ECS Meeting Abstracts

Abstract not Available.

Abstract not Available.

Next-generation solid-state batteries are expected to offer improved capacity and safety. The increase in capacity depends on the negative electrode material, and high-capacity materials such as Si, which can absorb large amounts of Li, are the subject of research. The amount of Li transferred can be measured electrically. However, it has not been possible to visualize where Li is distributed within the anode particles or to analyze the chemical state of the anode particles in real-time. Therefore, we installed a system on the SEM that enables real-time observation and analysis during charging and discharging (in-situ), which is an important technology in research and development.

This system has the following three features.

1) A tool that can maintain confining pressure and transport the battery from cross-section processing to SEM observation

2) Live imaging to visualize Li behavior during charging and discharging

3) Chemical state analysis of materials such as Si negative electrodes

The above three features are possible by combining the following devices and detectors; 1) a holder that maintains stack pressure and can be used together with processing and observation instruments, 2) a Windowless EDS detector "Gather-X" that can detect low characteristic X-ray energies like Li (54eV), and 3) a soft X-ray spectrometer (SXES) that enables local chemical state analysis.

Using this system, we were able to visualize the behavior and distribution of Li intercalating into Si particles during charging and discharging and analyze the transformation of anode particles into crystals, alloys, and amorphous states.

The Si anode composite was made by mixing Si particles and polyimide and applying a slurry. The cathode composite was made by mortar mixing the ternary oxide cathode material LiNi_1/3Mn_1/3Co_1/3O₂ (NMC), argyrodite sulfide solid electrolyte (SSE) and acetylene black (AB). Each component was put into a pelletizer, stacked, and pressurized at about 500 MPa to produce a full cell pellet. The pellet was cut into 4.8 mm squares using a precision punching tool for highly brittle materials (NOGAMIGIKEN, NC-CE-SS) and placed on a constrained charge/discharge holder, where a constraining pressure of 25 MPa was applied.

The cross-sections were prepared with an Ar ion beam (acceleration voltage: 5 kV, cooling temperature: -120 °C, processing time: 5 hr) using a cross-section preparation system (JEOL, Cooling Cross Section Polisher^TM, IB-19520CCP).

To minimize sample deterioration due to exposure to the atmosphere, glove boxes and transfer vessels that can be closed to the atmosphere were used for the entire process from pretreatment to processing to observation. A Schottky FE-SEM (JEOL, JSM-IT800) equipped with a Windowless EDS (JEOL, DrySD^TM Gather-X) and a soft X-ray spectrometer (JEOL, SS-94000SXES) was used for observation and analysis. SEM- EDS-SXES analysis was performed while charging and discharging at a C rate of 0.2 C (vs. NMC standard) using a battery charge/discharge device (HOKUTO DENKO, Hz-Pro) and a restrained charge-discharge holder in the SEM.

The result of SEM-Windowless EDS analysis (backscattered electron (BSE) and EDS MAP images) at SOC 0% to 10% is shown in Fig.1(a). Expansion of Si particles and changes in composition contrast were observed in the BSE composition image. From the EDS MAP, it was confirmed not only from contrast changes but also from characteristic X-ray information that Li was gradually inserted and alloyed toward the anode end of the solid electrolyte side of the Si particles in contact with the solid electrolyte interface. It was observed that Li was selectively inserted into some of the Si particles that were in contact with the solid electrolyte interface.

The results of SXES analysis of specific Si particles, when the sample was charged to 0%, 10%, 20%, and 40% SOC and then discharged, are shown in Fig.1(b). The peak intensity of Li-K gradually changed as the charge rate changed. The peak position of Li K is about 53.4 eV, suggesting that Li-Si alloying is in progress. On the other hand, the half-width and peak shape of Si-L also gradually changed with the change in charge rate. After discharge, the Li-K peak intensity became lower, and the Si-L peak shape was like that of amorphous silicon, indicating that the chemical state of the Si particles changed due to the desorption of Li.

These results show the continuous change of Si particle shape with Li insertion/extraction in the process of charging/discharging a single Si particle and the change of Si chemical state from crystalline silicon to amorphous state due to Li-Si alloying and discharge.

