XPS Investigation of the Electrolyte Induced Stabilization of LiCoO2and “AlPO4”-Coated LiCoO2Composite Electrodes

The “AlPO[subscript4]” coating has been shown to improve the electrochemical performance of LiCoO2 batteries. We previously showed that the “AlPO[subscript4]” coating promotes the formation of metal fluorides, which could act as a stable surface film and protect LiCoO[subscript2] from continuous degradation upon cycling. In this work, we removed the fluorine source in the LiPF[subscript6] salt by using the LiClO[subscript4] salt and investigated the effectiveness of the “AlPO[subscript4]” coating. Interestingly, the “AlPO[subscript4]” coating was found to improve the voltage efficiency and capacity retention when cycling in the LiPF[subscript6] electrolyte, but was detrimental when cycling in the LiClO[subscript4] electrolyte. XPS revealed that the “AlPO[subscript4]” coating promotes the formation of metal fluoride in both electrolytes, with the surface film formed in LiClO4 being more electrically resistive compared to that formed in LiPF[subscript6]. The source of fluorine in the coated electrode cycled in LiPF[subscript6] is largely attributed to the LiPF[subscript6] salt whereas the source of fluorine in the coated electrode cycled in LiClO[subscript4] is the binder PVDF. We believe that the coating could react with HF impurity in the LiPF[subscript6] electrolyte or from the binder PVDF and form stable metal fluoride films on the surface.National Science Foundation (U.S.). Materials Research Science and Engineering Centers (Program) (award number DMR-0819762)United States. Department of Energy. Office of FreedomCAR and Vehicle Technologies (contract no. DE-AC03-76SF00098)United States. Department of Energy. Office of Basic Energy Sciences (contract no. DE-AC02-98CH10886