Discharge reaction mechanism of room-temperature sodium-sulfur battery with tetra ethylene glycol dimethyl ether liquid electrolyte

摘要

The first discharge curve of a sodium-sulfur cell using a tetra ethylene glycol dimethyl ether liquid electrolyte at room temperature shows two different regions: a sloping region and a plateau region of 1.66 V. The first discharge capacity is 538mAhg~(-1) sulfur and then decreases with repeated charge-discharge cycling to give 240mAhg~(-1) after ten cycles. Elemental sulfur of the cathode changes to sodium polysul-fides Na_2S_2 and Na_2S_3, during full discharge. The sodium polysulfides, however, do not reduce completely to elemental sulfur after full charging. In summary, the mechanism of the battery with liquid electrolyte is 2Na + nS→Na_2S_n(4>n≥2) on discharge and Na_2S_n(4>n≥2)→x(2Na + nS) + (1 -x)Na_2S_n(5>n>2) on charge.