钠离子电池层状氧化物正极材料的表面修饰研究

Surface modification research of layered oxide materials for sodium-ion batteries

钠离子电池作为锂离子电池的有益补充,近几年获得了广泛研究。层状氧化物是其中最具发展潜力的正极材料,已经在100 kW·h级钠离子电池储能电站中获得演示验证,但目前仍存在碱性较高、循环不佳的弊端。得益于三元正极梯度分布材料的设计思路,通过液相包覆的方法在正极材料进行富锰壳层包覆降低材料表面残碱提升材料加工性能以及提升材料的电化学性能。借助扫描电子显微技术(SEM)、电化学技术等表征测试手段,综合评测不同包覆含量的正极材料,筛选得到最优比例为1%。X射线衍射(XRD)结果表明包覆前后的材料都属于O3相结构,空间群为R-3m。室温下的电化学性能测试表明1%Mn包覆样品在2.5~4 V下的有一定程度的提升:倍率性能上,1 C倍率保持率从85.4%提升至90.4%,100周循环保持率从81.5%提升至90.5%。通过残碱测试结果计算的pH值从11.74降至11.33,证明表面残碱会得到有效控制。本文综合研究了富锰壳层结构正极材料,验证了表面富锰壳层设计有利于降低残碱并提升电化学性能,为进一步设计表面改性的正极材料提供了新思路。

Sodium-ion batteries(SIBs),considered as potential supplement to lithium-ion batteries(LIBs),have been widely studied in recent years.Among all types of cathode materials,layered oxide material is the most promising kind and has been verified in 100 kW·h Sodium-ion battery energy storage station.However,it still suffers the disadvantages of high alkalinity and poor cycling performance.Benefited from the experience of gradient distribution design in ternary cathode materials for LIBs,liquid coating method was adopted to prepare manganese-rich shell coated layered oxide cathode material,so as to reduce the residue alkaline in the surface,to enhance the material process property during battery fabrication and to improve the electrochemical performance.Materials with different Mn contents were prepared and characterized by scanning electron microscope(SEM)and electrochemical examinations.The best performance is obtained when 1%Mn coating is utilized.The X-ray diffraction(XRD)results show that O3 structure(space group:R-3m)is maintained after coating.Moreover,the residual alkaline is reduced with calculated pH decreased from 11.74 to 11.33,proving the effectiveness of our design.At the same time,material with 1%Mn coating has the best electrochemical performance within the voltage of 2.5~4 V.The rate capability improved from 85.4%to 90.4%at 1 C rate after coating and the capacity retention after 100 cycles is also enhanced from 81.5%to 90.5%.In this paper,the Mn-rich shell coated positive electrode materials is studied comprehensively,which verifies the effect of our design and provides a new idea for the design of surface modified positive electrode materials.