JP2010176973A - Nonaqueous electrolyte secondary battery - Google Patents

Nonaqueous electrolyte secondary battery Download PDF

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JP2010176973A
JP2010176973A JP2009016997A JP2009016997A JP2010176973A JP 2010176973 A JP2010176973 A JP 2010176973A JP 2009016997 A JP2009016997 A JP 2009016997A JP 2009016997 A JP2009016997 A JP 2009016997A JP 2010176973 A JP2010176973 A JP 2010176973A
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carbon material
negative electrode
specific surface
electrolyte secondary
surface area
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Takuya Shinomiya
拓也 四宮
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Sanyo Electric Co Ltd
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Sanyo Electric Co Ltd
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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
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery having high adhesion between a negative electrode core and a negative electrode active material mix layer and high charge discharge cycle characteristics. <P>SOLUTION: In the nonaqueous electrolyte secondary battery including a positive electrode having a positive electrode active material, a negative electrode, and a nonaqueous electrolyte having a nonaqueous solvent and an electrolyte salt, a negative electrode active material is a mixture of a large particle carbon material having a median diameter in particle distribution of 30-50 μm and a specific surface area of 2.0-4.5 m<SP>2</SP>/g and a small particle carbon material having a median particle in particle distribution of 9-13 μm and a specific surface area of 6.5-7.8 m<SP>2</SP>/g in a mixing ratio of the large particle carbon material to the small particle carbon material of 8/2 to 6/4. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

本発明は、非水電解質二次電池に関し、特に、粒径分布が異なる複数種の炭素材料からなる負極活物質材料を用いた初期効率及びサイクル特性の良好な非水電解質二次電池に関する。   The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly, to a non-aqueous electrolyte secondary battery having good initial efficiency and cycle characteristics using a negative electrode active material made of a plurality of types of carbon materials having different particle size distributions.

今日の携帯電話機、携帯型パーソナルコンピューター、携帯型音楽プレイヤー等の携帯型電子機器の駆動電源として、更には、ハイブリッド電気自動車（ＨＥＶ）や電気自動車（ＥＶ）用の電源として、高エネルギー密度を有し、高容量であ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が広く利用されている。   It has high energy density as a driving power source for portable electronic devices such as today's mobile phones, portable personal computers, portable music players, and also as a power source for hybrid electric vehicles (HEV) and electric vehicles (EV). However, non-aqueous electrolyte secondary batteries represented by high-capacity lithium ion secondary batteries are widely used.

これらの非水電解質二次電池の正極活物質としては、リチウムイオンを可逆的に吸蔵・放出することが可能なＬｉｘＭｙＯ２（ただし、ＭはＣｏ、Ｎｉ、Ｍｎの少なくとも１種である）で表されるリチウム遷移金属複合酸化物、すなわち、ＬｉＣｏＯ２、ＬｉＮｉＯ２、ＬｉＮｉｘＣｏ１−ｘＯ２（ｘ＝０．０１〜０．９９）、ＬｉＭｎＯ２、ＬｉＭｎ２Ｏ４、ＬｉＣｏｘＭｎｙＮｉｚＯ２（ｘ＋ｙ＋ｚ＝１）又はＬｉＦｅＰＯ４などが一種単独もしくは複数種を混合して用いられている。 The positive electrode active material of these nonaqueous electrolyte secondary batteries is represented by LixMyO 2 (where M is at least one of Co, Ni, and Mn) capable of reversibly occluding and releasing lithium ions. Lithium transition metal composite oxides, that is, LiCoO 2 , LiNiO 2 , LiNixCo 1-x O 2 (x = 0.01 to 0.99), LiMnO 2 , LiMn 2 O 4 , LiCo x Mn y Ni z O 2 (x + y + z = 1), LiFePO 4 or the like is used singly or in combination.

このうち、特に各種電池特性が他のものに対して優れていることから、リチウムコバルト複合酸化物や異種金属元素添加リチウムコバルト複合酸化物が多く使用されている。しかしながら、コバルトは高価であると共に資源としての存在量が少ない。そのため、これらのリチウムコバルト複合酸化物や異種金属元素添加リチウムコバルト複合酸化物を非水電解質二次電池の正極活物質として使用し続けるには非水電解質二次電池の更なる高性能化が望まれている。   Among these, since various battery characteristics are particularly excellent with respect to others, lithium cobalt composite oxides and heterogeneous metal element-added lithium cobalt composite oxides are often used. However, cobalt is expensive and has a small abundance as a resource. Therefore, in order to continue to use these lithium cobalt composite oxides and lithium cobalt composite oxides with different metal elements added as the positive electrode active material of the non-aqueous electrolyte secondary battery, further enhancement of the performance of the non-aqueous electrolyte secondary battery is desired. It is rare.

一方、これらの非水電解質二次電池の負極活物質としては、リチウムの析出（デンドライトの生成）が少ないことから炭素材料が一般的に使われており、中でも黒鉛粒子を用いた非水電解質二次電池は、安全性が高く、かつ、高容量であるために広く用いられている。   On the other hand, as a negative electrode active material for these non-aqueous electrolyte secondary batteries, a carbon material is generally used because of a small amount of lithium deposition (dendritic generation), and in particular, a non-aqueous electrolyte 2 using graphite particles is used. Secondary batteries are widely used because of their high safety and high capacity.

例えば、下記特許文献１には、リチウムイオン二次電池の負極用材として、平均粒子径の異なる少なくとも２種の黒鉛粉を配合・充填することで、負極活物質の充填率を向上させ、リチウムイオン二次電池の放電容量を高めた非水電解質二次電池の発明が開示されている。具体的には、粉砕した黒鉛粒子を、平均粒子径が２５．８μｍでＢＥＴ比表面積が３．２１ｍ２／ｇの粗粒と、平均粒子径が１２．１μｍでＢＥＴ比表面積が２．９５ｍ２／ｇの中粒と、平均粒子径が５．１μｍでＢＥＴ比表面積が５．２４ｍ２／ｇの微粒とに分別し、粗粒と中粒、粗粒と微粒ないし中粒と微粒を混合して負極活物質として用いている。 For example, in Patent Document 1 below, as a negative electrode material for a lithium ion secondary battery, at least two kinds of graphite powders having different average particle diameters are blended and filled, thereby improving the filling rate of the negative electrode active material, and lithium ion An invention of a non-aqueous electrolyte secondary battery in which the discharge capacity of the secondary battery is increased is disclosed. Specifically, the pulverized graphite particles are coarse particles having an average particle diameter of 25.8 μm and a BET specific surface area of 3.21 m 2 / g, an average particle diameter of 12.1 μm and a BET specific surface area of 2.95 m 2. / G medium particles and fine particles having an average particle diameter of 5.1 μm and a BET specific surface area of 5.24 m 2 / g, and mixing coarse particles with medium particles, coarse particles with fine particles or medium particles with fine particles. And used as a negative electrode active material.

