JP2011044245A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery with suppressed discharge capacity deterioration due to repeated charge and discharge and with little electric resistance rise after repeated charge and discharge. <P>SOLUTION: The nonaqueous electrolyte secondary battery with a cathode containing iron phosphate lithium compound and lithium transition metal oxide which has an α-NaFeO<SB>2</SB>type crystal structure and with nonaqueous electrolyte, is characterized by the nonaqueous electrolyte which includes a fluorinated phosphoric ester compound. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery.

  In recent years, non-aqueous electrolyte secondary batteries represented by lithium ion secondary batteries having a relatively high energy density have attracted attention as power sources for portable devices such as mobile phones and notebook computers, or electric vehicles.

Conventionally, as a non-aqueous electrolyte secondary battery, for example, a lithium transition having an α-NaFeO ₂ type crystal structure such as a composite oxide containing Li, Mn, Ni, and Co in terms of a relatively high operating voltage. What is provided with the positive electrode material containing a metal oxide is known.
In addition, as the non-aqueous electrolyte secondary battery, for example, lithium iron phosphate (LiFePO ₄ ) is used in that it is difficult to release oxygen that can cause ignition even under relatively high temperature conditions, and the safety of the battery can be kept high. A material having a positive electrode material containing a Li-containing polyanionic phosphate compound is known.

On the other hand, in view of the performance of these conventional non-aqueous electrolyte secondary batteries, in order to provide a non-aqueous electrolyte secondary battery having both high operating voltage and battery safety, it has an α-NaFeO ₂ type crystal structure. A non-aqueous electrolyte secondary battery including a positive electrode material obtained by mixing a lithium transition metal oxide and a Li-containing polyanionic phosphate compound is known (for example, Patent Document 1).

  However, such a nonaqueous electrolyte secondary battery has a problem that the discharge capacity decreases with repeated charge / discharge, and the electrical resistance after repeated charge / discharge increases.

JP 2006-252895 A

Therefore, charging / discharging is repeated while providing a positive electrode material formed by mixing an active material containing a lithium transition metal oxide having an α-NaFeO ₂ type crystal structure and an active material containing a Li-containing polyanionic phosphate compound. There is a demand for a nonaqueous electrolyte secondary battery in which a decrease in discharge capacity accompanying the above is suppressed and an electrical resistance after repeated charge and discharge is hardly increased.

  The present invention provides a non-aqueous electrolyte secondary battery that suppresses a decrease in discharge capacity that accompanies repeated charge and discharge, and that does not easily increase the electrical resistance after repeated charge and discharge, in view of the above-described problems and demands. This is the issue.

In order to solve the above problems, a non-aqueous electrolyte secondary battery according to the present invention includes a positive electrode containing a Li-containing polyanionic phosphate compound and a lithium transition metal oxide having an α-NaFeO ₂ type crystal structure, and a non-aqueous solution. A non-aqueous electrolyte secondary battery including an electrolyte, wherein the non-aqueous electrolyte includes a fluorinated phosphate ester compound.

  In the nonaqueous electrolyte secondary battery according to the present invention, the fluorinated phosphate compound is preferably a trifluoroalkyl phosphate compound.

  In the nonaqueous electrolyte secondary battery according to the present invention, the Li-containing polyanionic phosphate compound is preferably a lithium iron phosphate compound.

  Moreover, it is preferable that the nonaqueous electrolyte secondary battery which concerns on this invention contains the said fluorinated phosphate ester compound 5-50 volume% in the said nonaqueous electrolyte.

  The nonaqueous electrolyte secondary battery according to the present invention has an effect that a decrease in discharge capacity due to repeated charge / discharge is suppressed and an increase in electrical resistance after repeated charge / discharge is suppressed.

  Hereinafter, an embodiment of a non-aqueous electrolyte secondary battery according to the present invention will be described.

The nonaqueous electrolyte secondary battery of the present embodiment is a nonaqueous electrolyte comprising a positive electrode containing a Li-containing polyanionic phosphate compound and a lithium transition metal oxide having an α-NaFeO ₂ type crystal structure, and a nonaqueous electrolyte. In the electrolyte secondary battery, the non-aqueous electrolyte includes a fluorinated phosphate compound.

