JP5448555B2 - Negative electrode for lithium ion secondary battery, lithium ion secondary battery using the same, slurry for preparing negative electrode for lithium ion secondary battery, and method for producing negative electrode for lithium ion secondary battery - Google Patents
Negative electrode for lithium ion secondary battery, lithium ion secondary battery using the same, slurry for preparing negative electrode for lithium ion secondary battery, and method for producing negative electrode for lithium ion secondary battery Download PDFInfo
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Description
本発明は、リチウムイオン二次電池用の負極などに関するものであり、特に、高容量かつ長寿命のリチウムイオン二次電池用の負極に関する。 The present invention relates to a negative electrode for a lithium ion secondary battery, and more particularly to a negative electrode for a lithium ion secondary battery having a high capacity and a long life.
従来、負極活物質としてグラファイトを用いたリチウムイオン二次電池が実用化されている。また、負極活物質と、カーボンブラック等の導電助剤と、樹脂の結着剤とを混練してスラリーを調製し、銅箔上に塗布・乾燥して、負極を形成することが行われている。 Conventionally, lithium ion secondary batteries using graphite as a negative electrode active material have been put into practical use. Also, a negative electrode is formed by kneading a negative electrode active material, a conductive aid such as carbon black, and a resin binder to prepare a slurry, and applying and drying on a copper foil. Yes.
一方、高容量化を目指し、負極活物質として金属、特にシリコン系合金を用いるリチウムイオン二次電池用の負極が開発されている。リチウムイオンを吸蔵して合金化したシリコンは、吸蔵前のシリコンに対して約４倍まで体積が膨張するため、シリコン系合金を負極活物質として用いた負極は、充放電サイクル時に膨張と収縮を繰り返す。 On the other hand, with the aim of increasing the capacity, negative electrodes for lithium ion secondary batteries using metals, particularly silicon alloys, as negative electrode active materials have been developed. Silicon alloyed by occlusion of lithium ions expands in volume up to about 4 times that of silicon before occlusion, so a negative electrode using a silicon-based alloy as a negative electrode active material expands and contracts during a charge / discharge cycle. repeat.
そこで、シリコン系活物質の表面にカーボンナノファイバーを成長させ、その弾性作用により負極活物質粒子の膨張と収縮による歪みを緩和し、サイクル特性を向上させるという非水電解液二次電池用負極が開示されている(例えば、特許文献１を参照)。 Therefore, a negative electrode for a non-aqueous electrolyte secondary battery that grows carbon nanofibers on the surface of a silicon-based active material, relaxes strain due to expansion and contraction of negative electrode active material particles by its elastic action, and improves cycle characteristics. It is disclosed (see, for example, Patent Document 1).
しかしながら、負極活物質と導電助剤と結着剤とのスラリーを塗布・乾燥して、負極を形成する従来の負極は、負極活物質と集電体とを樹脂の結着剤で結着しており、樹脂の結合力が弱い。また、粉末状の負極活物質を用いている。そのため、充放電時に、負極活物質の微粉化と負極活物質の剥離、負極の亀裂の発生、負極活物質間の導電性の低下などが発生して容量が低下する。それゆえ、サイクル特性が悪く、二次電池の寿命が短いという問題点があった。 However, a conventional negative electrode that forms a negative electrode by applying and drying a slurry of a negative electrode active material, a conductive additive, and a binder, binds the negative electrode active material and the current collector with a resin binder. The bonding strength of the resin is weak. In addition, a powdered negative electrode active material is used. Therefore, during charge and discharge, the negative electrode active material is pulverized, the negative electrode active material is peeled off, the negative electrode is cracked, the conductivity between the negative electrode active materials is reduced, and the capacity is reduced. Therefore, there are problems that the cycle characteristics are poor and the life of the secondary battery is short.
また、特許文献１に記載の発明は、負極活物質と集電体とを樹脂で結着するものであり、サイクル特性の劣化は十分には防げなかった。また、カーボンナノファイバーの形成工程があるため、生産性が悪かった。 In addition, the invention described in Patent Document 1 binds the negative electrode active material and the current collector with a resin, and the cycle characteristics cannot be sufficiently prevented from being deteriorated. In addition, the productivity was poor due to the formation process of carbon nanofibers.
本発明は、前述した問題点に鑑みてなされたもので、その目的とすることは、高容量と長寿命を実現し、生産性に優れるリチウムイオン二次電池用の負極を得ることである。 The present invention has been made in view of the above-described problems, and an object of the present invention is to obtain a negative electrode for a lithium ion secondary battery that realizes a high capacity and a long life and is excellent in productivity.
前述した目的を達成するために、第１の発明は、金属製の集電体と、前記集電体上に、結着剤で結合している負極活物質と導電助剤と、を有し、前記負極活物質が、ワイヤー形状の負極活物質を含み、金属ナノ粒子を介して、前記負極活物質と前記集電体または前記負極活物質と前記導電助剤とが、金属結合により結合しており、前記負極活物質が、シリコン、スズ、アンチモン、アルミニウム、鉛、ヒ素からなる群より選ばれた少なくとも１種の物質またはそれらの合金を含み、前記導電助剤が、炭素、銅、スズ、亜鉛、ニッケル、銀からなる群より選ばれた少なくとも１種の物質またはそれらの合金を含むことを特徴とするリチウムイオン二次電池用の負極である。なお、第１の発明に記載の「結着剤」とは、集電体上に負極活物質と導電助剤とを結合する物質を広く意味し、後述する樹脂の結着剤９だけでなく、後述する金属ナノ粒子２５も含む概念である。
前記第１の発明において、前記金属ナノ粒子の一次粒子の平均粒径は、２〜１００ｎｍであることが好ましい。また、前記金属ナノ粒子の金属の量が、前記導電助剤の金属の粉末に対して２〜４０重量％であることが好ましい。
In order to achieve the above-described object, the first invention includes a metal current collector, and a negative electrode active material and a conductive additive bonded on the current collector with a binder. the negative active material is observed including a negative electrode active material of the wire-shaped, through the metal nanoparticles, the negative active material and the current collector or the negative electrode active material and the conductive aid is bonded by a metal bond The negative electrode active material includes at least one material selected from the group consisting of silicon, tin, antimony, aluminum, lead, and arsenic, or an alloy thereof, and the conductive additive includes carbon, copper, A negative electrode for a lithium ion secondary battery comprising at least one substance selected from the group consisting of tin, zinc, nickel, and silver, or an alloy thereof . The “binder” described in the first invention broadly means a substance that binds the negative electrode active material and the conductive additive on the current collector, and includes not only the resin binder 9 described later. The concept includes the metal nanoparticles 25 described later.
In the first invention, the average particle diameter of primary particles of the metal nanoparticles is preferably 2 to 100 nm. Moreover, it is preferable that the quantity of the metal of the said metal nanoparticle is 2 to 40 weight% with respect to the metal powder of the said conductive support agent.
前記ワイヤー形状の負極活物質の長さが０．１μｍ〜２ｍｍであり、前記負極活物質の外径が４ｎｍ〜１０００ｎｍであることが好ましく、前記ワイヤー形状の負極活物質は、一部が直線状あるいは一部が縮れ形状であることが好ましく、前記導電助剤が、ワイヤー形状の導電助剤を含むことが好ましく、さらに負極活物質の体積膨張を吸収する十分な空隙を有することが好ましい。 The wire-shaped negative electrode active material has a length of 0.1 μm to 2 mm, and the negative electrode active material preferably has an outer diameter of 4 nm to 1000 nm. The wire-shaped negative electrode active material is partially linear. Or it is preferable that one part is a crimped shape, and it is preferable that the said conductive support agent contains a wire-shaped conductive support agent, and also has sufficient space | gap which absorbs the volume expansion of a negative electrode active material.
また、前記結着剤が金属ナノ粒子であり、前記金属ナノ粒子を介して、前記負極活物質と前記集電体または前記負極活物質と前記導電助剤とが、金属結合により結合していることが好ましい。 The binder is a metal nanoparticle, and the negative electrode active material and the current collector or the negative electrode active material and the conductive additive are bonded through a metal bond through the metal nanoparticle. It is preferable.
さらに、前記金属ナノ粒子は、銅、スズ、亜鉛、ニッケルおよび銀からなる群より選ばれた少なくとも１種の金属のナノ粒子であり、一次粒子の平均粒径が２ｎｍ〜１００ｎｍであり、前記金属結合が、前記金属ナノ粒子を焼結することにより形成され、前記集電体と前記負極活物質と前記導電助剤と前記金属ナノ粒子との一部または全部に取り囲まれた空隙を有することが好ましい。 Further, the metal nanoparticles are nanoparticles of at least one metal selected from the group consisting of copper, tin, zinc, nickel and silver, and the average particle size of primary particles is 2 nm to 100 nm, The bond is formed by sintering the metal nanoparticles, and has a void surrounded by part or all of the current collector, the negative electrode active material, the conductive additive, and the metal nanoparticles. preferable.
