JP4208451B2 - Polysulfide carbon and nonaqueous electrolyte battery using the same - Google Patents

Description

で示される繰り返し単位を有し、かつポリスルフィドセグメントを実質的に有しないことを特徴とする。
【００１７】
このポリ硫化カーボンは、充放電過程で側鎖中のＳ−Ｓ結合が切断されると同時に、主鎖に存在するＳ−Ｓ結合も切断され、それに伴って主鎖の重合と解重合が起こることを特徴としている。また、このポリ硫化カーボンをリチウム系非水電解質二次電池の正極活物質として用いた場合、その充放電過程でＬｉ_x Ｃ_y Ｓ_z （ｘ＝１〜ｚ、ｚ／ｙ＝１．５）を主成分とするイオウ化合物セグメントのリチウム塩が形成される。
【００１８】
上記構成からなる本発明のポリ硫化カーボンにおいて、特に下記に示す特徴を有するポリ硫化カーボンが好ましい。
【００１９】
すなわち、本発明の好ましい態様の一つは、炭素とイオウを主な構成元素とし、イオウの質量比率が７５質量％以上でかつ炭素とイオウの質量比率の合計が９５質量％以上であって、そのラマンスペクトルにおいて、ラマンシフトの１４４４ｃｍ^-1付近に主ピークが存在し、かつ４００ｃｍ^-1〜５２５ｃｍ^-1の範囲に存在するピークが実質的に４９０ｃｍ^-1付近のブロードなピークのみであり、かつ２１８ｃｍ^-1付近にシャープなピークを有しないことを特徴とするポリ硫化カーボンである。
【００２０】
また、本発明の他の好ましい態様の一つは、炭素とイオウを主な構成元素とし、イオウの質量比率が７５質量％以上でかつ炭素とイオウの質量比率の合計が９５質量％以上であって、そのＣｕＫα線によるＸ線回折において、回折角（２θ）が２０°〜３０°の範囲の回折パターンが、実質的に２５°付近にピークを有するブロードな回折ピークのみで表されることを特徴とするポリ硫化カーボンである。
【００２１】
本発明のさらに他の好ましい態様の一つは、炭素とイオウを主な構成元素とし、イオウの質量比率が７５質量％以上でかつ炭素とイオウの質量比率の合計が９５質量％以上であって、室温から３００℃まで１０℃／分の速度で加熱した際の熱質量分析による質量減少が１５％以下であることを特徴とするポリ硫化カーボンである。
【００２２】
上記のような炭素とイオウを主な構成元素とし、イオウの質量比率が６７質量％以上でかつ炭素とイオウの質量比率の合計が９５質量％以上であって、その分子中に式（１）で示される繰り返し単位を有するポリ硫化カーボンは、非水電解質電池の正極活物質として用いたときに、高容量で、可逆性が高く、かつ充放電サイクルに伴う容量低下が少ないので、信頼性の高い一次電池または二次電池を提供することができる。
【００２３】
【発明の実施の形態】
次に、本発明のポリ硫化カーボンの合成方法についての詳細と、非水電解質電池の活物質としての利用について具体的に説明する。
【００２４】
本発明の炭素とイオウを主な構成元素とし、イオウの質量比率が６７質量％以上でかつ炭素とイオウの質量比率の合計が９５質量％以上であって、かつ式（１）で示される繰り返し単位を有するポリ硫化カーボンは、例えば、次の方法によって合成することができる。まず、硫化ナトリウムなどのアルカリ金属硫化物とイオウをアルコール、アセトン、水などの溶媒中で、おおよそ０℃〜５０℃の温度範囲で１０分〜１０時間程度反応させた後、真空中で溶媒を揮発させて反応物を取り出す。次いで、これをＮ−メチル−２−ピロリドンなどの有機溶媒中で、おおよそ０℃〜５０℃の温度範囲で１０分〜３時間程度ヘキサクロロブタジエンなどのハロゲン化不飽和炭化水素と反応させる。その後、反応生成物を純水および有機溶媒で数回洗浄し、おおよそ１０℃〜８０℃で真空乾燥させることにより、中間生成物として茶色の固体化合物を得る。この茶色の固体化合物は、その分子中に多数のポリスルフィドセグメントを有しており、前記の特表平１１−５１４１２８号公報などに記載されている有機イオウ化合物に相当するものである。また、その合成反応の過程で生じるポリスルフィド化合物が多く混在していることも確認されている。この中間生成物を得る方法としては、上記方法以外にも、従来公知の種々の有機イオウ化合物の合成方法を採用することができる。
【００２５】
次に、上記中間生成物をアルミナ（酸化アルミニウム）などで作られた耐熱容器に入れ、真空中、１５０℃〜２５０℃の範囲内で加熱することにより、中間生成物中に混在しているポリスルフィド化合物などの不純物を蒸発させ、また、有機イオウ化合物分子中のポリスルフィドセグメントを切断して、余分なイオウを蒸発させて除去し、ほぼ炭素とイオウとの二元素のみからなり、分子内のほとんどあるいはすべての炭素原子がイオウ原子との結合を形成し、しかもイオウ原子のほとんどあるいはすべてが酸化および還元に対する高い可逆性を有するジスルフィド結合を形成した構造のポリ硫化カーボンが得られる。このようなポリ硫化カーボン中のイオウの含有比率は、質量基準で６７％〜８２％と高い値になる。
【００２６】
この化合物の分子構造を具体的に説明すると、前記したように、次の式（１）で表される繰り返し単位を有する構造が推定され、さらに炭素鎖間の結合は、例えば、式（２）、式（３）で示されるようなジスルフィド結合によりなされているものと推定される。
【化３】

【化４】

【化５】

【００２７】
上記ポリ硫化カーボンの分子内に炭素の二重結合（Ｃ＝Ｃ）やイオウのジスルフィド結合（Ｃ−Ｓ−Ｓ−Ｃ）が存在することは、後に詳記するラマン分析などによって確認することができる。
【００２８】
上記の加熱処理においては、加熱中の化合物の酸化を防ぐため、およそ５×１０³ Ｐａ以下の高真空度でかつ不活性ガス置換した後の真空雰囲気中などで加熱処理するのが好ましい。上記加熱温度としては、おおよそ１５０℃〜２５０℃が好ましく、１８０℃〜２２０℃がより好ましいが、真空度が高いほど、均一に熱が伝わるほど、また出発時の原材料が少ないほど、より低温で行うことができる。また、加熱時間は加熱処理の温度や雰囲気により調整すればよいが、おおよそ３０分〜５時間が適当である。中間生成物の組成、加熱温度や加熱時間などの相違により、得られるポリ硫化カーボンの組成は若干異なるが、イオウを質量比率で６７％〜８２％含有することにより高容量化が容易となり、化学的安定性の点からは炭素およびイオウ以外の元素の含有量が少ないこと、すなわちイオウと炭素の質量比率が９５質量％以上であることが必要である。
【００２９】
さらに、上記ポリ硫化カーボンの炭素とイオウの原子比率を１：ｘとしたときに、ｘが１．４〜１．６の範囲にある化合物は、分子構造の単一性が高く、充放電における可逆性が優れ、高容量の活物質となるので好ましい。これは、ｘの値が１．６より大きい化合物では、分子内にポリスルフィドセグメントが多く導入されてしまうからである。
【００３０】
また、上記ポリ硫化カーボンは、その化学的安定性や充放電の可逆性を害しない範囲で炭素およびイオウ以外の元素を含有してもよく、水素、窒素、ホウ素やハロゲン元素などを有する化合物とすることもできるが、炭素とイオウの二元素のみで構成されていることがより好ましい。例えば、ポリ硫化カーボンを一般式（ＣＳ_x ）_n で表した場合、ｘは１．４〜１．６で、ｎが４以上の化合物が好ましい。ｎが３の場合はジスルフィド結合を有する可逆性のトリチオン構造が形成することが困難であり、たとえ、そのようなトリチオン構造を有するものを合成できたとしても安定性が悪く有用性が低いと考えられる。本発明のポリ硫化カーボンは、有機溶剤などに対する溶解度が低く、その分子量を測定することが困難であるため、上記一般式におけるｎの値を正確に求めることは難しいが、前記のように、このｎは４以上であることが好ましく、また、ｎはいくら大きくなっても何ら問題が生じないと考えられるが、通常、ｎが１０万程度のものまでが合成しやすく実用的である。上記したｎが４以上のポリ硫化カーボンは、例えば、主鎖の炭素数が４以上のハロゲン化不飽和炭化水素を用いて合成することにより得ることができる。
【００３１】
また、上記ポリ硫化カーボンは、ポリスルフィドセグメントを有する有機イオウ化合物を容器中で溶解性を示す非水性溶媒に接触させるか、またはその非水性溶媒の蒸気に接触させることにより、カーボン骨格に繋がっていないイオウのセグメントと他の不純物を溶出し、かつカーボン骨格に繋がっていても不安定な長いイオウのセグメントを切断して除去することによっても得ることができる。すなわち、ポリスルフィドセグメントを有する有機イオウ化合物は、上記のような非水性溶媒との接触により、ほぼカーボンとイオウの二元素からなり、式（１）で表される繰り返し単位を主体とするポリ硫化カーボンに変化する。この溶媒抽出処理においては、溶媒の引火点を配慮して、雰囲気は酸素濃度の低い状態が好ましく、酸素濃度を４００ｐｐｍ以下に低減した不活性ガス雰囲気中で処理することがより好ましい。このような方法で合成したポリ硫化カーボンの分子量は低いと予想される。
【００３２】
上記溶媒抽出処理に使用する溶媒は、イオウやポリスルフィドセグメントを有するイオウ化合物に対して優れた溶解性を有する非水性有機溶媒であることが好ましい。特に、カーボン骨格に繋がっている不安定な長いイオウのセグメントを切断して除去するためには、強いドナー性の非水性有機溶媒であることが好ましい。その具体例としては、例えば、トルエン、ベンセ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、テトラメチルエチレンジアミン、ジオキソラン、テトラグリム（ｔｅｔｒａｇｌｙｍｅ）などの分子内に酸素または窒素を含有する脂肪族系または脂環族系の低分子量溶媒や、二硫化炭素、ジメチルスルホキシド、スルホランなどのイオウを含有する溶媒などが挙げられる。また、それらの溶媒の混合溶媒でもよい。前記の溶媒の中でも、特にジメチルスルホキシド、二硫化炭素、テトラヒドロフラン、トルエン、テトラグリムなどが好ましい。なお、上記のテトラグリムはビス〔（２−メトキシエトキシ）エチル〕エーテルと称される有機溶媒である。
【００３３】
上記溶媒による抽出温度は、特に限定されることはないが、室温から溶媒の沸点までの温度であり、特に溶媒を環流しながら抽出を行うことが好ましい。また、抽出時間は、温度および中間生成物である有機イオウ化合物の分子量にも依存するが、おおよそ１０分〜５時間が適当である。温度が高くなるほど、また中間生成物の分子量が小さいほど、抽出時間を短縮することができる。
【００３４】
上記ポリ硫化カーボンのラマン分析はアルゴンレーザーを光源として行われるが、本発明のポリ硫化カーボンは、そのラマン分析によれば、得られたラマンスペクトルにおいて、ラマンシフトの１４４４ｃｍ^-1付近に主なピークが存在し、かつ４００ｃｍ^-1〜５２５ｃｍ^-1の範囲に存在するピークが実質的に４９０ｃｍ^-1付近のブロードなピークのみで、かつ２１８ｃｍ^-1付近にシャープなピークを有しないことを特徴とする。ここで、１４４４ｃｍ^-1付近の主ピークはカーボン骨格中の炭素の不飽和結合（Ｃ＝Ｃ結合）に基づくものであり、ラマンスペクトルにおいてこのピークが最大強度となる。また、上記４００ｃｍ^-1〜５２５ｃｍ^-1の範囲には、カーボン骨格と繋がったジスルフィド結合に由来するピーク、あるいはポリスルフィドセグメントに由来するピークが現れるが、４９０ｃｍ^-1付近のピークはジスルフィド結合に由来するピークであり、ポリスルフィドセグメント中のＳ−Ｓ結合に由来するピークは、これとは別の位置に現れる（例えば、２１９ｃｍ^-1付近と４７０ｃｍ^-1付近などにシャープなピークを有する）。本発明において、「実質的に４９０ｃｍ^-1付近のピークのみ」としたのは、４９０ｃｍ^-1付近のピーク以外に微小なピークが存在していてもかまわないという意味である。すなわち、本発明のポリ硫化カーボンにおいては、その分子内にポリスルフィドセグメントが存在しないこと、すなわち、ラマンシフトの前記範囲内には４９０ｃｍ^-1付近のピーク以外のピークが存在しないことが好ましいが、要求される特性を劣化させない範囲内で、分子内に少量のポリスルフィドセグメントが存在していてもよいことを意味している。ここで、１４４４ｃｍ^-1付近とはおおよそ１４４４ｃｍ^-1±５０ｃｍ^-1の範囲に相当し、４９０ｃｍ^-1付近とはおおよそ４９０ｃｍ^-1±５０ｃｍ^-1の範囲に相当する。
【００３５】
これに対し、従来の有機イオウ化合物のラマンスペクトルでは、２００ｃｍ^-1〜５２５ｃｍ^-1の範囲に多数のピークがあり、特にイオウの含率が高い時、２１８ｃｍ^-1付近と２７０ｃｍ^-1付近などにシャープなピークを有する様子が認められる。これは、分子内に−Ｓ_m −（ｍ≧３）で表されるポリスルフィドセグメントが多く存在することを示しており、ｍは種々の値を有しているものと考えられる。
【００３６】
上記ポリ硫化カーボンについて、ＣｕＫα線を用いたＸ線回折を行うと、回折角（２θ）で２０°〜３０°の範囲の回折パターンは、実質的に、２５°付近にピーク位置を有する半値幅がおおよそ１．５°〜５°くらいの一つのブロードな回折ピークとして表すことができる。すなわち、前記回折角の範囲では、実質的に、前記回折ピークが一つ存在するだけである。ここで、上記のように「実質的に」と記載したのは、完全に一つだけであることは要求されず、ポリスルフィドセグメントに由来するピークすなわちイオウで同定されるピークが観察されないことが好ましいものの、たとえ観察されても微弱（ピーク強度が前記ピークのおおよそ１／１０以下の強度）であるものは本発明において許容されることを意味している。
【００３７】
また、上記した方法でポリ硫化カーボンを合成した場合、中間生成物である有機イオウ化合物の生成過程においてアルカリ金属のハロゲン化物も副生成物として生成するため、中間生成物あるいは最終的に得られるポリ硫化カーボンの洗浄を行った場合でも、ポリ硫化カーボンに少量の塩化ナトリウムなどが混在することがある。そのため、Ｘ線回折パターンにアルカリ金属のハロゲン化物のピークが現れることがあるが、この回折ピークは除外して考えればよい。
【００３８】
上記Ｘ線回折パターンにおいて、２５°付近のピークは、次の式（４）
【化６】

