JP7409132B2 - Nonaqueous electrolyte storage element - Google Patents

Description

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

Nonaqueous electrolyte secondary batteries, typified by lithium ion nonaqueous electrolyte secondary batteries, have high energy density and are widely used in electronic devices such as personal computers and communication terminals, automobiles, and the like. The non-aqueous electrolyte secondary battery generally includes an electrode body having a pair of electrodes electrically isolated by a separator, and a non-aqueous electrolyte interposed between the electrodes, and transfers ions between the two electrodes. It is configured to charge and discharge by doing so. Furthermore, capacitors such as lithium ion capacitors and electric double layer capacitors are also widely used as power storage elements other than non-aqueous electrolyte secondary batteries.

Carbon materials such as graphite are used as negative electrode active materials of the above-mentioned power storage elements for the purpose of improving the energy density of such power storage elements (see Patent Document 1).

Japanese Patent Application Publication No. 2005-222933

Non-aqueous electrolyte secondary batteries with rapid charging performance are required as an energy source for the above-mentioned automobiles and the like. However, when rapid charging is performed on a non-aqueous electrolyte secondary battery using graphite as the negative electrode active material, the decomposition reaction of the non-aqueous electrolyte is accelerated due to the negative electrode potential being base, resulting in a rapid charge-discharge cycle. There is a risk that the capacity retention rate during (high rate cycle) may decrease.

The present invention has been made based on the above circumstances, and an object of the present invention is to provide a non-aqueous electrolyte storage element that can suppress a decrease in capacity retention during rapid charge/discharge cycles.

A nonaqueous electrolyte storage device according to one aspect of the present invention includes a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and the negative electrode has a negative electrode active material layer containing graphite and an acrylic resin. The separator has an air permeability of 200 [sec/100 cm ³ ] or less.

The non-aqueous electrolyte storage element according to one aspect of the present invention can suppress a decrease in capacity retention rate during rapid charge/discharge cycles.

FIG. 1 is an external perspective view showing one embodiment of a non-aqueous electrolyte storage element. FIG. 2 is a schematic diagram showing an embodiment of a power storage device configured by collecting a plurality of non-aqueous electrolyte power storage elements.

A nonaqueous electrolyte storage device according to one aspect of the present invention includes a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and the negative electrode has a negative electrode active material layer containing graphite and an acrylic resin. The separator has an air permeability of 200 [sec/100 cm ³ ] or less.

Graphite, which has a large charge/discharge capacity per unit mass at a base potential close to the oxidation-reduction potential of lithium, is widely used as the negative electrode material used in non-aqueous electrolyte storage devices, and as a binder for the negative electrode, it can be added in a relatively small amount. Styrene-butadiene rubber, which is available in On the other hand, the present inventors have discovered that the negative electrode active material layer of the non-aqueous electrolyte storage element contains graphite as the negative electrode active material and acrylic resin as the binder, and that the air permeability of the separator interposed between the positive electrode and the negative electrode is It has been found that when the ratio is 200 [sec/100 cm ³ ] or less, it is possible to suppress a decrease in the capacity retention rate of the non-aqueous electrolyte storage element during rapid charge/discharge cycles. Although the reason for this is not certain, it is thought to be as follows. In a negative electrode containing graphite as the negative electrode active material, the potential for intercalation and desorption of metal ions such as lithium ions is very base, and when rapid charging is performed, the effect of polarization is added, so the negative electrode potential becomes even more base. , the reductive decomposition of non-aqueous electrolytes is further promoted. As a result, it is thought that the capacity retention rate during rapid charge/discharge cycles may decrease. A negative electrode using acrylic resin as a binder has lower resistance than a negative electrode using styrene-butadiene rubber as a binder. Therefore, in a negative electrode using an acrylic resin as a binder, the polarization during rapid charging is reduced, so that the negative electrode potential is relatively less likely to become base, and decomposition of the nonaqueous electrolyte is suppressed. However, when a negative electrode using acrylic resin as a binder is combined with a separator that has high air permeability and high tightness, the supply of lithium ions, etc. to the negative electrode cannot keep up with the negative electrode during rapid charging, resulting in repeated rapid charge/discharge cycles. The inventors discovered that the discharge capacity retention rate tends to decrease as the discharge capacity increases. Therefore, by combining a negative electrode using acrylic resin as a binder and a separator with an air permeability of 200 [sec/100 cm ³ ] or less, the non-aqueous electrolyte storage element can provide sufficient lithium ions to the negative electrode during rapid charging. can be supplied. As a result, it is presumed that the non-aqueous electrolyte storage element can suppress a decrease in capacity retention rate during rapid charge/discharge cycles. Here, "air permeability" is also called Gurley value, and indicates the number of seconds for a certain volume of air to pass through a certain area of paper under a certain pressure difference, and is measured in accordance with JIS-P8117 (2009). is the value to be used.

