Crossing the capacity threshold in Si-S batteries through mud-crack electrodes

Abstract

Silicon-Sulfur (Si-S) battery may promise high energy density and stability thanks to the high-capacity and less-dendrite-formation features of Si anode. However, current design principle for Si-S battery relies on a lab-scale, trial-and-error approach to designing and pairing sophisticated sulfur cathodes and Si/C anodes, lacking a feasible protocol to achieve practical application. Herein, we reveal that the Si-S battery made with commercially available Si/C and sulfur will reach a capacity (discharge) threshold that is independent of the mass of sulfur. This phenomenon is caused by the extremely sluggish Li⁺ diffusion at the charging plateaus (∼0.43 V) of silicon. In response to this challenge, we propose a dry-slurry process to fabricate a mud- crack structured Si electrode with significantly improved Li⁺ diffusion behavior, which could fully release the capacity of the full cell at low NP ratio by surpassing the capacity threshold. The resulting Si-S battery delivers a specific capacity of 1086 mAh g^-1 and 9.7 mAh cm^-2 with a sulfur loading of 8.9 mg cm^-2, which is much higher than the device based on the conventionally made Si/C electrode. Furthermore, the corresponding Si-S pouch cell achieves ∼600 mAh g^-1 after 200 cycles, showing a better stability compared to Li-S battery at a practical level. These findings suggest that charge transfer in the anode plays a decisive role in the overall performance and provides an overarching design protocol for fabricating practical Si-S full batteries.