JP2010267540A - Nonaqueous electrolyte secondary battery - Google Patents

Nonaqueous electrolyte secondary battery Download PDF

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JP2010267540A
JP2010267540A JP2009118965A JP2009118965A JP2010267540A JP 2010267540 A JP2010267540 A JP 2010267540A JP 2009118965 A JP2009118965 A JP 2009118965A JP 2009118965 A JP2009118965 A JP 2009118965A JP 2010267540 A JP2010267540 A JP 2010267540A
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negative electrode
active material
electrode active
material layer
graphite particles
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Yoshiyuki Muraoka
芳幸 村岡
Mitsuhiro Takeno
光弘 武野
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Panasonic Corp
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery with both cycle life characteristics and battery capacity compatible, through maintenance of battery capacity and restraint of lithium deposition on the surface of a negative electrode. <P>SOLUTION: The nonaqueous electrolyte secondary battery includes a cathode containing a cathode collector and a cathode active material layer, a negative electrode containing a negative electrode collector and a negative electrode active material layer, and a porous insulating layer as well as nonaqueous electrolyte intercalated between the cathode and the negative electrode. The negative electrode active material layer contains graphite particles, with a graphitization degree of the graphite particles distributed on a surface side of the negative electrode active material layer lower than that of the graphite particles distributed on a negative electrode collector side. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

本発明は、非水電解質二次電池の負極の改良に関し、特に負極活物質層に含まれる黒鉛粒子の改良に関する。   The present invention relates to an improvement in the negative electrode of a non-aqueous electrolyte secondary battery, and more particularly to an improvement in graphite particles contained in a negative electrode active material layer.

近年、非水電解質二次電池は、高い作動電圧と高エネルギー密度とを有する二次電池として、携帯電話、ノートパソコン、ビデオカムコーダなどのポータブル電子機器の駆動用電源として広く用いられている。最近では、上記のような小型民生用途のみならず、電力貯蔵用や電気自動車用の高出力型非水電解質二次電池の開発も急速に進められている。   In recent years, non-aqueous electrolyte secondary batteries have been widely used as driving power sources for portable electronic devices such as mobile phones, notebook computers, and video camcorders as secondary batteries having high operating voltage and high energy density. Recently, development of high-power non-aqueous electrolyte secondary batteries for electric power storage and electric vehicles as well as the above-described small-sized consumer applications has been rapidly advanced.

代表的な非水電解質二次電池であるリチウムイオン二次電池の正極活物質としては、金属リチウムに対して４Ｖ級の高電位を有するリチウム含有複合酸化物が用いられている。例えば、六方晶構造を有するＬｉＣｏＯ2、ＬｉＮｉＯ2、およびスピネル構造を有するＬｉＭｎ2Ｏ4が代表的なリチウム含有複合酸化物である。これらの中でも、作動電圧が高く、高エネルギー密度が得られるＬｉＣｏＯ2が主に正極活物質として用いられている。 As a positive electrode active material of a lithium ion secondary battery, which is a typical nonaqueous electrolyte secondary battery, a lithium-containing composite oxide having a high potential of 4 V class with respect to metallic lithium is used. For example, LiCoO 2 having a hexagonal crystal structure, LiNiO 2 , and LiMn 2 O 4 having a spinel structure are typical lithium-containing composite oxides. Among these, LiCoO 2 having a high operating voltage and a high energy density is mainly used as the positive electrode active material.

また、負極活物質としては、例えば、リチウムイオンを吸蔵および放出し得る炭素材料が用いられている。特に、フラットな放電電位と高容量とを実現する観点から、黒鉛粒子が主に用いられている。黒鉛化度が高いほど、すなわち、黒鉛の含有率が大きいほど、炭素材料は高い容量密度を有する。   Further, as the negative electrode active material, for example, a carbon material that can occlude and release lithium ions is used. In particular, graphite particles are mainly used from the viewpoint of realizing a flat discharge potential and a high capacity. The higher the degree of graphitization, that is, the higher the graphite content, the higher the capacity of the carbon material.

ここで、正極および負極を作製する際には、正極活物質層および負極活物質層の圧延を行う。ただし、黒鉛を含む負極活物質層を圧延すると、黒鉛のベーサル面が一方向に配向しやすい。その結果、リチウムイオンが挿入する入口となる黒鉛のエッジ面が負極表面側に配向しなくなり、充放電反応時の正負極間の反応抵抗が大きくなる傾向がある。反応抵抗が大きくなると、金属リチウムが負極表面に析出し、サイクル寿命特性が低下する。   Here, when producing a positive electrode and a negative electrode, the positive electrode active material layer and the negative electrode active material layer are rolled. However, when a negative electrode active material layer containing graphite is rolled, the basal plane of graphite is easily oriented in one direction. As a result, the edge surface of graphite serving as an entrance for inserting lithium ions is not oriented to the negative electrode surface side, and the reaction resistance between the positive and negative electrodes during the charge / discharge reaction tends to increase. When the reaction resistance is increased, metallic lithium is deposited on the negative electrode surface and the cycle life characteristics are lowered.

そこで、特許文献１は、黒鉛層とアモルファスカーボン層とを有する多層膜で構成された負極を用いることを提案している。アモルファスカーボン層は、電解液と接触しやすい位置に配置されている。   Therefore, Patent Document 1 proposes to use a negative electrode composed of a multilayer film having a graphite layer and an amorphous carbon layer. The amorphous carbon layer is disposed at a position where it can easily come into contact with the electrolytic solution.

特開平８−１５３５１４号公報JP-A-8-153514

特許文献１のように黒鉛層とアモルファスカーボン層とを有する多層膜を用いる場合、充放電反応時の正負極間の反応抵抗を小さくすることができると考えられる。しかし、アモルファスカーボン層は容量密度が小さいため、電池容量が大きく低下する。また、アモルファスカーボン層は不可逆容量が大きいため、電池のエネルギー密度が低下する。   When using a multilayer film having a graphite layer and an amorphous carbon layer as in Patent Document 1, it is considered that the reaction resistance between the positive and negative electrodes during charge / discharge reaction can be reduced. However, since the amorphous carbon layer has a small capacity density, the battery capacity is greatly reduced. In addition, since the amorphous carbon layer has a large irreversible capacity, the energy density of the battery decreases.

そこで、本発明は、電池容量を維持するとともに、負極活物質層の表面でのリチウムの析出を抑制することで、サイクル寿命特性と、電池容量とを優れたバランスで両立した非水電解質二次電池を提供することを目的とする。   Therefore, the present invention maintains a battery capacity and suppresses lithium precipitation on the surface of the negative electrode active material layer, thereby achieving a non-aqueous electrolyte secondary that balances cycle life characteristics and battery capacity in an excellent balance. An object is to provide a battery.

本発明は、正極集電体と正極活物質層とを含む正極、負極集電体と負極活物質層とを含む負極、正極と負極との間に介在する多孔質絶縁層および非水電解質を備え、
負極活物質層は、黒鉛粒子を含み、負極活物質層の表面側に分布する黒鉛粒子の黒鉛化度が、負極集電体側に分布する黒鉛粒子の黒鉛化度よりも低い、非水電解質二次電池を提供する。 The present invention provides a positive electrode including a positive electrode current collector and a positive electrode active material layer, a negative electrode including a negative electrode current collector and a negative electrode active material layer, a porous insulating layer interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte. Prepared,
The negative electrode active material layer includes graphite particles, and the graphitized degree of the graphite particles distributed on the surface side of the negative electrode active material layer is lower than the graphitized degree of the graphite particles distributed on the negative electrode current collector side. Provide the next battery.

