Photo-responsive electrode materials and multifunctional electrolytes for Li-ion batteries for multi-modal energy harvesting

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Self-sustained electrochemical energy storage systems are crucial to alleviate the barriers of energy transition toward future sustainable society. Lithium-ion rechargeable batteries represent a class of energy storage devices that are widely deployed due to high energy density, rate capability, and reliability. However, the autonomy of Li-ion batteries is limited due to the necessity of an external load that is required to reverse the electrochemical reactions responsible for power extraction (discharge). In this context, photochargeable batteries based on dual-mode electrode exhibiting photo- and electrochemical activities represent breakthrough energy technologies to simultaneously harvest and store solar energy. Electrochemical studies performed in light and under dark conditions demonstrate that photogenerated holes promotes the extraction of Li+ ions from the cathode material, which enables batteries solely rechargeable by light illumination. Within this bilateral project, new electrode materials (German Team) and photostable electrolytes (Japanese Team) will be studied to develop photo-rechargeable lithium-ion batteries that can be directly charged by visible light. Conventional lithium-ion batteries operate upon reversible Li+ transfer between a cathode and an anode through a liquid electrolyte. During charging process, Li+ extracted (de-intercalation) from the cathode migrates through an electrolyte for insertion (intercalation) into the anode. In photo-rechargeable lithium-ion batteries, the outward movement of Li+ (delithiation) is promoted by photooxidation of electrode material, however the mechanistic pathways (e.g., interdependence of bandgap of photoelectrode and battery voltage) for photo-induced Li+ extraction from the electrode are not well understood and will form a major aspect of this proposal. Although there are some reports on photo-switchable electrode materials, there is no insight into the role of liquid electrolyte that affects the photo-induced Li+ extraction. The originality of this project lies in its multidisciplinary approach in which the specialized know-how of the Japanese team in electrolyte development and solution/interfacial electrochemistry (PI: Prof. Y. Yamada) will be integrated with materials development and integration expertise of the German team (PI: Prof. S. Mathur) to realize a photobattery. The target of maximizing photo-charging efficiency will need adjustment of functional behavior of both electrode materials and electrolytes to accelerate Li+ extraction and prevent the recombination of photo-excited e-/h+, which cannot be achieved via conventional approach based only on electrode materials. The specific research objectives of this application include (i) fabrication of light active electrodes (ii) preparation of electrolytes and electrochemical assessment (iii) operando studies on interfacial electrode-electrolyte interactions under illumination and (iv) validation in full cell configuration.