JP2004095426A

JP2004095426A - Negative electrode and positive electrode for lithium secondary battery and lithium secondary battery

Info

Publication number: JP2004095426A
Application number: JP2002256462A
Authority: JP
Inventors: Takehiko Sawai; 澤井　岳彦; Shinji Saito; 斉藤　慎治
Original assignee: SEI KK
Current assignee: SEI KK
Priority date: 2002-09-02
Filing date: 2002-09-02
Publication date: 2004-03-25
Anticipated expiration: 2022-09-02
Also published as: JP3867030B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a negative electrode and a positive electrode for a lithium secondary battery having a long life and high safety as well as achieving high capacity, and the lithium secondary battery using the negative electrode and the positive electrode. <P>SOLUTION: A carbon material usable as the negative electrode for the lithium secondary battery has, as a main component, graphite particles formed by gathering or combining a plurality of particles, each of which has a specific surface area of 0.5-2m<SP>2</SP>/g, a total pore volume of 0.4-2.0ml/g in a range of 10<SP>1</SP>-10<SP>5</SP>nm, tap density of 0.5-1.2g/cm<SP>3</SP>, and a flat shape, so that their oriented surfaces are not in parallel with each other. The positive electrode material comprises lithium-contained metallic oxide particles obtained by mixing metallic oxide particles having a particle diameter of 7-12μm for D<SB>50</SB>and metallic oxide particles having a particle diameter of 4-5μm for D<SB>50</SB>. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明はリチウム二次電池用負極、正極および、該負極および正極を用いたリチウム二次電池に関する。
【０００２】
【従来の技術】
リチウムイオンの吸蔵、放出が可能な炭素材料を用いて負極材層を形成したリチウム二次電池は、金属リチウムを用いて負極材層を形成したリチウム二次電池に比べてデントライトの析出を抑制することができる。そのため、電池の短絡を防止して安全性を高めたうえで高容量な電池を提供できる利点を有している。
近年ではこのリチウムイオン電池の高容量化が求められ、電池反応物質である正極複合金属リチウム酸化物や負極炭素材自体の高容量化や電池設計による電極面積の増加、さらにはセパレータの薄形化による反応物質量の増加等の工夫がなされてきた。
【０００３】
例えば、負極炭素材として、アスペクト比が５以下、比表面積が　１０ｍ^２／ｇ　以下、１０^１〜１０^５ｎｍ　の範囲の全細孔容積が　０．４〜２．０　ｍｌ／ｇ　で、偏平状の粒子を複数配向面が非平行となるように集合または結合してなる形状を有してなる黒鉛粒子が知られている（例えば、特許文献１〜４参照）。
【０００４】
【特許文献１】
特開平１０−１５８００５号公報（特許請求の範囲）
【特許文献２】
特開平１０−２３６８０８号公報（特許請求の範囲）
【特許文献３】
特開平１０−２３６８０９号公報（特許請求の範囲）
【特許文献４】
特開２００１−０８９１１８号公報（特許請求の範囲）
【０００５】
【発明が解決しようとする課題】
しかしながら、負極炭素材として上記黒鉛粒子を用いた場合、高容量化は達成できるが、電池寿命性能や安全性が劣る場合があるという問題がある。リチウム二次電池が携帯電話やノートパソコンなどの一般民生用用途に多用されるようになると電池寿命性能や安全性は特に重要な電池特性となる。
本発明はこのような問題に対処するためになされたもので、高容量化を達成した上で長寿命かつ安全性の高いリチウム二次電池用負極、正極および、該負極および正極を用いたリチウム二次電池の提供を目的とする。
【０００６】
【課題を解決するための手段】
本発明に係るリチウム二次電池用負極材は、リチウムイオンの吸蔵、放出が可能な炭素材からなり、該炭素材は、比表面積が　０．５〜４　ｍ^２／ｇ　、１０^１〜１０^５ｎｍ　の範囲の全細孔容積が　０．４〜２．０　ｍｌ／ｇ　、タップ密度が　０．５〜１．２　ｇ／ｃｍ^３の偏平状の粒子を複数配向面が非平行となるように集合または結合してなる形状を有する主剤の黒鉛粒子と、メソフェーズ小球体炭素および気相成長炭素繊維状黒鉛から選ばれた少なくとも一つの配合材黒鉛とが配合されてなることを特徴とする。
また、上記炭素材は、上記主剤の黒鉛粒子が　７０〜９０　重量％、上記配合材黒鉛が　３０〜１０　重量％配合されてなることを特徴とする。
【０００７】
本発明に係るリチウム二次電池用正極材は、リチウム含有金属酸化物粒子からなり、該リチウム含有金属酸化物粒子は、粒径がＤ_５０で　７〜１２μｍ　の金属酸化物粒子と、粒径がＤ_５０で　４〜５μｍ　の金属酸化物粒子とを混合したことを特徴とする。
【０００８】
