JP6428151B2 - Negative electrode for lithium ion secondary battery and lithium ion secondary battery using the same - Google Patents

Description

  The present invention relates to a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery using the same.

2. Description of the Related Art Lithium ion secondary batteries, which are energy devices having a high energy density, are widely used as power sources for portable information terminals such as notebook computers, mobile phones, and PDAs. A typical lithium ion secondary battery (hereinafter also simply referred to as “lithium battery”) is a wound electrode group obtained by stacking and winding a positive electrode, an insulating layer, a negative electrode, and an insulating layer in this order, or A stacked electrode group in which a positive electrode, an insulating layer, and a negative electrode are stacked is used. The active material for the negative electrode is a carbon material having a multilayer structure capable of inserting and releasing lithium ions between layers (formation of a lithium intercalation compound) and the active material for the positive electrode is a lithium-containing metal composite oxide. For the layer, a polyolefin porous membrane is mainly used.
Most of the lithium secondary batteries currently on the market use graphite as the negative electrode active material except for a part, but the battery has already been designed with a utilization factor very close to the theoretical capacity of 372 mAh / g. In order to further increase the capacity, a new negative electrode material replacing graphite is required.
As such negative electrode materials, Sn (tin) alloy, Si (silicon) alloy, Si oxide, Li (lithium) nitride, Li metal, and the like have been studied. For example, ultrafine particles of Si are dispersed in SiO ₂ . SiO _x having a structure has attracted attention (for example, Patent Document 1).

JP 2012-14993 A

However, SiO _x, because the volume change due to charging and discharging of the battery as compared with the graphite is very large, the battery using the SiO _x in the anode active material, usually after repeated expansion and contraction due to charging and discharging, the negative electrode Strength and electronic conductivity are lowered, and charge / discharge cycle characteristics are deteriorated as compared with a battery using graphite as a negative electrode active material. Patent Document 1 describes that the charge / discharge cycle characteristics can be improved by using a specific conductive aid in the mixture. However, the conductive auxiliary agent described in Patent Document 1 is expected not to be involved in the charge / discharge capacity, and the charge / discharge capacity is expected to be lower than when the conductive auxiliary agent is not included.
The present invention has been made in view of the above problems, and in a lithium ion secondary battery using a silicon-based compound as a negative electrode active material, has excellent discharge capacity, suppresses large expansion and contraction due to charge and discharge, and conducts electrons. It is providing the negative electrode for lithium ion secondary batteries which is hard to deteriorate property, and a lithium ion secondary battery using the same.

That is, the present invention is a negative electrode for a lithium ion secondary battery in which a negative electrode active material layer is formed on at least one surface of a current collector, wherein the negative electrode active material layer includes a carbon material and a silicon compound, Provided is a negative electrode for a lithium ion secondary battery, in which the current collector has a plurality of through holes.
It is preferable that the area of the opening of the one through hole is 9 × 10 ⁻¹¹ to 8 × 10 ⁻⁷ m ² .
Moreover, it is preferable that the aperture ratio by the through-hole of the said collector is 10 to 50%.
The content ratio of the carbon material and the silicon compound is preferably carbon material: silicon compound = 99: 1 to 50:50 (mass ratio).
Furthermore, this invention provides a lithium ion secondary battery provided with the said negative electrode for lithium ion secondary batteries.

  According to the present invention, in a lithium ion secondary battery using a silicon-based compound as a negative electrode active material, the lithium ion secondary battery is excellent in discharge capacity, suppresses large expansion / contraction due to charge / discharge, and hardly deteriorates electronic conductivity. A negative electrode for a battery and a lithium ion secondary battery using the same can be provided.

It is sectional drawing of the cylindrical lithium ion secondary battery of embodiment which can apply this invention.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. Moreover, in the following drawings, the same code | symbol is attached | subjected to the member and site | part which show | plays the same effect | action, and the overlapping description may be abbreviate | omitted or simplified. The dimensional relationship (length, width, thickness, etc.) in each figure does not reflect the actual dimensional relationship.

  The technology disclosed herein can be widely applied to various nonaqueous secondary batteries including an electrode in a form in which an electrode active material is held on a current collector. Hereinafter, the present invention will be described in more detail mainly using an electrode mixture (negative electrode mixture) including a negative electrode active material and a lithium ion secondary battery including the negative electrode as an example. It is not intended to be limiting.

  The lithium ion secondary battery of the present invention is a nonaqueous electrolyte secondary battery having a positive electrode, a negative electrode, a nonaqueous electrolyte, and a separator containing a lithium-containing metal composite oxide as a positive electrode active material. The negative electrode for a lithium ion secondary battery of the present invention contains a material (silicon-based compound) containing Si and O as constituent elements and a carbon-based material (carbon material) as a negative electrode active material, and collects a negative electrode mixture layer. The non-aqueous electrolyte secondary battery is provided on one or both sides of the body, and the current collector has a plurality of through holes.

The negative electrode active material is a material capable of inserting and extracting lithium ions, and includes a carbon material and a silicon-based compound.
As the carbon material, graphite such as natural graphite (eg, flake graphite) and artificial graphite is preferable from the viewpoint of discharge capacity and charge / discharge cycle characteristics.
The average particle diameter of the carbon material is preferably 1 to 200 μm, more preferably 5 to 100 μm, and still more preferably 10 to 50 μm from the viewpoint of battery characteristics.
As the silicon-based compound, SiOx having a structure in which ultrafine particles of Si are dispersed in SiO ₂ is preferable (here, the atomic ratio x of O to Si is 0.5 ≦ x ≦ 1.5). . The silicon compound is a paint for forming a negative electrode mixture layer because the Six that reacts with Li is an ultrafine particle, so that charging and discharging are performed smoothly, while the SiOx particles having the above structure itself have a small surface area. The coating properties and the adhesion of the negative electrode mixture layer to the current collector are also good.
The average particle diameter of the SiOx particles is preferably 0.1 to 40 μm, more preferably 1 to 30 μm, and still more preferably 5 to 20 μm from the viewpoint of battery characteristics.
The content ratio of the carbon material and the silicon compound is preferably carbon material: silicon compound = 99: 1 to 50:50 (mass ratio), more preferably 97: 3 to 70:30, and 95: 5. 85:15 is more preferable.

