JP4479159B2 - Non-aqueous electrolyte battery - Google Patents

Description

【００２１】
常温溶融塩をこのように選択することにより、常温溶融塩の、常温で液状でありながら揮発性がほとんどなく、かつ、難燃性もしくは不燃性を有する特性を確実に備えたものとなる。従って、そのような非水電解質を備えた電池は、過充電、過放電やショートなどのアブユース時における安全性および高温環境下における安全性に優れたものとなる。
【００２２】
しかも、常温溶融塩が、非金属元素のみからなるアニオンを用いて形成されており、ハロゲン化アルミニウムイオンを含んでいないので、電池性能の劣化や取り扱いの困難さは生じない。
【００２３】
（化学式１）で示される骨格を有する「四級アンモニウム有機物カチオン」としては、ジアルキルイミダゾリウムイオン、トリアルキルイミダゾリウムイオンなどのイミダゾリウムイオン、テトラアルキルアンモニウムイオン、ピリジニウムイオン、ピラゾリウムイオン、ピロリウムイオン、ピロリニウムイオン、ピロリジニウムイオン、ピペリジニウムイオンなどが挙げられる。
【００２４】
なお、テトラアルキルアンモニウムイオンとしては、トリメチルエチルアンモニウム、トリメチルプロピルアンモニウム、トリメチルヘキシルアンモニウム、テトラペンチルアンモニウムなどが挙げられるが、これらに限定されるものではない。
【００２５】
前記「非金属元素のみからなるアニオン」とは、例えばハロゲン化アルミニウムイオンのように金属元素を含むアニオンではないものをいう。四級アンモニウム有機物カチオンと非金属元素のみからなるアニオンとが常温溶融塩を形成する組み合わせとしては、具体的には、次の（１）〜（４）に示すような組み合わせが挙げられるが、これらに限定されるものではない。
（１）Ｎ−ブチルピリジニウムカチオンとテトラフルオロホウ酸アニオン（ＢＦ₄ ^-）、トリフルオロメタンスルホン酸アニオン（ＣＦ₃ＳＯ₃ ^-）などとの組み合わせ。
（２）トリメチルヘキシルアンモニウムカチオンとトリフルオロメタンスルフォニルアミドアニオン（Ｎ（ＣＦ₃ＳＯ₂）₂ ^-）、ビスペンタフルオロエタンスルフォニルアミドアニオン（Ｎ（Ｃ₂Ｆ₅ＳＯ₂）₂ ^-）などとの組み合わせ。
（３）１−エチル−３−メチルイミダゾリウムカチオンとテトラフルオロホウ酸アニオン（ＢＦ₄ ^-）、トリフルオロメタンスルホン酸アニオン（ＣＦ₃ＳＯ₃ ^-）、トリフルオロメタンスルフォニルアミドアニオン（Ｎ（ＣＦ₃ＳＯ₂）₂ ^-）、ビスペンタフルオロエタンスルフォニルアミドアニオン（Ｎ（Ｃ₂Ｆ₅ＳＯ₂）₂ ^-）などとの組み合わせ。
（４）１−メチル−３−ブチルイミダゾリウムカチオンとテトラフルオロホウ酸アニオン（ＢＦ₄ ^-）、ヘキサフルオロリン酸アニオン（ＰＦ₆ ^-）などとの組み合わせ。
【００２６】
また、前記（化学式１）で示される骨格を有する四級アンモニウム有機物カチオンのなかでも、（化学式２）で示される骨格を有するイミダゾリウムカチオン、または、（化学式３）で示される骨格を有するピリジニウムカチオンのうち、少なくとも一方を有する常温溶融塩を含有するものであることが好ましい。
【００２７】
【化２】

（但し、化学式２において、Ｒ１とＲ２とは独立で、それぞれＣ_nＨ_2n+1、ｎ＝１〜６であり、Ｒ３はＨ又はＣ_nＨ_2n+1、ｎ＝１〜６である）
【００２８】
【化３】