で示されるジスルフィド結合により形成される平面がさらに層状構造を形成し、その層状構造により生じた回折ピークであると推定される。ピークがブロードな形になるのは、主として炭素で構成される主鎖が回転可能であるため、一つの分子内に存在する複数のジスルフィド結合により形成されるそれぞれの平面が、すべて同一平面になるわけではないことや、合成されるポリ硫化カーボンの分子量が一定の分布を有していることなどの理由によるものと考えられる。もちろん、上記理由から、このピークが完全に一つのピークとならずに若干の分離が生じることも考えられるが、全体としてほぼ一つのピークを形成していればよい。このピークの回折角から求まる層間距離は、０．３ｎｍ〜０．４４ｎｍ程度であり、黒鉛の層間距離（０．３３５ｎｍ）に近い値であるため、上記層状構造の層間ヘリチウムがインターカレートすることが考えられる。
【００３９】
これに対して、本発明での中間生成物をはじめとする従来の有機イオウ化合物では、そのＸ線回折パターンには多数のシャープなピークが存在するが、そのほとんどすべてが遊離したイオウまたはポリスルフィドセグメントのイオウによる回折ピークである。イオウに基づく回折ピーク以外の回折ピークは強度が小さいため判別しにくい。
【００４０】
さらに、従来の有機イオウ化合物では、窒素雰囲気下で熱質量−示差熱分析（ＴＧ−ＤＴＡ）を行うと、イオウに基づく１２２．７℃と３１４℃の強い吸熱ピークが存在し、また、温度の上昇とともに２００℃付近から質量減少も生じるが、本発明のポリ硫化カーボンでは、上記１２２．７°と３１４°のピークが消滅し、また、より高温まで質量減少が生じない。例えば、本発明のポリ硫化カーボンは、室温から３００℃まで１０℃／分の昇温速度で加熱した際の質量減少が２０％以下という優れた熱的安定性を示す。従って、結晶性がよく化学的安定性にも優れた本発明のポリ硫化カーボンを非水電解質電池の正極活物質として用いた場合は、硫化物の形成がないため長期にわたり良好な可逆性を維持することができる。
【００４１】
本発明のポリ硫化カーボンを非水電解質電池の正極活物質として用いた場合、その理論容量はおおよそ６７０ｍＡｈ／ｇであり、正極活物質として最も汎用されているＬｉＣｏＯ₂ （１３７ｍＡｈ／ｇ）の４倍以上の高容量化を実現できる。また、本発明のポリ硫化カーボンは、上記のような非水電解質電池の正極活物質としての用途以外に、負極活物質としての利用、あるいはその化学的安定性、半導電性、光吸収性などの特性を生かして、情報記憶素子、表示素子、電子材料などへの利用も可能であると考えられる。
【００４２】
次に、本発明のポリ硫化カーボンを正極活物質として用いた非水電解質電池（二次電池）の作製について述べる。
【００４３】
正極は、上記のポリ硫化カーボンと、必要に応じて用いる導電助剤、バインダー、添加剤などとで構成されるが、上記導電助剤としては、例えば、黒鉛、カーボンブラックのような炭素質材料や、導電性ポリマーなどが好適に用いられる。
【００４４】
上記バインダーとしては、例えば、ポリフッ化ビニリデン、ポリテトラフルオロエチレンなどのフッ素樹脂、無定形ポリエーテル、ポリアクリルアミド、ポリ−Ｎ−ビニルアセトアミド、溶媒に溶解性を有するポリアニリン、ポリピロールまたはそれらのコポリマーまたは架橋により形成される化合物などが挙げられ、これら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。
【００４５】
正極は、例えば、前記ポリ硫化カーボンからなる正極活物質に、必要に応じて、前記の導電助剤やバインダーなどを加え、混合して正極合剤を調製し、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させてから正極活物質などと混合してもよい）、その正極合剤含有ペーストを金属箔などからなる正極集電体に塗布し、乾燥して、正極集電体の少なくとも一部に正極合剤層を形成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。
【００４６】
負極の活物質としては、例えば、金属リチウム、リチウムのアルミニウムなどとの合金、リチウム含有複合化合物、黒鉛などの炭素質材料、スズ（錫）またはケイ素（珪素）などのリチウムと合金化可能な元素かまたはそれらを含む酸化物、リチウム含有窒素化合物などが挙げられる。
【００４７】
負極の作製方法は、用いる負極活物質の種類によって大別して２つに分けられる。その一つは、負極活物質として金属や合金を用いる場合、金網、エキスパンドメタル、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として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。そして、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助剤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させておいてから負極活物質などと混合してもよい）、その負極合剤含有ペーストを銅箔などからなる負極集電体に塗布し、乾燥して、負極集電体の少なくとも一部に負極合剤層を形成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。
【００４８】
非水電解質としては、非水系の液状電解質（以下、「電解液」という）、ポリマー電解質、固体電解質のいずれも用いることができる。
【００４９】
上記電解質として、まず、電解液から説明すると、電解液は非水性溶媒成分に電解質塩を溶解させることによって構成される。
【００５０】
電解質の非水性溶媒としては、リチウムの硫化物に対する良好な溶解性を有する主溶媒と、必要に応じて用いられる副溶媒とで構成される。前記主溶媒の具体例としては、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、テトラメチルエチレンジアミン、ジオキソラン、２−メチル−テトラヒドロフラン、テトラグリムなどを代表とする分子量１００００以下のポリオキサイドなど分子内に酸素または窒素を含有する脂肪族系または脂環族系の低分子量溶媒、ジメチルスルホキシド、スルホランなどのイオウを含有する溶媒などが挙げられ、これらの溶媒はそれぞれ単独でまたは２種以上の混合溶媒として用いることができる。また、これらの溶媒の中でも、特に１，２−ジメトキシエタン、ジメチルスルホキシド、スルホラン、テトラヒドロフラン、テトラグリムのようなドナー性（電子供与性）の強い溶媒が好ましく、とりわけ、こ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と組み合わせて用いることが好ましい。もちろん、この主溶媒だけで非水性溶媒を構成することもできる。
【００５１】
また、上記助溶媒としては、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エステルが用いられ、またエチレングリコール、サルファイトなどのイオウ系エステルなども用いることができる。さらに、これら以外にも、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、プロピオン酸メチルなどの鎖状エステル、リン酸トリメチルなどの鎖状リン酸トリエステルやジエチルエーテルなどを用いることができる。これらの助溶媒の添加により電解質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ので、副溶媒の添加量としては、主溶媒の性質にもよるが、全構成溶媒中の２０質量％以下が好ましい。
【００５２】
上記非水性溶媒に溶解させる電解質塩としては、例えば、リチウムのハロゲン塩または過塩素酸塩、有機ホウ素リチウム塩、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、ＬｉＣｌＯ₄ 、ＬｉＰＦ₆ 、ＬｉＢＦ₄ 、ＬｉＢ（ＯＣ₆ Ｈ₄ ＣＯＯ）₂ 、ＬｉＣＦ₃ ＳＯ₃ 、ＬｉＣ₄ Ｆ₉ ＳＯ₃ 、ＬｉＣＦ₃ ＣＯ₂ 、Ｌｉ₂ Ｃ₂ Ｆ₄ （ＳＯ₃ ）₂ 、ＬｉＮ（ＣＦ₃ ＳＯ₂ ）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または２種以上混合して用いることができる。そして、この電解質塩としては、特に炭素数２以上の含フッ素有機リチウム塩またはイミド塩が好ましい。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、上記非水性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ているからである。電解液中における電解質塩の濃度は、特に限定されるものではないが、０．５ｍｏｌ／ｌ以上が好ましく、１．７ｍｏｌ／ｌ以下が好ましい。
【００５３】
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。そのゲル化にあたっては、例えば、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またはそれらのコポリマー、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により得られるポリマー化合物などが用いられる。また、固体電解質としては、無機系のものと有機のものとがあり、無機系固体電解質としては、例えば、ナトリウムβアルミナ、６０ＬｉＩ−４０Ａｌ₂ Ｏ₃ 、Ｌｉ₃ Ｎ、５ＬｉＩ−４Ｌｉ₂ Ｓ−２Ｐ₂ Ｓ₅ 、Ｌｉ₃ Ｎ−ＬｉＩなどが挙げられ、また、有機系固体電解質としては、例えば、無定形、低相転移温度（Ｔｇ）のポリエーテル、無定形フッ化ビニリデンコポリマー、異種ポリマーのブレンドした物などが挙げられる。
【００５４】
上記のように、本発明のポリ硫化カーボンを非水電解質電池の活物質として用いる場合について説明してきたが、本発明のポリ硫化カーボンは、上記に例示したような非水電解質電池の活物質だけでなく、例えば、キャパシタなどの他の電気化学素子や、情報記録素子、表示素子、電子材料などにも利用可能である。
【００５５】
【実施例】
次に、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、以下の実施例において、溶液または分散液の濃度を示す％や、組成、収率などを示す％は、特にその基準を付記しないかぎり質量％である。
【００５６】
実施例１
硫化ナトリウムの九水和物（Ｎａ₂ Ｓ・９Ｈ₂ Ｏ）１００ｇを、体積比１：１で混合したエタノールと水との混合溶媒３００ｍｌに溶解させ、これに５３．４ｇのイオウを添加して室温下で１時間反応させた。次いで、溶媒を真空中で除去した後、残留物をＮ−メチル−２−ピロリドン７００ｍｌに溶解させ、ヘキサクロロブタジエンを１７．２ｇ添加して、室温下で１時間反応させた。その後、純水、アセトンおよびエタノールを用いて充分に洗浄し、真空中で４０℃に保ちながら１５時間乾燥して、中間生成物として茶色の化合物を得た。この化合物の合成方法は、特表平１１−５０６７９９号公報の実施例に記載の方法とほぼ同一である。
【００５７】
得られた化合物について元素分析を行い、その平均組成を求めた。その結果、Ｃ：７．０％、Ｓ：９２．３％、Ｎ：０．２％以下、Ｈ：０．３％以下であった。これに対応する一般式は（ＣＳ_6.2 ）_n であった（合成によって得られた化合物の平均組成は必ずしも一定ではない）。前記Ｃ、Ｎ、Ｈの分析結果は、全自動元素分析装置〔シーベルヘグナ社製、ｖａｒｉｏ ＥＬ〕により、試料分解炉温度：９５０℃、還元炉温度：５００℃、ヘリウム流量：２００ｍｌ／分、酸素流量：２０〜２５ｍｌ／分の条件下で元素分析を行った結果によるものであり、また、前記Ｓの分析結果は、フラスコ燃焼法−酢酸バリウム測定で、指示薬としてトリンメチレンブルーを用いて元素分析を行った結果によるものである。
【００５８】
次に、上記中間生成物４０ｇを船形のアルミナ（酸化アルミニウム）容器に入れ、その中間生成物を入れたアルミナ容器を真空乾燥炉に置き、真空度が１．３３×１０² Ｐａ（１ｔｏｒｒ）以下になるまで真空引きして純度９９．９％のアルゴンガスで一回置換した後、同様の真空度で以下に示す条件で温度を変化させて最終的に２０５℃で加熱処理を行った。すなわち、室温から６０℃まで０．５時間で昇温を行い、６０℃で１時間保持し、次いで２０５℃まで２時間で昇温を行い、２０５℃で５時間保持して加熱処理を行うことにより、中間生成物中のイオウの一部を除去することによって、中間生成物をポリ硫化カーボンに変化させた。
【００５９】
処理後に室温まで冷却してから反応生成物をアルミナ容器中から取り出し、外観が黒鉛に似た金属光沢を有する黒色のポリ硫化カーボン約１０．０ｇを得た。元素分析の結果、このポリ硫化カーボンの組成は、Ｃ：１９．９％、Ｓ：７９．８％であり、一般式で表すと（ＣＳ_1.50）_n となった。上記ポリ硫化カーボンの合成にあたって反応成分として用いたヘキサクロロブタジエンが炭素数４の化合物であることから、上記ポリ硫化カーボンの一般式（ＣＳ_1.50）_n のｎ値は４以上であり、主として４の倍数の化合物であると推定される。
【００６０】
次に、このポリ硫化カーボンについて、以下の装置および条件によりラマン分析を行った。その結果を図１に示す。
装置：Ｒａｍａｏｎｏｒ Ｔ−６４００（Ｊｏｂｉｎ Ｙｖｏｎ／愛宕物産）
光源：Ａｒレーザー〔ＧＬＧ３４６０（５１４．５ｎｍ、出力：１ｍＷ（ＮＥＣ）〕
【００６１】
図１において、横軸はラマンシフト（ｃｍ^-1）であり、縦軸は相対強度であるが、このポリ硫化カーボン（ＣＳ_1.50）_n のラマン分析の結果は、図１に示すように、１４４４ｃｍ^-1に炭素の不飽和結合（Ｃ＝Ｃ結合）に基づく主ピークを有し、また４００ｃｍ^-1〜５２５ｃｍ^-1の範囲内に存在するピークは、４９０ｃｍ^-1付近のブロードなピークが存在し、かつ２１９ｃｍ^-1付近にシャープなピークを有しなかった。すなわち、上記ポリ硫化カーボンには、ジスルフィド結合に基づくピークのみで、ポリスルフィドセグメントに基づくピークは認められなかった。一般に、炭素に繋がるジスルフィド結合の場合は、５０５ｃｍ^-1付近にジスルフィド結合に基づくピークが現れるが、本発明のポリ硫化カーボンでは、上記炭素の不飽和結合（Ｃ＝Ｃ結合）の影響を受けてピーク位置がシフトしたものと推定される。
【００６２】
また、上記ポリ硫化カーボンについて粉末Ｘ線回折装置〔ＲＩＮＴ２０００（リガク社製）〕により、ＣｕＫα線を用いてＸ線回折測定を行った。測定条件は、電圧：４０ｋＶ、電流：１５０ｍＡ、スキャン速度：２°／分、サンプリング：０．０２°、積算回数：５回で、回折角（２θ）が１０°〜８０°の範囲で測定を行った。上記Ｘ線回折測定により得られたポリ硫化カーボン（ＣＳ_1.50）_n の回折パターンを図２に示すが、回折角（２θ）が２０°〜３０°の範囲では、２５°付近にピーク位置を有するブロードな回折ピークだけが観察された。なお、３１．８°および４５．５°のピークは塩化ナトリウムによるものである。
【００６３】
さらに、上記ポリ硫化カーボンについて、リガク社製の熱分析計（ｔｈｅｒｍｏ Ｐｌｕｓ ＴＧ８１２０）を用いて熱質量−示差熱分析（ＴＧ−ＤＴＡ）を行った。すなわち、高純度窒素ガスを０．１５リットル／分の流量で流しながら１０℃／分の昇温速度で加熱を行い、温度と質量変化の関係を測定した。その結果を図３に示す。この図３には、後述する比較例１の化合物（ＣＳ_6.2 ）_n の熱質量−示差熱分析結果についても示している。図３に示す結果から明らかなように、従来公知の有機イオウ化合物（ＣＳ_6.2 ）_n は、２００℃以上になると急激に質量が減少するのに対して、本発明のポリ硫化カーボン（ＣＳ_1.50）_n は、３００℃付近まで質量減少が少なく（３００℃までの質量減少：２０％以下）、−Ｓｍ−（ｍは３以上）をほとんど含有しないことがわかる。
【００６４】
実施例２
実施例１の加熱処理において、処理温度を１９０℃とした以外は、実施例１と同様にしてポリ硫化カーボン（ＣＳ_1.58）_n を得た。このポリ硫化カーボンについて実施例１と同様にラマン分析とＸ線回折測定を行った。
【００６５】
このポリ硫化カーボン（ＣＳ_1.58）_n のラマン分析においては、前記（ＣＳ_1.50）_n と同様に１４４４ｃｍ^-1に主ピークを有し、また４００ｃｍ^-1〜５２５ｃｍ^-1の範囲には４９０ｃｍ^-1付近のブロードなピークが存在するだけで、かつ２１９ｃｍ^-1付近にシャープなピークを有しなかった。また、Ｘ線回折測定においても、前記（ＣＳ_1.50）_n の回折パターンとほぼ一致するパターンが得られた。
【００６６】
実施例３
実施例１の加熱処理において、処理温度を２２０℃とした以外は、実施例１と同様にしてポリ硫化カーボン（ＣＳ_1.42）_n を得た。このポリ硫化カーボンについて実施例１と同様にラマン分析とＸ線回折測定を行った。
【００６７】
このポリ硫化カーボン（ＣＳ_1.42）_n のラマン分析においては、前記（ＣＳ_1.50）_n と同様に１４４０ｃｍ^-1に主ピークを有し、また４９４ｃｍ^-1付近のブロードなピークが存在するだけで、かつ２１９ｃｍ^-1付近にシャープなピークを有しなかった。また、Ｘ線回折測定においても、前記（ＣＳ_1.50）_n の回折パターンと同様のパターンが得られ、２４．４°にブロードなピークを有するだけであった。
【００６８】
実施例４
実施例１と同様に中間生成物として得た一般式（ＣＳ_6.2 ) _n で表される化合物をボールミルで１０μｍ前後まで粉砕し、得られた粉末２０ｇを、冷却管と窒素置換口を取り付けた内容積３００ｍｌの三つ口フラスコ中に投入し、そこに１００ｍｌの二硫化炭素を加え、アルゴン雰囲気中で５時間環流することにより、上記化合物を構成するイオウの一部を除去し、ジスルフィド結合に変化させた。その後、室温まで冷却して遠心分離法で沈殿物を収集し、３０ｍｌの二硫化炭素とアセトンで洗浄してから、５０℃で１２時間真空乾燥して、黒茶色の金属光沢を有するポリ硫化カーボン（ＣＳ_1.54）_n を得た。このポリ硫化カーボンについて実施例１と同様にラマン分析とＸ線回折測定を行った。
【００６９】
このポリ硫化カーボンのラマン分析の結果を図４に示すが、このポリ硫化カーボン（ＣＳ_1.54）_n では、１４４７ｃｍ^-1の主ピークがブロードで１４４７ｃｍ^-1と１４６７ｃｍ^-1に分裂し、また４００ｃｍ^-1〜５２５ｃｍ^-1の範囲には４７２ｃｍ^-1にピークを有するのみで、かつ２１９ｃｍ^-1付近にシャープなピークを有しなかった。さらに、Ｘ線回折測定では、２５．６°にブロードなピークを有するのみであった。
【００７０】
比較例１
実施例１と同様にして、その中間生成物として一般式（ＣＳ_6.2 ）_n で表される有機イオウ化合物を得て、これを比較例１の有機イオウ化合物とした。
【００７１】
比較例２
実施例４と同様にして、その中間生成物として一般式（ＣＳ_2.6 ）_n で表される有機イオウ化合物を得て、これを比較例２の有機イオウ化合物とした。
【００７２】
これらの有機イオウ化合物（ＣＳ_6.2 ）_n および（ＣＳ_2.6 ）_n について、実施例１と同様にラマン分析とＸ線回折測定を行った。有機イオウ化合物（ＣＳ_6.2 ）_n のラマン分析の結果を図５に、Ｘ線回折の結果を図６に示す。有機イオウ化合物（ＣＳ_6.2 ）_n のラマン分析において、１４４０ｃｍ^-1に主ピークを有し、４００ｃｍ^-1〜５２５ｃｍ^-1の間での４９４ｃｍ^-1付近のピークも存在するものの、ポリスルフィドセグメントに基づく多数のピークも現れていた。例えば、２１９ｃｍ^-1付近のピークなどは本発明のポリ硫化カーボンでは見られなかったピークであり、本発明のポリ硫化カーボンとは分子構造がかなり異なるものと推定された。
【００７３】
また、（ＣＳ_6.2 ）_n のＸ線回折測定では、多数のシャープな回折ピークが認められたが、その回折ピークのほとんどがイオウまたはポリサルファイドの−Ｓｍ（ｍ＞３）の回折ピークで同定され、本発明のポリ硫化カーボンに見られるような、結晶構造に基づくと考えられる明瞭なピークは認められなかった。
【００７４】
以下の実施例５〜８および比較例３〜４では、上記実施例１〜４のポリ硫化カーボンおよび比較例１〜２の有機イオウ化合物をそれぞれ正極活物質として用いた非水電解質二次電池を作製し、その特性を評価した。
【００７５】
実施例５〜８および比較例３〜４
まず、正極は以下のようにして作製した。実施例１〜４のポリ硫化カーボンまたは比較例１〜２の有機イオウ化合物について、その１０質量部と、ロンザ社製グラファイト（ＫＳ−６）７．２質量部およびアセチレンブラック０．８質量部を混合用容器に入れ、乾式で１０分間混合した後、Ｎ−メチル−２−ピロリドン５０質量部を添加して３０分間混合した。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１６．７質量部を加え、さらに１時間混合して正極合剤含有ペーストを調製した。
【００７６】
得られた正極合剤含有ペーストを厚さ２０μｍのアルミニウム箔（サイズ：２５０ｍｍ×２２０ｍｍ）に塗布し、５０℃のホットプレート上で１０分間乾燥した後、さらに真空中で７０℃で１０時間乾燥してＮ−メチル−２−ピロリドンを除去することにより正極合剤層を形成した。乾燥後の電極体を１００℃に加温して加圧し、正極合剤層の厚みが４０μｍの正極を得た。
【００７７】
負極は、アルゴンガス雰囲気中で厚さ１２０μｍのリチウム箔を６０μｍのステンレス鋼製網（サイズ：２５０ｍｍ×２２０ｍｍ）上に載せ、ローラーで加圧して、リチウム箔をステンレス鋼製網に圧着することによって作製した。
【００７８】
電解液としては、テトラグリムと１，３−ジオキソランとの混合溶媒（質量比４：１）に、ＬｉＣＦ₃ ＳＯ₃ を１ｍｏｌ／ｌ溶解させた溶液を用いた。
【００７９】
そして、上記正極と負極を７０×４２ｍｍに裁断して、厚さ４０μｍの多孔質ポリエチレンフィルム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包装体に入れ、電解液を注入した後、密閉して非水電解質二次電池を作製した。この電池に、正極活物質１ｇあたり６０ｍＡに相当する電流値で充放電を行い（定電流定電圧の制限電圧：２．５Ｖ、定電流放電終止電圧：１．５Ｖ）、これを５サイクル繰り返し、サイクル初期の放電容量と５サイクル目の放電容量を測定し、正極活物質１ｇあたりの放電容量の変化を調べた。その結果を表１に示す。なお、実施例５〜８および比較例３〜４の電池と実施例１〜４のポリ硫化カーボンおよび比較例１〜２の有機イオウ化合物との関係について示すと、実施例５の電池の正極活物質は実施例１のポリ硫化カーボンで、実施例６の電池の正極活物質は実施例２のポリ硫化カーボンで、実施例７の電池の正極活物質は実施例３のポリ硫化カーボンで、実施例８の電池の正極活物質は実施例４のポリ硫化カーボンであり、比較例３の電池の正極活物質は比較例１の有機イオウ化合物で、比較例４の電池の正極活物質は比較例２の有機イオウ化合物である。
【００８０】
【表１】

