JP3683379B2 - Graphite for negative electrode of lithium secondary battery and method for producing the same - Google Patents
Graphite for negative electrode of lithium secondary battery and method for producing the same Download PDFInfo
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- JP3683379B2 JP3683379B2 JP11635197A JP11635197A JP3683379B2 JP 3683379 B2 JP3683379 B2 JP 3683379B2 JP 11635197 A JP11635197 A JP 11635197A JP 11635197 A JP11635197 A JP 11635197A JP 3683379 B2 JP3683379 B2 JP 3683379B2
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- Prior art keywords
- graphite
- negative electrode
- lithium secondary
- secondary battery
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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
Description
【0001】
【発明の属する分野】
本発明はリチウム二次電池負極用黒鉛及びその製造方法に係り、特に放電容量および初期充放電効率の高い黒鉛及びその製造方法に関する。
【0002】
【従来の技術】
近年の電子機器のポータブル化、コードレス化が進むにしたがい、これら機器の電源として小型・軽量かつ高エネルギー密度の高性能二次電池の開発が急がれ、その要望に応えるものとしてリチウム二次電池が提供されている。かかる二次電池用の負極材料には炭素質材料が使用されるが、中でも特公昭62−23433号公報に記載されるように、黒鉛の優位性が認められてきている。
この黒鉛質負極材料の特性としてはその層間距離(d)が小さいほど、またその結晶子の大きさ(Lc)が大きいほど二次電池の放電容量が大きく、初期充放電効率が大きいことが明らかとなっており、優れた性質を持った天然黒鉛の探索や、あるいは人造黒鉛の製造条件の改良などが進められてきている。
【0003】
【発明が解決しようとする課題】
しかしながら、天然黒鉛はたとえ優れた性質のものが発見されたとしても採掘場所の変化などにより性質が変化し、安定して供給するのが困難であり、一方、人造黒鉛は黒鉛の結晶性の発達のために易黒鉛化炭素を2500℃以上の温度で熱処理する必要があるが、それでもなお、放電容量が天然黒鉛に及んでいないのが現状である。ちなみに天然黒鉛の放電容量として370mAh/g、初期充放電効率92%が報告されているのに対し、人造黒鉛の場合は最も良い場合でも放電容量が350〜360mAh/g程度である。これは人造黒鉛の黒鉛の結晶性が天然黒鉛より低いためであると推察されている。
本発明は、従来技術の問題点を解決することを目的とし、天然黒鉛相当あるいはそれよりすぐれた性質を有するリチウム二次電池負極材料を工業製品として提供することを目的とし、安定して放電容量、初期充放電効率の高い黒鉛質負極材料およびその製造方法を提供することを目的とする。
【0004】
【課題を解決するための手段】
本発明者等は、リチウム二次電池負極用黒鉛について種々の材料を検討した結果、製鉄工程において発生するいわゆるキッシュグラファイトが上記リチウム二次電池負極用黒鉛として非常に好ましい性質を有していることに着目し、その利用手段について研究した結果、本発明を完成したものである。
【0005】
本発明は、リチウム二次電池負極用黒鉛を、過共晶組成の溶融銑鉄の冷却過程において生ずる鱗状黒鉛を主として含む生成物を処理して得た、Cを99%以上含有し、平均粒度が0.005mm以上であり、かつ層間距離(d)3.37Å以下、結晶子の大きさ(Lc)2000Å以上の鱗状黒鉛とするものであり、またその製造方法として、過共晶溶融銑鉄の冷却過程で得られる鱗状黒鉛を主として含有する生成物のうち粒径が0.044mmのものを回収し、化学処理を行なってCを99%以上するように精製し、しかる後粉砕と篩い分けを行なって平均粒度0.005mm以上、層間距離(d)3.37Å以下、結晶子の大きさ(Lc)2000Å以上の鱗状黒鉛を得るものである。またこの際、過共晶溶融銑鉄には高炉溶銑を用い、冷却過程で得られる生成物には製鉄ダスト、いわゆるキッシュグラファイトを利用するものである。
【0006】
【発明の実施の形態】
