JP3601265B2 - Collective battery and charging method thereof - Google Patents

Description

【００１８】
の反応式に対応する量として全固体リチウム二次電池を構成する。
また、結晶構造中のリチウムイオンサイトへのリチウムイオンの挿入脱離反応にともなう電位の不連続な変化を示す物質としてアルミニウムを用い、かつリチウムイオンの挿入脱離反応にともなう電位の不連続な変化を示す物質の電位が不連続に変化するまでのリチウムイオンの挿入量が、
【００１９】
【化４】

【００２０】
の反応式に対応する量として全固体リチウム二次電池を構成する。
【００２１】
また、さらにリチウムイオンサイトへのリチウムイオンの挿入脱離反応にともなう電位の不連続な変化を示す物質として、遷移金属酸化物、リチウム遷移金属酸化物、遷移金属硫化物、リチウム遷移金属硫化物の群より選ばれるものを用いる。
【００２２】
さらに、前記遷移金属酸化物あるいはリチウム遷移金属酸化物の遷移金属元素として、チタン、マンガン、タングステン、バナジウムの群より選ばれる少なくとも一種の元素を用いる。
【００２３】
また、前記遷移金属硫化物あるいはリチウム遷移金属硫化物の遷移金属元素として、チタン、モリブデン、ニオブ、タングステン、バナジウムの群より選ばれる少なくとも一種の元素を用いる。
【００２４】
また、正極に用いられるリチウム遷移金属酸化物の遷移金属元素として、コバルト、ニッケル、マンガン、鉄の群より選ばれる少なくとも一種類の元素を用いる。
【００２５】
また、リチウムイオン伝導性固体電解質として、無機化合物であるものを用いる。
【００２６】
さらに、前記無機化合物が、硫化物を主体とする非晶質のものを用いる。
さらに、前記無機化合物として、硫化リチウム、硫化ケイ素を主体とする物質より合成されるものを用いる。
【００２８】
さらに、複数の素電池を、気密性を有する同一の電池容器内に収納することで集合電池を構成する。
【００２９】
また本発明は、充電電気量に対して、電圧Ｖ_１から電圧Ｖ_２への不連続な電圧変化を生じるこれらの電池を、電圧Ｖ_２以下で充電する。
【００３０】
また、電解質として硫化物を主体とする非晶質リチウムイオン伝導性固体電解質を用い、電極活物質としてＬｉ_４／３Ｔｉ_５／３Ｏ_４を用いる。
【００３１】
【発明の実施の形態】
本発明の実施の形態について、正極活物質としてリチウムコバルト酸化物、負極としてインジウム−リチウム合金を用いた全固体リチウム二次電池を例に採り説明を行う。
【００３２】
リチウムイオン伝導性の固体電解質と、正極活物質としてリチウムコバルト酸化物（ＬｉＣｏＯ_２）、負極としてインジウムを用い全固体リチウム二次電池を構成すると、その充電時において、正極では（化５）で表される反応、負極では（化６）で表される反応が生じる。すなわち、正極ではリチウムコバルト酸化物からのリチウムイオンの脱離反応が生じ、一方負極では正極から脱離したリチウムイオンによりインジウム−リチウム合金が形成される。
【００３３】
【化５】

【００３４】
【化６】

【００３５】
ここで、リチウムコバルト酸化物への可逆的な挿入脱離反応が生じる範囲は、ｘ≦０．５の範囲であり、インジウム−リチウム合金の電位は、ｘ＝１．０付近で約０．６Ｖから約０．４Ｖへ不連続に変化する。
【００３６】
図１（ａ）は、負極活物質であるインジウムに対してモル比で２．１倍のリチウムコバルト酸化物を正極活物質として用いて構成した全固体リチウム二次電池の、充電における正極、負極の単極電位の変化を示した図である。また、電池の起電力の変化を図１（ｂ）に示した。リチウムコバルト酸化物の可逆的なリチウムイオンの挿入脱離を起こすリチウムイオンの最大脱離量は、Ｌｉ_０．５ＣｏＯ_２の組成となる量であり、一方インジウムの電位が不連続に変化するまでのリチウムイオンの挿入量はＩｎ−Ｌｉの組成となる量である。したがって、この全固体リチウム二次電池においては、リチウムコバルト酸化物の可逆的なリチウムイオンの挿入脱離を起こすリチウムイオンの最大脱離量に対して、インジウムの電位が不連続に変化するまでのリチウムイオンの挿入量がほぼ等しく若干小である構成となっている。
【００３７】
これに対して、負極であるインジウムに対してモル比で１．４倍のリチウムコバルト酸化物を正極活物質として用いて構成した全固体リチウム二次電池の、充電における正極、負極の単極電位の変化を図２（ａ）に、電池の起電力の変化を図２（ｂ）に示した。この全固体リチウム二次電池においては、リチウムコバルト酸化物の可逆的なリチウムイオンの挿入脱離を起こすリチウムイオンの最大脱離量に対して、インジウムの電位が不連続に変化するまでのリチウムイオンの挿入量が大となる構成となっている。
【００３８】
これらの構成の全固体リチウム二次電池において、リチウムコバルト酸化物がＬｉ_０．５ＣｏＯ_２の組成となるまでが最大の電池容量であるため、電池を図１あるいは図２におけるＡ点まで完全充電するためには、電池の完全充電時の正極電位（Ｅｐｏｓ）と負極電位（Ｅｎｅｇ）の差（Ｅｐｏｓ−Ｅｎｅｇ）に対応する電圧（Ｖｃｅｌｌ）の電圧で充電すればよいことになる。しかしながら実際には、充電時の電池には、内部抵抗に起因する直流分極成分や電極反応などに起因する過電圧（η）が生じているため、Ｖｃｅｌｌの電圧で充電した際には最大の電池容量までは充電されない。そのため、電池を充分に充電するためには、Ｖｃｅｌｌよりも高い電圧（Ｖｅｎｄ）で充電する必要がある。
【００３９】
しかしながら、ηの値は一定ではなく、つぎのように電池の充電にともない減少する傾向にある。
【００４０】
例えば定電圧で充電した場合、充電末期には充電電流の減衰にともないηは小さくなる。
【００４１】
また特に、電解質としてリチウムイオン伝導性固体電解質を用いた場合には、つぎのような機構によっても電池の充電にともないηが減少する。充電時の正極においては、先に述べたようにリチウムコバルト酸化物の層間距離が伸び、正極の体積は膨張する。それに対して、負極においても金属インジウムがインジウム−リチウム合金となることにより、体積膨張が生じる。その結果、電池素子には圧力が加わった状態となり、電池を構成する固体粒子間の接合状態が向上するとともに、電池素子内に存在した空隙の体積が減少する。その結果、電池の内部抵抗が低下し、ηも減少する。
【００４２】
ここでは、ηが極端に小さなものとなった場合、すなわちη→０となった場合について説明を続ける。
【００４３】
充電電圧をＶｅｎｄとした充電末期にη→０となると、正極電位と負極電位の差、すなわちＥｐｏｓ−Ｅｎｅｇの値がＶｅｎｄに近づく。その結果、図２においては本来Ａ点まで充電するべきものが、Ｂ点まで電池が深く充電されることになる。この例の場合リチウムコバルト酸化物からリチウムイオンが、最大でＬｉ_０．４ＣｏＯ_２の組成まで脱離する。その結果、リチウムコバルト酸化物でのリチウムイオンの挿入脱離反応の可逆性が損なわれ、充放電サイクル特性の低下が生じる。
【００４４】
これに対して、本発明による図１の構成とした場合、Ｖｅｎｄ−Ｖｃｅｌｌの値がインジウムの電位の不連続な変化量（ΔＶ）よりも小さければ、η→０となった場合も電池は図中のＢ点までしか充電されず、Ｖｅｎｄの電圧で充電した際にもリチウムコバルト酸化物からのリチウムイオンの脱離量は、可逆的な挿入脱離を生じる範囲に留まる。
【００４５】
また、このような電池構成とした場合、充電器の精度が低く、充電電圧に変動が生じた際にも、その変動がΔＶ以下である場合には、同様にリチウムコバルト酸化物からのリチウムイオンの脱離量は、可逆的な挿入脱離を生じる範囲に留まり、電池特性の低下は生じない。
【００４６】
以上の作用により、リチウムイオン伝導性固体電解質を主体とする電解質層と、結晶構造中のリチウムイオンサイトへのリチウムイオンの可逆的な電気化学的挿入脱離反応を生じるリチウム遷移金属酸化物を含む正極と、結晶構造中のリチウムイオンサイトへのリチウムイオンの挿入脱離反応にともない電位の不連続な変化を示す物質を含む負極を有する全固体リチウム二次電池において、前記リチウム遷移金属酸化物の可逆的なリチウムイオンの挿入脱離を起こすリチウムイオンの最大脱離量に対して、前記リチウムイオンの挿入脱離反応にともない電位の不連続な変化を示す物質の電位が不連続に変化するまでのリチウムイオンの挿入量が、等しいか又は小とすることで、充放電サイクル特性に優れた全固体リチウム二次電池を得ることができる。
【００４７】
また、上記の構成とした電池は、図１（ｂ）で示したように充電電気量に対して電池電圧がＶ_１からＶ_２への不連続な変化を示す。したがって、この電池においては充電電圧をＶ_２以下とすることが望ましい。
【００４８】
また、上記の深い充電により充放電サイクル特性が損なわれる現象は、電解質として有機電解質を用いたリチウム二次電池においても生じるが、下記の理由により、電解質として固体電解質を用いた全固体リチウム二次電池において顕著に現れる。
【００４９】
深い充電により充放電サイクル特性が損なわれる機構は、すでに述べたようにＬｉＣｏＯ_２からリチウムイオンを脱離すると、Ｏ−Ｌｉ−Ｏ構造中のＬｉが存在しなくなることにより、ＣｏＯ_２層内の酸素原子間の静電的反発力が増大し、結晶構造に不安定性が増加することによる。しかしながら有機溶媒を用いた電解質中においては、ＣｏＯ_２層間に有機溶媒分子も同時に挿入した状態となっているため、ＣｏＯ_２層間よりリチウムイオンが脱離した際も、有機溶媒分子が層間に存在している。この有機溶媒分子とＣｏＯ_２層内の酸素原子との間にも静電的な相互作用が生じ、有機溶媒分子に四重極モーメントが生じる。その結果、酸素原子間の静電的反発力は減少し、結晶構造の不安定性が減じられる。それに対して、全固体リチウム二次電池中においては、このような相互作用が生じないため、結晶の不安定性は有機電解質を用いた場合に比べ大きく、そのため、深い充電により充放電サイクル特性が損なわれやすい。
【００５０】
以上の理由により、本発明の効果は、電解質としてリチウムイオン伝導性固体電解質を用いた全固体リチウム二次電池において顕著なものとなる。
【００５１】
また、リチウムイオン伝導性固体電解質は、無機化合物よりなるものと有機高分子化合物を主体とするものに大別される。有機高分子化合物を主体とするものは、可塑剤として有機溶媒を含有しており、この有機溶媒分子が上記の結晶の不安定性を減じることに寄与する。したがって、リチウムイオン伝導性固体電解質としては、無機化合物のものを用いた全固体リチウム二次電池において、本発明の効果は特に顕著なものとなる。
【００５２】
さらに、無機化合物よりなるリチウムイオン伝導性固体電解質としては、高いイオン伝導性を持つものを用いることで、全固体リチウム二次電池の作動電流特性を優れたものにすることができる。そのため、無機化合物よりなるリチウムイオン伝導性固体電解質としては、高いイオン伝導性を示すものとして硫化物を主体とする非晶質のものが特に好ましく用いられる。これらは、ガラス形成能を持つ硫化物と可動イオンであるリチウムイオンをガラス構造中に生成するための硫化リチウムの混合物を、高温で溶融させ急冷することで得られるが、中でも硫化リチウム、硫化ケイ素を主体とする物質より合成されるものは、合成時における各成分の蒸気圧が低いものであり、成分の蒸散を抑えるために出発物質を密封する必要がなく、大量合成に適することから特に好ましい。
【００５３】
上記では、結晶構造中のリチウムイオンサイトへのリチウムイオンの挿入脱離反応にともない電位の不連続な変化を示す物質として、インジウムあるいはインジウム−リチウム合金を例に採り説明を行ったが、その他このような作用を示す物質としては、以下の物質が挙げられる。
【００５４】
まず、金属元素について説明する。
元素記号Ｍｅで表される金属中のリチウムイオンサイトへのリチウムイオンの挿入反応を一般的に（化７）で表すと、Ｍｅがアルミニウムの場合、ｘ＝１．０付近で電位は０．３５Ｖから０Ｖ付近への不連続な変化を生じる。このことより、上記で説明を行ったインジウムに代えて、アルミニウムを用いた場合も同様の効果を得ることができる。
【００５５】
【化７】

【００５６】
その他のＭｅとしては、鉛の場合にはｘ＝２．０において、ビスマスの場合にもｘ＝２．０、アンチモンの場合にはｘ＝２．５、ガリウムの場合にはｘ＝１．０、スズの場合にもｘ＝１．０で、不連続な電位の変化を生じる。また、銀、ケイ素、亜鉛、カドミウム、砒素、チタンなどもリチウムイオンの挿入反応により不連続な電位の変化を生じることから、これらの物質を用いた場合も同様の効果を得ることができる。
【００５７】
また、リチウムイオンの挿入脱離反応にともない、複数の電位の不連続な変化を示す物質の場合には、請求項１に記載の電位が不連続に変化するまでのリチウムイオンの挿入量として、いずれの電位の不連続な変化を生じる挿入量を用いてもよい。
【００５８】
例えば、（化７）においてＭｅがスズの場合には、ｘ＝１．０の他に、ｘ＝２．３、２．５、２．６、３．５、４．４などでも不連続な電位の変化を生じる。したがって、正極活物質にＬｉＣｏＯ_２、負極活物質にスズを用いた全固体リチウム二次電池の構成としては、正極で（化８）で表される反応が生じるのに対応するリチウムの脱離量に対して、負極で（化９）においてｘ＝１．０とした場合の反応が生じるのに対応するリチウムの挿入量が、等しい又は小なる構成とすることで、同様の効果が得られるのみならず、負極で（化８）においてＸ＝２．３、２．５、２．６、３．５、４．４とした場合の反応が生じるのに対応するリチウムの挿入量が、等しい又は小なる構成とすることでも同様の効果を得ることができる。
【００５９】
【化８】

【００６０】
【化９】

【００６１】
また、インジウム、アルミニウム、鉛、ビスマス、アンチモン、ガリウム、スズ、銀、ケイ素、亜鉛、カドミウム、砒素、チタンより選ばれる複数種の金属元素よりなる合金の場合にも、一般的にリチウムイオンの挿入脱離反応にともない、複数の電位の不連続な変化を示す。このような物質を負極活物質として用いた場合にも、同様に請求項１に記載の電位が不連続に変化するまでのリチウムイオンの挿入量として、いずれの電位の不連続な変化を生じる挿入量を用いてもよい。
【００６２】
また、上記の純金属、あるいは合金に代えて、これらの金属あるいは合金とリチウムとの合金を用いてもよい。
【００６３】
但し、例えば先に述べた、正極活物質としてＬｉＣｏＯ_２、負極活物質としてインジウムを用いた全固体リチウム二次電池の金属インジウムに代えてＩｎ−Ｌｉ_０．１で表されるインジウム−リチウム合金を用いた場合を例に採ると、（化６）に代わって（化１０）で表されるｙに対応する量、即ちｙ＝０．９に対応する量が電位が不連続に変化するまでのリチウムイオンの挿入量となる。
【００６４】
【化１０】

【００６５】
以上のような結晶構造中のリチウムイオンサイトへのリチウムイオンの挿入脱離反応にともない電位の不連続な変化を示す金属あるいは金属とリチウムの合金の中でも、金属元素としてインジウムを用いた場合、物質中でのリチウムイオンの拡散速度が大きなものとなり、大電流で作動可能な全固体リチウム二次電池を構成することができる。そのため、結晶構造中のリチウムイオンサイトへのリチウムイオンの挿入脱離反応にともない電位の不連続な変化を示す金属あるいは金属とリチウムの合金としては、インジウムあるいはインジウム−リチウム合金が好ましく用いられる。
【００６６】
また、結晶構造中のリチウムイオンサイトへのリチウムイオンの挿入脱離反応にともない電位の不連続な変化を示す金属あるいは金属とリチウムの合金の中でも、金属元素としてアルミニウムを用いた場合、アルミニウムが軽い元素であることからエネルギー密度の高い全固体リチウム二次電池を構成することができる。そのため、結晶構造中のリチウムイオンサイトへのリチウムイオンの挿入脱離反応にともない電位の不連続な変化を示す金属あるいは金属とリチウムの合金としては、アルミニウムあるいはアルミニウム−リチウム合金が好ましく用いられる。
【００６７】
つぎに、結晶構造中のリチウムイオンサイトへのリチウムイオンの挿入脱離反応にともない電位の不連続な変化を示す物質として、遷移金属酸化物、リチウム遷移金属酸化物、遷移金属硫化物、リチウム遷移金属硫化物について説明を行う。
【００６８】
これらの物質中で、例えばスピネル型構造を有するリチウムチタン酸化物（Ｌｉ_４／３Ｔｉ_５／３Ｏ_４）は、リチウムイオン伝導性の電解質中で（化１１）で表される電気化学的なリチウムイオンの挿入反応を生じ、その電位はｘ＝１．０で不連続な変化を生じる。そのため、上記のインジウムなどに代えてＬｉ_４／３Ｔｉ_５／３Ｏ_４を用いた場合も同様の効果を得ることができる。また、同じくリチウムチタン酸化物として、ＬｉＴｉ_２Ｏ_４も（化１２）において、ｘ＝１．０で電位の不連続な変化を生じる。
【００６９】
【化１１】