Specifically, the non-aqueous electrolyte secondary battery of the present embodiment includes a positive electrode containing a Li-containing polyanionic phosphate compound and a lithium transition metal oxide having an α-NaFeO ₂ type crystal structure, a negative electrode, an electrolyte salt, and A non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte containing a non-aqueous solvent, wherein the non-aqueous electrolyte contains a fluorinated phosphate compound.
Furthermore, the nonaqueous electrolyte secondary battery of the present embodiment can be provided with a separator between the positive electrode and the negative electrode. Moreover, the exterior body which packages these structures may be provided.
Further, the embodiment of the non-aqueous electrolyte secondary battery is not particularly limited. For example, a coin battery or a button battery having a positive electrode, a negative electrode, and a single-layer or multi-layer separator, a positive electrode, a negative electrode, and a roll. And a cylindrical battery, a square battery, a flat battery, and the like having a cylindrical separator.

  The fluorinated phosphate ester compound is preferably a fluoroalkyl phosphate ester compound, and more preferably a trifluoroalkyl phosphate ester compound.

  Examples of the trifluoroalkyl phosphate compound include tri (2,2-difluoroethyl phosphate), tri (2,2,3,3-tetrafluoropropyl) phosphate, and tri (2,2, 3,3,4,4-hexafluorobutyl), triphosphate (1H, 1H, 5H-octafluoropentyl), triphosphate (1H, 1H, 7H-dodecafluoroheptyl), triphosphate (1H, 1H, 3H, 7H-perfluoroheptyl), triphosphate (1H, 1H, 9H-hexadecafluorononyl), tri (2,2,2-trifluoroethyl) phosphate, tri (2,2 , 3,3,3-pentafluoropropyl), triphosphate (1H, 1H-perfluorobutyl), triphosphate (1H, 1H-perfluoropentyl), triphosphate (1H, 1H) Perfluoroheptyl), tri (1H, 1H-perfluorononyl) phosphate, tri (1,1-difluoroethyl) phosphate, tri (1,1,2,2-tetrafluoropropyl) phosphate alone Alternatively, a mixture of two or more thereof can be exemplified, but the invention is not limited to these. Among these, as the trifluoroalkyl phosphate compound, tri (2,2,3,3-tetrafluoropropyl) phosphate or tri (2,2,2-trifluoroethyl) phosphate is preferable, and phosphoric acid Tri (2,2,3,3-tetrafluoropropyl) is more preferred.

  The amount of the fluorinated phosphate compound contained in the non-aqueous electrolyte is not particularly limited, but it is 5 to 50 in that the cycle characteristics can be further improved while providing the basic performance of the battery. It is preferably volume%, more preferably 5 to 45 volume%, still more preferably 10 to 35 volume%, and most preferably 10 to 30 volume%.

  As the nonaqueous solvent other than the fluorinated phosphate ester compound and the electrolyte salt contained in the nonaqueous electrolyte, those generally used in nonaqueous electrolyte secondary batteries and the like are employed.

  The non-aqueous solvent is not particularly limited, and those generally used can be employed. Examples of the non-aqueous solvent include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, and chloroethylene carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; dimethyl carbonate, diethyl carbonate, Chain carbonates such as ethyl methyl carbonate; chain esters such as methyl formate, methyl acetate and methyl butyrate; tetrahydrofuran or derivatives thereof; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane, 1 Ethers such as 1,4-dibutoxyethane and methyldiglyme; nitriles such as acetonitrile and benzonitrile; dioxolane or derivatives thereof; ethylene sulfide, sulfolane, sultone or derivatives thereof A single substance or a mixture of two or more thereof can be exemplified.

Examples of the electrolyte salt include LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) ionic compounds such as (SO ₂ C ₄ F ₉ ), LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, NaBr, KClO ₄ , KSCN, etc. These ionic compounds may be used alone or as a mixture of two or more.

  The concentration of the electrolyte salt in the non-aqueous electrolyte is preferably 0.5 to 5.0 mol / l, more preferably 1.0 to 1.0 in order to reliably obtain a non-aqueous electrolyte battery having excellent battery characteristics. 2.5 mol / l.

