JP4170006B2 - Carbon material and negative electrode material for secondary battery using the same - Google Patents
Carbon material and negative electrode material for secondary battery using the same Download PDFInfo
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02E60/10—Energy storage using batteries
Description
【０００１】
【発明の属する技術分野】
本発明は、炭素材およびこれを用いた二次電池用負極材に関するものである。
【０００２】
【従来の技術】
近年、目覚ましい電子技術の発達に伴い電子機器の小型化、及び軽量化が要求項目として挙げられるようになってきている。それに伴い移動用電源に対しても更なる小型化、軽量化、且つ高エネルギー密度化が求められるようになった。従来使用されている二次電池としては鉛電池、ニカド電池などの水溶液系二次電池が主流である。しかし、これら水溶液系二次電池は優れたサイクル性を示すものの、電池質量やエネルギー密度の点で十分に満足できるものとはいえない。
【０００３】
その後、新たなる電極材としてリチウム、もしくはリチウム合金を負極材として用いるリチウム金属電池が開発された。これらの電池は従来と比較すると非常に高いエネルギー密度を有するものの、リチウム金属は非常に危険性が高く安全性に問題があり、実用化が困難とされている。そこで新たな負極材料として炭素材料を使用した非水電解液系のリチウムイオン二次電池が開発された。これは，炭素材の層間にリチウムがインターカレーション／デインターカレーションされることを利用したものであり、充放電サイクルが進行しても、炭素材料を使用した負極上にデンドライト状リチウムが析出する現象は見られず、高い安全性が保証される。そして高エネルギー密度を有し、軽量であると共に優れた充放電サイクル特性を示す。
【０００４】
上記の例としては、特開平５−７４５７号公報に記載の黒鉛が挙げられるが、理論充放電容量は３７２ｍＡｈ／ｇと限界が見られる。また，特開平５−２８９９６号公報，特開平７−７３８２８号公報に記載の易黒鉛化炭素材があるが、焼成温度が２０００度を越える条件では黒鉛化されるために充放電容量は決定され、それ以下の温度領域では充放電容量は高いもののサイクル性が乏しく、電池特性は低い。また，熱処理温度が５００℃〜７００℃程度の低温で処理された炭素負極は、充放電容量で８５０ｍＡｈ／ｇと重量当たりの容量で黒鉛を越え，低温処理のためにエネルギーメリットも良好ではあるが、電位が高く、充放電位における電位のヒステリシスが大きいというデメリットが挙げられる。
また電解液にプロピレンカーボネートが混合された液を用いた場合、黒鉛系炭素材を用いると電解液の分解反応が起こり特性低下が確認される。しかし非黒鉛系炭素材を用いた場合では分解反応は起こらず特性低下はほとんど確認されない。
【０００５】
このほか、炭素材以外のリチウムイオン負極材料として特開平５−１６６５３６号公報に示される金属酸化物などが挙げられる。金属酸化物を負極材として用いた場合では充放電容量８００ｍＡｈ／ｇと優れた特性を示すものの、瞬間放電容量が非常に高いために制御が困難であり，安全性に大きな問題が生じてくる。
【０００６】
非黒鉛系炭素材の特徴として、その立体構造は二次元性よりも三次元性が高い。黒鉛の場合は充電容量で３７２ｍＡｈ／ｇが上限とする理論容量が存在するのに対して、この特性を大きく超えることが可能である。しかしながら不可逆容量は通常の黒鉛系炭素材と比較して遥かに大きくこの点の改良が必須項目となっている。
【０００７】
【発明が解決しようとする課題】
本発明は、充放電効率が優れ不可逆容量が低く、かつ高エネルギー密度でありサイクル性が良く、さらには安全性の高い炭素材およびこれを用いた二次電池用負極材を提供するものである。
