JP6505464B2 - Negative electrode material for lithium secondary battery, composition for negative electrode active material layer for lithium secondary battery, negative electrode for lithium secondary battery, and method for producing lithium secondary battery - Google Patents
Negative electrode material for lithium secondary battery, composition for negative electrode active material layer for lithium secondary battery, negative electrode for lithium secondary battery, and method for producing 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、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の製造方法に関する。 The present invention relates to a negative electrode material for a lithium secondary battery, a composition for a negative electrode active material layer for a lithium secondary battery, a negative electrode for a lithium secondary battery, and a method for producing 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。 Nowadays, with the size and weight reduction of portable electronic devices represented by mobile phones and portable information devices (electronic notebooks, notebook computers, tablet computers, etc.) becoming remarkable, such portable electronic devices are being developed. There is a demand for development of a small and light secondary battery for driving equipment. Under such a background, a lithium secondary battery (lithium ion secondary battery etc.) which can be configured in a small size and has a high energy density has attracted attention, and its development is actively conducted. In addition to portable electronic devices as described above, needs for this lithium secondary battery are also expanding in electric vehicles and electric power storage of renewable energy, etc., and in order to meet these needs, one layer of the electrode material to be configured Energy density is required.
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 allowed to form dendrite, but as lithium ion batteries that can realize a lithium secondary battery with excellent cycle characteristics and safety, insertion and extraction of lithium ions A number of possible carbon materials have been proposed and are being put to practical use. Here, the negative electrode material for a lithium secondary battery made of a carbon material mainly includes 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 disadvantage that the change in potential accompanying the release of lithium ions is large, and it is difficult to form a stable lithium secondary battery. On the other hand, a graphite-based negative electrode material is advantageous over a carbon-based negative electrode material because such a change in potential is small and a stable lithium secondary battery can be constructed, and it is suitable for lithium secondary batteries. 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 graphite-based negative electrode material has a theoretical capacity of 372 mAh / g while silicon has a theoretical capacity of 4200 mAh / g, which is about 10 times the theoretical capacity of a graphite-based negative electrode material, so the use of a silicon negative electrode is expected (Non-Patent Documents 1 and 2). However, since silicon has a very large volume change due to charge and discharge, the negative electrode material may be cracked or peeled off from the electrode (Non-Patent Document 3) to reduce the actual capacity. 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 both sufficient charge and discharge capacity and cycle characteristics, it has been studied to combine silicon with a carbon material (Non-Patent Documents 4 to 5).
このようなシリコン材料と炭素材との複合化は、分散性と複合化しやすさの観点から、有機溶媒中で分散させる方法のみが検討されてきた。しかしながら、有機溶媒中でシリコン材料と炭素材とを複合化させるためには、高価なフィルターやエバポレーターが必要となる一方で十分な複合効果が得られなかった。このため、本発明は、簡便な方法で、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。 From the viewpoint of dispersibility and easiness of compounding such silicon materials and carbon materials, only a method of dispersing in an organic solvent has been studied. However, in order to combine the silicon material and the carbon material in the organic solvent, although an expensive filter and an evaporator are required, a sufficient combining effect can not be obtained. Therefore, the present invention aims to provide a negative electrode material for a lithium secondary battery, which has sufficient charge / discharge capacity, coulombic efficiency and cycle characteristics in a simple manner.
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、導電性炭素粒子、シリコン材料、及びカーボンナノチューブを混合（特に乾式混合）した後に、黒鉛及びピッチと乾式混合し、ピッチの熱分解温度以上に高めることにより、簡便に導電性炭素粒子、シリコン材料、及びカーボンナノチューブを複合化させることができ、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が得られることを見出した。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．導電性炭素粒子、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）導電性炭素粒子、シリコン材料、及びカーボンナノチューブを混合し複合体を得る工程、
（２）前記工程（１）で得た複合体と、黒鉛及びピッチとを乾式混合する工程、並びに
（３）前記工程（２）で得た混合物を前記ピッチの熱分解温度以上で熱処理する工程
を備える、製造方法。
項２．前記導電性炭素粒子の配合量が、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に記載の製造方法。
項３．前記カーボンナノチューブの配合量が、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に記載の製造方法。
項４．前記シリコン材料が、シリコン粒子である、項１〜３のいずれかに記載の製造方法。
項５．前記シリコン粒子の平均粒子径が、１ｎｍ〜１００μｍである、項４に記載の製造方法。
項６．前記カーボンナノチューブの平均外径が、１ｎｍ〜５００ｎｍである、項１〜５のいずれかに記載の製造方法。
項７．前記シリコン材料は、表面が酸化している、項１〜６のいずれかに記載の製造方法。
項８．前記ピッチの軟化点が１５０〜３００℃である、項１〜７のいずれかに記載の製造方法。
項９．前記工程（１）における混合が乾式混合である、項１〜８のいずれかに記載の製造方法。
項１０．前記工程（２）において、前記黒鉛の使用量が、前記複合体１００重量部に対して２５〜３５００重量部である、項１〜９のいずれかに記載の製造方法。
項１１．前記工程（２）において、前記ピッチの使用量が、前記複合体１００重量部に対して１０〜１００重量部である、項１〜１０のいずれかに記載の製造方法。
項１２．前記工程（３）において、前記閉空間内の雰囲気が不活性雰囲気又は還元性雰囲気である、項１〜１１のいずれかに記載の製造方法。
項１３．前記工程（３）における加熱温度が６００〜１１００℃である、項１〜１２のいずれかに記載の製造方法。
項１４．集電体上に、項１〜１３のいずれかに記載の製造方法により得ら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配置する工程
を備える、リチウム二次電池用負極の製造方法。
項１５．項１４に記載のリチウム二次電池用負極の製造方法により得られたリチウム二次電池用負極を形成する工程
を備える、リチウム二次電池の製造方法。
The present inventors have intensively researched in view of the above-mentioned problems. As a result, conductive carbon particles, a silicon material, and carbon nanotubes are mixed (especially dry mixing), then dry mixed with graphite and pitch, and raised to a temperature above the thermal decomposition temperature of pitch, so that conductive carbon particles can be simply and conveniently It has been found that it is possible to obtain a negative electrode material for a lithium secondary battery which can combine a silicon material and a carbon nanotube and has sufficient charge / discharge capacity, coulombic efficiency and cycle characteristics. The present invention has been completed by further research based on such findings. That is, the present invention includes the following configurations.
Item 1. What is claimed is: 1. A method for producing a negative electrode material for a lithium secondary battery, comprising conductive carbon particles, a silicon material, and carbon nanotubes,
(1) mixing conductive carbon particles, silicon material, and carbon nanotubes to obtain a composite,
(2) dry-mixing the composite obtained in step (1), graphite and pitch, and (3) heat-treating the mixture obtained in step (2) above the thermal decomposition temperature of the pitch A manufacturing method.
Item 2. Item 2. The method according to Item 1, wherein the content of the conductive carbon particles is 1 to 200 parts by weight with respect to 100 parts by weight of the silicon material.
Item 3. Item 3. The method according to Item 1 or 2, wherein the compounding amount 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 method according to any one of Items 1 to 3, wherein the silicon material is a silicon particle.
Item 5. Item 5. The production method according to Item 4, wherein the average particle diameter of the silicon particles is 1 nm to 100 μm.