本発明においては、過共晶組成の溶融銑鉄の冷却過程で生ずる黒鉛を利用する。本発明者等の調査によれば、かかる黒鉛は、鱗状黒鉛に属し、その性状は、表1に示すとおりである。ここに表1は、高炉による製鉄過程で得られる溶融銑鉄の冷却時に発生する製鉄ダスト、いわゆるキッシュグラファイトを精製し篩分けた場合の粒径ごとの性状を示したものであるが、キッシュグラファイトは黒鉛の層間距離(d)は3.37Å以下(実質的に3.36Å以下)となっており、また結晶子の大きさ(Lc)はその粒径が0.044mm以上のものを篩分けると2000Å以上となることが判明した。かかる性状を有するキッシュグラファイトは、従来知られている黒鉛の性状とその負極材としての特性値の相関関係図を基に考察すれば、これが優れた負極材となりうる可能性が示された。
【0007】
【表1】
【0008】
キッシュグラファイトがかかる優れた性状を呈する原因については、高温の溶融金属と一定の整合性を保ちながら、かつ、溶融鉄の圧力下で黒鉛結晶が成長することなどが考えられるが、正確な理由はなお不明である。しかし、粒径が極めて小さいもの、具体的には0.044mm未満のものは結晶子の大きさが比較的小さく、リチウム二次電池負極用黒鉛として十分な特性の向上が望めない上、不純物も多く精製コストもかかるので、本発明においてはキッシュグラファイトのうち粒径が0.044mm以上のもののみを原料として使用する。
【0009】
表2は上記によって得た粒径0.044mm以上のキッシュグラファイトを化学処理によってCを99%以上に精製し、それに対して粉砕と篩い分けを行なって平均粒度0.005mm以上のリチウム二次電池負極用黒鉛を得、その特性を調査した結果である。
ここに示されるように、キッシュグラファイトから得た鱗状黒鉛は最優秀の天然黒鉛に匹敵する二次電池負極材料特性を示し、従来の人造黒鉛の性能を凌ぐものであった。かかる結果は、高炉による製鉄過程で得られるキッシュグラファイトについて最初に認められたものであるが、過共晶銑鉄の冷却過程で得られるキッシュグラファイト全般に広く認められるものであることが確認されている。従って、黒鉛としては上記製鉄過程で得られるキッシュグラファイトのほか、過共晶溶融銑鉄の冷却過程で得られるキッシュグラファイトが広く利用できる。なお、高炉による製鉄過程で発生するキッシュグラファイトは大量かつ、安価に得られるのでこれを利用するのが経済的であることはいうまでもない。
【0010】
【表2】
【0011】
上記生成物(キッシュグラファイト)は、そのままでは不純物、すなわち鉄およびその酸化物、珪素(Si)、カルシウム(Ca)その他製鉄過程で精錬のため使用される副原料の微粉末などを多く含んでいるので、その除去を行い、純度を向上させる。一般に負極材料として使用するには、C含有量を99%(重量比)とすることが必要であるので、化学的処理を施して精製する。化学的処理としては、浮選および塩酸、弗酸による処理が含まれる。そのため特開昭63−151609号公報記載の方法を用いることができる。
【0012】
化学処理されたキッシュグラファイトはさらに適当なミル(例えばボールミル)等によって粉砕を行ない、篩い分けをする。これらの工程は、平均粒度が0.005mm以上となるように、かつ使用されるリチウム二次電池負極材料の要求特性に応じて行なえばよい。なお、平均粒度を0.005mm未満としないようにするのは、かかる粒度のものは一般に負極材料としても特性値が好ましくなく、また取り扱い上不便だからである。
【0013】
上記一連の工程によりリチウム二次電池負極用黒鉛として十分な層間距離と結晶子の大きさを有する黒鉛が得られる。特に、本発明によって提供可能な黒鉛の特性は原料となるキッシュグラファイトの特性を受けて実質的に層間距離3.36Å以下、結晶子の大きさ2000Å以上となり、そのため非常に優れた負極特性を呈することになる。
【0014】
【発明の効果】
本発明により、リチウム二次電池負極用黒鉛の特性が大きく改善され、リチウム二次電池の用途拡大、軽量化、長寿命化に資するところが大である。また本発明にかかる黒鉛は、天然産ではないので、極めて安定して供給することができ、リチウム二次電池の安定製造に寄与するものである。また、従来廃材として処理されていたキッシュグラファイトの有効活用を図ることができる。[0001]
[Field of the Invention]
The present invention relates to graphite for negative electrodes of lithium secondary batteries and a method for producing the same, and more particularly to graphite having a high discharge capacity and high initial charge / discharge efficiency and a method for producing the same.