（但し、化学式３において、Ｒ１はＣ_nＨ_2n+1、ｎ＝１〜６であり、Ｒ２とＲ３とは独立で、それぞれＨ又はＣ_nＨ_2n+1、ｎ＝１〜６である）
【００２９】
四級アンモニウム有機物カチオンをこのように選択することにより、非水電解質中のリチウムイオンの移動度を充分に得ることができるだけでなく、過充電、過放電やショートなどのアブユース時や高温環境下における安全性を充分に得ることができ、上記作用を効果的に得ることが可能となる。
【００３０】
前記イミダゾリウムカチオンとしては、例えば、ジアルキルイミダゾリウムイオンとしては、１、３−ジメチルイミダゾリウムイオン、１−エチル−３−メチルイミダゾリウムイオン、１−メチル−３−エチルイミダゾリウムイオン、１−ブチル−３−メチルイミダゾリウムイオンなどが、トリアルキルイミダゾリウムイオンとしては、１、２、３−トリメチルイミダゾリウムイオン、１、２−ジメチル−３−エチルイミダゾリウムイオン、１、２−ジメチル−３−プロピルイミダゾリウムイオン、１−ブチル−２、３−ジメチルイミダゾリウムイオンなどが挙げられるが、これらに限定されるものではない。
【００３１】
また前記アルキルピリジニウムイオンとしては、Ｎ−メチルピリジニウムイオン、Ｎ−エチルピリジニウムイオン、Ｎ−プロピルピリジニウムイオン、Ｎ−ブチルピリジニウムイオン１−エチル−２−メチルピリジニウム、１−ブチル−４−メチルピリジニウム、１−ブチル−２、４−ジメチルピリジニウムなどが挙げられるが、これらに限定されるものではない。
【００３２】
また、本発明に用いる常温溶融塩は、それぞれ１個もしくは２個以上のカチオンとアニオンが、適当なスペーサーを介して化学的に結合した状態で塩を形成していてもよく、多価アニオンが、複数の同一または異なる１価または多価カチオンと塩を形成していてもよい。
【００３３】
なお、これらの常温溶融塩は、単独で用いてもよく、２種以上混合して用いてもよい。
【００３４】
次に、本発明の非水電解質電池に用いる正極活物質について、詳述する。
【００３５】
正極活物質に用いる、層状のα−ＮａＦｅＯ_２型結晶構造を有し、化学組成式Ｌｉ_ａＭｎ_ｂＮｉ_ｃＣｏ_ｄＯ_２（但し、０＜ａ＜１．３、０．５≦ｄ≦０．８、｜ｂ−ｃ｜＜０．０３、ｂ＋ｃ＋ｄ＝１）で示される酸化物焼成体は、従来のＬｉＣｏＯ_２結晶構造において、α−ＮａＦｅＯ_２構造の６ｂサイトを占有するＣｏ部位をある特定の組成に規定される量のＭｎ及びＮｉ元素で置換した構造である。これにより、置換を行っていないＬｉＣｏＯ_２に比べて、高率放電性能が著しく向上し、なおかつ高温充電時におけるＬｉイオンの過度の引き抜きが抑制される。
【００３６】
このような作用が発現する機構については、必ずしも明らかではないが、以下のような仮説が可能である。Ｍｎ及びＮｉ元素がＬｉＣｏＯ₂結晶構造全体に何らかの影響を及ぼし、Ｌｉの拡散を促進している可能性が考えられる。また、Ｍｎ及びＮｉ元素がＬｉＣｏＯ₂結晶構造全体を安定化させている可能性が考えられる。あるいは、Ｍｎ及びＮｉ元素がＬｉＣｏＯ₂の結晶表面に局部的に何らかの作用を及ぼしている可能性が考えられる。あるいは、活物質の合成時、焼成過程で生じるＬｉとＣｏとの固相反応に対してＭｎ及びＮｉ元素が何らかの影響を及ぼし、最適な粒子形態を発現させている可能性が考えられる。
【００３７】
上記効果が好適に得られるためには、ＭｎとＮｉの構成比が重要である。即ち、本発明はＭｎとＮｉの元素比として｜ｂ−ｃ｜の値（ｂの値とｃの値との差の絶対値）を０．０３未満とすることで、上記効果が顕著に発揮される。即ち、高率放電性能が高く、なおかつ放電容量が高い正極活物質となる。
【００３８】
また、上記組成式において、Ｃｏの比率については、ｄ＜１とすることにより、高率放電性能を向上させ、高温充電時におけるＬｉイオンの過度の引き抜きを抑制する効果がある。また、０＜ｄとすることにより、やはり高率放電性能を向上させ、高温充電時におけるＬｉイオンの過度の引き抜きを抑制する効果がある。本発明におけるｄの範囲は、０．５≦ｄ≦０．８であり、好ましくは０．６≦ｄ≦０．７である。
【００３９】
また、上記組成式において、Ｌｉ量を表すａの値は、１．３以下の正の数であれば本発明の性能が発現する。ａが１．３を上回ると、過剰のＬｉが活物質表面で炭酸塩などのＬｉ化合物を形成し、電極作製時のみならず、電池性能、特に充放電サイクル性能に悪影響を及ぼすので好ましくない。
【００４０】
また、本発明電池に係る酸化物焼成体は、６ｂサイトを占める遷移金属の一部が異種元素Ｍで置換されていてもよい。このとき、化学組成式はＬｉ_aＭｎ_bＮｉ_cＣｏ_dＭ_eＯ₂（但し、０＜ａ＜１．３、０＜ｄ＋ｅ＜１、ｅ＜０．１、ｂ＋ｃ＋ｄ＋ｅ＝１）と表される。ここで、ＭはＭｎ、Ｎｉ、Ｃｏ、Ｌｉ及びＯを除く１〜１６族の１種以上の元素で、Ｍｎ、Ｎｉ、Ｃｏと交換しうる元素が好ましい。そのような元素としては、例えば、Ｂｅ、Ｂ、Ｖ、Ｃ、Ｓｉ、Ｐ、Ｓｃ、Ｃｕ、Ｚｎ、Ｇａ、Ｇｅ、Ａｓ、Ｓｅ、Ｓｒ、Ｍｏ、Ｐｄ、Ａｇ、Ｃｄ、Ｉｎ、Ｓｎ、Ｓｂ、Ｔｅ、Ｂａ、Ｔａ、Ｗ．Ｐｂ、Ｂｉ、Ｃｏ、Ｆｅ、Ｃｒ、Ｎｉ、Ｔｉ、Ｚｒ、Ｎｂ、Ｙ、Ａｌ、Ｎａ、Ｋ、Ｍｇ、Ｃａ、Ｃｓ、Ｌａ、Ｃｅ、Ｎｄ、Ｓｍ、Ｅｕ、Ｔｂ等が挙げられるが、これらに限定されるものではない。これらは単独で用いてもよく、２種以上混合して用いてもよい。なかでも、Ａｌ、Ｍｇ、Ｔｉ、Ｖ、Ｃｒ、Ｆｅ、Ｃｕ，Ｚｎ、Ｇａ，Ｉｎ，Ｓｎ，Ｙｂのいずれかを用いると、さらに好ましい。
次に、本発明の非水電解質電池を構成するその他の要素について詳述する。
【００４１】
本発明の非水電解質を構成するリチウム塩としては、一般に非水電解質電池に使用される広電位領域において安定であるリチウム塩が使用できる。例えば、ＬｉＢＦ₄、ＬｉＰＦ₆、ＬｉＣｌＯ₄、ＬｉＣＦ₃ＳＯ₃、ＬｉＮ（ＣＦ₃ＳＯ₂）₂、ＬｉＮ（Ｃ₂Ｆ₅ＳＯ₂）₂、ＬｉＮ（ＣＦ₃ＳＯ₂）（Ｃ₄Ｆ₉ＳＯ₂）、ＬｉＣ（ＣＦ₃ＳＯ₂）₃、ＬｉＣ（Ｃ₂Ｆ₅ＳＯ₂）₃などが挙げられるが、これらに限定されるものではない。これらは単独で用いてもよく、２種以上混合して用いてもよい。
【００４２】
非水電解質中のリチウム塩の含有量は、０．１〜３ｍｏｌ／ｌの範囲であることが望ましい。リチウム塩の含有量が０．１ｍｏｌ／ｌ未満になると、電解質抵抗が大きすぎ、電池の充放電効率が低下する。逆にリチウム塩の含有量が３ｍｏｌ／ｌを越えると、非水電解質の融点が上昇し、常温で液状を保つのが困難となる。さらにいうならば、非水電解質の還元電位が卑にシフトすることによる還元側の電位安定性の向上や、融点が消滅することによる低温下におけるリチウムイオンの移動度の確保が期待できることから、非水電解質中のリチウム塩の含有量は、０．５〜２ｍｏｌ／ｌの範囲であることが望ましい。
【００４３】
本発明における非水電解質は、リチウム塩と常温溶融塩の他、高分子を複合化させることにより、前記非水電解質をゲル状に固体化して使用してもよい。ここで、前記高分子としては、例えば、ポリエチレンオキサイド、ポリプロピレンオキサイド、ポリアクリロニトリル、ポリメタクリル酸メチル、ポリフッ化ビニリデン、各種アクリル系モノマー、メタクリル系モノマー、アクリルアミド系モノマー、アリル系モノマー、スチレン系モノマーの重合体などが挙げられるが、これらに限定されるものではない。これらは単独で用いてもよく、２種以上混合して用いてもよい。
【００４４】
本発明における非水電解質は、リチウム塩と常温溶融塩の他、常温で液状である有機溶媒を添加して使用してもよい。ここで、前記有機溶媒としては、一般に非水電解質電池用電解液に使用される有機溶媒が使用できる。例えば、エチレンカーボネート、プロピレンカーボネート、ジメチルカーボネート、ジエチルカーボネート、メチルエチルカーボネート、γ−ブチロラクトン、プロピロラクトン、バレロラクトン、テトラヒドロフラン、ジメトキシエタン、ジエトキシエタン、メトキシエトキシエタンなどが挙げられるが、これらに限定されるものではない。ただし、これらの有機溶媒は前述したとおり引火性があるため、添加量が多すぎると非水電解質が引火性を帯び、充分な安全性が得られなくなる可能性があり、好ましくない。また、一般に非水電解質電池用電解液に添加される難燃性溶媒である、リン酸エステルを使用することもできる。例えば、リン酸トリメチル、リン酸トリエチル、リン酸エチルジメチル、リン酸ジエチルメチル、リン酸トリプロピル、リン酸トリブチル、リン酸トリ（トリフルオロメチル）、リン酸トリ（トリフルオロエチル）、リン酸トリ（トリパーフルオロエチル）などが挙げられるが、これらに限定されるものではない。これらは単独で用いてもよく、２種以上混合して用いてもよい。
【００４５】
本発明の非水電解質電池に用いる負極材料の作動電位は、金属リチウムの電位に対して１Ｖよりも貴となるものを選択することが好ましい。このことにより、一般的な非水電解質電池用電解液に比較して還元電位が貴であるイミダゾリウムイオンやピリジニウムイオンを含有する非水電解質を用いた場合でも、サイクル性能や充放電効率性能に優れた非水電解質電池を得ることが可能となる。作動電位が、金属リチウムの電位に対して１Ｖよりも貴である負極活物質としては、ＷＯ₂、ＭｏＯ₂、ＴｉＳ₂、Ｌｉ_4/3Ｔｉ_5/3Ｏ₄、Ｌｉ_xＴｉ_5/3-yＬ_yＯ₄（Ｌは１種以上のＴｉ及びＯを除く２〜１６族の元素である。また、４／３≦ｘ≦７／３であり、０≦ｙ≦５／３である）などが挙げられるが、特にＬｉ_4/3Ｔｉ_5/3Ｏ₄、Ｌｉ_xＴｉ_5/3-yＬ_yＯ₄で表されるスピネル型構造を有する酸化物焼成体が好ましい。これらは単独で用いてもよく、２種以上混合して用いてもよい。
【００４６】
前記Ｌｉ_xＴｉ_5/3-yＬ_yＯ₄で表されるスピネル型構造を有する酸化物焼成体として、Ｌｉ_xＴｉ_5/3-yＬ_yＯ₄（Ｌは１種以上のＴｉ及びＯを除く２〜１６族の元素、４／３≦ｘ≦７／３、０≦ｙ≦５／３）で表されるスピネル型構造を有する酸化物焼成体を用いてもよい。
【００４７】
ここで、置換元素Ｌとしては、Ｂｅ、Ｂ、Ｃ、Ｍｇ、Ａｌ、Ｓｉ、Ｐ、Ｃａ、Ｓｃ、Ｖ、Ｃｒ、Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ、Ｃｕ、Ｚｎ、Ｇａ、Ｇｅ、Ａｓ、Ｓｅ、Ｓｒ、Ｙ、Ｚｒ、Ｎｂ、Ｍｏ、Ｐｄ、Ａｇ、Ｃｄ、Ｉｎ、Ｓｎ、Ｓｂ、Ｔｅ、Ｂａ、Ｌａ、Ｔａ、Ｗ、Ａｕ、Ｈｇ、Ｐｂなどが挙げられるが、これらに限定されるものではない。これらは単独で用いてもよく、２種以上混合して用いてもよい。
【００４８】
本発明における非水電解質電池を製造する方法や手段については、特に限定されるものではないが、例えば、正極、負極、セパレータから構成される発電要素を、外装材からなる電池用パッケージの内に入れ、次いで電池用パッケージの内に非水電解質を注液し、最終的に封止して得る方法を用いてもよく、また、例えばコイン型電池のように、正極，負極，セパレータを、正極収納部，負極収納部，セパレータ収納部を有する電池用パッケージの各収納部にそれぞれ独立して収納し、次いで外装材からなる電池用パッケージ内に非水電解質を注液し、最終的に封止して得る方法を用いても良い。
【００４９】
前記正極および負極は、主要構成成分である前記活物質の他に、導電剤および結着剤を構成成分として作製されることが好ましい。
【００５０】
導電剤としては、電池性能に悪影響を及ぼさない電子伝導性材料であれば限定されないが、通常、天然黒鉛（鱗状黒鉛，鱗片状黒鉛，土状黒鉛等）、人造黒鉛、カーボンブラック、アセチレンブラック、ケッチェンブラック、カーボンウイスカー、炭素繊維、金属（銅，ニッケル，アルミニウム，銀，金等）粉、金属繊維、導電性セラミックス材料等の導電性材料を１種またはそれらの混合物として含ませることができる。
【００５１】
これらの中で、導電剤としては、導電性及び塗工性の観点よりアセチレンブラックが望ましい。導電剤の添加量は、正極または負極の総重量に対して１〜５０重量％が好ましく、特に２重量％〜３０重量％が好ましい。これらの混合方法は、物理的な混合であり、その理想とするところは均一混合である。そのため、Ｖ型混合機、Ｓ型混合機、擂かい機、ボールミル、遊星ボールミルといったような粉体混合機を乾式、あるいは湿式で混合することが可能である。
【００５２】
結着剤としては、通常、ポリテトラフルオロエチレン，ポリフッ化ビニリデン，ポリエチレン，ポリプロピレン等の熱可塑性樹脂、エチレン−プロピレンジエンターポリマー（ＥＰＤＭ），スルホン化ＥＰＤＭ，スチレンブタジエンゴム（ＳＢＲ）、フッ素ゴム等のゴム弾性を有するポリマー、カルボキシメチルセルロース等の多糖類等を１種または２種以上の混合物として用いることができる。また、多糖類の様にリチウムと反応する官能基を有する結着剤をリチウム電池に用いる場合には、例えばメチル化するなどしてその官能基を失活させておくことが望ましい。結着剤の添加量は、正極または負極の総重量に対して１〜５０重量％が好ましく、特に２〜３０重量％が好ましい。
【００５３】
正極活物質または負極活物質、導電剤および結着剤をトルエン等の有機溶剤あるいは水を添加して混練し、電極形状に成形して乾燥することによって、それぞれ正極および負極を好適に作製できる。
【００５４】
なお、正極が正極用集電体に密着し、負極が負極用集電体に密着するように構成されるのが好ましく、例えば、正極用集電体としては、アルミニウム、チタン、ステンレス鋼、ニッケル、焼成炭素、導電性高分子、導電性ガラス等の他に、接着性、導電性および耐酸化性向上の目的で、アルミニウムや銅等の表面をカーボン、ニッケル、チタンや銀等で処理した物を用いることができる。負極用集電体としては、銅、ニッケル、鉄、ステンレス鋼、チタン、アルミニウム、焼成炭素、導電性高分子、導電性ガラス、Ａｌ−Ｃｄ合金等の他に、接着性、導電性、耐酸化性向上の目的で、銅等の表面をカーボン、ニッケル、チタンや銀等で処理した物を用いることができる。これらの材料については表面を酸化処理することも可能である。
【００５５】
集電体の形状については、フォイル状の他、フィルム状、シート状、ネット状、パンチ又はエキスパンドされた物、ラス体、多孔質体、発泡体、繊維群の形成体等が用いられる。厚さの限定は特にないが、１〜５００μｍのものが用いられる。これらの集電体の中で、正極用集電体としては、耐酸化性に優れているアルミニウム箔が、負極用集電体としては、還元場において安定であり、且つ導電性に優れ、安価な銅箔、ニッケル箔、鉄箔、およびそれらの一部を含む合金箔を使用することが好ましい。さらに、粗面表面粗さが０．２μｍＲａ以上の箔であることが好ましく、これにより正極および負極と集電体との密着性は優れたものとなる。よって、このような粗面を有することから、電解箔を使用するのが好ましい。特に、ハナ付き処理を施した電解箔は最も好ましい。
【００５６】
【実施例】
（実施例１）
本発明における非水電解質電池の断面図を図１に示す。本発明における非水電解質電池は、正極１、負極２、およびセパレータ３からなる極群４と、非水電解質と、金属樹脂複合フィルム５から構成されている。正極１は、正極合剤１１が正極集電体１２上に塗布されてなる。また、負極２は、負極合剤２１が負極集電体２２上に塗布されてなる。非水電解質は極群４に含浸されている。金属樹脂複合フィルム５は、極群４を覆い、その四方を熱溶着により封止されている。
【００５７】
次に、上記構成の非水電解質電池の製造方法を説明する。
【００５８】
層状のα−ＮａＦｅＯ₂型結晶構造を有し、ＬｉＭｎ_0.167Ｎｉ_0.167Ｃｏ_0.667Ｏ₂組成で表される酸化物焼成体を正極活物質として用いた。
【００５９】
前記正極活物質に、導電剤としてのアセチレンブラックを混合し、さらに結着剤としてのポリフッ化ビニリデンのＮ−メチル−２−ピロリドン溶液を混合し、この混合物をアルミ箔からなる正極集電体１２の片面に塗布した後、乾燥し、正極合剤１１の厚さが０．１ｍｍとなるようにプレスした。以上の工程により正極１を得た。
【００６０】
負極材料としてのＬｉ_4/3Ｔｉ_5/3Ｏ₄と、導電剤としてのケッチェンブラックを混合し、さらに結着剤としてのポリフッ化ビニリデンのＮ−メチル−２−ピロリドン溶液を混合し、この混合物を銅箔からなる負極集電体２２の片面に塗布した後、乾燥し、負極合剤２１厚さが０．１ｍｍとなるようにプレスした。以上の工程により負極２を得た。
【００６１】
セパレータ３は、次のようにして得た。まず、（化学式４）で示される構造を持つ２官能アクリレートモノマーを３重量パーセント溶解するエタノール溶液を作製し、多孔性基材であるポリエチレン微孔膜（平均孔径０．１ミクロン、開孔率５０％、厚さ２３ミクロン、重量１２．５２ｇ／ｍ²、透気度８９秒／１００ｍｌ）に塗布した後、電子線照射によりモノマーを架橋させて有機ポリマー層を形成し、温度６０℃で５分間乾燥させた。以上の工程により、セパレータ３を得た。なお、得られたセパレータ３は、厚さ２４ミクロン、重量１３．０４ｇ／ｍ²、透気度１０３秒／１００ｍｌであり、有機ポリマー層の重量は、多孔性材料の重量に対して約４重量％、架橋体層の厚さは約１ミクロンで、多孔性基材の孔がほぼそのまま維持されているものであった。
【００６２】
【化４】

