JP3621031B2 - Anode for non-aqueous electrolyte secondary battery - Google Patents
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- JP3621031B2 JP3621031B2 JP2000267627A JP2000267627A JP3621031B2 JP 3621031 B2 JP3621031 B2 JP 3621031B2 JP 2000267627 A JP2000267627 A JP 2000267627A JP 2000267627 A JP2000267627 A JP 2000267627A JP 3621031 B2 JP3621031 B2 JP 3621031B2
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Description
【０００１】
【発明の属する技術分野】
本発明は、非水電解質二次電池用負極に関する。
【０００２】
【従来の技術】
近年、携帯用電子機器の電源として利用されている非水電解質電池は、正極にリチウム含有遷移金属酸化物を用い、負極にリチウムの吸蔵・放出が可能な炭素材料を用いているため、高出力で高エネルギー密度である。ここで、これらの電池が有する電極は、活物質同士を結合するための結着剤を含んでおり、負極には、結着剤としてポリビニリデンジフルオライド（ＰＶＤＦ）やスチレンブタジエンゴム（ＳＢＲ）などが用いられている。
【０００３】
しかし、これらの結着剤を用いた場合、負極に充分な強度を付与し、かつ、充放電反応に寄与する活物質の表面積を充分に確保することは困難である。このことは、高率放電特性、低温特性、サイクル寿命等のバランスのよい電池を得る妨げとなっている。また、充放電反応に寄与する活物質の表面積が小さくなって活物質がＬｉを充分に吸蔵できなくなると、活物質表面に金属Ｌｉの析出が起こり、電池の安全性が損なわれる。
【０００４】
【発明が解決しようとする課題】
本発明は、負極に含まれる結着剤の量と負極に含まれる活物質が有する総表面積との関係を制御しつつ、結着剤として粒子状変性スチレンブタジエンゴムを用いることにより、効果的に負極の強度および充放電反応に寄与する活物質の表面積を確保することを目的とする。
【０００５】
【課題を解決するための手段】
本発明は、活物質として炭素材料を含み、結着剤として粒子状変性スチレンブタジエンゴムを含む非水電解質二次電池用負極であって、前記炭素材料の比表面積は、２〜５ｍ 2 ／ｇであり、前記粒子状変性スチレンブタジエンゴムの量は、前記炭素材料１００重量部に対して、０．６〜１．７重量部であり、前記粒子状変性スチレンブタジエンゴムは、コアシェル型粒子からなり、前記コアシェル型粒子は、コア部にアクリロニトリル単位を含み、前記負極が含有する前記炭素材料の表面積が、前記粒子状変性スチレンブタジエンゴム１ｇあたり３００〜６００ｍ2である非水電解質二次電池用負極に関する。
【０００６】
前記粒子状変性スチレンブタジエンゴムのＦＴ−ＩＲ測定で得られる吸収スペクトルにおいて、アクリロニトリル単位のＣ≡Ｎ伸縮振動に基づく吸収強度は、ブタジエン単位のＣ＝Ｃ伸縮振動に基づく吸収強度の０．１〜２倍であることが好ましい。
ここで、吸収強度とは、スペクトルのベースラインからみた吸収ピークの高さをいう。
【０００７】
前記粒子状変性スチレンブタジエンゴムの平均粒径の好適範囲は、０．０５〜０．４μｍである。
前記負極は、前記炭素材料１００重量部あたり、０．７〜１．２重量部の増粘剤を含んでいることが好ましい。
前記増粘剤は、カルボキシメチルセルロース（ＣＭＣ）であることが好ましい。
前記負極に含まれる前記粒子状変性スチレンブタジエンゴムおよび前記増粘剤の合計量は、前記炭素材料１００重量部あたり、合計１．３〜２．４重量部であることが好ましい。
【０００８】
【発明の実施の形態】
本発明の負極は、負極合剤と芯材（集電体）とからなり、例えば負極合剤を芯材の表面に塗着または芯材が有する細孔に充填し、圧延し、切断することで得られる。芯材としては、銅箔などの金属箔やパンチングメタルなどが用いられる。電池の小型軽量化の観点から、芯材の厚さは一般に８〜２０μｍ程度であり、負極の厚さは一般に８０〜２００μｍである。負極合剤は、負極活物質、結着剤としての粒子状変性スチレンブタジエンゴム、増粘剤などを所定の割合で配合して調製される。
【０００９】
負極活物質としては、黒鉛粉末などの炭素材料が用いられる。なかでも塊状人造黒鉛、鱗片状黒鉛、球状人造黒鉛などが好ましく用いられる。黒鉛粉末の平均粒径は、例えば２０〜３０μｍである。
【００１０】
粒子状変性スチレンブタジエンゴムは、アクリロニトリル単位、スチレン単位およびブタジエン単位を含む共重合体からなり、ゴム弾性を有するコア部分を有するコアシェル型粒子である。コア部分は、例えばアクリロニトリル単位、スチレン単位、ブタジエン単位、アクリレート単位などを含む共重合体を適当な架橋剤で架橋させたものが好ましい。また、シェル部分は、粘性の高い重合体であればよく、例えばアクリレート単位、スチレン単位などを含む共重合体が好ましい。
【００１１】
コアシェル型粒子は、例えば架橋剤を含むコア部分の原料モノマー混合物を重合させてラテックスを製造した後、ラテックス粒子にシェル部分の原料モノマー混合物をグラフト重合させる二段階の工程によって製造できる。このときコア部分の原料モノマーにアクリロニトリルを含有させると、弾性率の高いコア部分を得ることができる。
【００１２】
