JP2010262752A - Negative electrode for lithium ion secondary battery, lithium ion secondary battery using the same, and method of manufacturing negative electrode for lithium ion secondary battery - Google Patents
Negative electrode for lithium ion secondary battery, lithium ion secondary battery using the same, and method of manufacturing negative electrode for lithium ion secondary battery Download PDFInfo
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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、カーボンナノファイバー等の導電助剤と、樹脂の結着剤とを混練してスラリーを作製し、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 nanofiber, and a resin binder to form a slurry, and applying and drying on a copper foil. ing.
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).
また、結着剤、導電助剤を不要にするため、ＣＶＤ法などによりシリコンを集電体上に直接成膜し、リチウム電池用電極を製造する方法が知られている（例えば、特許文献２を参照）。 In addition, in order to eliminate the need for a binder and a conductive additive, a method of manufacturing a lithium battery electrode by directly depositing silicon on a current collector by a CVD method or the like is known (for example, Patent Document 2) See).
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。そのため、負極活物質の充放電時の剥離、負極の亀裂の発生、負極活物質間の導電性の低下などにより、容量が低下し、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. For this reason, there is a problem in that the capacity is reduced due to peeling during charging / discharging of the negative electrode active material, cracking of the negative electrode, conductivity decrease between the negative electrode active materials, the cycle characteristics are poor, and the life of the secondary battery is short. was there.
しかしながら、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。 However, 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.
また、集電体上にシリコン膜を直接形成する場合、十分なサイクル寿命を得るためには、シリコン膜の厚さを２μｍ以内にしなくてはならない。単位面積当たりの目標の容量を達成する厚さ８μｍのシリコン膜では、充放電を繰り返しているうちに、シリコン膜にシワが発生したり、クラックが発生したりして、シリコン膜が集電体から剥離し、容量が低下してサイクル特性が悪いという問題があった。 Further, when the silicon film is directly formed on the current collector, the thickness of the silicon film must be within 2 μm in order to obtain a sufficient cycle life. In a silicon film with a thickness of 8 μm that achieves the target capacity per unit area, the silicon film becomes a current collector because wrinkles or cracks occur in the silicon film during repeated charging and discharging. There was a problem that the capacity was reduced and the cycle characteristics were poor.
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す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.
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、前記集電体上に成長したシリコン線状体と、を有し、前記シリコン線状体の少なくとも一端が、前記集電体に金属結合で結合している、または前記集電体上の金属に金属結合で結合している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。 In order to achieve the above-described object, the first invention includes a metal current collector and a silicon linear body grown on the current collector, and at least one end of the silicon linear body is at least one end. A negative electrode for a lithium ion secondary battery, wherein the negative electrode is bonded to the current collector by a metal bond, or is bonded to a metal on the current collector by a metal bond.
さらに、前記負極に導電助剤が含まれることが好ましく、前記シリコン線状体の外径が４ｎｍ〜１０００ｎｍであることが好ましい。 Furthermore, the negative electrode preferably contains a conductive additive, and the outer diameter of the silicon linear body is preferably 4 nm to 1000 nm.
また、前記シリコン線状体の少なくとも一部が縮れ形状であることが好ましく、または前記シリコン線状体の少なくとも一部が直線状であることが好ましい。 Moreover, it is preferable that at least a part of the silicon linear body has a crimped shape, or at least a part of the silicon linear body has a linear shape.
第２の発明は、金属製の集電体と、前記集電体上に形成されたシリコン層または金属層と、前記シリコン層または前記金属層の上に成長したシリコン線状体とを有し、前記シリコン線状体の少なくとも一端が、前記シリコン層または前記金属層に金属結合で結合している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。また、前記シリコン層がポーラス形状または略石筍形状であることが好ましい。 A second invention includes a metal current collector, a silicon layer or a metal layer formed on the current collector, and a silicon linear body grown on the silicon layer or the metal layer. A negative electrode for a lithium ion secondary battery, wherein at least one end of the silicon linear body is bonded to the silicon layer or the metal layer by a metal bond. Moreover, it is preferable that the said silicon layer is a porous shape or a substantially sarcophagus shape.
また、第１の発明と、第２の発明において、前記シリコン線状体が、導電助剤で被覆されていることが好ましい。導電助剤は、例えば厚み２ｎｍ程度のカーボンや電解銅めっき、無電解銅めっきなどが好適である。本構成は、初回充電時のリチウム脱溶媒和を促進させ、良好な不導体被膜（ＳＥＩ）を形成することができるという効果を有する。 In the first invention and the second invention, it is preferable that the silicon linear body is coated with a conductive additive. As the conductive assistant, for example, carbon having a thickness of about 2 nm, electrolytic copper plating, electroless copper plating and the like are suitable. This configuration has the effect of promoting lithium desolvation during the initial charge and forming a good non-conductive coating (SEI).
また、第１の発明と、第２の発明において、前記シリコン線状体が、導電助剤で埋設されていることが好ましい。本構成により、実効表面積の低減により、初回充放電時の不可逆容量が低減でき、クーロン効率が向上する。また、電解液の不可逆反応が低減することで、電解液の消耗が抑えられ、高容量化が可能となる。 In the first invention and the second invention, it is preferable that the silicon linear body is embedded with a conductive additive. With this configuration, the effective surface area can be reduced to reduce the irreversible capacity during the first charge / discharge, and the coulomb efficiency can be improved. Further, since the irreversible reaction of the electrolytic solution is reduced, the consumption of the electrolytic solution can be suppressed and the capacity can be increased.
また、前記シリコン線状体を被覆または埋設する前記導電助剤が、ポーラスであることが好ましい。導電助剤が緻密な膜を形成している場合、リチウムの浸透に時間がかかり、内部抵抗が大きくなり、電極として使用できないという問題点を生じる。導電助剤が緻密な膜である場合、溶媒和したリチウムイオンが透過しにくいためである。 Moreover, it is preferable that the said conductive support agent which coat | covers or embeds the said silicon | silicone linear body is porous. When the conductive assistant forms a dense film, it takes time for the lithium to permeate, the internal resistance increases, and there is a problem that it cannot be used as an electrode. This is because solvated lithium ions are difficult to permeate when the conductive assistant is a dense film.
第３の発明は、第１の発明または第２の発明に係るリチウムイオン二次電池用の負極を用いるリチウムイオン二次電池である。 3rd invention is a lithium ion secondary battery using the negative electrode for lithium ion secondary batteries which concerns on 1st invention or 2nd invention.
第４の発明は、集電体上に金属触媒を担持する工程（ａ）と、チャンバー内の前記集電体を３５０〜８００℃の間のある温度に保ち、かつ前記チャンバー内の圧力を０．５〜５０Ｔｏｒｒの間のある圧力に保ちつつ、前記チャンバー内に２０分〜２時間原料ガスを供給し、前記集電体にシリコン線状体をＶＬＳ法により成長させる工程（ｂ）と、を有する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 step (a) of supporting a metal catalyst on a current collector, maintaining the current collector in the chamber at a temperature between 350 to 800 ° C., and reducing the pressure in the chamber to 0. (B) supplying a raw material gas into the chamber for 20 minutes to 2 hours while maintaining a certain pressure between 5 and 50 Torr, and growing a silicon linear body on the current collector by a VLS method; It is a manufacturing method of the negative electrode for lithium ion secondary batteries characterized by having.
