JP2017188203A - Method of evaluating stability of positive electrode material slurry for lithium ion secondary battery - Google Patents
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本発明は、スラリー粘度の経時変化により正極材スラリーの安定性を評価するリチウムイオン二次電池用正極材スラリーの安定性評価方法に関する。 The present invention relates to a stability evaluation method for a positive electrode material slurry for a lithium ion secondary battery, wherein the stability of the positive electrode material slurry is evaluated based on a change in slurry viscosity with time.
リチウムイオン二次電池は高いエネルギー密度を持つため、近年小型化や軽量化を要求される携帯電話やノートパソコンのような携帯電子機器に広く利用されている。また自動車用途ではクリーンなエネルギー源として開発が盛んであり、小型、軽量、高容量、高出力などの高性能化や低コスト化が求められている。 Since lithium ion secondary batteries have high energy density, they are widely used in portable electronic devices such as mobile phones and notebook computers that are required to be smaller and lighter in recent years. Moreover, development as a clean energy source is actively performed for automobile applications, and high performance and low cost such as small size, light weight, high capacity, and high output are required.
これらリチウムイオン二次電池に用いられる正極は、主に直径数μｍから数十μｍを持つコバルト酸リチウムなどのリチウム含有遷移金属酸化物と、電子伝導性を向上させるための直径数ｎｍ〜数百ｎｍでストラクチャー構造を持つカーボンブラックなどの導電助材と、それらを集電体に所望の厚みで固着させるためのポリフッ化ビニリデン（以下ＰＶＤＦともいう）などのバインダーの三つで構成される。これらの材料は一般的には粉体のまま使用されることはなく、Ｎ−メチル−２−ピロリドン（ＮＭＰ）などの有機溶媒で適正な粘度にスラリー化して扱われる。上記正極を構成する材料に有機溶媒を加えて混練して作製された正極材スラリーは、ダイコーターやロールコーターなどの精密塗工装置を用いて厚さ数十μｍのアルミニウム集電体上に精密に塗工され、その後、乾燥、圧縮、裁断工程を経て正極となる。 The positive electrode used in these lithium ion secondary batteries is mainly composed of a lithium-containing transition metal oxide such as lithium cobaltate having a diameter of several μm to several tens of μm, and a diameter of several nm to several hundreds for improving electron conductivity. It is composed of three conductive assistants such as carbon black having a structure structure at nm and a binder such as polyvinylidene fluoride (hereinafter also referred to as PVDF) for fixing them to a current collector with a desired thickness. These materials are generally not used as powders, and are handled by being slurried to an appropriate viscosity with an organic solvent such as N-methyl-2-pyrrolidone (NMP). The positive electrode material slurry produced by adding an organic solvent to the material constituting the positive electrode and kneading is precisely applied to an aluminum current collector with a thickness of several tens of μm using a precision coating device such as a die coater or a roll coater. After that, it becomes a positive electrode through drying, compression, and cutting processes.
現在、市場の多くを占めるリチウムイオン二次電池用正極活物質にはコバルト酸リチウムが主として用いられており、その容量は約１５０ｍＡｈ／ｇである。その中で、２００ｍＡｈ／ｇと高い容量が得られるリチウムニッケル系正極材料は、ハイブリッド車および電気自動車用電池の正極材料として開発が進んでいる。 Currently, lithium cobaltate is mainly used as a positive electrode active material for lithium ion secondary batteries, which occupies most of the market, and its capacity is about 150 mAh / g. Among them, a lithium nickel-based positive electrode material capable of obtaining a high capacity of 200 mAh / g has been developed as a positive electrode material for hybrid vehicles and electric vehicle batteries.
リチウムニッケル系正極材料は、容量の面では非常に魅力的な材料であるが、リチウムコバルト系正極材料と比べ吸水率が高くアルカリ性も高い（当該正極材料を浸漬した水のｐＨは約１１〜１２となる）。このような正極材料を一般的にバインダーとして用いられているポリフッ化ビニリデン（ＰＶＤＦ）と混練して正極を製造しようとした場合、急激な粘度上昇やゲル化（スラリーの非流動化）といった問題が起こる。この現象は正極活物質のアルカリとの反応でＰＶＤＦ内のＨＦが脱離することでＣ−Ｈ結合が切れ、Ｃ=Ｃ結合が生成し、この二重結合から架橋反応が一気に進行して起こるものと報告されている。また、リチウムニッケルコバルトマンガン三元系正極材料においても高容量化を狙い、組成をニッケルリッチに振る検討も進められているが、容量が上がる一方で、アルカリ性も高くなり、リチウムニッケル系正極材料と同様にゲル化等、スラリー安定性の問題が起こっている。 The lithium nickel-based positive electrode material is a very attractive material in terms of capacity, but has a higher water absorption and higher alkalinity than the lithium cobalt-based positive electrode material (the pH of water in which the positive electrode material is immersed is about 11 to 12). Becomes). When such a positive electrode material is kneaded with polyvinylidene fluoride (PVDF), which is generally used as a binder, to produce a positive electrode, there are problems such as rapid viscosity increase and gelation (slurry non-fluidization). Occur. This phenomenon occurs when the HF in PVDF is desorbed by the reaction with the alkali of the positive electrode active material, the C—H bond is cut, and the C═C bond is generated, and the crosslinking reaction proceeds at once from this double bond. It has been reported. In addition, lithium nickel cobalt manganese ternary positive electrode materials are also being studied for nickel-rich composition with the aim of increasing the capacity. However, while the capacity increases, the alkalinity also increases, Similarly, slurry stability problems such as gelation are occurring.
従って、リチウムニッケル系正極材料開発を迅速に進めるためには、通常の電池性能の評価だけでなくスラリー安定性評価も非常に重要な要素となる。 Therefore, in order to rapidly develop a lithium nickel-based positive electrode material, not only evaluation of normal battery performance but also evaluation of slurry stability is a very important factor.
