JP2012109280A - Negative electrode for lithium secondary battery and lithium secondary battery - Google Patents
Negative electrode for lithium secondary battery and lithium secondary battery Download PDFInfo
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本発明は、リチウム二次電池用負極及びリチウム二次電池に関する。さらに詳しくは、ポータブル機器、電気自動車、電力貯蔵等に用いるのに好適な、高容量でかつ急速充放電特性及びサイクル特性に優れたリチウム二次電池とそれを得るための負極及びその製造法に関する。 The present invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery. More specifically, the present invention relates to a lithium secondary battery having a high capacity and excellent in rapid charge / discharge characteristics and cycle characteristics suitable for use in portable equipment, electric vehicles, power storage, and the like, a negative electrode for obtaining the same, and a manufacturing method thereof. .
従来のリチウム二次電池の負極は、例えば天然黒鉛粒子、コークスを黒鉛化した人造黒鉛粒子、有機系高分子材料、ピッチ等を黒鉛化した人造黒鉛粒子、これらを粉砕した黒鉛粒子、メソフェーズカーボンを黒鉛化した球状黒鉛などがある。これらの黒鉛粒子は有機系結着剤及び有機溶剤と混合して黒鉛ペーストとし、この黒鉛ペーストを銅箔の表面に塗布し、溶剤を乾燥して、リチウム二次電池用負極として使用されている。 The negative electrode of a conventional lithium secondary battery includes, for example, natural graphite particles, artificial graphite particles graphitized with coke, organic polymer materials, artificial graphite particles graphitized with pitch, graphite particles obtained by pulverizing these, and mesophase carbon. Examples include graphitized spheroidal graphite. These graphite particles are mixed with an organic binder and an organic solvent to form a graphite paste. This graphite paste is applied to the surface of a copper foil, and the solvent is dried to be used as a negative electrode for a lithium secondary battery. .
例えば、特許文献１に示されるように、負極に黒鉛を使用することでリチウムのデンドライトによる内容短絡の問題を解消し、サイクル特性の改良を図っている。 For example, as disclosed in Patent Document 1, the use of graphite for the negative electrode eliminates the problem of content short circuit due to lithium dendrite and improves cycle characteristics.
しかしながら、黒鉛結晶が発達している天然黒鉛は、Ｃ軸方向の結晶の層間の結合力が、結晶の面方向の結合に比べて弱いため、粉砕により黒鉛層間の結合が切れ、アスペクト比が大きいいわゆる鱗状の黒鉛粒子となる。鱗状黒鉛は、アスペクト比が大きいために、バインダと混練して集電体に塗布して電極を作製したときに、鱗状黒鉛粒子が集電体の面方向に配向し、その結果、充放電容量や急速充放電特性が低下しやすいばかりでなく、黒鉛結晶へのリチウムの吸蔵・放出の繰り返しによって発生するＣ軸方向の膨張・収縮により電極内部の破壊が生じ、サイクル特性が低下する問題があるばかりでなく、負極密度を１．４５ｇ/ｃｍ3以上にすると、負極黒鉛にリチウムが吸蔵・放出されにくくなり、急速充放電特性、負極の重量当りの放電容量、サイクル特性が低下する問題がある。 However, natural graphite, which has developed graphite crystals, has weaker bond strength between crystal layers in the C-axis direction than the bond in the crystal plane direction. It becomes what is called scale-like graphite particles. Since scaly graphite has a large aspect ratio, when graphite is kneaded with a binder and applied to a current collector to produce an electrode, the scaly graphite particles are oriented in the surface direction of the current collector, resulting in a charge / discharge capacity. In addition to the rapid deterioration of the rapid charge / discharge characteristics, there is a problem in that the internal characteristics of the electrode are broken due to expansion and contraction in the C-axis direction caused by repeated insertion and extraction of lithium into and from the graphite crystal, resulting in deterioration of cycle characteristics. In addition, when the negative electrode density is 1.45 g / cm 3 or more, lithium is difficult to be occluded / released in the negative electrode graphite, and there is a problem that rapid charge / discharge characteristics, discharge capacity per weight of the negative electrode, and cycle characteristics are deteriorated. .
一方、リチウム二次電池は、負極密度を高くすることで、体積当りのエネルギー密度を大きくさせることが期待できる。そこでリチウム二次電池の体積当りのエネルギー密度を向上させるために、負極密度を高くした時に急速充放電特性及びサイクル特性に低下が少ない負極が要求されている。 On the other hand, the lithium secondary battery can be expected to increase the energy density per volume by increasing the negative electrode density. Therefore, in order to improve the energy density per volume of the lithium secondary battery, there is a demand for a negative electrode in which rapid charge / discharge characteristics and cycle characteristics are less deteriorated when the negative electrode density is increased.
本発明は、上記問題点に鑑み、急速充放電特性、サイクル特性に優れたリチウム二次電池に好適な負極を提供し、さらに高容量リチウム二次電池に好適な負極を提供するものである。 In view of the above problems, the present invention provides a negative electrode suitable for a lithium secondary battery excellent in rapid charge / discharge characteristics and cycle characteristics, and further provides a negative electrode suitable for a high capacity lithium secondary battery.
（１）本発明は、黒鉛粒子及び有機系結着剤の混合物と集電体とが加圧、一体化されてなるリチウム二次電池用負極において、負極のＸ線回折で測定される回折強度比（００２）／（１１０）が５００以下であるリチウム二次電池用負極に関する。 (1) The present invention relates to a diffraction intensity measured by X-ray diffraction of a negative electrode in a negative electrode for a lithium secondary battery in which a mixture of graphite particles and an organic binder and a current collector are pressed and integrated. The present invention relates to a negative electrode for a lithium secondary battery having a ratio (002) / (110) of 500 or less.
（２）また本発明は、黒鉛粒子及び有機系結着剤の混合物の密度が１．４５〜１．９５ｇ／ｃｍ3である前記（１）記載のリチウム二次電池用負極に関する。 (2) Moreover, this invention relates to the negative electrode for lithium secondary batteries as described in said (1) whose density of the mixture of a graphite particle and an organic type binder is 1.45-1.95g / cm < 3 >.
（３）また、本発明は、黒鉛粒子の平均粒径が１〜１００μｍ、結晶のＣ軸方向の結晶子サイズＬｃ（００２）が５００オングストローム以上である前記（１）又は（２）記載のリチウム二次電池用負極に関する。 (3) Further, the present invention provides the lithium according to the above (1) or (2), wherein the graphite particles have an average particle size of 1 to 100 μm and the crystallite size Lc (002) in the C-axis direction of the crystal is 500 angstroms or more. The present invention relates to a negative electrode for a secondary battery.
（４）さらに本発明は、前記（１）〜（３）いずれか記載の本発明のリチウム二次電池用負極とリチウム化合物を含む正極を有してなるリチウム二次電池に関する。 (4) Furthermore, this invention relates to the lithium secondary battery which has a positive electrode containing the negative electrode for lithium secondary batteries of this invention in any one of said (1)-(3), and a lithium compound.
本発明によれば、サイクル特性、急速放電特性に優れたリチウム二次電池用負極が得られ、高容量のリチウム二次電池に用いて好適である。 According to the present invention, a negative electrode for a lithium secondary battery excellent in cycle characteristics and rapid discharge characteristics can be obtained, which is suitable for use in a high capacity lithium secondary battery.
本発明のリチウム二次電池用負極は、黒鉛粒子及び有機系結着剤の混合物と集電体とが加圧、一体化されてなるリチウム二次電池用負極において、加圧、一体化された前記負極のＸ線回折で測定される回折強度比（００２）／（１１０）が５００以下であることを特徴とする。前記回折強度比（００２）／（１１０）は、好ましくは１０〜５００、より好ましくは１０〜４００、さらに好ましくは１０〜３００、特に好ましくは５０〜２００の範囲とされる。回折強度比（００２）／（１１０）が５００を超えると、作製するリチウム二次電池の急速充放電特性及びサイクル特性が低下する。 The negative electrode for a lithium secondary battery of the present invention is a negative electrode for a lithium secondary battery in which a mixture of graphite particles and an organic binder and a current collector are pressurized and integrated. The diffraction intensity ratio (002) / (110) measured by X-ray diffraction of the negative electrode is 500 or less. The diffraction intensity ratio (002) / (110) is preferably in the range of 10 to 500, more preferably 10 to 400, still more preferably 10 to 300, and particularly preferably 50 to 200. When the diffraction intensity ratio (002) / (110) exceeds 500, the rapid charge / discharge characteristics and cycle characteristics of the lithium secondary battery to be manufactured are deteriorated.
