JP4233800B2 - Lithium secondary battery negative electrode material and manufacturing method thereof - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、人造炭素系、特に人造黒鉛系リチウムイオン二次電池負極材料とその製造方法に関する。
【０００２】
近年、電子機器等の小型軽量化、省電力化及び環境保全の立場から、鉛蓄電池やニッケルカドミウム電池に替わるクリーンな非水系二次電池、特にリチウム二次電池が注目されている。そのため、現在では、ノート型パソコン、携帯電話等のいわゆるモバイル電子機器用電池として広く使用されている他、電気自動車のバッテリ用途でも検討が進められている。このリチウム二次電池に使用される負極材料としては、放電容量が高いこと、充填密度が高いこと、初期効率が高いこと、サイクル特性が優れること、そして安価であること等が要求される。
【０００３】
リチウム二次電池の負極材料としては、リチウム金属（合金）系と炭素材料系に大別されるが、リチウム金属（合金）系では、電池容量は非常に高くなるものの、充電時のリチウムのデンドライド（樹脂状結晶）状態での析出や微粉化のためにサイクル寿命及び安全性に問題を生じる。そのため、現在では炭素材料系が主流になっており、天然黒鉛系、メソカーボンマイクロビーズ（ＭＣＭＢ：球状炭素）系、人造黒鉛系、そして炭素繊維系がある。
このうち、結晶構造の優れている天然黒鉛系は、電池特性のうち放電容量は３５０mAhr/g以上の非常に高い特性が得られるが、粉体特性のうちTap嵩密度が低いことや電池特性のうち、充放電を繰り返した時のサイクル特性や急速な充放電による負荷特性に問題がある。また、表面積が大きいために１回目の充電容量と放電容量の差を示す不可逆容量が大きい問題もある。これらの問題は、天然黒鉛系材料は黒鉛化性が発達しているために扁平な構造となることから発生している。そこで、天然黒鉛系を使用する場合、ピッチと混練し、表面にピッチコートした材料を用いることが検討されているが、まだ充分な改善は出来ていない。ＭＣＭＢ系は球状の構造をしているために、サイクル特性や負荷特性には問題がないが、放電容量が３２０mAhr/g程度と低い。このため触媒黒鉛化を行うことが検討されているが、まだ十分な解決がされていない。
【０００４】
特開平８-２８７９１１号公報には、生コークスを微粉砕し、不活性ガス雰囲気下に700〜1500℃で加熱処理する方法が開示されている。また、特開平９−１５７０２２号公報には、生コークス粉末を、酸化熱処理し、黒鉛化した材料が記載されている。また、特開平１０−２２３２２３号公報には、炭素粉末にホウ素化合物を添加して黒鉛化することが記載されている。更に、特開２００１−２３６３８号公報には、ディレードコーカーで製造された生コークスを粉砕し、熱処理し、黒鉛化する方法が開示されている。これらの方法は、それなりに電池特性の改善がなされいるものの、モバイル機器の高機能化や超軽量化によって、消費電力が増大し充電時間あたりの使用時間増大等の要求がなされており、更なる高負荷電池特性に対応できる優れた負極材料が望まれている。
【０００５】
【発明が解決しようとする課題】
本発明は、モバイル機器の高機能化や超軽量化によって、消費電力が増大し充電時間あたりの使用時間増大等の要求がなされている現状下、更なる高負荷電池特性に対応できる優れた負極材料を提供することを目的とする。また、比表面積を小さくし、電池特性の中の初期効率を上げることや、粉体密度を上げることを目的とする。更に、電池内に充填される負極量を増加させ電池容量を増加させること、更に塗工スラリーの塗工性をあげることで、銅箔に負極ペーストを均一に塗工することが出来るようになることから、このような粉体特性に優れ、かつ放電容量、充放電効率等に代表される電池特性が優れた人造炭素系、特に人造黒鉛系リチウムイオン二次電池負極材料を提供することを目的とする。
【０００６】
【課題を解決するための手段】
本発明は、石炭系重質油及び石油系重質油から選択される少なくとも１つの重質油を原料とし、ディレードコーキングして生コークスを得て、これを熱処理して又は黒鉛化してリチウム二次電池負極材料を製造する方法において、キノリン不溶分が１ wt ％以下とされた重質油に、平均粒径が１〜５０μｍである黒鉛化の発達した黒鉛材料を、上記重質油に対して２〜３５ wt ％配合し、ディレードコーキングして生コークスを得た後、７００〜１５００℃で行う熱処理及び２５００℃以上で行う黒鉛化の少なくとも一の処理を行うことを特徴とするリチウム二次電池負極材料の製造方法である。
【０００７】
本発明において、a)重質油がキノリン不溶分が１０wt％以下の重質油であること、b)黒鉛化の発達した黒鉛材料がＸ線回折による結晶パラメーターにおけるｄ００２が０．３３６０ｎｍ以下で、Ｌｃが５０ｎｍ以上であること、c)黒鉛化の発達した黒鉛材料を重質油に対して１〜４０wt％配合すること、d)黒鉛化の発達した黒鉛材料が、平均粒径が１〜５０μｍであること、e)生コークスを平均粒径２０〜３０μmに粉砕し、７００〜１５００℃で熱処理、して、２６００℃以上の温度で黒鉛化すること、f)生コークスを平均粒径２０〜３０μmに粉砕し、熱処理することなく、直接２６００℃以上の温度で黒鉛化すること、g)黒鉛化時に、コークスに対して硼素、硼素化合物を硼素換算量で０．１〜５wt％配合すること、又は、h)硼素化合物がホウ酸、酸化硼素、炭化硼素、窒化硼素又はホウ酸塩であることは、好ましい例である。また、i)平均粒径２０〜３０μmに粉砕し、７００〜１５００℃で熱処理して、そのままリチウム二次電池負極材料として使用しても良いが、２６００℃以上の温度で熱処理するのが好ましい。