本発明に係るリチウム二次電池は、リチウムイオンの吸蔵、放出が可能な負極材と正極材とがリチウム塩含有非水電解質を介して積層あるいは捲回されてなり、上記負極材が本発明に係るリチウム二次電池用負極材であり、上記正極材が本発明に係るリチウム二次電池用正極材であることを特徴とする。すなわち、本発明に係るリチウム二次電池用負極材を用いたリチウム二次電池であるか、本発明に係るリチウム二次電池用正極材を用いたリチウム二次電池であるか、あるいは本発明に係るリチウム二次電池用負極材および本発明に係るリチウム二次電池用正極材を用いたリチウム二次電池である。
また、上記リチウム塩含有非水電解質の電解液にビニレンカーボネートを配合したことを特徴とする。
【０００９】
高容量で長寿命かつ安全性の高いリチウム二次電池の研究を進めたところ、所定の物性を有し、偏平状の粒子を複数配向面が非平行となるように集合または結合した形状の主剤となる黒鉛粒子と、メソフェーズ小球体炭素および気相成長炭素繊維状黒鉛から選ばれた少なくとも一つの配合材とを配合した負極材を用いることにより、初充電量に対する初回の放電量割合として定義される充放電効率が増加し、かつ高密度に炭素材を詰められることにより、容量が増大することが分かった。また、メソフェーズ小球体炭素および／または気相成長炭素繊維状黒鉛は、電子伝導性を向上させることに加えて、リチウムイオンを黒鉛エッジ部でＬｉＦやＬｉ_２ＣＯ_３の化合物に変化させないで速やかにリチウムイオンとして黒鉛層のステージに挿入するため、容量が増大することが分かった。
また、正極材として粒径が異なるリチウム含有金属酸化物粒子を用いることにより、最密充填が可能となり、正極の活物質量を増加させることができ、容量が増加した。
さらに、非水電解液にビニレンカーボネートを配合することにより、初回充放電中に生じる負極電極上でのＬｉＦ、Ｌｉ_２ＣＯ_３、金属リチウム等の生成を抑え、または電解液中のエチレンカーボネートが分解してＣＯ_２や水、エチレンガスに変化することを防止して効率よくリチウムイオンを充放電に関与させ、長寿命かつ安全性の高いリチウム二次電池が得られた。本発明はこのような知見に基づくものである。
【００１０】
【発明の実施の形態】
本発明に係るリチウム二次電池用負極材に使用できる炭素材は、比表面積が　０．５〜４　ｍ^２／ｇ　、および　１０^１〜１０^５ｎｍ　の範囲の全細孔容積が　０．４〜２．０　ｍｌ／ｇ　、タップ密度が　０．５〜１．２　ｇ／ｃｍ^３で、その形状は、偏平状の粒子を複数配向面が非平行となるように集合または結合している黒鉛粒子を主成分とする。
この黒鉛粒子の比表面積は、　０．５〜４　ｍ^２／ｇ　、好ましくは　０．７〜１．５　ｍ^２／ｇ　である。比表面積がこの範囲であると、充放電効率を高く維持しながら、高密度に詰まった負極材を得ることができる。なお、比表面積は、ＢＥＴ法（窒素ガス吸着法）などの既知の方法で測定できる。
また、黒鉛粒子における、１０^１ｎｍ〜１０^５ｎｍ　の範囲の全細孔容積は　０．４〜２．０　ｍｌ／ｇ　、好ましくは　０．４〜１．０　ｍｌ／ｇ　である。全細孔容積がこの範囲にあると、サイクル寿命を維持してリチウム二次電池の容量の低下を防ぐことができる。なお、全細孔容積は水銀圧入法による細孔径分布測定により求めることができる。細孔の大きさもまた水銀圧入法による細孔径分布測定により知ることができる。
【００１１】
上記黒鉛粒子は、偏平状の粒子を複数配向面が非平行となるように集合または結合している形状を有する。扁平状の粒子とは、鱗状、鱗片状、球形でない塊状等、粒子の径に長軸径と短軸径を有するものをいい、この粒子の配向面が非平行とは、扁平した面、換言すれば最も平らに近い面が相互に同一方向を有することなく集合または結合していることをいう。
また、この黒鉛粒子における結合とは互いの粒子が、タール、ピッチ等のバインダーを炭素化した炭素質を介して、化学的に結合している状態をいい、集合とは互いの粒子が化学的に結合してはないが、その形状等に起因して、その集合体としての形状を保っている状態をいう。機械的な強度の面から、黒鉛粒子同士が結合しているものが好ましい。１つの黒鉛粒子において、扁平状の粒子の集合または結合する数としては、３　個以上であることが好ましい。個々の扁平状の粒子の大きさとしては、粒径で　１〜１００μｍ　であることが好ましく、これらが集合または結合した黒鉛粒子の平均粒径の　２／３　以下であることが好ましい。
【００１２】
各黒鉛粒子のＸ線広角回析における結晶の層間距離ｄ（００２）は０．３３８ｎｍ　以下が好ましく、０．３３５〜０．３３７ｎｍ　の範囲がより好ましい。結晶の層間距離ｄ（００２）が　０．３３８ｎｍ　をこえると放電容量が小さくなる傾向がある。
また、黒鉛粒子のタップ密度は　０．５〜１．２　ｇ／ｃｍ^３である。タップ密度の測定は、容量　１００ｃｍ^３のメスシリンダーを斜めにし、これに試料粉末　１００ｃｍ^３をさじを用いて徐々に投入し、メスシリンダーに栓をした後、メスシリンダーを　５ｃｍ　の高さから　５０　回落下させた後の試料粉末の重量および容積から算出できる。
【００１３】
上記特性を有する黒鉛粒子の市販品としては、リチウムイオン電池負極材ＭＡＧＤ、ＭＡＧＣまたはＭＡＧＢ（日立化成社製）が挙げられる。
【００１４】
本発明に使用できるメソフェーズ小球体炭素は、例えば常圧または減圧されたアルゴンガス、窒素ガスなどの不活性ガス雰囲気中にてメソフェーズピッチ等を２８００〜３０００℃で熱処理することで得られる炭素粒子である。このメソフェーズ小球体炭素粒子の粒子径は炭素材の主成分となる上記黒鉛粒子が集合または結合した隙間に充填できる粒子径であれば使用でき、具体的には　５〜３０　μｍ　、好ましくは　１０〜２０　μｍ　である。黒鉛粒子の隙間に充填することで炭素材の最密充填が可能となり、電池寿命が向上する。
メソフェーズ小球体炭素の市販品としては、大阪ガス社製ＭＣＭＢなどが挙げられる。
【００１５】
本発明に使用できる気相成長炭素繊維状黒鉛は、いわゆる基板成長法または流動気相法いずれの方法で製造されたものであってもよい。また、この気相成長炭素繊維状黒鉛を　２０００℃以上、好ましくは　２０００℃〜３０００℃の範囲に加熱処理することにより黒鉛化することにより得られる黒鉛化気相成長炭素繊維状黒鉛であってもよい。
気相成長炭素繊維状黒鉛のＤ_５０は　１４〜２１　μｍ　であることが好ましい。また、これら気相成長炭素繊維状黒鉛にホウ素を添加したものは、炭素層間距離を広げることができ、リチウムのインターカレートを助長させ、容量増加できるので好ましい。
気相成長炭素繊維状黒鉛の市販品としては、メルブロンミルドＦＭ６２（ＢＭＣＦ）、ＸＭ６６（ペトカマテリアルズ社製）等が挙げられる。
【００１６】
本発明に係るリチウム二次電池用負極材に使用できる黒鉛炭素材は、上述したＭＡＧＣのような黒鉛粒子とメソフェーズ小球体炭素との組み合わせ、上述したＭＡＧＣのような黒鉛粒子と気相成長炭素繊維状黒鉛との組み合わせ、または上述したＭＡＧＣのような黒鉛粒子とメソフェーズ小球体炭素と気相成長炭素繊維状黒鉛との組み合わせとすることができる。
