The Design And Research Of Separator For High Performance Lithium Metal Battery

Lithium-ion batteries?LIBs?have been widely used in many fields including portable energy storage devices and new-energy vehicles.However,the theoretical capacity of the graphite-based negative electrode in LIBs only possesses 372mAh/g,which results in the request for developing new generation of lithium batteries with higher energy density and longer cycle life.Lithium metal anode has consequently been crutially important for the future energy storage investigation,due to its theoretical capacity of 3860 mAh/g and a chemical potential of-3.04 V?vs the standard hydrogen electrode?.However,lithium metal has extremely active reactivity and can easily react with electrolyte,leading to constant consumption of electrolyte.Secondly,the uncontrollable deposition would cause the formation of lithium dendrites.Further,huge volume expansion forces the lithium dendrites to break away,forming'dead lithium'and reducing the coulombic efficiency of lithium metal batteries?LMBs?.These problems have severely limited the commercial application of LMBs.In order to solve the above problems,scientific researchers have made a lot of efforts in designing and regulating electrolyte,current collector,artificial solid electrolyte interface layer?SEI?and solid electrolyte,resulting in tremendous breakthroughs.As an important part of batteries,separator can prevent short circuit,which is especially important for the safety of lithium batteries.However,few works focus on solving the problem of lithium metal anode through the separator design,and most of the work is to modify the original separator,which has problems such as insignificant effect,high cost and failed large scale production.Therefore,it is of great significance for the future development of lithium metal anode by designing a new separator to solve the problem.Based on the systematic discussion of the solution to the problem of lithium metal batteries in this paper,two simple and efficient methods for preparing new type of separators were designed.The separator designed here could effectively promote the lithium deposition.Moreover,the separator could induce artificial SEI to protect the lithium anode.In the first chapter of this paper,the research status of lithium metal anode and ceramic separator was discussed systematically,and the research scheme and purpose of designing novel separator for lithium metal anode were accordingly derived.In the third chapter of this paper,we synthesized the xonotlite nanowires to prepare the separator which was further used for lithium metal anode.The uniform porous xonotlite nanowires separator could lead to generate dendrite-free lithium deposition by inducing lithium nucleation and forming inducing Li₄SiO₄?Li₂SiO₃and Li₂Si₂O₅ enriched artificial SEI.When the deposition and extraction of lithium at the current density was 1 mA/cm²,3 mA/cm² and 5 mA/cm²,coulomb efficiency had98%,98%and 96%after 280 cycles,240 cycles and 200 cycles,respectively.For the full cell coupling with LiNi_0.8Co_0.1Mn_0.1O₂,the coulomb efficiency was 88%of the initial capacity after 400 cycles at 0.5 C.In the fourth chapter of the paper,the sea urchin shell with three-dimensional periodic minimal surface structure in nature was directly used as the separator of lithium metal batteries after simple mechanical treatment.When lithium was deposited and extracted at the current density of 2 mA/cm² and 5 mA/cm²,the coulomb efficiency was 95%after 400 cycles and 200 cycles,respectively.The full cell coupling with LiNi_0.8Co_0.1Mn_0.1O₂ exhibited the obtained capacity retention rate of 69.9%after 400 cycles at 0.5 C.Moreover,the flexible polymer polyvinylidene fluoride separator with the same structure was obtained by etching the sea urchin shell casting polyvinylidene fluoride?PVDF?with template method.The PVDF separator could further reduce the lithium dendrites and a uniform lithium deposition.When the current density was 2 mA/cm² and 5 mA/cm²,the coulomb efficiency of deposition and extraction of lithium both were 95%after 700 cycles and 400 cycles,respectively.The full cell coupling with LiNi_0.8Co_0.1Mn_0.1O₂ possessed the capacity retention rate of 69.9%after 400 cycles at 0.5 C.The fifth chapter records the conclusion and prospect.This thesis realized the regulation of lithium deposition behavior and solid electrolyte interface through the design of separator.This innovative research method and idea will provide novel thought and reference for the future development of lithium metal batteries.