従来から、リチウムイオン二次電池用正極材スラリー安定性評価は、粘度の経時変化をモニタリングする方法や、目視によるゲル化（スラリーの非流動化）の有無により評価されている。この粘度上昇や、ゲル化の主要因は先述の正極活物質中のアルカリによるものであることから、スラリーの安定性評価はそれらの性質の強弱と相関する評価が得られることが好ましい。しかし、正極活物質は吸水率が高く、また、溶媒として用いられているＮ−メチル−２−ピロリドンの吸水率は無限大であり、水分が存在する環境下では、それらが吸水し、水分によって正極活物質内部よりアルカリが抽出されゲル化が加速する。また、さらにスラリー中の水分率が高くなった場合には、アルカリがなくともＰＶＤＦが析出し、スラリーの非流動化が起こる。これらのことから従来の水分管理されていない環境で、正極活物質部材に水分が付着した状態での評価では、再現性の高い評価ができなかった。 Conventionally, the positive electrode material slurry stability evaluation for a lithium ion secondary battery has been evaluated by a method of monitoring a change in viscosity over time or by the presence or absence of visual gelation (non-fluidization of the slurry). Since the main cause of this increase in viscosity and gelation is due to the alkali in the positive electrode active material described above, it is preferable that the evaluation of the stability of the slurry is an evaluation that correlates with the strength of the properties. However, the positive electrode active material has a high water absorption rate, and the water absorption rate of N-methyl-2-pyrrolidone used as a solvent is infinite. In an environment where moisture exists, they absorb water, The alkali is extracted from the inside of the positive electrode active material and gelation is accelerated. In addition, when the moisture content in the slurry is further increased, PVDF is deposited even if there is no alkali, and the slurry becomes non-fluidized. From these facts, evaluation with high reproducibility could not be performed in the conventional environment where moisture management is not performed and when the moisture was attached to the positive electrode active material member.
例えば、特許文献１には、電池用正極シートの製造方法において、正極材ペーストの混練時、送液時、保管時の温度を低温度に保持し、雰囲気を低湿度雰囲気にすることが記載されている。 For example, Patent Document 1 describes that in a method for producing a positive electrode sheet for a battery, the temperature at the time of kneading, feeding, and storing positive electrode material paste is maintained at a low temperature, and the atmosphere is set to a low humidity atmosphere. ing.
また、他の評価方法として、正極活物質を水に浸漬させｐＨを測定する方法があるが、水分により正極活物質内部よりアルカリが抽出されることから、有機溶媒中でスラリーを製造する際に問題となるＰＶＤＦと接する正極活物質表面のアルカリ度との相関を得るのは難しかった。 In addition, as another evaluation method, there is a method of measuring the pH by immersing the positive electrode active material in water, but since alkali is extracted from the inside of the positive electrode active material by moisture, when producing a slurry in an organic solvent It was difficult to obtain a correlation with the alkalinity of the surface of the positive electrode active material in contact with the PVDF in question.
上述した通り、リチウムイオン二次電池用正極スラリーの安定性評価を再現性良く安定的に行うためには水分の制御は重要であり付着する水分は少ない程良い。しかしながら、水分を極少に抑えて評価を行うと、アルカリとの反応性（感度ともいう）が小さくなりすぎるため、評価サンプルのゲル化が発生せず、スラリー安定性評価ができないという問題が生じていた。 As described above, in order to perform stability evaluation of the positive electrode slurry for a lithium ion secondary battery stably with good reproducibility, control of moisture is important, and less moisture is better. However, when the evaluation is performed with a minimum amount of moisture, the reactivity with alkali (also referred to as sensitivity) becomes too small, and the gelation of the evaluation sample does not occur, and there is a problem that the slurry stability cannot be evaluated. It was.
特許文献１には、低湿度雰囲気で電池用正極シートを製造することは記載されているが、具体的な条件や、水分を極少に抑えた時に生じるアルカリへの感度の低下に対する対応については記載されていない。 Patent Document 1 describes that a positive electrode sheet for a battery is produced in a low-humidity atmosphere. However, specific conditions and a response to a decrease in sensitivity to alkali that occurs when moisture is minimized are described. It has not been.
本発明は、このような実情に鑑みて提案されたものであり、水分の影響を極少に抑えると共に、正極活物質表面のアルカリに対する感度を向上させ、再現性良く安定的な評価を行うことができるリチウムイオン二次電池用正極材料のスラリー安定性評価方法を提供する。 The present invention has been proposed in view of such circumstances, and can suppress the influence of moisture to the minimum, improve the sensitivity of the positive electrode active material surface to alkali, and perform stable evaluation with good reproducibility. Provided is a method for evaluating the slurry stability of a positive electrode material for a lithium ion secondary battery.
本発明者等は、上記課題の解決方法について詳細に検討した結果、リチウムイオン二次電池用正極材料のスラリー安定性評価を再現性良く安定的に行うには、水分の影響を極少に抑える方法として、正極材スラリーの製造と粘度測定を露点−３０℃以下に管理した環境下で行うことが有効であり、また、正極活物質表面のアルカリに対する感度を向上させるには、正極材スラリーの作製に用いるバインダーとして、官能基付きポリフッ化ビニリデンを用いることが有効である、との知見を得て、本発明の完成に至った。 As a result of examining the solution of the above problem in detail, the present inventors have conducted a method for minimizing the influence of moisture in order to stably evaluate the slurry stability of the positive electrode material for a lithium ion secondary battery with good reproducibility. In order to improve the sensitivity to the alkali on the surface of the positive electrode active material, it is effective to carry out the production of the positive electrode material slurry and the viscosity measurement in an environment in which the dew point is controlled to -30 ° C. or less. As a binder used in the above, the knowledge that it is effective to use a functionalized polyvinylidene fluoride was obtained, and the present invention was completed.
すなわち、本発明の一態様は、スラリー粘度の経時変化により正極材スラリーの安定性を評価するリチウムイオン二次電池用正極材スラリーの安定性評価方法であって、正極活物質と導電助材とバインダーを混練し、有機溶媒に分散させて正極材スラリーとするスラリー製造工程と、スラリー製造工程で得られた正極材スラリーのスラリー粘度の経時変化を測定することで評価を行う粘度測定工程を有し、正極材スラリー製造工程と粘度測定工程を露点−３０℃以下に管理した環境下で行い、バインダーに官能基付きポリフッ化ビニリデンを用いることを特徴とする。 That is, one aspect of the present invention is a method for evaluating the stability of a positive electrode material slurry for a lithium ion secondary battery, which evaluates the stability of the positive electrode material slurry by a change in slurry viscosity with time, and includes a positive electrode active material, a conductive additive, A slurry production process in which a binder is kneaded and dispersed in an organic solvent to form a positive electrode material slurry, and a viscosity measurement process in which evaluation is performed by measuring a change in slurry viscosity with time of the positive electrode material slurry obtained in the slurry production process. In addition, the positive electrode material slurry manufacturing step and the viscosity measuring step are performed in an environment where the dew point is controlled to -30 ° C. or lower, and the functionalized polyvinylidene fluoride is used as the binder.
