JP5573149B2 - Carbon material for negative electrode of lithium secondary battery, negative electrode of lithium secondary battery and lithium secondary battery - Google Patents
Carbon material for negative electrode of lithium secondary battery, negative electrode of lithium secondary battery and lithium secondary battery Download PDFInfo
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Description
本発明は、リチウム２次電池負極用炭素材、リチウム２次電池負極およびリチウム２次電池に関する。 The present invention relates to a carbon material for a lithium secondary battery negative electrode, a lithium secondary battery negative electrode, and a lithium secondary battery.
電子機器類のポータブル化、コードレス化が進むにつれ、リチウム２次電池の小型軽量化、或いは高エネルギー密度化が、より一層求められている。リチウム２次電池を高密度化するため、その負極材料として、リチウムと合金化するケイ素、スズ、ゲルマニウム、マグネシウム、鉛、およびアルミニウムまたはこれらの酸化物もしくは合金等を採用することが知られている。しかしながら、上述のような負極材料は、リチウムイオンを吸蔵する充電時に体積膨張し、反対にリチウムイオンを放出する放電時には体積収縮する。このため充放電サイクルの繰り返しに応じて負極電極の体積が変化し、その結果負極材料が微粉化し、電極から脱落するなどして負極が崩壊することが知られている。 As electronic devices become more portable and cordless, lithium secondary batteries are required to be smaller and lighter or have higher energy density. In order to increase the density of lithium secondary batteries, it is known to employ silicon, tin, germanium, magnesium, lead, and aluminum, or oxides or alloys thereof, which are alloyed with lithium, as the negative electrode material. . However, the negative electrode material as described above expands in volume during charging to occlude lithium ions, and conversely shrinks in volume during discharge to release lithium ions. For this reason, it is known that the volume of the negative electrode changes as the charge / discharge cycle repeats, and as a result, the negative electrode material is pulverized and falls off the electrode, causing the negative electrode to collapse.
上記問題を克服するため、さまざまな手法、手段が検討されているが、リチウム２次電池負極材料に金属、および酸化物を用いた場合に充放電特性を安定化させることは難しいのが現状である。そこで、例えば、特許文献１に開示されているように、充放電サイクル特性に優れたリチウム２次電池用負極材料として、リチウム合金を形成しうる金属の粒子表面を有機物で被覆し、リチウムイオンを吸蔵する際に起こる膨張を抑えるために、金属粒子の１次粒子平均粒径が５００ｎｍ以下、２次粒子平均粒径が１０μｍ以下のものが用いられると記載されている。しかし、用いる金属粒子の１次粒子径、２次粒子径を小さくしたのみでは、充電時のリチウム吸蔵における金属粒子の膨張を抑えることは難しく、また、負極活物質表面近傍の金属粒子の微細化による電極からの滑落も抑制できない。 In order to overcome the above problems, various methods and means have been studied. However, it is difficult to stabilize the charge / discharge characteristics when a metal and an oxide are used as a negative electrode material for a lithium secondary battery. is there. Therefore, for example, as disclosed in Patent Document 1, as a negative electrode material for a lithium secondary battery having excellent charge / discharge cycle characteristics, the surface of metal particles capable of forming a lithium alloy is coated with an organic substance, and lithium ions are formed. In order to suppress expansion that occurs during occlusion, it is described that a metal particle having a primary particle average particle size of 500 nm or less and a secondary particle average particle size of 10 μm or less is used. However, it is difficult to suppress the expansion of metal particles during lithium occlusion during charging only by reducing the primary particle size and secondary particle size of the metal particles used, and the metal particles near the negative electrode active material surface are made finer. Also, sliding from the electrode due to cannot be suppressed.
本発明は、前記従来の技術に鑑み、リチウムイオンの吸蔵・放出が可能なケイ素の合金、酸化物、窒化物もしくは炭化物を含むケイ素含有粒子と樹脂炭素材からなる複合粒子を包囲するナノファイバーおよび／またはナノチューブからなるケイ素含有網状構造体と、該複合粒子中の前記ケイ素含有粒子の２次凝集を抑制することによる、極めて優れた相乗効果により、リチウムイオン２次電池の充放電サイクル特性を一層向上させたリチウム２次電池負極用炭素材、リチウム２次電池負極およびこれを用いたリチウム２次電池を提供することを目的とする。 In view of the prior art, the present invention provides a nanofiber surrounding a composite particle composed of a silicon-containing particle containing an alloy, oxide, nitride, or carbide of silicon capable of occluding and releasing lithium ions and a resin carbon material, and The charge-discharge cycle characteristics of the lithium ion secondary battery are further enhanced by the extremely excellent synergistic effect by suppressing the secondary aggregation of the silicon-containing particles in the composite particles and the silicon-containing network structure composed of nanotubes. An object of the present invention is to provide an improved carbon material for a lithium secondary battery negative electrode, a lithium secondary battery negative electrode, and a lithium secondary battery using the same.
上述の目的は、以下の第（１）項〜第（８）項によって達成される。
（１）１次粒子平均粒径が５ｎｍ以上１．５μｍ以下のリチウムイオンの吸蔵・放出が可能なケイ素の合金、酸化物、窒化物もしくは炭化物を含むケイ素含有粒子と、該ケイ素含有粒子を包囲する樹脂炭素材とからなる複合粒子、ならびに
該複合粒子の表面に結合し、かつ、該複合粒子を包囲するナノファイバーおよび／またはナノチューブからなるケイ素含有網状構造体を含み、前記樹脂炭素材と前記網状構造体は、炭素前駆体を炭化処理することにより形成され、前記網状構造体は、見かけ上、複合粒子の表面を起点に形成され、
該複合粒子中の前記ケイ素含有粒子の２次粒子平均粒径が、１次粒子最小粒径以上、５μｍ以下であることを特徴とする、リチウム２次電池負極用炭素材。
The above object is achieved by the following items (1) to (8).
(1) Silicon-containing particles containing an alloy, oxide, nitride, or carbide of silicon capable of occluding and releasing lithium ions having an average primary particle diameter of 5 nm to 1.5 μm and surrounding the silicon-containing particles composite particles comprising a resin carbon material which, as well as bound to the surface of the composite particles, and includes a silicon-containing network structure consisting of nanofibers and / or nanotubes surrounding the composite particles, the said resin carbon material The network structure is formed by carbonizing a carbon precursor, and the network structure is apparently formed from the surface of the composite particle,
A carbon material for a lithium secondary battery negative electrode, wherein the silicon-containing particles in the composite particles have an average secondary particle size of not less than a minimum primary particle size of 5 μm or less.
（２）前記樹脂炭素材および前記網状構造体が、炭素前駆体の炭化処理により生成したものである、第（１）項に記載のリチウム２次電池負極用炭素材。 (2) The carbon material for a negative electrode of a lithium secondary battery according to item (1), wherein the resin carbon material and the network structure are generated by carbonizing a carbon precursor.
（３）前記ケイ素含有粒子がケイ素酸化物を含む、第（１）項または第（２）項に記載のリチウム２次電池負極用炭素材。 (3) The carbon material for a lithium secondary battery negative electrode according to (1) or (2), wherein the silicon-containing particles contain silicon oxide.
（４）前記網状構造体が更に炭素を含む、第（１）項〜第（３）項のいずれか１項に記載のリチウム２次電池負極用炭素材。 (4) The carbon material for a lithium secondary battery negative electrode according to any one of (1) to (3), wherein the network structure further contains carbon.
（５）平均粒子径が３μｍ〜１５μｍの範囲内である、第（１）項〜第（４）項のいずれか１項に記載のリチウム２次電池負極用炭素材。 (5) The carbon material for a lithium secondary battery negative electrode according to any one of (1) to (4), wherein the average particle diameter is in the range of 3 μm to 15 μm.
（６）前記炭素前駆体が、石油ピッチ、石炭ピッチ、フェノール樹脂、フラン樹脂、エポキシ樹脂およびポリアクリロニトリルからなる群より選択された易黒鉛化材料および／または難黒鉛化材料を含む、第（２）項〜第（５）項のいずれか１項に記載のリチウム２次電池負極用炭素材。 (6) The carbon precursor includes a graphitizable material and / or a non-graphitizable material selected from the group consisting of petroleum pitch, coal pitch, phenol resin, furan resin, epoxy resin and polyacrylonitrile. The carbon material for a lithium secondary battery negative electrode according to any one of items (1) to (5).
（７）第（１）項〜第（６）項のいずれか１項に記載のリチウム２次電池負極用炭素材を含むリチウム２次電池負極。 (7) A lithium secondary battery negative electrode comprising the carbon material for a lithium secondary battery negative electrode according to any one of items (1) to (6).
（８）第（７）項に記載のリチウム２次電池負極を含むリチウム２次電池。 (8) A lithium secondary battery including the lithium secondary battery negative electrode according to (7).
本発明によると、充放電サイクルによる負極用炭素材の微粉化が抑制されると共に、ナノファイバーおよび／またはナノチューブからなるケイ素含有網状構造体と複合粒子の間等の密着性が維持されることにより該炭素材の導電性の低下が抑えられるため、これまでにない優れた充放電サイクル特性を示すリチウム２次電池負極用炭素材が提供される。 According to the present invention, the pulverization of the carbon material for the negative electrode due to the charge / discharge cycle is suppressed, and the adhesion between the silicon-containing network structure composed of nanofibers and / or nanotubes and the composite particles is maintained. Since the decrease in conductivity of the carbon material is suppressed, a carbon material for a lithium secondary battery negative electrode that exhibits unprecedented excellent charge / discharge cycle characteristics is provided.
本発明によるリチウム２次電池負極用炭素材は、１次粒子平均粒径が５ｎｍ以上１．５μｍ以下のリチウムイオンの吸蔵・放出が可能なケイ素の合金、酸化物、窒化物もしくは炭化物を含むケイ素含有粒子と、該ケイ素含有粒子を包囲する樹脂炭素材とからなる複合粒子、ならびに該複合粒子の表面に結合し、かつ、該複合粒子を包囲するナノファイバーおよび／またはナノチューブ（以下、「ナノファイバー等」という場合がある）からなるケイ素含有網状構造体（以下「網状構造体」という場合がある）を含み、該複合粒子中の前記ケイ素含有粒子の２次粒子平均粒径が、１次粒子最小粒径以上、５μｍ以下であることを特徴とするものである。 The carbon material for a negative electrode of a rechargeable lithium battery according to the present invention is a silicon containing an alloy, oxide, nitride or carbide of silicon capable of occluding and releasing lithium ions having an average primary particle size of 5 nm to 1.5 μm. Composite particles composed of containing particles and a resin carbon material surrounding the silicon-containing particles, and nanofibers and / or nanotubes (hereinafter referred to as “nanofibers”) that bind to the surface of the composite particles and surround the composite particles Etc.), and a secondary particle average particle size of the silicon-containing particles in the composite particles is a primary particle (hereinafter also referred to as a “network structure”). The minimum particle size is 5 μm or less.
