JP3690128B2

JP3690128B2 - Non-aqueous secondary battery carbonaceous negative electrode material, method for producing the same, and non-aqueous secondary battery

Info

Publication number: JP3690128B2
Application number: JP21897898A
Authority: JP
Inventors: 明男加藤; 憲利高尾; 富行鎌田
Original assignee: Mitsubishi Chemical Corp
Current assignee: Mitsubishi Chemical Corp
Priority date: 1997-08-05
Filing date: 1998-08-03
Publication date: 2005-08-31
Anticipated expiration: 2018-08-03
Also published as: JPH11111296A

Description

【０００１】
【発明の属する技術分野】
本発明は、非水系二次電池用炭素質負極材料及びその製造方法並びに非水系二次電池に関するものである。より詳しくは、非水系二次電池用負極材料として特に好適な、特定のミクロポア分布、量を持つ炭素質材料及びその製造方法並びに、小型軽量の電子機器用として好適な、リチウムイオン二次電池をはじめとする非水系二次電池に関するものである。
【０００２】
【従来の技術】
近年、電子機器等の小型軽量化や高機能化の点から、繰り返し使用可能な二次電池の需要が高まってきている。このような要求に合致する電池として、省電力化及び環境保全の立場から、鉛蓄電池やニッカド電池に替わるニッケル−水素系やリチウム系等のクリーンな非水系電池、特に軽量化、高電圧の点からリチウムイオン二次電池が注目され、実用化されるに至っている。初期の電池では負極にリチウム金属を用いたが、充放電によってデンドライトを生成し、内部短絡を引き起こすという問題があった。その後、リチウム金属に代えて、リチウムイオンを吸収、放出することのできる材料の開発が行われ、コークス等や天然黒鉛等の炭素質あるいは黒鉛系の材料が主に使われる様になっている（特開平２−９０８６３号、特開平１−２２１８５９号、特開昭６３−１２１２５７号公報参照）。炭素質材料及び黒鉛系の材料の中でも、比較的低温で、例えば１５００℃以下の温度で焼成された炭素質材料を用いたものは低コスト、高容量という点で有望視されている。
【０００３】
【発明が解決しようとする課題】
しかし、炭素質材料は、比較的安価で安全性が高く初期充電量は高いものの、その後の充放電容量は、炭素黒鉛系材料の理論容量として提唱されている値（３７２ｍＡｈ／ｇ）の２／３程度で、電池を作成しても充放電容量、効率が充分満足するものではなく、改良が望まれている。
【０００４】
【課題を解決するための手段】
本発明者は、上記の課題を解決すべく種々検討を行い、炭素質材料中の揮発分が初期充電容量を大きくしていること、炭素質材料を高温で加熱処理する際に揮発分の一部が炭化して生じる成分が炭素質材料の容量の発現を阻害していること、さらに炭素質材料を微粉砕した後に高温加熱処理（仮焼）すれば、揮発分を効率的に除去でき、揮発分炭化成分の残留も抑制できることを見出し、先に特願平７−０９２６０６（特開平８−２８７９１１）として出願した。
【０００５】
その後さらに検討を続け、炭素質微粉に特定の加熱処理を行えば、揮発分、特に上記の問題の主原因となる遊離の有機高分子化合物をより効率的に除去できること、これによって、炭素質材料中の特定のミクロポアの分布量が制御されることで炭素質材料の充放電容量、効率を改良できることを見出して、本発明に至った。
すなわち、本発明の要旨は、窒素ガスのＢＥＴ吸着法によって求められる、（ｉ）直径８Å未満のポアが２×１０^-4ｃｃ／ｇ以上であり、（ii）直径８〜１８Åのポアが１５×１０^-4ｃｃ／ｇ以下であることを特徴とする非水系二次電池用炭素質負極材料、及び、該材料を負極材料として用いたことを特徴とする非水系二次電池、並びに、揮発分が３０重量％以下で平均粒度１００μｍ以下の微粉状の炭素質材料を、不活性ガス雰囲気下に２５０〜６５０℃の温度で第１段加熱処理を行い、さらに不活性ガス雰囲気下に７００〜１５００℃の温度で第２段加熱処理（焼成）を行うこと（第１製造方法）、又は、揮発分が３０重量％以下で平均粒度１００μｍ以下の微粉状の炭素質材料を、酸化性ガス雰囲気下に５０〜４００℃の温度で第１段加熱処理を行い、さらに不活性ガス雰囲気下に７００〜１５００℃の温度で第２段加熱処理を行うこと（第２製造方法）、又は、該第２製造方法において、揮発分が３０重量％以下で平均粒度１００μｍ以下の微粉状の炭素質材料を、酸化性ガス雰囲気下で５０〜４００℃の温度で加熱処理する前及び／又は後に不活性ガス雰囲気下で２５０〜６５０℃の温度で加熱処理を行い、さらに不活性ガス雰囲気下に７００〜１５００℃の温度で加熱処理（焼成）を行うこと（第３製造方法）を特徴とする非水系二次電池用炭素質負極材料の製造方法にある。
以下、本発明を詳細に説明する。
【０００６】
【発明の実施の形態】
まず本発明において用いられる炭素質材料としては、例えば、ＦＣＣ（流動接触分解）残渣油、ＥＨＥ油（エチレン製造時の副生油）、常圧残渣油、減圧残渣油等の石油系重質油やコールタール、コールタールピッチ等の石炭系重質油、さらにはナフタレンやアントラセンのような多環芳香族化合物を加熱処理して得られるタール状物質でディレードコーカー、オートクレーブ等により４００〜５００℃程度の温度でコーキングしたコークスが挙げられる。
また、フェノール樹脂やフラン樹脂、あるいは木材や竹材、さらには石炭等を比較的低温、例えば７００℃以下で炭素化して得られる炭素質材料も使用することができる。
【０００７】
本発明におけるこのような炭素質材料は、好適には、揮発分が３０重量％以下、中でも１５重量％以下、さらに好ましくは１０重量％以下であるものが用いられる。揮発分が３０重量％より多くても本発明の効果は得られるが、１回目の加熱処理に要する時間が長大になったり、加熱処理の際に微粉状の炭素質材料の熔融が生じて揮発分が脱離しにくくなったり、微粉砕の際に粉塵爆発を起こす恐れが生じる。
【０００８】
本発明の炭素質負極材料を得るには、上記の炭素質材料を微粉化し、得られた微粉状の炭素質材料を２段階の加熱処理を行うことに特徴を有する。すなわち、後述する加熱処理に先立ち、この炭素質材料を微粉砕することが重要である。粉砕は、平均粒径が１００μｍ以下、好ましくは５０μｍ以下、また下限としては実用上１μｍ以上になるように行われる。粉砕方法、粒度調整のための分級等の操作自体は特に限定されるものではなく常法によって行われ、衝撃式粉砕機、衝突式粉砕機、磨砕式粉砕機等の微粉砕機を使用して行うことができる。また、分級についても、ふるいを始め、各種風力式分級機が使用できる。なお、最大粒径は実質的に５００μｍ以上のものを含まない、中でも最大粒径２００μｍ以上のものを含まないようにするのが、揮発分の除去効率の点から好ましい。
また、最大粒径が実質的に５００μｍを越えると、揮発分の除去効率が低下しやすくなり、均一な厚さの電極を製造することが困難になったり、電極の厚みを薄くして表面積を大きくすることがより困難になる。
【０００９】
本発明の第１の製造方法では、微粉砕した炭素質材料を、不活性ガス雰囲気下で、２５０〜６５０℃の温度で、第１段加熱処理を行ってから７００〜１５００℃で不活性ガス雰囲気下で第２段の加熱処理を行う。第１段加熱処理は、ロータリーキルン、電気炉等により行われ、特に制限されない。第１段加熱処理は、好ましくは３００〜５５０℃、より好ましくは４００〜５５０℃の温度で行われる。加熱処理時間は微粉の粒度、どの様な状態で加熱されるかによって異なってくるが、加熱される温度で脱離すべき揮発分が実質的になくなるだけ、通常は２５０〜６５０℃の加熱で揮発する成分が３ｗｔ％以下、好ましくは１ｗｔ％以下の揮発分になるだけの時間で良く、通常５時間以下である。
【００１０】
また、この加熱処理に際しては、揮発分の脱離が行われやすい様に、微粉を５０ｍｍ以下程度の薄い積層状態にしたり、撹拌等により微粉表面が常に気中にさらされる様にしたり、さらにはガスの送り込みによって流動層状態にするのが好適である。また、減圧下に加熱したり、大量のガスをスイープしたりして、脱離される揮発分を積極的に取り除くことも好ましい。
この第１段加熱処理により、微粉に含まれている揮発分の大半以上、特に遊離の有機化合物に由来する揮発分の大部分を効率的に微粉中から脱離させることができる。
【００１１】
第１段加熱処理を行った微粉は、不活性ガス雰囲気下で、７００〜１５００℃の温度で、第２段加熱処理を行う。第２段加熱処理は第１段加熱処理と同様に、ロータリーキルン、電気炉等により行われ、特に制限はない。第２段加熱処理は、第１段の加熱処理とは別途に行っても良いし、第１段加熱処理と連続して行っても良い。ただし、後者の場合は、第１段加熱処理で脱離発生してくる揮発分が第２段加熱処理ゾーンに浸入しない様に例えば排気機構を設けることが、揮発分の再炭素化沈積を防ぐといった意味で好ましい。
【００１２】
第２段加熱処理は、実質的に不活性雰囲気であることが必要であり、好ましくは８００〜１２００℃の温度、さらに、目的の電池特性により異なるが、より好ましくは１０００〜１２００℃で行われる。加熱処理時間は、加熱される温度での炭素化反応が実質的に終了するだけの時間で良く、通常１５分から２時間の範囲である。
【００１３】
第１段加熱処理と同じ様に、微粉を５０ｍｍ以下の薄い積層状態にしたり、撹拌等により微粉表面が気中にさらされる様にしたり、さらにはガスの送り込みによって流動層状態にするのが第１段加熱処理後も残った揮発分を、早期に速やかに脱離させるために好ましい。また、減圧下に加熱したり、大量のガスをスイープしたりすることも同様の意味で好ましい。
【００１４】
本発明の第２の製造方法では、微粉砕した炭素質材料を、まず酸化性ガス雰囲気下で、５０〜４００℃の温度で、第１段加熱処理を行う。加熱処理は、通常ロータリーキルン、電気炉、あるいは乾燥設備等により行われるが、特に制限されない。