前記粒子状変性スチレンブタジエンゴムは、そのＦＴ−ＩＲ測定で得られる吸収スペクトルにおいて、アクリロニトリル単位のＣ≡Ｎ伸縮振動に基づく吸収強度が、ブタジエン単位のＣ＝Ｃ伸縮振動に基づく吸収強度の０．１〜２倍となる程度にアクリロニトリル単位とブタジエン単位を含んでいることが好ましい。アクリロニトリル単位のＣ≡Ｎ伸縮振動に基づく吸収強度が、ブタジエン単位のＣ＝Ｃ伸縮振動に基づく吸収強度の０．１倍未満になると、粒子状変性スチレンブタジエンゴムを用いても充分な強度の負極が得られなくなったり、活物質の表面が結着剤で覆われすぎたりする。一方、アクリロニトリル単位のＣ≡Ｎ伸縮振動に基づく吸収強度が、ブタジエン単位のＣ＝Ｃ伸縮振動に基づく吸収強度の２倍をこえると、粒子状変性スチレンブタジエンゴムのゴム弾性が低下し、芯材から合剤が剥離しやすくなる。
【００１３】
粒子状変性スチレンブタジエンゴムの平均粒径は、少量の使用で充分な強度の負極を得ることができることなどから、０．０５〜０．４μｍであることが好ましい。平均粒径が小さすぎると、活物質の表面の大部分が粒子状変性スチレンブタジエンゴムで被覆されてしまい、大きすぎると、活物質粒子間の距離が大きくなって負極内部の導電性が低下する。
【００１４】
負極合剤における粒子状変性スチレンブタジエンゴムの配合量は、負極活物質である炭素材料１００重量部に対して、０．６〜１．７重量部が適量である。粒子状変性スチレンブタジエンゴムの量が少なすぎると、充分な強度の負極が得られず、芯材から合剤が剥がれたりすることがあり、多すぎると、活物質の反応表面積が小さくなって高率放電特性がわるくなる。
なお、従来のＰＶＤＦの場合、負極合剤における好適配合量は、負極活物質１００重量部に対して、５〜１０重量部であり、ＳＢＲの場合でも２〜５重量部である。従って、本発明の負極は、結着剤の含有量が従来に比べて著しく低減されている。
【００１５】
負極が含有する炭素材料の表面積は、負極が含有する粒子状変性スチレンブタジエンゴム１ｇあたり３００〜６００ｍ２である必要がある。負極が含有する粒子状変性スチレンブタジエンゴム１ｇあたりの炭素材料の表面積が３００ｍ２未満になると、余剰の結着剤が活物質を被覆して電池の充電特性が低下するため、サイクル寿命が短くなってしまう。また、負極が含有する粒子状変性スチレンブタジエンゴム１ｇあたりの炭素材料の表面積が６００ｍ２をこえると、結着剤の不足により合剤層と芯材との密着性が低下する。また、炭素材料の比表面積は、２〜５ｍ２／ｇであることが好ましい。
【００１６】
負極合剤に用いる増粘剤としては、ＣＭＣなどのセルロース系増粘剤がよく用いられる。負極合剤における増粘剤の配合量は、負極活物質である炭素材料１００重量部に対して、０．７〜１．２重量部が適量である。増粘剤の配合量が少なすぎると、ペースト状の負極合剤が得られず、芯材から合剤が剥がれやすくなり、多すぎると、活物質が増粘剤で覆われてしまい、その反応表面積が小さくなる。
【００１７】
ただし、粒子状変性スチレンブタジエンゴムおよび増粘剤の合計量は、負極活物質である炭素材料１００重量部に対して、１．３〜２．４重量部である必要がある。前記合計量が１．３重量部未満になると、活物質粒子同士を充分に結着させることができず、負極の強度が不充分となり、多すぎると、活物質が粒子状変性スチレンブタジエンゴムや増粘剤で覆われてしまい、その反応表面積が小さくなる。
【００１８】
ＦＴ−ＩＲ測定において、粒子状変性スチレンブタジエンゴムの吸収スペクトルは、例えば粒子状変性スチレンブタジエンゴムをＫＢｒ板上に塗布したものを用いて測定すればよい。ここで、一般にブタジエン単位のＣ＝Ｃ伸縮振動に基づく吸収は、８８０〜９４０ｃｍ−１付近に見られ、アクリロニトリル単位のＣ≡Ｎ伸縮振動に基づく吸収は、２２００〜２２８０ｃｍ−１付近に見られる。
【００１９】
【実施例】
次に、本発明を実施例に基づいて具体的に説明する。ただし、本発明はこれらに限定されるものではない。
【００２０】
《実施例１〜５および比較例１〜８》
電池Ａ〜Ｍを以下に示すように作製し、その特性を評価した。
【００２１】
（ｉ）負極の作製
表１に示す性状の人造黒鉛を活物質として用い、表１に示す結着剤を用いて、各電池の負極に用いる負極合剤を調製した。活物質である人造黒鉛の比表面積、負極合剤における活物質１００重量部に対する結着剤の配合量、および合剤に含まれる活物質の総表面積を結着剤の配合量で割った値を表１に示す。ただし、結着剤としてＰＶＤＦを用いた場合以外は、活物質１００重量部あたり１．３重量部のＣＭＣを増粘剤として用いた。
【００２２】
【表１】
表１に示す結着剤について以下に説明する。
ＢＭ４００Ｂ：日本ゼオン（株）製のアクリロニトリル単位、スチレン単位およびブタジエン単位を含む共重合体からなる粒子状変性スチレンブタジエンゴム。平均粒径０．２μｍ。そのＦＴ−ＩＲ測定で得られる吸収スペクトルにおいて、アクリロニトリル単位のＣ≡Ｎ伸縮振動に基づく吸収強度は、ブタジエン単位のＣ＝Ｃ伸縮振動に基づく吸収強度の０．４倍である。その吸収スペクトルを図１に示す。
【００２４】
図１中、２２３７ｃｍ−１付近に見られる吸収ピークがアクリロニトリル単位のＣ≡Ｎ伸縮振動に基づくものであり、９１１ｃｍ−１付近に見られる吸収ピークがブタジエン単位のＣ＝Ｃ伸縮振動に基づくものである。
【００２５】
測定条件は、サンプルスキャン回数３２、バックグラウンドスキャン回数３２、分解能４０００、サンプルゲイン１．０であり、測定装置は、顕微ＦＴ−ＩＲ（Ｃｏｎｔｉｎｕμｍ（ニコレー社製）、光源：ＡＶＡＴＡＲ−３６０）を用いた。また、測定用の試料は、粒子状変性スチレンブタジエンゴムをＮ−メチルピロリドンに溶かしたものをＫＢｒ板上に塗布し、乾燥したものを用いた。