本発明の一態様によれば、正極材スラリー製造工程と粘度測定工程を露点−３０℃以下に管理した環境下で行うことで、水分の影響を極少に抑えると共に、バインダーに官能基付きポリフッ化ビニリデンを用いることで正極活物質表面のアルカリに対する感度を向上させることができる。 According to one aspect of the present invention, by performing the positive electrode material slurry manufacturing step and the viscosity measurement step in an environment in which the dew point is controlled to -30 ° C. or less, the influence of moisture is minimized, and the functional group is added to the polyfluorinated binder. By using vinylidene, the sensitivity to the alkali on the surface of the positive electrode active material can be improved.
このとき、本発明の一態様では、正極活物質は、１２０℃で３時間以上真空減圧乾燥されたものであるとしてもよい。 At this time, in one embodiment of the present invention, the positive electrode active material may be vacuum-dried at 120 ° C. for 3 hours or more.
正極活物質を真空減圧乾燥しておくことで、正極活物質に含まれる水分を除去することができる。 Moisture contained in the positive electrode active material can be removed by drying the positive electrode active material under vacuum under reduced pressure.
また、このとき、導電助材は、１２０℃で３時間以上真空減圧乾燥したカーボンブラックであるとしてもよい。 At this time, the conductive additive may be carbon black that has been vacuum-dried at 120 ° C. for 3 hours or more.
導電助材についても、同様に、真空減圧乾燥することで予め水分を除去しておくことが好ましい。 Similarly, it is preferable to remove moisture in advance by conducting vacuum drying under reduced pressure.
また、本発明の一態様では、有機溶媒は、水分含量が３０ｐｐｍ以下のＮ−メチル−２−ピロリドンであってもよい。 In one embodiment of the present invention, the organic solvent may be N-methyl-2-pyrrolidone having a water content of 30 ppm or less.
有機溶媒についても、水分含量が少ないものを用いることが好ましい。 It is preferable to use an organic solvent having a low water content.
本発明の一実施形態によれば、水分の影響を極少に抑えると共に、正極活物質表面のアルカリに対する感度を向上させ、再現性良く安定的な評価を行うことができるリチウムイオン二次電池用正極材料のスラリー安定性評価方法を提供することができる。 According to one embodiment of the present invention, a positive electrode for a lithium ion secondary battery that can suppress the influence of moisture to a minimum, improve sensitivity to alkali on the surface of the positive electrode active material, and perform stable evaluation with high reproducibility. A method for evaluating the slurry stability of a material can be provided.
以下、本発明の実施の形態について、図面を参照しながら下記順序にて詳細に説明する。なお、以下に説明する本実施形態は、特許請求の範囲に記載された本発明の内容を不当に限定するものではなく、本実施形態で説明される構成の全てが本発明の解決手段として必須であるとは限らない。
１．リチウムイオン二次電池用正極材料のスラリー安定性評価方法
１−１．スラリー製造工程
１−２．粘度測定工程
Hereinafter, embodiments of the present invention will be described in detail in the following order with reference to the drawings. The present embodiment described below does not unduly limit the contents of the present invention described in the claims, and all the configurations described in the present embodiment are essential as means for solving the present invention. Not necessarily.
1. 1. Slurry stability evaluation method of positive electrode material for lithium ion secondary battery 1-1. Slurry manufacturing process 1-2. Viscosity measurement process
＜１．リチウムイオン二次電池用正極材料のスラリー安定性評価方法＞
図１に、本発明の一実施の形態に係るリチウムイオン二次電池用正極材料のスラリー安定性評価方法のプロセスの概略を示す。
<1. Method for evaluating slurry stability of positive electrode material for lithium ion secondary battery>
In FIG. 1, the outline of the process of the slurry stability evaluation method of the positive electrode material for lithium ion secondary batteries which concerns on one embodiment of this invention is shown.
本発明の一実施形態は、スラリー粘度の経時変化により正極材スラリーの安定性を評価するリチウムイオン二次電池用正極材スラリーの安定性評価方法であって、正極活物質と導電助材とバインダーを混練し、有機溶媒に分散させて正極材スラリーとするスラリー製造工程Ｓ１と、スラリー製造工程で得られた正極材スラリーのスラリー粘度の経時変化を測定することで評価を行う粘度測定工程Ｓ２を有し、正極材スラリー製造工程と粘度測定工程を露点−３０℃以下に管理した環境下で行い、バインダーに官能基付きポリフッ化ビニリデンを用いることを特徴とする。 One embodiment of the present invention is a method for evaluating the stability of a positive electrode material slurry for a lithium ion secondary battery by evaluating the stability of the positive electrode material slurry by a change in slurry viscosity with time, comprising a positive electrode active material, a conductive additive, and a binder And a viscosity measurement step S2 in which the slurry viscosity is measured by measuring a change in slurry viscosity with time of the positive electrode material slurry obtained in the slurry production step. It is characterized in that it is carried out in an environment in which the positive electrode material slurry production step and the viscosity measurement step are controlled at a dew point of −30 ° C. or less, and the functionalized polyvinylidene fluoride is used as the binder.
このように、正極材スラリー製造工程と粘度測定工程を露点−３０℃以下に管理した環境下で行うことで、水分の影響を極少に抑えると共に、バインダーに官能基付きポリフッ化ビニリデンを用いることで正極活物質表面のアルカリに対する感度を向上させ、再現性良く安定的な正極材スラリーの安定性評価を行うことができる。 Thus, by performing the positive electrode material slurry manufacturing step and the viscosity measurement step in an environment where the dew point is controlled to -30 ° C. or less, the influence of moisture is suppressed to a minimum, and the functionalized polyvinylidene fluoride is used as the binder. The sensitivity to the alkali on the surface of the positive electrode active material can be improved, and the stability of the positive electrode material slurry can be evaluated with good reproducibility.
以下、各工程を順にそれぞれ説明する。 Hereafter, each process is demonstrated in order, respectively.