[0002]
[Prior art]
As electronic devices have become more portable and cordless in recent years, the development of compact, lightweight, high energy density, high performance secondary batteries has been urgently needed as the power source for these devices. Is provided. A carbonaceous material is used as the negative electrode material for the secondary battery, and among them, the superiority of graphite has been recognized as described in Japanese Patent Publication No. 62-23433.
It is clear that the characteristics of this graphite negative electrode material are that the smaller the interlayer distance (d) and the larger the crystallite size (Lc), the larger the discharge capacity of the secondary battery and the greater the initial charge / discharge efficiency. Accordingly, the search for natural graphite having excellent properties or the improvement of production conditions for artificial graphite has been promoted.
[0003]
[Problems to be solved by the invention]
However, even if natural graphite is found to have excellent properties, its properties change due to changes in the mining location, etc., and it is difficult to supply stably. On the other hand, artificial graphite develops the crystallinity of graphite. Therefore, it is necessary to heat treat graphitizable carbon at a temperature of 2500 ° C. or higher, but the current situation is that the discharge capacity does not reach natural graphite. Incidentally, while the discharge capacity of natural graphite is reported to be 370 mAh / g and the initial charge / discharge efficiency is 92%, artificial graphite has a discharge capacity of about 350 to 360 mAh / g even in the best case. It is presumed that this is because the graphite of artificial graphite has lower crystallinity than natural graphite.
An object of the present invention is to solve the problems of the prior art, and to provide a lithium secondary battery negative electrode material having properties equivalent to or superior to natural graphite as an industrial product, and stably discharge capacity. An object of the present invention is to provide a graphite negative electrode material having a high initial charge / discharge efficiency and a method for producing the same.
[0004]
[Means for Solving the Problems]
As a result of examining various materials for lithium secondary battery negative electrode graphite, the present inventors have found that so-called quiche graphite generated in the iron making process has very favorable properties as the above lithium secondary battery negative electrode graphite. The present invention has been completed as a result of investigating the means of use and studying its utilization means.
[0005]
The present invention relates to a lithium secondary battery negative electrode graphite obtained by treating a product mainly containing scaly graphite produced in the cooling process of a hypereutectic molten pig iron, containing 99% or more of C and having an average particle size of Scalar graphite having a distance of 0.005 mm or more and an interlayer distance (d) of 3.37 mm or less and a crystallite size (Lc) of 2000 mm or more is used, and as a manufacturing method thereof, cooling of hypereutectic molten pig iron is performed. Of the products mainly containing scaly graphite obtained in the process, those having a particle size of 0.044 mm are collected, purified by chemical treatment so that C is 99% or more, and then crushed and sieved. Thus, scaly graphite having an average particle size of 0.005 mm or more, an interlayer distance (d) of 3.37 mm or less, and a crystallite size (Lc) of 2000 mm or more is obtained. At this time, blast furnace hot metal is used for the hypereutectic molten pig iron, and iron-making dust, so-called quiche graphite, is used for the product obtained in the cooling process.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, graphite generated in the cooling process of molten pig iron having a hypereutectic composition is used. According to the investigation by the present inventors, such graphite belongs to scaly graphite, and its properties are as shown in Table 1. Table 1 shows the properties of each particle size when refined and sieved so-called quiche graphite, which is produced during the cooling of molten pig iron obtained in the blast furnace ironmaking process. The interlayer distance (d) of graphite is 3.37 mm or less (substantially 3.36 mm or less), and the crystallite size (Lc) is sieved when its particle size is 0.044 mm or more. It was found to be over 2000cm. When considering the correlation between the conventionally known properties of graphite and the characteristic values of the negative electrode material, quiche graphite having such properties has the potential to be an excellent negative electrode material.
[0007]
[Table 1]
[0008]
The reason why Kish graphite exhibits such excellent properties is that graphite crystals grow under the pressure of molten iron while maintaining a certain consistency with high-temperature molten metal, but the exact reason is It is unknown. However, those having a very small particle diameter, specifically those having a particle size of less than 0.044 mm, have a relatively small crystallite size, and it is not possible to improve the characteristics sufficiently as graphite for a lithium secondary battery negative electrode. Since many purification costs are required, in the present invention, only quiche graphite having a particle size of 0.044 mm or more is used as a raw material.
