JP4297673B2 - Non-aqueous secondary battery - Google Patents

Description

（前記式中、ｎは１以上１０００以下である。）
【００１３】
すなわち、本発明においては、ポリアニリン及び／又はポリアニリン誘導体と、前記一般式（１）で示されるトリチオン構造を有する有機硫黄化合物とを加熱反応させることによって、有機硫黄化合物をポリアニリン及び／又はポリアニリン誘導体で固定しているので、充放電を繰り返しても、有機硫黄化合物が電解液中に溶解しなくなり、その結果、充放電サイクル特性が優れた非水二次電池が得られるようになる。
【００１４】
【発明の実施の形態】
次に、本発明のポリアニリン及び／又はポリアニリン誘導体に有機硫黄化合物を結合させた化合物（以下、「ＰＡｎ−ＣＳ」で表す）を正極活物質として用いた非水二次電池について具体的に説明する。
【００１５】
上記ＰＡｎ−ＣＳは、例えば、ゲル透過クロマトグラフィー（ＧＰＣ）において、標準サンプルにポリスチレンを用いた場合、平均分子量が１０００〜１０万（以下、特別な説明が無い限り、平均分子量は、すべてはＧＰＣを用いて算出した数平均分子量である）の還元脱ドープ状態のポリアニリン及び／又はポリアニリン誘導体を出発原料として、溶媒にＮ−メチル−２−ピロリドン（ＮＭＰ）、ジメチルホルムアミド（ＤＭＦ）、ジメチルスルホキシド（ＤＭＳＯ）などの可溶性溶媒を用い、ポリアニリン及び／又はポリアニリン誘導体を有機硫黄化合物と加熱反応させることによって得られる。
【００１６】
このポリアニリン及び／又はポリアニリン誘導体と反応させる有機硫黄化合物としては、特にトリチオン構造を有する硫黄化合物が好ましく、また、トリチオン構造を有する硫黄化合物を合成する際に出発原料となるものも用いることができる。このトリチオン構造を有する硫黄化合物の出発原料となる化合物を用いる場合、ポリアニリン及び／又はポリアニリン誘導体に固定化後、余剰の硫黄分を取り除くことによって目的とする化合物を得ることができる。
【００１７】
また、低分子のポリアニリン及び／又はポリアニリン誘導体にトリチオン構造を有する硫黄化合物を固定化させてから、その母体をなす低分子のポリアニリン及び／又はポリアニリン誘導体を重合することによっても得ることができ、この場合もまた、トリチオン構造を有する硫黄化合物の出発原料となる化合物を用いてポリアニリン及び／又はポリアニリン誘導体に固定化後、余剰の硫黄分を取り除いてもよく、逆に固定化後、余剰の硫黄分を取り除いてから、低分子のポリアニリン及び／又はポリアニリン誘導体を重合して高分子化してもよい。
【００１８】
上記のトリチオン構造を有する硫黄化合物としては、例えば、前記のジチオロジチオールジチオン、すなわち、（１，２）−ジチオロ（４，３−ｃ）−１，２−ジチオール−３，６−ジチオンのほか、例えば、Ｓ＝（Ｃ_４ Ｓ_４ ）_２ ＝ＳなどのＳ＝（Ｃ_４ Ｓ_４ ）_ｎ ＝Ｓ（ｎは１以上で１０００以下）などが好適なものとして挙げられる。また、上記トリチオン構造を有する硫黄化合物の出発原料となるポリスルフィド、単体硫黄なども用いることができる。
【００１９】
上記一般式（１）において、式中のｎは１以上１０００以下であり、後記の実施例１で用いるものは、ｎ＝１のものに相当し、実施例２で用いるものは、ｎ＝２のものに相当する。そしてｎが１０００のものでも、ｎが１や２のものとほぼ同様の特性を有していて、ｎが１や２のものと同様に用いることができる。
【００２０】
また、上記有機硫黄化合物を結合させるポリアニリン及び／又はポリアニリン誘導体のうちポリアニリン誘導体としては、例えば、次の一般式（２）
【化３】

（ｍは１０以上１０００以下）で示されるもののほか、上記一般式（２）において置換基としてメチル基以外のアルキル基を有するものなどが挙げられる。
【００２１】
そして、ポリアニリン及び／又はポリアニリン誘導体は、還元ドープ状態にあるもの、すなわち、Ｎ−Ｈ結合を有しているものの方が、有機硫黄化合物との反応性が高いことから好ましい。また、ポリアニリン及び／又はポリアニリン誘導体としては、前記のように、平均分子量が１０００〜１０万の範囲のものが好ましい。
【００２２】
上記有機硫黄化のポリアニリン及び／又はポリアニリン誘導体への結合は、ポリアニリン及び／又はポリアニリン誘導体のＮ（チッ素）原子に有機硫黄化合物のＳ（硫黄）原子が結合することによって行なわれ、有機硫黄化合物のポリアニリン及び／又はポリアニリン誘導体への結合量としては、ポリアニリン及び／又はポリアニリン誘導体のＮ原子に対して有機硫黄化合物のＳ原子が０．３〜１の範囲が好ましい。
【００２３】
上記のようにして合成されたＰＡｎ−ＣＳ化合物は、精製過程を経て、真空乾燥処理し粉砕した後、正極活物質として使用に供される。
【００２４】
そして、正極は、上記ＰＡｎ−ＣＳからなる正極活物質と、必要に応じて添加される粉末状または繊維状の導電体、バインダーなどを用いて構成される。
【００２５】
上記の導電体としては、例えば、黒鉛、カーボンブラックのような炭素系のものが好適に用いられ、バインダーとしては、例えば、ポリフッ化ビニリデン、フッ化ビニリデンとヘキサフルオロプロピレンとの共重合体、無定形ポリエーテル、ポリアクリルアミド、フッ素ゴム、ジエン系ゴム、カルボキシメチルセルロースなどが好適に用いられ、これらのバインダーは正極活物質に対して化学的に安定でかつ強い接着力を有する高分子化合物であることが好ましい。
【００２６】
そして、正極は、上記ＰＡｎ−ＣＳからなる正極活物質と、必要に応じて添加される粉末状または繊維状の導電体と、バインダーなどとを混合して調製した正極合剤を、例えば、溶剤に分散させてぺースト状にし（バインダーはあらかじめ水または溶剤に溶解または分散させておいてから混合してもよい）、得られた正極合剤含有ぺーストをアルミニウム箔などからなる正極集電体に塗布し、乾燥して正極合剤層を形成し、必要に応じて加圧成形する工程を経ることによって作製される。ただし、正極の作製方法は、上記例示の方法に限られることなく、他の方法によってもよい。