The positive electrode contains, as a positive electrode material constituting the positive electrode, a Li-containing polyanionic phosphate compound and a lithium transition metal oxide having an α-NaFeO ₂ type crystal structure. In addition, the positive electrode may contain a current collector having electron conductivity.

Examples of the Li-containing polyanionic phosphate compound include those represented by the general formula LiMPO ₄ (M is one or more transition metal elements such as Fe, Mn, Co, Ni). Specific examples include lithium manganese phosphate compounds (LiMnPO ₄ ) and lithium iron phosphate compounds (LiFePO ₄ ). Here, the Li-containing polyanionic phosphate compound may contain a trace amount of metal elements such as Mg and Al in addition to the transition metal. Further, a part of PO ₄ may be substituted with BO ₃ , SiO ₄ or the like. The Li-containing polyanionic phosphate compound is preferably a lithium iron phosphate compound from the viewpoint of high electron conductivity and excellent high rate discharge characteristics.

The lithium iron phosphate compound has a chemical composition substantially represented by LiFePO ₄ and has an olivine type crystal structure.

The chemical composition of the lithium iron phosphate compound is not limited to LiFePO _4, and the coefficient of each element in the composition formula can vary. Specifically, the chemical composition of the lithium iron phosphate compound may be in the range of Li: P: Fe = 0.85 to 1.10: 1: 0.95 to 1.05.

The Li-containing polyanionic phosphate compound such as the lithium iron phosphate compound is usually in the form of particles. Particles of particle size, the value of D ₅₀ obtained by particle size distribution measurement, typically, a 3Myuemu～30myuemu, in that they may more improve the electron conductivity of the positive electrode material, preferably, the value of D ₅₀ a 3Myuemu～15myuemu, more preferably, the value of D ₅₀ is 10Myuemu～15myuemu.
The D ₅₀ value obtained by the particle size distribution measurement is determined by a laser diffraction / scattering type particle size distribution measuring apparatus after the sample and the surfactant are sufficiently kneaded and then ion-exchanged water is added and dispersed with ultrasonic waves. It is the value of D ₅₀ obtained by measurement at 20 ° C. using (SALD-2000J, manufactured by Shimadzu Corporation).

The lithium transition metal oxide having the α-NaFeO ₂ type crystal structure is a composite oxide containing lithium and a transition metal. Specifically, the chemical formula Li _p [Li _q Ni _r Mn _s Co _t ] O ₂ (q + r + s + t = 1). Here, the [] represents the atoms present in the transition metal sites in _type crystal structure alpha-NaFeO. Although the value of p varies depending on the charge / discharge depth, the value of p immediately after the synthesis corresponding to the complete discharge state is preferably 1.0 to 1.2. In addition, when q = 0 in Li _p [Li _q Ni _r Mn _s Co _t ] O ₂ , a material satisfying | r−s | ≦ 0.05 is excellent in thermal stability and charge / discharge cycle performance. preferable. When q ≠ 0, q = x / 3, r = y / 2, s = (2x / 3) + (y / 2), t = 1−xy, x ≧ 0, y ≧ 0 And satisfying x + y ≦ 1 at the same time are preferable in that a relatively large discharge capacity can be obtained, and those satisfying 1/3 <x <2/3 are more preferable.

Specifically, as the lithium transition metal oxide, those represented by the chemical formulas LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , LiNi _1/6 Mn _1/6 Co _2/3 O ₂ , etc. Is mentioned.

The lithium transition metal oxide has an α-NaFeO ₂ type crystal structure, that is, a layered rock salt type crystal structure. It can be recognized from the X-ray diffraction pattern obtained by general powder X-ray diffraction that the lithium transition metal oxide has an α-NaFeO ₂ type crystal structure.

