Fitness trackers, smart watches, virtual-reality headsets, smart clothing, and implants are becoming ubiquitous. These devices need more flexible and miniaturized energy storage mechanisms for improved comfort, reliability, and longevity. Enhancements must not compromise safety.
Recent battery research has focused on 'micro' flexible energy storage devices (MFESDs). Aqueous micro batteries offer distinct advantages among various structures and electrochemical foundations.
Aqueous batteries, which use a water-based solution as an electrolyte, have been around since the late 19th century. However, their energy density is too low for applications like electric vehicles. Lithium-ion batteries are more suitable for such uses.
Despite lower energy density, aqueous batteries are safer and cheaper than lithium-ion batteries. This makes them a viable option for MFESDs, known as aqueous micro batteries (AMBs).
"Up till now, sadly, AMBs have not lived up to their potential, said Ke Niu, a materials scientist with the Guangxi Key Laboratory of Optical and Electronic Materials and Devices at the Guilin University of Technology. "To be used in a wearable device, they need to withstand real-world bending and twisting. Most explored so far fail under such stress.
Self-healing AMBs are needed to overcome fractures from stress. However, current self-healing AMBs depend on metallic compounds, which react strongly with the electrode materials, reducing performance.
"So we started investigating the possibility of non-metallic charge carriers, added Junjie Shi, a researcher with the School of Physics and Center for Nanoscale Characterization and Devices (CNCD) at the Huazhong University of Science and Technology.
The research team identified ammonium ions, derived from ammonium salts, as optimal charge carriers. They are less corrosive and have a wide electrochemical stability window.
"But ammonium ions are not the only ingredient in the recipe needed to make our batteries self-healing, said Long Zhang, another leading team member at CNCD.
The team incorporated ammonium salts into a polyvinyl alcohol (PVA) hydrogel for its strength and low cost. Hydrogels can absorb and retain large amounts of water without disturbing their structure, providing flexibility and self-healing properties.
For the anode, titanium carbide, a 2D nanomaterial, was chosen for its conductivity. Manganese dioxide was woven into a carbon nanotube matrix for the cathode to improve conductivity.
Testing showed the prototype battery exhibited excellent energy density, power density, cycle life, flexibility, and self-healing after ten cycles.
The team aims to further develop and optimize their prototype for commercial production.
Research Report:A self-healing aqueous ammonium-ion micro battery based on PVA-NH4Cl hydrogel electrolyte and MXene-integrated perylene anode
Related Links
Huazhong University of Science and Technology
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