Novel Binary Binder PAA-SBR Towards Silicon Anodes in Li-Ion Batteries

Abstract

Silicon remains a promising anode material for next generation lithium-ion batteries, despite the well-documented issues associated with it, due to its abundance and high capacity (3579mAh/g: almost 10 times higher than the capacity of graphite). The problems still facing Si-based battery commercialization are volume expansion, which results in rapid capacity fade, and continued Li loss through SEI formation from electrolyte decomposition. To address this problem, effective binders are considered to be one solution, and could help to maintain good contact between the active material and current collector but also to generate effective, stable networks between silicon particles and conductive carbon additives. This work will introduce a new binder system: Polyacrylic Acid-Styrene Butadiene Rubber (PAA-SBR). PAA is an aqueous-based polymer and possesses a high concentration of carboxyl group, which effectively bonds with the surface of silicon but also can H-bond with other polar species contributing to a good cohesive composite. SBR (Styrene Butadiene Rubber) is well known for its good flexibility, which can improve the tensile property of the electrode towards volume expansion. Therefore, it is hypothesized that the binary binder PAA-SBR can help Si anode achieve an improved, more stable performance because it can preserve good adhesion and flexibility simultaneously under the stress of the Si expansion. A preliminary study was conducted on Si vs.Li/Li+ half cells with different binder systems: PAA, PAA-SBR (2:1 mass ratio) and PAA-SBR (5:1 mass ratio), where PAA-only is used as the control binder. Cells are tested under the maximum lithiation capacity of 1200mAh/g at a C rate of C/5. Electrochemical cycling data indicates that for first 100 charge-discharge cycles, the PAA-SBR (2:1) showed a similar level of performance compared with PAA in terms of specific capacity (~1194mAh/g) and columbic efficiency (~99.5%), while the PAA-SBR (5:1) displayed capacity fade after 80 cycles, as shown in Fig.1. We anticipate that an optimized PAA-SBR ratio will generate superior composite durability during longer-term electrochemical testing. To further approve the hypothesis, a comprehensive study based on PAA-SBR (2:1) will be followed including polymer stability in electrolyte solvents, tensile properties, adhesion and impedance testing. Figure 1