【０００８】
【問題を解決するための手段】
このような目的は、下記の本発明（１）〜（４）によって達成される。
（１）非水電解質二次電池の負極材に用いられる炭素材であって、該炭素材表面に形成された細孔が、
（ａ）０．４０ｎｍを越える細孔径を有する細孔容積が０．０００１〜０．０１０ｍｌ／ｇであり、
（ｂ）０．３３ｎｍ〜０．４０ｎｍの細孔径を有する細孔容積との比（ｂ／ａ）が１以上である
ことを特徴とする炭素材。
（２）前記（ａ）０．４０ｎｍを越える細孔径を有する細孔容積と、（ｂ）０．３３ｎｍ〜０．４０ｎｍの細孔径を有する細孔容積との比（ｂ／ａ）が５以上である上記（１）に記載の炭素材。
（３）前記炭素材が、フェノール樹脂を硬化し炭化処理したものである上記（１）または（２）に記載の炭素材。
（４）上記（１）ないし（３）のいずれかに記載の炭素材を含有する二次電池用負極材。
【０００９】
【発明の実施の形態】
以下に、本発明の炭素材およびこれを用いた二次電池用負極材について説明する。
本発明の炭素材は、非水電解質二次電池の負極材に用いられる炭素材であって、該炭素材表面に形成された細孔が、
（ａ）０．４０ｎｍを越える細孔径を有する細孔容積が０．０００１〜０．０１０ｍｌ／ｇであり、
（ｂ）０．３３ｎｍ〜０．４０ｎｍの細孔径を有する細孔容積との比（ｂ／ａ）が１以上である
ことを特徴とする。
また、本発明の二次電池用負極材は前記炭素材を用いたものである。
【００１０】
まず、本発明の炭素材について詳細に説明する。
本発明の炭素材表面に形成された細孔は、炭素材を製造する際の主に炭化処理工程において形成されるものであり、用いる炭素材原料の種類、炭素材原料の硬化条件、炭素材製造時の炭化処理条件などによって、様々な態様をなすと考えられる。本発明の炭素材において細孔とは、炭素材表面に形成されかつ外部と連通しているものを指し、細孔径とは、前記細孔が外部と連通している部分の孔径をいう。そして、細孔容積とは、前記細孔が炭素材内部に形成している空間容積の総和をいう。
【００１１】
本発明の炭素材は、表面に形成された細孔のうち、（ａ）０．４０ｎｍを越える細孔径を有する細孔容積が０．０００１〜０．０１０ｍｌ／ｇである。これにより、本発明の炭素材をリチウム二次電池の負極材に用いた場合、不可逆容量を低減させることができる。前記細孔容積が０．０１０ｍｌ／ｇを超えると、充電容量は増えるものの不可逆容量が増大し、充放電効率が低下する。また、０．０００１ｍｌ／ｇ未満である場合は、不可逆容量は減少するものの充電容量自体が低下するため、電池特性として適切なものではない。前記（ａ）の細孔径を有する細孔は、電解液中の有機溶媒が侵入しやすいために、リチウムイオンの存在下で電解液が分解、反応しリチウム塩としてトラップされることや不動態膜を形成することが考えられ、これにより不可逆容量が増大すると推定される。
【００１２】
また、本発明の炭素材は、表面に形成された細孔のうち、（ｂ）０．３３ｎｍ〜０．４０ｎｍの細孔径を有する細孔容積が、前記（ａ）の細孔径を有する細孔容積との比（ｂ／ａ）で１以上である。これにより、充電容量を確保し、充放電効率を良好なものにすることができる。前記容積比が１未満であると、充電容量が減少し、充放電効率もこれに伴って低下するようになる。
前記（ｂ）の細孔径を有する細孔は、充放電によるリチウムイオンの挿入・脱離が可逆的に起こりやすいと考えられるため、前記（ａ）の細孔径を有する細孔容積に対して大きいことが好ましい。
前記細孔容積比（ｂ／ａ）は、さらに好ましくは５以上である。これにより、さらに高い充放電効率を維持することができる。
【００１３】
本発明の炭素材は、特に限定されないが、平均粒径１〜５０μｍが好ましく、特に５〜３０μｍが好ましい。炭素材の粒径が前記範囲内であると、負極材作製時の取り扱い性が良く、また、作製後の負極材塗布面が平滑となる。炭素材の粒径が前記下限値未満では粉体の粉舞が発生するとともに負極材作製の作業性が低下しやすく、前記上限値を越えると負極材塗布面が凹凸となりやすい。
【００１４】
