Photorechargeable Lithium-Ion Battery Electrode Based on Nanocrystals of Anatase TiO2 Combining Energy Conversion and Storage

Abstract

The intermittent nature of renewable energies, in particular solar, limits its utilization at demand. Its hybridization with an energy storage reservoir is required, such as an electrochemical battery, to accommodate the balance between grid delivery and consumer demand. Although photovoltaic and batteries are two mature technologies widespread, their combination require electronics management, good assessment on both power dimensioning and ageing of each component, and still require a substantial cost reduction to become competitive with fossil fuels and nuclear. With long term view, the approach of bridging together the functions of solar conversion and its storage at the molecular level is worth attention for both scientific and technological point of view to pave the way towards photo-rechargeable ion batteries or non-intermittent photovoltaic displays. Tributsch in the early 80’s demonstrated the possibility to trigger light-induced interfacial ion transfer in mixed electronic/ionic semi-conductors as a result from the charge separation process within the depletion region (1). Up to now, the charges stored in such materials are only confined to the extreme surface (energy density less than 1 Wh/Kg), limited by the Debye length of the space charge layer (2). In this presentation, we will expose our strategy based on anatase TiO2 nanocrystals of 4 nm size assembled in carbon-free electrode to overcome this limitation. Anatase TiO2 with its n-type semi-conducting properties affords the de-insertion of lithium ions under illumination to counterbalance the hole transfer to Ti3+ induced by light. As a result from downsizing to such a nanoscale, surface reactions are promoted with respect to the total volume of particles. Consequently, our results, which will be discussed in-depth, show the possibility to quantitatively photorecharge an electrode of ca. 700 µAh/cm2 capacity in about one hour light exposure (Fig. 1). Both the mechanism and electrode performances will be discussed during this communication. Figure 1