本発明のケイ素含有網状構造体は、炭素前駆体を、炭化処理することにより上記樹脂炭素材とともに形成され、前記網状構造体は、見かけ上、ケイ素含有粒子と樹脂炭素材からなる複合粒子の表面を起点に形成される。特定の理論に束縛されることを意図するものではないが、前記ケイ素含有網状構造体は、リチウムイオンの吸蔵・放出が可能なケイ素の合金、酸化物、窒化物または炭化物を含むケイ素含有粒子と、該ケイ素含有粒子を包囲する樹脂炭素材とからなる複合粒子の表面に結合しているため、隣接する別の粒子に起因する網状構造体と交絡しているものと考えられる。このため、ナノファイバー等と複合粒子の間の密着性が高くなり、充放電によるケイ素含有粒子の体積膨張収縮に際してもナノファイバー等が複合粒子から離れにくくなる。また、隣接する複数の粒子の網状構造体同士が交絡することで全体として伸縮性のある網状構造体が形成されるため、充放電によるケイ素含有粒子の体積膨張収縮に際して負極全体の導電性が維持される。そして、負極の導電性が維持されることにより、充放電に伴う抵抗変化を抑制することができ、サイクル特性に優れたものとなる。このような本発明特有の網状構造体は、公知の別途気相法で形成されたカーボンナノファイバー等を添加しただけでは、形成されない。なお、網状構造体は見かけ上複合粒子の表面を起点に形成されるが、網状構造体がケイ素を含有することから、網状構造体の真の起点はケイ素含有粒子の表面であると考えられる。 The silicon-containing network structure of the present invention is formed together with the resin carbon material by carbonizing a carbon precursor, and the network structure is apparently a surface of a composite particle composed of silicon-containing particles and a resin carbon material. It is formed from the starting point. While not intending to be bound by any particular theory, the silicon-containing network is composed of silicon-containing particles containing an alloy, oxide, nitride, or carbide of silicon capable of occluding and releasing lithium ions. Since it is bonded to the surface of the composite particle composed of the resin carbon material surrounding the silicon-containing particle, it is considered that it is entangled with the network structure due to another adjacent particle. For this reason, the adhesion between the nanofibers and the composite particles becomes high, and the nanofibers and the like are hardly separated from the composite particles even during the volume expansion and contraction of the silicon-containing particles due to charge and discharge. In addition, because the network structure of a plurality of adjacent particles is entangled with each other to form a stretchable network structure as a whole, the conductivity of the entire negative electrode is maintained during the volume expansion and contraction of silicon-containing particles due to charge and discharge. Is done. And by maintaining the electroconductivity of a negative electrode, the resistance change accompanying charging / discharging can be suppressed and it becomes excellent in cycling characteristics. Such a network structure peculiar to the present invention cannot be formed only by adding a carbon nanofiber or the like formed by a known separate vapor phase method. The network structure is apparently formed starting from the surface of the composite particle, but since the network structure contains silicon, the true starting point of the network structure is considered to be the surface of the silicon-containing particle.
本発明による網状構造体を構成するナノファイバー等は、繊維直径１μｍ未満のケイ素含有繊維を含む。ナノファイバーとナノチューブとを厳密に区別する必要はないが、本明細書では特に、繊維直径１００ｎｍ以上のものをナノファイバーと、そして繊維直径１００ｎｍ以下のものをナノチューブとそれぞれ定義する。本発明によるナノファイバー等の元素組成としては、ケイ素含有粒子の元の組成により、炭化ケイ素、窒化ケイ素、炭窒化ケイ素等またはこれらの任意の組合せであることが想定される。本発明によるナノファイバー等の元素組成は、ナノファイバー等の全体にわたり均一であってもよいし、場所によって異なっていてもよい。さらに、本発明による網状構造体を構成するナノファイバー等には、カーボンナノファイバーおよび／またはカーボンナノチューブ（以下、「カーボンナノファイバー等」という。）が含まれていることが好ましい。カーボンナノファイバー等が存在することにより、ケイ素含有粒子を含む複合粒子間の導電性向上が期待される。 The nanofibers and the like constituting the network structure according to the present invention include silicon-containing fibers having a fiber diameter of less than 1 μm. Although it is not necessary to strictly distinguish between nanofibers and nanotubes, in the present specification, those having a fiber diameter of 100 nm or more are specifically defined as nanofibers, and those having a fiber diameter of 100 nm or less are defined as nanotubes. The elemental composition of the nanofiber or the like according to the present invention is assumed to be silicon carbide, silicon nitride, silicon carbonitride, or any combination thereof depending on the original composition of the silicon-containing particles. The elemental composition of the nanofiber or the like according to the present invention may be uniform throughout the nanofiber or the like, or may vary depending on the location. Furthermore, it is preferable that the nanofibers and the like constituting the network structure according to the present invention include carbon nanofibers and / or carbon nanotubes (hereinafter referred to as “carbon nanofibers”). The presence of carbon nanofibers is expected to improve the conductivity between composite particles including silicon-containing particles.
本発明の、１次粒子平均粒径が５ｎｍ以上１．５μｍ以下のリチウムイオンの吸蔵・放出が可能なケイ素の合金、酸化物、窒化物もしくは炭化物を含むケイ素含有（１次）粒子を構成するケイ素の合金、酸化物、窒化物もしくは炭化物の例としては、一酸化ケイ素（ＳｉＯ）、窒化ケイ素（Ｓｉ２Ｎ４）、炭化ケイ素（ＳｉＣ）、チタンシリコン合金（Ｔｉ−Ｓｉ系）等を挙げることができる。中でも、充電時の膨張率が小さいなどの理由で、一酸化ケイ素（ＳｉＯ）などのケイ素酸化物が好ましく、さらにＳｉＯが、より好ましい。
また前記ケイ素含有（１次）粒子は、その平均粒径が、５ｎｍ〜１．５μｍの範囲内にあることが好ましく、０．１μｍ〜１．２μｍの範囲内にあることがより好ましい。上記ケイ素含有粒子の平均粒径が５ｎｍ以上だと、リチウムイオンの吸蔵量が適正となり、粒子の膨張収縮を網状構造体により十分に抑制することができる。また上記ケイ素含有粒子の平均粒径が１．５μｍ以下だと、高い充放電容量を得ることができる。
The silicon-containing (primary) particles containing an alloy, oxide, nitride or carbide of silicon capable of occluding and releasing lithium ions having an average primary particle diameter of 5 nm to 1.5 μm of the present invention are constituted. Examples of silicon alloys, oxides, nitrides or carbides include silicon monoxide (SiO), silicon nitride (Si 2 N 4 ), silicon carbide (SiC), titanium silicon alloys (Ti—Si based), and the like. be able to. Among these, silicon oxides such as silicon monoxide (SiO) are preferable, and SiO is more preferable because the expansion coefficient during charging is small.
The silicon-containing (primary) particles preferably have an average particle size in the range of 5 nm to 1.5 μm, and more preferably in the range of 0.1 μm to 1.2 μm. When the average particle diameter of the silicon-containing particles is 5 nm or more, the amount of occlusion of lithium ions becomes appropriate, and the expansion and contraction of the particles can be sufficiently suppressed by the network structure. When the average particle size of the silicon-containing particles is 1.5 μm or less, a high charge / discharge capacity can be obtained.
本発明の複合粒子中の、前記ケイ素含有（１次）粒子が凝集した２次粒子については、その平均粒径は、１次粒子最小粒径以上、５μｍ以下が好ましく、さらに３．５μｍ以下がより好ましい。５μｍ以下だと、リチウムの吸蔵・放出に伴う膨張・収縮を樹脂炭素材が抑制できない部分を網状構造体で十分に抑制することができるため、優れた充放電サイクル特性を得ることができる。 Regarding the secondary particles in which the silicon-containing (primary) particles in the composite particles of the present invention are aggregated, the average particle size is preferably not less than the minimum primary particle size and not more than 5 μm, and more preferably not more than 3.5 μm. More preferred. When the thickness is 5 μm or less, the network structure can sufficiently suppress the portion where the resin carbon material cannot suppress the expansion / contraction associated with the insertion / extraction of lithium, and thus excellent charge / discharge cycle characteristics can be obtained.
本発明の網状構造体は前述のように、隣接する粒子に起因する網状構造体と交絡しているものと考えられるため、ナノファイバー等と複合粒子の間の密着性を向上させ、また、隣接する複数の粒子の網状構造体同士が交絡することで全体として伸縮性のある網状構造体が形成されるため、充放電による粒子の体積膨張収縮に際して負極全体の導電性が維持される効果があるが、前述のように、前記ケイ素含有（１次）粒子の凝集により、２次粒子が大きい場合、充放電に伴う膨張収縮が不均一になり、網状構造体の効果が十分に発現しなかったり、網状構造体自体が不均一となったりする可能性があるため、本発明の優れた効果を得るためには、本発明の網状構造体と、リチウムイオンの吸蔵・放出が可能なケイ素の合金、酸化物、窒化物もしくは炭化物を含むケイ素含有粒子の１次粒子径、および複合粒子中の該ケイ素含有粒子の２次粒子径、の両方を制御する技術が重要である。 Since the network structure of the present invention is considered to be entangled with the network structure caused by adjacent particles as described above, the adhesion between nanofibers and composite particles is improved, and Since the network structure of a plurality of particles entangled with each other forms a stretchable network structure as a whole, there is an effect that the conductivity of the whole negative electrode is maintained during the volume expansion / contraction of the particles due to charge / discharge However, as described above, when the secondary particles are large due to aggregation of the silicon-containing (primary) particles, the expansion and contraction associated with charge / discharge becomes uneven, and the effect of the network structure is not sufficiently exhibited. In order to obtain the excellent effect of the present invention, the network structure of the present invention and a silicon alloy capable of occluding and releasing lithium ions can be obtained. , Oxides and nitrides Ku is a technology for controlling both secondary particle diameter, of the silicon-containing particles of silicon primary particle diameter of the containing particles, and composite particles comprising a carbide is important.
