JP4721038B2 - Negative electrode carbon material for lithium secondary battery, method for producing the same, negative electrode for lithium secondary battery, and lithium secondary battery - Google Patents
Negative electrode carbon material for lithium secondary battery, method for producing the same, negative electrode for lithium secondary battery, and lithium secondary battery Download PDFInfo
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- JP4721038B2 JP4721038B2 JP2004208504A JP2004208504A JP4721038B2 JP 4721038 B2 JP4721038 B2 JP 4721038B2 JP 2004208504 A JP2004208504 A JP 2004208504A JP 2004208504 A JP2004208504 A JP 2004208504A JP 4721038 B2 JP4721038 B2 JP 4721038B2
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- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 title claims description 154
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- FSSPGSAQUIYDCN-UHFFFAOYSA-N 1,3-Propane sultone Chemical compound O=S1(=O)CCCO1 FSSPGSAQUIYDCN-UHFFFAOYSA-N 0.000 description 1
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- LNEPOXFFQSENCJ-UHFFFAOYSA-N haloperidol Chemical compound C1CC(O)(C=2C=CC(Cl)=CC=2)CCN1CCCC(=O)C1=CC=C(F)C=C1 LNEPOXFFQSENCJ-UHFFFAOYSA-N 0.000 description 1
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Classifications
-
- 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
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- Carbon And Carbon Compounds (AREA)
- Secondary Cells (AREA)
- Battery Electrode And Active Subsutance (AREA)
Description
本発明は、リチウム二次電池用負極炭素材料、その製造法、リチウム二次電池用負極及びリチウム二次電池に関する。さらに詳しくは、電気自動車、ハイブリッド型電気自動車、電力貯蔵等に用いるのに好適な、入出力特性、サイクル特性、保存特性に優れたリチウム二次電池とそれを得るための負極及びその製造法に関する。 The present invention relates to a negative electrode carbon material for a lithium secondary battery, a production method thereof, a negative electrode for a lithium secondary battery, and a lithium secondary battery. More particularly, the present invention relates to a lithium secondary battery excellent in input / output characteristics, cycle characteristics, and storage characteristics suitable for use in electric vehicles, hybrid electric vehicles, power storage, and the like, a negative electrode for obtaining the same, and a method for manufacturing the same. .
従来のリチウム二次電池の負極は、種々の有機物を２０００℃以下で焼成して炭素化した低結晶性炭素材料や、種々の有機物を２０００℃以上の温度で黒鉛化した結晶性黒鉛材料、天然黒鉛材料等がある。 A negative electrode of a conventional lithium secondary battery includes a low crystalline carbon material obtained by carbonizing various organic materials by firing at 2000 ° C. or lower, a crystalline graphite material obtained by graphitizing various organic materials at a temperature of 2000 ° C. or higher, natural There are graphite materials.
これらの炭素材料は有機系結着剤及び溶剤と混合して黒鉛ペーストとし、この黒鉛ペーストを銅箔の表面に塗布し、溶剤を乾燥したのちロール等で圧縮加工し、リチウム二次電池用負極として使用されている。 These carbon materials are mixed with an organic binder and a solvent to form a graphite paste. The graphite paste is applied to the surface of the copper foil, and after drying the solvent, it is compressed by a roll or the like, and the negative electrode for a lithium secondary battery. It is used as
例えば、特許文献１には、フラン樹脂を１１００℃で焼成した炭素材料が示されている。 For example, Patent Document 1 discloses a carbon material obtained by firing a furan resin at 1100 ° C.
特許文献２には、アントラセン油、テトラベンゾフェナジン、コールタール、塩化ビニル、塩化ビニリデン、アスファルトピッチ、原油分解ピッチ、コールタールピッチ、石油系コークス、石炭系コークス等の炭素前駆体を１１００〜１７００℃で炭素化した材料が示されている。 Patent Document 2 discloses carbon precursors such as anthracene oil, tetrabenzophenazine, coal tar, vinyl chloride, vinylidene chloride, asphalt pitch, crude oil cracking pitch, coal tar pitch, petroleum coke, and coal coke at 1100 to 1700 ° C. The material carbonized with is shown.
特許文献３には、自己焼結性を有する石油ピッチあるいは炭素質材料を、加圧成形し、次いで炭素化して得られる炭素材料を主として含む負極材料が示されている。
特許文献４には、フェノール樹脂を８００℃で炭素化した粒子の表面に７００℃でトルエンの熱分解により生じた炭素を析出させた材料が示されている。
特許文献５には、負極に黒鉛を使用した二次電池が示されている。
Patent Document 3 discloses a negative electrode material mainly including a carbon material obtained by press-molding a petroleum pitch or carbonaceous material having self-sintering properties and then carbonizing the material.
Patent Document 4 discloses a material in which carbon generated by thermal decomposition of toluene at 700 ° C. is deposited on the surface of particles obtained by carbonizing a phenol resin at 800 ° C.
Patent Document 5 discloses a secondary battery using graphite as a negative electrode.
しかしながら、従来の有機質材料を２０００℃以下の温度で炭素化したリチウム二次電池用負極炭素材料は、初回充放電効率が低く、その結果作製するリチウム二次電池の容量密度が小さくなるばかりでなく、サイクル特性、保存特性に問題がある。
一方、２０００℃以上の温度で黒鉛化された黒鉛材料や天然黒鉛は、初回充放電効率が高く、また、放電容量も３５０Ａｈ／ｋｇ以上の高容量が得られ作製するリチウム二次電池の高容量化には好適である。しかし、黒鉛材料を負極に使用した場合、充放電時に負極が膨張収縮するためサイクル特性が不十分であるばかりでなく、入力特性が劣る問題がある。
そこで、初回充放電効率が高く、サイクル特性、保存特性、入力特性に優れたリチウム二次電池用負極炭素材料が要求されている。
However, a negative electrode carbon material for a lithium secondary battery obtained by carbonizing a conventional organic material at a temperature of 2000 ° C. or lower has a low initial charge / discharge efficiency, and as a result, a capacity density of a lithium secondary battery to be manufactured is not only reduced. There are problems with cycle characteristics and storage characteristics.
On the other hand, a graphite material or natural graphite graphitized at a temperature of 2000 ° C. or higher has high initial charge / discharge efficiency, and a high capacity of a lithium secondary battery produced with a high discharge capacity of 350 Ah / kg or more. It is suitable for conversion. However, when a graphite material is used for the negative electrode, the negative electrode expands and contracts during charge and discharge, so that not only the cycle characteristics are insufficient, but also the input characteristics are inferior.
Therefore, a negative electrode carbon material for a lithium secondary battery having high initial charge / discharge efficiency and excellent cycle characteristics, storage characteristics, and input characteristics is required.
請求項１〜８記載の発明は、初回充放電効率が高く、サイクル特性、保存特性及び入力特性に優れたリチウム二次電池に好適な負極の製造法を提供するものである。 The inventions according to claims 1 to 8 provide a method for producing a negative electrode suitable for a lithium secondary battery having high initial charge / discharge efficiency and excellent cycle characteristics, storage characteristics, and input characteristics.
請求項９〜１２記載の発明は、初回充放電効率が高く、サイクル特性、保存特性及び入力特性に優れたリチウム二次電池に好適な負極炭素材料を提供するものである。 The invention according to claims 9 to 12 provides a negative electrode carbon material suitable for a lithium secondary battery having high initial charge / discharge efficiency and excellent cycle characteristics, storage characteristics, and input characteristics.
請求項１３記載の発明は、初回充放電効率が高く、サイクル特性、保存特性及び入力特性に優れたリチウム二次電池用負極を提供するものである。 The invention of claim 1 3 wherein is to initial charge and discharge efficiency is high, the cycle characteristics, to provide a negative electrode for a rechargeable lithium battery exhibiting good that the storage characteristics and input characteristics.
請求項１４及び１５記載の発明は、初回充放電効率が高く、サイクル特性、保存特性及び入力特性に優れた出力密度２０００Ｗ／ｋｇ以上のリチウム二次電池用負極を提供するものである。 The invention of claim 1 4 and 1 5, wherein is to initial charge and discharge efficiency is high, the cycle characteristics, provides excellent output density 2000 W / kg or more of a lithium secondary battery negative electrode storage characteristics and input characteristics.
