Novel strategies towards the realization of larger lithium sulfur/silicon pouch cells

Abstract

We report the fabrication of functional lithium sulfur full cells in button and pouch cell formats with the help of a prelithiation approach utilizing stabilized lithium metal powders (SLMP). A silicon electrode was prepared from silicon nanoparticles, carbon black and aqueous lithiated polyacrylic acid as a binder. The anode capacity was restricted to 900mAhg−1 based on the mass of composite. In a half cell configuration it may be cycled reversibly for at least 60 cycles at a specific current of 100mAg−1​ until the capacity starts to fade significantly. Coulombic efficiencies are well above 99%. However, the system possesses significant irreversible capacity of around 22%. For this reason a spray coating approach was used to coat the surface with SLMP. With this strategy the irreversible capacity could be compensated effectively. On the cathode side carbon/sulfur composites have been prepared by melt impregnation of activated charcoal. The composite was processed into electrodes with a polyethylene oxide/anisol binder solution. The composition ratio in wt% for the cathode was composite/carbon black/binder 80/10/10. At a specific current of 200mAg−1, the final electrode showed reversible capacities of 500mAhg−1 based on composite for at least 100 cycles with coulombic efficiencies above 90%. To add cycleable lithium into the cell, a slurry processing approach for the cathode was developed. SLMP was simply added to the cathode slurry. Resulting coatings have been stable under glove box conditions and could be further processed to full cells with the prelithiated anode as counter electrode. At first, button cell configurations were investigated. The cells showed higher initial discharge capacities of 400–500mAhg−1 based on the amount of cathode composite. Cells are relatively stable for 50 cycles. Larger single layer pouches with effective electrode areas of 24cm2 and an initial discharge capacity of 45 mAh at 200mAg−1 could successfully be assembled in a next step. The cells show almost the same performance as the smaller button cells.