Flexible lithium metal capacitors enabled by an in situ prepared gel polymer electrolyte

The rapid development of next-generation flexible electronics stimulates the growing demand for flexible and wearable power sources with high energy density. Li metal capacitor (LMC), combining with a Li metal anode and an activated carbon cathode, exhibits extremely high energy density and high power density due to the unique energy storage mechanism, thus showing great potential for powering wearable electronic devices. Herein, a flexible LMC based on an in situ prepared PETEA-based gel polymer electrolyte (GPE) was reported for the first time. Owing to the high ionic conductivity of PETEA-based GPE (5.75 × 10⁻³ S/cm at 20 °C), the assembled flexible LMC delivers a high capacitance of 210 F/g at 0.1 A/g within the voltage range from 1.5 V to 4.3 V vs. Li/Li⁺, a high energy density of 474 Wh/kg at 0.1 A/g and a high power density of 29 kW/kg at 10 A/g. More importantly, PETEA-based GPE endows the LMC with excellent flexibility and safety, which could work normally under abuse tests, such as bending, nail penetration and cutting. The in situ prepared PETEA-based GPE simplifies the fabrication process, avoids the risk of leakage and inhibits the growth of Li dendrite, making LMC a promising flexible energy storage device for the flexible electronic field.