JP2021153021A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

The present invention provides a non-aqueous electrolyte secondary battery that is excellent in maintaining discharge capacity while maintaining a high energy density. [Solution] A non-aqueous electrolyte secondary battery comprising a positive electrode including a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector, a negative electrode including a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector, a separator, and a non-aqueous electrolyte, wherein the positive electrode and the negative electrode are arranged such that the positive electrode active material layer and the negative electrode active material layer face each other via the separator, the non-aqueous electrolyte contains 0.1% by mass to 5.0% by mass of vinylene carbonate, 30% by mass to 60% by mass of ethyl methyl carbonate, and 0.1% by mass to 3.0% by mass of fluorinated ethylene carbonate, and when the separator is immersed in a solvent consisting of ethyl methyl carbonate, the penetration speed of the solvent in the surface direction is 0.1 cm2/sec to 5.0 cm2/sec [Selected Figure] FIG. 1

Description

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

Lithium-ion secondary batteries are characterized by higher energy density and electromotive force than lead-acid batteries and nickel-hydrogen batteries, and are therefore used in a wide variety of applications from portable devices to vehicles and aircraft. Most of these lithium ion secondary batteries use a non-aqueous electrolyte solution in which a lithium salt is dissolved in an organic solvent as an electrolyte. In a lithium ion secondary battery using such a non-aqueous electrolyte, a positive electrode having a positive electrode active material layer provided on a positive electrode current collector and a negative electrode having a negative electrode active material layer provided on a negative electrode current collector are provided. It has a structure in which a laminated body laminated via a separator is housed in an outer body, filled with a non-aqueous electrolyte solution, and sealed.

In a lithium ion secondary battery, lithium ions are released from the positive electrode and moved into the negative electrode during charging, and lithium ions are released from the negative electrode and moved into the positive electrode during discharging. Therefore, the separator is required to have ion permeability such as lithium ion. Therefore, as a separator for a lithium ion secondary battery using a non-aqueous electrolyte, a porous resin film, which is a material having insulating properties and ion permeability, is used. For example, in Patent Document 1 and the like, a polyolefin microporous membrane having an average pore diameter of 0.05 to 0.5 μm determined by a mercury press-fitting method is used as a separator for a non-aqueous secondary battery, and the polyolefin microporous membrane is used. A configuration has been proposed in which a porous layer made of a heat-resistant resin is provided on the surface.

However, in the conventional non-aqueous electrolyte secondary battery, a phenomenon in which lithium ions do not move sufficiently between the positive and negative electrodes (so-called “liquid withering”) occurs during repeated charging and discharging, especially in the central portion of the separator. It is known that this tendency becomes remarkable.

Further, in a conventional non-aqueous electrolyte secondary battery, a part of the non-aqueous electrolyte containing a non-aqueous solvent and a lithium salt reacts irreversibly on the surface of the negative electrode active material as the battery is charged and discharged. At this time, a solid electrolyte interface (SEI) is formed so as to cover the surface of the negative electrode active material. It is known that the larger the amount of SEI produced, the larger the irreversible capacity and the lower the discharge capacity.

Japanese Unexamined Patent Publication No. 2011-23162

If the movement of lithium ions between the positive and negative electrodes does not sufficiently occur due to repeated charging and discharging, the amount of lithium ions that can be supplied to the positive electrode per fixed time decreases, and there is a problem that the discharge capacity decreases. Further, when SEI is formed on the surface of the negative electrode active material, the discharge capacity is reduced as described above, and lithium ions are blocked by the negative electrode during discharge, so that the transport of lithium ions to the positive electrode is likely to be delayed. In this case, the separator made of the porous polyethylene film as described above has a problem that the pore diameter is small, the amount of lithium ions that can be supplied to the positive electrode per fixed time is small, and the discharge capacity is lowered. On the other hand, it is conceivable to reduce the thickness of the positive electrode active material layer in order to increase the amount of lithium ions that can be supplied to the positive electrode, but in that case, another problem such as a decrease in energy density occurs.

Therefore, an object of the present invention is to provide a non-aqueous electrolyte secondary battery which is excellent in maintaining the discharge capacity while maintaining a high energy density.

As a result of diligent studies to solve the above problems, the present inventors have maintained a high energy density by using a separator satisfying a specific Garley value and a non-aqueous electrolyte having a specific composition in combination. It was found that a non-aqueous electrolyte secondary battery with excellent maintenance of discharge capacity can be obtained. The present invention is based on such findings. That is, the gist of the present invention is as follows.

