JP2010177061A - Binder for negative electrode of battery - Google Patents
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- JP2010177061A JP2010177061A JP2009018871A JP2009018871A JP2010177061A JP 2010177061 A JP2010177061 A JP 2010177061A JP 2009018871 A JP2009018871 A JP 2009018871A JP 2009018871 A JP2009018871 A JP 2009018871A JP 2010177061 A JP2010177061 A JP 2010177061A
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
Description
本発明は、負極薄膜作成時に負極活物質をスラリー中に均一に分散させ、負極活物質と集電体との高い結着性を誘起し、且つ可撓性の優れた負極薄膜を提供可能なリチウムイオン二次電池負極用バインダーに関するものである。 The present invention can provide a negative electrode thin film having excellent flexibility in which a negative electrode active material is uniformly dispersed in a slurry at the time of preparation of the negative electrode thin film to induce high binding between the negative electrode active material and the current collector. The present invention relates to a binder for a negative electrode of a lithium ion secondary battery.
近年、電子機器の小型化、ポータブル化が進み、その電源としてエネルギー密度の高い電池の開発が強く要望されており、特に二次電池の開発が精力的に行われている。従来の二次電池としては、鉛蓄電他、ニッケル−カドミウム電池等が挙げられるが、高エネルギー密度の電池という点ではまだ不十分である。そこで、これらの電池に替わるものとして、近年、エネルギー密度を大幅に向上できるリチウムイオン二次電池が開発され、急速に普及してきた。 In recent years, electronic devices have become smaller and more portable, and there has been a strong demand for the development of a battery with high energy density as a power source. In particular, the development of secondary batteries has been vigorously conducted. Conventional secondary batteries include lead storage, nickel-cadmium batteries and the like, but they are still insufficient in terms of high energy density batteries. Therefore, as a replacement for these batteries, in recent years, lithium ion secondary batteries capable of greatly improving energy density have been developed and rapidly spread.
リチウムイオン二次電池は、銅箔等の集電体上にリチウムイオンを吸蔵・放出できる負極活物質をバインダーと共に薄膜化したものを負極としている。これらの負極活物質に用いるものとしては、天然黒鉛、人造黒鉛、ハードカーボン等の炭素材料やシリコンなどが挙げられる。これらの負極活物質とバインダーを溶媒と共に混練し、負極活物質を分散させてスラリーとする。このスラリーをドクターブレード法等によって集電体上に塗布し乾燥して薄膜化することにより、リチウムイオン二次電池の負極を形成する。 A lithium ion secondary battery uses a negative electrode active material that can occlude and release lithium ions on a current collector such as a copper foil and a thin film together with a binder as a negative electrode. Examples of materials used for these negative electrode active materials include carbon materials such as natural graphite, artificial graphite, and hard carbon, and silicon. These negative electrode active materials and a binder are kneaded with a solvent, and the negative electrode active materials are dispersed to form a slurry. This slurry is applied onto a current collector by a doctor blade method or the like, dried and thinned to form a negative electrode of a lithium ion secondary battery.
リチウムイオン二次電池負極用バインダーとして最も広範に用いられているのが、ポリフッ化ビニリデン（ＰＶＤＦ）に代表されるフッ素系樹脂である。 The most widely used binder for lithium ion secondary battery negative electrodes is a fluorine-based resin typified by polyvinylidene fluoride (PVDF).
フッ素系樹脂をバインダーとして用いた場合、可撓性を有する負極薄膜を作成可能な一方で、集電体と負極活物質の結着性が劣るため、電池製造工程時に負極活物質の一部又は全部が集電体から剥離・脱落する恐れがある。また、電池の充放電が行われる際、負極活物質内ではリチウムイオンの挿入・放出が繰り返され、それに伴い負極活物質の膨張・収縮が起こる。その場合も、集電体から負極活物質の剥離・脱落の問題が起こりうる。 When a fluorine-based resin is used as a binder, a flexible negative electrode thin film can be formed, but the binding property between the current collector and the negative electrode active material is inferior. There is a risk of all peeling or dropping from the current collector. Further, when the battery is charged / discharged, lithium ions are repeatedly inserted and released in the negative electrode active material, and the negative electrode active material expands and contracts accordingly. In such a case as well, there may be a problem that the negative electrode active material is peeled off from the current collector.
フッ素系樹脂以外のバインダーとしてスチレン−ブタジエンラバー（ＳＢＲ）を使用する場合があるが、スラリー中での負極活物質の安定性が著しく劣り、活物質の沈降が起こりやすい。この為、セルロース系増粘剤や界面活性剤などの添加が必要となるが、セルロース系増粘剤は乾燥過程の熱でそれ自身が分解し、水分が発生してしまう問題がある。 Styrene-butadiene rubber (SBR) may be used as a binder other than the fluorine-based resin, but the stability of the negative electrode active material in the slurry is extremely poor, and the active material tends to settle. For this reason, it is necessary to add a cellulosic thickener or a surfactant. However, the cellulosic thickener has a problem in that it decomposes itself by the heat of the drying process to generate moisture.
