JP2007305352A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery having high fire retardancy of an electrolyte and excellent high rate discharge characteristics. <P>SOLUTION: In the nonaqueous electrolyte secondary battery equipped with a positive electrode, a negative electrode, and a nonaqueous electrolyte, the nonaqueous electrolyte contains a fluorinated chain carbonate compound in which a methylene group is adjoined to a carbonate group, and having -CHF<SB>2</SB>at a molecule chain end; a cyclic carbonate compound having C-C π-bonding; and a cyclic compound having S=O bonding. A ratio of the fluorinated carbonate in an electrolyte solvent is ≥20 wt.%. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to improvement of a non-aqueous electrolyte solution of a non-aqueous electrolyte secondary battery.

  In recent years, non-aqueous electrolyte secondary batteries have attracted attention as power sources for portable devices such as mobile phones, PHS (simple mobile phones) and small computers, power storage power sources, and electric vehicle power sources.

  A nonaqueous electrolyte secondary battery generally includes a positive electrode, a negative electrode, and a nonaqueous electrolyte, the positive electrode includes a positive electrode active material, the negative electrode includes a negative electrode active material, and includes a nonaqueous solvent and a lithium salt. And a non-aqueous electrolyte.

Lithium-containing transition metal oxide is used as the positive electrode active material constituting the non-aqueous electrolyte secondary battery, carbon material typified by graphite as the negative electrode active material, and ethylene carbonate as the non-aqueous electrolyte. A solution in which an electrolyte such as lithium hexafluorophosphate (LiPF ₆ ) is dissolved in a nonaqueous solvent is widely known. These nonaqueous solvents are generally classified as flammable substances because they are easily volatile and have flammability.

  Therefore, the use of non-aqueous electrolytes that do not pose a risk of flammability is particularly desired for applications of relatively large non-aqueous electrolyte secondary batteries such as power storage power sources and electric vehicle power sources. In recent years, a technique using a non-aqueous electrolyte having flammability has attracted attention.

  In order to realize a non-aqueous electrolyte having flame retardancy, a technology for adding a fluorinated carbonate compound, which is a high flash point solvent, flame retardancy, and is less susceptible to oxidation and reduction electrochemically, has been studied. 1-3.

  In Patent Document 4, the non-aqueous solvent is selected from the group consisting of a fluorine-containing aromatic compound having 9 or less carbon atoms, an aliphatic hydrocarbon, and a fluorine-containing aliphatic hydrocarbon compound that is stable against oxidation and reduction. By containing at least one kind of compound, these compounds become active sites on the surfaces of the positive electrode and the negative electrode, which were insufficiently suppressed only by the cyclic carbonate or acid anhydride having an unsaturated bond and the sulfur-containing organic compound. Suppresses side reactions of cyclic carbonates or acid anhydrides having unsaturated bonds, sulfur-containing organic compounds, and other electrolyte components, and as a whole, side reactions that occur inside the battery during high-temperature storage. A non-aqueous electrolyte secondary battery that can suppress and improve large current discharge characteristics is disclosed.

  Furthermore, in patent document 5, by containing the compound (overcharge inhibitor) which reacts with the voltage more than the maximum operating voltage of a battery at the time of overcharge, such as biphenyl and alkylbiphenyl, in a nonaqueous solvent, A non-aqueous electrolyte secondary battery capable of securing a safety and producing a battery having a high capacity and excellent storage characteristics, load characteristics, and cycle characteristics is disclosed.

Patent Documents 4 and 5 disclose techniques for containing a cyclic carbonate having an unsaturated bond and a sulfur-containing organic compound in a non-aqueous solvent in a non-aqueous electrolyte secondary battery. The content of the cyclic carbonate having an unsaturated bond is preferably 0.01 to 5% by weight, the content of the sulfur-containing organic compound is preferably 0.01 to 5% by weight, and further, in the non-aqueous solvent. When 0.1 to 5% by weight of fluorinated carbonate such as fluoroethylene carbonate and trifluoropropylene carbonate is contained, the capacity retention characteristics and cycle characteristics may be better than when they are not contained. Are listed.
JP-A-10-116629 JP-A-10-116630 JP-A-11-307120 JP 2003-331915 A JP 2003-338317 A

  However, in order for the non-aqueous electrolyte proposed in Patent Documents 1 to 3 to exhibit sufficient flame retardancy, a large amount of fluorinated carbonate compound (for example, 35 to 70% by volume according to Patent Document 3). Since it is necessary to add, there has been a problem that sufficient battery characteristics such as high rate discharge characteristics cannot be obtained. Also, depending on the fluorinated carbonate compound, the solubility in lithium salts and other organic solvents constituting the non-aqueous electrolyte is low, and it cannot be added in a large amount, so that the non-aqueous electrolyte cannot exhibit sufficient flame retardancy. There was a problem.