It is preferable that the acrylic resin does not have a structural unit derived from butadiene. Since the acrylic resin does not have a structural unit derived from butadiene, initial resistance can be reduced, and a decrease in capacity retention rate during rapid charge/discharge cycles can be further suppressed.

It is preferable that the separator has a base layer in the form of a microporous membrane, and that the main component of the base layer is polyolefin. With the above configuration, even if excessive heat generation occurs due to an unintended reason such as a short circuit, the current shutdown function is activated and the increase in short circuit current can be suppressed, resulting in a high level of safety. .

It is preferable that the separator has a heat-resistant layer, and the heat-resistant layer contains inorganic particles and a binder. Since the separator has a heat-resistant layer containing inorganic particles and a binder, even if the temperature of the electricity storage element rises excessively due to unintended reasons, damage to the separator is suppressed and short circuits between the positive electrode and the negative electrode are more reliably suppressed. At the same time, the shape of the separator can be maintained. Furthermore, having a heat-resistant layer containing inorganic particles and a binder increases the shape retention of the separator, so it is possible to increase the porosity of the separator or base material layer and make the air permeability of the separator sufficiently low. It becomes possible.

Hereinafter, a non-aqueous electrolyte storage device according to an embodiment of the present invention will be explained in detail.
<Nonaqueous electrolyte storage element>
A non-aqueous electrolyte storage device according to an embodiment of the present invention includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. Hereinafter, a non-aqueous electrolyte secondary battery will be described as a preferable example of a non-aqueous electrolyte storage element. The above-mentioned positive electrode and negative electrode usually form an electrode body in which they are alternately stacked by stacking or winding with a separator in between. This electrode body is housed in a case, and the case is filled with a nonaqueous electrolyte. The non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. Further, as the case, a known metal case, resin case, etc. that are commonly used as cases for non-aqueous electrolyte secondary batteries can be used.

[Negative electrode]
The negative electrode includes a negative electrode base material and a negative electrode active material layer. The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer is laminated directly or via an intermediate layer on at least one surface of the negative electrode base material.

(Negative electrode base material)
The negative electrode base material is a conductive base material. As the material of the negative electrode base material, metals such as copper, nickel, stainless steel, nickel-plated steel, or alloys thereof are used, and copper or copper alloys are preferable. In addition, examples of the form of the negative electrode base material include foil, vapor deposited film, etc., and foil is preferable from the viewpoint of cost. In other words, copper foil is preferable as the negative electrode base material. Examples of the copper foil include rolled copper foil, electrolytic copper foil, and the like. Note that "conductive" means that the volume resistivity measured in accordance with JIS-H-0505 (1975) is 1 x 10 ⁷ Ω・cm or less, and "non-conductive" ” means that the volume resistivity is more than 1×10 ⁷ Ω·cm.

(Negative electrode active material layer)
The negative electrode active material layer is formed from a so-called negative electrode mixture containing a negative electrode active material. The negative electrode active material layer contains graphite and acrylic resin.

The non-aqueous electrolyte storage element contains graphite as a negative electrode active material. By including graphite as a negative electrode active material, energy density can be increased. Examples of graphite include natural graphite and artificial graphite. When graphite is included as the negative electrode active material, the movement speed of lithium ions on the surface of the negative electrode active material is slow, so the lithium concentration in the negative electrode surface layer becomes high. As a result, the decomposition reaction of the nonaqueous electrolyte on the surface of the negative electrode is promoted, and the capacity retention rate during rapid charge/discharge cycles tends to decrease. On the other hand, with non-graphitic carbon such as non-graphitizable carbon, the potential during charging and discharging changes slowly, so it is thought that the lithium concentration in the negative electrode active material layer is likely to be relaxed. Therefore, the lithium concentration in the negative electrode surface layer does not become high, and excessive decomposition reaction of the nonaqueous electrolyte can be suppressed, so it is presumed that the capacity retention rate during rapid charge/discharge cycles is unlikely to decrease. Therefore, the non-aqueous electrolyte storage element is effective in solving problems specific to negative electrodes having a negative electrode active material layer containing graphite.

"Graphite" refers to a carbon material having an average lattice spacing (d ₀₀₂ ) of the (002) plane of 0.33 nm or more and less than 0.34 nm before charging and discharging or in a discharge state, as determined by X-ray diffraction. Examples of graphite include natural graphite and artificial graphite. Artificial graphite is preferred from the viewpoint of being able to obtain a material with stable physical properties.

