JP6435235B2 - Fluorine-containing phosphate ester cyanoalkylamide, nonaqueous electrolyte containing the same, and nonaqueous secondary battery - Google Patents

Description

  The present invention relates to a fluorine-containing phosphate ester cyanoalkylamide. Specifically, fluorine-containing phosphoric acid ester cyanoalkylamide used in electrochemical energy conversion devices such as non-aqueous secondary batteries, capacitors and electrolytic capacitors, and non-aqueous electrolytes containing the same, and non-aqueous systems using the same The present invention relates to a secondary battery.

  Electrochemical energy conversion devices such as non-aqueous secondary batteries, capacitors, and electrolytic capacitors are used in various applications such as notebook PCs and mobile phones, backup power supplies, and smoothing of power supply circuits. In particular, non-aqueous secondary batteries represented by lithium ion secondary batteries have the characteristics of high output density and high energy density. In recent years, they have been put to practical use in large batteries as power storage power supplies and electric vehicle power supplies. The realization is getting into full swing.

  With the increase in size of non-aqueous secondary batteries, the batteries are required to have higher energy density and longer life, and in particular, it is important to extend the life at high temperatures (Non-Patent Document 1).

  To increase the energy density of non-aqueous secondary batteries, non-aqueous secondary batteries using positive electrode materials that can operate at a high potential (for example, 4.3 V or more based on metallic lithium in the case of lithium ion secondary batteries) are proposed. (Non-Patent Document 1).

  The electrolyte solution of such a non-aqueous secondary battery is obtained by dissolving an electrolyte salt in an organic solvent obtained by mixing a low dielectric solvent such as dimethyl carbonate or diethyl carbonate with a high dielectric constant solvent such as ethylene carbonate or propylene carbonate. Things are commonly used. However, these electrolyte solutions are not sufficient as electrolyte solutions for non-aqueous secondary batteries using a positive electrode material that can operate at a high potential. In particular, when charging / discharging is performed under high voltage conditions, the electrolytic solution is oxidized and decomposed on the positive electrode, causing the battery to swell due to the generation of decomposition gas, or increasing the electrical resistance due to the deposition of decomposition products, thereby increasing the charge / discharge cycle. There is a problem that tends to cause deterioration of characteristics (Non-Patent Documents 1 and 2).

On the other hand, as the electrolyte salt, for example, in the case of a lithium ion secondary battery, LiPF ₆ having excellent ionic conductivity and oxidation resistance is mainly used. This LiPF ₆ has a property of being easily decomposed by heat and moisture in the electrolytic solution, and it is known that this triggers the decomposition of the electrolytic solution to reduce the battery life. For such problems, phosphazenes, phosphites, hexamethylphosphoramide, and the like have been proposed (Non-Patent Documents 3 and 4 and Patent Document 1).

US Pat. No. 6,939,647 JP 2011-141974 A International Publication No. 2013/187073

“Development of materials for next-generation automotive lithium-ion batteries”, CMC Publishing Co., Ltd. (2008) p. 86-89 “Automotive Lithium Ion Battery”, Nikkan Kogyo Shimbun (2010) p. 20-25, p. 130-131 JornaI of PowerSources, 113, (2003), p. 166 JornaI of The Electrochemicala Society, vol. 152, (2005), p. A1361 JornaI of Fluorine chemistry, 113, 111-122 (2002)

Phosphazene, phosphite, and hexatyl phosphoramide, which are proposed for extending the life of lithium ion secondary batteries, supplement PF ₅ and HF generated by decomposition of LiPF ₆ with heat and moisture, It is thought that the mechanism is suppressing the decomposition, but because it is electrochemically unstable, when it coexists with the electrolyte of a non-aqueous secondary battery, the effect tends to be lost due to decomposition during charge / discharge was there. On the other hand, Patent Document 2 proposes a fluorine-containing phosphoric ester amide that does not decompose in the normal voltage range of lithium-ion batteries (4.2 V or less based on metallic lithium), but these materials also have a high energy density. In a battery having a positive electrode capable of operating at a high potential, such as LiNi _1/3 Co _1/3 Mn _1/3 O ₂ and LiNi _0.5 Mn _1.5 O ₄ Is not sufficient in terms of electrochemical stability (oxidation resistance).

  The present invention has been made in view of the above problems. That is, the present invention provides a fluorine-containing phosphoric ester amide that is excellent in an electrolytic solution decomposition inhibiting effect and can be used under high voltage conditions, and a non-aqueous solution that is excellent in high-temperature stability including the fluorine-containing phosphoric ester cyanoalkylamide. It is an object of the present invention to provide a non-aqueous secondary battery having improved electrolytic solution and further charge / discharge cycle characteristics under a high voltage condition of 4.3 V or higher.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have obtained a fluorine-containing phosphate ester cyanoalkylamide having a specific structure that is excellent in the effect of suppressing the decomposition of the electrolytic solution and can be used under high voltage conditions. I found. In addition, a non-aqueous electrolyte containing the fluorine-containing phosphate ester cyanoalkylamide and excellent in high-temperature stability, and further a non-aqueous secondary battery having improved charge / discharge cycle characteristics under a high voltage condition of 4.3 V or higher And the present invention has been completed. That is, the present invention relates to the following gist.