【００８１】
表１に示す結果から明らかなように、実施例５〜８の電池は、容量が大きく、かつ充放電サイクルに伴う容量低下が少なく、高容量でかつ充放電サイクル特性が優れた信頼性の高い非水電解質二次電池であった。すなわち、一般式（ＣＳ_x ）_n で表したときに、ｘが１．４〜１．６の範囲内にある実施例１〜４のポリ硫化カーボンは、従来の有機イオウ化合物（ＣＳ_2.6 ）_n および（ＣＳ_6.2 ）_n に比べて、実装電池化したときに、初期容量はあまり差がないものの、充放電サイクルに伴う容量低下が小さく、高容量でかつ充放電サイクル特性が優れた信頼性の高い非水電解質二次電池を構成できることがわかる。
【００８２】
実施例９
Ｈｕｎｔｓｍａｎ社製のアミン化合物（Ｊｅｆｆａｍｉｎｅ ＸＴＪ−５０２）１００ｇをテトラグリムと１，３−ジオキソランとの質量比４：１の混合溶媒１３０ｇに溶解し、これに坂本薬品社製のエポキシ樹脂（ＳＲ−８ＥＧ）２５．２ｇを添加して、室温下で攪拌しながら７日間反応させた。この反応により得られたアミン化合物の溶液に、ＬｉＣＦ₃ ＳＯ₃ を濃度が１．０ｍｏｌ／ｌになるように加え、均一に溶解するまで攪拌した。一方、三井化学社製のウレタン（ＡＸ−１０４３）をテトラグリムと１，３−ジオキソランとの質量比４：１の混合溶媒に溶解し、さらにＬｉＣＦ₃ ＳＯ₃ を濃度が１．０ｍｏｌ／ｌになるように加えた溶液を調製した。上記アミン化合物を含む溶液とウレタンを含む溶液とを、アミンの活性水素とウレタンのイソシアネート基とのモル比が１．１：１になるように混合し、その混合溶液に平均厚さが８０μｍのポリブチレンテレフタレート不織布を浸漬し、引き上げ後に２時間放置してポリブチレンテレフタレート不織布を支持体とするポリマー電解質を作製した。以上の操作はすべて露点温度が−６０℃以下のドライ雰囲気中で行った。
【００８３】
次に、電解液として、テトラグリムと１，３−ジオキソランとの質量比４：１の混合溶媒にＬｉＣＦ₃ ＳＯ₃ を濃度が１．０ｍｏｌ／ｌになるように加えた溶液を調製し、さらに実施例５において用いた（ＣＳ_1.50）_n を活物質とする正極と負極を用いて電池を組み立てた。上記正極および負極の表面を電解液で湿らせ、さらに、それらの正極と負極とを上記ポリマー電解質を介して積層し、その積層体を実施例５と同様の包装体に入れ、電解液を注入した後、密閉して非水電解質二次電池を作製した。
【００８４】
実施例１０
実施例５において、正極活物質として（ＣＳ_1.50）_n を用い、電解液の溶媒として、テトラグリムと１，３−ジオキソランとエチレンカーボネートとの質量比７５：２０：５の混合溶媒を用いた以外は、実施例５と同様に非水電解質二次電池を作製した。
【００８５】
実施例１１
実施例５において、正極活物質として（ＣＳ_1.50）_n を用い、電解液の溶媒として、ジメチルスルホキシドと１，３−ジオキソランとメチルエチルカーボネートとの質量比５０：４０：１０の混合溶媒を用いた以外は、実施例５と同様に非水電解質二次電池を作製した。
【００８６】
実施例１２
実施例５において、正極活物質として（ＣＳ_1.50）_n を用い、電解質塩として、１モル濃度の過塩素酸リチウムを用いた以外は、実施例５と同様にして非水電解質二次電池を作製した。
【００８７】
上記実施例９〜１２の電池に対して、実施例５と同様の充放電条件で充放電を５０サイクル繰り返し、５０サイクル目の放電容量を測定した。その結果を、正極活物質１ｇあたりの放電容量として表２に示す。
【００８８】
【表２】

