JP2008112734A - Carbon powder for lithium secondary battery negative electrode, manufacturing method therefor, negative electrode for the lithium secondary battery, and the lithium secondary battery - Google Patents
Carbon powder for lithium secondary battery negative electrode, manufacturing method therefor, negative electrode for the lithium secondary battery, and the lithium secondary battery Download PDFInfo
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Abstract
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本発明は、リチウム二次電池負極用炭素粉末の製造法、該製造法で作製したリチウム二次電池負極用炭素粉末、この炭素粉末を使用したリチウム二次電池用負極及びこの負極を使用した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、負極用炭素粉末及びその製造法に関する。 The present invention relates to a method for producing a carbon powder for a lithium secondary battery negative electrode, a carbon powder for a lithium secondary battery negative electrode produced by the production method, a lithium secondary battery negative electrode using the carbon powder, and a lithium using the negative electrode The present invention relates to a secondary battery. More specifically, the present invention relates to a lithium secondary battery having a high capacity and excellent cycle characteristics suitable for use in portable devices, electric vehicles, power storage, and the like, a negative electrode for obtaining the same, a carbon powder for the negative electrode, and a method for producing the same. .
従来のリチウム二次電池の負極材には、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している。例えば、特公昭６２−２３４３３号公報に示されるように、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。 Examples of conventional negative electrode materials for lithium secondary batteries include 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 the like. is there. These graphite particles are mixed with an organic binder and an organic solvent to form a graphite paste. The graphite paste is applied to the surface of the copper foil, the solvent is dried, and used as a negative electrode for a lithium secondary battery. Yes. For example, as disclosed in Japanese Examined Patent Publication No. 62-23433, the use of graphite for the negative electrode eliminates the content short circuit problem caused by lithium dendrite and improves the 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。 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. .
一方、コークス、ピッチ、有機系材料等を、２０００℃以上で焼成した人造黒鉛は、天然黒鉛に比べ、比較的アスペクト比を小さくすることができるが、黒鉛結晶の発達が悪いため、充放電容量が低い。そこで、高容量で、サイクル特性、急速充放電特性等が向上できるリチウム二次電池が作製できる負極用炭素材料が要求されている。 On the other hand, artificial graphite obtained by calcining coke, pitch, organic materials, etc. at 2000 ° C. or higher can have a relatively small aspect ratio compared to natural graphite, but its charge / discharge capacity is poor because of the poor development of graphite crystals. Is low. Therefore, there is a demand for a carbon material for a negative electrode that can produce a lithium secondary battery with high capacity and improved cycle characteristics, rapid charge / discharge characteristics, and the like.
本発明は、高容量で、サイクル特性及び急速充放電特性に優れたリチウム二次電池負極用炭素材料の製造法を提供するものである。また本発明は、高容量で、サイクル特性及び急速充放電特性に優れたリチウム二次電池負極用炭素材料を提供するものである。また本発明は、集電体と負極合剤の密着性に優れ、高容量で、サイクル特性及び急速充放電特性に優れたリチウム二次電池用負極を提供するものである。さらに本発明は、高容量で、サイクル特性及び急速充放電特性に優れたリチウム二次電池を提供するものである。 The present invention provides a method for producing a carbon material for a negative electrode of a lithium secondary battery having a high capacity and excellent cycle characteristics and rapid charge / discharge characteristics. The present invention also provides a carbon material for a negative electrode of a lithium secondary battery having a high capacity and excellent cycle characteristics and rapid charge / discharge characteristics. The present invention also provides a negative electrode for a lithium secondary battery having excellent adhesion between the current collector and the negative electrode mixture, high capacity, and excellent cycle characteristics and rapid charge / discharge characteristics. Furthermore, the present invention provides a lithium secondary battery having a high capacity and excellent cycle characteristics and rapid charge / discharge characteristics.
本発明は、炭素粉末を等方性加圧処理することを特徴とするリチウム二次電池負極用炭素粉末の製造法に関する。また本発明は、前記加圧処理のプレス圧力が５０〜２０００ｋｇｆ／ｃｍ２であるリチウム二次電池負極用炭素粉末の製造法に関する。また本発明は、前記の製造法により得られるリチウム二次電池負極用炭素粉末に関する。 The present invention relates to a method for producing carbon powder for a negative electrode of a lithium secondary battery, characterized by subjecting carbon powder to isotropic pressure treatment. Moreover, this invention relates to the manufacturing method of the carbon powder for lithium secondary battery negative electrodes whose press pressure of the said pressurization process is 50-2000 kgf / cm < 2 >. Moreover, this invention relates to the carbon powder for lithium secondary battery negative electrodes obtained by the said manufacturing method.
また本発明は、結晶の層間距離ｄ（００２）が３．３８Å以下、Ｃ軸方向の結晶子サイズＬｃ（００２）が５００Å以上、平均粒径が１０〜１００μｍ、比表面積が８ｍ２／ｇ以下、アスペクト比が１．１〜５、かさ密度が０．３ｇ／ｃｍ３以上の黒鉛粉末である前記の製造法により得られるリチウム二次電池負極用炭素粉末に関する。 In the present invention, the crystal interlayer distance d (002) is 3.38 mm or less, the crystallite size Lc (002) in the C-axis direction is 500 mm or more, the average particle size is 10 to 100 μm, and the specific surface area is 8 m 2 / g or less. Further, the present invention relates to a carbon powder for a lithium secondary battery negative electrode obtained by the above production method, which is a graphite powder having an aspect ratio of 1.1 to 5 and a bulk density of 0.3 g / cm 3 or more.