なお、「前記シリコン線状体の少なくとも一端が、前記集電体に金属結合で結合している」とは、ＶＬＳ（Ｖａｐｏｒ−Ｌｉｑｕｉｄ−Ｓｏｌｉｄ）機構により、前記集電体表面にシリコンが結晶成長したものを指しており、前記シリコン線状体が前記集電体に樹脂の結着剤で接着されたものや、物理吸着により接触している状態を指すものではない。すなわち、シランやジシランのような原料ガスとして供給されたシリコンは、液体状態の触媒表面に吸着し、水素を脱離して原子状のシリコンが触媒に溶解して合金化し、さらに原料ガスから過剰のシリコンが供給されることで、前記集電体の原子配列に応じて原子状のシリコンが規則正しく再配列して析出が進行する。シリコンの析出が繰り返し継続することで触媒は前記集電体表面から浮き上がり、線状にシリコンが結晶成長する。このとき、シリコンは液体から固体に変化するが集電体とは原子同士で結合し、自由電子は集電体とシリコン線状体の界面で自由に移動することができる。つまり、集電体とシリコン線状体は金属結合で結合している。直線状のシリコン線状体が集電体表面より成長し、シリコン線状体の一端が集電体表面に金属結合している場合以外にも、アーチ状のシリコン線状体が集電体表面から成長し、シリコン線状体の一端が集電体表面に金属結合し、さらにシリコン線状体の他端が集電体表面に接触している場合や、縮れたシリコン線状体が集電体表面より成長し、シリコン線状体の一端が集電体表面に金属結合し、さらにシリコン線状体の複数個所が集電体表面に接触している場合や、集電体表面より成長している二つのシリコン線状体が絡み合っている場合も含む。なお、シリコン線状体は、リチウムを吸蔵・脱離した後はアモルファスとなる。 Note that “at least one end of the silicon linear body is bonded to the current collector by a metal bond” means that silicon grows on the surface of the current collector by a VLS (Vapor-Liquid-Solid) mechanism. It does not indicate that the silicon linear body is bonded to the current collector with a resin binder or is in contact with physical adsorption. That is, silicon supplied as a source gas such as silane or disilane is adsorbed on the surface of the catalyst in a liquid state, desorbs hydrogen, and atomic silicon dissolves in the catalyst and forms an alloy. By supplying silicon, atomic silicon is regularly rearranged according to the atomic arrangement of the current collector, and precipitation proceeds. By repeating the deposition of silicon repeatedly, the catalyst is lifted from the surface of the current collector, and silicon crystal grows linearly. At this time, silicon changes from a liquid to a solid, but the current collector is bonded to each other by atoms, and free electrons can freely move at the interface between the current collector and the silicon linear body. That is, the current collector and the silicon linear body are bonded by a metal bond. In addition to the case where the linear silicon linear body grows from the current collector surface and one end of the silicon linear body is metal-bonded to the current collector surface, the arch-shaped silicon linear body is the current collector surface. When one end of the silicon linear body is metal-bonded to the current collector surface, and the other end of the silicon linear body is in contact with the current collector surface, or a crimped silicon linear body is It grows from the surface of the body, one end of the silicon linear body is metal-bonded to the current collector surface, and more than one part of the silicon linear body is in contact with the current collector surface. This includes the case where two silicon linear bodies are intertwined. Note that the silicon linear body becomes amorphous after insertion and extraction of lithium.
また、「シリコン線状体が縮れ形状である」とは、シリコン線状体が湾曲している形状、巻いている形状、ツイストしている形状、ねじれている形状、ひねられた形状、らせん形状、周期的でない形状などを指している。また、「前記シリコン線状体の少なくとも一部が縮れ形状である」とは、負極に縮れ形状であるシリコン線状体が含まれていることや、一本のシリコン線状体の一部が縮れ形状であることを意味し、「前記シリコン線状体の少なくとも一部が直線状である」とは、負極に直線状のシリコン線状体が含まれていることや、一本のシリコン線状体の一部が直線状であるを意味する。 In addition, “the silicon linear body has a crimped shape” means that the silicon linear body is curved, wound, twisted, twisted, twisted, or spiral. , Refers to non-periodic shapes and the like. In addition, “at least a part of the silicon linear body is a crimped shape” means that the negative electrode includes a silicon linear body that is a crimped shape, or a part of one silicon linear body is It means that it is a crimped shape, and “at least a part of the silicon linear body is linear” means that the negative electrode includes a linear silicon linear body or a single silicon wire. It means that a part of the shape is linear.
また、「前記シリコン層の少なくとも一部がポーラス形状である」とは、前記シリコン層の一部がポーラス形状であることを意味し、「前記シリコン層の少なくとも一部が略石筍形状である」とは、前記シリコン層の一部が略石筍形状であることを意味する。 Further, “at least a part of the silicon layer has a porous shape” means that a part of the silicon layer has a porous shape, and “at least a part of the silicon layer has a substantially sarcophagus shape”. The term “a part of the silicon layer” means a substantially sarcophagus shape.
本発明により、高容量と長寿命を実現す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 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。
第１の実施形態に係る負極１について説明する。
図１は、負極１を示す図である。負極１は、集電体３の上に、直接シリコン線状体１３が成長し、シリコン線状体１３の先端には触媒７を有する。
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.
The negative electrode 1 according to the first embodiment will be described.
FIG. 1 is a diagram showing a negative electrode 1. In the negative electrode 1, a silicon linear body 13 is grown directly on the current collector 3, and a catalyst 7 is provided at the tip of the silicon linear body 13.
集電体３は、銅、ニッケル、モリブデン、タングステン、タンタル、ステンレスなどの金属の箔である。これらを単独で用いてもよいし、これらの合金でもよい。厚さは４μｍ〜３５μｍが好ましく、特に８μｍ〜１８μｍがより好ましい。 The current collector 3 is a metal foil such as copper, nickel, molybdenum, tungsten, tantalum, and stainless steel. These may be used alone or an alloy thereof. The thickness is preferably 4 μm to 35 μm, and more preferably 8 μm to 18 μm.
シリコン線状体１３は、一次元のワイヤー状のシリコンであり、外径がナノサイズであれば、ナノワイヤーの他、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。シリコン線状体１３は、集電体３よりＶＬＳ機構により結晶成長しており、集電体３と直接金属結合をしている。シリコン線状体１３の外径は４ｎｍ〜１０００ｎｍであり、より好ましくは２５ｎｍ〜２００ｎｍである。シリコン線状体１３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。 The silicon linear body 13 is one-dimensional wire-like silicon, and if the outer diameter is nano-size, it is also called nanorod, nanowhisker, nanotube (hollow), nanofiber, nanobelt, etc. in addition to nanowire. The silicon linear body 13 is crystal-grown from the current collector 3 by the VLS mechanism, and is directly metal-bonded to the current collector 3. The outer diameter of the silicon linear body 13 is 4 nm to 1000 nm, and more preferably 25 nm to 200 nm. When the outer diameter of the silicon linear body 13 is thicker than 4 nm, 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.
シリコン線状体１３は、単結晶でも、多結晶でも、アモルファスでもよい。結晶性のシリコン線状体はリチウムを吸蔵・脱離すると、規則的な原子配列が乱れてアモルファスとなる。また、シリコン線状体１３の一部または全部が、直線状に成長していても、湾曲しながら縮れて成長していてもよい。 The silicon linear body 13 may be single crystal, polycrystalline, or amorphous. When a crystalline silicon linear body occludes or desorbs lithium, the regular atomic arrangement is disturbed and becomes amorphous. Moreover, even if a part or all of the silicon linear body 13 grows linearly, it may grow while shrinking while curving.
触媒７は、後述する触媒層５をスパッタリングあるいは蒸着することにより形成され、ＶＬＳ法によりシリコン線状体１３が成長するための触媒である。触媒７は銅、ニッケル、チタン、鉄、金、銀、パラジウム、マグネシウム、オスミウムなどや、それらの合金、例えば硫化銅、硫化銀、硫化金など、からなる直径４ｎｍ〜１０００ｎｍの粒子である。触媒７は、ＶＬＳ法により成長したシリコン線状体１３の先端に位置するが、途中に付着して観察されることもある。また、一部の触媒７が集電体３の表面に残り、触媒７よりシリコン線状体１３が成長していてもよい。この場合、集電体３と触媒７が金属結合を形成しており、さらに、触媒７とシリコン線状体１３とが金属結合を形成している。 The catalyst 7 is formed by sputtering or vapor-depositing a catalyst layer 5 described later, and is a catalyst for growing the silicon linear body 13 by the VLS method. The catalyst 7 is a particle having a diameter of 4 nm to 1000 nm made of copper, nickel, titanium, iron, gold, silver, palladium, magnesium, osmium, or an alloy thereof such as copper sulfide, silver sulfide, or gold sulfide. Although the catalyst 7 is located at the tip of the silicon linear body 13 grown by the VLS method, it may be observed attached to the middle. Further, a part of the catalyst 7 may remain on the surface of the current collector 3, and the silicon linear body 13 may grow from the catalyst 7. In this case, the current collector 3 and the catalyst 7 form a metal bond, and the catalyst 7 and the silicon linear body 13 form a metal bond.
次に、負極１の製造方法を説明する。
まず、図２（ａ）に示すように、集電体３の上に、触媒層５を形成する。触媒層５は、銅、ニッケル、チタン、鉄、金、銀、パラジウム、マグネシウム、オスミウムや、それらの合金、例えば、硫化銅、硫化銀、硫化金などの微粒子を散布したものであり、スパッタリング法や蒸着法、ＣＶＤ法により形成される。
Next, the manufacturing method of the negative electrode 1 is demonstrated.
First, as shown in FIG. 2A, the catalyst layer 5 is formed on the current collector 3. The catalyst layer 5 is obtained by spraying fine particles of copper, nickel, titanium, iron, gold, silver, palladium, magnesium, osmium, and alloys thereof, for example, copper sulfide, silver sulfide, gold sulfide, and the like. Or by vapor deposition or CVD.
