JP4852836B2 - Method for producing electrode plate for negative electrode of non-aqueous secondary battery - Google Patents
Method for producing electrode plate for negative electrode of non-aqueous secondary battery Download PDFInfo
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Description
本発明は、リチウムイオン電池に代表される非水系二次電池の負極用電極板の製造方法、特に、その塗膜形成用ペーストの混練工程に関する。 The present invention relates to a method for producing an electrode plate for a negative electrode of a non-aqueous secondary battery typified by a lithium ion battery, and more particularly to a kneading step of the coating film forming paste.
一般的にリチウムイオン電池に代表される非水系二次電池の極板は活物質に結着材と増粘剤を均一に高分散させて混練した高品質のペースト状の合材を集電体の両面に塗布し、乾燥して形成している。高分散されたペーストを得るために従来から各種の方法が提案されている。例えば、正極において第一工程で活物質と導電材および増粘剤を強い剪断力で混合処理させ、第二工程では増粘剤で希釈し、第三工程では結着材を添加し、弱い剪断力で混合処理することが提案されている。この高分散させる方法は同様に負極にも適用できることが報告されている（例えば、特許文献１参照）。 In general, the electrode plate of a non-aqueous secondary battery typified by a lithium ion battery is a current collector made of a high-quality paste-like compound in which a binder and a thickener are uniformly and highly dispersed in an active material. It is applied on both sides and dried to form. Various methods have been proposed in the past to obtain a highly dispersed paste. For example, in the positive electrode, the active material, the conductive material and the thickener are mixed with a strong shearing force in the first step, diluted with a thickener in the second step, a binder is added in the third step, and a weak shear is applied. It has been proposed to mix with force. It has been reported that this highly dispersed method can be applied to the negative electrode as well (see, for example, Patent Document 1).
また、負極において、黒鉛中の鉄などの不純物が少ないほどサイクル特性が向上することが報告されていた（例えば、特許文献２参照）。
以上述べた従来の方法では、負極用のペーストとして黒鉛とカルボキシル基を含む水溶性高分子の増粘剤を混練するにあたり、分散性を高めるために強い剪断力をかけても、逆に混練処理が不十分となり、高分散し、かつ安定したペーストを得ることができなかった。そのため、ペーストを集電体上に塗布する工程において塗布乾燥後の塗着重量が不安定となり、電池構成時に極板上でリチウムの受入れ性にバラツキが生じ、寿命特性が低下するなどの十分な電池特性を満たさなかった。 In the conventional method described above, when kneading a water-soluble polymer thickener containing graphite and a carboxyl group as a paste for a negative electrode, the kneading process is reversed even if a strong shearing force is applied to increase dispersibility. Was insufficient, and a highly dispersed and stable paste could not be obtained. Therefore, in the process of applying the paste on the current collector, the coating weight after coating and drying becomes unstable, and the lithium acceptability varies on the electrode plate at the time of battery construction, and the life characteristics are lowered. The battery characteristics were not met.
そこで本発明は、高分散かつ安定したペーストを作製することにより、塗着した際の重量バラツキが少ない負極用電極板を提供し、ひいてはこの負極用電極板を用いて電池を構成することで、良好な寿命特性を示す非水二次電池を提供することを目的とする。 Therefore, the present invention provides a negative electrode plate with less weight variation when applied by producing a highly dispersed and stable paste, and by using this negative electrode plate to constitute a battery, An object of the present invention is to provide a non-aqueous secondary battery exhibiting good life characteristics.
上記課題を解決するために、本発明の電池用負極合材の製造方法は、黒鉛を主剤とする炭素材料、増粘剤、および結着材を混練分散することにより構成されるペーストを用いる非水系二次電池の負極用電極板の製造方法において、黒鉛は鉄の含有量が５００ｐｐｍ以下であり、増粘剤はカルボキシル基を含む水溶性高分子であり、結着材は極性基を有する水分散性高分子であり、負極塗膜形成用の前記ペーストの混練工程は、黒鉛に増粘剤を粉末状態で添加し、分散媒と共に混練する初混練工程と、初混練工程の混練物を分散媒で希釈混練する希釈混練工程と、希釈混練工程の混練物に結着材を添加して混練し、ペーストを作製する仕上げ混練工程の少なくとも３つの工程を含み、初混練工程における混練の剪断力が、希釈混練工程および仕上げ混練工程における混練の剪断力の２．５倍以上であることを特徴としたものである。 In order to solve the above problems, the method for producing a negative electrode composite material for a battery according to the present invention uses a paste composed by kneading and dispersing a carbon material mainly composed of graphite, a thickener, and a binder. In the method for producing an electrode plate for a negative electrode of an aqueous secondary battery, graphite has an iron content of 500 ppm or less, the thickener is a water-soluble polymer containing a carboxyl group, and the binder is water having a polar group. The kneading process of the paste for forming a negative electrode coating film, which is a dispersible polymer, adds a thickener to the graphite in a powder state and kneads it with a dispersion medium, and disperses the kneaded material from the initial kneading process. The kneading shear force in the initial kneading step includes at least three steps of a dilution kneading step in which the mixture is diluted and kneaded, and a final kneading step in which a binder is added to the kneaded product in the dilution kneading step and kneaded to prepare a paste. The dilution kneading process and processing It is obtained by characterized in that 2.5 times the shear force of the kneading under kneading step.
本発明者らは、鋭意検討の結果、混練するにあたり、黒鉛中に含まれる鉄の含有量が多い場合に混練処理が不充分となることを見出した。そこで、使用する黒鉛は鉄の含有量が５００ｐｐｍ以下のものを使うことにより、より強い剪断力で混練することができ、分散性を高めることができる。 As a result of intensive studies, the present inventors have found that kneading treatment is insufficient when the content of iron contained in graphite is large. Therefore, by using graphite having an iron content of 500 ppm or less, the graphite used can be kneaded with a stronger shearing force and can improve dispersibility.
本発明によれば、均一に分散し、安定したペーストを得られることから、塗着重量バラツキが少ない負極用電極板を提供することができる。さらに、本発明によれば、良好な寿命特性及び初期の放電容量を示す非水系二次電池を提供することができる。 According to the present invention, it is possible to obtain a negative electrode plate with less coating weight variation since a uniform paste can be obtained that is uniformly dispersed. Furthermore, according to the present invention, it is possible to provide a non-aqueous secondary battery that exhibits good life characteristics and initial discharge capacity.
本発明の好ましい形態を以下に示す。 Preferred embodiments of the present invention are shown below.
カルボキシル基を含む水溶性高分子は、負極合材ペーストを作製する際に適度の粘性を付与する増粘剤として活用されてきたが、黒鉛を主剤としてペーストを作製した場合、条件によっては粘性が低下しペースト性状が不安定化する現象が多発した。発明者らが鋭意検討した結果、黒鉛中に含まれる鉄（製造過程における残渣）が５００ｐｐｍを超えた場合、鉄イオンが増粘剤に含まれるカルボキシル基と結合して錯体を形成し、増粘剤の粘性を低下させることを見出した。そこで鉄含有量が５００ｐｐｍ以下の黒鉛を選択し、初混練工程における混練の剪断力を高めることにより、鉄と増粘剤との錯形成を抑え、混練後のペーストを安定化させる本発明に至った。ここで黒鉛中に含まれる鉄は、酸処理あるいはアルカリ処理を施すことで減少させることができる。また鉄の含有量は、黒鉛を灰分にして蛍光Ｘ線により鉄の量を測定することで求まる。 A water-soluble polymer containing a carboxyl group has been used as a thickening agent for imparting an appropriate viscosity when preparing a negative electrode mixture paste. The phenomenon of degrading and destabilizing paste properties occurred frequently. As a result of intensive studies by the inventors, when iron (residue in the production process) contained in the graphite exceeds 500 ppm, iron ions are combined with a carboxyl group contained in the thickener to form a complex, thereby increasing the viscosity. It was found to reduce the viscosity of the agent. Therefore, by selecting graphite having an iron content of 500 ppm or less and increasing the shearing force of kneading in the initial kneading step, the complex formation between iron and the thickener is suppressed, and the paste after kneading is stabilized. It was. Here, iron contained in the graphite can be reduced by performing acid treatment or alkali treatment. Further, the iron content can be obtained by measuring the amount of iron by fluorescent X-ray using graphite as ash.
