High cyclability of LiCoO2 at high-voltage enabled by mixed ion and electron conductor Li7.5La3Zr1.5Co0.5O12 shell

LiCoO2 is dominantly used in electronic products due to the high energy density, which can be further improved by increasing the cut-off voltage. However, the capacity of LiCoO2 under high voltage deteriorates rapidly. In addition, the rate capability of LiCoO2 is also poor due to the high resistance of Cathode-Electrolyte Interphase (CEI). Insulator (ZrO2)0.9(MgO)0.1, ion conductor Li7La3Zr2O12, and ion-electron mixed conductor Li7.5La3Zr1.5Co0.5O12 are coated on the surface of LiCoO2 by coprecipitation method, respectively. Even (ZrO2)0.9(MgO)0.1 coating can obviously improve the electrochemical performances of LiCoO2, and the effect of Li7La3Zr2O12 coating is slightly better than that of (ZrO2)0.9(MgO)0.1. Since both ions and electrons must conduct through the surface, the poor electron conduction of the surface layer could limit their performances. By contrast, Li7.5La3Zr1.5Co0.5O12 coated LiCoO2 exhibits the best cycle stability and rate capability. The capacity retention is 94.6% at 1 C after 200 cycles.