In the current work, in-situ volume and pressure responses of pouch cells were carefully measured with specially designed in-house fixtures (Figure 1). Volume expansion of pouch cells was measured by tracking the buoyancy force with a high precision balance, giving volume change precision to 1 micro liter with a long-term drift of < 10 microliter/day. Cell stack loading pressure was investigated by constraining cells between two fixed plates and a floating plate under a load cell. We found that the volume and pressure fixtures provided very similar patterns during pouch cell charging and discharging. Commercially available NMC/Graphite pouch cells showed symmetric and reversible P/V responses, while in-house cells with silicon-composite anodes showed an asymmetric response and long-term drift associated with continued SEI formation and gas generation.
 L. Lu, X. Han, J. Li, J. Hua, M. Ouyang, J. Power Sources, (226) 2012, pp 272 - 288