本発明のリチウム２次電池負極用炭素材は、その形状に特に制限はなく、塊状、鱗片状、球状、繊維状等の任意の粒子形状を有することができる。また、これら炭素材粒子の大きさは、充放電特性の上で、平均粒子径が３μｍ以上、１５μｍ以下であることが好ましい。更に好ましくは５μｍ以上、１２μｍ以下である。また、より好ましくは、７μｍ以上、１０μｍ以下である。平均粒子径が１５μｍ以下であると、炭素材粒子間の間隙を小さくでき、リチウム２次電池負極用炭素材として用いた場合に、負極電極の密度を向上させることができる。また、平均粒子径が３μｍ以上だと、単位質量当たりで見た場合、炭素材粒子個数を抑制でき全体として嵩高くならず、取り扱いが容易になる。 The shape of the carbon material for a negative electrode of a lithium secondary battery of the present invention is not particularly limited, and can have any particle shape such as a lump shape, a scale shape, a spherical shape, or a fibrous shape. The carbon material particles preferably have an average particle size of 3 μm or more and 15 μm or less in view of charge / discharge characteristics. More preferably, it is 5 μm or more and 12 μm or less. More preferably, it is 7 μm or more and 10 μm or less. When the average particle size is 15 μm or less, the gap between the carbon material particles can be reduced, and when used as a carbon material for a negative electrode of a lithium secondary battery, the density of the negative electrode can be improved. Further, when the average particle diameter is 3 μm or more, the number of carbon material particles can be suppressed when viewed per unit mass, and the whole is not bulky and easy to handle.
本発明における炭素材およびケイ素の合金、酸化物、窒化物もしくは炭化物を含むケイ素含有（１次）粒子の粒子径の定義としては、粒子形状とＭｉｅ理論を用いて測定量を粒子径に算出した値とし、有効径と称されるものである。
本発明における前記ケイ素含有１次平均粒子径は、レーザー回折式粒度分布測定法による測定される体積換算で頻度が５０％となる粒子径を平均粒子径Ｄ５０％として定めた。
また、本発明の複合粒子中の前記ケイ素の合金、酸化物、窒化物もしくは炭化物を含むケイ素含有粒子の２次粒子平均粒径は、よく混合した炭素材粒子を１０サンプル任意に抽出し、その断面を走査型電子顕微鏡（ＳＥＭ）を用いて観察した際の２次凝集粒子の長径を測定、その平均値を２次粒子平均粒径とした。
As the definition of the particle size of silicon-containing (primary) particles containing carbon material and silicon alloy, oxide, nitride or carbide in the present invention, the measured amount was calculated as the particle size using the particle shape and Mie theory. The value is referred to as the effective diameter.
In the present invention, the silicon-containing primary average particle size was determined by setting the particle size having a frequency of 50% in terms of volume measured by a laser diffraction particle size distribution measurement method as an average particle size D50%.
Further, the secondary particle average particle size of the silicon-containing particles containing the alloy, oxide, nitride or carbide of silicon in the composite particles of the present invention is arbitrarily extracted from 10 samples of well-mixed carbon material particles. When the cross section was observed using a scanning electron microscope (SEM), the major axis of the secondary agglomerated particles was measured, and the average value was defined as the secondary particle average particle size.
本発明におけるリチウム２次電池負極用炭素材は、リチウムイオンの吸蔵・放出が可能なケイ素の合金、酸化物、窒化物もしくは炭化物を、負極用炭素材に対する質量比で５〜６０質量％含有することが好ましい。上記含有量が５質量％以上だと、リチウムイオンの吸蔵が十分なものとなり、高い充放電容量を得ることが期待できる。一方、上記含有量が６０質量％以下だと、リチウムイオンの吸蔵・放出における粒子の膨張収縮を網状構造体により抑えることが容易となり、十分な充放電サイクル特性を得ることができる。ここで、上記のケイ素の合金、酸化物、窒化物または炭化物の含有量は、ＪＩＳ Ｋ ２２７２：１９９８に従う灰分試験法によって測定される。 The lithium secondary battery negative electrode carbon material according to the present invention contains a silicon alloy, oxide, nitride or carbide capable of occluding and releasing lithium ions in a mass ratio of 5 to 60% by mass with respect to the negative electrode carbon material. It is preferable. When the content is 5% by mass or more, lithium ion storage is sufficient, and a high charge / discharge capacity can be expected. On the other hand, when the content is 60% by mass or less, it becomes easy to suppress the expansion and contraction of the particles during insertion and extraction of lithium ions by the network structure, and sufficient charge / discharge cycle characteristics can be obtained. Here, the content of the above-mentioned silicon alloy, oxide, nitride or carbide is measured by an ash test method according to JIS K 2272: 1998.
本発明によるリチウム２次電池負極用炭素材は、リチウムイオンの吸蔵・放出が可能なケイ素の合金、酸化物、窒化物もしくは炭化物を含むケイ素含有粒子と、炭素前駆体とを混合することにより、該ケイ素含有粒子が該炭素前駆体に分散された混合物を形成し、次いで該混合物に炭化処理を施すことにより製造される。この炭化処理により、炭素前駆体が樹脂炭素材に転化すると共に、転化した樹脂炭素材とリチウムイオンの吸蔵・放出が可能なケイ素含有粒子とからなる複合粒子を包囲するナノファイバー等からなる網状構造体が、該複合粒子の表面を起点に形成される。また必要に応じて炭素前駆体中に触媒を分散させて炭化処理を施すことにより、網状構造体を構成するナノファイバー等、特にカーボンナノファイバー等の生成量を増大させることができる。 The carbon material for a negative electrode of a lithium secondary battery according to the present invention is obtained by mixing silicon-containing particles containing an alloy, oxide, nitride, or carbide of silicon capable of occluding and releasing lithium ions, and a carbon precursor. The silicon-containing particles are produced by forming a mixture dispersed in the carbon precursor, and then subjecting the mixture to carbonization. This carbonization converts the carbon precursor into a resin carbon material, and a network structure comprising nanofibers surrounding composite particles composed of the converted resin carbon material and silicon-containing particles capable of occluding and releasing lithium ions. A body is formed starting from the surface of the composite particle. Further, if necessary, the amount of produced nanofibers constituting the network structure, particularly carbon nanofibers, can be increased by dispersing the catalyst in the carbon precursor and subjecting it to carbonization treatment.
炭素前駆体の例としては、石油ピッチ、石炭ピッチ、フェノール樹脂、フラン樹脂、エポキシ樹脂およびポリアクリロニトリルからなる群より選択された易黒鉛化材料および／または難黒鉛化材料を挙げることができる。易黒鉛化材料と難黒鉛化材料の混合物を使用してもよい。また、フェノール樹脂等に硬化剤（例、ヘキサメチレンテトラミン）を含めてもよく、その場合、硬化剤も炭素前駆体の一部となり得る。 Examples of the carbon precursor include an easily graphitized material and / or a hardly graphitized material selected from the group consisting of petroleum pitch, coal pitch, phenol resin, furan resin, epoxy resin, and polyacrylonitrile. A mixture of an easily graphitizable material and a hardly graphitized material may be used. Moreover, you may include a hardening | curing agent (for example, hexamethylenetetramine) in a phenol resin etc., In that case, a hardening | curing agent can also be a part of carbon precursor.
触媒を使用する場合、例として、銅（Ｃｕ）、鉄（Ｆｅ）、コバルト（Ｃｏ）、ニッケル（Ｎｉ）、モリブデン（Ｍｏ）およびマンガン（Ｍｎ）からなる群より選ばれた少なくとも１種の元素を含むものが挙げられる。触媒元素は、炭素前駆体に不純物として含まれるものであってもよく、その場合、意図的に別途触媒を用意して混合する必要のない場合もある。これらの触媒元素は、該ケイ素含有粒子と触媒とが炭素前駆体に分散された混合物を形成するように、溶液として粒子と混合することが好ましい。このような溶液を提供するため、触媒元素は金属塩化合物として用意することが好ましく、そのような金属塩化合物の例としては、上記元素の、硝酸塩、硫酸塩、塩酸塩等の無機酸根との塩、カルボン酸、スルホン酸、フェノール等の有機酸根との塩、等が挙げられる。また、このような溶液に用いる溶媒としては、水、有機溶媒および水と有機溶媒の混合物の中から適宜選択すればよく、特に有機溶媒の例としては、エタノール、イソプロピルアルコール、トルエン、ベンゼン、ヘキサン、テトラヒドロフラン等が挙げられる。 When using a catalyst, as an example, at least one element selected from the group consisting of copper (Cu), iron (Fe), cobalt (Co), nickel (Ni), molybdenum (Mo) and manganese (Mn) The thing containing is mentioned. The catalytic element may be contained as an impurity in the carbon precursor. In that case, it may not be necessary to intentionally prepare and mix a separate catalyst. These catalytic elements are preferably mixed with the particles as a solution so that the silicon-containing particles and the catalyst form a mixture dispersed in the carbon precursor. In order to provide such a solution, the catalyst element is preferably prepared as a metal salt compound. Examples of such metal salt compounds include the above-described elements and inorganic acid radicals such as nitrates, sulfates, and hydrochlorides. And salts with organic acid radicals such as salts, carboxylic acids, sulfonic acids and phenols. Further, the solvent used in such a solution may be appropriately selected from water, an organic solvent, and a mixture of water and an organic solvent. Particularly, examples of the organic solvent include ethanol, isopropyl alcohol, toluene, benzene, hexane. , Tetrahydrofuran and the like.