  In addition, the technique of adding 0.01 to 5% by weight of the fluorinated carbonate compound in the non-aqueous solvent disclosed in Patent Document 4 and Patent Document 5 is not intended to make the electrolyte solution flame-retardant. There was a problem that the obtained electrolyte did not exhibit flame retardancy and self-extinguishing properties.

  The present invention has been made in view of the above-mentioned problems, and its object is a non-aqueous electrolyte secondary battery having excellent electrolyte flame retardancy and good high rate discharge characteristics. Is to provide.

  In order to solve the above-mentioned problems, the present inventors have surprisingly made it difficult to make an excellent electrolyte solution by making a specific configuration of the non-aqueous solvent constituting the non-aqueous electrolyte solution as a result of intensive studies. The present inventors have found that a nonaqueous electrolyte secondary battery having flammability and having a high energy density and good high rate discharge characteristics can be obtained.

The invention of claim 1 is a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte has a carbonate group and a methylene group adjacent to each other and —CHF at the molecular chain end. _{It includes} a fluorinated chain carbonate compound having ₂ ; a cyclic carbonate compound having a carbon-carbon π bond; and a cyclic compound having an S═O bond.

According to the invention of claim 1, the non-aqueous electrolyte contains a fluorinated chain carbonate compound, whereby the flash point of the non-aqueous electrolyte rises or disappears, and the non-aqueous electrolyte is flame retardant or self-extinguishing. Will come to show. In addition, since the molecular chain terminal of the fluorinated chain carbonate compound is CF ₂ H, it is possible to maintain high solubility in lithium salts and other organic solvents constituting the non-aqueous electrolyte solution. A non-aqueous electrolyte secondary battery that can maintain good battery characteristics even when added in large quantities, is excellent in safety, and has good high-rate discharge characteristics. Can be provided.

  Furthermore, by simultaneously containing a carbonate compound having a carbon-carbon π bond and a cyclic compound having an S═O bond, these compounds are decomposed on the negative electrode during the initial charge, and the lithium ion permeability is excellent on the negative electrode surface. Therefore, the decomposition of other organic solvents constituting the non-aqueous electrolyte can be more effectively suppressed. Therefore, a non-aqueous electrolyte secondary battery having high charge / discharge efficiency, high energy density, and excellent high rate discharge characteristics can be obtained.

  According to a second aspect of the present invention, in the nonaqueous electrolyte secondary battery according to the first aspect, the proportion of the fluorinated chain carbonate compound in the electrolytic solution solvent is 20% by weight or more.

  According to the invention of claim 2, by setting the ratio of the fluorinated chain carbonate compound in the electrolytic solution solvent to 20% by weight or more, the flame retardancy of the electrolytic solution is increased, and the organic solvent is decomposed at the time of initial charge. It can be suppressed almost completely.

  The invention according to claim 3 is the nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the total of the cyclic carbonate compound having a carbon-carbon π bond and the cyclic compound having an S═O bond in the electrolyte solvent The ratio is 1% by weight or more and 20% by weight or less.

  According to the invention of claim 3, the total ratio of the carbonate compound having a carbon-carbon π bond and the cyclic compound having an S═O bond in the electrolyte solvent is 1 wt% or more and 20 wt% or less. A dense lithium ion-permeable protective coating is formed on the negative electrode surface.

  According to the non-aqueous electrolyte secondary battery of the present invention, it is possible to obtain a non-aqueous electrolyte secondary battery that is excellent in safety and has high energy density and excellent high rate discharge characteristics.

  Embodiments of the present invention are illustrated below, but the present invention is not limited to these descriptions. Moreover, although the technical structure of this invention and its effect are as follows, about an action mechanism, presumption is included and the right or wrong does not restrict | limit this invention.

The present invention relates to a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte has a carbonate group adjacent to a methylene group and a molecular chain terminal having —CHF ₂ . It includes a fluorinated chain carbonate compound, a cyclic carbonate compound having a carbon-carbon π bond, and a cyclic compound having an S═O bond.

  In the present invention, the fluorinated chain carbonate compound is, for example, a compound represented by the following general formula (1).