[0009]
Table 2 shows a lithium secondary battery having an average particle size of 0.005 mm or more by purifying the quiche graphite having a particle size of 0.044 mm or more obtained as described above by chemical treatment to 99% or more of C, and crushing and sieving it. It is the result of having obtained the graphite for negative electrodes, and having investigated the characteristic.
As shown here, the scaly graphite obtained from quiche graphite exhibited secondary battery negative electrode material characteristics comparable to the best natural graphite, and surpassed the performance of conventional artificial graphite. This result was first observed for quiche graphite obtained in the ironmaking process with a blast furnace, but it has been confirmed that it is widely recognized in general for quiche graphite obtained in the cooling process of hypereutectic pig iron. . Therefore, as the graphite, besides the quiche graphite obtained in the iron making process, quiche graphite obtained in the cooling process of the hypereutectic molten pig iron can be widely used. Needless to say, it is economical to use quiche graphite generated in the blast furnace ironmaking process in large quantities and at low cost.
[0010]
[Table 2]
[0011]
The product (quiche graphite) as it is contains a lot of impurities, that is, iron and its oxides, silicon (Si), calcium (Ca) and other fine powders of auxiliary materials used for refining in the iron making process. So it is removed and the purity is improved. In general, in order to use it as a negative electrode material, it is necessary to make the C content 99% (weight ratio), so that it is purified by chemical treatment. Chemical treatment includes flotation and treatment with hydrochloric acid and hydrofluoric acid. Therefore, the method described in JP-A No. 63-151609 can be used.
[0012]
The chemically treated quiche graphite is further pulverized by a suitable mill (for example, a ball mill) and sieved. These steps may be performed so that the average particle size is 0.005 mm or more and according to the required characteristics of the negative electrode material for the lithium secondary battery to be used. The reason why the average particle size is not set to less than 0.005 mm is that those having such a particle size are generally unfavorable for the negative electrode material and are inconvenient in handling.
[0013]
Through the above series of steps, graphite having sufficient interlayer distance and crystallite size as graphite for lithium secondary battery negative electrode is obtained. In particular, the characteristics of the graphite that can be provided by the present invention are substantially less than the 3.36 mm interlayer distance and the crystallite size of 2000 mm or more due to the characteristics of quiche graphite as a raw material, and therefore exhibit very excellent negative electrode characteristics. It will be.
[0014]
【The invention's effect】
According to the present invention, the characteristics of the graphite for lithium secondary battery negative electrodes are greatly improved, which greatly contributes to the expansion of use, weight reduction, and long life of lithium secondary batteries. Further, since the graphite according to the present invention is not a natural product, it can be supplied very stably and contributes to stable production of a lithium secondary battery. In addition, effective utilization of quiche graphite, which has been conventionally treated as waste material, can be achieved.
Claims (3)
Priority Applications (1)
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JP11635197A JP3683379B2 (en) | 1997-04-18 | 1997-04-18 | Graphite for negative electrode of lithium secondary battery and method for producing the same |
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JP11635197A JP3683379B2 (en) | 1997-04-18 | 1997-04-18 | Graphite for negative electrode of lithium secondary battery and method for producing the same |
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JPH10294101A JPH10294101A (en) | 1998-11-04 |
JP3683379B2 true JP3683379B2 (en) | 2005-08-17 |
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JP11635197A Expired - Fee Related JP3683379B2 (en) | 1997-04-18 | 1997-04-18 | Graphite for negative electrode of lithium secondary battery and method for producing the same |
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Families Citing this family (5)
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US6456484B1 (en) | 1999-08-23 | 2002-09-24 | Honda Giken Kogyo Kabushiki Kaisha | Electric double layer capacitor |
KR101874490B1 (en) | 2010-08-31 | 2018-08-02 | 가부시키가이샤 아데카 | Nonaqueous electrolyte secondary battery |
CN103597645B (en) * | 2011-06-03 | 2016-08-17 | 科学与工业研究委员会 | Preparation is for the method for the kish lithium insertion negative material of lithium ion battery |
US10403900B2 (en) | 2014-09-09 | 2019-09-03 | Tohoku Techno Arch Co., Ltd. | Method for producing porous graphite, and porous graphite |
CN106450331B (en) * | 2016-10-27 | 2019-02-05 | 萝北奥星新材料有限公司 | The method for preparing graphene conductive agent slurry with graphite tailing |
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1997
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