1. The following general formula (1)

(Wherein R ¹ and R ² are the same or non-identical and represent a linear or branched alkyl group having 1 to 6 carbon atoms, provided that R ¹ and R ² are a cyano group (—CN), a fluorine atom, And at least one of them may have a cyano group, Rf ¹ and Rf ² may be the same or non-identical, and a straight chain having 1 to 6 carbon atoms Or a branched alkyl group or a fluorine-containing alkyl group, at least one of which is a fluorine-containing alkyl group).

The fluorine-containing phosphate ester cyanoalkylamide of the present invention is characterized in that it has an amide group in the molecule, and in particular, the alkyl group bonded to the amide group has a cyano group as a substituent. This cyanoalkylamide group contributes to the electrochemical stability and the thermal stabilization effect of an electrolyte salt such as LiPF ₆ and a non-aqueous electrolyte containing the same. Further, by having a cyanoalkylamide group in the molecule, the physical properties are different from those of conventional fluorine-containing phosphoric ester amides such as high viscosity and high dielectric constant.

2. The following general formula (2)

(In the formula, R ^{1 ′} and R ^{2 ′} are the same or non-identical, and represent a linear or branched alkyl group having 1 to 6 carbon atoms. However, R ^{1 ′} and R ^{2 ′} are both cyano groups ( -CN), which may be further substituted by a fluorine atom, and Rf ¹ and Rf ² are the same as defined above). is there. That is, the two alkyl groups bonded to the amide group become cyanoalkyl groups each having at least one cyano group, thereby improving the oxidation resistance.

3. General formula (3)

(In the formula, R ^{1 ′} and R ^{2 ′} are the same as defined above. Rf ^{1 ′} and Rf ^{2 ′} are each independently a trifluoromethyl group, a 2-fluoroethyl group, or a 2,2-difluoroethyl group. Group, 2,2,2-trifluoroethyl group, 2,2,3,3-tetrafluoropropyl group, 2,2,3,3,3-pentafluoropropyl group, hexafluoroisopropyl group The fluorine-containing phosphoric acid ester cyanoalkylamide described in item 2).

4). A nonaqueous electrolytic solution comprising a nonaqueous solvent and an electrolyte salt, the nonaqueous electrolytic solution comprising the fluorine-containing phosphate ester cyanoalkylamide according to any one of Items 1 to 3.

5. Electrolyte salt is a non-aqueous electrolyte according to item 4 is LiPF _6.

6). A non-aqueous secondary battery comprising a negative electrode, a positive electrode, a separator, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte is the non-aqueous electrolyte according to item 3 or 4.

  According to the present invention, it is excellent in the decomposition inhibiting effect of the electrolytic solution, and is excellent in high-temperature stability including the fluorine-containing phosphate ester cyanoalkylamide that can be used under high voltage conditions and the fluorine-containing phosphate ester cyanoalkylamide. A nonaqueous secondary battery with improved charge / discharge cycle characteristics under high voltage conditions of nonaqueous electrolyte and 4.3 V or higher can be provided.

It is a schematic cross section which shows the structure of the battery of the coin cell used for Examples 9-10 and Comparative Examples 7-9.

  Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as “the present embodiment”) will be described in detail. The following embodiments are examples for explaining the present invention, and are not intended to limit the present invention to the following contents. The present invention can be implemented with appropriate modifications within the scope of the gist thereof.

The fluorine-containing phosphoric ester amide of the present invention is represented by the general formula (1). That is, it is a fluorine-containing phosphate ester cyanoalkylamide having a cyano group in the alkyl group bonded to the amide moiety. This cyanoalkylamide moiety contributes to the thermal stabilization effect of an electrolyte salt such as LiPF ₆ and a non-aqueous electrolyte containing the same. In particular, the cyanoalkylamide moiety has a cyano group so that the fluorine-containing phosphate amide molecule has a high voltage condition. It is thought that the electrochemical stability (oxidation resistance) in the case is improved. In addition, by having a cyanoalkylamide group, the physical properties are different from conventional fluorine-containing phosphoric ester amides such as high viscosity and high dielectric constant.

In the general formula (1), R ¹ and R ² are the same or non-identical and represent a linear or branched alkyl group having 1 to 6 carbon atoms. However, R ¹ and R ² may have a substituent selected from the group consisting of a cyano group (—CN) and a fluorine atom, and at least ^one of R ¹ and R ² has a cyano group. Examples of R ¹ and R ² are methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, t-butyl group, n-amyl group, t-amyl group. Group, n-hexyl group, cyclohexyl group, 2,2,2-trifluoroethyl group, cyanomethyl group, 2-cyanoethyl group, 4-cyanobutyl group and 6-cyanohexyl group. Among them, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, a cyanomethyl group and a 2-cyanoethyl group are preferable because the physical properties of the fluorine-containing phosphate ester cyanoalkylamide are good and the raw materials are easily available industrially. . Further, as shown in the general formula (2), when both of R ¹ and R ² have a cyano group, the electrolyte has a good electrolyte solution high-temperature stabilization function, and the fluorine-containing phosphate cyanoalkyl ester This is preferable because the oxidation resistance of the amide is further improved.