なお、一般式（１）において、ｘ、ｙはそれぞれ０〜２の整数であり、ｍ、ｎはそれぞれ０〜７の整数とする。ｍ、ｎを０〜７の整数とすることにより、電解液の粘度を低く保つことができ、良好な電池性能が得られる。また、（ＣＦ_ｘＨ_２−ｘ）_ｍおよび（ＣＦ_ｙＨ_２−ｙ）_ｎは直鎖または分岐のどちらの構造でもよい。

In the general formula (1), x and y are each an integer of 0 to 2, and m and n are each an integer of 0 to 7. By setting m and n to integers of 0 to 7, the viscosity of the electrolytic solution can be kept low, and good battery performance can be obtained. Further, (CF _x H _2−x ) _m and (CF _y H _2−y ) _n may have a linear or branched structure.

According to the present invention, by using a fluorinated chain carbonate compound having a methylene group adjacent to a carbonate group and having —CHF ₂ at the molecular chain terminal, a good battery can be obtained even when added in a large amount to a non-aqueous electrolyte. The characteristics can be maintained, and a non-aqueous electrolyte battery excellent in safety can be obtained.

  Furthermore, by containing both a cyclic carbonate compound having a carbon-carbon π bond and a cyclic compound having an S═O bond in the non-aqueous electrolyte, a lithium ion-permeable protective coating is formed on the negative electrode surface during initial charging. Therefore, the decomposition of other organic solvents including the fluorinated chain carbonate compound constituting the non-aqueous electrolyte can be reliably suppressed, so that the second and subsequent cycles can be sufficiently charged and discharged. The charge / discharge efficiency can be improved.

  Examples of the fluorinated chain carbonate compound used in the present invention include di (2,2-difluoroethyl) carbonate, di (2,2,3,3-tetrafluoropropyl) carbonate, di (2,2,3). , 3,4,4-hexafluorobutyl) carbonate, di (1H, 1H, 7H-dodecafluoroheptyl) carbonate, di (1H, 1H, 3H, 7H-perfluoroheptyl) carbonate, di (1H, 1H , 9H-hexadecafluorononyl) carbonate or the like, or a mixture of two or more thereof, but is not limited thereto.

  Among these, di (2,2-difluoroethyl) carbonate, di (2,2,3,3-tetrafluoropropyl) carbonate, di (2,2,3,3,4,4-hexafluoro Particularly preferred is at least one selected from butyl) carbonate and di (2,2-difluoroethyl) carbonate. The reason for this is that these compounds have a relatively low viscosity, so that when mixed in large quantities, the non-aqueous solution reliably combines excellent electrolyte flame retardancy and excellent high rate discharge characteristics. It can be set as an electrolyte secondary battery.

  The ratio of the fluorinated chain carbonate compound in the electrolyte solvent in the present invention is preferably 20% by weight or more. In order to obtain particularly excellent flame retardancy and high rate discharge characteristics of the electrolyte, 20 More preferably, it is at least 50% by weight. By setting the ratio of the fluorinated chain carbonate compound in the electrolytic solution solvent to 20% by weight or more, the flame retardancy of the electrolytic solution can be ensured. If the proportion of the fluorinated chain carbonate compound in the electrolyte solvent exceeds 50% by weight, the solubility of the lithium salt is lowered, and the battery performance may be lowered.

  The cyclic carbonate compound having a carbon-carbon π bond used in the present invention is at least one selected from vinylene carbonate, styrene carbonate, catechol carbonate, vinyl ethylene carbonate, 1-phenyl vinylene carbonate, and 1,2-diphenyl vinylene carbonate. Preferably there is.

  The cyclic compound having an S═O bond used in the present invention is at least one selected from ethylene sulfite, propylene sulfite, sulfolane, sulfolene, 1,3-propane sultone, 1,4-butane sultone, and derivatives thereof. It is preferable that

  Lithium ion-permeable protective coating formed on the surface of the negative electrode at the time of initial charge when the cyclic carbonate compound having a carbon-carbon π bond and the cyclic compound having an S═O bond are at least one selected from these compounds However, since it is denser and has superior lithium ion permeability, decomposition of other organic solvents constituting the non-aqueous electrolyte can be more effectively suppressed, and charge and discharge after the second cycle are sufficient. The charge / discharge efficiency can be improved, and a non-aqueous electrolyte secondary battery having high energy density and excellent high rate discharge characteristics can be obtained.

  In the present invention, the total proportion of the cyclic carbonate compound having a carbon-carbon π bond and the cyclic compound having an S═O bond in the electrolyte solution solvent is preferably 1% by weight or more and 20% by weight or less.

