KR100560210B1 - Electrolyte composition having high safety when overcharged and low swelling property at a high temperature - Google Patents

Abstract

The present invention relates to an electrolyte composition having high overcharging safety and low high temperature swelling properties, comprising a lithium salt and an organic solvent as a main component, and comprising an nitrogen-containing compound, biphenyl and propane sultone as additives. Lithium secondary batteries prepared by using not only shows excellent safety during overcharging but also has low swelling characteristics at high temperatures.

Description

ELECTROLYTE COMPOSITION HAVING HIGH SAFETY WHEN OVERCHARGED AND LOW SWELLING PROPERTY AT A HIGH TEMPERATURE

The present invention relates to an electrolyte composition that provides high safety during overcharging and low swelling properties at high temperatures, and a lithium secondary battery excellent in overcharge safety and high temperature swelling prevention capability using the composition.

Typically, a lithium secondary battery having a structure including a negative electrode, a positive electrode, an organic electrolyte, and a lithium ion-permeable separator between the electrodes is poor in safety, such as generating smoke or fire during overcharging, and thus, lithium secondary Biphenyl, 3-chlorothiophene, furan, and the like have been disclosed as additives for increasing the overcharge safety of batteries (see US Pat. Nos. 5,879,834 and 6,033,797).

These additives, during the overcharging of the lithium secondary battery, polymerize with the conductive polymer to generate hydrogen gas to operate the safety valve inside the battery to stabilize the battery or to soften the energy of the battery with a soft short by the conductive polymer. Diverge to stabilize the cell. However, these additives tend to oxidize prematurely by the catalysis of HF or Lewis acid present in the electrolyte, thereby rapidly increasing the self-discharge rate of the battery.

In addition, these additives are not only difficult to ensure overcharge safety of lithium secondary batteries in amounts conventionally used, such as 2.5 wt% or less for biphenyl, but also at high temperatures (eg, about 90 ° C.). The battery is greatly inflated by the hydrogen gas produced while polymerizing with the conductive polymer, and has a problem of far exceeding 10%, which is a degree of swelling normally required.

Regarding the high temperature swelling characteristics of the battery, propane sultone is known to have an effect of suppressing swelling by suppressing the reaction of the electrolyte and the electrode at high temperature to reduce the emission of gas (Japanese Patent Laid-Open No. 10-50342). , 12-3724, 12-123868, 12-323171 and 13-52738).

Therefore, studies on batteries having high overcharge safety and low high temperature swelling characteristics are continuing. For example, Japanese Patent Laid-Open No. 13-307773 (GS-Melcotech) adds lithium carbonate to an electrode to prevent overcharging. Disclosed is a method of producing a battery by adding propane sultone to an electrolyte. However, the battery produced by this method has a problem in that the battery capacity decreases with the loss of the amount of the electrode active material.

Accordingly, the present inventors have diligently studied to produce a lithium secondary battery having excellent overcharge safety and high temperature swelling properties when using an electrolyte composition containing a nitrogen-containing compound in a specific amount together with biphenyl and propane sultone. The present invention was completed.

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrolyte composition which provides high safety during overcharging and low swelling properties at high temperatures, and a lithium secondary battery excellent in overcharge safety and high temperature swelling prevention ability by using the composition.

In order to achieve the above object, the present invention provides an electrolyte composition comprising a lithium salt and an organic solvent as a main component, and containing a nitrogen-containing compound, biphenyl, and propane sultone as additives.

The present invention also provides a lithium secondary battery prepared using the composition.

Hereinafter, the present invention will be described in more detail.

The electrolyte composition according to the present invention is characterized in that it includes biphenyl as an overcharge safety additive and propane sultone as a high temperature swelling inhibitor together with a nitrogen-containing compound, wherein the nitrogen-containing compound, biphenyl and propane sultone are respectively composed as a whole composition. In amounts of 0.1 to 5% by weight, 4 to 10% by weight and 0.05 to 1.5% by weight. Furthermore, biphenyl may be preferably used in an amount of 5 to 8% by weight, and propane sultone may be preferably used in an amount of 0.05 to 1.0% by weight.

