Preparation And Properties Of Polyether Polyurethane-based Solid Polymer Electrolyte

Recently,most of lithium batteries in the market using liquid electrolytes have suffered safety problems such as inflammable,easy leakage and explosion.The solid polymer electrolyte(SPE)which obtained by mixing polymer matrix and lithium salt can solve the above problems well.The design and development of new solid polymer electrolytes is a hot topic in the study of all-solid-state lithium-ion batteries.In this paper,polyether polyurethane-based solid electrolytes were prepared with different polyether polyols.The relationships between the polyether types and properties of polyurethane-based solid electrolyte were discussed,which provided new ideas for the development of solid polymer electrolytes and all-solid-state lithium-ion batteries.In the first chapter,the progress of lithium batteries and the electrolytes were introduced.Meanwhile,the main contents of this article were discussed.In the second chapter,polypropylene glycol(PPG)based polyurethane(PU-PPG)was synthesized.Then different amounts of LiTFSI(5-25 wt%)were added into the PU-PPG to prepare the SPE.The FTIR shows that the polyurethane-based SPE was successfully synthesized.The Li+ can also coordinate with the-NH and-C-O-C-groups in the polyurethane.The XRD test indicates that the hydrogen bonding between intermolecular and intramolecular is destroyed by the complexation of Li?and C-O-C.The ionic conductivity of SPE increases with the increase of lithium salt content.The PU-PPG based SPE with 20 wt%lithium salt(SPE4)has the best comprehensive performance,its tensile strength is 0.5 MPa and the ionic conductivity of SPE4 is 7.94x10-5 S cm-1 at 80 ?.Then the SPE4 is assembled into a LiFePO4/SPE4/Li solid lithium battery,the initial discharge capacity is 25 mAh g-1 at 80 ?.In the third chapter,poly(ethylene glycol)(PEG)-based polyurethane(PU-PEG)was synthesized.The effects of LiTFSI concentration on properties of SPE were investigated.The FTIR shows that the addition of lithium salt makes the-NH move to high wavenumber and-C-O-C-to low wavenumber.The XRD results reveal that the crystallinity of PEG is destroyed by the addition of lithium salt.The ionic conductivities increase when the salt contents increase from 5 wt%to 25 wt%.Considering the comprehensive performance of the electrolyte,the SPE with 20wt%LiTFSI(SPE20)was selected to be assembled into a solid lithium battery.The results show that the battery has a discharge capacity of 163 mAh g-1 and its capacity retention close to 99%after 35 cycles at 0.2 C at 60 ?.In the fourth chapter,poly(ethylene glycol)-poly(propylene glycol)random copolymer(PEG-PPG)-based waterborne polyurethane(WPU)is synthesized.Then the WPU is used as solid polymer electrolyte(SPE).The effects of LiTFSI concentration on properties of SPE were investigated.The as-prepared WPU and SPE show amorphous structure as revealed by X-ray diffraction tests.The lithium salts can dissolve in WPU matrix well by the coordination of Li?ion with-NH,-C=O and-C-O-C-groups in polyurethane as confirmed by Fourier transform infrared spectroscopy.The SPE is thermal stability with a thermal decomposition temperature above 280 ?.The ionic conductivities increase firstly and then decreased when the salt contents increase from 10 wt%to 40 wt%.The WPU electrolyte with 30 wt%LiTFSI(WPU-30%Li)shows a superior comprehensive performance with an ionic conductivity of 1.02 x 10-4 S cm-1 and a electrochemical stable window up to 4.5 V at 80 ?.The battery using WPU-30%Li electrolyte exhibits a discharge capacity of 153 mAh g-1 and shows superior cycling performance with capacity retention close to 96%after 200 cycles at 0.2 C at 80 ?.These results suggested this environment-friendly electrolyte can be applied in all-solid-state lithium batteries.In the fifth chapter,poly(tetramethylene glycol)(PTMG)-based polyurethane(PU-PTMG)is synthesized.The effects of LiTFSI concentration on properties of SPE are investigated.The XRD test shows the crystallinity of PU-PTMG and the addition of lithium salts can destroy the crystallization of PU-PTMG to form more amorphous structures.The SPE is thermal stability with a thermal decomposition temperature above 200 °C.The ionic conductivities increase with the salt contents increase from 10 wt%to 40 wt%.The PU-PTMG electrolyte with 40 wt%LiTFSI(PU-40%Li)shows a superior comprehensive performance with an ionic conductivity of 1.80×10-4 S cm-1 and a electrochemical stable window up to 4.2 V at 60 ?.The battery using PU-40%Li electrolyte exhibits a discharge capacity of 153 mAh g-1 and shows poor cycling performance with capacity retention close to 70%after 100 cycles at 1 C at 60 ?.The bad cycling performance of the battery may due to its poor mechanical properties(only 0.2 MPa at room temperature).The sixth chapter of the paper summarizes the full text.