JP5220388B2 - Method for manufacturing lithium secondary battery - Google Patents

Method for manufacturing lithium secondary battery Download PDF

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JP5220388B2
JP5220388B2 JP2007293318A JP2007293318A JP5220388B2 JP 5220388 B2 JP5220388 B2 JP 5220388B2 JP 2007293318 A JP2007293318 A JP 2007293318A JP 2007293318 A JP2007293318 A JP 2007293318A JP 5220388 B2 JP5220388 B2 JP 5220388B2
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electrolytic solution
secondary battery
lithium secondary
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JP2009123382A (en
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哲彌 逢坂
聰之 門間
智香 巽
洋希 奈良
邦彦 小島
健太郎 多田
智 小原
仁 岩城
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Waseda University
Toyo Gosei Co Ltd
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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
    • 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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Description

本発明は、リチウム二次電池の製造方法に関し、特にイオン液体を含む電解液を用いたものに関するものである。 The present invention relates to a method for producing a Lithium secondary batteries, and in particular those using electrolyte containing an ionic liquid.

従来、リチウム二次電池は、電気自動車などの車載用、大型の電力貯蔵用などの大電流特性を要求される用途への適用が期待され、そのため、特に高い安全性が求められている。上記した従来のリチウム二次電池では、電解液に可燃性、揮発性を有する有機溶媒を用いるため、安全性の向上に対して限界があった。   Conventionally, lithium secondary batteries are expected to be applied to applications requiring high current characteristics such as in-vehicle use such as electric vehicles and large-scale power storage, and therefore, particularly high safety is required. In the above-described conventional lithium secondary battery, an organic solvent having flammability and volatility is used for the electrolytic solution, and thus there is a limit to improving safety.

これに対し、安全性を高めるための取り組みとして、イオン液体を電解液に用いたリチウム二次電池が開示されている（例えば特許文献１）。ここでイオン液体とは、１００℃以下で液体の塩をいう。このイオン液体は、一般に難燃性、不揮発性を有するので、有機溶媒を含む電解液を難燃性とすることにより、安全性を向上することができるだけでなく、電位窓（電位領域）が比較的広く、さらに比較的高いイオン伝導性示すという長所がある。この長所は、リチウム二次電池の電解液としての条件を備えており、長時間の安定動作に寄与できる可能性が高い。
特開２００６−２５３０８１号公報 On the other hand, a lithium secondary battery using an ionic liquid as an electrolyte has been disclosed as an effort to increase safety (for example, Patent Document 1). Here, the ionic liquid refers to a salt that is liquid at 100 ° C. or lower. Since this ionic liquid generally has flame retardancy and non-volatility, it is possible not only to improve safety by making the electrolyte containing an organic solvent flame retardant, but also the potential window (potential region) is compared. There is an advantage that it exhibits a relatively high ion conductivity. This advantage is provided with conditions as an electrolyte for a lithium secondary battery, and is highly likely to contribute to stable operation over a long period of time.
JP 2006-253081 A

しかしながら、上記特許文献１では、イオン液体は粘性が大きいため導電性が小さく、これによりリチウムが溶解・析出するサイクルのサイクル特性が悪化するという問題があった。また、負極と電解液界面との間に存在する表面被膜に大きく影響されることが知られている。すなわち、リチウム（以下、単に「Ｌｉ」ともいう）は反応性が強いので他の不純物と反応してしまい、充放電を繰り返すうちに電極の層間に出入りするリチウムが減少することによって、サイクル特性が低下するという問題があった。   However, in the above-mentioned Patent Document 1, there is a problem that the cycle characteristics of the cycle in which lithium is dissolved and precipitated is deteriorated due to the low viscosity of the ionic liquid because of its high viscosity. Moreover, it is known that it is greatly influenced by the surface film which exists between a negative electrode and electrolyte solution interface. That is, lithium (hereinafter also simply referred to as “Li”) is highly reactive and reacts with other impurities, and the cycle characteristics are reduced by reducing the amount of lithium entering and exiting the electrode layers as charge and discharge are repeated. There was a problem of lowering.