また混練方法において少なくとも３つの工程を含む。まず第一工程である初混練工程では、活物質と増粘剤の粉末に分散媒を加えたものを、第二、第三工程である希釈混練工程、仕上げ混練工程の２．５倍以上の剪断力で混練を行う。これにより増粘剤のカルボキシル基が活物質の活性面であるエッジ部のみならず、ベーサル面などの活物質表面に増粘剤を均質にコーティングすることができ、かつ均一に分散させることができる。希釈混練工程では、初混練工程より弱い剪断力で、増粘剤の水溶液を用い希釈を行う。仕上げ混練工程では、結着材を添加し、希釈混練工程とほぼ同じ剪断力で混練を行う。結着材は合成樹脂を界面活性剤や分散剤で水溶液中に分散した樹脂溶液であり、強い剪断力を加えると表面の界面活性剤が離脱し、エマルジョン樹脂の凝集が発生する。そのため、仕上げ混練工程において、弱い剪断力で混練する。また、結着材の極性基と増粘剤のカルボキシル基とが水素結合をするため、結着材は活物質に均一にコーティングされた増粘剤の皮膜へ結合し均一に分散する。このため、これにより得られたペーストは均一に分散し、安定している。また極板の合剤と集電体との結着力も向上する。電池特性においても優れた電池寿命特性および初期の放電容量を提供することができる。 The kneading method includes at least three steps. First, in the first kneading step, which is the first step, the active material and the thickener powder added with the dispersion medium are more than 2.5 times the second and third steps of the diluting kneading step and the finishing kneading step. Kneading with shearing force. As a result, the thickener can be uniformly coated on the active material surface such as the basal surface as well as the edge portion where the carboxyl group of the thickener is the active surface of the active material, and can be uniformly dispersed. . In the dilution kneading step, dilution is performed using an aqueous solution of a thickener with a weaker shear force than in the initial kneading step. In the final kneading step, a binder is added and kneading is performed with substantially the same shearing force as in the dilution kneading step. The binder is a resin solution in which a synthetic resin is dispersed in an aqueous solution with a surfactant or a dispersant. When a strong shearing force is applied, the surfactant on the surface is detached and aggregation of the emulsion resin occurs. Therefore, kneading is performed with a weak shearing force in the final kneading step. Further, since the polar group of the binder and the carboxyl group of the thickener form hydrogen bonds, the binder binds to the thickener film uniformly coated on the active material and is uniformly dispersed. For this reason, the paste thus obtained is uniformly dispersed and stable. Further, the binding force between the electrode plate mixture and the current collector is also improved. In terms of battery characteristics, excellent battery life characteristics and initial discharge capacity can be provided.
ここで、増粘剤を粉末状態で添加する理由について述べる。前述のように増粘剤水溶液自身が塗料化に適した粘性を有しており、ハンドリングも容易なため、負極塗膜形成用ペースト作製時には水溶液状態で投入し混練するのが一般的であった。しかし、その水溶液作製工程において、一般的に難溶性である増粘剤の溶解を促進するために、増粘作用の根源である分子間の絡みを破壊するような手法を採らざるを得なかった（例えばホモジナイザー処理）。このため増粘剤の部分的凝集が起こり、粘性の低下を伴うペースト性状の不安定化と、増粘剤が過剰に被覆された箇所での反応性低下に伴う充放電特性の悪化と、増粘剤が不足した箇所での密着性の低下（結着剤が増粘剤を頼って分散するため）が起こる。そこで、増粘剤を粉末状態で初混練工程時に投入し、水溶液とする工程での増粘剤の構造破壊を回避することにより、上述した課題が回避される。 Here, the reason why the thickener is added in a powder state will be described. As mentioned above, the thickener aqueous solution itself has a viscosity suitable for coating and is easy to handle. Therefore, it was common to add and knead in the aqueous solution state when preparing the paste for forming the negative electrode coating film. . However, in the aqueous solution preparation process, in order to promote the dissolution of thickeners that are generally poorly soluble, it has been necessary to adopt a technique that breaks the entanglement between molecules that is the basis of the thickening action. (For example, homogenizer treatment). For this reason, partial thickening of the thickener occurs, destabilizing the paste properties with a decrease in viscosity, deterioration of charge / discharge characteristics due to a decrease in reactivity at the place where the thickener is excessively coated, Decrease in adhesion at the place where the adhesive is insufficient (because the binder relies on the thickener to disperse). Therefore, the above-described problems can be avoided by introducing the thickener in the powder state during the initial kneading step to avoid structural destruction of the thickener in the aqueous solution step.
希釈混練工程では、初混練工程より弱い剪断力で、分散媒を添加し希釈混練を行う。仕上げ混練工程では、結着材を添加し、希釈混練工程と同等の剪断力で混練を行う。 In the dilution kneading step, the dispersion medium is added and diluted and kneaded with a shearing force weaker than that in the initial kneading step. In the final kneading step, a binder is added and kneading is performed with the same shearing force as in the dilution kneading step.
本発明の実施形態の攪拌混合機として、特殊機化製のミキサーを用いた。攪拌機構とし
て自転と公転機能を有する二つのブレード（羽根）が一対となったプラネタリーミキサー部とプラネタリー部と同様に自転しながら公転するディゾルバー部を有している混合攪拌機であり、双腕式練合機ともいう。
As a stirring mixer of the embodiment of the present invention, a special machine mixer was used. As a stirring mechanism, it is a mixing stirrer that has a planetary mixer section that has two blades (blades) that have rotation and revolution functions and a dissolver section that rotates and revolves like a planetary section. Also called a formula kneader.
ここで剪断力については、以下のように簡易的に測定し、その大小を論じた。すなわち、ニュートンの法則に則り、ｘ軸方向に流速ｖで流れている流体に対し、ｘ軸と垂直なｚ軸方向で流速を変化させた場合、剪断力τが流体の粘度ηおよび速度勾配ｄｖ／ｄｚに比例する形で発生する。その関係は以下の式に示すとおりである。 Here, the shearing force was simply measured as follows and the magnitude thereof was discussed. That is, according to Newton's law, when the flow velocity is changed in the z-axis direction perpendicular to the x-axis with respect to the fluid flowing at the flow velocity v in the x-axis direction, the shearing force τ becomes the fluid viscosity η and the velocity gradient dv. It is generated in a form proportional to / dz. The relationship is as shown in the following equation.
τ＝η×（ｄｖ／ｄｚ） ・・・ （式１）
これを本発明の構成要素に置き換えると、設備条件（羽根と攪拌容器との隙間など）が一定でｚ軸方向での流速変化が一定の場合、剪断力τは流体である混練物の粘度ηと、攪拌速度（羽根の周速）ｖとに比例することとなる。ここで第一工程における混練物はファニキュラー状態であり、通常の粘度計では粘度が測定できない。そこで剛性体を一定圧力で混練物に押し込み、その変位量を測ることで簡易的に粘度の代用値を求めた。具体的には各工程を経た後の混練物に対し、直径３ｍｍの銅製の丸棒を１０ｋｇｆ／ｃｍ２の圧力で５秒間押し込み、その変位量の逆数（単位は１／ｍ）を粘度ηの代用値として、混練時の攪拌羽根の周速に乗じることにより、当該工程の剪断力τの代用値を簡易的に求めた。
τ = η × (dv / dz) (Formula 1)
When this is replaced with the component of the present invention, when the equipment conditions (such as the gap between the blade and the stirring vessel) are constant and the flow rate change in the z-axis direction is constant, the shearing force τ is the viscosity η of the kneaded material that is a fluid. And the stirring speed (blade peripheral speed) v. Here, the kneaded material in the first step is in a funicular state, and the viscosity cannot be measured with a normal viscometer. Therefore, the substitute value of viscosity was simply obtained by pressing the rigid body into the kneaded material at a constant pressure and measuring the amount of displacement. Specifically, a copper round bar having a diameter of 3 mm is pushed into the kneaded material after passing through each step for 5 seconds at a pressure of 10 kgf / cm 2 , and the reciprocal of the amount of displacement (unit: 1 / m) is the viscosity η As a substitute value, the substitute value of the shearing force τ of the process was simply obtained by multiplying the peripheral speed of the stirring blade during kneading.