請求項１６記載の発明は、初回充放電効率が高く、サイクル特性、保存特性及び入力特性に優れたリチウム二次電池を提供するものである。 The invention according to claim 16 provides a lithium secondary battery having high initial charge / discharge efficiency and excellent cycle characteristics, storage characteristics, and input characteristics.
本発明は、デンプンを含む材料を、酸素を含む雰囲気下で加熱溶融した溶融処理物を作製し、該溶融処理物を焼成して炭素化する工程を含むことを特徴とするリチウム二次電池用負極炭素材料の製造法に関する。 The present invention includes a process for producing a melt-treated product obtained by heating and melting a material containing starch in an oxygen-containing atmosphere , and baking and carbonizing the melt-processed product. The present invention relates to a method for producing a negative electrode carbon material.
また、本発明は、デンプンを含む材料を、酸素を含む雰囲気下で加熱溶融した溶融処理物を作製し、該溶融処理物が固形化するまで加熱攪拌したのち、固形化した溶融処理物を焼成して炭素化する工程を含むことを特徴とするリチウム二次電池用負極炭素材料の製造法に関する。 In the present invention, a melt-treated product obtained by heating and melting a material containing starch in an atmosphere containing oxygen is heated and stirred until the melt-treated product is solidified, and then the solidified melt-treated product is fired. And a process for carbonizing the negative electrode carbon material for a lithium secondary battery.
また、本発明は、デンプンを含む材料を、酸素を含む雰囲気下で加熱溶融した溶融処理物を作製し、該溶融処理物が固形化するまで加熱攪拌したのち、固形化した溶融処理物を粉砕した後に焼成して炭素化する工程を含むことを特徴とするリチウム二次電池用負極炭素材料の製造法に関する。 In the present invention, a melt-treated product obtained by heating and melting a starch-containing material in an oxygen-containing atmosphere is heated and stirred until the melt-treated product is solidified, and then the solidified melt-treated product is pulverized. The present invention relates to a method for producing a negative electrode carbon material for a lithium secondary battery, which includes a step of firing and carbonizing the lithium secondary battery.
また、本発明は、デンプンを含む材料を加熱溶融する温度が、１５０〜５００℃であることを特徴とする前記リチウム二次電池用負極炭素材料の製造法に関する。 The present invention also relates to a method for producing a negative electrode carbon material for a lithium secondary battery, wherein the temperature at which the material containing starch is heated and melted is 150 to 500 ° C.
また、本発明は、焼成して炭素化する温度が、７００〜１７００℃であることを特徴とする前記リチウム二次電池用負極炭素材料の製造法に関する。 The present invention also relates to the above-described method for producing a negative electrode carbon material for a lithium secondary battery, wherein the temperature for firing and carbonizing is 700 to 1700 ° C.
また、本発明は、固形化した溶融処理物を平均粒径１〜５００μｍに粉砕することを特徴とする前記リチウム二次電池用負極炭素材料の製造法に関する。 The present invention also relates to a method for producing a negative electrode carbon material for a lithium secondary battery, wherein the solidified melt-treated product is pulverized to an average particle size of 1 to 500 μm.
また、本発明は、デンプンが、コーンスターチ、ライススターチ及びポテトスターチからなる群の少なくとも１種類以上であることを特徴とする前記リチウム二次電池用負極炭素材料の製造法に関する。 The present invention also relates to a method for producing a negative electrode carbon material for a lithium secondary battery, wherein the starch is at least one member selected from the group consisting of corn starch, rice starch and potato starch.
また、本発明は、デンプンを含む材料として、デンプンの他に、コークス粉末及び／又は黒鉛粉末を含むことを特徴とする前記リチウム二次電池用負極炭素材料の製造法に関する。 The present invention also relates to a method for producing a negative electrode carbon material for a lithium secondary battery, wherein the material containing starch includes coke powder and / or graphite powder in addition to starch.
また、本発明は、前記リチウム二次電池用負極炭素材料の製造法で作製したリチウム二次電池用負極炭素材料の平均粒径が１〜３０μｍであるリチウム二次電池用負極炭素材料に関する。 Moreover, this invention relates to the negative electrode carbon material for lithium secondary batteries whose average particle diameter of the negative electrode carbon material for lithium secondary batteries produced with the manufacturing method of the said negative electrode carbon material for lithium secondary batteries is 1-30 micrometers.
また、本発明は、前記リチウム二次電池用負極炭素材料の製造法で作製したリチウム二次電池用負極炭素材料の比表面積が１０ｍ２／ｇ以下であるリチウム二次電池用負極炭素材料に関する。 Moreover, this invention relates to the negative electrode carbon material for lithium secondary batteries whose specific surface area of the negative electrode carbon material for lithium secondary batteries produced with the manufacturing method of the said negative electrode carbon material for lithium secondary batteries is 10 m < 2 > / g or less.
また、本発明は、前記リチウム二次電池用負極炭素材料の製造法で作製したリチウム二次電池用負極炭素材料の真比重が１．４〜２．１であるリチウム二次電池用負極炭素材料に関する。 Further, the present invention provides a negative electrode carbon material for a lithium secondary battery in which the true specific gravity of the negative electrode carbon material for a lithium secondary battery produced by the method for producing a negative electrode carbon material for a lithium secondary battery is 1.4 to 2.1. About.
また、本発明は、前記リチウム二次電池用負極炭素材料の製造法で作製したリチウム二次電池用負極炭素材料の平均粒径が１〜３０μｍ、比表面積が１０ｍ２／ｇ以下、真比重が１．４〜２．１であるリチウム二次電池用負極炭素材料に関する。 In the present invention, the negative electrode carbon material for a lithium secondary battery produced by the method for producing a negative electrode carbon material for a lithium secondary battery has an average particle diameter of 1 to 30 μm, a specific surface area of 10 m 2 / g or less, and a true specific gravity of It is related with the negative electrode carbon material for lithium secondary batteries which is 1.4-2.1.
また、本発明は、集電体と前記リチウム二次電池用負極炭素材料の製造法で作製したリチウム二次電池用負極炭素材料又は前記リチウム二次電池用負極炭素材料を含んでなる炭素材料層とを一体化してなるリチウム二次電池用負極であって、該負極の炭素材料層の厚さが２０〜５５μｍであるリチウム二次電池用負極に関する。 Moreover, the present invention provides a negative electrode carbon material for a lithium secondary battery or a carbon material layer comprising the negative electrode carbon material for a lithium secondary battery produced by a method for producing a current collector and the negative electrode carbon material for a lithium secondary battery. And a negative electrode for a lithium secondary battery in which the thickness of the carbon material layer of the negative electrode is 20 to 55 μm.
また、本発明は、出力密度が２０００Ｗ／ｋｇ以上のリチウム二次電池に使用する前記リチウム二次電池用負極に関する。 Moreover, this invention relates to the said negative electrode for lithium secondary batteries used for a lithium secondary battery whose output density is 2000 W / kg or more.
また、本発明は、集電体上のリチウム二次電池用負極炭素材料と有機系結着剤を含んでなる層の密度が０．９５〜１．４ｇ／ｃｃである前記リチウム二次電池用負極に関する。 Further, the present invention provides the above lithium secondary battery in which the density of the layer comprising the negative electrode carbon material for a lithium secondary battery on the current collector and the organic binder is 0.95 to 1.4 g / cc. It relates to the negative electrode.
また、本発明は、前記リチウム二次電池用負極と正極とをセパレータを介し対向させて配置されたリチウム電池に関する。 The present invention also relates to a lithium battery in which the negative electrode for a lithium secondary battery and a positive electrode are arranged to face each other with a separator interposed therebetween.
請求項１〜８記載の製造法は、初回充放電効率が高く、サイクル特性、保存特性及び入力特性に優れたリチウム二次電池用炭素材料を製造可能である。 The production methods according to claims 1 to 8 can produce a carbon material for a lithium secondary battery having high initial charge / discharge efficiency and excellent cycle characteristics, storage characteristics, and input characteristics.
請求項９〜１２記載の負極炭素材料は、初回充放電効率が高く、サイクル特性、保存特性及び入力特性に優れたリチウム二次電池に好適である。 The negative electrode carbon material according to any one of claims 9 to 12 is suitable for a lithium secondary battery having high initial charge and discharge efficiency and excellent cycle characteristics, storage characteristics, and input characteristics.
