JP4096438B2

JP4096438B2 - Secondary power supply

Info

Publication number: JP4096438B2
Application number: JP04367299A
Authority: JP
Inventors: 学對馬; 剛森本; 勇車
Original assignee: Asahi Glass Co Ltd
Current assignee: AGC Inc
Priority date: 1998-03-17
Filing date: 1999-02-22
Publication date: 2008-06-04
Anticipated expiration: 2019-02-22
Also published as: JP2000106218A

Description

【０００１】
【発明の属する技術分野】
本発明は、抵抗が低く、耐電圧が高く、容量の大きい二次電源に関する。さらに、本発明は急速充放電サイクル信頼性の高い二次電源に関する。
【０００２】
【従来の技術】
従来の電気二重層キャパシタの電極には、正極、負極ともに活性炭を主体とする分極性電極が使用されている。電気二重層キャパシタの耐電圧は、水系電解液を使用すると１．２Ｖ、有機系電解液を使用すると２．５〜３．３Ｖである。電気二重層キャパシタのエネルギは耐電圧の２乗に比例するので、耐電圧の高い有機電解液の方が水系電解液より高エネルギである。しかし、有機電解液を使用した電気二重層キャパシタでもそのエネルギ密度は鉛蓄電池等の二次電池の１／１０以下であり、さらなるエネルギ密度の向上が必要とされている。
【０００３】
これに対し、特開昭６４−１４８８２には、活性炭を主体とする電極を正極とし、Ｘ線回折による［００２］面の面間隔が０．３３８〜０．３５６ｎｍである炭素材料にあらかじめリチウムイオンを吸蔵させた電極を負極とする上限電圧３Ｖの二次電源が提案されている。また、特開平８−１０７０４８には、リチウムイオンを吸蔵、脱離しうる炭素材料にあらかじめ化学的方法又は電気化学的方法でリチウムイオンを吸蔵させた炭素材料を負極に用いる電池が提案されている。また、特開平９−５５３４２には、リチウムイオンを吸蔵、脱離しうる炭素材料をリチウムと合金を形成しない多孔質集電体に担持させる負極を有する、上限電圧４Ｖの二次電源が提案されている。しかし、これらの二次電源にはあらかじめリチウムイオンを吸蔵させるという製造工程上の問題があった。
【０００４】
また、電気二重層キャパシタ以外に大電流充放電可能な電源にはリチウムイオン二次電池がある。リチウムイオン二次電池は電気二重層キャパシタに比べて高電圧かつ高容量という性質を有するが、抵抗が高く、急速充放電サイクルによる寿命が電気二重層キャパシタに比べ著しく短い問題があった。
【０００５】
【発明が解決しようとする課題】
そこで本発明は、急速充放電が可能で高耐電圧かつ高容量でエネルギ密度が高く、充放電サイクル信頼性の高い二次電源を提供することを目的とする。
【０００６】
【課題を解決するための手段】
本発明は、活性炭とリチウム含有遷移金属酸化物とを含む正極と、リチウムイオンを吸蔵、脱離しうる炭素材料を含む負極と、リチウム塩を含む有機電解液と、を有し、リチウム含有遷移金属酸化物は前記正極中に０．１〜８０重量％含まれることを特徴とする二次電源を提供する。
【０００７】
本明細書において、リチウムイオンを吸蔵、脱離しうる炭素材料を主体とする負極と集電体とを接合して一体化させたものを負極体という。正極体についても同様の定義とする。また、二次電池も電気二重層キャパシタも二次電源の１種であるが、本明細書では、正極に活性炭を含み、負極にリチウムイオンを吸蔵、脱離しうる炭素材料を含む特定の構成の二次電源を単に二次電源という。
【０００８】
本発明の二次電源では、充電したときに正極ではリチウム塩のアニオンの活性炭への吸着に加え、リチウム含有遷移金属酸化物からのリチウムイオンの脱離が起こる。負極では炭素材料にリチウムイオンが吸蔵される。ここで負極の炭素材料に吸蔵されるリチウムイオンは、電解液中のリチウム塩によるものとリチウム含有遷移金属酸化物からの脱離によるものの両方がある。
【０００９】
したがって、リチウム含有遷移金属酸化物を含まず活性炭を主体とする正極を有する従来の二次電源に比べ、本発明の二次電源では負極の炭素材料に充分にリチウムイオンを吸蔵させることができる。そのため、前記従来の二次電源のように負極にあらかじめリチウムイオンを吸蔵させておかなくても、正極と負極をセパレータを介して対向させて電解液に含浸させた後に充電することにより負極に充分な量のリチウムイオンを吸蔵できる。そして負極の電位は卑になり、二次電源の電圧を高くできる。
【００１０】
