KR100362282B1 - A composition for anodic-active materials and lithium secondary battery manufactured using the same - Google Patents

Abstract

The present invention relates to an anode active material composition and a lithium secondary battery, and provides an anode active material composition and a lithium secondary battery prepared using the anode active material, a conductive agent, a binder, a solvent and an inorganic acid. According to the present invention, by producing an anode with an anode active material composition further comprising an inorganic acid, the anode becomes acidic at the time of charging, thereby suppressing generation of fluoride gas, and as a result, side reactions due to hydrogen fluoride gas are effectively suppressed, thereby irreversible battery. It is possible to effectively suppress the internal pressure rise of the battery while reducing the reaction.

Description

A composition for anodic-active materials and lithium secondary battery manufactured using the same

The present invention relates to an anode active material composition and a lithium secondary battery manufactured by using the same. More particularly, the generation of hydrogen fluoride is suppressed to effectively suppress the internal pressure increase of the battery while reducing the irreversible reaction of the battery. It relates to a lithium secondary battery.

The lithium secondary battery includes a cathode and an anode, a separator inserted between the cathode and the anode, an organic electrolyte composed of a lithium salt and an organic solvent.

The cathode and anode are made by coating and drying the electrode active material composition on top of each current collector. In this case, the electrode active material composition includes a cathode active material such as a lithium-containing metal oxide or the like, an anode active material such as a lithium alloy or a carbon material, a conductive agent, a binder, and a solvent, among which a polyvinylidene fluoride, vinylidene fluoride It is common to use fluorine-containing compounds such as a lide-hexafluoropropylene copolymer and the like. And a lithium salt of LiPF ₆ , LiBF ₄ , LiCF ₃ SO _3, or the like, and a fluorine-containing lithium compound as the lithium salt of the organic electrolyte, and the separator forming material is a polyvinylidene fluoride material used as a binder of an electrode. Vinylidene fluoride-hexafluoropropylene copolymer and the like.

As described above, when the fluorine-containing compound is used in the preparation of the electrode, the separator, and the electrolyte, dehydrofluorination reaction occurs during charging or discharging of the battery, thereby generating hydrogen fluoride. Taking the polyvinylidene fluoride among the fluorine-containing compounds as an example, the mechanism of hydrogen fluoride generation in the electrode, the separator and the electrolyte is as follows.

In the case of the electrode and the separator, in the head-to-tail repeating structure, such as-(CH ₂ -CF ₂ )-(CH ₂ -CF ₂ )-, hydrogen of the hydrocarbon has an electrically equivalent structure. With inverted bonds, such as (CH ₂ -CF ₂ )-(CF ₂ -CH ₂ )-(CH ₂ -CF ₂ )-, ie head to head or tail to tail bonds Hydrogen in the sector is hydrogen fluoride is generated by increasing the acidity of the fluorine having a high electronegativity associated with it in the vicinity. The generation of hydrogen fluoride occurs mainly at the anode, which is electrically basic during charging.

When hydrogen fluoride is produced in accordance with the above-described mechanism, the hydrogen fluoride initiates a reaction for decomposing carbonate compounds such as ethylene carbonate and diethyl carbonate, which are organic solvent components of the electrolyte solution. As such, when the electrolyte is decomposed, the charging and discharging process is repeated to generate gases such as carbon dioxide, methane gas, and ethylene gas, and the gas increases the internal pressure of the battery, causing the battery to explode.

On the other hand, the battery packaging material generally includes a poly (ethylene acrylic acid: EAA) layer, which is a heat-adhesive material layer on the innermost layer with respect to the battery body, and on top of that, a polyethylene layer (polyethylene: PE), an EAA layer and an aluminum layer are sequentially stacked, and a pouch having a structure in which a nylon layer is laminated as the outermost layer is used. There is a problem that it is no longer possible to use the battery due to the pouch swelling during use due to no device or safety valve.

In order to solve the above problems, a method of removing a gas present in the pouch under vacuum conditions after the first chemical conversion of the battery has been proposed. However, even if this method is applied, it is practically difficult to completely solve the phenomenon of pouch swelling due to hydrogen fluoride gas generated from the binder of the electrode, the polymer resin of the separator and / or the lithium salt of the electrolyte component.

The technical problem to be achieved by the present invention is to provide an anode active material composition that can be acidic to the anode during charging in order to solve the above problems.

