JP4674883B2 - Polysulfide carbon, method for producing the same, and nonaqueous electrolyte battery using the same - Google Patents

Description

【化２】

【００２３】
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。
【００２４】
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、加熱雰囲気は酸素濃度の低い状態が好ましく、真空中かあるいは酸素濃度を低減した（例えば、４００ｐｐｍ以下にした）不活性ガス雰囲気中などで加熱処理するのが好ましい。
【００２５】
上記加熱温度としては、おおよそ３００℃〜４３０℃が好ましく、３２０℃〜４１０℃がより好ましいが、加熱を真空中あるいは減圧雰囲気中で行う場合は、より低温でも行うことができる。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１０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、イオウを重量比率で６７重量％以上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重量比率が９５重量％以上であることが好ましい。
【００２６】
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０．９〜１．５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、高容量な活物質となるために好ましく、ｘが１．３以下であることがより好ましい。特にｘが１．１以下の場合は、可逆的な充放電を可能にするジスルフィド結合の存在割合を最も高くできるため、高容量で安定性が最も優れた化合物となる。また、容量の点からは、ｘは０．９５以上が好ましく、さらに１以上とすることにより最も好ましい化合物となる。これは、ｘの値が小さくなると、充放電に関与するジスルフィド結合以外に、充放電に関与しないＣ−Ｓ−Ｃ結合が分子内に導入されるからであり、また、ｘが１．５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。
【００２７】
また、上記ポリ硫化カーボンには、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０．９〜１．５で、ｎは４以上となる化合物が好ましい。ｎが３でジスルフィド結合を有するポリ硫化カーボンの合成は困難であり、たとえ合成できたとしても安定性に劣り有用性は低いと考えられる。本発明のポリ硫化カーボンは、有機溶剤などに対する耐性が優れていて、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、このｎは４以上であることが好ましく、加工性を考えるとｎは１００以上であることがより好ましい。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。
【００２８】
また、上記ポリ硫化カーボンは、前述の方法以外に、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。
【００２９】
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。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、これらの溶媒からなる混合溶媒でもよい。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。
【００３０】
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。
【００３１】
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り得られる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付近のピークのみであることを特徴とする。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。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、前記４００ｃｍ^-1〜５２５ｃｍ^-1の範囲内には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±２０ｃｍ^-1の範囲に相当し、４９０ｃｍ^-1付近とはおおよそ４９０ｃｍ^-1±２０ｃｍ^-1の範囲に相当する。
【００３２】
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、４００ｃｍ^-1〜５２５ｃｍ^-1の範囲に多数のピークが重なり合ってい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。一方、４９０ｃｍ^-1付近のピークは明瞭ではなく、分子内にはジスルフィド結合はほとんど存在していないと考えられる。また、従来の有機イオウ化合物では、１４４４ｃｍ^-1付近のピークもブロードであるが、本発明のポリ硫化カーボンでは、それよりシャープであって、その組成と構造がより単一に近い化合物となっている。
【００３３】
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のみで表すことができる。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。「実質的に」と記載したのは、完全に一つだけである必要はなく、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が、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）であるものは本発明において許容されることを意味する。ここで、２５°付近とはおおよそ２５°±３．５°の範囲に相当する。
【００３４】
また、上述した方法を用いて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じるため、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もある。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。
【００３５】
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（３）
【化３】

で表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、０．３〜０．４４ｎｍ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。
【００３６】
これに対して、本発明における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ピークが存在しているが、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く、ポリスルフィドセグメントを有する従来の有機イオウ化合物は、本発明のポリ硫化カーボンより結晶性が低いと考えられる。
【００３７】
さらに、従来の有機イオウ化合物では、窒素雰囲気下で熱重量−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℃付近から重量減少も生じるが、本発明のポリ硫化カーボンでは、上記１２２．７°と３１４°のピークが消失し、また、より高温まで重量減少が生じない。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重量減少が５％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、充電あるいは放電における活物質の分解と、それに伴う電解液へのイオウの溶出および硫化物の生成が抑制されるため、長期にわたり良好な可逆性を維持することができる。
【００３８】
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５５０〜８９０ｍＡｈ／ｇであり、非水電解質電池の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。
【００３９】
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。
【００４０】
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。特に導電性ポリマーを含有させた場合は、大電流負荷での特性向上が期待できる。上記導電性ポリマーとしては、例えば、ポリアセン、ポリアセチレン、ポリアニリン、ポリピロールなどのような共役構造を有するポリマーやそれらのメチル、ブチル、ベンジルなどの側鎖を有する誘導体などが好適に用いられる。
【００４１】
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ポリマーの構成モノマー間もしくは他のモノマーと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。
【００４２】
また、正極の構成要素として、ニッケル、ニッケル合金、ニッケル複合体またはニッケル化合物のいずれかを含む場合は、ポリ硫化カーボンとの相互作用により正極の充放電可逆性が向上する。そのようなニッケル合金としては、例えば、ＬａＮｉ₅ 、ＬａＮｉ_4.6 Ａｌ_0.4 、Ｖ−Ｔｉ−Ｎｉ合金などが挙げられ、ニッケル複合体としては、例えば、ニッケルをアルミニウム箔、ステンレス鋼箔などの表面に蒸着したもの、ニッケルをポリプロピレンシート、ポリエチレンテレフタレートシート、ポリブチレンテレフタレートシートなどに蒸着したものなどのニッケルと無機材料または有機高分子材料との複合体などが挙げられ、ニッケル化合物としては、例えば、ＮｉＳ、Ｎｉ₂ Ｓ₂ 、ＮｉＳ₂ などのニッケルの硫化物などが挙げられる。中でも、一般式ＮｉＳ_z （ｚは１〜５である）で表される化合物が好ましく用いられる。これは、上記化合物が正極活物質としても作用すると考えられるからである。
【００４３】
上記ニッケル、ニッケル合金、ニッケル複合体またはニッケル化合物は、添加剤として正極合剤中に含有させればよく、正極合剤中の含有量は０．５〜４０重量％とすることが好ましく、３〜２５重量％とすることがより好ましい。この場合は、０．１〜１０μｍの粒子径のものを用いることが好ましい。また、ニッケルは電子伝導体としても機能するため、上記ニッケル系添加剤と併用してあるいは前記ニッケル系添加剤のかわりに、例えば、発泡体状あるいはシート状のニッケルを正極の集電体とするか、あるいは、ニッケルのリボンをリード体として使用することもできる。ニッケルを正極の集電体として用いた場合は、非水電解質電池の正極集電体として通常用いられるアルミニウムの場合に比べて、充放電サイクル特性を向上させることができる。また、電池の外装缶を正極の出力端子とする場合は、外装缶をニッケル缶、ニッケル合金缶またはニッケルメッキ層を有する金属缶としてもよい。
【００４４】
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。
【００４５】
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、カルシウム、マグネシウムなどのアルカリ土類金属、それらとアルミニウムなどとの合金、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、ポリアセン、ポリアセチレン、ポリアニリン、ポリチオフィン、ポリピロールなどのような共役構造を有するポリマーやそれらのメチル、ブチル、ベンジルなどの側鎖を有する誘導体などからなる導電性ポリマーなどを用いることができる。
【００４６】
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。
【００４７】
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。
【００４８】
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。
【００４９】
この溶媒成分としては、エーテル、エステル、カーボネート類などが好適に用いられる。特に誘電率が高いエステル（誘電率３０以上）を混合して用いることが好ましい。このような誘電率が高いエステルとしては、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、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が挙げられ、特に環状のエステルが好ましく、とりわけエチレンカーボネートなどの環状カーボネートが好ましい。
【００５０】
また、上記溶媒以外にも、例えば、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のアルキルエステル類やリン酸トリメチルなどの鎖状リン酸トリエステルなどを用いることができ、そのほか、１，２−ジメトキシエタン、１，３−ジオキソラン、テトラヒドロフラン、２−メチル−テトラヒドロフラン、ジエチルエーテル、テトラグリムなども用いることができる。さらに、アミン系またはイミド系有機溶媒やスルホラン、ジメチルスルホキシドなどの含イオウ有機溶媒なども用いることができる。
【００５１】
また、電解液への添加剤としてＣ＝Ｃ不飽和結合を有する化合物を電解液中に添加すると、サイクル特性の低下を抑制できる場合がある。このような不飽和結合を有する化合物としては、例えば、Ｃ₆ Ｈ₅ Ｃ₆ Ｈ₁₁（シクロヘキシルベンゼン）などの芳香族化合物や、Ｈ（ＣＦ₂ ）₄ ＣＨ₂ ＯＯＣＣＨ＝ＣＨ₂ 、Ｆ（ＣＦ₂ ）₈ ＣＨ₂ ＣＨ₂ ＯＯＣＣＨ＝ＣＨ₂ などのフッ素化された化合物が挙げられる。
【００５２】
上記溶媒成分に溶解させる電解質塩としては、例えば、リチウム、ナトリウムなどのアルカリ金属やマグネシウムなどのアルカリ土類金属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 、Ｍｇ（ＣｌＯ₄ ）₂ 、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、上記溶媒成分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構成モノマー間もしくは他のモノマーとのコポリマー、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】
本発明においては、前記ポリ硫化カーボンの可逆性および充放電での利用率をさらに向上させるために、電池内、特に正極または電解質に、前記ポリ硫化カーボン以外の有機イオウ化合物、−Ｓ_y −（ｙ≧３）で表される構造を有する化合物、リチウムの硫化物またはイオウのいずれかを含有させてもよい。特にリチウムの硫化物を含有させた場合には、以下のような相互作用が発揮されるため好適な特性が得られる。
【００５５】
すなわち、前記ポリ硫化カーボンとリチウムの硫化物とが電池内に共存する場合、ポリ硫化カーボンがリチウムの硫化物に対して高い触媒活性を示すため、リチウムの硫化物が可逆性に優れた活物質として作用するようになり、一方、リチウムの硫化物の存在によりポリ硫化カーボンの可逆性も高められるため、電池の高容量化と大電流での充放電におけるサイクル特性の向上を実現できる。上記リチウムの硫化物としては、一般式Ｌｉ₂ Ｓ_t （ｔ≧２）で表される化合物などを用いることができ、具体的には、Ｌｉ₂ Ｓ₄ 、Ｌｉ₂ Ｓ₈ 、Ｌｉ₂ Ｓ₁₈ などが挙げられる。
【００５６】
上記リチウムの硫化物は、電池内に存在すればよいが、正極または電解質に含有させることが好ましく、中でも電解液（液状電解質）に溶解させた状態で存在させることが最も好ましい。これは、リチウムの硫化物が電解液中の非水性溶媒への溶解性を有しており、電解液以外の構成部材に含有させても電解液に溶出し、正極においてポリ硫化カーボンと共に活物質として作用するからである。正極中に含有させた場合には、その体積分だけポリ硫化カーボンの充填量を減じる必要があるが、電解液中に含有させた場合には、正極のポリ硫化カーボンの充填量を低減する必要がないので、実質的に正極活物質の総量が増加することになり、電池の高容量化を容易に達成できる。
【００５７】
もちろん、この場合には、電解液の非水性溶媒として、リチウムの硫化物に対する溶解性の高い溶媒を用いることが好ましく、通常、その溶媒成分は、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、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、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、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。
【００５８】
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も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、リチウムの硫化物の溶解度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重量％以下が好ましい。
【００５９】
また、一般式Ｌｉ₂ Ｓ_t （ｔ≧２）で表されるリチウムの硫化物は、ｔの値が大きくなるほど電解液への溶解度が低下し、また電解液の粘度を上昇させてイオン伝導度を低下させる傾向があるため、ｔの値が５０以下の硫化物が実用的であり、さらに２０以下の硫化物がより好適である。
【００６０】
ここで、リチウムの硫化物の電解液中での濃度は、使用する溶媒の種類および硫化物の組成にもよるが、０．０１ｍｏｌ／ｌ以上が好ましく、１０ｍｏｌ／ｌ以下が好ましい。特に０．１ｍｏｌ／ｌ以上とすることにより電池の放電容量が大幅に増加し、４ｍｏｌ／ｌ以下にすることにより電解液のイオン伝導度およびポリ硫化カーボンの利用率を好適に保つことができる。
【００６１】
【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重量％を表している。
【００６２】
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。
【００６３】
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_4.9 ）_n であった。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。
【００６４】
次に、上記中間生成物１０ｇ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アルミナ加熱炉の炉心に置き、酸素濃度が１００ｐｐｍ以下になるまで純度９９．９９９％のアルゴンガスで置換した後、アルゴンガスを流しながら、以下に示す条件で温度を変化させて最終的に３８０℃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３８０℃まで２時間で昇温を行い、３８０℃で１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。
【００６５】
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３ｇ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：２６．０％、Ｓ：７３．９％であり、一般式で表すと（ＣＳ_1.06）_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_1.06）_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。
【００６６】
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）〕
【００６７】
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_1.06）_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のピークのみであった。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。
【００６８】
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_1.06）_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。
【００６９】
さらに、上記ポリ硫化カーボン（ＣＳ_1.06）_n について、リガク社製の熱分析計（ｔｈｅｒｍｏ Ｐｌｕｓ ＴＧ８１２０）を用いて熱重量−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、温度と重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_4.9 ）_n の熱重量−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_4.9 ）_n は、１００℃付近から重量減少が認められ、２００℃以上になると急激に重量が減少するのに対して、本発明のポリ硫化カーボン（ＣＳ_1.06）_n は、３００℃付近まで重量減少が少なく（３００℃までの重量減少：約０．５％）、安定な化合物であることがわかる。
【００７０】
また、（ＣＳ_1.06）_n をおおよそ７５μｍの粉末に粉砕し、直径５ｍｍのホルダーに上記粉末０．５ｇを採取して、２トンで加圧して成形した後、１００ｎＡの直流を印加して２５℃で電気伝導度を測定したところ、５×１０^-7Ｓｃｍ^-1であった。これに対して、後述する比較例１の化合物（ＣＳ_4.9 ）_n および比較例２の化合物（ＣＳ_2.6 ）_n についての同様の測定では、それらの電気伝導度が１０^-11 Ｓｃｍ^-1未満の値であったことから、本発明のポリ硫化カーボン（ＣＳ_1.06）_n は、従来の有機イオウ化合物よりも分子構造が単一化され、それによって、電気伝導度が向上したものと考えられる。
【００７１】
さらに、２５℃での真密度をガス置換法により測定したところ、１．９０３ｇ／ｃｍ³ であった。後述する比較例２の化合物（ＣＳ_2.6 ）_n の真密度２．０４７ｇ／ｃｍ³ や斜方晶のイオウの真密度２．０７ｇ／ｃｍ³ と比較して小さな値となったが、これは、式（３）
【化４】

