Covalently Bonded Electrochemical Interfaces for Flexible Aluminum–Graphite Electrodes

Flexible electronic systems require energy-dense batteries that can tolerate repeated mechanical deformation without loss of electrochemical performance. Conventional flexible battery architectures typically rely on weakly bound electrode–electrolyte interfaces, which are prone to interfacial resistance, disrupted mass transport, and mechanical failure under flexion. A covalent interface engineering strategy based on electrochemical sol–gel deposition is presented to create mechanically robust, chemically bonded electrochemical interfaces. In this approach, an ∼80 nm thick conformal silanol gel layer is electrochemically deposited to chemically anchor ionic liquid electrolytes to graphite cathodes in flexible aluminum–graphite batteries. This method enables precise control over interfacial thickness and chemistry while preserving electrode flexibility. Electrochemical characterizations using variable-rate cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic cycling demonstrate that covalent interface formation suppresses flex-induced interfacial resistance, shifts charge storage toward surface-controlled regimes, and enables rapid ion transport through ordered interfacial pathways without compromising electronic conductivity. Flexible full cells exhibit stable long-term cycling for >260 cycles with a specific capacity of 56 mAh/g of graphite. Individual electrodes retain electrochemical performance under bending up to 180°. By decoupling mechanical compliance from electrochemical stability, this work establishes a generalizable synthesis strategy for inherently flexible batteries and introduces an interface design paradigm for next-generation wearable and integrated energy storage devices.