JP2018081766A - Nonaqueous electrolyte power storage element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte power storage element having a high charge/discharge capacity retention rate and also having excellent repetition cycle characteristics.SOLUTION: A nonaqueous electrolyte power storage element 10 includes: a positive electrode 11 containing a positive electrode active material; a negative electrode 12 containing a negative electrode active material; an electrolyte containing a nonaqueous solvent and an electrolyte salt; and a separator 13 in which a plurality of layers formed using fibers are laminated, average fiber diameters of the fibers included in the respective layers being different from one another.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a non-aqueous electrolyte storage element.

  Conventionally, as a storage element using a non-aqueous electrolyte, for example, a lithium ion battery having a positive electrode such as a lithium cobalt composite oxide, a carbon negative electrode, and a non-aqueous electrolyte in which a lithium salt is dissolved in a non-aqueous solvent. Many secondary batteries are used (see Patent Document 1).

  In recent years, power storage devices have been used in a wide range of applications from portable devices to electric vehicles, and power storage devices having a high input / output density are required. As such a storage element, carbon is used for the positive electrode active material and the negative electrode active material, and anions in the non-aqueous electrolyte are inserted into or removed from the positive electrode, and lithium ions in the non-aqueous electrolyte are inserted into or removed from the negative electrode. There is a non-aqueous electrolyte secondary battery that is charged and discharged (see, for example, Non-Patent Document 1). The non-aqueous electrolyte secondary battery is also referred to as a dual carbon battery (DCB). In the dual carbon battery, the cations and anions in the non-aqueous electrolyte are inserted into the positive electrode active material and the negative electrode active material, so the internal resistance of the dual carbon battery is very small and the input / output density is very large. Therefore, the dual carbon battery has high input / output density while improving high-speed charge / discharge characteristics.

  As a method of increasing the discharge capacity of the dual carbon battery, for example, there is a method of increasing the amount of ions in the nonaqueous electrolytic solution and using a high concentration nonaqueous electrolytic solution. For example, the dual carbon battery can be charged at a high voltage of 5 V or more. However, the decomposition of the non-aqueous electrolyte increases under a high voltage. Therefore, if a high concentration non-aqueous electrolyte is used, hydrogen, carbon dioxide, etc. Bubbles may be generated. When the gas is generated, the gas accumulates between the positive electrode and the negative electrode, and the area of the electrode is reduced, so that the battery capacity may be reduced and cycle characteristics may be deteriorated.

  An object of this invention is to provide the non-aqueous-electrolyte electrical storage element which has a high charging / discharging capacity | capacitance maintenance factor and has the outstanding repetitive cycle characteristic.

  A nonaqueous electrolyte storage element according to an embodiment of the present invention includes a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, a nonaqueous electrolyte in which an electrolyte salt is dissolved in a nonaqueous solvent, and fibers. A plurality of layers formed using the separators, and separators having different average fiber diameters of the fibers contained in each layer.

  According to the embodiment of the present invention, it is possible to provide a nonaqueous electrolyte storage element that has a high charge / discharge capacity retention ratio and can have excellent repeated cycle characteristics.

FIG. 1 is a schematic view showing an example in which the nonaqueous electrolyte storage element according to one embodiment is applied as a dual carbon battery. FIG. 2 is a graph showing the discharge capacity retention rates of Examples 1 to 4 and Comparative Examples 1 and 2. FIG. 3 is a diagram showing the relationship between the charge / discharge cycle and the discharge capacity retention rate of Examples 1 to 3 and Comparative Example 1. FIG. 4 is a diagram showing the relationship between the charge / discharge cycle and the discharge capacity retention rate of Example 4 and Comparative Example 2.

  Embodiments according to the present invention will be described below. Note that it is easy for a person skilled in the art to make other embodiments by changing or correcting the present invention within the scope of the claims, and these changes and modifications are included in the scope of the claims. . The following description exemplifies an embodiment of the present invention and does not limit the scope of the claims.

(Non-aqueous electrolyte storage element)
The non-aqueous electrolyte storage element according to the embodiment includes a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator, and further includes other members as necessary. Hereinafter, each constituent member of the nonaqueous electrolyte storage element according to the present invention will be described in detail.

<Positive electrode>
The positive electrode contains a positive electrode active material. A positive electrode will not be restrict | limited especially if the positive electrode active material is included, According to the objective, it can select suitably. Examples of the positive electrode include an electrode including a positive electrode material layer having a positive electrode active material on a positive electrode current collector. There is no restriction | limiting in particular in the shape of a positive electrode, According to the objective, it can select suitably, For example, flat form etc. are mentioned.

[Positive electrode material layer]
The positive electrode material layer includes at least a positive electrode active material, and may further include a conductive agent, a binder, a thickener, and the like as necessary.

[Positive electrode active material]
The positive electrode active material is not particularly limited as long as it can insert or desorb anions, and can be appropriately selected depending on the purpose. Examples of the positive electrode active material include a carbonaceous material and a conductive polymer. These may be used alone or in combination of two or more. Among these, a carbonaceous material is preferable from the viewpoint of high input / output density.