に示されるように、分子内に炭素とイオウとで形成される環が多数存在することが影響しているものと推定される。
【００７２】
実施例２
実施例１の加熱処理において、処理温度を３７０℃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_1.1 ）_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。
【００７３】
このポリ硫化カーボン（ＣＳ_1.1 ）_n のラマン分析においては、前記（ＣＳ_1.06）_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にピークを有するだけであった。また、Ｘ線回折測定においても、前記（ＣＳ_1.06）_n の回折パターンとほぼ一致するパターンが得られた。
【００７４】
実施例３
実施例１の加熱処理において、処理温度を３９０℃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_0.9 ）_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。
【００７５】
このポリ硫化カーボン（ＣＳ_0.9 ）_n のラマン分析においては、前記（ＣＳ_1.06）_n とほぼ同様に１４４２ｃｍ^-1に主ピークを有し、また４００ｃｍ^-1〜５２５ｃｍ^-1の範囲には４９４ｃｍ^-1にピークを有するだけであった。また、Ｘ線回折測定においても、前記（ＣＳ_1.06）_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。
【００７６】
実施例４
実施例１で合成した中間生成物１０ｇを船形のアルミナ容器に入れ、その中間生成物を入れたアルミナ容器をアルミナ加熱炉の炉心に置き、酸素濃度が４００ｐｐｍ以下になるまで純度９９．９９９％のアルゴンガスで置換し、次いで２Ｐａ以下になるまで真空引きをし、真空を保ちながら実施例１と同じ条件で温度を変化させて加熱処理を行い、ポリ硫化カーボン（ＣＳ_1.02）_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。
【００７７】
このポリ硫化カーボン（ＣＳ_1.02）_n のラマン分析においては、前記（ＣＳ_1.06）_n とほぼ同様に１４４３ｃｍ^-1に主ピークを有し、また４００ｃｍ^-1〜５２５ｃｍ^-1の範囲には４９０ｃｍ^-1にピークを有するだけであった。また、Ｘ線回折測定においても、前記（ＣＳ_1.06）_n の回折パターンと同様のパターンが得られ、２５．５°にブロードなピークを有するのみであった。
【００７８】
実施例５
実施例４の加熱処理において、処理温度を３５５℃とし、処理温度での保持時間を５時間とした以外は、実施例４と同様にしてポリ硫化カーボン（ＣＳ_1.38）_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。
【００７９】
このポリ硫化カーボン（ＣＳ_1.38）_n のラマン分析においては、前記（ＣＳ_1.06）_n とほぼ同様に１４４２ｃｍ^-1に主ピークを有し、また４００ｃｍ^-1〜５２５ｃｍ^-1の範囲には４８８ｃｍ^-1にピークを有するだけであった。また、Ｘ線回折測定では、２４．７°にブロードなピークを有するのみであった。
【００８０】
実施例６
温度計、滴下漏斗、冷却管、窒素置換口および気密攪拌器を付けた５００ｍｌの四つ口フラスコに、窒素ガスを流しながら金属ナトリウムの切削片１５ｇを入れ、無水キシレン１００ｍｌを加えて１１０〜１２０℃のオイルバスにて加熱環流させた。金属ナトリウムが溶融した後、加熱を止めて強く攪拌した。次に、室温まで冷却してからキシレンを除去し、金属ナトリウムを１０ｍｌの無水エーテルで２回洗浄し、これに二硫化炭素２０４ｇを添加して５５℃のオイルバスにて加熱環流しながら、ジメチルスルホキシド１８０ｍｌを５時間かけてゆっくり滴下し、１５時間環流した。その後、室温まで冷却して２４時間放置した。
【００８１】
さらに、上記の反応液中の二硫化炭素を５５℃で蒸発させ、残った液状物をオイルバスにて１１０℃まで加熱した後、その温度で２０時間反応させた。次いで、室温まで冷却した後、反応生成物の入ったフラスコを氷冷しながら２５０ｍｌの純水を２０分間かけてゆっくり加えた。次いで、６０ｍｌの濃塩酸を１時間かけて滴下することにより、黒茶色の懸濁液を得た。上記黒茶色の懸濁液をデカンテーションして沈降した固形分を分離し、アセトンおよび水で充分に洗浄した。さらに、得られた赤茶色の固形物を真空中で１８５℃に保持しながら２時間乾燥して、中間生成物として一般式（ＣＳ_2.6 ）_n で表される黒茶色の化合物３３ｇを得た。この化合物の合成方法は、特表平１１−５１４１２８号公報の実施例に記載の方法とほぼ同一である。
【００８２】
上記化合物をボールミルで１０μｍ前後まで粉砕し、得られた粉末１０ｇ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、５０℃で１２時間真空乾燥して、黒い金属光沢を有するポリ硫化カーボン（ＣＳ_1.13）_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。ラマン分析の結果を図４に示す。
【００８３】
このポリ硫化カーボン（ＣＳ_1.13）_n のラマン分析においては、１４３８ｃｍ^-1に主ピークを有し、また４００ｃｍ^-1〜５２５ｃｍ^-1の範囲には４８９ｃｍ^-1にピークを有するだけであった。また、Ｘ線回折測定では、２５．５°にブロードなピークを有するのみであった。
【００８４】
実施例７
実施例６において、溶媒抽出により中間生成物をポリ硫化カーボンに変化させる過程で用いた二硫化炭素に代えて、ジメチルスルホキシドを用いた以外は、実施例６と同様に溶媒抽出処理を行い、ポリ硫化カーボン（ＣＳ_1.11）_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。
【００８５】
このポリ硫化カーボン（ＣＳ_1.11）_n のラマン分析においては、１４３９ｃｍ^-1に主ピークを有し、また４００ｃｍ^-1〜５２５ｃｍ^-1の範囲には４８９ｃｍ^-1にピークを有するだけであった。また、Ｘ線回折測定では、２５．５°にブロードなピークを有するのみであった。
【００８６】
実施例８
内容積２リットルの四つ口フラスコに、ドライアイスラック付きの冷却管を装着して窒素置換をした。これをメタノール−ドライアイスバスにより冷却し、バス温度−７５．５℃で５００ｍｌのアンモニアをゆっくりと仕込んで、−７０℃以下で一晩保存した。
【００８７】
その後、内温−６３℃で５５．１ｇのナトリウムを入れ、バス温度−７６℃でアセチレンガスを４７０ｍｌ／分で２．５時間吹き込んだ。３０分間攪拌後、内温−６３℃で１３５ｇのイオウを添加して、そのまま８時間反応させてから、７６ｇの塩化アンモニウムを添加し、−７０℃で一晩放置した。次に、室温まで昇温して３日間保存した。その後、塩酸で系のｐＨを２〜３に調整して生成物を沈殿させた。これを濾過後、７０℃で乾燥して黒緑色の化合物約７０ｇを得た。元素分析の結果、合成した化合物中の炭素とイオウとの比はモル比で１：５．５であった。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。
【００８８】
次に、上記の化合物１０ｇをトルエン中に入れ、室温下５時間反応させて、遠心分離して沈殿物を得た。得られた沈殿物をテトラグリム中に添加し、８０℃で８時間反応させて、ポリ硫化カーボン（ＣＳ_1.09）_n 約２．２ｇを得た。このポリ硫化カーボン（ＣＳ_1.09）_n のラマン分析では、１４３５ｃｍ^-1に主ピークを有し、また４００ｃｍ^-1〜５２５ｃｍ^-1の範囲には４９２ｃｍ^-1にピークを有するだけであった。
【００８９】
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_4.9 ）_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。
【００９０】
比較例２
実施例６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。
【００９１】
これらの化合物（ＣＳ_4.9 ）_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。化合物（ＣＳ_2.6 ）_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。化合物（ＣＳ_4.9 ）_n および化合物（ＣＳ_2.6 ）_n のいずれについても、ラマン分析において、４００ｃｍ^-1〜５２５ｃｍ^-1の間には、ポリスルフィドセグメントに基づく多数のピークが重なって現れており、ジスルフィド結合に対応するピークは認められなかった。また、１４４４ｃｍ^-1付近のピークは、本発明のポリ硫化カーボンのものよりブロードであることから、主として炭素で形成される骨格の構造があまり均一でないものと考えられる。さらに、本発明のポリ硫化カーボンでは見られなかったピーク（１０００ｃｍ^-1付近のピークなど）も認められ、本発明のポリ硫化カーボンとは分子構造がかなり異なっているものと推定された。
【００９２】
また、（ＣＳ_4.9 ）_n および（ＣＳ_2.6 ）_n のいずれについても、Ｘ線回折測定では、多数の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。
【００９３】
以下の実施例では、上記実施例１〜６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。
【００９４】
実施例９
まず、正極は以下のようにして作製した。実施例１〜６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重量部と、ロンザ社製グラファイト（ＫＳ−６）７．２重量部およびアセチレンブラック０．８重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重量部を添加して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重量部を加え、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。
【００９５】
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１２０℃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２０μｍの正極を得た。
【００９６】
負極は、アルゴンガス雰囲気中で厚さ２００μｍの金属リチウム箔をニッケル網（サイズ：２５０ｍｍ×２２０ｍｍ）上に載せ、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。
【００９７】
電解液としては、重量比１：１のプロピレンカーボネートとエチレンカーボネートとの混合溶媒に、ＬｉＰＦ₆ を１．４ｍｏｌ／ｌ溶解させた溶液を用いた。
【００９８】
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（放電の終止電圧は１．５Ｖ）、これを１０サイクル繰り返し、３サイクル目の放電容量と１０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。
【００９９】
【表１】