ここで、リチウム二次電池用負極の回折強度比（００２）／（１１０）は、ＣｕＫα線をＸ線源とするＸ線回折により、回折角２θ＝２６〜２７度付近に検出される（００２）面回折ピークと、回折角２θ＝７０〜８０度付近に検出される（１１０）面回折ピークの強度から下記（１）式により求めることができる。
（００２）面回折ピーク強度／（１１０）面回折ピーク強度 （１）式
Here, the diffraction intensity ratio (002) / (110) of the negative electrode for a lithium secondary battery is detected in the vicinity of a diffraction angle 2θ = 26 to 27 degrees by X-ray diffraction using CuKα rays as an X-ray source (002). ) The surface diffraction peak and the intensity of the (110) plane diffraction peak detected near the diffraction angle 2θ = 70 to 80 degrees can be obtained by the following equation (1).
(002) plane diffraction peak intensity / (110) plane diffraction peak intensity (1) Formula
本発明のリチウム二次電池用負極において、集電体と加圧、一体化された黒鉛粒子及び有機系結着剤の混合物の密度が１．４５〜１．９５ｇ/ｃｍ3であることが好ましい。前記密度は、１．５〜１．９ｇ/ｃｍ3がより好ましく、１．６〜１．８５ｇ/ｃｍ3がさらに好ましく、１．６５〜１．８ｇ/ｃｍ3が特に好ましい。本発明の負極における黒鉛粒子及び結着剤の混合物の密度を高くすることにより、この負極を用いて得られるリチウム二次電池の体積当りのエネルギー密度を大きくすることができる。前記黒鉛粒子及び有機系結着剤の混合物の密度が１．４５ｇ/ｃｍ3未満では得られるリチウム二次電池の体積当りのエネルギー密度が小さくなる。一方、前記黒鉛粒子及び有機系結着剤の混合物の密度が１．９５ｇ/ｃｍ3を超えると、リチウム二次電池を作製するときの電解液の注液性が悪くなるばかりでなく、作製するリチウム二次電池の急速充放電特性及びサイクル特性が低下しやすくなる。 In the negative electrode for a lithium secondary battery of the present invention, it is preferable that the density of the mixture of the current collector, the pressurized, integrated graphite particles and the organic binder is 1.45 to 1.95 g / cm 3. . The density is more preferably 1.5~1.9g / cm 3, more preferably 1.6~1.85g / cm 3, 1.65~1.8g / cm 3 is particularly preferred. By increasing the density of the mixture of the graphite particles and the binder in the negative electrode of the present invention, the energy density per volume of the lithium secondary battery obtained using this negative electrode can be increased. When the density of the mixture of the graphite particles and the organic binder is less than 1.45 g / cm 3 , the energy density per volume of the obtained lithium secondary battery becomes small. On the other hand, when the density of the mixture of the graphite particles and the organic binder exceeds 1.95 g / cm 3 , not only does the liquid injection property of the lithium secondary battery deteriorate, but it is also produced. The rapid charge / discharge characteristics and cycle characteristics of the lithium secondary battery are likely to deteriorate.
一体化後の該黒鉛粒子及び結着剤の混合物の密度は、例えば、一体化成形するときの圧力やロールプレス等の装置のクリアランス等により適宜調整することができる。 The density of the mixture of the graphite particles and the binder after the integration can be appropriately adjusted depending on, for example, the pressure at the time of integral molding, the clearance of an apparatus such as a roll press, and the like.
本発明で用いる黒鉛粒子の結晶のＣ軸方向の結晶子の大きさＬｃ（００２）は５００オングストローム以上が好ましく、８００オングストローム以上がより好ましく、１０００〜１００００オングストロームであることが特に好ましい。Ｃ軸方向の結晶子の大きさＬｃ（００２）が５００オングストローム未満では放電容量が小さくなる傾向がある。 The crystallite size Lc (002) in the C-axis direction of the graphite particles used in the present invention is preferably 500 angstroms or more, more preferably 800 angstroms or more, and particularly preferably 1000 to 10,000 angstroms. When the crystallite size Lc (002) in the C-axis direction is less than 500 angstroms, the discharge capacity tends to be small.
また、黒鉛粒子の結晶の層間距離ｄ（００２）は３．３８オングストローム以下が好ましく、３．３７オングストローム以下であることがより好ましく、３．３６オングストローム以下であることがさらに好ましい。結晶の層間距離ｄ（００２）が３．３８オングストロームを超えると放電容量が低下する傾向がある。前記Ｌｃ（００２）及びｄ（００２）はＸ線広角回折において測定できる。 Further, the interlayer distance d (002) of the graphite particle crystals is preferably 3.38 angstroms or less, more preferably 3.37 angstroms or less, and even more preferably 3.36 angstroms or less. When the interlayer distance d (002) between crystals exceeds 3.38 angstroms, the discharge capacity tends to decrease. The Lc (002) and d (002) can be measured by X-ray wide angle diffraction.
また、本発明のリチウム二次電池用負極に用いる黒鉛粒子は、加圧、一体化後の負極のＸ線回折で測定される回折強度比（００２）／（１１０）を５００以下に設定できるものであればよく、例えば鱗状黒鉛、球状黒鉛、鱗状黒鉛を機械的処理により粒子形状を改質した黒鉛や、複数の材料を混合して用いることもできるが、扁平状の一次粒子を複数、配向面が非平行となるように集合又は結合させた二次粒子の黒鉛粒子を用いることが好ましい。本発明において扁平状の粒子とは長軸と短軸を有する形状のことであり、完全な球状でないものをいう。例えば鱗状、鱗片状、一部の塊状等の形状のものがこれに含まれる。黒鉛粒子において、複数の扁平状の粒子の配向面が非平行とは、それぞれの粒子の形状において有する扁平した面、換言すれば最も平らに近い面を配向面として、複数の扁平状の粒子がそれぞれの配向面を一定の方向にそろうことなく集合し、黒鉛粒子を形成している状態をいう。 In addition, the graphite particles used in the negative electrode for a lithium secondary battery according to the present invention can set the diffraction intensity ratio (002) / (110) measured by X-ray diffraction of the negative electrode after pressing and integration to 500 or less. For example, scaly graphite, spheroidal graphite, graphite whose particle shape has been modified by mechanical treatment, or a mixture of a plurality of materials can be used, but a plurality of flat primary particles are oriented. It is preferable to use secondary graphite particles that are aggregated or bonded so that the surfaces are non-parallel. In the present invention, the flat particle means a shape having a major axis and a minor axis and is not completely spherical. For example, those having a shape such as a scale shape, a scale shape, or a part of a lump shape are included. In graphite particles, the orientation planes of a plurality of flat particles are non-parallel. The flat surfaces in the shape of each particle, in other words, the plane that is closest to the plane is the orientation plane, and the plurality of flat particles are A state in which the respective orientation surfaces are gathered without being aligned in a certain direction to form graphite particles.
この集合又は結合している扁平状の粒子において、結合とは互いの粒子が、例えばピッチ、タール等のバインダを炭素化した炭素質を介して、化学的に結合している状態をいい、集合とは互いの粒子が化学的に結合してはないが、その形状等に起因して、負極を作製する過程においてもその集合体としても形状を保っている状態をいう。機械的な強度の面から、結合しているものが好ましい。 In this aggregated or bound flat particle, the term “bond” refers to a state in which the particles are chemically bound, for example, via carbonaceous carbonized binder such as pitch and tar. Means that the particles are not chemically bonded to each other, but are maintained in the shape of the negative electrode as well as the aggregate due to its shape and the like. From the viewpoint of mechanical strength, those bonded are preferable.