Acknowledgments

We would like to thank Professor Nobuya Machida of Konan University for cooperation in some of the battery sample preparation.

Figure 1

Abstract not Available.

In recent years, the lithium iron phosphate battery is widely used in the fields of electric vehicles and energy storage because of its high energy density, long cycle life and safety^[1], but the existing battery technology was not enough to meet the requirements of electric vehicles^[2]. So it is of great importance to research performances of battery.

In this paper, the influence of different depth of discharge (DOD) on the cycle life of the battery was investigated. The specific research process is as follows, three kinds of LiFePO₄ batteries of the same type were charged and discharged at three different discharge depths (30% DOD, 50% DOD and 100% DOD) under constant conditions of 40℃and 1C (1.3A), and the discharge capacity decay curve and decay rate curve were measured after a certain number of cycles.

Discharge capacity decay curve and decay rate curve measured under different discharge depth are shown in Figure 1. As can be seen from the left graphic, the discharge capacity of the battery will have a slight increase in the early, this is because the battery anode material has not been fully activated during the initial cycle, as the cycle progresses, the electrolyte gradually penetrates into the interior of the electrode material, and the lithium ions smoothly migrate to the inside of the electrode material and undergo reversible deintercalation reaction, resulting in an increase in the capacity of the battery. In addition, At the beginning of the cycle, the depth of discharge has little effect on the capacity of the three groups of batteries. When the cycle continues, the discharge capacity of the LiFePO₄ battery gradually decreased, the attenuation of battery capacity by the depth of discharge is more and more obvious. The right capacity fading rate curve shows that battery capacity decay rate remained the same at the beginning of the cycle. At this time, the influence of the battery capacity by depth of discharge is almost independent. After the initial cycle, the deeper the depth of discharge, the faster the cell capacity decays, and there is a significant the positive correlation between the depth of discharge and the decay rate of battery capacity. Due to the different depth of discharge, the internal structure of the electrode material will occur to different degrees of deterioration.

Fig. 1 the discharge capacity decay curve and decay rate curve under different discharge depth.

It can be seen from the above studies that the effect of the battery cycle life by depth of discharge is various in different cycle stages. In the early cycle, LiFePO₄ battery capacity at different depth of discharge changes in the same law, indicating that the depth of discharge has no effect on the battery life in the early cycle. But as the cycle continues, the greater depth of discharge, the faster decay of battery capacity, the battery cycle life decline faster.

Acknowledgements

This work is financially supported by the National High Technology Research and Development Program of China (863Program, no.2015BAG01B01).

References

[1] Forgez C, Vinh Do D, Friedrich G, et al. Thermal modeling of a cylindrical LiFePO4/graphite lithium-ion battery[J]. Journal of Power Sources, 2010,195(9):2961-2968.

[2] Ritchie A, Howard W. Recent developments and likely advances in lithium-ion batteries[J]. Journal of Power Sources, 2006,162(2):809-812.

Figure 1

Blended cathodes are one of new approach for enhancing both characteristics of different cathode active materials. In previous study, a blended cathode between olivine structural cathode active materials and layered lock salt cathode active materials are applied to lithium ion cell to realize high thermal stability derived from olivine and large capacity derived from layered rock salt type. The blended cathode between lithium iron phosphate (LFP: LiFePO₄) and lithium nickel cobalt manganese oxide (NMC_{1-x-y, x, y}: LiNi_1-x-yMn_xCo_yO₂) shows a high stability of crystal structure and large specific capacity. However, an operation voltage of LFP and NMC is 3.3 V and 3.8 V, respectively. The difference in their operation voltage leads to a poor performance of cathode. Recently, lithium manganese iron phosphate (LMFP: LiMn_1-xFe_xPO₄ /C) has been expected as a excellent cathode active material due to higher operation voltage and higher energy density than those of LFP. LMFP is prepared by a replacing of Fe by Mn in LFP. The Mn²⁺/Mn³⁺ redox can be used, leading to higher operating average voltage of 3.8V with high stability of ordinary olivine structure features (high stability, capacity:170 mA h g^-1, long cycle performance). Therefore, the blended cathode between LMFP and NMC has been expected as a new cathode with high performances. The cathode performance depends on the blending ratio between LMFP and NMC. The effect of blending ratio on cathode performance have been reported in previous study. Various NMCs has been widely used as a cathode active material. Recently, a lithium ion battery using high nickel NMC811 cathode have been actively studied, due to its high specific capacity. However, NMC811 cathode has a low thermal stability due to weak chemical bond between Ni and O, elution of Ni and Mn in an electrolyte and a crack formation due to volume expansion and shrinkage during charge and discharge cycles. These problems have to be solved to realize lithium ion battery with NMC811 cathode. In previous study, Both LMFP and NMC cathodes have been made by solid-state process. The blended cathode using cathode active materials made by solid-state reactions shows a concern in a sense of a cathode layer density.

