KR101066390B1 - Polymer Electrolyte Composition for Lithium Battery Comprising Electrospun Polyvinylidene fluoride-Conducting Polyaniline Derivatives Composite Nanofibrous Membranes and Lithium Battery Employing the Same - Google Patents

Abstract

The present invention relates to a composition for forming a polymer electrolyte comprising an electrospun poly (vinylidene fluoride) -conductive polyaniline derivative composite nanofiber membrane which can be used as an electrolyte material for capacitors, sensors, batteries and the like. The present invention also relates to a polymer electrolyte composition for a lithium battery including a lithium salt dissolved in the composite nanofiber membrane and a solvent, and a lithium battery prepared using the same.

Electrospun nanofibers, poly (vinylidene fluoride), conductive polyaniline derivatives, polymer electrolytes, lithium batteries

Description

Polyelectrolyte Composition for Lithium Battery Comprising Electrospun Poly (vinylidene fluoride) -Conducting Polyaniline Derivatives Composite Nanofibrous Membranes and Lithium Battery Employing the Same}

The present invention provides a composition for forming a polymer electrolyte comprising an electrospun poly (vinylidene fluoride) -conductive polyaniline derivative composite nanofiber membrane that can be used as an electrolyte material for a capacitor, a sensor, a battery, and a lithium battery manufactured using the same. It is about.

Polymer electrolytes consist of dissolved salts in solid polymers that play a central role in achieving the main goals of all-solid-state rechargeable lithium batteries (DE Fenton et al., Polymer 14 (1973) 589; P. Santhosh et al., J. Power Sources 160 (2006) 609). Amorphous polymer electrolytes have been intensively studied for more than 30 years, but the performance of electrolytes has not improved substantially over the past period. In this system a conductivity of about ˜mScm ⁻¹ was achieved. For high performance of lithium batteries, the polymer electrolyte should have better ion conductivity than mScm ⁻¹ . Good steric and thermal stability, electrochemical stability window of ≧ 5.0 V, chemical compatibility with Li electrodes, Li circulation (recharge) with efficiency greater than 99%. Therefore, it is essential to develop a polymer electrolyte suitable for the modern demand of power sources.

Poly (vinylidene fluoride), (Poly (vinylidene fluoride): PVdF) with high mechanical stability and chemical inertness has been used as a polymer electrolyte in lithium batteries (SS Sekhon et al., Solid State Ionics 152.153 (2002) 169) . PVdF is inherently polar because of the presence of electronegative fluorine atoms in the backbone structure (E. Quartarone et al., J Phys. Chem. B 106 (2002) 10828). The crystal domain of PVdF inhibits the movement of lithium ions and lowers ionic conductivity.

Polydiphenylamine (PDPA), an N-substituted aniline polymer, is more stable to common organic solvents (TC Wen et al., Mater. Lett. 57 (2002) 280), and other poly (N-substituted anilines). Redox properties) (AV Orlov et al., Sci. Ser. B 48 (2006) 11; P. Santhosh et al., Mater. Chem. Phys. 85 (2004) 316). According to a recent study, PDPA backbone units are grafted with other polymer chains to have novel functional properties (F. Hua et al., Macromolecule 36 (2003) 9971).

Electrospinning is an efficient manufacturing process for producing fibrous and porous membranes with average diameters ranging from 100 nm to 5 μm (S. Adam, A fine set of threads, Nature 411 (2001) 236), produced by melting or solution spinning At least 10 to 100 times less than the finished fibers. Electrospinning technology has recently been extended to various fields such as porous fibers, biomedical materials, reinforcement components, fibers with electromagnetic shielding sensors, electrical circuits, etc. (KM Manesh et al., Biosens. Bioelectron. 23 (2008) 771; HS Kim et al., Macromol.Rapid Commun. 27 (2006) 146). There have been few reports of electrospinning to produce nonwoven mats of polymer composites containing conductive polymers and traditional polymers. A mixture of polyaniline with poly (ethylene) oxide (PEO) in chloroform has been reported to electrospin to produce filaments in the range of 4-20 nm (ID Norris et al., Synth. Met 114 (2000) 109). PEO provides an appropriate viscosity to the composite solution for electrospinning.

As an alternative to improve the performance of rechargeable lithium batteries, there is a need for the development of polymer electrolytes having improved physicochemical properties.

In order to improve the physicochemical properties of poly (vinylidene fluoride) (PVdF), which is used as a polymer component of electrolytes in lithium batteries, to prevent the migration of lithium ions and reduce ion conductivity, poly (vinylidene fluoride) Composite nanofiber membranes incorporating conductive polyaniline derivatives were prepared by electrospinning.