  By this, decomposition | disassembly of the other organic solvent which comprises the nonaqueous electrolyte at the time of first charge can be suppressed almost completely, and charge after the 2nd cycle can be performed more reliably. In addition, when the content is 20% by weight or less, the battery performance is almost deteriorated due to decomposition of the excessively contained cyclic carbonate compound having a carbon-carbon π bond or cyclic compound having an S═O bond on the positive electrode. Thus, a non-aqueous electrolyte battery having high energy density and excellent high rate discharge characteristics can be obtained.

  In addition, although the ratio of content of the cyclic carbonate compound having a carbon-carbon π bond and the cyclic compound having an S═O bond can be arbitrarily selected, it is preferably about 1: 1 by weight.

  In addition to the fluorinated chain carbonate compound, the cyclic carbonate compound having a carbon-carbon π bond, and the cyclic compound having an S═O bond, the organic solvent constituting the nonaqueous electrolyte is generally a nonaqueous electrolyte secondary solution. The organic solvent used for the non-aqueous electrolyte for batteries can be used.

  For example, cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, cyclic esters such as γ-butyrolactone, γ-valerolactone, propiolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, diphenyl carbonate, etc. Chain esters such as chain carbonate, methyl acetate, methyl butyrate, tetrahydrofuran or derivatives thereof, ethers such as 1,3-dioxane, dimethoxyethane, diethoxyethane, methoxyethoxyethane, methyldiglyme, acetonitrile, benzonitrile, etc. These nitriles, dioxalane or derivatives thereof may be used alone or as a mixture of two or more thereof, but are not limited thereto.

As the lithium salt constituting the non-aqueous electrolyte, a lithium salt that is stable in a wide potential region generally used for a non-aqueous electrolyte secondary battery can be used. For example, LiBF ₄ , LiPF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) _{3 and the} like, but are not limited thereto. These may be used alone or in combination of two or more.

  The concentration of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 mol / l to 5 mol / l, more preferably 1 mol / l in order to reliably obtain a non-aqueous electrolyte battery having excellent high rate discharge characteristics. 1 to 2.5 mol / l.

Examples of the positive electrode material used in the non-aqueous electrolyte secondary battery of the present invention include lithium manganate (LiMn ₂ O ₄ ), lithium cobaltate (LiCoO ₂ ), and lithium nickelate (LiNiO ₂ ) capable of inserting and extracting lithium. Lithium composite oxides that can occlude and release lithium, and lithium composite oxides in which the transition metal part of the above-mentioned various composite oxides is partially substituted with other transition metals or light metals to improve performance. It is done.

  In addition, as negative electrode materials, carbon materials such as natural graphite, artificial graphite, coke, non-graphitizable carbon, low-temperature calcinable graphitizable carbon, fullerene, carbon nanotube, carbon black, activated carbon, etc., capable of inserting and extracting lithium Is mentioned.

  As the separator used in the non-aqueous electrolyte secondary battery of the present invention, a microporous membrane mainly composed of a polyolefin resin such as polyethylene or polypropylene is used, and a plurality of microporous materials having different materials, weight average molecular weights and porosity are used. Those obtained by laminating films, or those containing a suitable amount of various plasticizers, antioxidants, flame retardants and the like in these microporous films may be used.

  Other battery components include a current collector, a terminal, an insulating plate, a battery case, and the like. However, these components may be used as they are.

  Hereinafter, although the further detail of this invention is demonstrated by an Example, this invention is not limited to these description.

[Examples 1 to 13 and Comparative Examples 1 to 5]
[Example 1]
A cross section of the non-aqueous electrolyte secondary battery of the present invention is shown in FIG. In FIG. 1, symbol 1 is a positive electrode, 2 is a negative electrode, 3 is a separator, 4 is an electrode group, 5 is a metal resin composite film, 11 is a positive electrode mixture, 12 is a positive electrode current collector, 21 is a negative electrode mixture, and 22 is It is a negative electrode current collector.

  The non-aqueous electrolyte secondary battery of the present invention is composed of an electrode group 4 including a positive electrode 1, a negative electrode 2, and a separator 3, a non-aqueous electrolyte (not shown), and a metal resin composite film 5. The positive electrode 1 is obtained by applying a positive electrode mixture 11 on a positive electrode current collector 12. The negative electrode 2 is obtained by applying a negative electrode mixture 21 on a negative electrode current collector 22. The non-aqueous electrolyte is impregnated in the electrode group 4. The metal resin composite film 5 covers the pole group 4 and is sealed on all four sides by heat welding.

