JP4765161B2

JP4765161B2 - Non-aqueous electrolyte battery

Info

Publication number: JP4765161B2
Application number: JP2000364204A
Authority: JP
Inventors: 忠義 ▲高▼橋; 真一川口; 信晴小柴
Original assignee: Panasonic Corp; Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Corp; Panasonic Holdings Corp
Priority date: 2000-11-30
Filing date: 2000-11-30
Publication date: 2011-09-07
Anticipated expiration: 2020-11-30
Also published as: JP2002170576A

Description

【０００１】
【発明の属する技術分野】
本発明は、フッ化炭素を正極活物質とする非水電解液電池に関し、特に高温保存特性及び間欠放電性能に優れた非水電解液電池に関する。
【０００２】
【従来の技術】
正極活物質にフッ化炭素を、負極にリチウム金属またはその合金を用いた非水電解液電池は、エネルギー密度が高く、また小型化および軽量化が可能であることから、小型の携帯機器の主電源をはじめとし、据置き型機器のバックアップ用電源などさまざまな用途に使用されている。これら機器からの要望に対して電池特性の改善に関する提案が種々なされ、実用化されてきた。例えば、正極活物質の利用率を向上させると共に４５℃の環境下における保存特性を改善するために、フッ化炭素の出発材料に（００２）面の面間隔が３．４０〜３．５０Åのコークスを用いた構成（特公昭５６−４６６７０号公報）、また強負荷放電特性を向上させるために、電解液にプロピレンカーボネートあるいはエチレンカーボネートと低粘度溶媒の１，２ジメトキシエタンとの混合溶媒を用いた構成（特公昭５８−１２９９１号公報）が提案されている。
【０００３】
しかしながら、近年では携帯機器の高機能化、多機能化に伴い、電源としての電池に対する要望も厳しさを増しており、６０℃以上に達する高温環境下での保存特性、及び高負荷での間欠放電特性の両立が求められている。然し乍、現状ではこれら特性を満たす電池は提供されていない。例えば、高温での保存特性、及び放電特性を個々に改善する前記の各構成を組み合わせた場合であっても、間欠放電がなされた電池を６０℃以上の環境下で保存後、強負荷放電に再度供した場合、放電初期に大幅な電圧の落込みが認められる。この電圧降下が顕著になると放電電圧が１．０Ｖ以下まで低下してしまい、機器の作動電圧を大幅に下まわるために動作不能に陥る問題が生ずる。この問題は、高温保存に伴う電池の内部抵抗の上昇に起因するが、具体的な改善策を見いだすことはできない。
【０００４】
【発明が解決しようとする課題】
上述のような問題に対し、非水系電解液電池の溶媒として、Ｓ−Ｏ結合を有するサルファイト化合物を用い、正極集電体や電池缶における電解液との接液部分の材料をＡｌ、Ｔｉ、Ｚｒ等の弁金属またはその合金に用いる構成が提案されている。この構成では、弁金属が電解液中での陽極酸化によって表面に不動態皮膜を形成しており、Ｓ−Ｏ結合を有する化合物の酸化分解が防止されるとしている。これにより、二次電池のサイクル特性と電池の長期保存特性とが向上出来ることも示されている（特開平１１−１６２５１１号公報）。しかし、電池ケース等の構成部材に弁金属の使用が不可欠であることから、ステンレス等の汎用的な金属材料が使用できず、生産性及び構成部材のコスト面で課題を有している。
【０００５】
本発明は、この種の非水電解液電池を高温環境下で保存した場合に生ずる電池の内部インピーダンスの上昇を抑制すると同時に、間欠放電特性に優れた安価な非水電解液電池を提供することを目的とする。
【０００６】
【課題を解決するための手段】
上記目的を達成するために鋭意検討を重ねた結果、本発明者らは正極のフッ化炭素の出発材料として（００２）面の面間隔の値が３．５０Å以下にある易黒鉛化性炭素または黒鉛質材料を用い、電解液としてプロパンサルトンを含有させると同時に、適切な予備放電を施すことで、高温保存特性及び間欠放電特性を満足する非水電解液電池が得られることを見いだした。すなわち、本発明の非水電解液電池は、金属リチウム又はリチウム合金からなる負極、フッ化炭素からなる正極、および有機電解液から構成されてなり、該フッ化炭素が（００２）面の面間隔が３．５０Å以下にある易黒鉛化性炭素または黒鉛質材料を出発炭素材料とし、且つ該有機電解液がプロパンサルトンを含有してなり、さらに予備放電後の開路電圧が３．５Ｖ以下にあることを特徴する。
【０００７】
本発明に係る非水電解液電池は、リチウムもしくはその合金からなる負極、フッ化炭素からなる正極及び非水電解液を基本構成してなり、フッ化炭素の出発材料として（００２）面の面間隔が３．５０Å以下にある易黒鉛化性炭素または黒鉛質材料を用い、得られたフッ化炭素とプロパンサルトンを含有させた有機電解液とを組み合わせることで、高温保存特性、及び間欠放電特性に優れた電池を得ることができる。このため、例えば放電後に６０℃以上の環境下で保存し、再度放電を行った場合でも電圧低下は小さく、且つ強負荷放電特性についても良好であった。さらに、保存前の放電状態についても放電深度に関係なく、従来構成に比べて大幅に向上した保存特性が得られた。これらの効果は、放電反応によってリチウムがフッ化炭素に挿入される時に、プロパンサルトンがフッ化炭素の表面に緻密な有機被膜を形成するためと考えられ、これにより電気抵抗の高い被膜の生成要因となる有機溶媒の分解が抑制される。さらにプロパンサルトンの被膜が良好な電導性を有するので高温保存後の放電特性、特に間欠放電特性が向上したと推察される。
【０００８】
また、本発明に係る非水電解液電池は、予備放電後の開路電圧を３．５Ｖ以下としている。一般に非水電解液を組み立てた後の開路電圧は約３．６Ｖであるが、上述したようにプロパンサルトンを含有する非水電解液を用いた電池は高温雰囲気での保存特性の悪化を招いてしまう。本発明者らの詳細な検討の結果、保存後の放電特性は保存前の開路電圧の値に左右され、その値が３．５Ｖ以下であると良好な特性が得られるのに対して、３．５Ｖを超えると性能劣化することを見出した。さらにこれらの現象が、正極側の構成部材が金属リチウムに対して３．５Ｖを超える電位に有り、且つ高温雰囲気、特に６０℃以上の雰囲気に曝された際に、プロパンサルトンによる正極側の構成部材の腐食に起因する知見も得た。これらの知見に基づき、プロパンサルトンを含有する電解液等を用いて電池を組み立てた後、予備放電にて電池の開路電圧を３．５Ｖ以下とすることで、正極集電体や正極缶等にオーステナイト系ステンレスや鉄など安価な材料の使用を可能としている。尚、予備放電の工程において放電される電気量は組立直後の放電容量に対して約１％程度であり、電池特性に与える影響は極めて小さいものである。
【０００９】
【発明の実施の形態】
以下、本発明の好ましい実施形態について説明する。
【００１０】
本発明の非水電解液電池に係るフッ化炭素の出発材料となる炭素材料は、熱処理によって易黒鉛化性炭素の結晶化度をあげた黒鉛に近い構造をもつものであり、（００２）面の面間隔の値が３．５０Å以下にある天然黒鉛、人造黒鉛等が好ましく、さらに面間隔の値が３．５０〜３．３５Åにあるものがより好ましい。易黒鉛化性炭素としては石油コークス、石炭コークス、メソカーボンマイクロビーズ、メゾフェーズピッチ系炭素繊維等があり、これらを１０００℃以上で熱処理することによって（００２）面の面間隔の値が３．５０Å以下の炭素材料を得られる。また、人造黒鉛はコークスを２８００℃以上で熱処理することによって得られる。
【００１１】
さらに、出発炭素材料の形状としては、フリュードコークス、ギルソナイトコークス等の球状コークス、およびピッチの炭素化過程で生じるメソフェーズ小球体を原料としたメソカーボンマイクロビーズ等の球状の材料が好ましい。
【００１２】