【００２６】
ＰＶＤＦ：ポリビニリデンジフルオライド。
ＳＢＲ：スチレンブタジエンゴム。
ＭＰＥ：変性ポリエチレン樹脂。
【００２７】
比較のためにＳＢＲのＦＴ−ＩＲ測定で得られる透過スペクトルを図２に示す。測定条件、測定装置等は図１の場合と同様である。図２中には、２２３７ｃｍ−１付近にアクリロニトリル単位のＣ≡Ｎ伸縮振動に基づく吸収ピークが見られない。
【００２８】
得られた負極合剤を、厚さ１５μｍの銅箔の芯材の両面に塗布し、厚さ１４０μｍに圧延し、所定の長さに切断し、負極を得た。負極には芯材と同材質の負極リードを接続した。
【００２９】
（ｉｉ）正極の作製
１００重量部のＬｉＣｏＯ２に対し、結着剤としてＰＶＤＦを４重量部および導電剤としてアセチレンブラック３重量部を配合し、正極合剤を得た。次いで、得られた正極合剤を、厚さ２０μｍのアルミニウム箔の芯材の両面に塗布し、所定の厚さに圧延し、所定の長さに切断し、正極を得た。正極には芯材と同材質の正極リードを接続した。
【００３０】
（ｉｉｉ）電池の作製
得られた正極および負極は、両者の間にセパレータを介在させて積層し、捲回して極板群を得た。セパレータとしては、厚さ２７μｍのポリエチレン製微多孔膜を用いた。捲回された極板群は、断面が略楕円形になるように一方向から圧縮した。
【００３１】
一方、非水溶媒である等体積のエチレンカーボネートとエチルメチルカーボネートとの混合物に、塩濃度１．０モル／リットルになるように、ＬｉＰＦ６を溶解した非水電解質を調製した。
【００３２】
前記極板群は、絶縁リングをその上部および底部に配して所定のアルミニウム製ケース内に３．２ｇの非水電解質とともに収容した。そして、負極リードおよび正極リードを所定の箇所に接続したのち、ケースの開口部を封口板で封口し、非水電解質電池Ａ〜Ｍを完成した。これらの電池は、幅３０ｍｍ、高さ４８ｍｍ、厚さ５ｍｍの角形であり、電池の公称容量は６００ｍＡｈである。
【００３３】
次に、得られた非水電解質電池の評価内容について説明する。
（ｉ）低温特性および容量回復率
電池Ａ〜Ｍについて、２０℃雰囲気下において、６００ｍＡで電池電圧が４．２Ｖになるまで充電し、１２０ｍＡで電池電圧が３Ｖになるまで放電した。次いで、０℃雰囲気下において、６００ｍＡで電池電圧が４．２Ｖになるまで充電し、６００ｍＡで電池電圧が３Ｖになるまで放電した。そして再び２０℃雰囲気下において、６００ｍＡで電池電圧が４．２Ｖになるまで充電し、１２０ｍＡで電池電圧が３Ｖになるまで放電した。
【００３４】
ここで、０℃雰囲気下において、６００ｍＡで電池電圧が４．２Ｖになるまで充電したときの充電容量を低温特性の指標として表１に示す。また、２０℃雰囲気下における１回目の充電で得られた容量および２０℃雰囲気下における２回目の充電で得られた容量を求め、後者の前者に対する比を求めた。結果を容量回復率として１００分率で表１に示す。
【００３５】
（ｉｉ）異常昇温の有無
容量回復率を調べた後の電池を２０℃で１２６０ｍＡで電池表面温度が８０℃になるまで充電した。そして、しばらく放置し、電池の表面温度の推移を確認した。その際、表面温度が９０℃以上になったものは有、それ以外は無とした。結果を表１に示す。
【００３６】
（ｉｉｉ）容量維持率
電池Ａ〜Ｍについて、６００ｍＡで電池電圧が４．２Ｖになるまで充電し、６００ｍＡで電池電圧が３Ｖになるまで放電する操作を２００回繰り返した。そして、一回目の放電容量に対する２００回目の放電容量の比を求めた。結果を１００分率で表１に示す。
【００３７】
表１の結果から、以下のことがわかる。
負極が含有する粒子状変性スチレンブタジエンゴム１ｇあたりの炭素材料の表面積が９００ｍ２になると芯材から合剤が剥離していることから、負極が含有する粒子状変性スチレンブタジエンゴム１ｇあたりの炭素材料の表面積が６００ｍ２をこえると、負極の強度が弱くなることがわかる。
【００３８】
負極が含有する粒子状変性スチレンブタジエンゴム１ｇあたりの炭素材料の表面積が２２５ｍ２になると、加熱試験で異常昇温が見られることから、負極が含有する粒子状変性スチレンブタジエンゴム１ｇあたりの炭素材料の表面積が３００ｍ２未満になると、電池の安全性が損なわれる可能性があることがわかる。これは、負極活物質にＬｉが吸蔵されにくくなり、活物質の表面に金属Ｌｉが析出するためと考えられる。また、この現象は、分極の大きい低温充電時に起こりやすいと考えられる。
【００３９】
低温特性の観点からは、負極が含有する粒子状変性スチレンブタジエンゴム１ｇあたりの炭素材料の表面積の最も好適な範囲は４５０〜６００ｍ２であることがわかる。
【００４０】
粒子状変性スチレンブタジエンゴム以外の結着剤を用いた場合、サイクル寿命が著しく低くなることがわかる。
【００４１】
【発明の効果】
本発明によれば、効果的に負極の強度および充放電反応に寄与する活物質の表面積を確保することができる。従って、本発明の負極を用いれば、高率放電特性、低温特性、サイクル寿命等のバランスがよく、安全性の高い非水電解質二次電池を得ることが可能になる。
【図面の簡単な説明】
【図１】粒子状変性スチレンブタジエンゴムのＦＴ−ＩＲ測定で得られた吸収スペクトルの一例である。
【図２】ＳＢＲのＦＴ−ＩＲ測定で得られた透過スペクトルの一例である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a negative electrode for a nonaqueous electrolyte secondary battery.
[0002]
[Prior art]
