JP2005353345A - Natural graphite negative electrode material and its manufacturing method - Google Patents
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Abstract
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本発明は、高容量、高クーロン効率で、電解液の吸液性に優れるリチウムイオン二次電池用の天然黒鉛負極材及びその製造方法に関する。 The present invention relates to a natural graphite negative electrode material for a lithium ion secondary battery having a high capacity, a high coulomb efficiency, and an excellent electrolyte absorption, and a method for producing the same.
電子機器の小型軽量化に伴い、電池の高エネルギー密度化が要求され、また省資源の面から繰り返し充放電可能な二次電池が求められている。この要求に対して、高エネルギー密度、軽量、小型、かつ充放電サイクル特性に優れたリチウム二次電池が提案され、開発されている。 With the reduction in size and weight of electronic devices, higher energy density of batteries is required, and secondary batteries that can be repeatedly charged and discharged are demanded from the viewpoint of resource saving. In response to this demand, lithium secondary batteries having high energy density, light weight, small size, and excellent charge / discharge cycle characteristics have been proposed and developed.
リチウム二次電池は、電解質の種類によってリチウムイオン二次電池、リチウムポリマー二次電池、全固体リチウム二次電池等がある。なかでも、リチウムイオン二次電池は、リチウム金属二次電池の有する急速充電性に劣る問題、サイクル寿命が短い問題、安全性に劣る問題等を解決するために開発されたものである。リチウム金属二次電池には負極に金属リチウムが用いられていたのに対し、リチウムイオン二次電池の場合には負極に炭素材料を用いることにより、上記の問題を解決しようとするものである。 Lithium secondary batteries include lithium ion secondary batteries, lithium polymer secondary batteries, all-solid lithium secondary batteries, etc., depending on the type of electrolyte. Among these, the lithium ion secondary battery has been developed to solve the problem of inferior rapid chargeability, the problem of short cycle life, the problem of inferior safety, etc. possessed by the lithium metal secondary battery. The lithium metal secondary battery uses metallic lithium for the negative electrode, whereas the lithium ion secondary battery uses a carbon material for the negative electrode in order to solve the above problem.
リチウムイオン二次電池用負極材として開発当初は炭素が用いられたが、現在は実用充電時間での容量が高く、かつクーロン効率の高い黒鉛が用いられている。 Carbon was used at the beginning of development as a negative electrode material for lithium ion secondary batteries, but currently, graphite having a high capacity during practical charging time and high coulomb efficiency is used.
負極材として用いられる黒鉛には、大別して人造黒鉛と天然黒鉛の２種類がある。人造黒鉛は概して質量当たりの容量が低く、高価格であるが、それにもかかわらず天然黒鉛より多く用いられている。人造黒鉛は密度が高いので、容積当たりの容量が天然黒鉛より高いことが一因として挙げられる。一方、天然黒鉛は安価であり、かつ質量当たりの容量は人造黒鉛に比較して大きいにもかかわらず負極材としての利用が進んでいない。その理由としては、容積当たりの容量が人造黒鉛より低いことに加えて、クーロン効率が低く、電極密度を上げるためにプレスを行うと黒鉛電極内で黒鉛結晶ＡＢ面がプレス方向に対し垂直に配列することが挙げられる。その結果、黒鉛電極内への電解液の浸透が困難になるのみならず、プレス方向の電気抵抗が大きくなり、リチウムイオン二次電池の負荷特性が悪くなる。 The graphite used as the negative electrode material is roughly classified into two types: artificial graphite and natural graphite. Although artificial graphite generally has a low capacity per mass and is expensive, it is nevertheless more used than natural graphite. One reason is that artificial graphite has a high density, and thus its capacity per volume is higher than that of natural graphite. On the other hand, natural graphite is inexpensive and its utilization as a negative electrode material is not progressing despite its large capacity per mass compared to artificial graphite. The reason is that in addition to the capacity per volume lower than that of artificial graphite, the Coulomb efficiency is low, and when pressing is performed to increase the electrode density, the graphite crystal AB plane is aligned perpendicular to the pressing direction in the graphite electrode. To do. As a result, not only is it difficult for the electrolyte solution to penetrate into the graphite electrode, but the electrical resistance in the pressing direction is increased, and the load characteristics of the lithium ion secondary battery are deteriorated.
リチウムイオン二次電池用負極材に対しては諸特性が要求されるが、なかでも高容量、高クローン効率はリチウムイオン二次電池用負極材の本質的な物性として常に改善が望まれている。 Various characteristics are required for the negative electrode material for lithium ion secondary batteries, but high capacity and high clone efficiency are always desired to be improved as essential physical properties of the negative electrode material for lithium ion secondary batteries. .