In the general formula (1), Rf ¹ and Rf ² are the same or non-identical and represent a linear or branched alkyl group or a fluorinated alkyl group having 1 to 6 carbon atoms, at least one of which is a fluorinated alkyl. It is a group. Examples of the linear or branched alkyl group having 1 to 6 carbon atoms include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, t-butyl group, Examples thereof include an n-amyl group, a t-amyl group, an n-hexyl group, and a cyclohexyl group. Examples of the linear or branched fluorine-containing alkyl group having 1 to 6 carbon atoms include a trifluoromethyl group, 2,2 , 2-trifluoroethyl group, 2,2-difluoroethyl group, 2-fluoroethyl group, perfluoroethyl group, 2,2,3,3-tetrafluoropropyl group, 2,2,3,3,3- Pentafluoropropyl group, 2,2,2,2 ′, 2 ′, 2′-hexafluoroisopropyl group, 1,1,2,2,3,3,4,4-octafluorobutyl group, perfluorobutyl group , 2, 2, 3 3,4,4,5,5- octafluoro pentyl group and a perfluorobutyl group and a 3,3,4,4,5,5,6,6,6-nonafluorohexyl group. Among the above fluorine-containing alkyl groups, trifluoromethyl group, 2-fluoroethyl group, 2,2-difluoroethyl group, 2,2,2-trifluoroethyl group, 2,2,3,3-tetrafluoropropyl group 2,2,3,3,3-pentafluoropropyl group and hexafluoroisopropyl group are particularly preferred from the viewpoint of physical properties and oxidation resistance of the fluorinated phosphoric acid ester cyanoalkylamide, and particularly shown in the general formula (3). As described above, the case where Rf ¹ and Rf ² are these fluorine-containing alkyl groups and both R ¹ and R ² have a cyano group is preferable from the viewpoint of oxidation resistance.

  Specific examples of the fluorine-containing phosphate ester cyanoalkylamide of the general formula (1) include the following compounds (A-1 to A7, B-1 to B-10, C-1 to C-9). However, the present invention is not limited to these.

  The fluorine-containing phosphoric acid ester dicyanoalkylamide represented by the general formula (1), (2) or (3) of the present invention can be synthesized according to the method shown in Non-Patent Document 5 or the like. That is, as shown in Scheme (4), synthesis can be performed by reacting a fluorine-containing chlorophosphate (5) derived from phosphorus trichloride and a fluorine-containing alcohol and a cyanoalkyl group-containing secondary amine (6). it can.

The obtained fluorine-containing phosphoric ester amide can be used as a crude purified product as an additive for electrolytes for non-aqueous secondary batteries as it is, but purified by a known extraction method, distillation method, recrystallization method, etc. The content of moisture, phosphoric acid, phosphoric acid condensate, chloride, raw material amine, raw material alcohol, and intermediate fluorine-containing chlorophosphate present as impurities can be reduced or substantially free of impurities. be able to.
Next, a method for using the fluorine-containing phosphate ester cyanoalkylamide of the present invention will be described.

The fluorine-containing phosphoric ester cyanoalkylamide of the present invention has higher oxidation resistance than other fluorine-containing phosphoric ester amides. Therefore, the fluorine-containing phosphoric acid ester cyanoalkylamide of the present invention is not only used for non-aqueous secondary batteries such as the current lithium ion secondary battery, but also for LiNi _1/3 Co which has been proposed to achieve high energy density. _It can also be used for non-aqueous secondary batteries having a positive electrode capable of operating at a high potential such as _1/3 Mn _1/3 O ₂ and LiNi _0.5 Mn _1.5 O _4. It is possible to contribute to the stabilization of the high temperature of the liquid and the extension of the life of the non-aqueous secondary battery (such as charge / discharge cycle characteristics).

  Moreover, the fluorine-containing phosphate ester cyanoalkylamide of the present invention has no flash point and is nonflammable. Non-aqueous secondary batteries such as lithium ion secondary batteries, sodium ion secondary batteries and magnesium ion secondary batteries, or electrochemical energy conversion devices such as lithium ion capacitors and electric double layer capacitors can be used as solvents for non-aqueous electrolytes. Inflammable solvents such as cyclic carbonates, chain carbonates and ethers are usually used. For this reason, the presence of the fluorine-containing phosphate ester cyanoalkylamide of the present invention in the electrolytic solution as a flame retardant can contribute to the improvement of the safety of the nonaqueous electrolytic solution.

  Further, the fluorine-containing phosphate ester cyanoalkylamide of the present invention has characteristics such as a high boiling point and a relatively high relative dielectric constant in terms of physical properties such as boiling point and relative dielectric constant. Electrolytic capacitors that are one of the electrochemical energy conversion devices also use flammable solvents such as diols and lactones. Especially as electrolyte materials for electrolytic capacitors, low volatility (high boiling point), A high dielectric constant and a high withstand voltage are required. For this reason, the fluorine-containing phosphoric acid ester cyanoalkylamide of the present invention can be suitably used as an electrolyte solution solvent or a flame retardant for an electrolytic capacitor.