The lithium transition metal oxide is usually in the form of particles. Particles of particle size, the value of D ₅₀ obtained by particle size distribution measurement, typically, a 3Myuemu～30myuemu, in that they may more improve the electron conductivity of the positive electrode material, preferably, the value of D ₅₀ a 3Myuemu～15myuemu, more preferably, the value of D ₅₀ is 5 m to 10 m.
Incidentally, in the lithium transition metal oxide, the value of D ₅₀ obtained by particle size distribution measurement is determined by the value a manner similar to D ₅₀ of the said Li-containing polyanionic phosphate compound.

  The amount ratio of the Li-containing polyanionic phosphate compound such as the lithium iron phosphate compound and the lithium transition metal oxide is such that the lithium transition metal oxide is 0 by mass with respect to the Li-containing polyanionic phosphate compound. It is preferably 25 to 9 times, more preferably 1 to 9 times, still more preferably 3 to 9 times, and most preferably 4 to 9 times. Such a configuration has the advantage that the operating voltage can be higher.

Examples of the material of the current collector used for the positive electrode include aluminum, titanium, stainless steel, nickel, calcined carbon, a conductive polymer, and conductive glass.
Examples of the shape of the current collector include a sheet shape and a net shape. The thickness of the current collector is not particularly limited, but usually 1 to 500 μm is employed.

Examples of the negative electrode include lithium metal and lithium alloys (lithium metal-containing alloys such as lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and wood alloys) and lithium.・ Dischargeable alloys, carbon materials (eg, graphite, hard carbon, low-temperature fired carbon, amorphous carbon, etc.), metal oxides, lithium metal oxides (Li ₄ Ti ₅ O ₁₂ etc.), negative electrodes such as polyphosphate compounds Material may be included. The negative electrode may contain a current collector having electronic conductivity.

  The negative electrode material is preferably composed of particles having an average particle diameter of 100 μm or less. In order to make the particles have a predetermined size, a pulverizer or a classifier can be used.

Examples of the material of the current collector used for the negative electrode include copper, nickel, iron, stainless steel, titanium, aluminum, baked carbon, conductive polymer, and conductive glass.
Examples of the shape of the current collector include a sheet shape and a net shape. The thickness of the current collector is not particularly limited, but usually 1 to 500 μm is employed.

  In addition to the positive electrode material and the negative electrode material described above, the positive electrode and the negative electrode may contain a conductive agent, a binder, a thickener, a filler, and the like as other components.

  These other components are usually mixed by a mixing method that can be physically and substantially uniformly mixed. As the mixing method, a mixing method in which a powder mixer such as a V-type mixer, an S-type mixer, a grinder, a ball mill, a planetary ball mill, or the like is mixed dry or wet may be employed.

  The conductive agent is not limited as long as it is an electron conductive material that does not adversely affect battery performance. For example, natural graphite (scale-like graphite, scale-like graphite, earth-like graphite, etc.), artificial graphite, carbon black, acetylene black , Ketjen black, carbon whisker, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.) powder, metal fiber, one type of conductive material such as conductive ceramic material, or a mixture thereof.

  Examples of the binder include thermoplastic resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene, and polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, and styrene butadiene. One type of a polymer having rubber elasticity such as rubber (SBR) or fluoro rubber, or a mixture of two or more types may be mentioned.

  As said thickener, 1 type, such as polysaccharides, such as carboxymethylcellulose and methylcellulose, or 2 or more types of mixtures is mentioned, for example. Moreover, it is preferable that the thickener which has a functional group which reacts with lithium like a polysaccharide deactivates the functional group, for example by methylating.

  The filler is not particularly limited as long as it does not adversely affect battery performance, and examples thereof include olefin polymers such as polypropylene and polyethylene, amorphous silica, alumina, zeolite, and glass.

  As the separator, those in which a porous film or a nonwoven fabric exhibiting excellent rate characteristics are used alone or in combination are preferable.

  Examples of the material of the separator include polyolefin resins typified by polyethylene and polypropylene, polyester resins typified by polyethylene terephthalate and polybutylene terephthalate, polyvinylidene fluoride, and vinylidene fluoride-hexafluoropropylene copolymer. , Vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, vinylidene fluoride-hexafluoro Acetone copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride-tetrafluoro Styrene - hexafluoropropylene copolymer, vinylidene fluoride - ethylene - can be mentioned tetrafluoroethylene copolymer.

