JP4729774B2 - Method for producing negative electrode material for lithium secondary battery - Google Patents
Method for producing negative electrode material for lithium secondary battery Download PDFInfo
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- JP4729774B2 JP4729774B2 JP2000051121A JP2000051121A JP4729774B2 JP 4729774 B2 JP4729774 B2 JP 4729774B2 JP 2000051121 A JP2000051121 A JP 2000051121A JP 2000051121 A JP2000051121 A JP 2000051121A JP 4729774 B2 JP4729774 B2 JP 4729774B2
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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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Description
【０００１】
【技術分野】
本発明は，カーボンを主体とする負極を構成する負極材料の製造方法に関する。
【０００２】
【従来技術】
負極にリチウム金属の代わりにカーボンを用いた二次電池が実用化されている。
リチウム金属負極は充放電に伴い，デンドライトが生成しこれが原因で，特性劣化や内部短絡などを引き起こす。
負極にカーボンを用いた電池においてはこのデンドライトは生成しにくい。
しかし，カーボンはリチウムを吸蔵した状態では電解液との反応性が高く，表面にリチウム含有被膜を形成し可動リチウム量を減少させるなどの問題点がある。
【０００３】
そこで従来では，
（１）このリチウム含有被膜の形成で消費されるリチウムを補充するために，負極活物質に金属リチウムを直接付着させておき，この負極活物質を電解液中に入れ，その時に生じる電位差と濃度差により，リチウムイオンを負極活物質に吸蔵させる方法。
（２）電解液との反応を抑制するためにカーボン上にリチウムと合金を作らない金属を薄く蒸着する方法。
などが提案されている。
【０００４】
【解決しようとする課題】
しかしながら，上記の従来法（１）においては，充放電に伴うリチウム含有被膜量の増加を本質的に抑制できておらず，長期的な安定性は得られない。また，上記の電解液との反応は高温において著しく，上記の従来法では解決しきれない。そのため，本質的な解決にはカーボンと電解液との界面に対する改良が課題となると考えられる。
【０００５】
また，上記の従来法（２）においては蒸着というプロセスを経なければならないため，コストが高く大量生産には向かない。さらに被膜する金属は導電性には優れるが，イオン導電性に乏しく，充放電の妨げとなる。
【０００６】
本発明は，かかる従来の問題点に鑑みてなされたもので，高温における安定性，長期保存における安定性が確保されると共に製造コスト安価で充放電性能を阻害しないリチウム二次電池用負極材料の製造方法を提供しようとするものである。
【０００７】
【課題の解決手段】
参考発明は，カーボンを主体とする負極と，リチウム含有遷移金属酸化物を主体とする正極と，有機電解液とから構成されるリチウム二次電池において，上記負極を構成する負極材料は，カーボン表面をスピネル型リチウムチタン酸化物で被覆した表面改質カーボンを含んでいることを特徴とするリチウム二次電池にある。
【０００８】
参考発明において最も注目すべきことは，表面改質カーボンよりなる負極材料で負極が構成されていることである。
【０００９】
次に，参考発明の作用につき説明する。
カーボンの表面はスピネル型リチウムチタン酸化物で被覆されている。
スピネル型リチウムチタン酸化物はリチウムに対し１．５Ｖ程度に酸化還元電位を持つ電子・イオン混合導電体である。リチウムが挿入されていない状態では絶縁体であるが，リチウムが挿入された１．５Ｖ（リチウムに対して）以上の電位では導電性を呈する。そのため，充放電を阻害しない。
【００１０】
一方，０．１Ｖ付近におもな電位を持つカーボンと比較して，スピネル型リチウムチタン酸化物は還元力が弱く，有機電解液との反応性も弱い。そのため，カーボンが直接電解液と接する場合と比較して，参考発明にかかるリチウム二次電池では，負極における電解液の分解，リチウム含有被膜生成量を少なくすることができる。そして，これらの反応が高温において特に顕著に発生することから，高温における安定性を高めることができる。
よって，高温における安定性，長期保存における安定性が確保されたリチウム二次電池を得ることができる。
【００１１】
以上，参考発明によれば，高温における安定性，長期保存における安定性が確保されると共に充放電性能を阻害しないリチウム二次電池を提供することができる。
【００１２】
また，上記表面改質カーボンであるが，カーボンの表面全体がスピネル型リチウムチタン酸化物で覆われている場合もあるが，カーボンの表面に部分的にスピネル型リチウムチタン酸化物が付着していることもある。
またバルク体にカーボンを成形して，その表面をスピネル型リチウムチタン酸化物で覆ってもよい。粒状カーボンの表面を上記酸化物で覆ってもよい。
【００１３】
また，上記スピネル型リチウムチタン酸化物としてはＬｉＴｉ2Ｏ4，Ｌｉ4/3Ｔｉ5/3Ｏ4など様々な組成のものを使用することができる。
また，正極の主体であるリチウム含有遷移金属酸化物には特に制限はなく，可逆的にリチウムが出入りできる材料であればよい。
【００１４】
次に，上記表面改質カーボンにおけるスピネル型リチウムチタン酸化物の割合はカーボンに対し重量比で２〜２０重量％であることが好ましい。
