JP4748949B2 - Nonaqueous electrolyte secondary battery - Google Patents
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Description
本発明は、急速充電時の安全性とサイクル特性の向上を目的とした非水電解質二次電池の負極の改良に関する。 The present invention relates to an improvement in the negative electrode of a nonaqueous electrolyte secondary battery for the purpose of improving safety and cycle characteristics during rapid charging.
近年、携帯電話やノートパソコン等の移動情報端末の小型・軽量化が急速に進展しており、その電源としての電池にはさらなる高容量化が要求されている。リチウムイオン二次電池に代表される非水電解質二次電池は、高いエネルギー密度を有し、高容量であるので、上記のような移動情報端末の駆動電源として広く利用されている。 In recent years, mobile information terminals such as mobile phones and notebook personal computers have been rapidly reduced in size and weight, and batteries as power sources are required to have higher capacities. A non-aqueous electrolyte secondary battery represented by a lithium ion secondary battery has a high energy density and a high capacity, and is therefore widely used as a driving power source for the mobile information terminal as described above.
リチウムイオン二次電池は、リチウムを吸蔵、放出する炭素材料が負極に使用されており、リチウムが金属状態で存在しないため、樹枝状（デンドライト状）リチウムの析出がない。よって、安全性に優れ、かつ電池寿命も長い。特に、天然黒鉛や人造黒鉛等の黒鉛系炭素材料は、リチウムイオンを吸蔵、放出できる量が多いため、高容量化の要求に応え易い。 In a lithium ion secondary battery, a carbon material that occludes and releases lithium is used for the negative electrode, and lithium does not exist in a metal state, so that dendritic (dendritic) lithium does not precipitate. Therefore, it is excellent in safety and has a long battery life. In particular, graphite-based carbon materials such as natural graphite and artificial graphite have a large amount of lithium ions that can be occluded and released, and therefore easily meet the demand for higher capacity.
このようなリチウムイオン二次電池に対して、近年では、より一層電池を急速に充電する要望が高まっている。この要望に応えるためには、高い電流値（ハイレート）で充電する必要があるが、黒鉛負極を用いたリチウムイオン二次電池をハイレート充電すると、黒鉛がリチウムイオンの全てを吸蔵することができないため、負極表面にリチウムが析出する。この析出したリチウムは、以後の充放電に寄与しないので、サイクル特性を低下させる。 In recent years, there has been an increasing demand for such a lithium ion secondary battery to rapidly charge the battery. In order to meet this demand, it is necessary to charge at a high current value (high rate), but if a lithium ion secondary battery using a graphite negative electrode is charged at a high rate, graphite cannot occlude all lithium ions. Lithium is deposited on the negative electrode surface. The deposited lithium does not contribute to the subsequent charge / discharge, so that the cycle characteristics are deteriorated.
ところで、炭素系負極の改良に関する技術としては、下記特許文献１、２が挙げられる。 By the way, the following patent documents 1 and 2 are mentioned as a technique regarding the improvement of a carbon-type negative electrode.
上記特許文献１は、球形、繊維状の人造グラファイト、芳香族炭化水素をＣＶＤ法で被覆するか、ピッチ・フェノール樹脂を表面に被覆・炭化して得られる粒状、多角形の天然グラファイト、球形、粒状、多角形の人造グラファイトからなる多重構造炭素材、コークスから選ばれた炭素材料を負極として用いる技術である。この技術によると、電池を高容量化、長寿命化できるとされる。 The above-mentioned Patent Document 1 discloses spherical, fibrous artificial graphite, granular particles obtained by coating aromatic carbon with a CVD method, or coating and carbonizing pitch / phenolic resin on the surface, polygonal natural graphite, spherical shape, This is a technique in which a carbon material selected from multi-structure carbon material made of granular and polygonal artificial graphite and coke is used as the negative electrode. According to this technology, it is said that the battery can have a higher capacity and a longer life.
上記特許文献２は、Ｘ線広角回折法による（００２）面の面間隔（ｄ００２）が０．３４ｎｍ未満である黒鉛系粒子の表面を、面間隔０．３４ｎｍ以上の非晶質炭素層で被覆した二重構造黒鉛粒子と、黒鉛化メソカーボンマイクロビーズとからなる混合物を負極活物質とし、電池の高容量化、長サイクル寿命化、安全性を向上させる技術である。この技術によると、高容量で、サイクル寿命及び安全性が向上するとされる。 In Patent Document 2, the surface of a graphite particle having a (002) plane spacing (d002) of less than 0.34 nm by an X-ray wide angle diffraction method is coated with an amorphous carbon layer having a plane spacing of 0.34 nm or more. This is a technique for improving the battery capacity, long cycle life, and safety by using a mixture of the double-structured graphite particles and graphitized mesocarbon microbeads as the negative electrode active material. According to this technology, the capacity is increased and the cycle life and safety are improved.
本発明は、ハイレート充電を行っても負極にリチウムが析出せず、且つサイクル劣化が生じない非水電解質二次電池を提供することを目的とする。 An object of the present invention is to provide a non-aqueous electrolyte secondary battery in which lithium is not deposited on the negative electrode even when high rate charging is performed and cycle deterioration does not occur.
上記目的の下、発明者らは、ハイレート充電時のリチウムの析出について鋭意研究を行った。その結果、表面が非晶質炭素で被覆された黒鉛を用いることにより、黒鉛と電解液との塗れ性が飛躍的に向上して、負極隅々にまで電解液を浸透させることができ、これにより負極表面でのリチウムの析出を抑制できることを知った。 Under the above purpose, the inventors have conducted intensive research on the precipitation of lithium during high rate charging. As a result, by using graphite whose surface is coated with amorphous carbon, the paintability of graphite and the electrolyte can be dramatically improved, and the electrolyte can penetrate into every corner of the negative electrode. It has been found that lithium deposition on the negative electrode surface can be suppressed.
しかしながら、表面が非晶質炭素で被覆された黒鉛のみを用いた負極は、黒鉛の表面に形成された非晶質炭素の導電性が悪いので、負極の内部抵抗が大きくなり、充放電サイクルによって、電池容量が大きく劣化するという問題が新たに生じるようになった。 However, the negative electrode using only the graphite whose surface is coated with amorphous carbon has poor conductivity of the amorphous carbon formed on the surface of the graphite, so the internal resistance of the negative electrode increases, and the charge / discharge cycle causes A new problem arises that the battery capacity is greatly deteriorated.
