Promoting long-term cycling performance of high-voltage Li2CoPO4F by the stabilization of electrode/electrolyte interface

Abstract

High-voltage Li₂CoPO₄F (∼5 V vs. Li/Li⁺) with double-layer surface coating has been successfully prepared for the first time. The Li₃PO₄-coated Li₂CoPO₄F shows a high reversible capacity of 154 mA h g⁻¹ (energy density up to 700 W h kg⁻¹) at 1 C current rate, and excellent rate capability (141 mA h g⁻¹ at 20 C). XRD and MAS NMR results show that Li₂CoPO₄F can be indexed as an orthorhombic structure with space group Pnma and coexists with Li₃PO₄. The XPS depth profiles and TEM analysis reveal that the as-prepared material has a double-layer surface coating, with a carbon outer layer and a Li₃PO₄ inner layer, which greatly enhances the transfer kinetics of the lithium ions and electrons in the material and stabilizes the electrode/electrolyte interface. Using LiBOB as an electrolyte additive is another way to further stabilize the electrode/electrolyte interface, and the LiBOB has a synergistic effect with the Li₃PO₄ coating layer. In this way, the Li₂CoPO₄F cathode material exhibits excellent long-term cycling stability, with 83.8% capacity retention after 150 cycles. The excellent cycling performance is attributed to the LiBOB electrolyte additive and the Li₃PO₄ coating layer, both of which play an important role in stabilizing the charge transfer resistance of Li₂CoPO₄F upon cycling.