Inhibiting degradation of LiCoO2 cathode material by anisotropic strain during delithiation

Lithium cobalt oxides (LiCoO 2 ) possess a high theoretical specific capacity of 274 mAhg −1 . However, when LiCoO 2 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 LiCoO 2 cathode material after 100 cycles, and found that LiCoO 2 phase would degrade to Co 3 O 4 phase. The phase transition of Co 3 O 4 from LiCoO 2 gave rise to lattice expansion, by which the anisotropic strain was proposed by first-principles calculation to inhibit LiCoO 2 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 LiCoO 2 during delithiation at high voltage. In this case, the elongation of interplanar spacing also increases the diffusivity of Li ions in LiCoO 2 , contributing to rate performance.