The nitrogen-containing compounds used in the present invention effectively remove HF or Lewis acids present in the electrolyte and inhibit premature oxidative polymerization of biphenyls by them, thereby helping the biphenyls play their original role in overcharging.

Specific examples of nitrogen-containing compounds according to the invention include monomers such as primary, secondary or tertiary amines, or polymers, copolymers or oligomers thereof, preferably 6-membered aromatic heterocycles, 5-membered fused. Aromatic heterocycles and monomers such as aromatic or non-aromatic secondary or tertiary amines, or polymers, copolymers or oligomers thereof. Preferred examples of 6-membered aromatic heterocycles include pyridine, pyridazine, pyrimidine, pyrazine and triazine compounds. Preferred examples of 5-membered fused aromatic heterocycles include triazole, thiazole and thiadiazole compounds. Aromatic or non-aromatic secondary and tertiary amine compounds preferably contain at least one nitrogen atom and at least five carbon atoms. If the amount of the nitrogen-containing compound is less than 0.1 wt%, it will not effectively capture HF or Lewis acid in the electrolyte, and if it is more than 5 wt%, the high rate discharge characteristics of the battery will be lowered.

The biphenyl used in the present invention converts into a conductive polymer during overcharging and generates a soft short to consume energy of an unstable battery, thereby improving overcharging safety of the battery. If the amount of the biphenyl is less than 4% by weight, it is difficult to secure overcharge safety. If the amount of the biphenyl is more than 10% by weight, the high rate discharge characteristic of the battery is reduced.

Propane sultone used in the present invention serves to suppress the generation of gas at a high temperature by forming a passive film on the surface of the electrode active material during initial charging of the battery so as not to react with the electrode active material and the electrolyte. When the amount of propane sultone is less than 0.05% by weight, it is impossible to form an inert film of high density and thus the reaction of the electrode active material and the electrolyte cannot be suppressed at high temperature. Increases the capacity, thereby decreasing the capacity.

In addition to the nitrogen-containing compounds, biphenyls and propane sultones described above, preferably, the electrolyte composition according to the invention may further comprise a halogen- or epoxy-containing compound as an additive. Since the halogen- or epoxy-containing compound reacts with the nitrogen-containing compound at a high temperature to advance the gelation, the electrolyte composition of the present invention can be converted into the gel polymer electrolyte by heating by adding the halogen- or epoxy-containing compound. have. The electrolyte composition according to the invention may comprise a halogen- or epoxy-containing compound in an amount of 0.02 to 1.5% by weight.

Specific examples of the halogen-containing compound used in the present invention include monomers such as substituted or unsubstituted alkylene halides or aromatic halides, or polymers, copolymers or oligomers thereof; Preferably, halomethylbenzene, halomethylnaphthalene, halomethylbiphenyl, bis (halomethyl) benzene, bis (halomethyl) naphthalene, bis (halomethyl) biphenyl, tris (halomethyl) benzene, tris (halomethyl ) Aromatic halides such as naphthalene, tris (halomethyl) biphenyl, tetrakis (halomethyl) benzene, tetrakis (halomethyl) naphthalene, tetrakis (halomethyl) biphenyl and halomethylstyrene, and diiodoalkanes, tri Monomers such as alkylene halides such as iodoalkanes and tetraiodoalkanes, or polymers, copolymers or oligomers thereof. In this case, preferably, the halomethyl group of the aromatic halide is a chloromethyl group, a bromomethyl group or an iodomethyl group, and the alkylene halide is a haloalkane containing two or more carbon atoms. Most preferred examples of substituted or unsubstituted alkylene halides or aromatic halides include bis (bromomethyl) benzene, α, α'-dibromoxylene and diiodoalkanes.

