Operando micro-computed tomography reveals temperature-dependent electrolyte movement dynamics in commercial NCR18650BD Li-ion cells

An operando micro-computed tomography (micro-CT) methodology is presented for characterizing and quantifying electrolyte movement within commercial Li-ion cells under laboratory conditions. We focus on temperature-dependent electrolyte dynamics, utilizing a commercial CT scanner and a specialized in-situ cycling stage for simultaneous 3D imaging (11.25 μm spatial, 4 min temporal resolution) and electrochemical testing. At 25 °C, electrolyte expulsion from the jellyroll into the upper donut region close to the positive terminal is observed at a rate of up to +0.69 V /V%⋅min −1 during charging, with partial reabsorption during discharge, thereby validating the electrolyte pumping concept. During discharge, a decrease in temperature leads to a reduction in both the electrolyte volume within the observed region and its outward movement rate (from −0.52 % V /V⋅min −1 at 25 °C to −0.32 % V/V⋅min −1 at −15 °C). A temporal lag between the cell voltage drop and the cessation of electrolyte movement is evident, particularly at lower temperatures. Pressure gradients driving the flow are estimated at 10–20 kPa⋅m −1 using Darcy's law. The temperature-dependent discharge dynamics allow for the calculation of an apparent activation energy of 7.80 kJ⋅mol −1 for the electrode assembly's overall contraction when discharging at 25 °C. • Operando micro-CT reveals Li-ion battery electrolyte dynamics in lab conditions • Temperature dependent electrode movement drives electrolyte motion • Electrolyte volume filling/emptying rates are in the 0.3-0.7 V /V% min -1 ⋅range • Electrode movement yields pressure gradients of 10-20 kPa⋅m -1 within the cell • Apparent activation energy of electrode movement is 7.8 kJ⋅mol -1 when discharging