（１−１．スラリー製造工程）
スラリー製造工程Ｓ１では、正極活物質と導電助材とバインダーを混練し、有機溶媒に分散させて正極材スラリーとする。
(1-1. Slurry manufacturing process)
In the slurry manufacturing step S1, a positive electrode active material, a conductive additive, and a binder are kneaded and dispersed in an organic solvent to obtain a positive electrode material slurry.
本発明で製造するリチウムイオン二次電池用正極材スラリーは、その基本的構成は、従来公知の電池と同様であり、正極活物質、導電助材、バインダーから構成される。それらの混合比については、最終製品である電池の混合比に合わせた混合比とすることができる。 The basic composition of the positive electrode slurry for a lithium ion secondary battery produced in the present invention is the same as that of a conventionally known battery, and is composed of a positive electrode active material, a conductive additive, and a binder. About those mixing ratios, it can be set as the mixing ratio matched with the mixing ratio of the battery which is a final product.
正極活物質は、リチウム含有遷移金属酸化物を用いることができる。例として、コバルト酸リチウム、マンガン酸リチウム、ニッケル酸リチウム、リン酸鉄リチウム、リチウム遷移金属複合酸化物（コバルト、ニッケル及びマンガンからなる群から選ばれる２種類以上を含むリチウム酸化物）などが挙げられる。これらのリチウム含有遷移金属酸化物から選択した正極活物質について、正極材スラリーの安定性評価を行う。 As the positive electrode active material, a lithium-containing transition metal oxide can be used. Examples include lithium cobaltate, lithium manganate, lithium nickelate, lithium iron phosphate, lithium transition metal composite oxide (lithium oxide containing two or more selected from the group consisting of cobalt, nickel, and manganese). It is done. For the positive electrode active material selected from these lithium-containing transition metal oxides, the stability of the positive electrode material slurry is evaluated.
導電助材は、アセチレンブラック、気相法炭素繊維（昭和電工（株）製ＶＧＣＦ（登録商標））、ケッチェンブランク等の炭素系のナノ粒子又はナノファイバーの他、人造黒鉛や、天然黒鉛を用いることができ、これらの導電助材を単独、あるいはこれらを組み合わせて用いることができる。 Conductive aids include carbon-based nanoparticles or nanofibers such as acetylene black, vapor grown carbon fiber (VGCF (registered trademark) manufactured by Showa Denko KK), Ketjen Blank, artificial graphite, and natural graphite. These conductive additives can be used alone or in combination.
バインダーには、ＰＶＤＦ分子に官能基を付加したＰＶＤＦ系バインダーを用いることが必要である。官能基の種類は特に限定はされないが、アルカリのアタックによりＰＶＤＦ内からＨＦが脱離するか、水が生成するか、又は酸素の付加反応により架橋が進むものであることが好ましい。 As the binder, it is necessary to use a PVDF binder in which a functional group is added to the PVDF molecule. The type of the functional group is not particularly limited, but it is preferable that HF is eliminated from the PVDF due to alkali attack, water is generated, or crosslinking proceeds by an oxygen addition reaction.
正極材スラリーの安定性評価を再現性良く安定的に行うためには水分の制御は重要であり付着する水分は少ない程良いが、水分を極少に抑えると、通常用いられる官能基の無いＰＤＶＦではアルカリと反応しなくなり、アルカリへの感度が小さくなりすぎるという問題が生じていた。本発明では、この問題を解決するために、通常は負極用のバインダーとして用いられ、アルカリに対する感度の高い官能基付きポリフッ化ビニリデン（ＰＶＤＦ）を正極材スラリーのバインダーとして適用する。これにより、水分の影響を極少に抑えた状態でも、正極活物質表面のアルカリに対する感度を向上させ、再現性良く安定的な評価を行うことができる。 In order to perform stability evaluation of the positive electrode material slurry stably with good reproducibility, it is important to control the moisture, and it is better that the amount of moisture adhering is small. There was a problem in that it no longer reacts with alkali and the sensitivity to alkali becomes too small. In the present invention, in order to solve this problem, it is usually used as a binder for a negative electrode, and a functionalized polyvinylidene fluoride (PVDF) having high sensitivity to alkali is applied as a binder for a positive electrode material slurry. Thereby, even in the state where the influence of moisture is suppressed to a minimum, the sensitivity to the alkali on the surface of the positive electrode active material can be improved, and stable evaluation can be performed with good reproducibility.
正極活物質と導電助材の付着水分は除去しておくことが好ましく、乾燥条件としては１２０〜２４０℃で３時間以上の真空減圧乾燥することが好ましい。 It is preferable to remove the moisture adhering to the positive electrode active material and the conductive additive, and it is preferable to dry under vacuum under reduced pressure at 120 to 240 ° C. for 3 hours or more.
有機溶媒は、脱水グレード（例えば、水分含量３０ｐｐｍ以下）、あるいは電池グレード（例えば、水分含量１００ｐｐｍ以下）のＮ−メチル−２−ピロリドンなど水分率の低いものを用いることが好ましいが、特に脱水グレードを用いることがより好ましい。 As the organic solvent, it is preferable to use a dehydrated grade (for example, moisture content of 30 ppm or less) or a battery grade (for example, moisture content of 100 ppm or less) N-methyl-2-pyrrolidone having a low moisture content. It is more preferable to use
スラリー製造工程Ｓ１では、これらの正極活物質、導電助材、及び、バインダーを混練し、有機溶媒中に分散させる。スラリー製造工程Ｓ１では、これらの作業を露点−３０℃以上の環境で行うことで、水分の混入を極少に抑える。 In the slurry production step S1, these positive electrode active material, conductive additive and binder are kneaded and dispersed in an organic solvent. In the slurry production step S1, these operations are performed in an environment having a dew point of −30 ° C. or higher, thereby minimizing moisture contamination.
正極材スラリーの作製には、プラネタリーミキサーや、二軸混練機、ホモジナイザー、自転公転ミキサーを用いることができるが、密閉容器で混練可能な自転公転ミキサーを用いることが好ましい。 In preparing the positive electrode material slurry, a planetary mixer, a twin-screw kneader, a homogenizer, and a rotation / revolution mixer can be used. It is preferable to use a rotation / revolution mixer that can be kneaded in a sealed container.
（１−２．粘度測定工程）
粘度測定工程Ｓ２では、スラリー製造工程Ｓ１で得られた正極材スラリーのスラリー粘度の経時変化を測定することで評価を行う。
(1-2. Viscosity measurement process)
In the viscosity measurement step S2, the evaluation is performed by measuring the change over time in the slurry viscosity of the positive electrode material slurry obtained in the slurry production step S1.
