Study On Protection And Performance Of Metal Lithium Anode

At present,lithium metal has attracted a lot of attention as one of the most negative electrode material with the highest specific mass energy.Although metal lithium has been studied as negative electrode material for nearly 40 years,there are still many problems in the commercialization process of lithium metal batteries.The volume change of lithium metal anode during deposition and stripping,growth of lithium dendrites and low coulombic efficiency in the long-term cycle have serious impact on the lifetime and safety of metal lithium batteries.In order to solve these problem,this paper improves the morphology and interfacial stability of lithium metal anode by using the Al₂O₃/PVDF modified separator and carbon cloth interlayer,improving the electrochemical properties of battery.In my paper,Al₂O₃/PVDF?the best mass ratio is 9:1?modified composite separator with the best mass ratio was successfully prepared by coating method.The structure of the membrane coating before and after electrochemical cycling was characterized by XRD.The surface of the metal lithium was characterized by SEM before and after electrochemical cycling.Li-Li symmetric battery,Li-Cu half-cell and lithium iron phosphate battery are assembled.Cycle testing and comparative analysis are carried out.The results show that the polarizatio n voltage of the Li-Li symmetric battery keeps 52 mV after 170 hours at current density of 0.5 mA cm^-2.At current density of 1.0 mA cm^-2,the Coulomb efficiency remains about 90%in Li-Cu half-cell after 100 cycles.The lithium iron phosphate battery has the first discharge specific capacity of 112.8 mA h g^-1 under 1C,and maintains 102 mA h g^-11 after 150 cycles.The capacity retention rate is 90.4%.This is because the nano-alumina has a porous structure,which facilitates uniform distribution of lithium ions and promotes uniform deposition of lithium.In addition,alumina also has excellent mechanical properties,effectively inhibits the growth of lithium dendrites and improves the surface morphology and electrochemical properties of metallic lithium.In addition,porous carbon cloth is disposed between lithium metal and separator as interlayer.The surface of metal lithium and carbon cloth before and after electrochemical cycling is characterized by SEM,Li@CC-Li@CC symmetrical battery and lithium iron phosphate battery are assembled,electrochemical cycle test and comparative analysis is carried out.The results show that the Li@CC-Li@CC symmetrical battery still maintains polarization voltage of 100 mV after 200 h cycling at current density of 2.0 mA cm^-2.when the battery capacity doubles,it remains smaller polarization voltage.The lithium iron phosphate battery has the first discharge specific capacity of 123.3 mA h g^-11 under 1 C and still maintains 110.5 mA h g^-1 after 150 cycles with the capacity retention rate of 89.6%.After cycles,the surface of the lithium metal negative electrode does not have lithium dendrite formation,because carbon cloth can reduce the local current density and its porous structure can effectively alleviate the volume change during charging and discharging process at the same time.Moreover,lithium dendrites can be confined in the interlayer to further prevent the formation of"dead lithium"and improve battery interface stability and cycle stability.