Cation Vacancies Enable Anion Redox in Li Cathodes

26 April 2024, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


Conventional Li-ion battery intercalation cathodes leverage charge compensation that is formally associated with redox on the transition metal. Employing the anions in the charge compensation mechanism, so-called anion redox, can yield higher capacities beyond the traditional limitations of intercalation chemistry. Here, we aim to understand the structural considerations that enable anion oxidation and focus on processes that result in structural changes such as the formation of persulfide bonds. Using a Li-rich metal sulfide as a model system, we present both first-principles simulations and experimental data that show cation vacancies are required for anion oxidation. First-principles simulations show that oxidation of sulfide to persulfide only occurs when a neighboring vacancy is present. To experimentally probe the role of vacancies in anion redox processes, we introduce vacancies into the Li2TiS3 phase while maintaining a high valency of Ti. When the cation sublattice is fully occupied and no vacancies can be formed through transition metal oxidation, the material is electrochemically inert. Upon introduction of vacancies, the material can support high degrees of anion redox even in the absence of transition metal oxidation. The model system offers fundamental insights to deepen our understanding of structure-property relationships that govern reversible anion redox in sulfides and demonstrates that cation vacancies are required for anion.


anion redox
cation vacancies
Li-rich cathodes
sulfide oxidation

Supplementary materials

Supplementary Materials for: Cation Vacancies Enable Anion Redox in Li Cathodes
XRD with Rietveld refinements and corresponding Vegard plots, high resolution TEM, parameters of Rietveld refinements, galvanostatic discharge curves of LiTi0.75_0.25S2 in a Mg electrolyte, 6Li and 7Li NMR, structural DFT enumerations, EPR sepctra, GITT, electrochemistry of LixTi0.75S2 materials, operando XRD of LiTi0.75S2, Ti XANES, S XES data.


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