【００７０】
【化１２】

【００７１】
このようなリチウムイオンの挿入反応にともなう不連続な電位変化を生じる遷移金属酸化物あるいはリチウム遷移金属酸化物としては、ＴｉＯ_２、ＭｎＯ_２、ＷＯ_３、ＷＯ_２、Ｖ_２Ｏ_５あるいはＬｉ_ｘＴｉＯ_２、Ｌｉ_ｘＭｎＯ_２、Ｌｉ_ｘＷＯ_３、Ｌｉ_ｘＷＯ_２、Ｌｉ_ｘＶ_２Ｏ_５なども挙げることができ、これらを用いた場合も同様の効果を得ることができる。
【００７２】
また、遷移金属硫化物あるいはリチウム遷移金属硫化物としては、ＴｉＳ_２、ＭｏＳ_２、ＮｂＳ_２、ＷＳ_２、ＦｅＭｏ_６Ｓ_８、Ｖ_２Ｓ_５あるいはＬｉ_ｘＴｉＳ_２、Ｌｉ_ｘＭｏＳ_２、Ｌｉ_ｘＮｂＳ_２、Ｌｉ_ｘＷＳ_２、Ｌｉ_ｘＭｏ_６Ｓ_８、Ｌｉ_ｘＶ_２Ｓ_５なども、リチウムイオンの挿入反応にともなう不連続な電位変化を示し、同様に用いることができる。
【００７３】
また、以上で述べたリチウム遷移金属化合物のリチウムイオンの脱離にともなう構造不安定性が原因となる電池のサイクル特性に関する問題は、電池を直列に積層した集合電池において、特に大きな問題となる。それに対して、集合電池の直列に接続された複数個の素電池のうち少なくとも最小の容量を有する素電池として、以上に記載の全固体リチウム二次電池を用いることで、充電末期には集合電池の電圧が不連続に変化するため、素電池を優れたサイクル性能を示す充電深度に保つことが容易となる。そのため、本発明は集合電池においてその効果を発揮する。
【００７４】
さらに、上記の全固体リチウム二次電池は共通電解質効果がないため、複数の素電池を、同一の気密性の電池容器内に収納することが可能であり、この構成とすることで電池ケースを簡単な構造とすることができ、安価な集合電池を構成することができる。
【００７５】
また、前述のような集合電池においても、充電電気量に対して、端子電圧は不連続な変化を示し、電圧Ｖ_１から電圧Ｖ_２への不連続な電圧変化を生じる集合電池においては、電圧Ｖ_２以下で充電することが好ましい。
【００７６】
なお、本明細書中において、電位とは、平衡電位のみを意味するものではなく、２相混合状態における混成電位などでもよい。
【００７７】
また、電位の不連続な変化とは、例えば（化６）においてｘの変化に対して急激な電位変化を生じることを示している。例えば、（化６）におけるＩｎ−Ｌｉ_ｘの電位をＥとすると、ｘの変化に対するＥの変化率（ｄＥ／ｄｘ）がピークを示すことを意味しており、厳密な数学的意味での不連続性、すなわちｄＥ／ｄｘが発散する場合のみを示すものではない。
【００７８】
また、上記の急激な電位変化としては、下記に示すような変化が好ましい。
全固体リチウム二次電池中で、正極活物質として用いられる結晶構造中のリチウムイオンサイトへのリチウムイオンの可逆的な電気化学的挿入脱離反応を生じるリチウム遷移金属酸化物と、負極に用いられるリチウムイオンの挿入脱離反応にともなう電位の不連続な変化を示す物質が（化１３）で表される電気化学反応を生じる場合、正極電位（Ｅ_Ｐ（ｘ））の変化率ｄＥ_Ｐ（ｘ）／ｄｘと負極電位（ｄＥ_ｎ（ｘ））の変化率ｄＥ_ｎ（ｘ）／ｄｘの間に、不連続な電位変化を示す組成ｘ＝ｘ_０において、少なくともｄＥ_ｎ（ｘ_０）／ｄｘ＞ｄＥ_Ｐ（ｘ_０）／ｄｘなる関係が成立することであり、さらに好ましくはｄＥ_ｎ（ｘ_０）／ｄｘ＞５Ｖの範囲である。
【００７９】
【化１３】

【００８０】
これに対してｄＥ_ｎ（ｘ）／ｄｘがこれらの関係を満たす値よりも小さな場合には、過電圧の変化、あるいは充電電圧の変動により電池が深く充電された状態となりやすく、充放電特性に優れた全固体リチウム二次電池を得ることが困難となる。
【００８１】
なお、（化１３）におけるＯｘは、Ｉｎ−Ｌｉ_Ｘ，Ａｌ−Ｌｉ_Ｘ合金などの場合には、Ｉｎ，Ａｌなどの母相の金属、遷移金属酸化物あるいは遷移金属硫化物などの場合には、（化１３）に記載の形式電価が変化する遷移金属原子を１個含む組成式である。すなわち、具体的にはＴｉ^４＋Ｓ_２，Ｌｉ［Ｌｉ_１／３Ｔｉ_２／３］Ｔｉ^４＋Ｏ_４などの組成式であり、これら組成式には形式電価の変化する遷移金属元素のみに価数を書き表してある。
【００８２】
また、電極活物質の体積変化が、固体電池のサイクル特性に大きな影響を与えることを指摘した。例えば、ＡｌとＬｉ^＋との電気化学反応によりアルミニウム−リチウム合金が形成される反応（化 ）において、Ａｌ，Ａｌ−Ｌｉともに結晶構造は立方晶であり、その格子定数はそれぞれ４．０４９Ａ、６．３７３Ａである。その結果、ＡｌがＬｉを吸蔵し、Ａｌ−Ｌｉ合金となることで、電極活物質の体積は約３．９倍にも膨張する。
【００８３】
【化１４】

【００８４】
このような大きな体積変化を生じる電極活物質がある一方、Ｌｉ^＋との電気化学反応にともなう体積変化が極めて小さい活物質として、スピネル構造を有するＬｉ_４／３Ｔｉ_５／３Ｏ_４が報告されている。Ｌｉ_４／３Ｔｉ_５／３Ｏ_４を電極活物質に用いて固体電池を構成した場合、先に指摘したような体積変化による影響がほとんど生じないことから、さらに優れたサイクル特性を有する固体電池が構成できることが期待される。
【００８５】
このＬｉ_４／３Ｔｉ_５／３Ｏ_４を電極活物質に用いた固体電池として、固体電解質にＬｉ０．３３Ｌａ０．５６ＴｉＯ３を用いたものが提案されている（Ｔ．Ｂｒｏｕｓｓｅ，Ｐ．Ｅｒａｇｎａｕｄ，Ｒ．Ｍａｒｃｈａｎｄ ａｎｄ Ｄ．Ｍ．Ｓｃｈｌｅｉｃｈ，Ｅｘｔｅｎｄｅｄ Ａｂｓｔｒａｃｔｓ ｏｆ ８ｔｈ Ｉｎｔｅｒｎａｔｉｏｎａｌ Ｍｅｅｔｉｎｇ ｏｎ Ｌｉｔｈｉｕｍ Ｂａｔｔｅｒｉｅｓ，３２４ （１９９６） Ｎａｇｏｙａ，以降引例１と記す）。しかし、Ｌｉ_０．３３Ｌａ_０．５６ＴｉＯ_３は遷移金属原子を含有する固体電解質であるため、電気化学的に還元されやすいという課題を有する。例えば、充電時に固体電解質が還元されてしまい、引例１中のＦｉｇ．１に示されたように、充電電気量に対して放電電気量が小さくなるなどの問題を有している。
【００８６】
このように、Ｌｉ_４／３Ｔｉ_５／３Ｏ_４を電極活物質とし用いた場合でも、固体電解質の選択によっては充放電効率が悪く、電池特性も不安定になってしまう問題があった。
【００８７】
これに対し、硫化物を主体とする非晶質リチウムイオン伝導性固体電解質は、Ｌｉ_４／３Ｔｉ_５／３Ｏ_４の還元電位付近においても電気化学的に安定であるため、 この固体電解質と組み合わせることにより初めてＬｉ_４／３Ｔｉ_５／３Ｏ_４が高い充放電効率を示し、その結果優れたサイクル特性を有する固体電池を構成することが可能となる。
【００８８】
【実施例】
以下、本発明について実施例を用いて詳細に説明するが、以下の操作はすべて乾燥アルゴン雰囲気下で行った。
【００８９】
（実施例１）
正極活物質として用いられる、結晶構造中のリチウムイオンサイトへのリチウムイオンの可逆的な電気化学的挿入脱離反応を生じるリチウム遷移金属酸化物としてＬｉＣｏＯ_２で表されるリチウムコバルト酸化物を、結晶構造中のリチウムイオンサイトへのリチウムイオンの挿入脱離反応にともなう電位の不連続な変化を示す物質としてインジウムを、リチウムイオン伝導性固体電解質として０．０１Ｌｉ_３ＰＯ_４−０．６３Ｌｉ_２Ｓ−０．３６ＳｉＳ_２で表される非晶質固体電解質を用いて、全固体リチウム二次電池を構成し、その特性を評価した。以下にその詳細を示す。
【００９０】
まず、下記の方法でリチウムイオン伝導性固体電解質を合成した。
硫化リチウムと硫化ケイ素、リン酸リチウムをモル比で６３：３６：１の割合で秤量混合した。この混合物をグラッシーカーボン製坩堝に充填し、アルゴンガス気流中で１０００℃で２時間溶融した。その後、溶融物を双ローラーで急冷することにより、リチウムイオン伝導性固体電解質を得た。
【００９１】
つぎに、ＬｉＣｏＯ_２は、酸化コバルト（Ｃｏ_３Ｏ_４）と炭酸リチウム（Ｌｉ_２ＣＯ_３）を、Ｃｏ／Ｌｉ＝１の比となるよう秤量、混合し、大気中９００℃で焼成することにより合成した。
【００９２】
このようにして得たリチウムイオン伝導性固体電解質、正極活物質、さらには金属インジウムの箔を用いて、下記の方法で全固体リチウム二次電池を構成した。
【００９３】
本実施例における全固体リチウム二次電池Ａの断面図を図３に示す。図３において、１は正極であり、上記で得たＬｉＣｏＯ_２と粉砕した固体電解質を重量比で６：４の比で混合した正極材料を３００ｍｇ秤量したものを用いた。２はリチウムイオン伝導性の固体電解質層であり、負極である重量９５ｍｇの金属インジウム箔３と一体に加圧成型した。この一体に成型したペレットをステンレス製の電池容器４に入れ、絶縁性ガスケット５を介しステンレス製の蓋６により密封した。
【００９４】
この全固体リチウム二次電池Ａにおいて、リチウムコバルト酸化物への可逆的なリチウムイオンの挿入脱離反応が起こる最大脱離量は、（化８）の反応に対応する２４．６ｍＡｈであり、それに対して、インジウムへのリチウムイオンの挿入脱離反応に対してインジウムの電位が不連続に変化するまでのリチウムイオンの挿入量は、（化３）の反応に対応する２２．２ｍＡｈである。したがって、この電池は、リチウム遷移金属酸化物の可逆的なリチウムイオンの挿入脱離を起こすリチウムイオンの最大脱離量に対して、リチウムイオンの挿入脱離反応にともない電位の不連続な変化を示す物質の電位が不連続に変化するまでのリチウムイオンの挿入量が、小である構成となっている。
【００９５】
つづいて比較のために、インジウム箔の重量を１９０ｍｇとした以外は、上記と同様の方法で全固体リチウム二次電池Ｂを構成した。この電池においては、インジウムの電位が不連続に変化するまでのリチウムイオンの挿入量が４４．４ｍＡｈであり、リチウム遷移金属酸化物の可逆的なリチウムイオンの挿入脱離を起こすリチウムイオンの最大脱離量に対して、リチウムイオンの挿入脱離反応にともない電位の不連続な変化を示す物質の電位が不連続に変化するまでのリチウムイオンの挿入量が、大である構成となっている。
【００９６】
このようにして構成した全固体リチウム二次電池を、５００μＡの電流値で充電した。図４は、これら電池の第１回目の充電曲線である。但し、全固体リチウム二次電池Ａについては、充電曲線が不連続な変化を生じた３．８５Ｖを充電の終止電圧とした。それに対して、全固体リチウム二次電池Ｂについては、２４．６ｍＡｈを充電した際の端子電圧を充電の終止電圧とした。
【００９７】
このようにして充電の終止電圧を決定し、さらに放電の終止電圧を２．０Ｖとし、充放電電流５００μＡの充放電サイクル試験を行った。その結果得られた、各サイクルにおける放電電気量を図５に示す。
【００９８】
本発明における全固体リチウム二次電池Ａでは、充放電サイクルにともなう放電電気量の変化がほとんど観測されなかったのに対し、比較のために構成した全固体リチウム二次電池Ｂでは、充放電サイクルにともなう放電容量の低下が観測された。
【００９９】
つぎに、以下の方法で、充電電圧に時間的な変動が生じた際の充放電サイクル挙動を調べた。
【０１００】
まず、充電器としては、３．７５Ｖの直流電圧に、振幅０．１Ｖ、周波数１ｍＨｚの交流電圧を重畳した電圧を発生する電源を用いた。各々の全固体リチウム二次電池を、この充電器で５０時間充電し、その後、５００μＡの定電流で２．０Ｖまで放電する充放電サイクル試験を行い、各サイクルにおける放電容量を記録した。その結果を図６に示す。
【０１０１】
全固体リチウム二次電池Ａでは、充放電サイクルにともなう放電容量の低下はほとんど観測されなかったのに対して、全固体リチウム二次電池Ｂでは、初期より放電容量が低く、さらに充放電サイクルにともなう放電容量の低下が観測された。
【０１０２】
以上のように本発明によると、充放電サイクル特性に優れた全固体リチウム二次電池が得られることがわかった。
【０１０３】
（実施例２）
結晶構造中のリチウムイオンサイトへのリチウムイオンの挿入脱離反応にともなう電位の不連続な変化を示す物質として実施例１で用いたインジウムに代えて、アルミニウムを用いた以外は、実施例１と同様の方法で、全固体リチウム二次電池を構成し、その特性を評価した。以下にその詳細を示す。
【０１０４】
リチウムイオン伝導性固体電解質、リチウムコバルト酸化物は、実施例１と同様の方法で合成、混合、秤量し、全固体リチウム二次電池の正極とした。
【０１０５】
負極材料としては、固体電解質粉末と、金属アルミニウム粉末を重量比で１：５の比率で混合したものを用いた。この負極材料を２５ｍｇ秤量し、全固体リチウム二次電池の負極とした。
【０１０６】
このようにして得た正極、負極を用い、実施例１と同様の方法で全固体リチウム二次電池Ｃを構成した。この全固体リチウム二次電池において、リチウムコバルト酸化物への可逆的なリチウムイオンの挿入脱離反応が起こる最大脱離量は、実施例１と同様に２４．６ｍＡｈであり、それに対して、アルミニウムへのリチウムイオンの挿入脱離反応においてアルミニウムの電位が不連続に変化するまでのリチウムイオンの挿入量は、（化４）の反応に対応する２０．７ｍＡｈである。したがって、この電池は、リチウム遷移金属酸化物の可逆的なリチウムイオンの挿入脱離を起こすリチウムイオンの最大脱離量に対して、リチウムイオンの挿入脱離反応にともなう電位の不連続な変化を示す物質の電位が不連続に変化するまでのリチウムイオンの挿入量が、小である構成となっている。
【０１０７】
つづいて比較のために、負極の重量を５０ｍｇとした以外は、上記と同様の方法で全固体リチウム二次電池Ｄを構成した。この電池においては、アルミニウムの電位が不連続に変化するまでのリチウムイオンの挿入量が４１．４ｍＡｈであり、リチウム遷移金属酸化物の可逆的なリチウムイオンの挿入脱離を起こすリチウムイオンの最大脱離量に対して、リチウムイオンの挿入脱離反応にともない電位の不連続な変化を示す物質の電位が不連続に変化するまでのリチウムイオンの挿入量が、大である構成となっている。
【０１０８】
このようにして構成した全固体リチウム二次電池を用いて、実施例１と同様の充放電試験を行った。但し、本発明による全固体リチウム二次電池Ｃについては、充電曲線が不連続な変化を生じた電圧を充電の終止電圧とし、それに対して、比較のための全固体リチウム二次電池Ｄについては、２４．６ｍＡｈを充電した際の端子電圧を充電の終止電圧とした。
【０１０９】
その結果、本発明における全固体リチウム二次電池Ｃでは、充放電サイクルにともなう放電電気量の変化がほとんど観測されなかったのに対し、比較のために構成した全固体リチウム二次電池Ｄでは、充放電サイクルにともなう放電容量の低下が観測された。
【０１１０】
つぎに、充電器の直流電圧値を４．０５Ｖとした以外は、実施例１と同様の方法で、充電電圧に時間的な変動が生じた際の充放電サイクル挙動を調べた。
【０１１１】
その結果、全固体リチウム二次電池Ｃでは、充放電サイクルにともなう放電容量の低下はほとんど観測されなかったのに対して、全固体リチウム二次電池Ｄでは、初期より放電容量が低く、さらに充放電サイクルにともなう放電容量の低下が観測された。
【０１１２】
以上のように本発明によると、充放電サイクル特性に優れた全固体リチウム二次電池が得られることがわかった。
【０１１３】
（実施例３〜実施例１３）
結晶構造中のリチウムイオンサイトへのリチウムイオンの挿入脱離反応にともなう電位の不連続な変化を示す物質として実施例２で用いたアルミニウムに代えて、（表１）に示す物質を用いた以外は実施例２と同様の方法で、全固体リチウム二次電池を構成し、実施例２と同様に定電流法による充放電サイクル挙動ならびに充電電圧に時間的な変動が生じた際の充放電サイクル挙動を調べた。なお、負極はこれら金属あるいは合金と固体電解質粉末を重量比で５：１に混合したものを用い、（表１）に記載の重量に秤量して用いた。なお、（表１）中には各電池においてリチウムコバルト酸化物への可逆的なリチウムイオンの挿入脱離反応が起こる最大脱離量Ｑ１、各負極へのリチウムイオンの挿入脱離反応に対して負極の電位が不連続に変化するまでのリチウムイオンの挿入量Ｑ２を示した。これらの電池はＱ２がＱ１より、小である構成となっている。
【０１１４】
その結果、充放電サイクルにともなう放電容量の低下はなく、本発明によると充放電サイクル特性に優れた全固体リチウム二次電池が得られることがわかった。
【０１１５】
【表１】