In recent years, non-aqueous electrolyte batteries used as power sources for portable electronic devices use a lithium-containing transition metal oxide for the positive electrode and a carbon material capable of occluding and releasing lithium for the negative electrode. High energy density. Here, the electrodes of these batteries include a binder for bonding active materials, and the negative electrode includes polyvinylidene difluoride (PVDF) or styrene butadiene rubber (SBR) as a binder. Etc. are used.
[0003]
However, when these binders are used, it is difficult to secure sufficient surface area of the active material that imparts sufficient strength to the negative electrode and contributes to the charge / discharge reaction. This hinders obtaining a battery having a good balance of high rate discharge characteristics, low temperature characteristics, cycle life, and the like. Further, when the surface area of the active material contributing to the charge / discharge reaction is reduced and the active material cannot sufficiently absorb Li, metal Li is deposited on the active material surface, and the safety of the battery is impaired.
[0004]
[Problems to be solved by the invention]
The present invention effectively uses the particulate modified styrene butadiene rubber as the binder while controlling the relationship between the amount of the binder contained in the negative electrode and the total surface area of the active material contained in the negative electrode. It aims at ensuring the surface area of the active material which contributes to the intensity | strength of a negative electrode, and charging / discharging reaction.
[0005]
[Means for Solving the Problems]
The present invention is a negative electrode for a non-aqueous electrolyte secondary battery including a carbon material as an active material and a particulate modified styrene butadiene rubber as a binder , and the specific surface area of the carbon material is 2 to 5 m 2 / g. The amount of the particulate modified styrene butadiene rubber is 0.6 to 1.7 parts by weight with respect to 100 parts by weight of the carbon material, and the particulate modified styrene butadiene rubber is composed of core-shell type particles. The core-shell type particle includes an acrylonitrile unit in the core portion, and the surface area of the carbon material contained in the negative electrode is 300 to 600 m 2 per 1 g of the particulate modified styrene butadiene rubber. About.