加熱温度と時間は、微粉の粒度、加熱される状態等、及び使用する酸化性ガスの種類によって異なってくるが、空気を使用した場合では、通常２５０〜４００℃の温度で、３０分から１０時間、ＮＯx 、ＳＯx 、ハロゲン等を使用（併用）した場合では通常５０〜２００℃の温度で、１５分から３時間程度である。勿論、この範囲に限定されるものではなく、必要とされる処理の程度に応じて適宜選択されるべきものであることは言うまでもない。
【００１５】
また、この加熱処理に際しては、均一な酸化反応の進行、揮発分の脱離が行われやすい様に、第１の製造方法の場合と同様に、微粉を５０ｍｍ以下程度の薄い積層状態にしたり、撹拌等により微粉表面が常に気中にさらされる様にしたり、さらにはガスの送り込みによって流動層状態にするのが好適である。
この加熱処理により、第１の製造方法の場合と同様に、加熱による揮発分の脱離が起こるが、同時に進行する酸化反応によって、揮発分自体に加熱によってより脱離しやすくなる構造（−Ｏ−結合等の化学結合形態）が生成されるため、揮発分の脱離はより容易になり、また第１段加熱処理で脱離しきれなかった揮発分も、続く不活性ガス雰囲気下の第２段加熱処理時の炭素化反応の進行が始まる大分前に脱離させることができる様になる。
【００１６】
また、炭素質微結晶の間にも酸化反応による結合が生成し、その構造が第２段加熱処理時の炭素化反応が始まる頃まで残るためかと思われるが、リチウムの吸蔵されるミクロポアの量も、第２の製造方法では増加する。
第１段加熱処理の終了後は、第１の製造方法における７００〜１５００℃での第２段加熱処理を行えば良い。
【００１７】
また、第３の製造方法として第２の製造方法の酸化性ガス雰囲気下での加熱処理に第１の製造方法と同様の２段階の不活性ガス雰囲気下での加熱処理を組合わせて行い、より一層の揮発分の脱離を行わせても良く、酸化性ガス雰囲気下での加熱処理温度が低かった場合や、使用した炭素質材料の揮発分量が多かった場合には特に有効である。この場合、酸化性ガス雰囲気下での加熱処理は、不活性ガス雰囲気下での２５０〜６５０℃での加熱処理の前及び／又は後に行うことができるが、前に行うことがより好ましい。その後に７００〜１５００℃での不活性ガス雰囲気下での加熱処理を行えばよい。
【００１８】
本発明の製造方法によれば炭素質材料微粉は、リチウムの吸蔵に適した８Å未満のミクロポアが、２×１０^-4ｃｃ/ ｇ以上存在し、リチウムの吸蔵に適した8 Å以下のミクロポアの失活を招く、より大きなサイズの直径８〜１８Åのポアが、１５×１０^-4ｃｃ/ ｇ以下となっている。また、揮発分が１重量％以下となったものが充放電容量の点から好適である。
【００１９】
また、８Å以下のミクロポアの量を決定する、一番大きな要因である炭素質微結晶の大きさは、原料とする炭素質材料によって異なってくるが、Ｘ線回折法で求められる結晶の厚さ（Ｌｃ）で、通常１０〜５０Å、００２格子の格子間間隔（ｄ００２）は通常３．４０〜３．５５Åの範囲となっている。
なお、ミクロポアの大きさ、量は窒素ガスのＢＥＴ吸着法によって測定することができ、その様な装置としては、例えば、ＱＵＡＮＴＡＣＨＲＯＭ社製のＡＵＴＯＳＯＲＢ−１が挙げられる。
【００２０】
本発明の新規な炭素質負極材料が本発明の選ばれた条件のもとに製造され、優れた性能を示す効果は以下の様に考えられる。
すなわち、高温処理をする前の炭素質材料中には、揮発分が含まれている。揮発分は比較的低分子量の遊離有機化合物や、加熱処理による炭素化反応の進行に伴い、炭素質骨格構造から分離してくる低分子量有機化合物等から成るが、これらは高温処理の際に、炭素質材料中からガス化脱離してくる。一方、加熱処理による炭素化反応の進行に伴い、炭素質骨格構造は収縮をするが、この収縮段階での揮発分の脱離があると、その脱離ルートの形成、あるいは揮発分のガス化脱離圧力と炭素質骨格構造の収縮圧力の相互作用により、炭素質骨格構造に微細な亀裂を生じて、比較的小さなサイズのポアを生じる。この傾向は炭素質材料の粒度が大である程顕著となる。
【００２１】
一方、リチウム二次電池における炭素質負極材料のリチウム吸蔵は、炭素質材料を構成する炭素質微結晶（黒鉛結晶の前駆体）の積層構造間、いわゆるＸ線回折法で求められる００２格子間に吸蔵されるものと、炭素質微結晶同士の間にある数Å程度のミクロポア内に吸蔵されるものとがある。この内ミクロポアに吸蔵されるものは、より大きなサイズのポアと繋がり、連続した開放ポアになってしまうと吸蔵活性、効率を失ってしまうので、ミクロポアの量が多くても、より大きなサイズのポアも多い場合には充放電容量の増加、効率の向上には結びつかない。
【００２２】
本発明の第１の製造方法では、微粉状態で加熱処理を行うことにより、揮発分を脱離しやすくさせ、炭素化反応の進行が加速される前に、揮発分の多くを脱離させて、炭素化反応進行時の揮発分脱離による、比較的大きなサイズのポアの生成を抑制するとともに、加熱処理の前期に生じた揮発分脱離によるポアを、炭素化反応進行時の収縮圧力で押しつぶして、消失、あるいはより小さなサイズのポアに変化させて、リチウムが吸蔵されるミクロポアと連続した開放ポアを生じることを防ぐことが可能となったものと考えられる。
【００２３】
特に不活性ガス雰囲気下、２５０〜６５０℃の温度での加熱処理を経ることによって、揮発分の脱離を炭素化反応の進行が始まる前にほぼ終了させてしまうことにより、不活性ガス雰囲気下での７００〜１５００℃での加熱処理の効果をより発現しやすくしているものと考えられる。
【００２４】
本発明における第２及び第３の製造方法での、酸化性ガス雰囲気下、５０〜４００℃の温度での加熱処理は、酸化性ガスと炭素質材料との反応で、揮発分内に加熱によってより脱離しやすくなる構造（化学結合形態）を生成させて、不活性ガス雰囲気下での、前記した２５０〜６５０℃あるいは７００〜１５００℃での加熱処理と同様の効果の発現をより促進させるとともに、リチウムが吸蔵されるミクロポアの量自体を増やすものと考えられる。
【００２５】
従って、不活性ガス雰囲気下での２５０〜６５０℃での加熱処理と、不活性ガス雰囲気下での７００〜１５００℃の加熱処理に加えて、酸化性ガス雰囲気下での５０〜４００℃での加熱処理を組合せて行うことが好適である。
得られた炭素質材料は、リチウムイオン二次電池等非水系二次電池の負極材として用いられる。
【００２６】
負極材として用いる場合には、前記炭素質材料を、バインダー、溶媒（支持媒）等と混合してペースト化し、これを銅等の金属箔上に塗布した後、乾燥、加圧プレス等を行う。バインダーとしてはポリフッ化ビニリデン、ポリテトラフルオロエチレン、ポリエチレン、又は合成ゴム等が用いられる。溶媒としてはＮ−メチル−２−ピロリドン、ジメチルホルムアミド、水等が用いられる。
【００２７】
正極及び非水溶媒中に電解質を溶解させてなる電解液については、従来、非水系二次電池に用いられているもので良く、特に限定されない。具体的には、正極としては、ＬｉＣｏＯ₂、ＭｎＯ₂、ＴｉＳ₂、ＦｅＳ₂、Ｎｂ₃Ｓ₄、Ｍｎ₃Ｓ₄、ＣｏＳ₂、Ｖ₂Ｏ₅、Ｐ₂Ｏ₅、ＣｒＯ₃、Ｖ₃Ｏ₈、ＴｅＯ₂、ＧｅＯ₂等が、電解質としては、ＬｉＣｌＯ₄、ＬｉＢＦ₄、ＬｉＰＦ₆等が、電解質を溶解する非水溶媒としては、プロピレンカーボネート、テトラヒドロフラン、１，２−ジメトキシエタン、ジメチルスルホキシド、ジオキソラン、ジメチルホルムアミド、ジメチルアセトアミド、及びこれらの２種以上の混合溶媒等が用いられる。
【００２８】
セパレータは、電池の内部抵抗を小さくするために多孔体が好適であり、ポリプロピレン等の不織布、ガラスフィルターなどの耐有機溶媒性材料のものが用いられる。
これらの負極、正極、電解液及びセパレータは、例えばステンレススチール又はこれにニッケルメッキした電池ケースに組み込むのが一般的である。
電池構造としては、帯状の正極、負極をセパレータを介して渦巻き状にしたスパイラル構造又はボタン型ケースにペレット状の正極、円盤状の負極をセパレータを介して挿入する方法などが採用される。
【００２９】
【実施例】
以下、本発明を実施例により、さらに詳細に説明するが、本発明は、その要旨を越えない限り、以下実施例によって限定されるものではない。
実施例１
コールタールをコーキングして得た、揮発分５．４重量％の生コークスを、ジェットミルにて微粉砕して、平均１２μｍ、最大粒度４０μｍ以下の生コークス微粉を得た。この生コークス微粉を、ステンレス製のトレイ中に１０ｍｍの厚さで入れ、箱形の電気炉中で、窒素流通雰囲気下、１０℃／分で４５０℃まで昇温し、その温度で１時間保持して第１段加熱処理を行った。
一旦冷却してトレイを取り出し、微粉を黒鉛製のトレイ中に１０ｍｍの厚さで入れ直した後、再び箱形の電気炉中に入れ、窒素流通雰囲気下１０℃／分で再昇温した。表１に示す通り、８００〜１２００℃で１時間の保持をして、第２段加熱処理を行い、炭素質負極材料を得た。
【００３０】
得られた炭素質負極材料を、３５０℃、１時間の真空脱気処理（乾燥）を行った後、ＱＵＡＮＴＡＣＨＲＯＭ社（米国）製のＡＵＴＯＳＯＲＢ−１を使用して、液体窒素温度での窒素ガス吸着を行い、吸着等温線、ＢＥＴプロットを求めた。これを、Ｈｏｒｖａｔｈ−Ｋａｗａｚｏｅ法で解析して１８Åまでのミクロポアを測定した。
【００３１】
また、得られた炭素質負極材料は、図１に示す構成のセルを使用して、その充放電容量を測定した。
負極材料は、１０％のＰＶＤＦ（ポリ弗化ビニリデン）をバインダーとして使用し、２０ｍｍφのステンレス金網上に圧着して負極１とした。対極としてはＬｉ金属箔を使用し、同じく２０ｍｍφのステンレス金網上に圧着して正極３とした。
【００３２】
電解液にはプロピレンカーボネート（ＰＣ）に、電解質としてＬｉＰＦ₆を１モル／リットルの割合で溶解したものを用いた（２はセパレータと電解液を示す）。なお、この電池の容量に関しては、正極に対して負極を十分に小さくしている。
４はステンレス製の電池筐体、５は絶縁体（ポリ四弗化エチレン製）、６は充放電端子、７はシールパッキンである。
【００３３】
この電池を充電電流０．５ｍＡ／ｃｍ²で、電圧（対Ｌｉ極）が０．０１Ｖになるまで充電し、さらに０．０１Ｖの電圧を保ったまま、充電電流が０．０３ｍＡ／ｃｍ²以下になるまで充電を続けた。続いて、放電電流０．５ｍＡ／ｃｍ²で１．５Ｖまでの放電を行って、容量（放電容量）と効率（放電容量／初充電容量）を測定した。
得られた炭素質負極材料について、ミクロポア量測定、充放電容量測定をした結果を表１に示す。
【００３４】
【表１】