上記割合が２％重量未満であると本発明の効果が得難く，２０重量％を越えた場合にはリチウム二次電池の初期容量の低下が生じるおそれがある。
また，上記割合は表面改質カーボンにおいて，その中のカーボンを100重量％とした場合の上記酸化物の割合である。
【００１５】
次に，上記リチウム含有遷移金属酸化物は，規則配列層状岩塩型構造を持つリチウムニッケル酸化物であることが好ましい。
中でも規則配列層状岩塩型構造であるリチウムニッケル酸化物は，正極の不可逆容量が大きく，被膜させたスピネル型リチウムチタン酸化物に対するリチウム挿入源となるため特に好ましい。
【００１６】
次に，スピネル型リチウムチタン酸化物はリチウムイオン過剰型のＬｉ4/3Ｔｉ5/3Ｏ4であることが好ましい。
この物質は，合成が容易で，安定性に優れているため好ましい。
【００１７】
次に，上記負極に対し，予めＬｉ金属を電気化学的に挿入してなることが好ましい。
これにより，正極との組み合わせや正負極の容量比のバランスによって発生する可能性がある初期容量の低下を防止することができる。
リチウム金属を挿入する方法は多数あるが，例えば負極表面にリチウム金属箔を接触させておき電解液の注入と共に電気化学的にリチウムを挿入する方法が挙げられる。
【００１８】
次に，本発明は，水酸化リチウムと酸化チタン粉末とを含有するゾル状混合物に対しカーボンを混合した混合物を準備し，該混合物を乾燥固化させた後，非酸化性雰囲気下，温度４００〜１０００℃において熱処理することを特徴とするリチウム二次電池用負極材料の製造方法にある。
【００１９】
本発明にかかる製造方法によれば，上述した表面をスピネル型リチウムチタン酸化物で被覆した表面改質カーボンよりなる負極材料を容易に製造することができる。
つまり，単純な混合や通常の固相応法ではカーボンの表面に均一にスピネル型リチウムチタン酸化物を被覆させたり，付着させたりすることは大変困難である。
また，スピネル型リチウムチタン酸化物の合成において，粉末を混合し熱処理する，通常の固相反応法を利用すると，特性に優れる高結晶性の結晶が構成される温度においては，共存するカーボンも焼失してしまう可能性が高かった。
【００２０】
本発明の製造法においてはこれらの問題点を鑑み，ゾル状のリチウム源，チタン源のゾル状混合物ををカーボンと一緒に混合することで，カーボン表面をリチウム源，チタン源等によって均一に覆うことが可能となった。
このような状態から乾燥固化，非酸化性雰囲気，４００〜１０００℃で熱処理するため，カーボンの焼失を防止しながら，表面改質カーボンを得ることができる。
【００２１】
また，ゾル状のチタン源として，反応性の高い酸化チタン粉末を用いるため，高結晶性で特性のよいスピネル型リチウムチタン酸化物を得ることができる。
また，上記酸化チタン粉末は超微粒子よりなるものが好ましい。これにより，より高結晶で特性に優れたスピネル型リチウムチタン酸化物を得ることができる。
また，この製造方法は，混合，熱処理といった単純な工程で製造できるため，蒸着等の工程と比べコストが安価である。
【００２２】
このように，本発明にかかる製造方法によれば，高温における安定性，長期保存における安定性が確保されると共に製造コスト安価で充放電性能を阻害しないリチウム二次電池用負極材料の製造方法を得ることができる。
【００２３】
また，上記熱処理の温度が４００℃未満である場合には，結晶性のリチウムチタン酸化物が合成されないおそれがある。一方，１０００℃を越えるとカーボン焼失やリチウムチタン酸化物の分解が生じるおそれがある。
【００２４】
【発明の実施の形態】
実施形態例
本発明の実施形態例にかかるリチウム二次電池と該リチウム二次電池の負極について説明する。
本例のリチウム二次電池は，カーボンを主体とする負極と，リチウム含有遷移金属酸化物を主体とする正極と，有機電解液とから構成される。
そして，上記負極を構成する負極材料は，表面をスピネル型リチウムチタン酸化物で被覆した表面改質カーボンを含んでいる。
また，この表面改質カーボンは，水酸化リチウムと酸化チタン粉末とを含有するゾル状混合物に対しカーボンを混合した混合物を準備し，該混合物を乾燥固化させた後，非酸化性雰囲気下，温度４００〜１０００℃において熱処理することにより作製される。
【００２５】
以下に実施例１及び２，またこれらと比較評価される比較例１を示す。
実施例１は，負極材料としてスピネル型リチウムチタン複合酸化物で表面を改質したカーボンを使用したリチウム二次電池である。実施例２は，実施例１に対してさらに負極表面上にリチウム金属薄膜を貼り付けたリチウム二次電池である。
比較例１は改質をしなかったカーボンを負極材料としたリチウム二次電池である。
【００２６】
（実施例１）
［負極材料の作製］
まず，石原産業製のチタニアゾル（ＳＴＳ−０１）と水酸化リチウム一水和物（ＬｉＯＨ・Ｈ2Ｏ）とを準備した。また，負極活物質として機能するカーボン原料として粒径が２５〜２８μｍである大阪ガス製のメソカーボンマイクロビーズ（以下ＭＣＭＢ）を準備した。
１０．９７ｇの上記水酸化リチウム一水和物とイオン交換水５０．０ｇとを混合し水溶液としたものに上記チタニアゾル（ＴｉＯ2２９．２３％溶液）を８９．３ｇ加えてよく混合し，ゾル状混合物を得た。
これに上記ＭＣＭＢを２７０ｇ加えてよく混合した後，乾燥固化させた。
【００２７】
この時のリチウムとチタンとのモル比は４：５である。
反応式を以下に記述する。
４ＬｉＯＨ＋５ＴｉＯ2→Ｌｉ4Ｔｉ5Ｏ12＋２Ｈ2Ｏ
上記の乾燥固化された混合物２５０ｇを，６００℃，８時間，窒素中で焼成した。これにより目的の負極材料を得た。
焼成後の重量は２４４．５ｇであり，焼成による質量減少は５．５ｇであった。
この質量減少は上記反応におけるＨ2Ｏの生成量とよく対応している。よって，この焼成によるＭＣＭＢの焼失は殆どないと考えられる。この作製した負極活物質は仕込み量から，カーボン１００ｗｔ％に対し１０ｗｔ％のＬｉ4Ｔｉ5Ｏ12を含んでいると計算される。
【００２８】
［リチウム二次電池の作製］
リチウム含有遷移金属酸化物を主体とする正極について説明する。