"Non-graphitic carbon" refers to a carbon material whose average lattice spacing (d ₀₀₂ ) of the (002) plane is 0.34 nm or more and 0.42 nm or less, as determined by X-ray diffraction before charging and discharging or in a discharge state. say. Examples of non-graphitic carbon include non-graphitizable carbon and easily graphitizable carbon. Examples of the non-graphitic carbon include resin-derived materials, petroleum pitch or petroleum pitch-derived materials, petroleum coke or petroleum coke-derived materials, plant-derived materials, alcohol-derived materials, and the like. "Non-graphitizable carbon" refers to a carbon material in which the above d ₀₀₂ is 0.36 nm or more and 0.42 nm or less. "Graphitizable carbon" refers to a carbon material in which the above d ₀₀₂ is 0.34 nm or more and less than 0.36 nm.

Here, the "discharge state" refers to a state in which the open circuit voltage is 0.7 V or more in a monopolar battery using a negative electrode containing a carbon material as a negative electrode active material as a working electrode and metallic lithium as a counter electrode. Since the potential of the metallic lithium counter electrode in an open circuit state is approximately equal to the redox potential of lithium, the open circuit voltage in the above-mentioned monopolar battery is approximately equivalent to the potential of the negative electrode containing the carbon material relative to the redox potential of lithium. . In other words, if the open circuit voltage of the monopolar battery is 0.7 V or more, it means that a sufficient amount of lithium ions, which can be intercalated and released during charging and discharging, is released from the carbon material that is the negative electrode active material. .

The lower limit of the graphite content in the negative electrode active material is preferably 60% by mass, more preferably 70% by mass, and even more preferably 80% by mass. On the other hand, the upper limit of this content is preferably 100% by mass, more preferably 95% by mass.

The content of the negative electrode active material in the negative electrode active material layer is not particularly limited, but its lower limit is preferably 50% by mass, more preferably 80% by mass, and even more preferably 90% by mass. On the other hand, the upper limit of this content is preferably 99% by mass, more preferably 98% by mass.

(binder)
The negative electrode mixture of the non-aqueous electrolyte storage element contains an acrylic resin as a binder. "Acrylic resin" excludes polyacrylic acid, and includes, for example, acrylic ester, methacrylic acid or a polymer of methacrylic ester, polyacrylamide, a copolymer containing acrylic acid, and the like.

It is preferable that the acrylic resin does not have a structural unit derived from butadiene. Since the acrylic resin does not have a structural unit derived from butadiene, initial resistance can be reduced.

The content of the acrylic resin in the binder is preferably 99% by mass or more, and may be 100% by mass.

The lower limit of the binder content in the negative electrode active material layer is preferably 0.2% by mass, more preferably 0.5% by mass, and even more preferably 1% by mass. On the other hand, the upper limit of this content is preferably 10% by mass, more preferably 5% by mass.

(Other optional ingredients)
The negative electrode mixture contains optional components such as a conductive agent, a thickener, and a filler, as necessary.

The conductive agent is not particularly limited as long as it is a conductive material. Examples of such a conductive agent include carbonaceous materials, metals, conductive ceramics, etc., although the graphite described above also has conductivity. Examples of the carbonaceous material include non-graphitized carbon, graphene-based carbon, and the like. Examples of non-graphitized carbon include carbon nanofibers, pitch-based carbon fibers, carbon black, and the like. Examples of carbon black include furnace black, acetylene black, Ketjen black, and the like. Examples of graphene-based carbon include graphene, carbon nanotubes (CNT), and fullerene. Examples of the shape of the conductive agent include powder, fiber, and the like. As the conductive agent, one type of these materials may be used alone, or two or more types may be used in combination. Further, these materials may be used in combination. For example, a composite material of carbon black and CNT may be used. Among these, carbon black is preferred from the viewpoint of electronic conductivity and coatability, and acetylene black is particularly preferred.

Examples of the thickener include polysaccharide polymers such as carboxymethylcellulose (CMC) and methylcellulose. Further, when the thickener has a functional group that reacts with lithium, it is preferable to deactivate this functional group by methylation or the like in advance.

The filler is not particularly limited. Main components of the filler include polyolefins such as polypropylene and polyethylene, silica, alumina, zeolite, and glass.

The lower limit of the basis weight of the negative electrode active material layer (mass per unit area of the negative electrode active material layer in the negative electrode) is preferably 0.3 mg/100 cm ² , more preferably 0.4 g/100 cm ² . On the other hand, the upper limit of this basis weight is preferably 2.0 g/100 cm ² , more preferably 1.5 g/100 cm ² . When the basis weight of the negative electrode active material layer is within the above range, it is possible to obtain a nonaqueous electrolyte storage element that has a high energy density and a high capacity retention rate during rapid charge/discharge cycles.