【００３５】
比較例１
実施例１で得た生コークスを、３０〜１５０ｍｍの大きさの塊のまま黒鉛製のトレイに入れ、箱形の電気炉中で、窒素流通雰囲気下、１０℃／分で表２に示すとおり８００〜１２００℃まで昇温し、その温度で１時間保持して加熱処理を行った。
次いで、得られた加熱処理コークスをジェットミルで微粉砕し、平均１１〜１２μｍ、最大粒度４５μｍ以下の炭素質負極材料を得た。
得られた炭素質負極材料について、実施例１と同様の、ミクロポア量測定、充放電容量測定をした結果を表２に示す。
【００３６】
【表２】

【００３７】
実施例２
コールタールをコーキングして得た、揮発分１８重量％の生コークスを、回転式衝撃粉砕機にて微粉砕した後、目開き８６μｍの篩を通し、平均１８μｍの生コークス微粉を得た。この生コークス微粉を、ステンレス製のトレイ中に１０ｍｍの厚さで入れ、箱形の電気炉中で、空気流通雰囲気下、１０℃／分で１５０℃まで昇温し、その後１℃／分の昇温速度に変えて、２５０〜４００℃まで昇温した後、その温度で３０分間保持して第１段加熱処理を行った。
一旦冷却してトレイを取り出した後、再び箱形の電気炉中に入れ、窒素流通雰囲気下、１０℃／分で再昇温し、１０００℃で１時間の保持をして、第２段加熱処理を行い、炭素質負極材料を得た。
得られた炭素質負極材料について、実施例１と同様の、ミクロポア量測定、充放電容量測定をした結果を表３に示す。
【００３８】
【表３】

