JP6241662B2 - Nonaqueous electrolyte secondary battery and power storage device - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte secondary battery characterized by a non-aqueous electrolyte.

  Nonaqueous electrolyte secondary batteries typified by lithium secondary batteries are widely used as power sources for mobile devices typified by mobile phones, taking advantage of their high energy density. In addition, in recent years, development has been made not only for power supplies for small devices, but also for medium and large-sized industrial applications such as power storage, electric vehicles, and hybrid vehicles.

A nonaqueous electrolyte secondary battery generally includes a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, a separator, and a nonaqueous electrolyte containing a nonaqueous solvent and a lithium salt.
The positive electrode active material constituting the nonaqueous electrolyte secondary battery is a lithium-containing transition metal oxide, the negative electrode active material is a carbon material typified by graphite, and the nonaqueous electrolyte is a cyclic carbonate such as ethylene carbonate and diethyl. A solution in which an electrolyte such as lithium hexafluorophosphate (LiPF ₆ ) is dissolved in a nonaqueous solvent containing a chain carbonate such as carbonate as a main constituent is widely known.

By the way, when considering the future expansion to medium-sized and large-sized, especially industrial applications where large demand is expected, there are applications where batteries are used in high-temperature environments that are not used in small-sized consumer applications. Safety is very important.
However, organic solvents conventionally used for non-aqueous solvents are generally volatile and flammable, and therefore are classified as flammable substances.

  Therefore, in order to improve the flame retardancy of the electrolyte solution of the non-aqueous electrolyte secondary battery and to improve the high-temperature charge / discharge cycle characteristics and the high-temperature storage characteristics, a phosphorus compound such as a fluorinated phosphonate ester is added to the non-aqueous electrolyte. The technique to add is known (for example, refer patent documents 1-5).

（式中、Ｒ¹は炭素原子数１〜８のアルキル基、ハロゲン化アルキル基、アリール基、アルキルアリール基、アラルキル基、または−ＣＨ₂−ＣＯＯＲ³−を示し、Ｒ²はメチル基、エチル基または炭素原子数１〜８のハロゲン化アルキル基を示す。Ｒ³は炭素原子数１〜８のアルキル基、ハロゲン化アルキル基を示す。但しＲ¹、Ｒ²、Ｒ³のうち、一つ以上がハロゲン化アルキル基である。ｍおよびｎはそれぞれ１または２を示し、ｍおよびｎの合計は３である。）」（請求項１）の発明が記載され、その実施例には、ジ−（２，２，２−トリフルオロエチル）メタンホスホネート、ジ−（２，２，２−トリフルオロエチル）エタンホスホネート、 ジ−（２，２，３，３，３−ペンタフルオロ−ｎ−プロピル）メタンホスホネート、ジ−メチルパーフルオロエタンホスホネート、ジメチルホスフィン酸−２，２，２−トリフルオロエチル等を３３重量％又は５０重量％含有した有機溶媒を用いること（段落［００１７］及び［００４２］）が示されている。
また、特許文献１には、この発明の目的として「電気特性に悪影響がなく、優れた難燃性を有する難燃性電解液およびこれを用いた非水電解液二次電池を提供すること」（段落［０００８］）が記載され、さらに、「上記リン化合物の存在割合（使用量）は、電解液を構成する有機溶媒中、５〜１００重量％が好ましく、１０〜１００重量％が更に好ましく、特に１０〜８０重量％が好ましい。該割合が５重量％未満では十分な難燃化効果が得られないことがある。」（段落［００２１］）と記載されている。 Patent Document 1 states that “in an electrolytic solution in which an electrolyte salt is dissolved in an organic solvent, the organic solvent contains at least one phosphorus compound represented by the following general formula (I): Flame retardant electrolyte.