【０１１６】
（実施例１４）
結晶構造中のリチウムイオンサイトへのリチウムイオンの挿入脱離反応にともなう電位の不連続な変化を示す物質として実施例１で用いたインジウムに代えて、鉛−インジウム合金を用いた以外は、実施例１と同様の方法で、全固体リチウム二次電池を構成し、その特性を評価した。以下にその詳細を示す。
【０１１７】
鉛−インジウム合金は、金属鉛と金属インジウムをモル比で１：１に混合したものをアルゴン気流中、８００℃で溶融させることによりＰｂ−Ｉｎの組成のものを得た。
【０１１８】
リチウムイオン伝導性固体電解質、リチウムコバルト酸化物は、実施例１と同様の方法で合成、混合、秤量し、全固体リチウム二次電池の正極とした。
【０１１９】
負極材料としては、固体電解質粉末と、鉛−インジウム合金粉末を重量比で１：５の比率で混合したものを用いた。この負極材料を１００ｍｇ秤量し、全固体リチウム二次電池の負極とした。
【０１２０】
この負極へのリチウムイオンの挿入反応において、負極の電位が不連続に変化するリチウムイオンの挿入量は、
【０１２１】
【化１５】

【０１２２】
の反応に対応する６．９４ｍＡｈ、ならびに
【０１２３】
【化１６】

【０１２４】
の反応に対応する２０．１８ｍＡｈである。
正極材料としては、実施例１で得たＬｉＣｏＯ_２と粉砕した固体電解質を重量比で６：４の比で混合したものを用いた。この正極材料を９１ｍｇ秤量し、実施例１と同様の方法で全固体リチウム二次電池Ｅを構成した。また、正極材料を３０４ｍｇ秤量し、同様に全固体リチウム二次電池Ｆを構成した。
【０１２５】
これらの全固体リチウム二次電池において、リチウムコバルト酸化物への可逆的なリチウムイオンの挿入脱離反応が起こるリチウムイオンの最大脱離量は、（化８）の反応に対応する全固体リチウム二次電池Ｅでは７．５ｍＡｈ、全固体リチウム二次電池Ｆでは２５ｍＡｈであり、各々負極の電位が不連続に変化する（化１５）あるいは（化１６）の反応に対応するリチウムイオンの挿入量に比べて大なる構成となっている。
【０１２６】
このようにして構成した全固体リチウム二次電池を用いて、実施例１と同様に定電流法による充放電サイクル挙動ならびに充電電圧に時間的な変動が生じた際の充放電サイクル挙動を調べた。
【０１２７】
その結果、充放電サイクルにともなう放電容量の低下はなく、本発明によると充放電サイクル特性に優れた全固体リチウム二次電池が得られることがわかった。
【０１２８】
（実施例１５）
結晶構造中のリチウムイオンサイトへのリチウムイオンの挿入脱離反応にともない電位の不連続な変化を示す物質として実施例１で用いたインジウムに代えて、リチウムチタン酸化物を用いた以外は、実施例１と同様の方法で、全固体リチウム二次電池を構成し、その特性を評価した。以下にその詳細を示す。
【０１２９】
最初に、リチウムチタン酸化物を下記の方法で合成した。
出発材料としては、水酸化リチウム（ＬｉＯＨ）と酸化チタン（ＴｉＯ_２）を用いた。まず、水酸化リチウムと酸化チタンが、Ｌｉ：Ｔｉ＝４：５となるよう秤量混合した。この混合物をペレット状に加圧成形し、空気中９００℃で２０時間加熱することで、Ｌｉ_４／３Ｔｉ_５／３Ｏ_４で表されるリチウムチタン酸化物を得た。
【０１３０】
リチウムイオン伝導性固体電解質、リチウムコバルト酸化物は、実施例１と同様の方法で合成、混合、秤量し、全固体リチウム二次電池の正極とした。
【０１３１】
負極材料としては、固体電解質粉末と、上記で得たリチウムチタン酸化物を重量比で２：３の比率で混合したものを用いた。この負極材料を２０９ｍｇ秤量し、全固体リチウム二次電池の負極とした。
【０１３２】
このようにして得た正極、負極を用い、実施例１と同様の方法で全固体リチウム二次電池Ｇを構成した。この全固体リチウム二次電池Ｇにおいて、リチウムコバルト酸化物への可逆的なリチウムイオンの挿入脱離反応が起こる最大脱離量は、実施例１と同様に２４．６ｍＡｈであり、それに対して、リチウムチタン酸化物へのリチウムイオンの挿入脱離反応においてリチウムチタン酸化物の電位が不連続に変化するまでのリチウムイオンの挿入量は、
【０１３３】
【化１７】

【０１３４】
の反応に対応する ２２ｍＡｈである。したがって、この電池は、リチウム遷移金属酸化物の可逆的なリチウムイオンの挿入脱離を起こすリチウムイオンの最大脱離量に対して、リチウムイオンの挿入脱離反応にともなう電位の不連続な変化を示す物質の電位が不連続に変化するまでのリチウムイオンの挿入量が、小である構成となっている。
【０１３５】
つづいて比較のために、負極の重量を５１８ｍｇとした以外は、上記と同様の方法で全固体リチウム二次電池Ｈを構成した。この電池においては、リチウムチタン酸化物の電位が不連続に変化するまでのリチウムイオンの挿入量が４４ｍＡｈであり、リチウム遷移金属酸化物の可逆的なリチウムイオンの挿入脱離を起こすリチウムイオンの最大脱離量に対して、リチウムイオンの挿入脱離反応にともなう電位の不連続な変化を示す物質の電位が不連続に変化するまでのリチウムイオンの挿入量が、大である構成となっている。
【０１３６】
このようにして構成した全固体リチウム二次電池を用いて、実施例１と同様の充放電試験を行った。但し、充電の終止電圧値は、本発明による全固体リチウム二次電池Ｇについては、充電曲線が不連続な変化を生じた電圧を充電の終止電圧とした。それに対して、比較のための全固体リチウム二次電池Ｈについては、２４．６ｍＡｈを充電した際の端子電圧を充電の終止電圧とした。
【０１３７】
その結果、本発明における全固体リチウム二次電池Ｇでは、充放電サイクルにともなう放電電気量の変化がほとんど観測されなかったのに対し、比較のために構成した全固体リチウム二次電池Ｈでは、充放電サイクルにともなう放電容量の低下が観測された。
【０１３８】
つぎに、充電器の直流電圧値を３．２５Ｖとした以外は、実施例１と同様の方法で、充電電圧に時間的な変動が生じた際の充放電サイクル挙動を調べた。
【０１３９】
その結果、全固体リチウム二次電池Ｇでは、充放電サイクルにともなう放電容量の低下はほとんど観測されなかったのに対して、全固体リチウム二次電池Ｈでは、初期より放電容量が低く、さらに充放電サイクルにともなう放電容量の低下が観測された。
【０１４０】
以上のように本発明によると、充放電サイクル特性に優れた全固体リチウム二次電池が得られることがわかった。
【０１４１】
（実施例１６）
結晶構造中のリチウムイオンサイトへのリチウムイオンの挿入脱離反応にともなう電位の不連続な変化を示す物質として実施例１で用いたインジウムに代えて、二硫化チタンを用いた以外は、実施例１と同様の方法で、全固体リチウム二次電池を構成し、その特性を評価した。以下にその詳細を示す。
【０１４２】
二硫化チタン（ＴｉＳ_２）は、硫黄と金属チタンを出発材料としＣＶＤ法により合成した。
【０１４３】
リチウムイオン伝導性固体電解質、リチウムコバルト酸化物は、実施例１と同様の方法で合成、混合、秤量し、全固体リチウム二次電池の正極とした。
【０１４４】
負極材料としては、固体電解質粉末と、上記で得た二硫化チタン酸化物を重量比で２：３の比率で混合したものを用いた。この負極材料を１５３ｍｇ秤量し、全固体リチウム二次電池の負極とした。
【０１４５】
このようにして得た正極、負極を用い、実施例１と同様の方法で全固体リチウム二次電池Ｉを構成した。この全固体リチウム二次電池Ｉにおいて、リチウムコバルト酸化物への可逆的なリチウムイオンの挿入脱離反応が起こる最大脱離量は、実施例１と同様に２４．６ｍＡｈであり、それに対して、二硫化チタンへのリチウムイオンの挿入脱離反応において二硫化チタンの電位が不連続に変化するまでのリチウムイオンの挿入量は、
【０１４６】
【化１８】

【０１４７】
の反応に対応する２２ｍＡｈである。したがって、この電池は、リチウム遷移金属酸化物の可逆的なリチウムイオンの挿入脱離を起こすリチウムイオンの最大脱離量に対して、リチウムイオンの挿入脱離反応にともなう電位の不連続な変化を示す物質の電位が不連続に変化するまでのリチウムイオンの挿入量が、小である構成となっている。
【０１４８】
つづいて比較のために、負極の重量を３０６ｍｇとした以外は、上記と同様の方法で全固体リチウム二次電池Ｊを構成した。この電池においては、リチウムチタン酸化物の電位が不連続に変化するまでのリチウムイオンの挿入量が４４ｍＡｈであり、リチウム遷移金属酸化物の可逆的なリチウムイオンの挿入脱離を起こすリチウムイオンの最大脱離量に対して、リチウムイオンの挿入脱離反応にともなう電位の不連続な変化を示す物質の電位が不連続に変化するまでのリチウムイオンの挿入量が、大である構成となっている。
【０１４９】
このようにして構成した全固体リチウム二次電池を用いて、実施例１と同様の充放電試験を行った。但し、充電の終止電圧値は、本発明による全固体リチウム二次電池Ｉについては、充電曲線が不連続な変化を生じた電圧を充電の終止電圧とした。それに対して、比較のための全固体リチウム二次電池Ｊについては、２４．６ｍＡｈを充電した際の端子電圧を充電の終止電圧とした。
【０１５０】
その結果、本発明における全固体リチウム二次電池Ｉでは、充放電サイクルにともなう放電電気量の変化がほとんど観測されなかったのに対し、比較のために構成した全固体リチウム二次電池Ｊでは、充放電サイクルにともなう放電容量の低下が観測された。
【０１５１】
つぎに、充電器の直流電圧値を２．５Ｖとした以外は、実施例１と同様の方法で、充電電圧に時間的な変動が生じた際の充放電サイクル挙動を調べた。
【０１５２】
その結果、全固体リチウム二次電池Ｉでは、充放電サイクルにともなう放電容量の低下はほとんど観測されなかったのに対して、全固体リチウム二次電池Ｊでは、初期より放電容量が低く、さらに充放電サイクルにともなう放電容量の低下が観測された。
【０１５３】
以上のように本発明によると、充放電サイクル特性に優れた全固体リチウム二次電池が得られることがわかった。
【０１５４】
（実施例１７）
正極活物質として、実施例１で用いたＬｉＣｏＯ_２で表されるリチウムコバルト酸化物に代えて、ＬｉＮｉＯ_２で表されるリチウムニッケル酸化物を用い、全固体リチウム二次電池を構成した。以下にその詳細を示す。
【０１５５】
まず、ＬｉＮｉＯ_２を、酸化ニッケル（ＮｉＯ）と水酸化リチウムを混合し、大気中８００℃で加熱することにより合成した。
【０１５６】
このようにして得たＬｉＮｉＯ_２を粉砕し、実施例１で得た固体電解質と重量比で３：２の比で混合し、正極材料とした。このようにして得た正極材料を３００ｍｇ秤量したものを正極とした以外は、実施例１と同様の方法で全固体リチウム二次電池Ｋを構成した。
【０１５７】
この全固体リチウム二次電池において、リチウムコバルト酸化物への可逆的なリチウムイオンの挿入脱離反応が起こる最大脱離量は、
【０１５８】
【化１９】

【０１５９】
の反応に対応する２４．７ｍＡｈであり、それに対して、インジウムへのリチウムイオンの挿入脱離反応に対してインジウムの電位が不連続に変化するまでのリチウムイオンの挿入量は、実施例１と同様に（化３）の反応に対応する２２．２ｍＡｈである。したがって、この電池は、リチウム遷移金属酸化物の可逆的なリチウムイオンの挿入脱離を起こすリチウムイオンの最大脱離量に対して、リチウムイオンの挿入脱離反応にともない電位の不連続な変化を示す物質の電位が不連続に変化するまでのリチウムイオンの挿入量が、小である構成となっている。
【０１６０】
つづいて比較のために、インジウム箔の重量を１９０ｍｇとした以外は、上記と同様の方法で全固体リチウム二次電池Ｌを構成した。この電池においては、インジウムの電位が不連続に変化するまでのリチウムイオンの挿入量が４４．４ｍＡｈであり、リチウム遷移金属酸化物の可逆的なリチウムイオンの挿入脱離を起こすリチウムイオンの最大脱離量に対して、リチウムイオンの挿入脱離反応にともない電位の不連続な変化を示す物質の電位が不連続に変化するまでのリチウムイオンの挿入量が、大である構成となっている。
【０１６１】
このようにして構成した全固体リチウム二次電池を用いて、実施例１と同様の充放電試験を行った。但し、充電の終止電圧値は、本発明による全固体リチウム二次電池Ｋについては、充電曲線が不連続な変化を生じた電圧を充電の終止電圧とした。それに対して、比較のための全固体リチウム二次電池Ｌについては、２４．６ｍＡｈを充電した際の端子電圧を充電の終止電圧とした。
【０１６２】
その結果、本発明における全固体リチウム二次電池Ｋでは、充放電サイクルにともなう放電電気量の変化がほとんど観測されなかったのに対し、比較のために構成した全固体リチウム二次電池Ｌでは、充放電サイクルにともなう放電容量の低下が観測された。
【０１６３】
つぎに、充電器の直流電圧値を３．５Ｖとした以外は、実施例１と同様の方法で、充電電圧に時間的な変動が生じた際の充放電サイクル挙動を調べた。
【０１６４】
その結果、全固体リチウム二次電池Ｋでは、充放電サイクルにともなう放電容量の低下はほとんど観測されなかったのに対して、全固体リチウム二次電池Ｌでは、初期より放電容量が低く、さらに充放電サイクルにともなう放電容量の低下が観測された。
【０１６５】
以上のように本発明によると、充放電サイクル特性に優れた全固体リチウム二次電池が得られることがわかった。
【０１６６】
（実施例１８）
正極活物質として、実施例１で用いたＬｉＣｏＯ_２で表されるリチウムコバルト酸化物に代えて、ＬｉＭｎ_２Ｏ_４で表されるリチウムマンガン酸化物を用い、全固体リチウム二次電池を構成した。以下にその詳細を示す。
【０１６７】
ＬｉＭｎ_２Ｏ_４は、炭酸リチウム（Ｌｉ_２ＣＯ_３）と酢酸マンガン（Ｍｎ（ＣＨ_３ＣＯＯ）_２）を混合し、大気中７５０℃で加熱することにより合成した。
【０１６８】
このようにして得たＬｉＭｎ_２Ｏ_４を粉砕し、実施例１で得た固体電解質、さらに電子導電材としてアセチレンブラックを重量比で３：１．９：０．１の比で混合し、正極材料とした。このようにして得た正極材料を４３２ｍｇ秤量したものを正極とした以外は、実施例１と同様の方法で全固体リチウム二次電池Ｍを構成した。
【０１６９】
この全固体リチウム二次電池Ｍにおいて、リチウムマンガン酸化物への可逆的なリチウムイオンの挿入脱離反応が起こる最大脱離量は、
【０１７０】
【化２０】

