JP5386802B2 - Graphite powder and method for producing the same - Google Patents

Graphite powder and method for producing the same Download PDF

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JP5386802B2
JP5386802B2 JP2007196427A JP2007196427A JP5386802B2 JP 5386802 B2 JP5386802 B2 JP 5386802B2 JP 2007196427 A JP2007196427 A JP 2007196427A JP 2007196427 A JP2007196427 A JP 2007196427A JP 5386802 B2 JP5386802 B2 JP 5386802B2
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graphite powder
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soluble polymer
graphite
carbon precursor
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浩司 山本
徹 藤原
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Chuo Denki Kogyo Co Ltd
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Description

本発明は、リチウムイオン二次電池などの非水系二次電池の負極材料として好適な黒鉛質粉末とその製造方法とに関する。   The present invention relates to a graphite powder suitable as a negative electrode material for a non-aqueous secondary battery such as a lithium ion secondary battery and a method for producing the same.

負極に炭素、正極にリチウム遷移金属酸化物、電解質にリチウム塩を溶解させた非水溶媒を使用した非水系二次電池であるリチウムイオン二次電池は、パソコン、携帯電話などの電子機器の電源として広く利用され、電気自動車への搭載の研究も進んでいる。   Lithium ion secondary batteries, which are nonaqueous secondary batteries that use nonaqueous solvents in which carbon is used for the negative electrode, lithium transition metal oxides are used for the positive electrode, and lithium salts are dissolved in the electrolyte, are power supplies for electronic devices such as personal computers and mobile phones. As a result, research on mounting on electric vehicles is also progressing.

リチウムイオン二次電池は、負極材料である炭素材料によって電池性能が左右されるため、高容量の負極を構成できる安価な炭素材料が求められている。また、自動車に搭載されるような大型電池向けには、信頼性の高い、すなわち電解液との反応性が低い炭素材料が求められている。   Since lithium ion secondary batteries have battery performance that depends on the carbon material that is the negative electrode material, an inexpensive carbon material that can form a high-capacity negative electrode is required. In addition, a carbon material that is highly reliable, that is, has low reactivity with an electrolyte, is required for a large battery that is mounted on an automobile.

現在のリチウムイオン二次電池では、電池電圧が高くなる黒鉛系の炭素粉末（黒鉛質粉末）が負極材料として一般に使用されている。高容量化のためには黒鉛化度の高い黒鉛粉末を使用することが有利であり、特に天然黒鉛の粉末は黒鉛化度が非常に高く、安価であるので、高容量で安価な負極材料となりうる。   In current lithium ion secondary batteries, graphite-based carbon powder (graphite powder) that increases battery voltage is generally used as a negative electrode material. In order to increase the capacity, it is advantageous to use graphite powder with a high degree of graphitization. In particular, natural graphite powder has a very high degree of graphitization and is inexpensive. sell.

しかし、負極炭素材料の黒鉛化度が高いと、電解液との反応性が高くなり、不可逆容量が増加する。そのため、正極に余分に正極活物質を詰め込まなければならず、体積が規定されている電池の容量が低下する。また、電解液との反応性が強く関与する電池の保存特性やサイクル特性といった電池の信頼性も低下する。そのため、高価であっても、電解液との反応性が比較的低い人造黒鉛がリチウムイオン二次電池の負極材料として主に使用されてきた。   However, when the degree of graphitization of the negative electrode carbon material is high, the reactivity with the electrolytic solution increases, and the irreversible capacity increases. For this reason, an extra positive electrode active material must be packed in the positive electrode, and the capacity of the battery whose volume is regulated is reduced. In addition, the reliability of the battery, such as the storage characteristics and cycle characteristics of the battery in which the reactivity with the electrolyte is strongly involved, also decreases. Therefore, artificial graphite, which is expensive but relatively low in reactivity with the electrolyte, has been mainly used as a negative electrode material for lithium ion secondary batteries.

黒鉛粉末の電解液との反応性を抑制するため、水溶性高分子材料で黒鉛粉末の表面を被覆することが提案されている。下記特許文献１には、黒鉛粉末の表面をカルボキシメチルセルロースなど水溶性高分子で被覆して、不可逆容量を低減させることが記載されている。下記特許文献２には、黒鉛粉末をカルボキシメチルセルロースなど水溶性高分子で被覆して、不可逆容量を低減させ、長期保存特性を改善することが記載されている。   In order to suppress the reactivity of the graphite powder with the electrolytic solution, it has been proposed to coat the surface of the graphite powder with a water-soluble polymer material. Patent Document 1 below describes that the surface of graphite powder is coated with a water-soluble polymer such as carboxymethyl cellulose to reduce the irreversible capacity. Patent Document 2 below describes that graphite powder is coated with a water-soluble polymer such as carboxymethyl cellulose to reduce irreversible capacity and improve long-term storage characteristics.

しかし、黒鉛粉末を水溶性高分子材料で単に被覆するだけでは、改善は不十分であった。また、被覆により黒鉛粉末と電解液との界面での電荷移動が阻害されるため、過電圧が大きくなり、レート特性が低下するという問題もあった。さらに、水系のバインダーを用いて電極を作製した場合、バインダー自体も黒鉛を被覆するため、黒鉛粉末を被覆する高分子の合計量が多くなりすぎ、放電容量が低下するという問題もあった。
特開２００１−１６７７５５号公報 ＷＯ９９／０１９０４パンフレット However, the improvement was insufficient by simply coating the graphite powder with a water-soluble polymer material. In addition, the charge transfer at the interface between the graphite powder and the electrolytic solution is hindered by the coating, so that there is a problem in that the overvoltage is increased and the rate characteristics are lowered. Further, when producing an electrode by using an aqueous binder, for the binder itself coated graphite, too many total amount of the high molecular you coat the graphite powder, the discharge capacity was also lowered.
JP 2001-167755 A WO99 / 01904 pamphlet

本発明の目的は、安価でありながら、高容量かつ不可逆容量が小さく、電解液との反応性が小さな非水系二次電池用負極材料となる黒鉛質粉末とその製造方法とを提供することである。   An object of the present invention is to provide a graphite powder as a negative electrode material for a non-aqueous secondary battery, which is inexpensive, has a high capacity, a small irreversible capacity, and a low reactivity with an electrolytic solution, and a method for producing the same. is there.

