<p>Thermocells are garnering increasing attention as a promising thermoelectric technology for harvesting low-grade heat. However, their performance is often limited by the scarcity of high-performance redox couples that possess both high thermopower and rapid redox kinetics. This work addresses this challenge by leveraging our recently developed copper (I/II) (Cu⁺/Cu²⁺) redox couple. We significantly enhance the performance of Cu-based liquid thermocells by integrating a thermosensitive crystallization process with etched carbon cloth electrodes, achieving synergistic improvements in thermodynamic and kinetic performance. The thermosensitive crystallization process establishes a persistent Cu²⁺ concentration gradient, boosting the thermopower from 1.47 to 2.93&#xa0;mV&#xa0;K⁻¹. Moreover, the etched carbon cloth electrodes provide a larger electroactive surface area and demonstrate a higher current density. Consequently, the optimized Cu⁺/Cu²⁺ system achieved an exceptional normalized power density <i>P</i>_max (<i>ΔT</i>)⁻² of 3.97&#xa0;mW&#xa0;m^‒2&#xa0;K⁻². A thermocell module comprised of 20 cells directly power various electronic devices at a temperature difference of 40&#xa0;K. This work successfully exhibits potential of Cu⁺/Cu²⁺ redox couple in thermoelectric conversion and introduces a valuable redox couple for high-performance thermocells.</p>