本発明の炭素材に用いられる原料としては特に限定されないが、フェノール樹脂，フラン樹脂，エポキシ樹脂などの熱硬化性樹脂、ポリスチレン、ポリアミドなどの熱可塑性樹脂のほか、石油ピッチ、石炭ピッチ、紡糸用ピッチ等が使用できる。これらの原料を単独または二種以上併用して用いることもできる。これらの中でも、フェノール樹脂を用いることが好ましい。これにより、三次元架橋の発達した構造を有する炭素材とすることができる。フェノール樹脂としては特に限定されないが、レゾール型フェノール樹脂、ノボラック型フェノール樹脂などを用いることができる。
炭素材の原料として熱硬化性樹脂を用いる場合、その硬化方法は特に限定されないが、例えばフェノール樹脂を用いた場合では、熱硬化、熱酸化、エポキシ硬化、イソシアネート硬化などが挙げられる。また、エポキシ樹脂を用いた場合では、フェノール樹脂硬化、酸無水物硬化、アミン硬化等が挙げられる。これらのいずれの硬化方法を用いることができる。
【００１５】
本発明の炭素材は、上記方法で得られた炭素材原料を炭化処理して得ることができる。本発明の炭素材を得るための炭化処理条件としては特に限定されないが、通常、１０００〜１５００℃で０．０１〜５０時間行われる。また，炭化処理時の雰囲気としては、大気中、窒素中、ヘリウムガスなどの不活性ガス中で行う方法などがある。
炭化処理時の条件は、本発明の炭素材を得る際に細孔制御を行うという点で重要な因子である。
例えば、炭素材の原料としてフェノール樹脂を用いた場合は、処理温度を高くするに従って細孔径が収縮し細孔容積が小さくなる傾向がある。また、処理時間については長くするほど細孔径が収縮し細孔容積が小さくなる傾向がある。これらの炭化処理条件を適宜選択することにより、目的とする細孔径及び細孔容積を有する炭素材を得ることができる。
【００１６】
なお、細孔制御された炭素材を得る方法は特に限定されるものではなく、前記炭化処理条件による方法のほか、炭素材原料として熱硬化性樹脂と熱可塑性樹脂との配合物を用いる方法、炭素材原料に添加剤を加えて硬化反応を制御する方法、あるいは炭素材の表面を樹脂で被覆して硬化・炭化処理を行う方法などがある。また、炭素材の製造時、硬化・炭化処理時に金属、あるいは他の炭素材料となりうる材料などで変性したり、顔料、滑剤、帯電防止剤、酸化防止剤など他の添加剤を添加しても差し支えない。
【００１７】
本発明の炭素材における、細孔径と細孔容積の測定方法については以下の通りである。
測定試料を島津製作所製・細孔分布測定装置装置「ＡＳＡＰ２０１０」を用いて、６２３Ｋで真空加熱前処理後、測定ガスとしてＣＯ2(分子径；０．３３ｎｍ)、Ｃ2Ｈ6（分子径；０．４０ｎｍ）を用い、各々についての２７３．１５Ｋでの吸着等温線を測定し、Dubinin-Radushkevich法によりそれぞれの吸着ガスの細孔容積を計算し、これをもとにそれぞれの細孔容積を次式に基づいて計算した。
Ｗ＝Ｗ0・ｅｘｐ［−（Ａ／Ｅ）ｎ］、Ａ＝ＲＴ［ｌｎ（Ｐｓ／Ｐ）］
Ｗ：吸着分子が占有しているエネルギー［ｍｌ／ｇ］
Ｅ：吸着特性エネルギー［Ｊ／ｍｏｌ］
Ｐ：平行蒸気圧［ｍｍＨｇ］
Ｔ：吸着温度［Ｋ］
Ｗ0：細孔容積［ｍｌ／ｇ］
Ｐｓ：飽和蒸気圧［ｍｍＨｇ］
ｎ：構造指数［−］、ｎ＝２とした
【００１８】
次に、本発明の二次電池用負極材について説明する。
本発明の二次電池用負極材は、以上に説明した炭素材を含有するものである。二次電池用負極材の製造方法としては特に限定されないが、例えば、前記炭素材１００重量部に対して、有機高分子結着剤（ポリエチレン、ポリプロピレン等を含むフッ素系高分子、ブチルゴム、ブタジエンゴム等のゴム状高分子等）１〜３０重量部、及び適量の粘度調整用溶剤（Ｎ−メチル−２−ピロリドン、ジメチルホルムアミド等）を添加して混練し、ペースト状にした混合物を圧縮成形，ロール成形等によりシート状、ペレット状等に成形して得ることができる。また、前記粘度調整用溶剤によりスラリー状にした混合物を銅箔、ニッケル箔等の集電体に塗布成形して得ることもできる。
【００１９】
【実施例】