【０１００】
表１に示す結果から明らかなように、本発明のポリ硫化カーボン（ＣＳ_0.9 ）_n 、（ＣＳ_1.02）_n 、（ＣＳ_1.06）_n 、（ＣＳ_1.1 ）_n 、（ＣＳ_1.13）_n および（ＣＳ_1.38）_n は、従来の有機イオウ化合物（ＣＳ_2.6 ）_n および（ＣＳ_4.9 ）_n に比べて実装電池での容量が大きく、また、電解液に対する安定性が高いので、充放電サイクルでの容量低下が少なく、信頼性の高い非水電解質二次電池を構成することができた。特にポリ硫化カーボンを一般式（ＣＳ_x ）_n で表したときに、ｘが０．９〜１．３の範囲内にあるポリ硫化カーボンが優れた特性を示し、中でも、ｘが１〜１．１の範囲内にあるポリ硫化カーボンが高い安定性を有していた。
【０１０１】
実施例１０
実施例９において、正極活物質として（ＣＳ_1.06）_n を用い、正極合剤含有ペーストの調製にあたってグラファイト７．２重量部の代わりに、グラファイト５．７重量部および平均粒径が５μｍのニッケル粉末１．５重量部を用いた以外は、実施例９と同様にして非水電解質二次電池を作製した。
【０１０２】
実施例１１
実施例９において、正極活物質として（ＣＳ_1.06）_n を用い、正極の集電体としてアルミニウム箔の代わりに、厚さ１０μｍのニッケル箔を用いた以外は、実施例９と同様にして非水電解質二次電池を作製した。
【０１０３】
上記実施例１０および実施例１１の電池と、実施例９において（ＣＳ_1.06）_n を正極活物質とした電池に対し、前記と同じ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。
【０１０４】
【表２】

【０１０５】
表２に示すように、実施例１０および実施例１１の電池は、実施例９の電池に比べて、５０サイクル目の放電容量が大きく、実施例１０および実施例１１の電池では、正極にニッケルを含有させたことにより、実施例９の電池に比べて充放電サイクル特性が大幅に向上していた。
【０１０６】
実施例１２
実施例９において、（ＣＳ_1.06）_n とＮｉＳを重量比で９：１〜４：６の範囲で含有する（ただし、両者の合計は１０重量部）正極合剤含有ペーストを調製し、実施例９と同様にして非水電解質二次電池を作製した。すなわち、この実施例１２ではポリ硫化カーボン（ＣＳ_1.06）_n の一部をニッケルの硫化物で置換した電池を作製した。
【０１０７】
上記実施例１２の電池と、実施例９において（ＣＳ_1.06）_n を正極活物質とした電池に対し、ポリ硫化カーボンとＮｉＳの合計重量１ｇあたり１５０ｍＡに相当する電流値で充放電を行い（放電終止電圧：１．０Ｖ）、これを１０サイクル繰り返し、１サイクル目の放電容量と１０サイクル目の放電容量を測定した。その結果を、（ＣＳ_1.06）_n とＮｉＳの合計重量１ｇ当たりの放電容量として表３に示す。なお、（ＣＳ_1.06）_n とＮｉＳとの合計は、前記のように１０重量部であり、この両者で正極合剤中の５０重量％を占めている。
【０１０８】
【表３】

【０１０９】
表３に示す結果から明らかなように、正極中にニッケルの硫化物を含有させることにより、充放電サイクルでの電流値を大きくした場合でも、正極の良好な可逆性が維持され、充放電サイクルに伴う容量低下が抑制されていた。また、ニッケルの硫化物の添加によりポリ硫化カーボンの含有量は減少するが、ニッケルの硫化物自身も活物質として作用するため、電池の放電容量がほとんど低下しないので好適である。
【０１１０】
また、（ＣＳ_1.06）_n とＮｉＳとの重量比を８：２にした正極を作用極とし、リチウムを対極とし、さらに別のリチウムを参照電極としてモデルセルを構成し、１０ｍＶ／秒の電位掃引速度でサイクリックボルタンメトリーの試験を行った。このときに得られた上記正極のサイクリックボルタモグラムを図７に示す。この図７に示すサイクリックボルタモグラムでは、酸化ピークと還元ピークの電位が接近しており、本発明のポリ硫化カーボンの酸化および還元に対する可逆性が高いことを示していた。
【０１１１】
実施例１３
以下の方法により、リチウムの硫化物を含有する電解液を調製した。すなわち、テトラグリムと１，３−ジオキソランとの体積比１：１の混合溶媒にＬｉＣＦ₃ ＳＯ₃ を１ｍｏｌ／ｌの濃度で溶解させて電解液とし、さらに、湿気を遮断した雰囲気中で８６．５ｇの前記電解液に２．３ｇのＬｉ₂ Ｓと１１．２ｇのイオウを添加し、８０℃で５時間環流して電解液中でＬｉ₂ Ｓ₈ を合成した。この電解液中におけるＬｉ₂ Ｓ₈ の含有量は０．５ｍｏｌ／ｌであり、Ｌｉ₂ Ｓ₈ の合成に伴ってＬｉＣＦ₃ ＳＯ₃ の濃度は０．８７ｍｏｌ／ｌに減少した。
【０１１２】
次に、実施例１１において、電解液として上記Ｌｉ₂ Ｓ₈ を含有する電解液を用いた以外は、実施例１１と同様にして非水電解質二次電池を作製した。
【０１１３】
実施例１４
実施例１３において、電解液中のＬｉ₂ Ｓ₈ の含有量を１．０ｍｏｌ／ｌとした以外は、実施例１３と同様にして非水電解質二次電池を作製した。
【０１１４】
実施例１５
実施例１４において、電解液の非水性溶媒としてジメチルスルホキシドと１，３−ジオキソランとの体積比１：１の混合溶媒を用いた以外は、実施例１４と同様にして非水電解質二次電池を作製した。
【０１１５】
実施例１６
実施例１３において、正極活物質として（ＣＳ_1.38）_n を用いた以外は、実施例１３と同様にして非水電解質二次電池を作製した。
【０１１６】
比較例３
実施例１５において、正極として以下に記載するカーボン電極を用いた以外は、実施例１５と同様にして非水電解質二次電池を作製した。この比較例３の電池における正極は、グラファイト（ＫＳ−６）：８２％、アセチレンブラック：８％、ポリフッ化ビニリデン：１０％の構成比で作製されたカーボン電極である。
【０１１７】
上記実施例１３〜１６の各電池に対し、定電流−定電圧充電と定電流放電による充放電サイクルを５０サイクル繰り返し、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、ポリ硫化カーボン１ｇあたりの放電容量の変化を調べた。なお、定電流−定電圧充電における定電流充電は、ポリ硫化カーボンとＬｉ₂ Ｓ₈ との合計重量１ｇ当たり６０ｍＡに相当する電流値とし、電圧の上限値を２．５Ｖに設定して行った。放電の電流値は、定電流充電での電流値と同じ値とし、電池電圧が１．５Ｖになるまで放電させた。その結果をポリ硫化カーボン１ｇあたりの放電容量として表４に示す。
【０１１８】
また、比較例３の電池に対しても、上記と同様に充放電を行ったが、２サイクル目に正極が崩壊して充放電が不可能になった。すなわち、Ｌｉ₂ Ｓ₈ のみを活物質として用いた場合は、二次電池として機能しなかった。また、このときの１サイクル目の放電容量は、Ｌｉ₂ Ｓ₈ の１ｇあたり１６７ｍＡｈ／ｇと低い値であった。
【０１１９】
【表４】

【０１２０】
前記した表１や表２に記載のように、ポリ硫化カーボンの放電容量は約６００ｍＡｈ／ｇであるが、電解液にリチウムの硫化物を含有させることにより、ポリ硫化カーボンの見かけの放電容量が大幅に増加し、電池の高容量化を容易に達成することができた。しかも、その大きな放電容量はサイクルを繰り返しても維持された。これは、リチウムの硫化物が活物質として作用しただけでなく、ポリ硫化カーボンと共存することにより、互いに可逆性を向上させる効果が生じたことによるものと考えられる。すなわち、上記実施例１３〜１６の電池は、固体の活物質（ポリ硫化カーボン）だけでなく、電解液中に溶解された液体状活物質（リチウムの硫化物）を用いたことにより、前記の実施例１１などと同一体積の電池でありながら、放電容量を大幅に増加させることに成功したものである。もちろん、ポリマー電解質の中にリチウムの硫化物を含有させることにより、ゲル状活物質として用いてもよい。
【０１２１】
実施例１７
実施例１および実施例３〜５のポリ硫化カーボンを用い、以下のようにして非水電解質二次電池を作製した。上記実施例１および実施例３〜５のポリ硫化カーボン１０重量部と、グラファイト（ＫＳ−６）２．２重量部およびアセチレンブラック０．８重量部と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２０重量部を添加して３０分間混合した。次いで、ポリアニリンを７．４％含有するＮ−メチル−２−ピロリドン溶液２１．６重量部と、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重量部を加え、さらに１時間混合して正極合剤含有ペーストを調製し、その正極合剤含有ペーストを用いた以外は、実施例９と同様に非水電解質二次電池を作製した。
【０１２２】
実施例１８
実施例１７において、導電性ポリマーとしてポリピロールを用いた以外は、実施例１７と同様にして非水電解質二次電池を作製した。
【０１２３】
実施例１９
Ｈｕｎｔｓｍａｎ社製のアミン化合物（Ｊｅｆｆａｍｉｎｅ ＸＴＪ−５０２）１００ｇをプロピレンカーボネートとエチレンカーボネートとの重量比１：１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）をメチルエチルカーボネートとエチレンカーボネートとの重量比２：１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。
【０１２４】
次に、電解液として、メチルエチルカーボネートとエチレンカーボネートとの重量比２：１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１７において用いた（ＣＳ_1.06）_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９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。
【０１２５】
実施例２０
実施例１７において、ポリアニリンを用いず、その代わりにグラファイトとアセチレンブラックを増量した以外は、実施例１７と同様にして非水電解質二次電池を作製した。
【０１２６】
上記実施例１７〜２０の各電池に対し、正極活物質１ｇあたり６０ｍＡに相当する電流値で初期放電を行った後、同様の電流値で充放電を行い（放電終止電圧：１．５Ｖ）、低電流の負荷での正極活物質１ｇあたりの放電容量を調べた。次いで、前記と同じ充電を行った後、正極活物質１ｇあたり３００ｍＡに相当する電流値で放電を行い、負荷が大きくなったときの放電容量の変化を調べた。その結果を表５に示す。
【０１２７】
【表５】