次いで、図２（ｂ）に示すように、集電体３を、チャンバー１０内に入れ、真空ポンプで減圧下、Ａｒガスをキャリアーとしてヒーター１１にて所定の温度まで加熱する。 Next, as shown in FIG. 2B, the current collector 3 is placed in a chamber 10 and heated to a predetermined temperature with a heater 11 using Ar gas as a carrier under reduced pressure by a vacuum pump.
次いで、図２（ｃ）に示すように、ヒーター１１でチャンバー１０内を所定の温度にした後、真空ポンプで減圧しながら、原料ガス９を導入し、シリコン線状体１３をＶＬＳ（Ｖａｐｏｒ−Ｌｉｑｕｉｄ−Ｓｏｌｉｄ）法で成長させる。 Next, as shown in FIG. 2 (c), after the temperature inside the chamber 10 is set to a predetermined temperature by the heater 11, the source gas 9 is introduced while the pressure is reduced by the vacuum pump, and the silicon linear body 13 is changed to VLS (Vapor− The growth is performed by a liquid-solid method.
チャンバー１０はヒーター１１に囲まれており、原料ガス９がチャンバー１０に供給されている。チャンバー１０での反応温度は、３５０℃〜８００℃であることが好ましく、より好ましくは、４００℃〜５００℃である。なお、反応温度はヒーターにより石英ガラス管などから形成されるチャンバー全体を加熱する方法の他に、集電体を設置する基板やドラムそのものを加熱して接触により反応温度を設定しても良い。また、圧力は０．５〜５０Ｔｏｒｒが好ましく、反応時間は２０分〜２時間程度であり、１時間程度が好ましい。 The chamber 10 is surrounded by a heater 11 and a source gas 9 is supplied to the chamber 10. The reaction temperature in the chamber 10 is preferably 350 ° C to 800 ° C, more preferably 400 ° C to 500 ° C. In addition to the method of heating the entire chamber formed from a quartz glass tube or the like with a heater, the reaction temperature may be set by contact by heating the substrate on which the current collector is installed or the drum itself. The pressure is preferably 0.5 to 50 Torr, the reaction time is about 20 minutes to 2 hours, and preferably about 1 hour.
原料ガス９としては、シラン、ジシラン、ジクロロシラン、トリクロロシランなどを用いることができる。また、原料ガス９は、水素ガスやアルゴンガスなどのガスで希釈することが好ましい。また、チャンバー１０は、原料ガス９を、設定された圧力を保つように調整される。 As the source gas 9, silane, disilane, dichlorosilane, trichlorosilane, or the like can be used. The source gas 9 is preferably diluted with a gas such as hydrogen gas or argon gas. The chamber 10 is adjusted so that the source gas 9 is maintained at a set pressure.
なお、反応速度を上げ、生産性を向上させるために、チャンバー１０内を、プラズマを発生可能にし、原料ガス９をプラズマによりラジカル化した後に触媒７と反応させてもよい。例えば、原料ガスとしてシランを用い、ＶＨＦ高周波発振器によりチャンバー１０内にシランプラズマを生成し、シランプラズマを原料としてＶＬＳ法によりシリコン線状体を成長させる。 In order to increase the reaction rate and improve the productivity, plasma may be generated in the chamber 10 and the source gas 9 may be radicalized by the plasma and then reacted with the catalyst 7. For example, silane is used as a source gas, silane plasma is generated in the chamber 10 by a VHF high frequency oscillator, and a silicon linear body is grown by the VLS method using silane plasma as a source.
次いで、図２（ｄ）に示すように、反応後に、シリコン線状体１３が成長する。 Next, as shown in FIG. 2D, after the reaction, the silicon linear body 13 grows.
次に、負極１の使用方法について説明する。
図３は負極１の使用状態を説明する図である。図３（ａ）はリチウムイオンの吸蔵前の負極１を示し、図３（ｂ）はリチウムイオンの吸蔵によりシリコン線状体１３の体積が膨張した負極１を示す。
Next, a method for using the negative electrode 1 will be described.
FIG. 3 is a diagram for explaining a use state of the negative electrode 1. 3A shows the negative electrode 1 before occlusion of lithium ions, and FIG. 3B shows the negative electrode 1 in which the volume of the silicon linear body 13 is expanded by occlusion of lithium ions.
負極１は、図１に示すように、導電助剤１５を添加しなくても良いが、図３（ａ）に示すように、導電助剤１５をシリコン線状体１３の間に添加しても良い。さらに、図４（ａ）に示すように、シリコン線状体１３の全面を導電助剤１５で被覆、あるいは図４（ｂ）に示すように、シリコン線状体１３を導電助剤１５で埋設しても良い。導電助剤１５を使用すると、負極１の内部抵抗を低減する作用が有り、高率での充放電特性に効果がある。また、導電助剤１５を使用すると、容量の増加、負極活物質の利用率の向上、電解液分解の低減などの効果がある。 As shown in FIG. 1, the negative electrode 1 does not need to add the conductive auxiliary 15, but as shown in FIG. 3A, the conductive auxiliary 15 is added between the silicon linear bodies 13. Also good. Further, as shown in FIG. 4 (a), the entire surface of the silicon linear body 13 is covered with the conductive auxiliary agent 15, or the silicon linear body 13 is embedded with the conductive auxiliary agent 15 as shown in FIG. 4 (b). You may do it. Use of the conductive additive 15 has an effect of reducing the internal resistance of the negative electrode 1 and is effective in charge / discharge characteristics at a high rate. In addition, when the conductive additive 15 is used, there are effects such as an increase in capacity, an improvement in the utilization rate of the negative electrode active material, and a reduction in decomposition of the electrolyte.
導電助剤１５は、導電剤とも呼ばれ、電極に添加されて導電性を高める物質である。導電助剤１５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種の導電性物質である。導電助剤１５は、炭素、銅、スズ、亜鉛、ニッケル、銀の単体の粉末でもよいし、これら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。また、導電助剤１５はこれらの導電性物質のナノワイヤーでもよく、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を用いることができる。 The conductive assistant 15 is also called a conductive agent, and is a substance that is added to the electrode to enhance conductivity. The conductive assistant 15 is at least one conductive material selected from the group consisting of carbon, copper, tin, zinc, nickel, and silver. The conductive additive 15 may be a single powder of carbon, copper, tin, zinc, nickel, or silver, or may be a powder of these alloys. For example, general carbon black such as furnace black and acetylene black can be used. Moreover, the conductive support agent 15 may be nanowires of these conductive substances, and carbon fibers, carbon nanotubes, copper nanowires, nickel nanowires, and the like can be used.
例えば、シリコン線状体１３に導電助剤１５を添加する場合には、導電助剤１５を水などの溶媒に分散してスラリーとして塗布し、乾燥すればよい。必要に応じて結着剤や増粘剤を添加してスラリーの粘度を調製したり、乾燥後の電極を強固な膜として２段ロール等でプレスして膜厚を調整したりしてもよい。 For example, when the conductive assistant 15 is added to the silicon linear body 13, the conductive assistant 15 may be dispersed in a solvent such as water, applied as a slurry, and dried. If necessary, a binder or thickener may be added to adjust the viscosity of the slurry, or the dried electrode may be pressed with a two-stage roll or the like as a strong film to adjust the film thickness. .
また、図４（ａ）に示すように、シリコン線状体１３を、導電助剤１５などの導電性材料で被覆してもよい。導電性材料としては、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。 Further, as shown in FIG. 4A, the silicon linear body 13 may be covered with a conductive material such as a conductive additive 15. Examples of the conductive material include carbon, copper, tin, zinc, nickel, silver, and alloys thereof.
