JP2011076897A - Negative electrode material for lithium ion secondary battery - Google Patents
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Abstract
Description
本発明は、リチウムイオン二次電池用負極材料に関するものであり、より詳細には、リチウムイオン二次電池用負極の極板強度を高める技術に関するものである。 The present invention relates to a negative electrode material for lithium ion secondary batteries, and more particularly to a technique for increasing the electrode plate strength of a negative electrode for lithium ion secondary batteries.
近年、電子機器等の小型化に伴い、電源となる電池も小型化が求められており、特に電池の高容量化の観点からリチウムイオン二次電池が注目されている。リチウムイオン二次電池の中でも、負極に黒鉛材料を用いたものは、大容量が得られやすく、かつ、安全で高電圧が得られやすいといった点でも有用である。このような観点から、リチウムイオン二次電池の負極材料として、さまざまな黒鉛材料が提案されている。 In recent years, with the miniaturization of electronic devices and the like, the battery serving as a power source is also required to be miniaturized, and in particular, lithium ion secondary batteries have attracted attention from the viewpoint of increasing the capacity of the battery. Among lithium ion secondary batteries, those using a graphite material for the negative electrode are also useful in that a large capacity can be easily obtained and a safe and high voltage can be easily obtained. From such a viewpoint, various graphite materials have been proposed as negative electrode materials for lithium ion secondary batteries.
例えば、特許文献１には、二次電池用電極を製造する際に用いる材料であって、酸性官能基が１．０ミリ当量／ｋｇ以下である球状化黒鉛粒子と、前記球状化黒鉛粒子より相対的に微細で、且つ、該球状化黒鉛粒子とは異なる導電性炭素質微粒子を混合状態で含有することを特徴とする二次電池用負極材料が開示されている。 For example, Patent Document 1 discloses a material used when manufacturing an electrode for a secondary battery, and the spheroidized graphite particles having an acidic functional group of 1.0 meq / kg or less and the spheroidized graphite particles. A negative electrode material for a secondary battery is disclosed, which contains conductive carbonaceous fine particles that are relatively fine and different from the spheroidized graphite particles in a mixed state.
特許文献２には、二次電池用の電極を製造する際に用いる黒鉛であって、前記黒鉛の酸性官能基量が、質量当たり５ミリ当量／ｋｇ以下で、且つ、比表面積当たり０．３μ当量／ｍ2以上であることを特徴とする二次電池電極用黒鉛が開示されている。 Patent Document 2 discloses graphite used when manufacturing an electrode for a secondary battery, wherein the amount of acidic functional groups of the graphite is 5 meq / kg or less per mass and 0.3 μm per specific surface area. There is disclosed a graphite for a secondary battery electrode characterized by being equivalent / m 2 or more.
特許文献３には、黒鉛粉末（Ａ）からなるリチウム二次電池用負極材料であって、該黒鉛粉末（Ａ）のタップ密度が０．８ｇ／ｃｍ3以上、１．３５ｇ／ｃｍ3以下であり、表面官能基量Ｏ／Ｃが０以上、０．０１以下であり、ＢＥＴ比表面積が２．５ｍ2／ｇ以上、７．０ｍ2／ｇ以下であり、ラマンＲ値が０．０２以上、０．０５以下であることを特徴とする、リチウム二次電池用負極材料が開示されている。 Patent Document 3 discloses a negative electrode material for a lithium secondary battery made of graphite powder (A), wherein the tap density of the graphite powder (A) is 0.8 g / cm 3 or more and 1.35 g / cm 3 or less. Yes, the surface functional group amount O / C is 0 or more and 0.01 or less, the BET specific surface area is 2.5 m 2 / g or more and 7.0 m 2 / g or less, and the Raman R value is 0.02 or more. A negative electrode material for a lithium secondary battery, which is 0.05 or less, is disclosed.
特許文献４には、第１および第２の電極と、上記第１の電極と第２の電極との間にセパレータを備えた電池であって、上記第１の電極と第２の電極の少なくともいずれかは、活物質と、この活物質に接触する電子導電材と、上記活物質および上記電子導電材の少なくともいずれかに接触する導電助剤を含有する活物質層を備え、上記電子導電材および上記導電助剤の一方は疎水性を有し、他方は親水性を備えたことを特徴とする電池が開示されている。 Patent Document 4 discloses a battery including a first and second electrode, and a separator between the first electrode and the second electrode, wherein the battery includes at least one of the first electrode and the second electrode. Any of the above-mentioned electronic conductive materials includes an active material containing an active material, an electronic conductive material in contact with the active material, and a conductive auxiliary agent in contact with at least one of the active material and the electronic conductive material. In addition, a battery is disclosed in which one of the conductive assistants has hydrophobicity and the other has hydrophilicity.
特許文献５には、バインダーの量を増加したり、導電助材の量を減少したりすることなく、電極の密着性を向上させることができる導電助材及び該導電助材を用いた正極及び／又は負極を備えた非水電池を提供することを目的として、正極と負極の少なくとも片方の電極が導電助材として、非水溶液中でイオン解離しうる官能基を表面に有したカーボンを含むことを特徴とする非水電池が開示されている。 Patent Document 5 discloses a conductive additive capable of improving the adhesion of an electrode without increasing the amount of the binder or decreasing the amount of the conductive additive, a positive electrode using the conductive additive, and For the purpose of providing a non-aqueous battery equipped with a negative electrode, at least one of the positive electrode and the negative electrode contains a carbon having a functional group capable of ion dissociation in a non-aqueous solution on the surface as a conductive additive. A non-aqueous battery is disclosed.
特許文献６には、集電体と炭素材料との密着性に優れた高容量のリチウムイオン二次電池用負極を提供することを目的として、集電体表面に炭素材料からなる塗布層を有するリチウムイオン二次電池用の負極において、炭素材料からなる塗布層を二層以上とし、集電体に接する塗布層の炭素材料として比表面積が２ｍ2／ｇ以下の炭素材料を用い、かつ該層の厚みを２０〜１００μｍの範囲としたことを特徴とするリチウムイオン二次電池用負極が開示されている。 Patent Document 6 has a coating layer made of a carbon material on the surface of a current collector for the purpose of providing a high-capacity negative electrode for a lithium ion secondary battery excellent in adhesion between the current collector and the carbon material. In a negative electrode for a lithium ion secondary battery, two or more coating layers made of a carbon material are used, and a carbon material having a specific surface area of 2 m 2 / g or less is used as the carbon material of the coating layer in contact with the current collector. The negative electrode for lithium ion secondary batteries characterized by having a thickness of 20 to 100 μm is disclosed.
リチウムイオン二次電池の負極を作製するには、黒鉛とバインダーとを混合して、スラリーを調製し、スラリーを集電体に塗布するのが一般的である。この際、負極材料である黒鉛と集電体との結着性能（極板強度）が低いと、電極の歩合低下、電池製造コストの増大をもたらすとともに、電池製造後に負極材料が、集電体から剥離する場合がある。バインダー量を増やすことにより、極板強度は向上するが、電池容量の低下、充放電特性の低下を引き起こす。そのため、黒鉛負極材料と集電体との結着性（極板強度）を向上させることが重要である。 In order to produce a negative electrode of a lithium ion secondary battery, it is common to prepare a slurry by mixing graphite and a binder, and apply the slurry to a current collector. At this time, if the binding performance (electrode plate strength) between graphite as the negative electrode material and the current collector is low, the yield of the electrode is reduced and the battery manufacturing cost is increased. May peel off. By increasing the amount of the binder, the electrode plate strength is improved, but the battery capacity and charge / discharge characteristics are reduced. Therefore, it is important to improve the binding property (electrode plate strength) between the graphite negative electrode material and the current collector.
本発明は上記事情に鑑みてなされたものであって、電池容量や充放電特性を維持しつつ、極板強度に優れたリチウムイオン二次電池用負極材料を提供することを目的とする。 This invention is made | formed in view of the said situation, Comprising: It aims at providing the negative electrode material for lithium ion secondary batteries excellent in electrode plate intensity | strength, maintaining battery capacity and charging / discharging characteristic.