本発明で用いる負極材は黒鉛を主剤とする炭素材料であり、中でも黒鉛は、レーザー光回折法における累積５０％径（Ｄ５０径）が８〜３０μmのものが好ましい。その範囲外のものでは、混練時に強い剪断力を与えにくく、分散不十分となりやすい。電池特性においても、電池寿命特性などの低下が僅かながら引き起こされる。窒素ガス吸着法における比表面積、タップ法における見掛け密度についても同様である。窒素ガス吸着法における比表面積が２．０〜５．５ｍ２／ｇ、タップ法における見掛け密度が０．６５〜１．５０ｇ／ｃｍ３である活物質が好ましい。それぞれの範囲外のものは、同様に混練時に強い剪断力を与えにくく、分散不十分となりやすい。電池特性においても、電池寿命特性などの低下が僅かながら引き起こされる。 The negative electrode material used in the present invention is a carbon material mainly composed of graphite. Among them, graphite preferably has a cumulative 50% diameter (D50 diameter) of 8 to 30 μm in the laser light diffraction method. If it is out of the range, it is difficult to give a strong shearing force during kneading and the dispersion tends to be insufficient. Even in the battery characteristics, a slight decrease in battery life characteristics and the like is caused. The same applies to the specific surface area in the nitrogen gas adsorption method and the apparent density in the tap method. An active material having a specific surface area of 2.0 to 5.5 m 2 / g in the nitrogen gas adsorption method and an apparent density of 0.65 to 1.50 g / cm 3 in the tap method is preferable. Those outside the respective ranges are similarly unlikely to give a strong shearing force during kneading and are likely to be insufficiently dispersed. Even in the battery characteristics, a slight decrease in battery life characteristics and the like is caused.
増粘剤としては、カルボキシル基を含む水溶性高分子を選択できる。有機溶剤に可溶な高分子は電池構成後に電解液を構成する非水溶媒にも溶けやすいが、水溶性高分子を用いればそのような不具合を回避できる。さらに詳しくは、カルボキシメチルセルロース（以下、ＣＭＣと略記）のナトリウム塩、またはアンモニウム塩であれば、ペーストに適度な粘性を与える上でも、カルボキシル基を多量に含有させる上でも好ましい。 As the thickener, a water-soluble polymer containing a carboxyl group can be selected. A polymer soluble in an organic solvent is easily soluble in a non-aqueous solvent that constitutes the electrolytic solution after the battery is constructed, but such a problem can be avoided by using a water-soluble polymer. More specifically, a sodium salt or ammonium salt of carboxymethyl cellulose (hereinafter abbreviated as CMC) is preferable for imparting an appropriate viscosity to the paste and for containing a large amount of carboxyl groups.
本発明の骨子は増粘剤を粉末状態で添加することであるが、この方法を採ることにより、密着性は高いが水溶液化が困難であった高粘度型のＣＭＣ、具体的には１％水溶液とした時の粘度（Ｂ型粘度計にて測定、２５℃環境下、溶液の調整法は後に詳述）が６〜１８Ｐａ・ｓのＣＭＣを用いることができ、負極板の剥離強度を増すことができるようになる。 The gist of the present invention is to add a thickener in powder form. By adopting this method, high viscosity CMC, which has high adhesion but difficult to form an aqueous solution, specifically 1% CMC with a viscosity of 6-18 Pa · s (measured with a B-type viscometer, in a 25 ° C. environment, and a method for preparing the solution will be described in detail later) can be used, and the peel strength of the negative electrode plate is increased. Will be able to.
結着材としては、極性基を有する水分散性高分子を選択することができる。アクリロニトリル単位を有するコアシェル型ゴム粒子結着材が好ましい。コア部にアクリロニトリル単位を含むコアシェル型ゴム粒子結着材は、粒子形状を保ちつつ、結着力を発現する粘着成分をシェル部に効果的に配置することができる。このシェル部の化学構造は、高分散した増粘剤のカルボキシル基と結合しやすいため、本発明の製造方法においては負極板の密着性を高めるために有効である。ここでシェル部に配置される単位としては、スチレン、ブタジエンの他、負極電位下において安定な極性基、または極性基の誘導体（不飽和結合を有する化学構造）を挙げることができる。 A water-dispersible polymer having a polar group can be selected as the binder. A core-shell type rubber particle binder having an acrylonitrile unit is preferred. The core-shell type rubber particle binder having an acrylonitrile unit in the core portion can effectively arrange an adhesive component that develops a binding force in the shell portion while maintaining the particle shape. Since the chemical structure of the shell portion is easily bonded to the carboxyl group of the highly dispersed thickener, it is effective for enhancing the adhesion of the negative electrode plate in the production method of the present invention. Examples of the unit disposed in the shell portion include styrene and butadiene, and polar groups that are stable under a negative electrode potential, or derivatives of polar groups (chemical structures having unsaturated bonds).
正極に関しては、本検討において何ら限定する要素は無いが一例を以下に示す。 As for the positive electrode, there are no limiting elements in this study, but an example is shown below.
さらに正極用活物質としては、コバルト酸リチウムおよびその変性体（アルミニウムやマグネシウムを共晶させたものなど）・ニッケル酸リチウムおよびその変性体（一部ニッケルをコバルト置換させたものなど）・マンガン酸リチウムおよびその変性体などの複合酸化物を挙げることができる。 In addition, active materials for positive electrodes include lithium cobaltate and modified products thereof (such as those obtained by eutectic aluminum and magnesium), lithium nickelate and modified products thereof (such as those in which nickel is partially substituted with cobalt), and manganic acid. A composite oxide such as lithium and a modified product thereof can be given.
このときの導電材種としてはアセチレンブラック等のカーボンブラック・各種グラファイトを単独、あるいは組み合わせて用いても良い。 At this time, carbon black such as acetylene black and various graphites may be used alone or in combination.
用いる増粘剤としてはメチルセルロースおよびその変性体が、ペースト増粘性、ペースト分散性の観点から好ましい。特にＣＭＣのナトリウム塩またはアンモニウム塩であると、本発明の効果が好適に現れる。 As the thickener to be used, methylcellulose and a modified product thereof are preferable from the viewpoints of paste thickening and paste dispersibility. In particular, when the sodium salt or ammonium salt of CMC is used, the effects of the present invention are suitably exhibited.
正極用結着材としては、アクリレート単位を有するゴム粒子結着剤であることが望ましい。アクリレート単位を有する結着材はガラス転移点が低く、分子鎖のからみ合いによる結着ではなく、主に結着材表面の粘着成分により結着するため、結着材の添加量の減量が可能となる。 The positive electrode binder is preferably a rubber particle binder having an acrylate unit. Binders with acrylate units have a low glass transition point and are not bonded by molecular chain entanglement, but are mainly bonded by the adhesive component on the binder surface, so the amount of binder added can be reduced. It becomes.
電解液については、塩としてＬｉＰＦ６およびＬｉＢＦ４などの各種リチウム化合物を用いることができる。また溶媒としてエチレンカーボネート（ＥＣ）、ジメチルカーボネート（ＤＭＣ）、ジエチルカーボネート（ＤＥＣ）、メチルエチルカーボネート（ＭＥＣ）を単独または組み合わせて用いることができる。また正負極上に良好な皮膜を形成させたり、過充電時の安定性を保証するために、ビニレンカーボネート（ＶＣ）やシクロヘキシルベンゼン（ＣＨＢ）およびその変性体を用いることも可能である。
セパレータについては、リチウムイオン二次電池の使用範囲に耐えうる組成であれば特に限定されないが、ポリエチレン・ポリプロピレンなどのオレフィン系樹脂の微多孔フィルムを、単一あるいは複合して用いるのが一般的でありまた態様として好ましい。このセパレータの厚みは特に限定されないが、１０〜２５μｍであることが好ましい。
For the electrolytic solution, it is possible to use various lithium compounds such as LiPF 6 and LiBF 4 as a salt. Further, ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), or methyl ethyl carbonate (MEC) can be used alone or in combination as a solvent. In addition, vinylene carbonate (VC), cyclohexylbenzene (CHB), and modified products thereof can be used in order to form a good film on the positive and negative electrodes and to ensure stability during overcharge.
The separator is not particularly limited as long as it has a composition that can withstand the range of use of the lithium ion secondary battery, but a microporous film of an olefin resin such as polyethylene / polypropylene is generally used singly or in combination. Also preferred as an embodiment. Although the thickness of this separator is not specifically limited, It is preferable that it is 10-25 micrometers.
以下、本発明を実施例および比較例を用いて詳細に説明するが、これらは本発明を何ら限定するものではない。 EXAMPLES Hereinafter, although this invention is demonstrated in detail using an Example and a comparative example, these do not limit this invention at all.