例えば、シリコン線状体１３へ炭素系の導電性材料で被覆する場合には、集電体３のシリコン線状体１３に高分子材料を含浸させ、焼成する方法が考えられる。例えば、３〜１５ｗｔ％のポリビニルアルコール水溶液を塗布した後、不活性雰囲気下で７００℃、３時間程度焼成してもよい。アルコール系樹脂のほかに、前記高分子材料としては、ビニル系樹脂、フェノール系樹脂、セルロース系樹脂、ピッチ系樹脂およびタール系樹脂などの、熱処理により炭素系物質に焼成される高分子材料を用いることができる。特に、炭素源としてショ糖や水あめなどの糖類を用いると図４（ｂ）のようにシリコン線状体を埋設することができる。シリコン線状体を導電性材料で埋設する方法として、例えば、５〜１０ｗｔ％のショ糖水溶液を塗布した後、不活性雰囲気下で７００℃、３時間程度焼成する方法がある。 For example, when the silicon linear body 13 is coated with a carbon-based conductive material, a method of impregnating the silicon linear body 13 of the current collector 3 with a polymer material and baking it can be considered. For example, after applying a 3 to 15 wt% polyvinyl alcohol aqueous solution, baking may be performed at 700 ° C. for about 3 hours in an inert atmosphere. In addition to the alcohol-based resin, as the polymer material, a polymer material that is fired into a carbon-based material by heat treatment, such as a vinyl-based resin, a phenol-based resin, a cellulose-based resin, a pitch-based resin, and a tar-based resin is used. be able to. In particular, when a saccharide such as sucrose or syrup is used as a carbon source, a silicon linear body can be embedded as shown in FIG. As a method for embedding the silicon linear body with a conductive material, for example, there is a method in which a 5 to 10 wt% sucrose aqueous solution is applied and then baked at 700 ° C. for about 3 hours in an inert atmosphere.
また、シリコン線状体１３を被覆や埋設する導電助剤１５は、空隙を有するポーラスな構造の膜を形成することが好ましい。導電助剤の膜が緻密な場合、溶媒和したリチウムイオンの浸透に時間がかかり、内部抵抗が大きくなるなど、電極として不利になるためである。 Moreover, it is preferable that the conductive additive 15 for covering or embedding the silicon linear body 13 forms a porous structure film having voids. This is because if the conductive assistant film is dense, it takes time for the solvated lithium ions to permeate and the internal resistance increases, which is disadvantageous as an electrode.
また、シリコン線状体１３を金属系の導電性物質で被覆する場合には、集電体３を真空チャンバー内にてスパッタリングや蒸着を用いて行う方法が考えられる。例えば、銅の被覆する場合には、銅ターゲットを設置し、集電体３を置いた基板間に直流高電圧を印加し、Ａｒガスを導入してシリコン線状体１３が形成された集電体３に銅を被覆することができる。 Further, when the silicon linear body 13 is covered with a metal-based conductive material, a method of performing the current collector 3 by using sputtering or vapor deposition in a vacuum chamber is conceivable. For example, in the case of covering with copper, a copper target is installed, a DC high voltage is applied between the substrates on which the current collector 3 is placed, and Ar gas is introduced to form a silicon linear body 13. The body 3 can be coated with copper.
図３（ｂ）に示すように、負極１にリチウムイオンを吸蔵させると、負極活物質であるシリコンが膨張し、シリコン線状体１３が太く長くなる。シリコン線状体１３は充電時にリチウムを吸蔵して合金化すると、体積膨張により、太く長くなるが、集電体３に金属結合で結合したままであるので、放電時にはリチウムを脱離して体積収縮して元のサイズに戻るのみで、集電体３との機械的、電気的接合は保持されたままである。このように、シリコン線状体１３は線状の形状であるため、負極活物質の体積変化に伴うひずみが吸収される。そのため、負極活物質の充放電時の微粉化や、負極活物質と集電体との剥離が抑制されるため、高容量かつ、サイクル寿命が長い。 As shown in FIG. 3B, when lithium ions are occluded in the negative electrode 1, silicon as the negative electrode active material expands, and the silicon linear body 13 becomes thick and long. When the silicon linear body 13 occludes lithium during charging and is alloyed, the silicon linear body 13 becomes thick and long due to volume expansion, but remains bonded to the current collector 3 by a metal bond. Then, the mechanical and electrical connection with the current collector 3 is maintained only by returning to the original size. Thus, since the silicon | silicone linear body 13 is a linear shape, the distortion accompanying the volume change of a negative electrode active material is absorbed. Therefore, since the pulverization of the negative electrode active material during charge / discharge and the peeling between the negative electrode active material and the current collector are suppressed, the capacity is high and the cycle life is long.
また、負極１は、図５に示すような装置でＲｏｌｅ ｔｏ Ｒｏｌｅでの大量生産が可能である。集電体３はドラム１７に巻きつけられたロール状の集電体３で供給される。集電体３は、ドラム１７から繰り出された後、触媒担持装置１９により、触媒層５が形成される。その後集電体３は、チャンバー１０に入り、ヒーター１１を内蔵したドラム上で所定の温度に保持されて、シリコン線状体１３が成長する。集電体３はチャンバー１０を出た後、ドラム２３に巻き取られる。 Moreover, the negative electrode 1 can be mass-produced by Role to Role with an apparatus as shown in FIG. The current collector 3 is supplied by a roll-shaped current collector 3 wound around a drum 17. After the current collector 3 is unwound from the drum 17, the catalyst support device 19 forms the catalyst layer 5. Thereafter, the current collector 3 enters the chamber 10 and is held at a predetermined temperature on a drum having a built-in heater 11, so that the silicon linear body 13 grows. After the current collector 3 exits the chamber 10, it is wound around the drum 23.
チャンバー１０は、真空排気装置により減圧環境におかれ、原料ガス９が供給される。チャンバー１０内の圧力は圧力計２１によりモニタリングされており、チャンバー１０内の圧力を一定に保つように、原料ガス９の供給や真空排気側のバルブが調整される。また、ドラム内に設置されたヒーター１１によりドラム上の集電体３は所定の反応温度に保たれている。なお、負極１は所定のサイズに裁断して枚葉でシリコン線状体１３を形成できることはいうまでも無い。 The chamber 10 is placed in a reduced pressure environment by a vacuum exhaust device, and the source gas 9 is supplied. The pressure in the chamber 10 is monitored by a pressure gauge 21, and the supply of the source gas 9 and the valve on the evacuation side are adjusted so as to keep the pressure in the chamber 10 constant. Further, the current collector 3 on the drum is maintained at a predetermined reaction temperature by the heater 11 installed in the drum. Needless to say, the negative electrode 1 can be cut into a predetermined size to form the silicon linear body 13 in a single sheet.
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、増粘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・乾燥して、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, a thickener, 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、増粘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, the thickener, and the solvent are at levels 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 ) (where x and y are natural numbers), one of electrolytes composed of lithium salts such as LiCl and LiI, or a mixture of two or more thereof can be dissolved and used.
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.
図６に、第１の実施形態に係る負極１の変形例を示す。図６（ａ）に示すように、負極２５は、集電体３の上に、シリコン層２７を有し、シリコン層２７からシリコン線状体１３が成長している。シリコン層２７は、シリコン線状体１３をＶＬＳ法にて成長させる際に、温度、圧力などの条件に応じて集電体３の表面にシリコンが析出して形成される。 FIG. 6 shows a modification of the negative electrode 1 according to the first embodiment. As shown in FIG. 6A, the negative electrode 25 has a silicon layer 27 on the current collector 3, and the silicon linear body 13 is grown from the silicon layer 27. The silicon layer 27 is formed by depositing silicon on the surface of the current collector 3 according to conditions such as temperature and pressure when the silicon linear body 13 is grown by the VLS method.
なお、シリコン層２７には、シリコンのみでなく、触媒層５や後述する金属層３１の金属が含まれていてもよい。また、シリコン層２７は、石筍状の形状を有していてもよく、細孔を有するポーラス形状であってもよい。石筍状とは、表面より突き出している突起状の形状である。 Note that the silicon layer 27 may contain not only silicon but also the metal of the catalyst layer 5 and the metal layer 31 described later. The silicon layer 27 may have a sarcophagus shape or a porous shape having pores. The sarcophagus is a protruding shape protruding from the surface.
