LiFePO4 Particles Embedded in Fast Bifunctional Conductor rGO&C@Li3V2 (PO4)3 Nanosheets as Cathodes for High-Performance Li-Ion Hybrid Capacitors

The sluggish kinetics of Faradaic reactions in bulk electrodes is a significant obstacle to achieve high energy and power density in energy storage devices. Herein, a composite of LiFePO4 particles trapped in fast bifunctional conductor rGO&C@Li3V2(PO4)(3) nanosheets is prepared through an in situ competitive redox reaction. The composite exhibits extraordinary rate capability (71 mAh g(-1) at 15 A g(-1)) and remarkable cycling stability (0.03% decay per cycle over 1000 cycles at 10 A g(-1) ). Improved extrinsic pseudocapacitive contribution is the origin of fast kinetics, which endows this composite with high energy and power density, since the unique 2D nanosheets and embedded ultrafine LiFePO4 nanoparticles can shorten the ion and electron diffusion length. Even applied to Li-ion hybrid capacitors, the obtained devices still achieve high power density of 3.36 kW kg(-1) along with high energy density up to 77.8 Wh kg(-1). Density functional theory computations also validate that the remarkable rate performance is facilitated by the desirable ionic and electronic conductivity of the composite.