【００２７】
上記正極集電体としては、例えば、アルミニウム、ニッケル、チタンなどの金属からなり、その形態としては、箔、パンチングメタル、エキスパンドメタル、網などを用い得るが、特に箔が好適に用いられる。
【００２８】
負極の活物質としては、例えば、リチウム、ナトリウムなどのアルカリ金属、それらとアルミニウムなどの合金、黒鉛、熱分解炭素類、コークス類、ガラス状炭素類、有機高分子化合物の焼成体、メソカーボンマイクロビーズ、炭素繊維、活性炭、グラファイトなどのリチウムイオンをドープ・脱ドープすることができる炭素質材料、スズ（錫）またはケイ素（珪素）を含む酸化物、リチウムコバルトの窒素化合物を用いることができ、特にリチウム、リチウム合金、リチウムイオンをドープ・脱ドープすることができる炭素質材料などが好ましい。
【００２９】
負極の作製方法は、用いる負極活物質の種類によって次の２つに大別される。例えば、負極活物質として金属や合金を用いる場合、金網、エキスパンドメチル、パンチングメタルなどの金属多孔体からなる負極集電体に負極活物質の金属や合金を圧着して負極を作製する方法が採用される。また、負極活物質として炭素質材料などを用いる場合は、上記炭素質材料などからなる負極活物質に、必要に応じて、正極の場合と同様の導電体やバインダーなどを加え、混合して負極合剤を調製し、それを溶剤に分散させてペーストにし（バインダーはあらかじめ溶剤に溶解または分散させておいてから混合してもよい）、得られたぺーストをニッケル箔や銅箔などからなる負極集電体に塗布し、乾燥して負極合剤層を形成し、必要に応じて加圧成形する工程を経ることによって作製される。ただし、負極の作製方法は、上記例示の方法に限られることなく、他の方法によってもよい。
【００３０】
本発明の非水二次電池を構成するにあたっては、上記正極と負極に加えて、非水系の電解質を要するが、その電解質としては、非水系の電解液（液体電解質）、ポリマー電解質のいずれも用いることができる。まず、電解液から説明すると、電解液は非水性溶媒に電解質塩を溶解させることによって調製される。この非水性溶媒としては、特に限定はされることはないが、硫黄に対する親和性を有する溶媒が好ましく、そのような溶媒としては、例えば、トルエン、ベンゼンなどの芳香族系溶媒、テトラヒドロフラン、ジメチルホルムアミド、１，２−ジメトキシエタン、１，３−ジオキソラン、２−メチル−テトラヒドロフラン、テトラグライムに代表される分子量１０００以下のポリオキサイドなど、分子内に酸素又は窒素を含有する脂肪族系又は脂環族系の溶媒、あるいは、ジメチルスルホキシド、スルホランなどの分子内に硫黄を含有する非水性溶媒などが挙げられる。これらの溶媒は、それぞれ単独で又は２種類以上の混合溶媒として用いることができるが、それらの中でも、特にジメチルスルホキシド、スルホラン（分子内に硫黄を含有する非水性溶媒）、グライム類（分子量１０００以下のポリオキサイド）、テトラヒドロフラン、ジオキソランなどのようなドナー性（電子供与性）の強い溶媒が好ましく、とりわけ、それらのドナー性の強い溶媒をテトラヒドロフラン、ジオキソランなどの低粘度エーテルなどの他の溶媒と組み合わせて用いることが好ましい。
【００３１】
また、上記溶媒以外にも、例えば、エチレンカーボネート、プロピレンカーボネート、ブチレンカーボネート、γ−ブチロラクトンなどの環状エステル、ジメチルカーボネート、ジエチルカーボネート、メチルエチルカーボネート、ビニレンカーボネート、プロピオン酸メチルなどの鎖状エステルやリン酸トリメチルなどのリン酸エステルなども用いることができる。ただし、これらの溶媒の添加により電解質塩のイオン伝導度は高まるが、活物質の反応性を低下させる傾向があるため、組み合わせる溶媒の性質にもよるが、上記溶媒の添加量としては全構成溶媒中の２０質量％以下が好ましい。
【００３２】
上記溶媒に溶解させる電解質塩としては、リチウムのハロゲン塩又は過塩素酸塩、有機ホウ素リチウム塩、リチウムのトリフロロメタンスルホン酸塩を代表とする含フッ素化合物の塩、イミド塩などが好適に用いられる。このような電解質塩の具体例としては、例えば、ＬｉＦ、ＬｉＣｌ、ＬｉＣｌＯ₄ 、ＬｉＰＦ₆ 、ＬｉＢＦ₄ 、ＬｉＡｓＦ₆ 、ＬｉＳｂＦ₆ 、ＬｉＣＦ₃ ＳＯ₃ 、ＬｉＣＦ₃ ＣＯ₂ 、Ｌｉ₂ Ｃ₂ Ｆ₄ （ＳＯ₃ ）₂ 、ＬｉＮ（ＲｆＳＯ₂ ）（Ｒｆ′ＳＯ₂ ）、ＬｉＮ（ＲｆＯＳＯ₂ ）（Ｒｆ′ＯＳＯ₂ ）、ＬｉＣ（ＲｆＳＯ₂ ）₃ 、ＬｉＣ_n Ｆ_2n+1ＳＯ₃ （ｎ≧２）、ＬｉＮ（ＲｆＯＳＯ₂ ）₂ 〔ここでＲｆとＲｆ′はフルオロアルキル基〕などが挙げられ、これらはそれぞれ単独で又は２種以上混合して用いることができる。
【００３３】
これらの中でも、上記電解質塩として、炭素数２以上の含フッ素有機リチウム塩又はイミド塩が好適に用いられる。これは、上記含フッ素有機リチウム塩はアニオン性が大きく、かつイオン分離しやすいので上記溶媒に溶解しやすいからであり、またイミド塩は安定性が優れるからである。なお、電解液中における電解質塩の濃度は、特に限定されることはないが、０．５ｍｏｌ／ｌ以上が好ましく、１．７ｍｏｌ／ｌ以下が好ましい。
【００３４】
次に、ポリマー電解質について説明する。ポリマー電解質は、上記電解液をゲル化したものに相当する。上記電解液をゲル化するためのゲル化剤としては、例えば、フッ化ビニリデンの共重合体、テトラフルオロエチレン−ヘキサフルオロプロピレン共重合体、ポリエチレンオキサイド、ポリアクリルニトリルなどの直鎖状ポリマー又はそれらの共重合体、多官能モノマー（例えば、ジペンタエリスリトールヘキサアクリレートなどの四官能以上のアクリレートなど）より得られるポリマー化合物やアミン化合物とウレタンとの反応より得られるポリマー化合物などが用いられる。
【００３５】
