JP2006179458A - Nonaqueous electrolyte for battery and nonaqueous electrolyte battery having the same - Google Patents
Nonaqueous electrolyte for battery and nonaqueous electrolyte battery having the same Download PDFInfo
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Abstract
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本発明は、電池用非水電解液及びそれを備えた非水電解液電池に関し、特に高い難燃性を有する電池用非水電解液及び優れた電池特性を有する非水電解液電池に関するものである。 The present invention relates to a battery non-aqueous electrolyte and a non-aqueous electrolyte battery including the same, and particularly relates to a battery non-aqueous electrolyte having high flame retardancy and a non-aqueous electrolyte battery having excellent battery characteristics. is there.
非水電解液は、リチウム電池やリチウムイオン２次電池、電気二重層キャパシタ等の電解質として使用されており、これらデバイスは、高電圧、高エネルギー密度を有することから、パソコン及び携帯電話等の駆動電源として広く用いられている。そして、これら非水電解液としては、一般にエステル化合物及びエーテル化合物等の非プロトン性有機溶媒に、ＬｉＰＦ6等の支持塩を溶解させたものが用いられている。しかしながら、非プロトン性有機溶媒は、可燃性であるため、上記デバイスから漏液した際に引火・燃焼する可能性があり、安全面での問題を有している。 Non-aqueous electrolytes are used as electrolytes for lithium batteries, lithium ion secondary batteries, electric double layer capacitors, etc., and these devices have high voltage and high energy density. Widely used as a power source. As these non-aqueous electrolytes, generally used are solutions in which a supporting salt such as LiPF 6 is dissolved in an aprotic organic solvent such as an ester compound and an ether compound. However, since the aprotic organic solvent is flammable, it may ignite and burn when leaked from the device, which has a safety problem.
この問題に対して、非水電解液を難燃化する方法が検討されており、例えば、非水電解液にリン酸トリメチル等のリン酸エステル類を用いたり、非プロトン性有機溶媒にリン酸エステル類を添加したりする方法が提案されている（特許文献１〜３参照）。しかしながら、これらリン酸エステル類は、充放電を繰り返すことで、徐々に負極で還元分解され、充放電効率及びサイクル特性等の電池特性が大きく劣化するという問題がある。 To solve this problem, methods for making non-aqueous electrolytes flame-retardant have been studied. For example, phosphoric acid esters such as trimethyl phosphate are used for non-aqueous electrolytes, or phosphoric acid is used for aprotic organic solvents. Methods for adding esters have been proposed (see Patent Documents 1 to 3). However, these phosphate esters have a problem in that they are gradually reduced and decomposed at the negative electrode by repeating charge and discharge, and battery characteristics such as charge and discharge efficiency and cycle characteristics are greatly deteriorated.
この問題に対して、非水電解液にリン酸エステルの分解を抑制する化合物を更に添加したり、リン酸エステルそのものの分子構造を工夫する等の方法も試みられている（特許文献４〜７参照）。しかしながら、この場合、リン酸エステルの添加量が増加するにつれて、その分解抑制効果が十分なものでなくなるため、リン酸エステルの添加量に制限があるのが現状である。また、リン酸エステルの還元分解の問題以外にも、リン酸トリエステルは高粘度、低導電率であるため、初期放電容量の低下や低温特性の低下等の他の電池性能の低下を招いてしまい、これも添加量を多くできない理由の一つとなっている。 In order to solve this problem, methods such as further adding a compound that suppresses the decomposition of the phosphate ester to the nonaqueous electrolytic solution or devising the molecular structure of the phosphate ester itself have been tried (Patent Documents 4 to 7). reference). However, in this case, as the addition amount of the phosphate ester is increased, the decomposition suppressing effect is not sufficient, so that the addition amount of the phosphate ester is currently limited. In addition to the problem of reductive decomposition of phosphate esters, phosphate triesters have high viscosity and low electrical conductivity, leading to other battery performance degradation such as reduced initial discharge capacity and low temperature characteristics. In other words, this is one of the reasons why the amount added cannot be increased.
このように、従来の技術では、電解液の安全性と電池性能の確保という点で必ずしも十分とはいえず、リン酸エステルの構造自体を根本から検討しなおす必要がある。 Thus, the conventional technology is not necessarily sufficient in terms of ensuring the safety of the electrolytic solution and the battery performance, and it is necessary to reexamine the phosphate ester structure itself.
そこで、本発明の目的は、上記従来技術の問題を解決し、高い難燃性を有する電池用非水電解液と、該電池用非水電解液を備え、優れた電池性能を有する非水電解液電池を提供することにある。 Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art and to provide a non-aqueous electrolyte for batteries having high flame retardancy, and a non-aqueous electrolysis having excellent battery performance, comprising the non-aqueous electrolyte for batteries. It is to provide a liquid battery.
本発明者らは、上記目的を達成するために鋭意検討した結果、従来のリン酸エステル類の欠点を解決できる構造を有したリン酸エステル化合物と、該リン酸エステル化合物の還元分解を効果的に抑制できる化合物を見出し、本発明を完成させるに至った。 As a result of intensive investigations to achieve the above object, the present inventors have found that a phosphoric acid ester compound having a structure capable of solving the disadvantages of conventional phosphoric acid esters and the reductive decomposition of the phosphoric acid ester compound are effective. The present inventors have found a compound that can be suppressed and have completed the present invention.
即ち、本発明の電池用非水電解液は、非水溶媒及び支持塩を含む電池用非水電解液において、該電池用非水電解液が下記一般式(I)：
本発明の電池用非水電解液の好適例においては、前記一般式(I)で表されるジフルオロリン酸エステル化合物の含有量が前記電池用非水電解液全体の20〜80体積％である。 In a preferred example of the battery non-aqueous electrolyte of the present invention, the content of the difluorophosphate compound represented by the general formula (I) is 20 to 80% by volume of the whole battery non-aqueous electrolyte. .
本発明の電池用非水電解液の他の好適例においては、前記一般式(II)で表される不飽和環状エステル化合物の含有量が前記電池用非水電解液全体の0.5〜10質量％である。 In another preferred embodiment of the battery non-aqueous electrolyte of the present invention, the content of the unsaturated cyclic ester compound represented by the general formula (II) is 0.5 to 10% by mass of the whole battery non-aqueous electrolyte. It is.
本発明の電池用非水電解液の他の好適例においては、前記一般式(III)で表される芳香族化合物の含有量が前記電池用非水電解液全体の0.05〜4質量％である。 In another preferred embodiment of the battery non-aqueous electrolyte of the present invention, the content of the aromatic compound represented by the general formula (III) is 0.05 to 4% by mass of the whole battery non-aqueous electrolyte. .
本発明の電池用非水電解液は、エチレンカーボネートを5体積％以上含むことが好ましい。 The non-aqueous electrolyte for a battery of the present invention preferably contains 5% by volume or more of ethylene carbonate.
また、本発明の非水電解液電池は、上記電池用非水電解液と、正極と、負極とを備えることを特徴とする。 Moreover, the non-aqueous electrolyte battery of the present invention comprises the above-described non-aqueous electrolyte for a battery, a positive electrode, and a negative electrode.