高い結着性と分散性を示す負極用バインダーを求めて研究が成される中、ポリアクリル酸をバインダーとして使用した場合、負極活物質と集電体を強固に結着させることができ、更に、剥離・脱落し難い負極薄膜を作成可能であることが見出された（特許文献１、特許文献２）。
ポリアクリル酸が、負極活物質と集電体を強固に結着させることが可能なのは、構造中に多量のカルボキシル基を含有するためであると考えられる。しかしながら、モノエチレン性不飽和ジカルボン酸であるイタコン酸のみ、もしくはイタコン酸を主成分とする水溶性合成高分子からなる負極用バインダー組成物は製造されていなかった。 It is considered that the polyacrylic acid can firmly bind the negative electrode active material and the current collector because it contains a large amount of carboxyl groups in the structure. However, a binder composition for a negative electrode comprising only itaconic acid which is a monoethylenically unsaturated dicarboxylic acid or a water-soluble synthetic polymer mainly composed of itaconic acid has not been produced.
本発明の課題は、負極薄膜作成時に負極活物質をスラリー中に均一に分散させ、且つ負極活物質と集電体との高い結着性を誘起し、且つ可撓性に優れる負極薄膜を作成可能なリチウムイオン二次電池負極用バインダー組成物を提供することにある。 An object of the present invention is to create a negative electrode thin film that uniformly disperses a negative electrode active material in a slurry at the time of preparing the negative electrode thin film, induces high binding properties between the negative electrode active material and the current collector, and is excellent in flexibility. The object is to provide a binder composition for a negative electrode of a lithium ion secondary battery.
上記課題の解決は、イタコン酸を必須として含有する水溶性単量体（混合物）
を（共）重合させることで得られるリチウムイオン二次電池負極用バインダーを用いることにより達成できることを見出し、本発明に到達した。
The solution to the above problem is a water-soluble monomer (mixture) containing itaconic acid as an essential component.
It has been found that this can be achieved by using a binder for a negative electrode of a lithium ion secondary battery obtained by (co) polymerizing the polymer.
イタコン酸を必須として含有する水溶性単量体（混合物）を（共）重合させることで得られるリチウムイオン二次電池負極用バインダーは、負極作成時の負極活物質、バインダー、溶媒を混錬しスラリーを作成する過程において、負極活物質を均一に分散させることができる。さらに、ポリアクリル酸をバインダーとして用いた場合よりも負極活物質と集電体を強固に結着させるため、極めて剥離・脱落し難い負極薄膜を得ることができる。加えて、本発明品を用いて作成した負極薄膜は、優れた可撓性を示すことが特徴である。 The binder for lithium ion secondary battery negative electrode obtained by (co) polymerizing a water-soluble monomer (mixture) containing itaconic acid as an essential component kneads the negative electrode active material, binder and solvent at the time of negative electrode preparation. In the process of creating the slurry, the negative electrode active material can be uniformly dispersed. Furthermore, since the negative electrode active material and the current collector are more firmly bound than when polyacrylic acid is used as a binder, a negative electrode thin film that is extremely difficult to peel and drop off can be obtained. In addition, the negative electrode thin film prepared using the product of the present invention is characterized by excellent flexibility.
以下、本発明をさらに記述する。 The invention is further described below.
本発明のリチウムイオン二次電池負極用バインダーは、イタコン酸を必須として含有する水溶性単量体を（共）重合させることで得られる。 The lithium ion secondary battery negative electrode binder of the present invention can be obtained by (co) polymerizing a water-soluble monomer containing itaconic acid as an essential component.
本発明のリチウムイオン二次電池負極用バインダーは、他の水溶性単量体との共重合物でも使用することができる。これらイタコン酸と共重合する水溶性単量体の例としては、（メタ）アクリルアミド、ジメチルアクリルアミド、ジエチルアクリルアミド、イソプロピルアクリルアミド、ヒドロキシエチルアクリルアミド、ビニルピロリドン、ビニルホルムアミド、ビニルアセトアミド、（メタ）アクリル酸、マレイン酸、無水マレイン酸、フマル酸、クロトン酸等が挙げられ、重合反応の容易さからアクリルアミドが最も好ましい。これらの水溶性単量体のうち、一つ、もしくは複数個用いてもよい。 The binder for a lithium ion secondary battery negative electrode of the present invention can also be used as a copolymer with other water-soluble monomers. Examples of water-soluble monomers that copolymerize with itaconic acid include (meth) acrylamide, dimethylacrylamide, diethylacrylamide, isopropylacrylamide, hydroxyethylacrylamide, vinylpyrrolidone, vinylformamide, vinylacetamide, (meth) acrylic acid, Maleic acid, maleic anhydride, fumaric acid, crotonic acid and the like can be mentioned, and acrylamide is most preferable from the viewpoint of easy polymerization reaction. Of these water-soluble monomers, one or more may be used.
