Safe and Deformable Li-Ion Battery Based on a High-Voltage Hydrogel Electrolyte

Safe and deformable soft batteries are desirable for future wearable electronic devices. However, current Li-ion batteries on the commercial market are rigidly packaged and hermetically sealed to prevent moisture penetration and the leakage of toxic and flammable organic electrolytes. Since the modulus of elasticity and gas permeability of materials are inextricably linked, stretchable batteries often experience significant performance degradation over time in the ambient due to inevitable moisture penetration. Furthermore, the polymer-based flexible packaging materials can be easily damaged resulting in electrolyte leakage that poses significant safety concerns. Here we report a non-toxic, aqueous hydrogel electrolyte instead of its organic counterpart that is demonstrated to 1) enable highly safe operations due to its non-toxic and non-flammable nature; 2) alleviate the moisture penetration problem from the outside environment; (3) have a high-voltage working window of ~2.97V; and (4) allow the construction of stretchable batteries by using elastic polymer packaging materials instead of rigid hermetic seals. The prototype batteries have shown good stretchability (50% strain) and flexibility (radius of curvature < 2mm) to enable conformal attachments to a wide range of geometric surfaces. The prototype battery also shows outstanding cyclic stability, retaining ~90% of the original capacity after 100 cycles for over 2 months in the ambient environment without using any rigid hermetic sealing package. Finally, a prototype battery with a self-healing elastomer package remains functional after being punctured by a needle 5 times at different locations in the package. Furthermore, it can recover >90% of its capacity after being cut through by a razor blade and subsequently healed at 70 for 10 minutes. Such safe and highly stretchable batteries would be useful for several wearable electronic applications such as blood glucose monitoring, hearing rate monitoring, temperature monitoring, wireless charging, smart clothing, etc.