Gas Evolution in Li-ion Rechargeable Batteries: A Review on Operando Sensing Technologies, Gassing Mechanisms, and Emerging Trends

Gas evolution is fundamentally problematic in rechargeable batteries, and may lead to swelling, smoking, and device-level failure. In laboratories, monitoring gas evolution can help understand dynamic chemical events inside battery cells, such as the formation of solid-electrolyte interphases, structural change of electrodes, and electrolyte degradation reactions. However, gassing in commercial batteries, discrete or continuous, is not monitored due to a lack of compatible sensing technologies. Here we describe the working principles of four real-time gas monitoring technologies for lithium-ion batteries. Gassing mechanisms and reaction pathways of five major gaseous species, namely H2, C2H4, CO, CO2, and O2, are comprehensively summarized. Since pertinent progress has been made on the optical fiber-based sensing of strain, pressure, and temperature of various battery cells recently, special emphasis has been given to fiber-based laser spectroscopy for gas detection. The technical details of the fiber-enhanced photothermal spectroscopy are compared with the four gas sensing technologies, and the commercialization possibilities are discussed. Owing to its small size, flexibility, and robustness, fiber-based sensing technology can be compatible with almost all kinds of battery cells, showcasing their great potential in various applications. It is envisioned that gas-event monitoring of rechargeable cells can be unlocked soon by utilizing fiber-based gas spectroscopy. Gas evolution is fundamentally problematic in rechargeable batteries. This paper reviews the real-time gas sensing technologies in laboratories, shedding light on the gassing mechanisms in battery cells with various cell chemistries. Herein, a new sensing method based on fiber-enhanced laser spectroscopy is proposed, which can potentially be used in commercial batteries. image