[1] A positive electrode, a negative electrode current collector, and a negative electrode current collector having a positive electrode active material layer provided on at least one surface of the positive electrode current collector and the positive electrode current collector are provided on at least one surface. A non-aqueous electrolyte secondary battery comprising a negative electrode with a negative electrode active material layer, a separator, and a non-aqueous electrolyte.
The positive electrode and the negative electrode are arranged so that the positive electrode active material layer and the negative electrode active material layer face each other via the separator.
The non-aqueous electrolyte contains vinylene carbonate of 0.1% by mass or more and 5.0% by mass or less, ethylmethyl carbonate of 30% by mass or more and 60% by mass or less, and fluorine of 0.1% by mass or more and 3.0% by mass or less. Contains ethylene carbonate carbonate
The non-aqueous electrolyte secondary is characterized in that the permeation rate of the solvent in the plane direction when the separator is immersed in a solvent made of ethyl methyl carbonate is 0.1 cm ² / sec or more and 5.0 cm ^{2 / sec or less.} battery.
[2] The non-aqueous electrolyte secondary battery according to [1], wherein the garley value of the separator is 1 second / 100 cc or more and 20 seconds / 100 cc or less.
[3] The non-aqueous electrolyte secondary battery according to [1] or [2], wherein the Garley value of the separator is 1 second / 100 cc or more and 5 seconds / 100 cc or less.
[4] The non-aqueous electrolyte is 1.0% by mass or more and 3.0% by mass or less of vinylene carbonate, 40% by mass or more and 50% by mass or less of ethylmethyl carbonate, and 1.0% by mass or more and 2.0% by mass. The non-aqueous electrolyte secondary battery according to any one of [1] to [3], which comprises the following fluorinated ethylene carbonate.
[5] The non-aqueous electrolyte secondary battery according to any one of [1] to [4], wherein the separator has a thickness of 10 μm or more and 30 μm or less.
[6] The non-aqueous electrolyte secondary battery according to any one of [1] to [5], wherein the positive electrode active material layer contains lithium iron phosphate.
[7] The non-aqueous electrolyte secondary battery according to any one of [1] to [6], wherein the positive electrode active material layer is made of positive electrode active material particles in which at least a part of the particle surface is coated with carbon. ..

According to the present invention, by using a separator having a specific solvent permeation property and a non-aqueous electrolyte having a predetermined composition in combination, a non-aqueous electrolyte excellent in maintaining a discharge capacity while maintaining a high energy density. A secondary battery can be realized.

FIG. 6 is a schematic cross-sectional view schematically showing an embodiment of the non-aqueous electrolyte secondary battery of the present invention. The figure which showed typically the procedure of measuring the solvent permeation rate of the separator of the non-aqueous electrolyte secondary battery of this invention.

The non-aqueous electrolyte secondary battery according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view schematically showing an embodiment of the non-aqueous electrolyte secondary battery of the present invention. In the non-aqueous electrolyte secondary battery 1 according to the present invention, one plate-shaped positive electrode 10, two plate-shaped negative electrodes 20, and two separators 30 are formed of a negative electrode / separator / positive electrode / separator / negative electrode. The laminated bodies laminated in this order are housed in the exterior body 40, and the non-aqueous electrolyte (not shown) is filled in the exterior body 40 and sealed. In this embodiment, the positive electrode 10, the negative electrode 20, and the separator 30 are all rectangular in a plan view.

The positive electrode 10 of the non-aqueous electrolyte secondary battery 1 includes a plate-shaped positive electrode current collector 11 and positive electrode active material layers 12 provided on both sides thereof. Although not shown, when the positive electrode and the negative electrode are paired, the positive electrode active material layer 12 may be provided on at least one surface of the positive electrode current collector 11 on the opposite negative electrode side. At the edge of one end of the positive electrode current collector 11, a positive electrode current collector exposed portion 13 in which the positive electrode active material layer 12 does not exist is provided. A leader line (not shown) is provided at an arbitrary portion of the exposed portion 13.

The negative electrode 20 of the non-aqueous electrolyte secondary battery 1 includes a plate-shaped negative electrode current collector 21 and negative electrode active material layers 22 provided on both sides thereof. Although not shown, when the positive electrode and the negative electrode are paired, the negative electrode active material layer 22 may be provided on at least one surface of the negative electrode current collector 21 on the opposite positive electrode side. At the edge of one end of the negative electrode current collector 21, a negative electrode current collector exposed portion 23 is provided so that the material layer 22 to buy the negative electrode does not exist. A leader line (not shown) is provided at an arbitrary portion of the exposed portion 23.

