JP2004253296A - Electrolyte for secondary battery and secondary battery using it - Google Patents
Electrolyte for secondary battery and secondary battery using it Download PDFInfo
- Publication number
- JP2004253296A JP2004253296A JP2003043813A JP2003043813A JP2004253296A JP 2004253296 A JP2004253296 A JP 2004253296A JP 2003043813 A JP2003043813 A JP 2003043813A JP 2003043813 A JP2003043813 A JP 2003043813A JP 2004253296 A JP2004253296 A JP 2004253296A
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- JP
- Japan
- Prior art keywords
- secondary battery
- electrolyte
- lithium
- battery according
- negative electrode
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
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Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
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- Battery Electrode And Active Subsutance (AREA)
- Secondary Cells (AREA)
Abstract
Description
【0001】
【発明の属する技術分野】
本発明は、二次電池用電解液およびそれを用いた二次電池に関する。
【0002】
【従来の技術】
負極に炭素材料、酸化物、リチウム合金またはリチウム金属を用いた非水電解液リチウムイオン電池またはリチウム二次電池は、高いエネルギー密度を実現できることから携帯電話、ノートパソコン用などの電源として注目されている。この二次電池において、負極の表面には表面膜または保護膜またはSEI(Solid Electrolyte Interface:固体電解質界面)または皮膜と呼ばれる膜が生成することが知られている。この表面膜は、充放電効率、サイクル寿命、安全性に大きな影響を及ぼすことから負極の高性能化には表面膜の制御が不可欠であることが知られている。炭素材料、酸化物材料についてはその不可逆容量の低減が必要であり、リチウム金属、合金負極においては充放電効率の低下とデンドライト生成による安全性の問題を解決する必要がある。
【0003】
これらの課題を解決する手法として様々な手法が提案されてきている。たとえば、リチウム金属またはリチウム合金の表面に、化学反応を利用してフッ化リチウム等からなる皮膜層を設けることによってデンドライトの生成を抑制することが提案されている。
【0004】
特許文献1には、フッ化水素酸を含有する電解液にリチウム負極を曝し、負極をフッ化水素酸と反応させることによりその表面をフッ化リチウムの膜で覆う技術が開示されている。フッ化水素酸は、LiPF6および微量の水の反応により生成する。一方、リチウム負極表面には、空気中での自然酸化により水酸化リチウムや酸化リチウムの表面膜が形成されている。これらが反応することにより、負極表面にフッ化リチウムの表面膜が生成するのである。ところが、このフッ化リチウム膜は、電極界面と液との反応を利用して形成されるものであり、副反応成分が表面膜中に混入しやすく、均一な膜が得られにくい。また、水酸化リチウムや酸化リチウムの表面膜が均一に形成されていない場合や一部リチウムがむきだしになっている部分が存在する場合もあり、これらの場合には均一な薄膜の形成ができないばかりか、水やフッ化水素等とリチウムが反応することによる安全性の問題が生じる。また、反応が不充分であった場合には、フッ化物以外の不要な化合物成分が残り、イオン伝導性の低下を招く等の悪影響が考えられる。さらに、このような界面での化学反応を利用してフッ化物層を形成する方法では、利用できるフッ化物や電解液の選択幅が限定され、安定な表面膜を歩留まり良く形成することは困難であった。
【0005】
特許文献2では、アルゴンとフッ化水素の混合ガスとアルミニウム−リチウム合金とを反応させ、負極表面にフッ化リチウムの表面膜を得ている。ところが、リチウム金属表面にあらかじめ表面膜が存在する場合、特に複数種の化合物が存在する場合には反応が不均一になり易く、フッ化リチウムの膜を均一に形成することが困難である。このため、充分なサイクル特性のリチウム二次電池を得ることが困難となる。
【0006】
特許文献3には、均一な結晶構造すなわち(100)結晶面が優先的に配向しているリチウムシートの表面に、岩塩型結晶構造を持つ物質を主成分とする表面皮膜構造を形成する技術が開示されている。こうすることにより、均一な析出溶解反応すなわち電池の充放電を行うことができ、リチウム金属のデンドライト析出を抑え、電池のサイクル寿命が向上できるとされている。表面膜に用いる物質としては、リチウムのハロゲン化物を有していることが好ましく、LiCl、LiBr、LiIより選ばれる少なくとも一種と、LiFとの固溶体を用いることが好ましいと述べられている。具体的には、LiCl、LiBr、LiIの少なくとも一種と、LiFとの固溶体皮膜を形成するために、押圧処理(圧延)により作製した(100)結晶面が優先的に配向しているリチウムシートを、塩素分子もしくは塩素イオン、臭素分子もしくは臭素イオン、ヨウ素分子もしくはヨウ素イオンのうち少なくとも一種とフッ素分子もしくはフッ素イオンを含有している電解液に浸すことにより非水電解質電池用負極を作製している。この技術の場合、圧延のリチウム金属シートを用いており、リチウムシートが大気中に曝され易いため表面に水分などに由来する皮膜が形成され易く、活性点の存在が不均一となり、目的とした安定な表面膜を作ることが困難となり、デントライトの抑制効果は必ずしも充分に得られなかった。
【0007】
また、リチウムイオンを吸蔵、放出し得る黒鉛やハードカーボン等の炭素材料を負極として用いた場合、容量および充放電効率の向上に係る技術が報告されている。
【0008】
特許文献4では、アルミニウムで炭素材料を被覆した負極が提案されている。これにより、リチウムイオンと溶媒和した溶媒分子の炭素表面での還元分解が抑制され、サイクル寿命の劣化を抑えられるとされている。ただし、アルミニウムが微量の水と反応してしまうため、サイクルを繰り返すと急速に容量が低下するという課題を有している。
【0009】
また、特許文献5では、炭素材料の表面をリチウムイオン伝導性固体電解質の薄膜を被覆した負極が提示されている。これにより、炭素材料を使用した際に生じる溶媒の分解を抑制し、特に炭酸プロピレンを使用できるリチウムイオン二次電池を提供できるとしている。しかしながら、リチウムイオンの挿入、脱離時の応力変化により固体電解質中に生じるクラックが特性劣化を導く。また、固体電解質の結晶欠陥等の不均一性により、負極表面において均一な反応が得られずサイクル寿命の劣化につながる。
【0010】
また、特許文献6では、負極がグラファイトを含む材料からなり、電解液として環状カーボネート及び鎖状カーボネートを主成分とし、且つ電解液中に0.1重量%以上4重量%以下の1,3−プロパンスルトン及び/または1,4−ブタンスルトンを含んだ二次電池が開示されている。ここで、1,3−プロパンスルトンや1,4−ブタンスルトンは、炭素材料表面での不働態皮膜形成に寄与し、天然黒鉛や人造黒鉛などの活性で高結晶化した炭素材料を不働態皮膜で被覆し、電池の正常な反応を損なうことなく電解液の分解を抑制する効果を有するものと考えられている。
【0011】
また、直井等は、第68回電気化学会(2000年9月、千葉工業大学、講演番号:2A24)、第41回電池討論会(2000年11月、名古屋国際会議場、講演番号:1E03)の学会発表で、ユーロピウム等のランタノイド系遷移金属とビス(パーフルオロアルキルスルフォン)イミドアニオンの錯体のリチウム金属負極への効果について報告している。ここでは、プロピレンカーボネートまたはエチレンカーボネートと1,2−ジメトキシエタンの混合溶媒にリチウム塩としてLiN(C2F5SO2)2を溶解させた電解液に、さらにEu(CF3SO3)3を添加剤として添加し鎖状ビス(パーフルオロアルキルスルフォン)イミド錯体、Eu[(C2F5SO2)2N]3を電解液中で in situ 合成する事により鎖状パーフルオロアルキルスルフォンイミドアニオンのEu錯体を得、電解液中に浸漬されたLi金属上に当該錯体からなる表面膜を形成している。
【0012】
【特許文献1】
特開平7−302617号公報
【特許文献2】
特開平8−250108号公報
【特許文献3】
特開平11−288706号公報
【特許文献4】
特開平5−234583号公報
【特許文献5】
特開平5−275077号公報
【特許文献6】
特開2000−3724号公報
【0013】
【発明が解決しようとする課題】
ところが、上記従来技術は、次のような課題を有していた。
【0014】
負極表面に生成する表面膜は、その性質によって充放電効率、サイクル寿命、安全性に深く関わっているが、その膜の制御を長期にわたって行える手法はまだ存在していない。たとえば、リチウムやその合金からなる層の上にリチウムハロゲン化物またはガラス状酸化物からなる表面膜を形成した場合、初期使用時にはデントライトの抑制効果が一定程度得られるものの、繰り返し使用していると、表面膜が劣化して保護膜としての機能が低下することが本発明者の検討により明らかになった。これは、リチウムやその合金からなる層は、リチウムを吸蔵、放出することにより体積変化する一方、その上部に位置するリチウムハロゲン化物等からなる被膜は体積変化がほとんどないため、これらの層およびこれらの界面に内部応力が発生することが原因と推察される。このような内部応力が発生することにより、特にリチウムハロゲン化物等からなる表面膜の一部が破損し、デンドライトの抑制機能が低下するものと考えられる。
