Preparation Of Carbon-based Membrane Materials By Phase Inversion Method And Study Of Electrochemical Performances

In recent years,lithium ion batteries and lithium sulfur batteries have been rapidly developed as representative energy storage devices,which put higher requirements on energy density,power density and stability of battery.It is very important for improving energy density,power density and stability to provide electrode materials with higher capacity,faster ion and electron transfer rates,longer cycle times.Conventional powder materials are easily peeled off from the current collector during charge and discharge process,and the non-conductive substance of binder is added,resulting in poor electrochemical performance.The use of a large amount of metal such as Al,Cu as a current collector increases the weight and cost of the electrodes.Asymmetric porous membranes constructed by phase inversion have been widely used in gas separation and water treatment,including thin skin layers and porous support layers.Due to the characteristics of the porous and interwoven skeleton,the dense layer acts a current collector and the porous layer carries the active materials,saving the use of the conductive agent,the binder and the current collector,so it has broad application propects as lithium ion battery and lithium sulfur battery electrodes.Firstly,the Fe₃C doped asymmetric porous carbon membrane?Fe₃C/APCM?integrated material was prepared by phase inversion method.By exploring the carbonization temperature and electrode thickness,it was found that the Fe₃C/APCM-100 electrode carbonized at 800°C has the highest rate performance and cycle stability.The integrated material consists of dense layer,finger pores and sponge pores structure.The porous structure shortens the ion transport distance and increases the specific surface area(134.9 m² g^-1).Under the rate performance test,the discharge capacities of Fe₃C/APCM-100 at current densities of 0.1,0.2,0.5,1.0 and 2.0 A g^-1 were 605.5,558.1,475.7,355.4 and 210.0 mAh g^-1,having high rate performances and cycle stability.Next,the APCM is loaded with high capacity Si active materials,Si@rGO/APCM integrated materials was prepared by freeze-drying and phase inversion methods.The stretched graphene sheet has wrinkles and folded morphology,which promotes uniform dispersion of the nano-silicon particles,and reduces the charge transfer resistance R_ctt from92.01?of the Si/APCM material to 85.58?.Si@rGO/APCM consists of dense layer and sponge pores,which can effectively accommodate the volume change of the Si nano particles during charge-discharge process.After 200 long cycles at 1.0 A g^-1 current density,the capacity of Si@rGO/APCM was remained at 881.2 mAh g^-1,and the Coulomb efficiency was remained above 99%.The capacity of Si@rGO/APCM was higher than the 316.3 mAh g^-1of the Si/APCM electrode.The rGO sheet structure effectively enhances the electrochemical performances of the electrode material.Finally,the APCM was modified by CNT,and then the high capacity S active meterials was loaded on the porous surface of the membrane to form a CNT/APCM/S electrode material.Both surfaces of CNT/APCM are porous and the specific surface area reaches49.103 m² g^-1,which enhances the adsorption of C/S composites.The introduction of the N element increases the chemisorption of polysulfides and electrochemical reactivity.At the current density of 0.5 C,the initial capacity of CNT/APCM/S is 1472.6 mAh g^-1,the capacity is remained at 869.9 mAh g^-1 after 100 cycles,and the Coulomb efficiency is remaining above99%,while The capacity of APCM/S and C/S electrodes decays to 733.3 mAh g^-1 and 589.2mAh g^-1.Even at the high current density of 1.0 C,the CNT/APCM/S capacity is remained at849.3 mAh g^-1 after 200 cycles.