KR101613766B1 - Gel polymer electrolyte and secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a gel polymer electrolyte composite comprising a gel polymer electrolyte composed of an organic electrolyte solution containing an ionic salt and a crosslinking polymer, and a porous support used as a support for mechanical properties, and an electrochemical device comprising the gel polymer electrolyte composite.

Description

[0001] GEL POLYMER ELECTROLYTE AND SECONDARY BATTERY COMPRISING SAME [0002]

The present invention relates to a gel polymer electrolyte composite having a thin thickness and excellent mechanical properties, and an electrochemical device comprising the gel polymer electrolyte composite.

Recently, with the development of wireless communication technology, electronic devices such as portable devices or automobile accessories are required to be made smaller and lighter, and studies on high energy density electrochemical devices used as energy sources thereof are being actively conducted.

A secondary battery known as a typical example of the electrochemical device is a device that converts external electrical energy into a form of chemical energy and generates electricity when necessary. The secondary battery is also called a "rechargeable battery " do. The secondary battery provides both an economical advantage and an environmental advantage over a single used primary battery.

Examples of the secondary battery include a lead-acid battery, a nickel-cadmium battery, a nickel-metal hydride battery, a lithium-ion battery, and a lithium-ion polymer battery.

The secondary battery is manufactured by mounting an electrode assembly composed of a cathode, an anode, and a separator in a pouch-shaped case of a metal can such as a cylindrical or angular shape or an aluminum laminate sheet, and injecting an electrolyte into the electrode assembly.

As the electrolyte for the secondary battery, a liquid electrolyte in which a salt is dissolved in a non-aqueous organic solvent is mainly used. However, such a liquid electrolyte has a great possibility of volatilizing the organic solvent, and causes various problems such as deterioration of the electrode material and generation of leakage, making it difficult to realize various types of electrochemical devices with high stability .

In recent years, gel polymer electrolytes or solid polymer electrolytes having no fear of leakage have been developed in order to solve the stability problem of such liquid electrolytes.

However, since the gel polymer electrolyte has high ion conductivity, the gel polymer electrolyte is very weak in mechanical properties, so it is not easy to use it alone. In order to introduce the gel polymer electrolyte into the secondary battery, there has been proposed a method in which a gel polymer electrolyte is coated on the surface of the electrode or separation membrane, and the monomers contained in the gel polymer electrolyte are crosslinked. However, when forming the polymer network due to the crosslinking reaction of the monomers, the gel polymer electrolyte layer formed on the surface of the electrode or the separator becomes thick, making it difficult to form a thin electrolyte layer having a thickness less than a certain level.

Therefore, it is urgent to develop a gel polymer electrolyte having a thin thickness and excellent mechanical properties while improving the above-mentioned conventional problems.

The present invention provides a gel polymer electrolyte composite which is not only thin but also excellent in mechanical properties and ionic conductivity.

The present invention also provides a secondary battery comprising the gel polymer electrolyte composite.

Hereinafter, the present invention will be described in detail.

In the present invention,

An organic electrolytic solution containing an ionic salt, a gel polymer electrolyte comprising a crosslinked polymer,

There is provided a gel polymer electrolyte composite comprising a porous support used as a support for mechanical properties.

Specifically, the gel polymer electrolyte composite of the present invention is preferably an electrolyte complex comprising a porous support impregnated with the gel polymer electrolyte.

In the gel polymer electrolyte composite of the present invention, ion seongyeom contained in the organic electrolyte solution is _{LiCl, LiBr, LiI, LiClO 4} , LiBF 4, LiB 10 Cl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, and 4-phenyl boric acid one selected from lithium or 2 The lithium salt may be a lithium salt of a species or more, but is not limited thereto.

In the gel polymer electrolyte of the present invention, the organic electrolytic solution may be at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), diethyl carbonate (DMC), ethylmethyl carbonate (EMC), methyl formate (MF), gamma-butyrolactone (γ-BL), sulfolane, MA (methylacetate) And methyl propionate (MP).

In the gel polymer electrolyte of the present invention, the crosslinked polymer may be obtained by polymerizing a monomer having two or more functional groups, or a polar monomer having one functional group and a polar monomer having two or more functional groups in the presence of a UV initiator (Co) polymers.

