Vanadium Dioxide Cathodes for High-Rate Photo-Rechargeable Zinc-Ion Batteries

Photovoltaics are an important source of renewable energy, but due to the intermittent nature of insolation, solar cells usually need to be connected to rechargeable batteries, electrochemical capacitors or other energy storage devices, which adds to the complexity and cost of these systems. In this work, a cathode design for photo-rechargeable zinc-ion batteries (photo-ZIBs) is reported, that is inherently capable of harvesting sunlight to recharge without the need for external solar cells. The proposed photocathodes, comprising a composite of vanadium dioxide nanorods and reduced graphene oxide, are engineered to provide the necessary charge separation and storage for photocharging under illumination. The photo-ZIBs achieve capacities of ≈282 mAh g⁻¹ in the dark and ≈315 mAh g⁻¹ under illumination, at 200 mA g⁻¹, demonstrating the use of light not only to charge the devices, but additionally to enhance their capacity. The photo-ZIBs also demonstrate enhanced high-rate capabilities under illumination, as well as a capacity retention of ≈90% over 1000 cycles. The proposed photo-ZIBs are considered a promising new technology for addressing energy poverty, due to their high performance and inherent cost-efficiency and safety.