正極活物質には液相法で合成されたＬｉＮｉ0.80Ｃｏ0.15Ａｌ0.05Ｏ2を用いた。正極活物質１００重量部に対して，導電材としてアセチレンブラックを１１．８重量部加えてよく混合し，その結着材としてポリフッ化ビニリデン（商品名「ＫＦポリマー」：呉羽化学工業）を５．９重量部，さらに溶剤としてＮ−メチル−２−ピロリドンを６０〜８０重量部とし，これらを混練して正極合材ペーストを作製した。
【００２９】
このペーストを厚さ２０μｍｍのＡｌ箔の両面に塗工・乾燥後，プレス・裁断して，幅５４ｍｍ，長さ４５０ｍｍ（塗工長さ４００ｍｍ）の正極を作製した。
この正極には，正極活物質の塗工量が片面単位面積当たり７．０ｍｇ／ｃｍ2となるように塗工されている。また，プレス圧，プレス回数等を調節して，最終的に選られる正極の正極合剤密度（集電体を除く）が２．８ｍｇ／ｃｍ3となるようにプレスされている。
【００３０】
次に，負極について説明する。
上記表面改質カーボンよりなる負極材料１００重量部に，結着材としてポリフッ化ビニリデン（商品名「ＫＦポリマー」：呉羽化学工業）を５．３重量部，さらに溶剤としてＮ−メチル−２−ピロリドンを６０〜７０重量部とし，これらを混練して負極合材ペーストを作製した。
【００３１】
このペーストを厚さ１０μｍのＣｕ箔の両面に塗工・乾燥後，プレス・裁断して，５６ｍｍ，長さ５２０ｍｍ（塗工長さ５００ｍｍ）の負極を作製した。
この負極には，負極材料の塗工量が片面単位面積当たり５．０ｍｇ／ｃｍ2となるように塗工されている。また，プレス圧，プレス回数等を調節して，最終的に得られる負極の負極合剤密度（集電体を除く）が１．３ｍｇ／ｃｍ3となるようにプレスされている。
【００３２】
そして，正極および負極を厚さ２５μｍｍ，幅５８ｍｍのポリエチレン製セパレーターを挟んで重ね合わせ，渦巻き状に捲回した電極ロールを作製した。
正極および負極の未塗工部には捲回前にあらかじめリードが溶接されている。
また，正極の両面の塗工部はセパレーターを介して必ず負極の塗工部が対向するように捲回がなされている。
【００３３】
電極ロールの両端にポリエチレン製の絶縁板を配した後，これをＮｉメッキの鉄製電池ケースに挿入し，負極リードを電池ケース内の底部に溶接し，正極リードを封口キャップに溶接した。
【００３４】
また，電極ロールが固定されるように電池ケースの開口部近くでネッキングを行なった。また，エチレンカーボネート（ＥＣ）とジエチルカーボネート（ＤＥＣ）を３：７の体積比で混合した溶媒に電解質としてＬｉＰＦ6を１モル／リットルの割合で溶解した有機電解液を用いた。
【００３５】
この有機電解液を電極ロールの挿入された電池ケース内に注入し，減圧と加圧を繰り返しながら電極とセパレーターとの空隙部分に電解液を浸透させた。余剰の電解液を排出したところ，約４ｇの電解液が注液できたことがわかった。注液後，封口キャップを電池ケースの開口部にかしめ，円筒型電池を作製した。
【００３６】
リチウム二次電池組み立て後，室温で約１日放置してから，最初の充放電を２０℃の恒温槽内で行なった。充電終止電圧を４．１Ｖとし，放電終止電圧を３．０Ｖとして，１００ｍｍＡの定電流充放電を１回行なった。
【００３７】
（実施例２）
作製した負極上に巻回前の段階で，厚さ４０μｍの金属リチウム薄膜を５０ｍｍ×５ｍｍの短冊状に切り，計３０枚をシートの横方向に対し垂直に縦にほぼ等間隔で貼り付けた。さらに電解液注入後，負極に対するリチウムの挿入反応促進のため，５０℃において３日間保存した。
上記の点以外は実施例１と同様である。
（比較例１）
負極材料として，実施例１に示すような表面改質を行なわない単なるＭＣＭＢを用いた。それ以外は実施例１と同様である。
【００３８】
このようにして作製した本発明品となる実施例１及び２と比較品である比較例１を評価するために，それぞれについて，６０℃環境下での保存試験及びサイクル特性評価を次のような要領で行った。
【００３９】
［性能評価］
（保存試験）
２０℃の環境下で４．１Ｖ，１００ｍＡの条件で定電流定電圧充電を８時間行い，５０ｍＡで３．０Ｖまで定電流放電を行って，満充電からの放電容量を確認した。その後，もう一度４．１Ｖ，１００ｍＡの条件で定電流定電圧充電を８時間行い満充電状態とした後，６０℃の環境下で３ケ月保存した。
保存後，２０℃の環境下に戻し，３．０Ｖまで５０ｍＡで定電流放電を行って残存している容量を測定した。この残存容量と保存前の満充電からの放電容量との比を容量残存率（＝保存後の残存容量／保存前の満容量×１００）と表現する。
さらにその後，４．１Ｖ，１００ｍＡの条件で定電流定電圧充電を８時間行い，５０ｍＡで３．０Ｖまで定電流放電を行い，保存前後での満充電からの放電容量の変化を測定した。この変化の比を容量回復率（＝保存後の満容量／保存前の満容量×１００）と表現する。
【００４０】
（サイクル特性評価試験）
６０℃の環境下に２時間放置した後，充放電を開始した。このときの充電終止電圧を４．ｌＶとし，放電終止電圧を３．０Ｖとして，９７２ｍＡの定電流充放電を行った。この充放電を５００サイクルまで行った。
そして，１サイクル目の放電時の電池容量を正極活物質量で割ったものを初期放電容量とする。また，この初期放電容量と５００サイクル後の放電容量との比を容量維持率と表現する。
これらの結果を表１にまとめて記載した。
【００４１】
同表より，比較例１に比べ，実施例１は初期容量が若干落ちるものの，容量維持率，容量残存率，容量回復率のすべてにおいて優れてていることが分かった。
また，実施例２においては，初期容量も比較例１と同等となり，かつ容量維持率，容量残存率，容量回復率は実施例１と同様に優れていることが分かった。
【００４２】
本例にかかるリチウム二次電池において，負極材料はスピネル型リチウムチタン酸化物で被覆された表面改質カーボンである。
スピネル型リチウムチタン酸化物はリチウムに対し１．５Ｖ程度に酸化還元電位を持つ電子・イオン混合導電体である。リチウムが挿入されていない状態では絶縁体であるが，リチウムが挿入された１．５Ｖ（リチウムに対して）以上の電位では導電性を呈する。そのため，充放電を阻害しない。
【００４３】
