JP2005011594A - Electrode mixture, electrode, and battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode mixture capable of improving fluidity and restraining the increase of viscosity. <P>SOLUTION: A positive electrode mixture contains a multivalent organic acid such as oxalic acid or a succinic acid in addition to a positive electrode active substance such as LiFePO<SB>4</SB>, a binder such as polyvinylidene fluoride, a conductive material such as carbon black and acetylene black, and a solvent such as N-methyl-2-pyrrolidone. A positive electrode mixture layer 21B is formed by coating the positive electrode mixture on a positive electrode collector 21A. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００５７】
この作製した正極合剤について、室温２５℃で２時間保存したのち、室温においてＢ型粘度計にて粘度を測定した。その結果を表１および図３に示す。なお、粘度が１５Ｐａ・ｓ以下の場合には、粘度上昇が殆ど見られないと判断し、表１には粘度上昇抑制効果が「 強い」 と記載し、１６Ｐａ・ｓ〜２５Ｐａ・ｓの場合には、やや粘度上昇抑制効果があると判断し、表１には粘度上昇抑制効果が「 有り」 と記載し、２６Ｐａ・ｓ以上の場合には、粘度上昇抑制効果がないものと判断し、表１には粘度上昇抑制効果が「 無し」 と記載した。
【００５８】
また、作製した正極合剤を用いて、次のようにしてリチウムイオン二次電池を作製した。まず、作製した正極合剤を厚み２０μｍの帯状のアルミニウム箔よりなる正極集電体２１Ａの両面に均一に塗布して乾燥させたのち、ローラープレス機により圧縮成型し、正極合剤層２１Ｂを形成した。そののち、適当な幅に裁断し、帯状の正極２１を作製した。作製した実施例１〜１５の正極２１について、ＪＩＳＢ ７７２１に規定される１８０°剥離強度測定法により正極合剤層２１Ｂの正極集電体２１Ａからの剥離強度を測定した。その結果を表１および図３に示す。
【００５９】
また、粉砕したピッチコークスを負極活物質とし、このピッチコークスと結着剤であるポリフッ化ビニリデン粉末とを９０：１０の質量比で混合し、溶剤であるＮ−メチル−２−ピロリドンに分散させて負極合剤を作製した。次いで、この負極合剤を厚み１０μｍの帯状の銅箔よりなる負極集電体２２Ａの両面に均一に塗布して乾燥させたのち、ローラープレス機により圧縮成型して負極合剤層２２Ｂを形成した。そののち、適当な幅に裁断し、帯状の負極２２を作製した。
【００６０】
更に、エチレンカーボネートとプロピレンカーボネートとを混合した溶媒に電解質塩であるＬｉＰＦ_６ を溶解させ電解液を作製した。そののち、この電解液と、高分子材料と、溶剤であるジメチルカーボネートとを混合攪拌し電解質を得た。続いて、正極集電体２１Ａに正極リード線１１を取り付けると共に、正極合剤層２１Ｂの上に電解質を塗布し、ジメチルカーボネートを揮発させ、電解質層２４を形成した。また、負極集電体２２Ａに負極リード線１２を取り付けると共に、負極合剤層２２Ｂの上に電解質を塗布し、ジメチルカーボネートを揮発させ、電解質層２４を形成した。続いて、厚み１０μｍの微孔性ポリプロピレンフィルムよりなるセパレータ２３を用意し、セパレータ２３，正極２１，セパレータ２３，負極２２の順に積層して巻回し、電池素子２０とした。次いで、この電池素子２０を、アルミラミネートフィルムよりなる外装部材３０の内部に真空パックした。以上の工程により図１および図２に示した二次電池を完成させた。
【００６１】
作製した実施例１〜１５の二次電池について、充電電流を１００ｍＡの定電流とし、電池電圧が３．６Ｖに達するまで充電を行ったのち、放電電流を１００ｍＡの定電流とし、電池電圧が２．０Ｖに達するまで放電を行うという充放電サイクル試験を行い、充放電容量が安定する１０サイクル目の放電容量を測定した。表１および図４にその１０サイクル目の放電容量を示す。また、充電電流を１００ｍＡの定電流とし、電池電圧が３．６Ｖに達するまで充電を行ったのち、放電電流を１０００ｍＡの定電流とし電池電圧が２．０Ｖに達するまで放電を行うという重負荷充放電試験を行い、放電容量を測定した。表１および図４にその重負荷放電容量を示す。
【００６２】
また、実施例１〜１５に対する比較例１として、多価の有機酸を添加しないことを除き、他は実施例１〜１５と同様にして正極合剤を作製すると共に、この正極合剤を用いて二次電池を作製した。更に、実施例１〜１５に対する比較例２として、多価の有機酸の代わりに１価の有機酸である酢酸を正極活物質１ｋｇに対して２．０×１０^−２ｍｏｌの割合で用いたことを除き、他は実施例１〜１５と同様にして正極合剤を作製すると共に、この正極合剤を用いて二次電池を作製した。比較例１，２についても、実施例１〜１５と同様にして、正極合剤の粘度、正極合剤層の正極集電体からの剥離強度、１０サイクル目の放電容量および重負荷放電容量を調べた。表１，図３および図４にそれらの結果を合わせて示す。
【００６３】
表１，図３および図４に示したように、多価の有機酸を用いた実施例１〜１５によれば、比較例１に比べて正極合剤の粘度を低くすることができた。また、比較例１に比べて、正極合剤層２１Ｂの正極集電体２１からの剥離強度および重負荷放電容量を向上させることができ、１０サイクル目の放電容量についても比較例１と同等あるいはそれよりも大きくすることができた。これに対して、１価の有機酸である酢酸を用いた比較例２では、正極合剤層の正極集電体からの剥離強度、１０サイクル目の放電容量および重負荷放電容量のいずれも大きく劣化してしまった。また、正極合剤作製時、塗布時および乾燥時に不快な刺激臭を伴うなどの不具合が生じた。すなわち、正極合剤に多価の有機酸を含むようにすれば、正極合剤の粘度を低下させることができ、正極合剤層２１Ｂの正極集電体２１からの剥離強度、充放電サイクル特性および重負荷放電特性を向上させることができると共に、プロセス的にも好ましいことが分かった。
