Mn/Fe浓度梯度LiMn1-xFexPO4原位晶格外延生长LiFePO4纳米保护层及其界面微观结构与电化学特性调控

橄榄石LiMn1-xFexPO4（0.5≥x>0）是非常有发展前景的高功率锂离子电池正极材料，其在能量密度上比LiFePO4更高在电化学反应动力学上比LiMnPO4更好。LiMn1-xFexPO4在充放电过程中常伴随Jahn-Teller畸变效应，易诱发电解液氧化分解，造成容量衰减，甚至引起电池爆炸起火事故。为此，本项目提出Mn/Fe浓度梯度LiMn1-xFexPO4原位晶格外延生长LiFePO4纳米保护层的研究思路。由于LiFePO4与LiMn1-xFexPO4在晶格构型上高度匹配，两相界面处可实现原子级无缝衔接，使材料中Mn元素与电解液完全隔离，充分消除Jahn-Teller畸变效应所诱发的一系列副反应。通过系统调节Mn/Fe高温互扩散行为来调控LiMn1-xFexPO4浓度梯度和LiFePO4纳米保护层厚度（界面调控），以此为基础构筑材料微观结构特性与电化学性能的之间的内在关联。

Olivine LiMn1-xFexPO4 (0.5≥x>0) is a very promising cathodes candidate for the high power lithium-ion batteries (LIBs), which can provide more energy density than that of LiFePO4 and feature more electrochemical reaction kinetics than that of LiMnPO4. The material often has trouble with Jahn-Teller effect upon charge and discharge, giving rise to organic electrolyte decomposition, capacity fade and even explosion/fire. Therefore, the project aims to modify Mn/Fe concentration-gradient LiMn1-xFexPO4 with LiFePO4 nano-protective layer by an in-situ epitaxial crystal growth way. In view of high compatibility in lattice structure between LiFePO4 and LiMn1-xFexPO4, seamless integration at the atomic level can be well achieved in their two-phase interfaces. As a result, Mn element in LiMn1-xFexPO4 can be totally insulated from the electrolyte, and the side effects caused by Jahn-Teller effect can be eliminated entirely. By systematically adjusting Mn/Fe interdiffusion behaviors at elevated temperatures, we regulate the Mn/Fe concentration gradient of LiMn1-xFexPO4 and the thickness of LiFePO4 nano-protective layer (interface regulations), and then establish the intrinsic relationship between microstructure characteristics and electrochemical performances.