  Examples of the material of the exterior body include nickel-plated iron, stainless steel, aluminum, a metal resin composite film, and glass.

  The nonaqueous electrolyte secondary battery of this embodiment can be manufactured by a conventionally known general method. For example, it can be manufactured by injecting the nonaqueous electrolyte before or after laminating the separator for the nonaqueous electrolyte battery, the positive electrode and the negative electrode, and finally sealing with an exterior material.

The non-aqueous electrolyte secondary battery of this embodiment is as illustrated above, but the present invention is not limited to the non-aqueous electrolyte secondary battery illustrated above.
That is, various modes used in a general nonaqueous electrolyte secondary battery can be adopted within a range that does not impair the effects of the present invention.

  EXAMPLES Next, although an Example is given and this invention is demonstrated in more detail, this invention is not limited to these.

  A nonaqueous electrolyte secondary battery was produced by the method described below.

Example 1
<Preparation of positive electrode>
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ 79.2% by mass (D ₅₀ = 10 μm)
LiFePO ₄ 8.8% by mass (D ₅₀ = 11 μm)
Carbon nanofiber (gas phase carbon fiber, trade name “VGCF”, manufactured by Showa Denko KK)
2% by mass
Acetylene black 5% by mass
Polyvinylidene fluoride (PVDF) 5% by mass
Was prepared in a N-methyl-2-pyrrolidone solution. Note that LiNi _1/3 Mn _1/3 Co _1/3 O ₂ was confirmed to have an α-NaFeO ₂ type crystal structure by an X-ray diffraction pattern.
This paste was applied onto a 15 μm thick aluminum foil as a current collector, and then dried at 130 ° C. to evaporate N-methyl-2-pyrrolidone.
This application and drying operation was performed on both sides of the aluminum foil, and further, both sides were compression molded by a roll press to produce a positive electrode.

<Production of negative electrode>
94% by mass of graphite
Polyvinylidene fluoride (PVDF) 6% by mass
Was prepared in a N-methyl-2-pyrrolidone solution.
This paste was applied on a copper foil having a thickness of 10 μm, and then dried at 150 ° C. to evaporate N-methyl-2-pyrrolidone.
This application and drying operations were performed on both sides of the copper foil, and further, both sides were compression-molded with a roll press to produce a negative electrode.

<Separator>
As the separator, a polyethylene microporous film having a thickness of 27 μm was used.

<Preparation of non-aqueous electrolyte>
Ethylene carbonate 20.3 (volume ratio)
Dimethyl carbonate 23.7 (volume ratio)
Ethyl methyl carbonate 23.9 (volume ratio)
Tri (2,2,3,3-tetrafluoropropyl) phosphate (TFPP)
30.0 (volume ratio)
A non-aqueous electrolyte was prepared by mixing 1 liter of a mixed solvent in which the above-mentioned ratio was mixed so that vinylene carbonate was 2% by mass and further dissolving 1 mol of LiPF ₆ . This electrolyte was designated as an electrolyte (a1).

<Production of secondary battery>
After winding the positive electrode, the negative electrode, and the separator so that the separator is positioned between the positive electrode and the negative electrode, a rectangular battery case made of aluminum (height 49.3 mm, width 33.7 mm, thickness is 5.17 mm). After the nonaqueous electrolyte (a1) was injected into the container, the battery was sealed.

(Example 2)
A battery was produced in the same manner as in Example 1 except that the following electrolyte (a2) was used as nonaqueous electrolysis. That is, the following composition was used as the non-aqueous electrolyte.
Ethylene carbonate 20.3 (volume ratio)
Dimethyl carbonate 23.7 (volume ratio)
Ethyl methyl carbonate 23.9 (volume ratio)
Tri (2,2,2-trifluoroethyl) phosphate (TFEP)
30.0 (volume ratio)

(Example 3)
A battery was produced in the same manner as in Example 1 except that the following electrolyte (a3) was used as nonaqueous electrolysis. That is, the following composition was used as the non-aqueous electrolyte.
Ethylene carbonate 26.3 (volume ratio)
Dimethyl carbonate 30.7 (volume ratio)
Ethyl methyl carbonate 31.0 (volume ratio)
Tri (2,2,3,3-tetrafluoropropyl) phosphate (TFPP)
10.0 (volume ratio)

