Internal Cooling of Lithium-Ion Batteries: Multi-Functional Electrolyte for Thermal Management
At A Glance
Researchers at Colorado State University have patented a method for a novel thermal management system in lithium-ion batteries. The solution can control high thermal conduction resistances and potential thermal runaway in lithium-ion batteries.
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Lithium-ion batteries continue to have inherent thermal limitations that severely affect their performance in large battery packs. Large battery packs can consist of tens to thousands of individual cells, all of which generate heat during normal operation. If not properly managed, this heat can cause significant capacity degradation, and, in some cases, the temperature of the cell can trigger thermal runaway. This can increase the temperature of neighboring cells and cause more thermal runaway to be triggered. As a result, these packs require a sophisticated thermal management system. However, no commercial thermal management system is capable of directly managing the internal cell temperature. A practical thermal management system that can provide internal cooling to an electrochemical cell to avoid overheating problems inherent with current battery technologies would be a benefit to many devices that depend on renewable energy.
The high thermal conduction resistances of lithium-ion batteries severely limit the effectiveness of conventional external thermal management systems. To remove heat from the insulated interior portions of the cell, a large temperature difference is required across the cell, and the center of the electrode stack can exceed the thermal runaway onset temperature even under normal cycling conditions. One potential solution is to remove heat locally inside the cell by evaporating a volatile component of the electrolyte. In this system, a high vapor pressure co-solvent evaporates at a low temperature prior to triggering thermal runaway. The vapor generated is transported to the skin of the cell, where it is condensed and transported back to the internal portion of the cell via surface tension forces. For this system to function, a co-solvent that has a boiling point below the thermal runaway onset temperature must also allow the cell to function under normal operating conditions.
Integrating a thermal management system internal to each cell by using a multi-functional electrolyte can serve two functions simultaneously: transport of lithium-ions and removal of heat through passive evaporation. As heat is generated within the cell, a volatile electrolyte co-solvent is evaporated in small channels located in the positive electrode. The evaporate co-solvent is the condensed on the skin of the cell and reincorporated into the liquid electrolyte. The liquid-vapor phase change process absorbs a significant amount of energy per unit mass of volatile co-solvent evaporated and occurs at a near constant temperature once the bubble point of a mixture is reached. This system has the potential to provide continuous, passive thermal management through the entirety of every cell within a large pack.
- Unique thermal management system internal to cell
- Significantly improves performance of large battery packs
- Lithium Ion Batteries, generally
- Electric Cars
Last updated: May 2020