そこで、発明者らは、サイクル劣化を解消するために更に研究を行った。その結果、表面が非晶質炭素で被覆された黒鉛と、表面が非晶質炭素で被覆されていない黒鉛とを混合して用いることにより、ハイレート充電時のリチウムの析出を抑制でき、且つ負極の内部抵抗が大幅に低下して、サイクル劣化を抑制できることを見いだし、本発明を完成させた。 Therefore, the inventors conducted further research to eliminate cycle deterioration. As a result, by using a mixture of graphite whose surface is coated with amorphous carbon and graphite whose surface is not coated with amorphous carbon, lithium deposition during high-rate charging can be suppressed, and the negative electrode As a result, the present invention was completed.
上記課題を解決するための本発明は、正極と、黒鉛粒子を活物質として含む負極と、非水電解質と、を有する非水電解質二次電池において、前記黒鉛粒子群は、表面が非晶質炭素で被覆されていない非被覆黒鉛粒子と、前記非被覆黒鉛粒子の表面が非晶質炭素で被覆された被覆黒鉛粒子と、が混合されてなるものであり、前記被覆黒鉛粒子及び非被覆黒鉛粒子のＬｃ値が１５ｎｍ以上であり、前記被覆黒鉛粒子及び前記非被覆黒鉛粒子のｄ002値が０．３３８ｎｍ以下であり、前記被覆黒鉛粒子及び前記非被覆黒鉛粒子の比表面積が２ｍ2／ｇ以上５ｍ2／ｇ以下であり、前記被覆黒鉛粒子及び前記非被覆黒鉛粒子の平均粒径が１５μｍ以上であり、前記被覆黒鉛粒子及び前記非被覆黒鉛粒子のＸ線回折法による００２面と１１０面とのピーク強度比Ｉh002／Ｉh110が２００以下である、ことを特徴とする。 The present invention for solving the above problems, a positive electrode, a negative electrode containing graphite particles as an active material, a non-aqueous electrolyte, the nonaqueous electrolyte secondary battery having the graphite particles, the surface is amorphous The uncoated graphite particles not coated with carbon and the coated graphite particles whose surfaces are coated with amorphous carbon are mixed, and the coated graphite particles and uncoated graphite are mixed. and the Lc value of the particle is 15nm or more, the d 002 value of the coated graphite particles and the non-coated graphite particles is less 0.338 nm, specific surface area of the coated graphite particles and the non-coated graphite particles 2m 2 / g 5 m 2 / g or less, the coated graphite particles and the uncoated graphite particles have an average particle size of 15 μm or more, and the 002 plane and 110 plane of the coated graphite particles and the uncoated graphite particles according to the X-ray diffraction method. And the peak Degrees ratio I h002 / I h110 is 200 or less, and wherein the.
ここで、被覆黒鉛粒子と、非被覆黒鉛粒子との違いを、以下のように定義する。 Here, the difference between coated graphite particles and uncoated graphite particles is defined as follows.
アルゴンレーザーによるラマン分光測定法を用いて黒鉛粒子の物性を測定した場合、波長１５８０ｃｍ-1付近の吸収ピークは黒鉛構造に起因するピークであり、波長１３６０ｃｍ-1付近の吸収ピークは黒鉛構造の乱れから生じるピークである。そして、これらのピーク比〔Ｉ1360／Ｉ1580〕は、被覆炭素材料層の結晶化（黒鉛化）の程度を表す指標となる。 When measuring the physical properties of the graphite particles using Raman spectroscopy with argon laser, the absorption peak near a wavelength of 1580 cm -1 is a peak due to the graphite structure, the absorption peak wavelength of around 1360 cm -1 is disturbed graphite structure The peak resulting from These peak ratios [I 1360 / I 1580 ] serve as an index representing the degree of crystallization (graphitization) of the coated carbon material layer.
ここで、非被覆黒鉛粒子とは、波長５１４５Åのアルゴンレーザーラマン分光測定における１３６０ｃｍ-1付近のピーク強度（Ｉ1360）と１５８０ｃｍ-1付近のピーク強度（Ｉ1580）の比〔Ｉ1360／Ｉ1580 〕が０．１０以下であるものをいう。 Here, the non-coated graphite particles, the ratio of the argon laser Raman spectroscopy 1360 cm -1 vicinity of the peak intensity (I 1360) and 1580 cm -1 vicinity of the peak intensity in the measurement of the wavelength 5145 Å (I 1580) [I 1360 / I 1580 ] Is 0.10 or less.
他方、被覆黒鉛粒子とは、波長５１４５Åのアルゴンレーザーラマン分光測定における１３６０ｃｍ-1付近のピーク強度（Ｉ1360）と１５８０ｃｍ-1付近のピーク強度（Ｉ1580）の比〔Ｉ1360／Ｉ1580〕が０．１３以上０．２３以下であるものをいう。 On the other hand, the coated graphite particles, the ratio [I 1360 / I 1580] of the peak intensity near 1360 cm -1 in an argon laser Raman spectroscopy in the wavelength 5145 Å (I 1360) and 1580 cm -1 vicinity of the peak intensity (I 1580) It means 0.13 or more and 0.23 or less.
上記構成において、前記非晶質炭素で被覆された黒鉛粒子と、前記表面が非晶質炭素で被覆されていない黒鉛粒子との質量比が３：７〜７：３である構成とすることができる。 In the above configuration, the mass ratio of the graphite particles coated with the amorphous carbon and the graphite particles whose surface is not coated with the amorphous carbon is 3: 7 to 7: 3. it can.
上記構成において、前記被覆黒鉛粒子１００質量部中に占める非晶質炭素の質量が、０．１〜１０質量部である構成とすることができる。 The said structure WHEREIN: The mass of the amorphous carbon which occupies for 100 mass parts of said coated graphite particles can be set as the structure which is 0.1-10 mass parts.
上記構成において、放電状態の前記負極の活物質充填密度が１．４０ｇ／ｍｌ以上であり、前記負極のＸ線回折法による００２面と１１０面とのピーク強度比Ｉh002／Ｉh110が３００以下である構成とすることができる。 In the above configuration, the active material filling density of the negative electrode in a discharged state is 1.40 g / ml or more, and the peak intensity ratio I h002 / I h110 between the 002 plane and the 110 plane according to the X-ray diffraction method of the negative electrode is 300 or less. It can be set as the structure which is.
ここで、放電状態とは、電池組み立て後一回以上充電を行い、その後電圧が２．７５Ｖ以下となるまで放電した状態のことをいう。 Here, the discharged state means a state in which the battery is charged once or more after assembling and then discharged until the voltage becomes 2.75 V or less.