本発明によれば、非水電解液電池の電解液に上記式(I)のジフルオロリン酸エステルを用いることにより、式(I)のジフルオロリン酸エステルが高含有率であっても、電池の低温放電特性を大幅に向上させることができ、また、電解液に式(I)の化合物と式(II)の不飽和環状エステル及び／又は式(III)の芳香族化合物を組み合わせて用いることにより、電池の放電容量及びサイクル特性を維持することが可能となる。また、式(I)のジフルオロリン酸エステルの添加により、電解液に高い難燃性を付与することができ、発火・引火の危険性が大幅に抑制された電池用非水電解液を提供することができ、該非水電解液を使用することで、安全性が著しく改善された非水電解液電池を提供することができる。 According to the present invention, by using the difluorophosphate ester of the above formula (I) in the electrolyte of the nonaqueous electrolyte battery, even if the difluorophosphate ester of the formula (I) has a high content, The low-temperature discharge characteristics can be greatly improved, and by using a combination of a compound of formula (I) and an unsaturated cyclic ester of formula (II) and / or an aromatic compound of formula (III) in the electrolyte The discharge capacity and cycle characteristics of the battery can be maintained. In addition, the addition of the difluorophosphate ester of formula (I) provides a non-aqueous electrolyte for a battery that can impart high flame retardancy to the electrolyte, and the risk of ignition and ignition is greatly suppressed. By using the non-aqueous electrolyte, a non-aqueous electrolyte battery with significantly improved safety can be provided.
理由は必ずしも明らかではないが、式(I)のジフルオロリン酸エステル化合物と、式(II)の不飽和環状エステル化合物及び／又は式(III)の芳香族化合物との相乗効果により生じた電極表面の皮膜が、式(I)のジフルオロリン酸エステル化合物の分解を特異的に抑制する効果を有し、式(I)のジフルオロリン酸エステル化合物が高含有率でも、安定した充放電特性を実現し、放電容量並びにサイクル特性を改善するものと考えられる。実際に、これまで提案された様々なリン酸トリエステル化合物又は１つのフッ素基を有するモノフルオロリン酸エステル化合物を用いた場合には、たとえ電極上での還元分解反応を抑制する物質を添加しても、電池性能が低下してしまう（特に高含有率で顕著である）。また、式(I)のジフルオロリン酸エステル分子が有する高誘電率で且つ低粘度であるという性質が、低温でも高いイオン導電性を発現し、これが低温特性を向上させているものと考えられる。 The reason is not necessarily clear, but the electrode surface produced by the synergistic effect of the difluorophosphate ester compound of formula (I) and the unsaturated cyclic ester compound of formula (II) and / or the aromatic compound of formula (III) This film has the effect of specifically suppressing the decomposition of the difluorophosphate compound of formula (I), and realizes stable charge / discharge characteristics even when the difluorophosphate compound of formula (I) is high in content Therefore, it is considered that the discharge capacity and the cycle characteristics are improved. In fact, when various phosphoric acid triester compounds proposed so far or monofluorophosphoric acid ester compounds having one fluorine group are used, a substance that suppresses the reductive decomposition reaction on the electrode is added. However, the battery performance is degraded (particularly at a high content). In addition, it is considered that the high dielectric constant and low viscosity of the difluorophosphate molecule of the formula (I) exhibits high ionic conductivity even at low temperatures, which improves the low temperature characteristics.
＜電池用非水電解液＞
以下に、本発明の電池用非水電解液を詳細に説明する。木発明の電池用非水電解液は、上記一般式(I)で表されるジフルオロリン酸エステル化合物と上記一般式(II)で表される不飽和環状エステル化合物及び／又は上記一般式(III)で表される芳香族化合物を含む非水溶媒と支持塩とからなる。
<Non-aqueous electrolyte for batteries>
Below, the non-aqueous electrolyte for batteries of the present invention will be described in detail. The non-aqueous electrolyte for a battery of the present invention comprises a difluorophosphate compound represented by the above general formula (I) and an unsaturated cyclic ester compound represented by the above general formula (II) and / or the above general formula (III). ) And a supporting salt.
本発明の電池用非水電解液に含まれるジフルオロリン酸エステル化合物は、上記一般式(I)で表される。式(I)において、Ｒlは、アルキル基、シクロアルキル基、アルケニル基、アルコキシ置換アルキル基又はアリール基である。式(I)のＲlにおけるアルキル基としては、メチル基、エチル基、プロピル基、ブチル基、ペンチル基、へキシル基等の炭素数１〜６のアルキル基が挙げられ、シクロアルキル基としては、シクロヘキシル基等が挙げられ、アルケニル基としては、アリル基、メタリル基等が挙げられ、アルコキシ置換アルキル基としては、メトキシエチル基、メトキシエトキシエチル基等が挙げられ、アリール基としては、フェニル基、メチルフェニル基、メトキシフェニル基等が挙げられる。上記置換基中の水素元素は、ハロゲン元素で置換されていてもよく、フッ素で置換されていることが好ましい。これらの中でも、難燃性に優れ且つ低粘度である点で、メチル基、エチル基、プロピル基、トルフルオロエチル基、フェニル基、３-フルオロフェニル基が好ましい。 The difluorophosphate compound contained in the battery non-aqueous electrolyte of the present invention is represented by the above general formula (I). In the formula (I), R 1 is an alkyl group, a cycloalkyl group, an alkenyl group, an alkoxy-substituted alkyl group or an aryl group. Examples of the alkyl group in R 1 of the formula (I) include C 1-6 alkyl groups such as a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, and a hexyl group. Cyclohexyl group, etc., alkenyl groups include allyl group, methallyl group, etc., alkoxy-substituted alkyl groups include methoxyethyl group, methoxyethoxyethyl group, etc., aryl groups include phenyl group , Methylphenyl group, methoxyphenyl group and the like. The hydrogen element in the substituent may be substituted with a halogen element, and is preferably substituted with fluorine. Among these, a methyl group, an ethyl group, a propyl group, a trifluoroethyl group, a phenyl group, and a 3-fluorophenyl group are preferable in terms of excellent flame retardancy and low viscosity.
式(I)のジフルオロリン酸エステル化合物の具体例としては、ジフルオロリン酸メチル、ジフルオロリン酸エチル、ジフルオロリン酸トリフルオロエチル、ジフルオロリン酸プロピル、ジフルオロリン酸アリル、ジフルオロリン酸ブチル、ジフルオロリン酸ペンチル、ジフルオロリン酸ヘキシル、ジフルオロリン酸シクロヘキシル、ジフルオロリン酸メトキシエチル、ジフルオロリン酸メトキシエトキシエチル、ジフルオロリン酸フェニル、ジフルオロリン酸フルオロフェニル等が挙げられる。これらジフルオロリン酸エステル化合物は、１種単独で使用してもよく、２種以上を混合して使用してもよい。 Specific examples of the difluorophosphate compound of formula (I) include methyl difluorophosphate, ethyl difluorophosphate, trifluoroethyl difluorophosphate, propyl difluorophosphate, allyl difluorophosphate, butyl difluorophosphate, difluorophosphoric acid. Examples include acid pentyl, hexyl difluorophosphate, cyclohexyl difluorophosphate, methoxyethyl difluorophosphate, methoxyethoxyethyl difluorophosphate, phenyl difluorophosphate, and fluorophenyl difluorophosphate. These difluorophosphate ester compounds may be used singly or in combination of two or more.