Examples of the carbonaceous material include graphite (graphite) such as artificial graphite and natural graphite, coke, soft carbon, and pyrolysis products of organic substances under various pyrolysis conditions. Among these, graphite or soft carbon is particularly preferable because it has a high discharge capacity. The carbonaceous material is preferably a carbonaceous material having high crystallinity. The crystallinity of the carbonaceous material can be evaluated by X-ray diffraction, Raman analysis, or the like. For example, the carbonaceous material has a diffraction peak intensity I _{2θ = 22.3 ° at 2θ = 22.3 °} and a diffraction peak intensity I _2θ at 2θ = 26.4 ° in a powder X-ray diffraction pattern using CuKα rays. _{= 26.4 °} Intensity ratio I _{2θ = 22.3 °} / I _{2θ = 26.4 °} is preferably 0.4 or less. The BET specific surface area by nitrogen adsorption of the carbonaceous material is preferably 1 m ² / g or more and 100 m ² / g or less, and the average particle diameter (median diameter) measured by the laser diffraction / scattering method is 0.1 μm or more and 100 μm or less. Preferably there is.

Soft carbon, for example, is a generic term for carbon in which a hexagonal network surface composed of carbon atoms is easy to form a regular laminated structure by heat treatment in an inert atmosphere. In the present embodiment, for example, when heat treatment is performed in an inert atmosphere, a crystal structure in which an average interplanar spacing d ₀₀₂ of (002) plane is 3.50 mm or less, preferably 3.35 mm or more and 3.45 mm or less. The soft carbon that forms is used. Examples of the raw material for soft carbon include graphitizable carbon such as petroleum pitch, coal pitch, coke, and anthracene. These may be used alone or in combination of two or more.

  Examples of the conductive polymer include polyaniline, polypyrrole, polyparaphenylene, and the like.

[Conductive agent]
Examples of the conductive agent include metal materials and carbonaceous materials. Examples of the metal material include copper and aluminum. Examples of the carbonaceous material include carbon black and acetylene black. These may be used alone or in combination of two or more.

[Binder]
The binder is not particularly limited as long as it is a material that is stable with respect to a solvent, a non-aqueous electrolyte, and an applied potential used in manufacturing the positive electrode, and can be appropriately selected according to the purpose. Examples of the binder include fluorine binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), acrylic binders, styrene-butadiene rubber (SBR), isoprene rubber, and polyacrylic acid esters. Examples of the fluorine-based binder include polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). These may be used alone or in combination of two or more.

[Thickener]
Examples of the thickener include carboxymethyl cellulose (CMC), polyethylene glycol (PEO), methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, sodium alginate and the like. These may be used alone or in combination of two or more.

[Positive electrode current collector]
The material of the positive electrode current collector is not particularly limited as long as it is made of a conductive material and is stable with respect to the applied potential, and can be appropriately selected according to the purpose. Examples of the positive electrode current collector include stainless steel, nickel, aluminum, copper, titanium, and tantalum. Among these, stainless steel and aluminum are particularly preferable, and aluminum that is easy to manufacture foil and inexpensive is particularly preferable. The size of the positive electrode current collector is not particularly limited as long as it is a size that can be used for the nonaqueous electrolyte storage element, and can be appropriately selected according to the purpose. There is no restriction | limiting in particular in the shape and structure of a positive electrode electrical power collector, According to the objective, it can select suitably.

<Method for producing positive electrode>
For the positive electrode, a positive electrode material layer coating liquid (slurry for positive electrode material layer) is added onto the positive electrode current collector by adding a binder, a thickener, a conductive agent, a solvent, etc. to the positive electrode active material as necessary. It can be produced by coating the film and then drying to form a positive electrode material layer. There is no restriction | limiting in particular as a solvent, According to the objective, it can select suitably, For example, an aqueous solvent, an organic solvent, etc. are mentioned. Examples of the aqueous solvent include water and alcohol. Examples of the organic solvent include N-methyl-2-pyrrolidone (NMP) and toluene. In addition, the composition for positive electrode material layers which added the binder, the electrically conductive agent, etc. to the positive electrode active material as needed can be roll-molded into a sheet electrode, or compression-molded into a pellet electrode.

<Negative electrode>
The negative electrode is not particularly limited as long as it contains a negative electrode active material, and can be appropriately selected according to the purpose. For example, an electrode having a negative electrode material layer containing a negative electrode active material on a negative electrode current collector, etc. Can be mentioned. There is no restriction | limiting in particular in the shape of a negative electrode, According to the objective, it can select suitably, For example, flat form etc. are mentioned.

[Negative electrode layer]
The negative electrode material layer includes a negative electrode active material, and includes a binder, a conductive agent, and the like as necessary. There is no restriction | limiting in particular in the average thickness of a negative electrode material layer, Although it can select suitably according to the objective, It is preferable that they are 10 micrometers or more and 450 micrometers or less, and it is more preferable that they are 20 micrometers or more and 200 micrometers or less. When the average thickness of the negative electrode material layer is 10 μm or more, a non-aqueous electrolyte storage element having good cycle characteristics is obtained, and when it is 450 μm or less, a non-aqueous electrolyte storage element having a sufficient input / output density is obtained.

