Rational design of surface reconstruction with pinning effect to relieving bulk fatigue for high energy single-crystal Ni-rich cathodes

Abstract

Single-crystal Ni-rich layered cathodes have become the mainstream commercial lithium ion batteries because of their structural and cyclic stability. In order to obtain a higher energy density, the cut-off voltage (>4.4 V) must be increased. However, the mechanism of capacity fading at high voltages remains unclear. This study proved that the capacity fading of single-crystal Ni-rich layered materials at high voltage is caused by the appearance of fatigued phases due to surface structure degradation. In particular, a structural evolution mechanism based on the premigration of rare earth elements to lithium sites to form reconstruction layers at the atomic scale was proposed in this paper. The introduction of rare earth element Sc leads to a nanoscale reconstruction layer with a pinning effect on the surface of the Ni-rich material, which alleviates the barriers of kinetic to lithium ions in the highly charged state, improves the reversibility phase transition of the H2 to H3 phase, and maintains structural stability. In particular, the Sc-doped cathodes have a superb capacity retention rate of 95.1% after 300 cycles at 5C under the voltage of 4.6 V with a loss of only 0.016% capacity per cycle. This study reveals the intrinsic link between the capacity fading and structural evolution, providing new insights for the research of Ni-rich layered cathode materials with high energy density.