【実施例】
つぎに、実施例を挙げて本発明をより具体的に説明する。ただし、本発明はそれらの実施例のみに限定されるものではない。なお、以下の実施例などにおいて、溶液や分散液の濃度を示す％は、特にその基準を付記しないかぎり、質量％である。
【００３６】
実施例１
還元脱ドープ状態のポリアニリン−ＮＭＰ溶液（固形分１０％、ポリアニリンの平均分子量５万、ＮＭＰはＮ−メチル−２−ピロリドン）５０ｇと硫黄化合物としてのジチオロジチオールジチオン〔すなわち、（１，２）−ジチオロ（４，３−ｃ）−１，２−ジチオール−３，６−ジチオン〕１９．８ｇを用い、それらを容器に入れ、さらに、Ｎ−メチル−２−ピロリドンを１７０ｇ加え、容器内を不活性ガスで置換した後、密閉し、その密閉容器中で８０℃、７２時間攪拌しながら加熱反応させることによって、ゲル状のポリマーを得た。このゲル状のポリマーをエタノール、Ｎ−メチル−２−ピロリドンおよび二硫化炭素で充分に洗浄・精製し、７０℃、１２時間以上真空乾燥した。得られた合成物（この合成物は、ポリアニリンにジチオロジチオールジチオンが結合したものであり、これを「ＰＡｎ−ＣＳ」で表す）を遊星ボールミルで粒径が約１０μｍ以下になるまで粉砕することによって黒色の粉末を得た。
【００３７】
そして、上記ＰＡｎ−ＣＳを正極活物質として以下に示すようにして非水二次電池を作製した。ＰＡｎ−ＣＳの黒色粉末１０ｇと、導電助剤としてグラファイト〔ロンザ社製のＫＳ−６（商品名）〕７．２ｇおよびアセチレンブラック０．８ｇを混合容器に入れ、乾式で１０分間混合してから、Ｎ−メチル−２−ピロリドン５０ｇを添加して３０分間混練した。次いで、ポリフッ化ビニリデンを１２％含有するＮ−メチル−２−ピロリドン溶液１６．７ｇを加え、さらに１時間混練して正極合剤含有ぺーストを調製した。
【００３８】
得られた正極合剤含有ぺーストを厚さ２０μｍのアルミニウム箔（サイズ：２５０ｍｍ×２２０ｍｍ）からなる正極集電体の一方の面に塗布し、５０℃のホットプレート上で１５分間乾燥したのち、さらに真空中で、１２０℃で１０時間乾燥してＮ−メチル−２−ピロリドンを除去して正極合剤層を形成した後、加圧成形して、正極合剤層の厚みを約２０μｍに調整して正極とした。
【００３９】
負極は、アルゴンガス雰囲気中で厚さ１２０μｍの金属リチウム箔をニッケル網（サイズ：２５０ｍｍ×２２０ｍｍ）上に載せてローラーで加圧して、金属リチウム箔をニッケル網に圧着することによって作製した。
【００４０】
電解液は、テトラグライム（テトラエチレングリコールジメチルエーテル）と１，３−ジオキソランとの体積比１：１の混合溶媒に、ＬｉＣｌＯ₄ を１．０ｍｏｌ／ｌ溶解させた溶液を用いた。
【００４１】
そして、上記正極と負極を厚さ８０μｍのポリプロピレン不織布からなるセパレータを介してアルゴンガス雰囲気中で積層し、その積層電極体をナイロンフィルム−アルミニウム箔−変性ポリオレフィン樹脂フィルムの三層ラミネートフィルムからなる一対の包装体に入れ、上記の電解液を注入した後、正極および負極からそれぞれ端子を引き出した状態で密閉して図１に示す非水二次電池を作製した。
【００４２】
ここで、図１に示す非水二次電池について説明すると、正極１は正極集電体１ａの一方の面にＰＡｎ−ＣＳを正極活物質とする正極合剤層１ｂを形成してなり、この実施例１の非水二次電池では上記正極集電体１ａにはアルミニウム箔が用いられている。負極２はニッケル網からなる負極集電体２ａの一方の面に金属リチウム箔２ｂを圧着してなり、これらの正極１と負極２はポリプロピレン不織布からなるセパレータ３を介して積層され、ナイロンフィルム−アルミニウム箔−変性ポリオレフィン樹脂フィルムの三層ラミネートフィルムからなる一対の包装体４、４内に収容され、また、その包装体４、４内には前記の電解液が注入され、正極１からは正極端子５を引き出し、負極２からは負極端子６を引き出した状態で密閉して非水二次電池が構成されている。
【００４３】
これをさらに詳しく説明すると、前記正極１と負極２との積層にあたっては、正極１の正極合剤層１ｂと負極２の金属リチウム箔２ｂとがセパレータ３を介して対向するようにして積層され、ナイロンフィルム−アルミニウム箔−変性ポリオレフィン樹脂フィルムの三層ラミネートフィルムからなる２枚の包装体４、４は、それらの変性ポリオレフィン樹脂フィルムが互いに向き合うように配置され、その接合部が熱融着されて電池内部が密閉状態になるようにしている。そして、正極端子５の一方の端部は正極集電体１ａに接続され、他方の端部は包装体４、４の接合部の一部を通って電池外部に引き出され、負極端子６の一方の端部は負極集電体２ａに接続され、他方の端部は包装体４、４の接合部の一部を通って電池外部に引き出されている。なお、この図１は実施例１の非水二次電池を模式的に示したものであり、各部材の厚みの比率などは必ずしも正確ではない。
【００４４】
実施例２
実施例１においてＰＡｎ−ＣＳの合成出発原料として用いたポリアニリンに代えて、還元脱ドープ状態のポリアニリン誘導体（平均分子量５万）であるＣ₇ Ｈ₇ Ｎを用いた以外は、実施例１と同様にして非水二次電池を作製した。上記Ｃ₇ Ｈ₇ Ｎは前記一般式（２）で示されるものであり、式中のｍは該ポリアニリン誘導体の平均分子量を５万にする値である。
【００４５】
実施例３
実施例１においてＰＡｎ−ＣＳの合成出発原料として用いたジチオロジチオールジチオンに代えて、Ｓ＝（Ｃ₄ Ｓ₄ ）₂ ＝Ｓを用いた以外は、実施例１と同様にして非水二次電池を作製した。
【００４６】
比較例１
ＰＡｎ−ＣＳに代えて、ジチオロジチオールジチオンのみを正極活物質として用いた以外は、実施例１と同様にして非水二次電池を作製した。
【００４７】
比較例２
ＰＡｎ−ＣＳに代えて、ポリアニリン（実施例１で用いたものと同様のもの）のみを正極活物質として用いた以外は、実施例１と同様にして非水二次電池を作製した。
【００４８】