以下，本発明を実施例により具体的に説明する。しかし、本発明は実施例に限定されるものでは無い。また「部」及び「％」はすべて「重量部」及び「重量％」を示す。
【００２０】
１．炭素材の製造
（実施例１）
フェノール樹脂（住友ベークライト製・ＰＲ-５１４６４）１００部を２００℃にて２時間硬化処理を行った後，窒素雰囲気下にて５℃／ｍｉｎで昇温し、１３００℃到達後１０時間保持して炭化処理した。その後、室温まで冷却し振動ボールミルを用い４５μｍ以下まで粉砕することにより炭素材５０部を得た。この炭素材を、島津製作所製・細孔分布測定装置「ＡＳＡＰ−２０１０」を用い、エタンガス吸着測定により前記（ａ）の細孔径を有する細孔について、及び炭酸ガス吸着測定により前記（ｂ）の細孔径を有する細孔について、それぞれ細孔容積を測定した。
（実施例２）
炭化処理工程において１℃／ｍｉｎで昇温した以外は、実施例１と同様の方法で炭素材を得た。
【００２１】
（比較例１）
炭化処理工程において２０℃／ｍｉｎで昇温した以外は、実施例１と同様の方法で炭素材を得た。
（比較例２）
炭化到達温度を２８００℃とした以外は、実施例１と同様の方法で炭素材を得た。
【００２２】
２．二次電池用負極材の評価（二次電池評価用二極式コインセルの製造）
（１）各実施例および比較例にて得られた炭素材に、これらに対して結合剤としてポリフッ化ビニリデン１０重量％、希釈溶媒としてＮ−メチル−２−ピロリドンを適量加え混合し、スラリー状の負極混合物を調製した。調製した負極スラリー状混合物を１８μｍの銅箔の両面に塗布し、その後、１１０℃で１時間真空乾燥した。真空乾燥後、ロールプレスによって電極を加圧成形した。これを直径００００ｍｍの円形として切り出し負極を作製した。
（２）正極はリチウム金属を用いて二極式コインセルにて評価を行った。電解液として体積比が１：１のエチレンカーボネートとジエチレンカーボネートの混合液に過塩素酸リチウムを１モル／リットル溶解させたものを用いた。
【００２３】
以上の方法で得られた炭素材及び二次電池評価用二極式コインセルについて、特性評価を行った。結果を表１に示す。
【表１】
（表の注）
３．測定方法
（１）Ｃ2Ｈ6細孔容積：前記方法により実施し、０．４０ｎｍを越える細孔径を有する細孔容積を測定した。
（２）ＣＯ2細孔容積：前記方法により実施し、０．３３ｎｍ〜０．４０ｎｍの細孔径を有する細孔容積を測定した。
（３）充電容量、放電容量：充電条件は電流２５ｍＡｈ／ｇの定電流で１ｍＶになるまで保持し，放電条件は １．２５ｍＡｈ／ｇ以下に電流が減衰するまでとした。また、放電条件のカットオフ電位は １．５Ｖとした。
（４）充放電効率：（充電容量／放電容量）により算出した。
【００２５】
実施例１及び２はいずれも、特定の細孔径を有する細孔容積が所定の範囲内である本発明の炭素材であり、これを負極材に用いて二次電池としての評価を行ったところ、充放電容量、充放電効率のバランスに優れたものであった。一方、比較例１、２はいずれも、細孔容積が適当でなかったため、いずれも充放電効率が低下したものとなった。本発明の炭素材をこのようにして検証したところ、実施例にて得られた細孔容積が制御された炭素材は、リチウムイオンの挿入・脱離がその細孔容積により制御されることが確認された。
【００２６】
【発明の効果】
本発明は、特定の細孔径を有する細孔容積が所定の範囲にあることを特徴とする炭素材であり、この炭素材を主成分とする非水電解質二次電池用電極材組成物は、充放電容量の理論値に限界点を有する黒鉛系組成物と比較して高エネルギー密度であり、充放電効率にも優れたものである。さらに、リチウムイオンのインターカレーション時に炭素材の膨張が起こらないなど電池特性としての安全性が高く再現性に優れているものであり、特にリチウムイオン二次電池の負極材として好適である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a carbon material and a negative electrode material for a secondary battery using the same.