In addition to the structure shown in FIG. 1, the non-aqueous electrolyte secondary battery according to the present invention may have a multilayer structure in which a plurality of negative electrodes and a plurality of positive electrodes are laminated. In this case, the negative electrode and the positive electrode may be provided alternately along the stacking direction. Further, the separator may be arranged between each negative electrode and each positive electrode.

The non-aqueous electrolyte secondary battery according to the present invention is characterized in that the separator 30 has a specific solvent permeation property. That is, the separator 30 in the present invention has a permeation rate in the plane direction when the separator 30 is immersed in a solvent made of ethyl methyl carbonate (hereinafter, also referred to as “solvent permeation rate” of the separator) of 0.1 cm ² / sec. One feature is that it is 5.0 cm ^{2 / sec or less.} In the non-aqueous electrolyte secondary battery according to the present invention, when the solvent permeation rate of the separator is in the above range, the non-aqueous electrolyte moves easily through the separator, and the movement of lithium ions between the positive and negative electrodes sufficiently occurs. it is conceivable that. As a result, even when charging and discharging are repeated, a high energy density is maintained and the maintenance rate of the discharge capacity is improved. A specific method for measuring the solvent permeation rate of the separator will be described below with reference to FIG. The following measurement method is preferably performed in a dry room having a dew point of −30 ° C. or lower.
First, a separator 30 having a size of 50 mm × 10 mm is prepared.
Next, a position 10 mm from both ends of the prepared separator 30 in the long side direction is marked with an oil-based magic.
The separator 30 is then vacuum dried at 120 ° C. for 4 hours.
Next, the glass rod 50 is fixed to the separator 30 with cellophane tape 60 so as to be perpendicular to the separator 30. At this time, the fixing position of the glass rod 50 is set to the outside in the long side direction (between the mark and the end portion close to the mark) with respect to the above mark of the separator 30.
Next, the weighting paper clip 70 is fixed to the outside in the long side direction (between the mark and the end close to the mark) with respect to the mark on the opposite side to which the glass rod 50 is fixed.
Next, the glass rod 60 fixed to the separator 30 is cross-linked to the 100 ml beaker 80 at the edge of the opening of the beaker, and the separator 30 is installed so that the side of the paper clip 70 enters the beaker 80.
Next, 50 ml of an electrolytic solution solvent (solvent composed of ethyl methyl carbonate) is prepared, and an ink for coloring is added so that it can be visually recognized.
Next, the colored electrolyte solvent is rapidly poured up to the mark on the lower part (Zem clip 70 side) of the separator 30 installed in the beaker 80.
Next, the time measurement is started from the time when the electrolytic solution solvent is started to be poured, and the time for the electrolytic solution solvent to permeate to the position marked on the upper part (glass rod 50 side) of the separator 30 is measured.
The time until the electrolyte solvent permeates all of the separator 30 marked on the upper part in the width direction is measured, and the permeation rate is calculated by setting the measurement time as the time required for permeation of an area of ^{3 cm 2.}

The range of the solvent permeation rate of the separator is preferably 0.5 cm ² / sec or more and 3.0 cm ² / sec or less, more preferably 1.0 cm ² / sec or more and 2.0 cm ² / sec or less, and even more preferably 1. It is 5 cm ² / sec.

In the non-aqueous electrolyte secondary battery according to the present invention, the Garley value of the separator 30 is preferably 1 second / 100 cc or more and 20 seconds / 100 cc or less. The Garley value is an index of air permeability, and the lower the Garley value, the higher the air permeability. In the non-aqueous electrolyte secondary battery according to the present invention, a higher energy density is maintained by using a separator having a lower Garley value (that is, higher air permeability) as compared with the conventional separator as described above. , The maintenance rate of the discharge capacity is further improved. The Garley value can be evaluated by a method based on JIS P 8117: 1998.

The range of the garley value of the separator is preferably 1 second / 100 cc or more and 10 seconds / 100 cc or less, more preferably 1 second / 100 cc or more and 5 seconds / 100 cc or less, and even more preferably 3 seconds / 100 cc.

The non-aqueous electrolyte secondary battery according to the present invention includes vinylene carbonate of 0.1% by mass or more and 5.0% by mass or less, ethylmethyl carbonate of 30% by mass or more and 60% by mass or less, and 0.1% by mass or more and 3.0. It has one feature in using a non-aqueous electrolyte containing fluorinated ethylene carbonate of mass% or less. By using an electrolyte having such a specific composition, it is possible to suppress the formation of a solid electrolyte interface (SEI) that is formed so as to cover the surface of the negative electrode active material. As a result, even when charging and discharging are repeated, a high energy density is maintained and the maintenance rate of the discharge capacity is improved. The content of each of the above components in the non-aqueous electrolyte can be measured by gas chromatography-mass spectrometry (GC-MS).