  In the present embodiment, the average thickness means an average value of thicknesses when the thickness of a layer as a measurement object is measured at several places with a micrometer. For example, the thickness of the layer is several places (for example, five places) in the longitudinal direction, several places in the width direction (for example, three places), and a total of 15 places are measured with a micrometer so that the measurement places are almost evenly spaced. When measured, it means the average value of the thickness at these 15 locations. In the present embodiment, the thickness means the length of the layer in the direction perpendicular to the contact surface of the electrode with the separator.

[Negative electrode active material]
The negative electrode active material is not particularly limited as long as it can insert or desorb cations such as lithium ions, and can be appropriately selected according to the purpose. Specifically, as the negative electrode active material, a carbonaceous material; a metal oxide capable of inserting or extracting lithium; a metal capable of being alloyed with lithium; a metal capable of being alloyed with lithium An alloy containing lithium; a metal that can be alloyed with lithium; a composite alloy compound of an alloy containing the metal with lithium; lithium metal nitride; and the like. These may be used alone or in combination of two or more.

Examples of the carbonaceous material include coke, artificial graphite, natural graphite, soft carbon, hard carbon, and pyrolysis products of organic substances under various pyrolysis conditions. Among these, artificial graphite, natural graphite, soft carbon, or hard carbon is particularly preferable. In the present embodiment, for example, when it is heat treated in an inert atmosphere, hard carbon is used in which the average spacing d ₀₀₂ of (002) plane to form a crystal structure of greater than 3.50 Å. Examples of hard carbon materials include thermosetting resins and carbon black. Examples of the thermosetting resin include a phenol resin, a melamine resin, a urea resin, an epoxy resin, and a urethane resin. Examples of carbon black include acetylene black and furnace black.

Examples of the metal oxide that can occlude or release lithium include lithium titanate, titanium oxide, antimony tin oxide, and silicon monoxide. Examples of lithium titanate include Li ₄ Ti ₅ O ₁₂ . Examples of the metal that can be alloyed with lithium include aluminum, tin, silicon, and zinc. Examples of the lithium metal nitride include cobalt lithium nitride.

  Among these, the negative electrode active material is particularly preferably a carbonaceous material or lithium titanate from the viewpoints of high safety and high input / output density of the nonaqueous electrolyte storage element.

[Binder]
The binder is not particularly limited as long as it is a material that is stable with respect to the solvent and non-aqueous electrolyte used in manufacturing the negative electrode, and can be appropriately selected according to the purpose. Examples of the binder include fluorine-based binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), ethylene-propylene-butadiene rubber (EPBR), styrene-butadiene rubber (SBR), isoprene rubber, carboxymethyl cellulose ( CMC) and polyethylene glycol (PEO). These may be used alone or in combination of two or more. Among these, fluorine-based binders such as PVDF and PTFE, and CMC are preferable, and CMC is particularly preferable from the viewpoint that the number of repeated charge / discharge cycles is improved as compared with other binders.

[Conductive agent]
Examples of the conductive agent include metal materials and carbonaceous materials. Examples of the metal material include copper and aluminum. Examples of the carbonaceous material include carbon black and acetylene black. These may be used alone or in combination of two or more.

[Negative electrode current collector]
The material of the negative electrode current collector is not particularly limited as long as it is a conductive material that is stable with respect to the applied potential, and can be appropriately selected according to the purpose. Examples of the material for the negative electrode current collector include stainless steel, nickel, aluminum, and copper. Among these, stainless steel and copper are particularly preferable. The shape of the negative electrode current collector is not particularly limited and can be appropriately selected depending on the purpose. The size of the negative electrode current collector is not particularly limited as long as it is a size that can be used for the nonaqueous electrolyte storage element, and can be appropriately selected according to the purpose. The structure of the negative electrode current collector is not particularly limited and can be appropriately selected according to the purpose.

<Method for producing negative electrode>
The negative electrode is prepared by applying a negative electrode material layer coating liquid in a slurry form by adding a binder, a conductive agent, a solvent, etc. to the negative electrode active material, if necessary, and then drying the negative electrode active material. It can be produced by forming a material layer. As the solvent, the same solvent as that for the positive electrode can be used. Moreover, the composition for negative electrode material layers which added the binder, the electrically conductive agent, etc. to the negative electrode active material as needed can be roll-molded into a sheet electrode, or compression-molded into a pellet electrode. In addition, a thin film electrode of a negative electrode active material can be formed on the negative electrode current collector by a method such as vapor deposition, sputtering, or plating.

<Non-aqueous electrolyte>
The nonaqueous electrolytic solution is an electrolytic solution containing a nonaqueous solvent and an electrolyte salt, and the electrolyte salt is dissolved in the nonaqueous solvent.