[0002]
[Prior art]
In recent years, along with the remarkable development of electronic technology, miniaturization and weight reduction of electronic devices have been mentioned as requirements. Along with this, further miniaturization, weight reduction, and higher energy density have been demanded for mobile power supplies. Conventionally used secondary batteries are aqueous secondary batteries such as lead batteries and nickel-cadmium batteries. However, these aqueous secondary batteries exhibit excellent cycle performance, but are not sufficiently satisfactory in terms of battery mass and energy density.
[0003]
Subsequently, lithium metal batteries using lithium or lithium alloys as negative electrode materials were developed as new electrode materials. Although these batteries have a very high energy density as compared with the conventional batteries, lithium metal is very dangerous and has a safety problem, and is difficult to put into practical use. Therefore, a non-aqueous electrolyte type lithium ion secondary battery using a carbon material as a new negative electrode material has been developed. This utilizes the fact that lithium is intercalated / deintercalated between carbon layers, and dendritic lithium is deposited on the negative electrode using the carbon material even if the charge / discharge cycle proceeds. This phenomenon is not seen and high safety is guaranteed. It has a high energy density, is lightweight, and exhibits excellent charge / discharge cycle characteristics.
[0004]
Examples of the above include graphite described in JP-A-5-7457, but the theoretical charge / discharge capacity has a limit of 372 mAh / g. Further, there are graphitizable carbon materials described in JP-A-5-28996 and JP-A-7-73828, but the charge / discharge capacity is determined because graphitization is performed under a condition where the firing temperature exceeds 2000 degrees. In the lower temperature range, the charge / discharge capacity is high, but the cycle characteristics are poor, and the battery characteristics are low. In addition, the carbon negative electrode treated at a low temperature of about 500 ° C. to 700 ° C. has a charge / discharge capacity of 850 mAh / g, exceeding the graphite per capacity, and has good energy merit for low temperature treatment. The disadvantage is that the potential is high and the potential hysteresis at the charge / discharge level is large.
Further, when a liquid in which propylene carbonate is mixed with the electrolytic solution is used, if a graphite-based carbon material is used, a decomposition reaction of the electrolytic solution occurs and a decrease in characteristics is confirmed. However, when a non-graphitic carbon material is used, no decomposition reaction occurs and almost no deterioration in characteristics is confirmed.
[0005]
In addition, examples of the lithium ion negative electrode material other than the carbon material include metal oxides disclosed in JP-A-5-166536. When a metal oxide is used as the negative electrode material, the charge / discharge capacity of 800 mAh / g is excellent. However, since the instantaneous discharge capacity is very high, it is difficult to control and a big problem arises in safety.
[0006]
As a feature of the non-graphite carbon material, its three-dimensional structure has higher three-dimensionality than two-dimensionality. In the case of graphite, there is a theoretical capacity whose upper limit is 372 mAh / g in charge capacity, but this characteristic can be greatly exceeded. However, the irreversible capacity is much larger than that of a normal graphite-based carbon material, and improvement of this point is an essential item.
[0007]
[Problems to be solved by the invention]
The present invention provides a carbon material having excellent charge / discharge efficiency, low irreversible capacity, high energy density, good cycleability, and high safety, and a negative electrode material for a secondary battery using the same. .
[0008]
[Means for solving problems]
Such an object is achieved by the following present inventions (1) to ( 4 ).
(1) A carbon material used for a negative electrode material of a nonaqueous electrolyte secondary battery, wherein pores formed on the surface of the carbon material are
(A) The pore volume having a pore diameter exceeding 0.40 nm is 0.0001 to 0.010 ml / g,
(B) A carbon material characterized in that a ratio (b / a) to a pore volume having a pore diameter of 0.33 nm to 0.40 nm is 1 or more.
( 2 ) The ratio (b / a) of (a) pore volume having a pore diameter exceeding 0.40 nm and (b) pore volume having a pore diameter of 0.33 nm to 0.40 nm is 5 or more. carbon material according to the above (1) is.
( 3 ) The carbon material according to (1) or (2) , wherein the carbon material is obtained by curing and carbonizing a phenol resin.
( 4 ) A negative electrode material for a secondary battery containing the carbon material according to any one of (1) to ( 3 ) above.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Below, the carbon material of this invention and the negative electrode material for secondary batteries using the same are demonstrated.
The carbon material of the present invention is a carbon material used for a negative electrode material of a nonaqueous electrolyte secondary battery, and pores formed on the surface of the carbon material are
(A) The pore volume having a pore diameter exceeding 0.40 nm is 0.0001 to 0.010 ml / g,
(B) A ratio (b / a) to a pore volume having a pore diameter of 0.33 nm to 0.40 nm is 1 or more.