上記実施例１〜３および比較例１の電池を、正極活物質中の有機硫黄化合物１ｇ当たり６０ｍＡに相当する電流値で、充放電を行い、比較例２の電池のみ正極活物質１ｇ当たり３０ｍＡに相当する電流値で充放電を行なった。この時、放電の終止電圧は１．５Ｖ、充電は３．０Ｖの定電流定電圧（ＣＣＣＶ）で容量の１１０％相当時間で充電を行なった。この充放電を５０サイクル繰り返し、その１サイクル目の放電容量と５０サイクル目の放電容量を測定し、１サイクル目の放電容量に対する５０サイクル目の放電容量の保持率を調べた。その結果を表１に示す。
【００４９】
【表１】

【００５０】
表１に示す結果から明かなように、正極活物質としてジチオロジチオールジチオンのみを用いた比較例１の電池では、ジチオロジチオールジチオンが６電子反応をすることから理論容量が６７０ｍＡｈ／ｇと高容量であるが、充放電を５０サイクル繰り返したときに、著しく放電容量が低下し、放電容量の保持率が低くなった。
【００５１】
これに対して、ＰＡｎ−ＣＳ（すなわち、ポリアニリン及び／又はポリアニリン誘導体に有機硫黄化合物を結合させた化合物）を正極活物質として用いた実施例１〜３の電池は、結合を形成した１電子反応分の容量損失があるものの、充放電を５０サイクル繰り返した場合でも、放電容量の低下が少なく、５０サイクル目の放電容量の保持率が比較例１の電池に比べて２倍近くに改善され、充放電サイクル特性が優れていた。なお、比較例２の電池のように、正極活物質がポリアニリンのみの場合は、理論容量こそ２９５ｍＡｈ／ｇと大きいものの、１．５〜３．０Ｖの範囲ではほとんど充放電しなかった。
【００５２】
【発明の効果】
以上説明したように、本発明によれば、充放電サイクルが優れた非水二次電池を提供することができる。
【図面の簡単な説明】
【図１】本発明に係る非水二次電池の一例を模式的に示す断面図である。
【符号の説明】
１ 正極
１ａ 正極集電体
１ｂ 正極合剤層
２ 負極
２ａ 負極集電体
２ｂ 負極合剤層
３ セパレータ
４ 包装体
５ 正極端子
６ 負極端子[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-aqueous secondary battery. More specifically, the present invention uses a compound in which an organic sulfur compound is bonded to polyaniline and / or a polyaniline derivative as a positive electrode active material, and suppresses deterioration of the positive electrode active material due to charge / discharge. The present invention relates to a non-aqueous secondary battery having improved charge / discharge cycle characteristics.
[0002]
[Prior art]
With the rapid expansion of portable electronic devices in the market, there is an increasing demand for higher performance of batteries used as power sources, and there is a demand for the development of more environmentally friendly batteries. Under such circumstances, as a positive electrode active material for a non-aqueous secondary battery, expectations are high for sulfur and its derivatives that are low in cost, have a low environmental load, and have a high capacity.
[0003]
If this two-electron reaction of sulfur can be utilized for a battery, elemental sulfur is theoretically an active material having a large capacity density of 1675 mAh / g. However, sulfur has a high insulating property, and in an alkali metal-sulfur battery using a reduction reaction to an alkali metal sulfide, it is necessary to coexist a large amount of a conductive auxiliary agent that is not reactive with sulfur. Currently, only a low utilization rate can be obtained. In addition, sulfur has poor reversibility, and sulfur and its derivatives at high temperatures have high activity, which causes the problem of erosion of battery cases and the like, making it difficult to apply to small consumer batteries.
