JP2004296269A - Negative electrode material for lithium ion secondary battery, its manufacturing method, and battery using the same - Google Patents
Negative electrode material for lithium ion secondary battery, its manufacturing method, and battery using the same Download PDFInfo
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- JP2004296269A JP2004296269A JP2003087188A JP2003087188A JP2004296269A JP 2004296269 A JP2004296269 A JP 2004296269A JP 2003087188 A JP2003087188 A JP 2003087188A JP 2003087188 A JP2003087188 A JP 2003087188A JP 2004296269 A JP2004296269 A JP 2004296269A
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- 239000007773 negative electrode material Substances 0.000 title claims abstract description 58
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims abstract description 20
- 229910001416 lithium ion Inorganic materials 0.000 title claims abstract description 20
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 12
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- 239000010703 silicon Substances 0.000 claims abstract description 23
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 23
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Classifications
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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
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Battery Electrode And Active Subsutance (AREA)
Abstract
Description
【０００１】
【技術分野】
本発明は、リチウムイオン二次電池用負極材に関し、より詳しくは黒鉛質粉末、
炭素前駆体、ポリカルボシラン（ポリメチルシリレンメチレン）微粉末、シリコン微粉末を加熱混合した後、焼成して得られ、４００ｍＡｈ／ｇ以上の高容量で、
容量ロスも少なく、かつサイクル特性にも優れた負極材とその製造方法に関する。
【０００２】
【従来の技術】
近年、リチウム二次電池はハイパワ−、高容量の二次電池として携帯電話、パソコン等の可搬型機器類に多く使用され、今後も需要がさらに高まると予想されている。
【０００３】
このような可搬型機器類の小型化への流れを受けて、リチウム二次電池も小型化、軽量化またさらなる高性能化への要請が強まっている。
【０００４】
そのため、リチウム二次電池を構成するパ−ツや材料も高性能化の動きが活発になっており、中でも負極材は電池の性能を左右する
ものとしてその重要性が高まっている。
【０００５】
この負極材としては、現在カ−ボン系材料（黒鉛質）が主流である。
負極材に要求される特
性は、まず放電容量が高容量であることで、また容量ロスの低減も重要であり、さらにサイクル特性にも優れることが必要である。
黒鉛質負極材は，放電容量が３５０〜３６０ｍＡｈ／ｇ程度と理論容量の３７２ｍＡｈ／ｇに
近いものが開発、実用化されており、これらの特性を十分備えた優れた材料である。
【０００６】
しかし乍ら将来的には、可般型機器類のさらなる高機能化に伴い、４００ｍＡｈ／ｇを超えるような超高容量の負極材が要請されることが確実とみられている。
そこでこのような高容量化を実現すると同時に、容量ロスも少なく、良好なサイクル特性を有し、電池として実用化できるような新規な負極材の開発が注目されている。
【０００７】
これまで高容量の負極材を得るため種々の試みがなされている。
まずカ−ボン系負極材の中には、黒鉛の理論容量３７２ｍｈ／ｇを上回る高容量のものがあるが、これらは、非晶質構造の炭素質材であるため、結晶中に大きな結晶が存在するため、リチウムイオンの充放電が円滑になされず、充放電ロスが大きくなる欠点を有する。（例えば特許文献１）
【０００８】
また近年には、黒鉛粉末にケイ素を混合させた 例えば、炭素材とケイ素粉末を混合熱処理したものがあるが、１０サイクル程度しか評価されておらず、実用化にはサイクル特性が不十分である。（特許文献２）
【０００９】
ケイ素粉末に替えて、ケイ化金属間化合物を負極材に用いることも提案されているがサイクル特性のみが検討されており、放電容量や充放電ロスについては考慮されていない。（特許文献３）
【００１０】
【特許文献１】
特許第３２６９４３０号公報