Moreover, the negative electrode material for secondary batteries of this invention uses the said carbon material.
[0010]
First, the carbon material of the present invention will be described in detail.
The pores formed on the surface of the carbon material according to the present invention are mainly formed in the carbonization process when the carbon material is manufactured. The type of carbon material used, the curing conditions of the carbon material, the carbon material It is considered that various modes are formed depending on the carbonization conditions at the time of manufacture. In the carbon material of the present invention, the pore refers to a material formed on the surface of the carbon material and communicates with the outside, and the pore diameter refers to a pore diameter of a portion where the pore communicates with the outside. And pore volume means the sum total of the space volume which the said pore forms in the carbon material inside.
[0011]
Of the pores formed on the surface of the carbon material of the present invention, (a) the pore volume having a pore diameter exceeding 0.40 nm is 0.0001 to 0.010 ml / g. Thereby, when the carbon material of this invention is used for the negative electrode material of a lithium secondary battery, an irreversible capacity | capacitance can be reduced. When the pore volume exceeds 0.010 ml / g, the charge capacity increases, but the irreversible capacity increases and the charge / discharge efficiency decreases. On the other hand, when it is less than 0.0001 ml / g, the irreversible capacity is reduced, but the charge capacity itself is lowered. The pores having the pore diameter of (a) are easily penetrated by the organic solvent in the electrolytic solution, so that the electrolytic solution is decomposed and reacted in the presence of lithium ions and trapped as a lithium salt. It is estimated that this increases the irreversible capacity .
[0012]
Moreover, the carbon material of the present invention has a pore volume (b) having a pore diameter of 0.33 nm to 0.40 nm among the pores formed on the surface, the pore volume having the pore diameter of (a). The ratio (b / a) to the volume is 1 or more. Thereby, charge capacity can be ensured and charging / discharging efficiency can be made favorable. When the volume ratio is less than 1, the charge capacity is reduced, and the charge / discharge efficiency is also lowered accordingly.
The pore having the pore diameter (b) is larger than the pore volume having the pore diameter (a) because the insertion / extraction of lithium ions due to charge / discharge is likely to occur reversibly. It is preferable.
The pore volume ratio (b / a) is more preferably 5 or more. Thereby, still higher charge / discharge efficiency can be maintained.
[0013]
The carbon material of the present invention is not particularly limited, but an average particle diameter of 1 to 50 μm is preferable, and 5 to 30 μm is particularly preferable. When the particle size of the carbon material is within the above range, the handleability during production of the negative electrode material is good, and the negative electrode material application surface after production is smooth. When the particle size of the carbon material is less than the lower limit, powder powder is generated and the workability of preparing the negative electrode material is likely to be deteriorated, and when the upper limit is exceeded, the negative electrode material application surface is likely to be uneven.
[0014]
Although it does not specifically limit as a raw material used for the carbon material of this invention, In addition to thermoplastic resins, such as thermosetting resins, such as a phenol resin, a furan resin, and an epoxy resin, polystyrene, polyamide, petroleum pitch, coal pitch, for spinning Pitch etc. can be used. These raw materials can be used alone or in combination of two or more. Among these, it is preferable to use a phenol resin. Thereby, it can be set as the carbon material which has the structure which the three-dimensional bridge | crosslinking developed. Although it does not specifically limit as a phenol resin, A resol type phenol resin, a novolak type phenol resin, etc. can be used.
When a thermosetting resin is used as the raw material for the carbon material, the curing method is not particularly limited. For example, when a phenol resin is used, thermal curing, thermal oxidation, epoxy curing, isocyanate curing, and the like can be given. Moreover, when an epoxy resin is used, phenol resin curing, acid anhydride curing, amine curing, and the like can be given. Any of these curing methods can be used.
[0015]
The carbon material of the present invention can be obtained by carbonizing the carbon material raw material obtained by the above method. Although it does not specifically limit as carbonization processing conditions for obtaining the carbon material of this invention, Usually, it is carried out at 1000-1500 degreeC for 0.01 to 50 hours. Moreover, as an atmosphere at the time of carbonization, there are a method in which it is performed in air, nitrogen, or an inert gas such as helium gas.
The conditions during the carbonization treatment are important factors in that pore control is performed when obtaining the carbon material of the present invention.