[0006]
In the absorption spectrum obtained in the previous SL FT-IR measurement of particulate modified styrene-butadiene rubber, the absorption intensity based on C≡N stretching vibration of acrylonitrile units, 0.1 of the absorption intensity based on C = C stretching vibration of the butadiene units It is preferable that it is -2 times.
Here, the absorption intensity refers to the height of the absorption peak viewed from the baseline of the spectrum.
[0007]
The suitable range of the average particle diameter of the particulate modified styrene butadiene rubber is 0.05 to 0.4 μm .
The negative electrode preferably contains 0.7 to 1.2 parts by weight of a thickener per 100 parts by weight of the carbon material.
The thickener is preferably carboxymethylcellulose (CMC).
The total amount of the particulate modified styrene butadiene rubber and the thickener contained in the negative electrode is preferably 1.3 to 2.4 parts by weight per 100 parts by weight of the carbon material.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The negative electrode of the present invention comprises a negative electrode mixture and a core material (current collector). For example, the negative electrode mixture is applied to the surface of the core material or filled into pores of the core material, rolled, and cut. It is obtained by. As the core material, metal foil such as copper foil or punching metal is used. From the viewpoint of reducing the size and weight of the battery, the thickness of the core is generally about 8 to 20 μm, and the thickness of the negative electrode is generally 80 to 200 μm. The negative electrode mixture is prepared by blending a negative electrode active material, particulate modified styrene butadiene rubber as a binder, a thickener, and the like at a predetermined ratio.
[0009]
A carbon material such as graphite powder is used as the negative electrode active material. Of these, massive artificial graphite, scaly graphite, spherical artificial graphite and the like are preferably used. The average particle diameter of the graphite powder is, for example, 20 to 30 μm.
[0010]
Particulate modified styrene-butadiene rubber, acrylonitrile units, Ri Do a copolymer comprising styrene units and butadiene units, a core-shell particles having a core portion having rubber elasticity. The core portion is preferably obtained by crosslinking a copolymer containing, for example, an acrylonitrile unit, a styrene unit, a butadiene unit, an acrylate unit, or the like with an appropriate crosslinking agent. Moreover, the shell part should just be a highly viscous polymer, for example, the copolymer containing an acrylate unit, a styrene unit, etc. is preferable.
[0011]
The core-shell type particles can be produced, for example, by a two-stage process in which a raw material monomer mixture in a core part containing a crosslinking agent is polymerized to produce a latex, and then a raw material monomer mixture in a shell part is grafted onto the latex particles. At this time, when acrylonitrile is contained in the raw material monomer of the core portion, a core portion having a high elastic modulus can be obtained.
[0012]
In the absorption spectrum obtained by FT-IR measurement, the particulate modified styrene butadiene rubber has an absorption intensity based on C≡N stretching vibration of acrylonitrile units of 0. It is preferable that the acrylonitrile unit and the butadiene unit are contained to the extent of 1 to 2 times. When the absorption strength based on the C≡N stretching vibration of the acrylonitrile unit is less than 0.1 times the absorption strength based on the C = C stretching vibration of the butadiene unit, a negative electrode having sufficient strength even if particulate modified styrene butadiene rubber is used. May not be obtained, or the surface of the active material may be excessively covered with a binder. On the other hand, when the absorption strength based on the C≡N stretching vibration of the acrylonitrile unit exceeds twice the absorption strength based on the C═C stretching vibration of the butadiene unit, the rubber elasticity of the particulate modified styrene butadiene rubber is reduced, and the core material The mixture becomes easy to peel off.
[0013]
The average particle diameter of the particulate modified styrene butadiene rubber is preferably 0.05 to 0.4 μm because a sufficiently strong negative electrode can be obtained with a small amount of use. If the average particle size is too small, most of the surface of the active material is covered with the particulate modified styrene butadiene rubber, and if it is too large, the distance between the active material particles increases and the conductivity inside the negative electrode decreases. .
[0014]
An appropriate amount of the particulate modified styrene butadiene rubber in the negative electrode mixture is 0.6 to 1.7 parts by weight with respect to 100 parts by weight of the carbon material as the negative electrode active material. If the amount of the particulate modified styrene butadiene rubber is too small, a sufficiently strong negative electrode may not be obtained, and the mixture may be peeled off from the core material. The rate discharge characteristic becomes unsatisfactory.
In addition, in the case of conventional PVDF, the suitable compounding quantity in a negative electrode mixture is 5-10 weight part with respect to 100 weight part of negative electrode active materials, and is 2-5 weight part also in the case of SBR. Therefore, in the negative electrode of the present invention, the content of the binder is significantly reduced as compared with the conventional case.
[0015]
The surface area of the carbon material contained in the negative electrode needs to be 300 to 600 m 2 per 1 g of the particulate modified styrene butadiene rubber contained in the negative electrode. If the surface area of the carbon material per 1 g of the particulate modified styrene butadiene rubber contained in the negative electrode is less than 300 m 2 , the surplus binder coats the active material and the charging characteristics of the battery deteriorate, so the cycle life is shortened. End up. On the other hand, when the surface area of the carbon material per 1 g of the particulate modified styrene butadiene rubber contained in the negative electrode exceeds 600 m 2 , the adhesion between the mixture layer and the core material decreases due to the shortage of the binder. Moreover, it is preferable that the specific surface area of a carbon material is 2-5 m < 2 > / g.