Another object of the present invention is to provide a lithium secondary battery prepared by using the anode active material composition is suppressed the generation of hydrogen fluoride.

In the present invention to achieve the above technical problem,

Provided is an anode active material composition comprising an anode active material, a conductive agent, a binder, a solvent, and an inorganic acid.

In the anode active material composition according to the present invention, the inorganic acid is preferably contained in more than 0% by weight, 10% by weight or less based on the solid content of the anode active material composition, and the inorganic acid is preferably silicic acid.

In the anode active material composition according to the present invention, the silicic acid is ortho silicic acid (H ₄ SiO ₄ ). Group consisting of metasilicate (H ₂ SiO ₃ ), meta-disilicate (H ₂ Si ₂ O ₅ ), meta-trisilicate (H ₂ Si ₃ O ₈ ) and meta tetrasilicate (H ₂ Si ₄ O ₁₁ ) It is preferably one or more selected from.

In order to achieve the above technical problem, the present invention is an anode active material layer formed on the current collector; A cathode having a cathode active material layer formed on a current collector; A separator inserted between both electrodes; And in the lithium secondary battery comprising an organic electrolyte consisting of an organic solvent and a lithium salt,

The anode active material layer is formed by the anode active material composition as described above provides a lithium secondary battery.

The present invention forms an anode active material layer by further adding an inorganic acid to a conventional anode active material composition composed of an anode active material, a conductive agent, a binder, and a solvent to impart acidity to an electrically basic anode during charging, thereby preventing decomposition of the electrolyte solution. It has the advantage of suppressing the generation of hydrogen fluoride acting as an initiator.

Hereinafter, an anode active material composition and a method of manufacturing a lithium secondary battery according to the present invention will be described in detail.

First, referring to the method for preparing the anode active material composition, the electrode binder is dissolved in a solvent, and then, an inorganic acid is added thereto, followed by vigorous stirring for a predetermined time. Here, as the electrode binder, a fluorine-containing polymer such as polyvinylidene fluoride or vinylidene fluoride-hexafluoropropylene copolymer is used, and a solvent is commonly used for the purpose in the art to which the present invention belongs. If that's all you can use. N-methylpyrrolidone (NMP), acetone, dimethylformamide. Dimethyl cellulose, methyl ethyl ketone, etc. are mentioned.

The inorganic acid is preferably contained in more than 0% by weight, 10% by weight or less based on the solid content of the anode active material composition. Herein, the inorganic acid may be included only a very small amount to allow the anode to be acidic when charged, but when the content exceeds 10% by weight, the amount of the active material is relatively decreased, causing a problem in battery performance. do.

In addition, silicic acid may be used as the inorganic acid, The silicic acid is ortho silicic acid (H₄SiO₄). Metasilicate (H₂SiO₃), Meta-dibasic silicate (H₂Si₂O₅), Meta-trisilicate (H₂Si₃O₈) And metaquatoxysilicate (H₂Si₄O₁₁It is preferably at least one selected from the group consisting of

Then, the resultant is left for a predetermined time, and then filtered through a filter paper to remove insoluble matters. The obtained filtrate is added to the mixture of the anode active material and the conductive agent, and then sufficiently mixed to prepare the anode active material composition. The anode active material and the conductive agent may be used without particular limitation as long as it is commonly used in the art to which the present invention pertains. For example, the anode active material may be carbon, graphite, etc., and the conductive agent may be carbon black or acetylene black. And the like can be used.

In some cases, a plasticizer may be further added to the mixture of the anode active material and the conductive agent described above. Here, as the plasticizer, organic solvent components of an electrolyte such as dibutyl phthalate (DBP), ethylene carbonate and diethyl carbonate may be used.

Next, a method of manufacturing a lithium secondary battery according to the present invention will be described.

The manufacturing steps of the lithium secondary battery according to the present invention may be divided into an anode manufacturing step, a cathode manufacturing step, a separator manufacturing step, a battery assembly manufacturing step, and an organic electrolyte impregnation step, wherein the anode comprises the anode active material composition prepared as described above. It is prepared by coating and drying on a copper current collector to form an anode active material layer. Impregnation of the cathode, the separator, the battery assembly, and the organic electrolyte solution will be briefly described since it follows a conventional method well known in the art.

