Nanofiber-based Self-supporting Interlayers For High Performance Of Lithium-sulfur Batteries

With the wide application and continuous development of various portable electronic devices and electric vehicles,the demand for high-energy-density secondary batteries is increasing,and the research of related technologies is in the ascendant.Based on the high theoretical energy density(2600 Wh kg^-1),lithium-sulfur batteries have become one of the candidates for next-generation high-energy-density secondary batteries.However,there are some problems to be solved in the practical application of lithium-sulfur batteries.The poor conductivity of sulfur and lithium sulfide causes severe battery polarization,the dissolution and diffusion of polysulfides reduces battery capacity and cycle life and the electrode materials are prone to collapse during continuous charge and discharge processes,decreasing battery stability.In this dissertation,in order to solve the above problems,several kinds of self-supporting carbon nanofibers were designed and prepared as the interlayers of lithium-sulfur batteries based on electrospinning technology,and the electrochemical properties of these interlayers was investigated.The main research contents and results obtained are as follows:1.Zn-N co-doped carbon nanofibers interlayerThe self-supporting cross-linked Zn-N co-doping carbon（ZnNC）nanofibers have been designed and used as the interlayers in Li-S batteries.The ZnNC nanofibers show a structure with pea-shaped voids derived from ZIF-8 nanoparticles,which provide more active sites for trapping and catalysis of polysulfides.The Zn-N co-doping endows the ZnNC nanofibers with improved adsorption and catalysis activity to Li PSs.The electrochemical performance of Li-S batteries is improved by addition of the ZnNC nanofibers interlayer.At 0.5 C,Li-S battery with the ZnNC nanofibers interlayer shows a high initial capacity of 1198.5 m Ah g^-1,a capacity of694.1 m Ah g^-1 can be retained after 500 cycles at 1 C,with a low capacity fading of0.073%per cycle.At a high sulfur loading of 6.19 mg cm^-2,a capacity of 754.8 m Ah g^-1 can be retained after 100 cycles at 0.2 C.2.Fe₃C@NC nanofibers interlayerThe self-supporting inter-crosslinked Fe₃C@NC nanofibers were designed to be used as interlayers for lithium-sulfur batteries.Dispersed Fe₃C nanoparticles can capture polysulfides and accelerate the conversion of polysulfides,N-doping enhances the conductivity of carbon-based nanofibers,and the nanofiber network structure also facilitates electrolyte penetration and ion transport.Li-S battery with the Fe₃C@NC nanofibers interlayer exhibits a high initial capacity of 1403.6 m Ah g^-1 at 0.2 C,a capacity of 724.4 m Ah g^-1 can be maintained after 500 cycles at 1 C,with a capacity fading of only 0.076%per cycle.At 4 C,the battery still displays a high capacity of682.3 m Ah g^-1,showing good rate performance.3.FeCo@NC nanofibers interlayerFeCo alloy phase nanoparticles-loaded N-dopedcarbon（FeCo@NC）nanofibers interlayers were designed and prepared for lithium-sulfur batteries,between which the comparative research was carried out andα-Co solid solution phase nanoparticles-loaded N-doped carbon（α-Co@NC）nanofibers interlayers.Electrochemical performance test analysis shows that the FeCo@NC nanofibers interlayer has stronger electrocatalytic activity and can effectively block the diffusion of polysulfide compared to theα-Co@NC nanofibers interlayer.At the same time the stronger promoting effect on ion transport and charge transfer can be realized by FeCo@NC nanofibers interlayer.Therefore,the battery with FeCo@NC nanofibers interlayer shows better rate capability(720.3 m Ah g^-1 at 4 C)and more stable long-cycle performance(a capacity of 680.6 m Ah g^-1 can be retained after 600 cycles at 1 C).