リチウムイオンの吸蔵・放出が可能な粒子と、炭素前駆体と、必要に応じて触媒とを混合する方法は、本発明のケイ素の合金、酸化物、窒化物もしくは炭化物を含む粒子等を前述のように十分に分散できれば特に制限はなく、ホモディスパー、ホモジナイザー等の撹拌機による溶融または溶液混合；遠心粉砕機、自由ミル、ジェットミル等の粉砕機による粉砕混合；乳鉢、乳棒による混練混合；等を採用することができる。上記粒子と樹脂炭素材からなる粒子において、樹脂炭素材により上記粒子を包囲する複合粒子を形成する上で、溶媒を用いて、上記粒子と炭素前駆体を混合し、スラリー状混合物としてもよいし、上記粒子に炭素前駆体を混合し、炭素前駆体を硬化させ、固形状にしてもよい。また、上記スラリーにおいて、炭素前駆体が液状であれば、溶媒を使用しなくても良い。また本発明のケイ素の合金、酸化物、窒化物もしくは炭化物を含むケイ素含有粒子を十分に分散させるための混合手順も特に制限はなく、該粒子を予めよく分散し得る溶媒に分散させた後、他の成分と混合する方法や他の成分と該粒子を同時に溶媒に混合する方法、他の成分と該粒子を同時に溶融混合する方法（その際少量の溶媒を使用することも含む）、該粒子と前記炭素前駆体の一部を予め溶融混合し、後で残りの成分を混合する方法、あるいは該粒子の表面にカップリング剤を付着させて分散させる方法など、特に制限はない。 The method of mixing particles capable of occluding / releasing lithium ions, a carbon precursor, and, if necessary, a catalyst, the particles containing an alloy, oxide, nitride, or carbide of silicon of the present invention are described above. As long as it can be sufficiently dispersed, there is no particular limitation, and melting or solution mixing with a stirrer such as a homodisper or homogenizer; pulverization and mixing with a pulverizer such as a centrifugal pulverizer, free mill or jet mill; kneading and mixing with a mortar or pestle; Can be adopted. In forming the composite particles that surround the particles with the resin carbon material in the particles composed of the particles and the resin carbon material, the particles and the carbon precursor may be mixed using a solvent to form a slurry mixture. The carbon precursor may be mixed with the particles, the carbon precursor may be cured, and solidified. Further, in the slurry, if the carbon precursor is liquid, it is not necessary to use a solvent. The mixing procedure for sufficiently dispersing the silicon-containing particles containing the silicon alloy, oxide, nitride or carbide of the present invention is not particularly limited, and after the particles are dispersed in a solvent that can be well dispersed in advance, A method of mixing with other components, a method of simultaneously mixing other components and the particles in a solvent, a method of simultaneously melting and mixing other components and the particles (including the use of a small amount of solvent), the particles There is no particular limitation such as a method in which a part of the carbon precursor is melt-mixed in advance and the remaining components are mixed later, or a method in which a coupling agent is attached to the surface of the particles and dispersed.
本発明のリチウム２次電池負極用炭素材の粒度分布を調整する場合は、公知の粉砕方法、分級方法を採用すればよい。粉砕装置の例としては、ハンマーミル、ジョークラッシャー、衝突式粉砕器等が挙げられる。また、分級方法の例としては、気流分級、篩による分級が可能であり、特に気流分級装置の例として、ターボクラシファイヤー、ターボプレックス等が挙げられる。 When adjusting the particle size distribution of the carbon material for a lithium secondary battery negative electrode of the present invention, a known pulverization method and classification method may be employed. Examples of the pulverizer include a hammer mill, a jaw crusher, and a collision pulverizer. Moreover, as an example of the classification method, air classification and classification with a sieve are possible. Particularly, examples of the air classification apparatus include a turbo classifier and a turboplex.
炭化処理のための加熱温度は、好ましくは４００〜１４００℃、より好ましくは６００〜１３００℃の範囲内で適宜設定すればよい。上記加熱温度に至るまでの昇温速度に特に制限はなく、好ましくは０．５〜６００℃／時、より好ましくは２０〜３００℃／時の範囲内で適宜設定すればよい。上記加熱温度での保持時間は、好ましくは４８時間以内、より好ましくは１〜１２時間の範囲内で適宜設定すればよい。また、炭化処理は、アルゴン、窒素、二酸化炭素等の還元雰囲気において実施すればよい。さらに、炭化処理を２段階以上に分けて実施することにより、得られる樹脂炭素材の物性を制御することが好ましい。例えば、４００〜７００℃の温度で１〜６時間程度処理（１次炭化）した後、上述の粉砕処理により所期の平均粒子径を有する炭素材を得、さらにその炭素材を１０００℃以上の温度で処理（２次炭化）することが好ましい。また炭化処理工程で本発明のケイ素の合金、酸化物、窒化物もしくは炭化物を含むケイ素含有粒子を凝集させない条件を適宜選択することも本発明に含まれる。 What is necessary is just to set the heating temperature for carbonization processing suitably in the range of preferably 400-1400 degreeC, More preferably, 600-1300 degreeC. There is no restriction | limiting in particular in the temperature increase rate until it reaches the said heating temperature, What is necessary is just to set suitably in the range of 0.5-600 degreeC / hour, More preferably, 20-300 degreeC / hour. The holding time at the heating temperature is suitably set within 48 hours, more preferably within a range of 1 to 12 hours. Moreover, what is necessary is just to implement carbonization processing in reducing atmosphere, such as argon, nitrogen, a carbon dioxide. Furthermore, it is preferable to control the physical properties of the obtained resin carbon material by carrying out the carbonization treatment in two or more stages. For example, after processing (primary carbonization) at a temperature of 400 to 700 ° C. for about 1 to 6 hours, a carbon material having an expected average particle diameter is obtained by the above-described pulverization treatment, and the carbon material is further heated to 1000 ° C. or more. It is preferable to perform the treatment (secondary carbonization) at a temperature. Further, the present invention includes appropriately selecting conditions that do not agglomerate silicon-containing particles containing an alloy, oxide, nitride or carbide of silicon of the present invention in the carbonization process.
このように、本発明よるリチウム２次電池負極用炭素材は、樹脂炭素材と、ナノファイバー等からなる網状構造体とが炭化処理により一緒に形成されるため、別途ナノファイバー等を気相法、アーク放電法、プラズマ処理法で用意する必要がなく、製造プロセスが簡便であり、且つコストを下げることができる。 As described above, the carbon material for a negative electrode of a lithium secondary battery according to the present invention is formed by carbonizing a resin carbon material and a network structure made of nanofibers together. Further, it is not necessary to prepare an arc discharge method or a plasma treatment method, the manufacturing process is simple, and the cost can be reduced.
上述のようにして得られた炭素材を負極活物質として用いることにより、本発明によるリチウム２次電池負極を作製することができる。本発明によるリチウム２次電池負極は、従来公知の方法で作製することができる。例えば、負極活物質としての本発明による炭素材に、バインダー、導電剤等を加えて適当な溶媒または分散媒で所定粘度としたスラリーを調製し、これを金属箔等の集電体に塗工し、厚さ数μｍ〜数百μｍのコーティングを形成させる。そのコーティングを５０〜２００℃程度で熱処理することにより溶媒または分散媒を除去することにより、本発明による負極を得ることができる。 By using the carbon material obtained as described above as a negative electrode active material, a lithium secondary battery negative electrode according to the present invention can be produced. The lithium secondary battery negative electrode according to the present invention can be produced by a conventionally known method. For example, a carbon material according to the present invention as a negative electrode active material is added with a binder, a conductive agent, etc. to prepare a slurry having a predetermined viscosity with an appropriate solvent or dispersion medium, and this is applied to a current collector such as a metal foil. Then, a coating having a thickness of several μm to several hundred μm is formed. The negative electrode according to the present invention can be obtained by heat-treating the coating at about 50 to 200 ° C. to remove the solvent or the dispersion medium.
本発明による負極の作製に用いられるバインダーは、従来公知の材料であればよく、例えば、ポリフッ化ビニリデン樹脂、ポリテトラフルオロエチレン、スチレン・ブタジエン共重合体、ポリイミド樹脂、ポリアミド樹脂、ポリビニルアルコール、ポリビニルブチラール等を使用することができる。また、本発明による負極の作製に用いられる導電剤は、導電補助材として通常使用されている材料であればよく、例として、黒鉛、アセチレンブラック、ケッチェンブラック等が挙げられる。さらに、本発明による負極の作製に用いられる溶媒または分散媒は、負極活物質、バインダー、導電剤等を均一に混合できる材料であればよく、例として、Ｎ−メチル−２−ピロリドン、メタノール、アセトニトリル等が挙げられる。 The binder used for preparing the negative electrode according to the present invention may be any conventionally known material, such as polyvinylidene fluoride resin, polytetrafluoroethylene, styrene / butadiene copolymer, polyimide resin, polyamide resin, polyvinyl alcohol, polyvinyl Butyral or the like can be used. In addition, the conductive agent used for producing the negative electrode according to the present invention may be any material that is usually used as a conductive auxiliary material, and examples thereof include graphite, acetylene black, and ketjen black. Furthermore, the solvent or dispersion medium used for the production of the negative electrode according to the present invention may be any material that can uniformly mix the negative electrode active material, the binder, the conductive agent, and the like. Examples thereof include N-methyl-2-pyrrolidone, methanol, Examples include acetonitrile.
さらに、本発明によるリチウム２次電池負極を用いることにより、本発明によるリチウム２次電池を作製することができる。本発明によるリチウム２次電池は、従来公知の方法で作製することができ、一般に、本発明による負極と、正極と、電解質とを含み、さらにこれらの負極と正極が短絡しないようにするセパレータを含む。電解質がポリマーと複合化された固体電解質であってセパレータの機能を併せ持つものである場合には、独立したセパレータは不要である。 Furthermore, the lithium secondary battery according to the present invention can be manufactured by using the lithium secondary battery negative electrode according to the present invention. The lithium secondary battery according to the present invention can be produced by a conventionally known method. In general, the lithium secondary battery includes a negative electrode according to the present invention, a positive electrode, and an electrolyte, and further includes a separator that prevents the negative electrode and the positive electrode from being short-circuited. Including. When the electrolyte is a solid electrolyte combined with a polymer and has the function of a separator, an independent separator is not necessary.
本発明によるリチウム２次電池の作製に用いられる正極は、従来公知の方法で作製することができる。例えば、正極活物質に、バインダー、導電剤等を加えて適当な溶媒または分散媒で所定粘度としたスラリーを調製し、これを金属箔等の集電体に塗工し、厚さ数μｍ〜数百μｍのコーティングを形成させ、そのコーティングを５０〜２００℃程度で熱処理することにより溶媒または分散媒を除去すればよい。正極活物質は、従来公知の材料であればよく、例えば、ＬｉＣｏＯ２等のコバルト複合酸化物、ＬｉＭｎ２Ｏ４等のマンガン複合酸化物、ＬｉＮｉＯ２等のニッケル複合酸化物、これら酸化物の混合物、ＬｉＮｉＯ２のニッケルの一部をコバルトやマンガンに置換したもの、ＬｉＦｅＶＯ４、ＬｉＦｅＰＯ４等の鉄複合酸化物、等を使用することができる。 The positive electrode used for the production of the lithium secondary battery according to the present invention can be produced by a conventionally known method. For example, a positive electrode active material is added with a binder, a conductive agent and the like to prepare a slurry having a predetermined viscosity with an appropriate solvent or dispersion medium, and this is applied to a current collector such as a metal foil, and a thickness of several μm to What is necessary is just to remove a solvent or a dispersion medium by forming several hundred micrometers coating and heat-processing the coating at about 50-200 degreeC. The positive electrode active material may be a conventionally known material, for example, a cobalt composite oxide such as LiCoO 2 , a manganese composite oxide such as LiMn 2 O 4 , a nickel composite oxide such as LiNiO 2 , and a mixture of these oxides. , LiNiO 2 in which part of nickel is replaced with cobalt or manganese, iron composite oxides such as LiFeVO 4 and LiFePO 4 , and the like can be used.
