高容量富锂锰基正极材料的研究进展

Research progress of high capacity Li-Mn-rich cathode materials

层状富锂锰基材料(LMR)凭借其高比容量(>250 mAh/g)和低成本等优点,有望成为新一代锂离子电池用正极材料。从该材料发现至今已有将近30年的时间,却始终没有实现真正商业化应用,主要原因包括:循环过程中,Mn^(3+)迁移进入锂空位,使层状结构向尖晶石结构转变,导致平均放电电压持续降低,造成能量损失严重且给电池管理带来巨大的挑战;Li_(2)MnO_(3)低的电子电导率使LMR材料具有差的倍率性能;较低的电极密度,造成材料的体积能量密度较低;此外,LMR材料需要在高电压下(>4.55 V)才能发挥高容量,但高电压下电解液容易氧化分解,同时伴随着晶格氧被氧化为O_(2)逸出,以上问题严重地影响了其商业化进程。本文基于多年来LMR材料的研究开发成果,综述了近年来LMR材料在充放电机理认识、前驱体工艺路线选择、体相掺杂、表面包覆、液相和气相后处理的作用效果和改性机理,以及O2/O3复合结构、单晶结构等新型特殊结构设计等方面的研究进展,并对LMR材料未来的发展方向和商业化前景进行展望,助力富锂锰基材料的产业化开发。

Layered Li-Mn-rich materials(LMR)are promising to be next generation cathodes for lithium-ion batteries due to their high specific capacity(>250 mAh/g)and low cost.It has been nearly 30 years since the discovery of LMR material,but it has never been commercialized for the following reasons:During the cycling process,Mn^(3+)migrates into Li sites makes the layered structure transform to spinel structure,resulting in a serious discharge voltage decay,which causing serious energy loss and bringing great challenges to battery management.The low electronic conductivity of Li_(2)MnO_(3) makes LMR material have poor rate capability and lower electrode density results in lower volume energy density of LMR.In addition,the LMR materials need to be at high voltage(>4.55 V)to show high capacity,but the electrolyte at high voltage is easy to oxidize and decompose,accompanied by the release of lattice oxygen into O_(2),the above problems seriously affected LMR commercialization process.Based on the research and development results of LMR materials over the years,this paper reviews the research progress of LMR materials in the understanding of charge and discharge mechanism,precursor process route selection,modification effect and mechanism of bulk doping,surface coating,liquid and gas phase post-treatment,and the design of new special structures such as O2/O3 composite structure and single crystal structure.In addition,the future development direction and commercial prospect of LMR materials are prospected to help the industrial development of LMR materials.