また、図６（ｂ）に示すように、負極２９は、集電体３の上に、金属層３１を有し、金属層３１からシリコン線状体１３が成長している。金属層３１は、集電体３とシリコン線状体１３とが剥離しないように形成されており、触媒層５の成膜に先立って集電体３の上に成膜される。金属層３１は、スパッタリング法や蒸着法、ＣＶＤ法により形成される。金属層３１は、チタン、バナジウム、ジルコニウム、イットリウム、タングステン、鉄、ニッケル、クロム、モリブデンからなる群より選ばれた少なくとも１種の金属またはそれらの合金である。金属層３１に用いられる金属は、シリコン（Ｓｉ）と金属（Ｍ）が２：１となるＳｉ２ＭあるいはＭＳｉ２となるシリサイドを形成しやすいものが好ましい。金属層３１が形成するシリサイドとしては、具体的にＴｉＳｉ２，ＶＳｉ２，Ｓｉ２Ｚｒ，Ｓｉ２Ｙ，ＷＳｉ２，ＦｅＳｉ２，ＮｉＳｉ２，ＣｒＳｉ２，ＭｏＳｉ２などが挙げられる。金属層３１により、集電体３とシリコン線状体１３の密着力が増す。さらに、これらのシリサイドはシリコンの１万倍から１０万倍のオーダーで電子導電性があり、集電体３の金属とシリコンとの電子伝導を促進するとともに、界面の近傍におけるシリコンの充放電に伴う体積変化を緩和する効果がある。特に、集電体３として電解銅箔の光沢面を使用するときには、シリコン線状体１３との密着力が向上して好適である。 Further, as shown in FIG. 6B, the negative electrode 29 has a metal layer 31 on the current collector 3, and the silicon linear body 13 is grown from the metal layer 31. The metal layer 31 is formed so that the current collector 3 and the silicon linear body 13 are not peeled off, and is formed on the current collector 3 prior to the formation of the catalyst layer 5. The metal layer 31 is formed by sputtering, vapor deposition, or CVD. The metal layer 31 is at least one metal selected from the group consisting of titanium, vanadium, zirconium, yttrium, tungsten, iron, nickel, chromium, and molybdenum, or an alloy thereof. The metal used for the metal layer 31 is preferably a metal that can easily form a silicide of Si 2 M or MSi 2 in which silicon (Si) and metal (M) are 2: 1. Specific examples of the silicide formed by the metal layer 31 include TiSi 2 , VSi 2 , Si 2 Zr, Si 2 Y, WSi 2 , FeSi 2 , NiSi 2 , CrSi 2 , and MoSi 2 . The metal layer 31 increases the adhesion between the current collector 3 and the silicon linear body 13. Furthermore, these silicides have electronic conductivity on the order of 10,000 to 100,000 times that of silicon, and promote the electron conduction between the metal of the current collector 3 and silicon, and charge and discharge of silicon in the vicinity of the interface. There is an effect to relieve the accompanying volume change. In particular, when the glossy surface of the electrolytic copper foil is used as the current collector 3, the adhesion with the silicon linear body 13 is improved, which is preferable.
なお、金属層３１の上に、さらにシリコン層２７を有し、シリコン層２７の上よりシリコン線状体１３を成長させていてもよい。 Note that a silicon layer 27 may be further provided on the metal layer 31, and the silicon linear body 13 may be grown on the silicon layer 27.
なお、図６（ａ）に示すような負極２５、図６（ｂ）に示すような負極２９についても、図３（ａ）に示すように、導電助剤をシリコン線状体の間に添加しても良いし、図４（ａ）に示すように、シリコン線状体を導電助剤で被覆しても良いし、図４（ｂ）に示すように、シリコン線状体を導電助剤で埋設しても良い。 For the negative electrode 25 as shown in FIG. 6 (a) and the negative electrode 29 as shown in FIG. 6 (b), as shown in FIG. 3 (a), a conductive additive is added between the silicon linear bodies. Alternatively, as shown in FIG. 4 (a), the silicon linear body may be coated with a conductive auxiliary agent, or as shown in FIG. 4 (b), the silicon linear body may be covered with a conductive auxiliary agent. It may be buried with.
本実施形態によれば、負極活物質としてシリコンを用いるため、グラファイトを負極活物質として用いる従来の負極よりも、高容量化が可能である。 According to this embodiment, since silicon is used as the negative electrode active material, the capacity can be increased as compared with the conventional negative electrode using graphite as the negative electrode active material.
また、本実施形態によれば、負極活物質が一次元のシリコン線状体であるため、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シリコン線状体の太さと長さで吸収され、シリコン線状体と集電体は金属結合のまま保持されるため、負極活物質と集電体との剥離が抑制される。そのため、負極の容量は大きく、寿命が長い。 Further, according to the present embodiment, since the negative electrode active material is a one-dimensional silicon linear body, even if the volume change of the negative electrode active material is large, the strain accompanying the volume change depends on the thickness and length of the silicon linear body. Since the silicon linear body and the current collector are absorbed and held in a metal bond, peeling between the negative electrode active material and the current collector is suppressed. Therefore, the capacity of the negative electrode is large and the life is long.
また、本実施形態によれば、シリコン線状体の一端と集電体とが金属結合しているため、シリコン線状体と集電体との間の電気的接続が良好であり、電極膜の電気抵抗が小さい。また、シリコン線状体と集電体とが強固に接合しており、シリコン線状体が負極より脱落しにくい。 In addition, according to the present embodiment, since one end of the silicon linear body and the current collector are metal-bonded, the electrical connection between the silicon linear body and the current collector is good, and the electrode film The electrical resistance is small. Further, the silicon linear body and the current collector are firmly bonded, and the silicon linear body is less likely to fall off from the negative electrode.
また、本実施形態によれば、バッチ処理ではなく連続処理で負極を製造できるため、生産性に優れ、大量生産が可能である。 Moreover, according to this embodiment, since a negative electrode can be manufactured not by batch processing but by continuous processing, it is excellent in productivity and mass production is possible.
また、本実施形態によれば、集電体とシリコン線状体が金属結合により直接結合しており、導電助剤１５を添加あるいは被覆、さらにシリコン線状体を導電助剤で埋設しているため、負極は内部抵抗を低く抑えることができ、負極を用いたリチウムイオン二次電池は、不可逆容量の低減が可能である。特にシリコン線状体を導電助剤で埋設すると、負極の実効表面積を低減することができ、不可逆容量の低減効果が大きい。不可逆容量とは、初回の充放電時の、充電容量と放電容量の容量差である。不可逆容量の原因の一つは、活物質となるシリコンが電解液に直接接することで電解液の電気化学的還元分解が生じてシリコン表面に不導体皮膜（ＳＥＩ）が形成されるときに生じるものであり、シリコン線状体に導電助剤を添加、導電助剤で被覆あるいは埋設することで、緩和することができる。このように、不可逆容量を低減することは、電解液の消耗を抑えることになり、リチウムイオン電池全体としての高容量化が可能となる。また、導電助剤１５でシリコン線状体１３を被覆あるいは埋設することで負極の内部抵抗をさらに低減することが可能となり高率での容量（ハイレート特性）に優れる。 Further, according to the present embodiment, the current collector and the silicon linear body are directly bonded by a metal bond, the conductive auxiliary agent 15 is added or covered, and the silicon linear body is embedded with the conductive auxiliary agent. Therefore, the negative electrode can keep internal resistance low, and the lithium ion secondary battery using the negative electrode can reduce irreversible capacity. In particular, when a silicon linear body is embedded with a conductive additive, the effective surface area of the negative electrode can be reduced, and the effect of reducing irreversible capacity is great. The irreversible capacity is a capacity difference between the charge capacity and the discharge capacity at the first charge / discharge. One of the causes of irreversible capacity occurs when silicon, which is the active material, is in direct contact with the electrolyte, causing electrochemical reductive decomposition of the electrolyte and forming a non-conductive film (SEI) on the silicon surface. It can be alleviated by adding a conductive additive to the silicon linear body and covering or burying it with the conductive additive. Thus, reducing the irreversible capacity suppresses the consumption of the electrolytic solution, and the capacity of the entire lithium ion battery can be increased. Further, by covering or embedding the silicon linear body 13 with the conductive auxiliary agent 15, the internal resistance of the negative electrode can be further reduced, and the capacity at a high rate (high rate characteristic) is excellent.
また、本実施形態によれば、集電体とシリコン線状体が金属結合しており、結着剤の量を減らすことができるため、負極中の負極活物質の割合が大きくなり、高容量化が可能である。 Further, according to the present embodiment, the current collector and the silicon linear body are metal-bonded, and the amount of the binder can be reduced, so that the ratio of the negative electrode active material in the negative electrode is increased, and the high capacity Is possible.
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.
以下、本発明について実施例および比較例を用いて具体的に説明する。
［実施例１］
電解銅箔（古河電気工業株式会社製 ＮＣ−ＷＳ 厚さ１０μｍ）のマット面（電析した側）を脱脂洗浄した後、金のスパッタを２０秒間行い、厚さ約２ｎｍの金の薄膜を形成した。その後、銅箔をチャンバー内に置き、チャンバー内を減圧してＡｒ雰囲気下で、チャンバー温度が４５０℃でチャンバー内圧力が５Ｔｏｒｒに到達したことを確認した後、原料ガスの供給を開始した。原料ガスとしてジシラン（１０％ 水素希釈）を供給し、チャンバー内が５Ｔｏｒｒになるようにした。原料ガスの供給を開始して１時間後に、原料ガスの供給を停止した。その後、チャンバーを常温常圧に戻した。ＶＬＳ機構により、電解銅箔のマット面上にシリコン線状体が成長した。
Hereinafter, the present invention will be specifically described using examples and comparative examples.