第２の発明は、前記リチウムイオン二次電池用の負極を用いたリチウムイオン二次電池である。 A second invention is a lithium ion secondary battery using the negative electrode for the lithium ion secondary battery.
第３の発明は、負極活物質と、導電助剤と、結着剤とが混在してなるスラリーであって、前記負極活物質が、ワイヤー形状の負極活物質を含み、前記結着剤が金属ナノ粒子を含み、前記負極活物質が、シリコン、スズ、アンチモン、アルミニウム、鉛およびヒ素からなる群より選ばれた少なくとも１種の物質またはそれらの合金を含み、前記導電助剤が、炭素、銅、スズ、亜鉛、ニッケル、銀からなる群より選ばれた少なくとも１種の物質またはそれらの合金を含むことを特徴とするリチウムイオン二次電池用の負極作製用のスラリーである。 A third invention is an anode active material, a conductive additive, a slurry is a binder comprising a mixture, the negative electrode active material, see it contains a negative electrode active material of the wire shape, the binder Includes metal nanoparticles, and the negative electrode active material includes at least one substance selected from the group consisting of silicon, tin, antimony, aluminum, lead, and arsenic, or an alloy thereof, and the conductive additive includes carbon. A slurry for preparing a negative electrode for a lithium ion secondary battery , comprising at least one substance selected from the group consisting of copper, tin, zinc, nickel, and silver, or an alloy thereof .
第４の発明は、負極活物質と導電助剤と結着剤とを混練してスラリーを調製する混練工程と、前記スラリーを集電体に塗布する塗布工程と、前記スラリーを塗布した前記集電体を乾燥する乾燥工程と、を具備し、前記負極活物質が、ワイヤー形状の負極活物質を含み、前記結着剤が金属ナノ粒子を含み、前記集電体が金属製であり、前記負極活物質が、シリコン、スズ、アンチモン、アルミニウム、鉛、ヒ素からなる群より選ばれた少なくとも１種の物質またはそれらの合金を含み、前記導電助剤が、炭素、銅、スズ、亜鉛、ニッケル、銀からなる群より選ばれた少なくとも１種の物質またはそれらの合金を含むことを特徴とするリチウムイオン二次電池用の負極の製造方法である。 According to a fourth aspect of the present invention, there is provided a kneading step of preparing a slurry by kneading a negative electrode active material, a conductive additive, and a binder, an application step of applying the slurry to a current collector, and the collector applied with the slurry. comprising the step of drying the collector and the negative electrode active material, see contains a negative electrode active material of the wire shape, the binder comprises a metal nanoparticle, the current collector is made of metal, The negative electrode active material includes at least one material selected from the group consisting of silicon, tin, antimony, aluminum, lead, and arsenic, or an alloy thereof, and the conductive additive includes carbon, copper, tin, zinc, A method for producing a negative electrode for a lithium ion secondary battery , comprising at least one substance selected from the group consisting of nickel and silver, or an alloy thereof .
また、前記乾燥工程後、前記金属ナノ粒子の金属のバルク体の融点（絶対温度）の１／２以下の温度の不活性雰囲気下で前記集電体を加熱する焼結工程をさらに具備することが好ましい。 Also, after pre-Symbol drying step, further comprising a sintering step of heating the current collector under an inert atmosphere of 1/2 or less of the temperature of the melting point (absolute temperature) of the bulk of the metal of the metal nanoparticles It is preferable.
本発明の特徴は、負極中にワイヤー形状（＝線形状、線状）の負極活物質を含んでいれば良く、粒子状の負極活物質が配合されていても、配合されていなくても良い。また、導電助剤はワイヤー形状であっても、粒子状であっても、あるいは粒子が連鎖してストラクチャーを形成していても、それらの単純な混合であっても、凝集体あるいは造粒体であってもよい。 The feature of the present invention is that the negative electrode contains a negative electrode active material in a wire shape (= linear shape, linear shape), and a particulate negative electrode active material may or may not be blended. . In addition, the conductive assistant may be in the form of a wire, a particle, a chain of particles to form a structure, or a simple mixture thereof. It may be.
本発明により、高容量と長寿命を実現し、生産性に優れるリチウムイオン二次電池用の負極を得ることができる。 According to the present invention, a negative electrode for a lithium ion secondary battery that achieves a high capacity and a long life and is excellent in productivity can be obtained.
以下図面に基づいて、本発明の実施形態を詳細に説明する。なお、各図は各構成要素を模式的に示したもので、実際の縮尺を表すものではない。 Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Each drawing schematically shows each component, and does not represent an actual scale.
本実施形態に係る負極１について説明する。図１（ａ）は、負極１を示す図である。負極１は、集電体３の上に、導電助剤７と負極活物質５と、結着剤９と、空隙１０とを有する。結着剤９は、集電体３、負極活物質５、導電助剤７を結着している。 The negative electrode 1 according to this embodiment will be described. FIG. 1A shows the negative electrode 1. The negative electrode 1 has a conductive additive 7, a negative electrode active material 5, a binder 9, and voids 10 on a current collector 3. The binder 9 binds the current collector 3, the negative electrode active material 5, and the conductive additive 7.
集電体３は、銅、ニッケル、ステンレスからなる群より選ばれた少なくとも1種の金属からなる箔である。それぞれを単独で用いてもよいし、それぞれの合金でもよい。厚さは４μｍ〜３５μｍが好ましく、さらに８μｍ〜１８μｍがより好ましい。 The current collector 3 is a foil made of at least one metal selected from the group consisting of copper, nickel, and stainless steel. Each may be used alone or may be an alloy of each. The thickness is preferably 4 μm to 35 μm, and more preferably 8 μm to 18 μm.
負極活物質５は、シリコン、スズ、アンチモン、アルミニウム、鉛、ヒ素からなる群より選ばれた少なくとも１種の物質のワイヤー形状の線状体である。それぞれを単独で用いてもよいし、それぞれの合金や酸化物でもよい。具体的には一酸化シリコン、チタンシリサイド、リンドープシリコン、スズ鉄合金、スズコバルト合金、アンチモンスズ合金、スズ銀合金、インジウムアンチモン合金などを用いることができる。また、線状体は、外径が１００ｎｍ以下であれば、ナノワイヤー、ナノロッド、ナノウィスカー、ナノチューブ（中空）、ナノファイバー、ナノベルトなどとも呼ばれる。 The negative electrode active material 5 is a wire-shaped linear body of at least one material selected from the group consisting of silicon, tin, antimony, aluminum, lead, and arsenic. Each of these may be used alone, or an alloy or oxide of each may be used. Specifically, silicon monoxide, titanium silicide, phosphorus-doped silicon, tin iron alloy, tin cobalt alloy, antimony tin alloy, tin silver alloy, indium antimony alloy, or the like can be used. In addition, the linear body is also called a nanowire, a nanorod, a nanowhisker, a nanotube (hollow), a nanofiber, a nanobelt or the like if the outer diameter is 100 nm or less.
負極活物質５、導電助剤７、結着剤９、空隙１０が形成する負極活物質の層の厚さは、５〜６０μｍであり、好ましくは１０〜２５μｍである。 The thickness of the negative electrode active material layer formed by the negative electrode active material 5, the conductive auxiliary agent 7, the binder 9, and the voids 10 is 5 to 60 μm, preferably 10 to 25 μm.
また、負極活物質５の長さは、好ましくは０．１μｍ〜２ｍｍである。負極活物質５の外径は、好ましくは４ｎｍ〜１０００ｎｍであり、より好ましくは２５ｎｍ〜２００ｎｍである。負極活物質５の長さが０．１μｍ以上であれば、負極活物質５の生産性を上げるのには十分な長さであり、負極活物質５の長さが２ｍｍ以下であれば、スラリーの塗布が容易である。また、負極活物質５の外径が４ｎｍより太い場合、合成が容易であり、外径が１０００ｎｍより細い場合、負極活物質の微粉化を防ぐことができる。負極活物質の外径と長さの測定方法は、ＳＥＭによる画像解析により行った。 Moreover, the length of the negative electrode active material 5 is preferably 0.1 μm to 2 mm. The outer diameter of the negative electrode active material 5 is preferably 4 nm to 1000 nm, more preferably 25 nm to 200 nm. If the length of the negative electrode active material 5 is 0.1 μm or more, the length is sufficient to increase the productivity of the negative electrode active material 5, and if the length of the negative electrode active material 5 is 2 mm or less, the slurry Is easy to apply. Moreover, when the outer diameter of the negative electrode active material 5 is thicker than 4 nm, the synthesis is easy, and when the outer diameter is thinner than 1000 nm, the negative electrode active material can be prevented from being pulverized. The measuring method of the outer diameter and length of the negative electrode active material was performed by image analysis using SEM.
