By Battery Power Online Staff
April 30, 2020 | Taking a cue from gimbap—Korean rice rolls—a research team from the Korea Institute of Science and Technology has developed a lithium-ion battery with both an electrolyte and packaging materials that are flexible enough to be stretched according to work published last month in ACS Nano (DOI:10.1021/acsnano.0c00187). The team hopes that the stretchable energy storage system can be further developed for wearable and body-implantable electronic devices.
The work was led by Dr. Jeong Gon Son and team at the Photo-Electronic Hybrids Research Center at the Korea Institute of Science and Technology (KIST). “Stretchable energy storage devices are of great interest because of their potential applications in body-friendly, skin-like, wearable devices,” the authors write in the paper’s abstract. “However, stretchable batteries are very challenging to fabricate. The electrodes must have a degree of stretchability because the active materials occupy most of the volume, and the separator and packaging should also be stretchable.”
In order to address these problems, the team focused on creating an accordion-like micro-structure, which gives structural stretchability to non-stretchable materials. They built a micro-inwardly curved electrode framework in a honeycomb shape. The inwardly protruded honeycomb framework consisted of atom-thick graphene, which serves as a curtain, and carbon nanotubes, which formed a nano-size rope. The honeycomb-shaped composite framework, made of active materials, graphene, and carbon nanotubes, was inwardly protruded like an accordion using a radial compression process, resembling the rolling of gimbap, which resulted in the creation of stretchable properties.
The electrodes developed by the research team do not contain any materials typically used for stretchability, such as rubber, that do not facilitate energy storage. All of the materials are used in energy storage and charge transport. In fact, the stretchable battery created by the team showed an energy storage capacity (5.05 mAh/cm2) that is as high as existing non-stretchable batteries.
The KIST newly introduced stretchable gel electrolytes and stretchable packaging materials, that block air and moisture, and keep the electrolytes from leaking.
“Our composite electrodes displayed little change in resistance when stretched, as well as long-term stability under repeated tensile testing,” the authors write. “A physically cross- linked gel electrolyte coated on the stretchable electrodes increased the mechanical stability upon deformation yet maintained high ionic conductivity; it also acted as a stretchable separator.”
The resulting stretchable battery showed a high areal capacity of 5.05 mAh/cm2, superior electrochemical performance up to 50% strain under repeated (up to 500) stretch-release cycles and long-term stability of 95.7% after 100 cycles in air conditions.