Safer and flexible battery developed for wearable technology
Researchers have developed a safer, cheaper and more flexible battery option for wearable devices.
Fitness trackers, smart watches, virtual reality headsets, smart clothing and implants are becoming ubiquitous. These devices require more flexible and miniaturized energy storage mechanisms for greater comfort, reliability and longer lifespan. Improvements must not endanger safety.
Recent battery research has focused on ‘micro’ flexible energy storage devices (MFESDs). Aqueous microbatteries offer distinct advantages between different structures and electrochemical bases.
Aqueous batteries, which use a water-based solution as the electrolyte, have been around since the late 19th century. However, their energy density is too low for applications such as electric vehicles. Lithium-ion batteries are more suitable for such use.
Despite the 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).
“Unfortunately, until now, AMBs have not lived up to their potential,” said Ke Niu, a materials scientist at the Guangxi Key Laboratory of Optical and Electronic Materials and Devices of Guilin University of Technology. “To use in a wearable device, they must withstand bending and twisting in the real world. Most tested to date fail under such stress.
Self-healing AMBs are needed to overcome stress fractures. However, current self-healing AMBs rely on metal compounds, which react strongly with the electrode materials, causing performance degradation.
“So we started exploring the possibility of non-metallic charge carriers,” added Junjie Shi, a researcher at the School of Physics and Center for Nanoscale Characterization and Devices (CNCD) at 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,” says 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 disrupting their structure, providing flexibility and self-healing properties.
Titanium carbide, a 2D nanomaterial, was chosen for the anode because of its conductivity. Manganese dioxide was woven into a carbon nanotube matrix for the cathode to improve conductivity.
Testing showed that the prototype battery showed excellent energy density, power density, longevity, flexibility and self-healing after ten cycles.
The team wants to further develop their prototype and optimize it for commercial production.
Research report:A self-healing aqueous ammonium-ion microbattery based on PVA-NH4Cl hydrogel electrolyte and MXene-integrated perylene anode
