Studies on fundamental materials degradation mechanisms in lithium-ion batteries via on-line electrochemical mass spectrometry

Lithium-ion batteries show various degradation phenomena during charge and discharge. In this thesis, we tackle the oxidative decomposition of battery components in high-voltage cells, and place a particular emphasis on gassing reactions and the role of contaminants. We employ On-line Electrochemical Mass Spectrometry, a novel technique for gas analysis in lithium-ion cells, and combine it with our unique two-compartment battery test cell, which enables the independent analysis of reactions at anode and cathode. With these tools, we accurately quantify the oxidative decomposition of carbonate electrolyte and conductive carbon to CO2/CO, and demonstrate its amplification by trace H2O contamination. Further, we investigate the influence of electrolyte additives, e. g., vinylene carbonate, on the gassing during the initial formation cycles of a lithium-ion cell. Eventually, we evidence that degradation phenomena in high-voltage battery cells involve a „crosstalk“ between anode and cathode, which is responsible for continuous H2 generation and deterioration of battery performance. The thesis also includes a critical assessment of silicon anodes and Li-O2 batteries.