上記ジフルオロリン酸エステル化合物の含有量は、本発明の目的から、非水電解液中10体積％以上であることを要し、10〜80体積％の範囲が好ましい。ジフルオロリン酸エステル化合物の含有量が10体積％未満では、十分な難燃性を得ることができず、一方、80体積％を超えると、式(II)の化合物及び／又は式(III)の化合物を用いても、非水電解液の還元分解が進行しはじめ、サイクル特性が低下する傾向がある。また、電池性能と難燃性の両立の観点から、非水電解液中の上記ジフルオロリン酸エステル化合物の含有量は、20〜80体積％の範囲が更に好ましい。 For the purpose of the present invention, the content of the difluorophosphate compound needs to be 10% by volume or more in the nonaqueous electrolytic solution, and is preferably in the range of 10 to 80% by volume. If the content of the difluorophosphate compound is less than 10% by volume, sufficient flame retardancy cannot be obtained, while if it exceeds 80% by volume, the compound of formula (II) and / or of formula (III) Even when the compound is used, the reductive decomposition of the non-aqueous electrolyte begins to progress, and the cycle characteristics tend to deteriorate. Moreover, from the viewpoint of achieving both battery performance and flame retardancy, the content of the difluorophosphate compound in the non-aqueous electrolyte is more preferably in the range of 20 to 80% by volume.
本発明の電池用非水電解液に含まれうる不飽和環状エステル化合物は、上記一般式(II)で表される。式(II)において、Ｒ2及びＲ3は、それぞれ独立して水素、フッ素又は炭素数１〜２のアルキル基であり、該アルキル基中の水素元素は、フッ素で置換されていてもよい。また、式(II)中のＲ2及びＲ3は、互いに結合して環を形成してもよく、この場合、不飽和結合を有していてもよい。Ｒ2及びＲ3が結合して形成する二価の基としては、トリメチレン基、テトラメチレン基、メチルトリメチレン基等のアルキレン基、プロペニレン基、ブテニレン基、メチルプロペニレン基等のアルケニレン基、ブタジエニレン基等のアルカジエニレン基等が挙げられる。 The unsaturated cyclic ester compound that can be contained in the battery non-aqueous electrolyte of the present invention is represented by the above general formula (II). In the formula (II), R 2 and R 3 are each independently hydrogen, fluorine or an alkyl group having 1 to 2 carbon atoms, and the hydrogen element in the alkyl group may be substituted with fluorine. R 2 and R 3 in formula (II) may be bonded to each other to form a ring, and in this case, may have an unsaturated bond. Examples of the divalent group formed by combining R 2 and R 3 include alkylene groups such as trimethylene group, tetramethylene group and methyltrimethylene group, alkenylene groups such as propenylene group, butenylene group and methylpropenylene group, butadienylene. And alkadienylene groups such as a group.
式(II)の不飽和環状エステル化合物の具体例としては、ビニレンカーボネート、４-フルオロビニレンカーボネート、４,５-ジフルオロビニレンカーボネート、４-メチルビニレンカーボネート、４,５-ジメチルビニレンカーボネート、４-フルオロメチルビニレンカーボネート、４-ジフルオロメチルビニレンカーボネート、４-トリフルオロメチルビニレンカーボネート、４-エチルビニレンカーボネート、４,５-ジエチルビニレンカーボネート、４-フルオロエチルビニレンカーボネート、４-ジフルオロエチルビニレンカーボネート、４-トリフルオロエチルビニレンカーボネート、４,５-ビストリフルオロメチルビニレンカーボネート、カテコールカーボネート、テトラヒドロカテコールカーボネート等が挙げられる。これらの中でも、ビニレンカーボネート、４-フルオロビニレンカーボネート、カテコールカーボネートが好ましい。これら不飽和環状エステル化合物は、１種単独で使用してもよく、２種以上を混合して使用してもよい。 Specific examples of the unsaturated cyclic ester compound of the formula (II) include vinylene carbonate, 4-fluorovinylene carbonate, 4,5-difluorovinylene carbonate, 4-methylvinylene carbonate, 4,5-dimethylvinylene carbonate, 4-fluoro Methyl vinylene carbonate, 4-difluoromethyl vinylene carbonate, 4-trifluoromethyl vinylene carbonate, 4-ethyl vinylene carbonate, 4,5-diethyl vinylene carbonate, 4-fluoroethyl vinylene carbonate, 4-difluoroethyl vinylene carbonate, 4-tri Examples include fluoroethyl vinylene carbonate, 4,5-bistrifluoromethyl vinylene carbonate, catechol carbonate, and tetrahydrocatechol carbonate. Among these, vinylene carbonate, 4-fluoro vinylene carbonate, and catechol carbonate are preferable. These unsaturated cyclic ester compounds may be used individually by 1 type, and 2 or more types may be mixed and used for them.
上記不飽和環状エステル化合物の含有量は、電池用非水電解液全体の0.5〜10質量％の範囲が好ましく、電池性能のバランスの観点から、1〜6質量％の範囲が更に好ましい。 The content of the unsaturated cyclic ester compound is preferably in the range of 0.5 to 10% by mass, and more preferably in the range of 1 to 6% by mass, based on the balance of battery performance.
本発明の電池用非水電解液に含まれうる芳香族化合物は、上記一般式(III)で表される。式(III)において、Ｒ4、Ｒ5及びＲ6は、それぞれ独立して水素、フッ素、炭素数１〜２のアルコキシ基、炭素数１〜６のアルキル基若しくはシクロアルキル基、又はアリール基である。 The aromatic compound that can be contained in the battery non-aqueous electrolyte of the present invention is represented by the above general formula (III). In the formula (III), R 4 , R 5 and R 6 are each independently hydrogen, fluorine, an alkoxy group having 1 to 2 carbon atoms, an alkyl group or cycloalkyl group having 1 to 6 carbon atoms, or an aryl group. is there.
式(III)の芳香族化合物として、具体的には、フルオロベンゼン、ジフルオロベンゼン、アニソール、フルオロアニソール、ジフルオロアニソール、フルオロベラトロール、フルオロエトキシベンゼン、ビフェニル、フルオロビフェニル、メトキシビフェニル、テルフェニル、シクロヘキシルベンゼン等が挙げられ、これら中でも、フルオロベンゼン、ビフェニル、フルオロビフェニル、フルオロアニソール、ジフルオロアニソール、フルオロベラトロールが好ましい。これら芳香族化合物は、１種単独で使用してもよく、２種以上を混合して使用してもよい。 Specific examples of aromatic compounds of formula (III) include fluorobenzene, difluorobenzene, anisole, fluoroanisole, difluoroanisole, fluoroveratrol, fluoroethoxybenzene, biphenyl, fluorobiphenyl, methoxybiphenyl, terphenyl, cyclohexylbenzene. Among these, fluorobenzene, biphenyl, fluorobiphenyl, fluoroanisole, difluoroanisole, and fluoroveratrol are preferable. These aromatic compounds may be used individually by 1 type, and 2 or more types may be mixed and used for them.
