WO2020026420A1 - Negative electrode binder for nonaqueous-electrolyte secondary battery, negative electrode for nonaqueous-electrolyte secondary battery, and nonaqueous-electrolyte secondary battery - Google Patents

Abstract

Provided is a negative electrode binder that is for a nonaqueous-electrolyte secondary battery and that can improve the coulombic efficiency and lifespan characteristics of the nonaqueous-electrolyte secondary battery. The negative electrode binder for a nonaqueous-electrolyte secondary battery according to an embodiment of the present invention, together with an active substance, form a mixture layer (13) of a negative electrode for a nonaqueous-electrolyte secondary battery, and contains: a main binder comprising a polymer which has a mass-average molecular weight of 1,000,000-5,000,000 and which has a repeating unit that is an ethylenically unsaturated carboxylic acid compound; and an auxiliary binder which is a polymer having a mass-average molecular weight of 1,000-10,000. The auxiliary binder comprises a copolymer including, in repeating units, an ethylenically unsaturated carboxylic acid compound, and an ethylenically unsaturated compound represented by chemical formula 1 (n = 1 to 10) or an ethylenically unsaturated carboxylic acid compound represented by chemical formula 2 (n = 1 to 10), or a polymer containing, as a repeating unit, an ethylenically unsaturated carboxylic acid compound represented by chemical formula 2 (n = 1 to 10).

Description

Negative electrode binder for non-aqueous electrolyte secondary batteries, negative electrode for non-aqueous electrolyte secondary batteries, non-aqueous electrolyte secondary batteries

The present invention relates to a negative electrode binder for a non-aqueous electrolyte secondary battery. More specifically, the present invention relates to a negative electrode binder for a non-aqueous electrolyte secondary battery capable of improving life characteristics.

In recent years, non-aqueous electrolyte secondary batteries (for example, Li-ion secondary batteries) have been used as secondary batteries that can be repeatedly charged and discharged, with the aim of reducing oil consumption and greenhouse gases, and further diversifying and improving the energy base. Attention is gathering. In particular, application development to electric vehicles, hybrid electric vehicles, and fuel cell vehicles is expected. In electric vehicles, improvement in cruising distance is required, and in the future, higher energy density of Li-ion secondary batteries will be further required.

As the negative electrode of the current Li-ion secondary battery, a graphite electrode is generally used. The theoretical capacity of graphite is 372 mAh / g (active material). On the other hand, Si and Sn have attracted attention in recent years as active materials having a capacity higher than graphite. The theoretical capacity of Si is 4200 mAh / g (active material), and the theoretical capacity of Sn is 990 mAh / g (active material).
However, an active material that alloys with Li, such as Si or Sn, has a large volume change due to Li occlusion and release, and has various adverse effects on battery characteristics. For example, since Si has a capacity about 11 times that of graphite, the volume increases about 3 times by Li occlusion. When a large volume change occurs in the active material due to charge / discharge, SEI (Solid Electrolyte Interphase) caused by reductive decomposition of the electrolyte cannot be obtained as a stable film. Along with this, continuous reductive decomposition of the electrolytic solution occurs due to repetition of charging and discharging, and Li is consumed, thereby lowering Coulomb efficiency. In other words, a large change in volume of the active material due to charge and discharge causes a decrease in life characteristics.

に 対 し On the other hand, in recent years, it has been reported that a polycarboxylic acid-based binder is applied to a binder constituting a mixture layer together with an active material, thereby improving coulomb efficiency and improving life characteristics. Non-Patent Document 1 reports that the use of polyacrylic acid as a binder for a natural graphite electrode improves Coulomb efficiency. Further, in Non-Patent Document 2, by using a binder obtained by block copolymerizing polyacrylic acid and acrylic acid / maleic acid copolymer, a Si negative electrode (Si or SiOx (X is larger than 0, 1.5 It has been reported that the life characteristics of a negative electrode using the following method can be improved.

