次世代冷却バッテリーの研究（Cool battery power）

2025-10-22 カリフォルニア大学リバーサイド校（UCR）

カリフォルニア大学リバーサイド校（UCR）の研究チームは、次世代リチウム固体電池の電解質材料「LLZTO（リチウム・ランタン・ジルコニウム・タンタル酸化物）」が発熱を抑える理由を原子レベルで解明した。研究はPRX Energy誌に掲載。LLZTOは銅の約250分の1という極めて低い熱伝導率を持ち、発火リスクを低減できる。単結晶解析と中性子散乱実験により、原子の振動（フォノン）のうち、光学モードが音響モードを散乱させ、熱輸送を妨げることが主因と判明。また、イオン移動に関連する強い非調和性も影響していた。この性質を利用すれば、エネルギー密度が高く安全性の高い固体電池設計が可能になる。研究はUCR電気・コンピュータ工学科のXi Chen准教授と大学院生Yitian Wangが主導し、米・欧・スイスの複数機関と協働して実施された。

Lithium batteries in laptop computers can sometimes heat up and cause fires. (Getty Images)

＜関連情報＞

ガーネット型固体電解質における本質的に低い熱伝導率の起源：格子およびイオンダイナミクスと熱輸送の関連 Origin of Intrinsically Low Thermal Conductivity in a Garnet-Type Solid Electrolyte: Linking Lattice and Ionic Dynamics with Thermal Transport

Yitian Wang, Yaokun Su, Jesús Carrete, Huanyu Zhang^,, Nan Wu, Yutao Li, Hongze Li, Jiaming He, Youming Xu et al.
PRX Energy Published: 17 July, 2025
DOI: https://doi.org/10.1103/6wj2-kzhh

Abstract

Understanding thermal transport in solid electrolytes is essential for improving the performance, reliability, and safety of all-solid-state batteries. Garnet-type lithium-ion conductors are promising candidates for solid electrolytes, yet their thermal-transport mechanisms remain poorly understood. Here, we connect the lattice and ion dynamics of single-crystal garnet-type Li6.5La3Zr1.5Ta0.5O12 to its intrinsically low thermal conductivity. Our study reveals that the single crystals grown by the floating-zone method exhibit remarkably low glasslike thermal conductivity. Using first-principles calculations and inelastic-neutron-scattering measurements, we identify both the acoustic and numerous optical phonon modes, which stem from the complex crystal structure of the material. Notably, a low-energy optical branch exhibits an avoided crossing with acoustic phonons near 7 meV. These optical modes can enhance the scattering of heat-carrying acoustic phonons and reduce thermal conductivity. Furthermore, the calculated Grüneisen parameters are large, especially for the vibrational modes around 6 meV, indicating strong anharmonicity, with a noticeable contribution from lithium-ion vibrations. A two-channel thermal-transport model is employed to describe the weak temperature dependence of the thermal conductivity, which can be attributed to the substantial contribution of diffuson transport facilitated by the abundance of optical phonons and intrinsic anharmonicity. These results offer valuable insights into the thermal transport in a broad class of ionic conductors of interest for energy conversion and storage applications.