イタコン酸と、それと共重合する水溶性単量体とのモル比は、１００：０〜２０：８０の範囲であるが、１００：０〜５０：５０が好ましい。さらにより好ましくは１００：０〜７０：３０である。この理由は、負極活物質と集電体を強固に結着させる作用、あるいは優れた可撓性を示す作用が、高分子中のイタコン酸構造単位に基くものと考えられるため一定以上のイタコン酸含有量が必要と考えられる。従って共重合率の範囲は、上記のようになる。 The molar ratio of itaconic acid and the water-soluble monomer copolymerized therewith is in the range of 100: 0 to 20:80, preferably 100: 0 to 50:50. Even more preferably, it is 100: 0 to 70:30. The reason for this is that the action of firmly binding the negative electrode active material and the current collector or the action of excellent flexibility is based on the itaconic acid structural unit in the polymer, so that a certain level of itaconic acid is obtained. Content is considered necessary. Therefore, the range of the copolymerization rate is as described above.
イタコン酸を必須として含有する水溶性単量体のうち、イタコン酸は水酸化ナトリウム等の適当なアルカリ剤を用いて中和する必要がある。イタコン酸に含まれるカルボン酸のモル数に対して、好ましい中和率は２０〜８０モル％である。中和率が低すぎると、イタコン酸の溶解性、及び反応性の低下に繋がる。また、中和率が高すぎると多量のイタコン酸塩が生成し、やはり溶解性が低下する。従って、より好ましい中和率は４０〜６０モル％である。 Of the water-soluble monomers containing itaconic acid as an essential component, itaconic acid needs to be neutralized using a suitable alkaline agent such as sodium hydroxide. A preferable neutralization rate is 20 to 80 mol% with respect to the number of moles of carboxylic acid contained in itaconic acid. When the neutralization rate is too low, it leads to a decrease in the solubility and reactivity of itaconic acid. On the other hand, if the neutralization rate is too high, a large amount of itaconic acid salt is produced, and the solubility is also lowered. Therefore, a more preferable neutralization rate is 40 to 60 mol%.
イタコン酸を必須として含有する水溶性単量体の（共）重合反応は、水媒体中にて溶解状態で行うが、反応に必要ならば水媒体中に少量のアルコール等水溶性有機溶媒を混在させることも可能である。反応濃度としては、水溶性単量体の合計の濃度として１０重量％〜８０重量％であるが、好ましくは４０重量％〜６０重量％である。反応時の温度は、イタコン酸が反応溶媒に充分に溶解する温度が必要で、３０〜１００℃の範囲で行う。 The (co) polymerization reaction of water-soluble monomers containing itaconic acid as an essential component is carried out in a dissolved state in an aqueous medium. If necessary for the reaction, a small amount of a water-soluble organic solvent such as alcohol is mixed in the aqueous medium. It is also possible to make it. The reaction concentration is 10% to 80% by weight as the total concentration of the water-soluble monomers, but preferably 40% to 60% by weight. The temperature at the time of reaction needs to be a temperature at which itaconic acid is sufficiently dissolved in the reaction solvent, and is carried out in the range of 30 to 100 ° C.
重合開始はラジカル重合開始剤を使用する。これら開始剤は、アゾ系、レドックス系、過酸化物系いずれでも重合することが可能である。水溶性アゾ系開始剤の例としては、２、２’−アゾビス（２−メチルプロピオンアミジン）二塩化水素化物、２、２’−アゾビス〔２−（２−イミダゾリン−２−イル）プロパン〕二塩化水素化物、４、４’−アゾビス（４−シアノ吉草酸）などが挙げられる。またレドックス系の例としては、過硫酸アンモニウムと亜硫酸ナトリウム、亜硫酸水素ナトリウム、トリメチルアミン、テトラメチルエチレンジアミンなどとの組み合わせがあげられる。さらに過酸化物の例としては、過硫酸アンモニウムあるいはカリウム、過酸化水素などを挙げることができる。 For the initiation of polymerization, a radical polymerization initiator is used. These initiators can be polymerized by any of azo, redox and peroxide. Examples of water-soluble azo initiators include 2,2′-azobis (2-methylpropionamidine) dichloride, 2,2′-azobis [2- (2-imidazolin-2-yl) propane] And hydrogen chloride, 4,4′-azobis (4-cyanovaleric acid), and the like. Examples of redox systems include a combination of ammonium persulfate and sodium sulfite, sodium hydrogen sulfite, trimethylamine, tetramethylethylenediamine, and the like. Further, examples of peroxides include ammonium or potassium persulfate, hydrogen peroxide, and the like.
イタコン酸を主成分とする水溶性単量体の（共）重合体の重量平均分子量は、２千〜３００万が好ましい。３００万以上になると、負極作成時の負極活物質、バインダー、溶媒を混錬する過程において、スラリーが粘調になり過ぎ扱い難くなる。そのため、さらに好ましくは２千〜１０万である。分子量を調整するために重合時に必要に応じた連鎖移動剤を加えることもできる。 As for the weight average molecular weight of the (co) polymer of the water-soluble monomer which has itaconic acid as a main component, 2,000-3 million are preferable. If it exceeds 3 million, the slurry becomes too viscous and difficult to handle in the process of kneading the negative electrode active material, the binder, and the solvent at the time of preparing the negative electrode. Therefore, it is more preferably 2,000 to 100,000. In order to adjust the molecular weight, a chain transfer agent can be added as needed during the polymerization.