また、正極をリチウム含有遷移金属酸化物を主体とする電極、負極をリチウムイオンを吸蔵、脱離しうる炭素材料を主体とする電極とするリチウムイオン二次電池では、急速充放電サイクルを行うと、緩やかな充放電サイクルを行った場合に比べて劣化が著しい。この主な原因は、正極活物質であるリチウム含有遷移金属酸化物の充放電による酸化還元反応にともなう劣化である。
【００１１】
一方、本発明の二次電源では、充分な量のリチウム含有遷移金属酸化物が正極に含まれている場合、大電流での急速充放電の場合は活性炭が関与し、比較的小さい電流の充放電の場合はリチウム含有遷移金属酸化物が関与する。そのため、正極のリチウム含有遷移金属酸化物は負担が小さくなり、充放電サイクルによる劣化を少なく抑えることができ、高電圧、高容量かつ充放電サイクルの寿命が長い二次電源が可能になる。
【００１２】
また、本発明の二次電源において正極に含まれるリチウム含有遷移金属酸化物の量を少なくすると、正極では充放電には電流の大きさにかかわらず実質的に活性炭のみが関与する。この場合、リチウム含有遷移金属酸化物の実質的な役割は、初期の充電で負極の炭素材料に吸蔵させるためのリチウムイオンを提供する役割と、二次電源の使用により電解液中のリチウムイオンが減少した場合にリチウムイオンを補う役割となる。したがって、リチウム含有遷移金属酸化物の含有量が多い場合に比べ容量は小さくなるが、充放電サイクルによる容量劣化は特に小さくなる。
【００１３】
正極中のリチウム含有遷移金属酸化物の量は０．１〜８０重量％が好ましい。０．１重量％未満であると、初めの充電において脱離されるリチウムイオンの量が負極が吸蔵できるリチウムイオンの量に対して充分ではなく、二次電源の電圧を高くできない。８０重量％を超えると、相対的に正極中の活性炭量が少なくなるため、充放電サイクルにおける容量減少が大きくなる。特に大容量化を重視し、小電流による充放電にリチウム含有遷移金属酸化物を関与させる場合、リチウム含有遷移金属酸化物の量は２０〜７０重量％であることが好ましい。また、特に充放電サイクルにおける容量減少を小さくし二次電源の耐久性を高めるには０．１〜１５重量％、特に１〜１０重量％が好ましい。
【００１４】
正極に含まれるリチウム含有遷移金属酸化物としては、Ｖ、Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ、Ｚｎ及びＷからなる群から選ばれる１種以上の遷移金属とリチウムとの複合酸化物が好ましい。特に好ましいのは、Ｍｎ、Ｃｏ及びＮｉからなる群から選ばれる１種以上とリチウムとの複合酸化物であり、さらにはＬｉ_xＣｏ_yＮｉ_(1-y)Ｏ₂又はＬｉ_zＭｎ₂Ｏ₄（ただし、０＜ｘ＜２、０≦ｙ≦１、０＜ｚ＜２。）が好ましい。
【００１５】
正極に含まれる活性炭は、比表面積が８００〜３０００ｍ²／ｇ、特に９００〜２１００ｍ²／ｇであることが好ましい。活性炭の原料、賦活条件は限定されないが、例えば原料としてはやしがら、フェノール樹脂、石油コークス等が挙げられ、賦活方法としては水蒸気賦活法、溶融アルカリ賦活法等が挙げられる。特に好ましいのはやしがらまたはフェノール樹脂を原料として水蒸気賦活して得られる活性炭である。正極の抵抗を低くするために、正極中に導電材として導電性のカーボンブラック又は黒鉛を含ませておくのも好ましく、このとき導電材は正極中に０．１〜２０重量％であることが好ましい。
【００１６】
正極体の作製方法としては、例えば活性炭粉末とリチウム含有遷移金属酸化物粉末との混合物にバインダとしてポリテトラフルオロエチレンを混合し、混練した後シート状に成形して正極とし、これを集電体に導電性接着剤を用いて固定する方法がある。また、バインダとしてポリフッ化ビニリデン、ポリアミドイミド、ポリイミド等を溶解したワニスに活性炭粉末とリチウム含有遷移金属酸化物粉末とを分散させ、この液をドクターブレード法等によって集電体上に塗工し、乾燥して得てもよい。正極中に含まれるバインダの量は、正極体の強度と容量等の特性とのバランスから１〜２０重量％であることが好ましい。
【００１７】
本発明におけるリチウムイオンを吸蔵、脱離しうる炭素材料は、Ｘ線回折の測定による［００２］面の面間隔が０．３３５〜０．４１０ｎｍ、特に０．３３５〜０．３３８ｎｍであることが好ましい。面間隔が０．４１０ｎｍ超の炭素材料は充放電サイクルにおいて劣化しやすい。具体的には石油コークス、メソフェーズピッチ系炭素材料又は気相成長炭素繊維を８００〜３０００℃で熱処理した材料、天然黒鉛、人造黒鉛、難黒鉛性炭素材料等が挙げられる。本発明ではこれらの材料はいずれも好ましく使用できる。
【００１８】
難黒鉛性炭素材料又は石油コークス等を低温処理した炭素材料を使用する場合、例えば気相成長炭素を黒鉛化した材料等の黒鉛性の炭素材料と混合して使用すると抵抗を低減できるので好ましい。この場合、難黒鉛性炭素材料等と黒鉛性の炭素材料とは重量比で９５：５〜７０：３０であることが好ましい。黒鉛性の炭素材料が５％未満では抵抗低減の効果が発揮できず、３０％超では負極の容量が低下する。
