JP6295975B2 - Lithium ion secondary battery - Google Patents
Lithium ion secondary battery Download PDFInfo
- Publication number
- JP6295975B2 JP6295975B2 JP2015027709A JP2015027709A JP6295975B2 JP 6295975 B2 JP6295975 B2 JP 6295975B2 JP 2015027709 A JP2015027709 A JP 2015027709A JP 2015027709 A JP2015027709 A JP 2015027709A JP 6295975 B2 JP6295975 B2 JP 6295975B2
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- Prior art keywords
- positive electrode
- formula
- fluorine
- secondary battery
- ion secondary
- Prior art date
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- 229910001416 lithium ion Inorganic materials 0.000 title claims description 32
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- 150000001875 compounds Chemical class 0.000 claims description 61
- 239000002904 solvent Substances 0.000 claims description 52
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- 229910052731 fluorine Inorganic materials 0.000 claims description 29
- 125000001153 fluoro group Chemical group F* 0.000 claims description 23
- 239000007774 positive electrode material Substances 0.000 claims description 22
- 239000011737 fluorine Substances 0.000 claims description 17
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 claims description 15
- 125000004435 hydrogen atom Chemical group [H]* 0.000 claims description 14
- 125000003709 fluoroalkyl group Chemical group 0.000 claims description 13
- -1 ether compound Chemical class 0.000 claims description 11
- 229910002099 LiNi0.5Mn1.5O4 Inorganic materials 0.000 claims description 8
- 125000004432 carbon atom Chemical group C* 0.000 claims description 7
- 229910003002 lithium salt Inorganic materials 0.000 claims description 7
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- 125000005010 perfluoroalkyl group Chemical group 0.000 claims description 6
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- 229920000642 polymer Polymers 0.000 description 1
- 229920005672 polyolefin resin Polymers 0.000 description 1
- 229920000069 polyphenylene sulfide Polymers 0.000 description 1
- 229920001282 polysaccharide Polymers 0.000 description 1
- 239000005017 polysaccharide Substances 0.000 description 1
- FOWDZVNRQHPXDO-UHFFFAOYSA-N propyl hydrogen carbonate Chemical compound CCCOC(O)=O FOWDZVNRQHPXDO-UHFFFAOYSA-N 0.000 description 1
- 239000002296 pyrolytic carbon Substances 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 229920005989 resin Polymers 0.000 description 1
- 239000011347 resin Substances 0.000 description 1
- 230000000630 rising effect Effects 0.000 description 1
- 238000007761 roller coating Methods 0.000 description 1
- 125000002914 sec-butyl group Chemical group [H]C([H])([H])C([H])([H])C([H])(*)C([H])([H])[H] 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 238000004528 spin coating Methods 0.000 description 1
- 229920005608 sulfonated EPDM Polymers 0.000 description 1
- 230000001629 suppression Effects 0.000 description 1
- 125000000999 tert-butyl group Chemical group [H]C([H])([H])C(*)(C([H])([H])[H])C([H])([H])[H] 0.000 description 1
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Classifications
-
- 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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- Secondary Cells (AREA)
- Battery Electrode And Active Subsutance (AREA)
Description
本発明は、リチウムイオン二次電池に関する。 The present invention relates to a lithium ion secondary battery.
近年、正極と負極との間に非水電解液が介在するリチウムイオン二次電池について、数多くの報告がなされている。例えば、特許文献１では、フッ素系のＣＦ3ＣＨ2ＯＣＦ2ＣＦ2Ｈと非フッ素系のジグライムとエチレンカーボネート（ＥＣ）とを混合した非水溶媒に、支持塩であるＬｉＰＦ6を溶解した非水電解液を用いている。特許文献２では、ジエチレングリコール（２，２，２−トリフルオロエチル）メチルエーテルとＣＦ3ＣＨ2ＯＣＦ2ＣＦ2Ｈとを混合した非水溶媒に、支持塩であるＬｉＰＦ6を溶解した非水電解液を用いている。特許文献３では、フッ素系エーテルと非フッ素系エーテルの混合溶媒に、支持塩であるＬｉＰＦ6を溶解した非水電解液を用いている。特許文献４〜６も、フッ素系溶媒を含有する非水溶媒に支持塩を溶解した非水電解液を用いている。一方、非特許文献１〜３には、リチウムイオン二次電池を金属リチウム基準で５Ｖ付近で充放電する例が開示されている。正極活物質としては、非特許文献１ではスピネル型リチウムニッケルマンガン酸化物（ＬｉＮｉ0.5Ｍｎ1.5Ｏ4）、非特許文献２ではオリビン型リチウムリン酸コバルト（ＬｉＣｏＰＯ4）、非特許文献３ではオリビン型リチウムリン酸ニッケル（ＬｉＮｉＰＯ4）を使用している。 In recent years, many reports have been made on lithium ion secondary batteries in which a non-aqueous electrolyte is interposed between a positive electrode and a negative electrode. For example, in Patent Document 1, non-aqueous solvent in which LiPF 6 as a supporting salt is dissolved in a non-aqueous solvent in which fluorine-based CF 3 CH 2 OCF 2 CF 2 H, non-fluorine-based diglyme and ethylene carbonate (EC) are mixed. A water electrolyte is used. In Patent Document 2, nonaqueous electrolysis in which LiPF 6 as a supporting salt is dissolved in a nonaqueous solvent in which diethylene glycol (2,2,2-trifluoroethyl) methyl ether and CF 3 CH 2 OCF 2 CF 2 H are mixed. Liquid is used. In Patent Document 3, a nonaqueous electrolytic solution in which LiPF 6 as a supporting salt is dissolved in a mixed solvent of a fluorinated ether and a non-fluorinated ether is used. Patent Documents 4 to 6 also use a nonaqueous electrolytic solution in which a supporting salt is dissolved in a nonaqueous solvent containing a fluorine-based solvent. On the other hand, Non-Patent Documents 1 to 3 disclose examples in which a lithium ion secondary battery is charged and discharged at around 5 V on the basis of metallic lithium. Examples of the positive electrode active material include spinel type lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O 4 ) in Non-Patent Document 1, olivine type lithium cobalt phosphate (LiCoPO 4 ) in Non-Patent Document 2, and olivine type in Non-Patent Document 3. Lithium nickel phosphate (LiNiPO 4 ) is used.
しかしながら、非特許文献１〜３では、５Ｖ付近で充放電した場合、サイクル特性が悪くなるという問題があった。一方、特許文献１〜７では、フッ素系の種々の非水電解液が開示されているが、５Ｖ付近で充放電した場合にサイクル特性が悪化するのを抑制する非水電解液については検討されていない。 However, Non-Patent Documents 1 to 3 have a problem that the cycle characteristics deteriorate when charging and discharging are performed in the vicinity of 5V. On the other hand, Patent Documents 1 to 7 disclose various fluorine-based non-aqueous electrolytes. However, non-aqueous electrolytes that suppress deterioration of cycle characteristics when charged and discharged near 5 V are studied. Not.
本発明はこのような課題を解決するためになされたものであり、５Ｖ級正極活物質を用いたリチウムイオン二次電池において、良好なサイクル特性を得ることを主目的とする。 The present invention has been made to solve such a problem, and a main object of the present invention is to obtain good cycle characteristics in a lithium ion secondary battery using a 5 V-class positive electrode active material.
上述した目的を達成するために、本発明者らは、５Ｖ級正極活物質を含む正極とリチウム金属箔からなる負極との間に、特定のフッ素化合物を含む溶媒に支持塩を溶解させた非水電解液を介在させた二極式評価セルを作製し、サイクル特性を調べたところ、良好なサイクル特性が得られることを見いだし、本発明を完成するに至った。 In order to achieve the above-described object, the present inventors have prepared a non-supporting salt dissolved in a solvent containing a specific fluorine compound between a positive electrode containing a 5V class positive electrode active material and a negative electrode made of a lithium metal foil. A bipolar evaluation cell interposing a water electrolyte was prepared and the cycle characteristics were examined. As a result, it was found that good cycle characteristics were obtained, and the present invention was completed.
即ち、本発明のリチウムイオン二次電池は、
正極と負極との間に非水電解液が介在するリチウムイオン二次電池であって、
前記正極は、金属リチウム電位基準で５Ｖ以上の電位まで充電可能な５Ｖ級正極活物質を含有し、
前記非水電解液は、式（Ｉ）で表される化合物を含む溶媒にリチウム塩を溶解したものである。
That is, the lithium ion secondary battery of the present invention is
A lithium ion secondary battery in which a non-aqueous electrolyte is interposed between a positive electrode and a negative electrode,
The positive electrode contains a 5 V class positive electrode active material that can be charged to a potential of 5 V or more on the basis of a metallic lithium potential,
The non-aqueous electrolyte is obtained by dissolving a lithium salt in a solvent containing a compound represented by the formula (I).
（Ｒ1及びＲ2は、それぞれ独立してフッ素原子又は炭素数１〜１０のフルオロアルキル基であり、前記フルオロアルキル基はエーテル結合、スルホニル結合及びビススルホニルイミド結合からなる群より選ばれた１つ以上を含んでいてもよい。） (R 1 and R 2 are each independently a fluorine atom or a fluoroalkyl group having 1 to 10 carbon atoms, and the fluoroalkyl group is selected from the group consisting of an ether bond, a sulfonyl bond and a bissulfonylimide bond. May contain more than one.)