一方，０．１Ｖ付近におもな電位を持つカーボンと比較して，スピネル型リチウムチタン酸化物は還元力が弱く，有機電解液との反応性も弱い。そのため，カーボンが直接電解液と接する場合と比較して，負極における電解液の分解，リチウム含有被膜生成量を少なくすることができる。そして，これらの反応が高温において特に顕著に発生することから，高温における安定性を高めることができる。
よって，高温における安定性，長期保存における安定性が確保され，高温保存時に失活するリチウム量が少なく容量残存率，容量回復率，サイクル特性に優れるリチウム二次電池を得ることができる。
【００４４】
以上，本例によれば，高温における安定性，長期保存における安定性が確保されると共に充放電性能を阻害しないリチウム二次電池及び製造コスト安価である負極材料の製造方法を提供することができる。
また，
【００４５】
更に，実施例１は初期容量が比較例よりも低いが，５００サイクル後の容量においては実施例１の方が比較例１に比べ大きく優るので，本例の利点は大変大きい。
また，実施例２のよううに負極上にリチウム金属薄膜を貼り付けて，初期容量を増加させることもできる。
【００４６】
【表１】
【発明の効果】
上述のごとく，本発明によれば，高温における安定性，長期保存における安定性が確保されると共に充放電性能を阻害しないリチウム二次電池及び製造コスト安価である負極材料の製造方法を提供することができる。[0001]
【Technical field】
The present invention, a negative electrode mainly composed of carbon method of manufacturing a negative electrode material that make up.
[0002]
[Prior art]
Secondary batteries using carbon as the negative electrode instead of lithium metal have been put into practical use.
When lithium metal negative electrode is charged and discharged, dendrite is generated, which causes deterioration of characteristics and internal short circuit.
In a battery using carbon for the negative electrode, this dendrite is hardly generated.
However, carbon has a high reactivity with an electrolytic solution in a state where lithium is occluded, and has a problem that a lithium-containing film is formed on the surface to reduce the amount of movable lithium.
[0003]
So in the past,
(1) In order to replenish the lithium consumed in the formation of the lithium-containing film, metallic lithium is directly attached to the negative electrode active material, and the negative electrode active material is placed in the electrolytic solution. A method of occluding lithium ions in the negative electrode active material due to the difference.
(2) A method of thinly depositing a metal that does not form an alloy with lithium on carbon in order to suppress the reaction with the electrolytic solution.
Etc. have been proposed.
[0004]
[Problems to be solved]
However, in the above conventional method (1), an increase in the amount of the lithium-containing film accompanying charge / discharge cannot be essentially suppressed, and long-term stability cannot be obtained. In addition, the reaction with the above electrolytic solution is remarkable at high temperatures and cannot be solved by the above conventional method. For this reason, an essential solution is to improve the carbon / electrolyte interface.
[0005]
In the above conventional method (2), since a process called vapor deposition must be performed, the cost is high and it is not suitable for mass production. Furthermore, the metal to be coated is excellent in conductivity, but is poor in ionic conductivity, and hinders charging and discharging.
