LiFePO ₄ Particles Embedded in Fast Bifunctional Conductor rGO&C@Li ₃ V ₂ (PO ₄ ) 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 LiFePO ₄ particles trapped in fast bifunctional conductor rGO&C@Li ₃ V ₂ (PO ₄ ) 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 LiFePO ₄ 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.