また本発明は、前記の製造法で作製した炭素粉末又は前記の炭素粉末を含有してなるリチウム二次電池用負極に関する。さらに本発明は、前記の負極及び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。 Moreover, this invention relates to the negative electrode for lithium secondary batteries formed by containing the carbon powder produced by the said manufacturing method, or the said carbon powder. Furthermore, this invention relates to the lithium secondary battery which has a positive electrode containing the said negative electrode and a lithium compound.
本発明の製造法によれば、高容量で、サイクル特性及び急速充放電特性に優れたリチウム二次電池負極用炭素材料が得られる。また本発明の二次電池負極用炭素材料は、高容量で、サイクル特性及び急速充放電特性に優れるものである。また本発明のリチウム二次電池用負極は、集電体と負極合剤の密着性に優れ、高容量で、サイクル特性及び急速充放電特性に優れるものである。さらに本発明のリチウム二次電池は、高容量で、サイクル特性及び急速充放電特性に優れるものである。 According to the production method of the present invention, a carbon material for a lithium secondary battery negative electrode having a high capacity and excellent cycle characteristics and rapid charge / discharge characteristics can be obtained. The carbon material for a secondary battery negative electrode of the present invention has a high capacity and is excellent in cycle characteristics and rapid charge / discharge characteristics. Moreover, the negative electrode for lithium secondary batteries of this invention is excellent in the adhesiveness of a collector and negative electrode mixture, is high capacity | capacitance, and is excellent in cycling characteristics and rapid charge / discharge characteristics. Furthermore, the lithium secondary battery of the present invention 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負極用炭素粉末の製造法は、炭素粉末を等方性加圧処理を行うことを特徴とする。ここで等方性加圧処理とは、一方向からの加圧のように、特定の方向からのみの加圧（異方性加圧処理）ではなく、一般に知られている、全方向から加圧する処理である。このように、炭素粉末に等方性加圧処理を行うと、得られるリチウム二次電池負極用炭素粉末のかさ密度及び流動性が向上し、作製するリチウム二次電池負極の密度バラツキが少なくかつ負極集電体との密着性が向上する。その結果、得られるリチウム二次電池のサイクル特性を向上させることができる。 The method for producing a carbon powder for a negative electrode of a lithium secondary battery according to the present invention is characterized by subjecting the carbon powder to an isotropic pressure treatment. Here, the isotropic pressurization is not a pressurization only from a specific direction (anisotropy pressurization) like a pressurization from one direction, but is generally applied from all directions. It is processing to press. Thus, when the isotropic pressure treatment is performed on the carbon powder, the bulk density and fluidity of the obtained carbon powder for a lithium secondary battery negative electrode are improved, and the resulting lithium secondary battery negative electrode has less density variation and Adhesion with the negative electrode current collector is improved. As a result, the cycle characteristics of the obtained lithium secondary battery can be improved.
なお、炭素粉末のかさ密度を向上させるために、加圧処理の方法として等方性加圧処理以外の、一方方向から加圧する一軸プレスやロールプレス等の異方性加圧処理を行うと、得られるリチウム二次電池の急速充放電特性が低下する問題がある。 In addition, in order to improve the bulk density of the carbon powder, other than isotropic pressure treatment as a method of pressure treatment, when performing anisotropic pressure treatment such as uniaxial press or roll press to press from one direction, There is a problem that the rapid charge / discharge characteristics of the obtained lithium secondary battery deteriorate.
炭素粉末の等方性加圧処理の方法としては、等方的に加圧できる方法であれば特に制限はなく、例えば炭素粉末をゴム型などの容器に入れ、水を加圧媒体とする静水圧等方性プレスや、空気等のガスを加圧媒体とする空圧による等方性プレスなどの加圧処理が挙げられる。 The method of isotropic pressure treatment of carbon powder is not particularly limited as long as it is an isotropic pressure method. For example, carbon powder is placed in a rubber mold or the like and water is used as a pressure medium. Examples of the pressure treatment include a water pressure isotropic press and a pneumatic isotropic press using a gas such as air as a pressure medium.
炭素粉末の等方性加圧処理の加圧媒体の圧力としては、５０〜２０００ｋｇｆ／ｃｍ２の範囲が好ましく、２００〜２０００ｋｇｆ／ｃｍ２の範囲であればより好ましく、５００〜１８００ｋｇｆ／ｃｍ２の範囲であればさらに好ましい。圧力が５０ｋｇｆ／ｃｍ２未満では、得られるリチウム二次電池のサイクル特性の向上の効果が小さくなる傾向にある。また、圧力が２０００ｋｇｆ／ｃｍ２を超えると、得られるリチウム二次電池負極用炭素材料の比表面積が大きくなり、その結果、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にある。 The pressure of the pressurized medium of isotropic pressure treatment of carbon powder, preferably in the range of 50~2000kgf / cm 2, more preferably be in the range of 200~2000kgf / cm 2, the 500~1800kgf / cm 2 If it is a range, it is still more preferable. When the pressure is less than 50 kgf / cm 2 , the effect of improving the cycle characteristics of the obtained lithium secondary battery tends to be small. In addition, when the pressure exceeds 2000 kgf / cm 2 , the specific surface area of the obtained carbon material for a lithium secondary battery negative electrode tends to increase, and as a result, the irreversible capacity at the first cycle of the obtained lithium secondary battery tends to increase. It is in.