上記課題を解決することのできた本発明のリチウムイオン二次電池用負極材料は、表面官能基量が２．０ｍｅｑ（ミリ当量）／ｋｇ以上の高官能基量黒鉛と、表面官能基量が２．０ｍｅｑ／ｋｇ未満の低官能基量黒鉛とを含有し、前記高官能基量黒鉛と前記低官能基量黒鉛の質量比（高官能基量黒鉛／低官能基量黒鉛）が、１０／９０〜８０／２０であることを特徴とする。前記高官能基量黒鉛の配合量が所定量以上であれば、黒鉛の表面官能基がバインダーと結合するようになり、バインダー量を増加させることなく集電体への結着性能（極板強度）を向上させることができる。また、前記低官能基量黒鉛の配合量が所定量以上であれば、電池容量や充放電特性の低下を抑制することができる。 The negative electrode material for a lithium ion secondary battery of the present invention, which has been able to solve the above problems, has a high functional group graphite having a surface functional group amount of 2.0 meq (milli equivalent) / kg or more and a surface functional group amount of 2 Less than 0.0 meq / kg, and the mass ratio of the high functional group graphite to the low functional group graphite (high functional group graphite / low functional group graphite) is 10/90. It is characterized by being 80/20. If the blending amount of the high functional group graphite is a predetermined amount or more, the surface functional group of the graphite will be bonded to the binder, and the binding performance to the current collector (electrode strength) without increasing the binder amount. ) Can be improved. Moreover, if the compounding quantity of the said low functional group amount graphite is more than predetermined amount, the fall of battery capacity or charging / discharging characteristics can be suppressed.
前記高官能基量黒鉛と前記低官能基量黒鉛とを混合した黒鉛混合粉全体の表面官能基量は２．０ｍｅｑ／ｋｇ以上８．０ｍｅｑ／ｋｇ以下であることが好ましい。前記高官能基量黒鉛および前記低官能基量黒鉛としては、鱗片状黒鉛を粉砕した後、球状化した球形化黒鉛粒子が好適である。 The surface functional group amount of the entire graphite mixed powder obtained by mixing the high functional group graphite and the low functional group graphite is preferably 2.0 meq / kg or more and 8.0 meq / kg or less. As the high functional group graphite and the low functional group graphite, spheroidized graphite particles obtained by pulverizing scaly graphite and then spheroidizing are preferable.
本発明には、前記リチウムイオン二次電池用負極材料を用いたことを特徴とするリチウムイオン二次電池用負極および、該リチウムイオン二次電池用負極を用いたリチウムイオン二次電池も含まれる。 The present invention also includes a negative electrode for a lithium ion secondary battery using the negative electrode material for a lithium ion secondary battery, and a lithium ion secondary battery using the negative electrode for a lithium ion secondary battery. .
本発明によれば、電池容量や充放電特性を維持しつつ、極板強度に優れたリチウムイオン二次電池用負極材料が得られる。 ADVANTAGE OF THE INVENTION According to this invention, the negative electrode material for lithium ion secondary batteries excellent in electrode plate intensity | strength is obtained, maintaining battery capacity and charging / discharging characteristics.
本発明のリチウムイオン二次電池用負極材料は、表面官能基量が２．０ｍｅｑ（ミリ当量）／ｋｇ以上の高官能基量黒鉛（以下、単に「高官能基量黒鉛」と称することがある）と、表面官能基量が２．０ｍｅｑ／ｋｇ未満の低官能基量黒鉛（以下、単に「低官能基量黒鉛」と称することがある）とを含有し、前記高官能基量黒鉛と前記低官能基量黒鉛の質量比（高官能基量黒鉛／低官能基量黒鉛）が、１０／９０〜８０／２０であることを特徴とする。前記高官能基量黒鉛を所定量以上配合することにより、これらの高官能基量黒鉛が有する表面官能基がバインダーと結合するようになるため、バインダー量を増加させることなく、黒鉛の集電体に対する結着性能を向上させることができる。また、本願発明では、負極材料に含有される全ての黒鉛の表面官能基量を増加させるのではなく、一部に高官能基量黒鉛を使用する、すなわち、表面官能基を一部の黒鉛に局所的に保持させるため、電池容量や充放電特性の低下を抑制することができる。 The negative electrode material for a lithium ion secondary battery of the present invention may be referred to as a high functional group graphite (hereinafter, simply referred to as “high functional group graphite”) having a surface functional group amount of 2.0 meq (milli equivalent) / kg or more. ) And a low functional group graphite having a surface functional group amount of less than 2.0 meq / kg (hereinafter sometimes simply referred to as “low functional group graphite”), the high functional group graphite and the above The mass ratio of the low functional group graphite (high functional group graphite / low functional group graphite) is 10/90 to 80/20. By blending a predetermined amount or more of the high functional group graphite, the surface functional groups of the high functional group graphite come to be bonded to the binder, so that the current collector of graphite can be obtained without increasing the binder amount. The binding performance with respect to can be improved. Further, in the present invention, rather than increasing the amount of surface functional groups of all graphite contained in the negative electrode material, high functional group weight graphite is used in part, that is, surface functional groups are converted into some graphite. Since it is held locally, a decrease in battery capacity and charge / discharge characteristics can be suppressed.
本発明で使用する高官能基量黒鉛および低官能基量黒鉛は、その表面官能基量が所定量に制御されていれば特に限定されず、天然黒鉛、人造黒鉛のいずれも使用することができる。前記表面官能基とは、例えば、黒鉛表面に存在する、カルボキシル基、フェノール性水酸基、カルボニル基などの酸性官能基であり、後述する方法により測定することができる。 The high functional group graphite and the low functional group graphite used in the present invention are not particularly limited as long as the surface functional group amount is controlled to a predetermined amount, and either natural graphite or artificial graphite can be used. . The surface functional group is, for example, an acidic functional group such as a carboxyl group, a phenolic hydroxyl group, or a carbonyl group present on the graphite surface, and can be measured by a method described later.
前記高官能基量黒鉛の表面官能基量は、２．０ｍｅｑ／ｋｇ以上であり、好ましくは５．０ｍｅｑ／ｋｇ以上、より好ましくは８．０ｍｅｑ／ｋｇ以上である。高官能基量黒鉛の表面官能基量が２．０ｍｅｑ／ｋｇ以上であれば、得られる黒鉛負極の極板強度を効率よく向上させることができる。また、高官能基量黒鉛の表面官能基量の上限は特に限定されないが、３０ｍｅｑ／ｋｇ以下が好ましく、より好ましくは２０ｍｅｑ／ｋｇ以下、さらに好ましくは１０ｍｅｑ／ｋｇ以下である。高官能基量黒鉛の表面官能基量が３０ｍｅｑ／ｋｇ以下であれば、一部の黒鉛に表面官能基が過剰に存在することを抑制できる。 The surface functional group amount of the high functional group graphite is 2.0 meq / kg or more, preferably 5.0 meq / kg or more, more preferably 8.0 meq / kg or more. If the surface functional group amount of the high functional group graphite is 2.0 meq / kg or more, the electrode plate strength of the obtained graphite negative electrode can be improved efficiently. The upper limit of the surface functional group amount of the high functional group graphite is not particularly limited, but is preferably 30 meq / kg or less, more preferably 20 meq / kg or less, and further preferably 10 meq / kg or less. If the surface functional group amount of the high functional group graphite is 30 meq / kg or less, it is possible to suppress the presence of excessive surface functional groups in some graphite.
前記低官能基量黒鉛の表面官能基量は、２．０ｍｅｑ／ｋｇ未満であり、好ましくは１．５ｍｅｑ／ｋｇ以下、より好ましくは１．０ｍｅｑ／ｋｇ以下である。低官能基量黒鉛の表面官能基量が２．０ｍｅｑ／ｋｇ未満であれば、得られるリチウムイオン二次電池の電池容量および充放電特性がより良好となる。なお、低官能基量黒鉛の表面官能基量の下限は特に限定されない。 The surface functional group amount of the low functional group graphite is less than 2.0 meq / kg, preferably 1.5 meq / kg or less, more preferably 1.0 meq / kg or less. If the surface functional group content of the low functional group graphite is less than 2.0 meq / kg, the battery capacity and charge / discharge characteristics of the obtained lithium ion secondary battery will be better. In addition, the minimum of the surface functional group amount of low functional group amount graphite is not specifically limited.