<Non-aqueous electrolyte>
The nonaqueous electrolytic solution of the present invention contains a fluorine-containing phosphate ester cyanoalkylamide represented by the above formula (1), a nonaqueous solvent, and an electrolyte salt. The nonaqueous electrolytic solution of the present embodiment is suitably used as a nonaqueous electrolytic solution for an electrochemical energy conversion device. Here, although it does not specifically limit as an electrochemical energy conversion device, For example, a lithium secondary battery, a lithium ion secondary battery, a sodium secondary battery, a sodium ion secondary battery, a magnesium secondary battery, a magnesium ion secondary battery And non-aqueous secondary batteries such as aluminum secondary batteries and aluminum ion secondary batteries, lithium ion capacitors, electric double layer capacitors, and electrolytic capacitors. Among the above, lithium secondary batteries and lithium ion secondary batteries in which LiPF ₆ is mainly used as an electrolyte salt are characterized in that high-temperature stability is improved by containing a fluorine-containing phosphate ester cyanoalkylamide. Since it is easily exhibited, it can be used more preferably.

  The addition amount of the fluorine-containing phosphate ester cyanoalkylamide of general formula (1) to the non-aqueous electrolyte is 0.01 to 50%, preferably 0.1 to 10% by weight with respect to the whole non-aqueous solvent. % Is desirable, and more preferably 0.5 to 5%. When the addition amount is less than 0.01%, the effect of adding the fluorine-containing phosphoric acid ester cyanoalkylamide, such as high-temperature stabilization and flame retardancy of the non-aqueous electrolyte, cannot be obtained sufficiently, and the addition amount is 50%. In the case of exceeding, the performance of the non-aqueous secondary battery may deteriorate.

  Various solvents can be used as the solvent for the nonaqueous electrolytic solution, but an aprotic polar solvent is preferred. Examples of the aprotic solvent include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, and fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, diphenyl carbonate, and bis (2,2,2). -Trifluoroethyl) carbonate and other chain carbonates, γ-butyrolactone, γ-valerolactone, cyclic esters such as propiolactone, methyl acetate, methyl butyrate, chain esters such as ethyl trifluoroacetate, diisopropyl ether, tetrahydrofuran, Ethers such as dioxolane, dimethoxyethane, diethoxyethane, methoxyethoxyethane, and nitriles such as acetonitrile and benzonitrile, phosphorus Examples thereof include phosphoric acid esters such as trimethyl acid and triethyl phosphate, and fluorine-containing phosphoric acid esters such as tris (2,2,2-trifluoroethyl) phosphate, or a mixture of two or more thereof. . Among these, it is particularly preferable from the viewpoint of electrolytic solution physical properties such as ion conductivity to use a solvent containing either one of cyclic carbonate and chain carbonate or a mixture of cyclic carbonate and chain carbonate. In particular, when the electrolytic solution is used under a high voltage condition of 4.3 V or higher, it is desirable from the viewpoint of the durability of the solvent to use a fluorine-containing phosphate ester for all or a part of the electrolytic solution.

  The nonaqueous electrolytic solution of the present invention can contain additives other than the fluorine-containing phosphate ester cyanoalkylamide of the present invention, if necessary. From the viewpoint of improving the cycle characteristics of the battery, it is preferable to contain compounds such as vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, and ethylene sulfite as additives. The concentration of the additive other than the phosphate ester cyanoalkylamide of the present invention is not particularly limited, but from the viewpoint of the solubility of the electrolyte, it is 0.1 to 10% by weight with respect to the total amount of the nonaqueous solvent with respect to the electrolyte solution. Desirably, it is preferably 0.5 to 5%.

As the electrolyte salt constituting the nonaqueous electrolytic solution of the present invention, lithium salt, sodium salt, magnesium salt, aluminum salt and the like that are stable in a wide potential region can be used depending on the type of electrochemical energy conversion device. Examples of the electrolyte salt include LiBF ₄ , LiPF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ). ₃ , NaPF ₆ , NaBF ₄ , NaClO ₄ and NaAsF ₆ , NaCF ₃ SO ₃ , NaN (CF ₃ SO ₂ ) ₂ , NaN (C ₂ F ₅ SO ₂ ) ₂ , NaC (CF ₃ SO ₂ ) ₃ , Mg ( ClO ₄ ) ₂ , Mg (CF ₃ SO ₃ ) ₂ , Mg (N (CF ₃ SO ₂ ) ₂ ) ₂ , Mg (ClO ₄ ) ₂ , MgBr ₂ , Mg (SO ₂ CF ₃ ) ₂ , Mg (BF _{4 ) 2, Mg (CF 3 SO} 3) 2, Mg (PF 6) 2, EtMgBr, Mg (AlCl 2 BuEt) 2, Al (CF 3 SO 3) 3 , and the like . These may be used alone or in combination of two or more. Among these electrolyte salts, as the electrolyte salt of the electrolyte solution for lithium secondary batteries or lithium ion secondary batteries in particular, when LiPF ₆ is used, high ion conductivity is easily obtained, and the fluorine-containing phosphate ester cyanoalkylamide is used. This is preferable because the problem of high temperature stability is also eliminated. In order to improve battery characteristics, it is desirable that the concentration of the electrolyte salt in the nonaqueous electrolytic solution be in the range of 0.1 to 2.5 mol / L.

<Non-aqueous secondary battery>
The non-aqueous secondary battery of the present invention is a generic name for secondary batteries that do not use an aqueous solution as the electrolyte in the secondary battery, and is not particularly limited. For example, a lithium secondary battery, a lithium ion secondary battery, sodium Secondary batteries, sodium ion secondary batteries, magnesium secondary batteries, magnesium ion secondary batteries, aluminum secondary batteries, aluminum ion secondary batteries, and the like can be given.

