Study On Preparation And Performance Of Flexible TiO₂ Ceramic Nanofiber Based Composite Lithium Anode

The development of portable electronic products,electric vehicles and large-scale energy storage systems put forward higher requirements for the energy density of batteries.Therefore,it is very important to develop new high-capacity electrodes.Although lithium metal batteries（LMBs）are most promising to become a new generation of high energy density batteries,lithium metal with high reactivity leads to lithium dendrite growth,which greatly reduces the reliability and safety of the battery.These methods are expected to solve the above problems by developing a 3D host framework to composite the host-free lithium metal,adding additives to the electrolyte or directly using solid electrolyte（SSEs）to design the solid electrolyte interface（SEI）.Different from the traditional and net lithium metal anode,the 3D porous lithium metal anode with a host framework can reduce the local current density and control the lithium deposition behavior.The widely reported 3D host framework can be divided into conductive and insulating framework.When the conductive framework is under high current,lithium ions are preferentially reduced on the surface of the framework,which weakens the confinement effect.However,the uneven distribution of electrons in the insulating framework will lead to the fracture of lithium metal and reduce the magnification performance of LMBs.New mixed ion electronic conductors can control lithium deposition and improve the rate capability.Nevertheless,how to balance the conductivity of electrons and ions is still a thorny problem.On the other hand,in order to reduce the continuous corrosion of lithium metal by electrolyte,SSEs is used in lithium metal batteries.However,for SSEs,there are concerns on high contact impedance,brittleness,and the noncompatible fabrication process with the mature roll-to-roll or lamination manufacturing.,which cannot be achieved and applied in practical LMBs.Based on the above problems,the flexible titanium dioxide（TiO₂）ceramic nanofiber membrane as the three-dimensional main framework of lithium metal anode was prepared by electrospinning and high-temperature calcination technology.The oxygen vacancy defect is introduced into TiO₂ by one-step hot-pressing lithium reduction method to form a conductive TiO_2-x fiber.At the same time,the lithium metal is fused and attached to the fiber surface,forming TiO_2-x@Li Composite anode.The TiO_2-x@Li composite anode and gel electrolyte were combined to form an integrated electrode/electrolyte structure with multiphase conduction network,and then a quasi-solid-state lithium metal battery is assembled.Here,we first explored the influence of different polymer templates on the morphology and structure of nanofibers,and prepared flexible TiO₂ nanofiber membranes with high specific surface area and three-dimensional structure.After that,it was compounded with lithium metal by hot-pressing lithium reduction method,and the influence of different hot-pressing parameters on the morphology and structure of composite anode was explored.The lithium metal in the TiO_2-x@Li composite anode is wrapped on the surface of the nanofiber,but still retains the three-dimensional pore structure between the fibers,forming a three-dimensional porous lithium nanofiber with TiO_2-x as the host framework.With this unique structure,the local current density and impedance were reduced,and the TiO_2-x@Li composite anode can stably cycle for more than 1600 h at a high current density of 10 m A/cm².The integrated electrode/electrolyte structure reduces the impedance of contact interface between the active lithium metal and the electrolyte.The multiphase conduction network can conduct electrons through three-dimensional TiO_2-x nanofibers and lithium ions through gel electrolyte.The quasi-solid lithium metal battery(TiO_2-x@Li//QSE//LFP)assembled with LiFePO₄ cathode can provide a stable discharge specific capacity of about 140 m A h/g after 500 cycles at 0.5 C and maintain a high coulomb efficiency of 99.8%.