Electrochemically driven thermomechanical energy harvesting

In an electrochemical cell, differences in the chemical potential of lithium (Li) between two electrodes drives Li ions (Li + ) across the electrolyte.Such differences can arise from mechanical or thermal loading, providing a basis for harvesting low-frequency mechanical energy and low-grade heat.Guided by this thermodynamic principle, we construct an electrochemical cell comprising lithium-tin (Li-Sn) and amorphous lithium-silicon (a-Li-Si) electrodes separated by an electrolyte-soaked separator.We examine three operating modes of the energy harvester: (i) uniform pressure applied to both electrodes, which exploits the partial molar-volume asymmetry, (ii) non-uniform temperature change across the two electrodes, which exploits the combined partial molar-entropy asymmetry and the imposed temperature difference, and (iii) simultaneous pressure-temperature stimulation.The pressure-only and temperatureonly loading each generate measurable short-circuit currents, demonstrating independent conversion of mechanical and thermal inputs into electrochemical current.Under combined loading, however, the resulting current deviates from a simple superposition of the two individual responses.We attribute this behavior to thermodynamic coupling: heating expands the electrodes, modifies the effective partial molar volume, and thus shifts the pressure-dependent Li chemical potential.These results establish a general thermodynamic framework for electrochemically driven energy harvesting across diverse external fields, while revealing the coupling complexities inherent to harvesting of low frequency mechanical and lowgrade thermal energies simultaneously.