Moreover, this invention may contain negative electrode active materials other than a carbon material and a silicon-type compound. Examples of such a negative electrode active material include metallic lithium, a lithium alloy, an organic compound, a metal complex, and an organic polymer compound. A negative electrode active material can be used individually by 1 type or in combination of 2 or more types. The conductive material may include acetylene black, ketjen black, channel black, furnace black, lamp black, carbon black such as thermal black, carbon fiber, and the like. From the viewpoint of further improving the cycle characteristics, acetylene black is preferable.
When acetylene black is included, the content of acetylene black is preferably 0.1 to 10% by mass and more preferably 1 to 7% by mass in the total amount of the negative electrode active material layer.

Incidentally, the negative electrode active material layer, negative electrode active material to each other or anode active material and purpose of bonding a current collector, it is preferable to use a binder.
Examples of the binder used for the negative electrode active material layer include polysaccharides such as starch, polyvinyl alcohol, polyacrylic acid, carboxymethyl cellulose (CMC), hydroxypropyl cellulose, regenerated cellulose, and diacetyl cellulose, and modified products thereof; polyvinyl Thermoplastic resins such as chloride, polyvinylpyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyamide, and their modified products; polyimide; ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, Polymers having rubber-like elasticity such as styrene butadiene rubber (SBR), butadiene rubber, polybutadiene, fluororubber, polyethylene oxide, acrylic polymer, and modified products thereof And the like, may be used alone or two or more thereof.

The acrylic polymer includes, for example, a structural unit derived from a monomer (meth) acrylonitrile and a structural unit derived from a compound having two or more ethylenically unsaturated bonds (hereinafter also referred to as “crosslinking agent”). It is preferable to include.
One type of monomer constituting each structural unit may be selected and used for polymerization in each structural unit, or a plurality of types may be selected and used for polymerization. Further, one type of monomer may be selected as a monomer constituting a specific structural unit, and a plurality of types of monomers may be selected as monomers constituting other structural units.
Moreover, the said acrylic polymer should just contain each structural unit mentioned above, and there is no restriction | limiting in particular about the coupling | bonding order of each structural unit. The specific copolymer may be either a block copolymer or a random copolymer, and is preferably a random copolymer.
The content of structural units derived from (meth) acrylonitrile in the acrylic polymer is the total structure derived from monomers of the acrylic polymer from the viewpoint of excellent adhesion between the current collector and the mixture layer in the energy device electrode. From the viewpoint of excellent adhesion and storage stability of the electrode mixture slurry, it is more preferably 30 to 60 mol% based on the number of units (100 mol%). More preferably, it is 35-45 mol%.
The compound having two or more ethylenically unsaturated bonds (crosslinking agent) includes two or more functional groups containing an ethylenically unsaturated bond and an organic group that is a divalent or higher linking group that links the functional groups to each other. If it is a compound which has this, there will be no restriction | limiting in particular. The compound having two or more ethylenically unsaturated bonds is preferably, for example, a compound represented by the following general formula (I).

一般式（Ｉ）中、Ｒ^１はそれぞれ独立に、水素原子又はメチル基を示す。Ｒ^２は、ｎ価の有機基を示す。ｎは２〜６の数を示し、３〜４であることが好ましい。ｎは一般式（Ｉ）で表される化合物が単一の分子種である場合、整数である。
Ｒ^２で示されるｎ価の有機基としては、炭素数２〜２０の脂肪族炭化水素からｎ個の水素原子を取り除いて構成される炭素数が２〜２０であるｎ価の脂肪族炭化水素基；炭素数２〜４のアルキレングリコールが２以上エーテル結合してなるポリアルキレングリコールの両末端からヒドロキシ基を取り除いて構成されるポリアルキレンオキシアルキレン基；グリセリン、ジグリセリン、ネオペンチルグリコール、ペンタエリスリトール、ジペンタエリスリトール、トリメチロールプロパン等の炭素数３〜２０の多価アルコール又はそのヒドロキシアルキル化物からｎ個のヒドロキシ基を取り除いて構成されるｎ価の有機基；イソシアヌル酸又はそのヒドロキシアルキル化物からｎ個のヒドロキシ基を取り除いて構成されるｎ価の有機基；などを挙げることができる。
これらの２以上のエチレン性不飽和結合を有する化合物は１種単独で又は２種類以上組み合わせて用いることができる。
上記アクリル系ポリマーにおける２以上のエチレン性不飽和結合を有する化合物由来の構造単位の含有量は、特定共重合体のゴム状領域における貯蔵弾性率を高めて、エネルギーデバイスの充放電における活物質の膨張収縮に追従しやすくさせるという観点から、アクリル系ポリマーにおける単量体由来の総質量１００質量部に対して、０．０１〜５．０質量部であることが好ましく、０．０５〜３．０質量部であることがより好ましく、０．０２〜０．２質量部であることが更に好ましい。
また、アクリル系ポリマーにおける２以上のエチレン性不飽和結合を有する化合物由来の構造単位の含有率をモル％で規定した場合、アクリル系ポリマーにおける単量体由来の総構造単位数（１００モル％）に対して、０．００１〜1．０モル％であることが好ましく、０．００５〜０．５モル％であることがより好ましく、０．０２〜０．２モル％であることが更に好ましい。
更にアクリル系ポリマーにおける（メタ）アクリロニトリル由来の構造単位の含有量に対する２以上のエチレン性不飽和結合を有する化合物由来の構造単位の含有量のモル比は特に制限されない。エネルギーデバイス電極における集電体と合剤層との密着性に優れる観点から、前記モル比は、０．００８〜０．８モル％であることが好ましく、０．０３〜０．３モル％であることがより好ましい。

