JP3958781B2 - Negative electrode for lithium secondary battery, method for producing negative electrode composition, and lithium secondary battery - Google Patents
Negative electrode for lithium secondary battery, method for producing negative electrode composition, and lithium secondary battery Download PDFInfo
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- JP3958781B2 JP3958781B2 JP2006183987A JP2006183987A JP3958781B2 JP 3958781 B2 JP3958781 B2 JP 3958781B2 JP 2006183987 A JP2006183987 A JP 2006183987A JP 2006183987 A JP2006183987 A JP 2006183987A JP 3958781 B2 JP3958781 B2 JP 3958781B2
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- Prior art keywords
- negative electrode
- lithium secondary
- secondary battery
- carbon fiber
- graphite
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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
Description
本発明は、負極中に天然黒鉛または人造黒鉛を用いた黒鉛質材料である負極活物質と、良好な導電性を持つ炭素繊維とを含む、サイクル寿命、大電流特性に優れたリチウム二次電池に関する。 The present invention relates to a lithium secondary battery excellent in cycle life and large current characteristics, comprising a negative electrode active material which is a graphite material using natural graphite or artificial graphite in a negative electrode, and carbon fiber having good conductivity. About.
携帯機器の小型軽量化及び高性能化が伴い、二次電池の高容量化と長サイクル寿命化が益々求められている。そのような背景で携帯電話やビデオカメラ等の小型携帯機器用二次電池として、非水系電解液を用いる円筒型・角型リチウムイオン電池やリチウムポリマー電池のようなリチウム二次電池がその高エネルギー密度、高電圧という特徴から多くの機器に使われるようになっている。 With the reduction in size, weight and performance of portable devices, there is an increasing demand for higher capacity and longer cycle life of secondary batteries. Under such circumstances, lithium secondary batteries such as cylindrical / rectangular lithium ion batteries and lithium polymer batteries using non-aqueous electrolytes are high energy as secondary batteries for small portable devices such as mobile phones and video cameras. Due to the characteristics of density and high voltage, it is used in many devices.
これらリチウム二次電池に用いられる正極活物質としては高電位での単位重量あたりの充放電容量が大きいコバルト酸リチウムに代表される金属酸化物系化合物が使用され、負極活物質としてはＬｉに近い卑な電位で単位重量あたりの充放電容量の大きい黒鉛に代表される炭素材料が用いられている。 As the positive electrode active material used in these lithium secondary batteries, a metal oxide compound represented by lithium cobaltate having a large charge / discharge capacity per unit weight at a high potential is used, and the negative electrode active material is close to Li. A carbon material typified by graphite having a low potential and a large charge / discharge capacity per unit weight is used.
従来、負極材には天然黒鉛、人造黒鉛、低結晶性炭素材料、非晶質炭素材料、表面被覆炭素材料、メソフェーズピッチ系炭素繊維、及びホウ素等の異種元素をドーピングさせた炭素材料等が用いられてきた。
当初、天然黒鉛は高い電池容量を出すことで注目されたが、電解液の分解反応が激しいためにサイクル寿命が短いという致命的な問題により、実用化が難しかった。
Conventional negative electrode materials include natural graphite, artificial graphite, low crystalline carbon materials, amorphous carbon materials, surface-coated carbon materials, mesophase pitch carbon fibers, and carbon materials doped with different elements such as boron. Has been.
Initially, natural graphite attracted attention because of its high battery capacity, but due to the fatal problem of short cycle life due to severe decomposition of the electrolyte, it was difficult to put it into practical use.
一方、コークス等を原料として熱処理することにより得られる人造黒鉛は、比較的サイクル特性が良好なため、現在負極活物質として広く使用されている。
更に高電池容量と長サイクル寿命である負極活物質を得るために、現在でも盛んに検討が続けられている。例えば、結晶性の高い黒鉛質材料に機械的処理を行うことで造粒、若しくは球状に加工したものであるとか、負極活物質表面の反応性を抑制するために、表面をピッチや樹脂で被覆し、熱処理を施した検討などがされている。
On the other hand, artificial graphite obtained by heat-treating coke or the like as a raw material is widely used as a negative electrode active material at present because of relatively good cycle characteristics.
Furthermore, in order to obtain a negative electrode active material having a high battery capacity and a long cycle life, studies are still actively conducted. For example, a highly crystalline graphite material is granulated or processed into a spherical shape by mechanical treatment, or the surface is coated with pitch or resin to suppress the reactivity of the negative electrode active material surface However, studies have been made with heat treatment.
一方、負極活物質同士間の導電性を維持・向上するためには、カーボンブラック、黒鉛微粉、炭素繊維、気相法炭素繊維など導電性炭素材料の添加が有効である。特に気相法炭素繊維は微細な繊維状物質であることから、活物質間の導電パス形成に有効であり、大電流を流す場合では、電極の電気抵抗を小さくすることができるため、大きなエネルギーを取り出すのに有利であろうと考えられてきた。また、充電放電サイクル寿命については、活物質自身の膨張収縮が起こってもなお、その繊維状であることから導電パスを維持できると考えられることから、サイクル寿命の向上という視点でも検討が行われてきた。 On the other hand, in order to maintain and improve the conductivity between the negative electrode active materials, it is effective to add a conductive carbon material such as carbon black, graphite fine powder, carbon fiber, and vapor grown carbon fiber. In particular, vapor grown carbon fiber is a fine fibrous material, so it is effective for forming a conductive path between active materials. When a large current is passed, the electrical resistance of the electrode can be reduced, so that a large amount of energy is required. It has been thought that it would be advantageous to take out. In addition, the charge / discharge cycle life is considered from the viewpoint of improving the cycle life because it is considered that the conductive path can be maintained because it is fibrous even if the active material itself expands and contracts. I came.
特許第３０３３１７５号（特許文献１）では、サイクル寿命向上について、気相法炭素繊維が重量で５％未満であると添加効果がないとされているが、添加量が多いと、塗工性が著しく低下する原因となる。また、気相炭素繊維の添加量が多いほど活物質の占める割合が減少することから電池容量が減少するため、さらに少ない添加量で効果を出す必要があった。 In Patent No. 3033175 (Patent Document 1), for improving the cycle life, it is said that there is no effect of addition when the vapor grown carbon fiber is less than 5% by weight. Causes a significant drop. Further, since the proportion of the active material decreases as the amount of the vapor-phase carbon fiber added increases, the battery capacity decreases. Therefore, it is necessary to obtain an effect with a smaller amount of addition.
特開２０００−１３３２６７号公報（特許文献２）では、気相法炭素繊維を０．５〜２２．５質量部添加することによりサイクル寿命を向上させている。電極中に平均粒径１２〜４８μｍの気相法炭素繊維からなる二次粒子を含んでいることが特徴として挙げられている。しかし、そのような条件の電極ではサイクル特性の向上は見られなかった（比較例７）。これは、気相法炭素繊維が局在していると、電流がその二次粒子に集中してしまい、その部分のみが集中的に劣化するためと考えられ、さらなる改良が必要であった。 In JP-A-2000-133267 (Patent Document 2), the cycle life is improved by adding 0.5 to 22.5 parts by mass of vapor grown carbon fiber. It is mentioned as a feature that the electrode contains secondary particles made of vapor grown carbon fiber having an average particle diameter of 12 to 48 μm. However, no improvement in cycle characteristics was observed with the electrode under such conditions (Comparative Example 7). This is considered to be because when the vapor grown carbon fiber is localized, the current concentrates on the secondary particles, and only that portion deteriorates intensively, and further improvement is necessary.
近年では、大電流特性とサイクル寿命を改善することを目的に、負極活物質の表面から直接炭素繊維を成長させた材料が報告されている（特許文献３；特開２００４−２５０２７５号公報）。効果の一つとして大電流特性の向上があるが、放電時間を５時間かけた場合の放電容量を１００％とした時の、放電時間を２０分間で行った場合（電流密度が１５倍の大電流条件）の放電容量の割合は８８％であるので（特許文献３の実施例）、未だ改善の余地がある。この原因として、化学蒸着処理のみであると生成した炭素繊維の結晶化度は一般に低く、導電性を付与するには不十分であることが考えられる。 In recent years, a material in which carbon fibers are grown directly from the surface of a negative electrode active material has been reported for the purpose of improving large current characteristics and cycle life (Patent Document 3; JP 2004-250275 A). One of the effects is the improvement of the large current characteristics, but when the discharge time is 20 minutes when the discharge capacity is 100% when the discharge time is 5 hours (the current density is 15 times larger). Since the ratio of the discharge capacity under the current condition is 88% (Example of Patent Document 3), there is still room for improvement. As a cause of this, it is considered that the crystallinity of the produced carbon fiber is generally low when it is only chemical vapor deposition, and is insufficient for imparting conductivity.
本発明は、負極中に天然黒鉛または人造黒鉛を用いた黒鉛質材料である負極活物質と、良好な導電性を持ち、１０μｍ以上の大きさの凝集体を形成することなく均一に分散している炭素繊維を含むリチウム二次電池用負極、その負極を製造するために必要な炭素繊維含有組成物、リチウム二次電池用負極組成物、及びその負極を使用した長サイクル寿命、大電流特性に優れたリチウム二次電池を提供することを目的とする。 The present invention has a negative electrode active material that is a graphite material using natural graphite or artificial graphite in the negative electrode, and has good conductivity and is uniformly dispersed without forming an aggregate having a size of 10 μm or more. A negative electrode for a lithium secondary battery containing carbon fibers, a carbon fiber-containing composition necessary for producing the negative electrode, a negative electrode composition for a lithium secondary battery, and a long cycle life and large current characteristics using the negative electrode An object is to provide an excellent lithium secondary battery.
本発明者らは、上記リチウム二次電池用電極の問題点に鑑みて、上記課題を解決するために鋭意検討を重ねた結果、天然黒鉛や人造黒鉛を負極活物質に使用し、導電性に優れた炭素繊維を１０μｍ以上の大きさの凝集体を形成することなく負極中に均一に分散させることにより、長いサイクル寿命を持ち、かつ大電流特性に優れたリチウム二次電池を実現させた。 In view of the problems of the lithium secondary battery electrode, the present inventors have made extensive studies to solve the above problems, and as a result, natural graphite or artificial graphite is used as the negative electrode active material, and the conductivity is improved. An excellent carbon fiber was uniformly dispersed in the negative electrode without forming an aggregate having a size of 10 μm or more, thereby realizing a lithium secondary battery having a long cycle life and excellent large current characteristics.
また、上記炭素繊維を１０μｍ以上の大きさの凝集体を形成することなく均一に分散した負極を実現するためには、この目的に適った組成物が必要であるが、以下の方法によりそれを実現した。
（１）バインダーにスチレンブタジエンゴム（以下ＳＢＲ）を用いる場合は、予め増粘剤水溶液中に気相法炭素繊維を分散させた液体（炭素繊維含有組成物）と、同じく増粘剤水溶液中に負極活物質とＳＢＲを分散させた液体を製造し、その後、これら二つの液体を所望の割合で撹拌混合する。
（２）バインダーにポリフッ化ビニリデン（以下ＰＶＤＦ）を用いる場合は、初めに負極活物質と炭素繊維を乾燥状態で混合し、その後、溶媒であるＮ−メチル−２−ピロリドンに溶解したＰＶＤＦを加え、撹拌混合する。
Further, in order to realize a negative electrode in which the carbon fiber is uniformly dispersed without forming an aggregate having a size of 10 μm or more, a composition suitable for this purpose is required. It was realized.
(1) When using styrene butadiene rubber (hereinafter referred to as SBR) as a binder, a liquid (carbon fiber-containing composition) in which vapor-grown carbon fibers are dispersed in a thickener aqueous solution in advance, and a thickener aqueous solution as well. A liquid in which the negative electrode active material and SBR are dispersed is manufactured, and then these two liquids are stirred and mixed in a desired ratio.
(2) When using polyvinylidene fluoride (hereinafter referred to as PVDF) as a binder, first, the negative electrode active material and carbon fiber are mixed in a dry state, and then PVDF dissolved in N-methyl-2-pyrrolidone as a solvent is added. Stir and mix.
すなわち本発明は、以下に示すリチウム二次電池用負極、その負極を製造するための炭素繊維含有組成物、リチウム二次電池用負極組成物、及びその負極を使用したリチウム二次電池を提供するものである。
［１］リチウムを吸蔵・放出できる負極活物質、導電性炭素材料、及びバインダーを含むリチウム二次電池用負極であって、負極活物質が、粉末Ｘ線回折による黒鉛構造の（００２）面の面間隔ｄ（００２）が０．３３５〜０．３３７ｎｍの天然黒鉛または人造黒鉛を用いた黒鉛質材料であり、導電性炭素材料が、平均繊維径１〜２００ｎｍで、内部に中空構造を有し、繊維の長さ方向に対して垂直方向にグラフェンシートが積層した構造を持ち、粉末Ｘ線回折による黒鉛構造の（００２）面の面間隔ｄ（００２）が０．３３６〜０．３４５ｎｍの範囲にある気相法炭素繊維であり、前記気相法炭素繊維が１０μｍ以上の大きさの凝集体を形成することなく負極全体の０．１〜１０質量％含まれているリチウム二次電池用負極。
［２］前記気相法炭素繊維の平均アスペクト比が２０〜２０００である前記１に記載のリチウム二次電池用負極。
［３］前記気相法炭素繊維において繊維が分岐している部分を含む前記１に記載のリチウム二次電池用負極。
［４］気相法炭素繊維と増粘剤水溶液を含む炭素繊維含有組成物であって、前記気相法炭素繊維は、平均繊維径１〜２００ｎｍで、内部に中空構造を有し、繊維の長さ方向に対して垂直方向にグラフェンシートが積層した構造を持ち、粉末Ｘ線回折による黒鉛構造の（００２）面の面間隔ｄ（００２）が０．３３６〜０．３４５ｎｍにあり、前記気相法炭素繊維は、前記増粘剤水溶液中に分散されており、２５℃での粘度が５０００ｍＰａ・ｓｅｃ以下である炭素繊維含有組成物。
［５］前記気相法炭素繊維の平均アスペクト比が２０〜２０００である前記４に記載の炭素繊維含有組成物。
［６］前記気相法炭素繊維において繊維が分岐している部分を含む前記４に記載の炭素繊維含有組成物。
［７］前記炭素繊維含有組成物中の気相法炭素繊維の濃度が１〜２０質量％、かつ前記増粘剤水溶液中の固形分濃度が０.３〜３.０質量％である前記４に記載の炭素繊維含有組成物。
［８］増粘剤水溶液がカルボキシメチルセルロース増粘剤水溶液である前記４に記載の炭素繊維含有組成物。
［９］粉末Ｘ線回折による黒鉛構造の（００２）面の面間隔ｄ（００２）が０．３３５〜０．３３７ｎｍの天然黒鉛または人造黒鉛を用いたリチウムを吸蔵・放出できる負極活物質、増粘剤水溶液、及びスチレンブタジエンゴム分散水を含む負極材含有増粘剤水溶液と、前記４に記載の炭素繊維含有組成物とを混合撹拌することを特徴とするリチウム二次電池用負極組成物の製造方法。
［１０］増粘剤水溶液がカルボキシメチルセルロース増粘剤水溶液である前記９に記載の製造方法。
［１１］粉末Ｘ線回折による黒鉛構造の（００２）面の面間隔ｄ（００２）が０．３３５〜０．３３７ｎｍの天然黒鉛または人造黒鉛を用いたリチウムを吸蔵・放出できる負極活物質と平均繊維径１〜２００ｎｍで、内部に中空構造を有し、繊維の長さ方向に対して垂直方向にグラフェンシートが積層した構造を持ち、粉末Ｘ線回折による黒鉛構造の（００２）面の面間隔ｄ（００２）が０．３３６〜０．３４５ｎｍの範囲にある気相法炭素繊維を乾燥状態で混合し、その後にポリフッ化ビニリデンを添加し、撹拌混合することを特徴とするリチウム二次電池用負極組成物の製造方法。
［１２］ポリフッ化ビニリデンが、Ｎ−メチル−２−ピロリドンに溶解した液体である前記１１に記載の製造方法。
［１３］前記９〜１２のいずれかに記載の製造方法で得られたリチウム二次電池用負極組成物を金属集電体箔上に塗布し、乾燥後、加圧成形してなるリチウム二次電池用負極。
［１４］金属集電体箔が厚み１〜５０μｍのＣｕ及びまたはＣｕ合金箔である前記１３に記載のリチウム二次電池用負極。
［１５］前記１、２、３、１３及び１４のいずれかに記載のリチウム二次電池用負極を構成要素として含むリチウム二次電池。
［１６］非水系電解液及び／または非水系ポリマー電解質を用い、前記非水系電解液及び／または非水系ポリマー電解質に用いられる非水系溶媒にエチレンカーボネート、ジエチルカーボネート、ジメチルカーボネート、メチルエチルカーボネート、プロピレンカーボネート、ブチレンカーボネート、γ−ブチロラクトン、及びビニレンカーボネートからなる群から選ばれる少なくとも１種が含まれる前記１５に記載のリチウム二次電池。
That is, the present invention provides the following negative electrode for a lithium secondary battery, a carbon fiber-containing composition for producing the negative electrode, a negative electrode composition for a lithium secondary battery, and a lithium secondary battery using the negative electrode. Is.
