JP6599106B2 - Negative electrode material for lithium secondary battery and method for producing the same, composition for negative electrode active material layer for lithium secondary battery using the negative electrode material, negative electrode for lithium secondary battery, and lithium secondary battery - Google Patents
Negative electrode material for lithium secondary battery and method for producing the same, composition for negative electrode active material layer for lithium secondary battery using the negative electrode material, negative electrode for lithium secondary battery, and lithium secondary battery Download PDFInfo
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Description
本発明は、リチウム二次電池用負極材料及びその製造方法、並びに該負極材料を用いたリチウム二次電池用の負極活物質層用組成物、リチウム二次電池用負極及びリチウム二次電池に関する。 The present invention relates to a negative electrode material for a lithium secondary battery, a method for producing the same, a composition for a negative electrode active material layer for a lithium secondary battery using the negative electrode material, a negative electrode for a lithium secondary battery, and a lithium secondary battery.
携帯電話や携帯用情報機器（電子手帳、ノートパソコン、タブレット型コンピュータ等）等に代表される携帯用電子機器類の小型化・軽量化が目覚しく進展しつつある今日では、そのような携帯用電子機器類を駆動するための小型で軽量な二次電池の開発が要望されている。このような背景の下、小型に構成でき、しかも高エネルギー密度を有するリチウム二次電池（リチウムイオン二次電池等）が注目を集めており、その開発が盛んに行われている。このリチウム二次電池は、上記のような携帯用電子機器の他、電気自動車や再生可能エネルギーの電力貯蔵等にもニーズが広がっており、これらのニーズに対応するため、構成する電極材料の一層の高エネルギー密度化が求められている。 Today, portable electronic devices such as mobile phones and portable information devices (electronic notebooks, notebook computers, tablet computers, etc.) are becoming increasingly smaller and lighter. Development of a small and lightweight secondary battery for driving devices has been demanded. Under such circumstances, lithium secondary batteries (lithium ion secondary batteries and the like) that can be configured in a small size and have a high energy density are attracting attention and are actively developed. In addition to the portable electronic devices as described above, the lithium secondary battery has a widespread need for electric vehicles and electric power storage for renewable energy. There is a demand for higher energy density.
一般的なリチウム二次電池としては、デンドライトを生成し易いリチウムではなく、サイクル特性及び安全性に優れたリチウム二次電池を実現可能な負極材料として、リチウムイオンの出入り、すなわち挿入・脱離が可能な炭素材料からなるものが数多く提案されており、実用化されつつある。ここで、炭素材料からなるリチウム二次電池用の負極材料は、主として、１０００℃程度で焼成された炭素系負極材料と、２０００℃を超える温度で焼成された黒鉛系負極材料との２種類に分類することができるが、炭素系負極材料は、リチウムイオンの放出に伴う電位の変化が大きく、安定なリチウム二次電池を構成し難いという欠点がある。これに対し、黒鉛系負極材料は、このような電位の変化が小さく、安定なリチウム二次電池を構成可能であるため、炭素系の負極材料に比べて有利であり、リチウム二次電池用の負極材料として主流になりつつある。 As a general lithium secondary battery, lithium ions are not easy to generate dendrite, but as a negative electrode material capable of realizing a lithium secondary battery with excellent cycle characteristics and safety, lithium ions can enter and exit, that is, insertion / extraction. Many possible carbon materials have been proposed and are being put into practical use. Here, the negative electrode material for a lithium secondary battery made of a carbon material is mainly divided into two types: a carbon-based negative electrode material fired at about 1000 ° C. and a graphite-based negative electrode material fired at a temperature exceeding 2000 ° C. Although it can be classified, the carbon-based negative electrode material has a drawback in that it has a large potential change due to the release of lithium ions and it is difficult to form a stable lithium secondary battery. On the other hand, the graphite-based negative electrode material is advantageous in comparison with the carbon-based negative electrode material because such a potential change is small and a stable lithium secondary battery can be configured. It is becoming mainstream as a negative electrode material.
上記の黒鉛系負極材料は、理論容量が３７２ｍＡｈ／ｇである一方、シリコンは理論容量４２００ｍＡｈ／ｇであり、実に黒鉛系負極材料の約１０倍の理論容量を有するため、シリコン負極の利用が期待されている（非特許文献１〜２）。しかしながら、シリコンは充放電に伴う体積変化が極めて大きいため、負極材料が割れたり、電極から剥がれたり（非特許文献３）して実際の容量が低下してしまうことから、十分な充放電容量及びサイクル特性を兼ね備える負極材料とはなり得なかった。 The above-mentioned graphite-based negative electrode material has a theoretical capacity of 372 mAh / g, while silicon has a theoretical capacity of 4200 mAh / g, and has a theoretical capacity approximately 10 times that of the graphite-based negative electrode material. (Non-patent Documents 1 and 2). However, since the volume change accompanying charging / discharging is extremely large in silicon, the negative electrode material is cracked or peeled off from the electrode (Non-Patent Document 3), and the actual capacity is reduced. It could not be a negative electrode material having cycle characteristics.
十分な充放電容量及びサイクル特性を兼ね備える負極材料を得るため、シリコンを炭素材と複合化させることが検討されている（非特許文献４〜５）。 In order to obtain a negative electrode material having sufficient charge / discharge capacity and cycle characteristics, it has been studied to combine silicon with a carbon material (Non-Patent Documents 4 to 5).
しかしながら、十分な充放電容量及びサイクル特性を兼ね備える負極材料は、いまだ得られていない。そこで、本発明は、十分な充放電容量、クーロン効率及びサイクル特性を兼ね備えるリチウム二次電池用の負極材料を提供することを目的とする。 However, a negative electrode material having sufficient charge / discharge capacity and cycle characteristics has not been obtained yet. Then, an object of this invention is to provide the negative electrode material for lithium secondary batteries which has sufficient charging / discharging capacity | capacitance, coulomb efficiency, and cycling characteristics.
本発明者らは、上記の課題に鑑み、鋭意研究を重ねてきた。その結果、グラフェンシート、シリコン材料、及び単層カーボンナノチューブを含ませることで、上記の課題を解決し、クーロン効率を維持しつつ、十分な充放電容量及びサイクル特性を兼ね備えるリチウム二次電池用の負極材料が得られることを見出した。また、この負極材料は、黒鉛と混合することで、シリコンのみの場合と比較し、特にサイクル特性を向上させることが可能である。本発明は、このような知見に基づき、さらに研究を重ね、完成したものである。すなわち、本発明は、以下の構成を包含する。
項１．ナノ炭素、シリコン材料、及びカーボンナノチューブを含む、リチウム二次電池用負極材料。
項２．前記ナノ炭素の含有量が、前記シリコン材料１００重量部に対して、１〜２００重量部である、項１に記載のリチウム二次電池用負極材料。
項３．前記カーボンナノチューブの含有量が、前記シリコン材料１００重量部に対して、１〜５０重量部である、項１又は２に記載のリチウム二次電池用負極材料。
項４．前記ナノ炭素がグラフェンシートである、項１〜３のいずれかに記載のリチウム二次電池用負極材料。
項５．前記グラフェンシートの層間に、前記シリコン材料及び前記カーボンナノチューブが存在する、項４に記載のリチウム二次電池用負極材料。
項６．前記シリコン材料が、シリコン粒子である、項１〜５のいずれかに記載のリチウム二次電池用負極材料。
項７．前記シリコン粒子の平均粒子径が、１ｎｍ〜１００μｍである、項６に記載のリチウム二次電池用負極材料。
項８．前記カーボンナノチューブの平均外径が、１ｎｍ〜５００ｎｍである、項１〜７のいずれかに記載のリチウム二次電池用負極材料。
項９．前記グラフェンシートにおけるグラフェンの大きさが１００ｎｍ〜１０００μｍである、項４〜８のいずれかに記載のリチウム二次電池用負極材料。
項１０．前記ナノ炭素が、空孔を有する、項１〜９のいずれかに記載のリチウム二次電池用負極材料。
項１１．前記シリコン材料は、表面が酸化している、項１〜１０のいずれかに記載のリチウム二次電池用負極材料。
項１２．ナノ炭素、シリコン材料、及びカーボンナノチューブを含むリチウム二次電池用負極材料の製造方法であって、
（１）ナノカーボン酸化物水分散液を第１有機溶媒で置換し、ナノカーボン酸化物分散液を得る工程、
（２）前記工程（１）で得たナノカーボン酸化物分散液に、シリコン材料及びカーボンナノチューブを添加し、ナノカーボン酸化物、シリコン材料及びカーボンナノチューブを含む分散液を得る工程、及び
（３）前記工程（２）で得た分散液に還元処理を施す工程
を備える、製造方法。
項１３．前記ナノカーボン酸化物が酸化グラフェンである、項１２に記載の製造方法。
項１４．前記工程（２）において、カーボンナノチューブは、あらかじめ第２有機溶媒に分散されている、項１２又は１３に記載の製造方法。
項１５．前記工程（３）は、８００〜１０００℃で焼成することにより、酸化グラフェンを還元する工程である、項１２〜１４のいずれかに記載の製造方法。
項１６．項１〜１１のいずれかに記載のリチウム二次電池用負極材料、又は項１２〜１５のいずれかに記載の製造方法により製造されたリチウム二次電池用負極材料と、黒鉛とを含有する、リチウム二次電池用の負極活物質層形成用組成物。
項１７．前記リチウム二次電池用負極材料と前記黒鉛との合計量１００重量％に対して、前記リチウム二次電池用負極材料の含有量が３〜８０重量％である、項１６に記載のリチウム二次電池用の負極活物質層形成用組成物。
項１８．集電体、及び前記集電体上に配置された項１〜１１のいずれかに記載のリチウム二次電池用負極材料、又は項１２〜１５のいずれかに記載の製造方法により製造されたリチウム二次電池用負極材料を含む負極活物質層を備える、リチウム二次電池用負極。
項１９．集電体、及び前記集電体上に配置された項１６又は１７に記載のリチウム二次電池用の負極活物質層形成用組成物からなる負極活物質層を備える、リチウム二次電池用負極。
項２０．項１８又は１９に記載のリチウム二次電池用負極を備えたリチウム二次電池。
In view of the above problems, the present inventors have made extensive studies. As a result, by including a graphene sheet, a silicon material, and a single-walled carbon nanotube, the lithium secondary battery has sufficient charge / discharge capacity and cycle characteristics while solving the above problems and maintaining coulomb efficiency. It has been found that a negative electrode material can be obtained. In addition, when this negative electrode material is mixed with graphite, the cycle characteristics can be particularly improved as compared with the case of using only silicon. The present invention has been completed by further research based on such knowledge. That is, the present invention includes the following configurations.
Item 1. A negative electrode material for a lithium secondary battery, comprising nanocarbon, silicon material, and carbon nanotube.
Item 2. Item 2. The negative electrode material for a lithium secondary battery according to Item 1, wherein the nanocarbon content is 1 to 200 parts by weight with respect to 100 parts by weight of the silicon material.
Item 3. Item 3. The negative electrode material for a lithium secondary battery according to Item 1 or 2, wherein the content of the carbon nanotube is 1 to 50 parts by weight with respect to 100 parts by weight of the silicon material.
Item 4. Item 4. The negative electrode material for a lithium secondary battery according to any one of Items 1 to 3, wherein the nanocarbon is a graphene sheet.
Item 5. Item 5. The negative electrode material for a lithium secondary battery according to Item 4, wherein the silicon material and the carbon nanotube are present between layers of the graphene sheet.
Item 6. Item 6. The negative electrode material for a lithium secondary battery according to any one of Items 1 to 5, wherein the silicon material is silicon particles.
Item 7. Item 7. The negative electrode material for a lithium secondary battery according to Item 6, wherein the silicon particles have an average particle diameter of 1 nm to 100 µm.
