Three Methods to Reduce Gas Evolution from a Lithium-Rich Manganese/Graphite Pouch Cell

The safety performance of batteries is known to be deteriorated by gas evolution. Lithium-rich manganese-based materials exhibit a serious gas evolution during high-voltage cycles, which hinders their applicability. Herein, a 400 mA h lithium–manganese/graphite pouch cell was investigated via a drainage method and electrochemical mass spectrometry. Carbon monoxide, carbon dioxide, and oxygen were observed to be the primary gases. The charging and discharging voltages exceeding 4.5 V were the main cause of gas evolution. In an oxygen-sintering atmosphere (method 3), gas evolution decreased by 10% approximately during the formation stage and no gas evolution was observed during cycling. Furthermore, lithium hydroxide (method 2) had no effect on gas evolution, while lithium carbonate decomposed into CO2 at 4.6 V and caused battery voltage hysteresis. Finally, a pouch cell that did not exhibit gas evolution was obtained by optimizing the voltage range (method 1, 2.0–4.6 V for the formation stage and 2.0–4.5 V for cycling). At a rate of 0.5 C, the specific capacity of the cathode was 192 mA h/g, of which 84.2% was retained after 900 cycles; the mid voltage of the cathode was 3.56 V, of which 95.5% was retained after 900 cycles; and the specific energy was 666 W h/kg, of which 80.1% was retained after 900 cycles. These results support the commercialization of the cell.