In this study, physical properties and electrochemical performance of the blended cathode between LMFP made by hydrothermal-synthesis and NMC811 made by solid-state reaction were investigated by using laminated cells at room and high temperatures.

Slurry of the blended cathode was prepared by mixing of PVdF, conductive additive, and two cathode active materials into NMP. The making slurry was coated on carbon coated Al foil and dried at 80 °C for 3hr under vacuum. The fabricated electrodes were evaluated by half-cells and full-cells. The sample name was added based on the blending ratio of LMFP.

The morphology of LMFP particles in the blended cathodes was changed by a press process. The specific capacity of the blended cathode of LMFP 20 wt.% was 182 mA h g^-1 which was a larger specific capacity than 180 mA h g^-1 of NMC811 cathode. The blended cathode of LMFP 20 wt.% exhibited the lowest porosity among various blended cathodes, suggesting that LMFP may play a role in the formation of conductive pathway. In addition, the blended cathode of LMFP 20wt.% exhibited a good cycle performance 80% discharge capacity retention (based on 0.2C)) at room temperature, which was better than that of NMC811 (65% discharge capacity retention). After disassembling the full-cell, the cross-section of the cathode was observed with SEM. Many cracks were observed in the NMC811 particles in the NMC811 cathode. On the other hand, no cracks were observed in the NMC811 particles of the blended cathode, indicating that LMFP could suppress the crack formation in NMC811 particles. This is one of reasons for the high cycle ability of the blended cathode. A cycle performance at 60 °C showed that the discharge capacity of NMC811 cathode decreased during 300 cycles, whereas that of the blended cathode of LMFP 20wt.% also decreased with much better discharge retention. From the cross-sectional SEM images, may cracks in NMC811 were observed in both pure NMC cathode and LMFP 20wt.% blended cathode. However, a less crack formation of NMC811 was confirmed in the blended cathode of LMFP 20wt.%. Based on these results, the effect of the blended cathode can be explained. Firstly, the improvement in specific capacity is due to the conductive pathway of the LMFP. Secondly, the improvement in cycle performance is due to the suppression of crack formation in the NMC811.

Figure 1

Abstract not Available.

Cell reversal in lithium ion (Li-ion) batteries is the condition of the anode electrochemical potential rising above that of the cathode, resulting in a negative voltage measured at the cell level. There are two primary reactions that occur at the anode at high potentials which increase cell impedance: oxidation of copper current collector, and oxidization of the carbonate electrolytes to CO₂. At the cathode, the reducing potential can lead to the electrodeposition of copper to form dendrites, which pose a shorting risk if they bridge the anode and cathode. Cell reversal can be caused by poorly matched cells, a failure of the battery management electronics, or a defective cell in a pack. Under these conditions, one or several of the cells can go into reversal causing performance decreases or even a dangerous thermal runaway event. This paper examines a pack of commercial 18650 Li-ion cells in simulated geosynchronous orbit (GEO) test under conditions where one or more cells were forced into reversal.

Panasonic B cells were matched and assembled into a pack to create a virtual cell. Measurements were collected using matched current shunts, and cells were cycled at a 60% DOD, but with only 90% of removed charge replaced each cycle to simulate a battery management system failure. After failure, cells were non-destructively examined using CT X-ray, and then dissected for failure analysis.