上記芳香族化合物の含有量は、電池用非水電解液全体の0.05〜4質量％の範囲が好ましく、電池性能のバランスの観点から、0.1〜2質量％の範囲が更に好ましい。 The content of the aromatic compound is preferably in the range of 0.05 to 4% by mass, and more preferably in the range of 0.1 to 2% by mass, based on the balance of battery performance.
上記式(II)の化合物及び式(III)の化合物は、それぞれ単独で式(I)の化合物と組み合わせて用いても効果があるが、式(I)の化合物を電池用非水電解液中30体積％以上の高含有率で用いる場合は、式(II)の化合物及び式(III)の化合物を併用することがより好ましい。 The compound of the above formula (II) and the compound of the formula (III) are effective even when used alone and in combination with the compound of the formula (I), but the compound of the formula (I) is used in the non-aqueous electrolyte for batteries. When used at a high content of 30% by volume or more, it is more preferable to use a compound of formula (II) and a compound of formula (III) in combination.
本発明の電池用非水電解液を調製するにあたり、上記化合物以外に使用する非水溶媒としては、従来より電池用非水電解液に使用されている種々の非プロトン性溶媒を使用することができる。該非プロトン性溶媒として具体的には、ジメチルカーボネート（ＤＭＣ）、ジエチルカーボネート（ＤＥＣ）、ジフェニルカーボネート、エチルメチルカーボネート（ＥＭＣ）、エチレンカーボネート（ＥＣ）、プロピレンカーボネート（ＰＣ）等の炭酸エステル類、１,２-ジメトキシエタン（ＤＭＥ）、テトラヒドロフラン（ＴＨＦ）、ジエチルエーテル（ＤＥＥ）等のエーテル類、γ-ブチロラクトン（ＧＢＬ）、γ-バレロラクトン、メチルフォルメート（ＭＦ）等のカルボン酸エステル類、アセトニトリル等のニトリル類、ジメチルホルムアミド等のアミド類、ジメチルスルホキシド等のスルホン類、Ｎ-ベンジルオキシカルボニルオキシサクシンイミド等のサクシンイミド類、エチレンスルフィド等のスルフィド類、Ｐ＝Ｎ結合を有するホスファゼン化合物等が挙げられる。これら非プロトン性溶媒の中でも、エチレンカーボネート（ＥＣ）が好ましく、電池用非水電解液がエチレンカーボネート（ＥＣ）を含む場合、式(I)の化合物の安定性が更に向上する。ここで、エチレンカーボネートの含有量は、電解液中5体積％以上であることが好ましい。これら非プロトン性溶媒は、１種単独で使用してもよく、２種以上を混合して用いてもよい。また、リチウム二次電池の形成に際して、本発明の非水電解液は、そのまま用いることも可能であるが、例えば、適当なポリマーや多孔性支持体、或いはゲル状物質に含浸させる等して保持させる方法等で用いることもできる。 In preparing the battery non-aqueous electrolyte of the present invention, various non-protic solvents conventionally used in battery non-aqueous electrolytes may be used as non-aqueous solvents other than the above compounds. it can. Specific examples of the aprotic solvent include carbonate esters such as dimethyl carbonate (DMC), diethyl carbonate (DEC), diphenyl carbonate, ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC). , 2-dimethoxyethane (DME), tetrahydrofuran (THF), diethyl ether (DEE) and other ethers, γ-butyrolactone (GBL), γ-valerolactone, carboxylic acid esters such as methyl formate (MF), acetonitrile Nitriles such as, amides such as dimethylformamide, sulfones such as dimethyl sulfoxide, succinimides such as N-benzyloxycarbonyloxysuccinimide, sulfides such as ethylene sulfide, P = N bond Sufazen compounds. Among these aprotic solvents, ethylene carbonate (EC) is preferable, and when the nonaqueous electrolytic solution for batteries contains ethylene carbonate (EC), the stability of the compound of formula (I) is further improved. Here, the content of ethylene carbonate is preferably 5% by volume or more in the electrolytic solution. These aprotic solvents may be used individually by 1 type, and 2 or more types may be mixed and used for them. In forming a lithium secondary battery, the nonaqueous electrolytic solution of the present invention can be used as it is. For example, it is retained by impregnating a suitable polymer, porous support, or gel material. It can also be used by the method of making it.
本発明の電池用非水電解液に用いる支持塩としては、リチウムイオンのイオン源となる支持塩が好ましい。該支持塩としては、特に制限はないが、例えば、ＬｉＣｌＯ4、ＬｉＢＦ4、ＬｉＰＦ6、ＬｉＣＦ3ＳＯ3、ＬｉＡｓＦ6、ＬｉＣ4Ｆ9ＳＯ3、Ｌｉ(ＣＦ3ＳＯ2)2Ｎ及びＬｉ(Ｃ2Ｆ5ＳＯ2)2Ｎ等のリチウム塩が好適に挙げられる。これらの中でも、不燃性に優れる点で、ＬｉＰＦ6が更に好ましい。これら支持塩は、１種単独で使用してもよく、２種以上を組み合わせて用いてもよい。 As the supporting salt used in the non-aqueous electrolyte for a battery of the present invention, a supporting salt serving as a lithium ion source is preferable. The supporting salt is not particularly limited, and for example, LiClO 4 , LiBF 4 , LiPF 6 , LiCF 3 SO 3 , LiAsF 6 , LiC 4 F 9 SO 3 , Li (CF 3 SO 2 ) 2 N and Li ( Preferable examples include lithium salts such as C 2 F 5 SO 2 ) 2 N. Among these, LiPF 6 is more preferable in terms of excellent nonflammability. These supporting salts may be used alone or in combination of two or more.
上記非水電解液中の支持塩の濃度としては、0.2〜1.5mol/L(Ｍ)が好ましく、0.5〜1mol/L(Ｍ)が更に好ましい。支持塩の濃度が0.2mol/L未満では、電解液の導電性を充分に確保することができず、電池の放電特性及び充電特性に支障をきたすことがあり、1.5mol/Lを超えると、電解液の粘度が上昇し、リチウムイオンの移動度を充分に確保できないため、前述と同様に電解液の導電性を充分に確保できず、電池の放電特性及び充電特性に支障をきたすことがある。 The concentration of the supporting salt in the non-aqueous electrolyte is preferably 0.2 to 1.5 mol / L (M), more preferably 0.5 to 1 mol / L (M). If the concentration of the supporting salt is less than 0.2 mol / L, the conductivity of the electrolyte cannot be sufficiently ensured, and the discharge characteristics and charging characteristics of the battery may be hindered. Since the viscosity of the electrolytic solution increases and the mobility of lithium ions cannot be ensured sufficiently, the conductivity of the electrolytic solution cannot be sufficiently ensured in the same manner as described above, which may hinder battery discharge characteristics and charge characteristics. .
