化学学报 ›› 2014, Vol. 72 ›› Issue (5): 537-551.DOI: 10.6023/A14010007 上一篇    下一篇

综述

锂离子电池正极材料磷酸锰锂研究进展

万洋, 郑荞佶, 赁敦敏   

  1. 四川师范大学化学与材料科学学院 成都 610066
  • 投稿日期:2014-01-03 发布日期:2014-04-18
  • 通讯作者: 赁敦敏 E-mail:ddmd222@sicnu.edu.cn
  • 基金资助:

    项目受四川师范大学研究生优秀学位论文培育基金(No. XYZ2013-14-38)资助.

Recent Development of LiMnPO4 as Cathode Materials of Lithium-ion Batteries

Wan Yang, Zheng Qiaoji, Lin Dunmin   

  1. College of Chemistry and Materials Science, Sichuan Normal University, Chengdu 610066
  • Received:2014-01-03 Published:2014-04-18
  • Supported by:

    Project supported by the Sichuan Normal University Graduate Dissertation Cultivation Fund (No. XYZ2013-14-38).

LiMnPO4具有环境友好、价格低廉及能量密度高(~700 Wh·kg-1)等优点,同时高强度的P—O共价键组成的PO4四面体构成了LiMnPO4稳定的骨架,使得LiMnPO4具有稳定的晶体结构,保证了LiMnPO4正极材料的安全性. 因此LiMnPO4被认为是具发展潜质的下一代候选正极材料之一,并有望应用到电动车(EV)领域. 本文系统地介绍了LiMnPO4的结构与性能的关系以及导电机制,并比较了LiMnPO4和LiFePO4动力学行为的异同;同时阐述了近年来关于LiMnPO4一些富有争议性的问题,如LiMnPO4中是否存在Jahn-Teller效应及LiMnPO4的热稳定性等. 此外,LiMnPO4改性措施比如形貌控制、表面改性和掺杂也会在文中得到详细评述.

关键词: LiMnPO4, Jahn-Teller效应, 热稳定性, 形貌, 表面改性, 掺杂改性

Similar to LiFePO4, LiMnPO4 possesses the following advantages: eco-friendliness, low cost and excellent safety performance. Moreover, high energy density (~700 Wh·kg-1) of LiMnPO4 is 20% larger than LiFePO4, which is due to LiMnPO4 with high operating voltage ~4.1 V vs. Li falling within the electrochemical stability window of conventional electrolyte solutions. Therefore, LiMnPO4 is considered as a next generation cathode material for lithium-ion batteries. However, the lithium ion conductivity of LiMnPO4 is lower than that of LiFePO4. The main difference between the kinetics in the initial stage of charging of two olivine materials may originate from the formation energy of vacancy-polaron complex in LiMnPO4 than in LiFePO4. In addition, the anisotropic lattice distortion of MnO6 octahedron during repeated charge/discharge process hinders lithium removal/uptake reactions in LiMnPO4 and thus leads to the large volume change. This distortion is not a strict Jahn-Teller effect but is a preferential elongation of two of the equatorial Mn—O bonds (edge-sharing with the PO4). These intrinsic defects result in rapid capacity fading upon extended cycling and poor rate capability during cycles. To overcome these problems, it is an effective approach to prepare nanometer-sized and rod/sheet-like materials through proper synthesis method. These special morphologies in LiMnPO4 can stimulate the rate of Li extraction/insertion. However, the surface structural instability of particles may occur at size d<35 nm. The awkward situation may be solved by effective surface coating. Surface coating can decrease the disorder toward amorphous state and the poison of impurities on the surface of particles; especially, coating can promote the ionic and electronic conductivity. Therefore, a coating leads to a remarkable improvement of the electrochemical performance of LiMnPO4. In addition, doping is also a method for improving the electrochemical property of LiMnPO4. As a Fe-doped material, LiMnyFe1-yPO4 has been widely investigated. In this paper, the recent advances in LiMnPO4 as cathode materials of lithium-ion batteries are reviewed. The characteristics, morphologies, and possible reaction mechanisms of the material were summarized systematically. Some open questions (e.g. the facticity of Jahn-Teller effect in LiMnPO4, the thermal stability of LiMnPO4, etc.) are discussed in detail. Moreover, some improved methods (controlling the particle morphology, surface coating, and doping) for the electrochemical property of LiMnPO4 are expounded.

Key words: LiMnPO4, Jahn-Teller effect, thermal stability, morphology, synthesis processes, surface coating, doping