Application Of Organic-inorganic Composite Artificial Interface Layer In Lithium Metal Anode

Due to the low theoretical specific capacity(372 m Ah g^-1)of the graphite,Li-ion batteries with graphite as anode cannot meet the demand for high energy density energy storage devices in emerging fields.Li metal had a high theoretical specific capacity(3860 m Ah g^-1)and the lowest redox potential（-3.04 V vs.standard hydrogen electrode）,which was regarded as one of the most potential anode materials.However,during the cycle,the instability of solid electrolyte interface（SEI）layer,uncontrollable dendritic growth and huge volume change seriously limited the practical application of Li metal anode.SEI layer played an important role in the processes of uniform Li plating/stripping.Nevertheless,the spontaneous SEI layer showed low mechanical strength,the fragmentation of SEI could aggravate the growth of dendrites and the corrosion of Li anode.Constructing a highly stable LIF artificial interface layer is one of the most effective strategies to improve the interface stability of lithium negative electrode and improve the cycle performance of battery.LIF artificial interface layer has high Young’s modulus and chemical stability,but it has low ionic conductivity and poor toughness,and cannot adapt to huge volume changes.In this paper,an in-situ organic-inorganic composite artificial interface layer was constructed on the surface of Li anode.Improve the ion transport and mechanical flexibility of LIF artificial interface layer,promote the uniform deposition of lithium on the electrode surface,inhibit the growth of dendrites and the generation of"dead lithium",and greatly improve the electrochemical performance of lithium metal battery.（1）Li₂S with high lithium-ion conductivity was compounded with polyvinylidene fluoride（PVDF）,and a sulfur-containing and fluorine element composite protective layer（F-organic/Li₂S）was constructed on the surface of lithium anode in situ.PVDF reacts with lithium to form Li F in-situ.The Li₂S improve the transmission rate of lithium-ion at the lithium metal anode interface,reduce the local concentration of lithium-ion,make lithium deposit evenly on the electrode surface and effectively inhibit the growth of dendrites.PVDF ensures the compactness of F-organic/Li₂S layer,reduces the contact between lithium metal and electrolyte and reduces the corrosion of lithium metal anode.The tests of full cell and symmetrical cell show that F-organic/Li₂S layer can effectively prolong the cycle life of lithium metal battery.（2）A composite protective layer GCSEI with gradient structure was prepared on the surface of Li metal by in-situ reaction.GCSEI was composed of inorganic components（Li₂S+Li F）and organic components（PVDF+PEO）,with a thickness of about 100 nm.The GCSEI layer after PEO composite is flexible and compact,which can effectively reduce the side reaction between lithium negative electrode and electrolyte.In addition,the gradient distribution structure made the high hardness inorganic components at the bottom of GCSEI effectively inhibit the growth of dendrites,while the organic components alleviate the stress and strain caused by the volume change of Li anode.XPS analysis of different etching depths proved that the concentration of inorganic components in GCSEI increased gradually from top to bottom,showing a gradient distribution.Li@GCSEI exhibited low interface impedance and good cyclic performance.Under the test conditions of current density of 3 m A cm^-2 and capacity of 2 m Ah cm^-2,it can cycle stably for 1000 hours.The full cell matched with the cathode electrode of NCM811 demonstrated a capacity retention rate of 81.4%after 500 cycles.In this thesis,an in-situ organic-inorganic composite artificial interface layer with low interface impedance,high ionic conductivity and high chemical stability was prepared in a mild and environment-friendly way,which greatly improved the cycle life of Li metal battery.