JP6395371B2 - Negative electrode active material layer for lithium ion secondary battery and lithium ion secondary battery - Google Patents

Description

  The present invention relates to 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 are widely used as power sources for portable devices such as notebook PCs and mobile phones. -Because of its high capacity, great expectations are placed on its development. 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 a new negative electrode active material, a tin (Sn) alloy, a silicon (Si) alloy, a silicon (Si) oxide, a lithium (Li) nitride, and the like have been attracting attention. Discharge cycle characteristics are inferior to graphitic carbon materials.

  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. On the other hand, the new negative electrode material, particularly the silicon-based active material, has a more complicated structure than the carbon-based active material, and has a large amount of Li inserted / desorbed per unit mass during charge / discharge. For this reason, the silicon-based active material is greatly expanded / contracted due to charge / discharge, and as a result, the silicon-based active material is disconnected in a charge / discharge cycle that repeats expansion / contraction. A silicon-based active material isolated from other silicon-based active materials has a reduced electron conductivity and cannot participate in charge / discharge. For this reason, it is considered that the charge / discharge cycle characteristics of the silicon-based active material are worse than those of the carbon-based active material.

  Patent Document 1 discloses a technique of using polyacrylic acid and polymethacrylic acid as a binder of a negative electrode active material layer containing a silicon-based active material.

JP 2007-115671 A

  However, even with the technique disclosed in Patent Document 1, the cycle characteristics have not been sufficiently improved. This is because polyacrylic acid and polymethacrylic acid have low flexibility and cannot follow the expansion and contraction of the silicon-based active material, thereby separating the silicon-based active materials. Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to improve cycle characteristics of a lithium ion secondary battery using a silicon-based active material as a negative electrode active material. It is an object of the present invention to provide a new and improved lithium ion secondary battery that can be used.

  In order to solve the above problems, according to an aspect of the present invention, a negative electrode active material including a silicon-based active material and a carbon-based active material, and a binder including a polyacrylic acid amine salt, A negative electrode active material layer for a lithium ion secondary battery is provided.

  According to this aspect, the negative electrode active material layer includes a polyacrylic acid amine salt having high flexibility and binding power as a binder. The polyacrylic acid amine salt can follow the expansion and contraction of the silicon-based active material during charge / discharge, and can maintain the connection between the silicon-based active materials. For this reason, the cycle life of the lithium ion secondary battery is improved.

  Here, the amine constituting the polyacrylic acid amine salt may have a hydrophilic group.

  According to this viewpoint, the binding force and flexibility of the polyacrylic acid amine salt are further improved.

  Further, the hydrocarbon group constituting the amine may have a side chain having a hydrophilic group.

  According to this viewpoint, the binding force and flexibility of the polyacrylic acid amine salt are further improved.

  The hydrophilic group may contain a hydroxyl group.

  According to this viewpoint, the binding force and flexibility of the polyacrylic acid amine salt are further improved.

  Further, the silicon-based active material may be contained in the negative electrode active material layer for a lithium ion secondary battery in an amount of 3 to 80% by mass with respect to the total mass of the negative electrode active material.

  According to this viewpoint, the binding force and flexibility of the polyacrylic acid amine salt are further improved.

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

  According to this aspect, the negative electrode active material layer includes a polyacrylic acid amine salt having high flexibility and binding power as a binder. The polyacrylic acid amine salt can follow the expansion and contraction of the silicon-based active material during charge / discharge, and can maintain the connection between the silicon-based active materials. For this reason, the cycle life of the lithium ion secondary battery is improved.

  According to another aspect of the present invention, a step of coating a slurry containing a silicon-based active material, a carbon-based active material, and a polyacrylic acid amine salt on a current collector, and a slurry on the current collector at 150 ° C. And a step of drying at the above temperature. A method for producing a negative electrode active material layer is provided.

  According to this aspect, since the drying temperature is set to 150 ° C. or higher, an amide bond is formed in a part of the polyacrylic acid amine salt, thereby improving the binding force and flexibility of the polyacrylic acid amine salt.

  As described above, according to the present invention, the cycle life of a lithium ion secondary battery using a silicon-based active material as a negative electrode active material is improved.

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

  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 includes a silicon-based active material and a carbon-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.

  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 content of the silicon-based active material in the negative electrode active material is not particularly limited, but as shown in the examples described later, the silicon-based active material is 3 to 80% by mass with respect to the total mass of the negative electrode active material. In the negative electrode active material layer 32, it is preferable. When the content of the silicon-based active material is within this range, the effect of improving the cycle life becomes more remarkable.

