Study On Construction And Energy Storage Of Electrode Materials For Mg-based Battery

Because of their high energy density and long cycle life,lithium-ion batteries have been widely used in portable electronic devices,electric vehicles and smart power grids.Nevertheless,safety concerns,the high Li anode cost and the environmental-unfriendly by-products dramatically hinder further development of lithium-ion batteries.With the growing requirements for advanced energy storage,environmental issues and population growth,there is an urgent need to pursue the design of new rechargeable battery systems with high energy density and high safety.Recently,multivalent cation rechargeable batteries using a zinc,aluminum,magnesium anode have received more attention.In particular,rechargeable magnesium-ion batteries have an appealing low cost,a high theoretical volumetric capacity(3833 m Ah cm^-3 for Mg and 2046 m Ah cm^-3for Li),and a low toxicity.In addition,they are made with an abundant natural source(1.94%for Mg and 0.006%for Li)and Mg is deposited without the formation of dendrites.In spite of these highly attractive features,rechargeable magnesium batteries still face a series of challenges to improve the kinetically sluggish Mg diffusion in solid hosts,the incompatibility between the Mg anode and non-aqueous electrolytes and the widening potential window.Therefore,it is necessary to find suitable electrode materials with an excellent electrochemical performance.In this dissertation,the preparation methods of electrode materials for magnesium-based batteries with high voltage,high energy storage performance and high electrolyte matching are explored.Moreover,it focuses on the researches of microstructure,composition and electrochemical properties of electrode materials.In addition,the energy storage mechanism of various types of electrode materials for magnesium-based batteries is discussed,and the influence of material modification strategies on energy storage performance is explored.The applications of magnesium-based batteries are further evaluated.The main work and results are as follows:(1)Ni Co₂S₄@Mn Mo O₄ core-shell structure composites are fabricated via a hydrothermal process.Urchin-like Ni Co₂S₄ microspheres are utilized as core material,where the ultrathin Mn Mo O₄ nanosheets are controllably deposited on the surface.This unique structure helps to increase the structural stability of spinel-Ni Co₂S₄ and inhabit the dissolution of sulfide in nucleophilic electrolyte.It is the first time to achieve an outstanding electrochemical performance in Mg-based batteries by combining Ni Co₂S₄@Mn Mo O₄ core-shell materials as the cathode.(2)Although the high specific capacity of the Ni Co₂S₄@Mn Mo O₄ electrode,it also has some problems such as complex synthesis method,low working voltage and instability in electrolyte.Oxide electrode can solve the above problems well.Ultrathin VO₂(B)nanosheets via one-step solvothermal method.Self-designed hybrid magnesium-lithium battery using ultrathin vanadium dioxide nanosheets as the cathode,magnesium as the anode,molybdenum as the current collector and an all-phenyl complex with lithium chloride as the electrolyte was assembled in the work.The battery delivers outstanding electrochemical performance with a high reversible capacity of 275m Ah g^-1,standout rate performance of 145 m Ah g^-1at a current density of 4 A g^-1,long cycle life and high energy density of 484 Wh kg^-1.(3)To further increase the working voltage,high-voltage spinel-Li₄Mn₅O₁₂cathode material with unique nano/microsphere via a novel low temperature method,offering short Li diffusion path and sufficient transport channels for electrolyte penetration into the electrode.For the first time,we demonstrate the feasibility of the spinel-Li₄Mn₅O₁₂ nano/microsphere with hierarchical architecture as cathode for 2 V hybrid Mg-Li batteries.It exhibits a reversible specific capacity of 155 m Ah g^-1 and a long discharge voltage platform exceeding 2.0 V(vs.Mg²⁺/Mg)with high energy density of 326 Wh kg^-1 at a current density of 0.1 C(1 C=163 m A g^-1).(4)The conventional electrolytes displayed very low compatibilities with Mg anode,which the formation of an insulating passivation layer on the surface of Mg metal anode would block the diffusion of Mg²⁺ions into Mg anode limiting reversible plating/stripping of Mg²⁺.Besides,the existence of free halogen ions in the electrolytes make highly corrosive with commonly used current collectors(such as stainless steel and nickel),hindering their broad applications in low cost magnesium ion batteries beyond 2 V.To enable the compatibility of conventional noncorrosive electrolytes in magnesium ion batteries,alloy-type anode materials have been proposed to replace Mg metal anodes.A novel bismuth–carbon composite,in which bismuth nanorods were anchored in a nitrogen-doped carbon matrix(Bi@NC),is proposed as anode for high performance magnesium ion batteries.Bi@NC composite was synthesized via pyrolyzation of dopamine-coated bismuth metal precursor,resulting in Bi nanorods anchored in the N-doped mesoporous carbon.The N-doped carbon matrix provides a highly electronic conductive network that facilitates the magnesiation/de-magnesiation of Bi.Additionally,it restrains aggregation of Bi nanorods and serves as a buffer layer to alleviate the mechanical strain of Bi nanorods upon Mg alloying/de-alloying.The Bi@NC core-shell nanorods as anode for magnesium ion batteries deliver a high reversible capacity of 360 m Ah g^-1 at current density of 100 m A g^-1 and maintaining 87%of the initial capacity after 100 cycles.Additional,standout rate performance of 275m Ah g^-1at a current density of 1 A g^-1.