本発明のリチウムイオン二次電池用負極材料中の前記高官能基量黒鉛と前記低官能基量黒鉛の質量比（高官能基量黒鉛／低官能基量黒鉛）は、１０／９０以上、好ましくは２０／８０以上、より好ましくは４０／６０以上であり、８０／２０以下、好ましくは７０／３０以下、より好ましくは６０／４０以下である。前記質量比が１０／９０未満では、黒鉛混合粉に導入される表面官能基量が少なすぎ、負極材料の集電体に対する結着性能が向上しない。一方、前記質量比が８０／２０を超えると、黒鉛混合粉に導入される表面官能基量が過剰となり、得られるリチウムイオン二次電池の電池容量や充放電特性が低下する。 The mass ratio of the high functional group graphite and the low functional group graphite (high functional group graphite / low functional group graphite) in the negative electrode material for a lithium ion secondary battery of the present invention is preferably 10/90 or more, preferably Is 20/80 or more, more preferably 40/60 or more, 80/20 or less, preferably 70/30 or less, more preferably 60/40 or less. When the mass ratio is less than 10/90, the amount of surface functional groups introduced into the graphite mixed powder is too small, and the binding performance of the negative electrode material to the current collector is not improved. On the other hand, when the mass ratio exceeds 80/20, the amount of surface functional groups introduced into the graphite mixed powder becomes excessive, and the battery capacity and charge / discharge characteristics of the obtained lithium ion secondary battery are lowered.
ここで、前記高官能基量黒鉛と前記低官能基量黒鉛とを混合した黒鉛混合粉全体の表面官能基量は２．０ｍｅｑ／ｋｇ以上が好ましく、より好ましくは４．０ｍｅｑ／ｋｇ以上であり、８．０ｍｅｑ／ｋｇ以下が好ましく、より好ましくは７．０ｍｅｑ／ｋｇ以下、さらに好ましくは６．０ｍｅｑ／ｋｇ以下である。前記黒鉛混合粉全体の表面官能基量を上記範囲内とすることにより、負極材料の集電体に対する結着性能と得られるリチウムイオン二次電池の電池容量や充放電特性とを、バランスよく両立させることができる。 Here, the surface functional group amount of the whole graphite mixed powder obtained by mixing the high functional group weight graphite and the low functional group weight graphite is preferably 2.0 meq / kg or more, more preferably 4.0 meq / kg or more. 8.0 meq / kg or less, more preferably 7.0 meq / kg or less, and still more preferably 6.0 meq / kg or less. By making the surface functional group amount of the entire graphite mixed powder within the above range, the binding performance of the negative electrode material to the current collector and the battery capacity and charge / discharge characteristics of the obtained lithium ion secondary battery are balanced in a balanced manner. Can be made.
以下、高官能基量黒鉛および低官能基量黒鉛について詳細に説明する。なお、以下で単に「黒鉛」という場合、高官能基量黒鉛および低官能基量黒鉛を含むものとする。 Hereinafter, the high functional group weight graphite and the low functional group weight graphite will be described in detail. In the following description, the term “graphite” includes high functional group graphite and low functional group graphite.
黒鉛の表面官能基量は、例えば、酸化性雰囲気下あるいは非酸化性雰囲気下で黒鉛を加熱処理することにより制御することができ、酸化性雰囲気下で加熱すれば、黒鉛の表面官能基量を増加させることができ、非酸化性雰囲気下で加熱すれば、黒鉛の表面官能基量を低減することができる。また、酸化性雰囲気下において、黒鉛を粉砕することによっても黒鉛の表面官能基量を増加させることができる。 The amount of surface functional groups of graphite can be controlled by, for example, heat-treating the graphite in an oxidizing atmosphere or a non-oxidizing atmosphere. The amount of surface functional groups of graphite can be reduced by heating in a non-oxidizing atmosphere. Moreover, the surface functional group amount of graphite can also be increased by pulverizing graphite in an oxidizing atmosphere.
前記酸化性雰囲気としては、例えば、空気、酸素、酸素と不活性ガスとの混合ガスなどの酸化性ガス雰囲気を挙げることができる。前記非酸化性雰囲気としては、例えば、アルゴン、窒素、ヘリウムなどの不活性ガス雰囲気を挙げることができる。 Examples of the oxidizing atmosphere include an oxidizing gas atmosphere such as air, oxygen, and a mixed gas of oxygen and an inert gas. Examples of the non-oxidizing atmosphere include an inert gas atmosphere such as argon, nitrogen, and helium.
黒鉛の表面官能基量を制御する際の加熱処理温度は、特に限定されないが、２００℃以上が好ましく、より好ましくは３００℃以上であり、８００℃以下が好ましく、より好ましくは６００℃以下である。表面官能基量を制御する際の加熱処理時間は、所望の表面官能基量に応じて適宜調節すればよいが、０．５時間以上が好ましく、１．０時間以上がより好ましい。 The heat treatment temperature for controlling the surface functional group amount of graphite is not particularly limited, but is preferably 200 ° C. or higher, more preferably 300 ° C. or higher, preferably 800 ° C. or lower, more preferably 600 ° C. or lower. . The heat treatment time for controlling the surface functional group amount may be appropriately adjusted according to the desired surface functional group amount, but is preferably 0.5 hours or longer, and more preferably 1.0 hour or longer.
前記黒鉛の比表面積は、１．０ｍ2／ｇ以上が好ましく、より好ましくは２．０ｍ2／ｇ以上、さらに好ましくは、３．０ｍ2／ｇ以上であり、５０ｍ2／ｇ以下が好ましく、より好ましくは２０ｍ2／ｇ以下、さらに好ましくは１０ｍ2／ｇ以下である。黒鉛の比表面積が１．０ｍ2／ｇ以上であれば、電解液との接触面積が大きくなり、得られるリチウムイオン二次電池の急速充放電特性がより良好となり、５０ｍ2／ｇ以下であれば、負極材料（黒鉛）の表面に生じる不動態膜を抑制でき、得られるリチウムイオン二次電池の初期効率がより良好となる。なお、比表面積は、Ｍｉｃｒｏｍｅｒｉｔｉｃｓ社製「ＡＳＡＰ−２４０５」装置を用い、Ｎ2吸着によるＢＥＴ法にて測定することができる。 The specific surface area of the graphite is preferably 1.0 m 2 / g or more, more preferably 2.0 m 2 / g or more, still more preferably 3.0 m 2 / g or more, and preferably 50 m 2 / g or less. More preferably, it is 20 m < 2 > / g or less, More preferably, it is 10 m < 2 > / g or less. If the specific surface area of graphite is 1.0 m 2 / g or more, the contact area with the electrolytic solution will be large, and the rapid charge / discharge characteristics of the resulting lithium ion secondary battery will be better, and it should be 50 m 2 / g or less. Thus, a passive film generated on the surface of the negative electrode material (graphite) can be suppressed, and the initial efficiency of the obtained lithium ion secondary battery becomes better. The specific surface area, using a Micromeritics Corp. "ASAP-2405" device, can be measured by BET method using N 2 adsorption.
前記黒鉛の平均粒子径は１μｍ以上が好ましく、より好ましくは５μｍ以上、さらに好ましくは１０μｍ以上であり、５０μｍ以下が好ましく、より好ましくは３０μｍ以下である。平均粒子径が、１μｍ以上であれば、比表面積が大きくなりすぎず、かつ、粒子間の通液性が良好となるため、得られるリチウムイオン二次電池の急速充放電特性がより良好となり、５０μｍ以下であれば、電極密度をより均一にすることができる。ここで、本願において平均粒子径とは、水に分散させた試料を、レーザー回折式粒度分布測定装置（例えば、島津製作所製の「ＳＡＬＤ（登録商標）−２０００」）により測定して、求められる体積基準メディアン径（Ｄ５０）である。 The average particle diameter of the graphite is preferably 1 μm or more, more preferably 5 μm or more, further preferably 10 μm or more, preferably 50 μm or less, more preferably 30 μm or less. If the average particle diameter is 1 μm or more, the specific surface area does not become too large, and the liquid permeability between the particles becomes good, so the rapid charge / discharge characteristics of the obtained lithium ion secondary battery become better, If it is 50 micrometers or less, an electrode density can be made more uniform. Here, in the present application, the average particle size is obtained by measuring a sample dispersed in water with a laser diffraction particle size distribution measuring device (for example, “SALD (registered trademark) -2000” manufactured by Shimadzu Corporation). Volume-based median diameter (D50).