(middle class)
The intermediate layer is a coating layer on the surface of the negative electrode base material, and contains conductive particles such as carbon particles to reduce contact resistance between the negative electrode base material and the negative electrode active material layer. The structure of the intermediate layer is not particularly limited, and can be formed, for example, from a composition containing a resin binder and conductive particles.

[Positive electrode]
The positive electrode has a positive electrode base material and a positive electrode active material layer. The positive electrode active material layer contains a positive electrode active material. The positive electrode active material layer is laminated directly or via an intermediate layer on at least one surface of the positive electrode base material.

(Positive electrode base material)
The positive electrode base material is a conductive base material. As the material of the positive electrode base material, metals such as aluminum, titanium, tantalum, stainless steel, or alloys thereof are used. Among these, aluminum and aluminum alloys are preferred from the viewpoint of potential resistance, high conductivity, and cost balance. In addition, examples of the form of the positive electrode base material include foil, vapor deposited film, etc., and foil is preferable from the viewpoint of cost. That is, aluminum foil is preferable as the positive electrode base material. Note that examples of aluminum or aluminum alloy include A1085, A3003, A1N30, etc. defined in JIS-H4000 (2014) or JIS-H-4160 (2006).

(Positive electrode active material layer)
The positive electrode active material layer is formed from a so-called positive electrode mixture containing a positive electrode active material. The positive electrode active material can be appropriately selected from known positive electrode active materials, for example. As a positive electrode active material for a lithium ion secondary battery, a material that can insert and release lithium ions is usually used. Examples of the positive electrode active material include a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure, a lithium transition metal oxide having a spinel type crystal structure, a polyanion compound, a chalcogen compound, and sulfur. Examples of lithium transition metal composite oxides having α-NaFeO ₂ type crystal structure include Li[Li _x Ni _1-x ]O ₂ (0≦x<0.5), Li[Li _x Ni _γ Co _{(1- x-γ)} ]O ₂ (0≦x<0.5, 0<γ<1), Li[Li _x Co _(1-x) ]O ₂ (0≦x<0.5), Li[Li _x Ni _γ Mn _(1-x-γ) ]O ₂ (0≦x<0.5, 0<γ<1), Li[Li _x Ni _γ Mn _β Co _(1-x-γ-β) ]O ₂ (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1), Li[Li _x Ni _γ Co _β Al _(1-x-γ-β) ]O ₂ (0≦ Examples include x<0.5, 0<γ, 0<β, 0.5<γ+β<1). Lithium transition metal oxides having a spinel crystal structure include Li _x Mn ₂ O ₄ , Li _x Ni _γ Mn _(2-γ) O ₄ and the like. Examples of the polyanion compound include LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , LiCoPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , Li ₂ MnSiO ₄ , Li ₂ CoPO ₄ F, and the like. Examples of chalcogen compounds include titanium disulfide, molybdenum disulfide, molybdenum dioxide, and the like. Atoms or polyanions in these materials may be partially substituted with atoms or anion species of other elements. Among these, the above-mentioned positive electrode active material is preferably the above-mentioned lithium-transition metal composite oxide from the viewpoint of high energy density, and a nickel-cobalt-manganese-containing lithium-transition metal composite containing nickel, cobalt, and manganese as constituent elements in addition to lithium. Oxides are more preferred.

The surface of the material listed as the positive electrode active material may be coated with another material. In the positive electrode active material layer, one type of these materials may be used alone, or two or more types may be used in combination.

The content of the positive electrode active material in the positive electrode active material layer is not particularly limited, but its lower limit is preferably 50% by mass, more preferably 80% by mass, and even more preferably 90% by mass. On the other hand, the upper limit of this content is preferably 99% by mass, more preferably 98% by mass.

(Other optional ingredients)
The positive electrode mixture contains optional components such as a conductive agent, a binder, a thickener, and a filler, as necessary. Optional components such as a conductive agent, a binder, a thickener, and a filler can be selected from the materials exemplified for the negative electrode.

(middle class)
The intermediate layer is a coating layer on the surface of the positive electrode base material, and contains conductive particles such as carbon particles to reduce contact resistance between the positive electrode base material and the positive electrode active material layer. Similar to the above negative electrode, the structure of the intermediate layer is not particularly limited, and can be formed, for example, from a composition containing a resin binder and conductive particles.
[Nonaqueous electrolyte]
As the non-aqueous electrolyte, a known non-aqueous electrolyte that is commonly used in general non-aqueous electrolyte secondary batteries (power storage elements) can be used. The nonaqueous electrolyte includes a nonaqueous solvent and an electrolyte salt dissolved in the nonaqueous solvent. Note that the non-aqueous electrolyte may be a solid electrolyte or the like.