一般に二次電池において、不可逆容量の低減は、電池容量の向上ばかりでなく、保存特性やサイクル特性など電池の信頼性の向上にも寄与する。
非水系二次電池の負極材料として使用される黒鉛粉末の場合、不可逆容量は主に表面で電解液が分解することにより生じる。従って、黒鉛粉末を不活性な材料で被覆することは効果がある。 In general, in secondary batteries, reduction of irreversible capacity contributes not only to improvement of battery capacity but also to improvement of battery reliability such as storage characteristics and cycle characteristics.
In the case of graphite powder used as a negative electrode material for non-aqueous secondary batteries, the irreversible capacity is generated mainly by the decomposition of the electrolyte solution on the surface. Therefore, it is effective to coat the graphite powder with an inert material.

上記特許文献１、２に提案されているように、水溶性高分子材料で黒鉛粉末を被覆すると、非水系二次電池の不可逆容量が低減できることを確認したが、不可逆容量を低減させるには被覆量を増大させる必要があり、そうなると放電容量やレート特性が悪化するため、十分なものではなかった。ところが、被覆後に熱処理することによって、水溶性高分子材料を熱分解させて炭素前駆体に変換させると、被覆量が少量でも不可逆容量の低減効果が著しく高まり、かつ被覆量を増大させても放電容量の低下が起こらないことが判明した。さらに、この熱処理による炭素前駆体への変換によって、水溶性高分子材料をそのまま被覆した場合に問題となる、過電圧の増加によるレート特性の低下を抑制できることも見出された。   As proposed in Patent Documents 1 and 2 above, it has been confirmed that irreversible capacity of a non-aqueous secondary battery can be reduced by coating graphite powder with a water-soluble polymer material. It is necessary to increase the amount, and the discharge capacity and rate characteristics are deteriorated. However, when the water-soluble polymer material is thermally decomposed and converted to a carbon precursor by heat treatment after coating, the effect of reducing the irreversible capacity is remarkably enhanced even if the coating amount is small, and even if the coating amount is increased, the discharge is performed. It was found that the capacity did not decrease. Furthermore, it has been found that the conversion to the carbon precursor by this heat treatment can suppress a decrease in rate characteristics due to an increase in overvoltage, which becomes a problem when the water-soluble polymer material is coated as it is.

その理由は明らかではないが、以下のメカニズムが推測される。
・熱分解により被覆層内に適度な隙間ができ、被覆層内でのリチウムイオンの移動がスムーズになる。 The reason is not clear, but the following mechanism is presumed.
-An appropriate gap is formed in the coating layer by thermal decomposition, and lithium ions move smoothly in the coating layer.

・水溶性高分子材料はリチウムを捕捉する酸素や水素といった元素を多量に有するが、熱処理によりこれらの元素が著しく低減し、不可逆容量が低減する。
ここに、本発明は、炭素前駆体を担持した黒鉛粉末からなり、平均粒径が３０μｍ以下であることを特徴とする黒鉛質粉末である。 The water-soluble polymer material has a large amount of elements such as oxygen and hydrogen that trap lithium, but these elements are remarkably reduced by heat treatment, and the irreversible capacity is reduced.
Here, the present invention is a graphite powder comprising a graphite powder supporting a carbon precursor and having an average particle size of 30 μm or less.

本発明の好適態様を列挙すれば次の通りである：
・炭素前駆体が水溶性高分子材料の熱分解生成物である；
・黒鉛粉末が天然黒鉛である；
・水溶性高分子材料がカルボキシメチルセルロースの塩である。 The preferred embodiments of the present invention are listed as follows:
The carbon precursor is a thermal decomposition product of a water-soluble polymer material;
The graphite powder is natural graphite;
The water-soluble polymer material is a carboxymethyl cellulose salt.

本発明において「炭素前駆体」とは、完全炭素化（実質的に炭素のみからなる）より前の段階にある炭素化中間体を意味する。すなわち、水溶性高分子材料といった有機化合物を熱処理して炭素化する場合、熱処理によってその有機化合物の熱分解が起こり、水素などの炭素以外の元素の少なくとも一部は失われたが、完全な炭素化（実質的に炭素からなる物質への変換）は起こっていない状態のものを意味する。組成的には、炭素前駆体は、炭素以外に、原料に含まれていた異種元素（水素、酸素、窒素など）の一部をなお含んでいる。   In the present invention, the “carbon precursor” means a carbonized intermediate in a stage prior to complete carbonization (substantially consisting only of carbon). That is, when an organic compound such as a water-soluble polymer material is carbonized by heat treatment, the organic compound is thermally decomposed by the heat treatment, and at least a part of the elements other than carbon such as hydrogen is lost. Chemical conversion (conversion to a substance consisting essentially of carbon) means that it has not occurred. In terms of composition, the carbon precursor still contains a part of different elements (hydrogen, oxygen, nitrogen, etc.) contained in the raw material in addition to carbon.

本発明はまた、黒鉛粉末の表面に水溶性高分子材料を付着させる工程と、付着した水溶性高分子材料の熱分解温度以上の温度で非酸化性雰囲気中にて黒鉛粉末を熱処理する工程とを有することを特徴とする、上記黒鉛質粉末の製造方法も提供する。この方法において、付着工程は、水溶性高分子材料の水溶液中に黒鉛粉末を分散させたスラリーを噴霧乾燥することにより行うことができる。   The present invention also includes a step of attaching a water-soluble polymer material to the surface of the graphite powder, and a step of heat-treating the graphite powder in a non-oxidizing atmosphere at a temperature equal to or higher than the thermal decomposition temperature of the attached water-soluble polymer material. There is also provided a method for producing the above graphite powder, characterized by comprising: In this method, the attaching step can be performed by spray drying a slurry in which graphite powder is dispersed in an aqueous solution of a water-soluble polymer material.

