High‐Temperature High‐Voltage Thermal Charging Cells Enabled by Ca–Li Dual‐Cationic Ionic Liquid Electrolytes and Anionophilic Separators

Abstract Thermoelectric technologies (TEs) offer immense potential for waste heat recovery and energy storage. However, the practical application of current TEs has been severely hampered by potential performance degradation in extreme environments, particularly at high temperatures, due to electrolyte flammability or poor carrier mobility. The development of high‐temperature, high‐performance TEs is crucial for broadening their operational range and enabling diverse applications. Here, practical high‐temperature high‐voltage thermal charging cells (HHTCCs) are reported, facilitated by a heat‐resistant trifluoromethanesulfonate‐based Ca–Li dual‐cationic ionic liquid electrolyte containing functionalized AmimCl solvent, together with a thermotolerant composite membrane, PEN(polyphenylene‐ether‐nitrile)@ZrBDC‐F‐4%. The dual‐cation mechanism enables high thermal voltage through cooperative energy storage, while the functionalized AmimCl accelerates the mobility of Ca 2+ and Li + ions by weakening the surrounding shielding effect. Additionally, the anionophilic ZrBDC‐F‐4% nanoparticles in the composite membrane enhance carrier migration. As a result, the HHTCCs exhibit an impressive thermal voltage of 1.138 V, a remarkable thermopower of 15.3 mV K −1 , and an outstanding Carnot‐relative efficiency of 9.56% over an unprecedented temperature range from 328.15 to 393.15 K, demonstrating the excellent safety and feasibility of HHTCCs. This work expands the service‐temperature range of i‐TEs, holding significant promise for high‐temperature, high‐performance waste heat harvesting.