Specifically, the content of each component in the non-aqueous electrolyte can be measured by GC-MS as follows.
First, the non-aqueous electrolyte secondary battery is disassembled, and the electrolytic solution is taken out from the laminate and / or the wound body. If the electrolytic solution cannot be taken out from the laminate or the wound body, it is taken out by centrifuging with a centrifuge. If the electrolytic solution cannot be taken out even after centrifugation, the electrolytic solution is taken out by using acetonitrile as an extraction solvent to sufficiently soak the laminate and / or the wound body, collect the electrolytic solution, and extract the electrolytic solution. ..
Next, the components of the removed electrolytic solution are analyzed by GC-MS.

The range of the content of vinylene carbonate in the non-aqueous electrolyte is preferably 0.5% by mass or more and 4.0% by mass or less, more preferably 1.0% by mass or more and 3.0% by mass or less, and even more preferably 1. It is 0% by mass or more and 2.0% by mass or less.

The range of the content of ethyl methyl carbonate in the non-aqueous electrolyte is preferably 35% by mass or more and 55% by mass or less, more preferably 35% by mass or more and 50% by mass or less, and further preferably 40% by mass or more and 50% by mass or less. be.

The range of the content of fluorinated ethylene carbonate in the non-aqueous electrolyte is preferably 0.5% by mass or more and 2.5% by mass or less, more preferably 1.5% by mass or more and 2.0% by mass or less, and even more preferably. It is 2.0% by mass or less.

_{Examples of the electrolyte salt include LiClO 4} , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₆ , LiCF ₃ CO ₂ , LiPF ₆ SO ₃ , LiN (SO ₃ CF ₃ ) ₂ , Li (in the case of a lithium ion secondary battery, for example. Examples thereof include salts containing lithium such as SO ₂ CF ₂ CF ₃ ) ₂ , LiN (COCF ₃ ) ₂ , and LiN (COCF ₂ CF ₃ ) ₂ , or a mixture of two or more of these salts.

<Separator>
The non-aqueous electrolyte secondary battery according to the present invention includes a separator arranged between the positive electrode and the negative electrode. The separator effectively prevents short circuits between the positive and negative electrodes. Further, the separator may retain the above-mentioned non-aqueous electrolyte.

Examples of the separator include a porous polymer film, a non-woven fabric, and glass fiber. Examples of the porous polymer film include an olefin-based porous film and a cellulosic-based porous film. Examples of the olefin-based porous film include an ethylene-based porous film and a polypropylene-based porous film. In the non-aqueous electrolyte secondary battery of the present invention, it is preferable to use a non-woven fabric as the separator from the viewpoint of the Garley value of the separator.

The fiber material that can be used for the non-woven fabric separator is not particularly limited as long as it is an insulating material, and either an inorganic fiber or an organic fiber can be used. Examples of inorganic fibers include microglass (small diameter glass fiber) and rock wool. Examples of organic fibers include cellulose esters such as cellulose, carboxymethyl cellulose and cellulose acetate, cellulose fiber materials such as lignocellulose, neutral mucopolysaccharide fiber materials such as chitin and chitosan, and aliphatic nylons. Examples thereof include polyamides such as aromatic nylon (aramid), polyolefins such as polyethylene and polypropylene, and synthetic resin-based fiber materials such as vinylon, polyester, polyimide, polyamideimide, and vinylidene fluoride. Among these, since it is easy to prepare and obtain a fiber material of a preferable size and it is easy to obtain a fiber material that is well dispersed in a dispersion medium by a modification treatment such as hydrophobicization, cellulose, carboxymethyl cellulose, cellulose acetate, etc. Cellulose-based fibers such as cellulose ester and lignocellulosic can be preferably used. Further, the cellulosic fiber is advantageous from the viewpoint of widening the selectivity of the electrolytic solution and heat resistance as compared with the conventional porous separator made of a polyolefin resin film.

The non-woven fabric is a cloth obtained by joining or entwining fibers with each other using a mechanical, chemical, solvent or the like without weaving or knitting the above-mentioned fiber materials. The non-woven fabric is a conventionally known method such as a dry method, a wet method, a thermal bond method, a chemical bond method, a needle punch method, a spunlace method (water flow entanglement method), a stitch bond method, a steam jet method, a spunbond method, and a melt blow method. Can be manufactured by. By appropriately adjusting the shape of the fiber material to be used, such as the fiber length and the fiber diameter, and the entanglement conditions when producing the non-woven fabric, the non-woven fabric separator can be obtained so as to satisfy the above-mentioned Garley value.

