Document Type

Article

Corresponding Author(s)

Yong Yang(yyang@xmu.edu.cn)

Abstract

With the rapid development of electric vehicles, higher requirements are put forward for the energy density, cycling performance and cost of lithium-ion batteries. As an important high capacity cathode material for lithium ion batteries,the high nickel layered oxide material LiNi0.8Co0.1Mn0.1O2 (NCM811) can reach an energy density of 760Wh·kg-1. The ultra-high nickel ternary positive electrode material (LiNi1-x-yCoxMnyO2, x≥0.90) has a specific capacity of more than 210mAh·g-1,and can realize higher energy density. Besides, ultra-high nickel material has lower cobalt content, which means lower material cost. However, there are still few researches on ultra-high nickel materials. Therefore, LiNi0.96Co0.02Mn0.02O2 (NCM96) is selected for the study of ultra-high nickel cathode materials. In order to improve the cycling performance of high specific capacity ultra-high nickel ternary cathode material, tungsten oxide and phosphotungstic acid are used to modify the surface of LiNi0.96Co0.02Mn0.02O2 material. The structure, morphology and electrochemical performance of the material prepared with the two modification methods are compared. Among them, tungsten oxide coating has been reported can effectively improve the electrochemical performance of ternary materials, but there are no reports of surface coating modification of ultra-high nickel cathode materials by tungsten oxide. Phosphate coating has been widely used in surface coating modification of high nickel cathode materials to improve their electrochemical performance, but it is difficult to achieve uniform coating. Phosphotungstic acid is a kind of substance that can realize double coated with tungsten oxide and phosphate at the same time, which is expected to achieve better electrochemical performance than single element coating. In this work, NCM96 precursor and phosphotungstic acid/tungsten oxide were dispersed in ethanol for mixing, after drying, mix with lithium source and sinter, so as to achieve tungsten oxide and phosphotungstic acid coating. The results show that, in the process of phosphotungstic acid and WO3 coating modification, W and P elements are not doped into the lattice of NCM96 material, but form a relatively uniform coating structure, in which WO3 coating modification is single element coating structure and PTA coating modification is P/W double element coating structure. Electrochemical test and analysis show that the two surface modification methods don’t affect the first cycle discharge capacity of the NCM96 material, while can effectively improve the long-term cycling performance. The high temperature electrochemical performance of the two modification methods is compared. It shows that, compared with the tungsten oxide coated NCM96@0.8wt%WO3 sample, the phosphotungstic acid coated NCM96@1wt%PTA material exhibits superior cycling stability at high-temperature (60 oC). indicating that the P/W two elementary surface modification of phosphotungstic acid is superior to the W single elementary modification of WO3.

Graphical Abstract

Keywords

Lithium ion battery, LiNi0.96Co0.02Mn0.02O2, Surface modification, Tungsten oxide coating, Phosphotungstic acid coating

Online Date

7-5-2022

2204281-SI.pdf (280 kB)

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