Item 6. Item 6. The method according to any one of Items 1 to 5, wherein the average outer diameter of the carbon nanotubes is 1 nm to 500 nm.
Item 7. Item 7. The method according to any one of Items 1 to 6, wherein the silicon material has a surface oxidized.
Item 8. Item 8. The method according to any one of Items 1 to 7, wherein the softening point of the pitch is 150 to 300 ° C.
Item 9. Item 9. The method according to any one of Items 1 to 8, wherein the mixing in the step (1) is dry mixing.
Item 10. The method according to any one of Items 1 to 9, wherein in the step (2), the amount of the graphite used is 25 to 3500 parts by weight with respect to 100 parts by weight of the composite.
Item 11. The method according to any one of Items 1 to 10, wherein in the step (2), the amount of the pitch used is 10 to 100 parts by weight with respect to 100 parts by weight of the composite.
Item 12. Item 12. The method according to any one of Items 1 to 11, wherein in the step (3), the atmosphere in the closed space is an inert atmosphere or a reducing atmosphere.
Item 13. Item 13. The method according to any one of Items 1 to 12, wherein the heating temperature in the step (3) is 600 to 1100 ° C.
Item 14. The negative electrode active material layer for lithium secondary batteries provided with the process of arrange | positioning the negative electrode active material layer containing the negative electrode material for lithium secondary batteries obtained by the manufacturing method in any one of claim 1-13 on a collector. Method.
Item 15. The manufacturing method of a lithium secondary battery including the process of forming the negative electrode for lithium secondary batteries obtained by the manufacturing method of the negative electrode for lithium secondary batteries of Claim 14.
本発明によれば、簡便にシリコン材料とカーボンナノチューブと導電性炭素粒子とを複合化することができるとともに、この複合体と、黒鉛及びピッチとを簡便に複合化することができる。 According to the present invention, the silicon material, the carbon nanotube, and the conductive carbon particle can be easily complexed, and the complex, the graphite and the pitch can be complexed simply.
このため、シリコン材料の膨張を、他材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、本発明によれば、カーボンナノチューブを含ませることにより、導電性炭素粒子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。 Therefore, since the expansion of the silicon material can be absorbed by the other material, it is considered that the negative electrode material can be prevented from cracking or peeling off from the electrode due to the volume expansion. Further, according to the present invention, it is considered that by including carbon nanotubes, conductive carbon particles can be easily bound to each other, and higher electron conductivity can be imparted.
このため、本発明によれば、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、より簡便な方法で製造することができ、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ことができる。 Therefore, according to the present invention, it can be manufactured by a simpler method than conventional silicon-based negative electrode materials for lithium secondary batteries, and has sufficient charge / discharge capacity, coulombic efficiency and cycle characteristics. be able to.
１．リチウム二次電池用負極材料の製造方法
本発明のリチウム二次電池用負極材料の製造方法は、各成分を乾式混合した後に熱処理する方法が簡便である。
1. Method for Producing Negative Electrode Material for Lithium Secondary Battery In the method for producing a negative electrode material for lithium secondary battery of the present invention, it is easy to carry out a heat treatment after dry-mixing the respective components.
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の製造方法は、
（１）導電性炭素粒子、シリコン材料、及びカーボンナノチューブを混合し複合体を得る工程、
（２）前記工程（１）で得た複合体と、黒鉛及びピッチとを乾式混合する工程、並びに
（３）前記工程（２）で得た混合物を前記ピッチの熱分解温度以上で熱処理する工程
を備える。
From such a viewpoint, the method for producing a negative electrode material for a lithium secondary battery of the present invention is
(1) mixing conductive carbon particles, silicon material, and carbon nanotubes to obtain a composite,
(2) dry-mixing the composite obtained in step (1), graphite and pitch, and (3) heat-treating the mixture obtained in step (2) above the thermal decomposition temperature of the pitch Equipped with
工程（１）において使用する導電性炭素粒子としては、特に制限はなく、例えば、アセチレンブラック、ケッチェンブラック、カーボンブラック、グラフェン、膨張黒鉛、微粉黒鉛等が挙げられる。 There is no restriction | limiting in particular as an electroconductive carbon particle used in a process (1), For example, acetylene black, ketjen black, carbon black, a graphene, an expanded graphite, fine powder graphite etc. are mentioned.
導電性炭素粒子の平均粒子径は、特に制限されないが、通常３ｎｍ〜１０μｍ程度が好ましく、５ｎｍ〜２μｍ程度がより好ましい。導電性炭素粒子の平均粒子径を上記範囲内とすることにより、シリコン、カーボンナノチューブの双方との密着性がさらに増す。なお、導電性炭素粒子の平均粒子径は、電子顕微鏡（ＳＥＭ）により測定されるものとする。 The average particle size of the conductive carbon particles is not particularly limited, but is preferably about 3 nm to 10 μm, and more preferably about 5 nm to 2 μm. By setting the average particle diameter of the conductive carbon particles in the above range, the adhesion to both silicon and carbon nanotubes is further enhanced. In addition, the average particle diameter of electroconductive carbon particle shall be measured by an electron microscope (SEM).
工程（１）において使用する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 used in the step (1) is not particularly limited as long as it is a material containing silicon (in particular, a material comprising silicon), but powder of silicon material (preferably silicon particles) such as crystalline silicon and amorphous silicon It can be mentioned.
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 a silicon material (preferably silicon particles) such as crystalline silicon or amorphous silicon is not particularly limited, but generally crystalline silicon, amorphous silicon or the like made into particles (or powder) by cutting etc. may be used it can. Non-standard products, wastes and the like generated in the process of manufacturing and processing crystalline silicon, amorphous silicon and the like may be used. In addition, crystalline silicon, amorphous silicon or 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 or the like at the time of formation. Also, the silicon material may have its surface oxidized. These silicon materials may be used alone or in combination of two or more.
ただし、特に制限されるわけではないが、シリコン材料としては、充放電に伴う退席変化により割れることをより抑制するために、粒径は小さいほうが好ましい。 However, although not particularly limited, as the silicon material, it is preferable that the particle diameter be smaller in order to further suppress the cracking due to the change in the seat accompanying the charge and discharge.
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、１０〜１５０ｎｍ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 about 1 nm to 100 μm, preferably about 5 nm to 10 μm, and more preferably about 10 to 150 nm. By setting the average particle diameter of the silicon material within the above range, cracking is less likely to occur. In addition, the average particle diameter of a silicon material shall be measured by an electron microscope (SEM).
本発明で用いられる上述のようなシリコン材料は、通常、リチウム二次電池において用いられる電解質、例えば、非プロトン性の有機溶媒と塩とを含む電解液やリチウムイオンに対する活性点、すなわち、当該電解液と反応して電解液を分解したり、充放電時に移動するリチウムイオンと反応したりする活性点を部分的に有している。この活性点は、詳細が明らかではないが、一般的には、シリコン材料の外側に配向している。結晶子の端面（edge plane）や、膨張等で生じた割れの端面であると理解されている。 The silicon material as described above used in the present invention is generally an electrolyte used in a lithium secondary battery, for example, an active solution for an electrolyte containing an aprotic organic solvent and a salt or a lithium ion, that is, the electrolysis It partially has an active point that reacts with the liquid to decompose the electrolytic solution, or reacts with lithium ions moving during charge and discharge. This active point is generally oriented outside the silicon material, although the details are not clear. It is understood to be the edge plane of a crystallite, or the end surface of a crack produced by expansion or the like.
