Improving structure stability of single-crystalline Ni-rich cathode at high voltage by element gradient doping and interfacial modification

Abstract

Single-crystalline Ni-rich cathodes can provide high energy density and capacity retention rates for lithium-ion batteries (LIBs). However, single-crystalline Ni-rich cathodes experience severe transition metal dissolution, irreversible phase transitions, and reduced structural stability during prolonged cycling at high voltage, which will significantly hinder their practical application. Herein, a Li₄TeO₅ surface coating along with bulk Te-gradient doping strategy is proposed and developed to solve these issues for single-crystalline Ni-rich LiNi_0.90Co_0.05Mn_0.05O₂ cathode (LTeO-1.0). It has been found that the bulk Te⁶⁺ gradient doping can lead to the formation of robust Te–O bonds that effectively inhibit H2-H3 phase transformations and reinforce the lattice framework, and the in-situ Li₄TeO₅ coating layer can act as a protective layer that suppresses the parasitic reactions and grain fragmentation. Besides, the modified material exhibits a higher Young’s modulus, which will be conducive to maintaining significant structural and electrochemical stability under high-voltage conditions. Especially, the LTeO-1.0 electrode shows the improved Li⁺ diffusion kinetics and thermodynamic stability as well as high capacity retention of 95.83% and 82.12% after 200 cycles at the cut-off voltage of 4.3 and 4.5 V. Therefore, the efficacious dual-modification strategy will definitely contribute to enhancing the structural and electrochemical stability of single-crystalline Ni-rich cathodes and developing their application in LIBs.