負極活物質層の表面側に黒鉛化度が低い黒鉛粒子を分布させることで、充放電反応時の反応抵抗を小さくすることができる。そのため、負極活物質層の表面におけるリチウムの析出が抑制され、電極の不可逆容量を小さくすることができる。よって、非水電解質二次電池のサイクル寿命特性が大きく向上する。
さらに、本発明によれば、圧延によるベーサル面の配向が起こりにくいため、負極活物質層の表面側においてリチウムイオンの負極への挿入が容易になる。これにより、非水電解質の粘度が高くなる低温でも良好な充放電特性が得られる。 By distributing graphite particles having a low graphitization degree on the surface side of the negative electrode active material layer, the reaction resistance during the charge / discharge reaction can be reduced. Therefore, lithium deposition on the surface of the negative electrode active material layer is suppressed, and the irreversible capacity of the electrode can be reduced. Therefore, the cycle life characteristics of the nonaqueous electrolyte secondary battery are greatly improved.
Furthermore, according to the present invention, since the orientation of the basal surface due to rolling hardly occurs, it is easy to insert lithium ions into the negative electrode on the surface side of the negative electrode active material layer. Thereby, favorable charge / discharge characteristics can be obtained even at a low temperature at which the viscosity of the nonaqueous electrolyte is increased.

また、負極活物質層の集電体側においては、黒鉛化度が高い黒鉛粒子が分布しているため、電池容量および活物質密度を良好に維持することができる。すなわち、本発明によれば、非水電解質二次電池のサイクル寿命特性と、電池容量とを優れたバランスで両立することができる。   In addition, since the graphite particles having a high graphitization degree are distributed on the current collector side of the negative electrode active material layer, the battery capacity and the active material density can be favorably maintained. That is, according to the present invention, both the cycle life characteristics of the nonaqueous electrolyte secondary battery and the battery capacity can be achieved with an excellent balance.

ここで、負極活物質層の表面側とは、負極活物質層の表面から、負極活物質層の全厚の５０％以下の領域をいい、負極活物質層の集電体側とは、負極活物質層の集電体との接触面から、負極活物質層の全厚の５０％未満の領域をいう。   Here, the surface side of the negative electrode active material layer means a region of 50% or less of the total thickness of the negative electrode active material layer from the surface of the negative electrode active material layer, and the current collector side of the negative electrode active material layer means the negative electrode active material layer. A region of less than 50% of the total thickness of the negative electrode active material layer from the contact surface of the material layer with the current collector.

負極活物質層の表面側に分布する黒鉛粒子としては、表面の少なくとも一部が、非晶質化した黒鉛粒子が好ましい。
黒鉛粒子の黒鉛化度は、負極活物質層の厚さ方向において、段階的に変化していてもよく、連続的に変化していてもよい。この場合、黒鉛化度は、平均的に負極活物質層の表面側から集電体側に向かって高くなっていればよい。
本発明の負極は、波長５１４３Åのアルゴンレーザー光を用いたラマンスペクトル分析において、Ｇバンドのピークの強度をＩＧとし、Ｄバンドのピークの強度をＩＤとするとき、前記負極活物質層の表面側におけるピーク強度比ＩＤ／ＩＧが、０．２５以上、１．０以下であり、負極活物質層の集電体側におけるピーク強度比ＩＤ／ＩＧが０．０１以上、０．２５未満であることが好ましい。 The graphite particles distributed on the surface side of the negative electrode active material layer are preferably graphite particles in which at least a part of the surface is amorphized.
The graphitization degree of the graphite particles may change stepwise or continuously in the thickness direction of the negative electrode active material layer. In this case, the graphitization degree should just become high toward the collector side from the surface side of a negative electrode active material layer on the average.
In the Raman spectrum analysis using an argon laser beam having a wavelength of 5143 nm, the negative electrode of the present invention has a G-band peak intensity as IG and a D-band peak intensity as ID. The peak intensity ratio ID / IG is 0.25 or more and 1.0 or less, and the peak intensity ratio ID / IG on the current collector side of the negative electrode active material layer is 0.01 or more and less than 0.25. preferable.

本発明によれば、電池容量を維持するとともに、負極活物質層の表面におけるリチウムの析出が抑制されるため、サイクル寿命特性と、電池容量とを優れたバランスで両立した非水電解質二次電池を提供することができる。   According to the present invention, since the battery capacity is maintained and lithium deposition on the surface of the negative electrode active material layer is suppressed, the non-aqueous electrolyte secondary battery that achieves both a good balance between cycle life characteristics and battery capacity Can be provided.

本発明の一実施形態に係る円筒型の非水電解質二次電池を概略的に示す縦断面図である。1 is a longitudinal sectional view schematically showing a cylindrical nonaqueous electrolyte secondary battery according to an embodiment of the present invention.

非水電解質二次電池の負極は、シート状の負極集電体と、この片面または両面に形成された負極活物質層とを含む。負極活物質層は、必須成分として負極活物質を含み、任意成分として結着剤等を含む。本発明の負極活物質は、黒鉛粒子を含む。ここでは、黒鉛粒子とは、黒鉛構造を有する領域を含む粒子の総称である。よって、黒鉛粒子には、天然黒鉛、人造黒鉛、黒鉛化メソフェーズカーボン粒子などの他に、任意の黒鉛化度を有する炭素粒子が含まれる。   The negative electrode of the nonaqueous electrolyte secondary battery includes a sheet-like negative electrode current collector and a negative electrode active material layer formed on one or both surfaces. The negative electrode active material layer includes a negative electrode active material as an essential component and a binder or the like as an optional component. The negative electrode active material of the present invention includes graphite particles. Here, the graphite particles are a general term for particles including a region having a graphite structure. Therefore, the graphite particles include carbon particles having an arbitrary degree of graphitization in addition to natural graphite, artificial graphite, graphitized mesophase carbon particles, and the like.

黒鉛粒子を含む負極活物質層は、通常、黒鉛粒子を含む負極合剤と、液状成分とを混合し、得られたペーストを負極集電体に塗布した後、乾燥させ、圧延することにより得られる。このような圧延工程を経て形成された負極活物質層は、黒鉛粒子の黒鉛化度が大きい場合、黒鉛のベーサル面が負極集電体表面と平行に配向しやすい。そのため、充放電反応時の反応抵抗が大きくなる傾向がある。反応抵抗が過剰に大きくなると、充放電に伴い、負極の表面側においてリチウムが析出し、電池のサイクル寿命特性が低下するおそれがある。   The negative electrode active material layer containing graphite particles is usually obtained by mixing a negative electrode mixture containing graphite particles and a liquid component, applying the obtained paste to the negative electrode current collector, drying, and rolling. It is done. In the negative electrode active material layer formed through such a rolling process, when the graphite particles have a high degree of graphitization, the basal surface of graphite is easily oriented parallel to the surface of the negative electrode current collector. Therefore, the reaction resistance during the charge / discharge reaction tends to increase. When the reaction resistance becomes excessively large, lithium is deposited on the surface side of the negative electrode along with charge / discharge, which may reduce the cycle life characteristics of the battery.

一方、負極活物質層において黒鉛粒子の黒鉛化度を過剰に小さくした場合、リチウムの析出の抑制には効果があるが、負極の容量密度が小さくなる。そのため、高容量かつ高出力が求められる非水電解質二次電池に適用することは難しい。   On the other hand, when the graphitization degree of the graphite particles is excessively reduced in the negative electrode active material layer, it is effective in suppressing lithium precipitation, but the capacity density of the negative electrode is reduced. Therefore, it is difficult to apply to a non-aqueous electrolyte secondary battery that requires high capacity and high output.

