JP2008016456A - Negative electrode material for lithium battery and lithium battery - Google Patents
Negative electrode material for lithium battery and lithium battery Download PDFInfo
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Abstract
Description
本発明は、体積あたりの充放電容量が大きく、充放電サイクル特性、大電流負荷特性に優れたリチウム電池用炭素系負極材、その負極材を得るための組成物、その製造方法、及びリチウム電池用炭素系負極材を用いたリチウム電池及びリチウム二次電池に関する。 The present invention relates to a carbon-based negative electrode material for a lithium battery having a large charge / discharge capacity per volume and excellent charge / discharge cycle characteristics and large current load characteristics, a composition for obtaining the negative electrode material, a production method thereof, and a lithium battery. The present invention relates to a lithium battery and a lithium secondary battery using a carbon-based negative electrode material.
携帯機器の小型軽量化及び高性能化に伴い、高いエネルギー密度を有する二次電池、二次電池の高容量化が益々求められている。このような背景の下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、高エネルギー密度、高電圧という特徴から非水系電解液を用いるリチウムイオン電池やリチウムポリマー電池のような非水系リチウム二次電池が多くの機器に使われるようになっている。これらリチウム二次電池に用いられる負極材料としては、リチウム(Li)に近い卑な電位で単位質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。しかしながらこれらの電極材料は質量あたりの充放電容量が理論値に近いところまで使われており、電池としての質量あたりのエネルギー密度は限界に近づいている。従って、電極としての利用率を上げるため、放電容量には寄与しない電極結着材や導電助剤を減らす試みが行われている。 2. Description of the Related Art As mobile devices become smaller and lighter and have higher performance, there is an increasing demand for secondary batteries having high energy density and higher capacities of secondary batteries. Under such circumstances, as secondary batteries for small portable devices such as mobile phones and video cameras, non-aqueous systems such as lithium ion batteries and lithium polymer batteries that use non-aqueous electrolytes due to the characteristics of high energy density and high voltage. Lithium secondary batteries are used in many devices. As a negative electrode material used for these lithium secondary batteries, a carbon material typified by graphite having a large potential charge / discharge capacity per unit mass at a base potential close to lithium (Li) is used. However, these electrode materials are used up to the point where the charge / discharge capacity per mass is close to the theoretical value, and the energy density per mass as a battery is approaching its limit. Therefore, in order to increase the utilization rate as an electrode, attempts have been made to reduce electrode binders and conductive aids that do not contribute to the discharge capacity.
負極用結着材としてはこれまではポリフッ化ビニリデン(PVDFと略す。)及びその共重合体に代表されるフッ素樹脂が主に用いられてきたが、最近ではスチレンブタジエン系ゴム(SBRと略す。)が添加量を少なくできることや、水系分散液で用いるため電極製造工程が簡易化されることなどのメリットから多く用いられるようになってきた。
また、導電助剤として、従来のアセチレンブラックのようなカーボンブラックに比較し、高導電性で電極強度にも効果のある気相成長炭素繊維が多く使われるようになっている。例えば、特開平4−155776号公報(特許文献1)、特開平4−237971号公報(特許文献2)等では黒鉛負極に気相成長炭素繊維を添加することにより、電極抵抗を下げ、電池の負荷特性を改善したり、電極の強度を上げ、電極の耐膨張収縮性を上げ、リチウム二次電池のサイクル寿命を向上させている。
しかしながら、気相成長炭素繊維は疎水性であるため結着材としては有機溶媒分散系のPVDFとの組み合わせで用いられており、水系分散液であるSBRとの併用は行われていない。
Up to now, polyvinylidene fluoride (abbreviated as PVDF) and fluororesins typified by copolymers thereof have been mainly used as the binder for the negative electrode, but recently it is abbreviated as styrene butadiene rubber (SBR). ) Has been widely used because of its merit such that the addition amount can be reduced and the electrode manufacturing process is simplified because it is used in an aqueous dispersion.
Further, as a conductive auxiliary agent, vapor grown carbon fibers that are highly conductive and effective in electrode strength are used more often than conventional carbon black such as acetylene black. For example, in JP-A-4-155576 (Patent Document 1), JP-A-4-237971 (Patent Document 2) and the like, by adding a vapor-grown carbon fiber to a graphite negative electrode, the electrode resistance is lowered, The load characteristics are improved, the strength of the electrode is increased, the expansion and contraction resistance of the electrode is increased, and the cycle life of the lithium secondary battery is improved.
However, since the vapor-grown carbon fiber is hydrophobic, it is used as a binder in combination with PVDF in an organic solvent dispersion, and is not used in combination with SBR as an aqueous dispersion.
また、小型携帯機器に用いられる二次電池として、よりコンパクトなものが要求され、質量あたりのエネルギー密度だけでなく、体積あたりのエネルギー密度も高いことが要求されている。従って、上述したように理論値に近づいてきている電極材料の電極密度を上げ、電池容器内の充填量を高め、電極及び電池としての体積あたりのエネルギー密度を高める検討がされ始めた。 Further, a secondary battery used in a small portable device is required to be more compact, and not only the energy density per mass but also the energy density per volume is required to be high. Therefore, studies have been started to increase the electrode density of electrode materials that are approaching the theoretical value as described above, to increase the filling amount in the battery container, and to increase the energy density per volume of the electrode and the battery.
例えば、現在負極材料として最も多く用いられている黒鉛はその真密度が2.2g/cm3程度であるが、これまで負極密度としては1.5g/cm3程度のものが用いられていた。負極密度を1.7g/cm3以上とすることにより電池体積あたりのエネルギー密度を向上させることが可能と考えられるが、負極密度を上げると、負極内の空孔は減少し、通常、空孔内に存在する電極反応に重要な電解液の不足を招いたり、電解液の負極内の浸透が遅くなるという問題が生じてくる。負極内の電解液が不足すると、電極反応が遅くなり、エネルギー密度の低下や高速充放電性能が低下し、また、電解液の浸透性が遅くなると電池製造時間が長くなり、製造コストアップにつながる。リチウムポリマー電池のような高粘性のポリマー電解液を用いる場合には、これらの問題がより顕著になってくる。 For example, graphite, which is most frequently used as a negative electrode material at present, has a true density of about 2.2 g / cm 3 , but so far, a negative electrode density of about 1.5 g / cm 3 has been used. It is considered that the energy density per battery volume can be improved by setting the negative electrode density to 1.7 g / cm 3 or more. However, when the negative electrode density is increased, the number of vacancies in the negative electrode is decreased. There arises a problem that the electrolyte solution that is important for the electrode reaction existing therein is insufficient, and the penetration of the electrolyte solution into the negative electrode is slow. When the electrolyte in the negative electrode is insufficient, the electrode reaction is delayed, the energy density is lowered and the high-speed charge / discharge performance is lowered, and when the permeability of the electrolyte is slow, the battery production time is prolonged, leading to an increase in production cost. . These problems become more prominent when a highly viscous polymer electrolyte solution such as a lithium polymer battery is used.
本発明は、サイクル特性、高速充放電性能に優れた高エネルギー密度リチウム電池を達成するために必要な、高エネルギー密度炭素系負極材を提供することを目的とする。 An object of this invention is to provide the high energy density carbon-type negative electrode material required in order to achieve the high energy density lithium battery excellent in cycling characteristics and high-speed charge / discharge performance.
本発明者らは、炭素系負極材の問題点に鑑みて、上記課題を解決するために鋭意検討を重ねた結果、炭素系負極材に、添加量が比較的少量で結着性のあるSBRを結着材として用い、導電助剤として繊維径1〜1000nmの炭素繊維を均一に分散させることにより、電極抵抗が低く、電極強度が良好で、電解液浸透性も高く、高エネルギー密度で高速充放電性能の良好な高性能の電池が得られることを見出し、本発明を完成した。
すなわち、本発明は、以下のリチウム電池用負極材、その製造方法及び用途等を提供するものである。
In light of the problems of the carbon-based negative electrode material, the present inventors have made extensive studies to solve the above problems, and as a result, the carbon-based negative electrode material has a relatively small addition amount and has a binding property. Is used as a binder, and carbon fibers having a fiber diameter of 1 to 1000 nm are uniformly dispersed as a conductive auxiliary agent, so that electrode resistance is low, electrode strength is good, electrolyte solution permeability is high, high energy density and high speed. The inventors have found that a high-performance battery with good charge / discharge performance can be obtained and completed the present invention.
That is, this invention provides the following negative electrode materials for lithium batteries, its manufacturing method, a use, etc.
[1]比表面積1m2/g以上の炭素系負極活物質、スチレンブタジエンゴムからなる結着材、及び繊維径1〜1000nmの炭素繊維を含有することを特徴とするリチウム電池用負極材。
[2]スチレンブタジエンゴムが平均粒径10〜500nmの微粒子である前記1に記載のリチウム電池用負極材。
[3]炭素系負極活物質、結着材及び炭素繊維の合計量に対して、炭素繊維の含有量が0.05〜20質量%であり、スチレンブタジエンゴムからなる結着材の含有量が0.1〜6.0質量%である前記1または2に記載のリチウム電池用負極材。
[4]さらに増粘剤を含む前記1乃至3のいずれかに記載のリチウム電池用負極材。
[5]増粘剤の含有量が、炭素系負極活物質、結着材、炭素繊維及び増粘剤の合計量に対して、0.1〜4質量%である前記4に記載のリチウム電池用負極材。
[6]増粘剤がカルボキシメチルセルロースである前記4に記載のリチウム電池用負極材。
[7]25℃での負極の比抵抗が0.5Ωcm以下である前記1乃至6のいずれかに記載のリチウム電池用負極材。
[8]炭素繊維が、2000℃以上で熱処理された黒鉛系炭素繊維である前記1乃至7のいずれかに記載のリチウム電池用負極材。
[9]炭素繊維が、酸化処理により表面に含酸素官能基が導入された黒鉛系炭素繊維である前記1乃至7のいずれかに記載のリチウム電池用負極材。
[10]炭素繊維が、ホウ素を0.1〜100000ppm含有する黒鉛系炭素繊維である前記1乃至7のいずれかに記載のリチウム電池用負極材。
[11]黒鉛系炭素繊維のX線回折法による(002)面の平均面間隔d002が、0.344nm以下である前記8に記載のリチウム電池用負極材。
[12]炭素繊維が内部に中空構造を有するものである前記1乃至11のいずれかに記載のリチウム電池用負極材。
[13]炭素繊維が分岐状炭素繊維を含む前記1乃至12のいずれかに記載のリチウム電池用負極材。
[14]炭素系負極活物質がSiを含む前記1乃至13のいずれかに記載のリチウム電池用負極材。
[15]炭素系負極活物質が非黒鉛系炭素材料であり、負極活物質、結着材、及び導電助剤からなる合剤層の密度が1.5g/cm3以上である前記1乃至14のいずれかに記載のリチウム電池用負極材。
[16]電極成形前の炭素系負極活物質が、以下の要件を満足する炭素質粒子である前記1乃至15のいずれかに記載のリチウム電池用負極材:
(1)フロー式粒子像解析装置によって測定される平均円形度が0.70〜0.99、
(2)レーザー回折法による平均粒子径が1〜50μm。
[17]炭素系負極活物質が50質量%以上の黒鉛炭素系材料を含む前記1乃至16のいずれかに記載のリチウム電池用負極材。
[18]黒鉛系材料がホウ素を含む前記17に記載のリチウム電池用負極材。
[19]電極活物質の電極成形前の炭素系負極活物質が、以下の要件を満足する黒鉛粒子を50質量%以上含む炭素質粒子である前記1乃至18のいずれかに記載のリチウム電池用負極材:
(1)フロー式粒子像解析装置によって測定される平均円形度が0.70〜0.99、
(2)レーザー回折法による平均粒子径が1〜50μm。
[20]黒鉛系炭素材料が、以下の要件を満足する黒鉛粒子を50質量%以上含む炭素質粒子である前記17に記載のリチウム電池用負極材:
(1)X線回折測定での(002)面のC0が0.6900nm以下、La(a軸方向の結晶子サイズ)>100nm、Lc(c軸方向の結晶子サイズ)>100nm、
(2)比表面積が1.0〜10m2/g、
(3)真密度が2.20g/cm3以上、
(4)レーザーラマンR値(レーザーラマンスペクトルによる1580cm-1のピーク強度に対する1360cm-1のピーク強度比)が0.01〜0.9。
[21]負極活物質、結着材、及び導電助剤からなる合剤層の密度が1.7g/cm3以上である前記15に記載のリチウム電池用負極材。
[22]増粘剤水溶液中に繊維径1〜1000nmの炭素繊維、比表面積1m2/g以上の炭素系負極活物質を分散してなる炭素繊維/活物質分散液に、スチレンブタジエンゴム水系分散液を添加し、撹拌混合することを特徴とするリチウム電池用負極材用組成物の製造方法。
[23]炭素繊維/活物質分散液が、増粘剤水溶液に繊維径1〜1000nmの炭素繊維を添加、撹拌して炭素繊維を分散させた後、比表面積1m2/g以上の炭素系負極活物質を添加し、撹拌混合することにより調製されるものである前記22に記載のリチウム電池用負極材用組成物の製造方法。
[24]炭素繊維/活物質分散液が、増粘剤水溶液に繊維径1〜1000nmの炭素繊維を添加、撹拌して炭素繊維を分散させた後、比表面積1m2/g以上の炭素系負極活物質を添加し、撹拌混合後、さらに増粘剤水溶液により調製されるものである前記22に記載のリチウム電池用負極材用組成物の製造方法。
[25]炭素繊維/活物質分散液が、増粘剤水溶液に比表面積1m2/g以上の炭素系負極活物質を添加し、撹拌混合後、繊維径1〜1000nmの炭素繊維を添加、撹拌して炭素繊維を分散させることにより調製されるものである前記22に記載のリチウム電池用負極材用組成物の製造方法。
[26]炭素繊維/活物質分散液が、比表面積1m2/g以上の炭素系負極活物質と繊維径1〜1000nmの炭素繊維を乾式撹拌し炭素繊維を分散させた後、増粘剤水溶液を添加、撹拌混合することにより調製されるものである前記22に記載のリチウム電池用負極材用組成物の製造方法。
[27]増粘剤水溶液中の増粘剤の濃度が0.3〜5質量%であり、スチレンブタジエンゴム水系分散液中のスチレンブタジエンゴムの濃度が10〜60質量%である前記22乃至26のいずれかに記載のリチウム電池用負極材用組成物の製造方法。
[28]増粘剤がカルボキシメチルセルロースである前記22乃至27のいずれかに記載のリチウム電池用負極材用組成物の製造方法。
[29]前記22乃至28のいずれかに記載の方法で得られるリチウム電池用負極材用組成物。
[30]増粘剤水溶液に繊維径1〜1000nmの炭素繊維が分散したリチウム電池用負極材組成物。
[31]増粘剤水溶液中の増粘剤の濃度が0.3〜5質量%であり、組成物全体に占める炭素繊維の割合が0.1〜10質量%である前記30に記載のリチウム電池用負極材組成物。
[32]増粘剤がカルボキシメチルセルロースである前記30または31に記載のリチウム電池用負極材組成物。
[33]前記29に記載のリチウム電池用負極材用組成物を金属集電体箔上に塗布し、乾燥後、加圧成形してなる前記1乃至21のいずれかに記載のリチウム電池用負極材。
[34]金属集電体箔が厚み1〜50μmの銅箔または銅合金箔である前記33に記載のリチウム電池用負極材。
[35]前記1乃至21、33及び34のいずれかに記載のリチウム電池用負極材を構成要素として含むリチウム電池。
[36]前記1乃至21、33及び34のいずれかに記載のリチウム電池用負極材を構成要素として含むリチウム二次電池。
[37]非水系電解質を用い、前記非水系電解質の非水系溶媒として、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、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種を用いる前記36に記載のリチウム二次電池。
以下、本発明を詳細に説明する。
[1] A negative electrode material for a lithium battery, comprising a carbon-based negative electrode active material having a specific surface area of 1 m 2 / g or more, a binder made of styrene butadiene rubber, and carbon fibers having a fiber diameter of 1 to 1000 nm.