【００６４】
また、正極合剤の粘度はシュウ酸またはコハク酸の含有量を増加させると低下し、極大値を示したのち増大する傾向が見られ、正極合剤層２１Ｂの正極集電体２１からの剥離強度、１０サイクル目放電容量および重負荷放電容量はシュウ酸またはコハク酸の含有量を増加させると増大し、極大値を示したのち低下する傾向が見られた。すなわち、多価の有機酸の含有量は、正極活物質１ｋｇに対して３．５×１０^−２ｍｏｌ以下とすることが好ましいことが分かった。また、シュウ酸の含有量は２．０×１０^−３ｍｏｌ以上とすることが好ましく、コハク酸の含有量は１．０×１０^−２ｍｏｌ以上とすることが好ましいことも分かった。
【００６５】
なお、上記実施例では、多価の有機酸について具体的に例を挙げて説明したが、他の多価の有機酸を用いても同様の結果を得ることができる。
【００６６】
以上、実施の形態および実施例を挙げて本発明を説明したが、本発明は上記実施の形態および実施例に限定されるものではなく、種々変形可能である。例えば、上記実施の形態および実施例では、いわゆるゲル状の電解質を用いる場合について説明したが、他の電解質を用いるようにしてもよい。他の電解質としては、電解液、窒化リチウムあるいはヨウ化リチウムなどの無機固体電解質、あるいは電解液，ゲル状の電解質，無機固体電解質のいずれか１種または２種以上を混合したものが挙げられる。
【００６７】
また、本発明は、正極合剤に限らず負極合剤などの電極合剤一般に適用することができる。
【００６８】
更に、上記実施の形態および実施例では、巻回ラミネート型の二次電池について説明したが、本発明は、積層ラミネート型の二次電池についても同様に適用することができる。加えて、いわゆる円筒型、角型、コイン型、ボタン型などの他の形状の二次電池についても適用することができる。更にまた、二次電池に限らず、一次電池についても適用することができる。
【００６９】
加えてまた、上記実施の形態および実施例では、電解質塩としてリチウム塩を用いる場合について説明したが、ナトリウム塩あるいはカリウム塩などの長周期型周期表における他の１族元素の塩、またはマグネシウム塩あるいはカルシウム塩などの長周期型周期表における他の２族元素の塩、またはアルミニウム塩などの他の軽金属塩を用いる場合についても本発明を適用することができる。その際、正極活物質、負極活物質および溶媒などは、その電解質塩に応じて選択される。
【００７０】
【発明の効果】
以上説明したように本発明による電極合剤によれば、多価の有機酸を含むようにしたので、流動性を向上させることができると共に、時間経過に伴う粘度の上昇を抑制することができる。よって、塗布精度を向上させることができる。
【００７１】
また、本発明による第１の電極によれば、多価の有機酸を含むようにしたので、また、本発明による第２の電極によれば、多価の有機酸を含む電極合剤を用いて形成されたものであるので、電極の表面性状を向上させることができ、それにより電極反応の均一性を高めることができると共に、強度を向上させることができる。
【００７２】
更に、本発明による第１の電池によれば、多価の有機酸を含む正極を備えるようにしたので、また、本発明による第２の電池によれば、多価の有機酸を含む電極合剤を用いて形成された正極を備えるようにしたので、充放電サイクル特性および重負荷放電特性などの電池特性を向上させることができる。
【００７３】
特に、多価の有機酸の含有量を、電極活物質１ｋｇに対して３．５ｍｏｌ×１０^−２ｍｏｌ以下とするようにすれば、より高い効果を得ることができる。
【図面の簡単な説明】
【図１】本発明の一実施の形態に係る二次電池を分解して表す斜視図である。
【図２】図１に示した電池素子のＩＩ−ＩＩ線に沿った断面図である。
【図３】本発明の実施例１〜１２に係る多価の有機酸の含有量と粘度および剥離強度との関係を示す特性図である。
【図４】本発明の実施例１〜１２に係る多価の有機酸の含有量と１０サイクル目の放電容量および重負荷放電容量との関係を示す特性図である。
【符号の説明】
１１…正極リード線、１２…負極リード線、２０…電池素子、２１…正極、２１Ａ…正極集電体、２１Ｂ…正極合剤層、２２…負極、２２Ａ…負極集電体、２２Ｂ…負極合剤層、２３…セパレータ、２４…電解質層、２５…保護テープ、３０…外装部材、３１…密着フィルム。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrode mixture containing an electrode active material and a binder, an electrode, and a battery.
[0002]
[Prior art]
In recent years, a lithium ion secondary battery using a lithium metal, a lithium compound, or a substance capable of inserting and extracting lithium ions as a negative electrode active material has attracted attention due to its high voltage and excellent reversibility. Among them, lithium ion secondary batteries using a composite oxide of lithium (Li) and a transition metal as a positive electrode active material and a carbon-based material as a negative electrode active material are conventional lead secondary batteries and nickel-cadmium secondary batteries. Since it is lighter and has a larger discharge capacity than batteries, it is widely used in electronic devices such as mobile phones and notebook personal computers.