そこで、本発明の非水電解質二次電池においては、負極活物質層の表面側に分布する黒鉛粒子の黒鉛化度を、負極活物質層の負極集電体側に分布する黒鉛粒子の黒鉛化度よりも低くしている。   Therefore, in the nonaqueous electrolyte secondary battery of the present invention, the degree of graphitization of the graphite particles distributed on the surface side of the negative electrode active material layer is the same as the degree of graphitization of the graphite particles distributed on the negative electrode current collector side of the negative electrode active material layer. Lower than.

黒鉛化度が低い黒鉛粒子を負極活物質層の表面側に分布させることで、負極表面におけるベーサル面の配向が抑制され、リチウムイオンが黒鉛のエッジ面に近づきやすくなる。そのため、充放電反応時の反応抵抗を小さくすることができ、負極活物質層の表面におけるリチウムの析出を抑制することができる。これにより、非水電解質二次電池のサイクル寿命特性が向上する。
また、黒鉛化度が高い黒鉛粒子を負極活物質層の集電体側に分布させているため、電池容量および活物質密度を高いレベルで維持することができる。 By distributing the graphite particles having a low degree of graphitization on the surface side of the negative electrode active material layer, the orientation of the basal surface on the negative electrode surface is suppressed, and lithium ions easily approach the graphite edge surface. Therefore, the reaction resistance during the charge / discharge reaction can be reduced, and lithium deposition on the surface of the negative electrode active material layer can be suppressed. This improves the cycle life characteristics of the nonaqueous electrolyte secondary battery.
Further, since the graphite particles having a high degree of graphitization are distributed on the current collector side of the negative electrode active material layer, the battery capacity and the active material density can be maintained at a high level.

集電体側に近づくほど、圧延によるベーサル面の配向が起こりにくい。そのため、集電体側の黒鉛粒子の黒鉛化度を高くし、表面側の黒鉛粒子の黒鉛化度を低くすることで、ベーサル面の配向を効率よく制御することができる。また、反応抵抗の増大の抑制と、高い電池容量とを、高いレベルで両立することができる。   The closer to the current collector side, the less likely the orientation of the basal surface is due to rolling. Therefore, the orientation of the basal plane can be efficiently controlled by increasing the graphitization degree of the graphite particles on the current collector side and decreasing the graphitization degree of the graphite particles on the surface side. Moreover, suppression of the increase in reaction resistance and high battery capacity can be achieved at a high level.

例えば、負極活物質層の表面側にアモルファス粒子と黒鉛粒子との混合物を分布させた場合、表面側の面の全体で黒鉛化度が不均一になる。この場合、電極表面で局所的な電圧の上昇等が起こり、反応が不均一になる。また、表面側に分布する黒鉛粒子のベーサル面は配向するので、充電受け入れ性の改善には限界がある。よって、本発明では、黒鉛化度が低い黒鉛粒子を負極活物質層の表面側の全面に分布させることが好ましい。黒鉛粒子の黒鉛化度は、負極活物質層の最表面の全面において、均一であることが好ましい。   For example, when a mixture of amorphous particles and graphite particles is distributed on the surface side of the negative electrode active material layer, the degree of graphitization is not uniform over the entire surface on the surface side. In this case, a local increase in voltage occurs on the electrode surface and the reaction becomes non-uniform. Further, since the basal plane of the graphite particles distributed on the surface side is oriented, there is a limit to the improvement in charge acceptance. Therefore, in the present invention, it is preferable to distribute graphite particles having a low degree of graphitization over the entire surface of the negative electrode active material layer. The degree of graphitization of the graphite particles is preferably uniform over the entire outermost surface of the negative electrode active material layer.

黒鉛化度は、平均的に負極活物質層の表面側から負極集電体側に向かって高くなっていればよく、負極活物質層の内部で局所的に黒鉛化度が低くなっている領域が含まれていてもよい。   The graphitization degree only needs to increase on the average from the surface side of the negative electrode active material layer to the negative electrode current collector side, and there is a region where the graphitization degree is locally low inside the negative electrode active material layer. It may be included.

表面側に分布する黒鉛粒子の黒鉛化度が、負極集電体側に分布する黒鉛粒子の黒鉛化度よりも低い負極活物質層は、例えば、以下の方法で作製することができる。
炭素材料を所定の条件（温度、圧力等）で焼成したり、黒鉛粒子に所定の非晶質化処理を施すことにより、所定の黒鉛化度を有する黒鉛粒子を得る。得られた黒鉛粒子と、結着剤と、液状成分とを混合して、負極活物質ペーストを調製する。このとき、黒鉛粒子の黒鉛化度を変化させて、黒鉛化度が異なる第１負極活物質ペーストおよび第２負極活物質ペーストをそれぞれ調製する。 The negative electrode active material layer in which the degree of graphitization of the graphite particles distributed on the surface side is lower than the degree of graphitization of the graphite particles distributed on the negative electrode current collector side can be produced, for example, by the following method.
The carbon material is fired under predetermined conditions (temperature, pressure, etc.), or a predetermined amorphization process is performed on the graphite particles to obtain graphite particles having a predetermined degree of graphitization. The obtained graphite particles, a binder, and a liquid component are mixed to prepare a negative electrode active material paste. At this time, a first negative electrode active material paste and a second negative electrode active material paste having different graphitization degrees are prepared by changing the graphitization degree of the graphite particles.

黒鉛化度が高い黒鉛粒子を含む第１負極活物質ペーストを集電体に塗布し、乾燥させて、第１層を形成する。その後、黒鉛化度が低い黒鉛粒子を含む第２負極活物質ペーストを、第１層に塗布することで、第２層を形成する。これにより、表面側に分布する黒鉛粒子の黒鉛化度が、負極集電体側に分布する黒鉛粒子の黒鉛化度よりも低い負極活物質層が得られる。   A first negative electrode active material paste containing graphite particles having a high degree of graphitization is applied to a current collector and dried to form a first layer. Thereafter, a second layer is formed by applying a second negative electrode active material paste containing graphite particles having a low degree of graphitization to the first layer. Thereby, the negative electrode active material layer in which the graphitization degree of the graphite particles distributed on the surface side is lower than the graphitization degree of the graphite particles distributed on the negative electrode current collector side is obtained.

黒鉛化度の異なる黒鉛粒子は、例えば、炭素材料を焼成する際の温度条件を変えたり、炭素材料を焼成する際の圧力を変えたり、結晶化しやすい炭素材料と、結晶化しにくい炭素材料とを併用したりすることで得られる。黒鉛化度が低い黒鉛粒子は、炭素材料を焼成する際の温度を低くしたり、炭素材料を焼成する際の圧力を低くしたり（例えば、真空下）、結晶化しにくい炭素材料を用いたりすることで得られる。   Graphite particles having different degrees of graphitization include, for example, a carbon material that is easily crystallized and a carbon material that is difficult to crystallize, such as changing the temperature conditions when firing the carbon material, changing the pressure when firing the carbon material. It is obtained by using together. Graphite particles having a low degree of graphitization lower the temperature when firing the carbon material, lower the pressure when firing the carbon material (for example, under vacuum), or use a carbon material that is difficult to crystallize. Can be obtained.

