Design and Validation of an Online Partial and Total Pressure Measurement System for Li-Ion Cells

Online Electrochemical Mass Spectrometry (OEMS) is capable of monitoring both partial and total gas pressure of Li-ion cells. Herein, the development and validation of an OEMS system along with detailed calibration protocols and limits of detection sensitivity are showcased. A full cell based on LiCoO₂/Graphite cell during overcharge to 4.9 V vs. Li/Li⁺ at 50 °C is investigated and the results are compared to LiCoO₂/LiFePO₄ and Graphite/LiFePO₄ cells in order to differentiate between gases forming at the anode and cathode. The release of O₂ from Li_xCoO₂ (x < 0.4) during both charge and discharge demonstrates that its degradation is dependent on composition rather than potential. Combining partial and total pressure measurements provides a clear advantage when detailing major and minor gas reactions as well as when determining unaccounted gases. The methodology presented herein provides a technical basis for deeper understanding of degradation reactions in batteries and electrochemical systems alike.