[0003]
Under such circumstances, various studies have been made on the positive electrode active material. For example, lithium cobalt composite oxide has been conventionally used as the positive electrode active material, but a lithium manganese composite oxide having a spinel crystal structure has also been studied from the viewpoint of cost and resource problems. In addition, lithium nickel-based composite oxides having a layered rock salt type crystal structure, which is said to be excellent in charge / discharge cycle characteristics at high temperatures, have attracted attention. Furthermore, olivine-type lithium oxide containing iron (Fe), which has a large production amount and is inexpensive, has also attracted attention in terms of cost and stable supply.
[0004]
Since these positive electrode active materials usually have low electron conductivity, they are used for positive electrodes together with conductive materials such as carbon black and acetylene black. The positive electrode is mainly produced by applying a positive electrode mixture obtained by mixing a positive electrode active material, a conductive material, and a binder using a solvent to a positive electrode current collector (see, for example, Patent Document 1). ).
[0005]
[Patent Document 1]
JP-A-6-333558
[0006]
[Problems to be solved by the invention]
However, since these conductive substances are bulky, if they are used in a large amount, the fluidity of the positive electrode mixture is lowered and the viscosity of the positive electrode mixture is increased with the passage of time. It becomes difficult to apply to the electric body. In order to improve the fluidity, it is necessary to use a large amount of a solvent. However, in this case, the solvent volatilizes all at once in the drying step, so that the positive electrode is severely cracked. This crack makes the positive electrode brittle, and as a result, the battery characteristics such as charge / discharge cycle characteristics or heavy load discharge characteristics are adversely affected.
[0007]
This invention is made | formed in view of this problem, The objective is to provide the electrode mixture which can improve a fluidity and can suppress a raise of a viscosity. Another object of the present invention is to provide an electrode having high strength and capable of improving charge / discharge cycle characteristics or heavy load discharge characteristics, and a battery using the electrode.
[0008]
[Means for Solving the Problems]
The electrode mixture according to the present invention contains a binder and a polyvalent organic acid together with an electrode active material.
[0009]
The 1st electrode by this invention contains a binder and a polyvalent organic acid with an electrode active material.
[0010]
The 2nd electrode by this invention is formed using the electrode mixture containing a binder and a polyvalent organic acid with an electrode active material.
[0011]
A first battery according to the present invention includes an electrolyte together with a positive electrode and a negative electrode, and the positive electrode includes a binder and a polyvalent organic acid together with an electrode active material.
[0012]
A second battery according to the present invention includes an electrolyte together with a positive electrode and a negative electrode, and the positive electrode includes a binder and a polyvalent organic acid together with an electrode active material.
[0013]
Since the electrode mixture according to the present invention contains a polyvalent organic acid, the fluidity is high and an increase in viscosity with time is suppressed.
[0014]
Since the first electrode according to the present invention contains a polyvalent organic acid, and the second electrode according to the present invention is formed using an electrode mixture containing a polyvalent organic acid, Surface properties and strength are improved.
[0015]
In the first battery according to the present invention, the positive electrode contains a polyvalent organic acid, and the surface properties and strength are improved. In the second battery according to the present invention, the positive electrode contains a polyvalent organic acid. Since it is formed using an electrode mixture and has improved surface properties and strength, excellent charge / discharge cycle characteristics and heavy load discharge characteristics can be obtained.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
[0017]
The positive electrode mixture according to one embodiment of the present invention includes a particulate positive electrode active material, a binder, and, if necessary, a conductive material and a solvent. Here, the positive electrode mixture corresponds to a specific example of “electrode mixture” in the present invention, and the positive electrode active material corresponds to a specific example of “electrode active material” in the present invention.
[0018]
As a positive electrode active material, the positive electrode material which can occlude and discharge | release lithium is mentioned, for example, These 1 type (s) or 2 or more types are used. As a positive electrode material capable of inserting and extracting lithium, for example, titanium sulfide (TiS ₂ ), Molybdenum sulfide (MoS) ₂ ), Niobium selenide (NbSe) ₂ ) Or vanadium oxide (V ₂ O ₅ ) And the like, or a lithium-containing metal sulfide or metal oxide, or a lithium composite oxide containing lithium, or a polymer material such as polyacetylene or polypyrrole.
[0019]
Among these, lithium composite oxides are preferable because there are those that can obtain a high voltage and a high energy density. Examples of such a lithium composite oxide include a chemical formula Li _x MIO ₂ Lithium oxide represented by _y MIIPO ₄ The lithium phosphorus oxide represented by these is mentioned. In the formula, MI and MII represent one or more transition metals, and preferably contain at least one of cobalt (Co), nickel (Ni), and manganese (Mn). The values of x and y vary depending on the charge / discharge state of the battery, and are generally 0.05 ≦ x ≦ 1.10 and 0.05 ≦ y ≦ 1.10. Chemical formula Li _x MIO ₂ As a specific example of the lithium oxide represented by the formula, lithium cobalt composite oxide (LiCoO ₂ ), Lithium nickel composite oxide (LiNiO) ₂ ), Lithium nickel cobalt composite oxide (LiNi _z Co _1-z O ₂ (0 <z <1)) or lithium manganese composite oxide (LiMn ₂ O ₄ ) And the like. Li _y MIIPO ₄ As the lithium phosphorus oxide represented by, for example, LiFePO ₄ Is mentioned.