【０００８】
【発明の実施の形態】
以下に本発明を具体的に説明する。
本発明のリチウム二次電池負極用材料となる炭素材料（以下、負極用材料ともいう）の製造方法は、生コークスを製造する工程、熱処理する工程、熱処理する工程と黒鉛化する工程又は黒鉛化する工程を有する。
【０００９】
本発明で使用する原料重質油は、石炭系又は石油系重質油又は両者の混合物であることが好ましい。
原料となる石炭系重質油には、コールタール、タール系重質油、タールピッチ等があり、石油系重質油には、石油系ピッチ、アスファルト、重油類、重質原油等がある。これらの原料の調製において、コーキング後の生コークス物性を制御するため、キノリン不溶分(QI)を10wt％以下、好ましくは1wt％以下に制御することがよい。また、ＣＣＲ(コンラドソン残留炭素)は１０％以上で、ｆa(芳香族指数)は、０．６５以上の原料でコーキングすることが望ましい。通常ディレードコーカーで製造される生コークスの組織制御は、ピッチ中のＱＩにより行われる。例えば、ピッチ中のQIが多いとメソフェースの発達を阻害し、等方性コークスとなる。ここで、ピッチ中のQIは石炭の微粒子や異物がほとんどであり、黒鉛化性の悪いものや黒鉛化しないものである。そのため、かかる原料から得られた生コークスを、黒鉛化しても天然黒鉛に近い結晶構造がとれない理由の一つとなると考えられる。
【００１０】
本発明では、上記原料重質油に黒鉛化の発達した黒鉛材料を配合する。黒鉛化の発達した黒鉛材料としては、Ｘ線回折による結晶パラメーターにおけるｄ００２が０．３３６０ｎｍ以下で、Ｌｃが５０ｎｍ以上であるものが好ましい。このｄ００２は理論値０．３３５４nmに近いものである。また、結晶の重なりの長さを表すＬｃは１００ｎｍを超えるものであることがより好ましい。かかる黒鉛材料としては、人造黒鉛や天然黒鉛やキッシュ黒鉛があるが、天然黒鉛やキッシュ黒鉛が好ましい。
【００１１】
また、この黒鉛材料は、平均粒径が１〜５０μｍの粉末であることが有利である。より好ましくは、リチウム電池に使用される負極用黒鉛材料の平均粒径に合わせることがよく、通常の負極用黒鉛材料の平均粒径が２０〜３０μｍである場合は、その範囲とすることがよい。また、入手可能なキッシュ黒鉛の平均粒径は約５μｍが最小であり、これより小さいものを使用するとキッシュ黒鉛の粉砕に負担がかかる。しかし、リチウム電池に使用される黒鉛材料等の負極用材料の平均粒径が２０〜３０μｍであることを考慮すると、５０μｍを超えるものは不利である。
【００１２】
QIを除去精製したピッチに、上記のような黒鉛材料を添加すると、黒鉛材料はQI成分であるので、QIが増大して良好な黒鉛化が進行しないとも考えられる。しかし、天然黒鉛、キッシュ黒鉛等の黒鉛化の発達した黒鉛材料を添加すると、黒鉛化性が良好に進行するばかりでなく、これらの黒鉛材料の配合量を調製することで種々組織のコントロールが可能であることが見出された。すなわち、最終的に得られる負極用材料は、黒鉛化の発達した黒鉛材料から生じる黒鉛と重質油から生じる炭素材料、好ましくは黒鉛からなるが、前者は黒鉛化が十分に発達しており、後者が黒鉛である場合、その黒鉛化はそれより劣るものの通常より発達するものと考えられ、配合量により性能調整が可能となると考えられる。しかし、得られる負極用材料はこれらの単なる混合物ではなく、ハイブリッドと考えられる。なお、黒鉛化の発達した黒鉛材料として、粒径の大きいものを添加すると、これは粉砕されるので、混合品になると考えられる。
【００１３】
黒鉛化の発達した黒鉛材料の配合量は、原料重質油に対して１〜４０wt％、好ましくは２〜３５wt％、より好ましくは５〜２５wt％であることがよい。
原料重質油と黒鉛化の発達した黒鉛材料の配合割合は、原料重質油をコーキングした時の重質油の炭化歩留りによっても変化する。ピッチ等の重質油の炭化歩留りが通常の５０〜６０％である場合、コーキング後の黒鉛材料と原料重質油から生成するコークスの割合が変化し、前者の割合が約２倍近く増加する。したがって、添加した黒鉛材料が全炭素分の２〜８０wt％を占めるようにするためには、黒鉛材料の配合割合を１〜４０wt％とすればよいことになる。
【００１４】
生コークスは、約４００〜５５０℃、好ましくは約４５０〜５００℃で、約２０〜５０hrでディレードコーキングして得られる。生コークスは通常、塊状として得られ、約５〜１５wt％の揮発分を含む。ディレードコーキングは、前記公報に記載されたように公知であり、かかる公知の装置及び条件を採用することができる。
【００１５】
