Research On The Preparation And Properties Of Phenolic Fiber Based Lithium Battery Separator Paper

With the rapid development of science and technology,lithium ion battery has been widely used in portable electronic equipment,pharmaceutical industry,electric vehicles,energy storage and other fields because of its advantages of high output voltage,large specific energy,good cycling performance,environmental friendliness and so on.The separator separates the positive and negative electrodes of the battery,provides channels for ion transmission,and realizes ion conduction,which is an important determinant of battery safety,capacity and life.This thesis mainly studied the structure and properties of phenolic fiber based lithium battery separator paper,with phenolic fiber as matrix material and aramide pulp as reinforced fiber,the battery separator paper was produced by traditional wet papermaking process,phenolic resin impregnation and hot pressing process,which had excellent mechanical properties,thermal stability,electrolyte wettability and flame retardant property.Firstly,the phenolic fibers were fibrilated by PFI pulping machine and analyzed by optical microscope and fiber morphology analyzer.The results showed that the phenolic fiber was the most suitable to be blended with other fibers at 20000r.The tensile index,burst index,porosity and absorbance of the separator paper reached the maximum when the ratio of phenolic fiber to aramong pulp was 4:6,which were 15.49 N·m·g^-1,0.99 k Pa·m²·g^-1,60%and 247.25%,respectively.When PEO content was 0.75%,the strength and evenness of separator paper were better.Then,through the study of the influence of phenolic resin impregnation on the properties of separator paper,it was found that with the increase of phenolic resin impregnation concentration solution,the viscosity also increased,the amount of glue,thickness,tensile index and rupture index of paper samples showed a rising trend,while the porosity gradually decreased,and the mean pore size showed a trend of decreasing first and then increasing.The battery separator material should have high liquid retention capacity and the mean pore size should be minimized while ensuring high porosity.Therefore,the concentration of phenolic resin impregnation solution 7%was selected.Under this concentration,the gelatinization amount of separator paper after impregnation reached 21.40%,the porosity reached 59.97%,and the mean pore size was 2.85μm.The comprehensive performance of separator paper was excellent.Further studied the optimum hot pressing process for the preparation of phenolic fiber based lithium battery separator paper.The results showed that when the hot pressing condition was adjusted to 180℃,10 MPa and 3 min,the strength performance of separator paper was excellent.Under this condition,the burst index was 1.20 k Pa·m²·g^-1,the tensile index was 24.67 N·m·g^-1,and the structure of the paper was compact.Therefore,the physical properties of phenolic fiber based lithium battery separator paper were improved.Finally,the physical properties,temperature resistance,flame retardancy and electrochemical properties of the separator paper and Celgard 2400 separator were compared.The results showed that the phenolic fiber based lithium battery separator paper has better electrolyte wettability,the electrolyte contact Angle was 88.9°,the highest porosity and absorbability were 62%and 248.5%,which were 1.48 times and 2.75 times of Celgard 2400separator.In addition,separator paper had excellent thermal stability,high initial decomposition temperature,high carbon residue rate,thermal shrinkage rate of 180℃was less than 3.5%;Separator paper had excellent flame retardant performance which can only be carbonized;Separator paper had lower dielectric constant and good insulation performance;The ionic conductivity was 1.36 m S·cm^-1,which was 4.9 times of Celgard 2400separator(0.28 m S·cm^-1).Most importantly,phenolic fiber based lithium battery separator paper can effectively inhibit the growth of lithium dendrite in the battery cycle and reduce the generation of dead lithium.In addition,the excellent mechanical strength of the separator paper can avoid the lithium dendrite piercing the separator and causing the battery internal short circuit,thus avoiding the thermal runaway accident of the battery.