Engineering news
A team of researchers from the University of California (UC) San Diego and California company ZPower developed the rechargeable silver oxide-zinc battery. It is reportedly easier to manufacture than other flexible batteries – which require sterile, vacuum conditions – and can be screen printed in normal laboratory conditions.
“Our batteries can be designed around electronics, instead of electronics… designed around batteries,” said Lu Yin, one of the paper's co-first authors.
The device, which could be used in flexible, stretchable electronics for wearables and soft robots, reportedly has an areal energy density that is five-to-10-times greater than the previous state of the art. The areal capacity is 50 milliamps per square centimetre at room temperature – 10-20-times greater than the areal capacity of typical Lithium ion batteries.
“This kind of areal capacity has never been obtained before,” said Yin. “And our manufacturing method is affordable and scalable.”
The new battery’s higher capacity is down to much lower impedance, the resistance of an electric circuit or device to alternative current. The lower the impedance, the better the battery performance against high current discharge.
The device’s high energy density is due to its silver oxide-zinc (AgO-Zn) chemistry, the team said. Most commercial flexible batteries use Ag2O-Zn chemistry, which the researchers said limited cycle life and capacity. AgO is traditionally considered unstable, but ZPower's AgO cathode material uses a proprietary lead oxide coating to improve its electrochemical stability and conductivity.
The AgO-Zn chemistry is also responsible for the battery's low impedance, while the battery's printed current collectors have excellent conductivity, helping achieve lower impedance.
By testing various solvents and binders, researchers in Professor Joseph Wang's lab at UC San Diego found an ink formulation that made AgO viable for printing. A research announcement said the battery can be printed onto a polymer film in “a few seconds” once the inks are prepared, and it is dry and ready to use in minutes. The battery could be printed in a roll-to-roll process, which would increase the speed and make manufacturing scalable.
The printed batteries powered a flexible display system equipped with a microcontroller and Bluetooth modules. The cells were recharged for more than 80 cycles, without any major signs of capacity loss. They kept working despite repeated bending and twisting.
The research was published in Joule.
Want the best engineering stories delivered straight to your inbox? The Professional Engineering newsletter gives you vital updates on the most cutting-edge engineering and exciting new job opportunities. To sign up, click here.
Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.