【０１７１】
の反応に対応する２５．０ｍＡｈであり、それに対して、インジウムへのリチウムイオンの挿入脱離反応に対してインジウムの電位が不連続に変化するまでのリチウムイオンの挿入量は、実施例１と同様に（化３）の反応に対応する２２．２ｍＡｈである。したがって、この電池は、リチウム遷移金属酸化物の可逆的なリチウムイオンの挿入脱離を起こすリチウムイオンの最大脱離量に対して、リチウムイオンの挿入脱離反応にともなう電位の不連続な変化を示す物質の電位が不連続に変化するまでのリチウムイオンの挿入量が、小である構成となっている。
【０１７２】
つづいて比較のために、インジウム箔の重量を１９０ｍｇとした以外は、上記と同様の方法で全固体リチウム二次電池Ｎを構成した。この電池においては、インジウムの電位が不連続に変化するまでのリチウムイオンの挿入量が４４．４ｍＡｈであり、リチウム遷移金属酸化物の可逆的なリチウムイオンの挿入脱離を起こすリチウムイオンの最大脱離量に対して、リチウムイオンの挿入脱離反応にともない電位の不連続な変化を示す物質の電位が不連続に変化するまでのリチウムイオンの挿入量が、大である構成となっている。
【０１７３】
このようにして構成した全固体リチウム二次電池を用いて、実施例１と同様の充放電試験を行った。但し、充電の終止電圧値は、本発明による全固体リチウム二次電池Ｍについては、充電曲線が不連続な変化を生じた電圧を充電の終止電圧とした。それに対して、比較のための全固体リチウム二次電池Ｎについては、２４．６ｍＡｈを充電した際の端子電圧を充電の終止電圧とした。
【０１７４】
その結果、本発明における全固体リチウム二次電池Ｍでは、充放電サイクルにともなう放電電気量の変化がほとんど観測されなかったのに対し、比較のために構成した全固体リチウム二次電池Ｎでは、充放電サイクルにともなう放電容量の低下が観測された。
【０１７５】
つぎに、充電器の直流電圧値を３．６５Ｖとした以外は、実施例１と同様の方法で、充電電圧に時間的な変動が生じた際の充放電サイクル挙動を調べた。
【０１７６】
その結果、全固体リチウム二次電池Ｍでは、充放電サイクルにともなう放電容量の低下はほとんど観測されなかったのに対して、全固体リチウム二次電池Ｎでは、初期より放電容量が低く、さらに充放電サイクルにともなう放電容量の低下が観測された。
【０１７７】
以上のように本発明によると、充放電サイクル特性に優れた全固体リチウム二次電池が得られることがわかった。
【０１７８】
（実施例１９）
リチウムイオン伝導性無機固体電解質として、実施例１で得た０．０１Ｌｉ_３ＰＯ_４−０．６３Ｌｉ_２Ｓ−０．３６ＳｉＳ_２に代えて０．０５Ｌｉ_２Ｏ−０．５７Ｌｉ_２Ｓ−０．３８ＳｉＳ_２で表される非晶質固体電解質を用いた以外は、実施例１と同様に、全固体リチウム電池を構成しその特性を評価した。以下に、その詳細を示す。
【０１７９】
硫化リチウムと硫化ケイ素、ならびに酸化リチウムををモル比で５７：３８：５の割合で秤量混合した。この混合物をグラッシーカーボン製坩堝に充填し、窒素ガス気流中で１０００℃で２時間溶融した。該溶融物を実施例１と同様に双ローラーで超急冷することにより、リチウムイオン伝導性固体電解質を得た。
【０１８０】
このようにして得たリチウムイオン伝導性固体電解質を用い、実施例１と同様のインジウム箔量をそれぞれ用いた本発明による全固体リチウム二次電池ならびに比較のための全固体リチウム二次電池を構成し、実施例１と同様の充放電試験を行った。
【０１８１】
その結果、本発明における全固体リチウム二次電池では、充放電サイクルにともなう放電電気量の変化がほとんど観測されなかったのに対し、比較のために構成した全固体リチウム二次電池では、充放電サイクルにともなう放電容量の低下が観測された。
【０１８２】
つぎに、実施例１と同様の方法で、充電電圧に時間的な変動が生じた際の充放電サイクル挙動を調べた。
【０１８３】
その結果、本発明における全固体リチウム二次電池では、充放電サイクルにともなう放電容量の低下はほとんど観測されなかったのに対して、比較のための全固体リチウム二次電池では、初期より放電容量が低く、さらに充放電サイクルにともなう放電容量の低下が観測された。
【０１８４】
以上のように本発明によると、充放電サイクル特性に優れた全固体リチウム二次電池が得られることがわかった。
【０１８５】
（実施例２０）
本実施例においては、実施例１と同様に正極活物質として用いられる、結晶構造中のリチウムイオンサイトへのリチウムイオンの可逆的な電気化学的挿入脱離反応を生じるリチウム遷移金属酸化物としてＬｉＣｏＯ_２で表されるリチウムコバルト酸化物を、結晶構造中のリチウムイオンサイトへのリチウムイオンの挿入脱離反応にともない電位の不連続な変化を示す物質としてインジウムを、リチウムイオン伝導性固体電解質として０．０１Ｌｉ_３ＰＯ_４−０．６３Ｌｉ_２Ｓ−０．３６ＳｉＳ_２で表される非晶質固体電解質を用いて、集合電池を構成し、その特性を評価した。以下にその詳細を示す。
【０１８６】
まず、本実施例における集合電池の断面図を図７に、集合電池を構成する素電池の構成を（表２）に示す。
【０１８７】
【表２】

【０１８８】
図７中、７、８は（表２）に構成を示した素電池（ｉ）ならびに素電池（ｉｉ）である。この２つの素電池をコネクター９により直列に接続し、ステンレス製の電池容器１０に入れ、絶縁性ガスケット１１を介しステンレス製の蓋１２により密封し、集合電池Ｓ１〜Ｓ４を構成した。
【０１８９】
なお、（表２）中には、正極ならびに負極の重量、各素電池においてリチウムコバルト酸化物への可逆的なリチウムイオンの挿入脱離反応が起こる最大脱離量Ｑ１、すなわち（化８）の反応に対応する電気量、インジウムへのリチウムイオンの挿入脱離反応に対してインジウムの電位が不連続に変化するまでのリチウムイオンの挿入量Ｑ２、すなわち（化３）の反応に対応する電気量を併せて示した。
【０１９０】
集合電池Ｓ１においては、素電池（ｉ）、（ｉｉ）ともにリチウム遷移金属酸化物の可逆的なリチウムイオンの挿入脱離を起こすリチウムイオンの最大脱離量Ｑ１に対して、リチウムイオンの挿入脱離反応にともない電位の不連続な変化を示す物質の電位が不連続に変化するまでのリチウムイオンの挿入量Ｑ２が、小である構成の集合電池となっている。また、集合電池Ｓ２においては、２つの素電池のうち容量の小さな素電池（ｉ）がＱ１＞Ｑ２の構成となっており、本発明の条件を満たす集合電池となっている。
【０１９１】
これらの集合電池に対して、集合電池Ｓ３では、容量の小さな素電池（ｉｉ）がＱ１＜Ｑ２の構成となっており、また集合電池Ｓ４では、いずれの素電池もＱ１＜Ｑ２の構成となっており、いずれも本発明の条件を満たさない。
【０１９２】
これらの集合電池を用い、下記の充放電サイクル試験を行った。
これらの電池を２５０μＡの定電流で充電した。なお、電池の充電終了電圧は、
（１）いずれかの素電池の正極中のリチウムコバルト酸化物が、Ｌｉ_０．５ＣｏＯ_２の組成となる反応に対応する電気量が流れた場合、
（２）充電時の充電曲線に不連続な変化が生じた場合、
の条件のうち、いずれか一方が生じた電圧とした。
【０１９３】
また、放電電流も２５０μＡとし、放電終了電圧は４．５Ｖとした。
上記の充放電条件でこれらの集合電池の充放電サイクル試験を行ったところ、集合電池Ｓ１、Ｓ２では、充放電サイクルにともなう充放電挙動の変化は観測されなかったのに対して、集合電池Ｓ３、Ｓ４では、充放電サイクルにともなう充放電容量の顕著な低下が観測された。
【０１９４】
つぎに、以下の方法で、充電電圧に時間的な変動が生じた際の充放電サイクル挙動を調べた。
【０１９５】
まず、充電器としては、上記定電流による充放電サイクル試験において決定された充電終了電圧に相当する電圧に、振幅０．１Ｖ、周波数１ｍＨｚの交流電圧を重畳した電圧を発生する電源を用いた。各々の集合電池を、この充電器で５０時間充電し、その後、２５０μＡの定電流で４．５Ｖまで放電する充放電サイクル試験を行った。
【０１９６】
その結果、集合電池Ｓ１、Ｓ２では、充放電サイクルにともなう放電容量の低下はほとんど観測されなかったのに対して、集合電池Ｓ３、Ｓ４では、初期より放電容量が低く、さらに充放電サイクルにともなう放電容量の低下が観測された。
【０１９７】
以上のように本発明によると、充放電サイクル特性に優れた集合電池が得られることがわかった。
【０１９８】
（実施例２１）
本実施例では、電極活物質の体積変化が充放電サイクル特性に及ぼす影響について調べた。他の実施例では、一体成形した全固体リチウム二次電池ペレットをコイン電池ケース内に封口することで全固体リチウム二次電池を構成していたが、ここではラミネート材の中に全固体リチウム二次電池ペレットを封入した電池の特性を調べた。
【０１９９】
負極活物質としてＬｉ_４／３Ｔｉ_５／３Ｏ_４、正極活物質としてＬｉＣｏＯ_２を用い、実施例１５の全固体リチウム二次電池Ｇと同様の全固体リチウム二次電池ペレットを成形した。成形した全固体リチウム二次電池ペレットの正負極それぞれに集電体として、ステンレス鋼製リードをスポット溶接したステンレス鋼製メッシュを圧着させ電極端子とした。これを、ステンレス箔にポリエチレンシートをラミネートしたフィルムに封入し、全固体リチウム二次電池Ｏとした。
【０２００】
つづいて比較のため、負極活物質としてＡｌ、正極活物質としてＬｉＣｏＯ_２を用い、実施例２の全固体リチウム二次電池Ｃと同様の全固体リチウム二次電池ペレットを成形し、全固体リチウム二次電池Ｏと同様にして全固体リチウム二次電池Ｐを構成した。
【０２０１】
このように構成した全固体リチウム二次電池を用いて、それぞれ実施例１５の全固体リチウム二次電池Ｇ、実施例２の全固体リチウム二次電池Ｃと同様の充放電試験を行った。
【０２０２】
その結果、本発明における全固体リチウム二次電池Ｏは充放電サイクルにともなう放電電気量の変化がほとんど観測されなかったのに対し、比較のため構成した全固体リチウム二次電池Ｐでは、初期の充電容量に対して放電容量が小さく、また充放電サイクルにともなう放電容量の低下が観測された。
【０２０３】
全固体リチウム二次電池Ｐで良好な電池特性が得られなかった原因としては、全固体リチウム二次電池のケースをラミネートフィルムに変更したため、電池ケース内に収納した場合に電池ペレットに加わっていたケースからの圧力が小さなものとなり、活物質の体積変化にともなう電池構成材料間の接合が失われやすくなったためと思われる。
【０２０４】
以上のように本発明によると、充放電サイクル特性に優れた全固体リチウム二次電池が得られることがわかった。
【０２０５】
なお、本発明の実施例においては、結晶構造中のリチウムイオンサイトへのリチウムイオンの挿入脱離反応にともなう電位の不連続な変化を示す物質として、インジウム、アルミニウム、鉛−インジウム合金、リチウムチタン酸化物、二硫化チタンなどを用いた全固体リチウム二次電池についてのみ説明を行ったが、その他の金属あるいは合金、ＭｎＯ_２、ＷＯ_３、ＷＯ_２、Ｖ_２Ｏ_５などの遷移金属酸化物、ＭｏＳ_２、ＮｂＳ_２、Ｖ_２Ｓ_４などの遷移金属硫化物、あるいは複合酸化物などを用いた場合も同様の効果が得られることはいうまでもなく、本発明は、結晶構造中のリチウムイオンサイトへのリチウムイオンの挿入脱離反応にともなう電位の不連続な変化を示す物質としてこれら実施例で説明を行ったものに限定されるものではない。
【０２０６】
また、本発明の実施例においては、正極に用いられる結晶構造中のリチウムイオンサイトへのリチウムイオンの可逆的な電気化学的挿入脱離反応を生じるリチウム遷移金属酸化物として、リチウムコバルト酸化物、リチウムニッケル酸化物、リチウムマンガン酸化物を用いたものについてのみ説明を行ったが、その他リチウム鉄酸化物、リチウムニッケルコバルト酸化物、リチウムニッケルバナジウム酸化物、リチウムマンガンクロム酸化物などの、本発明の実施例では説明を行わなかったリチウム遷移金属酸化物を用いた場合も同様の効果が得られることはいうまでもなく、本発明は、正極に用いられる結晶構造中のリチウムイオンサイトへのリチウムイオンの可逆的な電気化学的挿入脱離反応を生じるリチウム遷移金属酸化物としてこれら実施例で説明を行ったものに限定されるものではない。
【０２０７】
また、本発明の実施例においては、リチウムイオン伝導性無機固体電解質として、０．０１Ｌｉ_３ＰＯ_４−０．６３Ｌｉ_２Ｓ−０．３６ＳｉＳ_２、０．０５Ｌｉ_２Ｏ−０．５７Ｌｉ_２Ｓ−０．３８ＳｉＳ_２のリチウムイオン伝導性非晶質固体電解質について説明を行ったが、これらの固体電解質の各成分比の異なったもの、Ｌｉ_２Ｓ−ＧｅＳ_２、Ｌｉ_２Ｓ−Ｐ_２Ｓ_５、Ｌｉ_２Ｓ−Ｂ_２Ｓ_３など実施例では説明を行わなかった他の硫化物を含むもの、ＬｉＣｌ−Ｌｉ_２Ｓ−ＳｉＳ_２、ＬｉＢｒ−Ｌｉ_２Ｓ−Ｐ_２Ｓ_５など他のハロゲン化リチウムを含むもの、またＬｉＩ−Ｌｉ_２Ｓ−ＳｉＳ_２−Ｐ_２Ｓ_５、ＬｉＩ−Ｌｉ_３ＰＯ_４−Ｌｉ_２Ｓ−ＳｉＳ_２などの擬４元系のもの、あるいは酸化物を主体としたものなど、あるいはＬｉ_３Ｎ， Ｌｉ_１．３Ｓｃ_０．３Ｔｉ_１．７（ＰＯ_４）_３， Ｌｉ_０．２Ｌａ_０．６ＴｉＯ_３などの実施例では説明を行わなかった結晶質のリチウムイオン伝導性無機固体電解質を用いても同様の効果が得られることはいうまでもなく、本発明はリチウムイオン伝導性無機固体電解質として、これら実施例で説明を行ったものに限定されるものではない。
【０２０８】
また、本発明の実施例においては、全固体リチウム二次電池である２つの素電池を同一の電池容器内に直列接続に構成したものについてのみ説明を行ったが、その他、さらに多数の素電池を接続したもの、並列接続の構成を有するもの、複数容器内に構成された全固体リチウム二次電池を直列あるいは並列に接続したもの、あるいは有機溶媒電解質を用いたリチウム二次電池と接続したもの、またニッケル−カドミウム電池などの他の二次電池と接続したものにおいても同様の効果が得られることはいうまでもない。
【０２０９】
【発明の効果】
以上のように本発明によれば、リチウムイオン伝導性固体電解質を主体とする電解質層と、結晶構造中のリチウムイオンサイトへのリチウムイオンの可逆的な電気化学的挿入脱離反応を生じるリチウム遷移金属酸化物を含む正極と、結晶構造中のリチウムイオンサイトへのリチウムイオンの挿入脱離反応にともなう電位の不連続な変化を示す物質を含む負極を有する全固体リチウム二次電池が複数個、電気的に接続されて構成された集合電池であって、その一部に上記全固体リチウム二次電池が複数個、直列に接続された構造を有しており、前記直列に接続された複数個の電池のうち、最小の容量を有する電池を含む１個以上、全数未満の電池が、前記リチウム遷移金属酸化物の可逆的なリチウムイオンの挿入脱離を起こすリチウムイオンの最大脱離量に対して、前記リチウムイオンの挿入脱離反応にともなう電位の不連続な変化を示す物質の電位が不連続に変化するまでのリチウムイオンの挿入量が、等しいか又は小である構成とすることにより、充放電サイクル特性に優れた集合電池を得ることができた。
【０２１１】
また本発明によれば、充電電気量に対して、電圧Ｖ_１から電圧Ｖ_２への不連続な電圧変化を生じるこれらの電池を、電圧Ｖ_２以下で充電することにより、全固体リチウム二次電池の充放電サイクル特性を優れたものとすることができた。
【図面の簡単な説明】
【図１】（ａ）本発明における全固体リチウム二次電池の作動原理を説明した正極および負極の単極電位の変化を示した図
（ｂ）本発明における全固体リチウム二次電池の作動原理を説明した電池の起電力の変化を示した図
【図２】（ａ）比較例の全固体リチウム二次電池の作動原理を説明した正極および負極の単極電位の変化を示した図
（ｂ）比較例の全固体リチウム二次電池の作動原理を説明した電池の起電力の変化を示した図
【図３】本発明の一実施例における全固体リチウム二次電池の断面図
【図４】本発明の一実施例ならびに比較例における全固体リチウム二次電池の充電曲線を示した図
【図５】本発明の一実施例ならびに比較例における全固体リチウム二次電池の充放電サイクル特性を示した図
【図６】本発明の一実施例ならびに比較例における全固体リチウム二次電池の充放電サイクル特性を示した図
【図７】本発明の一実施例における集合電池の断面図
【符号の説明】
１ 正極
２ 固体電解質層
３ 負極
４ 電池容器
５ ガスケット
６ 蓋
７ 素電池（ｉ）
８ 素電池（ｉｉ）
９ コネクター
１０ 電池容器
１１ ガスケット
１２ 蓋[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an all-solid lithium secondary battery using a lithium ion conductive solid electrolyte as an electrolyte. Battery is configured by electrically connecting a plurality of , As well as these charging methods.
[0002]
[Prior art]
In recent years, with the development of portable devices such as personal computers and mobile phones, the demand for batteries as power sources has become extremely large. In particular, lithium batteries have been studied extensively as high energy density batteries because lithium has a small atomic weight and a large ionization energy. It has been used for.
[0003]
On the other hand, with the generalization of lithium batteries, interest in battery safety has recently increased due to an increase in internal energy due to an increase in the amount of active material contained and an increase in the content of organic solvents, which are flammable substances used in electrolytes. It has been a close-up. As a method for ensuring the safety of lithium batteries, it is extremely effective to use non-flammable solid electrolytes instead of organic solvent electrolytes. Is desired.
[0004]
Further, in order to increase the voltage of the battery, for example, lithium cobalt oxide (Li) _1-x CoO ₂ ) Is used. This material is a high temperature stable phase, LiCoO ₂ Is a metastable phase obtained by desorbing lithium ions from. LiCoO ₂ Has a structure in which triangular lattices of oxygen, lithium and cobalt are stacked in the order of O-Li-O-Co-O-Li-O, and the lithium ion is CoO ₂ Exist between the layers. Lithium ions are reversibly inserted and desorbed between the layers, thereby acting as an electrode material for a lithium battery.
[0005]
LiCoO ₂ Lithium ion inside is CoO ₂ CoO due to electrostatic attraction with anionic oxygen atoms in the layer ₂ It plays a role in attracting layers to each other. LiCoO ₂ When lithium ions are desorbed from O, Li in the O-Li-O structure disappears, and ₂ The electrostatic repulsion between the oxygen atoms in the layers increases, and elongation occurs between the layers. As a result, at the time of charging and discharging of the lithium battery, the expansion and contraction of the crystal lattice occur due to the insertion / desorption reaction of lithium ions.
[0006]
The interface between the electrode active material and the electrolyte in an all-solid battery using a solid electrolyte as the electrolyte is a solid / solid interface, and the contact area between the electrode active material and the electrolyte, that is, the electrical It tends to be difficult to enlarge the chemical reaction interface. Furthermore, when a material that undergoes a volume change due to charge and discharge, such as the lithium cobalt oxide described above, is used as the electrode active material, it is difficult to maintain a constant bonding state between the solid electrolyte and such an electrode active material. It is. As a result, during the operation of the battery, the joining state changes constantly, and the change in the joining state also changes the overvoltage of the electrode reaction.
[0007]
Battery charging methods include a constant current charging method and a constant voltage charging method.In the case of the constant current charging method, charging ends when the terminal voltage of the battery reaches a certain value. It is necessary to set the charging voltage of the battery also when using the charging method.
[0008]
[Problems to be solved by the invention]
However, as described above, since the overvoltage of the reaction is constantly changing in the electrodes of the all-solid-state battery, even when the terminal voltage of the battery at the time of charging is kept constant, the electrode at the end of charging is also maintained. The potential is not constant. That is, for example, when the reaction overvoltage is reduced in spite of charging at a constant voltage, the battery is deeply charged.
[0009]
LiCoO ₂ Desorbs lithium ions to form Li _1-x CoO ₂ Has a high equilibrium potential of 4 V or more based on the lithium electrode, but at the same time, instability occurs in the crystal structure due to the repulsive force between oxygen atoms described above. Therefore, in order to stably operate a battery using this material as an electrode active material, it is necessary to keep the amount of lithium ion insertion / desorption within a reversible range. On the other hand, if the amount of lithium ion desorption becomes too large, the crystal structure changes, and the reversible insertion / desorption reaction of lithium ion does not occur. Therefore, in the charge / discharge cycle of an all-solid-state lithium secondary battery using this material as a positive electrode active material, the overvoltage changes as described above, and when the battery is charged deeply, the reversible lithium ions A lithium ion elimination reaction exceeding an excessive insertion / desorption amount occurs, and the lithium ion insertion / elimination reaction between crystal layers does not proceed smoothly. As a result, there is a problem that the battery capacity is reduced with the charge / discharge cycle of the battery and the charge / discharge cycle life of the battery is shortened.
[0010]
Further, the phenomenon that the battery is deeply charged also occurs due to a variation in charging control of the charger or a temporal variation in charging voltage. Therefore, in order to extend the cycle life of the battery, it is necessary to perform precise charge control, and it is difficult to charge using a cheap charger, and there is a problem that the charger becomes expensive. I was
[0011]
As described above, Li as a positive electrode active material _x CoO ₂ Has been described, but as a positive electrode active material for a lithium battery showing an equilibrium potential exceeding 4 V, Li is used. _1-X NiO ₂ , Li _1-X Mn ₂ O ₄ These materials also have a metastable structure and exhibit an equilibrium potential exceeding 4 V. Therefore, even in an all-solid lithium secondary battery using these as a positive electrode active material, Li _1-X CoO ₂ The same problem as in the case of using as a positive electrode active material occurs.
[0012]
In addition to the above problems, a change in volume of the electrode active material due to charge and discharge has a great influence on the cycle characteristics of the all-solid-state battery. The all-solid-state battery is composed of solid particles. When no force acts on the solid particles in the direction of condensing the particles, the solid particles become plastic against displacement such as expansion and contraction. Therefore, in an all-solid-state battery that is not in a pressurized state, voids are generated between the electrode active material and the surrounding solid particles due to expansion and contraction of the electrode active material due to charge and discharge. As a result, there is a possibility that the battery performance may be reduced due to factors such as a reduction in the electrochemical reaction area due to repeated charging and discharging and a reduction in the current collection performance of the electrode active material.
[0013]
An object of the present invention is to solve the above-mentioned problems and to provide an all-solid lithium secondary battery and an assembled battery excellent in charge / discharge cycle characteristics, and a charging method thereof.
[0014]
[Means for Solving the Problems]
The present invention provides a positive electrode including a lithium ion conductive solid electrolyte-based electrolyte layer and a lithium transition metal oxide that causes a reversible electrochemical insertion / desorption reaction of lithium ions to lithium ion sites in a crystal structure. And a plurality of all-solid lithium secondary batteries having a negative electrode containing a substance exhibiting a discontinuous change in potential due to insertion and desorption of lithium ions into and from lithium ion sites in the crystal structure, which are electrically connected. It is a configured battery, having a structure in which a plurality of the all-solid lithium secondary batteries are partially connected in series, and among the plurality of batteries connected in series, , One or more batteries, including the battery with the smallest capacity, The potential of a substance exhibiting a discontinuous change in potential due to the lithium ion insertion / desorption reaction with respect to the maximum amount of lithium ions which cause reversible lithium ion insertion / desorption of the lithium transition metal oxide. Are equal or small until the amount of lithium ions changes discontinuously.
[0015]
In addition, indium, aluminum, lead, bismuth, antimony, gallium, tin, silver, silicon, zinc are substances that exhibit a discontinuous change in potential due to insertion and desorption of lithium ions into and from lithium ion sites in the crystal structure. At least one metal selected from the group consisting of cadmium, arsenic and titanium, an alloy of a metal selected from these groups, or an alloy of lithium and at least one metal selected from these groups is used.
[0016]
In addition, indium is used as a substance that exhibits a discontinuous change in potential due to insertion and desorption of lithium ions into and from lithium ion sites in the crystal structure, and a discontinuous change in potential due to insertion and desorption of lithium ions. The amount of lithium ion insertion until the potential of the substance showing
[0017]
Embedded image

