Synergistically dissipating the local strain and restraining lattice oxygen escape by fine-tuning of microstructure enabling Ni-rich cathodes with superior cyclabilities

Abstract

LiNi_xCo_yMn_zO₂ (NCM, x ≥ 0.8, x  + y + z = 1) cathodes have attracted much attention due to their high specific capacity and low cost. However, severe anisotropic volume changes and oxygen evolution induced capacity decay and insecurity have hindered their commercial application at scale. In order to overcome these challenges, a kind of tantalum (Ta) doped nickel-rich cathode with reduced size and significantly increased number of primary particles is prepared by combining mechanical fusion with high temperature co-calcination. The elaborately designed micro-morphology of small and uniform primary particles effectively eliminates the local strain accumulation caused by the random orientation of primary particles. Moreover, the uniform distribution of small primary particles stabilizes the spherical secondary particles, thus effectively inhibiting the formation and extension of microcracks. In addition, the formed strong Ta–O bonds restrain the release of lattice oxygen, which greatly increases the structural stability and safety of NCM materials. Therefore, the cathode material with the designed primary particle morphology shows superior electrochemical performance. The 1 mol% Ta-modified cathode (defined as 1% Ta-NCM) shows a capacity retention of 97.5% after 200 cycles at 1 C and a rate performance of 137.3 mAh g⁻¹ at 5 C. This work presents promising approach to improve the structural stability and safety of nickel-rich NCM.