In situ neutron radiography of lithium-ion batteries: the gas evolution on graphite electrodes during the charging

In situ neutron radiography (NR) was used to study the gas evolution on graphite electrodes in lithium-ion cells containing different PVDF-based gel-type electrolytes. The amount of gas bubbles and channels was calculated by image analysis. Gas production was extremely high in the case of the electrolyte containing ethylene carbonate (EC) and propylene carbonate (PC) (2:3, w/w), 1 M LiClO₄. About 60% of the electrode surface consisted of the gas phase which resulted in an inhomogeneous local current distribution. In contrast, the electrolyte containing EC and γ-butyrolactone (GBL) (1:1, w/w), 1 M LiBF₄ only showed a small increase of the gas volume between the electrodes of about 3%. In situ NR also revealed the displacement of the electrolyte due to gas evolution and volume changes of the electrodes.