NASICON-Structured LiZr2(PO4)3 Surface Modification Improves Ionic Conductivity and Structural Stability of LiCoO2 for a Stable 4.6 V Cathode.

Lithium cobalt oxide (LCO) as a classic layered oxide cathode for lithium-ion batteries is limited by the cutoff voltage, which only delivers about half of the theoretical capacity (∼4.2 V, 140 mA h g-1). Recently, raising the cutoff voltage to 4.6 V has been considered to further improve its specific capacity. However, LCO suffers from serious phase transition of O3 to H1-3, which leads to dramatic volume change and loss of cobalt, finally resulting in rapid capacity decay. In this work, we introduce the NASICON-structured LiZr2(PO4)3 (LZP), an ion conductor for lithium ion, to modify the surface of LCO by a wet-chemical method. Such a surface modification improves lithium-ion diffusion between the interface of LCO and electrolyte and restrains the O3 to H1-3 phase transition. As a result, the optimized LCO with 1 wt % coating (denoted as LCO@LZP-1%) demonstrates enhanced electrochemical performance in both half-cell and full-cell. To be specific, LCO@LZP-1% delivers a high specific capacity of 161.3 mA h g-1 and increases the capacity retention from 37.8 to 75.1% within 100 cycles. Importantly, the full-cell assembled by LCO@LZP-1% and artificial graphite can exhibit an outstanding energy density of 345.5 W h kg-1 (based on the total mass of cathode and anode).