【０１２８】
表５に示す結果から明らかなように、導電性ポリマーを正極に含有させることにより、放電時の電流値が大きくなっても放電容量の低下が少なく、大電流負荷の用途に適した電池を得ることができる。
【０１２９】
【発明の効果】
以上説明したように、本発明では、特に非水電解質電池の活物質として有用性の高いポリ硫化カーボンを提供することができた。すなわち、イオウを重量比率で６７重量％以上含有し、イオウと炭素の重量比率が９５重量％以上であって、かつ前記特定の物性を有する本発明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に伴う容量低下が少なく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。
【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_1.06）_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_1.06）_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_1.06）_n および比較例１で得られた有機イオウ化合物（ＣＳ_4.9 ）_n の熱重量−示差熱分析での重量変化を示す図である。
【図４】実施例６で得られたポリ硫化カーボン（ＣＳ_1.13）_n のラマンスペクトルを示す図である。
【図５】比較例２で得られた有機イオウ化合物（ＣＳ_2.6 ）_n のラマンスペクトルを示す図である。
【図６】比較例２で得られた有機イオウ化合物（ＣＳ_2.6 ）_n のＸ線回折パターンを示す図である。
【図７】実施例１２でポリ硫化カーボン（ＣＳ_1.06）_n とＮｉＳの重量比を８：２とした正極のサイクリックボルタモグラムを示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to carbon polysulfide that can be used as an active material of a battery, a method for producing the same, 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 power sources has become stronger, 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 sulfur can only be used at high temperatures, there is a problem that battery cases and the like are eroded by the high activity of sulfur and its derivatives, and it is said that application to small consumer batteries is difficult.
[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, as a positive electrode active material of a nonaqueous electrolyte battery, an organic sulfur compound containing carbon and sulfur as main constituent elements has been studied. In Japanese Patent Publication No. 60-502213 (WO85 / 01293), , 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 it had the following problems.
[0006]
In other words, it is impossible to completely replace halogen elements and hydrogen with sulfur in a synthesis method in which sulfur is added to a polymer such as a halogenated polyethylene such as polytetrafluoroethylene or polytrifluorochloroethylene or polyacetylene. , Organic sulfur compounds in which a lot of halogen elements and hydrogen remain in the molecule are likely to be formed. 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.
[0007]
In Example 6 of 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 obtained. Since this polysulfide compound cannot be removed by washing with water, the composition of the product described in Example 6 actually appears to 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) with the carbon skeleton 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, it is impossible to obtain a high-capacity organic sulfur compound composed of only two elements of carbon and sulfur and having a high sulfur content.
[0008]
On the other hand, as a compound different from the above, (CS _w ) _p Organic sulfur compounds represented by general formulas such as (w is about 2.5 to about 50, p is 2 or more) have attracted attention because they have a high energy density of 1000 to 1600 mAh / g. Scottheim et al. Have proposed a secondary battery that uses this compound as a positive electrode active material for a non-aqueous electrolyte battery and exhibits a high capacity even at room temperature (Japanese Patent Laid-Open No. 7-29599 (US 5441831)). Table No. 11-506799 (WO96 / 41388), JP-T 11-514128 (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”).
[0009]
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.
[0010]
In addition, the resulting compound generally contains a large amount of low molecular weight or high molecular weight polysulfide compounds, and the 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 charging and discharging, 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 has been a problem that not only the self-discharge of the battery becomes relatively large but also metal sulfides that inhibit reversibility of charge and discharge are formed, and the cycle life of the battery is shortened.
[0011]
The present invention eliminates the problems of the conventional organic sulfur compounds as described above, provides a polysulfide carbon having high reversibility, high capacity and excellent stability, and a method for producing the same, and further using this as an active material. By using it, an object is to realize a high-capacity nonaqueous electrolyte battery excellent in charge / discharge cycle characteristics and reliability.
[0012]
[Means for Solving the Problems]
As a result of intensive studies to solve the above-mentioned problems, the present inventors, based on an organic sulfur compound having carbon and sulfur as main constituent elements and having a polysulfide segment, are substantially composed of only two elements of carbon and sulfur. The present inventors have found a method for producing a novel organic sulfur compound (polysulfide carbon) having a high sulfur content and a higher molecular structure than that of conventional organic sulfur compounds. It was.
[0013]
That is, one of the present invention has carbon and sulfur as main constituent elements, the weight ratio of sulfur is 67% by weight or more, and the total weight ratio of carbon and sulfur is 95% by weight or more. In Raman shift of 1444cm ^-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 It is a polysulfide carbon characterized by having only a nearby peak.
[0014]
In another aspect of the present invention, carbon and sulfur are main constituent elements, the weight ratio of sulfur is 67% by weight or more and the total weight ratio of carbon and sulfur is 95% by weight or more. In X-ray diffraction using CuKα rays, a diffraction pattern having a diffraction angle (2θ) in the range of 20 ° to 30 ° is substantially represented only by a broad diffraction peak having a peak in the vicinity of 25 °. Polysulfide carbon.
[0015]
Still another aspect of the present invention is that carbon and sulfur are main constituent elements, the weight ratio of sulfur is 67% by weight or more, and the total weight ratio of carbon and sulfur is 95% by weight or more. The polysulfide carbon is characterized in that the weight loss by thermogravimetric analysis when heated to 300 ° C. at a rate of 10 ° C./min is 5% or less.
[0016]
Such a polysulfide having carbon and sulfur as main constituent elements, the weight ratio of sulfur being 67% by weight or more and the total weight ratio of carbon and sulfur being 95% by weight or more, and having the above specific physical properties Carbon has a high capacity when used as an active material for a non-aqueous electrolyte battery, has a high reversibility, and has a small capacity drop due to a charge / discharge cycle, thereby providing a highly reliable primary battery or secondary battery. be able to.
[0017]
The polysulfide carbon includes, for example, carbon and sulfur as main constituent elements, and —S _m It can synthesize | combine by removing a part of sulfur which comprises the polysulfide segment structure with respect to the organic sulfur compound which has a polysulfide segment represented by-(m> = 3), and making it change into a disulfide bond.
[0018]
In addition, the polysulfide carbon can be used not only for the active material of the nonaqueous electrolyte battery as illustrated, but also for other electrochemical elements such as capacitors, information storage elements, display elements, electronic materials, etc. is there.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Next, the details of the method for producing the polysulfide carbon of the present invention and the use as the active material of the nonaqueous electrolyte battery will be specifically described.
[0020]
Carbon and sulfur are the main constituent elements, the weight ratio of sulfur is 67% by weight or more, and the total weight ratio of carbon and sulfur is 95% by weight or more, and the polysulfide carbon having the above specific properties is: For example, it can be synthesized 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 and 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 number of polysulfide segments in the molecule, and corresponds to the organic sulfur compound described in the above-mentioned Japanese National Publication No. 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.
[0021]
Next, the intermediate product is put into a heat-resistant container made of alumina (aluminum oxide) or the like, and heated in a vacuum or in an inert atmosphere to remove impurities such as polysulfide compounds contained in the intermediate product. Evaporate and cleave the polysulfide segment in the organic sulfur compound molecule to evaporate and remove excess sulfur, consisting of only two elements, carbon and sulfur, with most or all carbon atoms in the molecule A carbon polysulfide having a structure in which a bond with a sulfur atom is formed and a disulfide bond in which most or all of the sulfur atom has high reversibility to oxidation and reduction is formed is obtained. The content ratio of sulfur in such polysulfurized carbon is a high value of 2/3 or more, that is, 67% by weight or more in weight ratio.
[0022]
Specifically explaining the molecular structure of this compound, a structure having a repeating unit represented by the following formula (1) is presumed, and the bond between carbon chains is, for example, a disulfide represented by the formula (2) It is presumed that it is made by combination.
[Chemical 1]

[Chemical 2]

