基于动力学性质的全固态锂电池界面层构筑及其锂枝晶抑制机理研究

All-solid-state lithium battery based on solid electrolyte Li7La3Zr2O12 (LLZO) has the advantages of high safety and high energy density, which is highly expected to meet the requirements of electric vehicles in the future. However, capacity fading or even battery failure caused by lithium dendrite growth has seriously hindered the development of all-solid-state lithium battery. Herein, from the perspective of dynamic properties of the interphase layer, this project proposes a LiPON thin film interphase layer at Li//LLZO interface with high lithium ionic conductivity and low electronic conductivity, which prevent the combination of Li+ and electrons in LLZO from forming lithium dendrites and fundamentally improve the inhibition ability of lithium dendrites. The effects of composition and microstructure of LiPON interphase layer on the interfacial contact state (lithium metal wettability, interfacial resistance, LiPON//LLZO interface chemical stability) and interfacial reaction process (occurring uniform lithium deposition reaction or lithium dendrite growth or LLZO electrochemical reduction reaction) are studied to reveal the lithium dendritic inhibition mechanism, thereby achieving controllability of the interfacial reaction process and improving battery cycling stability. On this basis, the relationship between the composition and microstructure of LiPON, the interfacial contact state and interfacial reaction process, and the electrochemical performance of all-solid-state lithium battery is established. The theory and method of constructing high-performance anodic interphase layer of all-solid-state lithium battery is obtained.

基于固体电解质Li7La3Zr2O12（LLZO）的全固态锂电池具有高安全性和高能量密度的优点，未来有望满足电动汽车的使用要求，然而锂枝晶生长导致的电池容量衰减甚至失效已严重阻碍了其发展。本课题从界面层动力学性质出发，提出在Li//LLZO界面构筑同时具有高锂离子电导率和低电子电导率的LiPON薄膜界面层，阻碍Li+与电子在LLZO中结合形成锂枝晶而从根本上提高锂枝晶抑制能力。通过LiPON界面层成分结构对界面接触状态（锂金属润湿性、界面电阻、LiPON//LLZO界面化学稳定性）和界面反应过程（发生锂均匀沉积反应还是锂枝晶生长或LLZO电化学还原反应）影响的研究，揭示其抑制锂枝晶生长的机理，达到界面反应过程可控并提高电池循环稳定性的目的。在此基础上建立LiPON成分结构、界面接触状态和界面反应过程、全固态锂电池电化学性能三者间的关联关系，获得高性能全固态锂电池负极界面层构筑理论与方法。

锂金属因其高能量密度成为全固态锂电池理想的负极材料，但其存在的锂枝晶生长问题却极易导致电池容量衰减甚至失效，已严重限制了全固态锂电池的发展。本研究在锂金属负极和固体电解质LLZO之间构筑Al金属界面层，Al2O3界面层以及LiPON界面层，通过研究不同动力学性质界面层的界面反应过程以及电池的电化学性能探究了锂枝晶生长的原因。研究结果显示，具有电子传导性质的Al金属界面层，由于电子可通过界面层到达LLZO与锂离子结合从而发生锂枝晶生长，电池循环95圈出现短路，在充放电后的LLZO晶界处可以清楚地观察到树枝状锂枝晶；而退火形成的Al2O3界面层，电池可稳定循环1000圈其极化电压低于0.1V且在0.05~0.5mA cm-2电流密度范围内具有良好的倍率性能。拉曼和XPS结果显示Al2O3界面层在充放电过程中与锂离子发生反应生成了一种具有锂离子传导性的Li-Al-O化合物。具有锂离子传导性和非电子传导性Li-Al-O界面层的锂枝晶抑制机理为：该化合物可促进Li+从固体电解质LLZO传导至锂金属发生锂的沉积反应，同时阻碍电子传导至LLZO而抑制锂枝晶生长。而基于LiPON界面层改性的XPS深度刻蚀研究结果显示，充放电后LiPON和LLZO界面保持稳定的化学和电化学状态；且基于该界面层改性的电池具有良好的充放电循环和倍率性能。LiPON同时具有高锂离子传导性和低电子传导性，该界面层可阻碍电子到达LLZO与锂离子结合发生锂枝晶生长同时可促进锂离子向锂金属负极传导从而促进目标锂沉积反应发生，该锂枝晶抑制机理与Li-Al-O化合物类似。因此，界面层的动力学性质对锂枝晶生长有很大的影响，具有低电子电导率和高锂离子传导率的界面层有利于提高抑制锂枝晶生长能力。