Inhibiting degradation of LiCoO2 cathode material by anisotropic strain during delithiation

Lithium cobalt oxides (LiCoO2) possess a high theoretical specific capacity of 274 mAhg(-1). However, when LiCoO2 is charged at the voltage higher than 4.2 V, there exist significant structure transition and capacity fade. In this study, we used HRTEM to observe the phase evolution of LiCoO2 cathode material after 100 cycles, and found that LiCoO2 phase would degrade to Co3O4 phase. The phase transition of Co3O4 from LiCoO2 gave rise to lattice expansion, by which the anisotropic strain was proposed by first-principles calculation to inhibit LiCoO2 degradation. Results show that the anisotropic strain via the extension of lattice parameter c and the compression of a enables to simultaneously impede lattice oxygen loss and structure transition of LiCoO2 during delithiation at high voltage. In this case, the elongation of interplanar spacing also increases the diffusivity of Li ions in LiCoO2, contributing to rate performance.