＜検討１．黒鉛中の鉄の含有量及び練合処方の検討＞
（実施例１）
まず、図１に示すフローチャートのように、負極を作製した。すなわち、初混練工程で（ｉ）鉄の含有量が３００ｐｐｍであり、粒径（ｄ５０）が２３μｍ、比表面積が２．３ｍ２／ｇ、タップ密度が１．００ｇ／ｍ３である黒鉛を負極用活物質として１００重量部、（ｉｉ）増粘剤として粘度（Ｂ型粘度計にて測定、２５℃環境下、溶液の調整法は後に詳述）が１．４〜１．８Ｐａ・ｓのカルボキシメチルセルロース（ＣＭＣ）のナトリウム塩を固形分換算で１．２重量部、固形分比が６２［％］となるように分散媒を加え双腕式練合機にて周速２０ｍ／秒で混練し一次混練物を得た。この混練物の粘度ηの代用値は７６５（１／ｍ）、剪断力τの代用値は１５３００（１／秒）であった。
<Study 1. Examination of iron content in graphite and kneading formulation>
Example 1
First, as shown in the flowchart of FIG. 1, a negative electrode was produced. That is, in the initial kneading step, (i) graphite having an iron content of 300 ppm, a particle size (d50) of 23 μm, a specific surface area of 2.3 m 2 / g, and a tap density of 1.00 g / m 3 is treated as a negative electrode. 100 parts by weight as an active material, and (ii) a viscosity as a thickener (measured with a B-type viscometer, in a 25 ° C. environment, a method for adjusting the solution will be described in detail later) of 1.4 to 1.8 Pa · s Carboxymethylcellulose (CMC) sodium salt was added in 1.2 parts by weight in terms of solid content, and a dispersion medium was added so that the solid content ratio was 62 [%], and kneaded at a peripheral speed of 20 m / sec in a double-arm kneader. A primary kneaded product was obtained. The substitute value of the viscosity η of this kneaded product was 765 (1 / m), and the substitute value of the shearing force τ was 15300 (1 / second).
次に希釈混練工程で前記初混練工程後の一次混練物に、固形分比が５１［％］となるように分散媒を加え双腕式練合機にて周速６０ｍ／秒で希釈混練した。この混練物の粘度ηの代用値は９０（１／ｍ）、剪断力τの代用値は５４００（１／秒）であった。 Next, a dispersion medium is added to the primary kneaded product after the initial kneading step in the dilution kneading step so that the solid content ratio is 51 [%], and the mixture is diluted and kneaded at a peripheral speed of 60 m / sec with a double-arm kneader. . The substitute value of the viscosity η of this kneaded product was 90 (1 / m), and the substitute value of the shearing force τ was 5400 (1 / second).
さらに仕上げ混練工程で前記希釈混練後の混練物に、（ｉｉｉ）結着材としてＳＢＲ変
性体（ＳＢＲ変性体固形分４０重量％）を固形分換算で１重量部を加え双腕式練合機にて混練し、固形分比が５０．６％の負極合材ペーストを作製した。この混練物の粘度ηおよび剪断力τの代用値は、希釈分散工程における混練物のそれとほぼ同等であった（以下の実施例および比較例についても同様）。
Furthermore, in the final kneading step, (iii) 1 part by weight of SBR modified material (SBR modified material solid content 40% by weight) as a binder is added to the kneaded material after dilution kneading in terms of solid content. To prepare a negative electrode mixture paste having a solid content ratio of 50.6%. The substitute values of the viscosity η and the shearing force τ of this kneaded product were almost equivalent to those of the kneaded product in the dilution dispersion process (the same applies to the following examples and comparative examples).
このペーストを１０μｍ厚の銅箔に塗布乾燥し、総厚が約２４０μｍの塗膜を、総厚が１６０μｍとなるようにプレスした後、５９ｍｍ幅にスリットし、負極電極板を得た。これを実施例１の負極電極板とする。 This paste was applied and dried on a 10 μm thick copper foil, and a coating having a total thickness of about 240 μm was pressed to a total thickness of 160 μm, and then slit to a width of 59 mm to obtain a negative electrode plate. This is the negative electrode plate of Example 1.
一方、正極は次のように作製した。すなわち、（ｉ）炭酸リチウムと４酸化３コバルトの混合物を７５０℃下で４．５時間仮焼きの後、９００℃下で７．５時間焼成したものを解砕して篩い、ＢＥＴ法で測定される比表面積が１．４ｍ２／ｇのコバルト酸リチウムを活物質として１００重量部、（ｉｉ）導電材としてＡＢを４重量部、（ｉｉｉ）増粘剤として粘度（Ｂ型粘度計にて測定、２５℃環境下、溶液の調整法は後に詳述）が１．７Ｐａ・ｓのＣＭＣのナトリウム塩の１重量％水溶液を固形分換算で０．４重量部、以上を双腕式練合機にて攪拌し、固形分比が７２．５％の一時混練物を得た。次に上記混練物に、（ｉｖ）結着材としてＰＴＦＥとヘキサフルオロエチレンの共重合体の水分散物（固形分重量６０重量％）を固形分換算で２．４重量部、以上を水とともに双腕式練合機にて攪拌し、固形分比が７０％の二次混練すなわち正極合材ペーストを作製した。このペーストを１５μｍ厚のアルミニウム箔に塗布乾燥し、総厚が約２５０μｍの塗膜を、総厚が１８０μｍとなるようにプレスした後、５６ｍｍ幅にスリットし、正極電極板を得た。 On the other hand, the positive electrode was produced as follows. That is, (i) a mixture of lithium carbonate and 3 cobalt tetroxide calcined at 750 ° C. for 4.5 hours, calcined at 900 ° C. for 7.5 hours, sieved, and measured by BET method 100 parts by weight of lithium cobaltate having a specific surface area of 1.4 m 2 / g as an active material, (ii) 4 parts by weight of AB as a conductive material, and (iii) viscosity as a thickener (with a B-type viscometer) Measurement, in a 25 ° C. environment, the method of adjusting the solution will be described in detail later.) 0.4 wt part of CMC sodium salt solution of 1.7 Pa · s in terms of solid content, the above being double arm kneaded The mixture was stirred in a machine to obtain a temporary kneaded product having a solid content ratio of 72.5%. Next, (iv) PTFE and hexafluoroethylene copolymer aqueous dispersion (solid weight 60% by weight) as a binder, 2.4 parts by weight in terms of solid content, and above with water The mixture was stirred with a double-arm kneader to prepare a secondary kneading, that is, a positive electrode mixture paste having a solid content ratio of 70%. This paste was applied to a 15 μm thick aluminum foil and dried. A coating film having a total thickness of about 250 μm was pressed to a total thickness of 180 μm, and then slit to a width of 56 mm to obtain a positive electrode plate.
ここで、ＣＭＣの粘度測定のための溶液調整法について詳述する。なおＣＭＣは水溶液の粘度が水溶液化時の攪拌法に大きく依存するため、以下の方法に準じて測定するのが好ましい。 Here, the solution adjustment method for measuring the viscosity of CMC will be described in detail. CMC is preferably measured according to the following method because the viscosity of the aqueous solution greatly depends on the stirring method at the time of making the aqueous solution.
すなわち、３００ｍｌ共栓三角フラスコ中にＣＭＣを２．３ｇ量り取り、蒸留水２００ｍｌを加えた後に激しく振とうした後、一夜（約１８〜２０時間）放置する。その後、不足分の蒸留水を１重量％溶液となるように追加し、マグネチックスターラーにて５分間攪拌し、膨潤状態の溶液を完全に分散溶解させて得られるというものである。この溶液を上述のようにＢ型粘度計にて粘度測定することにより、ＣＭＣに固有な増粘作用を数値化することができる。 Specifically, 2.3 g of CMC is weighed into a 300 ml stoppered Erlenmeyer flask, shaken vigorously after adding 200 ml of distilled water, and left overnight (about 18 to 20 hours). Thereafter, a short amount of distilled water is added so as to be a 1% by weight solution, and the mixture is stirred for 5 minutes with a magnetic stirrer to completely disperse and dissolve the swollen solution. By measuring the viscosity of this solution with a B-type viscometer as described above, the thickening action inherent to CMC can be quantified.
これらの正・負極の電極板を、２０μｍ厚のポリエチレン微多孔フィルム（セルガード製＃２３２０）をセパレータとして捲回構成し、所定の長さで切断してＮｉメッキしたＦｅを基材とする電槽缶内に挿入し、ＥＣ・ＤＭＣ・ＥＭＣ混合溶媒（体積比３：３：２）１００重量部にＶＣを３重量部添加し、さらにＬｉＰＦ６を１Ｍの濃度となるように溶解させた電解液を、５．５ｇ添加して封口し、公称容量２０００ｍＡｈの円筒型１８６５０リチウムイオン二次電池を作製した。これを実施例１のリチウムイオン電池とする。 These positive and negative electrode plates are wound using a polyethylene microporous film (Celgard # 2320) with a thickness of 20 μm as a separator, and a battery case using Ni plated Fe cut as a base material. Electrolyte inserted in can, 3 parts by weight of VC added to 100 parts by weight of EC / DMC / EMC mixed solvent (volume ratio 3: 3: 2), and further LiPF 6 was dissolved to a concentration of 1M Was added and sealed to prepare a cylindrical 18650 lithium ion secondary battery having a nominal capacity of 2000 mAh. This is the lithium ion battery of Example 1.
