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The Design, Preparation And Characterization Of Gel Polymer Electrolytes For Lithium Ion Batteries

Posted on:2011-12-09Degree:DoctorType:Dissertation
Country:ChinaCandidate:D LuoFull Text:PDF
GTID:1101330332983578Subject:Polymer Chemistry and Physics
Abstract/Summary:PDF Full Text Request
Novel gel polymer elelctrolytes (GPEs) for secondary lithium-ion batteries have been investigated. Five kinds of gel polymer electrolytes were prepared, i.e. semi-interpenetrating (semi-IPN) GPEs, amphiphilic conetwork GPEs, network-structured GPEs with polyetheramine as crosslinking agent, multiwall carbon nanotube/GPE hybrids and electrospun fibrous GPEs. The chemical structure and composition, morphology, thermal behavior, mechanical strength and ionic conductivity of these GPE membranes have been investigated by Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), X-ray diffraction pattern (XRD), stess-strain test and alternating current impedance (AC Impedance). The influences of the structure and compositions of the polymers on the properties of resulting GPEs were studied, aiming at obtaining GPEs with both good ionic conductivity at room temperature and good mechanical strength for practical application.Novel semi-IPN GPEs based on poly(acrylonitrile-co-glycidyl methacrylate)/poly(ethylene oxide) (P(AN-GMA)/PEO) crosslinked by diethylenetriamine (DETA) were synthesized. DSC and XRD measurements showed that the crystallization of PEO fraction in the semi-IPN polymer electrolyte was greatly impeded by the crosslinking of DETA with epoxy group, which facilitated the transportation of lithium ion. The tensil tests revealed that the critical strength of the membrane was enhanced. Moreover, the semi-IPN GPEs exhibited better absorptive ability of liquid electrolyte and higher ionic conductivity with the increased in the content of PEO. The ionic conductivity of the GPE at room temperature reached 1.25×10-4S/cm when the weight ration of P(AN-GMA)/PEO was 1/1.Novel amphiphilic conetwork GPEs based on (PEG200-b-GMA)-co-methyl methacrylate (MMA) and (PEG2000-b-GMA)-co-MMA have been investigated. Two glass transition temperatures were observed in the DSC curves. The measurements of the static contact angle of the polymer membranes revealed the amphiphilic nature of the polymers, and the contact angles were found to vary with the molecular weight of PEG-b-GMA and the mole ratio of PEG-b-GMA and MMA. With the increase of weight ratio of PEG-b-GMA, both the crosslinking degree and the ionic conductivity of the amphiphilic conetwork copolymer increased. And the ionic conductivity of (PEG2000-b-GMA)-co-MMA is higher than that of (PEG200-b-GMA)-co-MMA because of its longer ethylyne oxide (EO) chains.Crosslinked GPEs based on P(AN-GMA) and poly(glycidyl methacrylate-polyethylene glycol methyl ether methacrylate) (P(GMA-PEGMA)) with polyetheramine (Jeffamine D400, Jeffamine D2000) as crosslinking agents were prepared. The reaction degree of the epoxy group increased with the increase in the content of Jeffamine D400 and Jeffamine D2000 as indicated in FT-IR analysis. The stress-strain tests revealed that the critical strength of the crosslinked polymer membranes decreased with the weight content of polyetheramine, while their elongation at break increased accordingly. The DSC analysis of the resulting GPEs suggested that the compatibility between Jeffamine and P(AN-GMA) was worse than that between Jeffamine and P(GMA-PEGMA). The ionic conductivity of the crosslinked GPEs exhibited enhanced ionic conductivity with the increase in the molecular weight and weight ratio of Jeffamine, which is due to the fact that more PPO segments involved in the system facilitated the segment mobility of the crosslinked polymer.GPEs based on multiwall carbon nanotubes (MWCNTs)/polymer hybrids were prepared based on the blending of MWCNTs grafted with Jeffamine of different molecular weights with P(AN-GMA) and P(GMA-PEGMA), respectively. SEM images of the composite membranes showed that the MWCNTs were completely wrapped with polymers and dispersed finely in the polymer matrix. The stress-strain test revealed that the hybrids exhibited enhanced critical strength, which might be related to stronger binding force between MWCNTs and copolymer resulting from the chemical covalent crosslinking. Moreover the critical strength of the hybrids in which MWCNTs grafted with PPO of longer chains was higher due to stronger linkage between MWCNTs and copolymers. The elongation at break of P(GMA-PEGMA)/MWCNTs was higher than that of P(AN-GMA)/MWCNTs due to the different flexibility of the copolymers.higher content of Jeffamine grafted MWCNTs enhanced the ionophilicity of the hybrid GPEs and led to higher ionic conductivity. The GPEs based on Jeffamine D400 grafted MWCNTs exhibit higher ionic conductivity than that based on Jeffamine D2000 grafted MWCNTs. In contrast, the ionic conductivity of P(GMA-PEGMA)/MWCNTs was higher than that of P(AN-GMA)/MWCNTs due to its lower glass transition temperature of the former system. Electrospun PVdF/PEO and the composite of PVdF/PMMA and nano-SiO2 were fabricated. The resulting membranes were composed of fibers with smooth surface and large number of cavities of different sizes as indicated in SEM images. Moreover, it was found that the nano-SiO2 dispersed uniformly in PVdF/PMMA fiber. However, the nano particles tended to aggregate with the increase in its weight ratio. XRD and DSC results revealed that the crystallinity of PVdF decreased and the crystallinity of PEO increased with the increase in PEO in the PVdF/PEO fibrous membrane. The electrospun PVdF/PEO (3/1) exhibited the highest ionic conductivity. Better dispersity of nano-SiO2 led to lower crystallinity of PVdF. The electrospun composite of PVdF/PMMA and 6wt% of nano SiO2 showed the highest ionic conductivity of 2.55×10-3 S/cm at room temperature.
Keywords/Search Tags:lithium ion battery, gel polymer electrolytes, P(AN-GMA), P(GMA-PEGMA), polyetheramine, crosslinking, maltiwall carbon nano tube, nano SiO2, electrospun
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