JP6412689B2 - Lithium ion secondary battery negative electrode water based slurry (slurry), lithium ion secondary battery negative electrode active material layer, and lithium ion secondary battery - Google Patents

Description

  The present invention relates to an aqueous slurry for a negative electrode of a lithium ion secondary battery, a negative electrode active material layer for a lithium ion secondary battery, and a lithium ion secondary battery.

  Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries disclosed in Patent Document 1 are widely used as power sources for portable devices such as notebook PCs and mobile phones. Although it is used, it has high expectations for its development because of its high voltage and high capacity. As a negative electrode material (negative electrode active material) of such a non-aqueous electrolyte secondary battery, in addition to lithium metal and lithium alloy, a graphitic carbon material such as natural graphite or artificial graphite that can desorb and insert Li ions. Etc. are used.

  Recently, a further increase in capacity has been desired for batteries for portable devices that have become smaller and more multifunctional, and in response to this, carbon-based active materials (for example, graphitic carbon materials) that are widely used as negative electrode active materials. ) New negative electrode active materials have been investigated. As new negative electrode active materials, silicon (Si) -based active materials and tin (Sn) -based active materials have attracted attention. At present, any of the above-mentioned new negative electrode materials has a charge / discharge cycle (cycle) life of graphitic carbon. Inferior to the material.

  The carbon-based active material has a layered structure, and Li is inserted / extracted between the layers at the time of charge / discharge, so that expansion / contraction at the time of insertion / extraction of Li is small. In contrast, the new negative electrode material has a more complicated structure than the carbon-based active material, and has a large amount of Li insertion / desorption per unit mass during charge / discharge. For this reason, the new negative electrode material has a large expansion / contraction associated with charge / discharge, and as a result, in a charge / discharge cycle in which expansion / contraction is repeated, the structure of the electrode is broken and the electronic conductivity is lowered. For this reason, it is thought that charging / discharging cycle life worsens compared with a graphitic carbon material.

  On the other hand, in recent production of negative electrodes for non-aqueous electrolyte secondary batteries in recent years, production of negative electrodes using aqueous slurry (Slurry) has been required for reasons such as environmental considerations during production and cost reduction. Here, the aqueous slurry is obtained by dispersing a negative electrode mixture containing a negative electrode active material and an aqueous binder in water. A negative electrode is produced by applying an aqueous slurry to a current collector and drying. A negative electrode produced using an aqueous slurry is also referred to as an aqueous negative electrode.

JP 2007-52940 A

  However, the conventional aqueous binder cannot sufficiently follow the expansion and contraction of the above-described new negative electrode material. As a result, the cycle life of the lithium ion secondary battery using the new negative electrode material as the negative electrode active material of the water-based negative electrode was not sufficient.

  Accordingly, the present invention has been made in view of the above problems, and an object of the present invention is to provide an aqueous slurry for a negative electrode of a lithium ion secondary battery that can improve the cycle life of the lithium ion secondary battery. It is providing the negative electrode active material for lithium ion secondary batteries, and a lithium ion secondary battery.

  In order to solve the above problems, according to an aspect of the present invention, a carbon-based active material, a metal-based active material including at least one of a silicon-based active material and a tin-based active material, and acrylic acid (Acrylic acid) Alternatively, an aqueous slurry for a negative electrode of a lithium ion secondary battery including a salt of an acrylic acid derivative and a copolymer of acrylonitrile or an acrylonitrile derivative is provided.

  The copolymer according to this viewpoint has high flexibility and binding power. Therefore, even when the negative electrode active material layer produced using the aqueous slurry according to this viewpoint is repeatedly charged and discharged, the copolymer can follow the expansion and contraction of the silicon-based active material and the tin-based active material. Therefore, the copolymer can suppress dropping of the electrode layer due to expansion and contraction of the silicon-based active material and the tin-based active material. As a result, the cycle life is improved.

  Here, the acrylic acid derivative may contain methacrylic acid, and in this case, the cycle life is further improved.

  Further, the acrylonitrile derivative may contain methacrylonitrile, and in this case, the cycle life is further improved.

  The salt of acrylic acid or acrylic acid derivative is selected from the group consisting of lithium (Li) salt, sodium (Na) salt, ammonium salt, and amine salt of acrylic acid or acrylic acid derivative. Any one or more of them may be used, and in this case, the cycle life is further improved.