【００６３】
極群４は、正極合剤１１と負極合剤２１とを対向させ、その間にセパレータ３を配し、正極１、セパレータ３、負極２の順に積層することにより、構成した。
【００６４】
非水電解質は、１−エチル−３−メチルイミダゾリウムイオン（ＥＭＩ⁺）とテトラフルオロホウ酸イオン（ＢＦ₄ ^-）からなる常温溶融塩（ＥＭＩＢＦ₄）に、１モルのＬｉＢＦ₄を溶解させることにより得た。
【００６５】
次に、非水電解質中に極群４を浸漬させることにより、極群４に非水電解質を含浸させ、た。さらに、金属樹脂複合フィルム５で極群４を覆い、その四方を熱溶着により封止した。
【００６６】
以上の製法により得られた非水電解質電池を本発明電池１とする。
【００６７】
（実施例２）
非水電解液として、Ｎ−ブチルピリジニウムイオン（ＢＰｙ⁺）とＢＦ₄ ^-からなる常温溶融塩（ＢＰｙＢＦ₄）に、１モルのＬｉＢＦ₄を溶解したものを用いた以外、実施例１と同一の原料および製法により非水電解質電池を得た。これを本発明電池２とする。
【００６８】
（比較例１）
非水電解質として、エチレンカーボネートとジエチルカーボネートを体積比１：１で混合した混合溶媒１リットルに、１モルのＬｉＢＦ₄を溶解したものを用いた以外、実施例１と同一の原料および製法により非水電解質電池を得た。これを比較電池１とする。
【００６９】
（比較例２）
層状のα−ＮａＦｅＯ₂型結晶構造を有し、ＬｉＭｎ_0.5Ｎｉ_0.5Ｏ₂組成で表される酸化物焼成体を正極活物質として用いたことを除いては、実施例１と同一の原料および製法により非水電解質電池を得た。これを比較電池２とする。
【００７０】
（比較例３）
正極活物質として、ＬｉＣｏＯ₂を用いたことを除いては、実施例１と同一の原料および製法により非水電解質電池を得た。これを比較電池３とする。
【００７１】
（比較例４）
非水電解質として、エチレンカーボネートとジエチルカーボネートを体積比１：１で混合した混合溶媒１リットルに、１モルのＬｉＢＦ₄を溶解したものを用い、正極活物質として、ＬｉＣｏＯ₂を用いたことを除いては、実施例１と同一の原料および製法により非水電解質電池を得た。これを比較電池４とする。
【００７２】
本発明電池１，２及び比較電池１〜４に用いた非水電解質と正極活物質の組み合わせを整理して表１に示す。
【００７３】
【表１】