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。 In addition, as an aprotic organic solvent which comprises the above-mentioned electrolyte solution, ester, such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, gamma-butyrolactone, methyl formate, methyl acetate, is mentioned, for example. And the like; furans such as tetrahydrofuran and 2-methyltetrahydrofuran; ethers such as dioxolane, diethyl ether, dimethoxyethane, diethoxyethane and methoxyethoxyethane; dimethylsulfoxide; sulfolanes such as sulfolane and methylsulfolane; acetonitrile and the like . 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, salts dissolved in such aprotic organic solvents are, 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.
工程（１）において使用する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、より広い導電ネットワークの形成と、シリコン表面との密着性向上の点で、性能的には単層カーボンナノチューブが好ましく、入手のしやすさの点では多層カーボンナノチューブが好ましい。 The carbon nanotube used in the step (1) is a hollow carbon material in which a graphite sheet (that is, a carbon atom surface of a graphite structure or a graphene sheet) is closed in a tube shape, the diameter is a nanometer scale, and the wall structure is It has a graphite structure. A carbon nanotube whose shape is closed in a tube shape with a single graphite sheet (single-layer graphene sheet) is called single-walled carbon nanotube. On the other hand, carbon nanotubes in which a plurality of graphite sheets are closed in a tube shape and are nested are called multi-walled carbon nanotubes having a nested structure. In the present invention, although both single-walled carbon nanotubes and multi-walled carbon nanotubes can be adopted, single-walled carbon nanotubes are preferable in terms of performance in terms of forming a wider conductive network and improving adhesion with the silicon surface. Multi-walled carbon nanotubes are preferred in terms of ease of operation.
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。なお、カーボンナノチューブの平均外径は、電子顕微鏡（ＳＥＭ）により測定されるものとする。 In view of the fact that the average outer diameter of carbon nanotubes can be soft and cottony, and can be in various forms such as single or bundle, it becomes possible to embed silicon of various particle sizes, 1 -500 nm is preferable, 1-100 nm is more preferable, and 5-50 nm is more preferable. In addition, the average outer diameter of a carbon nanotube shall be measured by an electron microscope (SEM).
カーボンナノチューブの平均長さは、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。なお、カーボンナノチューブの平均長さは、電子顕微鏡（ＳＥＭ）により測定されるものとする。 The average length of the carbon nanotube makes it easier to absorb the volume change at the time of expansion of the silicon material, and further prevents the negative electrode material from cracking or peeling from the electrode due to the volume expansion, and the electricity by the expansion. From the viewpoint of preventing separation of the target conductive contact, 0.1 to 100 μm is preferable, and 1 to 10 μm is more preferable. In addition, the average length of a carbon nanotube shall be measured by an electron microscope (SEM).
カーボンナノチューブの平均アスペクト比は、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。なお、カーボンナノチューブの平均アスペクト比は、電子顕微鏡（ＳＥＭ）により測定されるものとする。 The average aspect ratio of the carbon nanotube makes it easier to absorb the volume change at the time of expansion of the silicon material, and from the viewpoint of suppressing further cracking or peeling of the negative electrode material due to the volume expansion, 5 to 100000. Is preferable, and 10 to 10000 is more preferable. In addition, the average aspect ratio of a carbon nanotube shall be measured by an electron microscope (SEM).
また、導電性炭素粒子、シリコン材料、及びカーボンナノチューブは、同時に混合してもよいし、逐次的に混合してもよい。なかでも、より簡便な工程となることから、導電性炭素粒子、シリコン材料、及びカーボンナノチューブを同時に混合することが好ましい。 Also, the conductive carbon particles, the silicon material, and the carbon nanotubes may be mixed simultaneously or may be mixed sequentially. Among them, it is preferable to simultaneously mix the conductive carbon particles, the silicon material, and the carbon nanotubes, since the process becomes simpler.
本発明では、各成分の配合量は、特に制限されない。具体的には、導電性炭素粒子の配合量は、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。導電性炭素粒子の配合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より追従してシリコンを包埋しやすくし、電気的コンタクトをより保持することができると考えられる。また、カーボンナノチューブの配合量は、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配合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より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より容易となる。 In the present invention, the blending amount of each component is not particularly limited. Specifically, the amount of the conductive carbon particles 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 amount of the conductive carbon particles in this range, it is considered that the expansion and contraction of silicon makes it easy to follow and embed the silicon, thereby further maintaining the electrical contact. The amount of carbon nanotubes is preferably 1 to 50 parts by weight, and more preferably 3 to 20 parts by weight with respect to 100 parts by weight of the silicon material. By setting the blending amount of carbon nanotubes within this range, it is considered that electrical contacts can be more retained even when silicon is expanded and shrunk, and at the same time, expensive conductive carbon nanotubes are not excessively used and alternative conductive materials are used. Is easier to add.
工程（１）において、混合の方法は特に制限されない。例えば、湿式混合であれば、適切な溶媒と混合後、溶媒を溜去すればよく、溶媒としては、エタノール、プロパノール、メタノール等のアルコール類、エチレンカーボネート、ジエチルカーボネート、ジメチルカーボネート、メチルエチルカーボネート、プロピレンカーボネート等のカーボネート類、その他、ジメチルホルムアミド（ＤＭＦ）、ジメチルスルホキシド（ＤＭＳＯ）、Ｎ−メチルピロリドン、ジオキサン等の極性溶媒等があげられる。この時の混合方法としては、一般的な撹拌、あるいは、超音波照射等、各種ホモジナイザーを使用できる。また、乾式混合であれば、高速気流に紛体粒子を吹き込み、粒子間衝突を促進する方法（高速気流紛体複合化法）や、紛体を混ぜるミキサーやナウター、さらには、シェアをかけて混ぜ合わせる、乳鉢、ボールミル、メカノフュージョン等を使用する方法を採用することができる。なかでも、簡便性を有し、量産化が容易で、且つ、ＣＮＴ等の原材料の損傷が少なく複合化できるという観点から、乾式混合が好ましく、乾式の高速気流紛体複合化法を使用する方法がより好ましい。具体的には、奈良機械製ハイブリダーゼーションシステムや、ホソカワミクロン製ファカルティ等がある。 In the step (1), the method of mixing is not particularly limited. For example, in the case of wet mixing, after mixing with a suitable solvent, the solvent may be distilled off, and as the solvent, alcohols such as ethanol, propanol and methanol, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, Carbonates such as propylene carbonate, and other polar solvents such as dimethylformamide (DMF), dimethylsulfoxide (DMSO), N-methylpyrrolidone, dioxane and the like can be mentioned. As a mixing method at this time, various homogenizers such as general stirring or ultrasonic irradiation can be used. Also, in the case of dry mixing, powder particles are blown into a high-speed air stream to promote collision between particles (high-speed air-flow powder composite method), a mixer or Nauta for mixing powders, and furthermore, they are mixed using shear. A method using mortar, ball mill, mechanofusion, etc. can be adopted. Among them, dry mixing is preferred from the viewpoint of simplicity, easy mass production, and less damage to raw materials such as CNTs, and a method using dry high-speed air-flow powder composite method is preferable. More preferable. Specifically, there are a hybridization system made by Nara Machine Co., Ltd., and a Faculty made by Hosokawa Micron.