本発明によると、負極はその表面が非晶質炭素で被覆された被覆黒鉛粒子と、表面が非晶質炭素で
被覆されていない非被覆黒鉛粒子とを有し、前記黒鉛粒子のＬｃ値が１５ｎｍ以上であり、前記黒鉛粒子のｄ 002 値が０．３３８ｎｍ以下であり、前記黒鉛粒子の比表面積が２ｍ 2 ／ｇ以上５ｍ 2 ／ｇ以下であり、前記黒鉛粒子の平均粒径が１５μｍ以上であり、前記黒鉛粒子のＸ線回折法による００２面と１１０面とのピーク強度比Ｉ h002 ／Ｉ h110 が２００以下である。
According to the present invention, the negative electrode has coated graphite particles whose surface is coated with amorphous carbon, and whose surface is composed of amorphous carbon.
And a uncoated uncoated graphite particles, the Lc value of the graphite particles is not less 15nm or more, the d 002 value of the graphite particles is not more than 0.338 nm, the specific surface area of said graphite particle is 2m 2 / g or more and 5 m 2 / g or less, the average particle diameter of the graphite particles is 15 μm or more, and the peak intensity ratio I h002 / I h110 of the 002 plane and the 110 plane according to the X-ray diffraction method of the graphite particles is 200 or less. It is .
非晶質炭素は、黒鉛に比べ容量が小さいものの、リチウムイオンの受け入れ性が高く、電解液との塗れ性が高い。よって、この非晶質炭素を黒鉛の表面に被覆することにより、高容量でかつ急速充電を行ってもリチウムが析出しない負極が得られる。 Although amorphous carbon has a smaller capacity than graphite, it has a high acceptability of lithium ions and a good coatability with an electrolytic solution. Therefore, by coating the amorphous carbon on the surface of the graphite, a negative electrode having a high capacity and no lithium deposition even when rapid charging is obtained.
しかし、炭素材料は黒鉛化の程度が高くなるにつれ、導電性に優れる傾向があり、黒鉛化の程度が低い、非晶質炭素で被覆した被覆黒鉛粒子は、非被覆黒鉛粒子に比べ導電性が低くなる。このため、単に被覆黒鉛粒子を用いたのみでは、サイクル特性を低下させることになる。 However, as the degree of graphitization increases, the carbon material tends to have better conductivity, and the coated graphite particles coated with amorphous carbon, which has a lower degree of graphitization, have a higher conductivity than the uncoated graphite particles. Lower. For this reason, simply using the coated graphite particles will degrade the cycle characteristics.
ここで、本発明では、被覆黒鉛粒子と非被覆黒鉛粒子とを混合して用いる。よって、被覆黒鉛粒子の優れたリチウムイオンの受け入れ性、電解液との塗れ性と、非被覆黒鉛粒子の優れた導電性とが相乗的に機能して、ハイレート充電特性とサイクル特性とをともに改善し得た非水電解質二次電池が実現する。 Here, in the present invention, coated graphite particles and uncoated graphite particles are mixed and used. Therefore, the excellent lithium ion acceptability of the coated graphite particles, the wettability with the electrolyte, and the excellent conductivity of the uncoated graphite particles function synergistically to improve both the high-rate charging characteristics and the cycle characteristics. Thus obtained non-aqueous electrolyte secondary battery is realized.
また、黒鉛粒子群に占める被覆黒鉛粒子の質量比が過小であると、リチウムイオンの受け入れ性が低下して、十分にリチウムの析出を抑制することができなくなる。他方、黒鉛粒子群に占める被覆黒鉛粒子の質量比が過大であると、負極中の非被覆黒鉛粒子による導電ネットワークが粗となり、ハイレート放電時の放電容量が低下する。したがって、被覆黒鉛粒子と非被覆黒鉛粒子との質量比は、好ましくは３：７〜７：３とする。 Further, if the mass ratio of the coated graphite particles in the graphite particle group is too small, the lithium ion acceptability is lowered, and the precipitation of lithium cannot be sufficiently suppressed. On the other hand, if the mass ratio of the coated graphite particles in the graphite particle group is excessive, the conductive network due to the uncoated graphite particles in the negative electrode becomes rough, and the discharge capacity during high-rate discharge decreases. Therefore, the mass ratio between the coated graphite particles and the uncoated graphite particles is preferably 3: 7 to 7: 3.
また、被覆黒鉛粒子中の非晶質炭素の質量割合が０．１質量％以下であると、非晶質炭素を被覆することによる効果が十分に得られない。他方、１０質量％以上であると、表面の非晶質炭素によって被覆黒鉛粒子が硬くなり、負極の高充填密度化が難しくなる。したがって、被覆黒鉛粒子中の非晶質炭素の質量割合は、０．１〜１０質量部とするのが好ましい。 Moreover, the effect by coat | covering amorphous carbon is not fully acquired as the mass ratio of the amorphous carbon in a covering graphite particle | grain is 0.1 mass% or less. On the other hand, if it is 10% by mass or more, the coated graphite particles are hardened by the amorphous carbon on the surface, and it is difficult to increase the packing density of the negative electrode. Accordingly, the mass ratio of amorphous carbon in the coated graphite particles is preferably 0.1 to 10 parts by mass.
また、被覆黒鉛粒子の核となる黒鉛粒子が、上記非被覆黒鉛粒子であると、電池の特性を制御しやすくなる。 Further, when the graphite particles serving as the core of the coated graphite particles are the above - mentioned uncoated graphite particles , it becomes easy to control the battery characteristics.
また、被覆黒鉛粒子及び非被覆黒鉛粒子のＬｃ値が１５ｎｍ未満または被覆黒鉛粒子及び非被覆黒鉛粒子のｄ002値が０．３３８ｎｍより大きいと、充放電に寄与しない不可逆容量が大きくなるので、サイクル特性が悪くなる。したがって黒鉛粒子のＬｃ値は１５ｎｍ以上かつ黒鉛粒子のｄ002値は０．３３８ｎｍ以下とする。 Further, the d 002 value is greater than 0.338nm of coated graphite particles and non coated graphite particles of Lc values 15nm less than or coated graphite particles and non coated graphite particles, since the irreversible capacity increases which does not contribute to charge and discharge cycle The characteristics deteriorate. Therefore Lc value of the graphite particles d 002 value of 15nm or more and graphite particles is not more than 0.338 nm.
また、被覆黒鉛粒子及び非被覆黒鉛粒子の比表面積が２ｍ2／ｇ未満であると、リチウムイオンの受け入れ性が低下してリチウムの析出が生じやすくなり、５ｍ2／ｇより大きいと、充放電に寄与しない不可逆容量が大きくので、サイクル特性が悪くなる。したがって、被覆黒鉛粒子及び非被覆黒鉛粒子の比表面積は２〜５ｍ2／ｇとする。 Further, the specific surface area of the coated graphite particles and non coated graphite particles is less than 2m 2 / g, lithium precipitation occurs easily acceptance of lithium ions is reduced, and greater than 5 m 2 / g, the charge-discharge Since the irreversible capacity that does not contribute to is large, the cycle characteristics deteriorate. Therefore, the specific surface area of the coated graphite particles and non coated graphite particles and 2 to 5 m 2 / g.