【特許文献２】
特許第３２６８７７０号公報
【特許文献３】
特許第３２８２５４６号公報
【００１１】
さらに、集電体である銅箔の上に、直接シリコン乃至シリコンとコバルト等の金属を複合メッキさせた電極材料等も検討されている。
しかし、リチウムのド−プ・アンドド−プに伴う体積変化に伴い、シリコン等の剥離によるサイクル特性の悪化を防止するため、この体積変化を吸収するのは困難で、実用化は容易ではない。
【００１２】
このように、現在の黒鉛質材を超える次世代の高容量の負極材の開発のために様々な試みがなされているが、かかる高容量であるとともに、電池として実用化できる負極材を得るのは、きわめて困難なのが現状である。
【００１３】
【発明の課題】
上記のような状況に鑑み、本発明者は４００ｍＡｈ／ｇを超える高容量で、容量ロスが少なく、サイクル特性にも優れ、電池として実用に供せるリチウムイオン二次電池用負極材とその製造方法を提供する。
【００１４】
【課題解決の手段】
上記のような課題を解決するために、本発明者が提案するのは、黒鉛質粉末、炭素前駆体、ポリカルボシラン微粉末、シリコン微粉末を加熱混合した後、焼成して得られるリチウムイオン二次電池用負極材である。
また、かかる負極材の製造方法として黒鉛質粉末に炭素前駆体をポリカルボシラン微粉末およびシリコン微粉末とともに加熱混合した後、８００〜１２００℃で焼成することを特徴とする製造方法である。
【００１５】
以下に本発明を詳細に説明する。
【００１６】
本発明の負極材は、基材である黒鉛質粉末と、主としてバインダ−として用いる炭素前駆体、そして高容量のための添加物質であるポリカルボシラン微粉末およびシリコン微粉末の四種の材料を混合、熱処理することにより得られる。
【００１７】
まず、基材として使用する黒鉛粉末は、天然黒鉛粉末、天然黒鉛粉末の造粒品、また人造黒鉛としてはコ−クスまたは生コ−クス、メソフェ−ズピッチ等を黒鉛化したものが代表的なものとして挙げられる。
これらの黒鉛粉末を単独か、二種以上を任意の割合で混合して用いてもよい。
【００１８】
黒鉛粉末の平均粒径は、市販の負極材と同程度であれば特に限定されないが２〜５０μｍ程度が適当である。
５μｍ以下では、比表面積が大きくなり、その結果負極材として用いても、充放電時の不可逆容量が大きくなり、好ましくない。
５０μｍを超えると、その粒度分布上、負極電極シ−トの厚さを超える粒子となる８０μｍ以上の粒子を多く含むため好ましくない。
【００１９】
また黒鉛化の程度は、炭素結晶面同士の間隔ｄ（００２）が０．３３７ｎｍ以下のものを用いるのが好ましい。
これにより、放電容量、電池効率等に優れた負極材を得ることができる。
【００２０】
次に、バインダ−である炭素前駆体については次のような樹脂、ピッチ、シリコン化合物を使用する。
樹脂ではフェノ−ル樹脂、セルロ−ス樹脂、フッ素樹脂等を使用し、ピッチではイソフェ−ズピッチ、メソフェ−ズピッチ等を使用する。
シリコン化合物としては、シリコ−ン、水ガラス等が用いられる。
【００２１】
ピッチを用いる場合は、その融点は３２０℃以下であるのが、好ましく、これ以上の融点を持ったものであると、黒鉛質粉末とのコ−テイングおよび含浸過程のニ−ダ−混合時に、実質上混ねつが不可能になったり、一部黒鉛質粉末の酸化が発生することがあり、好ましくない。
ピッチ以外の樹脂やシリコン化合物を用いる場合は、酸素含有量が後工程の８００〜１２００℃での焼成後に１．５％以下、より良くは０．１５％以下、更には０．０５％以下なることが好ましい。
酸素含有量が過剰であると、最終的に得られる負極材の放電容量や電池効率を低下させることがあるので好ましくない。
【００２２】
炭素前駆体の使用配合割合は、使用する黒鉛質粉末の比表面積、吸油量等により多少異なるが、一般には黒鉛粉末１００重量部に対して１０〜２５重量部程度が適当で、黒鉛質粉末の粉体特性により適宜増減させることが好ましい。
１０重量部以下では少量のため、混合による効果が十分ではなく、また２５重量部を超えると、混合熱処理後に仕上がるものが、粉末や軽い凝集体ではなく、大きな硬いブロック状のものとなるので好ましくない。
【００２３】
高容量化のために添加するポリカルボシラン微粉末、シリコン微粉末は、できる限り粒子径が小さい粒子であることが好ましい。
これは、最終製品の負極材の黒鉛粉末に被覆されたシリコン微粉末のリチウムの吸蔵・放出に伴う体積変化を抑えるために必要であり、粒子径が大き過ぎると、体積膨張のため剥離や粉化が生じサイクル特性に劣化をきたす。
【００２４】
従って、平均粒子径は５μｍ以下、より好ましくは、２μｍ以下であることが重要である。
なお、１μｍ以下の超微粉の場合、微粉間で凝集し合い均一な分散が難しいので、事前に分散媒との良分散体を作ってから、黒鉛粉末、バインダ−と混合することが必要になる。
【００２５】
平均粒子径５μｍ以下とするのは、ポリカルボシラン微粉末の場合、混合、熱処理時に溶融を容易にし、且つシリコン微粉末をばらつきなく均一に黒鉛質粉末に被覆させるためにも重要である。
被覆にばらつきがあると、容量やサイクル特性に悪影響を及ぼすので好ましくない。
【００２６】
最大粒子径については、ＳＥＭ観察において、１０μｍ以上、より好ましくは８μｍ以上、さらに好ましくは５μｍ以上の粒子が存在しないことが好ましい。粒子径の大なる粒子が存在すると、前記のように体積膨張によりサイクル特性に悪影響を与えるので好ましくない。
【００２７】
ポリカルボシラン微粉末およびシリコン微粉末の割合は、黒鉛粉末１００重量部に対し、３〜１５重量部が好ましい。
３重量部以下では容量増加に効果がなく、１５重量部を超えるとサイクル特性を劣化させるので好ましくない。
【００２８】
本発明において、有機ケイ素化合物であるポリカルボシラン微粉末は黒鉛質粉末とシリコン微粉末の密着性を増加させ、負極材のサイクル特性を向上させるために有効である。
【００２９】