（比較例１）
図１に示すフローチャートに従い、実施例１では鉄の含有量が３００ｐｐｍである黒鉛を用いたところを、鉄の含有量が１０００ｐｐｍである黒鉛を用い、初混練工程での固形分比を５５％とした以外は、実施例１と全く同様の作製手順で負極電極板を作製した。なおここで一次混練物の粘度ηの代用値は２６０（１／ｍ）で剪断力τの代用値は５２００（１／秒）、希釈混練工程後の混練物の粘度ηの代用値は１００（１／ｍ）で剪断力τの代用値は６０００（１／秒）であった。これを比較例１の負極電極板とする。
(Comparative Example 1)
In accordance with the flowchart shown in FIG. 1, in Example 1, the graphite having an iron content of 300 ppm was used, the graphite having an iron content of 1000 ppm was used, and the solid content ratio in the initial kneading step was 55%. A negative electrode plate was produced in the same production procedure as in Example 1 except that. Here, the substitute value of the viscosity η of the primary kneaded product is 260 (1 / m), the substitute value of the shearing force τ is 5200 (1 / second), and the substitute value of the viscosity η of the kneaded product after the dilution kneading step is 100 ( 1 / m) and the substitute value of the shearing force τ was 6000 (1 / second). This is the negative electrode plate of Comparative Example 1.
正極電極板は実施例１と同様に作製した極板を用い、また実施例１と同様に作製した電池を比較例１のリチウムイオン電池とする。 As the positive electrode plate, an electrode plate produced in the same manner as in Example 1 was used, and a battery produced in the same manner as in Example 1 was used as a lithium ion battery in Comparative Example 1.
（比較例２）
図１に示すフローチャートに従い、実施例１では第一工程で鉄の含有量が３００ｐｐｍである黒鉛を用いたところを、鉄の含有量が１０００ｐｐｍである黒鉛を用いた以外は、実施例１と全く同様の作製手順で負極を作製した。なおここで一次混練物の粘度ηの代用値は３７６（１／ｍ）で剪断力τの代用値は７５２０（１／秒）、希釈混練工程後の混練物の粘度ηの代用値は７２（１／ｍ）で剪断力τの代用値は４３２０（１／秒）であった。これを比較例２の負極板とする。
(Comparative Example 2)
In accordance with the flowchart shown in FIG. 1, Example 1 uses graphite with an iron content of 300 ppm in Example 1, except that graphite with an iron content of 1000 ppm is used. A negative electrode was produced in the same production procedure. Here, the substitute value of the viscosity η of the primary kneaded product is 376 (1 / m), the substitute value of the shearing force τ is 7520 (1 / second), and the substitute value of the viscosity η of the kneaded product after the dilution kneading step is 72 ( 1 / m) and the substitute value of the shearing force τ was 4320 (1 / second). This is the negative electrode plate of Comparative Example 2.
正極板は実施例１と同様に作製したものを用い、また実施例１と同様に作製した電池を比較例２のリチウムイオン電池とする。 A positive electrode plate produced in the same manner as in Example 1 was used, and a battery produced in the same manner as in Example 1 was used as a lithium ion battery in Comparative Example 2.
（比較例３）
図１に示すフローチャートに従い、実施例１では初混練工程で固形分比が６２［％］の混練物を得たところを、初混練工程で固形分比が５５％の混練物を得た以外は、実施例１と全く同様の作製手順で負極を作製した。なおここで一次混練物の粘度ηの代用値は２８５（１／ｍ）で剪断力τの代用値は５７００（１／秒）、希釈混練工程後の混練物の粘度ηの代用値は１２０（１／ｍ）で剪断力τの代用値は７２００（１／秒）であった。これを比較例３の負極電極板とする。
(Comparative Example 3)
According to the flowchart shown in FIG. 1, in Example 1, a kneaded material having a solid content ratio of 62 [%] was obtained in the initial kneading step, except that a kneaded material having a solid content ratio of 55% was obtained in the first kneading step. A negative electrode was produced in the same production procedure as in Example 1. Here, the substitute value of the viscosity η of the primary kneaded product is 285 (1 / m), the substitute value of the shearing force τ is 5700 (1 / second), and the substitute value of the viscosity η of the kneaded product after the dilution kneading step is 120 ( 1 / m) and the substitute value of the shearing force τ was 7200 (1 / second). This is the negative electrode plate of Comparative Example 3.
正極電極板は実施例１と同様に作製した極板を用い、また実施例１と同様に作製した電池を比較例３のリチウムイオン電池とする。 As the positive electrode plate, an electrode plate produced in the same manner as in Example 1 was used, and a battery produced in the same manner as in Example 1 was used as a lithium ion battery in Comparative Example 3.
（参考例１）
図２に示すフローチャートに従い、実施例１では初混練工程で黒鉛１００重量部にＣＭＣを粉末状態で固形分換算で１．２重量部添加して固形分比が６２［％］の混練物を得、希釈混練工程で分散媒のみを加えたところを、初混練工程で黒鉛１００重量部にＣＭＣの１重量％水溶液を固形分換算で０．５８重量部加え、固形分比が６３［％］の混練物を得（この混練物の粘度ηの代用値は６２５（１／ｍ）で剪断力τの代用値は１２５００（１／秒））、希釈混練工程で残りのＣＭＣ水溶液を加えた（この混練物の粘度ηの代用値は１００（１／ｍ）で剪断力τの代用値は６０００（１／秒））以外は、実施例１と全く同様の作製手順で負極を作製した。これを参考例１の負極電極板とする。
(Reference Example 1)
According to the flowchart shown in FIG. 2, in Example 1, 1.2 parts by weight of CMC in a powder state was added to 100 parts by weight of graphite in the initial kneading step to obtain a kneaded product having a solid content ratio of 62%. In the initial kneading step, 0.58 parts by weight of a 1% by weight aqueous solution of CMC in terms of solid content was added to a solid content ratio of 63 [%]. A kneaded product was obtained (the substitute value of the viscosity η of this kneaded product was 625 (1 / m) and the substitute value of the shearing force τ was 12500 (1 / second)), and the remaining CMC aqueous solution was added in the dilution kneading step (this A negative electrode was produced in exactly the same manner as in Example 1, except that the substitute value of the viscosity η of the kneaded product was 100 (1 / m) and the substitute value of the shearing force τ was 6000 (1 / second). This is the negative electrode plate of Reference Example 1.
正極電極板は実施例１と同様に作製した極板を用い、また実施例１と同様に作製した電池を参考例１のリチウムイオン電池とする。 As the positive electrode plate, an electrode plate produced in the same manner as in Example 1 is used, and a battery produced in the same manner as in Example 1 is a lithium ion battery of Reference Example 1.
前記のように作製した負極電極板を以下に示す方法にて評価した。その結果を（表１）に記す。
（ペースト沈降性）
混練直後の負極合材ペーストを塩化ビニール製のチュウブ管（φ１０、長さ１００ｍｍ）に入れ、上下部をテープで塞ぎ、密閉する。これを２本用意する。下部から１０ｍｍの位置をカッターで切断後、その箇所のペーストの固形分率を測定する。混練直後と混練して７日後とで測定した差の結果を（表１）に示した。
（塗着重量バラツキ）
負極合材ペーストをダイコート方式により、１０μｍ厚の銅箔に塗布乾燥する時に、βＸ線重量計により、幅方向および長手方向を含む２０００ｍでの電極板中の塗着重量バラツキを測定した結果を（表１）に示す。
（９０度剥離強度）
上記のように作製した負極板を用いて、集電体である銅箔と合剤部分とでの結着強度をＪＩＳ Ｋ６８５４に準拠して、９０度剥離によって測定した。試料片の寸法は幅が１２
．６５ｍｍ、接着部分の長さが７０ｍｍ〜８０ｍｍで行った。
The negative electrode plate produced as described above was evaluated by the following method. The results are shown in (Table 1).
(Paste sedimentation)
The negative electrode mixture paste immediately after kneading is put into a tube tube (φ10, length 100 mm) made of vinyl chloride, and the upper and lower parts are closed with tape and sealed. Prepare two of these. After cutting a position 10 mm from the bottom with a cutter, the solid content rate of the paste at that location is measured. The results of the difference measured immediately after kneading and after 7 days after kneading are shown in Table 1.