本発明で使用する黒鉛は、その形状は特に限定されず、例えば、鱗片状黒鉛、球形化黒鉛、およびこれらを併用することもできる。なお、本発明では、前記高官能基量黒鉛および前記低官能基量黒鉛の両方に、鱗片状黒鉛を粉砕した後、球状化した球形化黒鉛粒子を使用することが好ましい。本発明では、負極の極板強度を向上させるために、高官能基量黒鉛を多量に配合することが必要となる。ここで、高官能基量黒鉛として鱗片状黒鉛をそのまま使用した場合には、高官能基量黒鉛の配合量が増加するにつれて黒鉛粒子間の空隙が減少し、電極内部への電解液の通液性が悪くなり負荷特性が低下するおそれがある。しかし、高官能基量黒鉛および低官能基量黒鉛の両方に球形化黒鉛を使用すれば、高官能基量黒鉛の配合量が増加しても黒鉛粒子間の空隙を確保することができ、電極内部への電解液の通液性が良好となる。よって、得られるリチウムイオン二次電池用負極の極板強度および負荷特性をより向上させることができる。 The shape of the graphite used in the present invention is not particularly limited, and for example, flaky graphite, spheroidized graphite, and a combination thereof can be used. In the present invention, it is preferable to use spheroidized graphite particles obtained by pulverizing scaly graphite for both the high functional group weight graphite and the low functional group weight graphite. In the present invention, in order to improve the electrode plate strength of the negative electrode, it is necessary to blend a large amount of high functional group graphite. Here, when the scaly graphite is used as it is as the high functional group graphite, voids between the graphite particles decrease as the blending amount of the high functional group graphite increases, and the electrolyte solution flows into the electrode. May deteriorate and load characteristics may deteriorate. However, if spheroidized graphite is used for both high functional group weight graphite and low functional group weight graphite, it is possible to ensure voids between graphite particles even if the amount of high functional group graphite is increased. The liquid permeability of the electrolytic solution to the inside is improved. Therefore, the electrode plate strength and load characteristics of the obtained negative electrode for a lithium ion secondary battery can be further improved.
前記球形化黒鉛は、黒鉛粒子の形状が球状化されている黒鉛であれば特に限定されず、例えば、鱗片状黒鉛を球状化することにより得られるものであり、例えば、鱗片状黒鉛を粉砕した後、これらを球状化させることによって、球形化黒鉛を得ることができる。球形化黒鉛を製造する具体的な方法は特に限定されないが、例えば、本発明者らが先に提案した方法（特開平１１−２６３６１２号）やこれに類似する方法で製造できる。以下、図面を参酌しつつ製法の一例を説明する。 The spheroidized graphite is not particularly limited as long as the shape of the graphite particles is spheroidized. For example, the spheroidized graphite is obtained by spheroidizing flaky graphite, for example, pulverized flaky graphite. Thereafter, spheroidized graphite can be obtained by spheroidizing them. The specific method for producing the spheroidized graphite is not particularly limited, and for example, it can be produced by a method previously proposed by the present inventors (Japanese Patent Laid-Open No. 11-263612) or a method similar thereto. Hereinafter, an example of the manufacturing method will be described with reference to the drawings.
図１は、球形化黒鉛の製造に用いられる装置の概略説明図であり、１は槽、２はフィーダー、３は対向ノズル、４は分級機、５は吹き上げノズルを夫々示している。鱗片状黒鉛（原料）を、槽１に設けられたフィーダー２から槽１内へ供給する。フィーダー２は、ホッパー式のものを槽１の適当箇所に設置することが好ましく、球形化黒鉛の取出口としても利用できる。また、フィーダー２は、スクリュー式のものを槽１の下部に設けてもよい。槽１内への原料供給量は、槽１の容量を考慮して定めればよい。槽１の下部側には槽壁を貫通して対向ノズル３を設け、対向ノズル３からジェット気流を吹き込むことにより、槽１内の下部側に衝突域を形成する。衝突域の気流に入った前記鱗片状黒鉛は互いに衝突し、粉砕されながら再凝集して球状化する。対向ノズル３は、複数個（例えば、３〜４個）設けることが好ましい。対向ノズル３から吹き込むジェット気流の速度、吹き込みガス量、槽圧などは、円滑な衝突と流動が達成できるように設定され、操作時間を適宜に設定することにより鱗片状黒鉛を球状化する。例えば、ノズル吐出圧は０．０１ＭＰａ〜０．５０ＭＰａ程度、吹き込みガス量は０．２Ｎｍ3／ｍｉｎ〜１．０Ｎｍ3／ｍｉｎ程度、槽圧は−１０ｋＰａ〜３０ｋＰａ程度、操作時間は１分〜１００分程度とすればよい。なお、対向ノズル３から吹き込むガスとしては空気や窒素、水蒸気などを用いれば良く、また槽１内の温度は０℃〜６０℃程度とすればよい。槽１内では気体の対流が起こり、槽１の下部側の衝突域で互いに衝突して球状化した黒鉛は、槽１内の対流に沿って上部側へ吹き上げられ、その後再び沈降する。すなわち、粒子は槽１の中心部近傍で吹き上げられ、槽１の壁際に沿って降下して、槽１内に循環流動が起こる。槽１の上部には、分級機４を設けることで分級限界以下の微粉を槽１外に排出できる。分級機４は、公知のものを設ければよいが、高速回転分級機を用いるのが通常である。このときの排出量は、原料として用いる鱗片状黒鉛の粒度によって異なる。 FIG. 1 is a schematic explanatory view of an apparatus used for producing spheroidized graphite, wherein 1 is a tank, 2 is a feeder, 3 is a counter nozzle, 4 is a classifier, and 5 is a blowing nozzle. Scaly graphite (raw material) is fed into the tank 1 from a feeder 2 provided in the tank 1. The feeder 2 is preferably a hopper type one installed at an appropriate location in the tank 1 and can also be used as an outlet for spheroidized graphite. In addition, the feeder 2 may be a screw type provided in the lower part of the tank 1. The raw material supply amount into the tank 1 may be determined in consideration of the capacity of the tank 1. A counter nozzle 3 is provided on the lower side of the tank 1 through the tank wall, and a jet stream is blown from the counter nozzle 3 to form a collision area on the lower side of the tank 1. The scaly graphites that have entered the air current in the collision zone collide with each other, re-aggregate and spheroidize while being crushed. A plurality of (for example, 3 to 4) counter nozzles 3 are preferably provided. The speed of the jet stream blown from the facing nozzle 3, the amount of blown gas, the tank pressure, etc. are set so that smooth collision and flow can be achieved, and the flake graphite is spheroidized by appropriately setting the operation time. For example, the nozzle discharge pressure is about 0.01 MPa to 0.50 MPa, the amount of blown gas is about 0.2 Nm 3 / min to 1.0 Nm 3 / min, the tank pressure is about −10 kPa to 30 kPa, and the operation time is 1 minute to 100 It may be about minutes. In addition, what is necessary is just to use air, nitrogen, water vapor | steam etc. as a gas blown from the opposing nozzle 3, and the temperature in the tank 1 should just be about 0 degreeC-60 degreeC. Gas convection occurs in the tank 1, and the graphite spheroidized by colliding with each other in the collision area on the lower side of the tank 1 is blown up along the convection in the tank 1 and then sinks again. That is, the particles are blown up in the vicinity of the center of the tank 1 and descend along the wall of the tank 1 to cause a circulating flow in the tank 1. By providing a classifier 4 at the top of the tank 1, fine powder below the classification limit can be discharged out of the tank 1. The classifier 4 may be a known one, but a high-speed rotation classifier is usually used. The discharge amount at this time varies depending on the particle size of the flake graphite used as a raw material.
上記の操作はバッチで行なうことが好ましく、槽１の底部に設けられた吹き上げノズル５から槽１内へ空気を送り込むことにより球形化黒鉛粒子をフィーダー２から回収できる。 The above operation is preferably performed in a batch, and the spheroidized graphite particles can be recovered from the feeder 2 by sending air into the tank 1 from the blowing nozzle 5 provided at the bottom of the tank 1.
なお、球形化黒鉛粒子の原料としては、鱗片状の天然黒鉛や人造黒鉛を使用することができ、例えば、鱗片状天然黒鉛は、一般に８５％から９９％を上まわる純度で入手できるのでそのまま用いればよい。必要に応じて、公知の方法でさらに純度を高めることも好ましい。原料となる鱗片状黒鉛の粒度には種々のものがあるが、例えば、平均粒子径が１０μｍ〜６０μｍ程度の鱗片状黒鉛（原料）を用いるのがよい。 As a raw material for the spheroidized graphite particles, scaly natural graphite or artificial graphite can be used. For example, scaly natural graphite is generally used because it is available in a purity exceeding 85% to 99%. That's fine. If necessary, it is also preferred to further increase the purity by a known method. There are various particle sizes of the flake graphite used as a raw material. For example, flake graphite (raw material) having an average particle diameter of about 10 μm to 60 μm is preferably used.
