Understanding of pre-lithiation of poly(acrylic acid) binder: Striking the balances between the cycling performance and slurry stability for silicon-graphite composite electrodes in Li-ion batteries

Poly(acrylic acid) (PAA) is widely used as a polymer binder for high capacity silicon (Si) anodes in Li-ion batteries. When used, the carboxyl (-CO2H) groups of PAA can be partially lithiated (known as pre-lithiation treatment), which is believed to facilitates lamination process, especially for production on a large scale. However, such treatment impacts numerous physico-chemical properties of the PAA binder that affect the cycling performance of the electrode. Here we seek to quantify the pre-lithiation treatment effect on Li-ion cells containing Si-graphite composite electrodes. The electrochemical cycling results indicated that such pre-lithiation treatment of PAA can undermine the cycling performance, as more capacity loss was observed when pre-lithitated PAA binders were used. On the other hand, the same pre-lithiation practice is indeed beneficial for the lamination process, as it increases the viscosity of aqueous slurries at low shear rates (slows down sedimentation) and prompts the shear thinning (so that the slurries can be more easily mixed). Thus, there is an uneasy balance between the electrochemical performance that suffers from the pre-lithiation of PAA and the quality of slurry processing which benefits from the same practice. An alternative approach to slurry treatment would be desired to achieve better cycling performance without undermining the stability of slurry suspensions.