請求項１３記載のリチウム二次電池用負極は、初回充放電効率が高く、サイクル特性、保存特性及び入力特性に優れる。 Claim 1 3 The negative electrode for a lithium secondary battery according the high initial charge and discharge efficiency, excellent cycle characteristics, storage characteristics and input characteristics.
請求項１４及び１５記載のリチウム二次電池用負極は、初回充放電効率が高く、サイクル特性、保存特性及び入力特性に優れ、２０００Ｗ／ｋｇ以上の出力密度を得るのに有用である。 Claim 1 4 and 1 5 a negative electrode for lithium secondary battery according the high initial charge and discharge efficiency, excellent cycle characteristics, storage characteristics and input characteristics are useful for obtaining a power density of more than 2000 W / kg.
請求項１６記載のリチウム二次電池は、初回充放電効率が高く、サイクル特性、保存特性及び入力特性に優れる。 The lithium secondary battery according to claim 16 has high initial charge / discharge efficiency and is excellent in cycle characteristics, storage characteristics, and input characteristics.
本発明のリチウム二次電池用負極炭素材料の製造法は、デンプンを含む材料を、酸素を含む雰囲気下で加熱溶融した溶融処理物を作製し、該溶融処理物を焼成して炭素化する工程を含むことを特徴とする。
The method for producing a negative electrode carbon material for a lithium secondary battery according to the present invention includes a step of producing a melt-treated product obtained by heating and melting a material containing starch in an oxygen-containing atmosphere , and firing and carbonizing the melt-treated product. It is characterized by including.
デンプンを含む材料は、例えば、植物、穀物等から得られるデンプンが含まれることが好ましい。中でも穀物から得られるデンプンが好ましく、例えば、米類、豆類、いも類等から得られるデンプンが好ましい。
また、デンプンを含む材料としては、前記穀物を原料として作製したデンプンが好ましい。デンプンは、一般に食用、工業用等に使用されるデンプンが使用できる。
本発明で使用するデンプンとしては、例えば、米、もち米等を由来とするデンプン（いわゆるライススターチ）、トウモロコシ等を由来とするデンプン（いわゆるコーンスターチ）、じゃがいも等を由来とするデンプン（いわゆるポテトスターチ）が好ましく、初回充放電効率の点でコーンスターチが特に好ましい。
The starch-containing material preferably includes, for example, starch obtained from plants, grains and the like. Among them, starch obtained from cereals is preferable, and for example, starch obtained from rice, beans, potatoes and the like is preferable.
Moreover, as a material containing starch, the starch produced using the said grain as a raw material is preferable. As the starch, starch that is generally used for food, industry, etc. can be used.
Examples of the starch used in the present invention include starch derived from rice, glutinous rice, etc. (so-called rice starch), starch derived from corn, etc. (so-called corn starch), starch derived from potato, etc. (so-called potato starch) ) Is preferred, and corn starch is particularly preferred from the viewpoint of initial charge / discharge efficiency.
デンプンを含む材料は、デンプン単独でも良く、デンプンとデンプン以外の炭素化可能な材料又は炭素とともに使用することも可能である。デンプン以外の材料としては、例えば、フェノール樹脂、エポキシ樹脂、フラン樹脂等の熱硬化性樹脂、熱可塑性樹脂、ゴム、ピッチ、コールタール、これらの炭化物、コークス、黒鉛などが挙げられる。 The material containing starch may be starch alone, or may be used together with a carbonizable material or carbon other than starch and starch. Examples of materials other than starch include thermosetting resins such as phenol resins, epoxy resins, and furan resins, thermoplastic resins, rubber, pitch, coal tar, carbides thereof, coke, and graphite.
デンプン以外の炭素化可能な材料又は炭素は、焼成して炭素化してリチウム二次電池用負極炭素材料にした際に、炭素化後のデンプンの真比重より大きいものが作製するリチウム二次電池用負極炭素材料の体積当りの放電容量の点で好ましい。 For carbon materials that can be carbonized other than starch, or for carbon materials that are carbonized and calcined to produce a negative carbon material for lithium secondary batteries, a material that is larger than the true specific gravity of starch after carbonization is produced. This is preferable in terms of discharge capacity per volume of the negative electrode carbon material.
炭素化後のデンプンの真比重より大きいものとしては、例えば、熱可塑性樹脂、コールタール、ピッチ、コークス等の焼成物、黒鉛などが挙げられ、コークス、黒鉛の粉末が好ましい。
また、コークス粉末及び／又は黒鉛粉末の好ましい真比重は、１．９５〜２．２６である。該粉末の粒径は、平均粒径１〜３０μmが好ましく、３〜２０μmがより好ましく、５〜１５μmがさらに好ましい。また、該粉末の表面全て又は一部にデンプンが付着していることが好ましい。
Examples of the starch having a higher specific gravity than the carbonized starch include a thermoplastic resin, a fired product such as coal tar, pitch, coke, and graphite, and coke and graphite powder are preferable.
Moreover, the preferable true specific gravity of coke powder and / or graphite powder is 1.95-2.26. The average particle size of the powder is preferably 1 to 30 μm, more preferably 3 to 20 μm, and even more preferably 5 to 15 μm. Moreover, it is preferable that starch adheres to all or a part of the surface of the powder.
デンプンとデンプン以外の炭素化可能な材料又は炭素をともに使用する場合は、デンプンを少なくとも１重量％以上含むことが好ましく、１〜８５重量％含むことがより好ましく、３〜８５重量％含むことがさらに好ましく、５〜７５重量％含むことが特に好ましく、５〜６０重量％含むことが最も好ましい。１重量％未満では、作製するリチウム二次電池の急速充電特性が低下する。 When both starch and a carbonizable material other than starch or carbon are used, it is preferable to contain at least 1% by weight of starch, more preferably 1 to 85% by weight, and more preferably 3 to 85% by weight. More preferably, it is particularly preferably 5 to 75% by weight, and most preferably 5 to 60% by weight. If it is less than 1% by weight, the rapid charge characteristics of the lithium secondary battery to be produced are deteriorated.
デンプンを含む材料は、一部にデキストリンが含まれることが好ましい。デキストリンは、例えば、デンプンを分解することで作製することができる。デンプンを含む材料の一部にデキストリンが含まれることで、作製するリチウム二次電池用負極炭素材料の放電容量が大きくなる傾向がある。デキストリンを含むデンプンの作製方法は、例えば、前記のデンプンを含む材料を酸化性雰囲気で熱処理すること等で作製することができる。 The material containing starch preferably contains dextrin in part. Dextrins can be made, for example, by decomposing starch. When dextrin is contained in a part of the material containing starch, the discharge capacity of the negative electrode carbon material for a lithium secondary battery to be produced tends to increase. A method for producing starch containing dextrin can be produced by, for example, heat-treating the above-mentioned material containing starch in an oxidizing atmosphere.
デンプンを含む材料に含まれる金属不純物は灰分として、５％以下が好ましく、１％以下がより好ましく、０．１％以下がさらに好ましい。金属不純物は、炭素化後も残存しやすいため、あらかじめ金属不純物が少ない材料を使用することが好ましい。デンプンを含む植物や穀物等を直接使用するよりも、例えば、植物や穀物等を原料に作製したデンプンを使用すれば、作製するリチウム二次電池用負極炭素材料の金属不純物を減らすことが可能となる。ここで、金属不純物は、試料を空気雰囲気中、８００℃程度で恒量となるまで電気炉中で加熱し灰化した後の残渣重量から、加熱し灰化する前の試料全体量に対する灰分として算出した値である。 The metal impurity contained in the material containing starch is preferably 5% or less, more preferably 1% or less, and further preferably 0.1% or less as ash. Since metal impurities are likely to remain after carbonization, it is preferable to use a material with few metal impurities in advance. Rather than using starch-containing plants and grains directly, for example, if starch produced from plants or grains is used as a raw material, it is possible to reduce metal impurities in the anode carbon material for lithium secondary batteries to be produced Become. Here, the metal impurities are calculated as the ash content relative to the total amount of the sample before heating and ashing from the weight of the residue after ashing by heating in the electric furnace until the sample becomes constant at about 800 ° C. in an air atmosphere. It is a value.