黒鉛炭素材の配合割合は、主剤となる黒鉛粒子が　７０〜９０　重量％、配合材となるメソフェーズ小球体炭素および／または気相成長炭素繊維状黒鉛が　３０〜１０　重量％である。配合材が　３０　重量％をこえると充放電効率の低下や、材料そのものの放電能力が低いために高容量化に対して効果が小さくなり、逆に　１０　重量％未満であると充放電サイクル中にリチウムイオンが負極表面に集中して、金属リチウムの析出を助長させ電池寿命性能の劣化をきたす。また、配合材のより好ましい配合割合は　１０〜１５　重量％である。
【００１７】
リチウム二次電池用負極材は、活物質となる上記配合されたそれぞれの黒鉛粒と、結着剤と、分散溶媒とを混練してペースト状にし、集電体に塗布しシート状にすることで得られる。
結着剤としては、イオン伝導率の大きな高分子化合物等が使用できる。例えば、ポリフッ化ビニリデン、ポリテトラフルオロエチレン、ポリイミド、カルボニル化変性ポリフッ化ビニリデン、ポリアクリロニトリル、スチレンブタジエンゴム等が例示できる。結着剤の配合割合は炭素材　１００　重量部に対して、１〜２０　重量部用いることが好ましい。
用いる分散溶媒としては、炭素材と結着剤とをペースト状にできる溶媒であれば使用できる。好適な溶媒としては、Ｎ−メチル−２−ピロリドン、水等が挙げられる。
集電体としては、例えば銅の金属箔、金属メッシュなどの金属集電体が好適に使用できる。
【００１８】
本発明に係るリチウム二次電池用正極材に使用できるリチウム含有金属酸化物粒子は、リチウムを含有する金属酸化物粒子であれば特に制限なく使用できる。例えばＬｉＮｉＯ_２、ＬｉＣｏＯ_２、ＬｉＭｎ_２Ｏ_４等を単独または混合して、さらにはＮｉ、Ｃｏ、Ｍｎの複合金属酸化物を使用できる。
本発明に使用できるリチウム含有金属酸化物粒子は、粒径がＤ_５０で　７〜１２μｍ　の金属酸化物粒子と、粒径がＤ_５０で　４〜５μｍ　の金属酸化物粒子とを混合して使用する。上記範囲の粒径の異なるリチウム含有金属酸化物粒子を混合することにより、リチウム含有金属酸化物粒子の最密充填が可能となる。その結果、正極の活物質量が増加し、電極密度が増大する。
【００１９】
リチウム二次電池用正極材は、活物質となるリチウム含有金属酸化物粒子と、導電剤と、結着剤と、分散溶媒とを混練してペースト状にし、集電体に塗布しシート状にすることで得られる。
導電剤としては、黒鉛粉末、アセチレンブラック等の炭素材粉末などが挙げられる。結着剤、分散溶媒は負極材に用いたものを使用できる。集電体はアルミニウムの金属箔、金属メッシュなどを用いる。
【００２０】
本発明に係るリチウム二次電池は、上記負極材と上記正極材とを用いて、リチウム塩含有非水電解質を介して積層あるいは捲回されて得られる。
非水電解質の非水溶媒としては、エチレンカーボネート（ＥＣ）、プロピレンカーボネート（ＰＣ）、ジエチルカーボネート（ＤＥＣ）、ジメチルカーボネート（ＤＭＣ）、メチルエチルカーボネート（ＭＥＣ）等が挙げられる。
本発明は、特にビニレンカーボネートを上記非水溶媒に配合する。ビニレンカーボネートを配合することにより、効率よくリチウムイオンを充放電に関与させることができる。ビニレンカーボネートの配合割合は非水溶媒１００重量部に対して　０．５〜５　重量部、好ましくは　１〜３　重量部である。
【００２１】
非水溶媒に溶解できるリチウム塩としては、六フッ化燐酸リチウム（ＬｉＰＦ_６）、ホウ四フッ化リチウム（ＬｉＢＦ_４）、トリフルオロメタンスルホン酸リチウム（ＬｉＳＯ_３ＣＦ_４）等が挙げられる。リチウム塩の配合量としては非水溶媒１００　重量部に対して　０．６〜１．５　重量部、好ましくは　０．８〜１．２　重量部である。
【００２２】
【実施例】
実施例１
活物質として黒鉛粉末　９４．５　重量部に結着剤として　５．５　重量部のポリフッ化ビニリデンを添加し、これに分散溶媒としてＮ−メチル−２−ピロリドンを添加、混練したスラリを作製した。主剤の黒鉛粉末には比表面積が　０．５〜２　ｍ^２／ｇ　である黒鉛（ＭＡＧＣ、日立化成社製）を用いた。主剤の黒鉛粉末に対して、ホウ素添加の気相成長炭素繊維状黒鉛（ＢＭＣＦ、ペトカマテリアルズ社製）を　１０　重量％配合した。厚さ　１０μｍ　の圧延銅箔の両面に当該スラリを塗布・乾燥後、プレス、裁断することにより圧延銅箔を含む負極電極厚さ約　１３７μｍ　のリチウム二次電池用負極を得た。
【００２３】
実施例２
ホウ素添加の気相成長炭素繊維状黒鉛の代わりにメソフェーズ小球体炭素（ＭＣＭＢ、大阪ガス社製）を混合する以外は実施例１と同一の材料、方法でリチウム二次電池用負極を作製した。
【００２４】
実施例３
粒径がＤ_５０で　１０μｍ　のコバルト酸リチウム粒子と、粒径がＤ_５０で　５μｍ　のコバルト酸リチウム粒子との混合物を正極活物質とし、この活物質　９５．３　重量部に、導電剤　２．２　重量部と結着剤として　２．５　重量部のポリフッ化ビニリデンを添加し、これに分散溶媒としてＮ−メチル−２−ピロリドンを添加、混練した正極合剤（スラリ）を作製した。作製したスラリを厚さ　１５μｍ　の集電体としてのアルミニウム箔の両面に塗布、乾燥し、その後、プレス、裁断してアルミニウム箔を含む正極電極厚さ約　１４０μｍ　のリチウム二次電池用正極を得た。
【００２５】
実施例４
実施例１で得られたリチウム二次電池用負極と、粒径がＤ_５０で　１０μｍ　のコバルト酸リチウム粒子を用いる以外は実施例３と同一の材料、方法で得られたリチウム二次電池用正極を用いてリチウム二次電池を作製した。
上記のリチウム二次電池用正負極を、厚さ　１６〜２０μｍ　のポリエチレン製セパレータを介し捲回して電極群とし、この電極群を円筒形の電池容器に挿入、電解液を所定量注入後、上蓋をカシメ封口することにより円筒形リチウムイオン二次電池を得た。電解液にはＥＣ、ＤＭＣ、ＤＥＣを体積比で　２５：５０：１５　に混合した溶液中に６フッ化リン酸リチウム（ＬｉＰＦ_６）を　１　モル／リットル溶解し、さらにその溶液にビニレンカーボネートを電解液の　１　重量％混合したものを用いた。この電池の設計容量は　２２００　ｍＡｈである。
【００２６】
実施例５
実施例１の黒鉛粉末　９４．５　重量部に結着剤として　５．５　重量部のポリフッ化ビニリデンを添加するのは同一であるが、主剤の黒鉛（ＭＡＧＣ、日立化成社製）８５　重量部に、メソフェーズ小球体炭素（ＭＣＭＢ、大阪ガス社製）を　７．５　重量部、ホウ素添加の気相成長炭素繊維状黒鉛（ＢＭＣＦ、ペトカマテリアルズ社製）を　７．５　重量部混合して得られたリチウム二次電池用負極と、実施例３で得られたリチウム二次電池用正極を用いる以外は実施例４と同一の材料、方法で円筒形のリチウム二次電池を得た。この電池の設計容量は　２４００　ｍＡｈである。
【００２７】
比較例１
負極材料に比表面積が　０．５〜２　ｍ^２／ｇ　以外の通常市販されている人造黒鉛を用いた以外は実施例４と同様にして円筒形のリチウムイオン電池を得た。この電池の設計容量は　１８００　ｍＡｈである。
【００２８】
比較例２