本発明のイタコン酸を主成分とする水溶性単量体の（共）重合体を用いて負極薄膜を作成するには、負極活物質、バインダー、溶媒を混錬しスラリーを作成する過程、次いで得られたスラリーを集電体上に塗布し乾燥する過程が必要となる。このとき用いる負極活物質の具体例としては、ハードカーボン、フッ化カーボン、グラファイト、天然黒鉛、メソフェーズカーボンマイクロビーズ（ＭＣＭＢ）、ポリアクリロニトリル（ＰＡＮ）、ピッチ系炭素繊維などの炭素質材料；ポリアセンなどの導電性高分子；Ｌｉ３Ｎなどのチッ化リチウム化合物；リチウム金属、リチウム合金などのリチウム系金属；ＳｉＢ４、ＳｉＢ６、Ｍｇ２
Ｓｉ、Ｍｇ２ Ｓｎ、Ｎｉ２ Ｓｉ、ＴｉＳｉ２、ＭｏＳｉ２、ＣｏＳｉ２、ＮｉＳｉ２、ＣａＳｉ２、ＣｒＳｉ２、Ｃｕ５
Ｓｉ、ＦｅＳｉ２、ＭｎＳｉ２、ＮｂＳｉ２、ＴａＳｉ２、ＶＳｉ２、ＷＳｉ２、ＺｎＳｉ２、ＳｉＣ、Ｓｉ３
Ｎ４、Ｓｉ２ Ｎ２ Ｏ、ＳｉＯａ（０＜ａ≦２）、ＳｎＯｂ （０＜ｂ≦２）、ＳｎＳｉＯ３、ＬｉＳｉＯあるいはＬｉＳｎＯなどのケイ素またはスズの化合物、及びケイ素またはスズの単体；ＴｉＳ２、ＬｉＴｉＳ２などの金属化合物；Ｎｂ２Ｏ、ＦｅＯ、Ｆｅ２Ｏ、Ｆｅ３Ｏ４、ＣｏＯ、Ｃｏ２Ｏ３、Ｃｏ３Ｏ４などの金属酸化物；ＡｘＭｙＮｚＯ２（但
し、ＡはＬｉ、ＰおよびＢから選択された少なくとも一種、ＭはＣｏ、ＮｉおよびＭｎから選択された少なくとも一種、ＮはＡｌおよびＳｎから選択された少なくとも一種、Ｏは酸素原子を表わし、ｘ、ｙ、ｚは、それぞれ１．１０≧ｘ≧０．０５、４．００≧ｙ≧０．８５、２．００≧ｚ≧０の範囲の数である）で表わされる複合金属酸化物またはその他の金属酸化物；などが例示される。
In order to prepare a negative electrode thin film using a (co) polymer of a water-soluble monomer mainly composed of itaconic acid of the present invention, a process of kneading a negative electrode active material, a binder and a solvent to prepare a slurry, A process of applying and drying the obtained slurry on the current collector is required. Specific examples of the negative electrode active material used at this time include carbonaceous materials such as hard carbon, carbon fluoride, graphite, natural graphite, mesophase carbon microbeads (MCMB), polyacrylonitrile (PAN), and pitch-based carbon fibers; polyacene, etc. Conductive polymer: Lithium nitride compound such as Li 3 N; Lithium metal such as lithium metal and lithium alloy; 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
Silicon or tin compounds such as N 4 , Si 2 N 2 O, SiO a (0 <a ≦ 2), SnO b (0 <b ≦ 2), SnSiO 3, LiSiO or LiSnO, and a simple substance of silicon or tin; Metal compounds such as TiS 2 and LiTiS 2 ; Metal oxides such as Nb 2 O, FeO, Fe 2 O, Fe 3 O 4 , CoO, Co 2 O 3 , and Co 3 O 4 ; AxMyNzO 2 (where A is Li , P and B, at least one selected from Co, Ni and Mn, N at least one selected from Al and Sn, O represents an oxygen atom, x, y and z are 1.10 ≧ x ≧ 0.05, 4.00 ≧ y ≧ 0.85, and 2.00 ≧ z ≧ 0, respectively. Product; and the like are exemplified.