ディレードコーキングで得られた生コークスは、黒鉛化の発達した黒鉛材料を含むものであるが、塊状で得られるため、熱処理前又は黒鉛化前に粉砕することがよい。好ましくは、負極用黒鉛材料として必要な粒径に粉砕する。この必要な平均粒径は２０〜３０μｍであり、実際はこの粒径に粉砕することが有利である。しかも、生コークスの時点で粉砕をした後、熱処理としての焼成又は黒鉛化をすれば、粉体特性のうち、Ｔａｐかさ密度は高くなる効果も予想される。
【００１６】
生コークス、好ましくは粉砕した生コークスは、次に熱処理又は黒鉛化する。熱処理を行う場合は、次に黒鉛化を行うことが好ましいが、熱処理でとどめてもよい。この場合、添加した黒鉛材料と重質油から生じる熱処理コークスとからなる炭素材料が生じるが、これを負極用材料又はその中間体として使用することができる。更に、熱処理を行い、次に黒鉛化を行うことが好ましいが、熱処理を省略して直接黒鉛化することもできる。この場合、添加した黒鉛材料と重質油から生じる黒鉛とからなる炭素材料が生じるが、これは負極用材料として優れる。
【００１７】
熱処理は、約７００〜１５００℃、好ましくは８００〜１２００℃で行う。この熱処理されたコークス（熱処理コークスという）中の揮発分は１wt％以下にされる。熱処理炉としては、例えば、ロータリーキルン・カルサイナー、リードハンマー炉、流動層炉、トンネルキルン等が挙げられる。小規模的には、電気炉等の加熱装置を使用してもよい
【００１８】
熱処理コークスは、引き続いて又は一旦冷却後、解砕又は粉砕して２５００℃以上で黒鉛化することがよい。黒鉛化温度は高いほうがよく、好ましくは２６００〜３０００℃である。
熱処理を省略する場合は、生コークス、好ましくは粉砕した生コークスを、２５００℃以上で黒鉛化する。黒鉛化温度は高いほうがよく、好ましくは２６００〜３０００℃である。
【００１９】
この黒鉛化の際、硼素又は硼素化合物を添加することも有利である。硼素又は硼素化合物から選択される１種以上の硼素等の添加量は、硼素換算量で０．１〜５wt％が望ましい。０．１wt％未満では硼素等の添加による黒鉛化促進効果が得られず、高い放電容量をもつリチウム二次電池負極材料は得られない。硼素等の添加量が５wt％より多いと黒鉛化後の冷却時に析出したり、炭化硼素類が生成し負極材料に不純物として残存するために性能上好ましくない。また、硼素化合物としては、ホウ酸、酸化硼素、炭化硼素、窒化硼素又はホウ酸塩が好ましく挙げられる。
【００２０】
黒鉛化後に粒度調整を必要により行うこともよい。この粒度調整は約10〜50μm好ましくは２０〜３０μmの平均粒径とすることがよい。
このようにして得られた負極用材料は、正極活物質、負極活物質及び非水系電解質を含有するリチウム二次電池の負極活物質中に含む。
なお、リチウム二次電池の正極活物質、非水系電解質等は前記公報等で知られており、これらに記載のものを使用できる。
【００２１】
本発明の負極用材料を活物質に用いて負極を形成する方法も、前記公報等に記載の方法を採用できる。
例示すると、負極用材料にポリテトラフルオロエチレン等のフッ素系樹脂の粉末あるいはディスパージョン溶液を添加後、混合、混練する方法がある。また、負極用材料にポリフッ化ビニリデン(PVdF)等のフッ素系樹脂粉末あるいはカルボキシルメチルセルロース等の水溶性粘結剤をバインダーとして加えて、N-メチルピロリドン(NMP)、ジメチルホルムアミドあるいは水、アルコール等の溶媒を用いてスラリーを作成し、集電体上に塗布、乾燥する事により成型することもできる。
【００２２】
本発明の負極用材料は、重質油からの黒鉛又は熱処理コークスと、黒鉛化の発達した黒鉛材料とがハイブリッド化されているため、電池特性の放電容量は天然黒鉛等の黒鉛材料でカバーし、サイクル特性は重質油からの黒鉛系でカバーして、お互いに欠点を補うようにしたので、両方の電池特性が優れるものとなったと推測される。
【００２３】
実施例１
平均粒径１５μｍのキッシュ黒鉛（d002 : 0.3355nm , Lc : 100nm以上）を、キノリン不溶分を除去（QI：検出されず、TI：15％、軟化点38℃）した石炭系ピッチに５重量％添加し、５００℃で、２４hrディレードコーキングし生コークスとした。得られた生コークスの揮発分は、８％であった。この生コークスを粉砕して、平均粒径２５μｍとし、100℃/hrで９００℃まで昇温し、９００℃で１hr熱処理して熱処理コークスとした。この熱処理コークスを引き続いて、２６００℃で１hr黒鉛化して、負極用黒鉛材料を得た。
【００２４】
実施例２
平均粒径１５μｍのキッシュ黒鉛を、キノリン不溶分を除去した石炭系ピッチに３０重量％添加した他は、実施例１と同様にして負極用黒鉛材料を得た。
【００２５】
実施例３〜４
実施例１で得られた熱処理コークスに、炭化硼素を１重量％又は２重量％添加、混合して、実施例１と同様の温度、時間で黒鉛化して負極用黒鉛材料を得た。
【００２６】
比較例１
平均粒径１５μｍのキッシュ黒鉛を添加せず、キノリン不溶分を除去した石炭系ピッチを単独で使用した他は、実施例１と同様にして負極用黒鉛材料を得た。
比較例２
比較例１で得られた熱処理コークスに、炭化硼素を１重量％添加、混合して、実施例１と同様の温度、時間で黒鉛化して負極用黒鉛材料を得た。
【００２７】
分析方法は、次のとおり。
黒鉛化度(d002、Lc)：高純度シリコンを内部標準として加えた炭素粉末に単色のX線を照射し、黒鉛の002面に対応するピークを測定する。そのピークの位置及び半値幅を内部標準のシリコンのピークを標準として補正することによりを算出する。
