Stretchable lithium-Ion battery for wearables

Scientists at the Korea Institute of Science and Technology (KIST) have worked with graphene and carbon nanotubes to develop a working lithium-ion battery that can be stretched by up to 50% without damage to any of the components. The battery represents a significant step in the development of wearable or body-implantable electronic devices.

The design, described in the paper Stretchable Lithium-Ion Battery Based on Re-entrant Micro-honeycomb Electrodes and Cross-Linked Gel Electrolytepublished in ACS Nano, demonstrated a capacity of 5.05 milliamp hours per square centimeter, maintaining 95.7%  of this performance after 100  charge-discharge cycles. The battery also exhibited “superior electrochemical performance after 500 stretch-release cycles when the material was stretched up to 50%”.

Stretchable energy storage devices are of great interest because of their potential applications in body-friendly, skin-like, wearable devices. 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.

Here, an all-component stretchable lithium-ion battery was realized by leveraging the structural stretchability of re-entrant micro-honeycomb graphene–carbon nanotube (CNT)/active material composite electrodes and a physically cross-linked gel electrolyte, without using an inactive elastomeric substrate or matrix. Active materials interconnected via the entangled CNT and graphene sheets provided a mechanically stable porous network framework, and the inwardly protruding framework in the re-entrant honeycomb structure allowed for structural stretching during deformation.

The composite network consisting solely of binder-free, highly conductive materials provided superior electron transfer, and vertically aligned microchannels enabled facile ion transport. Additionally, the physically cross-linked gel electrolyte increased the mechanical stability upon deformation of the electrodes and was effective as a stretchable separator. The resulting stretchable battery showed a high areal capacity of 5.05 mAh·cm–2, 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.

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