本発明者は、高容量、低価格という天然黒鉛の特性を維持し、且つ電解液の分解の抑制を目的にした黒鉛系負極材の開発を行った。その結果、天然黒鉛粒子表面を２〜３０質量％の結晶性炭素で完全且つ均一に被覆した黒鉛−炭素複合材がリチウムイオン二次電池用負極材に好適であることを知得し、既に特許を取得した（特許文献１参照）。 The present inventor has developed a graphite-based negative electrode material that maintains the characteristics of natural graphite such as high capacity and low price and suppresses decomposition of the electrolyte. As a result, it has been known that a graphite-carbon composite material in which the surface of natural graphite particles is completely and uniformly coated with 2 to 30% by mass of crystalline carbon is suitable for a negative electrode material for a lithium ion secondary battery. (See Patent Document 1).
しかしながら、この複合材は、黒鉛表面を炭素で被覆することによって黒鉛の可撓性が損なわれ、プレス後の電極密度が上がりにくいという問題があった。 However, this composite material has a problem that the flexibility of graphite is impaired by coating the surface of graphite with carbon, and the electrode density after pressing is difficult to increase.
そこで、電極密度の向上と負荷特性の改善を目的として更に研究を重ねた結果、球形化した天然黒鉛を被覆量１〜１４質量％の炭素で被覆した球形天然黒鉛が負極材として好適であることを見出し先に特許出願を行った（特許文献２参照）。天然黒鉛を球形化することにより負極材における黒鉛粒子そのものの密度が向上することに加えて、黒鉛粒子の外表面積が減少するので、黒鉛粒子を被覆する炭素量を減少させることが可能となる。更に、この負極材は、プレスを行った場合であっても黒鉛ＡＢ面の配列を等方的とすることが可能である。これらの研究の中で、球形化黒鉛粒子の表面を炭素で被覆することにより、電解液の分解抑制効果のみならず、黒鉛−炭素複合材の圧縮強度を上げることができることが判明した。その結果、粒子間の連続した空隙が保持されるので、液速度が高められて電池の生産性が向上し、さらには負荷特性を高める効果がある。
一方、炭素のクーロン効率は黒鉛より低いため、元来黒鉛と同時に用いても分解しない電解液を用いた場合、黒鉛−炭素複合材の炭素被覆量を増加させると負極材全体のクーロン効率が低下することが明らかとなってきた。黒鉛の質量当たりの容量はほぼ理論容量に達していることから、今後は電極密度を上げ且つクーロン効率のより高い材料を使用することにより、容積当たりの容量を増加した負極材の開発が望まれている。 On the other hand, since the coulombic efficiency of carbon is lower than that of graphite, when using an electrolytic solution that does not decompose when used with graphite, increasing the carbon coverage of the graphite-carbon composite material decreases the coulomb efficiency of the entire negative electrode material. It has become clear to do. Since the capacity per mass of graphite has almost reached the theoretical capacity, it is desired to develop a negative electrode material with increased capacity per volume by increasing the electrode density and using a material with higher coulomb efficiency. ing.
炭素被覆量を減らすことはプロピレンカーボネート等の黒鉛により分解し易い溶媒を電解液とした場合に負極材の電解液分解耐性を減じることに繋がるが、電解液に元来黒鉛との反応性の低いエチレンカーボネートやその他の鎖状カーボネートを用いる電池ではクーロン効率を下げることになる。従って、電解液の分解が起きない電池システムである限り、炭素被覆はクーロン効率の見地からは最良の方法ではない。本発明者は研究を重ねた結果、電極塗工時の黒鉛００２面配列を考慮すると負極材として球形化した天然黒鉛粒子を使用することが好ましく、更に天然黒鉛粒子中に残存するフッ酸を除去することにより黒鉛粒子のクーロン効率が大きく向上することを見出し本発明を完成するに到った。 Reducing the carbon coating amount leads to a decrease in the electrolyte decomposition resistance of the negative electrode material when a solvent that is easily decomposed by graphite such as propylene carbonate is used as the electrolyte, but the electrolyte is originally low in reactivity with graphite. In batteries using ethylene carbonate or other chain carbonates, the Coulomb efficiency is lowered. Thus, carbon coating is not the best method from the viewpoint of Coulomb efficiency, as long as the battery system does not undergo electrolyte decomposition. As a result of repeated research, the present inventor preferably uses spherical natural graphite particles as the negative electrode material in consideration of the graphite 002 plane arrangement during electrode coating, and further removes hydrofluoric acid remaining in the natural graphite particles. As a result, it has been found that the Coulomb efficiency of the graphite particles is greatly improved, and the present invention has been completed.
