Benefits and drawbacks of high-temperature formation cycling for lithium-ion batteries

Formation is a key process in battery manufacturing. During this process the solid electrolyte interface (SEI) and cathode electrolyte interface (CEI) are formed influencing the performance and lifetime of the cell. In this work, we investigate the effects of three different formation temperatures (45 °C, 60 °C, and 80 °C) on cell properties after formation and degradation of the battery during cycle life testing. We found that formation at 80 °C causes a higher loss of lithium and active material during formation. Nonetheless, this high-temperature formation reduces capacity fade during cycling. By coupling degradation mode analysis, statistical tools, and analysing the composition of the electrolyte, we conclude that soluble SEI components cause faster capacity fade in cells formed at the two lower temperatures. In addition, transesterification was suppressed by the high temperature formation. This was confirmed by gas chromatography and Thermal Electrolyte Analysis (TEA).