本発明はさらに、上記黒鉛質粉末を用いて作製されたことを特徴とする非水系二次電池用負極、ならびにこの負極を備えた非水系二次電池もまた提供する。   The present invention further provides a negative electrode for a non-aqueous secondary battery produced using the above graphite powder, and a non-aqueous secondary battery provided with the negative electrode.

本発明に係る黒鉛質粉末は、天然黒鉛から製造できるため、安価で高容量を示すにもかかわらず、天然黒鉛の欠点であった電解液との反応性が抑えられ、不可逆容量が著しく低減され、レート特性も良好であるので、保存特性やサイクル特性など電池の信頼性向上が期待できる。   Since the graphite powder according to the present invention can be produced from natural graphite, the reactivity with the electrolytic solution, which was a disadvantage of natural graphite, is suppressed, and the irreversible capacity is remarkably reduced despite the fact that it is inexpensive and exhibits high capacity. Since the rate characteristics are also good, it can be expected to improve the reliability of the battery such as storage characteristics and cycle characteristics.

以下、本発明の好適態様について、より具体的に説明する。
本発明に係る黒鉛質粉末は、基材の黒鉛粉末に炭素前駆体を担持させたものからなる。基材の黒鉛粉末は、天然黒鉛、人造黒鉛、キッシュ黒鉛のいずれでもよく、これらの２種以上の混合物を使用することもできる。価格面からは安価な天然黒鉛を使用することが好ましい。 Hereinafter, preferred embodiments of the present invention will be described more specifically.
The graphite powder according to the present invention comprises a base material graphite powder supporting a carbon precursor. The graphite powder of the substrate may be any of natural graphite, artificial graphite, and quiche graphite, and a mixture of two or more of these may be used. In view of price, it is preferable to use cheap natural graphite.

天然黒鉛は、人造黒鉛より安価であるにもかかわらず、黒鉛化度が非常に高いため、電解液との反応性が高く、電解液分解に伴う不可逆容量が大きくなる、あるいは保存特性や安全性などの電池性能が損なわれる、という問題があり、リチウムイオン二次電池の負極材料としてはあまり使用されてこなかった。しかし、本発明では、炭素前駆体を黒鉛粉末に担持することにより、電解液との反応性が抑えられ、不可逆容量が著しく低減するので、より安価な天然黒鉛粉末も十分に使用できる。それにより、電極の製造コストを低減することが可能となる。   Although natural graphite is cheaper than artificial graphite, it has a very high degree of graphitization, so it is highly reactive with electrolytes, increases the irreversible capacity associated with electrolyte decomposition, or has storage characteristics and safety. However, it has not been used as a negative electrode material for lithium ion secondary batteries. However, in the present invention, by supporting the carbon precursor on the graphite powder, the reactivity with the electrolytic solution is suppressed and the irreversible capacity is remarkably reduced, so that cheaper natural graphite powder can be sufficiently used. Thereby, the manufacturing cost of the electrode can be reduced.

基材の黒鉛粉末は、平均粒径が３０μｍ以下のものを使用する。黒鉛粉末の平均粒径は好ましくは１〜３０μｍ、より好ましくは５〜２５μｍである。ここで平均粒径とは、質量中位径（メディアン径或いは５０％径といわれる）である。   The base graphite powder having an average particle size of 30 μm or less is used. The average particle size of the graphite powder is preferably 1 to 30 μm, more preferably 5 to 25 μm. Here, the average particle diameter is a mass median diameter (referred to as a median diameter or 50% diameter).

基材の黒鉛粉末の比表面積は、好ましくは２０ｍ2／g以下、より好ましくは１５ｍ2／ｇ以下である。比表面積が小さい天然黒鉛粉末として、粉砕により球形化処理された天然黒鉛粉末がある。 The specific surface area of the graphite powder of the base material is preferably 20 m 2 / g or less, more preferably 15 m 2 / g or less. As natural graphite powder having a small specific surface area, there is natural graphite powder that has been spheroidized by pulverization.

基材の黒鉛粉末が３０μｍを超えると、これに炭素前駆体を担持させて得られる本発明に係る黒鉛質粉末の平均粒径も３０μｍを超え、電極表面に凹凸が発生し易くなり、電池短絡の原因になる。一方、基材の黒鉛粉末の平均粒径が小さすぎると、粉末の凝集が起こりやすく、黒鉛質粉末製造において取扱いが難しいことがある。   If the graphite powder of the substrate exceeds 30 μm, the average particle size of the graphite powder according to the present invention obtained by supporting the carbon precursor on the substrate also exceeds 30 μm, and irregularities are likely to occur on the electrode surface, resulting in a battery short circuit. Cause. On the other hand, if the average particle size of the graphite powder of the base material is too small, the powder is likely to aggregate, which may be difficult to handle in the production of graphite powder.

基材の黒鉛粉末の比表面積が大き過ぎると、表面被覆に必要な炭素前駆体の量が多くなってしまう。黒鉛粉末の比表面積は、平均粒径に加えて、黒鉛粉末の細孔構造にも依存する。一般に、表面処理が施されていない未被覆の基材黒鉛粉末では、比表面積はかなり大きい。   If the specific surface area of the graphite powder of the substrate is too large, the amount of carbon precursor necessary for surface coating increases. The specific surface area of the graphite powder depends on the pore structure of the graphite powder in addition to the average particle diameter. In general, the specific surface area of the uncoated base graphite powder not subjected to surface treatment is considerably large.

この基材の黒鉛粉末に担持させる炭素前駆体は、水溶性高分子材料を熱処理して熱分解させた熱分解生成物であることが好ましい。この熱処理は、後で説明するように、基材の黒鉛粉末に水溶性高分子材料を付着させた後に行うことが好ましい。   The carbon precursor supported on the graphite powder of the base material is preferably a thermal decomposition product obtained by thermally decomposing a water-soluble polymer material. As will be described later, this heat treatment is preferably performed after the water-soluble polymer material is attached to the graphite powder of the base material.