また、負極活物質５は、直線状、曲線状あるいは三次元的に激しく折れ曲がった縮れ形状を含んでいても良い。線状体の負極活物質５を製造するときは直線状や曲線状、縮れ形状の混合物として得られることがあるが、これらの形状を特別な方法を用いて分離する必要はない。これらの形状は、単独で用いても良いし、混合物のまま用いても良い。 The negative electrode active material 5 may include a linear shape, a curved shape, or a crimped shape that is bent three-dimensionally. When the linear negative electrode active material 5 is produced, it may be obtained as a mixture of a linear shape, a curved shape, or a crimped shape, but it is not necessary to separate these shapes using a special method. These shapes may be used alone or as a mixture.
一例として、ＣＶＤ法で製造したシリコンの線状体のＴＥＭ写真とＳＥＭ写真を示す。図６は直線状あるいはほぼ直線状のシリコンが折れ曲がった形状をしている。外径は最大で１０００ｎｍ程度である。図７は、ほぼ直線状のシリコンと曲線状のシリコンの混合物である。外径は１０ｎｍ〜２００ｎｍ程度である。図８は、シリコンが三次元的に激しく折れ曲がり縮れ形状が単独のものである。外径は２０ｎｍ〜１５０ｎｍ程度である。 As an example, a TEM photograph and an SEM photograph of a silicon linear body manufactured by a CVD method are shown. FIG. 6 shows a shape in which silicon that is linear or substantially linear is bent. The maximum outer diameter is about 1000 nm. FIG. 7 is a mixture of substantially straight silicon and curved silicon. The outer diameter is about 10 nm to 200 nm. In FIG. 8, the silicon is bent three-dimensionally and the shape of the silicon is single. The outer diameter is about 20 nm to 150 nm.
導電助剤７は、炭素、銅、スズ、亜鉛、ニッケル、銀からなる群より選ばれた少なくとも１種の導電性物質からなる粉末である。炭素、銅、スズ、亜鉛、ニッケル、銀の単体の粉末でもよいし、それぞれの合金の粉末でもよい。例えば、ファーネスブラックやアセチレンブラックなどの一般的なカーボンブラックを使用できる。 The conductive assistant 7 is a powder made of at least one conductive material selected from the group consisting of carbon, copper, tin, zinc, nickel, and silver. A single powder of carbon, copper, tin, zinc, nickel, or silver may be used, or a powder of each alloy may be used. For example, general carbon black such as furnace black and acetylene black can be used.
結着剤９は、樹脂の結着剤であり、ポリフッ化ビニリデン（ＰＶｄＦ）、スチレンブタジエンゴム（ＳＢＲ）などのフッ素樹脂やゴム系の有機材料を用いることができる。 The binder 9 is a resin binder, and a fluororesin such as polyvinylidene fluoride (PVdF) and styrene butadiene rubber (SBR) or a rubber-based organic material can be used.
負極１は、負極活物質５と導電助剤７が結着剤９により緻密に詰まった状態で集電体３にスラリーを塗布・乾燥して形成された状態ではない。空隙１０は、集電体３、負極活物質５、導電助剤７の一部あるいは全てに取り囲まれた空間であり、負極１の体積に対して１０％〜８０％程度占有する。空隙１０の役割は、電解液を浸透させてリチウムイオンを通過させるとともに、充放電に伴う負極活物質５の体積変化を吸収して負極活物質５や導電助剤７の集電体３からの剥離や負極１のクラック発生を未然に防ぐことである。 The negative electrode 1 is not in a state where the negative electrode active material 5 and the conductive auxiliary agent 7 are densely packed with the binder 9 and the slurry is applied to the current collector 3 and dried. The void 10 is a space surrounded by part or all of the current collector 3, the negative electrode active material 5, and the conductive additive 7, and occupies about 10% to 80% with respect to the volume of the negative electrode 1. The role of the gap 10 is to allow the electrolytic solution to permeate and allow lithium ions to pass through, and to absorb the volume change of the negative electrode active material 5 that accompanies charging / discharging and from the current collector 3 of the negative electrode active material 5 and the conductive additive 7 This is to prevent peeling and occurrence of cracks in the negative electrode 1 in advance.
また、図１（ｂ）に示すように、ワイヤー形状の負極活物質５だけでなく、粒子状の負極活物質６を含んでいてもよい。負極活物質６は、負極活物質５に挙げられた物質と同様の物質で形成されており、粉末またはナノ粒子の負極活物質であり、一次粒子の平均粒径は１０ｎｍ〜２μｍ程度である。負極活物質６は、負極活物質５と同じ物質を用いても良いし、異なる物質を用いても良い。さらに、負極活物質６はグラファイトを用いても良い。なお、一次粒子とは、粒子の最小単位であって、それ以上分割されない粒子のことであり、凝集していない状態での粒子のことである。 Moreover, as shown in FIG.1 (b), not only the wire-shaped negative electrode active material 5 but the particulate negative electrode active material 6 may be included. The negative electrode active material 6 is formed of the same material as the material listed as the negative electrode active material 5, and is a powder or nanoparticle negative electrode active material. The average particle size of the primary particles is about 10 nm to 2 μm. As the negative electrode active material 6, the same material as the negative electrode active material 5 may be used, or a different material may be used. Furthermore, the negative electrode active material 6 may use graphite. The primary particles are particles that are the smallest unit of particles and are not further divided, and are particles that are not aggregated.
負極活物質６と、導電助剤７、後述する金属ナノ粒子２５と導電助剤２７の平均粒径に関して、微粒子は通常は凝集して存在しているので、ここでは一次粒子の平均粒径を指す。粒子の計測は、電子顕微鏡（ＳＥＭ）の画像情報と動的光散乱光度計（ＤＬＳ）の体積基準メディアン径を併用する。 Regarding the average particle diameter of the negative electrode active material 6, the conductive auxiliary agent 7, the metal nanoparticles 25 and the conductive auxiliary agent 27, which will be described later, the fine particles are usually present in an aggregated state. Point to. For particle measurement, image information of an electron microscope (SEM) and a volume-based median diameter of a dynamic light scattering photometer (DLS) are used in combination.
負極活物質６や、後述する金属ナノ粒子２５の平均粒径は、ＳＥＭ画像によりあらかじめ粒子形状を確認し、画像解析（例えば、旭化成エンジニアリング製Ａ像くん）で粒径を求めたり、粒子を溶媒に分散してＤＬＳ（例えば、大塚電子製ＤＬＳ−８０００）により測定したりすることが可能である。微粒子が十分に分散しており、凝集していなければ、ＳＥＭとＤＬＳでほぼ同じ測定結果が得られる。 The average particle diameter of the negative electrode active material 6 and the metal nanoparticles 25 described later is obtained by confirming the particle shape in advance using an SEM image, obtaining the particle diameter by image analysis (for example, A image manufactured by Asahi Kasei Engineering), And measured by DLS (for example, DLS-8000 manufactured by Otsuka Electronics Co., Ltd.). If the fine particles are sufficiently dispersed and not agglomerated, almost the same measurement results can be obtained with SEM and DLS.
導電助剤７や、後述する導電助剤２７の平均粒径も一次粒子の平均粒径を指す。アセチレンブラックのような高度にストラクチャー形状が発達している場合にも、ここでは一次粒径で平均粒径を定義し、ＳＥＭ写真の画像解析で平均粒径を求めることができる。 The average particle size of the conductive auxiliary agent 7 and the conductive auxiliary agent 27 described later also refers to the average particle size of the primary particles. Even when the structure shape is highly developed such as acetylene black, the average particle diameter can be defined by the primary particle diameter here, and the average particle diameter can be obtained by image analysis of the SEM photograph.