工程（１）において、混合（特に乾式混合）の雰囲気は、導電性炭素粒子、シリコン材料、及びカーボンナノチューブをより十分に複合化できれば特に制限されないが、大気雰囲気下とすることが簡便である。また、窒素ガス雰囲気下、アルゴンガス雰囲気下等の不活性ガス雰囲気下に行ってもよい。 In the step (1), the mixed (in particular, dry mixed) atmosphere is not particularly limited as long as the conductive carbon particles, the silicon material, and the carbon nanotube can be sufficiently compounded, but it is convenient to use an atmosphere. In addition, the reaction may be performed under an inert gas atmosphere such as a nitrogen gas atmosphere or an argon gas atmosphere.
工程（１）において、混合（特に乾式混合）時の温度は導電性炭素粒子、シリコン材料、及びカーボンナノチューブをより十分に複合化できれば特に制限されないが、室温付近とすることが簡便である。このような観点から、混合（特に乾式混合）時の温度は５〜８０℃が好ましく、１０〜５０℃がより好ましい。 In the step (1), the temperature during mixing (in particular, dry mixing) is not particularly limited as long as the conductive carbon particles, the silicon material, and the carbon nanotube can be sufficiently compounded, but it is convenient to set it around room temperature. From such a viewpoint, the temperature at the time of mixing (particularly, dry mixing) is preferably 5 to 80 ° C., and more preferably 10 to 50 ° C.
工程（１）において、混合（特に乾式混合）の時間は特に制限されないが、導電性炭素粒子、シリコン材料、及びカーボンナノチューブをより十分に複合化して充放電容量、クーロン効率及びサイクル特性をより向上させる観点から、０．２〜１０時間が好ましく、１〜３時間がより好ましい。 In the step (1), the time of mixing (in particular, dry mixing) is not particularly limited, but conductive carbon particles, silicon material, and carbon nanotubes are sufficiently compounded to further improve charge / discharge capacity, coulombic efficiency and cycle characteristics. It is preferable that the time be 0.2 to 10 hours, and more preferably 1 to 3 hours from the viewpoint of
工程（２）において使用する黒鉛としては、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 a graphite used in a process (2), 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 the graphite is not particularly limited, and may be, for example, a spherical shape, an elliptical shape, a square shape, a flake shape, a plate shape such as a flake shape, a rod shape, an amorphous shape, or the like. Those having a high specific surface area are preferable, and spherical or oval shapes are preferable.
工程（２）で用いられるピッチは、公知又は市販の各種ピッチを使用することができる。 As the pitch used in step (2), various known or commercially available pitches can be used.
このようなピッチの軟化点は、昇温過程で副反応をより抑制しつつより適切な温度でピッチのコーティングをより十分に行う観点から、１５０〜３００℃が好ましく、１８０〜２７０℃がより好ましい。なお、ピッチの軟化点は、ASTM D3104の規格にしたがって測定するものとする。 The softening point of such a pitch is preferably 150 to 300 ° C., more preferably 180 to 270 ° C., from the viewpoint of more sufficiently coating the pitch at a more appropriate temperature while suppressing side reactions in the temperature raising process. . In addition, the softening point of pitch shall be measured according to the specification of ASTM D3104.
上記のような条件を満たすピッチとしては、例えば、石炭系等方性ピッチ等の石炭系ピッチ；石油系等方性ピッチ等の石油系ピッチ等が挙げられるが、充放電容量、クーロン効率及びサイクル特性をより向上させる観点から、石炭系ピッチが好ましく、石炭系等方性ピッチがより好ましい。これらのピッチは、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 pitches that satisfy the above conditions include coal-based pitches such as coal-based isotropic pitch; petroleum-based pitches such as petroleum-based isotropic pitch, etc .; charge and discharge capacity, coulombic efficiency and cycle From the viewpoint of further improving the characteristics, a coal-based pitch is preferable, and a coal-based isotropic pitch is more preferable. These pitches may be used alone or in combination of two or more.
複合体と、黒鉛及びピッチとの混合比率は、特に制限されないが、より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さらに向上させる観点から、複合体１００重量部に対して、前記黒鉛の配合量が２５〜３５００重量部（特に５００〜２０００重量部）であることが好ましく、前記ピッチの配合量が１０〜１００重量部（特に２０〜８０重量部）がより好ましい。 The mixing ratio of the composite to the graphite and the pitch is not particularly limited, but from the viewpoint of further improving charge / discharge capacity and cycle characteristics while maintaining the coulombic efficiency, the above-mentioned graphite can be added to 100 parts by weight of the composite. The blending amount of is preferably 25 to 3500 parts by weight (especially 500 to 2000 parts by weight), and the blending amount of the pitch is more preferably 10 to 100 parts by weight (especially 20 to 80 parts by weight).
工程（２）において、乾式混合の方法は特に制限されない。例えば、高速気流に紛体粒子を吹き込み、粒子間衝突を促進する方法（高速気流紛体複合化法）や、紛体を混ぜるミキサーやナウター、さらには、シェアをかけて混ぜ合わせる、乳鉢、ボールミル、メカノフュージョン等を使用する方法を採用することができる。なかでも、簡便性を有し、量産化が容易で、且つ、ＣＮＴ等の原材料の損傷が少なく複合化できるという観点から、乾式の高速気流紛体複合化法を使用する方法が好ましい。具体的には、奈良機械製ハイブリダーゼーションシステムや、ホソカワミクロン製ファカルティ等がある。 In the step (2), the method of dry mixing is not particularly limited. For example, powder particles are blown into high-speed air flow to promote collision between particles (high-speed air-flow powder composite method), mixers and Nauta mixing powders, and further, shear and mix, mortar, ball mill, mechanofusion It is possible to adopt a method of using Among them, a method using a dry high-speed air-flow powder composite method is preferable from the viewpoint of simplicity, easy mass production, and little damage to raw materials such as CNTs. Specifically, there are a hybridization system made by Nara Machine Co., Ltd., and a Faculty made by Hosokawa Micron.
工程（２）において、乾式混合の雰囲気は、複合体、黒鉛、及びピッチを十分に混合できれば特に制限されないが、大気雰囲気下とすることが簡便である。また、窒素ガス雰囲気下、アルゴンガス雰囲気下等の不活性ガス雰囲気下に行ってもよい。 In the step (2), the dry mixing atmosphere is not particularly limited as long as the composite, the graphite, and the pitch can be sufficiently mixed, but it is convenient to use the atmosphere. In addition, the reaction may be performed under an inert gas atmosphere such as a nitrogen gas atmosphere or an argon gas atmosphere.
工程（２）において、乾式混合時の温度は複合体、黒鉛、及びピッチをより十分に複合化できれば特に制限されないが、室温付近とすることが簡便である。このような観点から、乾式混合時の温度は５〜８０℃が好ましく、１０〜５０℃がより好ましい。 In the step (2), the temperature during dry mixing is not particularly limited as long as the composite, the graphite, and the pitch can be sufficiently complexed, but it is convenient to set it around room temperature. From such a viewpoint, 5 to 80 ° C. is preferable, and 10 to 50 ° C. is more preferable as the temperature during dry mixing.
