Preparation Of Helical Polyurethane Derived Solid Electrolyte And Their Application In Lithium Batteries

Lithium batteries?LBs?with high energy density and safety are hot research topics in the field of energy storage.The utilization of solid polymer electrolyte?SPEs?without addition of liquild electrolytes can avoid the leakage issue,thus the safety of LBs is improved.Moreover,for Li metal anode with ultrahigh specific capacity(3860 mAh g^-1),SPEs can effectively restrict the generation of lituium dendrites,and the cycling stability and rate capacity of corresponding LBs are significantly enhanced.In this paper,the helical polyurethane@polyethylene oxide hybrid was firstly developed as SPE,and the SPE based on racemic polyurethane was also prepared for comparison.Subsequently,the network copolymer based on cross-linking of helical polyurethane and polyethylene glycol was prepared by condensation polymerization,and LiTFSI was added for developing of SPE.The structure and electrochemical properties of the obtained SPEs were characterized in detail,and the performance of the assembled LiFePO₄/Li cells were thoroughly evaluated.The details are as follows:?1?All solid-state electrolytes?SPEs?were developed by compositing of helical polyurethane?LPU?based on L-tyrosine,PEO and LiTFSI.The thermodynamic stability and mechanical properties of the prepared composite SPE have been significantly improved.At 60?,the electrochemical window of the optimized PEO@LPU?PEO:LPU=3:1?SPE is beyond 4.5 V?vs.Li⁺/Li?,and the ionic conductivity of PEO@LPU SPE achieves 4.92×10^-5S cm^-1.The lithium ion transference number(t _Li+)is 0.37.The LiFePO₄/Li cell assembled by PEO@LPU SPE presents the maxium discharge capacity of 153 mAh g^-11 at60?and 0.1 C.The capacity retention ratio is 83.6%after 80th cycles,and the coulombic efficiency is close to 100%.In contrast with the SPEs based on PEO@racemic polyurethane and the pristine PEO,PEO@LPU SPE shows obvious enhancement.?2?Network crosslinked copolymer based on helical polyurethane?LPU?and PEG was synthesized by using HDI trimers as the cross-linking agent,and then all solid-state PEG@LPU SPE was developed by addition of LiTFSI.The obtained PEG@LPU SPE exhibits higher thermodynamic stability and lower crystallinity than the pristine PEO SPE,and the interfacial compatibility between SPE and electrode is improved.At 60?,the electrochemical window and lithium ion transference number(t_Li+)of PEG@LPU SPE are4.62 V and 0.46,respectively,which are superior to pristine PEG SPE.The ionic conductivity of PEG@LPU SPE achieves 2.36×10^-6S cm^-1at 30?,which is 128 times that of PEG SPE(1.85×10^-88 S cm^-1).The LiFePO₄/Li cell assembled by PEG@LPU SPE presents initial discharge specific capacity of 143 mAh g^-11 at 60?and 0.2C,and the capacity retention ratio is 95.1%after 30th cycle.The coulomb efficiency is close to 100%.The battery performance of PEG@LPU SPE is evidently superior to the pristine PEG SPE.Therefore,the addition of helical polyurethane significantly improves the electrochemical properties of the pristine PEO and PEG scaffolds,the two types of PEO@LPU and PEG@LPU SPEs exhibit good battery performances,which can be recommended as potential all solid-state electrolytes for high performance LBs.