Example 4
A battery was produced in the same manner as in Example 1 except that the following electrolyte (a4) was used as nonaqueous electrolysis. That is, the following composition was used as the non-aqueous electrolyte.
Ethylene carbonate 14.3 (volume ratio)
Dimethyl carbonate 16.7 (volume ratio)
Ethyl methyl carbonate 16.8 (volume ratio)
Tri (2,2,3,3-tetrafluoropropyl) phosphate (TFPP)
50.0 (volume ratio)

(Example 5)
A battery was manufactured in the same manner as in Example 1 except that in preparing the positive electrode, a paste in which the following composition was dispersed in an N-methyl-2-pyrrolidone solution was prepared.
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ 70.4% by mass (D ₅₀ = 10 μm)
LiFePO ₄ 17.6% by mass (D ₅₀ = 11 μm)
Carbon nanofiber (gas phase carbon fiber, trade name “VGCF”, Showa Denko)
2% by mass
Acetylene black 5% by mass
Polyvinylidene fluoride (PVDF) 5% by mass

(Example 6)
A battery was manufactured in the same manner as in Example 1 except that in preparing the positive electrode, a paste in which the following composition was dispersed in an N-methyl-2-pyrrolidone solution was prepared. Note that LiNi _1/6 Mn _1/6 Co _2/3 O ₂ was confirmed to have an α-NaFeO ₂ type crystal structure by an X-ray diffraction pattern.
LiNi _1/6 Mn _1/6 Co _2/3 O ₂ 70.4% by mass (D ₅₀ = 5 μm)
LiFePO ₄ 17.6% by mass (D ₅₀ = 11 μm)
Carbon nanofiber (gas phase carbon fiber, trade name “VGCF”, Showa Denko)
2% by mass
Acetylene black 5% by mass
Polyvinylidene fluoride (PVDF) 5% by mass

(Comparative Example 1)
A battery was produced in the same manner as in Example 1 except that the following electrolyte (a5) was used as the nonaqueous electrolyte. That is, as a non-aqueous electrolyte,
Ethylene carbonate 20.3 (volume ratio)
Dimethyl carbonate 23.7 (volume ratio)
Ethyl methyl carbonate 23.9 (volume ratio)
Di (2,2,3,3-tetrafluoropropyl) carbonate (TFPC)
30.0 (volume ratio)
Into 1 liter of a mixed solvent mixed with the above ratio, vinylene carbonate was mixed to 2% by mass, and 1 mol of LiPF ₆ was further dissolved.

(Comparative Example 2)
A battery was produced in the same manner as in Example 1 except that the following electrolyte (a6) was used as the nonaqueous electrolyte. That is, as a non-aqueous electrolyte,
Ethylene carbonate 20.3 (volume ratio)
Dimethyl carbonate 23.7 (volume ratio)
Ethyl methyl carbonate 23.9 (volume ratio)
Di (2,2,2-trifluoroethyl) carbonate (TFEC)
30.0 (volume ratio)
A mixture of 1 liter of a mixed solvent in which the above-mentioned ratio was mixed with vinylene carbonate so as to be 2% by mass and further dissolved 1 mol of LiPF ₆ was used.

(Comparative Example 3)
A battery was produced in the same manner as in Example 1 except that the following electrolyte (a7) was used as the nonaqueous electrolyte. That is, as a non-aqueous electrolyte,
Ethylene carbonate 20.3 (volume ratio)
Dimethyl carbonate 23.7 (volume ratio)
Ethyl methyl carbonate 23.9 (volume ratio)
(2,2,3,3,3-pentafluoropropyl-1,1,2,2-tetrafluoroethyl) ether (FPFEE)
30.0 (volume ratio)
Into 1 liter of a mixed solvent mixed with the above ratio, vinylene carbonate was mixed to 2% by mass, and 1 mol of LiPF ₆ was further dissolved.