In general formula (I), R < ¹ > shows a hydrogen atom or a methyl group each independently. R ² represents an n-valent organic group. n shows the number of 2-6, and it is preferable that it is 3-4. n is an integer when the compound represented by formula (I) is a single molecular species.
The n-valent organic group represented by R ² is an n-valent aliphatic hydrocarbon having 2 to 20 carbon atoms formed by removing n hydrogen atoms from an aliphatic hydrocarbon having 2 to 20 carbon atoms. Group: a polyalkyleneoxyalkylene group formed by removing hydroxyl groups from both ends of a polyalkylene glycol formed by ether-linking two or more alkylene glycols having 2 to 4 carbon atoms; glycerin, diglycerin, neopentyl glycol, pentaerythritol N-valent organic group formed by removing n hydroxy groups from a polyhydric alcohol having 3 to 20 carbon atoms such as dipentaerythritol, trimethylolpropane or the like, or a hydroxyalkylated product thereof; from isocyanuric acid or a hydroxyalkylated product thereof n-valent organic group constituted by removing n hydroxy groups; Can be mentioned.
These compounds having two or more ethylenically unsaturated bonds can be used singly or in combination of two or more.
The content of the structural unit derived from the compound having two or more ethylenically unsaturated bonds in the acrylic polymer increases the storage elastic modulus in the rubber-like region of the specific copolymer, and the active material in charge / discharge of the energy device. From the viewpoint of easily following expansion and contraction, it is preferably 0.01 to 5.0 parts by mass with respect to 100 parts by mass of the monomer-derived total mass in the acrylic polymer, and 0.05 to 3. More preferably, it is 0 mass part, and it is still more preferable that it is 0.02-0.2 mass part.
Moreover, when the content rate of the structural unit derived from the compound having two or more ethylenically unsaturated bonds in the acrylic polymer is specified in mol%, the total number of structural units derived from the monomer in the acrylic polymer (100 mol%) Is preferably 0.001 to 1.0 mol%, more preferably 0.005 to 0.5 mol%, and still more preferably 0.02 to 0.2 mol%. .
Furthermore, the molar ratio of the content of the structural unit derived from the compound having two or more ethylenically unsaturated bonds to the content of the structural unit derived from (meth) acrylonitrile in the acrylic polymer is not particularly limited. From the viewpoint of excellent adhesion between the current collector and the mixture layer in the energy device electrode, the molar ratio is preferably 0.008 to 0.8 mol%, and 0.03 to 0.3 mol%. More preferably.

  The acrylic polymer contains structural units derived from other monomers other than structural units derived from (meth) acrylonitrile and structural units derived from compounds having two or more ethylenically unsaturated bonds, as necessary. May be. Examples of the other monomer include a monomer represented by the following general formula (II) and an acidic functional group-containing monomer.

In the general formula (II), R ²¹ represents a hydrogen atom or a methyl group. R ²² represents a 2-cyanoethyl group, an alkyl group having 3 to 20 carbon atoms, or a hydroxyalkyl group having 5 to 20 carbon atoms.
The alkyl group having 3 to 20 carbon atoms in R ²² may be a branched alkyl group or a linear alkyl group, and is preferably a linear alkyl group. The number of carbon atoms of the alkyl group represented by R ²² is preferably 3 to 12, and more preferably 3 to 8.
The total content of the structural unit derived from the monomer represented by the general formula (II) is a single amount in the specific copolymer from the viewpoint of excellent adhesion between the current collector and the mixture layer in the energy device electrode. From the viewpoint of excellent adhesion and storage stability of the electrode mixture slurry, it is preferably 40 to 70 mol%, based on the total structural unit amount derived from the body (100 mol%). More preferably, it is more preferably 55 to 65 mol%.

The acrylic polymer is preferably used as water-dispersed acrylic polymer particles.
The acrylic polymer particles preferably have a particle size of 500 nm or less, and more preferably 400 nm or less from the viewpoint of adhesion and battery characteristics. Although there is no restriction | limiting in particular in a lower limit, it is preferable that it is 100 nm or more from a practical viewpoint, and it is more preferable that it is 200 nm or more.
Here, the particle diameter is an average particle diameter, and can be measured using a commercially available measuring device by a dynamic light scattering method.
0.1-20 mass% is preferable in the total amount of a negative electrode active material layer, as for content of a binder, 0.5-10 mass% is more preferable, 1-5 mass% is still more preferable.

  The thickness of the negative electrode active material layer is preferably 1 to 150 μm, more preferably 5 to 130 μm, and still more preferably 10 to 120 μm.

