Ice, Ice Battery: Characterization of NMC532 Lithium-Ion Battery Electrolytes for Cold Climates : Electrochemical and Physicochemical Insights into Sub-Zero Battery Performance

Sammanfattning

The desire to reduce carbon consumption through renewable energy and electric systems has significantly expanded the applications of lithium-ion batteries. Commercial lithium-ion batteries are designed to operate between 15-35°C and will encounter difficulties in sub-zero environments. For applications where it is not sustainable to integrate a thermal management system to obtain the optimum temperature, new solutions are needed. The low temperature affects the entire battery, and in this thesis, a focus and investigation to find suitable electrolytes have been performed. Electrochemical and physiochemical properties have been evaluated for low viscosity solvents in an NMC532 vs. graphite system. Cyclic voltammetry was performed to investigate the electrochemical stability window, and constant current cycling against graphite to assess the extent of solvent co-intercalation. Full cell cycling was also performed in sub-zero temperature. Direct current internal resistance was performed to evaluate how the internal resistance is affected by the low temperature. The nail penetration tests were performed to investigate the full cells behaviour during short circuits. The result obtained showed that the low viscosity solvents could cycle better in sub-zero temperatures than the reference electrolyte containing ethylene carbonate (EC) and diethyl carbonate (DEC) with 1 M LiPF6-salt. The internal resistance was increasing for most electrolytes at -20°C. The nail penetration test showed no risk of thermal runaway. This thesis resulted in two ketone-based electrolytes combined with EC:DEC and 5 % fluoroethylene carbonate (FEC) have a good ability to cycle at -20°C. However, more measurements are necessary to provide better statistics.