Ionic thermoelectric osmotic energy conversion for waste heat recovery of lithium-ion battery through liquid cooling

With the widespread application of electrochemical energy storage, lithium-ion batteries have been extensively utilized due to their advantages such as high energy and power density. However, the huge amount of low-grade waste thermal energy generated inside lithium-ion batteries means that they remain ineffectively utilized. At the same time, traditional solid-state thermoelectric materials suffer from relatively low energy conversion efficiency under low-grade thermal sources. Hence, the current study proposes an ionic thermoelectric osmotic energy conversion (OEC) system to recover low-grade waste heat from a lithium-ion battery simulator via liquid cooling thermal management. The absorbed low-grade waste heat in the liquid is used to generate a temperature gradient across the ion exchange membrane of the ionic thermoelectric OEC device to drive ion migration for electricity generation. Through continuous operation for 90 min under the equivalent 3C rate heating condition of the lithium-ion battery simulator, its surface temperature is experimentally maintained at 59.0 °C, while the maximum output power density of the ionic thermoelectric OEC can achieve 68.23 mW m⁻² at an ionic solution concentration of 0.05 mol l⁻¹ and pH value of 7. In addition, the maximum output power density of the ionic thermoelectric OEC device increases with an elevated solution pH value. It reaches 84.87 mW m⁻² at a solution pH value of 11, which is improved by 24% compared to that at a solution pH value of 7. Furthermore, at a solution pH value of 11, when the ion concentration is raised from 0.01 to 0.05 mol l⁻¹, the maximum output power density increases from 16.18 to 84.87 mW m⁻² by 425%. In addition, when it is further increased to 0.1 mol l⁻¹, the power density drops to 42.44 mW m⁻². The current study provides a promising route for utilizing low-grade waste heat generated inside lithium-ion batteries through ionic thermoelectric energy conversion.