（００２）面の面間隔の値が３．５０Åより大きい易黒鉛化性炭素を出発炭素材料としたフッ化炭素の場合は、その面間隔が大きくなるに伴いフッ化炭素の表面に緻密な有機被膜を形成するプロパンサルトンの添加効果が低下するので望ましくない。尚、本発明のフッ化炭素（ＣＦｘ）ｎのフッ化度（ｘ）はｘ＝０．４〜１．０の範囲が好ましく、より好ましくはｘ＝０．５〜１．０である。
【００１３】
本発明の電池は組み立て後に予備放電を行い、電池電圧を３．５Ｖ以下、望ましくは３．５Ｖ〜３．４Ｖの範囲であって、予備放電電気量は正極設計容量の１〜５％の範囲が望ましい。なお、開路電圧を３．４Ｖ以下にした場合、腐食の抑制には十分効果を認められるが、５％以上の予備放電を必要とし、電池容量が減少するので好ましくない。尚、本実施形態に係る電池は負極に金属リチウムあるいはリチウム合金を用いており、電池電圧と正極電位とはほぼ同じ値を示すと考えられる。
【００１４】
プロパンサルトンの有機電解液中の含有量は０．１〜１５質量％であることが好ましい。含有量が０．１％未満でも効果は認められるが、フッ化炭素表面を完全に被覆できず、高温保存後の放電時に大きく電圧低下を起こす危険性がある。また、１５質量％より多くなると、有機被膜の厚みが厚くなり、有機被膜は良導電性ではあるものの抵抗性分が上昇し、有機被膜の厚みに起因する電圧低下が見られはじめる。
【００１５】
一方、負極に用いる材料としては、金属リチウムまたはＬｉ−Ａｌ、Ｌｉ−Ｓｉ、Ｌｉ−Ｓｎ、Ｌｉ−ＮｉＳｉ、Ｌｉ−Ｐｂなどのリチウム合金が挙げられる。
【００１６】
また、有機電解液の溶媒としてはこの種の電池に使用されている公知の溶媒（高誘電率溶媒や低粘度溶媒）を挙げることができる。高誘電率溶媒としては、例えばエチレンカーボネート（ＥＣ）、プロピレンカーボネート（ＰＣ）、ブチレンカーボネート（ＢＣ）、γ−ブチロラクトン（ＧＢＬ）等の環状エステルが挙げられる。低粘度溶媒としては、１、２ジメトキシエタン（ＤＭＥ）、１、２ジエトキシエタン（ＤＥＥ）、１、３ジオキソラン（ＤＯＬ）等の鎖状エーテル、およびジメチルカーボネート（ＤＭＣ）、エチルメチルカーボネート（ＥＭＣ）、ジエチルカーボネート（ＤＥＣ）等の鎖状エステルが挙げられる。高誘電率溶媒と低粘度溶媒とは、それぞれ単独で使用しても、複数の溶媒を組み合わせても使用してもよいが、低粘度溶媒を使用する場合には、低粘度溶媒の低電導性を補うために高誘電率溶媒と組み合わせて使用するのが好ましい。高誘電率溶媒と低粘度溶媒との組み合わせとしては、例えばＥＣ−ＤＭＥ、ＰＣ−ＤＭＥ、ＧＢＬ−ＤＭＥなどの２成分溶媒系、ＥＣ−ＰＣ−ＤＭＥ、ＥＣ−ＧＢＬ−ＤＭＥ、ＧＢＬ−ＢＣ−ＤＭＥ、ＰＣ−ＧＢＬ−ＤＭＥなどの３成分溶媒系などが挙げられる。なお、高誘電率溶媒と低粘度溶媒との割合は、たとえば体積比で４０：６０〜７０：３０が好ましい。
【００１７】
さらに、プロピレンカーボネート（ＰＣ）とγ−ブチロラクトン（ＧＢＬ）とは凝固点が−４０℃以下と低く、またエチレンカーボネート（ＥＣ）はリチウム塩の溶解能力が高く、さらに１、２ジメトキシエタン（ＤＭＥ）は低粘度エーテルの中でリチウム塩の溶解能力が比較的高い等の特徴を有することから、これら３成分を組み合わせたＰＣ−ＤＭＥ、ＧＢＬ−ＤＭＥ、ＥＣ−ＰＣ−ＤＭＥ、ＥＣ−ＧＢＬ−ＤＭＥ等が−２０℃〜８５℃と広範囲の使用環境に対応できる点で有利である。尚、これら２成分溶媒系あるいは３成分溶媒系においての混合割合は、プロピレンカーボネート（ＰＣ）あるいはγ−ブチロラクトン（ＧＢＬ）が体積比で５〜６０含むことがとくに好ましい。
【００１８】
有機電解液の溶質としては、ＬｉＣｌＯ₄、ＬｉＰＦ₆、ＬｉＢＦ₄、ＬｉＣＦ₃ＳＯ₃、ＬｉＢＢＢまたはイミド結合を有するリチウム塩、例えばＬｉＮ（ＣＦ₃ＳＯ₂）₂、ＬｉＮ（Ｃ₂Ｆ₅ＳＯ₂）₂、ＬｉＮ（ＣＦ₃ＳＯ₂）（Ｃ₄Ｆ₉ＳＯ₂）などが挙げられる。これらのリチウム塩は単独でも、組み合わせて使用してもよい。なかでもＬｉＰＦ₆またはＬｉＢＦ₄が好ましい。溶質の塩濃度としては、０．１〜２ｍｏｌ／ｌの範囲が好ましく、より好ましくは０．３〜１．５ｍｏｌ／ｌの範囲である。
【００１９】
【実施例】
以下、実施例により本発明を詳しく説明する。
【００２０】
（実施例１）
図１に本実施例で用いたコイン型電池の断面図を示す。正極ケース１、負極ケース２はそれぞれフェライト系ステンレス鋼（ＳＵＳ４４４）製であり、ポリプロピレン製の絶縁パッキング３を介して発電要素を密封口してなる。正極４、金属リチウムからなる負極５は、ポリプロピレン製の不織布からなるセパレータ６を介して対向配置されている。電解液は、環状エステルであるプロピレンカーボネート（ＰＣ）の単一溶媒に溶質としてホウフッ化リチウム（ＬｉＢＦ₄）を１ｍｏｌ／ｌの比率にて溶解させた。さらに調整された電解液に対してプロパンサルトン（ＰＳ）を３質量％の比率にて添加している。得られた電池の寸法は直径が２０ｍｍ、厚みが２．０ｍｍとした。以下、正極４の構成について詳しく説明する。
【００２１】
出発炭素として石油ピッチを用い、これを窒素雰囲気、２０００℃で焼成して得られた（００２）面の面間隔が３．４０Åの鱗片状の易黒鉛化性炭素を得た。さらにこの易黒鉛化炭素を４００℃でフッ素化させることによりフッ化炭素とした。このフッ化炭素に導電剤としてカーボンブラックを、結着剤としてフッ素系樹脂を重量比で８５：８：７の割合で混合し、正極合剤とした。この正極合剤を２ｔｏｎ／ｃｍ²で直径１６ｍｍのペレットに加圧成形した後、ドライ雰囲気中１１０℃で乾燥して重量１９０ｍｇの正極を得た。この正極の設計容量は１００ｍＡｈである。この正極を用い、上記組成の電解液を１６０μｌ注入して本発明の電池Ａを作製した。
【００２２】
電解液の溶媒をプロピレンカーボネートに変えてγ−ブチロラクトン（ＧＢＬ）とした以外は、電池Ａと同じ構成の電池を本発明の電池Ｂとする。
【００２３】
電解液の溶媒をプロピレンカーボネートに変えてプロピレンカーボネートと１，２ジメトキシエタン（ＤＭＥ）を体積比で５０：５０の混合溶媒とした以外は、電池Ａと同じ構成の電池を本発明の電池Ｃとする。
【００２４】
フッ化炭素の出発炭素源に（００２）面の面間隔が３．５０Åの鱗片状の易黒鉛化性炭素を用いた以外は、電池Ａと同じ構成の電池を本発明の電池Ｄとする。
【００２５】
フッ化炭素の出発炭素源にメソフェーズ小球体（ＭＣＭＢ）を２２００℃の焼成処理を施して得られた（００２）面の面間隔が３．４０Åのメソカーボンマイクロビーズを用い、電解液の溶媒をプロピレンカーボネートに変えてプロピレンカーボネートと１，２ジメトキシエタンとを体積比５０：５０の混合溶媒を用いた以外は、電池Ａと同じ構成の電池を本発明の電池Ｅとする。
【００２６】
フッ化炭素の出発炭素源に天然黒鉛を用い、電解液の溶媒をプロピレンカーボネートに変えてプロピレンカーボネートと１，２ジメトキシエタンを体積比で５０：５０の混合溶媒を用いた以外は、電池Ａと同じ構成の電池を本発明の電池Ｆとする。
【００２７】
本発明の電池Ａの有機電解液に変えて、プロピレンカーボネートの単一溶媒に溶質としてホウフッ化リチウムのみを１ｍｏｌ／ｌ溶解させ、プロパンサルトンを添加していない電解液を用いた以外は、電池Ａと同じ構成の電池を比較電池１とする。
【００２８】
本発明の電池Ａのフッ化炭素に変えて、アセチレンブラックを４００℃でフッ素化させて得られたフッ化炭素を用いた以外は、電池Ａと同じ構成の電池を比較電池２とする。
【００２９】
発明電池Ａのフッ化炭素に変えて、（００２）面の面間隔が３．５１Åの鱗片状の易黒鉛化性炭素を出発炭素源としたフッ化炭素を用いた以外は、電池Ａと同じ構成の電池を比較電池３とする。
【００３０】
上記本発明の電池Ａ、Ｂ、Ｃ、Ｄ、Ｅ、Ｆおよび比較電池１〜３は各１０個を１ｍＡで２時間（設計容量の２％）の予備放電と開路電圧の測定をした後、各５個は８５℃で２０日間の保存を行い、残りの各５個は室温で１０ｋΩの抵抗（高負荷）で放電終止電圧１．０Ｖまでの放電容量を調べた。８５℃保存後の電池各５個は上記と同条件で放電して、放電開始時の落込み電圧の最低値（以降放電初期電圧と称す）と放電維持電圧とを測定した。さらに、放電容量比率（％）（保存電池の放電容量／未保存電池の放電容量×１００）を算出した。これらの結果を表１に示す。
【００３１】
【表１】