【0015】
また、黒鉛等の炭素材料に関しては、溶媒分子またはアニオンの分解による電荷が不可逆容量成分として現れ、初回充放電効率の低下を導く。また、このとき生じた膜の組成、結晶状態、安定性等がその後の効率、サイクル寿命に大きな影響を及ぼす。
【0016】
また、直井等の検討したリチウム金属表面に有機表面膜を形成する方法は、上述の従来技術よりサイクル寿命の改善にある程度の効果が得られているが、まだ改良の余地があった。
【0017】
このように、負極表面に生成する皮膜は、その性質によって充放電効率、サイクル寿命、安全性等に深く関わっているが、その膜の制御を長期にわたって行える手法はまだ存在しておらず、負極に安定で充分な充放電効率を導く皮膜を形成させる技術が求められていた。
【0018】
本発明は上記事情に鑑みてなされたものであり、その目的は、二次電池のサイクル寿命を安定で優れたものとする二次電池用電解液を提供することにある。また、本発明の別の目的は、安定で優れたサイクル寿命と高い充放電効率を発揮する二次電池を提供することにある。
【0019】
【課題を解決するための手段】
本発明者は、LiN(C2F5SO2)2を含有しない電解液、たとえば現在市販されているリチウムイオン二次電池で汎用されている電解質(LiPF6)を適用する場合、事前に別途合成したEu[(C2F5SO2)2N]3錯体を電解液に直接溶解させることにより、容易に効果が得られること、さらには上述の直井らによる電解液中での in situ 錯体製造法に比べより優れた電解液を得られることを見出した。
【0020】
またさらに鋭意研究を重ねた結果、非プロトン性溶媒に、環状パーフルオロアルキレンジスルフォンイミドアニオンと、遷移金属イオンとが含まれる電解液を適用して二次電池を作製した場合に充放電効率に優れサイクル特性が良好となることを見出し本発明に至った。
【0021】
本発明によれば、非プロトン性溶媒と、環状パーフルオロアルキレンジスルフォンイミドアニオンと、遷移金属イオンとを含むことを特徴とする二次電池用電解液が提供される。
【0022】
環状パーフルオロアルキレンジスルフォンイミドアニオンおよび遷移金属イオンを含む電解液を用いることにより、従来のビス(鎖状パーフルオロアルキレンスルフォン)イミドアニオンおよび遷移金属イオンを含む電解液よりもさらに電池特性を向上させることが可能となる。なお、ここで言う鎖状パーフルオロアルキルスルフォンイミドアニオンとは−N(CkF2k+1SO2)2または−N(CkF2k+1SO2)(CmF2m+1SO2)(k、mは自然数)のことである。
【0023】
本発明によれば、非プロトン性溶媒と、リチウム塩と、環状パーフルオロアルキレンジスルフォンイミドアニオンおよび遷移金属イオンからなる金属錯体と、を含むことを特徴とする二次電池用電解液が提供される。本発明に係る二次電池用電解液は、環状パーフルオロアルキレンジスルフォンイミドアニオンおよび遷移金属イオンからなる金属錯体を含むため、電池のサイクル特性をより一層向上させることができる。
【0024】
本発明の二次電池用電解液において、前記環状パーフルオロアルキレンジスルフォンイミドアニオンは下記一般式(1)で表されてもよい。
【0025】
【化3】
【0026】
(ただし、上記一般式(1)において、Rfは炭素数2〜4の直鎖状または分岐状パーフルオロアルキレン基を表す。)
【0027】
本発明の二次電池用電解液において、環状パーフルオロアルキレンジスルフォンイミドアニオンおよび遷移金属イオンからなる前記金属錯体は、下記一般式(2)で表されてもよい。
【0028】
【化4】
【0029】
(ただし、上記一般式(2)において、Rfは炭素数2〜4の直鎖状または分岐状パーフルオロアルキレン基を表す。また、nは1〜3の整数であり、Mは遷移金属原子を表す。)
【0030】
本発明の二次電池用電解液において、前記遷移金属イオンがランタノイド系遷移金属イオンであってもよい。本発明の二次電池用電解液において、前記ランタノイド系遷移金属イオンが、ユウロピウムイオン、ネオジウムイオン、エルビウムイオンまたはホルミウムイオンのいずれかを含むことができる。
【0031】
Eu、Nd、Er、Hoの酸化還元電位は、負極活物質として用いられるリチウム金属またはその合金や黒鉛の酸化還元電位に等しいかまたは近く、リチウムよりも0V〜0.8V高い電位で還元可能である。このように負極活物質の酸化還元電位と近い金属を選択し、これらと安定な錯体を形成するアニオンを選ぶことにより、これらの金属が容易に還元されなくなる。従って、ランタノイド系金属カチオンとイミドアニオンからなる錯体は、負極と電解液の界面により安定に存在することができる。
【0032】
本発明の二次電池用電解液において、スルホン化合物をさらに含むことができる。
【0033】
環状パーフルオロアルキレンジスルフォンイミドアニオンおよび遷移金属イオンが形成する金属錯体と、スルホン化合物の二つの化合物が負極表面に存在することは次のような効果をもたらす。負極表面には、溶媒分子との反応を引き起こすダングリングボンドと、反応性のない部位が存在している。添加するイミド塩によって生成する金属錯体や、イミド塩と遷移金属イオンによって形成される金属錯体は上述の反応性のない部位に吸着するによって安定化皮膜を形成し、リチウムイオン伝導を行う。また、スルホン化合物は、負極表面での不働態皮膜形成に寄与し、結果として溶媒分子の分解を抑制する。
【0034】
本発明の二次電池用電解液において、前記スルホン化合物が、1,3−プロパンスルトン、1,4−ブタンスルトン、スルホラン、アルカンスルホン酸無水物、γ−スルトン化合物またはスルホレン化合物のいずれかを含むことができる。また、本発明の二次電池用電解液において、ビニレンカーボネートまたはその誘導体をさらに含んでもよい。こうすることにより、電池のサイクル特性をさらに向上させることができる。
【0035】
本発明の二次電池用電解液において、前記非プロトン性溶媒が、環状カーボネート類、鎖状カーボネート類、脂肪族カルボン酸エステル類、γ−ラクトン類、環状エーテル類、鎖状エーテル類またはそれらのフッ化誘導体のいずれかを含んでもよい。
【0036】
本発明の二次電池用電解液において、前記リチウム塩が、LIPF6、LiBF4、LiAsF6、LiSbF6、LiClO4、LiAlCl4、LiN(CkF2k+1SO2)2またはLiN(CkF2k+1SO2)(CmF2m+1SO2)(k、mは自然数)のいずれかを含んでもよい。
【0037】
本発明によれば、少なくとも正極と負極を備えた二次電池において、前記二次電池用電解液を有することを特徴とする二次電池が提供される。
【0038】
本発明に係る二次電池において、電解液は、安定な皮膜を与える環状パーフルオロアルキレンジスルフォンイミドアニオンと遷移金属イオン、または環状パーフルオロアルキレンジスルフォンイミドアニオンと遷移金属イオンからなる遷移金属錯体を電解液にあらかじめ添加することによりもたらされる。この錯体は、遷移金属カチオンにイミドアニオンが配位した安定な錯体である。この錯体が負極表面へ吸着することにより、負極表面が安定化される。また、この電解液にさらにスルホン化合物あるいはビニレンカーボネート化合物を加えることによりスルホン化合物あるいはビニレンカーボネート化合物を含有する電解液が得られる。スルホン化合物は負極界面でダングリングボンドと反応することにより、安定な皮膜を形成する。この二つの作用(吸着と反応)により、溶媒分子の分解を抑えることができサイクル特性が向上する。
【0039】
本発明の二次電池において、正極活物質として、リチウム含有複合酸化物を含むことができる。こうすることにより、電池のエネルギー密度を向上させることができる。
【0040】
本発明の二次電池において、負極活物質として、リチウムを吸蔵、放出できる材料、リチウム金属、リチウムと合金を形成しうる金属材料、および酸化物材料、からなる群から選択される一または二以上の物質を含んでもよい。
【0041】
特に負極が金属リチウムである場合には、負極表面のリチウムと負極表面に吸着した上記イミドアニオンとの反応生成物であるフッ化リチウムおよび遷移金属の一部がリチウムと合金化することにより、電流密度の分布を均一にし、デンドライト等の生成を抑える。
【0042】
さらに、皮膜が機械的に壊れた際には、その壊れた箇所において、上述のフッ化リチウムが、皮膜を修復する機能を有しており、皮膜が破壊された後においても、安定な表面化合物の生成を導く効果を有している。このため、イミドアニオンを含むことにより、長期にわたるサイクル寿命が実現される。
【0043】
本発明の二次電池において、前記負極活物質が炭素材料を含んでもよい。
【0044】
本発明の二次電池において、前記炭素材料が黒鉛であってもよい。また、本発明の二次電池において、前記炭素材料が非晶質炭素であってもよい。
【0045】
本発明において、リチウムを活物質とする負極と正極をセパレータを隔てて組み合わせ、電池外装体に挿入後、金属錯体を含む電解液を含浸させた後、電池外装体を封止または封止後に、電池を充電することにより、前記負極上に皮膜を形成させてもよい。こうすることによりサイクル特性に優れた電池が安定的に供給される。
【0046】
【発明の実施の形態】
図1に本発明に係る電池の一例について概略構造を示す。正極集電体11と、リチウムイオンを吸蔵、放出し得る酸化物またはイオウ化合物、導電性高分子、安定化ラジカル化合物のいずれかまたは混合物からなる正極活物質を含有する層12と、リチウムイオンを吸蔵、放出する炭素材料または酸化物、リチウムと合金を形成する金属、リチウム金属自身のいずれかもしくはこれらの混合物からなる負極活物質を含有する層13と、負極集電体14と、電解液15、およびこれを含む多孔質セパレータ16から構成されている。