【００３９】
比較例２
第２段加熱処理を４５０℃、３０分とした以外は、実施例３と全く同じ処理を行って炭素質負極材料を得た。
この炭素質負極材料について、実施例１と同様のミクロポア量測定、充放電容量測定を行った結果、８Å未満のポア量は２８．５×１０^-4ｃｃ／ｇ、８〜１８Åのポア量は４６．６×１０^-4ｃｃ／ｇであった。また、容量は３５５ｍＡｈ／ｇ、効率は７０％であった。
【００４０】
実施例３
実施例２で得た生コークス微粉を、ステンレス製のトレイ中に１０ｍｍの厚さで入れ、箱形の電気炉中で、１０容積％のＮＯ₂ガスを加えた空気流通雰囲気下、１０℃／分で１２０℃まで昇温し、その温度で３０分間保持して、第１段加熱処理を行った。
一旦冷却してトレイを取り出した後、再び箱形の電気炉中に入れ、窒素流通雰囲気下１０℃／分で再昇温し、１０００℃で１時間の保持をして、第２段加熱処理を行い、炭素質負極材料を得た。
得られた炭素質負極材料について、実施例１と同様の、ミクロポア量測定、充放電容量測定を行った結果、８Å未満のポア量は３．１×１０^-4ｃｃ／ｇ、８〜１８Åのポア量は６．１×１０^-4ｃｃ／ｇであった。また、容量は３８０ｍＡｈ／ｇ、効率は７１％であった。
【００４１】
実施例４
第１段加熱処理を行った後、窒素流通雰囲気下での４５０℃、１時間の、加熱処理を行い、次いで窒素流通雰囲気下での１０００℃、１時間の、最後の加熱処理を行った以外は、実施例３と全く同じ処理を行って炭素質負極材料を得た。
この炭素質負極材料について、実施例１と同様のミクロポア量測定、充放電容量測定を行った結果、８Å未満のポア量は３．９×１０^-4ｃｃ／ｇ、８〜１８Åのポア量は６．７×１０^-4ｃｃ／ｇであった。また、容量は４０５ｍＡｈ／ｇ、効率は７９％であった。
【００４２】
実施例５
コールタールをコーキングして得た、揮発分５．６重量％の生コークスを、ジェットミルにて微粉砕して、平均１１μｍ、最大粒度４０μｍ以下の生コークス微粉を得た。
この生コークス微粉を黒鉛製のトレイ中に４０ｍｍの厚さで入れ、箱形の電気炉中で、窒素流通雰囲気下、１０℃／分で４５０℃まで昇温し、４５０℃で１．５時間保持する第１段加熱処理を行った。
【００４３】
一旦冷却してトレイを取り出し、第１段加熱処理での収率を測定した後、トレイを再び箱形の電気炉中に入れ、窒素流通雰囲気下１０℃／分で再昇温した。表４に示す通り８００〜１２００℃で１時間の保持をして、第２段加熱処理を行い、負極材料を得た。得られた負極材料を図１に示す構成のセルを使用してその性能を評価した。
負極材料は、１０％のＰＶＤＦ（ポリ弗化ビニリデン）をバインダーとして使用し、２０ｍｍφのステンレス金網上に圧着して負極１とした。対極としてはＬｉ金属箔を使用し、同じく２０ｍｍφのステンレス金網上に圧着して正極３とした。
【００４４】
電解液にはプロピレンカーボネート（ＰＣ）に、電解質としてＬｉＰＦ₆を１モル／リットルの割合で溶解したものを用いた（２はセパレータと電解液を示す）。なお、この電池の容量に関しては、正極に対して負極を十分に小さくしている。
４はステンレス製の電池筐体、５は絶縁体（ポリ四弗化エチレン製）、６は充放電端子、７はシールパッキンである。
【００４５】
この電池を充電電流０．５ｍＡ／ｃｍ²で、電圧（対Ｌｉ極）が０．０１Ｖになるまで充電し、さらに０．０１Ｖの電圧を保ったまま、充電電流が０．０３ｍＡ／ｃｍ²以下になるまで充電を続けた。ついで、放電電流０．５ｍＡ／ｃｍ²で１．５Ｖまでの放電を行った。容量（放電容量）と効率（放電容量／初充電容量）の結果を表４に示す。
【００４６】
【表４】

【００４７】
比較例３
実施例５で得た生コークス微粉を、第１段加熱処理をすることなく、実施例５の場合と同様にして８００〜１２００℃で１時間の加熱処理を行い、負極材料を得た。
実施例５と同様の電池性能評価をした結果を表５に示す。
【００４８】
【表５】

【００４９】
比較例４
実施例５で得た生コークスを３０〜１５０ｍｍの大きさの塊のまま、比較例３の場合と同様の加熱処理をした。次いで、得られた加熱処理コークスをジェットミルで微粉砕し、平均１３μｍ、最大粒径４５μｍ以下の負極材料を得た。
実施例５と同様の電池性能評価をした結果を表６に示す。
【００５０】
【表６】

【００５１】
実施例６
実施例５で得た生コークス微粉を、実施例５の場合と同様な方法によって、３００〜６００℃、１．５時間の第１段加熱処理を行った。次いで、１０００℃、１時間の第２段加熱処理を行い、負極材料を得た。
実施例５と同様の電池性能評価をした結果を表７に示す。
【００５２】
【表７】

【００５３】
実施例７
実施例５で得た生コークス微粉を、実施例５の場合と同様な方法によって、４５０℃、０．５〜５時間の第１段加熱処理を行った。次いで、１０００℃、１時間の第２段加熱処理を行い、負極材料を得た。
実施例５と同様の電池性能評価をした結果を表８に示す。
【００５４】
【表８】

【００５５】
実施例８
実施例５で得た生コークスを、ジェットミルまたはサンプルミル（衝撃式粉砕機）で微粉砕して平均粒度１１〜１３５μｍの生コークス微粉を得た。この生コークス微粉を実施例５の場合と同様な方法によって、４５０℃、１．５時間の第１段加熱処理を行った。次いで、１０００℃、１時間の第２段加熱処理を行い、負極材料を得た。
実施例５と同様の電池性能評価をした結果を表９に示す。
【００５６】
【表９】

【００５７】
実施例９
コールタールをコーキングして得た、揮発分２５．２重量％の生コークスをステンレス製深皿に入れ、箱形電気炉中で、窒素雰囲気下４２５、４５０℃で５時間加熱処理をして、揮発分１９．１、１２．６重量％の生コークスを得た。
これらの生コークスに加えて、実施例５で使用した揮発分５．６重量％の生コークス及び本実施例（実施例９）の５時間の加熱処理をする前の揮発分２５．２重量％の生コークスの計４種について、それぞれ、ジェットミルで微粉砕して平均粒度１０〜１３μｍの生コークス微粉を得た。この生コークス微粉を実施例５におけるのと同様な方法によって、４５０℃、１．５時間の第１段加熱処理（不活性ガス処理）を行った。次いで、１０００℃、１時間の第２段加熱処理（不活性ガス処理）を行い、負極材料を得た。
実施例５と同様の電池性能評価をした結果を表１０に示す。
【００５８】
【表１０】

