Enhancing the structural stability and cycling performance of LiCoO2 at 4.55 V by YPO4 modification

To date, LiCoO2 has received extensive attention as a cathode material because of its unique characteristics. To satisfy the strong demand for high energy density, the cut-off voltage of LiCoO2 is continuously increased. However, the structural instability of LiCoO2 at a high cut-off voltage leads to capacity decay and many safety issues, which hinder further application of LiCoO2. Herein, YPO4 is used to achieve a better electrochemical performance for LiCoO2 at 4.55 V. In the synthesis process, YPO4 is transformed into the Li3PO4 and Y2O3 phases, which are basically uniformly incorporated into the particle and form a composite with LiCoO2. Owing to the synergistic modification of Li3PO4 and Y2O3 phases, YPO4-modified LiCoO2 materials show enhanced structural stability and excellent cycling performance. Particularly, 1.5% YPO4 modified LiCoO2 not only exhibits a reversible discharge capacity of 171.6 mAh g-1 over 500 cycles with 91.7% capacity retention, but also delivers a capacity of 144.5 mAh g-1 at 5 C (1 C = 274 mAh g-1). This work suggests that using rare-earth metal phosphates can be an effective strategy to improve the cycling performance of LiCoO2 at 4.55 V.