【００８９】
表２に示すように、実施例９〜１２の電池は、充放電サイクルの増加に伴う容量低下が小さく、高容量でかつ充放電サイクルが優れ、信頼性の高い非水電解質二次電池を提供することができた。つまり、実施例９〜１２の電池は、電解液の組成が変化しても、特性は実施例５の電池とほとんど変わらなかった。
【００９０】
【発明の効果】
以上説明したように、本発明では、高容量でかつ可逆性が高いポリ硫化カーボンと、そのポリ硫化カーボンを活物質として用いることにより、高容量でかつ充放電サイクルが優れ、信頼性の高い非水電解質電池を提供することができた。
【図面の簡単な説明】
【図１】実施例１で得られたポリ硫化カーボン（ＣＳ_1.50）_n のラマンスペクトルを示す図である。
【図２】実施例１で得られたポリ硫化カーボン（ＣＳ_1.50）_n のＸ線回折パターンを示す図である。
【図３】実施例１で得られたポリ硫化カーボン（ＣＳ_1.50）_n および比較例１で得られた有機イオウ化合物（ＣＳ_6.2 ）_n の熱質量−示差熱分析での質量変化を示す図である。
【図４】実施例４で得られたポリ硫化カーボン（ＣＳ_1.54）_n のラマンスペクトルを示す図である。
【図５】比較例１で得られた有機イオウ化合物（ＣＳ_6.2 ）_n のラマンスペクトルを示す図である。
【図６】比較例１で得られた有機イオウ化合物（ＣＳ_6.2 ）_n のＸ線回折パターンを示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a polysulfide carbon that can be used as an active material of a battery and a nonaqueous electrolyte battery using the same.
[0002]
[Prior art]
With the rapid expansion of portable electronic devices in the market, the demand for higher performance of batteries used as their power sources is increasing, while the development of more environmentally friendly batteries is required. . Under such circumstances, as a positive electrode active material for non-aqueous electrolyte batteries (primary batteries or secondary batteries), expectations are high for sulfur (sulfur) and its derivatives that are low in cost, have a low environmental impact, and have a high capacity. ing.
[0003]
If this two-electron reaction of sulfur can be used in a battery, theoretically, elemental sulfur becomes an active material having a large energy density of 1675 mAh / g. However, since sulfur is a highly insulating material and has a low reversibility, an alkali metal-sulfur battery actually provides only a low utilization rate. Moreover, since it can be used only at high temperatures, there is a problem that the battery case and the like are eroded by the high activity of sulfur and its derivatives, and it is said that it is difficult to apply to consumer small batteries.
[0004]
On the other hand, inorganic sulfur compounds soluble in organic solvents, such as alkali metal sulfides, are also used as positive electrode active materials for batteries (Japanese Patent Laid-Open No. 57-145272, etc.). In this battery using an inorganic sulfur compound, a porous carbon electrode is used for the positive electrode, and discharge can be performed with a larger current than a conventional sulfur battery, but the carbon constituting the electrode is likely to deteriorate during discharge. Have been used mainly as primary batteries.
[0005]
[Problems to be solved by the invention]
In addition, Japanese Patent Application Laid-Open No. 5-501937 discloses a general formula [R (S) _y ] _n (Y = 1 to 6, n = 2 to 20, R is an aliphatic, alicyclic or aromatic functional group having 1 to 20 carbon atoms, such as sulfur, oxygen, nitrogen, fluorine, etc. Batteries using an organic sulfur compound represented by the above formula as a positive electrode material have been studied. In this organic sulfur positive electrode material, the S—S bond in the charged state is cleaved in the discharged state to form an organic sulfur metal salt.
[0006]
However, this battery system has the following problems 1) and 2).
1) As a battery configuration, a solid polymer electrolyte / metal lithium battery configuration having organic sulfur / ion conductivity and a battery operating at 200 ° C. or lower can be configured, but this battery is difficult to operate at room temperature.
2) Since a solid polymer electrolyte is required, a liquid electrolyte cannot be used, and charging / discharging can be performed only with a minute current.
[0007]
Furthermore, studies on organic sulfur compounds containing carbon and sulfur as main constituent elements are also underway. JP-A-60-502213 (WO85 / 01293) discloses a general formula (R _a CS _b ) _c An organic sulfur compound represented by (where R is hydrogen, an alkali metal or a transition element) has been proposed. However, when the present inventors examined the method for synthesizing the organic sulfur compound disclosed in the above publication, it was found that the following problems were found.
[0008]
In other words, in the synthesis method in which sulfur is added to a polymer such as halogenated polyethylene or polyacetylene such as polytetrafluoroethylene or polytrifluorochloroethylene, the halogen element or hydrogen cannot be completely replaced with sulfur. Organic sulfur compounds in which a large amount of halogen elements, hydrogen, etc. remain are easily produced. Further, since the amount of sulfur to be added cannot be controlled, it is very difficult to obtain a compound having a uniform structure. Such a problem is also apparent from the fact that the organic sulfur compounds described in Examples 1 to 3 and Example 7 contain a large amount of elements other than carbon and sulfur in the above Japanese Patent Publication No. 60-502213. is there.
[0009]
In addition, in Example 6 of the above-mentioned JP-T-60-502213, the composition is CS. _0.98 H _0.009 A product composed only of two elements of carbon and sulfur is also described. However, according to the detailed examination by the present inventors, the synthesis method described in Example 6 is _0.98 H _0.009 It was found that a mixture of an organic sulfur compound having a low sulfur content and a polysulfide compound was actually obtained. Since this polysulfide compound cannot be removed by washing with water, the composition of the product described in Example 6 may actually represent the average composition of the above mixture. In addition, since a polymer containing no unsaturated bond is used as a starting material, the carbon skeleton of the organic sulfur compound having a low sulfur content to be synthesized is basically a saturated carbon chain and exists in the molecule. Since the number of disulfide bonds (C—S—S—C) between the carbon skeleton and sulfur is small, reversible charge / discharge is difficult and the discharge capacity is small. That is, according to the method described in JP-A-60-502213, a high-capacity organic sulfur compound consisting of only two elements of carbon and sulfur and having a high sulfur content ratio could not be obtained.
[0010]
On the other hand, as a compound different from the above, general formula (CS _w ) _p The organic sulfur compound represented by (w is 1.2 to about 50, p is 2 or more) has attracted attention because it has a high energy density of 1000 to 1600 mAh / g. Scottheim et al. Have proposed a secondary battery exhibiting a high capacity even at room temperature using this compound as a positive electrode active material of a nonaqueous electrolyte battery (Japanese Patent Laid-Open No. 7-29599 (US Pat. No. 5,441,831)). JP-T-11-506799 (WO96 / 41388), JP-T11-514128 (WO96 / 41387), etc.]. This organic sulfur compound is a method of reacting sodium sulfide with sulfur and further reacting with an organic chloride compound, or a method of reacting acetylene with sulfur in an ammonia solution of metal sodium, and using carbon sodium disulfide as a catalyst with metal sodium. It can be produced by a method of reacting with dimethyl sulfone. The molecular structure of the organic sulfur compound is a skeleton having a conjugated structure mainly formed of carbon, and -S bonded to the skeleton. _m It is characterized by having a structure represented by-(m ≧ 3) (hereinafter referred to as “polysulfide segment”). In addition, the organic sulfur compound strongly asserts that the main chain polymerization and depolymerization do not occur even when the SS bond is broken during the charge / discharge process, that is, the main chain does not break. Yes.
[0011]
However, the above general formula (CS _w ) _p Since the organic sulfur compound represented by the above formula 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 compound having a single structure cannot be obtained.
[0012]
In addition, the resulting compound generally contains a large amount of low molecular weight or high molecular weight polysulfide compounds, and the general formula (CS _w ) _p As the value of p in the medium increases, the proportion of the conjugated structure tends to decrease and the proportion of the polysulfide compound tends to increase. This polysulfide compound and the polysulfide segment in the molecule of the organic sulfur compound, particularly in a battery using an electrolytic solution (liquid electrolyte), are easily decomposed and dissolved in the electrolytic solution during charge and discharge, and the stability of the compound itself It becomes a big factor which lacks the stability of the battery which uses it. As a result, there is a problem that not only the self-discharge of the battery becomes relatively large but also a metal sulfide that inhibits reversibility of charge and discharge is formed, and the cycle life of the battery is shortened.
[0013]
The present inventors have synthesized a novel organic sulfur compound (polysulfide carbon) that is already composed of almost two elements of carbon and sulfur and has a higher unity of molecular structure than conventional organic sulfur compounds. By using it as a substance, a non-aqueous electrolyte battery having excellent charge / discharge cycle characteristics, high reliability, and high capacity has been realized, and a patent application has already been filed for it (Japanese Patent Application No. 2000-31305). This organic sulfur compound is characterized in that polymerization and depolymerization of the main chain do not occur even when the SS bond is broken in the charge / discharge process, that is, the main chain does not break. However, in the heat synthesis method, there is a problem in that the heat conductivity of the starting material is low, and it is difficult to obtain a large amount of an active material having uniform performance, and the cost is somewhat high. Moreover, since the temperature at the time of synthesis is high, the polyene structure in the molecule may be partially broken, so that the reversibility is not always sufficient.
[0014]
The present invention solves the problems of the conventional organic sulfur compounds as described above, provides a polysulfide carbon having higher reversibility, high capacity and high stability, and further using the polysulfide carbon as an active material. Accordingly, an object is to provide a non-aqueous electrolyte battery having a high capacity, excellent charge / discharge cycle characteristics, and high reliability.
[0015]
[Means for Solving the Problems]
As a result of intensive studies to solve the above-mentioned problems, the present inventors have improved the synthesis conditions of the synthesis method in particular in the present application of the present inventors, and the polysulfide segment is mainly composed of carbon and sulfur. Based on the organic sulfur compound it has, it consists of only two elements of carbon and sulfur, and the molar ratio of carbon to sulfur is about 1: 1.4 to 1.6, which is simpler in molecular structure than conventional organic sulfur compounds. It has been found that a novel polysulfide carbon having high uniformity can be synthesized, and the present invention has been completed.
[0016]
That is, the polysulfide carbon of the present invention has carbon and sulfur as main constituent elements, the mass ratio of sulfur is 67% by mass or more, and the total mass ratio of carbon and sulfur is 95% by mass or more. In the following formula (1)
[Chemical formula 2]