[2] The negative electrode material for a lithium battery as described in 1 above, wherein the styrene-butadiene rubber is fine particles having an average particle diameter of 10 to 500 nm.
[3] The carbon fiber content is 0.05 to 20% by mass with respect to the total amount of the carbon-based negative electrode active material, the binder and the carbon fiber, and the content of the binder made of styrene butadiene rubber is 3. The negative electrode material for a lithium battery as described in 1 or 2 above, which is 0.1 to 6.0% by mass.
[4] The negative electrode material for a lithium battery according to any one of 1 to 3, further comprising a thickener.
[5] The lithium battery as described in 4 above, wherein the content of the thickener is 0.1 to 4% by mass with respect to the total amount of the carbon-based negative electrode active material, the binder, the carbon fiber, and the thickener. Negative electrode material.
[6] The negative electrode material for a lithium battery as described in 4 above, wherein the thickener is carboxymethylcellulose.
[7] The negative electrode material for a lithium battery as described in any one of 1 to 6 above, wherein the specific resistance of the negative electrode at 25 ° C. is 0.5 Ωcm or less.
[8] The negative electrode material for a lithium battery according to any one of 1 to 7, wherein the carbon fiber is a graphite-based carbon fiber that has been heat-treated at 2000 ° C. or higher.
[9] The negative electrode material for a lithium battery as described in any one of 1 to 7 above, wherein the carbon fiber is a graphite-based carbon fiber having an oxygen-containing functional group introduced on the surface by oxidation treatment.
[10] The negative electrode material for a lithium battery according to any one of 1 to 7, wherein the carbon fiber is a graphite-based carbon fiber containing 0.1 to 100000 ppm of boron.
[11] The average spacing d 002 of (002) plane measured by X-ray diffraction of the graphite carbon fiber, a negative for a lithium battery according to the 8 or less 0.344nm electrode material.
[12] The negative electrode material for a lithium battery as described in any one of 1 to 11 above, wherein the carbon fiber has a hollow structure inside.
[13] The negative electrode material for a lithium battery according to any one of 1 to 12, wherein the carbon fiber includes a branched carbon fiber.
[14] The negative electrode material for a lithium battery as described in any one of 1 to 13, wherein the carbon-based negative electrode active material contains Si.
[15] The above 1 to 14, wherein the carbon-based negative electrode active material is a non-graphite carbon material, and the density of the mixture layer comprising the negative electrode active material, the binder, and the conductive additive is 1.5 g / cm 3 or more. The negative electrode material for lithium batteries according to any one of the above.
[16] The negative electrode material for a lithium battery as described in any one of 1 to 15 above, wherein the carbon-based negative electrode active material before forming the electrode is carbonaceous particles satisfying the following requirements:
(1) The average circularity measured by a flow type particle image analyzer is 0.70 to 0.99,
(2) The average particle diameter by laser diffraction method is 1-50 μm.
[17] The negative electrode material for a lithium battery according to any one of 1 to 16, wherein the carbon-based negative electrode active material contains a graphite carbon-based material of 50% by mass or more.
[18] The negative electrode material for a lithium battery as described in 17 above, wherein the graphite material contains boron.
[19] The lithium battery according to any one of 1 to 18 above, wherein the carbon-based negative electrode active material before forming the electrode of the electrode active material is a carbonaceous particle containing 50% by mass or more of graphite particles satisfying the following requirements: Anode material:
(1) The average circularity measured by a flow type particle image analyzer is 0.70 to 0.99,
(2) The average particle diameter by laser diffraction method is 1-50 μm.
[20] The negative electrode material for a lithium battery as described in 17 above, wherein the graphite-based carbon material is a carbonaceous particle containing 50% by mass or more of graphite particles satisfying the following requirements:
(1) C 0 of (002) plane in X-ray diffraction measurement is 0.6900 nm or less, La (crystallite size in the a-axis direction)> 100 nm, Lc (crystallite size in the c-axis direction)> 100 nm,
(2) A specific surface area of 1.0 to 10 m 2 / g,
(3) True density is 2.20 g / cm 3 or more,
(4) Laser Raman R value (peak intensity ratio of 1360 cm -1 to the peak intensity of 1580 cm -1 by laser Raman spectrum) 0.01 to 0.9.
[21] The negative electrode material for lithium batteries as described in 15 above, wherein the density of the mixture layer comprising the negative electrode active material, the binder, and the conductive additive is 1.7 g / cm 3 or more.
[22] A styrene-butadiene rubber aqueous dispersion in a carbon fiber / active material dispersion obtained by dispersing carbon fibers having a fiber diameter of 1 to 1000 nm and a carbon negative electrode active material having a specific surface area of 1 m 2 / g or more in a thickener aqueous solution. A method for producing a composition for a negative electrode material for a lithium battery, comprising adding a liquid and stirring and mixing.
[23] A carbon-based negative electrode having a specific surface area of 1 m 2 / g or more after a carbon fiber / active material dispersion is added to a thickener aqueous solution to stir the carbon fiber having a fiber diameter of 1-1000 nm and stirred to disperse the carbon fiber. 23. The method for producing a composition for a negative electrode material for a lithium battery as described in 22 above, which is prepared by adding an active material and stirring and mixing.
[24] A carbon-based negative electrode having a specific surface area of 1 m 2 / g or more after a carbon fiber / active material dispersion is added to a thickener aqueous solution and a carbon fiber having a fiber diameter of 1 to 1000 nm is added and stirred to disperse the carbon fiber. 23. The method for producing a composition for a negative electrode material for a lithium battery as described in 22 above, wherein the active material is added, stirred and mixed, and further prepared with an aqueous thickener solution.
[25] A carbon fiber / active material dispersion is added to a thickener aqueous solution with a carbon-based negative electrode active material having a specific surface area of 1 m 2 / g or more, and after stirring and mixing, carbon fibers having a fiber diameter of 1 to 1000 nm are added and stirred. The method for producing a composition for a negative electrode material for a lithium battery as described in 22 above, wherein the composition is prepared by dispersing carbon fibers.
[26] After the carbon fiber / active material dispersion is dry-stirred with a carbon-based negative electrode active material having a specific surface area of 1 m 2 / g or more and a carbon fiber having a fiber diameter of 1 to 1000 nm to disperse the carbon fiber, a thickener aqueous solution The method for producing a composition for a negative electrode material for a lithium battery as described in 22 above, wherein the composition is prepared by adding and stirring and mixing.
[27] The above 22 to 26, wherein the concentration of the thickener in the aqueous solution of the thickener is 0.3 to 5% by mass, and the concentration of the styrene butadiene rubber in the aqueous dispersion of styrene butadiene rubber is 10 to 60% by mass. The manufacturing method of the composition for negative electrode materials for lithium batteries in any one of these.
[28] The method for producing a composition for a negative electrode material for a lithium battery as described in any one of 22 to 27 above, wherein the thickener is carboxymethylcellulose.
[29] A composition for a negative electrode material for a lithium battery obtained by the method according to any one of 22 to 28 above.
[30] A negative electrode material composition for a lithium battery in which carbon fibers having a fiber diameter of 1 to 1000 nm are dispersed in a thickener aqueous solution.
[31] The lithium as described in 30 above, wherein the concentration of the thickener in the aqueous solution of the thickener is 0.3 to 5% by mass, and the proportion of the carbon fiber in the entire composition is 0.1 to 10% by mass. A negative electrode material composition for a battery.
[32] The negative electrode material composition for a lithium battery as described in 30 or 31, wherein the thickener is carboxymethylcellulose.
[33] The negative electrode for a lithium battery as described in any one of 1 to 21 above, wherein the composition for a negative electrode material for a lithium battery as described in 29 above is applied onto a metal current collector foil, dried and then pressure-molded. Wood.
[34] The negative electrode material for a lithium battery as described in 33 above, wherein the metal current collector foil is a copper foil or a copper alloy foil having a thickness of 1 to 50 μm.
[35] A lithium battery comprising the negative electrode material for a lithium battery according to any one of 1 to 21, 33 and 34 as a constituent element.
[36] A lithium secondary battery comprising the negative electrode material for a lithium battery according to any one of 1 to 21, 33, and 34 as a constituent element.
[37] At least one selected from the group consisting of ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate as a nonaqueous solvent for the nonaqueous electrolyte using a nonaqueous electrolyte. 37. The lithium secondary battery as described in 36 above, wherein
Hereinafter, the present invention will be described in detail.
1.炭素繊維
一般的に炭素系負極材は平均粒子径数〜数十μmの炭素系負極活物質粉末を結着材、導電助剤と湿式で混合し、それを金属集電体箔上に均一に塗布、乾燥後、加圧成形することにより得られる。
導電助剤としては従来、主にアセチレンブラック等のカーボンブラック粉末が用いられてきたが、炭素繊維のようなアスペクト比の高い導電助剤の方が、電極全体にネットワークを形成することができ、電極全体の導電性という観点から少ない添加量で導電性を高めることができる。一般にカーボンブラックは炭素系負極活物質、結着材、及び導電助剤の合計量に対して5質量%程度必要であるのに対し、気相成長炭素繊維のようなアスペクト比の大きい導電繊維は3質量%以下、例えば1質量%でも十分に効果を発揮する。また、前述したように最近は炭素系電極活物質のエネルギー密度が限界に近づいており、体積あたりのエネルギー密度を上げるために、電極を高密度化する試みがなされているが、従来のカーボンブラック系導電助剤では高密度化時の成形(高圧プレス)により変形し、電極中の導電パスや電解液浸透パスを阻害してしまう。一方、炭素繊維は圧力に対して変形しにくく、高密度電極においても、導電パスネットワーク及び電解液浸透パスを維持し、また、電極反応時に膨張収縮が起こっても、繊維によるネットワークにより電極強度を維持しており、高密度電極においても高容量で高速充放電性能の良好な炭素系負極材が得られる。
このような機能を顕現するには添加する炭素繊維自身が導電性に優れ、また導電パスを増やすためにできるだけ繊維径は細く、繊維長は長いことが好ましい。そのような観点から添加する導電繊維としては導電性で強靱で微細な炭素繊維を用いる必要がある。
1. Carbon fiber Generally, a carbon-based negative electrode material is obtained by mixing a carbon-based negative electrode active material powder having an average particle diameter of several to several tens of μm with a binder and a conductive additive in a wet manner, and uniformly mixing it on a metal current collector foil. It can be obtained by pressure molding after coating and drying.
Conventionally, carbon black powders such as acetylene black have been mainly used as the conductive auxiliary, but a conductive auxiliary having a higher aspect ratio such as carbon fiber can form a network on the entire electrode. From the viewpoint of the conductivity of the entire electrode, the conductivity can be increased with a small addition amount. In general, carbon black requires about 5% by mass based on the total amount of the carbon-based negative electrode active material, the binder, and the conductive additive, whereas conductive fibers having a large aspect ratio such as vapor-grown carbon fibers are used. Even if it is 3% by mass or less, for example, 1% by mass, the effect is sufficiently exhibited. In addition, as described above, the energy density of carbon-based electrode active materials has recently approached its limit, and attempts have been made to increase the density of electrodes in order to increase the energy density per volume. The system conductive auxiliary agent is deformed by molding (high-pressure press) at the time of densification, and the conductive path and the electrolyte penetration path in the electrode are hindered. On the other hand, carbon fibers are not easily deformed by pressure, and even in high-density electrodes, the conductive path network and electrolyte solution penetration path are maintained, and even if expansion and contraction occur during the electrode reaction, the strength of the electrodes is increased by the fiber network. Thus, a carbon-based negative electrode material having a high capacity and good high-speed charge / discharge performance can be obtained even in a high-density electrode.
In order to realize such a function, it is preferable that the added carbon fiber itself is excellent in conductivity, and that the fiber diameter is as thin as possible and the fiber length is long in order to increase the conductive path. From such a viewpoint, it is necessary to use conductive, tough and fine carbon fibers as the conductive fibers to be added.
1−1.炭素繊維の繊維径
本発明のリチウム電池用負極材に使用する炭素繊維の繊維径は、太過ぎると電極内の空隙が大きくなり過ぎ電極密度を高くできないため好ましくない。現在Liイオン電池やLiポリマー電池に使用されている炭素系電極活物質粒子の平均粒子径は数〜数十μm程度であるため、炭素繊維の繊維径は最大でも1μm程度である。また繊維径が細過ぎると活物質粒子間に埋没し、電極内のネットワークを形成できず、また活物質間の空隙生成が不能となるため好ましくなく、最小でも1〜数nm程度の繊維径が必要である。以上の理由から本発明のリチウム電池用負極材に使用することのできる炭素繊維の繊維径は1〜1000nmの範囲であり、好ましくは10〜500nmの範囲である。平均繊維径でいえば、5〜500nmの範囲が好ましく、10〜200nmの範囲がより好ましい。
1-1. Fiber diameter of carbon fiber If the fiber diameter of the carbon fiber used in the negative electrode material for a lithium battery of the present invention is too thick, voids in the electrode become too large to increase the electrode density, which is not preferable. Since the average particle diameter of carbon-based electrode active material particles currently used for Li ion batteries and Li polymer batteries is about several to several tens of micrometers, the fiber diameter of carbon fibers is about 1 μm at the maximum. Also, if the fiber diameter is too thin, it is buried between the active material particles and cannot form a network in the electrode, and void formation between the active materials becomes impossible. is necessary. For the above reasons, the fiber diameter of the carbon fiber that can be used for the negative electrode material for a lithium battery of the present invention is in the range of 1 to 1000 nm, preferably in the range of 10 to 500 nm. In terms of the average fiber diameter, a range of 5 to 500 nm is preferable, and a range of 10 to 200 nm is more preferable.
