Conductive Polypyrrole Coated Hollow NiCo2O4 Microspheres as Anode Material with Improved Pseudocapacitive Contribution and Enhanced Conductivity for Lithium-Ion Batteries

摘要

Conductive polypyrrole (PPy) coated urchin-like hollow NiCo2O4 (NCO) porous microspheres (NCO@PPy) were synthesized by an easy and cost-effective method. The NCO@PPy shows improved cycling stability and rate capability in comparison with the pure NiCo2O4 when used as anode material for lithium-ion batteries. In order to undersatnd the improvement of electrochemical performance of NCO@PPy, kinetic parameters and the lithium storage mechanism are investigated by EIS spectra and sweep voltammetry measurements. The sweep-rate-dependent CV (cyclic voltammetry) curves demonstrate an ever-increasing redox capacitive-controlled lithium storage originating from both, the hierarchical hollow structure and the effect of the PPy coating layer. The apparent Li+ ion diffusion coefficient of NCO@PPy and NCO derived from EIS and CV curves indicates that PPy coating layer reduces the charge-transfer resistances and improves the lithium-ion diffusion coefficient.