そこで本発明は上記した問題点に鑑み、上記サイクル特性を向上させることができるイオン液体を含む電解液を用いたリチウム二次電池の製造方法を提供することを目的とする。 The present invention has been made in view of the above problems, and an object thereof is to provide a method of manufacturing a Lithium secondary battery using the electrolyte containing an ionic liquid capable of improving the cycle characteristics.

上記目的を達成するために、請求項１に係る発明は、電解液にイオン液体を添加してイオン液体添加電解液を生成する工程を備えるリチウム二次電池の製造方法において、前記イオン液体は、１，３−ジアリルイミダゾリウムビス（トリフルオロメタンスルホニル）イミド、１−ブチル−１−メチルピロリジニウムビス（トリフルオロメタンスルホニル）イミドのいずれかであって、前記イオン液体添加電解液にバブリングにより酸素を溶存させる工程を備えることを特徴とする。 To achieve the above object, the invention provides method for producing a lithium secondary battery comprising the step of adding an ionic liquid to produce an ionic liquid added electrolyte electrolytic solution according to claim 1, wherein the ionic liquid 1,3-diallylimidazolium bis (trifluoromethanesulfonyl) imide, 1-butyl-1-methylpyrrolidinium bis (trifluoromethanesulfonyl) imide, and oxygenated by bubbling the ionic liquid-added electrolyte. The method is characterized by comprising a step of dissolving.

本発明によれば、イオン液体添加電解液にバブリングにより酸素を溶存させることにより、リチウムと不純物との反応を抑制し、結果としてリチウム二次電池のサイクル特性を向上させることができる。 According to the present invention, by dissolving oxygen in the ionic liquid-added electrolyte by bubbling , the reaction between lithium and impurities can be suppressed, and as a result, the cycle characteristics of the lithium secondary battery can be improved.

１．実施形態
以下図面を参照して、本発明の好適な実施形態について説明する。図１に示すリチウム二次電池１は、正極２、負極３、及びイオン液体添加電解液４を備え、リチウムイオンが正極及び負極を往復することにより、外部回路５に電流を供給し得るように構成されている。 1. Embodiment A preferred embodiment of the present invention will be described below with reference to the drawings. A lithium secondary battery 1 shown in FIG. 1 includes a positive electrode 2, a negative electrode 3, and an ionic liquid-added electrolyte solution 4, so that lithium ions can supply current to the external circuit 5 by reciprocating between the positive electrode and the negative electrode. It is configured.

正極２には、結晶層間にリチウムが自由に出入り可能な物質として、コバルト酸リチウム（ＬｉＣｏＯ２）や、マンガン酸リチウム（ＬｉＭｎ２Ｏ４）、リチウム鉄リン酸塩（ＬｉＦｅＰＯ４）などの遷移金属酸化物が用いられている。また、負極３にはリチウム金属を用いている。 In the positive electrode 2, transition metals such as lithium cobaltate (LiCoO 2 ), lithium manganate (LiMn 2 O 4 ), and lithium iron phosphate (LiFePO 4 ) that can freely enter and leave the crystal layer are used. An oxide is used. Further, lithium metal is used for the negative electrode 3.

イオン液体添加電解液４は、電解液にイオン液体を添加してなる。電解液は、エチレンカーボネート（ＥＣ）やジエチルカーボネート（ＤＥＣ）などの有機溶媒中に、六フッ化リン酸リチウム（ＬｉＰＦ６）などのリチウム塩を溶解したものが用いられる。 The ionic liquid-added electrolytic solution 4 is obtained by adding an ionic liquid to the electrolytic solution. As the electrolytic solution, a solution obtained by dissolving a lithium salt such as lithium hexafluorophosphate (LiPF 6 ) in an organic solvent such as ethylene carbonate (EC) or diethyl carbonate (DEC) is used.