(4) In natural graphite whose volume change due to charge and discharge is small, natural graphite can be coated with a polycarboxylic acid, and Li consumption due to reductive decomposition of the electrolyte can be suppressed. On the other hand, in Si, a brittle polycarboxylic acid film cannot be applied due to a large volume change accompanying charge / discharge, and a carboxyl group concentration is reduced by block copolymerizing polyacrylic acid and acrylic acid / maleic acid copolymer, It has been reported that the life characteristics of a Si negative electrode can be improved by using a binder having flexibility. However, even when block copolymerization of polyacrylic acid and acrylic acid-maleic acid copolymer was used, the Coulomb efficiency and life characteristics were not sufficient.

Journal of Power Resources, 2014, 247, 981-990. Physical Chemistry Chemical Physics, 2015, 17, 2388-2393.

課題 An object of the present invention is to provide a negative electrode binder for a non-aqueous electrolyte secondary battery capable of improving the coulomb efficiency and life characteristics of the non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery using the same.

In order to solve the above problem, one embodiment of the present invention is a binder which forms a mixture layer of a negative electrode for a nonaqueous electrolyte secondary battery together with an active material, and has a mass average molecular weight of 1,000,000 or more and 5,000,000 or less. A main binder comprising a polymer having a repeating unit of an ethylenically unsaturated carboxylic acid compound, and an auxiliary binder having a mass average molecular weight of 1,000 to 10,000, wherein the auxiliary binder has the following constitution (1) to A negative electrode binder for a non-aqueous electrolyte secondary battery comprising at least one of (3) is provided.

(1) Formula 1 below containing an ethylenically unsaturated carboxylic acid compound (a1) and an alkyl carboxylic acid ester group having an alkyl moiety (C _n H _{2n + 1-} ) having 1 to 10 carbon atoms n. A first copolymer containing, in a repeating unit, an ethylenically unsaturated compound (b).
(2) An ethylenically unsaturated carboxylic acid compound (a2) having an alkyl moiety (C _n H _{2n + 1-} ) having _{1 to} 10 carbon atoms on the α-carbon of the carboxy group, ) In a repeating unit.
(3) a second copolymer containing an ethylenically unsaturated carboxylic acid compound (a3) other than the ethylenically unsaturated carboxylic acid compound (a2) and an ethylenically unsaturated carboxylic acid compound (a2) in a repeating unit Coalescing.

According to one embodiment of the present invention, there is provided a negative electrode binder for a non-aqueous electrolyte secondary battery capable of improving the coulomb efficiency and life characteristics of the non-aqueous electrolyte secondary battery.

It is sectional drawing which shows typically the negative electrode for non-aqueous electrolyte secondary batteries of embodiment. 1 is a cross-sectional view schematically illustrating a non-aqueous electrolyte secondary battery according to an embodiment. 4 is a graph showing a result of a charge / discharge cycle test of the coin cell manufactured in the example.

[Inventor's knowledge]
The present inventor uses a polyacrylic acid-based binder with reduced hydrogen bonding ability as an auxiliary binder for coating the Si surface, thereby suppressing Li consumption on the Si surface due to reductive decomposition of the electrolytic solution and improving coulomb efficiency. It has been found that a stable film that can be formed is formed.

[Operation of Negative Electrode Binder for Nonaqueous Electrolyte Secondary Battery That Is One Embodiment of the Present Invention]
When the auxiliary binder is (1) (in the case of the first copolymerization), the auxiliary binder adheres to the surface of the active material due to the carboxy group of the ethylenically unsaturated carboxylic acid compound (a1). In addition, the alkyl moiety (C _n H _{2n + 1-} ) of the ethylenically unsaturated compound (b) inhibits the hydrogen bond due to the carboxy group of the auxiliary binder, so that the molecular chain tends to slip when a tensile load is applied. , The auxiliary binder is easily stretched.

The monomer blending ratio of the first copolymer is, for example, 20 to 90 mol% for the ethylenically unsaturated carboxylic acid compound (a1) and 10 to 80 mol% for the ethylenically unsaturated compound (b). Mol% or less.
When the auxiliary binder is (2), the auxiliary binder adheres to the surface of the active material due to the carboxy group of the ethylenically unsaturated carboxylic acid compound (a2). In addition, since the hydrogen bond due to the carboxy group of the auxiliary binder is inhibited by the alkyl moiety (C _n H _{2n + 1-} ) of the ethylenically unsaturated carboxylic acid compound (a2), the molecular chain slips when a tensile load is applied. And the auxiliary binder becomes easier to expand.