[0006]
The present invention has been made in view of such conventional problems, and is a negative electrode material for a lithium secondary battery that ensures stability at high temperatures and stability during long-term storage and is inexpensive to manufacture and does not impede charge / discharge performance. A manufacturing method is to be provided.
[0007]
[Means for solving problems]
The reference invention is a lithium secondary battery composed of a negative electrode mainly composed of carbon, a positive electrode mainly composed of a lithium-containing transition metal oxide, and an organic electrolyte, wherein the negative electrode material constituting the negative electrode is a carbon surface. In the lithium secondary battery, the surface-modified carbon is coated with spinel type lithium titanium oxide.
[0008]
What should be noted most in the reference invention is that the negative electrode is made of a negative electrode material made of surface-modified carbon.
[0009]
Next, the operation of the reference invention will be described.
The surface of carbon is coated with spinel type lithium titanium oxide.
Spinel type lithium titanium oxide is an electron / ion mixed conductor having a redox potential of about 1.5 V with respect to lithium. Although it is an insulator when lithium is not inserted, it is conductive at a potential of 1.5 V (relative to lithium) or higher when lithium is inserted. Therefore, charging and discharging are not hindered.
[0010]
On the other hand, compared with carbon having a main potential in the vicinity of 0.1 V, spinel type lithium titanium oxide has a weak reducing power and a low reactivity with an organic electrolyte. Therefore, compared with the case where carbon is in direct contact with the electrolytic solution, the lithium secondary battery according to the reference invention can reduce the decomposition of the electrolytic solution and the generation amount of the lithium-containing film in the negative electrode. And since these reactions generate | occur | produce especially notably at high temperature, stability at high temperature can be improved.
Therefore, it is possible to obtain a lithium secondary battery that ensures stability at high temperatures and long-term storage.
[0011]
As described above, according to the reference invention , it is possible to provide a lithium secondary battery that ensures stability at high temperatures and stability during long-term storage and does not impair charge / discharge performance.
[0012]
Although the surface-modified carbon is the above, the entire surface of the carbon may be covered with spinel type lithium titanium oxide, but the spinel type lithium titanium oxide is partially attached to the carbon surface. Sometimes.
Alternatively, carbon may be formed into a bulk body, and the surface thereof may be covered with spinel type lithium titanium oxide. The surface of the granular carbon may be covered with the oxide.
[0013]
As the spinel type lithium titanium oxide, those having various compositions such as LiTi 2 O 4 and Li 4/3 Ti 5/3 O 4 can be used.
Moreover, there is no restriction | limiting in particular in the lithium containing transition metal oxide which is the main body of a positive electrode, What is necessary is just a material which lithium can go in and out reversibly.
[0014]
Next , the proportion of the spinel type lithium titanium oxide in the surface modified carbon is preferably 2 to 20% by weight with respect to the carbon.
If the ratio is less than 2% by weight, it is difficult to obtain the effect of the present invention, and if it exceeds 20% by weight, the initial capacity of the lithium secondary battery may be reduced.
Further, the above ratio is the ratio of the oxide in the surface-modified carbon when the carbon in the carbon is 100% by weight.
[0015]
Next , the lithium-containing transition metal oxide is preferably a lithium nickel oxide having an ordered layered rock salt structure.
Among them, a lithium nickel oxide having a regular arrangement layered rock salt structure is particularly preferable because the irreversible capacity of the positive electrode is large and it becomes a lithium insertion source for the coated spinel type lithium titanium oxide.
[0016]
Next , the spinel type lithium titanium oxide is preferably lithium ion excess type Li 4/3 Ti 5/3 O 4 .
This material is preferred because it is easy to synthesize and has excellent stability.
[0017]
Next , it is preferable that Li metal is electrochemically inserted into the negative electrode in advance.
Thereby, it is possible to prevent a decrease in the initial capacity that may occur due to the combination with the positive electrode and the balance between the positive and negative electrode capacity ratios.
There are many methods for inserting lithium metal. For example, there is a method in which lithium metal foil is brought into contact with the negative electrode surface and lithium is electrochemically inserted together with the injection of the electrolyte.
[0018]
Next, the present invention provides a mixture in which carbon is mixed with a sol-like mixture containing lithium hydroxide and titanium oxide powder, and after the mixture is dried and solidified, in a non-oxidizing atmosphere, a temperature of 400 to It is in the manufacturing method of the negative electrode material for lithium secondary batteries characterized by heat-processing at 1000 degreeC.
[0019]
According to the production method of the present invention, a negative electrode material made of surface-modified carbon having the above-described surface coated with spinel type lithium titanium oxide can be easily produced.
In other words, it is very difficult to coat or adhere the spinel-type lithium titanium oxide uniformly to the carbon surface by simple mixing or ordinary solid corresponding methods.
Also, in the synthesis of spinel type lithium titanium oxide, if the ordinary solid phase reaction method, in which powder is mixed and heat-treated, is used, the coexisting carbon is also burned out at the temperature at which highly crystalline crystals with excellent characteristics are formed. There was a high possibility of it.
[0020]
In view of these problems, the production method of the present invention uniformly covers the carbon surface with a lithium source, a titanium source, etc. by mixing a sol-like mixture of a sol-like lithium source and a titanium source together with carbon. It became possible.