(Coating weight variation)
When the negative electrode mixture paste was applied to a 10 μm thick copper foil by a die coating method and dried, the result of measuring the coating weight variation in the electrode plate at 2000 m including the width direction and the longitudinal direction was measured by a βX-ray weight meter ( Table 1) shows.
(90 degree peel strength)
Using the negative electrode plate produced as described above, the binding strength between the copper foil as the current collector and the mixture portion was measured by 90-degree peeling according to JIS K6854. The dimension of the specimen is 12 width
. The length was 65 mm and the length of the bonded portion was 70 mm to 80 mm.
鉄の含有量が３００ｐｐｍの黒鉛を用い、かつ初混練工程における混練の剪断力が希釈混練工程の２．５倍以上になるよう作製した負極合材ペーストは、鉄の含有量が１０００ｐｐｍの黒鉛と比較して、ペースト安定性が飛躍的に向上し沈降が抑制され、密着性が向上している。この理由として、黒鉛に含有される鉄が増粘剤に含まれるカルボキシル基と錯形成反応を起こし増粘剤の機能が損失するのに対し、鉄が減少したことで上述した錯形成反応に伴うペーストの沈降が抑制されて塗着重量バラツキが激減する一方、増粘剤の凝集が抑制されて密着性が向上したと考えられる（実施例１と比較例２との対比）。 The negative electrode mixture paste prepared using graphite having an iron content of 300 ppm and having a shearing force of kneading in the initial kneading step at least 2.5 times that of the dilution kneading step is composed of graphite having an iron content of 1000 ppm. In comparison, paste stability is dramatically improved, settling is suppressed, and adhesion is improved. The reason for this is that the iron contained in the graphite causes a complex formation reaction with the carboxyl group contained in the thickener and the function of the thickener is lost. It is considered that the sedimentation of the paste is suppressed and the coating weight variation is drastically reduced, while the aggregation of the thickener is suppressed and the adhesion is improved (contrast with Example 1 and Comparative Example 2).
ただし鉄の含有量が３００ｐｐｍの黒鉛を用いた場合でも、初混練工程における剪断力が希釈混練工程のそれに対し２．５倍を下回った場合、ペーストの安定性低下に伴って塗着重量バラツキが増加し、密着性も低下した（実施例１と比較例３との対比）。さらには増粘剤を水溶液として添加した場合、初混練工程における増粘剤量が不足するため剪断力を希釈混練工程に対し２．５倍以上にすることができず、比較例１〜３ほどではないものの塗着重量ばらつきの増加と密着性の低下が見られた。この結果から、本発明の効果を現出させるためには、黒鉛中の鉄含有量が５００ｐｐｍ以下であることと、増粘剤を初混練工程にて粉末状態で添加することと、初混練工程における混練の剪断力を希釈混練工程における混練の剪断力の２．５倍以上とすることは必須であることがわかる。 However, even when graphite with an iron content of 300 ppm is used, if the shearing force in the initial kneading step is less than 2.5 times that in the dilution kneading step, there will be a variation in the coating weight due to a decrease in paste stability. It increased and the adhesiveness also decreased (contrast with Example 1 and Comparative Example 3). Furthermore, when the thickener is added as an aqueous solution, the amount of the thickener in the initial kneading step is insufficient, so the shearing force cannot be increased to 2.5 times or more that of the dilution kneading step. Although not, an increase in coating weight variation and a decrease in adhesion were observed. From this result, in order to bring out the effects of the present invention, the iron content in the graphite is 500 ppm or less, the thickener is added in the powder state in the initial kneading step, and the initial kneading step. It can be seen that it is essential to set the shearing force of kneading at 2.5 times or more of the shearing force of kneading in the dilution kneading step.
次に、これらの電池を、以下に示す方法にて評価した。その結果を（表２）に記す。
（２０℃ ５００サイクル容量維持率）
封口後の完成電池について、定電流充電１４００ｍＡ／４．１Ｖカット・定電流放電１４００ｍＡ／３Ｖカットの慣らし充放電を２度行い、２０℃環境で７日間保存した後、以下の充放電サイクルを５００回繰り返した。
充電：定電流１４００ｍＡ／４．２Ｖカットの後、定電圧４．２Ｖ保持／１００ｍＡカット
放電：定電流２０００ｍＡ／３Ｖカット
このときの１サイクル目に対する５００サイクル目の放電容量比を５００サイクル容量維持率として（表２）中に示した。
（４５℃ ３００サイクル容量維持率）
封口後の完成電池について、定電流充電１４００ｍＡ／４．１Ｖカット・定電流放電１４００ｍＡ／３Ｖカットの慣らし充放電を２度行い、４５℃環境で７日間保存した後、以下の充放電サイクルを３００回繰り返した。
充電：定電流１４００ｍＡ／４．２Ｖカットの後、定電圧４．２Ｖ保持／１００ｍＡカット
放電：定電流２０００ｍＡ／３Ｖカット
このときの１サイクル目に対する３００サイクル目の放電容量比を３００サイクル容量維持率として（表２）中に示した。
（０．２Ｃ 初期放電容量）
封口後の完成電池について、定電流充電１４００ｍＡ／４．１Ｖカット・定電流放電１４００ｍＡ／３Ｖカットの慣らし充放電を２度行い、４５℃環境で７日間保存した後、以下の充放電を行った。
充電：定電流１４００ｍＡ／４．２Ｖカットの後、定電圧４．２Ｖ保持／１００ｍＡカット
放電：定電流４００ｍＡ／３Ｖカット
このときの放電容量を０．２Ｃ初期放電容量として（表２）中に示した。
Next, these batteries were evaluated by the following methods. The results are shown in (Table 2).
(20 ° C 500 cycle capacity maintenance rate)
After completion of the sealing, the battery is subjected to constant charge / discharge of constant current charge 1400 mA / 4.1 V cut / constant current discharge 1400 mA / 3 V cut twice and stored in a 20 ° C. environment for 7 days. Repeated times.
Charging: After constant current 1400 mA / 4.2 V cut, constant voltage 4.2 V hold / 100 mA cut discharge: constant current 2000 mA / 3 V cut The ratio of discharge capacity at 500th cycle to the first cycle at this time is the capacity maintenance rate of 500 cycles As shown in (Table 2).
(45 ° C 300 cycle capacity maintenance rate)
The completed battery after sealing is subjected to constant charge and discharge of constant current charge 1400 mA / 4.1 V cut / constant current discharge 1400 mA / 3 V cut twice, stored for 7 days in a 45 ° C. environment, and then subjected to the following charge / discharge cycle of 300 Repeated times.
Charging: After constant current 1400 mA / 4.2 V cut, constant voltage 4.2 V hold / 100 mA cut discharge: constant current 2000 mA / 3 V cut At this time, the discharge capacity ratio of the 300th cycle to the first cycle is 300 cycle capacity maintenance rate As shown in (Table 2).
(0.2C initial discharge capacity)
The completed battery after sealing was subjected to constant charge / discharge of 1400 mA / 4.1 V cut / constant current discharge 1400 mA / 3 V cut twice and stored for 7 days in a 45 ° C. environment, followed by the following charge / discharge. .
Charging: After constant current 1400 mA / 4.2 V cut, constant voltage 4.2 V hold / 100 mA cut discharge: Constant current 400 mA / 3 V cut The discharge capacity at this time is shown as 0.2 C initial discharge capacity in Table 2 It was.
実施例１の電池はサイクル特性が良好であった。この理由として、塗着重量ばらつきが低減したために電極内の充放電反応が均一化したことと、極板の密着強度が向上したために活物質の脱落が減少したことが挙げられる。 The battery of Example 1 had good cycle characteristics. This is because the charge / discharge reaction in the electrode is made uniform because the coating weight variation is reduced, and the dropout of the active material is reduced because the adhesion strength of the electrode plate is improved.
この実施例１に対し、比較例１〜３および参考例１はサイクル特性の低下が見られた。特に比較例１および２に関しては、密着性が初期から低いために、初期放電容量の顕著な低下が見られた。以上の結果から、本発明の製造方法を用いることにより、サイクル特性及び、初期の放電容量に優れたリチウムイオン電池の実現が可能であることが分かった。 In contrast to Example 1, Comparative Examples 1 to 3 and Reference Example 1 showed a decrease in cycle characteristics. In particular, in Comparative Examples 1 and 2, since the adhesiveness was low from the beginning, the initial discharge capacity was significantly reduced. From the above results, it was found that a lithium ion battery excellent in cycle characteristics and initial discharge capacity can be realized by using the manufacturing method of the present invention.