[0018]
An all-solid-state lithium secondary battery is configured as an amount corresponding to the reaction formula (1).
In addition, aluminum is used as a substance that exhibits a discontinuous change in potential due to the insertion and desorption of lithium ions to and from lithium ion sites in the crystal structure, and a discontinuous change in potential due to the insertion and desorption of lithium ions. The amount of lithium ion insertion until the potential of the substance showing
[0019]
Embedded image

[0020]
An all-solid-state lithium secondary battery is configured as an amount corresponding to the reaction formula (1).
[0021]
Further, as a substance showing a discontinuous change in potential due to insertion and desorption of lithium ions into and from lithium ion sites, transition metal oxides, lithium transition metal oxides, transition metal sulfides, and lithium transition metal sulfides Use one selected from the group.
[0022]
Furthermore, at least one element selected from the group consisting of titanium, manganese, tungsten, and vanadium is used as the transition metal element of the transition metal oxide or lithium transition metal oxide.
[0023]
Further, as the transition metal element of the transition metal sulfide or the lithium transition metal sulfide, at least one element selected from the group consisting of titanium, molybdenum, niobium, tungsten, and vanadium is used.
[0024]
At least one element selected from the group consisting of cobalt, nickel, manganese, and iron is used as the transition metal element of the lithium transition metal oxide used for the positive electrode.
[0025]
As the lithium ion conductive solid electrolyte, an inorganic compound is used.
[0026]
Further, the inorganic compound is an amorphous compound mainly composed of sulfide.
Further, as the inorganic compound, a compound synthesized from a substance mainly composed of lithium sulfide and silicon sulfide is used.
[0028]
Furthermore, a plurality of unit cells are housed in the same battery container having airtightness to constitute an assembled battery.
[0029]
Also, the present invention provides a method in which the voltage V ₁ From the voltage V ₂ These cells, which produce a discontinuous voltage change to ₂ Charge below.
[0030]
In addition, an amorphous lithium ion conductive solid electrolyte mainly composed of sulfide is used as an electrolyte, and Li is used as an electrode active material. _4/3 Ti _5/3 O ₄ Is used.
[0031]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be described using an all-solid lithium secondary battery using a lithium cobalt oxide as a positive electrode active material and an indium-lithium alloy as a negative electrode as an example.
[0032]
Lithium ion conductive solid electrolyte and lithium cobalt oxide (LiCoO ₂ If an all-solid lithium secondary battery is formed using indium as the negative electrode, a reaction represented by the chemical formula (5) occurs on the positive electrode and a reaction represented by the chemical formula (6) on the negative electrode during charging. That is, in the positive electrode, a desorption reaction of lithium ions from the lithium cobalt oxide occurs, while in the negative electrode, an indium-lithium alloy is formed by lithium ions desorbed from the positive electrode.
[0033]
Embedded image