【００１９】
本発明における負極体は、活性炭を含む層の場合と同様に、リチウムイオンを吸蔵、脱離しうる材料にポリテトラフルオロエチレンをバインダとして混合し、混練してシート状に成形して負極を形成し、導電性接着剤を用いて集電体に接着させて得られる。また、ポリフッ化ビニリデン、ポリアミドイミド又はポリイミドをバインダとし、バインダとなる樹脂又はその前駆体を有機溶媒に溶解させた溶液に前記炭素材料を分散させ、集電体に塗工し、乾燥させて得る方法もある。これらの方法はいずれも好ましい。
【００２０】
集電体に負極層を塗工して得られる方法において、バインダとなる樹脂又はその前駆体を溶解させる溶媒は限定されないが、バインダを構成する樹脂又はその前駆体を容易に溶解でき、入手も容易であることからＮ−メチル−２−ピロリドン（以下、ＮＭＰという）が好ましい。ここで、ポリフッ化ビニリデンの前駆体、ポリアミドイミドの前駆体又はポリイミドの前駆体とは、加熱することにより重合してそれぞれポリフッ化ビニリデン、ポリアミドイミド又はポリイミドとなるものをいう。
【００２１】
上記のようにして得られるバインダは、加熱することにより硬化し、耐薬品性、機械的性質、寸法安定性に優れる。熱処理の温度は２００℃以上であることが好ましい。２００℃以上であれば、ポリアミドイミドの前駆体又はポリイミドの前駆体であっても通常重合して、それぞれポリアミドイミド又はポリイミドとなる。また、熱処理する雰囲気は窒素、アルゴン等の不活性雰囲気又は１ｔｏｒｒ以下の減圧下が好ましい。ポリアミドイミド又はポリイミドは、本発明で使用される有機電解液に対する耐性があり、また負極から水分を除去するために３００℃程度の高温加熱又は減圧下の加熱をしても充分耐性がある。
【００２２】
本発明において、負極と集電体の間にポリアミドイミド又はポリイミドからなる接着層を介在させると、負極と集電体の接着力はより強固になる。この場合、あらかじめ集電体にポリアミドイミド、ポリイミド又はこれらの前駆体を溶剤に溶解させたワニスを、ドクターブレード法等の塗工法で塗工し、乾燥して接着層を形成し、この上に負極を形成する。また、接着層を形成するワニスに銅、黒鉛等の導電材を分散させておくと、負極と集電体との接触抵抗を低減できるので好ましい。この導電材を含むワニスは、活性炭を含む層をシート状に成形した場合における該層と集電体との間にも導電性接着剤として介在させることもできる。
【００２３】
本発明における有機電解液に含まれるリチウム塩は、ＬｉＰＦ₆、ＬｉＢＦ₄、ＬｉＣｌＯ₄、ＬｉＮ（ＳＯ₂ＣＦ₃）₂、ＣＦ₃ＳＯ₃Ｌｉ、ＬｉＣ（ＳＯ₂ＣＦ₃）₃、ＬｉＡｓＦ₆及びＬｉＳｂＦ₆からなる群から選ばれる１種以上が好ましい。溶媒は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、ジメチルカーボネート、エチルメチルカーボネート、ジエチルカーボネート、スルホラン及びジメトキシエタンからなる群から選ばれる１種以上を含むことが好ましい。これらのリチウム塩と溶媒とからなる電解液は耐電圧が高く、電気伝導度も高い。リチウム塩の濃度は０．１〜２．５ｍｏｌ／Ｌ、さらには０．５〜２ｍｏｌ／Ｌが好ましい。
【００２４】
【実施例】
次に、実施例（例１〜６、例９〜１５）及び比較例（例７〜８、例１６〜１７）により本発明をさらに具体的に説明するが、本発明はこれらにより限定されない。なお、例１〜１７におけるセルの作製及び測定はすべて露点が−６０℃以下のアルゴングローブボックス中で行った。
【００２５】
［例１］
フェノール樹脂を原料として水蒸気賦活法によって得られた比表面積２０００ｍ²／ｇの活性炭４０重量％、ＬｉＣｏＯ₂４０重量％、導電性カーボンブラック１０重量％、及びバインダとしてポリテトラフルオロエチレン１０重量％からなる混合物をエタノールを加えて混練し、圧延した後、２００℃で２時間真空乾燥して電極シートを得た。このシートをポリアミドイミドをバインダとする導電性接着剤を用いてアルミニウム箔に接合し、減圧下で３００℃で２時間熱処理し、正極体とした。電極面積は１ｃｍ²、電極シートの厚さは１８０μｍであった。
【００２６】
次に、石油コークス系炭素材料を１０００℃で熱処理することによりリチウムイオンを吸蔵、脱離しうる炭素材料を得た。この炭素材料のＸ線回折による［００２］面の面間隔は０．３４１ｎｍであった。正極と同様にポリテトラフルオロエチレンをバインダとしてシート状に成形し、銅からなる集電体に導電性接着剤を用いて接合した。電極面積は１ｃｍ²、電極シートの厚さは６０μｍであった。
【００２７】
上記正極体と上記負極体とを、ポリプロピレン製セパレータを介して対向させて１ｃｍ角の素子を作製した。プロピレンカーボネートに１ｍｏｌ／ＬのＬｉＢＦ₄を溶解した溶液を電解液とし、該電解液に前記素子を充分に含浸させ、４．２Ｖから３Ｖまでの範囲で初期容量を測定した。その後、充放電電流１０ｍＡで、４．２Ｖから３Ｖまでの範囲で充放電サイクル試験を行い、１０００サイクル後の容量を測定し、変化率を算出した。結果を表１に示す。