[0023]
The presence of carbon double bonds (C═C) and sulfur disulfide bonds (C—S—S—C) in the molecule of the polysulfide carbon can be confirmed by Raman analysis, which will be described in detail later. it can.
[0024]
In the above heat treatment, in order to prevent oxidation of the compound during heating, the heating atmosphere is preferably in a low oxygen concentration state, in a vacuum or in an inert gas atmosphere with a reduced oxygen concentration (for example, 400 ppm or less). It is preferable to heat-process by.
[0025]
The heating temperature is preferably about 300 ° C. to 430 ° C. and more preferably 320 ° C. to 410 ° C. However, when heating is performed in a vacuum or a reduced pressure atmosphere, it can be performed at a lower temperature. The heating time may be adjusted depending on the temperature and atmosphere of the heat treatment, but approximately 10 minutes to 5 hours is appropriate. The composition of the polysulfide carbon obtained varies slightly 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 sulfur in a weight ratio of 67% by weight or more. From the viewpoint of stability, the content of elements other than carbon and sulfur is preferably small, that is, the weight ratio of sulfur to carbon is preferably 95% by weight or more.
[0026]
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 0.9 to 1.5 has high molecular structure unity, It is preferable because it is excellent in reversibility and becomes a high-capacity active material, and x is more preferably 1.3 or less. In particular, when x is 1.1 or less, since the abundance ratio of the disulfide bond that enables reversible charge / discharge can be maximized, the compound has the highest capacity and the highest stability. From the viewpoint of capacity, x is preferably 0.95 or more, and more preferably 1 or more to provide the most preferable compound. This is because when the value of x decreases, C—S—C bonds that do not participate in charge / discharge are introduced into the molecule in addition to disulfide bonds that participate in charge / discharge. This is because a large compound introduces many polysulfide segments in the molecule.
[0027]
In addition, 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 having 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 0.9 to 1.5, and n is preferably 4 or more. Synthesis of polysulfide carbon having n of 3 and having a disulfide bond is difficult, and even if it can be synthesized, it is considered to be inferior in stability and low in usefulness. The polysulfide carbon of the present invention has excellent resistance to organic solvents and the like, and it is difficult to measure its molecular weight. Therefore, it is difficult to accurately determine the value of n in the above general formula, but this n is 4 Preferably, n is 100 or more in view of workability. In addition, no matter how large n is, no problem is considered to occur. However, it is generally 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.
[0028]
In addition to the above-mentioned method, the polysulfide carbon is linked to the carbon skeleton by bringing an organic sulfur compound having a polysulfide segment into contact with a non-aqueous solvent in a container or with the vapor of the non-aqueous solvent. It can also be obtained by eluting the non-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.
[0029]
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 include, for example, aromatic solvents such as toluene and benzene, tetrahydrofuran, dimethylformamide, tetramethylethylenediamine, dioxolane, tetraglyme and the like aliphatic or alicyclic molecules containing oxygen or nitrogen in the molecule. And low molecular weight solvents of the family and solvents containing sulfur such as carbon disulfide, dimethyl sulfoxide and sulfolane. Moreover, the mixed solvent which consists of these 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.
[0030]
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.
[0031]
The Raman analysis of the polysulfide carbon is performed using an argon laser as a light source. The polysulfide carbon of the present invention has a Raman shift of 1444 cm in the Raman spectrum obtained by 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 It is characterized by only nearby peaks. 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. 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, the 400 cm ^-1 ~ 525cm ^-1 Within the range of 490cm ^-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 ± 20cm ^-1 Corresponds to the range of 490cm ^-1 The neighborhood is about 490cm ^-1 ± 20cm ^-1 It corresponds to the range.
[0032]
In contrast, the Raman spectrum of the conventional organic sulfur compound is 400 cm. ^-1 ~ 525cm ^-1 It can be seen that many peaks overlap in the range of. 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. On the other hand, 490cm ^-1 The nearby peak is not clear, and it is considered that there are almost no disulfide bonds in the molecule. In the conventional organic sulfur compound, 1444 cm. ^-1 Although the peak in the vicinity is broad, the polysulfide carbon of the present invention is sharper than that and has a composition and structure closer to a single unit.
[0033]
When the polysulfide carbon is subjected to X-ray diffraction using CuKα rays, the diffraction pattern of 20 ° to 30 ° at the diffraction angle (2θ) is substantially a half width having a peak position in the vicinity of 25 °. It can be represented by only one broad diffraction peak of about 1.5 ° to 5 °. That is, there is substantially only one diffraction peak in the diffraction angle range. The term “substantially” does not have to be exactly one, and it is preferable that a peak derived from a polysulfide segment, that is, a peak identified with sulfur is not observed. A thing whose intensity is approximately 1/10 or less of the peak) means that it is allowed in the present invention. Here, the vicinity of 25 ° corresponds to a range of approximately 25 ° ± 3.5 °.
[0034]
In addition, when carbon sulfide is synthesized using the above-described method, an alkali metal halide is also generated as a by-product in the process of producing an organic sulfur compound, which is an intermediate product. Even when the polysulfide carbon 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.
[0035]
In the X-ray diffraction pattern, the peak near 25 ° is expressed by the following formula (3):
[Chemical 3]

It is presumed that the plane formed by the disulfide bond represented by the formula 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 to 0.44 nm, which is close to the interlayer distance (0.335 nm) of graphite. Can be considered.
[0036]
On the other hand, in the conventional organic sulfur compounds including the intermediate product in the present invention, there are many peaks in the X-ray diffraction pattern, but almost all of the free sulfur or polysulfide segment is present. It is a diffraction peak due to sulfur. Diffraction peaks other than those based on sulfur are difficult to distinguish because of their low intensity, and the conventional organic sulfur compound having a polysulfide segment is considered to have lower crystallinity than the polysulfide carbon of the present invention.
[0037]
Furthermore, in the conventional organic sulfur compound, when thermogravimetric-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, Although the weight decreases from about 200 ° C. as the temperature rises, the 122.7 ° and 314 ° peaks disappear in the polysulfide carbon of the present invention, and the weight does not decrease to a higher temperature. For example, the polysulfide carbon of the present invention exhibits excellent thermal stability with a weight loss of 5% 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 having good crystallinity and excellent chemical stability is used as a positive electrode active material of a non-aqueous electrolyte battery, decomposition of the active material during charging or discharging and the accompanying electrolyte solution Since the elution of sulfur and the formation of sulfides are suppressed, good reversibility can be maintained over a long period of time.
[0038]
When the polysulfide carbon of the present invention is used as a positive electrode active material for a nonaqueous electrolyte battery, its theoretical capacity is approximately 550 to 890 mAh / g, and LiCoO that is most widely used as a positive electrode active material for a nonaqueous electrolyte battery. 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.
[0039]
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.
[0040]
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. In particular, when a conductive polymer is contained, an improvement in characteristics under a large current load can be expected. As the conductive polymer, for example, polymers having a conjugated structure such as polyacene, polyacetylene, polyaniline, polypyrrole and the like, derivatives thereof having a side chain such as methyl, butyl, and benzyl are preferably used.
[0041]
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, or a polymer composition thereof. Examples thereof include a copolymer formed between a monomer or a copolymer with other monomers, or a cross-linking compound. These are preferably polymer compounds that are chemically stable and have a strong adhesive force to the positive electrode active material.
[0042]
Moreover, when any of nickel, a nickel alloy, a nickel composite, or a nickel compound is included as a component of the positive electrode, the charge / discharge reversibility of the positive electrode is improved by the interaction with the polysulfide carbon. As such a nickel alloy, for example, LaNi _Five , LaNi _4.6 Al _0.4 V-Ti-Ni alloy, etc., and examples of nickel composites include nickel deposited on the surface of aluminum foil, stainless steel foil, nickel, polypropylene sheet, polyethylene terephthalate sheet, polybutylene terephthalate sheet, etc. Examples of the nickel compound include NiS, Ni, and the like. ₂ S ₂ , NiS ₂ And nickel sulfides. Among them, the general formula NiS _z A compound represented by (z is 1 to 5) is preferably used. This is because the above compound is considered to act as a positive electrode active material.
[0043]
The nickel, nickel alloy, nickel composite or nickel compound may be contained in the positive electrode mixture as an additive, and the content in the positive electrode mixture is preferably 0.5 to 40% by weight. More preferably, it is made into 25 weight%. In this case, it is preferable to use a particle having a particle size of 0.1 to 10 μm. In addition, since nickel also functions as an electron conductor, for example, nickel in the form of foam or sheet is used as the positive electrode current collector in combination with the nickel-based additive or in place of the nickel-based additive. Alternatively, a nickel ribbon can be used as the lead body. When nickel is used as the positive electrode current collector, the charge / discharge cycle characteristics can be improved as compared with the case of aluminum that is normally used as the positive electrode current collector of the nonaqueous electrolyte battery. When the battery outer can is used as the positive electrode output terminal, the outer can may be a nickel can, a nickel alloy can, or a metal can having a nickel plating layer.
[0044]
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.
[0045]
Examples of the active material for the negative electrode include alkali metals such as lithium and sodium, alkaline earth metals such as calcium and magnesium, alloys thereof with aluminum, carbonaceous materials such as graphite, tin (tin) or silicon (silicon). ) Elements that can be alloyed with lithium or oxides containing them, lithium-containing nitrogen compounds, polymers having a conjugated structure such as polyacene, polyacetylene, polyaniline, polythiophine, polypyrrole, and the like, methyl, butyl, benzyl, etc. For example, a conductive polymer composed of a derivative having a side chain of, for example, can be used.
[0046]
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.
[0047]
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.
[0048]
First, the electrolyte will be described as the electrolyte. The electrolyte is constituted by dissolving an electrolyte salt in a non-aqueous solvent component.
[0049]
As the solvent component, ethers, esters, carbonates and the like are preferably used. It is particularly preferable to use a mixture of esters having a high dielectric constant (dielectric constant of 30 or more). Examples of the ester having a high dielectric constant include sulfur-based esters such as ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, and ethylene glycol sulfite. Cyclic esters are particularly preferable, especially ethylene carbonate. Cyclic carbonates such as are preferred.
[0050]
In addition to the above solvents, for example, chain alkyl esters such as dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, vinylene carbonate, methyl propionate and chain phosphate triesters such as trimethyl phosphate are used. In addition, 1,2-dimethoxyethane, 1,3-dioxolane, tetrahydrofuran, 2-methyl-tetrahydrofuran, diethyl ether, tetraglyme and the like can also be used. Furthermore, amine-based or imide-based organic solvents, sulfur-containing organic solvents such as sulfolane and dimethyl sulfoxide, and the like can also be used.
[0051]
Moreover, when the compound which has a C = C unsaturated bond as an additive to electrolyte solution is added in electrolyte solution, the fall of cycling characteristics may be suppressed. As a compound having such an unsaturated bond, for example, C ₆ H _Five C ₆ H ₁₁ Aromatic compounds such as (cyclohexylbenzene) and H (CF ₂ ) _Four CH ₂ OOCCH = CH ₂ , F (CF ₂ ) ₈ CH ₂ CH ₂ OOCCH = CH ₂ Fluorinated compounds such as
[0052]
Examples of the electrolyte salt dissolved in the solvent component include, for example, alkali metals such as lithium and sodium, and alkaline earth metal halogen salts or perchlorates such as magnesium, lithium organic boron, and trifluoromethanesulfonate. Fluorine-containing compounds such as salts and imide salts are preferably used. Specific examples of such an electrolyte salt include, for example, LiF and LiClO. _Four Mg (ClO _Four ) ₂ , 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 solvent component, 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 above electrolytic solution. In the gelation, for example, a linear polymer such as tetrafluoroethylene-hexafluoropropylene copolymer, polyethylene oxide, polyacrylonitrile, a copolymer between those constituent monomers or with other monomers, a polyfunctional monomer (for example, In addition, a polymer compound obtained from a reaction of a tetrafunctional or higher functional acrylate such as dipentaerythritol hexaacrylate) or an amine compound with 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]
In the present invention, in order to further improve the reversibility of the polysulfide carbon and the utilization rate in charge and discharge, an organic sulfur compound other than the polysulfide carbon, -S, is used in the battery, particularly in the positive electrode or electrolyte. _y A compound having a structure represented by — (y ≧ 3), lithium sulfide, or sulfur may be contained. In particular, when lithium sulfide is contained, the following interaction is exhibited, so that preferable characteristics can be obtained.
[0055]
That is, when the polysulfide carbon and lithium sulfide coexist in the battery, the polysulfide carbon exhibits high catalytic activity for lithium sulfide, so that the lithium sulfide is an active material having excellent reversibility. On the other hand, since the reversibility of the polysulfide carbon is enhanced by the presence of lithium sulfide, it is possible to increase the capacity of the battery and to improve the cycle characteristics in charge / discharge with a large current. As the lithium sulfide, the general formula Li ₂ S _t A compound represented by (t ≧ 2) can be used. Specifically, Li ₂ S _Four , Li ₂ S ₈ , Li ₂ S ₁₈ Etc.
[0056]
The lithium sulfide may be present in the battery, but is preferably contained in the positive electrode or the electrolyte, and most preferably present in a state of being dissolved in an electrolytic solution (liquid electrolyte). This is because lithium sulfide has solubility in a non-aqueous solvent in the electrolytic solution, and even if it is contained in a component other than the electrolytic solution, it elutes into the electrolytic solution. Because it acts as. When it is contained in the positive electrode, it is necessary to reduce the filling amount of the polysulfide carbon by the volume, but when it is contained in the electrolyte, it is necessary to reduce the filling amount of the polysulfide carbon of the positive electrode. Therefore, the total amount of the positive electrode active material is substantially increased, and the battery can be easily increased in capacity.
[0057]
Of course, in this case, it is preferable to use a solvent having high solubility in lithium sulfide as the non-aqueous solvent of the electrolytic solution. Usually, the solvent component mainly has good solubility in lithium sulfide. It is comprised with the solvent and the subsolvent used as needed. Specific examples of the main solvent include, for example, aromatic solvents such as toluene and benzene, molecules such as 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, and solvents containing sulfur such as dimethyl sulfoxide, sulfolane, etc., and these solvents may be used alone or in combination of two or more. It can be used as a solvent. Among these solvents, solvents having strong donor properties (electron donating properties) such as dimethyl sulfoxide, sulfolane, tetrahydrofuran, and tetraglyme are particularly preferable. It is preferably used in combination with a viscosity ether. Of course, a non-aqueous solvent can also be comprised only with this main solvent.
[0058]
Examples of the cosolvent include esters such as ethylene carbonate, propylene carbonate, butylene carbonate, and γ-butyrolactone, and sulfur-based esters such as ethylene glycol 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 also be used. The addition of these cosolvents increases the ionic conductivity of the electrolyte, but it tends to reduce the solubility of lithium sulfide, so the amount of secondary solvent added depends on the nature of the main solvent, The content is preferably 20% by weight or less.
[0059]
In addition, the general formula Li ₂ S _t The lithium sulfide represented by (t ≧ 2) has a tendency that the solubility in the electrolytic solution decreases as the value of t increases, and the viscosity of the electrolytic solution increases to decrease the ionic conductivity. A sulfide having a value of t of 50 or less is practical, and a sulfide of 20 or less is more preferable.
[0060]
Here, the concentration of lithium sulfide in the electrolytic solution is preferably 0.01 mol / l or more, and preferably 10 mol / l or less, depending on the type of solvent used and the composition of the sulfide. In particular, by setting it to 0.1 mol / l or more, the discharge capacity of the battery is significantly increased, and by setting it to 4 mol / l or less, the ionic conductivity of the electrolyte and the utilization rate of carbon polysulfide can be suitably maintained.
[0061]
【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 composition, yield, etc., represent “% by weight” unless otherwise indicated.
[0062]
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 maintaining 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.
[0063]
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 _4.9 ) _n Met. 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 : 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.
[0064]
Next, 10 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 the core of an alumina heating furnace, and a purity of 99.999 is obtained until the oxygen concentration becomes 100 ppm or less. After substituting with% argon gas, the temperature was changed under the following conditions while flowing argon gas, and finally heat treatment was performed at 380 ° C. 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 up to 380 ° C. in 2 hours, and kept at 380 ° C. for 1 hour to perform heat treatment. The intermediate product was converted to carbon polysulfide by removing a portion of the sulfur in the intermediate product.
[0065]
After the treatment, the reaction product was taken out from the alumina container after cooling to room temperature, and about 3 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: 26.0% and S: 73.9%. _1.06 ) _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 _1.06 ) _n N value is 4 or more, and it is presumed that the compound is a compound which is mainly a multiple of 4.
[0066]
Next, this polysulfide carbon was subjected to Raman analysis using the following apparatus and conditions. The result is shown in FIG.
Apparatus: Ramaonor T-6400 (Jobin Yvon / Ehime Bussan) Light source: Ar laser [GLG3460 (514.5 nm, output: 1 mW (NEC)]
[0067]
In FIG. 1, the horizontal axis represents the Raman shift (cm ^-1 ) And the vertical axis is relative strength, but this polysulfide carbon (CS _1.06 ) _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 It was only the peak. 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.
[0068]
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) _1.06 ) _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.
[0069]
Furthermore, the above polysulfide carbon (CS _1.06 ) _n Was subjected to thermogravimetric-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 weight change was measured. The result is shown in FIG. FIG. 3 shows a compound (CS) of Comparative Example 1 described later. _4.9 ) _n The results of thermogravimetric-differential thermal analysis are also shown. As is apparent from the results shown in FIG. 3, conventionally known organic sulfur compounds (CS _4.9 ) _n Is observed to decrease in weight from around 100 ° C., while the weight decreases rapidly at 200 ° C. or higher, whereas the polysulfide carbon (CS _1.06 ) _n Is a stable compound with little weight loss up to around 300 ° C. (weight reduction up to 300 ° C .: about 0.5%).
[0070]
Also, (CS _1.06 ) _n Was pulverized into a powder of approximately 75 μm, 0.5 g of the above powder was collected in a holder having a diameter of 5 mm, molded by pressurizing with 2 tons, and then the electric conductivity was measured at 25 ° C. by applying a direct current of 100 nA. However, 5 × 10 ^-7 Scm ^-1 Met. In contrast, the compound of Comparative Example 1 (CS described later) _4.9 ) _n And the compound of Comparative Example 2 (CS _2.6 ) _n In a similar measurement for, their electrical conductivity is 10 ^-11 Scm ^-1 Since the value of the polysulfide carbon of the present invention (CS _1.06 ) _n It is considered that the molecular structure is unified as compared with the conventional organic sulfur compound, thereby improving the electric conductivity.
[0071]
Furthermore, when the true density at 25 ° C. was measured by a gas substitution method, 1.903 g / cm. ^Three Met. Compound (CS) of Comparative Example 2 described later _2.6 ) _n True density of 2.047 g / cm ^Three True density of orthorhombic sulfur 2.07g / cm ^Three Although it was a small value compared with, this is the formula (3)
[Formula 4]