また、被覆黒鉛粒子及び非被覆黒鉛粒子の平均粒径が１５μｍ未満であると、負極作製工程で圧縮を行った場合、黒鉛粒子群間の空隙が小さくなるため、電解液が浸透しにくくなる。このように電解液の浸透性が悪い負極を用いると、ハイレート充電時のサイクル特性が低下する。したがって、被覆黒鉛粒子及び非被覆黒鉛粒子の平均粒径は１５μｍ以上とする。 In addition, when the average particle diameter of the coated graphite particles and the uncoated graphite particles is less than 15 μm, when compression is performed in the negative electrode preparation step, the gap between the graphite particle groups becomes small, so that the electrolytic solution does not easily penetrate. If a negative electrode having poor electrolyte permeability is used in this way, cycle characteristics during high-rate charging are reduced. Therefore, the average particle diameter of the coated graphite particles and non coated graphite particles is not less than 15 [mu] m.
また、被覆黒鉛粒子及び非被覆黒鉛粒子のＸ線回折法による００２面と１１０面とのピーク強度比Ｉh002／Ｉh110は、被覆黒鉛粒子及び非被覆黒鉛粒子の結晶面（層面）の配向状態を示す指標となる値であるが、この値が２００より大きい被覆黒鉛粒子及び非被覆黒鉛粒子を用いて負極板を作製すると、負極作製時の圧延によって被覆黒鉛粒子及び非被覆黒鉛粒子の結晶面が集電体の面方向に配向しやすくなる。黒鉛粒子群の負極集電体の面方向への配向が大きくなると、リチウムイオンの受け入れ性が悪くなるので、ハイレート充電時のサイクル特性が低下する。したがって、ピーク強度比Ｉh002／Ｉh110は２００以下とする。 Further, the peak intensity ratio I h002 / I h110 between 002 plane and 110 plane measured by X-ray diffraction of the coated graphite particles and non coated graphite particles, the orientation state of the crystal surface of the coated graphite particles and non coated graphite particles (layer surface) However, when a negative electrode plate is produced using coated graphite particles and uncoated graphite particles having a value greater than 200, the crystal planes of the coated graphite particles and the uncoated graphite particles are obtained by rolling during the production of the negative electrode. Tends to be oriented in the surface direction of the current collector. When the orientation of the negative electrode current collector of the graphite particle group increases, the lithium ion acceptability deteriorates, and the cycle characteristics during high-rate charging deteriorate. Accordingly, the peak intensity ratio I h002 / I h110 is 200 or less.
また、放電状態の負極の活物質充填密度が１．４０ｇ／ｍｌ以上という高充填とすると、負極に充填された黒鉛粒子群の配向状態が、充填前の黒鉛粒子群の配向状態よりも更に大きくなる。 Further, when the active material filling density of the negative electrode in the discharged state is high as 1.40 g / ml or more, the orientation state of the graphite particle group filled in the negative electrode is larger than the orientation state of the graphite particle group before filling. Become.
ここで、放電状態の負極のＸ線回折法による００２面と１１０面とのピーク強度比Ｉh002／Ｉh110が３００より大きいと、この負極における黒鉛粒子群の結晶面が集電体の面方向への過度に配向しているので、リチウムイオンの受け入れ性が悪い。このため、ハイレート充電時のサイクル特性が低下する。したがって、ピーク強度比Ｉh002／Ｉh110が３００以下であることが好ましい。 Here, if the peak intensity ratio I h002 / I h110 between the 002 plane and the 110 plane according to the X-ray diffraction method of the negative electrode in the discharged state is larger than 300, the crystal plane of the graphite particle group in this negative electrode is the plane direction of the current collector Lithium ion acceptability is poor because of excessive orientation. For this reason, the cycle characteristics at the time of high-rate charging deteriorate. Therefore, the peak intensity ratio I h002 / I h110 is preferably 300 or less.
本発明を実施するための最良の形態を、実施例を用いて以下に詳細に説明する。本発明は下記実施の形態に何ら限定されるものではなく、その要旨を変更しない範囲において適宜変更して実施することができる。 The best mode for carrying out the present invention will be described in detail below using embodiments. The present invention is not limited to the following embodiments, and can be implemented with appropriate modifications within a range that does not change the gist thereof.
（実施例１）
〈正極の作製〉
平均粒径５μmのＬｉＣｏＯ2粉末と導電剤としての人造黒鉛粉末とを質量比９：１で混合して正極合剤となし、この正極合剤と、Ｎ−メチル−２−ピロリドン（ＮＭＰ）にポリフッ化ビニリデンを５質量％溶かした結着剤溶媒とを、固形分の質量比で９５：５となるように混練して正極活物質スラリーを調整した。
Example 1
<Preparation of positive electrode>
LiCoO 2 powder having an average particle size of 5 μm and artificial graphite powder as a conductive agent are mixed at a mass ratio of 9: 1 to form a positive electrode mixture, and this positive electrode mixture is mixed with N-methyl-2-pyrrolidone (NMP). A positive electrode active material slurry was prepared by kneading a binder solvent in which 5% by mass of polyvinylidene fluoride was dissolved so that the mass ratio of the solid content was 95: 5.
上記正極活物質スラリーをドクターブレード法により、正極集電体としてのアルミニウム箔の両面に塗布して乾燥した。この後１２０℃・２時間の真空乾燥を行い、次いでこれを充填密度が３．４ｇ／ｍｌとなるように圧縮して、正極を作製した。 The positive electrode active material slurry was applied to both surfaces of an aluminum foil as a positive electrode current collector by a doctor blade method and dried. Thereafter, vacuum drying was performed at 120 ° C. for 2 hours, and then this was compressed so that the packing density was 3.4 g / ml, thereby producing a positive electrode.
