Ionic Peltier Effect in Li Ion Battery Electrolytes

Thermoelectric transport, i.e., charge current driven by a temperature gradient (Seebeck effect) and heat current driven by an electric current (Peltier effect), provides fundamental insights on microscopic thermodynamics and kinetics of materials and enables devices that convert between heat and electrical work. The ionic Seebeck effect in ionic thermoelectric materials was reported more than one century ago while the reciprocal phenomenon, the ionic Peltier effect, remains unexplored due to experimental challenges. This work reports experimental observations and quantitative measurements of the ionic Peltier effect by an ultrasensitive temperature difference metrology (UTDM) with an extremely high temperature difference resolution up to 4 uK. UTDM enables the probing of sub-mK-level temperature responses of ionic Peltier effect even in the presence of parasitic Joule heat. We observe high ionic Peltier coefficients (up to 450 mV) in liquid electrolytes commonly used in Li-ion batteries. These high Peltier coefficients are approximately one order of magnitude greater than the Peltier coefficients of well-optimized electronic thermoelectric materials and comparable to Peltier coefficients of lightly doped silicon. Our work provides a platform to study the microscopic physics of ionic Peltier effect and understanding the thermodynamics and kinetics of ion transport in Li-ion batteries.