[0020]
The binder joins a positive electrode active material and a positive electrode current collector described later. Examples of the binder include a fluororesin such as polyvinylidene fluoride. Any one kind of binder may be used alone, or two or more kinds thereof may be mixed and used.
[0021]
The conductive substance is for improving the conductivity of the positive electrode. Examples of the conductive material include carbon black and acetylene black. Any one of the conductive substances may be used alone, or two or more kinds thereof may be mixed and used. The solvent is used for preparing the positive electrode mixture. Examples of the solvent include N-methyl-2-pyrrolidone. Any one kind of solvents may be used alone, or two or more kinds thereof may be mixed and used.
[0022]
This positive electrode mixture also contains a polyvalent organic acid. This is because the fluidity of the positive electrode mixture can be improved and an increase in the viscosity of the positive electrode mixture with time can be suppressed. As the polyvalent organic acid, for example, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid or fumaric acid is preferable. Any one kind of polyvalent organic acids may be used alone, or two or more kinds may be mixed and used.
[0023]
The content of the polyvalent organic acid is 3.5 mol × 10 5 per 1 kg of the positive electrode active material. ^-2 It is preferably less than or equal to mol. This is because the fluidity of the positive electrode mixture can be further improved, and an increase in the viscosity of the positive electrode mixture can be further suppressed.
[0024]
This positive electrode mixture is used as follows.
[0025]
FIG. 1 is an exploded view of a lithium ion secondary battery formed using the positive electrode mixture according to the present embodiment. In the secondary battery, a battery element 20 to which a positive electrode lead wire 11 and a negative electrode lead wire 12 are attached is enclosed in a film-shaped exterior member 30.
[0026]
The positive electrode lead wire 11 and the negative electrode lead wire 12 are led out from the inside of the exterior member 30 to the outside, for example, in the same direction. The positive electrode lead wire 11 and the negative electrode lead wire 12 are each made of a metal material such as aluminum (Al), copper (Cu), nickel, or stainless steel, and each have a thin plate shape or a mesh shape.
[0027]
The exterior member 30 is made of, for example, a rectangular aluminum laminated film in which a nylon film, an aluminum foil, and a polyethylene film are bonded together in this order. For example, the exterior member 30 is disposed so that the polyethylene film side and the battery element 20 face each other, and the outer edge portions are in close contact with each other by fusion bonding or an adhesive. An adhesive film 31 for preventing the entry of outside air is inserted between the exterior member 30 and the positive electrode lead wire 11 and the negative electrode lead wire 12. The adhesion film 31 is made of a material having adhesion to the positive electrode lead wire 11 and the negative electrode lead wire 12, for example, when the positive electrode lead wire 11 and the negative electrode lead wire 12 are made of the metal material described above, It is preferably composed of a polyolefin resin such as polyethylene, polypropylene, modified polyethylene, or modified polypropylene.
[0028]
The exterior member 30 may be made of a laminated film having another structure, a polymer film such as polypropylene, or a metal film instead of the above-described aluminum laminated film.
[0029]
FIG. 2 shows a cross-sectional structure along the line II-II of the battery element 20 shown in FIG. The battery element 20 is formed by laminating and winding a positive electrode 21 and a negative electrode 22 with a separator 23 and an electrolyte layer 24 interposed therebetween, and the outermost peripheral portion is protected by a protective tape 25.
[0030]
The positive electrode 21 includes, for example, a positive electrode current collector 21A having a pair of opposed surfaces and a positive electrode mixture layer 21B provided on both surfaces or one surface of the positive electrode current collector 21A. The positive electrode current collector 21A has an exposed portion where the positive electrode mixture layer 21B is not provided at one end in the longitudinal direction, and the positive electrode lead wire 11 is attached to the exposed portion. The positive electrode current collector 21A is made of, for example, a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil.
[0031]
The positive electrode mixture layer 21B is formed using the positive electrode mixture according to the present embodiment, and contains a polyvalent organic acid in addition to the particulate positive electrode active material, the binder, and the conductive material. . Therefore, the surface properties and strength, specifically, the peel strength from the positive electrode current collector 21A is greatly improved. The content of the polyvalent organic acid varies depending on its volatility, but in the case of a low volatility, for example, 3.5 mol × 10 5 per 1 kg of the positive electrode active material. ^-2 It is preferable to be less than mol.
[0032]
The negative electrode 22 includes, for example, a negative electrode current collector 22A having a pair of opposed surfaces, and a negative electrode mixture layer 22B provided on both surfaces or one surface of the negative electrode current collector 22A, similarly to the positive electrode 21. . The negative electrode current collector 22A has an exposed portion without being provided with the negative electrode mixture layer 22B at one end in the longitudinal direction, and the negative electrode lead wire 12 is attached to the exposed portion. The negative electrode current collector 22A is made of, for example, a metal foil such as a copper foil, a nickel foil, or a stainless steel foil.
[0033]
The negative electrode mixture layer 22B includes, for example, any one or two or more negative electrode materials capable of occluding and releasing lithium as a negative electrode active material, and a binder such as polyvinylidene fluoride as necessary. An agent may be included. Examples of the negative electrode material capable of inserting and extracting lithium include carbon materials, metal oxides, and polymer materials. Examples of the carbon material include artificial graphite, natural graphite, graphitizable carbon, and non-graphitizable carbon. In addition, examples of the metal oxide include iron oxide, ruthenium oxide, molybdenum oxide, and tungsten oxide, and examples of the polymer material include polyacetylene and polypyrrole.
