| In many batteries,lithium battery has been widely used in mobile phone,portable computer and other digital products and pharmaceutical industry,and electric vehicles as well as aerospace because of its advantages,such as high voltage,low self discharge,high specific energy and good cycle performance,and no memory effect,no pollution to the environment.As a key component of lithium batteries,the separator functions to prevents the electrons pass through,but allow the electrolyte ions through freely,so as to realize the ion conduction.The separator is a major determining factor of the battery’s capacity and safety performance.The polyolefin separators are the most common lithium-ion battery separator.The fibers used in this investigation are the polyolefin fiber,bacterial cellulose,dissolving pulp,which as the separator’s main structure materials,and though the wet papermaking and hot pressing processing to prepare battery separator.The main research work and results include the followings:The dissolving pulp was treated with a PFI refiner to achieve fibrillation,and then observed the fibers of the different beating degrees.The results show that the tensile index,permeability and absorption of dissolving pulp sheet at 60°SR are 0.75N﹒m∕g、31.14μm∕（pa﹒s）、6.8cm/10min,the dissolving pulp at 60°SR is most suitable for the preparation of battery separator.Bacterial cellulose was dispersed by mechanical mean with different speeds,then we observed the dispersed bacterial cellulose with microscope and FQA.The results showed that the dispersed bacterial cellulose by 10000r is the most suitable for papermaking.Average length and width of ES fiber are 4.373mm,16.21μm.The ES fibers which pretreated with sodium dodecyl benzene sulfonate were observed with electron microscope,showing that the flaky and granular impurities on the surface are removed.The main problem of ES fiber is the bad dispersion,when the additions of organic silicone defoamer and PEO dispersant are 0.05%,0.25%,the formation and strength of the paper are preferably.At140℃、3.12MPa,the tensile index,porosity,permeability,thickness,electrolyte absorbency of ES separator are 25.1N·m∕g,49%,4.2μm∕（pa·s）,45μm,189%.The ES fiber and dissolving pulp,bacterial cellulose were mixed with different proportions to make paper,when the content of dissolving pulp was 15%,the polyolefin/dissolving pulp composite membrane has better overall performance,the tensile index,porosity,permeability,electrolyte absorbency,thickness are 18.7N﹒m∕g,64%,5.1μm∕（Pa·s）,219%,48μm.When the bacterial cellulose content was 10%,the polyolefin/bacterial cellulose composite membrane has better overall performance,the tensile index,porosity,permeability,electrolyte absorbency,thickness were 25.6N·m∕g、58%、4.4μm∕（Pa·s）、218%、39μm.After 100 cycles at 10C,the specific discharge capacity of polyolefin/dissolving pulp（15%）composite membrane and polyolefin/bacterial cellulose（10%）composite membrane are 85mAhg-1,80mAhg-1 respectively.After 5 cycles at 0.1C,0.2C,0.5C,1C,2C,5C,10C,the capacity retention rate were 71%and 70%respectively,and the cellulose based battery separator showed higher capacity retention rate.The different thickness BC separators have greatly different physical properties.Results show that the thicker of film’s thickness,the higher the quantitative of BC separator,the greater the strength,as well as the smaller porosity,electrolyte absorbency,permeability.The tensile index,porosity,average pore size,electrolyte absorbency,permeability and thickness of 5mmBC membrane were 48.1 N·m∕g、44%、16.987nm、141%、1.02μm∕（Pa·s）、19μm.After 100 cycles at 10C,the specific discharge capacity was 40mAhg-1,after 5cycles at 0.1C,0.2C,0.5C,1C,2C,5C,10C,the capacity retention rate was 25%.Compared with ES fiber membrane and a business separator A,the thermal shrinkage of the polyolefin composite membrane with bacterial cellulose and dissolving pulp was relatively low.The composite membranes were added into the dissolving pulp with 5%,10%,15%,20%,30%,40%,the heat shrinkage rate,respectively,were 46.6%,45.5%,43.2%,38.6%,and 6.4%,at the temperature of 180℃.Adding bacterial cellulose into the composite membrane with 5%,10%,15%,and 20%,the thermal shrinkage were 50.2%,48.7%,38.4%,respectively,at the temperature of 180℃.The thermal shrinkage of the BC separator was0.3%at 200℃after 30min,and the thermal stability is excellent. |
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