Study On The Application Of Cellulose In Alkaline Polyelectrolyte

Alkaline polyelectrolyte(ASPE)is one of the key elements in electrochemical applications,which can be used to replace the traditional alkaline electrolyte.Alkaline polyelectrolyte not only has the advantages of environmental protection,low corrosivity and no leakage,but also has the advantages of bending resistance and no damage after repeated bending.So that it has a certain research potential in the field of flexible battery.Based on the conduction principle of alkaline polymer solid electrolyte membrane,natural polymer cellulose was introduced into traditional polyelectrolyte(PVA,PAA).Because of its high crystalline structure,cellulose has excellent alkali resistance and mechanical strength;Cellulose chain carries a large number of hydroxyl groups,and has excellent water absorption and retention,which can improve the OH^-and H₂O content of the membrane,so as to improve the ionic conductivity and mechanical strength of the membrane.PVA/QMCC/KOH polyelectrolyte membrane was prepared by mixing quaternary ammonium modified microcrystalline cellulose(QMCC)and PVA solution into membrane;In order to further improve the ionic conductivity and mechanical properties of the membrane,the regenerated absorbent cotton(RDC)was prepared by supercritical CO₂ to form RDC network,In situ polymerization was carried out in the presence of AA,initiator and N,N'-methylenebisacrylamide(MBA),RDC/PAA/KOH and RDC/N-PAA/KOH alkaline polyelectrolyte membranes with skin core structure were prepared.Through the structural characterization,electrochemical performance,mechanical properties and a series of performance tests of the alkaline polyelectrolyte,ASPE showed good alkali resistance,good electrochemical performance,stability and suitable mechanical properties,and was applied to flexible Zn-Air batteries.The main contents of this thesis are as follows:(1)Firstly,quaternary ammonium salt(QAS)was prepared by using epichlorohydrin and dodecyl tertiary amine as raw materials,and quaternary ammonium salt reacted with MCC to produce quaternized cellulose(QMCC).The PVA/QMCC/KOH composite film was obtained by mixing quaternized microcrystalline cellulose,PVA and KOH uniformly and casting.EDX and SEM scanning results showed that quaternary ammonium salt reacted successfully with MCC to obtain quaternized cellulose.Thermogravimetric analysis showed that the introduction of QMCC increased the water content of matrix.Electrochemical performance tests show that the ionic conductivity of alkaline polymer solid electrolyte membrane increases from 90 m S cm^-1to 238 m S cm^-1after QMCC is added.The stress-strain test showed good mechanical stability,and its tensile strength increased from 215KPa to 395KPa.(2)Firstly,absorbent cotton was dissolved by Li OH/Urea system,which was cast into a film and placed in an anhydrous ethanol coagulation bath.Regenerated absorbent cotton was dried by supercritical method to obtain regenerated absorbent cotton film(RDC).RDC was placed in acrylic acid and potassium persulfate(K₂S₂O₈)was used as initiator to initiate acrylic monomer to obtain RDC/PAA composite film.And then the RDC/PAA/KOH composite membrane is obtained by soaking the RDC/PAA composite membrane in KOH solution.SEM scanning results showed that a layer of polyacrylic acid was successfully coated on the surface of RDC.Thermogravimetric analysis showed that the water retention of matrix was obviously enhanced by the introduction of PAA.Electrochemical performance test showed that when RDC/PAA composite membrane was soaked in 10M KOH for 3h,the ionic conductivity of RDC/PAA/KOH could reach 308m S cm^-1.The stress-strain test showed good mechanical stability,and its tensile strength increased from 15KPa to26KPa.(3)Firstly,absorbent cotton was dissolved by Li OH/Urea system,which was cast into a film and placed in an anhydrous ethanol coagulation bath.Regenerated absorbent cotton was dried by supercritical method to obtain regenerated absorbent cotton film(RDC).RDC was placed in acrylic acid,K₂S₂O₈was used as initiator,and MBA was used as crosslinking agent to initiate acrylic acid,so as to obtain RDC/N-PAA composite film coated by polyacrylic acid crosslinking.Then RDC/N-PAA/KOH composite membrane was obtained by soaking RDC/N-PAA composite membrane in KOH solutions with different concentrations.SEM scanning results showed that RDC/N-PAA/KOH with sandwich structure was successfully formed after being coated by polyacrylic acid cross-linking.Thermogravimetric analysis showed that the introduction of PAA treated with N,N'-methylene bisacrylamide significantly enhanced the water retention of the matrix.Electrochemical performance test shows that when RDC/N-PAA composite membrane is soaked in 10M KOH for 3h,the ionic conductivity of RDC/N-PAA/KOH can reach430m S cm^-1.The stress-strain test showed that the existence of crosslinking agent greatly improved the mechanical stability of the composite membrane,and its tensile strength increased from 15KPa to 380KPa.