Preparation And Performance Control Of Lithium Battery Separator Based On CNF/aramid Fibe

With the development of economy and technology and the national call for green development,energy storage fields such as intelligent equipment and new energy electric vehicles are rising rapidly.According to what people need to use it,the market has put forward more stringent standards for the comprehensive performance of lithium-ion batteries,among which the traditional polyolefin separator can no longer meet the market demand for performance,and its low porosity,poor wettability and thermal stability restrict the development of lithium battery separator.In this paper,nanocellulose and aramid fibers were used as raw materials for preparing lithium battery separators.The blending and bio-stimulated mineralization modification methods were used to regulate and optimize the structure and performances of the separator by changing the concentration of each component.The lithium battery separators with high mechanical strength,high porosity,excellent wettability and thermal stability as well as good electrochemical performance were prepared.The main research contents are as follows:Firstly,the nanocellulose/aramid fiber lithium-ion battery separator（CPMP）designed the reinforced concrete structure was prepared by blending nanocellulose（CNF）and aramid fibers（PMIA chopped fiber and PPTA pulp）with polyimide（PI）as enhancer via the traditional heterogeneous paper-making process.The dispersion and stability of nanocellulose and aramid fibers suspensions were discussed,and the influence of regulating the concentration of each component on the mechanical properties of the CPMP separator was investigated by statistical analysis method of one-way ANOVA.The absorption rate,retention rate,porosity,thermal stability,contact angle,uniformity,SEM,POM,ATR-FTIR,TG and electrochemical properties of the CPMP separator were characterized and regulated.The results showed that nanocellulose and aramid fibers suspension had good dispersion and stability,and the optimal composition of CPMP separators was CNF（0.5wt%）,PMIA/PPTA（0.5wt%,5/5）,diatomite（0.05wt%）and PI（1.5wt%）.At this time,the tensile strength of the CPMP separator was 23.74MPa,elongation at break was 3.41%,and absorption rate,retention rate and porosity reached237.16%,152.88%and 69.34%,respectively.The thermal shrinkage rate was 0.31%,the contact angle was 0°,and the ionic conductivity was 1.041m S.cm^-1.The initial discharge capacity was 158.2m Ah.g^-1.The SEM results showed that CNF had good compatibility with PMIA/PPTA.The ART-FTIR showed that CNF and PMIA/PPTA successfully bonded with electrostatic attraction.The CPMP separator had excellent wettability and thermal stability,which met the technical safety requirements of lithium battery separator.Secondly,the porous nanocellulose/aramid fiber lithium-ion battery separator（p-CPMP）was prepared by blending CNF and aramid fibers with diatomite as filler via vacuum filtration.The effects of regulating three technological conditions,including the content of the filler（DTM）,the proportion of ethanol in solvent replacement medium and drying method,on the pore properties of p-CPMP separator were investigated.The basic physical properties,mechanical properties,absorption rate,retention rate,porosity,pore volume,specific surface area,average pore diameter,SEM,N2 adsorption isotherm and contact angle of p-CPMP separator were characterized and regulated.The results showed that the addition of DTM optimized and filled the large pore size of p-CPMP separator.The SEM results showed that the pore structure of p-CPMP separator was more uniform and compact when the content of DTM was 1wt%.The change of the proportion of ethanol in the solvent replacement medium helped to regulate the tightness and mechanical strength of p-CPMP separator with the ethanol as the porogen.When the proportion of ethanol was70%,the distribution range of porosity and pore size of p-CPMP separator was moderate.The drying method had a significant influence on the regulation of tightness and porosity of p-CPMP separator.Compared with five drying methods,the separator obtained by non-vacuum pre-drying and then felt drying had flat surface,high mechanical strength,and uniform pore structure.Thirdly,the mineralized modified nanocellulose/aramid fiber lithium-ion battery separator（pn-CPM）was prepared by bio-stimulated mineralization with sodium silicate（Na2SiO3）as silicon source and polydopamine（PDA）as mineralized inducer.Through response surface test design and regression equation model fitting,the influence of preparation process conditions on mechanical properties of pn-CPM separator was regulated and optimized,and the absorption rate,retention rate,porosity,thermal stability,contact angle,SEM,TG,ATR-FTIR and electrochemical properties of pn-CPM separator were characterized and regulated.The results showed that the optimal preparation conditions for the pn-CPM separator were obtained:the mass ratio of Laponite and CNF was 0.1:1,the Na2SiO3 concentration was 0.6%and the soaking time in PDA/Na2SiO3solution was 9h.At this time,the tensile strength and elongation at break of pn-CPM separator were 27.554MPa and 5.164%,respectively.The porosity was 63.15%,the thermal shrinkage was 0.24%,the contact Angle was 32.035°,and the ionic conductivity was 1.67m S.cm^-1.The results of SEM and FTIR showed that Laponite was well combined with CNF,PDA was deposited on the fiber surface and stimulated the in-situ growth of SiO2 particles,which confirmed the successful mineralization modification of pn-CPM separator.After mineralized modification,the mechanical properties,thermal stability and electrochemical properties of pn-CPM separator were improved.The mechanical properties,wettability,thermal stability and electrochemical performance of the separator are the key indexes to evaluate the excellent performance of lithium-ion battery separator.By comparing the performance of the lithium-ion battery separator prepared by the above three methods,the pn-CPM separator had high mechanical strength,excellent wettability,stable thermal performance and high ionic conductivity.The preparation process of pn-CPM separator was simple and the comprehensive property was the best.