[1] A negative electrode for a lithium secondary battery comprising a negative electrode active material capable of inserting and extracting lithium, a conductive carbon material, and a binder, wherein the negative electrode active material has a (002) plane of graphite structure by powder X-ray diffraction It is a graphite material using natural graphite or artificial graphite with an interplanar spacing d (002) of 0.335 to 0.337 nm, and the conductive carbon material has an average fiber diameter of 1 to 200 nm and a hollow structure inside. , Having a structure in which graphene sheets are laminated in a direction perpendicular to the length direction of the fiber, and the interplanar spacing d (002) of the (002) plane of the graphite structure by powder X-ray diffraction is in the range of 0.336 to 0.345 nm. The gas phase grown carbon fiber in which the gas phase grown carbon fiber is contained in an amount of 0.1 to 10% by mass of the whole negative electrode without forming an aggregate having a size of 10 μm or more. .
[2] The negative electrode for a lithium secondary battery as described in 1 above, wherein the vapor-grown carbon fiber has an average aspect ratio of 20 to 2000.
[3] The negative electrode for a lithium secondary battery as described in 1 above, comprising a portion where the fiber branches in the vapor grown carbon fiber.
[4] A carbon fiber-containing composition comprising vapor grown carbon fiber and a thickener aqueous solution, wherein the vapor grown carbon fiber has an average fiber diameter of 1 to 200 nm and has a hollow structure inside, It has a structure in which graphene sheets are laminated in a direction perpendicular to the length direction, and the interplanar spacing d (002) of the (002) plane of the graphite structure by powder X-ray diffraction is 0.336 to 0.345 nm. A phase-processed carbon fiber is a carbon fiber-containing composition that is dispersed in the thickener aqueous solution and has a viscosity at 25 ° C. of 5000 mPa · sec or less.
[5] The carbon fiber-containing composition as described in 4 above, wherein an average aspect ratio of the vapor grown carbon fiber is 20 to 2000.
[6] The carbon fiber-containing composition as described in 4 above, comprising a portion where the fiber is branched in the vapor grown carbon fiber.
[7] The 4 above, wherein the concentration of vapor grown carbon fiber in the carbon fiber-containing composition is 1 to 20% by mass, and the solid content concentration in the aqueous solution of the thickener is 0.3 to 3.0% by mass. The carbon fiber-containing composition described in 1.
[8] The carbon fiber-containing composition as described in 4 above, wherein the thickener aqueous solution is a carboxymethylcellulose thickener aqueous solution.
[9] Negative electrode active material capable of occluding / releasing lithium using natural graphite or artificial graphite having an interplanar spacing d (002) of 0.335 to 0.337 nm by graphite X-ray diffraction. A negative electrode composition for a lithium secondary battery, wherein the negative electrode material-containing thickener aqueous solution containing a viscous agent aqueous solution and a styrene-butadiene rubber-dispersed water and the carbon fiber-containing composition described in 4 above are mixed and stirred. Production method.
[10] The method according to 9 above, wherein the aqueous thickener solution is an aqueous carboxymethylcellulose thickener solution.
[11] Negative electrode active material capable of occluding / releasing lithium using natural graphite or artificial graphite having a (002) plane spacing d (002) of 0.335 to 0.337 nm by graphite X-ray diffraction A fiber diameter of 1 to 200 nm, a hollow structure inside, a structure in which graphene sheets are laminated in a direction perpendicular to the length direction of the fiber, and the spacing between (002) planes of the graphite structure by powder X-ray diffraction For lithium secondary battery, characterized in that vapor grown carbon fiber having d (002) in the range of 0.336 to 0.345 nm is mixed in a dry state, and then polyvinylidene fluoride is added and stirred and mixed. A method for producing a negative electrode composition.
[12] The production method as described in 11 above, wherein the polyvinylidene fluoride is a liquid dissolved in N-methyl-2-pyrrolidone.
[13] Lithium secondary formed by applying the negative electrode composition for a lithium secondary battery obtained by the production method according to any one of 9 to 12 above onto a metal current collector foil, followed by drying and pressing. Battery negative electrode.
[14] The negative electrode for a lithium secondary battery as described in 13 above, wherein the metal current collector foil is Cu and / or Cu alloy foil having a thickness of 1 to 50 μm.
[15] A lithium secondary battery comprising the negative electrode for a lithium secondary battery according to any one of 1, 2, 3, 13 and 14 as a constituent element.
[16] A non-aqueous electrolyte solution and / or a non-aqueous polymer electrolyte is used, and ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, propylene are used as the non-aqueous solvent used in the non-aqueous electrolyte solution and / or the non-aqueous polymer electrolyte. 16. The lithium secondary battery according to 15, wherein at least one selected from the group consisting of carbonate, butylene carbonate, γ-butyrolactone, and vinylene carbonate is included.
本発明により、導電性炭素材料として用いる気相法炭素繊維の１０μｍ以上の大きさの凝集体が含まれないリチウム二次電池用負極が得られた。これにより、放電電流密度１Ｃ下でのサイクル寿命では、従来の開示された技術（特開２０００−１３３２６７号公報）により作成したリチウム二次電池負極では３００サイクル時に放電容量保持率が４１％だったものを（比較例７）、７４％にまで改善できた（実施例７）。さらに、大電流特性については、特開２００４−２５０２７５号公報に記載された放電容量保持率８８％に対して、９５％以上を達成することができた。 According to the present invention, a negative electrode for a lithium secondary battery that does not contain an aggregate having a size of 10 μm or more of vapor grown carbon fiber used as a conductive carbon material was obtained. As a result, in the cycle life under the discharge current density of 1 C, the discharge capacity retention rate was 41% at 300 cycles in the lithium secondary battery negative electrode prepared by the conventionally disclosed technique (Japanese Patent Laid-Open No. 2000-133267). (Comparative Example 7), which was improved to 74% (Example 7). Furthermore, with respect to the large current characteristics, 95% or more can be achieved with respect to the discharge capacity retention rate of 88% described in JP-A-2004-250275.
本発明のリチウム二次電池用負極は、リチウムを吸蔵・放出できる負極活物質、導電性炭素材料、及びバインダーからなり、負極活物質に天然黒鉛または人造黒鉛といった黒鉛質材料を使用し、導電性炭素材料として炭素繊維を使用する。この炭素繊維は、負極中で１０μｍ以上の凝集体を形成していないことが必要である。 The negative electrode for a lithium secondary battery of the present invention comprises a negative electrode active material capable of occluding and releasing lithium, a conductive carbon material, and a binder. The negative electrode active material uses a graphite material such as natural graphite or artificial graphite, and is electrically conductive. Carbon fiber is used as the carbon material. This carbon fiber needs not to form an aggregate of 10 μm or more in the negative electrode.
前記負極活物質は天然黒鉛または人造黒鉛を用いた黒鉛質材料であって、粉末Ｘ線回折による黒鉛構造の（００２）面の面間隔ｄ（００２）が０．３３５〜０．３３７ｎｍにあることが必要である。この範囲を外れると電池容量の低下を招く。さらには、粉体特性として以下の条件を満たすものであることが望ましい。
（１）比表面積が大きいと、負極活物質表面での電解液分解反応が大きくなり、特にサイクル寿命が極端に短くなるため、ＢＥＴ法により測定される比表面積が１ｍ2／ｇ〜１０ｍ2／ｇ、より好ましくは１ｍ2／ｇ〜８ｍ2／ｇ、さらに好ましくは１ｍ2／ｇ〜６ｍ2／ｇであることが望ましい。
（２）粒子径が小さいと比表面積の増大を招き、また、嵩高くなるため電極密度を上げ難くなる。さらには、バインダーを多く必要とし、塗工性を低下させる原因となる。逆に粒子径が大きいと、比表面積が小さくなり過ぎてバインダー等と相互作用が少なくなり、電極剥離の原因となる。また、集電体上へリチウム二次電池用負極組成物を塗布する際に、大きな粒子が塗布膜を傷つける、あるいは溝を引いてしまうなどの弊害が現れるため、レーザー回折法により測定される粒子径が５μｍ〜６０μｍであることが望ましい。
（３）形状が平面状に近づくと、リチウム二次電池用負極の製造過程の加圧成形時に黒鉛結晶の配向が強くなり、サイクル寿命の低下を招く原因となる。また、黒鉛結晶を構成するグラフェンシートの反応活性な端（エッジ）部分が負極活物質表面に多く露出するため、電解液分解反応が促進してしまい、電池性能の低下や電池内部でのガス発生の要因となる。形状が真球状に近づくと、黒鉛結晶の配向抑えられ、またグラフェンシートの活性なエッジ部分の露出が少なくなることから、負極活物質の形状はフロー式粒子像解析装置により測定される平均円形度が０.７０〜０.９９であることが望ましい。
The negative electrode active material is a graphite material using natural graphite or artificial graphite, and the interplanar spacing d (002) of the (002) plane of the graphite structure by powder X-ray diffraction is 0.335 to 0.337 nm. is required. Outside this range, the battery capacity is reduced. Furthermore, it is desirable that the following characteristics are satisfied as powder characteristics.
(1) When the specific surface area is large, the electrolytic solution decomposition reaction on the surface of the negative electrode active material increases, and particularly the cycle life becomes extremely short. Therefore, the specific surface area measured by the BET method is 1 m 2 / g to 10 m 2 / g, it is preferable and more preferably 1m 2 / g~8m 2 / g, more preferably from 1m 2 / g~6m 2 / g.
(2) When the particle diameter is small, the specific surface area is increased, and it is bulky, which makes it difficult to increase the electrode density. Furthermore, a large amount of binder is required, which causes a decrease in coatability. On the contrary, if the particle size is large, the specific surface area becomes too small and the interaction with the binder or the like is reduced, which causes electrode peeling. In addition, when a negative electrode composition for a lithium secondary battery is applied on a current collector, particles such as large particles may damage the coating film or pull a groove. The diameter is desirably 5 μm to 60 μm.
(3) When the shape approaches a flat shape, the orientation of the graphite crystals becomes strong during pressure forming in the production process of the negative electrode for a lithium secondary battery, which causes a reduction in cycle life. In addition, the reactive active edge of the graphene sheet constituting the graphite crystal is exposed on the surface of the negative electrode active material, which accelerates the electrolyte decomposition reaction, lowers battery performance, and generates gas inside the battery. It becomes a factor of. As the shape approaches a true sphere, the orientation of the graphite crystal is suppressed, and the active edge portion of the graphene sheet is less exposed, so the shape of the negative electrode active material is the average circularity measured by a flow-type particle image analyzer Is preferably 0.70 to 0.99.
天然黒鉛とは、鉱石として天然に産出する黒鉛質材料のことをいう。天然黒鉛は、その外観と性状によって、結晶化度の高い鱗状黒鉛と結晶化度が低い土状黒鉛の二種類に分けられる。鱗状黒鉛はさらに外観が葉状の鱗片状黒鉛と、塊状である鱗状黒鉛に分けられる。天然黒鉛は、中国、ブラジル、マダガスカル、ジンバブエ、インド、スリランカ、メキシコ、朝鮮半島など世界中で産出するが、産地によって性状が少しずつ異なる。
本発明の黒鉛質材料となる天然黒鉛は、産地や性状、種類は特に制限されない。また、天然黒鉛または天然黒鉛を原料として製造した粒子に熱処理を施して用いても良い。
また、人造黒鉛とは、広く人工的な手法で作られた黒鉛及び黒鉛の完全結晶に近い黒鉛質材料をいう。代表的な例としては、石炭の乾留、原油の蒸留による残渣などから得られるタールやコークスを原料にして、５００〜１０００℃の焼成工程、２０００℃以上の黒鉛化工程を経て得たものが挙げられる。また、溶融鉄から炭素を再析出させることで得られるキッシュグラファイトも人造黒鉛の一種である。
Natural graphite refers to a graphite material that is naturally produced as ore. Natural graphite is classified into two types, scaly graphite having a high degree of crystallinity and earthy graphite having a low degree of crystallinity, depending on its appearance and properties. The scaly graphite is further divided into scaly graphite having a leafy appearance and massive scaly graphite. Natural graphite is produced all over the world, including China, Brazil, Madagascar, Zimbabwe, India, Sri Lanka, Mexico, and the Korean peninsula.
There are no particular restrictions on the origin, properties, and types of natural graphite that is the graphite material of the present invention. Further, natural graphite or particles produced using natural graphite as a raw material may be subjected to a heat treatment.
Artificial graphite refers to graphite made by a wide variety of artificial techniques and a graphite material close to a perfect crystal of graphite. Typical examples include those obtained from tar and coke obtained from coal residue, crude oil distillation residue, etc., and subjected to a calcination step at 500 to 1000 ° C. and a graphitization step at 2000 ° C. or higher. It is done. Kish graphite obtained by reprecipitation of carbon from molten iron is also a kind of artificial graphite.
