| Since the rapid development of emerging industries, lithium-ion batteries have been widely used in power applications because of its high operating voltage, stable discharge, long cycle life, high energy density, green environmental protection etc.. In the lithium-ion batteries, compared with the traditional liquid electrolyte, solid polymer electrolytes (SPEs) have some advantages such as light weight, films formated easily, good viscoelastic, use safety, etc., which not only solve liquid leakage and the heat decomposition problem in the working process of lithium batteries, but also have excellent thermal stability and mechanical properties. Therefore, it has become focus of electrolyte of lithium batteries development. Waterborne polyurethane (WPU) is a kind of large molecular materials with green environmental protection, adjustable structure, and good dispersion in water, especially nonionic type WPU (NPU) has the characteristics of good biocompatibility, resistance to electrolyte etc., which is widely used in medical science. The role of PEO and lithium salt "complexing-disintegrate " realize the migration of Li+ in PEO based on polymers, and then the ionic conductivity of SPE increase. But at present, the SPEs based on PEO have the problems of low crystallinity, electrical conductivity and mechanical strength. PEO through covalent bond is introduced into the NPU, not only can improve the low temperature ion conductivity of SPE, and mechanical strength is also improved. In this paper, the EO chain segment was introduced into NPU and, different series of solid electrolytes were prepared to take the NPU as polymer matrix, and the influence of salt content and structure of polyurethane on the properties of the solid electrolytes were explored. This paper is divided into three chapters:(1) The influence of different LiClO4 content on the performance of solid electrolytesIn this chapter, using isophorone diisocyanate (IPDI), poly (propylene oxide glycol (N 220), trimethylol propane poly(ethylene glycol monomethyl ether) (Ymer N-120), 1,4-butanediol (BDO) as raw material, nonionic waterborne polyurethane emulsion was synthesized firstly, and taking it as polymer matrix, a series of solid polymer electrolytes were prepared by adding LiClO4. Using the test methods such as Fourier transform infrared spectroscopy (FT-IR), dynamic thermodynamic analysis (DMA), thermogravimetric analysis (TGA), mechanical property analysis, and electrochemical workstation, and the effect of solid electrolytes properties were disscussed by changing the content of LiClO4. The result showed that, with the increase of the content of LiClO4, heat-resisting performance of solid electrolyte membranes decreases; The tensile strength of the electrolyte film increases gradually, while the elongation at break decreases, when LiClO4 content is 18%, the tensile strength of the electrolyte membrane reaches 18.2 MPa; Ion conductivity of solid electrolytes increase with temperature rising, and meet Arrhenius equation. At the same temperature, the ionic conductivity of electrolytes show a trend of increase firstly, then decrease with LiCO4 content rising; when LiCO4 content is 15%, the ionic conductivity of electrolyte reaches a maximum of 9.55×10-6 S/cm.(2) The effect of different polyurethane hard segment content on the properties of solid electrolytesIn this chapter, using isophorone diisocyanate (IPDI), poly (propylene oxide glycol (N 220), trimethylol propane poly(ethylene glycol monomethyl ether) (Ymer N-120), 1,4-butanediol (BDO) as raw material, nonionic waterborne polyurethane emulsion was synthesized firstly, and taking it as polymer matrix, a series of solid polymer electrolytes were prepared by adding LiClO4. The test methods such as Fourier transform infrared spectroscopy (FT-IR), thermodynamic analysis (DMA), thermogravimetric analysis (TGA), mechanical property analysis, and electrochemical workstation were used, and the effect of solid electrolytes properties were disscussed by changing the polyurethane hard segment content. The results show that, with the increase of polyurethane hard segment content, With the increase of polyurethane content, thermal properties of solid electrolyte decreased gradually; the tensile strength of the electrolyte film increases, while the elongation at break decreases, when the hard segment content is 44.81%, the tensile strength of the electrolyte membrane reaches 18.6 MPa; The ionic conductivity of solid electrolytes increase gradually with the increase of temperature and, meet the Arrhenius equation; At the same temperature, the ionic conductivity of the electrolyte increases first and then decreases with the increase of polyurethane hard segment content; When the hard segment content is 38.28%, the ionic conductivity of electrolytes reaches the maximum value of 1.55 × 10-5 S/cm.(3)The impact of different Ymer N-120 content on the properties of solid electrolytesIn this chapter, using isophorone diisocyanate (IPDI), poly (propylene oxide glycol (N 220), trimethylol propane poly(ethylene glycol monomethyl ether) (Ymer N-120), 1,4-butanediol (BDO) as raw material, nonionic waterborne polyurethane emulsion was synthesized firstly, and taking it as polymer matrix, a series of solid polymer electrolytes were prepared by adding LiClO4. Using the test methods such as Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), mechanical property analysis, and electrochemical workstation, and the effect of solid electrolytes properties were disscussed by changing the content of Ymer N-120. The results show that, with the increase of Ymer N-120 content, the glass transition temperature of the electrolyte decreases; the tensile strength of the film decreases, while elongation at break increases. Infrared peak results show that at room temperature, Li+mainly exist in the Li+ClO4-ion pair, free lithium ion occupy a small proportion; With the increase of Ymer N-120 content, the complexation numbers of Li+ and C-O-C increase at first and then decrease; When the content of Ymer N-120 is 24.88%, free Li+ is the largest, accounting for 24.35% of the total ion number, and the peak area of Li+ and C-O-C complex reach the largest value, which is 92.07%. The ionic conductivity of the solid electrolytes increase gradually with the increase of the temperature, and are consistent with the Arrhenius equation. At the same temperature, the ionic conductivity of the electrolytes increase at first and then decrease with the increase of Ymer N-120 content. When the content of Ymer N-120 is 24.88%, the ionic conductivity of electrolytes reach the maximum value (2.44×10-5 S/cm).(4) Assembly process and electrochemical performance of lithium ion batteriesIn the chapter, button-type model batteries were assembled by selecting three kinds of solid electrolytes (SPE5, SPE9, SPE15) with the highest ionic conductivity in the first three chapters, and using the Li/electrolyte/stainless steel sheet and the Li/ electrolyte/Li system, respectively. The assembly procedure was reviewed and electrochemical stability and ion transport number of three solid electrolytes were compared. The results show that the electrochemical stability of SPE15 (decomposition voltage is 4.7 V) is better than SPE9 (decomposition voltage is 4.5 V), SPE5 (decomposition voltage is 4.2 V), and ion transport number of SPE15 is 0.40, which was higher than SPE9 (0.34) and SPE5 (0.30). |