黒鉛粒子の黒鉛化度を測定する方法としては、例えばラマンスペクトル分析が挙げられる。波長５１４３Åのアルゴンレーザー光を用いたラマンスペクトル分析において、Ｇバンドのピークの強度をＩＧとし、Ｄバンドのピークの強度をＩＤとするとき、負極活物質層の表面側におけるピーク強度比Ｒ1（ＩＤ／ＩＧ）は０．２５以上、１．０以下であることが好ましく、０．４以上、１．０以下であることがより好ましい。また、負極活物質層の集電体側におけるピーク強度比Ｒ2（ＩＤ／ＩＧ）は０．０１以上、０．２５未満であることが好ましい。このようなピーク強度比を示す負極活物質層は、表面側に分布する黒鉛粒子の黒鉛化度が、負極集電体側に分布する黒鉛粒子の黒鉛化度よりも低くなっているといえる。上記のピーク強度比を示す負極活物質層は充放電反応時の反応抵抗がより小さくなるため、非水電解質二次電池のサイクル寿命特性が大きく向上する。ここで、ピークの強度とは、ピークの高さを意味する。 Examples of a method for measuring the degree of graphitization of the graphite particles include Raman spectrum analysis. In the Raman spectrum analysis using an argon laser beam having a wavelength of 5143 nm, when the intensity of the peak of the G band is IG and the intensity of the D band peak is ID, the peak intensity ratio R 1 on the surface side of the negative electrode active material layer ( ID / IG) is preferably 0.25 or more and 1.0 or less, and more preferably 0.4 or more and 1.0 or less. Further, the peak intensity ratio in the current collector side of the negative electrode active material layer R 2 (ID / IG) is 0.01 or more and less than 0.25. In the negative electrode active material layer exhibiting such a peak intensity ratio, it can be said that the graphitization degree of the graphite particles distributed on the surface side is lower than the graphitization degree of the graphite particles distributed on the negative electrode current collector side. Since the negative electrode active material layer exhibiting the above peak intensity ratio has a smaller reaction resistance during the charge / discharge reaction, the cycle life characteristics of the nonaqueous electrolyte secondary battery are greatly improved. Here, the peak intensity means the peak height.

Ｄバンドのピークは、およそ１３５０〜１３７０ｃｍ-1の範囲に現れるピークであり、結晶性が低い炭素が存在することを示す、欠陥由来のピークである。Ｇバンドのピークは、およそ１５８０〜１６２０ｃｍ-1の範囲に現れるピークであり、黒鉛構造に由来するピークである。 The peak of the D band is a peak appearing in a range of about 1350 to 1370 cm −1 and is a defect-derived peak indicating that carbon having low crystallinity exists. The peak of the G band is a peak appearing in the range of about 1580 to 1620 cm −1 and is a peak derived from the graphite structure.

負極活物質層の表面側におけるピーク強度比Ｒ1と、集電体側におけるピーク強度比Ｒ2との比（Ｒ1／Ｒ2）は、リチウムイオンの受入性および活物質容量が向上する観点から、１．５〜１００であることが好ましく、３〜２０であることがより好ましい。 A peak intensity ratio R 1 on the surface side of the negative electrode active material layer, the ratio of the peak intensity ratio R 2 at the collector side (R 1 / R 2), from the viewpoint of improving acceptance and active material capacity of the lithium ions 1.5 to 100 is preferable, and 3 to 20 is more preferable.

負極活物質層の表面側におけるピーク強度比は、負極活物質層のうち、負極集電体と対向していない面のラマンスペクトル分析を行うことで求められる。負極活物質層の集電体側におけるピーク強度比は、負極活物質層を負極集電体から剥離した後、集電体と接触していた面のラマンスペクトル分析を行うことで求められる。ラマンスペクトル分析は、例えば市販のレーザラマン分光装置（（株）堀場製作所製のLabRAM HR-800等）を用いて行えばよい。   The peak intensity ratio on the surface side of the negative electrode active material layer is obtained by performing a Raman spectrum analysis of the surface of the negative electrode active material layer that does not face the negative electrode current collector. The peak intensity ratio on the current collector side of the negative electrode active material layer is obtained by performing Raman spectrum analysis on the surface that has been in contact with the current collector after the negative electrode active material layer is peeled from the negative electrode current collector. The Raman spectrum analysis may be performed using, for example, a commercially available laser Raman spectrometer (LabRAM HR-800 manufactured by Horiba, Ltd.).

負極活物質層の表面側に分布する黒鉛粒子の表面の少なくとも一部は、非晶質化していることが好ましく、ほぼ全面が非晶質化していることがより好ましい。これにより、黒鉛粒子の表面の構造がランダムになり、リチウムイオンの挿入サイトが増加する。よって、充放電反応時の反応抵抗をより小さくすることができる。   At least a part of the surface of the graphite particles distributed on the surface side of the negative electrode active material layer is preferably amorphized, and more preferably almost the entire surface is amorphized. As a result, the surface structure of the graphite particles becomes random, and the number of lithium ion insertion sites increases. Therefore, the reaction resistance during the charge / discharge reaction can be further reduced.

黒鉛粒子の少なくとも一部が非晶質化している状態は、例えば市販のレーザラマン分光装置（（株）堀場製作所製のLabRAM HR-800等）により確認することができる。   The state in which at least a part of the graphite particles is amorphized can be confirmed by, for example, a commercially available laser Raman spectrometer (LabRAM HR-800 manufactured by Horiba, Ltd.).

表面の少なくとも一部が非晶質化した黒鉛粒子は、例えば黒鉛粒子の表面に非晶質層を付着させることで得られる。黒鉛粒子の表面に非晶質層を付着させる方法は特に限定されないが、例えば、天然黒鉛粒子の表面を、溶融ピッチ等のピッチ類で被覆する。その後、表面が被覆された天然黒鉛粒子の表面を、５００℃以上２０００℃以下程度の温度で焼成し、炭素化することで、表面の少なくとも一部が非晶質化した黒鉛粒子が得られる。なお、非晶質層は、このような液相中で形成されたものに限定されず、気相中で形成されたものであってもよい。   The graphite particles having at least a part of the surface made amorphous can be obtained, for example, by attaching an amorphous layer to the surface of the graphite particles. The method for attaching the amorphous layer to the surface of the graphite particles is not particularly limited. For example, the surface of the natural graphite particles is coated with pitches such as a molten pitch. Thereafter, the surface of the natural graphite particles coated with the surface is baked at a temperature of about 500 ° C. or more and 2000 ° C. or less and carbonized, whereby graphite particles having at least a part of the surface made amorphous are obtained. The amorphous layer is not limited to that formed in such a liquid phase, and may be formed in a gas phase.

また、黒鉛材料にメカニカル処理を行うことでも、表面の少なくとも一部が非晶質化した黒鉛粒子が得られる。メカニカル処理には、例えばボールミル等を用いればよい。   Further, by performing mechanical treatment on the graphite material, graphite particles having at least a part of the surface made amorphous can be obtained. For the mechanical treatment, for example, a ball mill or the like may be used.

本発明の一形態では、負極活物質層の表面側から集電体側に向かって、黒鉛粒子の黒鉛化度は段階的に変化している。リチウムイオン受入性が重要である負極活物質層の表面側において黒鉛化度を低くし、配向が起こりにくい集電体側において黒鉛化度を高くすることで、リチウムイオンの受入性と、電池容量とを高いレベルで両立することができる。
黒鉛粒子の黒鉛化度は、３段階以上に変化していてもよい。 In one embodiment of the present invention, the degree of graphitization of the graphite particles changes stepwise from the surface side of the negative electrode active material layer toward the current collector side. By reducing the degree of graphitization on the surface side of the negative electrode active material layer where lithium ion acceptance is important and increasing the degree of graphitization on the current collector side where orientation is difficult to occur, the lithium ion acceptance, battery capacity and Can be achieved at a high level.
The degree of graphitization of the graphite particles may change in three or more stages.