  Moreover, acrylonitrile or an acrylonitrile derivative may be contained in the copolymer at 10 to 50% by mass with respect to the total mass of the copolymer, and in this case, the cycle life is further improved.

  Further, it may contain a conductive assistant containing at least one selected from the group consisting of acetylene black, ketjenblack, and carbon nanotubes (CNT). In this case, the cycle life may be included. Is further improved.

  According to another aspect of the present invention, there is provided a negative electrode active material layer for a lithium ion secondary battery, which is produced using the above-described aqueous slurry for a lithium ion secondary battery negative electrode.

  By producing a lithium ion secondary battery using the negative electrode active material layer according to this viewpoint, the cycle life of the lithium ion secondary battery can be improved.

  According to another aspect of the present invention, there is provided a lithium ion secondary battery comprising the above negative electrode active material layer for a lithium ion secondary battery.

  The lithium ion secondary battery according to this viewpoint has improved cycle life.

  As described above, according to the present invention, the cycle life of the lithium ion secondary battery is improved.

It is a sectional side view which shows roughly the internal structure of a lithium ion secondary battery.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

(Configuration of lithium ion secondary battery)
First, based on FIG. 1, the structure of the lithium ion secondary battery 10 which concerns on this embodiment is demonstrated.

The lithium ion secondary battery 10 includes a positive electrode 20, a negative electrode 30, and a separator layer 40. The charge ultimate voltage (redox potential) of the lithium ion secondary battery 10 is, for example, 4.3 V (vs. Li ^/ Li ⁺ ) or more and 5.0 V or less, particularly 4.5 V or more and 5.0 V or less. The form of the lithium ion secondary battery 10 is not particularly limited. That is, the lithium ion secondary battery 10 may be any one of a cylindrical shape, a square shape, a laminate shape, a button shape, and the like.

  The positive electrode 20 includes a current collector 21 and a positive electrode active material layer 22. The current collector 21 may be any conductor as long as it is a conductor, and is made of, for example, aluminum, stainless steel, nickel-coated steel, or the like.

The positive electrode active material layer 22 includes at least a positive electrode active material, and may further include a conductive agent and a binder. The positive electrode active material is, for example, a solid solution oxide containing lithium, but is not particularly limited as long as the material can electrochemically occlude and release lithium ions. The solid solution oxide is, for example, Li _a Mn _x Co _y Ni _z O ₂ (1.150 ≦ a ≦ 1.430, 0.45 ≦ x ≦ 0.6, 0.10 ≦ y ≦ 0.15,. 20 ≦ z ≦ 0.28), LiMn _x Co _y Ni _z O ₂ (0.3 ≦ x ≦ 0.85, 0.10 ≦ y ≦ 0.3, 0.10 ≦ z ≦ 0.3), LiMn _1.5 Ni _0.5 O ₄ .

  The conductive agent is, for example, carbon black such as ketjen black or acetylene black, natural graphite, artificial graphite, or the like, but is not particularly limited as long as it is intended to increase the conductivity of the positive electrode.

  Examples of the binder include polyvinylidene fluoride, ethylene-propylene-diene terpolymer, styrene-butadiene rubber, acrylonitrile-butadiene rubber, and acrylonitrile-butadiene rubber. (Fluororubber), polyvinyl acetate, polymethylmethacrylate, polyethylene, polynitroethylene, nitrocellulose, and the like, and a positive electrode active material and a conductive agent are bound on the current collector 21. The There is no particular limitation as long as it can be applied.

  The positive electrode active material layer 22 is produced, for example, by the following manufacturing method. That is, first, a positive electrode mixture is prepared by dry-mixing a positive electrode active material, a conductive agent, and a binder. Next, the positive electrode mixture is dispersed in a suitable organic solvent to form a positive electrode mixture slurry (slurry). The positive electrode mixture slurry is applied onto the current collector 21, dried, and rolled to produce a positive electrode active slurry. A material layer is formed.

  The negative electrode 30 includes a current collector 31 and a negative electrode active material layer 32. The current collector 31 may be any conductor as long as it is a conductor, for example, aluminum, stainless steel, nickel-plated steel, or the like.

  The negative electrode active material layer 32 includes a negative electrode active material and a binder. The negative electrode active material layer 32 may further contain a conductive additive. The negative electrode active material includes a metal-based active material and a carbon-based active material. The metal-based active material includes at least one of a silicon-based active material and a tin-based active material.

