【０００１】
【発明の属する技術分野】
本発明は、非水電解質二次電池に用いる負極材料及び該負極材料を用いて作製した電極構造体、非水電解質二次電池に関する。
【０００２】
【従来の技術】
近年のビデオカメラやノート型パソコン等のポータブル機器の普及により薄型の電池に対する需要が高まっている。この薄型の電池として正極と負極を積層して形成されたリチウムイオン二次電池等の非水電解質二次電池が知られている。この正極は、シート状の正極集電体の表面に正極活物質層を形成することにより作られ、負極は、シート状の負極集電体の表面に負極活物質層を形成することにより作られる。正極の活物質層と負極の活物質層の間には電解質層が介装される。この電池では、それぞれの活物質における電位差を電流として取出すための正極端子及び負極端子が正極集電体及び負極集電体に設けられ、このように積層されたものをパッケージで密閉することによりリチウムイオン二次電池が形成されている。このリチウムイオン二次電池ではパッケージから引出された正極端子及び負極端子を電池の端子として使用することにより所望の電気が得られるようになっている。
【０００３】
このような構造を有するリチウムイオン二次電池は電池電圧が高く、エネルギー密度も大きいため、非常に注目されている。このリチウムイオン二次電池の放電容量を更に増大させるためにはシート状の正極又は負極の面積を拡大させる必要がある。この正極又は負極の面積を単純に拡大するだけでは広い面積のために、その取扱いが困難になる不具合がある。この点を解消するために、拡大したシート状の正極又は負極を所望の大きさに折畳んだり、捲回したりすることも考えられる。しかし、シート状の正極又は負極を積層した状態で折畳みや捲回を行うと、折目部分における正極又は負極に撓みが生じ、その部分におけるシートが電解質層から剥離して電極と電解質界面の有効表面積が減少して放電容量が減少するとともに、電池内部に抵抗を生じさせて放電容量のサイクル特性を悪化させる不具合がある。また同様に、折目部分に撓みが生じることにより正極又は負極をそれぞれ形成している活物質層が集電体より剥離する問題もあった。更に、この電池は充電及び放電過程において、正極及び負極活物質中へのリチウムイオンの吸蔵、放出によって正極及び負極活物質層の膨張、収縮が起こり、これにより発生する応力により、活物質層が集電体より剥離する問題もあった。
【０００４】
そこで上記諸問題を解決する技術として下記に示すように、活物質層の集電体からの剥離や密着性の低下を防止する技術がそれぞれ提案されている。
平均重合度２０以上のポリビニルアルコール単位を有し、水酸基の一部又は全部が平均モル置換度０．３以上のオキシアルキレン含有基で置換された高分子化合物、該高分子化合物からなるバインダ樹脂、及び高いイオン導電性と高い粘着性を備えているイオン導電性高分子電解質用組成物並びに二次電池が提案されている（例えば、特許文献１参照。）。この発明では、固体高分子電解質の材料やバインダ樹脂の材料としてポリオキシアルキレン部分の導入割合を上げた高分子化合物を用いることで、イオン移動し易くして高分子電解質用ポリマーのイオン導電性を高めている。
【０００５】
イソシアネート化合物とポリオール化合物とを反応させて得られたポリウレタン化合物中のイソシアネート基の一部又は全部に双極子モーメントの大きな置換基を有するアルコール化合物の水酸基を反応させた高分子化合物、バインダ樹脂、イオン導電性高分子電解質用組成物並びに二次電池が提案されている（例えば、特許文献２参照。）。この発明では、双極子モーメントの大きな置換基をポリウレタン中に導入することにより、高い誘電率とイオン導電性塩を高濃度に溶解する能力を保持しながら、電極と電解質間の密着性を良好にして、電解質溶液並みの界面インピーダンスを得ている。
イソシアネート化合物とポリオール化合物とを反応させて得られたポリウレタン化合物中のイソシアネート基の一部又は全部に双極子モーメントの大きな置換基を有するアルコール化合物の水酸基を反応させた高分子化合物と、イオン導電性塩と、架橋可能な官能基を有する化合物とを主成分としたイオン導電性固体高分子用組成物、イオン導電性固体高分子電解質、バインダ樹脂及び二次電池が提案されている（例えば、特許文献３参照。）。
【０００６】
リチウム二次電池の負極用電極材、該電極材を用いた電極構造体、該電極構造体を用いたリチウム二次電池、及び該電極構造体及び該リチウム二次電池の製造方法が提案されている（例えば、特許文献４参照。）。この発明では、電極材に非化学量論比組成の非晶質Ｍ・Ａ・Ｘ合金（ＭはＳｉ、Ｇｅ及びＭｇからなる群より選ばれた少なくとも一種の元素を示し、Ａは遷移金属元素の中から選ばれる少なくとも一種の元素を示し、Ｘは、Ｏ、Ｆ、Ｎ、Ｂａ、Ｓｒ、Ｃａ、Ｌａ、Ｃｅ、Ｃ、Ｐ、Ｓ、Ｓｅ、Ｔｅ、Ｂ、Ｂｉ、Ｓｂ、Ａｌ、Ｉｎ及びＺｎからなる群より選ばれる少なくとも一種の元素を示す。但し、Ｘは含有されていなくてもよく、合金の構成要素Ｍの含量はＭ／(Ｍ＋Ａ＋Ｘ)＝２０〜８０原子％である。）を含有する。このような合金を含有する電極材は優れた特性を有し、リチウム二次電池の負極活性物質として好適である。
【０００７】
リチウムを含有する正極活物質を備えた正極と、リチウムのドープ・脱ドープが可能なケイ素化合物と炭素材料との混合物が結着剤中に分散されてなる負極活物質層を備えた負極と、正極と負極との間に介在される非水電解質とを備え、上記結着剤は、ガラス転位温度が−４０℃以下である非水電解質電池が提案されている（例えば、特許文献５参照。）。この発明では、負極活物質中の結着剤として、ガラス転位温度が−４０℃以下のものを用いているので、リチウムのドープ・脱ドープ時のケイ素化合物負極の体積変化を結着剤が吸収し、負極活物質層全体としての体積変化が抑制されて、サイクル劣化が抑えられる。
更に、リチウムイオンを吸蔵・放出可能な正極及び負極と、リチウムイオン導電性の非水電解質から構成され、正極又は負極の電極合剤中に水溶性ポリマーを含有した非水電解質二次電池が提案されている（例えば、特許文献６参照。）。この発明では、電極合剤中に水溶性ポリマーを含有することにより、集電体への結着性が良好であり、かつ溶媒が水であることから製造コストを削減でき、製造工程における人体への影響等も抑制できる。また比較的低温で乾燥可能であり、合剤やシート電極を構成する材料への熱的ダメージを最小限に留めることができる。
【０００８】
【特許文献１】
ＰＣＴ国際公開番号ＷＯ００／５６７８０号公報
【特許文献２】
ＰＣＴ国際公開番号ＷＯ００／５６７９７号公報
【特許文献３】
ＰＣＴ国際公開番号ＷＯ００／５６８１５号公報
【特許文献４】
ＰＣＴ国際公開番号ＷＯ００／１７９４９号公報
【特許文献５】
特開２０００−２９９１０８号公報
【特許文献６】
特開平９−２８９０２２号公報
【０００９】
【発明が解決しようとする課題】
しかしながら、一般的に非水電解質を含む二次電池において、負極集電体と負極活物質層の接着は困難であり、上記特許文献４に示される負極用電極材では、例えば、Ｓｉ、Ｇｅ、Ａｌ、Ｓｎ等の元素を含む負極活物質の場合には、高い充放電容量が得られるものの、充放電に伴う活物質の体積変化が大きく、活物質層と集電体の剥離が生じる問題点があった。また特許文献５に示される結着剤では、柔軟性が特徴であり、活物質の体積変化をある程度吸収することができるが、この種の結着剤では集電体との接着強度が十分とはいえなかった。また特許文献１〜４及び６等は活物質と集電体の接着を向上することを目指して、結着剤の改良を行っているが、これらの結着剤は化学安定性が一般的に電池に使われるポリエチレン、ポリフッ化ビニリデン（以下、ＰＶｄＦという。）等の樹脂より劣ったり、電解質がある環境において接着性が足りなくなるというような問題が残っている。
【００１０】
本発明の目的は、高い化学安定性を備え、かつ無機質粒子への密着性に優れる、非水電解質二次電池用負極材料を提供することにある。
本発明の別の目的は、集電体と活物質との密着性に優れ、高い機械強度を保持し得る、負極材料を用いて作製した電極構造体、非水電解質二次電池を提供することにある。
本発明の更に別の目的は、充放電のリチウムイオンの挿入、脱離反応に伴うストレスを制御し、サイクル特性を向上できる、負極材料を用いて作製した電極構造体、非水電解質二次電池を提供することにある。
【００１１】
【課題を解決するための手段】
請求項１に係る発明は、樹脂結着剤と、Ｓｉ、Ｇｅ、Ｍｇ、Ｓｎ、Ｐｂ、Ａｇ、Ａｌ、Ｚｎ、Ｃｄ、Ｓｂ、Ｂｉ及びＩｎからなる群より選ばれた少なくとも１種の元素を含む無機質粒子の双方をそれぞれ含む非水電解質二次電池用負極材料の改良であり、その特徴ある構成は、樹脂結着剤がフッ素含有樹脂を変性物質により変性して得られた変性フッ素含有高分子化合物を含むところにある。
請求項１に係る発明では、樹脂結着剤に含まれるフッ素含有樹脂を変性物質により変性して得られた変性フッ素含有高分子化合物は、フッ素含有高分子化合物が有する高い化学安定性と同様の安定性を備えるだけでなく、無機質粒子への密着性に優れるため、充放電によるリチウムの吸蔵、脱離に伴う無機質粒子の体積変化に起因する無機質粒子の脱落や、電極の剥離等を防止し、サイクル特性を向上することができる。
【００１２】
請求項２に係る発明は、請求項１に係る発明であって、図３（ｃ）に示すように、変性フッ素含有高分子化合物２４がフッ素含有樹脂を幹重合体２２とし、幹重合体２２を変性物質２３によりグラフト変性させて得られる高分子化合物である負極材料である。
請求項３に係る発明は、請求項１又は２に係る発明であって、変性フッ素含有高分子化合物を構成する幹重合体が、ＰＶｄＦ、ポリフッ化ビニル（以下、ＰＶＦという。）、４フッ化エチレンポリマー、３フッ化エチレンポリマー、２フッ化エチレンポリマー、フッ化ビニリデン-ヘキサフルオロプロピレン共重合体（以下、ＶｄＦ-ＨＦＰ共重合体という。）、エチレン-４フッ化エチレン共重合体、４フッ化エチレン-６フッ化プロピレン共重合体、３フッ化塩化エチレンポリマー及びポリテトラフルオロエチレンからなる群より選ばれた少なくとも１種のフッ素含有樹脂を含む負極材料である。