このリチウムイオン二次電池では、良好なサイクル特性を得ることができる。ここで、サイクル特性とは、金属リチウム電位基準で５Ｖ以上の電位まで充電しその後放電するという操作を１サイクルとし、このサイクルを何度も繰り返したあとの充放電特性（例えば容量維持率やクーロン効率など）をいう。このような効果が得られる理由は定かではないが、式（Ｉ）で表される化合物が充電時に正極で酸化分解されてガス発生を伴うことなく正極に保護被膜を十分に形成し、その被膜が正極での非水電解液の更なる酸化分解を抑制したためと考えられる。 In this lithium ion secondary battery, good cycle characteristics can be obtained. Here, the cycle characteristic refers to the operation of charging to a potential of 5 V or higher on the basis of the metal lithium potential and then discharging, and the charge / discharge characteristics after repeating this cycle many times (for example, capacity maintenance rate and coulomb). Efficiency). The reason why such an effect can be obtained is not clear, but the compound represented by formula (I) is oxidized and decomposed at the positive electrode during charging to sufficiently form a protective film on the positive electrode without causing gas generation. This is thought to be due to the suppression of further oxidative decomposition of the non-aqueous electrolyte at the positive electrode.
本発明のリチウムイオン二次電池は、正極と負極との間に非水電解液が介在するリチウムイオン二次電池であって、前記正極は、金属リチウム電位基準で５Ｖ以上の電位まで充電可能な５Ｖ級正極活物質を含有し、前記非水電解液は、前記式（Ｉ）で表される化合物を含む溶媒にリチウム塩を溶解したものである。 The lithium ion secondary battery of the present invention is a lithium ion secondary battery in which a non-aqueous electrolyte is interposed between a positive electrode and a negative electrode, and the positive electrode can be charged to a potential of 5 V or more on the basis of a metallic lithium potential. 5V class positive electrode active material is contained, and the said non-aqueous electrolyte solution melt | dissolves lithium salt in the solvent containing the compound represented by the said Formula (I).
本発明のリチウムイオン二次電池の正極は、正極活物質として金属リチウム電位基準で５Ｖ以上の電位まで充電可能な５Ｖ級正極活物質を含有する。正極は、この５Ｖ級正極活物質と導電材と結着材とを混合し、適当な溶剤を加えてペースト状の正極材としたものを、集電体の表面に塗布乾燥し、必要に応じて電極密度を高めるべく圧縮して形成してもよい。５Ｖ級正極活物質としては、ＬｉaＮｉbＭｎcＭｅdＯe（ＭｅはＭｎ，Ｎｉ以外の遷移金属元素、Ａｌ及びアルカリ土類金属から選ばれる少なくとも１種の元素であり、ａ〜ｅは０．９≦ａ≦１．２、０．４５≦ｂ≦０．５５、１．４５≦ｃ≦１．５５、０≦ｄ≦５．００、３．８≦ｅ≦４．２）で表されるスピネル型リチウムニッケルマンガン酸化物、ＬｉＣｏＰＯ4で表されるオリビン型リチウムリン酸コバルト、ＬｉＮｉＰＯ4で表されるオリビン型リチウムリン酸ニッケルなどを用いることができる。なお、遷移金属としては、Ｖ，Ｔｉ，Ｃｒ，Ｆｅ，Ｃｏ，Ｃｕ等が挙げられる。このうち、スピネル型リチウムニッケルマンガン酸化物が好ましく、ＬｉＮｉ0.5Ｍｎ1.5Ｏ4がより好ましい。導電材は、正極の電池性能に悪影響を及ぼさない電子伝導性材料であれば特に限定されず、例えば、天然黒鉛（鱗状黒鉛、鱗片状黒鉛）や人造黒鉛などの黒鉛、アセチレンブラック、カーボンブラック、ケッチェンブラック、カーボンウィスカ、ニードルコークス、炭素繊維、金属（銅、ニッケル、アルミニウム、銀、金など）などの１種又は２種以上を混合したものを用いることができる。これらの中で、導電材としては、電子伝導性及び塗工性の観点より、カーボンブラック及びアセチレンブラックが好ましい。結着材は、活物質粒子及び導電材粒子を繋ぎ止める役割を果たすものであり、例えば、ポリテトラフルオロエチレン（ＰＴＦＥ）、ポリフッ化ビニリデン（ＰＶＤＦ）、フッ素ゴム等の含フッ素樹脂、或いはポリプロピレン、ポリエチレン等の熱可塑性樹脂、エチレンプロピレンジエンモノマー（ＥＰＤＭ）ゴム、スルホン化ＥＰＤＭゴム、天然ブチルゴム（ＮＢＲ）等を単独で、あるいは２種以上の混合物として用いることができる。また、水系バインダーであるセルロース系やスチレンブタジエンゴム（ＳＢＲ）の水分散体等を用いることもできる。正極活物質、導電材、結着材を分散させる溶剤としては、例えばＮ−メチルピロリドン、ジメチルホルムアミド、ジメチルアセトアミド、メチルエチルケトン、シクロヘキサノン、酢酸メチル、アクリル酸メチル、ジエチレントリアミン、Ｎ，Ｎ−ジメチルアミノプロピルアミン、エチレンオキシド、テトラヒドロフランなどの有機溶剤を用いることができる。また、水に分散剤、増粘剤等を加え、ＳＢＲなどのラテックスで活物質をスラリー化してもよい。増粘剤としては、例えば、カルボキシメチルセルロース、メチルセルロースなどの多糖類を単独で、あるいは２種以上の混合物として用いることができる。塗布方法としては、例えば、アプリケータロールなどのローラコーティング、スクリーンコーティング、ドクターブレイド方式、スピンコーティング、バーコータなどが挙げられ、これらのいずれかを用いて任意の厚さ・形状とすることができる。集電体としては、アルミニウム、チタン、ステンレス鋼、ニッケル、鉄、焼成炭素、導電性高分子、導電性ガラスなどのほか、接着性、導電性及び耐酸化性向上の目的で、アルミニウムや銅などの表面をカーボン、ニッケル、チタンや銀などで処理したものを用いることができる。これらについては、表面を酸化処理することも可能である。集電体の形状については、箔状、フィルム状、シート状、ネット状、パンチ又はエキスパンドされたもの、ラス体、多孔質体、発泡体、繊維群の形成体などが挙げられる。集電体の厚さは、例えば１〜５００μｍのものが用いられる。 The positive electrode of the lithium ion secondary battery of the present invention contains a 5 V class positive electrode active material that can be charged to a potential of 5 V or more on the basis of the metal lithium potential as a positive electrode active material. The positive electrode is prepared by mixing this 5V-class positive electrode active material, a conductive material and a binder, adding a suitable solvent to form a paste-like positive electrode material, applying and drying it on the surface of the current collector, and if necessary The electrode may be compressed to increase the electrode density. The 5V-class cathode active material, a Li a Ni b Mn c Me d O e ( at least one element Me is Mn, transition metal elements other than Ni, selected from Al and alkaline earth metals, a to e 0.9 ≦ a ≦ 1.2, 0.45 ≦ b ≦ 0.55, 1.45 ≦ c ≦ 1.55, 0 ≦ d ≦ 5.00, 3.8 ≦ e ≦ 4.2) Spinel type lithium nickel manganese oxide represented, olivine type lithium cobalt phosphate represented by LiCoPO 4 , olivine type lithium nickel phosphate represented by LiNiPO 4 and the like can be used. Examples of the transition metal include V, Ti, Cr, Fe, Co, and Cu. Among these, spinel type lithium nickel manganese oxide is preferable, and LiNi 0.5 Mn 1.5 O 4 is more preferable. The conductive material is not particularly limited as long as it is an electron conductive material that does not adversely affect the battery performance of the positive electrode. For example, graphite such as natural graphite (scale-like graphite, scale-like graphite) or artificial graphite, acetylene black, carbon black, What mixed 1 type (s) or 2 or more types, such as ketjen black, carbon whisker, needle coke, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.) can be used. Among these, as the conductive material, carbon black and acetylene black are preferable from the viewpoints of electron conductivity and coatability. The binder serves to bind the active material particles and the conductive material particles. For example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), fluorine-containing resin such as fluorine rubber, or polypropylene, Thermoplastic resins such as polyethylene, ethylene propylene diene monomer (EPDM) rubber, sulfonated EPDM rubber, natural butyl rubber (NBR) and the like can be used alone or as a mixture of two or more. In addition, an aqueous dispersion of cellulose or styrene butadiene rubber (SBR), which is an aqueous binder, can also be used. Examples of the solvent for dispersing the positive electrode active material, the conductive material, and the binder include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, and N, N-dimethylaminopropylamine. Organic solvents such as ethylene oxide and tetrahydrofuran can be used. Moreover, a dispersing agent, a thickener, etc. may be added to water, and an active material may be slurried with latex, such as SBR. As the thickener, for example, polysaccharides such as carboxymethyl cellulose and methyl cellulose can be used alone or as a mixture of two or more. Examples of the application method include roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coater, and the like, and any of these can be used to obtain an arbitrary thickness and shape. Current collectors include aluminum, titanium, stainless steel, nickel, iron, calcined carbon, conductive polymer, conductive glass, and aluminum, copper, etc. for the purpose of improving adhesion, conductivity, and oxidation resistance. A surface treated with carbon, nickel, titanium, silver or the like can be used. For these, the surface can be oxidized. Examples of the shape of the current collector include foil, film, sheet, net, punched or expanded, lath, porous, foam, and formed fiber group. The thickness of the current collector is, for example, 1 to 500 μm.