(Wherein R ¹ represents an alkyl group having 1 to 8 carbon atoms, a halogenated alkyl group, an aryl group, an alkylaryl group, an aralkyl group, or —CH ₂ —COOR ³ —, and R ² represents a methyl group, ethyl Or a halogenated alkyl group having 1 to 8 carbon atoms, R ³ represents an alkyl group or halogenated alkyl group having 1 to 8 carbon atoms, provided that ^one of R ¹ , R ² and R ³ The above is a halogenated alkyl group, and m and n each represent 1 or 2, and the sum of m and n is 3.) ”(Invention 1) is described. -(2,2,2-trifluoroethyl) methanephosphonate, di- (2,2,2-trifluoroethyl) ethanephosphonate, di- (2,2,3,3,3-pentafluoro-n-propyl ) Methanephosphonate, zime Helper tetrafluoroethane phosphonates, using a 33 wt% or 50 wt% containing organic solvents dimethyl phosphinic acid 2,2,2-trifluoroethyl and the like (paragraphs [0017] and [0042]) are shown.
In addition, Patent Document 1 describes as an object of the present invention “to provide a flame retardant electrolyte solution having no adverse effect on electrical characteristics and having excellent flame retardancy and a non-aqueous electrolyte secondary battery using the same”. (Paragraph [0008]) is described, and “the abundance ratio (amount used) of the phosphorus compound is preferably 5 to 100% by weight, more preferably 10 to 100% by weight in the organic solvent constituting the electrolytic solution. In particular, 10 to 80% by weight is preferable. If the ratio is less than 5% by weight, a sufficient flame retarding effect may not be obtained ”(paragraph [0021]).

（一般式（１）中、Ｒ^１〜Ｒ^４は、それぞれ独立して、水素原子、フッ素原子、又は炭素数１〜１２の一価の置換基のいずれかを示し、Ｒ^５はフッ素原子で置換されていてもよい炭素数１〜１２のアルキル基、フッ素原子で置換されていてもよい炭素数２〜１２のアルケニル基、フッ素原子で置換されていてもよい炭素数６〜１２のアリール基、又はフッ素原子で置換されていてもよい炭素数７〜１２のアラルキル基のいずれかを示す。ｎは０〜６の整数を示す。但し、Ｒ^１、Ｒ^２が共にアルコキシ基である場合、ｎは１〜６の整数を示し、Ｒ^３及びＲ^４の少なくとも一つは水素原子以外の基を示す。）」（請求項１）の発明が記載され、その実施例には、トリエチル−２−ホスホノプロピオネート、トリエチル−２−ホスホノブチレート、トリエチルホスホノフルオロアセテート、エチル（ジエチルホスフィニル）アセテート等が示されている（段落［０１１７］、［０１１９］〜［０１２２］）。
また、特許文献２には、この発明の目的として「ガス発生が少なく、高容量で、保存特性及びサイクル特性に優れた非水系電解液電池を実現することができる非水系電解液と、この非水系電解液を用いた非水系電解液電池を提供すること」（段落［００１０］）が記載され、さらに、「非水系電解液中の一般式（１）で表される化合物の割合（２種以上用いる場合はその合計の割合）は、通常０．００１重量％以上、好ましくは０．０１重量％以上、更に好ましくは０．０５重量％以上、特に好ましくは０．１重量％以上である。これより低濃度では、本発明の効果が発現しにくい場合がある。逆に濃度が高すぎると、電池の容量が低下する場合があるので、上限は、通常１０重量％以下、好ましくは４重量％以下、更に好ましくは２重量％、特に好ましくは１重量％以下、最も好ましくは０．８重量％以下である。」（段落［００６４］）と記載されている。 Patent Document 2 states that “in a nonaqueous electrolytic solution containing an electrolyte and a nonaqueous solvent, the nonaqueous electrolytic solution contains a compound represented by the following general formula (1)”. Non-aqueous electrolyte for liquid batteries.