実施例４の電解液にビニレンカーボネートを混合しない以外は上記比較例１と同様にして円筒形のリチウムイオン電池を得た。この電池の設計容量は　１８００　ｍＡｈである。
【００２９】
実施例４、５および比較例１、２で得られたリチウム二次電池の充放電試験を実施し、容量、サイクル寿命性能および安全性評価を比較した。
容量試験の測定では、４．２Ｖ　充電状態の電池を、それぞれ１時間率（１Ｃ）にて終止電圧である　２．７５Ｖ　まで放電し、電流値と時間との積にて求めた。結果を表１に示す。
【表１】

表１の結果より、実施例５は正極のコバルト酸リチウムの粒子が最密充填されて正極の電極密度が　３．７４ｇ／ｃｍ^３から　３．７７ｇ／ｃｍ^３に増大し、結果正極の活物質量が増加したためであると結論づけられる。一方比較例１および２に対して実施例４の容量が増加したのは負極の黒鉛を一般的に用いられる人造黒鉛の電極密度を増加したことに加えて比表面積が　０．５〜２　ｍ^２／ｇ　である炭素材にメソフェーズ小球体炭素材または気相成長炭素繊維状黒鉛を混合した材料を用いたことによる。これはＭＡＧＣのような黒鉛で比表面積を通常の人造黒鉛の　３　ｍ^２／ｇ　よりも小さくすることにより初充電量に対する初回の放電量割合（充放電効率）が増加し、結果容量が増大したものである。また、さらに当該充放電効率を増加させる目的でリチウムイオンのインターカレーションを効率よく行なわせるようにメソフェーズ小球体炭素材またはホウ素添加の気相成長炭素繊維状黒鉛を混合した材料を用いた。これらによりリチウムイオンが黒鉛エッジ部でＬｉＦやＬｉ_２ＣＯ_３の化合物に変化せずリチウムイオンとして黒鉛層のステージに挿入した結果容量を発現したものと考えられる。
【００３０】
サイクル寿命試験では、２５℃±２℃の雰囲気温度にて、１時間率（１Ｃ）、上限電圧　４．２Ｖ　で定電流定電圧充電し、１時間率（１Ｃ）で終止電圧　２．７５Ｖ　まで放電するサイクルを繰り返した。結果を図１に示す。
図１より、比較例２＜比較例１＜実施例４≒実施例５の順序で（ただし、容量は実施例５の方が大きい。）容量低下率が改善されていることがわかる。これは、まず比較例１と２では電解液にビニレンカーボネートを添加したことにより黒鉛表面部に初充電時、リチウムイオン伝導性の高分子被膜を生成し（学術的にはＳＥＩと呼ばれる被膜）、サイクル寿命中の充電時にリチウムイオンがＬｉＦやＬｉ_２ＣＯ_３の化合物を生成したり、金属リチウムを生成したり、または電解液中のエチレンカーボネートが分解してＣＯ_２や水、エチレンガスに変化することを防止して効率よくリチウムイオンを充放電に関与させることができたためである。
【００３１】
さらには実施例４および５が比較例２に比べて寿命特性が向上したのは、比表面積が　０．５〜２　ｍ^２／ｇ　である黒鉛材は充放電効率は高くなるが、充放電サイクルに対しては特に充電中に比表面積の小ささからリチウムイオンが黒鉛表面に集中して、場合によっては金属リチウムが生成し結果、正極から放出されたリチウムが充放電に関与できない状態になる。そこでメソフェーズ小球体炭素材またはホウ素添加の気相成長炭素繊維状黒鉛を混合した炭素材料を用いたことによって主剤である比表面積の小さい黒鉛の表面に集中したリチウムイオンを素早くメソフェーズ小球体や気相成長炭素繊維状黒鉛の炭素材の中に取り込んだために金属リチウムの生成を防止し、寿命性能が向上したものと考えられる。中でも気相成長炭素繊維状黒鉛炭素材にホウ素を添加したものは、炭素層間距離を広げたためにリチウムのインターカレートを助長させてさらに金属リチウムの生成を防止できた。このことは、充放電中の電池を解体して負極電極の表面を観察した結果、実施例４，５と比較例１，２で金属リチウムの生成状態からも顕著に違いを実証できた。
【００３２】
つぎに各電池を各種安全性試験に供して、安全性の確認を行なった。結果を表２に示す。
安全性試験は、リチウム二次電池を完全充電または完全放電の状態にして、試験温度、判定基準、試験個数を表２に示す条件で行なった。なお、安全性試験の各試験項目の試験方法はＵＬ規格（ＵＬ１６４２、ＵＬ２０５４）に準拠した。
【００３３】
【表２】

表２に示すように、比較例２＜比較例１＜実施例４≒実施例５の順序で（ただし、容量は実施例５の方が大きい。）安全性が確保されることがわかった。この理由は、上記サイクル寿命試験の結果において考察したように、ビニレンカーボネートによるＳＥＩの生成やリチウムイオンのメソフェーズ小球体やホウ素添加の気相成長炭素繊維状黒鉛材への取り込みにより金属リチウムの生成を防止して過充電試験や圧壊、衝突試験で安全性が確保されたものと考えられる。
【００３４】
【発明の効果】
本発明のリチウム二次電池用負極材は、比表面積が　０．５〜２　ｍ^２／ｇ　、１０^１〜１０^５ｎｍ　の範囲の全細孔容積が　０．４〜２．０　ｍｌ／ｇ　、タップ密度が　０．５〜１．２　ｇ／ｃｍ^３の偏平状の粒子を複数配向面が非平行となるように集合または結合してなる形状を有してなる主剤黒鉛粒子と、メソフェーズ小球体炭素および気相成長炭素繊維状黒鉛から選ばれた少なくとも一つの配合材黒鉛とが配合されてなる炭素材を用いるので、また、黒鉛粒子が　７０〜９０　重量％、配合材黒鉛が　３０〜１０　重量％配合されてなるので、充放電中に負極電極上でのＬｉＦ、Ｌｉ_２ＣＯ_３の化合物を生成したり、金属リチウムを生成したりする現象を抑える。その結果、高容量で長寿命かつ高安全性なリチウムイオン電池製造が可能になる。
【００３５】
本発明のリチウム二次電池用正極材は、粒径がＤ_５０で　７〜１２μｍ　の金属酸化物粒子と、粒径がＤ_５０で　４〜５μｍ　の金属酸化物粒子とを混合したリチウム含有金属酸化物粒子であるので、金属酸化物粒子の最密充填が可能となる。その結果、正極の活物質量が増加するため、高容量のリチウムイオン電池製造が可能になる。
【００３６】
本発明のリチウム二次電池は、上記負極材および／または正極材を用いるので、また、これら電極材とともに、電解液にビニレンカーボネートが配合されたリチウム塩含有非水電解質を用いるので、充放電中に負極電極上でのＬｉＦ、Ｌｉ_２ＣＯ_３の化合物を生成したり、金属リチウムを生成したり、または電解液中のエチレンカーボネートが分解してＣＯ_２や水、エチレンガスに変化することを防止して効率よくリチウムイオンを充放電に関与させることができ、結果、高容量で長寿命かつ高安全性なリチウム二次電池が得られる。
【図面の簡単な説明】
【図１】サイクル寿命試験結果を示す図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a negative electrode and a positive electrode for a lithium secondary battery, and a lithium secondary battery using the negative electrode and the positive electrode.