上記課題を解決する本発明は、以下に記載するものである。 The present invention for solving the above problems is described below.
〔１〕 球形天然黒鉛粒子からなる天然黒鉛負極材であって、該黒鉛粒子が黒鉛ＡＢ面が露出した外表面と、黒鉛ＡＢ面が褶曲したあるいは折り畳まれた内部構造とを有し、該黒鉛粒子１質量部を純水６０質量部で洗浄したときの洗浄水のｐＨが６．０以上であることを特徴とする天然黒鉛負極材。 [1] A natural graphite negative electrode material composed of spherical natural graphite particles, wherein the graphite particles have an outer surface with an exposed graphite AB surface and an inner structure in which the graphite AB surface is bent or folded. A natural graphite negative electrode material, wherein the pH of the washing water when washing 1 part by mass of the particles with 60 parts by mass of pure water is 6.0 or more.
〔２〕 平均粒子径５ｍｍ以下の天然黒鉛粒子を衝撃式粉砕機で粉砕処理することにより球形化した後、脱フッ酸処理することを特徴とする〔１〕に記載の天然黒鉛負極材の製造方法。 [2] The natural graphite negative electrode material according to [1], wherein natural graphite particles having an average particle diameter of 5 mm or less are spheroidized by pulverization with an impact pulverizer and then dehydrofluorinated. Method.
〔３〕 脱フッ酸処理を不活性ガス雰囲気中４００℃以上で熱処理することにより行う〔２〕に記載の天然黒鉛負極材の製造方法。 [3] The method for producing a natural graphite negative electrode material according to [2], wherein the hydrofluoric acid treatment is performed by heat treatment at 400 ° C. or higher in an inert gas atmosphere.
〔４〕 脱フッ酸処理を水洗により行う〔２〕に記載の天然黒鉛負極材の製造方法。 [4] The method for producing a natural graphite negative electrode material according to [2], wherein the hydrofluoric acid treatment is performed by washing with water.
〔５〕 〔１〕に記載の天然黒鉛負極材を用いたリチウムイオン二次電池。 [5] A lithium ion secondary battery using the natural graphite negative electrode material according to [1].
本発明の天然黒鉛負極材は、外表面に黒鉛ＡＢ面が露出し、黒鉛ＡＢ面が褶曲したあるいは折り畳まれた内部構造を有する球形天然黒鉛粒子からなる負極材である。本発明の天然黒鉛負極材は、粒子表面に被覆炭素層を有しておらず、鱗片状黒鉛に比較して外表面積が減少する結果、クーロン効率が大きい。また、球形化することによって電極塗工時の黒鉛００２面の選択的配列が抑制され電極抵抗が低下してハイレートのリチウムイオン二次電池とすることが可能である。同時に、球形化によりタップ密度が増加して電極密度が増加する。更に、カレンダープレスによる変形が抑えられるので、電極内の連続した空隙が確保されて吸液性が向上する。さらにフッ酸を除去した天然黒鉛粒子を負極材とすることにより一層クーロン効率が高められ、高エネルギー容量のリチウムイオン二次電池とすることが可能である。 The natural graphite negative electrode material of the present invention is a negative electrode material composed of spherical natural graphite particles having an internal structure in which the graphite AB surface is exposed on the outer surface and the graphite AB surface is bent or folded. The natural graphite negative electrode material of the present invention does not have a coating carbon layer on the particle surface, and as a result of a decrease in outer surface area compared with scaly graphite, the Coulomb efficiency is large. In addition, by making it spherical, the selective arrangement of the graphite 002 surface at the time of electrode coating is suppressed, and the electrode resistance is lowered, so that a high-rate lithium ion secondary battery can be obtained. At the same time, tap density increases due to spheroidization, and electrode density increases. Furthermore, since deformation due to the calendar press is suppressed, a continuous gap in the electrode is secured, and the liquid absorbency is improved. Furthermore, by using natural graphite particles from which hydrofluoric acid has been removed as a negative electrode material, the Coulomb efficiency can be further increased, and a lithium ion secondary battery having a high energy capacity can be obtained.