As shown in Fig. 2, it is presumed that there are many rings formed by carbon and sulfur in the molecule.
[0072]
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 370 ° C. _1.1 ) _n Got. The polysulfide carbon was subjected to Raman analysis and X-ray diffraction measurement in the same manner as in Example 1.
[0073]
This polysulfide carbon (CS _1.1 ) _n In the Raman analysis of _1.06 ) _n Same as 1444cm ^-1 Has a main peak at 400 cm ^-1 ~ 525cm ^-1 In the range of 490cm ^-1 Only had a peak. In the X-ray diffraction measurement, the above (CS _1.06 ) _n A pattern almost identical to the diffraction pattern was obtained.
[0074]
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 390 ° C. _0.9 ) _n Got. The polysulfide carbon was subjected to Raman analysis and X-ray diffraction measurement in the same manner as in Example 1.
[0075]
This polysulfide carbon (CS _0.9 ) _n In the Raman analysis of _1.06 ) _n Almost the same as 1442cm ^-1 Has a main peak at 400 cm ^-1 ~ 525cm ^-1 In the range of 494cm ^-1 Only had a peak. In the X-ray diffraction measurement, the above (CS _1.06 ) _n A pattern similar to the diffraction pattern was obtained, and only had a broad peak at 24.4 °.
[0076]
Example 4
10 g of the intermediate product synthesized in Example 1 was put in a ship-shaped alumina container, and the alumina container containing the intermediate product was placed in the core of an alumina heating furnace, and the purity was 99.999% until the oxygen concentration was 400 ppm or less. Substituting with argon gas, and then evacuating to 2 Pa or less, heat-treating by changing the temperature under the same conditions as in Example 1 while maintaining the vacuum, to obtain polysulfide carbon (CS _1.02 ) _n Got. The polysulfide carbon was subjected to Raman analysis and X-ray diffraction measurement in the same manner as in Example 1.
[0077]
This polysulfide carbon (CS _1.02 ) _n In the Raman analysis of _1.06 ) _n Almost the same as 1443cm ^-1 Has a main peak at 400 cm ^-1 ~ 525cm ^-1 In the range of 490cm ^-1 Only had a peak. In the X-ray diffraction measurement, the above (CS _1.06 ) _n A pattern similar to the diffraction pattern was obtained, and only had a broad peak at 25.5 °.
[0078]
Example 5
In the heat treatment of Example 4, carbon sulfide (CS) was obtained in the same manner as in Example 4 except that the treatment temperature was 355 ° C. and the holding time at the treatment temperature was 5 hours. _1.38 ) _n Got. The polysulfide carbon was subjected to Raman analysis and X-ray diffraction measurement in the same manner as in Example 1.
[0079]
This polysulfide carbon (CS _1.38 ) _n In the Raman analysis of _1.06 ) _n Almost the same as 1442cm ^-1 Has a main peak at 400 cm ^-1 ~ 525cm ^-1 In the range of 488cm ^-1 Only had a peak. Further, in the X-ray diffraction measurement, it had only a broad peak at 24.7 °.
[0080]
Example 6
A 500 ml four-necked flask equipped with a thermometer, a dropping funnel, a condenser, a nitrogen replacement port and an airtight stirrer was charged with 15 g of metal sodium cutting pieces while flowing nitrogen gas, and 100 ml of anhydrous xylene was added to add 110 to 120. The mixture was heated and refluxed in an oil bath at ° C. After the metallic sodium melted, the heating was stopped and the mixture was stirred vigorously. Next, after cooling to room temperature, xylene was removed, and sodium metal was washed twice with 10 ml of anhydrous ether, and then 204 g of carbon disulfide was added thereto, and dimethyl was added while heating and refluxing in an oil bath at 55 ° C. 180 ml of sulfoxide was slowly added dropwise over 5 hours and refluxed for 15 hours. Then, it cooled to room temperature and left to stand for 24 hours.
[0081]
Further, carbon disulfide in the reaction solution was evaporated at 55 ° C., and the remaining liquid was heated to 110 ° C. in an oil bath, and reacted at that temperature for 20 hours. Then, after cooling to room temperature, 250 ml of pure water was slowly added over 20 minutes while cooling the flask containing the reaction product with ice. Next, 60 ml of concentrated hydrochloric acid was added dropwise over 1 hour to obtain a black brown suspension. The black-brown suspension was decanted and the precipitated solid was separated and washed thoroughly with acetone and water. Further, the obtained reddish-brown solid was dried for 2 hours while maintaining at 185 ° C. in a vacuum to obtain a general formula (CS _2.6 ) _n As a result, 33 g of a black-brown compound represented by the formula: The method for synthesizing this compound is almost the same as the method described in the examples of JP-T-11-514128.
[0082]
The above compound was pulverized to about 10 μm with a ball mill, and 10 g of the obtained powder was put into a three-necked flask having an internal volume of 300 ml equipped with a condenser and a nitrogen substitution port, and 100 ml of carbon disulfide was added thereto, By refluxing in an argon atmosphere for 5 hours, a part of the sulfur constituting the compound was removed and changed to a disulfide bond. Thereafter, the mixture is cooled to room temperature, and the precipitate is collected by centrifugal separation. The precipitate is vacuum-dried at 50 ° C. for 12 hours to obtain a carbon sulfide (CS) having a black metallic luster. _1.13 ) _n Got. The polysulfide carbon was subjected to Raman analysis and X-ray diffraction measurement in the same manner as in Example 1. The result of Raman analysis is shown in FIG.
[0083]
This polysulfide carbon (CS _1.13 ) _n 1438cm for Raman analysis of ^-1 Has a main peak at 400 cm ^-1 ~ 525cm ^-1 In the range of 489cm ^-1 Only had a peak. Further, the X-ray diffraction measurement only had a broad peak at 25.5 °.
[0084]
Example 7
In Example 6, a solvent extraction treatment was performed in the same manner as in Example 6 except that dimethyl sulfoxide was used instead of carbon disulfide used in the process of changing the intermediate product to polysulfide carbon by solvent extraction. Carbon sulfide (CS _1.11 ) _n Got. The polysulfide carbon was subjected to Raman analysis and X-ray diffraction measurement in the same manner as in Example 1.
[0085]
This polysulfide carbon (CS _1.11 ) _n In the Raman analysis of ^-1 Has a main peak at 400 cm ^-1 ~ 525cm ^-1 In the range of 489cm ^-1 Only had a peak. Further, the X-ray diffraction measurement only had a broad peak at 25.5 °.
[0086]
Example 8
A four-necked flask with an internal volume of 2 liters was equipped with a cooling tube with a dry ice rack and was purged with nitrogen. This was cooled with a methanol-dry ice bath, slowly charged with 500 ml of ammonia at a bath temperature of −75.5 ° C., and stored overnight at −70 ° C. or lower.
[0087]
Thereafter, 55.1 g of sodium was added at an internal temperature of −63 ° C., and acetylene gas was blown in at 470 ml / min for 2.5 hours at a bath temperature of −76 ° C. After stirring for 30 minutes, 135 g of sulfur was added at an internal temperature of −63 ° C., and the reaction was allowed to proceed for 8 hours. Then, 76 g of ammonium chloride was added and left at −70 ° C. overnight. Next, the temperature was raised to room temperature and stored for 3 days. Thereafter, the pH of the system was adjusted to 2 to 3 with hydrochloric acid to precipitate the product. This was filtered and dried at 70 ° C. to obtain about 70 g of a blackish green compound. As a result of elemental analysis, the ratio of carbon to sulfur in the synthesized compound was 1: 5.5 in molar ratio. The method for synthesizing this compound is almost the same as the method described in the examples of JP-T-11-506799.
[0088]
Next, 10 g of the above compound was placed in toluene, reacted at room temperature for 5 hours, and centrifuged to obtain a precipitate. The obtained precipitate was added to tetraglyme and reacted at 80 ° C. for 8 hours to obtain polysulfide carbon (CS _1.09 ) _n About 2.2 g was obtained. This polysulfide carbon (CS _1.09 ) _n 1435cm for Raman analysis ^-1 Has a main peak at 400 cm ^-1 ~ 525cm ^-1 In the range of 492cm ^-1 Only had a peak.
[0089]
Comparative Example 1
In the same manner as in Example 1, the intermediate product is represented by the general formula (CS _4.9 ) _n The organic sulfur compound represented by the formula (1) was obtained and used as the organic sulfur compound of Comparative Example 1.
[0090]
Comparative Example 2
In the same manner as in Example 6, 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.
[0091]
These compounds (CS _4.9 ) _n And (CS _2.6 ) _n As in Example 1, Raman analysis and X-ray diffraction measurement were performed. Compound (CS _2.6 ) _n The results of Raman analysis are shown in FIG. 5, and the results of X-ray diffraction are shown in FIG. Compound (CS _4.9 ) _n And compounds (CS _2.6 ) _n For all of these, 400 cm ^-1 ~ 525cm ^-1 In between, a number of peaks based on the polysulfide segment appeared overlapping, and no peak corresponding to a disulfide bond was observed. 1444cm ^-1 Since the nearby peak is broader than that of the polysulfide carbon of the present invention, it is considered that the structure of the skeleton formed mainly of carbon is not so uniform. Furthermore, the peak (1000 cm) not seen in the polysulfide carbon of the present invention. ^-1 Nearby peaks were also observed, and it was estimated that the molecular structure was considerably different from that of the polysulfide carbon of the present invention.
[0092]
Also, (CS _4.9 ) _n And (CS _2.6 ) _n In any of these cases, many diffraction peaks were observed in the X-ray diffraction measurement, but most of the diffraction peaks were identified by sulfur diffraction peaks, and the crystal structure as seen in the polysulfide carbon of the present invention was observed. There was no clear peak considered to be based.
[0093]
In the following examples, non-aqueous electrolyte secondary batteries using the polysulfide carbons of Examples 1 to 6 and the organic sulfur compounds of Comparative Examples 1 and 2 as positive electrode active materials were produced and their characteristics were evaluated.
[0094]
Example 9
First, the positive electrode was produced as follows. About 10 parts by weight of the polysulfide carbon of Examples 1 to 6 or the organic sulfur compounds of Comparative Examples 1 to 2, 7.2 parts by weight of Lonza graphite (KS-6) and 0.8 parts by weight of acetylene black After putting into a mixing container and mixing for 10 minutes in a dry process, 50 parts by weight of N-methyl-2-pyrrolidone was added and mixed for 30 minutes. Next, 16.7 parts by weight 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.
[0095]
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 in vacuum at 120 ° C. 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 mixture layer with a thickness of 20 μm.
[0096]
The negative electrode was produced by placing a metal lithium foil having a thickness of 200 μm on a nickel mesh (size: 250 mm × 220 mm) in an argon gas atmosphere, pressurizing with a roller, and pressing the metal lithium foil onto the nickel mesh.
[0097]
As an electrolytic solution, a mixed solvent of propylene carbonate and ethylene carbonate having a weight ratio of 1: 1 is mixed with LiPF. ₆ A solution in which 1.4 mol / l was dissolved was used.
[0098]
And the said positive electrode and negative electrode are laminated | stacked in argon gas atmosphere through the separator which consists of a 80-micrometer-thick polypropylene nonwoven fabric, and the laminated electrode body consists of a three-layer laminate film of nylon film-aluminum foil-modified polyolefin resin film After putting in a package and injecting an electrolytic solution, it was sealed and a nonaqueous electrolyte secondary battery was produced. This battery is charged and discharged at a current value corresponding to 60 mA per 1 g of the positive electrode active material (the discharge end voltage is 1.5 V), and this is repeated for 10 cycles, and the discharge capacity at the third cycle and the discharge capacity at the 10th cycle. And the change in discharge capacity per gram of the positive electrode active material was examined. The results are shown in Table 1.
[0099]
[Table 1]