【００１３】
請求項４に係る発明は、請求項１又は２に係る発明であって、変性フッ素含有高分子化合物を構成する変性物質が、アクリル酸、アクリル酸メチル、メタクリル酸及びメタクリル酸メチルの少なくとも１種である負極材料である。
請求項５に係る発明は、請求項３又は４に係る発明であって、変性フッ素含有高分子化合物を構成する幹重合体がＰＶｄＦ又はＶｄＦ-ＨＦＰ共重合体のいずれか一方又は双方を含む混合物であって、変性物質がアクリル酸である負極材料である。
請求項６に係る発明は、請求項３又は５に係る発明であって、変性フッ素含有高分子化合物の幹重合体がフッ化ビニリデンであるとき、フッ化ビニリデンが変性フッ素含有高分子化合物に９５重量％〜６０重量％の割合で含まれる負極材料である。
【００１４】
請求項７に係る発明は、請求項１ないし６いずれか１項に係る発明であって、変性フッ素含有高分子化合物はフッ素含有樹脂と変性物質が放射線照射処理によってグラフト化される負極材料である。
請求項８に係る発明は、請求項７に係る発明であって、フッ素含有樹脂への放射線照射処理はγ線照射によって行われ、フッ素含有樹脂のγ線の吸収線量が１０〜９０ｋＧｙである負極材料である。
請求項９に係る発明は、請求項１ないし８いずれか１項に係る発明であって、樹脂結着剤に変性フッ素含有高分子化合物とは構造の異なるフッ素含有高分子化合物を更に含む負極材料である。
請求項９に係る発明では、変性フッ素含有高分子化合物だけでなく、フッ素含有高分子化合物を更に含むことで、化学安定性が更に高まり、集電体への密着性も向上する。また、変性フッ素含有高分子化合物よりも柔軟性に富むフッ素含有高分子化合物を含ませることで、充放電によるリチウムの吸蔵、脱離に伴う無機質粒子の体積変化を起因とするストレスを緩和する効果が得られる。
【００１５】
請求項１０に係る発明は、請求項９に係る発明であって、フッ素含有高分子化合物が、変性フッ素含有高分子化合物を構成するフッ素含有樹脂に含まれる反復単位をその反復単位として含む負極材料である。
請求項１０に係る発明では、フッ素含有高分子化合物の反復単位が、変性フッ素含有高分子化合物を構成するフッ素含有樹脂に含まれる反復単位を含むことで、樹脂結着剤の化学安定性が増すとともに、密着力がより強固になる。
【００１６】
請求項１１に係る発明は、請求項１ないし１０いずれか１項に係る発明であって、樹脂結着剤中の変性フッ素含有高分子化合物の含有割合が１０〜１００重量％である負極材料である。
請求項１２に係る発明は、請求項１に係る発明であって、無機質粒子の平均粒径が０．０１〜５０μｍである負極材料である。
請求項１３に係る発明は、請求項１又は１２に係る発明であって、無機質粒子はＳｉ、Ｇｅ、Ｍｇ、Ｓｎ、Ｐｂ、Ａｇ、Ａｌ、Ｚｎ、Ｃｄ、Ｓｂ、Ｂｉ及びＩｎからなる群より選ばれた少なくとも１種の元素が単体、酸化物又は他の金属との合金、単体とリチウムとの合金、及びこれらの金属、リチウムを含む多元合金で構成される負極材料である。
【００１７】
請求項１４に係る発明は、請求項１ないし１３いずれか１項に係る発明であって、材料中に導電助剤を更に含む負極材料である。
請求項１５に係る発明は、請求項１ないし１４いずれか１項に係る発明であって、材料中に塩及び相溶性有機溶媒を更に含む負極材料である。
請求項１６に係る発明は、請求項１ないし１５いずれか１項に係る発明であって、樹脂結着剤の割合が材料に含まれる固形物全体の１〜５０重量％である負極材料である。
【００１８】
請求項１７に係る発明は、図１に示すように、負極集電体１４と、この負極集電体１４の上に請求項１ないし１６いずれか１項に記載の負極材料を塗工して形成された負極活物質層１６とを備えた非水電解質二次電池用電極構造体である。
請求項１７に係る発明では、本発明の負極材料を用いて作製した電極構造体は、集電体と活物質との密着性に優れ、高い機械強度を保持できる。また、充放電のリチウムイオンの挿入、脱離反応に伴うストレスを制御し、サイクル特性を向上できる。
【００１９】
請求項１８に係る発明は、請求項１７に係る発明であって、図２に示すように、負極集電体１４と負極活物質層１６との間に、結着剤と導電助剤をそれぞれ含む密着層１９が設けられた電極構造体である。
請求項１９に係る発明は、図１又は図２に示すように、請求項１ないし１６いずれか１項に記載の負極材料、又は請求項１７又は１８記載の電極構造体を用いて負極１７を形成し、負極１７と非水電解質層１８と、正極集電体１１の上に正極活物質層１２を形成してなる正極１３とをそれぞれこの順に積層して形成された非水電解質二次電池である。
請求項１９に係る発明では、本発明の負極材料又は本発明の電極構造体を用いて作製した非水電解質二次電池は、集電体と活物質との密着性に優れ、高い機械強度を保持できる。また、充放電のリチウムイオンの挿入、脱離反応に伴うストレスを制御し、サイクル特性を向上できる。
【００２０】
請求項２０に係る発明は、請求項１９に係る発明であって、正極を構成する正極活物質層と、負極を構成する負極活物質層との間の非水電解質層が、高分子化合物からなるセパレータ層である非水電解質二次電池である。
請求項２１に係る発明は、請求項１９に係る発明であって、正極を構成する正極活物質層と、負極を構成する負極活物質層との間の非水電解質層が、塩及び相溶性有機溶媒をそれぞれ含むポリマー電解質である非水電解質二次電池である。
請求項２２に係る発明は、請求項２１に係る発明であって、ポリマー電解質に含まれるポリマーが請求項１ないし１６いずれか１項に記載の負極材料の樹脂結着剤に含まれる変性フッ素含有高分子化合物を構成するフッ素含有樹脂に含まれる反復単位をその反復単位として含む非水電解質二次電池である。
【００２１】
【発明の実施の形態】
次に本発明の実施の形態を図面に基づいて説明する。
本発明は、樹脂結着剤と、Ｓｉ、Ｇｅ、Ｍｇ、Ｓｎ、Ｐｂ、Ａｇ、Ａｌ、Ｚｎ、Ｃｄ、Ｓｂ、Ｂｉ及びＩｎからなる群より選ばれた少なくとも１種の元素を含む無機質粒子の双方をそれぞれ含む非水電解質二次電池用負極材料の改良であり、その特徴ある構成は、樹脂結着剤がフッ素含有樹脂を変性物質により変性して得られた変性フッ素含有高分子化合物を含むところにある。
ここで「変性」とは、性質が変わることを意味し、本明細書では、幹重合体である樹脂のところどころに変性物質が配列することにより、幹重合体である樹脂自身が持つ性質だけでなく、変性物質が持つ性質も併せ持ったり、両者にない性質を新たに持たせることを意味する。
【００２２】
樹脂結着剤に含まれるフッ素含有樹脂を変性物質により変性して得られた変性フッ素含有高分子化合物は、フッ素含有高分子化合物が有する高い化学安定性と同様の安定性を備えるだけでなく、無機質粒子への密着性に優れるため、充放電によるリチウムの吸蔵、脱離に伴う無機質粒子の体積変化に起因する無機質粒子の脱落や、電極の剥離等を防止し、サイクル特性を向上することができる。
負極活物質層を構成する負極材料の樹脂結着剤に含まれる高分子化合物に、分子内にフッ素を含む化合物を用いるのは、負極活物質層が電池内において化学的、電気化学的、熱的に安定性が要求されるためである。変性フッ素含有高分子化合物はフッ素含有樹脂を幹重合体とし、幹重合体を変性物質によりグラフト変性させて得られる。
【００２３】
幹重合体のところどころに変性物質を枝重合体として配列して変性させるには、グラフト重合を用いる。幹重合体には、ＰＶｄＦ、ＰＶＦ、４フッ化エチレンポリマー、３フッ化エチレンポリマー、２フッ化エチレンポリマー、ＶｄＦ-ＨＦＰ共重合体、エチレン-４フッ化エチレン共重合体、４フッ化エチレン-６フッ化プロピレン共重合体、３フッ化塩化エチレンポリマー及びポリテトラフルオロエチレンからなる群より選ばれた少なくとも１種のフッ素含有樹脂が含まれる。また変性物質には、アクリル酸、アクリル酸メチル、メタクリル酸及びメタクリル酸メチルの少なくとも１種が挙げられる。これらの変性物質を用いることで、無機質粒子や負極集電体と良好な密着性を得ることができる。
特に、幹重合体をＰＶｄＦ又はＶｄＦ-ＨＦＰ共重合体のいずれか一方又は双方を含む混合物とし、変性物質をアクリル酸とした変性フッ素含有高分子化合物は、ＰＶｄＦ又はＶｄＦ-ＨＦＰ共重合体のいずれか一方又は双方を含む混合物が無機質粒子と高い密着性を有し、アクリル酸基が負極集電体材料と高い密着性を有するため、樹脂結着剤に含まれる変性フッ素含有高分子化合物として優れた性質を有する。
【００２４】
変性フッ素含有高分子化合物の幹重合体がフッ化ビニリデンであるとき、フッ化ビニリデンが変性フッ素含有高分子化合物に９５重量％〜６０重量％の割合で含まれるのが好ましい。
グラフト重合させる方法としては放射線法がある。放射線法では、幹重合体となるフッ素含有樹脂と枝重合体となる変性物質とを混合して、混合物に放射線を連続的又は間欠的に放射することにより重合でき、変性物質とフッ素含有樹脂とを接触させる前にフッ素含有樹脂を予備放射することが好ましい。具体的には、フッ素含有樹脂に放射線を照射した後で、被照射物に変性物質を混合することにより、フッ素含有樹脂を幹重合体とし変性物質を枝重合体とした変性フッ素含有高分子化合物を得ることができる。グラフト重合に用いる放射線にはγ線を使用する。フッ素含有樹脂への吸収線量が１〜９０ｋＧｙになるようにγ線を照射する。幹重合体となるフッ素含有樹脂に放射線を照射することにより片末端にラジカルが形成され、変性物質が重合し易くなる。
【００２５】
