Preparation And Properties Of Polyurethane Solid Electrolyte Based On Poly (1,4-Butanediol Ester Diol)

Lithium battery is widely used in life,ranging from mobile phones,headphones,computers to electric vehicles,energy storage equipment,etc.The reason why lithium battery can be widely used in life is mainly because it has the advantages of environmental friendly,portability,easy to manufacture,etc.With the improvement of people’s safety awareness,solid lithium battery has become the most likely development direction of the next generation.In recent years,the research of solid-state polyurethane electrolyte has attracted many researchers’attention.Polyurethane has a designable soft and hard segment structure,which provides a channel for ion transport,while the hard segment gives the electrolyte ideal mechanical properties.In this paper,the hard segment content,lithium salt content（LiTFSI）,the type of chain extender and fluorine content in the polyurethane were investigated to find more excellent polyurethane based solid electrolyte.The main contents include the following:（1）Effect of different hard segment content and lithium salt content on the properties of polyurethane electrolyteIn the second chapter,poly1,4-butanediol glycol（PBA）and isoflurone diisocyanate（IPDI）were used to synthesize polyurethane（PU）with different hard segment content.Polyurethane with the best hard segment content was selected to prepare electrolyte membranes with different lithium salt（LiTFSI）content.The effects of hard segment content and lithium salt content on the comprehensive properties of polyurethane electrolyte were explored.The polyurethane film was tested by FTIR,tensile test,XRD,DSC and TG.The results show that the tensile strength increased first and then decreased with the increase of hard segment content.The tensile strength decreased with the increase of lithium salt content.At the same time,it is also confirmed that the crystallinity of polyurethane decreased with the increase of hard segment content,and the glass transition temperature of soft segment increased gradually.The electrochemical performance test showed that the composite of PU-3with 30wt%LiTFSI had the best ionic conductivity when the molar ratio n（IPDI）:n（PBA）=1.6 which reached 1.66×10^-44 S cm^-11 at 80℃.The electrochemical window is 4.3V at 80℃.The tensile strength is still 4.5 MPa and the comprehensive performance is the best.When the PU-3-30%Li electrolyte was assembled into a battery and tested at 80℃,the specific capacity of the battery was 164 mAh g^-11 at 0.2C and 121 mAh g^-11 at 1C after 300 cycles with the capacity retention of 93.1%.（2）Effects of chain extenders on properties of polyurethane and electrolyte membranesIn the third chapter,five kinds of chain extenders as EDA,IPDA,BDO,MPD and DEG were selected to synthesize five kinds of polyurethane with poly（1,4-butanediol ester glycol）（PBA）and hexamethylene diisocyanate（HDI）.The effect of chain extenders on the comprehensive properties of polyurethane solid electrolyte films was investigated.The polyurethane film was tested by FTIR,tensile test,XRD and DSC.The results show that the mechanical properties of amine chain extender are better than alcohol chain extender.The tensile strength of BDO chain extender is larger.Compared with PU synthesized by alcohol chain extender,amine chain extender has lower crystallinity and higher glass transition temperature.Among them,BDO chain extended PU has the best regularity with the highest crystallinity of 39.18%and the lowest glass transition temperature of-47.6℃.In the electrochemical test,the ionic conductivity of DEG chain extension PU was best at low temperature,but the mechanical properties are poor and the short circuit occurs at 80℃.While the ionic conductivity of PU-BDO-30%Li electrolyte membrane reached 1.78×10^-44 S cm^-11 at 80℃with the electrochemical window about 4.3V.Therefore,PU-BDO-30%Li electrolyte membrane was used to assemble the battery.The results showed that the specific discharge capacity of the battery can reach 164 mAh g^-11 and 150 mAh g^-11 at 80℃at 0.2C and1C,respectively.At the same time,the capacity retention was 99.3%after 300 cycles at 1C which showed the better cycling performance.（3）Study on the properties and electrolytes of fluorinated polyurethane with different fluorine contentIn the fourth chapter,polyurethane membranes with different fluorine content were synthesized by perfluorooctyl hexanediol,poly（1,4-butanediol）glycol（PBA）,hexamethylene diisocyanate（HDI）and 1,4-butanediol（BDO）.Then the fluorine-containing polyurethane electrolyte membranes were prepared with lithium salt（LiTFSI）.The influence of fluorine content on the comprehensive properties of polyurethane and electrolyte membranes was investigated.The polyurethane film was tested by FTIR,tensile test,XRD,contact angle test and DSC.The results show that the tensile strength of polyurethane film increased with the increase of fluorine content.When the fluorine content reached 7%,the tensile strength was24.5MPa.With the increase of fluorine content,the crystallinity of polyurethane was gradually destroyed.When the fluorine content was 5%,the fluorine migration reached saturation and the maximum contact angle was 111.9°.The electrochemical test showed that the ionic conductivity of PU-F5-30%Li with 5%fluorine content was the best,reaching 7.94×10^-44 S cm^-11 at 80℃.The electrochemical window test showed that the increase of fluorine content improved the stability of the electrolyte membrane and the electrochemical window reached 4.6V when the fluorine content was 7%.The discharge specific capacity of the battery assembled with PU-F5-30%Li electrolyte membrane at 80℃reached 164 mAh g^-1and 159 mAh g^-11 at 0.2C and 1C,respectively.The capacity retention was 99.7%after 200cycles at 1C.