Enhanced Electrochemical Performances of Silicon Based Anodes By Carbon-Coated Copper Current Collectors: Towards Effective Strategy for High-Capacity Lithium Ion Batteries

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Silicon, despite having a higher theoretical capacity and a lower operating voltage range compared to graphite, which is a typical anode material for lithium-ion batteries (LIBs), is gaining attention as the next-generation anode material for LIBs. However, due to its significant volume expansion from lithium-ion insertion/extraction, lower electrical conductivity compared to graphite, and poor bonding strength between active materials and adhesion to the current collector, it has not been widely adopted as the main anode material in LIBs. Numerous studies have been conducted to enhance the performance of silicon anodes. Research aimed at controlling the size of silicon has shown that electrode pulverization can be mitigated, reducing the incidence of electrode cracks or pulverization. To improve the electrical conductivity of silicon, methods such as coating the silicon surface with carbon or using highly conductive materials like graphene and carbon nanotubes (CNT) have been explored. The application of binders that can form crosslinking networks, such as Poly (acrylic acid) (PAA) or alginate, has been shown to enhance the bonding strength between active materials and improve lifespan characteristics. Delamination of electrodes from the current collector during repeated charging/discharging is also a factor that shortens the lifespan of silicon anodes. However, research on the adhesion between the current collector and the silicon electrode has been limited. Most studies have increased cohesiveness between the anode active material and the current collector by coating conductive carbon on copper foil. Using spherical conductive materials can cause point bonding between the anode active material and the current collector, potentially providing insufficient pathways for electron movement. Alternatively, using carbon rods of several millimeters can increase the thickness of the current collector, posing a problem. In this study, a carbon-coated Cu foil was fabricated to improve the mechanical adhesion, interfacial resistance and electrochemical properties of the silicon anode. A carbon paste was prepared by mixing carbon fibers and a resin-based binder in a solution, and a carbon layer was coated on the copper foil using the doctor blade method. The morphology of the carbon-coated Cu foil was observed using Scanning Electron Microscopy (SEM). The optimal carbon-binder formulation and thin film uniform-coating method are crucial factors for the effective under-layer coated current collector. The enhanced mechanical adhesion and surface roughness with proper corrugation reveal high electrochemical performances of silicon-based anodes. Specifically, the application of the carbon-coated Cu foil resulted in reduced interfacial resistance and improved adhesion between the current collector and the electrode. The carbon fibers coated on the current collector facilitated faster electron transport, which not only increased capacity but also improved lifespan characteristics. Fast charging performance were also enhanced, and it was evident that close contact and improved electron conductivity between the current collector and the anode electrode significantly enhanced the characteristics of the silicon electrode.