[0034]
Embedded image

[0035]
Here, the range in which the reversible insertion-desorption reaction to the lithium cobalt oxide occurs is in the range of x ≦ 0.5, and the potential of the indium-lithium alloy is about 0.6 V near x = 1.0. From about 0.4V to about 0.4V.
[0036]
FIG. 1A shows a positive electrode and a negative electrode in charging of an all-solid lithium secondary battery including a lithium cobalt oxide having a molar ratio of 2.1 times as much as indium as a negative electrode active material as a positive electrode active material. FIG. 4 is a diagram showing a change in the unipolar potential of FIG. FIG. 1B shows the change in the electromotive force of the battery. The maximum amount of lithium ion that causes reversible lithium ion insertion and desorption of lithium cobalt oxide is Li _0.5 CoO ₂ The amount of lithium ions inserted until the potential of indium changes discontinuously is the amount of the composition of In-Li. Therefore, in this all-solid-state lithium secondary battery, the maximum amount of lithium ion that causes reversible insertion and desorption of lithium cobalt oxide from lithium cobalt oxide until the potential of indium changes discontinuously changes. The configuration is such that the insertion amounts of lithium ions are almost equal and slightly smaller.
[0037]
On the other hand, the single-pole potential of the positive electrode and the negative electrode during charging of an all-solid lithium secondary battery constituted by using lithium cobalt oxide at a molar ratio of 1.4 times the indium serving as the negative electrode as a positive electrode active material. 2 (a) and FIG. 2 (b) show changes in the electromotive force of the battery. In this all-solid-state lithium secondary battery, the lithium ion until the potential of indium changes discontinuously with respect to the maximum desorption amount of lithium ion that causes reversible insertion and desorption of lithium ion of lithium cobalt oxide. Is configured to have a large insertion amount.
[0038]
In the all-solid-state lithium secondary battery having these configurations, the lithium cobalt oxide is Li _0.5 CoO ₂ Since the battery capacity is the maximum until the composition becomes, the battery needs to be fully charged up to the point A in FIG. 1 or FIG. It suffices to charge the battery with a voltage (Vcell) corresponding to the difference (Epos-Eneg). However, in practice, the battery at the time of charging has a DC polarization component due to internal resistance and an overvoltage (η) due to electrode reaction and the like. Is not charged until. Therefore, in order to charge the battery sufficiently, it is necessary to charge at a voltage (Vend) higher than Vcell.
[0039]
However, the value of η is not constant and tends to decrease as the battery is charged as follows.
[0040]
For example, when charging is performed at a constant voltage, η decreases at the end of charging due to the decay of the charging current.
[0041]
In particular, when a lithium ion conductive solid electrolyte is used as the electrolyte, η decreases as the battery is charged by the following mechanism. In the positive electrode at the time of charging, as described above, the interlayer distance of the lithium cobalt oxide increases, and the volume of the positive electrode expands. On the other hand, also in the negative electrode, when metal indium becomes an indium-lithium alloy, volume expansion occurs. As a result, pressure is applied to the battery element, the bonding state between the solid particles constituting the battery is improved, and the volume of the void existing in the battery element is reduced. As a result, the internal resistance of the battery decreases, and η also decreases.
[0042]
Here, the case where η becomes extremely small, that is, the case where η → 0, is continued.
[0043]
When η → 0 at the end of charging when the charging voltage is set to Vend, the difference between the positive electrode potential and the negative electrode potential, that is, the value of Epos−Eng approaches Vend. As a result, in FIG. 2, the battery is to be charged up to point A, but the battery is deeply charged up to point B. In this case, lithium ions are converted from lithium cobalt oxide up to Li _0.4 CoO ₂ To the composition of As a result, the reversibility of the lithium ion insertion / desorption reaction in the lithium cobalt oxide is impaired, and the charge / discharge cycle characteristics are reduced.
[0044]
On the other hand, in the case of the configuration of FIG. 1 according to the present invention, if the value of Vend-Vcell is smaller than the discontinuous change amount (ΔV) of the potential of indium, even if η → 0, the battery can be used. Only the middle point B is charged, and even when charged at the voltage of Vend, the amount of lithium ions desorbed from the lithium cobalt oxide remains within a range that causes reversible insertion and desorption.
[0045]
Further, in the case of such a battery configuration, when the accuracy of the charger is low and the charging voltage fluctuates, if the fluctuation is equal to or less than ΔV, the lithium ion Is limited to a range in which reversible insertion / desorption occurs, and the battery characteristics do not deteriorate.
[0046]
By the above action, an electrolyte layer mainly composed of a lithium ion conductive solid electrolyte and a lithium transition metal oxide which causes a reversible electrochemical insertion and desorption reaction of lithium ions to lithium ion sites in a crystal structure are included. A positive electrode, in an all-solid lithium secondary battery having a negative electrode containing a substance that shows a discontinuous change in potential due to insertion and desorption of lithium ions into lithium ion sites in the crystal structure, the lithium transition metal oxide With respect to the maximum amount of lithium ions that cause reversible insertion and removal of lithium ions, until the potential of a substance showing a discontinuous change in potential due to the lithium ion insertion / desorption reaction changes discontinuously. To obtain an all-solid-state lithium secondary battery with excellent charge-discharge cycle characteristics by making the amount of lithium ions inserted equal or smaller It can be.
[0047]
Further, in the battery having the above-described configuration, as shown in FIG. ₁ To V ₂ Indicates a discontinuous change to. Therefore, in this battery, the charging voltage is V ₂ It is desirable to make the following.
[0048]
In addition, the phenomenon in which the charge / discharge cycle characteristics are impaired by the deep charging described above also occurs in a lithium secondary battery using an organic electrolyte as an electrolyte, but for the following reasons, an all-solid lithium secondary battery using a solid electrolyte as an electrolyte is used. Appears prominently in batteries.
[0049]
The mechanism by which the charge / discharge cycle characteristics are impaired by deep charging is, as already described, LiCoO 2 ₂ When lithium ions are desorbed from O, Li in the O-Li-O structure disappears, and ₂ This is due to an increase in electrostatic repulsion between oxygen atoms in the layer and an increase in instability in the crystal structure. However, in an electrolyte using an organic solvent, CoO ₂ Since organic solvent molecules are also inserted between the layers at the same time, CoO ₂ Even when lithium ions are desorbed from the interlayer, the organic solvent molecules are present between the layers. This organic solvent molecule and CoO ₂ Electrostatic interaction also occurs between oxygen atoms in the layer and a quadrupole moment occurs in the organic solvent molecule. As a result, the electrostatic repulsion between oxygen atoms is reduced, and the instability of the crystal structure is reduced. On the other hand, in an all-solid lithium secondary battery, since such an interaction does not occur, the instability of the crystal is greater than that in the case of using an organic electrolyte. Easy to be.
[0050]
For the above reasons, the effect of the present invention is remarkable in an all solid lithium secondary battery using a lithium ion conductive solid electrolyte as an electrolyte.
[0051]
In addition, lithium ion conductive solid electrolytes are roughly classified into those composed of an inorganic compound and those mainly composed of an organic polymer compound. Those mainly composed of an organic polymer compound contain an organic solvent as a plasticizer, and the organic solvent molecules contribute to reducing the instability of the crystal. Therefore, the effect of the present invention is particularly remarkable in an all solid lithium secondary battery using an inorganic compound as the lithium ion conductive solid electrolyte.
[0052]
Further, by using a lithium ion conductive solid electrolyte made of an inorganic compound having high ion conductivity, the operating current characteristics of the all solid lithium secondary battery can be improved. Therefore, as a lithium ion conductive solid electrolyte made of an inorganic compound, an amorphous material mainly composed of a sulfide is particularly preferably used as having a high ion conductivity. These are obtained by melting and quenching a mixture of sulfide having glass-forming ability and lithium sulfide, which is a mobile ion, in a glass structure at a high temperature. Among them, lithium sulfide, silicon sulfide Those synthesized from substances mainly composed of are particularly preferable because the vapor pressure of each component at the time of synthesis is low, and there is no need to seal the starting material to suppress the evaporation of the components, which is suitable for mass synthesis. .
[0053]
In the above description, indium or indium-lithium alloy was used as an example of a substance showing a discontinuous change in potential due to insertion and desorption of lithium ions into and from lithium ion sites in the crystal structure. The following substances may be mentioned as substances exhibiting such actions.
[0054]
First, the metal element will be described.
Generally, the reaction of inserting a lithium ion into a lithium ion site in a metal represented by the element symbol Me is represented by the following formula (7). When Me is aluminum, the potential becomes 0.35 V near x = 1.0 From 0 to around 0V. Thus, the same effect can be obtained when aluminum is used instead of indium described above.
[0055]
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[0056]
As other Me, x = 2.0 for lead, x = 2.0 for bismuth, x = 2.5 for antimony, and x = 1.0 for gallium. , Tin also has a discontinuous potential change at x = 1.0. In addition, silver, silicon, zinc, cadmium, arsenic, titanium, and the like also cause a discontinuous change in potential due to the insertion reaction of lithium ions, and thus the same effect can be obtained when these substances are used.
[0057]
In addition, in the case of a substance showing a plurality of discontinuous changes in potential due to the insertion / desorption reaction of lithium ions, the amount of lithium ions inserted until the potential changes discontinuously according to claim 1 is: Any insertion amount that causes a discontinuous change in potential may be used.
[0058]
For example, when Me is tin in (Chem. 7), discontinuity is caused even when x = 2.3, 2.5, 2.6, 3.5, 4.4, etc. in addition to x = 1.0. This causes a change in potential. Therefore, LiCoO is used as the positive electrode active material. ₂ The structure of an all-solid lithium secondary battery using tin as the negative electrode active material is such that the amount of lithium released corresponding to the occurrence of the reaction represented by the formula In 9), by adopting a configuration in which the amount of lithium inserted corresponding to the reaction when x = 1.0 occurs is equal or smaller, not only the same effect can be obtained, but also the negative electrode has )), The same applies when the amount of lithium inserted corresponding to the reaction when X = 2.3, 2.5, 2.6, 3.5, 4.4 is equal or smaller. The effect of can be obtained.
[0059]
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[0060]
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[0061]
In addition, in the case of an alloy composed of a plurality of metal elements selected from indium, aluminum, lead, bismuth, antimony, gallium, tin, silver, silicon, zinc, cadmium, arsenic, and titanium, lithium ion insertion is generally performed. A plurality of discontinuous changes in potential are shown with the elimination reaction. Similarly, when such a material is used as the negative electrode active material, the amount of lithium ions inserted until the potential changes discontinuously according to claim 1 is an insertion that causes a discontinuous change in any potential. An amount may be used.
[0062]
Further, in place of the above pure metal or alloy, an alloy of these metal or alloy and lithium may be used.
[0063]
However, for example, as described above, LiCoO ₂ , In-Li instead of metal indium in an all-solid lithium secondary battery using indium as the negative electrode active material _0.1 Taking the case of using an indium-lithium alloy represented by the following formula as an example, the amount corresponding to y represented by (Formula 10) instead of (Formula 6), that is, the amount corresponding to y = 0.9, This is the amount of lithium ions inserted until the potential changes discontinuously.
[0064]
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[0065]
Among metals or alloys of metal and lithium, which show a discontinuous change in potential due to insertion and desorption of lithium ions into lithium ion sites in the crystal structure as described above, when indium is used as a metal element, The diffusion rate of lithium ions in the inside becomes large, and an all-solid-state lithium secondary battery operable with a large current can be constituted. Therefore, indium or an indium-lithium alloy is preferably used as a metal or an alloy of metal and lithium that exhibits a discontinuous change in potential due to insertion and desorption of lithium ions into and from lithium ion sites in the crystal structure.
[0066]
Also, among metals or alloys of metal and lithium, which show a discontinuous change in potential due to insertion and desorption of lithium ions into lithium ion sites in the crystal structure, when aluminum is used as the metal element, aluminum is light. Since the element is an element, an all-solid lithium secondary battery having a high energy density can be formed. Therefore, aluminum or an aluminum-lithium alloy is preferably used as a metal or an alloy of metal and lithium which exhibits a discontinuous change in potential due to insertion and desorption of lithium ions into and from lithium ion sites in the crystal structure.
[0067]
Next, substances showing a discontinuous change in potential due to insertion and desorption of lithium ions into and from lithium ion sites in the crystal structure include transition metal oxides, lithium transition metal oxides, transition metal sulfides, and lithium transition metals. The metal sulfide will be described.
[0068]
Among these substances, for example, lithium titanium oxide having a spinel structure (Li _4/3 Ti _5/3 O ₄ ) Causes an electrochemical lithium ion insertion reaction represented by Chemical Formula 11 in a lithium ion conductive electrolyte, and its potential changes discontinuously at x = 1.0. Therefore, instead of the indium or the like, Li _4/3 Ti _5/3 O ₄ The same effect can be obtained when using. Similarly, as lithium titanium oxide, LiTi ₂ O ₄ In (Formula 12), a discontinuous change in the potential occurs at x = 1.0.
[0069]
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[0070]
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[0071]
As a transition metal oxide or a lithium transition metal oxide that causes a discontinuous potential change due to such a lithium ion insertion reaction, TiO. ₂ , MnO ₂ , WO ₃ , WO ₂ , V ₂ O ₅ Or Li _x TiO ₂ , Li _x MnO ₂ , Li _x WO ₃ , Li _x WO ₂ , Li _x V ₂ O ₅ And the like, and when these are used, the same effect can be obtained.
[0072]
As the transition metal sulfide or lithium transition metal sulfide, TiS ₂ , MoS ₂ , NbS ₂ , WS ₂ , FeMo ₆ S ₈ , V ₂ S ₅ Or Li _x TiS ₂ , Li _x MoS ₂ , Li _x NbS ₂ , Li _x WS ₂ , Li _x Mo ₆ S ₈ , Li _x V ₂ S ₅ And the like show a discontinuous potential change due to a lithium ion insertion reaction, and can be used similarly.
[0073]
In addition, the above-described problem relating to the cycle characteristics of the battery due to structural instability due to the elimination of lithium ions from the lithium transition metal compound becomes a particularly serious problem in an assembled battery in which batteries are stacked in series. On the other hand, by using the all-solid lithium secondary battery described above as a unit cell having at least the minimum capacity among a plurality of unit cells connected in series in the unit cell, Since the voltage changes discontinuously, it is easy to maintain the unit cell at a charge depth that exhibits excellent cycle performance. Therefore, the present invention relates to Thigh Demonstrate the effect of.
[0074]
Further, since the above all-solid lithium secondary battery has no common electrolyte effect, it is possible to store a plurality of unit cells in the same airtight battery container. The structure can be simple, and an inexpensive assembled battery can be formed.
[0075]
Also, in the above-described assembled battery, the terminal voltage shows a discontinuous change with respect to the charged amount of electricity, and the voltage V ₁ From the voltage V ₂ In a battery pack that produces a discontinuous voltage change to ₂ It is preferable to charge the battery below.
[0076]
In this specification, the potential does not mean only the equilibrium potential, but may be a mixed potential in a two-phase mixed state.
[0077]
Further, the discontinuous change in the potential indicates that, for example, in (Formula 6), a sudden change in the potential occurs with respect to the change in x. For example, In-Li in (Chem. 6) _x Let the potential of E be E, which means that the rate of change of E with respect to the change of x (dE / dx) shows a peak. It does not indicate only.
[0078]
Further, as the above-mentioned rapid potential change, the following changes are preferable.
Lithium transition metal oxide that causes reversible electrochemical insertion and desorption of lithium ions into lithium ion sites in the crystal structure used as a positive electrode active material in an all-solid lithium secondary battery, and is used as a negative electrode When a substance showing a discontinuous change in potential due to the insertion / desorption reaction of lithium ions causes an electrochemical reaction represented by the following chemical formula (13), the positive electrode potential (E _P (X)) change rate dE _P (X) / dx and the negative electrode potential (dE _n (X)) change rate dE _n Composition (x = x) showing a discontinuous potential change between (x) / dx ₀ In at least dE _n (X ₀ ) / Dx> dE _P (X ₀ ) / Dx, and more preferably dE _n (X ₀ ) / Dx> 5V.
[0079]
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[0080]
On the other hand, dE _n If (x) / dx is smaller than the value satisfying these relationships, the battery is likely to be in a deeply charged state due to a change in overvoltage or a change in charging voltage, and an all-solid lithium secondary battery having excellent charge / discharge characteristics. It becomes difficult to obtain a battery.
[0081]
Note that Ox in the chemical formula (13) is In-Li _X , Al-Li _X In the case of an alloy or the like, in the case of a matrix metal such as In or Al, or in the case of a transition metal oxide or a transition metal sulfide, one of the transition metal atoms whose formal valence described in (Chem. This is a composition formula including That is, specifically, Ti ⁴⁺ S ₂ , Li [Li _1/3 Ti _2/3 ] Ti ⁴⁺ O ₄ In these composition formulas, the valence is written and expressed only for the transition metal element whose formal charge changes.
[0082]
He also pointed out that the volume change of the electrode active material has a large effect on the cycle characteristics of the solid-state battery. For example, Al and Li ⁺ In the reaction (chemical formula) in which an aluminum-lithium alloy is formed by an electrochemical reaction with Al and Al-Li, the crystal structures of both Al and Al-Li are cubic, and their lattice constants are 4.049A and 6.373A, respectively. As a result, Al occludes Li and becomes an Al-Li alloy, whereby the volume of the electrode active material expands about 3.9 times.
[0083]
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[0084]
While there is an electrode active material that produces such a large volume change, Li ⁺ Li having a spinel structure is used as an active material whose volume change accompanying the electrochemical reaction with _4/3 Ti _5/3 O ₄ Have been reported. Li _4/3 Ti _5/3 O ₄ When a solid-state battery is formed by using as the electrode active material, the effect of the volume change as described above hardly occurs, so that it is expected that a solid-state battery having more excellent cycle characteristics can be formed.
[0085]
This Li _4/3 Ti _5/3 O ₄ A battery using Li0.33La0.56TiO3 as a solid electrolyte has been proposed as a solid battery using as an electrode active material (T. Brousse, P. Eragnaud, R. Marchand and DM Schleich, Extended Abstracts of 8th International Meeting on Lithium Batteries, 324 (1996) Nagoya, hereinafter referred to as Reference 1.) However, Li _0.33 La _0.56 TiO ₃ Is a solid electrolyte containing a transition metal atom, and thus has a problem that it is easily electrochemically reduced. For example, the solid electrolyte is reduced during charging, and FIG. As shown in FIG. 1, there is a problem that the amount of discharged electricity is smaller than the amount of charged electricity.
[0086]
Thus, Li _4/3 Ti _5/3 O ₄ However, there is a problem that the charge / discharge efficiency is poor and the battery characteristics become unstable depending on the selection of the solid electrolyte even when is used as the electrode active material.
[0087]
On the other hand, the amorphous lithium ion conductive solid electrolyte mainly composed of sulfide is Li _4/3 Ti _5/3 O ₄ Is electrochemically stable even in the vicinity of the reduction potential of Li. _4/3 Ti _5/3 O ₄ Shows high charge and discharge efficiency, and as a result, it is possible to construct a solid state battery having excellent cycle characteristics.
[0088]
【Example】
Hereinafter, the present invention will be described in detail with reference to Examples, but the following operations were all performed in a dry argon atmosphere.
[0089]
(Example 1)
LiCoO is used as a positive electrode active material as a lithium transition metal oxide that causes a reversible electrochemical insertion / desorption reaction of lithium ions into lithium ion sites in a crystal structure. ₂ Is used as a substance showing a discontinuous change in potential due to insertion and desorption reactions of lithium ions into and from lithium ion sites in the crystal structure, and 0.1 as a lithium ion conductive solid electrolyte. 01Li ₃ PO ₄ -0.63Li ₂ S-0.36SiS ₂ An all-solid lithium secondary battery was constructed using the amorphous solid electrolyte represented by the following formula, and the characteristics thereof were evaluated. The details are shown below.
[0090]
First, a lithium ion conductive solid electrolyte was synthesized by the following method.
Lithium sulfide, silicon sulfide, and lithium phosphate were weighed and mixed at a molar ratio of 63: 36: 1. The mixture was filled in a glassy carbon crucible and melted at 1000 ° C. for 2 hours in an argon gas stream. Thereafter, the melt was quenched with a twin roller to obtain a lithium ion conductive solid electrolyte.
[0091]
Next, LiCoO ₂ Is cobalt oxide (Co ₃ O ₄ ) And lithium carbonate (Li ₂ CO ₃ ) Was weighed and mixed so that the ratio of Co / Li = 1 was obtained, and the mixture was baked at 900 ° C. in the atmosphere to synthesize.
[0092]
Using the lithium ion conductive solid electrolyte, the positive electrode active material, and the metal indium foil thus obtained, an all-solid lithium secondary battery was formed by the following method.
[0093]
FIG. 3 shows a cross-sectional view of the all-solid lithium secondary battery A in the present embodiment. In FIG. 3, reference numeral 1 denotes a positive electrode, and the LiCoO ₂ A positive electrode material obtained by mixing the solid electrolyte pulverized at a weight ratio of 6: 4 and weighing 300 mg was used. Reference numeral 2 denotes a lithium ion conductive solid electrolyte layer, which was integrally molded with a 95 mg metal indium foil 3 serving as a negative electrode under pressure. The integrally formed pellet was placed in a stainless steel battery container 4 and sealed with a stainless steel lid 6 via an insulating gasket 5.
[0094]
In this all-solid lithium secondary battery A, the maximum desorption amount at which a reversible insertion and desorption reaction of lithium ions into lithium cobalt oxide occurs is 24.6 mAh corresponding to the reaction of (Chem. 8). On the other hand, the insertion amount of lithium ions until the potential of indium changes discontinuously with respect to the insertion / desorption reaction of lithium ions into / from indium is 22.2 mAh corresponding to the reaction of (Chem. 3). Therefore, this battery shows a discontinuous change in potential due to the lithium ion insertion / desorption reaction with respect to the maximum lithium ion desorption amount that causes reversible lithium ion insertion / desorption of the lithium transition metal oxide. The configuration is such that the amount of lithium ions inserted until the potential of the indicated substance changes discontinuously is small.
[0095]
Subsequently, for comparison, an all-solid lithium secondary battery B was constructed in the same manner as described above except that the weight of the indium foil was changed to 190 mg. In this battery, the amount of lithium ions inserted before the potential of indium changes discontinuously is 44.4 mAh, and the maximum desorption of lithium ions causing reversible insertion and desorption of lithium ions of the lithium transition metal oxide. The amount of lithium ions inserted until the potential of a substance exhibiting a discontinuous change in potential due to the lithium ion insertion / desorption reaction changes discontinuously with respect to the separation amount is large.
[0096]
The all-solid lithium secondary battery thus configured was charged at a current value of 500 μA. FIG. 4 shows a first charging curve of these batteries. However, for the all-solid-state lithium secondary battery A, 3.85 V at which the charging curve changed discontinuously was set as the charging end voltage. On the other hand, for the all-solid-state lithium secondary battery B, the terminal voltage at the time of charging 24.6 mAh was taken as the charging end voltage.
[0097]
The end voltage of charging was determined in this way, and the end voltage of discharging was set to 2.0 V, and a charge / discharge cycle test was performed with a charge / discharge current of 500 μA. FIG. 5 shows the amount of electricity discharged in each cycle obtained as a result.
[0098]
In the all-solid lithium secondary battery A according to the present invention, almost no change in the amount of discharge electricity was observed with the charge / discharge cycle, whereas in the all solid lithium secondary battery B configured for comparison, the charge / discharge cycle As a result, a decrease in the discharge capacity was observed.
[0099]
Next, the charging / discharging cycle behavior when the charging voltage fluctuated with time was examined by the following method.
[0100]
First, as a charger, a power supply that generates a voltage in which an AC voltage having an amplitude of 0.1 V and a frequency of 1 mHz was superimposed on a DC voltage of 3.75 V was used. Each all-solid lithium secondary battery was charged with this charger for 50 hours, and then subjected to a charge / discharge cycle test in which the battery was discharged at a constant current of 500 μA to 2.0 V, and the discharge capacity in each cycle was recorded. FIG. 6 shows the result.
[0101]
In the all-solid lithium secondary battery A, almost no decrease in the discharge capacity due to the charge-discharge cycle was observed, whereas in the all-solid lithium secondary battery B, the discharge capacity was lower than the initial state, Accordingly, a decrease in discharge capacity was observed.
[0102]
As described above, according to the present invention, it has been found that an all-solid lithium secondary battery having excellent charge / discharge cycle characteristics can be obtained.
[0103]
(Example 2)
Example 1 was the same as Example 1 except that aluminum was used instead of indium used in Example 1 as a substance showing a discontinuous change in potential due to insertion and desorption of lithium ions into and from lithium ion sites in the crystal structure. An all-solid lithium secondary battery was constructed in the same manner, and its characteristics were evaluated. The details are shown below.
[0104]
The lithium ion conductive solid electrolyte and lithium cobalt oxide were synthesized, mixed and weighed in the same manner as in Example 1 to obtain a positive electrode of an all-solid lithium secondary battery.
[0105]
As the negative electrode material, a mixture of a solid electrolyte powder and a metal aluminum powder at a weight ratio of 1: 5 was used. 25 mg of this negative electrode material was weighed to obtain a negative electrode of an all solid lithium secondary battery.
[0106]
Using the positive electrode and the negative electrode thus obtained, an all-solid lithium secondary battery C was constructed in the same manner as in Example 1. In this all-solid lithium secondary battery, the maximum desorption amount at which a reversible insertion and desorption reaction of lithium ions into lithium cobalt oxide occurs is 24.6 mAh as in Example 1, whereas the maximum desorption amount is The amount of lithium ions inserted until the potential of aluminum changes discontinuously in the insertion / desorption reaction of lithium ions into the metal is 20.7 mAh corresponding to the reaction of Chemical Formula 4. Therefore, this battery shows a discontinuous change in potential due to the lithium ion insertion / desorption reaction with respect to the maximum lithium ion desorption amount that causes reversible lithium ion insertion / desorption of the lithium transition metal oxide. The configuration is such that the amount of lithium ions inserted until the potential of the indicated substance changes discontinuously is small.
[0107]
Subsequently, for comparison, an all-solid lithium secondary battery D was constructed in the same manner as described above except that the weight of the negative electrode was changed to 50 mg. In this battery, the amount of lithium ions inserted before the potential of aluminum changes discontinuously is 41.4 mAh, and the maximum lithium ion desorption that causes reversible insertion and desorption of lithium ions in the lithium transition metal oxide. The amount of lithium ions inserted until the potential of a substance exhibiting a discontinuous change in potential due to the lithium ion insertion / desorption reaction changes discontinuously with respect to the separation amount is large.
[0108]
The same charge / discharge test as in Example 1 was performed using the all-solid lithium secondary battery configured as described above. However, for the all-solid lithium secondary battery C according to the present invention, the voltage at which the charging curve has a discontinuous change is defined as the end-of-charge voltage, whereas for the all-solid lithium secondary battery D for comparison, , 24.6 mAh was used as the terminal voltage of charging.
[0109]
As a result, in the all-solid lithium secondary battery C of the present invention, almost no change in the amount of discharge electricity was observed with the charge / discharge cycle, whereas in the all-solid lithium secondary battery D configured for comparison, A decrease in the discharge capacity due to the charge / discharge cycle was observed.
[0110]
Next, the charging / discharging cycle behavior when the charging voltage fluctuated with time was examined in the same manner as in Example 1, except that the DC voltage value of the charger was 4.05 V.
[0111]
As a result, in the all-solid lithium secondary battery C, a decrease in the discharge capacity due to the charge / discharge cycle was hardly observed, whereas in the all-solid lithium secondary battery D, the discharge capacity was lower than the initial state, and the charge was further reduced. A decrease in discharge capacity with the discharge cycle was observed.
[0112]
As described above, according to the present invention, it has been found that an all-solid lithium secondary battery having excellent charge / discharge cycle characteristics can be obtained.
[0113]
(Examples 3 to 13)
Except for using the substances shown in (Table 1) in place of aluminum used in Example 2 as a substance showing a discontinuous change in potential due to insertion and desorption of lithium ions into and from lithium ion sites in the crystal structure In the same manner as in Example 2, a solid-state lithium secondary battery was constructed, and similarly to Example 2, the charge / discharge cycle behavior by the constant current method and the charge / discharge cycle when the charge voltage fluctuated over time. The behavior was examined. The negative electrode used was a mixture of these metals or alloys and the solid electrolyte powder at a weight ratio of 5: 1, and was weighed to the weight shown in Table 1 and used. In Table 1, the maximum desorption amount Q1 at which reversible insertion and desorption of lithium ions into lithium cobalt oxide occurs in each battery, and the maximum desorption amount of lithium ions at each negative electrode, The amount Q2 of lithium ion insertion until the potential of the negative electrode changes discontinuously is shown. These batteries are configured such that Q2 is smaller than Q1.
[0114]
As a result, it was found that there was no decrease in the discharge capacity due to the charge / discharge cycle, and that an all-solid lithium secondary battery having excellent charge / discharge cycle characteristics was obtained according to the present invention.
[0115]
[Table 1]