水溶性高分子材料は合成高分子、天然高分子、半合成高分子のいずれでもよく、１種または２種以上を使用することができる。本発明で使用するのが好ましい水溶性高分子材料は、セルロースエーテル類であり、中でもカルボキシメチルセルロース（ＣＭＣ）の塩が好ましい。カルボキシメチルセルロースの塩が特に好ましいのは、安価で無害（食品添加物としても用いられている）であることと、リチウムイオン電池などの電極作成時の添加剤として長年の使用実績があるためである。カルボキシメチルセルロースの塩としてはナトリウム塩、アンモニウム塩、カリウム塩が挙げられる。   The water-soluble polymer material may be any of a synthetic polymer, a natural polymer, and a semi-synthetic polymer, and one or more types can be used. Water-soluble polymer materials that are preferably used in the present invention are cellulose ethers, and among them, a salt of carboxymethyl cellulose (CMC) is preferable. The salt of carboxymethylcellulose is particularly preferable because it is inexpensive and harmless (it is also used as a food additive) and has been used for many years as an additive for making electrodes such as lithium ion batteries. . Examples of carboxymethylcellulose salts include sodium salts, ammonium salts, and potassium salts.

水溶性高分子材料は、基材の黒鉛粉末１００質量部に対して好ましくは０.２〜１０質量部、より好ましくは０.５〜５質量部の範囲内の量で使用する。水溶性高分子材料の量が少なすぎると、炭素前駆体の担持による黒鉛質粉末の不可逆容量低減効果が不十分となる。逆に、この量が多過ぎると、炭素前駆体は容量をもたないため、最終的に得られる黒鉛質粉末の容量が低下する。また、炭素前駆体は導電性に劣るので、電極のレート特性やサイクル特性も低下する。   The water-soluble polymer material is preferably used in an amount in the range of 0.2 to 10 parts by mass, more preferably 0.5 to 5 parts by mass with respect to 100 parts by mass of the graphite powder of the base material. If the amount of the water-soluble polymer material is too small, the effect of reducing the irreversible capacity of the graphite powder by supporting the carbon precursor becomes insufficient. Conversely, if the amount is too large, the carbon precursor does not have a capacity, so that the capacity of the finally obtained graphite powder decreases. Moreover, since a carbon precursor is inferior in electroconductivity, the rate characteristic and cycling characteristic of an electrode also fall.

水溶性高分子材料は基材の黒鉛粉末の表面を可及的に均一に被覆するように黒鉛粉末に付着させることが好ましい。具体的な付着方法としては、例えば次の方法が可能である。
(1)水溶性高分子材料を水に溶解させた水溶液中に黒鉛粉末を分散させたスラリーを調製し、このスラリーを乾燥させる。このスラリーは、先に水溶性高分子材料を水に溶解し、得られた水溶液に黒鉛粉末を添加して調製してもよく、あるいは、水溶性高分子材料と黒鉛粉末と水を混合して調製することもできる。スラリーの乾燥は、例えばマイクロミストドライヤ（藤崎電機社製）などによる噴霧乾燥を利用することができる。 The water-soluble polymer material is preferably attached to the graphite powder so as to cover the surface of the graphite powder as a base material as uniformly as possible. As a specific adhesion method, for example, the following method is possible.
(1) A slurry is prepared in which graphite powder is dispersed in an aqueous solution in which a water-soluble polymer material is dissolved in water, and the slurry is dried. This slurry may be prepared by first dissolving the water-soluble polymer material in water and adding graphite powder to the resulting aqueous solution, or mixing the water-soluble polymer material, graphite powder and water. It can also be prepared. For drying the slurry, spray drying using, for example, a micro mist dryer (manufactured by Fujisaki Electric Co., Ltd.) can be used.

(2)水溶性高分子材料を水に溶解させた水溶液を黒鉛粉末に吹き付ける。例えば、ニューグラーマシン（セイシン企業社製）のように容器内の回転羽根により黒鉛粉末を自転・公転させる装置を利用して水溶液を吹き付けると、黒鉛粉末の表面に均一に水溶液を付着させることができる。   (2) An aqueous solution in which a water-soluble polymer material is dissolved in water is sprayed on the graphite powder. For example, when an aqueous solution is sprayed using a device that rotates and revolves graphite powder by rotating blades in a container, such as a Newgler machine (manufactured by Seishin Enterprise Co., Ltd.), the aqueous solution can be uniformly attached to the surface of the graphite powder. it can.

(3)黒鉛粉末に固相の水溶性高分子材料を機械的な力を加えることにより付着させる。例えば、メカノフュージョン（ホソカワミクロン社製）のような回転容器内に黒鉛粉末と水溶性高分子材料の粉末を投入し、遠心力で両方の粉末を内壁に押し付けながら、曲率の異なるインナーピースとの間で強力な圧縮・剪断力を加えることにより、黒鉛粉末表面に固相の水溶性高分子材料を均一に付着させることができる。   (3) A solid water-soluble polymer material is adhered to the graphite powder by applying mechanical force. For example, graphite powder and water-soluble polymer powder are put into a rotating container such as Mechanofusion (made by Hosokawa Micron Corporation), and both powders are pressed against the inner wall by centrifugal force. By applying a strong compressive / shearing force, a solid water-soluble polymer material can be uniformly attached to the surface of the graphite powder.

表面に水溶性高分子材料が付着した黒鉛粉末を次いで熱処理する。この熱処理により、水溶性高分子材料は少なくとも部分的に熱分解して炭素前駆体に変換され、炭素前駆体が担持された黒鉛粉末からなる本発明の黒鉛質粉末が得られる。熱処理温度は使用した水溶性高分子材料の熱分解温度以上であればよい。熱分解温度とは、ある物質が加熱によって２種以上の物質に変化する温度のことである。熱分解温度は、熱天秤を利用した熱重量分析（ＴＧ）または示差熱分析（ＤＴＡ）といった熱的分析法で調べることができる。   Next, the graphite powder having the water-soluble polymer material attached to the surface is heat-treated. By this heat treatment, the water-soluble polymer material is at least partially pyrolyzed to be converted into a carbon precursor, and the graphite powder of the present invention comprising graphite powder supporting the carbon precursor is obtained. The heat treatment temperature should just be more than the thermal decomposition temperature of the water-soluble polymer material used. The thermal decomposition temperature is a temperature at which a certain substance changes into two or more kinds by heating. The thermal decomposition temperature can be examined by a thermal analysis method such as thermogravimetric analysis (TG) or differential thermal analysis (DTA) using a thermobalance.

