Li4Mn5O12包覆对三元正极材料结构和性能的影响

LiNi(1/3)Mn(1/3)Co(1/3)O2具有很高的理论比容量,但是三元正极材料在高电压下长循环时,其表面结构发生较大的衰退,导致电池的循环性能和倍率性能变差。本文采用耐高电压且结构稳定的富锂尖晶石Li4Mn5O(12)包覆LiNi(1/3)Mn(1/3)Co(1/3)O2可以有效改善材料的电化学性能。通过XRD、SEM、XPS和TEM等手段对包覆后的材料进行分析,证实了在LiNi(1/3)Mn(1/3)Co(1/3)O2的表面形成了10nm厚的均匀Li4Mn5O(12)的包覆层;在循环100圈后,包覆后的LiNi(1/3)Mn(1/3)Co(1/3)O2仍具有179.5m Ah/g的放电比容量和88.6%容量保持率,明显高于未包覆的LiNi(1/3)Mn(1/3)Co(1/3)O2的78.3%容量保持率。因此,利用富锂尖晶石Li4Mn5O(12)包覆LiNi(1/3)Mn(1/3)Co(1/3)O2为实现更高能量密度的锂离子电池提供了新的途径。

Effect of Li4Mn5O12 Coating on Structure and Performance of the Ternary Cathode Materials

LiNi_1/3Mn_1/3Co_1/3O₂ has high theoretical specific capacity. However, the surface structure of the cathode material greatly decays at high charging voltage, which leads to the deterioration of cycle performance and rate performance for batteries. Herein, LiNi_1/3Mn_1/3Co_1/3O₂coated with lithium-rich spinel Li₄Mn₅O₁₂ can effectively improve the electrochemical performance. X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and transmission electron microscopy are used to analyze the cathode material. It confirms that the surface of LiNi_1/3Mn_1/3Co_1/3O₂ is uniformly coated with 10nm thick coating of Li₄Mn₅O₁₂. At the same time, LiNi_1/3Mn_1/3Co_1/3O₂@Li₄Mn₅O₁₂ still possess 179.5mAh g^_-1 and high capacity retention (88.6 %) after 100 cycles, which is much higher than that of LiNi_1/3Mn_1/3Co_1/3O₂. EIS and GITT show that LiNi_1/3Mn_1/3Co_1/3O₂@Li₄Mn₅O₁₂ has better dynamic performance at high charge voltage. In addition, ex-suit XRD indicates that LiNi_1/3Mn_1/3Co_1/3O₂@Li₄Mn₅O₁₂ can improve the crystal structure stability of LiNi_1/3Mn_1/3Co_1/3O₂ at high charging voltage. Therefore, LiNi_1/3Mn_1/3Co_1/3O₂coated with lithium-rich spinel Li₄Mn₅O₁₂ provides a new way to achieve a high energy density of lithium-ion batteries.