[Example 1]
After degreasing and cleaning the mat surface (electrodeposited side) of electrolytic copper foil (Furukawa Electric Co., Ltd., NC-WS, 10 μm thick), gold sputtering is performed for 20 seconds to form a gold thin film with a thickness of about 2 nm. did. Thereafter, the copper foil was placed in the chamber, the pressure inside the chamber was reduced, and after confirming that the chamber temperature was 450 ° C. and the pressure in the chamber reached 5 Torr in an Ar atmosphere, the supply of the source gas was started. Disilane (10% hydrogen dilution) was supplied as a source gas so that the inside of the chamber was 5 Torr. One hour after starting the supply of the raw material gas, the supply of the raw material gas was stopped. Thereafter, the chamber was returned to normal temperature and pressure. A silicon linear body grew on the mat surface of the electrolytic copper foil by the VLS mechanism.
電極の特性試験は、以下の方法により行った。金属Ｌｉ箔を対照電極としてリチウムイオン２次電池を構成した。放電容量は、有効な活物質Ｓｉを基準として、設計値を１２００ｍＡｈ／ｇとした。まず、２５℃環境下において、電流値を０．１Ｃ、電圧値を０．０２Ｖまで定電流定電圧条件で充電を行い、電流値が０．０５Ｃに低下した時点で充電を停止した。次いで、電流値０．１Ｃの条件で、金属Ｌｉに対する電圧が１．５Ｖとなるまで放電を行った。なお、１Ｃとは、１時間で満充電できる電流値である。また、充電と放電はともに２５℃環境下において行った。次いで、０．２Ｃでの充放電速度で上記充放電を５０サイクル繰り返した。 The characteristic test of the electrode was performed by the following method. A lithium ion secondary battery was constructed using metal Li foil as a reference electrode. The discharge capacity was set to 1200 mAh / g based on the effective active material Si. First, in a 25 ° C. environment, charging was performed under constant current and constant voltage conditions until the current value was 0.1 C and the voltage value was 0.02 V, and the charging was stopped when the current value decreased to 0.05 C. Next, discharge was performed under the condition of a current value of 0.1 C until the voltage with respect to the metal Li became 1.5V. 1C is a current value that can be fully charged in one hour. Both charging and discharging were performed in a 25 ° C. environment. Next, the above charge / discharge cycle was repeated 50 cycles at a charge / discharge rate of 0.2C.
［実施例２］
反応温度を４００℃とした以外は、実施例１と同様の方法により負極を作製した。
[Example 2]
A negative electrode was produced in the same manner as in Example 1 except that the reaction temperature was 400 ° C.
［実施例３］
電解銅箔のシャイニー面（ドラムから引き剥がされた光沢面）を用いる以外は、実施例１と同様の方法により負極を作製した。
[Example 3]
A negative electrode was produced in the same manner as in Example 1 except that the shiny surface of the electrolytic copper foil (the glossy surface peeled off from the drum) was used.
［実施例４］
電解銅箔のシャイニー面を用い、反応温度を４００℃とする以外は、実施例１と同様の方法により負極を作製した。
[Example 4]
A negative electrode was produced in the same manner as in Example 1 except that the shiny surface of the electrolytic copper foil was used and the reaction temperature was 400 ° C.
［実施例５］
実施例１に記載の電解銅箔のマット面を用い、金のスパッタを２０秒間行い、厚さ約２ｎｍの金の薄膜を形成した。その後、銅箔をチャンバー内に置き、チャンバー内を減圧してＡｒ雰囲気下で、チャンバー温度が６００℃でチャンバー内圧力が１Ｔｏｒｒに到達したことを確認した後、実施例１に記載の原料ガスの供給を開始した。チャンバー内が１Ｔｏｒｒになるようにした。原料ガスの供給を開始して１時間後に、原料ガスの供給を停止した。その後、チャンバーを常温常圧に戻した。ＶＬＳ機構により、電解銅箔のマット面上にシリコン線状体が成長した。
[Example 5]
Using the matte surface of the electrolytic copper foil described in Example 1, gold was sputtered for 20 seconds to form a gold thin film having a thickness of about 2 nm. Thereafter, the copper foil was placed in the chamber, the pressure inside the chamber was reduced, and after confirming that the chamber temperature reached 600 ° C. and the chamber pressure reached 1 Torr in an Ar atmosphere, the raw material gas described in Example 1 was used. Supply started. The inside of the chamber was set to 1 Torr. One hour after starting the supply of the raw material gas, the supply of the raw material gas was stopped. Thereafter, the chamber was returned to normal temperature and pressure. A silicon linear body grew on the mat surface of the electrolytic copper foil by the VLS mechanism.
実施例１〜５の条件を表１にまとめた。 The conditions of Examples 1-5 are summarized in Table 1.
［比較例１］
（負極の作製）
導電助剤１として、平均粒径８０ｎｍのカーボンナノホーン（日本電気株式会社製、単層ＣＮＨ）よりなるカーボン１と、導電助剤２として平均粒径３５ｎｍのアセチレンブラック（電気化学工業株式会社製、粉状品）よりなるカーボン２と、平均粒径５μｍのシリコン粉末（株式会社高純度化学研究所製、ＳＩＥ２３ＰＢ）よりなる負極活物質と、スチレンブタジエンラバー（ＳＢＲ）４０ｗｔ％のエマルション（日本ゼオン株式会社製、ＢＭ４００Ｂ）よりなる樹脂系結着剤との水性スラリーを表２の固形分換算での配合比率（ｗｔ％）で調製した。水性スラリーは粘度を調整するため、カルボキシメチルセルロースナトリウム（ＣＭＣ、ダイセル化学工業株式会社製、＃２２００）１ｗｔ％溶液を増粘剤として使用した。
[Comparative Example 1]
(Preparation of negative electrode)
As conductive aid 1, carbon 1 composed of carbon nanohorns having an average particle size of 80 nm (manufactured by NEC Corporation, single-layer CNH), and acetylene black having an average particle size of 35 nm (made by Denki Kagaku Kogyo Co., Ltd., as conductive aid 2) Carbon 2 made of a powdery product), a negative electrode active material made of silicon powder having an average particle size of 5 μm (manufactured by High Purity Chemical Laboratory Co., Ltd., SIE23PB), and an emulsion of styrene butadiene rubber (SBR) 40 wt% (Nippon Zeon Corporation) An aqueous slurry with a resin binder made of BM400B) was prepared at a blending ratio (wt%) in terms of solid content in Table 2. In order to adjust the viscosity of the aqueous slurry, a 1 wt% solution of sodium carboxymethyl cellulose (CMC, manufactured by Daicel Chemical Industries, Ltd., # 2200) was used as a thickener.
調製したスラリーを自動塗工装置（テスター産業株式会社製、ＰＩ−１２１０型）のドクターブレードを用いて、厚み１０μｍのリチウムイオン２次電池用電解銅箔（古河電気工業株式会社製ＮＣ−ＷＳ）よりなる集電体上に、乾燥後膜厚が３０μｍとなる厚みで塗布し、７０℃で乾燥し、ロールプレスで厚み１５μｍに調厚してリチウムイオン二次電池用負極を製造した。 Using the prepared slurry, a doctor blade of an automatic coating apparatus (PI-1210 type, manufactured by Tester Sangyo Co., Ltd.), an electrolytic copper foil for lithium ion secondary batteries having a thickness of 10 μm (NC-WS, manufactured by Furukawa Electric Co., Ltd.) On the current collector, the film was applied with a thickness of 30 μm after drying, dried at 70 ° C., and adjusted to a thickness of 15 μm with a roll press to produce a negative electrode for a lithium ion secondary battery.
［比較例２］
比較例２においては、比較例１で用いられる平均粒径５μｍのシリコン粉末の代わりに、平均粒径６０ｎｍの球状シリコン粉末（Ｈｅｆｅｉ Ｋａｉ’ｅｒ社製）を用い、水性スラリーを表２の固形分換算での配合比率（ｗｔ％）で各種調製した。他の水性スラリーの原料、水性スラリーの塗布・乾燥方法、特性評価方法は、実施例と同様に行った。なお、比較例２においては、表２に記載の代表的な組成と、導電助剤１、導電助剤２、負極活物質の量を、表２に記載の所定の範囲内で変更した組成で負極を作製した。
[Comparative Example 2]
In Comparative Example 2, spherical silicon powder having an average particle diameter of 60 nm (manufactured by Hefei Kai'er) was used in place of the silicon powder having an average particle diameter of 5 μm used in Comparative Example 1, and the aqueous slurry was used as a solid content in Table 2. Various preparations were made at a conversion ratio (wt%) in terms of conversion. The other raw materials of the aqueous slurry, the application / drying method of the aqueous slurry, and the property evaluation method were performed in the same manner as in the examples. In Comparative Example 2, the representative composition described in Table 2 and the composition in which the amounts of the conductive auxiliary agent 1, the conductive auxiliary agent 2, and the negative electrode active material were changed within the predetermined range shown in Table 2 were used. A negative electrode was produced.