  The non-aqueous secondary battery of the present invention includes the non-aqueous electrolyte described above, a positive electrode, a negative electrode, and a separator.

The positive electrode material is not particularly limited as long as it has a positive electrode active material that absorbs and releases metals such as lithium, sodium, magnesium, and aluminum. For example, LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiFeO _2, LiFePO lithium composite oxide consisting of transition metals, such as _{4, NaFeO 2, NaNiO 2,} NaCoO 2, NaMnO 2, NaVO 2, Na (Ni X Mn (1-X)) O 2 (0 <X < _{1), Na (Fe X Mn} (1-X)) O 2 (0 <X <1), NaVPO 4 F, Na 2 FePO 4 F, Na 3 V 2 (PO 4) 3, fluorinated graphite ((CF ) n), manganese oxide such as manganese dioxide (MnO _2), vanadium pentoxide _(V 2 _{0 5)} vanadium oxides such as sulfur and vulcanization Compounds, magnesium copper oxide (Mg, Cu, Oz), magnesium iron oxide (Mg, Fe, Oz), and carbon materials such as activated carbon or the like.

The negative electrode material is not particularly limited as long as it has a negative electrode active material that occludes / releases metal such as lithium, sodium, magnesium, and aluminum. For example, metallic lithium and a carbon material capable of inserting / extracting lithium, Or lithium and transition metal composite oxides such as Li ₄ Ti ₅ O ₁₂ , sodium metal or alloys containing sodium, metal magnesium or alloys containing magnesium, metal aluminum, alloys containing aluminum, hard carbon, etc. Examples thereof include carbon materials.

As the separator, a microporous membrane or the like is used, and as a material, a polyolefin resin such as polyethylene or polypropylene, or a fluorine resin such as polyvinylidene fluoride is used.
As the shape and form of the nonaqueous electrolyte secondary battery, a cylindrical type, a square type, a coin type, a card type, a laminate type, and the like are usually selected.

EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these.
<Synthesis of fluorinated phosphate ester cyanoalkylamide>
[Example 1]
-Synthesis of bis (2,2,2-trifluoroethyl) diacetonitrile amide phosphate

  A four-necked flask equipped with a stirrer was charged with 1933 g of dichloromethane, 137 g of iminodiacetonitrile, and 218.8 g of triethylamine. 500 g of fert (purity 97%) was added dropwise over 3 hours. After completion of the dropping, heating and stirring were continued for 50 hours while controlling the reaction temperature at 45 ° C to 50 ° C. After completion of the reaction, 2000 g of 5% aqueous sodium hydrogen carbonate solution was added and stirred, and then the organic layer was separated. After distilling off dichloromethane from the organic layer, a fraction having a boiling point of 134 ° C./0.01 kPa was collected by distillation purification to obtain 362 g of a colorless liquid.

It was confirmed that the liquid obtained from NMR and GC-MS analysis was bis (2,2,2-trifluoroethyl) diacetonitrileamide phosphate.
¹ H-NMR (CDCl ₃ , TMS)
δ 4.37-4.46 (m, 4H), 4.14-4.16 (d, 4H)
¹⁹ F-NMR (CDCl ₃ , CFCl ₃ )
δ −75.60 (t, J = 9 Hz)
GC-MS (EI)
312, 293 (-F), 245, 225, 163, 94, 83
[Example 2]
-Synthesis of bis (2,2,2-trifluoroethyl) dipropionitrile amide phosphate

  A four-necked flask equipped with a stirrer was charged with 2130 g of chloroform, 266 g of iminodipropionitrile, and 238 g of triethylamine, and 1278 g of chloroform and bis (2, -2, -2, -trifluoroethyl) from a dropping funnel while stirring at room temperature. Chlorophosphate (purity 97%) 516 g was added dropwise over 3 hours. After completion of the dropwise addition, stirring was continued for 20 hours. After completion of the reaction, 3000 g of 5% aqueous sodium hydrogen carbonate solution was added and stirred, and then the organic layer was separated. After distilling off chloroform from the organic layer, a fraction having a boiling point of 160.8 ° C./0.01 kPa was fractionated by distillation purification to obtain 181 g of a colorless liquid.

It was confirmed that the liquid obtained from NMR and GC-MS analysis was bis (2,2,2-trifluoroethyl) dipropionitrileamide phosphate.
¹ H-NMR (CDCl ₃ , TMS)
δ 4.35 to 4.48 (m, 4H), 3.44 to 3.51 (m, 4H), 2.64 to 2.68 (t, 4H)
¹⁹ F-NMR (CDCl ₃ , CFCl ₃ )
δ −75.67 (t, J = 9 Hz)
GC-MS (EI)
367, 348 (-F), 327, 274, 246, 163, 83, 69, 54

<Physical properties of fluorine-containing phosphate ester cyanoalkylamide>
Example 3
○ Physical properties of bis (2,2,2-trifluoroethyl) diacetonitrileamide phosphate The flash point of bis (2,2,2-trifluoroethyl) diacetonitrileamide obtained in Example 1 is Measured with a flash point measuring device (RT-1 type, manufactured by Yoshida Scientific Instruments Co., Ltd.).
Moreover, the viscosity at 20 ° C. was measured using a cone plate viscometer (DV-1 PRIME type manufactured by BrookField).