1−2.炭素繊維の結晶化度
炭素繊維の結晶化度(いわゆる黒鉛化度)は高い方が望ましい。一般的に炭素材料の黒鉛化度が高いほど、層状構造が発達し、より硬くなり、また導電性も向上し、前述したようにリチウム電池用炭素系負極材の使用に適している。炭素材料を黒鉛化するには一般的に高温で処理すればよく、その場合の処理温度としては、用いる炭素繊維によっても異なるが、2000℃以上が好ましく、2500℃以上がさらに好ましい。また、この場合、黒鉛化度を促進させる働きのある黒鉛化助触媒であるホウ素やSiなどを熱処理前に添加しておくことが有効である。助触媒の添加量は特に限定されないが、添加量が少なすぎると効果がでず、多すぎると不純物として残るため好ましくない。好ましい添加量は0.1〜100000ppmであり、さらに好ましくは10〜50000ppmである。
1-2. The degree of crystallinity of carbon fiber It is desirable that the degree of crystallinity of carbon fiber (so-called graphitization degree) is higher. In general, the higher the degree of graphitization of the carbon material, the more the layered structure is developed, the harder the carbon material is, and the more the conductivity is improved. As described above, the carbon-based negative electrode material for lithium batteries is suitable for use. In order to graphitize the carbon material, it is generally sufficient to treat it at a high temperature. In this case, the treatment temperature varies depending on the carbon fiber used, but is preferably 2000 ° C. or higher, and more preferably 2500 ° C. or higher. In this case, it is effective to add boron or Si, which is a graphitization cocatalyst that works to promote the degree of graphitization, before the heat treatment. The addition amount of the cocatalyst is not particularly limited, but if the addition amount is too small, the effect is not obtained, and if it is too much, it remains as an impurity, which is not preferable. A preferable addition amount is 0.1 to 100,000 ppm, and more preferably 10 to 50,000 ppm.
これら炭素繊維の結晶化度は特に限定されないが、好ましくはX線回折法による平均面間隔d002が0.344nm以下、さらに好ましくは0.339nm以下であって、結晶のC軸方向の厚さLcが40nm以下のものである。 Although crystallinity of the carbon fibers is not particularly limited, preferably the average spacing d 002 is 0.344nm less by X-ray diffraction method, even more preferably less 0.339 nm, C-axis direction of the thickness of the crystal Lc is 40 nm or less.
1−3.炭素繊維の繊維長、アスペクト比
炭素繊維の繊維長は特に限定されない。前述したように繊維長は長いほど電極内の導電性、電極の強度、電解液保液性が増し好ましいが、長すぎると、電極内の繊維分散性が損なわれるため好ましくない。好ましい平均繊維長の範囲は、用いる炭素繊維の種類や繊維径によっても異なるが、0.5〜100μmであり、1〜50μmのものがさらに好ましい。この平均繊維長の好ましい範囲を平均アスペクト比(繊維径に対する繊維長の割合)で示すと、5〜50000の範囲であり、10〜15000の範囲がさらに好ましい。
1-3. Fiber length and aspect ratio of carbon fiber The fiber length of carbon fiber is not particularly limited. As described above, the longer the fiber length, the better the electrical conductivity in the electrode, the strength of the electrode, and the electrolyte solution retention, but this is not preferred because the fiber dispersibility in the electrode is impaired. Although the range of a preferable average fiber length changes with kinds and fiber diameter of the carbon fiber to be used, it is 0.5-100 micrometers, and the thing of 1-50 micrometers is more preferable. When the preferable range of this average fiber length is shown by the average aspect ratio (ratio of the fiber length to the fiber diameter), it is in the range of 5 to 50000, and more preferably in the range of 10 to 15000.
炭素繊維に枝分かれ(分岐状)したものが含まれていると、電極全体の導電性、電極の強度、電解液保液性がさらに増すため好ましい。但し、分岐状繊維が多すぎると繊維長同様、電極内の分散性が損なわれるため、適度な割合で含まれていることが好ましい。これら分岐状繊維の割合は製造法やその後の粉砕処理である程度制御できる。 It is preferable that the carbon fiber is branched (branched) because the conductivity of the entire electrode, the strength of the electrode, and the electrolyte solution retention are further increased. However, if there are too many branched fibers, the dispersibility in the electrode is impaired as in the fiber length, so it is preferable that they are contained in an appropriate ratio. The proportion of these branched fibers can be controlled to some extent by the production method and the subsequent pulverization treatment.
1−4.炭素繊維の製造方法
本発明で用いる炭素繊維の製造方法は特に限定されない。例えば紡糸法等で高分子を繊維状にし、不活性雰囲気中で熱処理する方法や、触媒存在下、高温で有機化合物を反応させる気相成長法などが挙げられる。気相成長法で得られる炭素繊維(気相法炭素繊維)は結晶成長方向は繊維軸に平行であり、黒鉛構造の繊維長方向の結晶性が高くなりやすく、比較的、短繊維径、高導電性、高強度の炭素繊維が得られる。
1-4. Carbon Fiber Manufacturing Method The carbon fiber manufacturing method used in the present invention is not particularly limited. Examples thereof include a method in which a polymer is formed into a fiber by a spinning method and heat-treated in an inert atmosphere, and a vapor phase growth method in which an organic compound is reacted at a high temperature in the presence of a catalyst. Carbon fiber obtained by vapor phase growth method (vapor phase growth carbon fiber) has a crystal growth direction parallel to the fiber axis, and the crystallinity in the fiber length direction of the graphite structure tends to be high. Conductive, high-strength carbon fibers can be obtained.
本発明の目的を達成するためには、繊維軸方向に結晶が成長し、繊維が枝分かれをしている気相法炭素繊維が適している。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ガス化された有機化合物を吹き込むことにより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℃で熱処理したもの、2000〜3000℃で黒鉛化処理したもののいずれも使用可能であり、使用する電極活物質粉末に適したものを用いるが、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。 In order to achieve the object of the present invention, vapor grown carbon fibers in which crystals grow in the fiber axis direction and the fibers branch are suitable. The vapor grown carbon fiber can be produced, for example, by blowing an organic compound gasified with iron serving as a catalyst in a high temperature atmosphere. Vapor-grown carbon fibers can be used as manufactured, those heat-treated at 800-1500 ° C., or graphitized at 2000-3000 ° C., and suitable for the electrode active material powder to be used. A material subjected to heat treatment or graphitization is preferable because it has advanced carbon crystallinity and high conductivity and high pressure resistance.
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ている箇所があってもよい。そのため繊維の円筒部分を構成している炭素層が連続している。中空構造と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形のものを含む。 Moreover, there exists a branched fiber as a preferable form of vapor grown carbon fiber. The branched portion may have a portion having a hollow structure in which the entire fiber including the portion is in communication with each other. Therefore, the carbon layer which comprises the cylindrical part of a fiber is continuing. The hollow structure is a structure in which the 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 laminated 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、そのため電極活物質との密着性が向上する利点もある。特に、電極活物質として炭素質粉体粒子を用い、二次電池の負極として使用する場合は、核となる炭素質材料との密着性が向上するため充放電を繰り返しても炭素質材料と導電性補助剤としての役割も兼ねている気相法炭素繊維とが解離せずに密着した状態を保つことができ、電子伝導性が保持できサイクル特性が向上する。
気相法炭素繊維が分岐状繊維を多く含む場合は、効率よくネットワークを形成することができ、高い電子伝導性や熱伝導性を得やすい。また、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、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 the advantage of improving the adhesion with the electrode active material. In particular, when carbonaceous powder particles are used as the electrode active material and used as the negative electrode of a secondary battery, the adhesion with the carbonaceous material serving as the nucleus is improved, so that the carbonaceous material and the conductive material are electrically conductive even after repeated charge and discharge. It is possible to maintain a close contact state without dissociating with the vapor grown carbon fiber which also serves as a conductivity aid, and to maintain electronic conductivity and to improve cycle characteristics.
When the vapor grown carbon fiber contains a lot of branched fibers, a network can be formed efficiently, and high electronic conductivity and thermal conductivity are easily obtained. In addition, the active material can be dispersed so as to wrap, increasing the strength of the electrode and maintaining good contact between the particles.
1−5.炭素繊維の添加量
炭素繊維の含有量は、炭素系負極活物質、結着材、炭素繊維及び所望により配合する増粘剤の合計量に対して、0.05〜20質量%の範囲がよく、好ましくは0.1〜15質量%、より好ましくは0.5〜10質量%である。含有量が20質量%を超えると、電極中の活物質比率が小さくなるため、電気容量が小さくなる。添加量が0.05質量%未満では本発明のリチウム電池用炭素系負極材に対する電気抵抗減や電解液浸透性向上等の効果が現れない。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。
1-5. Addition amount of carbon fiber The carbon fiber content is preferably in the range of 0.05 to 20% by mass with respect to the total amount of the carbon-based negative electrode active material, the binder, the carbon fiber, and the thickener optionally blended. The content is preferably 0.1 to 15% by mass, more preferably 0.5 to 10% by mass. If the content exceeds 20% by mass, the active material ratio in the electrode becomes small, and the electric capacity becomes small. When the addition amount is less than 0.05% by mass, effects such as reduction in electric resistance and improvement in electrolyte permeability with respect to the carbon-based negative electrode material for lithium batteries of the present invention do not appear. In order to adjust the content to this range, it can be carried out by adding the same ratio in the production method.
1−6.炭素繊維の表面処理
炭素繊維は、電極中での分散状態を制御するために表面処理したものも用いることができる。表面処理の方法は特に限定されないが、酸化処理により含酸素官能基を導入し親水性にしたものや、フッ化処理やシリコン処理により疎水性にしたものが挙げられる。また、フェノール樹脂等のコーティングやメカノケミカル処理等も挙げられる。表面処理しすぎると、炭素繊維の導電性や強度を著しく損なうことになるため、適度な処理が必要である。酸化処理は、例えば、炭素繊維を空気中で、500℃、1時間程度加熱することにより行なうことができる。この処理により炭素繊維の親水性度が向上する。
本発明においては、結着材としてのスチレンブタジエンゴムは水系分散液として使用されることが多いため、親水性の表面を有する、酸化処理された炭素繊維が好ましい。
1-6. Surface treatment of carbon fiber Carbon fiber having a surface treatment for controlling the dispersion state in the electrode can be used. The surface treatment method is not particularly limited, and examples thereof include those made hydrophilic by introducing an oxygen-containing functional group by oxidation treatment, and those made hydrophobic by fluorination treatment or silicon treatment. In addition, a phenol resin coating or a mechanochemical treatment may be used. If the surface treatment is excessively performed, the conductivity and strength of the carbon fiber are remarkably impaired, and therefore an appropriate treatment is required. The oxidation treatment can be performed, for example, by heating the carbon fiber in air at 500 ° C. for about 1 hour. This treatment improves the hydrophilicity of the carbon fiber.
In the present invention, styrene butadiene rubber as a binder is often used as an aqueous dispersion, and therefore, oxidized carbon fibers having a hydrophilic surface are preferable.
2.スチレンブタジエンゴム(SBR)(結着材)
本発明のリチウム電池用炭素系負極材の電極結着材にはSBRが使用される。SBRは、これまで主に用いられてきたPVDF等のフッ素樹脂系結着材に比べて使用量を少なくすることができ、また電極活物質との混合は水分散液が用いられるためPVDFのような有機溶媒系に比べて防爆設備が不要であるなど電極製造工程が簡易化される長所がある。また、SBRを結着材として使用した電極は、SBRのガラス転移点(Tg)が一般的に低いため、低温特性、高速充放電特性に優れる。
2. Styrene butadiene rubber (SBR) (binder)
SBR is used for the electrode binder of the carbon-based negative electrode material for lithium batteries of the present invention. SBR can be used in a smaller amount than fluororesin-based binders such as PVDF that have been mainly used so far, and is mixed with an electrode active material because an aqueous dispersion is used. Compared to the organic solvent system, there is an advantage that the electrode manufacturing process is simplified such that explosion-proof equipment is unnecessary. An electrode using SBR as a binder is excellent in low-temperature characteristics and high-speed charge / discharge characteristics because the glass transition point (Tg) of SBR is generally low.
SBRには乳化重合SBR、溶液重合SBRの二種類がある。乳化重合SBRは、ラテックス状で得られるが、乾燥してドライラバーとして用いてもよい。溶液重合SBRの中にはスチレンとブタジエンの共重合様式によって、ランダム型、ブロック型、対称ブロック型等がある。また、スチレン組成比が多く、ガラス転移点(Tg)の高いハイスチレンゴムもある。さらに、不飽和カルボン酸や不飽和ニトリル化合物を共重合させた変性SBRもある。これらはその重合様式、スチレン/ブタジエン共重合比によって接着性、強度、熱物性等の物性が少しずつ異なる。本発明のリチウム電池用炭素系負極材の結着材として用いるこれらのSBRは、用いる負極活物質の種類に合わせて適当なものを選択して用いることができる。 There are two types of SBR: emulsion polymerization SBR and solution polymerization SBR. The emulsion polymerization SBR is obtained in a latex form, but may be dried and used as a dry rubber. Among the solution polymerization SBRs, there are a random type, a block type, a symmetrical block type, and the like depending on a copolymerization mode of styrene and butadiene. There is also a high styrene rubber having a high styrene composition ratio and a high glass transition point (Tg). Furthermore, there is a modified SBR obtained by copolymerizing an unsaturated carboxylic acid or an unsaturated nitrile compound. These have slightly different physical properties such as adhesiveness, strength and thermophysical properties depending on the polymerization mode and styrene / butadiene copolymer ratio. These SBRs used as the binder for the carbon-based negative electrode material for lithium batteries of the present invention can be selected and used in accordance with the type of the negative electrode active material to be used.
その中でも乳化重合や溶液重合で得られるSBRを水に分散させたラテックスタイプの水分散液が炭素系負極活物質と混合しやすいため、本発明のリチウム電池用炭素系負極材に好適に用いることができる。また、得られる電極の電解液とのなじみや低温特性を良くするためには、スチレンの共重合割合は50質量%以下でガラス転移点が0℃以下のものが好ましい。 Among them, a latex type aqueous dispersion in which SBR obtained by emulsion polymerization or solution polymerization is dispersed in water is easy to mix with the carbon-based negative electrode active material, and therefore it is preferably used for the carbon-based negative electrode material for lithium batteries of the present invention. Can do. Further, in order to improve the compatibility of the obtained electrode with the electrolyte and the low temperature characteristics, it is preferable that the copolymerization ratio of styrene is 50% by mass or less and the glass transition point is 0 ° C. or less.
また、炭素系負極活物質中にSBRを均一に分散し、さらに炭素系負極活物質を効率的に接着するためには、分散液中のSBR粒子は大きすぎても、小さすぎても使いにくくなる。本発明のリチウム電池用炭素系負極材に用いる好適なSBRの個数平均粒径は、10〜500nmの範囲である。 Further, in order to uniformly disperse SBR in the carbon-based negative electrode active material and to adhere the carbon-based negative electrode active material efficiently, it is difficult to use whether the SBR particles in the dispersion are too large or too small. Become. The number average particle size of SBR suitable for use in the carbon-based negative electrode material for lithium batteries of the present invention is in the range of 10 to 500 nm.
SBRの負極材中の含量は混合する炭素繊維や炭素系負極活物質によって異なり、一概には限定できないが、多すぎると負極材中の炭素系負極活物質が少なくなり、負極としての容量が低下し、抵抗も増加する。また、負極反応部位が減少し、さらに容量が低下することにもなる。少なすぎると、結着材としての効果が低下し、電池組み立て時や充放電中に負極の崩壊が起こり、充放電サイクル寿命が低下するので好ましくない。好ましいSBRの添加量は、炭素系負極活物質、結着材、炭素繊維及び所望により配合する増粘剤の合計量に対して、0.1〜6.0質量%であり、さらに好ましくは0.3〜5.0質量%である。 The content of SBR in the negative electrode material varies depending on the carbon fiber and the carbon-based negative electrode active material to be mixed, and cannot be generally limited. And the resistance also increases. Moreover, the negative electrode reaction site is reduced, and the capacity is further reduced. If the amount is too small, the effect as a binder is reduced, and the negative electrode collapses during battery assembly or charge / discharge, which is not preferable because the charge / discharge cycle life is reduced. The amount of SBR added is preferably 0.1 to 6.0% by mass, more preferably 0%, based on the total amount of the carbon-based negative electrode active material, the binder, the carbon fiber, and the thickener optionally blended. It is 0.3-5.0 mass%.