[0004]
Polycarbon sulfide (CS _w ) _p (w is 2.3 to about 50, p is 2 or more) having a high capacity density of 1000 to 1600 mAh / g is attracting attention as a positive electrode active material for non-aqueous secondary batteries. Scottheim et al. Have announced a sulfur-based non-aqueous secondary battery that exhibits high capacity even at room temperature (see, for example, Patent Document 1).
[0005]
[Patent Document 1]
Japanese National Patent Publication No. 11-514128 (first page)
[0006]
The polysulfide described in JP 11-514128A is a method of reacting sodium sulfide with elemental sulfur and further reacting with an organic chloride compound, or acetylene and elemental sulfur in an ammonia solution of metallic sodium. It can be produced by a method of reacting, a method of reacting carbon disulfide and dimethyl sulfone using metallic sodium as a catalyst. The molecular structure of the polycarbon sulfide is characterized by having a conjugated structure mainly having carbon as a skeleton and polysulfide as a side chain.
[0007]
However, since the above-mentioned polysulfide cannot be molecularly designed in the synthesis process, it is difficult to control the sulfur content of the resulting compound, and there is a problem that a single structure compound cannot be obtained.
[0008]
In addition, the produced compound generally contains many low-molecular polysulfides and high-molecular polysulfides in addition to the polycarbon sulfide. This polysulfide molecule or the polysulfide segment constituting the side chain is easily dissolved in the electrolyte during charge / discharge, particularly in a battery using an electrolyte (liquid electrolyte), and lacks stability. In addition, conventional polysulfide is usually an amorphous or a solid with very poor crystallinity, and lack of a clear crystal structure is also a major factor that lacks stability in an electrolytic solution. Therefore, the self-discharge of the battery becomes relatively large, and a metal sulfide that inhibits the reversibility of the positive electrode is formed by charging and discharging, so that the cycle life of the battery is shortened.
[0009]
[Problems to be solved by the invention]
Therefore, the present inventors have made extensive studies to solve the above-described problems of the conventional carbon sulfide, and have a sulfur compound having a trithione structure such as (1,2) -dithiolo (4,3- c) -1,2-dithiol-3,6-dithione (hereinafter referred to as “dithiolodithioldithione”) was found to be suitable for use as a positive electrode active material for non-aqueous batteries, and has already filed a patent application. (Japanese Patent Application No. 2001-136585).
[0010]
However, even when a battery using the sulfur compound having the trithion structure as a positive electrode active material is charged and discharged over several tens of cycles using an electrolyte as an electrolyte, the sulfur compound having the trithione structure is greatly deteriorated. Therefore, it has been found that the characteristics are not always sufficient.
[0011]
Therefore, an object of the present invention is to provide a non-aqueous secondary battery excellent in charge / discharge cycle characteristics by suppressing deterioration of the positive electrode active material accompanying charge / discharge.
[0012]
[Means for Solving the Problems]
The present invention uses the compound obtained by heating and reacting polyaniline and / or a polyaniline derivative and an organic sulfur compound having a trithione structure represented by the following general formula (1) as a positive electrode active material. Is a solution.
[Chemical 1]

(In the above formula, n is 1 or more and 1000 or less.)
[0013]
That is, in the present invention, polyaniline and / or a polyaniline derivative and an organic sulfur compound having a trithione structure represented by the general formula (1) are heated and reacted to convert the organic sulfur compound into a polyaniline and / or a polyaniline derivative. Since it is fixed, even if charging / discharging is repeated, the organic sulfur compound does not dissolve in the electrolytic solution, and as a result, a nonaqueous secondary battery having excellent charge / discharge cycle characteristics can be obtained.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Next, a non-aqueous secondary battery using a compound obtained by binding an organic sulfur compound to the polyaniline and / or polyaniline derivative of the present invention (hereinafter referred to as “PAn-CS”) as a positive electrode active material will be specifically described. .
[0015]
For example, in the gel permeation chromatography (GPC), the above PAn-CS has an average molecular weight of 1,000 to 100,000 (hereinafter, unless otherwise specified), when polystyrene is used as a standard sample. Starting from a polyaniline and / or polyaniline derivative in a reductive dedope state (which is a number average molecular weight calculated using the above formula), N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethyl sulfoxide ( It is obtained by reacting polyaniline and / or a polyaniline derivative with an organic sulfur compound by using a soluble solvent such as DMSO).
[0016]
As the organic sulfur compound to be reacted with the polyaniline and / or the polyaniline derivative, a sulfur compound having a trithione structure is particularly preferable, and a starting material when a sulfur compound having a trithione structure is synthesized can also be used. When a compound that is a starting material for the sulfur compound having a trithione structure is used, the target compound can be obtained by removing excess sulfur after immobilization on the polyaniline and / or polyaniline derivative.
[0017]
It can also be obtained by immobilizing a sulfur compound having a trithione structure on a low molecular weight polyaniline and / or polyaniline derivative and then polymerizing the low molecular weight polyaniline and / or polyaniline derivative forming the matrix. In this case, after fixing the polyaniline and / or polyaniline derivative with a compound that is a starting material for the sulfur compound having a trithione structure, the excess sulfur content may be removed. After removing the polymer, low molecular weight polyaniline and / or polyaniline derivative may be polymerized to polymerize.
[0018]
Examples of the sulfur compound having a trithione structure include the dithiolodithioldithione, that is, (1,2) -dithiolo (4,3-c) -1,2-dithiol-3,6-dithione. For example, S = (C ₄ S ₄ ) ₂ = S or the like S = (C ₄ S ₄ ) _n = S (n is 1 or more and 1000 or less) is preferable. In addition, polysulfide, elemental sulfur, or the like, which is a starting material for the sulfur compound having the trithione structure, can also be used.