[Nonaqueous solvent]
There is no restriction | limiting in particular as a non-aqueous solvent, Although it can select suitably according to the objective, An aprotic organic solvent is preferable. As the aprotic organic solvent, carbonate-based organic solvents such as chain carbonates and cyclic carbonates are used, and low viscosity solvents are preferred. The aprotic organic solvent preferably contains a chain carbonate from the viewpoint of improving the dissolving power of the electrolyte salt.

  Examples of the chain carbonate include dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propionate (MP), and the like, and they can be used by appropriately mixing them. Among these, DMC and EMC are preferable.

  The content of the chain carbonate in the non-aqueous solvent is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 50% by mass or more, and more preferably 67% by mass or more. . When the content of the chain carbonate in the non-aqueous solvent is 50% by mass or more, the discharge capacity of the non-aqueous electrolyte storage element can be improved and the resistance of the non-aqueous electrolyte decreases, thereby reducing non-aqueous electrolysis. The input / output density of the liquid storage element can be improved.

  Examples of the cyclic carbonate include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), vinylene carbonate (VC), and fluoroethylene carbonate (FEC). Among these, PC is particularly preferable because of the high input / output density and discharge capacity of the nonaqueous electrolyte storage element.

  In the case of using a mixed solvent in which a chain carbonate and a cyclic carbonate are combined, the mixing ratio of the chain carbonate and the cyclic carbonate is preferably 1: 1 to 4: 1 by mass ratio, and 1: 1 to 3 is preferable. : 1 is more preferable. For example, when a mixed solvent in which DMC and EMC are combined as a chain carbonate and PC is used as a cyclic carbonate, the mixing ratio of DMC, EMC, and PC is 1: 1 to 2: 1 in terms of mass ratio. preferable.

  The non-aqueous solvent is an aprotic organic solvent other than the chain carbonate and the cyclic carbonate, if necessary, an ester organic solvent such as a cyclic ester and a chain ester, and an ether organic such as a cyclic ether and a chain ether. A solvent or the like can be used.

  Examples of the cyclic ester include γ-butyrolactone (γBL), 2-methyl-γ-butyrolactone, acetyl-γ-butyrolactone, and γ-valerolactone.

  Examples of chain esters include propionic acid alkyl esters, malonic acid dialkyl esters, acetic acid alkyl esters (such as methyl acetate (MA) and ethyl acetate), formic acid alkyl esters (such as methyl formate (MF) and ethyl formate), and the like. It is done.

  Examples of the cyclic ether include tetrahydrofuran, alkyltetrahydrofuran, alkoxytetrahydrofuran, dialkoxytetrahydrofuran, 1,3-dioxolane, alkyl-1,3-dioxolane, 1,4-dioxolane and the like.

  Examples of the chain ether include 1,2-dimethoxyethane (DME), diethyl ether, ethylene glycol dialkyl ether, diethylene glycol dialkyl ether, triethylene glycol dialkyl ether, and tetraethylene glycol dialkyl ether.

[Electrolyte salt]
The electrolyte salt is not particularly limited as long as it is dissolved in a non-aqueous solvent and ionized cations exhibit high ionic conductivity. Examples of the cation constituting the electrolyte salt include alkali metal ions, alkaline earth metal ions, tetraalkylammonium ions, spiro quaternary ammonium ions, and the like. Examples of the anion constituting the electrolyte salt include Cl ⁻ , Br ⁻ , I ⁻ , ClO ₄ ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , SbF ₆ ⁻ , AsF ₆ ⁻ , CF ₃ SO ₃ ⁻ , (CF ₃ SO ₂ ). _{^{2 N -, (C 2 F}} 5 SO 2) 2 N - , and the like. One electrolyte salt may be used alone, or two or more electrolyte salts may be used in combination. Especially, it is preferable that electrolyte salt is lithium salt from the point which improves the capacity | capacitance of a non-aqueous electrolyte electrical storage element.

Examples of the lithium salt include lithium hexafluorophosphate (LiPF ₆ ), lithium perchlorate (LiClO ₄ ), lithium chloride (LiCl), lithium borofluoride (LiBF ₄ ), and lithium arsenic hexafluoride (LiAsF ₆ ). , Lithium trifluorometasulfonate (LiCF ₃ SO ₃ ), lithium bistrifluoromethylsulfonylimide (LiN (C ₂ F ₅ SO ₂ ) ₂ ), lithium bisfurfluoroethylsulfonylimide (LiN (CF ₂ F ₅ SO ₂ ) ₂ ). These may be used alone or in combination of two or more. Among these, LiPF ₆ or a combination of LiPF ₆ and LiBF ₄ is particularly preferable from the viewpoint of the amount of occlusion of anions in the carbonaceous material.

  In the nonaqueous electrolyte storage element, charging is performed by co-insertion of an anion and a cation. Therefore, the concentration of the electrolyte salt in the nonaqueous electrolytic solution is preferably 1.5 mol / L or more, and more preferably 2.0 mol / L or more and 5 mol / L or less. When the concentration of the electrolyte salt in the nonaqueous electrolytic solution is 1.5 mol / L or more, a nonaqueous electrolytic solution storage element with high charge / discharge efficiency is obtained. On the other hand, if the concentration of the electrolyte salt is 5 mol / L or less, the viscosity of the non-aqueous electrolyte is increased and the ionic conductivity is suppressed from increasing, so that it is possible to suppress an increase in resistance and charge / discharge current. A nonaqueous electrolyte storage element having good characteristics can be obtained.