また、下記特許文献２には、特定の物理特性を有し、レーザー回折式粒度分布計を用いて測定した体積分率５０％時の粒子径Ｄ５０が１５〜３０μｍで、ＢＥＴ法を用いて測定した比表面積が１ｍ２／ｇ以下である大粒径の等方性人造黒鉛粒子Ａと、レーザー回折式粒度分布計を用いて測定した体積分率５０％時の粒子径Ｄ５０が５〜１５μｍで、ＢＥＴ法を用いて測定した比表面積が８ｍ２／ｇ以下である小粒径の球状黒鉛粒子Ｂとの混合物からなり、負極活物質全体に占める球状黒鉛粒子Ｂの混合比率が５〜 ４５重量％である負極合剤層を用いた非水電解質二次電池の発明が開示されている。下記特許文献２に開示されている発明によれば、初期不可逆容量が小さく、高率放電特性、低温放電特性、充放電サイクル特性及び安全性に優れた非水電解質二次電池が得られるとされている。 Patent Document 2 listed below has specific physical characteristics, and has a particle diameter D 50 at a volume fraction of 50% measured using a laser diffraction particle size distribution meter of 15 to 30 μm, using the BET method. Isotropic artificial graphite particles A having a large particle size with a measured specific surface area of 1 m 2 / g or less, and a particle size D 50 at a volume fraction of 50% measured using a laser diffraction particle size distribution meter is 5 to 5. It consists of a mixture with small graphite particles B having a specific surface area of 15 μm and a specific surface area measured using the BET method of 8 m 2 / g or less, and the mixing ratio of the spherical graphite particles B in the whole negative electrode active material is 5 to 5 An invention of a non-aqueous electrolyte secondary battery using a negative electrode mixture layer of 45% by weight is disclosed. According to the invention disclosed in the following Patent Document 2, a nonaqueous electrolyte secondary battery having a small initial irreversible capacity and excellent in high rate discharge characteristics, low temperature discharge characteristics, charge / discharge cycle characteristics and safety is obtained. ing.

なお、下記特許文献２に開示されている特定の物理特性を有する大粒径の等方性人造黒鉛粒子Ａは、バルクメソフェーズピッチを粉砕して作製した基材と、軟化状態にあるピッチ及び／又は熱硬化性樹脂とを混練・造粒し、得られた造粒物を７００〜１５００℃で炭素化し、更に２５００〜３０００℃で黒鉛化することによってのみ得られている。   The large-diameter isotropic artificial graphite particles A having specific physical properties disclosed in the following Patent Document 2 include a base material prepared by pulverizing a bulk mesophase pitch, a pitch in a softened state, and / or Or it knead | mixes and granulates with a thermosetting resin, and the obtained granulated material is carbonized at 700-1500 degreeC, and also is obtained only by graphitizing at 2500-3000 degreeC.

更に、下記特許文献３には、特定の物理特性を有し、高結晶性構造を有する黒鉛材料の表面を非黒鉛質炭素で被覆することにより得られる平均粒径が１０〜３０μｍ、比表面積が５ｍ２／ｇ以下の被覆炭素材料Ａと、特定の物理特性を有し、平均粒径が１０〜３０μｍ、比表面積が７ｍ２／ｇ以下である黒鉛材料Ｂを混合した混合物からなり、前記黒鉛材料Ｂの含有割合が２０〜８０ｗｔ％である負極活物質を用いた非水電解質二次電池の発明が開示されている。下記特許文献３に開示されている発明によれば、室温及び低温における充放電サイクル特性に優れた非水電解質二次電池が得られるとされている。 Further, Patent Document 3 below has an average particle size of 10 to 30 μm and a specific surface area obtained by coating the surface of a graphite material having specific physical characteristics and a highly crystalline structure with non-graphitic carbon. A mixture of a coated carbon material A of 5 m 2 / g or less and a graphite material B having specific physical characteristics, an average particle size of 10 to 30 μm, and a specific surface area of 7 m 2 / g or less, An invention of a nonaqueous electrolyte secondary battery using a negative electrode active material in which the content ratio of material B is 20 to 80 wt% is disclosed. According to the invention disclosed in the following Patent Document 3, a nonaqueous electrolyte secondary battery excellent in charge / discharge cycle characteristics at room temperature and low temperature is obtained.

特開平１１− ２５９８１号公報Japanese Patent Laid-Open No. 11-25981 特開２００４−１２９７１３号公報JP 2004-129713 A 特開２００１−１８５１４７号公報JP 2001-185147 A

従来から使用されている負極活物質としての炭素材料は、高密度領域において充放電を繰り返すことで、負極活物質表面にリチウム金属が析出し、液枯れや導電パスの遮断によるサイクル特性の低下といった劣化が生じる。また、負極活物質としての炭素材料は、粒子径を大きくすることで初期効率が向上し、粒子径を小さくすることで反応面積の増大によって負荷特性が向上することが知られている。   Conventionally used carbon materials as the negative electrode active material are repeatedly charged and discharged in a high density region, so that lithium metal is deposited on the surface of the negative electrode active material, resulting in deterioration of cycle characteristics due to liquid drainage or interruption of the conductive path. Deterioration occurs. In addition, it is known that the carbon material as the negative electrode active material is improved in initial efficiency by increasing the particle size and is improved in load characteristics by increasing the reaction area by decreasing the particle size.

しかし、負極活物質として大粒径の炭素材料を単独で使用した場合は、充放電による負極活物質の膨張・収縮の繰り返しにより導電パスが遮断され、サイクル特性が悪化する。また、負極活物質として小粒径の炭素材料を単独で使用した場合は、電解液との反応が過剰となり、液枯れ・ガス発生を引き起こすことで、やはりサイクル特性が劣化してしまう。   However, when a carbon material having a large particle size is used alone as the negative electrode active material, the conductive path is blocked by repeated expansion and contraction of the negative electrode active material due to charge and discharge, and the cycle characteristics deteriorate. In addition, when a carbon material having a small particle size is used alone as the negative electrode active material, the reaction with the electrolytic solution becomes excessive, causing liquid drainage and gas generation, resulting in deterioration of cycle characteristics.

これらの問題点を解決するためには、大粒径の炭素材料と小粒径の炭素材料を混合して用いることが考えられる。ところが、上記特許文献１に開示されている発明では、単に負極活物質材料として大粒径の炭素材料と小粒径の炭素材料とを混合して用いることにより負極活物質の充填密度を大きくして放電容量を高めているが、放電容量以外の電池特性については何も考慮されていない。また、上記特許文献２に開示されている発明では、負極活物質として特定の物理特性を有する大粒径の等方性人造黒鉛粒子と小粒径の球状黒鉛粒子とを用いているが、特に特定の物理特性を有する大粒径の等方性人造黒鉛粒子の製造工程が複雑であり、高価となるという問題点が存在する。   In order to solve these problems, it is conceivable to use a mixture of a carbon material having a large particle size and a carbon material having a small particle size. However, in the invention disclosed in Patent Document 1, the packing density of the negative electrode active material is increased by simply using a mixture of a large particle size carbon material and a small particle size carbon material as the negative electrode active material. However, no consideration is given to battery characteristics other than the discharge capacity. In the invention disclosed in Patent Document 2, isotropic artificial graphite particles having a large particle size and spherical graphite particles having a small particle size having specific physical characteristics are used as the negative electrode active material. There is a problem that the manufacturing process of isotropic artificial graphite particles having a large particle size having specific physical characteristics is complicated and expensive.