When the auxiliary binder is (3) (in the case of the second copolymerization), the auxiliary binder serves as an active material due to the carboxy group of the ethylenically unsaturated carboxylic acid compound (a3) and the ethylenically unsaturated carboxylic acid compound (a2). Attaches to surface. In addition, since the hydrogen bond due to the carboxy group of the auxiliary binder is inhibited by the alkyl moiety (C _n H _{2n + 1-} ) of the ethylenically unsaturated carboxylic acid compound (a2), the molecular chain slips when a tensile load is applied. And the auxiliary binder becomes easier to expand.

The monomer blending ratio of the second copolymer is, for example, 20 mol% or more and 90 mol% or less of the ethylenically unsaturated carboxylic acid compound (a3) and 10 mol% of the ethylenically unsaturated carboxylic acid compound (a2). It is at least 80 mol%.
Therefore, even when the active material contains Si, the auxiliary binders (1) to (3) form a stable film on the surface of the active material, suppress the Li consumption due to the reductive decomposition of the electrolyte, and reduce the Coulomb efficiency. Can be improved.
Further, since the main binder has a large number of carboxy groups and a high molecular weight, it is a binder having a high elastic modulus, and can suppress a change in the thickness of the mixture layer due to a change in the volume of Si.

Therefore, according to one embodiment of the present invention, the auxiliary binder covering the surface of the active material having a large volume change can form a stable film on the surface of the active material. It is possible to suppress. Thus, according to one embodiment of the present invention, a negative electrode binder for a nonaqueous electrolyte secondary battery having excellent life characteristics can be provided.
In the negative electrode binder for a nonaqueous electrolyte secondary battery of one embodiment of the present invention, the content of the main binder is 60% by mass or more and 99% by mass or less, and the content of the auxiliary binder is 1% by mass or more and 40% by mass or less. Is preferred. According to such a configuration, it is possible to maintain the shape of the mixture layer by the main binder and suppress the continuous destruction and generation of SEI due to repeated charging and discharging by the auxiliary binder.

[Embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the embodiments described below. In the embodiments described below, technically preferable limitations for carrying out the present invention are made, but this limitation is not an essential requirement of the present invention.
As shown in FIG. 1, the negative electrode 10 for a nonaqueous electrolyte secondary battery of the embodiment has a structure in which a mixture layer 13 is laminated on a current collector 12.
The mixture layer 13 contains a binder together with the active material. The binder is a main binder composed of a polymer composed of an ethylenically unsaturated carboxylic acid compound having a mass average molecular weight of 1,000,000 to 5,000,000 (high molecular weight), and a mass average molecular weight of 1,000 to 10,000 (lower molecular weight than the main binder). And an auxiliary binder comprising at least one of the above-mentioned (1) to (3). The main binder may have a crosslink containing either or both of a covalent bond and a metal ion bond. The auxiliary binder does not include a covalent bond but may include a metal ion bond.

As described above, in the present embodiment, the mixture contains the ethylenically unsaturated carboxylic acid compound having a mass average molecular weight of 1,000,000 or more and 5,000,000 or less, that is, a main binder having a high molecular weight and a molecular chain interaction network. Of the mixture layer can be suppressed, and a change in the thickness of the mixture layer can be suppressed. In addition, as a result, it is possible to suppress the sparseness of the conductive path, and to improve the life characteristics.
The mass average molecular weight of the main binder is in the range of 1,000,000 to 5,000,000. In the present embodiment, the “mass average molecular weight of the main binder” can be determined by a known method, and for example, GPC can be used. When the mass average molecular weight of the main binder is 1,000,000 or more, sufficient mechanical strength can be imparted to the mixture layer. When the mass average molecular weight of the main binder is 5,000,000 or less, the viscosity of the coating liquid decreases, and the dispersibility of the active material improves.