図７は、実施例１における、金触媒付与後の電解銅箔マット面の走査型電子顕微鏡（ＳＥＭ）写真（ａ）とその拡大図（ｂ）である。拡大図から粒径２０ｎｍ程度の金触媒が一面に分布していることがわかる。 FIG. 7 is a scanning electron microscope (SEM) photograph (a) and an enlarged view (b) of the electrolytic copper foil mat surface after application of the gold catalyst in Example 1. It can be seen from the enlarged view that gold catalysts having a particle size of about 20 nm are distributed over the entire surface.
図８は、実施例１に係る負極のＳＥＭ写真である。図８（ａ）において、突起状に形成されているものがシリコンナノワイヤー（シリコン線状体）である。図８（ｂ）において拡大して示すように、外径１００ｎｍ程度の縮れたシリコン線状体が密集して成長している。 FIG. 8 is an SEM photograph of the negative electrode according to Example 1. In FIG. 8A, what is formed in a protruding shape is a silicon nanowire (silicon linear body). As shown in an enlarged view in FIG. 8 (b), silicon linear bodies having a reduced outer diameter of about 100 nm are densely grown.
図９は、実施例１に係るシリコン線状体の透過型電子顕微鏡（ＴＥＭ）写真である。縮れたシリコン線状体の外径は６０〜７０ｎｍ程度であり、グレインバウンダリーや縞模様を観察できることから、縮れたシリコン線状体は多結晶であることがわかる。 FIG. 9 is a transmission electron microscope (TEM) photograph of the silicon linear body according to Example 1. The outer diameter of the crimped silicon linear body is about 60 to 70 nm, and the grain boundary and the striped pattern can be observed. Therefore, it is understood that the crimped silicon linear body is polycrystalline.
図１０は、実施例１に係るシリコン線状体の走査透過型電子顕微鏡（ＳＴＥＭ）観察結果である。明視野ＳＴＥＭ像にはシリコン線状体のところどころに黒いはん点が観察される。 FIG. 10 is a result of observation by a scanning transmission electron microscope (STEM) of the silicon linear body according to the first embodiment. In the bright field STEM image, black spots are observed in some places in the silicon linear body.
図１１は、実施例１に係るシリコン線状体のＳＴＥＭ−ＥＤＳ分析の結果である。シリコン線状体のところどころに観察される黒いはん点は銅であることが分かる。この銅は、電解銅箔のマット面に析出していた銅微粒子が、シリコン線状体の表面に付着したものである。 FIG. 11 shows the results of STEM-EDS analysis of the silicon linear body according to Example 1. It can be seen that the black spots observed in the silicon linear bodies are copper. In this copper, copper fine particles deposited on the mat surface of the electrolytic copper foil are attached to the surface of the silicon linear body.
図１２、図１３は、実施例１に係る負極を、０．２Ｃで５０サイクル充放電した後の負極のＳＥＭ写真である。シリコン線状体の表面に溶媒和リチウムイオンの電解液の電気化学的還元分解により形成される表面皮膜（ＳＥＩ）が観察される。
シリコン線状体を図４（ａ）に示すように、導電助剤で、特に厚さ２ｎｍ程度のカーボンで被覆すると少量で良好なＳＥＩが形成される。また、図４（ｂ）に示すように、カーボンなどの導電助剤で埋設することにより、より少量で良好なＳＥＩを形成することが可能となる。このときの導電助剤はポーラスであり、電解液が浸透することが必須である。
12 and 13 are SEM photographs of the negative electrode after charging and discharging the negative electrode according to Example 1 at 0.2 C for 50 cycles. A surface film (SEI) formed by electrochemical reductive decomposition of an electrolyte solution of solvated lithium ions is observed on the surface of the silicon linear body.
As shown in FIG. 4A, when a silicon linear body is coated with a conductive additive, particularly with a carbon having a thickness of about 2 nm, good SEI is formed in a small amount. Further, as shown in FIG. 4B, by embedding with a conductive aid such as carbon, it is possible to form a good SEI with a smaller amount. The conductive assistant at this time is porous, and it is essential that the electrolytic solution penetrates.
また、図１３に示すように、実施例１に係る、シリコン線状体を結晶成長させた負極を、５０サイクル充放電した後でも、活物質であるシリコンの微粉化や脱落、電極のクラック発生は観察されなかった。一方図２２〜図２６に示す比較例１や比較例２の結果とあわせると、活物質であるシリコンの形状は、三次元粒子状の形態より、一次元線状体のほうが、サイクル特性に優れることが分かる。 Moreover, as shown in FIG. 13, even after charging and discharging 50 cycles of the negative electrode on which the silicon linear body was crystal-grown according to Example 1, the active material silicon was pulverized and dropped, and cracks were generated in the electrode. Was not observed. On the other hand, when combined with the results of Comparative Example 1 and Comparative Example 2 shown in FIGS. 22 to 26, the shape of silicon, which is the active material, is more excellent in cycle characteristics in the one-dimensional linear body than in the three-dimensional particle form. I understand that.
図１４は、実施例２に係る負極のＳＥＭ写真である。図１４（ａ）において、縮れたシリコン線状体が観察される。図１４（ｂ）において拡大して示すように、シリコン線状体の外径は、４０ｎｍ〜９０ｎｍ程度である。 FIG. 14 is an SEM photograph of the negative electrode according to Example 2. In FIG. 14A, a crimped silicon linear body is observed. As shown in an enlarged view in FIG. 14B, the outer diameter of the silicon linear body is about 40 nm to 90 nm.
図１５は、実施例３に係る負極のＳＥＭ写真である。図１５（ａ）において、太くて縮れたシリコン線状体と細くて直線的なシリコン線状体が観察される。図１５（ｂ）において拡大して示すように、縮れたシリコン線状体の外径は１０〜２００ｎｍ程度であり、直線的なシリコン線状体の外径は、３０ｎｍ程度である。 FIG. 15 is a SEM photograph of the negative electrode according to Example 3. In FIG. 15A, a thick and crimped silicon linear body and a thin and linear silicon linear body are observed. As shown in an enlarged view in FIG. 15B, the outer diameter of the crimped silicon linear body is about 10 to 200 nm, and the outer diameter of the linear silicon linear body is about 30 nm.
図１６〜図１８は、実施例４に係る負極のＳＥＭ写真である。図１６（ａ）において、先端が平坦で、太さ５〜２０μｍの石筍状のシリコンの成長が観察される。図１６（ｂ）では、石筍状のシリコンの側面から、縮れたシリコン線状体の成長が観察される。図１７は、さらに縮れたシリコン線状体を拡大した図であり、縮れたシリコン線状体の外径は７０ｎｍ程度であることがわかる。また、図１８において、石筍状のシリコンの表面には細孔があり、石筍状のシリコンがポーラスであることが確認された。 16 to 18 are SEM photographs of the negative electrode according to Example 4. FIG. In FIG. 16 (a), the growth of stalagmite-like silicon having a flat tip and a thickness of 5 to 20 μm is observed. In FIG. 16B, the growth of the crimped silicon linear body is observed from the side surface of the stalagmite-like silicon. FIG. 17 is an enlarged view of the crimped silicon linear body, and it can be seen that the outer diameter of the crimped silicon linear body is about 70 nm. In FIG. 18, it was confirmed that the surface of the sarcophagus-like silicon had pores, and the sarcophagus-like silicon was porous.
図１９は、実施例５に係るシリコン線状体の視野（ａ）における電子線回折図形（ｂ）である。図１９において、視野内の電子線回折図形が示すように、シリコン線状体が多結晶であることがわかる。 FIG. 19 is an electron diffraction pattern (b) in the visual field (a) of the silicon linear body according to the fifth embodiment. In FIG. 19, it can be seen that the silicon linear body is polycrystalline, as shown by the electron diffraction pattern in the field of view.
図２０は、実施例５に係るシリコン線状体のＳＴＥＭ写真である。図２０（ａ）において、シリコン線状体の外径が、太いもので１μｍに近いことがわかる。 FIG. 20 is a STEM photograph of a silicon linear body according to Example 5. In FIG. 20A, it can be seen that the outer diameter of the silicon linear body is thick and close to 1 μm.
