Electrolyte engineering unlocks beyond 3.0 V voltage of V2O5 cathode for high-energy thermal batteries

High-voltage single cells (beyond 3 V) with V 2 O 5 cathode play a critical role in high-power, high-energy, and miniaturized applications of thermal batteries. However, V 2 O 5 obtains a bad discharge performance with a 2.5 V voltage plateau due to its poor incompatibility with LiBr in the traditional electrolyte LiF‒LiCl‒LiBr. This study substitutes LiBr with Li 2 SO 4 to form a LiF‒LiCl‒Li 2 SO 4 electrolyte, displaying excellent thermal stability with V 2 O 5 at high temperatures. The resulting V 2 O 5 /LiF-LiCl-Li 2 SO 4 /LiB cell achieves an initial discharge voltage of 3.53 V and a capacity of 359.8 mAh g −1 , which is 1.89 times higher than that of the LiBr‒based cell (189.95 mAh g −1 ). The self-discharge behavior of the cells is also systematically investigated, which is crucial for improving the longevity and thermal design of thermal batteries. A three‒cell prototype thermal battery delivers an output voltage of 10.35 V, with a discharge time for 150 s at a current density of 100 mA cm −2 . These measurements provide direct evidence that the V 2 O 5 /LiF‒LiCl‒Li 2 SO 4 /LiB cell becomes a promising high‒energy, miniaturized platform for next‒generation thermal batteries, justifying continued investigation and development.