Interfacial Coupling-Induced Pseudocapacitance in LiFePO4@Polypyrrole Heterostructures Toward High-Rate Lithium Storage

The olivine-structured LiFePO4 (LFP) materials are widely used as commercial cathodes due to its high thermal/chemical stability, long cycle life, low price, etc. However, the poor high-rate performance severely hinders its high-power applications due to intrinsically diffusion-controlled lithium storage. Herein, an interfacial coupling-induced pseudocapacitance (ICIPC) strategy to realize high-rate capacity lithium storage of LiFePO4@ polypyrrole (LFP@PPY) is provided. The strong interfacial coupling interaction between LFP and polypyrrole (PPY) promotes interfacial pseudocapacitance as a major Li+ storage mechanism during the charge/discharge process at high rates. The dynamic combination of interfacial and diffusion lithium storage of electrodes can enhance reaction kinetics, the rate capability and cyclic performance. In addition, the nanoscale PPY coating layer effectively improves the surface conductivity of the LFP particles and the charge transfer kinetics of electrochemical reactions. Therefore, the LFP@PPY cathode exhibits remarkable rate capability with a capacity of 105 mAh g(-1)at 10 A g(-1) and 84 mAh g(-1) at 20 A g(-1) and excellent cyclic stability performance with the initial capacity of 106.7 mAh g(-1) at 10 C (91.2 mAh g(-1) after 500 cycles). The ICIPC strategy may be extended to other cathodes (LiCoO2, etc.) to improve the high-rate performance.