【００５９】
【発明の効果】
本発明によれば、低コストの炭素質材料から容易に、容量が大きく、かつ効率の高い非水系二次電池用の負極材を提供しうる。
【図面の簡単な説明】
【図１】本発明の非水系二次電池の一例である、ボタン型非水電解液二次電池の断面説明図である。
【符号の説明】
１負極
２セパレータ及び電解液
３正極
４電池筐体
５絶縁体
６充放電端子
７シールパッキン[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a carbonaceous negative electrode material for a non-aqueous secondary battery, a method for producing the same, and a non-aqueous secondary battery. More specifically, a carbonaceous material having a specific micropore distribution and quantity, particularly suitable as a negative electrode material for a non-aqueous secondary battery, a method for producing the same, and a lithium ion secondary battery suitable for use in a small and light electronic device. The present invention relates to a non-aqueous secondary battery.
[0002]
[Prior art]
In recent years, the demand for secondary batteries that can be used repeatedly has increased from the viewpoint of reducing the size and weight of electronic devices and increasing the functionality. As a battery that meets these requirements, from the standpoint of power saving and environmental protection, clean non-aqueous batteries such as nickel-hydrogen and lithium that replace lead-acid batteries and nickel-cadmium batteries, especially weight reduction and high voltage Therefore, lithium ion secondary batteries have attracted attention and have been put to practical use. In early batteries, lithium metal was used for the negative electrode, but there was a problem that dendrites were generated by charging and discharging, causing internal short circuits. Later, instead of lithium metal, materials that can absorb and release lithium ions were developed, and carbonaceous or graphite-based materials such as coke and natural graphite are mainly used ( JP-A-2-90863, JP-A-1-221859, JP-A-63-1212257). Among carbonaceous materials and graphite-based materials, those using a carbonaceous material fired at a relatively low temperature, for example, a temperature of 1500 ° C. or less, are considered promising in terms of low cost and high capacity.
[0003]
[Problems to be solved by the invention]
However, although the carbonaceous material is relatively inexpensive and safe and has a high initial charge, the subsequent charge / discharge capacity is 2 / of the value (372 mAh / g) proposed as the theoretical capacity of the carbon graphite-based material. Even if a battery is prepared at about 3, the charge / discharge capacity and efficiency are not sufficiently satisfied, and improvements are desired.
[0004]
[Means for Solving the Problems]
The present inventor has made various studies to solve the above problems, and that the volatile matter in the carbonaceous material increases the initial charge capacity, and that the volatile matter in the carbonaceous material is heated at a high temperature. Volatile components can be removed efficiently if the components generated by carbonization inhibit the expression of the capacity of the carbonaceous material, and if the carbonaceous material is finely pulverized and then heat treated (calcined), It has been found that the residual volatile carbonization component can be suppressed, and previously filed as Japanese Patent Application No. 7-092606 (Japanese Patent Application Laid-Open No. 8-287911).
[0005]
After further investigation, if the carbonaceous fine powder is subjected to specific heat treatment, volatile components, especially free organic polymer compounds that are the main cause of the above problems, can be removed more efficiently. The inventors have found that the charge / discharge capacity and efficiency of the carbonaceous material can be improved by controlling the distribution amount of specific micropores therein, and have reached the present invention.
That is, the gist of the present invention is that (i) a pore having a diameter of less than 8 mm is obtained by a nitrogen gas BET adsorption method. ^-Four (ii) a pore having a diameter of 8 to 18 mm is 15 × 10 ^-Four Carbonaceous negative electrode material for non-aqueous secondary battery, characterized by being cc / g or less , And this material was used as a negative electrode material It is characterized by Non-aqueous secondary battery , And The volatile content is less than 30% by weight A finely powdered carbonaceous material having an average particle size of 100 μm or less at a temperature of 250 to 650 ° C. in an inert gas atmosphere. 1st stage Heat treatment, further At a temperature of 700-1500 ° C. in an inert gas atmosphere Second stage Performing heat treatment (firing) (first production method), or Volatile content is less than 30% by weight A finely powdered carbonaceous material having an average particle size of 100 μm or less at a temperature of 50 to 400 ° C. in an oxidizing gas atmosphere. 1st stage Heat treatment, Further, the second stage heat treatment is performed at 700 to 1500 ° C. in an inert gas atmosphere (second production method), or in the second production method, the volatile content is 30% by weight or less and the average particle size is 100 μm or less. A finely divided carbonaceous material at a temperature of 50 to 400 ° C. in an oxidizing gas atmosphere. Heat treatment Do Heat treatment is performed at a temperature of 250 to 650 ° C. in an inert gas atmosphere before and / or after. ,further Under inert gas atmosphere In Perform heat treatment (firing) at a temperature of 700 to 1500 ° C. (Third A method for producing a carbonaceous negative electrode material for a non-aqueous secondary battery.
Hereinafter, the present invention will be described in detail.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
First, as the carbonaceous material used in the present invention, for example, petroleum heavy oil such as FCC (fluid catalytic cracking) residue oil, EHE oil (by-product oil during ethylene production), atmospheric residue oil, decompression residue oil, etc. A coal-like heavy oil such as coal tar and coal tar pitch, and a tar-like substance obtained by heat-treating polycyclic aromatic compounds such as naphthalene and anthracene, etc., at about 400 to 500 ° C by delayed coker, autoclave, etc. Coke coked at a temperature of
In addition, a carbonaceous material obtained by carbonizing phenol resin, furan resin, wood, bamboo, or coal at a relatively low temperature, for example, 700 ° C. or less can be used.
[0007]
As such a carbonaceous material in the present invention, a material having a volatile content of 30% by weight or less, particularly 15% by weight or less, more preferably 10% by weight or less is used. Although the effect of the present invention can be obtained even if the volatile content is more than 30% by weight, the time required for the first heat treatment becomes longer, or the fine powdery carbonaceous material is melted during the heat treatment. There is a risk that it will be difficult for the components to be detached, or a dust explosion may occur during pulverization.
[0008]
In order to obtain the carbonaceous negative electrode material of the present invention, the above-mentioned carbonaceous material is pulverized and the obtained fine powdery carbonaceous material is subjected to two-stage heat treatment. That is, it is important to pulverize this carbonaceous material prior to the heat treatment described later. The pulverization is performed so that the average particle diameter is 100 μm or less, preferably 50 μm or less, and the lower limit is practically 1 μm or more. The operation itself, such as the pulverization method and classification for adjusting the particle size, is not particularly limited, and is performed by a conventional method, using a fine pulverizer such as an impact pulverizer, a collision pulverizer, or a grinding pulverizer. Can be done. For classification, various wind classifiers such as sieves can be used. In addition, it is preferable from the point of the removal efficiency of a volatile matter not to contain a thing with a maximum particle size of 500 micrometers or more substantially, especially not to have a maximum particle diameter of 200 micrometers or more.
Also, if the maximum particle size is substantially over 500 μm, the removal efficiency of volatile matter tends to be reduced, making it difficult to produce an electrode having a uniform thickness, or reducing the electrode thickness to reduce the surface area. It becomes more difficult to enlarge.
[0009]
In the first production method of the present invention, the finely pulverized carbonaceous material is subjected to a first stage heat treatment at a temperature of 250 to 650 ° C. in an inert gas atmosphere, and then an inert gas at 700 to 1500 ° C. A second stage heat treatment is performed under an atmosphere. The first stage heat treatment is performed by a rotary kiln, an electric furnace or the like, and is not particularly limited. The first stage heat treatment is preferably performed at a temperature of 300 to 550 ° C, more preferably 400 to 550 ° C. Although the heat treatment time varies depending on the particle size of the fine powder and in what state it is heated, it is usually volatilized by heating at 250 to 650 ° C. so that the volatile matter to be desorbed at the heating temperature is substantially eliminated. The time required for the component to become a volatile component of 3 wt% or less, preferably 1 wt% or less, is usually 5 hours or less.
[0010]
In this heat treatment, the fine powder is made into a thin laminated state of about 50 mm or less, the fine powder surface is always exposed to the air by stirring, etc. so that the volatile matter can be easily desorbed, It is preferable to make the fluidized bed state by feeding gas. Further, it is also preferable to positively remove the volatile components that are desorbed by heating under reduced pressure or sweeping a large amount of gas.
By this first stage heat treatment, most of the volatile matter contained in the fine powder, in particular, most of the volatile matter derived from the free organic compound can be efficiently desorbed from the fine powder.
[0011]
The fine powder subjected to the first stage heat treatment is subjected to the second stage heat treatment at a temperature of 700 to 1500 ° C. in an inert gas atmosphere. Similar to the first stage heat treatment, the second stage heat treatment is performed by a rotary kiln, an electric furnace or the like, and is not particularly limited. The second-stage heat treatment may be performed separately from the first-stage heat treatment, or may be performed continuously with the first-stage heat treatment. However, in the latter case, an evacuation mechanism, for example, is provided to prevent the volatile matter desorbed by the first stage heat treatment from entering the second stage heat treatment zone, thereby preventing recarbonization and deposition of the volatile matter. This is preferable.
[0012]
The second-stage heat treatment needs to be a substantially inert atmosphere, preferably at a temperature of 800 to 1200 ° C., and more preferably 1000 to 1200 ° C., depending on the intended battery characteristics. . The heat treatment time may be a time required for substantially completing the carbonization reaction at the heated temperature, and is usually in the range of 15 minutes to 2 hours.
[0013]
As with the first stage heat treatment, the fine powder is made into a thin laminated state of 50 mm or less, the surface of the fine powder is exposed to the air by stirring, etc. It is preferable to quickly desorb volatile components remaining after the first stage heat treatment at an early stage. Further, heating under reduced pressure or sweeping a large amount of gas is preferable in the same meaning.
[0014]
In the second production method of the present invention, the finely pulverized carbonaceous material is first subjected to first stage heat treatment at a temperature of 50 to 400 ° C. in an oxidizing gas atmosphere. The heat treatment is usually performed by a rotary kiln, an electric furnace, a drying facility or the like, but is not particularly limited.
The heating temperature and time vary depending on the particle size of the fine powder, the heated state, etc., and the type of oxidizing gas to be used. When air is used, the temperature is usually 250 to 400 ° C. for 30 minutes to 10 hours. When NOx, SOx, halogen or the like is used (combined), it is usually at a temperature of 50 to 200 ° C. and about 15 minutes to 3 hours. Of course, it is not limited to this range, and needless to say, it should be appropriately selected according to the degree of processing required.