The silicon-based active material is a material that contains silicon (atom) and can electrochemically occlude and release lithium ions. Examples of the silicon active material include fine particles of simple silicon, fine particles of silicon compound, and the like. A silicon compound will not be restrict | limited especially if it is used as a negative electrode active material of a lithium ion secondary battery. Examples of the silicon compound include silicon oxide and silicon alloy. The silicon oxide is represented by, for example, _{SiO x (0 <x ≦ 2} ). Examples of silicon alloys include Si—Ti—Ni alloys and Si—Al—Fe alloys.

The tin-based active material is a substance that contains tin (atom) and can electrochemically occlude and release lithium ions. Examples of the tin-based active material include fine particles of a simple substance of tin and fine particles of a tin compound. A tin compound will not be restrict | limited especially if used as a negative electrode active material of a lithium ion secondary battery. Examples of tin compounds include tin oxide and tin alloys. Examples of tin oxide include SnO _{2 and the} like. Examples of tin alloys include Sn—Ni alloys.

  On the other hand, the carbon-based active material is a material that contains carbon (atom) and can electrochemically occlude and release lithium ions. Examples of the carbon-based active material include graphite active materials (artificial graphite, natural graphite, a mixture of artificial graphite and natural graphite, natural graphite coated with artificial graphite, and the like).

  The binder is a so-called aqueous binder. The binder includes a copolymer of acrylic acid or a salt of an acrylic acid derivative and acrylonitrile or an acrylonitrile derivative. Here, the acrylic acid derivative includes methacrylic acid, and the acrylonitrile derivative includes methacrylonitrile. Since the copolymer has high flexibility and binding force, it can follow the expansion and contraction of the silicon-based active material and the tin-based active material, and maintain the connection between the silicon-based active material and the tin-based active material. be able to. As a result, the cycle life of the lithium ion secondary battery 10 is improved.

  Moreover, it is preferable that the salt of acrylic acid or an acrylic acid derivative is at least one selected from the group consisting of lithium salt, sodium salt, ammonium salt, and amine salt of acrylic acid or acrylic acid derivative.

  Moreover, it is preferable that acrylonitrile or an acrylonitrile derivative is contained in a copolymer at 10-50 mass% with respect to the total mass of a copolymer, and it is more preferable that it is contained in a copolymer at 20-30 mass%. When the content of acrylonitrile or an acrylonitrile derivative is a value within such a range, the peel strength of the negative electrode active material layer is particularly improved, and as a result, the cycle life can be improved.

  Further, the negative electrode active material layer 32 includes a conductive additive including at least one selected from the group consisting of acetylene black, ketjen black, and carbon nanotubes.

  The negative electrode active material layer 32 is produced by the following manufacturing method, for example. That is, first, a negative electrode mixture is prepared by dry-mixing a negative electrode active material, a binder, and a conductive additive. Next, the negative electrode mixture is dispersed in water to form a negative electrode mixture slurry (aqueous slurry), and this negative electrode mixture slurry is applied onto the current collector 31, dried and rolled to form the negative electrode An active material layer 32 is formed.

  The separator layer 40 includes a separator and an electrolytic solution. The separator is not particularly limited, and any separator can be used as long as it is used as a separator for a lithium ion secondary battery. As the separator, it is preferable to use a porous film or a non-woven fabric exhibiting excellent high rate discharge performance alone or in combination. Examples of the resin constituting the separator include polyolefin resins typified by polyethylene, polypropylene, etc., polyethylene terephthalate, polybutylene terephthalate, and the like represented by polybutylene terephthalate. (Polyester) resin, PVDF, vinylidene fluoride (VDF) -hexafluoropropylene (HFP) copolymer, vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene (tetrafluoroethylene) ) Copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, vinylidene fluoride-hexafluoroacetone copolymer, vinylidene fluoride- Ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene (tetrafluoroethylene-tetrafluoroethylene-tetrafluoroethylene-tetrafluoroethylene-tetrafluoroethylene-tetrafluoroethylene-tetrafluoroethylene-tetrafluoroethylene- (tetrafluoroethylene-tetrafluoroethylene) hexafluoropropylene copolymer, vinylidene fluoride-ethylene (ethy) ene) - can be exemplified tetrafluoroethylene (tetrafluoroethylene) copolymers.

