On the correlation between volume change of anode materials in Li-ion cells and their degradation and failure

Aiming at increasing the energy density of lithium ion batteries, a Si alloy/graphite blend was used as anode material, replacing traditional pure graphite anodes. For the first time an in-situ in-operando electrochemical dilatometry was used to evaluate the expansion and contraction of this novel Si-alloy anode materials during electrochemical cycling under constant temperature. The results show an increase in volume for the first cycle (80 %) with around 12 % irreversible expansion, while for graphite based anode these values are 10% and 3%, respectively. These volume variations require particular attention when producing commercial cells. As a complementary study, commercial 18650 cells with graphite anode were investigated and the mechanical effects – jelly roll deformation – after cycling were studied by X-ray computed tomography. The deformation found for graphite electrode elucidates the importance of understanding and quantifying swelling of Si electrodes for commercial cells.