硫化物系電池材料の特性を巡る長年の謎を解明
藪内直明教授（横浜国立大学：計画A02）
【概要】
横浜国立大学 藪内直明教授、名古屋工業大学 中山将伸教授、島根大学 尾原幸治教授、東北大学 髙橋幸生教授、群馬大学 鈴木宏輔准教授、立命館大学 SRセンター、National Synchrotron Radiation Research Center (台湾) からなる研究グループは、構造の規則・不規則性を制御したリチウム過剰系硫化物材料の充放電反応機構を実験・理論の観点から詳細に解析しました。その結果、構造の不規則化が鍵となり、硫化物イオンにおいて電子の非局在化が進行することで電子伝導性の向上と電池性能の高性能化に繋がることを明らかにしました。これは、従来層状構造の限界を超える、次世代の電池材料設計指針の確立とリチウムイオン電池の高性能化実現が期待できる研究成果です。
本研究成果は、米国化学会の科学雑誌 「Journal of the American Chemical Society」誌に2025年7月15日（米国東部時間）にオンラインで掲載されます。論文DOI: 10.1021/jacs.5c04018
Abstract
Extensive research efforts have been dedicated to Li-excess compounds with anionic redox reaction as potential high-capacity positive electrode materials for Li-ion battery applications. The origin of activation on anionic redox is still under debate, and a unified understanding is necessary, especially for sulfide-based compounds without conductive d electrons. Herein, joint experimental and theoretical study is conducted for Li-excess and stoichiometric compounds with different crystal structures, cation-disordered rocksalt, and cation-ordered layered structures. In contrast to the understanding of Li-excess oxides, sulfide-based compounds with ordered layered structures are electrochemically less active compared with the materials with disordered structure. Theoretical study reveals that a unique local structure for a sulfide ion coordinated by 6 Li ions, SLi6 configuration, is formed, which can be found only for the disordered structure and not for the layered structure. The unique local structure triggers electron delocalization for sulfide 3p orbitals, leading to superior electronic conductivity, as experimentally evidenced, and thus anionic redox is successfully activated. Furthermore, such nonuniform local structures lead to easier structural distortion and efficient S–S dimerization, and even trimerization (S32–), upon delithiation. Although sulfide-based compounds as battery electrode materials suffer from dissolution after oxidation, this practical problem is effectively mitigated by the use of highly concentrated electrolyte solutions with fewer free solvent molecules, leading to superior reversibility for anionic redox. The insights derived can guide the development of high-energy electrode materials with anionic redox with or without transition metal ions possessing conductive d electrons.
M. Shinoda, K. Matsunoshita, M. Nakayama, S. Hiroi, K. Ohara, M. Abe, N. Ishiguro, Y. Takahashi, G. Hasegawa, N. Kuwata, T. Iwama, T. Masuda, K. Suzuki, H. Ishii, Yu-C. Shao, D. Shibata, A. Irizawa, T. Ohta, I. Konuma, T. Ohno, Y. Ugata, *N. Yabuuchi, J. Am. Chem. Soc. (2025). "Activation of anionic redox for stoichiometric and Li-excess metal sulfides through structural disordering:joint experimental and theoretical study"