| Rechargeable Mg battery is regarded as a kind of ideal energy conversiondevice for a long time. Mg metal has the following virtues: Firstly, large volumespecific capacity (3833mAh cm-3); Secondly, high abundance in the earth crust(ranking5th); Thirdly, relatively low chemical activity and excellent safety.Therefore, it is hopeful that rechargeable Mg batteries will be applied in theenergy storage systems of Electric Vehicles.However, limited by the research of cathode material and electrolytesolution systems, the development of rechargeable Mg batteries is still on thestage of laboratory research. Mg has an active chemical property, thus in mostpolar aprotic solvents, a passive film forms on its surface. Unfortunately,comparing with the passive film of lithium ion battery, the film in rechargeableMg batteries is a poor conductor of Mg2+, as a result, Mg2+cannot get throughthe passive film and deposition and dissolution is impossible for Mg2+, whichseriously limits the electrochemical activity of the rechargeable Mg battery.Therefore, it is of great importance to find suitable electrolyte systems forrechargeable Mg batteries.Currently, the main problems which obstacle the research of rechargeableMg batteries are the following:1) the electrochemical windows of available electrolyte systems are too narrow, and they are also corrosive to non-novelmetal, which hardly fulfill the exploration of cathode material with high voltageplatform;2) the traditional solvent for rechargeable Mg batteries electrolyte saltis THF, which has a very low boiling point and strong volatility. Serious gasproblem will be gendered if THF is practically used in rechargeable Mgbatteries.Aiming at the above problems, in this paper, we prepared a novelboron-based electrolyte and studied its deposition-dissolution performance ofMg on non-novel current collector. In addition, we added Ionic Liquid PP14TFSIto THF, and this mixture of THF and PP14TFSI greatly enhanced the boilingpoint of pure THF and improved the safety of rechargeable Mg battery. Themain research contents are as follows:1）The second FPh group was introduced to Grignard reagent FPhMgBr toimprove the Mg electrochemical performance.(FPh)2Mg-Mes3B/THFelectrolyte was synthesized by complexing Mes3B and(FPh)2Mg in THF. In thispaper, we studied the Mg deposition-dissolution performance and the roomtemperature ionic conductivity in a variety of (FPh)2Mg-Mes3B/THF solutionwith different concentrations of Mg. The result showed that0.4mol L-1(FPh)2Mg-Mes3B/THF owns the widest electrochemical window (2.6vs. Mg)and highest ionic conductivity2.57mS cm-1. Meantime, by comparison with(FPh)2Mg/THF，(FPhMgBr)2-Mes3B/THF，FPhMgBr/THF, it was found thatthe introduction of4-FPh group did not broaden the electrochemical window of Grignard reagent FPhMgBr, on the other hand, the addition of Mes3B indeedgreatly optimized the deposition-dissolution performance of Mg in theelectrolyte.2）By adding Ionic Liquid PP14TFSI to THF, a mixture was provided as thesolvent for (BMPMC)2-AlCl3. DSC test indicated that after the addition of IonicLiquid, the boiling point of THF was greatly increased, and the thermal safety ofelectrolyte was greatly improved. Meantime, the cyclic voltammetry test showedthat when using the mixture as the solvent for (BMPMC)2-AlCl3, the electrolytehas excellent Mg deposition-dissolution performance. Comparing with pureTHF as the solvent, the new electrolyte has a wider electrochemical window.Besides, we assembled completed rechargeable Mg batteries with the electrolyte,and it was found that the new electrolyte was well compatible with the cathodematerial Mo6S8. Therefore, it is a good candidate for rechargeable Mg batterieselectrolyte solution. More importantly, because of the addition of Ionic Liquid,the volatility of electrolyte solution has been greatly depressed. This researchprovides a stepping stone for developing new less-volatile electrolyte systemsfor rechargeable Mg batteries. |
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