以上のように、基材である黒鉛質粉末、バインダ−であるピッチや樹脂、そしてポリカルボシラン微粉末およびシリコン微粉末の４種類の材料を５０℃〜３００℃で加熱混合する。
【００３０】
混合に使用する装置は、一般には加熱ニ−ダ−が量産に適しているが、これに限定はされない。
混合方法も特定されないが、一般には、バインダ−やポリカルボシラン微粉末を溶媒に溶解または分散させ、黒鉛質粉末とニ−ダ−で混合、攪拌しながら、加温し溶媒を蒸発、除去する方法が適当である。
【００３１】
混合、熱処理後は窒素等の非酸化性雰囲気または還元性雰囲気中で８００〜１２００℃、より好ましくは９００〜１１００℃で焼成する。
８００℃未満では完全に炭素化されず、残存元素が多く、この結果として電池効率が悪くなるので問題があり、１２００℃を超えると混入しているピッチとシリコン粉末がＳｉＣ化し、高容量を得ることができなくなるので、いずれも好ましくない。
最終的な熱処理として黒鉛化は行わず、上記のような焼成により負極材を得る。
以上のようにして本発明のリチウムイオン二次電池負極材が得られる。
【００３２】
本発明により得られる、リチウムイオン二次電池負極材は、基材である黒鉛質粉末にシリコン微粉末がばらつきなく均一に分散されることにより、高容量化を実現でき、また添加物質であるポリカルボシランの効果により、黒鉛質粉末とシリコン微粉末の密着性を向上させ、良好なサイクル特性も得ることもできる。
【００３３】
【発明の効果】
上記のようにして得られた本発明のリチウムイオン二次電池負極材は、４００ｍＡｈ／ｇ以上の高容量を実現できるとともに、充放電時の容量ロスが小さく、サイクル特性も優れている。
将来、可搬型機器類のさらなる高性能化に伴い要求される超高容量のリチウムイオン二次電池の負極材として有望である。
【００３４】
【実施例および比較例】
【実施例１】
平均粒子径１８．４μｍで軟化点３６０℃、メソフェ−ズ量９５％のメソフェ−ズピッチを空気中３５０℃にて熱処理し、不融化した。
これを解砕した後、不活性雰囲気下で１０００℃にて焼成し、更に黒鉛化炉に移して、アルゴン雰囲気下で３０００℃で黒鉛化処理した後、整粒して、平均粒子径１５．１μｍで平均層面間隔（以下ｄ（００２）と示す）が０．３３５８ｎｍの黒鉛質粉末とした。
この黒鉛質粉末１００重量部に対して、バインダ−としてストレ−ト型レゾ−ル樹脂を２０重量部、添加物質として、平均粒子径３．５μｍの金属シリコン粉末５重量部と平均粒径５μｍのポリカルボシラン３重量部（日本カ−ボン（株）製）を用いて、ニ−ダ−にて１５０℃で１時間、混合熱処理をし、更に水素ガス雰囲気中で、１０００℃で焼成して負極材を得た。
【００３５】
次に得られた負極材を用いて以下のように電池を作成し、電池特性を評価した。
本来、黒鉛粉末は負極として用いるが、本発明では対極にリチウム金属を使用したため、正極で電池の特性を評価した。
電極の製造は負極材１００重量部とポリフッ化ビニリデン８重量にＮ−メチル−２−ピロリドンを混合してペ−スト化した後、ドクタ−ブレ−ドを用いて銅箔上に塗布し、１５０℃で１時間熱処理し乾燥させた。
乾燥後、これを１ｃｍ２の面積になるように円形に打ち抜き、更に２ｔｏｎ／ｃｍ２の圧力でプレスしシ−ト化し、電極を調整した。
対極及び参照極としてリチウム金属を使用し、電解液として１ＭＬｉＰＦ６／ＥＣ：ＭＥＣ（体積比１：１）を用いてコインセルを組み立てた。
【００３６】
充電は０．５ｍＡ／ｃｍ２の電流密度で定電流充電後、１０ｍＶで定電圧充電に切り替え、０．０１ｍＡで終止した。
また、放電は、０．５ｍＡ／ｃｍ２の電流密度で定電流放電１．５Ｖまで行った。
更に放電レ−トを変えて５ｍＡ／ｃｍ２の電流密度での放電容量も測定した。
測定温度は３０℃である。
測定結果は放電容量が４６７ｍＡｈ／ｇ、容量ロスが少ないことを示す電池効率は９２．１％であった。
また、５０サイクル目の放電容量は４４４ｍＡｈ／ｇ、容量保持率は、９５％であった。
【００３７】
【実施例２】
平均粒径１５μｍ、ｄ（００２）が０．３３６ｎｍ、灰分０．１５％以下とした中国製鱗片状天然黒鉛１００重量部にバインダ−としてエチルセルロ−ス３重量部（ダウケミカル社製）を用いて造粒成形を行い、平均粒径２２μｍ、タッ
プ
密度が０．９４ｇ／ｃｍ３の略球形成形体を調整した。
この略球形成形体１００重量部に対して、バインダ−として軟化点１１０℃、メタフェ−ズ量（ＱＩ量）が１３％のコ−ルタ−タ−ルピッチ２０重量部を過剰
量のキシレンに溶解させ、そこに平均粒径０．４μｍの金属シリコン粉末６重量部、平均粒径５μｍのポリカルボシラン粉末を８重量部加えて、超音波分散させた。
次にこれらの原料を２軸ニ−ダ−に投入し、常温で２時間、さらに加熱し、１５０℃で２時間混熱を行いキシレンの除去と天然黒鉛成形体への被覆処理を行った。
被覆終了後は、窒素雰囲気下で熱処理し、最高温度１０００℃で６時間保持した後、放冷し、焼成品とした。
焼成品は粒子同士の強固な融着はなく、クイックミル（（株）セイシン企業製）で解砕するだけで、簡単に負極材が得られた。
次に得られた負極材を用いて、実施例１と同様にして、コインセルを構成し、充放電テストを行った結果、放電容量は４４２ｍＡｈ／ｇ、電池効率は９０．１％であった。
また５０サイクル目の放電容量は、４１６ｍＡｈ／ｇ、容量保持率は、９４％であった。
【００３８】
【実施例３】
実施例１で用いた黒鉛質粉末１００重量部に対して、ストレ−ト型シリコ−ン３０重量部と、粒径５μｍのポリカルボシラン微粉末５重量部、軟化点１００℃のピッチ１８重量部をニ−ダ−にて１５０℃で混合熱処理を行った後、水素雰囲気下１０００℃にて焼成し、負極材を得た。
得られた負極材を用いて、実施例１と同様に、コインセルを構成し、充放電テストを行った結果、放電容量は、４１８ｍＡｈ／ｇ、電池効率は８８．２％であった。
また５０サイクル目の放電容量は３９３ｍＡｈ／ｇ、容量保持率は、９４％であった。
【００３９】
【実施例４】
