Research On The Preparation Of Lithium Iron Phosphate Cathode Materials By Electrodeposition And Tunnel Hole Structure

In this paper,the lithium-aluminium iron phosphate matrix cathode composite was prepared by electrochemical deposition using propylene carbonate as electrolyte solvent and aluminium foil with porous structure as cathode.The effects of DC voltage,reaction time,electrolyte concentration and surface structure of cathode aluminium foil on the morphology and electrochemical properties of the prepared samples were studied.On this basis,in order to improve the electrochemical properties of the composites,nano-modification,carbon coating and metal ion doping were studied.The samples were analyzed by SEM,EDS,XPS,FTIR,XRD and electrochemical testing system,including element analysis,crystal structure analysis,micro-morphology analysis and electrochemical performance test.According to the results of characterization analysis and the phenomena observed during the experiment,the reaction mechanism of electrochemical deposition composite materials was studied.The experimental results show that the optimum electrodeposition conditions are as follows: DC voltage is 1.8 V,phosphoric acid concentration in electrolyte is 1mol/L,lithium nitrate concentration is 1 mol/L,electrodeposition time is 120 minutes,and the surface void morphology of negative aluminium foil has an important influence on the electrodeposition performance.The cathodic reduction conversion from trivalent iron to divalent iron was completed by XPS analysis of the valence state of iron.The particle size of the deposited particles on the electrode was 100-200 nm by scanning electron microscopy observation and analysis.The high frequency region of AC impedance was 600_by electrochemical measurement system,and the first discharge capacity was 60 mAh/g at 0.1 C rate.By adding cationic surfactant CTAB and basic yellow(BY)to the electrolyte,the particle size of lithium iron phosphate deposited particles was modified.The experimental results showed that the particle size of the sample prepared by electrodeposit was between 100-200 nm.The SEM micromorphology analysis showed that the sample prepared by adding basic yellow(BY)entered the aluminumfoil.The results of AC impedance analysis show that the impedance in high frequency region decreases from 600 ? before modification to 360? after modification,which reduces the interface impedance of lithium ion between electrode material and electrolyte.At the same time,the first charge-discharge capacities of the two modified lithium iron phosphate aluminum based cathode materials at 0.1 C ratio were compared.The first charge-discharge capacities of lithium iron phosphate composites(LFP-BY)prepared by adding alkaline yellowing were 80 mAh/g,and the first charge-discharge capacities of lithium iron phosphate composites(LFP-CTAB)prepared by adding hexadecyl trimethyl ammonium bromide were 60 mAh/g.By adding magnesium nitrate and cobalt nitrate into the electrolyte to dope metal ions,the experimental results show that the micro-morphology of the modified composite has little change.In the electrochemical performance,the interface impedance decreases from 600?to 250?after adding magnesium ions,and after doping cobalt ions,the interface impedance decreases to 100?,the first discharge performance has been greatly improved.After doping,the first charge and discharge at 0.1C ratio increased from 60 mAh/g to 130 mAh/g.In carbon-coated modification,propylene carbonate,an organic compound in the reaction system,can be used as a carbon source,so this topic only explores carbon-coated by adding glucose.The results show that the surface morphology of electrodeposits is smoother with the increase of glucose content.Under this system,the optimum addition of glucose is 0.03 mol/L.However,carbon coating has no significant effect on the electrochemical properties of composites.