なお、上記特許文献３に開示されている発明では、実質的に同粒径範囲で、特定の物理特性を有する天然黒鉛の表面を非晶質炭素により被覆したものと被覆しないものとを混合した負極活物質を用いているが、室温及び低温における充放電サイクル特性以外の電池特性については何も考慮されていない。   In the invention disclosed in Patent Document 3 above, the surface of natural graphite having specific physical characteristics in the substantially same particle diameter range is mixed with the one not coated with amorphous carbon. Although the negative electrode active material is used, no consideration is given to battery characteristics other than charge / discharge cycle characteristics at room temperature and low temperature.

上述のように、従来から非水電解質二次電の電池特性を改善すべく種々の改良が行われているが、非水電解質二次電池の用途の拡大に伴い、更なる電池特性の向上が望まれている。本発明者らは、上記のような従来技術に関する知見に基づき鋭意研究を重ねた結果、負極活物質としての炭素材料としてそれぞれ所定の粒子径及びＢＥＴ比表面積を持つ大粒子炭素材料及び小粒子炭素材料を所定の割合で混合することにより、負極極板の充填性が向上し、初期効率及びサイクル特性に優れた負極極板が得られることを見出し、本発明を完成させるに至ったのである。   As described above, various improvements have been made to improve the battery characteristics of nonaqueous electrolyte secondary batteries. However, with the expansion of applications of nonaqueous electrolyte secondary batteries, further improvements in battery characteristics have been made. It is desired. As a result of intensive studies based on the above-described knowledge about the prior art, the present inventors have found that as a carbon material as a negative electrode active material, a large particle carbon material and a small particle carbon having a predetermined particle diameter and a BET specific surface area, respectively. By mixing the materials at a predetermined ratio, it was found that the filling property of the negative electrode plate was improved, and a negative electrode plate excellent in initial efficiency and cycle characteristics was obtained, and the present invention was completed.

すなわち、本発明は、負極極板密度が高密度領域であってもリチウムの析出が抑えられ、液枯れや導電パスの遮断が起こり難く、初期効率及びサイクル特性に優れた非水電解質二次電池を提供することを目的とする。   That is, the present invention is a non-aqueous electrolyte secondary battery that is excellent in initial efficiency and cycle characteristics, in which lithium deposition is suppressed even when the negative electrode plate density is in a high density region, liquid drainage and conduction path blocking are unlikely to occur. The purpose is to provide.

上記目的を達成するため、本発明の非水電解質二次電池は、正極活物質を有する正極と、負極活物質を有する負極と、非水溶媒と電解質塩を有する非水電解質と、を備える非水電解質二次電池において、前記負極活物質は、粒度分布でメディアン径が３０〜５０μｍ、比表面積が２．０〜４．５ｍ２／ｇである大粒子炭素材料と、粒度分布でメディアン径が９〜１３μｍ、比表面積が６．５〜７．８ｍ２／ｇである小粒子炭素材料と、を大粒子炭素材料／小粒子炭素材料＝８／２〜６／４の割合で混合した混合物であることを特徴とする In order to achieve the above object, a nonaqueous electrolyte secondary battery of the present invention includes a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a nonaqueous electrolyte having a nonaqueous solvent and an electrolyte salt. In the water electrolyte secondary battery, the negative electrode active material includes a large particle carbon material having a median diameter of 30 to 50 μm and a specific surface area of 2.0 to 4.5 m 2 / g in a particle size distribution, and a median diameter in a particle size distribution. 9-13 μm, a small particle carbon material having a specific surface area of 6.5-7.8 m 2 / g, and a mixture of large particle carbon material / small particle carbon material = 8 / 2-6 / 4 It is characterized by being

本発明の非水電解質二次電池では、負極活物質として、粒度分布でメディアン径が３０〜５０μｍ、比表面積が２．０〜４．５ｍ２／ｇである大粒子炭素材料と、粒度分布でメディアン径が９〜１３μｍ、比表面積が６．５〜７．８ｍ２／ｇである小粒子炭素材料と、を大粒子炭素材料／小粒子炭素材料＝８／２〜６／４の割合で混合した混合物を用いている。なお、本発明における「メディアン径」とは、相対粒子量が５０％となる粒径を表し、上述したＤ５０と同意である。 In the nonaqueous electrolyte secondary battery of the present invention, as the negative electrode active material, a large particle carbon material having a median diameter of 30 to 50 μm and a specific surface area of 2.0 to 4.5 m 2 / g as a negative electrode active material, and a particle size distribution A small particle carbon material having a median diameter of 9 to 13 μm and a specific surface area of 6.5 to 7.8 m 2 / g is mixed at a ratio of large particle carbon material / small particle carbon material = 8/2 to 6/4. The mixture is used. The “median diameter” in the present invention represents a particle diameter at which the relative particle amount is 50%, and is the same as D 50 described above.

本発明で使用している大粒子炭素材料のメディアン径は３０〜５０μｍである。一方、上記引用文献１にかかる発明で使用されている大粒子炭素材料の平均粒径は２５．８μｍ（粗粒の場合）ないし１２．１μｍ（中粒の場合）であり、上記引用文献２にかかる発明で使用されている大粒子炭素材料のメディアン径は１５〜３０μｍであり、上記引用文献３にかかる発明で使用されている炭素材料の平均粒径は１０〜３０μｍである。従って、本発明で使用している大粒子炭素材料のメディアン径は従来例のものよりも大きくなっている。   The median diameter of the large particle carbon material used in the present invention is 30 to 50 μm. On the other hand, the average particle size of the large particle carbon material used in the invention according to the above cited reference 1 is 25.8 μm (in the case of coarse particles) to 12.1 μm (in the case of medium particles). The median diameter of the large particle carbon material used in the invention is 15 to 30 μm, and the average particle diameter of the carbon material used in the invention according to the above cited reference 3 is 10 to 30 μm. Therefore, the median diameter of the large particle carbon material used in the present invention is larger than that of the conventional example.

また、本発明で使用している大粒子炭素材料のＢＥＴ比表面積は２．０〜４．５ｍ２／ｇである。一方、上記引用文献１にかかる発明で使用されている大粒子炭素材料のＢＥＴ比表面積は３．２１ｍ２／ｇであり、上記引用文献２にかかる発明で使用されている大粒子炭素材料のＢＥＴ比表面積は１ｍ２／ｇ以下であり、更に、上記引用文献３にかかる発明で使用されている炭素材料の比表面積は５ｍ２／ｇ以下及び７ｍ２／ｇ以下である。従って、本発明で使用している大粒子炭素材料のＢＥＴ比表面積は、上記特許文献１に開示されているものとは実質的に同一であるが、上記特許文献２及び３に開示されているものとは相違している。 The BET specific surface area of the large particle carbon material used in the present invention is 2.0 to 4.5 m 2 / g. On the other hand, the BET specific surface area of the large particle carbon material used in the invention according to the cited document 1 is 3.21 m 2 / g, and the BET of the large particle carbon material used in the invention according to the cited document 2 is used. the specific surface area not more than 1 m 2 / g, further, the specific surface area of the carbon material used in the invention according to the cited document 3 is less than 5 m 2 / g or less and 7m 2 / g. Therefore, the BET specific surface area of the large particle carbon material used in the present invention is substantially the same as that disclosed in Patent Document 1, but is disclosed in Patent Documents 2 and 3 above. It is different from the one.