比表面積：窒素ガス吸着によるBET法によって測定した。
【００２８】
タップ密度：JIS-K1501による。セイシン企業社製タップ密度測定装置にて、100cm3の樹脂製メスシリンダーを用いて、20回タップ密度を測定した。
粒子径：レーザー回折法により測定した粒度分布から求め、体積に関して50％を平均粒径とした。
【００２９】
電極作製及び電極性能測定
ポリフッ化ビニリデンのNMP(N-メチル-2-ピロリドン)溶液に、本発明で得られた材料粉末とポリフッ化ビニリデンが質量比で95:5となる様加えて混練し、これを厚さ20μmの銅箔に塗布して負極電極箔を得た。この負極電極箔を、80℃で乾燥してNMPを蒸発させた後、10mm角に切り出して負極電極を作成した。この負極電極単極での電極特性を評価するために、対極、参照極にリチウム金属を用いた三極式セルを用いた。電解液には、エチレンカーボネートとジエチルカーボネ―トの混合溶媒(体積比で1:1混合)にLiClO4を1mol/lの割合で溶解したものを用いた。充放電試験に関しては、電位規制の下、充電、放電共に定電流(0.1mA/cm2)で行なった。電位範囲は0〜1.5V(リチウム金属基準)とした。
初期効率は、第１回目の充電容量と第１回目の放電容量の比である。
【００３０】
負極用黒鉛材料製造時のキッシュ黒鉛配合割合及び炭化硼素添加量と、負極用黒鉛材料の比表面積、タップ密度、放電容量及び初期効率を表１に示す。
【００３１】
【表１】
本発明の製造方法で得られるリチウム二次電池負極材料は、放電容量や初期効率で代表される電池特性が優れる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an artificial carbon-based, in particular, artificial graphite-based lithium ion secondary battery negative electrode material and a method for producing the same.
[0002]
In recent years, clean nonaqueous secondary batteries, particularly lithium secondary batteries, which replace lead-acid batteries and nickel-cadmium batteries have attracted attention from the standpoints of reducing the size and weight of electronic devices, saving power, and protecting the environment. Therefore, at present, the battery is widely used as a battery for so-called mobile electronic devices such as a notebook personal computer and a mobile phone, and is also being studied for a battery use of an electric vehicle. The negative electrode material used for the lithium secondary battery is required to have a high discharge capacity, a high packing density, high initial efficiency, excellent cycle characteristics, and low cost.
[0003]
Lithium secondary battery negative electrode materials can be broadly divided into lithium metal (alloy) and carbon material systems. Lithium metal (alloy) systems have very high battery capacity, but lithium dendrites during charging. Due to precipitation and pulverization in the (resin-like crystal) state, problems occur in cycle life and safety. Therefore, at present, carbon material systems are mainly used, and there are natural graphite systems, mesocarbon microbeads (MCMB: spherical carbon) systems, artificial graphite systems, and carbon fiber systems.