  As the non-aqueous electrolyte, the same non-aqueous electrolyte as conventionally used for lithium secondary batteries can be used without any particular limitation. The nonaqueous electrolytic solution has a composition in which an electrolyte salt is contained in a nonaqueous solvent. Examples of the non-aqueous solvent include propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, vinylene carbonate (vinyl carbonate), and the like. ); Cyclic esters such as γ-butyrolactone and γ-valerolactone; dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate chain carbonates such as ethyl carbonate; chain esters such as methyl formate, methyl acetate, butyric acid methyl; tetrahydrofuran (tetrahydrofuran) or derivatives thereof; 1,3- Ethers such as dioxane, 1,4-dioxane, 1,2-dimethoxyethane, 1,4-dibutoxyethane, methyl diglyme; Nitriles such as acetonitrile and benzonitrile e) class; dioxolane or a derivative thereof; ethylene sulfide, sulfolane, sultone, or a derivative thereof alone or a mixture of two or more thereof, etc. It is not limited to.

Examples of the electrolyte salt include LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiPF _6-x (C _n F _{2n + 1} ) _x [where 1 <x <6, n = 1or2], LiSCN, LiBr, Inorganic ions containing one kind of lithium (Li), sodium (Na) or potassium (K) such as LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, NaBr, KClO ₄ , KSCN Salt, LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) _{3, LiC (C 2 F 5} SO 2) 3, (CH 3) 4 NBF 4, (CH 3) 4 NBr, (C 2 H 5) 4 NClO 4, _{C 2 H 5) 4 NI,} (C 3 H 7) 4 NBr, (n-C 4 H 9) 4 NClO 4, (n-C 4 H 9) 4 NI, (C 2 H 5) 4 N-maleate , (C ₂ H ₅ ) ₄ N-benzoate, (C ₂ H ₅ ) ₄ N-phtalate, lithium stearyl sulfonate (octyl sulfonic acid), lithium dodecylbenzene sulfonate (lithium dodecylbenzene sulfonate) organic ion salts such as dodecyl benzene sulphonic acid) and the like, and these ionic compounds can be used alone or in admixture of two or more. The concentration of the electrolyte salt may be the same as that of the nonaqueous electrolytic solution used in the conventional lithium secondary battery, and is not particularly limited. In this embodiment, a nonaqueous electrolytic solution containing an appropriate lithium compound (electrolyte salt) at a concentration of about 0.8 to 1.5 mol / L can be used.

  Various additives may be added to the nonaqueous electrolytic solution. Examples of such additives include a negative electrode action additive, a positive electrode action additive, an ester additive, a carbonate ester additive, a sulfate ester additive, a phosphate ester additive, and a borate ester additive. Additive, acid anhydride additive, electrolyte additive and the like. Any one of these may be added to the non-aqueous electrolyte, or a plurality of types of additives may be added to the non-aqueous electrolyte.

(Method for producing lithium ion secondary battery)
Next, a method for manufacturing the lithium ion secondary battery 10 will be described. The positive electrode 20 is produced as follows. First, a slurry is formed by dispersing a mixture of a positive electrode active material, a conductive agent, and a binder in the above ratio in a solvent (for example, N-methyl-2-pyrrolidone). Next, the positive electrode active material layer 22 is formed by forming (for example, coating) the slurry on the current collector 21 and drying the slurry. The coating method is not particularly limited. Examples of the coating method include a knife coater method and a gravure coater method. The following coating steps are also performed by the same method. Next, the positive electrode active material layer 22 is pressed by a press machine so as to have a density within the above range. Thereby, the positive electrode 20 is produced.

  The negative electrode 30 is also produced in the same manner as the positive electrode 20. First, a negative electrode mixture slurry is formed by dispersing a negative electrode mixture in which a negative electrode active material, a binder, and a conductive additive are mixed in water. Next, the negative electrode mixture slurry is formed (for example, coated) on the current collector 31 and dried to form the negative electrode active material layer 32. Next, the negative electrode active material layer 32 is rolled by a press machine. Thereby, the negative electrode 30 is produced.

  Next, an electrode structure is produced by sandwiching the separator between the positive electrode 20 and the negative electrode 30. Next, the electrode structure is processed into a desired shape (for example, a cylindrical shape, a square shape, a laminate shape, a button shape, etc.) and inserted into a container of the shape. Next, by injecting the electrolytic solution having the above composition into the container, each pore in the separator is impregnated with the electrolytic solution. Thereby, a lithium ion secondary battery is produced.