電解質としては、公知の電解液、常温溶融塩（イオン液体）、及び有機系もしくは無機系の固体電解質などを用いることができる。公知の電解液としては、例えば、エチレンカーボネートおよびプロピレンカーボネートなどの環状炭酸エステル、エチルメチルカーボネートおよびジエチルカーボネートなどの鎖状炭酸エステルなどが挙げられる。また、常温溶融塩（イオン液体）としては、例えば、イミダゾリウム系塩、ピロリジニウム系塩、ピリジニウム系塩、アンモニウム系塩、ホスホニウム系塩、スルホニウム系塩などが挙げられる。前記固体電解質としては、例えば、ポリエーテル系ポリマー、ポリエステル系ポリマー、ポリイミン系ポリマー、ポリビニルアセタール系ポリマー、ポリアクリロニトリル系ポリマー、ポリフッ化アルケン系ポリマー、ポリ塩化ビニル系ポリマー、ポリ（塩化ビニル−フッ化ビニリデン）系ポリマー、ポリ（スチレン−アクリロニトリル）系ポリマー、及びニトリルゴムなどの直鎖型ポリマーなどに代表される有機系ポリマーゲル；ジルコニアなどの無機セラミックス；ヨウ化銀、ヨウ化銀硫黄化合物、ヨウ化銀ルビジウム化合物などの無機系電解質；などが挙げられる。また、前記電解質にリチウム塩を溶解したものを２次電池用の電解質として用いることができる。また、電解質に難燃性を付与するために難燃性電解質溶解剤を加えることもできる。同様に、電解質の粘度を低下させるために可塑剤を加えることもできる。 As the electrolyte, a known electrolytic solution, a room temperature molten salt (ionic liquid), an organic or inorganic solid electrolyte, and the like can be used. Examples of the known electrolyte include cyclic carbonates such as ethylene carbonate and propylene carbonate, and chain carbonates such as ethyl methyl carbonate and diethyl carbonate. Examples of the room temperature molten salt (ionic liquid) include imidazolium salts, pyrrolidinium salts, pyridinium salts, ammonium salts, phosphonium salts, sulfonium salts, and the like. Examples of the solid electrolyte include polyether polymers, polyester polymers, polyimine polymers, polyvinyl acetal polymers, polyacrylonitrile polymers, polyfluorinated alkene polymers, polyvinyl chloride polymers, poly (vinyl chloride-fluoride). Vinylidene) -based polymers, poly (styrene-acrylonitrile) -based polymers, and organic polymer gels represented by linear polymers such as nitrile rubber; inorganic ceramics such as zirconia; silver iodide, silver iodide sulfur compounds, iodine And inorganic electrolytes such as silver rubidium compounds. Moreover, what melt | dissolved lithium salt in the said electrolyte can be used as an electrolyte for secondary batteries. A flame retardant electrolyte solubilizer can also be added to impart flame retardancy to the electrolyte. Similarly, a plasticizer can be added to reduce the viscosity of the electrolyte.
電解質に溶解させるリチウム塩としては、例えば、ＬｉＰＦ６、ＬｉＣｌＯ４、ＬｉＣＦ３ＳＯ３、ＬｉＢＦ４、ＬｉＡｓＦ６、ＬｉＮ（ＣＦ３ＳＯ２）２、ＬｉＮ（Ｃ２Ｆ５ＳＯ２）２およびＬｉＣ（ＣＦ３ＳＯ２）３などが挙げられる。上記リチウム塩は、単独で用いても、また２種以上を組み合わせて用いてもよい。上記リチウム塩は、電解質全体に対して、一般に０．１質量％〜８９．９質量％、好ましくは１．０質量％〜７９．０質量％の含有量で用いられる。電解質のリチウム塩以外の成分は、リチウム塩の含有量が上記範囲内にあることを条件に、適当な量で添加することができる。 Examples of the lithium salt dissolved in the electrolyte include LiPF 6 , LiClO 4 , LiCF 3 SO 3 , LiBF 4 , LiAsF 6 , LiN (CF 3 SO 2 ) 2 , LiN (C 2 F 5 SO 2 ) 2 and LiC ( CF 3 SO 2 ) 3 and the like. The lithium salts may be used alone or in combination of two or more. The lithium salt is generally used in a content of 0.1% by mass to 89.9% by mass, preferably 1.0% by mass to 79.0% by mass, based on the entire electrolyte. Components other than the lithium salt of the electrolyte can be added in an appropriate amount on condition that the content of the lithium salt is within the above range.
上記電解質に用いられるポリマーとしては、電気化学的に安定であり、イオン伝導度が高いものであれば特に制限はなく、例えば、アクリレート系ポリマー、ポリフッ化ビニリデン等を使用することができる。また、重合性官能基を有するオニウムカチオンと重合性官能基を有する有機アニオンとから構成される塩モノマーを含むものから合成されたポリマーは、特にイオン伝導度が高く、充放電特性のさらなる向上に寄与し得る点で、より好ましい。電解質中のポリマー含有量は、好ましくは０．１質量％〜５０質量％、より好ましくは１質量％〜４０質量％の範囲内である。 The polymer used for the electrolyte is not particularly limited as long as it is electrochemically stable and has high ionic conductivity. For example, an acrylate polymer, polyvinylidene fluoride, or the like can be used. In addition, polymers synthesized from those containing a salt monomer composed of an onium cation having a polymerizable functional group and an organic anion having a polymerizable functional group have particularly high ionic conductivity, which further improves charge / discharge characteristics. It is more preferable at the point which can contribute. The polymer content in the electrolyte is preferably in the range of 0.1 mass% to 50 mass%, more preferably 1 mass% to 40 mass%.
上記難燃性電解質溶解剤としては、自己消火性を示し、かつ、電解質塩が共存した状態で電解質塩を溶解させることができる化合物であれば特に制限はなく、例えば、リン酸エステル、ハロゲン化合物、フォスファゼン等を使用することができる。 The flame retardant electrolyte solubilizer is not particularly limited as long as it is a compound that exhibits self-extinguishing properties and can dissolve the electrolyte salt in the presence of the electrolyte salt. For example, phosphate ester, halogen compound Phosphazene etc. can be used.
上記可塑剤の例としては、エチレンカーボネート、プロピレンカーボネート等の環状炭酸エステル、エチルメチルカーボネート、ジエチルカーボネート等の鎖状炭酸エステル、等が挙げられる。上記可塑剤は、単独で用いても、また２種以上を組み合わせて用いてもよい。 Examples of the plasticizer include cyclic carbonates such as ethylene carbonate and propylene carbonate, and chain carbonates such as ethyl methyl carbonate and diethyl carbonate. The above plasticizers may be used alone or in combination of two or more.
本発明によるリチウム２次電池にセパレータを用いる場合、正極と負極の間の短絡を防止することができ、電気化学的に安定である従来公知の材料を使用すればよい。セパレータの例としては、ポリエチレン製セパレータ、ポリプロピレン製セパレータ、セルロース製セパレータ、不織布、無機系セパレータ、グラスフィルター等が挙げられる。電解質にポリマーを含める場合には、その電解質がセパレータの機能を兼ね備える場合もあり、その場合、独立したセパレータは不要である。 When the separator is used in the lithium secondary battery according to the present invention, a conventionally known material that can prevent a short circuit between the positive electrode and the negative electrode and is electrochemically stable may be used. Examples of the separator include a polyethylene separator, a polypropylene separator, a cellulose separator, a nonwoven fabric, an inorganic separator, a glass filter, and the like. When a polymer is included in the electrolyte, the electrolyte may also have a separator function, and in that case, an independent separator is unnecessary.
本発明の２次電池の製造方法としては、公知な方法が適用できる。例えば、まず、上記で得た正極および負極を、所定の形、大きさに切断して用意し、次いで、正極と負極を直接接触しないように、セパレータを介して貼りあわせ、それを単層セルとする。次いで、この単層セルの電極間に、注液などの方法により、電解質を注入する。このようにして得られたセルを、例えば、ポリエステルフィルム／アルミニウムフィルム／変性ポリオレフィンフィルムの三層構造のラミネートフィルムからなる外装体に挿入し封止することにより、２次電池が得られる。得られた２次電池は、用途により、単セルとして用いても、複数のセルを繋いだモジュールとして用いてもよい。 As a method for producing the secondary battery of the present invention, a known method can be applied. For example, the positive electrode and the negative electrode obtained above are first prepared by cutting them into a predetermined shape and size, and then bonded via a separator so that the positive electrode and the negative electrode are not in direct contact with each other. And Next, an electrolyte is injected between the electrodes of the single-layer cell by a method such as injection. A secondary battery is obtained by inserting and sealing the thus obtained cell into an outer package made of a laminate film having a three-layer structure of polyester film / aluminum film / modified polyolefin film, for example. The obtained secondary battery may be used as a single cell or a module in which a plurality of cells are connected depending on the application.
以下、本発明をより具体的に説明するための実施例を提供する。 Hereinafter, an example for explaining the present invention more concretely is provided.