実施例１で用いた黒鉛質粉末１００重量部に対して、平均粒子径０．６μｍのケイ素粉末５重量部と、ポリカルボシラン微粉末重量部および軟化点１１０℃のピッチ２０重量部をニ−ダ−にて１５０℃で１時間、混合熱処理を行った後、窒素雰囲気下１０００℃で３時間熱処理し、負極材を得た。
得られた負極材を用いて、実施例１と同様にコインセルを構成し、充放電テストを行った結果、放電容量は、４５５ ｍＡｈ／ｇ、電池効率は８９．８％であった。
また５０サイクル目の放電容量は４３７ｍＡｈ／ｇ、容量保持率は、９６％であった。
【００４０】
【比較例１】
平均粒子径１９．２μｍの黒鉛粉末１００重量部に対し、平均粒子径２μｍのシリコン粉末１０重量部をニ−ダ−に投入し、室温にて１時間混合させ、平均粒子径１８．３μｍの黒鉛粉末とシリコン粉末を混合した負極材を得た。
得られた負極材を用いて、実施例１と同様にコインセルを構成し、充放電テストを行った結果、放電容量は、５１５ｍＡｈ／ｇ、電池効率は７８．２％であった。
また実施例と同様、サイクル特性を測定しようとしたが、５０サイクル目まで負極材がもたなかった。
【００４１】
【比較例２】
比較例１と同じ黒鉛粉末を用い、この黒鉛粉末１００重量部に対して、平均粒子径１６．７μｍのケイ素粉末３重量部とコ−ルタ−ルピッチ２０重量部とポリカルボシラン５重量部をニ−ダ−に投入し、１５０℃で１時間混合熱処理をした。
これをさらに窒素雰囲気下で１０００℃にて焼成し、平均粒子径１８．６μｍの負極材を得た。
得られた負極材を用いて、実施例１と同様にコインセルを構成し、充放電テストを行った結果、放電容量は、４２６ｍＡｈ／ｇ、電池効率は８２．９％であった。
また５０サイクル目の放電容量は２６９ｍＡｈ／ｇ、容量保持率は８７％であった。
【００４２】
【比較例３】
比較例１と同じ黒鉛質粉末１００重量部に対して、実施例４で用いたシリコ−ン１０重量部とポリカルボシラン３％と、軟化点１５０℃のメソフェ−ズピッチをニ−ダ−にて１８０℃で１時間混合熱処理を行った。
次に窒素雰囲気下、１０００℃で焼成し、負極材を得た。
得られた負極材を用いて、実施例１と同様にコインセルを作成し、充放電テストを行った結果、放電容量は３７２ｍＡｈ／ｇ、電池効率は８９．２ ％であった。
また５０サイクル目の放電容量は３５７ｍＡｈ／ｇ、容量保持率は９６％であった。
【００４３】
【比較例４】実施例１で使用した平均粒子径１５．１μｍの黒鉛質粉末１００重量部に対して
平均粒子径２．７μｍのシリコン微粉末５．３重量部、軟化点３５０℃のメソフェ−スピッチ１５重量部をらいかい機により、大気中で３時間反応させ、平均粒子径１４．６μｍの負極材を得た。
得られた負極材を用いて、実施例１と同様にコインセルを作成し、充放電テストを行った結果、放電容量は４３５ｍＡｈ／ｇ、電池効率は９０．０％であった。 また５０サイクル目の放電容量は３９６ｍＡｈ／ｇ、容量保持率は９１％であった。
【００４４】以上のように、本発明のいずれの実施例においても、放電容量が４００ｍＡｈ／ｇ以上で、電池効率が８８％以上と、容量ロスが少なく、しかも５０回サイクル後の放電容量の保持率が９４％以上のすぐれた負極材が得られた。[0001]
【Technical field】
The present invention relates to a negative electrode material for a lithium ion secondary battery, and more specifically, a graphite powder,
A carbon precursor, polycarbosilane (polymethylsilylene methylene) fine powder, and silicon fine powder are heated and mixed, and then calcined. At a high capacity of 400 mAh / g or more,
The present invention relates to a negative electrode material having a small capacity loss and excellent cycle characteristics and a method for producing the same.
[0002]
[Prior art]
2. Description of the Related Art In recent years, lithium secondary batteries are widely used as high-power, high-capacity secondary batteries in portable devices such as mobile phones and personal computers, and the demand is expected to increase in the future.
[0003]
In response to the trend toward miniaturization of such portable devices, there is an increasing demand for lithium secondary batteries to be smaller, lighter, and have higher performance.
[0004]
For this reason, the parts and materials constituting the lithium secondary battery have been actively moving toward higher performance. Among them, the negative electrode material has been increasing its importance as it affects the performance of the battery.