Of these, natural graphite, which has an excellent crystal structure, can provide very high battery capacity with a discharge capacity of 350 mAhr / g or more. However, among powder characteristics, tap bulk density is low and battery characteristics are low. Among them, there are problems in cycle characteristics when charging / discharging is repeated and load characteristics due to rapid charging / discharging. Moreover, since the surface area is large, there is also a problem that the irreversible capacity indicating the difference between the first charge capacity and the discharge capacity is large. These problems occur because the natural graphite material has a flat structure due to the development of graphitization. Thus, when natural graphite is used, it has been studied to use a material that is kneaded with pitch and pitch-coated on the surface, but sufficient improvement has not been achieved yet. Since the MCMB system has a spherical structure, there is no problem in cycle characteristics and load characteristics, but the discharge capacity is as low as about 320 mAhr / g. For this reason, it has been studied to perform catalytic graphitization, but a sufficient solution has not yet been made.
[0004]
Japanese Patent Application Laid-Open No. 8-287911 discloses a method in which raw coke is pulverized and heat-treated at 700 to 1500 ° C. in an inert gas atmosphere. Japanese Patent Application Laid-Open No. 9-157022 describes a material obtained by graphitizing raw coke powder by oxidation heat treatment. Japanese Patent Application Laid-Open No. 10-223223 describes that a boron compound is added to carbon powder for graphitization. Furthermore, JP-A-2001-23638 discloses a method of pulverizing, heat-treating and graphitizing raw coke produced by a delayed coker. Although these methods have improved battery characteristics as they are, there is a demand for increased power consumption and increased usage time per charging time due to higher functionality and ultra-lightweight mobile devices. An excellent negative electrode material capable of dealing with high load battery characteristics is desired.
[0005]
[Problems to be solved by the invention]
The present invention is an excellent negative electrode capable of dealing with further high load battery characteristics under the present situation where power consumption is increased and usage time per charging time is increased due to high functionality and ultra light weight of mobile devices. The purpose is to provide material. Another object is to reduce the specific surface area, increase the initial efficiency in battery characteristics, and increase the powder density. Furthermore, the negative electrode paste can be uniformly applied to the copper foil by increasing the amount of the negative electrode filled in the battery to increase the battery capacity and further improving the coating property of the coating slurry. Therefore, an object of the present invention is to provide an artificial carbon-based material, particularly an artificial graphite-based lithium ion secondary battery negative electrode material having excellent powder characteristics and excellent battery characteristics such as discharge capacity and charge / discharge efficiency. And
[0006]
[Means for Solving the Problems]
In the present invention, at least one heavy oil selected from coal-based heavy oil and petroleum-based heavy oil is used as a raw material, and delayed coking is performed to obtain raw coke, which is heat-treated or graphitized to obtain lithium secondary oil. In a method for producing a secondary battery negative electrode material, a graphitized material having an average particle size of 1 to 50 μm and having an average particle diameter of 1 to 50 μm is added to a heavy oil having a quinoline insoluble content of 1 wt % or less. Lithium secondary, characterized in that, after blending 2 to 35 wt % and obtaining raw coke by delayed coking , at least one of heat treatment performed at 700 to 1500 ° C and graphitization performed at 2500 ° C or higher is performed. It is a manufacturing method of battery negative electrode material .
[0007]
In the present invention, a) the heavy oil is a heavy oil having a quinoline insoluble content of 10 wt% or less, b) the graphitized material having developed graphitization has a d002 of 0.3360 nm or less in crystal parameters by X-ray diffraction, Lc is 50 nm or more, c) 1 to 40 wt% of graphitized graphite material is blended with heavy oil, and d) graphitized graphite material has an average particle diameter of 1 to 50 μm. E) crushed raw coke to an average particle size of 20-30 μm, heat-treated at 700-1500 ° C. and graphitized at a temperature of 2600 ° C. or higher, f) raw coke having an average particle size of 20-20 Grind to 30 μm and directly graphitize at a temperature of 2600 ° C. or higher without heat treatment. G) At the time of graphitization, boron and a boron compound are mixed with 0.1 to 5 wt% in terms of boron to coke. Or h) the boron compound is boric acid, Boron, boron carbide, it is boron nitride or boric acid salts are preferred. In addition, i) pulverized to an average particle size of 20 to 30 μm, heat treated at 700 to 1500 ° C., and used as it is as a lithium secondary battery negative electrode material, but is preferably heat treated at a temperature of 2600 ° C. or higher.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be specifically described below.
The method for producing a carbon material (hereinafter also referred to as a negative electrode material) as a material for a negative electrode of a lithium secondary battery of the present invention includes a step of producing raw coke, a step of heat treatment, a step of heat treatment and a step of graphitization or graphitization. The process of carrying out.
[0009]
The raw material heavy oil used in the present invention is preferably a coal-based or petroleum-based heavy oil or a mixture of both.
