Light vs Heat: Dissecting the De-intercalation in Photo-rechargeable Batteries

Does light or heat play a seminal role in photo-rechargeable batteries? This study unravels the effects of light in the exciton formation and separation processes in a photocathode, leading to the charging or de-intercalation of Li⁺ ions in a lithium-ion battery. Light induced oxidation of Ti³⁺ to Ti⁴⁺ in the Li_x(TiS₂-TiO₂) heterostructure cathode is shown here, while heating does not elicit such changes. With the aid of photogenerated electrons at the cathode, the de-lithiated Li⁺ ions from Li_x(TiS₂-TiO₂) get intercalated in the graphite anode during the photocharging process. Direct or passive heating leads to the degradation of the cathode electrolyte interface (CEI), instigating enhancement in open circuit potential. In contrast, photocharging leaves the organic electrolytes and CEI unaffected. Hence energy efficient photo-electrochemical energy systems can be built by carefully isolating the effects of heat and light in solar radiation, as dictated by this study.