The Exploration Of New Electrode Materials And Design Of Electrolytes For Rechargeable Magnesium Batteries

Rechargeable magnesium batteries(RMBs)are one of the most promising post lithium ion batteries(LIBs)with the the advantages of high safety,low cost,environmental friendliness and high specific energy density.However,due to the strong polarity Uf Mg2+,Uhe diffusion of Mg2+ in the solid material is rather slow,thus finding suitable electrode materials is very difficult.Among the developed electrode materials,the performances are not satisfying.On the other hand,Mg forms a passivation film in the conventional electrolyte system.Based on the current situation,the thesis focuses on the exploration of new electrode materials and the design of the electrolyte.The rearch content can be divided into the following four parts.(1)The Li3VO4/C was developed as a high-capacity anode material for the first time.The initial discharge capacity was 318 mAh g-1,higher than the developed intercalation anode material.Transmission electron microscope(TEM),ex-situ X-ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS)results demonstrate that the intercalation of Mg2+ into Li3VO4/C is not completely reversible.(2)The(Sodium super ionic conductor)NASICON structured Na3V2(PO4)3/C(NVP/C)was developed as a high voltage positive electrode material for the first time.The average discharge voltage of the electrochemically desodiated NVP/C(ED-NVP/C)in the half-cell is 2.5 V vs.Mg2+/Mg,higher than most of the cathode materials.The initial discharge capacity was 88.8 mAh g-1 and 81%of the capacity can be maintained after 100 cycles.Ex-situ XRD,XPS,Inductively coupled plasma-Atomic emission spectrometry(ICP-AES)and galvanostatic intermittent titration technique(GITT)results show that the intercalation of Mg2+ is based on two-phase reaction with good reversibility.After discharge process,0.8 Mg2+ were inserted into the ED-NVP/C structure.(3)Honeycomb-like structured NVP/C/G was constructed by spray drying method,which effectively improved the electrochemical performance of the NVP.The XRD refinement results indicate that Mg2+ tends to occupy the Na2 vacancy.The GITT and EIS tests reveal faster kinetics during Mg2+ extraction process and the increase of Rct is positively correlated with the content of the NaV2(PO4)3 phase.The constructed ED-Mg//0.1 M Mg(TFSI)2/triglyme//NVP/C/G full cell delivered a discharge capacity of 92 mAh g-1.(4)By designing a new Na-Mg hybrid electrolyte,the Na-Mg hybrid battery Mg//0.2 M Mg(TFSI)2+ 1 M NaBH4/triglyme-1,2-dimethoxyethane(DME)//NaTi2(PO4)3@C with excellent rate performance,long cycle life and high safety was developed.The capacity of the hybrid battery did not decay even after 26,000 cycles.The electrochemical performance is superior to traditional magnesium batteries.The result demonstrates that the Mg(TFSI)2 electrolyte can be used in a chlorine-free and has a magnesium metal as a negative electrode for long-term cycle for the first time.