The UV initiator may include benzophenone or benzoyl peroxide. The UV initiator may include about 3 wt% or less, specifically about 0.5 wt% to about 3 wt%, based on the total weight of the monomers.

The monomer having two or more functional groups may be selected from the group consisting of trimethylol propane ethoxylate triacrylate, polyethylene glycol dimethacrylate, polyethylene glycol diacrylate, divinylbenzene, polyester dimethacrylate, divinyl ether, Trimethylol propane, trimethylol propane trimethacrylate, and ethoxylated bisphenol A dimethacrylate. The monomer may be used alone or in combination of two or more. The polar monomers having one functional group may be selected from the group consisting of methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate, butyl acrylate, ethylene glycol methyl ether acrylate, ethylene glycol methyl ether methacrylate, acryl And at least one monomer selected from the group consisting of acrylonitrile, rhenitrile, vinyl acetate, vinyl chloride and vinyl fluoride.

The crosslinked polymer may be contained in an amount of about 2 to 5% by weight based on the total weight of the organic electrolytic solution. If the content of the crosslinking polymer is less than 2% by weight, a gel electrolyte may not be formed and the crosslinking polymer may not maintain its shape. If the content of the crosslinking polymer exceeds 5% by weight, A drawback that the conductivity is reduced may occur.

In the gel polymer electrolyte composite of the present invention, the porous support to be introduced into the support having mechanical properties may be a polyester, a polyacetal, a polyamide, a polycarbonate, a polyimide, a polyether ether ketone, a polyether sulfone, Oxide, polyphenylene sulfite, and polyethylene naphthalene. [0038] The term " polymer " Specifically, the porous substrate may be a porous nonwoven substrate or a porous nonwoven substrate formed of a mixture of inorganic particles and a binder polymer.

Further, in another embodiment of the present invention

Preparing a porous support;

Preparing a mixed solution containing an organic electrolyte solution containing an ionic salt, a crosslinking polymer and a UV initiator;

Immersing the porous support in the mixed solution; And

Removing the porous support immersed in the mixed solution, and irradiating ultraviolet light.

 The porous support is not particularly limited as long as it can be formed by a conventional method for producing a porous support used in the production of a secondary battery. For example, the porous support may be formed by electrospinning a nonwoven fabric or the like.

In addition, in the immersion step, the porous support is preferably immersed in the mixed solution for about 1 hour or more. By the immersion process, the gel polymer electrolyte may be contained in the porous support in an amount of about 50% or more based on the total volume of the porous support.

In addition, the thickness of the gel polymer electrolyte composite produced by the method of the present invention may be determined according to the thickness of the porous support. Specifically, the thickness of the porous support for determining the thickness of the gel polymer electrolyte composite of the present invention may be about 10 to 50 占 퐉, and the thickness is not limited to this, and a porous support having a thinner thickness may be used.

In another embodiment of the present invention,

1. An electrochemical device comprising an anode, a cathode, a separator and an electrolyte,

An electrochemical device comprising the gel polymer electrolyte composite of the present invention as the electrolyte is provided.

The positive electrode and the negative electrode are composed of a current collector and an electrode active material. For example, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li (Ni _a Co _b Mn _c ) O ₂ (0 < LiNi _{1 - y} MnyO ₂ , LiNi _{1- y} MnyO ₂ (O = y <1, 0 <b <1, 0 <c <1, a + b + c = 1), LiNi _{1 -y} CoyO ₂ , LiCo _{1- 1), Li (Ni a Co} b Mn c) O 4 (0 <a <2, 0 <b <2, 0 <c <2, a + b + c = 2), LiMn 2 - z Ni z O 4 , LiMn _{2- z} Co _z O ₄ (0 <z <2), LiCoPO ₄ and LiFePO ₄ , or a mixture of two or more thereof. In addition to these oxides, sulfide, selenide and halide may also be used.

