The battery cell uses aqueous electrolytes instead of flammable organic solvents with an energy density suitable for portable electronic devices. The team combined two cells in series to power a wearable LED sleeve (above) that can be fully charged in just 20s via USB or a photovoltaic cell.
Conventional aqueous electrolyte-based energy storage devices have a limitation for boosting charges and high energy density due to low driving voltage and a shortage of anode materials. Instead, Prof Jeung Ku Kang and his team from the Graduate School of Energy, Environment, Water, and Sustainability built the cell with fibre-like polymer chain anodes and sub-nanoscale metal oxide cathodes on graphene. The energy capacity is determined by the two electrodes, and the balance between cathode and anode leads to high stability. In general, two electrodes show differences in electrical properties and differ in ion storage mechanism processes, resulting in poor storage and stability from the imbalance.
So the team came up with new structures and materials to boost the speed in energy exchange on the surfaces of the electrodes and minimise the energy loss between the two electrodes. The web-like structure of graphene leads to a high surface area on the anode, allowing higher capacitance.
For cathode materials, the team used metal oxide in sub-nanoscale structures to elevate atom-by-ion redox reactions. This method produces a higher energy density and faster energy exchange while minimising energy loss.
The resulting cell can be charged within 20 to 30 seconds using a low-power charging system such as a USB switching charger or a flexible photovoltaic cell. It shows more than 100 times the power density of conventional aqueous batteries and can be rapidly recharged, with its capacity maintained at 100% at a high charge/discharge current across 100,000 cycles.
“This eco-friendly technology can be easily manufactured and is highly applicable,” said Prof Kang. “In particular, its high capacity and high stability, compared to existing technologies, could contribute to the commercialization of aqueous capacitors. The device can be rapidly charged using a low-power charging system, and thus can be applied to portable electronic device.”
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