(In General Formula (1), R ^{1 to} R ⁴ each independently represent a hydrogen atom, a fluorine atom, or a monovalent substituent having 1 to 12 carbon atoms, and R ⁵ is a fluorine atom. An optionally substituted alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms that may be substituted with a fluorine atom, and an aryl group having 6 to 12 carbon atoms that may be substituted with a fluorine atom Or an aralkyl group having 7 to 12 carbon atoms which may be substituted with a fluorine atom, n represents an integer of 0 to 6, provided that when R ¹ and R ² are both alkoxy groups, n represents an integer of 1 to 6, and at least one of R ³ and R ⁴ represents a group other than a hydrogen atom.) ”(Claim 1) is described, and examples thereof include triethyl-2. -Phosphonopropionate, triethyl-2-phosphonobutyle , Tri-ethyl phosphonoacetate trifluoroacetate, ethyl (diethyl phosphinyl) acetate and the like are indicated (paragraph [0117], [0119] - [0122]).
In addition, Patent Document 2 discloses, as an object of the present invention, “a non-aqueous electrolyte solution that can realize a non-aqueous electrolyte battery that generates less gas, has a high capacity, and has excellent storage characteristics and cycle characteristics; “Providing a non-aqueous electrolyte battery using an aqueous electrolyte” (paragraph [0010]) is further described, and “the ratio of the compound represented by the general formula (1) in the non-aqueous electrolyte (two types) When used above, the total ratio) is usually 0.001% by weight or more, preferably 0.01% by weight or more, more preferably 0.05% by weight or more, and particularly preferably 0.1% by weight or more. If the concentration is lower than this, the effect of the present invention may be difficult to be exhibited, whereas if the concentration is too high, the capacity of the battery may decrease, so the upper limit is usually 10% by weight or less, preferably 4% by weight. % Or less, more preferably 2% by weight Particularly preferably 1 wt% or less, most preferably 0.8 wt% or less. "Is described as (paragraph [0064]).

Patent Document 3 describes an invention of a non-aqueous electrolyte solution for a non-aqueous electrolyte battery containing a compound represented by the same general formula as that in [Chemical Formula 2]. Noacetate and the like are shown (paragraphs [0134] to [0136]).
Patent document 3 describes the effect of the present invention as “a non-aqueous electrolyte battery having a high capacity and excellent storage characteristics and cycle characteristics can be provided, and the non-aqueous electrolyte battery can be reduced in size and performance. Can be achieved ”(paragraph [0016]), and further,“ the content ratio of these compounds in the non-aqueous electrolyte solution is not particularly limited in order to exhibit the effects of the present invention ”. However, the total amount is generally 0.001% by weight or more, preferably 0.01% by weight or more, more preferably 0.1% by weight or more based on the total amount of the non-aqueous electrolyte. Usually 5% by weight or less, preferably 4% by weight or less, more preferably 3% by weight or less If the concentration of these compounds is too low, it may be difficult to obtain an improvement effect, while the concentration is too high. When charging and discharging efficiency is reduced There. "Is described as (paragraph [0075]).

Japanese Patent No. 4407847 Japanese Patent No. 5169091 JP 2013-080727 A

In conventional non-aqueous electrolyte secondary batteries to which phosphonates are added as specifically described in Patent Documents 1 to 3, flame retardancy, charge / discharge cycle performance during low voltage operation, and storage characteristics are improved. However, the positive electrode operating potential is 4.3 Vvs. When operating at a high voltage exceeding Li / Li ⁺ , the charge / discharge cycle performance was greatly reduced. Accordingly, an object of the present invention is to provide a nonaqueous electrolyte secondary battery having excellent charge / discharge cycle performance even during high voltage operation, in view of the above-described conventional technology.

（式中、Ｒ_１〜Ｒ_３は、それぞれ独立して、水素原子がフッ素原子で置換されていてもよい炭素数１〜８のアルキル基を示し、かつ、少なくともいずれか１つは、少なくとも１つの水素原子がフッ素原子で置換されている。）
で表される含フッ素ホスホン酸エステルを５質量％以下含有していることを特徴とする非水電解質二次電池。
〔２〕上記一般式（１）で表される含フッ素ホスホン酸エステルにおいて、Ｒ_３の少なくとも１つの水素原子がフッ素原子で置換されていることを特徴とする前記〔１〕の非水電解質二次電池。 In the present invention, in order to solve the above problems, the following means are adopted.
[1] A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte using a positive electrode material used for a battery operated at a potential of less than 4.5 V based on metallic lithium, The water electrolyte is represented by the following general formula (1)

(Wherein R _{1 to} R ₃ each independently represents a C 1-8 alkyl group in which a hydrogen atom may be substituted with a fluorine atom, and at least one of them is at least 1) Two hydrogen atoms are replaced by fluorine atoms.)
A non-aqueous electrolyte secondary battery comprising 5% by mass or less of a fluorine-containing phosphonic acid ester represented by the formula:
[2] The nonaqueous electrolyte 2 according to the above [1], wherein in the fluorine-containing phosphonate represented by the general formula (1), at least one hydrogen atom of R ₃ is substituted with a fluorine atom. Next battery.