工程（２）において、乾式混合の時間は特に制限されないが、複合体、黒鉛、及びピッチをより十分に複合化して充放電容量、クーロン効率及びサイクル特性をより向上させる観点から、１分〜１０時間が好ましく、３分〜３時間がより好ましい。 In the step (2), the dry mixing time is not particularly limited, but from the viewpoint of more fully complexing the composite, the graphite and the pitch to further improve the charge / discharge capacity, the coulombic efficiency and the cycle characteristics, 1 minute to 10 minutes. The time is preferred, and 3 minutes to 3 hours are more preferred.
次に、工程（３）においては、上記した工程（２）で得た混合物（導電性炭素粒子、シリコン材料、カーボンナノチューブ、黒鉛及びピッチを含有する混合物、特に導電性炭素粒子、シリコン材料、カーボンナノチューブ、黒鉛及びピッチを含有する複合体）を、熱処理する（具体的には、前記ピッチの熱分解温度以上に高める）ことで、リチウム二次電池用負極材料を得ることができる。 Next, in the step (3), the mixture obtained in the above step (2) (conductive carbon particles, silicon material, carbon nanotubes, a mixture containing graphite and pitch, particularly conductive carbon particles, silicon material, carbon Heat treatment (specifically, raising the temperature to a temperature above the thermal decomposition temperature of the pitch) of the composite containing nanotubes, graphite and pitch) can provide a negative electrode material for a lithium secondary battery.
このように、本発明においては、シリコン材料の膨張を、他材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ともに、シリコン材料の活性点をピッチの熱分解生成物により覆うことができることから電解液を分解したり充放電時に移動するリチウムイオンと反応したりすることを抑制することもできる。このため、本発明の製造方法は、非常に簡便な手法でありながら、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負極材料を得ることができる。 As described above, in the present invention, since the expansion of the silicon material can be absorbed by another material, it is possible to prevent the negative electrode material from being broken or peeled off from the electrode due to the volume expansion. Since the active point of the silicon material can be covered with the thermal decomposition product of the pitch, the decomposition of the electrolytic solution and the reaction with lithium ions moving during charge and discharge can be suppressed. Therefore, the production method of the present invention can provide a negative electrode material for a lithium secondary battery having sufficient charge / discharge capacity, coulombic efficiency and cycle characteristics while being a very simple method.
工程（３）において、加熱処理をする際の雰囲気は、シリコンの酸化被膜形成や炭素の燃焼をより避ける観点から、窒素ガス雰囲気、アルゴンガス雰囲気等の不活性ガス雰囲気や、上記した不活性ガスと水素との混合ガス等の還元性ガス雰囲気下等において熱処理することが好ましいが、厳密な雰囲気制御は必要ではない。 In the step (3), the atmosphere at the time of the heat treatment is an inert gas atmosphere such as a nitrogen gas atmosphere or an argon gas atmosphere or the above-mentioned inert gas from the viewpoint of avoiding formation of oxide film of silicon and combustion of carbon more. Heat treatment is preferably performed in a reducing gas atmosphere such as a mixed gas of hydrogen and hydrogen, but strict control of the atmosphere is not necessary.
また、加熱処理は、減圧又は常圧（０．１Ｐａ〜０．１５ＭＰａ程度）で行うのが好ましいが、常圧（０．０５〜０．１５ＭＰａ程度）で行うのが簡便である。また、加熱処理の温度は、特に（Ｂ）の方法を採用する場合にはピッチの熱分解温度以上であれば特に制限はないが、通常、６００〜１１００℃に設定するのが好ましく、８００〜１０００℃に設定するのがより好ましい。加熱温度をこの範囲とすることにより、充放電容量やクーロン効率をより維持しつつ、工程（２）で得た混合物（特に工程（２）で得た混合物中に含まれるシリコン材料）とピッチの熱分解生成物とをより十分に反応させてリチウムイオンや電解液とより反応しにくい負極材料が得られる。 The heat treatment is preferably carried out under reduced pressure or normal pressure (about 0.1 Pa to 0.15 MPa), but it is convenient to carry out heat treatment under normal pressure (about 0.05 to 0.15 MPa). The temperature of the heat treatment is not particularly limited as long as it is at least the thermal decomposition temperature of the pitch, particularly when the method (B) is adopted, but in general, the temperature is preferably set to 600 to 1100 ° C. It is more preferable to set to 1000 ° C. By keeping the heating temperature in this range, the charge / discharge capacity and the coulombic efficiency are maintained, and the mixture obtained in step (2) (particularly the silicon material contained in the mixture obtained in step (2)) and the pitch The thermal decomposition product is reacted more sufficiently to obtain a negative electrode material that is less likely to react with lithium ions and the electrolyte solution.
加熱時間は、加熱温度、得ようとする負極材料中のピッチの熱分解生成物の含有量等に応じて適宜設定すればよいが、０．１〜３０時間が好ましく、０．５〜５時間がより好ましい。 The heating time may be appropriately set according to the heating temperature, the content of the thermal decomposition product of the pitch in the negative electrode material to be obtained, etc., but 0.1 to 30 hours is preferable, and 0.5 to 5 hours Is more preferred.
これにより得られるリチウム二次電池用負極材料においては、混合物中のシリコン材料の主として活性点が選択的にピッチの熱分解生成物と反応し、電解液やリチウムイオンに対して不活性化されている。つまり、この負極材料は、混合物全体又はシリコン材料全体が、ピッチの熱分解生成物を含むコーティング層で完全に被覆されているわけではなく、シリコン材料表面の活性点が、ピッチの熱分解生成物を含むコーティング層で被覆されることにより不活性化されていると考えられる。 In the negative electrode material for a lithium secondary battery thus obtained, mainly the active site of the silicon material in the mixture selectively reacts with the thermal decomposition product of the pitch and is inactivated to the electrolytic solution and lithium ions. There is. That is, this negative electrode material is not completely covered with the entire mixture or the entire silicon material with the coating layer containing the thermal decomposition product of pitch, and the active point of the silicon material surface is the thermal decomposition product of pitch. It is considered to be inactivated by being coated with a coating layer containing
このようにして得られるリチウム二次電池用負極材料においては、シリコン材料の膨張を他材によって吸収することができることから割れたり剥がれたりしにくく、サイクル特性をより向上させることができる。また、上述のような電解液やリチウムイオンと反応しにくく、電解液を分解しにくく、充放電に関与するリチウムイオンを補足しにくいとともにそれ自体も電解液との反応による破壊を受け難い。また、特にシリコン材料の表面が部分的にしか被覆されないので、充放電時のリチウムイオンの通過を安定に確保することができ、充放電容量が低下しにくく、クーロン効率も高い。 In the negative electrode material for a lithium secondary battery thus obtained, since the expansion of the silicon material can be absorbed by another material, it is difficult to be broken or peeled off, and the cycle characteristics can be further improved. In addition, it is difficult to react with the above-described electrolytic solution and lithium ion, to decompose the electrolytic solution, to hardly capture lithium ions involved in charge and discharge, and to be destroyed by reaction with the electrolytic solution. Further, in particular, since the surface of the silicon material is only partially covered, the passage of lithium ions during charge and discharge can be stably ensured, the charge and discharge capacity is hardly reduced, and the coulombic efficiency is also high.
