Utilizing High Tensile Alloys of Copper to Eliminate Mechanical Degradation in High Loading Silicon Anodes

Silicon is a promising candidate to replace the conventionally used graphite anodes due to its high theoretical capacity (3579 mAh/g; Li_3.75Si), low cost, and abundance. However, silicon undergoes huge volumetric expansion (~300%) upon lithiation, which leads to particle isolation and thus, poor cycle life. Polymeric binders such as polyacrylic acid and carboxy methyl cellulose, have been used to overcome this problem by binding with silicon particles. However, these binders do not provide a strong adhesion between the coating and the current collector, which can lead to delamination upon prolonged cycling. Recently, stronger polymeric binders (such as polyimide, polyamide, etc.) have received attention due to their improved interfacial interactions and mechanical strength, creating a cohesive silicon anode with excellent coating adhesion to the current collector. However, at higher loadings the huge volumetric changes in the silicon combined with the strong adhesive properties of binders leads to plastic deformations in the current collector, which on extended cycling can significantly wrinkle or in the worst case shred the metal foil. We are investigating high tensile alloy (HTA) copper current collector foils, which have tensile strengths that are more than double that of conventional copper foils. Due to their improved mechanical properties, these foils do not undergo plastic deformation upon silicon lithiation and prevent shredding upon continuous cycling. Electrochemical testing data suggest that at moderate silicon loadings (2.5-3 mAh/cm²), electrodeposited or rolled copper show significant wrinkling after only 5 cycles in a half-cell, whereas the HTA foils show no wrinkling. This effect increases significantly at higher loadings (>5 mAh/cm²), where the conventional copper foils show significant wrinkling after just one lithiation-delithiation cycle, while the HTA copper shows no wrinkling. By utilizing this HTA copper foils, it is possible to eliminate mechanical issues in the anode current collector, especially in high loading silicon cells with strong polymeric binders.