本発明で好適に使用する球形化黒鉛の粒子形状は、サッカーボールやテニスボールの様な真球状のみならず、ラグビーボールの様な扁球状のものも含み、特に限定されないが、円形度が０．８６程度以上のものであることが好ましい。但し、円形度は三次元の黒鉛粒子を二次元平面に投影して算出される指標であるので、例えば一般的に入手できる鱗片状天然黒鉛粒子の円形度を算出すると０．８４程度になり、本発明で使用する球形化黒鉛の円形度と近似するが、鱗片状黒鉛粒子（原料）は平面的な粒子であるのに対し、本発明における二次電池用電極材料の実際の形状は立体的であり全く異なる。なお、円形度は、次式のようにして求めることができる（特開平１１−２６３６１２号参照）。
円形度＝（相当円の周囲長）／（粒子投影像の周囲長）
ここで、相当円とは、撮像した粒子像と同じ投影面積を持つ円であり、粒子投影像の周囲長とは、２値化された粒子像のエッジ点を結んで得られる輪郭線の長さである。
The particle shape of the spheroidized graphite preferably used in the present invention includes not only a spherical shape such as a soccer ball or a tennis ball but also a flat shape such as a rugby ball, and is not particularly limited. It is preferably about .86 or more. However, since the circularity is an index calculated by projecting three-dimensional graphite particles onto a two-dimensional plane, for example, when calculating the circularity of scaly natural graphite particles that are generally available, it becomes about 0.84, Although it approximates the circularity of the spheroidized graphite used in the present invention, the flaky graphite particles (raw material) are planar particles, whereas the actual shape of the secondary battery electrode material in the present invention is three-dimensional. And completely different. The circularity can be obtained by the following equation (see Japanese Patent Application Laid-Open No. 11-263612).
Circularity = (perimeter of equivalent circle) / (perimeter of particle projection image)
Here, the equivalent circle is a circle having the same projected area as the captured particle image, and the peripheral length of the particle projected image is the length of the contour line obtained by connecting the edge points of the binarized particle image. That's it.
球形化黒鉛として、上述した球形化黒鉛を等方的に加圧して成形した等方加圧処理球形化黒鉛も使用することができる。上述した球形化黒鉛を等方的に加圧することにより、得られる球形化黒鉛の等方性が一層高まるとともに、球形化黒鉛粒子の粒子内空隙が低減して高密度化する。等方性が高く、高密度化された球形化黒鉛粒子を使用することにより、得られるリチウムイオン二次電池の電池容量を大きくすることができる。等方的に加圧する方法は、特に限定されず、例えば、ガス、液体などの加圧媒体を用いて、球形化黒鉛を等方的に加圧する方法が挙げられ、例えば、高温で等方的に加圧する熱間等方加圧処理（Ｈｏｔ Ｉｓｏｔａｔｉｃ Ｐｒｅｓｓｉｎｇ）、水若しくはアルゴンなどを加圧媒体として用いて、室温で等方的に加圧する冷間等方加圧処理(Ｃｏｌｄ Ｉｓｏｔａｔｉｃ Ｐｒｅｓｓｉｎｇ)などが挙げられる。 As the spheroidized graphite, isotropic pressure-treated spheroidized graphite formed by isotropically pressing the above-described spheroidized graphite can also be used. By isotropically pressurizing the above-mentioned spheroidized graphite, the isotropic property of the obtained spheroidized graphite is further increased, and the voids in the particles of the spheroidized graphite particles are reduced to increase the density. By using highly isotropic and densified spherical graphite particles, the battery capacity of the obtained lithium ion secondary battery can be increased. The method of isotropically pressurizing is not particularly limited, and examples thereof include a method of isotropically pressurizing spheroidized graphite using a pressurizing medium such as a gas or a liquid. Hot isostatic pressing to pressurize to the surface, Cold isostatic pressing to pressurize isotropically at room temperature using water or argon as a pressurizing medium, etc. Can be mentioned.
球形化黒鉛を加圧する圧力は、特に限定されるものではないが、５０ｋｇｆ／ｃｍ2（４９０．５×１０4Ｐａ）以上、より好ましくは１００ｋｇｆ／ｃｍ2（９８１×１０4Ｐａ）以上、さらに好ましくは２００ｋｇｆ／ｃｍ2（１９６２×１０4Ｐａ）以上が好ましい。圧力が５０ｋｇｆ／ｃｍ2未満では、黒鉛粒子の密度や等方性を十分に高めることができないからである。 The pressure for pressurizing the spheroidized graphite is not particularly limited, but is 50 kgf / cm 2 (490.5 × 10 4 Pa) or more, more preferably 100 kgf / cm 2 (981 × 10 4 Pa) or more, 200 kgf / cm 2 (1962 × 10 4 Pa) or more is preferable. This is because if the pressure is less than 50 kgf / cm 2 , the density and isotropy of the graphite particles cannot be sufficiently increased.
球形化黒鉛を等方加圧して成形し、得られた成形体を解砕する。得られた成形体を解砕することによって、高密度で等方性の高い等方加圧処理球形化黒鉛が得られる。加圧処理に際してバインダーを使用しなければ、得られる成形体にわずかの剪断力を付与するだけで、成形体を容易に解砕できる。解砕の方法は特に限定されないが、例えば、撹拌羽根を有する撹拌機を用いて行うことができる。また、通常のジェットミル、振動ミル、ピンミル、ハンマーミルなどの公知の粉砕機を使用してもよい。 Spherical graphite is molded by isostatic pressing, and the resulting molded product is crushed. By crushing the obtained molded body, isotropic pressure-treated spheroidized graphite having high density and high isotropic property is obtained. If no binder is used in the pressure treatment, the molded body can be easily crushed by applying a slight shearing force to the obtained molded body. Although the method of crushing is not specifically limited, For example, it can carry out using the stirrer which has a stirring blade. Moreover, you may use well-known grinders, such as a normal jet mill, a vibration mill, a pin mill, a hammer mill.
リチウムイオン二次電池用負極
次に、本発明のリチウムイオン二次電池用負極について説明する。本発明のリチウムイオン二次電池用負極は、上述した本発明のリチウムイオン二次電池用負極材料を用いたことを特徴とする。本発明のリチウムイオン二次電池用負極は、例えば、上記負極材料と電極作製用バインダーとを水あるいは有機溶剤に分散させたスラリーを銅箔などの集電体に塗布した後、乾燥しプレスすることにより得られる。前記電極作製用バインダーとしては、ポリテトラフルオロエチレン、ポリフッ化ビニリデン、フッ化ビニリデン／ヘキサフルオロプロピレン共重合体、テトラフルオロエチレン／ヘキサフルオロプロピレン／フッ化ビニリデン共重合体などのフッ素系高分子化合物；カルボキシメチルセルロース、スチレン−ブタジエンゴム、アクリロニトリル−ブタジエンゴムなどが挙げられ、単独で、あるいは、二種以上を混合して使用してもよい。これらの中でも、電極作製用バインダーとしては、カルボキシメチルセルロースとスチレン−ブタジエンゴムとの混合物が好ましい。
Next, the negative electrode for lithium ion secondary batteries of the present invention will be described. The negative electrode for a lithium ion secondary battery of the present invention is characterized by using the above-described negative electrode material for a lithium ion secondary battery of the present invention. The negative electrode for a lithium ion secondary battery of the present invention is, for example, applied to a current collector such as a copper foil with a slurry in which the negative electrode material and the electrode-forming binder are dispersed in water or an organic solvent, and then dried and pressed. Can be obtained. Examples of the electrode-forming binder include fluorine-based polymer compounds such as polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride / hexafluoropropylene copolymer, tetrafluoroethylene / hexafluoropropylene / vinylidene fluoride copolymer; Examples thereof include carboxymethyl cellulose, styrene-butadiene rubber, acrylonitrile-butadiene rubber, and the like may be used alone or in admixture of two or more. Among these, as a binder for electrode preparation, a mixture of carboxymethyl cellulose and styrene-butadiene rubber is preferable.
電極作製用バインダーの使用量は、負極材料１００質量部に対して、固形分換算で０．５質量部以上が好ましく、より好ましくは１．０質量部以上であり、３．０質量部以下が好ましく、より好ましくは２．０質量部以下である。 The amount of the binder for electrode preparation is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, and 3.0 parts by mass or less in terms of solid content with respect to 100 parts by mass of the negative electrode material. Preferably, it is 2.0 parts by mass or less.
