Improved high-voltage cycling stability of single-crystalline LiNi0.8Co0.1Mn0.1O2 cathode by tantalum doping†

Abstract

The utilization of nickel-rich single-crystalline LiNi_1−x−yCo_xMn_yO₂ cathodes at elevated voltages encounters hindrances stemming from crack formation within micron-sized particles. While reducing particle dimensions offers a potential strategy to mitigate stress-induced cracking, it simultaneously exacerbates surface side reactions. Ta doping is presented to address these challenges, a Ta-doped single-crystalline LiNi_0.8Co_0.1Mn_0.1O₂ (Ta-SC) is engineered, integrating advantages of grain refinement and surface stability. Ta doping inhibits the growth of single crystals during sintering and suppresses the irreversible surface phase transition during cycling. Unlike the undoped SC cathode, which is susceptible to intragranular cracking, the Ta-SC cathode demonstrates excellent structural integrity upon high voltage cycling. This preservation of structural integrity in the Ta-SC cathode is attributed to homogeneous H2–H3 phase transition favoured by reduced kinetic barriers and short distance for Li⁺ diffusion. Benefitting from the structural stability, the Ta-SC cathode provides superior cycling stability. It maintains a coin cell capacity of 180.7 mA h g⁻¹ and retains an energy density of 679.8 W h kg⁻¹ after 200 cycles in the 2.8–4.8 V range at 1 C. This work highlights the potential of Ta doping as a general approach to improve the durability and electrochemical performance of layered cathode materials.