【００７４】
（初期放電容量試験）
本発明電池１，２および比較電池１〜４について、初期放電容量試験を行った。試験温度は２０℃とした。充電は、電流１ｍＡで、定電流充電とした。放電は、電流１ｍＡで、定電流放電とした。充放電の終止電圧は、充電終止電圧：２．７Ｖ；放電終止電圧：１．２Ｖ（Ａ）、又は、充電終止電圧：３．１Ｖ；放電終止電圧：１．５Ｖ（Ｂ）とした。充放電の終止電圧について、表１中にＡ，Ｂの符号で示した。得られた電池容量を、初期放電容量とした。なお、本発明電池１，２および比較電池１〜４の設計容量は、全て同一である。
【００７５】
ここで、充放電の終止電圧について、充電終止電圧：２．７Ｖ；放電終止電圧：１．２Ｖとした（Ａ）の条件においては、正極電位は２．７Ｖ−４．２Ｖ（ｖ．ｓ．Ｌｉ／Ｌｉ⁺）間で推移し、負極電位は１．５Ｖ（ｖ．ｓ．Ｌｉ／Ｌｉ⁺）付近で推移する。一方、充電終止電圧：３．１Ｖ；放電終止電圧：１．５Ｖとした（Ｂ）の条件においては、正極電位は３．０Ｖ−４．６Ｖ（ｖ．ｓ．Ｌｉ／Ｌｉ⁺）間で推移し、負極電位は１．５Ｖ（ｖ．ｓ．Ｌｉ／Ｌｉ⁺）付近で推移する。
【００７６】
（高率放電試験）
本発明電池１，２および比較電池１〜４について、高率放電試験を行った。試験温度は２０℃とした。充電は、電流１ｍＡで、定電流充電とした。放電は、電流５ｍＡで、定電流放電とした。充放電の終止電圧については、それぞれの電池について行った前記初期放電容量試験で採用した充放電の終止電圧と同一とした。得られた電池容量を、同一電池の同一条件における前記初期放電容量の値で除した百分率を高率放電性能（％）とした。
【００７７】
（高温保存試験）
本発明電池１，２および比較電池１〜４について、高温保存試験を行った。前述の初期放電容量試験と同様の条件で、初期容量の確認を行った電池を、前述した条件で充電後、１００℃で３時間保存後室温で２１時間保存する高温保存サイクルを３０日間繰り返し、前述した条件で保存後の放電容量を測定し、自己放電率を求めると共に、電池厚さの変化を測定した。なお、自己放電率および電池厚さ変化率は（式１）および（式２）により算出した。
【００７８】
【式１】

【００７９】
【式２】

【００８０】
以上の結果を表１にまとめて示す。
【００８１】
表１から、初期放電容量については、本発明電池１，２および比較電池１〜４のいずれの電池も、設計容量のほぼ１００％が得られ、充放電効率もほぼ１００％が得られていることがわかる。
【００８２】
次に、高率放電試験の結果について検討する。まず、非水電解質としてエチレンカーボネートとジエチルカーボネートの混合溶媒にＬｉＢＦ₄を溶解した電解液を用いた系において、正極活物質に本発明に係る酸化物焼成体を用いた比較電池１と、正極活物質に従来のＬｉＣｏＯ₂（組成式Ｌｉ_aＭｎ_bＮｉ_cＣｏ_dＯ₂においてｂ＋ｃ＋ｄ＝１、ｄ＝１としたものに相当）を用いた比較電池４とを比べると、両者の高率放電性能は同等である。このことから、本発明に係る酸化物焼成体も、従来のＬｉＣｏＯ₂も、正極活物質としては本質的に高率放電性能において同等の性能を有していることがわかる。
【００８３】
次に、それぞれの正極活物質を用いた場合において、非水電解質を本発明のものとしたときの高率放電性能を検討する。まず、正極活物質に従来のＬｉＣｏＯ₂を用いた系においては、非水電解質としてエチレンカーボネートとジエチルカーボネートの混合溶媒にＬｉＢＦ₄を溶解した電解液を用いた比較電池４の高率放電性能に比べ、非水電解質として常温溶融塩型非水電解質を用いた比較電池３の高率放電性能は、５７〜５９％と低い値になっている。ところが、正極に本発明に係る酸化物焼成体を用いた系においては、非水電解質としてエチレンカーボネートとジエチルカーボネートの混合溶媒にＬｉＢＦ₄を溶解した電解液を用いた比較電池１の高率放電性能に比べ、非水電解質として常温溶融塩型非水電解質を用いた本発明電池１の高率放電性能は、実に驚くべきことに、６４％という高い値が得られている。
【００８４】
以上の結果から、常温溶融塩型非水電解質を用いた場合の高率放電性能は、ひとり正極活物質自体が有する性能の差に依存するのではなく、常温溶融塩型非水電解質との組み合わせにおいて顕著な効果が発揮されるものであることがわかる。
【００８５】
また、常温溶融塩の種類を異なるものとした本発明電池２においても、本発明電池１と同様の効果が発揮されていることがわかる。
【００８６】
一方、組成式Ｌｉ_aＭｎ_bＮｉ_cＣｏ_dＯ₂においてｄ＝０としたものに相当するＬｉＭｎ_0.5Ｎｉ_0.5Ｏ₂を正極活物質として用いた比較電池２では高率放電性能が大きく劣るものとなっていることがわかる。
【００８７】
次に、充放電終止電圧の違いによる効果の現れ方について考察する。非水電解質に本発明に係る常温溶融塩を用い、正極活物質にＬｉＣｏＯ₂を用いた比較電池３においては、正極電位が２．７Ｖ−４．２Ｖ間で推移している（Ａ）の充放電条件では高温保存後の自己放電率は１３％と比較的低いのに対し、正極電位が３．０Ｖ−４．６Ｖ間で推移している（Ｂ）の充放電条件では高温保存後の自己放電率が４９％と著しく増大している。このように、正極電位を４．５Ｖ以上で作動させると保存性能に著しく低下している。一方、本発明電池１では、（Ｂ）の充放電条件においても高温保存後の自己放電は１８％と低いレベルに抑えられている。高温保存後の電圧厚さ変化率についても同様の効果が観察されている。
【００８８】
以上のことから、本発明によれば、高率放電性能に優れ、高い作動電位領域で用いても高温保存性能が良好な非水電解質電池を提供することができる。また、本発明による非水電解質電池は、不燃性の常温溶融塩を用いているので安全性にも優れる。
【００８９】
【発明の効果】
本発明によれば、常温溶融塩を非水電解質に用いることで得られる高い安全性を確保しながらも、高率放電性能に優れた非水電解質電池を提供することができる。また、高作動電圧を有し保存性能に優れた非水電解質電池を提供することができる。
【図面の簡単な説明】
【図１】 本発明の非水電解質電池の断面図である。
【符号の説明】
１ 正極
１１ 正極合剤
１２ 正極集電体
２ 負極
２１ 負極合剤
２２ 負極集電体
３ セパレータ
４ 極群
５ 金属樹脂複合フィルム[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-aqueous electrolyte battery, and more particularly to a positive electrode active material used for a non-aqueous electrolyte battery containing a room temperature molten salt in an electrolyte.
[0002]
[Prior art]
In recent years, non-aqueous electrolyte batteries using various non-aqueous electrolytes capable of obtaining a high energy density have attracted attention as power supplies for electronic devices, power storage power supplies, electric vehicle power supplies, etc., which are becoming higher performance and smaller. .
[0003]
Currently, a commercially available lithium ion battery has a lithium cobalt oxide (LiCoO) as a positive electrode.₂), A carbonaceous material that occludes and releases lithium ions is used for the negative electrode, and a nonaqueous electrolytic solution in which a lithium salt is dissolved in an organic solvent that is liquid at room temperature, such as ethylene carbonate and diethyl carbonate, is used as a nonaqueous electrolyte. ing.
[0004]
On the other hand, there is a lithium ion battery using a room temperature molten salt as a non-aqueous electrolyte. For example, Patent Document 1 discloses that a room temperature molten salt containing a quaternary ammonium organic cation such as an imidazolium cation and a lithium cation is used as a non-aqueous electrolyte, and the working potential of the negative electrode is metal lithium such as lithium titanium oxide. A positive electrode active material that is nobler than 1 V with respect to the potential of the positive electrode and an active potential that is nobler than 4.5 V with respect to the potential of metallic lithium, such as spinel type lithium nickel manganese oxide, is used for the positive electrode Batteries using materials have been proposed. According to this technique, since the electrolyte is flame retardant, a battery suitable for an application requiring particularly high safety can be obtained.
[0005]
However, when room temperature molten salt is used for the non-aqueous electrolyte, there is a problem that the discharge capacity during high-rate discharge is lower than when a general non-aqueous electrolyte is used.
[0006]
In order to obtain a battery having an excellent energy density, it is desirable to combine a positive electrode active material having a 4V class operating potential, and LiCoO as a positive electrode active material having a 4V class operating potential.₂Lithium cobalt composite oxides are widely used. However, charging over a specific operating potential causes the crystals to become unstable, causing rapid cycle capacity degradation and significant reduction in storage performance. There was a point. LiMn₂O_FourThe lithium manganese oxide having a spinel structure represented by the above is a cathode active material that is inexpensive and excellent in safety, but the energy density per weight is only about 70% as compared with the lithium cobalt composite oxide. However, the cycle performance and the high rate discharge performance are not sufficient, and although some have been put into practical use, they have not been widely used. In recent years, layered α-NaFeO₂LiMn_aNi_bCo_cO₂The use of a material represented by a composition (a + b + c = 1) composition as a positive electrode active material is proposed in Patent Document 2 and the like.
[0007]
[Patent Document 1]
JP 2002-110225 A
[Patent Document 2]
JP 2003-007298 A
[Non-Patent Document 1]
Study Group for Molten Salt / Thermal Technology "Basics of Molten Salt / Thermal Technology", Agne Technology Center, 1993, 313p (ISBN 4-900041-24-6)
[0008]
[Problems to be solved by the invention]
The present invention has been made in view of the above problems, and provides a nonaqueous electrolyte battery excellent in high-rate discharge performance while ensuring high safety obtained by using a room temperature molten salt as a nonaqueous electrolyte. The purpose is to do. Another object is to provide a nonaqueous electrolyte battery having a high operating voltage and excellent storage performance.
[0009]
[Means for Solving the Problems]
As a result of intensive studies to solve the above-mentioned problems, the present inventors were surprised when a material having a specific crystal structure and a specific composition ratio of its constituent elements was used for the positive electrode active material. In fact, it has been found that even when a room temperature molten salt type non-aqueous electrolyte is used in place of the conventional non-aqueous electrolyte, good high rate discharge performance can be obtained. The configuration of the present invention is as follows. However, the action mechanism includes estimation, and the success or failure of the action mechanism does not limit the present invention.
[0010]
The present invention relates to a non-aqueous electrolyte battery comprising a positive electrode and a negative electrode using a non-aqueous electrolyte containing a normal temperature molten salt containing a lithium salt as a main component, and the positive electrode active material constituting the positive electrode has a layered α- NaFeO₂Type crystal structure, Li_aMn_bNi_cCo_dO₂(However, 0 <a <1.3, 0.5 ≦ d ≦ 0.8,| B−c | <0.03,The nonaqueous electrolyte battery is characterized by mainly using an oxide fired body represented by b + c + d = 1).
[0011]
According to such a configuration, surprisingly, the capacity reduction during high-rate discharge, which was observed in the nonaqueous electrolyte battery using the room temperature molten salt, is remarkably improved.
[0013]
Also, aboveConstitutionBy doingIn particular, it is possible to provide a non-aqueous electrolyte battery having high discharge efficiency and high discharge capacity.
[0014]
In the nonaqueous electrolyte battery of the present invention, the positive electrode operating potential region is 4.5 V (vs. Li / Li⁺) It is characterized by being used over the above.
[0015]
According to such a configuration, layered α-NaFeO is applied to the positive electrode active material constituting the positive electrode.₂Type crystal structure, Li_aMn_bNi_cCo_dO₂(However, 0 <a <1.3, 0.5 ≦ d ≦ 0.8,| B−c | <0.03,b + c + d = 1) is used mainly, and the positive electrode operating potential region is 4.5 V (vs Li / Li).⁺) 4.5V (vs Li / Li)⁺Compared with the case where it is used in the positive electrode operating potential region of less than), not only the battery capacity is increased, but also good high rate discharge performance is maintained. Moreover, LiCoO₂Compared to the case where is used for the positive electrode, it is possible to obtain a non-aqueous electrolyte battery having a high battery voltage and also having good storage performance.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below, but the present invention is not limited to these descriptions.
[0017]
First, the room temperature molten salt used in the nonaqueous electrolyte battery of the present invention will be described in detail.
[0018]
In the present specification, the room temperature molten salt refers to a salt that is at least partially liquid at room temperature. The normal temperature is a temperature range in which the battery is assumed to normally operate. The upper limit is about 100 ° C., in some cases about 60 ° C., and the lower limit is about −50 ° C., and in some cases about −20 ° C. On the other hand, Li used for various electrodepositions as described in Non-Patent Document 1₂CO_Three-Na₂CO_Three-K₂CO_ThreeMost of the inorganic molten salts such as those having a melting point of 300 ° C. or higher are not in a liquid state within a temperature range in which the battery normally operates and are not included in the room temperature molten salt in the present invention. .
[0019]
As said normal temperature molten salt, the thing similar to what was shown in the said patent document 1 can be used. That is, it is preferable to use a material containing a room temperature molten salt formed of a quaternary ammonium organic cation having a skeleton represented by (Chemical Formula 1) and an anion composed only of a nonmetallic element.
[0020]
[Chemical 1]