  Moreover, the relative dielectric constant was measured under the following measurement conditions using an impedance analyzer (VersaSTAT4 manufactured by Toyo Technica, and electrode cell SR-C1 for liquid).

Measurement conditions: Measurement frequency 100kHz, temperature 25 ℃ ± 1 ℃
First, an empty cell (air) capacity (C-zero) was measured, and then the sample obtained in Example 1 (bis (2,2,2-trifluoroethyl) diacetonitrile amide phosphate) was filled in the electrode cell. Then, the relative dielectric constant was measured.

[Example 4, Comparative Examples 1-2]
For the fluorine-containing phosphoric ester amides of Example 4 and Comparative Examples 1 and 2 (compounds shown in Table 1), the flash point, viscosity, and relative dielectric constant were measured in the same manner as in Example 3.
The results are shown in Table 1.

  From Table 1, it can be seen that all of the fluorine-containing phosphate ester cyanoalkylamides of the present invention have no flash point and are nonflammable.

  Further, it can be seen that the fluorine-containing phosphoric acid ester cyanoalkylamide of the present invention has characteristics of high viscosity and high relative dielectric constant as compared with the conventional fluorine-containing phosphoric acid ester amides of Comparative Examples 1 and 2. .

<Measurement of oxidative decomposition potential of electrolyte>
Example 5
The electrochemical stability of the compounds was evaluated by linear sweep voltammetry (LSV) measurement.

The LSV was measured using a multichannel potentiostat / galvanostat (Biologic, VMP-3). Under an argon atmosphere, 5 ml of ethylene carbonate / ethyl methyl carbonate mixed solution (volume ratio: 3/7) was mixed with 5 ml of bis (2,2,2-trifluoroethyl) diacetonitrile amide phosphate to prepare a mixed solvent. . In this mixed solvent, lithium hexafluorophosphate (LiPF ₆ ) was dissolved so as to be 0.2 mol / L to obtain an electrolytic solution.

Into this electrolytic solution, platinum as a working electrode, lithium foil as a counter electrode, and lithium foil as a reference electrode were inserted, and the noble side was scanned at a scanning speed of 5 mV / sec to measure the oxidative decomposition potential. As a result, the potential when the current density exceeded 0.1 mA / cm ² was defined as the oxidative decomposition potential. All LSV measurements were performed in a glove box filled with an argon atmosphere.
[Example 6, Comparative Examples 3 to 5]
For Example 6 and Comparative Examples 3 to 5, the electrolytic solution was adjusted and the oxidative decomposition potential was measured in the same manner as in Example 5.

  Table 2 shows the types and amounts of additives such as fluorine-containing phosphoric ester amides used in Examples 5 to 6 and Comparative Examples 3 to 5, and the oxidative decomposition potential.

  From Comparative Example 3, it can be seen that EC / EMC undergoes oxidative decomposition at a potential of 6.42V. Further, the oxidative decomposition potential of bis (2,2,2-trifluoroethyl) dimethylamide phosphate, which is a conventional fluorine-containing phosphoric ester amide described in Comparative Example 4 and Comparative Example 5, is 4.87 V, phosphorus Whereas the oxidative decomposition potential of bis (2,2,2-trifluoroethyl) diethylamide is 4.81 V, the bisphosphate (Example 5) which is the fluorine-containing phosphate ester cyanoalkylamide of the present invention is used. The oxidative decomposition potential of 2,2,2-trifluoroethyl) diacetonitrileamide is 5.98 V, and the oxidative decomposition potential of bis (2,2,2-trifluoroethyl) dipropionitrileamide phosphate of Example 6 is 5. .45V. It can be seen that the fluorine-containing phosphoric ester cyanoalkylamide of the present invention is superior in oxidation resistance as compared with the conventional fluorine-containing phosphoric ester amide.

<< LiPF ₆ high temperature stability test >>
Example 7
In a glove box substituted with argon, put 3.8 g (25 mmol) of LiPF _{6 and} 1.55 g (4.6 mmol) of bis (2,2,2-trifluoroethyl) diacetonitrile amide in a 25 ml volumetric flask, While dissolving with a solvent in which ethylene carbonate (hereinafter abbreviated as EC) and ethyl methyl carbonate (hereinafter abbreviated as EMC) were mixed at a volume ratio of 3/7, the volume was adjusted to 25 ml to prepare a 1 mol / L LiPF ₆ solution. The resulting solution was clear and colorless.

This solution was placed in a glass sealed container and heated at 85 ° C. for 500 hours. After heating, the liquid turned pale yellow, and the peak of the LiPF ₆ decomposition product as measured by ¹⁹ F-NMR was 0.36% in terms of integral ratio with respect to the total of LiPF ₆ and decomposition product. The results are shown in Table 3.
Example 8
In a glove box substituted with argon, put 3.8 g (25 mmol) of LiPF _{6 and} 1.68 g (4.6 mmol) of bis (2,2,2-trifluoroethyl) dipropionitrile amide in a 25 ml volumetric flask. The solution was adjusted to 25 ml while dissolving with a solvent in which EC and EMC were mixed at a volume ratio of 3/7 to prepare a 1 mol / L LiPF ₆ solution. The resulting solution was clear and colorless.

