Preparation of Hydrophobic PPy Coated V2O5 Yolk-Shell Nanospheres-Based Cathode Materials with Excellent Cycling Performance

Vanadium pentoxide (V2O5) has been extensively used as the cathode material for lithium-ion batteries (LIBs). But the chemical dissolution of V2O5 in the electrolyte greatly restrains its electrochemical performance, especially cycling stability. In the present research, polypyrrole (PPy)-coated V2O5 yolk-shell nanospheres (V2O5@PPy) were synthesized by a simple solvothermal method in combination with the vapor deposition method. The density functional theory (DFT) analysis demonstrated that the PPy layer formed by oxidative polymerization manifested hydrophobicity and shielded the trace amount of water on electrode materials. Moreover, the polymerization process induced a gradient distribution of oxygen vacancies in the material and facilitated the rapid transfer of charges. The yolk-shell structure provided sufficient spaces to alleviate the structure change of electrode materials during lithiation/delithiation and inhibited the structural degradation. Hence, V2O5@PPy displayed an excellent cycling performance by improving the electrical conductivity and suppressing the chemical dissolution of V2O5. When the discharge current densities were 1 A g(-1) and 5 A g(-1), an ultralong cycling life of 1000 cycles (discharge specific capacity of 133.3 mAh g(-1)) and 5000 cycles (discharge specific capacity of 121 mAh g(-1)) was obtained in the voltage range of 2.5-4.0 V, respectively.