Long-Cycle Lithium Batteries with LiNi_0.8Co_0.1Mn_0.1O₂ Cathodes above 4.5V Enabled by Uniform Coating of Nanosized Garnet Electrolytes

Abstract

The pursuit of high-energy cathode materials has been focused on raising the charging cut-off voltage of Nickel(Ni)-rich layered oxide cathode such as LiNi0.8Co0.1Mn0.1O2 (NCM811). However, the NCM811 suffers from rapid capacity fading upon cycling at cut-off voltage higher than 4.5 V, owing to their structural degradation and labile surface reactivity. Surface-coating with solid electrolytes has been recognized as an effective method to mitigate the performance failure of NCM811 at high voltage. Herein, the nano-sized Li6.4La3Ta0.6Zr1.4O12 (LLZTO) is uniformly coated on the surface of single-crystal NCM811 particles, accompanied with the longrange Ta5+ diffusion into the transition metal layer of NCM811 lattice. It is revealed that the LLZTO coating can not only inhibit the surface reactions of NCM811 with liquid electrolytes but also play an important role in suppressing the bulk microcracking within the NCM811 particles. The incorporation of Ta5+ ion expands the lattice spacing and thereby improves the homogeneity of the Li+ diffusion in the single-crystal NCM811, which alleviates the mechanical strain and intragranular cracks caused by nonuniform phases-transformation at high charging voltage. The synergy of surface protection and structural stabilization realized by LLZTO coating enables the NCM811- based lithium batteries to achieve a remarkable electrochemical performance. Typically, LLZTO coated NCM811 delivers a high reversible specific capacity of 202.1 mAh g-1 with an excellent capacity retention as high as 70 % over 1000 cycles upon charging to 4.5 V at 1 C.