For example, when a phenol resin is used as the raw material for the carbon material, the pore diameter tends to shrink and the pore volume decreases as the processing temperature is increased. In addition, the longer the treatment time, the smaller the pore diameter and the smaller the pore volume. By appropriately selecting these carbonization conditions, a carbon material having a target pore diameter and pore volume can be obtained.
[0016]
In addition, the method for obtaining a carbon material with controlled pores is not particularly limited, in addition to the method based on the carbonization treatment conditions, a method using a blend of a thermosetting resin and a thermoplastic resin as a carbon material raw material, There are a method of controlling the curing reaction by adding an additive to the carbon material, or a method of coating the surface of the carbon material with a resin and performing a curing / carbonization treatment. In addition, it may be modified with a metal or other carbon material that can be used during curing and carbonization, or with other additives such as pigments, lubricants, antistatic agents, and antioxidants. There is no problem.
[0017]
The measuring method of the pore diameter and the pore volume in the carbon material of the present invention is as follows.
The measurement sample was pretreated by vacuum heating at 623 K using a pore distribution measuring device “ASAP2010” manufactured by Shimadzu Corporation, and then measured as CO 2 (molecular diameter; 0.33 nm), C 2 H 6 (molecular diameter; 0.40 nm), the adsorption isotherm at 273.15 K for each was measured, and the pore volume of each adsorbed gas was calculated by the Dubinin-Radushkevich method. Based on this, the pore volume of each was calculated. Calculation was based on the following formula.
W = W 0 · exp [− (A / E) n], A = RT [ln (Ps / P)]
W: Energy [ml / g] occupied by adsorbed molecules
E: Adsorption characteristic energy [J / mol]
P: Parallel vapor pressure [mmHg]
T: Adsorption temperature [K]
W 0 : pore volume [ml / g]
Ps: saturated vapor pressure [mmHg]
n: Structural index [−], n = 2.
Next, the negative electrode material for secondary batteries of the present invention will be described.
The negative electrode material for secondary batteries of the present invention contains the carbon material described above. Although it does not specifically limit as a manufacturing method of the negative electrode material for secondary batteries, For example, with respect to 100 weight part of said carbon materials, organic polymer binder (Fluorine polymer containing polyethylene, polypropylene, etc., butyl rubber, butadiene rubber) 1-30 parts by weight of a rubber-like polymer, etc.) and an appropriate amount of a viscosity adjusting solvent (N-methyl-2-pyrrolidone, dimethylformamide, etc.) are added and kneaded, and the mixture made into a paste is compression molded. It can be obtained by forming into a sheet form, a pellet form or the like by roll forming or the like. Moreover, the mixture made into the slurry form with the said solvent for viscosity adjustment can also be obtained by apply-molding on collectors, such as copper foil and nickel foil.
[0019]
【Example】
Hereinafter, the present invention will be specifically described by way of examples. However, the present invention is not limited to the examples. “Parts” and “%” indicate “parts by weight” and “% by weight”, respectively.
[0020]
1. Production of carbon material (Example 1)
After 2 hours curing at a 200 ° C. phenol resin (Sumitomo Bakelite · PR-51464) 100 parts, the temperature was raised at 5 ° C. / min under a nitrogen atmosphere, and held for 10 hours after 1300 ° C. reached Carbonized. Then, it cooled to room temperature and grind | pulverized to 45 micrometers or less using the vibration ball mill, and obtained 50 parts of carbon materials. Using this carbon material, a pore distribution measuring device “ASAP-2010” manufactured by Shimadzu Corporation, the pores having the pore diameter of the above (a) by the ethane gas adsorption measurement and the carbon dioxide adsorption measurement of the above (b) The pore volume was measured for each pore having a pore diameter.
(Example 2 )
A carbon material was obtained in the same manner as in Example 1 except that the temperature was raised at 1 ° C./min in the carbonization treatment step.
[0021]
(Comparative Example 1)
A carbon material was obtained in the same manner as in Example 1 except that the temperature was raised at 20 ° C./min in the carbonization process.
(Comparative Example 2)
A carbon material was obtained in the same manner as in Example 1 except that the carbonization temperature was 2800 ° C.