【0047】
電解液15は、電解質としてリチウム塩が溶解されており、環状パーフルオロアルキレンジスルフォンイミドアニオンと、遷移金属イオンとを含む。また、スルホン化合物またはビニレンカーボネート化合物をさらに含んでいてもよい。
【0048】
リチウム塩としては、たとえばLIPF6、LiBF4、LiAsF6、LiSbF6、LiClO4、LiAlCl4、LiN(CkF2k+1SO2)2、LiN(CkF2k+1SO2)(CmF2m+1SO2)(k、mは自然数)を用いることができる。特にLiPF6、LiBF4が好ましい。
【0049】
環状パーフルオロアルキレンジスルフォンイミドアニオンとして、たとえば下記一般式(1)で表される化合物が好適に用いられる。
【0050】
【化5】
【0051】
(ただし、上記一般式(1)において、Rfは炭素数2〜4の直鎖状または分岐状パーフルオロアルキレン基を表す。)
【0052】
上記一般式(1)で表される金属錯体はたとえば米国特許第4429093号、米国特許第4387222号、ドイツ公開特許第2239817号、特開2000―63682号公報などに記載の公知の方法により製造できる。
【0053】
本発明の一般式(1)の化合物の具体例を下記式(3)〜(6)に例示するが、本発明はこれらに限定されるものではない。
【0054】
【化6】
【0055】
【化7】
【0056】
【化8】
【0057】
【化9】
【0058】
なお、上記式(3)に示したイミドアニオンを以下A1とも表す。また、上記式(4)〜(6)に示したイミドアニオンを、以下同様にA2〜A4とも表す。
【0059】
遷移金属イオンとしては、ランタノイド系遷移金属のイオンを用いることが好ましい。たとえば、ユウロピウム(Eu)イオン、ネオジウム(Nd)イオン、エルビウム(Er)イオンまたはホルミウム(Ho)イオンのいずれかもしくは混合物とすることができる。
【0060】
環状パーフルオロアルキレンジスルフォンイミドアニオンと遷移金属イオンとは錯体を形成していてもよい。錯体は、たとえば下記一般式(2)で示される構造とすることができる。
【0061】
【化10】
【0062】
(ただし、上記一般式(2)において、Rfは炭素数2〜4の直鎖状または分岐状パーフルオロアルキレン基を表す。また、nは1〜3の整数であり、Mは遷移金属原子を表す。)
【0063】
環状パーフルオロアルキレンジスルフォンイミドアニオンまたはその金属錯体は、電解液15中に0.01〜10重量%含まれることが好ましい。0.01重量%以上とすることにより、負極表面への被膜形成効果を確実に発揮させることができる。また10重量%以下とすることにより、電解液15への溶解性が確保され、また電解液15の粘度上昇が好適に抑制される。より好ましくは、0.05〜5重量%の範囲で添加するとさらに充分な皮膜効果が得られる。
【0064】
また、スルホン化合物としては、具体的には特開昭60−154478号公報に示されるスルホラン、特開昭62−100948号公報、特開昭63−102173号公報、特開平11−339850号公報、特開2000−3724号公報に示される1,3−プロパンスルトンもしくは1,4−ブタンスルトン、特開平10−189041号公報に示されるアルカンスルホン酸無水物、特開平10−50342号公報に示される1,3,2−ジオキサホスホラン−2−オキサイド誘導体、特開2000−235866号公報に示されるγ−スルトン化合物、または特開2000−294278号公報に示されるスルホレン誘導体などが挙げられるがこれに限定されるものではない。
【0065】
スルホン化合物は電解液15中に0.01〜10重量%含まれることが好ましい。0.01重量%未満では負極表面での皮膜形成に充分効果がない。0.01重量%以上とすることにより、負極表面への被膜形成効果を確実に発揮させることができる。また10重量%以下とすることにより、電解液15への溶解性が確保され、また電解液15の粘度上昇による抵抗の増加が好適に抑制される。より好ましくは、0.05〜5重量%の範囲で添加するとさらに充分な皮膜効果が得られる。
【0066】
また、ビニレンカーボネートまたはその誘導体としては、たとえば特開平4−169075号公報、特開平7−122296号公報、特開平8−45545号公報、特開平5−82138号公報、特開平5−74486号公報、特開平6−52887号公報、特開平11−260401号公報、特開2000−208169号公報、特開2001−35530号公報、特開2000−138071号公報に示される化合物を適宜使用することができる。これらのビニレンカーボネートまたはその誘導体を後述の添加剤として使用する場合には、電解液15中に0.01〜10重量%含ませることで効果が得られる。また、溶媒として用いる場合には1〜5重量%含ませることで効果が得られる。
【0067】
電解液15に用いる溶媒としては、プロピレンカーボネート(PC)、エチレンカーボネート(EC)、ブチレンカーボネート(BC)、ビニレンカーボネート(VC)等の環状カーボネート類、ジメチルカーボネート(DMC)、ジエチルカーボネート(DEC)、エチルメチルカーボネート(EMC)、ジプロピルカーボネート(DPC)等の鎖状カーボネート類、ギ酸メチル、酢酸メチル、プロピオン酸エチル等の脂肪族カルボン酸エステル類、γ−ブチロラクトン等のγ−ラクトン類、1,2−エトキシエタン(DEE)、エトキシメトキシエタン(EME)等の鎖状エーテル類、テトラヒドロフラン、2−メチルテトラヒドロフラン等の環状エーテル類、ジメチルスルホキシド、1,3−ジオキソラン、ホルムアミド、アセトアミド、ジメチルホルムアミド、ジオキソラン、アセトニトリル、プロピルニトリル、ニトロメタン、エチルモノグライム、リン酸トリエステル、トリメトキシメタン、ジオキソラン誘導体、スルホラン、メチルスルホラン、1,3−ジメチル−2−イミダゾリジノン、3−メチル−2−オキサゾリジノン、プロピレンカーボネート誘導体、テトラヒドロフラン誘導体、エチルエーテル、1,3−プロパンスルトン、アニソール、N−メチルピロリドン、フッ素化カルボン酸エステルなどの非プロトン性有機溶媒を一種または二種以上を混合して使用し、これらの有機溶媒に溶解するリチウム塩を溶解させる。
【0068】
電解液15は、たとえば
(i)遷移金属イオンとイミドアニオンからなる金属錯体をあらかじめ溶解させ、さらに必要に応じスルホン化合物あるいはビニレンカーボネート化合物を溶解させる方法、
または、
(ii)環状パーフルオロアルキレンイミドリチウム塩と遷移金属イオンを溶解させさらにスルホン化合物あるいはビニレンカーボネート化合物を溶解させる方法、
の二つの方法により作製される。
【0069】
図1の二次電池において、負極は、上述のように、リチウム金属、リチウム合金または炭素材料や酸化物等のリチウムを吸蔵、放出できる材料により構成されている。
【0070】
この炭素材料としては、リチウムを吸蔵する黒鉛、非晶質炭素、ダイヤモンド状炭素、カーボンナノチューブ、カーボンナノホーンなど、あるいはこれらの複合物を用いることができる。
【0071】
また、酸化物としては、酸化シリコン、酸化スズ、酸化インジウム、酸化亜鉛、酸化リチウム、リン酸、ホウ酸のいずれか、あるいはこれらの複合物を用いてもよく、特に酸化シリコンを含むことが好ましい。構造としてはアモルファス状態であることが好ましい。これは、酸化シリコンが安定で他の化合物との反応を引き起こさないため、またアモルファス構造が結晶粒界、欠陥といった不均一性に起因する劣化を導かないためである。成膜方法としては、蒸着法、CVD法、スパッタリング法などの方法を用いることができる。
【0072】
リチウム合金は、リチウムおよびリチウムと合金形成可能な金属により構成される。たとえばAl、Si、Pb、Sn、In、Bi、Ag、Ba、Ca、Hg、Pd、Pt、Te、Zn、Laなどの金属とリチウムとの2元または3元以上の合金により構成される。リチウム金属乃至リチウム合金としては、特にアモルファス状合金が好ましい。これは、アモルファス構造により結晶粒界、欠陥といった不均一性に起因する劣化が起きにくいためである。
【0073】
リチウム金属またはリチウム合金は、融液冷却方式、液体急冷方式、アトマイズ方式、真空蒸着方式、スパッタリング方式、プラズマCVD方式、光CVD方式、熱CVD方式、ゾルーゲル方式、などの適宜な方式で形成することができる。
【0074】
負極は、遷移金属イオンと環状パーフルオロアルキルイミドアニオンからなる錯体を電解質溶液との界面に存在させることによって、金属、合金相の体積変化に対する柔軟性、イオン分布の均一性、物理的・化学的安定性に優れたものとなる。その結果、デンドライト生成やリチウムの微粉化を効果的に防止することができ、サイクル効率と寿命が向上する。また、炭素材料、酸化物材料の表面に存在する不可逆容量サイトは、化学的活性が高く、容易に溶媒が分解してしまう。この表面に、遷移金属カチオンとイミドアニオンからなる錯体を吸着させることによって、溶媒の分解が抑制され、不可逆容量が大きく減少されるため、充放電効率が減少しない。
【0075】
図1の二次電池において、正極活物質としては、LibZO2(ただしZは、少なくとも1種の遷移金属を表す。)である複合酸化物、たとえば、LibCoO2、LibNiO2、LibMn2O4、LibMnO3、LibNidCr1−dO2(ここで、0<b<1、0<d<1である。)など、または有機イオウ化合物、導電性高分子、有機ラジカル化合物などを用いることができる。また、金属リチウム対極電位で4.5V以上にプラトーを有するリチウム含有複合酸化物を用いることもできる。リチウム含有複合酸化物としては、スピネル型リチウムマンガン複合酸化物、オリビン型リチウム含有複合酸化物、逆スピネル型リチウム含有複合酸化物等が例示される。リチウム含有複合酸化物は、たとえば一般式Lia(AxMn2−x)O4(ここで、0<x<2、0<a<1.2である。Aは、Ni、Co、Fe、CrおよびCuよりなる群から選ばれる少なくとも一種である。)で表される化合物とすることができる。
【0076】