As the non-aqueous solvent, a known non-aqueous solvent that is commonly used as a non-aqueous solvent for a general non-aqueous electrolyte for a power storage device can be used. Examples of the nonaqueous solvent include cyclic carbonates, chain carbonates, esters, ethers, amides, sulfones, lactones, and nitriles. Among these, it is preferable to use at least a cyclic carbonate or a chain carbonate, and it is more preferable to use a cyclic carbonate and a chain carbonate in combination. When using a cyclic carbonate and a chain carbonate together, the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate: chain carbonate) is not particularly limited, but may be, for example, from 5:95 to 50:50. preferable.

Examples of the cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinylethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), and difluoroethylene. carbonate (DFEC), styrene carbonate, catechol carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate, etc. Among these, EC is preferred.

Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), and diphenyl carbonate, and among these, EMC is preferred.

As the electrolyte salt, a known electrolyte salt that is commonly used as an electrolyte salt of a general non-aqueous electrolyte for a power storage device can be used. Examples of the electrolyte salts include lithium salts, sodium salts, potassium salts, magnesium salts, onium salts, and the like, with lithium salts being preferred.

Examples of the lithium salt include inorganic lithium salts such as LiPF ₆ , LiPO ₂ F ₂ , LiBF ₄ , LiClO ₄ , LiN(SO ₂ F) ₂ , LiSO ₃ CF ₃ , LiN(SO ₂ CF ₃ ) ₂ , LiN(SO ₂ Hydrogen in C ₂ F ₅ ) ₂ , LiN(SO ₂ CF ₃ )(SO ₂ C ₄ F ₉ ), LiC(SO ₂ CF ₃ ) ₃ , LiC(SO ₂ C ₂ F ₅ ) ₃ is replaced with fluorine Examples include lithium salts having a hydrocarbon group. Among these, inorganic lithium salts are preferred, and LiPF ₆ is more preferred.

The lower limit of the concentration of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 mol/dm ³ , more preferably 0.3 mol/dm ³ , even more preferably 0.5 mol/dm ³ at 20°C and 1 atmosphere. , 0.7 mol/dm ³ is particularly preferred. On the other hand, this upper limit is not particularly limited, but is preferably 2.5 mol/dm ³ , more preferably 2.0 mol/dm ³ , and even more preferably 1.5 mol/dm ³ .

Other additives may be added to the non-aqueous electrolyte. Moreover, room temperature molten salts, ionic liquids, etc. can also be used as the non-aqueous electrolyte.

[Separator]
The separator can be appropriately selected from known separators. As the separator, for example, a separator consisting of only a base material layer, a separator in which a heat-resistant layer is formed on one surface or both surfaces of the base material layer, etc. can be used. Examples of the form of the base material layer of the separator include woven fabric, nonwoven fabric, and microporous membrane. Among these forms, microporous membranes are preferred from the viewpoint of safety. Examples of the material for the base layer of the separator include polyolefins such as polyethylene and polypropylene, polyimide, aramid, and composite materials of these resins. Among these, polyolefins are preferred. Since the main component of the base material layer is polyolefin, even if excessive heat generation occurs due to an unintentional short circuit, the current shutdown function works and suppresses the increase in short circuit current, resulting in high safety. can be provided.

The upper limit of the air permeability of the separator is 200 [seconds/100cm ³ ], preferably 150 [seconds/100cm ³ ], and more preferably 100 [seconds/100cm ³ ]. By setting the upper limit of the air permeability of the separator within the above range, it is possible to enhance the effect of suppressing a decrease in capacity retention rate during rapid charge/discharge cycles. On the other hand, the lower limit of the air permeability of the separator is preferably 40 [seconds/100cm ³ ] and more preferably 60 [seconds/100cm ³ ] from the viewpoint of maintaining the strength of the separator.

It is preferable that the separator has a heat-resistant layer. The heat-resistant layer includes inorganic particles and a binder. Since the separator has a heat-resistant layer containing inorganic particles and a binder, even if the temperature of the electricity storage element unintentionally rises excessively, damage to the separator is suppressed and short circuits between the positive electrode and the negative electrode are more reliably suppressed. At the same time, the shape of the separator can be maintained. This heat-resistant layer is a porous layer containing inorganic particles and a binder. Further, the heat-resistant layer may contain components other than the inorganic particles and the binder.