導電性炭素材料は、炭素繊維を用いる。炭素繊維は、太すぎると負極中への分散性が低下し、負電極の高密度化を阻害する。また、繊維長は短いと効果的な導電性維持効果が発現しなくなり、反対に長いと凝集体を形成し易くなるため負極中への分散性が低下する。よって、平均繊維径は１ｎｍ〜２００ｎｍ、好ましくは１０ｎｍ〜２００ｎｍ以下が望ましい。
また、平均繊維径と平均繊維長から算出されるアスペクト比（＝（繊維長）／（繊維径））は平均２０〜２００００、好ましくは平均２０〜４０００、さらに好ましくは平均２０〜２０００が望ましい。
Carbon fiber is used as the conductive carbon material. If the carbon fiber is too thick, the dispersibility in the negative electrode is lowered, and the densification of the negative electrode is hindered. On the other hand, if the fiber length is short, an effective conductivity maintaining effect is not exhibited, whereas if the fiber length is long, it becomes easy to form an aggregate, so that the dispersibility in the negative electrode is lowered. Therefore, the average fiber diameter is 1 nm to 200 nm, preferably 10 nm to 200 nm or less.
The aspect ratio (= (fiber length) / (fiber diameter)) calculated from the average fiber diameter and the average fiber length is 20 to 20000 on average, preferably 20 to 4000 on average, and more preferably 20 to 2000 on average.
炭素繊維は、良好な導電性を持つものであれば特に限定されないが、結晶化度が高く、繊維軸に対して垂直方向にグラフェンシートが積層した気相法炭素繊維が好ましい。
気相法炭素繊維は、例えば、高温雰囲気下に、触媒となる鉄と共に気化された有機化合物を吹き込む方法で製造することができる。気相法炭素繊維は、製造した状態のままのもの、８００〜１５００℃程度で熱処理したもの、２０００〜３０００℃程度で黒鉛化処理したもののいずれも使用可能であるが、熱処理さらには黒鉛化処理したものの方が、炭素の結晶性が進んでおり、高導電性及び高耐圧特性を有するため好ましい。
The carbon fiber is not particularly limited as long as it has good electrical conductivity, but a vapor grown carbon fiber having a high crystallinity and a graphene sheet laminated in a direction perpendicular to the fiber axis is preferable.
The vapor grown carbon fiber can be produced by, for example, a method in which an organic compound vaporized with iron serving as a catalyst is blown into a high temperature atmosphere. As the vapor grown carbon fiber, any of the as-produced carbon fiber, the one heat-treated at about 800 to 1500 ° C., and the one graphitized at about 2000 to 3000 ° C. can be used. This is preferable because the crystallinity of carbon is advanced and it has high conductivity and high withstand voltage characteristics.
結晶化度を高めるため、黒鉛化促進剤であるホウ素を黒鉛化前に混合して黒鉛化処理を行うことも有効である。ホウ素源は特に限定されないが、例えば酸化ホウ素、炭化ホウ素、窒化ホウ素などの粉末を黒鉛化前に気相法炭素繊維に混合することで、容易に結晶化度を上げることができる。この際、気相法炭素繊維中に残留するホウ素は、０.１ｐｐｍ〜１０００００ｐｐｍ以下にすることが好ましい。残留するホウ素が少ないと結晶化度向上の効果が薄く、また残留するホウ素が多いと結晶化促進に寄与せず、導電性の低い化合物として存在するホウ素が多くなり、かえって気相法炭素繊維の導電性を低減する原因となる。 In order to increase the degree of crystallinity, it is also effective to perform a graphitization treatment by mixing boron as a graphitization accelerator before graphitization. The boron source is not particularly limited, but the crystallinity can be easily increased by, for example, mixing powders such as boron oxide, boron carbide, and boron nitride with vapor grown carbon fiber before graphitization. At this time, boron remaining in the vapor grown carbon fiber is preferably 0.1 ppm to 100,000 ppm or less. If the amount of residual boron is small, the effect of improving the degree of crystallinity is low. If the amount of residual boron is large, it does not contribute to the promotion of crystallization, and more boron exists as a low-conductivity compound. It becomes a cause to reduce electrical conductivity.
また、気相法炭素繊維の好ましい形態として、分岐状繊維がある。分岐部分はその部分を含めて繊維全体が互いに連通した中空構造を有し、繊維の円筒部分を構成している炭素層は連続している。中空構造は炭素層が円筒状に巻いている構造であって、完全な円筒でないもの、部分的な切断箇所を有するもの、積層した２層の炭素層が１層に結合したものなどを含む。また、円筒の断面は完全な円に限らず楕円や多角化のものを含む。 Moreover, there exists a branched fiber as a preferable form of vapor grown carbon fiber. The branched portion has a hollow structure in which the entire fiber including the portion is in communication with each other, and the carbon layer constituting the cylindrical portion of the fiber is continuous. The hollow structure is a structure in which a carbon layer is wound in a cylindrical shape, and includes a structure that is not a complete cylinder, a structure having a partial cut portion, and a structure in which two stacked carbon layers are combined into one layer. Further, the cross section of the cylinder is not limited to a perfect circle, but includes an ellipse or a polygon.
気相法炭素繊維は、繊維表面に凹凸や乱れがあるものが多く、そのため負極活物質との密着性が向上する利点もある。この密着性により、負極活物質と気相法炭素繊維とが解離せず密着した状態を保つことができ、負極の導電性を維持できサイクル寿命が向上する。
気相法炭素繊維が分岐状繊維を多く含む場合は、効率よく負極中にネットワークを形成することができる。また、負極活物質を包むように分散することができ、電極の強度を高め、負極活物質粒子間の接触も良好に保てる。
Vapor-grown carbon fibers often have irregularities and disturbances on the fiber surface, and thus have an advantage of improving adhesion with the negative electrode active material. With this adhesion, the negative electrode active material and the vapor grown carbon fiber can be kept in close contact with each other without dissociating, so that the conductivity of the negative electrode can be maintained and the cycle life is improved.
When the vapor grown carbon fiber contains a lot of branched fibers, a network can be efficiently formed in the negative electrode. Moreover, it can disperse | distribute so that a negative electrode active material may be wrapped, the intensity | strength of an electrode can be raised, and the contact between negative electrode active material particles can also be maintained favorable.
炭素繊維の含有量は、負極中の０.１質量％〜２０質量％、好ましくは０.１質量％〜１０質量％である。含有量が多くなると、負極の電極密度の低下や、塗工性を低下させる原因となる。また、含有量が０.１質量％未満では負極の導電性維持効果が十分ではなく、サイクル寿命の急激な悪化に繋がる。炭素繊維の含有量をこの範囲に調整するには、製法において同比率となるように添加することにより行なうことができる。 Content of carbon fiber is 0.1 mass%-20 mass% in a negative electrode, Preferably it is 0.1 mass%-10 mass%. When the content increases, it causes a decrease in the electrode density of the negative electrode and a decrease in coatability. On the other hand, if the content is less than 0.1% by mass, the conductivity maintaining effect of the negative electrode is not sufficient, leading to a rapid deterioration of the cycle life. In order to adjust the content of the carbon fiber within this range, it can be carried out by adding the same ratio in the production method.
炭素繊維の導電性維持効果を発現させるためには、凝集体を形成させることなく負極中に均一に分散させる必要がある。元々繊維状であるため、負極組成物を製造する過程などで凝集体を形成しやすいが、本発明においては少なくとも１０μｍ以上の凝集体を形成させることなく負極を製造することが必要である。１０μｍ以上の凝集体が存在すると、結果的に導電性の高い炭素繊維が偏在することとなるため負極の導電性に分布が生じたり、負極電極密度が上げ難くなるといった弊害が発生する。この１０μｍ以上の炭素繊維の凝集体が存在しないリチウム二次電池用負極は、以下に示す本発明の炭素繊維含有組成物、及びリチウム二次電池用負極組成物を使用することで製造できる。 In order to develop the conductivity maintaining effect of the carbon fiber, it is necessary to uniformly disperse it in the negative electrode without forming an aggregate. Since it is originally fibrous, it is easy to form aggregates in the process of manufacturing the negative electrode composition, but in the present invention, it is necessary to manufacture the negative electrode without forming aggregates of at least 10 μm or more. If aggregates of 10 μm or more are present, carbon fibers with high conductivity are unevenly distributed, resulting in a problem that the conductivity of the negative electrode is distributed and the density of the negative electrode is difficult to increase. The negative electrode for a lithium secondary battery in which an aggregate of carbon fibers of 10 μm or more does not exist can be produced by using the following carbon fiber-containing composition of the present invention and the negative electrode composition for a lithium secondary battery.
本発明のリチウム二次電池用負極組成物の製造方法において、バインダーとして用いる材料及び溶媒として用いる材料によって混合する順序が異なる。 In the method for producing a negative electrode composition for a lithium secondary battery of the present invention, the mixing order differs depending on the material used as the binder and the material used as the solvent.
バインダーにスチレンブタジエンゴム（ＳＢＲ）を用いる場合、増粘剤としては、例えばポリエチレングリコール類、セルロース類、ポリアクリルアミド類、ポリＮ−ビニルアミド類、ポリＮ−ビニルピロリドン類等を用いることができるが、これらの中でも、ポリエチレングリコール類、カルボキシメチルセルロース（ＣＭＣ）等のセルロース類等が好ましく、特にＳＢＲに親和性の高いカルボキシメチルセルロース（ＣＭＣ）が特に好ましい。ＣＭＣにはナトリウム塩タイプとアンモニウム塩タイプがあるが、これは特に制限されない。
まず増粘剤水溶液を調製する。この際の水溶液中の増粘剤固形分濃度を０．３質量％〜３質量％に調整する。この固形分濃度が低いと増粘効果が薄いため、増粘材水溶液を多量に使用することとなり、密度の高いリチウム二次電池用負極を得ることができなくなる。また、反対に固形分濃度が高いと、リチウム二次電池用負極組成物の粘度が高くなり、集電体上への塗布ができなくなり、また炭素繊維が凝集体を形成する原因となる。
When styrene butadiene rubber (SBR) is used as the binder, examples of the thickener include polyethylene glycols, celluloses, polyacrylamides, poly N-vinyl amides, poly N-vinyl pyrrolidones, etc. Among these, celluloses such as polyethylene glycols and carboxymethyl cellulose (CMC) are preferable, and carboxymethyl cellulose (CMC) having a high affinity for SBR is particularly preferable. There are sodium salt type and ammonium salt type in CMC, but this is not particularly limited.
First, a thickener aqueous solution is prepared. The thickener solid content concentration in the aqueous solution at this time is adjusted to 0.3 mass% to 3 mass%. If this solid content concentration is low, the thickening effect is thin, so a large amount of the thickener aqueous solution is used, and a high density negative electrode for a lithium secondary battery cannot be obtained. On the other hand, when the solid content concentration is high, the viscosity of the negative electrode composition for a lithium secondary battery increases, which makes it impossible to apply it on the current collector, and causes carbon fibers to form aggregates.
次に、調製した増粘剤水溶液を炭素繊維に少量ずつ加えながら混練を行い、最終的に炭素繊維の濃度が１質量％〜２０質量％になるように、炭素繊維を分散させた炭素繊維含有組成物を調整する。この濃度が低いと後述する負極活物質を含んだ増粘剤水溶液へ多量に添加することが必要となるので、密度の高いリチウム二次電池用負極を得ることができなくなる。また、反対にこの濃度が高いと炭素繊維が凝集体を形成する原因となる。炭素繊維含有組成物の粘度は５０００ｍＰａ・ｓｅｃ以下になるよう調整することが望ましい。粘度が高いと、リチウム二次電池用負極中で炭素繊維が凝集体を形成しやすくなる。さらに好ましくは２０００ｍＰａ・ｓｅｃ〜５０００ｍＰａ・ｓｅｃの範囲に調整すると扱いやすくなる。 Next, kneading is carried out while adding the prepared thickener aqueous solution to the carbon fiber little by little, and the carbon fiber containing the carbon fiber is dispersed so that the concentration of the carbon fiber finally becomes 1% by mass to 20% by mass. Adjust the composition. If this concentration is low, it is necessary to add a large amount to a thickener aqueous solution containing a negative electrode active material, which will be described later, so that a high density negative electrode for a lithium secondary battery cannot be obtained. On the other hand, if this concentration is high, the carbon fibers cause agglomerates. It is desirable to adjust the viscosity of the carbon fiber-containing composition so as to be 5000 mPa · sec or less. When the viscosity is high, the carbon fibers easily form aggregates in the negative electrode for a lithium secondary battery. More preferably, it is easy to handle when adjusted to the range of 2000 mPa · sec to 5000 mPa · sec.
次に、負極活物質と増粘剤水溶液とＳＢＲを含む負極材含有増粘剤水溶液を調製する。負極活物質に前記の増粘剤水溶液を少しずつ添加しながら混練を行い、最終的に粘度が５０００ｍＰａ・ｓｅｃ以下となるように調製する。この粘度が高いと、集電体上への塗布が不可能となる。さらに、スチレンブタジエンゴム分散水（例えば日本ゼオン株式会社製のＢＭ−４００Ｂを用いることができる）を添加し、撹拌混合することにより、負極材含有増粘剤水溶液を得ることができる。 Next, a negative electrode material-containing thickener aqueous solution containing a negative electrode active material, a thickener aqueous solution, and SBR is prepared. Kneading is performed while gradually adding the above thickener aqueous solution to the negative electrode active material, and finally the viscosity is adjusted to 5000 mPa · sec or less. When this viscosity is high, coating on the current collector becomes impossible. Furthermore, a negative electrode material-containing thickener aqueous solution can be obtained by adding styrene-butadiene rubber dispersion water (for example, BM-400B manufactured by Nippon Zeon Co., Ltd.) and stirring and mixing.
次に、上記負極材含有増粘剤水溶液に、負極活物質と炭素繊維とＳＢＲとＣＭＣの合計を１００質量％とした場合に、炭素繊維の濃度が０．１質量％〜１０質量％となるよう、上記炭素繊維含有組成物を添加し、混合撹拌することで、リチウム二次電池用負極組成物を製造することができる。 Next, in the negative electrode material-containing thickener aqueous solution, when the total of the negative electrode active material, carbon fiber, SBR, and CMC is 100 mass%, the concentration of carbon fiber is 0.1 mass% to 10 mass%. Thus, the negative electrode composition for lithium secondary batteries can be manufactured by adding the said carbon fiber containing composition and mixing and stirring.
これら炭素繊維含有組成物及び負極材含有増粘剤水溶液の調整、さらにはリチウム二次電池用負極組成物を調製する混練方法は、公知の装置を用いて行うことができる。例えば、リボンミキサー、スクリュー型ニーダー、スパルタンリューザー、レディゲミキサー、プラネタリーミキサー、万能ミキサー、脱泡ニーダー等の装置を使用することができる。 The kneading method for preparing the carbon fiber-containing composition and the negative electrode material-containing thickener aqueous solution, and further preparing the negative electrode composition for a lithium secondary battery can be performed using a known apparatus. For example, apparatuses such as a ribbon mixer, a screw type kneader, a spartan luzer, a redige mixer, a planetary mixer, a universal mixer, and a defoaming kneader can be used.
次に、バインダーにポリフッ化ビニリデン（ＰＶＤＦ）を使用する場合のリチウム二次電池用負極組成物製造方法を以下に示す。
負極活物質と炭素繊維を、負極活物質と炭素繊維と後工程で添加するＰＶＤＦとの合計を１００質量％としたときの、炭素繊維濃度が０．１質量％〜１０質量％となるよう量り採り、乾燥状態のまま混合を行う。ここでの混合は、公知の装置を用いて行うことができる。例えば、リボンミキサー、スクリュー型ニーダー、スパルタンリューザー、レディゲミキサー、プラネタリーミキサー、万能ミキサー、脱泡ニーダー等の装置を使用することができる。用いる装置、容器の大きさによって最適な時間が異なることから一概には言えないが、通常５〜３０秒で十分な混合が可能である。
Next, a method for producing a negative electrode composition for a lithium secondary battery in the case of using polyvinylidene fluoride (PVDF) as a binder is shown below.