本発明の負極材の基材となる球形天然黒鉛は、本発明者が先に特許出願した方法、即ち特開２００２−３４８１１０号公報、及び特開２００２−４２２３４号公報記載の方法により製造することができる。これらの方法は、平均粒子径５ｍｍ以下の天然黒鉛粒子を衝撃式粉砕機に供給し、黒鉛ＡＢ面の平行方向より圧縮応力を加えることにより黒鉛粒子を球形化する方法である。この方法で製造した球形天然黒鉛粒子は、黒鉛ＡＢ面が積層した天然黒鉛に比較して外表面積が小さく、クーロン効率が高い。 The spherical natural graphite used as the base material of the negative electrode material of the present invention is manufactured by the method previously filed by the present inventor, that is, the method described in JP-A-2002-348110 and JP-A-2002-42234. Can do. In these methods, natural graphite particles having an average particle diameter of 5 mm or less are supplied to an impact pulverizer, and the graphite particles are spheroidized by applying a compressive stress in the parallel direction of the graphite AB surface. The spherical natural graphite particles produced by this method have a smaller outer surface area and higher coulomb efficiency than natural graphite with a graphite AB surface laminated.
球形天然黒鉛粒子の平均粒度は３〜５０μｍであることが好ましく、より好ましくは１０〜３０μｍである。平均粒度が３〜５０μｍの球形天然黒鉛粒子のタップ密度は０．８〜１．４ｇ／ｃｍ3程度である。この値は通常の鱗片状黒鉛の約２〜４倍である。 The average particle size of the spherical natural graphite particles is preferably 3 to 50 μm, more preferably 10 to 30 μm. The tap density of spherical natural graphite particles having an average particle size of 3 to 50 μm is about 0.8 to 1.4 g / cm 3 . This value is about 2 to 4 times that of ordinary flaky graphite.
球形天然黒鉛粒子のアスペクト比は１〜４が好ましく、１〜２が特に好ましい。 The aspect ratio of the spherical natural graphite particles is preferably 1 to 4, and particularly preferably 1 to 2.
また、球形天然黒鉛の純度（炭素含有量）は９９．９％以上が好ましく、９９．９５％以上がより好ましい。天然黒鉛は土中より採掘され、比重分離と重液分離を繰り返すことにより純度の高い天然黒鉛に精製される。リチウムイオン電池負極材に賞用される天然黒鉛の純度は、９９．９％以上が望まれるが、採掘された天然黒鉛に不純物として含まれるシリカは比重分離と重液分離では除去できず、９９．９％以上の純度を有する黒鉛を得るためには最終的にフッ酸を用いてシリカを除去し高純度化する必要がある。高純度化された天然黒鉛中にはフッ酸が残留し、高純度化天然黒鉛を水洗すると洗浄水のｐＨは通常６未満である。なお、本発明において洗浄水のｐＨとは、乾燥した天然黒鉛粒子１質量部を６０質量部の純水で洗浄したときの洗浄水のｐＨをいうものとする。黒鉛に残留するフッ酸はリチウムイオンのトラップ源、言い換えるとクーロン効率低下の原因となる不可逆容量となるので、負極材製造工程には残留フッ酸を除去する工程が必要になる。 Further, the purity (carbon content) of the spherical natural graphite is preferably 99.9% or more, and more preferably 99.95% or more. Natural graphite is mined from soil and purified to high purity natural graphite by repeating specific gravity separation and heavy liquid separation. The purity of natural graphite used for lithium ion battery negative electrode materials is preferably 99.9% or more, but silica contained as an impurity in mined natural graphite cannot be removed by specific gravity separation or heavy liquid separation. In order to obtain graphite having a purity of 9% or more, it is necessary to finally remove the silica using hydrofluoric acid to increase the purity. Hydrofluoric acid remains in the highly purified natural graphite, and when the highly purified natural graphite is washed with water, the pH of the washing water is usually less than 6. In the present invention, the pH of the washing water refers to the pH of the washing water when 1 part by mass of the dried natural graphite particles is washed with 60 parts by mass of pure water. Since the hydrofluoric acid remaining in the graphite becomes an irreversible capacity that causes a lithium ion trap source, in other words, a decrease in Coulomb efficiency, a process for removing the residual hydrofluoric acid is required in the negative electrode material manufacturing process.
フッ酸の除去工程としては、例えば球形天然黒鉛粒子を水洗する水洗法が挙げられる。この場合、球形天然黒鉛粒子を水で数回に分けて洗浄、脱水を繰り返すことが好ましい。また洗浄後は黒鉛粒子を乾燥し、水分０．０５％以下、さらに０．０１％以下とすることが好ましい。 Examples of the hydrofluoric acid removing step include a water washing method in which spherical natural graphite particles are washed with water. In this case, it is preferable that the spherical natural graphite particles are repeatedly washed and dehydrated with water several times. Moreover, after washing, the graphite particles are preferably dried to a moisture content of 0.05% or less, more preferably 0.01% or less.