【００２８】
［例２］
ＬｉＣｏＯ₂のかわりにＬｉＭｎ₂Ｏ₄を用いた以外は例１と同様にして正極体を得た。この正極体を用いた以外は例１と同様にして容量を測定した。結果を表１に示す。
【００２９】
［例３］
ＬｉＣｏＯ₂のかわりにＬｉＮｉＯ₂を用いた以外は例１と同様にして正極体を得た。この正極体を用いた以外は例１と同様にして容量を測定した。結果を表１に示す。
【００３０】
［例４］
ＬｉＣｏＯ₂のかわりにＬｉＣｏ_0.2Ｎｉ_0.8Ｏ₂を用いた以外は例１と同様にして正極体を得た。この正極体を用いた以外は例１と同様にして容量を測定した。結果を表１に示す。
【００３１】
［例５］
混合物中の活性炭を６０重量％かつＬｉＣｏＯ₂を２０重量％とした以外は例１と同様にして正極体を得た。この正極体を用いた以外は例１と同様にして容量を測定した。結果を表１に示す。
【００３２】
［例６］
混合物中の活性炭を２０重量％かつＬｉＣｏＯ₂を６０重量％とした以外は例１と同様にして正極体を得た。この正極体を用いた以外は例１と同様にして容量を測定した。結果を表１に示す。
【００３３】
［例７］
混合物中にＬｉＣｏＯ₂を加えずに活性炭を８０重量％とした以外は例１と同様にして正極体を得た。この正極体を用いた以外は例１と同様にして容量を測定した。結果を表１に示す。
【００３４】
［例８］
混合物中に活性炭を加えずにＬｉＣｏＯ₂を８０重量％とした以外は例１と同様にして正極体を得た。この正極体を用いた以外は例１と同様にして容量を測定した。結果を表１に示す。
【００３５】
［例９］
フェノール樹脂のかわりに、やしがらを原料として水蒸気賦活法によって得られた比表面積２０００ｍ²／ｇの活性炭を用いた以外は例１と同様にして正極体を作製した。
【００３６】
次に、メソフェーズピッチ系炭素材料を３０００℃で熱処理することにより、［００２］面の面間隔０．３３７ｎｍのリチウムイオンを吸蔵、脱離しうる炭素材料を得た。ポリアミドイミドをＮＭＰに溶解した溶液に上記炭素材料を分散させ、厚さ２０μｍのエッチングした銅箔にドクターブレード法で塗工し、空気中で１２０℃で２時間乾燥した後、０．２ｔｏｒｒの減圧下で３００℃で２時間熱処理し、負極体とした。乾燥後の塗工層の厚さは１００μｍであり、有効電極面積は１ｃｍ²、上記炭素材料とポリアミドイミドとの重量比は９：１であった。
【００３７】
上記正極体と上記負極体を厚さ２５μｍのポリプロピレン製セパレータを介して対向させて１ｃｍ角の素子を作製した。エチレンカーボネートとプロピレンカーボネートとの混合溶媒（容積比で１：１）に１ｍｏｌ／ＬのＬｉＢＦ₄を溶解した溶液を電解液とし、該電解液に前記素子を充分に含浸させ、４．２Ｖから３Ｖまでの範囲で初期容量を測定した。その後、充放電電流１０ｍＡで、４．２Ｖから３Ｖまでの範囲で充放電サイクル試験を行い、１万サイクル後の容量を測定し、さらに変化率を算出した。結果を表２に示す。
【００３８】
［例１０］
ＬｉＣｏＯ₂のかわりにＬｉＭｎ₂Ｏ₄を用いた以外は例９と同様にして正極体を得た。この正極体を用いた以外は例９と同様にして容量を測定した。結果を表２に示す。
【００３９】
［例１１］
ＬｉＣｏＯ₂のかわりにＬｉＮｉＯ₂を用いた以外は例９と同様にして正極体を得た。この正極体を用いた以外は例９と同様にして容量を測定した。結果を表２に示す。
【００４０】
［例１２］
ＬｉＣｏＯ₂のかわりにＬｉＣｏ_0.2Ｎｉ_0.8Ｏ₂を用いた以外は例１と同様にして正極体を得た。この正極体を用いた以外は例９と同様にして容量を測定した。結果を表２に示す。
【００４１】
［例１３］
混合物中の活性炭を６０重量％かつＬｉＣｏＯ₂を２０重量％とした以外は例９と同様にして正極体を得た。この正極体を用いた以外は例９と同様にして容量を測定した。結果を表２に示す。
【００４２】
［例１４］
混合物中の活性炭を２０重量％かつＬｉＣｏＯ₂を６０重量％とした以外は例９と同様にして正極体を得た。この正極体を用いた以外は例９と同様にして容量を測定した。結果を表２に示す。
【００４３】
［例１５］
混合物中の活性炭を７０重量％、かつＬｉＣｏＯ₂を１０重量％とした以外は例９と同様にして正極体を得た。また、塗工層の厚さを５０μｍとした以外は例９と同様にして負極体を得た。この正極体と負極体を用いた以外は例９と同様にして容量を測定した。結果を表２に示す。
【００４４】
［例１６］
混合物中にＬｉＣｏＯ₂を加えずに活性炭を８０重量％とした以外は例９と同様にして正極体を得た。この正極体を用いた以外は例９と同様にして容量を測定した。結果を表２に示す。
【００４５】
［例１７］
混合物中に活性炭を加えずにＬｉＣｏＯ₂を８０重量％とした以外は例９と同様にして正極体を得た。この正極体を用いた以外は例９と同様にして容量を測定した。結果を表２に示す。
【００４６】
【表１】

