Hierarchical Defect Engineering for LiCoO2 through Low-Solubility Trace Element Doping

Real-world industry-relevant battery composite electrodes are hierarchically structured. In particular for active cathode particles, there is a consensus that their structural and chemical defects could have a profound impact on battery performance. An in-depth understanding of the underlying mechanisms could critically inform cathode material engineering, which remains a daunting challenge at present. Herein, we tackle this question by studying LiCoO2 (LCO) with trace doping of Ti, which exhibits low solubility in the LCO-layered lattice. We observed the spontaneous and heterogeneous segregation of the dopant (Ti), which modified the particle surface and the buried grain boundaries while inducing a significant amount of lattice distortions. These multiscale structural defects promote the robustness of the LCO lattice at a deeply charged state (above 4.5 V). Our result formulates a multiscale defect-engineering strategy that could be applicable to the synthesis of a broad range of energy materials.