黒鉛粒子の黒鉛化度が、厚さ方向において段階的に変化している負極活物質層は、例えば、以下の方法で得られる。まず、それぞれ黒鉛化度が異なる黒鉛粒子を含む、複数の負極活物質ペーストを調製する。最も黒鉛化度が高い黒鉛粒子を含む第１負極活物質ペーストを負極集電体に塗布し、乾燥させて、第１層を形成する。次に、第１負極活物質ペーストよりも黒鉛化度が低い黒鉛粒子を含む、第２負極活物質ペーストを用いて、第１層の上に第２層を形成する。同様の工程を所定の回数繰り返した後、圧延する。これにより、黒鉛粒子の黒鉛化度が厚さ方向において段階的に変化している負極活物質層を作製することができる。   The negative electrode active material layer in which the degree of graphitization of the graphite particles changes stepwise in the thickness direction can be obtained, for example, by the following method. First, a plurality of negative electrode active material pastes containing graphite particles having different graphitization degrees are prepared. A first negative electrode active material paste containing graphite particles having the highest degree of graphitization is applied to the negative electrode current collector and dried to form the first layer. Next, a second layer is formed on the first layer using a second negative electrode active material paste containing graphite particles having a lower degree of graphitization than the first negative electrode active material paste. The same process is repeated a predetermined number of times and then rolled. Thereby, the negative electrode active material layer in which the graphitization degree of the graphite particles changes stepwise in the thickness direction can be produced.

本発明の別の一形態では、負極活物質層の表面側から集電体側に向かって、黒鉛粒子の黒鉛化度が連続的に変化している。負極活物質層の厚さ方向における黒鉛化度の変化の度合いは、一定であっても良く、一定でなくてもよい。このとき、負極活物質層の負極集電体側から表面側に向かって、黒鉛化度が平均的に減少していれば、局所的に黒鉛化度が増加していてもよい。   In another embodiment of the present invention, the degree of graphitization of the graphite particles continuously changes from the surface side of the negative electrode active material layer toward the current collector side. The degree of change in the graphitization degree in the thickness direction of the negative electrode active material layer may be constant or not constant. At this time, as long as the degree of graphitization decreases on the average from the negative electrode current collector side to the surface side of the negative electrode active material layer, the degree of graphitization may locally increase.

黒鉛粒子の形状は、例えば鱗片状、球状、針状等が挙げられる。なかでも、球状の黒鉛粒子は、充填性が向上するため好ましい。   Examples of the shape of the graphite particles include a scale shape, a spherical shape, and a needle shape. Among these, spherical graphite particles are preferable because the filling property is improved.

黒鉛粒子の平均粒径は、リチウムイオンの受け入れ性および黒鉛粒子の充填性が向上する点で、５〜５０μｍであることが好ましく、１５〜２５μｍであることがより好ましい。なお、ここで黒鉛粒子の平均粒径とは、黒鉛粒子の体積粒度分布におけるメディアン径（Ｄ５０）である。黒鉛粒子の体積粒度分布は、例えば市販のレーザー回折式の粒度分布測定装置により測定することができる。   The average particle diameter of the graphite particles is preferably 5 to 50 μm, and more preferably 15 to 25 μm, from the viewpoint of improving lithium ion acceptance and graphite particle filling. Here, the average particle diameter of the graphite particles is the median diameter (D50) in the volume particle size distribution of the graphite particles. The volume particle size distribution of the graphite particles can be measured by, for example, a commercially available laser diffraction type particle size distribution measuring apparatus.

負極活物質層全体に占める黒鉛粒子の重量割合は、電池の高容量化の観点から、例えば９０重量％以上であることが好ましく、９９重量％以上であることがより好ましい。結着剤の量は特に限定されないが、例えば負極活物質層全体の０．５〜７重量％であればよい。
負極活物質層の厚さは、例えば９０〜２２０μｍであり、負極活物質層の空隙率は、例えば５〜３０％である。 From the viewpoint of increasing the battery capacity, the weight ratio of the graphite particles in the entire negative electrode active material layer is preferably 90% by weight or more, and more preferably 99% by weight or more. The amount of the binder is not particularly limited, and may be, for example, 0.5 to 7% by weight of the whole negative electrode active material layer.
The thickness of the negative electrode active material layer is, for example, 90 to 220 μm, and the porosity of the negative electrode active material layer is, for example, 5 to 30%.

負極の結着剤は特に限定されないが、例えば、ポリエチレン、ポリプロピレン、ポリテトラフルオロエチレン（ＰＴＦＥ）、ポリフッ化ビニリデン（ＰＶＤＦ）、テトラフルオロエチレン−ヘキサフルオロプロピレン共重合体（ＦＥＰ）、フッ化ビニリデン−ヘキサフルオロプロピレン共重合体等が挙げられる。   The binder for the negative electrode is not particularly limited. For example, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), vinylidene fluoride- Examples include hexafluoropropylene copolymers.

負極集電体は特に限定されないが、例えば、ステンレス鋼、銅などからなるシートまたは箔を用いることができる。   The negative electrode current collector is not particularly limited. For example, a sheet or foil made of stainless steel, copper, or the like can be used.

本発明の非水電解質二次電池は、上記の負極を含むものであり、その他の構成は特に限定されない。
正極は、例えばシート状の正極集電体と、この片面または両面に形成された正極活物質層とを含む。正極活物質層は、必須成分として正極活物質を含み、任意成分として導電材や結着剤を含む。 The nonaqueous electrolyte secondary battery of the present invention includes the above-described negative electrode, and other configurations are not particularly limited.
The positive electrode includes, for example, a sheet-like positive electrode current collector and a positive electrode active material layer formed on one or both surfaces. The positive electrode active material layer includes a positive electrode active material as an essential component, and includes a conductive material and a binder as optional components.

正極は、例えば、正極活物質と、カーボンブラックなどの導電剤と、ポリフッ化ビニリデンなどの結着剤とを含むペーストを、アルミニウム箔などの正極集電体に塗布した後、乾燥させ、圧延することにより得られる。正極活物質としては、リチウム含有遷移金属酸化物が好ましい。リチウム含有遷移金属化合物の代表的な例としては、ＬｉＣｏＯ2、ＬｉＮｉＯ2、ＬｉＭｎ2Ｏ4、ＬｉＭｎＯ2、ＬｉＮｉ1-yＣｏyＯ2（０＜ｙ＜１）、ＬｉＮｉ1-y-zＣｏyＭｎzＯ2（０＜ｙ＋ｚ＜１）などを挙げることができる。正極の結着剤は、例えば、負極の結着剤として挙げたものと同様の結着剤を用いることができる。 For example, the positive electrode is applied by applying a paste containing a positive electrode active material, a conductive agent such as carbon black, and a binder such as polyvinylidene fluoride to a positive electrode current collector such as an aluminum foil, followed by drying and rolling. Can be obtained. As the positive electrode active material, a lithium-containing transition metal oxide is preferable. Typical examples of lithium-containing transition metal compounds include LiCoO 2 , LiNiO 2 , LiMn 2 O 4 , LiMnO 2 , LiNi 1-y Co y O 2 (0 <y <1), LiNi 1-yz Co y Mn and z O 2 (0 <y + z <1). As the positive electrode binder, for example, the same binders as those mentioned as the negative electrode binder can be used.