【００４７】
【表２】

【００４８】
【発明の効果】
本発明の二次電源は、耐電圧が高く容量が大きい。また、正極では急速充放電には活性炭が関与し、リチウム含有遷移金属酸化物は基本的に低電流による充放電に関与するか又は実質的に充放電に関与しないため、充放電サイクル耐久性に優れている。
【００４９】
また、二次電源の作製時の負極炭素材料へのリチウムイオンの吸蔵も、あらかじめ化学的方法又は電気化学的方法により行う必要がなく、二次電源として作製した後に充電により行うことができるため、二次電源の作製が容易である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a secondary power source with low resistance, high withstand voltage, and large capacity. Furthermore, the present invention relates to a secondary power source with high rapid charge / discharge cycle reliability.
[0002]
[Prior art]
As an electrode of a conventional electric double layer capacitor, a polarizable electrode mainly composed of activated carbon is used for both the positive electrode and the negative electrode. The withstand voltage of the electric double layer capacitor is 1.2 V when an aqueous electrolyte is used, and 2.5 to 3.3 V when an organic electrolyte is used. Since the energy of the electric double layer capacitor is proportional to the square of the withstand voltage, the organic electrolyte having a higher withstand voltage has a higher energy than the aqueous electrolyte. However, even in an electric double layer capacitor using an organic electrolyte, its energy density is 1/10 or less that of a secondary battery such as a lead storage battery, and further improvement in energy density is required.
[0003]
On the other hand, Japanese Patent Laid-Open No. 64-14882 discloses that a lithium ion is previously applied to a carbon material having an electrode mainly composed of activated carbon as a positive electrode and having a [002] plane spacing of 0.338 to 0.356 nm by X-ray diffraction. A secondary power source with an upper limit voltage of 3 V has been proposed in which the electrode that has occluded is used as a negative electrode. Japanese Patent Laid-Open No. 8-107048 proposes a battery using, as a negative electrode, a carbon material in which lithium ions are occluded in advance by a chemical method or an electrochemical method in a carbon material that can occlude and desorb lithium ions. Japanese Patent Laid-Open No. 9-55342 proposes a secondary power supply with an upper limit voltage of 4 V having a negative electrode that supports a porous current collector that does not form an alloy with lithium on a carbon material capable of absorbing and desorbing lithium ions. Yes. However, these secondary power sources have a problem in the manufacturing process of storing lithium ions in advance.
[0004]
In addition to the electric double layer capacitor, there is a lithium ion secondary battery as a power source capable of charging and discharging a large current. Lithium ion secondary batteries have the properties of higher voltage and higher capacity than electric double layer capacitors, but they have high resistance and have a problem that their life due to rapid charge / discharge cycles is significantly shorter than electric double layer capacitors.
[0005]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a secondary power source capable of rapid charge / discharge, high withstand voltage, high capacity, high energy density, and high charge / discharge cycle reliability.
[0006]
[Means for Solving the Problems]
The present invention includes a positive electrode and, occluding lithium ions, a negative electrode containing a carbon material capable desorbed have a, an organic electrolyte containing a lithium salt, a lithium-containing transition metal containing activated carbon and a lithium-containing transition metal oxides oxide provides a secondary power source, wherein Rukoto contains 0.1 to 80% by weight in the positive electrode.
[0007]
In this specification, a negative electrode body is formed by joining and integrating a negative electrode mainly composed of a carbon material capable of inserting and extracting lithium ions and a current collector. The same definition applies to the positive electrode body. A secondary battery and an electric double layer capacitor are both types of secondary power sources. In this specification, the positive electrode includes activated carbon, and the negative electrode includes a carbon material capable of inserting and extracting lithium ions. The secondary power source is simply called a secondary power source.
[0008]
In the secondary power source of the present invention, when charged, in addition to adsorption of lithium salt anions on activated carbon, lithium ions are desorbed from the lithium-containing transition metal oxide when charged. In the negative electrode, lithium ions are occluded in the carbon material. Here, the lithium ions occluded in the carbon material of the negative electrode are both due to the lithium salt in the electrolytic solution and due to desorption from the lithium-containing transition metal oxide.
[0009]
Therefore, compared with a conventional secondary power source having a positive electrode mainly composed of activated carbon that does not contain a lithium-containing transition metal oxide, the secondary power source of the present invention can sufficiently store lithium ions in the carbon material of the negative electrode. Therefore, even if the negative electrode is not previously occluded with lithium ions as in the conventional secondary power source, the negative electrode is sufficiently charged by charging after impregnating the electrolyte with the positive electrode and the negative electrode facing each other through a separator. A large amount of lithium ions can be occluded. And the electric potential of a negative electrode becomes base, and the voltage of a secondary power supply can be made high.
[0010]
Further, in a lithium ion secondary battery in which the positive electrode is an electrode mainly composed of a lithium-containing transition metal oxide and the negative electrode is an electrode mainly composed of a carbon material capable of occluding and desorbing lithium ions, when a rapid charge / discharge cycle is performed, Deterioration is remarkable compared to the case where a slow charge / discharge cycle is performed. The main cause is deterioration due to the oxidation-reduction reaction due to charging / discharging of the lithium-containing transition metal oxide as the positive electrode active material.
[0011]
On the other hand, in the secondary power source of the present invention, when a sufficient amount of a lithium-containing transition metal oxide is contained in the positive electrode, activated carbon is involved in the case of rapid charge / discharge at a large current, and charging of a relatively small current is performed. In the case of discharge, a lithium-containing transition metal oxide is involved. Therefore, the burden of the lithium-containing transition metal oxide of the positive electrode is reduced, the deterioration due to the charge / discharge cycle can be suppressed, and a secondary power source with a high voltage, a high capacity, and a long life of the charge / discharge cycle becomes possible.
[0012]
In addition, when the amount of the lithium-containing transition metal oxide contained in the positive electrode in the secondary power source of the present invention is reduced, only activated carbon is substantially involved in charge and discharge in the positive electrode regardless of the magnitude of the current. In this case, the substantial role of the lithium-containing transition metal oxide is to provide lithium ions for occlusion in the carbon material of the negative electrode in the initial charge, and to reduce the lithium ions in the electrolyte by using a secondary power source. When it decreases, it serves to supplement lithium ions. Therefore, the capacity is smaller than when the content of the lithium-containing transition metal oxide is large, but the capacity deterioration due to the charge / discharge cycle is particularly small.
[0013]