また、本発明で使用する黒鉛粒子は、アスペクト比が５以下であることが好ましく、１．２〜５であればより好ましく、１．２〜３であればさらに好ましく、１．３〜２．５であれば特に好ましい。アスペクト比が５以下の黒鉛粒子は、複数の一次粒子を集合又は結合させた二次粒子としてのものでもよく、また、１つの粒子を機械的な力を加えアスペクト比が５以下となるように形状を変えたものでもよく、さらに、これらを組合わせて作製したものでもよい。 The graphite particles used in the present invention preferably have an aspect ratio of 5 or less, more preferably 1.2 to 5, more preferably 1.2 to 3, and more preferably 1.3 to 2. 5 is particularly preferable. The graphite particles having an aspect ratio of 5 or less may be secondary particles in which a plurality of primary particles are aggregated or combined, and one particle is mechanically applied so that the aspect ratio is 5 or less. The shape may be changed, and further, a combination of these may be used.
このアスペクト比が５を超えると、加圧、一体化後の負極のＸ線回折で測定される回折強度比（００２）／（１１０）が大きくなりやすく、その結果、得られるリチウム二次電池の急速充放電特性及びサイクル特性が低下する傾向がある。このアスペクト比が１．２未満では、粒子間の接触面積が減ることにより、作製する負極の導電性が低下する傾向にある。 When this aspect ratio exceeds 5, the diffraction intensity ratio (002) / (110) measured by X-ray diffraction of the negative electrode after pressurization and integration tends to increase, and as a result, the obtained lithium secondary battery The rapid charge / discharge characteristics and cycle characteristics tend to deteriorate. When the aspect ratio is less than 1.2, the contact area between the particles decreases, and the conductivity of the negative electrode to be produced tends to decrease.
本発明において、使用する黒鉛粒子が複数の粒子の集合体または結合体として存在している場合は、黒鉛粒子の一次粒子とは、例えば走査型電子顕微鏡（ＳＥＭ）等により観察した際に認められる粒子単位をいう。また、二次粒子とは、この一次粒子が集合または結合している塊をいう。 In the present invention, when the graphite particles to be used are present as an aggregate or a combination of a plurality of particles, the primary particles of the graphite particles are recognized when observed with, for example, a scanning electron microscope (SEM). A particle unit. Further, the secondary particle refers to a mass in which the primary particles are aggregated or bonded.
また、アスペクト比は、粒子の長軸方向の長さをＡ、短軸方向の長さをＢとしたとき、Ａ／Ｂで表される。本発明における黒鉛粒子のアスペクト比は、顕微鏡で一次粒子または二次粒子の黒鉛粒子を拡大し、長軸の長さが１０〜５０μｍの大きさの粒子を任意に１０個選択し、Ａ／Ｂを測定し、その算術平均値をとったものである。 The aspect ratio is represented by A / B, where A is the length in the major axis direction of the particle and B is the length in the minor axis direction. The aspect ratio of the graphite particles in the present invention is such that the primary or secondary graphite particles are magnified with a microscope, and 10 particles having a major axis length of 10 to 50 μm are arbitrarily selected. Is measured and the arithmetic average value is taken.
１つの二次黒鉛粒子において、扁平状の一次粒子の集合又は結合する数としては、３個以上であることが好ましく、５個以上であればより好ましい。個々の扁平状の一次粒子の大きさとしては、粒径で１〜１００μｍの粒子を含むことが好ましく、５〜８０μｍであればより好ましく、５〜５０μｍであればさらに好ましく、これらが集合又は結合した二次黒鉛粒子の平均粒径の２／３以下であることが好ましい。また、個々の扁平状の一次粒子のアスペクト比は１００以下が好ましく、５０以下がより好ましく、２０以下がさらに好ましい。前記一次粒子のアスペクト比の好ましい下限としては１．２であり、球状でないことが好ましい。 In one secondary graphite particle, the number of flat primary particles aggregated or bonded is preferably 3 or more, more preferably 5 or more. The size of each flat primary particle is preferably 1 to 100 μm, more preferably 5 to 80 μm, and even more preferably 5 to 50 μm, and these are aggregates or bonds. It is preferable that it is 2/3 or less of the average particle diameter of the obtained secondary graphite particles. Further, the aspect ratio of each flat primary particle is preferably 100 or less, more preferably 50 or less, and further preferably 20 or less. A preferable lower limit of the aspect ratio of the primary particles is 1.2, and it is preferably not spherical.
さらに、本発明における黒鉛粒子は、二次粒子の比表面積が８ｍ2／ｇ以下のものが好ましく、より好ましくは５ｍ2/ｇ以下である。該黒鉛粒子を負極に使用すると、得られるリチウム二次電池の急速充放電特性及びサイクル特性を向上させることができ、また、第一サイクル目の不可逆容量を小さくすることができる。比表面積が、８ｍ2/ｇを超えると、得られるリチウム二次電池の第一サイクル目の不可逆容量が大きくなる傾向があり、エネルギー密度が小さく、さらに負極を作製する際多くの結着剤が必要になる傾向にある。得られるリチウム二次電池の急速充放電特性、サイクル特性等がさらに良好な点から、比表面積は、１．５〜５ｍ2／ｇであることがさらに好ましく、２〜５ｍ2／ｇであることが特に好ましい。比表面積の測定は、窒素ガス吸着によるＢＥＴ法など、既知の方法をとることができる。 Furthermore, the graphite particles in the present invention preferably have a specific surface area of secondary particles of 8 m 2 / g or less, more preferably 5 m 2 / g or less. When the graphite particles are used for the negative electrode, the rapid charge / discharge characteristics and cycle characteristics of the obtained lithium secondary battery can be improved, and the irreversible capacity in the first cycle can be reduced. If the specific surface area exceeds 8 m 2 / g, the irreversible capacity of the first cycle of the obtained lithium secondary battery tends to increase, the energy density is small, and a large number of binders are used when producing a negative electrode. It tends to be necessary. The specific surface area is more preferably 1.5 to 5 m 2 / g, more preferably 2 to 5 m 2 / g, from the viewpoint that the rapid charge / discharge characteristics, cycle characteristics, and the like of the obtained lithium secondary battery are further improved. Is particularly preferred. The specific surface area can be measured by a known method such as a BET method using nitrogen gas adsorption.
本発明のリチウム二次電池用負極の製造法は特に制限はないが、例えば、少なくとも黒鉛化可能な骨材又は黒鉛と黒鉛化可能なバインダを混合し、粉砕した後、該粉砕物と黒鉛化触媒１〜５０重量％を混合し、焼成して黒鉛粒子を得、ついで、該黒鉛粒子に有機系結着剤及び溶剤を添加して混合し、該混合物を集電体に塗布し、乾燥して溶剤を除去した後、加圧して一体化することで作製できる。 The method for producing the negative electrode for a lithium secondary battery of the present invention is not particularly limited. For example, at least a graphitizable aggregate or graphite and a graphitizable binder are mixed and pulverized, and then the pulverized product and graphitized are mixed. 1 to 50% by weight of catalyst is mixed and calcined to obtain graphite particles, and then the organic particles and a solvent are added to and mixed with the graphite particles, and the mixture is applied to a current collector and dried. Then, after removing the solvent, it can be manufactured by pressurizing and integrating.
