Unraveling the high expansion in low state of charge lithium-ion batteries after storage

Abstract

The higher expansion of low state of charge (SOC) lithium iron phosphate (LFP)/graphite prismatic batteries after storage has been a persistent concern for many battery manufacturers and users. This study successfully replicated the phenomenon using commercial LFP/graphite batteries. The post mortem analysis revealed that H₂O should be the main cause of gas evolution due to a lot of hydrogen was detected in the shelved 10 % SOC batteries. The Li₂CO₃ content on the anode surface of the 90 %SOC battery was higher than that of the 10 %SOC battery, which was speculated to be the reaction between the CO₂ generated by the side reaction of electrolyte with water and the lithium in the anode electrode of the 90 % SOC battery, thus consuming CO₂ to make the high SOC battery showed a lower expansion rate than the low SOC battery. Strictly controlling moisture during the manufacturing process of LFP/graphite batteries can effectively prevent the issue of low-SOC batteries exhibiting higher expansion after storage.