  In the present invention, a non-aqueous electrolyte secondary battery having better charge / discharge cycle performance than the case where no fluorine-containing phosphonate ester is contained can be obtained by containing 5% by mass or less of the fluorine-containing phosphonate ester in the non-aqueous electrolyte. It is done.

1 is an external perspective view showing an embodiment of a nonaqueous electrolyte secondary battery according to the present invention. Schematic which shows the electrical storage apparatus provided with multiple nonaqueous electrolyte secondary batteries which concern on this invention

  FIG. 1 shows an external perspective view of a rectangular nonaqueous electrolyte secondary battery 1 which is an embodiment of the nonaqueous electrolyte secondary battery according to the present invention. In the figure, the inside of the container is seen through. In the nonaqueous electrolyte secondary battery 1 shown in FIG. 1, an electrode group 2 is housed in a battery container 3. The electrode group 2 is formed by winding a positive electrode including a positive electrode active material and a negative electrode including a negative electrode active material via a separator. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 4 ′, and the negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 5 ′.

  Here, the non-aqueous electrolyte retained in the separator contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. In the present invention, the specific fluorine-containing phosphonic acid ester is further contained in an amount of 5% by mass. It is characterized by the following points.

  In the prior art, as shown in Patent Document 1, when a fluorine-containing phosphonate is added to the nonaqueous electrolyte of the nonaqueous electrolyte secondary battery, the flame retardancy is improved, but the charge / discharge cycle performance is decreased. It was thought to be. However, the present inventors unexpectedly added a small amount of the fluorine-containing phosphonic acid ester represented by the general formula (1) to the non-aqueous electrolyte of the non-aqueous electrolyte secondary battery, thereby unexpectedly charging / discharging cycle. Knowing that the performance is significantly improved, the present invention has been achieved. The content of the fluorine-containing phosphonate represented by the general formula (1) is 5 with respect to the total mass of the nonaqueous electrolyte in order to improve the high-temperature charge / discharge cycle performance and suppress the increase in battery thickness. The content is preferably not more than mass%, and in order to obtain the effect, it is more preferably 0.5 to less than 5 mass%, and particularly preferably 1 to 2 mass%.

In the general formula (1), R _{1 to} R ₃ each independently represent a C 1-8 alkyl group in which a hydrogen atom may be substituted with a fluorine atom, and at least any one of them. Has at least one hydrogen atom replaced with a fluorine atom. The alkyl group substituted with a fluorine atom may be an alkyl group (R ₁ or R ₂ ) bonded from P to O, but is an alkyl group (R ₃ ) bonded directly to P. It is particularly preferable in terms of improving the high temperature charge / discharge cycle performance.

  Examples of the fluorine-containing alkyl group having 1 to 8 carbon atoms that the fluorine-containing phosphonate represented by the general formula (1) has include a fluoromethyl group, a difluoromethyl group, a trifluoromethyl group, a 2-fluoroethyl group, 2,2-difluoroethyl group, 2,2,2-trifluoroethyl group, 2-fluoropropyl group, 3-fluoropropyl group, 2,2-difluoropropyl group, 3,3-difluoropropyl group, 3,3 , 3-trifluoropropyl group, 2,2,3,3-tetrafluoropropyl group, 2,2,3,3,3-pentafluoropropyl group, 2-fluorobutyl group, 3-fluorobutyl group, 4- Fluorobutyl group, 2,2-difluorobutyl group, 3,3-difluorobutyl group, 4,4-difluorobutyl group, 4,4,4-trifluorobutyl group, 2 2,3,3-tetrafluorobutyl group, 2,2,3,3,4,4-hexafluorobutyl group, 2,2,3,3,4,4,4-heptafluorobutyl group, 2-fluoro Pentyl group, 3-fluoropentyl group, 4-fluoropentyl group, 5-fluoropentyl group, 2,2-difluoropentyl group, 3,3-difluoropentyl group, 4,4-difluoropentyl group, 5,5-difluoro Pentyl group, 5,5,5-trifluoropentyl group, 1H, 1H, 5H, 5H, 5H-hexafluoropentyl group, 1H, 1H, 5H-octafluoropentyl group, 1H, 1H-nonafluoropentyl group, 1H , 1H, 7H-dodecafluoroheptyl group, 1H, 1H-tridecafluoroheptyl group, 1H, 1H, 8H-tridecafluorooctyl group, 1H, 1H Pentadecafluorooctyl group, and the like. Of these, fluoromethyl group, difluoromethyl group, 2,2,2-trifluoroethyl group, 2,2,3,3-tetrafluoropropyl group, 2,2,3,3,3-pentafluoropropyl group It is preferably selected from 1H, 1H, 5H-octafluoropentyl group, 1H, 1H-nonafluoropentyl group, 1H, 1H, 7H-dodecafluoroheptyl group, and 1H, 1H-tridecafluoroheptyl group.