２．リチウム二次電池用負極の製造方法
本発明では、集電体上に、上記のようにして得られるリチウム二次電池用負極材料を含む負極活物質層を配置する工程を備える本発明の製造方法により、リチウム二次電池用負極を簡便に得ることができる。
2. Method for Producing Negative Electrode for Lithium Secondary Battery In the present invention, the method for producing the present invention comprises the step of disposing a negative electrode active material layer containing the negative electrode material for lithium secondary battery obtained as described above on a current collector. Thus, the negative electrode for lithium secondary battery can be easily obtained.
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 metal such as copper, for example, in the form of a foil or a mesh.
また、負極活物質層は、上記リチウム二次電池用負極材料を含んでいてもよいし、上記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。 Further, the negative electrode active material layer may contain the above-mentioned negative electrode material for lithium secondary battery, or may be composed of the composition for forming a negative electrode active material layer for the above lithium secondary battery.
当該負極活物質層が上記リチウム二次電池用負極材料を含んでいる場合は、上記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 said negative electrode material for lithium secondary batteries, it is preferable to contain a binder besides the said negative electrode material for lithium secondary batteries. The binder is not particularly limited as long as it is a binder used in a lithium secondary battery, but specifically, fluorine-based polymers (polyvinylidene fluoride resin, polytetrafluoroethylene resin, etc.), polyolefin-based polymers, synthetic rubbers And the like 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 falls within the category generally understood as carbon, but, for example, carbon such as natural graphite, artificial graphite, mesocarbon microbeads, mesophase pitch powder, isotropic pitch powder, resin charcoal and the like What baked the precursor, etc. can be mentioned. These carbon materials may be used alone or in combination of two or more.
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。 Particularly preferable carbon materials used in the present invention are carbon materials having an average interplanar spacing d002 of 0.340 nm or less, particularly 0.335 to 0.340 nm, obtained by X-ray diffraction method. 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-mentioned carbon material are not particularly limited, and various materials such as scaly, massive, fibrous, whisker, spherical, crushed and the like can be used. The carbon material may be a mixture of two or more types of 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。 Further, the average particle diameter of such a carbon material is not particularly limited, and usually, about 1 to 50 μm is preferable, and about 5 to 30 μm is more preferable. In addition, the average particle diameter of a graphite-type carbon material shall be measured by 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、上記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。 The content of each component in the negative electrode active material layer as described above is not particularly limited, but 50 to 100 parts by weight (particularly 70 to 95 parts by weight) of the above-mentioned negative electrode material for lithium secondary battery, 0 to 30 binders. Weight parts (especially 3 to 15 parts by weight), 0 to 40 parts by weight (especially 0 to 5 parts by weight) of a carbon material, and 100 parts by weight in total, such as volume, coulombic efficiency, repetitive characteristics, energy efficiency, etc. It is preferable from the viewpoint of
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。 The thickness of the negative electrode active material layer is not particularly limited, but it is preferable to be thin in terms of securing ion penetration and electrical conductivity and reducing peeling even when rolled, but it is called energy density per electrode. From the viewpoint that the thicker one is better in point, 5 to 500 μm is preferable, and 10 to 250 μm is more preferable.
このようなリチウム二次電池用負極を形成する場合は、上記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、上記負極活物質層が上記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、上記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 above-mentioned negative electrode material for a lithium secondary battery is mixed with a binder and a graphite-based carbon material as required to form a paste, and the paste is placed on a current collector It is preferable to apply | coat to and to form a negative electrode active material layer. Moreover, when the said negative electrode active material layer consists of a composition for negative electrode active material layer formation for said lithium secondary batteries, it similarly collects the composition for negative electrode active material layers formation for said lithium secondary batteries. It is preferable to apply | coat on top and to form a negative electrode active material layer.
３．リチウム二次電池の製造方法
上記のようにして得られるリチウム二次電池用負極を形成する工程を備える製造方法により、リチウム二次電池を製造することができる。
3. Method of Manufacturing Lithium Secondary Battery A lithium secondary battery can be manufactured by the manufacturing method including the step of forming the negative electrode for a lithium secondary battery obtained as described above.
また、リチウム二次電池は、上記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。 In addition to the above-described negative electrode for lithium secondary battery, the lithium secondary battery can be provided with a positive electrode applied to a known lithium secondary battery, an electrolytic solution, and a container for containing these.
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 a mixture of a lithium-containing oxide, for example, a lithium composite oxide such as LiCoO 2 and a known binder to form a paste, which is applied onto a positive electrode current collector such as a metal. . In addition, although an aluminum foil is generally used as a collector, the thing similar to a negative electrode 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。この非プロトン性有機溶媒及び非プロトン性有機溶媒に溶解される塩としては、上記したものが挙げられる。 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 non-woven fabric or the like for preventing a short circuit between the positive electrode and the negative electrode. The separator is impregnated and held. Examples of the aprotic organic solvent and the salt dissolved in the aprotic organic solvent include those described above.
このようなリチウム二次電池は、負極に上記リチウム二次電池用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 such a lithium secondary battery uses the above-described negative electrode material for a lithium secondary battery as the negative electrode, the charge / discharge capacity and cycle characteristics of the negative electrode are high, and the active material mass of the positive electrode can be suppressed. For this reason, this lithium secondary battery does not need to use a large container for containing a large amount of positive electrode active material, and therefore, can be miniaturized as compared with the conventional one, and has a large charge / discharge capacity, In addition, since the negative electrode hardly reacts with the electrolyte, the safety is high.
なお、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, it can replace with the above-mentioned electrolyte solution, and lithium secondary battery can be implemented similarly, also when using other electrolytes, such as a well-known inorganic solid electrolyte and a solid polymer 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 by way of examples, but the present invention is not limited by these examples.
実施例１
入れ子構造の多層カーボンナノチューブ（ＡＬＫＥＭＡ社製Ｃ１００）４００ｍｇ、導電性炭素粒子（電気化学工業（株）製のデンカブラック）１２００ｍｇ、平均粒径２μｍのシリコン粉末２８００ｍｇをエタノール１６０ｍｌに入れ、超音波ホモジナイザーで２時間混合したのち、濾過し、複合固形物（４４００ｍｇ）を得た。
Example 1
Add 400 mg of multi-walled carbon nanotubes with nested structure (C100 made by ALKEMA), 1200 mg of conductive carbon particles (Denka Black made by Denki Kagaku Kogyo Co., Ltd.) and 2800 mg of silicon powder with an average particle diameter of 2 μm in 160 ml of ethanol After mixing for 2 hours, it was filtered to obtain a composite solid (4400 mg).
室温で、得られた混合物と平均粒径１７μｍの黒鉛３９．６ｇ、石炭系等方性ピッチ（軟化点２８５℃）２２００ｍｇとを同じ袋に入れて５分振ることで固体混合し、炭化炉内に配置した。そして、炭化炉内を窒素ガスで満たした後、常圧（０．１ＭＰａ）で１０リットル／分の窒素を流しながら、炭化炉内の温度を３００℃／時の昇温速度で９５０℃まで高めて１．０時間加熱処理し、実施例１のリチウム二次電池用負極材料を得た。この負極材料のリチウム電池としての特性を単セル評価した結果を表１に示す。 The mixture obtained at room temperature, 39.6 g of graphite having an average particle diameter of 17 μm, and 2200 mg of coal-based isotropic pitch (softening point 285 ° C.) are put in the same bag and shaken for 5 minutes to mix solids; Placed in Then, after the inside of the carbonization furnace is filled with nitrogen gas, the temperature in the carbonization furnace is raised to 950 ° C. at a temperature rising rate of 300 ° C./hour while flowing nitrogen at 10 liters / minute under normal pressure (0.1 MPa) The mixture was heat-treated for 1.0 hour to obtain a negative electrode material for a lithium secondary battery of Example 1. The results of single-cell evaluation of the characteristics of the negative electrode material as a lithium battery are shown in Table 1.