〈黒鉛の作製〉
平均粒径５μｍの鱗片状天然黒鉛に、石油ピッチ（軟化点：２５０℃）を加熱しながら混合し、不活性ガス（例えば、窒素ガス、アルゴン等）雰囲気中で３０００℃で焼成した。この後、粉砕・分級して、表面が非晶質炭素により被覆されていない黒鉛（非被覆黒鉛）を作製した。後述する物性値測定法による非被覆黒鉛の各物性値は、ｄ002＝０．３３５６ｎｍ、Ｌｃ＝１００ｎｍ、平均粒径＝２０μｍ、比表面積４．０ｍ2／ｇ、ピーク強度比Ｉh002／Ｉh110＝１５２であった。また、この非被覆黒鉛粒子について、波長５１４５Åのアルゴンレーザーラマン分光法でスペクトルを測定したところ、１３６０ｃｍ-1付近のピーク強度Ｉ1360に対する１５８０ｃｍ-1付近のピーク強度Ｉ1580の比〔Ｉ1360／Ｉ1580〕が０．０８であった。
<Production of graphite>
Petroleum pitch (softening point: 250 ° C.) was mixed with flaky natural graphite having an average particle diameter of 5 μm while heating, and fired at 3000 ° C. in an inert gas (eg, nitrogen gas, argon, etc.) atmosphere. Thereafter, pulverization and classification were performed to prepare graphite (non-coated graphite) whose surface was not coated with amorphous carbon. Each physical property value of the uncoated graphite by the physical property value measurement method described later is as follows: d 002 = 0.3356 nm, Lc = 100 nm, average particle size = 20 μm, specific surface area 4.0 m 2 / g, peak intensity ratio I h002 / I h110 = 152. As for the non-coated graphite particles was measured spectra by argon laser Raman spectroscopy in the wavelength 5145 Å, 1360 cm -1 ratio of the peak intensity I 1580 of around 1580 cm -1 to the peak intensity I 1360 near [I 1360 / I 1580 ] was 0.08.
この後、上記非被覆黒鉛に石油ピッチ（軟化点：２５０℃）を加熱しながら混合し、不活性ガス雰囲気で１０００℃で焼成した。この後、粉砕・分級して、表面が非晶質炭素により被覆された黒鉛（被覆黒鉛）を作製した。後述する物性値測定法による被覆黒鉛の各物性値は、ｄ002＝０．３３５６ｎｍ、Ｌｃ＝１００ｎｍ、平均粒径＝２０μｍ、比表面積３．０ｍ2／ｇ、ピーク強度比Ｉh002／Ｉh110＝１３８であった。 Thereafter, petroleum pitch (softening point: 250 ° C.) was mixed with the uncoated graphite while heating, and fired at 1000 ° C. in an inert gas atmosphere. Thereafter, pulverization and classification were performed to prepare graphite (coated graphite) whose surface was coated with amorphous carbon. Each physical property value of the coated graphite by the physical property value measurement method described later is as follows: d 002 = 0.3356 nm, Lc = 100 nm, average particle size = 20 μm, specific surface area 3.0 m 2 / g, peak intensity ratio I h002 / I h110 = 138.
この被覆黒鉛は、被覆前の非被覆黒鉛重量と被覆後の被覆黒鉛重量の質量変化から計算して、被覆黒鉛９７質量部に対して３質量部の非晶質炭素が被覆されたものである。また、この被覆黒鉛粒子について、波長５１４５Åのアルゴンレーザーラマン分光法でスペクトルを測定したところ、１３６０ｃｍ-1付近のピーク強度Ｉ1360に対する１５８０ｃｍ-1付近のピーク強度Ｉ1580の比〔Ｉ1360／Ｉ1580〕が０．２０であった。 This coated graphite is obtained by coating 3 parts by mass of amorphous carbon with respect to 97 parts by mass of coated graphite, calculated from the mass change of the weight of uncoated graphite before coating and the weight of coated graphite after coating. . As for the coated graphite particles was measured spectra by argon laser Raman spectroscopy in the wavelength 5145 Å, the ratio of the peak intensity I 1580 of around 1580 cm -1 to the peak intensity I 1360 of around 1360 cm -1 [I 1360 / I 1580 ] Was 0.20.
〈黒鉛粒子の物性値の測定〉
上記非被覆黒鉛粒子と被覆黒鉛粒子の各物性値を、以下の方法で測定した。
（１）ｄ002値は、理学社製Ｘ線回折装置「ＲＩＮＴ２１００」を用いて測定した。
（２）Ｌｃ値は、理学社製Ｘ線回折装置「ＲＩＮＴ２１００」を用いて測定した。
（３）平均粒径は、島津製作所製「ＳＡＬＤ−２０００Ｊ」を用いて測定した。
（４）比表面積は、島津製作所社製「ＡＳＡＰ２０１０」を用いて気体吸着法により測定 した。
（５）Ｘ線解析法によるピーク強度比Ｉh002／Ｉh110は、理学社製Ｘ線回折装置「ＲＩＮ Ｔ２１００」を用いて測定した。
<Measurement of physical properties of graphite particles>
The physical property values of the uncoated graphite particles and the coated graphite particles were measured by the following methods.
(1) The d 002 value was measured using an X-ray diffractometer “RINT2100” manufactured by Rigaku Corporation.
(2) The Lc value was measured using an X-ray diffractometer “RINT2100” manufactured by Rigaku Corporation.
(3) The average particle diameter was measured using “SALD-2000J” manufactured by Shimadzu Corporation.
(4) The specific surface area was measured by a gas adsorption method using “ASAP2010” manufactured by Shimadzu Corporation.
(5) The peak intensity ratio I h002 / I h110 by X-ray analysis was measured using an X-ray diffractometer “RIN T2100” manufactured by Rigaku Corporation.
〈負極の作製〉
上記非被覆黒鉛（Ａ）と被覆黒鉛（Ｂ）とを質量比で７：３の割合で混合し、固形分４８％のスチレン−ブタジエン（ＳＢＲ）のディスパージョンとを水に分散させ、さらに増粘剤としてカルボキシメチルセルロース（ＣＭＣ）を適量加えて、負極活物質スラリーを作製した。この負極活物質スラリーは乾燥後の固形分質量組成比が、活物質：ＳＢＲ：ＣＭＣ＝１００：３：２となるように調整した。
<Preparation of negative electrode>
The uncoated graphite (A) and the coated graphite (B) are mixed at a mass ratio of 7: 3, and a dispersion of styrene-butadiene (SBR) having a solid content of 48% is dispersed in water, and further increased. An appropriate amount of carboxymethylcellulose (CMC) was added as a sticking agent to prepare a negative electrode active material slurry. This negative electrode active material slurry was adjusted so that the solid mass composition ratio after drying was active material: SBR: CMC = 100: 3: 2.
上記スラリーをドクターブレード法により負極集電体としての銅箔の両面に塗布し、その後乾燥した。次いでこれを充填密度が１．６５ｇ／ｍｌとなるように圧縮して負極を作製した。 The slurry was applied to both surfaces of a copper foil as a negative electrode current collector by a doctor blade method, and then dried. Next, this was compressed so that the packing density was 1.65 g / ml to produce a negative electrode.
〈電解液の調製〉
非水溶媒として、エチレンカーボネート（ＥＣ）とジエチルカーボネート（ＤＥＣ）を体積比５：５で混合し、この混合溶媒に電解質塩として六フッ化リン酸リチウム（ＬｉＰＦ6）を１モル／ｌとなるように溶かしたものを電解液とした。
<Preparation of electrolyte>
As a non-aqueous solvent, ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a volume ratio of 5: 5, and lithium hexafluorophosphate (LiPF 6 ) is added to the mixed solvent as an electrolyte salt at 1 mol / l. The solution dissolved in this manner was used as the electrolyte.
