Preparation And Electrochemical Performances Of Porous Carbon-based Membranes By Phase Inversion

Lithium ion batteries are currently one of the most widely used energy storage equipment.However,as the demand for large energy storage systems continues to increase,the performance requirements of batteries'energy storage capacity and cycle stability are getting even higher.The theoretical capacity of the commercial lithium ion battery with graphite anode is only 372 mA h g^-1,which is far from meeting the actual needs.Lithium-sulfur batteries,as a typical lithium metal battery,have received widespread attention due to their high energy density(2.51 kW h kg^-1-Li₂S)and abundant sulfur resources.However,low sulfur-loading,"shuttle effect"and the growth of lithium dendrites,which is a common problem in lithium metal batteries,can result in a rapidly decaying capacity and short cycle life.To solve the above problems,membrane electrode and interlayer materials with a hierarchical pore structure are designed and prepared by phase inversion in this paper.The phase inversion method,which is the basis for the preparation of most commercial membrane synthesis,is simple and easy for large-scale production.Thanks to the large specific surface area,good conductivity and chemical stability,nanostructured carbon-based membrane with a hierarchical pore structure prepared by phase inversion can be used as a sulfur-loaded cathode and a polysulfide barrier interlayer for lithium-sulfur batteries,and can be used for the protection of negative electrodes of lithium metal batteries.Firstly,the Fe₃C-doped asymmetric porous carbon nanotube membrane?Fe₃C-C/CNT?was prepared by phase inversion method and water was used as the coagulation bath.The material was porous,and the sublayer was composed of finger pores,sponge pores and a coral-like interwoven structure with high porosity and good conductivity.It has dual adsorption of Li-N and Fe-S for polysulfide,which can effectively adsorb polysulfide and inhibit"shuttle effect".When the current density is 1 C,after 200 cycles,the battery with Fe₃C-C/CNT interlayer can still maintain a specific capacity of 751.5 mA hg^-1 and a Coulomb efficiency of96.6%,and the finger pores remains intact,which is beneficial to electrolyte infiltration and Li⁺transmission.To further increase the sulfur-loading of the cathode,using n-pentanol as the coagulation bath,the CNT@C?1:2?and CNT@C?1:1?membranes were prepared by changing the composition ratio of the casting solution.The CNT@C?1:2?membrane is suitable for the cathode of lithium-sulfur batteries because the dense layer can be used as a current collector,and the porous sublayer can be used to load sulfur.The CNT@C?1:1?membrane with cross-linked porous network is suitable for the interlayer of lithium-sulfur batteries to block polysulfides.The synergistic circulation groove constructed by the two membranes can effectively suppress the“shuttle effect”,reduce polarization and the loss of active materials.The CNT@C//CNT@C battery can maintain a specific capacity of 682.9 mA h g^-1 and a Coulomb efficiency of 96.2%at 400 cycles at 1 C.When the sulfur loading is 6.10 mg cm^-2,the areal capacity of the CNT@C//CNT@C battery can reach 5.4 mA h cm^-2.To suppress the growth of lithium dendrites of lithium metal batteries,the porous CNT@C?1:1?membrane is used as an interlayer to protect the anode,which can make lithium deposition more uniform,and act as a physical barrier to hinder the growth of lithium dendrites.Under the high plating/stripping capacity and current density of 8 mA h cm^-2 and 8 mA cm^-2,the polarization of Li/CNT@C was about 0.15 V after 500 h.In the full battery with LiFePO₄ as the cathode,the capacity retention rate of Li/CNT@C battery after 600 cycles was 82.5%.