有機物の場合、熱分解により、水、二酸化炭素などを生成しつつ、別の有機物に変化し、最終的に炭素になる。熱処理により炭素前駆体を生じさせるためには、熱処理条件を、熱分解が起こるが、完全な炭素化まで熱分解が進行しないように選択する。熱処理温度は、使用する水溶性高分子材料の熱分解温度以上の温度であって、かつ残留率（付着した水溶性高分子材料に対する熱処理後も黒鉛表面に残留する炭素前駆体の質量百分率、熱処理前後の質量変化から求められる）が４０％以上となる温度とすることが好ましい。水溶性高分子材料がカルボキシメチルセルロースＮａ塩である場合、好ましい熱処理温度は２５０〜７００℃の範囲である。   In the case of an organic substance, it is converted into another organic substance while producing water, carbon dioxide and the like by thermal decomposition, and finally becomes carbon. In order to generate a carbon precursor by heat treatment, the heat treatment conditions are selected so that thermal decomposition occurs but thermal decomposition does not proceed until complete carbonization. The heat treatment temperature is equal to or higher than the thermal decomposition temperature of the water-soluble polymer material to be used, and the residual ratio (the mass percentage of the carbon precursor remaining on the graphite surface after the heat treatment of the attached water-soluble polymer material, the heat treatment The temperature is preferably 40% or more (obtained from mass change before and after). When the water-soluble polymer material is carboxymethyl cellulose Na salt, the preferred heat treatment temperature is in the range of 250 to 700 ° C.

熱処理雰囲気は非酸化性雰囲気であり、好ましくはアルゴンや窒素等の不活性雰囲気である。熱処理を大気など酸素を多量に含有する雰囲気中で行うと、使用する水溶性高分子によっては、高分子鎖が切断されて昇温中に揮発しやすくなり、上記残留率が低くなってしまい、被覆効果がなくなるものがある。ただし、非酸化性雰囲気は少量の酸素を含有していても構わない。   The heat treatment atmosphere is a non-oxidizing atmosphere, preferably an inert atmosphere such as argon or nitrogen. When the heat treatment is performed in an atmosphere containing a large amount of oxygen such as the air, depending on the water-soluble polymer used, the polymer chain is easily broken and volatilizes during the temperature rise, and the residual rate becomes low. Some have lost the coating effect. However, the non-oxidizing atmosphere may contain a small amount of oxygen.

熱処理時間は上記残留率が４０質量％以上となるように選択することが好ましい。熱処理時間は、使用する水溶性高分子材料の熱分解温度および熱処理温度に応じて、実験により当業者が容易に決定することができる。   The heat treatment time is preferably selected so that the residual rate is 40% by mass or more. The heat treatment time can be easily determined by those skilled in the art through experiments according to the thermal decomposition temperature and heat treatment temperature of the water-soluble polymer material to be used.

熱処理は、黒鉛粉末を静置した状態で行うのでよいが、黒鉛粉末を撹拌または流動化させた状態で熱処理を行うことも可能である。熱処理後に必要であれば、熱処理中に融着した黒鉛粉末をほぐすように解砕を行ってもよい。それに加えて、またはそれに代えて、分級を行って、融着した粗大粒子を除去してもよい。   The heat treatment may be performed in a state where the graphite powder is allowed to stand, but it is also possible to perform the heat treatment in a state where the graphite powder is stirred or fluidized. If necessary after the heat treatment, the graphite powder fused during the heat treatment may be crushed so as to be loosened. In addition, or instead, classification may be performed to remove the fused coarse particles.

基材の黒鉛粉末への水溶性高分子材料の付着工程を、水溶性高分子材料の水溶液を使用した方法で行う場合には、付着工程において乾燥が必要になる。この乾燥を加熱により行う場合には、この付着工程における乾燥と熱処理とを１つの加熱装置内で続けて行うことも可能である。   When the adhesion process of the water-soluble polymer material to the graphite powder of the base material is performed by a method using an aqueous solution of the water-soluble polymer material, drying is required in the adhesion process. In the case where this drying is performed by heating, it is also possible to continuously perform the drying and heat treatment in this adhesion step in one heating device.

熱処理によって、炭素前駆体を担持した黒鉛粉末からなる本発明の黒鉛質粉末が得られる。炭素前駆体を担持させた黒鉛質粉末の平均粒径は、基材の黒鉛粉末と実質的には変化しない場合と、付着工程および／または熱処理工程中に造粒が起こって基材の黒鉛粉末より平均粒径が増加する場合とがある（特に基材が微粉の場合）。得られた黒鉛質粉末の平均粒径は３０μｍ以下であり、好ましくは１〜３０μｍ。より好ましくは５〜２５μｍである。平均粒径が３０μｍより大きいと、電極表面に凹凸が発生しやすくなり、電池短絡の原因となる恐れがある。平均粒径が小さすぎると、電極作製時にスラリー化した際に粉末が凝集しやすいなど、粉末の取り扱いが難しくなる。   By the heat treatment, the graphite powder of the present invention comprising the graphite powder supporting the carbon precursor is obtained. The average particle size of the graphite powder supporting the carbon precursor is substantially the same as that of the base material graphite powder, and granulation occurs during the adhesion process and / or the heat treatment process. In some cases, the average particle size may increase (especially when the substrate is fine powder). The average particle size of the obtained graphite powder is 30 μm or less, preferably 1 to 30 μm. More preferably, it is 5-25 micrometers. If the average particle size is larger than 30 μm, irregularities are likely to occur on the electrode surface, which may cause a battery short circuit. When the average particle size is too small, it becomes difficult to handle the powder, for example, the powder is likely to agglomerate when slurried at the time of electrode preparation.