なお、デンプンを含む材料を加熱溶融した溶融処理物とは、加熱によりデンプンを含む材料を溶解し液状化した状態、軟化した状態、これらの状態からさらに固化した状態等、加熱により形状変化した状態を言う。 The melt-processed product obtained by heating and melting a material containing starch is a state in which the material containing starch is dissolved and liquefied by heating, a softened state, a state solidified from these states, etc. Say.
デンプンを含む材料を加熱溶融する温度は１５０〜５００℃が好ましい。また、１５０〜４００℃が好ましく、１５０〜３５０℃がより好ましく、１８０〜３００℃がさらに好ましく、２００〜２８０℃が特に好ましい。加熱溶融する温度が１５０℃未満又は５００℃を超えると、作製するリチウム二次電池の初回充放電効率が低下する傾向がある。また、デンプンを含む材料を加熱溶融する方法としては、例えば、ニーダー等で攪拌しながら加熱することが挙げられる。静置した状態で加熱するとデンプンが発泡しやすく、デンプンが発泡すると、作製するリチウム二次電池の初回充放電効率が低下する傾向がある。 As for the temperature which heat-melts the material containing starch, 150-500 degreeC is preferable. Moreover, 150-400 degreeC is preferable, 150-350 degreeC is more preferable, 180-300 degreeC is further more preferable, 200-280 degreeC is especially preferable. When the temperature for heating and melting is less than 150 ° C. or exceeds 500 ° C., the initial charge / discharge efficiency of the lithium secondary battery to be produced tends to decrease. Moreover, as a method of heating and melting a material containing starch, for example, heating while stirring with a kneader or the like can be mentioned. When heated in a stationary state, starch tends to foam, and when starch foams, the initial charge / discharge efficiency of the lithium secondary battery to be produced tends to decrease.
また、加熱溶融時の雰囲気としては、酸素を含む雰囲気であることが好ましく、酸素濃度が１体積％以上であることが好ましく、１０体積％以上であればより好ましく、２０体積％以上であればさらに好ましい。酸素を含む雰囲気としては、各種ガスを所定の濃度に調整してもよく、また、空気中でもよく、水分を含んでいてもよい。酸素濃度が１体積％未満であると、作製するリチウム二次電池の充放電容量が低下する傾向がある。 The atmosphere at the time of heating and melting is preferably an atmosphere containing oxygen, the oxygen concentration is preferably 1% by volume or more, more preferably 10% by volume or more, and 20% by volume or more. Further preferred. As the atmosphere containing oxygen, various gases may be adjusted to a predetermined concentration, or may be in air or may contain moisture. When the oxygen concentration is less than 1% by volume, the charge / discharge capacity of the lithium secondary battery to be produced tends to decrease.
また、１５０〜５００℃で加熱溶融する時間は特に制限は無いが、溶融処理物が加熱状態において固形化するまで加熱撹拌することが好ましい。加熱状態で固形化する前に加熱を止めると、作製するリチウム二次電池の充放電容量が低下するばかりでなく、初回充放電効率が低下する傾向がある。 The time for heating and melting at 150 to 500 ° C. is not particularly limited, but it is preferable to heat and stir until the melted product is solidified in the heated state. If the heating is stopped before solidification in the heated state, not only the charge / discharge capacity of the lithium secondary battery to be produced is lowered, but also the initial charge / discharge efficiency tends to be lowered.
固形化した溶融処理物は粉砕することが好ましく、さらに、冷却した後粉砕することがより好ましい。なお、冷却方法は特に制限は無く、例えば、強制的に冷却しても良く、自然放冷でも良い。粉砕方法としては、例えば、ピンミル、ジェットミル、ボールミル、ハンマーミル、カッターミル等の衝撃粉砕方式、水等の液体中で粉砕する湿式粉砕、冷却しながら粉砕する凍結粉砕などによって行うことが可能である。
粉砕は、デンプンを含む材料の溶融処理物を焼成して炭素化した後に行うことも可能であるが、焼成して炭素化する前に平均粒径１〜５００μｍに粉砕しておくほうが、作製するリチウム二次電池の初回充放電効率の点で好ましい。また、粉砕後の平均粒径は、１〜１００μｍが好ましく、１〜５０μｍがより好ましく、１〜３０μｍがさらに好ましく、３〜２０μｍであれば特に好ましく、５〜１６μｍであれば最も好ましい。
The solidified melt-treated product is preferably pulverized, and more preferably pulverized after cooling. In addition, there is no restriction | limiting in particular in the cooling method, For example, you may cool forcibly and natural cooling may be sufficient. As the pulverization method, for example, an impact pulverization method such as a pin mill, jet mill, ball mill, hammer mill, cutter mill, etc., wet pulverization in a liquid such as water, freeze pulverization in which cooling is performed can be performed. is there.
The pulverization can be performed after the melt-processed material of the starch-containing material is baked and carbonized, but it is produced by pulverizing to an average particle diameter of 1 to 500 μm before calcination and carbonization. It is preferable in terms of the initial charge / discharge efficiency of the lithium secondary battery. Moreover, 1-100 micrometers is preferable, as for the average particle diameter after a grinding | pulverization, 1-50 micrometers is more preferable, 1-30 micrometers is more preferable, It is especially preferable if it is 3-20 micrometers, and it is most preferable if it is 5-16 micrometers.
デンプンを含む材料を加熱溶融した溶融処理物を焼成して炭素化する温度は、７００〜１７００℃で行うことが好ましい。また、９００〜１６００℃がより好ましく、１０００〜１５００℃がさらに好ましく、１１００〜１４００℃が特に好ましい。焼成して炭素化する温度が７００℃未満では、作製するリチウム二次電池用負極炭素材料の第一サイクル目の充放電効率が低下するばかりでなく、作製するリチウム二次電池の出力特性が低下する傾向がある。１７００℃を超えると作製するリチウム二次電池用負極炭素材料の放電容量が小さくなる傾向がある。 The temperature at which the melt-treated product obtained by heating and melting the material containing starch is baked and carbonized is preferably 700 to 1700 ° C. Moreover, 900-1600 degreeC is more preferable, 1000-1500 degreeC is further more preferable, and 1100-1400 degreeC is especially preferable. If the temperature for firing and carbonization is less than 700 ° C, not only the charge / discharge efficiency of the first cycle of the negative electrode carbon material for the lithium secondary battery to be produced is lowered, but also the output characteristics of the produced lithium secondary battery are lowered. Tend to. When the temperature exceeds 1700 ° C., the discharge capacity of the negative electrode carbon material for a lithium secondary battery to be produced tends to be small.
焼成して炭素化する時の雰囲気は非酸化性雰囲気中で行うことが好ましく、非酸化性雰囲気とは、例えば、窒素ガス雰囲気、アルゴンガス雰囲気、炭素化する材料をコークスや砂等で囲い加熱することで得られる自己揮発性ガス雰囲気などがあげられる。
焼成して炭素化する時の昇温速度は、０．１〜２０００℃／時間が好ましく、１〜１０００℃／時間がより好ましく、１０〜５００℃／時間がさらに好ましい。昇温速度が０．１℃／時間未満であると作製するリチウム二次電池用負極炭素材料の第一サイクル目の充放電効率が低下する傾向がある。２０００℃／時間を超えると作製するリチウム二次電池用負極炭素材料の放電容量が低下する傾向がある。
The atmosphere when firing and carbonizing is preferably performed in a non-oxidizing atmosphere. The non-oxidizing atmosphere is, for example, a nitrogen gas atmosphere, an argon gas atmosphere, or a material to be carbonized surrounded by coke or sand and heated. The self-volatile gas atmosphere obtained by doing is mention | raise | lifted.
The rate of temperature rise when firing and carbonizing is preferably from 0.1 to 2000 ° C / hour, more preferably from 1 to 1000 ° C / hour, and even more preferably from 10 to 500 ° C / hour. When the rate of temperature increase is less than 0.1 ° C./hour, the charge / discharge efficiency of the first cycle of the negative electrode carbon material for a lithium secondary battery to be produced tends to decrease. When it exceeds 2000 ° C./hour, the discharge capacity of the negative electrode carbon material for a lithium secondary battery to be produced tends to decrease.