<Separator>
The separator is provided between the positive electrode and the negative electrode in order to prevent a short circuit between the positive electrode and the negative electrode. The separator is configured by laminating a plurality of layers formed using fibers, and the average fiber diameter of the fibers contained in each layer is different. Even if gas is generated between the electrodes, the bubbles (gas) such as hydrogen and carbon dioxide generated between the electrodes are formed between the fibers by forming a plurality of layers formed of fibers having different average fiber diameters. The separator can be smoothly passed through the gap. For this reason, it can suppress that the gas produced between electrodes accumulates between electrodes. Thereby, since it can suppress that the area of the positive electrode and negative electrode which contribute to charging / discharging reaction falls, the discharge capacity maintenance factor of a non-aqueous electrolyte electrical storage element becomes high, and it contributes to the improvement of repeated cycle characteristics.

  In the present embodiment, the average fiber diameter is an average value obtained by selecting a plurality of fibers having a cross section perpendicular to or substantially perpendicular to the fiber length direction and measuring the fiber diameter. The fiber may be melted or deformed by heat or pressure. In that case, the cross-sectional area is measured, and the fiber diameter in terms of a perfect circle is calculated. The fibers are observed using, for example, a scanning electron microscope (SEM).

  The fiber of the layer constituting the separator is obtained by spinning a cellulose resin, a polybutylene terephthalate resin, a polyolefin resin such as a polypropylene resin, a polyamide resin, glass or the like into a fiber shape. These may be used alone or in combination of two or more. The layer which comprises a separator is obtained by forming the fiber obtained by spinning in the form of a nonwoven fabric, a textile fabric, or a knitted fabric, for example. Examples of the shape of the separator include a sheet shape. The size of the separator may be any size as long as it can be used for the nonaqueous electrolyte storage element, and can be appropriately selected according to the purpose.

  The layers constituting the separator may be formed of fibers of different materials, but the layers constituting the separator are made of the same material from the viewpoint of producing a separator having stable strength while ensuring air permeability. It is preferably formed of fibers.

The separator has a first layer containing fibers having an average fiber diameter of Y μm and a second layer containing fibers having an average fiber diameter of X μm, and satisfies the following formulas (1) and (2). It is preferable. If the average fiber diameter of the fibers constituting the second layer is 5 μm or less, the gas generated between the electrodes can pass through the gap between the fibers and smoothly pass through the separator. For this reason, it can suppress that the gas produced between electrodes accumulates between electrodes, and can maintain the holding | maintenance amount of the non-aqueous electrolyte in a separator. Further, if the average fiber diameter of the fibers constituting the first layer is 1.3 times or more than the average fiber diameter of the fibers constituting the second layer, the electrolyte solution can be retained, and the mechanical strength of the separator can be secured. Reduction is suppressed.
0 <X ≦ 5 μm (1)
1.3X ≦ Y (2)

Moreover, it is more preferable that the second layer satisfies the following formula (1) ′, and it is more preferable that the first layer satisfies the following formula (2) ′. Thereby, the retention amount of the non-aqueous electrolyte in the separator can be maintained more stably.
0 <X ≦ 3 μm (1) ′
1.3X ≦ Y ≦ 10X (2) ′

  The thickness of the first layer is preferably 6 to 50 μm, and more preferably 10 to 30 μm. When the thickness of the first layer is 6 μm or more, the gas generated between the electrodes can be prevented from accumulating between the electrodes, and the amount of nonaqueous electrolyte retained in the separator can be maintained. The diffusion coefficient can be increased. In addition, when the thickness of the first layer is 30 μm or less, it is possible to reduce the battery resistance and reduce the size of the separator while maintaining the amount of nonaqueous electrolyte retained in the separator.

  The thickness of the second layer is preferably 5 to 25 μm, and more preferably 10 to 20 μm. When the thickness of the second layer is 5 μm or more, a decrease in strength of the separator can be suppressed and a short circuit can be prevented. Further, when the thickness of the second layer is 25 μm or less, it is possible to reduce battery resistance and reduce the size of the separator while suppressing a decrease in the strength of the separator.

  The ratio of the thickness of the first layer to the thickness of the second layer is preferably 1: 2 to 5: 1, more preferably 1: 1 to 4: 1. If the ratio of the thickness of the first layer to the thickness of the second layer is 1: 2 or more, the outgassing effect in the first layer can be supported. On the other hand, if the ratio of the thickness of the first layer to the thickness of the second layer is 5: 1 or less, the outgassing effect can be supported while maintaining the short-circuit prevention effect in the second layer.

  When a separator is comprised by two types of layers, a 1st layer and a 2nd layer, each layer may be arrange | positioned so that either a positive electrode or a negative electrode may be contacted. From the viewpoint of the charge / discharge mechanism of the nonaqueous electrolyte storage element, the first layer is preferably disposed so as to be in contact with the positive electrode side, and the second layer is preferably disposed so as to be in contact with the negative electrode side.