比較例１
平均粒径２μｍのシリコン粒子２．８ｇ、アセチレンブラック１．２ｇ、カーボンナノチューブ０．４ｇをエタノール１６０ｍｌに入れ、超音波ホモジナイザーで２時間混合したのち、ろ過し、混合固形物（４．４ｇ）を得た。
Comparative Example 1
2.8 g of silicon particles having an average particle diameter of 2 μm, 1.2 g of acetylene black and 0.4 g of carbon nanotubes are put into 160 ml of ethanol, mixed with an ultrasonic homogenizer for 2 hours, and filtered to obtain a mixed solid (4.4 g) Obtained.
混合固形物を１２時間真空乾燥したのち、炭化炉内に配置した。そして、炭化炉内を窒素ガスで満たした後、常圧（０．１ＭＰａ）で１０リットル／分の窒素を流しながら、９５０℃まで昇温し９５０℃で１時間保持後、放冷したものを、予め、室温で、平均粒径１７μｍの黒鉛３９．６ｇ、軟化点２８５℃のピッチ２．０ｇを５分固体混合し、常圧（０．１ＭＰａ）で９５０℃まで昇温し９５０℃で１時間保持後放冷したものと混合することで、負極材料を得た。この負極材料のリチウム電池としての特性を単セル評価した結果を表１に示す。 The mixed solid was vacuum dried for 12 hours and then placed in a carbonizing furnace. Then, after the inside of the carbonization furnace is filled with nitrogen gas, the temperature is raised to 950 ° C. and held at 950 ° C. for 1 hour while flowing nitrogen at a normal pressure (0.1 MPa) at 10 liters / min. In advance, 39.6 g of graphite having an average particle diameter of 17 μm at room temperature, and 2.0 g of pitch at a softening point of 285 ° C. are solid mixed for 5 minutes, heated to 950 ° C. under normal pressure (0.1 MPa), and 1 at 950 ° C. The negative electrode material was obtained by mixing with what was stood to cool after hold | maintaining time. The results of single-cell evaluation of the characteristics of the negative electrode material as a lithium battery are shown in Table 1.
実施例２
平均粒径２μｍのシリコン粒子２．８ｇ、アセチレンブラック１．２ｇ、カーボンナノチューブ０．４ｇをエタノール１６０ｍｌに入れ、超音波ホモジナイザーで２時間混合したのち、ろ過し、混合固形物を得た（４．４ｇ）。
Example 2
2.8 g of silicon particles having an average particle diameter of 2 μm, 1.2 g of acetylene black and 0.4 g of carbon nanotubes were placed in 160 ml of ethanol, mixed by an ultrasonic homogenizer for 2 hours, and filtered to obtain a mixed solid (4. 4g).
混合固形物を１２時間真空乾燥したのち、室温で、平均粒径１７μｍの黒鉛３９．６ｇ、軟化点２８５℃のピッチ２．２ｇと５分固体混合し、常圧（０．１ＭＰａ）で１０リットル／分の窒素を流しながら、１０００℃まで昇温し１０００℃で１時間保持後放冷することで、負極材料を得た。この負極材料のリチウム電池としての特性を単セル評価した結果を表１に示す。 The mixed solid is vacuum dried for 12 hours, then mixed with 39.6 g of graphite having an average particle diameter of 17 μm, 2.2 g of pitch having a softening point of 285 ° C. and solid for 5 minutes at room temperature, and 10 liters under normal pressure (0.1 MPa) While flowing nitrogen per minute, the temperature was raised to 1000 ° C., held at 1000 ° C. for 1 hour, and allowed to cool, thereby obtaining an anode material. The results of single-cell evaluation of the characteristics of the negative electrode material as a lithium battery are shown in Table 1.
実施例３
平均粒径２μｍのシリコン粒子２．８ｇ、アセチレンブラック１．２ｇ、カーボンナノチューブ０．４ｇをエタノール１６０ｍｌに入れ、超音波ホモジナイザーで１時間混合したのち、ろ過し、混合固形物を得た（４．４ｇ）。
Example 3
2.8 g of silicon particles having an average particle diameter of 2 μm, 1.2 g of acetylene black and 0.4 g of carbon nanotubes were added to 160 ml of ethanol, mixed with an ultrasonic homogenizer for 1 hour, and filtered to obtain a mixed solid (4. 4g).
混合固形物を１２時間真空乾燥したのち、室温で、平均粒径１７μｍの黒鉛３９．６ｇ、軟化点２８５℃のピッチ２．２ｇと５分固体混合し、常圧（０．１ＭＰａ）で１０リットル／分の窒素を流しながら、９５０℃まで昇温し９５０℃で１時間保持後放冷することで、負極材料を得た。この負極材料のリチウム電池としての特性を単セル評価した結果を表１に示す。 The mixed solid is vacuum dried for 12 hours, then mixed with 39.6 g of graphite having an average particle diameter of 17 μm, 2.2 g of pitch having a softening point of 285 ° C. and solid for 5 minutes at room temperature, and 10 liters under normal pressure (0.1 MPa) While flowing nitrogen per minute, the temperature was raised to 950 ° C., held at 950 ° C. for 1 hour, and allowed to cool, whereby a negative electrode material was obtained. The results of single-cell evaluation of the characteristics of the negative electrode material as a lithium battery are shown in Table 1.
実施例４
平均粒径２μｍのシリコン粒子２．８ｇ、アセチレンブラック１．２ｇ、カーボンナノチューブ０．４ｇをエタノール１６０ｍｌに入れ、超音波ホモジナイザーで１時間混合したのち、ろ過し、混合固形物を得た（４．４ｇ）。
Example 4
2.8 g of silicon particles having an average particle diameter of 2 μm, 1.2 g of acetylene black and 0.4 g of carbon nanotubes were added to 160 ml of ethanol, mixed with an ultrasonic homogenizer for 1 hour, and filtered to obtain a mixed solid (4. 4g).
混合固形物を１２時間真空乾燥したのち、室温で、平均粒径１７μｍの黒鉛３９．６ｇ、軟化点２８５℃のピッチ２．２ｇを５分固体混合し、常圧（０．１ＭＰａ）で１０リットル／分の窒素を流しながら、１０００℃まで昇温し１０００℃で１時間保持後放冷することで、負極材料を得た。この負極材料のリチウム電池としての特性を単セル評価した結果を表１に示す。 The mixed solid is vacuum dried for 12 hours, and then 39.6 g of graphite having an average particle diameter of 17 μm and a pitch of 2.2 g with a softening point of 285 ° C. are mixed for 5 minutes at room temperature for 10 liters under normal pressure (0.1 MPa). While flowing nitrogen per minute, the temperature was raised to 1000 ° C., held at 1000 ° C. for 1 hour, and allowed to cool, whereby a negative electrode material was obtained. The results of single-cell evaluation of the characteristics of the negative electrode material as a lithium battery are shown in Table 1.