上記の如く炭素化した後、必要に応じて粉砕又は解砕する。炭素化後、得られた粒子同士が凝集しない場合や、得られた粒子同士の凝集又は固化が少ない場合は粉砕又は解砕をしなくても良い。また、必要に応じて篩い処理、風力分級等を行うことが好ましい。 After carbonization as described above, it is pulverized or crushed as necessary. After carbonization, when the obtained particles do not aggregate or when there is little aggregation or solidification of the obtained particles, crushing or crushing is not necessary. Moreover, it is preferable to perform a sieving process, an air classification, etc. as needed.
本発明のリチウム二次電池用負極炭素材料の平均粒径は、１〜３０μｍが好ましく、３〜２５μｍがより好ましく、５〜２５μｍがさらに好ましく、８〜２０μｍが特に好ましい。平均粒径が１μｍ未満であると、作製する負極に多くの結着剤が必要になり、その結果、作製するリチウム二次電池の入力特性、サイクル特性が低下する傾向がある。また、平均粒径が３０μｍを超えると出力特性が低下する傾向がある。また、本発明のリチウム二次電池用負極炭素材料の９０％累積粒径は５０μｍ以下が好ましく、４０μｍ以下がより好ましく、３０μｍ以下が特に好ましい。９０％累積粒径が５０μｍを超えると、集電体上に塗布するときの作業性が低下する傾向がある。 1-30 micrometers is preferable, as for the average particle diameter of the negative electrode carbon material for lithium secondary batteries of this invention, 3-25 micrometers is more preferable, 5-25 micrometers is more preferable, and 8-20 micrometers is especially preferable. If the average particle size is less than 1 μm, a large amount of binder is required for the negative electrode to be produced, and as a result, the input characteristics and cycle characteristics of the lithium secondary battery to be produced tend to deteriorate. Further, when the average particle size exceeds 30 μm, the output characteristics tend to be lowered. In addition, the 90% cumulative particle size of the negative electrode carbon material for a lithium secondary battery of the present invention is preferably 50 μm or less, more preferably 40 μm or less, and particularly preferably 30 μm or less. When the 90% cumulative particle size exceeds 50 μm, workability when applied on the current collector tends to be lowered.
本発明のリチウム二次電池用負極炭素材料の平均粒径及び累積９０％粒径は、例えば、水中に粉末を分散させた分散液をレーザー回折式粒度分布計で測定することができる。 The average particle size and the cumulative 90% particle size of the negative electrode carbon material for lithium secondary batteries of the present invention can be measured, for example, with a laser diffraction particle size distribution meter in a dispersion in which powder is dispersed in water.
本発明のリチウム二次電池用負極炭素材料は、比表面積が１０ｍ２／ｇ以下であることが好ましく、０．１〜６ｍ２／ｇであればより好ましく、０．１〜５ｍ２／ｇであればさらに好ましい。比表面積が０．１ｍ２／ｇ未満であると、作製するリチウム二次電池の出力特性が低下する傾向がある。１０ｍ２／ｇを超えると作製するリチウム二次電池の保存特性が低下する傾向がある。なお、比表面積は、例えば、試料を２００℃で真空乾燥した後、窒素ガス吸着によるＢＥＴ５点法によって測定することができる。 Negative electrode carbon material for a lithium secondary battery of the present invention preferably has a specific surface area of less 10 m 2 / g, more preferably if 0.1~6m 2 / g, with 0.1 to 5 m 2 / g More preferably. When the specific surface area is less than 0.1 m 2 / g, the output characteristics of the produced lithium secondary battery tend to be reduced. If it exceeds 10 m 2 / g, the storage characteristics of the produced lithium secondary battery tend to be reduced. The specific surface area can be measured, for example, by the BET 5-point method by nitrogen gas adsorption after the sample is vacuum dried at 200 ° C.
また、本発明のリチウム二次電池用負極炭素材料の真比重は１．４〜２．１が好ましく、１．４５〜１．９がより好ましく、１．５〜１．８がさらに好ましい。真比重が１．４未満であると作製するリチウム二次電池の初回充放電効率が低下する傾向があり、２．１を超えるとサイクル特性が低下する傾向がある。なお、真比重は、例えば、ＪＩＳ−Ｒ−７２１２に規定されるブタノール置換法によって測定することができる。 Moreover, 1.4-2.1 are preferable, as for the true specific gravity of the negative electrode carbon material for lithium secondary batteries of this invention, 1.45-1.9 are more preferable, and 1.5-1.8 are further more preferable. When the true specific gravity is less than 1.4, the initial charge / discharge efficiency of the lithium secondary battery to be produced tends to decrease, and when it exceeds 2.1, the cycle characteristics tend to decrease. In addition, true specific gravity can be measured by the butanol substitution method prescribed | regulated to JIS-R-7212, for example.
また、本発明のリチウム二次電池用負極炭素材料は、励起波長５３２ｎｍのレーザーラマン分光測定において、１３００〜１４００ｃｍ−１と１５５０〜１６５０ｃｍ−１にピークが観測され、高い結晶性を有するグラファイト構造に関連する１５５０〜１６５０ｃｍ−１のピークトップ強度ＩＧと結晶構造の乱れや低結晶成分の増減に関連する１３００〜１４００ｃｍ−１のピークトップ強度ＩＤの強度比ＩＤ／ＩＧが０．２〜１．５であることが好ましく、０．３〜１．０であればより好ましく、０．４〜０．９であればさらに好ましい。強度比ＩＤ／ＩＧが０．２未満であると作製するリチウム二次電池の放電容量が低下する傾向があり、１．５を超えると出力特性、初回充放電効率が低下する傾向がある。 The negative electrode carbon material for a lithium secondary battery of the present invention, in the laser Raman spectrometry excitation wavelength 532 nm, peaks were observed at 1300～1400Cm -1 and 1550～1650Cm -1, the graphite structure with high crystallinity associated intensity ratio ID / IG of the peak top intensity ID of 1300～1400Cm -1 related to increase or decrease the turbulence and low crystalline component peak top intensities IG and crystal structure of 1550～1650Cm -1 is 0.2 to 1.5 Preferably, it is 0.3 to 1.0, more preferably 0.4 to 0.9. When the intensity ratio ID / IG is less than 0.2, the discharge capacity of the lithium secondary battery to be produced tends to decrease, and when it exceeds 1.5, the output characteristics and the initial charge / discharge efficiency tend to decrease.
本発明のリチウム二次電池用負極炭素材料は、例えば、有機系結着剤及び溶剤と混練して、ペースト状にし、シート状、ペレット状等の形状に成形され、リチウム電池負極として使用される。
有機系結着剤としては、例えば、ポリエチレン、ポリプロピレン、エチレンプロピレンターポリマー、ブタジエンゴム、スチレンブタジエンゴム、ブチルゴム、イオン伝導率の大きな高分子化合物等を使用することができる。
前記イオン伝導率の大きな高分子化合物としては、例えば、ポリフッ化ビニリデン、ポリエチレンオキサイド、ポリエピクロルヒドリン、ポリファスファゼン、ポリアクリロニトリル等を使用することができる。
The negative electrode carbon material for a lithium secondary battery of the present invention is used, for example, as a lithium battery negative electrode by kneading with an organic binder and a solvent to form a paste, a sheet, a pellet or the like. .
As the organic binder, for example, polyethylene, polypropylene, ethylene propylene terpolymer, butadiene rubber, styrene butadiene rubber, butyl rubber, a polymer compound having a high ion conductivity, or the like can be used.
Examples of the polymer compound having a high ionic conductivity include polyvinylidene fluoride, polyethylene oxide, polyepichlorohydrin, polyphasphazene, polyacrylonitrile, and the like.
本発明のリチウム二次電池用負極炭素材料と有機系結着剤との混合比率は、炭素材料１００重量部に対して、有機系結着剤を０．５〜２０重量部用いることが好ましい。
溶剤としては、例えば、Ｎ−メチル−２−ピロリドン、ジメチルホルムアミド、イソプロパノール、水等が挙げられる。溶剤として水を使用する結着剤の場合は、増粘剤を併用することが好ましい。
The mixing ratio of the negative electrode carbon material for a lithium secondary battery of the present invention and the organic binder is preferably 0.5 to 20 parts by weight of the organic binder with respect to 100 parts by weight of the carbon material.