本発明のリチウム二次電池の負極は、例えば、負極活物質と集電体とを密着させて形成してもよいし、負極活物質と導電材と結着材とを混合し、適当な溶剤を加えてペースト状の負極材としたものを、集電体の表面に塗布乾燥し、必要に応じて電極密度を高めるべく圧縮して形成してもよい。負極活物質としては、リチウム、リチウム合金、スズ化合物などの無機化合物、リチウムイオンを吸蔵・放出可能な炭素質材料、複数の元素を含む複合酸化物、導電性ポリマーなどが挙げられる。炭素質材料は、例えば、コークス類、ガラス状炭素類、グラファイト類、難黒鉛化性炭素類、熱分解炭素類、炭素繊維などが挙げられる。このうち、人造黒鉛、天然黒鉛などのグラファイト類が、金属リチウムに近い作動電位を有し、高い作動電圧での充放電が可能であり支持塩としてリチウム塩を使用した場合に自己放電を抑え、且つ充電時おける不可逆容量を少なくできるため、好ましい。複合酸化物としては、例えば、リチウムチタン複合酸化物やリチウムバナジウム複合酸化物などが挙げられる。負極活物質としては、このうち、炭素質材料が安全性の面から見て好ましい。また、負極に用いられる導電材、結着材、溶剤などは、それぞれ正極で例示したものを用いることができる。負極の集電体には、銅、ニッケル、ステンレス鋼、チタン、アルミニウム、焼成炭素、導電性高分子、導電性ガラス、Ａｌ−Ｃｄ合金などのほか、接着性、導電性及び耐還元性向上の目的で、例えば銅などの表面をカーボン、ニッケル、チタンや銀などで処理したものも用いることができる。これらについては、表面を酸化処理することも可能である。集電体の形状は、正極と同様のものを用いることができる。 The negative electrode of the lithium secondary battery of the present invention may be formed, for example, by adhering a negative electrode active material and a current collector, or by mixing a negative electrode active material, a conductive material, and a binder, and an appropriate solvent. A paste-like negative electrode material may be applied to the surface of the current collector and dried, and may be compressed to increase the electrode density as necessary. Examples of the negative electrode active material include lithium, lithium alloys, tin compounds and other inorganic compounds, carbonaceous materials capable of inserting and extracting lithium ions, composite oxides containing a plurality of elements, and conductive polymers. Examples of the carbonaceous material include cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, and carbon fibers. Of these, graphites such as artificial graphite and natural graphite have an operating potential close to that of metallic lithium, can be charged and discharged at a high operating voltage, and suppresses self-discharge when a lithium salt is used as a supporting salt. In addition, the irreversible capacity during charging can be reduced, which is preferable. Examples of the composite oxide include lithium titanium composite oxide and lithium vanadium composite oxide. Among these, as the negative electrode active material, a carbonaceous material is preferable from the viewpoint of safety. In addition, as the conductive material, binder, solvent, and the like used for the negative electrode, those exemplified for the positive electrode can be used. The negative electrode current collector includes copper, nickel, stainless steel, titanium, aluminum, calcined carbon, conductive polymer, conductive glass, Al-Cd alloy, etc., as well as improved adhesion, conductivity and reduction resistance. For the purpose, for example, a copper surface treated with carbon, nickel, titanium, silver or the like can be used. For these, the surface can be oxidized. The shape of the current collector can be the same as that of the positive electrode.
本発明のリチウムイオン二次電池の非水電解液は、式（Ｉ）で表される化合物を含む溶媒にリチウム塩（支持塩）を溶解したものである。式（Ｉ）中、Ｒ1及びＲ2は、それぞれ独立してフッ素原子又は炭素数１〜１０（好ましくは炭素数１〜４）のフルオロアルキル基であり、フルオロアルキル基はエーテル結合、スルホニル結合及びビススルホニルイミド結合からなる群より選ばれた１つ以上を含んでいてもよい。フルオロアルキル基は、アルキル基の水素原子の少なくとも１つがフッ素原子に置換されたものであり、このうち、アルキル基の水素原子のすべてがフッ素原子に置換されたパーフルオロアルキル基が好ましい。エーテル結合を含むフルオロアルキル基は、−Ｏ−Ｒ（Ｒは炭素数１〜１０のフルオロアルキル基、以下同じ）で表され、スルホニル結合を含むフルオロアルキル基は、−Ｓ（＝Ｏ）2Ｒで表され、ビススルホニルイミド結合を含むフルオロアルキル基は、−Ｓ（＝Ｏ）2ＮＬｉＳ（＝Ｏ）2Ｒで表される。Ｒとしては、炭素数１〜４のフルオロアルキル基、すなわち、メチル基、エチル基、ｎ−プロピル基、イソプロピル基、ｎ−ブチル基、イソブチル基、ｓｅｃ−ブチル基及びｔｅｒｔ−ブチル基からなる群より選ばれた一つの基の少なくとも１つの水素原子がフッ素原子に置換されたものが好ましい。 The non-aqueous electrolyte of the lithium ion secondary battery of the present invention is obtained by dissolving a lithium salt (supporting salt) in a solvent containing a compound represented by the formula (I). In formula (I), R 1 and R 2 are each independently a fluorine atom or a fluoroalkyl group having 1 to 10 carbon atoms (preferably 1 to 4 carbon atoms), and the fluoroalkyl group is an ether bond or a sulfonyl bond. And one or more selected from the group consisting of bissulfonylimide bonds may be included. The fluoroalkyl group is one in which at least one hydrogen atom of the alkyl group is substituted with a fluorine atom, and among these, a perfluoroalkyl group in which all of the hydrogen atoms of the alkyl group are substituted with fluorine atoms is preferable. The fluoroalkyl group containing an ether bond is represented by —O—R (R is a fluoroalkyl group having 1 to 10 carbon atoms, the same applies hereinafter), and the fluoroalkyl group containing a sulfonyl bond is —S (═O) 2 R. And a fluoroalkyl group containing a bissulfonylimide bond is represented by —S (═O) 2 NLiS (═O) 2 R. R is a group consisting of a fluoroalkyl group having 1 to 4 carbon atoms, that is, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, and a tert-butyl group. A group in which at least one hydrogen atom of one selected group is substituted with a fluorine atom is preferable.
式（Ｉ）で表される化合物としては、例えば下記式（１）〜（４）の化合物が好ましい。これらの化合物は、本発明の効果を得るうえで適切な耐酸化性及び耐還元性を有しているからである。これに対して、例えば、式（Ｉ）においてＲ1及びＲ2がともに水素原子又はともにアルキル基である溶媒や、Ｒ1がパーフルオロアルキル基でＲ2が水素原子又は塩素原子である溶媒の場合、適切な耐酸化性及び耐還元性を有していないため、好ましくない。 As the compound represented by the formula (I), for example, compounds of the following formulas (1) to (4) are preferable. This is because these compounds have appropriate oxidation resistance and reduction resistance in obtaining the effects of the present invention. In contrast, for example, in the formula (I), R 1 and R 2 are both hydrogen atoms or alkyl groups, or R 1 is a perfluoroalkyl group and R 2 is a hydrogen atom or chlorine atom. The case is not preferable because it does not have appropriate oxidation resistance and reduction resistance.
非水電解液に用いられる溶媒は、フッ素基を有するフッ素系溶媒に、式（Ｉ）で表される化合物を含ませたものが好ましい。この場合、式（Ｉ）で表される化合物は、フッ素系溶媒１００質量部に対して１〜２質量部の割合で添加されていることが好ましい。フッ素系溶媒としては、少なくとも１つの水素原子がフッ素原子で置換されたカーボネートが好ましい。こうしたカーボネートとしては、例えば、エチレンカーボネート、プロピレンカーボネート、ブチレンカーボネート、ビニレンカーボネートなどの環状カーボネートのうち少なくとも１つの水素原子がフッ素原子で置換された化合物や、ジメチルカーボネート、エチルメチルカーボネート、ジエチルカーボネート、エチル−ｎ−ブチルカーボネート、メチル−ｔ−ブチルカーボネート、ジ−ｉ−プロピルカーボネート、ｔ−ブチル−ｉ−プロピルカーボネートなどの鎖状カーボネートのうち少なくとも１つの水素原子がフッ素原子で置換された化合物や、これらの２種以上を混合したものなどが挙げられる。このうち、エチレンカーボネートやエチルメチルカーボネートのうち少なくとも１つの水素原子がフッ素原子で置換された化合物がより好ましい。なお、こうしたカーボネートのほかに、ガンマブチロラクトン，ガンマバレロラクトンなどの環状エステルのうち少なくとも１つの水素原子がフッ素で置換された化合物などを用いてもよい。 The solvent used for the nonaqueous electrolytic solution is preferably a fluorine-based solvent having a fluorine group containing the compound represented by the formula (I). In this case, it is preferable that the compound represented by the formula (I) is added at a ratio of 1 to 2 parts by mass with respect to 100 parts by mass of the fluorinated solvent. As the fluorine-based solvent, carbonate in which at least one hydrogen atom is substituted with a fluorine atom is preferable. Examples of such carbonates include compounds in which at least one hydrogen atom is substituted with a fluorine atom among cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl A compound in which at least one hydrogen atom is substituted with a fluorine atom among chain carbonates such as -n-butyl carbonate, methyl-t-butyl carbonate, di-i-propyl carbonate, and t-butyl-i-propyl carbonate; What mixed these 2 or more types is mentioned. Among these, a compound in which at least one hydrogen atom is substituted with a fluorine atom among ethylene carbonate and ethyl methyl carbonate is more preferable. In addition to these carbonates, compounds in which at least one hydrogen atom is substituted with fluorine among cyclic esters such as gamma butyrolactone and gamma valerolactone may be used.