[0002]
[Prior art]
Lithium secondary batteries with a negative electrode material layer made of a carbon material capable of occluding and releasing lithium ions reduce the precipitation of dentite compared to lithium secondary batteries with a negative electrode material layer made of metallic lithium can do. Therefore, there is an advantage that a high-capacity battery can be provided while preventing a short circuit of the battery and improving safety.
In recent years, the capacity of this lithium ion battery has been required to increase, and the capacity of the cathode composite metal lithium oxide and the anode carbon material itself, which are battery reactants, the electrode area has increased due to battery design, and the separator has been made thinner. Some measures have been taken, such as an increase in the amount of reactants.
[0003]
For example, as the negative electrode carbon material having an aspect ratio of 5 or less and a specific surface area of 10 m ² / g or ^less, 10 1 ^{to 10} at 5 nm total pore volume of 0.4 to 2.0 ml / g in the range of, flat Graphite particles having a shape formed by assembling or bonding particles having a plurality of non-parallel orientation planes are known (for example, see Patent Documents 1 to 4).
[0004]
[Patent Document 1]
JP-A-10-158005 (Claims)
[Patent Document 2]
JP-A-10-236808 (Claims)
[Patent Document 3]
JP-A-10-236809 (Claims)
[Patent Document 4]
JP 2001-089118 A (Claims)
[0005]
[Problems to be solved by the invention]
However, when the graphite particles are used as the negative electrode carbon material, a high capacity can be achieved, but there is a problem that the battery life performance and safety may be inferior. When lithium secondary batteries are widely used in general consumer applications such as mobile phones and notebook computers, battery life performance and safety are particularly important battery characteristics.
The present invention has been made to address such a problem, and has achieved a high capacity, a long life and a high safety negative electrode for a lithium secondary battery, a positive electrode, and lithium using the negative electrode and the positive electrode. The purpose is to provide secondary batteries.
[0006]
[Means for Solving the Problems]
The negative electrode material for a lithium secondary battery according to the present invention is made of a carbon material capable of inserting and extracting lithium ions, and the carbon material has a specific surface area of 0.5 to 4 m ² / g and 10 ¹ to 10 ^5. A plurality of flat particles having a total pore volume of 0.4 to 2.0 ml / g and a tap density of 0.5 to 1.2 g / cm ³ in the range of nm are arranged so that a plurality of orientation planes are non-parallel. It is characterized in that graphite particles of a main agent having a shape formed by assembling or bonding are blended with at least one blending material graphite selected from mesophase small spherical carbon and vapor-grown carbon fibrous graphite.
Further, the carbon material is characterized in that 70 to 90% by weight of the graphite particles of the main agent and 30 to 10% by weight of the compounding material graphite are blended.
[0007]
Positive electrode material for lithium secondary battery according to the present invention comprises a lithium-containing metal oxide particles, the lithium-containing metal oxide particles, metal oxide particles of 7~12μm in particle size D _50, is the particle size It is characterized by being mixed with metal oxide particles having a D50 of 4 to ₅ μm.
[0008]
The lithium secondary battery according to the present invention is formed by laminating or winding a negative electrode material capable of inserting and extracting lithium ions and a positive electrode material via a lithium salt-containing nonaqueous electrolyte, and the negative electrode material according to the present invention. This is a negative electrode material for a lithium secondary battery, wherein the positive electrode material is the positive electrode material for a lithium secondary battery according to the present invention. That is, a lithium secondary battery using the negative electrode material for a lithium secondary battery according to the present invention, a lithium secondary battery using the positive electrode material for a lithium secondary battery according to the present invention, or the present invention A lithium secondary battery using the negative electrode material for a lithium secondary battery and the positive electrode material for a lithium secondary battery according to the present invention.
Further, vinylene carbonate is blended in the electrolyte of the lithium salt-containing nonaqueous electrolyte.
[0009]
Research into high-capacity, long-life, and high-safety lithium rechargeable batteries has progressed.As a result, the main agent has the specified physical properties and is formed by combining or combining flat particles with multiple orientation planes that are non-parallel. By using a negative electrode material blended with graphite particles and at least one blended material selected from mesophase small spherical carbon and vapor-grown carbon fibrous graphite, it is defined as a ratio of an initial discharge amount to an initial charge amount. It has been found that the charge / discharge efficiency increases and the carbon material can be packed at a high density to increase the capacity. In addition to the improvement in electron conductivity, the mesophase small spherical carbon and / or vapor-grown carbon fibrous graphite can be used quickly without changing lithium ions into LiF or Li ₂ CO ₃ compounds at the graphite edge. It was found that the capacity was increased because lithium ions were inserted into the graphite layer stage.
In addition, by using lithium-containing metal oxide particles having different particle diameters as the positive electrode material, close-packing became possible, the amount of active material of the positive electrode could be increased, and the capacity increased.
Furthermore, by blending vinylene carbonate with the non-aqueous electrolyte, the production of LiF, Li ₂ CO ₃ , lithium metal, etc. on the negative electrode generated during the initial charge / discharge is suppressed, or ethylene carbonate in the electrolyte is decomposed. Thus, conversion to CO ₂ , water, and ethylene gas was prevented, and lithium ions were efficiently involved in charging and discharging. As a result, a lithium secondary battery having a long life and high safety was obtained. The present invention is based on such findings.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Carbon material that can be used in the negative electrode material for lithium secondary battery according to the present invention has a specific surface area of the total pore volume in the range from 0.5 to 4 m ² / g, and 10 ¹ ~10 ⁵ nm 0.4~ 2.0 ml / g, tap density 0.5-1.2 g / cm ³ , and its shape is graphite particles that are flat particles aggregated or bonded so that multiple orientation planes are non-parallel. As a main component.
The specific surface area of the graphite particles is 0.5 to 4 m ² / g, preferably 0.7 to 1.5 m ² / g. When the specific surface area is within this range, it is possible to obtain a densely packed negative electrode material while maintaining high charge and discharge efficiency. The specific surface area can be measured by a known method such as a BET method (nitrogen gas adsorption method).
