摘要/Abstract
随着电动汽车和储能电站等电力设备的快速发展，对高能量密度的锂离子电池的需求日益增加.高比容量（>250 mAh·g-1）的富锂锰基正极材料，有望成为锂离子电池实现高比能量（>350 Wh·kg-1）的关键正极材料.富锂锰基正极材料的Li2MnO3相和晶格氧参与电化学反应使其拥有了高容量，但这也导致表面结构和成分容易发生变化，进而造成富锂锰基正极材料存在着诸如首次库伦效率低、倍率性能差和循环后电压和容量衰减严重等问题.因此，本文综述了富锂锰基正极材料的表面包覆、表面掺杂和表面化学处理三种表面改性方法，并进一步讨论了三种表面改性方法对材料性能提升的机制机理和优缺点.在此基础上，介绍了近些年基于多方法的表面联合改性工作.通过对富锂锰基正极材料进行表面联合改性，不仅可以改善其结构稳定性和抑制电极/电解液界面副反应，而且可以缓解其在循环过程中不断发生的结构转变和晶格氧的析出问题.最后，对富锂锰基正极材料表面改性研究方向进行了总结和展望.
关键词: 富锂锰基正极材料, 表面包覆, 表面掺杂, 表面化学处理, 表面联合改性
With the rapid development of electric cars and energy storage power stations, there is an increasing demand for lithium ion batteries with high energy density. Li- and Mn-rich (LMR) cathode materials with large specific capacity (>250 mAh·g-1) are supposed to accomplish lithium ion batteries with high energy density (>350 Wh·kg-1). The high capacity performance of LMR cathode materials are resulted from the lattice oxygen redox reaction induced by the electrochemical activation of the Li2MnO3 phase. However, the activation of the Li2MnO3 phase and oxygen redox reaction lead to lattice oxygen release and structure transformation, which cause some serious problems such as low initial columbic efficiency, poor rate capability, voltage and capacity degradation after subsequent cycles. The oxygen release and structure transformation always start from the surface, indicating that the surface stability is significant to LMR cathode materials. In this paper, surface modifications such as surface coating, surface doping and surface chemical treatment are reviewed and the mechanism of three surface modification methods for LMR cathode materials are discussed in further. Surface coating is one of the most widely surface modification methods, which can suppress the electrode/electrolyte side reaction and reduce the transition metal dissolution. The effect of surface coating on improving electrochemical performance of LMR cathode materials is always determined by the characteristic of coating layer materials including non-active coating layer, electrochemical active coating layer, Li+ conductive coating layer and electronic conductive coating layer. Surface doping has shown to be an effective method in suppressing oxygen release and structural transformation. Surface chemical treatment has resulted in reducing irreversible capacity loss by activating Li2MnO3 phase. On this basis, surface integrated strategies combined several surface modified methods are introduced and discussed in recent years. The surface intergrated strategies not only enhance the structural stability and suppress electrode/electrolyte surface-interface reaction, but also have an effective role on mitigating structure transformation and lattice oxygen release. Finally, we wish that our review would provide research directions for surface modified strategies of LMR cathode materials in future.
Key words: Li- and Mn-rich cathode materials, surface coating, surface doping, surface chemical treatment, surface integrated strategies
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