  Examples of the fluorine-containing phosphonate represented by the general formula (1) include dimethyl (fluoromethyl) phosphonate, dimethyl (difluoromethyl) phosphonate, dimethyl (2,2,2-trifluoroethyl) phosphonate, dimethyl (2, 2,3,3-tetrafluoropropyl) phosphonate, dimethyl (2,2,3,3,3-pentafluoropropyl) phosphonate, diethyl (fluoromethyl) phosphonate, diethyl (difluoromethyl) phosphonate, diethyl (2,2, 2-trifluoroethyl) phosphonate, diethyl (2,2,3,3-tetrafluoropropyl) phosphonate, diethyl (2,2,3,3,3-pentafluoropropyl) phosphonate, bis (2,2,2- Trifluoroethyl) methylphosphonate, bis ( , 2,2-trifluoroethyl) ethyl phosphonate, bis (2,2,3,3-tetrafluoropropyl) methyl phosphonate, bis (2,2,3,3,3-pentafluoropropyl) methyl phosphonate and the like are preferable. .

  In the present invention, other organic solvents constituting the non-aqueous electrolyte are not limited, and organic solvents generally used for non-aqueous electrolytes for non-aqueous electrolyte secondary batteries can be used. For example, cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, styrene carbonate, catechol carbonate, 1-phenyl vinylene carbonate, 1,2-diphenyl vinylene carbonate, γ-butyrolactone, γ-valerolactone, propio Cyclic carboxylic acid esters such as lactone, chain carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and diphenyl carbonate, chain carboxylic acid esters such as methyl acetate and methyl butyrate, tetrahydrofuran or derivatives thereof, 1,3-dioxane, Ethers such as dimethoxyethane, diethoxyethane, methoxyethoxyethane, methyldiglyme, acetonitrile, benzonite Examples thereof include nitriles such as ril, dioxalane or a derivative thereof alone or a mixture of two or more thereof. In particular, those containing a cyclic carbonate such as ethylene carbonate and a chain carbonate such as diethyl carbonate are preferred. Moreover, these organic solvents can be mixed and used in arbitrary ratios.

  The non-aqueous electrolyte of the present invention contains the fluorine-containing phosphonic acid ester represented by the above general formula (1) and the above organic solvent. If necessary, other compounds can be added to the effect of the present invention. It can be contained in any amount as long as it is not impaired.

  Examples of such other compounds include aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; Partially fluorinated products of the above aromatic compounds such as -fluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene; 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, 3,5 -Overcharge inhibitors such as fluorine-containing anisole compounds such as difluoroanisole; vinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, trifluoropropylene carbonate Negative electrode film forming agents such as succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, propane sultone, Propene sultone, butane sultone, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, thioanisole, diphenyl disulfide, Examples include positive electrode protective agents such as dipyridinium disulfide.

  The content ratio of these other compounds in the non-aqueous electrolyte is not particularly limited, but is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and still more preferably, with respect to the entire non-aqueous electrolyte. The upper limit is preferably 5% by mass or less, more preferably 3% by mass or less, and still more preferably 2% by mass or less. By containing these compounds, safety can be further improved, and capacity maintenance performance and cycle performance after high-temperature storage can be improved.