黒鉛化可能な骨材としては、例えば、コークス粉末、樹脂の炭化物等が使用できるが、黒鉛化できる粉末材料であれば特に制限はない。中でも、ニードルコークス等の黒鉛化しやすいコークス粉末が好ましい。また黒鉛としては、例えば天然黒鉛粉末、人造黒鉛粉末等が使用できるが粉末状であれば特に制限はない。黒鉛化可能な骨材又は黒鉛の粒径は、作製する黒鉛粒子の粒径より小さいことが好ましく、平均粒径で１〜８０μｍがより好ましく、１〜５０μｍであればさらに好ましく、５〜５０μｍであれば特に好ましい。また、黒鉛化可能な骨材又は黒鉛のアスペクト比は、１．２〜５００が好ましく、１．５〜３００の範囲であればより好ましく、１．５〜１００の範囲であればさらに好ましく、２〜５０の範囲であれば特に好ましい。ここでアスペクト比測定は、前記と同様の方法で行う。黒鉛化可能な骨材又は黒鉛のアスペクト比が大きくなると、加圧、一体化後の負極のＸ線回折で測定される回折強度比（００２）／（１１０）が大きくなる傾向があり、１．２未満では黒鉛粒子重量当りの放電容量が小さくなる傾向がある。 Examples of the aggregate that can be graphitized include coke powder and resin carbide, but there is no particular limitation as long as it is a powder material that can be graphitized. Among these, coke powder that is easily graphitized such as needle coke is preferable. Moreover, as graphite, natural graphite powder, artificial graphite powder, etc. can be used, for example, but there is no restriction | limiting in particular if it is a powder form. The particle size of the graphitizable aggregate or graphite is preferably smaller than the particle size of the graphite particles to be produced, the average particle size is more preferably 1 to 80 μm, more preferably 1 to 50 μm, and more preferably 5 to 50 μm. It is particularly preferable if it is present. The aspect ratio of the graphitizable aggregate or graphite is preferably from 1.2 to 500, more preferably from 1.5 to 300, and even more preferably from 1.5 to 100. A range of ˜50 is particularly preferable. Here, the aspect ratio measurement is performed by the same method as described above. When the aspect ratio of graphitizable aggregate or graphite increases, the diffraction intensity ratio (002) / (110) measured by X-ray diffraction of the negative electrode after pressurization and integration tends to increase. If it is less than 2, the discharge capacity per graphite particle weight tends to be small.
バインダとしては、例えば、タール、ピッチの他、熱硬化性樹脂、熱可塑性樹脂等の有機系材料が好ましい。バインダの配合量は、黒鉛化可能な骨材又は黒鉛に対し、５〜８０重量％添加することが好ましく、１０〜８０重量％添加することがより好ましく、２０〜８０重量％添加することがさらに好ましく、３０〜８０重量％添加することが特に好ましい。バインダの量が多すぎたり少なすぎたりすると、作製する黒鉛粒子のアスペクト比及び比表面積が大きくなり易い傾向がある。黒鉛化可能な骨材又は黒鉛とバインダの混合方法は、特に制限はなく、例えばニーダー等を用いて行うことができるが、バインダの軟化点以上の温度で混合することが好ましい。具体的にはバインダがピッチ、タール等の際には、５０〜３００℃が好ましく、熱硬化性樹脂の場合は２０〜１８０℃が好ましい。 As the binder, for example, an organic material such as a thermosetting resin and a thermoplastic resin is preferable in addition to tar and pitch. The blending amount of the binder is preferably 5 to 80% by weight, more preferably 10 to 80% by weight, and further preferably 20 to 80% by weight based on the graphitizable aggregate or graphite. It is preferable to add 30 to 80% by weight. If the amount of the binder is too large or too small, the aspect ratio and specific surface area of the graphite particles to be produced tend to increase. The method of mixing the graphitizable aggregate or graphite and the binder is not particularly limited and can be performed using, for example, a kneader, but is preferably mixed at a temperature equal to or higher than the softening point of the binder. Specifically, when the binder is pitch, tar or the like, 50 to 300 ° C is preferable, and when the binder is a thermosetting resin, 20 to 180 ° C is preferable.
次に上記混合物を粉砕し、該粉砕物と黒鉛化触媒とを混合する。該粉砕物の粒径は１〜１００μｍが好ましく、５〜８０μｍであればより好ましく、５〜５０μｍであればさらに好ましく、１０〜３０μｍが特に好ましい。 Next, the mixture is pulverized, and the pulverized product and the graphitization catalyst are mixed. The particle size of the pulverized product is preferably 1 to 100 μm, more preferably 5 to 80 μm, further preferably 5 to 50 μm, and particularly preferably 10 to 30 μm.
該粉砕物の粒径が１００μｍを超えると得られる黒鉛粒子の比表面積が大きくなる傾向があり、１μｍ未満では得られる負極の（００２）／（１１０）比が大きくなる傾向がある。また、該粉砕物の揮発分は０．５〜５０重量％であることが好ましく、１〜３０重量％であればより好ましく、５〜２０重量％であればさらに好ましい。揮発分の測定は、該粉砕物を８００℃で１０分間加熱した時の重量減少が求められる。該粉砕物と混合する黒鉛化触媒としては、黒鉛化触媒としての機能があるものであれば特に制限はないが、例えば鉄、ニッケル、チタン、ケイ素、ホウ素等の金属、これらの炭化物、酸化物などの黒鉛化触媒が使用できる。これらの中で、鉄又はケイ素の化合物が好ましい。また化合物の化学構造としては炭化物が好ましい。これらの黒鉛化触媒の添加量は、黒鉛化触媒と混合する粉砕物と黒鉛化触媒の総量を１００重量％としたとき、１〜５０重量％が好ましく、５〜３０重量％であればより好ましく、７〜２０重量％であればさらに好ましい。黒鉛化触媒の量が１重量％未満であると作製する黒鉛粒子の結晶の発達が悪くなるばかりでなく、比表面積が大きくなる傾向があり、一方５０重量％を超えると作製する黒鉛粒子に黒鉛化触媒が残存しやすくなる。使用する黒鉛化触媒は粉末状が好ましく、平均粒径が0.1〜200μｍの粉末状が好ましく、1〜100μｍであればより好ましく、1〜５０μｍであればより好ましい。 When the particle size of the pulverized product exceeds 100 μm, the specific surface area of the obtained graphite particles tends to increase, and when it is less than 1 μm, the (002) / (110) ratio of the obtained negative electrode tends to increase. The volatile matter of the pulverized product is preferably 0.5 to 50% by weight, more preferably 1 to 30% by weight, and even more preferably 5 to 20% by weight. The volatile matter is measured by weight reduction when the pulverized product is heated at 800 ° C. for 10 minutes. The graphitization catalyst to be mixed with the pulverized product is not particularly limited as long as it has a function as a graphitization catalyst. For example, metals such as iron, nickel, titanium, silicon and boron, carbides and oxides thereof Graphitization catalysts such as can be used. Of these, iron or silicon compounds are preferred. The chemical structure of the compound is preferably a carbide. The addition amount of these graphitization catalysts is preferably 1 to 50% by weight, more preferably 5 to 30% by weight, when the total amount of the pulverized product mixed with the graphitization catalyst and the graphitization catalyst is 100% by weight. 7 to 20% by weight is more preferable. When the amount of the graphitization catalyst is less than 1% by weight, not only the crystal development of the graphite particles to be produced deteriorates but also the specific surface area tends to increase. The catalyst becomes easier to remain. The graphitization catalyst used is preferably in the form of a powder, preferably in the form of a powder having an average particle size of 0.1 to 200 μm, more preferably 1 to 100 μm, and even more preferably 1 to 50 μm.
次に上記混合物を焼成し、黒鉛化処理を行うが、焼成を行う前に、前記粉砕物と黒鉛化触媒の混合物をプレス等により所定形状に成形してから、焼成してもよい。この場合の成形圧力は１〜３００ＭＰａ程度が好ましい。焼成は前記混合物が酸化し難い条件で焼成することが好ましく、例えば窒素雰囲気中、アルゴン雰囲気中、真空中、自己揮発性雰囲気中で焼成する方法が挙げられる。黒鉛化の温度は、２０００℃以上が好ましく、２５００℃以上であることがより好ましく、２７００℃以上であればさらに好ましく、２８００〜３２００℃であることが特に好ましい。黒鉛化の温度が低いと、黒鉛の結晶の発達が悪く、放電容量が低くなる傾向があるとともに添加した黒鉛化触媒が作製する黒鉛粒子に残存し易くなる傾向がある。黒鉛化触媒が作製する黒鉛粒子中に多く残存すると、黒鉛粒子重量当りの放電容量が低下する。黒鉛化の温度が高すぎると、黒鉛が昇華することがある。焼成を、プレス等により所定形状に成形した成形物で行う場合は、黒鉛化後の成形物の見掛け密度は１．６５g/cｍ3以下が好ましく、１．５５g/cｍ3以下であればより好ましく、１．５０g/cｍ3以下であればさらに好ましく、１．４５g/cｍ3以下であれば特に好ましい。黒鉛化後の成形物の密度が１．６５g/cｍ3以上では作製する黒鉛粒子の比表面積が大きくなる傾向がある。黒鉛化後の成形物の見掛け密度は、例えば、前記黒鉛化触媒と混合する粉砕物の粒径及び、プレス等により所定形状に成形するときの圧力等により適宜調整することができる。 Next, the mixture is fired and graphitized, and before firing, the mixture of the pulverized product and the graphitized catalyst may be formed into a predetermined shape by a press or the like and then fired. The molding pressure in this case is preferably about 1 to 300 MPa. Firing is preferably performed under conditions where the mixture is not easily oxidized, and examples thereof include a method of firing in a nitrogen atmosphere, an argon atmosphere, a vacuum, and a self-volatile atmosphere. The graphitization temperature is preferably 2000 ° C or higher, more preferably 2500 ° C or higher, further preferably 2700 ° C or higher, and particularly preferably 2800 to 3200 ° C. When the graphitization temperature is low, the development of graphite crystals tends to be poor, the discharge capacity tends to be low, and the added graphitization catalyst tends to remain in the graphite particles produced. When a large amount of the graphitization catalyst remains in the graphite particles produced, the discharge capacity per graphite particle weight decreases. If the graphitization temperature is too high, the graphite may sublime. Firing, if performed in the molding prepared by molding into a predetermined shape by pressing or the like, the apparent density is preferably 1.65 g / cm 3 or less of the molded product after graphitization, more preferably if 1.55 g / cm 3 or less , more preferably if 1.50 g / cm 3 or less, particularly preferred if the 1.45 g / cm 3 or less. When the density of the molded product after graphitization is 1.65 g / cm 3 or more, the specific surface area of the produced graphite particles tends to increase. The apparent density of the molded product after graphitization can be appropriately adjusted by, for example, the particle size of the pulverized product mixed with the graphitization catalyst and the pressure when forming into a predetermined shape by a press or the like.