上記のように炭素粉末を等方性加圧処理を行うと、粒子同士が凝集しやすくなるため、等方性加圧処理後に、解砕、篩い等の処理を行うことが好ましい。なお、粒子同士が凝集しないときは解砕をしなくともよい。 When carbon powder is subjected to isotropic pressure treatment as described above, the particles are likely to aggregate with each other. Therefore, it is preferable to perform treatment such as crushing and sieving after the isotropic pressure treatment. In addition, when the particles do not aggregate, it is not necessary to crush.
以上の方法により、サイクル特性等を大幅に向上させることが可能であるが、このようにして作製したリチウム二次電池負極用炭素粉末は、結晶の層間距離ｄ（００２）が３．３８Å以下、Ｃ軸方向の結晶子サイズＬｃ（００２）が５００Å以上、平均粒径が１０〜１００μｍ、比表面積が８ｍ２／ｇ以下、アスペクト比が１．１〜５、真比重が２．２以上、かさ密度が０．３ｇ／ｃｍ３以上の黒鉛粉末であると、高容量で、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が得られるので好ましい。 Although the cycle characteristics and the like can be greatly improved by the above method, the carbon powder for a lithium secondary battery negative electrode produced in this way has a crystal interlayer distance d (002) of 3.38 mm or less, The crystallite size Lc (002) in the C-axis direction is 500 mm or more, the average particle size is 10 to 100 μm, the specific surface area is 8 m 2 / g or less, the aspect ratio is 1.1 to 5, the true specific gravity is 2.2 or more, the bulk A graphite powder having a density of 0.3 g / cm 3 or more is preferable because a lithium secondary battery having a high capacity and excellent rapid charge / discharge characteristics and cycle characteristics can be obtained.
ここで結晶の層間距離ｄ（００２）はリチウム二次電池負極用炭素粉末の広角Ｘ線回折の測定から算出される値で、この値が３．３８Åを超えると放電容量が小さくなる傾向がある。ｄ（００２）の下限値に特に制限はないが、通常３．３５Å以上とされる。また、Ｃ軸方向の結晶子サイズＬｃ（００２）も広角Ｘ線回折の測定から算出される値で、この値が５００Å未満であると放電容量が小さくなる傾向がある。Ｌｃ（００２）の上限値に特に制限はないが、通常１００００Å以下とされる。 Here, the interlayer distance d (002) of the crystal is a value calculated from the measurement of wide-angle X-ray diffraction of the carbon powder for a lithium secondary battery negative electrode. When this value exceeds 3.38%, the discharge capacity tends to decrease. . There is no particular limitation on the lower limit of d (002), but it is usually 3.35 mm or more. Also, the crystallite size Lc (002) in the C-axis direction is a value calculated from the measurement of wide-angle X-ray diffraction, and when this value is less than 500 mm, the discharge capacity tends to be small. There is no particular limitation on the upper limit value of Lc (002), but it is usually set to 10000 kg or less.
また、アスペクト比が１．１未満では、粒子間の接触面積が減ることにより、導電性が低下する傾向にある。一方、アスペクトが５より大きくなると、急速充放電特性が低下し易くなる傾向がある。なお、アスペクト比は、リチウム二次電池負極用炭素粉末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。本発明におけるアスペクト比は、顕微鏡でリチウム二次電池負極用炭素粉末を拡大し、任意に１０個の粒子を選択し、Ａ／Ｂを測定し、その平均値をとったものである。 On the other hand, if the aspect ratio is less than 1.1, the contact area between particles tends to decrease, and the conductivity tends to decrease. On the other hand, when the aspect is larger than 5, the rapid charge / discharge characteristics tend to be deteriorated. The aspect ratio is represented by A / B, where A is the length in the major axis direction and B is the length in the minor axis direction of the carbon powder for a lithium secondary battery negative electrode. The aspect ratio in the present invention is obtained by enlarging the carbon powder for a lithium secondary battery negative electrode with a microscope, arbitrarily selecting 10 particles, measuring A / B, and taking the average value.
また、リチウム二次電池負極用炭素粉末の比表面積が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。比表面積は１ｍ２／ｇ以上であることがより好ましい。比表面積の測定は、ＢＥＴ法（窒素ガス吸着法）などの既知の方法をとることができる。 Further, when the specific surface area of the carbon powder for a lithium secondary battery negative electrode exceeds 8 m 2 / g, the irreversible capacity at the first cycle of the obtained lithium secondary battery is increased, the energy density is small, and the negative electrode is produced. Many binders tend to be required. The specific surface area is more preferably 1 m 2 / g or more. The specific surface area can be measured by a known method such as the BET method (nitrogen gas adsorption method).