Examples of the inorganic particles contained in the heat-resistant layer include inorganic compounds. Examples of inorganic compounds include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, barium titanate, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, aluminosilicate; magnesium hydroxide, water Hydroxides such as calcium oxide and aluminum hydroxide; Nitrides such as aluminum nitride and silicon nitride; Carbonates such as calcium carbonate; Sulfates such as barium sulfate; Hardly soluble ionic crystals such as calcium fluoride and barium fluoride Covalent crystals such as silicon and diamond; Substances derived from mineral resources such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof. . As the inorganic compound, these substances may be used alone or in combination, or two or more types may be used in combination. Among these inorganic compounds, silicon oxide, aluminum oxide, boehmite, or aluminum silicate are preferred from the viewpoint of secondary battery characteristics. The inorganic particles contained in the heat-resistant layer preferably have a mass loss of 5% or less at 500° C. under atmospheric pressure, and more preferably have a mass loss of 5% or less at 800° C. under atmospheric pressure.

[Specific configuration of non-aqueous electrolyte storage element]
The shape of the power storage element of this embodiment is not particularly limited, and examples include a cylindrical battery, a laminate film battery, a square battery, a flat battery, a coin battery, a button battery, and the like.

FIG. 1 shows a schematic diagram of a rectangular nonaqueous electrolyte storage device 1 (nonaqueous electrolyte secondary battery), which is an embodiment of the nonaqueous electrolyte storage device according to the present invention. Note that this figure is a transparent view of the inside of the case. An electrode body 2 having a positive electrode and a negative electrode wound with a separator in between is housed in a rectangular case 3. The positive electrode is electrically connected to the positive electrode terminal 4 via a positive electrode lead 41. The negative electrode is electrically connected to the negative electrode terminal 5 via a negative electrode lead 51. Furthermore, a non-aqueous electrolyte is injected into the case 3.

The range of the positive electrode potential at the end-of-charge voltage during normal use of the nonaqueous electrolyte storage element is preferably 4.2V (vs. Li/Li ⁺ ) or higher, and 4.2V (vs. Li/Li ⁺ ) or higher 4 .5V (vs. Li/Li ⁺ ) or less is more preferable. By having the above-mentioned configuration, the non-aqueous electrolyte storage element suppresses a decrease in capacity retention rate during rapid charge/discharge cycles even when operated at high voltage. Therefore, the non-aqueous electrolyte storage element can more fully exhibit the effect of improving rapid charge/discharge cycle performance when the positive electrode potential at the end-of-charge voltage during normal use is within the above range.

[Method for manufacturing non-aqueous electrolyte storage element]
A method for manufacturing a non-aqueous electrolyte energy storage device according to an embodiment of the present invention includes manufacturing the positive electrode, manufacturing the negative electrode, preparing the non-aqueous electrolyte, and laminating or winding the positive electrode and the negative electrode through a separator. The method includes forming alternately stacked electrode bodies by rotating the electrode bodies, housing the electrode bodies in a container, and injecting the non-aqueous electrolyte into the container. The above-mentioned positive electrode can be obtained by laminating the above-mentioned positive electrode active material layer on a positive electrode base material directly or via an intermediate layer. The above-mentioned positive electrode active material layer is laminated by applying a positive electrode mixture paste to the positive electrode base material. Further, the negative electrode can be obtained by laminating the negative electrode active material layer on the negative electrode base material directly or via an intermediate layer, similarly to the positive electrode. The negative electrode active material layer is laminated by applying a negative electrode mixture paste containing graphite and acrylic resin to the negative electrode base material. The positive electrode mixture paste and the negative electrode mixture paste may contain a dispersion medium. As the dispersion medium, for example, aqueous solvents such as water and a mixed solvent mainly composed of water; organic solvents such as N-methylpyrrolidone and toluene can be used.

The above-mentioned negative electrode, positive electrode, non-aqueous electrolyte, etc. can be housed in a case by a known method. After housing, a non-aqueous electrolyte storage element can be obtained by sealing the housing opening. The details of each element constituting the non-aqueous electrolyte storage device obtained by the above manufacturing method are as described above.

According to the non-aqueous electrolyte storage device, the negative electrode active material layer contains graphite as the negative electrode active material and acrylic resin as the binder, and the separator interposed between the positive electrode and the negative electrode has an air permeability of 200 seconds. /100cm ³ ] or less, it is possible to suppress a decrease in the capacity retention rate of the nonaqueous electrolyte storage element during rapid charge/discharge cycles.

[Other embodiments]
The non-aqueous electrolyte storage device of the present invention is not limited to the above embodiments.

Further, in the above embodiments, the non-aqueous electrolyte storage element is mainly a non-aqueous electrolyte secondary battery, but other non-aqueous electrolyte storage elements may be used. Other nonaqueous electrolyte storage devices include capacitors (electric double layer capacitors, lithium ion capacitors), and the like. Examples of nonaqueous electrolyte secondary batteries include lithium ion nonaqueous electrolyte secondary batteries.