The thickness of the non-woven fabric separator is preferably 10 μm or more and 30 μm or less, and more preferably 12 μm or more and 24 μm or less from the viewpoint of mechanical strength.

The non-woven fabric separator may contain various plasticizers, antioxidants, flame retardants, and the fiber surface may be coated with a metal oxide or the like. For example, the antioxidants include hindered phenolic antioxidants, monophenolic antioxidants, bisphenolic antioxidants, and phenolic antioxidants such as polyphenolic antioxidants, hindered amines, and phosphorus. Examples include phenol-based antioxidants, sulfur-based antioxidants, benzotriazole-based antioxidants, benzophenone-based antioxidants, triazine-based antioxidants, salicylate-based antioxidants, and phenol-based antioxidants and phosphorus-based antioxidants. Antioxidants can be preferably used.

<Positive electrode>
The positive electrode constituting the non-aqueous electrolyte secondary battery according to the present invention has a structure in which a positive electrode active material layer is provided on a positive electrode current collector, and includes, for example, a positive electrode active material, a binder resin, a conductive auxiliary agent, and a solvent. It can be prepared by preparing a composition, applying it on a positive electrode current collector, and drying it.

The positive electrode active material is not particularly limited as long as it is a lithium transition metal compound, but a layered rock salt type compound represented by lithium cobalt oxide, an olivine type compound represented by lithium iron phosphate, and a spinel type lithium manganate are more suitable. preferable.

The layered rock salt type compound refers to a compound having a layered rock salt type structure, and is not particularly limited, but is a lithium nickel composite oxide represented by _{LiMeO 2 (Me is a transition metal), a lithium cobalt composite oxide (for example, LiNiO 2} ), or a lithium cobalt composite. oxides (e.g. LiCoO _2), lithium nickel cobalt composite oxide (e.g., _{LiNi 1-y Co y O 2} ), lithium-nickel-cobalt-manganese composite oxide (e.g., _{LiNi x Co y Mn 1-y} -z O 2, where, x + y + z = 1), for example _{, a solid solution of LiMnO 3} and Li ₂ MnO ₃ and LixMeO ₂ in excess of lithium, but since structural deterioration due to long-term use is less, LiCoO ₂ and LiNi _0.8 Co _{0 .15 Al 0.05 O 2, LiNi x} Co y Mn 1-y-z O 2 ( where, x + y + z = 1 ) are preferred.

The olivine-type compound is a compound having an olivine-type structure, and is not particularly limited, but _{is represented by LiMePO 4} (Me is a transition metal), LiFePO ₄ , LiMn _1-x Fe _x PO ₄ , LiMnPO ₄ , LiCoPO. ₄ , LiNiPO _{4 and the} like can be mentioned.

_{In the present invention, LiFePO 4} (lithium iron phosphate) can be preferably used as the positive electrode active material from the viewpoint of battery characteristics such as durability and charge / discharge. Further, as the positive electrode active material, one having a granular form having an average particle diameter D50 in the range of 0.1 μm or more and 5 μm or less can be preferably used. In the present specification, the average particle size means the cumulative average particle size (D50) by the laser diffraction / scattering method. The average particle size can be appropriately adjusted depending on the crushing conditions when crushing (crushing) the raw material. When the crushing time is short, the particle size of the object to be crushed tends to be large, and when the crushing time is long, the particle size tends to be small.

When the granular form of lithium iron phosphate is used, at least a part of the particle surface is coated with an organic substance such as polyethylene glycol, an inorganic substance such as aluminum oxide, magnesium oxide, zirconium oxide or titanium oxide, or a carbon material. May be. In particular, lithium iron phosphate particles in which at least a part of the particle surface is coated with carbon can be preferably used. The amount of carbon coated is preferably 4% or more and 8% or less with respect to the mass of the lithium iron phosphate particles.

Examples of the conductive auxiliary agent include carbon materials such as graphite, graphene, hard carbon, Ketjen black, and acetylene black.

Examples of the binder resin include polyacrylic acid, lithium polyacrylate, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, styrene butadiene rubber, polyvinyl alcohol, polyvinyl acetal, polyethylene oxide, polyethylene glycol, carboxymethyl cellulose, and poly. Acrylic nitrile, polyimide and the like can be mentioned.

The solvent is preferably a non-aqueous solvent, for example, alcohols such as methanol, ethanol, 1-propanol and 2-propanol; chain or cyclic amides such as N-methylpyrrolidone, N, N-dimethylformamide; and ketones such as acetone. Can be mentioned.

Examples of the material constituting the positive electrode current collector include conductive metals such as copper, aluminum, titanium, nickel, and stainless steel.