Examples of the solvent include N-methyl-2-pyrrolidone, dimethylformamide, isopropanol, water and the like. In the case of a binder that uses water as a solvent, it is preferable to use a thickener together.
本発明のリチウム二次電池用負極炭素材料は、例えば、有機系結着剤及び溶剤と混練し、粘度を調整した後、集電体に塗布し、該集電体と本発明のリチウム二次電池用負極炭素材料を含む炭素材料層とを一体化して負極とされる。集電体としては、例えば、ニッケル、銅等の箔、メッシュ等の金属集電体などを使用することができる。なお、一体化は、例えば、ロール、プレス等の成形法で行うことができ、また、これらを組み合わせて一体化しても良い。 The negative electrode carbon material for a lithium secondary battery of the present invention is, for example, kneaded with an organic binder and a solvent, adjusted in viscosity, and then applied to a current collector, and then the current collector and the lithium secondary material of the present invention. A carbon material layer containing a negative electrode carbon material for a battery is integrated into a negative electrode. As the current collector, for example, a foil such as nickel or copper, or a metal current collector such as a mesh can be used. The integration can be performed by a molding method such as a roll or a press, or may be integrated by combining them.
また、本発明のリチウム二次電池用負極炭素材料は、単独でリチウム二次電池用負極を構成することができるが、本発明のリチウム二次電池用負極炭素材料以外の材料と混合して使用することもできる。本発明のリチウム二次電池用負極炭素材料以外の材料は、例えば、カーボンブラック、コークス、黒鉛、金属微粉、金属担持炭素材等が挙げられ、導電性を有する材料又はリチウムを電気化学的に吸蔵・放出する材料が好ましい。これらの平均粒径は２０μｍ以下であることが好ましく、１０μｍ以下がより好ましい。平均粒径が２０μｍを超えると、作製するリチウム二次電池の出力特性が低下する傾向がある。また、混合量としては、本発明のリチウム二次電池用負極炭素材料の全体量に対して０．１〜８０重量％が好ましく、１〜５０重量％がより好ましい。 Moreover, the negative electrode carbon material for lithium secondary batteries of the present invention can be used alone to constitute a negative electrode for lithium secondary batteries, but is used by mixing with materials other than the negative electrode carbon material for lithium secondary batteries of the present invention. You can also Examples of the material other than the negative electrode carbon material for a lithium secondary battery of the present invention include carbon black, coke, graphite, metal fine powder, metal-supported carbon material, and the like. -Material to be released is preferred. These average particle diameters are preferably 20 μm or less, and more preferably 10 μm or less. When the average particle size exceeds 20 μm, the output characteristics of the lithium secondary battery to be manufactured tend to be lowered. Moreover, as a mixing amount, 0.1 to 80 weight% is preferable with respect to the whole quantity of the negative electrode carbon material for lithium secondary batteries of this invention, and 1 to 50 weight% is more preferable.
本発明のリチウム二次電池用負極炭素材へのリチウム二次電池用負極炭素材料以外の材料の混合方法としては、例えば、リチウム二次電池用負極炭素材料とそれ以外の材料を粉体同士で事前に混合してから、有機系結着剤及び溶剤を混合する方法、本発明のリチウム二次電池用負極炭素材料と有機系結着剤及び溶剤を混合する際に同時に混合する方法等が挙げられる。 Examples of the method of mixing materials other than the negative electrode carbon material for lithium secondary battery into the negative electrode carbon material for lithium secondary battery of the present invention include, for example, a negative electrode carbon material for lithium secondary battery and other materials in powder form. A method of mixing the organic binder and the solvent after mixing in advance, a method of mixing the negative electrode carbon material for the lithium secondary battery of the present invention, the organic binder and the solvent at the same time, etc. It is done.
本発明のリチウム二次電池用負極は、集電体上のリチウム二次電池用負極炭素材料を含む炭素材料層の厚みが２０〜５５μｍであることが好ましく、２０〜５０μｍであればより好ましく、２５〜４０μｍであればさらに好ましい。前記炭素材料層の厚みが２０μｍ未満では作製するリチウム二次電池のエネルギー密度が低下する傾向があり、５５μｍを超えると作製するリチウム二次電池の入出力特性が低下する傾向がある。
また、本発明のリチウム二次電池用負極は、前記層の密度が０．９５〜１．５０ｇ／ｃｃであることが好ましく、１．００〜１．４５ｇ／ｃｃであればより好ましく、１．００〜１．４０ｇ／ｃｃであればさらに好ましい。前記層の密度が０．９５ｇ／ｃｃ未満又は１．５０ｇ／ｃｃを超えると作製するリチウム二次電池の入出力特性が低下する傾向がある。
In the negative electrode for lithium secondary battery of the present invention, the thickness of the carbon material layer containing the negative electrode carbon material for lithium secondary battery on the current collector is preferably 20 to 55 μm, more preferably 20 to 50 μm, More preferably, it is 25-40 micrometers. When the thickness of the carbon material layer is less than 20 μm, the energy density of the lithium secondary battery to be manufactured tends to decrease, and when it exceeds 55 μm, the input / output characteristics of the lithium secondary battery to be manufactured tend to decrease.
In the negative electrode for a lithium secondary battery of the present invention, the density of the layer is preferably 0.95 to 1.50 g / cc, more preferably 1.00 to 1.45 g / cc. More preferably, it is 00-1.40 g / cc. When the density of the layer is less than 0.95 g / cc or more than 1.50 g / cc, the input / output characteristics of the lithium secondary battery to be manufactured tend to be lowered.
このようにして得られたリチウム二次電池用負極は、例えば、リチウム化合物を含む正極とともに、本発明のリチウム二次電池に用いられる。
リチウム二次電池は、例えば、正極と負極とをセパレータを介して対向して配置し、かつ電解液を注入することにより得ることができる。これは従来の負極を使用したリチウム二次電池に比較して、初回充放電効率が高く、サイクル特性、保存特性及び入力特性に優れる。
The negative electrode for a lithium secondary battery thus obtained is used for the lithium secondary battery of the present invention together with a positive electrode containing a lithium compound, for example.
A lithium secondary battery can be obtained, for example, by arranging a positive electrode and a negative electrode to face each other with a separator interposed therebetween and injecting an electrolytic solution. This has higher initial charge / discharge efficiency and superior cycle characteristics, storage characteristics, and input characteristics as compared with a lithium secondary battery using a conventional negative electrode.
本発明のリチウム二次電池用負極は、出力密度が２０００Ｗ／ｋｇ以上で使用されるリチウム二次電池に使用することが好ましい。本発明の負極を使用した出力密度２０００Ｗ／ｋｇ以上のリチウム二次電池は、初期出力が高いばかりでなく、高い出力密度を持続することが可能であり、かつ、サイクル特性及び保存特性が特に優れる。
本発明におけるリチウム二次電池の正極はリチウム化合物を含むが、その材料に特に制限はなく、例えば、ＬｉＮｉＯ２、ＬｉＣｏＯ２、ＬｉＭｎ２Ｏ４等を単独で又は２種以上を組み合わせて使用することができる。また、それぞれＮｉ、Ｃｏ，Ｍｎ元素を異種元素に置換したものでも良い。
The negative electrode for a lithium secondary battery of the present invention is preferably used for a lithium secondary battery used at an output density of 2000 W / kg or more. A lithium secondary battery having an output density of 2000 W / kg or more using the negative electrode of the present invention not only has a high initial output, but also can maintain a high output density, and is particularly excellent in cycle characteristics and storage characteristics. .
The positive electrode of the lithium secondary battery in the present invention contains a lithium compound, but the material is not particularly limited. For example, LiNiO 2 , LiCoO 2 , LiMn 2 O 4, etc. may be used alone or in combination of two or more. Can do. Further, Ni, Co, and Mn elements may be substituted with different elements.