Coal heavy oil, tar heavy oil, tar pitch, and the like are used as raw materials for coal heavy oil, and petroleum heavy oil includes petroleum pitch, asphalt, heavy oil, heavy crude oil, and the like. In the preparation of these raw materials, the quinoline insoluble content (QI) is preferably controlled to 10 wt% or less, preferably 1 wt% or less in order to control the physical properties of raw coke after coking. Further, it is desirable to coke with a raw material having CCR (Conradson residual carbon) of 10% or more and fa (aromatic index) of 0.65 or more. Ordinary coke produced by a delayed coker is controlled by QI in the pitch. For example, if the QI in the pitch is large, the development of mesophase is inhibited and isotropic coke. Here, the QI in the pitch is mostly coal fine particles and foreign matter, and is poor in graphitization or not graphitized. Therefore, it is considered that the raw coke obtained from such raw materials is one of the reasons that a crystal structure close to that of natural graphite cannot be obtained even when graphitized.
[0010]
In the present invention, the above-mentioned raw material heavy oil is blended with a graphite material having developed graphitization. As the graphite material that has been graphitized, a material having d002 of 0.3360 nm or less and Lc of 50 nm or more in crystal parameters by X-ray diffraction is preferable. This d002 is close to the theoretical value of 0.3354 nm. Further, it is more preferable that Lc representing the overlap length of the crystal exceeds 100 nm. Such graphite materials include artificial graphite, natural graphite, and quiche graphite, with natural graphite and quiche graphite being preferred.
[0011]
The graphite material is advantageously a powder having an average particle size of 1 to 50 μm. More preferably, the average particle size of the negative electrode graphite material used in the lithium battery is adjusted to be in the range when the average particle size of the normal negative electrode graphite material is 20 to 30 μm. . In addition, the average particle diameter of available quiche graphite is about 5 μm, and if a smaller particle size is used, the pulverization of quiche graphite is burdened. However, when the average particle diameter of the negative electrode material such as graphite material used in the lithium battery is 20 to 30 μm, it is disadvantageous if it exceeds 50 μm.
[0012]
If the graphite material as described above is added to the pitch from which QI has been removed and purified, the graphite material is a QI component, so it is considered that QI increases and good graphitization does not proceed. However, when graphitized materials such as natural graphite and quiche graphite are added, not only the graphitization progresses well, but also the various structures can be controlled by adjusting the amount of these graphite materials. It was found that That is, the negative electrode material finally obtained is composed of graphite produced from graphitized graphite material and carbon material produced from heavy oil, preferably graphite, but the former has sufficiently developed graphitization, When the latter is graphite, its graphitization is inferior to that, but it is thought that it develops more than usual, and it is considered that the performance can be adjusted by the blending amount. However, the obtained negative electrode material is not a simple mixture of these, but is considered to be a hybrid. If a graphite material with a large particle size is added as a graphitized material with advanced graphitization, it is considered to be a mixed product because it is pulverized.
[0013]
The blending amount of the graphitized material having developed graphitization is 1 to 40 wt%, preferably 2 to 35 wt%, more preferably 5 to 25 wt% with respect to the raw heavy oil.
The mixing ratio of the raw material heavy oil and the graphitized material with advanced graphitization also varies depending on the carbonization yield of the heavy oil when the raw material heavy oil is coked. When the carbonization yield of heavy oil such as pitch is 50 to 60% of normal, the ratio of coke produced from graphite material after coking and raw heavy oil changes, and the former ratio increases nearly twice. . Therefore, in order for the added graphite material to occupy 2 to 80 wt% of the total carbon content, the blending ratio of the graphite material may be set to 1 to 40 wt%.
[0014]
The raw coke is obtained by delayed coking at about 400 to 550 ° C., preferably about 450 to 500 ° C. for about 20 to 50 hours. Raw coke is usually obtained as a block and contains about 5-15 wt% volatiles. Delayed coking is known as described in the above publication, and such known apparatus and conditions can be employed.
[0015]
The raw coke obtained by delayed coking contains a graphite material that has been graphitized, but is obtained in the form of a lump, so that it may be pulverized before heat treatment or before graphitization. Preferably, it grind | pulverizes to a particle size required as a graphite material for negative electrodes. The required average particle size is 20-30 μm, and in practice it is advantageous to grind to this particle size. In addition, if the powder is pulverized at the time of raw coke and then fired or graphitized as a heat treatment, the effect of increasing the Tap bulk density is expected among the powder characteristics.
[0016]
The green coke, preferably ground green coke, is then heat treated or graphitized. When heat treatment is performed, graphitization is preferably performed next, but the heat treatment may be performed. In this case, a carbon material composed of the added graphite material and heat-treated coke generated from heavy oil is produced, and this can be used as a negative electrode material or an intermediate thereof. Further, it is preferable to perform heat treatment and then graphitize, but it is also possible to perform graphitization directly without heat treatment. In this case, a carbon material composed of the added graphite material and graphite generated from heavy oil is produced, which is excellent as a negative electrode material.