図３（ａ）に示すように、変性フッ素含有高分子化合物を構成する幹重合体２２は、繰返し単位Ａを基本単位とする。幹重合体の基本単位は、図３（ａ）に示すように１種類でもよいし、図示しないが２種類以上の基本単位を用いてもよい。この基本単位は幹重合体中に５０分子量％以上の割合で含まれることが好ましい。６０〜１００分子量％の割合で含まれるのがより好ましい。図３（ｂ）に示すように、この幹重合体２２に放射線を照射して基本単位Ａの片末端のところどころにラジカル２２ａを形成する。図３（ｃ）に示すように、ラジカルを形成した幹重合体２２に変性物質２３（図３中のＣ）を接触させることにより、ラジカル部分２２ａに変性物質２３が配列して変性フッ素含有高分子化合物２４が形成される。変性物質２３は変性フッ素含有高分子化合物中に２〜５０分子量％の割合で含まれることが好ましい。変性フッ素含有高分子化合物中に５〜３０分子量％の割合で含まれるのがより好ましい。
グラフト重合は活性化した幹重合体となる樹脂が枝重合体となる変性物質と接触している時間の長さ、放射線による予備活性の程度、枝重合体となる変性物質が幹重合体となる樹脂を透過できるまでの程度、樹脂及び変性物質が接触しているときの温度等によりそれぞれ重合生成が異なる。変性物質が酸である場合、変性物質である化合物を含有する溶液をサンプリングして、アルカリにより滴定し、残留する酸化合物濃度を測定することにより、グラフト化の程度を観測することができる。得られた組成物中のグラフト化の割合は、最終重量の２〜５０分子量％が望ましい。
【００２６】
樹脂結着剤には、変性フッ素含有高分子化合物とは構造の異なるフッ素含有高分子化合物を更に含むことが好ましい。樹脂結着剤に変性フッ素含有高分子化合物だけでなく、フッ素含有高分子化合物を更に含むことで、化学安定性が更に高まり、集電体への密着性も向上する。また、変性フッ素含有高分子化合物よりも柔軟性に富むフッ素含有高分子化合物を含むことで、充放電によるリチウムの吸蔵、脱離に伴う無機質粒子の体積変化を起因とするストレスを緩和する効果が得られる。
フッ素含有高分子化合物は、変性フッ素含有高分子化合物を構成するフッ素含有樹脂に含まれる反復単位をその反復単位として含むことが好ましい。これにより樹脂結着剤の化学安定性が更に増すとともに、密着力がより強固になる。樹脂結着剤中に含まれる変性フッ素含有高分子化合物の含有割合は１０〜１００重量％である。好ましくは４０重量％〜１００重量％である。
【００２７】
無機質粒子はＳｉ、Ｇｅ、Ｍｇ、Ｓｎ、Ｐｂ、Ａｇ、Ａｌ、Ｚｎ、Ｃｄ、Ｓｂ、Ｂｉ及びＩｎからなる群より選ばれた少なくとも１種の元素が単体、酸化物又は他の金属との合金、単体とリチウムとの合金、及びこれらの金属、リチウムを含む多元合金で構成される。この無機物粒子はリチウムを吸蔵・放出可能な機能を有する。Ｓｉをベースにした無機質粒子としては、Ｓｉ単結晶、ポリシリコン、アモルファスシリコン、Ｃａ、Ｆｅ、Ｎｉ、Ｃｏ、Ｍｎ、Ｍｇ等と形成するＳｉシリサイド、シリコンオキシカーバイド、シリコンカーバイド等が挙げられる。この無機質粒子の平均粒径は０．０１〜５０μｍである。好ましい平均粒径は０．２〜３０μｍである。
【００２８】
本発明の負極材料には導電助剤が更に含まれる。導電助剤には、粒径０．５〜３０μｍ、黒鉛化度５０％以上の炭素材が用いられる。具体的には、アセチレンブラック（以下、ＡＢという。）が挙げられる。また本発明の負極材料には塩及び相溶性有機溶媒が更に含まれる。塩及び相溶性有機溶媒としては、ジメチルアセトアミド、アセトン、ジメチルフォルムアミド、Ｎ-メチルピロリドン（以下、ＮＭＰという。）、テトラヒドロフラン等が挙げられる。
本発明の負極材料に含まれる樹脂結着剤の割合は負極材料中に含まれる固形物全体の１〜５０重量％が好適である。１重量％未満であると、負極集電体と負極活物質層との密着性に劣り、５０重量％を越えると、充放電容量が低下する。より好ましくは、３〜４０重量％である。
【００２９】
負極を構成する本発明の非水電解質二次電池用電極構造体は、図１に示すように、負極集電体１４と、負極集電体１４の上に本発明の負極材料を塗工して形成された負極活物質層１６とを備える。本発明の負極材料を用いて作製した電極構造体は、集電体と活物質との密着性に優れ、高い機械強度を保持できる。また、充放電のリチウムイオンの挿入、脱離反応に伴うストレスを制御し、サイクル特性を向上できる。
本発明の電極構造体は、図２に示すように、負極集電体１４と負極活物質層１６との間に、結着剤と導電助剤をそれぞれ含む密着層１９を設けることで、負極集電体１４と負極活物質層１６との密着性が更に高まる。
【００３０】
本発明の非水電解質二次電池は、図１に示すように、本発明の負極材料、又は本発明の電極構造体を用いて負極１７を形成し、この負極１７と非水電解質層１８と、正極集電体１１の上に正極活物質層１２を形成してなる正極１３とをそれぞれこの順に積層して形成される。本発明の負極材料又は本発明の電極構造体を用いて作製した非水電解質二次電池は、集電体と活物質との密着性に優れ、高い機械強度を保持できる。また、充放電のリチウムイオンの挿入、脱離反応に伴うストレスを制御し、サイクル特性を向上できる。
非水電解質層としては、高分子化合物からなるセパレータ層、塩及び相溶性有機溶媒をそれぞれ含むポリマー電解質等が挙げられる。ポリマー電解質に含まれるポリマーは、本発明の負極材料の樹脂結着剤に含まれる変性フッ素含有高分子化合物を構成するフッ素含有樹脂に含まれる反復単位をその反復単位として含むことで、非水電解質層と負極活物質層との密着性が更に向上する。
【００３１】
次に、本発明の非水電解質二次電池の製造手順をリチウムイオンポリマー二次電池を例にとって説明する。
先ず、シート状の正極及び負極集電体をそれぞれ用意する。シート状の正極集電体としてはＡｌ箔が、負極集電体としてはＣｕ箔がそれぞれ挙げられる。
次いで、負極活物質層に必要な成分として本発明の負極材料、具体的には、Ｓｉ粒子等の無機質粒子、変性フッ素含有高分子化合物を含む樹脂結着剤、ＡＢ等の導電助剤及びＮＭＰ等の溶媒等をそれぞれ混合して、本発明の負極材料のスラリーを調製する。
【００３２】
次に、正極活物質層及び電解質層に必要な成分をそれぞれ混合して正極活物質層塗工用スラリー及び電解質層塗工用スラリーをそれぞれ調製する。
得られた負極材料のスラリーを負極集電体上にドクターブレード法により塗布して乾燥し、圧延することにより負極を形成する。ここでドクターブレード法とは、キャリアフィルムやエンドレスベルト等のキャリア上に載せて運ばれるスリップの厚さをドクターブレードと呼ばれるナイフエッジとキャリアとの間隔を調整することによってシートの厚さを精密に制御する方法である。
【００３３】
また正極も同様にして、得られた正極活物質層塗工用スラリーを正極集電体上にドクターブレード法により塗布して乾燥し、圧延することにより正極を形成する。正極又は負極活物質層は乾燥後の厚さが、２０〜２５０μｍとなるように形成する。電解質層は得られた電解質層塗工用スラリーを剥離紙上に電解質層の乾燥厚さが１０〜１５０μｍとなるようにドクターブレード法により塗工及び乾燥し、剥離紙より剥がして形成する。また、電解質層塗工用スラリーを正極表面や負極表面に塗工及び乾燥して電解質層を形成してもよい。それぞれ形成した正極と電解質層と負極を順に積層し、積層物を熱圧着することにより、図１に示すように、シート状の電極体が形成される。
最後に、この電極体にＮｉからなる正極リード及び負極リードをそれぞれ正極集電体及び負極集電体に溶接し、開口部を有する袋状に加工したラミネートパッケージ材に収納し、減圧条件下で熱圧着により開口部を封止して、シート状のリチウムイオンポリマー二次電池が作製できる。
【００３４】
【実施例】
次に本発明の実施例を比較例とともに詳しく説明する。
＜変性フッ素含有高分子化合物Ａの合成＞
先ず、幹重合体を構成する材料としてＰＶｄＦ粉末５０ｇを、変性物質を構成する材料として１５重量％アクリル酸水溶液４００ｇをそれぞれ用意した。ＰＶｄＦ粉末をポリエチレン製パックに入れて真空パックし、ＰＶｄＦへの吸収線量が５０ｋＧｙとなるように60Ｃｏをγ線源としてγ線を照射した。γ線照射したＰＶｄＦ粉末をポリエチレン製パックより取出して窒素雰囲気に移し、１５重量％アクリル酸水溶液４００ｇ中にＰＶｄＦ粉末を供給してアクリル酸水溶液と反応させた。反応中は反応溶液のサンプルを逐次採取し、この採取液に水酸化ナトリウムを用いて滴定を行い、ＰＶｄＦと反応したアクリル酸量を算出した。アクリル酸の消耗量がＰＶｄＦ重量の２０．４８％になった時点で反応を止めて、得られた固体状生成物を純水で洗浄して乾燥させ、変性フッ素含有高分子化合物Ａ（以下、変性化合物Ａという。）を得た。この変性化合物Ａ中の変性物質割合は１７重量％であった。
【００３５】
＜変性フッ素含有高分子化合物Ｂの合成＞
変性物質を構成する材料としてメタクリル酸を用いた以外は変性化合物Ａの合成と同様にして合成を行い、変性フッ素含有高分子化合物Ｂ（以下、変性化合物Ｂという。）を得た。
＜変性フッ素含有高分子化合物Ｃの合成＞
幹重合体を構成する材料としてＶｄＦ-ＨＦＰ共重合体粉末を用いた以外は変性化合物Ａの合成と同様にして合成を行い、変性フッ素含有高分子化合物Ｃ（以下、変性化合物Ｃという。）を得た。
＜変性フッ素含有高分子化合物Ｄの合成＞
ＰＶｄＦへの吸収線量が７０ｋＧｙとなるようにγ線を照射し、変性フッ素含有高分子化合物中のＰＶｄＦ割合を８０重量％、アクリル酸割合を２０重量％となるように合成した以外は変性化合物Ａの合成と同様にして合成を行い、変性フッ素含有高分子化合物Ｄ（以下、変性化合物Ｄという。）を得た。
【００３６】
＜実施例１＞
先ず、正極集電体として厚さ２０μｍ、幅２５０μｍのＡｌ箔を、負極集電体として厚さ１４μｍ、幅２５０μｍのＣｕ箔をそれぞれ用意した。
次いで、無機質粒子として平均粒径０．４μｍのＳｉ粒子を、樹脂結着剤の変性フッ素含有高分子化合物として変性化合物Ａを、導電助剤としてＡＢを、溶媒としてＮＭＰをそれぞれ用意した。無機質粒子を５０重量部、樹脂結着剤を１０重量部、導電助剤を４０重量部及び溶媒を５０重量部それぞれ混合してボールミルで２時間混合することにより、負極材料のスラリーを調製した。
次に、表１に示される各成分をボールミルで２時間混合することにより、正極活物質層塗工用スラリー及び電解質層塗工用スラリーをそれぞれ調製した。
【００３７】
【表１】
【００３８】
