2-mercaptobenzothiazole as a surface modifier to improve the electrochemical properties of Li1.2Ni0.2Mn0.6O2 cathode materials

Abstract

Li-rich layered oxides (LLO), like Li1.2Ni0.6Mn0.2O2, have certain disadvantages such as poor cycle stability and fast voltage decay. Herein, we attempt to employ simple methods, the Li1.2Ni0.2Mn0.6O2 material is modified by self-assembly of 2-mercaptobenzothiazole (MBT), to improve the electrochemical properties. The cycling stability of Li1.2Ni0.2Mn0.6O2 cathodes (LLC) is significantly increased by modified MBT, and its capacity retention increases from 52.64 to 88.47% after 125 cycles. In the meantime, the rate of medium voltage decay slows down. Lithium-deficient layer and spinel phase were formed by H+/Li+ exchange in the process of surface molecule self-assembly. In the first charge/discharge cycle, H+ in the material is removed and forms H2O molecule on the material surface, which leads to more surface spinel phase and the formation of LiF/LixPOyFz films, hereby reducing the contact between electrolyte and cathode. The phase transition and voltage decay have been suppressed by the surface spinel phase and LiF/LixPOyFz films which also improve the rate capacity. The -N=, -N+= functional groups in the modified films stabilize the PF6− and PF5, which can inhibit the decomposition of LiPF6 in the electrolyte and then reduce the content of LiF in SEI film.