3.炭素系負極活物質
炭素系負極活物質とは、炭素を含み、電気化学的にイオンを吸蔵、放出できるものである。
本発明では、電極の結着材としてSBR、好ましくはSBRの水系分散液を用いるため、炭素系負極活物質の比表面積はできるだけ高い方が濡れ性が改善され、扱いやすく、電極強度や電解液保持性にも有利である。具体的には、BET法で測定される比表面積(BET比表面積)で1m2/g以上のものを用いる。しかし、比表面積があまり高すぎると、電解液と副反応を起こしやすい。好ましいBET比表面積の範囲としては、1.0〜7.0m2/gであり、さらに好ましくは1.5〜6.0m2/gである。
3. Carbon-based negative electrode active material A carbon-based negative electrode active material contains carbon and can electrochemically occlude and release ions.
In the present invention, since an aqueous dispersion of SBR, preferably SBR, is used as the electrode binder, the higher the specific surface area of the carbon-based negative electrode active material, the better the wettability, the easier to handle, the electrode strength and the electrolyte solution It is also advantageous for retention. Specifically, a specific surface area (BET specific surface area) measured by the BET method is 1 m 2 / g or more. However, if the specific surface area is too high, side reactions with the electrolytic solution are likely to occur. A preferable range of the BET specific surface area is 1.0 to 7.0 m 2 / g, and more preferably 1.5 to 6.0 m 2 / g.
炭素系負極活物質材料としては、非黒鉛系炭素材料を主成分とするもの及び黒鉛系炭素材料を主成分とするもののいずれもが使用できる。
非黒鉛系炭素材料とは、黒鉛の三次元的結晶規則性を有しない炭素材料であり、乱層構造炭素材料、非晶質炭素材料がこれに含まれ、例えばガラス状炭素や、熱処理温度が低いために結晶化の進んでいない炭素材料も含まれる。
黒鉛系炭素材料とは、黒鉛の三次元的結晶規則性を有する炭素材料であり、天然に産出する天然黒鉛、易黒鉛化性炭素材料を熱処理して得られる人造黒鉛がこれに含まれ、鉄融体中から黒鉛が再析出して得られるキッシュ黒鉛も含まれる。
また、「主成分とするもの」とは全体の50質量%以上、好ましくは60質量%以上、さらに好ましくは80質量%以上、特に好ましくは90質量%以上をその材料が占めることを意味する。
As the carbon-based negative electrode active material, both a material mainly composed of a non-graphite carbon material and a material mainly composed of a graphite-based carbon material can be used.
Non-graphitic carbon materials are carbon materials that do not have the three-dimensional crystal regularity of graphite, and include turbulent structure carbon materials and amorphous carbon materials, such as glassy carbon and heat treatment temperature. A carbon material that has not been crystallized because it is low is also included.
The graphite-based carbon material is a carbon material having three-dimensional crystal regularity of graphite, and includes natural graphite produced naturally, artificial graphite obtained by heat-treating a graphitizable carbon material, and iron. Kish graphite obtained by reprecipitation of graphite from the melt is also included.
Further, the “main component” means that the material occupies 50% by mass or more of the whole, preferably 60% by mass or more, more preferably 80% by mass or more, and particularly preferably 90% by mass or more.
非黒鉛系炭素材料を主成分とするものとしては、フェノール樹脂等の難黒鉛系高分子を熱処理した炭素材料や、ピッチやコークスを1000℃程度で熱処理したもの、導電性高分子等の共役系高分子を熱処理したもの、熱CVD法により基板に堆積させたCVD炭素等が挙げられる。また、これらの材料の熱処理時にSiを混入して、負極としての電気容量を増加させたものが挙げられる。
これら非黒鉛系炭素材料はできるだけ円形度が高い球状のものが電極シートを作成する場合の取扱いや電池に用いる場合の電解液との副反応が抑えられ好ましい。
好ましい円形度は、フロー式粒子像解析装置によって測定される平均円形度として0.70〜0.99である。
これら非黒鉛系炭素材料の平均粒子径は目的とする電極シート形状によって異なり、特に限定されないが、一般的には、レーザー回折法による平均粒子径が1〜50μmの範囲で用いられる。
これら非黒鉛系炭素材料を用いる負極材の嵩密度については、炭素系活物質の真密度が様々であり、特に限定されないが、一般には非黒鉛系炭素材料の真密度は1.9g/cm3以上であり、負極活物質、結着材、及び導電助剤からなる合剤層の密度(電極嵩密度)は1.5g/cm3以上、さらには1.7g/cm3以上のものが好ましい。
Non-graphite carbon materials as main components include carbon materials obtained by heat-treating non-graphite polymers such as phenol resins, pitch and coke heat-treated at about 1000 ° C., and conjugated systems such as conductive polymers. Examples include heat-treated polymers and CVD carbon deposited on a substrate by a thermal CVD method. In addition, a material in which Si is mixed during heat treatment of these materials to increase the electric capacity as a negative electrode can be mentioned.
Of these non-graphitic carbon materials, spherical ones having as high a degree of circularity as possible are preferable because they can suppress side reactions with the electrolytic solution when used when producing electrode sheets and when used in batteries.
A preferable circularity is 0.70 to 0.99 as an average circularity measured by a flow type particle image analyzer.
The average particle diameter of these non-graphitic carbon materials varies depending on the target electrode sheet shape, and is not particularly limited, but is generally used in the range of an average particle diameter by laser diffraction of 1 to 50 μm.
The bulk density of the negative electrode material using these non-graphitic carbon materials varies depending on the true density of the carbon-based active material and is not particularly limited. Generally, the true density of the non-graphitic carbon material is 1.9 g / cm 3. The density of the mixture layer composed of the negative electrode active material, the binder, and the conductive additive (electrode bulk density) is 1.5 g / cm 3 or more, more preferably 1.7 g / cm 3 or more. .
黒鉛系炭素材料を主成分とするものとしては、一般にLiイオン電池の炭素系活物質材料として使用されている黒鉛系炭素材料が本発明においても使用できる。黒鉛系活物質材料は結晶性が発達し、Liイオンの挿入脱離が均一に起こり、拡散も早いため、電池の放電電位の変化が少なく、また高負荷特性も優れるという特徴を有している。これらは真密度が2.2g/cm3程度と高く、電極嵩密度も1.5g/cm3で使われる。本発明においては、さらに空隙率を減らし、電極嵩密度1.7g/cm3以上とすることもできる。
この黒鉛系活物質材料もできるだけ円形度が高いものが好ましく、フロー式粒子像解析装置によって測定される平均円形度が0.70〜0.99、レーザー回折法による平均粒子径が1〜50μm程度のものが用いられる。
黒鉛系材料はできるだけ結晶性が高いことが好ましく、X線回折測定での002面のC0が0.6900nm(d002=0.3450nm)以下であり、La(a軸方向の結晶子サイズ)が100nmより大きく、Lc(c軸方向の結晶子サイズ)も100nmより大きいことが好ましい。また、レーザーラマンR値は0.01〜0.9(R値:レーザーラマンスペクトルによる1580cm-1のピーク強度に対する1360cm-1のピーク強度比)が好ましく、真密度は2.20g/cm3以上が好ましい。
As the main component of the graphite-based carbon material, a graphite-based carbon material that is generally used as a carbon-based active material of a Li ion battery can also be used in the present invention. The graphite-based active material has the characteristics that the crystallinity develops, the insertion and release of Li ions occur uniformly, and the diffusion is fast, so that the change in the discharge potential of the battery is small and the high load characteristics are excellent. . These are used at a true density as high as about 2.2 g / cm 3 and an electrode bulk density of 1.5 g / cm 3 . In the present invention, the porosity can be further reduced to an electrode bulk density of 1.7 g / cm 3 or more.
This graphite-based active material is also preferably as high as possible in the circularity, the average circularity measured by a flow type particle image analyzer is 0.70 to 0.99, and the average particle diameter by laser diffraction is about 1 to 50 μm. Is used.
The graphite material preferably has as high crystallinity as possible, and the C 0 of the 002 plane in X-ray diffraction measurement is 0.6900 nm (d 002 = 0.3450 nm) or less, and La (crystallite size in the a-axis direction) Is preferably larger than 100 nm, and Lc (crystallite size in the c-axis direction) is preferably larger than 100 nm. The laser Raman R value is 0.01 to 0.9 (R value: peak intensity ratio of 1360 cm -1 to the peak intensity of 1580 cm -1 by laser Raman spectrum) are preferred, true density 2.20 g / cm 3 or more Is preferred.
黒鉛系活物質材料にホウ素を加えて熱処理すると、結晶性向上や、電解液とのなじみや安定性が改善されるため好ましい。ホウ素の添加量は特に限定されないが、添加量が少なすぎると効果がでず、多すぎると不純物として残るため好ましくない。好ましい添加量は、0.1質量ppm〜100000質量ppm、さらに好ましくは10質量ppmから50000質量ppmの範囲である。 Heat treatment by adding boron to the graphite-based active material is preferable because crystallinity is improved and compatibility with the electrolyte and stability are improved. The addition amount of boron is not particularly limited, but if the addition amount is too small, the effect is not obtained, and if it is too much, it remains as an impurity, which is not preferable. A preferable addition amount is in the range of 0.1 mass ppm to 100,000 mass ppm, more preferably 10 mass ppm to 50,000 mass ppm.
4.リチウム電池用負極
4−1.炭素系負極活物質/電極結着材/炭素繊維を含む負極材用組成物
リチウム電池用炭素系負極材は、一般には、炭素系負極活物質と電極結着材、場合によってはカーボンブラックや黒鉛微粉等の他の導電助剤を加え、湿式または乾式で所定の比率で混合後、Cu等の金属集電体上に塗布後、乾燥、プレスすることにより製造される。しかしながら、本発明のリチウム電池用炭素系負極材では、アスペクト比の大きい炭素繊維を添加するために、これまでの一般的な方法では炭素繊維を均一に分散することができない。また、電極結着材としてSBR水分散液を用いるため、疎水性の炭素繊維、特に黒鉛化した炭素繊維を十分に分散させることができない。
4). Negative electrode for lithium battery 4-1. Carbon-based negative electrode active material / electrode binder / composition for negative electrode material containing carbon fiber Generally, a carbon-based negative electrode material for a lithium battery is a carbon-based negative electrode active material and an electrode binder, and in some cases, carbon black or graphite. It is manufactured by adding other conductive aids such as fine powder, mixing in a predetermined ratio in a wet or dry manner, applying on a metal current collector such as Cu, and drying and pressing. However, in the carbon-based negative electrode material for a lithium battery according to the present invention, carbon fibers having a large aspect ratio are added, so that carbon fibers cannot be uniformly dispersed by conventional methods. In addition, since the SBR aqueous dispersion is used as the electrode binder, hydrophobic carbon fibers, particularly graphitized carbon fibers cannot be sufficiently dispersed.
本発明のリチウム電池用炭素系負極材は、炭素系負極活物質、炭素繊維及びSBRからなる結着材を混合した負極材用組成物を、集電体上に塗布、成形することによって得られるが、この負極材用組成物の調製を従来知られていない方法、すなわち、繊維径1〜1000nmの炭素繊維、BET比表面積1m2/g以上の炭素系負極活物質及び所望により他の炭素系粉末導電助剤を増粘剤水溶液(例えばカルボキシメチルセルロース化合物水溶液)に充分に分散させた後、スチレンブタジエンゴムの水系分散液を添加し、比較的短時間で撹拌混合する方法により行なう。
この方法は、炭素繊維を水系溶液に予め十分に分散させた後、SBR水分散液を添加し、その際の撹拌混合を簡単に行なうことを意図した方法である。SBR結着材添加後の撹拌混合に時間をかけると、一度分散した炭素繊維が再度凝集することがあり、その結果、電極比抵抗が増加したり、電解液浸透性が低下したりし、電池性能を悪化させる。炭素繊維が再度凝集する理由としては、後から添加した結着材と増粘剤水溶液との親和性が高いため、増粘剤中に分散していた疎水性の炭素繊維が増粘剤から徐々に分離していくためと考えられる。具体的な方法としては、例えば以下の(A)〜(D)の方法がある。
The carbon-based negative electrode material for a lithium battery of the present invention is obtained by applying and molding on a current collector a composition for a negative electrode material in which a binder composed of a carbon-based negative electrode active material, carbon fiber, and SBR is mixed. However, the preparation of this negative electrode material composition is not conventionally known, that is, carbon fibers having a fiber diameter of 1 to 1000 nm, carbon-based negative electrode active materials having a BET specific surface area of 1 m 2 / g or more, and other carbon-based materials if desired. The powder conductive assistant is sufficiently dispersed in a thickener aqueous solution (for example, a carboxymethyl cellulose compound aqueous solution), and then an aqueous dispersion of styrene butadiene rubber is added and stirred and mixed in a relatively short time.
This method is a method intended to easily disperse the carbon fiber in an aqueous solution in advance and then add an SBR aqueous dispersion and stir and mix at that time. When it takes time to stir and mix after the addition of the SBR binder, the carbon fibers once dispersed may agglomerate again. As a result, the electrode specific resistance increases or the electrolyte permeability decreases. Degrading performance. The reason why the carbon fibers agglomerate again is that the affinity between the binder added later and the aqueous solution of the thickener is high, so that the hydrophobic carbon fibers dispersed in the thickener are gradually removed from the thickener. This is thought to be due to separation. Specific methods include, for example, the following methods (A) to (D).
(A) 増粘剤水溶液に炭素繊維を添加、撹拌して炭素繊維を十分に分散させた後、炭素系負極活物質及び所望により他の炭素系粉末導電助剤を添加し、撹拌混合後、SBR水分散液を添加し、比較的短時間で撹拌混合する方法。
(B) 増粘剤水溶液に炭素繊維を添加、撹拌して炭素繊維を十分に分散させた後、炭素系負極活物質及び所望により他の炭素系粉末導電助剤を添加し、撹拌混合後、増粘剤水溶液を添加して粘度調整をし、SBR水分散液を添加し、比較的短時間で撹拌混合する方法。
(C) 増粘剤水溶液に炭素系負極活物質及び所望により他の炭素系粉末導電助剤を添加し、撹拌混合し、次いで炭素繊維を添加、撹拌して炭素繊維を十分に分散させた後に、SBR水分散液を添加し、比較的短時間で撹拌混合する方法。
(D) 炭素系負極活物質粉末と炭素繊維及び所望により他の炭素系粉末導電助剤とを乾式撹拌して、炭素繊維を十分に分散させた後、増粘剤水溶液を添加し撹拌混合し、次いでSBR水分散液を添加し、比較的短時間で撹拌混合する方法。
(A) After adding carbon fiber to the thickener aqueous solution and stirring to sufficiently disperse the carbon fiber, adding the carbon-based negative electrode active material and optionally other carbon-based powder conductive aid, stirring and mixing, A method of adding an SBR aqueous dispersion and stirring and mixing in a relatively short time.
