Analysis of Photo-Intercalation Towards Photo-Charging Lithium-Ion Battery
Authors: Chamidah Nur , Orikasa Yuki 
Published: December 2020

The energy conversion of light energy into electricity is one of the most promising studies to meet the increasing world energy demands. Solar cell is one of the spread energy devices where light energy converts to electrical energy to be used directly or to be stored as chemical energy for later use by using a rechargeable battery. However, the latter case including two steps of energy conversion in the basic solar cell drives to the low efficiency during device-to-device transfer. The efficient establishment of solar cell technology on a global scale requires an efficient improvement concerning materials and devices to increase the power conversion efficiency. The integration of light-harvesting solar energy with the battery system was expected to enhance the performance of the light energy conversion.
The photo-electrochemical reaction of lithium-ion insertion and deinsertion has been reported by employing dye-sensitized battery material under light irradiation [1]. The light energy generated electron-hole pairs with the holes aiding the chemical conversion. Nevertheless, energy efficiency and reaction kinetics should be improved by investigating the appropriate anode material for the system. By utilizing the photo-intercalation and photo-deintercalation concept that has been proposed by H. Tributsch in 1983 [2], the light energy can induce the transfer of ions between the electrode and electrolyte when there is a difference of fermi level energy between electrolyte and electrodes in semiconductor materials. Hence, to investigate the basic fundamental studies of the photo-intercalation reaction, active battery materials and semiconductors were utilized in the photochemical cell. A photo-sensitized LiFePO4 has been prepared to be applied as the working electrode, while a silicon p-type semiconductor has a role as the counter electrode in three electrodes battery system. The electrochemical transparent cell was utilized in order to observe the electrical current response from the energy produced by the reaction that takes place under the light irradiation.
The experiment was done by observing the current response of the LiFePO4/Si and the potential changes of LiFePO4 vs. Li+/Li full cell system under light irradiation. There was no electrochemical activation involved in the system. When there was no light irradiation, there was no current response observed. Meanwhile, there was a distinct current and voltage changes marked once the light was irradiating the photochemical cell. For further analysis, the chemical state changes of the electrode materials in the photo-electrochemical system were investigated by conducting an experiment using X-ray absorption spectroscopy. The experiment was done after the irradiation of light energy towards the material. It showed that there was peak changes shape of the X-ray absorption spectrum which corresponds to the lithiation of silicon. By this result, we acquired the possibility of advancing the design principles for photo-assisted rechargeable batteries by using prospective materials.
Reference:
[1] A. Paolella, et al, Nature Communication, 8 , (2017).
[2] H. Tributsch, Solid State Ionics, 9-10 , 41-58 (1983).