High-Ni cathode material improved with Zr for stable cycling of Li-ion rechargeable batteries

Abstract

The Zr solvent solution method, which allows primary and secondary particles of LiNi_0.90Co_0.05Mn_0.05O₂ (NCM) to be uniformly doped with Zr and simultaneously to be coated with an Li₂ZrO₃ layer, is introduced in this paper. For Zr doped NCM, which is formed using the Zr solvent solution method (L-NCM), most of the pinholes inside the precursor disappear owing to the diffusion of the Zr dopant solution compared with Zr-doped NCM, which is formed using the dry solid mixing method from the (Ni_0.90Co_0.05Mn_0.05)(OH)₂ precursor and the Zr source (S-NCM), and Li₂ZrO₃ is formed at the pinhole sites. The mechanical strength of the powder is enhanced by the removal of the pinholes by the formation of Li₂ZrO₃ resulting from diffusion of the solvent during the mixing process, which provides protection from cracking. The coating layer functions as a protective layer during the washing process for removing the residual Li. The electrochemical performance is improved by the synergetic effects of suitable coatings and the enhanced structural stability. The capacity-retentions for 2032 coin cells are 86.08%, 92.12%, and 96.85% at the 50^th cycle for pristine NCM, S-NCM, and L-NCM, respectively. The superiority of the liquid mixing method is demonstrated for 18 650 full cells. In the 300^th cycle in the voltage range of 2.8–4.35 V, the capacity-retentions for S-NCM and L-NCM are 77.72% and 81.95%, respectively.