• Proceedings of the KIEE Conference
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• 1994.07b
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• pp.1229-1232
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• 1994

The purpose of this study is to research and develop solid polymer electrolyte(SPE) for Li secondary battery. This paper describes the effects of lithium salts, plasticizer addition and temperature dependence of conductivity of PEO electrolytes. Polyethylene oxide(PEO) based polymer electrolyte films were prepared by solution casting an acetonitrile solution of preweighed PEO and Li salt. After solvent evaporation, the electrolyte films were vacuum-dried at $60^{\circ}C$ for 48h, the thickness of the films were $90{\sim}110{\mu}m$. The conductivity properties of prepared PEO electrolytes are summarized as follows. PEO electrolyte complexed with $LiClO_4$ shows the better conductivity of the others. $PEO-LiClO_4$ electrolyte when $EO/Li^+$ ratio is 8, showed the best conductivity. Optimum operating temperature of PEO electrolyte is $60^{\circ}C$. By adding propylene carbonate and ethylene carbonate to $PEO-LiClO_4$ electrolyte, its conductivity was higher than $PEO-LiClO_4$ without those. Also $PEO_8LiClO_4$ electrolyte remains static up to 4.5V vs. $Li/Li^+$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.11a
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• pp.374-377
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• 1999

The purpose of this study is to research and develop solid polymer electrolyte(SPE) for Li polymer battery. This paper describes temperature dependence of conductivity, impedance spectroscopy, electrochemical properties of PVDF/PAN electrolytes as a function of a mixed ratio. PVDF/PAN based polymer electrolyte films were prepared by thermal gellification method of preweighed PVDF/PAN, plasticizer and Li salt. The conductivity of PVDF/PAN electrolytes was 10-3S/cm. 20PVDF5PANLiCIO$_4$PC$\sub$10//EC$\sub$10/ electrolyte shows the better conductivity of the others. 20P7DF5PANLiCI$_4$PC$\sub$10//EC$\sub$10/ electrolyte remains stable up to 5V vs. Li/Li$\^$+/. Steady state current method and ac impedance used for the determination of transference numbers in PVDF/PAN electrolyte film. The transference number of 20PVDF5ANLICIO$_4$/PC $\sub$10//EC$\sub$10/ electrolyte is 0.48

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.12
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• pp.45-51
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• 2019

As the separator becomes thinner, the role of thermal stability becomes more important in ensuring the high capacity of medium- and large-sized lithium-ion secondary batteries. In this study, we researched coating technology to improve the separator's thermal stability. We minimized the coating time by optimizing the design of a vertical two-stage coater that was thin, uniform, and capable of coating on both sides at the same time with a maximum 2㎛ thickness coating layer of fluorinated polymer (PVdF-HFP) on the bare polyethylene (PE) separator, which increased the thermal stability. In addition, during the coating process, a dual-jacket-roll method of drying was developed that increased the drying effectiveness without thermal damage to the separator. We also investigated the thermal stability of the separator manufactured from a coating machine, and studied the battery-applied performance by making a lithium-ion pouch battery.

• Proceedings of the Polymer Society of Korea Conference
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• 2006.10a
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• pp.69-70
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• 2006

In lithium-ion batteries, separator membrane's, main role is to physically isolate a cathode and an anode while maintaining rapid transport of ionic charge carriers during the passage of electric current. As far as battery safety is concerned, the electrical isolation of electrodes is most crucial since unexpected short-circuits across the membrane induces hot spots where thermal runaway may break out. Internal short-circuits are generally believed to occur by protrusions on the electrode surface either by unavoidable deposits of metallic impurities or by dendritic lithium growth during battery operation. Another cause is shrinkage of the separator membrane when exposed to heat. If separator membrane can be engineered to prevent the internal short-circuit, it will not be difficult to improve lithium-ion batteries' safety. Commonly the separators employed in lithium-ion batteries are made of polyethylene (PE) and/or polypropylene (PP). These materials have terrible limitations in preventing the fore-mentioned internal short-circuit between electrodes due to their poor dimensional stability and mechanical strength. In this study we have developed a novel separator membrane that possesses very high thermal and mechanical stability. The cells employing this separator provided noticeable safety improvement in the various abuse tests.

• Korean Journal of Materials Research
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• v.32 no.10
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• pp.429-434
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• 2022

There is ongoing research to develop lithium ion batteries as sustainable energy sources. Because of safety problems, solid state batteries, where electrolytes are replaced with solids, are attracting attention. Sulfide electrolytes, with a high ion conductivity of 10^-3 S/cm or more, have the highest potential performance, but the price of the main materials is high. This study investigated lithium hydride materials, which offer economic advantages and low density. To analyze the change in ion conductivity in polymer electrolyte composites, PVDF, a representative polymer substance was used at a certain mass ratio. XRD, SEM, and BET were performed for metallurgical analyses of the materials, and ion conductivity was calculated through the EIS method. In addition, thermal conductivity was measured to analyze thermal stability, which is a major parameter of lithium ion batteries. As a result, the ion conductivity of LiH was found to be 10^-6 S/cm, and the ion conductivity further decreased as the PVDF ratio increased when the composite was formed.