  The binder includes a polyacrylic acid amine salt. Preferably, the binder is composed of a polyacrylic acid amine salt. That is, the present inventor found that the flexibility and binding force of the polyacrylic acid amine salt were very good, and tried to use the polyacrylic acid amine salt as a binder for the negative electrode active material layer 32. As a result, the present inventors succeeded in dramatically improving the cycle life of the lithium ion secondary battery. Since the polyacrylic acid amine salt has high flexibility and binding power, it can follow the expansion and contraction of the silicon-based active material, and can maintain the connection between the silicon-based active materials. As a result, it is considered that the cycle life of the lithium ion secondary battery 10 is improved.

  The amine constituting the polyacrylic acid amine salt preferably has a hydrophilic group. In this case, the binding force and flexibility of the polyacrylic acid amine salt are further improved, and as a result, the cycle life of the lithium ion secondary battery 10 is further improved. The greater the number of hydrophilic groups, the better the binding force and flexibility. Further, the hydrocarbon group constituting the amine preferably has a side chain having a hydrophilic group. In this case, the polyacrylic acid amine salt has a more three-dimensional structure (network structure) by bonding the hydroxyl groups of each amine. Therefore, the binding force and flexibility of the polyacrylic acid amine salt are further improved, and the cycle life of the lithium ion secondary battery 10 is further improved. Here, the hydrophilic group is preferably a hydroxyl group. Accordingly, a preferred example of the polyacrylic acid amine salt is an amino alcohol salt of polyacrylic acid. The upper limit of the temperature during drying is, for example, about 200 ° C.

  Specific examples of the polyacrylic acid amine salt include trishydroxymethylaminomethane (Tris hydroxymethylaminomethane), ethanolamine, ethylmethane, and the like. According to the above characteristics, among these polyacrylic acid amine salts, trishydroxymethylaminomethane is most preferred, ethanolamine is next preferred, and ethylamine is next preferred.

  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 and a binder. Subsequently, the negative electrode mixture is dispersed in a suitable solvent to form a negative electrode mixture slurry (slurry). The negative electrode mixture slurry is coated on the current collector 31, dried, and rolled to form a negative electrode active material. Layer 32 is formed. Here, the temperature during drying is not particularly limited as long as it is a temperature applied to the negative electrode active material layer of the lithium ion secondary battery, but it is particularly preferably 150 ° C. or higher. This is because the cycle characteristics of the lithium ion secondary battery 10 are further improved by drying the negative electrode mixture slurry at a temperature of 150 ° C. or higher. The reason is considered that when the negative electrode mixture slurry is dried at a temperature of 150 ° C. or higher, an amide bond is formed by a dehydration bond between a carboxyl group of acrylic acid and an amine. By forming such an amide bond, the flexibility and binding force of the polyacrylic acid amine salt can be further improved, and can be reliably followed by expansion and contraction of the silicon-based active material.

  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 slurry is formed by dispersing a mixture of a negative electrode active material and a binder in the above ratio in a solvent (for example, N-methyl-2-pyrrolidone). Next, the negative electrode active material layer 32 is formed by forming (for example, coating) the slurry on the current collector 31 and drying the slurry. The temperature during drying is preferably 150 ° C. or higher. Next, the negative electrode active material layer 32 is pressed by a press machine so as to have a density within the above range. 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
(Creation of silicon-based active material)
First, production of a silicon-based active material (silicon-based alloy) was performed using a gas atomizing method with reference to a 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. Subsequently, this molten metal was poured into a tundish, and a trickle of molten metal was formed through pores provided at the bottom of the tundish. And the molten metal was pulverized by spraying high pressure argon gas to this molten metal trickle. This powder becomes a silicon-based alloy. The cooling rate was 103 to 105 ° C./sec by measuring the distance between secondary arms of the dendrite 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.

(Preparation of polyacrylic acid amine salt)
A polyacrylic acid amine salt was obtained by neutralizing polyacrylic acid and trishydroxymethylaminomethane at a monomer conversion of 1: 1.

(Preparation of slurry for negative electrode)
Next, the silicon-based active material, artificial graphite (carbon-based active material), acetylene black, and the acrylate amine salt prepared above were mixed at a mass ratio of 45.5: 45.5: 1.0: 8.0. Thus, a negative electrode mixture was produced. Then, a negative electrode mixture slurry was prepared by adding water to the negative electrode mixture to adjust the viscosity suitable for coating.