[0116]
(Example 14)
A lead-indium alloy was used in place of indium used in Example 1 as a substance showing a discontinuous change in potential due to insertion and desorption of lithium ions into and from lithium ion sites in the crystal structure. An all-solid lithium secondary battery was constructed in the same manner as in Example 1, and its characteristics were evaluated. The details are shown below.
[0117]
The lead-indium alloy was obtained by melting a mixture of metal lead and metal indium at a molar ratio of 1: 1 at 800 ° C. in an argon stream to obtain a Pb—In composition.
[0118]
The lithium ion conductive solid electrolyte and lithium cobalt oxide were synthesized, mixed and weighed in the same manner as in Example 1 to obtain a positive electrode of an all-solid lithium secondary battery.
[0119]
As the negative electrode material, a mixture of a solid electrolyte powder and a lead-indium alloy powder at a weight ratio of 1: 5 was used. 100 mg of this negative electrode material was weighed to obtain a negative electrode of an all-solid lithium secondary battery.
[0120]
In the lithium ion insertion reaction into the negative electrode, the amount of lithium ion insertion at which the potential of the negative electrode changes discontinuously is:
[0121]
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[0122]
6.94 mAh corresponding to the reaction of
[0123]
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[0124]
20.18 mAh corresponding to the reaction of
As the positive electrode material, LiCoO 2 obtained in Example 1 was used. ₂ And a solid electrolyte pulverized at a weight ratio of 6: 4. 91 mg of this positive electrode material was weighed, and an all-solid lithium secondary battery E was constructed in the same manner as in Example 1. Further, 304 mg of the positive electrode material was weighed, and an all solid lithium secondary battery F was similarly formed.
[0125]
In these all-solid-state lithium secondary batteries, the maximum amount of lithium ion that undergoes a reversible insertion / desorption reaction of lithium ion into lithium-cobalt oxide is determined by the all-solid-state lithium secondary battery corresponding to the reaction of formula (8). The rechargeable battery E has a current of 7.5 mAh, and the all-solid lithium secondary battery F has a current of 25 mAh. The amount of lithium ion insertion corresponding to the reaction (Chem. 15) or (Chem. 16) in which the potential of the negative electrode changes discontinuously, respectively The configuration is larger than that.
[0126]
Using the thus configured all-solid lithium secondary battery, the charge / discharge cycle behavior by the constant current method and the charge / discharge cycle behavior when the charge voltage fluctuated with time were examined in the same manner as in Example 1. .
[0127]
As a result, it was found that there was no decrease in the discharge capacity due to the charge / discharge cycle, and that an all-solid lithium secondary battery having excellent charge / discharge cycle characteristics was obtained according to the present invention.
[0128]
(Example 15)
The procedure was repeated except that lithium titanium oxide was used instead of indium used in Example 1 as a substance showing a discontinuous change in potential due to insertion and desorption of lithium ions into and from lithium ion sites in the crystal structure. An all-solid lithium secondary battery was constructed in the same manner as in Example 1, and its characteristics were evaluated. The details are shown below.
[0129]
First, a lithium titanium oxide was synthesized by the following method.
Starting materials include lithium hydroxide (LiOH) and titanium oxide (TiO2). ₂ ) Was used. First, lithium hydroxide and titanium oxide were weighed and mixed so that Li: Ti = 4: 5. This mixture was pressed into a pellet and heated in air at 900 ° C. for 20 hours to obtain Li _4/3 Ti _5/3 O ₄ Was obtained.
[0130]
The lithium ion conductive solid electrolyte and lithium cobalt oxide were synthesized, mixed and weighed in the same manner as in Example 1 to obtain a positive electrode of an all-solid lithium secondary battery.
[0131]
As the negative electrode material, a mixture of the solid electrolyte powder and the lithium titanium oxide obtained above in a weight ratio of 2: 3 was used. 209 mg of this negative electrode material was weighed to obtain a negative electrode of an all-solid lithium secondary battery.
[0132]
Using the positive electrode and the negative electrode thus obtained, an all-solid lithium secondary battery G was constructed in the same manner as in Example 1. In this all-solid-state lithium secondary battery G, the maximum desorption amount at which reversible insertion and desorption of lithium ions into lithium cobalt oxide occurs is 24.6 mAh as in Example 1, whereas The amount of lithium ions inserted until the potential of the lithium titanium oxide changes discontinuously in the insertion / desorption reaction of lithium ions into lithium titanium oxide is as follows:
[0133]
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[0134]
22 mAh corresponding to the reaction of Therefore, this battery shows a discontinuous change in potential due to the lithium ion insertion / desorption reaction with respect to the maximum lithium ion desorption amount that causes reversible lithium ion insertion / desorption of the lithium transition metal oxide. The configuration is such that the amount of lithium ions inserted until the potential of the indicated substance changes discontinuously is small.
[0135]
Subsequently, for comparison, an all-solid lithium secondary battery H was configured in the same manner as described above except that the weight of the negative electrode was changed to 518 mg. In this battery, the insertion amount of lithium ions until the potential of the lithium titanium oxide changes discontinuously is 44 mAh, and the maximum amount of lithium ions that cause reversible insertion and desorption of lithium ions in the lithium transition metal oxide is obtained. With respect to the amount of desorption, the amount of lithium ion insertion until the potential of a substance showing a discontinuous change in potential due to the insertion / desorption reaction of lithium ions changes discontinuously is large. .
[0136]
The same charge / discharge test as in Example 1 was performed using the all-solid lithium secondary battery configured as described above. However, for the all-solid lithium secondary battery G according to the present invention, the voltage at which the charging curve changed discontinuously was taken as the charging end voltage. On the other hand, for the all-solid lithium secondary battery H for comparison, the terminal voltage at the time of charging 24.6 mAh was taken as the charging end voltage.
[0137]
As a result, in the all-solid-state lithium secondary battery G of the present invention, almost no change in the amount of discharge electricity due to the charge / discharge cycle was observed, whereas in the all-solid-state lithium secondary battery H configured for comparison, A decrease in the discharge capacity due to the charge / discharge cycle was observed.
[0138]
Next, the charging / discharging cycle behavior when the charging voltage fluctuated with time was examined in the same manner as in Example 1 except that the DC voltage value of the charger was 3.25 V.
[0139]
As a result, in the all-solid lithium secondary battery G, a decrease in the discharge capacity due to the charge / discharge cycle was hardly observed, whereas in the all-solid lithium secondary battery H, the discharge capacity was lower than the initial one, and A decrease in discharge capacity with the discharge cycle was observed.
[0140]
As described above, according to the present invention, it has been found that an all-solid lithium secondary battery having excellent charge / discharge cycle characteristics can be obtained.
[0141]
(Example 16)
Example 1 was repeated except that titanium disulfide was used in place of indium used in Example 1 as a substance showing a discontinuous change in potential due to insertion and desorption of lithium ions into lithium ion sites in the crystal structure. An all-solid lithium secondary battery was constructed in the same manner as in Example 1, and its characteristics were evaluated. The details are shown below.
[0142]
Titanium disulfide (TiS ₂ ) Was synthesized by a CVD method using sulfur and metallic titanium as starting materials.
[0143]
The lithium ion conductive solid electrolyte and lithium cobalt oxide were synthesized, mixed and weighed in the same manner as in Example 1 to obtain a positive electrode of an all-solid lithium secondary battery.
[0144]
As the negative electrode material, a mixture of the solid electrolyte powder and the titanium disulfide oxide obtained above in a weight ratio of 2: 3 was used. 153 mg of this negative electrode material was weighed to obtain a negative electrode of an all-solid lithium secondary battery.
[0145]
Using the positive electrode and the negative electrode thus obtained, an all-solid lithium secondary battery I was constructed in the same manner as in Example 1. In this all-solid lithium secondary battery I, the maximum desorption amount at which a reversible insertion and desorption reaction of lithium ions into lithium cobalt oxide occurs is 24.6 mAh as in Example 1, whereas Insertion amount of lithium ion until the potential of titanium disulfide changes discontinuously in the insertion / desorption reaction of lithium ion into titanium disulfide,
[0146]
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[0147]
22 mAh corresponding to the reaction of Therefore, this battery shows a discontinuous change in potential due to the lithium ion insertion / desorption reaction with respect to the maximum lithium ion desorption amount that causes reversible lithium ion insertion / desorption of the lithium transition metal oxide. The configuration is such that the amount of lithium ions inserted until the potential of the indicated substance changes discontinuously is small.
[0148]
Subsequently, for comparison, an all-solid lithium secondary battery J was configured in the same manner as described above except that the weight of the negative electrode was 306 mg. In this battery, the insertion amount of lithium ions until the potential of the lithium titanium oxide changes discontinuously is 44 mAh, and the maximum amount of lithium ions that cause reversible insertion and desorption of lithium ions in the lithium transition metal oxide is obtained. With respect to the amount of desorption, the amount of lithium ion insertion until the potential of a substance showing a discontinuous change in potential due to the insertion / desorption reaction of lithium ions changes discontinuously is large. .
[0149]
The same charge / discharge test as in Example 1 was performed using the all-solid lithium secondary battery configured as described above. However, for the all-solid lithium secondary battery I according to the present invention, the voltage at which the charging curve caused a discontinuous change was defined as the charging end voltage. On the other hand, for the all-solid lithium secondary battery J for comparison, the terminal voltage at the time of charging 24.6 mAh was taken as the charging end voltage.
[0150]
As a result, in the all-solid-state lithium secondary battery I of the present invention, almost no change in the amount of discharge electricity due to the charge / discharge cycle was observed, whereas in the all-solid-state lithium secondary battery J configured for comparison, A decrease in the discharge capacity due to the charge / discharge cycle was observed.
[0151]
Next, the charging / discharging cycle behavior when the charging voltage fluctuated with time was examined in the same manner as in Example 1 except that the DC voltage value of the charger was set to 2.5 V.
[0152]
As a result, in the all-solid lithium secondary battery I, almost no decrease in the discharge capacity due to the charge / discharge cycle was observed, whereas in the all-solid lithium secondary battery J, the discharge capacity was lower than the initial period, and A decrease in discharge capacity with the discharge cycle was observed.
[0153]
As described above, according to the present invention, it has been found that an all-solid lithium secondary battery having excellent charge / discharge cycle characteristics can be obtained.
[0154]
(Example 17)
LiCoO used in Example 1 as a positive electrode active material ₂ In place of the lithium cobalt oxide represented by ₂ An all solid lithium secondary battery was constructed using the lithium nickel oxide represented by The details are shown below.
[0155]
First, LiNiO ₂ Was synthesized by mixing nickel oxide (NiO) and lithium hydroxide and heating at 800 ° C. in the air.
[0156]
LiNiO thus obtained ₂ Was ground and mixed with the solid electrolyte obtained in Example 1 at a weight ratio of 3: 2 to obtain a positive electrode material. An all-solid-state lithium secondary battery K was constructed in the same manner as in Example 1, except that 300 mg of the positive electrode material thus obtained was weighed to obtain a positive electrode.
[0157]
In this all-solid lithium secondary battery, the maximum desorption amount at which reversible insertion and desorption of lithium ions into lithium cobalt oxide occurs is as follows:
[0158]
Embedded image

[0159]
24.7 mAh corresponding to the reaction of Example 1. On the other hand, the insertion amount of lithium ions until the potential of indium changes discontinuously with respect to the insertion / desorption reaction of lithium ions into indium is the same as in Example 1. Similarly, it is 22.2 mAh corresponding to the reaction of (Chem. 3). Therefore, this battery shows a discontinuous change in potential due to the lithium ion insertion / desorption reaction with respect to the maximum lithium ion desorption amount that causes reversible lithium ion insertion / desorption of the lithium transition metal oxide. The configuration is such that the amount of lithium ions inserted until the potential of the indicated substance changes discontinuously is small.
[0160]
Subsequently, for comparison, an all-solid lithium secondary battery L was constructed in the same manner as described above except that the weight of the indium foil was changed to 190 mg. In this battery, the amount of lithium ions inserted before the potential of indium changes discontinuously is 44.4 mAh, and the maximum desorption of lithium ions causing reversible insertion and desorption of lithium ions of the lithium transition metal oxide. The amount of lithium ions inserted until the potential of a substance exhibiting a discontinuous change in potential due to the lithium ion insertion / desorption reaction changes discontinuously with respect to the separation amount is large.
[0161]
The same charge / discharge test as in Example 1 was performed using the all-solid lithium secondary battery configured as described above. However, for the all-solid lithium secondary battery K according to the present invention, the voltage at which the charging curve caused a discontinuous change was defined as the charging end voltage. On the other hand, for the all-solid-state lithium secondary battery L for comparison, the terminal voltage when 24.6 mAh was charged was taken as the charge termination voltage.
[0162]
As a result, in the all-solid-state lithium secondary battery K of the present invention, almost no change in the amount of discharge electricity due to the charge / discharge cycle was observed, whereas in the all-solid-state lithium secondary battery L configured for comparison, A decrease in the discharge capacity due to the charge / discharge cycle was observed.
[0163]
Next, the charging / discharging cycle behavior when the charging voltage fluctuated with time was examined in the same manner as in Example 1 except that the DC voltage value of the charger was 3.5 V.
[0164]
As a result, in the all-solid lithium secondary battery K, a decrease in the discharge capacity due to the charge / discharge cycle was hardly observed, whereas in the all-solid lithium secondary battery L, the discharge capacity was lower than in the initial stage, and the charge was further reduced. A decrease in discharge capacity with the discharge cycle was observed.
[0165]
As described above, according to the present invention, it has been found that an all-solid lithium secondary battery having excellent charge / discharge cycle characteristics can be obtained.
[0166]
(Example 18)
LiCoO used in Example 1 as a positive electrode active material ₂ Instead of the lithium cobalt oxide represented by ₂ O ₄ An all-solid lithium secondary battery was constructed using the lithium manganese oxide represented by The details are shown below.
[0167]
LiMn ₂ O ₄ Is lithium carbonate (Li ₂ CO ₃ ) And manganese acetate (Mn (CH ₃ COO) ₂ ) Was mixed and heated at 750 ° C. in the atmosphere to synthesize.
[0168]
LiMn thus obtained ₂ O ₄ Was ground, and the solid electrolyte obtained in Example 1 and acetylene black as an electronic conductive material were mixed at a weight ratio of 3: 1.9: 0.1 to obtain a positive electrode material. An all-solid-state lithium secondary battery M was constructed in the same manner as in Example 1, except that 432 mg of the positive electrode material thus obtained was weighed and used as the positive electrode.
[0169]
In this all-solid-state lithium secondary battery M, the maximum desorption amount at which a reversible insertion and desorption reaction of lithium ions into lithium manganese oxide occurs is as follows:
[0170]
Embedded image

[0171]
25.0 mAh, which corresponds to the reaction of Example 1. On the other hand, the amount of lithium ions inserted until the potential of indium changes discontinuously with respect to the insertion and desorption reactions of lithium ions into indium is the same as in Example 1. Similarly, it is 22.2 mAh corresponding to the reaction of (Chem. 3). Therefore, this battery shows a discontinuous change in potential due to the lithium ion insertion / desorption reaction with respect to the maximum lithium ion desorption amount that causes reversible lithium ion insertion / desorption of the lithium transition metal oxide. The configuration is such that the amount of lithium ions inserted until the potential of the indicated substance changes discontinuously is small.
[0172]
Subsequently, for comparison, an all-solid lithium secondary battery N was configured in the same manner as described above except that the weight of the indium foil was changed to 190 mg. In this battery, the amount of lithium ions inserted before the potential of indium changes discontinuously is 44.4 mAh, and the maximum desorption of lithium ions causing reversible insertion and desorption of lithium ions of the lithium transition metal oxide. The amount of lithium ions inserted until the potential of a substance exhibiting a discontinuous change in potential due to the lithium ion insertion / desorption reaction changes discontinuously with respect to the separation amount is large.
[0173]
The same charge / discharge test as in Example 1 was performed using the all-solid lithium secondary battery configured as described above. However, for the all-solid lithium secondary battery M according to the present invention, the voltage at which the charging curve caused a discontinuous change was defined as the charging end voltage. On the other hand, for the all-solid-state lithium secondary battery N for comparison, the terminal voltage when 24.6 mAh was charged was used as the charging end voltage.
[0174]
As a result, in the all-solid-state lithium secondary battery M of the present invention, a change in the amount of discharge electricity due to the charge / discharge cycle was hardly observed, whereas in the all-solid-state lithium secondary battery N configured for comparison, A decrease in the discharge capacity due to the charge / discharge cycle was observed.
[0175]
Next, the charging / discharging cycle behavior when the charging voltage fluctuated with time was examined in the same manner as in Example 1 except that the DC voltage value of the charger was changed to 3.65 V.
[0176]
As a result, in the all-solid lithium secondary battery M, a decrease in the discharge capacity due to the charge / discharge cycle was hardly observed, whereas in the all-solid lithium secondary battery N, the discharge capacity was lower than the initial state, and the charge was further reduced. A decrease in discharge capacity with the discharge cycle was observed.
[0177]
As described above, according to the present invention, it has been found that an all-solid lithium secondary battery having excellent charge / discharge cycle characteristics can be obtained.
[0178]
(Example 19)
As the lithium ion conductive inorganic solid electrolyte, 0.01Li obtained in Example 1 was used. ₃ PO ₄ -0.63Li ₂ S-0.36SiS ₂ Instead of 0.05Li ₂ O-0.57Li ₂ S-0.38SiS ₂ All solid-state lithium batteries were constructed and their characteristics were evaluated in the same manner as in Example 1, except that the amorphous solid electrolyte represented by the following formula was used. The details are described below.
[0179]
Lithium sulfide, silicon sulfide, and lithium oxide were weighed and mixed in a molar ratio of 57: 38: 5. The mixture was filled in a glassy carbon crucible and melted at 1000 ° C. for 2 hours in a nitrogen gas stream. The melt was ultra-quenched with twin rollers in the same manner as in Example 1 to obtain a lithium ion conductive solid electrolyte.
[0180]
Using the lithium ion conductive solid electrolyte thus obtained, an all-solid lithium secondary battery according to the present invention using the same amount of indium foil as in Example 1 and an all-solid lithium secondary battery for comparison were constructed. Then, the same charge / discharge test as in Example 1 was performed.
[0181]
As a result, in the all-solid lithium secondary battery of the present invention, almost no change in the amount of discharge electricity was observed with the charge / discharge cycle, whereas in the all-solid lithium secondary battery configured for comparison, A decrease in the discharge capacity with the cycle was observed.
[0182]
Next, in the same manner as in Example 1, the charge / discharge cycle behavior when the charging voltage fluctuated over time was examined.
[0183]
As a result, in the all-solid lithium secondary battery of the present invention, almost no decrease in the discharge capacity due to the charge / discharge cycle was observed, whereas in the all-solid lithium secondary battery for comparison, the discharge capacity was increased from the beginning. , And a decrease in discharge capacity with charge / discharge cycles was observed.
[0184]
As described above, according to the present invention, it has been found that an all-solid lithium secondary battery having excellent charge / discharge cycle characteristics can be obtained.
[0185]
(Example 20)
In this embodiment, LiCoO 2 is used as the positive electrode active material, as in the first embodiment, as a lithium transition metal oxide that causes a reversible electrochemical insertion / desorption reaction of lithium ions into lithium ion sites in the crystal structure. ₂ Is used as a substance which shows a discontinuous change in potential due to insertion and desorption of lithium ions into and from lithium ion sites in the crystal structure, and 0.1 as a lithium ion conductive solid electrolyte. 01Li ₃ PO ₄ -0.63Li ₂ S-0.36SiS ₂ The assembled battery was constructed using the amorphous solid electrolyte represented by the following formula, and its characteristics were evaluated. The details are shown below.
[0186]
First, FIG. 7 shows a cross-sectional view of the assembled battery in this example, and (Table 2) shows the configuration of the unit cells constituting the assembled battery.
[0187]
[Table 2]