＜実施例１＞
ノボラック型フェノール樹脂（住友ベークライト株式会社製ＰＲ−５１５３０）１００質量部およびヘキサメチレンテトラミン（三菱瓦斯化学株式会社製）１０質量部、メタノール１０質量部、さらに一酸化ケイ素２５質量部（平均粒子径０．６μｍ）をニーダーで、回転数５０ｒｐｍ、４０℃、３０分間混合し、樹脂スラリーを得た。攪拌終了後、得られた樹脂スラリーを１７５℃にて５時間硬化処理を行った。硬化処理後、窒素雰囲気下にて昇温し、５００℃到達後３時間の炭化を行った。得られた炭素材を平均粒子径が９μｍになるまで粉砕処理を行い、粉砕処理により得られた炭素材を、さらに昇温し、１１００℃到達後３時間の炭化処理を行い、２次電池負極用炭素材を得た。得られた炭素材について、走査型電子顕微鏡（ＳＥＭ）を用いて炭素材表面の観察を行ったところ、図１に示すように白く写った繊維状のナノファイバー等からなる網状構造体が炭素材の粒子表面から発生し、これらの粒子を包囲していることが確認された。また、ＳＥＭで観察されたナノファイバー等をエネルギー分散型Ｘ線分析装置（ＥＤＸ）を用いて元素分析を行ったところ、ケイ素のピークが確認された（図２のグラフに代表例を示す）。また、炭素材断面のＳＥＭ観察を行ったところ、炭素材中の一酸化ケイ素粒子の２次粒子平均粒径は３μｍであった（図３の写真に代表例を示す）。また、得られた炭素材には一酸化ケイ素が２６．８質量％含有されていた。
<Example 1>
100 parts by weight of a novolac type phenolic resin (PR-51530 manufactured by Sumitomo Bakelite Co., Ltd.), 10 parts by weight of hexamethylenetetramine (manufactured by Mitsubishi Gas Chemical Co., Inc.), 10 parts by weight of methanol, and 25 parts by weight of silicon monoxide (average particle size 0) .6 μm) was mixed with a kneader at a rotation speed of 50 rpm and 40 ° C. for 30 minutes to obtain a resin slurry. After the stirring was completed, the obtained resin slurry was cured at 175 ° C. for 5 hours. After the curing treatment, the temperature was raised in a nitrogen atmosphere, and carbonization was performed for 3 hours after reaching 500 ° C. The obtained carbon material is pulverized until the average particle size becomes 9 μm, and the carbon material obtained by the pulverization is further heated, and carbonized for 3 hours after reaching 1100 ° C. Carbon material for use was obtained. The obtained carbon material was observed on the surface of the carbon material using a scanning electron microscope (SEM). As shown in FIG. 1, a network structure composed of fibrous nanofibers and the like appearing in white was a carbon material. It was confirmed that these particles were generated from the particle surface and surrounded these particles. Further, when elemental analysis was performed on nanofibers and the like observed by SEM using an energy dispersive X-ray analyzer (EDX), silicon peaks were confirmed (a representative example is shown in the graph of FIG. 2). Moreover, when SEM observation of the carbon material cross section was performed, the secondary particle average particle size of the silicon monoxide particles in the carbon material was 3 μm (a representative example is shown in the photograph of FIG. 3). The obtained carbon material contained 26.8% by mass of silicon monoxide.
本発明の炭素材およびケイ素の合金、酸化物、窒化物もしくは炭化物を含む（１次）粒子の粒子径は、レーザー回折折散乱粒度分布測定装置（ベックマン・コールター（株）社製ＬＳ−２３０）を用いて測定した。平均粒子径は体積換算とし、頻度が累積で５０％になったところを平均粒子径と定義した。
また、本発明の複合粒子中の前記ケイ素含有粒子の２次粒子平均粒径は、よく混合した炭素材粒子を１０サンプル任意に抽出し、その断面を走査型電子顕微鏡（ＳＥＭ）を用いて観察した際の２次凝集粒子の長径を測定、その平均値を２次粒子平均粒径とした。
The particle diameter of the (primary) particles containing the carbon material and silicon alloy, oxide, nitride or carbide of the present invention is measured by a laser diffraction diffraction scattering particle size distribution analyzer (LS-230 manufactured by Beckman Coulter, Inc.). It measured using. The average particle diameter was converted to volume, and the place where the frequency reached 50% cumulatively was defined as the average particle diameter.
Further, the secondary particle average particle size of the silicon-containing particles in the composite particles of the present invention is obtained by arbitrarily extracting 10 samples of well-mixed carbon material particles and observing the cross section using a scanning electron microscope (SEM). The major axis of the secondary agglomerated particles was measured, and the average value was defined as the average secondary particle size.
充放電特性の評価
（１）負極の作製
上記で得られた炭素材を用い、これに対して結着剤としてポリフッ化ビニリデン１０％、アセチレンブラック３％の割合で、それぞれ配合し、さらに、希釈溶媒としてＮ−メチル−２−ピロリドンを適量加え混合し、スラリー状の負極用混合物を調製した。
この負極スラリー状混合物を１０μｍの銅箔の両面に塗布し、その後、１１０℃で１時間真空乾燥した。真空乾燥後、ロールプレスによって電極を１００μｍに加圧成形した。これを幅４０ｍｍで長さ２９０ｍｍの大きさに切り出し負極を作製した。この負極を用いて、リチウムイオン２次電池用電極としてφ１３ｍｍの径で打ち抜き負極とした。
Evaluation of charge / discharge characteristics (1) Production of negative electrode Using the carbon material obtained above, the binder was blended at a ratio of 10% polyvinylidene fluoride and 3% acetylene black, respectively, and further diluted. An appropriate amount of N-methyl-2-pyrrolidone as a solvent was added and mixed to prepare a slurry-like negative electrode mixture.
This negative electrode slurry mixture was applied to both sides of a 10 μm copper foil, and then vacuum dried at 110 ° C. for 1 hour. After vacuum drying, the electrode was pressure-formed to 100 μm by a roll press. This was cut into a size of 40 mm in width and 290 mm in length to produce a negative electrode. Using this negative electrode, a negative electrode was punched out with a diameter of 13 mm as an electrode for a lithium ion secondary battery.
（２）リチウムイオン２次電池の作製
上記負極、セパレータ（ポリプロピレン製多孔質フィルム：直径φ１６、厚さ２５μｍ）、作用極としてリチウム金属（直径φ１２、厚さ１ｍｍ）の順で、宝泉製２０３２型コインセル内の所定の位置に配置した。さらに、電解液としてエチレンカーボネートとジエチレンカーボネートの混合液（体積比が１：１）に、過塩素酸リチウムを１［モル／リットル］の濃度で溶解させたものを注液し、リチウムイオン２次電池を作製した。
(2) Production of Lithium Ion Secondary Battery The negative electrode, separator (polypropylene porous film: diameter φ16, thickness 25 μm), and lithium metal (diameter φ12, thickness 1 mm) as the working electrode in order of Hosen 2032 The coin cell was placed at a predetermined position in the coin cell. Further, an electrolyte solution in which lithium perchlorate is dissolved at a concentration of 1 [mol / liter] in a mixed solution of ethylene carbonate and diethylene carbonate (volume ratio is 1: 1) is injected into a lithium ion secondary. A battery was produced.
（３）電池特性の評価
〈初期充放電特性評価〉
充電容量については、充電時の電流密度を２５ｍＡ／ｇとして定電流充電を行い、電位が０Ｖに達した時点から、０Ｖで定電圧充電を行い、電流密度が１．２５ｍＡ／ｇになるまでに充電した電気量を充電容量とした。
一方、放電容量については、放電時の電流密度も２５ｍＡ／ｇとして定電流放電を行い、電位が２．５Ｖに達した時点から、２．５Ｖで定電圧放電を行い、電流密度が１．２５ｍＡ／ｇになるまでに放電した電気量を放電容量とした。
なお、充放電特性の評価は、充放電特性評価装置（北斗電工（株）製：ＨＪＲ−１０１０ｍＳＭ８）を用いて行った。
また、以下の式により初回の充放電効率を定義した。
初回充放電効率（％）＝初回放電容量（ｍＡｈ／ｇ）／初回充電容量（ｍＡｈ／ｇ）×１００
(3) Evaluation of battery characteristics <Evaluation of initial charge / discharge characteristics>
Regarding the charging capacity, constant current charging is performed with the current density at the time of charging being 25 mA / g, and from the time when the potential reaches 0 V, constant voltage charging is performed at 0 V until the current density reaches 1.25 mA / g. The amount of electricity charged was taken as the charge capacity.
On the other hand, with respect to the discharge capacity, constant current discharge was performed with a current density at the time of discharge of 25 mA / g, and constant voltage discharge was performed at 2.5 V from the time when the potential reached 2.5 V, and the current density was 1.25 mA. The amount of electricity discharged up to / g was taken as the discharge capacity.
In addition, evaluation of the charging / discharging characteristic was performed using the charging / discharging characteristic evaluation apparatus (Hokuto Denko Co., Ltd. product: HJR-1010mSM8).
The initial charge / discharge efficiency was defined by the following equation.
Initial charge / discharge efficiency (%) = initial discharge capacity (mAh / g) / initial charge capacity (mAh / g) × 100
〈サイクル性評価〉
初期充放電特性評価条件を３００回繰り返し測定した後に得られた放電容量を３００サイクル目の放電容量とした。また、以下の式によりサイクル性（３００サイクル容量維持率）を定義した。
サイクル性（％、３００サイクル容量維持率）＝３００サイクル目の放電容量（ｍＡｈ／ｇ）／初回放電容量（ｍＡｈ／ｇ）×１００
<Cycle evaluation>
The discharge capacity obtained after repeatedly measuring the initial charge / discharge characteristic evaluation conditions 300 times was defined as the discharge capacity at the 300th cycle. In addition, the cycle property (300 cycle capacity maintenance rate) was defined by the following equation.
Cycle performance (%, 300 cycle capacity retention rate) = 300th cycle discharge capacity (mAh / g) / initial discharge capacity (mAh / g) × 100
＜実施例２＞
ノボラック型フェノール樹脂（住友ベークライト株式会社製ＰＲ−５１５３０）１００質量部およびヘキサメチレンテトラミン（三菱瓦斯化学株式会社製）１０質量部、メタノール１０質量部、さらに一酸化ケイ素２５質量部（平均粒子径１．２μｍ）をニーダーで、回転数５０ｒｐｍ、４０℃、３０分間混合し、樹脂スラリーを得た。攪拌終了後、得られた樹脂スラリーを１７５℃にて５時間硬化処理を行った。硬化処理後、窒素雰囲気下にて昇温し、５００℃到達後３時間の炭化を行った。得られた炭素材を平均粒子径が１０μｍになるまで粉砕処理を行い、粉砕処理により得られた炭素材を、さらに昇温し、１１００℃到達後３時間の炭化処理を行い、２次電池負極用炭素材を得た。得られた炭素材について、走査型電子顕微鏡（ＳＥＭ）を用いて炭素材表面の観察を行ったところ、炭素材粒子表面にナノファイバー等の生成が確認され、観察されたナノファイバー等をエネルギー分散型Ｘ線分析装置（ＥＤＸ）を用いて元素分析を行ったところ、ケイ素のピークが確認された。また、炭素材の断面のＳＥＭ観察を行ったところ、炭素材中の金属粒子の２次粒子平均粒径は３．３μｍであった。また、得られた炭素材には一酸化ケイ素が２７．０質量％含有されていた。
<Example 2>
100 parts by weight of a novolac type phenolic resin (PR-51530, manufactured by Sumitomo Bakelite Co., Ltd.), 10 parts by weight of hexamethylenetetramine (manufactured by Mitsubishi Gas Chemical Co., Inc.), 10 parts by weight of methanol, and 25 parts by weight of silicon monoxide (average particle size 1) 2 μm) was mixed with a kneader at a rotation speed of 50 rpm and 40 ° C. for 30 minutes to obtain a resin slurry. After the stirring was completed, the obtained resin slurry was cured at 175 ° C. for 5 hours. After the curing treatment, the temperature was raised in a nitrogen atmosphere, and carbonization was performed for 3 hours after reaching 500 ° C. The obtained carbon material is pulverized until the average particle size becomes 10 μm. The carbon material obtained by the pulverization is further heated, and carbonized for 3 hours after reaching 1100 ° C. Carbon material for use was obtained. About the obtained carbon material, when the carbon material surface was observed using a scanning electron microscope (SEM), the production | generation of nanofiber etc. was confirmed on the carbon material particle surface, and energy dispersion was performed for the observed nanofiber etc. When elemental analysis was performed using a type X-ray analyzer (EDX), a silicon peak was confirmed. Moreover, when the SEM observation of the cross section of a carbon material was performed, the secondary particle average particle diameter of the metal particle in a carbon material was 3.3 micrometers. The obtained carbon material contained 27.0% by mass of silicon monoxide.