粘度測定は、露点−３０℃に管理されたドライルーム内で粘度計を用いて行い、正極材スラリーのスラリー粘度の経時変化を測定する。測定時以外の保管時においても、露点−３０℃に管理する。すなわち、粘度測定工程Ｓ２では、スラリー粘度測定環境及びスラリーの保管環境を露点−３０℃以下とする。 Viscosity is measured using a viscometer in a dry room controlled at a dew point of −30 ° C., and a change with time in the slurry viscosity of the positive electrode material slurry is measured. Even during storage other than during measurement, the dew point is controlled to -30 ° C. That is, in the viscosity measurement step S2, the slurry viscosity measurement environment and the slurry storage environment are set to a dew point of −30 ° C. or lower.
正極材スラリーの粘度は、１，０００〜８，０００ｃｐｓに調整することが好ましく、ゲル化の判断の容易さから２，０００〜３，０００ｃｐｓに調整することがさらに好ましい。正極材スラリーの粘度がスラリー作製時の粘度から上昇傾向を示すことでゲル化の判断ができる。粘度測定工程Ｓ２では、正極材スラリーの粘度がスラリー作製時の粘度からの変化率が２０〜３０％の範囲にあるかによりゲル化を判断し、ゲル化までの経過時間を見てスラリーの安定性評価を行うことができる。 The viscosity of the positive electrode material slurry is preferably adjusted to 1,000 to 8,000 cps, and more preferably adjusted to 2,000 to 3,000 cps from the ease of determination of gelation. The determination of gelation can be made when the viscosity of the positive electrode material slurry shows a rising tendency from the viscosity at the time of slurry preparation. In the viscosity measuring step S2, gelation is judged based on whether the viscosity of the positive electrode material slurry is within a range of 20 to 30% from the viscosity at the time of slurry preparation, and the stability of the slurry is determined by checking the elapsed time until gelation. Sexual evaluation can be performed.
以上説明したように、本発明の一実施形態に係るリチウムイオン二次電池用正極材料のスラリー安定性評価方法によれば、露点−３０℃に管理することで水分の影響を極少に抑えると共に、官能基付きポリフッ化ビニリデンを用いることで正極活物質表面のアルカリに対する感度を向上させ、再現性良く安定的な評価を行うことができるリチウムイオン二次電池用正極材料のスラリー安定性評価方法を提供することができる。 As described above, according to the slurry stability evaluation method for a positive electrode material for a lithium ion secondary battery according to an embodiment of the present invention, the influence of moisture is minimized by controlling the dew point to -30 ° C. Providing a slurry stability evaluation method for positive electrode materials for lithium ion secondary batteries that improves the sensitivity to alkali on the surface of the positive electrode active material by using polyvinylidene fluoride with a functional group and enables stable evaluation with high reproducibility. can do.
なお、本発明の一実施形態に係るリチウムイオン二次電池用正極材料のスラリー安定性評価方法で製造した、正極材スラリーは評価用のものではあるが、実際にリチウムイオン二次電池用正極材料として用いても良い。すなわち、上述した正極活物質と導電助材とバインダーを混練し、有機溶媒に分散させて正極材スラリーを製造し、シート法又は塗工法によりリチウムイオン二次電池用の正極を製造することもできる。 In addition, although the positive electrode material slurry manufactured with the slurry stability evaluation method of the positive electrode material for lithium ion secondary batteries according to one embodiment of the present invention is for evaluation, the positive electrode material for lithium ion secondary batteries is actually used. It may be used as That is, the above-described positive electrode active material, conductive additive and binder are kneaded and dispersed in an organic solvent to produce a positive electrode material slurry, and a positive electrode for a lithium ion secondary battery can be produced by a sheet method or a coating method. .
以下に、本発明の実施例及び比較例によって本発明をさらに詳細に説明するが、本発明は、これらの実施例によって何ら限定されるものではない。 EXAMPLES The present invention will be described in further detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.
（実施例１）
［正極活物質水分除去］
実施例１では、正極活物質としてニッケル酸リチウムを用いた。正極活物質は、真空乾燥機にて１２０℃で８時間真空減圧乾燥を行うことで水分を除去した。
Example 1
[Moisture removal of positive electrode active material]
In Example 1, lithium nickelate was used as the positive electrode active material. The positive electrode active material was subjected to vacuum reduced pressure drying at 120 ° C. for 8 hours with a vacuum dryer to remove moisture.
［導電助材水分除去］
導電助材は、カーボンブラック（デンカ工業製デンカブラック（登録商標）、型番ＨＳ１００）を用い、真空乾燥機にて１２０℃で８時間真空減圧乾燥を行った。
[Moisture removal for conductive material]
Carbon black (Denka Black (registered trademark), model number HS100, manufactured by Denka Kogyo Co., Ltd.) was used as the conductive additive, and vacuum drying was performed at 120 ° C. for 8 hours in a vacuum dryer.
［正極材スラリー作製］
正極材スラリー作製は、露点−３０℃以下に管理されたドライルーム内で、上述の水分除去した正極活物質と導電助材とバインダーが固体質量比９１：６：３になるように撹拌機（シンキー社製、あわとり練太郎（登録商標）（型番：ＡＲＥ−３１０））を用いて混練した。バインダーは、官能基付きＰＶＤＦ溶液（クレハ製、ＮＭＰ溶液タイプ型番＃Ｌ９３０５）を用いた。その後、脱水グレード（水分含量３０ｐｐｍ以下）のＮＭＰ（関東化学製）を適量添加し、同装置を用いて混練して所望の粘度の正極材スラリーを得た。
[Cathode slurry production]
The positive electrode material slurry was prepared in a dry room controlled at a dew point of −30 ° C. or lower by using a stirrer so that the above-mentioned positive electrode active material, conductive additive, and binder removed from water had a solid mass ratio of 91: 6: 3. It knead | mixed using the Shinkey Co., Ltd. product made from Awatori Nertaro (trademark) (model number: ARE-310). As the binder, a PVDF solution with a functional group (manufactured by Kureha, NMP solution type model number # L9305) was used. Thereafter, an appropriate amount of dehydrated grade (moisture content of 30 ppm or less) NMP (manufactured by Kanto Chemical Co., Inc.) was added and kneaded using the same device to obtain a positive electrode material slurry having a desired viscosity.
