Lithium Substituted Poly(acrylic acid) as a Mechanically Robust Binder for Low-Cost Silicon Microparticle Electrodes

Silicon microparticles (SiMPs) are attractive anode materials for lithium ion batteries due to their high theoretical capacity, low cost, high initial Coulombic efficiency, and large packaging density. However, the substantial volume change induced by lithiation/delithiation causes the pulverization and loss of electronic conductivity of SiMPs, which lead to the fast capacity fading. In this study, we report that the cycling stability of SiMP electrodes can be effectively improved by using environmentally friendly and cost-efficient lithium (Li) substituted poly(acrylic acid) (PAA-xLi, x ≤ 1) as binders. Noticeably, the SiMP/PAA-0.75Li electrode with a mass loading of ∼0.9 mg/cm² can deliver a significantly higher capacity (2125 mAh/g, 100 cycles) at C/3 (1200 mA/g) than that (730 mAh/g) made of the pristine PAA (i.e., PAA-0Li) binder. We focused on understanding the mechanism of PAA-xLi binders by correlating the mechanical properties of SiMP/PAA-xLi electrodes with their electrochemical stability. The effectiveness of PAA-0.75Li can be attributed to its high elasticity and strong adhesion with SiMPs, both of which greatly enhance the mechanical integrity of SiMP electrodes and help keep pulverized SiMPs coalesced during cycling. These findings offer important design principles of binders for low-cost SiMP electrodes.