And having substantially no polysulfide segment.
[0017]
In this polysulfide carbon, the S—S bond in the side chain is cleaved during the charge / discharge process, and at the same time, the S—S bond present in the main chain is cleaved, and accordingly, polymerization and depolymerization of the main chain occur. It is characterized by that. In addition, when this polysulfide carbon is used as a positive electrode active material of a lithium-based nonaqueous electrolyte secondary battery, Li _x C _y S _z A lithium salt of a sulfur compound segment mainly composed of (x = 1 to z, z / y = 1.5) is formed.
[0018]
In the polysulfide carbon of the present invention having the above-described structure, a polysulfide carbon having the following characteristics is particularly preferable.
[0019]
That is, one of the preferred embodiments of the present invention has carbon and sulfur as main constituent elements, the mass ratio of sulfur is 75 mass% or more, and the total mass ratio of carbon and sulfur is 95 mass% or more, In the Raman spectrum, 1444 cm of Raman shift. ^-1 There is a main peak in the vicinity and 400cm ^-1 ~ 525cm ^-1 The peak existing in the range is substantially 490 cm ^-1 There is only a broad peak nearby, and 218cm ^-1 It is a polysulfide carbon characterized by not having a sharp peak in the vicinity.
[0020]
In another preferred embodiment of the present invention, carbon and sulfur are the main constituent elements, the mass ratio of sulfur is 75% by mass or more, and the total mass ratio of carbon and sulfur is 95% by mass or more. In the X-ray diffraction using the CuKα ray, the diffraction pattern having a diffraction angle (2θ) in the range of 20 ° to 30 ° is substantially expressed only by a broad diffraction peak having a peak in the vicinity of 25 °. It is a featured polysulfide carbon.
[0021]
In another preferred embodiment of the present invention, carbon and sulfur are the main constituent elements, the mass ratio of sulfur is 75 mass% or more, and the total mass ratio of carbon and sulfur is 95 mass% or more. The polysulfide carbon is characterized in that the mass loss by thermal mass spectrometry when heated from room temperature to 300 ° C. at a rate of 10 ° C./min is 15% or less.
[0022]
Carbon and sulfur as described above are the main constituent elements, the mass ratio of sulfur is 67 mass% or more, and the total mass ratio of carbon and sulfur is 95 mass% or more, and the formula (1) The carbonized polysulfide having a repeating unit represented by the following formula is reliable when used as a positive electrode active material for a non-aqueous electrolyte battery because it has a high capacity, a high reversibility, and a small capacity drop due to a charge / discharge cycle. A high primary battery or a secondary battery can be provided.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Next, the details of the method for synthesizing the polysulfide carbon of the present invention and the use as the active material of the nonaqueous electrolyte battery will be specifically described.
[0024]
Carbon and sulfur of the present invention are the main constituent elements, the mass ratio of sulfur is 67 mass% or more, and the total mass ratio of carbon and sulfur is 95 mass% or more, and the repetition represented by the formula (1) The polysulfide carbon having units can be synthesized, for example, by the following method. First, an alkali metal sulfide such as sodium sulfide and sulfur are reacted in a solvent such as alcohol, acetone or water at a temperature range of approximately 0 ° C. to 50 ° C. for about 10 minutes to 10 hours, and then the solvent is removed in a vacuum. Volatilize to remove reactants. Next, this is reacted with a halogenated unsaturated hydrocarbon such as hexachlorobutadiene in an organic solvent such as N-methyl-2-pyrrolidone at a temperature range of about 0 ° C. to 50 ° C. for about 10 minutes to 3 hours. Thereafter, the reaction product is washed several times with pure water and an organic solvent and vacuum dried at approximately 10 ° C. to 80 ° C. to obtain a brown solid compound as an intermediate product. This brown solid compound has a large number of polysulfide segments in the molecule, and corresponds to the organic sulfur compound described in JP-A-11-514128. It has also been confirmed that many polysulfide compounds produced in the course of the synthesis reaction are mixed. As a method for obtaining this intermediate product, in addition to the above methods, conventionally known methods for synthesizing various organic sulfur compounds can be employed.
[0025]
Next, the intermediate product is put in a heat-resistant container made of alumina (aluminum oxide) or the like, and heated in a range of 150 ° C. to 250 ° C. in a vacuum, so that the polysulfide mixed in the intermediate product is mixed. Impurities such as compounds are evaporated, polysulfide segments in organic sulfur compound molecules are cleaved, and excess sulfur is removed by evaporation, consisting of almost only two elements of carbon and sulfur. A carbon polysulfide having a structure in which all carbon atoms form bonds with sulfur atoms and most or all of the sulfur atoms form disulfide bonds having high reversibility to oxidation and reduction is obtained. The sulfur content in such polysulfide carbon is as high as 67% to 82% on a mass basis.
[0026]
Specifically describing the molecular structure of this compound, as described above, a structure having a repeating unit represented by the following formula (1) is presumed, and the bond between carbon chains is represented by, for example, formula (2) , It is presumed to be formed by a disulfide bond as represented by the formula (3).
[Chemical 3]

[Formula 4]

[Chemical formula 5]

