Fully coating of Mg3B2O6 in nonaqueous solution on Ni-rich LiNi0.8Co0.1Mn0.1O2 secondary particles to improve cycling stability of lithium-ion batteries

Surface coating is an effective strategy to suppress side reactions at the electrode/electrolyte interface and improve cycling stability of the Ni-rich LiNixCoyMn1-x-yO2 electrodes. It is difficult to prepare a complete coating layer on the secondary particles by traditional methods, due to the alkaline substances and oxidative property on surface. In this work, a coating process of Mg3B2O6 running counter to traditional routes was designed to modify LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode material. In a weak polar ethanol medium, BH4- ions are uniformly lain on particle surface by the interaction between its electronegativity and oxidizing surface, which also change the charge state into negative atmosphere around the NCM811 surface. Then Mg2+ ions are also completely dispersed by the mutual attraction between metal cations and the hydrolyzed BO3-. Then a full surface coverage of Mg3B2O6 was prepared in situ on the NCM811 secondary particles. The complete coating layer protects the surface crystal structure of the NCM811 and limits the irreversible phase transition. The optimized composite with a suitable coverage of 1 % Mg3B2O6 exhibits enhanced rate capability and excellent cycling performance. At a high current density of 10C, it delivers a specific capacity of 162.7 mAh g−1. Especially, it maintains 160.6 mAh g−1 after 400 cycles at a high cut-off voltage of 4.5 V at 1C with a retention of 80.3 %. In addition, Mg3B2O6 is a non-toxic and non-polluting material. The simple coating process with low-cost raw materials as well as mild operating conditions endow this technology with potential practical application value.