Hereinafter, the present invention will be described in detail.

The present invention relates to a composite nanofiber membrane that can be used as an electrolyte component of batteries, capacitors and sensors, and provides an electrospun poly (vinylidene fluoride) -conductive polyaniline derivative composite nanofiber membrane.

The conductive polyaniline derivatives may include, but are not limited to, polyolso phenyldiamine, poly N-methylaniline, polyaniline or polydiphenylamine (PDPA).

The conductive polyaniline derivative is characterized in that it is included from 0.1 wt.% To 10.0 wt.% With respect to the total weight of the poly (vinylidene fluoride) and the conductive polyaniline derivative mixture.

The nanofibrous membrane is prepared by a general electrospinning process of the art for spinning a polymer in a viscous state instantaneously into a fiber form, a process for preparing a spinning solution having a viscosity by dissolving the polymer in a solvent, and the spinning solution with a constant voltage and Solvent type, solvent concentration, spinning distance, radiation voltage, spinning method, etc. in the process of electrospinning at a range can be appropriately adjusted for various purposes and various applications.

In one aspect, the present invention relates to a composition for forming a polymer electrolyte comprising an electrospun poly (vinylidene fluoride) -conductive polyaniline derivative composite nanofiber membrane.

In general, functional groups of PVdF react with lithium or lithiated graphite, cause instability in negative electrodes of lithium and lithium ion batteries and cause rapid thermal reaction problems. On the other hand, the poly (vinylidene fluoride) -polydiphenylamine composite electrospun membrane (PVdF-PDPA-CFM) of the present invention prepared by the electrospinning method is the mutual interaction between PDPA and PVdF. By the formation of the connected network and the functional group of PDPA, it has the following physical and chemical properties.

PVdF and PDPA in the composite has a uniform shape without phase-separated microstructure, and as the PDPA content in the composite increases, the fiber diameter decreases and the twist between fibers increases. In addition, the PVdF-PDPA-CFM of the present invention exhibits the highest absorption of the electrolyte among the known PVdF-based polymers due to the interconnected network, and shows excellent steric stability in the expanded state.

In addition, due to the interconnected network form between PDPA and PVdF, the dense pore structure capable of maintaining a large amount of liquid electrolyte, and the freely movable Li ⁺ ions in the PVdF-PDPA membrane matrix, high ion conductivity is achieved. It also exhibits improved performance in electrospun PVdF and other PVdF-based polymers, such as being electrochemically stable and highly compatible with electrode materials.

More specifically, since the composite nanofiber membrane having the composition of the present invention has excellent physicochemical properties suitable for a rechargeable secondary lithium battery, it can be used to prepare a polymer electrolyte of a lithium battery.

Accordingly, as another aspect, the present invention relates to a polymer electrolyte composition for lithium batteries comprising an electrospun poly (vinylidene fluoride) -conductive polyaniline derivative composite nanofiber membrane and a lithium salt dissolved in a solvent.

Lithium salts dissolve in a solvent to act as a source of lithium ions in the cell to enable operation of a basic lithium secondary battery and to promote the movement of lithium ions between the positive and negative electrodes. Such lithium salts include LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₄ , LiAlCl ₄ , LiCl, LiI, and LiN (C _x F _{2x + 1} SO ₂ ) (C _x F _{2y + 1} SO ₂ ), where x and y are natural numbers Can be. The mixing ratio in the case where a lithium salt component is mixed and used for one or more components can be appropriately adjusted according to the desired battery performance. The concentration of the lithium salt may be used in a range commonly used in the art, but generally, a range of 0.1 to 2.0 M is preferred. If the concentration of the lithium salt is less than 0.1 M, the conductivity of the electrolyte is lowered to reduce the electrolyte performance, and if the concentration exceeds 2.0 M, the viscosity of the electrolyte is increased to reduce the mobility of lithium ions.

The solvent used in the preparation of the electrolyte is a non-aqueous organic solvent, and serves as a medium for transferring ions involved in the electrochemical reaction of the battery. The organic solvent is preferably phase separation does not occur when mixing with a component such as a polymer, it may be used at least one component selected from the group consisting of carbonate, ester, ether and ketone.

Specifically, propylene carbonate, ethylene carbonate, γ-butyroacetone, dimethoxyethane, dimethylcarbonate, diethylcarbonate, tetrahydro and tetrahydro At least one component from the group consisting of tetrahydrofuran, dimethylsulfoxide, polyethylene glycol, dimethylether, ethylmethyl carbonate and gamma-caprolactone Can be selected. The mixing ratio in the case of mixing one or more organic solvents can be appropriately adjusted according to the desired battery performance.