[0016]
As the thickener used in the negative electrode mixture, a cellulose-based thickener such as CMC is often used. The blending amount of the thickener in the negative electrode mixture is appropriately 0.7 to 1.2 parts by weight with respect to 100 parts by weight of the carbon material as the negative electrode active material. If the blending amount of the thickener is too small, a paste-like negative electrode mixture cannot be obtained and the mixture is easily peeled off from the core material. If it is too much, the active material is covered with the thickener, and the reaction The surface area is reduced.
[0017]
However, the total amount of the particulate modified styrene butadiene rubber and the thickener needs to be 1.3 to 2.4 parts by weight with respect to 100 parts by weight of the carbon material which is the negative electrode active material. When the total amount is less than 1.3 parts by weight, the active material particles cannot be sufficiently bonded to each other, and the strength of the negative electrode becomes insufficient. It is covered with a thickener, and its reaction surface area becomes small.
[0018]
In the FT-IR measurement, the absorption spectrum of the particulate modified styrene butadiene rubber may be measured, for example, by using a particulate modified styrene butadiene rubber coated on a KBr plate. Here, in general, absorption based on C═C stretching vibration of butadiene units is observed in the vicinity of 880 to 940 cm −1 , and absorption based on C≡N stretching vibration of acrylonitrile units is observed in the vicinity of 2200 to 2280 cm −1 .
[0019]
【Example】
Next, the present invention will be specifically described based on examples. However, the present invention is not limited to these.
[0020]
<< Examples 1-5 and Comparative Examples 1-8 >>
Batteries A to M were produced as shown below and their characteristics were evaluated.
[0021]
(I) Production of Negative Electrode Using artificial graphite having the properties shown in Table 1 as an active material, a negative electrode mixture used for the negative electrode of each battery was prepared using the binder shown in Table 1. The value obtained by dividing the specific surface area of artificial graphite as the active material, the blending amount of the binder with respect to 100 parts by weight of the active material in the negative electrode mixture, and the total surface area of the active material contained in the mixture by the blending amount of the binder. Table 1 shows. However, 1.3 parts by weight of CMC per 100 parts by weight of the active material was used as a thickener except when PVDF was used as the binder.
[0022]
[Table 1]
The binder shown in Table 1 will be described below.
BM400B: A particulate modified styrene butadiene rubber made of a copolymer containing acrylonitrile units, styrene units and butadiene units manufactured by Nippon Zeon Co., Ltd. Average particle size 0.2 μm. In the absorption spectrum obtained by the FT-IR measurement, the absorption intensity based on the C≡N stretching vibration of the acrylonitrile unit is 0.4 times the absorption intensity based on the C═C stretching vibration of the butadiene unit. The absorption spectrum is shown in FIG.
[0024]
In FIG. 1, the absorption peak observed near 2237 cm −1 is based on the C≡N stretching vibration of the acrylonitrile unit, and the absorption peak observed near 911 cm −1 is based on the C═C stretching vibration of the butadiene unit. is there.
[0025]
The measurement conditions are a sample scan count of 32, a background scan count of 32, a resolution of 4000, and a sample gain of 1.0. The measurement apparatus uses a microscopic FT-IR (Continuum (manufactured by Nicolet), light source: AVATAR-360). It was. Moreover, the sample for measurement used what melt | dissolved particulate modified styrene butadiene rubber in N-methylpyrrolidone, apply | coated on the KBr board, and dried.
[0026]
PVDF: polyvinylidene difluoride.
SBR: Styrene butadiene rubber.
MPE: Modified polyethylene resin.
[0027]
For comparison, a transmission spectrum obtained by FT-IR measurement of SBR is shown in FIG. The measurement conditions, measurement apparatus, etc. are the same as in the case of FIG. In FIG. 2, an absorption peak based on C≡N stretching vibration of acrylonitrile units is not observed in the vicinity of 2237 cm −1 .
[0028]
The obtained negative electrode mixture was applied to both surfaces of a core material of copper foil having a thickness of 15 μm, rolled to a thickness of 140 μm, and cut into a predetermined length to obtain a negative electrode. A negative electrode lead made of the same material as the core material was connected to the negative electrode.
[0029]
(Ii) Production of positive electrode 4 parts by weight of PVDF as a binder and 3 parts by weight of acetylene black as a conductive agent were blended with 100 parts by weight of LiCoO 2 to obtain a positive electrode mixture. Next, the obtained positive electrode mixture was applied to both surfaces of a 20 μm thick aluminum foil core, rolled to a predetermined thickness, cut into a predetermined length, and a positive electrode was obtained. A positive electrode lead made of the same material as the core material was connected to the positive electrode.
[0030]
(Iii) Production of Battery The obtained positive electrode and negative electrode were laminated with a separator interposed therebetween, and wound to obtain an electrode plate group. As the separator, a polyethylene microporous film having a thickness of 27 μm was used. The wound electrode plate group was compressed from one direction so that the cross section was substantially elliptical.