[0017]
The heat treatment is performed at about 700 to 1500 ° C., preferably 800 to 1200 ° C. The volatile content in the heat-treated coke (referred to as heat-treated coke) is 1 wt% or less. Examples of the heat treatment furnace include a rotary kiln / calciner, a lead hammer furnace, a fluidized bed furnace, and a tunnel kiln. On a small scale, a heating device such as an electric furnace may be used.
The heat-treated coke is preferably graphitized at 2500 ° C. or higher after being cooled or once cooled and then crushed or pulverized. The graphitization temperature should be higher, preferably 2600 to 3000 ° C.
When the heat treatment is omitted, raw coke, preferably crushed raw coke is graphitized at 2500 ° C. or higher. The graphitization temperature should be higher, preferably 2600 to 3000 ° C.
[0019]
It is also advantageous to add boron or a boron compound during the graphitization. The addition amount of one or more kinds of boron selected from boron or a boron compound is preferably 0.1 to 5 wt% in terms of boron. If it is less than 0.1 wt%, the effect of promoting graphitization by adding boron or the like cannot be obtained, and a lithium secondary battery negative electrode material having a high discharge capacity cannot be obtained. If the added amount of boron or the like is more than 5 wt%, it is not preferable in terms of performance because it precipitates during cooling after graphitization or boron carbides are generated and remain as impurities in the negative electrode material. Further, preferred examples of the boron compound include boric acid, boron oxide, boron carbide, boron nitride, and borate.
[0020]
If necessary, the particle size may be adjusted after graphitization. The particle size is adjusted to an average particle size of about 10 to 50 μm, preferably 20 to 30 μm.
The negative electrode material thus obtained is contained in a negative electrode active material of a lithium secondary battery containing a positive electrode active material, a negative electrode active material, and a non-aqueous electrolyte.
In addition, the positive electrode active material of a lithium secondary battery, a non-aqueous electrolyte, etc. are known by the said gazette etc., The thing as described in these can be used.
[0021]
As a method for forming a negative electrode using the negative electrode material of the present invention as an active material, the method described in the above publication can be employed.
For example, there is a method of mixing and kneading after adding a powder of a fluororesin such as polytetrafluoroethylene or a dispersion solution to the negative electrode material. Also, fluorine resin powder such as polyvinylidene fluoride (PVdF) or water-soluble binder such as carboxymethyl cellulose is added as a binder to the negative electrode material, and N-methylpyrrolidone (NMP), dimethylformamide or water, alcohol, etc. It is also possible to form a slurry by preparing a slurry using a solvent, and applying and drying on a current collector.
[0022]
Since the negative electrode material of the present invention is a hybrid of graphite or heat-treated coke from heavy oil and graphite material with advanced graphitization, the discharge capacity of battery characteristics is covered with graphite material such as natural graphite. Since the cycle characteristics were covered with a graphite system from heavy oil and compensated for each other's defects, it is presumed that both battery characteristics were excellent.
[0023]
Example 1
Quiche graphite (d002: 0.3355nm, Lc: 100nm or more) with an average particle size of 15μm, 5% by weight in coal-based pitch from which quinoline insolubles have been removed (QI: not detected, TI: 15%, softening point 38 ° C) The mixture was added and subjected to delayed coking at 500 ° C. for 24 hours to obtain raw coke. The raw coke obtained had a volatile content of 8%. The green coke was pulverized to an average particle size of 25 μm, heated to 900 ° C. at 100 ° C./hr, and heat-treated at 900 ° C. for 1 hr to obtain heat-treated coke. This heat-treated coke was subsequently graphitized at 2600 ° C. for 1 hr to obtain a negative electrode graphite material.
[0024]
Example 2
A graphite material for a negative electrode was obtained in the same manner as in Example 1 except that 30% by weight of quiche graphite having an average particle size of 15 μm was added to the coal-based pitch from which the quinoline insoluble matter was removed.
[0025]
Examples 3-4
Boron carbide was added at 1% by weight or 2% by weight to the heat-treated coke obtained in Example 1, mixed, and graphitized at the same temperature and time as in Example 1 to obtain a graphite material for a negative electrode.
[0026]
Comparative Example 1
A graphite material for a negative electrode was obtained in the same manner as in Example 1 except that quiche graphite having an average particle size of 15 μm was not added and a coal-based pitch from which quinoline-insoluble components were removed was used alone.
Comparative Example 2
1% by weight of boron carbide was added to and mixed with the heat-treated coke obtained in Comparative Example 1, and graphitized at the same temperature and time as in Example 1 to obtain a graphite material for a negative electrode.
[0027]
The analysis method is as follows.
Degree of graphitization (d002, Lc): Carbon powder added with high-purity silicon as an internal standard is irradiated with monochromatic X-rays, and a peak corresponding to the 002 plane of graphite is measured. The peak position and half width are calculated by correcting the peak of the internal standard silicon as a standard.
Specific surface area: Measured by BET method by nitrogen gas adsorption.
[0028]
Tap density: According to JIS-K1501. The tap density was measured 20 times using a 100 cm 3 resin graduated cylinder with a tap density measuring device manufactured by Seishin Enterprise Co., Ltd.
