LiTFSI-H₂O As The Electrolyte For Studying Electrochemical Properties Of Aqueous Lithium-ion Battery

Aqueous lithium-ion battery has shown a wide range of application prospects due to its unique advantages such as safety,environment protection and low price.Unfortunately,the voltage window of the aqueous electrolyte cannot reach 1.23 V,which extremely limits the energy density of the aqueous lithium-ion battery.In this essay,to improve the voltage window of the aqueous lithium-ion battery,a new type of high concentration aqueous electrolyte based on lithium bistrifluorosulfimide?LiTFSI?is chosen.The voltage window of the aqueous battery is expanded leading to an improved the energy density.At the same time,we investigate the electrochemical performance of electrode materials of different aqueous battery in the electrolyte and the effect of electrolyte concentration on the properties of materials.The concrete research contents are as following:The electrochemical performance of commercial cathode material LiMn₂O₄ in different concentrations of LiTFSI electrolyte was studied.The potential range of LiMn₂O₄ is 0.4¹.2V,0.4¹.2 V,0.4¹.2 V,0.4¹.3 V,0.4¹.4 V in 1,5,10,15,22 mol kg^-1 LiTFSI electrolyte,respectively.In 15 mol·kg^-1 LiTFSI electrolyte,LiMn₂O₄ shows the best electrochemical performance.At the rate of 0.1 C,LiMn2O4 display a capacity of 119.5mAh·g^-1.Moreover,LiMn₂O₄ in 15 mol·kg^-1 LiTFSI electrolyte shows the best rate ability.In addition,LiMn₂O₄ shows excellent cycling performance in 15 mol·kg^-1 LiTFSI electrolyte.After 400 cycles,discharge specific capacity of 78.5 mAh·g^-1 is obtained and the capacity retention is 85%.A new type octahedral molecular sieve?Mg-OMS-1?was prepared by ion exchange method and selected as cathode material.We also studied the influence of its electrochemical performance in the high concentration aqueous electrolyte.The samples were characterization by XRD,SEM and TEM.The samples were assembled into a three-electrode system and tested for electrochemical properties.The electrochemical performance of Mg-OMS-1 in 1,5,10,15 and 22 mol·kg^-11 LiTFSI electrolytes are obtained through cyclic voltammetry,constant current charge/discharge and electrochemical impedance spectroscopy test.The potential range of Mg-OMS-1 is-0.7¹.3 V,-0.7¹.45 V,-0.7¹.5 V,-0.7¹.55 V,-0.7¹.65 V in the 1,5,10,15,22 mol kg^-1 LiTFSI electrolyte,respectively.Mg-OMS-1 in 15 mol·kg^-1LiTFSI electrolyte shows a better electrochemical performance.At the rate of 0.1 C,the first discharge capacity in 15 mol·kg^-1 LiTFSI electrolyte is 222.5 mAh·g^-1.Even at rate of 10 C,the discharge capacity of 50.4 mAh·g^-1 is obtained.After 1000 cycle,the materials show a specific discharge capacity of 92.6 mAh·g^-1 and an excellent cycling stability with a high coulombic efficiency of¹00%.Meanwhile,the temperature has a large influence on specific capacity of Mg-OMS-1 in 1 and 5 mol·kg^-1 LiTFSI.However,the Mg-OMS-1 in 22 mol·kg^-1LiTFSI electrolyte,the specific capacity of the cycle increases sharply at 70 ^oC.In contrast,the specific capacity is gradually reduced due to strong acidity damages to the internal structure of Mg-OMS-1.The Mg-OMS-1//AC capacitor battery was assembled,and the electrochemical performance of the capacitor battery under high concentration electrolyte was investigated.The Mg-OMS-1//AC capacitor battery were tested in 15 mol·kg^-11 LiTFSI and 0.5 mol?dm^-3MgCl₂ electrolyte,respectively.At the rate of 0.1 C,the assembled capacitor battery shows capacities of 153.7 mAh·g^-1and 96.3 mAh·g^-11 in 15 mol·kg^-11 LiTFSI and 0.5 mol?dm^-3 MgCl₂electrolyte,respectively.After 400 cycles at 0.5 C and 500 cycles at 1 C,the capacitor battery in 15 mol·kg^-1 LiTFSI displays a high capacity retention of¹00%.In contrast,in 0.5mol·dm^-3 MgCl₂,an obvious attenuation of capacity is observed at different rates.It shows that the high concentration electrolyte is beneficial to improve the cycling stability of the aqueous capacitor batteries.