Further, in the graphite ^particles, the total pore volume in the range from 10 1 nm~10 ⁵ nm is 0.4 to 2.0 ml / g, preferably from 0.4 to 1.0 ml / g. When the total pore volume is in this range, the cycle life can be maintained and the capacity of the lithium secondary battery can be prevented from lowering. The total pore volume can be determined by measuring the pore size distribution by the mercury intrusion method. The size of the pores can also be determined by measuring the pore size distribution by the mercury intrusion method.
[0011]
The graphite particles have a shape in which flat particles are aggregated or bonded such that a plurality of orientation planes are non-parallel. Flat particles refers to those having a major axis diameter and a minor axis diameter relative to the particle diameter, such as scaly, squamous, non-spherical lump, and the like. In other words, it means that the surfaces that are almost flat are gathered or connected without having the same direction as each other.
Also, the bond in the graphite particles refers to a state in which the particles are chemically bonded to each other via carbonaceous material obtained by carbonizing a binder such as tar and pitch.Assembling means that the particles are chemically bonded to each other. , But a state in which the shape of the aggregate is maintained due to its shape and the like. From the viewpoint of mechanical strength, those in which graphite particles are bonded to each other are preferable. In one graphite particle, the number of flat particles aggregated or bonded is preferably 3 or more. The size of each flat particle is preferably 1 to 100 μm in particle size, and is preferably 2/3 or less of the average particle size of the aggregated or bonded graphite particles.
[0012]
The interlayer distance d (002) between crystals in the X-ray wide angle diffraction of each graphite particle is preferably 0.338 nm or less, more preferably in the range of 0.335 to 0.337 nm. When the interlayer distance d (002) of the crystal exceeds 0.338 nm, the discharge capacity tends to decrease.
The tap density of the graphite particles is 0.5 to 1.2 g / cm ³ . To measure the tap density, a graduated cylinder with a capacity of 100 cm ³ was slanted, and 100 cm ³ of sample powder was gradually poured into the graduated cylinder using a spoon. After the graduated cylinder was plugged, the graduated cylinder was dropped 50 times from a height of 5 cm. It can be calculated from the weight and volume of the sample powder after dropping.
[0013]
Commercially available graphite particles having the above characteristics include lithium ion battery negative electrode materials MAGD, MAGC and MAGB (manufactured by Hitachi Chemical Co., Ltd.).
[0014]
Mesophase small spherical carbon that can be used in the present invention is, for example, carbon particles obtained by heat-treating mesophase pitch or the like at 2800 to 3000 ° C. in an inert gas atmosphere such as argon gas or nitrogen gas at normal pressure or reduced pressure. is there. The particle size of the mesophase small sphere carbon particles can be used as long as the particle size can fill the gaps where the graphite particles as the main component of the carbon material are aggregated or bonded, and specifically 5 to 30 μm, preferably 10 to 10 μm. 20 μm. By filling the gaps between the graphite particles, the closest packing of the carbon material becomes possible, and the battery life is improved.
Commercial products of mesophase small spherical carbon include MCMB manufactured by Osaka Gas Co., Ltd.
[0015]
The vapor-grown carbon fibrous graphite that can be used in the present invention may be produced by any of the so-called substrate growth method and the fluidized gas-phase method. Graphite-grown vapor-grown carbon fibrous graphite obtained by heat-treating this vapor-grown carbon fibrous graphite to 2,000 ° C. or more, preferably in the range of 2,000 ° C. to 3000 ° C. Good.
Vapor _{D 50} carbon fibrous graphite is preferably 14 to 21 [mu] m. Further, those obtained by adding boron to these vapor-grown carbon fibrous graphites are preferable because the carbon interlayer distance can be increased, lithium intercalation can be promoted, and the capacity can be increased.
Commercial products of vapor-grown carbon fibrous graphite include Melbron Milled FM62 (BMCF) and XM66 (manufactured by Petka Materials).
[0016]
Graphite carbon materials that can be used for the negative electrode material for lithium secondary batteries according to the present invention include a combination of graphite particles such as the above-mentioned MAGC and mesophase small spherical carbon, and graphite particles such as the above-described MAGC and vapor-grown carbon fibers. Or a combination of graphite particles such as the above-mentioned MAGC, mesophase small spherical carbon, and vapor-grown carbon fibrous graphite.
The mixing ratio of the graphite carbon material is 70 to 90% by weight of the graphite particles as the main agent, and 30 to 10% by weight of the mesophase spheroidal carbon and / or the vapor grown carbon fibrous graphite as the compounding material. When the amount of the compounded material exceeds 30% by weight, the charge / discharge efficiency is reduced, and the effect of increasing the capacity is reduced due to the low discharge capacity of the material itself. Lithium ions are concentrated on the surface of the negative electrode, which promotes the deposition of metallic lithium, thereby deteriorating battery life performance. Further, a more preferable compounding ratio of the compounding material is 10 to 15% by weight.
[0017]
The negative electrode material for a lithium secondary battery is obtained by kneading the above-mixed graphite particles to be an active material, a binder, and a dispersion solvent to form a paste, and applying the mixture to a current collector to form a sheet. Is obtained.
As the binder, a polymer compound having a high ionic conductivity can be used. For example, polyvinylidene fluoride, polytetrafluoroethylene, polyimide, carbonylated modified polyvinylidene fluoride, polyacrylonitrile, styrene butadiene rubber and the like can be exemplified. The compounding ratio of the binder is preferably 1 to 20 parts by weight based on 100 parts by weight of the carbon material.
As a dispersion solvent to be used, any solvent can be used as long as the carbon material and the binder can be made into a paste. Suitable solvents include N-methyl-2-pyrrolidone, water and the like.
As the current collector, for example, a metal current collector such as a copper metal foil or a metal mesh can be suitably used.
[0018]
The lithium-containing metal oxide particles that can be used in the positive electrode material for a lithium secondary battery according to the present invention can be used without particular limitation as long as they are lithium-containing metal oxide particles. For example, LiNiO ₂ , LiCoO ₂ , LiMn ₂ O ₄ , or the like can be used alone or in combination, and a composite metal oxide of Ni, Co, and Mn can be used.
Lithium-containing metal oxide particles for use in the present invention, the particle size and the metal oxide particles of 7~12μm at D ₅₀ particle size is used by mixing the metal oxide particles 4~5μm at D ₅₀ . By mixing lithium-containing metal oxide particles having different particle diameters in the above range, close-packing of the lithium-containing metal oxide particles becomes possible. As a result, the amount of the active material of the positive electrode increases, and the electrode density increases.
[0019]
The positive electrode material for a lithium secondary battery is formed by kneading lithium-containing metal oxide particles serving as an active material, a conductive agent, a binder, and a dispersion solvent into a paste, applying the paste to a current collector, and forming a sheet. It is obtained by doing.
Examples of the conductive agent include a carbon material powder such as graphite powder and acetylene black. As the binder and the dispersion solvent, those used for the negative electrode material can be used. As the current collector, an aluminum metal foil, a metal mesh, or the like is used.
