Table of contents

Capacity fading on cycling of lithium/sulfur batteries may result from at least four processes: increase of SEI thickness resistance, loss of cathode capacity (precipitation of sulfur species outside the cathode), agglomeration and thickening of sulfur species and increase in cell impedance as a result of reduction of the electrolyte. A very important issue that has not been properly addressed up to now is the influence of the type and content of the cathode binder on the cell parameters and on the electrochemical performance of lithium/sulfur batteries. We present here a detailed analysis and discussion of the electrochemical behavior, during prolonged cycling, of Li₂S-based cathodes containing five different binders. The binders under investigation are: poly(vinylidene fluoride) (PVDF-HFP), polyvinylpyrrolidone (PVP), mix of PVP with polyethylene imine (PEI), polyaniline (PANI) and lithium polyacrylate (LiPAA). Sulfur utilization in the cathode follows the order of LiPAA > PVP:PEI > PVP > PVDF-HFP > PANI. Depending on the type of binder, cells provide 500 to 1400 mAh/g (S), 94.6–98.0% faradaic efficiency and enable more than 500 reversible cycles.

Li[Ni_0.42Mn_0.42Co_0.16]O₂ (NMC442)/graphite pouch cells demonstrate superb performance at high voltage when ethylene carbonate (EC)-free electrolytes, using a solvent mixture that is >95% ethyl methyl carbonate (EMC) and between 2 and 5% of an "enabler", are used. The "enablers", required to passivate graphite during formation, can be vinylene carbonate (VC), methylene-ethylene carbonate (MEC), fluoroethylene carbonate (FEC) or difluoro ethylene carbonate (DiFEC), among others. In order to optimize the amount of "enabler" added to EMC, gas chromatography coupled with mass spectrometry (GC-MS) was used to track the consumption of "enabler" during the formation step. Storage tests, electrochemical impedance spectroscopy (EIS), ultrahigh precision coulometry (UHPC), long-term cycling, differential voltage analysis and isothermal microcalorimetry were used to determine the optimum amount of enabler to add to the cells. It was found that the graphite negative electrode cannot be fully passivated when the amount of "enabler" is too low resulting in gas production and capacity fade. Using excess "enabler" can cause large impedance and gas production in most cases. The choice of "enabler" also impacts cell performance. A solvent blend of 5% FEC with 95% EMC (by weight) provides the best combination of properties in NMC442/graphite cells operated to 4.4 V. It is our opinion that the experiments and their interpretation presented here represent a primer for the design of EC-free electrolytes.

This year, the battery industry celebrates the 25^th anniversary of the introduction of the lithium ion rechargeable battery by Sony Corporation. The discovery of the system dates back to earlier work by Asahi Kasei in Japan, which used a combination of lower temperature carbons for the negative electrode to prevent solvent degradation and lithium cobalt dioxide modified somewhat from Goodenough's earlier work. The development by Sony was carried out within a few years by bringing together technology in film coating from their magnetic tape division and electrochemical technology from their battery division. The past 25 years has shown rapid growth in the sales and in the benefits of lithium ion in comparison to all the earlier rechargeable battery systems. Recent work on new materials shows that there is a good likelihood that the lithium ion battery will continue to improve in cost, energy, safety and power capability and will be a formidable competitor for some years to come.

A high areal capacity lithium-sulfur battery making use of mass produced aluminum metal foam as a current collector was investigated. A sulfur/Ketjenblack (KB) composite was filled and deposited into the aluminum foam current collector via a predetermined filling procedure, resulting in high sulfur loading. The value for this loading was found to be 17.7 mg sulfur/cm² by using carboxymethyl cellulose and styrene butadiene rubber (CMC + SBR) as a binder. An operating single-layer pouch-type cell with an S/KB-CMC+SBR on Al foam cathode was created as a result of this synthesis and found to possess an unprecedentedly high areal capacity of 21.9 mAh/cm². On the basis of the achieved areal capacity, the energy density of a theoretical lithium-sulfur battery was estimated with the assumption of an electrolyte/sulfur ratio of 2.7 μL/mg. This was calculated upon 100% of the pore volume in the S/KB-CMC + SBR on Al foam cathodes and polyolefin separator, along with the inclusion of the weights of the tabs for the current lead and pouch film packaging in the case of a seven-layer pouch-type battery. With this calculation, it was determined that the creation of a lithium-sulfur battery with an energy density of greater than 200 Wh/kg is plausible.

Energy storage related to transient energy sources, such as solar and wind, and their integration with the energy distribution grid is getting increased attention. The characteristics required for this type of storage are quite different from those for energy storage in portable devices. Size and weight are not so important. Instead, matters such as power, cost, calendar life, cycle life, and safety are critical. A new family of hexacyanoferrate materials with the same type of open framework crystal structure as Prussian Blue has been recently developed with characteristics ideally suited for this type of application. Several monovalent cations can be rapidly and reversibly inserted into these materials, with very little crystallographic distortion. This can result in high rates and long cycle lives. A new type of composite negative electrode materials has also been developed that has the rapid kinetics typical of carbon electrodes, with a potential that varies little with the state of charge. The result is the development of a new battery system, the ferrocyanide / stabilized carbon, MHCF-SC, system. It is the purpose of this paper to review these developments.

Li₃VO₄ is a promising insertion anode material for lithium ion batteries (LIBs), but has the drawback of low electronic conductivity. Here, we have developed a facile spray drying route to synthesize Li₃VO₄/C/CNTs (carbon nanotubes) composites with hollow spherical morphology. In this composite, Li₃VO₄ nanocrystals are interconnected by CNTs to form an integrated electronic conducting particle. Owing to the high specific surface and hierarchical porous structure, Li₃VO₄/C/CNTs composites also possess higher apparent Li⁺ ions diffusion coefficient. The resulting Li₃VO₄/C/CNTs composites exhibit much better rate capability than the pristine Li₃VO₄. A high reversible capacity of 272 mAh g⁻¹ can be maintained up to 500 cycles at 10 C (86.1% retention of the 2nd charge capacity). Moreover, the synthetic method is facile and scalable, thus as-prepared LVO/C/CNTs composites can be a promising anode material for high-safety LIBs.

Ag_0.50VOPO₄·1.8H₂O (silver vanadium phosphate, SVOP) demonstrates a counterintuitive higher initial loaded voltage under higher discharge current. Energy dispersive X-ray diffraction (EDXRD) from synchrotron radiation was used to create tomographic profiles of cathodes at various depths of discharge for two discharge rates. SVOP displays two reduction mechanisms, reduction of a vanadium center accompanied by lithiation of the structure, or reduction-displacement of a silver cation to form silver metal. In-situ EDXRD provides the opportunity to observe spatially resolved changes to the parent SVOP crystal and formation of Ag⁰ during reduction. At a C/170 discharge rate V⁵⁺ reduction is the preferred initial reaction resulting in higher initial loaded voltage. At a discharge rate of C/400 reduction of Ag⁺ with formation of conductive Ag⁰ occurs earlier during discharge. Discharge rate also affects the spatial location of reduction products. The faster discharge rate initiates reduction close to the current collector with non-uniform distribution of silver metal resulting in isolated cathode areas. The slower rate develops a more homogenous distribution of reduced SVOP and silver metal. This study illuminates the roles of electronic and ionic conductivity limitations within a cathode at the mesoscale and how they impact the course of reduction processes and loaded voltage.

Organic radical polymers (ORP) and conjugated polymers provide exceptional rate capability as cathode materials for lithium-ion batteries, albeit low volumetric energy density. To optimize overall power and energy density, we consider a composite of ORP with oxide cathode. Upon charge (oxidation), ORP absorb anions from the electrolyte, which causes the salt content in the cell to decrease during charge. Even if the ORP is only 10 volume% of the cathode, the cell's salt content will decrease by >0.6 M in practical cell designs. Furthermore, the conductivity of typical electrolytes varies strongly with concentration. We use electrochemical modeling of a composite positive electrode containing both lithium-releasing and anion-absorbing active materials to explore the tradeoffs and design implications among salt concentration, porosity, and volume fraction of ORP.

