Design of Liquid Metal/Ionic Liquid Composite Gel Electrodes for Stretchable Li-Ion Battery Applications

Abstract

Stretchable Li-ion batteries are promising power sources for next-generation wearable and deformable electronics; however, designing battery electrodes that simultaneously provide electronic conductivity, ionic conductivity, and mechanical stretchability remains challenging. Here, we develop liquid metal/ionic liquid composite gel electrodes containing Li4Ti5O12 as stretchable mixed electronic–ionic conducting electrodes for Li-ion batteries. Ag powder was introduced as a filler for Ga-In liquid metal, enabling partial alloying at the Ag/LM interface; the resulting improved wettability enhanced the continuity of the metallic conductive network. Consequently, the electronic conductivity reached the order of 103 S cm–1, substantially higher than that of Ni-based counterparts. Tensile and electromechanical measurements showed that the liquid metal (LM) phase maintained stretchability (>50% strain) and suppressed resistance increases during deformation by bridging gaps between metallic particles. Selection of the ionic liquid (IL) component further improved ionic conductivity and charge–discharge performance. Using a thermoplastic polyurethane (TPU)-based composite gel electrode, reversible charge–discharge operation was demonstrated even under 50% strain. However, post-cycling analysis revealed electrochemically induced degradation of TPU, accompanied by deterioration in mechanical integrity. These results demonstrate IL/LM composite gel electrodes as a promising materials platform for stretchable Li-ion battery electrodes while identifying polymer electrochemical stability as a key requirement for durable deformable energy-storage devices.