Study On Stabilizing The Metal Lithium Anode And Its Application In High Specific Energy Battery

With the rapid development of electric vehicles and consumer electronics,the demand for high energy density batteries is being under a high intense.Metallic lithium is the most ideal negative electrode material for high-energy density battery based on the highest theoretical specific capacity(3860 m Ah/g)and the most negative electrode potential(-3.04 V vs.standard hydrogen electrode).However,the lithium metal anode will produce volume expansion effect during the cycle,which will lead to "dead lithium" in the reaction process,and even lead to the collapse of the negative pole structure.Besides,the battery produces lithium dendrites during the cycle and the continuous growth of the dendrites can pierce the diaphragm,causing to short circuited and even explode of the battery.The above two problems are the main reasons that impede the commercialization of lithium battery.The preparation of the composite lithium negative electrode and the surface modification of lithium metal is an effective way to inhibit the growth of the lithium dendrite and alleviate the volume expansion effect of the electrode.Based on the above research solutions,safety design and related research have been carried out and the following conclusions have been obtained in this work.(1)Li/CNF composite anode was prepared by vacuum filtration.First of all,the lithium powder in the dispersions was dispersed uniformly in the 3D carbon framework by vacuum filtration.Then it was pressed into Li/CNF composite anode.After 500 h cycle,the voltage plateau of the pure lithium anode has been over 2.1 V,but the voltage plateau of the Li/CNF composite anode was only 38 m V.By observing the surface and cross section of the negative electrode,it is found that the surface of the pure lithium anode has a large number of lithium dendrites and the cross section of pure lithium anode has obvious collapse.However,the surface and section morphology of the Li/CNF composite anode remain in good condition.This is mainly due to the fact that the 3D carbon framework can not only alleviate the volume expansion of the negative electrode,but also improve the conductivity of the negative electrode.(2)Li/GO composite anode was prepared by mechanical pressing.The lithium powder and graphite were mixed uniformly through ball milling.The mixture was pressed into Li/GO anode.High cycling stability of the cell is obtained when the mass percentage of the graphite was 30 wt.%.As the symmetric cells was tested for 500 h,the voltage plateau of pure lithium electrode increased and the potential of Li/GO anode remained stable.The voltage plateau of Li/GO anode was much lower than that of pure lithium.SEM analysis shows that the surface morphology of the Li/GO anode was obviously improved.This is due to that the Li/GO anode has a large specific surface,which can effectively alleviate the growth of lithium dendrite,and graphite as a supporting skeleton can alleviate the negative volume expansion effect.(3)CNF/Li anode was obtained by the preparation of carbon fiber film on the surface of lithium metal by means of coating.The lithium-ion deposition efficiency test shows that the deposition efficiency has been reduced to 2% after 90 cycles of pure lithium negative collector.However,the efficiency of the cells can remain 95% after 100 cycles after collector is modified by carbon fiber film.It is found that the number of dendrites on the CNF/Li anode surface was far less than that of the pure lithium anode.It is indicated that the preparation of carbon fiber film on the surface of metal lithium anode can improve the deposition efficiency of the negative electrode and effectively inhibit the growth of dendrite.This is because carbon fibers can provide a deposition site for the lithium metal,which is beneficial to the uniform deposition of metal lithium.(4)The CPF/Li anode was prepared by the preparation of copper powder film on the surface of lithium metal via a casting way.The discharge capacity of the pure lithium anode battery attenuates to 24 m Ah/g after 1500 cycles,meanwhile the discharge capacity of the CPF/Li anode battery can still remain 74 m Ah/g.It is found that the number of dendrites on the surface of the CPF/Li anode decreases obviously by the surface morphology test of the negative electrode.It is proved that the preparation of copper powder film on the surface of lithium metal anode can inhibit the formation of the lithium dendrite and improve the cycle stability of the battery.That is due to the anode surface area reduces the effective current density on the surface of the electrode and inhibits the formation of dendrite.