The parallel cell pack operated far into reversal, with up to four complete cycles (Fig. 1) completed before all cells shorted. CT X-ray scans of the cells after shorting detectable amounts of copper dendrites in the cell, and demonstrated the first nondestructive test for cell reversal in Li-ion (Fig. 2). Destructive physical analysis of the cells showed extensive copper corrosion at the anode current collector as well as copper dendrites that were found to have fully penetrated the separator in selected areas.

These results show that these cells can operate several cycles into deep reversal without going into thermal runaway, despite the observed growth of copper dendrites which pierce the cell separator. This has strong implications on cell safety and battery management.

Figure 1

Molten salts have physical properties that include thermal stability over a large temperature range, low vapor pressure at high temperature, and are nearly immune to radiological effects. Due to these favorable properties, molten salts are being considered as a promising candidate for next generation heat transfer fluids for use in generation IV nuclear reactors. One drawback of molten chloride salts thermo-physical properties is their low specific heat capacity (around 1.0–1.5 (J/(g×K)). It has been shown that addition of nanoparticles in molten salts leads to a large increasing in the specific heat capacity of these salts, once melted with the particles. The aim of this study is to investigate the effect that nanoparticles have on specific heat capacity of zinc potassium chloride solutions. The hollow carbon nanospheres (hCNS, outer diameter is 20–30 nm; wall thickness 7 nm) and zeolite nanoparticles (ZSM-5, size 10–30 nm) were chosen for this study. The colloidal solutions of ZnCl₂–KCl (46 mol% KCl) eutectic melt (T_m.p. = 220 ^oC) with different amounts, 0.3 to 2 wt% of nanoparticles, were prepared by mechanical mixing of required amount of salt with nanoparticles at 350^oC for at least 24 hours until stable colloidal solutions were formed. Specific heat capacity of the samples was measured using a differential scanning calorimeter (HDSC; PT1000, Linseis Inc.) under the argon atmosphere according to established literature procedures. Measurements were carried out between 250–350^oC temperature region with 10^oC/min temperature rate using platinum crucibles with platinum lids for containment. The obtained experimental results (fig. 1) demonstrate that specific heat capacity of ZnCl₂–KCl eutectic melt increases with increasing amounts of both types of nanoparticles used to form the colloidal solution.

Figure 1

A multi-metric armband system capable of simultaneous measurement of electrocardiogram (ECG) and electrodermal activity (EDA) from left arm is presented for the assessment of sympathetic nervous response. The performance of of EDA module was validated against a BIOPAC MP160 system while a single-lead ECG module was used to capture heart rate variations simultaneously. The presented armband is anticipated to provide reliable data for the detection and prognosis of different physical and neuropsychological disorders such as autism and Alzheimer's disease.

Keywords: Sympathetic Nervous System; EDA; ECG; Left Arm; I. Introduction

Sympathetic nervous response (SNR) has been found to be correlated with numerous bodily and mental health disorders. Frequency analysis of heart rate variability (HRV) and electrodermal activity (EDA) are the only non-invasive methods to assess the dynamics of the autonomic nervous system. However, frequency analysis of the HRV method cannot separate the dynamics of the sympathetic and parasympathetic nervous systems. EDA is a reflection of the autonomic innervation of sweat glands resulting in the reflection of activity within the sympathetic branch of the autonomic nervous system. EDA, however, suffers from motion artifact and movement. Therefore, the simultaneous monitoring of EDA and electrocardiogram (ECG) will provide more reliable and comprehensive indices of sympathetic nerve activities. Time-domain features of EDA along with ECG has been commonly utilized to assess the overall SNR.

The mere relationship between the EDA and SNR has been investigated via different approaches such as the analysis of power spectral density and time-varying analysis of EDA. The combined use of ECG/HRV and EDA has lent itself to assessing mental stress and numerous mental disorders such as schizophrenia, autism, Down syndrome. Also, it was found that EDA and SNR are heavily invested in the volume of white matter in the cingulum and inferior parietal and thus with Alzheimer's disease.