正極は、これらの活物質を、カーボンブラック等の導電性物質、ポリビニリデンフルオライド(PVDF)等の結着剤とともにN−メチル−2−ピロリドン(NMP)等の溶剤中に分散混練し、これをアルミニウム箔等の基体上に塗布するなどの方法により得ることができる。
【0077】
図1の二次電池は、乾燥空気または不活性ガス雰囲気において、負極および正極を、セパレータを介して積層、あるいは積層したものを捲回した後に、電池缶に収容したり、合成樹脂と金属箔との積層体からなる可撓性フィルム等によって封口することによって製造することができる。なお、セパレータとしては、ポリプロピレン、ポリエチレン等のポリオレフィン、フッ素樹脂等の多孔性フィルムが用いられる。
【0078】
本発明に係る二次電池の形状に特に制限はなく、たとえば、円筒型、角型、コイン型、ラミネート型などがあげられる。
【0079】
以上、本発明を実施の形態をもとに説明した。この実施の形態は例示であり、それらの各構成要素や各処理プロセスの組合せにいろいろな変形例が可能なこと、またそうした変形例も本発明の範囲にあることは当業者に理解されるところである。
【0080】
【実施例】
(実施例1)
(電池の作製)
正極集電体11に厚さ20μmのアルミニウム箔、正極中の正極活物質にLiMn2O4、負極に負極集電体14の10μmの銅箔上に蒸着した20μmのリチウム金属を用いた。また電解液15については、溶媒としてECとDEC混合溶媒(体積比:30/70)を用い、この溶媒中に1molL−1のLiPF6を溶解させた。添加剤として、上記式(3)に示される1,2−パーフルオロエチレンジスルフォンイミドのユーロピニウム錯体(以下、「Eu(A1)3」とも記す。)を、電解液15全体の0.5重量%含まれるように加え、溶解した。そして、負極と正極とをポリエチレンからなる多孔質セパレータ16を介して積層し、コイン型二次電池を作製した。
【0081】
(充放電サイクル試験)
温度20℃において、充電レート0.05C、放電レート0.1C、充電終止電圧4.2V、放電終止電圧3.0Vとし、リチウム金属負極の利用率(放電深度)は33%とした。容量維持率(%)は300サイクル後の放電容量(mAh)を、10サイクル目の放電容量(mAh)で割った値である。サイクル試験で得られた結果を下記表1に示す。
【0082】
(実施例2〜4)
実施例1に示したEu(A1)3の代わりに、表1に示す添加剤で電池を構成した。これ以外は、実施例1と同様にして電池を作製し評価した。実施例1と同様にサイクル特性を調べた結果を表1に示す。
【0083】
(比較例1)
電解液中に、遷移金属イミドアニオン錯体を添加しないこと以外、実施例1と同様の電池を作製した。実施例1と同様にサイクル特性を調べた結果を表1に示す。
【0084】
(比較例2)
電解液中に、環状パーフルオロアルキレンジスルフォンイミド遷移金属錯体に代えて、ビス(鎖状パーフルオロアルキルスルフォン)イミド錯体であるEu[N(C2F5SO2)2]3を用いたこと以外、実施例1と同様にして電池を作製した。実施例1と同様にサイクル特性を調べた結果を表1に示す。
【0085】
【表1】
【0086】
表1より、実施例1〜4における容量維持率は、比較例1のそれらよりも大きく上回っている。これは、負極表面と電解質との界面に存在する表面膜の安定化と、その膜の高いイオン伝導性によって、不可逆反応およびデンドライト生成が抑制されたためと考えられる。さらに比較例2の鎖状パーフルオロアルキルスルフォンイミド錯体に比べ優れた特性を示すことは明らかである。実際に、各実施例に示した電池について、サイクル後の負極表面をX線光電子分光法(XPS)とエネルギー分散型X線分析(EDX)を用いて調べたところ、LiF、ランタノイド系金属、イミドアニオン分子の存在が示された。
【0087】
(実施例5)
Eu(A1)3錯体に代えてEu(A2)3錯体を用い、負極活物質として黒鉛材料で構成すること以外、実施例1と同様の電池を作製し、実施例1と同様にサイクル特性を調べた。結果を表2に示す。本実施例に示した電池について、サイクル後の負極表面をX線光電子分光法(XPS)とエネルギー分散型X線分析(EDX)を用いて調べたところ、LiF、ランタノイド系金属、イミドアニオン分子の存在が示された。
【0088】
(実施例6)
電解質溶媒をECとDEC混合溶媒(体積比:30/70)に代えてPCとECとDEC混合溶媒(体積比:20/20/60)を用い、負極活物質として非晶質炭素を用い、Eu(A1)3錯体に代えてNd(A2)3錯体を用いること以外、実施例1と同様に電池を作製し、実施例1と同様にサイクル特性を調べた。結果を表2に示す。本実施例に示した電池について、サイクル後の負極表面をX線光電子分光法(XPS)とエネルギー分散型X線分析(EDX)を用いて調べたところ、LiF、ランタノイド系金属、イミドアニオン分子の存在が示された。
【0089】
(比較例3)
添加剤を加えないこと以外は実施例5と同様にして比較例3の電池を作製した。得られた電池について実施例1と同様の評価を行った。結果を表2に示す。
【0090】
(比較例4)
添加剤を加えないこと以外は実施例6と同様にして比較例4の電池を作製した。得られた電池について実施例1と同様の評価を行った。結果を表2に示す。
【0091】
(比較例5)
添加剤としてEu(A2)3に代えてEu[N(C2F5SO2)2]3を加えること以外は実施例5と同様にして比較例5の電池を作製した。得られた電池について実施例1と同様の評価を行った。結果を表2に示す。
【0092】
(比較例6)
添加剤としてNd(A2)3に代えてNd[N(C2F5SO2)2]3を加えること以外は実施例6と同様にして比較例6の電池を作製した。得られた電池について実施例1と同様の評価を行った。結果を表2に示す。
【0093】
【表2】
【0094】
表2に結果を示した。実施例5〜6と比較例3〜6とを比較すると、環状パーフルオロアルキレンジスルフォンイミド錯体を用いることにより、比較例と比べて容量維持率が高いことがわかる。この結果から、リチウム金属のみだけでなく、黒鉛、非晶質炭素のいずれかを負極活物質として用いた場合にも、実施例1と同様の効果があった。
【0095】
(実施例7)
(電池の作製)
本実施例の電池の作製について説明する。正極集電体に厚さ20μmのアルミニウム箔、正極中の正極活物質にLiMn2O4を用いた。また。負極中の負極活物質に、負極集電体14となる10μmの銅箔上に蒸着した20μmのリチウム金属を用いた。電解液15の溶媒として、ECとDEC混合溶媒(体積比:30/70)を用い、支持電解質として1molL−1のLiPF6を用いた。添加剤としてEu3+の遷移金属塩すなわちEu(A3)3を用い、これを電解液15全体の0.3重量%となるよう溶解させた。さらに、1,3−プロパンスルトン(以下、1,3−PSとも記す)を電解液15全体の1重量%含むように添加した。そして、負極と正極とをポリエチレンからなる多孔質セパレータ16を介して積層し、二次電池を作製した。
【0096】
(充放電サイクル試験)
実施例1に記載の方法と同様にして得られた電池の評価を実施した。結果を下記表3に示す。
【0097】
(実施例8)
実施例7のEu(A3)3に代えてNd(A3)3を用い、電解質溶媒をECとDEC混合溶媒(体積比:30/70)に代えてPCとECとDEC混合溶媒(体積比:20/20/60)を用いる以外は、実施例7と同様にして電池を作製し評価した。実施例7と同様にサイクル特性を調べた結果を表3に示す。
【0098】
【表3】
【0099】
表3より、実施例7および実施例8におけるサイクル試験後の容量維持率は、それぞれ実施例1あるいは実施例6に比較して上回っている。これは、負極表面と電解質との界面に存在する皮膜の安定化と、その膜の高いイオン伝導性によって、不可逆反応が抑制されたためと考えられる。
【0100】
(実施例9)
本実施例では、添加剤として遷移金属錯体、1,3−PSおよびビニレンカーボネート(VC)を含有させた電解液15を用いた。正極集電体に厚さ20μmのアルミニウム箔、正極中の正極活物質にLiMn2O4を用いた。また、負極中の負極活物質に、負極集電体14となる厚さ10μmの銅箔上に蒸着した20μmのリチウム金属を用いた。
電解液15の溶媒として、ECとDEC混合溶媒(体積比:30/70)を用い、この溶媒中に1molL−1のLiPF6を溶解させた。添加剤として、Eu(A4)3錯体を用い、これを電解液15全体の0.3重量%含まれるように加えた。次に、1,3−PSとVCを電解液15中にそれぞれ1重量%含まれるよう加え、本実施例の電解液15を得た。そして、負極と正極とをポリエチレンからなる多孔質セパレータ16を介して積層し、二次電池を作製した。
【0101】
(充放電サイクル試験)
実施例1に記載の方法と同様にして得られた電池の評価を実施した。得られた結果を表4に示す。
【0102】
(実施例10)
実施例9においてVCを添加しないこと以外は実施例9と同様にして二次電池を作製した。
【0103】
【表4】
【0104】
表4より、実施例9に示した電池は、実施例10の電池と比較して、サイクル試験後の容量維持率がさらに向上していること、すなわち金属錯体とスルホン化合物が含まれる電解液にVCをさらに添加することでサイクル特性がより改善されていることが確認された。
【0105】
【発明の効果】
以上説明したように本発明によれば、非プロトン性溶媒と、環状パーフルオロアルキレンジスルフォンイミドアニオンと、遷移金属イオンと、を含むことにより、二次電池のサイクル寿命を安定で優れたものとする二次電池用電解液が実現される。また、本発明によれば、安定で優れたサイクル寿命と高い充放電効率を発揮する二次電池が実現される。
【図面の簡単な説明】
【図1】本実施形態に係る二次電池の概略構成図である。
【符号の説明】
11 正極集電体
12 正極活物質を含有する層
13 負極活物質を含有する層
14 負極集電体
15 電解液
16 多孔質セパレータ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electrolyte for a secondary battery and a secondary battery using the same.