＜実施例３＞
ノボラック型フェノール樹脂（住友ベークライト株式会社製ＰＲ−５１５３０）１００質量部およびヘキサメチレンテトラミン（三菱瓦斯化学株式会社製）１０質量部、メタノール１０質量部、さらに一酸化ケイ素４０質量部（平均粒子径０．７μｍ）をニーダーで、回転数５０ｒｐｍ、４０℃、３０分間混合し、樹脂スラリーを得た。攪拌終了後、得られた樹脂スラリーを１７５℃にて５時間硬化処理を行った。硬化処理後、窒素雰囲気下にて昇温し、５００℃到達後３時間の炭化を行った。得られた炭素材を平均粒子径が１０μｍになるまで粉砕処理を行い、粉砕処理により得られた炭素材を、さらに昇温し、１１００℃到達後３時間の炭化処理を行い、２次電池負極用炭素材を得た。得られた炭素材について、走査型電子顕微鏡（ＳＥＭ）を用いて炭素材表面の観察を行ったところ、炭素材粒子表面にナノファイバー等の生成が確認され、観察されたナノファイバー等をエネルギー分散型Ｘ線分析装置（ＥＤＸ）を用いて元素分析を行ったところ、ケイ素のピークが確認された。また、炭素材の断面のＳＥＭ観察を行ったところ、炭素材中の金属粒子の２次粒子平均粒径は４μｍであった。また、得られた炭素材には一酸化ケイ素が４１．１質量％含有されていた。
<Example 3>
100 parts by weight of novolak type phenolic resin (PR-51530 manufactured by Sumitomo Bakelite Co., Ltd.), 10 parts by weight of hexamethylenetetramine (manufactured by Mitsubishi Gas Chemical Co., Inc.), 10 parts by weight of methanol, and 40 parts by weight of silicon monoxide (average particle size 0) 0.7 μm) was mixed with a kneader at a rotation speed of 50 rpm and 40 ° C. for 30 minutes to obtain a resin slurry. After the stirring was completed, the obtained resin slurry was cured at 175 ° C. for 5 hours. After the curing treatment, the temperature was raised in a nitrogen atmosphere, and carbonization was performed for 3 hours after reaching 500 ° C. The obtained carbon material is pulverized until the average particle size becomes 10 μm. The carbon material obtained by the pulverization is further heated, and carbonized for 3 hours after reaching 1100 ° C. Carbon material for use was obtained. About the obtained carbon material, when the carbon material surface was observed using a scanning electron microscope (SEM), the production | generation of nanofiber etc. was confirmed on the carbon material particle surface, and energy dispersion was performed for the observed nanofiber etc. When elemental analysis was performed using a type X-ray analyzer (EDX), a silicon peak was confirmed. Moreover, when the SEM observation of the cross section of a carbon material was performed, the secondary particle average particle diameter of the metal particle in a carbon material was 4 micrometers. The obtained carbon material contained 41.1% by mass of silicon monoxide.
＜実施例４＞
メタクレゾール（関東化学株式会社製）１００質量部と４３％ホルムアルデヒド水溶液（住友ベークライト株式会社製）５３．３質量部、しゅう酸（関東化学株式会社製）３質量部を攪拌機及び冷却管を備えた３つ口フラスコに入れ、１００℃で３時間反応後、昇温脱水し、メタクレゾール樹脂９０質量部を得た。上記操作を繰り返して得られたメタクレゾール樹脂１００質量部およびヘキサメチレンテトラミン（三菱瓦斯化学株式会社製）１０質量部、ジメチルスルホアミド１０質量部、さらに一酸化ケイ素２５質量部（平均粒子径１．２μｍ）をニーダーで、回転数５０ｒｐｍ、４０℃、３０分間混合し、樹脂スラリーを得た。攪拌終了後、得られた樹脂スラリーを１７５℃にて５時間硬化処理を行った。硬化処理後、窒素雰囲気下にて昇温し、５００℃到達後３時間の炭化を行った。得られた炭素材を平均粒子径が９μｍになるまで粉砕処理を行い、粉砕処理により得られた炭素材を、さらに昇温し、１１００℃到達後３時間の炭化処理を行い、２次電池負極用炭素材を得た。得られた炭素材について、走査型電子顕微鏡（ＳＥＭ）を用いて炭素材表面の観察を行ったところ、炭素材粒子表面にナノファイバー等の生成が確認され、観察されたナノファイバー等をエネルギー分散型Ｘ線分析装置（ＥＤＸ）を用いて元素分析を行ったところ、ケイ素のピークが確認された。また、炭素材の断面のＳＥＭ観察を行ったところ、炭素材中の金属粒子の２次粒子平均粒径は３．５μｍであった。また、得られた炭素材には一酸化ケイ素が２６．７質量％含有されていた。
<Example 4>
100 parts by mass of metacresol (manufactured by Kanto Chemical Co., Inc.), 53.3 parts by mass of a 43% formaldehyde aqueous solution (manufactured by Sumitomo Bakelite Co., Ltd.), and 3 parts by mass of oxalic acid (manufactured by Kanto Chemical Co., Ltd.) were equipped with a stirrer and a condenser. The mixture was placed in a three-necked flask and reacted at 100 ° C. for 3 hours, followed by dehydration at elevated temperature to obtain 90 parts by mass of a metacresol resin. 100 parts by mass of a metacresol resin obtained by repeating the above operation, 10 parts by mass of hexamethylenetetramine (manufactured by Mitsubishi Gas Chemical Co., Inc.), 10 parts by mass of dimethylsulfamide, and 25 parts by mass of silicon monoxide (average particle diameter of 1. 2 μm) was mixed with a kneader at a rotation speed of 50 rpm and 40 ° C. for 30 minutes to obtain a resin slurry. After the stirring was completed, the obtained resin slurry was cured at 175 ° C. for 5 hours. After the curing treatment, the temperature was raised in a nitrogen atmosphere, and carbonization was performed for 3 hours after reaching 500 ° C. The obtained carbon material is pulverized until the average particle size becomes 9 μm, and the carbon material obtained by the pulverization is further heated, and carbonized for 3 hours after reaching 1100 ° C. Carbon material for use was obtained. About the obtained carbon material, when the carbon material surface was observed using a scanning electron microscope (SEM), the production | generation of nanofiber etc. was confirmed on the carbon material particle surface, and energy dispersion was performed for the observed nanofiber etc. When elemental analysis was performed using a type X-ray analyzer (EDX), a silicon peak was confirmed. Moreover, when the SEM observation of the cross section of a carbon material was performed, the secondary particle average particle diameter of the metal particle in a carbon material was 3.5 micrometers. Further, the obtained carbon material contained 26.7% by mass of silicon monoxide.
＜実施例５＞
メタクレゾール（関東化学株式会社製）１００質量部と４３％ホルムアルデヒド水溶液（住友ベークライト株式会社製）５３．３質量部、しゅう酸（関東化学株式会社製）３質量部を攪拌機及び冷却管を備えた３つ口フラスコに入れ、１００℃で３時間反応後、昇温脱水し、メタクレゾール樹脂９０質量部を得た。上記操作を繰り返して得られたメタクレゾール樹脂１００質量部およびヘキサメチレンテトラミン（三菱瓦斯化学株式会社製）１０質量部、ジメチルスルホアミド１０質量部、さらに一酸化ケイ素３５質量部（平均粒子径０．５μｍ）をニーダーで、回転数５０ｒｐｍ、４０℃、３０分間混合し、樹脂スラリーを得た。攪拌終了後、得られた樹脂スラリーを１７５℃にて５時間硬化処理を行った。硬化処理後、窒素雰囲気下にて昇温し、５００℃到達後３時間の炭化を行った。得られた炭素材を平均粒子径が１０μｍになるまで粉砕処理を行い、粉砕処理により得られた炭素材を、さらに昇温し、１１００℃到達後３時間の炭化処理を行い、２次電池負極用炭素材を得た。得られた炭素材について、走査型電子顕微鏡（ＳＥＭ）を用いて炭素材表面の観察を行ったところ、炭素材粒子表面にナノファイバー等の生成が確認され、観察されたナノファイバー等をエネルギー分散型Ｘ線分析装置（ＥＤＸ）を用いて元素分析を行ったところ、ケイ素のピークが確認された。また、炭素材の断面のＳＥＭ観察を行ったところ、炭素材中の金属粒子の２次粒子平均粒径は５μｍであった。また、得られた炭素材には一酸化ケイ素が３６．５質量％含有されていた。
<Example 5>
100 parts by mass of metacresol (manufactured by Kanto Chemical Co., Inc.), 53.3 parts by mass of a 43% formaldehyde aqueous solution (manufactured by Sumitomo Bakelite Co., Ltd.), and 3 parts by mass of oxalic acid (manufactured by Kanto Chemical Co., Ltd.) were equipped with a stirrer and a condenser. The mixture was placed in a three-necked flask and reacted at 100 ° C. for 3 hours, followed by dehydration at elevated temperature to obtain 90 parts by mass of a metacresol resin. 100 parts by mass of a metacresol resin obtained by repeating the above operation, 10 parts by mass of hexamethylenetetramine (manufactured by Mitsubishi Gas Chemical Co., Inc.), 10 parts by mass of dimethylsulfamide, and 35 parts by mass of silicon monoxide (average particle size of 0. 5 μm) was mixed with a kneader at 50 rpm and 40 ° C. for 30 minutes to obtain a resin slurry. After the stirring was completed, the obtained resin slurry was cured at 175 ° C. for 5 hours. After the curing treatment, the temperature was raised in a nitrogen atmosphere, and carbonization was performed for 3 hours after reaching 500 ° C. The obtained carbon material is pulverized until the average particle size becomes 10 μm. The carbon material obtained by the pulverization is further heated, and carbonized for 3 hours after reaching 1100 ° C. Carbon material for use was obtained. About the obtained carbon material, when the carbon material surface was observed using a scanning electron microscope (SEM), the production | generation of nanofiber etc. was confirmed on the carbon material particle surface, and energy dispersion was performed for the observed nanofiber etc. When elemental analysis was performed using a type X-ray analyzer (EDX), a silicon peak was confirmed. Moreover, when the SEM observation of the cross section of a carbon material was performed, the secondary particle average particle diameter of the metal particle in a carbon material was 5 micrometers. The obtained carbon material contained 36.5% by mass of silicon monoxide.