However, the electrospun composite nanofiber membrane of the present invention is not limited to the production of a battery, and electrolytes of various devices and systems, such as capacitors and sensors, which require thermodynamic ion transfer over a wide temperature range. Can be used as a component.

In another embodiment, a high molecular electrolyte composition for a lithium battery comprising (i) an electrospun poly (vinylidene fluoride) -conductive polyaniline derivative composite nanofiber membrane and a lithium salt dissolved in a solvent, (ii) a cathode and (iii) an anode It relates to a lithium battery prepared from a battery assembly comprising a.

As discussed above, the electrospun poly (vinylidene fluoride) -conductive polyaniline derivative composite nanofiber membrane of the present invention has suitable physical and chemical properties as a material for high performance lithium batteries, particularly rechargeable high performance secondary lithium batteries, It can be made into a high performance lithium battery with cathode and anode material materials known in the art.

The cathode material material is not particularly limited, but is preferably lithium cobalt (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), or lithium manganate (LiMn ₂ O ₄ ), which is a rechargeable lithium secondary battery material material. Co, Ni, and Mn may be added to these lithium oxides to improve capacity and lifetime, such as LiNi _{1 - x} CoxO ₂ .

As the anode material, both low crystalline carbon and high crystalline carbon may be used depending on the microstructure. Low crystalline carbon includes hard carbon, soft carbon, and bar carbon. High crystalline carbon includes natural graphite, Kish graphite, pyrolytic carbon, and liquid crystal pitch. Mesophase pitch based carbon fiber, Meso-carbon microbeads, Mesophase pitches, petroleum or coal tar pitch derived cokes, and the like.

The process of manufacturing a battery using the above materials may be performed by a general method known in the art, and the shape of the lithium battery is not particularly limited.

Electrospun poly (vinylidene fluoride) -conductive polyaniline derivative composite nanofiber membrane-based polymer electrolytes of the present invention exhibit enhanced ion transport, ion conductivity, and expanded electrochemical stability windows, and thus electrospun poly (vinylidene fluoride) -The lithium battery manufactured using the conductive polyaniline derivative-based composite nanofiber membrane-based polymer electrolyte also has greatly improved functions in terms of interfacial properties, impedances, discharge capacity ratio, and cyclability.

Hereinafter, the present invention will be described in more detail with reference to Examples. The examples are intended to illustrate the present invention in more detail, and the scope of the present invention is not limited by the following examples.

Example  One

1-1: Preparation of Polymer Electrolyte

Polydiphenylamine was prepared by oxidative polymerization of diphenylamine (50 mM in 1M NSA) with potassium peroxodisulfate (0.2M in 1M NSA) at 5 ° C. (S. Nagarajan et al., Acta A , 62 (2005) 420). Green precipitate (NSA-doped PDPA) was filtered off, washed with 1M NSA and dried in a vacuum oven. Appropriate quantities of PVdF and NSA-doped PDPA were dissolved in a DMF / acetone mixture (7: 3 v / v). Electrospun composite membranes were prepared by known methods (KM Manesh et al., Anal. Biochem. 360 (2007) 189). Electrospinning of the complex solution was performed at a flow rate of 10 mL / h with a potential difference of 25 kV. The silage tip and collector were kept 15 cm away. The film was accumulated in aluminum foil of the collector (drum). The amount of PDPA was adjusted (0.5%, 1% and 2% w / w) to produce an electrospinning membrane. Electrospinning times were also manipulated to produce membranes with other thicknesses ranging from 10 μm to 100 μm. A polymer electrolyte was prepared by immersing electrospun PVdF-PDPA-CFM at 25 ° C. in a 1M LiClO ₄ -PC solution in a glove box. PVdF-PDPA-CFM manufacturing method is shown in FIG.

1-2: membrane properties

Membrane morphology was observed with a field emission scanning electron microscope (FESEM) -Hitachi S-4300 equipped with a field emission gun (FEG) operated at 200 kV. Fourier transform infrared (FT-IR) spectra were recorded at ambient temperature using a Bruker IFS 66vFT-IR spectrophotometer with 4 cm ⁻¹ wave resolution. Samples for FT-IR were prepared by casting the membrane directly to KBr pellets and simultaneously dried at 120 ° C. for 48 hours.