【００３２】
表１からも明らかなように、本発明の電池Ａ、Ｂ、Ｃ、Ｄ、Ｅ、Ｆはいずれも放電初期電圧が２．０Ｖ以上で放電維持電圧と同等で、電圧低下が少なく、また放電容量比率においても９０％以上の高い値を示す。また、有機電解液の溶媒が環状エステルのみとした電池Ａ、Ｂ、Ｄよりも、環状エステルに低粘度エーテルの１，２ジメトキシエタンを混合した混合溶媒を用いた電池Ｃ、Ｅ、Ｆがより良好な結果が得られた。また、出発炭素材料に球状の易黒鉛化性炭素を用いた電池Ｅは最も優れた高負荷放電特性が得られた。
【００３３】
これらに対してプロパンサルトンが添加されていない比較電池１は、放電初期の電圧低下が大きく、加えて容量劣化も激しい。また、プロパンサルトンを添加した場合においても、出発材料が非晶質炭素のアセチレンブラックの比較電池２、および（００２）の面間隔が３．５１Åの易黒鉛化性炭素の比較電池３は、いずれも本発明の電池に比べていずれの特性も劣る。このように出発材料の比表面積が非常に大きい場合、あるいは（００２）の面間隔が３．５０Åを超える場合には、プロパンサルトンの添加の効果が得られない。尚、比較電池２および３も開路電圧は３．５Ｖ以下で構成部材の腐食は認められなかった。
【００３４】
（実施例２）
実施例２として、有機電解液へのプロパンサルトンの添加量を変化させ、その影響を検討した。有機電解液に対するプロパンサルトン（ＰＳ）の添加量を、０．０５〜１８質量％の範囲で変化させた以外は実施例１の本発明の電池Ａと同じ構成とした本発明の電池Ｇ〜Ｋを作製し、実施例１と同様の評価をおこなった、その結果を表２に示す。
【００３５】
【表２】