(B) After adding carbon fiber to the thickener aqueous solution and stirring to sufficiently disperse the carbon fiber, adding the carbon-based negative electrode active material and optionally other carbon-based powder conductive assistant, stirring and mixing, A method of adjusting the viscosity by adding a thickener aqueous solution, adding an SBR aqueous dispersion, and stirring and mixing in a relatively short time.
(C) After adding a carbon-based negative electrode active material and optionally another carbon-based powder conductive additive to the thickener aqueous solution, stirring and mixing, and then adding and stirring the carbon fiber to sufficiently disperse the carbon fiber A method of adding an SBR aqueous dispersion and stirring and mixing in a relatively short time.
(D) Dry-stir the carbon-based negative electrode active material powder, carbon fiber, and optionally other carbon-based powder conductive auxiliary agent to sufficiently disperse the carbon fiber, and then add the thickener aqueous solution and stir and mix. Then, a method of adding an SBR aqueous dispersion and stirring and mixing in a relatively short time.
SBR水分散液を添加後に撹拌する時間の目安は、炭素繊維の種類、撹拌方法、量等によるので一概には限定できないが、撹拌後に静置した場合の組成物の状態により随時判断する。一般的には120分以内であり、好ましくは10〜90分である。
上記方法の中では、炭素繊維の分散が比較的容易な(A)及び(B)が特に好ましい。その場合の炭素繊維の添加は、炭素繊維の占める割合が炭素系負極活物質、結着材、及び導電助剤の合計量に対して0.1〜10質量%となるように行なうことが好ましい。
The standard of the stirring time after the addition of the SBR aqueous dispersion depends on the type of carbon fiber, the stirring method, the amount, etc., and thus cannot be limited in general, but is determined as needed depending on the state of the composition when allowed to stand after stirring. Generally, it is within 120 minutes, preferably 10 to 90 minutes.
Among the above methods, (A) and (B) are particularly preferable because the dispersion of carbon fibers is relatively easy. In this case, the addition of the carbon fiber is preferably performed so that the proportion of the carbon fiber is 0.1 to 10% by mass with respect to the total amount of the carbon-based negative electrode active material, the binder, and the conductive additive. .
上記方法で増粘剤は、負極材用組成物を集電体上に塗布可能な粘度に制御するために用いられる非イオン性ポリマーである。
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が挙げられるが、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、カルボキシメチルセルロース(CMC)が特に好ましい。増粘剤の配合量は、増粘剤の種類によるので一概に言えないが、通常、炭素系負極活物質、結着材、炭素繊維及び増粘剤の合計量に対して、0.1〜4質量%が好ましく、0.3〜3質量%がより好ましい。また、増粘剤は水溶液として用いることが好ましい。増粘剤水溶液中の増粘剤の濃度は、粘度として室温で50〜5000mPa・s、好ましくは100〜3000mPa・sとできる濃度であり、通常0.3〜5質量%の範囲が好ましい。
以下好ましい増粘剤であるカルボキシメチルセルロース(CMC)化合物を例に挙げて説明する。
CMC化合物の分子量等の物性は特に限定されず、使用する炭素繊維や負極活物質の種類によって異なるが、CMC化合物は電池反応に関与せず、多すぎると電極中の負極活物質割合が小さくなるため添加量はできるだけ少ない方がよい。またCMC化合物水溶液中のCMC化合物濃度も増粘剤の効果が発揮できる範囲でできるだけ低い方がよい。好ましいCMC化合物の配合量は炭素系負極活物質、結着材、炭素繊維及びCMC化合物の合計量に対して、0.1〜4.0質量%であり、さらに好ましくは0.3〜3質量%である。CMC化合物は0.3〜5質量%、好ましくは1質量%程度の水溶液として使用し、その場合の粘度は室温で50〜5000mPa・sであり、100〜3000mPa・sが好ましい。
In the above method, the thickener is a nonionic polymer used to control the viscosity of the negative electrode material composition so that it can be applied to the current collector.
Examples of the thickener include polyethylene glycols, celluloses, polyacrylamides, poly N-vinyl amides, poly N-vinyl pyrrolidones, etc. Among them, polyethylene glycols, carboxymethyl cellulose (CMC), etc. Celluloses and the like are preferable, and carboxymethyl cellulose (CMC) is particularly preferable. The blending amount of the thickener depends on the type of the thickener and cannot be generally specified, but is usually 0.1 to the total amount of the carbon-based negative electrode active material, the binder, the carbon fiber, and the thickener. 4 mass% is preferable and 0.3-3 mass% is more preferable. The thickener is preferably used as an aqueous solution. The concentration of the thickener in the aqueous solution of the thickener is a concentration that allows the viscosity to be 50 to 5000 mPa · s, preferably 100 to 3000 mPa · s at room temperature, and is usually in the range of 0.3 to 5% by mass.
Hereinafter, the carboxymethyl cellulose (CMC) compound which is a preferable thickener will be described as an example.
The physical properties such as the molecular weight of the CMC compound are not particularly limited and vary depending on the type of carbon fiber and negative electrode active material used. However, the CMC compound does not participate in the battery reaction, and if it is too much, the proportion of the negative electrode active material in the electrode decreases. Therefore, the addition amount should be as small as possible. The CMC compound concentration in the CMC compound aqueous solution is preferably as low as possible within the range in which the effect of the thickener can be exhibited. A preferable blending amount of the CMC compound is 0.1 to 4.0% by mass, and more preferably 0.3 to 3% by mass with respect to a total amount of the carbon-based negative electrode active material, the binder, the carbon fiber, and the CMC compound. %. The CMC compound is used as an aqueous solution of 0.3 to 5% by mass, preferably about 1% by mass, and the viscosity in that case is 50 to 5000 mPa · s at room temperature, preferably 100 to 3000 mPa · s.
SBR水分散液中のSBR濃度は、高すぎると短時間での混合がしにくく、また低すぎるとCMC水溶液で増粘した組成物粘度をまた低下させることになるので好ましくない。従って、SBR水分散液中のSBR濃度は10〜60質量%が好ましい。
各々の材料の種類や組成比、組み合わせ等で電極内の分散状態が異なり、電極抵抗、吸液性等に影響してくるので、最適な組成及び濃度条件を選択する必要がある。
If the SBR concentration in the SBR aqueous dispersion is too high, mixing in a short time is difficult, and if it is too low, the viscosity of the composition thickened with the CMC aqueous solution is lowered, which is not preferable. Therefore, the SBR concentration in the SBR aqueous dispersion is preferably 10 to 60% by mass.
Since the dispersion state in the electrode differs depending on the type, composition ratio, combination, and the like of each material and affects electrode resistance, liquid absorbency, etc., it is necessary to select optimum composition and concentration conditions.
撹拌機としては、種々のものを使用することができる。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、脱泡ニーダー、撹拌羽根つき万能ミキサー、ペイントシェーカー等の装置を使用することができる。これらのなかで上述した4通りの方法の撹拌が比較的容易にできるものとして、プラネタリーミキサー、脱泡ニーダー、撹拌羽根つき万能ミキサーが挙げられ、脱泡ニーダー、撹拌羽根つき万能ミキサーが好ましく、撹拌羽根つき万能ミキサーが特に好ましい。 A variety of stirrers can be used. For example, apparatuses such as a ribbon mixer, a screw-type kneader, a Spartan-Luzer, a Redige mixer, a planetary mixer, a defoaming kneader, a universal mixer with stirring blades, and a paint shaker can be used. Among these, the one that can be stirred relatively easily in the four methods described above includes a planetary mixer, a defoaming kneader, and a universal mixer with stirring blades, and a defoaming kneader and a universal mixer with stirring blades are preferable. A universal mixer with stirring blades is particularly preferred.
4−2.シート状負極材の作製
上述の方法で得た負極材組成物を集電体箔に塗布することにより、本発明のリチウム電池用のシート状負極材を作製できる。
組成物の集電体箔への塗布は、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後、ロールプレス等で成形する方法等が挙げられる。
集電体としては、現在のLiイオン電池では銅箔が用いられているが、銅箔、アルミニウム箔、ステンレス箔、ニッケル箔、チタン箔及びそれらの合金箔、カーボンシートなど公知の材料が使用できる。これらの中では、強度、電気化学安定性、コスト等の面から、銅箔や銅合金箔が好ましい。
本発明で用いられる集電体箔の厚みに特に制限はないが、薄すぎると強度が低下し、シート状負極材の強度や塗布時の取扱い性に問題が生じる。また、厚すぎると、電池構成体中の集電体箔の質量、体積の割合が高くなり、電池のエネルギー密度が低下し、さらに電池作製時のシート状電極が堅くなり、捲回に支障をきたす。従って集電体箔の厚みは、0.5〜100μmが好ましく、1〜50μmが特に好ましい。
これら塗布した電極シートを公知の方法で乾燥後、ロールプレス、加圧プレス等公知の方法で所望の厚み、密度に成形する。
4-2. Preparation of sheet-like negative electrode material By applying the negative electrode material composition obtained by the above-described method to the current collector foil, the sheet-like negative electrode material for the lithium battery of the present invention can be produced.
Application of the composition to the current collector foil can be carried out by a known method, and examples thereof include a method of applying the composition with a doctor blade, a bar coater, or the like and then forming it with a roll press or the like.
As the current collector, a copper foil is used in the current Li ion battery, but a known material such as a copper foil, an aluminum foil, a stainless steel foil, a nickel foil, a titanium foil and an alloy foil thereof, and a carbon sheet can be used. . Among these, copper foil and copper alloy foil are preferable from the viewpoints of strength, electrochemical stability, cost, and the like.
Although there is no restriction | limiting in particular in the thickness of the collector foil used by this invention, when too thin, intensity | strength will fall and the problem will arise in the intensity | strength of a sheet-like negative electrode material, and the handleability at the time of application | coating. On the other hand, if the thickness is too thick, the ratio of the mass and volume of the current collector foil in the battery structure is increased, the energy density of the battery is decreased, and the sheet-like electrode at the time of battery production becomes stiff, which hinders winding. Come on. Therefore, the thickness of the current collector foil is preferably from 0.5 to 100 μm, particularly preferably from 1 to 50 μm.
These coated electrode sheets are dried by a known method, and then formed into a desired thickness and density by a known method such as a roll press or a pressure press.
プレス圧力は使用する負極活物質材料によって異なり、また、目的とする電極密度によるため、特に限定されないが、通常は1ton/cm2以上の加圧条件で行なう。また、電極シート厚みは目的とする電池の形状によって異なり、特に限定されないが、通常は0.5〜2000μm、好ましくは5〜1000μmに成形される。 The pressing pressure varies depending on the negative electrode active material used, and is not particularly limited because it depends on the target electrode density. Usually, the pressing pressure is 1 ton / cm 2 or more. The thickness of the electrode sheet varies depending on the shape of the intended battery and is not particularly limited, but is usually formed to 0.5 to 2000 μm, preferably 5 to 1000 μm.
4−3.負極材の特性
上述した方法で得られる本発明のリチウム電池用炭素系負極材は、炭素繊維が良好に分散して存在するため、電極としての比抵抗が低い。電極比抵抗が低いほど電池充放電での電流密度を高くすることができ、高速充放電が可能になる。また、電極比抵抗が低いということは、炭素繊維のネットワークが十分に広がっており、電極強度が増していることになり、電池の充放電サイクル寿命が長くなる。
本発明負極材の電極比抵抗は、25℃で0.5Ωcm以下、さらには0.3Ωcm以下を示す。
4-3. Characteristics of Negative Electrode Material The carbon-based negative electrode material for a lithium battery of the present invention obtained by the method described above has a low specific resistance as an electrode because carbon fibers are well dispersed. The lower the electrode specific resistance, the higher the current density in charging / discharging the battery, enabling high-speed charging / discharging. Also, the low electrode specific resistance means that the carbon fiber network is sufficiently widened, the electrode strength is increased, and the charge / discharge cycle life of the battery is prolonged.
The electrode specific resistance of the negative electrode material of the present invention is 0.5 Ωcm or less and further 0.3 Ωcm or less at 25 ° C.
また、上記(A)〜(D)の製法においてSBRを添加した後の撹拌混合に時間をかけると、前述したように一度分散した炭素繊維が再度凝集し易くなり、その結果、得られる負極材の比抵抗が高くなる。具体的には、上記(A)〜(D)の方法においてSBR添加後の撹拌に時間をかけた組成物からなる負極材の比抵抗は、上記(A)〜(D)の方法において炭素繊維を用いない組成物からなる負極材の比抵抗に比べて、せいぜい10%程度しか改善しない。それに対して、上記(A)〜(D)の方法による本発明負極材の比抵抗は、上記(A)〜(D)の方法において炭素繊維を用いない組成物からなる負極材の比抵抗に比べて、少なくとも20%改善し、多くは40%以上改善する。言い換えれば、本発明負極材は、その負極材から繊維径1〜1000nmの炭素繊維を除いた電極に比べて、電極比抵抗を80%以下、さらには60%以下にまで低減することが可能である。 In addition, when it takes time to stir and mix after adding SBR in the production methods (A) to (D), the carbon fibers once dispersed easily aggregate as described above, and as a result, a negative electrode material obtained as a result. The specific resistance increases. Specifically, in the methods (A) to (D) above, the specific resistance of the negative electrode material composed of a composition that takes time for stirring after the addition of SBR is the carbon fiber in the methods (A) to (D). Compared to the specific resistance of a negative electrode material made of a composition that does not use, it improves only about 10% at most. On the other hand, the specific resistance of the negative electrode material of the present invention by the methods (A) to (D) is the specific resistance of the negative electrode material made of a composition not using carbon fiber in the methods (A) to (D). Compared to at least 20% improvement, many improve more than 40%. In other words, the negative electrode material of the present invention can reduce the electrode specific resistance to 80% or less, and further to 60% or less, compared to an electrode obtained by removing carbon fibers having a fiber diameter of 1 to 1000 nm from the negative electrode material. is there.
電解液の浸透性についても、同様のことが言える。すなわち、上記(A)〜(D)の方法においてSBRを添加した後の撹拌混合に時間をかけると、得られる負極材の電解液浸透性を十分に改善させることができない。これは電極の密度を高くしたときに顕著である。具体的には、例えば、黒鉛系負極において電極密度を1.7g/cm3以上とした場合、上記(A)〜(D)の方法においてSBR添加後の撹拌に時間をかけた組成物からなる負極材の電解液浸透速度は、上記(A)〜(D)の方法において炭素繊維を用いない組成物からなる負極材の電解液浸透速度に比べて、最大でも30%程度しか改善されない。これに対して、上記(A)〜(D)の方法による本発明負極材の電解液浸透速度は、上記(A)〜(D)の方法において炭素繊維を用いない組成物からなる負極材の電解液浸透速度に比べて、少なくとも35%改善し、多くは60%以上改善される。 The same can be said for the permeability of the electrolyte. That is, if it takes time to stir and mix after adding SBR in the methods (A) to (D), the electrolyte permeability of the obtained negative electrode material cannot be sufficiently improved. This is remarkable when the density of the electrode is increased. Specifically, for example, when the electrode density of a graphite-based negative electrode is 1.7 g / cm 3 or more, the method is composed of a composition that takes time for stirring after the addition of SBR in the methods (A) to (D). The electrolyte solution permeation rate of the negative electrode material is improved only by about 30% at the maximum compared to the electrolyte solution permeation rate of the negative electrode material made of a composition not using carbon fiber in the methods (A) to (D). On the other hand, the electrolyte solution permeation rate of the negative electrode material of the present invention by the methods (A) to (D) is that of the negative electrode material made of a composition not using carbon fiber in the methods (A) to (D). Compared to the electrolyte penetration rate, it is improved by at least 35%, and many are improved by 60% or more.