1-3 Electrochemical Properties

The polymer electrolyte membrane for electrochemical measurement was obtained by immersing electrospun PVdF-PDPA-CFM in 1 M LiClO ₄ -PC solution at 25 ° C. for 24 hours. Ionic conductivity of PVdF-PDPA-CFM was measured by recording the ac impedance spectra of symmetrical SUS316 cells (area: 3.14 cm ² ) over a temperature range of 0-80 ° C. (sweep: 0.1 MHz at 100 Hz, ac amplitude: 5 mV). The symmetric cell was then fixed to a sealed double walled glass tube through an outer jacket in which constant temperature water circulated at different temperatures. All electrochemical measurements were performed using EG and G PAR 283 Potentiostat / Galvanostat equipped with FRA 1025. For electrochemical measurements, cells were prepared by sandwiching an electrospun membrane electrolyte between two symmetrical lithium metal electrodes. Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were performed at a sweep rate of ¹ mVs ^{- 1} . For dc polarization measurements, a small potential difference of about 10 mV was applied to the cell and the current was measured as a function of time until a constant value was reached. The cation transport number, t ₊ was measured in consideration of the potential drop occurring in the electrode surface layer. The ac impedance spectra were measured before and after current relaxation measurements, without modulation of dc bias (P. Santhosh et al., A. Mater. Res. Bull. 41 (2006) 1023). For charge-discharge studies, a pouch cell battery prototype was assembled by laminating LiCoO ₂ in order of three components, graphite anode, PVdF-PDPA-CFM (thickness of about 60 μm) as the electrolyte and cathode.

Example  2: form and structure

FIG. 2 is an FESEM image of an electrospun fiber membrane showing the morphological differences between the original PVdF (pristine PVdF) membrane and PVdF-PDPA-CFM. The PVdF film color is white (when viewed under an optical microscope), while PVdF-PDPA-CFM is green. FESEM images clearly show the morphological differences between the original PVdF membrane and PVdF-PDPA-CFM. The electrospun PVdF fibrous membrane was a nearly straight and tubular structure with an average diameter of ˜500 nm (FIG. 2A). However, PVdF-PDPA-CFM has an interconnected multifiber layer with a microporous structure (FIGS. 2B and C). The average diameter of PVdF-PDPA-CFM (˜200 nm) with 0.5 wt.% PDPA in the composite (FIG. 2B) is much less than the original PVdF membrane (FIG. 2A). PVdF-PDPA-CFM has interfiber twists that produce micropores. PVdF-PDPA-CFM with 1.0 wt.% PDPA in the composite has less fiber diameter (<200 nm) and more twist between fibers (FIG. 2C). The composite fibers were constant without phase separated microstructures or beads due to the miscibility of PVdF and PDPA.

Reason analysis of the morphological differences between PVdF membranes and PVdF-PDPA-CFM is important. It is generally known that the distance between the syringe nozzle and the collector, the applied voltage, the viscosity of the polymer solution and the dielectric constant of the solvent are parameters that affect the shape of the electrospun fiber. In this study, the first three elements in the list remained constant during electrospinning, and thus could not be the reason for morphological differences. Therefore, the following reason was anticipated. Introduction of PDPA can increase the insulation of the electrospinning medium. Electrospin jets were readily formed in the syringe nozzles of the PVdF-PDPA composite solution (compared to less insulated PVdF solutions) and induced small diameter fiber formation without beads (KM Manesh et al., Anal. Biochem. 360 (2007) 189). The interconnected fiber forms of PVdF-PDPA-CFM are amine or imine groups quantized in PDPA (AV Orlov et al., Polym. Sci. Ser. B 48 (2006) 11; P. Santhosh et al., Mater. Chem. Phys. 85 (2004) 316) and is expected to be due to intermolecular interactions between electronegative fluorine atoms in PVdF.

The FT-IR spectrum of PVdF-PDPA-CFM (FIG. 3) shows that the main bands correspond to the oxidized form of PDPA consisting of diphenoquinodimine (quinoid) and diphenylbenzidine (benzenoid) (AV Orlov et. al., Polym. Sci. Ser.B 48 (2006) 11; P. Santhosh et al., Mater. Chem. Phys. 85 (2004) 316). However, benje cannabinoid and quinoid C = N appeared in the vibration band at 1494cm ^-1 and 1595cm ^-1, respectively PDPA are respectively 1498 cm ^-1 and 1598cm from PVdF-PDPA-CFM ^- was found, go to ^1. Similarly, for PVdF, the bands corresponding to the CF ₂ bending mode of vibration appearing at 1400 cm ⁻¹ are shown in (Y. Bormashenko et al., Polym. Test. 23 (2004) 791; YJ Shen et al., Solid State Ionics It was moved to ^1-175 (2004) 747) at 1375cm PVdF-PDPA-CFM. In addition, the new vibration bands were found in the vicinity of 1670cm ^-1 and 1734cm ^-1 of the complex. These observations indicate that there is a molecular level of interaction between the benzenoid or quinoid structure nitrogen atoms of PDPA and the electronegative fluorine atoms of PVdF in PVdF-PDPA-CFM.