［粘度測定］
正極材スラリーの粘度測定は、露点−３０℃に管理されたドライルーム内で粘度計（ブルックフィールド社製、ＤＶ−II+ＰＲＯ）を用いてせん断速度１／５０ｓで、得られた正極材スラリーの粘度を測定した。初期粘度は２，０７１ｃｐｓであった。スラリーはポリプロピレン製密閉容器に入れ、露点−３０℃に管理されたドライルーム内で保管した。その後、継続的に粘度の測定を行った結果、２８時間経過後の粘度は４，７３９ｃｐｓであり、アルカリ性の高いリチウムニッケル系正極材料では、粘度が大きく上昇した。実施例１における正極材スラリーの粘度の継時変化を図２に示す。
[Viscosity measurement]
The positive electrode material slurry was measured at a shear rate of 1/50 s using a viscometer (manufactured by Brookfield, DV-II + PRO) in a dry room controlled at a dew point of −30 ° C. The viscosity of was measured. The initial viscosity was 2,071 cps. The slurry was placed in a polypropylene sealed container and stored in a dry room controlled at a dew point of −30 ° C. After that, as a result of continuously measuring the viscosity, the viscosity after 28 hours was 4,739 cps, and the viscosity of the lithium nickel-based positive electrode material having high alkalinity was greatly increased. FIG. 2 shows changes over time in the viscosity of the positive electrode material slurry in Example 1.
（実施例２）
［正極活物質水分除去］
実施例２では、正極活物質としてコバルト酸リチウムを用いた。正極活物質は、真空乾燥機にて１２０℃で８時間真空減圧乾燥を行うことで水分を除去した。
(Example 2)
[Moisture removal of positive electrode active material]
In Example 2, lithium cobalt oxide was used as the positive electrode active material. The positive electrode active material was subjected to vacuum reduced pressure drying at 120 ° C. for 8 hours with a vacuum dryer to remove moisture.
［導電助材水分除去］
導電助材は、カーボンブラック（デンカ工業製デンカブラック（登録商標）、型番ＨＳ１００）を用い、真空乾燥機にて１２０℃で８時間真空減圧乾燥を行った。
[Moisture removal for conductive material]
Carbon black (Denka Black (registered trademark), model number HS100, manufactured by Denka Kogyo Co., Ltd.) was used as the conductive additive, and vacuum drying was performed at 120 ° C. for 8 hours in a vacuum dryer.
［正極材スラリー作製］
正極材スラリー作製は実施例１と同条件とした。
[Cathode slurry production]
The positive electrode material slurry was prepared under the same conditions as in Example 1.
［粘度測定］
露点−３０℃に管理されたドライルーム内で粘度計（ブルックフィールド社製、ＤＶ−II+ＰＲＯ）を用いてせん断速度１／５０ｓで得られた正極スラリーの粘度を測定した。初期粘度は１,６５１ｃｐｓであった。スラリーはポリプロピレン製密閉容器に入れ、露点−３０℃に管理されたドライルーム内で保管した。その後、継続的に粘度の測定を行った結果、２８時間経過後の粘度は１，７０６ｃｐｓであり、リチウムコバルト系正極材料では粘度上昇は見られなかった。実施例２における正極材スラリーの粘度の継時変化を図２に示す。
[Viscosity measurement]
The viscosity of the positive electrode slurry obtained at a shear rate of 1/50 s was measured using a viscometer (manufactured by Brookfield, DV-II + PRO) in a dry room controlled at a dew point of −30 ° C. The initial viscosity was 1,651 cps. The slurry was placed in a polypropylene sealed container and stored in a dry room controlled at a dew point of −30 ° C. Thereafter, the viscosity was continuously measured. As a result, the viscosity after 28 hours was 1,706 cps, and no increase in viscosity was observed in the lithium cobalt-based positive electrode material. FIG. 2 shows changes in the viscosity of the positive electrode material slurry in Example 2 over time.
（実施例３）
［正極活物質水分除去］
実施例３では、正極活物質としてリチウム遷移金属複合酸化物（ニッケル：コバルト：マンガン比１：１：１）を用い、真空乾燥機にて１２０℃で８時間真空減圧乾燥を行った。
(Example 3)
[Moisture removal of positive electrode active material]
In Example 3, lithium transition metal composite oxide (nickel: cobalt: manganese ratio 1: 1: 1) was used as the positive electrode active material, and vacuum vacuum drying was performed at 120 ° C. for 8 hours in a vacuum dryer.
［導電助材水分除去］
導電助材は、カーボンブラック（デンカ工業製デンカブラック（登録商標）、型番ＨＳ１００）を用い、真空乾燥機にて１２０℃で８時間真空減圧乾燥を行った。
[Moisture removal for conductive material]
Carbon black (Denka Black (registered trademark), model number HS100, manufactured by Denka Kogyo Co., Ltd.) was used as the conductive additive, and vacuum drying was performed at 120 ° C. for 8 hours in a vacuum dryer.
［正極材スラリー作製］
正極材スラリー作製は実施例１と同条件とした。
[Cathode slurry production]
The positive electrode material slurry was prepared under the same conditions as in Example 1.
［粘度測定］
露点−３０℃に管理されたドライルーム内で粘度計（ブルックフィールド社製、ＤＶ−II+ＰＲＯ）を用いてせん断速度１/５０ｓで、得られた正極スラリーの粘度を測定した。初期粘度は１，５６３ｃｐｓであった。スラリーはポリプロピレン製密閉容器に入れ、露点−３０℃に管理されたドライルーム内で保管した。その後、継続的に粘度の測定を行った結果、２８時間経過後の粘度は２,８６５ｃｐｓであった。実施例３における正極材スラリーの粘度の継時変化を図２に示す。リチウム遷移金属複合酸化物（ニッケル：コバルト：マンガン比１：１：１）材料の粘度上昇は、実施例１のリチウムニッケル系正極材料と比べると小さいが、実施例２のリチウムコバルト系正極材料と比べると大きい結果となった。
[Viscosity measurement]
The viscosity of the resulting positive electrode slurry was measured at a shear rate of 1/50 s using a viscometer (Brookfield, DV-II + PRO) in a dry room controlled at a dew point of -30 ° C. The initial viscosity was 1,563 cps. The slurry was placed in a polypropylene sealed container and stored in a dry room controlled at a dew point of −30 ° C. Thereafter, the viscosity was continuously measured, and as a result, the viscosity after 28 hours was 2,865 cps. FIG. 2 shows changes over time in the viscosity of the positive electrode material slurry in Example 3. The increase in viscosity of the lithium transition metal composite oxide (nickel: cobalt: manganese ratio 1: 1: 1) material is small compared to the lithium nickel positive electrode material of Example 1, but the lithium cobalt based positive electrode material of Example 2 It was a big result when compared.
