Photon-assisted charging in thin-film lithium-ion batteries using LiMn2O4 cathodes

In pursuit of alternative strategies to probe the optoelectronic properties of lithium-ion battery materials, this study presents the fabrication and photoelectrochemical evaluation of a CR2032-type coin cell featuring a nanostructured LiMn 2 O 4 thin-film cathode (∼500 nm thick) with an optical quartz window for in situ light exposure. The LiMn 2 O 4 film, with a direct bandgap of 2.08 eV and grain size ∼67 nm, was irradiated using a 532 nm laser (37 mW) to investigate the effect of photoexcitation on battery performance. Under illumination, a photomodulated electrochemical response was observed, attributed to the generation of electron–hole pairs within the LiMn 2 O 4 layer. This photogeneration led to (i) a shift in the quasi-Fermi level, resulting in an increase in open-circuit voltage from 2.9168 V (Light-OFF) to 2.9183 V (Light-ON), and (ii) enhanced charge transfer kinetics, evidenced by a decrease in charge-transfer resistance at the electrode/electrolyte interface from 1905 Ω to 1742 Ω. Furthermore, the lithium-ion diffusion coefficient increased from 2.92 × 10 −9 to 9.15 × 10 −9 cm 2 /s—under green laser illumination. These results highlight how bandgap-matched photon excitation can be employed as a probe of carrier dynamics and interfacial transport phenomena in LiMn 2 O 4 , providing new insights into the fundamental light–matter interactions that govern energy storage processes. • LiMn 2 O 4 thin films show photoactivity under 532 nm laser illumination. • Light exposure increases cathode voltage from 2.9168 V to 2.9183 V (OCV). • Charge transfer resistance drops from 1905 Ω to 1742 Ω under light. • Photon-induced carriers enhance Li-ion transport and kinetics. • Real-time current modulation confirms light-driven electrochemical effects.