Example  3: expansion phenomenon ( Swelling behaviour )

PVdF-PDPA-CFM was transformed into a polymer electrolyte membrane by immersing porous mats in electrolyte solution (1M LiClO ₄ of propylene carbonate) (FIG. 4). PVdF-PDPA-CFM with 2% PDPA (w / w) for liquid electrolytes has a higher liquid absorption than (> 280 wt.%) PVdF membranes (-200 wt.%). To the best of our knowledge, PVdF-PDPA-CFM has the highest absorption for PVdF-based polymer electrolytes (A. Magistris et al., Solid State Ionics 152.153, (2002) 347; T. Godz et al., US Patent) 5,418,091; Y. Liu et al., Solid State Ionics 150 (2002) 317; JM Tarascon et al., Solid State Ionics 86.88 (1996) 49; SW Choi et al., Adv. Mater. 15 (2003) 202). Up to 70% liquid uptake was reported for PVdF and PVdF-HFP membranes (A. Magistris et al., Solid State Ionics 152.153 (2002) 347; T. Godz et al., US Patent 5,418,091). For PVdF-HFP and PVdF-HFP-g-PMMA membranes, liquid uptake of about 45% and 75% was reported, respectively (Y. Liu et al., Solid State Ionics 150 (2002) 317; JM Tarascon et al., Solid State Ionics 86.88 (1996) 49). A maximum liquid uptake of about 260 wt.% Was reported for electrospun PVdF (SW Choi et al., Adv. Mater. 15 (2003) 2027). In the expanded state, PVdF-PDPA-CFM shows excellent steric stability. The high liquid absorption of PVdF-PDPA-CFM is mainly due to the interconnected network form which increased pore stability.

Example  4: ionic conductivity ( ionic conductivity )

The ion conductivity of the polymer electrolyte membrane depends on the efficient number of carrier ions and ion mobility. The effective number of carrier ions is related to the concentration of dissolved ions. Ion mobility in the polymer electrolyte formed by dissolution of ions in the polymer is promoted by the segment mobility of the polymer chain.

The ion conductivity of PVdF-PDPA-CFM was measured by ac impedance spectroscopy as a function of temperature. The PVdF-PDPA-CFM ion conduction mechanism is mainly consistent with the Vogel-Tammann-Fulcher (VTF) relationship. The relationship of VTF to ion transport in PVdF-PDPA-CFM implies the coupling of the potential carrier and the symmetrical movement of the polymer chain. 2% PVdF-PDPA-CFM ( 60-μm thickness) having the PDPA is from 25 ℃, the reported value is the highest, 3.6mScm against the PVdF-based ^electrolyte exhibited ionic conductivity of ¹ (SW Choi et al,. Adv. Mater. 15 (2003) 2027; CY Chiang et al., J. Power Sources 123 (2003) 222; S. Panero et al., Electrochim. Acta 48 (2003) 2009; HS Choe et al., Electrochim. Acta 40 (1995) 2289; SS Choi et al., Electrochim. Acta 50 (2004) 339).

The high ionic conductivity of PVdF-PDPA-CFM (2% PDPA) is due to the high content of electrolyte (> 280 wt.%) Inserted into the membrane pores and the increased lithium ion mobility in the membrane. Doped PDPA is a positively charged nitrogen site (protonated diphenoquinone diimine unit) (AV Orlov et al., Polym. Sci.) Having a molecular level interaction with electronegative fluorine atoms present in PVdF. Ser.B 48 (2006) 11; P. Santhosh et al., Mater. Chem. Phys. 85 (2004) 316). This environment provides a dense pore structure capable of (i) a novel pathway of Li ⁺ ion migration in the complex, (ii) an interconnected network form between PDPA and PVdF, and (iii) a large amount of liquid electrolyte. The possibility of binding ClO ₄ ^- ions to Li ⁺ ions is expected to be disturbed in the presence of PDPA, thus allowing Li ⁺ ion migration. Some ClO ₄ ^- ions are expected to be immobilized by replacing organic dopants, naphthalene sulfonate anions at the protonated amine or imine sites of PDPA. Bulky naphthalene sulfonate anions have less mobility than ClO ₄ ⁻ ions. As a result, Li ⁺ ions in the PVdF-PDPA membrane matrix are freely movable to have high ionic conductivity.