＜非水電解液電池＞
次に、本発明の非水電解液電池を詳細に説明する。本発明の非水電解液電池は、上述の電池用非水電解液と、正極と、負極とを備え、必要に応じて、セパレーター等の非水電解液電池の技術分野で通常使用されている他の部材を備える。この場合、本発明の非水電解液電池は、１次電池としても、２次電池としても構成することができる。
<Nonaqueous electrolyte battery>
Next, the nonaqueous electrolyte battery of the present invention will be described in detail. The non-aqueous electrolyte battery of the present invention includes the above-described non-aqueous electrolyte for a battery, a positive electrode, and a negative electrode, and is usually used in the technical field of non-aqueous electrolyte batteries such as a separator as necessary. Other members are provided. In this case, the non-aqueous electrolyte battery of the present invention can be configured as a primary battery or a secondary battery.
本発明の非水電解液電池の正極活物質としては、Ｖ2Ｏ5、Ｖ6Ｏ13、ＭｎＯ2、ＭｎＯ3等の金属酸化物、ＬｉＣｏＯ2、ＬｉＮｉＯ2、ＬｉＭｎ2Ｏ4、ＬｉＦｅＯ2及びＬｉＦｅＰＯ4等のリチウム含有複合酸化物、ＴｉＳ2、ＭｏＳ2等の金属硫化物、ポリアニリン等の導電性ポリマー等が好適に挙げられる。上記リチウム含有複合酸化物は、Ｆｅ、Ｍｎ、Ｃｏ及びＮｉからなる群から選択される２種又は３種の遷移金属を含む複合酸化物であってもよく、この場合、該複合酸化物は、ＬｉＦｅxＣｏyＮｉ(1-x-y)Ｏ2［式中、０≦ｘ＜１、０≦ｙ＜１、０＜ｘ＋ｙ≦１］、或いはＬｉＭｎxＦｅyＯ2-x-y等で表される。これらの中でも、高容量で安全性が高く、更には電解液の濡れ性に優れる点で、ＬｉＣｏＯ2、ＬｉＮｉＯ2、ＬｉＭｎ2Ｏ4が特に好適である。これら正極活物質は、１種単独で使用してもよく、２種以上を併用してもよい。 As the positive electrode active material of the nonaqueous electrolyte battery of the present invention, metal oxides such as V 2 O 5 , V 6 O 13 , MnO 2 , MnO 3 , LiCoO 2 , LiNiO 2 , LiMn 2 O 4 , LiFeO 2 and Preferable examples include lithium-containing composite oxides such as LiFePO 4 , metal sulfides such as TiS 2 and MoS 2 , and conductive polymers such as polyaniline. The lithium-containing composite oxide may be a composite oxide containing two or three transition metals selected from the group consisting of Fe, Mn, Co, and Ni. In this case, the composite oxide includes: LiFe x Co y Ni [wherein, 0 ≦ x <1,0 ≦ y <1,0 <x + y ≦ 1] (1-xy) O 2, or represented by LiMn x Fe y O 2-xy like. Among these, LiCoO 2 , LiNiO 2 , and LiMn 2 O 4 are particularly preferable in terms of high capacity, high safety, and excellent electrolyte wettability. These positive electrode active materials may be used individually by 1 type, and may use 2 or more types together.
本発明の非水電解液電池の負極活物質としては、リチウム金属自体、リチウムとＡｌ、Ｉｎ、Ｓｎ、Ｓｉ、Ｐｂ又はＺｎ等との合金、リチウムイオンをドープした黒鉛等の炭素材料等が好適に挙げられ、これらの中でも安全性がより高く、電解液の滞れ性に優れる点で、黒鉛等の炭素材料が好ましく、黒鉛が特に好ましい。ここで、黒鉛としては、天然黒鉛、人造黒鉛、メソフェーズカーボンマイクロビーズ（ＭＣＭＢ）等、広くは易黒鉛化カーボンや難黒鉛化カーボンが挙げられる。これら負極活物質は、１種単独で使用してもよく、２種以上を併用してもよい。 As the negative electrode active material of the non-aqueous electrolyte battery of the present invention, lithium metal itself, an alloy of lithium and Al, In, Sn, Si, Pb, Zn or the like, a carbon material such as graphite doped with lithium ions, etc. are suitable. Among them, a carbon material such as graphite is preferable, and graphite is particularly preferable in view of higher safety and excellent stagnation of the electrolyte. Here, examples of graphite include natural graphite, artificial graphite, mesophase carbon microbeads (MCMB), and the like, and widely include graphitizable carbon and non-graphitizable carbon. These negative electrode active materials may be used individually by 1 type, and may use 2 or more types together.
上記正極及び負極には、必要に応じて導電剤、結着剤を混合することができ、導電剤としてはアセチレンブラック等が挙げられ、結着剤としてはポリフッ化ビニリデン（ＰＶＤＦ）、ポリテトラフルオロエチレン（ＰＴＦＥ）、スチレン・ブタジエンゴム（ＳＢＲ）、カルボキシメチルセルロース（ＣＭＣ）等が挙げられる。これらの添加剤は、従来と同様の配合割合で用いることができる。 The positive electrode and the negative electrode can be mixed with a conductive agent and a binder as necessary. Examples of the conductive agent include acetylene black, and the binder includes polyvinylidene fluoride (PVDF) and polytetrafluoro. Examples include ethylene (PTFE), styrene / butadiene rubber (SBR), carboxymethyl cellulose (CMC), and the like. These additives can be used at a blending ratio similar to the conventional one.
本発明の非水電解液電池に使用できる他の部材としては、非水電解液電池において、正負極間に、両極の接触による電流の短絡を防止する役割で介在させるセパレーターが挙げられる。セパレーターの材質としては、両極の接触を確実に防止し得、且つ電解液を通したり含んだりできる材料、例えば、ポリテトラフルオロエチレン、ポリプロピレン、ポリエチレン、セルロース系、ポリブチレンテレフタレート、ポリエチレンテレフタレート等の合成樹脂製の不織布、薄層フィルム等が好適に挙げられる。これらは、単体でも、混合物でも、共重合体でもよい。これらの中でも、厚さ20〜50μm程度のポリプロピレン又はポリエチレン製の微孔性フィルム、セルロース系、ポリブチレンテレフタレート、ポリエチレンテレフタレート等のフィルムが特に好適である。本発明では、上述のセパレーターの他にも、通常電池に使用されている公知の各部材が好適に使用できる。 Other members that can be used in the non-aqueous electrolyte battery of the present invention include a separator that is interposed between positive and negative electrodes in a role of preventing current short-circuiting due to contact between both electrodes in the non-aqueous electrolyte battery. As the material of the separator, it is possible to reliably prevent contact between the two electrodes and to allow the electrolyte to pass through or to contain, for example, synthesis of polytetrafluoroethylene, polypropylene, polyethylene, cellulose, polybutylene terephthalate, polyethylene terephthalate, etc. Preferred examples include resin non-woven fabrics and thin layer films. These may be a single substance, a mixture or a copolymer. Of these, polypropylene or polyethylene microporous films having a thickness of about 20 to 50 μm, cellulose-based films, polybutylene terephthalate, polyethylene terephthalate, and the like are particularly suitable. In the present invention, in addition to the separators described above, known members that are normally used in batteries can be suitably used.