[0015]
In addition, in this heat treatment, as in the case of the first manufacturing method, the fine powder is made into a thin laminated state of about 50 mm or less, so that the uniform oxidation reaction proceeds and volatile components are easily desorbed. It is preferable that the surface of the fine powder is always exposed to the air by stirring or the like, or further, a fluidized bed state is obtained by feeding gas.
As in the case of the first production method, this heat treatment causes desorption of volatile components by heating. However, the structure (-O-) in which the volatile components themselves are more easily desorbed by heating due to the simultaneous oxidation reaction. The volatile matter is more easily desorbed, and the volatile matter that could not be desorbed by the first stage heat treatment is also present in the second stage under the inert gas atmosphere. It can be desorbed much before the start of the carbonization reaction during the heat treatment.
[0016]
In addition, it is thought that a bond due to an oxidation reaction is generated between carbonaceous microcrystals, and the structure remains until the carbonization reaction in the second stage heat treatment starts, but the amount of micropores in which lithium is occluded However, it increases in the second manufacturing method.
After the completion of the first stage heat treatment, the second stage heat treatment at 700 to 1500 ° C. in the first manufacturing method may be performed.
[0017]
Further, as the third production method, the heat treatment in the oxidizing gas atmosphere of the second production method is combined with the heat treatment in an inert gas atmosphere in the same two steps as the first production method, Further desorption of volatile components may be performed, which is particularly effective when the heat treatment temperature in an oxidizing gas atmosphere is low or when the amount of volatile components of the carbonaceous material used is large. In this case, the heat treatment in an oxidizing gas atmosphere can be performed before and / or after the heat treatment at 250 to 650 ° C. in an inert gas atmosphere, but is more preferably performed before. Thereafter, heat treatment in an inert gas atmosphere at 700 to 1500 ° C. may be performed.
[0018]
According to the production method of the present invention, the carbonaceous material fine powder has 2 × 10 micropores of less than 8 mm suitable for lithium storage. ^-Four Larger sized pores having a diameter of 8 to 18 mm, which are present in the presence of cc / g or more and cause inactivation of micropores of 8 mm or less suitable for lithium occlusion, are 15 × 10 ^-Four cc / g or less. Moreover, the thing whose volatile content became 1 weight% or less is suitable from the point of charge / discharge capacity.
[0019]
In addition, the size of carbon microcrystals, which is the biggest factor that determines the amount of micropores of 8 cm or less, differs depending on the carbonaceous material used as a raw material, but the crystal thickness required by the X-ray diffraction method In (Lc), the inter-lattice spacing (d002) of 10 to 50 cm and 002 lattice is usually in the range of 3.40 to 3.55 cm.
The size and amount of micropores can be measured by the BET adsorption method of nitrogen gas. As such an apparatus, for example, AUTOSORB-1 manufactured by QUANTACHROM can be mentioned.
[0020]
The novel carbonaceous negative electrode material of the present invention is produced under the selected conditions of the present invention, and the effect of exhibiting excellent performance is considered as follows.
That is, the volatile matter is contained in the carbonaceous material before the high temperature treatment. Volatile components are composed of relatively low molecular weight free organic compounds and low molecular weight organic compounds that are separated from the carbonaceous skeleton structure as the carbonization reaction proceeds by heat treatment. It gasifies and desorbs from the carbonaceous material. On the other hand, the carbonaceous skeletal structure contracts as the carbonization reaction proceeds by heat treatment, but if there is volatile desorption at this contraction stage, formation of the desorption route or gasification of the volatiles will occur. The interaction between the desorption pressure and the shrinkage pressure of the carbonaceous skeleton structure causes fine cracks in the carbonaceous skeleton structure, resulting in relatively small size pores. This tendency becomes more prominent as the particle size of the carbonaceous material increases.
[0021]
On the other hand, the lithium occlusion of the carbonaceous negative electrode material in the lithium secondary battery is performed between laminated structures of carbonaceous microcrystals (precursor of graphite crystals) constituting the carbonaceous material, between 002 lattices obtained by so-called X-ray diffraction method. Some are occluded, and some are occluded in a few micropores between carbonaceous microcrystals. Of these, what is occluded in the micropore is connected to a larger pore and loses its occlusion activity and efficiency if it becomes a continuous open pore, so even if the amount of micropores is large, the larger pore If the amount is too large, the charge / discharge capacity is not increased and the efficiency is not improved.
[0022]
In the first production method of the present invention, by performing heat treatment in a fine powder state, it is easy to desorb volatile matter, and before the progress of the carbonization reaction is accelerated, most of the volatile matter is desorbed, Suppresses the generation of relatively large pores due to volatile desorption during the carbonization reaction, and crushes pores due to volatile desorption generated in the first half of the heat treatment with the shrinkage pressure during the carbonization reaction. Thus, it is considered that it is possible to prevent the generation of an open pore continuous with the micropore in which lithium is occluded by disappearing or changing to a pore having a smaller size.
[0023]
In particular, by performing heat treatment at a temperature of 250 to 650 ° C. under an inert gas atmosphere, the elimination of volatile matter is almost completed before the progress of the carbonization reaction starts, so that the inert gas atmosphere It is considered that the effect of the heat treatment at 700 to 1500 ° C. is more easily expressed.
[0024]
In the second and third production methods of the present invention, the heat treatment at a temperature of 50 to 400 ° C. in an oxidizing gas atmosphere is a reaction between the oxidizing gas and the carbonaceous material, and heating is performed in the volatile matter. A structure (chemically bonded form) that is more easily desorbed is generated to further promote the expression of the same effect as the heat treatment at 250 to 650 ° C. or 700 to 1500 ° C. in an inert gas atmosphere. It is considered that the amount of micropores in which lithium is occluded is increased.
[0025]
Therefore, in addition to the heat treatment at 250 to 650 ° C. in an inert gas atmosphere and the heat treatment at 700 to 1500 ° C. in an inert gas atmosphere, the heat treatment at 50 to 400 ° C. in an oxidizing gas atmosphere is performed. It is preferable to perform the heat treatment in combination.
The obtained carbonaceous material is used as a negative electrode material for non-aqueous secondary batteries such as lithium ion secondary batteries.
[0026]
When used as a negative electrode material, the carbonaceous material is mixed with a binder, a solvent (support medium), etc. to form a paste, and this is applied onto a metal foil such as copper, followed by drying, pressing and the like. . As the binder, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, synthetic rubber, or the like is used. As the solvent, N-methyl-2-pyrrolidone, dimethylformamide, water or the like is used.
[0027]
The electrolytic solution obtained by dissolving the electrolyte in the positive electrode and the non-aqueous solvent may be conventionally used in non-aqueous secondary batteries and is not particularly limited. Specifically, as the positive electrode, LiCoO ₂ , MnO ₂ TiS ₂ , FeS ₂ , Nb _Three S _Four , Mn _Three S _Four , CoS ₂ , V ₂ O _Five , P ₂ O _Five , CrO _Three , V _Three O ₈ , TeO ₂ , GeO ₂ Etc., as the electrolyte, LiClO _Four , LiBF _Four , LiPF ₆ As the non-aqueous solvent for dissolving the electrolyte, propylene carbonate, tetrahydrofuran, 1,2-dimethoxyethane, dimethyl sulfoxide, dioxolane, dimethylformamide, dimethylacetamide, and a mixed solvent of two or more thereof are used.
[0028]
The separator is preferably a porous body in order to reduce the internal resistance of the battery, and a non-woven fabric such as polypropylene or an organic solvent-resistant material such as a glass filter is used.
These negative electrode, positive electrode, electrolytic solution and separator are generally incorporated into, for example, a stainless steel or a battery case plated with nickel.
As the battery structure, a belt-shaped positive electrode, a spiral structure in which the negative electrode is spiraled through a separator, or a method of inserting a pellet-shaped positive electrode and a disk-shaped negative electrode through a separator into a button-type case, etc. are adopted.
[0029]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited by the following Examples, unless the summary is exceeded.
Example 1
Raw coke having a volatile content of 5.4% by weight obtained by coking coal tar was finely pulverized by a jet mill to obtain raw coke fine powder having an average of 12 μm and a maximum particle size of 40 μm or less. This raw coke fine powder is put into a stainless steel tray at a thickness of 10 mm, heated to 450 ° C. at 10 ° C./min in a nitrogen flow atmosphere in a box-shaped electric furnace, and held at that temperature for 1 hour. Then, the first stage heat treatment was performed.
Once cooled, the tray was taken out, and the fine powder was reinserted into a graphite tray at a thickness of 10 mm, and then again placed in a box-shaped electric furnace, and the temperature was raised again at 10 ° C./min in a nitrogen flow atmosphere. As shown in Table 1, it was held at 800 to 1200 ° C. for 1 hour, and the second stage heat treatment was performed to obtain a carbonaceous negative electrode material.
[0030]
The obtained carbonaceous negative electrode material is subjected to vacuum degassing treatment (drying) at 350 ° C. for 1 hour, and then, using an AUTOSORB-1 manufactured by QUANTACHROM (USA), nitrogen gas adsorption at liquid nitrogen temperature The adsorption isotherm and the BET plot were obtained. This was analyzed by the Horvath-Kawazoe method, and micropores up to 18 cm were measured.
[0031]
Moreover, the obtained carbonaceous negative electrode material measured the charging / discharging capacity using the cell of the structure shown in FIG.
As the negative electrode material, 10% PVDF (polyvinylidene fluoride) was used as a binder, and a negative electrode 1 was obtained by pressure bonding onto a 20 mmφ stainless steel wire mesh. Li metal foil was used as the counter electrode, and was pressed onto a stainless steel wire mesh of 20 mmφ to form the positive electrode 3.
[0032]
The electrolyte is propylene carbonate (PC) and the electrolyte is LiPF. ₆ Was dissolved at a rate of 1 mol / liter (2 represents a separator and an electrolytic solution). Regarding the capacity of this battery, the negative electrode is made sufficiently smaller than the positive electrode.
4 is a stainless steel battery housing, 5 is an insulator (made of polytetrafluoroethylene), 6 is a charge / discharge terminal, and 7 is a seal packing.
[0033]
This battery has a charging current of 0.5 mA / cm. ² Then, the battery was charged until the voltage (with respect to the Li electrode) reached 0.01 V, and the charging current was 0.03 mA / cm while maintaining the voltage of 0.01 V. ² Charging continued until: Subsequently, a discharge current of 0.5 mA / cm ² The battery was discharged up to 1.5 V and the capacity (discharge capacity) and efficiency (discharge capacity / initial charge capacity) were measured.
Table 1 shows the results of measurement of the micropore amount and charge / discharge capacity of the obtained carbonaceous negative electrode material.
[0034]
[Table 1]