[0034]
Examples of the negative electrode material capable of inserting and extracting lithium include simple elements, alloys or compounds of metal elements or metalloid elements capable of forming an alloy with lithium. In addition to the alloy composed of two or more metal elements, the alloy includes an alloy composed of one or more metal elements and one or more metalloid elements. There are structures in which a solid solution, a eutectic (eutectic mixture), an intermetallic compound, or two or more of them coexist.
[0035]
Examples of metal elements or metalloid elements capable of forming an alloy with lithium include magnesium (Mg), boron (B), arsenic (As), aluminum, gallium (Ga), indium (In), silicon (Si), Germanium (Ge), tin (Sn), lead (Pb), antimony (Sb), bismuth (Bi), cadmium (Cd), silver (Ag), zinc (Zn), hafnium (Hf), zirconium (Zr), Examples thereof include yttrium (Y), palladium (Pd), and platinum (Pt). These alloys or compounds include, for example, the chemical formula Ma _s Mb _t The thing represented by is mentioned. In this chemical formula, Ma represents at least one of a metal element and a metalloid element capable of forming an alloy with lithium, and Mb represents at least one of elements other than Ma. The values of s and t are s> 0 and t ≧ 0, respectively.
[0036]
Among them, a simple substance, alloy or compound of a group 14 metal element or metalloid element in the long-period periodic table is preferable, and silicon or tin, or an alloy or compound thereof is particularly preferable. These may be crystalline or amorphous.
[0037]
Specific examples of such alloys or compounds include LiAl, AlSb, CuMgSb, SiB. ₄ , SiB ₆ , Mg ₂ Si, Mg ₂ Sn, Ni ₂ Si, TiSi ₂ , MoSi ₂ , CoSi ₂ , NiSi ₂ , CaSi ₂ , CrSi ₂ , Cu ₅ Si, FeSi ₂ , MnSi ₂ , NbSi ₂ , TaSi ₂ , VSi ₂ , WSi ₂ , ZnSi ₂ , SiC, Si ₃ N ₄ , Si ₂ N ₂ O, SiO _v (0 <v ≦ 2), SnO _w (0 <w ≦ 2), SnSiO ₃ , LiSiO or LiSnO.
[0038]
The separator 23 is made of, for example, a porous film made of synthetic resin such as polytetrafluoroethylene, polypropylene, or polyethylene, or a porous film made of ceramic, and has a structure in which two or more kinds of porous films are laminated. May be.
[0039]
The electrolyte layer 24 is configured by a so-called gel electrolyte in which an electrolytic solution is held in a polymer material. Examples of the polymer material include polyvinylidene fluoride and a copolymer of polyvinylidene fluoride, and examples of the copolymer monomer include hexafluoropropylene and tetrafluoroethylene. These polyvinylidene fluorides and copolymers thereof are preferable because high battery characteristics can be obtained, and among them, a copolymer of vinylidene fluoride and hexafluoropropylene is particularly preferable.
[0040]
As the polymer material, for example, polyacrylonitrile and a copolymer of polyacrylonitrile can be used, and the copolymer monomers such as vinyl monomers include vinyl acetate, methyl methacrylate, butyl methacrylate, acrylic Examples include methyl acrylate, butyl acrylate, itaconic acid, hydrogenated methyl acrylate, hydrogenated ethyl acrylate, acrylamide, vinyl chloride, vinylidene fluoride, and vinylidene chloride. In addition, acrylonitrile butadiene rubber, acrylonitrile butadiene styrene resin, acrylonitrile chlorinated polyethylene propylene diene styrene resin, acrylonitrile chlorinated polyethylene propylene diene styrene resin, acrylonitrile vinyl chloride resin, acrylonitrile methacrylate resin or acrylonitrile acrylate resin may be used.
[0041]
As the polymer material, for example, polyethylene oxide and a copolymer of polyethylene oxide may be used. Examples of the copolymerized monomer include polypropylene oxide, methyl methacrylate, butyl methacrylate, methyl acrylate, and butyl acrylate. Is mentioned. In addition, polyether-modified siloxane and copolymers thereof may be used.
[0042]
The electrolytic solution contains a solvent and an electrolyte salt dissolved in the solvent, and may contain various additives as necessary. Examples of the solvent include propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, sulfolane, 2-methyltetrahydrofuran, and dimethoxyethane. Any one type of solvent may be used alone, or two or more types may be mixed and used.
[0043]
Any electrolyte salt may be used as long as it dissolves in a solvent to generate ions, and one kind may be used alone, or two or more kinds may be used in combination. For example, in the case of a lithium salt, lithium hexafluorophosphate (LiPF ₆ ), Lithium tetrafluoroborate (LiBF) ₄ ), Lithium hexafluoroarsenate (LiAsF) ₆ ), Lithium perchlorate (LiClO) ₄ ), Lithium trifluoromethanesulfonate (LiCF) ₃ SO ₃ ), Bis (trifluoromethanesulfonyl) imidolithium (LiN (SO ₂ CF ₃ ) ₂ ), Tris (trifluoromethanesulfonyl) methyllithium (LiC (SO ₂ CF ₃ ) ₃ ), Lithium tetrafluoroaluminate (LiAlCl) ₄ ) Or lithium hexafluorosilicate (LiSiF) ₆ ) And the like.
[0044]
In the secondary battery, when charged, for example, lithium ions are released from the positive electrode mixture layer 21 </ b> B and inserted into the negative electrode mixture layer 22 </ b> B through the electrolyte layer 24. When discharging is performed, for example, lithium ions are released from the negative electrode mixture layer 22 </ b> B and inserted into the positive electrode mixture layer 21 </ b> B through the electrolyte layer 24. Here, since the surface property of the positive electrode mixture layer 21B and the peel strength of the positive electrode mixture layer 21B from the positive electrode current collector 21A are improved, excellent charge / discharge cycle characteristics and heavy load discharge characteristics can be obtained.