5.リチウム電池
本発明のリチウム電池用負極材をコバルト酸リチウム等の各種正極材と組み合わせることにより、高性能のリチウム電池を作製できる。特に本発明のリチウム電池用負極材は、現在、市場で伸びているLiイオン電池やLiポリマー電池等の高エネルギー密度非水系二次電池へのニーズが大きい。
以下、本発明負極材を用いたLiイオン電池及びLiポリマー電池の製造方法について説明するが、電池の製造法はこれらに限定されるものではない。
5. Lithium battery A high-performance lithium battery can be produced by combining the negative electrode material for a lithium battery of the present invention with various positive electrode materials such as lithium cobalt oxide. In particular, the negative electrode material for lithium batteries of the present invention has a great need for high energy density non-aqueous secondary batteries such as Li ion batteries and Li polymer batteries that are currently growing in the market.
Hereinafter, although the manufacturing method of Li ion battery and Li polymer battery using this invention negative electrode material is demonstrated, the manufacturing method of a battery is not limited to these.
5−1.正極活物質材料
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及びこれらの複合酸化物や混合物等が現在、Liイオン電池の正極活物質材料として用いられている。
5-1. Cathode active material materials Cobalt-based oxides such as lithium cobaltate, manganese-based oxides such as lithium manganate, nickel-based oxides such as lithium nickelate, and composite oxides and mixtures thereof are currently positive electrodes for Li-ion batteries. Used as an active material.
本発明のリチウム電池用炭素系負極材を用いたリチウム電池の正極活物質としては、上記金属酸化物系材料以外にも種々のものを用いることができる。本発明のリチウム電池の正極活物質として用いられるリチウム含有遷移金属酸化物は、好ましくは、Ti、V、Cr、Mn、Fe、Co、Ni、Mo及びWから選ばれる少なくとも1種の遷移金属元素とリチウムとを主として含有する酸化物であって、リチウムと遷移金属のモル比が0.3〜2.2の化合物である。より好ましくは、V、Cr、Mn、Fe、Co及びNiから選ばれる少なくとも1種の遷移金属元素とリチウムとを主として含有する酸化物であって、リチウムと遷移金属のモル比が0.3〜2.2の化合物である。なお、主として存在する遷移金属に対し30モルパーセント未満の範囲でAl、Ga、In、Ge、Sn、Pb、Sb、Bi、Si、P、Bなどを含有していても良い。上記の正極活物質の中で、一般式LixMO2(MはCo、Ni、Fe、Mnの少なくとも1種、x=0〜1.2)、またはLiyN2O4(Nは少なくともMnを含む。y=0〜2)で表されるスピネル構造を有する材料の少なくとも1種を用いることが好ましい。 As a positive electrode active material of a lithium battery using the carbon-based negative electrode material for a lithium battery of the present invention, various materials other than the metal oxide material can be used. The lithium-containing transition metal oxide used as the positive electrode active material of the lithium battery of the present invention is preferably at least one transition metal element selected from Ti, V, Cr, Mn, Fe, Co, Ni, Mo and W And an oxide mainly containing lithium and a compound having a molar ratio of lithium to transition metal of 0.3 to 2.2. More preferably, it is an oxide mainly containing at least one transition metal element selected from V, Cr, Mn, Fe, Co and Ni and lithium, and the molar ratio of lithium to transition metal is 0.3 to 0.3. The compound of 2.2. In addition, Al, Ga, In, Ge, Sn, Pb, Sb, Bi, Si, P, B, or the like may be contained in a range of less than 30 mole percent with respect to the transition metal present mainly. Among the above positive electrode active materials, the general formula Li x MO 2 (M is at least one of Co, Ni, Fe, and Mn, x = 0 to 1.2), or Li y N 2 O 4 (N is at least It is preferable to use at least one of materials having a spinel structure represented by y = 0 to 2).
さらに、正極活物質はLiyMaD1-aO2(MはCo、Ni、Fe、Mnの少なくとも1種、DはCo、Ni、Fe、Mn、Al、Zn、Cu、Mo、Ag、W、Ga、In、Sn、Pb、Sb、Sr、B、Pの中のM以外の少なくとも1種、y=0〜1.2、a=0.5〜1)を含む材料、またはLiz(NbE1-b)2O4(NはMn、EはCo、Ni、Fe、Mn、Al、Zn、Cu、Mo、Ag、W、Ga、In、Sn、Pb、Sb、Sr、B、Pの少なくとも1種、b=1〜0.2、z=0〜2)で表されるスピネル構造を有する材料の少なくとも1種を用いることが特に好ましい。 Further, the positive electrode active material Li y M a D 1-a O 2 (M is Co, Ni, Fe, at least one of Mn, D is Co, Ni, Fe, Mn, Al, Zn, Cu, Mo, Ag , W, Ga, In, Sn, Pb, Sb, Sr, B, P, at least one material other than M, y = 0 to 1.2, a = 0.5 to 1), or Li z (N b E 1-b ) 2 O 4 (N is Mn, E is Co, Ni, Fe, Mn, Al, Zn, Cu, Mo, Ag, W, Ga, in, Sn, Pb, Sb, Sr It is particularly preferred to use at least one material having a spinel structure represented by at least one of B, P, b = 1 to 0.2, z = 0 to 2).
具体的には、LixCoO2、LixNiO2、LixMnO2、LixCoaNi1-aO2、LixCobV1-bOz、LixCobFe1-bO2、LixMn2O4、LixMncCo2-cO4、LixMncNi2-cO4、LixMncV2-cO4、LixMncFe2-cO4(ここでx=0.02〜1.2、a=0.1〜0.9、b=0.8〜0.98、c=1.6〜1.96、z=2.01〜2.3)が挙げられる。最も好ましいリチウム含有遷移金属酸化物としては、LixCoO2、LixNiO2、LixMnO2、LixCoaNi1-aO2、LixMn2O4、LixCobV1-bOz(x=0.02〜1.2、a=0.1〜0.9、b=0.9〜0.98、z=2.01〜2.3)が挙げられる。なお、xの値は充放電開始前の値であり、充放電により増減する。 Specifically, Li x CoO 2, Li x NiO 2, Li x MnO 2, Li x Co a Ni 1-a O 2, Li x Co b V 1-b O z, Li x Co b Fe 1-b O 2, Li x Mn 2 O 4, Li x Mn c Co 2-c O 4, Li x Mn c Ni 2-c O 4, Li x Mn c V 2-c O 4, Li x Mn c Fe 2- c O 4 (where x = 0.02 to 1.2, a = 0.1 to 0.9, b = 0.8 to 0.98, c = 1.6 to 1.96, z = 2. 01-2.3). The most preferred lithium-containing transition metal oxides, Li x CoO 2, Li x NiO 2, Li x MnO 2, Li x Co a Ni 1-a O 2, Li x Mn 2 O 4, Li x Co b V 1 -b O z (x = 0.02-1.2, a = 0.1-0.9, b = 0.9-0.98, z = 2.01-2.3). In addition, the value of x is a value before the start of charging / discharging, and increases / decreases by charging / discharging.
その他の次世代Li電池正極材料として、硫化チタン、硫化モリブデン等の金属硫化物、LiFePO4等の鉄オリビン系化合物等も使用可能である。特に、LiFePO4等の鉄オリビン系化合物は理論容量が高く、鉄を用いており、資源性、環境安全性、耐熱性等に優れている。 As other next-generation Li battery positive electrode materials, metal sulfides such as titanium sulfide and molybdenum sulfide, and iron olivine compounds such as LiFePO 4 can also be used. In particular, iron olivine compounds such as LiFePO 4 have a high theoretical capacity, use iron, and are excellent in resource, environmental safety, heat resistance, and the like.
正極活物質の平均粒子サイズは特に限定されないが、0.1〜50μmが好ましい。0.5〜30μmの粒子の体積が95%以上であることが好ましい。粒径3μm以下の粒子群の占める体積が全体積の18%以下であり、かつ15μm以上25μm以下の粒子群の占める体積が、全体積の18%以下であることがさらに好ましい。比表面積は特に限定されないが、BET法で0.01〜50m2/gが好ましく、特に0.2〜10m2/gが好ましい。 The average particle size of the positive electrode active material is not particularly limited, but is preferably 0.1 to 50 μm. It is preferable that the volume of particles of 0.5 to 30 μm is 95% or more. More preferably, the volume occupied by a particle group having a particle diameter of 3 μm or less is 18% or less of the total volume, and the volume occupied by a particle group of 15 μm or more and 25 μm or less is 18% or less of the total volume. Although the specific surface area is not particularly limited, but is preferably 0.01 to 50 m 2 / g by the BET method, in particular 0.2 to 10 m 2 / g are preferred.
5−2.正極シートの作製
本発明のリチウム電池の正極シートの作製法は、特に限定されない。一般的にはコバルト酸リチウム等の正極活物質と電極結着材、場合によってはカーボンブラックや黒鉛微粉等の導電助剤、または本発明のリチウム電池用炭素系負極材に用いるような炭素繊維を加え、湿式または乾式で所定の比率で混合し、Al等の集電体上に塗布後、乾燥、プレスすることにより作製することができる。
5-2. Production of positive electrode sheet The production method of the positive electrode sheet of the lithium battery of the present invention is not particularly limited. In general, a positive electrode active material such as lithium cobaltate and an electrode binder, and in some cases, a conductive additive such as carbon black or graphite fine powder, or a carbon fiber used for the carbon-based negative electrode material for a lithium battery of the present invention are used. In addition, it can be produced by mixing it at a predetermined ratio in a wet or dry manner, applying it on a current collector such as Al, drying and pressing.
例えば、コバルト酸リチウム粉末、アセチレンブラック(ABと略す。)を所定の組成比で乾式で、羽根つき高速小形ミキサー(IKミキサー)で混合後、この正極用混合物に電極結着材としてポリビニリデンフルオライド(PVDF)を含有したN−メチルピロリドン(NMP)溶液を所定の質量比になるように加え、プラネタリーミキサーにて混練りし、正極材用組成物とする。 For example, lithium cobaltate powder and acetylene black (abbreviated as AB) are dry-mixed at a predetermined composition ratio and mixed with a high-speed small-sized mixer with a blade (IK mixer), and then the polyvinylidene fluoride as an electrode binder is mixed with the positive electrode mixture. An N-methylpyrrolidone (NMP) solution containing a ride (PVDF) is added so as to have a predetermined mass ratio, and is kneaded with a planetary mixer to obtain a composition for a positive electrode material.
この正極材用組成物にNMPをさらに加え、粘度を調整した後、正極用に圧延Al箔(25μm)上でドクターブレードを用いて所定の厚みに塗布し、これを加熱減圧乾燥後、プレスにより所望の厚み、密度に成形する。プレス圧は特に限定はないが、1×103〜3×103kg/cm2程度が一般的である。その後、さらに加熱減圧乾燥し、正極シートを作製することができる。 NMP is further added to this composition for a positive electrode material, the viscosity is adjusted, and then applied to a predetermined thickness on a rolled Al foil (25 μm) for a positive electrode by using a doctor blade. Mold to desired thickness and density. The press pressure is not particularly limited, but is generally about 1 × 10 3 to 3 × 10 3 kg / cm 2 . Then, it can further heat-dry under reduced pressure and a positive electrode sheet can be produced.
正極材の電極結着材としては、上記したPVDFの他、ポリテトラフルオロエチレン等のフッ素系ポリマーや、上記炭素系負極材に用いたSBRやアクリレート系重合体等のゴムが使用できる。溶媒には、各々の電極結着材に適した公知のもの、例えばフッ素系ポリマーの場合なら上記のN−メチルピロリドンや、トルエン、アセトン等、SBRの場合なら水等、公知のものが使用できる。
正極材での電極結着材の使用量は、正極活物質を100質量部とした場合、0.5〜20質量部が適当であるが、特に1〜15質量部程度が好ましい。
As the electrode binder of the positive electrode material, in addition to the above-described PVDF, fluorine-based polymers such as polytetrafluoroethylene, and rubbers such as SBR and acrylate polymers used for the carbon-based negative electrode material can be used. As the solvent, a known solvent suitable for each electrode binder, for example, the above-mentioned N-methylpyrrolidone in the case of a fluorine-based polymer, toluene, acetone or the like, or water in the case of SBR can be used. .
The amount of the electrode binder used in the positive electrode material is suitably 0.5 to 20 parts by mass, particularly preferably about 1 to 15 parts by mass, when the positive electrode active material is 100 parts by mass.
溶媒添加後の混練り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、撹拌はね付き万能ミキサー等公知の装置が使用できる。 The kneading method after the addition of the solvent is not particularly limited. For example, a known apparatus such as a ribbon mixer, a screw kneader, a Spartan rewinder, a Redige mixer, a planetary mixer, a universal mixer with stirring and splashing can be used.
以上説明した本発明のリチウム電池用負極材シート及び正極材シートを所望の形状に加工し、正極材シート/セパレータ/負極材シートに積層し、正極と負極が接触しないようにし、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。次いで、電解液を注入し、容器を封印することにより、Liイオン電池及び/またはLiポリマー電池が作製できる。 The negative electrode material sheet and the positive electrode material sheet of the present invention described above are processed into a desired shape and laminated on the positive electrode material sheet / separator / negative electrode material sheet so that the positive electrode and the negative electrode are not in contact with each other. Store in containers such as molds, cylinders, and sheet molds. 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. Next, by injecting an electrolytic solution and sealing the container, a Li ion battery and / or a Li polymer battery can be produced.
セパレータ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、特に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、負極の短絡の原因となり、通常は30〜90%で用いられ、好ましくは50〜80%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、負極の短絡の原因となるため、通常は5〜100μm、好ましくは5〜50μm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と併用して用いることができる。 Although a well-known separator can be used, polyethylene and polypropylene porous microporous films are particularly preferable from the viewpoint of being thin and having high strength. The porosity is preferably higher from the viewpoint of ion conduction. However, if the porosity is too high, it causes a decrease in strength and a short circuit between the positive electrode and the negative electrode, and is usually used at 30 to 90%, preferably 50 to 80%. The thickness is preferably thin from the viewpoints of ionic conduction and battery capacity, but if it is too thin, it causes a decrease in strength and a short circuit between the positive electrode and the negative electrode, so that the thickness is usually 5-100 μm, preferably 5-50 μm. These microporous films can be used in combination of two or more kinds or other separators such as a nonwoven fabric.
本発明の非水系二次電池、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質としては、公知の非水系電解質が使用できる。
本発明の非水系電解質としては、電解質塩を非水系溶媒に溶解してなる非水系電解液、高分子固体電解質を非水系溶媒で膨潤させてなる非水系ポリマー電解質など公知のものが使用できる。
As the electrolyte in the non-aqueous secondary battery of the present invention, particularly a lithium ion battery and / or a Li polymer battery, a known non-aqueous electrolyte can be used.