(Example 1: Silicon-based active material + copolymer binder)
(Synthesis Example 1)
In Synthesis Example 1, a copolymer binder of lithium acrylate / acrylonitrile = 70/30% by mass was synthesized.

  Specifically, 270 g of water was added into a 0.5 liter four-necked flask (Flash) equipped with a stirrer, a thermometer, a condenser, and a liquid feed pump. Then, the operation of reducing the internal pressure to 20 mmHg with an aspirator and returning the internal pressure to normal with nitrogen was repeated three times. The flask was then kept in a nitrogen atmosphere and heated to 60 ° C. in an oil bath while stirring the water. Thereafter, 0.12 g of ammonium persulfate was dissolved in 5 g of water to prepare an aqueous ammonium persulfate solution, and the aqueous ammonium persulfate solution was added to the flask. Immediately after the ammonium persulfate aqueous solution was added to the water in the flask, a mixture of 19.4 g of acrylic acid (manufactured by Wako Pure Chemical Industries, Ltd.) and 9.0 g of acrylonitrile (manufactured by Wako Pure Chemical Industries, Ltd.) was added dropwise over a period of 2 hours with a liquid feed pump. did.

  The aqueous solution in the flask was continuously stirred for 4 hours, and then the aqueous solution in the flask was heated to 80 ° C. The aqueous solution was further stirred for 2 hours. After the aqueous solution was cooled to room temperature, 11.3 g (1.0 equivalent to acrylic acid) of lithium hydroxide monohydrate (manufactured by Wako Pure Chemical Industries, Ltd.) was added and stirred until everything was completely dissolved. Thus, a copolymer of lithium acrylate / acrylonitrile = 70/30% by mass was synthesized.

  After the aqueous solution in the flask was cooled to room temperature, about 1 ml of the aqueous solution was weighed in an aluminum pan and dried on a hot plate heated to 160 ° C. for 15 minutes. Next, the mass of the residue was measured, and based on the measured value, the mass% of the residue (that is, the mass% of the non-volatile content) was calculated. As a result, the mass% of the non-volatile content was 9.98 mass% with respect to the total mass of the aqueous solution. The mass% of the non-volatile content is calculated by dividing the mass of the residue by the mass of the aqueous solution. In addition, size exclusion chromatography (SEC, converted to polyethylene glycol) was performed, and the weight average molecular weight of the organic acid was calculated based on the result. As a result, the weight average molecular weight of the copolymer binder of lithium acrylate / acrylonitrile = 70/30% by mass produced in Synthesis Example 1 was 56000.

(Synthesis Example 2)
In Synthesis Example 2, a copolymer binder of lithium acrylate / acrylonitrile = 50/50 mass% was synthesized. Specifically, the same treatment as in Synthesis Example 1 was performed except that 13.9 g of acrylic acid, 15 g of acrylonitrile, and 8.1 g of lithium lithium hydroxide monohydrate (1.0 equivalent to acrylic acid) were added. It was. The mass% of the nonvolatile content was 9.98% by mass. The weight average molecular weight of the copolymer binder was 57000.

(Synthesis Example 3)
In Synthesis Example 3, a copolymer binder of lithium acrylate / acrylonitrile = 80/20% by mass was synthesized. Specifically, the same treatment as in Synthesis Example 1 was performed except that 22.2 g of acrylic acid, 6 g of acrylonitrile, and 12.9 g of lithium lithium hydroxide monohydrate (1.0 equivalent to acrylic acid) were added. It was. The mass% of non-volatile content was 9.97 mass%. The weight average molecular weight of the copolymer binder was 55000.

(Synthesis Example 4)
In Synthesis Example 4, a copolymer binder of lithium acrylate / acrylonitrile = 90/10% by mass was synthesized. Specifically, the same treatment as in Synthesis Example 1 was performed except that 24.9 g of acrylic acid, 3 g of acrylonitrile, and 14.5 g of lithium lithium hydroxide monohydrate (1.0 equivalent to acrylic acid) were added. It was. The mass% of the nonvolatile content was 9.98% by mass. The weight average molecular weight of the copolymer binder was 53000.