[0021]
By selecting the room temperature molten salt in this way, the room temperature molten salt is surely provided with the property of being hardly volatile while being liquid at room temperature and having flame retardancy or nonflammability. Therefore, a battery equipped with such a non-aqueous electrolyte is excellent in safety at the time of abuse such as overcharge, overdischarge and short circuit and in a high temperature environment.
[0022]
Moreover, since the room temperature molten salt is formed using an anion consisting of only a nonmetallic element and does not contain an aluminum halide ion, battery performance is not deteriorated and handling is not difficult.
[0023]
Examples of the “quaternary ammonium organic cation” having a skeleton represented by (chemical formula 1) include imidazolium ions such as dialkylimidazolium ions and trialkylimidazolium ions, tetraalkylammonium ions, pyridinium ions, pyrazolium ions, and pyrrolium ions. , Pyrrolinium ion, pyrrolidinium ion, piperidinium ion, and the like.
[0024]
Examples of the tetraalkylammonium ion include, but are not limited to, trimethylethylammonium, trimethylpropylammonium, trimethylhexylammonium, and tetrapentylammonium.
[0025]
The “anion consisting only of a nonmetallic element” refers to an anion that does not contain a metal element, such as an aluminum halide ion. Specific examples of combinations in which a quaternary ammonium organic cation and an anion consisting only of a nonmetallic element form a room temperature molten salt include the combinations shown in the following (1) to (4). It is not limited to.
(1) N-butylpyridinium cation and tetrafluoroborate anion (BF_Four ^-), Trifluoromethanesulfonate anion (CF_ThreeSO_Three ^-) Etc.
(2) Trimethylhexylammonium cation and trifluoromethanesulfonylamide anion (N (CF_ThreeSO₂)₂ ^-), Bispentafluoroethanesulfonylamide anion (N (C₂F_FiveSO₂)₂ ^-) Etc.
(3) 1-ethyl-3-methylimidazolium cation and tetrafluoroborate anion (BF_Four ^-), Trifluoromethanesulfonate anion (CF_ThreeSO_Three ^-), Trifluoromethanesulfonylamide anion (N (CF_ThreeSO₂)₂ ^-), Bispentafluoroethanesulfonylamide anion (N (C₂F_FiveSO₂)₂ ^-) Etc.
(4) 1-methyl-3-butylimidazolium cation and tetrafluoroborate anion (BF_Four ^-), Hexafluorophosphate anion (PF)₆ ^-) Etc.
[0026]
Among the quaternary ammonium organic cations having the skeleton represented by (Chemical Formula 1), the imidazolium cation having the skeleton represented by (Chemical Formula 2) or the pyridinium cation having the skeleton represented by (Chemical Formula 3) Among them, it is preferable to contain a room temperature molten salt having at least one of them.
[0027]
[Chemical 2]

(However, in Chemical Formula 2, R1 and R2 are independent and_nH_{2n + 1}, N = 1 to 6, and R3 is H or C_nH_{2n + 1}N = 1-6)
[0028]
[Chemical Formula 3]