[0002]
[Prior art]
Non-aqueous electrolyte lithium-ion batteries or lithium secondary batteries using carbon materials, oxides, lithium alloys or lithium metal for the negative electrode have been attracting attention as power sources for mobile phones and notebook computers because of their high energy density. I have. In this secondary battery, it is known that a film called a surface film or a protective film or a SEI (Solid Electrolyte Interface) or a film is formed on the surface of the negative electrode. It is known that control of the surface film is indispensable for improving the performance of the negative electrode because the surface film has a large effect on charge / discharge efficiency, cycle life, and safety. It is necessary to reduce the irreversible capacity of carbon materials and oxide materials, and it is necessary to solve the problems of safety due to reduction in charge / discharge efficiency and generation of dendrites in lithium metal and alloy negative electrodes.
[0003]
Various methods have been proposed as methods for solving these problems. For example, it has been proposed to suppress the generation of dendrites by providing a coating layer made of lithium fluoride or the like on the surface of lithium metal or a lithium alloy using a chemical reaction.
[0004]
Patent Literature 1 discloses a technique in which a lithium negative electrode is exposed to an electrolytic solution containing hydrofluoric acid, and the negative electrode is reacted with hydrofluoric acid to cover the surface with a lithium fluoride film. Hydrofluoric acid is LiPF 6 And a small amount of water. On the other hand, a surface film of lithium hydroxide or lithium oxide is formed on the surface of the lithium negative electrode by natural oxidation in air. When these react, a surface film of lithium fluoride is formed on the surface of the negative electrode. However, this lithium fluoride film is formed by utilizing the reaction between the electrode interface and the liquid, and the side reaction components easily mix into the surface film, and it is difficult to obtain a uniform film. In addition, there are cases where the surface film of lithium hydroxide or lithium oxide is not formed uniformly, or where there is a part where lithium is exposed, and in these cases, a uniform thin film cannot be formed. Alternatively, there is a safety problem due to the reaction of lithium with water or hydrogen fluoride. In addition, when the reaction is insufficient, unnecessary compound components other than the fluoride remain, which may adversely affect the ion conductivity. Furthermore, in the method of forming a fluoride layer using such a chemical reaction at the interface, the selection range of available fluorides and electrolytes is limited, and it is difficult to form a stable surface film with high yield. there were.
[0005]
In Patent Document 2, a mixed gas of argon and hydrogen fluoride is reacted with an aluminum-lithium alloy to obtain a lithium fluoride surface film on the negative electrode surface. However, when a surface film is present on the lithium metal surface in advance, particularly when a plurality of compounds are present, the reaction tends to be nonuniform, and it is difficult to form a lithium fluoride film uniformly. For this reason, it is difficult to obtain a lithium secondary battery having sufficient cycle characteristics.
[0006]
Patent Literature 3 discloses a technique for forming a surface film structure mainly composed of a material having a rock salt type crystal structure on the surface of a lithium sheet in which a uniform crystal structure, that is, a (100) crystal plane is preferentially oriented. It has been disclosed. By doing so, a uniform precipitation-dissolution reaction, that is, charge / discharge of the battery can be performed, dendrite precipitation of lithium metal can be suppressed, and the cycle life of the battery can be improved. It is stated that the material used for the surface film preferably has a halide of lithium, and it is preferable to use a solid solution of LiF and at least one selected from LiCl, LiBr and LiI. Specifically, in order to form a solid solution film of at least one of LiCl, LiBr, and LiI and LiF, a lithium sheet having a (100) crystal plane preferentially oriented by pressing treatment (rolling) produced by pressing (rolling) is used. A negative electrode for a non-aqueous electrolyte battery is manufactured by immersing in an electrolytic solution containing at least one of chlorine molecules or chlorine ions, bromine molecules or bromine ions, iodine molecules or iodine ions, and fluorine molecules or fluorine ions. . In the case of this technique, a rolled lithium metal sheet is used, and since the lithium sheet is easily exposed to the air, a film derived from moisture or the like is easily formed on the surface, and the existence of active points becomes non-uniform, and the intended purpose is obtained. It became difficult to form a stable surface film, and the effect of suppressing dentite was not always sufficiently obtained.
[0007]
In addition, when a carbon material such as graphite or hard carbon capable of occluding and releasing lithium ions is used as a negative electrode, a technique relating to improvement in capacity and charge / discharge efficiency has been reported.
[0008]
Patent Literature 4 proposes a negative electrode in which a carbon material is coated with aluminum. Thereby, reductive decomposition of solvent molecules solvated with lithium ions on the carbon surface is suppressed, and deterioration of cycle life is suppressed. However, since aluminum reacts with a very small amount of water, there is a problem that the capacity is rapidly reduced when the cycle is repeated.
[0009]
Patent Literature 5 discloses a negative electrode in which a surface of a carbon material is coated with a thin film of a lithium ion conductive solid electrolyte. It is stated that this can suppress the decomposition of the solvent that occurs when the carbon material is used, and provide a lithium ion secondary battery that can use propylene carbonate in particular. However, cracks generated in the solid electrolyte due to stress changes at the time of lithium ion insertion and desorption lead to characteristic deterioration. In addition, due to non-uniformity such as crystal defects of the solid electrolyte, a uniform reaction cannot be obtained on the negative electrode surface, leading to a deterioration in cycle life.
[0010]
Further, in Patent Document 6, the negative electrode is made of a material containing graphite, and mainly contains cyclic carbonate and chain carbonate as an electrolytic solution, and 0.1 to 4 wt% of 1,3- in the electrolytic solution. A secondary battery containing propane sultone and / or 1,4-butane sultone is disclosed. Here, 1,3-propane sultone and 1,4-butane sultone contribute to the formation of a passive film on the surface of the carbon material, and passivate the active and highly crystallized carbon material such as natural graphite and artificial graphite. It is considered that the coating has the effect of suppressing the decomposition of the electrolytic solution without impairing the normal reaction of the battery.
[0011]
Naoi et al. Are the 68th Electrochemical Society of Japan (September 2000, Chiba Institute of Technology, lecture number: 2A24), and the 41st Battery Symposium (November 2000, Nagoya International Convention Center, lecture number: 1E03). Report on the effect of a complex of a lanthanoid transition metal such as europium and a bis (perfluoroalkylsulfone) imide anion on a lithium metal anode. Here, LiN (C) is used as a lithium salt in a mixed solvent of propylene carbonate or ethylene carbonate and 1,2-dimethoxyethane. 2 F 5 SO 2 ) 2 Is further added to the electrolyte in which Eu (CF) is dissolved. 3 SO 3 ) 3 Is added as an additive to form a chain bis (perfluoroalkylsulfone) imide complex, Eu [(C 2 F 5 SO 2 ) 2 N] 3 Is synthesized in situ in an electrolytic solution to obtain an Eu complex of a chain perfluoroalkylsulfonimide anion, and a surface film made of the complex is formed on Li metal immersed in the electrolytic solution.
[0012]
[Patent Document 1]
JP-A-7-302617
[Patent Document 2]
JP-A-8-250108
[Patent Document 3]
JP-A-11-288706
[Patent Document 4]
JP-A-5-234585
[Patent Document 5]
JP-A-5-275077
[Patent Document 6]
JP-A-2000-3724
[0013]
[Problems to be solved by the invention]
However, the above-described prior art has the following problems.
