Anion Redox in an Amorphous Titanium Polysulfide

Keiji Shimoda; Kentaro Kuratani; Shunsuke Kobayashi; Tomonari Takeuchi; Miwa Murakami; Akihide Kuwabara; Hikari Sakaebe

doi:10.1021/acsami.2c07337

Anion Redox in an Amorphous Titanium Polysulfide

ACS Appl Mater Interfaces. 2022 Jul 13. doi: 10.1021/acsami.2c07337. Online ahead of print.

Authors

Keiji Shimoda¹, Kentaro Kuratani², Shunsuke Kobayashi³, Tomonari Takeuchi², Miwa Murakami¹, Akihide Kuwabara³, Hikari Sakaebe²

Affiliations

¹ Office of Society-Academia Collaboration for Innovation, Kyoto University, Uji, Kyoto 611-0011, Japan.
² National Institute of Advanced Industrial Science and Technology, Ikeda, Osaka 563-8577, Japan.
³ Nanostructures Research Laboratory, Japan Fine Ceramics Center, Atsuta, Nagoya 456-8587, Japan.

PMID: 35829727
DOI: 10.1021/acsami.2c07337

Abstract

Amorphous transition-metal polysulfides are promising positive electrode materials for next-generation rechargeable lithium-ion batteries because of their high theoretical capacities. In this study, sulfur anion redox during lithiation of amorphous TiS₄ (a-TiS₄) was investigated by using experimental and theoretical methods. It was found that a-TiS₄ has a variety of sulfur valence states such as S^2-, S^-, and S^δ-. The S^2- species became the main component in the Li₄TiS₄ composition, indicating that sulfur is a redox-active element up to this composition. The simulated a-TiS₄ structure changed gradually by lithium accommodation to form a-Li₄TiS₄: S-S bonds in the disulfide units and polysulfide chains were broken. Bader charge analysis suggested that the average S valency decreased drastically. Moreover, deep lithiation of a-TiS₄ provided a conversion reaction to metallic Ti and Li₂S, with a high practical capacity of ∼1000 mAh g^-1 when a lower cutoff voltage was applied.

Keywords: X-ray photoelectron spectroscopy; amorphous transition-metal polysulfides; anion redox; density functional calculations; lithium−sulfur batteries; operando NMR spectroscopy.