Charging 'Battery' with Indoor Lighting

This image shows a battery that stores electrical energy converted from light energy produced by indoor lighting, connected to an IoT device to monitor indoor environmental information (temperature, humidity) in real time.

[Asia Economy Reporter Junho Hwang] Domestic researchers have developed a secondary battery that can be wirelessly charged using indoor lighting. This technology responds even to dim lighting, producing and storing electricity. It is expected to enable energy recycling by converting urban lighting into electricity and using it when needed.

Ulsan National Institute of Science and Technology (UNIST) announced on the 21st that a research team led by Professors Song Hyungon and Kwon Taehyuk developed a dye-sensitized photocharging battery that combines a fuel-sensitized solar cell and a lithium-ion battery, which produces electricity using light.

Structure and Operating Principle of Dye-Sensitized Photorechargeable Secondary Battery.

The research team improved the system by attaching a secondary battery to a fuel-sensitized solar cell (photovoltaic cell) that can generate electricity even under low-brightness indoor lighting, enabling stable power supply and reliable electricity storage. The electrode of the photovoltaic cell and the anode of the secondary battery have different energy levels, making it difficult to combine them, but this issue was resolved.

Co-first author Myunghee Lee, a doctoral researcher in the Department of Energy Engineering at UNIST, explained, "To fuse the photovoltaic cell and the secondary battery, electrons generated at the photoelectrode must move stably to the anode of the secondary battery. By injecting carbon into the surface of 'lithium manganese oxide,' which is mainly used as the cathode of lithium secondary batteries and has reactivity on both sides, we were able to align the energy levels of the two systems."

Performance of Fuel-Responsive Photocharged Cells with Redox Mediators under Varying Illumination Conditions

The research team also identified an effective 'redox mediator' that operates well in low-light environments. Fuel-sensitized solar cells operate by producing electricity through an oxidation reaction where the dye loses electrons upon receiving light. In this process, the redox mediator replenishes the electrons lost by the dye.

Co-first author Byungman Kim, an assistant professor in the Department of Natural Sciences at UNIST, stated, "In low-light environments where the number of light particles reaching the dye is small, the discharge voltage (thermodynamic property) was more important than how fast the redox mediator moves (kinetic property). We proposed criteria for selecting 'redox mediators' based on illuminance when designing photocharging devices."

Professor Kwon Tae-hyuk (from the left), Researcher Kim Byung-man, Researcher Lee Myung-hee, Professor Song Hyun-gon

The research team succeeded in operating a commercial IoT sensor after charging six photocharging batteries connected in series for 10 minutes under indoor LED lighting.

Professor Song Hyungon said, "The newly developed dye-sensitized photocharging battery achieved a high energy conversion and storage efficiency of 11.5% under indoor lighting, which is the highest in the world for low-light environments." Professor Kwon Taehyuk explained, "Indoor lighting accounts for nearly 10% of total energy consumption, so the effect of energy recycling will be enormous."

The research results were published as a cover paper in the academic journal 'Energy & Environmental Science.'

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