本発明におけるリチウム二次電池は、正極及び負極とともに、通常リチウム化合物を含む電解液を含む。
電解液としては、ＬｉＣｌＯ４、ＬｉＰＦ６、ＬｉＡｓＦ、ＬｉＢＦ４、ＬｉＳＯ３ＣＦ４等のリチウム塩を、例えば、エチレンカーボネート、プロピレンカーボネート、ジエチルカーボネート、ジメトキシエタン、ジメチルカーボネート、メチルエチルカーボネート、テトラヒドロフラン等の非水系溶剤に溶かしたいわゆる有機電解液や、固体若しくはゲル状のいわゆるポリマー電解質などを使用することができる。また、電解液には、リチウム二次電池の初回充電時に分解反応を示す添加剤を少量添加することが好ましい。このような添加剤としては、例えば、ビニレンカーボネート、ビフェニール、プロパンスルトン等が挙げられ、添加量としては０．０１〜５重量％が好ましい。
セパレータとしては、例えば、ポリエチレン、ポリプロピレン等のポリオレフィンを主成分とした不織布、クロス、微孔フィルム又はそれらを組み合わせたものなどを使用することができる。なお、作製するリチウム二次電池の正極と負極が直接接触しない構造にした場合は、セパレータを使用する必要はない。
The lithium secondary battery in this invention contains the electrolyte solution which contains a lithium compound normally with a positive electrode and a negative electrode.
Examples of the electrolyte include lithium salts such as LiClO 4 , LiPF 6 , LiAsF, LiBF 4 , LiSO 3 CF 4 , such as ethylene carbonate, propylene carbonate, diethyl carbonate, dimethoxyethane, dimethyl carbonate, methyl ethyl carbonate, and tetrahydrofuran. A so-called organic electrolytic solution dissolved in a non-aqueous solvent or a so-called polymer electrolyte in a solid or gel form can be used. Moreover, it is preferable to add a small amount of an additive that exhibits a decomposition reaction when the lithium secondary battery is initially charged to the electrolytic solution. Examples of such additives include vinylene carbonate, biphenyl, propane sultone, and the addition amount is preferably 0.01 to 5% by weight.
As the separator, for example, a nonwoven fabric, a cloth, a microporous film, or a combination thereof having a polyolefin as a main component such as polyethylene or polypropylene can be used. In addition, when it is set as the structure where the positive electrode and negative electrode of a lithium secondary battery to produce are not in direct contact, it is not necessary to use a separator.
以下、本発明の実施例を説明する。
（実施例１）
コーンスターチを２７０℃のニーダーによって攪拌しながら溶融させ、溶融したコーンスターチが固形化するまで加熱攪拌した。次いで、ジェットミルで粉砕し、平均粒径１３μｍ、累積９０％粒径２９μｍの粉末を得た。なお、本実施例及び比較例での平均粒径及び累積９０％粒径は、レーザー回折式粒度分布計（株式会社島津製作所 製品名ＳＡＬＤ−３０００）を用い、５０％Ｄでの粒子径を平均粒径とし、９０％Ｄでの粒子径を累積９０％粒径とした。また、得られた粉末の、窒素ガス吸着によるＢＥＴ５点法で測定した比表面積は０．９ｍ２／ｇであった（マイクロメリテックス社製 製品名ＡＳＡＰ２０１０）。該粉末の金属不純物は灰分で０．０３％であった。本実施例及び比較例における金属不純物は得られた粉末を空気雰囲気中、８００℃で恒量となるまで電気炉中で加熱し灰下した後の残渣量から灰分として算出した。
該粉末を、窒素雰囲気で、昇温速度３００℃／時間で１３００℃まで昇温し、１時間保持した。次いで、３００メッシュの篩を通して、リチウム二次電池用負極炭素材料を作製した。
Examples of the present invention will be described below.
Example 1
The corn starch was melted with stirring by a 270 ° C. kneader and heated and stirred until the melted corn starch solidified. Subsequently, it was pulverized by a jet mill to obtain a powder having an average particle size of 13 μm and a cumulative 90% particle size of 29 μm. In addition, the average particle diameter and the cumulative 90% particle diameter in this example and the comparative example are obtained by using a laser diffraction particle size distribution meter (product name: SALD-3000, Ltd.) and averaging the particle diameter at 50% D. The particle size at 90% D was the cumulative 90% particle size. Moreover, the specific surface area of the obtained powder measured by the BET 5-point method by nitrogen gas adsorption was 0.9 m 2 / g (product name ASAP2010 manufactured by Micromeritex Corporation). The metal impurity of the powder was 0.03% in terms of ash. The metal impurities in Examples and Comparative Examples were calculated as ash from the amount of residue after the obtained powder was heated in an electric furnace in an air atmosphere until it became a constant weight at 800 ° C. and ashed.
The powder was heated to 1300 ° C. at a heating rate of 300 ° C./hour in a nitrogen atmosphere and held for 1 hour. Subsequently, the negative electrode carbon material for lithium secondary batteries was produced through the 300 mesh sieve.
次いで、得られた負極炭素材料９０重量％に、Ｎ−メチル−２−ピロリドンに溶解したポリフッ化ビニリデン（ＰＶＤＦ）を固形分で１０重量％加えて混練して黒鉛ペーストを作製した。この黒鉛ペーストを厚さが１０μｍの圧延銅箔に塗布し、さらに、１２０℃で乾燥してＮ−メチル−２−ピロリドンを除去し、ロールプレスで圧縮加工し、試験電極を得た。得られた試験電極の、炭素材料とＰＶＤＦとを含んでなる炭素材料層の厚みは３５μｍ、密度は１．０５ｇ／ｃｃであった。 Next, 10% by weight of polyvinylidene fluoride (PVDF) dissolved in N-methyl-2-pyrrolidone was added to 90% by weight of the obtained negative electrode carbon material in a solid content and kneaded to prepare a graphite paste. This graphite paste was applied to a rolled copper foil having a thickness of 10 μm, and further dried at 120 ° C. to remove N-methyl-2-pyrrolidone, followed by compression with a roll press to obtain a test electrode. In the obtained test electrode, the carbon material layer including the carbon material and PVDF had a thickness of 35 μm and a density of 1.05 g / cc.
電気化学的測定は、作製した試料電極を面積２ｃｍ２に打ち抜き、対極、セパレータ、電解液とともにアルゴン循環型グローブボックス内でＣＲ２０１６型コイン電池による充放電試験を２５℃で行った。コイン電池は試料電極、セパレータ、対極の順に積層した。対極には、表面を研磨して酸化皮膜を除去した金属リチウムを使用した。セパレータには厚み１２μｍのポリエチレン微孔膜を使用した。電解液には、ＬｉＰＦ６をエチレンカーボネート（ＥＣ）及びメチルエチルカーボネート（ＭＥＣ）（ＥＣとＭＥＣは体積比で１：２）の混合溶媒に１モル／リットルの濃度になるように溶解した溶液を使用した。得られたコイン電池を用いて試料電極と対極の間に、試料電極の面積に対して、０．２ｍＡ／ｃｍ２の定電流で０Ｖ（Ｖ ｖｓ. Ｌｉ／Ｌｉ＋）まで充電し、次いで０Ｖの定電圧で電流が０．０２ｍＡ／ｃｍ２になるまで充電した。次に３０分間の休止時間後に０．２ｍＡ／ｃｍ２の定電流で１．５Ｖ（Ｖ ｖｓ. Ｌｉ／Ｌｉ＋）まで放電する１サイクル試験を行い、放電容量及び充放電効率を測定した。充放電効率は、（放電容量）／（充電容量）×１００として算出した。 The electrochemical measurement was performed by punching out the produced sample electrode to an area of 2 cm 2 and conducting a charge / discharge test using a CR2016 type coin battery at 25 ° C. in an argon circulation type glove box together with a counter electrode, a separator and an electrolytic solution. The coin battery was laminated in the order of the sample electrode, separator, and counter electrode. As the counter electrode, metallic lithium whose surface was polished to remove the oxide film was used. A polyethylene microporous film having a thickness of 12 μm was used as the separator. For the electrolytic solution, a solution obtained by dissolving LiPF 6 in a mixed solvent of ethylene carbonate (EC) and methyl ethyl carbonate (MEC) (EC and MEC are 1: 2 by volume) to a concentration of 1 mol / liter is used. used. Using the obtained coin battery, the sample electrode and the counter electrode were charged to 0 V (V vs. Li / Li + ) with a constant current of 0.2 mA / cm 2 with respect to the area of the sample electrode, and then 0 V The battery was charged at a constant voltage of until the current reached 0.02 mA / cm 2 . Next, after a 30-minute rest period, a one-cycle test was performed to discharge to 1.5 V (V vs. Li / Li + ) at a constant current of 0.2 mA / cm 2 , and the discharge capacity and charge / discharge efficiency were measured. The charge / discharge efficiency was calculated as (discharge capacity) / (charge capacity) × 100.