また、リチウム二次電池負極用炭素粉末のかさ密度は０．３ｇ／ｃｍ３未満であると負極を作製する際多くの結着剤が必要になり易く、その結果作製するリチウム二次電池のエネルギー密度が小さくなる。かさ密度の上限値に特に制限はないが、通常１．５ｇ／ｃｍ３以下とされる。かさ密度の測定は、容量１００ｃｍ３のメスシリンダーを斜めにし、これに試料粉末１００ｃｍ３をさじを用いて徐々に投入し、メスシリンダーに栓をした後、メスシリンダーを５ｃｍの高さから５０回落下させた後の試料粉末の重量及び容積から算出することができる。 Moreover, when the bulk density of the carbon powder for a lithium secondary battery negative electrode is less than 0.3 g / cm 3 , many binders are likely to be required when preparing the negative electrode. As a result, the energy of the lithium secondary battery produced Density decreases. The upper limit of the bulk density is not particularly limited, but is usually 1.5 g / cm 3 or less. To measure the bulk density, graduated a 100 cm 3 graduated cylinder, slowly put 100 cm 3 of sample powder into it using a spoon, plugged the graduated cylinder, and dropped the graduated cylinder 50 times from a height of 5 cm. It can be calculated from the weight and volume of the sample powder after being lowered.
また、真比重は通常２．３以下とされる。そして、得られるリチウム二次電池負極用炭素粉末の平均粒径は、１０〜１００μｍが好ましく、１０〜５０μｍがより好ましい。本発明における平均粒径は、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。 The true specific gravity is usually 2.3 or less. And the average particle diameter of the carbon powder for lithium secondary battery negative electrodes obtained is preferably 10 to 100 μm, and more preferably 10 to 50 μm. The average particle diameter in the present invention can be measured with a laser diffraction particle size distribution analyzer.
また、等方性加圧処理を行う前の炭素粉末として、上記各特性を備えた黒鉛粉末を用いると、高容量で、急速充放電特性及びサイクル特性に特に優れたリチウム二次電池が得られるので好ましい。上記の等方性加圧処理を行う前の炭素粉末は、特に制限はなく、天然黒鉛、コークスを黒鉛化した人造黒鉛、有機系高分子材料、ピッチ等を黒鉛化した人造黒鉛、非晶質炭素、低温処理炭素などが挙げられるが、人造黒鉛であることが好ましく、中でも、黒鉛化可能な骨材又は黒鉛と黒鉛化可能なバインダと黒鉛化触媒を混合し、焼成及び粉砕工程を経て作製したものが好ましい。黒鉛化可能な骨材又は黒鉛と黒鉛化可能なバインダを、混合することで、得られる炭素粉末のアスペクト比を小さくするができ、その結果、作製するリチウム二次電池の急速充放電特性を向上させることができる。 Moreover, when the graphite powder having the above characteristics is used as the carbon powder before the isotropic pressure treatment, a lithium secondary battery having a high capacity and particularly excellent in rapid charge / discharge characteristics and cycle characteristics can be obtained. Therefore, it is preferable. Carbon powder before the above isotropic pressure treatment is not particularly limited, natural graphite, artificial graphite graphitized coke, organic polymer material, artificial graphite graphitized pitch, etc., amorphous Carbon, low-temperature treated carbon, etc. are mentioned, but it is preferable that it is artificial graphite. Among them, graphitizable aggregate or graphite, graphitizable binder, and graphitization catalyst are mixed, and manufactured through firing and pulverization steps. Is preferred. The aspect ratio of the resulting carbon powder can be reduced by mixing graphitizable aggregate or graphite and graphitizable binder, resulting in improved rapid charge / discharge characteristics of the lithium secondary battery produced. Can be made.
黒鉛化可能な骨材としては、例えば、コークス粉末、樹脂炭化物等が挙げられる。黒鉛化可能なバインダとしては、ピッチ、タールの他、熱硬化性樹脂、熱可塑性樹脂等の有機系材料があげられる。また、黒鉛化触媒を添加することで、得られる炭素粉末の結晶が発達しやすくなり、得られるリチウム二次電池の放電容量を向上させることができる。 Examples of the aggregate that can be graphitized include coke powder and resin carbide. Examples of the binder that can be graphitized include organic materials such as thermosetting resins and thermoplastic resins in addition to pitch and tar. Moreover, by adding a graphitization catalyst, the crystal | crystallization of the carbon powder obtained becomes easy to develop and the discharge capacity of the obtained lithium secondary battery can be improved.
黒鉛化触媒としては、Ｔｉ、Ｓｉ、Ｆｅ、Ｎｉ、Ｂ等の金属又はその酸化物若しくは炭化物が好ましい。黒鉛化触媒は、骨材とバインダを混合する際に添加し、同時に混合することが好ましい。混合する温度は、黒鉛化可能なバインダが軟化溶融する温度であることが好ましく、その温度は使用する材料によってことなるが、５０〜３５０℃の範囲が好ましい。また、黒鉛化可能なバインダを溶剤等によって、溶液にする場合には、黒鉛化触媒を常温で混合しても良い。 As the graphitization catalyst, metals such as Ti, Si, Fe, Ni, and B, or oxides or carbides thereof are preferable. The graphitization catalyst is preferably added when the aggregate and the binder are mixed, and mixed at the same time. The mixing temperature is preferably a temperature at which the graphitizable binder is softened and melted. The temperature varies depending on the material used, but is preferably in the range of 50 to 350 ° C. When the graphitizable binder is made into a solution with a solvent or the like, the graphitization catalyst may be mixed at room temperature.