図２１は、実施例５に係るシリコン線状体のＳＴＥＭ像と、エネルギー分散型Ｘ線分光分析（ＥＤＳ）結果を示す図である。図２１において、シリコン線状体の先端に触媒としての金（図示せず）の他に銅が存在していることがわかる。この銅は、電解銅箔の製造時に析出した微粒子の銅であると考えられる。 FIG. 21 is a diagram illustrating an STEM image of a silicon linear body according to Example 5 and an energy dispersive X-ray spectroscopic analysis (EDS) result. In FIG. 21, it can be seen that copper exists in addition to gold (not shown) as a catalyst at the tip of the silicon linear body. This copper is considered to be fine-particle copper deposited during the production of the electrolytic copper foil.
実施例１〜５において、シリコン線状体の結晶成長を確認できた。また、これらのシリコン線状体は、電極試験の結果、高容量かつ長寿命であることが確認できた。 In Examples 1-5, the crystal growth of the silicon linear body was confirmed. Further, as a result of the electrode test, it was confirmed that these silicon linear bodies had a high capacity and a long life.
図２２は、比較例１に係る負極のＳＥＭ写真である。図２２（ａ）、（ｂ）において、矢印で示したとおり、電極の表面に露出した平滑なシリコン粉末の表面が観察される。 FIG. 22 is an SEM photograph of the negative electrode according to Comparative Example 1. 22A and 22B, the surface of the smooth silicon powder exposed on the surface of the electrode is observed as indicated by the arrows.
図２３は、比較例１に係る負極を、０．２Ｃで５０サイクル充放電した後の負極のＳＥＭ写真である。図２３（ａ）において、矢印で示した箇所に、電極の表面に露出したシリコン粉末が微粉化していることが観察された。また、図２３（ｂ）において、矢印で示した箇所に、クラックの発生とともに電極の一部に、負極活物質膜の脱落が観察された。このような負極活物質の微粉化や脱落は、一部の負極活物質で電気的な接続が遮断されることを意味しており、容量低下の主な原因となる。 FIG. 23 is a SEM photograph of the negative electrode after charging and discharging the negative electrode according to Comparative Example 1 at 0.2 C for 50 cycles. In FIG. 23A, it was observed that the silicon powder exposed on the surface of the electrode was pulverized at the position indicated by the arrow. Further, in FIG. 23B, the negative electrode active material film was observed to drop off at a part of the electrode along with the occurrence of cracks at the position indicated by the arrow. Such pulverization or dropping off of the negative electrode active material means that a part of the negative electrode active material is disconnected from the electrical connection, which is a main cause of capacity reduction.
図２４（ａ）は、比較例２に係る負極の負極活物質のＳＥＭ写真であり、図２４（ｂ）は、同じ負極を０．２Ｃで５０サイクルの充放電を行った後の負極活物質のＳＥＭ写真である。図２３（ａ）に示すように比較例１において、活物質である粒径５μｍのシリコン粉末の微粉化が観察されたが、図２４（ｂ）に示すように比較例２において、活物質である粒径６０ｎｍのシリコンの微粉化は、観察されなかった。ミクロンサイズの活物質で微粉化が生じ、ナノサイズの活物質で微粉化が生じないのは、ホールペッチ則により、降伏点が結晶粒径の１／２乗に逆比例して高くなったものと考えられる。 24A is an SEM photograph of the negative electrode active material of the negative electrode according to Comparative Example 2, and FIG. 24B is a negative electrode active material after charging and discharging the same negative electrode at 0.2C for 50 cycles. It is a SEM photograph of. As shown in FIG. 23 (a), in Comparative Example 1, the pulverization of silicon powder having a particle size of 5 μm, which is an active material, was observed. However, in Comparative Example 2, as shown in FIG. No micronization of silicon with a particle size of 60 nm was observed. Micron-sized active material causes pulverization and nano-sized active material does not pulverize because of the Hall Petch rule, the yield point is increased in inverse proportion to the 1/2 power of the crystal grain size. Conceivable.
図２５は、比較例２に係る負極を、０．２Ｃで５０サイクル充放電した後の負極のＳＥＭ写真である。図２５（ａ）において、矢印で示した箇所に、クラックの発生とともに部分的な浮き上がりが観察された。また、図２５（ｂ）において、矢印で示した箇所に、部分的な盛り上がりが観察された。 FIG. 25 is an SEM photograph of the negative electrode after charging and discharging the negative electrode according to Comparative Example 2 at 0.2 C for 50 cycles. In FIG. 25 (a), partial lifting was observed along with the occurrence of cracks at the locations indicated by arrows. In addition, in FIG. 25 (b), partial swells were observed at the locations indicated by arrows.
図２６は、比較例２に係る負極を、０．２Ｃで５０サイクル充放電した後の負極の別のＳＥＭ写真である。図２６において、矢印で示した箇所に、断層のように見える大きなクラックや小さなクラックが無数に観察された。これらのクラックや負極活物質の脱落は、充放電を繰り返すとさらに拡大する傾向があり、活物質の電気的接続が破壊されることによって、容量が低下し、寿命が短くなる。 FIG. 26 is another SEM photograph of the negative electrode after charging and discharging the negative electrode according to Comparative Example 2 at 0.2 C for 50 cycles. In FIG. 26, countless large cracks and small cracks that look like faults were observed at locations indicated by arrows. These cracks and falling off of the negative electrode active material tend to further expand when charging and discharging are repeated, and the electrical connection of the active material is broken, thereby reducing the capacity and shortening the life.
１………負極
３………集電体
５………触媒層
７………触媒
９………原料ガス
１０………チャンバー
１１………ヒーター
１３………シリコン線状体
１５………導電助剤
１７………ドラム
１９………触媒担持装置
２１………圧力計
２３………ドラム
２５………負極
２７………シリコン層
２９………負極
３１………金属層
DESCRIPTION OF SYMBOLS 1 ......... Negative electrode 3 ......... Current collector 5 ......... Catalyst layer 7 ......... Catalyst 9 ......... Source gas 10 ......... Chamber 11 ......... Heater 13 ......... Silicon linear body 15 ... ... Conductive aid 17 ......... Drum 19 ......... Catalyst carrier 21 ......... Pressure gauge 23 ......... Drum 25 ......... Negative electrode 27 ......... Silicone layer 29 ......... Negative electrode 31 ......... Metal layer
Claims (16)
前記集電体上に成長したシリコン線状体と、を有し、
前記シリコン線状体の少なくとも一端が、前記集電体に金属結合で結合している、または前記集電体上の金属に金属結合で結合している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,
A silicon linear body grown on the current collector,
At least one end of the silicon linear body is bonded to the current collector by a metal bond, or is bonded to a metal on the current collector by a metal bond. Negative electrode.
前記集電体上に形成されたシリコン層と、
前記シリコン層の上に成長したシリコン線状体と、を有し、
前記シリコン線状体の少なくとも一端が、前記シリコン層に金属結合で結合している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,
A silicon layer formed on the current collector;
A silicon linear body grown on the silicon layer,
A negative electrode for a lithium ion secondary battery, wherein at least one end of the silicon linear body is bonded to the silicon layer by a metal bond.
前記集電体上に形成された金属層と、
前記金属層の上に成長したシリコン線状体と、を有し、
前記金属層が、チタン、バナジウム、ジルコニウム、イットリウム、タングステン、鉄、ニッケル、クロムおよびモリブデンからなる群より選ばれた少なくとも１種の金属またはそれらの合金であり、
前記シリコン線状体の少なくとも一端が、前記金属層に金属結合で結合している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,
A metal layer formed on the current collector;
A silicon linear body grown on the metal layer,
The metal layer is at least one metal selected from the group consisting of titanium, vanadium, zirconium, yttrium, tungsten, iron, nickel, chromium and molybdenum, or an alloy thereof;
A negative electrode for a lithium ion secondary battery, wherein at least one end of the silicon linear body is bonded to the metal layer by a metal bond.
チャンバー内の前記集電体を３５０〜８００℃の間のある温度に保ち、かつ前記チャンバー内の圧力を０．５〜５０Ｔｏｒｒの間のある圧力に保ちつつ、前記チャンバー内に２０分〜２時間、原料ガスを供給し、シリコン線状体をＶＬＳ法により成長させる工程（ｂ）と、
を有する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 step (a) of supporting a metal catalyst on a current collector;
The current collector in the chamber is kept at a certain temperature between 350-800 ° C., and the pressure in the chamber is kept at a certain pressure between 0.5-50 Torr, and 20 minutes-2 hours in the chamber. Supplying a source gas and growing a silicon linear body by the VLS method (b);
The manufacturing method of the negative electrode for lithium ion secondary batteries characterized by having.
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