In-situ differential electrochemical mass spectrometry study on the effects of negative/positive ratios on gas evolution in lithium-ion full batteries

Gas generation in Li-ion batteries has a negative impact on their electrochemical performance and safety characteristics, the accumulation of flammable gases may result in explosion and combustion. In this work, we investigated the electrochemical performance and gas behavior of LiFePO4// Li4Ti5O12 lithium-ion full batteries with varying negative/positive(N/P) ratios. Firstly, studied their initial capacity, initial efficiency, multiplicity, and cycling performance. Additionally, we employed in situ differential electrochemical mass spectrometry (DEMS) to analyze the gas precipitation behavior of the full cell during charging and discharging at varying N/P ratios. Electrochemistry data indicate that excessively high or low N/P ratios impact the capacity performance, cycle stability, and gas behavior of the materials. DEMS monitoring revealed that as the N/P ratio increases, so do the production rates of H2, CO2, and CO. However, the production rate of C2H4 increases as the N/P ratio decreases. The continuous accumulation of gases can adversely affect battery performance. The optimal N/P ratio for achieving maximum performance with minimal gas production is found to be 0.95. This suggests that the N/P design is crucial in optimizing the electrochemical performance of the complete battery, particularly its safety performance.