The negative electrode current collector is not particularly limited as long as it has a plurality of through holes, but a metal material is preferably used. Examples of the metal material include metal foils such as aluminum foil, copper foil, and electrolytic copper foil, expanded metal, punch metal, and foam metal. The thickness of the metal foil is preferably 1 to 500 μm, more preferably 2 to 50 μm, and still more preferably 5 to 30 μm. The negative electrode active material layer is formed on one or both surfaces in the thickness direction of the negative electrode current collector.
The shape of the through hole is not particularly limited, and examples thereof include a circle, an ellipse, a quadrangle, a triangle, and a polygon.
The area of the opening of the one through hole is preferably 9 × 10 ⁻¹¹ to 8 × 10 ⁻⁷ m ² from the viewpoint of charge / discharge cycle characteristics, and 1 × 10 ^{−10 to} 3 × 10 ^−8. m ² is more preferable, and 4 × 10 ⁻¹⁰ to 1 × 10 ⁻⁸ m ² is even more preferable.
Further, the aperture ratio due to the through holes of the current collector is preferably 5 to 50%, more preferably 10 to 50%, from the viewpoint of charge / discharge cycle characteristics and the strength of the negative electrode current collector, 15 More preferably, it is -40%.
Further, the ten-point average roughness (Rz) of the current collector forming surface forming the negative electrode active material layer is preferably 1.5 μm or more, more preferably 1.6 μm or more, and even more preferably 1.7 μm or more. . The upper limit of the ten-point average roughness (Rz) of the current collector forming surface is not particularly limited, but is 5 μm or less from a practical viewpoint.
The ten-point average roughness (Rz) is, for example, using Handy Surf E-35B (manufactured by Tokyo Seimitsu Co., Ltd.), JIS standard (JISB 0633: 2001), “Product geometric characteristic specification (GPS) —Surface property: Contour”. The measurement can be carried out according to the curve method—surface texture evaluation method and procedure ”).

The lithium ion secondary battery of this invention can take the structure similar to the conventional lithium ion secondary battery except a negative electrode. For example, the lithium ion secondary battery of the present invention includes (a) a positive electrode, (b) a negative electrode, (c) an insulating layer, and (d) a nonaqueous electrolyte.
The positive electrode includes a positive electrode current collector and a positive electrode active material layer.
The positive electrode active material layer is formed on one or both surfaces in the thickness direction of the positive electrode current collector, contains a positive electrode active material, and further contains a conductive material, a binder, and the like as necessary. Good. As the positive electrode active material, those commonly used in this field can be used, and examples thereof include lithium-containing composite metal oxides, olivine-type lithium salts, chalcogen compounds, and manganese dioxide. The lithium-containing composite metal oxide is a metal oxide containing lithium and a transition metal or a metal oxide in which a part of the transition metal in the metal oxide is substituted with a different element. Here, examples of the different elements include Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, V, and B. Mn, Al, Co, Ni, Mg and the like are preferable. One kind or two or more kinds of different elements may be used.
Among these, lithium-containing composite metal oxides can be preferably used. Specific examples of the lithium-containing composite metal oxide, for _{example, LixCoO 2, LixNiO 2, LixMnO} 2, LixCoyNi 1 -yO 2, LixCoyM 1 -yOz, LixNi 1 -yMyOz, LixMn 2 O 4, LixMn 2 -yMyO 4, LiMPO ₄ , Li ₂ MPO ₄ F (in the above formulas, M is a group consisting of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, V, and B) At least one element selected from: x = 0 to 1.2, y = 0 to 0.9, and z = 2.0 to 2.3). Here, x value which shows the molar ratio of lithium increases / decreases by charging / discharging. Further, as the olivine type lithium salts such as LiFePO _4. Examples of the chalcogen compound include titanium disulfide and molybdenum disulfide. A positive electrode active material can be used individually by 1 type, or can use 2 or more types together.

  As the conductive material, for example, carbon black, graphite, carbon fiber, or metal fiber can be used. Examples of carbon black include acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black. Examples of graphite include natural graphite and artificial graphite. A conductive material can be used individually by 1 type or in combination of 2 or more types.

  As the binder, for example, polyethylene, polypropylene, polyvinyl acetate, polymethyl methacrylate, nitrocellulose, fluororesin, and rubber particles can be used. Examples of the fluororesin include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and vinylidene fluoride-hexafluoropropylene copolymer. Examples of the rubber particles include styrene-butadiene rubber particles and acrylonitrile rubber particles. Among these, in consideration of improving the oxidation resistance of the positive electrode active material layer, a binder containing fluorine is preferable. A binder can be used individually by 1 type, or can be used in combination of 2 or more type as needed.

The positive electrode active material layer can be formed, for example, by applying a positive electrode mixture paste on the surface of the conductive layer that is a positive electrode current collector, drying, and rolling as necessary. The positive electrode mixture paste can be prepared, for example, by adding a positive electrode active material to a dispersion medium together with a binder, a conductive material, and the like, if necessary. For example, N-methyl-2-pyrrolidone (NMP), tetrahydrofuran, or dimethylformamide can be used as the dispersion medium.
Examples of the positive electrode current collector include stainless steel, aluminum, a sheet containing titanium, and foil. Among these, aluminum is preferable. Although the thickness of a sheet | seat and foil is not specifically limited, For example, it is preferable that it is 1-500 micrometers, it is more preferable that it is 2-50 micrometers, and it is still more preferable that it is 5-30 micrometers.

  The insulating layer is provided so as to be interposed between the positive electrode and the negative electrode, and insulates the positive electrode from the negative electrode. As the insulating layer, an ion permeable material such as a separator or an inorganic porous film can be used. As the separator, those commonly used in the field of non-aqueous electrolyte secondary batteries can be used, and examples thereof include a resin porous sheet. Examples of the resin constituting the resin porous sheet include polyolefins such as polyethylene and polypropylene, polyamides, and polyamideimides. Non-woven fabrics, woven fabrics and the like are included in the resin porous sheet. Among these, a porous sheet in which the diameter of pores formed inside is about 0.05 to 0.15 μm is preferable. Such a porous sheet has high levels of ion permeability, mechanical strength, and insulation. Further, the thickness of the porous sheet is not particularly limited.