Item 8. Item 8. The negative electrode material for a lithium secondary battery according to any one of Items 1 to 7, wherein the carbon nanotube has an average outer diameter of 1 nm to 500 nm.
Item 9. Item 9. The negative electrode material for a lithium secondary battery according to any one of Items 4 to 8, wherein the graphene in the graphene sheet has a size of 100 nm to 1000 μm.
Item 10. Item 10. The negative electrode material for a lithium secondary battery according to any one of Items 1 to 9, wherein the nanocarbon has pores.
Item 11. Item 11. The negative electrode material for a lithium secondary battery according to any one of Items 1 to 10, wherein a surface of the silicon material is oxidized.
Item 12. A method for producing a negative electrode material for a lithium secondary battery comprising nanocarbon, a silicon material, and a carbon nanotube,
(1) replacing the nanocarbon oxide aqueous dispersion with a first organic solvent to obtain a nanocarbon oxide dispersion;
(2) A step of adding a silicon material and a carbon nanotube to the nanocarbon oxide dispersion obtained in the step (1) to obtain a dispersion containing the nanocarbon oxide, the silicon material and the carbon nanotube, and (3) A production method comprising a step of subjecting the dispersion obtained in the step (2) to a reduction treatment.
Item 13. Item 13. The method according to Item 12, wherein the nanocarbon oxide is graphene oxide.
Item 14. Item 14. The method according to Item 12 or 13, wherein in the step (2), the carbon nanotubes are dispersed in advance in a second organic solvent.
Item 15. Item 15. The manufacturing method according to any one of Items 12 to 14, wherein the step (3) is a step of reducing graphene oxide by baking at 800 to 1000 ° C.
Item 16. The negative electrode material for a lithium secondary battery according to any one of Items 1 to 11, or the negative electrode material for a lithium secondary battery produced by the production method according to any one of Items 12 to 15, and graphite. A composition for forming a negative electrode active material layer for a lithium secondary battery.
Item 17. Item 17. The lithium secondary according to Item 16, wherein the content of the negative electrode material for a lithium secondary battery is 3 to 80% by weight with respect to 100% by weight of the total amount of the negative electrode material for the lithium secondary battery and the graphite. A composition for forming a negative electrode active material layer for a battery.
Item 18. Item 15. The negative electrode material for a lithium secondary battery according to any one of Items 1 to 11 disposed on the current collector, or lithium produced by the production method according to any one of Items 12 to 15 A negative electrode for a lithium secondary battery, comprising a negative electrode active material layer containing a negative electrode material for a secondary battery.
Item 19. A negative electrode for a lithium secondary battery, comprising: a current collector; and a negative electrode active material layer comprising the composition for forming a negative electrode active material layer for a lithium secondary battery according to Item 16 or 17 disposed on the current collector. .
Item 20. Item 20. A lithium secondary battery comprising the lithium secondary battery negative electrode according to Item 18 or 19.
本発明のリチウム二次電池用負極材料は、シリコン材料の膨張を、ナノ炭素の変形により吸収することができることから、体積膨張を原因として負極材料が割れたり、電極から剥がれたりすることを抑制することができると考えられる。また、ナノ炭素としてグラフェンシートを使用する場合は、グラフェンシートの層間隔をカーボンナノチューブにより拡張して、シリコン材料をその空間に閉じ込め、膨張時の体積変化を吸収しやすくし、体積膨張を原因として負極材料が割れたり、電極から剥がれたりすることを抑制することができると考えられる。 Since the negative electrode material for a lithium secondary battery of the present invention can absorb the expansion of the silicon material by the deformation of nanocarbon, the negative electrode material is prevented from cracking or peeling off from the electrode due to volume expansion. It is considered possible. Also, when using graphene sheets as nanocarbon, the layer spacing of the graphene sheets is expanded by carbon nanotubes, confining the silicon material in the space, making it easier to absorb volume changes during expansion, and causing volume expansion It is considered that the negative electrode material can be prevented from cracking or peeling off from the electrode.
さらに、本発明のリチウム二次電池用負極材料は、カーボンナノチューブを含ませることにより、ナノ炭素同士を結着しやすくし、より高い電子伝導性を付与することができると考えられる。 Furthermore, it is considered that the negative electrode material for a lithium secondary battery of the present invention can easily bind nanocarbons and impart higher electronic conductivity by including carbon nanotubes.
このため、本発明のリチウム二次電池用負極材料は、従来のリチウム二次電池用のシリコン系負極材料に比べても、クーロン効率を維持しつつ、非常に高い充放電容量及びサイクル特性を有している。また、本発明のリチウム二次電池用負極材料を黒鉛と混合することで、シリコンのみの場合と比較し、特にサイクル特性を向上させることが可能である。 For this reason, the negative electrode material for lithium secondary batteries of the present invention has very high charge / discharge capacity and cycle characteristics while maintaining coulomb efficiency as compared with conventional silicon negative electrode materials for lithium secondary batteries. is doing. In addition, by mixing the negative electrode material for a lithium secondary battery of the present invention with graphite, it is possible to improve the cycle characteristics in particular as compared with the case of using only silicon.
１．リチウム二次電池用負極材料
本発明のリチウム二次電池用負極材料は、ナノ炭素、シリコン材料、及びカーボンナノチューブを含む。
1. Negative electrode material for lithium secondary battery The negative electrode material for lithium secondary battery of the present invention includes nanocarbon, silicon material, and carbon nanotube.
本発明で用いるナノ炭素は、直径１００ｎｍ以下のナノ炭素粒子、又は１０層以下（つまり１〜１０層）のグラフェンが積層した層状構造を持つシート（グラフェンシート）が好ましい。なお、ナノ炭素として複数のグラフェンを有するグラフェンシートを使用する場合には、その層間に、グラフェン以外の物質を含有することも可能である。こうしたグラフェンは、多くの凸角と凹角をもつ平面形状をしているため、その大きさは一概には規定できない。本明細書では、一枚のグラフェンにおいて最も離れている凸角間の距離をそのグラフェンの大きさとする。 The nanocarbon used in the present invention is preferably a nanocarbon particle having a diameter of 100 nm or less, or a sheet (graphene sheet) having a layered structure in which 10 layers or less (that is, 1 to 10 layers) of graphene are laminated. Note that in the case where a graphene sheet having a plurality of graphenes as nanocarbon is used, a substance other than graphene can be contained between the layers. Since such graphene has a planar shape with many convex and concave angles, its size cannot be defined unconditionally. In this specification, the distance between the convex angles that are the farthest in one graphene is the size of the graphene.
グラフェンの大きさとしては、１００ｎｍ以上が好ましく、１０００ｎｍ以上がより好ましい。この範囲とすることで、より十分な導電性が得られる。なお、グラフェンの大きさは、大きい方が電気的物性等の諸物性が優れていることが知られているため、大きさの上限は限定されないが、グラフェンの大きさは１０００μｍ以下が好ましく、１００μｍ以下がより好ましい。なお、グラフェンの大きさは、顕微鏡（原子間力顕微鏡、レーザー顕微鏡、電子顕微鏡等、特に原子間力顕微鏡）観察により測定するものとする。 The size of graphene is preferably 100 nm or more, and more preferably 1000 nm or more. By setting it in this range, more sufficient conductivity can be obtained. In addition, since it is known that the larger the size of graphene, the better the physical properties such as electrical properties, the upper limit of the size is not limited, but the size of graphene is preferably 1000 μm or less, 100 μm The following is more preferable. In addition, the magnitude | size of a graphene shall be measured by microscope (atomic force microscope, a laser microscope, an electron microscope etc., especially atomic force microscope) observation.
ナノ炭素は、空孔を有していてもよい。このように、ナノ炭素が空孔を有することにより、電解液の通りをよくし、レート特性の向上も期待できる。なお、ナノ炭素に空孔を空けるためには、例えば、ナノ炭素に酸化処理を施せばよい。 Nanocarbon may have a void | hole. As described above, since nanocarbon has pores, the electrolyte solution can be improved and the rate characteristics can be improved. In order to make a hole in the nanocarbon, for example, the nanocarbon may be oxidized.
このようなナノ炭素（特にグラフェンシート）としては、ＣＶＤ法、機械的剥離法等の公知の方法で得られた単層又は多層のグラフェン等が使用できる。また、グラファイトを酸化・剥離して得られる酸化グラフェンから化学的及び／又は熱的還元処理を経て作製されたナノ炭素（特にグラフェンシート）も使用できる。 As such nanocarbon (particularly graphene sheet), single-layer or multi-layer graphene obtained by a known method such as a CVD method or a mechanical peeling method can be used. In addition, nanocarbon (particularly graphene sheet) produced by chemical and / or thermal reduction treatment from graphene oxide obtained by oxidizing and peeling graphite can also be used.
本発明のリチウム二次電池用負極材料においては、ナノ炭素と後述のカーボンナノチューブとの高い親和性のため、カーボンナノチューブがバンドル状又は綿状になった状態、さらには、単独で直線性の高い状態でも、ナノ炭素（特にグラフェンシート）はカーボンナノチューブと接することができ、結果、ナノ炭素（特にグラフェンシート）の炭素面で挟まれ、カーボンナノチューブ単体又は集合体を、ナノ炭素（特にグラフェンシート）に挟まれた柱とするような、数ｎｍ〜数百ｎｍの、隙間のある空間が確保され、そこにシリコン材料が入り込むことができ、シリコン材料の充放電に伴う体積膨張及び収縮に、ナノ炭素（特にグラフェンシート）が追従しながら電気コンタクトを保つ機構を有することができる。 In the negative electrode material for a lithium secondary battery of the present invention, the carbon nanotubes are in a bundle-like or cotton-like state due to the high affinity between nanocarbon and the carbon nanotubes described later, and moreover, the single linearity is high. Even in the state, nanocarbon (especially graphene sheet) can be in contact with carbon nanotubes. As a result, the carbon surface of nanocarbon (particularly graphene sheet) is sandwiched between carbon nanotubes alone or aggregates, and nanocarbon (particularly graphene sheet) A space with a gap of several nanometers to several hundred nanometers, such as a pillar sandwiched between layers, is secured, and a silicon material can enter into the space. It can have a mechanism that keeps electrical contact while carbon (particularly graphene sheet) follows.
シリコン材料としては、シリコンを含む材料（特にシリコンからなる材料）であれば特に制限されないが、結晶シリコン、アモルファスシリコン等のシリコン材料（好ましくはシリコン粒子）の粉末等が挙げられる。 The silicon material is not particularly limited as long as it is a material containing silicon (particularly a material made of silicon), and examples thereof include powder of silicon material (preferably silicon particles) such as crystalline silicon and amorphous silicon.
結晶シリコン、アモルファスシリコン等のシリコン材料（好ましくはシリコン粒子）の粉末としては、特に制限されないが、汎用の結晶シリコン、アモルファスシリコン等を切削等により粒子（又は粉末）にしたもの等を用いることができる。結晶シリコン、アモルファスシリコン等の製造、加工等の過程において発生する規格外の製品、廃棄物等を使用してもよい。また、本発明において使用する結晶シリコン、アモルファスシリコン等は、形成時にリン系、ホウ素系化合物等の導入によりｎ型半導体又はｐ型半導体になっていてもよい。また、シリコン材料は、その表面が酸化されていてもよい。これらのシリコン材料は、単独で用いてもよいし、２種以上を組合せて用いてもよい。 The powder of silicon material (preferably silicon particles) such as crystalline silicon and amorphous silicon is not particularly limited, but it is possible to use general crystalline silicon, amorphous silicon or the like made into particles (or powder) by cutting or the like. it can. Non-standard products, waste, etc. generated in the process of manufacturing and processing crystalline silicon, amorphous silicon, etc. may be used. In addition, crystalline silicon, amorphous silicon, and the like used in the present invention may be an n-type semiconductor or a p-type semiconductor by introducing a phosphorus-based or boron-based compound at the time of formation. Further, the surface of the silicon material may be oxidized. These silicon materials may be used alone or in combination of two or more.
