The Controllable Preparation Of Three Dimensional Composite Lithium Anodes And Their Performances

Li metal batteries(LMBs)composed of a Li metal anode and a high-capacity cathode,have been considered as a promising energy storage device candidate.Lithium metal has a high theoretical capacity(3860 m A h g^-1),a low redox potential(-3.045 V vs.the standard hydrogen electrode),and a light theoretical density(0.534 g cm^-3).Nevertheless,the uneven deposition and huge volume change of the lithium metal anode during the charging and discharging process result in low Coulombic efficiency and poor cycle life.The three dimensional framework structures with a high specific surface area and high pore volume can reduce local current density,relieve the volume change of lithium anode,and achieve uniform deposition of lithium.To solve the problems existing in the lithium anode and improve its safety,the thesis focuses on the following work:(1)Preparation of super-lithophilic three dimensional composite lithium anodes and its performancesThe three-dimensional composite lithium anode can induce the uniform deposition and dissolution of lithium metallic inside the host,but it remains a challenge to effectively construct the three-dimensional composite lithium anode.Infusing molten strategy related to encapsulate molten lithium metal into a lithophilic host shows its practical application potential.In this work,commercial nickel foam is used as a host,and magnesium-aluminum layered double oxide arrays are subsequently grown on its surface by wet chemical method.During the melting process,the magnesium-aluminum-layered double oxides spontaneously react with lithium to form a lithophilic coating.Besides,the porous arrays on the surface can form a strong capillary force.Driven by the lithophilic coating and capillary force,molten lithium can achieve an instant infiltration on the nickel foam(220?for 1s).Symmetric batteries based on the composite lithium anodes cycle stably for more than 1000 h under a current density of 1m A cm^-2,and exhibit a low polarization voltage of less than 40 m V.Full cells assembled with the composite anode in combination with a high areal Li Fe PO₄ cathode(3 m A h cm^-2)exhibits a high capacity retention rate of 89%after stable cycling for 100 cycles at0.5 C.(2)Preparation of carbon fiber/lithium composite anode and its performancesThe metal hosts with high structural stability can maintain the long-term cycling of batteries without significantly structural collapse.However,metals usually have heavy weight and large thickness,which may decrease the Li utilization and the overall gravimetric energy density of batteries.Carbon-based materials have received widespread attention because of their lightweight,abundant resources,and low cost.In this work,an electrospinning technology in combination of a high-temperature carbonization method is used to prepare a cobalt-doped and thickness-controllable three dimensional carbon nanofiber membrane.The large specific surface area of the three dimensional carbon fiber skeleton can help reduce the local current density of the current collector and thus inhibit the growth of lithium dendrites.The voids inside the skeleton can provide sufficient space for lithium deposition,ensuring a high areal Li deposition and small volume change of lithium anode.The light weight of the three dimensional carbon skeleton can ensure a high composite specific capacity and high gravimetric energy density of batteries.The cobalt nanoparticles uniformly dispersed on the skeleton can improve the wettability of the carbon fiber surface and realize the rapid spreading of molten lithium at a temperature of 220?within 30 s.Compared with commercial lithium foil,the lithium anode based on cobalt-doped carbon fibers effectively reduce the nucleation overpotential,and can induce the uniform lithium deposition in the current collector.Therefore,the composite lithium anode can cycle for over 1000 hours at 0.5 C.This work provides a new idea for the large-scale preparation of lightweight and thin lithium metal anodes.