Particle diameter: The particle diameter was determined from the particle size distribution measured by the laser diffraction method, and 50% of the volume was defined as the average particle diameter.
[0029]
Electrode preparation and electrode performance measurement In a NMP (N-methyl-2-pyrrolidone) solution of polyvinylidene fluoride, the material powder obtained in the present invention and polyvinylidene fluoride were added and kneaded in a mass ratio of 95: 5, This was applied to a copper foil having a thickness of 20 μm to obtain a negative electrode foil. This negative electrode foil was dried at 80 ° C. to evaporate NMP, and then cut into 10 mm squares to form negative electrodes. In order to evaluate the electrode characteristics of the single electrode of the negative electrode, a tripolar cell using lithium metal as a counter electrode and a reference electrode was used. The electrolyte used was a solution in which LiClO4 was dissolved at a rate of 1 mol / l in a mixed solvent of ethylene carbonate and diethyl carbonate (mixed 1: 1 by volume). The charge / discharge test was conducted at a constant current (0.1 mA / cm2) for both charging and discharging under potential regulation. The potential range was 0 to 1.5 V (lithium metal reference).
The initial efficiency is a ratio between the first charge capacity and the first discharge capacity.
[0030]
Table 1 shows the ratio of the quiche graphite and the amount of boron carbide added during the production of the graphite material for the negative electrode, the specific surface area, the tap density, the discharge capacity and the initial efficiency of the graphite material for the negative electrode.
[0031]
[Table 1]
The lithium secondary battery negative electrode material obtained by the production method of the present invention is excellent in battery characteristics represented by discharge capacity and initial efficiency.
Claims (9)
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| JP4915687B2 (en) * | 2005-12-28 | 2012-04-11 | 東海カーボン株式会社 | Method for producing negative electrode material for lithium ion secondary battery |
| US7597999B2 (en) * | 2006-06-07 | 2009-10-06 | Conocophillips Company | Methods of preparing carbonaceous anode materials and using same |
| JP5415684B2 (en) * | 2007-10-02 | 2014-02-12 | Ｊｘ日鉱日石エネルギー株式会社 | Artificial graphite for negative electrode of lithium ion secondary battery and method for producing the same |
| JP5270906B2 (en) | 2007-11-08 | 2013-08-21 | Ｊｘ日鉱日石エネルギー株式会社 | Raw material carbon composition for negative electrode material of lithium ion secondary battery and method for producing the same |
| JP5242210B2 (en) * | 2008-03-24 | 2013-07-24 | 新日鉄住金化学株式会社 | Non-aqueous electrolyte secondary battery negative electrode active material and method for producing non-aqueous electrolyte secondary battery |
| JP5603589B2 (en) | 2009-05-15 | 2014-10-08 | 新日鉄住金化学株式会社 | Negative electrode active material for lithium secondary battery and in-vehicle lithium secondary battery using the same |
| JP5662698B2 (en) * | 2009-05-15 | 2015-02-04 | 新日鉄住金化学株式会社 | Negative electrode active material for lithium secondary battery and in-vehicle lithium secondary battery using the same |
| JP5603590B2 (en) * | 2009-05-29 | 2014-10-08 | 新日鉄住金化学株式会社 | Negative electrode active material for lithium secondary battery and in-vehicle lithium secondary battery using the same |
| KR101096936B1 (en) * | 2009-07-23 | 2011-12-22 | 지에스칼텍스 주식회사 | Negative active material for rechargeable lithium battery, method of manufacturing the same and rechargeable lithium battery having the same |
| WO2011068097A1 (en) * | 2009-12-02 | 2011-06-09 | 新日鐵化学株式会社 | Negative electrode for secondary battery, and secondary battery using same |
| DK2715855T3 (en) * | 2011-06-03 | 2015-10-19 | Council Scient Ind Res | PROCEDURE FOR THE MANUFACTURING OF VARIETY GRAPH-CONTAINED LITHIUM INSTALLATION ANODEMATERIALS FOR LITHIUM-ION BATTERIES |
| JP6274390B2 (en) * | 2012-10-24 | 2018-02-07 | 東海カーボン株式会社 | Method for producing graphite powder for negative electrode material of lithium secondary battery |
| CN104813518B (en) * | 2012-11-21 | 2017-10-20 | 昭和电工株式会社 | The manufacture method of cathode material of lithium ion battery |
| JP7009049B2 (en) * | 2016-07-07 | 2022-02-10 | 日鉄ケミカル＆マテリアル株式会社 | Lithium-ion secondary battery Carbon material for negative electrode, its intermediate, its manufacturing method, and negative electrode or battery using it |
| KR20190019430A (en) * | 2017-08-17 | 2019-02-27 | 주식회사 포스코 | Method for manufacturing negative electrode active material for rechargeable lithium battery, and rechargeable lithium battery including the same |
| US11274042B2 (en) * | 2018-01-19 | 2022-03-15 | Alliance For Sustainable Energy, Llc | Valorization of bio-oils |
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