得られた負極材料のスラリーを負極集電体表面に負極活物質層の乾燥厚さが８０μｍとなるようにドクターブレード法により塗工及び乾燥し、圧延することにより負極を形成した。同様に、正極活物質層塗工用スラリーを正極集電体表面に塗工及び乾燥し、圧延することにより正極を形成した。更に電解質層塗工用スラリーを乾燥厚さが５０μｍになるように上記正極にドクターブレード法により塗工し、電解質層を有する正極と負極を積層して熱圧着することにより、シート状の電極体を作製した。作製した電極体にＮｉからなる正極リード及び負極リードをそれぞれ正極集電体、負極集電体に溶接し、開口部を有する袋状に加工したラミネートパッケージ材に収納し、減圧条件下で開口部を熱圧着して封止し、シート状電池を作製した。
【００３９】
＜実施例２＞
無機質粒子として平均粒径１μｍのＳｉ粒子を、樹脂結着剤には変性フッ素含有高分子化合物として変性化合物Ａを、フッ素含有高分子化合物としてＶｄＦ-ＨＦＰ共重合体をそれぞれ用意し、無機質粒子を５０重量部、変性化合物Ａを１０重量部、ＶｄＦ-ＨＦＰ共重合体を５重量部、導電助剤を３５重量部及び溶媒を６０重量部となるようにそれぞれ混合して負極材料のスラリーを調製した以外は実施例１と同様にしてシート状電池を作製した。
＜実施例３＞
無機質粒子として平均粒径１μｍのＳｉ粒子を、樹脂結着剤には変性フッ素含有高分子化合物として変性化合物Ｂをそれぞれ用意し、無機質粒子を４０重量部、変性化合物Ｂを２０重量部、導電助剤を４０重量部及び溶媒を８０重量部となるようにそれぞれ混合して負極材料のスラリーを調製した以外は実施例１と同様にしてシート状電池を作製した。
＜実施例４＞
無機質粒子として平均粒径１μｍのＳｉ粒子を、樹脂結着剤には変性フッ素含有高分子化合物として変性化合物Ｃをそれぞれ用意し、無機質粒子を６０重量部、変性化合物Ｃを１０重量部、導電助剤を３０重量部及び溶媒を５０重量部となるようにそれぞれ混合して負極材料のスラリーを調製した以外は実施例１と同様にしてシート状電池を作製した。
【００４０】
＜実施例５＞
無機質粒子として平均粒径１０μｍのＳｉ粒子を、樹脂結着剤には変性フッ素含有高分子化合物として変性化合物Ｄをそれぞれ用意し、無機質粒子を５０重量部、変性化合物Ｄを１０重量部、導電助剤を４０重量部及び溶媒を５０重量部となるようにそれぞれ混合して負極材料のスラリーを調製した以外は実施例１と同様にしてシート状電池を作製した。
＜実施例６＞
無機質粒子として平均粒径１５μｍのＳｉ粒子を、樹脂結着剤には変性フッ素含有高分子化合物として変性化合物Ｄを、フッ素含有高分子化合物としてＶｄＦ-ＨＦＰ共重合体をそれぞれ用意し、無機質粒子を５０重量部、変性化合物Ｄを７重量部、ＶｄＦ-ＨＦＰ共重合体を３重量部、導電助剤を４０重量部及び溶媒を５０重量部となるようにそれぞれ混合して負極材料のスラリーを調製した以外は実施例１と同様にしてシート状電池を作製した。
【００４１】
＜比較例１＞
無機質粒子として平均粒径１０μｍのＳｉ粒子を、樹脂結着剤にはＰＶｄＦをそれぞれ用意し、無機質粒子を５０重量部、ＰＶｄＦを１０重量部、導電助剤を４０重量部及び溶媒を５０重量部となるようにそれぞれ混合して負極材料のスラリーを調製した以外は実施例１と同様にしてシート状電池を作製した。
＜比較例２＞
無機質粒子として平均粒径５μｍのＳｉ粒子を、樹脂結着剤にはＰＴＦＥをそれぞれ用意し、無機質粒子を５０重量部、ＰＴＦＥを１０重量部、導電助剤を４０重量部及び溶媒を５０重量部となるようにそれぞれ混合して負極材料のスラリーを調製した以外は実施例１と同様にしてシート状電池を作製した。
＜比較例３＞
無機質粒子として平均粒径１μｍのＳｉ粒子を、樹脂結着剤にはＶｄＦ-ＨＦＰ共重合体をそれぞれ用意し、無機質粒子を４０重量部、ＶｄＦ-ＨＦＰ共重合体を１５重量部、導電助剤を４５重量部及び溶媒を５０重量部となるようにそれぞれ混合して負極材料のスラリーを調製した以外は実施例１と同様にしてシート状電池を作製した。
【００４２】
＜比較試験及び評価＞
実施例１〜６及び比較例１〜３でそれぞれ得られたシート状電池を用いて以下の評価試験を行った。
(1) 電池のサイクル容量維持特性試験
得られたシート状の電池を充放電サイクル試験にかけ、最大充電電圧４Ｖ、負極活物質の充電電流が４００ｍＡｈ／ｇとなるような条件で１０時間の充電を行う充電工程と、充電工程と同様の電流の条件で放電電圧が最低放電電圧となる２．０Ｖまで放電を行う放電工程とを１サイクルとして充放電サイクルを繰返し、充放電試験を行う際に、各サイクルの充放電容量をそれぞれ測定して、１０サイクル目の放電容量保持率（(１０サイクル目の放電容量／初期放電容量)×１００）を求めた。
【００４３】
(2) 密着層の集電体及び活物質層に対する密着性試験
得られたシート状の電池に対して上記評価試験(1)と同様の条件での充放電サイクルを１０サイクル行った。その後、１０サイクルの充放電を終えたシート状電池の収納パッケージを除去し、電池の正極と負極を引き剥がしてそれぞれを分離した。分離した負極をピンセットでつまんで引っ張ったときに、負極活物質層と負極集電体とが剥離するか否かを確認した。またそのときの負極活物質層の状況を目視により確認した。
【００４４】
実施例１〜６及び比較例１〜３のシート状電池でそれぞれ用いた負極材料スラリーの組成を次の表２にそれぞれ示す。また、上記評価試験(1)及び(2)における評価結果を表３にそれぞれ示す。なお、表３中の密着性評価における記号は、次の意味である。◎：密着が良好である。×：完全に剥離されている。○：活物質層自身が一定な機械強度を持つシート状である。×：活物質層は機械強度が失われ、シート状ではない。
【００４５】
【表２】
【００４６】
【表３】
【００４７】
表３より明らかなように、評価試験(1)のサイクル容量維持特性試験では、比較例１〜３のシート状電池による放電容量保持率は大幅に低下していた。放電容量保持率の低下の原因としては、活物質である無機質粒子の充放電による膨張収縮が、活物質と集電体の界面で発生する剥離を引起こしたと考えられる。この剥離が電池の活物質と集電体の間の電子の流れを止めてしまったので、１０サイクル目における容量保持率を大幅に低下させたと考えられる。これに対して実施例１〜６のシート状電池による放電容量保持率はそれぞれ高い値を示していた。これは、実施例１〜６の樹脂結着剤に含まれる変性フッ素含有高分子化合物が無機質粒子と高い密着性を有しているため、充放電に伴う無機質粒子の体積膨張収縮による無機質粒子の剥離を防止し、サイクル容量を維持したのではないかと考えられる。また各実施例を比較すると、変性フッ素含有高分子化合物とフッ素含有高分子化合物をそれぞれ含む樹脂結着剤を用いた実施例２と実施例６の放電容量保持率が特に高い保持率が得られた。これはフッ素含有高分子化合物を含むことで、変性フッ素含有高分子化合物だけの結着剤に比べて化学安定性が更に高まったことと、集電体への密着性が向上したことによると推察される。
【００４８】
また比較例１〜３のシート状電池における評価試験(2)の１０サイクル後における密着性試験では、負極集電体と負極活物質層とが完全に剥離してしまっていた。これは負極活物質層内部において、無機質粒子と樹脂結着剤との接着面が充放電サイクルによる膨張収縮により剥がれてしまい、活物質層自体の凝集強度が失われたと考えられる。また数回の充放電によって本来はシート状であった活物質層が、破片状或いは砂状の形状に変化したのではないかと推察される。これに対して、実施例１〜６のシート状電池では、負極活物質層は負極集電体から剥離し難く、負極活物質層自体の凝集強度も維持していた。このように負極活物質層を形成する負極材料に変性フッ素含有高分子化合物を含む樹脂結着剤を含ませることによって、負極活物質層と負極集電体の接着を向上させ、無機質粒子を含む負極活物質層の体積変化に起因する剥離を防止することができる。
【００４９】
【発明の効果】
以上述べたように、本発明の非水電解質二次電池用負極材料は、樹脂結着剤と、Ｓｉ、Ｇｅ、Ｍｇ、Ｓｎ、Ｐｂ、Ａｇ、Ａｌ、Ｚｎ、Ｃｄ、Ｓｂ、Ｂｉ及びＩｎからなる群より選ばれた少なくとも１種の元素を含む無機質粒子の双方をそれぞれ含む負極材料の改良であり、その特徴ある構成は、樹脂結着剤がフッ素含有樹脂を変性物質により変性して得られた変性フッ素含有高分子化合物を含むところにある。
樹脂結着剤に含まれるフッ素含有樹脂を変性物質により変性して得られた変性フッ素含有高分子化合物は、フッ素含有高分子化合物が有する高い化学安定性を備えるだけでなく、無機質粒子への密着性に優れるため、充放電によるリチウムの吸蔵、脱離に伴う無機質粒子の体積変化に起因する無機質粒子の脱落や、電極の剥離等を防止し、サイクル特性を向上することができる。
従って、本発明の負極材料を用いて作製した電極構造体、非水電解質二次電池は、集電体と活物質との密着性に優れ、高い機械強度を保持できる。また、充放電のリチウムイオンの挿入、脱離反応に伴うストレスを制御し、サイクル特性を向上できる。
【図面の簡単な説明】
【図１】本発明の非水電解質二次電池の電極体を示す部分断面構成図。
【図２】本発明の別の非水電解質二次電池の電極体を示す部分断面構成図。
【図３】変性フッ素含有高分子化合物の合成を示す模式図。
【符号の説明】
１１ 正極集電体
１２ 正極活物質層
１３ 正極
１４ 負極集電体
１６ 負極活物質層
１７ 負極（電極構造体）
１８ 非水電解質層[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a negative electrode material used for a non-aqueous electrolyte secondary battery, an electrode structure manufactured using the negative electrode material, and a non-aqueous electrolyte secondary battery.