更に、熱処理を行って残留フッ酸を蒸発除去する熱処理法によってもフッ酸を除去することが可能である。キルン内部に球形天然黒鉛を連続的に投入し、内部を常に窒素ガスなどの不活性ガスでパージする方法が簡便である。 Furthermore, hydrofluoric acid can be removed by a heat treatment method in which heat treatment is performed to evaporate and remove residual hydrofluoric acid. A simple method is one in which spherical natural graphite is continuously charged into the kiln and the inside is always purged with an inert gas such as nitrogen gas.
熱処理は球形天然黒鉛を撹拌しながら行うことが望ましいが、プッシャー炉等の黒鉛が流動しない方法でも熱処理が可能である。また、縦型炉上部から球形天然黒鉛を挿入し、順次下部から熱処理した球形天然黒鉛を抜き出す方法も簡便である。この場合縦型炉底部より不活性ガスを導入することが望ましい。 The heat treatment is desirably performed while stirring the spherical natural graphite, but the heat treatment can be performed by a method such as a pusher furnace where the graphite does not flow. Further, a method of inserting spherical natural graphite from the upper part of the vertical furnace and sequentially extracting the heat-treated spherical natural graphite from the lower part is also simple. In this case, it is desirable to introduce an inert gas from the bottom of the vertical furnace.
熱処理温度は４００℃以上とするが、好ましくは１０００〜１５００℃である。なお、１５００℃以下では熱処理温度が増加するに従い天然黒鉛粒子のクーロン効率が増加し、１５００℃を超えるとほぼクーロン効率が飽和する傾向にある。 Although the heat processing temperature shall be 400 degreeC or more, Preferably it is 1000-1500 degreeC. When the heat treatment temperature is increased at 1500 ° C. or lower, the Coulomb efficiency of the natural graphite particles increases, and when it exceeds 1500 ° C., the Coulomb efficiency tends to be saturated.
熱処理法において使用する不活性ガスは安価な窒素ガスが好ましい。窒素ガス中の酸素含有量は０．１％以下とすることが望ましい。７００℃以下では５％程度の酸素の混入も許容される。６００℃以下では空気で処理することも可能である。 The inert gas used in the heat treatment method is preferably an inexpensive nitrogen gas. The oxygen content in the nitrogen gas is desirably 0.1% or less. When the temperature is 700 ° C. or lower, about 5% of oxygen is allowed to be mixed. It is possible to treat with air at 600 ° C. or lower.
熱処理時間は、熱処理温度等の条件により異なるが、熱処理温度が１０００〜１５００℃の場合には１〜１２０分とすることが好ましく、１０〜４０分とすることがより好ましい。 Although heat processing time changes with conditions, such as heat processing temperature, when heat processing temperature is 1000-1500 degreeC, it is preferable to set it as 1 to 120 minutes, and it is more preferable to set it as 10 to 40 minutes.
このように、熱処理法あるいは水洗法でフッ酸を除去することにより、球形天然黒鉛の洗浄水のｐＨを６．０以上とするが、好ましくは６．３以上である。 Thus, by removing hydrofluoric acid by a heat treatment method or a water washing method, the pH of the spherical natural graphite washing water is adjusted to 6.0 or more, preferably 6.3 or more.
上記のようにして得た球形天然黒鉛粒子を用いてリチウム二次電池の負極を調製する方法は特に限定されないが、例えば、天然黒鉛粒子にバインダーを溶解した溶剤を加えて十分に混練後、金属箔等の集電体に塗膜することにより負極とすることができる。 The method of preparing the negative electrode of the lithium secondary battery using the spherical natural graphite particles obtained as described above is not particularly limited. For example, after adding a solvent in which a binder is dissolved in natural graphite particles and sufficiently kneading, a metal A negative electrode can be obtained by coating a current collector such as a foil.
バインダーには公知の材料、例えば各種ピッチ、ラバー、合成樹脂等を用いることができるが、なかでもポリビニリデンフルオライド（ＰＶＤＦ）、エチレンプロピレンジエンポリマー（ＥＰＤＭ）、カルボキシメチルセルロース（ＣＭＣ）、スチレンブタジエンラテックス（ＳＢＲ）等が好適である。 Known materials such as various pitches, rubbers and synthetic resins can be used for the binder. Among them, polyvinylidene fluoride (PVDF), ethylene propylene diene polymer (EPDM), carboxymethyl cellulose (CMC), styrene butadiene latex, among others. (SBR) and the like are preferable.