  In addition, the first layer or the second layer is not limited to a single layer, and a plurality of layers may be provided, and the separator may be composed of three or more layers.

  The average thickness of the entire separator is preferably 30 μm or more. The upper limit of the overall average thickness of the separator is not particularly limited, but is appropriately adjusted depending on the size of the nonaqueous electrolyte storage element. If the average thickness of the entire separator is 30 μm or more, the amount of nonaqueous electrolyte retained in the separator can be sufficiently maintained, so that the bias of ions in the nonaqueous electrolyte and depletion of the electrolyte during full charge can be avoided. Can be suppressed.

The separator preferably has a Gurley value of 230 to 290 μm / Pa · s. Thereby, air permeability, retention ability of the non-aqueous electrolyte, and strength can be ensured. In the present embodiment, the Gurley value is obtained in accordance with a method specified in JISP 8117: 2009 (Gurley test machine method), and is 100 cc of air mL under a pressure of 0.879 gf / mm ² in accordance with JISP 8117. It means the number of seconds that air passes through the membrane. Therefore, in this embodiment, when the Gurley value is 230 μm / Pa · s or more, a decrease in the strength of the separator can be suppressed. On the other hand, when the Gurley value is 290 μm / Pa · s or less, the ion permeability and the decrease in the electrolyte holding capacity of the separator are suppressed.

<Other members>
Other members are not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include an outer can and a lead wire.

<Method for Manufacturing Nonaqueous Electrolyte Storage Element>
The nonaqueous electrolyte storage element of the embodiment can be manufactured, for example, by assembling a positive electrode, a negative electrode, a nonaqueous electrolyte, and a separator into an appropriate shape. When manufacturing the non-aqueous electrolyte storage element, an outer can or the like can be further used as necessary. There is no restriction | limiting in particular as a method of assembling a non-aqueous electrolyte electrical storage element, It can select suitably from the method employ | adopted normally.

<Operation method of nonaqueous electrolyte storage element>
The working voltage range of the non-aqueous electrolyte storage element of the embodiment is preferably 2.5V to 5.5V. If the voltage during charging / discharging is less than 2.5 V, sufficient anion cannot be accumulated, and the discharge capacity of the nonaqueous electrolyte storage element may be reduced. Moreover, when the voltage at the time of charging / discharging exceeds 5.5V, decomposition | disassembly of a non-aqueous solvent and electrolyte salt will occur easily, and deterioration of a non-aqueous electrolyte electrical storage element may be accelerated.

<Application example of nonaqueous electrolyte storage element>
Here, an example in which the nonaqueous electrolyte storage element according to the embodiment is applied as a dual carbon battery is shown in FIG. As shown in FIG. 1, the dual carbon battery 10 is configured by housing a positive electrode 11, a negative electrode 12, and a separator 13 in an outer can 14. The separator 13 is composed of two layers, a first layer 13 a and a second layer 13 b, and is disposed between the positive electrode 11 and the negative electrode 12. The first layer 13a is a layer including fibers having an average fiber diameter of X μm, and the second layer 13b is a layer including fibers having an average fiber diameter of Y μm. A nonaqueous electrolytic solution obtained by dissolving a lithium salt in a nonaqueous solvent is injected into the outer can 14, and the positive electrode 11, the negative electrode 12, and the separator 13 are immersed in the nonaqueous electrolytic solution. Is impregnated in a non-aqueous electrolyte. In addition, lead wires 15 and 16 are provided on the positive electrode 11 and the negative electrode 12, respectively, and the lead wires 15 and 16 are connected to, for example, an external power source.

<Shape of nonaqueous electrolyte storage element>
The shape of the nonaqueous electrolyte storage element of the embodiment can be appropriately selected from various shapes that are generally employed according to the application. Examples of the shape of the nonaqueous electrolyte storage element include a laminate type, a cylinder type, a cylinder type, and a coin type. The laminate type has a structure in which sheet electrodes and separators are laminated. The cylinder type has a structure in which the sheet electrode and the separator are spiral. The cylinder type is an inside-out structure in which a pellet electrode and a separator are combined. The coin type has a structure in which pellet electrodes and separators are stacked.

<Application of non-aqueous electrolyte storage element>
The application of the nonaqueous electrolyte storage element of the embodiment is not particularly limited, and can be used for various applications. Examples of the use of the non-aqueous electrolyte storage element of the embodiment include a notebook computer, a pen input personal computer, a mobile personal computer, an electronic book player, a cellular phone, a portable fax machine, a portable copy, a portable printer, a headphone stereo, a video movie, and a liquid crystal television. , Handy cleaners, portable CDs, mini-discs, transceivers, electronic notebooks, calculators, memory cards, portable tape recorders, radios, motors, lighting equipment, toys, game equipment, clocks, strobes, cameras, electric bicycles, electric tools, etc. Or a backup power source.

