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.
Publication Date: 2026