[0002]
[Prior art]
With the spread of portable devices such as video cameras and notebook computers in recent years, demand for thin batteries has been increasing. As this thin battery, a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery formed by laminating a positive electrode and a negative electrode is known. The positive electrode is formed by forming a positive electrode active material layer on the surface of a sheet-shaped positive electrode current collector, and the negative electrode is formed by forming a negative electrode active material layer on the surface of a sheet-shaped negative electrode current collector. . An electrolyte layer is interposed between the positive electrode active material layer and the negative electrode active material layer. In this battery, a positive electrode terminal and a negative electrode terminal for taking out a potential difference in each active material as a current are provided on a positive electrode current collector and a negative electrode current collector, and the thus stacked ones are sealed in a package to make lithium. An ion secondary battery is formed. In this lithium ion secondary battery, desired electricity can be obtained by using the positive electrode terminal and the negative electrode terminal drawn out of the package as terminals of the battery.
[0003]
Lithium ion secondary batteries having such a structure have attracted much attention because of their high battery voltage and high energy density. In order to further increase the discharge capacity of this lithium ion secondary battery, it is necessary to increase the area of the sheet-like positive electrode or negative electrode. If the area of the positive electrode or the negative electrode is simply enlarged, the handling becomes difficult due to the large area. In order to solve this problem, it is conceivable to fold or wind the enlarged sheet-like positive electrode or negative electrode to a desired size. However, when folding or winding is performed in a state where the sheet-like positive electrode or negative electrode is laminated, the positive electrode or the negative electrode at the fold portion is bent, and the sheet at that portion is peeled off from the electrolyte layer and the effective interface between the electrode and the electrolyte is formed. There is a problem that the surface area is reduced and the discharge capacity is reduced, and resistance is generated inside the battery to deteriorate the cycle characteristics of the discharge capacity. Similarly, there is also a problem that the active material layer forming the positive electrode or the negative electrode is separated from the current collector due to the bending at the fold portion. Further, in this battery, during the charging and discharging process, the positive and negative electrode active materials absorb and release lithium ions, which causes the positive and negative electrode active material layers to expand and contract. There was also a problem of peeling from the current collector.
[0004]
Therefore, as a technique for solving the above-mentioned problems, as described below, techniques for preventing the active material layer from peeling off from the current collector and reducing the adhesion have been proposed.
A polymer compound having a polyvinyl alcohol unit having an average degree of polymerization of 20 or more, and a part or all of hydroxyl groups substituted with an oxyalkylene-containing group having an average degree of molar substitution of 0.3 or more, a binder resin comprising the polymer compound, Also, a composition for an ion-conductive polymer electrolyte having high ionic conductivity and high adhesiveness and a secondary battery have been proposed (for example, see Patent Document 1). In the present invention, by using a polymer compound in which the introduction ratio of a polyoxyalkylene moiety is increased as a material of a solid polymer electrolyte or a material of a binder resin, ion transfer is facilitated and the ionic conductivity of the polymer for a polymer electrolyte is improved. Is increasing.
[0005]
A polymer compound obtained by reacting a hydroxyl group of an alcohol compound having a substituent having a large dipole moment with a part or all of an isocyanate group in a polyurethane compound obtained by reacting an isocyanate compound and a polyol compound, a binder resin, and an ion. A composition for a conductive polymer electrolyte and a secondary battery have been proposed (for example, see Patent Document 2). In the present invention, by introducing a substituent having a large dipole moment into the polyurethane, the adhesion between the electrode and the electrolyte is improved while maintaining a high dielectric constant and the ability to dissolve the ionic conductive salt at a high concentration. As a result, an interface impedance comparable to that of the electrolyte solution is obtained.
A polymer compound obtained by reacting a hydroxyl group of an alcohol compound having a large dipole moment with a part or all of the isocyanate groups in a polyurethane compound obtained by reacting an isocyanate compound with a polyol compound; A composition for an ionic conductive solid polymer, a ionic conductive solid polymer electrolyte, a binder resin, and a secondary battery mainly comprising a salt and a compound having a crosslinkable functional group have been proposed (eg, patents). Reference 3).
[0006]
An electrode material for a negative electrode of a lithium secondary battery, an electrode structure using the electrode material, a lithium secondary battery using the electrode structure, and a method for manufacturing the electrode structure and the lithium secondary battery have been proposed. (For example, see Patent Document 4). In the present invention, an amorphous M.A.X alloy having a non-stoichiometric composition (M is at least one element selected from the group consisting of Si, Ge and Mg, and A is a transition metal element) X represents O, F, N, Ba, Sr, Ca, La, Ce, C, P, S, Se, Te, B, Bi, Sb, Al, In And at least one element selected from the group consisting of Zn and Zn, provided that X does not need to be contained, and the content of the constituent element M of the alloy is M / (M + A + X) = 20 to 80 atomic%.) It contains. An electrode material containing such an alloy has excellent characteristics and is suitable as a negative electrode active material of a lithium secondary battery.
[0007]
A positive electrode provided with a positive electrode active material containing lithium, a negative electrode provided with a negative electrode active material layer in which a mixture of a silicon compound and a carbon material capable of doping / dedoping lithium are dispersed in a binder, A non-aqueous electrolyte battery including a non-aqueous electrolyte interposed between a positive electrode and a negative electrode and having a glass transition temperature of −40 ° C. or lower as the binder has been proposed (for example, see Patent Document 5). ). In the present invention, the binder in the negative electrode active material has a glass transition temperature of −40 ° C. or less, so that the binder absorbs the volume change of the silicon compound negative electrode during lithium doping and undoping. However, a change in volume of the entire negative electrode active material layer is suppressed, and cycle deterioration is suppressed.
Furthermore, a non-aqueous electrolyte secondary battery comprising a positive electrode and a negative electrode capable of inserting and extracting lithium ions, and a non-aqueous electrolyte having lithium ion conductivity, and containing a water-soluble polymer in the electrode mixture of the positive electrode or the negative electrode is proposed. (See, for example, Patent Document 6). In the present invention, the water-soluble polymer is contained in the electrode mixture, so that the binding property to the current collector is good, and since the solvent is water, the production cost can be reduced. Can be suppressed. Further, drying can be performed at a relatively low temperature, and thermal damage to the mixture and the material constituting the sheet electrode can be minimized.
[0008]
[Patent Document 1]
PCT International Publication No. WO00 / 56780
[Patent Document 2]
PCT International Publication No. WO 00/56797
[Patent Document 3]
PCT International Publication No. WO00 / 56815
[Patent Document 4]
PCT International Publication No. WO00 / 17949
[Patent Document 5]
JP-A-2000-299108
[Patent Document 6]
JP-A-9-289022
[0009]
[Problems to be solved by the invention]
However, in a secondary battery including a non-aqueous electrolyte, it is generally difficult to bond the negative electrode current collector and the negative electrode active material layer. In the negative electrode material disclosed in Patent Document 4, for example, Si, Ge, In the case of a negative electrode active material containing elements such as Al and Sn, although a high charge / discharge capacity can be obtained, the volume change of the active material due to charge / discharge is large, and the active material layer and the current collector are separated. was there. The binder disclosed in Patent Document 5 is characterized by flexibility and can absorb a change in volume of the active material to some extent. However, this type of binder has a sufficient adhesive strength with the current collector. I could not say. Patent Documents 1 to 4 and 6 and the like aim at improving the adhesion between the active material and the current collector, and improve the binder. However, these binders generally have chemical stability. There remain problems such as inferiority to resins such as polyethylene and polyvinylidene fluoride (hereinafter referred to as PVdF) used for batteries, and insufficient adhesiveness in an environment in which an electrolyte exists.
[0010]
An object of the present invention is to provide a negative electrode material for a non-aqueous electrolyte secondary battery, which has high chemical stability and excellent adhesion to inorganic particles.
Another object of the present invention is to provide an electrode structure and a non-aqueous electrolyte secondary battery that are manufactured using a negative electrode material and have excellent adhesion between a current collector and an active material and can maintain high mechanical strength. It is in.
Still another object of the present invention is to provide an electrode structure and a non-aqueous electrolyte secondary battery manufactured using a negative electrode material, which can control the stress associated with the insertion and desorption reactions of lithium ions during charge and discharge and can improve cycle characteristics. Is to provide.
[0011]
[Means for Solving the Problems]
The invention according to claim 1 includes a resin binder and at least one element selected from the group consisting of Si, Ge, Mg, Sn, Pb, Ag, Al, Zn, Cd, Sb, Bi, and In. The present invention is an improvement of a negative electrode material for a non-aqueous electrolyte secondary battery including both of the inorganic particles including a modified fluorine-containing resin obtained by modifying a fluorine-containing resin with a modifying substance using a resin binder. Contains molecular compounds.
In the invention according to claim 1, the modified fluorine-containing polymer obtained by modifying the fluorine-containing resin contained in the resin binder with a modifying substance has the same high chemical stability that the fluorine-containing polymer has. In addition to having stability, it also has excellent adhesion to inorganic particles, preventing omission of inorganic particles due to volume change of inorganic particles due to occlusion and desorption of lithium due to charge and discharge, peeling of electrodes, etc. Cycle characteristics can be improved.
[0012]
The invention according to claim 2 is the invention according to claim 1, wherein the modified fluorine-containing polymer compound 24 is formed of a fluorine-containing resin as the trunk polymer 22 as shown in FIG. Is a negative electrode material which is a polymer compound obtained by graft-modifying with a modifying substance 23.
The invention according to claim 3 is the invention according to claim 1 or 2, wherein the trunk polymer constituting the modified fluorine-containing polymer compound is PVdF, polyvinyl fluoride (hereinafter, referred to as PVF), and tetrafluoride. Ethylene polymer, trifluorinated ethylene polymer, difluoroethylene polymer, vinylidene fluoride-hexafluoropropylene copolymer (hereinafter referred to as VdF-HFP copolymer), ethylene-tetrafluoroethylene copolymer, 4-fluoroethylene A negative electrode material containing at least one fluorine-containing resin selected from the group consisting of a fluorinated ethylene-6-fluoropropylene copolymer, a trifluorinated ethylene polymer, and polytetrafluoroethylene.
[0013]
The invention according to claim 4 is the invention according to claim 1 or 2, wherein the modified substance constituting the modified fluorine-containing polymer compound is at least one of acrylic acid, methyl acrylate, methacrylic acid, and methyl methacrylate. The negative electrode material is as follows.