Example  5: Anodized  stability ( Anodic stability )

The electrochemical stability window of the polymer electrolyte is one of the important parameters to be considered for the application of rechargeable lithium batteries. This parameter can be measured via linear sweep voltammetry (LSV). In general, LSV prepared laminated electrode cells having two inactive blocking electrodes and performed at ambient temperature. The blocking electrode is polarized and the electrochemical stability is confirmed by the rapid increase in the anodic current observed when decomposition of the polymer electrolyte, ie oxidation of typical electrolyte anions, occurs. Operating potential ranges or commercially available rechargeable lithium batteries are typically + 1.8V and + 3.5V vs. Between Li.

In this study, LSV was performed to confirm the electrochemical stability of PVdF-PDPA-CFM. 5 shows the current-voltage response obtained in PVdF-PDPA-CFM electrolyte. Initiation of current flow is related to the decomposition voltage of the electrolyte. In the importance of the current response, the decomposition voltages of PVdF-PDPA-CFM are 5.0 V, 5.1 V and 5.18 V vs. It was found to be Li (PDPA: 0.5%, 1% and 2%, respectively). Electrochemical stability of the membrane is affected by the PDPA content. LSV measurements of PVdF-PDPA-CFM showed an increased anodical limit voltage (5.18 V), which was higher than reported values in electrospun PVdF membranes (4.6 V; FIG. 5A) and in the reported PVdF-based electrolyte (SW Choi et al., Adv. Mater. 15 (2003) 2027; JR Kim et al., Electrochim. Acta 50 (2004) 69; Z. Wang et al., Mater. Chem. Phys. 82 (2003) 16) . The composite nanofiber structure increased the oxidation potential of the liquid electrolyte to ˜1.6 V (typically 3.6 V vs. Li) and provided high anodic stability to the electrolyte membrane. The negligible current distribution above 4.3 V for PVdF-PDPA-CFM results from the electrical distribution of the PDPA. The presence of PDPA has the beneficial effect of expanding the electrochemical stability window of the resulting electrolyte membrane.

Example  6: Li Of Li ⁺ Couple reversible

Cyclic voltammetry was performed to study the reversibility of the Li deposition-peeling process of PVdF-PDPA-CFM. FIG. 6 shows repetitive cyclic current voltage curves (Cyclic voltammograms) for Li / PVdF-PDPA-CFM / Li electrode cells performed at ambient temperature. The sweep rate was maintained at ¹ mVs ⁻¹ . The starting potential for Li deposition was about -0.4 V and can be seen as the cathodic limit for the membrane electrolyte.

At one point of the electrode potential, a cathodic peak was observed at about -0.4 V, corresponding to plating of lithium onto the electrode. In reverse scan, peeling of lithium was observed around 0.38 V. High currents with peaks in all anodical and cathodic directions mean the establishment of the reversibility of the Li / Li ⁺ couples. The reaction, Li ⁺ + e ^- ↔ Li, is easy at the interface between the lithium electrode and PVdF-PDPA-CFM. The large separation at the peak potential is due to the fact that no reference electrode is used.

While the process remained reversible during the cycle, it was observed that the amount of lithium circulated gradually decreased. This phenomenon may be due to the formation of a passive layer of the electrode, which is similar to that commonly found in liquid organic electrolytes. Passive layer formation can also be observed from the impedance response of lithium electrodes with PVdF-PDPA-CFM. Membrane reversibility demonstrates that PVdF-PDPA-CFM is electrochemically stable and therefore can be used stably as a polymer electrolyte in rechargeable lithium batteries.

Example  7: transportation number ( transport number )

The number of transports of the electrolyte is an important indicator of the conductive behavior. A: (t ₊ Li + transference number) to avoid a concentration gradient during the discharge cycle, constant Li ⁺ be transported - for the host compound grid lithium ion intercalation / de-intercalation of the via (host compound lattice), charge Eggplants require an electrolyte. Therefore, transport water irradiation is important for the characterization of electrolyte materials for lithium polymer batteries.