  Examples of the present invention will be described below, but the present invention is not limited to these examples. In addition, a present Example is an example which uses the nonaqueous electrolyte storage element by this invention as a nonaqueous electrolyte secondary battery. Further, “%” in this example means “mass%”.

<Preparation of positive electrode A>
Carbon powder (KS-6, manufactured by TIMCAL) was used as the positive electrode active material. This carbon powder had a BET specific surface area of 20 m ² / g by nitrogen adsorption and an average particle diameter (median diameter) measured by a laser diffraction particle size distribution meter (SALD-2200, manufactured by Shimadzu Corporation) was 3.4 μm.

  Carbon powder (KS-6, manufactured by TIMCAL) and acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive agent are kneaded with water, and then 3% by mass of carboxymethyl cellulose (CMC) as a thickener. 19 g of an aqueous solution (Daiichi Kogyo Seiyaku Co., Ltd.) was added and kneaded. Subsequently, 0.75 g of an acrylate binder (manufactured by JSR Corporation) as a binder was added and kneaded to prepare a slurry for a positive electrode material layer.

  Next, a positive electrode material layer slurry was applied on an aluminum sheet (thickness 20 μm) as a positive electrode current collector, and then vacuum dried at 150 ° C. for 20 hours to form a positive electrode material layer. The aluminum foil on which the positive electrode material layer was formed was punched into 83 mm × 101 mm to produce a positive electrode A.

<Preparation of negative electrode A>
After adding and kneading water to 10 g of lithium titanate (LTO, manufactured by Ishihara Sangyo Co., Ltd.) as a negative electrode active material and 0.5 g of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive agent, carboxy as a thickener. 10 g of a 3% by weight aqueous solution of methylcellulose (CMC) was added and kneaded. Subsequently, 0.75 g of the acrylate binder was added to prepare a negative electrode material layer slurry.

  Next, a slurry for a negative electrode material layer was applied on a copper foil as a negative electrode current collector, and then vacuum dried at 150 ° C. for 20 hours to form a negative electrode material layer. The copper foil on which the negative electrode material layer was formed was punched into 83 mm × 101 mm to produce a negative electrode A.

<Preparation of non-aqueous electrolyte A>
DMC / PC / EMC weight ratio 1: 1: a mixed solvent of 1, so that the concentration is a concentration of 1.8 mol / L and LiBF ₄ of LiPF ₆ becomes 0.2 mol / L, the LiPF ₆ and LiBF ₄ Dissolved to prepare a non-aqueous electrolyte A.

<Preparation of separator A>
A cellulose separator A comprising a first layer having an average fiber diameter of 1.5 μm and a second layer having an average fiber diameter of 1 μm was prepared. The separator A had an average thickness of 40 μm and a Gurley value of 239.2 μm / Pa · s.

<Preparation of separator B>
A separator B having an average fiber diameter of 1.5 μm and a first layer having an average thickness of 20 μm and an average fiber diameter of 1 μm and a second layer having an average thickness of 10 μm and an average thickness of 30 μm was prepared. The Gurley value of this separator B was 237.55 μm / Pa · s.

<Preparation of separator C>
A separator C having an average fiber diameter of 1.5 μm and an average thickness of 25 μm and an average fiber diameter of 1 μm and a second layer having an average thickness of 10 μm and an average thickness of 35 μm was prepared. The Gurley value of this separator C was 237.55 μm / Pa · s.

<Preparation of separator D>
Instead of the separator A, a polybutylene terephthalate separator (average thickness: 20 μm) having an average fiber diameter of 4 μm and a polybutylene terephthalate separator (average thickness: 20 μm, manufactured by Tapils) having an average fiber diameter of 3 μm. A separator D was prepared. The separator D had an average thickness of 39 μm and a Gurley value of 1.7 μm / Pa · s.

<Preparation of separator a>
A cellulose-based separator (manufactured by Nippon Kogyo Paper Co.) a having an average fiber diameter of 1 μm was prepared. This separator a had an average thickness of 25 μm and a Gurley value of 298.3 μm / Pa · s.

<Preparation of separator b>
A separator (manufactured by Tapirs) b made of polybutylene terephthalate was prepared. The separator b had an average thickness of 20 μm and a Gurley value of 2.2 μm / Pa · s.

<Example 1>
A negative electrode A, a separator A, and a positive electrode A were repeatedly laminated in this order to produce an electrode group. At this time, the negative electrode A was positioned on the outermost side using 20 positive electrodes A, 40 separators A, and 20 negative electrodes A. The obtained electrode group was accommodated in a laminate film. Next, after filling the outer can with the non-aqueous electrolyte A, the laminate film was sealed to produce the non-aqueous electrolyte storage element A.

<Example 2>
A nonaqueous electrolyte storage element B was produced in the same manner as in Example 1 except that the separator B was used instead of the separator A.

<Example 3>
A nonaqueous electrolyte storage element C was produced in the same manner as in Example 1 except that the separator C was used instead of the separator A.

<Example 4>
A nonaqueous electrolytic solution storage element D was produced in the same manner as in Example 1 except that the separator D was used instead of the separator A.