また、非水電解液に用いられる溶媒は、フッ素基を有さない非フッ素系溶媒に、式（Ｉ）で表される化合物を含ませたものも好ましい。この場合、式（Ｉ）で表される化合物は、非フッ素系溶媒１００質量部に対して１〜５質量部の割合で添加されていることが好ましい。非フッ素系溶媒としては、フッ素基を有さないカーボネートが好ましい。こうしたカーボネートとしては、エチレンカーボネート、プロピレンカーボネート、ブチレンカーボネート、ビニレンカーボネートなどの環状カーボネートや、ジメチルカーボネート、エチルメチルカーボネート、ジエチルカーボネート、エチル−ｎ−ブチルカーボネート、メチル−ｔ−ブチルカーボネート、ジ−ｉ−プロピルカーボネート、ｔ−ブチル−ｉ−プロピルカーボネートなどの鎖状カーボネートや、これらの２種以上を混合したものなどがあげられる。なお、非フッ素系溶媒を用いた場合に比べて、フッ素系溶媒を用いた方がより良好なサイクル特性が得られるため好ましい。 The solvent used for the non-aqueous electrolyte is preferably a non-fluorinated solvent having no fluorine group containing the compound represented by the formula (I). In this case, the compound represented by the formula (I) is preferably added at a ratio of 1 to 5 parts by mass with respect to 100 parts by mass of the non-fluorinated solvent. As the non-fluorinated solvent, a carbonate having no fluorine group is preferable. Examples of such carbonates include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl-n-butyl carbonate, methyl-t-butyl carbonate, and di-i-. Examples thereof include chain carbonates such as propyl carbonate and t-butyl-i-propyl carbonate, and mixtures of two or more of these. Note that it is preferable to use a fluorinated solvent as compared with the case of using a non-fluorinated solvent because better cycle characteristics can be obtained.
リチウム塩としては、例えば、ＬｉＰＦ6、ＬｉＣｌＯ4、ＬｉＢＦ4、ＬｉＡｓＦ6、ＬｉＳｂＦ6、ＬｉＣＦ3ＳＯ3、ＬｉＮ（ＣＦ3ＳＯ2）2、ＬｉＣ（ＣＦ3ＳＯ2）3、ＬｉＳｉＦ6、ＬｉＡｌＦ4、ＬｉＳＣＮ、ＬｉＣｌ、ＬｉＦ、ＬｉＢｒ、ＬｉＩ、ＬｉＡｌＣｌ4などが挙げられる。支持塩は、非水電解液中の濃度が０．１Ｍ以上５Ｍ以下であることが好ましく、０．５Ｍ以上２Ｍ以下であることがより好ましい。支持塩の濃度が０．１Ｍ以上では、十分な電流密度を得ることができ、５Ｍ以下では、電解液をより安定させることができる。 Examples of the lithium salt, LiPF 6, LiClO 4, LiBF 4, LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiN (CF 3 SO 2) 2, LiC (CF 3 SO 2) 3, LiSiF 6, LiAlF 4 , LiSCN, LiCl, LiF, LiBr, LiI, LiAlCl 4 and the like. The concentration of the supporting salt in the nonaqueous electrolytic solution is preferably 0.1 M or more and 5 M or less, and more preferably 0.5 M or more and 2 M or less. When the concentration of the supporting salt is 0.1 M or more, a sufficient current density can be obtained, and when it is 5 M or less, the electrolytic solution can be made more stable.
式（Ｉ）で表される化合物であってＲ1，Ｒ2が炭素数１〜１０のパーフルオロアルキル基の化合物については、米国特許第３３２４１４５号及びMacromolecules vol. 26, 1993, pp.5829-5834に記載されている方法を参考にして合成可能である。なお、原料として用いられるパーフルオロアセトンについては、国際公開第２００２／０４６８１号のパンフレットに記載されている方法を参考にして合成可能である。また、Ｒ1がフッ素原子でＲ2がパーフルオロアルキル基の化合物については、特開平９−２８６７８５号公報に記載されている方法を参考にして合成可能である。その他に、Ｒ1が水素原子でＲ2がフッ素原子の化合物については、Tetrahedron Letters vol. 43, 2002, pp.1503-1505に記載されている方法で、また、Ｒ1が水素原子でＲ2がパーフルオロアルキル基の化合物については、Macromoleculs vol. 26, 1993, pp.5829-5834に記載されている方法で合成可能である。 Regarding the compound represented by the formula (I) in which R 1 and R 2 are perfluoroalkyl groups having 1 to 10 carbon atoms, US Pat. No. 3,324,145 and Macromolecules vol. 26, 1993, pp. 5829- It can be synthesized with reference to the method described in 5834. The perfluoroacetone used as a raw material can be synthesized with reference to the method described in the pamphlet of International Publication No. 2002/04681. A compound in which R 1 is a fluorine atom and R 2 is a perfluoroalkyl group can be synthesized with reference to the method described in JP-A-9-286785. In addition, for compounds in which R 1 is a hydrogen atom and R 2 is a fluorine atom, the method described in Tetrahedron Letters vol. 43, 2002, pp. 1503-1505 is used, and R 1 is a hydrogen atom and R 2 A compound having a perfluoroalkyl group can be synthesized by the method described in Macromoleculs vol. 26, 1993, pp. 5829-5834.
本発明のリチウムイオン二次電池は、負極と正極との間にセパレータを備えていてもよい。セパレータとしては、リチウムイオン二次電池の使用範囲に耐えうる組成であれば特に限定されないが、例えば、ポリプロピレン製不織布やポリフェニレンスルフィド製不織布などの高分子不織布、ポリエチレンやポリプロピレンなどのオレフィン系樹脂の薄い微多孔膜が挙げられる。これらは単独で用いてもよいし、複数を混合して用いてもよい。 The lithium ion secondary battery of the present invention may include a separator between the negative electrode and the positive electrode. The separator is not particularly limited as long as the composition can withstand the use range of the lithium ion secondary battery. For example, a polymer nonwoven fabric such as a polypropylene nonwoven fabric or a polyphenylene sulfide nonwoven fabric, or a thin olefin resin such as polyethylene or polypropylene is used. A microporous membrane is mentioned. These may be used alone or in combination.
本発明のリチウムイオン二次電池の形状は、特に限定されないが、例えばコイン型、ボタン型、シート型、積層型、円筒型、偏平型、角型などが挙げられる。また、電気自動車等に用いる大型のものなどに適用してもよい。図１は、本発明のリチウムイオン二次電池の一例を示す模式図である。このリチウムイオン二次電池１０は、集電体１１に正極活物質１２を形成した正極シート１３と、集電体１４の表面に負極活物質１７を形成した負極シート１８と、正極シート１３と負極シート１８との間に設けられたセパレータ１９と、正極シート１３と負極シート１８の間を満たす非水電解液２０と、を備えたものである。このリチウムイオン二次電池１０では、正極シート１３と負極シート１８との間にセパレータ１９を挟み、これらを捲回して円筒ケース２２に挿入し、正極シート１３に接続された正極端子２４と負極シート１８に接続された負極端子２６とを配設して形成されている。ここでは、正極シート１３には、５Ｖ級正極活物質が含まれている。また、非水電解液２０は、式（Ｉ）で表される化合物を含む溶媒に支持塩を溶解させたものである。 The shape of the lithium ion secondary battery of the present invention is not particularly limited, and examples thereof include a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, and a square type. Moreover, you may apply to the large sized thing etc. which are used for an electric vehicle etc. FIG. 1 is a schematic view showing an example of the lithium ion secondary battery of the present invention. The lithium ion secondary battery 10 includes a positive electrode sheet 13 in which a positive electrode active material 12 is formed on a current collector 11, a negative electrode sheet 18 in which a negative electrode active material 17 is formed on the surface of the current collector 14, a positive electrode sheet 13 and a negative electrode A separator 19 provided between the sheet 18 and a nonaqueous electrolytic solution 20 that fills between the positive electrode sheet 13 and the negative electrode sheet 18 are provided. In this lithium ion secondary battery 10, a separator 19 is sandwiched between a positive electrode sheet 13 and a negative electrode sheet 18, and these are wound and inserted into a cylindrical case 22, and a positive electrode terminal 24 and a negative electrode sheet connected to the positive electrode sheet 13. And a negative electrode terminal 26 connected to 18. Here, the positive electrode sheet 13 contains a 5V class positive electrode active material. The nonaqueous electrolytic solution 20 is obtained by dissolving a supporting salt in a solvent containing a compound represented by the formula (I).
本実施形態のリチウムイオン二次電池１０によれば、良好なサイクル特性を得ることができる。ここで、サイクル特性とは、金属リチウム電位基準で５Ｖ以上の電位まで充電しその後放電するという操作を１サイクルとし、このサイクルを何度も繰り返したあとの充放電特性（例えば容量維持率やクーロン効率など）をいう。 According to the lithium ion secondary battery 10 of the present embodiment, good cycle characteristics can be obtained. Here, the cycle characteristic refers to the operation of charging to a potential of 5 V or higher on the basis of the metal lithium potential and then discharging, and the charge / discharge characteristics after repeating this cycle many times (for example, capacity maintenance rate and coulomb). Efficiency).
なお、本発明は上述した実施形態に何ら限定されることはなく、本発明の技術的範囲に属する限り種々の態様で実施し得ることはいうまでもない。 It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.
本発明を実証する実施例について、比較例と対比しながら以下に説明する。各実施例、各比較例で使用した電解液溶媒や電極を表１に示した。尚、本発明はこの実施例に限定されるものではない。 Examples demonstrating the present invention will be described below in comparison with comparative examples. Table 1 shows the electrolyte solvents and electrodes used in the examples and comparative examples. In addition, this invention is not limited to this Example.