In this paper we report on the investigation of ionic liquid-based electrolytes with enhanced characteristics. In particular, we have studied ternary mixtures based on the lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt and two ionic liquids sharing the same cation (N-methyl-N-propyl pyrrolidinium, PYR₁₃), but different anions, bis(trifluoromethanesulfonyl)imide (TFSI) and bis(fluorosulfonyl)imide (FSI). The LiTFSI-PYR₁₃TFSI-PYR₁₃FSI mixtures, found to be ionically dissociated, exhibit better ion transport properties (about 10⁻³ S cm⁻¹ at −20°C) with respect to similar ionic liquid electrolytes till reported in literature. An electrochemical stability window of 5 V is observed in carbon working electrodes. Preliminary battery tests confirm the good performance of these ternary electrolytes with high-voltage NMC cathodes and graphite anodes.

Ionic liquid electrolyte mixtures, PYR₁₃TFSI, PYR₁₃FSI.

In this study we present a novel method of lithium ion battery electrode sample preparation with a new type of epoxy impregnation, brominated (Br) epoxy, which is introduced here for the first time for this purpose and found suitable for focused ion beam scanning electron microscope (FIB-SEM) tomography. The Br epoxy improves image contrast, which enables higher FIB-SEM resolution (3D imaging), which is amongst the highest ever reported for composite LFP cathodes using FIB-SEM. In turn it means that the particles are well defined and the size distribution of each phase can be analyzed accurately from the complex 3D electrode microstructure using advanced quantification algorithms.

The authors present for the first time a new methodology of contrast enhancement for 3D imaging, including novel advanced quantification, on a commercial Lithium Iron Phosphate (LFP) LiFePO₄ cathode. The aim of this work is to improve the quality of the 3D imaging of challenging battery materials by developing methods to increase contrast between otherwise previously poorly differentiated phases. This is necessary to enable capture of the real geometry of electrode microstructures, which allows measurement of a wide range of microstructural properties such as pore/particle size distributions, surface area, tortuosity and porosity. These properties play vital roles in determining the performance of battery electrodes.

Many transition metal sulfides are electronically conductive, electrochemically active and reversible in reactions with lithium. However, the application of transition metal sulfides as sulfur cathode additives in lithium-sulfur (Li-S) batteries has not been fully explored. In this study, Pyrite (FeS₂) is studied as a capacity contributing conductive additive in sulfur cathode for Li-S batteries. Electrochemically discharging the S-FeS₂ composite electrodes to 1.0 V activates the FeS₂ component, contributing to the improved Li-S cell discharge energy density. However, direct activation of the FeS₂ component in a fresh S-FeS₂ cell results in a significant shuttling effect in the subsequent charging process, preventing further cell cycling. The slight FeS₂ solubility in electrolyte and its activation alone in S-FeS₂ cells are not the root causes of the severe shuttling effect. The observed severe shuttling effect is strongly correlated to the 1^st charging of the activated S-FeS₂ electrode that promotes iron dissolution in electrolyte and the deposition of electronically conductive FeS on the anode SEI. Pre-cycling of the S-FeS₂ cell prior to the FeS₂ activation or the use of LiNO₃ electrolyte additive help to prevent the severe shuttling effect and allow the cell to cycle between 2.6 V to 1.0 V with an extra capacity contribution from the FeS₂ components. However, a more effective method of anode pre-passivation is still needed to fully protect the lithium surface from FeS deposition and allow the S-FeS₂ electrode to maintain high energy density over extended cycles. A mechanism explaining the observed phenomena based on the experimental data is proposed and discussed.

We report about a cost-effective synthesis approach for obtaining layered lithium vanadium monodiphosphate Li₉V₃(P₂O₇)₃(PO₄)₂ (LVPP) as cathode material for lithium-ion batteries. This polyanionic cathode framework can exchange more than one electron per transition metal at high potentials versus lithium. The influence of crystallite size, carbon coating and working potential window on the electrochemical performance of Li₉V₃(P₂O₇)₃(PO₄)₂ is reported. The extraction of nearly 5 Li⁺ ions during the first cycle between 2 and 4.8 V is reached for LVPP with crystallite size of 40 nm and 4.4% carbon coating. A stable reversible specific capacity of 115 mA h g⁻¹ is achieved when cycled between 2 and 4.8 V.

Energy density of full cells containing layered-oxide positive electrodes can be increased by raising the upper cutoff voltage above the present 4.2 V limit. In this article we examine aging behavior of cells, containing LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523)-based positive and graphite-based negative electrodes, which underwent up to ∼400 cycles in the 3–4.4 V range. Electrochemistry results from electrodes harvested from the cycled cells were obtained to identify causes of cell performance loss; these results were complemented with data from X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) measurements. Our experiments indicate that the full cell capacity fade increases linearly with cycle number and results from irreversible lithium loss in the negative electrode solid electrolyte interphase (SEI) layer. The accompanying electrode potential shift reduces utilization of active material in both electrodes and causes the positive electrode to cycle at higher states-of-charge. Full cell impedance rise on aging arises primarily at the positive electrode and results mainly from changes at the electrode-electrolyte interface; the small growth in negative electrode impedance reflects changes in the SEI layer. Our results indicate that cell performance loss could be mitigated by modifying the electrode-electrolyte interfaces through use of appropriate electrode coatings and/or electrolyte additives.

Calendar aging of lithium-ion cells is investigated by storing commercial 18650 cells with NCA cathode and graphite anode at different states of charge and temperatures. The resulting capacity fades are analyzed by differential voltage analysis (DVA) and coulometry. DVA reveals that the capacity fade results mainly from a shift in the electrode balancing due to a reduced inventory of cyclable lithium. Moreover, DVA confirms that the capacity fade strongly correlates with the anode potential. The observed loss of cyclable lithium is further analyzed by coulomb tracking, which stands for creating a continuous ampere-hour balance from all individual measurements performed with an examined cell and tracking the slippage of charging and discharging endpoints. It reveals the extent of anodic and cathodic side reactions during the storage periods and their effect on the inventory of cyclable lithium. Anodic side reactions, which are related to electrolyte reduction and passivation layer growth, can be identified as the main driver of capacity fade. Coulomb tracking also discloses that increasing cathodic side reactions can reduce the irreversible capacity fade, particularly for storage at very high SoC, which is likely to be misinterpreted as decelerated aging reactions. Evaluating also the reversible capacity fade prevents such a misconception.

A series of Si/graphene sheet/carbon (Si/GS/C) composites was prepared by electrostatic self-assembly between amine-grafted silicon nanoparticles (SiNPs) and graphene oxide (GO). The Si/GS derived from carbonization of Si/GO assemblies showed limited cycling stability owing to loose cohesion between SiNPs and graphene, and increased impedances during cycling. To counteract the cycling instability of Si/GS, an additional carbon-gel coating was applied to the Si/GO assemblies in situ in solution followed by carbonization to yield dense three-dimensional particulate Si/GS/C composite with many internal voids. The obtained Si/GS/C composites showed much better electrochemical performances than the Si/GS owing to enhanced cohesion between the SiNPs and the carbon structures, which reduced the impedance buildup and protected the SiNPs from direct exposure to the electrolyte. A strategy for practical use of a high-capacity Si/GS/C composite was also demonstrated using a hybrid composite prepared by mixing it with commercial graphite. The hybrid composite electrode showed specific and volumetric capacities that were 200% and 12% larger, respectively, than those of graphite, excellent cycling stability, and CEs (>99.7%) exceeding those of graphite. Hence, electrostatic self-assembly of SiNPs and GO followed by in situ carbon coating can produce reliable, high-performance anodes for high-energy LIBs.