イオン液体は、特に限定されるものではないが、例えば、ＥＭＩＴＦＳＩ（1-Ethyle-3-methylimidazolium bis (trifluoromethanesulfonyl) imide）、ＤＡＩＴＦＳＩ（1,3-Diallylimidazolium bis (trifluoromethanesulfonyl) imide）や、ＢＭＰＴＦＳＩ（1-Butyl-1-methylpyrrolidinium bis (trifluoromethanesulfonyl) imide）を挙げることができる。ここに例示したイオン液体は、アニオン部位が共通しており、その構造式は、化１に示す通りである。また、ＥＭＩＴＦＳＩのカチオン部位であるＥＭＩカチオンの構造式を化２に、ＤＡＩＴＦＳＩのカチオン部位であるＤＡＩカチオンの構造式を化３に、ＢＭＰＴＦＳＩのカチオン部位であるＢＭＰカチオンの構造式を化４にそれぞれ示す。このＢＭＰカチオンは、リチウムの溶解・析出電位において安定であることが、一般に知られている。また、ＥＭＩカチオンは、Ｌｉの溶解・析出電位よりも貴な電位で還元分解反応をすることが知られている。   The ionic liquid is not particularly limited, and examples thereof include EMITFSI (1-Ethyle-3-methylimidazolium bis (trifluoromethanesulfonyl) imide), DAITFSI (1,3-Diallylimidazolium bis (trifluoromethanesulfonyl) imide), BMPTFSI (1- Butyl-1-methylpyrrolidinium bis (trifluoromethanesulfonyl) imide). The ionic liquid exemplified here has a common anion moiety, and the structural formula is as shown in Chemical Formula 1. Also, the structural formula of the EMI cation, which is the cation site of EMITFSI, is represented by Chemical Formula 2, the structural formula of the DAI cation, which is the cationic site of DAITFSI, is represented by Chemical Formula 3, and the structural formula of the BMP cation, which is the cationic site of BMPTFSI, Show. It is generally known that this BMP cation is stable at the dissolution / precipitation potential of lithium. EMI cations are known to undergo a reductive decomposition reaction at a potential nobler than the Li dissolution / precipitation potential.

また、本発明に係るリチウム二次電池１に用いるイオン液体添加電解液４には、酸素を溶存させてなる。イオン液体添加電解液４に酸素を溶存させる方法は、酸素を含む気体中にイオン液体添加電解液４を開放した状態で保持し、さらに酸素を含む気体中にイオン液体添加電解液４を開放した状態で充放電を行う方法が好適に用いられる。   Moreover, oxygen is dissolved in the ionic liquid addition electrolyte 4 used for the lithium secondary battery 1 which concerns on this invention. In the method of dissolving oxygen in the ionic liquid-added electrolytic solution 4, the ionic liquid-added electrolytic solution 4 is kept open in a gas containing oxygen, and the ionic liquid-added electrolytic solution 4 is opened in a gas containing oxygen. A method of charging and discharging in a state is preferably used.

尚、イオン液体添加電解液４に酸素を溶存させる方法は、特に限定されるものではない。例えば、充放電に先立ち、予め製造段階において、イオン液体添加電解液４中にバブリング等により酸素を強制的に送り込むことによって、イオン液体添加電解液４中に酸素を溶存させておく方法でもよい。   The method for dissolving oxygen in the ionic liquid-added electrolytic solution 4 is not particularly limited. For example, prior to charge / discharge, a method may be used in which oxygen is dissolved in the ionic liquid-added electrolyte solution 4 by forcibly sending oxygen into the ionic liquid-added electrolyte solution 4 by bubbling or the like in the manufacturing stage.

このように、イオン液体添加電解液４を用いたリチウム二次電池１において、本発明者らは、イオン液体添加電解液４に酸素を溶存させることにより、サイクル特性の低下を抑制できることを見出した。   As described above, in the lithium secondary battery 1 using the ionic liquid-added electrolyte solution 4, the present inventors have found that the deterioration of the cycle characteristics can be suppressed by dissolving oxygen in the ionic liquid-added electrolyte solution 4. .

