无钴富锂锰基正极材料Li1.2Ni0.2Mn0.6O2的表面改性及电化学性能研究

Surface Modification and Electrochemical Properties of Cobalt-Free Lithium-Rich Manganese-Based Cathode Material Li1.2Ni0.2Mn0.6O2

摘要:

无钴富锂锰基正极材料Li_1.2Ni_0.2Mn_0.6O₂因高比容量、低成本等优点备受关注，是极具潜力的下一代锂离子电池正极材料。然而，Li_1.2Ni_0.2Mn_0.6O₂材料存在首次库伦效率低、倍率性能差及容量衰减等问题，限制了其进一步发展。为解决此问题，采用柠檬酸溶液表面处理结合再重新煅烧方法，通过在其表面包覆一层尖晶石相，对Li_1.2Ni_0.2Mn_0.6O₂开展了表面改性研究，并对改性前后样品进行物理表征和电化学测试分析。结果表明，改性前后的Li_1.2Ni_0.2Mn_0.6O₂正极材料，形貌基本一致，均为尺寸100—400 nm的不规则颗粒，改性后的粉末颗粒边缘略有不平整。使用柠檬酸溶液表面处理后，Li_1.2Ni_0.2Mn_0.6O₂材料形成了內部为层状相、表面为尖晶石相的结构。尖晶石相的存在不仅为锂离子扩散提供了三维离子扩散通道、提高倍率性能，还可充当正极材料表面与电解液间的保护层，提高首次库伦效率，改善循环性能。改性后的Li_1.2Ni_0.2Mn_0.6O₂的首次库伦效率为92. 4%，可逆比容量为292 mAh?g^-1， 与改性前相比分别提高了13.8%和22 mAh?g^-1，并且在不同倍率下的可逆比容量和长循环容量保持率均有明显提升，表明其具有更好的倍率性能和更优的循环稳定性能。本研究提出了一种无钴富锂锰基正极材料表面改性方法，该改性方法操作简单、效果明显，可应用于不同组分的富锂正极材料，为富锂锰基正极材料的进一步发展提供了新的思路 。

Abstract:

Cobalt-free lithium-rich manganese-based cathode materials have attracted much attention as potential next-generation cathode materials for lithium-ion batteries due to their high specific capacity and low-cost advantages. However，problems such as low first-cycle Coulombic efficiency，poor rate performance，and capacity attenuation limit the further development of cobalt-free lithium-rich manganese-based cathode materials. A spinel phase was successfully coated on the surface of cobalt-free Li_1.2Ni_0.2Mn_0.6O₂ cathode material by the method of surface treatment with citric acid and then re-calcination. The physical characterization and electrochemical test analysis were carried out on the samples before and after modification. The results show that the morphology of cobalt-free Li_1.2Ni_0.2Mn_0.6O₂ cathode material before and after modification is basically the same，which is irregular particles with the size of 100—400 nm. The modified powder particles have slightly uneven edges. The surface treatment of cobalt-free lithium-rich manganese cathode material Li_1.2Ni_0.2Mn_0.6O₂ with citric acid solution formed a structure with layered phase inside and spinel phase on the surface. The presence of spinel phase not only provides a three-dimensional ion diffusion channel for lithium ion diffusion，but also improves the rate performance. It can also act as a protective layer between the material surface and the electrolyte to improve the first coulomb efficiency and improve the cycle performance. The first coulomb efficiency and reversible specific capacity of the modified Li_1.2Ni_0.2Mn_0.6O₂ are 92.4% and 292 mAh?g^-1，respectively，which are 13.8% and 22 mAh?g^-1 higher than those before modification，and the reversible specific capacity and long-cycle capacity retention rate are significantly improved at different magnifications. It shows that it has better rate performance and cycle stability performance. The modification method is simple and effective，and can be applied to different components of Li-rich cathode materials. It provides a new idea for the further development of Li-rich manganese-based cathode materials.