Looking at the manufacturing method of the cathode, the binder is dissolved in an organic solvent, and the above solution is added to the mixture obtained by dry mixing the cathode active material and the conductive agent separately and uniformly mixed to prepare an anode active material composition, which is then It is prepared by applying and then drying. In some cases, a plasticizer may be further added to the mixture of the cathode active material and the conductive agent.

The conductive agent, the organic solvent, and the binder may be the same as those used in the preparation of the above-described anode active material composition, and as the cathode active material, LiMn ₂ O ₄ , LiNiO ₂ commonly used in the art to which the present invention pertains. LiCoO ₂ and the like may be used, and an expanded metal, a punched metal, and a foil made of aluminum may be used as the cathode current collector.

Next, looking at the method for producing a separator, a binder composition, an inorganic filler, and a solvent are mixed to prepare a separator composition. In some cases, a plasticizer may be further added to the composition. Herein, the binder, the inorganic filler and the solvent are not particularly limited as long as they are materials commonly used in the technical field to which the present invention belongs. For example, the binder may be vinyl chloride, hexafluoropropylene, perfluoroalkoxy, hexa Homopolymers or copolymers of monomers selected from fluoroisobutene and acrylonitrile, or mixtures thereof may be used. As inorganic fillers, silica and alumina may be used, and acetone and tetrahydrofuran may be used as a solvent. .

The separator composition is directly coated and dried on the electrode to obtain a separator film. Alternatively, the separator composition may be cast on a separate support and hot-air dried, and then peeled off from the support to obtain a separator film. In this case, a glass substrate, a polyethylene terephthalate (PET) electrode plate, a mylar film, or the like is used as the support.

Electrodes and separators obtained according to the above-described process are laminated and laminated in the order of cathode / separator / anode / separator / cathode to form a bicell structure. Subsequently, when a plasticizer is added, when the plasticizer needs to be extracted and removed, an organic solvent such as ether or methanol is used to remove the plasticizer from the battery structure thus obtained.

An aluminum tab and a copper tab are respectively welded to the resultant, and then the lithium secondary battery according to the present invention is completed by impregnating an electrolyte solution.

The electrolyte is composed of a lithium salt and an organic solvent, all of which can be used as long as it is commonly used in lithium secondary batteries. The organic solvent is propylene carbonate (PC), ethylene carbonate, γ-butyrolactone, 1,3-dioxolane, dimethoxyethane, dimethyl carbonate, methylethyl carbonate and diethyl carbonate, tetrahydrofuran, dimethyl sulfoxide And at least one solvent selected from polyethylene glycol dimethyl ether. And the content of the solvent is the usual level used in the lithium secondary battery. Lithium salts include lithium perchlorate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ) and lithium bistrifluoromethanesulfonyl At least one ionic lithium salt selected from the group consisting of amides (LiN (CF ₃ SO ₂ ) ₂ ) is used and its content is at the usual level used in lithium secondary batteries.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited only to the following Examples.

Example 1

8 g of polyvinylidene fluoride was dissolved in 92 g of NMP, and then 0.2 g of ortho-silicate (H ₄ SiO ₄ ) was added to the mixture and stirred vigorously for 2 to 4 hours, and then stirred slowly in a closed container for 10 hours. To prepare a binder solution.

Subsequently, the binder solution was filtered to remove insoluble matters, and then the filtrate was added to a mixture of 65 g of mesocarbon fiber (MCF) as an anode active material, 8 g of conductive carbon black, and 27 g of dibutylphthalate as a plasticizer, followed by sufficient mixing. An active material composition was formed.

The anode active material composition was coated and dried on a copper expanded metal to make an anode electrode plate.

Separately, the binder solution prepared during the production of the anode electrode plate was filtered to remove the insoluble material, and the obtained filtrate was then filtered to remove the insoluble material, and then the filtrate was used as a cathode active material 65 g of LiCoO ₂ and the conductive agent. 10 g of carbon black and 25 g of dibutyl phthalate as a plasticizer were added to the mixture, and then sufficiently mixed to prepare a cathode active material composition.

The cathode active material composition was coated and dried on a pretreated aluminum expanded metal to form a cathode electrode plate.