【００３６】
表２からも明らかなように０．１〜１５ｗｔ％の範囲にある電池Ｈ、Ａ、Ｉ、Ｊは、電圧及び保存特性の両面で優れている。一方、電池Ｇは高温保存による内部抵抗の上昇を抑制できるが、放電初期電圧及び容量比率の面で他の電池に比べて特性が劣っており、電池Ｋも同様の傾向を示している。このことから、０．１ｗｔ％以下および１５ｗｔ％を超えた場合には、添加による改善を認められるがその効果が不十分である。このことから、電解液に対してプロパンサルトンの含有量は０．１〜１５ｗｔ％の範囲が好ましいことがわかる。
【００３７】
（実施例３）
実施例３として、溶媒組成の影響について検討をした。本実施例３に係る電解液には、高誘電率溶媒としてプロピレンカーボネート（ＰＣ）およびエチレンカーボネート（ＥＣ）を用い、低粘度溶媒として１、２ジメトキシエタン（ＤＭＥ）を用い、これらを選択した２成分系及び３成分系の溶媒を作成し、それぞれの溶媒にフッ化リチウム（ＬｉＢＦ₄）を１ｍｏｌ／ｌになるように溶解したものを使用した。さらに各電解液にプロパンサルトンを電解液に対して３質量％の比率にて添加した。これら電解液を用いた以外は、実施例１の電池Ａと構成が同じである電池Ｌ〜Ｒを作製し、実施例１と同様の評価を行った。尚、実施例３では高温保存が保存後の低温放電特性への影響を明確にするために、保存後の放電条件を雰囲気温度−２０℃で負荷抵抗３０ｋΩで行った。その結果を表３に示す。
【００３８】
【表３】

【００３９】
表３からも明らかなように、高誘電率溶媒のプロピレンカーボネートの体積比が５〜６０％の電池Ｎ〜Ｑは、いずれの特性も優れている。これに対して溶媒に占めるＰＣの比率が５％未満の電池Ｌ及び電池Ｍ、加えてＰＣの比率が７０％以上の電池Ｒでは、放電電圧および放電容量比率も大幅に低下している。これは、プロパンサルトンの添加によって高温保存時の内部抵抗の上昇は抑制できているが、低温での放電特性が他の電池に比べて劣る。これは、−２０℃の低温における電解液の導電性による影響が顕著になり、凝固点の低いプロピレンカーボネートの比率が５％未満の場合、あるいはプロピレンカーボネートが７０％の高率で添加されているにも関わらず低粘度溶媒の１、２ジメトキシエタン（ＤＭＥ）の比率が低くなる場合には、電解液の電導性が低下し、これにより低温での放電特性の悪化を招いたと考えられる。したがって、溶媒組成が２成分系、３成分系のいずれにおいてもプロピレンカーボネートは体積比で５〜６０％の範囲が好ましい。なお、本実施例は高誘電率溶媒にプロピレンカーボネートを使用したが、γ−ブチロラクトン（ＧＢＬ）の場合も同様の結果が得られる。
【００４０】
（実施例４）
実施例４として、本発明の電池Ａを用いて高温保存前の開路電圧が保存特性に及ぼす影響を調べた。実施例１で作成した電池を用い、組み立て後の約３．６Ｖの電池を予備放電（部分放電）することによって、異なる開路電圧を有する電池を得た。具体的には、１ｍＡの定電流放電で時間を変えることで予備放電深度を正極設計容量（１００ｍＡｈ）の０〜５％の範囲に設定して、開路電圧が３．６〜３．４Ｖとなる電池を各１０個作製した。これら電池は実施例１と同様の評価を行い、その結果の放電容量比率を表４に示す。
【００４１】
【表４】