Further, since the auxiliary binder is a polymer having a mass average molecular weight of 1,000 or more and 10,000 or less and is made of at least one of the above-mentioned (1) to (3), it easily adheres to the surface of the active material as described above, A stable film that can withstand a volume change can be formed on the active material surface. In addition, since this film is made of a polymer having a carboxy group, it can transmit Li ions and act as SEI, and can also be expected to have an effect of suppressing impregnation of the film with the electrolytic solution.
The weight average molecular weight of the auxiliary binder is in the range of 1,000 to 10,000. In the present embodiment, the “weight average molecular weight of the auxiliary binder” can be obtained by a known method, and for example, GPC can be used. When the mass average molecular weight of the auxiliary binder is 1000 or more, it is possible to prevent the auxiliary binder that has not adhered to the active material surface from being dissolved in the electrolytic solution. When the mass average molecular weight of the auxiliary binder is 10,000 or less, the auxiliary binder easily adheres to the active material surface.

Further, since the polymer and copolymer constituting the auxiliary binder of (1) to (3) contain, in the repeating unit, a monomer having an alkyl moiety that inhibits hydrogen bonding by a carboxy group, the active material is composed of Si. Even in this case, it can be expected that a stable film that can follow the volume change of Si is formed on the surface of the active material. As a result, continuous destruction and generation of SEI due to repeated charging and discharging are suppressed, and the life characteristics can be improved.

ポ リ マ ー As the polymer constituting the main binder, a polymer containing a carboxylate in a repeating unit is desirable. Specific examples include polyacrylic acid, acrylic acid-maleic acid copolymer, acrylate styrene copolymer, and vinyl acrylate acetate polymer in which the hydroxyl group of the repeating unit is a salt. Carboxylates include sodium, lithium, potassium, magnesium, calcium, and ammonium salts. Particularly preferably, sodium polyacrylate is used as the polymer constituting the main binder.

主 The main binder may be subjected to a crosslinking treatment. Crosslinking may use either a covalent bond or a metal ion bond, or both. For example, an aziridine compound or a carbodiimide compound can be used for the covalent bond. For the metal ion bond, a polyvalent cation can be used, and a calcium ion, a magnesium ion, or the like can be used.

As the ethylenically unsaturated carboxylic acid compounds (a1) and (a3) constituting the repeating units of the auxiliary binders (1) and (3), for example, acrylic acid, methacrylic acid, maleic acid, fumaric acid, and the like are preferable. In particular, acrylic acid is desirable.
The active material is not particularly limited as long as it can reversibly occlude and release Li, and a known material can be used. However, it is preferable to use a material alloyable with Li. In particular, if a material having a larger capacity than graphite is used as the active material, the effect of the present embodiment can be remarkably obtained. Examples of a material that alloys with Li include Si, Ge, Sn, Pb, Al, Ag, Zn, Hg, and Au.

It is particularly preferable to use pure silicon (Si) or SiO _x (0 <x ≦ 1.5) as the active material. If x is greater than 1.5, it is not possible to secure a sufficient amount of Li occlusion and release. Further, graphite may be added as an active material other than the above.

As the conductive additive, carbon black, natural graphite, artificial graphite, metal oxides such as titanium oxide and ruthenium oxide, and metal fibers can be used. Among them, carbon black having a structure structure is preferable, and furnace black, Ketjen black, and acetylene black, which are one of them, are particularly preferable. Note that a mixed system of carbon black and another conductive agent, for example, vapor grown carbon fiber (VGCF), graphene, or carbon nanotube is also preferable.

(Non-aqueous electrolyte secondary battery)
FIG. 2 is a cross-sectional view schematically illustrating a configuration example of the nonaqueous electrolyte secondary battery 100 according to the embodiment of the present invention. As shown in FIG. 2, the non-aqueous electrolyte secondary battery 100 includes a negative electrode 10 for a non-aqueous electrolyte secondary battery, a positive electrode 20 for a non-aqueous electrolyte secondary battery, and a negative electrode 10 for a non-aqueous electrolyte secondary battery. An electrolyte layer 30 disposed between the positive electrode 20 for a water electrolyte secondary battery.
When the electrolyte layer 30 is a liquid electrolyte (that is, an electrolytic solution), a separator may be provided between the negative electrode 10 for a non-aqueous electrolyte secondary battery and the positive electrode 30 for a non-aqueous electrolyte secondary battery. In this case, the nonaqueous electrolyte secondary battery includes, for example, a negative electrode 10 for a nonaqueous electrolyte secondary battery, an electrolyte layer 30, a separator, an electrolyte layer 30, and a positive electrode 20 for a nonaqueous electrolyte secondary battery in this order. Hereinafter, the case where the electrolyte layer 30 is an electrolytic solution will be described. Further, the positive electrode 20 for a non-aqueous electrolyte secondary battery will also be briefly described.