[0020]
The lithium secondary battery according to the present invention is obtained by laminating or winding the above negative electrode material and the above positive electrode material via a lithium salt-containing nonaqueous electrolyte.
Examples of the non-aqueous solvent of the non-aqueous electrolyte include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC).
In the present invention, particularly, vinylene carbonate is blended with the above non-aqueous solvent. By blending vinylene carbonate, lithium ions can be efficiently involved in charge and discharge. The mixing ratio of vinylene carbonate is 0.5 to 5 parts by weight, preferably 1 to 3 parts by weight, based on 100 parts by weight of the nonaqueous solvent.
[0021]
Examples of the lithium salt that can be dissolved in the non-aqueous solvent include lithium hexafluorophosphate (LiPF ₆ ), lithium borotetrafluoride (LiBF ₄ ), and lithium trifluoromethanesulfonate (LiSO ₃ CF ₄ ). The compounding amount of the lithium salt is 0.6 to 1.5 parts by weight, preferably 0.8 to 1.2 parts by weight, based on 100 parts by weight of the nonaqueous solvent.
[0022]
【Example】
Example 1
A slurry was prepared by adding 5.5 parts by weight of polyvinylidene fluoride as a binder to 94.5 parts by weight of graphite powder as an active material, adding N-methyl-2-pyrrolidone as a dispersion solvent thereto, and kneading the mixture. Graphite having a specific surface area of 0.5 to 2 m ² / g (MAGC, manufactured by Hitachi Chemical Co., Ltd.) was used as the graphite powder of the main agent. 10% by weight of boron-added vapor-grown carbon fibrous graphite (BMCF, manufactured by Petka Materials Co., Ltd.) was blended with the graphite powder as the main agent. The slurry was applied to both sides of a rolled copper foil having a thickness of 10 μm, dried, pressed and cut to obtain a negative electrode for a lithium secondary battery having a negative electrode thickness of about 137 μm including the rolled copper foil.
[0023]
Example 2
A negative electrode for a lithium secondary battery was produced using the same materials and method as in Example 1, except that mesophase microsphere carbon (MCMB, manufactured by Osaka Gas Co., Ltd.) was mixed instead of boron-added vapor-grown carbon fibrous graphite.
[0024]
Example 3
10μm lithium cobaltate particles in particle size _{D 50,} the particle size mixtures of 5μm of lithium cobalt oxide particles _{D 50} as the positive electrode active material, 95.3 parts by weight of the active material, conductive agent 2.2 A positive electrode mixture (slurry) was prepared by adding 2.5 parts by weight of polyvinylidene fluoride as a binder and 2.5 parts by weight of a binder and N-methyl-2-pyrrolidone as a dispersion solvent and kneading the mixture. The prepared slurry was applied to both sides of an aluminum foil as a current collector having a thickness of 15 μm, dried, and then pressed and cut to obtain a positive electrode for a lithium secondary battery having a thickness of about 140 μm including the aluminum foil. .
[0025]
Example 4
A negative electrode for a lithium secondary battery obtained in Example 1, the same material as in Example 3 except that the particle size used lithium cobalt oxide particles 10μm in D _50, the positive electrode for the obtained lithium secondary battery in a way Was used to produce a lithium secondary battery.
The positive and negative electrodes for a lithium secondary battery are wound around a polyethylene separator having a thickness of 16 to 20 μm to form an electrode group. The electrode group is inserted into a cylindrical battery container, and after a predetermined amount of electrolyte is injected, the top cover is removed. Was caulked to obtain a cylindrical lithium ion secondary battery. Lithium hexafluorophosphate (LiPF ₆ ) was dissolved at 1 mol / liter in a solution obtained by mixing EC, DMC, and DEC at a volume ratio of 25:50:15, and vinylene carbonate was further dissolved in the solution. A mixture of 1% by weight of the liquid was used. The design capacity of this battery is 2200 mAh.
[0026]
Example 5
The addition of 5.5 parts by weight of polyvinylidene fluoride as a binder to 94.5 parts by weight of the graphite powder of Example 1 was the same, but 85 parts by weight of graphite (MAGC, manufactured by Hitachi Chemical Co., Ltd.) as a main agent was added. 7.5 parts by weight of mesophase microsphere carbon (MCMB, manufactured by Osaka Gas Co., Ltd.) and 7.5 parts by weight of boron-added vapor-grown carbon fibrous graphite (BMCF, manufactured by Petka Materials Co., Ltd.) A cylindrical lithium secondary battery was obtained by the same materials and method as in Example 4 except that the obtained negative electrode for a lithium secondary battery and the positive electrode for a lithium secondary battery obtained in Example 3 were used. The design capacity of this battery is 2400 mAh.
[0027]
Comparative Example 1
A cylindrical lithium ion battery was obtained in the same manner as in Example 4 except that a commercially available artificial graphite having a specific surface area other than 0.5 to 2 m ² / g was used as the negative electrode material. The design capacity of this battery is 1800 mAh.
[0028]
Comparative Example 2
A cylindrical lithium ion battery was obtained in the same manner as in Comparative Example 1 except that vinylene carbonate was not mixed in the electrolyte of Example 4. The design capacity of this battery is 1800 mAh.
[0029]
Charge / discharge tests were performed on the lithium secondary batteries obtained in Examples 4 and 5 and Comparative Examples 1 and 2, and the capacity, cycle life performance and safety evaluation were compared.
In the measurement of the capacity test, the batteries in the 4.2 V charged state were each discharged at an hourly rate (1 C) to a final voltage of 2.75 V, and the battery was obtained by multiplying the current value by the time. Table 1 shows the results.
[Table 1]

From the results shown in Table 1, in Example 5, the lithium cobalt oxide particles of the positive electrode were closest packed, and the electrode density of the positive electrode increased from 3.74 g / cm ³ to 3.77 g / cm ^3, and as a result, the active material of the positive electrode It is concluded that the amount was increased. On the other hand, the capacity of Example 4 increased with respect to Comparative Examples 1 and 2 in addition to the increase in the electrode density of artificial graphite, which is generally used as graphite for the negative electrode, and the specific surface area of 0.5 to 2 m ^2. / G of a carbon material having a mixture of a mesophase small sphere carbon material or a vapor-grown carbon fibrous graphite. This is because the ratio of the initial discharge amount to the initial charge amount (charge / discharge efficiency) is increased by reducing the specific surface area of graphite such as MAGC to less than 3 m ² / g of ordinary artificial graphite, resulting in an increase in capacity. Things. Further, for the purpose of further increasing the charge / discharge efficiency, a material mixed with a mesophase small spherical carbon material or a boron-added vapor-grown carbon fibrous graphite was used so as to efficiently perform lithium ion intercalation. It is considered that, due to these, the lithium ions did not change into a compound of LiF or Li ₂ CO ₃ at the graphite edge portion, and the lithium ions were inserted into the stage of the graphite layer as a result of expressing the capacity.
