KR100467689B1 - Organic electrolyte solution and lithium battery adopting the same - Google Patents

Abstract

The present invention provides an organic electrolyte solution comprising an organic acid peroxide capable of forming radicals by heat or light in an organic electrolyte solution containing a lithium salt and an organic solvent. The lithium battery employing the organic electrolyte according to the present invention has an effect of forming a film on the interface between the electrode plate and the organic electrolyte to suppress decomposition of the organic electrolyte and to improve the life characteristics of the battery.

Description

Organic electrolyte solution and lithium battery adopting the same

The present invention relates to an organic electrolyte and a lithium battery employing the same, and more particularly, to an organic electrolyte containing an organic acid peroxide capable of forming radicals by heat or light, and to the charge and discharge at the same time inhibiting decomposition of the electrolyte. The present invention relates to a lithium battery having excellent characteristics.

Recently, as the electronic equipment becomes smaller and lighter due to the development of advanced electronic devices, the use of portable electronic devices is gradually increasing. Therefore, the necessity of a battery having high energy density characteristics used as a power source for such an electronic device is increasing, and research on a lithium secondary battery is being actively conducted.

Lithium secondary battery is a battery manufactured by forming a separator, an organic electrolyte and a separator that provides a movement path of lithium ions between the cathode, the anode and the cathode and the anode, the lithium ion intercalation / de-insertion at the cathode and the anode Electrical energy is generated by oxidation and reduction reactions when deintercalation. Such lithium secondary batteries can be classified into lithium ion batteries using liquid electrolytes and lithium ion polymer batteries using solid electrolytes, depending on the type of separator. Among them, the lithium ion polymer battery uses a solid electrolyte, so there is little risk of leakage of the electrolyte, and the processability can be made into a battery pack. It is light in weight, low in volume, and has a very small self-discharge rate. Due to these characteristics, lithium ion polymer batteries are not only safer than lithium ion batteries, but also easy to manufacture into square and large cells.

In a lithium secondary battery, the cathode and the anode are made of a material capable of inserting and deinserting lithium ions. Looking at the forming material of the electrode, a lithium-containing metal oxide such as LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiMnO ₂ and the like as the cathode active material forming material. Among such lithium-containing metal oxides, manganese-based materials such as LiMn ₂ O ₄ , LiMnO _2, and the like are easy to synthesize, relatively inexpensive, and preferable for environmental protection, but have a small capacity. Cobalt-based materials such as LiCoO ₂ have good electrical conductivity and excellent voltage characteristics, but have a disadvantage of being expensive. Nickel-based materials such as LiNiO ₂ are relatively inexpensive and have a high discharge capacity, but are difficult to synthesize. Due to the difficult and high discharge capacity, there is a problem in that the stability of the battery must be secured.

Lithium metal, lithium alloy, or carbon material is used as the anode active material forming material. When lithium metal is used as the anode forming material, dendrite is formed, and there is a risk of explosion due to battery short circuit. Use it.

On the other hand, an organic electrolyte commonly used in a lithium secondary battery composed of a cathode / electrolyte and an anode / electrolyte is an ion conductor in which lithium salt is dissolved in an organic solvent. Must be excellent One problem that has arisen in this organic electrolyte solution is decomposition of the organic electrolyte solution during battery charging and discharging and storage. In particular, upon initial charging of the cell, the organic electrolyte reacts with the electrode and partially decomposes, which produces gas by-products that adversely affect the initial charge and discharge efficiency of the cell. In addition, as the charge and discharge cycle of the battery continues during storage, the organic electrolyte solution is continuously decomposed to generate gas, thereby providing a cause of deterioration of battery performance.

As a solution to the decomposition of the organic electrolyte solution has been actively researched to suppress the decomposition of the organic electrolyte using an additive that reacts faster than the organic electrolyte. However, most of the additives remain an unsolved problem in that the gas generated by the decomposition of the additive itself adversely affects the performance of the battery.

Accordingly, the technical problem to be achieved by the present invention is to provide an organic electrolyte solution in which the above decomposition is suppressed.

Another object of the present invention is to provide a lithium battery having improved charge and discharge characteristics by employing the organic electrolyte.

1 shows a change in the slope of a charging curve due to decomposition of an electrolyte during initial charging in an embodiment of the present invention and a conventional battery.