Examples of the solvent for the electrolytic solution used in the nonaqueous electrolyte secondary battery include low-viscosity chain carbonates such as dimethyl carbonate and diethyl carbonate, high dielectric constant cyclic carbonates such as ethylene carbonate, propylene carbonate and butylene carbonate, and γ-carbonate. Examples thereof include butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolan, methyl acetate, methyl propionate, vinylene carbonate, dimethylformamide, sulfolane, and a mixed solvent thereof.

The electrolyte contained in the electrolyte is not particularly limited, and a known electrolyte can be used. Specifically, LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiI, LiAlCl _{4 and the} like, and mixtures thereof can be used. Preferably, a lithium salt obtained by mixing one or more of LiBF ₄ and LiPF ₆ is used.

(Positive electrode for non-aqueous electrolyte secondary battery)
The positive electrode 20 for a nonaqueous electrolyte secondary battery includes a positive electrode current collector (not shown) and a positive electrode active material layer (not shown) formed on one surface of the positive electrode current collector. As the positive electrode current collector, a material known as a current collector material of the above-described negative electrode 10 for a nonaqueous electrolyte secondary battery can be used. That is, the positive electrode current collector may be formed of, for example, aluminum, nickel, copper, iron, stainless steel (SUS), titanium, or the like. The positive electrode current collector is preferably aluminum from the viewpoints of electron conductivity and battery operating potential.

The positive electrode active material layer includes at least a positive electrode active material and a binder, and is in direct contact with the positive electrode current collector. Further, the positive electrode active material layer may contain a conductive auxiliary. The positive electrode active material contained in the positive electrode active material layer is not particularly limited as long as it is a material capable of inserting and extracting lithium, and a positive electrode active material generally used for a lithium ion secondary battery that is a nonaqueous electrolyte secondary battery may be appropriately used. Can be adopted.
Specifically, lithium-manganese composite oxides (such as LiMn ₂ O ₄ ), lithium-nickel composite oxides (such as LiNiO ₂ ), lithium-cobalt composite oxides (such as LiCoO ₂ ), Iron composite oxide (such as LiFeO ₂ ), lithium-nickel-manganese composite oxide (such as LiNi _0.5 Mn _0.5 O ₂ ), lithium-nickel-cobalt composite oxide (such as LiNi _0.8 Co _0.2 O ₂ ), lithium-transition metal A phosphoric acid compound (such as LiFePO ₄ ) or a lithium-transition metal sulfate compound (such as Li _x Fe ₂ (SO ₄ ) ₃ ) can be used. Each of these positive electrode active materials may be included alone in the positive electrode active material layer, or may be included in the form of a mixture of two or more.

Hereinafter, Examples and Comparative Examples of the present invention will be described.
[Preparation of main binder]
To 96.54 g of water, 4.96 g of sodium polyacrylate (manufactured by Nippon Shokubai Co., Ltd., mass average molecular weight: 5,000,000) was added, and the mixture was stirred by a disper equipped with a disk turbine blade as a stirring blade. Subsequently, 0.15 g of a 10-fold diluted aqueous solution of an aziridine compound (Nippon Shokubai Co., Ltd., PZ-33) was added to the polymer solution, followed by stirring for 20 minutes. Subsequently, 2.34 g of a 100-fold diluted aqueous solution of calcium chloride was added, followed by further stirring. Thereby, a crosslinked sodium polyacrylate aqueous solution having a concentration of 5% by mass was obtained.

[Auxiliary binder]
As the auxiliary binder A used in Example 1, poly (ethyl acrylate-acrylic acid) having a mass average molecular weight of 5000 was prepared. The auxiliary binder A is a copolymer of ethyl acrylate and acrylic acid. That is, the auxiliary binder A is the above-mentioned first copolymer (auxiliary binder (1)), in which acrylic acid corresponds to the ethylenically unsaturated carboxylic acid compound (a1) and ethyl acrylate is This corresponds to 2 ethylenically unsaturated compounds (b). The monomer mixing ratio of the auxiliary binder A (copolymer) is acrylic acid: ethyl acrylate = 50: 50 in molar ratio.