１．正極がＬｉＮｉ0.5Ｍｎ1.5Ｏ4、負極が黒鉛の組合せ−その１
［実施例１−１］
（正極の作製）
５Ｖ級正極活物質としてＬｉＮｉ0.5Ｍｎ1.5Ｏ4（戸田工業製）を、導電助材として炭素を、バインダとしてポリフッ化ビニリデン（クレハ製、ＫＦポリマ）を用い、正極活物質と導電助材とバインダとを質量比で８５：１０：５となるように混合することで、正極合材を作製した。その正極合材をＮ−メチル−２−ピロリドン（ＮＭＰ）で分散させたペーストを、厚さ２０μｍのアルミニウム箔の両面に塗工乾燥させた。その後、塗布シートを加圧プレス処理し、１０ｃｍ2の面積に打ち抜いて円盤状の正極を得た。
1. Combination of LiNi 0.5 Mn 1.5 O 4 for positive electrode and graphite for negative electrode-part 1
[Example 1-1]
(Preparation of positive electrode)
LiNi 0.5 Mn 1.5 O 4 (manufactured by Toda Kogyo Co., Ltd.) as a 5V class positive electrode active material, carbon as a conductive additive, and polyvinylidene fluoride (manufactured by Kureha, KF polymer) as a binder, positive electrode active material, conductive additive and binder Were mixed so that the mass ratio was 85: 10: 5, to produce a positive electrode mixture. The paste in which the positive electrode mixture was dispersed with N-methyl-2-pyrrolidone (NMP) was applied and dried on both sides of an aluminum foil having a thickness of 20 μm. Thereafter, the coated sheet was pressure-pressed and punched out to an area of 10 cm 2 to obtain a disc-shaped positive electrode.
（非水電解液の作製）
モノフルオロエチレンカーボネートとトリフルオロエチルメチルカーボネートとを体積比で５０：５０の割合で混合した溶媒に、ＬｉＰＦ6を１ｍｏｌ／Ｌになるように加えて混合溶液とした。その後、この混合溶液１００質量部に対して、式（１）に示す２，２−ビストリフルオロメチル−１，３−ジオキソランを１質量部含有させて、非水電解液を得た。
(Preparation of non-aqueous electrolyte)
LiPF 6 was added to a solvent in which monofluoroethylene carbonate and trifluoroethyl methyl carbonate were mixed at a volume ratio of 50:50 so as to be 1 mol / L to obtain a mixed solution. Thereafter, 1 part by mass of 2,2-bistrifluoromethyl-1,3-dioxolane represented by the formula (1) was added to 100 parts by mass of the mixed solution to obtain a nonaqueous electrolytic solution.
（負極の作製）
ｄ002＝０．３８８ｎｍ以下の黒鉛１００質量部に対して、ｄ002＝０．３４ｎｍ以上の易黒鉛化炭素を４０質量部混合して負極活物質とした。バインダにポリフッ化ビニリデン（クレハ製、ＫＦポリマ）を用い、負極活物質とバインダとを質量比で９５：５となるように混合することで、負極合材を作製した。その負極合材をＮＭＰで分散させたペーストを、厚さ１０μｍの銅箔の両面に塗工乾燥させた。その後、塗布シートを加圧プレス処理し、１０ｃｍ2の面積に打ち抜いて円盤状の負極を得た。
(Preparation of negative electrode)
40 parts by mass of graphitizable carbon having d 002 = 0.34 nm or more was mixed with 100 parts by mass of graphite having d 002 = 0.388 nm or less to obtain a negative electrode active material. Polyvinylidene fluoride (manufactured by Kureha, KF polymer) was used as the binder, and the negative electrode active material and the binder were mixed at a mass ratio of 95: 5 to prepare a negative electrode mixture. The paste in which the negative electrode mixture was dispersed with NMP was applied and dried on both sides of a 10 μm thick copper foil. Thereafter, the coated sheet was pressure-pressed and punched out to an area of 10 cm 2 to obtain a disc-shaped negative electrode.
（二極式評価セルの作製）
上述した正極と負極との間に、上述した非水電解液を含浸させたセパレータ（東レ東燃製）を挟んで二極式評価セルを作製した。
(Preparation of bipolar evaluation cell)
A bipolar evaluation cell was produced by sandwiching a separator (manufactured by Toray Tonen) impregnated with the above-described non-aqueous electrolyte between the positive electrode and the negative electrode.
（充放電試験）
上述した二極式評価セルを用い、２０℃の温度環境下、１．０ｍＡで４．９Ｖまで充電した後、１．０ｍＡで３．５Ｖまで放電させた。この操作を１５０サイクル行った。初回の放電容量をＱ1st、１５０サイクル後の放電容量をＱ150thとして、（Ｑ150th／Ｑ1st）×１００（％）を１５０サイクル後の容量維持率とした。
(Charge / discharge test)
Using the above-described bipolar evaluation cell, the battery was charged to 4.9 V at 1.0 mA in a temperature environment of 20 ° C., and then discharged to 3.5 V at 1.0 mA. This operation was performed for 150 cycles. The initial discharge capacity was Q 1st , the discharge capacity after 150 cycles was Q 150th , and (Q 150th / Q 1st ) × 100 (%) was the capacity maintenance rate after 150 cycles.
［実施例１−２］
非水電解液を作製する際に混合溶液１００質量部に対して式（１）の化合物を２質量部含有させた以外は、実施例１−１と同様にして二極式評価セルを作製し、充放電試験を行った。
[Example 1-2]
A bipolar evaluation cell was prepared in the same manner as in Example 1-1, except that 2 parts by mass of the compound of the formula (1) was added to 100 parts by mass of the mixed solution when producing the non-aqueous electrolyte. A charge / discharge test was conducted.
［比較例１−１］
非水電解液を作製する際に式（１）の化合物を含有させなかった以外は、実施例１−１と同様にして二極式評価セルを作製し、充放電試験を行った。
[Comparative Example 1-1]
A bipolar evaluation cell was produced in the same manner as in Example 1-1 except that the compound of formula (1) was not included when producing the nonaqueous electrolytic solution, and a charge / discharge test was performed.
［充放電試験の評価］
５Ｖ級正極活物質を含有する正極と炭素質材料の負極との間に非水電解液が介在するリチウムイオン二次電池において、主たる電解液溶媒としてフッ素系溶媒を用いた実施例１−１，１−２及び比較例１−１の充放電試験の結果を図２及び表２に示す。図２及び表２から、フッ素系溶媒に式（１）の化合物を添加した場合、添加しない場合に比べてサイクル特性が向上することがわかった。これは、フッ素系溶媒の耐酸化性が高いことに加えて、式（１）の化合物がフッ素系溶媒の分解を抑制したことによるものと推察される。この場合、フッ素系溶媒１００質量部に対して式（１）の化合物を１〜５質量部添加するのが好ましく、１〜２質量部添加するのがより好ましい。
[Evaluation of charge / discharge test]
In a lithium ion secondary battery in which a non-aqueous electrolyte is interposed between a positive electrode containing a 5 V class positive electrode active material and a negative electrode of a carbonaceous material, Example 1-1 using a fluorine-based solvent as a main electrolyte solvent The results of the charge / discharge test of 1-2 and Comparative Example 1-1 are shown in FIG. From FIG. 2 and Table 2, it was found that when the compound of the formula (1) was added to the fluorinated solvent, the cycle characteristics were improved as compared with the case where the compound was not added. This is presumably due to the fact that the compound of formula (1) suppressed the decomposition of the fluorine-based solvent in addition to the high oxidation resistance of the fluorine-based solvent. In this case, it is preferable to add 1-5 mass parts of compounds of Formula (1) with respect to 100 mass parts of fluorine-type solvents, and it is more preferable to add 1-2 mass parts.
２．正極がＬｉＮｉ0.5Ｍｎ1.5Ｏ4、負極が黒鉛の組合せ−その２
［実施例２−１］
非水電解液を作製する際に、エチレンカーボネートとジメチルカーボネートとエチルメチルカーボネートとを体積比で３０：４０：３０の割合で混合した溶媒に、ＬｉＰＦ6を１ｍｏｌ／Ｌになるように加えて混合溶液とし、この混合溶液１００質量部に対して、式（１）の化合物を１質量部含有させて、非水電解液を得た。それ以外は、実施例１−１と同様にして二極式評価セルを作製し、充放電試験を行った。充放電試験では、１５０サイクル後の容量維持率に加えて、５００サイクル後の容量維持率も測定した。なお、５００サイクル後の容量維持率は、５００サイクル後の放電容量をＱ500thとして、（Ｑ500th／Ｑ1st）×１００（％）として求めた。
2. Combination of LiNi 0.5 Mn 1.5 O 4 for positive electrode and graphite for negative electrode-Part 2
[Example 2-1]
When preparing a non-aqueous electrolyte, LiPF 6 is added to a solvent in which ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate are mixed at a volume ratio of 30:40:30 so that the concentration is 1 mol / L. A nonaqueous electrolyte solution was obtained by adding 1 part by mass of the compound of formula (1) to 100 parts by mass of the mixed solution. Other than that produced the bipolar evaluation cell similarly to Example 1-1, and performed the charging / discharging test. In the charge / discharge test, in addition to the capacity retention rate after 150 cycles, the capacity retention rate after 500 cycles was also measured. Incidentally, the capacity retention after 500 cycles, the discharge capacity after 500 cycles as Q 500th, was determined as (Q 500th / Q 1st) × 100 (%).
［実施例２−２］
非水電解液を作製する際に、混合溶液１００質量部に対して、式（１）の化合物を５質量部含有させて、非水電解液を得た。それ以外は、実施例２−１と同様にして二極式評価セルを作製し、充放電試験を行った。
[Example 2-2]
When producing the non-aqueous electrolyte, 5 parts by mass of the compound of the formula (1) was added to 100 parts by mass of the mixed solution to obtain a non-aqueous electrolyte. Other than that produced the bipolar evaluation cell similarly to Example 2-1, and performed the charging / discharging test.