シリコン材料としてシリコン粒子を使用する場合、その平均粒子径は、特に制限されないが、通常１ｎｍ〜１００μｍ程度が好ましく、５ｎｍ〜１０μｍ程度がより好ましく、１０ｎｍ〜５μｍ程度がさらに好ましい。シリコン材料の平均粒子径を上記範囲内とすることにより、割れが発生しにくくなる。なお、シリコン材料の平均粒子径は、電子顕微鏡（ＳＥＭ）により測定されるものとする。 When silicon particles are used as the silicon material, the average particle diameter is not particularly limited, but is usually preferably about 1 nm to 100 μm, more preferably about 5 nm to 10 μm, and further preferably about 10 nm to 5 μm. By making the average particle diameter of the silicon material within the above range, cracks are less likely to occur. In addition, the average particle diameter of a silicon material shall be measured with an electron microscope (SEM).
カーボンナノチューブは、黒鉛シート（即ち、黒鉛構造の炭素原子面又は単層のグラフェンシート）がチューブ状に閉じた中空炭素物質であり、その直径はナノメートルスケールであり、壁構造は黒鉛構造を有している。壁構造が一枚の黒鉛シート（単層のグラフェンシート）でチューブ状に閉じた形状のカーボンナノチューブは単層カーボンナノチューブと呼ばれている。一方、複数枚の黒鉛シートがそれぞれチューブ状に閉じて、入れ子状になっているカーボンナノチューブは入れ子構造の多層カーボンナノチューブと呼ばれている。本発明では、単層カーボンナノチューブ及び多層カーボンナノチューブいずれも採用できるが、多層カーボンナノチューブよりも単層カーボンナノチューブが好ましい。 A carbon nanotube is a hollow carbon material in which a graphite sheet (that is, a carbon atom plane of a graphite structure or a single-layer graphene sheet) is closed in a tube shape, its diameter is nanometer scale, and the wall structure has a graphite structure. is doing. A carbon nanotube having a wall structure closed in a tube shape with a single graphite sheet (single-layer graphene sheet) is called a single-walled carbon nanotube. On the other hand, a plurality of graphite sheets each closed in a tube shape, and the carbon nanotubes nested are called nested carbon nanotubes. In the present invention, both single-walled carbon nanotubes and multi-walled carbon nanotubes can be adopted, but single-walled carbon nanotubes are preferable to multi-walled carbon nanotubes.
カーボンナノチューブの平均外径は、柔軟で綿状にもなり、かつ、単独又はバンドル状と多様な形態になり得ることで、様々な粒径のシリコンが包埋できるようになるという観点から、１〜５００ｎｍが好ましく、１〜１００ｎｍがより好ましく、５〜５０ｎｍがさらに好ましい。 The average outer diameter of the carbon nanotube is flexible and cotton-like, and can be in a variety of forms such as a single or a bundle, so that silicon having various particle diameters can be embedded. -500 nm is preferable, 1-100 nm is more preferable, and 5-50 nm is further more preferable.
カーボンナノチューブの平均長さは、グラフェンシートの層間隔をより拡張し、シリコン材料の膨張時の体積変化をより吸収しやすくし、体積膨張を原因として負極材料が割れたり、電極から剥がれたりすることをより抑制する観点、及び膨張によって電気的導電コンタクトが離れないようする観点から、０．１〜１００μｍが好ましく、１〜１０μｍがより好ましい。 The average length of the carbon nanotubes increases the inter-layer spacing of the graphene sheet, makes it easier to absorb the volume change when the silicon material expands, and causes the negative electrode material to crack or peel off from the electrode due to volume expansion From the viewpoint of further suppressing the resistance and from the viewpoint of preventing the electrically conductive contact from separating due to expansion, 0.1 to 100 μm is preferable, and 1 to 10 μm is more preferable.
カーボンナノチューブの平均アスペクト比は、グラフェンシートの層間隔をより拡張し、シリコン材料の膨張時の体積変化をより吸収しやすくし、体積膨張を原因として負極材料が割れたり、電極から剥がれたりすることをより抑制する観点から、５〜１０００００が好ましく、１０〜１００００がより好ましい。 The average aspect ratio of the carbon nanotubes increases the layer spacing of the graphene sheet, makes it easier to absorb volume changes when the silicon material expands, and causes the negative electrode material to crack or peel off from the electrode due to volume expansion From a viewpoint of suppressing more, 5-100,000 are preferable and 10-10000 are more preferable.
本発明のリチウム二次電池用負極材料は、上述のように、シリコン材料の膨張を、ナノ炭素とカーボンナノチューブの複合壁の変形により吸収することができることから、体積膨張を原因として負極材料が割れたり、電極から剥がれたりすることを抑制し、導電バスの欠落を抑制することができると考えられる。 As described above, the negative electrode material for a lithium secondary battery of the present invention can absorb the expansion of the silicon material by the deformation of the composite wall of nanocarbon and carbon nanotubes, so that the negative electrode material cracks due to volume expansion. Or peeling from the electrode, it is considered that the loss of the conductive bus can be suppressed.
また、ナノ炭素としてグラフェンシートを使用する場合はグラフェンシートの層間隔をカーボンナノチューブにより拡張して、シリコン材料をその空間に閉じ込め、膨張時の体積変化を吸収しやすくし、体積膨張を原因として負極材料が割れたり、電極から剥がれたりすることを抑制するとともに、導電ネットワークを形成することができると考えられる。 In addition, when using graphene sheets as nanocarbon, the layer spacing of the graphene sheets is expanded by carbon nanotubes, confining the silicon material in the space, making it easy to absorb volume changes during expansion, and negative electrode due to volume expansion It is considered that the material can be prevented from being broken or peeled off from the electrode, and a conductive network can be formed.
本発明のリチウム二次電池用負極材料において、各成分の含有量は、特に制限されない。 In the negative electrode material for a lithium secondary battery of the present invention, the content of each component is not particularly limited.
具体的には、ナノ炭素の含有量は、シリコン材料１００重量部に対して、１〜２００重量部が好ましく、３〜５０重量部がより好ましい。ナノ炭素の含有量をこの範囲内とすることにより、シリコンの膨張収縮に追従してシリコンを包埋し、電気的コンタクトを保持することができると考えられ、同時に、高価なナノ炭素を過剰に使用せず代替導電材の添加が可能となる。また、カーボンナノチューブの含有量は、シリコン材料１００重量部に対して、１〜５０重量部が好ましく、３〜２０重量部がより好ましい。カーボンナノチューブの含有量をこの範囲内とすることにより、シリコンの膨張収縮に際しても、電気的コンタクトを保持することができると考えられ、同時に、高価なカーボンナノチューブを過剰に使用せず代替導電材の添加が可能となる。 Specifically, the content of nanocarbon is preferably 1 to 200 parts by weight and more preferably 3 to 50 parts by weight with respect to 100 parts by weight of the silicon material. By setting the nanocarbon content within this range, it is thought that silicon can be embedded following the expansion and contraction of silicon, and electrical contact can be maintained, and at the same time, expensive nanocarbon is excessively contained. An alternative conductive material can be added without using it. Moreover, 1-50 weight part is preferable with respect to 100 weight part of silicon materials, and, as for content of a carbon nanotube, 3-20 weight part is more preferable. By setting the content of carbon nanotubes within this range, it is considered that electrical contact can be maintained even during silicon expansion and contraction, and at the same time, an alternative conductive material can be used without excessively using expensive carbon nanotubes. Addition becomes possible.
本発明のリチウム二次電池用負極材料は、上記のような構成を採用することにより、特にナノ炭素としてグラフェンシートを使用する場合には、シリコン材料の体積膨張を、カーボンナノチューブにより層間隔を拡張したグラフェンシートの変形により吸収することができるため、体積膨張を原因として負極材料が割れたり、電極から剥がれたりすることを抑制することができる。このため、従来のリチウム二次電池用負極材料と比較すると、クーロン効率を維持しつつ、充放電容量及びサイクル特性を向上させることができる。より具体的には、本発明のリチウム二次電池用負極材料は、
（Ｉ）シリコン材料の容量に対して１／４０Ｃの定電流で０．０１Ｖになるまで充電
（ＩＩ）０．０１Ｖの定電圧で、電流値がシリコン材料の容量に対して１／６０Ｃになるまで充電
（ＩＩＩ）シリコン材料の容量に対して１／４０Ｃの定電流で１．５Ｖになるまで放電
（ＩＶ）１．５Ｖの定電圧で、電流値がシリコン材料の容量に対して１／６０Ｃになるまで放電
の条件で８回充放電試験を行った際に、初期放電容量３０００ｍＡｈ／ｇ以上、好ましくは３３００ｍＡｈ／ｇ以上の放電容量でかつ、９５．１％以上のクーロン効率（８回目）、及び初回から８回目までの放電容量比較で８０％以上（好ましくは９０％以上）の容量維持率を達成することができる。
The negative electrode material for a lithium secondary battery according to the present invention adopts the above-described configuration, particularly when a graphene sheet is used as nanocarbon, and the volume expansion of the silicon material is expanded by the carbon nanotubes. Therefore, the negative electrode material can be prevented from cracking or peeling from the electrode due to volume expansion. For this reason, compared with the conventional negative electrode material for lithium secondary batteries, the charge / discharge capacity and the cycle characteristics can be improved while maintaining the Coulomb efficiency. More specifically, the negative electrode material for a lithium secondary battery of the present invention is
(I) Charge until a constant current of 1 / 40C with respect to the capacity of the silicon material is 0.01V. (II) At a constant voltage of 0.01V, the current value is 1 / 60C with respect to the capacity of the silicon material. Charge (III) Discharge (IV) at a constant voltage of 1.5V until a constant current of 1 / 40C with respect to the capacity of the silicon material, and a current value of 1 / 60C with respect to the capacity of the silicon material. When the charge / discharge test was conducted 8 times under the discharge conditions until the time reached, the initial discharge capacity was 3000 mAh / g or more, preferably 3300 mAh / g or more and the coulombic efficiency of 95.1% or more (8th) In addition, a capacity maintenance ratio of 80% or more (preferably 90% or more) can be achieved by comparing the discharge capacity from the first time to the eighth time.
２．リチウム二次電池用負極材料の製造方法
上記した本発明のリチウム二次電池用負極材料は、特に制限されるわけではない。例えば、上記各成分を混合することにより製造してもよいが、酸化グラフェン等のナノカーボン酸化物の水分散液を利用してもよい。特に、ナノ炭素は凝集しやすいため、ナノカーボン酸化物水分散液（特に酸化グラフェン水分散液）を利用する方法が好ましい。
2. Method for producing negative electrode material for lithium secondary battery The negative electrode material for a lithium secondary battery of the present invention described above is not particularly limited. For example, although it may manufacture by mixing said each component, you may utilize the aqueous dispersion of nanocarbon oxides, such as a graphene oxide. In particular, since nanocarbon easily aggregates, a method using a nanocarbon oxide aqueous dispersion (particularly, graphene oxide aqueous dispersion) is preferable.
このような観点から、本発明のリチウム二次電池用負極材料は、好ましくは、
（１）ナノカーボン酸化物水分散液（特に酸化グラフェン水分散液）を第１有機溶媒で置換し、ナノカーボン酸化物分散液（特に酸化グラフェン分散液）を得る工程、
（２）前記工程（１）で得たナノカーボン酸化物分散液に、シリコン材料及びカーボンナノチューブを添加し、ナノカーボン酸化物、シリコン材料及びカーボンナノチューブを含む分散液を得る工程、及び
（３）前記工程（２）で得た分散液に還元処理を施す工程
を備える方法により得ることができる。
From such a viewpoint, the negative electrode material for a lithium secondary battery of the present invention is preferably
(1) A step of replacing the nanocarbon oxide aqueous dispersion (particularly graphene oxide aqueous dispersion) with a first organic solvent to obtain a nanocarbon oxide dispersion (particularly graphene oxide dispersion),
(2) A step of adding a silicon material and a carbon nanotube to the nanocarbon oxide dispersion obtained in the step (1) to obtain a dispersion containing the nanocarbon oxide, the silicon material and the carbon nanotube, and (3) It can be obtained by a method comprising a step of subjecting the dispersion obtained in the step (2) to a reduction treatment.