[0031]
On the other hand, a nonaqueous electrolyte in which LiPF 6 was dissolved in a mixture of an equal volume of ethylene carbonate and ethyl methyl carbonate as a nonaqueous solvent so as to have a salt concentration of 1.0 mol / liter was prepared.
[0032]
The electrode plate group was accommodated together with 3.2 g of a non-aqueous electrolyte in a predetermined aluminum case with insulating rings arranged on the top and bottom. And after connecting a negative electrode lead and a positive electrode lead to a predetermined location, the opening part of the case was sealed with the sealing board, and nonaqueous electrolyte battery AM was completed. These batteries are rectangular with a width of 30 mm, a height of 48 mm, and a thickness of 5 mm, and the nominal capacity of the battery is 600 mAh.
[0033]
Next, the evaluation content of the obtained nonaqueous electrolyte battery will be described.
(I) Low-temperature characteristics and capacity recovery rate The batteries A to M were charged in a 20 ° C atmosphere at 600 mA until the battery voltage reached 4.2 V, and discharged at 120 mA until the battery voltage reached 3 V. Next, in an atmosphere of 0 ° C., the battery was charged at 600 mA until the battery voltage reached 4.2 V, and discharged at 600 mA until the battery voltage reached 3 V. Then, in an atmosphere of 20 ° C., the battery was charged at 600 mA until the battery voltage reached 4.2 V, and discharged at 120 mA until the battery voltage reached 3 V.
[0034]
Here, Table 1 shows the charge capacity when charged at 600 mA until the battery voltage reaches 4.2 V in an atmosphere of 0 ° C. as an index of low temperature characteristics. Further, the capacity obtained by the first charge in the 20 ° C. atmosphere and the capacity obtained by the second charge in the 20 ° C. atmosphere were determined, and the ratio of the latter to the former was determined. The results are shown in Table 1 as the capacity recovery rate in terms of 100 minutes.
[0035]
(Ii) Presence / absence of abnormal temperature rise After the capacity recovery rate was examined, the battery was charged at 1260 mA at 20 ° C. until the battery surface temperature reached 80 ° C. Then, after standing for a while, the transition of the surface temperature of the battery was confirmed. At that time, the surface temperature was 90 ° C. or higher, and there were no others. The results are shown in Table 1.
[0036]
(Iii) Capacity maintenance rate For batteries A to M, an operation of charging at 600 mA until the battery voltage reached 4.2 V, and discharging at 600 mA until the battery voltage reached 3 V was repeated 200 times. Then, the ratio of the 200th discharge capacity to the first discharge capacity was determined. The results are shown in Table 1 in terms of 100 minutes.
[0037]
From the results in Table 1, the following can be understood.
When the surface area of the carbon material per gram of the particulate modified styrene butadiene rubber contained in the negative electrode becomes 900 m 2 , the mixture is peeled off from the core material. Therefore, the carbon material per gram of the particulate modified styrene butadiene rubber contained in the negative electrode It can be seen that when the surface area exceeds 600 m 2 , the strength of the negative electrode decreases.
[0038]
When the surface area of the carbon material per gram of the particulate modified styrene butadiene rubber contained in the negative electrode is 225 m 2 , an abnormal temperature rise is observed in the heating test. Therefore, the carbon material per gram of the particulate modified styrene butadiene rubber contained in the negative electrode It can be seen that when the surface area of the battery is less than 300 m 2 , the safety of the battery may be impaired. This is presumably because Li is less likely to be occluded in the negative electrode active material, and metal Li is deposited on the surface of the active material. In addition, this phenomenon is likely to occur during low temperature charging with large polarization.
[0039]
From the viewpoint of low temperature characteristics, it can be seen that the most preferable range of the surface area of the carbon material per 1 g of the particulate modified styrene butadiene rubber contained in the negative electrode is 450 to 600 m 2 .
[0040]
It can be seen that when a binder other than the particulate modified styrene butadiene rubber is used, the cycle life is remarkably lowered.
[0041]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the surface area of the active material which contributes to the intensity | strength of a negative electrode and charge / discharge reaction effectively can be ensured. Therefore, by using the negative electrode of the present invention, it is possible to obtain a highly safe non-aqueous electrolyte secondary battery having a good balance of high rate discharge characteristics, low temperature characteristics, cycle life, and the like.
[Brief description of the drawings]
FIG. 1 is an example of an absorption spectrum obtained by FT-IR measurement of particulate modified styrene butadiene rubber.
FIG. 2 is an example of a transmission spectrum obtained by FT-IR measurement of SBR.