[0027]
The presence of carbon double bonds (C═C) and sulfur disulfide bonds (C—S—S—C) in the polysulfide carbon molecule can be confirmed by Raman analysis and the like which will be described in detail later. it can.
[0028]
In the above heat treatment, in order to prevent oxidation of the compound during heating, approximately 5 × 10 ^Three Heat treatment is preferably performed in a high vacuum degree of Pa or less and in a vacuum atmosphere after replacement with an inert gas. The heating temperature is preferably about 150 ° C to 250 ° C, more preferably 180 ° C to 220 ° C. However, the higher the degree of vacuum, the more uniformly the heat is transferred, and the lower the starting raw material, the lower the temperature. It can be carried out. The heating time may be adjusted depending on the temperature and atmosphere of the heat treatment, but approximately 30 minutes to 5 hours is appropriate. The composition of the polysulfide carbon obtained is slightly different depending on the composition of the intermediate product, the heating temperature, the heating time, etc., but it is easy to increase the capacity by containing 67 to 82% by mass of sulfur. From the viewpoint of mechanical stability, it is necessary that the content of elements other than carbon and sulfur is small, that is, the mass ratio of sulfur to carbon is 95% by mass or more.
[0029]
Furthermore, when the atomic ratio of carbon to sulfur in the polysulfide carbon is 1: x, a compound in which x is in the range of 1.4 to 1.6 has high molecular structure, The reversibility is excellent and a high capacity active material is preferable. This is because a compound having a value of x greater than 1.6 introduces many polysulfide segments in the molecule.
[0030]
The polysulfide carbon may contain elements other than carbon and sulfur as long as the chemical stability and reversibility of charge / discharge are not impaired, and a compound containing hydrogen, nitrogen, boron, halogen elements, etc. However, it is more preferably composed of only two elements of carbon and sulfur. For example, polysulfide carbon can be represented by the general formula (CS _x ) _n X is 1.4 to 1.6, and n is preferably 4 or more. When n is 3, it is difficult to form a reversible trithione structure having a disulfide bond, and even if a compound having such a trithione structure can be synthesized, the stability is poor and its usefulness is low. It is done. Since the polysulfide carbon of the present invention has low solubility in organic solvents and it is difficult to measure its molecular weight, it is difficult to accurately determine the value of n in the above general formula. n is preferably 4 or more, and no problem is considered to occur no matter how large n is. However, it is usually practical to synthesize up to n of about 100,000. The above-mentioned polysulfide carbon having n of 4 or more can be obtained, for example, by synthesizing using a halogenated unsaturated hydrocarbon having 4 or more carbon atoms in the main chain.
[0031]
Further, the polysulfide carbon is not connected to the carbon skeleton by bringing the organic sulfur compound having a polysulfide segment into contact with a non-aqueous solvent exhibiting solubility in the container or by contacting with the vapor of the non-aqueous solvent. It can also be obtained by eluting the sulfur segment and other impurities and cutting and removing the unstable long sulfur segment even though it is connected to the carbon skeleton. That is, the organic sulfur compound having a polysulfide segment is substantially composed of two elements of carbon and sulfur by contact with a non-aqueous solvent as described above, and is a polysulfide carbon mainly composed of a repeating unit represented by the formula (1). To change. In this solvent extraction treatment, in consideration of the flash point of the solvent, the atmosphere is preferably in a low oxygen concentration state, and more preferably in an inert gas atmosphere in which the oxygen concentration is reduced to 400 ppm or less. The molecular weight of carbon polysulfide synthesized by such a method is expected to be low.
[0032]
The solvent used for the solvent extraction treatment is preferably a non-aqueous organic solvent having excellent solubility with respect to sulfur or a sulfur compound having a polysulfide segment. In particular, in order to cut and remove the unstable long sulfur segment connected to the carbon skeleton, a strong donor non-aqueous organic solvent is preferable. Specific examples thereof include aliphatic solvents such as aromatic solvents such as toluene and benzene, tetrahydrofuran, dimethylformamide, tetramethylethylenediamine, dioxolane, tetraglyme and the like containing oxygen or nitrogen in the molecule. Examples thereof include cyclic low molecular weight solvents and sulfur-containing solvents such as carbon disulfide, dimethyl sulfoxide, and sulfolane. Moreover, the mixed solvent of those solvents may be sufficient. Among the above solvents, dimethyl sulfoxide, carbon disulfide, tetrahydrofuran, toluene, tetraglyme and the like are particularly preferable. The above tetraglyme is an organic solvent called bis [(2-methoxyethoxy) ethyl] ether.
[0033]
The extraction temperature with the solvent is not particularly limited, but is a temperature from room temperature to the boiling point of the solvent, and it is particularly preferable to perform extraction while refluxing the solvent. The extraction time depends on the temperature and the molecular weight of the organic sulfur compound, which is an intermediate product, but approximately 10 minutes to 5 hours is appropriate. The higher the temperature and the lower the molecular weight of the intermediate product, the shorter the extraction time.
[0034]
The Raman analysis of the above polysulfide carbon is carried out using an argon laser as the light source. The polysulfide carbon of the present invention has a Raman shift of 1444 cm in the obtained Raman spectrum according to the Raman analysis. ^-1 There is a main peak in the vicinity and 400cm ^-1 ~ 525cm ^-1 The peak existing in the range is substantially 490 cm ^-1 218cm only at a broad peak nearby ^-1 It does not have a sharp peak in the vicinity. Where 1444 cm ^-1 The main peak in the vicinity is based on an unsaturated bond (C═C bond) of carbon in the carbon skeleton, and this peak has the maximum intensity in the Raman spectrum. Also, 400cm above ^-1 ~ 525cm ^-1 In this range, a peak derived from a disulfide bond connected to a carbon skeleton or a peak derived from a polysulfide segment appears, but 490 cm ^-1 A nearby peak is a peak derived from a disulfide bond, and a peak derived from an SS bond in a polysulfide segment appears at a different position (for example, 219 cm). ^-1 Near and 470cm ^-1 It has a sharp peak in the vicinity.) In the present invention, “substantially 490 cm ^-1 “Only the peak near” is 490cm ^-1 This means that there may be a minute peak in addition to the nearby peak. That is, in the polysulfide carbon of the present invention, there is no polysulfide segment in the molecule, that is, within the above range of Raman shift, 490 cm. ^-1 Although it is preferable that no peaks other than nearby peaks exist, it means that a small amount of polysulfide segments may be present in the molecule within a range not deteriorating the required characteristics. Where 1444 cm ^-1 The neighborhood is approximately 1444cm ^-1 ± 50cm ^-1 Corresponds to the range of 490cm ^-1 The neighborhood is about 490cm ^-1 ± 50cm ^-1 It corresponds to the range.
[0035]
In contrast, the Raman spectrum of a conventional organic sulfur compound is 200 cm. ^-1 ~ 525cm ^-1 There are many peaks in the range of 218 cm, especially when the sulfur content is high ^-1 Near and 270cm ^-1 There is a sharp peak in the vicinity. This is because -S _m This indicates that there are many polysulfide segments represented by-(m ≧ 3), and m is considered to have various values.
[0036]
When the above polysulfide carbon is subjected to X-ray diffraction using CuKα rays, the diffraction pattern in the range of 20 ° to 30 ° at the diffraction angle (2θ) is substantially a half-value width having a peak position in the vicinity of 25 °. Can be expressed as one broad diffraction peak of approximately 1.5 ° to 5 °. That is, there is substantially only one diffraction peak in the diffraction angle range. Here, as described above, “substantially” is not required to be completely one, and it is preferable that a peak derived from a polysulfide segment, that is, a peak identified with sulfur is not observed. However, even if observed, it is weak (peak intensity is approximately 1/10 or less of the peak), which means that it is acceptable in the present invention.
[0037]
In addition, when carbon polysulfide is synthesized by the above-described method, an alkali metal halide is also produced as a by-product in the production process of the organic sulfur compound, which is an intermediate product. Even when carbon sulfide is washed, a small amount of sodium chloride or the like may be mixed in the polysulfide carbon. Therefore, an alkali metal halide peak may appear in the X-ray diffraction pattern, but this diffraction peak may be excluded.
[0038]
In the X-ray diffraction pattern, the peak near 25 ° is expressed by the following formula (4):
[Chemical 6]