＜検討２．黒鉛中の鉄の含有量の検討＞
（実施例２〜５、比較例４）
図１に示すフローチャートに従い、実施例１において第一工程で黒鉛中の鉄の含有量が３００ｐｐｍであったところを、６００、５００、１００、５０ｐｐｍ、検出限界未満（Ｎ．Ｄ．）とした以外は、実施例１と全く同様の作成手順で負極を作成した。各々を比較例４、実施例２〜５の負極電極板とする。
<Study 2. Examination of iron content in graphite>
(Examples 2 to 5, Comparative Example 4)
According to the flowchart shown in FIG. 1, in Example 1, the iron content in the graphite in the first step was 300 ppm, except that it was 600, 500, 100, 50 ppm, less than the detection limit (ND). Produced a negative electrode by the same production procedure as in Example 1. Each is made into the negative electrode plate of the comparative example 4 and Examples 2-5.
正極電極板は実施例１と同様に作製したものを用い、前記負極電極板と組み合わせ、実施例１と同様の手順で作製した電池を、比較例４、実施例２〜５のリチウムイオン電池とする。 The positive electrode plate produced in the same manner as in Example 1 was used, and the battery produced in the same procedure as in Example 1 in combination with the negative electrode plate was compared with the lithium ion batteries in Comparative Example 4 and Examples 2-5. To do.
これらの負極電極板を以下に示す方法にて評価した。その結果を（表３）に記す。
（ペースト沈降性）
検討１と同様の方法にて評価した。
（塗着重量バラツキ）
検討１と同様の方法にて評価した。
（９０度剥離強度）
検討１と同様の方法にて評価した。
These negative electrode plates were evaluated by the following methods. The results are shown in (Table 3).
(Paste sedimentation)
Evaluation was performed in the same manner as in Study 1.
(Coating weight variation)
Evaluation was performed in the same manner as in Study 1.
(90 degree peel strength)
Evaluation was performed in the same manner as in Study 1.
鉄の含有量が５００ｐｐｍ以下の黒鉛を用いて作製した負極合材ペーストは、経時変化（ペースト沈降性）が少なく、塗着重量バラツキが小さい上に、９０度剥離強度による結着力も強いことが判る（実施例１〜５）。一方、鉄の含有量が６００ｐｐｍ以上の黒鉛を用いて作製した負極合材ペーストは、経時変化（ペースト沈降性）が大きく、塗着重量バラツキが大きい上に、９０度剥離強度も小さい（比較例２および４）。これは、鉄の含有量が５００ｐｐｍを越えると、鉄とＣＭＣとが結合して錯体を形成し、増粘剤の増粘作用を低下させ、ペーストが不安定になったためである。 The negative electrode mixture paste produced using graphite with an iron content of 500 ppm or less has little change over time (paste sedimentation), small variation in coating weight, and strong binding strength due to 90 ° peel strength. It can be seen (Examples 1 to 5). On the other hand, the negative electrode mixture paste produced using graphite having an iron content of 600 ppm or more has a large change with time (paste sedimentation), a large coating weight variation, and a small 90 ° peel strength (Comparative Example). 2 and 4). This is because when the iron content exceeds 500 ppm, iron and CMC are combined to form a complex, the thickening action of the thickener is lowered, and the paste becomes unstable.
次に、これらの電池を、以下に示す方法にて評価した。その結果を（表４）に記す。
（２０℃ ５００サイクル容量維持率）
検討１と同様の方法にて評価した。
（４５℃ ５００サイクル容量維持率）
検討１と同様の方法にて評価した。
（０．２Ｃ 初期放電容量）
検討１と同様の方法にて評価した。
Next, these batteries were evaluated by the following methods. The results are shown in (Table 4).
(20 ° C 500 cycle capacity maintenance rate)
Evaluation was performed in the same manner as in Study 1.
(45 ° C 500 cycle capacity maintenance rate)
Evaluation was performed in the same manner as in Study 1.
(0.2C initial discharge capacity)
Evaluation was performed in the same manner as in Study 1.
鉄の含有量が５００ｐｐｍ以下の場合、２０℃および４５℃の電池のサイクル特性及び
０．２Ｃ初期の放電容量において良好であることが判る（実施例１〜５）。一方、鉄の含有量が６００ｐｐｍ以上の場合、５００サイクル後の容量維持率が低く、初期の放電容量も低い（比較例２および４）。上述したような不安定なペーストからなる負極板を用いた場合、負荷が局所的に大きくなるところが存在するため、負極活物質の層間に挿入しきれなかったリチウムイオンがリチウム金属として析出しやすい。また、結着材も均一に分散されていないことから、極板強度の値も小さく、充放電時の極板の膨張、収縮の際に集電体から合剤が剥がれやすくなる。そのため、サイクル特性及び初期の放電容量が低下したと推測できる。
It can be seen that when the iron content is 500 ppm or less, the cycle characteristics of the batteries at 20 ° C. and 45 ° C. and the discharge capacity at the initial stage of 0.2 C are good (Examples 1 to 5). On the other hand, when the iron content is 600 ppm or more, the capacity retention rate after 500 cycles is low, and the initial discharge capacity is also low (Comparative Examples 2 and 4). When the negative electrode plate made of the unstable paste as described above is used, there are places where the load is locally increased, so that lithium ions that could not be inserted between the layers of the negative electrode active material tend to precipitate as lithium metal. Further, since the binder is not uniformly dispersed, the value of the electrode plate strength is small, and the mixture is easily peeled off from the current collector when the electrode plate expands or contracts during charge / discharge. Therefore, it can be estimated that the cycle characteristics and the initial discharge capacity have decreased.
以上の結果から、黒鉛中に含まれる鉄の許容量は、５００ｐｐｍであることが分かった。 From the above results, it was found that the allowable amount of iron contained in graphite was 500 ppm.
＜検討３．増粘剤種の検討＞
（実施例６〜７、比較例５〜６）
図１に示すフローチャートに従い、実施例１ではＣＭＣのナトリウム塩（第一工業製薬製セロゲン４Ｈ）を黒鉛１００重量部あたり１．２重量部用いたところを、ＣＭＣのアンモニウム塩、ポリアクリル酸、ポリエチレンオキシド（ＰＥＯ）、ポリビニルアルコール（ＰＶＡ）を各々１．２重量部、１．２重量部、０．７２重量部、０．７２重量部（ＣＭＣのナトリウム塩と同等の体積）を用い、実施例１と同様の手順で負極を作製した。各々を実施例６、７、比較例５、６の負極電極板とする。
<Study 3. Examination of thickener types>
(Examples 6-7, Comparative Examples 5-6)
In accordance with the flowchart shown in FIG. 1, in Example 1, 1.2 parts by weight of CMC sodium salt (Delogen Kogyo Serogen 4H) per 100 parts by weight of graphite was used. Examples using ethylene oxide (PEO) and polyvinyl alcohol (PVA) in an amount of 1.2 parts by weight, 1.2 parts by weight, 0.72 parts by weight, and 0.72 parts by weight (volume equivalent to the sodium salt of CMC), respectively A negative electrode was prepared in the same procedure as in 1. The negative electrode plates of Examples 6 and 7 and Comparative Examples 5 and 6 are respectively used.
正極電極板は実施例１と同様に作製したものを用い、前記負極電極板と組み合わせ、実施例１と同様の手順で作製した電池を、実施例６、７、比較例５、６のリチウムイオン電池とする。 The positive electrode plate produced in the same manner as in Example 1 was used. The batteries produced in the same procedure as in Example 1 were combined with the negative electrode plate, and lithium ions in Examples 6 and 7 and Comparative Examples 5 and 6 were used. Use batteries.
次に、これらの負極電極板および電池を以下に示す方法にて評価した。その結果を（表５）に記す
（９０度剥離強度）
検討１と同様の方法にて評価した。
（２０℃ ５００サイクル容量維持率）
検討１と同様の方法にて評価した。
（４５℃ ３００サイクル容量維持率）
検討１と同様の方法にて評価した。
Next, these negative electrode plates and batteries were evaluated by the following methods. The results are shown in (Table 5) (90 degree peel strength)
Evaluation was performed in the same manner as in Study 1.
(20 ° C 500 cycle capacity maintenance rate)
Evaluation was performed in the same manner as in Study 1.
(45 ° C 300 cycle capacity maintenance rate)
Evaluation was performed in the same manner as in Study 1.