また、図１（ｃ）に示すように、粒子状の導電助剤７とワイヤー形状の導電助剤８の両方を用いても良い。導電助剤８は導電性物質のワイヤーであり、導電助剤７に挙げられた導電性物質を用いることができる。導電助剤８は、カーボンファイバー、カーボンナノチューブ、銅ナノワイヤー、ニッケルナノワイヤーなどの外径が３００ｎｍ以下の線状体を用いることができる。ワイヤー形状の導電助剤８を用いることで、負極活物質５、６や集電体３などと電気的接続が保持しやすくなり集電性能が向上するとともに、ポーラス膜状の負極１に繊維状物質が増え、負極１にクラックが生じにくくなる。導電助剤８は、導電助剤７と同じ導電性物質を用いても良いし、異なる物質を用いても良い。例えば粒子状の導電助剤７として銅粉末を用い、ワイヤー形状の導電助剤８として気相成長炭素繊維（ＶＧＣＦ）を用いることが考えられる。なお、粒子状の導電助剤７を加えずに、ワイヤー形状の導電助剤８のみを用いても良い。 Moreover, as shown in FIG.1 (c), you may use both the particulate-form conductive support agent 7 and the wire-shaped conductive support agent 8. FIG. The conductive assistant 8 is a wire made of a conductive substance, and the conductive substances listed in the conductive assistant 7 can be used. As the conductive additive 8, a linear body having an outer diameter of 300 nm or less, such as carbon fiber, carbon nanotube, copper nanowire, or nickel nanowire, can be used. By using the wire-shaped conductive auxiliary agent 8, the electrical connection with the negative electrode active materials 5, 6 and the current collector 3 can be easily maintained and the current collecting performance is improved, and the negative electrode 1 in the porous film shape is fibrous. A substance increases and it becomes difficult to produce a crack in the negative electrode 1. The conductive auxiliary agent 8 may use the same conductive material as the conductive auxiliary agent 7 or a different substance. For example, it is conceivable to use copper powder as the particulate conductive aid 7 and use vapor grown carbon fiber (VGCF) as the wire-shaped conductive aid 8. In addition, you may use only the wire-shaped conductive support agent 8 without adding the particulate-form conductive support agent 7. FIG.
導電助剤８の長さは、好ましくは０．１μｍ〜２ｍｍである。導電助剤８の外径は、好ましくは４ｎｍ〜１０００ｎｍであり、より好ましくは２５ｎｍ〜２００ｎｍである。導電助剤８の長さが０．１μｍ以上であれば、導電助剤８の生産性を上げるのには十分な長さであり、長さが２ｍｍ以下であれば、スラリーの塗布が容易である。また、導電助剤８の外径が４ｎｍより太い場合、合成が容易であり、外径が１０００ｎｍより細い場合、スラリーの混練が容易である。導電物質８の外径と長さの測定方法は、ＳＥＭによる画像解析により行った。 The length of the conductive auxiliary agent 8 is preferably 0.1 μm to 2 mm. The outer diameter of the conductive auxiliary agent 8 is preferably 4 nm to 1000 nm, more preferably 25 nm to 200 nm. If the length of the conductive additive 8 is 0.1 μm or more, the length is sufficient to increase the productivity of the conductive additive 8, and if the length is 2 mm or less, the slurry can be easily applied. is there. Moreover, when the outer diameter of the conductive auxiliary agent 8 is thicker than 4 nm, the synthesis is easy, and when the outer diameter is thinner than 1000 nm, the kneading of the slurry is easy. The measuring method of the outer diameter and length of the conductive material 8 was performed by image analysis using SEM.
また、図２に示すように、負極活物質５の粒子の表面を、導電性材料１１により被覆してもよい。さらに、図２に示すように、導電性材料１１により被覆した負極活物質５と導電助剤７を造粒し、造粒体１３として負極活物質５を用いてもよい。なお、造粒体１３を構成する負極活物質は、ワイヤー形状の負極活物質５と粒子状の負極活物質６の混合物であってもよく、造粒体１３を構成する導電助剤は、粒子状の導電助剤７とワイヤー形状の導電助剤８の混合物であっても良い。造粒体１３の直径は０．２μｍ〜１０μｍであることが好ましい。 In addition, as shown in FIG. 2, the surface of the particles of the negative electrode active material 5 may be covered with a conductive material 11. Furthermore, as shown in FIG. 2, the negative electrode active material 5 coated with the conductive material 11 and the conductive additive 7 may be granulated, and the negative electrode active material 5 may be used as the granulated body 13. In addition, the negative electrode active material which comprises the granulated body 13 may be a mixture of the wire-shaped negative electrode active material 5 and the particulate negative electrode active material 6, and the conductive auxiliary agent which comprises the granulated body 13 is a particle It may be a mixture of the conductive aid 7 having a shape and the conductive aid 8 having a wire shape. The diameter of the granulated body 13 is preferably 0.2 μm to 10 μm.
導電性材料１１としては、炭素、銅、スズ、亜鉛、ニッケル、銀または、これらの合金などが挙げられる。 Examples of the conductive material 11 include carbon, copper, tin, zinc, nickel, silver, and alloys thereof.
負極活物質５の導電性材料１１の被覆は、ＣＶＤ法、液相法、焼成法、乾式法を用いて行うことができる。また、ボールミルなどを用いたメカニカルアロイング法により被覆することもできる。これらの方法によれば、負極活物質５の粒子の表面の少なくとも一部に導電性材料１１を被覆することができる。 Coating of the negative electrode active material 5 with the conductive material 11 can be performed using a CVD method, a liquid phase method, a firing method, or a dry method. Moreover, it can also coat | cover by the mechanical alloying method using a ball mill etc. According to these methods, the conductive material 11 can be coated on at least a part of the surface of the particles of the negative electrode active material 5.
造粒体１３の作製は、乾式と湿式の一般的な造粒方法を用いることができるが、例えば、乾式では圧縮とせん断力をかけるメカニカルアロイング法や、気流中で粉体同士を高速で衝突させるハイブリダイゼーション法がある。さらに、湿式では無電解めっき法やスプレードライ法を単独あるいは組み合わせて用いることができる。例えば、負極活物質５にカーボン系の導電性材料１１を乾式で被覆させて複合体とし、さらに、導電性材料１１や結着剤９を水に分散させてサスペンションとして所定のサイズとなるようにスプレードライ法により造粒する方法がある。また、負極活物質５を硫酸銅溶液に分散させた後、水素化ホウ素ナトリウムなどの還元剤を用いて負極活物質５の表面に銅を析出させて導電性材料の被覆を形成する方法などがある。また、負極活物質をポリビニルアルコール水溶液（ＰＶＡ水溶液）に分散した後、不活性雰囲気下でＰＶＡを焼成し、炭素で被覆させる方法などもある The granulated body 13 can be produced by using dry and wet general granulation methods. For example, in the dry process, the mechanical alloying method in which compression and shearing force is applied, or the powders are rapidly moved together in an air current. There is a hybridization method for collision. Furthermore, in the wet process, an electroless plating method or a spray drying method can be used alone or in combination. For example, the negative electrode active material 5 is dry-coated with a carbon-based conductive material 11 to form a composite, and the conductive material 11 and the binder 9 are dispersed in water so that the suspension has a predetermined size. There is a method of granulation by spray drying. In addition, there is a method in which after the negative electrode active material 5 is dispersed in a copper sulfate solution, copper is deposited on the surface of the negative electrode active material 5 using a reducing agent such as sodium borohydride to form a conductive material coating. is there. In addition, there is a method in which the negative electrode active material is dispersed in an aqueous polyvinyl alcohol solution (PVA aqueous solution), and then PVA is fired in an inert atmosphere and coated with carbon.
炭素の被覆方法としては、例えば、以下のような方法が挙げられる。負極活物質と１０％ポリビニルアルコール水溶液を混練後、７００℃で３時間、不活性雰囲気下（真空、窒素雰囲気、アルゴン雰囲気等）で焼成する。ポリビニルアルコール中の炭素が炭化し、酸素と水素は水となって気化し、負極活物質は、炭素で被覆され、導電性が向上する。 Examples of the carbon coating method include the following methods. The negative electrode active material and a 10% aqueous polyvinyl alcohol solution are kneaded and then fired at 700 ° C. for 3 hours in an inert atmosphere (vacuum, nitrogen atmosphere, argon atmosphere, etc.). Carbon in the polyvinyl alcohol is carbonized, oxygen and hydrogen are vaporized as water, and the negative electrode active material is coated with carbon to improve conductivity.
次に、負極１の製造方法を説明する。図３に示すように、ミキサー１５に、スラリー原料１９を投入し、混練してスラリー１７を形成する。スラリー原料１９は、負極活物質５、導電助剤７、結着剤９、増粘剤、溶媒などである。 Next, the manufacturing method of the negative electrode 1 is demonstrated. As shown in FIG. 3, a slurry raw material 19 is put into a mixer 15 and kneaded to form a slurry 17. The slurry raw material 19 is the negative electrode active material 5, the conductive additive 7, the binder 9, a thickener, a solvent, and the like.