次いで、黒鉛化可能な骨材又は黒鉛と黒鉛化可能なバインダと黒鉛化触媒を混合した混合物を、２５００℃以上の温度で焼成して黒鉛化することが好ましい。本発明において、該混合物を２５００℃以上の温度で黒鉛化する前に、粉砕、成形を行い、さらに７００〜１３００℃程度の温度で焼成しておいてもよい。また、７００〜１３００℃程度の温度で焼成した後、粉砕し、粒度を調整してから、粉体で２５００℃以上の温度で焼成して黒鉛化してもよい。黒鉛化時の焼成温度は、得られる負極炭素材料の結晶性及び放電容量の点で２５００℃以上が好ましく、２８００℃以上であればより好ましく、３０００℃以上であればさらに好ましい。焼成時の雰囲気は、酸化しにくい条件であれば特に制限はなく、例えば、自己揮発性ガス雰囲気、窒素雰囲気、アルゴン雰囲気、真空中等があげられる。 Next, it is preferable to perform graphitization by firing a graphitizable aggregate or a mixture obtained by mixing graphite, a graphitizable binder, and a graphitization catalyst at a temperature of 2500 ° C. or more. In the present invention, before graphitization of the mixture at a temperature of 2500 ° C. or higher, the mixture may be pulverized and molded and further baked at a temperature of about 700 to 1300 ° C. Moreover, after baking at the temperature of about 700-1300 degreeC, after grind | pulverizing and adjusting a particle size, it may calcinate and graphitize with a powder at the temperature of 2500 degreeC or more. The firing temperature during graphitization is preferably 2500 ° C. or higher, more preferably 2800 ° C. or higher, and even more preferably 3000 ° C. or higher in terms of the crystallinity and discharge capacity of the obtained negative electrode carbon material. The atmosphere during firing is not particularly limited as long as it is difficult to oxidize, and examples thereof include a self-volatile gas atmosphere, a nitrogen atmosphere, an argon atmosphere, and a vacuum.
次いで、粉砕し、粒度を調整して炭素粉末とするが、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。粉砕後の炭素粉末の平均粒径は、１０〜１００μｍが好ましい。なお、黒鉛化前に粉砕し、粒度を調整してある場合は、黒鉛化後に粉砕しなくとも良い。 Next, the powder is pulverized and the particle size is adjusted to obtain carbon powder, but the pulverization method is not particularly limited, and for example, an impact pulverization method such as a jet mill, a hammer mill, or a pin mill can be employed. The average particle size of the pulverized carbon powder is preferably 10 to 100 μm. In addition, when it grind | pulverizes before graphitization and the particle size is adjusted, it is not necessary to grind | pulverize after graphitization.
以上の如く作製した炭素粉末は、等方性加圧処理を施すことで、サイクル特性及び急速充放電特性に優れたリチウム二次電池に好適なリチウム二次電池負極用炭素粉末とすることができる。 The carbon powder produced as described above can be made into a carbon powder for a negative electrode of a lithium secondary battery suitable for a lithium secondary battery excellent in cycle characteristics and rapid charge / discharge characteristics by performing isotropic pressure treatment. .
本発明になるリチウム二次電池負極用炭素粉末は、有機系結着剤及び溶剤と混練して、ペースト状の負極合剤にし、シート状、ペレット状等の形状に成形することができる。有機系結着剤としては、例えば、ポリエチレン、ポリプロピレン、エチレンプロピレンターポリマー、ブタジエンゴム、スチレンブタジエンゴム、ブチルゴム、イオン伝導率の大きな高分子化合物等が使用できる。 The carbon powder for a negative electrode of a lithium secondary battery according to the present invention can be kneaded with an organic binder and a solvent to form a paste-like negative electrode mixture, which can be formed into a sheet shape, a pellet shape, or the like. 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。炭素粉末と有機系結着剤との混合比率は、炭素粉末１００重量部に対して、有機系結着剤を１〜２０重量部とすることが好ましい。 As the polymer compound having a high ion conductivity, polyvinylidene fluoride, polyethylene oxide, polyepichlorohydrin, polyphasphazene, polyacrylonitrile and the like can be used. The mixing ratio of the carbon powder and the organic binder is preferably 1 to 20 parts by weight of the organic binder with respect to 100 parts by weight of the carbon powder.
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、イソプロパノール等があげられる。溶剤の量も特に制限はない。炭素粉末は、有機系結着剤及び溶剤と混練し、粘度を調整した後、集電体に塗布し、該集電体と一体化して負極とすることができる。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、またこれらの成形法を組み合わせて一体化しても良い。 There is no restriction | limiting in particular as a solvent, N-methyl- 2-pyrrolidone, a dimethylformamide, isopropanol etc. are mention | raise | lifted. The amount of the solvent is not particularly limited. The carbon powder can be kneaded with an organic binder and a solvent, adjusted in viscosity, then applied to a current collector, and integrated with the current collector to form 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, and these molding methods may be combined to be integrated.
このようにして得られた負極は、リチウム化合物を含む正極とともに、本発明のリチウム二次電池に用いられる。リチウム二次電池は、例えば、正極と負極をセパレータを介して対向して配置し、かつ電解液を注入することにより得ることができる。本発明のリチウム二次電池は、従来の炭素粉末を負極に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 the lithium secondary battery of the present invention together with the positive electrode containing a lithium compound. A lithium secondary battery can be obtained, for example, by arranging a positive electrode and a negative electrode to face each other with a separator interposed therebetween and injecting an electrolytic solution. The lithium secondary battery of the present invention has a high capacity and excellent cycle characteristics and rapid charge / discharge characteristics as compared with a lithium secondary battery using a conventional carbon powder as a negative electrode.