Specific examples of epoxy-containing compounds include 3,4-epoxycyclohexylmethyl-3 ', 4'-epoxycyclohexane carboxylate, glycidyl dodecafluoroheptyl ether, polypropylene glycol diglycidyl ether, glycy Dyl dodecafluoroheptyl ether, butadiene diepoxide, butanediol diglycidyl ether, cyclohexene oxide, cyclopentene oxide, diepoxy cyclooctane, ethylene glycol diglycidyl ether and 1,2-epoxy hexane Can be mentioned.

In addition, the lithium salt and the organic solvent used in the present invention may be a conventional one used in the electrolyte, specific examples of the lithium salt are LiPF ₆ , LiAsF ₆ , LiClO ₄ , LiN (CF ₃ SO ₂ ) ₂ , LiBF ₄ , LiCF ₃ SO ₃ , LiSbF _6, and mixtures thereof. The electrolyte composition according to the present invention may contain lithium salt in an organic solvent at a concentration of 0.5 to 2M.

The electrolyte composition according to the present invention can be obtained by dissolving the above amounts of additives in an organic solvent containing a lithium salt, and using the electrolyte composition, a lithium 2 comprising a separator between the negative electrode, the positive electrode, and the electrodes. A primary battery can be manufactured. Specifically, the electrode stack composed of the negative electrode, the positive electrode, and the separator is wound to make a jelly roll, which is then placed in a battery container, and a portion thereof is sealed. Subsequently, the electrolyte composition is injected into a container, and then heated to 30 to 130 ° C. as necessary (if it contains a halogen- or epoxy-containing compound) to soak / gel the electrolyte composition to form a lithium secondary battery. Can be prepared.

In the present invention, electrodes of conventional lithium ion batteries can be used. The positive electrode composition used in the present invention includes 100 parts by weight of a positive electrode active material (eg, LiCoO ₂ ), 1 to 10 parts by weight of a conductive agent (eg, carbon black), 2 to 2 parts by weight of a binder (eg, polyvinylidene fluoride (PVDF)). 10 parts by weight and 30-100 parts by weight of a solvent, such as N-methylpyrrolidone (NMP). The negative electrode composition used in the present invention is 100 parts by weight of the negative electrode active material (e.g. carbon), 10 parts by weight or less of the conductive agent (e.g. carbon black), 2 to 10 parts by weight of the binder (e.g. polyvinylidene fluoride (PVDF)) Parts and 30 to 100 parts by weight of a solvent, such as N-methylpyrrolidone (NMP).

In addition, the separator used in the present invention may be a microporous plate made of a polymeric material such as polyethylene or polypropylene, which is commonly used in lithium ion batteries. The container used in the present invention is preferably made of thermoplastic material which can be heat sealed and inert to the battery contents.

As such, the lithium secondary battery prepared using the electrolyte composition according to the present invention not only shows excellent safety during overcharging but also has low swelling characteristics at high temperatures.

Hereinafter, the present invention will be described in more detail based on the following examples. However, the following examples are only for illustrating the present invention, and the scope of the present invention is not limited thereto.

Reference Example 1 Change of Battery Characteristics According to Biphenyl Addition (No Propane Sultone)

2 g poly (2-vinylpyridine-co-styrene) (PVPS, Aldrich), 0.5 g butanediol diglycidyl ether (BDDGE, Aldrich), biphenyl (aldrich) in 1: 1 volume percent ethylene carbonate: An electrolyte precursor solution was prepared by dissolving in 1M LiPF ₆ liquid electrolyte in diethyl carbonate (EC: DEC, Merck). At this time, the amount of biphenyl was changed to 0, 2, 3, 4, 5, 6, 8, and 10 g, so that the amount of liquid electrolyte was also 97.5, 95.5, 94.5, 93.5, 92.5, 91.5, 89.5, and 87.5 g. Changed to.