（実施例４）
［正極活物質水分除去］
実施例４では、正極活物質として、ニッケル比率の高いリチウム遷移金属複合酸化物（ニッケル：コバルト：マンガン比５：１：２）を用い、真空乾燥機にて１２０℃で８時間真空減圧乾燥を行った。
Example 4
[Moisture removal of positive electrode active material]
In Example 4, a lithium transition metal composite oxide having a high nickel ratio (nickel: cobalt: manganese ratio 5: 1: 2) was used as the positive electrode active material, and vacuum vacuum drying at 120 ° C. for 8 hours in a vacuum dryer. went.
［導電助材水分除去］
導電助材は、カーボンブラック（デンカ工業製デンカブラック（登録商標）、型番ＨＳ１００）を用い、真空乾燥機にて１２０℃で８時間真空減圧乾燥を行った。
[Moisture removal for conductive material]
Carbon black (Denka Black (registered trademark), model number HS100, manufactured by Denka Kogyo Co., Ltd.) was used as the conductive additive, and vacuum drying was performed at 120 ° C. for 8 hours in a vacuum dryer.
［正極材スラリー作製］
正極スラリー作製は実施例１と同条件とした。
[Cathode slurry production]
The positive electrode slurry was prepared under the same conditions as in Example 1.
［粘度測定］
露点−３０℃に管理されたドライルーム内で粘度計（ブルックフィールド社製、ＤＶ−II+ＰＲＯ）を用いてせん断速度１/５０ｓで、得られた正極スラリーの粘度を測定した。初期粘度は１,９１２ｃｐｓであった。スラリーはポリプロピレン製密閉容器に入れ、露点−３０℃に管理されたドライルーム内で保管した。その後、継続的に粘度の測定をおこなった結果、２８時間経過後の粘度は４，２７８ｃｐｓであった。実施例４における正極材スラリーの粘度の継時変化を図２に示す。ニッケル比率の高いリチウム遷移金属複合酸化物（ニッケル：コバルト：マンガン比５：１：２）では、リチウムニッケル系正極材料に次ぐ大きな粘度上昇が見られた。
[Viscosity measurement]
The viscosity of the resulting positive electrode slurry was measured at a shear rate of 1/50 s using a viscometer (Brookfield, DV-II + PRO) in a dry room controlled at a dew point of -30 ° C. The initial viscosity was 1,912 cps. The slurry was placed in a polypropylene sealed container and stored in a dry room controlled at a dew point of −30 ° C. Thereafter, the viscosity was continuously measured, and as a result, the viscosity after 28 hours was 4,278 cps. The change over time of the viscosity of the positive electrode material slurry in Example 4 is shown in FIG. In the lithium transition metal composite oxide having a high nickel ratio (nickel: cobalt: manganese ratio 5: 1: 2), a large increase in viscosity was observed after the lithium nickel positive electrode material.
以上より、水分を極小に抑えた環境下で正極材スラリーの安定性評価を行った実施例１〜４においては、アルカリ性の高いニッケルの比率が高いほど大きな粘度上昇が見られた。したがって、本発明の一実施の形態に係るリチウムイオン二次電池用正極材料のスラリー安定性評価方法を適用することで、正極活物質表面のアルカリ度と相関の取れた定量的な評価ができていることが分かる。 From the above, in Examples 1 to 4 in which the stability evaluation of the positive electrode material slurry was performed in an environment in which moisture was suppressed to a minimum, a larger increase in viscosity was observed as the ratio of nickel having high alkalinity was higher. Therefore, by applying the slurry stability evaluation method for the positive electrode material for a lithium ion secondary battery according to an embodiment of the present invention, a quantitative evaluation correlated with the alkalinity of the positive electrode active material surface can be performed. I understand that.
（比較例１）
［正極活物質水分除去］
比較例１では、正極活物質として実施例４と同じリチウム複合酸化物（ニッケル：コバルト：マンガン比５：１：２）を用い、真空乾燥機にて１２０℃で８時間真空減圧乾燥を行った。
(Comparative Example 1)
[Moisture removal of positive electrode active material]
In Comparative Example 1, the same lithium composite oxide as in Example 4 (nickel: cobalt: manganese ratio 5: 1: 2) was used as the positive electrode active material, and vacuum vacuum drying was performed at 120 ° C. for 8 hours in a vacuum dryer. .
［導電助材水分除去］
導電助材は、カーボンブラック（デンカ工業製デンカブラック（登録商標）、型番ＨＳ１００）を用い、真空乾燥機にて１２０℃で８時間真空減圧乾燥を行った。
[Moisture removal for conductive material]
Carbon black (Denka Black (registered trademark), model number HS100, manufactured by Denka Kogyo Co., Ltd.) was used as the conductive additive, and vacuum drying was performed at 120 ° C. for 8 hours in a vacuum dryer.
［正極材スラリー作製］
正極スラリー作製は露点−３０℃以下に管理されたドライルーム内で、上述の水分除去した正極活物質と導電助材とバインダーが固体質量比９１：６：３になるように撹拌機（シンキー社製、あわとり練太郎（登録商標）（型番：ＡＲＥ−３１０））を用いて混練した。バインダーとして官能基の無いＰＶＤＦ溶液（クレハ製、ＮＭＰ溶液タイプ型番＃Ｌ７２０８）を用いた。その後、脱水グレード（水分含量３０ｐｐｍ以下）のＮＭＰ（関東化学製）を適量添加し、同装置を用いて混練して所望の粘度の正極スラリーを得た。
[Cathode slurry production]
The positive electrode slurry was prepared in a dry room controlled at a dew point of −30 ° C. or lower, and the agitator (Sinky Corp.) was used so that the positive electrode active material, the conductive additive and the binder were removed at a solid mass ratio of 91: 6: 3. Kneaded using Awatori Nertaro (registered trademark) (model number: ARE-310). A PVDF solution having no functional group (manufactured by Kureha, NMP solution type model number # L7208) was used as a binder. Thereafter, an appropriate amount of dehydrated grade (water content 30 ppm or less) NMP (manufactured by Kanto Chemical Co., Inc.) was added and kneaded using the same device to obtain a positive electrode slurry having a desired viscosity.