【００４２】
表４からも明らかなように、開路電圧の値が３．４６Ｖ以下の電池は高温保存による容量劣化もなくプロパンサルトンの添加効果が認められる。一方、３．５１Ｖ以上の電池では容量劣化が激しく、分解して調べたところリチウム表面に正極ケース材質のステンレスの析出が認められた。以上のことから、開路電圧を３．５〜３．４Ｖにすることでエチレンサルファイ添加の効果を十分に発揮させることができることがわかる。また、この電圧値を得るには、正極設計容量の１〜５％の容量を予備放電することが好ましい。
【００４３】
尚、本実施例ではコイン型電池について述べたが、本発明は円筒型など様々な形状の電池についても同様の結果が得られる。
【００４４】
【発明の効果】
以上の説明から明らかなように、（００２）面の面間隔が３．５０Å以下である易黒鉛化性炭素または黒鉛質材料を出発炭素材料としたフッ化炭素からなる正極、リチウムイオンを放出可能な負極とプロパンサルトンを含有する有機電解液を組み合わせて電池を構成し、開路電圧を３．５Ｖ以下にすることにより、高温保存特性に優れ、保存後の高負荷放電においても電圧低下が生じず、且つ間欠放電特性に優れる非水電解液電池が得られる。同時にステンレス鋼等を電池構成部材に用いても特性の劣化を招かず、その工業的価値は大なるものである。
【図面の簡単な説明】
【図１】本実施例における非水電解液電池の構成を示す断面図
【符号の説明】
１正極缶
２負極缶
３ガスケット
４正極
５負極
６セパレータ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-aqueous electrolyte battery using fluorocarbon as a positive electrode active material, and particularly to a non-aqueous electrolyte battery excellent in high-temperature storage characteristics and intermittent discharge performance.
[0002]
[Prior art]
Non-aqueous electrolyte batteries that use fluorocarbon as the positive electrode active material and lithium metal or an alloy thereof as the negative electrode have high energy density and can be reduced in size and weight. It is used for various purposes such as power supplies and backup power supplies for stationary devices. In response to requests from these devices, various proposals for improving battery characteristics have been made and put into practical use. For example, in order to improve the utilization rate of the positive electrode active material and to improve the storage characteristics in an environment of 45 ° C., coke having a (002) plane spacing of 3.40 to 3.50 mm as a fluorocarbon starting material. In order to improve the heavy load discharge characteristics, a mixed solvent of propylene carbonate or ethylene carbonate and a low viscosity solvent 1,2 dimethoxyethane was used as an electrolyte. A configuration (Japanese Patent Publication No. 58-12991) has been proposed.
[0003]
However, in recent years, the demand for batteries as a power source has been severer with the increase in functionality and functionality of portable devices, and the storage characteristics in a high temperature environment reaching 60 ° C. or higher, and intermittent at high loads. There is a need for both discharge characteristics. However, no battery that satisfies these characteristics is provided at present. For example, even when the above-described configurations that individually improve storage characteristics at high temperatures and discharge characteristics are combined, batteries that have been subjected to intermittent discharge are stored in an environment of 60 ° C. or higher and then subjected to heavy load discharge. When it is used again, a significant drop in voltage is observed at the beginning of discharge. When this voltage drop becomes significant, the discharge voltage decreases to 1.0 V or less, and the operating voltage of the device is greatly reduced, resulting in a problem of inoperability. This problem is caused by an increase in the internal resistance of the battery due to high-temperature storage, but no specific improvement measures can be found.
[0004]
[Problems to be solved by the invention]
To solve the above-described problems, a sulfite compound having an S—O bond is used as a solvent for a non-aqueous electrolyte battery, and the material in contact with the electrolyte in the positive electrode current collector or the battery can is made of Al, Ti. A structure used for a valve metal such as Zr or an alloy thereof has been proposed. In this configuration, the valve metal forms a passive film on the surface by anodic oxidation in the electrolytic solution, and oxidative decomposition of the compound having an S—O bond is prevented. This also shows that the cycle characteristics of the secondary battery and the long-term storage characteristics of the battery can be improved (Japanese Patent Laid-Open No. 11-162511). However, since it is indispensable to use a valve metal for a constituent member such as a battery case, a general-purpose metal material such as stainless steel cannot be used, and there are problems in terms of productivity and cost of the constituent member.
[0005]
The present invention provides an inexpensive nonaqueous electrolyte battery excellent in intermittent discharge characteristics while suppressing an increase in internal impedance of the battery that occurs when this type of nonaqueous electrolyte battery is stored in a high temperature environment. With the goal.
[0006]
[Means for Solving the Problems]
As a result of intensive studies to achieve the above object, the present inventors have used graphitizable carbon having a (002) plane spacing value of 3.50 mm or less as a starting material for the fluorocarbon of the positive electrode. It has been found that a non-aqueous electrolyte battery satisfying high-temperature storage characteristics and intermittent discharge characteristics can be obtained by using graphite material and containing propane sultone as an electrolyte and at the same time performing appropriate preliminary discharge. That is, the nonaqueous electrolyte battery of the present invention is composed of a negative electrode made of metallic lithium or a lithium alloy, a positive electrode made of fluorocarbon, and an organic electrolyte, and the fluorocarbon has a spacing of (002) planes. Is a graphitizable carbon or graphite material having a carbon dioxide content of 3.50% or less as a starting carbon material, the organic electrolyte contains propane sultone, and the open circuit voltage after preliminary discharge is 3.5 V or less. It is characterized by being.
[0007]
The non-aqueous electrolyte battery according to the present invention basically comprises a negative electrode made of lithium or an alloy thereof, a positive electrode made of fluorocarbon and a non-aqueous electrolyte, and has a (002) plane as a starting material for fluorocarbon. By using a graphitizable carbon or graphite material with an interval of 3.50 mm or less and combining the obtained fluorocarbon and an organic electrolyte containing propane sultone, high temperature storage characteristics and intermittent discharge A battery having excellent characteristics can be obtained. For this reason, for example, even when stored in an environment of 60 ° C. or higher after discharge and then discharged again, the voltage drop is small and the heavy load discharge characteristics are also good. Furthermore, the storage characteristics before storage were greatly improved compared to the conventional configuration regardless of the depth of discharge. These effects are thought to be because propane sultone forms a dense organic film on the surface of the fluorocarbon when lithium is inserted into the fluorocarbon by a discharge reaction, thereby producing a film with high electrical resistance. Decomposition of the organic solvent which becomes a factor is suppressed. Furthermore, since the propane sultone coating has good electrical conductivity, it is presumed that the discharge characteristics after high-temperature storage, particularly the intermittent discharge characteristics, have been improved.
[0008]
In the nonaqueous electrolyte battery according to the present invention, the open circuit voltage after the preliminary discharge is 3.5 V or less. Generally, the open circuit voltage after assembling the non-aqueous electrolyte is about 3.6 V. However, as described above, the battery using the non-aqueous electrolyte containing propane sultone causes deterioration of the storage characteristics in a high temperature atmosphere. I will. As a result of detailed investigations by the present inventors, the discharge characteristics after storage depend on the value of the open circuit voltage before storage, and when the value is 3.5 V or less, good characteristics are obtained. It was found that the performance deteriorates when the voltage exceeds .5V. Further, these phenomena are caused when the positive side component is at a potential exceeding 3.5 V with respect to metallic lithium and is exposed to a high temperature atmosphere, particularly an atmosphere of 60 ° C. or higher. The knowledge resulting from the corrosion of the components was also obtained. Based on these findings, after assembling the battery using an electrolyte containing propane sultone, etc., the open circuit voltage of the battery is set to 3.5 V or less by preliminary discharge, so that the positive electrode current collector, the positive electrode can, etc. In addition, inexpensive materials such as austenitic stainless steel and iron can be used. The amount of electricity discharged in the preliminary discharge process is about 1% of the discharge capacity immediately after assembly, and the influence on the battery characteristics is extremely small.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described.
[0010]
The carbon material used as the starting material for the fluorocarbon according to the non-aqueous electrolyte battery of the present invention has a structure close to that of graphite obtained by increasing the crystallinity of graphitizable carbon by heat treatment, and has a (002) plane. Natural graphite, artificial graphite and the like having a face spacing value of 3.50 mm or less are preferred, and those having a face spacing value of 3.50 to 3.35 kg are more preferred. Examples of graphitizable carbon include petroleum coke, coal coke, mesocarbon microbeads, and mesophase pitch-based carbon fiber. When these are heat-treated at 1000 ° C. or higher, the value of the (002) plane spacing is 3. A carbon material of 50 cm or less can be obtained. Artificial graphite can be obtained by heat treating coke at 2800 ° C. or higher.
[0011]
Furthermore, as the shape of the starting carbon material, spherical materials such as spherical coke such as fried coke and gilsonite coke, and mesocarbon microbeads made from mesophase microspheres generated in the carbonization process of pitch are preferable.
[0012]