[0014]
The surface film formed on the negative electrode surface is closely related to the charge / discharge efficiency, cycle life and safety by its properties, but there is no method capable of controlling the film for a long time. For example, when a surface film made of a lithium halide or a glassy oxide is formed on a layer made of lithium or an alloy thereof, although the effect of suppressing dentite can be obtained to a certain extent at the time of initial use, it may be repeatedly used. The present inventors have found that the surface film is deteriorated and the function as a protective film is deteriorated. This is because a layer made of lithium or an alloy thereof changes its volume by occluding and releasing lithium, while a film made of lithium halide or the like located on the top hardly changes its volume. It is presumed that internal stress is generated at the interface of. It is considered that the generation of such internal stress particularly damages a part of the surface film made of lithium halide or the like, and reduces the function of suppressing dendrite.
[0015]
In addition, in the case of a carbon material such as graphite, an electric charge resulting from the decomposition of a solvent molecule or an anion appears as an irreversible capacity component, leading to a decrease in initial charge / discharge efficiency. Further, the composition, crystal state, stability, and the like of the film generated at this time have a great effect on the subsequent efficiency and cycle life.
[0016]
The method of forming an organic surface film on a lithium metal surface studied by Naoi et al. Has a certain effect in improving the cycle life than the above-described conventional technology, but there is still room for improvement.
[0017]
As described above, the film formed on the negative electrode surface is deeply related to the charge / discharge efficiency, cycle life, safety, etc., depending on its properties.However, there is no method capable of controlling the film over a long period of time, and the negative electrode has not yet been developed. There has been a demand for a technique for forming a film that leads to a stable and sufficient charge / discharge efficiency.
[0018]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electrolyte solution for a secondary battery which makes the cycle life of the secondary battery stable and excellent. Another object of the present invention is to provide a secondary battery that exhibits stable and excellent cycle life and high charge / discharge efficiency.
[0019]
[Means for Solving the Problems]
The present inventor has proposed that LiN (C 2 F 5 SO 2 ) 2 , An electrolyte commonly used in currently marketed lithium ion secondary batteries (LiPF 6 ) Is applied, Eu [(C 2 F 5 SO 2 ) 2 N] 3 It has been found that the effect can be easily obtained by directly dissolving the complex in the electrolytic solution, and furthermore, it is possible to obtain an electrolytic solution which is superior to the above-described method for producing an in situ complex in an electrolytic solution by Naoi et al. .
[0020]
In addition, as a result of further intensive studies, it was found that the charge / discharge efficiency was improved when a secondary battery was manufactured by applying an electrolyte containing a cyclic perfluoroalkylene disulfonimide anion and a transition metal ion to an aprotic solvent. The inventors have found that excellent cycle characteristics are improved, and have reached the present invention.
[0021]
According to the present invention, there is provided an electrolyte solution for a secondary battery, comprising an aprotic solvent, a cyclic perfluoroalkylene disulfonimide anion, and a transition metal ion.
[0022]
By using an electrolytic solution containing a cyclic perfluoroalkylene disulfonimide anion and a transition metal ion, battery characteristics are further improved as compared with a conventional electrolytic solution containing a bis (chain perfluoroalkylene sulfone) imide anion and a transition metal ion. It becomes possible. Here, the chain perfluoroalkylsulfonimide anion referred to herein is − N (C k F 2k + 1 SO 2 ) 2 Or − N (C k F 2k + 1 SO 2 ) (C m F 2m + 1 SO 2 ) (K and m are natural numbers).
[0023]
According to the present invention, there is provided an electrolyte solution for a secondary battery, comprising: an aprotic solvent; a lithium salt; and a metal complex comprising a cyclic perfluoroalkylene disulfonimide anion and a transition metal ion. You. Since the electrolyte solution for a secondary battery according to the present invention contains a metal complex composed of a cyclic perfluoroalkylene disulfonimide anion and a transition metal ion, the cycle characteristics of the battery can be further improved.
[0024]
In the electrolytic solution for a secondary battery of the present invention, the cyclic perfluoroalkylene disulfonimide anion may be represented by the following general formula (1).
[0025]
Embedded image
[0026]
(In the general formula (1), Rf represents a linear or branched perfluoroalkylene group having 2 to 4 carbon atoms.)
[0027]
In the electrolyte solution for a secondary battery of the present invention, the metal complex comprising a cyclic perfluoroalkylene disulfonimide anion and a transition metal ion may be represented by the following general formula (2).
[0028]
Embedded image
[0029]
(However, in the general formula (2), Rf represents a linear or branched perfluoroalkylene group having 2 to 4 carbon atoms. In addition, n is an integer of 1 to 3, and M represents a transition metal atom. Represents.)
[0030]
In the electrolyte for a secondary battery of the present invention, the transition metal ion may be a lanthanoid-based transition metal ion. In the electrolyte solution for a secondary battery of the present invention, the lanthanoid-based transition metal ion may include any of europium ion, neodymium ion, erbium ion and holmium ion.
[0031]
The oxidation-reduction potential of Eu, Nd, Er, and Ho is equal to or close to the oxidation-reduction potential of lithium metal or its alloy or graphite used as a negative electrode active material, and can be reduced at a potential higher by 0 V to 0.8 V than lithium. is there. As described above, by selecting metals close to the oxidation-reduction potential of the negative electrode active material and selecting anions that form stable complexes with these metals, these metals are not easily reduced. Therefore, the complex comprising the lanthanoid metal cation and the imide anion can be more stably present at the interface between the negative electrode and the electrolyte.
[0032]
The electrolyte solution for a secondary battery of the present invention may further include a sulfone compound.
[0033]
The presence of the metal complex formed by the cyclic perfluoroalkylene disulfonimide anion and the transition metal ion and the sulfone compound on the negative electrode surface has the following effects. On the surface of the negative electrode, there are dangling bonds that cause a reaction with solvent molecules, and non-reactive sites. The metal complex formed by the imide salt to be added or the metal complex formed by the imide salt and the transition metal ion forms a stabilized film by adsorbing to the above-mentioned non-reactive site, thereby performing lithium ion conduction. Further, the sulfone compound contributes to the formation of a passive film on the surface of the negative electrode, and as a result, suppresses the decomposition of solvent molecules.
[0034]
In the electrolyte solution for a secondary battery according to the present invention, the sulfone compound contains any of 1,3-propane sultone, 1,4-butane sultone, sulfolane, alkanesulfonic anhydride, a γ-sultone compound, and a sulfolene compound. Can be. Further, the electrolyte solution for a secondary battery of the present invention may further include vinylene carbonate or a derivative thereof. By doing so, the cycle characteristics of the battery can be further improved.
[0035]
In the electrolyte solution for a secondary battery of the present invention, the aprotic solvent is a cyclic carbonate, a chain carbonate, an aliphatic carboxylic acid ester, a γ-lactone, a cyclic ether, a chain ether or a mixture thereof. Any of the fluorinated derivatives may be included.
[0036]
In the electrolyte for a secondary battery according to the present invention, the lithium salt may be LIPF 6 , LiBF 4 , LiAsF 6 , LiSbF 6 , LiClO 4 , LiAlCl 4 , LiN (C k F 2k + 1 SO 2 ) 2 Or LiN (C k F 2k + 1 SO 2 ) (C m F 2m + 1 SO 2 ) (K and m are natural numbers).
[0037]
According to the present invention, there is provided a secondary battery including at least a positive electrode and a negative electrode, the secondary battery including the secondary battery electrolyte.
[0038]
In the secondary battery according to the present invention, the electrolyte is a cyclic perfluoroalkylene disulfonimide anion and a transition metal ion that provide a stable film, or a transition metal complex including a cyclic perfluoroalkylene disulfonimide anion and a transition metal ion. It is brought about by previously adding to the electrolyte. This complex is a stable complex in which an imide anion is coordinated with a transition metal cation. The complex is adsorbed on the surface of the negative electrode, whereby the surface of the negative electrode is stabilized. Further, by adding a sulfone compound or a vinylene carbonate compound to this electrolyte solution, an electrolyte solution containing a sulfone compound or a vinylene carbonate compound can be obtained. The sulfone compound reacts with the dangling bond at the negative electrode interface to form a stable film. By these two actions (adsorption and reaction), decomposition of the solvent molecules can be suppressed, and the cycle characteristics are improved.
[0039]
In the secondary battery of the present invention, a lithium-containing composite oxide can be included as the positive electrode active material. By doing so, the energy density of the battery can be improved.
[0040]
In the secondary battery of the present invention, as the negative electrode active material, one or more selected from the group consisting of a material capable of inserting and extracting lithium, a lithium metal, a metal material capable of forming an alloy with lithium, and an oxide material May be included.
[0041]
In particular, when the negative electrode is metallic lithium, the lithium fluoride, which is a reaction product of the lithium on the negative electrode surface with the imide anion adsorbed on the negative electrode surface, and a part of the transition metal are alloyed with lithium, so that the current is reduced. Density distribution is made uniform and generation of dendrites and the like is suppressed.
[0042]
Further, when the film is mechanically broken, the above-mentioned lithium fluoride has a function of repairing the film at the broken point, and a stable surface compound is maintained even after the film is broken. Has the effect of leading to the generation of For this reason, by including the imide anion, a long cycle life is realized.
[0043]
In the secondary battery of the present invention, the negative electrode active material may include a carbon material.
[0044]
In the secondary battery of the present invention, the carbon material may be graphite. In the secondary battery of the present invention, the carbon material may be amorphous carbon.