Since it is heat-treated at 400 to 1000 ° C. in a dry solidified, non-oxidizing atmosphere from such a state, surface-modified carbon can be obtained while preventing carbon from being burned out.
[0021]
In addition, since highly reactive titanium oxide powder is used as the sol-like titanium source, a spinel type lithium titanium oxide having high crystallinity and good characteristics can be obtained.
The titanium oxide powder is preferably made of ultrafine particles. As a result, a spinel type lithium titanium oxide having higher crystallinity and excellent characteristics can be obtained.
Further, since this manufacturing method can be manufactured by simple processes such as mixing and heat treatment, the cost is lower than that of processes such as vapor deposition.
[0022]
As described above, according to the manufacturing method of the present invention, there is provided a method for manufacturing a negative electrode material for a lithium secondary battery that ensures stability at high temperatures and stability during long-term storage and is inexpensive to manufacture and does not hinder charge / discharge performance. Obtainable.
[0023]
Moreover, when the temperature of the heat treatment is less than 400 ° C., crystalline lithium titanium oxide may not be synthesized. On the other hand, if it exceeds 1000 ° C., carbon may be burned out or lithium titanium oxide may be decomposed.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment Examples A lithium secondary battery and an anode of the lithium secondary battery according to an embodiment of the present invention will be described.
The lithium secondary battery of this example includes a negative electrode mainly composed of carbon, a positive electrode mainly composed of a lithium-containing transition metal oxide, and an organic electrolyte.
And the negative electrode material which comprises the said negative electrode contains the surface modification carbon which coat | covered the surface with the spinel type lithium titanium oxide.
The surface-modified carbon is prepared by preparing a mixture of carbon in a sol-like mixture containing lithium hydroxide and titanium oxide powder, drying and solidifying the mixture, and then subjecting it to a temperature in a non-oxidizing atmosphere. It is produced by heat treatment at 400 to 1000 ° C.
[0025]
Examples 1 and 2 and Comparative Example 1 to be compared and evaluated are shown below.
Example 1 is a lithium secondary battery using carbon whose surface is modified with a spinel type lithium titanium composite oxide as a negative electrode material. Example 2 is a lithium secondary battery in which a lithium metal thin film is further bonded on the negative electrode surface with respect to Example 1.
Comparative Example 1 is a lithium secondary battery using unmodified carbon as a negative electrode material.
[0026]
(Example 1)
[Production of negative electrode material]
First, titania sol (STS-01) manufactured by Ishihara Sangyo Co., Ltd. and lithium hydroxide monohydrate (LiOH.H 2 O) were prepared. In addition, Osaka Gas mesocarbon microbeads (hereinafter referred to as MCMB) having a particle size of 25 to 28 μm were prepared as a carbon raw material that functions as a negative electrode active material.
Add 89.3 g of the above titania sol (TiO 2 29.23% solution) to a solution prepared by mixing 10.97 g of the above lithium hydroxide monohydrate and 50.0 g of ion-exchanged water, and mix well. A gaseous mixture was obtained.
270 g of the above MCMB was added thereto and mixed well, and then dried and solidified.
[0027]
At this time, the molar ratio of lithium to titanium is 4: 5.
The reaction formula is described below.
4LiOH + 5TiO 2 → Li 4 Ti 5 O 12 + 2H 2 O
250 g of the dried and solidified mixture was calcined in nitrogen at 600 ° C. for 8 hours. This obtained the target negative electrode material.
The weight after firing was 244.5 g, and the mass loss due to firing was 5.5 g.
This decrease in mass corresponds well with the amount of H 2 O produced in the above reaction. Therefore, it is considered that there is almost no burning of MCMB by this firing. It is calculated that the produced negative electrode active material contains 10 wt% Li 4 Ti 5 O 12 with respect to 100 wt% carbon based on the charged amount.
[0028]
[Production of lithium secondary battery]
A positive electrode mainly composed of a lithium-containing transition metal oxide will be described.
LiNi 0.80 Co 0.15 Al 0.05 O 2 synthesized by the liquid phase method was used as the positive electrode active material. 4. Add 11.8 parts by weight of acetylene black as a conductive material to 100 parts by weight of the positive electrode active material and mix well. Polyvinylidene fluoride (trade name “KF polymer”: Kureha Chemical Industries) is used as the binder. 9 parts by weight and further 60 to 80 parts by weight of N-methyl-2-pyrrolidone as a solvent were kneaded to prepare a positive electrode mixture paste.
[0029]
This paste was coated on both sides of an Al foil having a thickness of 20 μm, dried, pressed and cut to produce a positive electrode having a width of 54 mm and a length of 450 mm (coating length of 400 mm).
The positive electrode is coated such that the amount of the positive electrode active material applied is 7.0 mg / cm 2 per unit area on one side. In addition, pressing is performed such that the positive electrode mixture density (excluding the current collector) of the positive electrode finally selected is 2.8 mg / cm 3 by adjusting the pressing pressure, the number of times of pressing, and the like.
[0030]
Next, the negative electrode will be described.
100 parts by weight of the negative electrode material made of the above surface-modified carbon, 5.3 parts by weight of polyvinylidene fluoride (trade name “KF polymer”: Kureha Chemical Industries) as a binder, and N-methyl-2-pyrrolidone as a solvent Was mixed to prepare a negative electrode mixture paste.
[0031]
This paste was applied to both sides of a 10 μm thick Cu foil, dried, pressed and cut to produce a negative electrode of 56 mm length 520 mm (coating length 500 mm).