<Comparative Example 1>
A nonaqueous electrolytic solution storage element a was produced in the same manner as in Example 1 except that the separator a was used instead of the separator A.

<Comparative example 2>
A nonaqueous electrolytic solution storage element b was produced in the same manner as in Example 1 except that the separator b was used instead of the separator A.

  Table 1 shows the configurations of the nonaqueous electrolyte electricity storage devices A to D, a, and b of each of the above examples and comparative examples.

<Charge / discharge test>
Using a charge / discharge measuring device (TOSCAT3001, manufactured by Toyo System Co., Ltd.), the obtained nonaqueous electrolyte storage element was charged at a constant current of 0.2 mA / cm ² at room temperature (25 ° C.) to a charge end voltage of 3.5 V. Charged. After the first charge, the battery was discharged at a constant current of 0.2 mA / cm ² to 1.5 V, and a charge / discharge test was performed.

<Charge / discharge cycle test>
Using a charge / discharge measuring apparatus (TOSCAT3001, manufactured by Toyo System Co., Ltd.), the obtained nonaqueous electrolyte storage element was charged at a constant current of 1.0 mA / cm ² at room temperature (25 ° C.) to a charge end voltage of 3.5 V. Charged. After the first charge, the battery was discharged to 1.5 V with a constant current of 1.0 mA / cm ² . This constant current discharge was defined as one cycle. This charge / discharge cycle was repeated 1000 times in Examples 1 to 3 and Comparative Example 1, and 700 times in Example 4 and Comparative Example 2, and the charge / discharge cycle test was performed.

<Discharge capacity maintenance rate>
In the charge / discharge test, the discharge capacity retention rate of the nonaqueous electrolyte storage element was calculated when charge / discharge was performed for only one cycle. The measurement results are shown in FIG. In the charge / discharge cycle test, the discharge capacity retention rate of the non-aqueous electrolyte storage element at the 1st to 1000th cycles was calculated. The measurement results are shown in FIGS. The discharge capacity maintenance rate was the ratio of the discharge capacity to the charge capacity of the same cycle (discharge capacity / charge capacity × 100)%.

  2, the nonaqueous electrolyte storage elements of Examples 1 to 4 had a higher discharge capacity retention rate after the charge / discharge test than the nonaqueous electrolyte storage batteries of Comparative Examples 1 and 2. 3 and 4, the nonaqueous electrolyte storage elements of Examples 1 to 4 have a higher discharge capacity retention rate after the charge / discharge cycle test than the nonaqueous electrolyte storage batteries of Comparative Examples 1 and 2. It was. Therefore, it can be said that the nonaqueous electrolyte storage element according to the embodiment is superior in cycle characteristics because the discharge capacity maintenance rate is higher and the discharge capacity decrease rate is lower than the conventional nonaqueous electrolyte storage element. This is because, in the nonaqueous electrolyte storage element according to the embodiment, a gas pool between positive and negative electrodes can be suppressed by combining two layers formed of fibers having different average fiber diameters to form a separator. This is considered to be due to maintaining the positive and negative electrode areas contributing to the discharge reaction.

10 Nonaqueous electrolyte storage element (dual carbon battery)
DESCRIPTION OF SYMBOLS 11 Positive electrode 12 Negative electrode 13 Separator 13a 1st layer 13b 2nd layer 14 Outer can 15, 16 Lead line

JP 2012-199225 A

Journal of The Electrochemical Society, 147 (3) 899-901 (2000).

Claims (9)

A positive electrode including a positive electrode active material;
A negative electrode containing a negative electrode active material;
A non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent;
A separator in which a plurality of layers formed using fibers are stacked, and the average fiber diameter of the fibers included in each layer is different, and
A nonaqueous electrolyte storage element, comprising: The separator includes a first layer including fibers having an average fiber diameter of Y μm, and a second layer including fibers having an average fiber diameter of X μm,
The non-aqueous electrolyte storage element according to claim 1, wherein the following formula (1) and formula (2) are satisfied.
0 <X ≦ 5 μm (1)
1.3X ≦ Y (2)   The non-aqueous electrolyte storage element according to claim 2, wherein the ratio of the thickness of the first layer to the thickness of the second layer is 1: 2 to 5: 1.   The non-aqueous electrolyte storage element according to any one of claims 1 to 3, wherein the fiber is a cellulose resin or a polybutylene terephthalate resin.   The non-aqueous electrolyte storage element according to claim 1, wherein the separator has a thickness of 30 μm or more.   The nonaqueous electrolyte storage element according to claim 1, wherein the separator has a Gurley value of 230 to 290 μm / Pa · s.   The nonaqueous electrolyte storage element according to any one of claims 1 to 6, wherein the nonaqueous solvent includes an aprotic organic solvent containing a chain carbonate or a cyclic carbonate.   The non-aqueous electrolyte storage element according to claim 1, wherein the electrolyte salt includes a lithium salt.   The nonaqueous electrolyte storage element according to any one of claims 1 to 8, wherein the concentration of the electrolyte salt is 1.5 mol / L or more.

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