The invention according to claim 5 is the invention according to claim 3 or 4, wherein the backbone polymer constituting the modified fluorine-containing polymer compound contains one or both of PVdF and VdF-HFP copolymer. Wherein the modifying substance is acrylic acid.
The invention according to claim 6 is the invention according to claim 3 or 5, wherein when the backbone polymer of the modified fluorine-containing polymer compound is vinylidene fluoride, 95% of vinylidene fluoride is added to the modified fluorine-containing polymer compound. It is a negative electrode material contained at a ratio of from 60% by weight to 60% by weight.
[0014]
The invention according to claim 7 is the invention according to any one of claims 1 to 6, wherein the modified fluorine-containing polymer compound is a negative electrode material in which a fluorine-containing resin and a modified substance are grafted by radiation irradiation treatment. .
The invention according to claim 8 is the invention according to claim 7, wherein the irradiation of the fluorine-containing resin with radiation is performed by γ-ray irradiation, and the absorption dose of γ-ray of the fluorine-containing resin is 10 to 90 kGy. Material.
The invention according to claim 9 is the invention according to any one of claims 1 to 8, wherein the resin binder further comprises a fluorine-containing polymer compound having a structure different from that of the modified fluorine-containing polymer compound. It is.
According to the ninth aspect of the present invention, by further containing not only the modified fluorine-containing polymer compound but also the fluorine-containing polymer compound, the chemical stability is further improved, and the adhesion to the current collector is also improved. In addition, by including a fluorine-containing polymer compound that is more flexible than the modified fluorine-containing polymer compound, the effect of alleviating the stress caused by the volume change of the inorganic particles due to the occlusion and desorption of lithium due to charge and discharge. Is obtained.
[0015]
The invention according to claim 10 is the invention according to claim 9, wherein the fluorine-containing polymer compound includes, as a repeating unit, a repeating unit contained in a fluorine-containing resin constituting the modified fluorine-containing polymer compound. It is.
In the invention according to claim 10, the chemical stability of the resin binder is increased by the fact that the repeating unit of the fluorine-containing polymer compound contains a repeating unit contained in the fluorine-containing resin constituting the modified fluorine-containing polymer compound. At the same time, the adhesion becomes stronger.
[0016]
An invention according to claim 11 is the invention according to any one of claims 1 to 10, wherein the content of the modified fluorine-containing polymer compound in the resin binder is 10 to 100% by weight. is there.
A twelfth aspect of the present invention is the negative electrode material according to the first aspect, wherein the average particle diameter of the inorganic particles is 0.01 to 50 μm.
The invention according to claim 13 is the invention according to claim 1 or 12, wherein the inorganic particles are selected from the group consisting of Si, Ge, Mg, Sn, Pb, Ag, Al, Zn, Cd, Sb, Bi, and In. At least one selected element is a negative electrode material composed of a simple substance, an alloy of an oxide or another metal, an alloy of a simple substance and lithium, and a multi-element alloy containing these metals and lithium.
[0017]
The invention according to claim 14 is the invention according to any one of claims 1 to 13, which is a negative electrode material further including a conductive auxiliary in the material.
The invention according to claim 15 is the invention according to any one of claims 1 to 14, wherein the material further comprises a salt and a compatible organic solvent in the material.
A sixteenth aspect of the present invention is the negative electrode material according to any one of the first to fifteenth aspects, wherein the ratio of the resin binder is 1 to 50% by weight of the entire solid contained in the material. .
[0018]
According to a seventeenth aspect of the present invention, as shown in FIG. 1, a negative electrode current collector 14 and the negative electrode material according to any one of the first to sixteenth aspects are coated on the negative electrode current collector 14. An electrode structure for a non-aqueous electrolyte secondary battery including the formed negative electrode active material layer 16.
In the invention according to claim 17, the electrode structure manufactured using the negative electrode material of the present invention has excellent adhesion between the current collector and the active material, and can maintain high mechanical strength. In addition, the stress associated with the insertion and desorption reactions of lithium ions during charge and discharge can be controlled, and cycle characteristics can be improved.
[0019]
The invention according to claim 18 is the invention according to claim 17, wherein a binder and a conductive assistant are provided between the negative electrode current collector 14 and the negative electrode active material layer 16, respectively, as shown in FIG. This is an electrode structure provided with an adhesion layer 19 including the same.
According to a nineteenth aspect of the present invention, as shown in FIG. 1 or FIG. 2, the negative electrode 17 is formed by using the negative electrode material according to any one of the first to sixteenth aspects or the electrode structure according to the seventeenth or eighteenth aspects. A non-aqueous electrolyte secondary battery formed by laminating a negative electrode 17, a non-aqueous electrolyte layer 18, and a positive electrode 13 having a positive electrode active material layer 12 formed on a positive electrode current collector 11 in this order. It is.
In the invention according to claim 19, the non-aqueous electrolyte secondary battery manufactured using the negative electrode material of the present invention or the electrode structure of the present invention has excellent adhesion between the current collector and the active material, and has high mechanical strength. Can be retained. In addition, the stress associated with the insertion and desorption reactions of lithium ions during charge and discharge can be controlled, and cycle characteristics can be improved.
[0020]
The invention according to claim 20 is the invention according to claim 19, wherein the nonaqueous electrolyte layer between the positive electrode active material layer forming the positive electrode and the negative electrode active material layer forming the negative electrode is made of a polymer compound. A non-aqueous electrolyte secondary battery as a separator layer.
The invention according to claim 21 is the invention according to claim 19, wherein the non-aqueous electrolyte layer between the positive electrode active material layer forming the positive electrode and the negative electrode active material layer forming the negative electrode has a salt and compatibility. This is a non-aqueous electrolyte secondary battery that is a polymer electrolyte containing an organic solvent.
The invention according to claim 22 is the invention according to claim 21, wherein the polymer contained in the polymer electrolyte contains modified fluorine contained in the resin binder of the negative electrode material according to any one of claims 1 to 16. A non-aqueous electrolyte secondary battery including a repeating unit contained in a fluorine-containing resin constituting a polymer compound as the repeating unit.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, an embodiment of the present invention will be described with reference to the drawings.
The present invention relates to a method of preparing a resin binder and inorganic particles containing at least one element selected from the group consisting of Si, Ge, Mg, Sn, Pb, Ag, Al, Zn, Cd, Sb, Bi and In. It is an improvement of a negative electrode material for a non-aqueous electrolyte secondary battery including both of them, and a characteristic configuration thereof includes a modified fluorine-containing polymer compound obtained by modifying a fluorine-containing resin with a modifying substance in a resin binder. There.
Here, `` modified '' means that the property changes, and in this specification, the modified substance is arranged everywhere in the resin that is the trunk polymer, so that only the property of the resin itself that is the trunk polymer is obtained. In other words, it means that the properties of the denatured substance are combined, or new properties that are not present in both are added.
[0022]
The modified fluorine-containing polymer compound obtained by modifying the fluorine-containing resin contained in the resin binder with a modifying substance has not only the same high chemical stability as the fluorine-containing polymer compound but also the same stability, Because of its excellent adhesion to inorganic particles, it is possible to prevent the loss of the inorganic particles due to the volume change of the inorganic particles due to the occlusion and desorption of lithium due to charge and discharge, the separation of the electrodes, etc., and to improve the cycle characteristics. it can.
The use of a compound containing fluorine in the molecule as the polymer compound contained in the resin binder of the negative electrode material constituting the negative electrode active material layer is because the negative electrode active material layer is chemically, electrochemically, and thermally formed in the battery. This is because stability is required. The modified fluorine-containing polymer compound is obtained by using a fluorine-containing resin as a trunk polymer and graft-modifying the trunk polymer with a modifying substance.
[0023]
Graft polymerization is used for arranging and modifying a modified substance as a branch polymer in some places of the backbone polymer. The backbone polymer includes PVdF, PVF, tetrafluoroethylene polymer, trifluoride ethylene polymer, difluoroethylene polymer, VdF-HFP copolymer, ethylene tetrafluoroethylene copolymer, and tetrafluoroethylene copolymer. At least one fluorine-containing resin selected from the group consisting of hexafluoropropylene copolymer, trifluorinated ethylene polymer and polytetrafluoroethylene is included. In addition, examples of the modified substance include at least one of acrylic acid, methyl acrylate, methacrylic acid, and methyl methacrylate. By using these modified substances, good adhesion to the inorganic particles and the negative electrode current collector can be obtained.
In particular, a modified fluorine-containing polymer compound in which the trunk polymer is a mixture containing one or both of PVdF and VdF-HFP copolymer, and the modifying substance is acrylic acid, is any of PVdF or VdF-HFP copolymer. A mixture containing one or both has high adhesion to the inorganic particles, and the acrylic acid group has high adhesion to the negative electrode current collector material, so that it is excellent as a modified fluorine-containing polymer compound contained in the resin binder. It has properties.
[0024]
When the backbone polymer of the modified fluorine-containing polymer compound is vinylidene fluoride, it is preferable that vinylidene fluoride is contained in the modified fluorine-containing polymer compound at a ratio of 95% by weight to 60% by weight.
As a method for graft polymerization, there is a radiation method. In the radiation method, a fluorine-containing resin serving as a trunk polymer and a modifying material serving as a branch polymer are mixed, and the mixture can be polymerized by continuously or intermittently emitting radiation to the mixture. It is preferred that the fluorine-containing resin be pre-radiated before contacting the substrate. Specifically, after irradiating the fluorine-containing resin with radiation, a modified substance is mixed into the irradiation target, so that the fluorine-containing resin is a trunk polymer, and the modified substance is a branched polymer. Can be obtained. Γ-rays are used for radiation used for graft polymerization. Irradiation with γ-rays is performed so that the absorbed dose to the fluorine-containing resin is 1 to 90 kGy. By irradiating the fluorine-containing resin serving as the backbone polymer with radiation, a radical is formed at one end, and the modified substance is easily polymerized.
[0025]
As shown in FIG. 3A, the trunk polymer 22 constituting the modified fluorine-containing polymer compound has a repeating unit A as a basic unit. The basic unit of the backbone polymer may be one type as shown in FIG. 3A, or two or more types of basic units (not shown). This basic unit is preferably contained in the backbone polymer in a proportion of at least 50 molecular weight%. More preferably, it is contained at a ratio of 60 to 100 molecular weight%. As shown in FIG. 3B, the backbone polymer 22 is irradiated with radiation to form a radical 22a at one end of the basic unit A. As shown in FIG. 3 (c), when the modifying substance 23 (C in FIG. 3) is brought into contact with the backbone polymer 22 which has formed a radical, the modifying substance 23 is arranged in the radical portion 22a, and the modified fluorine A molecular compound 24 is formed. The modified substance 23 is preferably contained in the modified fluorine-containing polymer at a ratio of 2 to 50% by weight. More preferably, it is contained in the modified fluorine-containing polymer compound at a ratio of 5 to 30 molecular weight%.