Next, a method for manufacturing a nonaqueous electrolyte secondary battery will be described. The positive electrode 1 was obtained as follows. First, LiCoO ₂ and acetylene black, which is a conductive agent, are mixed, and a N-methyl-2-pyrrolidone (NMP) solution of polyvinylidene fluoride is further mixed as a binder, and this mixture is a positive electrode current collector made of an aluminum foil. After apply | coating to the single side | surface of the body 12, it dried and pressed so that the thickness of the positive mix 11 might be set to 0.09 mm.

  Moreover, the negative electrode 2 was obtained as follows. First, graphite, which is a negative electrode active material, and an aqueous solution of carboxymethyl cellulose (CMC), which is a binder, and styrene butadiene rubber (SMR) are mixed, and this mixture is applied to one side of a negative electrode current collector 22 made of copper foil. Then, it dried and pressed so that the negative mix 21 might be set to 0.08 mm.

  On the other hand, a polyethylene microporous film (thickness: 25 μm, porosity: 50%) was used for the separator 3. And the pole group 4 was comprised by making the positive electrode mixture 11 and the negative electrode mixture 21 oppose, arranging the separator 3 between them, and laminating | stacking the positive electrode 1, the separator 3, and the negative electrode 2 in order.

The non-aqueous electrolyte was prepared as follows. First, a mixed solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 1: 1 was prepared. Next, the mixed solvent of EC and DEC, di (2,2,3,3-tetrafluoropropyl) carbonate (TFPC), vinylene carbonate (VC), and 1,3-propane sultone (PS) are mixed in a weight ratio. It mixed so that it might become 86: 10: 2: 2. LiPF ₆ was dissolved in the mixed solvent containing the obtained EC, DEC, TFPC, VC and PS so as to be 1 mol / L.

In this way, EC, DEC, TFPC, VC and PS are included as non-aqueous solvents, the concentration of LiPF ₆ is 1 mol / l, and the proportion of the electrolyte solvent is TFPC 10 wt%, VC 2 wt%, PS 2 wt. % Non-aqueous electrolyte was obtained. This is designated as non-aqueous electrolyte a.

  Next, the electrode group 4 is immersed in the non-aqueous electrolyte solution a, the electrode group 4 is impregnated with the non-aqueous electrolyte solution, and the electrode group 4 is covered with the metal resin composite film 5, and the four sides thereof are thermally welded. Sealed. The battery with the designed capacity of 30 mAh thus produced is referred to as non-aqueous electrolyte secondary battery A of Example 1.

[Example 2]
Nonaqueous electrolysis that includes EC, DEC, TFPC, VC and PS as nonaqueous solvents, the concentration of LiPF ₆ is 1 mol / l, and the proportion of the electrolyte solvent is 20% by weight of TFPC, 2% by weight of VC, and 2% by weight of PS A liquid was obtained. This is designated as non-aqueous electrolyte b.

  A nonaqueous electrolyte secondary battery B of Example 2 was produced in the same manner as Example 1 except that the nonaqueous electrolyte b was used.

[Example 3]
Nonaqueous electrolysis that includes EC, DEC, TFPC, VC and PS as nonaqueous solvents, the concentration of LiPF ₆ is 1 mol / l, and the proportion of the electrolyte solvent is 50% by weight of TFPC, 2% by weight of VC, and 2% by weight of PS A liquid was obtained. This is designated as non-aqueous electrolyte c.

  A nonaqueous electrolyte secondary battery C of Example 3 was produced in the same manner as Example 1 except that the nonaqueous electrolyte c was used.

[Example 4]
Nonaqueous electrolysis that includes EC, DEC, TFPC, VC and PS as nonaqueous solvents, the concentration of LiPF ₆ is 1 mol / l, and the proportion of the electrolyte solvent is 70% by weight of TFPC, 2% by weight of VC, and 2% by weight of PS A liquid was obtained. This is designated as non-aqueous electrolyte d.

  A nonaqueous electrolyte secondary battery D of Example 4 was produced in the same manner as in Example 1 except that the nonaqueous electrolyte d was used.

[Example 5]
EC, DEC, TFPC, VC and PS are included as non-aqueous solvents, the concentration of LiPF ₆ is 1 mol / l, and the proportion of the electrolyte solvent is 50% by weight of TFPC, 0.5% by weight of VC, and 0.5% by weight of PS. A non-aqueous electrolyte was obtained. This is designated as a non-aqueous electrolyte e.