In the case of fluorocarbons starting from graphitizable carbon having a (002) plane spacing value greater than 3.50 mm as the starting carbon material, a dense organic surface is formed on the surface of the fluorocarbon as the spacing increases. This is not desirable because the effect of adding propane sultone to form a film is reduced. The degree of fluorination (x) of the fluorocarbon (CFx) n of the present invention is preferably in the range of x = 0.4 to 1.0, more preferably x = 0.5 to 1.0.
[0013]
The battery of the present invention performs preliminary discharge after assembly, and the battery voltage is 3.5 V or less, preferably in the range of 3.5 V to 3.4 V, and the amount of preliminary discharge electricity is in the range of 1 to 5% of the positive electrode design capacity. Is desirable. Note that when the open circuit voltage is set to 3.4 V or less, a sufficient effect can be recognized for suppressing corrosion, but it is not preferable because 5% or more of preliminary discharge is required and the battery capacity is reduced. Note that the battery according to the present embodiment uses metallic lithium or a lithium alloy for the negative electrode, and the battery voltage and the positive electrode potential are considered to exhibit substantially the same value.
[0014]
The content of propane sultone in the organic electrolyte is preferably 0.1 to 15% by mass. Although the effect is recognized even when the content is less than 0.1%, the surface of the fluorocarbon cannot be completely covered, and there is a risk of causing a large voltage drop during discharge after high-temperature storage. On the other hand, when the content is more than 15% by mass, the thickness of the organic coating increases, and although the organic coating has good conductivity, the resistance component increases, and voltage reduction due to the thickness of the organic coating begins to be observed.
[0015]
On the other hand, examples of the material used for the negative electrode include metallic lithium or lithium alloys such as Li—Al, Li—Si, Li—Sn, Li—NiSi, and Li—Pb.
[0016]
Examples of the solvent for the organic electrolyte include known solvents (high dielectric constant solvents and low viscosity solvents) used in this type of battery. Examples of the high dielectric constant solvent include cyclic esters such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and γ-butyrolactone (GBL). Examples of the low viscosity solvent include linear ethers such as 1,2 dimethoxyethane (DME), 1,2 diethoxyethane (DEE), and 1,3 dioxolane (DOL), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). ) And chain esters such as diethyl carbonate (DEC). The high dielectric constant solvent and the low viscosity solvent may be used alone or in combination with a plurality of solvents, but when using a low viscosity solvent, the low conductivity of the low viscosity solvent is low. In order to compensate, it is preferably used in combination with a high dielectric constant solvent. Examples of the combination of the high dielectric constant solvent and the low viscosity solvent include two-component solvent systems such as EC-DME, PC-DME, and GBL-DME, EC-PC-DME, EC-GBL-DME, and GBL-BC-DME. And a three-component solvent system such as PC-GBL-DME. In addition, the ratio of the high dielectric constant solvent and the low viscosity solvent is preferably, for example, 40:60 to 70:30 in volume ratio.
[0017]
Furthermore, propylene carbonate (PC) and γ-butyrolactone (GBL) have a low freezing point of −40 ° C. or lower, ethylene carbonate (EC) has a high lithium salt solubility, and 1,2 dimethoxyethane (DME) PC-DME, GBL-DME, EC-PC-DME, EC-GBL-DME, etc., which combine these three components, have characteristics such as relatively high lithium salt solubility in low-viscosity ethers. This is advantageous in that it can be used in a wide range of use environments such as -20 ° C to 85 ° C. The mixing ratio in these two-component solvent system or three-component solvent system is particularly preferably 5 to 60 propylene carbonate (PC) or γ-butyrolactone (GBL) in volume ratio.
[0018]
As the solute of the organic electrolyte, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiBBB or a lithium salt having an imide bond, for example, LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ and LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ). These lithium salts may be used alone or in combination. Of these, LiPF ₆ or LiBF ₄ is preferable. The salt concentration of the solute is preferably in the range of 0.1 to 2 mol / l, more preferably in the range of 0.3 to 1.5 mol / l.
[0019]
【Example】
Hereinafter, the present invention will be described in detail by way of examples.
[0020]
Example 1
FIG. 1 shows a cross-sectional view of a coin-type battery used in this example. Each of the positive electrode case 1 and the negative electrode case 2 is made of ferritic stainless steel (SUS444), and has a power generation element sealed through a polypropylene insulating packing 3. The positive electrode 4 and the negative electrode 5 made of metallic lithium are disposed to face each other with a separator 6 made of a nonwoven fabric made of polypropylene. The electrolytic solution was prepared by dissolving lithium borofluoride (LiBF ₄ ) as a solute in a single solvent of propylene carbonate (PC), which is a cyclic ester, at a ratio of 1 mol / l. Furthermore, propane sultone (PS) is added at a ratio of 3% by mass to the adjusted electrolyte. The dimensions of the obtained battery were 20 mm in diameter and 2.0 mm in thickness. Hereinafter, the configuration of the positive electrode 4 will be described in detail.
[0021]
Petroleum pitch was used as the starting carbon, and this was calcined at 2000 ° C. in a nitrogen atmosphere to obtain scaly graphitizable carbon having a (002) plane spacing of 3.40 mm. Further, this easily graphitized carbon was fluorinated at 400 ° C. to obtain fluorocarbon. Carbon black as a conductive agent and a fluorine-based resin as a binder were mixed at a weight ratio of 85: 8: 7 to the carbon fluoride to obtain a positive electrode mixture. This positive electrode mixture was pressure-molded into pellets having a diameter of 16 mm at ² ton / cm ² and then dried at 110 ° C. in a dry atmosphere to obtain a positive electrode having a weight of 190 mg. The design capacity of this positive electrode is 100 mAh. Using this positive electrode, 160 μl of an electrolyte solution having the above composition was injected to produce Battery A of the present invention.
[0022]
A battery having the same configuration as the battery A is referred to as the battery B of the present invention except that the solvent of the electrolytic solution is changed to propylene carbonate to obtain γ-butyrolactone (GBL).
[0023]
A battery having the same configuration as the battery A is the same as the battery C of the present invention except that the solvent of the electrolytic solution is changed to propylene carbonate to make a mixed solvent of propylene carbonate and 1,2 dimethoxyethane (DME) in a volume ratio of 50:50. To do.
[0024]
The battery having the same configuration as the battery A is referred to as the battery D of the present invention, except that scaly graphitizable carbon having a (002) plane spacing of 3.50 mm is used as the starting carbon source of fluorocarbon.
[0025]
Mesophase microspheres (MCMB) were calcined at 2200 ° C. as the starting carbon source of fluorocarbon, and mesocarbon microbeads having a (002) plane spacing of 3.40 mm were used, and the solvent of the electrolyte was changed. A battery E having the same configuration as the battery A is referred to as the battery E of the present invention except that a mixed solvent of propylene carbonate and 1,2 dimethoxyethane in a volume ratio of 50:50 is used instead of propylene carbonate.
[0026]
Batteries A and A were used except that natural graphite was used as the starting carbon source for fluorocarbon, the solvent of the electrolyte was changed to propylene carbonate, and a mixed solvent of propylene carbonate and 1,2 dimethoxyethane in a volume ratio of 50:50 was used. A battery having the same configuration is referred to as a battery F of the present invention.
[0027]
A battery except that instead of the organic electrolytic solution of the battery A of the present invention, only 1 mol / l of lithium borofluoride was dissolved as a solute in a single solvent of propylene carbonate, and an electrolytic solution not added with propane sultone was used. A battery having the same configuration as A is referred to as a comparative battery 1.
[0028]
A battery having the same configuration as that of the battery A is used as the comparative battery 2 except that carbon fluoride obtained by fluorinating acetylene black at 400 ° C. is used instead of the carbon fluoride of the battery A of the present invention.
[0029]
The same as battery A, except that in place of the fluorocarbon of invention battery A, a fluorocarbon having a (002) plane spacing of 3.51 mm and having a scale-like graphitizable carbon as a starting carbon source was used. The battery having the configuration is referred to as a comparative battery 3.
[0030]
The batteries A, B, C, D, E, F of the present invention and the comparative batteries 1 to 3 were each subjected to preliminary discharge and open circuit voltage measurement at 10 mA for 2 hours (2% of the design capacity). Each of the five pieces was stored at 85 ° C. for 20 days, and the remaining five pieces were examined for a discharge capacity up to a discharge end voltage of 1.0 V with a resistance of 10 kΩ (high load) at room temperature. Each of the five batteries after storage at 85 ° C. was discharged under the same conditions as described above, and the lowest drop voltage (hereinafter referred to as initial discharge voltage) and the discharge sustaining voltage at the start of discharge were measured. Furthermore, the discharge capacity ratio (%) (discharge capacity of storage battery / discharge capacity of non-storage battery × 100) was calculated. These results are shown in Table 1.
[0031]
[Table 1]