[0019]
In the general formula (1), n in the formula is 1 or more and 1000 or less, and what is used in Example 1 described later corresponds to n = 1, and what is used in Example 2 is n = 2. Corresponds to Even when n is 1000, the characteristics are almost the same as those when n is 1 or 2, and n can be used in the same manner as when n is 1 or 2.
[0020]
Moreover, as polyaniline derivatives among the polyaniline and / or polyaniline derivatives to which the organic sulfur compound is bonded, for example, the following general formula (2)
[Chemical 3]

In addition to those represented by (m is 10 or more and 1000 or less), those having an alkyl group other than a methyl group as a substituent in the general formula (2) can be used.
[0021]
The polyaniline and / or polyaniline derivative is preferably in a reduction-doped state, that is, having an N—H bond, because the reactivity with the organic sulfur compound is high. As the polyaniline and / or polyaniline derivative, those having an average molecular weight in the range of 1,000 to 100,000 are preferable as described above.
[0022]
The organic sulfuration is bonded to the polyaniline and / or polyaniline derivative by bonding an S (sulfur) atom of the organic sulfur compound to an N (nitrogen) atom of the polyaniline and / or polyaniline derivative. As the amount of binding to the polyaniline and / or polyaniline derivative, the S atom of the organic sulfur compound is preferably in the range of 0.3 to 1 with respect to the N atom of the polyaniline and / or polyaniline derivative.
[0023]
The PAn-CS compound synthesized as described above is subjected to a purification process, vacuum dried and pulverized, and then used as a positive electrode active material.
[0024]
And a positive electrode is comprised using the positive electrode active material which consists of said PAn-CS, and the powder-form or fiber-like conductor, binder, etc. which are added as needed.
[0025]
As the conductor, for example, carbon-based materials such as graphite and carbon black are preferably used. As the binder, for example, polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, Regular polyethers, polyacrylamides, fluororubbers, diene rubbers, carboxymethylcellulose, etc. are preferably used, and these binders are polymer compounds that are chemically stable and have strong adhesive strength to the positive electrode active material. Is preferred.
[0026]
The positive electrode is a positive electrode mixture prepared by mixing a positive electrode active material composed of the above PAn-CS, a powdery or fibrous conductor added as necessary, and a binder, for example, a solvent A positive electrode current collector made of an aluminum foil or the like, and the resulting positive electrode mixture-containing paste is mixed in a paste form (the binder may be previously dissolved or dispersed in water or a solvent and then mixed). It is produced by applying to the substrate and drying to form a positive electrode mixture layer and, if necessary, pressure forming. However, the method for manufacturing the positive electrode is not limited to the above-described method, and other methods may be used.
[0027]
The positive electrode current collector is made of, for example, a metal such as aluminum, nickel, or titanium. As the form thereof, a foil, a punching metal, an expanded metal, a net, or the like can be used, and a foil is particularly preferably used.
[0028]
Examples of the active material for the negative electrode include alkali metals such as lithium and sodium, alloys thereof such as aluminum, graphite, pyrolytic carbons, cokes, glassy carbons, fired bodies of organic polymer compounds, mesocarbon micro Carbonaceous materials that can be doped / undoped with lithium ions such as beads, carbon fiber, activated carbon, graphite, etc., oxides containing tin (tin) or silicon (silicon), nitrogen compounds of lithium cobalt can be used, In particular, lithium, a lithium alloy, a carbonaceous material that can be doped / undoped with lithium ions, and the like are preferable.
[0029]
The method for producing the negative electrode is roughly classified into the following two types depending on the type of the negative electrode active material to be used. For example, when a metal or alloy is used as the negative electrode active material, a method is adopted in which the negative electrode active material metal or alloy is pressure-bonded to a negative electrode current collector made of a porous metal such as a wire mesh, expanded methyl, or punching metal. Is done. When a carbonaceous material or the like is used as the negative electrode active material, a negative electrode active material made of the above carbonaceous material or the like is added with the same conductor or binder as in the case of the positive electrode, if necessary, and mixed to form the negative electrode Prepare a mixture, disperse it in a solvent to make a paste (the binder may be dissolved or dispersed in the solvent before mixing), and the resulting paste consists of nickel foil, copper foil, etc. It is produced by applying to a negative electrode current collector, drying to form a negative electrode mixture layer, and subjecting to pressure forming as necessary. However, the method for manufacturing the negative electrode is not limited to the above-described method, and other methods may be used.
[0030]
In constructing the non-aqueous secondary battery of the present invention, a non-aqueous electrolyte is required in addition to the positive electrode and the negative electrode. As the electrolyte, both non-aqueous electrolyte (liquid electrolyte) and polymer electrolyte are used. Can be used. First, from an electrolytic solution, the electrolytic solution is prepared by dissolving an electrolyte salt in a non-aqueous solvent. The non-aqueous solvent is not particularly limited, but a solvent having affinity for sulfur is preferable. Examples of such a solvent include aromatic solvents such as toluene and benzene, tetrahydrofuran, dimethylformamide, and the like. 1,2-dimethoxyethane, 1,3-dioxolane, 2-methyl-tetrahydrofuran, polyoxides having a molecular weight of 1000 or less typified by tetraglyme, etc., aliphatic or alicyclic compounds containing oxygen or nitrogen in the molecule And non-aqueous solvents containing sulfur in the molecule such as dimethyl sulfoxide and sulfolane. These solvents can be used singly or as a mixed solvent of two or more kinds, among which dimethyl sulfoxide, sulfolane (non-aqueous solvent containing sulfur in the molecule), glyme (molecular weight of 1000 or less) Polyoxides), tetrahydrofuran, dioxolane, and other solvents with strong donor properties (electron-donating properties) are preferred, and especially those solvents with strong donor properties are combined with other solvents such as tetrahydrofuran, dioxolane, and other low-viscosity ethers. Are preferably used.