(Preparation of negative electrode)
The negative electrode mixture slurry was applied to one side of a copper foil, dried for 15 minutes with a blow-type dryer set at 80 ° C., rolled, and then vacuum dried at 150 ° C. for 6 hours to prepare a negative electrode active material layer. . The packing density of the negative electrode active material layer was 1.50 g / cm ³ . The negative electrode was produced by the above steps.

(Preparation of positive electrode)
A positive electrode mixture was prepared by mixing solid solution oxide Li _1.20 Mn _0.55 Co _0.10 Ni _0.15 O ₂ , Ketjen Black, and polyvinylidene fluoride in a mass ratio of 96: 2: 2. A positive electrode mixture slurry was prepared by dispersing the positive electrode mixture in N-methyl-2-pyrrolidone. Next, the positive electrode mixture slurry was uniformly coated on an aluminum foil, dried for 15 minutes with a blow-type dryer set at 80 ° C., rolled, and then vacuum dried at 100 ° C. for 6 hours. This produced the positive electrode active material layer. The positive electrode was produced by the above steps. The packing density of the positive electrode active material layer was 3.0 g / cm ³ .

(Production of coin cell)
The positive electrode was cut to a diameter of 13 mm, and the negative electrode of Example 1 was cut to a diameter of 15.5 mm. A separator made of a polyethylene microporous film having a diameter of 19 mm and a thickness of 25 μm was sandwiched between the positive electrode and the negative electrode, and accommodated in a CR2032 coin cell battery case. .

Inject nonaqueous electrolyte (1.5M LiPF ₆ ethylene carbonate (EC) / diethyl carbonate (DEC) / fluoroethylene carbonate (FEC) = 10/70/20 mixed solution (volume ratio)) into the battery case and seal Thus, a lithium ion secondary battery according to Example 1 was produced.

(Peel strength (adhesion) evaluation)
The negative electrode produced in Example 1 was cut into a strip shape having a width of 25 mm and a length of 100 mm. Next, a double-sided tape was used to attach the active material surface to the glass plate as the adherend surface, and a peel strength test sample was obtained. 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. It can be said that the higher the peel strength, the greater the binding force and flexibility of the binder.

(Evaluation of cycle characteristics)
A lithium ion secondary battery is charged to 4.2 V with a constant current of 1 It = 5 mA at 25 ° C., charged to 4.20 V with a constant current of 1/50 It = 0.1 mA, and a 10-minute pause is inserted. It discharged until it became 2.75V with the constant current of 1 It. The discharge capacity at this time was taken as the discharge capacity of the first cycle, and the charge / discharge cycle was repeated 100 times, and the 100-minute ratio of the discharge capacity of the 100th cycle to the discharge capacity of the first cycle was determined.

(Example 2)
The same treatment as in Example 1 was performed except that trishydroxymethylaminomethane was changed to ethanolamine.

(Example 3)
The same treatment as in Example 1 was performed except that the vacuum drying temperature at the time of preparing the negative electrode was 100 ° C.

(Example 4)
The same treatment as in Example 1 was performed except that trishydroxymethylaminomethane was changed to ethylamine.

(Example 5)
The same treatment as in Example 1 was performed except that the silicon-based alloy was silicon oxide (SiO).

(Comparative Example 1)
The same treatment as in Example 1 was performed except that polyacrylic acid was used as the binder for the negative electrode active material layer.

(Comparative Example 2)
The same treatment as in Example 1 was performed except that polyacrylic acid was used as the binder of the negative electrode active material layer, and the vacuum drying temperature at the time of producing the negative electrode was set to 100 ° C.

(Comparative Example 3)
The same treatment as in Comparative Example 1 was performed except that the silicon-based alloy was changed to silicon oxide (SiO).

(Contrast)
Table 1 shows the peel strength and cycle characteristics of Examples 1 to 5 and Comparative Examples 1 to 3.

  In Table 1, “Si species” indicates a silicon-based active material, and “Gr: Si” indicates a mass ratio between the carbon-based active material and the silicon-based active material.

  In Examples 1 to 5, the peel strength was higher than in Comparative Examples 1 to 3, and the cycle characteristics were also improved. Trishydroxymethylaminomethane has a side chain having a hydroxyl group, and this side chain is long. Therefore, since trishydroxymethylaminomethane has a more steric structure, the negative electrode active material can be bound with a stronger binding force and has high flexibility. For this reason, the polyacrylic acid amine salt which has trishydroxymethylaminomethane has high peel strength, and can improve the cycling characteristics of a lithium ion secondary battery.