In this paper we have laid out the groundwork required for SNR evaluation, which takes advantage of the simultaneous EDA and ECG data acquisition from the left arm. II. System Design

The wearable armband system, Gen2.0, is constructed with commercial off-the-shelf components (COTS) and equipped with a BLE-enabled Nordic nRF51822 microcontroller unit (MCU) and is considered low-power [1]. We custom designed the filters for the AD8232 ECG analog frontend chip so that the left arm ECG signal is clear and reliable. The analog frontend for EDA was also custom designed using LTC 6081 op-amp to achieve a sufficiently high resolution. The MCU interfaces with an ADC 1114 for ECG measurement and uses an internal ADC for interfacing the EDA signal. Under the control of an internal timer, the ADC chip examples voltage and conductance signals from ECG and EDA frontends at a specific point depending on sampling frequency. Then the signals are converted into digital data and fed into the MCU. The MCU stores it inside buffers (capacity of 64 data samples) for ECG and EDA data separately. Every time the buffer is full, data will be either stored in a flash or transmitted via BLE. Figure 1 shows the system and the optimal ECG electrodes' positions. III. EDA Optimization And Validation

The performance of our armband ECG was validated against the BIOPAC direct ECG1 system. The optimal positions for EDA electrodes were determined through a set of external physical stimuli (pinch) tests. The accuracy of the used ECG module has already been verified in our previous study [2]. Figure 2 shows the system diagram and the candidate EDA electrode positions. Both the BIOPAC and our Gen2.0 modules were assigned an equal sample rate of 10Hz. IV. Results And Discussion B. EDA Validation

EDA curves were collected from a 38YO non-smoker male subject by both the BIOPAC and our proposed systems in an IRB- approved study (12418, North Carolina State University). The subject relaxed for an undisclosed amount of time (about 25s) and was then pinched in the right hand for 1s and relaxed for the rest of the test. The optimal electrodes' positions for our EDA module were found to be positions 10&13 or 1&2 (Figure 2). Figure 3 shows that the EDA obtained by the proposed system was more stable than that of BIOPAC addressing the relaxation and tension periods more distinctively. C. Simultaneous EDA and ECG

A testing protocol including resting, reading Latin, and being pinched (for 1s) and resting each for about 60s was followed. The ECG and EDA measurements were both carried out using the same armband and in real-time (Figures 4).

Considering the EDA results, the nervous response to the physical stimulus (being pinched) was stronger than the cognitive stimulus (reading). HRV analysis was done in time domain by detecting RR intervals in order to capture instant changes in heart rate in the ECG data. V. Conclusions

A wearable and low-power multi bio-metric armband system was proposed and validated for simultaneous monitoring of ECG and EDA. The current research lays out the groundwork for more in-depth characterization of the autonomic sympathetic nervous system and its relationship to both bodily and neurological disorders obtained from the left arm.

References

• Nozariasbmarz et al, "Review of wearable thermoelectric energy harvesting: From body temperature to electronic systems," Applied Energy, vol. 258, pp. 114069, 2020.

• Mohaddes et al, "A Pipeline for Adaptive Filtering and Transformation of Noisy Left-Arm ECG to Its Surrogate Chest Signal," Electronics (Basel), vol. 9, (5), pp. 866, 2020.

Figure 1

Electrifying mobility and implementing more renewable energies in our energy mix to reduce global warming and limit the climate crisis will be two targets that will require massive energy storage devices in the near future. Li batteries is one of the most promising technology for electrochemical storage to meet these challenges requiring safe and high performance cells. Li metal batteries and solid state electrolytes SSE may try to tackle these safety[1] and energy densities[2] challenges. Research pay attention to the development of several families of SSE based on oxide, sulfur or polymer moieties exhibiting pros and cons in terms of stability, safety, processability and cell and module integration. Despite their ease of processability, polymer based SSE suffur from their low ionic conductivity at room temperature and poor chemical stability towards Li metal[3]. Recently, a new class of organic materials based on charge-transfer complexes (CTCs) is drawing attention. The donor / acceptor couple associated with a lithium salt shows great ionic conduction properties up to 0,1-1 mS.cm-1 at room temperature[4]. This complexes are widely studied as fast electronic conductors for decades while their potential for ionic electrolytes, where low electronic conductivity is mandatory to prevent self-discharge, has to be studied in depth [5].