The cation transport number, t ₊ , of the composite electrolyte was measured by applying a 10 mV dc potential to the test cell (Li / (PVdF-PDPA-CFM) / Li). The current state immediately reached a steady state. The current immediately decayed and reached steady state. The decrease in current is due to the growth of a passivating LATER at the electrode (P. Santhosh et al., Mater. Sci. Eng. B 135 (2006) 65; P. Santhosh et al., J. Power Sources 160 ( 2006) 609). Li ⁺ ion transport water was measured and shown in Table 1. The t ₊ value of PVdF-PDPA-CFM containing 2% PDPA was determined to be 0.48. The t ₊ values reported for SPE range from 0.06 to 0.2 (T. Godz et al., US Patent 5,418,091). In gel polymer systems, t ₊ values of 0.4-0.5 have been reported. Cathodic transport numbers between 0.2 and 0.4 have been reported for PVdF-HFP based electrolyte membranes (E. Quartarone et al., Electrochim. Acta 44 (1988) 677; M. Stolarska et al., Electrochim. Acta 53 (2007) 1512; H. Dai et al., J. Electroanal. Chem. 459 (1998) 111; H. Kataoka et al., Solid State Ionics 152.153 (2002) 175).

Example  8: Interface phenomenon Interfacial behaviour )

The mixing of the electrode materials is a critical parameter of the cyclability and reliability of rechargeable lithium batteries. The ac impedance studies performed on symmetrical non-blocking Li / PVdF-PDPA-CFM / Li and Li / PVdF membranes / Li cells under open-circuit conditions are known as charge transfer of lithium ions. And useful information on diffusion and diffusion (KP Lee et al.,, IEEE Trans. Nanotechnol. 6 (2007) 362). Intercept at high frequencies gives bulk resistance ( R _b ) and at low frequencies the intercept corresponds to the resistance at the interface caused by the passivation ( R _i ) of the film at the electrode. The PVdF electrospinning film had R _i of 0.46 k (at 25 ° C.) and PVdF-PDPA-CFM (2% PDPA) showed a low R _i of about 0.32 k (at 25 ° C.) (FIG. 7A). In addition, R _i increased as a function of time and decreased with the content of PDPA in the membrane. The increase in R _i can be attributed to the increase in passivating film at the lithium surface. In general, CF bonds in PVdF react with lithium or lithiated graphite to form stable LiF and / or unsaturated bonds of &gt; C = CF-type (AD Pasquier et al., J. Electrochem. Soc. 145 ( 1988) 472), causing instability and negative thermal runaway problems for negative electrodes of lithium and lithium ion batteries. In PVdF-PDPA-CFM, some of the CF bonds are intermolecularly bound to the protonated amine or imine part of the PDPA unit and thus inhibit the various effects of CF interactions with the Li electrode.

In addition, to understand the effect of temperature at the Li / PVdF-PDPA-CFM interface, impedance measurements were performed at temperatures between 25 ° C. and 70 ° C. (FIG. 7B). In the Nyquist plot, the interfacial resistance ( R _i ) decreases with temperature and consequently the alternating current density, i ₀ , increases with temperature. It can be seen that at high temperatures the boundary film portion properties are conductive so that easy charge transfer is due to the collapse of the passivating film. It is clear from the impedance results that PVdF-PDPA-CFM has good compatibility with lithium metal electrodes.

PVdF-PDPA-CFM shows improved performance characteristics over electrospun PVdF and other PVdF-based polymer electrolyte membranes. A comparison of the electrochemical properties of PVdF-based electrolytes and VdF-PDPA-CFM is shown in Table 2.

Example 9: Battery Performance

In order to confirm the usefulness of PVdF-PDPA-CFM as an electrolyte of a rechargeable lithium battery, a pouch cell containing graphite as an anode, LiCoO ₂ as a cathode, and PVdF-PDPA-CFM as an electrolyte was fabricated and evaluated for performance. . A typical charge and discharge curve at 25 ° C. of a pouch cell with PVdF-PDPA-CFM (2% PDPA) is shown in FIG. 8. The cells cycled between cut-off voltages, 4.2 V and 3.0 V at 1 C rate. The charge-discharge profile is similar to that observed in conventional lithium ion batteries (LJ Fu et al., Prog. Mater. Sci. 50 (2005) 881), which shows good contact between the electrode and PVdF-PDPA-CFM. To convince them to have An open circuit voltage as high as 4.15V was achieved at 25 ° C. and the charge-discharge voltage was reproducible through the entire cycle.

