Preparation And Properties Of Polyurethanebased Gel Polymer Electrolyte

Polymer electrolyte can overcome the shortcomings of flammability and leakage caused by traditional liquid electrolytes?LEs?.However,the low ionic conductivity of solid polymer electrolyte at room temperature greatly limits its application.Thus,gel polymer electrolyte?GPE?becomes a more practical substitute for LEs due to its high ionic conductivity at room temperature.Among different polymer matrix materials,thermoplastic polyurethane?TPU?,due to its special two-phase microstructure,that is,hard segment and soft segment,becomes an excellent polymer matrix material.The soft segment with ether bonds can hold ionic liquid,which is helpful to promote the dissociation of alkali metal salt,leading to the improvement of ionic conductivity,the hard segment can provide sufficient strength and dimensional stability because of?-?interaction and hydrogen bond interaction between polyurethane groups.Therefore,in this thesis,TPU was used as the main matrix material to prepare a variety of gel electrolytes:?1?A series of membrane materials were successfully prepared by solution casting method with TPU,PMMA,and TiO₂ nanoparticles as raw materials.By adding TiO₂and PMMA,the ionic conductivity of PUMAT reaches 3.9×10^-3 S cm^-1 at room temperature,and its electrochemical stability is as high as 5.2 V.Moreover,the Li/GPE/LiFePO₄ cell delivers excellent cycle performance at 0.1 C and stable rate performance?the retention of capacity is nearly 92%after 60 cycles?with high coulombic efficiency.?2?Two kinds of semi-IPNs polymer membrane were prepared by photoinitiation polymerization.The results of SEM show that the surface of the membranes is smooth without phase separation,which indicates that the cross-linked PMMA has a good compatibility with the linear TPU.Meanwhile,TG,mechanical properties test and crosslinking degree test also prove the formation of the interpenetrating network structure.The porous structure and the presence of PMMA promote the absorption of electrolytes.By comparing the two kinds of semi-IPNs electrolyte membranes,it is found that the porous structure is beneficial to the transport of lithium ions and to the reduction of the interfacial impedance between GPE and lithium metal.Thus,the porous semi-IPNs membrane has higher ionic conductivity and easier migration for lithium ions.The maximum ionic conductivity of semi-IPNs films is up to 3.8×10^-3S cm^-1.The electrochemical stability of all semi-IPNs films is above 5 V.The batteries with semi-IPNs film as electrolyte show good specific capacity during cycle test.?3?Carboxylated multiwalled carbon nanotubes?O-MWCNTs?doped polymer films were prepared by electrospinning.The composite films own porous structure which are observed by SEM.TG and mechanical properties test show that the addition of O-MWCNTs can improve the thermal stability and mechanical properties.The maximum tensile strength reaches 8.7 MPa when the amount of O-MWCNTs is 2%.The ionic conductivity is up to 3.8×10^-3 S cm^-1 and the electrochemical stability is 5.0V.The capacity retention rate of the button battery during charge/discharge cycles is as high as 97%,showing excellent cycle stability.