Flexible, Biocompatible Supercapacitors Weaved from Layered Phyllosilicates and Zwitterions via Ionicity

Limited resources impede the long-term viability of supercapacitors and batteries, underscoring the urgent need for next-generation energy storage alternatives. Phyllosilicates, e.g., bentonite clay, are among the most abundant natural minerals that could offer an attractive option; however, their brittleness and poor conductivity necessitate the use of harmful solvents and binders to develop durable membranes for energy applications. We present a polymer-free, aqueous-based approach in which betaine serves as a “molecular weaver” that simultaneously bridges clay platelets and enables ion transport and storage into free-standing, mechanically robust ion-conducting membranes and supercapacitors. Molecular dynamics simulations, rheo-impedance, and electroimpedance spectroscopies reveal that betaine intercalation creates ion-conductive pathways while preserving the clay structure. Further, the addition of transition-metal ions introduces redox-active sites, thereby yielding pseudocapacitive charge storage. The all-clay supercapacitors serve as electrodes (113 mAh/g vs. NMC811) and separators, delivering an energy density of 158 mWh/cm3 and a power density of 5688 mW/cm3, while retaining ~75% of their initial capacitance after 30,000 cycles, and can power LEDs up to 2.2 V after a brief charge. We show, for the first time, that zwitterions and clay can provide a simple, scalable, and sustainable avenue to engineer biocompatible, flexible supercapacitors for low-carbon innovations and energy applications.