Preparation And Energy Storage Properties Of PAN/CNT-based Integrated Membrane

At present,the theoretical specific capacity of commercial lithium-ion batteries are only274 m A h g^-1,while the lithium-sulfur batteries are expected to become the development direction of a new generation of lithium batteries with a higher theoretical specific capacity(1675 m A h g^-1).In addition,lithium-sulfur batteries also have the advantages of low price,abundant storage of sulfur and environmental friendliness,which has great potential for development.However,the practical application of lithium-sulfur batteries are still faced with many problems:Charging and discharging products S and Li₂S/Li₂S₂ have poor electrical conductivity and are easy to deposit on the membrane surface to hinder the transfer of lithium ions.The volume expansion of sulfur active substances are up to 80%during the cycles.The dissolution and diffusion of intermediate polysulfides causes the shuttle effect.In order to solve the above problems,MoNCNTs/CNTs-PAN porous network electrode membrane(MoNCNTs)with CNT as the skeleton and Mo and N co-doped carbon as the cross-linked coating layer were prepared by phase inversion method.Furthermore,CNTs-PAN membrane(CNTs-PAN)with CNT as the skeleton and PAN as the cross-linked coating layer were constructed on the surface of the electrode membrane.The interface between electrode membrane and interlayer is naturally connected by cross-connecting holes,which effectively reduces the internal resistance of the batteries and accelerates the diffusion rate of ions through the interface.The good pore space in the material is favorable to the load of sulfur,and at the same time,it can effectively buffer the volume expansion of the active substances.Mo and N doping can effectively improve the polysulfides adsorption performance of the electrode membrane,effectively inhibit the shuttle effect,and can effectively catalyze the transformation of polysulfides and decomposition of lithium sulfide,accelerate the reaction rate of the batteries,with excellent performance.Firstly,N-doped electrode membrane-interlayer integrated membrane(NCNTs/CNTs-PAN)was prepared by phase inversion method.Based on the advantages of integrated structure,abundant pore space and N chemisorption performance,the batteries showed good electrochemical performance.At 0.5 C current density,the discharge capacity remains at 820.1m A h g^-1 after 100 cycles,and the coulomb efficiency is 99.9%.At 1 C current density,the average capacity decay rate per cycle is only 0.04%after 250 cycles.Compared with the traditional discrete stacked batteries,the performance is greatly improved.Mo and N co-doped integrated membrane(MoNCNTs/CNTs-PAN)was prepared by further doping Mo elemental substance in the electrode membrane.There was a stronger interaction between Mo and polysulfides,and the adsorption and catalytic properties of the electrode membrane material were significantly improved.The electrocatalytic capacity of Mo in lithium-sulfur batteries was confirmed by DFT simulation,and the conversion reaction of active substances was promoted by reducing the dissociation energy barrier of Li₂S and the Gibbs free energy of polysulfides conversion,thus inhibiting the shuttle effect..Based on the advantages of electrocatalysis,the performance of the batteries is greatly improved.At the current density of 0.5 C,the discharge capacity reaches 927.2 m A h g^-1 after 100 cycles.At a high sulfur load of 3 mg cm^-2,the discharge capacity remains at 755.9 m A h g^-1 after 100 cycles.At a high sulfur load of 4 mg cm^-2,the average capacity decay rate per cycle is only 0.09%after 100 cycles.