電極作製時に使用する溶媒は、常圧での沸点が８０℃以上であるものが好ましく、より好ましくは１００℃以上である。沸点が低過ぎると、本発明のスラリーを電極製造に用いるときに集電体への塗布が困難なことがあり、また、スラリーを集電体に塗布した後の乾燥工程でポリマー粒子が移動して電極表面に集中する現象が発生し、電極の強度が低下する、あるいは結着力が低下するなどの問題が生じやすい。ただし、電極作製時の乾燥工程では、集電体を劣化させない条件以下に溶媒分子を除去する必要があることから、沸点は３００℃以下であることが好ましい。溶媒の具体例としては、水、もしくはメチルエチルケトン、メチルイソブチルケトン、シクロペンタノン、シクロヘキサノン、シクロヘプタノン等のケトン類；ジメチルホルムアミド、Ｎ−メチル−２−ピロリドンなどの鎖状または環状のアミド類；ブチルアルコール、アミルアルコール、ヘキシルアルコール等のアルコール類；乳酸メチル、乳酸エチル、乳酸ブチル、酢酸ブチル、安息香酸メチル等のエステル類；等、各種の極性液状物質が挙げられる。取り扱いの容易さ、安全性等を考慮し、特に水が好ましい。 The solvent used at the time of electrode preparation is preferably a solvent having a boiling point of 80 ° C. or higher at normal pressure, more preferably 100 ° C. or higher. If the boiling point is too low, the slurry of the present invention may be difficult to apply to the current collector when used for electrode production, and the polymer particles may move during the drying process after the slurry is applied to the current collector. As a result, a phenomenon of concentration on the electrode surface occurs, and problems such as a decrease in the strength of the electrode or a decrease in the binding force tend to occur. However, the boiling point is preferably 300 ° C. or lower because it is necessary to remove solvent molecules under conditions that do not deteriorate the current collector in the drying step during electrode preparation. Specific examples of the solvent include water or ketones such as methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, cyclohexanone, and cycloheptanone; linear or cyclic amides such as dimethylformamide and N-methyl-2-pyrrolidone; Various polar liquid substances such as alcohols such as butyl alcohol, amyl alcohol, and hexyl alcohol; esters such as methyl lactate, ethyl lactate, butyl lactate, butyl acetate, and methyl benzoate; Considering ease of handling, safety, etc., water is particularly preferable.
集電体は、ある程度の強度があり、導電率が高い材料により構成されていることが好ましく、例えば、銅（Ｃｕ）、ステンレス、ニッケル、チタン（Ｔｉ）、タングステン（Ｗ）、モリブデン（Ｍｏ）およびアルミニウムからなる群のうちの少なくとも１種を含むことが好ましい。特に好ましくは銅である。形状も特に制限されないが、通常、厚さ０．００１〜０．５ｍｍ程度のシート状のものである。 The current collector is preferably made of a material having a certain degree of strength and high conductivity. For example, copper (Cu), stainless steel, nickel, titanium (Ti), tungsten (W), molybdenum (Mo) And at least one selected from the group consisting of aluminum. Particularly preferred is copper. Although the shape is not particularly limited, it is usually a sheet having a thickness of about 0.001 to 0.5 mm.
スラリーの集電体への塗布方法は特に制限されない。例えば、ドクターブレード法、ディップ法、リバースロール法、ダイレクトロール法、グラビア法、エクストルージョン法、浸漬方、ハケ塗りなどによって塗布される。塗布する量も特に制限されないが、溶媒を乾燥等の方法によって除去した後に形成される活物質層の厚さが０．００５〜５ｍｍ、好ましくは０．０１〜２ｍｍになる量が一般的である。乾燥方法も特に制限されず、例えば温風、熱風、低湿風による乾燥、真空乾燥、（遠）赤外線や電子線などの照射による乾燥が挙げられる。乾燥条件は、応力集中によって活物質層に亀裂が入る、あるいは活物質層が集電体から剥離する問題が生じない程度の速度範囲の中で、できるだけ早く溶媒が除去できるように調整する。更に、乾燥後の集電体をプレスすることにより負極活物質の密度を高めてもよい。プレス方法は、金型プレスやロールプレスなどの方法が挙げられる。 The method for applying the slurry to the current collector is not particularly limited. For example, it is applied by a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a dipping method, a brush coating, or the like. The amount to be applied is not particularly limited, but the amount of the active material layer formed after removing the solvent by a method such as drying is generally 0.005 to 5 mm, preferably 0.01 to 2 mm. . The drying method is not particularly limited, and examples thereof include drying with warm air, hot air, low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays or electron beams. The drying conditions are adjusted so that the solvent can be removed as quickly as possible within a speed range that does not cause a problem that the active material layer cracks due to stress concentration or the active material layer peels from the current collector. Further, the density of the negative electrode active material may be increased by pressing the dried current collector. Examples of the pressing method include a mold press and a roll press.
（実施例）
以下、合成例によって本発明をさらに詳しく説明するが、本発明はその要旨を超えない限り、以下の実施例に制約されるものではない。
(Example)
EXAMPLES Hereinafter, although this invention is demonstrated in more detail by a synthesis example, this invention is not restrict | limited to a following example, unless the summary is exceeded.