(Synthesis Example 5)
In Synthesis Example 5, a copolymer binder of lithium acrylate / methacrylonitrile = 70/30 mass% was synthesized. Specifically, the same treatment as in Synthesis Example 1 was performed except that 11.4 g of methacrylonitrile was added instead of acrylonitrile. The mass% of the nonvolatile content was 10.57% by mass. The weight average molecular weight of the copolymer binder was 500,000.

(Synthesis Example 6)
In Synthesis Example 6, a copolymer binder of lithium methacrylate / acrylonitrile = 70/30% by mass was synthesized. Specifically, the procedure was the same as in Synthesis Example 1 except that 23.2 g of methacrylic acid was added instead of acrylic acid. The mass% of the non-volatile content was 11.05 mass%. The weight average molecular weight of the copolymer binder was 53000.

(Synthesis Example 7)
In Synthesis Example 7, a copolymer binder of lithium methacrylate / methacrylonitrile = 70/30% by mass was synthesized. Specifically, the same treatment as in Synthesis Example 1 was performed except that 23.2 g of methacrylic acid instead of acrylic acid and 11.4 g of acrylonitrile were added. The mass% of the nonvolatile content was 11.61% by mass. The weight average molecular weight of the copolymer binder was 53000.

(Synthesis Example 8)
In Synthesis Example 8, a copolymer binder of ammonium acrylate / acrylonitrile = 70/30% by mass was synthesized. Specifically, all was the same as in Synthesis Example 1 except that 15.3 g of 30% aqueous ammonia (1.0 equivalent to acrylic acid) was added instead of lithium hydroxide monohydrate (manufactured by Wako Pure Chemical Industries, Ltd.). Was processed. The mass% of the nonvolatile content was 10.34% by mass. The weight average molecular weight of the copolymer binder was 560000.

(Synthesis Example 9)
In Synthesis Example 9, a copolymer binder of sodium acrylate / acrylonitrile = 70/30% by mass was synthesized. Specifically, the same as Synthesis Example 1 except that 10.8 g of sodium hydroxide (1.0 equivalent to acrylic acid) was added instead of lithium hydroxide monohydrate (manufactured by Wako Pure Chemical Industries, Ltd.). Processed. The mass% of the nonvolatile content was 9.98% by mass. The weight average molecular weight of the copolymer binder was 56000.

(Synthesis Example 10)
In Synthesis Example 10, a copolymer binder of triethylamine acrylate salt / acrylonitrile = 70/30% by mass was synthesized. Specifically, the same treatment as in Synthesis Example 1 was performed except that 27.2 g of triethylamine (1.0 equivalent to acrylic acid) was added instead of lithium hydroxide monohydrate (manufactured by Wako Pure Chemical Industries, Ltd.). went. The mass% of the non-volatile content was 16.90 mass%. The weight average molecular weight of the copolymer binder was 56000.

(Synthesis Example 11)
In Synthesis Example 11, a copolymer binder of triethanolamine acrylate salt / acrylonitrile = 70/30% by mass was synthesized. Specifically, the same as Synthesis Example 1 except that 40.2 g of triethanolamine (1.0 equivalent to acrylic acid) was added instead of lithium hydroxide monohydrate (manufactured by Wako Pure Chemical Industries, Ltd.). Processed. The mass% of the non-volatile content was 19.97 mass%. The weight average molecular weight of the copolymer binder was 56000.

(Synthesis Example 12 (Comparative Example))
In Synthesis Example 12, a polyacrylic acid lithium binder was prepared. Specifically, 27.7 g of polyacrylic acid (manufactured by Aldrich, MW 450,000) is dissolved in 270 g of water, and 16.1 g of lithium hydroxide monohydrate (manufactured by Wako Pure Chemical Industries, Ltd.) (1 with respect to acrylic acid). 0.0 equivalents) and stirred until completely dissolved. The mass% of non-volatile content was 9.97 mass%. The results of Synthesis Examples 1 to 12 are summarized in Table 1.