比較例２
平均粒径２μｍのシリコン粒子２．８ｇ、アセチレンブラック１．２ｇをエタノール１６０ｍｌに入れ、超音波ホモジナイザーで２時間混合したのち、ろ過し、混合固形物を得た（４．４ｇ）。
Comparative example 2
2.8 g of silicon particles having an average particle diameter of 2 μm and 1.2 g of acetylene black were added to 160 ml of ethanol, mixed with an ultrasonic homogenizer for 2 hours, and filtered to obtain a mixed solid (4.4 g).
混合固形物を１２時間真空乾燥したのち、室温で、平均粒径１７μｍの黒鉛３６ｇ、軟化点２８５℃のピッチ２．０ｇを５分固体混合し、常圧（０．１ＭＰａ）で１０リットル／分の窒素を流しながら、９５０℃まで昇温し９５０℃で１時間保持後放冷することで、負極材料を得た。この負極材料のリチウム電池としての特性を単セル評価した結果を表１に示す。 The mixed solid is vacuum dried for 12 hours, and then, at room temperature, 36 g of graphite having an average particle diameter of 17 μm and a 2.0 g pitch having a softening point of 285 ° C. are solid mixed for 5 minutes. The negative electrode material was obtained by raising the temperature to 950.degree. C. and holding at 950.degree. C. for 1 hour while flowing nitrogen. The results of single-cell evaluation of the characteristics of the negative electrode material as a lithium battery are shown in Table 1.
実施例５
入れ子構造の多層カーボンナノチューブ（ＡＬＫＥＭＡ社製Ｃ１００）１ｇ、平均粒径２μｍのシリコン粉末５ｇ、平均粒径１７μｍの黒鉛１００ｇを、奈良機械製ハイブリダイゼーションシステムＮＨＳ−１を用いて混合した。ローター回転速度：４８００回転／分、処理時間：５分の条件とした。
Example 5
1 g of nested carbon nanotubes (C100 manufactured by ALKEMA), 5 g of silicon powder having an average particle diameter of 2 μm, and 100 g of graphite having an average particle diameter of 17 μm were mixed using a hybridization system NHS-1 manufactured by Nara Machine Co., Ltd. Rotor rotational speed: 4800 rpm, processing time: 5 minutes.
室温で、得られた混合物１０ｇと石炭系等方性ピッチ（軟化点２８５℃）０．５ｇとを同じ袋に入れて振ることで５分固体混合し、炭化炉内に配置した。そして、常圧（０．１ＭＰａ）で１０リットル／分の窒素を流しながら、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１．０時間加熱処理し、実施例５のリチウム二次電池用負極材料を得た。この負極材料のリチウム電池としての特性を単セル評価した結果を表１に示す。 At room temperature, 10 g of the obtained mixture and 0.5 g of a coal-based isotropic pitch (softening point 285 ° C.) were put in the same bag, shaken for 5 minutes, and mixed for 5 minutes, and placed in a carbonization furnace. Then, after filling the inside of the carbonizing furnace with nitrogen gas while flowing nitrogen at 10 liters / minute under normal pressure (0.1 MPa), the temperature in the carbonizing furnace is raised to 950 ° C. at a temperature rising rate of 300 ° C./hour. The mixture was heat-treated for 1.0 hour to obtain a negative electrode material for a lithium secondary battery of Example 5. The results of single-cell evaluation of the characteristics of the negative electrode material as a lithium battery are shown in Table 1.
［充放電試験用セルの製造］
上記の実施例１〜５又は比較例１〜２で得た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、ガラスセルにセットした。この際、電極厚みは６０μｍ、電極密度は１．６ｇ／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のエチレンカーボネート／エチルメチルカーボネート（ＥＣ／ＭＥＣ）＝１：２（体積比）を電解液 とし、対極はリチウム金属（１１ｍｍ×１１ｍｍ×０．２ｍｍ）を用いた。組み立ては、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]
The negative electrode composite material for lithium secondary batteries (composition for negative electrode active material layer formation for lithium secondary batteries) obtained in Examples 1 to 5 or Comparative Examples 1 and 2 described above was set in a glass cell. At this time, the electrode thickness was adjusted to 60 μm, and the electrode density was adjusted to 1.6 g / cm 3 . A glass filter is used for the separator, and ethylene carbonate / ethyl methyl carbonate (EC / MEC) = 1: 2 (volume ratio) of 1 M LiPF 6 is used as an electrolyte solution, and the counter electrode is lithium metal (11 mm × 11 mm × 0.2 mm) Was used. The assembly was performed in a glove box with a dew point of −80 ° C. or less under an argon atmosphere.
これにより、実施例１〜５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 charge / discharge tests was obtained about Examples 1-5 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２５℃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）負極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）さらに、０．００１Ｖの定電圧で、８時間充電
（ＩＩＩ）負極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 1: Charge and Discharge Test]
The charge / discharge test cell obtained above was placed in a thermostat of 25 ° C., and the charge / discharge test was performed. The conditions of charge and discharge are as follows:
(I) Charge to a constant current of 0.2 C with respect to the capacity of the negative electrode material until it reaches 0.001 V (II) Furthermore, with a constant voltage of 0.001 V, charge for 8 hours with respect to the capacity of the negative electrode material (III) The discharge was performed at a constant current of 0.2 C until it reached 2.5 V.
上記の充放電を１０回繰り返し、特性評価を行った。結果を表１に示す。表１の結果は、測定を２回行い、平均値を取ったものである。なお、表１において、放電容量の単位はｍＡｈ／ｇ、クーロン効率及び容量維持率の単位は％である。 The above-mentioned charge and discharge were repeated 10 times to evaluate the characteristics. The results are shown in Table 1. The results in Table 1 are obtained by measuring twice and taking an average value. In Table 1, the unit of discharge capacity is mAh / g, and the unit of coulombic efficiency and capacity maintenance rate is%.
このように、本発明によれば、簡便な方法で製造できるにもかかわらず、有機溶媒を使用した場合と同程度の性能を得ることができた。 As described above, according to the present invention, although it can be manufactured by a simple method, the same performance as when using an organic solvent could be obtained.
Claims (15)
（１）導電性炭素粒子、シリコン材料、及びカーボンナノチューブを混合し複合体を得る工程、
（２）前記工程（１）で得た複合体と、黒鉛及びピッチとを乾式混合する工程、並びに
（３）前記工程（２）で得た混合物を前記ピッチの熱分解温度以上で熱処理する工程
を備える、製造方法。 What is claimed is: 1. A method for producing a negative electrode material for a lithium secondary battery, comprising conductive carbon particles, a silicon material, and carbon nanotubes,
(1) mixing conductive carbon particles, silicon material, and carbon nanotubes to obtain a composite,
(2) dry-mixing the composite obtained in step (1), graphite and pitch, and (3) heat-treating the mixture obtained in step (2) above the thermal decomposition temperature of the pitch A manufacturing method.
を備える、リチウム二次電池用負極の製造方法。 A negative electrode for a lithium secondary battery, comprising a step of arranging a negative electrode active material layer containing a negative electrode material for a lithium secondary battery obtained by the method according to any one of claims 1 to 13 on a current collector. Production method.
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