[0005]
As the negative electrode material, a carbon-based material (graphite) is mainly used at present.
The characteristics required of the negative electrode material are that the discharge capacity is high, the reduction of the capacity loss is also important, and the cycle characteristics must also be excellent.
Graphite-based negative electrode materials have been developed and put to practical use with a discharge capacity of about 350 to 360 mAh / g, which is close to the theoretical capacity of 372 mAh / g, and are excellent materials sufficiently provided with these characteristics.
[0006]
However, in the future, with the further enhancement of the functions of general-purpose devices, it is surely required that an anode material having an ultra-high capacity exceeding 400 mAh / g is required.
Therefore, attention has been paid to the development of a new negative electrode material that realizes such a high capacity, has a small capacity loss, has good cycle characteristics, and can be practically used as a battery.
[0007]
Various attempts have been made to obtain a high-capacity negative electrode material.
First, some carbon-based negative electrode materials have a high capacity exceeding the theoretical capacity of graphite of 372 mh / g. However, since these are carbonaceous materials having an amorphous structure, large crystals are contained in the crystals. Since it is present, there is a disadvantage that charging and discharging of lithium ions are not performed smoothly, and charging and discharging loss is increased. (For example, Patent Document 1)
[0008]
In recent years, graphite powder mixed with silicon, for example, a carbon material and silicon powder mixed and heat treated has been evaluated, but only about 10 cycles have been evaluated, and the cycle characteristics are insufficient for practical use. . (Patent Document 2)
[0009]
The use of an intermetallic silicide compound as a negative electrode material instead of silicon powder has also been proposed, but only cycle characteristics have been studied, and the discharge capacity and charge / discharge loss have not been considered. (Patent Document 3)
[0010]
[Patent Document 1]
Japanese Patent No. 3269430 [Patent Document 2]
Japanese Patent No. 3268770 [Patent Document 3]
Japanese Patent No. 3282546
Further, an electrode material or the like in which silicon or a metal such as silicon and cobalt is directly plated on a copper foil as a current collector has been studied.
However, in order to prevent the deterioration of the cycle characteristics due to exfoliation of silicon or the like due to the volume change caused by the lithium doping and doping, it is difficult to absorb the volume change, and practical application is not easy.
[0012]
As described above, various attempts have been made to develop a next-generation, high-capacity negative electrode material that exceeds the current graphite materials, but it is necessary to obtain such a high-capacity negative electrode material that can be practically used as a battery. Is extremely difficult at present.
[0013]
[Problems of the Invention]
In view of the above situation, the present inventor has a high capacity exceeding 400 mAh / g, a small capacity loss, excellent cycle characteristics, and a negative electrode material for a lithium ion secondary battery that can be put to practical use as a battery, and a method for producing the same. I will provide a.
[0014]
[Means for solving the problem]
In order to solve the above problems, the present inventors propose that graphite powder, carbon precursor, polycarbosilane fine powder, heat-mixed silicon powder, lithium ion obtained by firing It is a negative electrode material for a secondary battery.
In addition, as a method for producing such a negative electrode material, a carbon precursor is mixed with graphite powder together with polycarbosilane fine powder and silicon fine powder by heating, followed by firing at 800 to 1200 ° C.
[0015]
Hereinafter, the present invention will be described in detail.
[0016]
The negative electrode material of the present invention comprises a graphite powder as a base material, a carbon precursor mainly used as a binder, and four kinds of materials, polycarbosilane fine powder and silicon fine powder, which are additives for high capacity. It is obtained by mixing and heat treating.
[0017]
First, the graphite powder used as a base material is typically natural graphite powder, a granulated product of natural graphite powder, and artificial graphite is graphitized coke or raw coke, mesophase pitch, or the like. Are listed.
These graphite powders may be used alone or as a mixture of two or more kinds at an arbitrary ratio.
[0018]
The average particle size of the graphite powder is not particularly limited as long as it is substantially the same as that of a commercially available negative electrode material, but is suitably about 2 to 50 μm.
When the thickness is 5 μm or less, the specific surface area increases, and as a result, even when used as a negative electrode material, the irreversible capacity at the time of charging and discharging increases, which is not preferable.
If it exceeds 50 μm, the particle size distribution is not preferred because it contains many particles of 80 μm or more which exceed the thickness of the negative electrode sheet.
[0019]
The degree of graphitization is preferably such that the distance d (002) between carbon crystal planes is 0.337 nm or less.
Thereby, a negative electrode material excellent in discharge capacity, battery efficiency, and the like can be obtained.
[0020]
Next, for the carbon precursor as the binder, the following resin, pitch and silicon compound are used.
As the resin, phenol resin, cellulose resin, fluororesin or the like is used, and as the pitch, an isophase pitch, a mesophase pitch, or the like is used.
As the silicon compound, silicon, water glass or the like is used.
[0021]
When a pitch is used, its melting point is preferably 320 ° C. or lower, and if it has a melting point higher than that, when the powder is coated with graphite powder and kneaded during the impregnation process, In some cases, mixing becomes impossible, or oxidation of the graphitic powder partially occurs, which is not preferable.
When a resin or a silicon compound other than the pitch is used, the oxygen content becomes 1.5% or less, more preferably 0.15% or less, and further 0.05% or less after firing at 800 to 1200 ° C. in the subsequent step. Is preferred.
If the oxygen content is excessive, the discharge capacity and battery efficiency of the finally obtained negative electrode material may decrease, which is not preferable.