スラリー１７中の固形分において、負極活物質５は２５〜９０重量％、導電助剤７は５〜７０重量％、結着剤９は１〜１０重量％を含む。例えば、負極活物質５を６０重量％、導電助剤７は３３重量％、結着剤９は２重量％、増粘剤は５重量％である。 In the solid content in the slurry 17, the negative electrode active material 5 includes 25 to 90 wt%, the conductive auxiliary agent 7 includes 5 to 70 wt%, and the binder 9 includes 1 to 10 wt%. For example, the negative electrode active material 5 is 60% by weight, the conductive additive 7 is 33% by weight, the binder 9 is 2% by weight, and the thickener is 5% by weight.
ミキサー１５は、スラリーの調製に用いられる一般的な混練機を用いることができ、ニーダー、撹拌機、分散機、混合機などと呼ばれるスラリーを調製可能な装置を用いてもよい。また、増粘剤としてはカルボキシメチルセルロース、メチルセルロース等の多糖類等を１種又は２種以上の混合物として用いることが適している。また、溶媒としては水を用いることができる。 As the mixer 15, a general kneader used for preparing a slurry can be used, and an apparatus capable of preparing a slurry called a kneader, a stirrer, a disperser, a mixer, or the like may be used. Moreover, as a thickener, it is suitable to use polysaccharides, such as carboxymethylcellulose and methylcellulose, as a 1 type, or 2 or more types of mixture. Moreover, water can be used as a solvent.
次に、図４に示すように、コーター２１を用いて、集電体３の片面に、スラリー１７を塗布する。コーター２１は、スラリーを集電体に塗布可能な一般的な塗工装置を用いることができ、例えばロールコーターやドクターブレードによるコーターである。 Next, as shown in FIG. 4, slurry 17 is applied to one surface of current collector 3 using coater 21. The coater 21 can use a general coating apparatus that can apply slurry to a current collector, and is, for example, a coater using a roll coater or a doctor blade.
その後、７０℃程度で乾燥し、厚みを調整するため、ロールプレスを通して、負極１を得る。また、空隙１０はスラリー原料１９の主要成分となる負極活物質５、６や導電助剤７、８のサイズや配合比率でコントロールすることが可能であるほか、ロールプレスで厚みを調整するときの圧下率やスラリー１７の厚み調整により、所望のサイズや量を設定することができる。 Then, in order to dry at about 70 degreeC and adjust thickness, the negative electrode 1 is obtained through a roll press. Further, the gap 10 can be controlled by the size and blending ratio of the negative electrode active materials 5 and 6 and the conductive assistants 7 and 8 which are the main components of the slurry raw material 19, and when the thickness is adjusted by a roll press. A desired size and amount can be set by adjusting the rolling reduction and the thickness of the slurry 17.
次に、本発明の負極１を用いた、リチウムイオン二次電池の製造方法を説明する。 Next, a method for producing a lithium ion secondary battery using the negative electrode 1 of the present invention will be described.
まず、正極活物質、導電助剤、結着剤及び溶媒を混合して正極活物質の組成物を準備する。前記正極活物質の組成物をアルミ箔などの金属集電体上に直接塗布・乾燥し、正極を準備する。なお、前記正極活物質の組成物を別途の支持体上にキャスティングした後、その支持体から剥離して得たフィルムを金属集電体上にラミネーションして正極を製造することも可能である。 First, a positive electrode active material, a conductive additive, a binder, and a solvent are mixed to prepare a positive electrode active material composition. The composition of the positive electrode active material is directly applied on a metal current collector such as an aluminum foil and dried to prepare a positive electrode. It is also possible to manufacture a positive electrode by casting the composition of the positive electrode active material on a separate support, and then laminating the film obtained by peeling from the support on a metal current collector.
前記正極活物質としては、リチウム含有の金属酸化物であって、一般的に使われるものであればいずれも使用可能であり、例えばＬｉＣｏＯ２，ＬｉＭｎｘＯ２ｘ，ＬｉＮｉ１−ｘＭｎｘＯ２ｘ（ｘ＝１，２），Ｎｉ１−ｘ−ｙＣｏｘＭｎｙＯ２（０≦ｘ≦０．５，０≦ｙ≦０．５）などを挙げることができ、さらに具体的には、ＬｉＭｎ２Ｏ４，ＬｉＭｎＯ２，ＬｉＮｉＯ２，ＬｉＦｅＯ２，ＬｉＦｅＰＯ４，Ｌｉ２ＦｅＰＯ４Ｆ，Ｖ２Ｏ５，ＴｉＳ及びＭｏＳ２などリチウムの酸化還元が可能な化合物である。 As the positive electrode active material, any lithium-containing metal oxide that is generally used can be used. For example, LiCoO 2 , LiMn x O 2x , LiNi 1-x Mn x O 2x (X = 1, 2), Ni 1-xy Co x Mn y O 2 (0 ≦ x ≦ 0.5, 0 ≦ y ≦ 0.5), etc., more specifically, LiMn 2 O 4, it is a LiMnO 2, LiNiO 2, LiFeO 2 , LiFePO 4, Li 2 FePO 4 F, V 2 O 5, TiS and MoS 2 and compounds capable redox lithium.
導電助剤としては、カーボンブラックを使用し、結着剤としては、フッ化ビニリデン／ヘキサフルオロプロピレンコポリマー、ポリフッ化ビニリデン（ＰＶｄＦ）、ポリアクリロニトリル、ポリメチルメタクリレート、ポリテトラフルオロエチレン（ＰＴＦＥ）及びその混合物、スチレンブタジエンゴム系ポリマーを使用し、溶媒としては、Ｎ−メチルピロリドン（ＮＭＰ）、アセトン、水などを使用する。このとき、正極活物質、導電助剤、結着剤及び溶媒の含量は、リチウムイオン二次電池で通常的に使用するレベルである。 Carbon black is used as a conductive additive, and vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride (PVdF), polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene (PTFE) and the like are used as a binder. A mixture and a styrene butadiene rubber-based polymer are used, and N-methylpyrrolidone (NMP), acetone, water and the like are used as a solvent. At this time, the contents of the positive electrode active material, the conductive additive, the binder, and the solvent are at levels that are normally used in lithium ion secondary batteries.
セパレータとしては、正極と負極の電子伝導を絶縁する機能を有し、リチウムイオン二次電池で通常的に使われるものであればいずれも使用可能である。特に、電解質のイオン移動に対して低抵抗であり、かつ、電池の高容量の観点から厚みは２０ミクロン程度と薄いものが好ましい。代表的なセパレータは、ポリプロピレン（ＰＰ）／ポリエチレン（ＰＥ）／ポリプロピレン（ＰＰ）微多孔膜の３層ラミネート膜となっており、ＰＰとＰＥは熱可塑性の樹脂でそれぞれ約１７０℃、約１３０℃の融点となるように重合度などが材料設計されている。電池内部の温度が１３０℃を超えるとＰＥ膜が溶融し、微孔が目詰まりしてリチウムイオンが透過できなくなり、電池反応を停止することができる。 Any separator can be used as long as it has a function of insulating electronic conduction between the positive electrode and the negative electrode and is usually used in a lithium ion secondary battery. In particular, it is preferable that the thickness is as low as about 20 microns from the viewpoint of the high capacity of the battery because of its low resistance to ion migration of the electrolyte. A typical separator is a three-layer laminate film of polypropylene (PP) / polyethylene (PE) / polypropylene (PP) microporous film, and PP and PE are thermoplastic resins of about 170 ° C. and about 130 ° C., respectively. The degree of polymerization and the like are designed so that the melting point becomes. When the temperature inside the battery exceeds 130 ° C., the PE film melts, the micropores are clogged and lithium ions cannot permeate, and the battery reaction can be stopped.