This solution was placed in a glass sealed container and heated at 85 ° C. for 500 hours. After heating, the liquid turned pale yellow, and the peak of the LiPF ₆ decomposition product as measured by ¹⁹ F-NMR was 0.37% in terms of integral ratio with respect to the total of LiPF ₆ and decomposition product. The results are shown in Table 3.

[Comparative Example 6]
A 1 mol / L LiPF ₆ solution was prepared in the same manner as in Example 7 except that bis (2,2,2-trifluoroethyl) diacetonitrileamide phosphate was not used. The resulting solution was clear and colorless.

When this solution was put into a glass-made airtight container and heated at 85 ° C. for 500 hours in the same manner as in Example 7, a dark brown liquid was obtained. The peak of the LiPF ₆ decomposition product measured by 19F-NMR was 12.8% in terms of integral ratio with respect to the total of LiPF 6 and the decomposition product. The results are shown in Table 3.
(Examples 7 to 8 and Comparative Example 6)
The solutions to which the fluorine-containing phosphoric ester cyanoalkylamides of the present invention of Examples 7 to 8 were added were all decomposed after heating compared to the solution of Comparative Example 6 in which the phosphoric ester cyanoalkylamide was not added. It can be seen that the rate is low. It was shown that the high temperature stabilization effect of LiPF6 of the fluorine-containing phosphate ester cyanoalkylamide of the present invention is high.

《Battery charge / discharge test》
Example 1 Preparation of Coin Cell Type Lithium Secondary Battery Lithium cobaltate (LiNi _1/3 Mn _1/3 Co _1/3 O ₂ ) is used as a positive electrode active material, acetylene black is used as a conductive aid, and polyvinylidene fluoride (PVDF is used as a binder). ) LiNi _1/3 Mn _1/3 Co _1/3 O ₂ : Acetylene black: PVDF = 86: 7: 7 Blended so as to be slurried with 1-methyl-2-pyrrolidone made of aluminum The positive electrode was obtained by applying a constant film thickness on the current collector and drying it. Natural negative graphite is used as a negative electrode active material, PVDF is blended as a binder so that graphite: PVDF = 9: 1, and slurried using 1-methyl-2-pyrrolidone is placed on a copper current collector. It apply | coated with the fixed film thickness, it was made to dry and the negative electrode was obtained. As the separator, an inorganic filler-containing polyolefin porous membrane was used. Using the above components, a lithium secondary battery using a coin-type cell having the structure shown in FIG. 1 was produced. In the lithium secondary battery, a positive electrode 1 and a negative electrode 5 are disposed opposite to each other with a separator 8 interposed therebetween, a stainless steel plate spring 7 is installed on a negative electrode stainless steel cap 4, and a laminate including the negative electrode 5, the separator 8, and the positive electrode 1 is coin-shaped. Stored in the cell. After injecting a non-aqueous electrolyte into this laminate, the gasket 9 was placed, then the cap 3 made of positive stainless steel was put on, and the coin-type cell case was crimped.
Test Example 1 Charge / Discharge Test of Coin Cell Type Lithium Secondary Battery A coin cell type lithium secondary battery prepared with a lithium nickel manganese composite oxide (LiNi _1/3 Mn _1/3 Co _1/3 O ₂ ) positive electrode and a carbon negative electrode is kept at 25 ° C. Under the conditions, the battery was charged with an upper limit voltage of 4.4 V with a charging current of 0.1 C, and then discharged to 3.0 V with a discharging current of 0.1 C. After performing this operation three times, a constant current-constant voltage charge of 4.4V is performed with a charging current of 0.2C under a constant temperature condition of 60 ° C., and a constant current up to a final voltage of 3.0V with a discharging current of 0.2C. Discharge was performed. The discharge capacity at this time was used as the initial discharge capacity, the discharge capacity when this operation was repeated 20 times was measured, and the comparison was made using the discharge capacity / initial discharge capacity ratio after 20 cycles as the capacity retention rate.
Test Example 2 Charge / Discharge Test of Coin Cell Type Lithium Secondary Battery A coin cell type lithium secondary battery prepared with a lithium nickel manganese composite oxide (LiNi _1/3 Mn _1/3 Co _1/3 O ₂ ) positive electrode and a carbon negative electrode is kept at 25 ° C. Under the conditions, the battery was charged with an upper limit voltage of 4.4 V with a charging current of 0.1 C, and then discharged to 3.0 V with a discharging current of 0.1 C. After performing this operation three times, under a constant temperature condition of 25 ° C., a constant current-constant voltage charge of 4.4 V is performed with a charge current of 0.2 C, and a constant current is reached to a final voltage of 3.0 V with a discharge current of 0.2 C. Discharge was performed. The discharge capacity at this time was used as the initial discharge capacity, the discharge capacity when this operation was repeated 20 times was measured, and the comparison was made using the discharge capacity / initial discharge capacity ratio after 20 cycles as the capacity retention rate.

Example 9
Ethylene carbonate (hereinafter abbreviated as EC) and tris phosphate (2,2,2-trifluoroethyl) (hereinafter abbreviated as TFEP) as a solvent were mixed at a weight ratio of 1: 1. The acid bis (2,2,2-trifluoroethyl) diacetonitrile amide was added at 2% by weight. Next, a nonaqueous electrolytic solution was prepared by dissolving lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte salt at a concentration of 1.0 mol / L.

