Cationic Doped Manganese Oxides As Cathode Materials For Aqueous Magnesium Ion Batteries

Due to the volatility and intermittent,the development of clean energy has been restricted.Large-scale storage energy battery is the key to solve the problem.Aqueous magnesium ion batteries,in the advantage of simple preparation,low production cost,high safety coefficient,have gotten widely attentions in a large-scale energy storage battery.In this article,through reflux method for Nb and V doping modification manganese oxide K-OMS-2 with 2 x 2 channel structure,physical characterizations such as SEM,TEM,XRD,BET,are used to characterize the physical structure,and electrochemical characterizations such as cyclic voltammograms,constant current charge-discharge test are employed to characterize the electrochemical performances as the aqueous magnesium ion battery cathode material in Mg?NO₃?₂ and Mg?CH₃COO?₂ electrolytes.K-OMS-2 material,prepared by reflux method,has a morphology structure of nanowire rod morphology structure,the range of length between 220-320 nm and approximately 24 nm in diameter.Based on the results of TEM,XRD that the material keeps the hidden potassium 2 x 2channel structure.The discharge specific capacity of K-OMS-2 is 155.9 mAh/g in the current density of 20 mA/g and in 1 mol/L Mg?NO₃?₂ electrolyte.When the current density is 100 mA/g and in 1 mol/L Mg?NO3?2 electrolyte,the initial discharge specific capacity of K-OMS-2 is 92.2mAh/g,after 200 times of cycle stability test,residual specific capacity is 29.4 mAh/g.Nb K-OMS-2 material is prepared by reflux method,and when the molar ratio of doping Nb:Mn=1:10?10%Nb K-OMS-2?,material has a uniform nanoparticle,particle size range about 90nm,and shows the best electrochemical performance.In the current density of 20 mA/g and 1mol/L Mg?NO3?2 electrolyte,10%Nb K-OMS-2 material has a discharge specific capacity of252.6 mAh/g.When in the current density of 100 mA/g,1 mol/L Mg?NO₃?₂ electrolyte,the initial discharge specific capacity of K-OMS-2 is 168.7 mAh/g,after 200 times of cycle stability test,residual specific capacity is 65.1 mAh/g.Nb element doping promotes the electrochemical performance of K-OMS-2 material.V K-OMS-2 material is prepared by reflux method,and when the molar ratio of doping V:Mn=1:10?10%V K-OMS-2?,the material has a uniform nanoparticle,a particle size is about 30nm,and shows the best electrochemical performance.In the current density of 20 mA/g,1 mol/L Mg?NO3?2 electrolyte,10%V K-OMS-2 material has a discharge specific capacity of 265.9mAh/g.When in the current density of 100 mA/g,1 mol/L Mg?NO₃?₂ electrolyte,the initial discharge specific capacity of 10%V K-OMS-2 is 178.7 mAh/g,after 200 times of cycle stability test,residual specific capacity is 65mAh/g.V element doping also promotes the electrochemical performance of K-OMS-2 material.Using Mg?CH₃COO?₂ aqueous solution as the electrolyte,examines the electrochemical properties of K-OMS-2,10%Nb K-OMS-2 and 10%V K-OMS-2 three materials,under the stability test condition that current density of 100 mA/g,1 mol/L Mg?CH₃COO?₂ electrolyte.The initial discharge specific capacity respectively is 97.1 mAh/g,100.6 mAh/g and 221.8 mAh/g.After 200 cycles,residual specific capacity respectively is 97 mAh/g,122.4 mAh/g and 122.9mAh/g.Compared with the test results in Mg?NO3?2 electrolyte,the capacity retention has been increased by about 2³ times.In Mg?CH₃COO?₂ electrolyte,parents type of acetic acid-base can adsorb on the surface of electrode materials and provides the protection to improve the cycle stability of the battery.