Figure 2 shows the change according to the charge and discharge cycle of the battery capacity in the embodiment of the present invention and the conventional battery.

The present invention to achieve the above technical problem,

In an organic electrolyte solution containing a lithium salt and an organic solvent,

It provides an organic electrolytic solution, characterized in that it further comprises an organic acid peroxide capable of forming radicals by heat or light.

The present invention to achieve the above other technical problem,

A cathode comprising a lithium-containing metal oxide or sulfur compound;

An anode comprising a metallic lithium, a lithium alloy or a carbon material;

A separator interposed between the cathode and the anode; And

A lithium battery comprising a lithium salt, an organic solvent, and an organic acid peroxide is provided.

In the organic electrolyte and lithium battery according to the present invention, the organic acid peroxide is dilauroyl peroxide, benzoyl peroxide, m-toluoyl peroxide, t-butyl peroxy-2-ethyl hexanoate, t-butylper Oxy bibarate, t-butylperoxy neodecanoate, diisopropyl peroxy dicarbonate, diethoxy peroxy dicarbonate, bis- (4-t-butylcyclohexyl) peroxy dicarbonate, dimethoxy isopropyl per It is preferably at least one selected from the group consisting of oxy dicarbonate, dicyclohexylperoxy dicarbonate, and C3-C30 dialkyl or dialkoxy peroxides.

Preferably, the C3 to C30 dialkyl or dialkoxy peroxide is at least one selected from the group consisting of isobutyl peroxide, and 3,3,5-trimethylhexanoyl peroxide.

In the organic electrolyte and lithium battery according to the present invention, the content of the organic acid peroxide is preferably 100ppm to 50000ppm with respect to the organic solvent.

In the organic electrolyte and the lithium battery according to the present invention, the lithium salt is LiPF₆, LiBF₄, LiAsF₆, LiClO₄, CF₃SO₃Li, LiC (CF₃SO₂)₃, LiN (C₂F₅SO₂)₂, LiN (CF₃SO₂)₂, LiI, and It is preferably at least one selected from the group consisting of LiSCN.

In the organic electrolytic solution and lithium battery according to the present invention, the organic solvent is oligoether such as tetrahydrofran, 2-methyltetrahydrofran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, or the like. Ester carbonate compounds such as dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate and methyl propyl carbonate, alkyl ester compounds such as methyl permate, methyl acetate, methyl propionate, aromatic nitrile compounds, It is preferably at least one selected from the group consisting of lactone compounds such as amide compounds, butyl lactones, and sulfur compounds.

In the lithium battery according to the present invention, it is preferable that the organic acid peroxide generates CO ₂ gas at 30 to 90 ° C.

Hereinafter, an organic electrolyte solution and a lithium battery according to the present invention will be described.

First, the organic electrolyte solution according to the present invention is composed of a lithium salt and an organic solvent, and further includes an organic acid peroxide. This organic acid peroxide is dissociated when energy is received by heat or light, as shown in Formula 1, to form radicals. The radicals thus liberated are in an unstable state and again dissociate to produce CO ₂ gas. This CO ₂ gas is dissolved in the organic electrolyte which is a polar solvent, and this dissolved gas forms a film of lithium carbonate on the surface of the negative electrode plate. The film thus formed suppresses decomposition of the organic electrolyte solvent to improve charge and discharge performance. In addition, the chemical structure of the organic acid peroxide is divided into a polar portion and a non-polar portion, and has a function to suppress the decomposition of the organic electrolyte by reducing the resistance generated between the negative electrode active material-containing anode and the organic electrolyte. In order to obtain such an effect, the nonpolar part constituting the organic acid peroxide is an alkyl group having 3 or more carbon atoms, and thus serves as a surfactant between the negative electrode and the electrolyte solution.

The organic acid peroxides include dilauroyl peroxide, benzoyl peroxide, m-toluoyl peroxide, t-butyl peroxy-2-ethyl hexanoate, t-butylperoxy bibarate, t-butylperoxy neo Decanate, diisopropyl peroxy dicarbonate, diethoxy peroxy dicarbonate, bis- (4-t-butylcyclohexyl) peroxy dicarbonate, dimethoxy isopropyl peroxy dicarbonate, dicyclohexyl peroxy dicarbonate And C3-C30 dialkyl or alkoxy peroxides can be used. When the carbon number of the alkyl group of the dialkyl or alkoxy peroxide is C3 or less, it cannot function as a surfactant between the active material in the negative electrode and the organic electrolyte solution, and when it exceeds C30, the balance between polarity and nonpolarity is broken and nonpolarity is also exceeded. Becomes relatively large and is difficult to dissolve in a highly polar organic electrolyte. In particular, in the case of the dialkyl peroxide having a polyfunctional group, the carbon number of the alkyl group or the alkoxy group may be C3 to C30.