（合成例1）
攪拌機、還流冷却管、単量体滴下口、および窒素導入管を備えた４つ口５００ｍｌセパラブルフラスコに脱イオン２５％水酸化ナトリウム水溶液５０．００ｇ、イタコン酸５０．０ｇを加え、均一な混合溶液とした。攪窒素導入管より窒素を導入し、恒温水槽により６０℃に内部温度を調整した。窒素導入３０分後、２％過硫酸アンモニウム水溶液１．００ｇと２％亜硫酸ナトリウム水溶液１．００ｇを添加し重合を開始させた。反応開始５時間後再度２％過硫酸アンモニウム水溶液１．００ｇと２％亜硫酸ナトリウム水溶液１．００ｇを添加し、さらに１７時間重合を継続し反応を終了した。得られた反応溶液に過剰量のメタノールを加え、生成した白色固体をろ過により採取した。これを重合体１とする。こ重合体１を乾燥後、０．０５％水溶液を作成し、ＧＰＣ-ＭＡＬＳにて分子量測定を行ったところ、重量平均分子量５千を示した。
(Synthesis Example 1)
Add 50.00 g of deionized 25% sodium hydroxide aqueous solution and 50.0 g of itaconic acid to a 4-neck 500 ml separable flask equipped with a stirrer, reflux condenser, monomer dropping port, and nitrogen inlet tube, and mix evenly. It was set as the solution. Nitrogen was introduced from the stirred nitrogen introducing tube, and the internal temperature was adjusted to 60 ° C. by a constant temperature water bath. 30 minutes after the introduction of nitrogen, 1.00 g of a 2% aqueous ammonium persulfate solution and 1.00 g of a 2% aqueous sodium sulfite solution were added to initiate polymerization. Five hours after the start of the reaction, 1.00 g of a 2% aqueous ammonium persulfate solution and 1.00 g of a 2% aqueous sodium sulfite solution were added again, and polymerization was continued for 17 hours to complete the reaction. An excess amount of methanol was added to the resulting reaction solution, and the resulting white solid was collected by filtration. This is designated as Polymer 1. The polymer 1 was dried, a 0.05% aqueous solution was prepared, and molecular weight measurement was performed with GPC-MALS. The weight average molecular weight was 5,000.
（合成例２）
攪拌機、還流冷却管、単量体滴下口、および窒素導入管を備えた４つ口５００ｍｌセパラブルフラスコに脱イオン２５％水酸化ナトリウム水溶液５０．００ｇ、イタコン酸４７．０ｇを加え、均一な混合溶液とした後、５０％アクリルアミド溶液６ｇを加え、さらに攪拌した。攪窒素導入管より窒素を導入し、恒温水槽により６０℃に内部温度を調整した。窒素導入３０分後、２％２、２’−アゾビス（２−メチルプロピオンアミジン）二塩化水素化物１．００ｇを添加し重合を開始させた。反応開始５時間後再度％２、２’−アゾビス（２−メチルプロピオンアミジン）二塩化水素化物１．００ｇを添加し、さらに１７時間重合を継続し反応を終了した。得られた反応溶液に過剰量のメタノールを加え、生成した白色固体をろ過により採取した。この固体を重合体２とする。重合体２を乾燥後、０．０５％水溶液を作成し、ＧＰＣ-ＭＡＬＳにて分子量測定を行ったところ、重量平均分子量１０万を示した。
(Synthesis Example 2)
Add 40.00 g of deionized 25% aqueous sodium hydroxide and 47.0 g of itaconic acid to a 4-neck 500 ml separable flask equipped with a stirrer, reflux condenser, monomer dropping port, and nitrogen inlet tube, and mix uniformly. After preparing the solution, 6 g of 50% acrylamide solution was added and further stirred. Nitrogen was introduced from the stirred nitrogen introducing tube, and the internal temperature was adjusted to 60 ° C. with a constant temperature water bath. After 30 minutes from the introduction of nitrogen, 1.00 g of 2% 2,2′-azobis (2-methylpropionamidine) dichloride was added to initiate polymerization. 5 hours after the start of the reaction, 1.00 g of% 2,2′-azobis (2-methylpropionamidine) dihydrochloride was added again, and the polymerization was continued for another 17 hours to complete the reaction. An excessive amount of methanol was added to the obtained reaction solution, and the produced white solid was collected by filtration. This solid is designated as Polymer 2. After drying the polymer 2, a 0.05% aqueous solution was prepared, and molecular weight measurement was performed with GPC-MALS. The weight average molecular weight was 100,000.
実施例及び比較例中の評価条件は以下の通りである。
（１）スラリーの混合性
バインダーと負極活物質に溶媒を添加したとき、均一に混合できたものをＡ、少し不均一な部分があったものをＢ、ほぼ不均一になったものをＣと評価した。
（２）スラリーの保存安定性
作製した負極電極用スラリー状態のまま密封して室温下で３日間保存し、スラリーの状態に変化がみられなかったものをＡ、一部変化がみられたものをＢ、大部分が変化したものをＣと評価した。
（３）スラリーの集電体への塗布性
作製した負極電極用スラリーを、ドクターブレードを用いて厚さ２００μｍになるように銅箔上に塗布した。このとき、均一に塗布できたものをＡ、均一に塗布するのに数回の操作が必要だったものをＢ、均一に塗布できなかったものをＣと評価した。
（４）乾燥後の負極電極の表面状態
作製した負極電極用スラリーを、ドクターブレードを用いて厚さ２００μｍになるように銅箔上に塗布し、溶媒に水を使用したものは８０℃、溶媒にＮ−メチル−２−ビロリドンを使用したものは１２０℃で1時間乾燥させた。乾燥後の負極電極表面が、均一であるものをＡ、一部不均一な部分があるものをＢ、大部分が不均一となったものをＣと評価した。
（５）折り曲げ試験
長さ８０ｍｍ、幅２０ｍｍの負極電極片を２０枚作製し、負極電極片の活物質層を外側にして、直径１５ｍｍのガラス棒を芯にして電極面が接するまで折り曲げた。その後、同じ折り曲げ部分を、負極電極片が内側になるようにして同様に折り曲げた。この操作を３回繰り返した後に、活物質層にヒビが生じたもの、もしくは活物質が集電体から剥離したものの負極電極片の枚数を数えた。ヒビや剥離した枚数が一枚もないものをＡ、５枚以下のものをＢ、それ以外のものをＣと評価した。
（６）負極活物質と集電体の結着性試験
作製した負極電極の表面にセロハンテープを一定の大きさで貼り付け、一定の速度で剥がしたときに、銅箔から剥がれた負極活物質の様子を観察した。銅箔上に結着している負極活物質がほとんど剥がれなかったものをＡ、部分的に剥がれてしまったものをＢ、銅箔部分からほとんど剥がれてしまったものをＣと評価した。
The evaluation conditions in the examples and comparative examples are as follows.