[0188]
7, reference numerals 7 and 8 denote a unit cell (i) and a unit cell (ii) whose configuration is shown in (Table 2). The two unit cells were connected in series by a connector 9, placed in a battery case 10 made of stainless steel, and sealed with a lid 12 made of stainless steel via an insulating gasket 11, thereby forming assembled batteries S1 to S4.
[0189]
In Table 2, the weights of the positive electrode and the negative electrode, the maximum desorption amount Q1 at which the reversible insertion / removal reaction of lithium ions into lithium cobalt oxide occurs in each unit cell, that is, (Formula 8) The amount of electricity corresponding to the reaction, the amount of lithium ion insertion Q2 until the potential of indium changes discontinuously with respect to the insertion / desorption of lithium ion into / from the indium, that is, the amount of electricity corresponding to the reaction of (Chem. 3) Are also shown.
[0190]
In the assembled battery S1, in each of the unit cells (i) and (ii), the maximum amount of lithium ions Q1 causing reversible insertion / desorption of lithium ions of the lithium transition metal oxide is larger than the maximum amount of lithium ions Q1. A configuration in which the insertion amount Q2 of lithium ions until the potential of a substance showing a discontinuous change in potential due to the separation reaction changes discontinuously is small. of It is a collective battery. In the battery pack S2, Is Among the two unit cells, the unit cell (i) having a small capacity has a configuration of Q1> Q2, and is an assembled cell satisfying the conditions of the present invention.
[0191]
With respect to these assembled batteries, in the assembled battery S3, the unit cells (ii) having a small capacity have a configuration of Q1 <Q2, and in the assembled battery S4, all of the unit cells have a configuration of Q1 <Q2. None of them satisfy the conditions of the present invention.
[0192]
The following charge / discharge cycle test was performed using these assembled batteries.
These batteries were charged at a constant current of 250 μA. Note that the charge end voltage of the battery is
(1) Lithium cobalt oxide in the positive electrode of any of the unit cells is Li _0.5 CoO ₂ When the amount of electricity corresponding to the reaction that results in the composition of
(2) When a discontinuous change occurs in the charging curve during charging,
The voltage at which any one of the conditions was generated.
[0193]
Also, the discharge current was set to 250 μA, and the discharge end voltage was set to 4.5V.
When a charge / discharge cycle test of these assembled batteries was performed under the above charge / discharge conditions, no change in the charge / discharge behavior due to the charge / discharge cycle was observed in the assembled batteries S1 and S2, whereas the assembled battery S3 , S4, a remarkable decrease in the charge / discharge capacity accompanying the charge / discharge cycle was observed.
[0194]
Next, the charging / discharging cycle behavior when the charging voltage fluctuated with time was examined by the following method.
[0195]
First, as the charger, a power supply that generates a voltage in which an AC voltage having an amplitude of 0.1 V and a frequency of 1 mHz was superimposed on a voltage corresponding to the charge end voltage determined in the charge / discharge cycle test using the constant current described above was used. Each of the assembled batteries was charged with this charger for 50 hours, and then subjected to a charge / discharge cycle test in which the battery was discharged to 4.5 V at a constant current of 250 μA.
[0196]
As a result, in the assembled batteries S1 and S2, almost no decrease in the discharge capacity due to the charge / discharge cycle was observed, whereas in the assembled batteries S3 and S4, the discharge capacity was lower than the initial state, and furthermore, the discharge capacity was further increased. A decrease in discharge capacity was observed.
[0197]
As described above, according to the present invention, it was found that an assembled battery having excellent charge / discharge cycle characteristics was obtained.
[0198]
(Example 21)
In this example, the effect of a change in the volume of the electrode active material on the charge / discharge cycle characteristics was examined. In other embodiments, the all-solid lithium secondary battery was formed by sealing the integrally formed all-solid lithium secondary battery pellet in a coin battery case. The characteristics of the battery in which the secondary battery pellet was sealed were examined.
[0199]
Li as negative electrode active material _4/3 Ti _5/3 O ₄ , LiCoO as a positive electrode active material ₂ Was used to form an all-solid lithium secondary battery pellet similar to the all-solid lithium secondary battery G of Example 15. As a current collector, a stainless steel mesh obtained by spot welding a stainless steel lead was pressure-bonded to each of the positive and negative electrodes of the molded all-solid lithium secondary battery pellet to form electrode terminals. This was sealed in a film in which a polyethylene sheet was laminated on a stainless steel foil, to obtain an all-solid lithium secondary battery O.
[0200]
Subsequently, for comparison, Al was used as the negative electrode active material, and LiCoO was used as the positive electrode active material. ₂ Was used to form an all-solid lithium secondary battery pellet similar to the all-solid lithium secondary battery C of Example 2, and an all-solid lithium secondary battery P was constructed in the same manner as the all-solid lithium secondary battery O.
[0201]
Using the thus configured all-solid lithium secondary battery, the same charge / discharge test as the all-solid lithium secondary battery G of Example 15 and the all-solid lithium secondary battery C of Example 2 was performed.
[0202]
As a result, in the all-solid-state lithium secondary battery O of the present invention, a change in the amount of discharge electricity due to the charge / discharge cycle was hardly observed, whereas in the all-solid-state lithium secondary battery P configured for comparison, the initial It was observed that the discharge capacity was smaller than the charge capacity, and that the discharge capacity decreased with the charge / discharge cycle.
[0203]
The reason why good battery characteristics could not be obtained with the all-solid lithium secondary battery P was that the case of the all-solid lithium secondary battery was changed to a laminated film, so that it was added to the battery pellet when stored in the battery case. This is probably because the pressure from the case became small, and the connection between the battery constituent materials due to the change in volume of the active material was easily lost.
[0204]
As described above, according to the present invention, it has been found that an all-solid lithium secondary battery having excellent charge / discharge cycle characteristics can be obtained.
[0205]
In the examples of the present invention, indium, aluminum, lead-indium alloy, lithium titanium, and the like are used as substances that show a discontinuous change in potential due to insertion / desorption of lithium ions into / from lithium ion sites in the crystal structure. Although only an all-solid lithium secondary battery using oxides, titanium disulfide, etc. has been described, other metals or alloys, MnO 2 ₂ , WO ₃ , WO ₂ , V ₂ O ₅ Transition metal oxides such as MoS ₂ , NbS ₂ , V ₂ S ₄ Needless to say, the same effect can be obtained when a transition metal sulfide such as a transition metal sulfide or a composite oxide is used, and the present invention relates to the insertion / desorption reaction of lithium ions into lithium ion sites in the crystal structure. However, the substance showing a discontinuous change in potential with the above is not limited to those described in these examples.
[0206]
Further, in an embodiment of the present invention, lithium cobalt oxide as a lithium transition metal oxide that causes a reversible electrochemical insertion / desorption reaction of lithium ions to lithium ion sites in a crystal structure used for a positive electrode, Although only those using lithium nickel oxide and lithium manganese oxide have been described, other lithium iron oxide, lithium nickel cobalt oxide, lithium nickel vanadium oxide, lithium manganese chromium oxide, etc. Needless to say, the same effect can be obtained even when a lithium transition metal oxide, which has not been described in Examples, is used. As a lithium transition metal oxide causing a reversible electrochemical insertion-desorption reaction of It is not limited to those been described in the Examples.
[0207]
In the embodiment of the present invention, as the lithium ion conductive inorganic solid electrolyte, 0.01Li ₃ PO ₄ -0.63Li ₂ S-0.36SiS ₂ , 0.05Li ₂ O-0.57Li ₂ S-0.38SiS ₂ The lithium ion conductive amorphous solid electrolytes described above were described, but those having different component ratios of these solid electrolytes, Li ₂ S-GeS ₂ , Li ₂ SP ₂ S ₅ , Li ₂ SB ₂ S ₃ Examples including other sulfides not described in Examples, such as LiCl-Li ₂ S-SiS ₂ , LiBr-Li ₂ SP ₂ S ₅ Including other lithium halides, such as LiI-Li ₂ S-SiS ₂ -P ₂ S ₅ , LiI-Li ₃ PO ₄ −Li ₂ S-SiS ₂ Such as pseudo-quaternary, oxide-based, or Li ₃ N, Li _1.3 Sc _0.3 Ti _1.7 (PO ₄ ) ₃ , Li _0.2 La _0.6 TiO ₃ Needless to say, the same effect can be obtained by using a crystalline lithium ion conductive inorganic solid electrolyte which was not described in the examples such as the present invention. The invention is not limited to those described in the embodiments.
[0208]
Further, in the embodiments of the present invention, only the case where two unit cells, which are all solid-state lithium secondary batteries, are connected in series in the same battery container has been described. Connected, connected in parallel, connected in series or in parallel with all solid lithium secondary batteries configured in multiple containers, or connected to a lithium secondary battery using an organic solvent electrolyte Needless to say, the same effect can be obtained in a battery connected to another secondary battery such as a nickel-cadmium battery.
[0209]
【The invention's effect】
As described above, according to the present invention, an electrolyte layer mainly composed of a lithium ion conductive solid electrolyte and a lithium transition which causes a reversible electrochemical insertion / desorption reaction of lithium ions to / from lithium ion sites in a crystal structure. A plurality of all-solid lithium secondary batteries having a positive electrode containing a metal oxide and a negative electrode containing a substance showing a discontinuous change in potential due to insertion and desorption of lithium ions into lithium ion sites in the crystal structure, An assembled battery that is configured to be electrically connected, and has a structure in which a plurality of the all-solid lithium secondary batteries are partially connected in series, and the plurality is connected in series. Out of batteries , One or more batteries, including the battery with the smallest capacity, With respect to the maximum desorption amount of lithium ions causing reversible insertion and desorption of lithium ions of the lithium transition metal oxide, Said A charge / discharge cycle is performed by adopting a configuration in which the amount of lithium ion insertion until the potential of a substance exhibiting a discontinuous change in potential due to the insertion / desorption reaction of lithium ion changes discontinuously is equal or small. A collective battery having excellent characteristics was obtained.
[0211]
Further, according to the present invention, the voltage V ₁ From the voltage V ₂ These cells, which produce a discontinuous voltage change to ₂ By charging below, the charge / discharge cycle characteristics of the all-solid lithium secondary battery could be improved.
[Brief description of the drawings]
FIG. 1 (a) is a diagram illustrating a change in the single-electrode potential of a positive electrode and a negative electrode illustrating the operation principle of an all-solid lithium secondary battery according to the present invention.
(B) A diagram showing a change in the electromotive force of the battery for explaining the operation principle of the all-solid-state lithium secondary battery in the present invention.
FIG. 2 (a) is a diagram illustrating a change in single-electrode potential of a positive electrode and a negative electrode illustrating the operation principle of an all-solid-state lithium secondary battery of a comparative example.
(B) A diagram showing a change in electromotive force of a battery explaining the operation principle of the all-solid lithium secondary battery of the comparative example.
FIG. 3 is a cross-sectional view of an all-solid lithium secondary battery according to one embodiment of the present invention.
FIG. 4 is a diagram showing a charging curve of an all-solid-state lithium secondary battery in one example and a comparative example of the present invention.
FIG. 5 is a diagram showing charge / discharge cycle characteristics of an all-solid lithium secondary battery in one example and a comparative example of the present invention.
FIG. 6 is a diagram showing charge / discharge cycle characteristics of an all-solid-state lithium secondary battery in one example and a comparative example of the present invention.
FIG. 7 is a sectional view of an assembled battery according to an embodiment of the present invention.
[Explanation of symbols]
1 positive electrode
2 Solid electrolyte layer
3 Negative electrode
4 Battery case
5 Gasket
6 Lid
7. Cell (i)
8. Unit cell (ii)
9 Connector
10 Battery case
11 Gasket
12 lid

Claims (14)

An electrolyte layer mainly composed of a lithium ion conductive solid electrolyte, a positive electrode containing a lithium transition metal oxide that causes a reversible electrochemical insertion and desorption reaction of lithium ions into lithium ion sites in the crystal structure, and a crystal structure Composed of a plurality of all-solid-state lithium secondary batteries that have a negative electrode containing a substance that exhibits a discontinuous change in potential due to insertion and removal of lithium ions into and from lithium ion sites in the battery a battery a plurality of the all-solid lithium secondary battery in a part, has a connection structure in series, among a plurality of batteries connected in the series, the capacitance of the minimum 1 or more, including a battery having a battery of less than total number, the maximum amount of released lithium ions causing deintercalation of reversible lithium ion of the lithium transition metal oxide, said lithium Insertion amount of lithium ions to the potential of a substance that shows a discontinuous change in potential due to intercalation and deintercalation reactions Ion changes discontinuously, assembled battery is a battery which is equal to or smaller. Indium, aluminum, lead, bismuth, antimony, gallium, tin, silver, silicon, zinc, cadmium are substances that exhibit a discontinuous change in potential due to insertion and desorption of lithium ions into and from lithium ion sites in the crystal structure. , Arsenic, at least one metal selected from the group of titanium, an alloy of a metal selected from these groups, or an alloy of lithium and at least one metal selected from these groups. Item 7. The assembled battery according to Item 1. Indium is a substance that exhibits a discontinuous change in potential due to insertion and desorption of lithium ions into and from lithium ion sites in the crystal structure, and exhibits a discontinuous change in potential due to insertion and desorption of lithium ions. The amount of lithium ions inserted until the potential of the substance changes discontinuously,

2. The assembled battery according to claim 1, wherein the amount corresponds to the reaction formula: Aluminum is a substance that exhibits a discontinuous change in potential due to insertion and desorption of lithium ions into and from lithium ion sites in the crystal structure, and exhibits a discontinuous change in potential due to insertion and desorption of lithium ions The amount of lithium ions inserted until the potential of the substance changes discontinuously,

2. The assembled battery according to claim 1, wherein the amount corresponds to the reaction formula: Substances that show a discontinuous change in potential due to insertion and desorption of lithium ions into and from lithium ion sites in the crystal structure include transition metal oxides, lithium transition metal oxides, transition metal sulfides, and lithium transition metal sulfides. 2. The battery pack according to claim 1, wherein the battery is selected from the group consisting of: The assembled battery according to claim 5, wherein the transition metal element of the transition metal oxide or the lithium transition metal oxide is at least one element selected from the group consisting of titanium, manganese, tungsten, and vanadium. The assembled battery according to claim 5, wherein the transition metal element of the transition metal sulfide or the lithium transition metal sulfide is at least one element selected from the group consisting of titanium, molybdenum, niobium, tungsten, and vanadium. 2. The assembled battery according to claim 1, wherein the transition metal element of the lithium transition metal oxide is at least one element selected from the group consisting of cobalt, nickel, manganese, and iron. The battery assembly according to claim 1, wherein the lithium ion conductive solid electrolyte is an inorganic compound. The assembled battery according to claim 9, wherein the inorganic compound is amorphous mainly composed of sulfide. The assembled battery according to claim 9, wherein the inorganic compound is synthesized from a substance mainly composed of lithium sulfide and silicon sulfide. The assembled battery according to claim 1, wherein the plurality of batteries are housed in the same airtight battery case. The lithium-ion conductive solid electrolyte is an amorphous lithium-ion conductive solid electrolyte mainly composed of sulfides, and exhibits a discontinuous change in potential due to insertion and desorption of lithium ions into and from lithium ion sites in the crystal structure. battery assembly according to claim 1, wherein substances showing is Li _4/3 Ti _5/3 O _4. The voltage V One From the voltage V Two The battery pack according to any one of claims 1 to 13, which causes a discontinuous voltage change to Two The method for charging a battery pack according to any one of claims 1 to 12, wherein the battery is charged as follows.

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