Solid Polymer Electrolyte Based On Polyurethane For All-solid-state Lithium Batteries

The traditional lithium ion batteries have been suffered from some safety problems like leakage and flame which caused by the use of organic liquid electrolytes.Solid polymer electrolytes(SPEs)have been considered as the promising candidates for the next-generation lithium ion batteries due to its advantages of nonvolatile,nonflammable,high energy density,easy to prepare in large area and safety.In order to develop novel solid state polymer electrolytes and all-solid-state lithium ion batteries,a series of polyurethane based solid polymer electrolytes are prepared by designing different soft and hard segments in this paper.The polyurethane based flexible cathode membranes and flexible all-solid-state lithium batteries are also fabricated.In Chapter 1,the different types of lithium ion batteries and the ion transfer mechanisms of solid polymer electrolytes have been introduced.The development of polymer matrix and all-solid-state lithium batteries base on innovative design concepts are reviewed in this section.In Chapter 2,the materials and equipment used in this paper are listed.The testing methods and the assemble procedure of coin cells are introduced.In Chapter 3,a series of solid polymer electrolytes based on comb-like nonionic waterborne polyurethane(NWPU)and LiClO4 are fabricated by isophorone diisocyanate,poly(propylene oxide glycol),1,4-butandiol and poly(ethylene glycol monomethyl ether)-based trimethyllolpropane.Lithium salts can be dissolved in the NWPU matrix by the coordination of Li+ with soft and hard segments.The Li+transfer occurs mainly in the soft segments of polyurethane.The SPE15(with 15 wt%LiClO4)possesses the best comprehensive performance with the ionic conductivity of 5.44×10-6 S cm-1 and 2.35x103 S cm-1 at 60? and 80?,respectively.In Chapter 4,a series of NWPU/PEO-based solid polymer electrolytes are prepared by blending NWPU(as prepared in Chapter 3),poly(ethylene oxide)(PEO)and lithium bis(trifluoromethane sulfonimide)(LiTFSI)via an organic solvent free process.The NWPU acts as the rigid skeleton for the NWPU/PEO blends,improving the mechanical properties and electrochemical stability of the solid polymer electrolytes.The SPE2(30 wt%LiTFSI in NWPU:PEO=1:3)electrolyte presents the superior comprehensive performance with a stress of 1.3 MPa.The ionic conductivity of SPE2 reach to 8.2×10-4 S cm-1 at 60? with electrochemical window exceeding 4.8 V.All-solid-state LiFePO4/SPE2/Li cell exhibits discharge capacity of 160 mAh g-1 at 0.2C and 96%capacity retention after 100 cycles at 1C at 80?.In Chapter 5,four kinds of polycarbonate-based polyurethane with different content of hard segments are synthesized by 1,6-hexamethylene diisocyanate,polycarbonatediol and diethylene glycol.The stress of the PCPU increases with the increase of hard segments content.The PCPU-based SPEs composed of PCPU10(with 10 wt%hard segments content)and 20 wt%LiTFSI shows high ionic conductivity of 1.58×10-5 S cm-1 and 1.12×10-4 S cm-1 at 60 ? and 80?,respectively.The all-solid-state batteries using PCPU-based SPEs and LiFePO4 cathode possess excellent cycling performance both at 60? and 80?.In Chapter 6,a series of polyurethane-based flexible cathodes with different mass ratios of thermoplastic polyurethane(TPU),LiFePO4 and super P(SP)are fabricated by a phase separation process.The obtained cathode membranes show flexible characteristic with abundant porous structure.Compared with the traditional cathode,the polyurethane-based flexible cathodes possess excellent rate performance,which may attribute to the porous networks can promote the electrolyte infiltration and accelerate Li+ transformation.In Chapter 7,flexible all-solid-state lithium batteries are fabricated by the polyurethane-based flexible cathodes and hybrid solid polymer electrolytes.The porous structure of the cathode membranes has been optimized by using different amount of N,N-dimethylformamide(DMF)during the phase separation process.With the increase of the content of DMF,the flexible cathodes membrane can form large finger-like holes.The integrated design of the flexible lithium battery structure is realized by casting the SPEs on the channel of the flexible cathodes,and the flexible all-solid-state lithium batteries show excellent cycling performance at 80?.