The amounts of adsorbed water on several kinds of carbon and silicon materials including Si nano-flake powder (Si LeafPowder, Si-LP) were determined at 250°C. It was found that nano-sized Si materials adsorb a large amount of water even after being dried at 120°C because of the hydrophilicity of the surface and the high specific surface area. The adsorbed water on Si-LP can be removed, but not completely, after drying at a 180°C. The charge and discharge characteristics of Si-LP, especially the initial irreversible capacity and the coulombic efficiencies upon repeated cycling, were significantly improved by removal of the adsorbed water at 180°C. The 180°C-dried sample also suppressed gas evolution during the initial charging and discharging cycle. From the results of gas analysis, it was found that gases evolved from the Si-LP electrodes were mainly H₂ and CO₂. From the results of charge and discharge tests and gas analysis, the effect of the adsorbed water on the irreversible decomposition of the electrolyte solution was discussed.

An equimolar mixture of lithium bis(trifluoromethylsulfonyl)amide (Li[TFSA]) and triglyme (G3) or tetraglyme (G4) yields the stable molten complexes, [Li(G3)][TFSA] or [Li(G4)][TFSA], respectively, classified into solvate ionic liquids (SILs). The Li-conducting SIL electrolytes have favorable thermal and electrochemical properties, but their intrinsic high viscosities and low ionic conductivities impede widespread application. In this study, SILs were diluted with organic solvents, such as toluene, hydrofluoroether (HFE) and propylene carbonate (PC), to enhance their ionic conductivity. Subsequently, the performance of a battery consisting of diluted SILs, LiCoO₂, and graphite electrodes was evaluated. The electrochemical stability and charge/discharge behavior of the LiCoO₂ cathode and graphite anode were greatly influenced by the stability of the complex cations, [Li(G3)]⁺ or [Li(G4)]⁺, in the diluted SILs. Unfavorable ligand exchange between the glyme and PC occurred in PC-diluted SILs. Oxidative decomposition of the uncoordinated glyme and pitting corrosion of Al current collector deteriorated the battery performance of LiCoO₂ half-cell with PC-diluted SILs. We demonstrate that toluene- and HFE-diluted SILs, which do not contain chemicals such as carbonate solvent and LiPF₆ used in commercialized Li-ion batteries, allow both LiCoO₂ cathode and graphite anode to operate stably.

The electrochemical performance of cells with a Li_1.03(Ni_0.5Co_0.2Mn_0.3)_0.97O₂ (NCM523) positive electrode and a blended silicon-graphite (Si-Gr) negative electrode are investigated using various electrolyte compositions and voltage cycling windows. Voltage profiles of the blended Si-Gr electrode show a superposition of graphite potential plateaus on a sloped Si profile with a large potential hysteresis. The effect of this hysteresis is seen in the cell impedance versus voltage data, which are distinctly different for the charge and discharge cycles. We confirm that the addition of compounds, such as vinylene carbonate (VC) and fluoroethylene carbonate (FEC) to the baseline 1.2 M LiPF₆ in ethylene carbonate (EC): ethyl methyl carbonate (EMC) (3:7 w/w) electrolyte, improves cell capacity retention with higher retention seen at higher additive contents. We show that reducing the lower cutoff voltage (LCV) of full cells to 2.5 V increases the Si-Gr electrode potential to 1.12 V vs. Li/Li⁺; this relatively-high delithiation potential correlates with the lower capacity retention displayed by the cell. Furthermore, we show that raising the upper cutoff voltage (UCV) can increase cell energy density without significantly altering capacity retention over 100 charge-discharge cycles.

This work demonstrates that the mechanical damage of surface passivation films plays an underlying role in the failure of nano-sized Si electrodes in lithium-ion batteries. The surface film derived from the standard electrolyte (1.3 M LiPF₆ dissolved in ethylene carbonate/diethyl carbonate) during the first lithiation step is damaged by the mechanical stress caused by the volume contraction of Si particles during the subsequent de-lithiation period. The electrolyte decomposes on the newly exposed Si surface and film deposition occurs, which is then mechanically damaged again owing to volume change of the Si particles. Such film deposition/damage cycles are repeated until the mechanical stress becomes insignificant as a result of capacity decay. Continued electrolyte decomposition, which prevails in the early cycling period, produces electronically insulating films located between Si particles, which cause Li trapping within the Si matrix. Li trapping is found to be responsible for the rapid decrease in capacity and Coulombic efficiency in the intermediate period of cycling. When fluoroethylene carbonate (FEC) is added to the electrolyte, a surface film that is robust against mechanical stress is produced. As a result, the FEC-derived surface film maintains its passivating ability and suppresses the irreversible reactions, resulting in a better cycling performance.

Anode materials with high capacity are urgently required to substitute graphite. The theoretical gravimetric and volumetric capacities of Bi₂S₃ are much higher than those of graphite, but the cycling performance of Bi₂S₃ is poor due to its large volumetric expansion. Amorphous SiO₂ is mechanically rigid, which can buffer the volume change. A novel Bi₂S₃@SiO₂ core-shell microwire is firstly designed and synthesized in this work. The composite exhibits excellent electrochemical performances. The discharge capacity is 379 mA h g⁻¹ after 4000 cycles at the current density of 1 A g⁻¹.

The degradation behaviors of bare and Al-oxide coated LiCoO₂ in the high-voltage phase transition region were investigated at the charge voltage of 4.7 V. In both materials, two voltage plateaus that indicate phase transitions from the O3 to H1-3 and O1 phases were observed in the first charge/discharge. Bare LiCoO₂ exhibited considerably decreased capacity, and increased polarization and charge transfer resistance in the cycle test, whereas these changes were remarkably suppressed in the coated LiCoO₂. The phase transitions of the coated LiCoO₂ can be assumed to be fairly reversible, since the voltage plateaus remained even after 20 cycles. After the cycle tests, stacking faults were observed throughout the bare LiCoO₂ particle. Pitting corrosion occurred on the faults, and the formation of a spinel-like layer was observed on the surface of the cycled bare LiCoO₂. The pitting corrosion caused intrinsic capacity fading by Co dissolution. The formation of the spinel-like layer also resulted in effective capacity fading due to the increased polarization. Both the pitting corrosion and the formation of the spinel-like layer were markedly suppressed by the surface coating. Therefore, a surface coating that stabilizes the electrode/electrolyte interface greatly affects the charge/discharge characteristics, even in the high-voltage phase transition region.

Herein, an investigation of the impact of the dopant and carbon content in iron-doped zinc oxide/carbon composites is presented. For this purpose, a comprehensive morphological, structural, and electrochemical characterization of a series of different compounds is reported, including techniques like X-ray diffraction (XRD), transmission electron microscopy (TEM), inductively coupled plasma optical emission spectroscopy (ICP-OES), thermogravimetric analysis (TGA), specific surface area using the Brunauer-Emmett-Teller (BET) algorithm, pycnometry, small-angle X-ray scattering (SAXS), cyclic voltammetry (CV), and galvanostatic cycling. The obtained results reveal an impact of the iron-dopant content on the crystallite and particle size as well as the detailed de-/lithiation mechanism. The effect on the cycling stability, however, appears to be rather minor. The carbon coating content, on the contrary, has a significant influence on the cycling stability and rate capability. According to these results, a carbon content of about 10 wt% is sufficient to achieve stable cycling at lower current densities, while a carbon content of 15–20 wt% allows for specific capacities of 425–500 mAh g⁻¹, when applying a specific current of 1 A g⁻¹, for instance.