以上に説明した本発明の非水電解液電池の形態としては、特に制限はなく、コインタイブ、ボタンタイプ、ペーパータイプ、角型又はスパイラル構造の円筒型電池等、種々の公知の形態が好適に挙げられる。ボタンタイプの場合は、シート状の正極及び負極を作製し、該正極及び負極でセパレーターを挟む等して、非水電解液電池を作製することができる。また、スパイラル構造の場合は、例えば、シート状の正極を作製して集電体を挟み、これにシート状の負極を重ね合わせて巻き上げる等して、非水電解液電池を作製することができる。 The form of the non-aqueous electrolyte battery of the present invention described above is not particularly limited, and various known forms such as a coin-type, button type, paper type, prismatic or spiral structure cylindrical battery are preferably mentioned. It is done. In the case of the button type, a non-aqueous electrolyte battery can be produced by preparing a sheet-like positive electrode and negative electrode and sandwiching a separator between the positive electrode and the negative electrode. In the case of the spiral structure, for example, a non-aqueous electrolyte battery can be manufactured by preparing a sheet-like positive electrode, sandwiching a current collector, and stacking and winding up the sheet-like negative electrode on the current collector. .
以下に、実施例を挙げて本発明を更に詳しく説明するが、本発明は下記の実施例に何ら限定されるものではない。 Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.
（実施例１）
ジフルオロリン酸メチル30体積％、エチレンカーボネート23体積％、ジエチルカーボネート47体積％からなる混合溶媒に、ＬｉＰＦ6を1mol/Lになるように溶解させて、これに３-フルオロビニレンカーボネート2質量％、フルオロベンゼン1質量％を添加して非水電解液を調製した。次に、得られた非水電解液の難燃性を下記の方法で評価し、表１に示す結果を得た。
(Example 1)
In a mixed solvent consisting of 30% by volume of methyl difluorophosphate, 23% by volume of ethylene carbonate, and 47% by volume of diethyl carbonate, LiPF 6 was dissolved so as to be 1 mol / L, and 2% by mass of 3-fluorovinylene carbonate was added thereto. A non-aqueous electrolyte was prepared by adding 1% by mass of fluorobenzene. Next, the flame retardancy of the obtained non-aqueous electrolyte was evaluated by the following method, and the results shown in Table 1 were obtained.
（１）難燃性の評価
ＵＬ（アンダーライティングラボラトリー）規格のＵＬ９４ＨＢ法をアレンジした方法で、大気環境下において着火した炎の燃焼長及び燃焼時間を測定・評価した。具体的には、ＵＬ試験基準に基づき、127mm×12.7mmのＳｉＯ2シートに上記電解液1.0mLを染み込ませて試験片を作製して評価を行った。以下に不燃性・難燃性・自己消火性・燃焼性の評価基準を示す。
＜不燃性の評価＞試験炎を点火しても全く着火しなかった場合（燃焼長：0mm）を不燃性ありと評価した。
＜難燃性の評価＞着火した炎が、装置の25mmラインまで到達せず且つ網からの落下物にも着火が認められなかった場合を難燃性ありと評価した。
＜自己消火性の評価＞着火した炎が25〜100mmラインで消火し且つ網からの落下物にも着火が認められなかった場合を自己消火性ありと評価した。
＜燃焼性の評価＞着火した炎が、100mmラインを超えた場合を燃焼性と評価した。
(1) Flame Retardancy Evaluation The combustion length and combustion time of a flame ignited in an atmospheric environment were measured and evaluated by a method in which the UL94HB method of UL (Underwriting Laboratory) standard was arranged. Specifically, based on the UL test standard, a test piece was prepared by impregnating a 127 mm × 12.7 mm SiO 2 sheet with the above electrolytic solution 1.0 mL, and evaluated. The evaluation criteria for nonflammability, flame retardancy, self-extinguishing properties, and flammability are shown below.
<Evaluation of Nonflammability> A case where the test flame did not ignite at all (ignition length: 0 mm) was evaluated as nonflammable.
<Evaluation of Flame Retardancy> The case where the ignited flame did not reach the 25 mm line of the apparatus and the fallen object from the net was not ignited was evaluated as flame retardant.
<Evaluation of self-extinguishing property> When the ignited flame was extinguished in the 25 to 100 mm line and no ignition was observed on the falling object from the net, it was evaluated as having self-extinguishing property.
<Evaluation of combustibility> The case where the ignited flame exceeded the 100 mm line was evaluated as combustible.
次に、ＬｉＣｏＯ2（正極活物質）94質量部に対して、アセチレンブラック（導電剤）3質量部と、ポリフッ化ビニリデン（結着剤）3質量部とを添加し、有機溶媒（酢酸エチルとエタノールとの50/50質量％混合溶媒）で混練した後、該混練物を厚さ25μmのアルミニウム箔（集電体）にドクターブレードで塗工し、更に熱風乾燥（100〜120℃）して、厚さ80μmの正極シートを作製した。また、人造グラファイト（負極活物質）90質量部に対してポリフッ化ビニリデン（結着剤）10質量部を添加し、有機溶媒（酢酸エチルとエタノールとの50/50質量％混合溶媒）で混練した後、該混練物を厚さ25μmの銅箔（集電体）にドクターブレードで塗工し、更に熱風乾燥（100〜120℃）して、厚さ80μmの負極シートを作製した。 Next, 3 parts by mass of acetylene black (conductive agent) and 3 parts by mass of polyvinylidene fluoride (binder) are added to 94 parts by mass of LiCoO 2 (positive electrode active material), and an organic solvent (ethyl acetate and (50/50 mass% mixed solvent with ethanol), and the kneaded product is applied to a 25 μm thick aluminum foil (current collector) with a doctor blade and further dried with hot air (100 to 120 ° C.). A positive electrode sheet having a thickness of 80 μm was prepared. Also, 10 parts by weight of polyvinylidene fluoride (binder) was added to 90 parts by weight of artificial graphite (negative electrode active material), and kneaded with an organic solvent (50/50% by weight mixed solvent of ethyl acetate and ethanol). Thereafter, the kneaded product was applied to a copper foil (current collector) having a thickness of 25 μm with a doctor blade, and further dried with hot air (100 to 120 ° C.) to prepare a negative electrode sheet having a thickness of 80 μm.
得られた正極シートに、厚さ25μmのセパレーター（微孔性フィルム：ポリプロピレン製）を介して負極シートを重ね合わせて巻き上げ、円筒型電極を作製した。該円筒型電極の正極長さは約260mmであった。該円筒型電極に、上記電解液を注入して封口し、単三型リチウム電池（非水電解液２次電池）を作製した。得られた電池の初期放電容量、サイクル特性及び低温特性を下記の方法で測定し、表１に示す結果を得た。 On the obtained positive electrode sheet, a negative electrode sheet was overlapped and wound up via a separator (microporous film: made of polypropylene) having a thickness of 25 μm to produce a cylindrical electrode. The positive electrode length of the cylindrical electrode was about 260 mm. The above electrolytic solution was injected into the cylindrical electrode and sealed to prepare an AA lithium battery (non-aqueous electrolyte secondary battery). The initial discharge capacity, cycle characteristics, and low temperature characteristics of the obtained battery were measured by the following methods, and the results shown in Table 1 were obtained.