It is presumed that the plane formed by the disulfide bond shown in (2) further forms a layered structure and is a diffraction peak generated by the layered structure. The peak is broad because the main chain composed mainly of carbon is rotatable, so that each plane formed by multiple disulfide bonds in one molecule is all the same plane. This is probably because the molecular weight of the synthesized polysulfide carbon has a certain distribution. Of course, for the reasons described above, it is conceivable that the peak does not become a single peak, but a slight separation occurs. However, it is sufficient that almost one peak is formed as a whole. The interlayer distance obtained from the diffraction angle of this peak is about 0.3 nm to 0.44 nm, which is close to the interlayer distance (0.335 nm) of graphite, so that the interlayer helium in the above layered structure intercalates. Can be considered.
[0039]
In contrast, in the conventional organic sulfur compounds including the intermediate product of the present invention, there are many sharp peaks in the X-ray diffraction pattern, but almost all of them are free sulfur or polysulfide segments. This is a diffraction peak due to sulfur. Diffractive peaks other than sulfur-based diffraction peaks are difficult to distinguish because of their low intensity.
[0040]
Furthermore, in the conventional organic sulfur compound, when thermal mass-differential thermal analysis (TG-DTA) is performed in a nitrogen atmosphere, strong endothermic peaks of 122.7 ° C. and 314 ° C. based on sulfur exist, As the temperature rises, the mass decreases from around 200 ° C., but in the polysulfide carbon of the present invention, the 122.7 ° and 314 ° peaks disappear, and the mass does not decrease to a higher temperature. For example, the polysulfide carbon of the present invention exhibits excellent thermal stability with a mass loss of 20% or less when heated from room temperature to 300 ° C. at a heating rate of 10 ° C./min. Therefore, when the polysulfide carbon of the present invention, which has good crystallinity and excellent chemical stability, is used as the positive electrode active material of a non-aqueous electrolyte battery, there is no sulfide formation, so that good reversibility is maintained over a long period of time. can do.
[0041]
When the polysulfide carbon of the present invention is used as a positive electrode active material of a nonaqueous electrolyte battery, its theoretical capacity is approximately 670 mAh / g, and LiCoO that is most widely used as a positive electrode active material. ₂ It is possible to realize a capacity increase of 4 times or more of (137 mAh / g). The polysulfide carbon of the present invention can be used as a negative electrode active material in addition to the above-described use as a positive electrode active material of a non-aqueous electrolyte battery, or its chemical stability, semiconductivity, light absorption, etc. It is considered that it can be used for information storage elements, display elements, electronic materials and the like by taking advantage of the above characteristics.
[0042]
Next, preparation of a nonaqueous electrolyte battery (secondary battery) using the polysulfide carbon of the present invention as a positive electrode active material will be described.
[0043]
The positive electrode is composed of the above polysulfide carbon and conductive aids, binders, additives and the like used as necessary. Examples of the conductive aid include carbonaceous materials such as graphite and carbon black. Alternatively, a conductive polymer or the like is preferably used.
[0044]
Examples of the binder include fluororesins such as polyvinylidene fluoride and polytetrafluoroethylene, amorphous polyether, polyacrylamide, poly-N-vinylacetamide, polyaniline having solubility in a solvent, polypyrrole, copolymers thereof, or cross-linking. And the like. These are preferably polymer compounds that are chemically stable and have a strong adhesive force to the positive electrode active material.
[0045]
The positive electrode is, for example, a positive electrode active material composed of the above polysulfide carbon, and if necessary, the above-mentioned conductive auxiliary or binder is added and mixed to prepare a positive electrode mixture, which is dispersed in a solvent and pasted (The binder may be dissolved in a solvent in advance and then mixed with the positive electrode active material, etc.), and the positive electrode mixture-containing paste is applied to a positive electrode current collector made of a metal foil and dried. It is produced by undergoing a step of forming a positive electrode mixture layer on at least a part of the body. However, the method for manufacturing the positive electrode is not limited to the above-described method, and other methods may be used.
[0046]
Examples of the active material of the negative electrode include metal lithium, lithium alloys with aluminum, lithium-containing composite compounds, carbonaceous materials such as graphite, and elements that can be alloyed with lithium such as tin (tin) or silicon (silicon). Or oxides containing them, lithium-containing nitrogen compounds, and the like.
[0047]
The method for producing the negative electrode is roughly divided into two types depending on the type of the negative electrode active material to be used. One of them is that when using a metal or alloy as the negative electrode active material, the negative electrode is made by pressing the metal or alloy as the negative electrode active material on the negative electrode current collector made of a metal porous body such as a wire mesh, expanded metal or punching metal. Is adopted. And when using a carbonaceous material etc. as a negative electrode active material, if necessary, the same conductive assistant or binder as in the case of the positive electrode is added to the negative electrode active material made of the above carbonaceous material, and mixed. Prepare a negative electrode mixture, disperse it in a solvent to make a paste (the binder may be dissolved in the solvent in advance and then mixed with the negative electrode active material), and the negative electrode mixture-containing paste is made of copper foil, etc. The negative electrode current collector is applied to the negative electrode current collector and dried to form a negative electrode mixture layer on at least a part of the negative electrode current collector. However, the method for manufacturing the negative electrode is not limited to the above-described method, and other methods may be used.
[0048]
As the non-aqueous electrolyte, any of a non-aqueous liquid electrolyte (hereinafter referred to as “electrolytic solution”), a polymer electrolyte, and a solid electrolyte can be used.
[0049]
First, the electrolyte will be described as the electrolyte. The electrolyte is constituted by dissolving an electrolyte salt in a non-aqueous solvent component.
[0050]
The non-aqueous solvent for the electrolyte is composed of a main solvent having good solubility in lithium sulfide and a sub-solvent used as necessary. Specific examples of the main solvent include aromatic solvents such as toluene and benzene, tetrahydrofuran, dimethylformamide, 1,2-dimethoxyethane, tetramethylethylenediamine, dioxolane, 2-methyl-tetrahydrofuran, and tetraglyme. Examples include aliphatic or alicyclic low molecular weight solvents containing oxygen or nitrogen in the molecule, such as polyoxide having a molecular weight of 10,000 or less, and solvents containing sulfur such as dimethyl sulfoxide, sulfolane, etc. It can be used alone or as a mixed solvent of two or more. Among these solvents, solvents having strong donor properties (electron-donating properties) such as 1,2-dimethoxyethane, dimethyl sulfoxide, sulfolane, tetrahydrofuran, and tetraglyme are particularly preferable. Is preferably used in combination with a low viscosity ether such as tetrahydrofuran or dioxolane. Of course, a non-aqueous solvent can also be comprised only with this main solvent.
[0051]
Examples of the co-solvent include esters such as ethylene carbonate, propylene carbonate, butylene carbonate, and γ-butyrolactone, and sulfur-based esters such as ethylene glycol and sulfite. In addition to these, chain esters such as dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and methyl propionate, chain phosphate triesters such as trimethyl phosphate, and diethyl ether can be used. Although the ionic conductivity of the electrolyte is increased by the addition of these cosolvents, the reactivity of the active material tends to be reduced. Therefore, the amount of the auxiliary solvent added depends on the nature of the main solvent, but in all the constituent solvents. Is preferably 20% by mass or less.
[0052]
As the electrolyte salt to be dissolved in the non-aqueous solvent, for example, a halogen salt or perchlorate of lithium, a lithium salt of an organic boron, a salt of a fluorine-containing compound typified by trifluoromethanesulfonate, an imide salt and the like are preferable. Used for. Specific examples of such an electrolyte salt include, for example, LiF and LiClO. _Four , LiPF ₆ , LiBF _Four , LiB (OC ₆ H _Four COO) ₂ , LiCF _Three SO _Three , LiC _Four F ₉ SO _Three , LiCF _Three CO ₂ , Li ₂ C ₂ F _Four (SO _Three ) ₂ , LiN (CF _Three SO ₂ ) ₂ , LiN (RfSO ₂ ) (Rf'SO ₂ ), LiN (RfOSO) ₂ ) (Rf'OSO ₂ ), LiC (RfSO ₂ ) _Three , LiC _n F _{2n + 1} SO _Three (N ≧ 2), LiN (RfOSO ₂ ) ₂ [Wherein Rf and Rf ′ are fluoroalkyl groups] and the like, and these can be used alone or in combination of two or more. The electrolyte salt is particularly preferably a fluorine-containing organic lithium salt or imide salt having 2 or more carbon atoms. 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 non-aqueous 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.
[0053]
The polymer electrolyte corresponds to a gelled version of the electrolytic solution. In the gelation, for example, a linear polymer such as tetrafluoroethylene-hexafluoropropylene copolymer, polyethylene oxide, polyacrylonitrile, or a copolymer thereof, or a polyfunctional monomer (for example, four polymers such as dipentaerythritol hexaacrylate) is used. A polymer compound obtained from a reaction between a polymer compound obtained from a functional acrylate or higher) or an amine compound and urethane is used. In addition, the solid electrolyte includes an inorganic type and an organic type, and examples of the inorganic solid electrolyte include sodium β alumina, 60LiI-40Al. ₂ O _Three , Li _Three N, 5LiI-4Li ₂ S-2P ₂ S _Five , Li _Three In addition, examples of the organic solid electrolyte include amorphous, low phase transition temperature (Tg) polyethers, amorphous vinylidene fluoride copolymers, blends of different polymers, and the like. .
[0054]
As described above, the case where the polysulfide carbon of the present invention is used as the active material of the nonaqueous electrolyte battery has been described. However, the polysulfide carbon of the present invention is only the active material of the nonaqueous electrolyte battery as exemplified above. In addition, for example, it can be used for other electrochemical elements such as capacitors, information recording elements, display elements, electronic materials, and the like.
[0055]
【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, “%” indicating the concentration of a solution or dispersion, and “%” indicating the composition, yield, etc. are mass% unless otherwise specified.
[0056]
Example 1
Sodium sulfide nonahydrate (Na ₂ S • 9H ₂ 100 g of O) was dissolved in 300 ml of a mixed solvent of ethanol and water mixed at a volume ratio of 1: 1, and 53.4 g of sulfur was added thereto and reacted at room temperature for 1 hour. Then, after removing the solvent in vacuum, the residue was dissolved in 700 ml of N-methyl-2-pyrrolidone, 17.2 g of hexachlorobutadiene was added, and the mixture was reacted at room temperature for 1 hour. Thereafter, it was thoroughly washed with pure water, acetone and ethanol, and dried for 15 hours while keeping the temperature at 40 ° C. in a vacuum to obtain a brown compound as an intermediate product. The method for synthesizing this compound is almost the same as the method described in the examples of JP-T-11-506799.
[0057]
Elemental analysis was performed on the obtained compound to obtain an average composition. As a result, C: 7.0%, S: 92.3%, N: 0.2% or less, and H: 0.3% or less. The corresponding general formula is (CS _6.2 ) _n (The average composition of the compounds obtained by synthesis is not always constant). The analysis results of C, N, and H were analyzed using a fully automatic elemental analyzer (manufactured by Siebel Hegna, vario EL), sample decomposition furnace temperature: 950 ° C., reducing furnace temperature: 500 ° C., helium flow rate: 200 ml / min, oxygen flow rate : Based on the results of elemental analysis performed under conditions of 20 to 25 ml / min. The analysis result of S is the flask combustion method-barium acetate measurement, and the elemental analysis was performed using trimethylene blue as an indicator. It depends on the result.
[0058]
Next, 40 g of the intermediate product is placed in a ship-shaped alumina (aluminum oxide) container, the alumina container containing the intermediate product is placed in a vacuum drying furnace, and the degree of vacuum is 1.33 × 10 6. ² After evacuating to Pa (1 torr) or less and replacing with argon gas having a purity of 99.9% once, the temperature is changed under the following conditions with the same degree of vacuum, and finally heat treatment is performed at 205 ° C. Went. That is, the temperature is raised from room temperature to 60 ° C. in 0.5 hours, held at 60 ° C. for 1 hour, then heated to 205 ° C. in 2 hours, and kept at 205 ° C. for 5 hours for heat treatment The intermediate product was converted to carbon polysulfide by removing a portion of the sulfur in the intermediate product.
[0059]
After the treatment, the reaction product was taken out from the alumina container after cooling to room temperature, and about 10.0 g of black polysulfide carbon having a metallic luster similar in appearance to graphite was obtained. As a result of elemental analysis, the composition of this polysulfide carbon is C: 19.9% and S: 79.8%. _1.50 ) _n It became. Since hexachlorobutadiene used as a reaction component in the synthesis of the polysulfide carbon is a compound having 4 carbon atoms, the general formula (CS _1.50 ) _n N value is 4 or more, and it is presumed that the compound is a compound which is mainly a multiple of 4.
[0060]
Next, this polysulfide carbon was subjected to Raman analysis using the following apparatus and conditions. The result is shown in FIG.
Device: Ramaonor T-6400 (Jobin Yvon / Ehime Bussan)
Light source: Ar laser [GLG3460 (514.5 nm, output: 1 mW (NEC)]
[0061]
In FIG. 1, the horizontal axis represents the Raman shift (cm ^-1 ) And the vertical axis is relative strength, but this polysulfide carbon (CS _1.50 ) _n As shown in FIG. 1, the result of Raman analysis is 1444 cm. ^-1 Has a main peak based on an unsaturated bond of carbon (C = C bond) and 400 cm ^-1 ~ 525cm ^-1 The peak existing in the range of 490 cm ^-1 There is a broad peak nearby and 219cm ^-1 There was no sharp peak in the vicinity. That is, the polysulfide carbon had only peaks based on disulfide bonds and no peaks based on polysulfide segments. In general, for disulfide bonds that lead to carbon, 505 cm ^-1 A peak based on a disulfide bond appears in the vicinity. However, in the polysulfide carbon of the present invention, it is presumed that the peak position is shifted under the influence of the unsaturated bond (C═C bond) of the carbon.
[0062]
Further, the polysulfide carbon was subjected to X-ray diffraction measurement using CuKα rays by a powder X-ray diffractometer [RINT2000 (manufactured by Rigaku Corporation)]. Measurement conditions are voltage: 40 kV, current: 150 mA, scan speed: 2 ° / min, sampling: 0.02 °, number of integrations: 5 times, and measurement within a diffraction angle (2θ) of 10 ° to 80 °. went. Polysulfide carbon (CS obtained by X-ray diffraction measurement) _1.50 ) _n FIG. 2 shows the diffraction pattern of FIG. 2. When the diffraction angle (2θ) is in the range of 20 ° to 30 °, only a broad diffraction peak having a peak position in the vicinity of 25 ° was observed. The peaks at 31.8 ° and 45.5 ° are due to sodium chloride.
[0063]
Further, the polysulfide carbon was subjected to thermal mass-differential thermal analysis (TG-DTA) using a thermal analyzer (thermo plus TG8120) manufactured by Rigaku Corporation. That is, heating was performed at a heating rate of 10 ° C./min while flowing high-purity nitrogen gas at a flow rate of 0.15 liter / min, and the relationship between temperature and mass change was measured. The result is shown in FIG. FIG. 3 shows a compound (CS) of Comparative Example 1 described later. _6.2 ) _n The results of the thermal mass-differential thermal analysis are also shown. As is apparent from the results shown in FIG. 3, conventionally known organic sulfur compounds (CS _6.2 ) _n While the mass rapidly decreases at 200 ° C. or higher, the polysulfide carbon (CS) of the present invention _1.50 ) _n Shows that there is little mass loss up to around 300 ° C. (mass loss up to 300 ° C .: 20% or less), and hardly contains -Sm- (m is 3 or more).
[0064]
Example 2
In the heat treatment of Example 1, carbon sulfide (CS) was obtained in the same manner as in Example 1 except that the treatment temperature was 190 ° C. _1.58 ) _n Got. The polysulfide carbon was subjected to Raman analysis and X-ray diffraction measurement in the same manner as in Example 1.
[0065]
This polysulfide carbon (CS _1.58 ) _n In the Raman analysis of _1.50 ) _n Same as 1444cm ^-1 Has a main peak at 400 cm ^-1 ~ 525cm ^-1 In the range of 490cm ^-1 There is only a broad peak nearby and 219cm ^-1 There was no sharp peak in the vicinity. In the X-ray diffraction measurement, the above (CS _1.50 ) _n A pattern almost identical to the diffraction pattern was obtained.
[0066]
Example 3
In the heat treatment of Example 1, carbon sulfide (CS) was obtained in the same manner as in Example 1 except that the treatment temperature was 220 ° C. _1.42 ) _n Got. The polysulfide carbon was subjected to Raman analysis and X-ray diffraction measurement in the same manner as in Example 1.
[0067]
This polysulfide carbon (CS _1.42 ) _n In the Raman analysis of _1.50 ) _n Like 1440cm ^-1 Has a main peak at 494 cm ^-1 There is only a broad peak nearby and 219cm ^-1 There was no sharp peak in the vicinity. In the X-ray diffraction measurement, the above (CS _1.50 ) _n A pattern similar to the diffraction pattern was obtained, and only had a broad peak at 24.4 °.
[0068]
Example 4
The general formula (CS) obtained as an intermediate product in the same manner as in Example 1. _6.2 ) _n The compound represented by the above is pulverized to about 10 μm with a ball mill, and 20 g of the obtained powder is put into a 300 ml three-necked flask equipped with a cooling tube and a nitrogen substitution port, and 100 ml of carbon disulfide is added thereto. Was added and refluxed in an argon atmosphere for 5 hours to remove a part of the sulfur constituting the compound and change it to a disulfide bond. Thereafter, the precipitate is collected by centrifugation after cooling to room temperature, washed with 30 ml of carbon disulfide and acetone, and then vacuum-dried at 50 ° C. for 12 hours to obtain a polysulfide carbon having a black-brown metallic luster. (CS _1.54 ) _n Got. The polysulfide carbon was subjected to Raman analysis and X-ray diffraction measurement in the same manner as in Example 1.
[0069]
The result of Raman analysis of this polysulfide carbon is shown in FIG. _1.54 ) _n Then, 1447cm ^-1 The main peak of the broad is 1447cm ^-1 And 1467cm ^-1 Split into 400cm ^-1 ~ 525cm ^-1 In the range of 472cm ^-1 Only has a peak at 219 cm ^-1 There was no sharp peak in the vicinity. Furthermore, the X-ray diffraction measurement only had a broad peak at 25.6 °.
[0070]
Comparative Example 1
In the same manner as in Example 1, the intermediate product is represented by the general formula (CS _6.2 ) _n The organic sulfur compound represented by the formula (1) was obtained and used as the organic sulfur compound of Comparative Example 1.
[0071]
Comparative Example 2
In the same manner as in Example 4, the intermediate product is represented by the general formula (CS _2.6 ) _n The organic sulfur compound represented by the formula (1) was obtained and used as the organic sulfur compound of Comparative Example 2.
[0072]
These organic sulfur compounds (CS _6.2 ) _n And (CS _2.6 ) _n As in Example 1, Raman analysis and X-ray diffraction measurement were performed. Organic sulfur compounds (CS _6.2 ) _n The results of Raman analysis are shown in FIG. 5, and the results of X-ray diffraction are shown in FIG. Organic sulfur compounds (CS _6.2 ) _n 1440cm in Raman analysis ^-1 Has a main peak at 400 cm ^-1 ~ 525cm ^-1 494cm between ^-1 Although there are nearby peaks, many peaks based on the polysulfide segment also appeared. For example, 219cm ^-1 The nearby peaks and the like were peaks that were not seen in the polysulfide carbon of the present invention, and it was estimated that the molecular structure was quite different from that of the polysulfide carbon of the present invention.
[0073]
Also, (CS _6.2 ) _n In the X-ray diffraction measurement, a large number of sharp diffraction peaks were observed, but most of the diffraction peaks were identified by sulfur or polysulfide -Sm (m> 3) diffraction peaks, and the polysulfide carbon of the present invention was identified. As can be seen, no clear peak considered to be based on the crystal structure was observed.
[0074]
In the following Examples 5 to 8 and Comparative Examples 3 to 4, non-aqueous electrolyte secondary batteries using the polysulfide carbon of Examples 1 to 4 and the organic sulfur compounds of Comparative Examples 1 and 2 as positive electrode active materials were used. It was prepared and its characteristics were evaluated.
[0075]
Examples 5-8 and Comparative Examples 3-4
First, the positive electrode was produced as follows. About the polysulfide carbon of Examples 1-4 or the organic sulfur compounds of Comparative Examples 1-2, 10 parts by mass thereof, 7.2 parts by mass of Lonza graphite (KS-6) and 0.8 parts by mass of acetylene black After putting into a mixing container and mixing for 10 minutes by dry process, 50 parts by mass of N-methyl-2-pyrrolidone was added and mixed for 30 minutes. Next, 16.7 parts by mass of an N-methyl-2-pyrrolidone solution containing 12% polyvinylidene fluoride was added, and further mixed for 1 hour to prepare a positive electrode mixture-containing paste.
[0076]
The obtained positive electrode mixture-containing paste was applied to an aluminum foil (size: 250 mm × 220 mm) having a thickness of 20 μm, dried on a hot plate at 50 ° C. for 10 minutes, and further dried at 70 ° C. in vacuum for 10 hours. The positive electrode mixture layer was formed by removing N-methyl-2-pyrrolidone. The electrode body after drying was heated to 100 ° C. and pressurized to obtain a positive electrode having a positive electrode material mixture layer with a thickness of 40 μm.
[0077]
The negative electrode is formed by placing a 120 μm-thick lithium foil on a 60 μm stainless steel net (size: 250 mm × 220 mm) in an argon gas atmosphere, pressurizing it with a roller, and pressing the lithium foil onto the stainless steel net Produced.
[0078]
As an electrolytic solution, a mixed solvent of tetraglyme and 1,3-dioxolane (mass ratio 4: 1), LiCF _Three SO _Three A solution in which 1 mol / l was dissolved was used.
[0079]
Then, the positive electrode and the negative electrode are cut into 70 × 42 mm and laminated in an argon gas atmosphere through a separator made of a porous polyethylene film having a thickness of 40 μm, and the laminated electrode body is nylon film-aluminum foil-modified polyolefin. A non-aqueous electrolyte secondary battery was produced by placing the resin film in a package made of a three-layer laminate film, injecting an electrolytic solution, and sealing it. This battery was charged and discharged at a current value corresponding to 60 mA per 1 g of the positive electrode active material (constant current and constant voltage: 2.5 V, constant current discharge end voltage: 1.5 V), and this was repeated for 5 cycles. The discharge capacity at the beginning of the cycle and the discharge capacity at the fifth cycle were measured, and the change in the discharge capacity per gram of the positive electrode active material was examined. The results are shown in Table 1. In addition, when it shows about the relationship between the battery of Examples 5-8 and Comparative Examples 3-4, the polysulfide carbon of Examples 1-4, and the organic sulfur compound of Comparative Examples 1-2, the positive electrode activity of the battery of Example 5 is shown. The material is the polysulfide carbon of Example 1, the positive electrode active material of the battery of Example 6 is the polysulfide carbon of Example 2, and the positive electrode active material of the battery of Example 7 is the polysulfide carbon of Example 3. The positive electrode active material of the battery of Example 8 is the polysulfide carbon of Example 4, the positive electrode active material of the battery of Comparative Example 3 is the organic sulfur compound of Comparative Example 1, and the positive electrode active material of the battery of Comparative Example 4 is the comparative example 2 organic sulfur compounds.
[0080]
[Table 1]