The negative electrode active material and the carbon fiber are weighed so that the carbon fiber concentration is 0.1% by mass to 10% by mass when the total of the negative electrode active material, the carbon fiber and PVDF added in the subsequent step is 100% by mass. Take and mix in dry state. Mixing here can be performed using a well-known apparatus. For example, apparatuses such as a ribbon mixer, a screw type kneader, a spartan luzer, a redige mixer, a planetary mixer, a universal mixer, and a defoaming kneader can be used. Although the optimum time varies depending on the apparatus used and the size of the container, it cannot be generally stated, but usually sufficient mixing is possible in 5 to 30 seconds.
次に、Ｎ−メチル−２−ピロリドンに溶解したＰＶＤＦ（例えば、呉羽化学工業株式会社製のＫＦ−ポリマーを使用することができる）を所定量加えて、撹拌混合を行うことで、リチウム二次電池用負極組成物を得ることができる。この際にも公知の装置を用いて撹拌混合を行うことができ、例えば、リボンミキサー、スクリュー型ニーダー、スパルタンリューザー、レディゲミキサー、プラネタリーミキサー、万能ミキサー、脱泡ニーダー等の装置を使用することができる。 Next, by adding a predetermined amount of PVDF dissolved in N-methyl-2-pyrrolidone (for example, KF-polymer manufactured by Kureha Chemical Industry Co., Ltd.) and stirring and mixing, lithium secondary A negative electrode composition for a battery can be obtained. Also in this case, stirring and mixing can be performed using a known device, for example, using a device such as a ribbon mixer, a screw type kneader, a spartan luzer, a redige mixer, a planetary mixer, a universal mixer, a defoaming kneader, etc. can do.
本発明のリチウム二次電池用負極組成物を使用することで、リチウム二次電池用負極を製造できる。上記リチウム二次電池用負極組成物を、厚み１〜５０μｍのＣｕ箔上またはＣｕ合金箔上へ塗布し、乾燥、加圧成形することで、本発明のリチウム二次電池用負極材を得ることができる。この箔が薄過ぎると機械的な強度が落ち、厚いと剛直性が増加するため、どちらも電池作成が困難となる。
上記の塗布工程は、公知の方法により実施できるが、例えばドクターブレードやバーコーターなどが使用できる。その後の加圧成形工程では、ロールプレス等を使用することができる。
By using the negative electrode composition for a lithium secondary battery of the present invention, a negative electrode for a lithium secondary battery can be produced. The negative electrode composition for a lithium secondary battery of the present invention is obtained by applying the negative electrode composition for a lithium secondary battery on a Cu foil or Cu alloy foil having a thickness of 1 to 50 μm, followed by drying and pressure molding. Can do. If this foil is too thin, the mechanical strength is reduced, and if it is thick, the rigidity increases, so that it is difficult to produce a battery in both cases.
The application step can be performed by a known method, and for example, a doctor blade or a bar coater can be used. In the subsequent pressure forming step, a roll press or the like can be used.
本発明のリチウム二次電池は、本発明の製造方法により得たリチウム二次電池用負極組成物を原料に用いたリチウム二次電池用負極を構成要素とすることにより実現する。以下に、リチウム二次電池の製造方法を示す。 The lithium secondary battery of this invention is implement | achieved by making into a component the negative electrode for lithium secondary batteries which used the negative electrode composition for lithium secondary batteries obtained by the manufacturing method of this invention as a raw material. Below, the manufacturing method of a lithium secondary battery is shown.
正極に用いることのできるリチウムを吸蔵、放出可能な正極活物質材料例としては、コバルト酸リチウム等のコバルト系酸化物、マンガン酸リチウム等のマンガン系酸化物、ニッケル酸リチウム等のニッケル系酸化物、五酸化バナジウム等のバナジウム系酸化物及びこれらの複合酸化物や混合物等が挙げられるが、これらに限定されるものではない。
正極活物質として使用できる。
正極活物質の粒子の大きさは特に限定されないが、通常０.１〜５０μｍが好ましく、比表面積は特に限定されないが、ＢＥＴ法で測定した値で０.２ｍ2／ｇ〜１０ｍ2／ｇが好ましい。
Examples of positive electrode active material materials capable of inserting and extracting lithium that can be used for the positive electrode include cobalt-based oxides such as lithium cobaltate, manganese-based oxides such as lithium manganate, and nickel-based oxides such as lithium nickelate. And vanadium oxides such as vanadium pentoxide, and complex oxides and mixtures thereof, but are not limited thereto.
It can be used as a positive electrode active material.
Is not particularly limited the size of the positive electrode active material particles, is usually preferably 0.1 to 50 [mu] m, the specific surface area is not particularly limited, but 0.2m 2 / g~10m 2 / g by a value measured by the BET method preferable.
正極の製造方法は特に限定されないが、一般的には前述した正極活物質材料、導電性炭素材料及びバインダー材料を混合後、金属集電体等の担持基材上に塗布後、乾燥、プレスすることにより製造することができる。
導電性炭素材料には、カーボンブラック、アセチレンブラック、炭素繊維、気相法炭素繊維、カーボンナノチューブなどが使用できる。また、バインダーにはＰＶＤＦを使用することができる。
正極活物質材料、導電性炭素材料及びバインダー材料を混合する方法は、例えばミキサー等で撹拌すればよい。撹拌方法は特に限定されないが、例えば、リボンミキサー、スクリュー型ニーダー、スパルタンリューザー、レディゲミキサー、プラネタリーミキサー、万能ミキサー、脱泡ニーダー等の装置を使用することができる。
バインダーの使用量は、正極活物質と導電性炭素材料とＰＶＤＦの合計を１００質量％とした場合に、１質量％以上１５質量％以下となるよう調整することが好ましい。
集電体への塗布は、公知の方法により実施できるが、例えばドクターブレードやバーコーターなどで塗布、乾燥後、ロールプレス等で加圧成形する方法等が挙げられる。
集電体としては、アルミニウム、ステンレス、ニッケル、チタン及びそれらの合金、白金、カーボンシートなど公知の材料が使用できる。
The method for producing the positive electrode is not particularly limited, but generally, after mixing the positive electrode active material, the conductive carbon material and the binder material described above, the mixture is applied onto a support substrate such as a metal current collector, and then dried and pressed. Can be manufactured.
As the conductive carbon material, carbon black, acetylene black, carbon fiber, vapor grown carbon fiber, carbon nanotube, or the like can be used. PVDF can be used as the binder.
The method of mixing the positive electrode active material, the conductive carbon material, and the binder material may be agitated with, for example, a mixer. Although the stirring method is not specifically limited, For example, apparatuses, such as a ribbon mixer, a screw-type kneader, a Spartan luzer, a redige mixer, a planetary mixer, a universal mixer, a defoaming kneader, can be used.
The amount of the binder used is preferably adjusted to be 1% by mass or more and 15% by mass or less when the total of the positive electrode active material, the conductive carbon material, and PVDF is 100% by mass.
Application to the current collector can be carried out by a known method, and examples thereof include a method of applying and drying with a doctor blade, a bar coater or the like, and then press-molding with a roll press or the like.
As the current collector, known materials such as aluminum, stainless steel, nickel, titanium and alloys thereof, platinum, and a carbon sheet can be used.
本発明のリチウム二次電池は、公知の方法により製造することができる。リチウムイオン電池及び／またはリチウムポリマー電池の代表的な製造方法を以下に述べるが、これに限定されない。
上記で作製した負極を所望の形状に加工し、正極と組み合わせて、正極／セパレータ／負極に積層し、正極と負極がふれないようにし、コイン型、角型、円筒型、シート型等の容器の中に収納する。積層、収納で水分や酸素を吸着した可能性がある場合はこのまま減圧及びまたは低露点（−５０℃以下）不活性雰囲気中で再度乾燥後、低露点の不活性雰囲気内に移す。ついで電解液を注入し容器を封印することにより、リチウムイオン電池またはリチウムポリマー電池が作製できる。
The lithium secondary battery of the present invention can be produced by a known method. Although the typical manufacturing method of a lithium ion battery and / or a lithium polymer battery is described below, it is not limited to this.
The negative electrode produced above is processed into a desired shape, combined with the positive electrode, laminated on the positive electrode / separator / negative electrode, so that the positive electrode and the negative electrode do not come into contact with each other, and a container of coin type, square type, cylindrical type, sheet type, etc. Store inside. If there is a possibility that moisture or oxygen has been adsorbed during stacking and storage, it is dried again in an inert atmosphere under reduced pressure and / or a low dew point (-50 ° C. or lower), and then transferred to an inert atmosphere with a low dew point. Subsequently, a lithium ion battery or a lithium polymer battery can be produced by injecting an electrolytic solution and sealing the container.
セパレーターは公知のものが使用できるが、薄くて強度が高いという観点から、ポリエチレンやポリプロピレン性の多孔性のマイクロポーラスフィルムが好ましい。多孔度は、イオン伝導という観点から高い方がよいが、高すぎると強度の低下や正極と負極の短絡の原因となるので、通常は３０％以上９０％以下で用いられ、好ましくは５０以上８０％以下である。また厚みもイオン伝導、電池容量という観点から薄い方がよいが、薄すぎると強度の低下や正極と負極の短絡の原因となるので、通常は５μｍ以上１００μｍ以下、好ましくは５μｍ以上５０μｍ以下で用いられる。これらマイクロポーラスフィルムは二種以上の併用や不織布等の他のセパレーターと併用して用いることができる。 A known separator can be used, but from the viewpoint of being thin and having high strength, a polyethylene or polypropylene porous microporous film is preferable. The porosity is preferably higher from the viewpoint of ionic conduction, but if it is too high, it will cause a decrease in strength and a short circuit between the positive electrode and the negative electrode, so it is usually used in a range of 30% to 90%, preferably 50 to 80. % Or less. The thickness is preferably thin from the viewpoints of ion conduction and battery capacity. However, if it is too thin, it may cause a decrease in strength or a short circuit between the positive electrode and the negative electrode. Therefore, the thickness is usually 5 μm to 100 μm, preferably 5 μm to 50 μm. It is done. These microporous films can be used in combination of two or more kinds or other separators such as a nonwoven fabric.
非水系二次電池、特にリチウムイオン電池及び／またはＬｉポリマー電池における電解液及び電解質は公知の有機電解液、無機固体電解質、高分子固体電解質が使用できる。
有機電解液としては、ジエチルエーテル、ジブチルエーテル、エチレングリコールモノメチルエーテル、エチレングリコールモノエチルエーテル、エチレングリコールモノブチルエーテル、ジエチレングリコールモノメチルエーテル、ジエチレングリコールモノエチルエーテル、ジエチレングリコールモノブチルエーテル、ジエチレングリコールジメチルエーテル、エチレングリコールフェニルエーテル等のエーテル；ホルムアミド、Ｎ−メチルホルムアミド、Ｎ，Ｎ−ジメチルホルムアミド、Ｎ−エチルホルムアミド、Ｎ，Ｎ−ジエチルホルムアミド、Ｎ−メチルアセトアミド、Ｎ，Ｎ−ジメチルアセトアミド、Ｎ−エチルアセトアミド、Ｎ，Ｎ−ジエチルアセトアミド、Ｎ，Ｎ−ジメチルプロピオンアミド、ヘキサメチルホスホリルアミド等のアミド；ジメチルスルホキシド、スルホラン等の含硫黄化合物；メチルエチルケトン、メチルイソブチルケトン等のジアルキルケトン；エチレンオキシド、プロピレンオキシド、テトラヒドロフラン、２−メトキシテトラヒドロフラン、１，２−ジメトキシエタン、１，３−ジオキソラン等の環状エーテル；エチレンカーボネート、プロピレンカーボネート等のカーボネート；γ−ブチロラクトン；Ｎ−メチルピロリドン；アセトニトリル、ニトロメタン等の有機溶媒の溶液が好ましい。さらに、好ましくはエチレンカーボネート、ブチレンカーボネート、ジエチルカーボネート、ジメチルカーボネート、プロピレンカーボネート、ビニレンカーボネート、γ−ブチロラクトン等のエステル類、ジオキソラン、ジエチルエーテル、ジエトキシエタン等のエーテル類、ジメチルスルホキシド、アセトニトリル、テトラヒドロフラン等が挙げられ、特に好ましくはエチレンカーボネート、プロピレンカーボネート等のカーボネート系非水溶媒を用いることができる。これらの溶媒は、単独でまたは２種以上を混合して使用することができる。
これらの溶媒の溶質（電解質）には、リチウム塩が使用される。一般的に知られているリチウム塩にはＬｉＣｌＯ4、ＬｉＢＦ4、ＬｉＰＦ6、ＬｉＡｌＣｌ4、ＬｉＳｂＦ6、ＬｉＳＣＮ、ＬｉＣｌ、ＬｉＣＦ3ＳＯ3、ＬｉＣＦ3ＣＯ2、ＬｉＮ（ＣＦ3ＳＯ2）2等がある。
高分子固体電解質としては、ポリエチレンオキサイド誘導体及び該誘導体を含む重合体、ポリプロピレンオキサイド誘導体及び該誘導体を含む重合体、リン酸エステル重合体、ポリカーボネート誘導体及び該誘導体を含む重合体等が挙げられる。
上記以外の電池構成上必要な部材の選択についてはなんら制約を受けるものではない。
As the electrolyte and electrolyte in a non-aqueous secondary battery, particularly a lithium ion battery and / or a Li polymer battery, known organic electrolytes, inorganic solid electrolytes, and polymer solid electrolytes can be used.
Examples of organic electrolytes include diethyl ether, dibutyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, and ethylene glycol phenyl ether. Ether; formamide, N-methylformamide, N, N-dimethylformamide, N-ethylformamide, N, N-diethylformamide, N-methylacetamide, N, N-dimethylacetamide, N-ethylacetamide, N, N-diethyl Acetamide, N, N-dimethylpropionamide, hexamethylphosphorylamide Amides such as dimethyl sulfoxide, sulfolane, etc .; dialkyl ketones such as methyl ethyl ketone, methyl isobutyl ketone; ethylene oxide, propylene oxide, tetrahydrofuran, 2-methoxytetrahydrofuran, 1,2-dimethoxyethane, 1,3-dioxolane, etc. Cyclic ethers; carbonates such as ethylene carbonate and propylene carbonate; γ-butyrolactone; N-methylpyrrolidone; solutions of organic solvents such as acetonitrile and nitromethane are preferred. Furthermore, preferably ethylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate, propylene carbonate, vinylene carbonate, esters such as γ-butyrolactone, ethers such as dioxolane, diethyl ether, diethoxyethane, dimethyl sulfoxide, acetonitrile, tetrahydrofuran, etc. Particularly preferred are carbonate-based non-aqueous solvents such as ethylene carbonate and propylene carbonate. These solvents can be used alone or in admixture of two or more.