電解液としては、炭酸プロピレン、炭酸エチレン、炭酸ジエチル、炭酸エチルメチル、炭酸メチルプロピル、炭酸ブチレン、ベンゾニトリル、アセトニトリル、テトラヒドロフラン、２−メチルテトラヒドロフラン、γ−ブチロラクトン、ジオキソラン、４−メチルオキソラン、Ｎ，Ｎ−ジメチルホルムアミド、ジメチルアセトアミド、ジメチルスルホキシド、ジオキサン、１，２−ジメトキシエタン、スルホラン、ジクロロエタン、クロロベンゼン、ニトロベンゼン、炭酸ジメチル、炭酸メチルエチル、炭酸ジエチル、炭酸メチルプロピル、炭酸メチルイソプロピル、炭酸エチルプロピル、炭酸ジプロピル、炭酸ジブチル、ジエチレングリコールまたはジメチルエーテルなどの溶媒またはそれらの混合溶媒にＬｉＰＦ６，ＬｉＢＦ４，ＬｉＳｂＦ６，ＬｉＡｓＦ６，ＬｉＣｌＯ４，ＬｉＣＦ３ＳＯ３，Ｌｉ（ＣＦ３ＳＯ２）２Ｎ，ＬｉＣ４Ｆ９ＳＯ３，ＬｉＡｌＯ４，ＬｉＡｌＣｌ４，ＬｉＮ（ＣｘＦ２ｘ＋１ＳＯ２）（ＣｙＦ２ｙ＋１ＳＯ２）（ただし、ｘ，ｙは自然数），ＬｉＣｌ，ＬｉＩなどのリチウム塩からなる電解質のうち一つまたはそれらを二つ以上混合したものを溶解して使用できる。 Examples of the electrolyte include propylene carbonate, ethylene carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butylene carbonate, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4-methyloxolane, N , N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl propyl carbonate , dipropyl carbonate, LiPF 6 dibutyl carbonate, in a solvent or a mixed solvent thereof and the like diethylene glycol or dimethyl ether, LiBF 4, L SbF 6, LiAsF 6, LiClO 4 , LiCF 3 SO 3, Li (CF 3 SO 2) 2 N, LiC 4 F 9 SO 3, LiAlO 4, LiAlCl 4, LiN (C x F 2x + 1 SO 2) (C y F 2y + 1 SO 2) (however, x, y are natural numbers), LiCl, can be used by dissolving a mixture of one or thereof two or more of the electrolyte comprising a lithium salt such as LiI.
前述したような正極と負極との間にセパレータを配置して、電池構造体を形成する。このような電池構造体を巻くか、または折って円筒形の電池ケースや角形の電池ケースに入れた後、電解液を注入すれば、リチウムイオン二次電池が完成する。 A separator is disposed between the positive electrode and the negative electrode as described above to form a battery structure. When such a battery structure is wound or folded and placed in a cylindrical battery case or a rectangular battery case, an electrolyte is injected to complete a lithium ion secondary battery.
また、前記電池構造体をバイセル構造で積層した後、それを有機電解液に含浸させ、得られた結果物をポーチに入れて密封すれば、リチウムイオンポリマー電池が完成する。 Further, after the battery structure is laminated in a bicell structure, it is impregnated with an organic electrolyte, and the resultant product is put in a pouch and sealed to complete a lithium ion polymer battery.
負極活物質５は、リチウムの吸蔵・脱離で体積が変わるが、負極活物質５がサブミクロンあるいはナノレベルの外径を有するワイヤー形状であるため、負極活物質５が体積変化を起こしても、負極活物質５の微粉化は生じない。例えば、シリコンはリチウムを吸収すると体積が最大で４倍まで膨張するが、シリコンのワイヤー径が太くなったり、曲線部の曲率が変化したり、ワイヤーの長さが変化したりしても空隙１０のスペースで吸収され、負極の破壊（集電体からの活物質の剥離や脱落）が回避される。寿命特性に関しては、負極にクラックを生じさせないことが特に重要となる。 The volume of the negative electrode active material 5 changes due to insertion / extraction of lithium. However, since the negative electrode active material 5 has a wire shape having a submicron or nano level outer diameter, even if the negative electrode active material 5 undergoes a volume change. Further, pulverization of the negative electrode active material 5 does not occur. For example, when silicon absorbs lithium, the volume expands up to 4 times, but even if the wire diameter of silicon increases, the curvature of the curved portion changes, or the length of the wire changes, the void 10 In this space, the negative electrode is prevented from being broken (the active material is peeled off or dropped from the current collector). Regarding the life characteristics, it is particularly important not to cause cracks in the negative electrode.
第１の実施形態によれば、負極活物質にシリコン系合金を用いているため、炭素系材料を負極活物質として用いる従来の負極に比べて、高容量化が可能である。 According to the first embodiment, since a silicon-based alloy is used as the negative electrode active material, the capacity can be increased as compared with a conventional negative electrode using a carbon-based material as the negative electrode active material.
また、第１の実施形態によれば、ワイヤー形状の負極活物質を用いているため、負極活物質の体積変化が大きくとも、一次元形状の負極活物質の太さと長さで空隙に吸収される。そのため、負極活物質の微粉化や、負極膜の亀裂の発生、負極活物質と集電体との剥離や脱落、負極活物質間の導電性の低下などの問題点が抑制され、負極の寿命が長くなる。 Further, according to the first embodiment, since the wire-shaped negative electrode active material is used, even if the volume change of the negative electrode active material is large, the negative electrode active material is absorbed into the gap with the thickness and length of the one-dimensional negative electrode active material. The As a result, problems such as pulverization of the negative electrode active material, generation of cracks in the negative electrode film, peeling and dropping of the negative electrode active material and the current collector, and decrease in conductivity between the negative electrode active materials are suppressed, and the life of the negative electrode is suppressed. Becomes longer.
また、第１の実施形態によれば、スラリーの塗布・乾燥という製造方法でリチウムイオン二次電池用の負極を製造するため、真空系が必要なく、連続的に負極を製造でき、生産性に優れる。 In addition, according to the first embodiment, since the negative electrode for a lithium ion secondary battery is manufactured by the manufacturing method of applying and drying the slurry, a vacuum system is not necessary, and the negative electrode can be manufactured continuously, thereby improving productivity. Excellent.
次に、第２の実施形態について説明する。
図５は、第２の実施形態にかかる、負極２３、負極２９、負極３１を示す図である。以下の実施形態で第１の実施形態にかかる負極１と同一の様態を果たす要素には同一の番号を付し、重複した説明は避ける。
Next, a second embodiment will be described.
FIG. 5 is a diagram illustrating the negative electrode 23, the negative electrode 29, and the negative electrode 31 according to the second embodiment. In the following embodiment, the same number is attached | subjected to the element which fulfill | performs the same aspect as the negative electrode 1 concerning 1st Embodiment, and the duplicate description is avoided.
図５（ａ）に示すように、第２の実施形態に係る負極２３においては、結着剤９に代えて金属ナノ粒子２５を用いる点が第１の実施形態に係る負極１と異なる。 As shown in FIG. 5A, the negative electrode 23 according to the second embodiment is different from the negative electrode 1 according to the first embodiment in that metal nanoparticles 25 are used instead of the binder 9.
金属ナノ粒子２５は、銅、スズ、亜鉛、ニッケル、銀からなる群より選ばれた少なくとも１種の金属のナノ粒子であり、一次粒子の平均粒径は２ｎｍ〜１００ｎｍであることが好ましい。不活性雰囲気下での焼結により、金属ナノ粒子２５は、集電体３と負極活物質５と導電助剤７との接点近傍で金属結合を形成し、負極活物質５と導電助剤７とを集電体３に接合する。また、金属ナノ粒子２５の焼結により負極には強固な空隙２８が形成され、電解液の浸透や負極活物質の体積変化を緩和し、負極にクラックが発生するのを抑止する役割を担う。 The metal nanoparticles 25 are nanoparticles of at least one metal selected from the group consisting of copper, tin, zinc, nickel, and silver, and the average particle size of the primary particles is preferably 2 nm to 100 nm. By sintering in an inert atmosphere, the metal nanoparticles 25 form a metal bond in the vicinity of the contact point between the current collector 3, the negative electrode active material 5, and the conductive additive 7, and the negative electrode active material 5 and the conductive additive 7. Are joined to the current collector 3. In addition, strong voids 28 are formed in the negative electrode due to the sintering of the metal nanoparticles 25, and it plays a role of suppressing the penetration of the electrolytic solution and the volume change of the negative electrode active material, and suppressing the generation of cracks in the negative electrode.
金属ナノ粒子２５は、一次粒子の平均粒径が２ｎｍ以上であれば、より容易に製造が可能であり、一次粒子の平均粒径が１００ｎｍ以下であれば、より低温での焼結が可能である。 The metal nanoparticles 25 can be manufactured more easily if the average particle size of the primary particles is 2 nm or more, and can be sintered at a lower temperature if the average particle size of the primary particles is 100 nm or less. is there.