次いで、粉砕し、粒度を調整して負極炭素材料である黒鉛粒子とするが、粉砕方法としては、特に制限はなく、例えば、ジェットミル、ハンマーミル、ピンミル等の衝撃粉砕方式をとることができる。粉砕後の負極炭素材料の平均粒径は、１〜１００μｍが好ましく、５〜５０μｍがより好ましく、１０〜３０μｍが特に好ましい。平均粒径が大きくなりすぎると作製する負極の表面に凹凸ができ易くなり、その結果作製するリチウム二次電池がミクロ短絡しやすくなりサイクル特性が低下する傾向がある。 Next, the powder is pulverized and the particle size is adjusted to obtain graphite particles that are the negative electrode carbon material. . The average particle diameter of the negative electrode carbon material after pulverization is preferably 1 to 100 μm, more preferably 5 to 50 μm, and particularly preferably 10 to 30 μm. If the average particle size becomes too large, the surface of the negative electrode to be produced is likely to be uneven, and as a result, the lithium secondary battery to be produced tends to be short-circuited and the cycle characteristics tend to deteriorate.
なお、本発明において平均粒径は、レーザー回折式粒度分布計により測定することができる。 In the present invention, the average particle diameter can be measured by a laser diffraction particle size distribution meter.
得られた前記黒鉛粒子は、有機系結着剤及び溶剤と混練して、ペースト状にし、シート状、ペレット状等の形状に成形される。 The obtained graphite particles are kneaded with an organic binder and a solvent to form a paste, and are formed into a sheet shape, a pellet shape, or the like.
有機系結着剤としては、例えば、ポリエチレン、ポリプロピレン、エチレンプロピレンターポリマー、ブタジエンゴム、スチレンブタジエンゴム、ブチルゴム、イオン伝導率の大きな高分子化合物等が使用できる。 As the organic binder, for example, polyethylene, polypropylene, ethylene propylene terpolymer, butadiene rubber, styrene butadiene rubber, butyl rubber, a high molecular compound having high ionic conductivity, and the like can be used.
前記イオン伝導率の大きな高分子化合物としては、ポリフッ化ビニリデン、ポリエチレンオキサイド、ポリエピクロルヒドリン、ポリファスファゼン、ポリアクリロニトリル等が使用できる。 As the polymer compound having a high ion conductivity, polyvinylidene fluoride, polyethylene oxide, polyepichlorohydrin, polyphasphazene, polyacrylonitrile and the like can be used.
炭素材料と有機系結着剤との混合比率は、炭素材料１００重量部に対して、有機系結着剤を０．５〜２０重量部用いることが好ましい。 The mixing ratio of the carbon material and the organic binder is preferably 0.5 to 20 parts by weight of the organic binder with respect to 100 parts by weight of the carbon material.
溶剤としては、特に制限はなく、Ｎ−メチル−２−ピロリドン、ジメチルホルムアミド、イソプロパノール、水等が挙げられる。溶剤として水を使用するバインダの場合は、増粘剤を併用することが好ましい。 There is no restriction | limiting in particular as a solvent, N-methyl- 2-pyrrolidone, a dimethylformamide, isopropanol, water etc. are mentioned. In the case of a binder using water as a solvent, it is preferable to use a thickener together.
溶剤の量も特に制限はなく、炭素材料は、有機系結着剤及び溶剤と混練して混合物を作製し、粘度を適宜調整した後、集電体に塗布し、該集電体と加圧、一体化して負極とされる。集電体としては、例えばニッケル、銅等の箔、メッシュなどの金属集電体が使用できる。なお一体化は、例えばロール、プレス等の成形法で行うことができ、またこれらを組み合わせて一体化しても良い。この一体化する際の圧力は１〜２００ＭＰａ程度が好ましい。 The amount of the solvent is not particularly limited, and the carbon material is kneaded with an organic binder and a solvent to prepare a mixture, the viscosity is appropriately adjusted, and then applied to the current collector. , Integrated into a negative electrode. As the current collector, for example, a metal current collector such as a foil or mesh of nickel, copper or the like can be used. The integration can be performed by a molding method such as a roll or a press, or a combination of them may be integrated. The pressure during the integration is preferably about 1 to 200 MPa.
このようにして得られた負極は、リチウム二次電池に用いられる。本発明のリチウム二次電池は、リチウム化合物を含む正極と前記本発明の負極を有してなるもので、例えば、正極と負極をセパレータを介して対向して配置し、かつ電解液を注入することにより得ることができ、これは従来の負極を使用したリチウム二次電池に比較して、高容量でサイクル特性、急速充放電特性に優れる。 The negative electrode thus obtained is used for a lithium secondary battery. The lithium secondary battery of the present invention comprises a positive electrode containing a lithium compound and the negative electrode of the present invention. For example, the positive electrode and the negative electrode are arranged to face each other with a separator interposed therebetween and an electrolyte is injected. Compared to a lithium secondary battery using a conventional negative electrode, it has a high capacity and excellent cycle characteristics and rapid charge / discharge characteristics.
本発明におけるリチウム二次電池の正極はリチウム化合物を含むが、その材料に特に制限はなく、例えばＬｉＮｉＯ２、ＬｉＣｏＯ２、ＬｉＭｎ２Ｏ４等を単独又は混合して使用することができる。 The positive electrode of the lithium secondary battery in the present invention contains a lithium compound, but the material thereof is not particularly limited. For example, LiNiO 2 , LiCoO 2 , LiMn 2 O 4 and the like can be used alone or in combination.
リチウム二次電池は、正極及び負極とともに、通常、リチウム化合物を含む電解液を含む。 Lithium secondary batteries usually contain an electrolyte containing a lithium compound together with a positive electrode and a negative electrode.
電解液としては、ＬｉＣｌＯ４、ＬｉＰＦ６、ＬｉＡｓＦ６、ＬｉＢＦ４、ＬｉＳＯ３ＣＦ３、ＣＨ３ＳＯ３Ｌｉ、ＣＦ３ＳＯ３Ｌｉ等のリチウム塩を、例えば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、アセトニトリル、プロピロニトリル、ジメトキシエタン、テトラヒドロフラン、γ―ブチロラクトン等の非水系溶剤に溶かしたいわゆる有機電解液や、固体若しくはゲル状のいわゆるポリマー電解質を使用することができる。 As the electrolytic solution, lithium salts such as LiClO 4 , LiPF 6 , LiAsF 6 , LiBF 4 , LiSO 3 CF 3 , CH 3 SO 3 Li, CF 3 SO 3 Li, for example, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl A so-called organic electrolytic solution dissolved in a non-aqueous solvent such as ethyl carbonate, propylene carbonate, acetonitrile, propironitrile, dimethoxyethane, tetrahydrofuran, or γ-butyrolactone, or a so-called polymer electrolyte in a solid or gel form can be used.