非水電解質としては、非水溶媒およびこれに溶解するリチウム塩からなる液状の電解質が好ましい。非水溶媒としては、エチレンカーボネート、プロピレンカーボネートなどの環状カーボネート類と、ジメチルカーボネート、ジエチルカーボネート、エチルメチルカーボネートなどの鎖状カーボネート類との混合溶媒が一般的に用いられる。また、γ−ブチロラクトンやジメトキシエタンなども用いられる。リチウム塩としては、無機リチウムフッ化物やリチウムイミド化合物などが挙げられる。無機リチウムフッ化物としては、ＬｉＰＦ6、ＬＩＢＦ4等が挙げられ、リチウムイミド化合物としてはＬｉＮ（ＣＦ3ＳＯ2）2等が挙げられる。 As the non-aqueous electrolyte, a liquid electrolyte comprising a non-aqueous solvent and a lithium salt dissolved therein is preferable. As the non-aqueous solvent, a mixed solvent of cyclic carbonates such as ethylene carbonate and propylene carbonate and chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate is generally used. Further, γ-butyrolactone, dimethoxyethane and the like are also used. Examples of the lithium salt include inorganic lithium fluoride and a lithium imide compound. Examples of the inorganic lithium fluoride include LiPF 6 and LIBF 4 , and examples of the lithium imide compound include LiN (CF 3 SO 2 ) 2 .

多孔質絶縁層（セパレータ）としては、ポリエチレン、ポリプロピレンなどからなる微多孔性フィルムが一般に用いられている。多孔質絶縁層の厚みは、例えば１０〜３０μｍである。   As the porous insulating layer (separator), a microporous film made of polyethylene, polypropylene or the like is generally used. The thickness of the porous insulating layer is, for example, 10 to 30 μm.

本発明は、円筒型、扁平型、コイン型、角形など、様々な形状の非水電解質二次電池に適用可能であり、電池の形状は特に限定されない。   The present invention can be applied to non-aqueous electrolyte secondary batteries having various shapes such as a cylindrical shape, a flat shape, a coin shape, and a square shape, and the shape of the battery is not particularly limited.

次に、本発明を実施例および比較例に基づいて具体的に説明する。ただし、本発明が下記の実施例に限定されるわけではない。   Next, the present invention will be specifically described based on examples and comparative examples. However, the present invention is not limited to the following examples.

《実施例１》
（ａ）負極の作製
第１黒鉛粒子として、平均粒径２０μｍの球状天然黒鉛を用いた。第１黒鉛粒子と、結着剤であるスチレンブタジエンゴム（ＳＢＲ）と、水とを混合して、第１負極活物質ペーストを調製した。ここで、ＳＢＲの量は、第１黒鉛粒子１００重量部あたり１．０重量部とした。 Example 1
(A) Production of negative electrode Spherical natural graphite having an average particle diameter of 20 μm was used as the first graphite particles. First graphite particles, styrene butadiene rubber (SBR) as a binder, and water were mixed to prepare a first negative electrode active material paste. Here, the amount of SBR was 1.0 part by weight per 100 parts by weight of the first graphite particles.

また、上記の第１黒鉛粒子と同じ球状天然黒鉛をボールミルで１２時間メカニカル処理することにより、平均粒径２０μｍの第２黒鉛粒子を調製した。(株)堀場製作所製のレーザラマン分光装置であるLabRAM HR-800を用いて確認したところ、得られた第２黒鉛粒子は、その表面の一部が非晶質化していた。第２黒鉛粒子と、結着剤であるＳＢＲと、水とを混合して、第２負極活物質ペーストを調製した。ここで、ＳＢＲの量は、第２黒鉛粒子１００重量部あたり１．０重量部とした。   Further, second natural graphite particles having an average particle diameter of 20 μm were prepared by mechanically treating the same spherical natural graphite as the first graphite particles with a ball mill for 12 hours. As a result of confirmation using LabRAM HR-800, a laser Raman spectroscope manufactured by Horiba, Ltd., the obtained second graphite particles were partially amorphous. The second negative electrode active material paste was prepared by mixing the second graphite particles, SBR as the binder, and water. Here, the amount of SBR was 1.0 part by weight per 100 parts by weight of the second graphite particles.

第１負極活物質ペーストを、負極集電体である電解銅箔（厚さ８μｍ）の両面に塗布した後、１１０℃で乾燥させて、第１層を形成した。次に、第２負極活物質ペーストを、第１層の上に塗布した後、１１０℃で乾燥させて、第２層を形成した。その後、圧延を行い、厚さ１８８μｍの負極を得た。第１層および第２層からなる負極活物質層の厚さは、片面あたり９０μｍであった。なお、第１層の厚さは片面あたり４５μｍであり、第２層の厚さは片面あたり４５μｍであった。   After apply | coating the 1st negative electrode active material paste on both surfaces of the electrolytic copper foil (thickness 8 micrometers) which is a negative electrode electrical power collector, it was made to dry at 110 degreeC and the 1st layer was formed. Next, after apply | coating the 2nd negative electrode active material paste on the 1st layer, it was made to dry at 110 degreeC and the 2nd layer was formed. Thereafter, rolling was performed to obtain a negative electrode having a thickness of 188 μm. The negative electrode active material layer composed of the first layer and the second layer had a thickness of 90 μm per side. The thickness of the first layer was 45 μm per side, and the thickness of the second layer was 45 μm per side.

得られた負極について、波長５１４３Åのアルゴンレーザー光を用いてラマンスペクトル分析を行い、Ｄバンドのピークの強度ＩＤと、Ｇバンドのピークの強度ＩＧとのピーク強度比（ＩＤ／ＩＧ）を求めた。負極活物質層の表面側におけるピーク強度比（Ｒ1）ＩＤ／ＩＧは０．５であり、負極活物質層の集電体側におけるピーク強度比（Ｒ2）ＩＤ／ＩＧは、０．１５であった。これにより、実施例１の負極は、負極活物質層の表面側に分布する黒鉛粒子の黒鉛化度が、負極集電体側に分布する黒鉛粒子の黒鉛化度よりも低くなっていることがわかった。負極活物質層の表面側におけるピーク強度比Ｒ1と、集電体側におけるピーク強度比Ｒ2との比（Ｒ1／Ｒ2）は、３．３であった。 The obtained negative electrode was subjected to Raman spectrum analysis using an argon laser beam having a wavelength of 5143 nm, and the peak intensity ratio (ID / IG) between the intensity ID of the D band peak and the intensity IG of the G band peak was determined. . The peak intensity ratio (R 1 ) ID / IG on the surface side of the negative electrode active material layer is 0.5, and the peak intensity ratio (R 2 ) ID / IG on the current collector side of the negative electrode active material layer is 0.15. there were. Thus, in the negative electrode of Example 1, the graphitization degree of the graphite particles distributed on the surface side of the negative electrode active material layer is found to be lower than the graphitization degree of the graphite particles distributed on the negative electrode current collector side. It was. A peak intensity ratio R 1 on the surface side of the negative electrode active material layer, the ratio of the peak intensity ratio R 2 at the collector side (R 1 / R 2) was 3.3.