この黒鉛質粉末の比表面積は１.０〜１２.５ｍ2／ｇの範囲内が好ましく、より好ましくは１.０〜１０ｍ2／ｇの範囲内である。水溶性高分子材料の付着と熱処理を経ることにより、黒鉛質粉末の比表面積は基材の黒鉛粉末の比表面積より小さくなる傾向がある。電極作製の用いる黒鉛質粉末の比表面積が小さすぎると、リチウムイオンが進入するサイトが減少し、レート特性が低下する。一方、この比表面積が大きすぎると、不可逆容量が増加する。 The specific surface area of the graphite powder is preferably in the range of 1.0 to 12.5 m 2 / g, more preferably in the range of 1.0 to 10 m 2 / g. The specific surface area of the graphite powder tends to be smaller than the specific surface area of the graphite powder of the base material through the adhesion of the water-soluble polymer material and the heat treatment. If the specific surface area of the graphite powder used for electrode preparation is too small, the sites into which lithium ions enter will decrease and the rate characteristics will deteriorate. On the other hand, if this specific surface area is too large, the irreversible capacity increases.

黒鉛粉末に担持された炭素前駆体の量は、黒鉛粉末１００質量部に対して０.０８〜６質量部の範囲内であることが好ましく、より好ましくは０.２〜３質量部である。炭素前駆体の担持量が少なすぎると、炭素前駆体の担持による不可逆容量の低減効果が不十分となる。逆に担持量が多過ぎると、炭素前駆体は容量もたないため、黒鉛質粉末の容量が低下する。また、炭素前駆体は導電性に劣るのでレート特性やサイクル特性が低下する。   The amount of the carbon precursor supported on the graphite powder is preferably in the range of 0.08 to 6 parts by mass, more preferably 0.2 to 3 parts by mass with respect to 100 parts by mass of the graphite powder. When the loading amount of the carbon precursor is too small, the effect of reducing the irreversible capacity due to the loading of the carbon precursor becomes insufficient. On the other hand, if the loading amount is too large, the carbon precursor has no capacity, and the capacity of the graphite powder decreases. Moreover, since a carbon precursor is inferior in electroconductivity, a rate characteristic and cycling characteristics will fall.

本発明の黒鉛質粉末を負極材料として用いた非水系二次電池の負極の製造や二次電池の作成は、従来公知のように実施すればよい。以下に、この点についても簡単に説明するが、この説明は例示にすぎず、他の方法や構成も可能である。   Production of the negative electrode of a non-aqueous secondary battery using the graphite powder of the present invention as a negative electrode material and preparation of the secondary battery may be carried out as conventionally known. Although this point will be briefly described below, this description is only an example, and other methods and configurations are possible.

負極材料の黒鉛質粉末に適当な結着剤とその溶媒を混合し、必要に応じて導電性向上のために適当な導電剤を混合して、塗工用のスラリーを形成する。混合は、必要であれば、ホモジナイザーあるいはガラスビーズを用いて行うことができる。このスラリーを適当な集電体（圧延銅箔、銅電析銅箔など）にドクターブレード法等を用いて塗工し、乾燥した後、ロール圧延等で圧密化させると、負極用の電極が製造される。   An appropriate binder and its solvent are mixed with the graphite powder of the negative electrode material, and an appropriate conductive agent is mixed as necessary to improve conductivity, thereby forming a slurry for coating. If necessary, mixing can be performed using a homogenizer or glass beads. When this slurry is applied to a suitable current collector (rolled copper foil, copper electrodeposited copper foil, etc.) using a doctor blade method, etc., dried, and then consolidated by roll rolling or the like, the electrode for the negative electrode becomes Manufactured.

結着剤としてはポリフッ化ビニリデン、ポリテトラフルオロエチレン等のフッ素系高分子、カルボキシメチルセルロース（ＣＭＣ）等の樹脂系高分子、スチレンーブタジエンゴム（ＳＢＲ）等のゴム状高分子などの１種または２種以上を使用することができる。結着剤の溶媒はＮ−メチルピロリドン、水などでよい。必要に応じて使用しうる導電剤は、炭素材料、金属（Ｎｉ等）でよく、このときの炭素材料には人造黒鉛、天然黒鉛、カーボンブラック、アセチレンブラック等が包含され、粉末だけでなく繊維状のものを用いても良い。   As the binder, one kind of fluorine polymer such as polyvinylidene fluoride and polytetrafluoroethylene, resin polymer such as carboxymethylcellulose (CMC), rubbery polymer such as styrene-butadiene rubber (SBR), or the like Two or more types can be used. The binder solvent may be N-methylpyrrolidone, water or the like. The conductive agent that can be used as necessary may be a carbon material or a metal (Ni, etc.), and the carbon material at this time includes artificial graphite, natural graphite, carbon black, acetylene black, etc. A shape may be used.

電池は、その基本構造として、負極、正極、セパレーター、非水系電解液を含んでいる。本発明にあっても、そのような構成に特に制限はされず、また、電池の形状も特に制限されず、円筒型、角形、コイン型、シート型等何れでも良い。電解液は、例えば、エチレンカーボネート（ＥＣ）やエチルメチルカーボネート（ＥＭＣ）などのアルキルカーボネートから選ばれた１種または２種以上を使用できる。   The battery includes a negative electrode, a positive electrode, a separator, and a non-aqueous electrolyte as its basic structure. Even in the present invention, such a configuration is not particularly limited, and the shape of the battery is not particularly limited, and may be any of a cylindrical shape, a square shape, a coin shape, a sheet shape, and the like. As the electrolytic solution, for example, one or more selected from alkyl carbonates such as ethylene carbonate (EC) and ethyl methyl carbonate (EMC) can be used.