[0035]
Comparative Example 1
The raw coke obtained in Example 1 was put in a graphite tray as a lump with a size of 30 to 150 mm, as shown in Table 2 in a box-shaped electric furnace at 10 ° C./min in a nitrogen flow atmosphere. The temperature was raised to 800 to 1200 ° C., and the heat treatment was performed by maintaining the temperature for 1 hour.
Next, the obtained heat-treated coke was finely pulverized with a jet mill to obtain a carbonaceous negative electrode material having an average of 11 to 12 μm and a maximum particle size of 45 μm or less.
About the obtained carbonaceous negative electrode material, the result of having performed the micropore amount measurement and the charge / discharge capacity measurement similar to Example 1 is shown in Table 2.
[0036]
[Table 2]

[0037]
Example 2
Raw coke having a volatile content of 18% by weight obtained by coking coal tar was finely pulverized by a rotary impact pulverizer and then passed through a sieve having an aperture of 86 μm to obtain raw coke fine powder having an average of 18 μm. This raw coke fine powder is put into a stainless steel tray at a thickness of 10 mm, heated in a box-shaped electric furnace to 150 ° C. at 10 ° C./min in an air circulation atmosphere, and then 1 ° C./min. The temperature was raised to 250 to 400 ° C. in place of the rate of temperature rise, and then held at that temperature for 30 minutes to perform the first stage heat treatment.
After cooling and taking out the tray, it is placed in a box-shaped electric furnace again, heated again at 10 ° C / min in a nitrogen flow atmosphere, held at 1000 ° C for 1 hour, and second stage heating Treatment was performed to obtain a carbonaceous negative electrode material.
About the obtained carbonaceous negative electrode material, the result of having performed the micropore amount measurement and the charge / discharge capacity measurement similar to Example 1 is shown in Table 3.
[0038]
[Table 3]