Using this non-aqueous electrolyte, a coin cell type lithium secondary battery was prepared according to Preparation Example 1, and a 20-cycle charge / discharge test was performed according to Test Example 1. The results are shown in Table 4.
Example 10
A non-aqueous electrolyte was prepared in the same manner as in Example 9, a coin cell type lithium secondary battery was prepared in the same manner as in Example 9, and a 20-cycle charge / discharge test was performed according to Test Example 2. The results are shown in Table 4.
[Comparative Example 7]
A nonaqueous electrolytic solution was prepared in the same manner as in Example 9 except that bis (2,2,2-trifluoroethyl) dimethylamide phosphate was added as a fluorine-containing phosphoric ester amide compound. A coin cell type lithium secondary battery was prepared in the same manner as described above, and a charge / discharge test was performed. The results are shown in Table 4.
[Comparative Example 8]
A non-aqueous electrolyte solution was prepared in the same manner as in Example 9, except that bis (2,2,2-trifluoroethyl) diacetonitrileamide phosphate was not added. Type lithium secondary battery was prepared and a charge / discharge test was conducted. The results are shown in Table 4.
[Comparative Example 9]
A non-aqueous electrolyte solution was prepared in the same manner as in Example 10 except that bis (2,2,2-trifluoroethyl) diacetonitrileamide phosphate was not added. Type lithium secondary battery was prepared and a charge / discharge test was conducted. The results are shown in Table 4.

From Table 4, the EC-TFEP mixed solvent was used as the non-aqueous solvent, and among the results under the charge / discharge conditions at a test temperature of 60 ° C. and 4.4 V, the non-containing solvent containing the fluorine-containing phosphate ester cyanoalkylamide of the present invention. In Example 9 using an aqueous electrolyte, Comparative Example 7 in which a fluorinated phosphoric acid ester dimethylamide was added instead of the fluorinated phosphoric acid ester cyanoalkylamide, and Comparative Example 8 which did not contain a fluorinated phosphoric acid ester cyanoalkylamide The capacity maintenance rate was higher than This is presumed to be due to the fact that the fluorine-containing phosphate ester cyanoalkylamide of the present invention contributed to the thermal decomposition of LiPF ₆ and the accompanying suppression of the decomposition of the electrolyte solvent without oxidative decomposition at this voltage. Is done.

  On the other hand, Example 10 and Comparative Example 9 are tests at room temperature, but here, Example 10 containing the fluorine-containing phosphate ester cyanoalkylamide of the present invention is also a comparison not containing the fluorine-containing phosphate ester cyanoalkylamide. Compared to Example 9, the capacity retention rate was higher. Although this factor is unknown, a cyano group in the molecule of the fluorine-containing phosphate ester cyanoalkylamide acts on the positive electrode active material to form a kind of film that prevents decomposition of the electrolyte solution on the positive electrode surface. It is inferred that the cycle characteristics were improved by suppressing the decomposition of the electrolytic solution on the surface.

  The fluorine-containing phosphoric acid ester cyanoalkylamide of the present invention has an electrolyte decomposition inhibiting effect and can be used under high voltage conditions, and is stable at high temperature containing the fluorine-containing phosphoric acid ester cyanoalkylamide. This is extremely useful because it can provide a non-aqueous electrolyte excellent in the charge and discharge cycle characteristics under a high voltage condition of 4.3 V or higher.

DESCRIPTION OF SYMBOLS 1 Positive electrode active material 2 Positive electrode collector 3 Positive electrode stainless steel cap 4 Negative electrode stainless steel cap 5 Negative electrode material 6 Negative electrode current collector 7 Stainless steel leaf spring 8 Inorganic filler containing polyolefin porous separator 9 Gasket

Claims (5)

The following general formula (2)

(In the formula, R ^{1 ′} and R ^{2 ′} are the same or non-identical, and represent a linear or branched alkyl group having 1 to 6 carbon atoms. However, R ^{1 ′} and R ^{2 ′} are both cyano groups ( -CN) and may be further substituted by a fluorine atom, Rf ¹ and Rf ² are the same or non-identical, and a linear or branched alkyl group or fluorine-containing alkyl group having 1 to 6 carbon atoms. the stands, at least one is a fluorine-containing alkyl group. fluorinated phosphate ester cyanoalkyl amides you express in). The following general formula (3)

(In the formula, R ^{1 ′} and R ^{2 ′} are the same as defined above. Rf ^{1 ′} and Rf ^{2 ′} are each independently a trifluoromethyl group, a 2-fluoroethyl group, or a 2,2-difluoroethyl group. Group, 2,2,2-trifluoroethyl group, 2,2,3,3-tetrafluoropropyl group, 2,2,3,3,3-pentafluoropropyl group, hexafluoroisopropyl group The fluorine-containing phosphate ester cyanoalkylamide according to claim 1 , which is represented by: A nonaqueous electrolytic solution comprising a nonaqueous solvent and an electrolyte salt, wherein the nonaqueous electrolytic solution comprises the fluorine-containing phosphate ester cyanoalkylamide according to claim 1 or 2 . The nonaqueous electrolytic solution according to claim 3 , wherein the electrolyte salt is LiPF ₆ . A non-aqueous secondary battery comprising a negative electrode, a positive electrode, a separator, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte is the non-aqueous electrolyte according to claim 3 or 4 .