In graft polymerization, the length of time during which the activated stem polymer resin is in contact with the modified material that becomes a branch polymer, the degree of preliminary activity by radiation, and the modified material that becomes a branched polymer becomes the stem polymer Polymerization differs depending on the degree to which the resin can pass through, the temperature when the resin and the modified substance are in contact, and the like. When the denaturing substance is an acid, the degree of grafting can be observed by sampling a solution containing the compound as a denaturing substance, titrating the solution with an alkali, and measuring the concentration of the remaining acid compound. The proportion of grafting in the obtained composition is desirably 2 to 50 molecular weight% of the final weight.
[0026]
It is preferable that the resin binder further contains a fluorine-containing polymer compound having a structure different from that of the modified fluorine-containing polymer compound. By further containing not only the modified fluorine-containing polymer compound but also the fluorine-containing polymer compound in the resin binder, the chemical stability is further improved, and the adhesion to the current collector is also improved. In addition, by including a fluorine-containing polymer compound that is more flexible than the modified fluorine-containing polymer compound, the effect of relieving stress caused by a change in volume of the inorganic particles due to occlusion and desorption of lithium due to charge and discharge is obtained. can get.
The fluorine-containing polymer compound preferably contains a repeating unit contained in the fluorine-containing resin constituting the modified fluorine-containing polymer compound as the repeating unit. Thereby, the chemical stability of the resin binder is further increased, and the adhesion is further strengthened. The content of the modified fluorine-containing polymer compound contained in the resin binder is 10 to 100% by weight. Preferably it is 40% by weight to 100% by weight.
[0027]
As the inorganic particles, at least one element selected from the group consisting of Si, Ge, Mg, Sn, Pb, Ag, Al, Zn, Cd, Sb, Bi and In is a simple substance, an oxide or an alloy with another metal. , An alloy of a simple substance and lithium, and a multi-element alloy containing these metals and lithium. These inorganic particles have a function of inserting and extracting lithium. Examples of the inorganic particles based on Si include Si single crystal, polysilicon, amorphous silicon, Si silicide formed with Ca, Fe, Ni, Co, Mn, Mg, etc., silicon oxycarbide, silicon carbide, and the like. The average particle size of the inorganic particles is 0.01 to 50 μm. The preferred average particle size is 0.2 to 30 μm.
[0028]
The negative electrode material of the present invention further contains a conductive auxiliary. As the conductive additive, a carbon material having a particle size of 0.5 to 30 μm and a degree of graphitization of 50% or more is used. Specific examples include acetylene black (hereinafter, referred to as AB). The negative electrode material of the present invention further contains a salt and a compatible organic solvent. Examples of the salt and the compatible organic solvent include dimethylacetamide, acetone, dimethylformamide, N-methylpyrrolidone (hereinafter, referred to as NMP), tetrahydrofuran, and the like.
The proportion of the resin binder contained in the negative electrode material of the present invention is preferably from 1 to 50% by weight of the entire solid contained in the negative electrode material. If it is less than 1% by weight, the adhesion between the negative electrode current collector and the negative electrode active material layer is poor. If it exceeds 50% by weight, the charge / discharge capacity is reduced. More preferably, it is 3 to 40% by weight.
[0029]
As shown in FIG. 1, the electrode structure for a nonaqueous electrolyte secondary battery of the present invention, which constitutes the negative electrode, includes a negative electrode current collector 14, and a negative electrode material of the present invention coated on the negative electrode current collector 14. And a negative electrode active material layer 16 formed by the above method. The electrode structure manufactured using the negative electrode material of the present invention has excellent adhesion between the current collector and the active material, and can maintain high mechanical strength. In addition, the stress associated with the insertion and desorption reactions of lithium ions during charge and discharge can be controlled, and cycle characteristics can be improved.
As shown in FIG. 2, the electrode structure of the present invention has a structure in which an adhesion layer 19 containing a binder and a conductive auxiliary agent is provided between a negative electrode current collector 14 and a negative electrode active material layer 16, respectively. The adhesion between the current collector 14 and the negative electrode active material layer 16 is further increased.
[0030]
As shown in FIG. 1, the nonaqueous electrolyte secondary battery of the present invention forms a negative electrode 17 using the negative electrode material of the present invention or the electrode structure of the present invention, and the negative electrode 17 and the nonaqueous electrolyte layer 18 And a positive electrode 13 in which a positive electrode active material layer 12 is formed on a positive electrode current collector 11. The nonaqueous electrolyte secondary battery manufactured using the negative electrode material of the present invention or the electrode structure of the present invention has excellent adhesion between the current collector and the active material, and can maintain high mechanical strength. In addition, the stress associated with the insertion and desorption reactions of lithium ions during charge and discharge can be controlled, and cycle characteristics can be improved.
Examples of the non-aqueous electrolyte layer include a separator layer made of a polymer compound, a polymer electrolyte containing a salt and a compatible organic solvent, and the like. The polymer contained in the polymer electrolyte is a non-aqueous electrolyte containing the repeating unit contained in the fluorine-containing resin constituting the modified fluorine-containing polymer compound contained in the resin binder of the negative electrode material of the present invention as the repeating unit. The adhesion between the layer and the negative electrode active material layer is further improved.
[0031]
Next, the procedure for manufacturing the nonaqueous electrolyte secondary battery of the present invention will be described by taking a lithium ion polymer secondary battery as an example.
First, a sheet-shaped positive electrode current collector and a negative electrode current collector are prepared. The sheet-shaped positive electrode current collector includes an Al foil, and the negative electrode current collector includes a Cu foil.
Next, the negative electrode material of the present invention as a component necessary for the negative electrode active material layer, specifically, inorganic particles such as Si particles, a resin binder containing a modified fluorine-containing polymer compound, a conductive auxiliary agent such as AB, and NMP Are mixed to prepare a slurry of the negative electrode material of the present invention.
[0032]
Next, the components required for the positive electrode active material layer and the electrolyte layer are respectively mixed to prepare a slurry for coating the positive electrode active material layer and a slurry for coating the electrolyte layer.
The obtained slurry of the negative electrode material is applied on a negative electrode current collector by a doctor blade method, dried, and rolled to form a negative electrode. Here, the doctor blade method precisely adjusts the sheet thickness by adjusting the gap between the knife edge and the carrier, called the doctor blade, by adjusting the thickness of the slip carried on a carrier such as a carrier film or endless belt. How to control.
[0033]
Similarly, the positive electrode is formed by applying the obtained slurry for coating a positive electrode active material layer on a positive electrode current collector by a doctor blade method, drying, and rolling to form a positive electrode. The positive electrode or negative electrode active material layer is formed so that the thickness after drying is 20 to 250 μm. The electrolyte layer is formed by applying and drying the obtained slurry for coating an electrolyte layer on release paper by a doctor blade method so that the dry thickness of the electrolyte layer becomes 10 to 150 μm, and peeling off the release paper. Further, the electrolyte layer coating slurry may be applied to the positive electrode surface or the negative electrode surface and dried to form the electrolyte layer. The formed positive electrode, electrolyte layer, and negative electrode are sequentially laminated, and the laminate is subjected to thermocompression bonding to form a sheet-like electrode body as shown in FIG.
Finally, the positive electrode lead and the negative electrode lead made of Ni are welded to the positive electrode current collector and the negative electrode current collector, respectively, and are housed in a bag-shaped laminated package material having an opening. By sealing the opening by thermocompression bonding, a sheet-shaped lithium ion polymer secondary battery can be manufactured.
[0034]
【Example】
Next, examples of the present invention will be described in detail together with comparative examples.
<Synthesis of modified fluorine-containing polymer compound A>
First, 50 g of PVdF powder was prepared as a material constituting the trunk polymer, and 400 g of a 15% by weight aqueous solution of acrylic acid was prepared as a material constituting the modified substance. The PVdF powder is placed in a polyethylene pack and vacuum-packed so that the absorbed dose to PVdF becomes 50 kGy. 60 Irradiation was performed using Co as a γ-ray source. The gamma-irradiated PVdF powder was taken out of a polyethylene pack, transferred to a nitrogen atmosphere, and supplied with 400 g of a 15% by weight aqueous acrylic acid solution to react with the aqueous acrylic acid solution. During the reaction, samples of the reaction solution were sequentially sampled, and the sampled solution was titrated with sodium hydroxide to calculate the amount of acrylic acid reacted with PVdF. When the consumption of acrylic acid reaches 20.48% of the weight of PVdF, the reaction is stopped, and the obtained solid product is washed with pure water and dried, and the modified fluorine-containing polymer compound A (hereinafter, referred to as “the modified fluorine-containing polymer compound A”) is used. Modified Compound A) was obtained. The modified substance ratio in the modified compound A was 17% by weight.
[0035]
<Synthesis of modified fluorine-containing polymer compound B>
Synthesis was carried out in the same manner as in the synthesis of the modified compound A, except that methacrylic acid was used as a material constituting the modified substance, to obtain a modified fluorine-containing polymer compound B (hereinafter, referred to as modified compound B).
<Synthesis of modified fluorine-containing polymer compound C>
The synthesis is performed in the same manner as the synthesis of the modified compound A except that the VdF-HFP copolymer powder is used as a material constituting the backbone polymer, and a modified fluorine-containing polymer compound C (hereinafter, referred to as a modified compound C) is obtained. Obtained.
<Synthesis of modified fluorine-containing polymer compound D>
Modified compound A except that it was irradiated with γ-rays so that the absorbed dose to PVdF was 70 kGy, and synthesized so that the PVdF ratio in the modified fluorine-containing polymer was 80% by weight and the acrylic acid ratio was 20% by weight. Was synthesized in the same manner as in the synthesis of, to obtain a modified fluorine-containing polymer compound D (hereinafter, referred to as modified compound D).
[0036]
<Example 1>
First, an Al foil having a thickness of 20 μm and a width of 250 μm was prepared as a positive electrode current collector, and a Cu foil having a thickness of 14 μm and a width of 250 μm was prepared as a negative electrode current collector.
Next, Si particles having an average particle diameter of 0.4 μm were prepared as inorganic particles, modified compound A as a modified fluorine-containing polymer compound as a resin binder, AB as a conductive auxiliary, and NMP as a solvent. A slurry of the negative electrode material was prepared by mixing 50 parts by weight of the inorganic particles, 10 parts by weight of the resin binder, 40 parts by weight of the conductive auxiliary agent, and 50 parts by weight of the solvent and mixing them in a ball mill for 2 hours.
Next, the respective components shown in Table 1 were mixed by a ball mill for 2 hours to prepare a slurry for coating a positive electrode active material layer and a slurry for coating an electrolyte layer, respectively.