Further, although a wound type electrode body is used in the above embodiment, a laminated type electrode body formed from a laminated body in which a plurality of sheet bodies each including a positive electrode, a negative electrode, and a separator are stacked may be provided.

The present invention can also be realized as a power storage device including a plurality of the above non-aqueous electrolyte power storage elements. In this case, the technology of the present invention may be applied to at least one non-aqueous electrolyte power storage element included in the power storage device. Moreover, a battery assembly can be constructed by using one or more non-aqueous electrolyte power storage elements (cells) of the present invention, and furthermore, a power storage device can be constructed using this battery assembly. The power storage device described above can be used as a power source for automobiles such as electric vehicles (EVs), hybrid vehicles (HEVs), and plug-in hybrid vehicles (PHEVs). Further, the power storage device can be used in various power supply devices such as an engine starting power supply device, an auxiliary machine power supply device, and an uninterruptible power supply (UPS).

FIG. 2 shows an example of a power storage device 30 in which a power storage unit 20 in which two or more electrically connected non-aqueous electrolyte power storage elements 1 are assembled is further assembled. The power storage device 30 may include a bus bar (not shown) that electrically connects two or more non-aqueous electrolyte power storage elements 1 and a bus bar (not shown) that electrically connects two or more power storage units 20. good. The power storage unit 20 or the power storage device 30 may include a state monitoring device (not shown) that monitors the state of one or more power storage elements.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples.

[Example 1 and Comparative Examples 1 to 3]
(Negative electrode)
Acrylic resin or styrene-butadiene copolymer was used as a binder for the negative electrode active material layer. A negative electrode mixture paste containing graphite as a negative electrode active material, the binder listed in Table 1, and CMC as a thickener, and using water as a dispersion medium was prepared. The mixing ratio of the negative electrode active material, binder, and thickener was 98:1:1 by mass. The negative electrode mixture paste was applied to both sides of a copper foil base material with a thickness of 10 μm at a coating weight of 13 mg/cm ² (fabric weight, solid content equivalent), dried to form a negative electrode active material layer, and the packing density was Negative electrodes of Examples and Comparative Examples were obtained by pressing so that the density was 1.5 g/cm ³ .
(Nonaqueous electrolyte)
A non-aqueous electrolyte was prepared by dissolving 1.0 mol/dm ³ of LiPF ₆ in a non-aqueous solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 30:70.
(positive electrode)
A positive electrode containing NCM (LiNi _0.5 Co _0.2 Mn _0.3 O ₂ ) having an α-NaFeO ₂ type crystal structure as a positive electrode active material was produced. The positive electrode is a positive electrode mixture paste containing the above positive electrode active material, polyvinylidene fluoride (PVDF) as a binder, and acetylene black as a conductive agent, and using N-methyl-2-pyrrolidone (NMP) as a dispersion medium. was prepared. The mixing ratio of the positive electrode active material, binder, and conductive agent was 93:4:3 in terms of mass ratio. A positive electrode mixture paste is applied to both sides of a positive electrode base material made of aluminum foil with a thickness of 15 μm at a coating weight of 25 mg/cm ² (fabric weight, solid content equivalent), dried, and pressed to form a positive electrode active material layer. was formed.

(Production of non-aqueous electrolyte storage element)
Next, as a separator, a separator consisting of a microporous film-like base material layer made of polyethylene and an inorganic layer formed on one side of the base material layer, and having the air permeability shown in Table 1, was used. The positive electrode and the negative electrode were laminated with the separator interposed therebetween to produce an electrode body. This electrode body was housed in a rectangular case made of aluminum, and a positive electrode terminal and a negative electrode terminal were attached to it. After injecting the non-aqueous electrolyte into the case, the case was sealed and a non-aqueous electrolyte secondary battery with a rated capacity of 0.9 Ah was produced to obtain non-aqueous electrolyte storage elements of Examples and Comparative Examples.

[evaluation]
(Initial charging/discharging process)
Each of the obtained non-aqueous electrolyte storage elements was subjected to constant current and constant voltage charging at 0.18 A in a temperature environment of 25° C. with a charging end voltage of 4.25 V until a total charging time of 7 hours. Next, a 10-minute pause was provided after charging. Thereafter, constant current discharge was performed at a current value of 0.18A with a discharge end voltage of 2.75V. Next, with a charging end voltage of 4.25 V, constant current and constant voltage charging was performed at 0.9 A in a temperature environment of 25° C. until the total charging time reached 3 hours. After a 10-minute break, constant current discharge was performed at a current value of 0.9A. It was confirmed that these discharge capacities were equivalent to the rated capacities.

