The instrumentation and in-situ gas pressure monitoring of Li-ion pouch cells

Internal gas pressure monitoring during lithium-ion battery (LIB) operation is a key area of interest, it has the potential to provide a better in-depth understanding of battery operating status, as it varies with state of charge (SOC), electrical and thermal dynamic loading, and ageing. For the first time, we present a methodology that directly measures the internal gas pressure via a bespoke interphase fitting on different laboratory-scale pouch cell variants. This method provides an accurate representation of the internal gas pressure within pouch cells compared to current state-of-the-art methodologies that measure the change in the volume of the pouch bag and do not directly sample the internal gas. This methodology also offers the potential for adaptation for simultaneous gas composition analysis. Initial results from this work highlight the extensive gas generation observed during formation of lithium iron phosphate (LFP)/graphite pouch cells (12 cm × 5 cm) and nickel manganese cobalt (NMC)622/graphite A7 pouch cells. The reversible pressure change due to lithiation/delithiation of the electrodes is also observed with the SOC dependant trends in pressure for both cell chemistries. Our study further highlights the non-linear relationship between gas pressure and temperature under no electrical load and verifies the instrumentation methodology does not have an adverse effect on battery performance. • Novel, robust methodology to probe internal gas pressure of Li-ion pouch cells • Operando gas pressure evolution during cell formation monitored for the first time • Distinct SOC dependent pressure trends observed during cycling at different c-rates