[0037]
[Table 1]
[0038]
The obtained slurry of the negative electrode material was applied to the surface of the negative electrode current collector by a doctor blade method such that the dry thickness of the negative electrode active material layer became 80 μm, dried, and then rolled to form a negative electrode. Similarly, the positive electrode active material layer coating slurry was coated on the surface of the positive electrode current collector, dried, and rolled to form a positive electrode. Further, an electrolyte layer coating slurry is applied to the positive electrode by a doctor blade method so that the dry thickness becomes 50 μm, and a positive electrode having an electrolyte layer and a negative electrode are laminated and thermocompression-bonded to form a sheet-like electrode body. Was prepared. The positive electrode lead and the negative electrode lead made of Ni were welded to the positive electrode current collector and the negative electrode current collector, respectively, and housed in a bag-shaped laminated package material having an opening, and the opening was opened under reduced pressure. Was sealed by thermocompression bonding to produce a sheet-shaped battery.
[0039]
<Example 2>
Si particles having an average particle diameter of 1 μm as inorganic particles, a modified compound A as a modified fluorine-containing polymer compound as a resin binder, and a VdF-HFP copolymer as a fluorine-containing polymer compound are prepared. A slurry of the negative electrode material was prepared by mixing 50 parts by weight, 10 parts by weight of the modified compound A, 5 parts by weight of the VdF-HFP copolymer, 35 parts by weight of the conductive additive and 60 parts by weight of the solvent. A sheet-like battery was produced in the same manner as in Example 1 except that the above procedure was repeated.
<Example 3>
Si particles having an average particle diameter of 1 μm are prepared as inorganic particles, and modified compound B is prepared as a modified fluorine-containing polymer compound as a resin binder. 40 parts by weight of inorganic particles, 20 parts by weight of modified compound B, A sheet-shaped battery was produced in the same manner as in Example 1 except that the slurry was prepared by mixing the agent to 40 parts by weight and the solvent to 80 parts by weight, respectively, to prepare a slurry of the negative electrode material.
<Example 4>
Si particles having an average particle size of 1 μm are prepared as inorganic particles, and modified compound C is prepared as a modified fluorine-containing polymer compound as a resin binder. 60 parts by weight of inorganic particles, 10 parts by weight of modified compound C, A sheet-shaped battery was produced in the same manner as in Example 1, except that the slurry was prepared by mixing the agents to 30 parts by weight and the solvent to 50 parts by weight, respectively, to prepare a slurry of the negative electrode material.
[0040]
<Example 5>
Si particles having an average particle diameter of 10 μm are prepared as inorganic particles, and modified compound D is prepared as a modified fluorine-containing polymer compound as a resin binder. 50 parts by weight of inorganic particles, 10 parts by weight of modified compound D, A sheet-shaped battery was produced in the same manner as in Example 1, except that the slurry was prepared by mixing the agents to 40 parts by weight and the solvent to 50 parts by weight, respectively, to prepare a slurry of the negative electrode material.
<Example 6>
Si particles having an average particle size of 15 μm as inorganic particles, a modified compound D as a modified fluorine-containing polymer compound as a resin binder, and a VdF-HFP copolymer as a fluorine-containing polymer compound were prepared. A slurry of the negative electrode material was prepared by mixing 50 parts by weight, 7 parts by weight of the modified compound D, 3 parts by weight of the VdF-HFP copolymer, 40 parts by weight of the conductive additive and 50 parts by weight of the solvent. A sheet-like battery was produced in the same manner as in Example 1 except that the above procedure was repeated.
[0041]
<Comparative Example 1>
Si particles having an average particle diameter of 10 μm are prepared as inorganic particles, and PVdF is prepared as a resin binder. 50 parts by weight of inorganic particles, 10 parts by weight of PVdF, 40 parts by weight of a conductive auxiliary agent, and 50 parts by weight of a solvent. A sheet-shaped battery was produced in the same manner as in Example 1 except that the respective materials were mixed so as to prepare a slurry of the negative electrode material.
<Comparative Example 2>
Si particles having an average particle diameter of 5 μm were prepared as inorganic particles, and PTFE was prepared as a resin binder. 50 parts by weight of inorganic particles, 10 parts by weight of PTFE, 40 parts by weight of a conductive auxiliary agent, and 50 parts by weight of a solvent were used. A sheet-shaped battery was produced in the same manner as in Example 1 except that the respective materials were mixed so as to prepare a slurry of the negative electrode material.
<Comparative Example 3>
Si particles having an average particle diameter of 1 μm were prepared as inorganic particles, and a VdF-HFP copolymer was prepared as a resin binder, 40 parts by weight of inorganic particles, 15 parts by weight of VdF-HFP copolymer, and a conductive additive. Was prepared in the same manner as in Example 1 except that a slurry of a negative electrode material was prepared by mixing each of 45 parts by weight and a solvent to 50 parts by weight.
[0042]
<Comparison test and evaluation>
The following evaluation tests were performed using the sheet batteries obtained in Examples 1 to 6 and Comparative Examples 1 to 3, respectively.
(1) Battery cycle capacity maintenance characteristics test
The obtained sheet-shaped battery is subjected to a charge / discharge cycle test, and a charging step of charging for 10 hours under conditions such that the maximum charging voltage is 4 V and the charging current of the negative electrode active material is 400 mAh / g, and a charging step similar to the charging step. The charge and discharge cycle is repeated with the discharge step of discharging the discharge voltage to 2.0 V at which the discharge voltage becomes the minimum discharge voltage under the current conditions as one cycle. When performing the charge and discharge test, the charge and discharge capacity of each cycle is measured. Thus, the discharge capacity retention rate at the 10th cycle ((discharge capacity at the 10th cycle / initial discharge capacity) × 100) was determined.
[0043]
(2) Adhesion test of adhesion layer to current collector and active material layer
The obtained sheet-shaped battery was subjected to 10 charge / discharge cycles under the same conditions as in the evaluation test (1). Thereafter, the storage package of the sheet-shaped battery after the completion of 10 cycles of charging and discharging was removed, and the positive electrode and the negative electrode of the battery were separated by separating. When the separated negative electrode was pinched with tweezers and pulled, it was confirmed whether or not the negative electrode active material layer and the negative electrode current collector were separated. The state of the negative electrode active material layer at that time was visually confirmed.
[0044]
The compositions of the negative electrode material slurries used in the sheet batteries of Examples 1 to 6 and Comparative Examples 1 to 3 are shown in Table 2 below. Table 3 shows the results of the evaluation tests (1) and (2). The symbols in the evaluation of adhesion in Table 3 have the following meanings. A: Good adhesion. ×: Completely peeled. ：: The active material layer itself is a sheet having a certain mechanical strength. ×: The active material layer loses mechanical strength and is not sheet-shaped.
[0045]
[Table 2]
[0046]
[Table 3]
[0047]
As is clear from Table 3, in the cycle capacity maintenance characteristic test of the evaluation test (1), the discharge capacity retention by the sheet batteries of Comparative Examples 1 to 3 was significantly reduced. It is considered that the cause of the decrease in the discharge capacity retention ratio is that the expansion and contraction of the inorganic particles as the active material due to charge and discharge caused peeling occurring at the interface between the active material and the current collector. It is considered that this peeling stopped the flow of electrons between the active material of the battery and the current collector, and thus greatly reduced the capacity retention at the tenth cycle. On the other hand, the discharge capacity retention rates of the sheet batteries of Examples 1 to 6 showed high values. This is because the modified fluorine-containing polymer compound contained in the resin binders of Examples 1 to 6 has high adhesion to the inorganic particles, so that the volume of the inorganic particles due to the volume expansion and contraction of the inorganic particles accompanying charge and discharge is increased. It is considered that peeling was prevented and the cycle capacity was maintained. In addition, when the respective examples are compared, particularly high retention rates of the discharge capacity retention rates of Examples 2 and 6 using the modified fluorine-containing polymer compound and the resin binder containing the fluorine-containing polymer compound respectively are obtained. Was. This is presumed to be due to the fact that the inclusion of the fluorine-containing polymer compound further enhanced the chemical stability compared to the binder containing only the modified fluorine-containing polymer compound, and improved adhesion to the current collector. Is done.
[0048]
In the adhesion test after 10 cycles of the evaluation test (2) in the sheet batteries of Comparative Examples 1 to 3, the negative electrode current collector and the negative electrode active material layer were completely peeled off. This is considered to be because the adhesive surface between the inorganic particles and the resin binder was peeled off due to expansion and contraction due to the charge / discharge cycle inside the negative electrode active material layer, and the cohesive strength of the active material layer itself was lost. It is also assumed that the active material layer, which was originally in the form of a sheet, was changed to a fragment-like or sand-like form by several times of charge and discharge. On the other hand, in the sheet batteries of Examples 1 to 6, the negative electrode active material layer was hard to peel off from the negative electrode current collector, and the cohesive strength of the negative electrode active material layer itself was maintained. By including the resin binder containing the modified fluorine-containing polymer compound in the negative electrode material forming the negative electrode active material layer in this way, the adhesion between the negative electrode active material layer and the negative electrode current collector is improved, and the inorganic particles are included. Peeling due to a change in volume of the negative electrode active material layer can be prevented.
[0049]
【The invention's effect】
As described above, the negative electrode material for a non-aqueous electrolyte secondary battery of the present invention comprises a resin binder and Si, Ge, Mg, Sn, Pb, Ag, Al, Zn, Cd, Sb, Bi, and In. The present invention is an improvement of a negative electrode material containing both of inorganic particles containing at least one element selected from the group consisting of a resin binder and a resin binder modified by modifying a fluorine-containing resin with a modifying substance. Containing modified fluorine-containing polymer compounds.
The modified fluorine-containing polymer obtained by modifying the fluorine-containing resin contained in the resin binder with a modifying substance has not only the high chemical stability of the fluorine-containing polymer but also the adhesion to the inorganic particles. Because of the excellent properties, it is possible to prevent the inorganic particles from dropping due to the volume change of the inorganic particles due to occlusion and desorption of lithium due to charge and discharge, peeling of electrodes, and the like, and to improve cycle characteristics.
Therefore, the electrode structure and the non-aqueous electrolyte secondary battery manufactured using the negative electrode material of the present invention have excellent adhesion between the current collector and the active material, and can maintain high mechanical strength. In addition, the stress associated with the insertion and desorption reactions of lithium ions during charge and discharge can be controlled, and cycle characteristics can be improved.
[Brief description of the drawings]
FIG. 1 is a partial cross-sectional configuration diagram showing an electrode body of a nonaqueous electrolyte secondary battery of the present invention.
FIG. 2 is a partial cross-sectional configuration diagram showing an electrode body of another nonaqueous electrolyte secondary battery of the present invention.
FIG. 3 is a schematic view showing the synthesis of a modified fluorine-containing polymer compound.
[Explanation of symbols]
11 positive electrode current collector
12 Positive electrode active material layer
13 Positive electrode
14 Negative electrode current collector
16 Negative electrode active material layer
17 Negative electrode (electrode structure)
18 Non-aqueous electrolyte layer