The amount of the lithium-containing transition metal oxide in the positive electrode is preferably 0.1 to 80% by weight. If it is less than 0.1% by weight, the amount of lithium ions desorbed in the first charge is not sufficient relative to the amount of lithium ions that can be occluded by the negative electrode, and the voltage of the secondary power source cannot be increased. If it exceeds 80% by weight, the amount of activated carbon in the positive electrode is relatively reduced, and thus the capacity reduction in the charge / discharge cycle is increased. In particular, when emphasizing the increase in capacity and involving the lithium-containing transition metal oxide in charging and discharging with a small current, the amount of the lithium-containing transition metal oxide is preferably 20 to 70% by weight. Moreover, 0.1 to 15 weight%, especially 1 to 10 weight% is preferable in order to reduce the capacity | capacitance reduction especially in a charging / discharging cycle and to improve durability of a secondary power supply.
[0014]
The lithium-containing transition metal oxide contained in the positive electrode is preferably a composite oxide of lithium and one or more transition metals selected from the group consisting of V, Mn, Fe, Co, Ni, Zn, and W. Particularly preferred is a composite oxide of lithium and at least one selected from the group consisting of Mn, Co and Ni, and Li _x Co _y Ni _(1-y) O ₂ or Li _z Mn ₂ O _4. (However, 0 <x <2, 0 ≦ y ≦ 1, 0 <z <2.) Is preferable.
[0015]
The activated carbon contained in the positive electrode preferably has a specific surface area of 800 to 3000 m ² / g, particularly 900 to 2100 m ² / g. Although the raw material of activated carbon and activation conditions are not limited, For example, as a raw material, a phenol resin, petroleum coke, etc. are mentioned, As a activation method, a steam activation method, a molten alkali activation method, etc. are mentioned. Particularly preferred is activated carbon obtained by steam activation using coconut or phenol resin as a raw material. In order to reduce the resistance of the positive electrode, it is also preferable to include conductive carbon black or graphite as a conductive material in the positive electrode. At this time, the conductive material should be 0.1 to 20% by weight in the positive electrode. preferable.
[0016]
As a method for producing the positive electrode, for example, a mixture of activated carbon powder and lithium-containing transition metal oxide powder is mixed with polytetrafluoroethylene as a binder, kneaded, and then molded into a sheet to obtain a positive electrode. There is a method of fixing using a conductive adhesive. In addition, activated carbon powder and lithium-containing transition metal oxide powder are dispersed in a varnish in which polyvinylidene fluoride, polyamideimide, polyimide, etc. are dissolved as a binder, and this liquid is applied onto a current collector by a doctor blade method or the like, It may be obtained by drying. The amount of the binder contained in the positive electrode is preferably 1 to 20% by weight from the balance between the strength of the positive electrode body and characteristics such as capacity.
[0017]
The carbon material capable of inserting and extracting lithium ions in the present invention preferably has a [002] plane spacing of 0.335 to 0.410 nm, particularly 0.335 to 0.338 nm as measured by X-ray diffraction. . A carbon material having an interplanar spacing of more than 0.410 nm is likely to deteriorate in a charge / discharge cycle. Specifically, petroleum coke, mesophase pitch-based carbon material or vapor-grown carbon fiber is heat-treated at 800 to 3000 ° C., natural graphite, artificial graphite, non-graphitizable carbon material, and the like. In the present invention, any of these materials can be preferably used.
[0018]
In the case of using a low-graphite carbon material or a carbon material obtained by subjecting petroleum coke or the like to a low temperature, it is preferable to mix vapor-grown carbon with a graphitic carbon material such as a graphitized material because the resistance can be reduced. In this case, the weight ratio of the non-graphitizable carbon material and the like to the graphitic carbon material is preferably 95: 5 to 70:30. If the graphitic carbon material is less than 5%, the effect of reducing the resistance cannot be exhibited, and if it exceeds 30%, the capacity of the negative electrode decreases.
[0019]
In the negative electrode body of the present invention, as in the case of the layer containing activated carbon, polytetrafluoroethylene is mixed as a binder with a material capable of inserting and extracting lithium ions, kneaded and formed into a sheet to form a negative electrode. It is obtained by adhering to a current collector using a conductive adhesive. In addition, polyvinylidene fluoride, polyamideimide, or polyimide is used as a binder, and the carbon material is dispersed in a solution in which a binder resin or its precursor is dissolved in an organic solvent, applied to a current collector, and dried. There is also a method. Any of these methods is preferred.
[0020]
In the method obtained by applying the negative electrode layer to the current collector, the solvent that dissolves the binder resin or its precursor is not limited, but the resin constituting the binder or its precursor can be easily dissolved and is also available. N-methyl-2-pyrrolidone (hereinafter referred to as NMP) is preferable because it is easy. Here, the precursor of polyvinylidene fluoride, the precursor of polyamideimide or the precursor of polyimide means a polymer which is polymerized by heating to become polyvinylidene fluoride, polyamideimide or polyimide, respectively.
[0021]
The binder obtained as described above is cured by heating and is excellent in chemical resistance, mechanical properties, and dimensional stability. It is preferable that the temperature of heat processing is 200 degreeC or more. If it is 200 degreeC or more, even if it is a polyamideimide precursor or a polyimide precursor, it will superpose | polymerize normally and it will become a polyamideimide or a polyimide, respectively. The atmosphere for the heat treatment is preferably an inert atmosphere such as nitrogen or argon, or a reduced pressure of 1 torr or less. Polyamideimide or polyimide is resistant to the organic electrolyte used in the present invention, and is sufficiently resistant to high temperature heating at about 300 ° C. or heating under reduced pressure in order to remove moisture from the negative electrode.
[0022]
In the present invention, when an adhesive layer made of polyamideimide or polyimide is interposed between the negative electrode and the current collector, the adhesive force between the negative electrode and the current collector becomes stronger. In this case, a varnish obtained by dissolving polyamideimide, polyimide or a precursor thereof in a current collector in a solvent in advance is applied by a coating method such as a doctor blade method, and dried to form an adhesive layer. A negative electrode is formed. In addition, it is preferable to disperse a conductive material such as copper or graphite in the varnish forming the adhesive layer because the contact resistance between the negative electrode and the current collector can be reduced. The varnish containing this conductive material can be interposed as a conductive adhesive also between the layer and the current collector when the layer containing activated carbon is formed into a sheet.
[0023]
The lithium salt contained in the organic electrolyte in the present invention includes LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN (SO ₂ CF ₃ ) ₂ , CF ₃ SO ₃ Li, LiC (SO ₂ CF ₃ ) ₃ , LiAsF ₆ and LiSbF. One or more selected from the group consisting of ₆ are preferred. The solvent preferably contains one or more selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, sulfolane, and dimethoxyethane. Electrolytic solutions composed of these lithium salts and solvents have high withstand voltage and high electrical conductivity. The concentration of the lithium salt is preferably 0.1 to 2.5 mol / L, more preferably 0.5 to 2 mol / L.
[0024]
【Example】
Next, although an Example (Examples 1-6, Examples 9-15) and a comparative example (Examples 7-8, Examples 16-17) demonstrate this invention further more concretely, this invention is not limited by these. In addition, all the manufacture and measurement of the cell in Examples 1-17 were performed in the argon glove box whose dew point is -60 degrees C or less.
[0025]
[Example 1]