[0100]
As is clear from the results shown in Table 1, the polysulfide carbon (CS) of the present invention _0.9 ) _n , (CS _1.02 ) _n , (CS _1.06 ) _n , (CS _1.1 ) _n , (CS _1.13 ) _n And (CS _1.38 ) _n The conventional organic sulfur compound (CS _2.6 ) _n And (CS _4.9 ) _n As compared with the battery, the capacity of the mounted battery is large and the stability to the electrolytic solution is high. Therefore, the capacity decrease in the charge / discharge cycle is small, and a highly reliable nonaqueous electrolyte secondary battery can be constructed. In particular, polysulfide carbon is represented by _x ) _n The polysulfide carbon having x in the range of 0.9 to 1.3 exhibits excellent characteristics, and among them, the polysulfide carbon in which x is in the range of 1 to 1.1 is highly stable. Had sex.
[0101]
Example 10
In Example 9, as the positive electrode active material (CS _1.06 ) _n In the preparation of the positive electrode mixture-containing paste, Example 9 was used except that instead of 7.2 parts by weight of graphite, 5.7 parts by weight of graphite and 1.5 parts by weight of nickel powder having an average particle size of 5 μm were used. A nonaqueous electrolyte secondary battery was produced in the same manner as described above.
[0102]
Example 11
In Example 9, as the positive electrode active material (CS _1.06 ) _n A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 9, except that a nickel foil having a thickness of 10 μm was used as the positive electrode current collector instead of the aluminum foil.
[0103]
In the batteries of Examples 10 and 11 above and Example 9 (CS _1.06 ) _n For the battery using the positive electrode active material, charge and discharge were repeated 50 cycles under the same charge and discharge conditions as above, and the discharge capacity at the 50th cycle was measured. The results are shown in Table 2 as the discharge capacity per gram of the positive electrode active material.
[0104]
[Table 2]

[0105]
As shown in Table 2, the batteries of Example 10 and Example 11 had a larger discharge capacity at the 50th cycle than the battery of Example 9, and the batteries of Examples 10 and 11 had nickel as the positive electrode. As a result, the charge / discharge cycle characteristics were greatly improved as compared with the battery of Example 9.
[0106]
Example 12
In Example 9, (CS _1.06 ) _n And NiS in a weight ratio of 9: 1 to 4: 6 (however, the total of both is 10 parts by weight) to prepare a positive electrode mixture-containing paste, and in the same manner as in Example 9, a non-aqueous electrolyte secondary A battery was produced. That is, in Example 12, polysulfide carbon (CS _1.06 ) _n A battery in which a part of the battery was replaced with nickel sulfide was produced.
[0107]
The battery of Example 12 above and in Example 9 (CS _1.06 ) _n Is charged and discharged at a current value corresponding to 150 mA per 1 g total weight of polysulfide carbon and NiS (discharge end voltage: 1.0 V), and this is repeated 10 cycles. And the discharge capacity at the 10th cycle were measured. The result is (CS _1.06 ) _n Table 3 shows the discharge capacity per gram of NiS and NiS. (CS _1.06 ) _n The total amount of NiS and NiS is 10 parts by weight as described above, and both account for 50% by weight in the positive electrode mixture.
[0108]
[Table 3]

[0109]
As is apparent from the results shown in Table 3, by including nickel sulfide in the positive electrode, even when the current value in the charge / discharge cycle is increased, good reversibility of the positive electrode is maintained, and the charge / discharge cycle is maintained. The decrease in capacity accompanying this was suppressed. Although the content of polysulfide carbon is reduced by the addition of nickel sulfide, the nickel sulfide itself acts as an active material, so that the discharge capacity of the battery is hardly lowered, which is preferable.
[0110]
Also, (CS _1.06 ) _n A cyclic voltammetry test at a potential sweep rate of 10 mV / sec with a positive electrode with a weight ratio of NiS and NiS of 8: 2 as the working electrode, lithium as the counter electrode, and another lithium as the reference electrode. Went. A cyclic voltammogram of the positive electrode obtained at this time is shown in FIG. In the cyclic voltammogram shown in FIG. 7, the potentials of the oxidation peak and the reduction peak are close to each other, indicating that the polysulfide carbon of the present invention is highly reversible with respect to oxidation and reduction.
[0111]
Example 13
An electrolytic solution containing lithium sulfide was prepared by the following method. That is, LiCF was added to a mixed solvent of tetraglyme and 1,3-dioxolane in a volume ratio of 1: 1. _Three SO _Three Is dissolved at a concentration of 1 mol / l to form an electrolyte, and 2.3 g of Li is added to 86.5 g of the electrolyte in an atmosphere where moisture is blocked. ₂ S and 11.2 g of sulfur were added and refluxed at 80 ° C. for 5 hours in the electrolyte. ₂ S ₈ Was synthesized. Li in this electrolyte ₂ S ₈ The content of is 0.5 mol / l and Li ₂ S ₈ LiCF with the synthesis of _Three SO _Three The concentration of was reduced to 0.87 mol / l.
[0112]
Next, in Example 11, the above Li as the electrolyte ₂ S ₈ A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 11 except that the electrolyte solution containing was used.
[0113]
Example 14
In Example 13, Li in the electrolyte solution ₂ S ₈ A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 13 except that the content of was changed to 1.0 mol / l.
[0114]
Example 15
In Example 14, a nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 14 except that a mixed solvent having a volume ratio of 1: 1 of dimethyl sulfoxide and 1,3-dioxolane was used as the nonaqueous solvent for the electrolytic solution. Produced.
[0115]
Example 16
In Example 13, (CS _1.38 ) _n A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 13 except that was used.
[0116]
Comparative Example 3
In Example 15, a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 15 except that the carbon electrode described below was used as the positive electrode. The positive electrode in the battery of Comparative Example 3 is a carbon electrode manufactured with a composition ratio of graphite (KS-6): 82%, acetylene black: 8%, and polyvinylidene fluoride: 10%.
[0117]
For each of the batteries of Examples 13 to 16, charge / discharge cycles by constant current-constant voltage charge and constant current discharge were repeated 50 times, and the discharge capacity at the first cycle and the discharge capacity at the 50th cycle were measured. The change in discharge capacity per gram of carbon was examined. In addition, constant current charging in constant current-constant voltage charging is performed using polysulfide carbon and Li ₂ S ₈ And a current value corresponding to 60 mA per 1 g of the total weight, and the upper limit value of the voltage was set to 2.5V. The discharge current value was set to the same value as the current value in constant current charging, and the battery was discharged until the battery voltage became 1.5V. The results are shown in Table 4 as the discharge capacity per gram of polysulfide carbon.
[0118]
In addition, the battery of Comparative Example 3 was charged and discharged in the same manner as described above, but the positive electrode collapsed in the second cycle, making charging and discharging impossible. That is, Li ₂ S ₈ When only was used as the active material, it did not function as a secondary battery. In addition, the discharge capacity of the first cycle at this time is Li ₂ S ₈ The value was as low as 167 mAh / g per gram of the above.
[0119]
[Table 4]