As the auxiliary binder B used in Example 2, polymethacrylic acid having a weight average molecular weight of 5000 was prepared. That is, the auxiliary binder B is the above-mentioned auxiliary binder (2), and the methacrylic acid as a monomer corresponds to the ethylenically unsaturated carboxylic acid compound (a2) where n = 1 in Chemical Formula 2.
As an auxiliary binder C used in Example 3, poly (acrylic acid-methacrylic acid) having a mass average molecular weight of 5000 was prepared. The auxiliary binder C is a copolymer of acrylic acid and methacrylic acid. That is, this auxiliary binder is the above-mentioned second copolymer (auxiliary binder (3)), in which acrylic acid corresponds to the ethylenically unsaturated carboxylic acid compound (a3), and methacrylic acid is This corresponds to 1 ethylenically unsaturated carboxylic acid compound (a2). The monomer mixing ratio of the auxiliary binder C (copolymer) is acrylic acid: methacrylic acid = 20: 80 in molar ratio.

[Preparation of negative electrode slurry]
(Example 1)
6.48 g of water was added to 26.82 g of the obtained aqueous solution of crosslinked sodium polyacrylate (aqueous solution of the main binder), and the mixture was stirred with a disper equipped with a disk turbine blade as a stirring blade. Subsequently, 0.07 g of the above-mentioned auxiliary binder A was added and further stirred. Next, 4.71 g of Si particles (average particle diameter 200 nm), 0.94 g of acetylene black and 0.94 of vapor grown carbon fiber were added and stirred. Subsequently, the mixture was fully dispersed using Fillmix (registered trademark of Primix Co., Ltd.) to obtain a negative electrode slurry.

(Example 2)
The same amount of the above-mentioned auxiliary binder B was used in place of the auxiliary binder A. Except for this, a negative electrode slurry was obtained in the same manner as in Example 1.
(Example 3)
The same amount of the above-mentioned auxiliary binder C was used in place of the auxiliary binder A. Except for this, a negative electrode slurry was obtained in the same manner as in Example 1.

(Comparative Example 1)
6.45 g of water was added to 26.82 g of the obtained aqueous solution of crosslinked sodium polyacrylate (aqueous solution of the main binder), and the mixture was stirred with a disper equipped with a disk turbine blade as a stirring blade. Subsequently, 0.14 g of an aqueous solution of acrylic acid / maleic acid copolymer having a concentration of 50% by mass was added, and the mixture was further stirred. Except for this, a negative electrode slurry was obtained in the same manner as in Example 1.

[Preparation of negative electrode]
Each of the negative electrode slurries obtained in Example 1, Example 2, Example 3, and Comparative Example 1 was applied to each current collector made of a copper foil having a thickness of 12 μm to have a basis weight of 1.0 mg / cm ^2. And then preliminarily dried at 80 ° C. for 30 minutes. Next, the current collector having the dried negative electrode slurry layer was punched into a disk having a diameter of 15 mm, and dried under reduced pressure at 105 ° C. for 5 hours. Thereby, the negative electrode was obtained.

[Cell fabrication and charge / discharge evaluation]
A coin cell was manufactured using the negative electrode and the Li electrode, which are the electrodes of Example 1, Example 2, Example 3, and Comparative Example 1 described above. The coin cell used was type 2032. The Li pole has a disk shape with a diameter of 18 mm. The basic configuration of the coin cell was each electrode, Li electrode, and separator (Asahi Kasei, Hypore ND525). The electrolytic solution was prepared by adding LiPF ₆ to a solution obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) at a mass ratio of 3: 7 to 1 M, and further adding fluoroethylene carbonate (FEC). What was added so that it might be set to 10 mass% was used.

