Preparation Of Hierarchical Porous Membrane And Application In Lithium Metal Batteries

With the development and progress of society,the requirements for energy storage technology are getting higher and higher.Lithium-ion batteries are currently one of the most widely used energy storage components.However,as the demand for large-scale energy storage continues to increase,lithium-ion batteries cannot meet the status quo,and lithium metal batteries with much higher energy density than lithium-ion batteries are expected.Lithium-sulfur batteries are a typical representative of lithium metal batteries,but problems such as the growth of lithium dendrites in the negative electrode and the shuttle effect of the positive electrode have seriously affected the performance and safety of lithium-sulfur batteries,and are the shackles of the industrialization of lithium-sulfur batteries.Relieving the growth of lithium dendrites and inhibiting the shuttle effect is an urgent need for breakthroughs in lithium-sulfur batteries.Adding a barrier layer with high porosity and excellent conductivity to disperse the lithium ions flux is a simple and effective means of preventing dendrite.The functionalized electrode is designed to absorb polysulfides while ensuring the uniform deposition of lithium,which can effectively improve the performance of lithium-sulfur batteries.In this article,we first configured PAN:CNT(1:1 wt%)casting solution,and prepared nitrogen-doped hierarchical porous carbon membrane(NHPM)by phase inversion method using n-pentanol as the gel bath for lithium metal batteries Negative protective barrier.The main body of the material is composed of an interwoven CNT skeleton with a symmetrical structure,and the channels are connected to each other.The porous network structure can redistribute the uneven lithium ions flux inside the battery,make it uniform and reversible deposition on the surface of the negative electrode,and inhibit the growth of lithium dendrites.PAN is used as a coating to coat the CNT framework and introduce large number of nitrogen atoms after carbonization.XPS experiments and theoretical calculations prove that the doped nitrogen atoms have a strong adsorption effect on lithium ions,which induces some lithium ions to be deposited on the interlayer,which relieves the deposition pressure on the negative electrode surface.NHPM is applied to a variety of lithium metal batteries for testing.At a high current density of 8 m A cm^-2,a symmetrical battery with NHPM added can run up to 500 hours with an overpotential of 0.15 V.In the LiFePO₄ full battery,the NHPM-Li battery cycles more than 600 cycles,and the capacity decay rate is 0.03%.Even if the LiFePO₄ load is increased or replaced with a high working voltage NCM full battery,the NHPM-Li battery still runs stably,and the coulombic efficiency is close to 100%.On the basis of the above-mentioned NHPM,a tin metal coating was further coated on the film frame to prepare Sn@NHPM and used for the positive and negative electrodes of lithium-sulfur batteries.The membrane has high porosity and sufficient space for deposition.The experimental results show that Sn@NHPM as a positive electrode has a dual adsorption effect of Li-N and Sn-S,which effectively inhibits the shuttle of polysulfides,and has excellent lithium affinity as a negative electrode,promotes uniform and reversible deposition of lithium ions,and is beneficial to inhibit lithium dendrites.The capacity of Li/Sn@NHPM-S/Sn@NHPM battery can reach617.1 mAh g^-1 after 200 cycles at 1 C current density,and the efficiency remains 99.5%.In addition,the lithium load of the composite negative electrode is controlled to 5 mAh cm^-2,which reduces the N/P ratio of the lithium-sulfur battery to 3.7,which greatly improves the utilization rate of lithium.