As the negative electrode active material, a carbonaceous material, lithium-containing titanium composite oxide (LTO) which can normally store and discharge lithium ions; Metals (Me) having Si, Sn, Li, Zn, Mg, Cd, Ce, Ni and Fe; An alloy composed of the metal (Me); An oxide of the metal (Me) (MeOx); And a composite of the metal (Me) and carbon; May be used. Preferably, carbon materials can be used, and carbon materials such as low-crystalline carbon and highly-crystalline carbon can be used. Examples of low crystalline carbon are soft carbon and hard carbon. Examples of highly crystalline carbon include natural graphite, Kish graphite, pyrolytic carbon, liquid crystal pitch carbon fiber mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch derived cokes. The negative electrode may include a binder. Examples of the binder include polyvinylidene fluoride, polyacrylonitrile, vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polymethylmethacrylate Various kinds of binder polymers such as acrylate and acrylate can be used.

The separator is a thin porous polymer thin film of an insulating material applicable to a lithium secondary battery. Specifically, the separator is an ethylene homopolymer, a propylene homopolymer, an ethylene-butene copolymer, an ethylene-hexene copolymer and an ethylene-methacrylate copolymer A porous substrate made of a polyolefin-based polymer selected from the group consisting of polyolefin-based polymers; A porous substrate made of a polymer selected from the group consisting of polyester, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyethersulfone, polyphenylene oxide, polyphenylsulfite and polyethylene naphthalene; Or a porous substrate formed of a mixture of inorganic particles and a binder polymer, and the like, but are not limited thereto.

In addition, the electrochemical device of the present invention is preferably a lithium secondary battery, and its outer shape is not particularly limited, but may be a cylindrical shape, a square shape, a pouch shape, a coin shape, or the like using a can.

As described above, the conventional gel polymer electrolyte for electrochemical devices has difficulty in reducing the thickness to 100 μm to 200 μm or less. On the other hand, in the present invention, by impregnating the gel polymer electrolyte into the thin porous support, The thickness of the electrolyte can be reduced to about 50 탆 or less, while the gel polymer electrolyte composite for an electrochemical device having improved strength and flexibility can be produced.

On the other hand, the ionic conductivity (s / cm) of the electrochemical device, that is, the lithium secondary battery, is a kind of proportional constant that is not affected by the thickness or the area, and the conventional gel polymer electrolyte and the gel polymer electrolyte of the present invention are impregnated It is meaningless to compare the ionic conductivities because the gel polymer electrolyte composites composed of the porous support have different thicknesses. Therefore, in order to comparatively analyze the effects and effects of the gel polymer electrolytes of the two inventions on the thickness, ionic conductance (S) was taken into consideration in consideration of the thickness of the electrolyte membrane.

A method of measuring the ion conductance S can be found by the following equation (1).

[Formula 1]

G = K * A / I

Where G is ion conductance (S), K is ionic conductivity (K), A is surface area and I is the thickness of the electrolyte layer.

In other words, when the gel polymer electrolyte is coated on the surface of an electrode or a separator by conventional methods, the thickness of the electrolyte layer is increased, so that the ionic conductance of the electrolyte layer is reduced, and the internal resistance of the electrochemical device system is increased. On the other hand, in the present invention, since the gel polymer electrolyte is impregnated into the porous support, it is possible to provide a gel polymer electrolyte composite in which the thickness of the electrolyte layer is affected by the thickness of the porous support and the thickness thereof is reduced. Therefore, according to the present invention, it is possible to provide an electrolyte for an electrochemical device which is excellent in not only ion conductivity, but also flexibility and mechanical properties, and thereby, the effect of ensuring the stability of the interface between the electrode and the electrolyte can be obtained. Therefore, a secondary battery having improved stability and mechanical properties can be produced.

The present invention provides a gel polymer electrolyte composite comprising a porous support impregnated with a gel polymer electrolyte having a thin thickness and excellent ionic conductivity and mechanical strength, whereby a secondary battery having stability and high performance characteristics can be manufactured.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments of the invention and, together with the description of the invention, It should not be construed as limited.
1 is an electron micrograph (SEM) photograph showing a cross section of an electrolyte complex of the present invention.
FIGS. 2A and 2B are graphs showing ionic conductivity measurement results of respective gel polymer electrolytes according to Experimental Example 1 of the present invention. FIG.
3 is a graph showing the electrochemical stability measurement results of the respective electrolytes according to Experimental Example 2 of the present invention.
4 is a graph showing the performance test results of a battery using each of the gel polymer electrolytes according to Experimental Example 3 of the present invention.
5A and 5B are graphs showing performance test results of a cell using each gel polymer electrolyte according to Experimental Example 3 of the present invention.