[0031]
In addition to the above solvents, for example, cyclic esters such as ethylene carbonate, propylene carbonate, butylene carbonate, and γ-butyrolactone, chain esters such as dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, vinylene carbonate, and methyl propionate, phosphorus Phosphate esters such as trimethyl acid can also be used. However, although the ionic conductivity of the electrolyte salt is increased by the addition of these solvents, there is a tendency to reduce the reactivity of the active material. The content is preferably 20% by mass or less.
[0032]
As the electrolyte salt to be dissolved in the above-mentioned solvent, lithium halogen salt or perchlorate, organic boron lithium salt, fluorine-containing compound salt represented by lithium trifluoromethanesulfonate, imide salt, etc. are preferably used. It is done. Specific examples of the electrolyte salt, for _{example, LiF, LiCl, LiClO 4,} LiPF 6, LiBF 4, LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiCF 3 CO 2, Li 2 C 2 F 4 (SO _{3) 2, LiN (RfSO 2} ) (Rf'SO 2), LiN (RfOSO 2) (Rf'OSO 2), LiC (RfSO 2) 3, LiC n F 2n + 1 SO 3 (n ≧ 2), LiN (RfOSO ₂ ) ₂ [wherein Rf and Rf ′ are fluoroalkyl groups] and the like can be used, and these can be used alone or in admixture of two or more.
[0033]
Among these, as the electrolyte salt, a fluorine-containing organic lithium salt or imide salt having 2 or more carbon atoms is preferably used. This is because the fluorine-containing organic lithium salt has a large anionic property and is easily ion-separated, so that it is easily dissolved in the solvent, and the imide salt is excellent in stability. The concentration of the electrolyte salt in the electrolytic solution is not particularly limited, but is preferably 0.5 mol / l or more, and preferably 1.7 mol / l or less.
[0034]
Next, the polymer electrolyte will be described. The polymer electrolyte corresponds to a gelled version of the electrolytic solution. Examples of the gelling agent for gelling the electrolytic solution include linear polymers such as vinylidene fluoride copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyethylene oxide, and polyacrylonitrile. And a polymer compound obtained from a reaction between an amine compound and urethane, or a polymer compound obtained from a polyfunctional monomer (for example, a tetrafunctional or higher functional acrylate such as dipentaerythritol hexaacrylate).
[0035]
【Example】
Next, the present invention will be described more specifically with reference to examples. However, this invention is not limited only to those Examples. In the following examples and the like,% indicating the concentration of a solution or dispersion is mass% unless otherwise noted.
[0036]
Example 1
Reductive dedoped polyaniline-NMP solution (solid content 10%, polyaniline average molecular weight 50,000, NMP is N-methyl-2-pyrrolidone) and dithiodithioldithione as a sulfur compound [ie, (1,2) -Dithiolo (4,3-c) -1,2-dithiol-3,6-dithione] 19.8 g, put them in a container, and further add 170 g of N-methyl-2-pyrrolidone. After substituting with an inert gas, it was sealed, and a gel-like polymer was obtained by reacting with heating in the sealed container with stirring at 80 ° C. for 72 hours. The gel polymer was thoroughly washed and purified with ethanol, N-methyl-2-pyrrolidone and carbon disulfide, and vacuum dried at 70 ° C. for 12 hours or more. Grinding the resultant compound (this compound is a polyaniline bonded with dithiolodithioldithione, represented by “PAn-CS”) with a planetary ball mill until the particle size is about 10 μm or less. Gave a black powder.
[0037]
And the non-aqueous secondary battery was produced as follows using the said PAn-CS as a positive electrode active material. After putting 10 g of PAn-CS black powder and 7.2 g of graphite [KS-6 (trade name) manufactured by Lonza Co., Ltd.] and 0.8 g of acetylene black in a mixing container and mixing them for 10 minutes in a dry process. Then, 50 g of N-methyl-2-pyrrolidone was added and kneaded for 30 minutes. Next, 16.7 g of an N-methyl-2-pyrrolidone solution containing 12% polyvinylidene fluoride was added, and the mixture was further kneaded for 1 hour to prepare a positive electrode mixture-containing paste.
[0038]
The obtained positive electrode mixture-containing paste was applied to one surface of a positive electrode current collector made of an aluminum foil having a thickness of 20 μm (size: 250 mm × 220 mm) and dried on a hot plate at 50 ° C. for 15 minutes, Furthermore, after drying at 120 ° C. for 10 hours in vacuum to remove N-methyl-2-pyrrolidone to form a positive electrode mixture layer, pressure molding is performed to adjust the thickness of the positive electrode mixture layer to about 20 μm. Thus, a positive electrode was obtained.
[0039]
The negative electrode was prepared by placing a metal lithium foil having a thickness of 120 μm on a nickel mesh (size: 250 mm × 220 mm) in a argon gas atmosphere, pressing the metal lithium foil with a roller, and pressing the metal lithium foil onto the nickel mesh.
[0040]
As the electrolytic solution, a solution obtained by dissolving 1.0 mol / l of LiClO ₄ in a 1: 1 mixed solvent of tetraglyme (tetraethylene glycol dimethyl ether) and 1,3-dioxolane was used.
[0041]
Then, the positive electrode and the negative electrode are laminated in an argon gas atmosphere through a separator made of polypropylene nonwoven fabric having a thickness of 80 μm, and the laminated electrode body is made of a three-layer laminate film of nylon film-aluminum foil-modified polyolefin resin film. After injecting the above electrolytic solution, the battery was sealed with the terminals pulled out from the positive electrode and the negative electrode, respectively, to produce the nonaqueous secondary battery shown in FIG.