The electrolyte salt (lithium salt) constituting the nonaqueous electrolyte of the present invention is not limited, and lithium salts that are stable in a wide potential region generally used for nonaqueous electrolyte secondary batteries can be used. For example, LiBF ₄ , LiPF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN (FSO ₂ ) ₂ , 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. These may be used alone or in combination of two or more.

  The concentration of the electrolyte salt in the nonaqueous electrolyte is preferably 0.1 mol / l to 5.0 mol / l, more preferably, in order to reliably obtain a nonaqueous electrolyte secondary battery having excellent high rate discharge characteristics. 1.0 mol / l to 2.0 mol / l.

The positive electrode material ( positive electrode active material ) used for the positive electrode constituting the nonaqueous electrolyte secondary battery of the present invention is one that can insert and desorb lithium ions electrochemically, and is 4. Any positive electrode active material that is generally used for a positive electrode active material for a nonaqueous electrolyte secondary battery can be used as long as it is used for a battery operated at a potential of less than 5 V. Examples include transition metal oxides, transition metal sulfides, lithium transition metal composite oxides, lithium-containing polyanion metal composite compounds, and the like. Examples of the transition metal oxide include manganese oxide, iron oxide, copper oxide, nickel oxide, vanadium oxide, and examples of the transition metal sulfide include molybdenum sulfide and titanium sulfide. Examples of the lithium transition metal composite oxide include lithium manganese composite oxide, lithium nickel composite oxide, lithium cobalt composite oxide, lithium nickel cobalt composite oxide, lithium nickel manganese composite oxide, and lithium nickel cobalt manganese composite oxide. Can be mentioned. Examples of the lithium-containing polyanion metal complex compounds, and the like iron phosphate lithium is. Further, conductive polymer compounds such as disulfide, polypyrrole, polyaniline, polyparastyrene, polyacetylene, and polyacene materials, pseudographite-structured carbonaceous materials, and the like can be given.

  There is no restriction | limiting in particular as a material of a positive electrode electrical power collector, A well-known thing can be used arbitrarily. Specific examples include metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum; and carbonaceous materials such as carbon cloth and carbon paper. Of these, metal materials, particularly aluminum, are preferred.

  The negative electrode active material used for the negative electrode constituting the non-aqueous electrolyte secondary battery of the present invention is not particularly limited as long as it can electrochemically insert and desorb lithium ions, and is a carbonaceous material, oxidized Examples thereof include metal oxides such as tin and silicon oxide, metal composite oxides, lithium alloys such as lithium alone and lithium aluminum alloys, and metals that can form alloys with lithium such as Sn and Si. Examples of the carbonaceous material include natural graphite, artificial graphite, coke, non-graphitizable carbon, low-temperature calcinable graphitizable carbon, fullerene, carbon nanotube, carbon black, activated carbon and the like. These may be used individually by 1 type, or may use 2 or more types together by arbitrary combinations and a ratio. Of these, carbonaceous materials or lithium composite oxides are preferably used from the viewpoint of safety.

  As the current collector for the negative electrode, a known one can be arbitrarily used. For example, metal materials such as copper, nickel, stainless steel, nickel-plated steel and the like can be mentioned, and copper is particularly preferable from the viewpoint of ease of processing and cost.

  As the separator, it is preferable to use a microporous membrane or a nonwoven fabric alone or in combination. Examples of the material constituting 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 Ethylene - hexafluoropropylene copolymer, vinylidene fluoride - ethylene - can be mentioned tetrafluoroethylene copolymer. Among these, a microporous film mainly composed of a polyolefin resin typified by polyethylene, polypropylene and the like is preferable.

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

  The shape of the nonaqueous electrolyte secondary battery according to the present invention is not particularly limited, and examples thereof include a cylindrical battery, a square battery (rectangular battery), a flat battery, and the like. The present invention can also be realized as a power storage device including a plurality of the above non-aqueous electrolyte secondary batteries. One embodiment of a power storage device is shown in FIG. In FIG. 2, the power storage device 30 includes a plurality of power storage units 20. Each power storage unit 20 includes a plurality of nonaqueous electrolyte secondary batteries 1. The power storage device 30 can be mounted as a power source for vehicles such as an electric vehicle (EV), a hybrid vehicle (HEV), and a plug-in hybrid vehicle (PHEV).

