Evaluation of multiple cooling strategies identify anti-freeze liquid FRAM® and paraffin wax as promising stabilizers of lithium-ion battery energy efficiency

Abstract

Rechargeable lithium-ion batteries are widely used in vertical lift drones and electric vehicles, owing to 10 times longer shelf life than lead-acid batteries. While lithium-ion batteries are climate-friendly, statistics point to growing fire-risk, as their performance drops  25% below 41°F and explosions occur above 95°F. Their greatest caveat is “thermal runaway,” an exothermic reaction chain which sharply increases the internal temperature causing destabilization. Multiple cooling strategies (air, liquid, or phase-change materials) differentially impact optimal battery temperature, and the resulting safety, durability, and performance efficiency of these batteries. To harness greater cost-benefit economics, this study evaluates cooling strategies to optimize energy efficiency of lithium-ion batteries. Fully-charged lithium-ion battery was connected to the discharger and examined at low, moderate, or high temperatures (~50ºF, 70ºF or 80ºF), mirroring mild winters and summers while maintaining safety standards. Using infra-red thermometer, surface thermal uniformity of the battery was recorded at 0, 10, 15, 20 minutes along with corresponding amperage indicating energy efficiency. Procedure was repeated with forced air cooling (small fan), indirect liquid cooling (water or anti-freeze liquid FRAM^®), or using phase change materials (paraffin wax). Lowered thermal uniformity due to air- or water-cooling decreased energy efficiency, while FRAM^® or paraffin wax cooling increased the energy efficiency irrespective of the ambient temperatures. These findings indicate that anti-freeze liquid FRAM® and paraffin wax cooling strategies at varied temperature zones each positively impact thermal uniformity and energy efficiency, warranting applied investigations of numerous configurations of lithium-ion containing batteries.