Revealing the heat contribution and thermal behavior of individual electrode and electrolyte for sodium-ion batteries

Sodium-ion batteries (SIBs) with lower costs and longer cycle lives have remarkable advantages in large-scale energy storage. With their commercial application, thermal safety assessment is of significant importance to the large-scale development of SIBs. Herein, we conduct a detailed investigation into the heat contribution and thermal behavior of each electrode and electrolyte for SIBs. It is revealed that SIBs release substantial heat during discharging, originating from the more negative cathode entropy change. Furthermore, the source of irreversible heat is the Joule effect of ohmic and polarization resistance, with a greater proportion at low states of charge and low temperatures. The total heat is a superposition of reversible and irreversible heat, increasing at low temperatures and high current densities. Additionally, from the thermal stability evaluation results of the battery, it can be found that the cathode and anode in the charged battery exhibit poor thermal stability, and the electrolyte significantly weakens the stability of the electrode by corroding the cathode and forming the fragile SEI. Therefore, the design of thermal management systems guided by heat contribution, and the optimization of electrodes and electrolytes based on thermal stability are essential for developing thermally safe SIBs.