[0022]
The mixing ratio of the carbon precursor is slightly different depending on the specific surface area of the graphite powder to be used, the oil absorption and the like, but generally about 10 to 25 parts by weight is appropriate for 100 parts by weight of the graphite powder. It is preferable to increase or decrease as appropriate according to the powder characteristics.
When the amount is less than 10 parts by weight, the effect of mixing is not sufficient because the amount is small, and when the amount exceeds 25 parts by weight, the finished product after the heat treatment for mixing is not a powder or a light agglomerate but a large hard block. Absent.
[0023]
The polycarbosilane fine powder and silicon fine powder added for increasing the capacity are preferably particles having the smallest possible particle diameter.
This is necessary in order to suppress the volume change accompanying the occlusion and release of lithium in the silicon fine powder coated on the graphite powder of the negative electrode material of the final product.If the particle size is too large, peeling or powdering occurs due to volume expansion. And the cycle characteristics deteriorate.
[0024]
Therefore, it is important that the average particle diameter is 5 μm or less, more preferably 2 μm or less.
In the case of an ultrafine powder of 1 μm or less, it is difficult to uniformly disperse the fine powder and uniformly disperse the fine powder. Therefore, it is necessary to prepare a good dispersion with a dispersion medium before mixing with the graphite powder and the binder. .
[0025]
In the case of polycarbosilane fine powder, it is important that the average particle diameter is 5 μm or less in order to facilitate melting during mixing and heat treatment and to coat the silicon fine powder uniformly and uniformly with the graphite powder.
Variations in the coating are undesirable because they have an adverse effect on capacity and cycle characteristics.
[0026]
Regarding the maximum particle size, it is preferable that no particles having a size of 10 μm or more, more preferably 8 μm or more, and still more preferably 5 μm or more do not exist in SEM observation. The presence of particles having a large particle diameter is not preferable because the cycle characteristics are adversely affected by volume expansion as described above.
[0027]
The proportion of the polycarbosilane fine powder and the silicon fine powder is preferably 3 to 15 parts by weight based on 100 parts by weight of the graphite powder.
If the amount is less than 3 parts by weight, there is no effect on increasing the capacity, and if it exceeds 15 parts by weight, the cycle characteristics deteriorate, which is not preferable.
[0028]
In the present invention, polycarbosilane fine powder, which is an organosilicon compound, is effective for increasing the adhesion between the graphite powder and the silicon fine powder and improving the cycle characteristics of the negative electrode material.
[0029]
As described above, graphite powder as a base material, pitch and resin as binders, and four kinds of materials of polycarbosilane fine powder and silicon fine powder are heated and mixed at 50 ° C to 300 ° C.
[0030]
As for an apparatus used for mixing, a heating kneader is generally suitable for mass production, but is not limited to this.
Although the mixing method is not specified, generally, the binder or the polycarbosilane fine powder is dissolved or dispersed in a solvent, mixed with a graphite powder and kneaded with a kneader, heated and evaporated to remove the solvent. The method is appropriate.
[0031]
After mixing and heat treatment, firing is performed at 800 to 1200 ° C, more preferably 900 to 1100 ° C, in a non-oxidizing atmosphere such as nitrogen or a reducing atmosphere.
If the temperature is lower than 800 ° C., the carbon is not completely carbonized, and there are many residual elements. As a result, the battery efficiency deteriorates. There is a problem. If the temperature exceeds 1200 ° C., the mixed pitch and silicon powder are converted into SiC to obtain a high capacity. Are not preferred.
Graphitization is not performed as a final heat treatment, and a negative electrode material is obtained by the above-described firing.
As described above, the lithium ion secondary battery negative electrode material of the present invention is obtained.
[0032]
The negative electrode material of a lithium ion secondary battery obtained by the present invention can realize high capacity by uniformly dispersing silicon fine powder without variation in graphite powder as a base material, By the effect of carbosilane, the adhesion between the graphite powder and the silicon fine powder can be improved, and good cycle characteristics can be obtained.
[0033]
【The invention's effect】
The lithium ion secondary battery negative electrode material of the present invention obtained as described above can realize a high capacity of 400 mAh / g or more, has a small capacity loss at the time of charge and discharge, and has excellent cycle characteristics.
In the future, it is promising as a negative electrode material for ultra-high capacity lithium-ion secondary batteries required for higher performance of portable devices.
[0034]
[Examples and Comparative Examples]
Embodiment 1
A mesophase pitch having an average particle diameter of 18.4 μm, a softening point of 360 ° C. and a mesophase amount of 95% was heat-treated at 350 ° C. in air to make it infusible.
After being crushed, it is baked at 1000 ° C. in an inert atmosphere, further transferred to a graphitization furnace, graphitized at 3000 ° C. in an argon atmosphere, sized, and sized to have an average particle diameter of 15. Graphite powder having an average layer spacing (hereinafter referred to as d (002)) of 1 μm and 0.3358 nm was obtained.
With respect to 100 parts by weight of the graphite powder, 20 parts by weight of a straight type resin as a binder and 5 parts by weight of a metal silicon powder having an average particle diameter of 3.5 μm and an average particle diameter of 5 μm as additive substances. Using 3 parts by weight of polycarbosilane (manufactured by Nippon Carbon Co., Ltd.), a mixture is heat-treated at 150 ° C. for 1 hour with a kneader, and further fired at 1000 ° C. in a hydrogen gas atmosphere. A negative electrode material was obtained.
[0035]
Next, a battery was prepared as follows using the obtained negative electrode material, and the battery characteristics were evaluated.
