Cation Vacancies Enable Anion Redox in Li Cathodes

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Conventional lithium-ion battery cathodes rely on transition metal redox for charge compensation.
• Anion redox offers a pathway to exceed capacity limitations of traditional intercalation chemistry.
• Understanding structural requirements for anion redox is crucial for developing advanced battery materials.

Purpose of the Study:

• To investigate the structural prerequisites for anion oxidation in battery materials.
• To elucidate the role of cation vacancies in enabling anion redox processes.
• To explore persulfide bond formation during anion oxidation in a Li-rich metal sulfide.

Main Methods:

• First-principles simulations to model anion oxidation mechanisms.
• Experimental synthesis and electrochemical characterization of Li-rich metal sulfides.
• Introduction of controlled cation vacancies in Li2TiS3 to probe their effect on anion redox.

Main Results:

• First-principles simulations confirm that anion oxidation to persulfide requires a neighboring cation vacancy.
• Experimental data shows that Li2TiS3 with a fully occupied cation sublattice is electrochemically inert.
• Introduction of cation vacancies enables significant anion redox activity, even without transition metal oxidation.

Conclusions:

• Cation vacancies are a fundamental requirement for enabling reversible anion redox in metal sulfides.
• Persulfide formation is directly linked to the presence of cation vacancies.
• This research provides critical insights into structure-property relationships for high-capacity anion redox materials.