[0032]
As is clear from Table 1, the batteries A, B, C, D, E, and F of the present invention all have an initial discharge voltage of 2.0 V or more, which is equivalent to the sustaining voltage, little voltage drop, and discharge. The capacity ratio also shows a high value of 90% or more. In addition, batteries C, E, and F using a mixed solvent in which 1,2 dimethoxyethane of low-viscosity ether is mixed with cyclic ester are more than batteries A, B, and D in which the solvent of organic electrolyte is only cyclic ester. Good results were obtained. In addition, the battery E using spherical easily graphitizable carbon as the starting carbon material has the most excellent high-load discharge characteristics.
[0033]
On the other hand, the comparative battery 1 to which propane sultone is not added has a large voltage drop at the initial stage of discharge, and in addition, the capacity deterioration is severe. Further, even when propane sultone is added, the comparative battery 2 of acetylene black whose starting material is amorphous carbon, and the comparative battery 3 of graphitizable carbon having a (002) plane spacing of 3.51 mm, All of these characteristics are inferior to the battery of the present invention. Thus, when the specific surface area of the starting material is very large, or when the (002) plane spacing exceeds 3.50 mm, the effect of adding propane sultone cannot be obtained. Incidentally, in the

comparative batteries

2 and 3, the open circuit voltage was 3.5 V or less, and no corrosion of the constituent members was observed.
[0034]
(Example 2)
As Example 2, the amount of propane sultone added to the organic electrolyte was changed, and the effect was examined. The battery G of the present invention having the same configuration as the battery A of the present invention of Example 1 except that the amount of propane sultone (PS) added to the organic electrolyte was changed in the range of 0.05 to 18% by mass. K was prepared and evaluated in the same manner as in Example 1. Table 2 shows the results.
[0035]
[Table 2]