Charge / discharge evaluation was performed using the manufactured coin cell. The first charge / discharge was performed under the conditions that the current density was 160 mA / g for both charge and discharge, and the voltage range was 0.01 V to 1.2 V. Subsequently, charging and discharging were repeatedly performed under the conditions of a current density of 1600 mA / g for both charging and discharging and a voltage range of 0.03 V to 1.0 V.
FIG. 3 is a graph showing the change in cell capacity due to repeated charging and discharging. Table 1 shows the coulomb efficiencies of the coin cells when the number of times of repetitive charge / discharge is 1 cycle to 5 cycles.

分 か る As can be seen from FIG. 3, the coin cells of Example 1, Example 2, and Example 3 have a smaller change in capacity than the coin cell of Comparative Example 1. This is considered to be because a stable film was formed on the Si surface by using the auxiliary binders A, B, and C satisfying the above (1), (2), and (3). Furthermore, as can be seen from Table 1, the coin cells of Example 1, Example 2, and Example 3 exhibited values higher in Coulomb efficiency than the coin cell of Comparative Example 1.

初 回 Further, the initial coulomb efficiency was 80% in Example 1, 79% in Example 2, 78% in Example 3, and 75% in Comparative Example 1. This is probably because the auxiliary binders A, B, and C formed a stable film on the surface of the Si particles as the active material, and suppressed Li consumption.

A negative electrode having a mixture layer containing a negative electrode binder for a nonaqueous electrolyte secondary battery of one embodiment of the present invention is a power source for various portable electronic devices, and a storage battery for driving an electric vehicle or the like in which high energy density is required. It is used as a power storage device for various energies such as solar energy and wind power, or as an electrode for a storage power source of household electric appliances.

Reference Signs List 10 Negative electrode for non-aqueous electrolyte secondary battery 12 Current collector 13 Mixture layer 20 Positive electrode for non-aqueous electrolyte secondary battery 30 Electrolyte layer 100 Non-aqueous electrolyte secondary battery

Claims (5)

A binder constituting a mixture layer of the negative electrode for a non-aqueous electrolyte secondary battery together with the active material,
A main binder comprising a polymer having a mass average molecular weight of 1,000,000 or more and 5,000,000 or less and a repeating unit being an ethylenically unsaturated carboxylic acid compound,
An auxiliary binder which is a polymer having a weight average molecular weight of 1,000 or more and 10,000 or less,
Including
The auxiliary binder is
(1) Formula 1 below containing an ethylenically unsaturated carboxylic acid compound (a1) and an alkyl carboxylic acid ester group having an alkyl moiety (C _n H _{2n + 1-} ) having 1 to 10 carbon atoms n. An ethylenically unsaturated compound (b), and a first copolymer containing a repeating unit thereof,
(2) An ethylenically unsaturated carboxylic acid compound (a2) having an alkyl moiety (C _n H _{2n + 1-} ) having _{1 to} 10 carbon atoms on the α-carbon of the carboxy group, ), A polymer containing a repeating unit,
and
(3) The ethylenically unsaturated carboxylic acid compound (a3) other than the ethylenically unsaturated carboxylic acid compound (a2), and the ethylenically unsaturated carboxylic acid compound (a2), the second unit containing in the repeating unit A negative electrode binder for a non-aqueous electrolyte secondary battery comprising at least one of a copolymer.

The monomer blending ratio of the first copolymer is 20 mol% or more and 90 mol% or less of the ethylenically unsaturated carboxylic acid compound (a1) and 10 mol% or more of the ethylenically unsaturated compound (b). 80 mol% or less,
The monomer blending ratio of the second copolymer is such that the ethylenically unsaturated carboxylic acid compound (a3) is 20 mol% or more and 90 mol% or less, and the ethylenically unsaturated carboxylic acid compound (a2) is 10 mol%. 2. The negative electrode binder for a non-aqueous electrolyte secondary battery according to claim 1, wherein the amount of the binder is not less than 80% by mole. 3. The negative electrode for a nonaqueous electrolyte secondary battery according to claim 1, wherein the content of the main binder is 60% by mass or more and 99% by mass or less, and the content of the auxiliary binder is 1% by mass or more and 40% by mass or less. Binder. A negative electrode for a non-aqueous electrolyte secondary battery having a mixture layer containing the negative electrode binder for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3. A non-aqueous electrolyte secondary battery comprising the negative electrode for a non-aqueous electrolyte secondary battery according to claim 4.

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