The negative electrode is coated such that the amount of the negative electrode material applied is 5.0 mg / cm 2 per unit area of one side. Further, the negative electrode mixture density (excluding the current collector) of the negative electrode finally obtained is adjusted to 1.3 mg / cm 3 by adjusting the press pressure, the number of presses, and the like.
[0032]
Then, the positive electrode and the negative electrode were overlapped with a polyethylene separator having a thickness of 25 μm and a width of 58 mm, and an electrode roll wound in a spiral shape was produced.
Leads are welded to the uncoated portions of the positive electrode and the negative electrode in advance before winding.
In addition, the coated portions on both sides of the positive electrode are wound so that the coated portions of the negative electrode always face each other via a separator.
[0033]
A polyethylene insulating plate was placed on both ends of the electrode roll, which was then inserted into a Ni-plated iron battery case, the negative electrode lead was welded to the bottom of the battery case, and the positive electrode lead was welded to the sealing cap.
[0034]
In addition, necking was performed near the opening of the battery case so that the electrode roll was fixed. Further, an organic electrolytic solution in which LiPF 6 was dissolved at a rate of 1 mol / liter as an electrolyte in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 3: 7 was used.
[0035]
This organic electrolyte was poured into the battery case in which the electrode roll was inserted, and the electrolyte was infiltrated into the gap between the electrode and the separator while repeatedly reducing pressure and pressurizing. When the excess electrolyte solution was discharged, it was found that about 4 g of electrolyte solution could be injected. After injection, the sealing cap was caulked into the opening of the battery case to produce a cylindrical battery.
[0036]
After assembling the lithium secondary battery, it was left at room temperature for about 1 day, and then the first charge / discharge was performed in a constant temperature bath at 20 ° C. The charge end voltage was 4.1 V, the discharge end voltage was 3.0 V, and constant current charge / discharge of 100 mmA was performed once.
[0037]
(Example 2)
On the prepared negative electrode, a 40 μm-thick metal lithium thin film was cut into a 50 mm × 5 mm strip shape at the stage before winding, and a total of 30 sheets were attached vertically at almost equal intervals vertically to the lateral direction of the sheet. . Further, after injecting the electrolyte, it was stored at 50 ° C. for 3 days to promote the insertion reaction of lithium into the negative electrode.
Except for the above points, the second embodiment is the same as the first embodiment.
(Comparative Example 1)
As the negative electrode material, simple MCMB without surface modification as shown in Example 1 was used. The rest is the same as in the first embodiment.
[0038]
In order to evaluate Examples 1 and 2 which are the products of the present invention thus produced and Comparative Example 1 which is a comparative product, a storage test and a cycle characteristic evaluation in a 60 ° C. environment are as follows. I went there.
[0039]
[Performance evaluation]
(Preservation test)
Constant current and constant voltage charging was performed for 8 hours under conditions of 4.1 V and 100 mA in an environment of 20 ° C., and constant current discharging was performed up to 3.0 V at 50 mA to confirm the discharge capacity from full charge. After that, constant current and constant voltage charging was performed again under conditions of 4.1 V and 100 mA for 8 hours, and the battery was stored for 3 months in a 60 ° C. environment.
After storage, it was returned to an environment of 20 ° C., a constant current discharge was performed at 50 mA up to 3.0 V, and the remaining capacity was measured. The ratio between the remaining capacity and the discharge capacity from the full charge before storage is expressed as capacity remaining rate (= remaining capacity after storage / full capacity before storage × 100).
Thereafter, constant current and constant voltage charging was performed for 8 hours under conditions of 4.1 V and 100 mA, constant current discharging was performed to 3.0 V at 50 mA, and the change in discharge capacity from full charge before and after storage was measured. The ratio of this change is expressed as a capacity recovery rate (= full capacity after storage / full capacity before storage × 100).
[0040]
(Cycle characteristic evaluation test)
After being left in a 60 ° C. environment for 2 hours, charging / discharging was started. The charging end voltage at this time is set to 4. A constant current charge / discharge of 972 mA was performed at 1 V and a final discharge voltage of 3.0 V. This charging / discharging was performed up to 500 cycles.
Then, the initial discharge capacity is obtained by dividing the battery capacity at the first cycle discharge by the positive electrode active material amount. The ratio between the initial discharge capacity and the discharge capacity after 500 cycles is expressed as a capacity maintenance rate.
These results are summarized in Table 1.
[0041]
From the table, it can be seen that, compared with Comparative Example 1, Example 1 is superior in all of the capacity retention rate, the capacity remaining rate, and the capacity recovery rate, although the initial capacity is slightly reduced.
Further, in Example 2, the initial capacity was the same as that of Comparative Example 1, and it was found that the capacity maintenance rate, the capacity remaining rate, and the capacity recovery rate were excellent as in Example 1.
[0042]
In the lithium secondary battery according to this example, the negative electrode material is surface-modified carbon coated with spinel type lithium titanium oxide.
Spinel type lithium titanium oxide is an electron / ion mixed conductor having a redox potential of about 1.5 V with respect to lithium. Although it is an insulator when lithium is not inserted, it is conductive at a potential of 1.5 V (relative to lithium) or higher when lithium is inserted. Therefore, charging and discharging are not hindered.