Lithium salts are used as solutes (electrolytes) for these solvents. Commonly known lithium salts include LiClO 4 , LiBF 4 , LiPF 6 , LiAlCl 4 , LiSbF 6 , LiSCN, LiCl, LiCF 3 SO 3 , LiCF 3 CO 2 , LiN (CF 3 SO 2 ) 2 and the like. is there.
Examples of the polymer solid electrolyte include a polyethylene oxide derivative and a polymer containing the derivative, a polypropylene oxide derivative and a polymer containing the derivative, a phosphate ester polymer, a polycarbonate derivative and a polymer containing the derivative.
There are no restrictions on the selection of members necessary for battery configuration other than those described above.
以下に本発明について代表的な例を示し、さらに具体的に説明する。なお、これらは説明のための単なる例示であって、本発明はこれらに何等制限されるものではない。
下記例で用いた物性等は以下の方法、装置により測定した。
［１］平均粒子径：
レーザー回析散乱式粒度分布測定装置マイクロトラックＨＲＡ（日機装株式会社製）を用いて測定した。
［２］比表面積：
比表面積測定装置ＮＯＶＡ−１２００（ユアサアイオニクス株式会社製）を用いて、一般的な比表面積の測定方法である、液体窒素を用いるＢＥＴ法により測定した。
［３］円形度評価：
フロー式粒子像分析装置ＦＰＩＡ−２１００（シスメックス社製）を用いて、以下の方法で評価を行った。黒鉛微粉試料を界面活性剤入りの水に分散させ、フロー式粒子像分析装置のシリンジより吸引させた。フローセルの中心を流れる試料流（微粉の分散液）をＣＣＤカメラで１／３０秒毎に撮像し、静止画像をリアルタイムに画像処理し、下記式によって算出した。
円形度＝（円相当径から求めた円の周囲長）／（粒子投影像の周囲長）
円相当径とは実際に撮像された粒子の周囲長さと同じ投影面積を持つ真円の直径であり、この円相当径から求めた円の周囲長を実際に撮像された粒子の周囲長で割った値である。例えば真円で１、形状が複雑になるほど小さい値となる。平均円形度は、測定された粒子個々に円形度の平均値である。
［４］粘度測定：
粘度測定は、Ｂ型回転式粘度計ＬＶ−型（Brookfield Engineering laboratories, Inc.）を用いて行った。初めに、測定するサンプルをステンレス容器に入れ、測定装置に取り付けた。サンプルの温度を一定にするため、２５℃に調整された恒温槽にステンレス容器部分を浸した。その次に、ローターを回転させ、回転開始から三分後に粘度を測定した。それぞれのサンプルについての測定は二度行い、その平均値を用いた。ローターはＮｏ．４を用い、ローター回転数は６ｒｐｍにて行った。
The present invention will be described in more detail below with typical examples. Note that these are merely illustrative examples, and the present invention is not limited thereto.
The physical properties used in the following examples were measured by the following methods and apparatuses.
[1] Average particle size:
It measured using the laser diffraction scattering type particle size distribution measuring apparatus Microtrac HRA (made by Nikkiso Co., Ltd.).
[2] Specific surface area:
Using a specific surface area measuring apparatus NOVA-1200 (manufactured by Yuasa Ionics Co., Ltd.), measurement was performed by a BET method using liquid nitrogen, which is a general method for measuring a specific surface area.
[3] Circularity evaluation:
Evaluation was performed by the following method using a flow type particle image analyzer FPIA-2100 (manufactured by Sysmex Corporation). The graphite fine powder sample was dispersed in water containing a surfactant and sucked from a syringe of a flow type particle image analyzer. A sample flow (fine powder dispersion) flowing through the center of the flow cell was imaged every 1/30 seconds with a CCD camera, a still image was processed in real time, and calculated according to the following equation.
Circularity = (circle circumference obtained from equivalent circle diameter) / (perimeter of particle projection image)
The equivalent circle diameter is the diameter of a true circle having the same projected area as the circumference of the actually imaged particle, and the circumference of the circle obtained from this equivalent circle diameter is divided by the circumference of the actually imaged particle. Value. For example, it is 1 for a perfect circle, and the value becomes smaller as the shape becomes more complicated. The average circularity is an average value of circularity of each measured particle.
[4] Viscosity measurement:
The viscosity was measured using a B-type rotary viscometer LV-type (Brookfield Engineering laboratories, Inc.). First, a sample to be measured was placed in a stainless steel container and attached to a measuring device. In order to keep the temperature of the sample constant, the stainless steel container portion was immersed in a thermostatic chamber adjusted to 25 ° C. Next, the rotor was rotated, and the viscosity was measured 3 minutes after the start of rotation. Each sample was measured twice, and the average value was used. The rotor is no. No. 4 was used, and the rotational speed of the rotor was 6 rpm.
［５］電池評価方法：
（１）負極の作製
負極の作製工程は、負極組成物の作製、塗布、乾燥、加圧成形の順序で行う。以下には、塗布工程以降の作製方法を示す。
それぞれの方法で得た負極組成物を、負極用として日本製箔株式会社製圧延銅箔（厚み１８μｍ）に、それぞれドクターブレードを用いて所定の厚みに塗布した。これを１２０℃で、１時間真空乾燥し、１８ｍｍΦに打ち抜いた。さらに、打ち抜いた電極を超鋼製プレス板で挟み、プレス圧が電極に対して約１×１０2〜３×１０2Ｎ／ｍｍ2（１×１０3〜３×１０3ｋｇ／ｃｍ2）となるようにプレスし、目付け量７〜９ｍｇ／ｃｍ2、厚さ４０〜６０μｍで、電極密度を１．６ｇ／ｃｍ3とした。その後、真空乾燥器で１２０℃、１２時間乾燥し、評価用とした。
[5] Battery evaluation method:
(1) Production of negative electrode The production process of the negative electrode is carried out in the order of production of the negative electrode composition, application, drying, and pressure molding. Below, the preparation methods after a coating process are shown.
The negative electrode composition obtained by each method was applied to a rolled copper foil (thickness: 18 μm) manufactured by Nippon Foil Co., Ltd. to a predetermined thickness using a doctor blade. This was vacuum-dried at 120 ° C. for 1 hour and punched out to 18 mmΦ. Further, the punched electrode is sandwiched between super steel press plates, and the press pressure is about 1 × 10 2 to 3 × 10 2 N / mm 2 (1 × 10 3 to 3 × 10 3 kg / cm 2 ) with respect to the electrode. Then, the weight per unit area was 7 to 9 mg / cm 2 , the thickness was 40 to 60 μm, and the electrode density was 1.6 g / cm 3 . Then, it dried for 120 hours and 120 degreeC with the vacuum dryer, and it was for evaluation.
（２）正極の作製
上記（１）で作成した負極と組み合わせる正極の作成を以下にしめす。
ＬｉＣｏＯ4セルシードＣ−１０（日本化学工業株式会社製）、アセチレンブラック（電気化学工業株式会社製）を質量比９５：５で乾式、羽根つき高速小形ミキサーIKA Labotechnik Staufen（Janke & Kunkel GmbH）を用いて１００００ｒｐｍで１０秒混合し、正極材混合物を調製した。これに呉羽化学製ＫＦポリマーL＃１３２０（ポリビニリデンフルオライド（ＰＶＤＦ）を１２質量％含有したＮ−メチル−２−ピロリドン（ＮＭＰ）溶液）を正極材混合物とＰＶＤＦの質量比が９５：３になるように加え、これを脱泡ニーダーＮＢＫ−１（日本精機製作所製）を用いて撹拌球１個（φ１２ｍｍ）を入れて５００ｒｐｍで５分間混練し、ペースト状の正極組成物を得た。
上記、正極組成物を昭和電工株式会社製圧延アルミ箔（厚み２５μｍ）に、ドクターブレードを用いて所定の厚みに塗布した。これを１２０℃で、１時間真空乾燥し、１８ｍｍΦに打ち抜いた。さらに、打ち抜いた電極を超鋼製プレス板で挟み、プレス圧が電極に対して約１×１０2〜３×１０2Ｎ／ｍｍ2（１×１０3〜３×１０3ｋｇ／ｃｍ2）となるようにプレスした。その後、真空乾燥器で１２０℃、１２時間乾燥し、評価用とした。厚さ約８０μｍ、電極密度は約３．５ｇ／ｃｍ3であった。
(2) Production of positive electrode Production of a positive electrode combined with the negative electrode produced in (1) above is shown below.
LiCoO 4 cell seed C-10 (manufactured by Nippon Kagaku Kogyo Co., Ltd.), acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) at a mass ratio of 95: 5, using a high-speed small bladed mixer IKA Labotechnik Staufen (Janke & Kunkel GmbH) The mixture was mixed at 10,000 rpm for 10 seconds to prepare a positive electrode material mixture. KF polymer L # 1320 (N-methyl-2-pyrrolidone (NMP) solution containing 12% by mass of polyvinylidene fluoride (PVDF)) was added to Kureha Chemical Co., Ltd., and the mass ratio of the positive electrode material mixture to PVDF was 95: 3. Then, using a defoaming kneader NBK-1 (manufactured by Nippon Seiki Seisakusho), one stirring ball (φ12 mm) was added and kneaded at 500 rpm for 5 minutes to obtain a paste-like positive electrode composition.
The positive electrode composition was applied to a rolled aluminum foil (thickness 25 μm) manufactured by Showa Denko KK to a predetermined thickness using a doctor blade. This was vacuum-dried at 120 ° C. for 1 hour and punched out to 18 mmΦ. Further, the punched electrode is sandwiched between super steel press plates, and the press pressure is about 1 × 10 2 to 3 × 10 2 N / mm 2 (1 × 10 3 to 3 × 10 3 kg / cm 2 ) with respect to the electrode. It pressed so that it might become. Then, it dried for 120 hours and 120 degreeC with the vacuum dryer, and it was for evaluation. The thickness was about 80 μm, and the electrode density was about 3.5 g / cm 3 .
（３）リチウムイオン電池試験３極式セル作製
下記のようにして３極式セルを作製した。なお以下の操作は露点−８０℃以下の乾燥アルゴン雰囲気下に保ったグローブボックス内で実施した。
ポリプロピレン製のねじ込み式フタ付きのセル（内径約１８ｍｍ）内において、上記（１）で作製した銅箔付き負極と対極用金属リチウム箔をセパレーター（ポリプロピレン製マイクロポーラスフィルム（セルガード２４００；東燃株式会社製）で挟み込んで積層した。さらにリファレンス用の金属リチウム箔（５０μｍ）を同様に積層した。これに電解液を加えて試験用セルとした。
(3) Lithium-ion battery test tripolar cell production A tripolar cell was produced as follows. The following operation was performed in a glove box kept in a dry argon atmosphere with a dew point of -80 ° C or lower.
In a polypropylene-made cell with a screw-in lid (inner diameter of about 18 mm), the negative electrode with copper foil prepared in (1) above and a metallic lithium foil for counter electrode were separated by a separator (polypropylene microporous film (Cell Guard 2400; manufactured by Tonen Corporation). In addition, a reference metal lithium foil (50 μm) was laminated in the same manner, and an electrolytic solution was added thereto to form a test cell.
（４）リチウムイオン電池試験コインセル作製
下記のようにしてコインセルを作製した。なお以下の操作は露点−８０℃以下の乾燥アルゴン雰囲気下に保ったグローブボックス内で実施した。
円筒形をしたＳＵＳ３０４製の受け外装材の中に、スペーサー、板バネ、上記（１）で作製した銅箔付き負極と上記（２）で作製したアルミ箔付き正極をセパレーター（ポリプロピレン製マイクロポーラスフィルム（セルガード２４００；東燃株式会社製）で挟み込んで積層した。さらにその上から円筒形をしたＳＵＳ３０４の上蓋外装材を乗せた。
次に、これを電解液の中に浸して、真空含浸を５分間行った。この後、コインかしめ機を用いてコインセルをかしめることで、評価用のコインセルを得た。
（５）電解液
ＥＣ（エチレンカーボネート）８質量部及びＥＭＣ（エチルメチルカーボネート）１２質量部の混合品で、電解質としてＬｉＰＦ6を１．０モル／リットル溶解したのもを電解液とした。
（６）高率電池特性評価試験
評価セルには３極式セルを用い、定電流定電圧充放電試験を行った。
充電はレストポテンシャルから２ｍＶまで０.２ｍＡ／ｃｍ2でＣＣ（コンスタントカレント：定電流）充電を行った。次に２ｍＶでＣＶ（コンスタントボルト：定電圧）充電に切り替え、電流値が１２.０μＡに低下した時点で停止させた。
放電は各電流密度（０.２ｍＡ／ｃｍ2、（０．１Ｃに相当）、及び４．０ｍＡ／ｃｍ2（２．０Ｃに相当））でそれぞれＣＣ放電を行い、電圧１．５Ｖでカットオフした。
０．１Ｃ時の放電容量に対する２．０Ｃ時の放電容量の割合を、高率放電容量保持率として評価を行った。
（７）充放電サイクル試験
評価セルにはコインセルを用い、定電流低電圧充放電試験を行った。
２回の充放電サイクルまでは、充電はレストポテンシャルから４.２Ｖまで０．２ｍＡ／ｃｍ2でＣＣ（コンスタントカレント：定電流）充電し、次に４.２ＶでＣＶ（コンスタントボルト：定電圧）充電に切り替え、電流値が２５.４μＡに低下した時点で停止させた。次いで、放電は０．２ｍＡ／ｃｍ2でＣＣ放電を行い、電圧２.７Ｖでカットオフした。
３サイクル目以降からは、充電はレストポテンシャルから４.２Ｖまで１．０ｍＡ／ｃｍ2（０．５Ｃに相当）でＣＣ（コンスタントカレント：定電流）充電し、次に４.２ＶでＣＶ（コンスタントボルト：定電圧）充電に切り替え、電流値が２５.４μＡに低下した時点で停止させた。次いで、放電は電流密度２．０ｍＡ／ｃｍ2（１．０Ｃに相当）でＣＣ放電を行い、電圧２.７Ｖでカットオフした。２サイクル目の放電容量に対する３００サイクル目の放電容量の割合を、サイクル放電容量保持率として評価を行った。
(4) Preparation of lithium ion battery test coin cell A coin cell was prepared as follows. The following operation was performed in a glove box kept in a dry argon atmosphere with a dew point of -80 ° C or lower.
In a cylindrical outer casing made of SUS304, a spacer, a leaf spring, a negative electrode with copper foil prepared in (1) above, and a positive electrode with aluminum foil prepared in (2) above were separated by a separator (polypropylene microporous film). (Celguard 2400; manufactured by Tonen Co., Ltd.) The laminate was sandwiched between them, and a cylindrical SUS304 top cover exterior material was placed thereon.
Next, this was immersed in an electrolytic solution and vacuum impregnation was performed for 5 minutes. Then, the coin cell for evaluation was obtained by caulking the coin cell using a coin caulking machine.
(5) Electrolyte Solution A mixture of 8 parts by mass of EC (ethylene carbonate) and 12 parts by mass of EMC (ethyl methyl carbonate), in which LiPF 6 was dissolved in an amount of 1.0 mol / liter as an electrolyte, was used as an electrolyte.
(6) High-rate battery characteristic evaluation test A tripolar cell was used as the evaluation cell, and a constant current constant voltage charge / discharge test was performed.