なお、本発明で使用している小粒子炭素材料のメディアン径は９〜１３μｍである。一方、上記引用文献１にかかる発明で使用されている小粒子炭素材料の平均粒径は１２．１μｍ（中粒の場合）ないし５．１μｍ（細粒の場合）であり、上記引用文献２にかかる発明で使用されている小粒子炭素材料のメディアン径が５〜１５μｍであり、上記引用文献３にかかる発明で使用されている炭素材料の平均粒径が１０〜３０μｍである。従って、本発明で使用している小粒子炭素材料のメディアン径はこれらの従来例のものと実質的に同等となっている。   The median diameter of the small particle carbon material used in the present invention is 9 to 13 μm. On the other hand, the average particle size of the small particle carbon material used in the invention according to the above cited reference 1 is 12.1 μm (in the case of medium grains) to 5.1 μm (in the case of fine grains). The median diameter of the small particle carbon material used in this invention is 5 to 15 μm, and the average particle diameter of the carbon material used in the invention according to the above cited reference 3 is 10 to 30 μm. Therefore, the median diameter of the small particle carbon material used in the present invention is substantially equal to those of these conventional examples.

また、本発明で使用している小粒子炭素材料のＢＥＴ比表面積は６．５〜７．８ｍ２／ｇである。一方、上記引用文献１にかかる発明で使用されている小粒子炭素材料のＢＥＴ比表面積は２．９５ｍ２／ｇ（中粒の場合）又は５．２４ｍ２／ｇ（細粒の場合）であり、上記引用文献２にかかる発明で使用されている小粒子炭素材料のＢＥＴ比表面積は８ｍ２／ｇ以下であり、更に、上記引用文献３にかかる発明で使用されている炭素材料の比表面積は５ｍ２／ｇ以下及び７ｍ２／ｇ以下である。従って、本発明で使用している小粒子炭素材料のＢＥＴ比表面積は少なくとも従来例のものと実質的に同等となっている。 Further, BET specific surface area of small particles of carbon material used in the present invention is 6.5~7.8m 2 / g. On the other hand, BET specific surface area of small particles of carbon material used in the invention according to the cited document 1 (in the case of medium grain) 2.95m 2 / g or 5.24m be 2 / g (in the case of fine granules) The BET specific surface area of the small particle carbon material used in the invention according to the above cited reference 2 is 8 m 2 / g or less, and the specific surface area of the carbon material used in the invention according to the above cited reference 3 is 5 m 2 / g or less and 7 m 2 / g or less. Therefore, the BET specific surface area of the small particle carbon material used in the present invention is at least substantially equal to that of the conventional example.

このように、本発明の非水電解質二次電池は、大粒子炭素材料のメディアン径が従来のものよりも大きいものを使用することにより、その他の物性が従来例のものと同等であっても、以下に各種実施例及び比較例によって説明するように、初期効率及びサイクル特性に優れた非水電解質二次電池が得られるようになる。   Thus, the non-aqueous electrolyte secondary battery of the present invention uses a large particle carbon material having a median diameter larger than that of the conventional one, so that other physical properties are equivalent to those of the conventional example. As will be described below with reference to various examples and comparative examples, a nonaqueous electrolyte secondary battery having excellent initial efficiency and cycle characteristics can be obtained.

なお、本発明の非水電解質二次電池においては、大粒子炭素材料のメディアン径が３０μｍ未満では、比表面積が２．０〜４．５ｍ２／ｇの範囲内に入っていても、初期効率及び容量維持率ともに小さくなるので、好ましくない。同じく、大粒子炭素材料のメディアン径が５０μｍを超えると、初期効率は良好であるが、容量維持率が低下し出すので、好ましくない。 In the nonaqueous electrolyte secondary battery of the present invention, when the median diameter of the large particle carbon material is less than 30 μm, even if the specific surface area is within the range of 2.0 to 4.5 m 2 / g, the initial efficiency In addition, both the capacity retention ratio and the capacity retention ratio are not preferable. Similarly, if the median diameter of the large particle carbon material exceeds 50 μm, the initial efficiency is good, but the capacity retention rate starts to decrease, which is not preferable.

また、本発明の非水電解質二次電池においては、前記大粒子炭素材料及び小粒子炭素材料は、天然黒鉛からなることが好ましい。   In the nonaqueous electrolyte secondary battery of the present invention, the large particle carbon material and the small particle carbon material are preferably made of natural graphite.

本発明で使用する大粒子炭素材料及び小粒子炭素材料は、天然黒鉛を粉砕した後に分粒し、適宜所定の粒径範囲のものを所定のメディアン径及び比表面積となるように混合することによって容易に得ることができる。   The large particle carbon material and the small particle carbon material used in the present invention are pulverized after pulverizing natural graphite and appropriately mixed in a predetermined particle size range so as to have a predetermined median diameter and specific surface area. Can be easily obtained.

黒鉛系炭素材料は従来から安全性が高く、かつ、高容量であるために広く用いられている負極活物質材料である。本発明の非水電解質二次電池においても、黒鉛系炭素材料を負極活物質として用いているので、上記効果を奏しながらも、安全性が高く高容量な非水電解質二次電池が得られる。   Graphite-based carbon material is a negative electrode active material that has been widely used because of its high safety and high capacity. Also in the nonaqueous electrolyte secondary battery of the present invention, since the graphite-based carbon material is used as the negative electrode active material, a non-aqueous electrolyte secondary battery with high safety and high capacity can be obtained while exhibiting the above effects.

また、本発明の非水電解質二次電池で使用し得る正極活物質としては、上述のような従来から普通に使用されているリチウムイオンを可逆的に吸蔵・放出することが可能なＬｉｘＭｙＯ２（ただし、ＭはＣｏ、Ｎｉ、Ｍｎの少なくとも１種である）で表されるリチウム遷移金属複合酸化物、すなわち、ＬｉＣｏＯ２、ＬｉＮｉＯ２、ＬｉＮｉｘＣｏ１−ｘＯ２（ｘ＝０．０１〜０．９９）、ＬｉＭｎＯ２、ＬｉＭｎ２Ｏ４、ＬｉＣｏｘＭｎｙＮｉｚＯ２（ｘ＋ｙ＋ｚ＝１）又はＬｉＦｅＰＯ４などを一種単独もしくは複数種を混合して用いることができる。 Moreover, as a positive electrode active material which can be used in the nonaqueous electrolyte secondary battery of the present invention, LixMyO 2 (which can reversibly occlude / release lithium ions that have been conventionally used as described above). However, M is a lithium transition metal complex oxide represented by Co, Ni, Mn), that is, LiCoO 2 , LiNiO 2 , LiNixCo 1-x O 2 (x = 0.01-0. 99), LiMnO 2 , LiMn 2 O 4 , LiCo x Mn y Ni z O 2 (x + y + z = 1), or LiFePO 4 can be used singly or in combination.