以下の実施例は本発明の例示にすぎず、本発明はそれによって制限を受けない。実施例中、部は全て質量部の意味である。
（実施例１）
平均粒径２０μｍ、比表面積５.４ｍ2／ｇの球形化処理された天然黒鉛粉末１００部にカルボキシメチルセルロースナトリウムＮａ塩（ＣＭＣ−Ｎａ）粉末０.５部を混合し、この混合物を純水１００部に投入し、攪拌混合して、スラリーを得た。得られたスラリーをマイクロミストドライヤ（藤崎電機社製）を用いて噴霧乾燥させた。 The following examples are merely illustrative of the invention and the invention is not limited thereby. In the examples, all parts mean parts by mass.
Example 1
0.5 parts of carboxymethyl cellulose sodium Na salt (CMC-Na) powder is mixed with 100 parts of natural graphite powder having an average particle diameter of 20 μm and a specific surface area of 5.4 m 2 / g, and the mixture is mixed with 100 parts of pure water. The resulting mixture was stirred and mixed to obtain a slurry. The obtained slurry was spray-dried using a micro mist dryer (Fujisaki Electric Co., Ltd.).

得られた混合粉末を黒鉛るつぼに入れ、窒素気流下、３００℃で１時間熱処理した。熱処理により得られた粉末をふるい目７５μｍのふるいで分級して、炭素前駆体が担持された黒鉛質粉末を得た。使用したＣＭＣ−Ｎａの熱分解温度を熱重量分析（ＴＧ）で調べたところ、３００℃より低かったので、熱処理温度を３００℃とした（図１）。   The obtained mixed powder was put into a graphite crucible and heat-treated at 300 ° C. for 1 hour under a nitrogen stream. The powder obtained by the heat treatment was classified with a sieve having a sieve size of 75 μm to obtain a graphite powder carrying a carbon precursor. When the thermal decomposition temperature of CMC-Na used was examined by thermogravimetric analysis (TG), it was lower than 300 ° C., so the heat treatment temperature was set to 300 ° C. (FIG. 1).

この黒鉛質粉末の平均粒径は２０μｍ、比表面積は４.５ｍ2／ｇ、炭素前駆体の担持量は黒鉛粉末１００部に対して０.２５部であった。
（実施例２および３）
ＣＭＣ−Ｎａ粉末の量をそれぞれ１部および２部に変更し、純水の量をそれぞれ１５０部および１７５部に変更した以外は実施例１と同様にして、炭素前駆体が担持された黒鉛質粉末を得た。この黒鉛質粉末の平均粒径、比表面積、炭素前駆体の担持量はそれぞれ表１に示す通りである。 The average particle diameter of this graphite powder was 20 μm, the specific surface area was 4.5 m 2 / g, and the amount of the carbon precursor supported was 0.25 part with respect to 100 parts of graphite powder.
(Examples 2 and 3)
Graphite with a carbon precursor supported in the same manner as in Example 1 except that the amount of CMC-Na powder was changed to 1 part and 2 parts, respectively, and the amount of pure water was changed to 150 parts and 175 parts, respectively. A powder was obtained. Table 1 shows the average particle diameter, specific surface area, and supported amount of carbon precursor of the graphite powder.

（比較例１）
実施例１で用いた球形化粉砕処理された天然黒鉛粉末（未処理品）をそのまま、あるいは熱処理のみを実施例１と同じ条件で実施して、負極材料として使用した。 (Comparative Example 1)
The spheroidized and ground natural graphite powder (untreated product) used in Example 1 was used as a negative electrode material as it was, or only by heat treatment under the same conditions as in Example 1.

（比較例２〜４）
実施例１〜３において、３００℃での熱処理を実施しなかった。従って、得られた黒鉛質粉末は、表面にＣＭＣ−Ｎａを担持していた。このような熱分解させていない水溶性高分子材料を担持させた黒鉛粉末は、上記特許文献１および２に開示されているものと同じである。 (Comparative Examples 2 to 4)
In Examples 1 to 3, the heat treatment at 300 ° C. was not performed. Therefore, the obtained graphite powder supported CMC-Na on the surface. Such graphite powder carrying a water-soluble polymer material not thermally decomposed is the same as that disclosed in Patent Documents 1 and 2 above.

以上の実施例及び比較例で得られた黒鉛質粉末の電極性能を次のようにして調査した。
黒鉛質粉末９７部に結着剤として実施例で用いたのと同じＣＭＣ−Ｎａ粉末（以下では単にＣＭＣという）を混合した後、ＳＢＲ（スチレン−ブタジエンゴム）を水に分散させた液を加え、攪拌してスラリーを得た。配合比は炭素：ＣＭＣ：ＳＢＲ＝９７：１：２（質量比）であった。このスラリーを厚み１７μｍの圧延銅箔上にドクターブレード法により塗布し（塗布量は１０ｍｇ／ｃｍ2）、加熱乾燥後、直径１３ｍｍに打ち抜き、プレス成形機にて加圧して電極を作製した。 The electrode performance of the graphite powder obtained in the above Examples and Comparative Examples was investigated as follows.
The same CMC-Na powder (hereinafter simply referred to as CMC) used in the examples as a binder was mixed with 97 parts of graphite powder, and then a solution in which SBR (styrene-butadiene rubber) was dispersed in water was added. And stirred to obtain a slurry. The blending ratio was carbon: CMC: SBR = 97: 1: 2 (mass ratio). This slurry was applied onto a rolled copper foil having a thickness of 17 μm by a doctor blade method (coating amount: 10 mg / cm 2 ), heat-dried, punched to a diameter of 13 mm, and pressed with a press molding machine to produce an electrode.

以下の評価には、電極密度１.７ｇ／ｃｍ3の電極を１００℃で真空乾燥したものを用いた。
ポリオレフィン製セパレーターを用い、その両側に上記電極と対極のＬｉ金属箔とを配置し、電解液にはエチレンカーボネート（ＥＣ）：エチルメチルカーボネート（ＥＭＣ）＝１：３（体積比）の混合溶媒に支持電解質ＬｉＰＦ6を１Ｍ濃度で溶解した非水溶液を用いて、コイン型の非水試験セルを作製した。 In the following evaluation, an electrode having an electrode density of 1.7 g / cm 3 was vacuum-dried at 100 ° C.
Using a separator made of polyolefin, the electrode and the Li metal foil of the counter electrode are arranged on both sides of the separator, and the electrolyte is a mixed solvent of ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 1: 3 (volume ratio). A coin-type non-aqueous test cell was prepared using a non-aqueous solution in which the supporting electrolyte LiPF 6 was dissolved at a concentration of 1M.

