Nb包覆对富锂锰基材料电化学性能的影响

Effects of Nb coating on the performance of Li-rich manganese layered oxide material

为了提高富锂锰基材料的循环稳定性,以Nb_(2)O_(5)作为包覆剂,采用高温固相反应法对富锂锰基材料进行包覆改性。研究发现,Nb能够与材料表面的残存锂反应,生成LiNbO_(3);当Nb包覆量为0.2%时样品性能最佳:0.1C下放电比容量为285.6 mA·h/g,1C循环100次后的容量保持率为85.9%,且表现出较好的倍率性能和较低的电压衰减。富锂锰基材料的循环稳定性能的提升可能归因于高温热处理使Nb扩散进入材料表层晶格,形成了较强的Nb—O键,减缓了循环过程中晶格氧的流失,从而稳定结构;同时,表面生成的快离子导体LiNbO_(3)不仅阻止了电解液对材料的侵蚀,而且促进了锂离子的扩散和电子的传导。

To improve the cycle stability of Li-rich manganese layered oxide(LLO)material,the Nb_(2)O_(5) was used as coating agent to improve the electrochemical performance of LLO material by the high temperature solid state reaction method.It is found that Nb could react with residual lithium on the surface of materials to form LiNbO_(3),which reduced the residual alkali content.The performance of the sample with 0.2%Nb coating is the best:the specific discharge capacity is 285.6 mA·h/g at 0.1C,and the capacity retention rate is 85.9%after 100 cycles at 1C,which shows good rate capability and lowe voltage decay.The performance improvement may be attributed to the diffusion of Nb into the surface lattice of the material during the heat treatment and form strong Nb—O bond,which alleviate the loss of lattice oxygen during the cycles,thus stabilizing the structure.Moreover,the fast ion conductor LiNbO_(3) coated on the surface not only prevents the corrosion of the electrolyte on the material surface,but also promotes the diffusion of lithium ion and electron conduction.