Using CoS cathode materials with 3D hierarchical porosity and an ionic liquid (IL) as an electrolyte additive for high capacity rechargeable magnesium batteries

Abstract

Developing high capacity, rechargeable magnesium batteries is highly desired to meet increasing energy demands while targeting viable replacements for lithium batteries.

Lithium‐Salt Controlled Electrolyte and Flower‐Like Cobalt Sulfide Cathode for High‐Performance Magnesium Lithium Dual Ion Batteries

“…In the following two cycles, the strength and peak position change gradually until the cathodic peaks gradually stabilize at about 0.4 V indicating the kinetic enhancement during initial cycling. Besides, the small reduction peaks at 0.95 V are getting a little stronger after three cycles, which could be assigned to the insertion of Mg 2+ ions in the CoS cathodes following conversion of CoS to Co and MgS [24] . In contrast, for cell using APC/THF electrolyte, Figure S3 displays small reduction peaks at 0.95 V and high oxidation peaks near 1.8 V are derived from the Mg 2+ ions reaction with CoS during the initial three cycles.…”

“…These spheres are composed of large quantities of nanosheets. The formation mechanism of flower‐like CoS may involve: the Co 2+ ions coordinate with ethylene glycol (EG solvent) to form a complex, while thiourea is pyrolyzed to give H 2 S in the solvothermal environment [24] . Then Co 2+ ions are slowly released from the complex and react with H 2 S to form CoS metastable nanosheets and self‐assemble to form the flower‐like CoS [23,28] .…”

“…Furthermore, CV curve area of the cells using APC‐0.8 LiCl/THF electrolyte is much larger than those using APC/THF electrolyte without LiCl additive, implying that LiCl takes a significant role in enhancing the electrochemical performance of CoS for MLIBs. Previous works [28,31] have reported the conversion reaction of CoS electrode with Li + and Mg 2+ ions for LIBs and MIBs [24] …”

“…It indicates that more CoS materials are exposed to electrolyte owing to the gap caused by volume expansion during cycling. As a result, Li + and Mg 2+ ions can react with more active materials including CoS and Co 9 S 8 [24,38] . At the same time, the Li 2 S and MgS concentration in the electrolyte increases with the cycling, which is conducive to slow down the dissolution and help increase the reaction reversibility of Li 2 S and MgS [38–39] .…”

“…CoS was synthesized by He using hydrothermal method to control the ratio of ethanol and water, then to be used in MIBs [23] . The hierarchical cobalt sulfide (CoS) spheres were prepared by solute thermal method, [24] not only facilitating the transport of magnesium ions but also alleviating volume expansion during discharge/charge. The CoS cathodes enables a high capacity (up to 370 mAh g −1 at 20 mA g −1 ) and good rate performance (300 mAh g −1 at 50 mA g −1 ).…”