40% by weight of activated carbon having a specific surface area of 2000 m ² / g obtained by a steam activation method using phenol resin as a raw material, 40% by weight of LiCoO _2, 10% by weight of conductive carbon black, and 10% by weight of polytetrafluoroethylene as a binder. The mixture was kneaded with ethanol, rolled, and then vacuum dried at 200 ° C. for 2 hours to obtain an electrode sheet. This sheet was bonded to an aluminum foil using a conductive adhesive containing polyamideimide as a binder, and heat treated at 300 ° C. for 2 hours under reduced pressure to obtain a positive electrode body. The electrode area was 1 cm ² and the thickness of the electrode sheet was 180 μm.
[0026]
Next, the petroleum coke carbon material was heat-treated at 1000 ° C. to obtain a carbon material capable of inserting and extracting lithium ions. The surface spacing of the [002] plane by X-ray diffraction of this carbon material was 0.341 nm. In the same manner as the positive electrode, polytetrafluoroethylene was used as a binder to form a sheet and joined to a current collector made of copper using a conductive adhesive. The electrode area was 1 cm ² and the thickness of the electrode sheet was 60 μm.
[0027]
The positive electrode body and the negative electrode body were opposed to each other through a polypropylene separator to produce a 1 cm square element. A solution in which 1 mol / L LiBF ₄ was dissolved in propylene carbonate was used as an electrolytic solution, the device was sufficiently impregnated with the electrolytic solution, and the initial capacity was measured in the range from 4.2V to 3V. Thereafter, a charge / discharge cycle test was performed at a charge / discharge current of 10 mA in a range from 4.2 V to 3 V, the capacity after 1000 cycles was measured, and the rate of change was calculated. The results are shown in Table 1.
[0028]
[Example 2]
A positive electrode body was obtained in the same manner as in Example 1 except that LiMn ₂ O ₄ was used instead of LiCoO ₂ . The capacity was measured in the same manner as in Example 1 except that this positive electrode was used. The results are shown in Table 1.
[0029]
[Example 3]
A positive electrode body was obtained in the same manner as in Example 1 except that LiNiO ₂ was used instead of LiCoO ₂ . The capacity was measured in the same manner as in Example 1 except that this positive electrode was used. The results are shown in Table 1.
[0030]
[Example 4]
A positive electrode body was obtained in the same manner as in Example 1 except that LiCo _0.2 Ni _0.8 O ₂ was used instead of LiCoO ₂ . The capacity was measured in the same manner as in Example 1 except that this positive electrode was used. The results are shown in Table 1.
[0031]
[Example 5]
A positive electrode body was obtained in the same manner as in Example 1 except that the activated carbon in the mixture was 60 wt% and LiCoO ₂ was 20 wt%. The capacity was measured in the same manner as in Example 1 except that this positive electrode was used. The results are shown in Table 1.
[0032]
[Example 6]
A positive electrode body was obtained in the same manner as in Example 1 except that the activated carbon in the mixture was 20 wt% and LiCoO ₂ was 60 wt%. The capacity was measured in the same manner as in Example 1 except that this positive electrode was used. The results are shown in Table 1.
[0033]
[Example 7]
A positive electrode was obtained in the same manner as in Example 1 except that the activated carbon was changed to 80% by weight without adding LiCoO ₂ to the mixture. The capacity was measured in the same manner as in Example 1 except that this positive electrode was used. The results are shown in Table 1.
[0034]
[Example 8]
A positive electrode body was obtained in the same manner as in Example 1 except that the activated carbon was not added to the mixture and LiCoO ₂ was changed to 80% by weight. The capacity was measured in the same manner as in Example 1 except that this positive electrode was used. The results are shown in Table 1.
[0035]
[Example 9]
A positive electrode body was prepared in the same manner as in Example 1 except that instead of the phenol resin, activated carbon having a specific surface area of 2000 m ² / g obtained by steam activation using coconut palm as a raw material was used.
[0036]
Next, the mesophase pitch-based carbon material was heat-treated at 3000 ° C. to obtain a carbon material capable of inserting and extracting lithium ions having a [002] plane spacing of 0.337 nm. The above carbon material is dispersed in a solution of polyamideimide in NMP, coated on a 20 μm thick etched copper foil by the doctor blade method, dried in air at 120 ° C. for 2 hours, and then decompressed at 0.2 torr. Under heat treatment at 300 ° C. for 2 hours, a negative electrode body was obtained. The thickness of the coating layer after drying was 100 μm, the effective electrode area was 1 cm ² , and the weight ratio of the carbon material to polyamideimide was 9: 1.
[0037]
The positive electrode body and the negative electrode body were opposed to each other through a polypropylene separator having a thickness of 25 μm to produce a 1 cm square element. A solution obtained by dissolving 1 mol / L LiBF ₄ in a mixed solvent of ethylene carbonate and propylene carbonate (volume ratio of 1: 1) is used as an electrolytic solution. The electrolytic solution is sufficiently impregnated with the element, and 4.2V to 3V. The initial capacity was measured in the range up to. Thereafter, a charge / discharge cycle test was performed at a charge / discharge current of 10 mA in a range from 4.2 V to 3 V, the capacity after 10,000 cycles was measured, and the rate of change was further calculated. The results are shown in Table 2.
[0038]
[Example 10]
A positive electrode body was obtained in the same manner as in Example 9 except that LiMn ₂ O ₄ was used instead of LiCoO ₂ . The capacity was measured in the same manner as in Example 9 except that this positive electrode was used. The results are shown in Table 2.
[0039]
[Example 11]
A positive electrode body was obtained in the same manner as in Example 9, except that LiNiO ₂ was used instead of LiCoO ₂ . The capacity was measured in the same manner as in Example 9 except that this positive electrode was used. The results are shown in Table 2.
[0040]
[Example 12]
A positive electrode body was obtained in the same manner as in Example 1 except that LiCo _0.2 Ni _0.8 O ₂ was used instead of LiCoO ₂ . The capacity was measured in the same manner as in Example 9 except that this positive electrode was used. The results are shown in Table 2.
[0041]
[Example 13]
A positive electrode body was obtained in the same manner as in Example 9 except that the activated carbon in the mixture was 60% by weight and LiCoO ₂ was 20% by weight. The capacity was measured in the same manner as in Example 9 except that this positive electrode was used. The results are shown in Table 2.
[0042]
[Example 14]
A positive electrode body was obtained in the same manner as in Example 9 except that the activated carbon in the mixture was 20 wt% and LiCoO ₂ was 60 wt%. The capacity was measured in the same manner as in Example 9 except that this positive electrode was used. The results are shown in Table 2.
[0043]
[Example 15]
A positive electrode body was obtained in the same manner as in Example 9, except that the activated carbon in the mixture was 70 wt% and LiCoO ₂ was 10 wt%. Further, a negative electrode body was obtained in the same manner as in Example 9 except that the thickness of the coating layer was 50 μm. The capacity was measured in the same manner as in Example 9 except that this positive electrode body and negative electrode body were used. The results are shown in Table 2.
[0044]
[Example 16]
A positive electrode body was obtained in the same manner as in Example 9 except that LiCoO ₂ was not added to the mixture and the activated carbon was changed to 80% by weight. The capacity was measured in the same manner as in Example 9 except that this positive electrode was used. The results are shown in Table 2.
[0045]
[Example 17]
A positive electrode body was obtained in the same manner as in Example 9 except that LiCoO ₂ was changed to 80% by weight without adding activated carbon to the mixture. The capacity was measured in the same manner as in Example 9 except that this positive electrode was used. The results are shown in Table 2.
[0046]
[Table 1]

