The integration of silicon into anode materials for lithium-ion batteries (LIBs) promises a significant leap in energy density, but it comes with the substantial challenge of managing silicon's pronounced volume expansion during cycling. A key strategy to mitigate this issue involves the use of electrolyte additives, with Vinylene Carbonate (VC) being one of the most effective and widely studied. This article delves into the chemical mechanisms by which VC contributes to the stabilization of silicon anodes.

Silicon anodes undergo a dramatic change in volume as they alloy with lithium during the charging process. This expansion and contraction cycle can mechanically fracture the anode particles and disrupt the protective layer that forms between the anode and the electrolyte – the Solid Electrolyte Interphase (SEI). A compromised SEI layer leads to continuous electrolyte decomposition, consuming active lithium and electrolyte components, which in turn causes a rapid decrease in battery capacity and lifespan. The primary role of Vinylene Carbonate is to influence the formation and structure of this critical SEI layer.

Chemically, VC is a cyclic carbonate with a vinyl group. During the initial electrochemical reduction on the anode surface, VC undergoes a reductive decomposition. Unlike linear carbonates, VC's structure allows it to polymerize into a more compact and mechanically robust SEI layer. Theoretical calculations and experimental observations suggest that VC can undergo single-electron transfer (SET) to form radical anions, which then react with other VC molecules or form polymeric species. These polymers create a more resilient barrier compared to the SEIs formed from simpler carbonate solvents. This polymeric SEI is better able to accommodate the physical stresses imposed by the silicon anode's volume changes, thereby preventing cracking and maintaining electrical connectivity.

Furthermore, the reduction pathway of VC can lead to the formation of lithium carbonate (Li2CO3) and other lithium organic species within the SEI. These components contribute to the SEI's passivating properties, reducing its impedance to lithium ion transport while effectively blocking electron transfer. The presence of the vinyl group in VC also makes it susceptible to reactions with other radical species, which can lead to cross-linking and further enhance the mechanical strength and chemical stability of the SEI. When used in combination with other additives like DMVC-OCF3 and DMVC-OTMS, the synergistic effects further refine the SEI's composition and properties, leading to even greater stability and performance improvements for silicon anodes.

In summary, Vinylene Carbonate stabilizes silicon anodes primarily by participating in electrochemical reactions that yield a more robust, polymeric SEI layer. This chemically and mechanically stable interface is crucial for managing silicon's volume expansion, preventing electrolyte decomposition, and ensuring the long-term performance and durability of lithium-ion batteries. The chemical understanding of VC's role is fundamental to designing next-generation battery electrolytes that can harness the full potential of silicon anodes.