The above-mentioned positive electrode active material, binder resin, conductive auxiliary agent and solvent may be used alone or in combination of two or more.

The content of the positive electrode active material in the positive electrode active material layer is preferably 50% or more and 99% or less, and more preferably 60% or more and 98% or less on a mass basis with respect to the entire positive electrode active material layer.

The positive electrode active material layer which is manufactured as described above, in view of enhancing the electrode density, it is preferable density of 1.90 g / cm ³ or more 2.30 g / cm ³ or less.

The thickness of the positive electrode active material layer is not particularly limited as long as the effects of the present invention are exhibited, and can be appropriately set from the viewpoint of maintaining the energy density and the like.

The porosity (%) of the positive electrode active material layer is not particularly limited as long as the effects of the present invention are exhibited, but is preferably 20% or more and 60% or less. The porosity of the positive electrode active material layer can be measured by a mercury injection method using a mercury injection porosimeter. Specifically, a test piece obtained by cutting out each layer to a predetermined size is prepared, the pore distribution of the test piece is measured by the mercury intrusion method using a mercury intrusion porosimeter, and the pore diameter is calculated from the pressure value and the pressure amount is used. The porosity can be calculated by obtaining the pore volume. Specifically, it can be calculated as follows.
First, the sample to be measured is constantly dried at a temperature of 110 ° C. for 12 hours. Subsequently, the pore distribution in the pore diameter range of about 0.0036 μm to 200 μm is measured using a measuring device such as Autopore IV9520 (manufactured by micromerits). The pore diameter is determined by the Washburn formula:
PD = -4σcosθ
(In the formula, P is the pressure, D is the pore diameter, σ is the surface tension of mercury (480 days / cm), and θ is the contact angle between mercury and the sample (140 °).)
It can be calculated from.
The porosity (%) can be calculated by dividing the obtained pore volume by the volume specified by the outer dimensions of the sample (however, the current collector shall have no voids and shall be calculated from the volume of the sample. Calculate by excluding in advance.).

<Negative electrode>
The negative electrode constituting the non-aqueous electrolyte secondary battery according to the present invention has a structure in which a negative electrode active material layer is provided on the negative electrode current collector, and includes, for example, a negative electrode active material, a binder resin, a conductive auxiliary agent, and a solvent. It can be prepared by preparing a composition, applying it on a positive electrode current collector, and drying it.

Examples of the negative electrode active material and the conductive auxiliary agent include carbon materials such as graphite, graphene, hard carbon, Ketjen black, and acetylene black.

Examples of the binder resin, the conductive auxiliary agent, the solvent, and the current collector are the same as those of the above-mentioned positive electrode. As the negative electrode active material, the conductive auxiliary agent, the binder resin, and the solvent, one kind may be used alone, or two or more kinds may be used in combination.

The content of the negative electrode active material in the negative electrode active material layer is preferably 50% or more and 99% or less, and more preferably 60% or more and 98% or less on a mass basis with respect to the entire negative electrode active material layer.

The negative electrode active material layer produced as described above has a density of preferably 1.3 g / cc or more and 1.8 g / cc or less, and more preferably 1.5 g / cc or more and 1.7 g / cc or less.

The thickness of the negative electrode active material layer is not particularly limited as long as the effects of the present invention are exhibited, and can be appropriately set.

The porosity (%) of the negative electrode active material layer is not particularly limited as long as the effects of the present invention are exhibited, but is preferably 25% or more and 60% or less, and more preferably 30% or more and 50% or less. The porosity here means a value measured by a mercury injection method using a mercury injection porosimeter, as in the case of the positive electrode active material layer.

In the non-aqueous electrolyte secondary battery according to the present invention, for example, a laminate in which a separator is arranged between a positive electrode and a negative electrode is prepared, and the electrode laminate is enclosed in an exterior body (housing) such as an aluminum laminate bag to be non-aqueous. It can be produced by injecting a water electrolyte.

The non-aqueous electrolyte secondary battery according to the present invention has been described above, but the present invention is not limited thereto. The non-aqueous electrolyte secondary battery according to the present invention may have any other configuration or may be replaced with any configuration that exhibits the same function. Further, in addition to the lithium ion secondary battery, it can also be applied to a secondary battery such as a silver ion secondary battery.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these examples.