[0043]
On the other hand, compared with carbon having a main potential in the vicinity of 0.1 V, spinel type lithium titanium oxide has a weak reducing power and a low reactivity with an organic electrolyte. Therefore, compared with the case where carbon is in direct contact with the electrolytic solution, the decomposition of the electrolytic solution in the negative electrode and the generation amount of the lithium-containing film can be reduced. And since these reactions generate | occur | produce especially notably at high temperature, stability at high temperature can be improved.
Therefore, it is possible to obtain a lithium secondary battery that ensures stability at high temperatures and stability during long-term storage, has a small amount of lithium deactivated during high-temperature storage, and has excellent capacity remaining rate, capacity recovery rate, and cycle characteristics.
[0044]
As described above, according to this example, it is possible to provide a lithium secondary battery that ensures stability at high temperatures and stability during long-term storage and does not hinder charge / discharge performance, and a method for producing a negative electrode material that is inexpensive in production cost. .
Also,
[0045]
Further, although the initial capacity of Example 1 is lower than that of the comparative example, the advantage of this example is very great because the capacity of Example 1 is significantly superior to that of Comparative Example 1 in the capacity after 500 cycles.
Also, as in Example 2, a lithium metal thin film can be attached on the negative electrode to increase the initial capacity.
[0046]
[Table 1]
【The invention's effect】
As described above, according to the present invention, a lithium secondary battery that ensures stability at high temperatures and stability during long-term storage and does not hinder charge / discharge performance, and a method for manufacturing a negative electrode material that is inexpensive to manufacture are provided. Can do.
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| KR100424643B1 (en) * | 2002-03-20 | 2004-03-25 | 삼성에스디아이 주식회사 | Negative active material for rechargeable lithium battery |
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| KR100838165B1 (en) * | 2004-09-24 | 2008-06-13 | 주식회사 엘지화학 | Titanium Compound-Coated Cathode Active Material And Lithium Secondary Battery Comprising The Same |
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| KR101105878B1 (en) * | 2008-12-02 | 2012-01-16 | 주식회사 코캄 | Core-shell type anode active material for lithium secondary batteries and Method of preparing for the same and Lithium secondary batteries comprising the same |
| JP5319312B2 (en) | 2009-01-21 | 2013-10-16 | 株式会社東芝 | Negative electrode active material for batteries, non-aqueous electrolyte battery and battery pack |
| EP2450988A4 (en) | 2009-05-26 | 2014-06-04 | Kokam Co Ltd | Anode active material for lithium secondary battery, preparation method thereof, and lithium secondary battery containing same |
| KR101105875B1 (en) | 2009-05-26 | 2012-01-16 | 주식회사 코캄 | Anode active material for lithium secondary batteries and Method of preparing for the same and Lithium secondary batteries comprising the same |
| KR101112754B1 (en) | 2010-05-18 | 2012-02-24 | 삼화콘덴서공업주식회사 | Active material for Anode, Method for manufacturing the same, And Secondary Battery and Super Capacitor including the Same |
| KR101308677B1 (en) * | 2011-05-31 | 2013-09-13 | 주식회사 코캄 | Lithium secondary batteries |
| JP6301619B2 (en) | 2013-09-20 | 2018-03-28 | 株式会社東芝 | Non-aqueous electrolyte secondary battery, battery pack and car |
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| JPH05275077A (en) * | 1992-03-24 | 1993-10-22 | Agency Of Ind Science & Technol | Negative electrode for lithium secondary battery |
| JPH1040960A (en) * | 1996-07-23 | 1998-02-13 | Matsushita Electric Ind Co Ltd | Nonaqueous electrolyte secondary battery |
| JPH1069922A (en) * | 1996-08-27 | 1998-03-10 | Matsushita Electric Ind Co Ltd | Non-aqueous electrolyte lithium secondary battery |
| JPH1179751A (en) * | 1997-09-02 | 1999-03-23 | Toda Kogyo Corp | Production of lithium-nickel oxide particulate powder |
| JPH1196995A (en) * | 1997-09-22 | 1999-04-09 | Toyota Motor Corp | Manufacture of negative electrode for lithium ion secondary battery |
| JPH1196993A (en) * | 1997-09-22 | 1999-04-09 | Toyota Motor Corp | Negative electrode for lithium ion secondary battery |
-
2000
- 2000-02-28 JP JP2000051121A patent/JP4729774B2/en not_active Expired - Fee Related
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH05275077A (en) * | 1992-03-24 | 1993-10-22 | Agency Of Ind Science & Technol | Negative electrode for lithium secondary battery |
| JPH1040960A (en) * | 1996-07-23 | 1998-02-13 | Matsushita Electric Ind Co Ltd | Nonaqueous electrolyte secondary battery |
| JPH1069922A (en) * | 1996-08-27 | 1998-03-10 | Matsushita Electric Ind Co Ltd | Non-aqueous electrolyte lithium secondary battery |
| JPH1179751A (en) * | 1997-09-02 | 1999-03-23 | Toda Kogyo Corp | Production of lithium-nickel oxide particulate powder |
| JPH1196995A (en) * | 1997-09-22 | 1999-04-09 | Toyota Motor Corp | Manufacture of negative electrode for lithium ion secondary battery |
| JPH1196993A (en) * | 1997-09-22 | 1999-04-09 | Toyota Motor Corp | Negative electrode for lithium ion secondary battery |
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| Publication number | Publication date |
|---|---|
| JP2001243950A (en) | 2001-09-07 |
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