Confined sulfur electrode to achieve quasi-solid state sulfur conversion reaction in Li[sbnd]S battery

Abstract

An ordered mesoporous carbon (OMC) inlaid with micropores was derived via a hard template method. OMC micropores loaded with sulfur (S-OMC) were used as a cathode for the LiS battery. A comparison of UV–Visible analysis of S, S-OMC and S-loaded carbon nanotube (S-CNT) indicated lower solubility of S into the electrolyte from S-OMC. Controlling the solubility of S into the electrolyte is important to reduce the polysulfide concentration in the electrolyte. Cyclic voltammetry and galvanostatic charge-discharge measurements of S-OMC indicated the merging of solid-S → polysulfide and liquid-polysulfide → lower-order lithium sulfide transitions. Instead of the two-plateau discharge curve normally observed in S‑carbon composite electrodes, a single sloppy discharge curve was observed with S-OMC. Which possibly due to lower S concentration in the electrolyte, which results in reduced polysulfide concentration and lowers dynamic viscosity of the electrolyte. At 0.2C, nearly 1254 mAh g−1 of capacity was realized with capacity loss <5 mAh g−1 even after 50 cycles in lean electrolyte condition (3 μL/mgS). Distributed relaxation time analysis performed using a series of Nyquist plots recorded at various stages of charging and discharging indicate sudden decrease in the solution+contact resistance as a result of improved electrolyte access into the pores due to sudden volume contraction associated with Li2S → S at potentials >2.2 V in the confined zone. Due to the confinement effect, the growth of Li2S occurs slowly both at the anode and cathode, thereby enabling high voltage and capacity discharge with S-OMC compared to the S-CNT.