［比較例２−１］
非水電解液を作製する際に式（１）の化合物を含有させなかった以外は、実施例２−１と同様にして二極式評価セルを作製し、充放電試験を行った。
[Comparative Example 2-1]
A bipolar evaluation cell was prepared in the same manner as in Example 2-1, except that the compound of formula (1) was not included when preparing the nonaqueous electrolytic solution, and a charge / discharge test was performed.
［充放電試験の評価］
５Ｖ級正極活物質を含有する正極と炭素質材料の負極との間に非水電解液が介在するリチウムイオン二次電池において、主たる電解液溶媒として非フッ素系溶媒を用いた実施例２−１，２−２及び比較例２−１の充放電試験の結果を表２に示す。非フッ素系溶媒に式（１）の化合物を添加した場合、添加しない場合に比べてサイクル特性が向上することが分かった。これは、式（１）の化合物が非フッ素系溶媒の分解を抑制したことによるものと推察される。この場合、非フッ素系溶媒１００質量部に対して式（１）の化合物を１〜５質量部添加するのが好ましい。
[Evaluation of charge / discharge test]
In a lithium ion secondary battery in which a nonaqueous electrolytic solution is interposed between a positive electrode containing a 5V class positive electrode active material and a negative electrode of a carbonaceous material, Example 2-1 using a non-fluorinated solvent as a main electrolytic solution solvent Table 2 shows the results of the charge and discharge tests of 2-2 and Comparative Example 2-1. It was found that when the compound of formula (1) was added to the non-fluorinated solvent, the cycle characteristics were improved as compared with the case where it was not added. This is presumably due to the fact that the compound of formula (1) suppressed the decomposition of the non-fluorinated solvent. In this case, it is preferable to add 1 to 5 parts by mass of the compound of the formula (1) with respect to 100 parts by mass of the non-fluorinated solvent.
３．作用極がＬｉＮｉ0.5Ｍｎ1.5Ｏ4、対極がリチウム金属箔の組合せ
［実施例３−１］
（作用極の作製）
５Ｖ級正極活物質としてＬｉＮｉ0.5Ｍｎ1.5Ｏ4（戸田工業製）を、導電助材として炭素を、バインダとしてポリフッ化ビニリデン（クレハ製、ＫＦポリマ）を用い、正極活物質と導電助材とバインダとを質量比で８５：１０：５となるように混合することで、正極合材を作製した。その正極合材をＮ−メチル−２−ピロリドンで分散させたペーストを、厚さ２０μｍのアルミニウム箔の両面に塗工乾燥させた。その後、塗布シートを加圧プレス処理し、２．０５ｃｍ2の面積に打ち抜いて円盤状の作用極を得た。
3. Combination of working electrode LiNi 0.5 Mn 1.5 O 4 and counter electrode lithium metal foil [Example 3-1]
(Production of working electrode)
LiNi 0.5 Mn 1.5 O 4 (manufactured by Toda Kogyo Co., Ltd.) as a 5V class positive electrode active material, carbon as a conductive additive, and polyvinylidene fluoride (manufactured by Kureha, KF polymer) as a binder, positive electrode active material, conductive additive and binder Were mixed so that the mass ratio was 85: 10: 5, to produce a positive electrode mixture. The paste in which the positive electrode mixture was dispersed with N-methyl-2-pyrrolidone was applied and dried on both sides of an aluminum foil having a thickness of 20 μm. Thereafter, the coated sheet was pressure-pressed and punched out to an area of 2.05 cm 2 to obtain a disk-shaped working electrode.
（非水電解液の作製）
式（１）に示す２，２−ビストリフルオロメチル−１，３−ジオキソランと式（５）に示す１，２−ジフルオロエチレンカーボネートとを質量比で５０：５０の割合で混合した非水溶媒に、ＬｉＰＦ6を１ｍｏｌ／ｋｇになるように加えて、非水電解液を作製した。
(Preparation of non-aqueous electrolyte)
To a non-aqueous solvent in which 2,2-bistrifluoromethyl-1,3-dioxolane represented by formula (1) and 1,2-difluoroethylene carbonate represented by formula (5) were mixed at a mass ratio of 50:50 LiPF 6 was added to 1 mol / kg to prepare a non-aqueous electrolyte.
（二極式評価セルの作製）
上述した円盤状の作用極とリチウム金属箔（厚み３００μｍ）からなる対極との間に、上述した非水電解液を含浸させたセパレータ（東レ東燃製）を挟んで二極式評価セルを作製した。
(Preparation of bipolar evaluation cell)
A bipolar evaluation cell was produced by sandwiching the separator impregnated with the non-aqueous electrolyte described above (manufactured by Toray Tonen) between the disk-shaped working electrode and the counter electrode made of lithium metal foil (thickness 300 μm). .
（充放電試験）
上述した二極式評価セルを用い、２０℃の温度環境下、０．１４ｍＡで５．０Ｖまで酸化（充電）した後、０．１４ｍＡで３．０Ｖまで還元（放電）させた。この操作を１サイクル行った。その後、同様の充放電試験の条件において７０サイクルの試験を行った。サイクル毎の充電容量をＱc、放電容量をＱdiscとして、（Ｑdisc／Ｑc）×１００（％）を各サイクルのクーロン効率とした。また、１サイクル目の放電容量を初期容量として、（７０サイクル目の放電容量／初期容量）×１００（％）を容量維持率とした。
(Charge / discharge test)
Using the above-mentioned bipolar evaluation cell, after oxidation (charging) to 5.0 V at 0.14 mA in a temperature environment of 20 ° C., reduction (discharging) was performed to 3.0 V at 0.14 mA. This operation was performed for one cycle. Thereafter, a 70-cycle test was performed under the same charge / discharge test conditions. The charge capacity per cycle was Q c , the discharge capacity was Q disc , and (Q disc / Q c ) × 100 (%) was the Coulomb efficiency of each cycle. Further, the discharge capacity at the first cycle was defined as the initial capacity, and the discharge capacity at the 70th cycle / initial capacity) × 100 (%) was defined as the capacity retention rate.
［比較例３−１］
エチレンカーボネートとジメチルカーボネート、エチルメチルカーボネートを体積比で３０：４０：３０の割合で混合した非水溶媒に、ＬｉＰＦ6を１ｍｏｌ／Ｌになるように加えて調整した非水電解液を用いた以外は、実施例３−１と同じである。ここで使用した各溶媒は、リチウムイオン二次電池において通常よく使用されるものである。
[Comparative Example 3-1]
Other than using a nonaqueous electrolytic solution prepared by adding LiPF 6 to 1 mol / L to a nonaqueous solvent in which ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed at a volume ratio of 30:40:30. Is the same as in Example 3-1. Each solvent used here is usually used in a lithium ion secondary battery.
［比較例３−２］
１，２−ジフルオロエチレンカーボネートとジメチルカーボネート、エチルメチルカーボネートを体積比で３０：４０：３０の割合で混合した非水溶媒に、ＬｉＰＦ6を１ｍｏｌ／Ｌになるように加えて調整した非水電解液を用いた以外は、実施例３−１と同じである。
[Comparative Example 3-2]
Nonaqueous electrolysis prepared by adding LiPF 6 to 1 mol / L to a nonaqueous solvent in which 1,2-difluoroethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate are mixed at a volume ratio of 30:40:30. The same as Example 3-1, except that the liquid was used.
［充放電試験の評価］
実施例３−１及び比較例３−１，３−２のサイクル試験結果を図３及び図４に示す。具体的には、図３には、サイクル数に対する放電容量の変化を示し、図４には、サイクル数に対するクーロン効率の変化を示す。また、表３に初期容量と７０サイクル目の放電容量、容量維持率及び７０サイクル目のクーロン効率を示す。
[Evaluation of charge / discharge test]
The cycle test results of Example 3-1 and Comparative Examples 3-1 and 3-2 are shown in FIGS. Specifically, FIG. 3 shows a change in discharge capacity with respect to the number of cycles, and FIG. 4 shows a change in coulomb efficiency with respect to the number of cycles. Table 3 shows the initial capacity, the discharge capacity at the 70th cycle, the capacity retention rate, and the Coulomb efficiency at the 70th cycle.
表３からわかるように、比較例３−１及び比較例３−２に比べて、実施例３−１は容量維持率が高かった。なお、比較例３−２については、５サイクル目の放電容量が初期容量と比べて大きく落ち込んだことから、５サイクル目でサイクル試験を打ち切った。比較例３−１で用いた電解液を用いてＬｉＣｏＯ2やＬｉＮｉＯ2のような４Ｖで動作する正極活物質を含む正極と金属リチウム負極からなるセルで評価した場合、サイクル特性は良好であった。このことから、比較例１−１での容量維持率の低下は、５Ｖで動作する際に電解液が酸化分解を起こしてＣＯガスやＣＯ2ガスが発生し、被膜が作用極に十分形成されなかったためと考えられる。また、図４及び表３からわかるように、比較例３−１に比べて実施例３−１は全てのサイクルにおいて高いクーロン効率を示した。また、比較例３−２に比べて実施例３−１は初回から５サイクル目までのクーロン効率が高かった。 As can be seen from Table 3, the capacity retention rate of Example 3-1 was higher than that of Comparative Example 3-1 and Comparative Example 3-2. In Comparative Example 3-2, the cycle test was aborted at the 5th cycle because the discharge capacity at the 5th cycle was significantly lower than the initial capacity. When evaluated in a cell comprising a positive electrode containing a positive electrode active material that operates at 4 V, such as LiCoO 2 or LiNiO 2 , using the electrolytic solution used in Comparative Example 3-1, the cycle characteristics were good. . From this, the decrease in capacity retention rate in Comparative Example 1-1 is that the electrolyte solution undergoes oxidative decomposition when operating at 5 V to generate CO gas and CO 2 gas, and the coating film is sufficiently formed on the working electrode. It is thought that there was not. Further, as can be seen from FIG. 4 and Table 3, Example 3-1 showed higher Coulomb efficiency in all cycles than Comparative Example 3-1. Moreover, compared with Comparative Example 3-2, Example 3-1 had higher Coulomb efficiency from the first time to the fifth cycle.
