Stabilizing Ketone-Based Electrolytes for Low Temperature Lithium-Ion Batteries

Sammanfattning

The need for long-term energy storage on all scales is increasing, as society moves towards a more fossil-free economy. Lithium-ion batteries are considered promising for such applications due to their widespread applicability, including portable electronics, military applications and electric vehicles. Current lithium-ion batteries operate well within the 20-60 ℃ temperature range but suffer from significant performance degradation at sub-zero temperatures. Efforts to mitigate this degradation have focused on developing electrolytes suitable for low temperature operation. Ketone-based electrolytes have been suggested as a potential solvent for these applications. This thesis focuses on investigating the long-term stability of ketone-based electrolytes in an NMC532/Graphite system. Galvanostatic cycling was performed in both room temperature and -20 ℃, alongside cyclic voltammetry and pressure cell measurements. The stability of the electrolytes was also evaluated by analyzing gases formed during cycling using GC-MS. The results showed that ketone-based electrolytes are unstable at room temperature, as they produce gas during cycling. However, the gas formation can be mitigated by adding co- solvents and additives, though this comes at the expense of the performance in sub-zero temperatures. Analysis of the decomposition products through GC-MS showed that there are several gases produced during cycling. To further characterize decomposition products and propose a reaction pathway for ketone-based electrolytes, additional measurements are required.