（ｂ）正極の作製
正極活物質には、ＬｉＮｉ0.33Ｍｎ0.33Ｃｏ0.33Ｏ2を用いた。
正極活物質１００重量部と、導電材であるアセチレンブラック１．３重量部と、結着剤であるＰＶＤＦのＮ−メチル−２−ピロリドン（ＮＭＰ）溶液とを混合して、正極活物質ペーストを調製した。ここで、ＰＶＤＦの量は、正極活物質１００重量部あたり１．０重量部とした。 (B) Production of positive electrode LiNi 0.33 Mn 0.33 Co 0.33 O 2 was used as the positive electrode active material.
A positive electrode active material paste was prepared by mixing 100 parts by weight of a positive electrode active material, 1.3 parts by weight of acetylene black as a conductive material, and an N-methyl-2-pyrrolidone (NMP) solution of PVDF as a binder. Prepared. Here, the amount of PVDF was 1.0 part by weight per 100 parts by weight of the positive electrode active material.

正極活物質ペーストを、正極集電体であるアルミニウム箔の両面に塗布した後、１１０℃で乾燥させ、圧延を行った。これにより、厚さ１５５μｍの正極を得た。正極集電体に形成された正極活物質層の厚さは、片面あたり７０μｍであった。   After apply | coating the positive electrode active material paste to both surfaces of the aluminum foil which is a positive electrode electrical power collector, it dried at 110 degreeC and rolled. As a result, a positive electrode having a thickness of 155 μm was obtained. The thickness of the positive electrode active material layer formed on the positive electrode current collector was 70 μm per side.

（ｃ）非水電解質の調製
エチレンカーボネートとジメチルカーボネートとの体積比が１：３である混合溶媒に、５重量％のビニレンカーボネートを添加し、１．４ｍｏｌ／Ｌの濃度でＬｉＰＦ6を溶解し、非水電解質を得た。 (C) Preparation of non-aqueous electrolyte 5 wt% vinylene carbonate was added to a mixed solvent having a volume ratio of ethylene carbonate and dimethyl carbonate of 1: 3, and LiPF 6 was dissolved at a concentration of 1.4 mol / L. A non-aqueous electrolyte was obtained.

（ｄ）円筒型リチウムイオン二次電池の作製
以下の手順で図１に示すような円筒型リチウムイオン二次電池を作製した。 (D) Production of Cylindrical Lithium Ion Secondary Battery A cylindrical lithium ion secondary battery as shown in FIG. 1 was produced by the following procedure.

正極５の集電体にアルミニウム製の正極リード５ａを取り付け、負極６の集電体にニッケル製の負極リード６ａを取り付けた。その後、正極と負極との間に厚さ２０μｍのポリエチレン製の微多孔質フィルムからなるセパレータ７を介して捲回し、電極群を構成した。   The positive electrode lead 5 a made of aluminum was attached to the current collector of the positive electrode 5, and the negative electrode lead 6 a made of nickel was attached to the current collector of the negative electrode 6. Then, it wound between the positive electrode and the negative electrode through the separator 7 which consists of a 20-micrometer-thick polyethylene microporous film, and comprised the electrode group.

次に、電極群の上部および下部には、上部絶縁板８ａおよび下部絶縁板８ｂをそれぞれ配置した。負極リード６ａを電池ケース１の内側に溶接し、正極リード５ａを、内圧作動型の安全弁を有する封口板２に溶接した。電極群を電池ケース１の内部に収納し、非水電解質を減圧方式により注入した。
最後に、電池ケース１の開口端部を、ガスケット３を介して封口板２にかしめることにより、円筒型リチウムイオン二次電池を完成させた。 Next, an upper insulating plate 8a and a lower insulating plate 8b were arranged above and below the electrode group, respectively. The negative electrode lead 6a was welded to the inside of the battery case 1, and the positive electrode lead 5a was welded to the sealing plate 2 having an internal pressure actuated safety valve. The electrode group was accommodated in the battery case 1 and a nonaqueous electrolyte was injected by a reduced pressure method.
Finally, the cylindrical lithium ion secondary battery was completed by caulking the open end of the battery case 1 to the sealing plate 2 via the gasket 3.

［評価］
（i）電池容量
２５℃環境下で、電池電圧が４．２Ｖになるまで１．４Ａの定電流で充電を行い、その後４．２Ｖの定電圧で電流値が５０ｍＡになるまで充電を行った。その後、０．５６Ａの定電流で２．５Ｖになるまで放電を行い、得られた電池の容量を求めた。結果を表１に示す。電池容量は２．４Ａｈであり、ＬｉＮｉ0.33Ｍｎ0.33Ｃｏ0.33Ｏ2の活物質容量は１５０ｍＡｈ／ｇであった。 [Evaluation]
(I) Battery capacity In a 25 ° C environment, charging was performed at a constant current of 1.4 A until the battery voltage reached 4.2 V, and then charging was performed at a constant voltage of 4.2 V until the current value reached 50 mA. . Then, it discharged until it became 2.5V with the constant current of 0.56A, and the capacity | capacitance of the obtained battery was calculated | required. The results are shown in Table 1. The battery capacity was 2.4 Ah, and the active material capacity of LiNi 0.33 Mn 0.33 Co 0.33 O 2 was 150 mAh / g.

（ii）サイクル特性
２５℃環境下で、電池電圧が４．２Ｖになるまで１．４Ａの定電流で充電を行い、その後４．２Ｖの定電圧で電流値が５０ｍＡになるまで充電を行った。その後、２．８Ａの定電流で２．５Ｖになるまで放電した。このサイクルを、５００サイクル繰り返した。初回サイクル時の電池容量を１００％とし、５００サイクル経過したときの電池容量からサイクル容量維持率（％）を求めた。結果を表１に示す。 (Ii) Cycle characteristics Under a 25 ° C environment, charging was performed at a constant current of 1.4 A until the battery voltage reached 4.2 V, and then charging was performed at a constant voltage of 4.2 V until the current value reached 50 mA. . Then, it discharged until it became 2.5V with the constant current of 2.8A. This cycle was repeated 500 cycles. The battery capacity at the first cycle was taken as 100%, and the cycle capacity maintenance rate (%) was determined from the battery capacity after 500 cycles. The results are shown in Table 1.

Figure 2010267540
Figure 2010267540

《比較例１》
実施例１と同様の球状天然黒鉛１００重量部と、結着剤であるＳＢＲと、水とを混合して、第１負極活物質ペーストを調製した。ここで、ＰＶＤＦの量は、第１黒鉛粒子１００重量部あたり１重量部とした。
また、非晶質の材料である平均粒径２０μｍの難黒鉛化性炭素５０重量部と、上記の球状天然黒鉛５０重量部と、結着剤であるＳＢＲと、水とを混合して、第２負極活物質ペーストを調製した。ここで、ＳＢＲの量は、難黒鉛化性炭素と球状天然黒鉛の合計１００重量部あたり１重量部とした。 << Comparative Example 1 >>
A first negative electrode active material paste was prepared by mixing 100 parts by weight of the same spherical natural graphite as in Example 1, SBR as a binder, and water. Here, the amount of PVDF was 1 part by weight per 100 parts by weight of the first graphite particles.
Further, 50 parts by weight of non-graphitizable carbon having an average particle diameter of 20 μm which is an amorphous material, 50 parts by weight of the above spherical natural graphite, SBR which is a binder, and water are mixed, 2 A negative electrode active material paste was prepared. Here, the amount of SBR was 1 part by weight per 100 parts by weight of the total of non-graphitizable carbon and spherical natural graphite.