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。本発明におけるリチウム二次電池は、正極及び負極とともに、通常リチウム化合物を含む電解液を含む。電解液としては、ＬｉＣｌＯ４、ＬｉＰＦ６、ＬｉＡｓＦ、ＬｉＢＦ４、ＬｉＳＯ３ＣＦ４等のリチウム塩を、例えばエチレンカーボネート、ジエチルカーボネート、ジメトキシエタン、ジメチルカーボネート、メチルエチルカーボネート、メチルエチルカーボネート、テトラヒドロフラン等の非水系溶剤に溶かしたいわゆる有機電解液や、固体若しくはゲル状のいわゆるポリマー電解質を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 is not particularly limited, and for example, LiNiO 2 , LiCoO 2 , LiMn 2 O 4 or the like can be used alone or in combination. The lithium secondary battery in this invention contains the electrolyte solution which contains a lithium compound normally with a positive electrode and a negative electrode. Examples of the electrolyte include lithium salts such as LiClO 4 , LiPF 6 , LiAsF, LiBF 4 , LiSO 3 CF 4 , such as ethylene carbonate, diethyl carbonate, dimethoxyethane, dimethyl carbonate, methyl ethyl carbonate, methyl ethyl carbonate, and tetrahydrofuran. A so-called organic electrolytic solution dissolved in a non-aqueous solvent or a so-called polymer electrolyte in solid or gel form can be used.
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使用中も直接接触しない構造にした場合は、セパレータを使用しなくとも良い。 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 do not contact directly during use, 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 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
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
〔加圧処理用炭素粉末の作製〕
平均粒径１５μｍのコークス粉末５０重量部と、ピッチ１５重量部と、コールタール２０重量部と、炭化けい素１０重量部を、２３０℃で１時間混合した。次いで、この混合物を平均粒径２５μｍに粉砕し、該粉砕物を金型に入れプレス成形し、直方体に成形した。この成形体を１０００℃で熱処理した後、さらに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、炭素粉末を得た。
Example 1
[Production of carbon powder for pressure treatment]
50 parts by weight of coke powder having an average particle size of 15 μm, 15 parts by weight of pitch, 20 parts by weight of coal tar, and 10 parts by weight of silicon carbide were mixed at 230 ° C. for 1 hour. Next, this mixture was pulverized to an average particle size of 25 μm, and the pulverized product was put into a mold and press-molded to form a rectangular parallelepiped. This molded body was heat treated at 1000 ° C., and further heat treated at 3000 ° C. to obtain a graphite molded body. Furthermore, this graphite molded body was pulverized to obtain a carbon powder.
〔リチウム二次電池負極用炭素粉末の作製〕
前記で得られた炭素粉末をゴム製の容器に充填、密閉したのち、該ゴム製容器を静水圧プレス機で、加圧媒体の圧力１５００ｋｇｆ／ｃｍ２で、等方性加圧処理を行った。ついで、カッターミルで解砕して、リチウム二次電池負極用炭素粉末を得た。得られたリチウム二次電池負極用炭素粉末のかさ密度、平均粒径、比表面積、ｄ（００２）、Ｌｃ（００２）、アスペクト比を表１に示す。
[Production of carbon powder for negative electrode of lithium secondary battery]
After filling and sealing the carbon powder obtained above in a rubber container, the rubber container was subjected to isotropic pressure treatment with a hydrostatic pressure press at a pressure of 1500 kgf / cm 2 of a pressure medium. . Subsequently, it was crushed with a cutter mill to obtain a carbon powder for a negative electrode of a lithium secondary battery. Table 1 shows the bulk density, average particle diameter, specific surface area, d (002), Lc (002), and aspect ratio of the obtained carbon powder for a lithium secondary battery negative electrode.
次いで、得られた負極用炭素粉末を使用して負極及びリチウム二次電池を作製した。図１に示した本発明のリチウム二次電池を以下のようにして作製した。正極活物質としてＬｉＣｏＯ２ ８８重量％を用いて、導電剤として平均粒径２μｍの鱗片状黒鉛を７重量％、結着剤としてポリフッ化ビニリデン（ＰＶＤＦ）５重量％添加して、これにＮ−メチル−２−ピロリドンを加えて混合して正極合剤のペーストを調整した。同様に負極活物質として、前記の方法で作製した負極炭素材料に、結着剤としてＰＶＤＦを１０重量％添加して、これにＮ−メチル−２−ピロリドンを加えて混合して負極合剤のペーストを調整した。 Subsequently, the negative electrode and lithium secondary battery were produced using the obtained carbon powder for negative electrodes. The lithium secondary battery of the present invention shown in FIG. 1 was produced as follows. Using 88% by weight of LiCoO 2 as a positive electrode active material, 7% by weight of scaly graphite having an average particle diameter of 2 μm as a conductive agent, and 5% by weight of polyvinylidene fluoride (PVDF) as a binder, N— Methyl-2-pyrrolidone was added and mixed to prepare a positive electrode mixture paste. Similarly, 10% by weight of PVDF as a binder is added to the negative electrode carbon material produced by the above method as a negative electrode active material, and N-methyl-2-pyrrolidone is added thereto and mixed to form a negative electrode mixture. The paste was adjusted.