The detailed characterization of garnet-type Li-ion conducting Li₇La₃Zr₂O₁₂ (LLZO) solid electrolyte thin films grown by novel CO₂-laser assisted chemical vapor deposition (LA-CVD) is reported. A deposition process parameter study reveals that an optimal combination of deposition temperature and oxygen partial pressure is essential to obtain high quality tetragonal LLZO thin films. The polycrystalline tetragonal LLZO films grown on platinum have a dense and homogeneous microstructure and are free of cracks. A total lithium ion conductivity of 4.2·10⁻⁶ S·cm⁻¹ at room temperature, with an activation energy of 0.50 eV, is achieved. This is the highest total lithium ion conductivity value reported for tetragonal LLZO thin films so far, being about one order of magnitude higher than previously reported values for tetragonal LLZO thin films prepared by sputtering and pulsed laser deposition. The results of this study suggest that the tetragonal LLZO thin films grown by LA-CVD are applicable for the use in all-solid-state thin film lithium ion batteries.

We report an advanced device based on a Nitrogen-doped Carbon Nanopipes (N-CNP) negative electrode and a lithium iron phosphate (LiFePO₄) positive electrode. We carefully balanced the cell composition (charge balance) and suppressed the initial irreversible capacity of the anode in the round of few cycles. We demonstrated an optimal performance in terms of specific capacity 170 mAh/g of LiFePO₄ with energy density of about 203 Wh kg⁻¹ and a stable operation for over 100 charge−discharge cycles. The components of this device (combining capacitive and faradaic electrodes) are low cost and easily scalable. This device has a performance comparable to those offered by the present technology of LIBs with the potential for faster charging; hence, we believe that the results disclosed in this work may open up new opportunities for energy storage devices.

The synthesis, characterization and electrochemical sodiation/desodiation performance of two novel disodium diimide carboxylates, disodium salt of N,N'-bis (glycinyl) pyromellitic diimide (Na₂-BPDI) and disodium salt of N,N'-bis (glycinyl) naphthalene diimide (Na₂-BNDI) were reported for the first time. The Na₂-BNDI electrode material delivers a reversible capacity of 122 mAh g⁻¹ in the first cycle and retains a reasonable capacity of 92 mAh g⁻¹ after 50 cycles at a current density of 50 mA g⁻¹, whereas a rapid capacity fading is observed in the case of Na₂-BPDI electrode material in subsequent cycles. Ex-situ NMR and FT-IR studies confirmed that the decomposition of Na₂-BPDI electrode material upon continuous electrochemical sodiation/desodiation process. These results demonstrate that the importance of extended conjugation, as in Na₂-BNDI, for efficient electrochemical sodium storage in the redox active aromatic compound.

In order to examine the controversial hypothesis put forward to explain the entropy step experimentally observed for the stage II to stage I transition for lithium intercalation in graphite, a transparent statistical mechanical model is developed. The results obtained show that the entropy increase can be explained by the change of configurational entropy occurring at occupation of half of the lattice. Comparison with experimental data shows that attractive interactions between intercalated particles in the same layer must be assumed, in agreement with the ansatz made in the original experimental work.

Safety remains a significant concern for the lithium-ion battery industry, despite over twenty five years of development since their commercial introduction [R. Spotnitz and J. Franklin, J. Power Sources, 113, 81, (2003)]. Many abusive conditions (such as overheating, overcharge, overdischarge, and electrical short) can give rise to gas evolution in lithium ion batteries, which causes increased pressure and/or expansion of the cell leading to changes in the electrode geometry that can lead to significantly different electrochemical performance and safety characteristics [Y. Qi, S. S. J. Harris, J. Electrochem. Soc., 157, A741 (2010)]. In order to characterize the cell-level changes that occur during gas evolution, a non-destructive technique is required that can image the internal components of the cell at high spatial resolution without perturbing the electrode assembly itself. This paper demonstrates the use of synchrotron-based computed tomography to characterize the changes in electrode geometry that occur during gas evolution in a commercial aluminum pouch cell.

Efficient conduction of both electrons and cations (e.g., Li⁺) has a profound effect on the current and capacity of lithium-based batteries. With this study, we focus on cathode effects, with the preparation of pure silver hollandite materials with variable silver ion content within (intra-tunnel) and on the surface of α-MnO₂ tunneled materials, followed by the measurement and analysis of impedance and electrochemistry data. Specifically, pure Ag_xMn₈O_16-y materials with low (x = 1.13) and high (x = 1.54) intra-tunnel silver content are compared with Ag_xMn₈O_16-y·aAg₂O (a = 0.25, 0.63, 1.43) composites prepared via a new Ag₂O coating strategy. When the Ag₂O (a = 0, 0.25) content is low, the material with higher intra-tunnel silver (x = 1.53) content delivers up to ∼5-fold higher capacity accounted for by a ∼10-fold lower impedance than its lower intra-tunnel silver (x = 1.13) counterpart. In the presence of high Ag₂O content (a = 0.63, 1.43), both composites exhibit comparable impedance but the lower intra-tunnel silver (x = 1.13) composite delivers up to ∼1.5-fold higher capacity than higher intra-tunnel silver composite, highlighting the key role of Li⁺ transport under those conditions. Our results demonstrate material design strategies which can significantly increase electronic and ionic conductivities.

Binders are electrochemically inactive electrode components. However, their chemical and physical nature greatly affects battery performance and plays a key role in electrode integrity and interface reactivity. The binders thus have a strong impact on battery capacity retention and cycle life. Water-processable binders would make the electrode preparation process cheap and environmentally friendly and provide a viable alternative to polyvinylidene difluoride (PVdF). Here we report the use of sodium alginate (SA) as binder for LiNi_0.5Mn_1.5O₄ (LNMO), one of the most promising cathode materials for high-voltage and high-energy LIBs. We demonstrate that electrodes with high mass loading containing SA have excellent specific discharge capacity (120 mAh g⁻¹ at C/3 and 100 mAh g⁻¹ at 5C) with negligible overpotentials in conventional electrolyte based on ethylene carbonate (EC): dimethyl carbonate (DMC) and 1 M LiPF₆, where the reactivity of LNMO is known to negatively affect stability. The electrodes with SA also show a good stability over subsequent cycles of charge and discharge at 1C with capacity retention of 95% and 86% with respect to the initial cycles at the 100th and 200th cycle.

Carbon replica constructed of three-dimensional, ordered mesopores was employed as the conductive framework for the composite electrode in Li-sulfur all-solid-state batteries. Using a gas-phase mixing method under various conditions, elemental sulfur was introduced into the mesopores with an average diameter of 12 nm. The all-solid-state cells consisted of the sulfur-carbon replica composite cathode, thio-LISICON solid electrolyte, and Li-Al alloy anode. The cells produced discharge capacities of approximately 1500 mAh g⁻¹ in the 1^st cycle, which is comparable to the theoretical capacity of sulfur. Thermogravimetric and X-ray diffraction analyses revealed that sulfur deposited inside the mesopores is the main contributor to the excellent performance of the battery. However, sulfur strongly interacted with the carbon replica, reducing the thickness of the carbon wall from 7 to 4 nm. This structural change in the carbon matrix triggered the deterioration of battery performance, especially the cycling capability. Optimizing the sulfur deposition conditions could therefore enhance the performance of batteries using such composite electrodes.

The increasing usage of electrical drive systems and stationary energy storage worldwide lead to a high demand of raw materials for the production of lithium-ion batteries. To prevent further shortage of these crucial materials, ecological and efficient recycling processes of lithium-ion batteries are needed. Nowadays industrial processes are mostly pyrometallurgical and as such energy and cost intensive. The LithoRec projects, funded by the Federal Ministry for the Environment, Nature Conservation, Building and Nuclear Safety (BMUB), aimed at a realization of a new energy-efficient recycling process, abstaining high temperatures and tracing mechanical process-steps. The conducted mechanical processes were thoroughly investigated by experiments in a laboratory and within technical scale, describing gas release of aged and non-aged lithium-ion batteries during dry crushing, intermediates, and products of the mechanical separation. Conclusively, we found that applying a second crushing step increases the yield of the coating materials, but also enables more selective separation. This work identifies the need for recycling of lithium-ion batteries and its challenges and hazard potential in regards to the applied materials. The outlined results show a safe and ecological recycling process with a material recycling rate of at least 75%.