  A nonaqueous electrolyte secondary battery E of Example 5 was produced in the same manner as Example 1 except that the nonaqueous electrolyte e was used.

[Example 6]
Nonaqueous electrolysis that includes EC, DEC, TFPC, VC and PS as nonaqueous solvents, the concentration of LiPF ₆ is 1 mol / l, and the proportion of the electrolyte solution is 50% by weight of TFPC, 10% by weight of VC, and 10% by weight of PS. A liquid was obtained. This is designated as non-aqueous electrolyte f.

  A nonaqueous electrolyte secondary battery F of Example 6 was produced in the same manner as in Example 1 except that the nonaqueous electrolyte f was used.

[Example 7]
Di (2,2-difluoroethyl) carbonate (DFEC) is used in place of TFPC, EC, DEC, DFEC, VC and PS are included as non-aqueous solvents, the concentration of LiPF ₆ is 1 mol / l, and the electrolyte solvent A non-aqueous electrolyte having a proportion of 20% by weight of DFEC, 2% by weight of VC, and 2% by weight of PS was obtained. This is designated as non-aqueous electrolyte g.

  A nonaqueous electrolyte secondary battery G of Example 7 was produced in the same manner as Example 1 except that the nonaqueous electrolyte solution g was used.

[Example 8]
Styrene carbonate (SC) is used instead of VC, sulfolane (SF) is used instead of PS, EC, DEC, DFEC, SC and SF are included as non-aqueous solvents, and the concentration of LiPF ₆ is 1 mol / l. A nonaqueous electrolytic solution having a ratio of 20% by weight of DFEC, 2% by weight of SC, and 2% by weight of SF was obtained. This is designated as a non-aqueous electrolyte h.

  A nonaqueous electrolyte secondary battery H of Example 8 was produced in the same manner as Example 1, except that the nonaqueous electrolyte h was used.

[Example 9]
Di (2,2,3,3,4,4-hexafluorobutyl) carbonate (HFBC) instead of TFPC, vinyl ethylene carbonate (VEC) instead of VC, and ethylene sulfite (ES) instead of PS Non-aqueous solvent containing EC, DEC, HFBC, VEC and ES as the non-aqueous solvent, the concentration of LiPF ₆ is 1 mol / l, and the proportion of the electrolyte solvent is 20% by weight, 2% by weight of VEC, and 2% by weight of ES An electrolytic solution was obtained. This is designated as non-aqueous electrolyte i.

  A nonaqueous electrolyte secondary battery I of Example 9 was produced in the same manner as in Example 1 except that the nonaqueous electrolyte i was used.

[Example 10]
EC, DEC, TFPC, VC and PS are included as non-aqueous solvents, the concentration of LiPF ₆ is 1 mol / l, and the proportion of the electrolyte solvent is 20% by weight of TFPC, 0.5% by weight of VC, and 0.3% by weight of PS. A non-aqueous electrolyte was obtained. This is designated as non-aqueous electrolyte j.

  A nonaqueous electrolyte secondary battery J of Example 10 was produced in the same manner as in Example 1 except that the nonaqueous electrolyte j was used.

[Example 11]
EC, DEC, TFPC, VC and PS are included as non-aqueous solvents, the concentration of LiPF ₆ is 1 mol / l, and the proportion of the electrolyte solvent is 20% by weight of TFPC, 0.3% by weight of VC, and 0.5% by weight of PS. A non-aqueous electrolyte was obtained. This is designated as non-aqueous electrolyte k.

  A nonaqueous electrolyte secondary battery K of Example 11 was produced in the same manner as Example 1 except that the nonaqueous electrolyte k was used.

[Example 12]
Nonaqueous electrolysis that includes EC, DEC, TFPC, VC and PS as nonaqueous solvents, the concentration of LiPF ₆ is 1 mol / l, and the proportion of the electrolyte solvent is 20% by weight of TFPC, 15% by weight of VC, and 10% by weight of PS. A liquid was obtained. This is designated as non-aqueous electrolyte 1.

  A nonaqueous electrolyte secondary battery L of Example 12 was produced in the same manner as Example 1 except that the nonaqueous electrolyte solution l was used.

[Example 13]
Nonaqueous electrolysis that includes EC, DEC, TFPC, VC and PS as nonaqueous solvents, the concentration of LiPF ₆ is 1 mol / l, and the proportion of the electrolyte solution solvent is 20% by weight of TFPC, 10% by weight of VC, and 15% by weight of PS. A liquid was obtained. This is designated as non-aqueous electrolyte m.