工程（１）において、ナノカーボン酸化物（特に酸化グラフェン）は、従来公知の方法により、水分散液として製造することができる。例えば、酸化グラフェンを使用する場合は、ハマーズ法により酸化グラファイトを作製し、これを溶媒（水性溶媒）に展開して超音波を照射することで、酸化グラファイトが層方向に剥離され、酸化グラフェンの水分散液が得られる。 In the step (1), the nanocarbon oxide (particularly graphene oxide) can be produced as an aqueous dispersion by a conventionally known method. For example, when graphene oxide is used, graphite oxide is produced by the Hammers method, and this is developed in a solvent (aqueous solvent) and irradiated with ultrasonic waves. An aqueous dispersion is obtained.
具体的には、グラファイトを濃硫酸中に浸し、過マンガン酸カリウムを加えて酸化させた後、反応物を希硫酸／過酸化水素でクエンチした後、蒸留水で洗浄して酸化グラファイトを得ることができる。グラファイトを濃硫酸中で過マンガン酸カリウムを加えて反応させることで、炭素原子に酸素原子が結合し、層間に酸素原子が導入されて酸化グラファイトが得られる。次いで、このようにして得られる酸化グラファイトを水性溶媒に分散させることで、層間に溶媒分子が挿入され、層方向にのみ剥離させることができ、面方向のサイズが大きい酸化グラフェンを高い収率で回収できる。必要に応じて、水性溶媒に分散後の溶液を遠心分離し、上澄み液を回収してもよい。 Specifically, after immersing graphite in concentrated sulfuric acid and adding potassium permanganate to oxidize, quench the reaction with dilute sulfuric acid / hydrogen peroxide and then wash with distilled water to obtain graphite oxide. Can do. By reacting graphite by adding potassium permanganate in concentrated sulfuric acid, oxygen atoms are bonded to carbon atoms, and oxygen atoms are introduced between layers to obtain graphite oxide. Next, by dispersing the graphite oxide thus obtained in an aqueous solvent, solvent molecules are inserted between the layers and can be peeled only in the layer direction, and the graphene oxide having a large size in the plane direction can be obtained in a high yield. Can be recovered. If necessary, the solution after dispersion in an aqueous solvent may be centrifuged to recover the supernatant.
この際使用される水性溶媒としては、例えば、水、エタノール、メタノール、エチレングリコール、グリセリン、２−メトキシエタノール等が使用できる。 As the aqueous solvent used at this time, for example, water, ethanol, methanol, ethylene glycol, glycerin, 2-methoxyethanol and the like can be used.
ナノカーボン酸化物水分散液中のナノカーボン酸化物の濃度は、０．００１〜２重量％が好ましく、０．００５〜１．５重量％がより好ましい。ナノカーボン酸化物の濃度をこの範囲とすることで、安定な分散液とすることができる。 The concentration of the nanocarbon oxide in the nanocarbon oxide aqueous dispersion is preferably 0.001 to 2% by weight, and more preferably 0.005 to 1.5% by weight. By setting the concentration of the nanocarbon oxide within this range, a stable dispersion can be obtained.
ここで使用できる第１有機溶媒としては、ナノカーボン酸化物を分散させることができる溶媒であれば特に制限はないが、例えば、メタノール、エタノール、イソプロピルアルコール（ＩＰＡ）等のアルコール（特に炭素数１〜６の低級アルコール）、アセトン等が使用できる。これらは１種単独で用いてもよいし、２種以上を組合せて用いてもよい。 The first organic solvent that can be used here is not particularly limited as long as it is a solvent that can disperse nanocarbon oxides. For example, alcohols such as methanol, ethanol, and isopropyl alcohol (IPA) (particularly those having 1 carbon atom). ˜6 lower alcohols), acetone and the like. These may be used individually by 1 type and may be used in combination of 2 or more type.
ナノカーボン酸化物水分散液と第１有機溶媒とを混合する際の混合比は特に限定されないが、安定な分散液を得る観点から、例えばナノカーボン酸化物水分散液１０ｍＬに対して第１有機溶媒は５〜１０００ｍＬが好ましく、１０〜５００ｍＬがより好ましい。 The mixing ratio when mixing the nanocarbon oxide aqueous dispersion and the first organic solvent is not particularly limited, but from the viewpoint of obtaining a stable dispersion, for example, the first organic is added to 10 mL of the nanocarbon oxide aqueous dispersion. The solvent is preferably 5 to 1000 mL, more preferably 10 to 500 mL.
工程（２）において、シリコン材料及びカーボンナノチューブは上記したものである。 In the step (2), the silicon material and the carbon nanotube are as described above.
シリコン材料及びカーボンナノチューブの形態は特に制限されない。例えば、シリコン材料及びカーボンナノチューブの片方又は双方は、そのまま投入してもよいし、第２有機溶媒に分散された状態で投入してもよい。 The form of the silicon material and the carbon nanotube is not particularly limited. For example, one or both of the silicon material and the carbon nanotube may be added as it is, or may be added in a state dispersed in the second organic solvent.
この際使用される第２有機溶媒としては、シリコン材料及び／又はカーボンナノチューブを分散させることができる溶媒であれば特に制限はないが、例えば、メタノール、エタノール、イソプロピルアルコール（ＩＰＡ）等のアルコール（特に炭素数１〜６の低級アルコール）、アセトン等が使用できる。これらは１種単独で用いてもよいし、２種以上を組合せて用いてもよい。 The second organic solvent used in this case is not particularly limited as long as it is a solvent that can disperse a silicon material and / or carbon nanotubes. For example, alcohol (eg, methanol, ethanol, isopropyl alcohol (IPA)) ( In particular, C1-6 lower alcohols), acetone, and the like can be used. These may be used individually by 1 type and may be used in combination of 2 or more type.
シリコン材料及びカーボンナノチューブの添加量は特に制限はなく、最終的に得られる本発明のリチウム二次電池用負極材料におけるシリコン材料及びカーボンナノチューブの含有量に応じた添加量とすればよい。具体的には、シリコン材料の添加量は、ナノカーボン酸化物水分散液中のナノカーボン酸化物１００重量部に対して１００〜１００００重量部とすることが好ましく、２００〜５０００重量部とすることがより好ましい。また、カーボンナノチューブの添加量は、ナノカーボン酸化物水分散液中のナノカーボン酸化物１００重量部に対して１〜１００重量部とすることが好ましく、１０〜５０重量部とすることがより好ましい。 The addition amount of the silicon material and the carbon nanotube is not particularly limited, and may be an addition amount corresponding to the content of the silicon material and the carbon nanotube in the finally obtained negative electrode material for a lithium secondary battery of the present invention. Specifically, the addition amount of the silicon material is preferably 100 to 10,000 parts by weight, and 200 to 5000 parts by weight with respect to 100 parts by weight of the nanocarbon oxide in the nanocarbon oxide aqueous dispersion. Is more preferable. The amount of carbon nanotube added is preferably 1 to 100 parts by weight and more preferably 10 to 50 parts by weight with respect to 100 parts by weight of the nanocarbon oxide in the nanocarbon oxide aqueous dispersion. .
このようにして、ナノ炭素（特にグラフェンシート）、シリコン材料及びカーボンナノチューブを含む分散液が得られるが、この後、乾燥処理を施すことが好ましい。 In this way, a dispersion containing nanocarbon (particularly graphene sheet), a silicon material, and carbon nanotubes can be obtained. However, it is preferable to perform a drying treatment thereafter.
より具体的には、例えば、上記の工程（２）で得た分散液を通常の固液分離を行ってもよく、濾過、又は溶媒溜去した後真空乾燥すること、あるいは基板上に塗布及び乾燥させることが好ましい。 More specifically, for example, the dispersion obtained in the above step (2) may be subjected to ordinary solid-liquid separation, and may be filtered or vacuum-dried after removing the solvent, or applied onto a substrate and It is preferable to dry.
基板上に上記分散液を塗布する場合の基板の形状や材質は特に限定されないが、例えば、アルミニウム等の金属；プラスチック；木；セラミック；紙等からなる板状、塊状（ブロック状等）、フィルム状、又はこれらが組み合わされた形状等が挙げられる。 There are no particular limitations on the shape and material of the substrate when the dispersion is applied onto the substrate, but for example, metal such as aluminum; plastic; wood; ceramic; paper, etc., plate-like, lump-like (block-like, etc.), film Or a combination of these.
基板表面は特に制限はなく、平滑でも多孔質でもよい。 The substrate surface is not particularly limited and may be smooth or porous.
塗布方法は基板の材質や形状によって適宜選択でき、特に限定されないが、例えば、キャスト、スピンコート、スプレーコート、ディップコート等を挙げることができる。特に、基材形状を選ばないこと、構造体を多孔質にすることもできること等からスプレーコートが好ましい。 The coating method can be appropriately selected depending on the material and shape of the substrate, and is not particularly limited. Examples thereof include casting, spin coating, spray coating, and dip coating. In particular, spray coating is preferred because the substrate shape is not selected and the structure can be made porous.
塗布の際、基板を加熱して本発明のリチウム二次電池用負極材料の形成を促進することもできる。加熱方法は特に限定されないが、例えばヒーター等で間接又は直接基板を加熱することができる。この時の加熱温度は、３０℃〜分散液の溶媒の沸点＋３０℃の範囲が好ましく、４０℃〜有機分散液の有機溶媒の沸点＋２０℃の範囲がより好ましい。 At the time of application, the substrate can be heated to promote the formation of the negative electrode material for a lithium secondary battery of the present invention. Although the heating method is not particularly limited, for example, the substrate can be heated indirectly or directly with a heater or the like. The heating temperature at this time is preferably in the range of 30 ° C. to the boiling point of the solvent of the dispersion liquid + 30 ° C., more preferably in the range of 40 ° C. to the boiling point of the organic solvent of the organic dispersion liquid + 20 ° C.
塗布後の乾燥条件は、特に制限されないが、この後の工程で還元させるために酸素のない雰囲気が好ましく、具体的には、真空乾燥が好ましい。また、温度と時間は、特に制限されないが、３０〜３００℃の範囲で１０分〜２４時間が好ましく、基板の材質と分散液の溶媒の沸点に応じて適宜選択すればよい。 The drying conditions after application are not particularly limited, but an oxygen-free atmosphere is preferable for reduction in the subsequent steps, and specifically, vacuum drying is preferable. The temperature and time are not particularly limited, but are preferably in the range of 30 to 300 ° C. for 10 minutes to 24 hours, and may be appropriately selected according to the material of the substrate and the boiling point of the solvent of the dispersion.
次に、工程（３）においては、工程（２）で得た分散液に還元処理を施す。 Next, in step (3), the dispersion obtained in step (2) is subjected to reduction treatment.
なお、本発明においては、カーボン材料であるカーボンナノチューブが弱い還元剤として機能するため、焼成処理の際に、不活性ガス雰囲気下での焼成としてもよく、あるいは、水素等の還元性ガス雰囲気としてもよい。さらには、還元剤を別途投入してもよいし、投入しなくてもよい。 In the present invention, since the carbon nanotube, which is a carbon material, functions as a weak reducing agent, it may be fired in an inert gas atmosphere during the firing process, or as a reducing gas atmosphere such as hydrogen. Also good. Furthermore, a reducing agent may be added separately or not.
