Breaking the capacity limit for WO₃ anode-based Li-ion batteries using photo-assisted charging

The capacity of a metal ion battery is limited by fundamental parameters. Various strategies have been employed to maximise energy storage, including manufacturing control and investigating the components within the battery system. Recent developments have focused on incorporating photoactive materials into battery architectures to enhance energy density. However, challenges remain in material selection and processing for high-performance electrodes. Here, we show that hydrothermally produced WO3 is a safe, low-cost material with excellent photo-battery performance. Under illumination, the battery achieves a capacity of 1150 mAh g⁻¹ at 0.1C and 800 mAh g⁻¹ at 1C, exceeding the theoretical limit (693 mAh g⁻¹). The battery exhibits excellent cycling stability, retaining a capacity of 623 mAh g⁻¹ after 400 cycles at 1C. Using Randles-Sevcik and electrochemical impedance spectroscopy, we show that enhanced carrier mobility contributes to the observed capacity beyond the theoretical limit. The photo-conversion efficiency of the battery is 5.96%. Our results demonstrate that light can be used to enhance the capacity of an ion battery system beyond its theoretical limit. This approach can significantly boost the energy storage density of various metal-ion batteries. Moreover, in systems with inherently slow metal-ion diffusion, such as multi-valent systems, photoenhanced charging can make these technologies more competitive.