因みに、イオン液体添加電解液４を使用した従来のリチウム二次電池では、この正極２及び負極３の間をリチウムが移動する際、上述した通りリチウムは反応性が高いので、イオン液体添加電解液４中の不純物と容易に反応し得る。不純物と反応したリチウムは、電極の層間に挿入されず、結果として電極間を往復するリチウムの量が減るので、サイクル特性が悪化してしまう。   Incidentally, in the conventional lithium secondary battery using the ionic liquid-added electrolytic solution 4, when lithium moves between the positive electrode 2 and the negative electrode 3, the lithium is highly reactive as described above. Can easily react with impurities in 4. Lithium that has reacted with the impurities is not inserted between the layers of the electrodes, and as a result, the amount of lithium reciprocating between the electrodes is reduced, resulting in deterioration of cycle characteristics.

これに対し、本発明のリチウム二次電池１では、酸素を含む気体中にイオン液体添加電解液４を開放した状態で保持し、さらに酸素を含む気体中にイオン液体添加電解液４を開放した状態で充放電を行うことにより、イオン液体添加電解液４中に酸素を溶存させた。これにより、このイオン液体添加電解液４中に溶存している酸素が、上記したリチウムと不純物との反応を抑制しているものと考えられる。抑制のメカニズムとしては、種々考えられるが、例えば、溶存酸素により電極表面に被膜を形成していることが考えられる。この被膜は、充放電中にリチウムイオンと他の物質との反応を防止すると共に、イオントンネル（Ion Tunnel）の役割を果たして、リチウムイオンだけを通過させるＳＥＩ（Solid Electrolyte Interface）と呼ばれる。溶存酸素により電極表面にＳＥＩが形成されているとすれば、ＳＥＩがリチウム金属表面における不純物やイオン液体の分解を抑制するので、リチウムイオンの量が維持されることとなり、サイクル特性を向上させることができる。   On the other hand, in the lithium secondary battery 1 of the present invention, the ionic liquid-added electrolytic solution 4 is held open in a gas containing oxygen, and the ionic liquid-added electrolytic solution 4 is opened in a gas containing oxygen. By performing charge and discharge in the state, oxygen was dissolved in the ionic liquid-added electrolytic solution 4. Thereby, it is considered that the oxygen dissolved in the ionic liquid-added electrolyte 4 suppresses the reaction between lithium and impurities described above. Various suppression mechanisms are conceivable. For example, it is conceivable that a film is formed on the electrode surface by dissolved oxygen. This coating is called SEI (Solid Electrolyte Interface) that prevents lithium ions from reacting with other substances during charge and discharge, and plays the role of ion tunnel, allowing only lithium ions to pass through. If SEI is formed on the electrode surface by dissolved oxygen, SEI suppresses decomposition of impurities and ionic liquid on the surface of the lithium metal, so that the amount of lithium ions is maintained and cycle characteristics are improved. Can do.

このように、本発明に係るリチウム二次電池１によれば、イオン液体添加電解液４に酸素を溶存させることにより、有機溶媒を含む電解液を難燃性とすることができる。また、電極表面にＳＥＩが形成されているとすれば、放電によって電解液中に放出されたリチウムイオンが充電で負極表面に析出するときに平滑な面を形成しないで樹の枝のように析出するデンドライトの発生を抑制できる。そうすると、デンドライトがセパレータ（図示しない）を突き破って内部短絡を起こすことによる発火事故を防止することができる。   Thus, according to the lithium secondary battery 1 which concerns on this invention, the electrolyte solution containing an organic solvent can be made flame-retardant by dissolving oxygen in the ionic liquid addition electrolyte solution 4. FIG. Also, if SEI is formed on the electrode surface, lithium ions released into the electrolytic solution by discharge will be deposited like a tree branch without forming a smooth surface when deposited on the negative electrode surface by charging. Generation of dendrite can be suppressed. If it does so, a fire accident by a dendrite breaking through a separator (not shown) and causing an internal short circuit can be prevented.