88 g of LiCoO ₂ (Seimi), 6.8 g of carbon black (Cabot) and 5.2 g of polyvinylidene fluoride (PVDF, Solvay) were added to N-methylpyrrolidone (NMP, Aldrich). ) To 200 g to prepare a positive electrode composition. The prepared positive electrode slurry was coated on a surface of an aluminum foil (current collector) using a die coater, dried, and pressed to prepare a positive electrode having a thickness of 122 μm.

93.76 g of mesophase carbon micro beads (MCMB 25-28, Osaka gas) and 6.24 g of polyvinylidene fluoride (PVDF, Solvay) were added to N-methylpyrrolidone (NMP). , Aldrich) was dissolved in 180 g to prepare a negative electrode composition. The prepared negative electrode composition slurry was coated on the surface of a copper foil (current collector) using a die coater, dried and pressed to prepare a negative electrode having a thickness of 120 μm.

The electrode laminate made by placing a polypropylene separator (25 μm, Celgard 2300 microporous film) between the prepared cathode and anode was wound up to make jelly roll, and then placed in a heat sealable plastic container. A portion of the vessel was sealed at 170 ° C. using a bar sealer. Subsequently, the electrolyte precursor solution prepared above was injected into a container, and then gelled at 65 ° C. for 24 hours to prepare a lithium secondary battery.

For manufactured cells, the capacity (mAh, 225 mAh discharge standard) was used with Maccor test equipment, and the overcharge (12 V) safety (1 C-mA and power supply was used with Power Supply, Hewlett Packard). 2C-mA current) was measured at 90 ° C. for 4 hours, and then the degree of swelling (%) was measured.

Biphenyl addition amount (g) 0 4 5 6 8 10 Capper City 918 913 920 916 918 912 Overcharge safety ^* 1C 0/3 3/3 3/3 3/3 3/3 2/3 2C 0/3 0/3 2/3 3/3 2/3 0/3 High temperature swelling (%) 9 30 29 30 45 56 Overcharge safety: Performs three cells each at 1C- and 2C-current to indicate the number of cells that did not produce smoke and fire (safe)

From Table 1, it can be seen that the overcharge safety is increased by the addition of biphenyl, while the degree of high temperature swelling is significantly increased as the amount of use is increased.

Reference Example 2 Change of Battery Characteristics According to Propane Sultone Addition (No Biphenyl)

Instead of using biphenyl, the amount of propane sultone (Aldrich) was changed to 0, 0.5, 1.0 and 1.5 g to prepare an electrolyte precursor solution in the same manner as in Reference Example 1, and then using the prepared electrolyte precursor solution. To prepare a lithium secondary battery in the same manner as in Reference Example 1.

For manufactured cells, the capacity (mAh, 225 mAh discharge basis) was used with a Marko test equipment, and the overcharge (12 V) safety (currents of 1 C-mA and 2 C-mA) was measured using a power supply (Hewlett-Packard) at 90 ° C. After standing for 4 hours at measured the degree of swelling (%), the results are shown in Table 2 below.

Propane sultone addition amount (g) 0 0.5 1.0 1.5 Capper City 918 925 923 921 Overcharge safety ^* 1C 0/3 0/3 0/3 0/3 2C 0/3 0/3 0/3 0/3 High temperature swelling (%) 9 8 7 7 Overcharge safety: Performs three cells each at 1C- and 2C-current to indicate the number of cells that did not produce smoke and fire (safe)

From Table 2, it can be seen that the high temperature swelling degree is lowered by adding propane sultone.

Example: Change of battery characteristics according to the amount of propane sultone added (biphenyl 6% by weight)

The amount of propane sultone (Aldrich) was changed to 0, 0.5, 1.0 and 1.5 g while using biphenyl in an amount of 6 g to prepare an electrolyte precursor solution in the same manner as in Reference Example 1, and then prepared electrolyte precursor solution was prepared. A lithium secondary battery was prepared in the same manner as in Reference Example 1 above.