  Examples of the non-aqueous electrolyte include a liquid non-aqueous electrolyte, a gel-like non-aqueous electrolyte, and a solid electrolyte (for example, a polymer solid electrolyte). The liquid non-aqueous electrolyte contains a solute (supporting salt) and a non-aqueous solvent, and further contains various additives as necessary. Solutes usually dissolve in non-aqueous solvents. For example, the insulating layer is impregnated with the liquid non-aqueous electrolyte.

As the solute, those commonly used in this field can be used. For example, LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiB ₁₀ Cl ₁₀ , lower aliphatic lithium carboxylates, LiCl, LiBr, LiI, chloroborane lithium, borates and imide salts. Examples of borates include lithium bis (1,2-benzenediolate (2-)-O, O ') and bis (2,3-naphthalenedioleate (2-)-O, O') boric acid. Lithium, bis (2,2'-biphenyldiolate (2-)-O, O ') lithium borate, bis (5-fluoro-2-olate-1-benzenesulfonic acid-O, O') lithium borate Etc. Examples of the imide salts include lithium bistrifluoromethanesulfonate imide ((CF ₃ SO ₂ ) ₂ NLi), lithium trifluoromethanesulfonate nonafluorobutanesulfonate ((CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ) NLi) ), Lithium bispentafluoroethanesulfonate imide ((C ₂ F ₅ SO ₂ ) ₂ NLi), and the like. A solute may be used individually by 1 type, or may be used in combination of 2 or more type as needed. The amount of the solute dissolved in the non-aqueous solvent is preferably in the range of 0.5 to 2 mol / L.

  As the non-aqueous solvent, those commonly used in this field can be used, and examples thereof include cyclic carbonate esters, chain carbonate esters, and cyclic carboxylic acid esters. Examples of the cyclic carbonate include propylene carbonate (PC) and ethylene carbonate (EC). Examples of the chain carbonate include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). Examples of the cyclic carboxylic acid ester include γ-butyrolactone (GBL) and γ-valerolactone (GVL). A non-aqueous solvent may be used individually by 1 type, or may be used in combination of 2 or more type as needed.

(Lithium ion secondary battery)
An embodiment in which the present invention is applied to a laminated battery will be described.
A laminate-type lithium ion secondary battery can be manufactured, for example, as follows. First, the positive electrode and the negative electrode are cut into squares, and tabs are welded to the respective electrodes to produce positive and negative electrode terminals. A laminated body in which the positive electrode, the insulating layer, and the negative electrode are laminated in this order is prepared, and in that state, accommodated in an aluminum laminate pack, and the positive and negative electrode terminals are taken out of the aluminum laminate pack and sealed. Next, the nonaqueous electrolyte is poured into the aluminum laminate pack, and the opening of the aluminum laminate pack is sealed. Thereby, a lithium ion secondary battery is obtained.

Next, an embodiment in which the present invention is applied to a 18650 type cylindrical lithium ion secondary battery will be described with reference to the drawings.
As shown in FIG. 1, the lithium ion secondary battery 1 of this embodiment has a bottomed cylindrical battery case 6 made of steel plated with nickel. The battery container 6 accommodates an electrode group 5 in which a strip-like positive electrode plate 2 and a negative electrode plate 3 are wound in a spiral shape with a separator 4 interposed therebetween. In the electrode group 5, the positive electrode plate 2 and the negative electrode plate 3 are wound in a spiral shape in cross section via a separator 4 made of a polyethylene porous sheet. For example, the separator 4 has a width of 58 mm and a thickness of 30 μm. A ribbon-like positive electrode tab terminal made of aluminum and having one end fixed to the positive electrode plate 2 is led out on the upper end surface of the electrode group 5. The other end of the positive electrode tab terminal is joined by ultrasonic welding to the lower surface of a disk-shaped battery lid that is disposed on the upper side of the electrode group 5 and serves as a positive electrode external terminal. On the other hand, a ribbon-like negative electrode tab terminal made of copper with one end fixed to the negative electrode plate 3 is led out on the lower end surface of the electrode group 5. The other end of the negative electrode tab terminal is joined to the inner bottom of the battery container 6 by resistance welding. Therefore, the positive electrode tab terminal and the negative electrode tab terminal are respectively led out to the opposite sides of the both end surfaces of the electrode group 5. In addition, the insulation coating which abbreviate | omitted illustration is given to the outer peripheral surface whole periphery of the electrode group 5. FIG. The battery lid is caulked and fixed to the upper part of the battery container 6 via an insulating resin gasket. For this reason, the inside of the lithium ion secondary battery 1 is sealed. In addition, a non-aqueous electrolyte (not shown) is injected into the battery container 6.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. (Examples 1-3, Comparative Example 1 and Reference Examples 1-2)
(1) Production of positive electrode A positive electrode plate was produced as follows. Layered lithium-nickel-manganese-cobalt composite oxide (NMC) to (positive electrode active material, Mitsubishi Chemical Corporation) 87 parts by mass of acetylene black (conductive material as the conductive material, trade name: HS-100, average particle size 48 nm (manufactured by Denki Kagaku Kogyo Co., Ltd. catalog value) produced by Denki Kagaku Kogyo Kabushiki Kaisha) 7 parts by mass of polyvinylidene fluoride (binder, trade name: Kureha KF polymer # 1120, manufactured by Kureha Corporation) 6 parts by mass of N- Methyl-2-pyrrolidone (NMP) was thoroughly mixed to prepare a positive electrode mixture paste. This positive electrode mixture paste was applied to the surface of the conductive layer of the positive electrode current collector (aluminum foil), dried at 80 ° C. and rolled to form a positive electrode mixture layer having a total thickness of about 200 μm, thereby producing a positive electrode. .
Then, the drying process was performed and it consolidated by the press to the predetermined density. The density of the positive electrode mixture was 2.55 g / cm ³ and the coating amount of the positive electrode mixture was 342 g / m ² . The aluminum foil had a rectangular shape with a short side (width) of 350 mm, and an uncoated portion with a width of 50 mm was left along the long side on one side. Then, the drying process was performed and it consolidated by the press to the predetermined density. Next, a positive electrode plate having a width of 350 mm was obtained by cutting. At this time, a notch was made in the uncoated part, and the remaining part of the notch was used as a lead piece. The width of the lead piece was 10 mm, and the interval between adjacent lead pieces was 20 mm.

