Photo-Rechargeable Sodium-Ion Batteries with a Two-Dimensional MoSe₂ Crystal Cathode

Combining energy harvesting with energy storage systems in a single device could offer great advantages for continuous power supply in both indoor and outdoor electric applications. In this work, we demonstrate a photochargeable sodium-ion battery (PSIB) based on a photoactive cathode of two-dimensional crystals of MoSe₂. This photocathode enables spontaneous photodriven charging of a sodium-ion battery cathode under illumination and an increase in the reversible capacity to 29% at 600 mA g^-1 compared to that under dark conditions during galvanostatic cycling. Exposure of MoSe₂ to light drives the Na⁺ extraction, prompted by photogenerated holes, and accelerates the charge transfer kinetics with improved ion diffusion, which leads to an increased capacity. Moreover, the PSIB can be charged to 1.68 V under light illumination without applying an external current. Our work paves the way for the development of light-driven rechargeable batteries, which can benefit off-grid technologies such as the Internet of Things.