具体的には以下のように調製することが可能である。まず、球形天然黒鉛粒子に例えばバインダーとしてＰＶＤＦ３〜１５質量％又はＣＭＣ１〜７質量％と、任意によりＳＢＲラテックス２質量％以下を添加した溶剤を加えてスラリー化する。得られたスラリーをドクターブレードを用いて銅箔上に塗工後乾燥し、更にはロールプレスすることで負極を調製することができる。 Specifically, it can be prepared as follows. First, the spherical natural graphite particles are slurried by adding, for example, a solvent containing 3 to 15% by mass of PVDF or 1 to 7% by mass of CMC as a binder and optionally 2% by mass or less of SBR latex. The obtained slurry is coated on a copper foil using a doctor blade, dried, and then roll-pressed to prepare a negative electrode.
本発明の球形天然黒鉛負極材は、炭素で被覆した黒鉛粒子に比較して柔らかく、プレスによって電極密度を１．８〜１．８５ｇ／ｃｍ3程度にまで上げることができる。本発明の負極材の好ましい電極密度の範囲は、粒子間にある程度の空隙を維持し、かつ高容量の負極材を得る観点から１．６〜１．８ｇ／ｃｍ3である。 The spherical natural graphite negative electrode material of the present invention is softer than graphite particles coated with carbon, and the electrode density can be increased to about 1.8 to 1.85 g / cm 3 by pressing. A preferable electrode density range of the negative electrode material of the present invention is 1.6 to 1.8 g / cm 3 from the viewpoint of maintaining a certain amount of voids between particles and obtaining a high capacity negative electrode material.
この密度では電極負極材中に空隙率２０〜３０体積％の空間が存在しているが、この空隙率は電解液の保持に最適な空間容量である。電極密度を１．７ｇ／ｃｍ3以上にすると、通常はプレス表面で黒鉛が潰れ電極内部に電解液を浸透させることが困難になるが、本発明の方法では球形化した黒鉛粒子により粒子間の連続した空隙が形成され、かつタップ密度が高いためロールプレス時の粒子変形が少ない。従って、プレスによっても粒子間の細孔が維持されて良好な吸液特性が維持される。 At this density, a space with a porosity of 20 to 30% by volume exists in the electrode negative electrode material, and this porosity is the optimum space capacity for holding the electrolytic solution. If the electrode density is 1.7 g / cm 3 or more, the graphite is usually crushed on the press surface and it becomes difficult to permeate the electrolyte inside the electrode. Since continuous voids are formed and the tap density is high, there is little particle deformation during roll pressing. Therefore, the pores between the particles are maintained even by pressing, and good liquid absorption characteristics are maintained.
正極材料は特に限定されないが、ＬｉＣｏＯ2、ＬｉＮｉＯ2、ＬｉＭｎ2Ｏ4、ＬｉＦｅＰＯ4等やこれらの混合物が好適である。粉末状の正極材料は必要があれば導電材を加えてバインダーを溶解した溶剤と十分に混練後、集電体とともに成形して調製することができる。これらは公知の技術である。 The positive electrode material is not particularly limited, but LiCoO 2 , LiNiO 2 , LiMn 2 O 4 , LiFePO 4 and the like, and mixtures thereof are suitable. If necessary, the powdered positive electrode material can be prepared by adding a conductive material and sufficiently kneading with a solvent in which a binder is dissolved, and then molding with a current collector. These are known techniques.
また、セパレーターについても特に限定はなく、ポリプロピレンやポリエチレン等の公知の材料を用いることができる。 The separator is not particularly limited, and a known material such as polypropylene or polyethylene can be used.