リチウムイオン二次電池
本発明のリチウムイオン二次電池は、上記本発明の負極を使用することを特徴とする。本発明のリチウムイオン二次電池は、本発明の負極を用いたものであれば、特に限定されず、例えば、円筒（乾電池）型、角型、ボタン型、コイン型などの形状を有することができる。図２は、円筒（乾電池）型のリチウムイオン二次電池の内部構造を例示する斜視図であり、シート状の正極体１４と負極体１５との間にセパレータ１６を挟んで渦巻状に巻いたスパイラル構造になっている。図３は、コイン型のリチウムイオン二次電池の内部構造を例示する断面図であり、正極体１４と負極体１５と電解液とを備え、正極体１４と負極体１５とはセパレータ１６によって分離されており、リチウムイオンが、電解液を介して正極体と負極体とを行き来することにより、起電反応が行われる。
Lithium ion secondary battery The lithium ion secondary battery of the present invention uses the negative electrode of the present invention. The lithium ion secondary battery of the present invention is not particularly limited as long as the negative electrode of the present invention is used. For example, the lithium ion secondary battery may have a cylindrical (dry cell) type, a square type, a button type, a coin type, or the like. it can. FIG. 2 is a perspective view illustrating the internal structure of a cylindrical (dry cell) type lithium ion secondary battery, which is wound in a spiral shape with a separator 16 interposed between a sheet-like positive electrode body 14 and a negative electrode body 15. It has a spiral structure. FIG. 3 is a cross-sectional view illustrating the internal structure of a coin-type lithium ion secondary battery, which includes a positive electrode body 14, a negative electrode body 15, and an electrolyte solution, and the positive electrode body 14 and the negative electrode body 15 are separated by a separator 16. Thus, the lithium ions move back and forth between the positive electrode body and the negative electrode body through the electrolytic solution, whereby an electromotive reaction is performed.
リチウムイオン二次電池における正極材料としては、例えば、ＬｉＣｏＯ2、ＬｉＮｉＯ2、ＬｉＮｉ1-yＣｏyＯ2、ＬｉＭｎＯ2、ＬｉＭｎ2Ｏ4、ＬｉＦｅＯ2などのリチウム複合酸化物などが挙げられる。これらの中でも好ましいのは、リチウムコバルト複合酸化物である。正極用のバインダーとしては、ポリフッ化ビニリデンやポリ四フッ化エチレンなどを挙げることができる。電解液としては、エチレンカーボネート、メチルエチルカーボネートなどの有機溶媒や、該有機溶媒と、ジメチルカーボネート、ジエチルカーボネート、１，２−ジメトキシエタン、１，２−ジエトキシメタン、エトキシメトキシエタンなどの低沸点溶媒との混合溶媒に、ＬｉＰＦ6、ＬｉＢＦ4、ＬｉＣｌＯ4、ＬｉＣＦ3ＳＯ3、ＬｉＡｓＦ6などの電解液溶質（電解質塩）を溶解した溶液が用いられる。また、電解液の代わりに固体電解質を使用してもよい。正極体と負極体とを分離するセパレータとしては、例えば、ポリエチレンやポリプロピレンなどのポリオレフィンを主成分とした不織布、クロス、微孔フィルムなどを用いることができる。 As the cathode material in a lithium ion secondary battery, for example, LiCoO 2, LiNiO 2, LiNi 1 -y Co y O 2, LiMnO 2, LiMn 2 O 4, a lithium composite oxide such as LiFeO 2 and the like. Among these, lithium cobalt composite oxide is preferable. Examples of the binder for the positive electrode include polyvinylidene fluoride and polytetrafluoroethylene. As an electrolytic solution, an organic solvent such as ethylene carbonate and methyl ethyl carbonate, and a low boiling point such as the organic solvent and dimethyl carbonate, diethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxymethane, ethoxymethoxyethane, etc. A solution obtained by dissolving an electrolyte solution solute (electrolyte salt) such as LiPF 6 , LiBF 4 , LiClO 4 , LiCF 3 SO 3 , LiAsF 6 in a mixed solvent with a solvent is used. Moreover, you may use a solid electrolyte instead of electrolyte solution. As a separator which isolate | separates a positive electrode body and a negative electrode body, the nonwoven fabric, cloth, microporous film, etc. which have polyolefins, such as polyethylene and a polypropylene, as a main component can be used, for example.
以下に実施例を挙げて本発明をより具体的に説明するが、本発明は、下記実施例によって限定されるものではなく、前・後記の趣旨に適合しうる範囲で適宜変更して実施することも可能であり、それらはいずれも本発明の技術的範囲に包含される。 The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to the following examples, and may be appropriately modified and implemented within a range that can meet the purpose described above and below. All of which are within the scope of the present invention.
［評価方法］
１．表面官能基量の測定
薬包紙の上で、黒鉛試料をそれぞれ１０．００ｇ秤量し、１００ｍｌの褐色フラスコに入れた。そこにホールピペットを用いて０．００２ｍｏｌ／ｌ ＮａＯＥｔ水溶液を５０ｍｌ入れ、黒鉛の酸性表面官能基を反応させた。褐色フラスコにサイズ２５の撹拌子を入れ、軽く振り混ぜて黒鉛を沈めた後、空気抜きをして栓をした。それぞれの三角フラスコをマグネティックスターラーに載せ、５００ｒｐｍで２時間撹拌させた後、撹拌を停止して約２２時間放置した。黒鉛を濾過して得られた反応液から２５ｍｌをとり、０．００２ｍｏｌ／ｌ ＨＣｌ水溶液を用いて、滴定装置にてＮａＯＥｔ残量を測定し、下記式（１）により黒鉛の表面官能基量を算出した。
[Evaluation methods]
1. Measurement of the amount of surface functional groups 10.00 g of each graphite sample was weighed on a medicine wrapping paper and placed in a 100 ml brown flask. 50 ml of 0.002 mol / l NaOEt aqueous solution was put there using a hole pipette, and the acidic surface functional group of graphite was made to react. A stir bar of size 25 was placed in a brown flask and lightly shaken to submerge the graphite, then the air was vented and stoppered. Each Erlenmeyer flask was placed on a magnetic stirrer and stirred at 500 rpm for 2 hours, after which stirring was stopped and left for about 22 hours. Take 25 ml from the reaction solution obtained by filtering graphite, measure the remaining amount of NaOEt with a titration device using 0.002 mol / l HCl aqueous solution, and calculate the surface functional group amount of graphite by the following formula (1). Calculated.
２．平均粒子径
レーザー回折式粒度分布測定装置（島津製作所製、「ＳＡＬＤ（登録商標）−２０００」）を用いて測定を行い、体積基準メディアン径（Ｄ５０）を求めた。
2. Average particle diameter Measurement was carried out using a laser diffraction particle size distribution measuring apparatus (manufactured by Shimadzu Corporation, “SALD (registered trademark) -2000”) to obtain a volume-based median diameter (D50).
３．比表面積
比表面積測定装置（Ｍｉｃｒｏｍｅｒｉｔｉｃｓ社製、「ＡＳＡＰ ２４０５」）を用いて、ＢＥＴ法による比表面積を測定した。
3. Specific surface area The specific surface area by the BET method was measured using a specific surface area measurement device (manufactured by Micromeritics, "ASAP 2405").
４．極板強度試験
黒鉛試料１０ｇに対して、純水２．１ｇ±０．１ｇ、ＣＭＣ（カルボキシメチルセルロース）水溶液（ダイセル化学株式会社製、ＣＭＣ濃度：２．０質量％）５ｇ、ＳＢＲ（スチレンブタジエンゴム）分散液（日本合成ゴム株式会社製、ＳＢＲ含有率；５．０質量％、溶媒；水）２ｇを加えてスラリー状にしたものを厚さ１８μｍの銅箔上に自動コーター（松尾産業株式会社製）を用いて塗布し、乾燥機で８０℃１０分間乾燥後、さらに１００℃１０分間乾燥して負極を作製した。作製した極板を直径１．６ｃｍの円盤状に打ち抜き、ローラープレス機を用いて１．６ｇ／ｃｍ2〜１．８ｇ／ｃｍ2の間で種々の電極密度になるようにプレスを行い、極板強度測定用円盤状電極を作製した。
4). Electrode strength test With respect to 10 g of graphite sample, pure water 2.1 g ± 0.1 g, CMC (carboxymethylcellulose) aqueous solution (manufactured by Daicel Chemical Industries, CMC concentration: 2.0 mass%), 5 g, SBR (styrene butadiene rubber) ) Dispersion (manufactured by Nippon Synthetic Rubber Co., Ltd., SBR content: 5.0 mass%, solvent: water) 2 g of slurry was added to an automatic coater (Matsuo Sangyo Co., Ltd.) on 18 μm thick copper foil And then dried at 80 ° C. for 10 minutes with a dryer, and further dried at 100 ° C. for 10 minutes to produce a negative electrode. Punching The prepared plate into a disk shape having a diameter of 1.6 cm, subjected to pressing so that a variety of electrode density between 1.6g / cm 2 ~1.8g / cm 2 using a roller press, pole A disk-shaped electrode for measuring plate strength was produced.