また、本発明の非水電解質二次電池で使用し得る非水溶媒（有機溶媒）としては、カーボネート類、ラクトン類、エーテル類、エステル類などを使用することができ、これら溶媒の２種類以上を混合して用いることもできる。これらの中では、特に誘電率が大きく、非水電解液のイオン伝導度が大きいカーボネート類が好ましい。   Further, as the non-aqueous solvent (organic solvent) that can be used in the non-aqueous electrolyte secondary battery of the present invention, carbonates, lactones, ethers, esters and the like can be used, and two or more of these solvents can be used. Can also be used in combination. Among these, carbonates having a large dielectric constant and a high ionic conductivity of the nonaqueous electrolytic solution are preferable.

具体例としては、エチレンカーボネート（ＥＣ）、プロピレンカーボネート（ＰＣ）、ブチレンカーボネート（ＢＣ）、ビニレンカーボネート（ＶＣ）、シクロペンタノン、スルホラン、３−メチルスルホラン、２、４−ジメチルスルホラン、３−メチル−１，３オキサゾリジン−２−オン、ジメチルカーボネート（ＤＭＣ）、メチルエチルカーボネート（ＭＥＣ）、ジエチルカーボネート（ＤＥＣ）、メチルプロピルカーボネート、メチルブチルカーボネート、エチルプロピルカーボネート、エチルブチルカーボネート、ジプロピルカーボネート、γ−ブチロラクトン、γ−バレロラクトン、１、２−ジメトキシエタン、テトラヒドロフラン、２−メチルテトラヒドロフラン、１、３−ジオキソラン、酢酸メチル、酢酸エチル、１、４−ジオキサンなどを挙げることができる。   Specific examples include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), cyclopentanone, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, 3-methyl. -1,3-oxazolidine-2-one, dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), methyl propyl carbonate, methyl butyl carbonate, ethyl propyl carbonate, ethyl butyl carbonate, dipropyl carbonate, γ -Butyrolactone, γ-valerolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, ethyl acetate, 1,4-dio Xanthan can be mentioned.

なお、本発明における非水電解質の溶質としては、非水電解質二次電池において一般に溶質として用いられるリチウム塩を用いることができる。このようなリチウム塩としては、ＬｉＰＦ６、ＬｉＢＦ４、ＬｉＣＦ３ＳＯ３、ＬｉＮ（ＣＦ３ＳＯ２）２、ＬｉＮ（Ｃ２Ｆ５ＳＯ２）２、ＬｉＮ（ＣＦ３ＳＯ２）（Ｃ４Ｆ９ＳＯ２）、ＬｉＣ（ＣＦ３ＳＯ２）３、ＬｉＣ（Ｃ２Ｆ５ＳＯ２）３、ＬｉＡｓＦ６、ＬｉＣｌＯ４、Ｌｉ２Ｂ１０Ｃｌ１０、Ｌｉ２Ｂ１２Ｃｌ１２など及びそれらの混合物が例示される。これらの中でも、ＬｉＰＦ６（ヘキサフルオロリン酸リチウム）が特に好ましい。前記非水溶媒に対する溶質の溶解量は、０．５〜２．０ｍｏｌ／Ｌとするのが好ましい。 In addition, as a solute of the nonaqueous electrolyte in the present invention, a lithium salt generally used as a solute in a nonaqueous electrolyte secondary battery can be used. Such lithium salts include LiPF 6 , LiBF 4 , LiCF 3 SO 3 , LiN (CF 3 SO 2 ) 2 , LiN (C 2 F 5 SO 2 ) 2 , LiN (CF 3 SO 2 ) (C 4 F 9 SO 2 ), LiC (CF 3 SO 2 ) 3 , LiC (C 2 F 5 SO 2 ) 3 , LiAsF 6 , LiClO 4 , Li 2 B 10 Cl 10 , Li 2 B 12 Cl 12 , and mixtures thereof Illustrated. Among these, LiPF 6 (lithium hexafluorophosphate) is particularly preferable. The amount of solute dissolved in the non-aqueous solvent is preferably 0.5 to 2.0 mol / L.

以下、本願発明を実施するための形態を実施例及び比較例を用いて詳細に説明する。ただし、以下に示す実施例は、本発明の技術思想を具体化するための非水電解質二次電池の一例を例示するものであって、本発明をこの実施例に限定することを意図するものではなく、本発明は特許請求の範囲に示した技術思想を逸脱することなく種々の変更を行ったものにも均しく適用し得るものである。   Hereinafter, the form for implementing this invention is demonstrated in detail using an Example and a comparative example. However, the examples shown below are examples of non-aqueous electrolyte secondary batteries for embodying the technical idea of the present invention, and are intended to limit the present invention to these examples. Rather, the present invention can be equally applied to a variety of modifications without departing from the technical idea shown in the claims.

最初に、実施例１〜６及び比較例１〜１２に共通する非水電解質二次電池の具体的製造方法について説明する。
［正極極板の作製］
正極活物質としてのコバルト酸リチウム（ＬｉＣｏＯ２）、導電剤としての黒鉛粉末、結着剤としてのポリフッ化ビニリデン（ＰＶｄＦ）粉末を、９５：３：２（質量比）の割合で均一に混合した後、Ｎ−メチル−２−ピロリドン（ＮＭＰ）に分散させて正極活物質スラリーを調製した。この正極活物質スラリーを厚さ１５μｍのアルミホイル製の正極集電体の両面にドクターブレード法により均一な厚みで塗布した後、乾燥機内に通してＮＭＰを乾燥除去することで、正極集電体の両面に正極活物質層を形成した。その後、この正極極板をロールプレス機を用いて圧延し、所定の大きさに切り出して、実施例１〜６及び比較例１〜１２で共通して使用する各正極極板を作成した。 Initially, the specific manufacturing method of the nonaqueous electrolyte secondary battery common to Examples 1-6 and Comparative Examples 1-12 is demonstrated.
[Preparation of positive electrode plate]
Lithium cobaltate (LiCoO 2 ) as a positive electrode active material, graphite powder as a conductive agent, and polyvinylidene fluoride (PVdF) powder as a binder were uniformly mixed at a ratio of 95: 3: 2 (mass ratio). Thereafter, a positive electrode active material slurry was prepared by dispersing in N-methyl-2-pyrrolidone (NMP). The positive electrode active material slurry was applied to both surfaces of a positive electrode current collector made of aluminum foil having a thickness of 15 μm with a uniform thickness by a doctor blade method, and then passed through a dryer to dry and remove NMP. A positive electrode active material layer was formed on both sides. Then, this positive electrode plate was rolled using a roll press machine, cut into a predetermined size, and each positive electrode plate used in common with Examples 1-6 and Comparative Examples 1-12 was created.