Examples of the C3 to C30 dialkyl or alkoxy peroxides include isobutyl peroxide and 3,3,5-trimethylhexanoyl peroxide.

The organic acid peroxide may be used in an amount of 100 ppm to 50000 ppm with respect to the organic solvent. If the content of the organic acid peroxide is less than 100ppm, it is not preferable because the entire electrode plate may not be coated. If the content of the organic acid peroxide exceeds 50000ppm, it is not preferable because the excess additives act as impurities in the battery.

There is no particular limitation on the type of lithium salt that can be used in the present invention, but the greater the dissociation constant of lithium ions in the electrolyte, the better, and the corresponding lithium salt is LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ , CF ₃ SO ₃ Li , LiC (CF ₃ SO ₂ ) ₃ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiI, and LiSCN can be used. It is preferable that the concentration of this lithium salt is 0.5 to 2.0 M. When the concentration of the lithium salt is less than 0.5 M, the battery capacity characteristics are poor, and when the concentration of the lithium salt is higher than 2.0 M, the life characteristics are lowered.

Organic solvents that may be used in the present invention include oligoether compounds such as tetrahydrofran, 2-methyltetrahydrofran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, dimethyl carbonate, Ester carbonate compounds such as diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate and methyl propyl carbonate, alkyl ester compounds such as methyl permate, methyl acetate, methyl propionate, aromatic nitrile compounds, amide compounds, and butyl lactones And at least one selected from the group consisting of lactone compounds and sulfur compounds such as these.

Next, a lithium battery according to the present invention using the above-described organic electrolyte solution will be described.

First, a cathode active material composition is prepared by mixing a cathode active material, a conductive agent, a binder, and a solvent. The cathode active material composition is directly coated and dried on an aluminum current collector to prepare a cathode electrode plate. Alternatively, the cathode active material composition may be cast on a separate support, and then the film obtained by peeling from the support may be laminated on an aluminum current collector to manufacture a cathode electrode plate. Here, a mylar film or the like is used as the support.

Lithium-containing metal oxides or sulfur compounds are used as the cathode active material, and in particular, lithium-containing metal oxides include LiNi _1-x Co _x M _y O ₂ , (x = 0 to 0.2, M = Mg, Ca, Sr, Ba or La, y = 0.001 to 0.02), LiCoO ₂ , LiMn _x O _2x (x = 1 or 2), LiNi _1-x Mn _x O _2x (x = 1 or 2), and the like. desirable. Carbon black is used as the conductive agent, and vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene, and mixtures thereof are used. N-methylpyrrolidone, acetone, and the like are used as the solvent. At this time, the content of the cathode active material, the conductive agent, the binder, and the solvent is at a level commonly used in lithium batteries.

As in the case of manufacturing the cathode electrode plate described above, an anode active material composition is prepared by mixing an anode active material, a conductive agent, a binder, and a solvent, which is directly coated on a copper current collector or cast on a separate support and peeled from the support. The film is laminated on a copper current collector to obtain an anode plate.

As the anode active material, a lithium metal, a lithium alloy, or a carbon material is used. In the anode active material composition, the conductive agent, the binder, and the solvent are used in the same manner as in the case of the cathode. In some cases, a plasticizer is further added to the cathode electrode active material composition and the anode electrode active material composition to form pores inside the electrode plate.

On the other hand, any separator can be used as long as it is commonly used in lithium batteries. That is, as a separator, a coilable separator such as polyethylene (PE), polypropylene (PP) film, or the like is used, or a gelling polymer layer is laminated on both sides of the PE or PP film. Such a separator forms a gel polymer layer on a PE or PP film by coating a gelling polymer on the PE or PP film or injecting a composition containing a polymerizable monomer for gelling polymer formation into a cell and then performing polymerization.