In this work, XRD, EDX, Mössbauer and NMR spectroscopy were used to study chemical and electrochemical Na⁺/Li⁺ ion exchange in the sodium iron pyrophosphate Na_1.56Fe_1.22P₂O₇ with a triclinic symmetry, S. G. P-1, and sodium vanadium fluorophosphate Na₃V₂(PO₄)₂F₃ with a tetragonal symmetry, S. G. P4₂/mnm, cathode materials. Electrochemical Na⁺/Li⁺ ion exchange was performed in hybrid-ion cells with Li metal anode and LiPF₆-based electrolyte, while chemical ion exchange was realized in the solution of LiBr in acetonitrile. A facile electrochemical and chemical Na⁺/Li⁺ ion exchange was observed for both cathode materials, resulting in the formation of the mixed Na-Li compositions: ∼Na_1.2Li_0.36Fe_1.22P₂O₇ and ∼Na_2.47Li_0.53V₂(PO₄)₂F_3, respectively. Partial Na⁺/Li⁺ ion exchange did not cause noticeable structural changes to the pristine sodium-based materials. Both materials showed an excellent electrochemical performance in hybrid-ion cells. It was suggested that during cycling, a mixed Na⁺/Li⁺ cathode reactions occurred.

Li-insertion studies were performed on V₄O₃(PO₄)₃ that belongs to the libscombite/lazulite family. Availability of multiple oxidation states and vacancies in crystal structure allows for the insertion of more than 7 lithium ions per formula unit. We will show that in the voltage window of 1–4 V vs. Li⁺/Li, 6.0 Li-ions could be inserted leading to a reversible capacity of 195 mAh/g at a C/5 rate. A structural transformation is observed from ex-situ XRD patterns after the insertion of 2 lithium at 2.4 V vs. Li⁺/Li, consistent with the available crystallographic sites in the structure. Interestingly we show that from this phase Li₂V₄O₃(PO₄)₃, further lithium insertion lead to an amorphous material but the structure is completely recovered on charge.

Silicon electrodes can give high capacity as anodes for lithium-ion batteries. However, there has not been much work quantifying the different contributions to the reversible and irreversible capacities. Here, we report the use of an electrochemical approach – depth of discharge test – to separate the charge-discharge capacities of crystalline silicon electrodes into four contributions: (1) SEI formation, (2) lithium accommodation in carbon and binder, (3) lithiation and delithiation of the Si active material, and (4) capacity loss associated with particle cracking and isolation. We find that the intrinsic coulombic efficiency for the crystalline-to-amorphous transition of Si during initial cycle is about 90%, which is independent of particle size. SEI formation is estimated to be about 10 mAh per square meters of active material surface and scales with BET surface area. Mechanical issues and particle isolation are observed in fully discharged electrode when the amount of binder is less than 20%. Capacity limitation prolongs lifetime of Si electrode, but the overall performance is governed by the coulombic efficiency (CE) during cycle. Low CE is due to continual SEI formation with cycling, increase utilization of Si upon cycling, trapping of Li in the material and mechanical failure of the electrode.

In this manuscript is reported a thermal and impedance spectroscopy investigation carried out on quaternary polymer electrolytes, to be addressed as separators for lithium solid polymer batteries, containing large amount of the N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide ionic liquid. The target is the development of Li⁺ conducting membranes with enhanced ion transport even below room temperature. Polyethylene oxide and polymethyl methacrylate were selected as the polymeric hosts. A fully dry, solvent-free procedure was followed for the preparation of the polymer electrolytes, which were seen to be self-consistent and handled even upon prolonged storage periods (more than 1 year). Appealing ionic conductivities were observed especially for the PEO electrolytes, i.e., 1.6 × 10⁻³ and 1.5 × 10⁻⁴ S cm⁻¹ were reached at 20 and −20°C, respectively, which are ones the best, if not the best ion conduction, never detected for polymer electrolytes.

Lithium ion batteries have become an integral part of our daily lives. Among a number of different cathode materials nickel-rich LiNi_xCo_yMn_zO₂ is particularly interesting. The material can deliver high capacities of ∼195 mAh g⁻¹ putting it on the map for electric vehicles. With an increasing nickel content, a number of issues arise in the material limiting its performance. The Li/Ni mixing, highly reactive surface and formation of micro cracks are the most pressing ones. An overview of recent literature exploring these phenomena is herein summarized and were applicable solutions will be highlighted.

We report about the electrochemical performance in the potential range 1.5 to 4.9 V of highly ordered, stoichiometric LiNi_0.5Mn_1.5O₄ with spinel structure and tailored morphology. Structural and morphological parameters are optimized for obtaining maximum energy density in Li-ion cell applications. The effect of the discharge cutoff on the cathode capacity, cycling stability and coulombic efficiency is discussed. Li-rich structures with composition Li_1+xNi_0.5Mn_1.5O₄ (0 < × < 1) obtained via electrochemical lithiation are investigated via ex-situ XRD and SEM analysis. The results are compared with those obtained via a chemical lithiation method, showing that the phase transition from cubic LiNi_0.5Mn_1.5O₄ to tetragonal Li₂Ni_0.5Mn_1.5O₄ occurs via a two-phase mechanism with no evidence of intermediate phases. The superior electrochemical performance of the synthesized cathode material is ascribed to its specific morphology that provides suitable properties for reduced side-reactions with the electrolyte and low impact of the volumetric changes during cycling.

LiMn_1.5Ni_0.5O₄ (LMNO) has a huge potential for use as a cathode material in electric vehicular applications. However, it could face discharge capacity degradation with cycling at elevated temperatures due to attacks by hydrofluoric acid (HF) from the electrolyte, which could cause cationic dissolution. To overcome this barrier, we coated 3–5 micron sized LMNO particles with a ∼3 nm optimally thick and conductive CeO₂ film prepared by atomic layer deposition (ALD). This provided optimal thickness for mass transfer resistance, species protection, and mitigation of cationic dissolution at elevated temperatures. After 1,000 cycles of charge-discharge between 3.5 V–5 V (vs. Li⁺/Li) at 55°C, the optimally coated sample, 50Ce (50 cycles of CeO₂ ALD coated) had a capacity retention of ∼97.4%, when tested at a 1C rate, and a capacity retention of ∼83% at a 2C rate. This was compared to uncoated LMNO particles that had a capacity retention of only ∼82.7% at a 1C rate, and a capacity retention of ∼40.8% at a 2C rate.

In this work we analyzed the phenomenon of quasi solid state (QSS) lithiation of sulfur-carbon (S/C) composite electrodes with sulfur confined in the micropores of carbon matrices based on our recent studies and data published in literature. We demonstrated that the existence of sulfur in the form of small molecules is not a necessary condition for the realization of QSS mechanism. QSS operation behavior was demonstrated both for carbons with small up to 1nm micropores and for carbons with larger pore size up to 2–3 nm. A key role in the operation of S/C electrodes via a QSS mechanism plays surface electrolyte interphase (SEI) which is formed on the surface of S/C composite during the initial discharge. The formation of SEI was supported by X-ray photoelectron spectroscopy and by scanning electron microscopy. Small pore size (up to 1 nm) of the carbon matrices has a positive effect on the cycling of S/C electrodes. A superior cycling performance for more than 3500 charge-discharge cycles was demonstrated for S/C composite electrodes based on carbons synthesized by carbonization of polyvinylidene dichloride (PVDC) resin.