第１負極活物質ペーストを、負極集電体である電解銅箔（厚さ８μｍ）の両面に塗布した後、１１０℃で乾燥させて、第１層を形成した。その後、第２負極活物質ペーストを、第１層の上に塗布した後、１１０℃で乾燥させて、第２層を形成した。その後、圧延を行い、厚さ１８８μｍの負極を得た。第１層および第２層からなる負極活物質層の厚さは、片面あたり９０μｍであった。なお、第１層の厚さは片面あたり４５μｍであり、第２層の厚さは片面あたり４５μｍであった。   After apply | coating the 1st negative electrode active material paste on both surfaces of the electrolytic copper foil (thickness 8 micrometers) which is a negative electrode electrical power collector, it was made to dry at 110 degreeC and the 1st layer was formed. Then, after apply | coating the 2nd negative electrode active material paste on the 1st layer, it was made to dry at 110 degreeC and the 2nd layer was formed. Thereafter, rolling was performed to obtain a negative electrode having a thickness of 188 μm. The negative electrode active material layer composed of the first layer and the second layer had a thickness of 90 μm per side. The thickness of the first layer was 45 μm per side, and the thickness of the second layer was 45 μm per side.

比較例１の負極活物質層において、第２層は難黒鉛化性炭素と球状天然黒鉛との混合物を含み、第１層および第２層は、同じ球状天然黒鉛を含む。   In the negative electrode active material layer of Comparative Example 1, the second layer includes a mixture of non-graphitizable carbon and spherical natural graphite, and the first layer and the second layer include the same spherical natural graphite.

得られた負極について、波長５１４３Åのアルゴンレーザー光を用いてラマンスペクトル分析を行い、Ｄバンドのピークの強度ＩＤと、Ｇバンドのピークの強度ＩＧとのピーク強度比（ＩＤ／ＩＧ）を求めた。負極活物質層の表面側におけるピーク強度比ＩＤ／ＩＧは０．５であり、負極活物質層の集電体側におけるピーク強度比は、０．１５であった。   The obtained negative electrode was subjected to Raman spectrum analysis using an argon laser beam having a wavelength of 5143 nm, and the peak intensity ratio (ID / IG) between the intensity ID of the D band peak and the intensity IG of the G band peak was determined. . The peak intensity ratio ID / IG on the surface side of the negative electrode active material layer was 0.5, and the peak intensity ratio on the current collector side of the negative electrode active material layer was 0.15.

上記の負極を用いたこと以外、実施例１と同様にして、円筒型リチウムイオン二次電池を作製した。得られた電池について、実施例１と同様にして評価を行った。結果を表１に示す。なお、電池容量は２．３Ａｈであった。   A cylindrical lithium ion secondary battery was produced in the same manner as in Example 1 except that the above negative electrode was used. The obtained battery was evaluated in the same manner as in Example 1. The results are shown in Table 1. The battery capacity was 2.3 Ah.

実施例１と比較例１とで、負極活物質層の表面側および集電体側ＩＤ／ＩＧ比はそれぞれ同じであるにもかかわらず、特にサイクル寿命特性に大きな差が生じた。実施例１の負極は、表面側の全面において、黒鉛化度がほぼ均一であるため、比較例の負極よりも充電受け入れ性が向上すると共に、負極の不可逆容量が少なくなったと考えられる。これにより、実施例１の電池は高容量と優れたサイクル寿命特性とを実現することができたと考えられる。   Although the surface side of the negative electrode active material layer and the current collector side ID / IG ratio were the same in Example 1 and Comparative Example 1, particularly a great difference in cycle life characteristics occurred. Since the negative electrode of Example 1 has a substantially uniform degree of graphitization over the entire surface, the charge acceptability is improved and the irreversible capacity of the negative electrode is reduced compared to the negative electrode of the comparative example. Thereby, it is considered that the battery of Example 1 was able to realize high capacity and excellent cycle life characteristics.

本発明によれば、サイクル寿命特性と、電池容量とを優れたバランスで両立した非水電解質二次電池を提供することができる。本発明の非水電解質二次電池は、例えば民生用電源、自動車搭載用の電源、大型工具用の電源などに有用である。   According to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery in which cycle life characteristics and battery capacity are both balanced with an excellent balance. The nonaqueous electrolyte secondary battery of the present invention is useful, for example, as a power source for consumer use, a power source for mounting on automobiles, and a power source for large tools.

１ 電池ケース
２ 封口板
３ ガスケット
５ 正極
５ａ 正極リード
６ 負極
６ａ 負極リード
７ セパレータ
８ａ 上部絶縁板
８ｂ 下部絶縁板 DESCRIPTION OF SYMBOLS 1 Battery case 2 Sealing plate 3 Gasket 5 Positive electrode 5a Positive electrode lead 6 Negative electrode 6a Negative electrode lead 7 Separator 8a Upper insulating plate 8b Lower insulating plate

Claims (5)

正極集電体と正極活物質層とを含む正極、負極集電体と負極活物質層とを含む負極、前記正極と前記負極との間に介在する多孔質絶縁層および非水電解質を備え、
前記負極活物質層は、黒鉛粒子を含み、
前記負極活物質層の表面側に分布する前記黒鉛粒子の黒鉛化度が、前記負極集電体側に分布する前記黒鉛粒子の黒鉛化度よりも低い、非水電解質二次電池。 A positive electrode including a positive electrode current collector and a positive electrode active material layer, a negative electrode including a negative electrode current collector and a negative electrode active material layer, a porous insulating layer interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte,
The negative electrode active material layer includes graphite particles,
A non-aqueous electrolyte secondary battery in which a graphitization degree of the graphite particles distributed on the surface side of the negative electrode active material layer is lower than a graphitization degree of the graphite particles distributed on the negative electrode current collector side. 前記負極活物質層の表面側に分布する前記黒鉛粒子の表面の少なくとも一部が非晶質化している、請求項１記載の非水電解質二次電池。   The nonaqueous electrolyte secondary battery according to claim 1, wherein at least a part of the surface of the graphite particles distributed on the surface side of the negative electrode active material layer is amorphized. 前記負極活物質層の厚さ方向において、前記黒鉛粒子の黒鉛化度が段階的に変化している、請求項１または２記載の非水電解質二次電池。   The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the graphitization degree of the graphite particles changes stepwise in the thickness direction of the negative electrode active material layer. 前記負極活物質層の厚さ方向において、前記黒鉛粒子の黒鉛化度が連続的に変化している、請求項１または２記載の非水電解質二次電池。   The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the graphitization degree of the graphite particles continuously changes in the thickness direction of the negative electrode active material layer. 波長５１４３Åのアルゴンレーザー光を用いたラマンスペクトル分析において、Ｇバンドのピークの強度をＩＧとし、Ｄバンドのピークの強度をＩＤとするとき、前記負極活物質層の表面側におけるピーク強度比ＩＤ／ＩＧが０．２５以上、１．０以下であり、負極活物質層の集電体側におけるピーク強度比ＩＤ／ＩＧが０．０１以上、０．２５未満である、請求項１〜４のいずれかに記載の非水電解質二次電池。   In the Raman spectrum analysis using an argon laser beam having a wavelength of 5143 nm, when the intensity of the peak of the G band is IG and the intensity of the peak of the D band is ID, the peak intensity ratio ID / on the surface side of the negative electrode active material layer The IG is 0.25 or more and 1.0 or less, and the peak intensity ratio ID / IG on the current collector side of the negative electrode active material layer is 0.01 or more and less than 0.25. The non-aqueous electrolyte secondary battery described in 1.
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