従って、本発明に係るリチウム二次電池１によれば、安全性を向上させることができると共に、サイクル特性を向上させることができる。   Therefore, according to the lithium secondary battery 1 of the present invention, safety can be improved and cycle characteristics can be improved.

２．実施例
次に本発明に係るリチウム二次電池１の実施例について図２を参照して説明する。リチウム二次電池１のサイクル特性評価は、Ｋｏｃｈらが提案した充放電試験法（STATUS OF THE SECONDARY LITHIUMU ELECTRODE、V.R.KOCH、Journal of Power Source,6(1981)357-370、Elsevier Sequoia S.A.,Lausanne-Printed in The Netherlands）により行った。 2. EXAMPLE Next, an example of the lithium secondary battery 1 according to the present invention will be described with reference to FIG. The cycle characteristics evaluation of the lithium secondary battery 1 is based on the charge / discharge test method proposed by Koch et al. in The Netherlands).

まず、評価方法の概略について説明する。評価の内訳としては、電解液にイオン液体を添加し酸素を溶存させた場合（実施例１〜３）、電解液にイオン液体を添加せずに酸素を溶存させた場合（比較例１）、電解液にイオン液体を添加せずに酸素を溶存させない場合（比較例２）、電解液にイオン液体を添加し酸素を溶存させない場合（比較例３〜５）の合計８種類の評価を行った。尚、以下に示す実験において、雰囲気及び電解液の温度は室温とした。   First, an outline of the evaluation method will be described. As a breakdown of the evaluation, when an ionic liquid is added to the electrolytic solution and oxygen is dissolved (Examples 1 to 3), oxygen is dissolved without adding the ionic liquid to the electrolytic solution (Comparative Example 1), A total of eight kinds of evaluations were performed, in which oxygen was not dissolved without adding the ionic liquid to the electrolytic solution (Comparative Example 2), and when oxygen was not dissolved by adding the ionic liquid to the electrolytic solution (Comparative Examples 3 to 5). . In the experiments shown below, the atmosphere and the temperature of the electrolytic solution were room temperature.

サイクル特性評価は、三極式セルを用い、リチウム金属を対極12及び参照極11とした。作用極13には、以下の手順により作成したＮｉ電極を使用した。まずＮｉ電極を、希塩酸にて５分間超音波洗浄してエッチングをした。水洗い後、粒径が０．３μｍのアルミナにて表面を研磨し鏡面に仕上げた。該鏡面仕上げをしたＮｉ電極をエタノールにて超音波洗浄した後、アセトンで洗浄しエタノールを除去した。このＮｉ電極に窒素を吹きかけることにより残留したアセトンを乾燥させ、一晩真空乾燥を行った。このようにして得られたＮｉ電極を容器14に入れた電解液（１Ｍ ＬｉＰＦ６／ＥＣ−ＤＥＣ（１：１ｖｏｌ．％））10の中で、Ｎｉ電極上にＬｉを５．１Ｃｃｍ−２相当電析させて、作用極13を得た。尚、作用極13は、所定面積のみを表出させておくため、エポキシ樹脂によりその余の部分を被覆し、予め表面積を規定した。 In the cycle characteristics evaluation, a triode cell was used, and lithium metal was used as a counter electrode 12 and a reference electrode 11. As the working electrode 13, a Ni electrode prepared by the following procedure was used. First, the Ni electrode was etched by ultrasonic cleaning with dilute hydrochloric acid for 5 minutes. After washing with water, the surface was polished with alumina having a particle size of 0.3 μm to finish a mirror surface. The mirror-finished Ni electrode was ultrasonically cleaned with ethanol and then washed with acetone to remove the ethanol. The remaining acetone was dried by blowing nitrogen on the Ni electrode, and vacuum drying was performed overnight. In the electrolyte solution (1M LiPF 6 / EC-DEC (1: 1 vol.%)) 10 in which the Ni electrode thus obtained was put in the container 14, Li was equivalent to 5.1 Ccm −2 on the Ni electrode. Electrodeposition was performed to obtain a working electrode 13. The working electrode 13 was covered with an epoxy resin so that only a predetermined area was exposed, and the surface area was defined in advance.