[0036]
As is clear from Table 2, the batteries H, A, I, and J in the range of 0.1 to 15 wt% are excellent in both voltage and storage characteristics. On the other hand, the battery G can suppress an increase in internal resistance due to high-temperature storage, but the characteristics are inferior to those of other batteries in terms of the initial discharge voltage and capacity ratio, and the battery K shows the same tendency. From this, when it is 0.1 wt% or less and exceeds 15 wt%, improvement by addition is recognized, but the effect is insufficient. This indicates that the content of propane sultone is preferably in the range of 0.1 to 15 wt% with respect to the electrolytic solution.
[0037]
(Example 3)
As Example 3, the influence of the solvent composition was examined. In the electrolyte solution according to Example 3, propylene carbonate (PC) and ethylene carbonate (EC) were used as the high dielectric constant solvent, and 1,2 dimethoxyethane (DME) was used as the low viscosity solvent, and these were selected 2 Component-type and ternary-type solvents were prepared, and lithium fluoride (LiBF ₄ ) dissolved in each solvent to 1 mol / l was used. Further, propane sultone was added to each electrolytic solution at a ratio of 3 mass% with respect to the electrolytic solution. Except for using these electrolytic solutions, batteries L to R having the same configuration as the battery A of Example 1 were produced and evaluated in the same manner as in Example 1. In Example 3, in order to clarify the effect of high temperature storage on low temperature discharge characteristics after storage, the discharge conditions after storage were performed at an ambient temperature of -20 ° C and a load resistance of 30 kΩ. The results are shown in Table 3.
[0038]
[Table 3]

[0039]
As is apparent from Table 3, the batteries N to Q having a volume ratio of propylene carbonate as a high dielectric constant solvent of 5 to 60% are excellent in all characteristics. On the other hand, in the battery L and the battery M in which the proportion of PC in the solvent is less than 5%, and in the battery R in which the proportion of PC is 70% or more, the discharge voltage and the discharge capacity ratio are also greatly reduced. Although the increase of internal resistance at the time of high temperature storage can be suppressed by adding propane sultone, the discharge characteristics at low temperature are inferior to those of other batteries. This is markedly affected by the conductivity of the electrolyte solution at a low temperature of −20 ° C. When the proportion of propylene carbonate having a low freezing point is less than 5%, or when propylene carbonate is added at a high rate of 70%. Nevertheless, when the ratio of 1,2 dimethoxyethane (DME), which is a low-viscosity solvent, becomes low, the conductivity of the electrolytic solution is lowered, which is considered to have caused the deterioration of discharge characteristics at low temperatures. Therefore, propylene carbonate is preferably in the range of 5 to 60% in volume ratio regardless of whether the solvent composition is a two-component system or a three-component system. In addition, although the present Example used propylene carbonate for the high dielectric constant solvent, the same result is obtained also in the case of (gamma) -butyrolactone (GBL).
[0040]
Example 4
As Example 4, the influence of the open circuit voltage before high-temperature storage on the storage characteristics was examined using the battery A of the present invention. Using the battery prepared in Example 1, a battery having different open circuit voltages was obtained by pre-discharging (partial discharge) the battery of about 3.6 V after assembly. Specifically, the preliminary discharge depth is set in the range of 0 to 5% of the positive electrode design capacity (100 mAh) by changing the time with a constant current discharge of 1 mA, and the open circuit voltage becomes 3.6 to 3.4 V. Ten batteries were produced. These batteries were evaluated in the same manner as in Example 1. The resulting discharge capacity ratios are shown in Table 4.
[0041]
[Table 4]

[0042]
As is apparent from Table 4, batteries having an open circuit voltage value of 3.46 V or less have an effect of adding propane sultone without capacity deterioration due to high temperature storage. On the other hand, when the battery was 3.51 V or more, the capacity was severely deteriorated, and when it was disassembled and examined, precipitation of stainless steel as the positive electrode case material was observed on the lithium surface. From the above, it can be seen that the effect of addition of ethylene sulfide can be sufficiently exhibited by setting the open circuit voltage to 3.5 to 3.4 V. In order to obtain this voltage value, it is preferable to pre-discharge a capacity of 1 to 5% of the positive electrode design capacity.
[0043]
In this embodiment, the coin type battery is described. However, the present invention can obtain the same result for various shapes of batteries such as a cylindrical type.
[0044]
【The invention's effect】
As is clear from the above description, a positive electrode made of graphitizable carbon having a (002) plane spacing of 3.50 mm or less or a fluorocarbon starting from a graphite material, and lithium ions can be released. A negative electrode and an organic electrolyte containing propane sultone to form a battery, and by making the open circuit voltage 3.5 V or less, it has excellent high-temperature storage characteristics, and voltage drops even during high-load discharge after storage In addition, a non-aqueous electrolyte battery excellent in intermittent discharge characteristics can be obtained. At the same time, even if stainless steel or the like is used as a battery constituent member, the characteristics are not deteriorated, and its industrial value is great.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing the configuration of a nonaqueous electrolyte battery in this embodiment.
1 Positive electrode can 2 Negative electrode can 3 Gasket 4 Positive electrode 5 Negative electrode 6 Separator

Claims

A nonaqueous electrolyte battery comprising a negative electrode made of metallic lithium or a lithium alloy, a positive electrode made of carbon fluoride, and an organic electrolyte, wherein the surface spacing of the (002) plane is 3.50 mm. The following graphitized carbon or graphite material is used as a starting carbon material, the organic electrolyte contains propane sultone, and the open circuit voltage after preliminary discharge is 3.5 V or less. Non-aqueous electrolyte battery.

The nonaqueous electrolyte battery according to claim 1, wherein propane sultone is contained at a ratio of 0.1 to 15 mass% with respect to the organic electrolyte.

The non-aqueous electrolyte battery according to claim 2, wherein the organic solvent constituting the organic electrolyte comprises a cyclic ester.

The non-aqueous electrolyte battery according to claim 3, wherein the organic solvent is at least one cyclic ester selected from ethylene carbonate, propylene carbonate, butylene carbonate, and γ-butyrolactone.

The non-aqueous electrolyte battery according to claim 2, wherein the organic electrolytic solution is a mixed solvent of a low-viscosity ether or chain ester and a cyclic ester.

6. The nonaqueous electrolyte battery according to claim 5, wherein the low viscosity ether is 1,2 dimethoxyethane.

The nonaqueous electrolyte battery according to claim 5, wherein the cyclic ester of the mixed solvent is at least one of γ-butyrolactone and propylene carbonate, and the cyclic ester is contained in a ratio of 5 to 60% by volume.

The non-aqueous electrolyte battery according to claim 3, wherein the graphitizable carbon has a spherical shape.