正極合剤を厚み２５μｍのアルミニウム箔の両面に塗付し、その後１２０℃で１時間真空乾燥した後、ロールプレスによって電極を加圧成形し、さらに巾４０ｍｍ長さ２８５ｍｍの大きさに切り出して正極を作製した。但し、正極の両端の長さ１０ｍｍの部分は正極合剤が塗布されておらずアルミニウム箔が露出しており、この一方に正極タブを超音波接合によって圧着している。 The positive electrode mixture was applied to both sides of an aluminum foil having a thickness of 25 μm, and then vacuum-dried at 120 ° C. for 1 hour, and then the electrode was pressure-molded by a roll press, and further cut into a size of 40 mm wide and 285 mm long. Was made. However, the positive electrode mixture is not applied to the 10 mm long portions at both ends of the positive electrode, and the aluminum foil is exposed, and a positive electrode tab is pressure-bonded to this one by ultrasonic bonding.
一方、負極合剤は厚み１０μｍの銅箔の両面に塗布し、その後１２０℃で１時間真空乾燥した。真空乾燥後、ロールプレスによって電極を加圧成形し、さらに巾４０ｍｍ長さ２９０ｍｍの大きさに切り出して負極を作製した。正極と同様に、負極の両端の長さ１０ｍｍの部分は負極合剤が塗布されておらず銅箔が露出しており、この一方に負極タブを超音波接合によって圧着した。 On the other hand, the negative electrode mixture was applied on both sides of a copper foil having a thickness of 10 μm and then vacuum-dried at 120 ° C. for 1 hour. After vacuum drying, the electrode was pressure-formed by a roll press, and further cut into a size of 40 mm wide and 290 mm long to produce a negative electrode. As with the positive electrode, the negative electrode mixture was not applied to the 10 mm long portions at both ends of the negative electrode, and the copper foil was exposed, and a negative electrode tab was pressure bonded to this one by ultrasonic bonding.
セパレータは、厚み２５μｍ巾４４ｍｍのポリエチレン製の微孔膜を用いた。正極、セパレータ、負極、セパレータの順で重ね合わせ、これを捲回して電極群とした。これを単三サイズの電池缶に挿入して、負極タブを缶底溶接し、正極蓋をかしめるための絞り部を設けた。体積比が１：２のエチレンカーボネートとジメチルカーボネートの混合溶媒に六フッ化リン酸リチウムを１モル／リットル溶解させた電解液を電池缶に注入した後、正極タブを正極蓋に溶接した後、正極蓋をかしめ付けて電池を作製した。 As the separator, a microporous membrane made of polyethylene having a thickness of 25 μm and a width of 44 mm was used. The positive electrode, the separator, the negative electrode, and the separator were stacked in this order, and this was wound to form an electrode group. This was inserted into an AA size battery can, and the negative electrode tab was welded to the bottom of the can to provide a throttle for caulking the positive electrode lid. After injecting into the battery can an electrolytic solution in which 1 mol / liter of lithium hexafluorophosphate was dissolved in a mixed solvent of ethylene carbonate and dimethyl carbonate having a volume ratio of 1: 2, the positive electrode tab was welded to the positive electrode lid, A positive electrode lid was caulked to prepare a battery.
この電池を用いて、充放電特性を評価した。作製したリチウム二次電池の充電条件は、電流３００ｍＡで電池電圧４．２Ｖまで定電流で充電した後、電池電圧４．２Ｖで電流が３０ｍＡになるまで定電圧充電した。電流３００ｍＡで電池電圧が２．８Ｖになるまで定電流放電した時の放電容量を表２に示す。また、電流３００ｍＡの時の放電容量に対し、電流９００ｍＡで電池電圧が２．８Ｖになるまで定電流放電した時の放電容量維持率を表２に示す。また、電流３００ｍＡで電池電圧４．２Ｖまで定電流で充電した後、電池電圧４．２Ｖで電流が３０ｍＡになるまで定電圧充電し、電流３００ｍＡで電池電圧が２．８Ｖになるまで定電流放電するサイクルを３００回及び５００回繰り返した時の放電容量維持率を表２に示す。 Using this battery, charge / discharge characteristics were evaluated. The lithium secondary battery thus manufactured was charged at a constant current up to a battery voltage of 4.2 V at a current of 300 mA, and then charged at a constant voltage until the current reached 30 mA at a battery voltage of 4.2 V. Table 2 shows the discharge capacity when a constant current is discharged until the battery voltage reaches 2.8 V at a current of 300 mA. Table 2 shows the discharge capacity retention rate when the constant current discharge is performed until the battery voltage becomes 2.8 V at a current of 900 mA with respect to the discharge capacity at a current of 300 mA. Also, after charging with a constant current up to a battery voltage of 4.2V at a current of 300mA, the battery is charged at a constant voltage until the current reaches 30mA at a battery voltage of 4.2V and discharged at a constant current until the battery voltage reaches 2.8V at a current of 300mA. Table 2 shows the discharge capacity retention ratio when the cycle is repeated 300 times and 500 times.