サイクル特性評価においては、イオン液体添加電解液４と、イオン液体を添加しないままの未添加電解液10とにより評価を行った。イオン液体添加電解液４に添加するイオン液体としてはＴＦＳＩアニオン系イオン液体、すなわち上述した、ＥＭＩＴＦＳＩ、ＤＡＩＴＦＳＩ、及び、ＢＭＰＴＦＳＩの三種を用いた。実際には、上記のようにＬｉをＮｉ電極上に電析した後、上記電解液に２０ｖｏｌ．％の上記イオン液体を添加して三種類のイオン液体添加電解液４を生成した。また、未添加電解液には、ＬｉをＮｉ電極上に電析した後の電解液10をそのまま使用した。   In the cycle characteristic evaluation, evaluation was performed using the ionic liquid-added electrolytic solution 4 and the non-added electrolytic solution 10 without adding the ionic liquid. As the ionic liquid added to the ionic liquid-added electrolytic solution 4, TFSI anionic ionic liquid, that is, the above-described three types of EMITFSI, DAITFSI, and BMPTFSI were used. Actually, after depositing Li on the Ni electrode as described above, 20 vol. % Of the ionic liquid was added to produce three types of ionic liquid-added electrolytes 4. Further, as the non-added electrolytic solution, the electrolytic solution 10 after Li was electrodeposited on the Ni electrode was used as it was.

また、本実施例では、酸素を含む気体としてドライエア（酸素２０体積％、窒素８０体積％、露点：−６０℃）を用い、酸素を含まない気体としてＡｒガス（露点：−９５℃）を用いた。気液界面の面積は約１６ｃｍ２、電解液の体積は４０ｍＬとした。 In this embodiment, dry air (20% by volume of oxygen, 80% by volume of nitrogen, dew point: −60 ° C.) is used as the gas containing oxygen, and Ar gas (dew point: −95 ° C.) is used as a gas not containing oxygen. It was. The area of the gas-liquid interface was about 16 cm 2 , and the volume of the electrolyte was 40 mL.

酸素を溶存させる場合（実施例１〜３、比較例１）において、電析及び後述するサイクル特性評価は、電解液を収容した容器14を、ドライエア中に所定時間開放して行った。尚、本実施例では、電解液は、上記電析に先立ち、５分間ドライエア中に開放した。また、実施例１〜３については、後述するサイクル特性評価を行う前に、ドライエア中でイオン液体を添加し、攪拌した（図２（Ｂ））。   In the case of dissolving oxygen (Examples 1 to 3, Comparative Example 1), electrodeposition and cycle characteristic evaluation described later were performed by opening the container 14 containing the electrolytic solution in dry air for a predetermined time. In this example, the electrolyte was released in dry air for 5 minutes prior to the electrodeposition. Moreover, about Examples 1-3, the ionic liquid was added and stirred in dry air before performing the cycling characteristics evaluation mentioned later (FIG. 2 (B)).

酸素を溶存させない場合（比較例２〜５）において、容器14内を電解液10と、その余の部分ＡをＡｒガスとで充満させ、該容器14を蓋15で密閉して行った（図２（Ａ））。次いで、Ａｒガス雰囲気を保持したままの状態で後述する充放電評価を行った。尚、比較例３〜５については、サイクル特性評価を行う前に、Ａｒガス雰囲気を保持したままイオン液体を添加した。   When oxygen was not dissolved (Comparative Examples 2 to 5), the inside of the container 14 was filled with the electrolytic solution 10 and the remaining portion A with Ar gas, and the container 14 was sealed with a lid 15 (see FIG. 2 (A)). Next, the charge / discharge evaluation described later was performed while the Ar gas atmosphere was maintained. In Comparative Examples 3 to 5, the ionic liquid was added while maintaining the Ar gas atmosphere before performing the cycle characteristics evaluation.