[0047]
[Table 2]

[0048]
【The invention's effect】
The secondary power supply of the present invention has a high withstand voltage and a large capacity. In the positive electrode, activated carbon is involved in rapid charge / discharge, and lithium-containing transition metal oxides are basically involved in charge / discharge due to low current or substantially not involved in charge / discharge. Are better.
[0049]
In addition, the insertion of lithium ions into the negative electrode carbon material during the production of the secondary power source does not need to be performed in advance by a chemical method or an electrochemical method, and can be performed by charging after the production of the secondary power source, A secondary power supply can be easily manufactured.

Claims

A positive electrode containing a activated carbon and the lithium-containing transition metal oxide, absorb lithium ions, possess a negative electrode containing a carbon material capable of elimination, and an organic electrolyte containing a lithium salt, a lithium-containing transition metal oxide is the secondary power source, wherein Rukoto contains 0.1 to 80 wt% in the positive electrode.

The secondary power supply according to claim 1, wherein the lithium-containing transition metal oxide is a composite oxide of lithium and at least one selected from the group consisting of V, Mn, Fe, Co, Ni, Zn, and W.

The lithium-containing transition metal oxide is Li _x Co _y Ni _1-y O ₂ or Li _z Mn ₂ O ₄ (where 0 <x <2, 0 ≦ y ≦ 1, 0 <z <2). Item 2. The secondary power source according to Item 1.

Activated carbon of the positive electrode, a secondary power supply having a specific surface area of claim 1, 2 or 3 is 800~3000m ² / g.

The secondary power source according to claim 1, 2, 3, or 4 , wherein the carbon material has a [002] plane spacing of 0.335 to 0.410 nm.