The gelling polymer may be polyethylene oxide, polyurethane, epoxy, polyacrylonitrile, polyvinylidene fluoride and mixtures thereof. Among them, polyethylene oxide, polyurethane, epoxy, polyacrylonitrile, polyvinylidene fluoride and the like are preferably used in a gel system having a content of 2 to 25% by weight.

The separator is disposed between the cathode electrode plate and the anode electrode plate as described above to form an electrode assembly. The electrode assembly is wound or folded and placed in a cylindrical battery case or a square battery case, and then the organic electrolyte solution of the present invention is injected to complete a lithium ion battery.

In the lithium battery of the present invention, when the organic electrolyte solution according to the present invention is put into the electrode case and heated for 20 minutes to 4 hours between 50 ° C. and 90 ° C., CO ₂ is generated by decomposition of the organic acid peroxide in the electrolyte and thus the surface of the negative electrode. A lithium carbonate film is formed on the film.

Hereinafter, the present invention will be described in detail with reference to the following examples, but the present invention is not limited to the following examples.

EXAMPLE

<Example 1>

0.15 g of dilauroyl peroxide was added to 300 ml of 1.3 mol / liter LiPF ₆ mixed solution in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 3: 7 to prepare an organic electrolyte solution.

94 parts by weight of LiCoO _{2 as a} cathode active material, ₂ parts by weight of isetylene black (Super-P) (MMM) as a conductive material, and 2 parts by weight of polyvinylidene fluoride (PVDF) 30 parts by weight of N-methylpyrrolidone (NMP) Dispersion produced a cathode active material slurry. The cathode active material slurry was applied to an aluminum foil having a thickness of 20 μm, dried, rolled, and cut to a predetermined dimension to prepare a cathode electrode plate.

An anode active material slurry was prepared by dispersing 95 parts by weight of crystalline graphite (mesocarbon fiber: Petoca) as an anode active material and 4 parts by weight of PVDF in 25 parts by weight of NMP. The anode active material slurry was applied to a copper foil having a thickness of 15 μm, dried, rolled, and cut into a predetermined dimension to prepare an anode electrode plate.

A polyethylene separator (Cellgard) having a thickness of 25 μm is disposed between the cathode electrode plate and the anode electrode plate thus prepared, wound and pressed, inserted into a cylindrical can, and then 2.4 g of the organic electrolyte solution according to the present invention is injected into lithium 2. The primary battery was completed.

<Example 2>

Polyethylene glycol diacrylate was added to the electrolyte of the battery system as in Example 1 to 5% of the electrolyte content to prepare a lithium secondary battery, and then heated at 75 ° C. for 4 hours to complete the gel polymer battery.

Comparative Example 1

A battery was manufactured in the same manner as in Example 1, except that dilauroyl peroxide was not added when preparing the organic electrolyte solution in Example 1.

The performance of the batteries prepared in Examples and Comparative Examples was tested as follows. FIG. 1 is a graph of the voltage of dQ / dV and shows the change in the slope of the charge curve due to electrolyte decomposition during initial charging. This graph can show the extent to which the decomposition of the organic electrolyte proceeds with voltage. Referring to FIG. 1, it can be seen that in Examples 1 and 2, decomposition of the organic electrolyte is started at a higher voltage than the comparative example. This suggests that the film formed on the surface of the electrode plate when dilauroyl peroxide, which is a radical initiator, is added, suppresses decomposition of the electrolyte solution.

In addition, the life characteristics of the battery prepared in the above example were investigated. 2 shows the change according to the charge / discharge cycle of the battery capacity. Curve a shows the case of the battery prepared in Example 1, curve b shows the case of the battery prepared in Example 2, and curve c shows the case of the battery prepared in Comparative Example 1. As can be seen in Figure 2, it can be seen that when the organic acid peroxide is added, that is, the capacity in the case of curves a and b is much more stable than curve c without addition of the peroxide. It can be reconfirmed that the long-life characteristics of such batteries are due to the presence of a film formed at the interface between the organic electrolyte solution and the electrode plate.

The lithium battery employing the organic electrolyte according to the present invention has an effect of forming a film on the interface between the electrode plate and the organic electrolyte to suppress decomposition of the organic electrolyte and to improve the life characteristics of the battery.