この試験セルを、２５ｍＡ／ｇの電流値で、対極に対して電位差０（ゼロ）Ｖになるまで定電流でドープし（充電に相当）、さらに０Ｖを保持したまま、５μＡ／ｃｍ2になるまで定電圧でドープを続けた。次に、２５ｍＡ／ｇの定電流で、電位差１.５Ｖになるまで脱ドープを行って（放電に相当）、脱ドープ容量を測定した。この時の脱ドープ容量は、二次電池の負極として用いた時の放電容量に相当するのでこれを放電容量とした。充電容量から放電容量を差し引いた値を不可逆容量とした。 The test cell is doped with a constant current at a current value of 25 mA / g until the potential difference becomes 0 (zero) V with respect to the counter electrode (corresponding to charging), and further becomes 5 μA / cm 2 while maintaining 0 V. Continued doping at a constant voltage until. Next, dedoping was performed at a constant current of 25 mA / g until the potential difference became 1.5 V (corresponding to discharge), and the dedoping capacity was measured. The dedope capacity at this time corresponds to the discharge capacity when used as the negative electrode of the secondary battery, and this was used as the discharge capacity. The value obtained by subtracting the discharge capacity from the charge capacity was defined as the irreversible capacity.

また放電曲線（脱ドープ側）において、比較例２〜３の材料では比較例１に比べて、僅かな電流にもかかわらず貴な電位側にシフトした。これは非常にレート特性が悪いことを示している。数値化するため、放電スタートから１００ｍＡｈ／ｇのところの電圧を読み取り、比較例１からの電圧差を比較した。以上の結果を表１に示す。   Further, in the discharge curve (undoped side), the materials of Comparative Examples 2 to 3 were shifted to a noble potential side despite a slight current as compared with Comparative Example 1. This indicates that the rate characteristic is very bad. In order to quantify, the voltage at 100 mAh / g was read from the discharge start, and the voltage difference from Comparative Example 1 was compared. The results are shown in Table 1.

Figure 0005386802
Figure 0005386802

表１に示すように、本発明に従って、黒鉛粉末にＣＭＣの熱分解生成物からなる炭素前駆体を担持した実施例１〜３の黒鉛質粉末では、放電容量が３６０ｍＡｈ／ｇを越え、不可逆容量も小さくなっている。また、電圧降下も認められない。ＣＭＣの添加量が増大しても、不可逆容量の低下はごくわずかにとどまっている。   As shown in Table 1, according to the present invention, in the graphite powders of Examples 1 to 3 in which the carbon precursor made of the thermal decomposition product of CMC was supported on the graphite powder, the discharge capacity exceeded 360 mAh / g, and the irreversible capacity. Is also getting smaller. Also, no voltage drop is observed. Even when the amount of CMC added increases, the irreversible capacity decreases only slightly.

これに対し、比較例を見ると、未被覆の比較例１の黒鉛粉末に比べて、比較例２〜４ではＣＭＣによる被覆によって不可逆容量を低減することはできるものの、添加量を多くしないと十分な不可逆容量の低減が得られない。一方、ＣＭＣの添加量を多くすると、放電容量が著しく低下し、電圧降下が大きくなり、レート特性の低下が顕著となる。   On the other hand, compared with the uncoated graphite powder of Comparative Example 1, in Comparative Examples 2 to 4, the irreversible capacity can be reduced by coating with CMC, but it is sufficient if the amount added is not increased. A significant reduction in irreversible capacity cannot be obtained. On the other hand, when the amount of CMC added is increased, the discharge capacity is remarkably reduced, the voltage drop is increased, and the rate characteristic is significantly reduced.

実施例１において水溶性高分子材料として使用したＣＭＣ−Ｎａの熱重量分析（ＴＧ）曲線である。2 is a thermogravimetric analysis (TG) curve of CMC-Na used as a water-soluble polymer material in Example 1. FIG.

Claims (5)

炭素前駆体を担持した黒鉛粉末からなる黒鉛質粉末であって、
平均粒径が３０μｍ以下であり、
前記炭素前駆体が、カルボキシメチルセルロース塩の残留率４０％以上の熱分解生成物である、
ことを特徴とする黒鉛質粉末。 A graphitic powder ing graphite powder carrying a carbon precursor,
Average particle diameter of Ri der less 30 [mu] m,
The carbon precursor is a thermal decomposition product having a residual ratio of carboxymethyl cellulose salt of 40% or more.
Graphite powder characterized by that. 黒鉛粉末の表面にカルボキシメチルセルロース塩を付着させる工程と、付着したカルボキシメチルセルロース塩の熱分解温度以上の温度で非酸化性雰囲気中にて黒鉛粉末を熱処理する工程とを有することを特徴とする、請求項１記載の黒鉛質粉末の製造方法。 The method comprises: attaching a carboxymethyl cellulose salt to the surface of the graphite powder; and heat treating the graphite powder in a non-oxidizing atmosphere at a temperature equal to or higher than a thermal decomposition temperature of the attached carboxymethyl cellulose salt. Item 2. A method for producing a graphite powder according to Item 1. 前記付着工程が、カルボキシメチルセルロース塩の水溶液中に黒鉛粉末を分散させたスラリーを噴霧乾燥することにより行われる、請求項２記載の黒鉛質粉末の製造方法。 The method for producing a graphite powder according to claim 2 , wherein the attaching step is performed by spray drying a slurry in which graphite powder is dispersed in an aqueous solution of carboxymethylcellulose salt . 請求項１記載の黒鉛質粉末を用いて作製されたことを特徴とする非水系二次電池用負極。   A negative electrode for a non-aqueous secondary battery, characterized by being produced using the graphite powder according to claim 1. 請求項４記載の負極を備えた非水系二次電池。
A non-aqueous secondary battery comprising the negative electrode according to claim 4.
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