For manufactured cells, using Mako test equipment, the capacity (mAh, 225 mAh discharge basis), the high rate characteristic (%, 2C discharge basis), and the lifetime characteristic (%, 150 cycles) were determined using a power supply (Hewlett-Packard). The overcharge (12V) safety (currents of 1 C-mA and 2 C-mA) was measured at swelling degree (%) after 4 hours at 90 ° C., and the results are shown in Table 3 below.

Propane sultone addition amount (g) 0 0.5 1.0 1.5 Capper City 916 929 924 907 Overcharge safety ^* 1C 3/3 3/3 3/3 3/3 2C 3/3 3/3 3/3 3/3 High temperature swelling (%) 30 10 8 11 High rate characteristic (%) 96.5 96.8 96.9 95.8 Life Characteristics (%) 91.8 92.6 91.9 92.2 Overcharge safety: Performs three cells each at 1C- and 2C-current to indicate the number of cells that did not produce smoke and fire (safe)

From Table 3, when using a nitrogen-containing compound and biphenyl and propane sultone according to the present invention, not only can provide a battery excellent in capacity, overcharge safety, high rate characteristics and life characteristics, but also the degree of high temperature swelling of the battery. It can be seen that can be maintained at the level of 10% that is normally required. On the other hand, when propane sultone is not added, it can be seen that the high temperature swelling degree is excessively increased to 30%.

 The electrolyte composition of the present invention can provide high overcharge safety and low low-temperature swelling characteristics, so that the lithium secondary battery prepared using the same shows excellent safety during overcharging as well as low swelling characteristics at high temperatures.

Claims (13)

Electrolyte composition comprising a lithium salt and an organic solvent as main components and comprising, as an additive, a nitrogen-containing compound, biphenyl and propane sultone at 0.1 to 5% by weight, 4 to 10% by weight and 0.05 to 1.5% by weight, respectively, based on the total amount of the composition. . delete The method of claim 1, 5 to 8 wt% and 0.05 to 1.0 wt% of biphenyl and propane sultone, respectively. The method of claim 1, A composition characterized in that the nitrogen-containing compound is a primary, secondary or tertiary amine, or a polymer, copolymer or oligomer thereof. The method of claim 4, wherein Wherein the primary, secondary or tertiary amine is a compound selected from at least one of six-membered aromatic heterocycles, five-membered fused aromatic heterocycles, and aromatic or non-aromatic secondary or tertiary amines. The method of claim 5, Of compounds wherein the primary, secondary or tertiary amine contains pyridine, pyridazine, pyrimidine, pyrazine, triazine, triazole, thiazole, thiadiazole, and at least one nitrogen atom and at least five carbon atoms At least one compound selected. The method of claim 1, The composition further comprises from 0.02 to 1.5% by weight of halogen- or epoxy-containing compound, based on the total amount of the composition. delete The method of claim 1, Lithium salt is selected from LiPF ₆ , LiAsF ₆ , LiClO ₄ , LiN (CF ₃ SO ₂ ) ₂ , LiBF ₄ , LiCF ₃ SO ₃ and LiSbF ₆ , characterized in that contained in a concentration of 0.5 to 2.0M in an organic solvent Composition. The electrolyte composition according to any one of claims 1, 3 to 7, and 9 is poured into a battery container containing a negative electrode, a positive electrode, and a separator, and the container is sealed and heated to 30 to 130 ° C. to prepare the electrolyte composition. A method for producing a lithium secondary battery, comprising gelling. delete A lithium secondary battery, comprising a negative electrode, a positive electrode, and a separator, produced by the method of claim 10, wherein both electrodes are filled with the composition of any one of claims 1, 3-7, and 9. The method of claim 12, A lithium secondary battery, wherein both electrodes are filled with a gel polymer electrolyte obtained by gelling the composition of any one of claims 1, 3-7, and 9.