Room temperature rechargeable magnesium (Mg) batteries are constructed from Mg as a negative material, sulfur (S)-containing composite prepared from elemental sulfur and the bis(alkenyl) compound having a crown ether unit (BUMB18C6) or linear ether unit (UOEE) as a positive material and the simple electrolyte (0.7 mol dm-3 Mg[N(SO 2 CF 3) 2 ] 2-triglyme (G3) solution). The reaction between molten S and the bis(alkenyl) compound (BUMB18C6 or UOEE) provides the sulfur-containing composite, S-BUMB18C6 or S-UOEE. Both of the sulfur-containing composites are electrochemically active in the Mg salt-based electrolyte, acetonitrile-or G3-Mg[N(SO 2 CF 3) 2 ] 2 electrolyte. The first discharge capacity of the test cells with the sulfur-containing composite is 460 Ah kg-1 (per the weight of sulfur in the composite) with the S-BUMB18C6 electrode and 495 Ah kg-1 with the S-UOEE electrode. According to the continuous charge-discharge cycle tests (at 10th cycle), the discharge capacity of the test cell with the S-BUMB18C6 electrode (68.1Ah kg-1) is higher than that with the S-UOEE electrode (0.18Ah kg-1). The crown ether units in the S-BUMB18C6 composite may create ion-conducting paths in the cathode, prevent rise in the internal resistance of the cathode, and provide better cycle performance of the test cells with the S-BUMB18C6 composite electrode than that with the S-UOEE electrode.
We prepared random copolymers from elemental sulfur (S) and bis(alkenyl) compound with crown ether (BUMB18C6). The resulted random copolymers, poly(S-r-BUMB18C6) were soluble in the organic solvents, tetrahydrofuran, N-methyl-2-pyrrolidone, and chloroform. The Ketjenblack (KB) and acetylene black (AB) particles were treated with the copolymer solution. TEM and EDS results of the treated carbon particles indicate that the incorporation of the copolymer into the KB cavities. The attachment of the copolymer to the AB particles was not observed, obviously. The copolymers in the KB particles showed the electrochemical responses based on the redox reaction of their polysulfide chains in organic electrolyte solution (1.0 mol dm-3 lithium bis(trifluoromethane)sulfonamide in 1:1 (v/v) mixture of 1,3-dioxolane and 1,2-dimethoxy-ethane). The lithium coin cells having the copolymer electrode were constructed and their charge-discharge behaviors were also tested under constant current conditions. Coulombic efficiency the test cells with poly(S-r-BUMB18C6-0.5)/KB electrode was over 95 % at 100th cycle and the average capacity through the 100 cycles was 286 Ah kg-1 .
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