さらに同様の方法で５０サイクル充放電を繰り返し、第一サイクル目の放電容量を１００とした時の放電容量維持率を測定した。
また、０．２ｍＡ／ｃｍ２の定電流で０Ｖ（Ｖ ｖｓ. Ｌｉ／Ｌｉ＋）まで充電し、３０分間の休止時間後に０．２ｍＡ／ｃｍ２の定電流で１．５Ｖ（Ｖ ｖｓ. Ｌｉ／Ｌｉ＋）まで放電する試験を２サイクル行い、さらに３サイクル目充電を３ｍＡ／ｃｍ２の定電流で０Ｖまで行った。この試験において、２サイクル目充電容量を１００としたときの３サイクル目の充電容量を算出し、充電負荷時の充電容量維持率とした。
これらの結果を表１に示す。
Furthermore, 50 cycles of charge and discharge were repeated by the same method, and the discharge capacity retention rate when the discharge capacity of the first cycle was set to 100 was measured.
Further, 0.2 mA / cm was charged to 0V (V vs. Li / Li + ) in the second constant current, after 30 minutes dwell time at a constant current of 0.2mA / cm 2 1.5V (V vs. Li / Li + ) was tested for 2 cycles, and the third cycle charge was performed to 0 V with a constant current of 3 mA / cm 2 . In this test, the charge capacity at the third cycle when the charge capacity at the second cycle was set to 100 was calculated as the charge capacity maintenance rate at the time of charge load.
These results are shown in Table 1.
（実施例２）
コーンスターチ１００重量部と中国産鱗片状天然黒鉛１００重量部を、２７０℃のニーダーによって攪拌しながらコーンスターチを溶融させ、溶融軟化したコーンスターチが固形化するまで加熱攪拌した以外は、実施例１と同様の方法でリチウム二次電池用負極炭素材料を作製した。
得られたリチウム二次電池用負極炭素材料を実施例１と同様方法で試験電極、及びコイン電池を作製し、実施例１と同様の試験を行った。得られた試験電極の、炭素材料とＰＶＤＦとを含んでなる炭素材料層の厚みは３３μｍ、密度は１．３５ｇ／ｃｃであった。この試験結果を表１に示す。
(Example 2)
Example 1 except that 100 parts by weight of corn starch and 100 parts by weight of Chinese flake-like natural graphite were stirred with a kneader at 270 ° C. and the corn starch was melted and heated and stirred until the melted and softened corn starch was solidified. The negative electrode carbon material for lithium secondary batteries was produced by the method.
A test electrode and a coin battery were produced from the obtained negative electrode carbon material for a lithium secondary battery in the same manner as in Example 1, and the same test as in Example 1 was performed. In the obtained test electrode, the carbon material layer including the carbon material and PVDF had a thickness of 33 μm and a density of 1.35 g / cc. The test results are shown in Table 1.
（比較例１）
フラン樹脂を１８０℃のオーブン中で５時間処理して硬化させた後、該硬化物をハンマーで解砕し、さらにジェットミルで粉砕し、平均粒径１５μｍ、累積９０％粒径３３μｍの粉末を得た。該粉末を、窒素雰囲気で、昇温速度３００℃／時間で１３００℃まで昇温し、１時間保持した。次いで、３００メッシュの篩を通して、リチウム二次電池用負極炭素材料を作製した。
得られたリチウム二次電池用負極炭素材料を実施例１と同様方法で試験電極、及びコイン電池を作製し、実施例１と同様の試験を行った。得られた試験電極の、炭素材料とＰＶＤＦとを含んでなる炭素材料層の厚みは３４μｍ、密度は０．９６ｇ／ｃｃであった。この試験結果を表１に示す。
(Comparative Example 1)
The furan resin was cured in a 180 ° C. oven for 5 hours, and then the cured product was crushed with a hammer and further pulverized with a jet mill to obtain a powder having an average particle size of 15 μm and a cumulative 90% particle size of 33 μm. Obtained. The powder was heated to 1300 ° C. at a heating rate of 300 ° C./hour in a nitrogen atmosphere and held for 1 hour. Subsequently, the negative electrode carbon material for lithium secondary batteries was produced through the 300 mesh sieve.
A test electrode and a coin battery were produced from the obtained negative electrode carbon material for a lithium secondary battery in the same manner as in Example 1, and the same test as in Example 1 was performed. In the obtained test electrode, the carbon material layer including the carbon material and PVDF had a thickness of 34 μm and a density of 0.96 g / cc. The test results are shown in Table 1.
（比較例２）
フェノール樹脂を１８０℃のオーブン中で５時間処理して硬化させた後、該硬化物をハンマーで解砕し、さらにジェットミルで粉砕し、平均粒径１５μｍ、累積９０％粒径３４μｍの粉末を得た。該粉末を、窒素雰囲気で、昇温速度３００℃／時間で１３００℃まで昇温し、１時間保持した。次いで、３００メッシュの篩を通して、リチウム二次電池用負極炭素材料を作製した。
得られたリチウム二次電池用負極炭素材料を実施例１と同様方法で試験電極、及びコイン電池を作製し、実施例１と同様の試験を行った。得られた試験電極の、炭素材料とＰＶＤＦとを含んでなる炭素材料層の厚みは３８μｍ、密度は０．９８ｇ／ｃｃであった。この試験結果を表１に示す。
(Comparative Example 2)
After the phenol resin was cured by treatment in an oven at 180 ° C. for 5 hours, the cured product was crushed with a hammer and further pulverized with a jet mill to obtain a powder having an average particle size of 15 μm and a cumulative 90% particle size of 34 μm. Obtained. The powder was heated to 1300 ° C. at a heating rate of 300 ° C./hour in a nitrogen atmosphere and held for 1 hour. Subsequently, the negative electrode carbon material for lithium secondary batteries was produced through the 300 mesh sieve.
A test electrode and a coin battery were produced from the obtained negative electrode carbon material for a lithium secondary battery in the same manner as in Example 1, and the same test as in Example 1 was performed. In the obtained test electrode, the carbon material layer including the carbon material and PVDF had a thickness of 38 μm and a density of 0.98 g / cc. The test results are shown in Table 1.
（比較例３）
純度９９．９９％の中国産鱗片状天然黒鉛をジェットミルで粉砕し、３００メッシュの篩を通し平均粒径１６μｍのリチウム二次電池用負極炭素材料を作製した。
得られたリチウム二次電池用負極炭素材料を実施例１と同様方法で試験電極、及びコイン電池を作製し、実施例１と同様の試験を行った。得られた試験電極の、炭素材料とＰＶＤＦとを含んでなる炭素材料層の厚みは３８μｍ、密度は１．４６ｇ／ｃｃであった。この試験結果を表１に示す。
(Comparative Example 3)
A Chinese scale flake-like natural graphite having a purity of 99.99% was pulverized by a jet mill, and passed through a 300 mesh sieve to prepare a negative electrode carbon material for lithium secondary batteries having an average particle size of 16 μm.
A test electrode and a coin battery were produced from the obtained negative electrode carbon material for a lithium secondary battery in the same manner as in Example 1, and the same test as in Example 1 was performed. In the obtained test electrode, the carbon material layer including the carbon material and PVDF had a thickness of 38 μm and a density of 1.46 g / cc. The test results are shown in Table 1.
表１に示されるように、本発明のリチウム二次電池用負極炭素材料は、初回充放電効率が高く、サイクル特性及び急速充電特性に優れたリチウム二次電池として好適であることが示された。 As shown in Table 1, it was shown that the negative electrode carbon material for lithium secondary batteries of the present invention has high initial charge / discharge efficiency and is suitable as a lithium secondary battery excellent in cycle characteristics and rapid charge characteristics. .
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