9A shows the discharge curves of cells with PVdF-PDPA-CFM (PDPA: 1.0% and 2.0%) as electrolytes at various rates. High-speed performance has been achieved in cells where the electrolyte is PVdF-PDPA-CFM, due to the high ion conductivity and high porosity form of PVdF-PDPA-CFM. Sufficient capacity of the capacity moves at 0.2 C, and the cell is operable at 2 C. Typically, at 1 C rate the cell is movable about 90% of the 0.2 C capacity. Even at 2 C rate, the cell is capable of moving about 0.2% of the 0.2 C capacity. In addition, cycle tests were conducted with cut-off voltages of 4.2 V (upper limit) and 3.0 V (lower limit) at 1 C rate. FIG. 9B shows that cells with PVdF-PDPA-CFM as electrolyte have a very stable charge-discharge phenomenon without significant loss of capacity under voltage conditions (1 C rate at 25 ° C.). In addition, high charge-discharge efficiency (ratio between charge and discharge capacity) was observed, confirming the excellent interfacial stability between the electrode and PVdF-PDPA-CFM. Therefore, the pouch cell having PVdF-PDPA-CFM as an electrolyte shows low impedance, excellent rate capability and excellent cyclability and shows excellent potential as a rechargeable lithium battery.

The composition for forming a polymer electrolyte including the electrospun poly (vinylidene fluoride) -conductive polyaniline derivative composite nanofiber membrane of the present invention is not only a material of a polymer electrolyte for lithium batteries but also an electrolyte material such as a capacitor and a sensor. Can be.

1 is a schematic diagram showing a process for producing PVdF-PDPA-CFM.

FIG. 2 shows FESEM images of PVdF-PDPA-CFM with (a) electrospinning PVdF, (B) PDPA wt.% 0.5, and (C) PDPA wt.% 1.

3 shows the FT-IR spectra of (a) electrospinning PVdF, (b) original PDPA and PVdF-PDPA-CFM (0.5% PDPA).

4 shows the expansion characteristics of (a) electrospun PVdF and (b) PVdF-PDPA-CFM (2% PDPA) in 1M LiClO ₄ -PC.

FIG. 5 shows electrochemical measurements performed with linear sweep current measurements of (a) PVdF membrane and (b) 0.5 PDPA wt.% (C) 1 PDPA wt.% And (d) PVdF-PDPA-CFM of 2 PDPA wt.% Results for stability

6 is a cyclic current voltage curve of PVdF-PDPA-CFM with 2% PDPA.

Figure 7 is (i) interfacial resistance ( R i) curve according to PDPA content in PVdF-PDPA-CFM, (ii) (a) 25 ℃, (b) 30 ℃, (c) 40 ℃, (d) 50 ℃ , (e) the impedance spectra of Li / PVdF-PDPA-CFM (2% PDPA) / Li cells at temperatures of 60 ° C and (f) 70 ° C. Insertion degree R _i And i _o Show the effect of temperature on.

8 shows the charge-discharge voltage profile of graphite / PVdF-PDPA-CFM (2% PDPA) / LiCoO ₂ cells.

9 is a discharge voltage profile measured at various rates at 25 ° C. of a pouch cell having PVdF-PDPA-CFM (PDPA: 1% and 2%) as the electrode, graphite as the anode, and LiCoO ₂ as the cathode. Pouch cells were charged at 0.5C rate. (b) Cycle number versus volume measured at 25 ° C. of a pouch cell with PVdF-PDPA-CFM (PDPA 2%) as the electrolyte, graphite as the anode, and LiCoO ₂ as the cathode. The cells cycled between 3.0 V and 4.2 V at 1 C rate.

Claims (9)

delete delete delete Poly (vinylidene fluoride) -conducting polyaniline derivatives composite electrospun membrane (PVDF-PDPA-CFM) and a polymer electrolyte for a lithium battery including a lithium salt dissolved in a solvent Composition. The composition of claim 4 wherein the conductive polyaniline derivative is polyolso phenyldiamine, poly N-methylaniline, polyanisyrin or polydiphenylamine. 5. The composition of claim 4, wherein the conductive polyaniline derivative is included at a ratio of 0.1 wt.% To 10.0 wt.% Relative to the total weight of the poly (vinylidene fluoride) and conductive polyaniline derivative mixtures. The method of claim 4, wherein the lithium salt is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₄ , LiAlCl ₄ , LiCl, LiI and LiN (C _x F _{2x + 1} SO ₂ ) (C _x F _{2y + 1} SO ₂ ), where x and y are natural numbers At least one composition selected. The solvent of claim 4 wherein the solvent is propylene carbonate, ethylene carbonate, γ-butyroacetone, dimethoxyethane, dimethyl carbonate, diethyl carbonate, tetrahydrofuran, dimethyl sulfoxide, polyethylene glycol dimethyl ether, ethyl methyl carbonate and gamma- At least one selected from the group consisting of caprolactone. A lithium battery prepared from a battery assembly comprising (i) the polymer electrolyte composition for lithium batteries according to claim 4, (ii) a cathode and (iii) an anode.

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