還元剤を投入する場合、使用できる還元剤は、特に制限されないが、ヒドラジン、水素化ホウ素ナトリウム、シュウ酸、ギ酸等が挙げられる。 When the reducing agent is added, the reducing agent that can be used is not particularly limited, and examples thereof include hydrazine, sodium borohydride, oxalic acid, formic acid and the like.
還元剤を投入する場合、還元剤の量は、より確実に還元させるために、ナノカーボン酸化物１００重量部に対して、０．１〜２０重量部が好ましく、１〜１０重量部がより好ましい。 In the case of introducing a reducing agent, the amount of the reducing agent is preferably 0.1 to 20 parts by weight, more preferably 1 to 10 parts by weight with respect to 100 parts by weight of the nanocarbon oxide in order to reduce more reliably. .
還元処理の際の処理条件は特に制限されないが、窒素雰囲気、アルゴン雰囲気等の不活性気体雰囲気下での加熱処理（特に焼成処理）とすることが好ましい。 The treatment conditions for the reduction treatment are not particularly limited, but it is preferable to perform heat treatment (particularly firing treatment) in an inert gas atmosphere such as a nitrogen atmosphere or an argon atmosphere.
また、還元処理の際の圧力、温度及び時間は、特に制限されないが、ＳｉＣの生成を抑制するために温度は高すぎないほうがよく、大気圧下での不活性気体流通下において、８００〜１０００℃、好ましくは８５０〜９７０℃の範囲で３０分〜１０時間が好ましい。 Further, the pressure, temperature, and time during the reduction treatment are not particularly limited, but the temperature should not be too high in order to suppress the formation of SiC, and 800 to 1000 under an inert gas flow at atmospheric pressure. C., preferably 30 to 10 hours in the range of 850 to 970.degree.
３．リチウム二次電池用の負極活物質層形成用組成物
本発明のリチウム二次電池用負極材料は、上記のような構成を有するため、シリコン材料とナノ炭素、及びカーボンナノチューブのコンポジット自身が、シリコン材料の膨張や割れを抑制、捕捉するだけでなく、黒鉛と混合する場合は、シリコンコンポジットを囲む周りの黒鉛がシリコンの膨張や割れを抑制、捕捉するという理由から、黒鉛と混合したリチウム二次電池用の負極活物質層形成用組成物は、シリコン単独の場合と比較し、特にサイクル特性を向上させることができる。より具体的には、本発明のリチウム二次電池用の負極活物質層形成用組成物を負極に用いることで、充放電を行った際に、初期充電容量６５０ｍＡｈ／ｇ以上（特に６７０〜３０００ｍＡｈ／ｇ）、初期放電容量６００ｍＡｈ／ｇ以上（特に６１０〜３０００ｍＡｈ／ｇ）で、且つ、初回から１０回目までの充電容量比較で７５％以上（特に８０％以上）、初回から１０回目までの充電容量比較で８５％以上（特に９０％以上）の容量維持率を達成することができる。
3. Composition for Forming Negative Electrode Active Material Layer for Lithium Secondary Battery Since the negative electrode material for lithium secondary battery of the present invention has the above-described configuration, the composite of silicon material, nanocarbon, and carbon nanotube itself is silicon. In addition to suppressing and capturing material expansion and cracking, when mixed with graphite, lithium secondary mixed with graphite is used because the graphite surrounding the silicon composite suppresses and captures silicon expansion and cracking. The composition for forming a negative electrode active material layer for a battery can particularly improve the cycle characteristics as compared with the case of using silicon alone. More specifically, when the composition for forming a negative electrode active material layer for a lithium secondary battery of the present invention is used for a negative electrode, an initial charge capacity of 650 mAh / g or more (especially 670 to 3000 mAh) is obtained when charging and discharging are performed. / G), an initial discharge capacity of 600 mAh / g or more (especially 610 to 3000 mAh / g), and a charge capacity comparison from the first time to the 10th time is 75% or more (especially 80% or more). A capacity retention rate of 85% or more (particularly 90% or more) can be achieved by comparing the capacity.
黒鉛としては、特に制限はなく、天然黒鉛及び人造黒鉛のいずれも使用できる。 There is no restriction | limiting in particular as graphite, Both natural graphite and artificial graphite can be used.
黒鉛の形状は特に制限されず、例えば、球状、楕円状、方形等の他、鱗片、薄片状等の板状、ロッド状、無定形状等であってもよい。比表面積が高いものが好ましく、球状又は楕円状が好ましい。 The shape of graphite is not particularly limited, and may be, for example, a spherical shape, an elliptical shape, a rectangular shape, a plate shape such as a scale or a flake shape, a rod shape, an amorphous shape, or the like. Those having a high specific surface area are preferred, and spherical or elliptical shapes are preferred.
本発明のリチウム二次電池用負極材料と、黒鉛との混合比率は、特に制限されないが、より充放電容量を維持しつつ、サイクル特性をより向上させる観点から、本発明のリチウム二次電池用負極材料と前記黒鉛との合計量１００重量％に対して、前記リチウム二次電池用負極材料の含有量が３〜８０重量％であることが好ましく、５〜５０重量％がより好ましい。 The mixing ratio of the negative electrode material for a lithium secondary battery of the present invention and graphite is not particularly limited, but from the viewpoint of further improving the cycle characteristics while maintaining the charge / discharge capacity, it is used for the lithium secondary battery of the present invention. The content of the negative electrode material for a lithium secondary battery is preferably 3 to 80% by weight and more preferably 5 to 50% by weight with respect to 100% by weight of the total amount of the negative electrode material and the graphite.
本発明のリチウム二次電池用の負極活物質層形成用組成物には、本発明のリチウム二次電池用負極材料及び黒鉛以外にも、バインダーや、メソフェーズピッチ粉末、等方性ピッチ粉末、樹脂炭等の炭素前駆体を焼成したもの等の炭素材料等の導電材等を含ませてもよい。なお、これらの炭素材料は、単独で用いてもよいし、２種以上を組合せて用いてもよい。 The composition for forming a negative electrode active material layer for a lithium secondary battery of the present invention includes a binder, mesophase pitch powder, isotropic pitch powder, resin in addition to the negative electrode material for lithium secondary battery of the present invention and graphite. You may include electrically conductive materials, such as carbon materials, such as what baked carbon precursors, such as charcoal. In addition, these carbon materials may be used independently and may be used in combination of 2 or more type.
バインダーとしては、リチウム二次電池に使用されるバインダーであれば特に制限はないが、具体的には、フッ素系ポリマー（ポリフッ化ビニリデン樹脂、ポリテトラフルオロエチレン樹脂等）、ポリオレフィン系ポリマー、合成ゴム等の公知のバインダーを使用することができる。 The binder is not particularly limited as long as it is a binder used in a lithium secondary battery, and specifically, fluorine-based polymers (polyvinylidene fluoride resin, polytetrafluoroethylene resin, etc.), polyolefin-based polymers, synthetic rubbers. A known binder such as can be used.
導電材の形状・形態は特に限定されるものではなく、鱗片状、塊状、繊維状、ウイスカー状、球状、破砕状等の各種のものが使用できる。なお、導電材は、２種以上の形状・形態のものの混合物であってもよい。 The shape and form of the conductive material are not particularly limited, and various types such as a scale shape, a lump shape, a fiber shape, a whisker shape, a spherical shape, and a crushed shape can be used. The conductive material may be a mixture of two or more shapes and forms.
また、このような導電材の平均粒径は、特に制限されず、通常、１〜５０μｍ程度が好ましく、５〜３０μｍ程度がより好ましい。なお、黒鉛系炭素材料の平均粒子径は、電子顕微鏡（ＳＥＭ）により測定されるものとする。 Moreover, the average particle diameter of such a conductive material is not particularly limited, and is usually preferably about 1 to 50 μm, more preferably about 5 to 30 μm. In addition, the average particle diameter of a graphite-type carbon material shall be measured with an electron microscope (SEM).
本発明のリチウム二次電池用の負極活物質層形成用組成物において、本発明のリチウム二次電池用負極材料及び黒鉛以外の含有量は、特に制限されないが、バインダーを０〜３０重量％（特に３〜１５重量％）、導電材を０〜４０重量％（特に０〜５重量％）とすることが、容量、クーロン効率、繰り返し特性、エネルギー効率等の観点から好ましい。 In the composition for forming a negative electrode active material layer for a lithium secondary battery of the present invention, the contents other than the negative electrode material for a lithium secondary battery of the present invention and graphite are not particularly limited, but the binder is 0 to 30% by weight ( In particular, 3 to 15% by weight) and 0 to 40% by weight (particularly 0 to 5% by weight) of the conductive material are preferable from the viewpoints of capacity, coulomb efficiency, repeatability, energy efficiency, and the like.
４．リチウム二次電池用負極
本発明のリチウム二次電池用負極は、集電体及び前記集電体上に配置された負極活物質層を主に備えている。
4). Negative electrode for lithium secondary battery The negative electrode for lithium secondary battery of the present invention mainly comprises a current collector and a negative electrode active material layer disposed on the current collector.
集電体は、銅等の金属からなる、例えば箔状、メッシュ状等の部材である。 The current collector is a member made of a metal such as copper, for example, a foil shape or a mesh shape.
また、負極活物質層は、本発明のリチウム二次電池用負極材料を含んでいてもよいし、本発明のリチウム二次電池用の負極活物質層形成用組成物からなるものでもよい。 Moreover, the negative electrode active material layer may contain the negative electrode material for lithium secondary batteries of this invention, and may consist of the composition for negative electrode active material layer formation for lithium secondary batteries of this invention.
当該負極活物質層が本発明のリチウム二次電池用負極材料を含んでいる場合は、本発明のリチウム二次電池用負極材料以外にも、バインダーを含むことが好ましい。バインダーとしては、リチウム二次電池に使用されるバインダーであれば特に制限はないが、具体的には、フッ素系ポリマー（ポリフッ化ビニリデン樹脂、ポリテトラフルオロエチレン樹脂等）、ポリオレフィン系ポリマー、合成ゴム等の公知のバインダーを使用することができる。 When the said negative electrode active material layer contains the negative electrode material for lithium secondary batteries of this invention, it is preferable that a binder is included besides the negative electrode material for lithium secondary batteries of this invention. The binder is not particularly limited as long as it is a binder used in a lithium secondary battery, and specifically, fluorine-based polymers (polyvinylidene fluoride resin, polytetrafluoroethylene resin, etc.), polyolefin-based polymers, synthetic rubbers. A known binder such as can be used.
さらに、負極活物質層には、さらに、導電材として、炭素材料を含ませてもよい。 Furthermore, the negative electrode active material layer may further contain a carbon material as a conductive material.
炭素材料は、炭素として一般に理解される範疇に入る材料であれば特に制限されないが、例えば、天然黒鉛、人造黒鉛、メソカーボンマイクロビーズ、メソフェーズピッチ粉末、等方性ピッチ粉末、樹脂炭等の炭素前駆体を焼成したもの等を挙げることができる。なお、これらの炭素材料は、単独で用いてもよいし、２種以上を組合せて用いてもよい。 The carbon material is not particularly limited as long as it is a material that is in a category generally understood as carbon. For example, carbon such as natural graphite, artificial graphite, mesocarbon microbeads, mesophase pitch powder, isotropic pitch powder, resin charcoal, etc. The thing which baked the precursor can be mentioned. In addition, these carbon materials may be used independently and may be used in combination of 2 or more type.
なお、本発明で用いられる炭素材料として特に好ましいものは、Ｘ線回折法により得られる（００２）面の平均面間隔ｄ００２が０．３４０ｎｍ以下の炭素材料、特に、０．３３５〜０．３４０ｎｍの炭素材料である。 A carbon material particularly preferable as the carbon material used in the present invention is a carbon material having an average interplanar spacing d002 of (002) plane obtained by X-ray diffraction method of 0.340 nm or less, particularly 0.335 to 0.340 nm. It is a carbon material.
