Computational Design and Preparation of Cation‐Disordered Oxides for High‐Energy‐Density Li‐Ion Batteries

Abstract

also been experimentally verifi ed. [ 1,7 ] This is in line with the general strategy to utilize Li-excess chemistries to achieve higher energy densities. [13][14][15] However, Li-excess materials often suffer from structural instabilities that give rise to phase transitions and degradation upon repeated cycling. [16][17][18][19] As a possible remedy, cation disorder was found to enhance the structural stability upon Li extraction, which makes it possible to achieve high reversible capacities and reduces the overall volume change with varying lithium content. [ 1 ] Minimizing volume fl uctuations is benefi cial for all electrodes, but is especially important for solid-state batteries in order to prevent fracturing of the solid/solid electrode/electrolyte interfaces, [ 20,21 ] and as such cation-disordered electrodes are particularly attractive for all-solid batteries.The stringent electronic structure requirements on TM ions in structures that need to remain well layered [ 22,23 ] have limited the active chemistry of cathode oxides to just a few elements such as Co and Ni. On the other hand, the composition space for potential cation-disordered oxides is vast, as TM mobility is not a constraint. Indeed, many of the new disordered cathodes contain elements such as Cr, Mo, Ti, and Nb, which were usually not used in well-ordered cathodes. Because of this, identifying the compositions of new cation-disordered oxides is a critical bottleneck for the discovery of improved disordered cathode materials. One successful strategy for the rational design of new cation-disordered Li-excess cathode materials has been to introduce excess Li into known stoichiometric disordered compositions, such as LiTi 0.5 Ni 0.5 O 2 [ 8,24,25 ] and LiTi 0.5 Fe 0.5 O 2 . [ 7,26,27 ] This approach is, however, limited by the small number of presently known cation-disordered Li-TM oxides. While it is in some cases possible to impose cation disorder to otherwise ordered crystal structures by means of mechanochemical synthesis routes, [ 28 ] a complete library of materials that potentially form in the disordered rocksalt structure would accelerate the development of cation-disordered cathode materials.With this motivation in mind, the objective of the present work is to introduce a straightforward methodology for the computational prediction of new disordered rocksalts and to demonstrate its practicality by identifying and synthesizing a novel cation-disordered oxide. In the following Section 2 the computational methods, synthesis procedures, and characterization techniques are outlined. This is followed by a report of Cation-disordered lithium-excess metal oxides have recently emerged as a promising new class of high-energy-density cathode materials for Li-ion batteries, but the exploration of disordered materials has been hampered by their vast and unexplored composition space. This study proposes a practical methodology for the identifi cation of stable cation-disordered rocksalts. Here, it is established that the effi cient method, which makes...

Fluorination of Lithium‐Excess Transition Metal Oxide Cathode Materials

“…The trends in disordering temperature are in line with previous DFT results on the stoichiometric LMOs [32,39] and with the experimental observation that the titanium compound forms in a disordered state upon solid-state synthesis. Since the high temperature miscibility gap is between two compositions of the disordered rock salt phase, above the eutectic point this phase boundary is identical between the equilibrium and disordered phase diagrams.…”

Reversible Delithiation of Disordered Rock Salt LiVO2

“…[33] Changes during discharge, charge and upon extended cycling could thus contribute to deviations. Liion diffusion, which could change upon cycling due to disorder [5,34] may increase the kinetic polarization. Besides these reversible changes in LiVO 2 , irreversible changes could also occur during cycling: e. g., vanadium dissolution and electrolyte degradation.…”

Combined Theoretical and Experimental Studies of Sodium Battery Materials

“…Now, real‐time collaboration of theorists and experimentalists is commonplace in efforts to understand the mechanism of battery reactions. Density functional theory (DFT) provides insight into essential battery properties such as average voltages, activation energy of ion‐diffusion, thermodynamic stability, spatial distribution of electrons, lattice vibrations, elastic properties, and spectroscopic assignments . These features are determined from static calculations through total energy and/or Kohn‐Sham orbitals with moderate calculation costs.…”