[0045]
The secondary battery having such a configuration can be manufactured, for example, as follows using the positive electrode mixture of the present embodiment.
[0046]
First, after mixing a positive electrode material capable of inserting and extracting lithium, which is a positive electrode active material, a binder and a conductive material, a polyvalent organic acid is added, and N-methyl-2-pyrrolidone, etc. The positive electrode mixture according to the present embodiment is prepared by dispersing in a solvent. Subsequently, the positive electrode mixture is applied to both surfaces or one surface of the positive electrode current collector 21A, dried, and compression molded to form the positive electrode mixture layer 21B, whereby the positive electrode 21 is manufactured.
[0047]
Also, for example, a negative electrode material can be prepared by mixing a negative electrode material capable of occluding and releasing lithium, which is a negative electrode active material, and a binder, and dispersing in a solvent such as N-methyl-2-pyrrolidone. To do. Subsequently, the negative electrode mixture is applied to both surfaces or one surface of the negative electrode current collector 22A, dried, and compression-molded to form the negative electrode mixture layer 22B, whereby the negative electrode 22 is manufactured.
[0048]
Next, the electrolyte layer 24 is formed on each of the positive electrode 21 and the negative electrode 22. After that, the positive electrode lead wire 11 is attached to the end portion of the positive electrode current collector 21A by welding, and the negative electrode lead wire 12 is attached to the end portion of the negative electrode current collector 22A by welding.
[0049]
Next, the positive electrode 21 and the negative electrode 22 on which the electrolyte layer 24 is formed are stacked and wound with a separator 23 interposed therebetween, and a protective tape 25 is adhered to the outermost peripheral portion to form the battery element 20.
[0050]
Finally, for example, the battery element 20 is sandwiched between the exterior members 30, and the outer edges of the exterior members 30 are brought into close contact with each other by thermal fusion or the like. At that time, an adhesion film 31 is inserted between the positive electrode lead wire 11 and the negative electrode lead wire 12 and the exterior member 30. Thereby, the secondary battery shown in FIGS. 1 and 2 is completed.
[0051]
As described above, since the positive electrode mixture according to the present embodiment includes a polyvalent organic acid, the fluidity can be improved and the increase in viscosity with time can be suppressed. Therefore, for example, when a bulky positive electrode active material such as lithium phosphorus oxide or a bulky conductive material such as carbon black or acetylene black is used, the fluidity is low, and the viscosity tends to increase with time. However, also in this case, the coating accuracy can be improved, the surface property of the positive electrode mixture layer 21B can be improved, and the uniformity of the electrode reaction can be improved. Further, the peel strength of the positive electrode mixture layer 21B from the positive electrode current collector 21A can be improved. Therefore, battery characteristics such as charge / discharge cycle characteristics and heavy load discharge characteristics of the battery can be improved.
[0052]
In particular, the polyvalent organic acid content is 3.5 mol × 10 5 per 1 kg of the positive electrode active material. ^-2 If the amount is less than or equal to mol, a higher effect can be obtained.
[0053]
【Example】
Further, specific embodiments of the present invention will be described in detail.
[0054]
(Examples 1 to 15)
First, lithium phosphate and iron (II) phosphate octahydrate are mixed so that the element ratio of lithium and iron becomes 1: 1, and acetylene black powder is added to this mixture to obtain a mixed sample. . At that time, the amount of acetylene black powder added was 10% by mass of the entire mixed sample. Next, this mixed sample was put into an alumina container, and alumina balls were used at a mass ratio of 50 mass% with respect to the mixed sample, and milling was performed using a planetary ball mill under conditions of a rotational speed of 250 rpm and an operating time of 10 hours. After that, this was put into a ceramic crucible and baked at 600 ° C. for 5 hours in an electric furnace in a nitrogen atmosphere. ₄ Got.
[0055]
Next, LiFePO ₄ LiFePO as a positive electrode active material ₄ 85 parts by mass, 10 parts by mass of acetylene black as a conductive material, and 5 parts by mass of polyvinylidene fluoride powder as a binder are added, and after adding a polyvalent organic acid, N- A paste-like positive electrode mixture was prepared by dispersing in methyl-2-pyrrolidone. At that time, the type and content of the polyvalent organic acid were changed as shown in Table 1 in Examples 1-15. In Table 1, the content of polyvalent organic acid is shown as a ratio with respect to 1 kg of the positive electrode active material.
[0056]
[Table 1]

[0057]
The prepared positive electrode mixture was stored at room temperature of 25 ° C. for 2 hours, and then the viscosity was measured with a B-type viscometer at room temperature. The results are shown in Table 1 and FIG. In addition, when the viscosity is 15 Pa · s or less, it is determined that almost no increase in viscosity is observed. Table 1 describes that the effect of suppressing the increase in viscosity is “strong”, and in the case of 16 Pa · s to 25 Pa · s. Is determined to have a slight viscosity increase inhibitory effect, and Table 1 describes that the viscosity increase inhibitory effect is “Yes”. If the viscosity is 26 Pa · s or more, it is determined that the viscosity increase inhibitory effect is not present. In No. 1, the viscosity increase inhibiting effect was described as “None”.