［粘度測定］
露点−３０℃に管理されたドライルーム内で粘度計（ブルックフィールド社製、ＤＶ−II+ＰＲＯ）を用いてせん断速度１/５０ｓで得られた正極スラリーの粘度を測定した。初期粘度は２，３０２ｃｐｓであった。スラリーはポリプロピレン製密閉容器に入れ露点−３０℃に管理されたドライルーム内で保管した。その後、継続的に粘度の測定をおこなった結果、４８時間経過後の粘度は初期粘度と変わらない２，１０３ｃｐｓであった。比較例１における正極材スラリーの粘度の継時変化を図３に示す。実施例１ではリチウム複合酸化物（ニッケル：コバルト：マンガン比５：１：２）にて粘度上昇が見られたが、−３０℃環境で官能基の無い一般的なＰＶＤＦを用いて作製、保管したスラリーの粘度上昇は見られず、正極活物質表面のアルカリ度と相関の取れる定量的な評価とはならなかった。
[Viscosity measurement]
The viscosity of the positive electrode slurry obtained at a shear rate of 1/50 s was measured using a viscometer (manufactured by Brookfield, DV-II + PRO) in a dry room controlled at a dew point of −30 ° C. The initial viscosity was 2,302 cps. The slurry was put in a polypropylene sealed container and stored in a dry room controlled at a dew point of -30 ° C. Thereafter, the viscosity was continuously measured, and as a result, the viscosity after 48 hours was 2,103 cps which was the same as the initial viscosity. The change over time of the viscosity of the positive electrode material slurry in Comparative Example 1 is shown in FIG. In Example 1, an increase in viscosity was observed in the lithium composite oxide (nickel: cobalt: manganese ratio 5: 1: 2), but it was prepared and stored using general PVDF having no functional group in a -30 ° C environment. As a result, no increase in viscosity of the slurry was observed, and the quantitative evaluation could not be correlated with the alkalinity of the surface of the positive electrode active material.
（比較例２）
［正極活物質水分除去］
比較例２では、正極活物質として実施例２と同じコバルト酸リチウムを用い、真空乾燥機にて１２０℃で８時間真空減圧乾燥を行った。
(Comparative Example 2)
[Moisture removal of positive electrode active material]
In Comparative Example 2, the same lithium cobalt oxide as in Example 2 was used as the positive electrode active material, and vacuum vacuum drying was performed at 120 ° C. for 8 hours in a vacuum dryer.
［導電助材水分除去］
導電助材は、カーボンブラック（デンカ工業製デンカブラック（登録商標）、型番ＨＳ１００）を用い、真空乾燥機にて１２０℃で８時間真空減圧乾燥を行った。
[Moisture removal for conductive material]
Carbon black (Denka Black (registered trademark), model number HS100, manufactured by Denka Kogyo Co., Ltd.) was used as the conductive additive, and vacuum drying was performed at 120 ° C. for 8 hours in a vacuum dryer.
［正極材スラリー作製］
正極スラリー作製は実施例１と同条件とした。
[Cathode slurry production]
The positive electrode slurry was prepared under the same conditions as in Example 1.
［粘度測定］
露点−３０℃に管理されたドライルーム内で粘度計（ブルックフィールド社製、ＤＶ−II+ＰＲＯ）を用いてせん断速度１/５０ｓで得られたスラリーの粘度を測定した。その際、初期粘度は２，１８３ｃｐｓであった。スラリーは湿度４０〜５０％に制御された環境下でポリプロピレン製容器に蓋をしない状態で保管し、継続的に粘度の測定を行った結果、２６時間後には粘度が６，２３４ｃｐｓまで粘上昇し、その後、２７時間経過後にはスラリーのゲル化が起こった。比較２における正極材スラリーの粘度の継時変化を図４に示す。湿度４０〜５０％でスラリーを保管した場合には、ゲル化が起こりにくいコバルト系材料であってもゲル化が発生してしまい、正極活物質表面のアルカリ度と相関の取れる定量的な評価とはならなかった。
[Viscosity measurement]
The viscosity of the slurry obtained at a shear rate of 1/50 s was measured using a viscometer (manufactured by Brookfield, DV-II + PRO) in a dry room controlled at a dew point of −30 ° C. At that time, the initial viscosity was 2,183 cps. The slurry was stored in a condition where the humidity was controlled at 40-50% without covering the polypropylene container, and the viscosity was continuously measured. As a result, the viscosity increased to 6,234 cps after 26 hours. Thereafter, gelation of the slurry occurred after 27 hours. FIG. 4 shows changes in the viscosity of the positive electrode material slurry in comparison 2 over time. When the slurry is stored at a humidity of 40 to 50%, even if it is a cobalt-based material that hardly undergoes gelation, gelation occurs, and quantitative evaluation that can be correlated with the alkalinity of the surface of the positive electrode active material I didn't.
Claims (4)
正極活物質と導電助材とバインダーを混練し、有機溶媒に分散させて正極材スラリーとするスラリー製造工程と、
前記スラリー製造工程で得られた前記正極材スラリーのスラリー粘度の経時変化を測定することで評価を行う粘度測定工程を有し、
前記正極材スラリー製造工程と前記粘度測定工程を露点−３０℃以下に管理した環境下で行い、前記バインダーに官能基付きポリフッ化ビニリデンを用いることを特徴とするリチウムイオン二次電池用正極材スラリーの安定性評価方法。 A method for evaluating the stability of a positive electrode material slurry for a lithium ion secondary battery, wherein the stability of the positive electrode material slurry is evaluated by a change in slurry viscosity with time,
A slurry manufacturing process in which a positive electrode active material, a conductive additive and a binder are kneaded and dispersed in an organic solvent to form a positive electrode material slurry;
Having a viscosity measurement step of performing evaluation by measuring a change in slurry viscosity with time of the positive electrode material slurry obtained in the slurry production step;
A positive electrode material slurry for a lithium ion secondary battery, wherein the positive electrode material slurry production step and the viscosity measurement step are performed in an environment where the dew point is controlled to -30 ° C. or less, and a functionalized polyvinylidene fluoride is used as the binder. Stability evaluation method.
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