In this presentation, we will share our latest results on solid electrolytes made up of organic charge-transfer complexes. Both small molecules and polymers will be investigated to synthesize SSE by mixing it with a lithium salt. Donor and acceptor chemical structures, CTC / Li salt molar ratios will be modified to tune salt dissociation and ionic conductive properties of the SSE. While these electrolytes are currently processed as powders, fabricating films thanks to the use of binders will further improve the overall ionic conductivity. Molar ratio of CTC / binder and salt will be modified to develop optimized formulations allowing to easily process electrolytes and catholytes for full cell characterization. Ionic conductivities up to 0,02 mS.cm-1 were obtained at room temperature and are currently being improved with work on formulation and sample processing. Incorporate very low content of plasticizers might be used to improve room temperature properties. Electrochemical stability in full cell integration and competitive SSE ionic conductivity will also be shown. Advanced characterization will be used to understand the way it works to reduce the lack of sample reproducibility and to investigate these new ionic transport mechanisms involved through these materials.

[1] L. Yue et al, Energy Storage Mater, 5 (2016) 139-165.

[2] X. Cheng et al, Chem. Rev., 117 (2017) 10403-10473.

[3] J. Mindemark et al, Prog. Polym. Sci., 81 (2018) 114-143.

[4] K. Hatakeyama-Sato et al, ACS Appl. Electron. Mater., 2 (2020) 2211-2217.

[5] Yang et al., ASC Energy letters, (2023), 8, 2426-2431.

Lithium-sulfur batteries (LSBs) are a promising technology for electrochemical energy storage, particularly for portable electronics and electric vehicles due to their high theoretical energy density and cost-effectiveness of sulfur. However, they face limitations in rate capability and lifespan due to the sluggish conversion kinetics of sulfur and the soluble lithium polysulfide (LiPS) intermediate. In this presentation, we will discuss various approaches that utilize modified interlayers, especially mesoporous materials, to overcome the challenges associated with lithium-sulfur batteries (LSBs) and enhance their performance. These approaches have been proposed as potential solutions to improve the efficiency and overall capabilities of LSBs.

Sodium metal batteries (SMBs) have been considered as one of the most favorable and economic candidates for next generation batteries to overcome low enenrgy density limitation of sodium ion batteries (SIBs) due to high theoretical specific capacity (1166 mAh g^-1), low electrochemical redox potential (-2.71 V vs. SHE). However, 'moss-like' dendrite growth that occurs during continuous charging and discharging processes not only threatens the safety of batteries, but also poses several problems to be solved, such as electrolyte consumption, hugh volume expansion, dead Na formation, and low coulombic efficiency. The dendrite problem in the SMBs is similr to that of lithium-metal batteries (LMBs), yet the degree of the issue is further severe than LMBs. Surface stabilization of sodium metal anode should be achieved to realize SMB technologies.

The introduction of functional electrolyte additives is an effective and economical way to overcome these problems and improve the cyclability of SMBs. Based on the similarity between electroplating and sodium deposition reaction, utilization of surface leveler additive in the electrolyte could allow a substantial impact to stabilize sodium metal surface during repeated deposition and stripping process.

In this presentation, we confirmed the surface flattening effect of molecular dipole electrolyte additives at the anode through the Na-Na symmetric cell test. Sodium metal deposition and stripping behavior has been successfully controlled by introducing surface leveler additives for realization of SMBs. Even under rapid charging and discharging situations, additive containing Na-Na symmetric cells showed stable performance for over 2000 hours, which is 5 times longer than the pristine cell without the additive. We confirmed that controlling intrinsic properties of surface leveler additive can effectively further improve cycle performance of SMBs.