(2) Production of negative electrode A negative electrode plate was produced as follows. Artificial graphite (average particle size 20 μm) 88 parts by mass as a carbon material and carbon-coated SiO (average particle size 10 μm) 9 parts by mass as a silicon compound, carboxymethyl cellulose (thickener, trade name: CMC # 2200, Daicel Corporation) Ltd.) 1 part by mass, the acrylic polymer 2 parts by weight obtained in the following synthesis example as a binder (solid content) were added sequentially to give a mixture of the negative electrode material by mixing. Further, water as a dispersion solvent was added to the mixture and kneaded to form a slurry. This slurry was applied substantially uniformly and uniformly on one side of a copper foil as a negative electrode current collector. The copper foil is an electrolytic copper foil having a through-hole (thickness 10 μm, through-hole diameter 90.9 μm, through-hole area 6.4 × 10 ⁻⁹ m ² , aperture ratio 34.7%, ten-point surface roughness of the slurry application surface. (Rz) = 1.75 μm, manufactured by Hitachi Chemical Co., Ltd., trade name: TH-2090) was used. Then, after drying at 80 ° C., consolidation was performed, the negative electrode mixture density was 1.8 g / cm ^3, and the single-side coating amount was 100 g / m ² on the current collector of the negative electrode mixture. The copper foil had a rectangular shape with a short side (width) of 350 mm, and an uncoated portion with a width of 50 mm was left along the long side on one side. Then, the drying process was performed and it consolidated by the press to the predetermined density. Next, a negative electrode plate having a width of 350 mm was obtained by cutting. At this time, a notch was made in the uncoated part, and the remaining part of the notch was used as a lead piece. The width of the lead piece was 10 mm, and the interval between adjacent lead pieces was 20 mm.

Synthesis example <acrylic polymer>
In a 0.5 liter three-necked flask equipped with a stirrer, thermometer, condenser, and liquid feed pump, 335 g of water and 2 masses of carboxymethyl cellulose (trade name: CMC # 2200, manufactured by Daicel Finechem Co., Ltd.) as an emulsifier 21.46 g of a% aqueous solution was added, and the operation of reducing the pressure to 2.6 kPa (20 mmHg) with an aspirator and then returning to normal pressure with nitrogen was repeated three times to remove dissolved oxygen. The flask was maintained in a nitrogen atmosphere, heated to 60 ° C. with an oil bath while stirring, and 0.26 g of potassium persulfate was dissolved in 8 g of water and added to the three-necked flask.
After adding potassium persulfate, 16.98 g of acrylonitrile (manufactured by Wako Pure Chemical Industries, Ltd.) (a proportion of 40 mol% in the total monomer amount (100 mol%)), represented by the general formula (II) 68.26 g of butyl methacrylate (manufactured by Wako Pure Chemical Industries, Ltd.) which is a monomer (R ²¹ is a methyl group and R ²² is a butyl group having 4 carbon atoms) (60% in total monomer amount (100 mol%)) Mol%), an ethoxylated pentaerythritol tetraacrylate (Shin Nakamura Chemical Co., Ltd.), which is a compound represented by the general formula (I) (R ¹ is a hydrogen atom, n is 4, and R ² is an ethoxylated pentaerythritol group) Product name: ATM-4E (product name: ATM-4E) 0.34 g (0.04 mol% relative to the total monomer amount (100 mol%)) Drop emulsion over time to conduct emulsion polymerization . The reaction conversion rate of the monomer after completion of dropping of the monomer composition was 51%. After stirring for 1 hour, the temperature was raised to 80 ° C., and stirring was further continued for 2 hours to obtain an aqueous dispersion of acrylic polymer particles. About 1 ml of the obtained aqueous dispersion was weighed in an aluminum pan, dried on a hot plate heated to 160 ° C. for 15 minutes, and the non-volatile content was calculated from the weight of the residue to find 15.3% by mass (copolymer yield). 98%).