A combination of a Li₄Ti₅O₁₂ (LTO) anode and 4 V-class cathodes has been electrochemically studied with a view to its adoption for 12 V-class bipolar batteries. Five series-connected LTO/LiMn_0.85Fe_0.1Mg_0.05PO₄ (LMFP) cells harmonized well with a useable voltage range of 12 V lead-acid batteries, which is suitable for low-voltage system applications. The LMFP cathode had excellent cycle life performance during high-temperature cycling at 60°C and over-discharge cycling tests. In the case of the LTO/Al and the LMFP/Al electrode using an Al current collector in a hybrid solid electrolyte consisting of a cubic garnet-type Li₇La₃Zr₂O₁₂ and a gel polymer, lithium insertion and extraction occurred smoothly without irreversible reactions in the potential range of 1 to 4.5 V vs. Li/Li⁺. The thin hybrid solid electrolyte with thickness of a few micrometer exhibited not only high-rate discharge but also a low self-discharge for practical use. It was demonstrated that the fabricated 12 V-class bipolar LTO/LMFP battery with a capacity of 102 mAh had the average discharge voltage of 12.5 V, the energy density of 90 Wh kg⁻¹, and the output power density of 1500 W kg⁻¹ for 10 s. The 12 V-class bipolar LTO/LMFP battery is expected to be suitable for low-voltage systems.

Two series of magnetite (Fe₃O₄) composite electrodes, one group with and one group without added carbon, containing varying quantities of polypyrrole (PPy), and a non-conductive polyvinylidene difluoride (PVDF) binder were constructed and then analyzed using electrochemical and spectroscopic techniques. Galvanostatic cycling and alternating current (AC) impedance measurements were used in tandem to measure delivered capacity, capacity retention, and the related impedance at various stages of discharge and charge. Further, the reversibility of Fe₃O₄ to iron metal (Fe⁰) conversion observed during discharge was quantitatively assessed ex-situ using X-ray Absorption Spectroscopy (XAS). The Fe₃O₄ composite containing the largest weight fraction of PPy (20 wt%) with added carbon demonstrated reduced irreversible capacity on initial cycles and improved cycling stability over 50 cycles, attributed to decreased reaction with the electrolyte in the presence of PPy. This study illustrated the beneficial role of PPy addition to Fe₃O₄ based electrodes was not strongly related to improved electrical conductivity, but rather to improved ion transport related to the formation of a more favorable surface electrolyte interphase (SEI).

Lithium lanthanum titanate (LLTO) is a promising solid state electrolyte for solid state batteries due to its demonstrated high bulk ionic conductivity. However, crystalline LLTO has a relatively low grain boundary conductivity, limiting the overall material conductivity. In this work, we investigate amorphous LLTO (a-LLTO) thin films grown by pulsed laser deposition (PLD). By controlling the background pressure and temperature we are able to optimize the ionic conductivity to 3 × 10⁻⁴ S/cm and electronic conductivity to 5 × 10⁻¹¹ S/cm. XRD, TEM, and STEM/EELS analysis confirm that the films are amorphous and indicate that oxygen background gas is necessary during the PLD process to decrease the oxygen vacancy concentration, decreasing the electrical conductivity. Amorphous LLTO is deposited onto high voltage LiNi_0.5Mn_1.5O₄ (LNMO) spinel cathode thin films and cycled up to 4.8 V vs. Li showing excellent capacity retention. These results demonstrate that a-LLTO has the potential to be integrated into high voltage thin film batteries.

This work presents life cycle analysis, the primary energy demand and balance, as well as overall sustainability of using Pb-acid and Li-ion technology in residential photovoltaic systems. It is shown that the ecological amortization in residential storage occurs after only a few months of operation. The Li-ion storage system becomes environmentally positive after 0.6 years while Pb-acid systems require 1.8 years of operation before it becomes environmentally positive.

The consumption via reductive and oxidative decompositions of vinylene carbonate (VC) molecules as an electrolyte additive at the anode and cathode in a 18650 lithium-ion battery was quantitatively analyzed with charge-discharge tests, NMR spectroscopy, and gas chromatography. It was unambiguously concluded that the molar number of VC reductively decomposed at the anode has the upper limit whereas that of VC oxidatively decomposed at the cathode depended highly upon the initial VC concentration. The excess amount of VC molecules causes the increase in oxidative decomposition at the cathode surface eventually reducing the Columbic efficiency at the first cycle.

Catastrophic failure concerns of Li-ion batteries create anxiety in electric vehicle and energy storage markets. Currently, no fast method to forecast catastrophic failure has existed for lithium ion or other battery types. This work presents a solution by very early detection of nascent internal shorts that are precursors of catastrophic failure. The new metric, the self-discharge current, which is determined under potentiostatic conditions at a slight discharge overvoltage, is proposed as a fast metric for detection of shorts and assessment of battery safety that can be completed in minutes. The assessment time for self-discharge analysis can be further shortened by at least two times using a sigmoidal model that displays only 5.6% variation from experimental values. The method is non-invasive and applicable to any battery chemistry or design. It can be easily adapted to any battery management system for monitoring battery state of health at any time and at any battery state of charge. The technology based on this method can be used in electric drive vehicles, stationary energy storage, military, aeronautic, as final control in battery production, for first responders in electric vehicle accidents, and many other applications.

New sulfur-carbon composite positive electrode materials were synthesized through sulfurizing primary alcohols, and their electrochemical properties were examined. The sulfurized alcohol composites (SACs) showed relatively higher sulfur contents (more than 60 wt%) and were revealed to be an amorphous structure by high-resolution TEM observations. Raman and XAFS spectra showed the presence of S – S, C – S, and C – C bonds, and the C – C bonds mainly consisted of sp³ components, which makes a clear contrast to the previously reported organosulfur materials where the C – C bonds mainly consisted of sp² components. The SAC positive electrode cells showed discharge capacities of more than 900 mAh·g⁻¹ with relatively reduced cycle degradation.

Increasing the energy density of Li-ion batteries is very crucial for the success of electric vehicles, grid-scale energy storage, and next-generation consumer electronics. One popular approach is to incrementally increase the capacity of the graphite anode by integrating silicon into composites with capacities between 500 and 1000 mAh/g as a transient and practical alternative to the more-challenging, silicon-only anodes. In this work, we have calculated the percentage of improvement in the capacity of silicon:graphite composites and their impact on energy density of Li-ion full cell. We have used the Design of Experiment method to optimize composites using data from half cells, and it is found that 16% improvements in practical energy density of Li-ion full cells can be achieved using 15 to 25 wt% of silicon. However, full-cell assembly and testing of these composites using LiNi_0.5Mn_0.5Co_0.5O₂ cathode have proven to be challenging and composites with no more than 10 wt% silicon were tested giving 63% capacity retention of 95 mAh/g at only 50 cycles. The work demonstrates that introducing even the smallest amount of silicon into graphite anodes is still a challenge and to overcome that improvements to the different components of the Li-ion battery are required.

Li–oxygen (Li-O₂) cathodes using palladium-coated and palladium-filled carbon nanotubes (CNTs) were investigated for their battery performance. The full discharge of batteries in the 2–4.5 V range showed 6-fold increase in the first discharge cycle of the Pd-filled over the pristine CNTs and 35% increase over their Pd-coated counterparts. The Pd-filled also exhibited improved cyclability with 58 full cycles of 500 mAh·g⁻¹ at current density of 250 mA·g⁻¹ versus 35 and 43 cycles for pristine and Pd-coated CNTs, respectively. In this work, the effect of encapsulating the Pd catalysts inside the CNTs proved to increase the stability of the electrolyte during both discharging and charging. Voltammetry, Raman spectroscopy, FTIR, XRD, UV/Vis spectroscopy and visual inspection of the discharge products using scanning electron microscopy confirmed the improved stability of the electrolyte due to this encapsulation and suggest that this approach could lead increasing the Li-O₂ battery capacity and cyclability performance.