  EXAMPLES Hereinafter, although this invention is demonstrated concretely using an Example and a comparative example, this invention is not limited to these Examples, unless the summary is exceeded.

Example 1
In Example 1, diethyl (difluoromethyl) phosphonate was used as the fluorine-containing phosphonate represented by the above general formula (1).
(Example 1-1)
0.5% by mass of diethyl (difluoromethyl) phosphonate having the following chemical formula in a mixed solvent of ethylene carbonate (EC): ethyl methyl carbonate (EMC) containing 1 mol / L LiPF ₆ in a volume ratio of 30:70 By adding, a nonaqueous electrolyte according to Example 1-1 was produced.

(Examples 1-2 to 1-4)
According to Examples 1-2, 1-3, and 1-4, the addition amount of diethyl (difluoromethyl) phosphonate was changed from 0.5% by mass to 1% by mass, 2% by mass, and 5% by mass, respectively. A non-aqueous electrolyte was produced.

(Example 2)
In Example 2, bis (2,2,2-trifluoroethyl) methylphosphonate was used as the fluorine-containing phosphonate represented by the general formula (1).
(Example 2-1)
Example 2-1 was carried out in the same manner as Example 1-1 except that bis (2,2,2-trifluoroethyl) methylphosphonate having the following chemical formula was added instead of diethyl (difluoromethyl) phosphonate. The non-aqueous electrolyte which concerns on was produced.

(Examples 2-2 to 2-4)
The addition amount of bis (2,2,2-trifluoroethyl) methylphosphonate was changed from 0.5% by mass to 1% by mass, 2% by mass, and 5% by mass, respectively. -3 and 2-4 were produced.

(Comparative Example 1)
A nonaqueous electrolyte according to Comparative Example 1 was produced in the same manner as in Example 1-1 except that diethyl (difluoromethyl) phosphonate was not added.

(Comparative Example 2)
A nonaqueous electrolyte according to Comparative Example 2 was produced in the same manner as in Example 1-3 except that diethylmethylphosphonate having the following chemical formula was added instead of diethyl (difluoromethyl) phosphonate.

(Preparation of non-aqueous electrolyte secondary battery)
Using the nonaqueous electrolytes of Examples 1 and 2 and Comparative Examples 1 and 2, nonaqueous electrolyte secondary batteries were produced. The non-aqueous electrolyte secondary battery according to the example includes a positive electrode obtained by applying a positive electrode active material to a positive electrode current collector and a negative electrode obtained by applying a negative electrode active material to a negative electrode current collector through a separator. The electrode group formed by stacking and winding in a flat shape is housed in a battery case.

Next, a method for manufacturing the nonaqueous electrolyte secondary battery having the above configuration will be described.
The positive electrode was obtained as follows. First, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ and acetylene black as a conductive agent are mixed, and further, an N-methyl-2-pyrrolidone solution of polyvinylidene fluoride as a binder is mixed. The mixture (positive electrode mixture) was applied to both surfaces of a positive electrode current collector made of an aluminum foil, dried, and pressed so that the thickness of the positive electrode mixture became a predetermined thickness. The positive electrode was obtained by the above process.

  The negative electrode was obtained as follows. First, graphite (negative electrode active material (002) plane spacing of 0.336 nm by X-ray wide angle diffraction method) and styrene-butadiene rubber and carboxymethylcellulose aqueous solution as a binder were mixed, and this mixture (negative electrode The mixture was applied to both sides of a negative electrode current collector made of copper foil, dried, and pressed so that the thickness of the negative electrode mixture became a predetermined thickness. The negative electrode was obtained by the above process.

  As the separator, a polyethylene microporous membrane was used. The electrode group was configured by facing the positive electrode mixture and the negative electrode mixture, placing a separator therebetween, and laminating and winding the positive electrode, the separator, and the negative electrode in this order. Next, the electrode group was housed in an aluminum battery case, and positive and negative electrode terminals were attached. The battery case was sealed after injecting the nonaqueous electrolytes of Examples 1 and 2 and Comparative Examples 1 and 2, respectively. As described above, the nonaqueous electrolyte secondary batteries of Examples 1 and 2 and Comparative Examples 1 and 2 were produced.