（２）初期放電容量及びサイクル特性評価
20℃の環境下で、上限電圧4.2Ｖ、下限電圧3.0Ｖ、放電電流50mA、充電電流50mAの条件で充放電を行い、この時の放電容量を既知の電極重量で除することにより初期放電容量（mAh/g）を求めた。更に、同様の充放電条件で50サイクルまで充放電を繰り返して、50サイクル後の放電容量を求め、下記の式：
容量残存率Ｓ＝50サイクル後の放電容量／初期放電容量×100（％）
に従って容量残存率Ｓを算出し、電池のサイクル特性の指標とした。
(2) Initial discharge capacity and cycle characteristics evaluation
Under an environment of 20 ° C, charge and discharge are performed under the conditions of an upper limit voltage of 4.2 V, a lower limit voltage of 3.0 V, a discharge current of 50 mA, and a charge current of 50 mA. By dividing the discharge capacity by the known electrode weight, (MAh / g) was determined. Furthermore, charge / discharge was repeated up to 50 cycles under the same charge / discharge conditions, and the discharge capacity after 50 cycles was determined.
Capacity remaining rate S = discharge capacity after 50 cycles / initial discharge capacity × 100 (%)
The capacity remaining rate S was calculated according to the above and used as an index of the cycle characteristics of the battery.
（３）低温特性の評価（低温放電容量残存率の測定）
20℃と−10℃の環境下で、上限電圧4.2Ｖ、下限電圧3.0Ｖ、放電電流50mA、充電電流50mAの条件で充放電を5サイクル行い、20℃と−10℃において測定した5サイクル後の放電容量と比較し、下記の式：
容量残存率Ｌ＝5サイクル後放電容量(-10℃)／5サイクル後放電容量(20℃)×100（％）
に従って容量残存率Ｌを算出し、電池の低温特性の指標とした。
(3) Evaluation of low-temperature characteristics (measurement of residual rate of low-temperature discharge capacity)
After 5 cycles measured at 20 ° C and -10 ° C under the conditions of 20 ° C and -10 ° C, 5 cycles of charge / discharge under conditions of upper limit voltage 4.2V, lower limit voltage 3.0V, discharge current 50mA, charge current 50mA Compared with the discharge capacity of the following formula:
Capacity remaining rate L = Discharge capacity after 5 cycles (-10 ° C) / Discharge capacity after 5 cycles (20 ° C) x 100 (%)
The capacity remaining rate L was calculated according to the above and used as an index of the low temperature characteristics of the battery.
（実施例２）
ジフルオロリン酸エチル50体積％、エチレンカーボネート25体積％、ジメチルカーボネート25体積％からなる混合溶媒に、ＬｉＰＦ6を1mol/Lになるように溶解させて、これにビニレンカーボネート3質量％、３-フルオロビフェニル1質量％を添加して非水電解液を調製し、得られた非水電解液の難燃性を評価した。また、実施例１と同様にして非水電解液２次電池を作製し、初期放電容量、サイクル特性及び低温特性をそれぞれ測定・評価した。結果を表１に示す。
(Example 2)
LiPF 6 is dissolved in a mixed solvent consisting of 50% by volume of ethyl difluorophosphate, 25% by volume of ethylene carbonate, and 25% by volume of dimethyl carbonate so as to be 1 mol / L, and 3% by weight of vinylene carbonate is added thereto. A non-aqueous electrolyte was prepared by adding 1% by mass of biphenyl, and the flame retardancy of the obtained non-aqueous electrolyte was evaluated. Further, a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, and the initial discharge capacity, cycle characteristics, and low temperature characteristics were measured and evaluated. The results are shown in Table 1.
（実施例３）
ジフルオロリン酸プロピル80体積％、エチレンカーボネート20体積％からなる混合溶媒に、ＬｉＰＦ6を1mol/Lになるように溶解させて、これに４-フルオロビニレンカーボネート3質量％、３-フルオロアニソール1質量％を添加して非水電解液を調製し、得られた非水電解液の難燃性を評価した。また、実施例１と同様にして非水電解液２次電池を作製し、初期放電容量、サイクル特性及び低温特性をそれぞれ測定・評価した。結果を表１に示す。
(Example 3)
LiPF 6 is dissolved in a mixed solvent consisting of 80% by volume of propyl difluorophosphate and 20% by volume of ethylene carbonate so as to be 1 mol / L, and then 3% by mass of 4-fluorovinylene carbonate and 1% by mass of 3-fluoroanisole. % Was added to prepare a non-aqueous electrolyte, and the flame retardancy of the obtained non-aqueous electrolyte was evaluated. In addition, a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, and the initial discharge capacity, cycle characteristics, and low temperature characteristics were measured and evaluated. The results are shown in Table 1.
（実施例４）
ジフルオロリン酸トリフルオロエチル80体積％、エチレンカーボネート5体積％、エチルメチルカーボネート15体積％からなる混合溶媒に、ＬｉＰＦ6を1mol/Lになるように溶解させて、これにカテコールカーボネート5質量％、フルオロベラトロール0.1質量％を添加して非水電解液を調製し、得られた非水電解液の難燃性を評価した。次に、実施例１で用いた人造グラファイト製の負極に代えて、厚さ1.0mmのリチウム金属シートを負極として用いる以外は実施例１と同様にして非水電解液２次電池を作製し、初期放電容量、サイクル特性及び低温特性をそれぞれ測定・評価した。結果を表１に示す。
Example 4
In a mixed solvent consisting of 80% by volume of trifluoroethyl difluorophosphate, 5% by volume of ethylene carbonate, and 15% by volume of ethyl methyl carbonate, LiPF 6 was dissolved so as to be 1 mol / L. A non-aqueous electrolyte was prepared by adding 0.1% by mass of fluoroveratrol, and the flame retardancy of the obtained non-aqueous electrolyte was evaluated. Next, instead of the artificial graphite negative electrode used in Example 1, a non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1 except that a 1.0 mm thick lithium metal sheet was used as the negative electrode. Initial discharge capacity, cycle characteristics, and low temperature characteristics were measured and evaluated. The results are shown in Table 1.
（実施例５）
ジフルオロリン酸フェニル10体積％、エチレンカーボネート30体積％、エチルメチルカーボネート60体積％からなる混合溶媒に、ＬｉＰＦ6を1mol/Lになるように溶解させて、これにビニレンカーボネート2質量％を添加して非水電解液を調製し、得られた非水電解液の難燃性を評価した。また、実施例１と同様にして非水電解液２次電池を作製し、初期放電容量、サイクル特性及び低温特性をそれぞれ測定・評価した。結果を表１に示す。
(Example 5)
In a mixed solvent consisting of 10% by volume of phenyl difluorophosphate, 30% by volume of ethylene carbonate, and 60% by volume of ethyl methyl carbonate, LiPF 6 is dissolved to 1 mol / L, and 2% by mass of vinylene carbonate is added thereto. A non-aqueous electrolyte solution was prepared, and the flame retardancy of the obtained non-aqueous electrolyte solution was evaluated. Further, a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, and the initial discharge capacity, cycle characteristics, and low temperature characteristics were measured and evaluated. The results are shown in Table 1.