(Rapid charge/discharge cycle test)
A charge/discharge cycle test was conducted on the nonaqueous electrolyte storage elements of Example 1 and Comparative Examples 1 to 3 completed through the above initial charge/discharge process under the following conditions. The following cycle test was conducted in a constant temperature bath at 25°C. Constant current and constant voltage charging was performed at 1.8 A until the total charging time was 3 hours until the voltage reached 100% SOC (State of Charge). Next, a 10-minute pause was provided after charging. Thereafter, constant current discharge was performed at a discharge current of 1.8 A until the voltage reached SOC 0%, and a 10-minute pause was provided. Further, constant current discharge was performed at a discharge current of 0.045 A until the voltage reached SOC 0%, and a rest period of 10 minutes was performed. These charging and discharging steps were considered as one cycle, and this cycle was repeated 10 times.

(Capacity retention rate during rapid charge/discharge cycles)
Regarding the nonaqueous electrolyte storage elements of Example 1 and Comparative Examples 1 to 3, the discharge capacity at 1.8 A discharge in the 10th cycle versus the discharge capacity at 1.8 A discharge in the 1st cycle during the rapid charge/discharge cycle test The capacity was determined as a capacity retention rate. The results are shown in Table 1 below.

As shown in Table 1, Example 1, in which the negative electrode active material layer contains an acrylic resin and the separator has an air permeability of 200 seconds/100 cm ³ or less, has a good capacity retention rate during rapid charge/discharge cycles. Met. In addition, in Example 1 and Comparative Example 1, which include a separator with an air permeability of 200 seconds/100 cm ³ or less, Comparative Example 1, in which the negative electrode active material layer contains a styrene-butadiene copolymer, has a separator with an acrylic resin. The capacity retention rate was lower than that of Example 1, which included the following. On the other hand, in Comparative Examples 2 and 3 that include separators with an air permeability exceeding 200 seconds/100 cm ³ , Comparative Example 3 in which the negative electrode active material layer contains a styrene-butadiene copolymer contains more acrylic resin. The capacity retention rate was higher than that of Comparative Example 2. For these reasons, by using a negative electrode having a negative electrode active material layer containing a binder made of acrylic resin in combination with a separator having an air permeability of 200 seconds/100 cm ³ or less, the capacity during rapid charge/discharge cycles can be increased. It can be seen that the improvement effect on the decline in retention rate is extremely high.

As described above, it has been shown that the non-aqueous electrolyte storage element can suppress a decrease in capacity retention rate during rapid charge/discharge cycles.

The present invention relates to non-aqueous electrolyte storage elements such as non-aqueous electrolyte secondary batteries used as power sources for electronic devices such as personal computers and communication terminals, and automobiles such as EVs, HEVs, and PHEVs that require rapid charging. It is suitably used as
Moreover, a large-sized lithium ion secondary battery is mentioned as a preferable application target of the present invention. For example, it is a large capacity type with a battery capacity of 5.0 Ah or more (for example, 5.0 Ah or more and 100 Ah or less), and can be used in charge/discharge cycles that include high-rate discharge of 3 C or more (for example, from 3 C to 50 C). A hypothetical large-sized lithium ion secondary battery is exemplified. The non-aqueous electrolyte storage device according to the present invention has an excellent capacity retention rate during rapid charge/discharge cycles, and therefore can be suitably applied to the above-mentioned large lithium ion secondary battery.

1 Energy storage element 2 Electrode body 3 Case 4 Positive electrode terminal 41 Positive electrode lead 5 Negative electrode terminal 51 Negative electrode lead 20 Energy storage unit 30 Energy storage device

Claims (4)

a positive electrode;
a negative electrode;
and a separator interposed between the positive electrode and the negative electrode,
The negative electrode has a negative electrode active material layer containing graphite and acrylic resin,
A non-aqueous electrolyte storage element in which the separator has an air permeability of 200 seconds/100 cm ³ or less (provided that a positive electrode comprising a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and a negative electrode An electrode body comprising: a negative electrode including a current collector and a negative electrode active material layer formed on the negative electrode current collector; and a separator disposed between the positive electrode and the negative electrode, the electrode body comprising: The negative electrode active material layer includes an electrode body in which the surface roughness of the negative electrode active material layer is 0.2 to 5 μm, and the separator has a surface roughness of 0.06 μm or more, and the negative electrode active material layer is made of fluorine-modified (meth)acrylic. (Excluding cases including binders). The non-aqueous electrolyte storage device according to claim 1, wherein the acrylic resin does not have a structural unit derived from butadiene. The separator has a microporous membrane-like base material layer,
3. The non-aqueous electrolyte storage device according to claim 1, wherein the main component of the base layer is polyolefin. The separator has a heat-resistant layer,
4. The non-aqueous electrolyte storage device according to claim 1, wherein the heat-resistant layer contains inorganic particles and a binder.

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