(3) Production of Laminate Battery The produced negative electrode was cut into a 13.9 cm ² square to obtain an evaluation electrode. Next, the positive electrode produced above was cut into a 13.5 cm ² square, and a separator made of a polyethylene microporous film (trade name: Hypore, manufactured by Asahi Kasei Co., Ltd., “Hypore” is a registered trademark), 13.9 cm ² A laminated body in which negative electrodes cut into squares were superposed was produced. This laminate is put into an aluminum laminate container (trade name: aluminum laminate film, manufactured by Dai Nippon Printing Co., Ltd.), and an electrolytic solution (ethylene carbonate / methyl ethyl carbonate containing 1M LiPF ₆ = 3/7 mixed solution (volume ratio)). 1 mL of vinylene carbonate added to the total amount of the mixed solution was added, and 1 mL of Kishida Chemical Co., Ltd.) was added, and an aluminum laminate container was thermally welded to produce a battery for electrode evaluation.
The negative electrode produced above was cut into a 13.9 cm ² square to obtain an evaluation electrode. A positive electrode similar to the positive electrode (13.5 cm ² square) used in Example 1 was produced, and this positive electrode and a polyethylene porous sheet separator (trade name: Hypore, manufactured by Asahi Kasei Co., Ltd., thickness: 30 μm) And the laminated body which piled up the negative electrode cut | disconnected in the square of 13.9cm < ² > in this order was produced. This laminate is placed in an aluminum laminate container (trade name: Aluminum Laminate Film, Dai Nippon Printing Co., Ltd.), and a non-aqueous electrolyte (ethylene carbonate / methyl ethyl carbonate / dimethyl carbonate = 2/1/3 containing 1M LiPF ₆ ). 1 mL of a mixed solution (volume ratio) with 0.8% by mass of vinylene carbonate added to the total amount of the mixed solution, trade name: Sollite, Mitsubishi Chemical Corporation, “Sollite” is a registered trademark), and aluminum A laminate container was thermally welded to prepare a battery for evaluating cycle characteristics.

(Example 2)
Electrolytic copper foil having through-holes (thickness 15 μm, through-hole diameter 31.8 μm, through-hole area 7.9 × 10 ⁻¹⁰ m ² , aperture ratio 18.7%, ten-point surface of slurry application surface A laminated battery of the present invention was produced in the same manner as in Example 1, except that the copper foil having a roughness (Rz) of 2.05 μm (made by Hitachi Chemical Co., Ltd.) was used.

Example 3
As shown in Table 1, 92 parts by mass of artificial graphite, 5 parts by mass of SiO, 2 parts by mass of an acrylic polymer, and 1 part by mass of CMC were mixed to obtain a mixture of negative electrode materials. Further, water as a dispersion solvent was added to this mixture and kneaded to form a slurry. This slurry was applied substantially evenly and uniformly to one surface of an electrolytic copper foil (through-hole diameter 90.9 μm) similar to that of Example 1 serving as a negative electrode current collector. And it processed like Example 1, the negative electrode was produced, and the laminate type battery was produced.

(Example 4)
(1) Production of positive electrode A positive electrode plate was produced as follows. Layered lithium-cobalt oxide (LCO) to (positive electrode active material, Nichia Corporation) 95 parts by mass of acetylene black as a conductive material (conductive material, trade name: HS-100, average particle size 48 nm (electric chemical industry Co., Ltd. catalog value), manufactured by Denki Kagaku Kogyo Co., Ltd.) 2.5 parts by mass of polyvinylidene fluoride (binder, trade name: Kureha KF polymer # 1120, manufactured by Kureha Corporation) 2.5 parts by mass of N -Methyl-2-pyrrolidone (NMP) was thoroughly mixed to prepare a positive electrode mixture paste. This positive electrode mixture paste was applied to the surface of the conductive layer of the positive electrode current collector (aluminum foil), dried at 80 ° C. and rolled to form a positive electrode mixture layer having a total thickness of about 200 μm, thereby producing a positive electrode. .
Then, the drying process was performed and it consolidated by the press to the predetermined density. The density of the positive electrode mixture was 3.7 g / cm ³ and the coating amount of the positive electrode mixture was 295 g / m ² . Thereafter, the same procedure as in the preparation of the positive electrode in Example 1 was performed.
(2) Production of negative electrode A negative electrode plate was produced as follows. The carbon-coated SiO (average particle size 10 [mu] m) 5 parts by weight of artificial graphite (average particle size 20 [mu] m) 87 parts by weight and the silicon compound as the carbon material, acetylene black (conductive material as the conductive material, trade name: HS-100, average Particle size 48nm (Electrochemical Industry Co., Ltd. catalog value), Electrochemical Industry Co., Ltd. 5 parts by mass, Carboxymethylcellulose (Thickener, Trade name: CMC # 2200, Daicel Chemical Co., Ltd.) 1 part, acrylic polymer 2 parts by mass obtained in synthesis example (solid content) were added sequentially as adherend to obtain a mixture of the negative electrode material by mixing. This slurry was applied substantially uniformly and uniformly on one side of a copper foil as a negative electrode current collector. The copper foil is an electrolytic copper foil having a through-hole (thickness 10 μm, through-hole diameter 90.9 μm, through-hole area 6.4 × 10 ⁻⁹ m ² , aperture ratio 34.7%, ten-point surface roughness of the slurry application surface. (Rz) = 1.75 μm, manufactured by Hitachi Chemical Co., Ltd., trade name: TH-2090) was used. Then, after drying at 80 ° C., consolidation was performed, the negative electrode mixture density was 1.8 g / cm ^3, and the single-side coating amount was 120 g / m ² to the negative electrode current collector. Thereafter, the same procedure as in the preparation of the negative electrode of (Example 1) was performed.
(3) Production of Laminate Type Battery A laminate type battery was produced in the same manner as in Example 1 except that the positive electrode and the negative electrode were used.

(Comparative Example 1)
The same as Example 1 except that it was applied to an electrolytic copper foil having a thickness of 11 μm having no through-holes (ten-point surface roughness (Rz) of slurry applied surface = 1.20 μm, manufactured by Nihon Electrolytic Co., Ltd.) Thus, a laminate type battery was produced.