実施例２及び実施例３
実施例１において、静水圧プレス機による加圧媒体の圧力を、６００ｋｇｆ／ｃｍ２（実施例２）及び１０００ｋｇｆ／ｃｍ２（実施例３）の圧力に変えた以外は、全く同様に炭素粉末の等方性加圧処理を行い、得られた炭素粉末を用いて実施例１と同様にリチウム二次電池を作製し、充放電特性を評価した。炭素粉末のかさ密度、平均粒径、比表面積、ｄ（００２）、Ｌｃ（００２）、アスペクト比を表１に示す。また実施例１と同様の方法で評価した充放電特性評価結果を表２に示す。
Example 2 and Example 3
In Example 1, the pressure of the pressurizing medium by the hydrostatic press was changed to 600 kgf / cm 2 (Example 2) and 1000 kgf / cm 2 (Example 3). An isotropic pressure treatment was performed, and using the obtained carbon powder, a lithium secondary battery was produced in the same manner as in Example 1, and the charge / discharge characteristics were evaluated. Table 1 shows the bulk density, average particle diameter, specific surface area, d (002), Lc (002), and aspect ratio of the carbon powder. Table 2 shows the results of charging / discharging characteristics evaluation performed by the same method as in Example 1.
比較例１
実施例１で作製した炭素粉末を等方性加圧処理を行わず、そのままリチウム二次電池負極用炭素粉末として使用した以外は、実施例１と同様にリチウム二次電池を作製し、充放電特性を評価した。炭素粉末のかさ密度、平均粒径、比表面積、ｄ（００２）、Ｌｃ（００２）、アスペクト比を表１に示す。また実施例１と同様の方法で評価した充放電特性評価結果を表２に示す。
Comparative Example 1
A lithium secondary battery was produced in the same manner as in Example 1 except that the carbon powder produced in Example 1 was not subjected to isotropic pressure treatment and was used as it was as a carbon powder for a lithium secondary battery negative electrode. The characteristics were evaluated. Table 1 shows the bulk density, average particle diameter, specific surface area, d (002), Lc (002), and aspect ratio of the carbon powder. Table 2 shows the results of charging / discharging characteristics evaluation performed by the same method as in Example 1.
比較例２
実施例１と同様の方法で作製した炭素粉末を、金型に充填し、一軸プレスで上部から１５００ｋｇｆ／ｃｍ２の圧力で一定方向に加圧処理を行った以外は、実施例１と同様の方法でリチウム二次電池負極炭素粉末を作製した。得られたリチウム二次電池負極用炭素粉末のかさ密度、平均粒径、比表面積、ｄ（００２）、Ｌｃ（００２）、アスペクト比を表１に示す。また実施例１と同様の方法で評価した充放電特性評価結果を表２に示す。
The carbon powder produced by the same method as in Example 1 was filled in a mold, and the same treatment as in Example 1 was performed except that the uniaxial press was pressurized in a fixed direction at a pressure of 1500 kgf / cm 2 from above. A negative electrode carbon powder of a lithium secondary battery was prepared by the method. Table 1 shows the bulk density, average particle diameter, specific surface area, d (002), Lc (002), and aspect ratio of the obtained carbon powder for a lithium secondary battery negative electrode. Table 2 shows the results of charging / discharging characteristics evaluation performed by the same method as in Example 1.
表２から明らかなように、本発明のリチウム二次電池負極用炭素粉末は、高容量で、サイクル特性、急速充放電特性に優れたリチウム二次電池として好適であることが示された。 As is apparent from Table 2, the carbon powder for a negative electrode of a lithium secondary battery of the present invention was shown to be suitable as a lithium secondary battery having a high capacity and excellent cycle characteristics and rapid charge / discharge characteristics.
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
DESCRIPTION OF SYMBOLS 1 Positive electrode 2
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Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
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| JPH07335216A (en) * | 1994-06-07 | 1995-12-22 | Fuji Elelctrochem Co Ltd | Nonaqueous electrolytic secondary battery |
| JPH0982326A (en) * | 1995-07-10 | 1997-03-28 | Nikkiso Co Ltd | Graphitized vapor phase epitaxy carbon fiber for lithium ion secondary battery negative electrode, and lithium ion secondary battery |
| JPH0992286A (en) * | 1995-07-18 | 1997-04-04 | Nikkiso Co Ltd | Graphitized vapor phase epitaxy carbon fiber for lithium ion secondary battery and lithium ion secondary battery |
| JPH10255803A (en) * | 1997-03-14 | 1998-09-25 | Nikkiso Co Ltd | Carbon material for negative electrode of secondary battery and its manufacture |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH07335216A (en) * | 1994-06-07 | 1995-12-22 | Fuji Elelctrochem Co Ltd | Nonaqueous electrolytic secondary battery |
| JPH0982326A (en) * | 1995-07-10 | 1997-03-28 | Nikkiso Co Ltd | Graphitized vapor phase epitaxy carbon fiber for lithium ion secondary battery negative electrode, and lithium ion secondary battery |
| JPH0992286A (en) * | 1995-07-18 | 1997-04-04 | Nikkiso Co Ltd | Graphitized vapor phase epitaxy carbon fiber for lithium ion secondary battery and lithium ion secondary battery |
| JPH10255803A (en) * | 1997-03-14 | 1998-09-25 | Nikkiso Co Ltd | Carbon material for negative electrode of secondary battery and its manufacture |
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