• Journal of Electrochemical Science and Technology
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• v.2 no.1
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• pp.26-31
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• 2011

We have prepared siloxane polymers grafted with trifluoromethane-sulfonylamide and oligoether side chains for solid polymer electrolytes with enhanced ionic conductivity. The grafted trifluoromethane sulfonylamide groups seem to be effective as an anion recepting site to enhance the ionic conductivity of the solid polymer electrolyte. The anion receptor grafted siloxane polymers showed one order of magnitude higher ionic conductivity than the siloxane polymers without anion receptor grafts. The fitting parameter A of the VTF plot which was related to the carrier density of the electrolyte increased with increasing the number of grafted anion receptor. The results of experiment indicate that the anion-complexing site of the anion receptor grafted polymer host effectively traps the anions. The anion receptor grafted polymer was found to be a promising material for lithium polymer batteries.

• The Transactions of the Korean Institute of Power Electronics
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• v.14 no.6
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• pp.457-465
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• 2009

Lithium batteries are widely used in mobile electronic devices due to their higher voltage and energy density, lighter weight and longer life cycle compared to other secondary batteries. In particular, high demand for lithium batteries is expected for electric cars. In case of lithium batteries used in electric cars, driving distance must be calculated accurately and discharging should not be done below the level of making it impossible to crank. Therefore, accurate information about state of charge (SOC) becomes an essential element for reliable driving. In this paper, a new method of estimating the SOC of lithium polymer batteries by using AC impedance is proposed. In the proposed method, parameters are extracted by fitting a curve of impedance measured at each frequency on the equivalent impedance model and extracted parameters are used to estimate SOC. Experiments were conducted on lithium polymer batteries with similar capacities made by different manufacturers to prove the validity of the proposed method.

• Polymer(Korea)
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• v.32 no.6
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• pp.598-602
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• 2008

In this study we prepared crosslinked separators with the improved thermal stability by irradiating a commercial polyethylene (PE) separator for lithium secondary battery with an electron beam, and the thermal and mechanical properties of the prepared separators were evaluated as a function of the absorption dose. The thermal shrinkage of electron beam irradiated separator was decreased with increasing absorption dose. As a result of the shutdown behavior using an AC impedance, it was observed that the irradiated separator had the better shutdown function than the unirradiated separator. The modulus of the irradiated separator was enhanced as the absorption dose was increased, while the tensile strength and the break elongation of the irradiated separator were decreased.

• Applied Chemistry for Engineering
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• v.7 no.3
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• pp.433-442
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• 1996

Electrochemical characteristics and physical properties of polymer electrolyte which immobilized lithium salts such as $LiClO_4$ and $LiCF_3SO_3$ and plasticizers such as ethylene carbonate(EC) and propylene carbonate(PC) in high molecular weight poly(ethylene oxide)[PEO] polymer was investigated. PEO-Li based polymer electrolyte with plasticizers showed ionic conductivity of $10^{-4}S/cm$ at room temperature and high electrochemical stability up to 4.5 V(vs. $Li^+/Li$), so it can be applied to lithium secondary battery. The crystallinity of PEO decreased with the addition of lithium salts and plasticizers, especially $LiClO_4$ and PC showed more effective than and $LiCF_3SO_3$ and EC. Glass transition temperature($T_g$) of polymer electrolyte increased with increasing lithium salt concentration whereas melting temperature ($T_m$) decreased. Polymer electrolyte with plasticizers crystallized at $6^{\circ}C$.

• Applied Chemistry for Engineering
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• v.33 no.3
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• pp.289-295
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• 2022

In this study, we intend to fabricate an all solid polymer battery with a reduced interfacial resistance between the solid electrolyte and the electrode by applying thiophene based polymers as both electrode and electrolyte materials. In order to minimize the interfacial resistance with the poly(3,4-ethylenedioxy thiophene) (PEDOT) based electrode, 3,4-ethylenedioxy thiophene (EDOT) oligomer was introduced into the solid electrolyte. Also, to improve the lithium salt dissociation ability of the EDOT oligomer [oligo(EDOT)] electrolyte, it was blended with poly(vinylidene fluoride) (PVdF). As a result, the ionic conductivity of the solid polymer electrolyte increased by introducing PVdF into the oligo (EDOT). From the result of evaluating the electrochemical properties of an all solid polymer battery, the interfacial resistance significantly decreased by introducing a thiophene based polymer to the electrode and electrolyte.