Charging was performed by CC (constant current) at 0.2 mA / cm 2 from the rest potential to 2 mV. Next, it switched to CV (constant volt | bolt: constant voltage) charge at 2 mV, and stopped when the electric current value fell to 12.0 microamperes.
Discharging each current density perform CC discharge respectively (0.2mA / cm 2, (equivalent to 0.1 C), and 4.0 mA / cm 2 (equivalent to 2.0 C)), cut off at a voltage of 1.5V did.
The ratio of the discharge capacity at 2.0 C to the discharge capacity at 0.1 C was evaluated as a high rate discharge capacity retention rate.
(7) Charge / Discharge Cycle Test A coin cell was used as the evaluation cell, and a constant current low voltage charge / discharge test was performed.
Up to two charge / discharge cycles, the charge is CC (constant current: constant current) at 0.2 mA / cm 2 from the rest potential to 4.2 V, and then CV (constant voltage: constant voltage) at 4.2 V. Switching to charging was stopped when the current value dropped to 25.4 μA. Subsequently, CC discharge was performed at 0.2 mA / cm 2 and cut off at a voltage of 2.7 V.
From the 3rd cycle onward, the charge is CC (constant current) at 1.0mA / cm 2 (equivalent to 0.5C) from the rest potential to 4.2V, and then at CV (constant current) at 4.2V. The voltage was switched to (volt: constant voltage) charging and stopped when the current value dropped to 25.4 μA. Subsequently, CC discharge was performed at a current density of 2.0 mA / cm 2 (corresponding to 1.0 C), and cut off at a voltage of 2.7 V. The ratio of the discharge capacity at the 300th cycle to the discharge capacity at the second cycle was evaluated as the cycle discharge capacity retention rate.
［６］炭素繊維の凝集状態確認方法：炭素繊維の凝集状態の観察は、走査型電池顕微鏡Ｔ−２０（日本電子製）を用いて以下の方法により行った。
サンプル電極を１ｔ／ｃｍ2でプレスし、観察用試料台にセットした。試料台を水平状態から３０から６０℃傾け、最低倍率（３５倍）にて広くすべての電極表面が見えるように調節した。その際、サンプル表面の突起部分（盛り上がり部分）の存在の有無を観察した。炭素繊維の凝集体が存在していた場合、その部分が他の部分よりも盛り上がって見えることで判別できる。
[6] Aggregation state confirmation method of carbon fiber: The aggregation state of the carbon fiber was observed by the following method using a scanning battery microscope T-20 (manufactured by JEOL Ltd.).
The sample electrode was pressed at 1 t / cm 2 and set on an observation sample stage. The sample stage was tilted from 30 to 60 ° C. from a horizontal state, and adjusted so that all electrode surfaces could be seen widely at the minimum magnification (35 times). At that time, the presence or absence of a protruding portion (swelled portion) on the sample surface was observed. When an aggregate of carbon fibers is present, it can be identified by the fact that the part appears to be raised more than the other part.
［７］負極使用材料：
（１）負極活物質
ＬＢ−ＣＧ：球状天然黒鉛（日本黒鉛株式会社製）
Ｘ線ｄ（００２）：０．３３５９ｎｍ
比表面積：６ｍ2／ｇ
平均粒子径：２０μｍ
円形度：０．９０
ＭＣＭＢ（２５−２８）：メソフェーズ系球状人造黒鉛（大阪ガス株式会社製）
Ｘ線ｄ（００２）：０．３３６３ｎｍ
比表面積：０．９ｍ2／ｇ
平均粒子径：２５μｍ
円形度：０．９３
ＳＣＭＧ−Ａ：塊状人造黒鉛（昭和電工株式会社製）
Ｘ線ｄ（００２）：０．３３６７ｎｍ
比表面積：２．２ｍ2／ｇ
平均粒子径：２０μｍ
円形度：０．８６
（２）炭素繊維
ＶＧＣＦ：気相成長黒鉛繊維（昭和電工株式会社製）
平均繊維径（ＳＥＭ画像解析より）：１５０ｎｍ、
平均繊維長（ＳＥＭ画像解析より）：８μｍ、
平均アスペクト比：５３
分岐度：約０.１個／μｍ
（ＳＥＭ画像解析より繊維長１μｍ当たりの分岐数を算出；以下同様）
Ｘ線ｄ（００２）：０.３３８４ｎｍ、Ｌｃ（結晶子サイズ）：４８ｎｍ。
ＶＧＣＦ−Ｈ：気相成長黒鉛ナノファイバー（昭和電工株式会社製）
平均繊維径（ＳＥＭ画像解析より）：１５０ｎｍ、
平均繊維長（ＳＥＭ画像解析より）：６μｍ、
平均アスペクト比：４０
分岐度：０.０５個／μｍ、
Ｘ線ｄ（００２）：０.３３８４ｎｍ、Ｌｃ：３５ｎｍ。
ＶＧＣＦ−Ｓ：気相成長黒鉛繊維（昭和電工株式会社製）
平均繊維径（ＳＥＭ画像解析より）：１２０ｎｍ、
平均繊維長（ＳＥＭ画像解析より）：１２μｍ、
平均アスペクト比：１００
分岐度：約０.０２個／μｍ、
Ｘ線ｄ（００２）：０.３３８５ｎｍ、Ｌｃ：４８ｎｍ。
ＶＧＮＴ：気相成長黒鉛ナノチューブ（昭和電工株式会社製）
平均繊維径（ＳＥＭ画像解析より）：２５ｎｍ、
平均繊維長（ＳＥＭ画像解析より）：５μｍ、
平均アスペクト比：２００、
分岐度：０.１個／μｍ、
Ｘ線ｄ（００２）：０.３４４９ｎｍ、Ｌｃ：３０ｎｍ。
（３）バインダー
スチレンブタジエンゴム（ＳＢＲ）：ＢＭ−４００Ｂ（日本ゼオン株式会社製）
ポリフッ化ビニリデン（ＰＶＤＦ）：ＫＦ−ポリマーＬ＃９２１０（呉羽化学工業株式会社製）
（４）増粘剤
カルボキシメチルセルロース（ＣＭＣ）：ＷＳ−Ｃ（第一工業製薬株式会社製）
（５）溶剤
Ｎ−メチル−２−ピロリドン（ＮＭＰ）：ＥＰ−II（昭和電工株式会社製）
[7] Material used for negative electrode:
(1) Negative electrode active material LB-CG: Spherical natural graphite (manufactured by Nippon Graphite Co., Ltd.)
X-ray d (002): 0.3359 nm
Specific surface area: 6 m 2 / g
Average particle size: 20 μm
Circularity: 0.90
MCMB (25-28): Mesophase spherical artificial graphite (Osaka Gas Co., Ltd.)
X-ray d (002): 0.3363 nm
Specific surface area: 0.9 m 2 / g
Average particle size: 25 μm
Circularity: 0.93
SCMG-A: Bulk artificial graphite (made by Showa Denko KK)
X-ray d (002): 0.3367 nm
Specific surface area: 2.2 m 2 / g
Average particle size: 20 μm
Circularity: 0.86
(2) Carbon fiber VGCF: Vapor growth graphite fiber (manufactured by Showa Denko KK)
Average fiber diameter (from SEM image analysis): 150 nm,
Average fiber length (from SEM image analysis): 8 μm,
Average aspect ratio: 53
Branching degree: about 0.1 / μm
(SEM image analysis calculates the number of branches per 1 μm fiber length; the same applies hereinafter)
X-ray d (002): 0.3384 nm, Lc (crystallite size): 48 nm.
VGCF-H: Vapor growth graphite nanofiber (made by Showa Denko KK)
Average fiber diameter (from SEM image analysis): 150 nm,
Average fiber length (from SEM image analysis): 6 μm,
Average aspect ratio: 40
Branching degree: 0.05 / μm,
X-ray d (002): 0.3384 nm, Lc: 35 nm.
VGCF-S: Vapor growth graphite fiber (made by Showa Denko KK)
Average fiber diameter (from SEM image analysis): 120 nm,
Average fiber length (from SEM image analysis): 12 μm,
Average aspect ratio: 100
Branching degree: about 0.02 pieces / μm,
X-ray d (002): 0.3385 nm, Lc: 48 nm.
VGNT: Vapor growth graphite nanotube (made by Showa Denko KK)
Average fiber diameter (from SEM image analysis): 25 nm,
Average fiber length (from SEM image analysis): 5 μm,
Average aspect ratio: 200,
Branching degree: 0.1 / μm,
X-ray d (002): 0.3449 nm, Lc: 30 nm.
(3) Binder Styrene butadiene rubber (SBR): BM-400B (manufactured by Nippon Zeon Co., Ltd.)
Polyvinylidene fluoride (PVDF): KF-polymer L # 9210 (Kureha Chemical Industries, Ltd.)
(4) Thickener Carboxymethylcellulose (CMC): WS-C (Daiichi Kogyo Seiyaku Co., Ltd.)
(5) Solvent N-methyl-2-pyrrolidone (NMP): EP-II (manufactured by Showa Denko KK)
実施例１
ＶＧＣＦ２０ｇに、予め調製しておいたＣＭＣ１質量％水溶液を少しずつ加えながら、万能型ミキサーＴ.Ｋ.ハイビスミックス（登録商標）f-model ０３型（特殊機化工業株式会社製）を用いて、９０分間混練を行った。最終的に、ＶＧＣＦが８．５質量％の炭素繊維含有組成物を調製した。この水溶液の粘度は、４０００ｍＰａ・ｓｅｃであった。
球状天然黒鉛ＬＢ−ＣＧ７０ｇに、予め調製しておいたＣＭＣ１質量％水溶液を少しずつ加えながら、Ｔ.Ｋ.ハイビスミックス（登録商標）f-model ０３型を用いて、２時間混練を行った。最終的に、球状天然黒鉛ＬＢ−ＣＧが５０質量％のＣＭＣ水溶液を調製した。この水溶液にＳＢＲ分散水ＢＭ−４００Ｂを、ＳＢＲ固形分が１．５質量％となるよう加えて、１時間混練を行った。この負極材含有増粘剤水溶液の粘度は、３５００ｍＰａ・ｓｅｃであった。
次に、ＬＢ−ＣＧとＶＧＣＦとＳＢＲとＣＭＣの合計を１００質量％とした時に、ＶＧＣＦ含有量が２質量％となるよう、炭素繊維含有組成物と負極材含有増粘剤水溶液を加え合わせ、さらに１５分間混練した。
このようにして得たリチウム二次電池用負極組成物を用いて、先述の「負極の作成」方法にしたがってリチウム二次電池用負極を作製した。
プレス前の負極材の状態を拡大観察した電子顕微鏡写真を図３に、プレス後の負極の表面状態を観察した電子顕微鏡写真を図４に示す。図３から明らかなように負極材中の炭素繊維は良好に分散しており、図４に示すプレス後の負極表面には直径１０μｍを超える炭素繊維凝集体はなかった。
Example 1
Using a universal mixer TK Hibismix (registered trademark) f-model 03 (manufactured by Tokushu Kika Kogyo Co., Ltd.) while adding a 1% by weight aqueous solution of CMC prepared in advance little by little to 20 g of VGCF, Kneading was performed for 90 minutes. Finally, a carbon fiber-containing composition having a VGCF of 8.5% by mass was prepared. The viscosity of this aqueous solution was 4000 mPa · sec.
The mixture was kneaded for 2 hours using TK Hibismix (registered trademark) f-model 03 type while gradually adding a 1% by weight aqueous solution of CMC prepared in advance to 70 g of spherical natural graphite LB-CG. Finally, a CMC aqueous solution containing 50% by mass of spherical natural graphite LB-CG was prepared. SBR dispersion water BM-400B was added to this aqueous solution so that SBR solid content might be 1.5 mass%, and it knead | mixed for 1 hour. The viscosity of this negative electrode material-containing thickener aqueous solution was 3500 mPa · sec.
Next, when the total of LB-CG, VGCF, SBR and CMC is 100% by mass, the carbon fiber-containing composition and the negative electrode material-containing thickener aqueous solution are added together so that the VGCF content is 2% by mass, The mixture was further kneaded for 15 minutes.
Using the thus obtained negative electrode composition for a lithium secondary battery, a negative electrode for a lithium secondary battery was prepared according to the above-described “preparation of negative electrode” method.
FIG. 3 shows an electron micrograph obtained by observing the state of the negative electrode material before pressing, and FIG. 4 shows an electron micrograph obtained by observing the surface state of the negative electrode after pressing. As is clear from FIG. 3, the carbon fibers in the negative electrode material were well dispersed, and there were no carbon fiber aggregates having a diameter exceeding 10 μm on the negative electrode surface after pressing shown in FIG.
実施例２
塊状人造黒鉛ＳＣＭＧ−Ａ７０ｇに、予め調製しておいたＣＭＣ１質量％水溶液を少しずつ加えながら、Ｔ.Ｋ.ハイビスミックス（登録商標）f-model ０３型を用いて、２時間混練を行った。最終的に、塊状人造黒鉛ＳＣＭＧ−Ａが６０質量％のＣＭＣ水溶液を調製した。この水溶液にＳＢＲ分散水ＢＭ−４００Ｂを、ＳＢＲ固形分が１．５質量％となるよう加えて、１時間混練を行った。この負極材含有増粘剤水溶液の粘度は、３０００ｍＰａ・ｓｅｃであった。
他は、実施例１と同じ方法に従って、リチウム二次電池用負極を作製した。
得られた負極を実施例１と同様に電子顕微鏡にて観察したところ、炭素繊維は負極材中に良好に分散しており、プレス後の負極表面には直径１０μｍを超える炭素繊維凝集体はなかった。
Example 2
The mixture was kneaded for 2 hours using TK Hibismix (registered trademark) f-model 03 type while gradually adding a 1% by weight aqueous solution of CMC prepared in advance to 70 g of massive artificial graphite SCMG-A. Finally, a CMC aqueous solution containing 60% by mass of massive artificial graphite SCMG-A was prepared. SBR dispersion water BM-400B was added to this aqueous solution so that SBR solid content might be 1.5 mass%, and it knead | mixed for 1 hour. The viscosity of this negative electrode material-containing thickener aqueous solution was 3000 mPa · sec.
Others produced a negative electrode for a lithium secondary battery according to the same method as in Example 1.
When the obtained negative electrode was observed with an electron microscope in the same manner as in Example 1, the carbon fibers were well dispersed in the negative electrode material, and there was no carbon fiber aggregate exceeding 10 μm in diameter on the negative electrode surface after pressing. It was.
実施例３
ＶＧＣＦにＢ4Ｃを１質量％添加し、小型黒鉛化炉（株式会社サン理工電機）を用いてアルゴンガス気流下２８００℃において熱処理を行った。冷却、回収後、粉末Ｘ線回折法によりｄ（００２）を測定した結果、０．３３７６ｎｍであった。このＶＧＣＦホウ素処理品を用いて、実施例１と同じ方法に従ってリチウム二次電池用負極を作製した。
得られた負極を実施例１と同様に電子顕微鏡にて観察したところ、炭素繊維は負極材中に良好に分散しており、プレス後の負極表面には直径１０μｍを超える炭素繊維凝集体はなかった。
Example 3
1 mass% of B 4 C was added to VGCF, and heat treatment was performed at 2800 ° C. under an argon gas stream using a small graphitization furnace (Sun Riko Electric Co., Ltd.). After cooling and recovery, d (002) was measured by powder X-ray diffraction method and found to be 0.3376 nm. Using this VGCF boron-treated product, a negative electrode for a lithium secondary battery was produced according to the same method as in Example 1.