黒鉛が塗布されたこの円盤状電極をＳＵＳ板上に両面テープで貼り付け、ＳＵＳ板上の電極に１０ｍｍ×５ｍｍの接触面積となるように短冊状に切ったテープを貼り付けた。ＳＵＳ板を引張試験機（東京試験機社製ＬＳＣ−１／３０−２）の下部治具に固定し、電極に貼り付けられたテープを試験機の上部治具（上下可動）に固定し、引張速度３０ｍｍ／ｍｉｎにて引っ張り、テープが極板から剥がれたときの力（最大引張力）を記録した。この値から式（２）により単位当りの極板強度（ｇ／ｃｍ2）を計算した。
極板強度（ｋｇ／ｃｍ2）＝最大引張力（ｋｇ）／（１ｃｍ×０．５ｃｍ）・・・（２）
１．６ｇ／ｃｍ2〜１．８ｇ／ｃｍ2の電極密度の電極に対して得られたそれぞれの極板密度の値を電極密度に対してプロットし、線形最小二乗法による近似曲線の式から、電極密度１．７ｇ／ｃｍ2における極板強度を算出した。
This disk-like electrode coated with graphite was stuck on a SUS plate with a double-sided tape, and a tape cut into a strip shape so as to have a contact area of 10 mm × 5 mm was stuck on the electrode on the SUS plate. The SUS plate is fixed to the lower jig of a tensile tester (Tokyo Testing Machine Co., Ltd. LSC-1 / 30-2), and the tape attached to the electrode is fixed to the upper jig (movable up and down) of the tester. The film was pulled at a tensile speed of 30 mm / min, and the force (maximum tensile force) when the tape was peeled off from the electrode plate was recorded. From this value, the electrode plate strength (g / cm 2 ) per unit was calculated according to the formula (2).
Electrode plate strength (kg / cm 2 ) = Maximum tensile force (kg) / (1 cm × 0.5 cm) (2)
The value of each plate density obtained for 1.6g / cm 2 ~1.8g / cm 2 of electrode density of the electrode was plotted against the electrode density, the equation of the approximate curve by linear least squares The electrode plate strength at an electrode density of 1.7 g / cm 2 was calculated.
５．初期効率
電池の充電を、電流密度０．７２ｍＡ／ｃｍ2（０．２Ｃ）の定電流値で電圧が０．００７Ｖになるまで行い、続けて、０．００７Ｖの定電圧で電流値が０．１４ｍＡになるまで行った。次に、電池の放電を、電流密度０．７２ｍＡ／ｃｍ2（０．２Ｃ）の定電流値で電圧が１．１Ｖになるまで行った。なお、電池の充放電は、２５℃で行った。電池の初期効率を、一回目の充電容量と一回目の放電容量から下記式（３）により算出した。
5). Initial efficiency The battery was charged until the voltage reached 0.007 V at a constant current value of 0.72 mA / cm 2 (0.2 C), and then the current value reached 0.007 V at a constant voltage of 0.007 V. It went until it became 14 mA. Next, the battery was discharged until the voltage became 1.1 V at a constant current value of a current density of 0.72 mA / cm 2 (0.2 C). In addition, charging / discharging of the battery was performed at 25 degreeC. The initial efficiency of the battery was calculated by the following formula (3) from the first charge capacity and the first discharge capacity.
６．負荷特性
電池の充電を、電流密度０．７２ｍＡ／ｃｍ2（０．２Ｃ）の定電流値で電圧が０．００７Ｖになるまで行い、続けて、０．００７Ｖの定電圧で電流値が０．１４ｍＡになるまで行った。次に、電流密度０．７２ｍＡ／ｃｍ2（０．２Ｃ）の定電流値で電圧が１．１Ｖになるまで放電を行い、放電容量を測定した。続いて、上記と同様にして電池の充電を行った後、電流密度１４．４ｍＡ／ｃｍ2（２．０Ｃ）の定電流値で電圧が１．１Ｖになるまで放電を行い、放電容量を測定した。なお、電池の充放電は、２５℃で行った。
電池の負荷特性を、下記式（４）により算出した。
6). Load characteristics The battery was charged at a constant current value of 0.72 mA / cm 2 (0.2 C) until the voltage reached 0.007 V, and then at a constant voltage of 0.007 V, the current value was set to 0.00. It went until it became 14 mA. Next, discharging was performed at a constant current value of 0.72 mA / cm 2 (0.2 C) until the voltage became 1.1 V, and the discharge capacity was measured. Subsequently, after charging the battery in the same manner as described above, discharging was performed until the voltage became 1.1 V at a constant current value of 14.4 mA / cm 2 (2.0 C), and the discharge capacity was measured. did. In addition, charging / discharging of the battery was performed at 25 degreeC.
The load characteristics of the battery were calculated by the following formula (4).
球形化黒鉛の作製
球形化黒鉛Ａ（高官能基量黒鉛）
平均粒子径２０μｍの鱗片状天然黒鉛をホソカワミクロン社製「カウンタージェットミル１００ＡＦＧ」を用いて、試料量２００ｇ、ノズル吐出空気圧０．２０ＭＰａ、操作時間２０分の条件で球状化し、球形化黒鉛Ａを得た。得られた球形化黒鉛Ａの表面官能基量は、９．９ｍｅｑ／ｋｇであった。
Production of spheroidized graphite Spheronized graphite A (high functional group graphite)
Spherical graphite having an average particle diameter of 20 μm is spheroidized using “Counter Jet Mill 100AFG” manufactured by Hosokawa Micron Corporation under the conditions of a sample amount of 200 g, a nozzle discharge air pressure of 0.20 MPa, and an operation time of 20 minutes to obtain spherical graphite A. It was. The surface functional group amount of the obtained spheroidized graphite A was 9.9 meq / kg.
球形化黒鉛Ｂ（低官能基量黒鉛）
前記球形化黒鉛Ａを窒素雰囲気下、１２００℃で２時間加熱処理して、球形化黒鉛Ｂを得た。得られた球形化黒鉛Ｂの表面官能基量は、０．６ｍｅｑ／ｋｇであった。
Spherical graphite B (low functional group graphite)
The spheroidized graphite A was heat-treated at 1200 ° C. for 2 hours in a nitrogen atmosphere to obtain spheroidized graphite B. The surface functional group amount of the obtained spheroidized graphite B was 0.6 meq / kg.
球形化黒鉛Ｃ（高官能基量黒鉛）
前記球形化黒鉛Ｂを空気雰囲気下、２００℃で２時間加熱処理して、球形化黒鉛Ｃを得た。得られた球形化黒鉛Ｃの表面官能基量は、２．３ｍｅｑ／ｋｇであった。
Spherical graphite C (high functional group graphite)
The spheroidized graphite B was heat-treated at 200 ° C. for 2 hours in an air atmosphere to obtain spheroidized graphite C. The amount of surface functional groups of the obtained spheroidized graphite C was 2.3 meq / kg.
球形化黒鉛Ｄ（高官能基量黒鉛）
前記球形化黒鉛Ｂを空気雰囲気下、２７０℃で２時間加熱処理して、球形化黒鉛Ｄを得た。得られた球形化黒鉛Ｄの表面官能基量は、５．８ｍｅｑ／ｋｇであった。
Spheroidized graphite D (high functional group graphite)
The spheroidized graphite B was heat-treated at 270 ° C. for 2 hours in an air atmosphere to obtain spheroidized graphite D. The surface functional group amount of the obtained spheroidized graphite D was 5.8 meq / kg.