また、電解液には、リチウム二次電池の初回充電時に分解反応を示す添加剤を少量添加することが好ましい。添加剤としては例えば、ビニレンカーボネート、ビフェニール、プロパンスルトン等があげられ、添加量としては０．０１〜５重量％が好ましい。 Moreover, it is preferable to add a small amount of an additive that exhibits a decomposition reaction when the lithium secondary battery is initially charged to the electrolytic solution. Examples of the additive include vinylene carbonate, biphenyl, propane sultone, and the addition amount is preferably 0.01 to 5% by weight.
セパレータとしては、例えばポリエチレン、ポリプロピレン等のポリオレフィンを主成分とした不織布、クロス、微孔フィルム又はそれらを組み合わせたものを使用することができる。なお、作製するリチウム二次電池の正極と負極が直接接触しない構造にした場合は、セパレータを使用する必要はない。 As the separator, for example, a nonwoven fabric mainly composed of polyolefin such as polyethylene or polypropylene, cloth, microporous film, or a combination thereof can be used. In addition, when it is set as the structure where the positive electrode and negative electrode of a lithium secondary battery to produce are not in direct contact, it is not necessary to use a separator.
図１に円筒型リチウム二次電池の一例の一部断面正面の概略図を示す。図１に示す円筒型リチウム二次電池は、薄板状に加工された正極１と、同様に加工された負極２がポリエチレン製微孔膜等のセパレータ３を介して重ねあわせたものを捲回し、これを金属製等の電池缶７に挿入し、密閉化されている。正極１は正極タブ４を介して正極蓋６に接合され、負極２は負極タブ５を介して電池底部へ接合されている。正極蓋６はガスケット８にて電池缶（正極缶）７へ固定されている。 FIG. 1 shows a schematic diagram of a partial cross-sectional front view of an example of a cylindrical lithium secondary battery. The cylindrical lithium secondary battery shown in FIG. 1 is obtained by winding a positive electrode 1 processed into a thin plate shape and a negative electrode 2 processed in the same manner through a separator 3 such as a polyethylene microporous membrane, This is inserted into a battery can 7 made of metal or the like and sealed. The positive electrode 1 is bonded to the positive electrode lid 6 via the positive electrode tab 4, and the negative electrode 2 is bonded to the battery bottom via the negative electrode tab 5. The positive electrode lid 6 is fixed to a battery can (positive electrode can) 7 with a gasket 8.
以下、本発明の実施例を説明する。 Examples of the present invention will be described below.
実施例１
平均粒径１０μｍのコークス粉末５０重量部と、コールタールピッチ３０重量部を２３０℃で２時間混合した。次いで、この混合物を平均粒径２５μｍに粉砕した後、該粉砕物８０重量部と平均粒径２５μｍの炭化珪素２０重量部をブレンダーで混合し、該混合物を金型に入れ、１００ＭＰａでプレス成形し、直方体に成形した。この成形体を窒素雰囲気中で１０００℃で熱処理した後、さらに窒素雰囲気中で３０００℃で熱処理し、黒鉛成形体を得た。さらにこの黒鉛成形体を粉砕して負極炭素材料である黒鉛粒子を得た。得られた負極炭素材料から、以下の測定を行った。(1)レーザー回折式粒度分布計による平均粒径、(2)ＢＥＴ法による比表面積、(3)アスペクト比（１０個分の平均値）、(4)Ｘ線広角回折による結晶の層間距離ｄ（００２）及び(5)結晶のＣ軸方向の結晶子サイズＬｃ（００２）。これらの測定値を表１に示す。
Example 1
50 parts by weight of coke powder having an average particle size of 10 μm and 30 parts by weight of coal tar pitch were mixed at 230 ° C. for 2 hours. Next, after pulverizing this mixture to an average particle size of 25 μm, 80 parts by weight of the pulverized product and 20 parts by weight of silicon carbide having an average particle size of 25 μm were mixed with a blender, and the mixture was put into a mold and press-molded at 100 MPa. And formed into a rectangular parallelepiped. This molded body was heat-treated at 1000 ° C. in a nitrogen atmosphere, and further heat-treated at 3000 ° C. in a nitrogen atmosphere to obtain a graphite molded body. Furthermore, this graphite molded body was pulverized to obtain graphite particles as a negative electrode carbon material. The following measurements were performed from the obtained negative electrode carbon material. (1) Average particle diameter by laser diffraction particle size distribution meter, (2) Specific surface area by BET method, (3) Aspect ratio (average value for 10 pieces), (4) Interlayer distance d of crystals by X-ray wide angle diffraction (002) and (5) Crystallite size Lc (002) in the C-axis direction of the crystal. These measured values are shown in Table 1.
平均粒径は、レーザー回折粒度分布測定装置（株式会社島津製作所製品名SALD-3000）を用い、５０％Dでの粒子径を平均粒径とした。層間距離ｄ(002)はＸ線回折装置を用い、Ｃｕ-Ｋα線をＮｉフィルターで単色化し、高純度シリコンを標準物質として測定した。比表面積は、micromeritics社製品名ASAP 2010を用い、液体窒素温度での窒素吸着を多点法で測定、BET法に従って算出した。 The average particle size was determined by using a laser diffraction particle size distribution analyzer (product name: SALD-3000, Shimadzu Corporation), and the particle size at 50% D was defined as the average particle size. The interlayer distance d (002) was measured using an X-ray diffractometer, using Cu-Kα rays as a single color with a Ni filter, and using high-purity silicon as a standard substance. The specific surface area was calculated according to the BET method by measuring the nitrogen adsorption at the liquid nitrogen temperature by a multipoint method using the product name ASAP 2010 of micromeritics.
次いで、得られた負極炭素材料９０重量％に、Ｎ−メチル−２ピロリドンに溶解した有機系結着剤ポリフッ化ビニリデン（ＰＶＤＦ）を固形分で１０重量％加えて混練して黒鉛ペーストを作製した。この黒鉛ペーストを厚さが１０μｍの圧延銅箔に塗布し、さらに、１２０℃で乾燥してＮ−メチル−２ピロリドンを除去し、垂直プレスで１０ＭＰａで圧縮して試料電極を得た。この試料電極の、(6)黒鉛粒子とPVDFの混合物層の密度を測定したところ、１．２０g/cｍ3であり、厚さは９６μｍであった。得られた試験電極を、Ｘ線回折装置により、（００２）及び（１１０）回折ピークを測定し、各ピークトップ強度から、(7)（００２）／（１１０）強度比を測定した。その結果を表１に併記する。なお、(4)、(5)及び(6)のＸ線回折において、Ｘ線源：ＣｕＫα線／４０ＫＶ／２０ｍＡ、ステップ幅０．０２°とした。 Subsequently, 10% by weight of organic binder polyvinylidene fluoride (PVDF) dissolved in N-methyl-2-pyrrolidone was added to 90% by weight of the obtained negative electrode carbon material and kneaded to prepare a graphite paste. . This graphite paste was applied to a rolled copper foil having a thickness of 10 μm, further dried at 120 ° C. to remove N-methyl-2pyrrolidone, and compressed at 10 MPa with a vertical press to obtain a sample electrode. When the density of the mixed layer of (6) graphite particles and PVDF of this sample electrode was measured, it was 1.20 g / cm 3 and the thickness was 96 μm. The (002) and (110) diffraction peaks of the obtained test electrode were measured with an X-ray diffractometer, and the (7) (002) / (110) intensity ratio was measured from each peak top intensity. The results are also shown in Table 1. In the X-ray diffraction of (4), (5), and (6), the X-ray source was CuKα ray / 40 KV / 20 mA, and the step width was 0.02 °.