Unstable and deficient supplies of lithium resources have led to the development of alternative battery systems such as sodium-ion batteries. Herein, P-type Na_0.6Mn_0.65Ni_0.25Co_0.10O₂ cathode materials were synthesized by a co-precipitation and solid-state reaction method. When the calcination temperature was changed from 700 to 1000°C, Na_0.6Mn_0.65Ni_0.25Co_0.10O₂ had a different morphology and crystalline structure; however, a P3-type structure was formed only at 700°C, and P2-type structured cathodes could be obtained at 800, 900, and 1000°C. Their electrochemical performances were evaluated with 2032 coin-type half cells. Among them, the P2-type cathode calcinated at 900°C, exhibited a high specific discharge capacity of 148 mAh g⁻¹, and a stable cycling performance at a 0.2 C rate for 150 cycles.

Transition metal (TM) ions dissolution from positive electrodes, migration to and deposition on negative electrodes, followed by Mn-catalyzed reactions of solvents and anions, with loss of Li⁺ ions, is a major degradation (DMDCR) mechanism in Li-ion batteries (LIBs) with spinel positive electrode materials. While the details of the DMDCR mechanism are still under debate, it is clear that HF and other acid species' attack is the main cause in solutions with LiPF₆ electrolyte. We first review the work on various mitigation measures for the DMDCR mechanism, now spanning more than two decades. We then discuss recent progress on our understanding of Mn species in electrolyte solutions and the extension of a mitigation measure first proposed by Tarascon and coworkers in 1999, namely chelation of TM cations, to Mn cation trapping, HF scavenging, and alkali metal ions dispensing multi-functional materials. We focus on practicable, drop-in technical solutions, based on placing such materials in the inter-electrode space, with significant benefits for LIBs performance: increased capacity retention during operation at room and above-ambient temperatures as well as robust (both maximally ionically conducting and electronically insulating) solid-electrolyte interfaces, having reduced charge transfer and film resistances at both negative and positive electrodes. We illustrate the multifunctional materials approach with both new and previously published data. We also discuss and offer our evaluation regarding the merits and drawbacks of the various mitigation measures, with an eye for practically relevant technical solutions capable to meet both the performance requirements and cost constraints for commercial LIBs, and end with recommendations for future work.

A single-layered NMC/graphite pouch cell is investigated by means of differential local potential measurements during various operation scenarios. 44 tabs in total allow for a highly resolved potential measurement along the electrodes whilst the single layer configuration guarantees the absence of superimposed thermal gradients. By applying a multi-dimensional model framework to this cell, the current density and SOC distribution are analyzed quantitatively. The study is performed for four C-rates (0.1C, 0.5C, 1C, 2C) at three temperatures (5°C, 25°C, 40°C). The maximum potential drop as well the corresponding SOC deviation are characterized. The results indicate that cell inhomogeneity is positively coupled to temperature, i.e. the lower the temperature, the more uniform the electrodes will be utilized.

The charge–discharge behavior of a Si-C mixed electrode (Si:graphite = 20:80 or 30:70 (wt%)) was investigated using in situ solid-state ⁷Li nuclear magnetic resonance (NMR) spectroscopy. The spectra revealed the formation of Li-Si alloys and the intercalation of Li into graphite during the charge process and the corresponding reverse process (Li extraction) during discharge. Li was mainly stored as a Li-Si alloy (Li₁₅Si₄ or Li_15+δSi₄) at high SOC (state of charge) values (above 80% SOC, low cell voltage region) and could be released from the alloy. The cell resistance measured by electrochemical impedance spectroscopy (EIS) increased steeply at high SOC values, revealing that structural changes in the Li-Si alloy may influence the electrode resistance. The NMR peaks observed upon formation of Li₁₅Si₄ or Li_15+δSi₄ shifted and decreased gradually, indicating that the Li-Si alloys are not sufficiently stable in the cell.

Electrodes prepared from lithium-rich (Li-rich) xLi₂MnO₃⋅(1-x)LiNi_aCo_bMn_cO₂ materials (a + b + c = 1) show extremely high discharge capacities, arising from excess Li⁺ present in their Li₂MnO₃ component, and the ability to reversibly store charge with O²⁻ anions. These electrodes suffer serious voltage and capacity fading however, due to the migration of transition metals to the Li-layer at advanced states of charging, partial structural layered-to-spinel transformation and other reasons. In this focus paper, the current understanding of the above materials is summarized, briefly concluding with attempts by our groups to mitigate the voltage and capacity fade of these electrodes.

The high voltage LiNi_0.5Mn_1.5O₄ spinel suffers from severe capacity fade when cycled against a graphitic anode as well as a relatively low theoretical capacity. Using metallic lithium as counter electrode, the stability is improved and the ability of the spinel structure to host 2 Li eq. can be used to improve the capacity. This leads to a theoretical specific energy of ∼1000 Wh kg⁻¹. Unfortunately, the cycling of 2 Li eq. involves a phase transition from cubic to tetragonal associated with material degradation. In this work doping is used to improve capacity retention when cycling between 2.0 and 5.0 V. Initial capacities and stabilities are directly dependent on synthesis conditions and doping elements. Therefore, Fe- and Ti-doped spinels are compared with Ru- and Ti-doped spinels and tested at different cycling conditions. The cycling stability can be improved significantly by using reannealed material and by changing the discharge cutoff criteria. Thus a capacity of 190 mAh g⁻¹ is achieved at a rate of C/2 with a capacity retention of ∼92% after 100 cycles. Furthermore, differences in the discharge behavior between the differently treated Ru- and Ti- doped materials are discussed based on the electrochemical behavior, the particle morphology and in-situ XRD analysis.

One of the prevailing approaches to tune properties of materials is lattice doping with metal cations. Aluminum is a common choice, and numerous studies have demonstrated the ability of Al³⁺ doping to stabilize different positive electrode materials, such as Li[Ni-Co-Mn]O₂ (NCMs). Currently, an atomic level understanding of the stabilizing effect of Al doping in NCMs is limited. In this work, we investigate the effect of Al doping on Ni-rich-NCM-523 (LiNi_0.5Co_0.2Mn_0.3O₂). Our results suggest that Al stabilizes the structure of the cathode material via strong Al-O iono-covalent bonding due to a significant Al(s)-O(p) overlap, as well as significant charge transfer capabilities of Al. The calculated formation energies suggest that Al doping results in stabilization of partially lithiated states of NCM-523. On the other hand, calculated voltages indicate only a minor change in the voltage profiles as a function of the state-of-charge due to Al doping, and a modest increase in the Li diffusion barrier was observed. We note that high doping concentrations might mitigate the Li diffusion rates.

In this work, various electrolyte additives designed for enhanced performance at high voltages were evaluated with elevated temperature potentiostatic holds with LiNi_0.5Co_0.2Mn_0.3/Li₄Ti₅O₁₂ full cells to determine their effect on the high voltage stability. Of the additives investigated, many showed increased oxidation current through the 60 hour potentiostatic holds test, and adversely affected both the capacity retention and interfacial impedance. Improved high voltage performance was observed with two additives, vinylene carbonate (VC) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), which was attributed to two different mechanisms of improvement. This work investigates some conclusions in the available literature of an additive molecule that decomposes on the charged cathode surface and passivates the surface against electrolyte oxidation.

