高エネルギー密度蓄電池材料の発見 ～高いエネルギー密度と低コストの両立を実現～
藪内 直明 教授（横国大：計画A04）中山 将伸 教授（名工大：計画A03）
【概要】
横浜国立大学の藪内直明教授らの研究グループは、マンガンとチタンから構成されたナノサイズ試料を合成することで、大きな放電容量と高いエネルギー密度を実現する新しい電池材料の開発に成功しました。既存の電気自動車で用いられているコバルトやニッケルを利用しない低価格・高性能なリチウムイオン蓄電池の実現は、電気自動車の普及にも繋がると期待できます。
本研究成果は、国際科学雑誌「Materials Today」(2018 年度インパクトファクター 24.372)に掲載されました (2020年3月25日付)。
Abstract
A binary system of Li2TiO3–LiMnO2 is systematically examined by joint experimental and theoretical studies as electrode materials for Li storage applications. Increase in a fraction of Li2TiO3 effectively activates anionic redox, and thus holes are reversibly formed on oxygen by electrochemical oxidation. Such holes are energetically stabilized through π-type interaction with Mn t2g orbital as suggested by theoretical calculation. However, excess enrichment of Li2TiO3 fractions in this binary system results in the oxygen loss as an irreversible process on delithiation because of a non-bonding character for Ti–O bonds coupled with the formation of O–O dimers, which are chemically and electrochemically unstable species. Additionally, detailed electrochemical study clearly shows that Li migration kinetics is relatively slow, presumably coupled with low electronic conductivity. Nevertheless, nanosizing of primary particles is an effective strategy to overcome this limitation. The nanosized sample prepared by mechanical milling delivers a large reversible capacity, ∼300 mA h g−1, even at room temperature and shows much improved capacity retention. Formation and stabilization of holes for the nanosized sample are also directly evidenced by soft X-ray absorption spectroscopy. From these results, factors affecting the reversibility of anionic redox as emerging new chemistry and its possibility for energy storage applications are discussed in more details.
Yuki Kobayashi, Miho Sawamura, Sayaka Kondo, Maho Haradam Yusuke Noda, Masanobu Nakayama, Sho Kobayakawa, Wenwen Zhao, Aiko Nakao, Akira Yasui, Hongahally Basappa Rajendra, Keisuke Yamanaka, Toshiaki Ohta, Naoaki Yabuuchi, Mater. Today 37, 43-55 (2020). "Activation and stabilization mechanisms of anionic redox for Li storage applications: Joint experimental and theoretical study on Li2TiO3-LiMnO2 binary system",
DOI: 10.1016/j.mattod.2020.03.002
Available online on March 25, 2020