ところで、図示しないが、実施例３−１では、比較例３−１，３−２に比べて、初回の充電過程（酸化）において大きな分極挙動を示し、２サイクル目以降は比較例３−１と実施例３−１はほぼ同様の充放電カーブを示した。このことから、実施例３−１では、初回の充電過程において式（１）の２，２−ビストリフルオロメチル−１，３−ジオキソランが酸化分解して作用極上に保護被膜が形成され、その被膜が非水電解液の更なる酸化分解を抑制することでサイクル毎のクーロン効率が高くなり、容量維持率も良好になったものと推察される。比較例３−１のように式（１）のフッ素化合物を含まない非水電解液を用いた場合、作用極に被膜が十分形成されず、作用極上にて継続的に非水電解液の酸化分解が起こるために、容量維持率が低下したものと推察される。 By the way, although not shown, in Example 3-1, compared with Comparative Examples 3-1 and 3-2, the first charging process (oxidation) shows a large polarization behavior, and Comparative Example 3-1 after the second cycle. And Example 3-1 exhibited substantially the same charge / discharge curves. Therefore, in Example 3-1, 2,2-bistrifluoromethyl-1,3-dioxolane of the formula (1) is oxidized and decomposed in the initial charging process to form a protective film on the working electrode. However, by suppressing further oxidative decomposition of the non-aqueous electrolyte, it is presumed that the Coulomb efficiency for each cycle is increased and the capacity retention rate is also improved. When a non-aqueous electrolyte not containing the fluorine compound of formula (1) was used as in Comparative Example 3-1, a sufficient film was not formed on the working electrode, and the non-aqueous electrolyte was continuously oxidized on the working electrode. It is inferred that the capacity retention rate decreased due to the decomposition.
また、図示しないが、１０サイクル目の充電末期において、比較例３−１では、実施例３−１に比べて充電電位の立ち上がり分の容量が大きかった。これは、比較例３−１では、実施例に比べて電解液の酸化分解量が多かったためと推察される。そのため、実施例３−１では、比較例３−１に比べてクーロン効率が向上したものと考えられる。 Although not shown, at the end of charging at the 10th cycle, in Comparative Example 3-1, the capacity for the rising of the charging potential was larger than that in Example 3-1. This is presumably because in Comparative Example 3-1, the amount of oxidative decomposition of the electrolytic solution was larger than that in Example. Therefore, in Example 3-1, it is thought that the coulomb efficiency improved compared with the comparative example 3-1.
以上のように、５Ｖ級の正極活物質を含む正極を備えたリチウムイオン二次電池において、式（Ｉ）で表される化合物を含むフッ素系溶媒にリチウム塩を溶解した非水電解液を用いた場合には、金属リチウム電位基準で５Ｖ以上の電位まで充電しその後放電するという操作を１サイクルとし、このサイクルを何度も繰り返したあとの充放電特性（サイクル特性）が向上することが分かった。 As described above, in a lithium ion secondary battery provided with a positive electrode containing a 5 V-class positive electrode active material, a nonaqueous electrolytic solution in which a lithium salt is dissolved in a fluorine-based solvent containing a compound represented by formula (I) is used. In this case, the operation of charging to a potential of 5 V or higher on the basis of the lithium metal potential and then discharging is regarded as one cycle, and the charge / discharge characteristics (cycle characteristics) after repeating this cycle many times are improved. It was.
４．作用極が黒鉛、対極がリチウム金属箔の組合せ
［実施例４−１］
（二極式評価セルの作製）
黒鉛を作用極とし、リチウム金属箔（厚み３００μｍ）を対極として、両電極の間に実施例１−１の非水電解液を含浸させたセパレータ（東レ東燃製）を挟んで二極式評価セルを作製した。
4). Combination of working electrode as graphite and counter electrode as lithium metal foil [Example 4-1]
(Preparation of bipolar evaluation cell)
Bipolar evaluation cell with graphite as working electrode, lithium metal foil (thickness 300 μm) as the counter electrode, and a separator (manufactured by Toray Tonen) impregnated with the non-aqueous electrolyte of Example 1-1 between both electrodes Was made.
（充放電試験）
上述した二極式評価セルを用い、２０℃の温度環境下、０．１７ｍＡで０．０５Ｖまで放電（還元）した後、０．１７ｍＡで１．５Ｖまで充電（酸化）させた。この操作を１０サイクル行った。１サイクル目の充電容量をＱ1st、１０サイクル後の放電容量をＱ10thとして、（Ｑ10th／Ｑ1st）×１００（％）を１０サイクル後の容量維持率とした。
(Charge / discharge test)
Using the above-described bipolar evaluation cell, the battery was discharged (reduced) to 0.05 V at 0.17 mA in a temperature environment of 20 ° C., and then charged (oxidized) to 1.5 V at 0.17 mA. This operation was performed for 10 cycles. The charge capacity at the first cycle was Q 1st , the discharge capacity after 10 cycles was Q 10th , and (Q 10th / Q 1st ) × 100 (%) was the capacity maintenance rate after 10 cycles.
［比較例４−１］
非水電解液を作製する際に、エチレンカーボネートとジメチルカーボネートとエチルメチルカーボネートとを体積比で３０：４０：３０の割合で混合した溶媒に、ＬｉＰＦ6を１ｍｏｌ／Ｌになるように加えて混合溶液とし、この混合溶液をそのまま非水電解液とした以外は、実施例４−１と同様にして二極式評価セルを作製し、充放電試験を行った。
[Comparative Example 4-1]
When preparing a non-aqueous electrolyte, LiPF 6 is added to a solvent in which ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate are mixed at a volume ratio of 30:40:30 so that the concentration is 1 mol / L. A bipolar evaluation cell was prepared and a charge / discharge test was conducted in the same manner as in Example 4-1, except that this was used as a solution and the mixed solution was used as a non-aqueous electrolyte.
［比較例４−２］
非水電解液を作製する際に、１，３−ジオキソランと１，２−ジメトキシエタンとを体積比で５０：５０の割合で混合した溶媒に、ＬｉＰＦ6を１ｍｏｌ／Ｌになるように加えて混合溶液とし、この混合溶液をそのまま非水電解液とした以外は、実施例４−１と同様にして二極式評価セルを作製し、充放電試験を行った。
[Comparative Example 4-2]
When preparing the non-aqueous electrolyte, LiPF 6 was added to a solvent in which 1,3-dioxolane and 1,2-dimethoxyethane were mixed at a volume ratio of 50:50 so as to be 1 mol / L. A bipolar evaluation cell was prepared and a charge / discharge test was conducted in the same manner as in Example 4-1, except that a mixed solution was used and the mixed solution was directly used as a nonaqueous electrolytic solution.
［充放電試験の評価］
実施例４−１及び比較例４−１の１〜１０サイクル目の充放電カーブをそれぞれ図５及び図６に示す。図５及び図６の結果から、比較例４−１に比べて、実施例４−１は、電解液溶媒に式（１）の化合物を含有させたことで、安定した充放電を繰り返すことがわかった。また、比較例４−２の１サイクル目の充放電カーブを図７に示す。図７から、１，３−ジオキソランのようなフッ素基を有さない環状エーテルを溶媒として用いると、Ｌｉ吸蔵に相当する還元反応は進行するものの、その後のＬｉ放出に相当する酸化反応は起こりにくくなり、容量が著しく減少することがわかった。これはフッ素基を有さない環状エーテルを含む電解液の場合、Ｌｉ吸蔵時に溶媒がＬｉイオンに溶媒和したままの状態で黒鉛の層間に挿入され、その後、Ｌｉ放出が困難になり劣化するコ・インターカレーション（co-intercalation）と称される現象の結果であると思われる（参考文献 Journal of Power Sources 54 (1995) 228-231）。一方、１，３−ジオキソランにフッ素基が導入された式（１）の化合物では、フッ素基により分子のサイズが大きくなるために、黒鉛の層間時に溶媒が挿入されずにＬｉ吸蔵放出を起こすものと推察される。更に、式（１）の化合物を含む電解液では、式（１）の化合物を含まないカーボネート系電解液に比べて、黒鉛と電解液とのより安定な界面を付与することでサイクル性が向上したものと思われる。
[Evaluation of charge / discharge test]
The charge / discharge curves in the 1st to 10th cycles of Example 4-1 and Comparative Example 4-1 are shown in FIGS. 5 and 6, respectively. From the results of FIGS. 5 and 6, compared to Comparative Example 4-1, Example 4-1 can repeat stable charge and discharge by containing the compound of formula (1) in the electrolyte solvent. all right. Moreover, the charge / discharge curve of the first cycle of Comparative Example 4-2 is shown in FIG. From FIG. 7, when a cyclic ether having no fluorine group such as 1,3-dioxolane is used as a solvent, a reduction reaction corresponding to Li occlusion proceeds, but an oxidation reaction corresponding to subsequent Li release hardly occurs. As a result, it was found that the capacity was remarkably reduced. In the case of an electrolytic solution containing a cyclic ether that does not have a fluorine group, the solvent is inserted between the graphite layers while being solvated with Li ions when Li is occluded.・ It seems to be the result of a phenomenon called co-intercalation (Reference Journal of Power Sources 54 (1995) 228-231). On the other hand, in the compound of formula (1) in which a fluorine group is introduced into 1,3-dioxolane, the size of the molecule is increased by the fluorine group, and therefore, Li is occluded and released without insertion of a solvent between graphite layers. It is guessed. Furthermore, in the electrolytic solution containing the compound of the formula (1), the cycle performance is improved by providing a more stable interface between the graphite and the electrolytic solution compared to the carbonate-based electrolytic solution not containing the compound of the formula (1). It seems to have done.