＜比較例１＞
ノボラック型フェノール樹脂（住友ベークライト株式会社製ＰＲ−５１５３０）１００質量部およびヘキサメチレンテトラミン（三菱瓦斯化学株式会社製）１０質量部、メタノール１０質量部、さらに一酸化ケイ素２５質量部（平均粒子径１．２μｍ）をニーダーで、回転数２５ｒｐｍ、４０℃、１０分間混合し、樹脂スラリーを得た。攪拌終了後、得られた樹脂スラリーを１７５℃にて５時間硬化処理を行った。硬化処理後、窒素雰囲気下にて昇温し、５００℃到達後３時間の炭化を行った。得られた炭素材を平均粒子径が１５μｍになるまで粉砕処理を行い、粉砕処理により得られた炭素材を、さらに昇温し、１１００℃到達後３時間の炭化処理を行い、２次電池負極用炭素材を得た。得られた炭素材について、走査型電子顕微鏡（ＳＥＭ）を用いて炭素材表面の観察を行ったところ、炭素材粒子表面にナノファイバー等の生成が確認され、観察されたナノファイバー等をエネルギー分散型Ｘ線分析装置（ＥＤＸ）を用いて元素分析を行ったところ、ケイ素のピークが確認された。また、炭素材の断面のＳＥＭ観察を行ったところ、炭素材中の金属粒子の２次粒子平均粒径は９μｍであった。また、得られた炭素材には一酸化ケイ素が２６．４質量％含有されていた。
<Comparative Example 1>
100 parts by weight of a novolac type phenolic resin (PR-51530, manufactured by Sumitomo Bakelite Co., Ltd.), 10 parts by weight of hexamethylenetetramine (manufactured by Mitsubishi Gas Chemical Co., Inc.), 10 parts by weight of methanol, and 25 parts by weight of silicon monoxide (average particle size 1) .2 μm) was mixed with a kneader at a rotational speed of 25 rpm, 40 ° C. for 10 minutes to obtain a resin slurry. After the stirring was completed, the obtained resin slurry was cured at 175 ° C. for 5 hours. After the curing treatment, the temperature was raised in a nitrogen atmosphere, and carbonization was performed for 3 hours after reaching 500 ° C. The obtained carbon material is pulverized until the average particle size becomes 15 μm, and the carbon material obtained by the pulverization is further heated, and carbonized for 3 hours after reaching 1100 ° C. Carbon material for use was obtained. About the obtained carbon material, when the carbon material surface was observed using a scanning electron microscope (SEM), the production | generation of nanofiber etc. was confirmed on the carbon material particle surface, and energy dispersion was performed for the observed nanofiber etc. When elemental analysis was performed using a type X-ray analyzer (EDX), a silicon peak was confirmed. Moreover, when the SEM observation of the cross section of a carbon material was performed, the secondary particle average particle diameter of the metal particle in a carbon material was 9 micrometers. The obtained carbon material contained 26.4% by mass of silicon monoxide.
＜比較例２＞
ノボラック型フェノール樹脂（住友ベークライト株式会社製ＰＲ−５１５３０）１００質量部およびヘキサメチレンテトラミン（三菱瓦斯化学株式会社製）１０質量部、メタノール１０質量部、さらにケイ素（株式会社高純度化学研究所製のものを粉砕）２０質量部（平均粒子径１．０μｍ）をニーダーで、回転数５０ｒｐｍ、４０℃、３０分間混合し、樹脂スラリーを得た。攪拌終了後、得られた樹脂スラリーを１７５℃にて５時間硬化処理を行った。硬化処理後、窒素雰囲気下にて昇温し、５００℃到達後３時間の炭化を行った。得られた炭素材を平均粒子径が９μｍになるまで粉砕処理を行い、粉砕処理により得られた炭素材を、さらに昇温し、１１００℃到達後３時間の炭化処理を行い、２次電池負極用炭素材を得た。得られた炭素材について、走査型電子顕微鏡（ＳＥＭ）を用いて炭素材表面の観察を行ったところ、炭素材粒子表面にナノファイバー等の生成が確認されなかった。また、炭素材の断面のＳＥＭ観察を行ったところ、炭素材中の金属粒子の２次粒子平均粒径は３μｍであった。また、得られた炭素材にはケイ素が２０．９質量％含有されていた。
<Comparative example 2>
100 parts by weight of a novolac type phenolic resin (PR-51530 manufactured by Sumitomo Bakelite Co., Ltd.), 10 parts by weight of hexamethylenetetramine (manufactured by Mitsubishi Gas Chemical Co., Ltd.), 10 parts by weight of methanol, and silicon (manufactured by High Purity Chemical Research Laboratory) 20 parts by mass (average particle size: 1.0 μm) was mixed with a kneader at 50 rpm, 40 ° C. for 30 minutes to obtain a resin slurry. After the stirring was completed, the obtained resin slurry was cured at 175 ° C. for 5 hours. After the curing treatment, the temperature was raised in a nitrogen atmosphere, and carbonization was performed for 3 hours after reaching 500 ° C. The obtained carbon material is pulverized until the average particle size becomes 9 μm, and the carbon material obtained by the pulverization is further heated, and carbonized for 3 hours after reaching 1100 ° C. Carbon material for use was obtained. About the obtained carbon material, when the carbon material surface was observed using the scanning electron microscope (SEM), the production | generation of nanofiber etc. was not confirmed on the carbon material particle surface. Moreover, when the SEM observation of the cross section of a carbon material was performed, the secondary particle average particle diameter of the metal particle in a carbon material was 3 micrometers. The obtained carbon material contained 20.9% by mass of silicon.
上記各実施例、比較例について、炭素材の電池特性の評価結果を表１に示す。 Table 1 shows the evaluation results of the battery characteristics of the carbon material for each of the above Examples and Comparative Examples.
表１から明らかなように、実施例１〜５のリチウムイオン２次電池は、３００サイクル
後の容量維持率が８０％以上あり、同５０％以下の比較例１、２と比べ、充放電サイクル特性が顕著に向上した。これは、図１、図３に代表されるように、実施例ではナノファイバー等からなる網状構造体が複合粒子の表面から発生し、これらの粒子を包囲し、さらには本発明のリチウムイオンの吸蔵・放出が可能なケイ素の合金、酸化物、窒化物もしくは炭化物を含むケイ素含有（１次）粒子がよく分散して２次粒子が小さくなっている結果、充放電サイクルによる負極用炭素材の膨張収縮に伴う微粉化が抑制されたためであると考えられる。これに対し、比較例１では、ナノファイバー等からなる網状構造体が複合粒子の表面から発生し、これらの粒子を包囲しているものの、本発明のリチウムイオンの吸蔵・放出が可能なケイ素の合金、酸化物、窒化物もしくは炭化物を含むケイ素含有（１次）粒子の凝集が著しく、２次粒子が大きくなっており、比較例２では、粒子を包囲する網状構造体が存在しないため、前記２次粒子が小さくなっているにもかかわらず、前記充放電サイクルによる負極用炭素材の膨張収縮に伴う微粉化が進行し、実質的に電極が崩壊した。
As is clear from Table 1, the lithium ion secondary batteries of Examples 1 to 5 have a capacity maintenance rate of 80% or more after 300 cycles, and charge / discharge cycles as compared with Comparative Examples 1 and 2 of 50% or less. The characteristics were significantly improved. As represented by FIG. 1 and FIG. 3, in this embodiment, a network structure composed of nanofibers or the like is generated from the surface of the composite particles, surrounds these particles, and further, the lithium ion of the present invention. As a result of the well-dispersed silicon-containing (primary) particles containing silicon alloys, oxides, nitrides or carbides that can be occluded / released, the secondary particles become smaller. This is considered to be because the pulverization accompanying expansion and contraction was suppressed. On the other hand, in Comparative Example 1, although a network structure composed of nanofibers or the like is generated from the surface of the composite particle and surrounds these particles, the silicon of the present invention capable of occluding and releasing lithium ions is used. Aggregation of silicon-containing (primary) particles containing an alloy, oxide, nitride, or carbide is remarkably large, and the secondary particles are large. In Comparative Example 2, there is no network structure surrounding the particles. Despite secondary particles becoming smaller, pulverization accompanying the expansion and contraction of the carbon material for a negative electrode due to the charge / discharge cycle proceeded, and the electrode substantially collapsed.
Claims (6)
該複合粒子の表面に結合し、かつ、該複合粒子を包囲するナノファイバーおよび／またはナノチューブからなるケイ素含有網状構造体を含み、前記樹脂炭素材と前記網状構造体は、炭素前駆体を炭化処理することにより形成され、前記網状構造体は、見かけ上、複合粒子の表面を起点に形成され、
該複合粒子中の前記ケイ素含有粒子の２次粒子平均粒径が、１次粒子最小粒径以上、５μｍ以下であることを特徴とする、リチウム２次電池負極用炭素材。 Silicon-containing particles containing an alloy, oxide, nitride or carbide of silicon capable of occluding and releasing lithium ions having an average primary particle diameter of 5 nm to 1.5 μm, and resin charcoal surrounding the silicon-containing particles A composite particle composed of a raw material, and a silicon-containing network composed of nanofibers and / or nanotubes that bind to and surround the surface of the composite particle, the resin carbon material and the network structure Is formed by carbonizing a carbon precursor, and the network structure is apparently formed from the surface of the composite particle,
A carbon material for a lithium secondary battery negative electrode, wherein the silicon-containing particles in the composite particles have an average secondary particle size of not less than a minimum primary particle size of 5 μm or less.
A lithium secondary battery comprising the lithium secondary battery negative electrode according to claim 5 .
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