まず、ナトリウム塩・アンモニウム塩の何れであっても、増粘剤としてＣＭＣを用いた場合、９０度剥離強度は強く、２０℃および４５℃での容量維持率も良好であることが判る（実施例１および６）。また、カルボキシル基を有するポリアクリル酸を増粘剤に用いた場合も、同様に９０度剥離強度やサイクル特性が良好である（実施例７）。一方、増粘
剤としてＰＥＯやＰＶＡを用いた場合、９０度剥離強度の値は小さく、２０℃および４５℃での容量維持率も低かった（比較例５〜６）。このような負極板を用いた場合、結着材の極性基との結合が困難となり、結着材が均一に分散しないため、極板強度の値も小さく、充放電時の極板の膨張、収縮の際に集電体から合剤が剥がれやすくなる。そのため、サイクル特性及び初期の放電容量が低下したと推測できる。
First, it can be seen that when CMC is used as a thickener, the 90 degree peel strength is strong and the capacity retention rate at 20 ° C. and 45 ° C. is good for both sodium salts and ammonium salts. Examples 1 and 6). Also, when polyacrylic acid having a carboxyl group is used as a thickener, the 90-degree peel strength and cycle characteristics are also good (Example 7). On the other hand, when PEO or PVA was used as the thickener, the 90-degree peel strength was small, and the capacity retention at 20 ° C. and 45 ° C. was also low (Comparative Examples 5 to 6). When such a negative electrode plate is used, it becomes difficult to bond with the polar group of the binder, and the binder does not disperse uniformly, so the value of the electrode plate strength is also small, the expansion of the electrode plate during charging and discharging, During the shrinkage, the mixture is easily peeled off from the current collector. Therefore, it can be estimated that the cycle characteristics and the initial discharge capacity have decreased.
以上の結果から、本発明の製造方法を充分に活用するためには、カルボキシル基を含む増粘剤であることが好ましいことがわかる。 From the above results, it can be seen that a thickener containing a carboxyl group is preferable in order to fully utilize the production method of the present invention.
＜検討４．結着材種の検討＞
（実施例８、比較例７）
図１に示すフローチャートに従い、実施例１では結着材としてＳＢＲ変性体（固形分４０重量％）を用いたところを、ポリオレフィン系ディスパージョン（固形分４０重量％）、ポリテトラフルオロエチレン（ＰＴＦＥ）とヘキサフルオロエチレンの共重合体の水酸化物（固形分６０重量％）を用いた以外は、実施例１と全く同様の作製手順で負極を作製した。各々を実施例８、比較例７の負極電極板とする。
<Study 4. Examination of binder type>
(Example 8, Comparative Example 7)
According to the flowchart shown in FIG. 1, in Example 1, the SBR modified material (solid content 40% by weight) was used as the binder, and the polyolefin dispersion (solid content 40% by weight) and polytetrafluoroethylene (PTFE) were used. A negative electrode was produced in exactly the same production procedure as in Example 1 except that a hydroxide of a copolymer of hexafluoroethylene (solid content: 60% by weight) was used. The negative electrode plates of Example 8 and Comparative Example 7 are used as these.
正極板は実施例と同様に作製したものを用い、実施例１と同様の手順で作製した電池を実施例８、比較例７のリチウムイオン電池とする。 The positive electrode plate produced in the same manner as in the example was used, and the battery produced in the same procedure as in Example 1 was used as the lithium ion battery in Example 8 and Comparative Example 7.
これらの負極電極板および電池を以下に示す方法にて評価した。その結果を（表６）に記す。
（９０度剥離強度）
検討１と同様の方法にて評価した。
（２０℃ ５００サイクル容量維持率）
検討１と同様の方法にて評価した。
（４５℃ ３００サイクル容量維持率）
検討１と同様の方法にて評価した。
These negative electrode plates and batteries were evaluated by the methods shown below. The results are shown in (Table 6).
(90 degree peel strength)
Evaluation was performed in the same manner as in Study 1.
(20 ° C 500 cycle capacity maintenance rate)
Evaluation was performed in the same manner as in Study 1.
(45 ° C 300 cycle capacity maintenance rate)
Evaluation was performed in the same manner as in Study 1.
結着材がＳＢＲ変性体である場合、ゴム粒子表面が極性基からなる粘着成分で覆われている。またポリオレフィン系結着材の場合も、粒子表面がカルボキシル基などの極性基で覆われている。これらを結着材として用いた場合、９０度剥離強度は強く、２０℃および４５℃での容量維持率も良好であることが判る（実施例１および８）。中でも実施例１の方が、サイクル特性が僅かながら実施例８よりも良好な結果を示した。 When the binder is an SBR modified body, the rubber particle surface is covered with an adhesive component made of a polar group. In the case of a polyolefin-based binder, the particle surface is covered with a polar group such as a carboxyl group. When these are used as the binder, it can be seen that the 90 ° peel strength is strong and the capacity retention at 20 ° C. and 45 ° C. is also good (Examples 1 and 8). In particular, Example 1 showed better results than Example 8 with a slight cycle characteristic.
一方、結着材がＰＴＦＥである場合、９０度剥離強度の値は小さく、２０℃および４５℃での容量維持率も低かった（比較例７）。ＰＴＦＥは極性基を有さないため、ＣＭＣの極性基との結合が困難となり、均一に分散しないため、極板強度の値も小さく、充放電時の極板の膨張、収縮の際に集電体から合剤が剥がれやすくなる。そのため、サイクル特性及び初期放電容量が低下したと推測できる。 On the other hand, when the binder was PTFE, the 90 ° peel strength value was small, and the capacity retention at 20 ° C. and 45 ° C. was also low (Comparative Example 7). Since PTFE does not have a polar group, it becomes difficult to bond with the polar group of CMC and does not disperse uniformly. Therefore, the value of the electrode plate strength is small, and current is collected during expansion and contraction of the electrode plate during charge and discharge. The mixture is easy to peel off from the body. Therefore, it can be estimated that the cycle characteristics and the initial discharge capacity are reduced.
以上の結果から、本発明の製造方法を充分に活用するためには、結着材として極性基を有する水分散性高分子を用いるのが好ましく、さらにはアクリロニトリル単位を含むコアシェル型ゴム粒子を用いるのがより好ましいことがわかる。 From the above results, in order to fully utilize the production method of the present invention, it is preferable to use a water-dispersible polymer having a polar group as a binder, and further use core-shell type rubber particles containing acrylonitrile units. It can be seen that is more preferable.
本発明の非水系二次電池は、容量バラツキが少なく、サイクル特性に優れたポータブル用高容量電源等として有用である。 The non-aqueous secondary battery of the present invention is useful as a portable high-capacity power source with little capacity variation and excellent cycle characteristics.
Claims (4)
前記黒鉛は鉄の含有量が５００ｐｐｍ以下であり、前記増粘剤はカルボキシル基を含む水溶性高分子であり、前記結着材は極性基を有する水分散性高分子であり、
負極塗膜形成用の前記ペーストの混練工程は、少なくとも前記黒鉛に前記増粘剤を粉末状態で添加し、前記分散媒と共に混練する初混練工程と、前記初混練工程の混練物を前記分散媒で希釈し混練する希釈混練工程と、前記希釈混練工程の混練物に前記結着材を添加し、混練することによりペーストを作成する仕上げ混練工程の３つの工程を含み、
初混練工程における混練の剪断力が、希釈混練工程および仕上げ混練工程における混練の剪断力の２．５倍以上であることを特徴とする非水系二次電池の負極用電極板の製造方法。 In the method for producing a negative electrode plate for a non-aqueous secondary battery using a paste constituted by kneading and dispersing a carbon material mainly composed of graphite, a thickener, and a binder,
The graphite has an iron content of 500 ppm or less, the thickener is a water-soluble polymer containing a carboxyl group, and the binder is a water-dispersible polymer having a polar group,
The paste kneading step for forming the negative electrode coating film includes an initial kneading step in which the thickener is added in powder form to at least the graphite and kneading with the dispersion medium, and a kneaded product of the initial kneading step is used as the dispersion medium. Including a dilution kneading step for diluting and kneading, and a final kneading step for adding a binder to the kneaded product of the dilution kneading step and creating a paste by kneading,
A method for producing an electrode plate for a negative electrode of a nonaqueous secondary battery, wherein the kneading shear force in the initial kneading step is 2.5 times or more the kneading shear force in the dilution kneading step and the finish kneading step.
その１％水溶液とした時の粘度が６〜１８Ｐａ・ｓであることを特徴とする請求項１に記載の非水系二次電池の負極用電極板の製造方法。 The thickener is a sodium salt and / or an ammonium salt of carboxymethylcellulose;
2. The method for producing a negative electrode plate for a non-aqueous secondary battery according to claim 1, wherein the 1% aqueous solution has a viscosity of 6 to 18 Pa · s.
The method for producing a negative electrode plate for a non-aqueous secondary battery according to claim 1, wherein the binder is a core-shell type rubber particle-based binder containing an acrylonitrile unit.
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