(1) When a solvent is added to the slurry binder and the negative electrode active material, A can be uniformly mixed, B can be a little uneven, and C can be a little uneven. evaluated.
(2) Storage stability of slurry Sealed in the state of the prepared negative electrode slurry and stored at room temperature for 3 days. A when the state of the slurry was not changed and A was partially changed. Was evaluated as B, and most changed as C.
(3) Applyability of slurry to current collector The prepared slurry for negative electrode was applied on a copper foil using a doctor blade so as to have a thickness of 200 μm. At this time, A was evaluated for uniform application, B was evaluated for several operations for uniform application, and C was evaluated for non-uniform application.
(4) The surface state of the negative electrode after drying The negative electrode slurry prepared was applied on a copper foil to a thickness of 200 μm using a doctor blade, and water was used as the solvent at 80 ° C. Those using N-methyl-2-pyrrolidone were dried at 120 ° C. for 1 hour. A negative electrode surface after drying was evaluated as A, a portion having a partially non-uniform portion as B, and a portion having a non-uniform portion as a non-uniform portion as C.
(5) Bending test Twenty negative electrode pieces with a length of 80 mm and a width of 20 mm were produced, and the active material layer of the negative electrode piece was placed outside, and a glass rod with a diameter of 15 mm was used as a core until the electrode surface was in contact. Thereafter, the same bent portion was bent in the same manner with the negative electrode piece on the inside. After repeating this operation three times, the number of negative electrode pieces of the active material layer cracked or the active material peeled from the current collector was counted. The case where there was no crack or peeled sheet was evaluated as A, 5 or less was evaluated as B, and the others were evaluated as C.
(6) Binding test of negative electrode active material and current collector The negative electrode active material peeled off from the copper foil when cellophane tape was affixed to the surface of the prepared negative electrode in a certain size and peeled at a constant speed The state of was observed. The negative electrode active material bound on the copper foil was evaluated as “A” when the negative electrode active material was hardly peeled off, “B” when it was partially peeled off, and “C” when the material was almost peeled off from the copper foil portion.
上記重合体１をバインダーとして５重量部、天然黒鉛(ＬＦ−１８Ａ)を負極活物質として９５重量部の割合で混合し、更に水を加えてスラリー中の全固形分が２５％になるまで水を加えて十分攪拌し、負極電極用スラリーを得た。得られたスラリーを銅箔上にドクターブレード法によって均一に塗布し、８０℃に調整した乾燥機で１時間乾燥した。さらに真空乾燥機にて１００℃減圧乾燥をした後、ロールプレスによって圧縮し、活物質層の厚さ１００μｍの負極電極を得た。各種評価結果を表１に示す。 5 parts by weight of the polymer 1 as a binder and 95 parts by weight of natural graphite (LF-18A) as a negative electrode active material are added, and water is added until the total solid content in the slurry is 25%. Was added and sufficiently stirred to obtain a slurry for negative electrode. The obtained slurry was uniformly coated on a copper foil by a doctor blade method, and dried for 1 hour with a drier adjusted to 80 ° C. Furthermore, after drying at 100 ° C. under reduced pressure with a vacuum dryer, the film was compressed by a roll press to obtain a negative electrode having an active material layer thickness of 100 μm. Various evaluation results are shown in Table 1.
上記重合体２をバインダーとして５重量部、天然黒鉛(ＬＦ−１８Ａ)を負極活物質として９５重量部の割合で混合し、更に水を加えてスラリー中の全固形分が２５％になるまで水を加えて十分攪拌し、負極電極用スラリーを得た。得られたスラリーを銅箔上にドクターブレード法によって均一に塗布し、８０℃に調整した乾燥機で１時間乾燥した。さらに真空乾燥機にて１００℃減圧乾燥をした後、ロールプレスによって圧縮し、活物質層の厚さ１００μｍの負極電極を得た。各種評価結果を表１に示す。 5 parts by weight of the above polymer 2 as a binder and 95 parts by weight of natural graphite (LF-18A) as a negative electrode active material are added, and water is added until the total solid content in the slurry becomes 25%. Was added and sufficiently stirred to obtain a slurry for negative electrode. The obtained slurry was uniformly coated on a copper foil by a doctor blade method, and dried for 1 hour with a drier adjusted to 80 ° C. Furthermore, after drying at 100 ° C. under reduced pressure with a vacuum dryer, the film was compressed by a roll press to obtain a negative electrode having an active material layer thickness of 100 μm. Various evaluation results are shown in Table 1.
