Study On The Preparation And Performances Of TPU-based Composite Microporous Polymer Electrolytes For Lithium-ion Batteries

The history of human society in thousands of years is not only the history of scientific progress,but also the history of blood and tears of exhaustion of resources and environmental pollution.As time goes into the 21st century,mankind has to face the problem of increasingly serious resource shortage and environmental pollution.Therefore,it is particularly important to develop the new clean energy.Among the much new clean energy,lithium ion battery has many excellent performances,such as high energy density,good cycle stability,low self-discharge,and no pollution,which has made it get a lot of attention from researchers and companies.Lithium ion battery also becomes the main sources of electrochemical source of some traditional electronic equipment.In this paper,thermoplastic polyurethane elastomer(TPU)was selected as the polymer matrix,based on electrostatic spinning technology,which a new type of porous polymer electrolyte was prepared.The influence of spinning process on the microstructure and comprehensive performance of TPU based multi-pore fiber membrane was also discussed.In order to improve the comprehensive performance of lithium ion batteries,organic silicon/TPU based multi-pore fiber membrane was prepared,and the effect of organosilicon on the properties of polymer electrolyte was discussed in the fourth chapter.In the fifth chapter,the nano-inorganic SiO2 modified composite polymer electrolyte was prepared by in-situ polymerization.Finally,considering the excellent safety performance of solid polymer electrolyte,a new type of "rigid-flexible coupling" all-solid-state polymer electrolyte was prepared in the end of this article.Suffer from the hidden trouble in the liquid electrolyte and the improvement of people environmental protection consciousness that make more and more enterprises have turned to use the gel polymer electrolytes and solid-state electrolyte for lithium ion batteries.Come to light,electrostatic spinning technology is one of the simple and effective methods for preparing porous membrane.Therefore,we adopt the electrostatic spinning method and selected the TPU as the polymer matrix to prepare the porous polymer electrolyte for lithium ion battery in the third chapter.By analyzing the scanning electron micrograph,we identified the best electrostatic spinning process:DMF/Ac(7/3)was the mixed solvent,TPU concentration was controlled at 17 wt%,the spinning voltage was 20 kV,and the receiving distance of the drum was 15 cm,the drum speed was 600 rmp.Physical and chemical performance and battery performance test showed that the polymer electrolyte of TPU substrate has a good porosity(54.5%)and ionic conductivity was 3.2×10-3 S cm-1 at room temperature.Nevertheless,porous polymer electrolytes had poor electrochemical stability(4.1 V).Compared with commercial lithium-ion battery separator(PP),the cycling performance of TPU based polymer electrolytes is not good.To sum up,improve the electrochemical stability of TPU based polymer electrolyte is an effective way to make the assembly of the lithium ion battery has a good cycle performance.In the fourth chapter,a series of polyurethane/organosilicon composite fiber membranes were prepared by adopt the electrostatic spinning process in chapter 3.Compared with the fiber membrane prepared by pure TPU,adding appropriate amount of organic silicon will reduces the mechanical properties of the material,but can improve the comprehensive performance of composite fiber membranes.Among them,the composite fiber membrane(TPU/DC51-10%)has the best porosity and the absorption rate(60.9%,428.7%),and the ionic conductivity at room temperature can reach 4.5×10-3 S cm-1.The battery performance test showed that TPU/DC51-10%has better initial charge and discharge performance,and the circulation of 80 times of discharge capacity was higher than those assembled by commercial separator(PP).In order to improve the electrochemical stability of porous polymer electrolyte,nano silica was introduced in chapter 5.The preparation process of TPU/SiO2 composite electrolyte with porous structure also adopts the electrostatic spinning process in chapter 3.Compared with the pure TPU porous membrane,due to the enhancement of inorganic filler,the comprehensive performance of the electrolyte was significantly improved.When adding TEOS content is 5%,the fluid absorption rate and the maximum tensile strength of composite electrolyte,are 542.3%and 25.7 MPa,ionic conductivity at room temperature is 6.02×10-3 S cm-1,electrochemical stability window were 4.72 V.The battery performance test showed charge and discharge 80 times of coulomb efficiency remained at 98.2%.Whether commercial liquid electrolyte or gel polymer electrolytes(GPEs)have safety problems.The all solid polymer electrolyte(SPEs)is widely investigated due to its excellent performances,especially its safety improvement for Li-ion batteries.A kind of "rigid-flexible coupling" composite polymer electrolytes(CPEs)was successfully prepared by using the TPU porous fibrous membrane as the skeleton.By analyzing the structural and thermal performance tests,we found that the addition of nano-SiO2 can reduce the crystallinity and melting temperature of PEO.As is known to all,the conduction of ions in the polymer matrix occurs in the amorphous region.The low crystallinity of PEO will increase the amorphous region in the polymer matrix,which increases the ionic conductivity at room temperature.Besides,PEO has extremely strong crystallization that shows poor mechanical properties.While in CPEs,TPU porous fibrous membrane as the skeleton provides excellent mechanical properties for composite polymer electrolyte membranes.Compared to pure PEO-based polymer electrolyte,CPEs also have good thermal dimensional stability at 140 ?.In the end,in order to evaluate the battery performance of CPEs,we using the CPE3 assembled the all solid state lithium ion battery.Battery performance test result showed CPE3 has excellent first charge and discharge performance(154 mAh g-1)at 60 ?.When the current density up to 1C,CPE3 charge and discharge 100 times the capacity is still maintain in 110 mAh g-1 and coulomb efficiency remained at 91.2%.Through the battery performance test,we found that all solid state composite polymer electrolytes have excellent battery performance,is expected to be applied in polymer lithium ion battery.