Hereinafter, the present invention will be described in detail with reference to examples and comparative examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Example

Example  One.

The mixture was homogeneously mixed with an organic electrolytic solution (1M, LiPF ₆ , EC: DEC = 1: 1 (vol)) and trimethylolpropane ethoxylate triacrylate (TMPEOTA) 97.5: 2.5 parts by weight, Was added to 1% by weight of TMPEOTA to prepare a mixture. A porous nonwoven fabric made of PET having a thickness of 20 탆 was immersed in the mixture for 1 hour to impregnate the porous nonwoven fabric with the mixture. Thereafter, the porous nonwoven fabric impregnated with the mixture was taken out and irradiated / crosslinked with ultraviolet rays for 1 minute to prepare an electrolyte complex comprising the porous support impregnated with the gel polymer electrolyte (see FIG. 1).

Comparative Example  One.

A gel polymer electrolyte was prepared in the same manner as in Example 1 except that the organic electrolyte doped with the ionic salt and the TMPEOTA mixture were directly cast on a glass plate without immersing the porous nonwoven fabric.

Comparative Example 2

In order to compare the electrochemical stability with the gel polymer electrolyte composite of Example 1, organic electrolytes of 1M, LiPF ₆ , EC: DEC = 1: 1 (vol) without TMPEOTA were prepared.

Experimental Example  1. Ion conductivity test

The ionic conductivity of the electrolyte composite of Example 1 and the gel polymer electrolyte of Comparative Example 1 was measured. As a result, the ionic conductivity (S / cm) of the gel polymer electrolyte of Comparative Example 1 was high, but the ionic conductance (S) of the membrane excluding the thickness portion was high, confirming that the electrolyte complex of Example 1 was high (See Figs. 2A and 2B).

That is, in the case of the electrolyte of Comparative Example 1, it is difficult to manufacture the membrane under 100 to 200 μm, whereas the electrolyte composite of Example 1 is highly dependent on the thickness of the nonwoven fabric, so that a thin film can be produced. It was confirmed that the electrolyte complex of practical example 1 is superior in ion conductivity because the factor associated with battery resistance applied to an actual battery is ion conductance.

Experimental Example  2. Electrochemical stability experiment

A coin-type battery was prepared by using stainless steel as a measuring electrode and lithium metal as a counter electrode, and the electrolyte composite of Example 1 and the organic electrolyte of Comparative Example 2 were inserted between these electrodes.

The electrochemical stability of the coin-type cells was then measured using a linear sweep voltammetry (LSV) up to 6V with a scan rate of 5 mV / s.

As a result, it was found that the electrolyte complex of Example 1 of the present invention had similar oxidation stability to that of Comparative Example 2, and the electrolyte complex of Example 1 exhibited excellent electrochemical stability up to 5 V 3).

Experimental Example  3. Battery performance experiment

The negative electrode and the positive electrode were prepared by coating LTO / acetylene black / PVDF as the negative electrode active material and LiCoO ₂ / acetylene black / PVDF as the positive electrode active material, respectively, on the aluminum foil.

The electrolyte composite of Example 1 and the gel polymer electrolyte of Comparative Example 1 were inserted between the electrodes thus prepared to prepare a coin-type battery.

Charge-discharge experiments were conducted on the prepared coin-type battery under a voltage of 1.5 V to 2.72 V at a predetermined current density. The current density was changed by 0.1C, 0.2C, 0.3C, 0.4C, 0.5C, 1C and 2C for each 5 cycles in order to confirm the performance change of the battery by the capacity rate (FIG. 4 Reference).

As a result, the discharge characteristics of the electrolyte complex of Example 1 (see FIG. 5B) were improved compared with the electrolyte of Comparative Example 1 (see FIG. 5B), which was attributable to the improvement in ion conductance due to the introduction of the porous support Respectively.