[0045]
In the present invention, a negative electrode and a positive electrode using lithium as an active material are combined with a separator interposed therebetween, and after insertion into the battery exterior, after impregnation with an electrolytic solution containing a metal complex, after sealing or sealing the battery exterior, A film may be formed on the negative electrode by charging the battery. By doing so, a battery having excellent cycle characteristics can be supplied stably.
[0046]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows a schematic structure of an example of the battery according to the present invention. A positive electrode current collector 11, a
[0047]
The electrolytic solution 15 has a lithium salt dissolved therein as an electrolyte, and contains a cyclic perfluoroalkylene disulfonimide anion and a transition metal ion. Further, a sulfone compound or a vinylene carbonate compound may be further included.
[0048]
As the lithium salt, for example, LIPF 6 , LiBF 4 , LiAsF 6 , LiSbF 6 , LiClO 4 , LiAlCl 4 , LiN (C k F 2k + 1 SO 2 ) 2 , LiN (C k F 2k + 1 SO 2 ) (C m F 2m + 1 SO 2 ) (K and m are natural numbers). Especially LiPF 6 , LiBF 4 Is preferred.
[0049]
As the cyclic perfluoroalkylene disulfonimide anion, for example, a compound represented by the following general formula (1) is suitably used.
[0050]
Embedded image
[0051]
(In the general formula (1), Rf represents a linear or branched perfluoroalkylene group having 2 to 4 carbon atoms.)
[0052]
The metal complex represented by the general formula (1) can be produced by a known method described in, for example, U.S. Pat. No. 4,429,093, U.S. Pat. No. 4,387,222, German Offenlegungsschrift No. 2,239,817, JP-A-2000-63682. .
[0053]
Specific examples of the compound of the general formula (1) of the present invention are shown in the following formulas (3) to (6), but the present invention is not limited to these.
[0054]
Embedded image
[0055]
Embedded image
[0056]
Embedded image
[0057]
Embedded image
[0058]
The imide anion represented by the above formula (3) is represented by A 1 Also represented. Further, the imide anion represented by the above formulas (4) to (6) 2 ~ A 4 Also represented.
[0059]
As the transition metal ion, a lanthanoid-based transition metal ion is preferably used. For example, any one or a mixture of europium (Eu) ion, neodymium (Nd) ion, erbium (Er) ion, and holmium (Ho) ion can be used.
[0060]
The cyclic perfluoroalkylene disulfonimide anion and the transition metal ion may form a complex. The complex can have, for example, a structure represented by the following general formula (2).
[0061]
Embedded image
[0062]
(However, in the general formula (2), Rf represents a linear or branched perfluoroalkylene group having 2 to 4 carbon atoms. In addition, n is an integer of 1 to 3, and M represents a transition metal atom. Represents.)
[0063]
The electrolytic solution 15 preferably contains the cyclic perfluoroalkylene disulfonimide anion or its metal complex in an amount of 0.01 to 10% by weight. When the content is 0.01% by weight or more, the effect of forming a film on the negative electrode surface can be reliably exhibited. By setting the content to 10% by weight or less, the solubility in the electrolyte 15 is ensured, and the increase in the viscosity of the electrolyte 15 is suitably suppressed. More preferably, if it is added in the range of 0.05 to 5% by weight, a further sufficient film effect can be obtained.
[0064]
Specific examples of the sulfone compound include sulfolane described in JP-A-60-154478, JP-A-62-100948, JP-A-63-102173, and JP-A-11-339850. 1,3-propane sultone or 1,4-butane sultone described in JP-A-2000-3724, alkanesulfonic anhydride described in JP-A-10-189041, and 1 described in JP-A-10-50342. , 3,2-dioxaphosphorane-2-oxide derivatives, γ-sultone compounds disclosed in JP-A-2000-235866, and sulfolene derivatives disclosed in JP-A-2000-294278. It is not limited.
[0065]
It is preferable that the sulfone compound is contained in the electrolytic solution 15 at 0.01 to 10% by weight. If the amount is less than 0.01% by weight, the film formation on the negative electrode surface is not sufficiently effective. When the content is 0.01% by weight or more, the effect of forming a film on the negative electrode surface can be reliably exhibited. When the content is 10% by weight or less, solubility in the electrolyte 15 is ensured, and an increase in resistance due to an increase in the viscosity of the electrolyte 15 is suitably suppressed. More preferably, if it is added in the range of 0.05 to 5% by weight, a further sufficient film effect can be obtained.
[0066]
Examples of vinylene carbonate or derivatives thereof include, for example, JP-A-4-169,075, JP-A-7-122296, JP-A-8-45545, JP-A-5-82138, and JP-A-5-74486. The compounds described in JP-A-6-52887, JP-A-11-260401, JP-A-2000-208169, JP-A-2001-35530, and JP-A-2000-138071 can be appropriately used. it can. When these vinylene carbonates or derivatives thereof are used as additives described below, the effect can be obtained by including 0.01 to 10% by weight in the electrolyte 15. When used as a solvent, the effect can be obtained by adding 1 to 5% by weight.
[0067]
Examples of the solvent used for the electrolytic solution 15 include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), and vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), Chain carbonates such as ethyl methyl carbonate (EMC) and dipropyl carbonate (DPC); aliphatic carboxylic acid esters such as methyl formate, methyl acetate and ethyl propionate; γ-lactones such as γ-butyrolactone; Chain ethers such as 2-ethoxyethane (DEE) and ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolan, formamide, and acetamide Dimethylformamide, dioxolane, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl- Aprotic organic solvents such as 2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ethyl ether, 1,3-propane sultone, anisole, N-methylpyrrolidone, and fluorinated carboxylic acid ester; Used to dissolve the lithium salts that dissolve in these organic solvents.
[0068]
The electrolyte 15 is, for example,
(I) a method of previously dissolving a metal complex comprising a transition metal ion and an imide anion, and further dissolving a sulfone compound or a vinylene carbonate compound, if necessary;
Or
(Ii) a method of dissolving a lithium salt of a cyclic perfluoroalkyleneimide and a transition metal ion, and further dissolving a sulfone compound or a vinylene carbonate compound;
It is produced by the following two methods.
[0069]
In the secondary battery of FIG. 1, the negative electrode is made of a material capable of inserting and extracting lithium, such as lithium metal, a lithium alloy, or a carbon material or an oxide, as described above.
[0070]
As the carbon material, graphite that absorbs lithium, amorphous carbon, diamond-like carbon, carbon nanotube, carbon nanohorn, or a composite thereof can be used.
[0071]
Further, as the oxide, any of silicon oxide, tin oxide, indium oxide, zinc oxide, lithium oxide, phosphoric acid, boric acid, or a composite thereof may be used, and it is particularly preferable to include silicon oxide. . The structure is preferably in an amorphous state. This is because silicon oxide is stable and does not cause a reaction with another compound, and the amorphous structure does not lead to deterioration due to non-uniformity such as crystal grain boundaries and defects. As a film formation method, a method such as an evaporation method, a CVD method, or a sputtering method can be used.
[0072]
The lithium alloy is composed of lithium and a metal capable of forming an alloy with lithium. For example, it is formed of a binary or ternary or more alloy of lithium and a metal such as Al, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, Zn, or La. As the lithium metal or lithium alloy, an amorphous alloy is particularly preferable. This is because deterioration due to non-uniformity such as crystal grain boundaries and defects is unlikely to occur due to the amorphous structure.
[0073]
Lithium metal or lithium alloy should be formed by an appropriate method such as a melt cooling method, a liquid quenching method, an atomizing method, a vacuum evaporation method, a sputtering method, a plasma CVD method, an optical CVD method, a thermal CVD method, a sol-gel method, etc. Can be.
[0074]
The negative electrode has a complex consisting of a transition metal ion and a cyclic perfluoroalkylimide anion at the interface with the electrolyte solution, which allows the metal and alloy phases to have flexibility in volume change, uniform ion distribution, physical and chemical properties. It is excellent in stability. As a result, generation of dendrite and pulverization of lithium can be effectively prevented, and cycle efficiency and life are improved. Further, the irreversible capacity site existing on the surface of the carbon material or oxide material has high chemical activity, and the solvent is easily decomposed. By adsorbing a complex composed of a transition metal cation and an imide anion on this surface, the decomposition of the solvent is suppressed and the irreversible capacity is greatly reduced, so that the charge / discharge efficiency does not decrease.
[0075]
In the secondary battery of FIG. 1, the positive electrode active material is Li b ZO 2 (Where Z represents at least one transition metal), for example, Li b CoO 2 , Li b NiO 2 , Li b Mn 2 O 4 , Li b MnO 3 , Li b Ni d Cr 1-d O 2 (Here, 0 <b <1, 0 <d <1), or an organic sulfur compound, a conductive polymer, an organic radical compound, or the like can be used. Further, a lithium-containing composite oxide having a plateau at 4.5 V or more in terms of the counter electrode potential of metallic lithium can also be used. Examples of the lithium-containing composite oxide include a spinel-type lithium-manganese composite oxide, an olivine-type lithium-containing composite oxide, and an inverse spinel-type lithium-containing composite oxide. The lithium-containing composite oxide has, for example, the general formula Li a (A x Mn 2-x ) O 4 (Here, 0 <x <2 and 0 <a <1.2. A is at least one selected from the group consisting of Ni, Co, Fe, Cr, and Cu.) can do.
[0076]
The positive electrode is prepared by dispersing and kneading these active materials together with a conductive material such as carbon black and a binder such as polyvinylidene fluoride (PVDF) in a solvent such as N-methyl-2-pyrrolidone (NMP). Is applied on a substrate such as an aluminum foil.
