Ultrafast Li⁺ Diffusion Kinetics of 2D Oxidized Phosphorus for Quasi-Solid-State Bendable Batteries with Exceptional Energy Densities

Phosphorus has drawn much attention for energy storage applications due to its high theoretical capacity while its surface is prone to oxidization, causing alterations of its physicochemical properties. Herein, we report a previously overlooked Li storage mechanism in the oxidized 2D black phosphorus/graphene oxide (BP/GO) heterostructure, where Li⁺ ions transport at an ultralow diffusion barrier of 80 meV and an ultrafast diffusion kinetics of 2.5 × 10^-6 cm² s^-1 according to the ab initio molecular dynamics simulations. Furthermore, significant synergy arises when the 2D BP sheets chemically bind with GO layers, giving rise to an exceptional mechanical strength and flexibility of the BP/GO paper. The BP/GO composite anode sustains 500 stable cycles with Coulombic efficiencies as high as 99.6% in a Li ion half-cell. A quasi-solid-state, bendable Li-ion full-cell battery is assembled for the first time by using the BP/GO anode, a V₂O₅/CNT cathode, and a gel polymer electrolyte. It delivers simultaneously high gravimetric and volumetric energy densities of 389 Wh kg^-1 and 498 Wh L^-1, respectively, with a high retention rate of 92.3% even after 100 cycles of repeated folding and unfolding. The foregoing discovery makes the current flexible battery ideally suited for powering wearable electronics that require both high energy densities and mechanical robustness.