Your search for "Gerbrand Ceder" returned 37 results

solid solutions of structure type have been synthesized from homogeneous hydroxide precursors. X‐ray powder diffraction and scanning transmission electron microscopy show that single‐phase solid solutions are formed up to y ≈ 0.5 at 800°C in air. Electrochemical tests using nonaqueous liquid electrolyte cells shows that the open‐circuit voltage and working voltage increase with Al content as predicted by ab initio calculations [Ceder et al., Nature, 392, 694 (1998)], while capacity fade was significant during cycling at room temperature. However, both the absolute capacity and cycleability were improved at 55°C. © 1999 The Electrochemical Society. All rights reserved.

We have investigated phase stability in the layered intercalation compound for x < 0.4 from first principles. By combining a lattice model description of the Li‐vacancy configurational degrees of freedom with first‐principles pseudopotential calculations, we have calculated the free energy of the material as a function of Li concentration in three different host structures: (i) the rhombohedral form of , (ii) the hexagonal form of , and (iii) a stage II compound of in which the host structure can be considered as a hybrid of the rhombohedral and hexagonal host structures. The first‐principles free energies indicate that the stage II compound is the most stable of the three phases for Li concentrations ranging between 0.12 and 0.19. This result is consistent with the experimental observation by Ohzuku and Ueda and Amatucci et al. that the rhombohedral form of transforms to a new phase at Li concentrations around x = 0.15. We find that the calculated X‐ray powder diffraction patterns of the stage II structure agree qualitatively with those observed experimentally at low Li concentration.

NaTi_0.25Fe_0.25Co_0.25Ni_0.25O₂ is explored as a cathode material for Na-ion batteries. Synthesized by a solid-state reaction, the compound is phase-pure with the O3-type layered structure and consists of Ti⁴⁺, Fe³⁺, Co³⁺, and Ni²⁺ according to X-ray absorption spectroscopy. The cathode delivers 163 mAh/g and 504 Wh/kg at C/20 in the first discharge with 89% capacity retention after 20 cycles and demonstrates superior rate capability with micron sized particles, in which discharge capacity at 30 C is 80 mAh/g. Our results indicate that the Ti-containing quaternary material can be a potential cathode composition for Na-ion batteries.

Short-range ordering in was investigated with NMR and first principles structure computations. NMR indicates that the tendency for to replace in the layers decreases with decreasing nickel content. Li in the Ni/Mn layers preferentially occupies sites near and avoids the ions, leading to nonrandom configurations. Calculations indicate that the ground state of contains zigzag rows of and ions. Although a disordering temperature of approximately 1000 K is calculated, ordered fragments persist above the phase transition and these materials contain significant short-range order, even when quenched from high temperature. © 2004 The Electrochemical Society. All rights reserved.

An initial search with density functional theory to sort through potential cathode materials based on their Li intercalation potentials and electronic structures was carried on systems, where TM1 is a 3+ transition metal etc.) and TM2 is a 4+ transition metal etc.). Fe substitution is found to be advantageous because among the compounds investigated it shows the lowest voltage at the last stage of the charge. was synthesized by a sol-gel method and used to confirm that Fe substitution leads to a lower potential at the end of charge. Both X-ray photoelectron spectroscopy and first principles electronic structure computations indicate that Ni and Fe are simultaneously oxidized in this material. Computations further indicate that Co will only be oxidized at the very end of charge. The compound synthesized at 750°C shows reversible capacity of 150 mAh/g with reasonably good capacity retention. © 2004 The Electrochemical Society. All rights reserved.

A combination of first principles calculations and lithium NMR spectroscopy was used to examine the effect of electrochemical cycling on lithium ions located in the transition metal layers in layered lithium nickel manganates. These lithium ions participate in the electrochemical process with NMR results showing that they are removed from the octahedral sites on charging, but return on discharging. Calculations indicate that the lithium ions become increasingly unstable, as the concentration of vacancies in the lithium layers increases. A lithium ion nearby three vacancies in the lithium layers drops immediately, with no activation barrier, into the adjacent tetrahedral site in the lithium layers; charging to higher potentials is then required to remove this lithium ion. © 2004 The Electrochemical Society. All rights reserved.

First principles calculations have been used to explore the Li–Bi–F ternary phase diagram. Our results confirm the thermodynamic stability of previously observed phases and find no new phases in this system. Electrochemical voltage profiles for the reaction of Li and are in reasonable agreement with experiment. The driving force to form ternary Li–Bi–F intermediates is small. We also investigated the effect of particle size on the reaction voltage and find a potential decrease when nanoscale vs bulk Bi forms upon reacting with Li.

was synthesized from an off-stoichiometric mix of starting materials with nominal composition . Stoichiometric with particle size was found with X-ray diffraction even with the large overall deviation from stoichiometry in the sample, indicating that other noncrystalline compounds are present. The off-stoichiometric sample had a discharge capacity of 145 mAh/g at C/10 and at 2C after a constant current constant voltage charge. Capacity retention was excellent without a significant capacity loss at 1C. The performance of could not be significantly improved by diluting the electrode with more carbon, indicating a more intrinsic kinetic limitation of the material for in contrast to [ Nature (London) , 458 , 190 (2009) ]. This is further corroborated by the difference in the overpotential between the two materials. Although has a sloping voltage profile, tends to have a constant overpotential at high rate.