金属ナノ粒子２５は、重量に比べて、表面積が非常に大きいため、表面に存在する原子の比率が高くなり、融点が低下する。例えば、金の融点は１３３７Ｋであるが、直径５ｎｍの金ナノ粒子の融点は１１００Ｋ程度と、約２００Ｋ低いという報告がある。そのため、金属ナノ粒子２５を用いることで、バルク体の金属の融点の１／２以下の温度でも金属ナノ粒子２５の表面が活性となり、焼結可能となるため、金属ナノ粒子２５と集電体３、負極活物質５または導電助剤７は、金属結合で接合する。 Since the metal nanoparticles 25 have a very large surface area compared to the weight, the ratio of atoms present on the surface is increased and the melting point is lowered. For example, although the melting point of gold is 1337K, there is a report that the melting point of gold nanoparticles having a diameter of 5 nm is about 1100K, which is about 200K lower. Therefore, by using the metal nanoparticles 25, the surface of the metal nanoparticles 25 becomes active and can be sintered even at a temperature of 1/2 or less of the melting point of the metal of the bulk body. 3. The negative electrode active material 5 or the conductive additive 7 is bonded by a metal bond.
また、図５（ｂ）に示すように、導電助剤７に代えて、導電助剤２７を用いても良い。導電助剤２７は、銅、スズ、亜鉛、ニッケル、銀からなる群より選ばれた少なくとも１種の金属からなる粉末である。銅、スズ、亜鉛、ニッケル、銀の単体の粉末でもよいし、それぞれの合金の粉末でもよい。導電助剤２７の平均粒径は１μｍ〜１０μｍであることが好ましい。導電助剤７の一次粒子の平均粒径が１μｍ以上であれば、負極活物質５が膨張しても負極２９にクラックを生じないような強固でより大きな空隙２８を持った負極２９をより確実に形成可能である。導電助剤２７の平均粒径が１０μｍ以下である場合、スラリーがより均一に混練され、均質な厚みの電極が得られる。 Further, as shown in FIG. 5B, a conductive auxiliary agent 27 may be used instead of the conductive auxiliary agent 7. The conductive auxiliary agent 27 is a powder made of at least one metal selected from the group consisting of copper, tin, zinc, nickel, and silver. A single powder of copper, tin, zinc, nickel, or silver may be used, or a powder of each alloy may be used. The average particle diameter of the conductive auxiliary agent 27 is preferably 1 μm to 10 μm. If the average particle size of the primary particles of the conductive additive 7 is 1 μm or more, the negative electrode 29 having a strong and larger void 28 that does not crack in the negative electrode 29 even when the negative electrode active material 5 expands is more sure. Can be formed. When the average particle diameter of the conductive auxiliary agent 27 is 10 μm or less, the slurry is kneaded more uniformly, and an electrode having a uniform thickness is obtained.
また、図５（ｃ）に示すように、導電助剤２７には、さらにカーボン材料３３を加えてもよく、負極３１は空隙２８を有する。添加するカーボン材料３３の量は、負極活物質５と導電助剤２７と金属ナノ粒子２５との合計の１０〜７０重量％であることが好ましい。添加するカーボン材料３３としては、ファーネスブラックやアセチレンブラック、カーボンファイバーなどの一般的なカーボンブラックを使用できる。 Further, as shown in FIG. 5C, a carbon material 33 may be further added to the conductive auxiliary agent 27, and the negative electrode 31 has a gap 28. The amount of the carbon material 33 to be added is preferably 10 to 70% by weight of the total of the negative electrode active material 5, the conductive additive 27 and the metal nanoparticles 25. As the carbon material 33 to be added, general carbon black such as furnace black, acetylene black and carbon fiber can be used.
導電助剤２７と負極活物質５とは、金属ナノ粒子２５を介して金属結合で結ばれており、集電体３の上に空隙２８の多いポーラス構造の膜を形成している。また、焼結後の２５が形成する金属結合は、結着剤９の有機物より強度が高く、負極２３、負極２９、負極３１はクラックが発生しにくく、サイクル特性に優れる。 The conductive additive 27 and the negative electrode active material 5 are connected by metal bonds through the metal nanoparticles 25, and a porous structure film having many voids 28 is formed on the current collector 3. Moreover, the metal bond formed by the sintered 25 is higher in strength than the organic material of the binder 9, and the negative electrode 23, the negative electrode 29, and the negative electrode 31 are less prone to cracking and have excellent cycle characteristics.
金属ナノ粒子２５の金属の量は、焼結前において導電助剤２７の金属の粉末に対して２〜４０重量％であることが好ましい。前記範囲において、十分な空隙２８を有する好適なポーラス構造を形成可能である。なお、空隙２８は、スラリーに配合する原料の粒径やワイヤー径および組成比率により調節が可能であるとともに、スラリーの塗布・乾燥後の負極をロールプレスに通して厚みを調整する際にも好適なポーラス構造を形成することができる。 The amount of metal of the metal nanoparticles 25 is preferably 2 to 40% by weight with respect to the metal powder of the conductive additive 27 before sintering. Within the above range, a suitable porous structure having a sufficient gap 28 can be formed. The void 28 can be adjusted by the particle size, wire diameter, and composition ratio of the raw material blended in the slurry, and is also suitable for adjusting the thickness by passing the negative electrode after applying and drying the slurry through a roll press. A porous structure can be formed.
負極２３、負極２９、負極３１は、結着剤９に代えて金属ナノ粒子２５を用い、必要に応じて導電助剤７に代えて導電助剤２７やカーボン材料３３を用いる点以外は、負極１と同様の工程で製造される。なお、金属ナノ粒子２５は、粉末のほかに、酸化防止を目的としたサスペンションの状態でスラリー１７に配合してミキサー１５で混練してもよい。金属ナノ粒子２５を含むサスペンションには水やアルコールなどの溶媒に酸化防止剤や還元剤が添加されていてもよい。 The negative electrode 23, the negative electrode 29, and the negative electrode 31 are the same except that the metal nanoparticles 25 are used instead of the binder 9, and the conductive assistant 27 and the carbon material 33 are used instead of the conductive assistant 7 as necessary. 1 in the same process. In addition to the powder, the metal nanoparticles 25 may be blended in the slurry 17 in a suspension state for the purpose of preventing oxidation and kneaded by the mixer 15. In the suspension containing the metal nanoparticles 25, an antioxidant or a reducing agent may be added to a solvent such as water or alcohol.
また、負極２３、負極２９、負極３１の製造方法において、スラリーの塗布・乾燥後、不活性雰囲気（真空、窒素、アルゴンなど）下において、焼結工程を有する。焼結温度は、金属ナノ粒子２５に用いる金属のバルクでの融点（絶対温度）の半分以下であることが好ましい。仮に、金属ナノ粒子２５に銅ナノ粒子を用いる場合には、バルクでの銅の融点が１３５７Ｋであるので、焼結温度は、６７８Ｋ（＝４０５℃）である。焼結温度はさらに、３５０℃以下であることが好ましく、実用的に２００℃〜３００℃であることがより好ましい。 Moreover, in the manufacturing method of the negative electrode 23, the negative electrode 29, and the negative electrode 31, after application | coating and drying of a slurry, it has a sintering process under inert atmosphere (vacuum, nitrogen, argon, etc.). The sintering temperature is preferably not more than half the melting point (absolute temperature) of the metal used for the metal nanoparticles 25 in the bulk. If copper nanoparticles are used for the metal nanoparticles 25, the melting point of copper in the bulk is 1357K, so the sintering temperature is 678K (= 405 ° C.). Further, the sintering temperature is preferably 350 ° C. or lower, and more preferably 200 ° C. to 300 ° C. practically.
仮に、金属ナノ粒子２５を加えないで導電助剤２７のみを焼結した場合、高温にしなければ焼結しない。一方、導電助剤２７を加えずに金属ナノ粒子２５のみを焼結した場合、空隙の少ない緻密な膜が得られることとなる。 If only the conductive auxiliary agent 27 is sintered without adding the metal nanoparticles 25, it is not sintered unless the temperature is raised. On the other hand, when only the metal nanoparticles 25 are sintered without adding the conductive additive 27, a dense film with few voids can be obtained.
なお、第２の実施形態において、ワイヤー形状の負極活物質５に加えて、粒子状の負極活物質６を加えても良いし、粒子状の導電助剤７に代えて、ワイヤー形状の導電助剤８を用いても良く、粒子状の導電助剤７とワイヤー形状の導電助剤８の混合物を用いても良い。 In the second embodiment, a particulate negative electrode active material 6 may be added in addition to the wire shaped negative electrode active material 5, or a wire shaped conductive aid may be used instead of the particulate conductive aid 7. The agent 8 may be used, or a mixture of the particulate conductive additive 7 and the wire-shaped conductive additive 8 may be used.