上記のように準備されたそれぞれの電極及び電解液中において、図３に示すように、電流密度２ｍＡｃｍ−２を作用極13及び対極12に通電し、溶解・析出（充放電）を繰り返した（溶解：Ｌｉ→Ｌｉ＋＋ｅ−，析出：Ｌｉ＋＋ｅ−→Ｌｉ）。尚、充放電は、上記電析後、１５分後に開始することとした。 In each of the electrodes and the electrolyte prepared as described above, a current density of 2 mAcm −2 was passed through the working electrode 13 and the counter electrode 12 as shown in FIG. 3, and dissolution / precipitation (charging / discharging) was repeated ( Dissolution: Li → Li + + e − , precipitation: Li + + e − → Li). The charge / discharge was started 15 minutes after the electrodeposition.

この充放電において、過電圧が１．０Ｖ ｖｓ．Ｌｉ／Ｌｉ＋を超えたときを、そのセルの充放電挙動（サイクル回数）とした（図４〜図７）。その結果を表１に示す。このサイクル回数を比較し、イオン液体を添加することによる影響、及び電解液中に酸素を溶存させることによる効果について評価を行った。 In this charging / discharging, the overvoltage is 1.0 V vs. When Li / Li + was exceeded, the charge / discharge behavior (number of cycles) of the cell was determined (FIGS. 4 to 7). The results are shown in Table 1. The number of cycles was compared, and the effect of adding an ionic liquid and the effect of dissolving oxygen in the electrolyte were evaluated.

表１に示すように、Ａｒガス雰囲気下では、イオン液体を添加することにより、サイクル回数が減少するが（比較例３〜５）、イオン液体添加電解液４をドライエアに開放することにより、サイクル回数の減少を抑制できることが分かった（実施例１〜３）。   As shown in Table 1, in an Ar gas atmosphere, the number of cycles is reduced by adding an ionic liquid (Comparative Examples 3 to 5), but by opening the ionic liquid-added electrolyte 4 to dry air, the cycle is reduced. It turned out that the reduction | decrease in frequency | count can be suppressed (Examples 1-3).

Ａｒガス雰囲気においては、イオン液体としてＢＭＰＴＦＳＩを添加した場合においてもサイクル回数が減少した（比較例５）。これに対し、ドライエア中において、イオン液体としてＢＭＰＴＦＳＩを添加した場合のサイクル回数は、未添加電解液（比較例１）と同等の結果を得た。   In the Ar gas atmosphere, the number of cycles was reduced even when BMPTFSI was added as the ionic liquid (Comparative Example 5). In contrast, in dry air, the number of cycles when BMPTFSI was added as the ionic liquid was the same as the non-added electrolyte (Comparative Example 1).

さらに、Ａｒ雰囲気下においては、イオン液体としてＥＭＩＴＦＳＩを添加すると、未添加電解液（比較例２）に比べ、サイクル回数は、ほぼ半分となることが確認された（比較例３）。イオン液体を添加することでサイクル回数が減少することは予想された結果であるが、イオン液体としてＥＭＩＴＦＳＩを添加した場合であっても、ドライエア中では、未添加電解液と同等のサイクル回数（３１回）を得られることが分かった（実施例１）。   Further, it was confirmed that when EMITFSI was added as an ionic liquid in an Ar atmosphere, the number of cycles was almost halved as compared with the non-added electrolyte (Comparative Example 2) (Comparative Example 3). Although it is an expected result that the number of cycles is reduced by adding the ionic liquid, even when EMITFSI is added as the ionic liquid, in dry air, the number of cycles equivalent to the non-added electrolyte (31 (Example 1).

以上より、本発明に係るリチウム二次電池１において、イオン液体添加電解液４を用いることにより、安全性を高めることができると共に、イオン液体添加電解液４に酸素を溶存させることにより、サイクル回数の低減を抑制できることが分かった。   As described above, in the lithium secondary battery 1 according to the present invention, the safety can be improved by using the ionic liquid-added electrolytic solution 4, and the number of cycles can be increased by dissolving oxygen in the ionic liquid-added electrolytic solution 4. It was found that the reduction of the amount can be suppressed.