(Reference Example 1)
As shown in Table 1, 97 parts by mass of artificial graphite, 2 parts by mass of acrylic polymer, and 1 part by mass of CMC were mixed without using SiO to obtain a mixture of negative electrode materials. Further, water as a dispersion solvent was added to this mixture and kneaded to form a slurry. This slurry was applied substantially evenly and uniformly to one surface of an electrolytic copper foil (through-hole diameter 90.9 μm) similar to that of Example 1 serving as a negative electrode current collector. And it processed like Example 1, the negative electrode was produced, and the laminate type battery was produced.

(Reference Example 2)
Using the same slurry as in Reference Example 1, a negative electrode was prepared using an electrolytic copper foil having a thickness of 11 μm and having no through holes as in Comparative Example 1, and a laminate type battery was prepared in the same manner as in Example 1. .

(Evaluation of initial discharge capacity)
For the lithium ion secondary batteries obtained in Examples 1 to 4, Comparative Example 1 and Reference Examples 1 to 2, the initial discharge capacity at 25 ° C. was charged / discharged (Toyo System Co., Ltd., trade name: TOSCAT-3200, “TOSCAT” was measured using a registered trademark. First, in an environment of 25 ° C., a charge / discharge cycle was repeated twice with a current value of 0.1 C (11.56 mA) in a voltage range of 2.7 to 4.2 V. Further, constant current and constant voltage charging (CCCV) was performed to a current value of 4.2 V and 0.01 C (1.156 mA) at a current value of 0.1 C. Subsequently, discharge was performed by constant current discharge (CC) with a current value of 0.1 C (11.56 mA) and a final voltage of 2.7 V. The discharge capacity at this time was defined as the initial discharge capacity. The measurement results are shown in Table 1.

(Evaluation of discharge capacity at 1C)
Using the battery whose initial discharge capacity was evaluated, constant current and constant voltage charging (CCCV) was performed at a current value of 0.1 C to a current value of 4.2 V and 0.01 C (1.156 mA). Subsequently, discharging was performed by constant current discharge with a current value of 1C (115.6 mA) and a final voltage of 2.7 V. The discharge capacity at this time was defined as the discharge capacity at 1C. The measurement results are shown in Table 1.

(100th discharge capacity with 1C charge / discharge)
Furthermore, after evaluating the discharge capacity at 1C, the charge / discharge current value was set to 1C, and the charge / discharge test was performed 100 times under the same conditions as the evaluation of the initial discharge capacity. The discharge capacity for the 100th time was taken. The measurement results are shown in Table 1.

  The batteries of Examples 1 to 4 had higher discharge capacities than those of Comparative Example 1 and Reference Example 2 having no through holes in the capacity at the 100th cycle of 1C cycle. Moreover, it was high discharge capacity also compared with the reference example 2 which has a through-hole. From this, the copper foil of the present invention relieves stress during expansion and contraction of SiOx, thereby excellent discharge capacity after multiple cycles, suppresses large expansion and contraction due to charge and discharge, and deteriorates electronic conductivity. It is possible to provide a negative electrode for a lithium ion secondary battery that is difficult to cause, and a lithium ion secondary battery using the negative electrode.

  The non-aqueous electrolyte secondary battery of the present invention is excellent in cycle characteristics as compared with a copper foil having no through-hole, and can be suitably used for the same applications as conventional non-aqueous electrolyte secondary batteries. In particular, it can be suitably used as a power source for various portable electronic devices such as a mobile phone, a notebook personal computer, a portable information terminal, an electronic dictionary, and a game device. When used in such applications, stress due to expansion and contraction of SiOx is relieved. The nonaqueous electrolyte secondary battery of the present invention can also be applied to uses such as for transportation equipment such as electric vehicles and hybrid vehicles.

DESCRIPTION OF SYMBOLS 1 ... Lithium ion secondary battery 2 ... Positive electrode plate 3 ... Negative electrode plate 4 ... Separator 5 ... Electrode group 6 ... Battery container

Claims (10)

A negative electrode for a lithium ion secondary battery in which a negative electrode active material layer is formed on at least one surface of a current collector, wherein the negative electrode active material layer includes a carbon material and a silicon-based compound, and the current collector includes a plurality of current collectors have a through-hole, the content of the carbon material and the silicon-based compound, a carbon material: silicon compound = 95: 5-85: 15 negative electrode for a lithium ion secondary battery as (mass ratio). ^{2. The} negative electrode for a lithium ion secondary battery according to claim 1, wherein an area of an opening of one of the through holes is 9 × 10 ⁻¹¹ to 8 × 10 ⁻⁷ m ² .   The negative electrode for a lithium ion secondary battery according to claim 1 or 2, wherein an aperture ratio of the current collector through the through hole is 10 to 50%. The average particle diameter of the carbon material, a negative electrode for a lithium ion secondary battery according to any one of claims 1 to 3, which is 1 to 200 [mu] m. The silicon-based compound, a negative electrode for a lithium ion secondary battery according to any one of claims. 1 to 4 Si in SiO ₂ are dispersed structure. The silicon-based compound, SiOx (0.5 ≦ x ≦ 1.5 ) and a claim from 1 to 5 or the negative electrode for a lithium ion secondary battery according to one of. The negative electrode for a lithium ion secondary battery according to claim 6 , wherein the average particle diameter of the SiOx is 0.1 to 40 μm. The lithium ion secondary according to any one of claims 1 to 7 , wherein a ten-point average roughness (Rz) of a surface of the current collector on a side on which the negative electrode active material layer is formed is 1.5 µm or more. Battery negative electrode. The negative electrode for a lithium ion secondary battery according to any one of claims 1 to 8 , wherein a ten-point average roughness (Rz) of a surface of the current collector on which the negative electrode active material layer is formed is 5 µm or less. Lithium-ion secondary battery comprising a negative electrode for a lithium ion secondary battery according to any one of claims 1-9.

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