[0058]
Moreover, the lithium ion secondary battery was produced as follows using the produced positive electrode mixture. First, the prepared positive electrode mixture was uniformly applied to both surfaces of a positive electrode current collector 21A made of a strip-shaped aluminum foil having a thickness of 20 μm and dried, and then compression-molded with a roller press to form the positive electrode mixture layer 21B. did. Then, it cut | judged to the appropriate width | variety and the strip-shaped positive electrode 21 was produced. About the produced positive electrode 21 of Examples 1-15, the peeling strength from 21 A of positive electrode collectors 21A of the positive mix layer 21B was measured by the 180 degree peeling strength measuring method prescribed | regulated to JISB7721. The results are shown in Table 1 and FIG.
[0059]
The pulverized pitch coke is used as a negative electrode active material, and the pitch coke and the polyvinylidene fluoride powder as a binder are mixed at a mass ratio of 90:10 and dispersed in N-methyl-2-pyrrolidone as a solvent. Thus, a negative electrode mixture was prepared. Next, the negative electrode mixture was uniformly applied to both surfaces of a negative electrode current collector 22A made of a strip-shaped copper foil having a thickness of 10 μm, dried, and then compression molded by a roller press to form the negative electrode mixture layer 22B. . After that, it was cut into an appropriate width to produce a strip-shaped negative electrode 22.
[0060]
Furthermore, LiPF which is an electrolyte salt is added to a solvent in which ethylene carbonate and propylene carbonate are mixed. ₆ Was dissolved to prepare an electrolytic solution. After that, this electrolytic solution, the polymer material, and dimethyl carbonate as a solvent were mixed and stirred to obtain an electrolyte. Subsequently, the positive electrode lead wire 11 was attached to the positive electrode current collector 21 </ b> A, and an electrolyte was applied on the positive electrode mixture layer 21 </ b> B, and dimethyl carbonate was volatilized to form the electrolyte layer 24. Moreover, while attaching the negative electrode lead wire 12 to the negative electrode collector 22A, the electrolyte was apply | coated on the negative mix layer 22B, dimethyl carbonate was volatilized, and the electrolyte layer 24 was formed. Subsequently, a separator 23 made of a microporous polypropylene film having a thickness of 10 μm was prepared, and the separator 23, the positive electrode 21, the separator 23, and the negative electrode 22 were laminated and wound in this order to obtain the battery element 20. Next, the battery element 20 was vacuum packed inside an exterior member 30 made of an aluminum laminate film. The secondary battery shown in FIGS. 1 and 2 was completed through the above steps.
[0061]
For the fabricated secondary batteries of Examples 1 to 15, the charging current was set to a constant current of 100 mA, the battery was charged until the battery voltage reached 3.6 V, the discharging current was set to a constant current of 100 mA, and the battery voltage was 2 A charge / discharge cycle test was performed in which discharge was performed until the voltage reached 0.0 V, and the discharge capacity at the 10th cycle at which the charge / discharge capacity was stabilized was measured. Table 1 and FIG. 4 show the discharge capacity at the 10th cycle. Moreover, the charging current is set to a constant current of 100 mA, charging is performed until the battery voltage reaches 3.6 V, and then the discharging current is set to a constant current of 1000 mA and discharging is performed until the battery voltage reaches 2.0 V. A discharge test was performed and the discharge capacity was measured. Table 1 and FIG. 4 show the heavy load discharge capacity.
[0062]
Further, as Comparative Example 1 with respect to Examples 1 to 15, a positive electrode mixture was prepared in the same manner as in Examples 1 to 15 except that a polyvalent organic acid was not added, and this positive electrode mixture was used. A secondary battery was manufactured. Furthermore, as Comparative Example 2 with respect to Examples 1 to 15, acetic acid, which is a monovalent organic acid, was used instead of the polyvalent organic acid in an amount of 2.0 × 10 × ^-2 A positive electrode mixture was prepared in the same manner as in Examples 1 to 15 except that it was used in a molar ratio, and a secondary battery was prepared using this positive electrode mixture. For Comparative Examples 1 and 2, as in Examples 1 to 15, the viscosity of the positive electrode mixture, the peel strength from the positive electrode current collector of the positive electrode mixture layer, the discharge capacity at the 10th cycle, and the heavy load discharge capacity Examined. These results are shown together in Table 1, FIG. 3 and FIG.
[0063]
As shown in Table 1, FIG. 3 and FIG. 4, according to Examples 1 to 15 using a polyvalent organic acid, the viscosity of the positive electrode mixture could be lowered as compared with Comparative Example 1. Compared with Comparative Example 1, the peel strength and heavy load discharge capacity of the positive electrode mixture layer 21B from the positive electrode current collector 21 can be improved, and the discharge capacity at the 10th cycle is equivalent to that of Comparative Example 1 or It could be bigger than that. On the other hand, in Comparative Example 2 using acetic acid, which is a monovalent organic acid, both the peel strength from the positive electrode current collector of the positive electrode mixture layer, the discharge capacity at the 10th cycle, and the heavy load discharge capacity are both large. It has deteriorated. In addition, problems such as an unpleasant irritating odor occurred during the preparation of the positive electrode mixture, the application and the drying. That is, if a polyvalent organic acid is included in the positive electrode mixture, the viscosity of the positive electrode mixture can be reduced, and the peel strength of the positive electrode mixture layer 21B from the positive electrode current collector 21 and the charge / discharge cycle characteristics. It was also found that the heavy load discharge characteristics can be improved and that the process is preferable.