[0039]
Comparative Example 2
Except that the second stage heat treatment was performed at 450 ° C. for 30 minutes, the same treatment as in Example 3 was performed to obtain a carbonaceous negative electrode material.
With respect to this carbonaceous negative electrode material, the same micropore amount measurement and charge / discharge capacity measurement as in Example 1 were performed. As a result, the pore amount of less than 8 mm was 28.5 × 10. ^-Four cc / g, 8-18cm pore volume is 46.6 × 10 ^-Four cc / g. The capacity was 355 mAh / g, and the efficiency was 70%.
[0040]
Example 3
The raw coke fine powder obtained in Example 2 was placed in a stainless steel tray at a thickness of 10 mm, and 10% by volume of NO in a box-shaped electric furnace. ₂ The temperature was raised to 120 ° C. at 10 ° C./min in an air circulation atmosphere to which gas was added, and kept at that temperature for 30 minutes to perform the first stage heat treatment.
After cooling and taking out the tray, it is placed in a box-shaped electric furnace again, heated again at 10 ° C / min in a nitrogen flow atmosphere, held at 1000 ° C for 1 hour, and second stage heat treatment The carbonaceous negative electrode material was obtained.
The obtained carbonaceous negative electrode material was subjected to the same micropore measurement and charge / discharge capacity measurement as in Example 1. As a result, the pore volume of less than 8 mm was 3.1 × 10. ^-Four cc / g, pore volume of 8-18cm is 6.1 × 10 ^-Four cc / g. The capacity was 380 mAh / g, and the efficiency was 71%.
[0041]
Example 4
After performing the first stage heat treatment, heat treatment was performed at 450 ° C. for 1 hour in a nitrogen flow atmosphere, and then the final heat treatment was performed at 1000 ° C. for 1 hour in a nitrogen flow atmosphere. The same treatment as in Example 3 was performed to obtain a carbonaceous negative electrode material.
With respect to this carbonaceous negative electrode material, the same micropore amount measurement and charge / discharge capacity measurement as in Example 1 were conducted. As a result, the pore amount of less than 8 mm was 3.9 × 10. ^-Four cc / g, 8-18cm pore volume is 6.7 × 10 ^-Four cc / g. The capacity was 405 mAh / g, and the efficiency was 79%.
[0042]
Example 5
Raw coke having a volatile content of 5.6% by weight obtained by coking coal tar was finely pulverized by a jet mill to obtain raw coke fine powder having an average of 11 μm and a maximum particle size of 40 μm or less.
This raw coke fine powder is put into a graphite tray at a thickness of 40 mm, heated in a box-shaped electric furnace to 450 ° C. at 10 ° C./min in a nitrogen flow atmosphere, and at 450 ° C. for 1.5 hours. The first stage heat treatment to be held was performed.
[0043]
After cooling and taking out the tray, and measuring the yield in the first stage heat treatment, the tray was again placed in a box-shaped electric furnace and reheated at 10 ° C./min in a nitrogen flow atmosphere. As shown in Table 4, it was held at 800 to 1200 ° C. for 1 hour, and the second stage heat treatment was performed to obtain a negative electrode material. The performance of the obtained negative electrode material was evaluated using a cell having the configuration shown in FIG.
As the negative electrode material, 10% PVDF (polyvinylidene fluoride) was used as a binder, and a negative electrode 1 was obtained by pressure bonding onto a 20 mmφ stainless steel wire mesh. Li metal foil was used as the counter electrode, and was pressed onto a stainless steel wire mesh of 20 mmφ to form the positive electrode 3.
[0044]
The electrolyte is propylene carbonate (PC) and the electrolyte is LiPF. ₆ Was dissolved at a rate of 1 mol / liter (2 represents a separator and an electrolytic solution). As for the capacity of this battery, the negative electrode is made sufficiently smaller than the positive electrode.
4 is a stainless steel battery housing, 5 is an insulator (made of polytetrafluoroethylene), 6 is a charge / discharge terminal, and 7 is a seal packing.
[0045]
This battery has a charging current of 0.5 mA / cm. ² Then, the battery was charged until the voltage (with respect to the Li electrode) reached 0.01 V, and the charging current was 0.03 mA / cm while maintaining the voltage of 0.01 V. ² Charging continued until: Next, a discharge current of 0.5 mA / cm ² Was discharged to 1.5V. Table 4 shows the results of capacity (discharge capacity) and efficiency (discharge capacity / initial charge capacity).
[0046]
[Table 4]

[0047]
Comparative Example 3
The raw coke fine powder obtained in Example 5 was subjected to a heat treatment at 800 to 1200 ° C. for 1 hour without subjecting the first stage heat treatment to obtain a negative electrode material.
Table 5 shows the results of battery performance evaluation similar to that of Example 5.
[0048]
[Table 5]

[0049]
Comparative Example 4
The raw coke obtained in Example 5 was subjected to the same heat treatment as that in Comparative Example 3 while maintaining a lump with a size of 30 to 150 mm. Subsequently, the obtained heat-treated coke was finely pulverized with a jet mill to obtain a negative electrode material having an average of 13 μm and a maximum particle size of 45 μm or less.
Table 6 shows the results of battery performance evaluation similar to that of Example 5.
[0050]
[Table 6]

[0051]
Example 6
The raw coke fine powder obtained in Example 5 was subjected to the first stage heat treatment at 300 to 600 ° C. for 1.5 hours by the same method as in Example 5. Next, second-stage heat treatment at 1000 ° C. for 1 hour was performed to obtain a negative electrode material.
Table 7 shows the results of battery performance evaluation similar to that of Example 5.
[0052]
[Table 7]

[0053]
Example 7
The raw coke fine powder obtained in Example 5 was subjected to the first stage heat treatment at 450 ° C. for 0.5 to 5 hours by the same method as in Example 5. Next, second-stage heat treatment at 1000 ° C. for 1 hour was performed to obtain a negative electrode material.
Table 8 shows the results of battery performance evaluation similar to that of Example 5.
[0054]
[Table 8]

[0055]
Example 8
The raw coke obtained in Example 5 was finely pulverized with a jet mill or a sample mill (impact pulverizer) to obtain raw coke fine powder having an average particle size of 11 to 135 μm. The raw coke fine powder was subjected to the first stage heat treatment at 450 ° C. for 1.5 hours by the same method as in Example 5. Next, second-stage heat treatment at 1000 ° C. for 1 hour was performed to obtain a negative electrode material.
Table 9 shows the results of battery performance evaluation similar to that of Example 5.
[0056]
[Table 9]

[0057]
Example 9
Raw coke obtained by coking coal tar and having a volatile content of 25.2% by weight is placed in a stainless steel deep dish, and heated in a box-shaped electric furnace at 425, 450 ° C. for 5 hours in a nitrogen atmosphere. Raw coke having a volatile content of 19.1 and 12.6% by weight was obtained.
In addition to these raw cokes, the raw coke having a volatile content of 5.6% by weight used in Example 5 and the volatile content of 25.2% by weight before the heat treatment for 5 hours of this example (Example 9) were used. A total of four types of raw coke were finely pulverized with a jet mill to obtain raw coke fine powder having an average particle size of 10 to 13 μm. This raw coke fine powder was subjected to a first stage heat treatment (inert gas treatment) at 450 ° C. for 1.5 hours by the same method as in Example 5. Next, second-stage heat treatment (inert gas treatment) at 1000 ° C. for 1 hour was performed to obtain a negative electrode material.
Table 10 shows the results of battery performance evaluation similar to that of Example 5.
[0058]
[Table 10]

[0059]
【The invention's effect】
According to the present invention, it is possible to easily provide a negative electrode material for a non-aqueous secondary battery that has a large capacity and high efficiency, easily from a low-cost carbonaceous material.
[Brief description of the drawings]
FIG. 1 is a cross-sectional explanatory view of a button type non-aqueous electrolyte secondary battery which is an example of a non-aqueous secondary battery of the present invention.
[Explanation of symbols]
1 Negative electrode
2 Separator and electrolyte
3 Positive electrode
4 Battery housing
5 Insulator
6 Charge / discharge terminals
7 Seal packing

Claims

(I) pores having a diameter of less than 8 mm are 2 × 10 ⁻⁴ cc / g or more, and (ii) pores having a diameter of 8 to 18 mm are calculated to be 15 × 10 ⁻⁴ cc / g or less. A carbonaceous negative electrode material for a non-aqueous secondary battery.

The carbonaceous negative electrode material for a non-aqueous secondary battery according to claim 1, wherein the carbonaceous negative electrode material is a fine powder having an average particle size of 100 µm or less.

A pulverized carbonaceous material having a volatile content of 30% by weight or less and an average particle size of 100 μm or less is subjected to a first stage heat treatment at a temperature of 250 to 650 ° C. in an inert gas atmosphere, and further to 700 in an inert gas atmosphere. A method for producing a carbonaceous negative electrode material for a non-aqueous secondary battery, wherein the second stage heat treatment is performed at a temperature of ˜1500 ° C.

A finely pulverized carbonaceous material having a volatile content of 30% by weight or less and an average particle size of 100 μm or less is subjected to a first stage heat treatment in an oxidizing gas atmosphere at a temperature of 50 to 400 ° C., and further to 700 in an inert gas atmosphere. A method for producing a carbonaceous negative electrode material for a non-aqueous secondary battery, wherein the second stage heat treatment is performed at a temperature of ˜1500 ° C.

5. The method for producing a carbonaceous negative electrode material for a non-aqueous secondary battery according to claim 4, wherein a pulverized carbonaceous material having a volatile content of 30% by weight or less and an average particle size of 100 μm or less is 50 to 50 % in an oxidizing gas atmosphere. Before and / or after heat treatment at a temperature of 400 ° C., heat treatment is performed at a temperature of 250 to 650 ° C. in an inert gas atmosphere, and further heat treatment is performed at a temperature of 700 to 1500 ° C. in an inert gas atmosphere. The manufacturing method of the carbonaceous negative electrode material for non-aqueous secondary batteries characterized by these.

A non-aqueous secondary battery using the carbonaceous negative electrode material for a non-aqueous secondary battery according to claim 1 or 2 as a negative electrode material.