第２の実施形態によれば、第１の実施形態で得られる効果に加えて、集電体３と導電助剤７や導電助剤２７とが、金属ナノ粒子２５を介して金属結合で結合しており、負極２３、負極２９、負極３１は多数の空隙２８を有するポーラス構造を形成しているため、負極活物質の体積変化が大きくとも体積変化に伴うひずみが吸収され、負極膜に亀裂が入らず、負極活物質と集電体との剥離が抑制されるため、さらに負極の寿命が長い。 According to the second embodiment, in addition to the effects obtained in the first embodiment, the current collector 3 and the conductive auxiliary agent 7 and the conductive auxiliary agent 27 are bonded by metal bonds via the metal nanoparticles 25. Since the negative electrode 23, the negative electrode 29, and the negative electrode 31 form a porous structure having a large number of voids 28, even when the volume change of the negative electrode active material is large, strain accompanying the volume change is absorbed, and the negative electrode film cracks. Does not enter and the peeling between the negative electrode active material and the current collector is suppressed, and the life of the negative electrode is further long.
また、第２の実施形態によれば、集電体３と導電助剤７や導電助剤２７、負極活物質５が金属ナノ粒子を介して金属結合でつながっているため、電極膜の内部抵抗が小さくなり、高率での充放電特性が改善する。 In addition, according to the second embodiment, the current collector 3, the conductive assistant 7, the conductive assistant 27, and the negative electrode active material 5 are connected by metal bonds through the metal nanoparticles, so that the internal resistance of the electrode film And the charge / discharge characteristics at a high rate are improved.
以上、添付図面を参照しながら、本発明にかかるリチウムイオン二次電池用の負極の好適な実施形態について説明したが、本発明は係る例に限定されない。当業者であれば、本願で開示した技術的思想の範疇内において、各種の変更例または修正例に想到しえることは明らかであり、それらについても当然に本発明の技術的範囲に属するものと了解される。 As mentioned above, although preferred embodiment of the negative electrode for lithium ion secondary batteries concerning this invention was described referring an accompanying drawing, this invention is not limited to the example which concerns. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the technical idea disclosed in the present application, and these are naturally within the technical scope of the present invention. Understood.
１、２………負極
３………集電体
４………負極
５………ワイヤー形状の負極活物質
６………粒子状の負極活物質
７………粒子状の導電助剤
８………ワイヤー形状の導電助剤
９………結着剤
１０………空隙
１１………導電性材料
１３………造粒体
１５………ミキサー
１７………スラリー
１９………スラリー原料
２１………コーター
２３………負極
２５………金属ナノ粒子
２７………金属の導電助剤
２８………空隙
２９………負極
３１………負極
３３………カーボン材料
1, 2 ......... Negative electrode 3 ......... Current collector 4 ......... Negative electrode 5 ......... Wire-shaped negative electrode active material 6 ......... Particulate negative electrode active material 7 ......... Particulate conductive auxiliary agent 8 ……… Wire-shaped conductive aid 9 ……… Binder 10 ……… Void 11 ……… Conductive material 13 ……… Granulated material 15 ……… Mixer 17 ……… Slurry 19 ……… Slurry Raw material 21 ......... Coater 23 ......... Negative electrode 25 ......... Metal nanoparticles 27 ......... Metal conductive aid 28 ......... Void 29 ......... Negative electrode 31 ......... Negative electrode 33 ......... Carbon material
Claims (12)
前記集電体上に、結着剤で結合している負極活物質と導電助剤と、を有し、
前記負極活物質が、ワイヤー形状の負極活物質を含み、
金属ナノ粒子を介して、前記負極活物質と前記集電体または前記負極活物質と前記導電助剤とが、金属結合により結合しており、
前記負極活物質が、シリコン、スズ、アンチモン、アルミニウム、鉛およびヒ素からなる群より選ばれた少なくとも１種の物質またはそれらの合金を含み、
前記導電助剤が、炭素、銅、スズ、亜鉛、ニッケル、銀からなる群より選ばれた少なくとも１種の物質またはそれらの合金を含むことを特徴とするリチウムイオン二次電池用の負極。 A metal current collector,
On the current collector, a negative electrode active material bonded with a binder and a conductive additive,
The negative electrode active material, see contains a negative electrode active material of the wire shape,
Via the metal nanoparticles, the negative electrode active material and the current collector or the negative electrode active material and the conductive additive are bonded by a metal bond,
The negative electrode active material includes at least one substance selected from the group consisting of silicon, tin, antimony, aluminum, lead and arsenic or an alloy thereof;
The negative electrode for a lithium ion secondary battery, wherein the conductive auxiliary agent includes at least one substance selected from the group consisting of carbon, copper, tin, zinc, nickel, and silver, or an alloy thereof .
前記金属結合が、前記金属ナノ粒子を焼結することにより形成され、
前記集電体と前記負極活物質と前記導電助剤と前記金属ナノ粒子との一部または全部に取り囲まれた空隙を有することを特徴とする請求項１に記載のリチウムイオン二次電池用の負極。 The metal nanoparticles are nanoparticles of at least one metal selected from the group consisting of copper, tin, zinc, nickel and silver, and the average particle size of primary particles is 2 nm to 100 nm,
The metal bond is formed by sintering the metal nanoparticles;
2. The lithium ion secondary battery according to claim 1 , wherein the current collector, the negative electrode active material, the conductive additive, and the metal nanoparticles have a void surrounded by part or all of the current collector, the negative electrode active material, the conductive auxiliary agent, and the metal nanoparticles. Negative electrode.
前記負極活物質が、ワイヤー形状の負極活物質を含み、
前記結着剤が金属ナノ粒子を含み、
前記負極活物質が、シリコン、スズ、アンチモン、アルミニウム、鉛およびヒ素からなる群より選ばれた少なくとも１種の物質またはそれらの合金を含み、
前記導電助剤が、炭素、銅、スズ、亜鉛、ニッケル、銀からなる群より選ばれた少なくとも１種の物質またはそれらの合金を含むことを特徴とするリチウムイオン二次電池用の負極作製用のスラリー。 A slurry in which a negative electrode active material, a conductive additive, and a binder are mixed,
The negative electrode active material, see contains a negative electrode active material of the wire shape,
The binder comprises metal nanoparticles;
The negative electrode active material includes at least one substance selected from the group consisting of silicon, tin, antimony, aluminum, lead and arsenic or an alloy thereof;
For producing a negative electrode for a lithium ion secondary battery, wherein the conductive additive contains at least one substance selected from the group consisting of carbon, copper, tin, zinc, nickel, and silver, or an alloy thereof . Slurry.
前記スラリーを集電体に塗布する塗布工程と、
前記スラリーを塗布した前記集電体を乾燥する乾燥工程と、
を具備し、
前記負極活物質が、ワイヤー形状の負極活物質を含み、
前記結着剤が金属ナノ粒子を含み、
前記集電体が金属製であり、
前記負極活物質が、シリコン、スズ、アンチモン、アルミニウム、鉛、ヒ素からなる群より選ばれた少なくとも１種の物質またはそれらの合金を含み、
前記導電助剤が、炭素、銅、スズ、亜鉛、ニッケル、銀からなる群より選ばれた少なくとも１種の物質またはそれらの合金を含むことを特徴とするリチウムイオン二次電池用の負極の製造方法。 A kneading step of kneading a negative electrode active material, a conductive additive and a binder to prepare a slurry;
An application step of applying the slurry to a current collector;
A drying step of drying the current collector coated with the slurry;
Comprising
The negative electrode active material, see contains a negative electrode active material of the wire shape,
The binder comprises metal nanoparticles;
The current collector is made of metal;
The negative electrode active material includes at least one substance selected from the group consisting of silicon, tin, antimony, aluminum, lead, and arsenic, or an alloy thereof.
Production of a negative electrode for a lithium ion secondary battery, wherein the conductive additive contains at least one substance selected from the group consisting of carbon, copper, tin, zinc, nickel, and silver, or an alloy thereof. Method.
After pre-Symbol drying step, and characterized by further comprising a sintering step of heating the negative electrode in an inert atmosphere of 1/2 or less of the temperature of the melting point (absolute temperature) of the bulk of the metal of the metal nanoparticles The manufacturing method of the negative electrode for lithium ion secondary batteries of Claim 11.
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| US9373838B2 (en) * | 2009-09-29 | 2016-06-21 | Georgia Tech Research Corporation | Electrodes, lithium-ion batteries, and methods of making and using same |
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