锂离子电池富镍正极基础科学问题：前驱体高温锂化过程结构演变及调控

Basic scientific problems of nickel-rich cathode for lithium-ion battery: Structural evolution and regulation of intermediate during high temperature lithiation process

摘要:

为合成高性能富镍正极,需采用较优的煅烧温度、煅烧时间、降温程序等锂化特定形态的氢氧化物前驱体,以可控形成具有较优晶体结构及晶粒形态的正极材料。然而,由于煅烧过程涉及参数多且变化范围大,合理设计制备具有理想结构和形态的富镍正极所需煅烧工艺仍然具有挑战性。为此,需深入理解前驱体和锂盐高温煅烧为正极过程的物相、结构、形貌等的演变方式及形成规律,以为富镍正极煅烧工艺设计及材料定向调控提供参考。本文首先介绍了前驱体高温锂化过程物相、结构演变及反应机制,包括从热力学相平衡角度简要分析的相组成变化、基于原位测试及理论计算分析的前驱体锂化过程反应机制及物相演变以及降温过程发生的显著影响富镍正极材料性能的表面重构现象。其次,介绍了前驱体锂化过程的形貌影响因素及演变方式。最后,对富镍正极煅烧过程面临的问题进行了探讨。本文系统总结前驱体煅烧过程结构演变及调控规律,以期为相关专业人员开发富镍正极提供参考。

Abstract:

In order to synthesize high performance nickel-rich cathode, it is necessary to adopt favorable calcination temperature, calcination time and cooling procedure to lithiate hydroxide precursor, so as to form cathode material with better crystal structure and grain morphology in a controlled way. However, due to the large number of parameters involved in the calcination process, it is still challenging to reasonably design the calcination process which is required for preparing nickel-rich positive electrode with ideal structure and morphology. Therefore, it is necessary to deeply understand the evolution and formation rule of the phase, structure and morphology of intermediate during high temperature calcination, so as to provide reference for the design of nickel-rich cathode calcination process and directional control of structure. In this paper, the phase composition changes of precursor during the lithiation are briefly introduced from the point view of thermodynamic phase equilibrium. Secondly, the reaction mechanism and phase evolution of the intermediate are introduced based on in situ testing and theoretical calculation analysis. Then, the surface reconstruction phenomenon which is occurred in cooling process and significantly affects the properties of nickel-rich cathode materials is introduced, and the reasons for surface reconstruction are summarized. Finally, the morphology evolution and factors that affect the morphology during lithiation are introduced. Finally, the problems in the calcination process of nickel-rich cathode are discussed. The structural evolution and regulation of intermediate during high temperature lithiation process introduced in the paper could provide reference for relevant professionals to develop nickel-rich cathodes.