When the obtained negative electrode was observed with an electron microscope in the same manner as in Example 1, the carbon fibers were well dispersed in the negative electrode material, and there was no carbon fiber aggregate exceeding 10 μm in diameter on the negative electrode surface after pressing. It was.
実施例４
ＶＧＣＦ−Ｈ２０ｇに、予め調製しておいたＣＭＣ１質量％水溶液を少しずつ加えながら、万能型ミキサーＴ.Ｋ.ハイビスミックス（登録商標）f-model ０３型（特殊機化工業株式会社製）を用いて、９０分間混練を行った。最終的に、ＶＧＣＦ―Ｈが１４．０質量％の炭素繊維含有組成物を調製した。この水溶液の粘度は、３０００ｍＰａ・ｓｅｃであった。
これ以降は、実施例１と同じ方法に従ってリチウム二次電池用負極を作製した。
得られた負極を実施例１と同様に電子顕微鏡にて観察したところ、炭素繊維は負極材中に良好に分散しており、プレス後の負極表面には直径１０μｍを超える炭素繊維凝集体はなかった。
Example 4
Using a universal mixer TK Hibismix (registered trademark) f-model 03 (manufactured by Tokushu Kika Kogyo Co., Ltd.) while adding a 1% by weight aqueous solution of CMC prepared in advance to 20 g of VGCF-H And kneading for 90 minutes. Finally, a carbon fiber-containing composition having VGCF-H of 14.0% by mass was prepared. The viscosity of this aqueous solution was 3000 mPa · sec.
Thereafter, a negative electrode for a lithium secondary battery was produced according to the same method as in Example 1.
When the obtained negative electrode was observed with an electron microscope in the same manner as in Example 1, the carbon fibers were well dispersed in the negative electrode material, and there was no carbon fiber aggregate exceeding 10 μm in diameter on the negative electrode surface after pressing. It was.
実施例５
ＶＧＣＦ−Ｓ２０ｇに、予め調製しておいたＣＭＣ１質量％水溶液を少しずつ加えながら、万能型ミキサーＴ.Ｋ.ハイビスミックス（登録商標）f-model ０３型（特殊機化工業株式会社製）を用いて、９０分間混練を行った。最終的に、ＶＧＣＦ−Ｓが５．３質量％の炭素繊維含有組成物を調製した。この水溶液の粘度は、４９００ｍＰａ・ｓｅｃであった。
これ以降は、実施例１と同じ方法に従ってリチウム二次電池用負極を作製した。
得られた負極を実施例１と同様に電子顕微鏡にて観察したところ、炭素繊維は負極材中に良好に分散しており、プレス後の負極表面には直径１０μｍを超える炭素繊維凝集体はなかった。
Example 5
Using a universal mixer TK Hibismix (registered trademark) f-model 03 (manufactured by Tokushu Kika Kogyo Co., Ltd.) while adding a 1% by weight aqueous solution of CMC prepared in advance little by little to 20 g of VGCF-S And kneading for 90 minutes. Finally, a carbon fiber-containing composition having VGCF-S of 5.3% by mass was prepared. The viscosity of this aqueous solution was 4900 mPa · sec.
Thereafter, a negative electrode for a lithium secondary battery was produced according to the same method as in Example 1.
When the obtained negative electrode was observed with an electron microscope in the same manner as in Example 1, the carbon fibers were well dispersed in the negative electrode material, and there was no carbon fiber aggregate exceeding 10 μm in diameter on the negative electrode surface after pressing. It was.
実施例６
ＶＧＮＴ２０ｇに、予め調製しておいたＣＭＣ１質量％水溶液を少しずつ加えながら、万能型ミキサーＴ.Ｋ.ハイビスミックス（登録商標）f-model ０３型（特殊機化工業株式会社製）を用いて、９０分間混練を行った。最終的に、ＶＧＮＴが５．３質量％の炭素繊維含有組成物を調製した。この水溶液の粘度は、４８００ｍＰａ・ｓｅｃであった。
これ以降は、実施例１と同じ方法に従ってリチウム二次電池用負極を作製した。
プレス前の負極材の状態を拡大観察した電子顕微鏡写真を図５に、プレス後の負極の表面状態を観察した電子顕微鏡写真を図６に示す。図５から明らかなように負極材中の炭素繊維は良好に分散しており、図６に示すプレス後の負極表面には直径１０μｍを超える炭素繊維凝集体はなかった。
Example 6
Using a universal mixer TK Hibismix (registered trademark) f-model 03 type (manufactured by Tokushu Kika Kogyo Co., Ltd.) while adding a 1% by weight aqueous solution of CMC prepared in advance little by little to VGNT 20 g, Kneading was performed for 90 minutes. Finally, a carbon fiber-containing composition having a VGNT of 5.3% by mass was prepared. The viscosity of this aqueous solution was 4800 mPa · sec.
Thereafter, a negative electrode for a lithium secondary battery was produced according to the same method as in Example 1.
FIG. 5 shows an electron micrograph obtained by observing the state of the negative electrode material before pressing, and FIG. 6 shows an electron micrograph obtained by observing the surface state of the negative electrode material after pressing. As is clear from FIG. 5, the carbon fibers in the negative electrode material were well dispersed, and there were no carbon fiber aggregates having a diameter exceeding 10 μm on the negative electrode surface after pressing shown in FIG.
実施例７
球状人造黒鉛ＭＣＭＢ（２５−２８）とＶＧＣＦを、乾燥状態で羽根つき高速小形ミキサーIKA Labotechnik Staufen（Janke & Kunkel GmbH）で１００００ｒｐｍで１０秒混合した。次に、ＰＶＤＦのＮＭＰ溶液（ＫＦ−ポリマー）を添加した。このとき、前記ＭＣＭＢとＶＧＣＦとＰＶＤＦの質量比が、９３：２：５となるように予め計算をして、調製した。
次いで、ＮＭＰを少量ずつ添加しながら負極組成物の粘度を調整した。このようにして得たリチウム二次電池用負極組成物を用いて、先述の「負極の作成」方法にしたがってリチウム二次電池用負極を作製した。
得られた負極を実施例１と同様に電子顕微鏡にて観察したところ、炭素繊維は負極材中に良好に分散しており、プレス後の負極表面には直径１０μｍを超える炭素繊維凝集体はなかった。
Example 7
Spherical artificial graphite MCMB (25-28) and VGCF were mixed in a dry high-speed small-sized mixer IKA Labotechnik Staufen (Janke & Kunkel GmbH) for 10 seconds at 10,000 rpm. Next, an NMP solution of PVDF (KF-polymer) was added. At this time, the mass ratio of MCMB, VGCF and PVDF was calculated in advance so as to be 93: 2: 5.
Subsequently, the viscosity of the negative electrode composition was adjusted while adding NMP little by little. Using the thus obtained negative electrode composition for a lithium secondary battery, a negative electrode for a lithium secondary battery was prepared according to the above-described “preparation of negative electrode” method.
When the obtained negative electrode was observed with an electron microscope in the same manner as in Example 1, the carbon fibers were well dispersed in the negative electrode material, and there was no carbon fiber aggregate exceeding 10 μm in diameter on the negative electrode surface after pressing. It was.
比較例１
球状天然黒鉛ＬＢ−ＣＧ２０ｇとＶＧＣＦ０．４ｇを、乾燥状態で羽根つき高速小形ミキサーIKA Labotechnik Staufen（Janke & Kunkel GmbH）で１００００ｒｐｍで１０秒混合した。予め調製しておいた１質量％ＣＭＣ水溶液をこの混合物に少しずつ加えながら、万能型ミキサーＴ.Ｋ.ハイビスミックス（登録商標）f-model ０３型（特殊機化工業株式会社製）を用いて、９０分間混練を行った。この水溶液にＳＢＲ分散水ＢＭ−４００Ｂを、ＳＢＲ固形分が１．５質量％となるよう加えて、１時間混練を行った。最終的にこの水溶液の粘度は、４６００ｍＰａ・ｓｅｃであった。
このようにして得たリチウム二次電池用負極組成物を用いて、先述の「負極の作成」方法にしたがってリチウム二次電池用負極を作製した。
プレス前の負極材の状態を拡大観察した電子顕微鏡写真を図７に、プレス後の負極の表面状態を観察した電子顕微鏡写真を図８に示す。図７から理解されるように負極材中の炭素繊維は凝集した状態で観察され、図８に示すプレス後の負極表面には多くの凸部分が目立っている。図８の凸部分を拡大した写真を図９に示す。図９から、その凸部は炭素繊維凝集体であり、その大きさは直径で２０μｍ程度であることが分かる。
Comparative Example 1
Spherical natural graphite LB-CG (20 g) and VGCF (0.4 g) were mixed at 10,000 rpm for 10 seconds in a dry high-speed small-sized mixer IKA Labotechnik Staufen (Janke & Kunkel GmbH). Using a universal mixer TK Hibismix (registered trademark) f-model 03 (manufactured by Tokushu Kika Kogyo Co., Ltd.) while adding 1% by weight CMC aqueous solution prepared in advance to this mixture little by little. And kneading for 90 minutes. SBR dispersion water BM-400B was added to this aqueous solution so that SBR solid content might be 1.5 mass%, and it knead | mixed for 1 hour. Finally, the viscosity of this aqueous solution was 4600 mPa · sec.
Using the thus obtained negative electrode composition for a lithium secondary battery, a negative electrode for a lithium secondary battery was prepared according to the above-described “preparation of negative electrode” method.
FIG. 7 shows an electron micrograph obtained by observing the state of the negative electrode material before pressing, and FIG. 8 shows an electron micrograph obtained by observing the surface state of the negative electrode material after pressing. As understood from FIG. 7, the carbon fibers in the negative electrode material are observed in an aggregated state, and many convex portions are conspicuous on the negative electrode surface after pressing shown in FIG. The photograph which expanded the convex part of FIG. 8 is shown in FIG. From FIG. 9, it can be seen that the convex portions are carbon fiber aggregates, and the size thereof is about 20 μm in diameter.
比較例２
ＶＧＣＦ２０ｇに、予め調製しておいたＣＭＣ１質量％水溶液を少しずつ加えながら、万能型ミキサーＴ.Ｋ.ハイビスミックス（登録商標）f-model ０３型（特殊機化工業株式会社製）を用いて、９０分間混練を行った。最終的に、ＶＧＣＦが２５質量％の炭素繊維含有組成物を調製した。この水溶液の粘度は、１２０００ｍＰａ・ｓｅｃであった。
球状天然黒鉛ＬＢ−ＣＧ７０ｇに、予め調製しておいたＣＭＣ１質量％水溶液を少しずつ加えながら、Ｔ.Ｋ.ハイビスミックス（登録商標）f-model ０３型を用いて、２時間混練を行った。最終的に、球状天然黒鉛ＬＢ−ＣＧが５０質量％のＣＭＣ水溶液を調製した。この水溶液にＳＢＲ分散水ＢＭ−４００Ｂを、ＳＢＲ固形分が１．５質量％となるよう加えて、１時間混練を行った。この負極材含有増粘剤水溶液の粘度は、３５００ｍＰａ・ｓｅｃであった。
次に、ＬＢ−ＣＧとＶＧＣＦとＳＢＲとＣＭＣの合計を１００質量％とした時に、ＶＧＣＦ含有量が２質量％となるよう、炭素繊維含有組成物と負極材含有増粘剤水溶液を加え合わせ、さらに１５分間混練した。
このようにして得たリチウム二次電池用負極組成物を用いて、先述の「負極の作成」方法にしたがってリチウム二次電池用負極を作製した。
得られた負極を電子顕微鏡にて観察したところ、炭素繊維は負極材中に凝集した状態で存在し、プレス後には負極表面に直径２０μｍを超える炭素繊維凝集体が多く点在していた。
Comparative Example 2
Using a universal mixer TK Hibismix (registered trademark) f-model 03 (manufactured by Tokushu Kika Kogyo Co., Ltd.) while adding a 1% by weight aqueous solution of CMC prepared in advance little by little to 20 g of VGCF, Kneading was performed for 90 minutes. Finally, a carbon fiber-containing composition having a VGCF of 25% by mass was prepared. The viscosity of this aqueous solution was 12000 mPa · sec.
The mixture was kneaded for 2 hours using TK Hibismix (registered trademark) f-model 03 type while gradually adding a 1% by weight aqueous solution of CMC prepared in advance to 70 g of spherical natural graphite LB-CG. Finally, a CMC aqueous solution containing 50% by mass of spherical natural graphite LB-CG was prepared. SBR dispersion water BM-400B was added to this aqueous solution so that SBR solid content might be 1.5 mass%, and it knead | mixed for 1 hour. The viscosity of this negative electrode material-containing thickener aqueous solution was 3500 mPa · sec.
Next, when the total of LB-CG, VGCF, SBR and CMC is 100% by mass, the carbon fiber-containing composition and the negative electrode material-containing thickener aqueous solution are added together so that the VGCF content is 2% by mass, The mixture was further kneaded for 15 minutes.
Using the thus obtained negative electrode composition for a lithium secondary battery, a negative electrode for a lithium secondary battery was prepared according to the above-described “preparation of negative electrode” method.
When the obtained negative electrode was observed with an electron microscope, the carbon fibers were present in an aggregated state in the negative electrode material, and many carbon fiber aggregates having a diameter exceeding 20 μm were scattered on the negative electrode surface after pressing.
比較例３
ＶＧＣＦ２０ｇに、予め調製しておいたＣＭＣ１質量％水溶液を少しずつ加えながら、万能型ミキサーＴ.Ｋ.ハイビスミックス（登録商標）f-model ０３型（特殊機化工業株式会社製）を用いて、９０分間混練を行った。最終的に、ＶＧＣＦが８．５質量％の炭素繊維含有組成物を調製した。この水溶液の粘度は、４０００ｍＰａ・ｓｅｃであった。
球状天然黒鉛ＬＢ−ＣＧ７０ｇに、予め調製しておいたＣＭＣ１質量％水溶液を少しずつ加えながら、Ｔ.Ｋ.ハイビスミックス（登録商標）f-model ０３型を用いて、２時間混練を行った。最終的に、球状天然黒鉛ＬＢ−ＣＧが６０質量％のＣＭＣ水溶液を調製した。この水溶液にＳＢＲ分散水ＢＭ−４００Ｂを、ＳＢＲ固形分が１．５質量％となるよう加えて、１時間混練を行った。この負極材含有増粘剤水溶液の粘度は、１００００ｍＰａ・ｓｅｃであった。
次に、ＬＢ−ＣＧとＶＧＣＦとＳＢＲとＣＭＣの合計を１００質量％とした時に、ＶＧＣＦ含有量が２質量％となるよう、炭素繊維含有組成物と負極材含有増粘剤水溶液を加え合わせ、さらに１５分間混練した。
このようにして得たリチウム二次電池用負極組成物を用いて、先述の「負極の作成」方法にしたがってリチウム二次電池用負極を作製した。
得られた負極を電子顕微鏡にて観察したところ、炭素繊維は負極材中に凝集した状態で存在し、プレス後には負極表面に直径２０μｍを超える炭素繊維凝集体が多く点在していた。
Comparative Example 3
Using a universal mixer TK Hibismix (registered trademark) f-model 03 (manufactured by Tokushu Kika Kogyo Co., Ltd.) while adding a 1% by weight aqueous solution of CMC prepared in advance little by little to 20 g of VGCF, Kneading was performed for 90 minutes. Finally, a carbon fiber-containing composition having a VGCF of 8.5% by mass was prepared. The viscosity of this aqueous solution was 4000 mPa · sec.