(However, in Chemical Formula 3, R1 is C_nH_{2n + 1}, N = 1 to 6, R2 and R3 are independent of each other, and H or C_nH_{2n + 1}N = 1-6)
[0029]
By selecting the quaternary ammonium organic cation in this way, not only can the mobility of lithium ions in the non-aqueous electrolyte be sufficiently obtained, but also during overuse, overdischarge, short-circuiting, etc., and in high temperature environments Safety can be sufficiently obtained, and the above action can be effectively obtained.
[0030]
Examples of the imidazolium cation include 1,3-dimethylimidazolium ion, 1-ethyl-3-methylimidazolium ion, 1-methyl-3-ethylimidazolium ion, and 1-butyl as dialkylimidazolium ions. Examples of trialkylimidazolium ions include 1,2,3-trimethylimidazolium ion, 1,2-dimethyl-3-ethylimidazolium ion, 1,2-dimethyl-3- Examples thereof include, but are not limited to, propyl imidazolium ion, 1-butyl-2, 3-dimethylimidazolium ion, and the like.
[0031]
Examples of the alkylpyridinium ion include N-methylpyridinium ion, N-ethylpyridinium ion, N-propylpyridinium ion, N-butylpyridinium ion 1-ethyl-2-methylpyridinium, 1-butyl-4-methylpyridinium, 1 -Butyl-2,4-dimethylpyridinium and the like are exemplified, but not limited thereto.
[0032]
The room temperature molten salt used in the present invention may form a salt in a state where one or two or more cations and anions are chemically bonded via an appropriate spacer. A salt may be formed with a plurality of the same or different monovalent or polyvalent cations.
[0033]
In addition, these normal temperature molten salts may be used independently and may be used in mixture of 2 or more types.
[0034]
Next, the positive electrode active material used for the nonaqueous electrolyte battery of the present invention will be described in detail.
[0035]
Layered α-NaFeO used for positive electrode active material₂Type crystal structure, chemical composition formula Li_aMn_bNi_cCo_dO₂(However, 0 <a <1.3, 0.5 ≦ d ≦ 0.8,| B−c | <0.03,An oxide fired body represented by b + c + d = 1) is a conventional LiCoO.₂In the crystal structure, α-NaFeO₂This is a structure in which the Co site occupying the 6b site of the structure is replaced with Mn and Ni elements in amounts specified in a specific composition. Thereby, LiCoO which has not performed substitution₂As compared with the above, the high rate discharge performance is remarkably improved, and excessive extraction of Li ions during high temperature charging is suppressed.
[0036]
The mechanism by which such an action appears is not necessarily clear, but the following hypothesis is possible. Mn and Ni elements are LiCoO₂There is a possibility that some influence is exerted on the entire crystal structure and the diffusion of Li is promoted. In addition, Mn and Ni elements are LiCoO.₂There is a possibility that the entire crystal structure is stabilized. Alternatively, the Mn and Ni elements are LiCoO₂There is a possibility that some kind of action is locally exerted on the crystal surface. Alternatively, during synthesis of the active material, there is a possibility that Mn and Ni elements have some influence on the solid phase reaction between Li and Co that occurs in the firing process, and that an optimal particle form is expressed.
[0037]
In order to obtain the above effect suitably, the composition ratio of Mn and Ni is important. That is, according to the present invention, when the value of | b−c | (the absolute value of the difference between the value of b and the value of c) is less than 0.03 as the element ratio of Mn and Ni, the above-described effects are remarkably exhibited. Is done. That is, it becomes a positive electrode active material having high discharge performance and high discharge capacity.
[0038]
In the above composition formula, the ratio of Co is, DBy setting it to <1, it has the effect of improving high-rate discharge performance and suppressing excessive extraction of Li ions during high-temperature charging. Further, by setting 0 <d, the high-rate discharge performance is also improved, and there is an effect of suppressing excessive extraction of Li ions during high-temperature charging.In the present inventionThe range of d is, 0. 5 ≦ d ≦ 0.8GoodPreferably, 0.6 ≦ d ≦ 0.7.
[0039]
Moreover, in the said composition formula, if the value of a showing the amount of Li is a positive number of 1.3 or less, the performance of this invention will express. If a exceeds 1.3, excess Li forms a Li compound such as carbonate on the surface of the active material, which adversely affects not only the electrode production but also battery performance, particularly charge / discharge cycle performance.
[0040]
Moreover, in the oxide fired body according to the battery of the present invention, a part of the transition metal occupying the 6b site may be substituted with a different element M. At this time, the chemical composition formula is Li_aMn_bNi_cCo_dM_eO₂(However, 0 <a <1.3, 0 <d + e <1, e <0.1, b + c + d + e = 1). Here, M is one or more elements of Group 1 to 16 excluding Mn, Ni, Co, Li and O, and elements that can be exchanged for Mn, Ni, and Co are preferable. Examples of such elements include Be, B, V, C, Si, P, Sc, Cu, Zn, Ga, Ge, As, Se, Sr, Mo, Pd, Ag, Cd, In, Sn, and Sb. , Te, Ba, Ta, W. Pb, Bi, Co, Fe, Cr, Ni, Ti, Zr, Nb, Y, Al, Na, K, Mg, Ca, Cs, La, Ce, Nd, Sm, Eu, Tb and the like can be mentioned. It is not limited to. These may be used alone or in combination of two or more. Among these, it is more preferable to use any of Al, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, In, Sn, and Yb.
Next, other elements constituting the nonaqueous electrolyte battery of the present invention will be described in detail.
[0041]
As the lithium salt constituting the nonaqueous electrolyte of the present invention, a lithium salt that is stable in a wide potential region generally used for a nonaqueous electrolyte battery can be used. For example, LiBF_Four, LiPF₆LiClO_Four, LiCF_ThreeSO_Three, LiN (CF_ThreeSO₂)₂, LiN (C₂F_FiveSO₂)₂, LiN (CF_ThreeSO₂) (C_FourF₉SO₂), LiC (CF_ThreeSO₂)_Three, LiC (C₂F_FiveSO₂)_ThreeHowever, it is not limited to these. These may be used alone or in combination of two or more.
[0042]
The lithium salt content in the non-aqueous electrolyte is preferably in the range of 0.1 to 3 mol / l. When the content of the lithium salt is less than 0.1 mol / l, the electrolyte resistance is too large, and the charge / discharge efficiency of the battery decreases. On the contrary, if the content of the lithium salt exceeds 3 mol / l, the melting point of the non-aqueous electrolyte rises and it becomes difficult to maintain a liquid state at room temperature. Furthermore, since the reduction potential of the nonaqueous electrolyte shifts to the base, the potential stability on the reduction side can be improved, and the mobility of lithium ions at low temperatures can be expected due to the disappearance of the melting point. The lithium salt content in the water electrolyte is desirably in the range of 0.5 to 2 mol / l.
[0043]
The non-aqueous electrolyte in the present invention may be used by solidifying the non-aqueous electrolyte into a gel by combining a polymer other than a lithium salt and a room temperature molten salt. Here, examples of the polymer include, for example, polyethylene oxide, polypropylene oxide, polyacrylonitrile, polymethyl methacrylate, polyvinylidene fluoride, various acrylic monomers, methacrylic monomers, acrylamide monomers, allyl monomers, and styrene monomers. Examples include, but are not limited to, polymers. These may be used alone or in combination of two or more.
[0044]
The nonaqueous electrolyte in the present invention may be used by adding an organic solvent that is liquid at room temperature in addition to the lithium salt and the room temperature molten salt. Here, as said organic solvent, the organic solvent generally used for the electrolyte solution for nonaqueous electrolyte batteries can be used. Examples include, but are not limited to, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, propyrolactone, valerolactone, tetrahydrofuran, dimethoxyethane, diethoxyethane, methoxyethoxyethane, and the like. Is not to be done. However, since these organic solvents are flammable as described above, if the addition amount is too large, the non-aqueous electrolyte may be flammable and sufficient safety may not be obtained, which is not preferable. Moreover, the phosphate ester which is a flame-retardant solvent generally added to the electrolyte solution for nonaqueous electrolyte batteries can also be used. For example, trimethyl phosphate, triethyl phosphate, ethyl dimethyl phosphate, diethyl methyl phosphate, tripropyl phosphate, tributyl phosphate, tri (trifluoromethyl) phosphate, tri (trifluoroethyl) phosphate, triphosphate (Triperfluoroethyl) and the like may be mentioned, but are not limited thereto. These may be used alone or in combination of two or more.
[0045]
The operating potential of the negative electrode material used in the nonaqueous electrolyte battery of the present invention is preferably selected so that it is nobler than 1 V with respect to the potential of metallic lithium. This makes it possible to achieve cycle performance and charge / discharge efficiency performance even when using non-aqueous electrolytes containing imidazolium ions and pyridinium ions, which have a noble reduction potential compared to common electrolyte solutions for non-aqueous electrolyte batteries. An excellent nonaqueous electrolyte battery can be obtained. As a negative electrode active material having an operating potential nobler than 1 V with respect to the potential of metallic lithium, WO₂, MoO₂TiS₂, Li_4/3Ti_5/3O_Four, Li_xTi_{5 / 3-y}L_yO_Four(L is a group 2-16 element excluding one or more of Ti and O. Also, 4/3 ≦ x ≦ 7/3 and 0 ≦ y ≦ 5/3). , Especially Li_4/3Ti_5/3O_Four, Li_xTi_{5 / 3-y}L_yO_FourAn oxide fired body having a spinel structure represented by: These may be used alone or in combination of two or more.
[0046]
Li_xTi_{5 / 3-y}L_yO_FourAs an oxide fired body having a spinel structure represented by Li_xTi_{5 / 3-y}L_yO_FourAn oxide fired body having a spinel structure represented by (L is an element of group 2 to 16 excluding one or more of Ti and O, 4/3 ≦ x ≦ 7/3, 0 ≦ y ≦ 5/3) May be used.
[0047]
Here, as the substitution element L, Be, B, C, Mg, Al, Si, P, Ca, Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se , Sr, Y, Zr, Nb, Mo, Pd, Ag, Cd, In, Sn, Sb, Te, Ba, La, Ta, W, Au, Hg, Pb, etc., but are not limited thereto is not. These may be used alone or in combination of two or more.
[0048]
The method and means for producing the nonaqueous electrolyte battery in the present invention are not particularly limited. For example, a power generation element composed of a positive electrode, a negative electrode, and a separator is placed in a battery package made of an exterior material. Then, a method may be used in which a nonaqueous electrolyte is injected into the battery package and finally sealed, and the positive electrode, the negative electrode, and the separator are connected to the positive electrode as in, for example, a coin-type battery. Each of the battery packages having a storage unit, a negative electrode storage unit, and a separator storage unit is stored independently, and then a nonaqueous electrolyte is injected into the battery package made of an exterior material, and finally sealed. You may use the method obtained by doing.
[0049]
The positive electrode and the negative electrode are preferably produced using a conductive agent and a binder as constituent components in addition to the active material as a main constituent component.
[0050]
The conductive agent is not limited as long as it is an electron conductive material that does not adversely affect the battery performance. Usually, natural graphite (such as scaly graphite, scaly graphite, earthy graphite), artificial graphite, carbon black, acetylene black, Conductive materials such as ketjen black, carbon whisker, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.) powder, metal fiber, and conductive ceramic material can be included as one kind or a mixture thereof. .
[0051]
Among these, as the conductive agent, acetylene black is desirable from the viewpoints of conductivity and coating properties. The addition amount of the conductive agent is preferably 1 to 50% by weight, particularly preferably 2 to 30% by weight, based on the total weight of the positive electrode or the negative electrode. These mixing methods are physical mixing, and the ideal is uniform mixing. Therefore, powder mixers such as V-type mixers, S-type mixers, crackers, ball mills, and planetary ball mills can be mixed dry or wet.
[0052]
As the binder, usually, thermoplastic resins such as polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, and polypropylene, ethylene-propylene diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, and the like These polymers having rubber elasticity, polysaccharides such as carboxymethylcellulose, and the like can be used as one or a mixture of two or more. When a binder having a functional group that reacts with lithium, such as a polysaccharide, is used in a lithium battery, it is desirable to deactivate the functional group by, for example, methylation. The addition amount of the binder is preferably 1 to 50% by weight, particularly preferably 2 to 30% by weight, based on the total weight of the positive electrode or the negative electrode.
[0053]
A positive electrode and a negative electrode active material, a conductive agent, and a binder are added to an organic solvent such as toluene or water, kneaded, formed into an electrode shape, and dried, whereby the positive electrode and the negative electrode can each be suitably produced.
[0054]
The positive electrode is preferably in close contact with the positive electrode current collector and the negative electrode is preferably in close contact with the negative electrode current collector. For example, the positive electrode current collector may be aluminum, titanium, stainless steel, nickel In addition to baked carbon, conductive polymer, conductive glass, etc., the surface of aluminum, copper, etc. treated with carbon, nickel, titanium, silver, etc. for the purpose of improving adhesion, conductivity and oxidation resistance Can be used. In addition to copper, nickel, iron, stainless steel, titanium, aluminum, calcined carbon, conductive polymer, conductive glass, Al-Cd alloy, etc., the negative electrode current collector is adhesive, conductive, and oxidation resistant. For the purpose of improving the property, a material obtained by treating the surface of copper or the like with carbon, nickel, titanium, silver or the like can be used. The surface of these materials can be oxidized.
[0055]
Regarding the shape of the current collector, a film shape, a sheet shape, a net shape, a punched or expanded material, a lath body, a porous body, a foamed body, a formed body of fiber groups, and the like are used in addition to the foil shape. The thickness is not particularly limited, but a thickness of 1 to 500 μm is used. Among these current collectors, an aluminum foil excellent in oxidation resistance is used as a positive electrode current collector, and as a negative electrode current collector, it is stable in a reducing field, has excellent conductivity, and is inexpensive. It is preferable to use a copper foil, a nickel foil, an iron foil, and an alloy foil containing a part thereof. Further, the foil is preferably a foil having a rough surface surface roughness of 0.2 μmRa or more, whereby the adhesion between the positive electrode and the negative electrode and the current collector is excellent. Therefore, it is preferable to use an electrolytic foil because it has such a rough surface. In particular, an electrolytic foil that has been subjected to a cracking treatment is most preferable.
[0056]
【Example】
Example 1
A cross-sectional view of the nonaqueous electrolyte battery in the present invention is shown in FIG. The nonaqueous electrolyte battery according to the present invention includes a pole group 4 including a positive electrode 1, a negative electrode 2, and a separator 3, a nonaqueous electrolyte, and a metal resin composite film 5. The positive electrode 1 is formed by applying a positive electrode mixture 11 on a positive electrode current collector 12. The negative electrode 2 is formed by applying a negative electrode mixture 21 on a negative electrode current collector 22. The nonaqueous electrolyte is impregnated in the pole group 4. The metal resin composite film 5 covers the pole group 4 and is sealed on all four sides by heat welding.
[0057]
Next, a method for manufacturing the nonaqueous electrolyte battery having the above configuration will be described.
[0058]
Layered α-NaFeO₂LiMn_0.167Ni_0.167Co_0.667O₂An oxide fired body represented by the composition was used as the positive electrode active material.
[0059]
The positive electrode active material is mixed with acetylene black as a conductive agent, further mixed with an N-methyl-2-pyrrolidone solution of polyvinylidene fluoride as a binder, and this mixture is used as a positive electrode current collector 12 made of aluminum foil. After being coated on one side, the film was dried and pressed so that the thickness of the positive electrode mixture 11 was 0.1 mm. The positive electrode 1 was obtained by the above process.
[0060]
Li as negative electrode material_4/3Ti_5/3O_FourAnd ketjen black as a conductive agent are mixed, and an N-methyl-2-pyrrolidone solution of polyvinylidene fluoride as a binder is further mixed, and this mixture is applied to one side of a negative electrode current collector 22 made of copper foil. After the coating, it was dried and pressed so that the thickness of the negative electrode mixture 21 was 0.1 mm. The negative electrode 2 was obtained by the above process.
[0061]
Separator 3 was obtained as follows. First, an ethanol solution in which 3% by weight of a bifunctional acrylate monomer having a structure represented by (Chemical Formula 4) is dissolved is prepared, and a polyethylene microporous membrane (average pore diameter of 0.1 micron, porosity of 50) is used as a porous substrate. %, Thickness 23 microns, weight 12.52 g / m²The air permeability was 89 seconds / 100 ml), and the monomer was crosslinked by electron beam irradiation to form an organic polymer layer, which was dried at a temperature of 60 ° C. for 5 minutes. The separator 3 was obtained by the above process. The obtained separator 3 has a thickness of 24 microns and a weight of 13.04 g / m.²The air permeability is 103 seconds / 100 ml, the weight of the organic polymer layer is about 4% by weight with respect to the weight of the porous material, the thickness of the crosslinked layer is about 1 micron, and the pores of the porous substrate are It was maintained almost as it was.
[0062]
[Formula 4]

