LiMnPO4/C多孔微球的可控构筑及储锂性能研究

Nanocrystallization of cathode is in favor of the high power density for lithium ion battery. However, its volumetric energy density can be inevitably decreased. The power density and the volumetric energy density for cathodes with structures of porous microspheres can be considered simultaneously. Nevertheless, it is a great challenge to achieve the high power density for cathodes with structures of porous microspheres according to the current literatures. Porous microspheres of LiMnPO4/C cathodes as our research object are studied for controllable construction and lithium storage property. Here, we intend to synthesize porous microspheres of LiMnPO4/C cathodes by solvothermal method. The effect laws of the processes parameters and conditions on the structures of the microspheres and the carbon lays of the porous microspheres of LiMnPO4/C cathodes, the interfacial bonds with carbon nanotubes and crystallographic orientations of LiMnPO4 crystals are revealed. The growth mechanism for the porous microspheres of LiMnPO4/C cathodes is elucidated. The corresponding results are expected to achieve controllable construction of the porous microspheres of LiMnPO4/C which can provide the reference for controllable fabrication of porous microspheres. Furthermore, the influence rules of the structures of the microspheres, the carbon lays, the interfacial bonds and crystallographic orientations on the rate capabilities of the porous microspheres of LiMnPO4/C cathodes are demonstrated. The high rate capabilities with the international advanced level are obtained. The mechanism with the high volumetric energy density as well as the high power density for the porous microspheres of LiMnPO4/C cathodes is elucidated, which may afford the theoretical support for the developing design and the performance prediction of lithium ion batteries with the double high performance.

正极材料的纳米化会提高电池的功率密度，但也会降低电池的体积能量密度。多孔微球结构可以同时兼顾到正极材料的功率密度与体积能量密度，但目前对多孔微球正极材料高功率密度的研究还面临着巨大挑战。本项目以LiMnPO4/C多孔微球为研究对象，进行多孔微球的可控构筑及储锂性能研究。拟采用溶剂热法制备多孔微球，揭示工艺参数及条件对LiMnPO4/C多孔微球的微球结构、碳层结构、LiMnPO4与碳纳米管间的界面结合、LiMnPO4晶体结晶取向的影响规律，阐明生长机理，实现LiMnPO4/C多孔微球的可控构筑，为多孔微球的可控制备提供参考依据；揭示微球结构、碳层结构、界面结合及结晶取向对电池倍率性能的影响规律，获得国际先进水平的高倍率性能，阐明LiMnPO4/C多孔微球能够兼顾高功率密度与高体积能量密度的作用机理，为“双高”锂离子电池的开发设计和性能预测提供理论支持。

针对纳米化的LiMnPO4正极材料会导致电池体积能量密度降低的问题，提出通过构筑LiMnPO4/C多孔微球来消除弊端，同时尽可能地增强多孔微球的倍率性能。为此，探讨了碳纳米管的纯化、酸化、接枝以及与LiMnPO4的复合，研究了LiMnPO4/C空心微球的制备，对比了具有不同尺寸、结构及取向特征LiMnPO4/C空心微球的储锂性能。通过本项目的研究，取得的重要结果有：①实现了LiMnPO4空心微球尺寸在600nm~3μm内的可控制备。对比分析直径600nm与直径3μm空心微球的储锂性能表明，两者倍率性能相近，不同倍率下直径600nm空心微球的放电容量稍大些，但3μm空心微球的循环性能更稳定。此外，3μm空心微球分散性好、流动性强，便于加工、易于密堆，利于电池体积能量密度的提升。综合考虑性能和加工因素，直径3μm的LiMnPO4空心微球能同时兼顾到高倍率性能与高体积能量性能，具有潜在推广应用价值。②实现了LiMnPO4空心微球结构有序/无序的可控构筑。对比分析有序组装、无序组装空心微球的储锂性能表明，低倍率下两者放电比容量相近，但随着倍率的增强，两者放电容量的差距越来越大，有序组装空心微球的倍率性能表现更优。③实现了LiMnPO4空心微球组装晶粒不同结晶取向的可控调节。对比分析具有不同(010)暴露面积及[010]晶向尺寸组装晶粒的空心微球储锂性能表明，扩大(010)晶面的暴露面积、减小[010]晶向的厚度尺寸，有利于改善LiMnPO4电池的倍率性能。所得到的由大量暴露有(010)晶面且[010]晶向厚度为60nm纳米片有序组装的空心微球，在1、2、5、10C充放电下，比容量分别为130、121、106、81 mA h g−1，在1C循环200圈后容量保持率为90%。本项目的实施为高性能LiMnPO4正极材料的可控合成提供新方法，同时为其它锂离子电池材料的设计开发提供新思路。