The mixture was kneaded for 2 hours using TK Hibismix (registered trademark) f-model 03 type while gradually adding a 1% by weight aqueous solution of CMC prepared in advance to 70 g of spherical natural graphite LB-CG. Finally, a CMC aqueous solution containing 60% by mass of spherical natural graphite LB-CG was prepared. SBR dispersion water BM-400B was added to this aqueous solution so that SBR solid content might be 1.5 mass%, and it knead | mixed for 1 hour. The viscosity of this negative electrode material-containing thickener aqueous solution was 10,000 mPa · sec.
Next, when the total of LB-CG, VGCF, SBR and CMC is 100% by mass, the carbon fiber-containing composition and the negative electrode material-containing thickener aqueous solution are added together so that the VGCF content is 2% by mass, The mixture was further kneaded for 15 minutes.
Using the thus obtained negative electrode composition for a lithium secondary battery, a negative electrode for a lithium secondary battery was prepared according to the above-described “preparation of negative electrode” method.
When the obtained negative electrode was observed with an electron microscope, the carbon fibers were present in an aggregated state in the negative electrode material, and many carbon fiber aggregates having a diameter exceeding 20 μm were scattered on the negative electrode surface after pressing.
比較例４
ＶＧＣＦ２０ｇに、予め調製しておいたＣＭＣ１質量％水溶液を少しずつ加えながら、万能型ミキサーＴ.Ｋ.ハイビスミックス（登録商標）f-model ０３型（特殊機化工業株式会社製）を用いて、９０分間混練を行った。最終的に、ＶＧＣＦが８．５質量％の炭素繊維含有組成物を調製した。この水溶液の粘度は、４０００ｍＰａ・ｓｅｃであった。
球状天然黒鉛ＬＢ−ＣＧ７０ｇにＶＧＣＦの割合が２質量％となるように炭素繊維含有組成物を加えて、Ｔ.Ｋ.ハイビスミックス（登録商標）f-model ０３型を用いて２時間混練を行った。このとき、１質量％ＣＭＣ水溶液を粘度調製のために追加使用した。次いで、この水溶液にＳＢＲ分散水ＢＭ−４００ＢをＳＢＲ固形分が１．５質量％となるよう加えて、１時間混練を行った。この時リチウム二次電池用負極組成物の粘度は、４０００ｍＰａ・ｓｅｃであった。
このようにして得たリチウム二次電池用負極組成物を用いて、先述の「負極の作成」方法にしたがってリチウム二次電池用負極を作製した。
得られた負極を電子顕微鏡にて観察したところ、炭素繊維は負極材中に凝集した状態で存在し、プレス後には負極表面に直径２０μｍを超える炭素繊維凝集体が多く点在していた。
Comparative Example 4
Using a universal mixer TK Hibismix (registered trademark) f-model 03 (manufactured by Tokushu Kika Kogyo Co., Ltd.) while adding a 1% by weight aqueous solution of CMC prepared in advance little by little to 20 g of VGCF, Kneading was performed for 90 minutes. Finally, a carbon fiber-containing composition having a VGCF of 8.5% by mass was prepared. The viscosity of this aqueous solution was 4000 mPa · sec.
A carbon fiber-containing composition is added to 70 g of spherical natural graphite LB-CG so that the ratio of VGCF is 2% by mass, and kneading is performed for 2 hours using TK Hibismix (registered trademark) f-model 03 type. It was. At this time, a 1 mass% CMC aqueous solution was additionally used for viscosity adjustment. Subsequently, SBR dispersion water BM-400B was added to this aqueous solution so that SBR solid content might be 1.5 mass%, and it knead | mixed for 1 hour. At this time, the viscosity of the negative electrode composition for a lithium secondary battery was 4000 mPa · sec.
Using the thus obtained negative electrode composition for a lithium secondary battery, a negative electrode for a lithium secondary battery was prepared according to the above-described “preparation of negative electrode” method.
When the obtained negative electrode was observed with an electron microscope, the carbon fibers were present in an aggregated state in the negative electrode material, and many carbon fiber aggregates having a diameter exceeding 20 μm were scattered on the negative electrode surface after pressing.
比較例５
球状天然黒鉛ＬＢ−ＣＧ７０ｇに、予め調製しておいたＣＭＣ１質量％水溶液を少しずつ加えながら、Ｔ.Ｋ.ハイビスミックス（登録商標）f-model ０３型を用いて、２時間混練を行った。最終的に、球状天然黒鉛ＬＢ−ＣＧが５０質量％のＣＭＣ水溶液を調製した。
これにＶＧＣＦを加えて、粘度調製のために１質量％ＣＭＣ水溶液を少しずつ加えながら２時間混練を行った。次いで、この水溶液にＳＢＲ分散水ＢＭ−４００ＢをＳＢＲ固形分が１．５質量％となるよう加えて、１時間混練を行った。この時リチウム二次電池用負極組成物の粘度は、４０００ｍＰａ・ｓｅｃであった。
このようにして得たリチウム二次電池用負極組成物を用いて、先述の「負極の作成」方法にしたがってリチウム二次電池用負極を作製した。
得られた負極を電子顕微鏡にて観察したところ、炭素繊維は負極材中に凝集した状態で存在し、プレス後には負極表面に直径２０μｍを超える炭素繊維凝集体が多く点在していた。
Comparative Example 5
The mixture was kneaded for 2 hours using TK Hibismix (registered trademark) f-model 03 type while gradually adding a 1% by weight aqueous solution of CMC prepared in advance to 70 g of spherical natural graphite LB-CG. Finally, a CMC aqueous solution containing 50% by mass of spherical natural graphite LB-CG was prepared.
VGCF was added thereto, and kneading was performed for 2 hours while adding a 1% by mass CMC aqueous solution little by little to adjust the viscosity. Subsequently, SBR dispersion water BM-400B was added to this aqueous solution so that SBR solid content might be 1.5 mass%, and it knead | mixed for 1 hour. At this time, the viscosity of the negative electrode composition for a lithium secondary battery was 4000 mPa · sec.
Using the thus obtained negative electrode composition for a lithium secondary battery, a negative electrode for a lithium secondary battery was prepared according to the above-described “preparation of negative electrode” method.
When the obtained negative electrode was observed with an electron microscope, the carbon fibers were present in an aggregated state in the negative electrode material, and many carbon fiber aggregates having a diameter exceeding 20 μm were scattered on the negative electrode surface after pressing.
比較例６
球状人造黒鉛ＭＣＭＢ（２５−２８）にＫＦ−ポリマーを添加し、Ｔ.Ｋ.ハイビスミックス（登録商標）f-model ０３型を用いて、１５時間混練を行った。その後、この混練物にＶＧＣＦを添加し、さらに混練を行った。このとき、ＭＣＭＢとＶＧＣＦとＰＶＤＦの質量比が、９３：２：５となるように予め計算をして、調製した。
次いで、ＮＭＰを少量ずつ添加しながら負極組成物の粘度を調整した。このようにして得たリチウム二次電池用負極組成物を用いて、先述の「負極の作成」方法にしたがってリチウム二次電池用負極を作製した。
プレス前の負極材の状態を拡大観察した電子顕微鏡写真を図１０に示す。図１０から明らかなように負極材中の炭素繊維は凝集した状態となっている。また、プレス後には負極表面に直径２０μｍを超える炭素繊維凝集体が多く点在していた。
Comparative Example 6
KF-polymer was added to spherical artificial graphite MCMB (25-28), and kneading was performed for 15 hours using a TK Hibismix (registered trademark) f-model 03 type. Thereafter, VGCF was added to the kneaded material and further kneaded. At this time, it was prepared by calculating in advance such that the mass ratio of MCMB, VGCF, and PVDF was 93: 2: 5.
Subsequently, the viscosity of the negative electrode composition was adjusted while adding NMP little by little. Using the thus obtained negative electrode composition for a lithium secondary battery, a negative electrode for a lithium secondary battery was prepared according to the above-described “preparation of negative electrode” method.
The electron micrograph which expandedly observed the state of the negative electrode material before a press is shown in FIG. As is clear from FIG. 10, the carbon fibers in the negative electrode material are in an aggregated state. Further, after the pressing, many carbon fiber aggregates having a diameter exceeding 20 μm were scattered on the negative electrode surface.
比較例７
ＶＧＣＦにＫＦ−ポリマーを添加し、Ｔ.Ｋ.ハイビスミックス（登録商標）f-model ０３型を用いて、１５時間混練を行った。その後、この混練物に球状人造黒鉛ＭＣＭＢ（２５−２８）を添加し、さらに混練を行った。このとき、ＭＣＭＢとＶＧＣＦとＰＶＤＦの質量比が、９３：２：５となるように予め計算をして、調製した。
次いで、ＮＭＰを少量ずつ添加しながら負極組成物の粘度を調整した。このようにして得たリチウム二次電池用負極組成物を用いて、先述の「負極の作成」方法にしたがってリチウム二次電池用負極を作製した。
得られた負極を電子顕微鏡にて観察したところ、炭素繊維は負極材中に凝集した状態で存在し、プレス後には負極表面に直径２０μｍを超える炭素繊維凝集体が多く点在していた。
Comparative Example 7
KF-polymer was added to VGCF, and kneading was performed for 15 hours using TK Hibismix (registered trademark) f-model 03 type. Thereafter, spherical artificial graphite MCMB (25-28) was added to this kneaded product, and further kneaded. At this time, it was prepared by calculating in advance such that the mass ratio of MCMB, VGCF, and PVDF was 93: 2: 5.
Subsequently, the viscosity of the negative electrode composition was adjusted while adding NMP little by little. Using the thus obtained negative electrode composition for a lithium secondary battery, a negative electrode for a lithium secondary battery was prepared according to the above-described “preparation of negative electrode” method.
When the obtained negative electrode was observed with an electron microscope, the carbon fibers were present in an aggregated state in the negative electrode material, and many carbon fiber aggregates having a diameter exceeding 20 μm were scattered on the negative electrode surface after pressing.
比較例８
球状天然黒鉛ＬＢ−ＣＧ７０ｇに、予め調製しておいたＣＭＣ１質量％水溶液を少しずつ加えながら、Ｔ.Ｋ.ハイビスミックス（登録商標）f-model ０３型を用いて、２時間混練を行った。最終的に、球状天然黒鉛ＬＢ−ＣＧが５０質量％のＣＭＣ水溶液を調製した。この水溶液にＳＢＲ分散水ＢＭ−４００Ｂを、ＳＢＲ固形分が１．５質量％となるよう加えて、１時間混練を行った。このＣＭＣ水溶液の粘度は、３５００ｍＰａ・ｓｅｃであった。
このようにして得たリチウム二次電池用負極組成物を用いて、先述の「負極の作成」方法にしたがってリチウム二次電池用負極を作製した。
Comparative Example 8
The mixture was kneaded for 2 hours using TK Hibismix (registered trademark) f-model 03 type while gradually adding a 1% by weight aqueous solution of CMC prepared in advance to 70 g of spherical natural graphite LB-CG. Finally, a CMC aqueous solution containing 50% by mass of spherical natural graphite LB-CG was prepared. SBR dispersion water BM-400B was added to this aqueous solution so that SBR solid content might be 1.5 mass%, and it knead | mixed for 1 hour. The viscosity of this CMC aqueous solution was 3500 mPa · sec.
Using the thus obtained negative electrode composition for a lithium secondary battery, a negative electrode for a lithium secondary battery was prepared according to the above-described “preparation of negative electrode” method.
比較例９
塊状人造黒鉛ＳＣＭＧ−Ａ７０ｇに、予め調製しておいたＣＭＣ１質量％水溶液を少しずつ加えながら、Ｔ.Ｋ.ハイビスミックス（登録商標）f-model ０３型を用いて、２時間混練を行った。最終的に、塊状人造黒鉛ＳＣＭＧ−Ａが６０質量％のＣＭＣ水溶液を調製した。この水溶液にＳＢＲ分散水ＢＭ−４００Ｂを、ＳＢＲ固形分が１．５質量％となるよう加えて、１時間混練を行った。このＣＭＣ水溶液の粘度は、３０００ｍＰａ・ｓｅｃであった。
このようにして得たリチウム二次電池用負極組成物を用いて、先述の「負極の作成」方法にしたがってリチウム二次電池用負極を作製した。
Comparative Example 9
The mixture was kneaded for 2 hours using TK Hibismix (registered trademark) f-model 03 type while gradually adding a 1% by weight aqueous solution of CMC prepared in advance to 70 g of massive artificial graphite SCMG-A. Finally, a CMC aqueous solution containing 60% by mass of massive artificial graphite SCMG-A was prepared. SBR dispersion water BM-400B was added to this aqueous solution so that SBR solid content might be 1.5 mass%, and it knead | mixed for 1 hour. The viscosity of this CMC aqueous solution was 3000 mPa · sec.
Using the thus obtained negative electrode composition for a lithium secondary battery, a negative electrode for a lithium secondary battery was prepared according to the above-described “preparation of negative electrode” method.
比較例１０
球状人造黒鉛ＭＣＭＢ（２５−２８）にＫＦ−ポリマーを添加し、Ｔ.Ｋ.ハイビスミックス（登録商標）f-model ０３型を用いて、１５時間混練を行った。このとき、ＭＣＭＢ（２５−２８）とＰＶＤＦの質量比が、９５：５となるように予め計算をして、調製した。
次いで、ＮＭＰを少量ずつ添加しながら負極組成物の粘度を調整した。このようにして得たリチウム二次電池用負極組成物を用いて、先述の「負極の作成」方法にしたがってリチウム二次電池用負極を作製した。
Comparative Example 10
KF-polymer was added to spherical artificial graphite MCMB (25-28), and kneading was performed for 15 hours using a TK Hibismix (registered trademark) f-model 03 type. At this time, it was prepared in advance so that the mass ratio of MCMB (25-28) to PVDF was 95: 5.
Subsequently, the viscosity of the negative electrode composition was adjusted while adding NMP little by little. Using the thus obtained negative electrode composition for a lithium secondary battery, a negative electrode for a lithium secondary battery was prepared according to the above-described “preparation of negative electrode” method.
本発明はあらゆる形式、様式のリチウム二次電池に適用でき、そのリチウム二次電池は携帯電話やモバイル電子機器の電源、自動車用バッテリー、電動工具用バッテリーなどに使用できる。 The present invention can be applied to lithium secondary batteries of all types and styles, and the lithium secondary batteries can be used as power sources for mobile phones and mobile electronic devices, automobile batteries, electric tool batteries, and the like.
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| WO2013085241A1 (en) * | 2011-12-09 | 2013-06-13 | 주식회사 엘지화학 | Lithium secondary battery comprising spherical natural graphite as anode active material |
| US9853289B2 (en) | 2011-12-09 | 2017-12-26 | Lg Chem, Ltd. | Lithium secondary battery comprising spherical graphite as anode active material |
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