上述の炭素材料の形状・形態は特に限定されるものではなく、鱗片状、塊状、繊維状、ウイスカー状、球状、破砕状等の各種のものが使用できる。なお、炭素材料は、２種以上の形状・形態のものの混合物であってもよい。 The shape and form of the above-described carbon material are not particularly limited, and various types such as a scale shape, a lump shape, a fiber shape, a whisker shape, a spherical shape, and a crushed shape can be used. The carbon material may be a mixture of two or more shapes and forms.
また、このような炭素材料の平均粒径は、特に制限されず、通常、１〜５０μｍ程度が好ましく、５〜３０μｍ程度がより好ましい。なお、黒鉛系炭素材料の平均粒子径は、電子顕微鏡（ＳＥＭ）により測定されるものとする。 Moreover, the average particle diameter of such a carbon material is not particularly limited, and is usually preferably about 1 to 50 μm, and more preferably about 5 to 30 μm. In addition, the average particle diameter of a graphite-type carbon material shall be measured with an electron microscope (SEM).
上記のような負極活物質層において、各成分の含有量は、特に制限されないが、本発明のリチウム二次電池用負極材料を５０〜１００重量部（特に７０〜９５重量部）、バインダーを０〜３０重量部（特に３〜１５重量部）、炭素材料を０〜４０重量部（特に０〜５重量部）とし、合計を１００重量部とすることが、容量、クーロン効率、繰り返し特性、エネルギー効率等の観点から好ましい。 In the negative electrode active material layer as described above, the content of each component is not particularly limited, but the negative electrode material for a lithium secondary battery of the present invention is 50 to 100 parts by weight (particularly 70 to 95 parts by weight), and the binder is 0. ~ 30 parts by weight (especially 3 to 15 parts by weight), 0 to 40 parts by weight (especially 0 to 5 parts by weight) of carbon material, and 100 parts by weight in total, capacity, coulomb efficiency, repeatability, energy It is preferable from the viewpoint of efficiency and the like.
また、負極活物質層の厚みは、特に制限されないが、イオンの浸透と電気伝導度を確保しかつロールした際にも剥がれが少ないという点では薄い方が良い一方で、電極あたりのエネルギー密度という点では厚い方が良いという観点から、５〜５００μｍが好ましく、１０〜２５０μｍがより好ましい。 Further, the thickness of the negative electrode active material layer is not particularly limited, but it is preferable to be thin in terms of ensuring ion penetration and electrical conductivity and less peeling even when rolled, on the other hand, the energy density per electrode From the standpoint that the thicker is better, the thickness is preferably 5 to 500 μm, more preferably 10 to 250 μm.
このようなリチウム二次電池用負極を形成する場合は、本発明のリチウム二次電池用負極材料を、必要に応じてバインダー及び黒鉛系炭素材料と混合してペースト状にし、そのペーストを集電体上に塗布して負極活物質層を形成することが好ましい。また、本発明の負極活物質層が本発明のリチウム二次電池用の負極活物質層形成用組成物からなる場合は、同様に、本発明のリチウム二次電池用の負極活物質層形成用組成物を集電体上に塗布して負極活物質層を形成することが好ましい。 When forming such a negative electrode for a lithium secondary battery, the negative electrode material for a lithium secondary battery of the present invention is mixed with a binder and a graphite-based carbon material as necessary to form a paste, and the paste is collected. It is preferable to form a negative electrode active material layer by coating on the body. When the negative electrode active material layer of the present invention is composed of the composition for forming a negative electrode active material layer for a lithium secondary battery of the present invention, similarly, for forming a negative electrode active material layer for the lithium secondary battery of the present invention It is preferable to form the negative electrode active material layer by applying the composition onto a current collector.
５．リチウム二次電池
本発明のリチウム二次電池は、上記した本発明のリチウム二次電池用負極を備えている。また、本発明のリチウム二次電池は、本発明のリチウム二次電池用負極以外に、公知のリチウム二次電池に適用される正極、電解液及びこれらを収納するための容器を備えることができる。
5. Lithium secondary battery The lithium secondary battery of the present invention includes the above-described negative electrode for a lithium secondary battery of the present invention. Moreover, the lithium secondary battery of this invention can be equipped with the positive electrode applied to a well-known lithium secondary battery, electrolyte solution, and the container for accommodating these other than the negative electrode for lithium secondary batteries of this invention. .
正極は、リチウムを含有する酸化物、例えば、ＬｉＣｏＯ２等のリチウム複合酸化物と公知のバインダーとを混合してペースト状にしたものを金属製等の正極集電体上に塗布したものである。なお、集電体は、一般的にはアルミ箔が用いられるが、負極集電体と同様のものを使用することもできる。 The positive electrode is obtained by applying a paste containing a lithium-containing oxide, for example, a lithium composite oxide such as LiCoO 2 and a known binder, and applying the mixture onto a positive electrode current collector made of metal or the like. . In addition, although the aluminum foil is generally used for the current collector, the same material as the negative electrode current collector can also be used.
また、電解液は、非プロトン性有機溶媒に塩を溶解した電解液であって、正極と負極との間に配置されており、例えば、正極と負極との短絡を防止するための不織布等からなるセパレータに含浸されて保持されている。 The electrolytic solution is an electrolytic solution in which a salt is dissolved in an aprotic organic solvent, and is disposed between the positive electrode and the negative electrode. For example, from a nonwoven fabric for preventing a short circuit between the positive electrode and the negative electrode The separator is impregnated and held.
なお、上述の電解液を構成する非プロトン性有機溶媒としては、例えば、エチレンカーボネート、プロピレンカーボネート、ブチレンカーボネート、ジメチルカーボネート、ジエチルカーボネート、メチルエチルカーボネート、γ−ブチロラクトン、ギ酸メチル、酢酸メチル等のエステル類；テトラヒドロフランや２−メチルテトラヒドロフラン等のフラン類；ジオキソラン、ジエチルエーテル、ジメトキシエタン、ジエトキシエタン、メトキシエトキシエタン等のエーテル類；ジメチルスルホキシド；スルホラン、メチルスルホラン等のスルホラン類；アセトニトリル等が挙げられる。これらの非プロトン性有機溶媒は、単独で用いてもよいし、２種以上を組合せて用いてもよい。 Examples of the aprotic organic solvent that constitutes the above electrolyte include esters such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, methyl formate, and methyl acetate. Furans such as tetrahydrofuran and 2-methyltetrahydrofuran; Ethers such as dioxolane, diethyl ether, dimethoxyethane, diethoxyethane, and methoxyethoxyethane; Dimethyl sulfoxide; Sulfolanes such as sulfolane and methylsulfolane; Acetonitrile . These aprotic organic solvents may be used alone or in combination of two or more.
一方、このような非プロトン性有機溶媒に溶解される塩は、例えば、過塩素酸リチウム、ホウフッ化リチウム、６フッ化リン酸リチウム、６フッ化砒酸リチウム、トリフルオロメタンスルホン酸リチウム、ハロゲン化リチウム、塩化アルミン酸リチウム等のリチウム塩が挙げられる。これらの塩は、単独で用いてもよいし、２種以上を組合せて用いてもよい。 On the other hand, the salt dissolved in such an aprotic organic solvent is, for example, lithium perchlorate, lithium borofluoride, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, lithium halide. And lithium salts such as lithium chloroaluminate. These salts may be used alone or in combination of two or more.
このような本発明のリチウム二次電池は、負極に本発明の負極材料を用いているため、負極の充放電容量及びサイクル特性が高く、正極の活物質量を抑制することができる。このため、このリチウム二次電池は、多量の正極活物質を収容するための大型の容器を用いる必要がないので、従来のものに比べて小型化することができ、且つ充放電容量が大きく、また、負極が電解液と反応しにくいため安全性が高い。 Since the lithium secondary battery of the present invention uses the negative electrode material of the present invention for the negative electrode, the charge / discharge capacity and cycle characteristics of the negative electrode are high, and the amount of the active material of the positive electrode can be suppressed. For this reason, since this lithium secondary battery does not need to use a large container for accommodating a large amount of positive electrode active material, it can be downsized compared to the conventional one, and has a large charge / discharge capacity, Moreover, since the negative electrode hardly reacts with the electrolyte, safety is high.
なお、本発明のリチウム二次電池は、上述の電解液に代えて、公知の無機固体電解質や高分子固体電解質等の他の電解質を用いた場合も同様に実施することができる。 In addition, the lithium secondary battery of the present invention can be implemented in the same manner when another electrolyte such as a known inorganic solid electrolyte or polymer solid electrolyte is used instead of the above-described electrolyte.
以下、実施例によって本発明を具体的に説明するが、本発明はこれら実施例によって制限されるものではない。 EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.
［実施例１］
＜グラフェンの調製＞
温度計及び冷却管を備えた５００ｍＬ三口フラスコに濃硫酸２３ｍＬを入れ氷冷し、日本黒鉛工業株式会社製薄片化黒鉛粉末ＣＭＸ（０．５ｇ）を加え、撹拌した。ここに、ＮａＮＯ３（０．５ｇ）、ＫＭｎＯ４（３．０ｇ）をゆっくり添加し、３５℃で１時間撹拌した。さらに、蒸留水１４０ｍＬを加え、３０％Ｈ２Ｏ２（３ｍＬ）を滴下し、９０℃で３０分間撹拌した。
[Example 1]
<Preparation of graphene>
A 500 mL three-necked flask equipped with a thermometer and a condenser tube was charged with 23 mL of concentrated sulfuric acid and cooled with ice, and exfoliated graphite powder CMX (0.5 g) manufactured by Nippon Graphite Industries Co., Ltd. was added and stirred. To this, NaNO 3 (0.5 g) and KMnO 4 (3.0 g) were slowly added and stirred at 35 ° C. for 1 hour. Furthermore, 140 mL of distilled water was added, 30% H 2 O 2 (3 mL) was added dropwise, and the mixture was stirred at 90 ° C. for 30 minutes.
得られた溶液を、１８０００ｒｐｍで９０分間遠心分離し、固形分に蒸留水１５０ｍＬを加えて撹拌し、再度遠心分離して固形分を得た。この遠心分離操作を計６回し、固形分を再度水に分散させ、酸化グラフェンの水分散液（０．５７重量％）を得た。 The obtained solution was centrifuged at 18000 rpm for 90 minutes, 150 mL of distilled water was added to the solid content, stirred, and centrifuged again to obtain a solid content. This centrifugation operation was performed a total of 6 times, and the solid content was again dispersed in water to obtain an aqueous dispersion of graphene oxide (0.57% by weight).
＜負極材料の調製＞
上述で得られた酸化グラフェン水分散液（１０．０ｍＬ）をイソプロピルアルコール（ＩＰＡ）（１１．５ｍＬ）で置換し、１重量％の酸化グラフェンＩＰＡ分散液（９．０ｇ）を得た。
<Preparation of negative electrode material>
The graphene oxide aqueous dispersion (10.0 mL) obtained above was replaced with isopropyl alcohol (IPA) (11.5 mL) to obtain a 1 wt% graphene oxide IPA dispersion (9.0 g).