５．本発明で使用可能なフッ素化合物
上述した実施例で使用した式（１）の２，２−ビストリフルオロメチル−１，３−ジオキソランと同等の性質を有するフッ素化合物を探索した。具体的には、表４に示した式（１）〜（４）、式（Ｃ１）〜（Ｃ５）の化合物について、ＨＯＭＯ−ＬＵＭＯ準位を計算した。計算には、Gaussian 09（ＨＰＣシステムズ社製）を使用し、計算レベルはB3LYP/6-31Gにより構造最適化した。計算結果を表４に示す。なお、ＨＯＭＯエネルギーは酸化性の程度を示し、数値が小さいほど耐酸化性に優れ、ＬＵＭＯエネルギーは還元性の程度を示し、数値が大きいほど耐還元性に優れている。
5. Fluorine compounds usable in the present invention Fluorine compounds having properties equivalent to those of 2,2-bistrifluoromethyl-1,3-dioxolane of formula (1) used in the above-described examples were searched. Specifically, HOMO-LUMO levels were calculated for the compounds of formulas (1) to (4) and formulas (C1) to (C5) shown in Table 4. For the calculation, Gaussian 09 (manufactured by HPC Systems) was used, and the structural level was optimized by B3LYP / 6-31G. Table 4 shows the calculation results. The HOMO energy indicates the degree of oxidation, and the smaller the value, the better the oxidation resistance. The LUMO energy indicates the degree of reduction, and the higher the value, the better the reduction resistance.
表４から明らかなように、式（１）の化合物は、比較例２−１等で使用した式（Ｃ１）のエチレンカーボネートに比べて、ＨＯＭＯエネルギーが同等でＬＵＭＯエネルギーが大きいことから、耐酸化性は同等で耐還元性は優れているといえる。式（Ｃ１）のような環状カーボネートの場合、カルボニル基（Ｃ＝Ｏ）の部分で酸化分解して、ＣＯガスやＣＯ2ガスが生成することが報告されている（例えばJ. Electrochem. Soc., 156, A563-A571(2009)）。充電時に正極で式（Ｃ１）の化合物が酸化分解する際にガスが発生すると、正極上の被膜を十分に形成することが困難になると推察される。一方、式（１）の化合物は、構造からみて酸化分解の際にガスが発生しないため、正極上の被膜が十分に形成され、良好なサイクル特性が得られたと推察される。このように、式（１）と式（Ｃ１）とは、ＨＯＭＯエネルギーがほぼ同じであるため耐酸化性は同等と考えられるが、酸化分解時のガスの発生の有無によりサイクル特性に差が生じたと考えられる。式（２）〜（４）の化合物は、式（１）の化合物と比べて、ＨＯＭＯエネルギーが小さくＬＵＭＯエネルギーが大きいことから、耐酸化性も耐還元性も優れているといえる。したがって、式（２）〜（４）の化合物を非水電解液の溶媒に用いた場合には、式（１）の化合物を使用した上述の実施例と同等かそれ以上のサイクル特性が得られると予測される。 As is clear from Table 4, the compound of formula (1) has an equivalent HOMO energy and a large LUMO energy compared to ethylene carbonate of formula (C1) used in Comparative Example 2-1, etc. Therefore, it can be said that the reduction resistance is excellent. In the case of a cyclic carbonate such as the formula (C1), it is reported that CO gas and CO 2 gas are generated by oxidative decomposition at the carbonyl group (C═O) (see, for example, J. Electrochem. Soc. , 156, A563-A571 (2009)). If gas is generated when the compound of the formula (C1) undergoes oxidative decomposition at the positive electrode during charging, it is assumed that it is difficult to sufficiently form a coating film on the positive electrode. On the other hand, since the compound of formula (1) does not generate gas during the oxidative decomposition in view of the structure, it is presumed that the coating on the positive electrode was sufficiently formed and good cycle characteristics were obtained. Thus, although the HOMO energy is almost the same between the formula (1) and the formula (C1), it is considered that the oxidation resistance is equivalent. However, there is a difference in cycle characteristics depending on whether or not gas is generated during oxidative decomposition. It is thought. Since the compounds of the formulas (2) to (4) have a small HOMO energy and a large LUMO energy compared to the compound of the formula (1), it can be said that the compounds have excellent oxidation resistance and reduction resistance. Therefore, when the compounds of the formulas (2) to (4) are used as the solvent for the non-aqueous electrolyte, cycle characteristics equivalent to or higher than those of the above-described example using the compound of the formula (1) can be obtained. It is predicted.
一方、式（Ｃ２）及び式（Ｃ３）の化合物は、式（１）や式（Ｃ１）の化合物に比べて、ＨＯＭＯエネルギーが大きいことから耐酸化性が劣る。したがって、これらを式（１）の化合物の代わりに用いたとしても、式（１）の化合物を使用した上述の実施例の性能は得られないと予測される。式（Ｃ４）及び式（Ｃ５）の化合物は、フッ素化された１，３−ジオキソランではあるが２位に塩素原子又は水素原子を有している。式（Ｃ４）の化合物は、式（１）の化合物と比べてＨＯＭＯエネルギーが大きいことから耐酸化性が劣り、式（Ｃ５）の化合物は式（１）の化合物と比べてＬＵＭＯエネルギーが小さいことから耐還元性が劣る。耐酸化性が劣ると、充電時に正極で容易に酸化分解されてしまい、耐還元性が劣ると、充電時に負極で容易に還元分解されてしまうため、いずれも良好なサイクル特性が得られない。したがって、これらを式（１）の化合物の代わりに用いたとしても、式（１）の化合物を使用した上述の実施例の性能は得られないと予測される。 On the other hand, the compounds of formula (C2) and formula (C3) are inferior in oxidation resistance due to their higher HOMO energy than the compounds of formula (1) and formula (C1). Therefore, even if these are used instead of the compound of the formula (1), it is expected that the performance of the above-described example using the compound of the formula (1) cannot be obtained. The compounds of formula (C4) and formula (C5) are fluorinated 1,3-dioxolanes but have a chlorine atom or a hydrogen atom at the 2-position. The compound of the formula (C4) has a lower HOMO energy than the compound of the formula (1) and thus has poor oxidation resistance, and the compound of the formula (C5) has a lower LUMO energy than the compound of the formula (1). Therefore, the resistance to reduction is inferior. If the oxidation resistance is inferior, it is easily oxidized and decomposed at the positive electrode during charging, and if the reduction resistance is inferior, it is easily reduced and decomposed at the negative electrode during charging. Therefore, even if these are used instead of the compound of the formula (1), it is expected that the performance of the above-described example using the compound of the formula (1) cannot be obtained.
１０ リチウムイオン二次電池、１１ 集電体、１２ 正極活物質、１３ 正極シート、１４ 集電体、１７ 負極活物質、１８ 負極シート、１９ セパレータ、２０ 非水電解液、２２ 円筒ケース、２４ 正極端子、２６ 負極端子。 DESCRIPTION OF SYMBOLS 10 Lithium ion secondary battery, 11 Current collector, 12 Positive electrode active material, 13 Positive electrode sheet, 14 Current collector, 17 Negative electrode active material, 18 Negative electrode sheet, 19 Separator, 20 Nonaqueous electrolyte, 22 Cylindrical case, 24 Positive electrode Terminal, 26 Negative terminal.
Claims (4)
前記正極は、正極活物質としてＬｉＮｉ0.5Ｍｎ1.5Ｏ4を含有し、
前記非水電解液は、フッ素基を有するフッ素系溶媒に式（Ｉ）で表される化合物を含ませた溶媒にリチウム塩を溶解したものであり、前記フッ素系溶媒は、少なくとも１つの水素原子がフッ素原子で置換されたカーボネートであり、前記溶媒は、フッ素含有鎖状エーテル化合物および／またはフッ素含有リン酸エステル化合物を含むものを除く、
リチウムイオン二次電池。
The positive electrode contains LiNi 0.5 Mn 1.5 O 4 as a positive electrode active material,
The non-aqueous electrolyte is obtained by dissolving a lithium salt in a solvent in which a compound represented by the formula (I) is contained in a fluorine-based solvent having a fluorine group, and the fluorine-based solvent includes at least one hydrogen atom. Is a carbonate substituted with a fluorine atom, and the solvent excludes those containing a fluorine-containing chain ether compound and / or a fluorine-containing phosphate compound,
Lithium ion secondary battery.
請求項１に記載のリチウムイオン二次電池。
The lithium ion secondary battery according to claim 1.
請求項１又は２に記載のリチウムイオン二次電池。 The compound represented by the formula (I) is added in a ratio of 1 to 2 parts by mass with respect to 100 parts by mass of the fluorinated solvent.
The lithium ion secondary battery according to claim 1 or 2.
請求項１〜３のいずれか１項に記載のリチウムイオン二次電池。 The fluoroalkyl group is a perfluoroalkyl group,
The lithium ion secondary battery of any one of Claims 1-3 .
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