[Example 1]
<Preparation of positive electrode>
A solid component containing 100 parts by mass of a positive electrode active material, 5 parts by mass of acetylene black as a conductive auxiliary agent, 5 parts by mass of polyvinylidene fluoride as a binder, and NMP as a solvent are mixed to obtain a solid content of 45%. A prepared slurry was obtained. This slurry was applied to an aluminum foil, pre-dried, and then vacuum dried at 120 ° C. The electrode was pressure-pressed at 4 kN and further punched to a 40 mm square electrode size to prepare a positive electrode.
Lithium iron olivine was used as the positive electrode active material and mixed in the following mass ratio.
Positive electrode active material: Binder (PVdF): Conductive aid = 90: 5: 5
The thickness of the positive electrode active material layer was 58.5 μm. The porosity was measured with a mercury polysimeter and found to be 41.6%.

<Manufacturing of negative electrode>
100 parts by mass of a solid component containing a negative electrode active material, 1.5 parts by mass of styrene-butadiene rubber as a binder, 1.5 parts by mass of carboxymethyl cellulose Na as a thickener, and water as a solvent are mixed and solid. A slurry adjusted to a minute of 50% was obtained. This slurry was applied to a copper foil and vacuum dried at 100 ° C. The electrode was pressure-pressed at 2 kN and further punched to a 42 mm square electrode size to prepare a negative electrode.
Graphite was used as the negative electrode active material and mixed at the following mass ratio.
Negative electrode active material: Binder (CMC): Binder (SBR) = 98: 1: 1
The thickness of the negative electrode active material layer was 39 μm. The porosity was measured with a mercury polysimeter and found to be 36.4%.

<Preparation of separator>
As a separator, a cellulose non-woven fabric having a thickness of 15 μm was used. The solvent permeation rate of the non-woven fabric separator was 1.5 cm ² / sec. The non-woven fabric separator had a Garley value of 3 as measured by a method based on JIS P 8117: 1998. The solvent permeation rate of the separator was measured by the following method.
First, a separator having a size of 50 mm × 1 mm was prepared.
Next, oil-based magic marks were made at positions 10 mm from both ends of the prepared separator in the long side direction.
The separator was then vacuum dried at 120 ° C. for 4 hours.
Next, a glass rod was fixed to the separator with cellophane tape so as to be perpendicular to the separator. At this time, the fixing position of the glass rod was set to the outside in the long side direction with respect to the above mark of the separator (between the mark and the end portion close to the mark).
Next, a weight paper clip was fixed to the outside in the long side direction (between the mark and the end near the mark) with respect to the mark on the opposite side to which the glass rod was fixed.
Next, a glass rod fixed to the separator was cross-linked to the edge of the opening of the beaker in a 100 ml beaker (2-5091-03, manufactured by AS ONE Corporation), and the separator was installed so that the side of the paper clip was inside the beaker.
Next, 50 ml of an electrolytic solution solvent (solvent composed of ethyl methyl carbonate) was prepared, and an ink for coloring (XR-2N red, manufactured by Shachihata x Stamp Co., Ltd.) was added so as to be visually recognizable.
Then, the colored electrolyte solvent was rapidly poured up to the mark on the lower part (Zemclip side) of the separator installed in the beaker.
Next, the time measurement was started from the time when the electrolytic solution solvent was started to be poured, and the time for the electrolytic solution solvent to permeate to the position marked on the upper part (glass rod side) of the separator was measured.
The time required for the electrolytic solution solvent to permeate into all of the width directions of the separator marked on the upper part was measured, and the permeation rate was calculated with the measurement time as the time required for permeation of an area of ^{3 cm 2.}

<Manufacturing of non-aqueous electrolyte secondary battery>
As shown in FIG. 1, the two negative electrodes, one positive electrode, and two non-woven fabric separators described above were laminated in the order of negative electrode / separator / positive electrode / separator / negative electrode. At this time, the separator and the positive electrode were laminated in advance and thermocompression bonded at 90 ° C. for 1 Mpa for 2 minutes to bond the separator to the surface of the positive electrode active material layer. Next, the terminal tabs are electrically connected to each of the positive electrode current collector exposed portion and the negative electrode current collector exposed portion, and the laminate is sandwiched between aluminum laminate films so that the terminal tabs project to the outside. The sides were sealed by laminating.
Subsequently, from one side left unsealed, a mixed solution containing 2% by mass of vinylene carbonate, 50% by mass of ethylmethyl carbonate, and 2% by mass of fluorinated ethylene carbonate was mixed with 1 mol / liter _{of LiPF 6 as an electrolyte.} A secondary battery (laminate cell) was manufactured by injecting a non-aqueous electrolyte solution dissolved in such a manner and vacuum-sealing.

[Example 2]
_{Non-aqueous electrolyte solution containing LiPF 6} as an electrolyte at 1 mol / liter in a mixed solution containing 1% by mass of vinylene carbonate, 40% by mass of ethylmethyl carbonate, and 2% by mass of fluorinated ethylene carbonate. A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the aqueous electrolyte solution was used.