The effect of the cation nature is explored for the reaction of alkali metal ions intercalation into the AVPO₄F material. Application of electrochemical methods allowed determining the key diffusional and kinetic parameters for Li⁺, Na⁺ and K⁺ intercalation reactions. The obtained formal redox potential values, apparent diffusion coefficients and charge transfer resistance values are contrasted, providing the possibility to assess the variation in the reaction energetics for metal ion insertion/extraction. The observed differences in reaction rates are rationalized in terms of different contributions of ion desolvation and transition through adsorbate layer/electrode interface for various ions.

A stable electrolyte system at a charge voltage over 4.5 V is the key to successfully obtaining higher energy density by raising the charging cutoff voltage. We demonstrate a fluorinated electrolyte (1 M LiPF₆ fluoroethylene carbonate (FEC) and methyl (2,2,2-trifluoroethyl) carbonate (FEMC) (FEC/FEMC = 1/9, v/v)) for a high-voltage LiNi_0.5Mn_0.3Co_0.2O₂/graphite system. The stability of the fluorinated electrolyte for the LiNi_0.5Mn_0.3Co_0.2O₂ (NMC532) cathode was investigated using scanning electron microscopy, X-ray photoelectron spectroscopy, and electrochemical impedance spectroscopy. The charge-discharge performance of the fluorinated electrolyte was superior to the corresponding non-fluorinated electrolyte system at a charging cutoff voltage of 4.7 V.

Recent experimental literature reports the solid state electrolyte properties of Li₄SnS₄ and Li₄SnSe₄, identifying interesting questions regarding their structural details and motivating our first principles simulations. Together with Li₄GeS₄, these materials are all characterized by the orthorhombic space group Pnma and are found to be isostructural. They have a ground state crystal structure (denoted Li₄SnS⁰₄) having interstitial sites in void channels along the c-axis. They also have a meta-stable structure (denoted Li₄SnS*₄) which is formed by moving one fourth of the Li ions from their central sites to the interstitial positions, resulting in a 0.5 Å  contraction of the a lattice parameter. Relative to their ground states, the meta-stable structures are found to have energies 0.25 eV, 0.02 eV, and 0.07 eV for Li₄GeS*₄, Li₄SnS*₄, and Li₄SnSe*₄, respectively. Consistent with these simulation results, the ground state forms for Li₄GeS⁰₄, Li₄SnS⁰₄ and Li₄SnSe⁰₄ and the meta-stable form for Li₄SnS*₄ have been reported in the experimental literature. In addition, simulations of Li ion migration in these materials are also investigated.

The development of all solid-state lithium batteries is reliant on suitable high performance solid state electrolytes. Here, we present the synthesis and ionic conductivity of the In- and Y-doped Li₆Hf₂O₇ materials; Li_6+xHf_2-xM_xO₇ (M = In³⁺, Y³⁺). Microwave-assisted synthesis was used to give phase pure material after heating for 4 hours at 850°C. The ionic conductivity of the materials is increased with the insertion of interstitial lithium ion within the structure from 0.02 to 0.25 mS cm⁻¹ at 174°C and the activation energy for ionic conduction is lowered from 0.97(4) eV to 0.42(3) eV with respect to the undoped material.

State-of-Health (SoH) is a critical parameter for determining the safe operating area of a battery cell and battery packs to avoid abuse and prevent failure and accidents. Experiments were performed at the US Naval Research Laboratory (NRL) on a 4P1S cell array using pulsed discharge and electrochemical impedance spectra (EIS) to determine a single-point SoH frequency for the array as a whole. Individual cell EIS measurements were taken, as well as measurements of the array as a whole. This work will discuss experimental results to date.

Various kinds of fluoroalkyl ethers were investigated as diluents to reduce the high viscosity of highly concentrated LiBF₄/PC electrolyte solutions. 1,1,2,2–tetrafluoroethyl 2,2,3,3–tetrafluoropropyl ether (HFE) was the most suitable diluent because of a high solubility of LiBF₄. 2.50 mol kg⁻¹ LiBF₄/PC+HFE (2:1 by volume) was a reasonable compromise to attain a low viscosity (51.7 mPa s) and a low PC/Li molar ratio (2.39). Raman spectroscopy revealed that the fraction of free PC molecules in 2.50 mol kg⁻¹ LiBF₄/PC+HFE (2:1) was much smaller than 2.50 mol kg⁻¹ LiBF₄/PC (PC/Li molar ratio = 4.00), and that the interactions of HFE with Li⁺ cations and BF₄⁻ anions were very weak. LiNi_0.5Mn_1.5O₄ positive electrodes showed high charge/discharge performance with low irreversible capacities in 2.50 mol kg⁻¹ LiBF₄/PC+HFE (2:1), which showed that the highly concentrated LiBF₄/PC system can be diluted with HFE without losing the high stability against oxidation.

The lithium-sulfur battery has received much attention in recent years owing to its high gravimetric capacity, far beyond that of current Li-ion batteries. Overcoming the shuttling effect caused by the dissolution of polysulfides during the charge-discharge process is a major challenge for the realization of Li-S cells. Here we report transfer-printing of a conductive polymer to cover and securely passivate the surface of sulfur electrodes to prevent the dissolution of polysulfides and, simultaneously, to provide high electronic conductivity of sulfur cathodes. Highly uniform polyaniline film can be controllably formed on sulfur cathodes via the transfer printing method, and a sulfur cathode with the printed polyaniline layer showed improved cycle performance (capacity retention of 96.4% and an average Coulombic efficiency of 99.6% for 200 cycles) compared to conventional sulfur cathodes. In situ measurement of transmittance during discharge demonstrated that the dissolution of sulfur in electrolytes is considerably suppressed by the printed polyaniline layer, substantiating that transfer-printed polyaniline film can provide robust protection as well as supplement electrical conductivity to the sulfur cathode. This strategy could be extensively applied to sulfur cathodes of diverse morphology and further extended to large-scale production.

With the goal of creating a model of a Li-air battery that is consistent with voltammetry data, we develop a full battery model capable of giving insight into details of cell operation otherwise inaccessible to common experimental techniques. With this model, we investigate the dependence of the current on: the diffusion characteristics of the electrolyte, the solubility of the ambient oxygen, the structure of the cathode, and aspects of the primary surface reaction. We explore modifications to a basic reaction-diffusion model of a full cell that bring better agreement with experimental data, including gas-electrolyte surface limited diffusion and a partially active cathode. We discuss how the basic form of the model and the simulated reaction and concentration profiles affect cell dynamics.

Polyvinylidenedifluoride (PVdF) and polyethyleneoxide (PEO) are blended and electrospun in order to obtain membranes suitable as Li-ion battery separators. The separators are characterized, and their properties investigated and compared with those of PVdF and commercial separators. The PVdF-PEO based separators ensure increased conductivities, greater electrolyte uptake and higher porosities than commercial polyolefines, all factors that improve cell performance. They are also safer than PVdF separators thanks to lower shutdown temperature, even if their mechanical properties are not yet comparable with those of the latter.

The development process of electrified vehicles can benefit significantly from computer-aided engineering tools that predict the multi-physics response of batteries during abusive events. A coupled structural, electrical, electrochemical, and thermal model framework has been developed within the commercially available LS-DYNA software. The finite element model leverages a three-dimensional mesh structure that fully resolves the unit cell components. The mechanical solver predicts the distributed stress and strain response with failure thresholds leading to the onset of an internal short circuit. In this implementation, an arbitrary compressive strain criterion is applied locally to each unit cell. A spatially distributed equivalent circuit model provides an empirical representation of the electrochemical response with minimal computational complexity. The thermal model provides state information to index the electrical model parameters, while simultaneously accepting irreversible and reversible sources of heat generation. The spatially distributed models of the electrical and thermal dynamics allow for the localization of current density and corresponding temperature response. The ability to predict the distributed thermal response of the cell as its stored energy is completely discharged through the short circuit enables an engineering safety assessment. A parametric analysis of an exemplary model is used to demonstrate the simulation capabilities.