| With the increasing demand for energy,traditional fossil energy can no longer meet the need of human beings,and new types of energy technologies represented by lithium-ion batteries（LIBs）have set off an upsurge.Nowadays,LIBs have been widely applied in our daily life,such as mobile phone batteries and new energy vehicles.However,the energy density of traditional LIBs is increasingly difficult to meet the operating requirements with the rapid growth of market.In order to further improve the energy density of batteries,it is a hot research topic to explore new electrode materials to replace the graphite anode,such as metal-organic frameworks（MOFs）,lithium metals,etc.Unfortunately,these LIBs anode materials have unavoidable interface problems including the solid-liquid interface between the electrode and electrolyte,and the solid-solid interface between the current collector and active material,which seriously restrict the cycling life and stability of the battery.MOFs have been commonly studied in the field of LIBs owing to their large specific surface area,versatile chemical properties,adjustable porous structure,and abundant reaction sites.In particular,the numerous active sites and structural adjustability provide unlimited possibilities for constructing the stable interfaces.In this thesis,three key problems including the poor stability of solid-liquid interface between MOFs-based anode material and the electrolyte,the interface incompatibility of current collector/deposited lithium metal,and the easy breaking of lithium metal/electrolyte interface are investigated.MOFs and their derivatives are utilized to optimize the interface structure and construct a stable and compatible two-phase interface,improving the performance of LIBs.The specific research contents are as follows:（1）A fluorinated MOF material,copper tetrafluoroterephthalate（Cu TFBDC）,is designed and prepared,aiming at the problem that the poor cycle stability of the battery is caused by the fragility of solid electrolyte interface（SEI）film when MOFs are directly employed as the negative electrode of LIBs.Based on the abundant fluorine species in Cu TFBDC,the increasing Li F content in SEI film results in a highly electrochemical stability.The studies reveal that the specific capacity of fluorine-free copper1,4-benzenedicarboxylate（Cu BDC）without fluorine rapidly decreases to 99.5 m Ah g-1 after21 cycles at a current density of 100 m A g-1,while a reversible specific capacity of 575.5m Ah g-1 is achieved for the fluorinated Cu TFBDC after 500 cycles.This effective fluorination strategy can be extended to a wider range of applications for MOF materials.（2）The Cu-TCNQ materials as the template are grown on pure copper foil followed by a calcined treatment,aiming at addressing the issues of lithium dendrites,dead lithium and poor cycle life which are caused by the incompatibility of the Cu/Li interface.The branched nitrogen-doped carbon network structure is constructed on the surface of copper foil by repeating the growth and calcination process.The high specific surface area of current collector effectively reduces the local current density,and lithium metals are uniformly nucleated and grown on the surface of current collector.In the subsequent cycling process,the branched nitrogen-doped carbon network is well preserved and a dense Cu/Li interface is generated.The results show that the symmetric cell constructed based on the branched structure of current collector operates stably for 3000 hours at a current density of 0.5 m A cm-2 with a small hysteresis voltage of 14.4 m V.The controlled strategy on uniform depostion of lithium metal by fabricating branched nitrogen-doped carbon network provides a basis for artificially constructing copper-based current collection with a high specific surface area of lithium metal batteries.（3）An in-situ liquid phase growth technique is employed to construct a stable and safe Cu/Li interface as well as a robust SEI film.The stable cycle of lithium metal batteries can be ensured by a coating of copper tetrafluoroterephthalate on the copper current collector,aiming at adressing two problems including the incompatibility Cu/Li interface and the fragile SEI film.A thin copper tetrafluoroterephthalate film is in situ formed on the modified current collector,which induces the uniform deposition of lithium on Cu TFBDC@Cu current collector,meanwhile reduces the generation of lithium dendrites.In addition,the rich F elements within Cu TFBDC can increase the content of Li F in SEI film,which effectively passivates the lithium metal electrodes,restrains the side reactions between electrolyte and electrode,thus promoting the diffusion of lithium in the SEI film.The results reveal that the symmetric cell based on Cu TFBDC@Cu current collector can run stably for 3000 hours at a current density of 0.5 m A cm-2 with a smaller hysteresis voltage of 11.5 m V,compared to the pure copper foil.Furthermore,the as-assembled full battery is capable of running smoothly for 250 cycles at 2 C with a specific capacity of 125.29 m Ah g-1.This strategy provides ideas for the design and development of practical lithium metal batteries. |
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