[0064]
Further, the viscosity of the positive electrode mixture decreases when the content of oxalic acid or succinic acid is increased, and shows a tendency to increase after showing a maximum value. The peeling of the positive electrode mixture layer 21B from the positive electrode current collector 21 is observed. The strength, the 10th cycle discharge capacity, and the heavy load discharge capacity increased when the content of oxalic acid or succinic acid was increased, and showed a tendency to decrease after showing the maximum value. That is, the content of the polyvalent organic acid is 3.5 × 10 5 with respect to 1 kg of the positive electrode active material. ^-2 It turned out that it is preferable to set it as mol or less. The content of oxalic acid is 2.0 × 10 ^-3 Preferably, the content of succinic acid is 1.0 × 10. ^-2 It was also found that it is preferable to make it at least mol.
[0065]
In the above-described examples, the polyvalent organic acid has been described with specific examples. However, similar results can be obtained using other polyvalent organic acids.
[0066]
Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the above embodiments and examples, and various modifications can be made. For example, in the above-described embodiments and examples, the case where a so-called gel electrolyte is used has been described, but another electrolyte may be used. Examples of other electrolytes include an electrolyte, an inorganic solid electrolyte such as lithium nitride or lithium iodide, or a mixture of one or more of an electrolyte, a gel electrolyte, and an inorganic solid electrolyte.
[0067]
In addition, the present invention is not limited to the positive electrode mixture, and can be generally applied to electrode mixtures such as a negative electrode mixture.
[0068]
Further, in the above-described embodiments and examples, the wound laminate type secondary battery has been described. However, the present invention can be similarly applied to a laminated laminate type secondary battery. In addition, the present invention can also be applied to secondary batteries having other shapes such as a so-called cylindrical shape, square shape, coin shape, and button shape. Furthermore, not only the secondary battery but also the primary battery can be applied.
[0069]
In addition, in the above-described embodiment and examples, the case where a lithium salt is used as the electrolyte salt has been described. However, a salt of another group element in a long-period periodic table such as a sodium salt or a potassium salt, or a magnesium salt Alternatively, the present invention can also be applied to the case of using a salt of another group 2 element in a long-period periodic table such as a calcium salt, or another light metal salt such as an aluminum salt. In that case, a positive electrode active material, a negative electrode active material, a solvent, etc. are selected according to the electrolyte salt.
[0070]
【The invention's effect】
As described above, according to the electrode mixture of the present invention, since it contains a polyvalent organic acid, it is possible to improve fluidity and to suppress an increase in viscosity over time. . Therefore, application accuracy can be improved.
[0071]
Also, according to the first electrode of the present invention, since the polyhydric organic acid is included, the electrode mixture containing the polyvalent organic acid is used according to the second electrode of the present invention. Therefore, the surface properties of the electrode can be improved, whereby the uniformity of the electrode reaction can be improved and the strength can be improved.
[0072]
Furthermore, according to the first battery of the present invention, since the positive electrode containing a polyvalent organic acid is provided, the second battery according to the present invention also has an electrode combination containing a polyvalent organic acid. Since the positive electrode formed using the agent is provided, battery characteristics such as charge / discharge cycle characteristics and heavy load discharge characteristics can be improved.
[0073]
In particular, the polyvalent organic acid content is 3.5 mol × 10 5 per 1 kg of the electrode active material. ^-2 If the amount is less than or equal to mol, a higher effect can be obtained.
[Brief description of the drawings]
FIG. 1 is an exploded perspective view showing a secondary battery according to an embodiment of the present invention.
2 is a cross-sectional view taken along line II-II of the battery element shown in FIG.
FIG. 3 is a characteristic diagram showing the relationship between the content of a polyvalent organic acid, viscosity, and peel strength according to Examples 1 to 12 of the present invention.
FIG. 4 is a characteristic diagram showing the relationship between the content of polyvalent organic acid according to Examples 1 to 12 of the present invention, the discharge capacity at the 10th cycle, and the heavy load discharge capacity.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Positive electrode lead wire, 12 ... Negative electrode lead wire, 20 ... Battery element, 21 ... Positive electrode, 21A ... Positive electrode collector, 21B ... Positive electrode mixture layer, 22 ... Negative electrode, 22A ... Negative electrode collector, 22B ... Negative electrode combination Agent layer, 23 ... separator, 24 ... electrolyte layer, 25 ... protective tape, 30 ... exterior member, 31 ... adhesion film.

Claims (11)

An electrode mixture comprising a binder and a polyvalent organic acid together with an electrode active material. The electrode mixture according to claim 1, further comprising a conductive substance. 2. The electrode mixture according to claim 1, wherein the content of the polyvalent organic acid is 3.5 mol × 10 ⁻² mol or less with respect to 1 kg of the electrode active material. An electrode comprising a binder and a polyvalent organic acid together with an electrode active material. The electrode according to claim 4, further comprising a conductive substance. The electrode according to claim 4, wherein the content of the polyvalent organic acid is 3.5 mol × 10 ⁻² mol or less with respect to 1 kg of the electrode active material. An electrode formed using an electrode mixture containing a binder and a polyvalent organic acid together with an electrode active material. A battery comprising an electrolyte together with a positive electrode and a negative electrode,
The battery, wherein the positive electrode contains a binder and a polyvalent organic acid together with an electrode active material. The battery according to claim 8, wherein the positive electrode further includes a conductive substance. The battery according to claim 8, wherein a content of the polyvalent organic acid is 3.5 mol × 10 ⁻² mol or less with respect to 1 kg of the electrode active material. A battery comprising an electrolyte together with a positive electrode and a negative electrode,
The battery, wherein the positive electrode is formed using an electrode mixture containing a binder and a polyvalent organic acid together with an electrode active material.

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