リチウムイオン二次電池用の電解液用非水系溶媒としてはリチウム塩を溶解できる非プロトン性低誘電率の公知の溶媒が用いられる。例えばエチレンカーボネート、ジメチルカーボネート、ジエチレンカーボネート、アセトニトリル、プロピオニトリル、テトラヒドロフラン、γ−ブチロラクトン、２−メチルテトラヒドロフラン、１，３−ジオキソラン、４−メチル−１，３−ジオキソラン、１，２−ジメトキシエタン、１，２−ジエトキシエタン、ジエチルエーテル、スルホラン、メチルスルホラン、ニトロメタン、Ｎ，Ｎ−ジメチルホルムアミド、ジメチルスルホキシド等の溶媒が単独で又は二種類以上が混合して用いられる。溶媒としてプロピレンカーボネートを用いることも可能であるが、プロピレンカーボネートを用いる場合には電解液中の濃度を２５体積％以下とすることが好ましい。 As a non-aqueous solvent for an electrolyte solution for a lithium ion secondary battery, a known aprotic low dielectric constant solvent capable of dissolving a lithium salt is used. For example, ethylene carbonate, dimethyl carbonate, diethylene carbonate, acetonitrile, propionitrile, tetrahydrofuran, γ-butyrolactone, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-dimethoxyethane, Solvents such as 1,2-diethoxyethane, diethyl ether, sulfolane, methyl sulfolane, nitromethane, N, N-dimethylformamide, dimethyl sulfoxide and the like may be used alone or in admixture of two or more. Propylene carbonate can be used as the solvent, but when propylene carbonate is used, the concentration in the electrolytic solution is preferably 25% by volume or less.
電解質として用いられるリチウム塩には、ＬｉＣｌＯ4、ＬｉＡｓＦ5、ＬｉＰＦ6、ＬｉＢＦ4、ＬｉＢ（Ｃ6Ｈ5）、ＬｉＣｌ、ＬｉＢｒ、ＣＨ3ＳＯ3Ｌｉ、ＣＦ3ＳＯ3Ｌｉ、Ｌｉ（ＣＦ3ＳＯ2）2Ｎ、Ｌｉ（Ｃ2Ｆ5ＳＯ2）2Ｎ等があり、これらの塩が単独に、あるいは二種類以上の塩が混合して用いられる。 The lithium salt used as the electrolyte includes LiClO 4 , LiAsF 5 , LiPF 6 , LiBF 4 , LiB (C 6 H 5 ), LiCl, LiBr, CH 3 SO 3 Li, CF 3 SO 3 Li, Li (CF 3 SO 2 ) 2 N, Li (C 2 F 5 SO 2 ) 2 N, etc., and these salts are used alone or in admixture of two or more kinds.
また、上記電解液と電解質をゲル化したゲル電解質やポリエチレンオキサイド、ポリアクリロニトリル等の高分子電解質等を用いてリチウムポリマー二次電池とすることもできる。 Moreover, it can also be set as a lithium polymer secondary battery using the gel electrolyte which gelatinized the said electrolyte solution and electrolyte, polymer electrolytes, such as a polyethylene oxide and polyacrylonitrile.
さらには固体電解質を用いてリチウム全固体二次電池とすることもできる。 Furthermore, it can also be set as a lithium all-solid-state secondary battery using a solid electrolyte.
実施例１〜５
ブラジル産鱗片状天然黒鉛をピンミルを用いて球形化した後、５３μｍで篩い分けを行い、その篩い下粒子を球形天然黒鉛粒子とした。この球形天然黒鉛粒子のタップ密度は１．１５ｇ／ｃｍ3、平均粒子径は２５μｍであった。プッシャー式トンネルキルンに球形天然黒鉛粒子を順次挿入し、９９．９vol％の窒素を高温側から流しながら熱処理を行った。熱処理温度は、最高温度をそれぞれ４００℃、６００℃、８００℃、１０００℃、１２００℃とした。なお、熱処理時間は３０分間であった。
Examples 1-5
Brazilian scale-like natural graphite was spheroidized using a pin mill and then sieved at 53 μm, and the particles under the sieve were made into spherical natural graphite particles. The spherical natural graphite particles had a tap density of 1.15 g / cm 3 and an average particle size of 25 μm. Spherical natural graphite particles were sequentially inserted into a pusher-type tunnel kiln, and heat treatment was performed while flowing 99.9 vol% nitrogen from the high temperature side. The heat treatment temperatures were set to 400 ° C., 600 ° C., 800 ° C., 1000 ° C., and 1200 ° C., respectively. The heat treatment time was 30 minutes.
実施例６、７
実施例１〜５と同様にして得た球形天然黒鉛粒子を用い、タンマン炉にて熱処理した。熱処理温度は、最高温度を２０００℃、２５００℃とした。なお、熱処理時間は３０分間であった。
Examples 6 and 7
Using spherical natural graphite particles obtained in the same manner as in Examples 1 to 5, heat treatment was performed in a Tamman furnace. The maximum heat treatment temperature was 2000 ° C and 2500 ° C. The heat treatment time was 30 minutes.