リチウムイオン二次電池用負極材料の作製
上記で得た球形化黒鉛Ａ〜Ｄを使用して、表２に示す配合組成を有するリチウムイオン二次電池用負極材料を作製した。リチウムイオン二次電池用負極材料Ｎｏ．１〜７について評価した結果を表２に示した。
Production of Negative Electrode Material for Lithium Ion Secondary Battery A negative electrode material for a lithium ion secondary battery having the composition shown in Table 2 was produced using the spheroidized graphites AD obtained above. Negative electrode material No. for lithium ion secondary battery The results of evaluation for 1 to 7 are shown in Table 2.
リチウムイオン二次電池用負極および二次電池の作製
リチウムイオン二次電池用負極材料Ｎｏ．１〜７を用いて、リチウムイオン二次電池用負極を次のようにして作製した。まず、リチウムイオン二次電池用負極材料１００質量部、ＣＭＣ（カルボキシメチルセルロース）水溶液（濃度２．０質量％）５０質量部、ＳＢＲ（スチレンブタジエンゴム）分散液（ＳＢＲ含有率；５．０質量％、溶媒；水）２０質量部、純水３０質量部を、撹拌機を用いて１０分間撹拌し電極材スラリーを調製した。
Preparation of negative electrode for lithium ion secondary battery and secondary battery Anode material No. for lithium ion secondary battery A negative electrode for a lithium ion secondary battery was produced using 1 to 7 as follows. First, 100 parts by mass of a negative electrode material for a lithium ion secondary battery, 50 parts by mass of a CMC (carboxymethylcellulose) aqueous solution (concentration: 2.0% by mass), an SBR (styrene butadiene rubber) dispersion (SBR content: 5.0% by mass) , Solvent; water) 20 parts by mass and 30 parts by mass of pure water were stirred for 10 minutes using a stirrer to prepare an electrode material slurry.
得られた電極材スラリーを銅箔（厚み；１８μｍ）上に塗布した後、１００℃に設定した乾燥機で乾燥することにより電極材付着量１０ｍｇ／ｃｍ2、電極材面積２．０ｃｍ2の電極を得た。この電極材を、プレス機を用いて加圧することにより極板密度を１．７ｇ／ｃｍ3に調製し、リチウムイオン二次電池用負極を得た。 The obtained electrode material slurry was applied on a copper foil (thickness: 18 μm), and then dried with a drier set at 100 ° C., whereby an electrode material adhesion amount of 10 mg / cm 2 and an electrode material area of 2.0 cm 2 was obtained. Got. The electrode material was pressurized using a press to adjust the electrode plate density to 1.7 g / cm 3 to obtain a negative electrode for a lithium ion secondary battery.
得られたリチウムイオン二次電池用負極を用いて、リチウムイオン二次電池を次のようにして作製した。リチウムイオン二次電池用負極を作用極とし、対極および参照極に金属リチウムを用いて３電極式セルを組み立てた。電解液としては、１Ｍ ＬｉＰＦ6／（ＥＣ＋ＭＥＣ）（宇部興産社製）０．２ｍｌを用いた。ここで、１Ｍ ＬｉＰＦ6／（ＥＣ＋ＭＥＣ）とは、エチレンカーボネート（ＥＣ）とメチルエチルカーボネート（ＭＥＣ）を容積比１：１で混合した溶媒に、ＬｉＰＦ6を濃度１Ｍとなるように溶解させたものである。得られたリチウムイオン二次電池についての評価結果を表２に示した。 Using the obtained negative electrode for a lithium ion secondary battery, a lithium ion secondary battery was produced as follows. A three-electrode cell was assembled using a negative electrode for a lithium ion secondary battery as a working electrode and metallic lithium as a counter electrode and a reference electrode. As an electrolytic solution, 0.2 ml of 1M LiPF 6 / (EC + MEC) (manufactured by Ube Industries) was used. Here, 1M LiPF 6 / (EC + MEC) is obtained by dissolving LiPF 6 to a concentration of 1M in a solvent in which ethylene carbonate (EC) and methyl ethyl carbonate (MEC) are mixed at a volume ratio of 1: 1. It is. The evaluation results for the obtained lithium ion secondary battery are shown in Table 2.
リチウムイオン二次電池Ｎｏ．１〜３は、負極材料が高官能基量黒鉛と低官能基量黒鉛とを２０／８０〜８０／２０の質量比で含有する場合である。これらのＮｏ．１〜３の電池は、いずれも負極の極板強度が高く、且つ、電池の初期効率および負荷特性にも優れている。リチウムイオン二次電池Ｎｏ．４は負極材料が高官能基量黒鉛のみを含有する場合であるが、これは負極の極板強度には優れるものの、初期効率や負荷特性が劣る。一方、リチウムイオン二次電池Ｎｏ．５は負極材料が低官能基量黒鉛のみを含有する場合であるが、これは初期効率や負荷特性には優れるものの、負極の極板強度が劣る。リチウムイオン二次電池Ｎｏ．６，７は、負極材料に含有される全ての黒鉛の表面官能基量を増加させた場合であるが、これらは負極の極板強度または電池性能が不十分であった。 Lithium ion secondary battery No. 1-3 are cases where the negative electrode material contains high functional group weight graphite and low functional group weight graphite in a mass ratio of 20/80 to 80/20. These No. The batteries 1 to 3 all have a high negative electrode plate strength and are excellent in the initial efficiency and load characteristics of the battery. Lithium ion secondary battery No. Although 4 is a case where the negative electrode material contains only high functional group weight graphite, this is excellent in the electrode plate strength of the negative electrode, but is inferior in initial efficiency and load characteristics. On the other hand, lithium ion secondary battery no. Although 5 is a case where the negative electrode material contains only low functional group weight graphite, this is excellent in initial efficiency and load characteristics but is inferior in the electrode plate strength of the negative electrode. Lithium ion secondary battery No. 6 and 7 are cases where the amount of surface functional groups of all graphite contained in the negative electrode material was increased, but these had insufficient electrode plate strength or battery performance of the negative electrode.
本発明は、リチウムイオン二次電池用負極材料として好適である。 The present invention is suitable as a negative electrode material for a lithium ion secondary battery.
１：槽、２：フィーダー、３：対向ノズル、４：分級機、５：吹き上げノズル、１３：集電体、１３ａ：負極集電体、１３ｂ：正極集電体、１４：正極体、１５：負極体、１６：セパレータ、１７：電池ケース、１８：絶縁ガスケット 1: tank, 2: feeder, 3: counter nozzle, 4: classifier, 5: blowing nozzle, 13: current collector, 13a: negative electrode current collector, 13b: positive electrode current collector, 14: positive electrode body, 15: Negative electrode body, 16: separator, 17: battery case, 18: insulating gasket
Claims (5)
前記高官能基量黒鉛と前記低官能基量黒鉛の質量比（高官能基量黒鉛／低官能基量黒鉛）が、１０／９０〜８０／２０であることを特徴とするリチウムイオン二次電池用負極材料。 A high functional group weight graphite having a surface functional group amount of 2.0 meq / kg or more, and a low functional group graphite having a surface functional group amount of less than 2.0 meq / kg,
A lithium ion secondary battery, wherein a mass ratio of the high functional group graphite and the low functional group graphite (high functional group graphite / low functional group graphite) is 10/90 to 80/20 Negative electrode material.
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| JP2013001582A (en) * | 2011-06-13 | 2013-01-07 | Kansai Coke & Chem Co Ltd | Isotropic graphite material, and method for producing the same |
| JP2014127313A (en) * | 2012-12-26 | 2014-07-07 | Toyota Motor Corp | Nonaqueous electrolyte secondary battery and manufacturing method of the battery |
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| JP2005108456A (en) * | 2003-09-26 | 2005-04-21 | Kansai Coke & Chem Co Ltd | Graphite for secondary battery electrode, secondary battery electrode containing the same, and lithium ion secondary battery using the electrode |
| 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 |
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| JP2005108456A (en) * | 2003-09-26 | 2005-04-21 | Kansai Coke & Chem Co Ltd | Graphite for secondary battery electrode, secondary battery electrode containing the same, and lithium ion secondary battery using the electrode |
| 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 |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP2013001582A (en) * | 2011-06-13 | 2013-01-07 | Kansai Coke & Chem Co Ltd | Isotropic graphite material, and method for producing the same |
| JP2014127313A (en) * | 2012-12-26 | 2014-07-07 | Toyota Motor Corp | Nonaqueous electrolyte secondary battery and manufacturing method of the battery |
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