(Comparative Example 4)
A battery was produced in the same manner as in Example 1 except that the following electrolyte (a8) was used as the nonaqueous electrolyte. That is, as a non-aqueous electrolyte,
Ethylene carbonate 29.4 (volume ratio)
Dimethyl carbonate 34.3 (volume ratio)
Ethyl methyl carbonate 34.5 (volume ratio)
Into 1 liter of a mixed solvent mixed with the above ratio, vinylene carbonate was mixed to 2% by mass, and 1 mol of LiPF ₆ was further dissolved.

(Comparative Example 5)
In using the electrolyte (a8) instead of the electrolyte (a1) as the nonaqueous electrolyte, in the production of the positive electrode, the following composition (similar to Example 5) was dispersed in the N-methyl-2-pyrrolidone solution. A battery was manufactured in the same manner as in Example 1 except that the paste was prepared.
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ 70.4% by mass (D ₅₀ = 10 μm)
LiFePO ₄ 17.6% by mass (D ₅₀ = 11 μm)
Carbon nanofiber (gas phase carbon fiber, trade name “VGCF”, Showa Denko)
2% by mass
Acetylene black 5% by mass
Polyvinylidene fluoride (PVDF) 5% by mass

(Comparative Example 6)
A paste in which the following composition is dispersed in an N-methyl-2-pyrrolidone solution in the production of a positive electrode in that the electrolyte (a8) is used instead of the electrolyte (a1) as a nonaqueous electrolyte (Example 6 and A battery was produced in the same manner as in Example 1 except that the same was prepared.
LiNi _1/6 Mn _1/6 Co _2/3 O ₂ 70.4% by mass (D ₅₀ = 5 μm)
LiFePO ₄ 17.6% by mass (D ₅₀ = 11 μm)
Carbon nanofiber (gas phase carbon fiber, trade name “VGCF”, Showa Denko)
2% by mass
Acetylene black 5% by mass
Polyvinylidene fluoride (PVDF) 5% by mass

(Comparative Example 7)
In making the positive electrode,
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ 90% by mass (D ₅₀ = 10 μm)
Acetylene black 5% by mass
Polyvinylidene fluoride (PVDF) 5% by mass
A battery was produced in the same manner as in Example 1 except that a paste was prepared in which N was dispersed in an N-methyl-2-pyrrolidone solution.

(Comparative Example 8)
In using the electrolyte (a8) instead of the electrolyte (a1) as the nonaqueous electrolyte,
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ 90% by mass
Acetylene black 5% by mass
Polyvinylidene fluoride (PVDF) 5% by mass
A battery was produced in the same manner as in Example 1 except that a paste was prepared in which N was dispersed in an N-methyl-2-pyrrolidone solution.

(Comparative Example 9)
In making the positive electrode,
LiFePO ₄ 90% by mass (D ₅₀ = 11 μm)
Acetylene black, 5% by mass
Polyvinylidene fluoride (PVDF) 5% by mass
A paste prepared by dispersing in a N-methyl-2-pyrrolidone solution, using a polyethylene microporous film having a thickness of 22 μm instead of a 27 μm polyethylene microporous film as a separator, and A battery was produced in the same manner as in Example 1 except that a 20 μm thick aluminum foil was used instead of the 15 μm thick aluminum foil as the current collector.

(Comparative Example 10)
A battery was produced in the same manner as in Comparative Example 9, except that the electrolyte (a8) was used instead of the electrolyte (a1) as the nonaqueous electrolyte.