実施例８
実施例１〜５と同様にして得た球形天然黒鉛粒子５００ｇを１リットルガラスビーカーに入れ、純水を３ｌ加えて１時間撹拌した。その後、バケットフィルターでろ過を行い、さらに付着水を遠心分離した。この操作を４回繰り返した後、水分が０．０１％以下となるまで１１０℃乾燥機で乾燥した。
Example 8
500 g of spherical natural graphite particles obtained in the same manner as in Examples 1 to 5 were placed in a 1 liter glass beaker, 3 l of pure water was added and stirred for 1 hour. Then, it filtered with the bucket filter and also adhered water was centrifuged. After this operation was repeated four times, it was dried with a 110 ° C. drier until the water content was 0.01% or less.
比較例１
実施例１で原料として用いたブラジル産鱗片状天然黒鉛をジェットミルで粉砕し、タップ密度０．６１ｇ／ｃｍ3、平均粒子径２５μｍの鱗片状黒鉛を得た。
Comparative Example 1
The Brazilian scale-like natural graphite used as a raw material in Example 1 was pulverized with a jet mill to obtain scale-like graphite having a tap density of 0.61 g / cm 3 and an average particle diameter of 25 μm.
比較例２
実施例１〜５と同様にして得た球形天然黒鉛粒子をそのまま比較例２として使用した。
Comparative Example 2
Spherical natural graphite particles obtained in the same manner as in Examples 1 to 5 were used as Comparative Example 2 as they were.
実施例１〜８及び比較例１、２で得られた黒鉛粒子を用いて、表１に示す条件で電池評価試験を行った。また、洗浄水のｐＨ、吸液性について、以下の方法で測定した。結果を表２に示す。 Using the graphite particles obtained in Examples 1 to 8 and Comparative Examples 1 and 2, a battery evaluation test was performed under the conditions shown in Table 1. Further, the pH and liquid absorbency of the washing water were measured by the following methods. The results are shown in Table 2.
洗浄水のｐＨ：乾燥試料５ｇと純水３００ｇを密閉容器中で８０℃で２４時間スタラーで撹拌し、試料中から溶出する成分を純水中に溶出させた。同洗浄水の水素イオン濃度をｐＨメーターで直読した。 PH of washing water: 5 g of dried sample and 300 g of pure water were stirred with a stirrer at 80 ° C. for 24 hours in a sealed container to elute components eluted from the sample into pure water. The hydrogen ion concentration of the washing water was read directly with a pH meter.
吸液性：ＣＭＣ１質量％、ＳＢＲラテックス２質量％を添加して調製した試料の水スラリーをドクターブレードを用いて銅箔上に塗工した。乾燥後、一軸プレスで所定圧力をかけ、試料の電極密度を１．７ｇ／ｃｃに調節した。この電極表面にプロピレンカーボネート／メチルエチルカーボネート＝１／１（体積比）の混合溶媒を３μｌ滴下し、溶媒が全て電極内に吸収される時間を計測した。 Liquid absorbency: A water slurry of a sample prepared by adding 1% by mass of CMC and 2% by mass of SBR latex was coated on a copper foil using a doctor blade. After drying, a predetermined pressure was applied with a uniaxial press to adjust the electrode density of the sample to 1.7 g / cc. 3 μl of a mixed solvent of propylene carbonate / methyl ethyl carbonate = 1/1 (volume ratio) was dropped on the electrode surface, and the time taken for all the solvent to be absorbed in the electrode was measured.
Claims (5)
A lithium ion secondary battery using the natural graphite negative electrode material according to claim 1.
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| JP2006049288A (en) * | 2004-06-30 | 2006-02-16 | Mitsubishi Chemicals Corp | Negative electrode material for lithium secondary battery, its manufacturing method, negative electrode for the lithium secondary battery using it and the lithium secondary battery |
| JP2017157571A (en) * | 2011-11-09 | 2017-09-07 | Ｎｅｃエナジーデバイス株式会社 | Negative electrode for lithium ion secondary battery, method of manufacturing the same, and lithium ion secondary battery |
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| JP2006049288A (en) * | 2004-06-30 | 2006-02-16 | Mitsubishi Chemicals Corp | Negative electrode material for lithium secondary battery, its manufacturing method, negative electrode for the lithium secondary battery using it and the lithium secondary battery |
| US8637187B2 (en) | 2004-06-30 | 2014-01-28 | Mitsubishi Chemical Corporation | Negative electrode material for lithium secondary battery, method for producing same, negative electrode for lithium secondary battery using same and lithium secondary battery |
| JP2017157571A (en) * | 2011-11-09 | 2017-09-07 | Ｎｅｃエナジーデバイス株式会社 | Negative electrode for lithium ion secondary battery, method of manufacturing the same, and lithium ion secondary battery |
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