Claims (18)

1. An electrochemical device comprising an anode, a cathode, a separator and an electrolyte,
Wherein the electrolyte comprises a gel polymer electrolyte comprising an organic electrolyte solution containing an ionic salt and a crosslinked polymer; And a porous support, wherein the gel polymer electrolyte complex is a gel polymer electrolyte composite comprising:
Wherein the separation membrane is a porous substrate made of a polyolefin-based polymer selected from the group consisting of an ethylene homopolymer, a propylene homopolymer, an ethylene-butene copolymer, an ethylene-hexene copolymer, and an ethylene-methacrylate copolymer; A porous substrate made of a polymer selected from the group consisting of polyester, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyethersulfone, polyphenylene oxide, polyphenylsulfite and polyethylene naphthalene; Or a porous substrate formed of a mixture of inorganic particles and a binder polymer,
The porous support may be a porous nonwoven substrate or a porous nonwoven substrate formed of a mixture of inorganic particles and a binder polymer,
Wherein the porous nonwoven substrate comprises one or two selected from the group consisting of polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfite and polyethylene naphthalene Wherein at least one of the first electrode and the second electrode is formed of at least one polymer. The method according to claim 1,
Ion seongyeom contained in the organic electrolyte solution is _{LiCl, LiBr, LiI, LiClO 4} , LiBF 4, LiB 10 Cl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiAlCl 4, CH 3 Wherein the lithium salt is at least one lithium salt selected from the group consisting of SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, chloroborane lithium, lower aliphatic carboxylate lithium and lithium 4-phenylborate. Chemical device. The method according to claim 1,
The organic electrolytic solution may be at least one selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, methyl formate, gamma-butyrolactone, sulfolane, Wherein the organic electrolyte solution is one or more organic electrolytic solutions selected from the group consisting of sodium carbonate, potassium carbonate, and sodium carbonate. The method according to claim 1,
Wherein the crosslinked polymer comprises a copolymer obtained by polymerization of a monomer having two or more functional groups or a polar monomer having two or more functional groups and a functional group having one functional group in the presence of a UV initiator, device. The method of claim 4,
Wherein the UV initiator comprises benzophenone or benzoyl peroxide. The method of claim 4,
Wherein the UV initiator is contained in an amount of 3 wt% or less based on the total weight of the monomers. The method of claim 4,
The monomer having two or more functional groups is selected from the group consisting of trimethylol propane ethoxylate triacrylate, polyethylene glycol dimethacrylate, polyethylene glycol diacrylate, divinylbenzene, polyester dimethacrylate, divinyl ether, trimethylol Is at least one monomer selected from the group consisting of propane, trimethylolpropane trimethacrylate, and ethoxylated bisphenol A dimethacrylate. The method of claim 4,
The polar monomer having one functional group may be selected from the group consisting of methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate, butyl acrylate, ethylene glycol methyl ether acrylate, ethylene glycol methyl ether methacrylate, acrylonitrile , Vinyl acetate, vinyl chloride, and vinyl fluoride. The method according to claim 1,
Wherein the crosslinked polymer is contained in an amount of 2 to 5 wt% based on the total weight of the organic electrolytic solution. delete delete The method according to claim 1,
Wherein the gel polymer electrolyte is impregnated into the porous support in an amount of not more than 50% based on the total volume of the porous support. The method according to claim 1,
Wherein the porous support has a thickness of 10 to 50 占 퐉. delete The method according to claim 1,
The positive electrode may be made of LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li (Ni _a Co _b Mn _c ) O ₂ where 0 <a <1, 0 <b < _{+ c = 1), LiNi 1} -y CoyO 2, LiCo 1-y MnyO 2, LiNi 1-y MnyO 2 (O = y <1), Li (Ni a Co b Mn c) O 4 (0 <a < 2, 0 <b <2, 0 <c <2, a + b + c = 2), LiMn 2-z Ni z O 4, LiMn 2-z Co z O 4 (0 <z <2), LiCoPO 4 And LiFePO ₄ , or a mixture of two or more thereof, is used as the positive electrode active material. The method according to claim 1,
The negative electrode is made of a carbon material, a lithium-containing titanium composite oxide (LTO); Metals (Me) having Si, Sn, Li, Zn, Mg, Cd, Ce, Ni and Fe; An alloy composed of the metal (Me); An oxide of the metal (Me) (MeOx); And a composite of the metal (Me) and carbon. The electrochemical device according to claim 1, delete The method according to claim 1,
Wherein the electrochemical device is a lithium secondary battery.

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