[1] S.-Y. Jun, K. Shin, C. Y. Son, J. Park, H.-S. Kim, J.-Y. Hwang, W.-H. Ryu, Advanced Energy Materials, 2024, 2304504

[2] S.-Y. Jun, K. Shin, Y. Lim, S. Kim, H. Kim, C. Y. Son, W.-H. Ryu, Small Structures, 2024, 5, 2300578

[3] S.-Y. Jun, K. Shin, J.-S. Lee, S. Kim, J. Chun, W.-H. Ryu, Advanced Science, 2023, 10, 2301426

[4] J.-S. Lee, K. Shin, S.-Y. Jun, S. Kim, W.-H. Ryu, Chemical Engineering Journal, 2023, 458, 141383

Figure 1

With the advancement of the automobile and aerospace industries, carbon fiber reinforced plastic (CFRP), known for its high specific stiffness and strength, has been utilized to construct lightweight structures. Research is now focusing on structural batteries that combine CFRP structures with energy storage capabilities. Among these, sandwich-type structural batteries, which embed commercial batteries between CFRP skins, are nearing industrialization due to their high energy density and stability. However, a significant limitation is that these structural batteries cannot be replaced once the embedded battery's lifespan is exhausted. To address this issue and maximize the lifespan of the embedded battery, we propose a sandwich-type structural battery with integrated pressurization and preheating functions. By applying pressure through the fastening force of curved CFRP skins, the capacity retention of the embedded battery is enhanced, thereby extending its lifespan. Additionally, we developed a thermal management system for the structural battery using hybrid composites made of carbon paper and glass fabric as compression pads. The integrated pressurization and thermal management system are secured with CFRP brackets, completing the structural battery design.

Since the use of tricarbonyl compounds (e.g. dichloroisocyanuric acid) as electrode materials for primary lithium batteries dates back to the 1960s, organic molecules have received significant attention as a means to further advance the state-of-the-art electrode materials for rechargeable batteries due to their advantages, including abundance, high energy density, design flexibility, environmentally benign nature, mild synthesis processes, and cost competitiveness. Numerous molecular design strategies have been employed to achieve high performance in organic electrode materials for rechargeable batteries. For examples, the organic molecular structure can be optimized to provide high specific capacity by minimizing the redox-inactive parts, exploiting multiactive centers, or introducing electron activating and deactivating groups. In addition, cycle stability can be controlled by polymerization of the active-molecules and electrical conductivity can be increased by enhancing electron delocalization, inter- (p-d) and intra-molecular (p-p) conjugation in aromatic rings of the organic molecules.

Herein, we provide a novel design of organic electrode for high discharge voltage with superior cycling stability in rechargeable battery by using steric effect of substituted the single molecule. 16,17-dihydroxyviolanthrone (DHV) molecule was used as a single molecule model for control group because the violanthrone compound has a planar conformation overlapping sp² hybridized carbon and its hydroxyl groups that can be substituted with a variety of substituents. The electrochemical performance of DHV cathode and its reversible redox process in rechargeable battery system were demonstrated through experimental and theoretical identification at the first time. To further advance the battery performance of the DHV through the steric hindrance effect, we substituted main functional group (-OH) of DHV nearby p-type redox center with long-chain alkoxy group (-OC₈H₁₇ or -OC₁₀H₂₁) leading to ether, which are dioctiloxyviolanthrone (DOV) and didecyloxyviolanthrone (DDV), respectively.

In comparison to DHV, DOV and DDV showed significant increase of redox potential of the oxidation reaction allowing battery with around 0.6 V higher operating voltage. We further substantiated the steric hindrance effect from long-chain alkoxy groups on coupling electrolyte anion (PF₆^-) with charged DOV and DDV via computational simulation and theoretical studies based on density functional theory (DFT). Moreover, we showed that the bipolar nature of the violanthrones allows its application in symmetrical cells, though the cycling performance was limited by the reduction reaction stability. Additionally, we demonstrated that finding of the more suitable electrolyte could lead to greatly enhanced stability of the violanthrone electrodes allowing up to 2000 cycles without capacity reduction and reduced voltage decay. Finally, based on various analytical methods, we demonstrated that the oxidation occurs through withdrawing of the delocalized electrons from the large conjugated structure of the violanthrones, and that the main the p-type redox site could be determined to be the moiety of (-(ROC)C-C-C-C(COR)-). Thus, this molecular design approach allows development of organic cathode with a high redox potential, comparable to the conventional cathode materials, and potentially may lead to future all-organic symmetric batteries.