[0063]
The pole group 4 was configured by facing the positive electrode mixture 11 and the negative electrode mixture 21, placing the separator 3 therebetween, and laminating the positive electrode 1, the separator 3, and the negative electrode 2 in this order.
[0064]
The non-aqueous electrolyte is 1-ethyl-3-methylimidazolium ion (EMI⁺) And tetrafluoroborate ion (BF_Four ^-Room temperature molten salt (EMIBF)_Four) 1 mol of LiBF_FourWas obtained by dissolving.
[0065]
Next, the electrode group 4 was impregnated with the non-aqueous electrolyte by immersing the electrode group 4 in the non-aqueous electrolyte. Furthermore, the pole group 4 was covered with the metal resin composite film 5, and the four sides were sealed by heat welding.
[0066]
The nonaqueous electrolyte battery obtained by the above production method is referred to as the battery 1 of the present invention.
[0067]
(Example 2)
As non-aqueous electrolyte, N-butylpyridinium ion (BPy⁺) And BF_Four ^-Room temperature molten salt (BPyBF_Four) 1 mol of LiBF_FourA non-aqueous electrolyte battery was obtained using the same raw materials and production method as in Example 1 except that a solution obtained by dissolving was used. This is referred to as the battery 2 of the present invention.
[0068]
(Comparative Example 1)
As a nonaqueous electrolyte, 1 mol of LiBF was added to 1 liter of a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1._FourA non-aqueous electrolyte battery was obtained using the same raw materials and production method as in Example 1 except that a solution obtained by dissolving was used. This is referred to as comparative battery 1.
[0069]
(Comparative Example 2)
Layered α-NaFeO₂LiMn_0.5Ni_0.5O₂A nonaqueous electrolyte battery was obtained using the same raw materials and production method as in Example 1 except that the oxide fired body represented by the composition was used as the positive electrode active material. This is referred to as comparative battery 2.
[0070]
(Comparative Example 3)
LiCoO as positive electrode active material₂A non-aqueous electrolyte battery was obtained using the same raw materials and production method as in Example 1 except that was used. This is referred to as comparative battery 3.
[0071]
(Comparative Example 4)
As a nonaqueous electrolyte, 1 mol of LiBF was added to 1 liter of a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1._FourLiCoO as a positive electrode active material₂A non-aqueous electrolyte battery was obtained using the same raw materials and production method as in Example 1 except that was used. This is referred to as a comparative battery 4.
[0072]
Table 1 summarizes the combinations of the nonaqueous electrolyte and the positive electrode active material used in the batteries 1 and 2 of the present invention and the comparative batteries 1 to 4.
[0073]
[Table 1]