上記正極板と負極板とを両者の間にポリプロピレン製微多孔膜からなるセパレータを介在させて巻回して電極体となし、これを円筒型外装缶に収納した後、上記電解液を注液し、その後開口部をカシメ封口することにより、実施例１に係る電池（設計容量１０００ｍＡｈ）を作製した。 The positive electrode plate and the negative electrode plate are wound with a separator made of a polypropylene microporous film interposed therebetween to form an electrode body, which is stored in a cylindrical outer can, and then the electrolyte solution is injected. Then, the battery according to Example 1 (design capacity 1000 mAh) was manufactured by sealing the opening with caulking.
（実施例２〜９，比較例１、２）
下記表１に示すように、非被覆黒鉛（Ａ）と被覆黒鉛（Ｂ）との質量比を下記表１に示すように変更したこと以外は、上記実施例１同様にして実施例２〜９、比較例１、２に係る電池を作製した。
(Examples 2 to 9, Comparative Examples 1 and 2)
As shown in Table 1 below, Examples 2 to 9 were conducted in the same manner as in Example 1 except that the mass ratio of uncoated graphite (A) and coated graphite (B) was changed as shown in Table 1 below. Then, batteries according to Comparative Examples 1 and 2 were produced.
以上で作製した電池を用いて、以下の実験を行った。その結果を下記表１に示す。 The following experiment was conducted using the battery fabricated as described above. The results are shown in Table 1 below.
〔放電容量の測定〕
充電：定電流１Ｉｔ（１０００ｍＡ）で４．２Ｖ、定電圧４．２Ｖで１００ｍＡまで
放電；定電流１Ｉｔ（１０００ｍＡ）で２．７５Ｖまで。
[Measurement of discharge capacity]
Charge: 4.2V at a constant current of 1 It (1000 mA), discharge to 100 mA at a constant voltage of 4.2 V; discharge to 2.75 V at a constant current of 1 It (1000 mA).
〔ハイレート充電時の放電容量の測定〕
充電：定電流２Ｉｔ（２０００ｍＡ）で４．２Ｖ、定電圧４．２Ｖで１００ｍＡまで
放電；定電流１Ｉｔ（１０００ｍＡ）で２．７５Ｖまで。
[Measurement of discharge capacity during high-rate charging]
Charging: 4.2 V at a constant current of 2 It (2000 mA), discharging to 100 mA at a constant voltage of 4.2 V; discharging to 2.75 V at a constant current of 1 It (1000 mA).
〔ハイレート充電時のサイクル特性の測定〕
充電：定電流２Ｉｔ（２０００ｍＡ）で４．２Ｖ、定電圧４．２Ｖで１００ｍＡまで
放電；定電流１Ｉｔ（１０００ｍＡ）で２．７５Ｖまで。
サイクル特性（％）＝５０サイクル目放電容量÷１サイクル目放電容量×１００
[Measurement of cycle characteristics during high-rate charging]
Charging: 4.2 V at a constant current of 2 It (2000 mA), discharging to 100 mA at a constant voltage of 4.2 V; discharging to 2.75 V at a constant current of 1 It (1000 mA).
Cycle characteristics (%) = 50th cycle discharge capacity / first cycle discharge capacity × 100
上記表１から、非被覆黒鉛のみを用いた比較例１は、２Ｉｔ放電容量が７６０ｍＡと、被覆黒鉛を含む実施例１〜１０、比較例２の８２０〜９３０ｍＡよりも大幅に低いことがわかる。 From Table 1 above, it can be seen that Comparative Example 1 using only uncoated graphite has a 2It discharge capacity of 760 mA, which is significantly lower than 820 to 930 mA of Examples 1 to 10 and Comparative Example 2 containing coated graphite.
このことは次のように考えられる。非被覆黒鉛は被覆黒鉛よりもリチウムイオンの受け入れ性が低い。このため、非被覆黒鉛のみを用いた負極に対して２Ｉｔという大電流（ハイレート）で充電を行うと、リチウムが負極表面に析出する。この析出したリチウムは、以降の放電に寄与しないので、放電容量が低下する。
他方、被覆黒鉛は非被覆黒鉛よりもリチウムイオンの受け入れ性が高いので、２Ｉｔという大電流で充電を行っても、リチウムが負極表面に析出することがない。このため、放電容量が高まる。
This is considered as follows. Uncoated graphite has a lower lithium ion acceptability than coated graphite. For this reason, when a negative electrode using only uncoated graphite is charged with a large current (high rate) of 2 It, lithium is deposited on the negative electrode surface. Since the deposited lithium does not contribute to the subsequent discharge, the discharge capacity is reduced.
On the other hand, coated graphite has higher acceptability of lithium ions than uncoated graphite, so that lithium is not deposited on the negative electrode surface even when charged with a large current of 2 It. For this reason, the discharge capacity increases.
また、被覆黒鉛のみを用いた比較例２は、２Ｉｔサイクル特性が６７％と、非被覆黒鉛を含む実施例１〜１０、比較例１の７３〜８５％よりも大幅に低いことがわかる。 Moreover, it turns out that the comparative example 2 using only a covering graphite is 2% cycling characteristics 67%, and is significantly lower than 73 to 85% of Examples 1-10 and the comparative example 1 containing uncoated graphite.
このことは次のように考えられる。被覆黒鉛は非被覆黒鉛よりも導電性が低い。このため、被覆黒鉛のみを用いた負極は、内部抵抗が大きく、サイクル特性を劣化させる。
他方、非被覆黒鉛は導電性が被覆黒鉛よりも高く、負極に非被覆黒鉛からなる導電ネットワークが形成され、サイクル劣化が生じない。
This is considered as follows. Coated graphite is less conductive than uncoated graphite. For this reason, a negative electrode using only coated graphite has a large internal resistance and deteriorates cycle characteristics.
On the other hand, uncoated graphite has higher conductivity than coated graphite, and a conductive network composed of uncoated graphite is formed on the negative electrode, so that cycle deterioration does not occur.