[0042]
Here, the nonaqueous secondary battery shown in FIG. 1 will be described. The positive electrode 1 is formed by forming a positive electrode mixture layer 1b using PAn-CS as a positive electrode active material on one surface of a positive electrode current collector 1a. In the nonaqueous secondary battery of Example 1, an aluminum foil is used for the positive electrode current collector 1a. The negative electrode 2 is formed by press-bonding a metal lithium foil 2b to one surface of a negative electrode current collector 2a made of a nickel mesh, and the positive electrode 1 and the negative electrode 2 are laminated via a separator 3 made of a polypropylene non-woven fabric. It is accommodated in a pair of packaging bodies 4 and 4 made of a three-layer laminate film of an aluminum foil-modified polyolefin resin film, and the electrolyte solution is injected into the packaging bodies 4 and 4. A non-aqueous secondary battery is configured by drawing out the terminal 5 and sealing it with the negative electrode terminal 6 drawn out from the negative electrode 2.
[0043]
More specifically, in laminating the positive electrode 1 and the negative electrode 2, the positive electrode mixture layer 1b of the positive electrode 1 and the metal lithium foil 2b of the negative electrode 2 are laminated so as to face each other with the separator 3 therebetween, Two packages 4 and 4 made of a three-layer laminate film of nylon film-aluminum foil-modified polyolefin resin film are arranged so that the modified polyolefin resin films face each other, and the joints are heat-sealed. The inside of the battery is sealed. One end of the positive electrode terminal 5 is connected to the positive electrode current collector 1 a, and the other end is pulled out of the battery through a part of the joint of the packaging bodies 4, 4. Is connected to the negative electrode current collector 2a, and the other end is drawn out of the battery through a part of the joint of the packaging bodies 4 and 4. FIG. 1 schematically shows the nonaqueous secondary battery of Example 1, and the ratio of the thickness of each member is not necessarily accurate.
[0044]
Example 2
The same as Example 1 except that C ₇ H ₇ N, which is a polyaniline derivative (average molecular weight 50,000) in a reduced dedope state, was used in place of the polyaniline used as the starting material for the synthesis of PAn-CS in Example 1. Thus, a non-aqueous secondary battery was produced. The C ₇ H ₇ N are those represented by the general formula (2), m in the formula is a value of the average molecular weight of the polyaniline derivative in 50,000.
[0045]
Example 3
Non-aqueous secondary in the same manner as in Example 1 except that S = (C ₄ S ₄ ) ₂ = S was used instead of dithiodithioldithione used as the starting material for the synthesis of PAn-CS in Example 1. A battery was produced.
[0046]
Comparative Example 1
A nonaqueous secondary battery was produced in the same manner as in Example 1 except that only dithiolodithioldithione was used as the positive electrode active material instead of PAn-CS.
[0047]
Comparative Example 2
A nonaqueous secondary battery was produced in the same manner as in Example 1 except that only polyaniline (same as that used in Example 1) was used as the positive electrode active material instead of PAn-CS.
[0048]
The batteries of Examples 1 to 3 and Comparative Example 1 were charged and discharged at a current value corresponding to 60 mA per gram of organic sulfur compound in the positive electrode active material, and only the battery of Comparative Example 2 was adjusted to 30 mA per gram of positive electrode active material. Charging / discharging was performed at a corresponding current value. At this time, the discharge was stopped at a constant current constant voltage (CCCV) of 1.5 V and the charge was performed at a time corresponding to 110% of the capacity. This charge / discharge was repeated 50 cycles, the discharge capacity of the first cycle and the discharge capacity of the 50th cycle were measured, and the retention rate of the discharge capacity of the 50th cycle with respect to the discharge capacity of the 1st cycle was examined. The results are shown in Table 1.
[0049]
[Table 1]

[0050]
As is clear from the results shown in Table 1, in the battery of Comparative Example 1 using only dithiolodithioldithione as the positive electrode active material, the theoretical capacity is as high as 670 mAh / g because dithiolodithioldithione undergoes a six-electron reaction. Although it was a capacity | capacitance, when charging / discharging was repeated 50 cycles, discharge capacity fell remarkably and the retention rate of discharge capacity became low.
[0051]
On the other hand, the batteries of Examples 1 to 3 using PAn-CS (that is, a compound obtained by binding an organic sulfur compound to polyaniline and / or a polyaniline derivative) as a positive electrode active material are one-electron reaction in which a bond is formed. Although there is a capacity loss of 50 minutes, even when charging and discharging are repeated 50 cycles, the decrease in the discharge capacity is small, and the retention rate of the discharge capacity at the 50th cycle is improved to nearly twice that of the battery of Comparative Example 1, The charge / discharge cycle characteristics were excellent. In addition, when the positive electrode active material was only polyaniline as in the battery of Comparative Example 2, the theoretical capacity was as large as 295 mAh / g, but was hardly charged or discharged in the range of 1.5 to 3.0 V.
[0052]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a non-aqueous secondary battery having an excellent charge / discharge cycle.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view schematically showing an example of a non-aqueous secondary battery according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Positive electrode 1a Positive electrode collector 1b Positive electrode mixture layer 2 Negative electrode 2a Negative electrode collector 2b Negative electrode mixture layer 3 Separator 4 Package 5 Positive electrode terminal 6 Negative electrode terminal

Claims (3)

To a polyaniline and / or a polyaniline derivative, characterized in that the organic sulfur compound having a trithiones structure represented by the following general formula (1), a compound obtained by heating the reaction using the positive electrode to the positive electrode active material Non-aqueous secondary battery.

(In the above formula, n is 1 or more and 1000 or less.) Polyaniline and / or a polyaniline derivative, a non-aqueous secondary battery according to claim 1 Symbol mounting, characterized in that in a reduced undoped state. 3. The non-aqueous solution according to claim 1, wherein the negative electrode contains at least one selected from the group consisting of lithium, a lithium alloy, and a carbonaceous material capable of doping and dedoping lithium ions. Secondary battery.

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