（比較例１）
エチレンカーボネート33体積％、ジエチルカーボネート67体積％からなる混合溶媒に、ＬｉＰＦ6を1mol/Lになるように溶解させて非水電解液を調製し、得られた非水電解液の難燃性を評価した。また、実施例１と同様にして非水電解液２次電池を作製し、初期放電容量、サイクル特性及び低温特性をそれぞれ測定・評価した。結果を表１に示す。
(Comparative Example 1)
A non-aqueous electrolyte was prepared by dissolving LiPF 6 in a mixed solvent consisting of 33% by volume of ethylene carbonate and 67% by volume of diethyl carbonate so as to be 1 mol / L, and the flame resistance of the obtained non-aqueous electrolyte was reduced. evaluated. In addition, a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, and the initial discharge capacity, cycle characteristics, and low temperature characteristics were measured and evaluated. The results are shown in Table 1.
（比較例２）
リン酸トリエチル30体積％、エチレンカーボネート23体積％、エチルメチルカーボネート47体積％からなる混合溶媒に、ＬｉＰＦ6を1mol/Lになるように溶解させて、これにビニレンカーボネート2質量％、３-フルオロベンゼン1質量％を添加して非水電解液を調製し、得られた非水電解液の難燃性を評価した。また、実施例１と同様にして非水電解液２次電池を作製し、初期放電容量、サイクル特性及び低温特性をそれぞれ測定・評価した。結果を表１に示す。
(Comparative Example 2)
LiPF 6 was dissolved in a mixed solvent consisting of 30% by volume of triethyl phosphate, 23% by volume of ethylene carbonate, and 47% by volume of ethyl methyl carbonate so as to be 1 mol / L, and 2% by weight of vinylene carbonate and 3-fluoro A nonaqueous electrolytic solution was prepared by adding 1% by mass of benzene, and the flame retardancy of the obtained nonaqueous electrolytic solution was evaluated. In addition, a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, and the initial discharge capacity, cycle characteristics, and low temperature characteristics were measured and evaluated. The results are shown in Table 1.
（比較例３）
フルオロリン酸ジエチル30体積％、エチレンカーボネート23体積％、エチルメチルカーボネート47体積％からなる混合溶媒に、ＬｉＰＦ6を1mol/Lになるように溶解させて、これに３-フルオロビニレンカーボネート2質量％、３-フルオロアニソール1質量％を添加して非水電解液を調製し、得られた非水電解液の難燃性を評価した。また、実施例１と同様にして非水電解液２次電池を作製し、初期放電容量、サイクル特性及び低温特性をそれぞれ測定・評価した。結果を表１に示す。
(Comparative Example 3)
LiPF 6 is dissolved in a mixed solvent consisting of 30% by volume of diethyl fluorophosphate, 23% by volume of ethylene carbonate, and 47% by volume of ethyl methyl carbonate so as to be 1 mol / L, and then 2% by mass of 3-fluorovinylene carbonate. A non-aqueous electrolyte was prepared by adding 1% by mass of 3-fluoroanisole, and the flame retardancy of the obtained non-aqueous electrolyte was evaluated. In addition, a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, and the initial discharge capacity, cycle characteristics, and low temperature characteristics were measured and evaluated. The results are shown in Table 1.
（比較例４）
ジフルオロリン酸プロピル70体積％、エチレンカーボネート30体積％からなる混合溶媒に、ＬｉＰＦ6を1mol/Lになるように溶解させて非水電解液を調製し、得られた非水電解液の難燃性を評価した。また、実施例１と同様にして非水電解液２次電池を作製し、初期放電容量、サイクル特性及び低温特性をそれぞれ測定・評価した。結果を表１に示す。
(Comparative Example 4)
A non-aqueous electrolyte solution was prepared by dissolving LiPF 6 in a mixed solvent consisting of 70% by volume of propyl difluorophosphate and 30% by volume of ethylene carbonate so as to be 1 mol / L, and the flame retardant of the obtained non-aqueous electrolyte solution Sex was evaluated. Further, a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, and the initial discharge capacity, cycle characteristics, and low temperature characteristics were measured and evaluated. The results are shown in Table 1.
表１の実施例１〜４に示すように、式(I)〜式(III)の化合物を含む非水電解液が高い難燃性を示すと共に、該非水電解液を用いた電池が優れた電池性能を示すことが分る。また、実施例５から、式(I)の化合物を10体積％以上用いれば、非水電解液に自己消火性以上の難燃効果を付与できることが分る。このように、本発明の非水電解液により、難燃、不燃性を発現しつつ、放電容量、サイクル特性及び低温特性に優れた非水電解液電池が得られることが確認された。 As shown in Examples 1 to 4 in Table 1, the non-aqueous electrolyte containing the compounds of formula (I) to formula (III) showed high flame retardancy, and the battery using the non-aqueous electrolyte was excellent. It can be seen that the battery performance is shown. In addition, it can be seen from Example 5 that if the compound of formula (I) is used in an amount of 10% by volume or more, the non-aqueous electrolyte can be provided with a flame-retardant effect of self-extinguishing property or more. As described above, it was confirmed that the nonaqueous electrolyte battery of the present invention can provide a nonaqueous electrolyte battery excellent in discharge capacity, cycle characteristics and low temperature characteristics while exhibiting flame retardancy and nonflammability.
一方、比較例２及び３に示すように、非水電解液に通常のリン酸トリエステル又はモノフルオロリン酸エステルを30体積％含有する非水電解液は、式(II)の化合物や式(III)の化合物を添加しても、初期放電容量が小さく、また、サイクル特性が大幅に低下してしまうことが分る。また、比較例４に示すように、式(I)のジフルオロリン酸エステルを用いても、式(II)の化合物や式(III)の化合物を加えない場合には、実施例３と比較して、初期放電容量やサイクル特性が低下してしまうことが分る。 On the other hand, as shown in Comparative Examples 2 and 3, a non-aqueous electrolyte solution containing 30% by volume of a normal phosphoric acid triester or monofluorophosphate ester in the non-aqueous electrolyte solution is a compound of the formula (II) or a formula ( It can be seen that even when the compound of III) is added, the initial discharge capacity is small and the cycle characteristics are greatly deteriorated. Further, as shown in Comparative Example 4, when the difluorophosphate ester of the formula (I) is used and the compound of the formula (II) or the compound of the formula (III) is not added, it is compared with Example 3. As a result, the initial discharge capacity and cycle characteristics are deteriorated.
以上の結果から、式(I)で表されるジフルオロリン酸エステルと式(II)で表される不飽和環状エステル及び／又は式(III)で表される芳香族化合物を含有することを特徴とする非水電解液を用いることにより、高い難燃性と優れた電池性能を両立させた非水電解液電池を提供できることが分る。 From the above results, it contains a difluorophosphate ester represented by the formula (I) and an unsaturated cyclic ester represented by the formula (II) and / or an aromatic compound represented by the formula (III). It can be seen that a non-aqueous electrolyte battery having both high flame retardancy and excellent battery performance can be provided by using the non-aqueous electrolyte.
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