As the non-aqueous electrolyte of the present invention, known ones such as a non-aqueous electrolyte obtained by dissolving an electrolyte salt in a non-aqueous solvent and a non-aqueous polymer electrolyte obtained by swelling a polymer solid electrolyte with a non-aqueous solvent can be used.
非水系溶媒としては、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。 Non-aqueous solvents 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, ethylene glycol phenyl ether, etc. 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.
電解質塩には、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。 A lithium salt is used as the electrolyte salt. 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.
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に上記の電解質塩を含有させたものが挙げられる。
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。
Examples of the polymer solid electrolyte include polyethylene oxide derivatives and polymers containing the derivatives, polypropylene oxide derivatives and polymers containing the derivatives, phosphate ester polymers, polycarbonate derivatives and polymers containing the derivatives, and the electrolyte salts described above. Can be mentioned.
There are no restrictions on the selection of members necessary for battery configuration other than those described above.
本発明のリチウム電池用負極材は、SBRを結着材として用い、それに導電助剤として繊維径1〜1000nmの炭素繊維を高度に分散させてなるものであり、電極抵抗が低く、電極強度が良好で、電解液浸透性に優れ、高エネルギー密度で高速充放電性能の良好な高性能の電池とすることができる。 The negative electrode material for a lithium battery according to the present invention uses SBR as a binder, and carbon fibers having a fiber diameter of 1 to 1000 nm are highly dispersed as a conductive auxiliary agent, and has low electrode resistance and electrode strength. It is possible to obtain a high-performance battery that is good, excellent in electrolyte permeability, high energy density, and high-speed charge / discharge performance.
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。 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.
[1]平均円形度:
炭素材料の平均円形度は、フロー式粒子像分析装置FPIA−2100(シスメックス(株)製)を用いて以下のように測定した。
測定用試料は106μmのフィルターを通して微細なゴミを取り除いて精製した。その試料0.1gを20mlのイオン交換水中に添加し、陰・非イオン界面活性剤0.1〜0.5質量%加えることによって均一に分散させ、測定用試料分散液を調製した。分散は、超音波洗浄機UT−105S(シャープマニファクチャリングシステム(株)製)を用い、5分間処理することにより行った。
測定原理等の概略は、「粉体と工業」,VOL.32,No.2,2000、特開平8−136439号公報(米国特許第5,721,433号)などに記載されているが、具体的には以下の通りである。
測定試料の分散液がフラットで透明なフローセル(厚み約200μm)の流路を通過したときにストロボ光が1/30秒間隔で照射され、CCDカメラで撮像される。その静止画像を一定枚数撮像し画像解析し、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。
[1] Average circularity:
The average circularity of the carbon material was measured as follows using a flow particle image analyzer FPIA-2100 (manufactured by Sysmex Corporation).
The sample for measurement was purified by removing fine dust through a 106 μm filter. A sample dispersion for measurement was prepared by adding 0.1 g of the sample into 20 ml of ion-exchanged water and uniformly dispersing 0.1 to 0.5% by mass of an anionic / nonionic surfactant. Dispersion was performed by treating for 5 minutes using an ultrasonic cleaner UT-105S (manufactured by Sharp Manufacturing System Co., Ltd.).
The outline of the measurement principle and the like is described in “Powder and Industry”, VOL.32, No. 2,2000, JP-A-8-136439 (US Pat. No. 5,721,433), etc. Specifically, it is as follows.
When the dispersion liquid of the measurement sample passes through the flow path of a flat and transparent flow cell (thickness: about 200 μm), strobe light is irradiated at 1/30 second intervals and imaged with a CCD camera. A certain number of the still images were taken and analyzed, and calculated according to the following formula.
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, the value 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.
[2]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)製)を用いて測定した。
[2] Average particle size:
It measured using the laser diffraction scattering type particle size distribution measuring apparatus Microtrac HRA (made by Nikkiso Co., Ltd.).
[3]比表面積:
比表面積測定装置NOVA−1200(ユアサアイオニクス(株)製)を用いて、一般的な比表面積の測定方法であるBET法により測定した。
[3] Specific surface area:
Using a specific surface area measuring device NOVA-1200 (manufactured by Yuasa Ionics Co., Ltd.), the measurement was performed by the BET method, which is a general method for measuring the specific surface area.
[4]炭素系負極材用組成物の調製
方法A:
室温で、撹拌羽根付き万能ミキサー(T.K.ハイビスミックス,特殊機化工業(株)製)中で1質量%CMC水溶液(ダイセル化学工業(株)製、ダイセル2200)に炭素繊維を所定の比率で添加し、回転速度25rpmで30分撹拌し分散した後に、所定量の炭素系負極活物質粉末を添加し、30分撹拌混合した。その後40質量%SBR水分散液(日本ゼオン(株)製、BM400B)を添加、15分撹拌混合し、炭素系負極材用組成物を得た。
[4] Method A for preparing a composition for a carbon-based negative electrode material:
At room temperature, carbon fiber is added to a 1% by mass CMC aqueous solution (manufactured by Daicel Chemical Industries, Ltd., Daicel 2200) in a universal mixer with stirring blades (TK Hibismix, manufactured by Tokushu Kika Kogyo Co., Ltd.). After adding at a ratio and stirring and dispersing for 30 minutes at a rotational speed of 25 rpm, a predetermined amount of carbon-based negative electrode active material powder was added and mixed by stirring for 30 minutes. Thereafter, 40% by mass SBR aqueous dispersion (manufactured by Zeon Corporation, BM400B) was added and mixed with stirring for 15 minutes to obtain a composition for a carbon-based negative electrode material.
方法A−2:
40質量%SBR水分散液(日本ゼオン(株)製、BM400B)を添加後、100分撹拌混合した以外は方法Aと同様の方法で、炭素系負極材用組成物を得た。
Method A-2:
After adding a 40 mass% SBR aqueous dispersion (manufactured by Nippon Zeon Co., Ltd., BM400B), a carbon-based negative electrode material composition was obtained in the same manner as in Method A except that the mixture was stirred and mixed for 100 minutes.
方法A−3:
40質量%SBR水分散液(日本ゼオン(株)製、BM400B)を添加後、150分撹拌混合した以外は方法Aと同様の方法で、炭素系負極材用組成物を得た。
Method A-3:
A carbon-based negative electrode material composition was obtained in the same manner as in Method A, except that 40% by mass SBR aqueous dispersion (manufactured by Nippon Zeon Co., Ltd., BM400B) was added and stirred for 150 minutes.
方法B:
室温で、撹拌羽根付き万能ミキサー(T.K.ハイビスミックス,特殊機化工業(株)製)中で1質量%のCMC水溶液(ダイセル化学工業(株)製、ダイセル2200)に炭素繊維を所定の比率で添加し、回転速度25rpmで30分撹拌し分散した後に、所定量の炭素系負極活物質粉末を添加し、30分撹拌混合した。さらに粘度調整として同様の1質量%CMC水溶液を所定量添加し、その後40質量%SBR水系分散液(日本ゼオン(株)製、BM400B)を添加、15分撹拌混合し、炭素系負極材用組成物を得た。
Method B:
Predetermined carbon fiber in a 1% by mass CMC aqueous solution (manufactured by Daicel Chemical Industries, Ltd., Daicel 2200) in a universal mixer with stirring blades (TK Hibismix, manufactured by Tokushu Kika Kogyo Co., Ltd.) at room temperature After stirring for 30 minutes at a rotational speed of 25 rpm and dispersing, a predetermined amount of carbon-based negative electrode active material powder was added and mixed with stirring for 30 minutes. Furthermore, a predetermined amount of the same 1% by mass CMC aqueous solution is added for viscosity adjustment, and then 40% by mass SBR aqueous dispersion (manufactured by Nippon Zeon Co., Ltd., BM400B) is added and mixed by stirring for 15 minutes, and the composition for carbon-based negative electrode material I got a thing.
方法C:
室温で、撹拌羽根付き万能ミキサー(T.K.ハイビスミックス,特殊機化工業(株)製)中で1質量%のCMC水溶液(ダイセル化学工業(株)製、ダイセル2200)に炭素系負極活物質粉末を所定の比率で添加し、回転速度25rpmで30分撹拌混合後、所定量の炭素繊維を添加し、30分撹拌し分散した後に、40質量%SBR水系分散液(日本ゼオン(株)製、BM400B)を添加、15分撹拌混合し、炭素系負極材用組成物を得た。
Method C:
At room temperature, in a universal mixer with a stirring blade (TK Hibismix, manufactured by Tokushu Kika Kogyo Co., Ltd.), a 1% by mass CMC aqueous solution (manufactured by Daicel Chemical Industries, Ltd., Daicel 2200) is used as a carbon-based negative electrode active. After adding the substance powder at a predetermined ratio and stirring and mixing at a rotational speed of 25 rpm for 30 minutes, adding a predetermined amount of carbon fiber, stirring and dispersing for 30 minutes, and then dispersing a 40% by mass SBR aqueous dispersion (Nippon Zeon Corporation) Manufactured, BM400B) was added and mixed with stirring for 15 minutes to obtain a composition for a carbon-based negative electrode material.
方法D:
羽根付き卓上高速ミキサー(IKAミキサー)中で炭素系負極活物質粉末と炭素繊維を所定の比率で、10000rpmで1分を2回乾式撹拌混合した。この混合物を撹拌羽根付き万能ミキサー(T.K.ハイビスミックス,特殊機化工業(株)製)に移し、1質量%のCMC水溶液(ダイセル化学工業(株)製、ダイセル2200)を所定量添加し、室温で30分撹拌混合後、40質量%SBR水系分散液(日本ゼオン(株)製、BM400B)を添加、15分撹拌混合し、炭素系負極材用組成物を得た。
Method D:
The carbon-based negative electrode active material powder and the carbon fiber were dry-stirred and mixed twice at a predetermined ratio at 10000 rpm for 2 minutes in a desktop high-speed mixer with blades (IKA mixer). This mixture was transferred to a universal mixer with stirring blades (TK Hibismix, manufactured by Tokushu Kika Kogyo Co., Ltd.), and a predetermined amount of 1% by mass CMC aqueous solution (manufactured by Daicel Chemical Industries, Ltd., Daicel 2200) was added. Then, after stirring and mixing at room temperature for 30 minutes, 40% by mass SBR aqueous dispersion (manufactured by Nippon Zeon Co., Ltd., BM400B) was added and mixed by stirring for 15 minutes to obtain a composition for a carbon-based negative electrode material.
方法Ref(炭素繊維を添加しない場合):
室温、撹拌羽根付き万能ミキサー(T.K.ハイビスミックス,特殊機化工業(株)製)中で1質量%CMC水溶液(ダイセル化学工業(株)製、ダイセル2200)に、所定量の炭素系負極活物質粉末を添加し、30分撹拌混合した。その後40質量%SBR水系分散液(日本ゼオン(株)製、BM400B)を添加、15分撹拌混合し、炭素系負極材用組成物を得た。
Method Ref (when no carbon fiber is added):
At room temperature, in a universal mixer with stirring blades (TK Hibismix, manufactured by Tokushu Kika Kogyo Co., Ltd.), a 1% by mass CMC aqueous solution (manufactured by Daicel Chemical Industries, Ltd., Daicel 2200) is charged with a predetermined amount of carbon. The negative electrode active material powder was added and mixed with stirring for 30 minutes. Thereafter, 40% by mass SBR aqueous dispersion (manufactured by Zeon Corporation, BM400B) was added and mixed with stirring for 15 minutes to obtain a composition for a carbon-based negative electrode material.
[5]電極及び電池の製造及び評価
(1)炭素系負極シートの製造
上記の方法で作成した炭素系負極材用組成物を日本製箔(株)製圧延銅箔(18μm)上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℃、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1×103〜3×103kg/cm2となるようにプレスし、約100μmで、所望の電極密度(1.6g/cm3または1.8g/cm3)とした。
その後、真空乾燥器で120℃、12時間乾燥し、電池評価用炭素系負極シートとした。
[5] Manufacture and evaluation of electrodes and batteries (1) Manufacture of carbon-based negative electrode sheet The composition for carbon-based negative electrode material prepared by the above method is doctor blade on a rolled copper foil (18 μm) manufactured by Nippon Foil Co., Ltd. Was applied to a predetermined thickness. 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 pressed so that the press pressure is 1 × 10 3 to 3 × 10 3 kg / cm 2 with respect to the electrode, and a desired electrode density (about 100 μm) 1.6 g / cm 3 or 1.8 g / cm 3 ).
Then, it dried at 120 degreeC for 12 hours with the vacuum dryer, and was set as the carbon type negative electrode sheet for battery evaluation.
(2)正極材組成物の調製
正極活物質LiCoO2、電気化学工業(株)製アセチレンブラック、昭和電工(株)製気相法黒鉛繊維を93:1:2(質量比)で乾式で羽根付き卓上高速ミキサー(IKミキサー)で10000rpmで1分×2回混合した正極混合物に呉羽化学工業(株)製KFポリマーL1320(ポリビニリデンフルオライド(PVDF)を12質量%含有したN−メチルピロリドン(NMP)溶液)を正極混合物とPVDFの質量比が96:4になるように加え、プラネタリーミキサーにて混練し、正極材組成物を得た。
(2) Preparation of positive electrode material composition Cathode active material LiCoO 2 , acetylene black manufactured by Denki Kagaku Kogyo Co., Ltd., and vapor-phase-processed graphite fiber manufactured by Showa Denko Co., Ltd. were dry-blown at 93: 1: 2 (mass ratio). N-methylpyrrolidone containing 12% by mass of KF polymer L1320 (polyvinylidene fluoride (PVDF)) manufactured by Kureha Chemical Industry Co., Ltd. in a cathode mixture mixed at 10000 rpm for 1 minute × 2 times with a desktop high speed mixer (IK mixer). NMP) solution) was added so that the mass ratio of the positive electrode mixture to PVDF was 96: 4, and kneaded with a planetary mixer to obtain a positive electrode material composition.
(3)正極シートの製造
正極材組成物にNMPをさらに加え、粘度を調整した後、昭和電工(株)製圧延Al箔(25μm)上で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℃、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1×103kg/cm2となるようにプレスし、約100μmで、電極密度3.3g/cm3とした。
その後、真空乾燥器で120℃、12時間乾燥し、評価用電極とした。
(3) Manufacture of positive electrode sheet NMP was further added to the positive electrode material composition to adjust the viscosity, and then applied to a predetermined thickness on a rolled Al foil (25 μm) manufactured by Showa Denko KK using a doctor blade. This was vacuum-dried at 120 ° C. for 1 hour and punched out to 18 mmφ. Further, the punched electrode was sandwiched between super steel press plates and pressed so that the pressing pressure was 1 × 10 3 kg / cm 2 with respect to the electrode, and the electrode density was 3.3 g / cm 3 at about 100 μm. .
Then, it dried at 120 degreeC for 12 hours with the vacuum dryer, and was set as the electrode for evaluation.