また、非被覆黒鉛と被覆黒鉛との質量混合比が３：７〜７：３である実施例１、実施例４〜７は、２Ｉｔ放電容量が９１０〜９２０ｍＡで、且つサイクル特性が８３〜８５％と、非被覆黒鉛の配合比が０：１０〜２：８である比較例１、実施例２、３の２Ｉｔ放電容量（７６０〜８４０ｍＡ）、非被覆黒鉛の配合比が８：２〜１０：０である比較例２、実施例８、９のサイクル特性（６７〜７３％）よりも優れていることがわかる。 In Examples 1 and 4 to 7, in which the mass mixing ratio of uncoated graphite and coated graphite is 3: 7 to 7: 3, the 2It discharge capacity is 910 to 920 mA, and the cycle characteristics are 83 to 85. %, 2It discharge capacity (760-840 mA) of Comparative Example 1, Examples 2 and 3 in which the blending ratio of uncoated graphite is 0:10 to 2: 8, and the blending ratio of uncoated graphite is 8: 2 to 10 0: It is understood that the cycle characteristics (67 to 73%) of Comparative Example 2 and Examples 8 and 9 which are 0 are superior.
このことは次のように考えられる。非被覆黒鉛の混合比が低いと、リチウムイオンの受け入れ性が十分に向上しないため、２Ｉｔという大電流で充電を行うと負極にリチウムが析出する。他方被覆黒鉛の混合比が低いと、負極に形成される被覆黒鉛からなる導電ネットワークが粗であり、サイクル劣化が大きくなる。 This is considered as follows. When the mixing ratio of the uncoated graphite is low, the lithium ion acceptability is not sufficiently improved, so that lithium is deposited on the negative electrode when charged with a large current of 2 It. On the other hand, when the mixing ratio of the coated graphite is low, the conductive network made of the coated graphite formed on the negative electrode is rough, and the cycle deterioration becomes large.
また、上記条件で充電、放電を行った実施例１に係る電池（電圧が２．７５Ｖになるまで放電した電池：電池電圧３．３Ｖ）を分解し、その負極を取り出し、乾燥した後の活物質充填密度は１．５１ｇ／ｍｌであり、Ｘ線回折法によるピーク強度比Ｉh002／Ｉh110は２２３であった。 Also, the battery according to Example 1 charged and discharged under the above conditions (battery discharged until the voltage reached 2.75 V: battery voltage 3.3 V) was disassembled, and the negative electrode was taken out and dried. The material packing density was 1.51 g / ml, and the peak intensity ratio I h002 / I h110 by X-ray diffraction method was 223.
〔その他の事項〕
尚、上記実施の形態では円筒型外装缶を使用したが、角型、ラミネート外装体等種々の形状にすることができることは当然のことである。また、電池内重合により形成される固体高分子電解質電池にも適用することができる。
[Other matters]
In the above embodiment, a cylindrical outer can is used. However, it is a matter of course that various shapes such as a rectangular shape and a laminate outer can be used. It can also be applied to a solid polymer electrolyte battery formed by in-battery polymerization.
また、上記の実施の形態ではドクターブレードによりスラリーを塗布したが、ダイコーターであってもよい。また、活物質スラリーのかわりに活物質ペーストを用い、ローラコーティング法により塗布することもできる。また、アルミニウム箔のかわりにアルミニウムメッシュ、発泡ニッケルを用いても同様に作製することができる。 Moreover, although slurry was apply | coated with the doctor blade in said embodiment, a die coater may be sufficient. Further, an active material paste can be used in place of the active material slurry, and it can be applied by a roller coating method. Moreover, it can produce similarly even if it uses an aluminum mesh and nickel foam instead of an aluminum foil.
また、正極活物質としては、リチウム含有遷移金属複合酸化物から選択される一種の化合物、あるいは二種以上の化合物を混合して用いることができ、例えば、コバルト酸リチウム・ニッケル酸リチウム・マンガン酸リチウム・鉄酸リチウム、またはこれらの酸化物に含まれる遷移金属の一部を他の元素で置換した酸化物等が用いることができる。 Further, as the positive electrode active material, one kind of compound selected from lithium-containing transition metal composite oxides, or a mixture of two or more kinds of compounds can be used. For example, lithium cobaltate / lithium nickelate / manganate Lithium / lithium ferrate or an oxide obtained by substituting a part of the transition metal contained in these oxides with other elements can be used.
また、非被覆黒鉛、被覆黒鉛ともに、２種以上の黒鉛の混合物であってもよい。 Further, both uncoated graphite and coated graphite may be a mixture of two or more types of graphite.
また、負極活物質として、黒鉛材料（被覆黒鉛及び非被覆黒鉛）以外に、カーボンブラック・コークス・ガラス状炭素・炭素繊維、またはこれらの焼成体等の炭素材料、あるいはこれらの混合物等を含んでいてもよいが、本発明の効果を十分に得るためには全炭素材料１００質量部中に占める黒鉛材料の質量が９０質量部以上であることが好ましく、９５質量部以上であることがさらに好ましい。 In addition to graphite materials (coated graphite and uncoated graphite), the negative electrode active material includes carbon materials such as carbon black, coke, glassy carbon, carbon fiber, or a fired body thereof, or a mixture thereof. However, in order to sufficiently obtain the effects of the present invention, the mass of the graphite material in 100 parts by mass of the total carbon material is preferably 90 parts by mass or more, and more preferably 95 parts by mass or more. .
また、被覆する非晶質炭素の材料としては非晶質炭素化が可能な有機物であれば、各種の気相材料、液相材料、固相材料が使用可能であり、被覆方法も上記実施例に限定されるものではない。また、上記実施例では１０００℃で焼成したが、例えば７００〜１４００℃の範囲で焼成してもよい。 As the amorphous carbon material to be coated, various vapor phase materials, liquid phase materials, and solid phase materials can be used as long as they are organic materials that can be converted into amorphous carbon. It is not limited to. Moreover, in the said Example, it baked at 1000 degreeC, However, You may bak in 700-1400 degreeC, for example.
また、負極活物質スラリーに用いる結着剤としては、スチレン−ブタジエン共重合体・メチル（メタ）アクリレート・エチル（メタ）アクリレート・ブチル（メタ）アクリレート・（メタ）アクリロニトリル・ヒドロキシエチル（メタ）アクリレート等のエチレン性不飽和カルボン酸エステル、アクリル酸・メタクリル酸・イタコン酸・フマル酸・マレイン酸等のエチレン性不飽和カルボン酸等を、一種または二種以上混合して用いることができる。 The binder used for the negative electrode active material slurry is styrene-butadiene copolymer, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, (meth) acrylonitrile, hydroxyethyl (meth) acrylate. Ethylenically unsaturated carboxylic acid esters such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid and the like can be used singly or in combination.
また、負極活物質スラリーに用いる増粘剤しては、カルボキシメチルセルロース、メチルセルロース、ヒドロキシメチルセルロース、エチルセルロース、ポリビニルアルコール、ポリアクリル酸（塩）、酸化スターチ、リン酸化スターチ、カゼイン等を単独で、もしくは二種以上混合して使用することができる。しかし、増粘剤は本発明の必須の構成要素ではない。 Further, as the thickener used in the negative electrode active material slurry, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, polyacrylic acid (salt), oxidized starch, phosphorylated starch, casein, etc. may be used alone or in combination. A mixture of more than one species can be used. However, thickeners are not an essential component of the present invention.