作製した試料電極を２ｃｍ2の大きさに打ち抜き、３端子法による定電流充放電を行い、下記のように充放電容量及び放電容量維持率の測定を行った。図２に、本測定に用いたリチウム二次電池の概略図を示す。試料電極の評価は、図２に示すようにビーカ型ガラスセル９に電解液１０としてＬｉＰＦ６をエチレンカーボネート（ＥＣ）及びメチルエチルカーボネート（ＭＥＣ）（ＥＣとＭＥＣは体積比で１：２）の混合溶媒に１モル／リットルの濃度になるように溶解した溶液を入れ、試料電極１１、セパレータ１２及び対極１３を積層して配置し、さらに参照極１４を上部から吊るしてモデル電池を作製した。なお、対極１３及び参照極１４には金属リチウムを使用し、セパレータ４にはポリエチレン微孔膜を使用した。得られたモデル電池を用いて試料電極１１と対極１３の間に、試料電極の面積に対して、０．２ｍＡ／ｃｍ2の定電流で０Ｖ（Ｖ vs. Ｌｉ／Ｌｉ＋）まで充電し、０．２ｍＡ／ｃｍ2の定電流で１Ｖ（Ｖ vs. Ｌｉ／Ｌｉ＋）まで放電する試験を行い、(8)単位体積当りの放電容量を測定した。 The produced sample electrode was punched out to a size of 2 cm 2 and subjected to constant current charge / discharge by the three-terminal method, and the charge / discharge capacity and discharge capacity retention rate were measured as follows. FIG. 2 shows a schematic diagram of the lithium secondary battery used in this measurement. As shown in FIG. 2, the sample electrode was evaluated as follows: LiPF 6 as an electrolytic solution 10 in a beaker type glass cell 9 with ethylene carbonate (EC) and methyl ethyl carbonate (MEC) (EC and MEC are in a volume ratio of 1: 2). A solution dissolved to a concentration of 1 mol / liter was added to the mixed solvent, the sample electrode 11, the separator 12 and the counter electrode 13 were stacked and arranged, and the reference electrode 14 was suspended from the top to prepare a model battery. The counter electrode 13 and the reference electrode 14 were made of metallic lithium, and the separator 4 was made of a polyethylene microporous film. Using the obtained model battery, the sample electrode 11 and the counter electrode 13 were charged to 0 V (V vs. Li / Li +) with a constant current of 0.2 mA / cm 2 with respect to the area of the sample electrode. A test was conducted to discharge to 1 V (V vs. Li / Li +) at a constant current of 2 mA / cm 2 , and (8) discharge capacity per unit volume was measured.
さらに同様の方法で１００サイクル充放電を繰り返し、(9)第一サイクル目の放電容量を１００とした時の放電容量維持率を測定した。 Further, 100 cycles of charge and discharge were repeated in the same manner, and (9) the discharge capacity retention rate when the discharge capacity in the first cycle was set to 100 was measured.
また、０．２ｍＡ／ｃｍ2の定電流で０Ｖ（Ｖ vs. Ｌｉ／Ｌｉ＋）まで充電し、６．０ｍＡ／ｃｍ2の定電流で１Ｖ（Ｖ vs. Ｌｉ／Ｌｉ＋）まで放電する試験を行い、(10)０．２ｍＡ／ｃｍ2の定電流で放電した時の放電容量を１００とした時の放電容量維持率を測定した。 In addition, the battery was charged to 0 V (V vs. Li / Li +) at a constant current of 0.2 mA / cm 2 and discharged to 1 V (V vs. Li / Li +) at a constant current of 6.0 mA / cm 2. (10) The discharge capacity retention rate was measured when the discharge capacity when discharged at a constant current of 0.2 mA / cm 2 was taken as 100.
各測定結果を表１に併記する。 The measurement results are also shown in Table 1.
実施例２
垂直プレスの圧力を１０ＭＰａの代わりに２３ＭＰａとすることにより黒鉛粒子とPVDFの混合物層の密度を１．４５g/cｍ3にした以外は、実施例１と同様の方法で試験電極を作製し、実施例１と同様の方法で、（００２）／（１１０）強度比、単位体積当りの放電容量、１００サイクル後の放電容量維持率、放電電流６．０ｍＡ／ｃｍ2時の放電容量維持率を測定した。測定結果を表１に併記する。
Example 2
A test electrode was prepared in the same manner as in Example 1 except that the density of the mixture layer of graphite particles and PVDF was changed to 1.45 g / cm 3 by changing the pressure of the vertical press to 23 MPa instead of 10 MPa. In the same manner as in Example 1, the (002) / (110) intensity ratio, discharge capacity per unit volume, discharge capacity maintenance rate after 100 cycles, and discharge capacity maintenance rate at a discharge current of 6.0 mA / cm 2 were measured. did. The measurement results are also shown in Table 1.
実施例３
垂直プレスの圧力を３１ＭＰａとすることにより黒鉛粒子とPVDFの混合物層の密度を１．５５g/cｍ3にした以外は、実施例１と同様の方法で試験電極を作製し、実施例１と同様の方法で、（００２）／（１１０）強度比、単位体積当りの放電容量、１００サイクル後の放電容量維持率、放電電流６．０ｍＡ／ｃｍ2時の放電容量維持率を測定した。測定結果を表１に併記する。
Example 3
A test electrode was prepared in the same manner as in Example 1 except that the density of the mixture layer of graphite particles and PVDF was changed to 1.55 g / cm 3 by setting the pressure of the vertical press to 31 MPa. (002) / (110) intensity ratio, discharge capacity per unit volume, discharge capacity maintenance rate after 100 cycles, and discharge capacity maintenance rate at a discharge current of 6.0 mA / cm 2 were measured. The measurement results are also shown in Table 1.
実施例４
垂直プレスの圧力を５０ＭＰａとすることにより黒鉛粒子とPVDFの混合物層の密度を１．６５g/cｍ3にした以外は、実施例１と同様の方法で試験電極を作製し、実施例１と同様の方法で、（００２）／（１１０）強度比、単位体積当りの放電容量、１００サイクル後の放電容量維持率、放電電流６．０ｍＡ／ｃｍ2時の放電容量維持率を測定した。測定結果を表１に併記する。
Example 4
A test electrode was prepared in the same manner as in Example 1 except that the density of the mixture layer of graphite particles and PVDF was changed to 1.65 g / cm 3 by setting the pressure of the vertical press to 50 MPa. (002) / (110) intensity ratio, discharge capacity per unit volume, discharge capacity maintenance rate after 100 cycles, and discharge capacity maintenance rate at a discharge current of 6.0 mA / cm 2 were measured. The measurement results are also shown in Table 1.
実施例５
垂直プレスの圧力を８５ＭＰａとすることにより黒鉛粒子とPVDFの混合物層の密度を１．７５g/cｍ3にした以外は、実施例１と同様の方法で試験電極を作製し、実施例１と同様の方法で、（００２）／（１１０）強度比、単位体積当りの放電容量、１００サイクル後の放電容量維持率、放電電流６．０ｍＡ／ｃｍ2時の放電容量維持率を測定した。測定結果を表１に併記する。
Example 5
A test electrode was prepared in the same manner as in Example 1 except that the density of the mixture layer of graphite particles and PVDF was changed to 1.75 g / cm 3 by setting the pressure of the vertical press to 85 MPa. (002) / (110) intensity ratio, discharge capacity per unit volume, discharge capacity maintenance rate after 100 cycles, and discharge capacity maintenance rate at a discharge current of 6.0 mA / cm 2 were measured. The measurement results are also shown in Table 1.
実施例６
垂直プレスの圧力を１４３ＭＰａとすることにより黒鉛粒子とPVDFの混合物層の密度を１．８５g/cｍ3にした以外は、実施例１と同様の方法で試験電極を作製し、実施例１と同様の方法で、（００２）／（１１０）強度比、単位体積当りの放電容量、１００サイクル後の放電容量維持率、放電電流６．０ｍＡ／ｃｍ2時の放電容量維持率を測定した。測定結果を表１に併記する。
Example 6
A test electrode was prepared in the same manner as in Example 1 except that the density of the mixture layer of graphite particles and PVDF was changed to 1.85 g / cm 3 by setting the pressure of the vertical press to 143 MPa. (002) / (110) intensity ratio, discharge capacity per unit volume, discharge capacity maintenance rate after 100 cycles, and discharge capacity maintenance rate at a discharge current of 6.0 mA / cm 2 were measured. The measurement results are also shown in Table 1.
