Preparation And Electrochemical Properties Of Magnesium Vanadate Anode Materials

It is well known that the performance of the electrode material determines the performance of the battery.Vanadium-based anode materials（MV_xO_y type）,with multiple redox states and strong V-O bonding enable them to output higher specific capacity and better long-term cycle stability,which have successfully stood out among various candidate electrode materials.To date,the development of lithium-ion battery anode materials with simple processes,low cost,long cycle life,and excellent multiplicative performance without sacrificing other key properties remains a key challenge.Herein,this work report for the first time the synthesis of Mg V₃O₈,Mg V₂O₆,and Mg VO₃ as durable high-magnification anode materials based on a simple and scalable solution combustion method combined with solid-phase sintering.This work investigated the reaction mechanism during the low-temperature combustion synthesis as well as explored the advantages and lithium storage mechanisms of each of the three different anode materials through relevant tests.It is concluded that Mg V₃O₈ anode material with a mixed vanadium valence state has the most potential as anode material for Li-ion batteries due to the simplest preparation process and the best electrochemical performance.The main research of this thesis includes the following aspects:（1）The effects of combustion agent and other parameters on the physical phase and electrochemical properties of Mg V₃O₈ powder were investigated,and high purity Mg V₃O₈was successfully prepared by solution combustion method,and it was used for the first time as anode material for lithium-ion batteries.The powder with a specific surface area of 22.05m² g^–1 Mg V₃O₈ was prepared by using citric acid monohydrate as the combustion agent,magnesium nitrate hexahydrate and ammonium metavanadate as the magnesium and vanadium sources,respectively,in a molar ratio of 4:1:3.When used as an anode material for Li-ion batteries,the Mg V₃O₈ electrode exhibits small volume changes（<10%,1000cycles）during the lithiation/delithiation process.This is due to the reaction process as a simple solid-solution Li⁺storage mechanism,resulting in an electrode with excellent cycling stability.Thus,the Mg V₃O₈ electrode provided a remarkable specific capacity of～102.6 m A h g^–1 at 2.0 A g^–1 and a decay rate of only 0.001%per cycle over 3000 cycles.（2）Using citric acid monohydrate as the combustant,magnesium nitrate hexahydrate and ammonium metavanadate as the magnesium and vanadium sources,respectively,in a molar ratio of 3:1:2,the precursor was first prepared by solution combustion,and then the single-phase Mg V₂O₆ was prepared by annealing the precursor at 550°C for two hours in combination with solid-phase sintering,and it was used for the first time as an anode material for LIBs.This work has probed the Mg V₂O₆ electrode as a lithium intercalation storage mechanism during lithiation/delithiation.The corresponding discharge capacities of Mg V₂O₆ were 306.2,249.3,220.6,158.8,128.7,and 96.1 m A h g^–1 when the current densities were set to 0.05,0.1,0.2,0.5,1,and 2 A g^–1,respectively.The Mg V₂O₆ electrode provided a significant specific capacity of about 141.2 m A h g^–1 at 1.0 A g^–1,and there is no significant attenuation in 700 cycles.（3）Mg VO₃ powder was prepared by solid-phase sintering in one step after grinding at a molar ratio of 2:1 using magnesium nitrate hexahydrate as the magnesium source and vanadium dioxide tetra oxide as the vanadium source.The electrochemical properties of Mg VO₃ powder as anode material for LIBs were investigated.The reversible capacity of the Mg VO₃ electrode reached 162.3 m A h g^–1 after 50 cycles at 0.2 A g^–1.In addition,the reversible capacity of the Mg VO₃ electrode was 98.2 m A h g^–1 after 100 cycles at 0.5 A g^–1.