"High temperature cycle test"
Each manufactured battery was subjected to a high-temperature cycle test.
In the batteries of Examples and Comparative Examples 1 to 8, the high-temperature cycle test was performed at 45 ° C. with a charging current of 600 mA, a charging voltage of 4.20 V, a charging time of 3.0 hours, and a discharging current of 600 mA The charge / discharge consisting of constant current discharge with a final voltage of 2.00 V was repeated 50 cycles.
In the batteries of Comparative Examples 9 and 10, the high-temperature cycle test was performed at 45 ° C. with a charging current of 500 mA, a charging voltage of 3.60 V, a constant current and constant voltage charging of 3.0 hours, a discharging current of 500 mA, and a termination voltage. Charging / discharging consisting of a constant current discharge of 2.00 V was repeated 50 cycles.
For each battery, the ratio of the initial discharge capacity at 25 ° C. to the design capacity was calculated as “initial capacity (%) with respect to the design capacity”.
In addition, the ratio of the discharge capacity at the 50th cycle to the first cycle was calculated as “capacity holding ratio (%)”. A higher “capacity retention ratio (%)” is preferable as battery performance.
Further, each battery was cooled to 25 ° C., and the direct current resistance of the battery was measured at an SOC of 50%, and the ratio of direct current resistance at the 50th cycle with respect to the initial stage (before the cycle test) was calculated as “DC resistance increase rate”.
Further, the internal resistance of the battery after discharge was measured using a 1 kHz impedance meter, and the ratio of the internal resistance at the 50th cycle relative to the initial stage (before the cycle test) was calculated as “1 kHz AC resistance increase rate”.
A lower “DC resistance increase rate” and “1 kHz AC resistance increase rate” are preferable as battery performance.

  Similarly, a high-temperature cycle test was conducted up to the 150th cycle.

  Similarly, a high-temperature cycle test was conducted up to the 500th cycle.

  Tables 1 and 2 show the evaluation results of the 50th cycle with respect to the initial stage (before the cycle test).

As can be seen from Table 1, in a battery using a positive electrode material in which a lithium transition metal oxide having an α-NaFeO ₂ type crystal structure and LiFePO ₄ are mixed, an electrolyte (a1) added with a fluorinated phosphate compound or When the electrolyte (a2) is used, the capacity retention is high compared to the case where the electrolyte (a5), the electrolyte (a6), the electrolyte (a7), and the electrolyte (a8) are used, and the electric resistance (DC and 1kHz AC resistance) increase suppression effect is large.

  As can be seen from Table 2, the addition of the fluorinated phosphate ester to the nonaqueous electrolyte can improve the capacity retention of the battery. Moreover, it is preferable that the addition ratio of a fluorinated phosphate ester is 50 volume% or less at the point that the initial capacity of a battery can become a comparatively high thing.

  Table 3 shows the evaluation results at the 150th cycle with respect to the initial stage (before the cycle test).

From Table 3, the electrolyte (a1) was used in the batteries (Comparative Examples 7 to 10) using either the lithium transition metal oxide having an α-NaFeO ₂ type crystal structure or LiFePO ₄ alone for the positive electrode. In this case, it can be seen that the capacity retention is lower than that in the case of using the electrolyte (a8). On the other hand, in batteries (Examples 5, 6, Comparative Examples 5 and 6) using a positive electrode material in which a lithium transition metal oxide having an α-NaFeO ₂ type crystal structure and LiFePO ₄ are mixed, the electrolyte ( It can be seen that the capacity retention is higher when a1) is used than when the electrolyte (a8) is used.

  Table 4 shows the evaluation results of the 500th cycle with respect to the initial stage (before the cycle test).

From Table 4, in a battery using a positive electrode material in which a lithium transition metal oxide having an α-NaFeO ₂ type crystal structure and LiFePO ₄ are mixed, a lithium transition metal oxide having an α-NaFeO ₂ type crystal structure, or Compared with a battery using any one of LiFePO ₄ alone as a positive electrode, the effect of suppressing an increase in electrical resistance (direct current and 1 kHz alternating current resistance) by adding a fluorinated phosphate compound to the non-aqueous electrolyte is greater. I understand.

Claims (4)

A non-aqueous electrolyte secondary battery comprising a positive electrode containing a Li-containing polyanionic phosphate compound and a lithium transition metal oxide having an α-NaFeO ₂ type crystal structure, and a non-aqueous electrolyte,
The non-aqueous electrolyte secondary battery, wherein the non-aqueous electrolyte contains a fluorinated phosphate compound.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the fluorinated phosphate ester compound is a trifluoroalkyl phosphate ester compound.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the Li-containing polyanionic phosphate compound is a lithium iron phosphate compound.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte contains the fluorinated phosphate ester compound in an amount of 5 to 50% by volume.