Originally, graphite powder was used as the negative electrode, but in the present invention, lithium metal was used for the counter electrode, and thus the battery characteristics were evaluated using the positive electrode.
An electrode was manufactured by mixing N-methyl-2-pyrrolidone with 100 parts by weight of a negative electrode material and 8 parts by weight of polyvinylidene fluoride to form a paste, and then applying the paste on a copper foil using a doctor blade. C. for 1 hour and dried.
After drying, this was punched out into a circular shape so as to have an area of 1 cm 2 , and further pressed at a pressure of 2 ton / cm 2 to form a sheet, thereby preparing an electrode.
A coin cell was assembled using lithium metal as a counter electrode and a reference electrode, and using 1M LiPF6 / EC: MEC (volume ratio 1: 1) as an electrolyte.
[0036]
After charging at a constant current of 0.5 mA / cm 2, the charging was switched to constant voltage charging at 10 mV and terminated at 0.01 mA.
The discharge was performed at a current density of 0.5 mA / cm 2 up to a constant current discharge of 1.5 V.
Further, the discharge capacity was measured at a current density of 5 mA / cm 2 while changing the discharge rate.
The measurement temperature is 30 ° C.
The measurement results showed that the discharge capacity was 467 mAh / g and the battery efficiency, which indicates that the capacity loss was small, was 92.1%.
The discharge capacity at the 50th cycle was 444 mAh / g, and the capacity retention was 95%.
[0037]
Embodiment 2
3 parts by weight of ethyl cellulose (manufactured by Dow Chemical Company) is used as a binder in 100 parts by weight of flake natural graphite made in China having an average particle size of 15 μm, d (002) of 0.336 nm and an ash content of 0.15% or less. Granulation molding was performed to prepare a substantially spherical form having an average particle diameter of 22 μm and a tap density of 0.94 g / cm 3 .
With respect to 100 parts by weight of the substantially spherical body, 20 parts by weight of a cold roll pitch having a softening point of 110 ° C. and a metaphase amount (QI amount) of 13% as a binder are dissolved in an excessive amount of xylene. Then, 6 parts by weight of a metal silicon powder having an average particle diameter of 0.4 μm and 8 parts by weight of a polycarbosilane powder having an average particle diameter of 5 μm were added thereto and ultrasonically dispersed.
Next, these raw materials were put into a biaxial kneader, further heated at room temperature for 2 hours, and further mixed at 150 ° C. for 2 hours to remove xylene and coat natural graphite compacts.
After the coating was completed, it was heat-treated in a nitrogen atmosphere, kept at a maximum temperature of 1000 ° C. for 6 hours, and then allowed to cool to obtain a fired product.
The calcined product did not have strong fusion between the particles, and the negative electrode material was easily obtained only by pulverizing with a quick mill (manufactured by Seishin Enterprise Co., Ltd.).
Next, a coin cell was formed using the obtained negative electrode material in the same manner as in Example 1, and a charge / discharge test was performed. As a result, the discharge capacity was 442 mAh / g, and the battery efficiency was 90.1%.
The discharge capacity at the 50th cycle was 416 mAh / g, and the capacity retention was 94%.
[0038]
Embodiment 3
For 100 parts by weight of the graphite powder used in Example 1, 30 parts by weight of a straight type silicone, 5 parts by weight of a polycarbosilane fine powder having a particle size of 5 μm, and 18 parts by weight of a pitch having a softening point of 100 ° C. Was subjected to a mixed heat treatment at 150 ° C. with a kneader, and then fired at 1000 ° C. in a hydrogen atmosphere to obtain a negative electrode material.
A coin cell was formed using the obtained negative electrode material in the same manner as in Example 1, and a charge / discharge test was performed. As a result, the discharge capacity was 418 mAh / g, and the battery efficiency was 88.2%.
The discharge capacity at the 50th cycle was 393 mAh / g, and the capacity retention was 94%.
[0039]
Embodiment 4
To 100 parts by weight of the graphite powder used in Example 1, 5 parts by weight of silicon powder having an average particle diameter of 0.6 μm, fine parts by weight of polycarbosilane fine powder and 20 parts by weight of a pitch having a softening point of 110 ° C. were used. The mixture was heat-treated at 150 ° C. for 1 hour in a durer, and then heat-treated at 1000 ° C. for 3 hours in a nitrogen atmosphere to obtain a negative electrode material.
A coin cell was formed using the obtained negative electrode material in the same manner as in Example 1, and a charge / discharge test was performed. As a result, the discharge capacity was 455 mAh / g, and the battery efficiency was 89.8%.
The discharge capacity at the 50th cycle was 437 mAh / g, and the capacity retention was 96%.
[0040]
[Comparative Example 1]
100 parts by weight of graphite powder having an average particle diameter of 19.2 μm is charged into a kneader with 10 parts by weight of silicon powder having an average particle diameter of 2 μm and mixed at room temperature for 1 hour to obtain graphite having an average particle diameter of 18.3 μm. A negative electrode material obtained by mixing powder and silicon powder was obtained.
A coin cell was formed using the obtained negative electrode material in the same manner as in Example 1, and a charge / discharge test was performed. As a result, the discharge capacity was 515 mAh / g, and the battery efficiency was 78.2%.
As in the case of the example, the cycle characteristics were measured, but the negative electrode material did not remain until the 50th cycle.