[0022]
2. Evaluation of secondary battery negative electrode materials (production of bipolar coin cells for secondary battery evaluation)
(1) To the carbon materials obtained in each of the examples and comparative examples, 10% by weight of polyvinylidene fluoride as a binder and an appropriate amount of N-methyl-2-pyrrolidone as a diluting solvent are added to and mixed with these carbon materials. A negative electrode mixture was prepared. The prepared negative electrode slurry-like mixture was applied to both sides of 18 μm copper foil, and then vacuum-dried at 110 ° C. for 1 hour. After vacuum drying, the electrode was pressure-formed by a roll press. This was cut out as a circle having a diameter of 0000 mm to produce a negative electrode.
(2) The positive electrode was evaluated with a bipolar coin cell using lithium metal. As the electrolytic solution, a solution obtained by dissolving 1 mol / liter of lithium perchlorate in a mixed solution of ethylene carbonate and diethylene carbonate having a volume ratio of 1: 1 was used.
[0023]
Characteristic evaluation was performed about the carbon material obtained by the above method and the bipolar coin cell for secondary battery evaluation. The results are shown in Table 1.
[Table 1]
(Note to table)
3. Measurement method (1) C 2 H 6 pore volume: The pore volume having a pore diameter exceeding 0.40 nm was measured by the method described above.
(2) CO 2 pore volume: carried out by the method, the pore volume was measured with a pore size of 0.33Nm～0.40Nm.
(3) Charging capacity, discharging capacity: Charging conditions were maintained at a constant current of 25 mAh / g until 1 mV, and discharging conditions were set until the current decayed to 1.25 mAh / g or less. The cut-off potential under discharge conditions was 1.5V.
(4) Charging / discharging efficiency: It was calculated by (charging capacity / discharging capacity).
[0025]
Each of Examples 1 and 2 is a carbon material of the present invention in which the pore volume having a specific pore diameter is within a predetermined range, and when this was used as a negative electrode material, evaluation as a secondary battery was performed. It was excellent in balance between charge / discharge capacity and charge / discharge efficiency. On the other hand, since the comparative examples 1 and 2 were not suitable for the pore volume, the charge / discharge efficiency was lowered. As a result of verifying the carbon material of the present invention in this way, the carbon material with controlled pore volume obtained in the examples is that the insertion / desorption of lithium ions is controlled by the pore volume. confirmed.
[0026]
【The invention's effect】
The present invention is a carbon material characterized in that the pore volume having a specific pore diameter is in a predetermined range, the electrode material composition for a non-aqueous electrolyte secondary battery mainly comprising this carbon material, Compared to a graphite-based composition having a limit point in the theoretical value of charge / discharge capacity, it has a higher energy density and excellent charge / discharge efficiency. Furthermore, since the carbon material does not expand during lithium ion intercalation, it has high battery safety and excellent reproducibility, and is particularly suitable as a negative electrode material for lithium ion secondary batteries.
Claims (4)
（ａ）０．４０ｎｍを越える細孔径を有する細孔容積が０．０００１〜０．０１０ｍｌ／ｇであり、
（ｂ）０．３３ｎｍ〜０．４０ｎｍの細孔径を有する細孔容積との比（ｂ／ａ）が１以上である
ことを特徴とする炭素材。A carbon material used for a negative electrode material of a non-aqueous electrolyte secondary battery, wherein pores formed on the surface of the carbon material,
(A) The pore volume having a pore diameter exceeding 0.40 nm is 0.0001 to 0.010 ml / g,
(B) A carbon material characterized in that a ratio (b / a) to a pore volume having a pore diameter of 0.33 nm to 0.40 nm is 1 or more.
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| JP4967316B2 (en) * | 2005-06-28 | 2012-07-04 | 日立化成工業株式会社 | Carbon particle for lithium secondary battery negative electrode, carbon negative electrode for lithium secondary battery using the same, and lithium secondary battery |
| JP5233314B2 (en) * | 2008-02-25 | 2013-07-10 | 住友ベークライト株式会社 | Carbon material for secondary battery, electrode for secondary battery, and secondary battery |
| CN102549813B (en) | 2009-09-28 | 2014-02-26 | 丰田自动车株式会社 | Lithium secondary battery and manufacturing method therefor |
| EP3691001A1 (en) * | 2010-07-30 | 2020-08-05 | Hitachi Chemical Company, Ltd. | Anode material for lithium ion secondary battery, anode for lithium ion secondary battery, and lithium ion secondary battery |
| KR102477729B1 (en) | 2014-07-07 | 2022-12-14 | 미쯔비시 케미컬 주식회사 | Carbon material, method for producing carbon material, and non-aqueous secondary battery using carbon material |
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