本発明は、本実施形態に限定されるものではなく、本発明の要旨の範囲内で種々の変形実施が可能である。   The present invention is not limited to this embodiment, and various modifications can be made within the scope of the gist of the present invention.

本発明に係るリチウム二次電池の構成を示す模式図である。It is a schematic diagram which shows the structure of the lithium secondary battery which concerns on this invention. 同上、実施例に用いたリチウム二次電池の構成を示す模式図であり、（Ａ）電析の様子を示す図、（Ｂ）充放電を行う場合の様子を示す図である。It is a schematic diagram which shows the structure of the lithium secondary battery used for the Example same as the above, (A) The figure which shows the mode of electrodeposition, (B) The figure which shows the mode in the case of charging / discharging. 電析及び充放電を行う場合の通電時間−電流密度曲線である。It is an energization time-current density curve in the case of performing electrodeposition and charging / discharging. 同上、未添加電解液を用いた場合のサイクル特性の結果を示すデータであり、（Ａ）ドライエア中（比較例１）、（Ｂ）Ａｒガス雰囲気下（比較例２）のデータである。Same as above, it is data showing the results of the cycle characteristics when using the non-added electrolyte, (A) data in dry air (Comparative Example 1), (B) data in an Ar gas atmosphere (Comparative Example 2). 同上、イオン液体（ＥＭＩＴＦＳＩ）添加電解液を用いた場合のサイクル特性の結果を示すデータであり、（Ａ）ドライエア中（実施例１）、（Ｂ）Ａｒガス雰囲気下（比較例３）のデータである。Same as above, data showing results of cycle characteristics when using an ionic liquid (EMITFSI) -added electrolyte, (A) data in dry air (Example 1), (B) data in an Ar gas atmosphere (Comparative Example 3) It is. 同上、イオン液体（ＤＡＩＴＦＳＩ）添加電解液を用いた場合のサイクル特性の結果を示すデータであり、（Ａ）ドライエア中（実施例２）、（Ｂ）Ａｒガス雰囲気下（比較例４）のデータである。Same as above, it is data showing the results of cycle characteristics when an ionic liquid (DAITFSI) -added electrolytic solution is used, (A) data in dry air (Example 2), (B) data in an Ar gas atmosphere (Comparative Example 4) It is. 同上、イオン液体（ＢＭＰＴＦＳＩ）添加電解液を用いた場合のサイクル特性の結果を示すデータであり、（Ａ）ドライエア中（実施例３）、（Ｂ）Ａｒガス雰囲気下（比較例５）のデータである。Same as above, data showing the results of cycle characteristics when using an ionic liquid (BMPTFSI) -added electrolyte, (A) data in dry air (Example 3), (B) data in an Ar gas atmosphere (Comparative Example 5) It is.

１ リチウム二次電池
２ 正極
３ 負極
４ イオン液体添加電解液 1 Lithium secondary battery 2 Positive electrode 3 Negative electrode 4 Electrolyte added with ionic liquid

Claims (1)

電解液にイオン液体を添加してイオン液体添加電解液を生成する工程を備えるリチウム二次電池の製造方法において、
前記イオン液体は、１，３−ジアリルイミダゾリウムビス（トリフルオロメタンスルホニル）イミド、１−ブチル−１−メチルピロリジニウムビス（トリフルオロメタンスルホニル）イミドのいずれかであって、
前記イオン液体添加電解液にバブリングにより酸素を溶存させる工程を備えることを特徴とするリチウム二次電池の製造方法。 In a method for producing a lithium secondary battery comprising a step of adding an ionic liquid to an electrolytic solution to generate an ionic liquid-added electrolytic solution,
The ionic liquid is either 1,3-diallylimidazolium bis (trifluoromethanesulfonyl) imide or 1-butyl-1-methylpyrrolidinium bis (trifluoromethanesulfonyl) imide,
A method for producing a lithium secondary battery, comprising the step of dissolving oxygen in the ionic liquid-added electrolyte by bubbling .
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