Structural Design Of Anode And Optimization Of Carbonate-Based Electrolyte For Lithium Metal Battery

With the rapid development of electric vehicles and high-tech such as 5G and AI terminals,it is urgent to develop a new type of high-performance and safe energy storage equipment.The lithium metal anode has an ultra-high theoretical specific capacity(3,860 mAh g-1),low redox potential(-3.04 V vs.SHE),and light weight(0.534 g cm-3),which is an ideal anode for higher energy density lithium batteries.However,lithium dendrite growth,electrode volume expansion,and low utilization efficiency during the cycling of lithium metal anode hinder its practical application.In view of above problems,our paper firstly protects the lithium metal anode through structural design,and then further improves the performance of the lithium metal anode through electrolyte additive.The main research contents are as follows:1.A composite lithium metal anode with a high specific area capacity(10 mAh cm-2)was prepared by electrodeposition using three-dimensional carbon paper(3DCP)current collector.2.The results of scanning electron microscope(SEM),high-resolution transmission electron microscopy(HRTEM),X-ray photoelectron spectroscopy(XPS),x-ray diffraction(XRD)and Raman spectrometry(Raman)indicate that 3DCP consists of a cross-link framework of car'bon fibers and graphene nanosheets(GNs).Carbon fibers can greatly enhance the mechanical strength of the composite lithium metal anode.GNs can provide a great lithiophilicity,which can induce the uniform deposition of lithium metal.This unique structure can reduce the local current density during Li+deposition and promote its uniform deposition,which can suppress the generation of lithium dendrites.3.The morphology of lithium metal deposited on the surface of 3DCP substrate and Cu foil was compared by SEM.3DCP can effectively improve the deposition behavior of lithium metal and induce the uniform deposition of lithium metal.By observing the surface and cross-sectional morphologies of three lithium metal anodes after 1000 cycles(4 C)in 3DCP@Li/LFP,Cu@Li/LFP and Li foil/LFP full cells,it indicated that 3DCP can effectively inhibit the formation of lithium dendrites and alleviate the volume expansion of the lithium metal anode.4.By comparing the nucleation overpotential of lithium metal deposited on Cu and 3DCP substrates at different current densities combined with the SEM images of lithium metal deposition.It is founded that 3DCP can significantly reduce the voltage platform(2 mA cm-2,<20 mV)and increase its cyclic life(>1000 h)of the half cell.The Coulombic efficiency is 99.0%when half cell cycling at a large capacity of 10 mAh cm-2.When Li@3DCP composite lithium metal anode is matched with LiNi0.8Co0.15Al0.05O2 and LiFePO4 cathode materials,respectively,the full cells exhibit good large-rate performance and still have good performance advantage under high temperature condition(60 ?).5.By using a novel polymer(PTE)and fluoroethylene carbonate(FEC)as electrolyte additives,the utilization efficiency of lithium metal in the carbonate electrolyte can be greatly improved.It was found that the optimal performance was achieved when the content of PTE and FEC was 2%and 5%,respectively.Under this condition,when the Li/3DCP half cell cycling with capacity of 1 mAh cm-2 at 0.5 mA cm-2,the average Coulombic efficiency was as high as 99.93%in 400 cycles.6.The cyclic voltammetry(CV)method was used to study the influence mechanism of PTE and FEC dual additives on the deposition/dissolution process of lithium metal in carbonate electrolytes.PTE and FEC can decompose before the solvent and form a more stable SEI film on the 3DCP electrode,reducing the irreversible consumption of the electrolyte.In addition,PTE and FEC can increase the electrochemical polarization of lithium ions deposited on the 3DCP substrate,which can reduce the size of the lithium nucleus.So PTE and FEC can induce uniform deposition of lithium metal and inhibit the formation of lithium dendrites.7.Based on the excellent synergy between PTE,FEC double additives and 3DCP.Lithium metal anode can harvest an ultra-high utilization efficiency with the using of our unique carbonate electrolyte and 3DCP current collector.The full cell assembled with LiFePO4 cathode and Li@3DCP with ultra-low lithium metal loading(0.5 mAh cm-2)can cycle stably for 100 cycles.