[0074]
(Initial discharge capacity test)
The inventive batteries 1 and 2 and the comparative batteries 1 to 4 were subjected to an initial discharge capacity test. The test temperature was 20 ° C. Charging was performed at a constant current of 1 mA. The discharge was a constant current discharge at a current of 1 mA. The charge / discharge end voltage was set to charge end voltage: 2.7 V; discharge end voltage: 1.2 V (A), or charge end voltage: 3.1 V; discharge end voltage: 1.5 V (B). The end voltage of charge / discharge is indicated by the symbols A and B in Table 1. The obtained battery capacity was defined as the initial discharge capacity. The design capacities of the inventive batteries 1 and 2 and the comparative batteries 1 to 4 are all the same.
[0075]
Here, with regard to the charge / discharge end voltage, the positive electrode potential is 2.7 V-4.2 V (vs. V.s.) under the condition (A) in which the charge end voltage is 2.7 V and the discharge end voltage is 1.2 V. Li / Li⁺), And the negative electrode potential is 1.5 V (vs. Li / Li⁺) It moves around. On the other hand, the positive electrode potential is 3.0 V to 4.6 V (vs Li / Li) under the condition (B) in which the charge end voltage is 3.1 V and the discharge end voltage is 1.5 V.⁺), And the negative electrode potential is 1.5 V (vs. Li / Li⁺) It moves around.
[0076]
(High rate discharge test)
The inventive batteries 1 and 2 and the comparative batteries 1 to 4 were subjected to a high rate discharge test. The test temperature was 20 ° C. Charging was performed at a constant current of 1 mA. The discharge was a constant current discharge at a current of 5 mA. The final charge / discharge voltage was the same as the final charge / discharge voltage employed in the initial discharge capacity test performed for each battery. A percentage obtained by dividing the obtained battery capacity by the value of the initial discharge capacity under the same conditions of the same battery was defined as high rate discharge performance (%).
[0077]
(High temperature storage test)
Inventive batteries 1 and 2 and comparative batteries 1 to 4 were subjected to a high-temperature storage test. Under the same conditions as the initial discharge capacity test described above, the battery whose initial capacity was confirmed was charged under the above-described conditions, then stored at 100 ° C. for 3 hours and then stored at room temperature for 21 hours, repeated for 30 days, The discharge capacity after storage was measured under the conditions described above to determine the self-discharge rate, and the change in battery thickness was measured. The self-discharge rate and the battery thickness change rate were calculated by (Equation 1) and (Equation 2).
[0078]
[Formula 1]

[0079]
[Formula 2]

[0080]
The above results are summarized in Table 1.
[0081]
From Table 1, as for the initial discharge capacity, almost 100% of the design capacity is obtained and the charge / discharge efficiency is also almost 100% for any of the batteries of the present invention 1, 2 and the comparative batteries 1-4. I understand that.
[0082]
Next, the results of the high rate discharge test are examined. First, as a nonaqueous electrolyte, a mixed solvent of ethylene carbonate and diethyl carbonate is mixed with LiBF._FourIn the system using the electrolytic solution in which the electrolyte is dissolved, the comparative battery 1 using the fired oxide according to the present invention as the positive electrode active material and the conventional LiCoO as the positive electrode active material.₂(Composition Formula Li_aMn_bNi_cCo_dO₂In comparison with the comparative battery 4 using b + c + d = 1 and d = 1), the high-rate discharge performance is the same. From this, the oxide fired body according to the present invention is also a conventional LiCoO.₂However, it can be seen that the positive electrode active material has essentially the same performance in terms of high rate discharge performance.
[0083]
Next, in the case of using each positive electrode active material, the high rate discharge performance when the non-aqueous electrolyte is the present invention is examined. First, conventional LiCoO is used as the positive electrode active material.₂In a system using a non-aqueous electrolyte, a mixed solvent of ethylene carbonate and diethyl carbonate is mixed with LiBF._FourCompared with the high-rate discharge performance of the comparative battery 4 using the electrolyte solution in which the electrolyte is dissolved, the high-rate discharge performance of the comparative battery 3 using the room temperature molten salt type non-aqueous electrolyte as the non-aqueous electrolyte is as low as 57 to 59%. It has become. However, in the system using the oxide fired body according to the present invention for the positive electrode, a mixed solvent of ethylene carbonate and diethyl carbonate as a non-aqueous electrolyte is LiBF._FourCompared with the high rate discharge performance of the comparative battery 1 using the electrolytic solution in which the electrolyte solution is dissolved, the high rate discharge performance of the battery 1 of the present invention using the room temperature molten salt type non-aqueous electrolyte as the non-aqueous electrolyte is surprisingly surprising. A high value of 64% is obtained.
[0084]
From the above results, the high rate discharge performance when using a room temperature molten salt type non-aqueous electrolyte is not dependent on the performance difference of the positive electrode active material itself, but the combination with the room temperature molten salt type non-aqueous electrolyte It can be seen that a remarkable effect is exhibited.
[0085]
In addition, it can be seen that the same effect as that of the battery 1 of the present invention is exhibited in the battery 2 of the present invention in which the kind of the room temperature molten salt is different.
[0086]
On the other hand, the composition formula Li_aMn_bNi_cCo_dO₂LiMn corresponding to d = 0_0.5Ni_0.5O₂It can be seen that the comparative battery 2 using as the positive electrode active material has a significantly poor high rate discharge performance.
[0087]
Next, how the effect due to the difference in the charge / discharge end voltage appears will be considered. The normal temperature molten salt according to the present invention is used for the nonaqueous electrolyte, and the positive electrode active material is LiCoO.₂In the comparative battery 3 using the battery, the self-discharge rate after high-temperature storage is relatively low at 13% under the charge / discharge conditions (A) in which the positive electrode potential changes between 2.7 V and 4.2 V. Under the charge / discharge conditions (B) in which the positive electrode potential changes between 3.0V and 4.6V, the self-discharge rate after high-temperature storage is significantly increased to 49%. As described above, when the positive electrode potential is operated at 4.5 V or more, the storage performance is remarkably deteriorated. On the other hand, in the battery 1 of the present invention, the self-discharge after high-temperature storage is suppressed to a low level of 18% even under the charge / discharge conditions of (B). Similar effects have been observed for the voltage thickness change rate after high temperature storage.
[0088]
From the above, according to the present invention, it is possible to provide a nonaqueous electrolyte battery that is excellent in high-rate discharge performance and excellent in high-temperature storage performance even when used in a high operating potential region. Moreover, since the nonaqueous electrolyte battery according to the present invention uses a nonflammable room temperature molten salt, it is excellent in safety.
[0089]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the nonaqueous electrolyte battery excellent in the high rate discharge performance can be provided, ensuring the high safety | security obtained by using normal temperature molten salt for a nonaqueous electrolyte. In addition, a nonaqueous electrolyte battery having a high operating voltage and excellent storage performance can be provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a nonaqueous electrolyte battery of the present invention.
[Explanation of symbols]
1 Positive electrode
11 cathode mix
12 Positive current collector
2 Negative electrode
21 Negative electrode mix
22 Negative electrode current collector
3 Separator
4 pole group
5 Metal resin composite film

Claims (2)

In a non-aqueous electrolyte battery comprising a positive electrode and a negative electrode using a non-aqueous electrolyte containing a lithium salt and having a normal temperature molten salt as a main component , a layered α-NaFeO is used as a positive electrode active material constituting the positive electrode. has a ₂ type crystal _{structure, Li a Mn b Ni c Co} d O 2 ( where, 0 <a <1.3,0.5 ≦ d ≦ 0.8, | b-c | <0.03, b + c + d = 1) A non-aqueous electrolyte battery characterized by mainly using a fired oxide body represented by 1). The nonaqueous electrolyte battery, the nonaqueous electrolyte battery according to claim 1 Symbol placement operating potential region of the positive electrode, characterized by being used spans 4.5V (v.s.Li/Li ⁺⁾ or more.

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