Improved Cycling Stability of Ni-Rich Cathode Material by In Situ Introduced TM-B-O Amorphous Surface Structure.

Current research has found the amorphous/crystal interface has some unexpected electrochemical behaviors. This work designed a surface modification strategy using NaBH ₄ to induce in situ conversion of the surface structure of Ni-rich LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (NCM811) into TM-B-O amorphous interface layer. Oxidizing the surface from transition metals (TM) with high valence and reductive BH ₄ ^- in a weak polar medium of ethanol results in an easy redox reacton. A TM-B-O amorphous structure is formed on NCM811 surface. The action of reactive wetting ensures a complete and uniform structure evolution of the surface crystals. The complete coverage protects the outer crystal and the heterogeneous interface impedance between the modified layer and bulk is reduced. More importantly, this amorphous interface layer through in situ conversion enhances the heterogeneous link at interface and its own structural stability. The modified NCM811 (TB2@NCM) treated with 1 wt % NaBH ₄ shows excellent electrochemical performance, especially cyclic stability. At a high cutoff voltage of 4.5 V, the capacity retention was 72.5% at 1 C after 500 cycles. The electrode achieves 173.7 mAh·g ^-1 at 10 C. This work creates a modifying strategy with potential application prospect due to simple technology with low-cost raw material under mild operating conditions.