［負極極板の作製］
負極活物質としての炭素材料には、それぞれ所定のメディアン径を持つ大粒子黒鉛及び小粒子黒鉛を所定の割合（質量比）で混合したものを使用し、この炭素材料混合物と、増粘剤としてのカルボキシメチルセルロース（ＣＭＣ）と、結着剤としてのスチレン−ブタジエンゴム（ＳＢＲ）とを、９５：３：２（質量比）の割合で均一に混合した後、水に分散させて負極活物質スラリーを調製した。この負極活物質スラリーを厚さ１０μｍの銅製の負極集電体の両面に、ドクターブレード法により均一な厚みで塗布した後、乾燥機内に通して水を乾燥除去することで、負極集電体の両面に負極活物質層を形成した。その後、この負極極板をロールプレス機を用いて充填密度が１．７０ｇ／ｃｍ３となるように圧延し、所定の大きさに切り出して、実施例１〜６及び比較例１〜１２で使用するそれぞれの負極極板を作成した。なお、正極と負極の充電容量比は、充電時の電池電圧を４．２Ｖとしたときに、負極充電容量／正極充電容量＝１．１となるように、調整した。 [Production of negative electrode plate]
For the carbon material as the negative electrode active material, a mixture of large particle graphite and small particle graphite each having a predetermined median diameter in a predetermined ratio (mass ratio) is used. Carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) as a binder were uniformly mixed at a ratio of 95: 3: 2 (mass ratio) and then dispersed in water to prepare a negative electrode active material slurry. Was prepared. The negative electrode active material slurry was applied to both surfaces of a copper negative electrode current collector having a thickness of 10 μm with a uniform thickness by a doctor blade method, and then passed through a dryer to dry and remove water, thereby removing the negative electrode current collector. Negative electrode active material layers were formed on both sides. Thereafter, this negative electrode plate was rolled using a roll press so that the packing density was 1.70 g / cm 3 , cut into a predetermined size, and used in Examples 1 to 6 and Comparative Examples 1 to 12. Each negative electrode plate was prepared. The charge capacity ratio between the positive electrode and the negative electrode was adjusted so that the negative electrode charge capacity / the positive electrode charge capacity = 1.1 when the battery voltage during charging was 4.2 V.

［巻回電極体の作製］
上記のようにして作製された正極極板と各負極極板とセパレータとしてのポリエチレン製微多孔膜とを、巻き取り機により巻回し、巻回終端部に絶縁性の巻き止めテープを取り付け、プレスすることによって、実施例１〜６及び比較例１〜１２で使用する各偏平状の巻回電極体をそれぞれ作製した。 [Production of wound electrode body]
The positive electrode plate manufactured as described above, each negative electrode plate, and a polyethylene microporous membrane as a separator are wound by a winder, and an insulating winding tape is attached to the winding end portion, and the press Thus, each flat wound electrode body used in Examples 1 to 6 and Comparative Examples 1 to 12 was produced.

［非水電解質の調製］
非水電解質としては、エチレンカーボネ一ト、プロピレンカーボネート、エチルメチルカーボネートを、１０：１０：８０（１気圧、２５℃での体積比）となるよう混合した非水溶媒に、電解質塩としての六フッ化燐酸リチウム（ＬｉＰＦ６）を１ｍｏｌ／Ｌとなるように溶解させ、実施例１〜６及び比較例１〜１２で共通して使用する電解質とした。 [Preparation of non-aqueous electrolyte]
As a non-aqueous electrolyte, ethylene carbonate, propylene carbonate, and ethyl methyl carbonate are mixed in a non-aqueous solvent mixed at 10:10:80 (1 atm, volume ratio at 25 ° C.) as an electrolyte salt. Lithium hexafluorophosphate (LiPF 6 ) was dissolved so as to be 1 mol / L to obtain an electrolyte commonly used in Examples 1 to 6 and Comparative Examples 1 to 12.

［電池の作製］
上記のようにして得られた巻回電極体と非水電解質とを角形外装缶内に挿入し、外装缶の開口部に封口板を嵌め合わせてレーザー溶接することにより、実施例１〜６及び比較例１〜１２で使用する厚み４．３ｍｍ×幅３４ｍｍ×高さ４３ｍｍの角形の非水電解質二次電池をそれぞれ作製した。得られた各非水電解質二次電池の公称容量は８００ｍＡｈである。 [Production of battery]
By inserting the wound electrode body and the nonaqueous electrolyte obtained as described above into a rectangular outer can, fitting a sealing plate into the opening of the outer can and laser welding, Examples 1 to 6 and Square non-aqueous electrolyte secondary batteries each having a thickness of 4.3 mm, a width of 34 mm, and a height of 43 mm used in Comparative Examples 1 to 12 were produced. The nominal capacity of each obtained nonaqueous electrolyte secondary battery is 800 mAh.

以上のようにして作製した、実施例１〜６及び比較例１〜１２のそれぞれの負極極板を用いて作製された非水電解質二次電池について、以下に示す各試験をそれぞれ実施した。   Each test shown below was implemented about the nonaqueous electrolyte secondary battery produced using each negative electrode plate of Examples 1-6 and Comparative Examples 1-12 produced as mentioned above.

［初期効率の測定］
実施例１〜６及び比較例１〜１２の各非水電解質二次電池を、２５℃に維持された恒温槽中において、０．２Ｉｔ（１６０ｍＡ）の定電流で電池電圧が４．２Ｖに達するまで充電し、電池電圧が４．２Ｖに達した後は、更に、４．２Ｖの定電圧で電流値が１／５０Ｉｔ（１６ｍＡ）になるまで充電した。このときの全充電容量を初期充電容量として用いた。次いで、０．２Ｉｔの定電流で電池電圧が２．７５Ｖになるまで放電し、このときの放電容量を初期放電容量として求めた。そして、以下の計算式により初期効率を求めた。
初期効率（％）＝（初期放電容量／初期充電容量）×１００ [Measurement of initial efficiency]
In each of the nonaqueous electrolyte secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 12, the battery voltage reaches 4.2 V at a constant current of 0.2 It (160 mA) in a thermostat maintained at 25 ° C. After the battery voltage reached 4.2V, the battery was further charged with a constant voltage of 4.2V until the current value reached 1/50 It (16 mA). The total charge capacity at this time was used as the initial charge capacity. Next, the battery was discharged at a constant current of 0.2 It until the battery voltage reached 2.75 V, and the discharge capacity at this time was determined as the initial discharge capacity. And the initial efficiency was calculated | required with the following formulas.
Initial efficiency (%) = (initial discharge capacity / initial charge capacity) × 100