実施例７
中国産天然黒鉛をジェットミルで粉砕して、鱗片状天然黒鉛粒子を作製した。該黒鉛粒子の平均粒径、比表面積、アスペクト比、ｄ（００２）、Ｌｃ（００２）測定結果を表１に併記する。該黒鉛粒子を用いて、垂直プレスの圧力を２ＭＰａとすることにより黒鉛粒子とPVDFの混合物層の密度を１．００g/cｍ3にした以外は実施例１と同様の方法で試験電極を作製した。実施例１と同様の方法で、（００２）／（１１０）強度比、単位体積当りの放電容量、１００サイクル後の放電容量維持率、放電電流６．０ｍＡ／ｃｍ2時の放電容量維持率を測定した。測定結果を表１に併記する。
Example 7
Chinese natural graphite was pulverized with a jet mill to produce scaly natural graphite particles. The average particle diameter, specific surface area, aspect ratio, d (002), and Lc (002) measurement results of the graphite particles are also shown in Table 1. A test electrode was prepared in the same manner as in Example 1 except that the density of the mixture layer of graphite particles and PVDF was changed to 1.00 g / cm 3 by using the graphite particles at a vertical press pressure of 2 MPa. . In the same manner as in Example 1, the (002) / (110) intensity ratio, the discharge capacity per unit volume, the discharge capacity maintenance rate after 100 cycles, and the discharge capacity maintenance rate at a discharge current of 6.0 mA / cm 2 were obtained. It was measured. The measurement results are also shown in Table 1.
比較例１
垂直プレスの圧力を２７ＭＰａとすることにより黒鉛粒子とPVDFの混合物層の密度を１．５０g/cｍ3にした以外は、実施例７と同様の方法で試験電極を作製し、実施例１と同様の方法で、（００２）／（１１０）強度比、単位体積当りの放電容量、１００サイクル後の放電容量維持率、放電電流６．０ｍＡ／ｃｍ2時の放電容量維持率を測定した。測定結果を表１に併記する。
Comparative Example 1
A test electrode was prepared in the same manner as in Example 7 except that the density of the mixture layer of graphite particles and PVDF was changed to 1.50 g / cm 3 by setting the pressure of the vertical press to 27 MPa. (002) / (110) intensity ratio, discharge capacity per unit volume, discharge capacity maintenance rate after 100 cycles, and discharge capacity maintenance rate at a discharge current of 6.0 mA / cm 2 were measured. The measurement results are also shown in Table 1.
比較例２
垂直プレスの圧力を４２ＭＰａとすることにより黒鉛粒子とPVDFの混合物層の密度を１．６５g/cｍ3にした以外は、実施例７と同様の方法で試験電極を作製し、実施例１と同様の方法で、（００２）／（１１０）強度比、単位体積当りの放電容量、１００サイクル後の放電容量維持率、放電電流６．０ｍＡ／ｃｍ2時の放電容量維持率を測定した。測定結果を表１に併記する。
A test electrode was prepared in the same manner as in Example 7 except that the density of the mixture layer of graphite particles and PVDF was changed to 1.65 g / cm 3 by setting the pressure of the vertical press to 42 MPa. (002) / (110) intensity ratio, discharge capacity per unit volume, discharge capacity maintenance rate after 100 cycles, and discharge capacity maintenance rate at a discharge current of 6.0 mA / cm 2 were measured. The measurement results are also shown in Table 1.
表１に示されるように、本発明のリチウム二次電池用負極は、高容量で、サイクル特性及び急速放電特性に優れ、リチウム二次電池に用いて好適であることが示された。 As shown in Table 1, it was shown that the negative electrode for a lithium secondary battery of the present invention has a high capacity, excellent cycle characteristics and rapid discharge characteristics, and is suitable for use in a lithium secondary battery.
１ 正極 ２ 負極
３ セパレータ ４ 正極タブ
５ 負極タブ ６ 正極蓋
７ 電池缶 ８ ガスケット
９ ガラスセル １０ 電解液
１１ 試料電極（負極） １２ セパレータ
１３ 対極（正極） １４ 参照極
DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Positive electrode tab 5 Negative electrode tab 6 Positive electrode lid 7 Battery can 8 Gasket 9 Glass cell 10 Electrolytic solution 11 Sample electrode (negative electrode) 12 Separator 13 Counter electrode (positive electrode) 14 Reference electrode
Claims (4)
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| JP2012054325A JP2012109280A (en) | 2012-03-12 | 2012-03-12 | Negative electrode for lithium secondary battery and lithium secondary battery |
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| JP2008265688A Division JP4985611B2 (en) | 2008-10-14 | 2008-10-14 | Negative electrode for lithium secondary battery and lithium secondary battery |
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| JP2014140282A Division JP5776823B2 (en) | 2014-07-08 | 2014-07-08 | Negative electrode for lithium secondary battery and lithium secondary battery |
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| JP2012109280A true JP2012109280A (en) | 2012-06-07 |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9627682B2 (en) | 2012-12-26 | 2017-04-18 | Sanyo Electric Co., Ltd. | Negative electrode for nonaqueous electrolyte secondary batteries and nonaqueous electrolyte secondary battery including the same |
Citations (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH10255767A (en) * | 1997-03-11 | 1998-09-25 | Sanyo Electric Co Ltd | Set battery for use in electric vehicle |
| JPH11283622A (en) * | 1998-03-31 | 1999-10-15 | Sanyo Electric Co Ltd | Nonaqueous electrolyte secondary battery |
| JPH11317229A (en) * | 1998-03-10 | 1999-11-16 | Samsung Display Devices Co Ltd | Negative active material for lithium secondary battery, lithium secondary battery and production of negative active material for lithium secondary battery |
| JP2001114505A (en) * | 1999-10-15 | 2001-04-24 | Osaka Gas Co Ltd | Carbonaceous material, method for controlling particle diameter of the carbonaceous material, carbonaceous material for negative electrode of lithium secondary battery and lithium secondary battery |
| JP2001283844A (en) * | 2000-03-29 | 2001-10-12 | Sanyo Electric Co Ltd | Nonaqueous electrolyte battery |
| WO2002059040A1 (en) * | 2001-01-25 | 2002-08-01 | Hitachi Chemical Co., Ltd. | Artificial graphite particle and method for producing the same, nonaqueous electrolyte secondary battery negative electrode and method for producing the same, and lithium secondary battery |
| JP2003197182A (en) * | 2001-12-21 | 2003-07-11 | Samsung Sdi Co Ltd | Graphite-containing composition, negative electrode for lithium secondary battery, and lithium secondary battery |
-
2012
- 2012-03-12 JP JP2012054325A patent/JP2012109280A/en not_active Withdrawn
Patent Citations (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH10255767A (en) * | 1997-03-11 | 1998-09-25 | Sanyo Electric Co Ltd | Set battery for use in electric vehicle |
| JPH11317229A (en) * | 1998-03-10 | 1999-11-16 | Samsung Display Devices Co Ltd | Negative active material for lithium secondary battery, lithium secondary battery and production of negative active material for lithium secondary battery |
| JPH11283622A (en) * | 1998-03-31 | 1999-10-15 | Sanyo Electric Co Ltd | Nonaqueous electrolyte secondary battery |
| JP2001114505A (en) * | 1999-10-15 | 2001-04-24 | Osaka Gas Co Ltd | Carbonaceous material, method for controlling particle diameter of the carbonaceous material, carbonaceous material for negative electrode of lithium secondary battery and lithium secondary battery |
| JP2001283844A (en) * | 2000-03-29 | 2001-10-12 | Sanyo Electric Co Ltd | Nonaqueous electrolyte battery |
| WO2002059040A1 (en) * | 2001-01-25 | 2002-08-01 | Hitachi Chemical Co., Ltd. | Artificial graphite particle and method for producing the same, nonaqueous electrolyte secondary battery negative electrode and method for producing the same, and lithium secondary battery |
| JP2003197182A (en) * | 2001-12-21 | 2003-07-11 | Samsung Sdi Co Ltd | Graphite-containing composition, negative electrode for lithium secondary battery, and lithium secondary battery |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9627682B2 (en) | 2012-12-26 | 2017-04-18 | Sanyo Electric Co., Ltd. | Negative electrode for nonaqueous electrolyte secondary batteries and nonaqueous electrolyte secondary battery including the same |
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