Claims (13)

Lithium salts; Organic solvents; And It is dissociated by heat or light to form a radical, and the radicals are dissociated to generate CO ₂ gas, and the resulting CO ₂ gas is an organic electrolyte consisting of organic peroxides to form a lithium carbonate film on the negative electrode plate surface. The method of claim 1, wherein the organic acid peroxide is dilauroyl peroxide, benzoyl peroxide, m-toluoyl peroxide, t-butyl peroxy-2-ethyl hexanoate, t-butylperoxy bibarate, t-butylperoxy neodecanate, diisopropyl peroxy dicarbonate, diethoxy peroxy dicarbonate, bis- (4-t-butylcyclohexyl) peroxy dicarbonate, dimethoxy isopropyl peroxy dicarbonate, di At least one selected from the group consisting of cyclohexyl peroxy dicarbonate, and C3 to C30 dialkyl or dialkoxy peroxide. The organic electrolyte of claim 2, wherein the C3 to C30 dialkyl or dialkoxy peroxide is at least one selected from the group consisting of isobutyl peroxide and 3,3,5-trimethylhexanoyl peroxide. The organic electrolytic solution according to claim 1, wherein the content of the organic acid peroxide is greater than 100 ppm and less than 50000 ppm with respect to the organic solvent. The method of claim 1, wherein the lithium salt is LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ , CF ₃ SO ₃ Li, LiC (CF ₃ SO ₂ ) ₃ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN ( Organic electrolyte solution, characterized in that at least one selected from the group consisting of CF ₃ SO ₂ ) ₂ , LiI, and LiSCN. The method of claim 1, wherein the organic solvent is at least one oligoether compound selected from tetrahydroran, 2-methyltetrahydrofran, 1,3-dioxolane, and 4-methyl-1,3-dioxolane; At least one ester carbonate compound selected from dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, and methyl propyl carbonate; At least one alkyl ester compound selected from methyl permate, methyl acetate, and methyl propionate; Aromatic nitrile compounds; Amide compounds; Lactone compounds such as butyl lactone; And an organic electrolyte solution, characterized in that at least one selected from the group consisting of sulfur-based compounds. A cathode comprising a lithium-containing metal oxide or sulfur compound; An anode comprising a metallic lithium, a lithium alloy or a carbon material; A separator interposed between the cathode and the anode; And A lithium battery comprising an organic electrolyte comprising a lithium salt, an organic solvent and an organic acid peroxide. 8. The method of claim 7, wherein the organic acid peroxide is dilauroyl peroxide, benzoyl peroxide, m-toluoyl peroxide, t-butyl peroxy-2-ethyl hexanoate, t-butylperoxy bibarate, t -Butyl peroxy neodecanate, diisopropyl peroxy dicarbonate, diethoxy peroxy dicarbonate, bis- (4-t-butylcyclohexyl) peroxy dicarbonate, dimethoxy isopropyl peroxy dicarbonate, dicyclo Hexyl peroxy dicarbonate, and a lithium battery characterized in that at least one selected from the group consisting of C3 to C30 dialkyl or dialkoxy peroxide. 9. The lithium battery of claim 8, wherein the C3 to C30 dialkyl or dialkoxy peroxide is at least one selected from the group consisting of isobutyl peroxide and 3,3,5-trimethylhexanoyl peroxide. The lithium battery according to claim 7, wherein the content of the organic acid peroxide is greater than 100 ppm and less than 50000 ppm with respect to the organic solvent. The method of claim 7, wherein the lithium salt is LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ , CF ₃ SO ₃ Li, LiC (CF ₃ SO ₂ ) ₃ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN ( Lithium battery, characterized in that at least one selected from the group consisting of CF ₃ SO ₂ ) ₂ , LiI, and LiSCN. The method of claim 7, wherein the organic solvent is at least one oligoether compound selected from tetrahydrofran, 2-methyltetrahydrofran, 1,3-dioxolane, and 4-methyl-1,3-dioxolane; At least one ester carbonate compound selected from dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, and methyl propyl carbonate; At least one alkyl ester compound selected from methyl permate, methyl acetate, and methyl propionate; Aromatic nitrile compounds; Amide compounds; Lactone compounds such as butyl lactone; And at least one selected from the group consisting of sulfur compounds. The lithium battery according to claim 7, wherein the organic acid peroxide generates CO ₂ gas at 30 to 90 ° C.