Overall structural modification of a layered Ni-rich cathode for enhanced cycling stability and rate capability at high voltage†
The vital challenge in relation to layered Ni-rich cathodes is their pronounced structural degradation originating from cation mixing at high voltage, which causes serious electrode polarization and electrochemical deterioration. Herein, an overall structural modification strategy, which integrates a Li2GeO3 coating with gradient Ge-doping, was developed to improve the structural stability and create ordered diffusion channels in a layered Ni-rich cathode via interfacial fusion at high temperature. This effective strategy significantly enhances the reversible capacity retention, voltage stability and rate capability of the layered Ni-rich cathode at high voltage. We find that the Li2GeO3 coating inhibits interfacial side reactions to enhance the surface structural stability of the cathode materials. More importantly, the gradient Ge-doping plays a critical role in suppressing cation mixing to improve the ordered channels available for Li+ ion transport. The experimental observations, corroborated by first principle calculations, further reveal that Ge-doping not only alleviates structural degradation by increasing the phase transition energy barrier for layers to form spinel-like or rock-salt phases, but also facilitates fast Li+ diffusion kinetics via reducing the diffusion barrier. Our work provides a design idea for stabilizing the surface/bulk structure of advanced cathodes for high-performance Li-ion batteries.