Investigation on the Gas Saturation of Electrolyte on the Performance of Lithium-Ion Batteries

Summary:

Plenty of research and development about electrolytes in lithium-ion batteries has been published over the past years, for instance on conducting salts, solvents, and additives. It is well known that gases are formed during formation and operation of a lithium-ion battery. Mainly, those gases are attributed as products of SEI formation, and they are not considered to have a major influence on the performance. Some research groups, however, reported on the improvement of performance using carbon dioxide. So far, there is no reference in the literature to a systematic investigation of pre-gas saturation with different gases of the lithium-ion battery electrolyte. Therefore, we decided to systematically investigate the influence of pre-gas saturation on the performance of lithium-ion batteries. Here an electrolyte was saturated with different gases, that were observed to occur in lithium-ion batteries: argon, carbon dioxide, carbon monoxide, ethene, acetylene, hydrogen, methene, and oxygen. Charge/discharge characteristics, C-rate influence, coulombic/energy efficiency, and electrochemical impedance spectroscopy were examined for a detailed understanding.

Through this detailed investigation we proved that gases vary significantly in their influence on performance and cycling stability of the battery. Especially, the use of carbon dioxide revealed a remarkable increase in performance and a decrease in aging. These cells, as well as the cells with saturated electrolyte with hydrogen and oxygen, showed a higher C-rate capability and a decrease of irreversible loss in the first cycle. Carbon dioxide also showed a notable decrease of impedance in halving the impedance of the cell compared to our reference argon. Oxygen also showed a positive effect on the performance of the cell. In contrast to that the gases argon, ethene, carbon monoxide, methene and hydrogen showed a similar impedance after formation and similar capacity. On the other hand, acetylene showed a large decrease of performance, impedance, and a strong increase of aging.
We were able to determine by impedance measurements that differences attributed to the SEI and the charge transfer revealing the diverging influences of the gases. For example, some gases influenced the charge transfer processes in a positive way.
In that respect, we can display that each type of gas saturated electrolyte has an influence on the electrochemical behavior. Based on these results, positive effects on lithium-ion batteries and thus on performance can be achieved by a purposefully pre-gassing saturation.