また、電解質に使用する非水溶媒としては、カーボネート類・ラクトン類・エーテル類、ケトン類・ニトリル類・アミド類・スルホン系化合物・エステル類・芳香族炭化水素等から選択される化合物の一種、あるいは二種以上混合して用いることができる。これらの内でも、カーボネート類・ラクトン類・エーテル類・ケトン類・ニトリル類が好ましく、特にカーボネート類がさらに好ましい。これらの具体例としては、エチレンカーボネート・プロピレンカーボネート・ブチレンカーボネート・ジエチルカーボネート・ジメチルカーボネート・エチルメチルカーボネート・γ−ブチロラクトン・１，２−ジメトキシエタン・テトラヒドロフラン・アニソール・１，４−ジオキサン・４−メチル−２−ペンタノン・シクロヘキサノン・アセトニトリル・プロピオニトリル・ジメチルホルムアミド・スルホラン・蟻酸メチル・蟻酸エチル・酢酸メチル・酢酸エチル・酢酸プロピル・プロピオン酸エチルなどがあげられる。 In addition, as the non-aqueous solvent used for the electrolyte, carbonates, lactones, ethers, ketones, nitriles, amides, sulfone compounds, esters, aromatic hydrocarbons, etc. Or it can use in mixture of 2 or more types. Among these, carbonates, lactones, ethers, ketones, and nitriles are preferable, and carbonates are more preferable. Specific examples thereof include ethylene carbonate, propylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, anisole, 1,4-dioxane, 4-methyl. -2-pentanone, cyclohexanone, acetonitrile, propionitrile, dimethylformamide, sulfolane, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, ethyl propionate, and the like.
また、電解質塩としては、ＬｉＮ（Ｃ2Ｆ5ＳＯ2）2・ＬｉＮ（ＣＦ3ＳＯ2）2・ＬｉＣＦ3ＳＯ3・ＬｉＰＦ6・ＬｉＢＦ4・ＬｉＡｓＦ6・ＬｉＣｌＯ4等のリチウム塩から選択される化合物の一種単独で、あるいは二種以上混合して使用することができる。また、前記非水溶媒に対する電解質塩の溶解量は０．５〜２．０モル／リットルとすることが好ましい。 As the electrolyte salt, selected from LiN (C 2 F 5 SO 2 ) 2 · LiN (CF 3 SO 2) lithium salt such as 2 · LiCF 3 SO 3 · LiPF 6 · LiBF 4 · LiAsF 6 · LiClO 4 These compounds can be used alone or in combination of two or more. The amount of electrolyte salt dissolved in the non-aqueous solvent is preferably 0.5 to 2.0 mol / liter.
上記の結果から明らかなように、本発明によると、ハイレート充電を行っても負極にリチウムが析出せず、且つサイクル劣化が生じない非水電解質二次電池を提供できるという優れた効果を奏する。よって、産業上の利用可能性は大きい。
As is clear from the above results, according to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery in which lithium is not deposited on the negative electrode even when high rate charging is performed and cycle deterioration does not occur. Therefore, industrial applicability is great.
Claims (4)
前記黒鉛粒子群は、表面が非晶質炭素で被覆されていない非被覆黒鉛粒子と、前記非被覆黒鉛粒子の表面が非晶質炭素で被覆された被覆黒鉛粒子と、が混合されてなるものであり、
前記被覆黒鉛粒子及び前記非被覆黒鉛粒子のＬｃ値が１５ｎｍ以上であり、
前記被覆黒鉛粒子及び前記非被覆黒鉛粒子のｄ002値が０．３３８ｎｍ以下であり、
前記被覆黒鉛粒子及び前記非被覆黒鉛粒子の比表面積が２ｍ2／ｇ以上５ｍ2／ｇ以下であり、
前記被覆黒鉛粒子及び前記非被覆黒鉛粒子の平均粒径が１５μｍ以上であり、
前記被覆黒鉛粒子及び前記非被覆黒鉛粒子のＸ線回折法による００２面と１１０面とのピーク強度比Ｉh002／Ｉh110が２００以下である、
ことを特徴とする非水電解質二次電池。 In a non-aqueous electrolyte secondary battery having a positive electrode, a negative electrode including a graphite particle group as an active material, and a non-aqueous electrolyte,
The graphite particle group is a mixture of uncoated graphite particles whose surface is not coated with amorphous carbon and coated graphite particles whose surface is coated with amorphous carbon. And
Lc value of the coated graphite particles and the uncoated graphite particles is 15 nm or more,
The d 002 value of the coated graphite particles and the uncoated graphite particles is 0.338 nm or less,
The specific surface areas of the coated graphite particles and the uncoated graphite particles are 2 m 2 / g or more and 5 m 2 / g or less,
The coated graphite particles and the uncoated graphite particles have an average particle size of 15 μm or more,
The peak intensity ratio I h002 / I h110 between the 002 plane and the 110 plane according to the X-ray diffraction method of the coated graphite particles and the uncoated graphite particles is 200 or less.
A non-aqueous electrolyte secondary battery.
前記被覆黒鉛粒子と、前記非被覆黒鉛粒子との質量比が３：７〜７：３である、
ことを特徴とする非水電解質二次電池。 The nonaqueous electrolyte secondary battery according to claim 1,
The mass ratio of the coated graphite particles to the uncoated graphite particles is 3: 7 to 7: 3.
A non-aqueous electrolyte secondary battery.
前記被覆黒鉛粒子１００質量部中に占める非晶質炭素の質量が、０．１〜１０質量部である、
ことを特徴とする非水電解質二次電池。 The nonaqueous electrolyte secondary battery according to claim 1 or 2,
The mass of amorphous carbon in 100 parts by mass of the coated graphite particles is 0.1 to 10 parts by mass.
A non-aqueous electrolyte secondary battery.
放電状態の前記負極の活物質充填密度が１．４０ｇ／ｍｌ以上であり、かつ前記負極のＸ線回折法による００２面と１１０面とのピーク強度比Ｉh002／Ｉh110が３００以下である、
ことを特徴とする非水電解質二次電池。 The nonaqueous electrolyte secondary battery according to claim 1, 2 or 3 ,
The active material filling density of the negative electrode in a discharged state is 1.40 g / ml or more, and the peak intensity ratio I h002 / I h110 between the 002 plane and the 110 plane according to the X-ray diffraction method of the negative electrode is 300 or less.
A non-aqueous electrolyte secondary battery.
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