Preparation Of Polymer Porous Membranes And Research On The Protection Mechanism Of Metal Lithium

With the excessive consumption of fossil fuels and serious environmental pollution,promote the rapid development of clean and sustainable energy.Lithium-ion batteries(LIBs)are widely used in electric vehicles and portable electronic products due to the advantages of high safety,long service life and environmental protection.It is currently one of the most rapidly developing energy equipment.The cathode and anode materials of lithium-ion batteries are close to the theoretical limit,which cannot meet people's demand for high energy density energy storage equipment.Lithium metal is considered as the ideal electrode of rechargeable batteries because of its high theoretical capacity.However,lithium metal battery have an unstable solid electrolyte interphase(SEI)and lithium dendrites formed on lithium electrode during the electrochemical cycle.Lithium metal has high reactivity,which will lead to continuous consumption of liquid electrolyte,resulting in high over potential and low coulomb efficiency of LMBS.In this paper,the Poly(vinylidene fluoride)(PVDF)porous membrane and the Polyacrylonitrile(PAN)oxide porous membrane were prepared by using a simple phase replacement method as lithium protective layers.The main contents are as follows:PVDF Porous membranes were prepared by phase replacement method with different content of PVP pore-forming agent,including 10%,12% and 14% PVDF Porous membranes.Scanning electron microscope(SEM)clearly characterize the microstructure of PVDF membranes before and after cycling,and the PVDF membranes is three-dimensional layered membranes.Compared with PVDF membranes using other PVP pore formers,the PVDF membranes obtained with 12%pore formers have greater porosity.During the preparation of membranes,the surface in contact with water has nano-pores and the surface in contact with glass it is a micron hole.In order to explore the effect of the PVDF porous membranes on suppressing lithium dendrites,it was studied as lithium protective layers.It can be seen from the electrochemical performance results that the improved lithium anode of PVDF porous membrane has excellent sedimentary capacity,high Coulomb efficiency and good cycling after adding a protective layer of PVDF porous membrane.This is mainly due to the excellent mechanical properties of porous PVDF,and the existence of porous structure reduces the local current density and constrains the growth of lithium dendrites.PAN porous membranes were prepared by the phase replacement method and then annealing at 300 °C to obtain oxidized PAN porous membrane.The layered porous structure of PAN was observed by SEM,and the structure will also remain unchanged after the oxidation.The oxidized PAN membrane formed new O-H,C=O and C-N functional groups observed by IR,proving that the oxidized PAN porous membrane already has polar functional groups.According to the electrochemical performance of the materials,porous PAN oxide has better effect of inhibiting the formation of lithium dendrite and better cycling performance.Polar functional groups and porous structure promotes the lithium ion flow uniformly deposited on the lithium surface.