Synthesis,Structure And Electrochemical Properties Of Novel Transition Metal Borates For Li-ion Batteries

Due to the advantages of high output voltage,large energy density and long cycle life,lithium-ion batteries are widely used in portable electronic devices,electric vehicles and defense industries.With the development and application of smart electronic products and electric vehicles,people have put forward higher requirements for the performance of lithium-ion batteries.The anode materials of the transition metal borate system use the smaller molecular weight of the borate and the multi-electron reaction of the transition metal to increase its specific lithium storage capacity,and the appropriate‘induction'to obtain a safe lithium insertion potential,so it has important research significance.This paper mainly studies the synthesis methods,crystal structures and electrochemical properties of two novel transition metal borates V₃BO₆and Mn VBO₄.Firstly,the vanadium borate V₃BO₆with norbergite structure was synthesized for the first time by the high temperature solid-phase method,and the influence of various factors was discussed;the electrochemical performance of the V₃BO₆/C nanocomposite as an anode material for lithium-ion batteries and its lithium storage process were explored.Secondly,the bimetallic borate Mn VBO₄with zircon structure was obtained for the first time,its crystal structure was analyzed and its electrochemical performance as an anode material was tested.In this paper,the novel compound vanadium borate V₃BO₆was synthesized by high-temperature solid-phase method,and the effects of different raw materials,V:B ratio,addition amount of nucleating agent Al₂O₃and sintering temperature on V₃BO₆synthesis and purity were investigated.Adding trace Al₂O₃can promote the formation of BO₄tetrahedron,and finally synthesize V₃BO₆/C nanocomposites with a purity of 76%.Combining refinement results and bond price theory,it is known that the reason why V₃BO₆is difficult to obtain pure phase is its unstable VO₆distortion octahedral structure.V₃BO₆/C nanocomposites have a specific discharge capacity of 1071 m Ah g^-1for the first time at a current density of 10 m A g^-1within a voltage window of 0.05-3 V.After 50 cycles at a current density of 10 m A g^-1,the specific capacity of material is stable at 416 m Ah g^-1,and it has a rate capacity of 329 m Ah g^-1at a current density of 0.5 A g^-1.In-situ XRD results indicate that V₃BO₆/C nanocomposites can store lithium through conversion reactions.The above results indicate that V₃BO₆/C nanocomposites can be high-performance anode materials for lithium-ion batteries.Through the sol-gel method,we synthesized the bimetallic borate Mn VBO₄with zircon structure for the first time,using citric acid as a carbon source and chelating agent optimized the performance of Mn VBO₄as an anode material for lithium batteries.Charged and discharged at a constant current density of 50 m A g^-1within a voltage window of0.01-2.5 V,Mn VBO₄has first discharge specific capacity of 850 m Ah g^-1and the reversible charge specific capacity of 498 m Ah g^-1.And there is a clear discharge platform at 0.8 V.The research results show that Mn VBO₄is a lithium battery anode material with development potential.It is urgent to study the lithium storage process to further improve its electrochemical performance.