Separately, the binder solution in which 8 g of vinylidene fluoride-hexafluoropropylene copolymer was dissolved in 92 g of NMP was filtered to remove the insoluble material, and then the filtrate was added to a mixture of 34 g of silica and 40 g of dibutylphthalate and mixed sufficiently. The separator composition was formed. The separator composition was cast and dried on a polyethylene terephthalate (PET) electrode plate, and then peeled from the PET electrode plate to obtain a separator film.

The bipolar structure was formed by laminating the cathode electrode plate, the anode electrode plate, and the separator obtained according to the above procedure in the order of cathode / separator / anode / separator / cathode. Subsequently, the plasticizer was extracted and removed from the battery structure of the bicell structure thus obtained using ether.

An aluminum tab and a copper tab were welded to the resultant, and then a lithium secondary battery was formed by impregnating an electrolyte solution (Merck, 1.5M LiPF ₆ in ethylene carbonate: dimethyl carbonate: diethyl carbonate = 3: 3: 4) for 3 hours. Completed.

Example 2

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the amount of ortho-silicate (H ₄ SiO ₄ ) was changed to 0.5 g when the anode active material composition was prepared.

Example 3

A lithium secondary battery was manufactured in the same manner as in Example 1, except that metasilicate (H ₂ SiO ₃ ) was used instead of ortho silicic acid (H ₄ SiO ₄ ) to prepare the anode active material composition.

Example 4

A lithium secondary battery was manufactured in the same manner as in Example 1, except that meta-disilicate (H ₂ Si ₂ O ₅ ) was used instead of ortho silicic acid (H ₄ SiO ₄ ) to prepare the anode active material composition.

Example 5

Instead of ortho-silicate (H ₄ SiO ₄ ) in the preparation of the anode active material composition. A lithium secondary battery was manufactured in the same manner except that metasilic acid (H ₂ SiO ₃ ) and metatrititric acid (H ₂ Si ₃ O ₈ ) were used.

Example 6

A lithium secondary battery was manufactured in the same manner as in Example 1, except that meta tetrasilic acid (H ₂ Si ₄ O ₁₁ ) was used instead of ortho silicic acid (H ₄ SiO ₄ ) to prepare the anode active material composition.

Comparative Example 1

A lithium secondary battery was manufactured in the same manner as in Example 1, except that ortho-silicate (H ₄ SiO ₄ ) was not added at the time of preparing the anode active material composition.

In the lithium secondary battery prepared according to Example 1-6 and Comparative Example 1, the degassing process was carried out under vacuum conditions after the first chemical conversion. Then, the phenomenon of pouch swelling due to HF gas generation was investigated.

As a result, in the lithium secondary battery according to Example 1-6, unlike the case of the comparative example, the increase in the internal pressure of the battery was suppressed, so that the pouch was almost not swollen.

According to the present invention, by producing an anode with an anode active material composition further comprising an inorganic acid, the anode becomes acidic during charging, thereby suppressing generation of fluoride gas, and as a result, effectively inhibiting side reactions due to hydrogen fluoride gas, thereby effectively reversing the battery. It is possible to effectively suppress the internal pressure rise of the battery while reducing the reaction.

Although described with reference to the embodiment of the present invention, this is merely exemplary, those skilled in the art will understand that various modifications and equivalent other embodiments are possible from this. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

Claims (6)

An anode active material composition comprising an anode active material, a conductive agent, a binder, a solvent and an inorganic acid. The anode active material composition of claim 1, wherein the inorganic acid is included in an amount of more than 0 wt% and 10 wt% or less based on the solid content of the anode active material composition. The anode active material composition according to claim 1, wherein the inorganic acid is silicic acid. The method of claim 3, wherein the silicic acid is ortho silicate (H ₄ SiO ₄ ). Group consisting of metasilicate (H ₂ SiO ₃ ), meta-disilicate (H ₂ Si ₂ O ₅ ), meta-trisilicate (H ₂ Si ₃ O ₈ ) and meta tetrasilicate (H ₂ Si ₄ O ₁₁ ) An anode active material composition, characterized in that at least one selected from. An anode having an anode active material layer formed on a current collector, wherein the anode active material layer is formed of the anode active material composition according to any one of claims 1 to 4. An anode having an anode active material layer formed on a current collector; A cathode having a cathode active material layer formed on a current collector; A separator inserted between both electrodes; And In a lithium secondary battery comprising an organic electrolyte composed of an organic solvent and a lithium salt, The anode is a lithium secondary battery, characterized in that the anode according to claim 5.