Effect of the PrPO4 Modification on the Structure and Electrochemical Performance of LiCoO2

Increasing interest in LiCoO2 as a cathode material for Li-ion batteries has recently arisen due to its high operating voltage, high energy density and long cycle life. However, irreversible structural damage and severe side reactions at high cut-off voltages severely deteriorate the electrochemical performance of LiCoO2 materials, resulting in a series of safety issues when used in batteries. In this work, PrPO4, Li2CO3 and Co3O4 are mixed and then treated at a high temperature to obtain PrPO4-modified LiCoO2 with improved electrochemical performance at 4.55 V. XRD and Rietveld refinement results confirm that the modified LiCoO2 materials exhibit well-ordered structures with compact unit cells. PrPO4 is not incorporated into the crystal lattice of LiCoO2 but converted by Li2O and Co3O4 into PrCoO3 and Li3PO4 phases during the reaction. Additionally, these two phases are well-incorporated into the LiCoO2 particle. Electrochemical tests indicate that the irreversible capacity during cycling is significantly reduced by PrPO4 modification. Benefiting from the enhanced interface stability induced by Li3PO4 and PrCoO3, the 1 mol% PrPO4-modified LiCoO2 sample exhibits an initial discharge capacity of 185 mAhg-1 at 0.5C with a capacity retention of 92.4% after 100 cycles, as well as an excellent rate capability with a capacity of 128 mAhg-1 even at 5C.