［容量維持率］
上述のようにして初期効率を測定したそれぞれの電池について、１Ｉｔ（８００ｍＡ）の定電流で電池電圧が４．２Ｖに達するまで充電し、電池電圧が４．２Ｖに達した後は、更に、４．２Ｖの定電圧で電流値が１／５０Ｉｔ（１６ｍＡ）になるまで充電した後、１Ｉｔの定電流で電池電圧が２．７５Ｖになるまで放電し、このときの放電容量を１サイクル目の放電容量として求めた。この充放電サイクルを１００回繰り返して１００回目の放電容量を求め、以下の計算式に基づいて１００サイクル目の容量維持率を求めた。
容量維持率（％）
＝（１００サイクル目の放電容量／１サイクル目の放電容量）×１００ [Capacity maintenance rate]
For each battery whose initial efficiency was measured as described above, the battery was charged at a constant current of 1 It (800 mA) until the battery voltage reached 4.2 V. After the battery voltage reached 4.2 V, the battery was further charged with 4 The battery is charged until the current value becomes 1/50 It (16 mA) at a constant voltage of 2 V, and then discharged until the battery voltage becomes 2.75 V at a constant current of 1 It. The discharge capacity at this time is discharged in the first cycle. Calculated as capacity. This charge / discharge cycle was repeated 100 times to determine the discharge capacity at the 100th time, and the capacity retention rate at the 100th cycle was determined based on the following calculation formula.
Capacity maintenance rate (%)
= (Discharge capacity at the 100th cycle / discharge capacity at the first cycle) × 100

［実施例１〜３、比較例１〜６］
実施例１〜３及び比較例１〜６としては、天然黒鉛より作製した小粒子炭素材料のメディアン径を１０μｍ一定、比表面積を７．２ｍ２／ｇ一定とし、天然黒鉛より作製した大粒子炭素材料と小粒子炭素材料の混合比（質量比）を８：２一定とし、大粒子炭素材料のメディアン径及び比表面積を種々変更して作製したそれぞれの非水電解質二次電池を用いて初期効率及び容量維持率を測定した。結果を各大粒子炭素材料のメディアン径及び比表面積と共に表１に纏めて示した。 [Examples 1 to 3, Comparative Examples 1 to 6]
In Examples 1 to 3 and Comparative Examples 1 to 6, a small particle carbon material prepared from natural graphite has a median diameter of 10 μm constant, a specific surface area of 7.2 m 2 / g constant, and a large particle carbon prepared from natural graphite. Initial efficiency using each non-aqueous electrolyte secondary battery produced by varying the median diameter and specific surface area of the large-particle carbon material with the mixing ratio (mass ratio) of the material and small-particle carbon material constant at 8: 2. And the capacity maintenance rate was measured. The results are shown in Table 1 together with the median diameter and specific surface area of each large particle carbon material.

Figure 2010176973
Figure 2010176973

表１に示した結果から以下のことが分かる。すなわち、大粒子炭素材料のメディアン径が１５μｍ〜６０μｍへと大きくなっていくと、大粒子炭素材料のメディアン径に比例して初期効率が上昇していく。一方、大粒子炭素材料のメディアン径が２０μｍと同一であるが、比表面積が０．８ｍ２／ｇ及び５．２ｍ２／ｇである比較例２及び比較例３では、初期効率及び容量維持率ともに実質的に同一となっている。また、大粒子炭素材料のメディアン径が３０μｍと同一であるが、比表面積が０．７ｍ２／ｇ及び４．５ｍ２／ｇである比較例４及び実施例１では、初期効率はほぼ同一であるが、比較例４では容量維持率が大きく低下している。更に、大粒子炭素材料のメディアン径が４０μｍと同一であるが、比表面積が１．５ｍ２／ｇ及び３．２ｍ２／ｇである比較例５及び実施例２では、初期効率は実質的に同一であるが、比較例５では容量維持率が大きく低下している。なお、大粒子メディアン径が６０μｍと大きい比較例６では、比表面積は１．６ｍ２／ｇであり、初期効率は最も良好であるが、容量維持率は大きく低下している。 From the results shown in Table 1, the following can be understood. That is, as the median diameter of the large particle carbon material increases from 15 μm to 60 μm, the initial efficiency increases in proportion to the median diameter of the large particle carbon material. On the other hand, in Comparative Example 2 and Comparative Example 3 in which the median diameter of the large-particle carbon material is the same as 20 μm but the specific surface areas are 0.8 m 2 / g and 5.2 m 2 / g, the initial efficiency and capacity retention rate Both are substantially the same. In addition, although the median diameter of the large particle carbon material is the same as 30 μm, in Comparative Example 4 and Example 1 in which the specific surface areas are 0.7 m 2 / g and 4.5 m 2 / g, the initial efficiency is almost the same. However, in Comparative Example 4, the capacity retention rate is greatly reduced. Furthermore, in Comparative Example 5 and Example 2 in which the median diameter of the large particle carbon material is the same as 40 μm, but the specific surface areas are 1.5 m 2 / g and 3.2 m 2 / g, the initial efficiency is substantially Although the same, in Comparative Example 5, the capacity retention rate is greatly reduced. In Comparative Example 6 where the large particle median diameter is as large as 60 μm, the specific surface area is 1.6 m 2 / g and the initial efficiency is the best, but the capacity retention ratio is greatly reduced.

そうすると、大粒子炭素材料は、メディアン径が３０μｍ〜５０μｍの範囲及び比表面積が２．０ｍ２／ｇ〜４．５ｍ２／ｇの両条件を満たす場合において、初期効率及び容量維持率共に良好な結果が得られることが分かる。 Then, the large particle carbon material, when the median diameter is in the range and specific surface area of 30μm~50μm both meet the 2.0m 2 /g~4.5m 2 / g, a both initial efficiency and capacity retention good It turns out that a result is obtained.

［実施例４，５及び比較例７〜１０］
実施例４，５及び比較例７〜１０としては、天然黒鉛より作製した大粒子炭素材料のメディアン径を４０μｍ一定、比表面積を３．２ｍ２／ｇ一定とし、大粒子炭素材料と天然黒鉛より作製した小粒子炭素材料の混合比（質量比）を８：２一定とし、小粒子炭素材料のメディアン径及び比表面積を種々変更して作製したそれぞれの非水電解質二次電池を用いて初期効率及び容量維持率を測定した。結果を各小粒子炭素材料のメディアン径及び比表面積と共に表２に纏めて示した。なお、表２には実施例２の結果をも纏めて示してある。 [Examples 4 and 5 and Comparative Examples 7 to 10]
In Examples 4 and 5 and Comparative Examples 7 to 10, the median diameter of a large particle carbon material made from natural graphite is constant at 40 μm, the specific surface area is constant at 3.2 m 2 / g, and the large particle carbon material and natural graphite are used. Initial efficiency using each non-aqueous electrolyte secondary battery produced by changing the median diameter and specific surface area of the small particle carbon material while keeping the mixing ratio (mass ratio) of the produced small particle carbon material constant at 8: 2. And the capacity maintenance rate was measured. The results are shown in Table 2 together with the median diameter and specific surface area of each small particle carbon material. Table 2 also summarizes the results of Example 2.