[0081]
As is clear from the results shown in Table 1, the batteries of Examples 5 to 8 have a large capacity, a small capacity decrease accompanying the charge / discharge cycle, a high capacity, and a high reliability with excellent charge / discharge cycle characteristics. It was a non-aqueous electrolyte secondary battery. That is, the general formula (CS _x ) _n The polysulfide carbons of Examples 1 to 4 having x in the range of 1.4 to 1.6 are represented by conventional organic sulfur compounds (CS _2.6 ) _n And (CS _6.2 ) _n Compared to, the initial capacity is not much different when mounted batteries, but the capacity drop associated with charge / discharge cycles is small, the capacity is high, and the secondary battery is highly reliable and has excellent charge / discharge cycle characteristics. It can be seen that the battery can be constructed.
[0082]
Example 9
100 g of an amine compound (Jeffamine XTJ-502) manufactured by Huntsman was dissolved in 130 g of a mixed solvent of tetraglyme and 1,3-dioxolane in a mass ratio of 4: 1, and an epoxy resin (SR-8EG manufactured by Sakamoto Yakuhin Co., Ltd.) ) 25.2 g was added and reacted at room temperature with stirring for 7 days. To the solution of the amine compound obtained by this reaction, LiCF _Three SO _Three Was added to a concentration of 1.0 mol / l and stirred until it was uniformly dissolved. On the other hand, urethane (AX-1043) manufactured by Mitsui Chemicals, Inc. is dissolved in a mixed solvent of tetraglyme and 1,3-dioxolane in a mass ratio of 4: 1. _Three SO _Three Was added so that the concentration was 1.0 mol / l. The solution containing the amine compound and the solution containing urethane are mixed so that the molar ratio of active hydrogen of amine and isocyanate group of urethane is 1.1: 1, and the average thickness of the mixed solution is 80 μm. A polybutylene terephthalate nonwoven fabric was dipped and left for 2 hours after being pulled up to prepare a polymer electrolyte using the polybutylene terephthalate nonwoven fabric as a support. All the above operations were performed in a dry atmosphere having a dew point temperature of −60 ° C. or lower.
[0083]
Next, as an electrolytic solution, a mixed solvent of tetraglyme and 1,3-dioxolane in a mass ratio of 4: 1 was mixed with LiCF. _Three SO _Three Was added to a concentration of 1.0 mol / l and used in Example 5 (CS _1.50 ) _n A battery was assembled by using a positive electrode and a negative electrode each having an active material. The surfaces of the positive electrode and the negative electrode are moistened with an electrolytic solution, and further, the positive electrode and the negative electrode are laminated through the polymer electrolyte, and the laminated body is put in the same package as in Example 5, and the electrolytic solution is injected. After that, it was sealed to produce a nonaqueous electrolyte secondary battery.
[0084]
Example 10
In Example 5, as the positive electrode active material (CS _1.50 ) _n And a nonaqueous electrolyte secondary battery in the same manner as in Example 5 except that a mixed solvent of tetraglyme, 1,3-dioxolane and ethylene carbonate in a mass ratio of 75: 20: 5 was used as the solvent of the electrolytic solution. Was made.
[0085]
Example 11
In Example 5, as the positive electrode active material (CS _1.50 ) _n And a nonaqueous electrolyte secondary as in Example 5 except that a mixed solvent of dimethyl sulfoxide, 1,3-dioxolane, and methyl ethyl carbonate in a mass ratio of 50:40:10 was used as a solvent for the electrolytic solution. A battery was produced.
[0086]
Example 12
In Example 5, as the positive electrode active material (CS _1.50 ) _n A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 5 except that 1 molar lithium perchlorate was used as the electrolyte salt.
[0087]
For the batteries of Examples 9 to 12, charging and discharging were repeated 50 cycles under the same charging and discharging conditions as in Example 5, and the discharge capacity at the 50th cycle was measured. The results are shown in Table 2 as the discharge capacity per 1 g of the positive electrode active material.
[0088]
[Table 2]

[0089]
As shown in Table 2, the batteries of Examples 9 to 12 provide a highly reliable non-aqueous electrolyte secondary battery that has a small capacity drop with an increase in charge / discharge cycle, high capacity, excellent charge / discharge cycle, and high reliability. We were able to. That is, the batteries of Examples 9 to 12 had almost the same characteristics as the battery of Example 5 even when the composition of the electrolytic solution was changed.
[0090]
【The invention's effect】
As described above, in the present invention, high-capacity and highly reversible polysulfide carbon and the use of the polysulfide carbon as an active material have high capacity, excellent charge / discharge cycle, and high reliability. A water electrolyte battery could be provided.
[Brief description of the drawings]
FIG. 1 shows a polysulfide carbon (CS) obtained in Example 1. _1.50 ) _n It is a figure which shows a Raman spectrum.
FIG. 2 shows polysulfide carbon (CS) obtained in Example 1. _1.50 ) _n It is a figure which shows X-ray diffraction pattern of these.
FIG. 3 shows polysulfide carbon (CS) obtained in Example 1. _1.50 ) _n And the organic sulfur compound (CS) obtained in Comparative Example 1 _6.2 ) _n It is a figure which shows the mass change in thermal mass-differential thermal analysis.
FIG. 4 shows polysulfide carbon (CS) obtained in Example 4. _1.54 ) _n It is a figure which shows a Raman spectrum.
FIG. 5 shows an organic sulfur compound (CS) obtained in Comparative Example 1. _6.2 ) _n It is a figure which shows a Raman spectrum.
6 shows an organic sulfur compound (CS) obtained in Comparative Example 1. FIG. _6.2 ) _n It is a figure which shows X-ray diffraction pattern of these.

Claims (2)

Carbon and sulfur are the main constituent elements, the mass ratio of sulfur is 67 mass% or more, and the total mass ratio of carbon and sulfur is 95 mass% or more. In the molecule, the following formula (1)

Polysulfide carbon have a in the repeating unit represented and characterized in that substantially no polysulfide segments. A nonaqueous electrolyte battery comprising an electrode comprising the polysulfide carbon of claim 1 as an active material and a nonaqueous electrolyte.

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