（比較例１）
バインダーとしてＰＶＤＦ（ＫＦ−１１００）を５重量部、天然黒鉛(ＬＦ−１８Ａ)を９５重量部の割合で混合し、更に水を加えてスラリー中の全固形分が３０％になるまでＮ−メチル−２−ピロリドン（ＮＭＰ）を加えて十分攪拌し、負極電極用スラリーを得た。得られたスラリーを銅箔上にドクターブレード法によって均一に塗布し、１２０℃に調整した乾燥機で１時間乾燥した。さらに真空乾燥機にて１５０℃減圧乾燥をした後、ロールプレスによって圧縮し、活物質層の厚さ１００μｍの負極電極を得た。各種評価結果を表１に示す。
(Comparative Example 1)
As a binder, 5 parts by weight of PVDF (KF-1100) and 95 parts by weight of natural graphite (LF-18A) are mixed, and water is further added until the total solid content in the slurry becomes 30%. 2-Pyrrolidone (NMP) was added and stirred sufficiently to obtain a slurry for negative electrode. The obtained slurry was uniformly coated on a copper foil by a doctor blade method, and dried for 1 hour with a drier adjusted to 120 ° C. Furthermore, after drying under reduced pressure at 150 ° C. with a vacuum dryer, the resultant was compressed by a roll press to obtain a negative electrode having an active material layer thickness of 100 μm. Various evaluation results are shown in Table 1.
（比較例２）
バインダーとしてポリアクリル酸（和光純薬工業製、重量平均分子量１，０００，０００）を使用した以外は比較例２と同様にして負極電極を得た。各種評価結果を表１に示す。
(Comparative Example 2)
A negative electrode was obtained in the same manner as in Comparative Example 2 except that polyacrylic acid (manufactured by Wako Pure Chemical Industries, Ltd., weight average molecular weight 1,000,000) was used as a binder. Various evaluation results are shown in Table 1.
（表１）
(Table 1)
これらの結果から、イタコン酸を必須として含有する水溶性単量体（混合物）を（共）重合させることで得られるリチウムイオン二次電池負極用バインダー（合成例１・２）は、負極薄膜作成時に負極活物質をスラリー中に均一に分散させ、負極活物質と集電体とを強く結着させることが分かった。その結着性はポリアクリル酸をバインダーとして用いた場合よりも高く、得られる負極薄膜は、可撓性も優れていることがわかった。 From these results, a binder for a lithium ion secondary battery negative electrode (Synthesis Examples 1 and 2) obtained by (co) polymerizing a water-soluble monomer (mixture) containing itaconic acid as an essential component was prepared as a negative electrode thin film. It has been found that sometimes the negative electrode active material is uniformly dispersed in the slurry, and the negative electrode active material and the current collector are strongly bound. The binding property was higher than when polyacrylic acid was used as a binder, and the obtained negative electrode thin film was found to be excellent in flexibility.
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| CN103733289A (en) * | 2011-06-24 | 2014-04-16 | 三菱丽阳株式会社 | Binder for electrode of electrochemical element, composition for electrode of electrochemical element, electrode of electrochemical element, and electrochemical element |
| JPWO2012176895A1 (en) * | 2011-06-24 | 2015-02-23 | 三菱レイヨン株式会社 | Electrode element electrode binder, electrochemical element electrode composition, electrochemical element electrode and electrochemical element |
| EP2725644A4 (en) * | 2011-06-24 | 2015-05-27 | Mitsubishi Rayon Co | Binder for electrode of electrochemical element, composition for electrode of electrochemical element, electrode of electrochemical element, and electrochemical element |
| WO2013018887A1 (en) * | 2011-08-03 | 2013-02-07 | 日本ゼオン株式会社 | Conductive adhesive composition for electrochemical element electrode, collector with adhesive layer, and electrochemical element electrode |
| JPWO2013018887A1 (en) * | 2011-08-03 | 2015-03-05 | 日本ゼオン株式会社 | Conductive adhesive composition for electrochemical element electrode, current collector with adhesive layer, and electrochemical element electrode |
| US10014528B2 (en) | 2011-08-03 | 2018-07-03 | Zeon Corporation | Conductive adhesive composition for electrochemical element electrode, collector with adhesive layer, and electrochemical element electrode |
| JP2013065493A (en) * | 2011-09-20 | 2013-04-11 | Toyota Industries Corp | Binder for negative electrode of lithium ion secondary battery, and lithium ion secondary battery using binder for negative electrode |
| JP2013065494A (en) * | 2011-09-20 | 2013-04-11 | Toyota Industries Corp | Binder for negative electrode of lithium ion secondary battery, manufacturing method of the same, and lithium ion secondary battery using binder for negative electrode |
| CN103351448A (en) * | 2013-06-28 | 2013-10-16 | 中国科学院青岛生物能源与过程研究所 | High-temperature resistance lithium ion secondary battery adhesive and preparation method thereof |
| JP2020123590A (en) * | 2014-06-04 | 2020-08-13 | 日本ゼオン株式会社 | Binder composition for lithium-ion secondary battery electrode, slurry composition for lithium-ion secondary battery electrode, lithium-ion secondary battery electrode and lithium-ion secondary battery |
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