(4)電解液浸透速度の評価
各種負極シート(18mmφ)上に25℃の大気中で、各種電解液とほぼ同等の粘度を有し、揮発性の低いプロピレンカーボネート(PCと略す。)を電解液としてマイクロシリンジで3μl適下し、PCが電極内に浸透する時間を比較した(各水準で3回の平均値)。
(4) Evaluation of electrolyte solution permeation rate Electrolysis of propylene carbonate (abbreviated as PC) having a viscosity almost equal to that of various electrolyte solutions and low volatility on various negative electrode sheets (18 mmφ) in air at 25 ° C. As a solution, 3 μl was appropriately reduced with a microsyringe, and the time required for the PC to penetrate into the electrode was compared (average value of three times at each level).
(5)電極比抵抗の測定
各種負極シートについて4探針法で体積固有抵抗値(25℃)を測定した。
(5) Measurement of electrode specific resistance The volume specific resistance value (25 degreeC) was measured by the 4-probe method about various negative electrode sheets.
(6)Liイオン電池試験セルの作製
露点−80℃以下の乾燥アルゴン雰囲気下、下記のようにして三極セルを作製した。
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シート、上記(3)で作製したAl箔付き正極シートをセパレータ(ポリプロピレン製マイクロポ−ラスフィルム(セルガ−ド2400)、25μm)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。
(6) Production of Li-ion battery test cell A triode cell was produced as follows under a dry argon atmosphere with a dew point of -80 ° C or lower.
In a polypropylene screw-attached lid cell (inner diameter: about 18 mm), the negative electrode sheet with copper foil prepared in (1) above and the positive electrode sheet with Al foil prepared in (3) above were separated by separators (polypropylene microporous). A film (Selgard 2400), 25 μm) was sandwiched and laminated. Further, a reference metal lithium foil (50 μm) was laminated in the same manner. An electrolytic solution was added thereto to obtain a test cell.
(7)電解液
EC系:EC(エチレンカーボネート)8質量部及びDEC(ジエチルカーボネート)12質量部の混合品で、電解質としてLiPF6を1モル/リットル溶解した。
(7) Electrolytic solution EC system: A mixed product of 8 parts by mass of EC (ethylene carbonate) and 12 parts by mass of DEC (diethyl carbonate), and 1 mol / liter of LiPF 6 was dissolved as an electrolyte.
(8)充放電サイクル試験
電流密度0.6mA/cm2(0.3C相当)で定電流低電圧充放電試験を行った。
充電レストポテンシャルから4.2Vまで0.6mA/cm2でCC(コンスタントカレント:定電流)充電を行った。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。
放電は0.6mA/cm2(0.3C相当)でCC放電を行い、電圧2.7Vでカットオフした。
(8) Charging / discharging cycle test A constant current low voltage charging / discharging test was conducted at a current density of 0.6 mA / cm 2 (equivalent to 0.3 C).
CC (constant current: constant current) charging was performed at 0.6 mA / cm 2 from the charging rest potential to 4.2 V. Next, it switched to CV (constant volt: constant voltage) charge at 4.2 V, and stopped when the current value dropped to 25.4 μA.
As the discharge, CC discharge was performed at 0.6 mA / cm 2 (equivalent to 0.3 C), and cut off at a voltage of 2.7 V.
使用した材料:
<負極活物質>
SCMG−1:昭和電工(株)製球状黒鉛粒子、
平均粒径:24.5μm、 平均円形度:0.93、
X線C0:0.6716nm、 Lc:459nm、
ラマンR値:0.05、
比表面積:1.2m2/g、 真密度:2.17g/cm3
Materials used:
<Negative electrode active material>
SCMG-1: Spherical graphite particles manufactured by Showa Denko KK
Average particle size: 24.5 μm, Average circularity: 0.93
X-ray C 0 : 0.6716 nm, Lc: 459 nm,
Raman R value: 0.05,
Specific surface area: 1.2 m 2 / g, True density: 2.17 g / cm 3
SCMG−2:昭和電工(株)製球状黒鉛粒子、
平均粒径:19.0μm、 平均円形度:0.91、
X線C0:0.6716nm、 Lc:489nm、
ラマンR値:0.06、
比表面積:2.5m2/g、 真密度:2.17g/cm3
SCMG-2: Spheroidal graphite particles manufactured by Showa Denko KK
Average particle size: 19.0 μm, Average circularity: 0.91
X-ray C 0 : 0.6716 nm, Lc: 489 nm,
Raman R value: 0.06
Specific surface area: 2.5 m 2 / g, True density: 2.17 g / cm 3
MAG :日立化成工業(株)製黒鉛粒子、
平均粒径:20.1μm、 平均円形度:0.85、
X線C0:0.6716nm、 Lc:420nm、
ラマンR値:0.10、
比表面積:3.2m2/g、 真密度:2.20g/cm3
MAG: Graphite particles manufactured by Hitachi Chemical Co., Ltd.
Average particle size: 20.1 μm, Average circularity: 0.85,
X-ray C 0 : 0.6716 nm, Lc: 420 nm,
Raman R value: 0.10
Specific surface area: 3.2 m 2 / g, True density: 2.20 g / cm 3
上海MC :上海杉杉社製メソフェーズ黒鉛粒子、
平均粒径17.4μm、 平均円形度0.88、
X線C0:0.6732nm、 Lc:82.0nm、
ラマンR値:0.15、
比表面積:1.3m2/g、 真密度:2.15g/cm3
Shanghai MC: Mesophase graphite particles made by Shanghai Sugisugi,
Average particle size 17.4 μm, average circularity 0.88,
X-ray C 0 : 0.6732 nm, Lc: 82.0 nm,
Raman R value: 0.15
Specific surface area: 1.3 m 2 / g, True density: 2.15 g / cm 3
MCMB :大阪ガスケミカル(株)製メソフェーズ球状黒鉛粒子、
平均粒径16.6μm、 平均円形度0.94、
X線C0:0.6729nm、 Lc:84.4nm、
ラマンR値:0.12、
比表面積:1.1m2/g、 真密度:2.19g/cm3
MCMB: Osaka Gas Chemical Co., Ltd. mesophase spherical graphite particles,
Average particle size 16.6 μm, average circularity 0.94,
X-ray C 0 : 0.6729 nm, Lc: 84.4 nm,
Raman R value: 0.12,
Specific surface area: 1.1 m 2 / g, True density: 2.19 g / cm 3
LBCG :日本黒鉛工業(株)製球状天然黒鉛、
平均粒径24.0μm、 平均円形度0.85、
X線C0:0.6717nm、 Lc:283.5nm、
ラマンR値:0.23、
比表面積:4.6m2/g、 真密度:2.27g/cm3
LBCG: Spherical natural graphite manufactured by Nippon Graphite Industry Co., Ltd.
Average particle size 24.0 μm, average circularity 0.85,
X-ray C 0 : 0.6717 nm, Lc: 283.5 nm,
Raman R value: 0.23
Specific surface area: 4.6 m 2 / g, True density: 2.27 g / cm 3
<正極活物質材料>
LiCoO2:日本化学工業(株)製、平均粒径28.9μm、平均円形度0.96
<Positive electrode active material>
LiCoO 2 : manufactured by Nippon Chemical Industry Co., Ltd., average particle size 28.9 μm, average circularity 0.96
<炭素繊維>
VG :気相成長黒鉛繊維、
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:60、
分岐度(SEM画像解析より):0.1%、
X線C0:0.6767nm、Lc:48.0nm
<Carbon fiber>
VG: Vapor growth graphite fiber,
Average fiber diameter (from SEM image analysis): 150 nm,
Average fiber length (from SEM image analysis): 8 μm,
Average aspect ratio: 60,
Branch degree (from SEM image analysis): 0.1%
X-ray C 0 : 0.6767 nm, Lc: 48.0 nm
VG−A :気相成長炭素繊維(未黒鉛化品、1200℃焼成)、
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:65、
分岐度(SEM画像解析より):0.1%、
X線C0:0.6992nm、Lc:3.0nm
VG-A: Vapor growth carbon fiber (non-graphitized product, fired at 1200 ° C.),
Average fiber diameter (from SEM image analysis): 150 nm,
Average fiber length (from SEM image analysis): 8 μm,
Average aspect ratio: 65,
Branch degree (from SEM image analysis): 0.1%
X-ray C 0 : 0.6922 nm, Lc: 3.0 nm
VG−B :気相成長黒鉛繊維(黒鉛化時ホウ素2%添加)、
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:60、
分岐度(SEM画像解析より):0.1%、
X線C0:0.6757nm、Lc:72.0nm
VG-B: Vapor growth graphite fiber (2% boron added during graphitization),
Average fiber diameter (from SEM image analysis): 150 nm,
Average fiber length (from SEM image analysis): 8 μm,
Average aspect ratio: 60,
Branch degree (from SEM image analysis): 0.1%
X-ray C 0 : 0.6757 nm, Lc: 72.0 nm
VG−H :気相成長黒鉛繊維(ジェットミル粉砕)、
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):5μm、
平均アスペクト比:37、
分岐度(SEM画像解析より):0.1%、
X線C0:0.6769nm、Lc:47.0nm
VG-H: Vapor growth graphite fiber (jet mill pulverization),
Average fiber diameter (from SEM image analysis): 150 nm,
Average fiber length (from SEM image analysis): 5 μm,
Average aspect ratio: 37,
Branch degree (from SEM image analysis): 0.1%
X-ray C 0 : 0.6769 nm, Lc: 47.0 nm
VG−O :気相成長黒鉛繊維(500℃酸化処理品)、
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:55、
分岐度(SEM画像解析より):0.1%、
X線C0:0.6769nm、Lc:42.0nm
VG-O: Vapor-grown graphite fiber (500 ° C. oxidized product),
Average fiber diameter (from SEM image analysis): 150 nm,
Average fiber length (from SEM image analysis): 8 μm,
Average aspect ratio: 55,
Branch degree (from SEM image analysis): 0.1%
X-ray C 0 : 0.6769 nm, Lc: 42.0 nm
VG−F :気相成長黒鉛繊維、
平均繊維径(SEM画像解析より):80nm、
平均繊維長(SEM画像解析より):6μm、
平均アスペクト比:90、
分岐度(SEM画像解析より):0.1%、
X線C0:0.6801nm、Lc:35.0nm
VG-F: Vapor growth graphite fiber,
Average fiber diameter (from SEM image analysis): 80 nm,
Average fiber length (from SEM image analysis): 6 μm,
Average aspect ratio: 90,
Branch degree (from SEM image analysis): 0.1%
X-ray C 0 : 0.6801 nm, Lc: 35.0 nm
VG−T :気相成長黒鉛繊維、
平均繊維径(SEM画像解析より):20nm、
平均繊維長(SEM画像解析より):6μm、
平均アスペクト比:150、
分岐度(SEM画像解析より):0.1%、
X線C0:0.6898nm、Lc:30.0nm
VG-T: Vapor growth graphite fiber,
Average fiber diameter (from SEM image analysis): 20 nm
Average fiber length (from SEM image analysis): 6 μm,
Average aspect ratio: 150,
Branch degree (from SEM image analysis): 0.1%
X-ray C 0 : 0.6898 nm, Lc: 30.0 nm
<SBR電極結着材>
BM−400B:日本ゼオン(株)製40質量%水系分散液、ガラス転移点−5℃(DSCより)、平均粒径120nm。
<SBR electrode binder>
BM-400B: 40 mass% aqueous dispersion manufactured by Nippon Zeon Co., Ltd., glass transition point-5 ° C. (from DSC), average particle size 120 nm.
実施例:負極及び電池の作製・評価
表1(表1−1:負極材密度1.6g/cm3,表1−2:負極材密度1.8g/cm3)に示す組成及び方法により、炭素系負極材を作製し、電極比抵抗及び電解液浸透速度を測定した。次に、上記の正極材と組み合わせてLiイオン電池試験セルを作製し、負極容量密度と(充放電)サイクル特性を測定評価した。結果を表1に併せて示す。
表1から明らかなように、(A)〜(D)及び(A−2)〜(A−3)の方法で調製した負極材用組成物から作製した負極は、炭素繊維未添加品に比較して電解液浸透性が改善され、電池としたときのサイクル特性が向上している。特に(A)〜(D)の方法を用いた場合には、電極比抵抗、電解液浸透性及び容量密度のいずれもが改善し、電池としたときのサイクル特性も大幅に向上していることが分かる。また、混合方法としては(A)=(B)>(C)>(D)の順で効果があった。
Example: Production and Evaluation of Negative Electrode and Battery According to the composition and method shown in Table 1 (Table 1-1: Negative electrode material density 1.6 g / cm 3 , Table 1-2: Negative electrode material density 1.8 g / cm 3 ) A carbon-based negative electrode material was prepared, and the electrode specific resistance and the electrolyte penetration rate were measured. Next, a Li ion battery test cell was prepared in combination with the above positive electrode material, and the negative electrode capacity density and (charge / discharge) cycle characteristics were measured and evaluated. The results are also shown in Table 1.
As is clear from Table 1, the negative electrode produced from the negative electrode material composition prepared by the methods (A) to (D) and (A-2) to (A-3) was compared with a carbon fiber-free product. Thus, the electrolyte permeability is improved, and the cycle characteristics of the battery are improved. In particular, when the methods (A) to (D) are used, all of the electrode specific resistance, electrolyte permeability and capacity density are improved, and the cycle characteristics when a battery is obtained are also greatly improved. I understand. Further, the mixing method was effective in the order of (A) = (B)>(C)> (D).
Claims (24)
(1)フロー式粒子像解析装置によって測定される平均円形度が0.70〜0.99、
(2)レーザー回折法による平均粒子径が1〜50μm。 The negative electrode material for a lithium battery according to any one of claims 1 to 14, wherein the carbon-based negative electrode active material before forming the electrode is a carbonaceous particle satisfying the following requirements:
(1) The average circularity measured by a flow type particle image analyzer is 0.70 to 0.99,
(2) The average particle diameter by laser diffraction method is 1-50 μm.
(1)フロー式粒子像解析装置によって測定される平均円形度が0.70〜0.99、
(2)レーザー回折法による平均粒子径が1〜50μm。 The negative electrode material for a lithium battery according to any one of claims 1 to 17, wherein the carbon-based negative electrode active material of the electrode active material before forming the electrode is a carbonaceous particle containing 50% by mass or more of graphite particles satisfying the following requirements. :
(1) The average circularity measured by a flow type particle image analyzer is 0.70 to 0.99,
(2) The average particle diameter by laser diffraction method is 1-50 μm.
(1)X線回折測定での(002)面のC0が0.6900nm以下、La(a軸方向の結晶子サイズ)>100nm、Lc(c軸方向の結晶子サイズ)>100nm、
(2)比表面積が1.0〜10m2/g、
(3)真密度が2.20g/cm3以上、
(4)レーザーラマンR値(レーザーラマンスペクトルによる1580cm-1のピーク強度に対する1360cm-1のピーク強度比)が0.01〜0.9。 The negative electrode material for a lithium battery according to claim 16, wherein the graphite-based carbon material is a carbonaceous particle containing 50% by mass or more of graphite particles satisfying the following requirements:
(1) C 0 of (002) plane in X-ray diffraction measurement is 0.6900 nm or less, La (crystallite size in the a-axis direction)> 100 nm, Lc (crystallite size in the c-axis direction)> 100 nm,
(2) A specific surface area of 1.0 to 10 m 2 / g,
(3) True density is 2.20 g / cm 3 or more,
(4) Laser Raman R value (peak intensity ratio of 1360 cm -1 to the peak intensity of 1580 cm -1 by laser Raman spectrum) 0.01 to 0.9.
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