Figure 2010176973
Figure 2010176973

大粒子炭素材料のメディアン径が４０μｍ一定、比表面積が３．２ｍ２／ｇ一定である実施例２，４，５及び比較例７〜１０共に初期効率は良好な結果が得られている。一方、小粒子炭素材料のメディアン径が５μｍと同一であるが、比表面積が７．３ｍ２／ｇ及び１０．８ｍ２／ｇである比較例７及び比較例８では、初期効率及び容量維持率ともにほぼ同一となっている。また、小粒子炭素材料のメディアン径が１０μｍと同一であるが、比表面積が５．５ｍ２／ｇ及び７．２ｍ２／ｇである比較例９及び実施例２では、比較例９の方が初期効率は優れているが、容量維持率が大きく劣っている。更に、小粒子炭素材料のメディアン径８μｍであり、比表面積が７．８ｍ２／ｇである実施例４、小粒子炭素材料のメディアン径１３μｍであり、比表面積が６．５ｍ２／ｇである実施例５では、良好な容量維持率が得られている。なお、小粒子メディアン径が１５μｍと大きい比較例１０では、比表面積は６．１ｍ２／ｇであり、初期効率は最も良好であるが、容量維持率は大きく低下している。 In Examples 2, 4, 5 and Comparative Examples 7-10 in which the median diameter of the large particle carbon material is constant at 40 μm and the specific surface area is constant at 3.2 m 2 / g, good results are obtained in the initial efficiency. On the other hand, the small but median diameter of the particles of carbon material is identical to the 5 [mu] m, in Comparative Examples 7 and 8 having a specific surface area of 7.3 m 2 / g and 10.8 m 2 / g, initial efficiency and capacity retention rate Both are almost identical. Further, in Comparative Example 9 and Example 2 in which the median diameter of the small particle carbon material is the same as 10 μm but the specific surface areas are 5.5 m 2 / g and 7.2 m 2 / g, Comparative Example 9 is more preferable. The initial efficiency is excellent, but the capacity maintenance rate is greatly inferior. Further, Example 4 in which the median diameter of the small particle carbon material is 8 μm and the specific surface area is 7.8 m 2 / g, the median diameter of the small particle carbon material is 13 μm, and the specific surface area is 6.5 m 2 / g. In Example 5, a good capacity retention rate is obtained. In Comparative Example 10 in which the small particle median diameter is as large as 15 μm, the specific surface area is 6.1 m 2 / g and the initial efficiency is the best, but the capacity retention rate is greatly reduced.

そうすると、小粒子炭素材料は、メディアン径が８μｍ〜１３μｍの範囲及び比表面積が６．５ｍ２／ｇ〜７．８ｍ２／ｇの両条件を満たす場合において、初期効率及び容量維持率共に良好な結果が得られることが分かる。 Then, small particle carbon material, when the median diameter is in the range and specific surface area of 8μm~13μm both meet the 6.5m 2 /g~7.8m 2 / g, both good initial efficiency and capacity retention It turns out that a result is obtained.

［実施例６、比較例１１及び１２］
実施例６、比較例１１及び１２としては、天然黒鉛より作製した大粒子炭素材料のメディアン径を４０μｍ一定、比表面積を３．２ｍ２／ｇ一定とし、天然黒鉛より作製した小粒子炭素材料のメディアン径を１０μｍ一定、比表面積を７．２ｍ２／ｇ一定とし、大粒子炭素材料と小粒子炭素材料の混合比（質量比）を５：５（比較例１１）、６：４（実施例６）及び９：１（比較例１２）と変化させた場合の結果を表３に纏めて示した。なお、表３には大粒子炭素材料と小粒子炭素材料の混合比が８：２である実施例２の結果も纏めて示してある。 [Example 6, Comparative Examples 11 and 12]
Example 6 As Comparative Examples 11 and 12, the median diameter of the large particle carbon material prepared from natural graphite 40μm constant, the specific surface area and 3.2 m 2 / g constant, small particle carbon material prepared from natural graphite The median diameter is constant at 10 μm, the specific surface area is constant at 7.2 m 2 / g, and the mixing ratio (mass ratio) of the large particle carbon material and the small particle carbon material is 5: 5 (Comparative Example 11), 6: 4 (Example) The results when changed to 6) and 9: 1 (Comparative Example 12) are summarized in Table 3. Table 3 also shows the results of Example 2 in which the mixing ratio of the large particle carbon material and the small particle carbon material is 8: 2.

Figure 2010176973
Figure 2010176973

表３に示した結果から、大粒子炭素材料と小粒子炭素材料の混合比は、８：２〜６：４であれば、初期効率及び容量維持率共に良好な結果が得られることが分かる。   From the results shown in Table 3, it can be seen that if the mixing ratio of the large particle carbon material and the small particle carbon material is 8: 2 to 6: 4, good results can be obtained in both the initial efficiency and the capacity retention rate.

以上述べたとおり、負極活物質として、粒度分布でメディアン径が３０〜５０μｍ、比表面積が２．０〜４．５ｍ２／ｇである大粒子炭素材料と、粒度分布でメディアン径が９〜１３μｍ、比表面積が６．５〜７．８ｍ２／ｇである小粒子炭素材料と、を大粒子炭素材料／小粒子炭素材料＝８／２〜６／４の割合で混合した混合物を用いると、初期効率及び容量維持率共に良好な非水電解質二次電池が得られることが分かる。 Above mentioned as hereinbefore, as an anode active material, a median diameter of 30~50μm with a particle size distribution, and large particle carbon material having a specific surface area is 2.0~4.5m 2 / g, the median diameter in particle size distribution 9~13μm When a mixture obtained by mixing a small particle carbon material having a specific surface area of 6.5 to 7.8 m 2 / g and a large particle carbon material / small particle carbon material = 8/2 to 6/4 is used, It can be seen that a non-aqueous electrolyte secondary battery with good initial efficiency and capacity retention rate can be obtained.

Claims (2)

正極活物質を有する正極と、負極活物質を有する負極と、非水溶媒と電解質塩を有する非水電解質と、を備える非水電解質二次電池において、
前記負極活物質は、粒度分布でメディアン径が３０〜５０μｍ、比表面積が２．０〜４．５ｍ２／ｇである大粒子炭素材料と、粒度分布でメディアン径が９〜１３μｍ、比表面積が６．５〜７．８ｍ２／ｇである小粒子炭素材料と、を大粒子炭素材料／小粒子炭素材料＝８／２〜６／４の割合で混合した混合物であることを特徴とする非水電解質二次電池。 In a nonaqueous electrolyte secondary battery comprising a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a nonaqueous electrolyte having a nonaqueous solvent and an electrolyte salt,
The negative electrode active material includes a large particle carbon material having a median diameter of 30 to 50 μm and a specific surface area of 2.0 to 4.5 m 2 / g in a particle size distribution, a median diameter of 9 to 13 μm and a specific surface area of a particle size distribution. A non-particle carbon material having a particle size of 6.5 to 7.8 m 2 / g and a mixture of a large particle carbon material / small particle carbon material = 8/2 to 6/4. Water electrolyte secondary battery. 前記大粒子炭素材料及び小粒子炭素材料は、天然黒鉛からなることを特徴とする請求項１に記載の非水電解質二次電池。   The non-aqueous electrolyte secondary battery according to claim 1, wherein the large particle carbon material and the small particle carbon material are made of natural graphite.
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