[0077]
In the secondary battery of FIG. 1, the negative electrode and the positive electrode are laminated via a separator in a dry air or inert gas atmosphere, or the laminated product is wound, and then housed in a battery can or a synthetic resin and metal foil. Can be manufactured by sealing with a flexible film or the like made of a laminate of the above. As the separator, a porous film such as a polyolefin such as polypropylene or polyethylene, or a fluororesin is used.
[0078]
The shape of the secondary battery according to the present invention is not particularly limited, and examples thereof include a cylindrical type, a square type, a coin type, and a laminate type.
[0079]
The present invention has been described based on the embodiments. This embodiment is an exemplification, and it is understood by those skilled in the art that various modifications can be made to the combination of each component and each processing process, and that such modifications are also within the scope of the present invention. is there.
[0080]
【Example】
(Example 1)
(Production of battery)
A 20 μm-thick aluminum foil is used for the positive electrode current collector 11, and LiMn is used for the positive electrode active material in the positive electrode. 2 O 4 For the negative electrode, 20 μm of lithium metal deposited on a 10 μm copper foil of the negative electrode
[0081]
(Charge / discharge cycle test)
At a temperature of 20 ° C., the charge rate was 0.05 C, the discharge rate was 0.1 C, the charge end voltage was 4.2 V, the discharge end voltage was 3.0 V, and the utilization rate (depth of discharge) of the lithium metal negative electrode was 33%. The capacity retention ratio (%) is a value obtained by dividing the discharge capacity (mAh) after 300 cycles by the discharge capacity (mAh) at the 10th cycle. The results obtained in the cycle test are shown in Table 1 below.
[0082]
(Examples 2 to 4)
Eu (A) shown in Example 1 1 ) 3 , Instead of the additives shown in Table 1. Except for this, a battery was prepared and evaluated in the same manner as in Example 1. Table 1 shows the results of examining the cycle characteristics in the same manner as in Example 1.
[0083]
(Comparative Example 1)
A battery was manufactured in the same manner as in Example 1, except that the transition metal imide anion complex was not added to the electrolytic solution. Table 1 shows the results of examining the cycle characteristics in the same manner as in Example 1.
[0084]
(Comparative Example 2)
In the electrolytic solution, instead of the cyclic perfluoroalkylene disulfonimide transition metal complex, Eu [N (C 2 F 5 SO 2 ) 2 ] 3 A battery was fabricated in the same manner as in Example 1, except that was used. Table 1 shows the results of examining the cycle characteristics in the same manner as in Example 1.
[0085]
[Table 1]
[0086]
From Table 1, the capacity retention rates in Examples 1 to 4 are much higher than those of Comparative Example 1. This is probably because the stabilization of the surface film existing at the interface between the negative electrode surface and the electrolyte and the high ionic conductivity of the film suppressed the irreversible reaction and dendrite formation. Further, it is clear that it shows superior properties as compared with the chain perfluoroalkylsulfonimide complex of Comparative Example 2. Actually, when the surface of the negative electrode after the cycle was examined using X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray analysis (EDX) for the batteries shown in each example, it was found that LiF, lanthanoid-based metal, imide The presence of an anionic molecule was indicated.
[0087]
(Example 5)
Eu (A 1 ) 3 Eu (A) instead of complex 2 ) 3 A battery was manufactured in the same manner as in Example 1 except that the complex was used and a graphite material was used as the negative electrode active material, and cycle characteristics were examined in the same manner as in Example 1. Table 2 shows the results. When the surface of the negative electrode after cycling of the battery shown in this example was examined using X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray analysis (EDX), it was found that LiF, lanthanoid metal, and imide anion molecules Existence was indicated.
[0088]
(Example 6)
Using PC, EC and DEC mixed solvent (volume ratio: 20/20/60) instead of EC and DEC mixed solvent (volume ratio: 30/70) as the electrolyte solvent, using amorphous carbon as the negative electrode active material, Eu (A 1 ) 3 Nd (A 2 ) 3 A battery was fabricated in the same manner as in Example 1 except that the complex was used, and cycle characteristics were examined in the same manner as in Example 1. Table 2 shows the results. When the surface of the negative electrode after cycling of the battery shown in this example was examined using X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray analysis (EDX), it was found that LiF, lanthanoid metal, and imide anion molecules Existence was indicated.
[0089]
(Comparative Example 3)
A battery of Comparative Example 3 was produced in the same manner as in Example 5, except that no additive was added. The same evaluation as in Example 1 was performed on the obtained battery. Table 2 shows the results.
[0090]
(Comparative Example 4)
A battery of Comparative Example 4 was made in the same manner as in Example 6, except that no additive was added. The same evaluation as in Example 1 was performed on the obtained battery. Table 2 shows the results.
[0091]
(Comparative Example 5)
Eu (A) as an additive 2 ) 3 Instead of Eu [N (C 2 F 5 SO 2 ) 2 ] 3 A battery of Comparative Example 5 was made in the same manner as in Example 5 except that was added. The same evaluation as in Example 1 was performed on the obtained battery. Table 2 shows the results.
[0092]
(Comparative Example 6)
Nd (A 2 ) 3 Instead of Nd [N (C 2 F 5 SO 2 ) 2 ] 3 A battery of Comparative Example 6 was produced in the same manner as in Example 6, except for adding. The same evaluation as in Example 1 was performed on the obtained battery. Table 2 shows the results.
[0093]
[Table 2]
[0094]
Table 2 shows the results. Comparing Examples 5 to 6 with Comparative Examples 3 and 6, it is understood that the use of the cyclic perfluoroalkylene disulfonimide complex has a higher capacity retention ratio than that of the comparative example. From this result, the same effect as in Example 1 was obtained when not only lithium metal but also graphite or amorphous carbon was used as the negative electrode active material.
[0095]
(Example 7)
(Production of battery)
The fabrication of the battery of this example will be described. A 20 μm-thick aluminum foil is used for the positive electrode current collector, and LiMn is used for the positive electrode active material in the positive electrode. 2 O 4 Was used. Also. As the negative electrode active material in the negative electrode, 20 μm of lithium metal deposited on a 10 μm copper foil serving as the negative electrode
[0096]
(Charge / discharge cycle test)
The battery obtained in the same manner as described in Example 1 was evaluated. The results are shown in Table 3 below.
[0097]
(Example 8)
Eu (A) of Example 7 3 ) 3 Instead of Nd (A 3 ) 3 In the same manner as in Example 7, except that the electrolyte solvent is replaced with a mixed solvent of PC, EC and DEC (volume ratio: 20/20/60) instead of the mixed solvent of EC and DEC (volume ratio: 30/70). A battery was prepared and evaluated. Table 3 shows the results of examining the cycle characteristics in the same manner as in Example 7.
[0098]
[Table 3]
[0099]
Table 3 shows that the capacity retention rates after the cycle test in Example 7 and Example 8 were higher than those in Example 1 or Example 6, respectively. This is probably because the irreversible reaction was suppressed by the stabilization of the film existing at the interface between the negative electrode surface and the electrolyte and the high ionic conductivity of the film.
[0100]
(Example 9)
In this example, the electrolyte solution 15 containing a transition metal complex, 1,3-PS, and vinylene carbonate (VC) as additives was used. A 20 μm-thick aluminum foil is used for the positive electrode current collector, and LiMn is used for the positive electrode active material in the positive electrode. 2 O 4 Was used. In addition, as the negative electrode active material in the negative electrode, 20 μm of lithium metal deposited on a 10 μm thick copper foil to be the negative electrode
As a solvent for the electrolytic solution 15, a mixed solvent of EC and DEC (volume ratio: 30/70) was used. -1 LiPF 6 Was dissolved. As an additive, Eu (A 4 ) 3 A complex was used and added so as to contain 0.3% by weight of the entire electrolyte 15. Next, 1,3-PS and VC were added so as to be contained at 1% by weight in the electrolytic solution 15, respectively, to obtain the electrolytic solution 15 of this example. And the negative electrode and the positive electrode were laminated | stacked via the porous separator 16 which consists of polyethylene, and the secondary battery was produced.
[0101]
(Charge / discharge cycle test)
The battery obtained in the same manner as described in Example 1 was evaluated. Table 4 shows the obtained results.
[0102]
(Example 10)
A secondary battery was fabricated in the same manner as in Example 9 except that VC was not added.
[0103]
[Table 4]
[0104]
From Table 4, the battery shown in Example 9 has a further improvement in the capacity retention rate after the cycle test as compared with the battery of Example 10, that is, in the electrolyte containing the metal complex and the sulfone compound. It was confirmed that the cycle characteristics were further improved by further adding VC.
[0105]
【The invention's effect】
As described above, according to the present invention, by including an aprotic solvent, a cyclic perfluoroalkylene disulfonimide anion, and a transition metal ion, the cycle life of the secondary battery is stable and excellent. Thus, an electrolyte solution for a secondary battery is realized. Further, according to the present invention, a secondary battery exhibiting stable and excellent cycle life and high charge / discharge efficiency is realized.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a secondary battery according to an embodiment.
[Explanation of symbols]
11 positive electrode current collector
12 Layer containing positive electrode active material
13 Layer containing negative electrode active material
14 Negative electrode current collector
15 Electrolyte
16 Porous separator
Claims (17)
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