(Charge / discharge test)
The batteries of Examples 1 and 2 and Comparative Examples 1 and 2 were subjected to a charge / discharge test.
First, at 25 ° C., a constant current and constant voltage charge with a current of 1.0 CmA and a final voltage of 4.35 V and a constant current discharge with a current of 1.0 CmA and a final voltage of 2.75 V were performed for one cycle.
Next, at 45 ° C., 75 cycles of constant current and constant voltage charging with a current of 1.0 CmA and a final voltage of 4.35 V and constant current discharge with a current of 1.0 CmA and a final voltage of 2.75 V were performed, and one cycle at 45 ° C. First and 75th cycle 1C discharge capacities were measured.

(Measurement of battery thickness)
In the above charge / discharge test, the thickness of the battery at room temperature before measuring the 1.0C discharge capacity at the first cycle at 45 ° C. and after measuring the 1.0C discharge capacity at the 75th cycle at 45 ° C. It measured using.

  The above results are summarized in Table 1 and Table 2. In Table 1, the 1.0C discharge capacity at the first cycle and the 75th cycle at 45 ° C. is expressed with the value of the 1.0C discharge capacity at the first cycle of Comparative Example 1 as 100%. In Table 2, the battery thickness before measuring the 1.0C discharge capacity at the first cycle at 45 ° C. is “battery thickness first cycle”, and after measuring the 1.0C discharge capacity at the 75th cycle at 45 ° C. The battery thickness was expressed as “battery thickness 75th cycle”, and the value of the battery thickness before measuring the 1.0C discharge capacity in the first cycle at 45 ° C. of Comparative Example 1 was expressed as 100%.

As shown in Tables 1 and 2, the fluorine-containing phosphonic acid ester represented by the above general formula (1) having an alkyl group in which at least one of the hydrogen atoms of R _{1 to} R ₃ is substituted with a fluorine atom is 5 The secondary battery using the non-aqueous electrolytes of Examples 1 and 2 contained in mass% or less was charged at a higher temperature than the secondary battery using the non-aqueous electrolyte of Comparative Example 1 containing no fluorine-containing phosphonate. It can be seen that the discharge cycle performance is remarkably improved and the increase in battery thickness is remarkably suppressed. On the other hand, the nonaqueous electrolyte secondary battery of Comparative Example 2 containing a phosphonic acid ester having an alkyl group in which the hydrogen atoms of R _{1 to} R ₅ are not substituted with fluorine atoms is the nonaqueous electrolyte of Comparative Example 1. Compared to the secondary battery, the high-temperature charge / discharge cycle performance is not improved, and the increase in battery thickness is comparable and not suppressed. Even when the fluorine-containing phosphonate represented by the general formula (1) is contained, if the content exceeds 5% by mass of the non-aqueous electrolyte, the high-temperature charge / discharge cycle performance is not sufficiently improved. The content is 5% by mass or less. It is preferable to be less than 5% by mass. Moreover, it is preferable to set it as 0.5 mass% or more.

(Explanation of symbols)
DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte secondary battery 2 Electrode group 3 Battery container 4 Positive electrode terminal 4 'Positive electrode lead 5 Negative electrode terminal 5' Negative electrode lead 20 Power storage unit 30 Power storage device

  Since the nonaqueous electrolyte secondary battery according to the present invention has excellent charge / discharge cycle performance, it is useful as a power source for vehicles such as electric vehicles, hybrid vehicles, plug-in hybrid vehicles and the like.

Claims (2)

A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte using a positive electrode material used for a battery operated at a potential of less than 4.5 V based on metallic lithium , wherein the non-aqueous electrolyte is The following general formula (1)

(Wherein R _{1 to} R ₃ each independently represents a C 1-8 alkyl group in which a hydrogen atom may be substituted with a fluorine atom, and at least one of them is at least 1) Two hydrogen atoms are replaced by fluorine atoms.)
A non-aqueous electrolyte secondary battery comprising 5% by mass or less of a fluorine-containing phosphonic acid ester represented by the formula: 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein in the fluorine-containing phosphonate represented by the general formula (1), at least one hydrogen atom of R ₃ is substituted with a fluorine atom. _3. .

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