A Flexible and Stretchable Battery Inspired by Snake Scales
The KIMM research team developed a flexible, stretchable and safe battery inspired by the scales and flexible joints found on the scale structure of snakes.
With advancements in soft robotics and ultra-lightweight wearable devices, there is a challenge for developing lightweight flexible batteries that can be integrated into a small area. As a result, there is increasing research attention towards developing high-performance pliable lithium-ion batteries that can be useful in wearable devices, soft robotics, and implantable biomedical devices. These batteries need to exhibit flexibility and even stretchability along with high performance, reliability, and safety.
Lithium-ion batteries available commercially possess the high energy density required by compact power-intensive applications for reliable operation, but they suffer from the insecurity of electrolytes. Moreover, the development of flexible lithium-ion batteries strongly relies on the development of flexible electrodes and battery chemistries to achieve high reliability and stability under mechanical stress and deformation.
The research team from the Korea Institute of Machinery and Materials (KIMM), led by Senior Researcher Dr. Bongkyun Jang and Principal Researcher Dr. Seungmin Hyun at the Department of Nano-Mechanics, suggest that geometrically designed structures incorporating bioinspiration and mechanical metamaterials are promising solutions for integrating the components of soft robots. They developed a flexible, stretchable battery inspired by scales of snakes. The individual scales/cells, though being rigid, can be folded together to protect thinner material from external impacts. Moreover, these scales possess properties that make them stretchable so that they can move flexibly.
They created a highly stretchable battery with high stability and performance using shape-morphing, mechanical metamaterials based on origami and kirigami. In this technology, several small rigid batteries are connected in a snake-like structure; as compared to integrating a battery in a tight formation.
The image depicts the similarity of the shape-morphing battery developed to snake skin. Image Courtesy of KIMM.
The structure encompasses hexagonal cells consisting of batteries and interconnections between them. Here, the shape of each battery was optimized for high energy density. The hexagonal cells are connected with polymer and copper that use folding hinges, allowing the cells to deform freely. The structure ensures stability and durability under multi-axial deformation.
The hexagonal cells consist of a cathode (aluminum foil coated in lithium cobalt oxide [LCO]), an anode (copper foil coated in graphite), a separator, and an electrolyte solution of LiPF6 in ethylene carbonate (EC)/dimethyl carbonate (DMC) (1:1). The cells, along with the interconnections, are cut to the desired shape and size by using a cutting plotter and are sealed in an aluminum pouch.
The shape morphing battery was tested using an in-situ electrochemical testing apparatus. The cell demonstrated high performance even when subjected to a stretching ratio of 90% and a 10 mm radius bending curve across more than 36,000 charge/discharge cycles.
This technology can be implemented as an energy storage solution for wearables that require flexible and soft energy storage devices and for biomedical devices for the elderly and sick. Moreover, the developed batteries can power soft robots that can move flexibly and freely change shape.
Image Courtesy of KIMM.
The KIMM research team hopes to develop solutions that can increase the energy storage capacity of soft and flexible energy storage devices. In addition, they also plan to create multi-functional soft robots that combine artificial muscles with soft robot actuation technology.
Dr. Bongkyun Jang stated that, by applying the structure and design of snake scales, the KIMM research team developed a battery that is not only safe to use, but also retains its flexibility and stretchability. He also added that, down the road, he and his team aim to continue conducting follow-up research and development, so that this technology can be used for rehabilitation medical care and disaster relief and help ensure the health and safety of the general public.