  A nonaqueous electrolyte secondary battery M of Example 13 was produced in the same manner as Example 1 except that the nonaqueous electrolyte m was used.

[Comparative Example 1]
A non-aqueous electrolyte solution containing EC, DEC and TFPC as the non-aqueous solvent, the LiPF ₆ concentration being 1 mol / l, and the proportion of the electrolyte solvent being TFPC was 20% by weight was obtained. This is designated as non-aqueous electrolyte n.

  A nonaqueous electrolyte secondary battery N of Comparative Example 1 was produced in the same manner as in Example 1 except that the nonaqueous electrolyte n was used.

[Comparative Example 2]
A nonaqueous electrolytic solution containing EC, DEC, TFPC, and VC as the nonaqueous solvent, the concentration of LiPF ₆ being 1 mol / l, and the proportion of the electrolyte solution being 20% by weight of TFPC and 2% by weight of VC was obtained. This is designated as non-aqueous electrolyte o.

  A nonaqueous electrolyte secondary battery O of Comparative Example 2 was produced in the same manner as in Example 1 except that the nonaqueous electrolyte o was used.

[Comparative Example 3]
A nonaqueous electrolytic solution containing EC, DEC, TFPC, and PS as the nonaqueous solvent, the concentration of LiPF ₆ being 1 mol / l, and the proportion of the electrolyte solution being 20% by weight of TFPC and 2% by weight of PS was obtained. This is designated as non-aqueous electrolyte p.

  A nonaqueous electrolyte secondary battery P of Comparative Example 3 was produced in the same manner as in Example 1 except that the nonaqueous electrolyte p was used.

[Comparative Example 4]
Di (2,2,2-trifluoroethyl) carbonate (TFE) is used instead of TFPC, and EC, DEC, TFE, VC and PS are used as non-aqueous solvents, and the concentration of LiPF ₆ is 1 mol / l. A nonaqueous electrolytic solution having a ratio of 20% by weight of TFE, 2% by weight of VC, and 2% by weight of PS was obtained in the liquid solvent. This is designated as non-aqueous electrolyte q.

  A nonaqueous electrolyte secondary battery Q of Comparative Example 4 was produced in the same manner as in Example 1 except that the nonaqueous electrolyte solution q was used.

[Comparative Example 5]
A nonaqueous electrolytic solution containing EC and DEC as a nonaqueous solvent and having a LiPF ₆ concentration of 1 mol / l was obtained. This is designated as non-aqueous electrolyte r. A nonaqueous electrolyte secondary battery R of Comparative Example 5 was produced in the same manner as in Example 1 except that the nonaqueous electrolyte r was used.

  In Examples 1 to 13 and Comparative Examples 1 to 5, the mixing ratio of EC and DEC in the electrolyte was all 1: 1 by volume.

  Types and compositions of solvents other than EC and DEC contained in the electrolytes of the nonaqueous electrolyte secondary batteries A to M of Examples 1 to 13 and the nonaqueous electrolyte secondary batteries N to R of Comparative Examples 1 to 5 (% By weight) are summarized in Table 1.

  In Table 1, TFPC is di (2,2,3,3-tetrafluoropropyl) carbonate, DFEC is di (2,2-difluoroethyl) carbonate, and HFBC is di (2,2,3,3). , 4,4-hexafluorobutyl) carbonate, TFE is di (2,2,2-trifluoroethyl) carbonate, VC is vinylene carbonate, SC is styrene carbonate, VEC is vinylethylene carbonate, PS Represents 1,3-propane sultone, SF represents sulfolane, and ES represents ethylene sulfite.

[Electrolyte flammability test]
First, the non-aqueous electrolytes a to r used in the non-aqueous electrolyte secondary batteries A to M of Examples 1 to 13 and the non-aqueous electrolyte secondary batteries N to R of Comparative Examples 1 to 5 were subjected to electrolyte combustion. A sex test was performed. The glass solution was infiltrated with an electrolyte solution, and exposed to a test flame in the atmosphere for 10 seconds. Then, the test flame was moved away, and the state of ignition was visually observed.

  In this test, when the test flame is moved away 10 seconds later, if the flame ignited by the electrolyte immediately disappears, it is judged as “showing flame retardancy”, and the test flame is moved away and ignited 3 seconds later. When the flame had disappeared, it was judged that “flame retardance was insufficient”, and when the flame did not disappear even after 5 seconds from the test flame, it was judged as “having combustibility”.