ここに、Nanostructured & Amorphous Materials, Inc.社製 Silicon Powder（平均粒子径３０〜５０ｎｍ）を０．２１ｇ、１重量％の単層カーボンナノチューブ（Nano Integris社製 Super Pure Tubs；平均外径１．４ｎｍ、平均長さ約０．５μｍ、平均アスペクト比３５７）のＩＰＡ分散液を３．０ｇ加えて、氷冷下でホモジナイザー処理を２時間行い、グラフェン−ナノシリコン−単層カーボンナノチューブのＩＰＡ分散液を得た。この分散液をガラス基板上に滴下し、１２０℃で１．５時間真空乾燥した後、アルゴン雰囲気下で９５０℃に昇温し、１時間保持することで、実施例１の負極材料（グラフェン−ナノシリコン−単層カーボンナノチューブ複合体）を得た。この負極材料において、各成分の混合比率は、グラフェン：シリコン：単層カーボンナノチューブ＝３０：７０：１０（重量比）であった。 Here, 0.21 g of Silicon Powder (average particle size 30-50 nm) manufactured by Nanostructured & Amorphous Materials, Inc., 1 wt% single-walled carbon nanotube (Super Pure Tubs manufactured by Nano Integris; average outer diameter 1.4 nm) Then, 3.0 g of an IPA dispersion having an average length of about 0.5 μm and an average aspect ratio of 357) is added, and homogenizer treatment is performed for 2 hours under ice-cooling to obtain an IPA dispersion of graphene-nanosilicon-single-walled carbon nanotubes Obtained. This dispersion was dropped on a glass substrate and vacuum-dried at 120 ° C. for 1.5 hours, and then heated to 950 ° C. in an argon atmosphere and held for 1 hour, whereby the negative electrode material (graphene- Nanosilicon-single wall carbon nanotube composite) was obtained. In this negative electrode material, the mixing ratio of each component was graphene: silicon: single-walled carbon nanotubes = 30: 70: 10 (weight ratio).
［比較例１］
単層カーボンナノチューブを用いなかったこと以外は実施例１と同様に、比較例１の負極材料を得た。この負極材料において、各成分の混合比率は、グラフェン：シリコン：単層カーボンナノチューブ＝３０：７０：０（重量比）であった。
[Comparative Example 1]
A negative electrode material of Comparative Example 1 was obtained in the same manner as in Example 1 except that the single-walled carbon nanotube was not used. In this negative electrode material, the mixing ratio of each component was graphene: silicon: single-walled carbon nanotubes = 30: 70: 0 (weight ratio).
［比較例２］
単層カーボンナノチューブを用いず、１重量％の酸化グラフェンＩＰＡ分散液（９．０ｇ）の代わりに１重量％のアセチレンブラックＩＰＡ分散液（９．０ｇ）を用いたこと以外は実施例１と同様に、比較例２の負極材料を得た。この負極材料において、各成分の混合比率は、アセチレンブラック：シリコン：単層カーボンナノチューブ＝３０：７０：０（重量比）であった。
[Comparative Example 2]
Example 1 except that single-walled carbon nanotubes were not used and 1 wt% acetylene black IPA dispersion (9.0 g) was used instead of 1 wt% graphene oxide IPA dispersion (9.0 g). In addition, a negative electrode material of Comparative Example 2 was obtained. In this negative electrode material, the mixing ratio of each component was acetylene black: silicon: single-walled carbon nanotubes = 30: 70: 0 (weight ratio).
［充放電試験用セルの製造（その１）］
上記の実施例１又は比較例１〜２で得た負極材料（シリコンとグラフェン又はアセチレンブラックの合計量を１００重量部とする）に対し、バインダーとして２０重量部のポリフッ化ビニリデン（ＰＶＤＦ）を加え、メノウ乳鉢で混合し、リチウム二次電池用負極合材を得た。
[Manufacture of charge / discharge test cell (1)]
20 parts by weight of polyvinylidene fluoride (PVDF) is added as a binder to the negative electrode material obtained in Example 1 or Comparative Examples 1 and 2 above (the total amount of silicon and graphene or acetylene black is 100 parts by weight) The mixture was mixed in an agate mortar to obtain a negative electrode composite material for a lithium secondary battery.
この合材１２ｇを、東洋システム（株）製コインセル評価治具にセットした。セパレータにはグラスフィルターを使用し、１Ｍ ＬｉＰＦ６を約３００μＬ添加したエチレンカーボネート／ジエチルカーボネート（ＥＣ／ＤＥＣ）＝１：１（体積比）を電解液 とし、対極はリチウム金属（φ１６ｍｍ×１ｍｍ）を用いた。組み立ては、内部圧１０Ｎ／ｃｍ２となるよう、アルゴン雰囲気下、露点−８０℃以下のグローブボックス内で行った。 12 g of this composite material was set in a coin cell evaluation jig manufactured by Toyo System Co., Ltd. A glass filter is used as the separator. Ethylene carbonate / diethyl carbonate (EC / DEC) = 1: 1 (volume ratio) to which about 300 μL of 1M LiPF 6 is added is used as an electrolyte, and lithium metal (φ16 mm × 1 mm) is used as a counter electrode. Using. The assembly was performed in a glove box having a dew point of −80 ° C. or lower under an argon atmosphere so that the internal pressure was 10 N / cm 2 .
これにより、実施例１及び比較例１〜２について、充放電試験用セルを得た。 Thereby, the cell for a charging / discharging test was obtained about Example 1 and Comparative Examples 1-2.
［試験例１：充放電試験］
上記で得た充放電試験用セルを３０℃の恒温槽内に設置し、充放電試験を実施した。充放電の条件は以下：
（Ｉ）シリコン材料の容量に対して１／４０Ｃの定電流で０．０１Ｖになるまで充電
（ＩＩ）０．０１Ｖの定電圧で、電流値がシリコン材料の容量に対して１／６０Ｃになるまで充電
（ＩＩＩ）シリコン材料の容量に対して１／４０Ｃの定電流で１．５Ｖになるまで放電
（ＩＶ）１．５Ｖの定電圧で、電流値がシリコン材料の容量に対して１／６０Ｃになるまで放電
のとおりとした。
[Test Example 1: Charge / Discharge Test]
The charge / discharge test cell obtained above was placed in a thermostatic bath at 30 ° C., and a charge / discharge test was performed. The charge / discharge conditions are as follows:
(I) Charge until a constant current of 1 / 40C with respect to the capacity of the silicon material is 0.01V. (II) At a constant voltage of 0.01V, the current value is 1 / 60C with respect to the capacity of the silicon material. Charge (III) Discharge (IV) at a constant voltage of 1.5V until a constant current of 1 / 40C with respect to the capacity of the silicon material, and a current value of 1 / 60C with respect to the capacity of the silicon material. It was set as the discharge until it became.
上記の（Ｉ）〜（ＩＶ）の充放電を８回繰り返し、特性評価を行った。充放電第１回目の初期充放電容量と初期クーロン効率、最終サイクル８回目の充放電容量とクーロン効率、放電容量の容量維持率を表１に示す。 Charging / discharging of said (I)-(IV) was repeated 8 times, and the characteristic evaluation was performed. Table 1 shows the initial charge / discharge capacity and initial coulomb efficiency for the first charge / discharge, the charge / discharge capacity and coulomb efficiency for the eighth cycle, and the capacity retention rate of the discharge capacity.
［実施例２：グラフェン＋ＣＮＴ］
＜負極合材の調製＞
黒鉛（大阪ガスケミカル（株）製のＯＭＡＣ−Ｒ）８０．０重量部、平均粒子径が２μｍのシリコン粒子を用いたこと以外は実施例１と同様に作製したグラフェン−ナノシリコン−単層カーボンナノチューブ複合体９．０重量部、アセチレンブラック６．０重量部、バインダーとしてシリコンブタジエンゴム（ＳＢＲ）２．０重量部、及び造粘剤としてカルボキシメチルセルロース（ＣＭＣ）２．０重量部をメノウ乳鉢で混合し、実施例２のリチウム二次電池用負極合材（リチウム二次電池用の負極活物質層形成用組成物）を得た。
[Example 2: Graphene + CNT]
<Preparation of negative electrode mixture>
Graphene-nanosilicon-single-layer carbon produced in the same manner as in Example 1 except that 80.0 parts by weight of graphite (OMAC-R manufactured by Osaka Gas Chemical Co., Ltd.) and silicon particles having an average particle diameter of 2 μm were used. In an agate mortar, 9.0 parts by weight of a nanotube composite, 6.0 parts by weight of acetylene black, 2.0 parts by weight of silicon butadiene rubber (SBR) as a binder, and 2.0 parts by weight of carboxymethyl cellulose (CMC) as a thickener By mixing, a negative electrode mixture for a lithium secondary battery of Example 2 (a composition for forming a negative electrode active material layer for a lithium secondary battery) was obtained.
［比較例３：処理なし］
グラフェン−ナノシリコン−単層カーボンナノチューブ複合体ではなく、シリコン粒子（平均粒子径２μｍ）を使用したこと以外は実施例２と同様に、比較例３のリチウム二次電池用負極合材（リチウム二次電池用の負極活物質層形成用組成物）を得た。
[Comparative Example 3: No treatment]
The negative electrode composite material for lithium secondary batteries of Comparative Example 3 (lithium secondary battery) was used in the same manner as in Example 2 except that silicon particles (average particle diameter 2 μm) were used instead of the graphene-nanosilicon-single-walled carbon nanotube composite. A composition for forming a negative electrode active material layer for a secondary battery) was obtained.
［比較例４：ピッチベーパー］
シリコン粒子（平均粒子径２μｍ）と軟化点が２８５℃の石炭系等方性ピッチとを炭化炉内に別々に配置した。ここでは、炭化炉内に配置されたメッシュ上にシリコンを載置し、また、当該メッシュ下に、シリコンとピッチとの重量比が７：３となるように石炭系等方性ピッチを入れたトレーを配置した。そして、炭化炉内を窒素ガスで満たした後、炭化炉内の温度を３００℃／時の昇温速度で９５０℃まで高めてシリコンを１．５時間加熱処理し、シリコンにピッチベーパーされたリチウム二次電池用負極材料を得た。
[Comparative Example 4: Pitch vapor]
Silicon particles (average particle diameter 2 μm) and coal-based isotropic pitch having a softening point of 285 ° C. were separately arranged in the carbonization furnace. Here, silicon was placed on a mesh placed in the carbonization furnace, and a coal-based isotropic pitch was placed under the mesh so that the weight ratio of silicon to pitch was 7: 3. A tray was placed. Then, after filling the inside of the carbonization furnace with nitrogen gas, the temperature inside the carbonization furnace was increased to 950 ° C. at a temperature increase rate of 300 ° C./hour, and the silicon was heat-treated for 1.5 hours. A negative electrode material for a secondary battery was obtained.
グラフェン−ナノシリコン−単層カーボンナノチューブ複合体ではなく、シリコンにピッチベーパーされたリチウム二次電池用負極材料を使用したこと以外は実施例２と同様に、比較例４のリチウム二次電池用負極合材（リチウム二次電池用の負極活物質層形成用組成物）を得た。 A negative electrode for a lithium secondary battery of Comparative Example 4 as in Example 2 except that a negative electrode material for lithium secondary battery pitch-vaporized in silicon was used instead of the graphene-nanosilicon-single-walled carbon nanotube composite. A composite (a composition for forming a negative electrode active material layer for a lithium secondary battery) was obtained.
［比較例５：ピッチコート］
シリコン粒子（平均粒子径２μｍ）と軟化点が２８５℃の石炭系等方性ピッチとを炭化炉内に別々に配置した。ここでは、炭化炉内に配置されたメッシュ上にシリコンを載置し、また、当該メッシュ下に、シリコンとピッチとの重量比が５：５となるようにミル混合し、るつぼに入れて炭化炉にセットした。そして、炭化炉内を窒素ガスで満たした後、炭化炉内の温度を３００℃／時の昇温速度で９５０℃まで高めてシリコンを１．５時間加熱処理し、シリコンにピッチコートされたリチウム二次電池用負極材料を得た。
[Comparative Example 5: Pitch coat]
Silicon particles (average particle diameter 2 μm) and coal-based isotropic pitch having a softening point of 285 ° C. were separately arranged in the carbonization furnace. Here, silicon is placed on a mesh placed in a carbonization furnace, and under the mesh, mill-mixed so that the weight ratio of silicon to pitch is 5: 5, and placed in a crucible and carbonized. Set in the furnace. Then, after filling the inside of the carbonization furnace with nitrogen gas, the temperature in the carbonization furnace was increased to 950 ° C. at a temperature rising rate of 300 ° C./hour, and the silicon was heat-treated for 1.5 hours. A negative electrode material for a secondary battery was obtained.