[0030]
In the cycle life test, constant-current and constant-voltage charging was performed at an ambient temperature of 25 ° C. ± 2 ° C. at an hourly rate (1C) and an upper limit voltage of 4.2V, and discharged to a final voltage of 2.75V at an hourly rate (1C). The cycle was repeated. The results are shown in FIG.
From FIG. 1, it can be seen that the capacity reduction rate is improved in the order of Comparative Example 2 <Comparative Example 1 <Example 4 実施 Example 5 (however, the capacity is larger in Example 5). First, in Comparative Examples 1 and 2, a lithium ion conductive polymer film was formed on the graphite surface at the time of the first charge by adding vinylene carbonate to the electrolyte (a film called SEI academically). At the time of charging during the cycle life, lithium ions generate compounds of LiF or Li ₂ CO ₃ , generate metal lithium, or decompose ethylene carbonate in the electrolyte to change to CO ₂ , water, and ethylene gas. This is because lithium ions can be efficiently involved in charge and discharge by preventing the occurrence of such a phenomenon.
[0031]
Further, the life characteristics of Examples 4 and 5 were improved as compared with Comparative Example 2 because the graphite material having a specific surface area of 0.5 to 2 m ² / g had higher charge / discharge efficiency, but the charge / discharge cycle was higher. In particular, during charging, lithium ions concentrate on the graphite surface due to the small specific surface area, and in some cases, metallic lithium is generated. As a result, lithium released from the positive electrode cannot participate in charging and discharging. Therefore, by using mesophase spheroidal carbon material or carbon material mixed with boron-added vapor-grown carbon fibrous graphite, lithium ions concentrated on the surface of graphite with a small specific surface area, which is the main agent, can be quickly converted to mesophase spheroids and gas phase. It is considered that the incorporation of the grown carbon fibrous graphite into the carbon material prevented the formation of lithium metal and improved the life performance. Above all, in the case where boron was added to the vapor-grown carbon fibrous graphite carbon material, the intercalation of lithium was promoted because the distance between carbon layers was widened, thereby further preventing the generation of lithium metal. As a result of disassembling the battery during charging / discharging and observing the surface of the negative electrode, a remarkable difference was also demonstrated in Examples 4 and 5 and Comparative Examples 1 and 2 from the state of metal lithium generation.
[0032]
Next, each battery was subjected to various safety tests to confirm its safety. Table 2 shows the results.
The safety test was performed under the conditions shown in Table 2 in which the lithium secondary battery was fully charged or completely discharged, and the test temperature, the criterion, and the number of test pieces were shown. In addition, the test method of each test item of the safety test conformed to UL standard (UL1642, UL2054).
[0033]
[Table 2]

As shown in Table 2, it was found that safety was ensured in the order of Comparative Example 2 <Comparative Example 1 <Example 4 ≒ Example 5 (however, the capacity was larger in Example 5). The reason for this is that, as discussed in the results of the above cycle life test, the generation of metallic lithium is caused by the generation of SEI by vinylene carbonate and the incorporation of lithium ions into mesophase spheres or boron-added vapor-grown carbon fibrous graphite material. It is considered that the safety was secured by overcharge test, crushing and collision test.
[0034]
【The invention's effect】
The negative electrode material for lithium secondary battery of the present invention has a specific surface area of ^{^{0.5~2 m 2 / g, 10 1}} ~10 5 total pore volume of the nm range is 0.4 to 2.0 ml / g, Main graphite particles having a shape in which flat particles having a tap density of 0.5 to 1.2 g / cm ³ are aggregated or bonded so that a plurality of orientation planes are non-parallel, and mesophase small spheres Since a carbon material obtained by blending at least one blending material graphite selected from carbon and vapor-grown carbon fibrous graphite is used, the graphite particles are 70 to 90% by weight, and the blending material graphite is 30 to 10% by weight. %, It suppresses a phenomenon that a compound of LiF and Li ₂ CO ₃ is formed on the negative electrode during charge and discharge, and a phenomenon that metal lithium is formed. As a result, high-capacity, long-life and high-safety lithium-ion batteries can be manufactured.
[0035]
Positive electrode material for lithium secondary battery of the present invention, the metal oxide particles of 7~12μm in particle size D _50, the lithium-containing metal oxide having a particle size was mixed with the metal oxide particles 4~5μm at D ₅₀ Since it is an object particle, close packing of metal oxide particles is possible. As a result, the amount of the active material of the positive electrode increases, so that a high-capacity lithium-ion battery can be manufactured.
[0036]
Since the lithium secondary battery of the present invention uses the above-described negative electrode material and / or positive electrode material, and also uses a lithium salt-containing nonaqueous electrolyte in which vinylene carbonate is blended in the electrolytic solution together with these electrode materials, the lithium secondary battery is charged and discharged. Prevents the formation of LiF and Li ₂ CO ₃ compounds on the negative electrode, the formation of lithium metal, and the decomposition of ethylene carbonate in the electrolyte into CO ₂ , water and ethylene gas As a result, lithium ions can be efficiently involved in charge and discharge, and as a result, a high capacity, long life and high safety lithium secondary battery can be obtained.
[Brief description of the drawings]
FIG. 1 is a diagram showing a cycle life test result.

Claims

A negative electrode material for a lithium secondary battery comprising a carbon material capable of inserting and extracting lithium ions,
The carbon material has a specific surface area of ^{^{0.5~4 m 2 / g, 10 1}} ~10 5 total pore volume of the nm range is 0.4 to 2.0 ml / g, a tap density of 0.5 A main graphite particle having a shape formed by assembling or bonding 1.2 g / cm ³ flat particles so that a plurality of orientation planes are non-parallel, and mesophase small spherical carbon and vapor-grown carbon fibrous graphite. A negative electrode material for a lithium secondary battery, characterized by being mixed with at least one selected compounding material.

2. The negative electrode material for a lithium secondary battery according to claim 1, wherein the carbon material comprises {70 to 90% by weight} of the base graphite particles and {30 to 10% by weight} of the compounded graphite. 3.

A positive electrode material for a lithium secondary battery comprising lithium-containing metal oxide particles,
The lithium-containing metal oxide particles, a lithium secondary particle size, wherein the metal oxide particles of 7~12μm at D _50, that particle size by mixing a metal oxide particle 4~5μm at D ₅₀ Positive electrode material for secondary batteries.

A lithium secondary battery in which a negative electrode material and a positive electrode material capable of inserting and extracting lithium ions are laminated or wound via a lithium salt-containing nonaqueous electrolyte,
At least one electrode of the negative electrode material and the positive electrode material is the negative electrode material for a lithium secondary battery according to claim 1 or 2, and the positive electrode material for a lithium secondary battery according to claim 3. Rechargeable lithium battery.

5. The lithium ion secondary battery according to claim 4, wherein the electrolyte of the lithium salt-containing non-aqueous electrolyte contains vinylene carbonate.