Effect of Si layer thickness on the cycling stability and aging behavior of Li-ion capacitors with micrometer-sized Si anodes

Si is utilized as the active anode material of lithium-ion capacitors (LICs) to increase their energy and power densities. The main drawback of industrial Si-based LICs is their insufficient cycling stability resulting from the limited life of Si anodes. In this study, cell design parameters required for 10,000 stable cycles were determined using inexpensive unmodified 2 μm Si particles and a polyimide binder. Three cathode-to-anode capacity ratios were investigated by varying the thickness of a Si coating layer at a constant mass of the cathode fabricated from activated carbon (AC). The thickest Si coating with a thickness of 48 μm resulted in the anode/cathode capacity ratio of 56.4, which was calculated based on the apparent Si specific capacity of 3000 mAh g⁻¹ and AC specific capacity of 60 mAh g⁻¹. Conversely, the thinnest Si coating with a thickness of 10 μm exhibited a capacity ratio of 14.2 and highest energy density of 97.4 Wh kg⁻¹ at a power density of ∼1 kW kg⁻¹ during the first cycle, and the highest cycling stability corresponding to a retention of 78.3% after 30,000 cycles. Additionally, the aging behavior of the produced anodes and cathodes was examined via postmortem material characterization.