(Negative electrode slurry preparation example 1)
First, a silicon-based active material (silicon-based alloy) was produced by the following treatment. Here, the production of the silicon alloy was performed using a gas atomization (GAS ATOMIZING) method with reference to the method described in Japanese Patent Publication No. 2001-297757. Specifically, a molten metal was formed by high-frequency melting 60 mass% of Si powder, 20 mass% of Ti powder, and 20 mass% of Ni powder in an argon atmosphere. Next, this molten metal was poured into a tundish and a trickle of molten metal was formed through the pores provided at the bottom of the tundish. The molten metal was pulverized by spraying high pressure argon gas onto the molten metal stream. This powder becomes a silicon-based alloy. The cooling rate was 103-105 ° C./sec as measured by measuring the distance between the secondary arms (arm) of dendrites of aluminum-4 mass% copper alloy solidified under the same conditions. That is, the cooling rate was sufficiently faster than 100 ° C./sec. No heat treatment was performed. Next, 45.5% by mass of the silicon-based active material, 45.5% by mass of artificial graphite, 0.3% by mass of CNT, 2.7% by mass of acetylene black, lithium acrylate / acrylonitrile of Synthesis Example 1 = 70/30% by mass 6% by mass of a copolymer binder was mixed, and water was further added to adjust the viscosity to prepare a negative electrode mixture slurry. In addition, the non volatile matter in a negative mix slurry was 45 mass%. The method for measuring the nonvolatile content was the same as the method described in Synthesis Example 1.

(Negative electrode production example 1)
Next, the gap (gap) of the bar coater (gap) is adjusted so that the coating amount (area density) after drying is 4.5 mg / cm ^2, and the negative electrode mixture slurry is copper foil (collected) with this bar coater. (Electric body, 10 μm). Next, the negative electrode mixture slurry was dried for 15 minutes by a blow type dryer set at 80 ° C. Next, the dried negative electrode mixture was pressed by a roll press machine so that the mixture density was 1.53 g / cm ³ . Next, the negative electrode mixture is vacuum-dried at 150 ° C. for 6 hours (that is, the negative electrode active material binder is thermally cured), whereby a sheet-shaped negative electrode including a negative electrode current collector and a negative electrode active material layer is formed. Produced.

(Negative electrode slurry preparation examples 2-14 and negative electrode preparation examples 2-14)
Except for changing the binder and the conductive aid to those shown in Table 2, the same treatment as in Slurry Preparation Example 1 for Negative Electrode and Preparation Example 1 for Negative Electrode was performed.

(Peel strength (adhesion) evaluation)
The negative electrodes produced in each of the negative electrode production examples 1 to 14 were cut into strips having a width of 25 mm and a length of 100 mm. Then, using a double-sided tape, the active material surface was bonded to a glass plate as the adherend surface to obtain a sample for peel strength test. A peel strength test sample was attached to a peel tester (SHIMAZU EZ-S manufactured by Shimadzu Corporation), and the peel strength at 180 ° peel was measured. The results are summarized in Table 2.

  As shown in Table 2, since the negative electrode preparation examples 1 to 13 use the negative electrode mixture slurry (aqueous slurry) according to this embodiment, they correspond to the examples of this embodiment. Anode preparation example 14 corresponds to a comparative example.

(Cell production example 1)
First, a positive electrode was produced. 96 parts by mass (mass%) of solid solution oxide Li _1.20 Mn _0.55 Co _0.10 Ni _0.15 O _{2, 2} parts by mass of ketjen black, 2 parts by mass of polyvinylidene fluoride (PVDF) were added to N-methyl- A slurry was formed by dispersing in 2-pyrrolidone (N-methyl-2-pyrrolidone). Next, the positive electrode active material layer is formed by coating the slurry on an aluminum current collector foil, which is a current collector, so that the coating amount (area density) after drying is 14.7 mg / cm ² and drying. Formed. Next, the positive electrode active material layer was pressed by a press machine, so that the mixture density of the positive electrode active material layer was 3.0 g / cm ³ . This was cut into a diameter of 1.3 cm to produce a positive electrode.

Next, the negative electrode produced in the negative electrode production example 1 was cut into a circle having a diameter of 1.55 cm. Then, in a stainless steel coin outer container having a diameter of 2.0 cm, a positive electrode having a diameter of 1.3 cm and a polyethylene microfiber having a thickness of 25 μm cut into a circle having a diameter of 1.6 cm are prepared. A separator made of a porous film, a negative electrode cut into a circle having a diameter of 1.55 cm, and a copper foil having a thickness of 200 μm cut into a circle having a diameter of 1.5 cm as a spacer were stacked in this order. Next, the container is filled with electrolyte (1.5M LiPF ₆ ethylene carbonate (EC) / diethyl carbonate (DEC) / fluoroethylene carbonate (FEC) = 10/70/20 mixed solution (volume ratio)) so that it does not overflow. Dripping. Next, a stainless steel cap was placed on the container via a polypropylene packing, and the container was sealed with a caulking device for producing a coin battery. Thereby, a lithium ion secondary battery according to Cell Production Example 1 was produced.

