Synthesis And Modification Study Of Li Metal Anode And VPO₄ Anode For Lithium Batteries With High Energy Density

As a green and safe new-generation energy storage device,lithium batteries have been given high expectations by researchers.Lithium-ion batteries have been widely used in electric vehicles(EVs)and plug-in hybrid electric vehicles(PHEVs).With the popularization of EVs in daily life,people have more and more urgent demands for high energy density energy storage batteries.As for the anode materials,the traditional anode materials for lithium-ion battery cannot meet the performance of high energy density,fast-charging and long-cycle simultaneously.The development of new type of lithium-ion battery anode material has become the direction of researchers.In order to develop higher energy density lithium batteries,the development of lithium metal batteries has become an inevitable trend.As the core material of lithium metal batteries,lithium metal anode(with theoretical capacity of3860 m Ah g^-1)is the inevitable choice for high specific energy Lithium-sulfur battery,Lithium-oxygen battery and all solid Lithium metal battery.However,it still faces a series of safety problems,such as side reaction,lithium dendrite,dead lithium and so on.The topic of this thesis focuses on high specific energy lithium metal battery anode materials and fast charge and discharge Lithium-ion battery anode materials.1.Research on the design and modification of Lithium metal anode protected by gradient solid electrolyte interphase layer in carbonate electrolyte.The solid electrolyte interface(SEI)is an effective method to improve the safety problems of metal lithium negative electrodes.We have prepared a gradient polymer/inorganic(Polyethylene glycol diacrylate-co-Vinylene carbonate,PEGDA-co-VC/Cu F₂/Li NO₃)composite solid electrolyte interphase layer(PIG-SEI)to protect the lithium anode by in-situ polymerization.In the PIG-SEI,from the outer layer to the inner layer,the content of polymer(PEGDA-co-VC)is decreasing,and the content of inorganic substances(Li F,Li₃N,Cu)is increasing,they change in a gradient trend.The outer layer is mainly polymer,showing good flexibility and mechanical stability,and the inner layer is mainly nano-scale Li F,Li₃N,Cu and lithiated PEGDA-co-VC.There is a chemical interaction between PIG-SEI and lithium metal,which makes PIG-SEI contact lithium metal closely without gap,and inhibits the side reaction between electrolyte and lithium anode and the formation of lithium dendrite.Li Fe PO₄(LFP)and Li Ni_0.8Co_0.1Mn_0.1O₂(NCM811)full batteries assembled with Lithium metal anode protected by PIG-SEI exhibit excellent electrochemical performance under a small amount of carbonate electrolyte.2.Application of artificial solid electrolyte interphase layer in ultra-thin Lithium metal anode.The metal lithium anode used in the laboratory is 400-600?m,which has greatly exceeded the commercial standard(the thickness of the lithium metal anode is less than 50?m).We designed and prepared PEGDA-co-VC/Li DFOB[Lithium difluoro(oxalato)borate]composite artificial SEI(PEVB-SEI)on ultra-thin lithium metal anode(20?m).It combines the advantages of inorganic and polymer.After charging and discharging,the interior is rich in Li F,Li_xBO_yF_zintermediates and PEGDA-co-VC-Li intermediates,improving the physical contact between PEVB-SEI and ultra-thin lithium metal,and the PEVB-SEI has high lithium-ion conductivity.The LFP and Li Ni_0.6Co_0.2Mn_0.2O₂(NCM622)full batteries assembled with Lithium metal anode protected by PEVB-SEI show excellent electrochemical performance.Especially,the assembled LFP soft pack batteries assembled also show excellent charge-discharge performance.3.Research on the design and modification of polymer/inorganic composite solid electrolyte interphase layer to protect lithium metal anode in Lithium-Sulfur batteries with ether-based electrolyte.The biggest problem in Lithium-Sulfur batteries is the“shuttle effect”of polysulfide.Polysulfide will dissolve in the electrolyte and shuttle to the surface of lithium metal anode and react with lithium metal to generate non-conductive Li₂S.Therefore,the artificial SEI can effectively inhibit the side reaction between polysulfide and lithium metal.We designed a PMMA/PPC/Li NO₃polymer/inorganic composite SEI(PMCN-SEI)to protect the lithium metal anode.The PMMA and PPC are carbonate electrolytes,and polysulfides are insoluble in carbonate polymers,which can effectively inhibit the penetration of polysulfides and side reaction between polysulfides and lithium metal anode.In addition,with the charging and discharging process,the PMCN-SEI can generate Li₃N and Li-PPC-Li intermediates to promote uniform deposition of lithium ions.The Lithium-Sulfur battery has excellent electrochemical performance.4.Application research of 3D mutually embedded VPO₄/r GO anode in fast charging and long-life Lithium-ion batteries.VPO₄ is a promising anode material for fast charging,due to its excellent chemical activity and relatively high theoretical specific capacity(550 m Ah g^-1).We successfully synthesized a new type of 3D mutually embedded VPO₄/r GO(VG-MS)composite electrode by in-situ solvothermal reduction method.The porous hydrangea-like VPO₄/r GO microspheres are formed by the nano VPO₄particles and the interlaced r GO conduction network,and the microspheres are embedded in the interlaced porous r GO frame to form a self-supporting composite electrode.The unique porous VG-MS electrode can adapt to the volume change in the lithiation-delithiation reaction process,improve the electronic conductivity and improve the electrochemical reaction kinetics.More importantly,this mutually embedded nanostructure enables VG-MS to exhibit the best pseudocapacitation-controlled fast-charging lithium transport kinetics and excellent cycling stability,enabling it to have the performance of long-cycling and fast-charging.