[Battery performance test]
Next, for the non-aqueous electrolyte secondary batteries A to M of Examples 1 to 13 and the non-aqueous electrolyte secondary batteries N to R of Comparative Examples 1 to 5, the initial discharge capacity and the high-rate discharge capacity were measured. It was. First, at 20 ° C., the battery was charged with a constant current of 30 mA up to 4.2 V, and further with a constant voltage of 4.2 V for a total of 2.5 hours, and then discharged at 20 ° C. with a constant current of 6 mA up to a final voltage of 3 V. The discharge capacity at that time was defined as “initial discharge capacity” (mAh). Next, at 20 ° C., the battery was charged at a constant current of 30 mA to 4.2 V, and further at a constant voltage of 4.2 V for a total of 2.5 hours, and then discharged at 20 ° C. at a constant current of 90 mA to a final voltage of 3 V. The discharge capacity at this time was defined as “high rate discharge capacity”.

  The results of the electrolyte flammability test and the battery performance test are summarized in Table 2. In Table 2, in the “Flame Retardancy” column, a symbol “◯” indicates flame retardancy, a symbol “Δ” indicates insufficient flame retardancy, and a symbol “×” indicates combustibility. .

  As shown in Table 2, the initial discharge capacity and the high rate discharge capacity of the battery A of Example 1 and the battery R of Comparative Example 5 of the present invention were good. However, while the electrolysis solution r used in the battery R of Comparative Example 5 had combustibility, the electrolytic solution a used in the battery A of Example 1 did not show combustibility, but it was flame retardant. Was insufficient.

  Further, in the batteries B to M of Examples 2 to 13 of the present invention, not only the initial discharge capacity and the high rate discharge capacity are both excellent, but also the electrolytes b to m used in these batteries are all flame retardant. The results of the flammability test were also good, and it was confirmed that the battery was a non-aqueous electrolyte battery having both excellent flame retardancy of the electrolyte and high rate discharge characteristics.

  In contrast, the electrolytes n to q used in the batteries N to Q of Comparative Examples 1 to 4 showed flame retardancy, but the initial discharge capacity was slightly lower than the design capacity, and was inferior to the high rate discharge capacity. I understood it.

  In the batteries A to M of Examples 1 to 13, in the batteries B to M of Examples 2 to 13 in which the content of the fluorinated chain carbonate compound is 20% by weight or more, the electrolyte solution is flame retardant. In addition, non-aqueous electrolyte secondary batteries excellent in high rate discharge characteristics are obtained, and among these, the content of the fluorinated chain carbonate compound is 50% by weight or less, Examples 2, 3, and Examples 6 to 10 The batteries C, D and F to J were particularly excellent in high rate discharge characteristics.

  Therefore, it was confirmed that the content of the fluorinated chain carbonate compound in the electrolytic solution is preferably 20% by weight or more, more preferably 20% by weight or more and 50% by weight or less.

  Further, when the batteries B, E, and F of Examples 2, 5, and 6 were compared with the batteries J to M of Examples 10 to 13, the high rate discharge characteristics were the batteries B and E of Examples 2, 5, and 6, respectively. Since F was superior, the ratio of the total of the cyclic compound having a carbon-carbon π bond and the cyclic compound having an S═O bond in the electrolyte solvent was 1% by weight or more and 20% by weight or less. In some cases, it was confirmed that a non-aqueous electrolyte secondary battery having a nonflammable electrolyte, excellent high-rate discharge characteristics, and high charge / discharge efficiency can be obtained.

The figure which shows the cross section of the nonaqueous electrolyte secondary battery of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode 11 Positive electrode mixture 12 Positive electrode collector 2 Negative electrode mixture 21 Negative electrode mixture 22 Negative electrode collector 3 Separator 4 Electrode group 5 Metal resin composite film

Claims (3)

In a nonaqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a nonaqueous electrolyte, the nonaqueous electrolyte is a fluorinated chain having a carbonate group adjacent to a methylene group and having —CHF ₂ at the molecular chain end. A non-aqueous electrolyte secondary battery comprising a carbonate compound, a cyclic carbonate compound having a carbon-carbon π bond, and a cyclic compound having an S═O bond. The nonaqueous electrolyte secondary battery according to claim 1, wherein the proportion of the fluorinated chain carbonate compound in the electrolyte solvent is 20% by weight or more. 3. The total proportion of a cyclic carbonate compound having a carbon-carbon π bond and a cyclic compound having an S═O bond in the electrolyte solvent is 1% by weight or more and 20% by weight or less. A nonaqueous electrolyte secondary battery according to 1.

Images