Electrospun Flexible Self-supporting Materials For Lithium-sulfur Battery

In order to cope with the increasingly severe climate change and develop efficient and clean energy storage systems,battery energy storage systems need to achieve higher energy density,cycle life and safety.The lithium-sulfur（Li-S）battery using sulfur as the cathode material has a high material theoretical specific capacity(1675 m Ah g^-1)and battery theoretical specific energy(2600 Wh kg^-1),which converts the earth’s abundant Sulfur as a cathode combined with a high-energy lithium metal anode is considered a next-generation battery technology superior to state-of-the-art lithium-ion batteries（LIBs）.However,there are still some obstacles on the road to commercial application of lithium-sulfur batteries:"shuttle effect"of soluble lithium polysulfide（Li PS）and slow kinetics of sulfur redox conversion;Dendritic lithium formed by uneven deposition of lithium on the negative side,etc.In this paper,carbon fiber is used to construct a three-dimensional conductive framework to achieve excellent electrical conductivity and good mechanical properties.The firm internal network structure can improve the inherent defects of volume expansion before and after charging and discharging of the electrode.The transformation of polysulfides and the uniform deposition of lithium guides provide more active sites to achieve the"shuttle effect"of lithium polysulfides and inhibit the growth of lithium dendrites in the negative electrode.The main research work and conclusions of this paper are as follows:（1）Flexible self-supporting Ni Se₂-Co Se₂@CNF nanofiber membranes were prepared by electrospinning and subsequent selenization treatment.Ni Se₂-Co Se₂@CNF uses a carbon nanofiber network as the skeleton,and the fiber surface extends a layered heterostructure Ni Se₂/Co Se₂.When used as a positive electrode,the initial capacity of the electrode can reach 1004 m Ah g^-1in 500 cycles at a rate of 1 C,and the decay rate per cycle is only 0.03%.When used as a negative electrode,it can significantly reduce the overpotential of lithium nucleation and inhibit the formation of lithium dendrites.When used as a general electrode,the S/Ni Se₂-Co Se₂@CNF|Li/Ni Se₂-Co Se₂@CNF battery has an initial capacity of 943 m Ah g^-1at a rate of 1 C,and can still maintain a capacity of 732m Ah g^-1after 500 cycles.The retention rate is 77.6%,and the overall coulombic efficiency can be maintained above 99%.When the universal electrode is applied to the pouch battery,the cycle loss per cycle is 0.19%at a rate of 0.05 C,and the normal operation of the battery is hardly affected at different bending angles,reflecting the excellent electrochemistry of the integrated flexible electrode in lithium-sulfur batteries.Performance and the potential to fabricate flexible devices.（2）The flexible self-supporting Zn O-Co₃O₄@CNF material was also prepared by electrospinning and evaporation treatment.A solid and large lithium storage space is provided by the three-dimensional conductive framework of carbon fiber,and the lithiophilic gradient on the fiber is composed of Zn O and Co₃O₄.Effectively reduce the local current on the material surface of lithium during electroplating/stripping,so that the deposition of lithium is smoother and more uniform.The electrochemical performance test proves that Zn O-Co₃O₄@CNF has excellent lithium storage and dendrite-free deposition characteristics.When used as an anode,the nucleation overpotential/rate performance/reversibility of the battery is significantly better than that of pure lithium anode.Symmetric cells exhibit ultra-low voltage polarization of 12 m V at 1 m A cm^-2,1m Ah cm^-2,and can maintain a low voltage of 19 m V at current densities of 5 m A cm^-2,5m Ah cm^-2polarization.