Claims (2)
前記炭素材料の比表面積は、２〜５ｍ 2 ／ｇであり、
前記粒子状変性スチレンブタジエンゴムの量は、前記炭素材料１００重量部に対して、０．６〜１．７重量部であり、
前記粒子状変性スチレンブタジエンゴムは、コアシェル型粒子からなり、
前記コアシェル型粒子は、コア部にアクリロニトリル単位を含み、
前記負極が含有する前記炭素材料の表面積が、前記粒子状変性スチレンブタジエンゴム１ｇあたり３００〜６００ｍ2である非水電解質二次電池用負極。A negative electrode for a non-aqueous electrolyte secondary battery comprising a carbon material as an active material and a particulate modified styrene butadiene rubber as a binder,
The carbon material has a specific surface area of 2 to 5 m 2 / g,
The amount of the particulate modified styrene butadiene rubber is 0.6 to 1.7 parts by weight with respect to 100 parts by weight of the carbon material,
The particulate modified styrene butadiene rubber is composed of core-shell type particles,
The core-shell type particle includes an acrylonitrile unit in the core part,
The negative electrode for a nonaqueous electrolyte secondary battery, wherein the carbon material contained in the negative electrode has a surface area of 300 to 600 m 2 per gram of the particulate modified styrene butadiene rubber.
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| Application Number | Priority Date | Filing Date | Title |
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| JP2000267627A JP3621031B2 (en) | 2000-09-04 | 2000-09-04 | Anode for non-aqueous electrolyte secondary battery |
| US09/845,265 US6773838B2 (en) | 2000-09-04 | 2001-05-01 | Non-aqueous electrolyte secondary battery and negative electrode for the same |
| DE2001629482 DE60129482T2 (en) | 2000-09-04 | 2001-05-14 | Non-aqueous electrolyte secondary battery and negative electrode for it |
| EP20010304270 EP1184921B1 (en) | 2000-09-04 | 2001-05-14 | Non-aqueous electrolyte secondary battery and negative electrode for the same |
| DE60134432T DE60134432D1 (en) | 2000-09-04 | 2001-05-14 | Nonaqueous electrolyte secondary battery and negative electrode therefor |
| EP20040077458 EP1492182B1 (en) | 2000-09-04 | 2001-05-14 | Non-aqueous electrolyte secondary battery and negative electrode for the same |
| DE2001630296 DE60130296T2 (en) | 2000-09-04 | 2001-05-14 | Nonaqueous electrolyte secondary battery and negative electrode therefor |
| EP20040018679 EP1478039B1 (en) | 2000-09-04 | 2001-05-14 | Non-aqueous electrolyte secondary battery and negative electrode for the same |
| CNB011211687A CN1233056C (en) | 2000-09-04 | 2001-06-04 | Nonaqueous electrolyte secondary battery and negative electrode for nonaqueous electrolyte secondary battery |
| CNB2004100699563A CN1253955C (en) | 2000-09-04 | 2001-06-04 | Non-aqueous electrolyte secondary battery and negative electrode for the same |
| CNB2004100699578A CN1249834C (en) | 2000-09-04 | 2001-06-04 | Non-aqueous electrolyte secondary battery |
| US10/883,727 US7147964B2 (en) | 2000-09-04 | 2004-07-06 | Non-aqueous electrolyte secondary battery and negative electrode for the same |
| US10/943,839 US7150937B2 (en) | 2000-09-04 | 2004-09-20 | Non-aqueous electrolyte secondary battery and negative electrode for the same |
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| JP2004259121A Division JP3637351B2 (en) | 2004-09-07 | 2004-09-07 | Nonaqueous electrolyte secondary battery |
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| JP2005032688A (en) * | 2003-07-11 | 2005-02-03 | Toshiba Corp | Non-aqueous electrolyte secondary battery |
| JP4852836B2 (en) * | 2004-10-05 | 2012-01-11 | パナソニック株式会社 | Method for producing electrode plate for negative electrode of non-aqueous secondary battery |
| JP5879673B2 (en) | 2009-09-03 | 2016-03-08 | ソニー株式会社 | Method for producing negative electrode for non-aqueous electrolyte secondary battery |
| WO2017056466A1 (en) | 2015-09-28 | 2017-04-06 | 日本ゼオン株式会社 | Binder composition for nonaqueous secondary battery electrodes, slurry composition for nonaqueous secondary battery electrodes, electrode for nonaqueous secondary batteries, and nonaqueous secondary battery |
| KR20210110295A (en) | 2018-12-27 | 2021-09-07 | 니폰 제온 가부시키가이샤 | A binder composition for a secondary battery electrode, a conductive material paste composition for a secondary battery electrode, a slurry composition for a secondary battery electrode, an electrode for a secondary battery, and a secondary battery |
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| EP0603397B2 (en) * | 1991-09-13 | 2002-12-18 | Asahi Kasei Kogyo Kabushiki Kaisha | Secondary cell |
| JP4473967B2 (en) * | 1997-03-04 | 2010-06-02 | 日本ゼオン株式会社 | Binder for battery, binder composition for battery, slurry for battery electrode, electrode for lithium secondary battery, and lithium secondary battery |
| JPH11111300A (en) * | 1997-09-30 | 1999-04-23 | Sanyo Electric Co Ltd | Negative electrode for nonaqueous secondary battery |
| JPH11288718A (en) * | 1998-04-01 | 1999-10-19 | Toyota Central Res & Dev Lab Inc | Nonaqueous solvent secondary battery |
| JP4482953B2 (en) * | 1998-06-09 | 2010-06-16 | パナソニック株式会社 | Anode for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery using the same |
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