グラフェン−ナノシリコン−単層カーボンナノチューブ複合体ではなく、シリコンにピッチコートされたリチウム二次電池用負極材料を使用したこと以外は実施例２と同様に、比較例５のリチウム二次電池用負極合材（リチウム二次電池用の負極活物質層形成用組成物）を得た。 A negative electrode for a lithium secondary battery of Comparative Example 5 in the same manner as in Example 2, except that a negative electrode material for lithium secondary battery that was pitch coated on silicon was used instead of the graphene-nanosilicon-single-walled carbon nanotube composite. A composite (a composition for forming a negative electrode active material layer for a lithium secondary battery) was obtained.
［比較例６：グラフェン］
グラフェン−ナノシリコン−単層カーボンナノチューブ複合体ではなく、平均粒子径が２μｍのシリコン粒子を用いたこと以外は比較例１と同様に作製した負極材料を使用したこと以外は実施例２と同様に、比較例６のリチウム二次電池用負極合材（リチウム二次電池用の負極活物質層形成用組成物）を得た。
[Comparative Example 6: Graphene]
Similar to Example 2 except that the negative electrode material prepared in the same manner as in Comparative Example 1 was used except that silicon particles having an average particle diameter of 2 μm were used instead of the graphene-nanosilicon-single-walled carbon nanotube composite. The negative electrode mixture for lithium secondary batteries of Comparative Example 6 (a composition for forming a negative electrode active material layer for lithium secondary batteries) was obtained.
［比較例７：グラフェン＋ＶＧＣＦ］
単層カーボンナノチューブの代りに、平均繊維径が１５０ｎｍの気相成長法炭素繊維を用い、平均粒子径が２μｍのシリコン粒子を用いること以外は実施例１と同様に、負極材料を得た。
[Comparative Example 7: Graphene + VGCF]
A negative electrode material was obtained in the same manner as in Example 1 except that vapor-grown carbon fibers having an average fiber diameter of 150 nm were used instead of single-walled carbon nanotubes, and silicon particles having an average particle diameter of 2 μm were used.
次に、グラフェン−ナノシリコン−単層カーボンナノチューブ複合体ではなく、上記で得た負極材料を使用したこと以外は実施例２と同様に、比較例７のリチウム二次電池用負極合材（リチウム二次電池用の負極活物質層形成用組成物）を得た。 Next, the negative electrode mixture for lithium secondary batteries of Comparative Example 7 (lithium) was used in the same manner as in Example 2 except that the negative electrode material obtained above was used instead of the graphene-nanosilicon-single-walled carbon nanotube composite. A composition for forming a negative electrode active material layer for a secondary battery) was obtained.
［比較例８：膨張黒鉛（その１）］
ＳＡＮＹＯ ＳＹＺＲ５０２Ｈを、６００℃で焼成（空気中、６００℃／時間昇温−６００℃保持１時間）したものを、１重量％でジオキサンに分散し、分散液（９．０ｇ）を得た。
[Comparative Example 8: Expanded graphite (Part 1)]
SANYO SYZR502H calcined at 600 ° C. (in the air, 600 ° C./hour temperature rise-600 ° C. hold 1 hour) was dispersed in dioxane at 1% by weight to obtain a dispersion (9.0 g).
ここに、平均粒子径２μｍのシリコンを０．２１ｇ加えて、氷冷下でホモジナイザー処理を２時間行い、膨張黒鉛−微粉シリコンのジオキサン分散液を得た。この分散液をガラス基板上に滴下し、１２０℃で１．５時間真空乾燥した後、アルゴン雰囲気下で９５０℃に昇温し、１時間保持することで、比較例８の負極材料（膨張黒鉛−微粉シリコン複合体）を得た。 0.21 g of silicon having an average particle diameter of 2 μm was added thereto, and homogenizer treatment was performed for 2 hours under ice-cooling to obtain a dioxane dispersion of expanded graphite-fine powder silicon. This dispersion was dropped onto a glass substrate and vacuum-dried at 120 ° C. for 1.5 hours, then heated to 950 ° C. under an argon atmosphere and held for 1 hour, whereby the negative electrode material (expanded graphite) of Comparative Example 8 was obtained. -Fine silicon composite).
次に、グラフェン−ナノシリコン−単層カーボンナノチューブ複合体ではなく、上記で得た負極材料を使用したこと以外は実施例２と同様に、比較例８のリチウム二次電池用負極合材（リチウム二次電池用の負極活物質層形成用組成物）を得た。 Next, the negative electrode mixture for lithium secondary batteries of Comparative Example 8 (lithium) was used in the same manner as in Example 2 except that the negative electrode material obtained above was used instead of the graphene-nanosilicon-single-walled carbon nanotube composite. A composition for forming a negative electrode active material layer for a secondary battery) was obtained.
［比較例９：膨張黒鉛（その２）］
日本黒鉛（株）製のＥＸＰ−ＳＭを、６００℃で焼成（空気中、６００℃／時間昇温−６００℃保持１時間）したものを、１重量％でジオキサンに分散し、分散液（９．０ｇ）を得た。この分散液をガラス基板上に滴下し、１２０℃で１．５時間真空乾燥した後、アルゴン雰囲気下で９５０℃に昇温し、１時間保持することで、比較例９の負極材料（膨張黒鉛−微粉シリコン複合体）を得た。
[Comparative Example 9: Expanded graphite (2)]
EXP-SM manufactured by Nippon Graphite Co., Ltd. was baked at 600 ° C. (in air, 600 ° C./hour temperature rise—600 ° C. hold for 1 hour), dispersed in dioxane at 1% by weight, and dispersion (9 0.0 g) was obtained. This dispersion was dropped onto a glass substrate and vacuum-dried at 120 ° C. for 1.5 hours, and then heated to 950 ° C. under an argon atmosphere and held for 1 hour, whereby the negative electrode material (expanded graphite) of Comparative Example 9 was obtained. -Fine silicon composite).
次に、グラフェン−ナノシリコン−単層カーボンナノチューブ複合体ではなく、上記で得た負極材料を使用したこと以外は実施例２と同様に、比較例９のリチウム二次電池用負極合材（リチウム二次電池用の負極活物質層形成用組成物）を得た。 Next, the negative electrode mixture for lithium secondary battery of Comparative Example 9 (lithium) was used in the same manner as in Example 2 except that the negative electrode material obtained above was used instead of the graphene-nanosilicon-single-walled carbon nanotube composite. A composition for forming a negative electrode active material layer for a secondary battery) was obtained.
［比較例１０：アセチレンブラック］
グラフェン−ナノシリコン−単層カーボンナノチューブ複合体ではなく、比較例２で得た負極材料を使用したこと以外は実施例２と同様に、比較例１０のリチウム二次電池用負極合材（リチウム二次電池用の負極活物質層形成用組成物）を得た。
[Comparative Example 10: Acetylene black]
A negative electrode mixture for lithium secondary battery of Comparative Example 10 (lithium secondary battery) of Example 10 except that the negative electrode material obtained in Comparative Example 2 was used instead of the graphene-nanosilicon-single-walled carbon nanotube composite. A composition for forming a negative electrode active material layer for a secondary battery) was obtained.
［充放電試験用セルの製造（その２）］
実施例２及び比較例３〜１０で得た負極合材１２ｇを、コインセル評価治具にセットした。この際、電極厚みは５０μｍ、電極密度は１．５９ｇ／ｃｍ３となるように調整した。セパレータにはグラスフィルターを使用し、１Ｍ ＬｉＰＦ６を添加したエチレンカーボネート／メチルエチルカーボネート（ＥＣ／ＭＥＣ）＝３：７（体積比）を電解液 とし、対極はリチウム金属（φ１６ｍｍ×１ｍｍ）を用いた。組み立ては、内部圧１０Ｎ／ｃｍ２となるよう、アルゴン雰囲気下、露点−８０℃以下のグローブボックス内で行った。
[Manufacture of charge / discharge test cell (2)]
12 g of the negative electrode mixture obtained in Example 2 and Comparative Examples 3 to 10 was set in a coin cell evaluation jig. At this time, the electrode thickness was adjusted to 50 μm, and the electrode density was adjusted to 1.59 g / cm 3 . Glass separator is used as separator, ethylene carbonate / methyl ethyl carbonate (EC / MEC) added with 1M LiPF 6 = 3: 7 (volume ratio) is used as electrolyte, and counter electrode is lithium metal (φ16mm × 1mm) It was. The assembly was performed in a glove box having a dew point of −80 ° C. or lower under an argon atmosphere so that the internal pressure was 10 N / cm 2 .
［試験例２：充放電試験］
上記で得た充放電試験用セルを３０℃の恒温槽内に設置し、充放電試験を実施した。充放電の条件は以下：
（Ｉ）シリコン材料の容量に対して０．２Ｃの定電流で０．００１Ｖになるまで充電
（ＩＩ）０．００１Ｖの定電圧で、８時間充電
（ＩＩＩ）シリコン材料の容量に対して０．２Ｃの定電流で２．５Ｖになるまで放電
のとおりとした。
[Test Example 2: Charge / Discharge Test]
The charge / discharge test cell obtained above was placed in a thermostatic bath at 30 ° C., and a charge / discharge test was performed. The charge / discharge conditions are as follows:
(I) Charged to 0.001 V at a constant current of 0.2 C with respect to the capacity of the silicon material (II) Charged for 8 hours at a constant voltage of 0.001 V (III) 0. The discharge was continued until it reached 2.5 V at a constant current of 2C.
上記の（Ｉ）〜（ＩＩＩ）の充放電を１０回繰り返し、特性評価を行った。充放電第１回目の初期充放電容量と最終サイクル１０回目の充放電を表２に示す。 Charging / discharging of said (I)-(III) was repeated 10 times, and the characteristic evaluation was performed. Table 2 shows the initial charge / discharge capacity at the first charge / discharge and the charge / discharge at the 10th final cycle.
Claims (17)
前記ナノ炭素がグラフェンシートであり、
該グラフェンシートの層間に、前記シリコン材料及び前記カーボンナノチューブが存在する、
リチウム二次電池用負極材料。 Including nanocarbon, silicon material, and carbon nanotubes,
The nano carbon is a graphene sheet,
Between the layers of the graphene sheet, the silicon material and the carbon nanotube are present.
Negative electrode material for lithium secondary battery.
（１）ナノカーボン酸化物水分散液を第１有機溶媒で置換し、ナノカーボン酸化物分散液を得る工程、
（２）前記工程（１）で得たナノカーボン酸化物分散液に、シリコン材料及びカーボンナノチューブを添加し、ナノカーボン酸化物、シリコン材料及びカーボンナノチューブを含む分散液を得る工程、及び
（３）前記工程（２）で得た分散液に還元処理を施す工程
を備え、
前記ナノカーボン酸化物が酸化グラフェンである、製造方法。 A method for producing a negative electrode material for a lithium secondary battery comprising nanocarbon, a silicon material, and a carbon nanotube,
(1) replacing the nanocarbon oxide aqueous dispersion with a first organic solvent to obtain a nanocarbon oxide dispersion;
(2) A step of adding a silicon material and a carbon nanotube to the nanocarbon oxide dispersion obtained in the step (1) to obtain a dispersion containing the nanocarbon oxide, the silicon material and the carbon nanotube, and (3) Comprising a step of subjecting the dispersion obtained in the step (2) to a reduction treatment,
The manufacturing method whose said nano carbon oxide is a graphene oxide.
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