| With the rapid development of modern technology,lithium ion battery have been used in all aspects of life,such as electric vehicles,mobile phones,energy storage power stations,etc.However,the slow development of traditional lithium secondary batteries,especially the limited energy density is now difficult to meet the demand of social life,which has also prompted scientists to explore new and safer rechargeable battery systems with higher energy density.Magnesium metal,has a specific volume capacity of 8056 m Ah cm–3 and a mass specific capacity of 2205 m Ah g–1 when used as anode material.More importantly,the content of magnesium in the earth’s crust is also much higher than that of lithium,so the price is also much cheaper than lithium.The biggest obstacle that restricting the development of rechargeable magnesium batteries(RMB)comes from the sluggish kinetic of Mg2+.Based on this,we tried to design new electrochemical reaction mechanisms,develop new organic electrode materials and new electrolyte systems,and optimize the electrode composition preparation process to conquering the sluggish kinetic of Mg2+.The results are as follows:(1)We tried to use simple and cheap Mg Cl2/THF as the electrolyte for the first time in RMB,which with a deposition over potential of just 0.07 V.The deposition efficiency of Mg Cl2/THF electrolyte in SS,Mo and Cu substrates were all above 95%,and the oxidation window of 0.5 M Mg Cl2/THF electrolyte was around 2.3 V vs.Mg.Subsequently,three organic materials,Mo6S8,P14 AQ and PBV-Cl2,were applied to the 0.5 M Mg Cl2/THF electrolyte.Which with a reversible capacity of 80,160,and 157 m Ah g–1,respectively,and 62.5%,61.5% and 91.2% of the theoretical capacity.Gravimetric analysis SEM-EDS and XPS characterization conformed that the charge carrier of Mg–PBV-Cl2 battery is Mg Cl3– during the cycling process,while the Mo6S8 and P14 AQ were Mg2+ and Mg Cl+,respectively,this was also the key factors for the big difference of the electrochemical performance.Mg–PBV-Cl2 battery showed excellent electrochemistry performance in 0.5 M Mg Cl2/THF electrolyte including a capacity of 120 m Ah g–1 at a high current density of 500 m A g–1,a capacity retention of 81% at the current density of 200 m A g–1 for 500 cycles,and an average coulombic efficiency as high as 99.94%.CV demonstrated that the discharge capacity of Mg–PBV-Cl2 battery was contributed by both the diffusion and the pseudo capacitance behavior.(2)Simple and cheap 1.0 M Mg Cl2–Li Cl/THF was used as the electrolyte for RMB for the first time.The conductivity of this electrolyte wss as high as 1.25 m S cm–1.The deposition efficiency of this electrolyte in Mo substrates was Above 93%,and with a electrochemistry window of 2.2 V vs.Mg.Subsequently,three organic materials,PAQS,P14 AQ and Li2 PDHBQS,were applied to 1.0 M Mg Cl2–Li Cl/THF electrolyte.The capacity utilization rates of PAQS and P14 AQ in Mg Cl2–Li Cl/THF electrolyte were 51.5% and 44.2% respectively,However Li2 PDHBQS was as high as 100%.XPS and EDS showed that the charge carrier of PAQS and P14 AQ were Mg Cl+,while Li2 PDHBQS was Li+.Mg–Li2PDHBQS battery showed the best electrochemical performance in the voltage range of 0.6–2.0 V with an excellent rate performance of 190 m Ah g–1 at a high current density of even 2000 m A g–1.CV demonstrated that the discharge capacity of Mg–Li2PDHBQS was contributed by the pseudo capacitance behavior.(3)Mg(BH4)2 was used to prepare Mg(HFPB)2 electrolyte in one step,and then,refined by recrystallization to prepare 0.6 M Mg(HFPB)2/G2 electrolyte with an electrochemical window as high as 3.2 V vs Mg2+/Mg,the overpotential of symmetrical battery for this electrolyte was just 0.08 V at the current density of 100 μA cm–2.Small organic molecules NTCDI and PTCDI were used as cathode materials for the first time.For cathode cathodes,concentrated sulfuric acid was used to dissolve NTCDI and PTCDI,and then deposited on KB,both Mg–NTCDI and Mg–PTCDI were exhibited the discharged capacity of 120 m Ah g–1 and with the average discharge voltag of 1.52 V and 1.50 V,respectively.Mg–PTCDI@KB battery showed excellent cycling performance with a capacity retention of 70% at the current density of 100 m A g–1 in 200 cycles.When RGO was used to replace the position of KB,Mg–PTCDI@RGO battery even exhibited a capacity utilization as high as theoretical capacity at the current density of 20 m A g–1.However,the cycling performance and rate performance including coulombic efficiency were all declined.CV demonstrated that the discharge capacity of Mg–NTCDI and Mg–PTCDI battery was contributed by both the diffusion and the pseudo capacitance behavior. |