[Comparative Example 1]
A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that a polyethylene separator was used instead of the non-woven fabric separator. The solvent permeation rate of the polyethylene separator was 170 cm ² / sec. Moreover, the galley value of the polyethylene separator measured by the method based on JIS P 8117: 1998 was 170.

[Comparative Example 2]
As the non-aqueous electrolyte solution, a non-aqueous electrolyte secondary solution was used in the same manner as in Example 1 except that a mixture containing 10% by mass of lithium hexafluorophosphate, 43% by mass of dimethyl carbonate, and 47% by mass of ethylene carbonate was used. A battery was manufactured.

<Evaluation of cycle characteristics>
The cycle characteristics (capacity retention rate) of each of the obtained non-aqueous electrolyte secondary batteries (cells) of the obtained Examples and Comparative Examples were evaluated by the following methods.
When the cells of Examples 1 and 2 and Comparative Examples 1 and 2 were prepared, the area of the laminate was adjusted to prepare the cells so that the rated capacity was 1 Ah.
First, the obtained cell is charged with a constant current at a constant current of 3.6 V at a constant current of 0.2 C rate (that is, 200 mA), and then at a constant voltage of 0.05 C rate (that is, 20 mA). ) Was charged.
Next, discharge for checking the capacity was performed at a rate of 0.2 C at a constant current and a final voltage of 2.5 V. The discharge capacity at this time was set as the reference capacity, and the reference capacity was set as the current value of 1C rate (that is, 1,000 mA).
Next, a cycle test was conducted with the following charge / discharge as one cycle. That is, charging was performed at a constant current at a constant voltage of 3.6 V at a constant voltage, charging was performed at a constant current of 0.05 C rate (that is, 20 mA) at a constant voltage, and then a rest was performed for 10 minutes. Subsequently, the battery was discharged at a constant current at a rate of 1 C at a final voltage of 2.5 V, and then paused for 10 minutes.
The above charging / discharging was repeated 1,000 times (cycles).
Then, the capacity was confirmed by the same method as described above.
The value obtained by dividing the discharge capacity measured in the capacity confirmation by the reference capacity before the cycle test to obtain a percentage was defined as the capacity retention rate after 1,000 cycles. The evaluation results of the cycle characteristics (capacity retention rate) of each non-aqueous electrolyte secondary battery are as shown in Table 1 below.

1 Non-aqueous electrolyte secondary battery 10 Positive electrode 11 Positive electrode current collector 12 Positive electrode active material layer 13 Positive electrode current collector exposed part 20 Negative electrode 21 Negative electrode current collector 22 Negative electrode active material layer 23 Negative electrode current collector exposed part 30 Separator 40 Exterior 50 Glass electrode 60 Cellophane tape 70 Zem clip 80 Beaker

Claims (7)

A positive electrode having a positive electrode active material layer provided on at least one surface of the positive electrode current collector and the positive electrode current collector, a negative electrode current collector, and a negative electrode active material provided on at least one surface of the negative electrode current collector. A non-aqueous electrolyte secondary battery with a layered negative electrode, a separator, and a non-aqueous electrolyte.
The positive electrode and the negative electrode are arranged so that the positive electrode active material layer and the negative electrode active material layer face each other via the separator.
The non-aqueous electrolyte contains vinylene carbonate of 0.1% by mass or more and 5.0% by mass or less, ethylmethyl carbonate of 30% by mass or more and 60% by mass or less, and fluorine of 0.1% by mass or more and 3.0% by mass or less. Contains ethylene carbonate carbonate
The non-aqueous electrolyte secondary is characterized in that the permeation rate of the solvent in the plane direction when the separator is immersed in a solvent made of ethyl methyl carbonate is 0.1 cm ² / sec or more and 5.0 cm ^{2 / sec or less.} battery. The non-aqueous electrolyte secondary battery according to claim 1, wherein the Garley value of the separator is 1 second / 100 cc or more and 20 seconds / 100 cc or less. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the Garley value of the separator is 1 second / 100 cc or more and 5 seconds / 100 cc or less. The non-aqueous electrolyte contains 1.0% by mass or more and 3.0% by mass or less of vinylene carbonate, 40% by mass or more and 50% by mass or less of ethylmethyl carbonate, and 1.0% by mass or more and 2.0% by mass or less of fluorine. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, which comprises ethylene carbonate carbonate. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the thickness of the separator is 10 μm or more and 30 μm or less. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein the positive electrode active material layer contains lithium iron phosphate. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 6, wherein the positive electrode active material layer is made of positive electrode active material particles in which at least a part of the particle surface is coated with carbon.

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