[0041]
[Comparative Example 2]
The same graphite powder as in Comparative Example 1 was used, and 100 parts by weight of the graphite powder were mixed with 3 parts by weight of silicon powder having an average particle diameter of 16.7 μm, 20 parts by weight of coal pitch, and 5 parts by weight of polycarbosilane. And subjected to mixed heat treatment at 150 ° C. for 1 hour.
This was further fired at 1000 ° C. in a nitrogen atmosphere to obtain a negative electrode material having an average particle diameter of 18.6 μm.
A coin cell was formed using the obtained negative electrode material in the same manner as in Example 1, and a charge / discharge test was performed. As a result, the discharge capacity was 426 mAh / g, and the battery efficiency was 82.9%.
The discharge capacity at the 50th cycle was 269 mAh / g, and the capacity retention was 87%.
[0042]
[Comparative Example 3]
To 100 parts by weight of the same graphite powder as in Comparative Example 1, 10 parts by weight of the silicone used in Example 4, 3% of polycarbosilane, and a mesophase pitch having a softening point of 150 ° C. were kneaded. The mixed heat treatment was performed at 180 ° C. for 1 hour.
Next, firing was performed at 1000 ° C. in a nitrogen atmosphere to obtain a negative electrode material.
A coin cell was prepared using the obtained negative electrode material in the same manner as in Example 1, and a charge / discharge test was performed. As a result, the discharge capacity was 372 mAh / g, and the battery efficiency was 89.2%.
The discharge capacity at the 50th cycle was 357 mAh / g, and the capacity retention was 96%.
[0043]
Comparative Example 4 5.3 parts by weight of silicon fine powder having an average particle diameter of 2.7 μm and 100 parts by weight of graphite powder having an average particle diameter of 15.1 μm used in Example 1 and a mesophase having a softening point of 350 ° C. 15 parts by weight of the s pitch was reacted in the air for 3 hours by a grinder to obtain a negative electrode material having an average particle diameter of 14.6 µm.
A coin cell was prepared using the obtained negative electrode material in the same manner as in Example 1, and a charge / discharge test was performed. As a result, the discharge capacity was 435 mAh / g, and the battery efficiency was 90.0%. The discharge capacity at the 50th cycle was 396 mAh / g, and the capacity retention was 91%.
As described above, in any of the embodiments of the present invention, the discharge capacity is 400 mAh / g or more, the battery efficiency is 88% or more, the capacity loss is small, and the discharge capacity is maintained after 50 cycles. An excellent negative electrode material having a rate of 94% or more was obtained.
Claims (7)
法。The method for producing a negative electrode material for a lithium ion secondary battery according to claim 2, wherein the carbon precursor is selected from the group consisting of a pitch, a resin, and a silicon compound.
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| JP2006228640A (en) * | 2005-02-21 | 2006-08-31 | Nippon Carbon Co Ltd | Silicon-added graphite cathode material for lithium-ion secondary battery, and manufacturing method |
| JP2006253126A (en) * | 2005-02-14 | 2006-09-21 | Matsushita Electric Ind Co Ltd | Anode active material for nonaqueous electrolyte secondary cell, anode for nonaqueous electrolyte secondary cell using same, and nonaqueous electrolyte secondary cell |
| JP2008112710A (en) * | 2006-10-03 | 2008-05-15 | Hitachi Chem Co Ltd | Negative electrode material for lithium secondary battery, negative electrode for lithium secondary battery using this, and lithium secondary battery |
| JP2011048992A (en) * | 2009-08-26 | 2011-03-10 | Sekisui Chem Co Ltd | Carbon material, electrode material, and lithium ion secondary battery negative electrode material |
| CN102376944A (en) * | 2011-11-24 | 2012-03-14 | 深圳市贝特瑞新能源材料股份有限公司 | Method for preparing silicon carbide alloy negative electrode material for lithium ion battery |
| US9543079B2 (en) | 2013-08-19 | 2017-01-10 | Jsr Corporation | Production process for electrode material, electrode and electric storage device |
| CN113991092A (en) * | 2021-09-27 | 2022-01-28 | 杭州电子科技大学 | Preparation method of silicon electrode material |
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- 2003-03-27 JP JP2003087188A patent/JP3915072B2/en not_active Expired - Fee Related
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP2006253126A (en) * | 2005-02-14 | 2006-09-21 | Matsushita Electric Ind Co Ltd | Anode active material for nonaqueous electrolyte secondary cell, anode for nonaqueous electrolyte secondary cell using same, and nonaqueous electrolyte secondary cell |
| JP2006228640A (en) * | 2005-02-21 | 2006-08-31 | Nippon Carbon Co Ltd | Silicon-added graphite cathode material for lithium-ion secondary battery, and manufacturing method |
| JP2008112710A (en) * | 2006-10-03 | 2008-05-15 | Hitachi Chem Co Ltd | Negative electrode material for lithium secondary battery, negative electrode for lithium secondary battery using this, and lithium secondary battery |
| JP2011048992A (en) * | 2009-08-26 | 2011-03-10 | Sekisui Chem Co Ltd | Carbon material, electrode material, and lithium ion secondary battery negative electrode material |
| CN102376944A (en) * | 2011-11-24 | 2012-03-14 | 深圳市贝特瑞新能源材料股份有限公司 | Method for preparing silicon carbide alloy negative electrode material for lithium ion battery |
| US9543079B2 (en) | 2013-08-19 | 2017-01-10 | Jsr Corporation | Production process for electrode material, electrode and electric storage device |
| CN113991092A (en) * | 2021-09-27 | 2022-01-28 | 杭州电子科技大学 | Preparation method of silicon electrode material |
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