  In addition, Example 1 had higher peel strength than Example 2, and was most excellent in cycle characteristics. This is because trishydroxymethylaminomethane has more side chains having a hydroxy group than ethanolamine and thus has high flexibility and binding power. Also, the higher the heat treatment temperature, the better the peel strength. The reason for this is considered that a dehydration reaction is caused with a salt composed of an amino group and a carboxyl group, and a part of an amide bond is formed.

  Further, when Examples 1 to 3 were compared with Example 4, Examples 1 to 3 had better peel strength and cycle characteristics than Example 4. As this reason, since the amine of Examples 1-3 has a hydroxyl group, it can be considered that the binding force is further improved. Further, when Example 5 and Comparative Example 3 were compared, it was found that peel strength and cycle characteristics were improved even when the silicon-based active material was silicon oxide.

(Examples 6 to 9)
The same treatment as in Example 1 was performed except that the mass ratio of the carbon-based active material and the silicon-based active material was changed as shown in Table 2.

(Comparative Examples 4-7)
The same treatment as in Comparative Example 1 was performed except that the mass ratio of the carbon-based active material and the silicon-based active material was changed as shown in Table 2.

  According to Table 2, when the examples in which the mass ratio of the silicon-based active material and the carbon-based active material are the same are compared with the comparative example, the peel strength and the cycle characteristics of the examples are compared at any mass ratio. Better than the example. In particular, when the mass% of the silicon-based active material is 3 to 80 mass%, the difference between the example and the comparative example becomes significant.

  As described above, according to the present embodiment, the negative electrode active material layer 32 includes a polyacrylic acid amine salt having high flexibility and binding force as a binder. The polyacrylic acid amine salt can follow the expansion and contraction of the silicon-based active material during charging and discharging, and as a result, the cycle life of the lithium ion secondary battery 10 is improved.

  Here, the amine constituting the polyacrylic acid amine salt may have a hydrophilic group, and in this case, the binding force and flexibility of the polyacrylic acid amine salt are further improved.

  The hydrocarbon group constituting the amine may have a side chain having a hydrophilic group, and in this case, the binding force and flexibility of the polyacrylic acid amine salt are further improved.

  Further, the hydrophilic group may contain a hydroxyl group, and in this case, the binding force and flexibility of the polyacrylic acid amine salt are further improved.

  Further, the silicon-based active material may be included in the negative electrode active material layer 32 in an amount of 3 to 80% by mass with respect to the total mass of the negative electrode active material. In this case, the cycle characteristics of the lithium ion secondary battery 10 are further increased. improves.

  In addition, since the vacuum drying temperature is set to 150 ° C. or higher when the negative electrode is manufactured, an amide bond is formed in a part of the polyacrylic acid amine salt, thereby improving the binding force and flexibility of the polyacrylic acid amine salt. .

  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 40 Separator layer

Claims (6)

A negative electrode active material comprising a silicon-based active material and a carbon-based active material;
A binder containing a polyacrylic acid amine salt, and a negative electrode active material layer for a lithium ion secondary battery,
The negative electrode for a lithium ion secondary battery, wherein the silicon-based active material is included in the negative electrode active material layer for a lithium ion secondary battery in an amount of 3 to 80% by mass with respect to the total mass of the negative electrode active material. Active material layer.   The negative electrode active material layer for a lithium ion secondary battery according to claim 1, wherein the amine constituting the polyacrylic acid amine salt has a hydrophilic group.   The negative electrode active material layer for a lithium ion secondary battery according to claim 2, wherein the hydrocarbon group constituting the amine has a side chain having the hydrophilic group.   The negative electrode active material layer for a lithium ion secondary battery according to claim 2, wherein the hydrophilic group includes a hydroxyl group. A lithium ion secondary battery comprising the negative electrode active material layer for a lithium ion secondary battery according to any one of claims 1 to 4 . Applying a slurry containing a silicon-based active material, a carbon-based active material, and a polyacrylic acid amine salt on a current collector;
Drying the slurry on the current collector at a temperature of 150 ° C. or higher, and a method for producing a negative electrode active material layer for a lithium ion secondary battery,
The silicon-based active material is included in the negative electrode active material layer for a lithium ion secondary battery in an amount of 3 to 80% by mass based on the total mass of the silicon-based active material and the carbon-based active material. The manufacturing method of the negative electrode active material layer for ion secondary batteries.