Impact of the Slurry pH on the Expansion/Contraction Behavior of Silicon/Carbon/Carboxymethylcellulose Electrodes for Li-Ion Batteries

Electrochemical dilatometry experiments were performed on silicon/carbon/carboxymethylcellulose (Si/C/CMC) composite electrodes prepared with pH7 and buffered pH3 slurries. It was shown that the pH3 electrode better accommodates the severe volume change of the micrometric Si particles, inducing a much better capacity retention with cycling (70% after 10 cycles compared to only 6% for the pH7 electrode). During the first discharge (lithiation), a maximum electrode thickness expansion of ∼170% was observed for the pH3 electrode compared to ∼330% for the pH7 electrode. A lower irreversible expansion was also observed at the end of the 1 st cycle (∼50% compared to ∼180% for the pH7 electrode). It was explained by the fact that the pH3 of the slurry, which is known to favor the formation covalent bonds between the Si particles and the CMC chains, greatly improves the cohesive strength of the electrode as supported by the higher hardness and elastic modulus of the pH3 electrode. When the discharge capacity was limited to 1200 mAh g −1 , a progressive and irreversible swelling of the pH3 electrode was observed upon prolonged cycling, which was attributed to the accumulation of solid electrolyte interface (SEI) products.