複雑な固体材料界面の電子・イオン状態の高精度シミュレーション手法を開発 〜全固体電池の電極—固体電解質ヘテロ固固界面の最適設計が加速〜

館山佳尚GL（物質・材料研究機構：計画A03）

【概要】

NIMSは、全固体電池などの蓄電固体デバイス内に存在する異なる材料間のヘテロ固固界面の電子・イオン状態を高精度・高効率に解析可能な計算手法の開発に成功しました。これにより、例えば全固体電池のイオン伝導に関するボトルネックである電極—固体電解質ヘテロ固固界面のミクロレベルでの制御指針の獲得が進み、蓄電固体デバイス開発の更なる加速が期待されます。

Abstract

High interfacial resistance between a cathode and solid electrolyte (SE) has been a long-standing problem for all-solid-state batteries (ASSBs). Though thermodynamic approaches suggested possible phase transformations at the interfaces, direct analyses of the ionic and electronic states at the solid/solid interfaces are still crucial. Here, we used our newly constructed scheme for predicting heterogeneous interface structures via the swarm-intelligence-based crystal structure analysis by particle swarm optimization method, combined with density functional theory calculations, and systematically investigated the mechanism of Li-ion (Li⁺) transport at the interface in LiCoO₂ cathode/β-Li₃PS₄ SE, a representative ASSB system. The sampled favorable interface structures indicate that the interfacial reaction layer is formed with both mixing of Co and P cations and mixing of O and S anions. The calculated site-dependent Li chemical potentials μ_Li(r) and potential energy surfaces for Li⁺ migration across the interfaces reveal that interfacial Li⁺ sites with higher μ_Li(r) values cause dynamic Li⁺ depletion with the interfacial electron transfer in the initial stage of charging. The Li⁺-depleted space can allow oxidative decomposition of SE materials. These pieces of evidence theoretically confirm the primary origin of the observed interfacial resistance in ASSBs and the mechanism of the resistance decrease observed with oxide buffer layers (e.g., LiNbO₃) and oxide SE. The present study also provides a perspective for the structure sampling of disordered heterogeneous solid/solid interfaces on the atomic scale.

Bo Gao, Randy Jalem, Yanming Ma, Yoshitaka Tateyama, Chem. Mater. 32, 85-96 (2020). "Li⁺ Transport Mechanism at Heterogeneous Cathode / Solid Electrolyte Interface in All-Solid-State Battery via First-Principles Structure Prediction Scheme"

DOI: 10.1021/acs.chemmater.9b02311

Published on November 20, 2019

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