(Cell production examples 2 to 14)
Lithium ion secondary batteries according to Cell Preparation Examples 2-14 were manufactured by performing the same treatment as in Cell Preparation Example 1 except that the negative electrodes according to Negative Electrode Preparation Examples 2-14 were used.

(Evaluation of cycle life)
After charging the lithium ion secondary battery according to each Example and Comparative Example at a constant current-constant voltage with a capacity of 0.2 C at 25 ° C., a charge / discharge cycle for discharging to 0.01 C with a constant current of 1.0 C Repeated 300 times. On the other hand, the discharge capacity after 1 cycle and the discharge capacity after 300 cycles were measured. The measurement of the discharge capacity was performed by TOSCAT3000 Toyo System Corporation.

  Next, the discharge capacity retention rate (percentage) was calculated by dividing the discharge capacity after 300 cycles by the discharge capacity after 1 cycle. The larger the capacity retention rate, the better the cycle life. The evaluation results are summarized in Table 3.

  Since the cell preparation examples 1 to 13 use the negative electrodes according to the negative electrode preparation examples 1 to 13 (examples), they correspond to the examples of this embodiment. Since cell preparation example 14 uses the negative electrode according to negative electrode preparation example 14 (comparative example), it corresponds to a comparative example.

  As can be seen from Tables 1 to 3, it can be seen that the electrode produced using the negative electrode mixture slurry according to the present embodiment achieves high peel strength and cycle life. In particular, it can be seen that when the content of acrylonitrile or acrylonitrile derivative in the copolymer is 20 to 30% by mass, the peel strength and the cycle life are dramatically improved.

(Example 2: Tin-based active material + copolymer binder)
The same treatment as in Example 1 was performed except that the silicon-based active material in Example 1 was changed to a tin-based active material (SnO ₂ ). As a result, almost the same result as in Example 1 was obtained.

  As described above, according to the present embodiment, the negative electrode mixture slurry includes a copolymer of acrylic acid or a salt of an acrylic acid derivative and acrylonitrile or an acrylonitrile derivative. This copolymer can follow the expansion and contraction of the silicon-based active material and the tin-based active material. Therefore, the electrode layer can be prevented from falling off due to expansion and contraction of the silicon-based active material and the tin-based active material. As a result, the cycle life is improved.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 10 Lithium ion secondary battery 20 Positive electrode 21 Current collector 22 Positive electrode active material layer 30 Negative electrode 31 Current collector 32 Negative electrode active material layer

Claims (6)

A carbon-based active material,
A metal-based active material containing at least one of a silicon-based active material and a tin-based active material;
Includes a salt of acrylic acid or acrylic acid derivative, a copolymer comprising acrylonitrile or acrylonitrile derivative, and,
The salt of acrylic acid or acrylic acid derivative is any one or more selected from the group consisting of sodium salt, ammonium salt, and amine salt of acrylic acid or acrylic acid derivative,
The acrylonitrile or the acrylonitrile derivative is an aqueous slurry for a negative electrode of a lithium ion secondary battery that is contained in the copolymer at 10 to 50% by mass with respect to the total mass of the copolymer.   The aqueous slurry for a negative electrode of a lithium ion secondary battery according to claim 1, wherein the acrylic acid derivative contains methacrylic acid.   3. The aqueous slurry for a negative electrode of a lithium ion secondary battery according to claim 1, wherein the acrylonitrile derivative contains methacrylonitrile. 4.   The lithium ion secondary material according to any one of claims 1 to 3, further comprising a conductive additive containing at least one selected from the group consisting of acetylene black, ketjen black, and carbon nanotubes. Aqueous slurry for secondary battery negative electrode.   A negative electrode active material layer for a lithium ion secondary battery, produced using the aqueous slurry for a negative electrode of a lithium ion secondary battery according to any one of claims 1 to 4. A lithium ion secondary battery comprising the negative electrode active material layer for a lithium ion secondary battery according to claim 5.

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