[0120]
As described in Tables 1 and 2 above, the discharge capacity of polysulfide carbon is about 600 mAh / g. However, by including lithium sulfide in the electrolyte, the apparent discharge capacity of polysulfide carbon can be reduced. The battery capacity was greatly increased, and the battery capacity could be easily increased. Moreover, the large discharge capacity was maintained even after repeated cycles. This is presumably because the lithium sulfide not only acted as an active material, but also coexisted with the polysulfide carbon to improve the reversibility of each other. That is, in the batteries of Examples 13 to 16, not only the solid active material (polysulfide carbon) but also the liquid active material (lithium sulfide) dissolved in the electrolytic solution was used. Although the battery has the same volume as that of Example 11 and the like, it has succeeded in greatly increasing the discharge capacity. Of course, lithium sulfide may be included in the polymer electrolyte to be used as a gel active material.
[0121]
Example 17
Using the polysulfide carbons of Example 1 and Examples 3 to 5, nonaqueous electrolyte secondary batteries were produced as follows. 10 parts by weight of the polysulfide carbon of Example 1 and Examples 3 to 5, 2.2 parts by weight of graphite (KS-6) and 0.8 parts by weight of acetylene black are placed in a mixing container, and dried for 10 minutes. After mixing, 20 parts by weight of N-methyl-2-pyrrolidone was added and mixed for 30 minutes. Next, 21.6 parts by weight of an N-methyl-2-pyrrolidone solution containing 7.4% polyaniline and 16.7 parts by weight of an N-methyl-2-pyrrolidone solution containing 12% polyvinylidene fluoride were added. A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 9 except that a positive electrode mixture-containing paste was prepared by mixing for 1 hour, and that the positive electrode mixture-containing paste was used.
[0122]
Example 18
In Example 17, a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 17 except that polypyrrole was used as the conductive polymer.
[0123]
Example 19
100 g of an amine compound (Jeffamine XTJ-502) manufactured by Huntsman was dissolved in 130 g of a mixed solvent of propylene carbonate and ethylene carbonate in a weight ratio of 1: 1. 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 is dissolved in a mixed solvent of methyl ethyl carbonate and ethylene carbonate in a weight ratio of 2: 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.
[0124]
Next, as an electrolytic solution, a mixed solvent of methyl ethyl carbonate and ethylene carbonate having a weight ratio of 2: 1 was mixed with LiCF _Three SO _Three Was added to a concentration of 1.0 mol / l and used in Example 17 (CS _1.06 ) _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 9, and the electrolytic solution is injected After that, it was sealed to produce a nonaqueous electrolyte secondary battery.
[0125]
Example 20
In Example 17, a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 17 except that polyaniline was not used and graphite and acetylene black were increased instead.
[0126]
For each of the batteries of Examples 17 to 20, after initial discharge was performed at a current value corresponding to 60 mA per 1 g of the positive electrode active material, charge and discharge were performed at the same current value (discharge end voltage: 1.5 V), The discharge capacity per gram of the positive electrode active material under a low current load was examined. Next, after performing the same charging as described above, discharging was performed at a current value corresponding to 300 mA per 1 g of the positive electrode active material, and the change in the discharge capacity when the load increased was examined. The results are shown in Table 5.
[0127]
[Table 5]

[0128]
As is apparent from the results shown in Table 5, by containing a conductive polymer in the positive electrode, even when the current value at the time of discharge increases, there is little decrease in discharge capacity, and a battery suitable for high current load applications is obtained. be able to.
[0129]
【The invention's effect】
As described above, according to the present invention, it is possible to provide polysulfide carbon that is particularly useful as an active material for a nonaqueous electrolyte battery. That is, by using as an active material the polysulfide carbon of the present invention containing 67% by weight or more of sulfur by weight, the weight ratio of sulfur to carbon being 95% by weight or more, and having the above specific physical properties, It was possible to provide a highly reliable non-aqueous electrolyte secondary battery that has a high capacity and little reduction in capacity due to charge / discharge cycles.
[Brief description of the drawings]
FIG. 1 shows a polysulfide carbon (CS) obtained in Example 1. _1.06 ) _n It is a figure which shows a Raman spectrum.
FIG. 2 shows polysulfide carbon (CS) obtained in Example 1. _1.06 ) _n It is a figure which shows the X-ray-diffraction pattern of.
FIG. 3 shows polysulfide carbon (CS) obtained in Example 1. _1.06 ) _n And the organic sulfur compound (CS) obtained in Comparative Example 1 _4.9 ) _n It is a figure which shows the weight change in a thermogravimetric-differential thermal analysis.
FIG. 4 shows polysulfide carbon (CS) obtained in Example 6. _1.13 ) _n It is a figure which shows a Raman spectrum.
FIG. 5 shows an organic sulfur compound (CS) obtained in Comparative Example 2. _2.6 ) _n It is a figure which shows a Raman spectrum.
6 is an organic sulfur compound (CS) obtained in Comparative Example 2. FIG. _2.6 ) _n It is a figure which shows the X-ray-diffraction pattern of.
FIG. 7 shows carbon polysulfide (CS) in Example 12. _1.06 ) _n It is a figure which shows the cyclic voltammogram of the positive electrode which made 8: 2 the weight ratio of NiS.

Claims (20)

Carbon and sulfur as the main component elements, der total 95% or more by weight of the weight ratio of the weight ratio and the carbon and sulfur in 67% or more by weight of sulfur is, the atomic ratio of carbon to sulfur was 1: x sometimes, x is 0.9 to 1.5 der in its Raman spectrum, a peak exists mainly peak near 1444cm ^-1 of Raman shift, and present in the range of ^{400cm -1 ~525cm} -1 4 Polysulfide carbon characterized by having only a peak near 90 cm ⁻¹ . Carbon and sulfur as the main component elements, der total 95% or more by weight of the weight ratio of the weight ratio and the carbon and sulfur in 67% or more by weight of sulfur is, the atomic ratio of carbon to sulfur was 1: x sometimes, x I is 0.9 to 1.5 der, in X-ray diffraction by the CuKα ray diffraction pattern in the range of diffraction angles (2 [Theta]) is 20 ° to 30 ° is a peak near 2 5 ° Yes and, and, either having no peaks at diffraction angles other than near 25 °, or, the peak intensity of the peaks present in the diffraction angle other than near 25 ° is a peak intensity of the peak in the vicinity of 25 ° 1 / 10 polysulfide carbon, characterized by being represented by der Ru broad diffraction peaks below. Carbon and sulfur as the main component elements, der total 95% or more by weight of the weight ratio of the weight ratio and the carbon and sulfur in 67% or more by weight of sulfur is, the atomic ratio of carbon to sulfur was 1: x sometimes, that x is I 0.9-1.5 der, weight loss by thermogravimetric analysis when heated at a rate of 10 ° C. / min up to 300 ° C. from room temperature under a nitrogen atmosphere of 5% or less Characteristic polysulfide carbon. The carbon polysulfide according to any one of claims 1 to 3, which is represented by a general formula (CS _x ) _n (x is 0.9 to 1.5, and n is a number of 4 or more). polysulfide carbon according to any one of claims 1 to 4, x is equal to or more than 1.3. The polysulfide carbon according to any one of claims 1 to 5, which has a repeating unit represented by the following formula (1).

For organic sulfur compounds having a structure represented by -S _m- (m ≧ 3) with carbon and sulfur as main constituent elements, removing a part of the sulfur having the structure to change to a disulfide bond. A method for producing carbon polysulfide, characterized in that the carbon polysulfide according to any one of claims 1 to 6 is used.   8. The method for producing carbon polysulfide according to claim 7, wherein the method for removing a part of sulfur constituting the structure is by heating.   8. The method for producing carbon polysulfide according to claim 7, wherein a method of removing a part of sulfur constituting the structure is a solvent extraction method.   A non-aqueous electrolyte battery using an electrode comprising the carbon polysulfide according to claim 1 as an active material and a non-aqueous electrolyte.   The positive electrode containing the polysulfide carbon according to any one of claims 1 to 6 and at least one of nickel, a nickel alloy, a nickel composite, or a nickel compound is used. Non-aqueous electrolyte battery.   The non-aqueous electrolyte battery according to claim 11, wherein the nickel compound is nickel sulfide. The non-aqueous electrolyte battery according to claim 12, wherein the nickel sulfide is a compound represented by a general formula NiS _z (z is 1 to 5). Organic sulfur compound other than polysulfide carbon according to any one of claims 1 to 6, -S y _- a compound having a structure represented by (y ≧ 3), at least one of a sulfide or sulfur lithium The nonaqueous electrolyte battery according to claim 10, wherein the battery is contained in the battery.   15. The nonaqueous electrolyte battery according to claim 14, wherein lithium sulfide is contained in the positive electrode or the nonaqueous electrolyte. The non-aqueous electrolyte battery according to claim 15, wherein the lithium sulfide is a compound represented by a general formula Li ₂ S _t (t ≧ 2).   The nonaqueous electrolyte battery according to claim 10, wherein a positive electrode containing the polysulfide carbon according to claim 1 and a conductive polymer is used.   The nonaqueous electrolyte battery according to claim 10, wherein a negative electrode using any one of lithium, a lithium alloy, a lithium-containing composite compound, or a carbonaceous material as an active material is used.   The nonaqueous electrolyte battery according to any one of claims 10 to 18, wherein a polymer electrolyte is used as the nonaqueous electrolyte.   The nonaqueous electrolyte battery according to any one of claims 10 to 19, wherein a nonaqueous electrolyte containing a fluorine-containing organic lithium salt or an imide salt is used.

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