SPECIFIC CHARACTERISTICS OF SULFUR ELECTRODES IN SALT-SOLVATE ELECTROLYTES

Abstract

The influence of the technological parameters of the positive electrode and the composition of the salt-solvate electrolyte LiTFSI – TEGDME on the specific characteristics of sulfur electrodes during galvanostatic cycling in lithium-sulfur cells was studied. The dependences of the change in specific capacity on the cathode composition, the charge-discharge current density, and the preservation of the charged state were discussed. It was found that the concentration of salt in salt-solvate electrolyte determines the specific characteristics of sulfur and affects its stability during cycling. It was determined that the most stable specific capacity and high Coulombic efficiency of the discharge/charge process of lithium-sulfur cells under long-term cycling conditions were ensured at lithium salt concentration of 0.4 molar fractions (m.f.) in the salt-solvate electrolyte. The positive effect of reducing the size of sulfur particles and optimizing its concentration and the composition of conductive additives in the cathode on the specific characteristics of sulfur-containing electrodes during cycling was shown. It was determined that reducing the size of sulfur particles from δS ≤ 150 μm to δS ≤ 40 μm contributes to an increase in the specific capacity of lithium-sulfur cells by approximately 20% and had a positive effect on their stability during cycling. It was established that increasing the concentration of sulfur in the cathode from 50% to 70% by mass leads to a significant decreased in the specific capacity of lithium-sulfur cells as a result of accelerated passivation of the electrode by poorly soluble lithium polysulfides. It was shown that in salt-solvate electrolytes a high level of retention of specific capacity was achieved under the conditions of long-term storage of a charged sulfur cathode at the temperature of ~30 °C. With a sulfur content of 50% and 70% by mass in the composition of the cathode with a fractional composition of δS ≤ 80 μm, the return of the specific capacity was over 97%.