JP2022065561A - Positive electrode for power storage element and power storage element - Google Patents

Abstract

To provide a positive electrode for a power storage element, capable of suppressing an increase in current collection resistance associated with charge/discharge cycles.SOLUTION: A positive electrode for a power storage element includes a positive electrode active material layer containing a positive electrode active material and a conductive agent, and, when, in the log differential pore volume distribution of the positive electrode active material layer, A represents the maximum value of a differential pore volume in the range of a pore diameter of 0.04 μm or more and 0.1 μm or less, and B represents the maximum value of a differential pore volume in the range of a pore diameter of more than 0.1 μm and 1.0 μm or less, the sum of the A and the B is 0.60 cm3/g or more.SELECTED DRAWING: None

Description

The present invention relates to a positive electrode for a power storage element and a power storage element.

Non-aqueous electrolyte secondary batteries typified by lithium ion secondary batteries are widely used in personal computers, electronic devices such as communication terminals, automobiles, etc. due to their high energy density. The non-aqueous electrolyte secondary battery generally has a pair of electrodes electrically separated 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. In addition, 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.

In the positive electrode of such a power storage element, the output characteristics of the battery are improved by setting the pore diameter of the positive electrode mixture layer or the pore volume per unit weight of the positive electrode active material in the positive electrode mixture layer within a predetermined range. It is known to do so (see Patent Document 1).

International Publication WO2006 / 129756

On the other hand, in the power storage element, it is desirable that the internal resistance does not increase even if the charge / discharge cycle is repeated. However, in the conventional power storage element using a positive electrode having a positive electrode active material layer, the current collecting resistance may increase with the charge / discharge cycle, and one of the factors is the increase in the electronic resistance in the positive electrode active material layer. Further improvement is required for suppressing the increase in current collection resistance.

The present invention has been made based on the above circumstances, and an object of the present invention is to provide a positive electrode for a power storage element capable of suppressing an increase in current collection resistance due to a charge / discharge cycle of the power storage element.

The positive electrode for a power storage element according to one aspect of the present invention includes a positive electrode active material layer containing a positive electrode active material and a conductive agent, and has a pore diameter of 0.04 μm or more and 0 in the Log differential pore volume distribution of the positive electrode active material layer. When the maximum value of the differential pore volume in the range of 1 μm or less is A and the maximum value of the differential pore volume in the range of more than 0.1 μm and 1.0 μm or less is B, the above A and B are The total is 0.60 cm ³ / g or more.

The positive electrode for a power storage element according to one aspect of the present invention can suppress an increase in current collection resistance due to a charge / discharge cycle of the power storage element.

FIG. 1 is a perspective perspective view showing an embodiment of a power storage element. FIG. 2 is a schematic view showing an embodiment of a power storage device in which a plurality of power storage elements are assembled. FIG. 3 is a graph showing the relationship between the total maximum value of the differential pore volume and the rate of increase in AC resistance after the charge / discharge cycle.

First, the outline of the positive electrode for a power storage element and the power storage element disclosed by the present specification will be described.

The positive electrode for a power storage element according to one aspect of the present invention includes a positive electrode active material layer containing a positive electrode active material and a conductive agent, and has a pore diameter of 0.04 μm or more and 0 in the Log differential pore volume distribution of the positive electrode active material layer. When the maximum value of the differential pore volume in the range of 1 μm or less is A and the maximum value of the differential pore volume in the range of more than 0.1 μm and 1.0 μm or less is B, the above A and B are The total is 0.60 cm ³ / g or more.

The positive electrode for the power storage element has the maximum differential pore volume in the range of the pore diameter of 0.04 μm or more and 0.1 μm or less (hereinafter, also referred to as the first range) in the Log differential pore volume distribution of the positive electrode active material layer. The total of the value A and the maximum value B of the differential pore volume in the range of more than 0.1 μm and 1.0 μm or less (hereinafter, also referred to as the second range) is 0.60 cm ³ / g or more. , It is possible to suppress an increase in the current collecting resistance due to the charge / discharge cycle of the power storage element. The reason for this is not clear, but the following reasons are presumed. In the Log differential pore volume distribution, the differential pore volume in the first range of 0.04 μm or more and 0.1 μm or less is based on the pores of the conductive agent, and the pore diameter is more than 0.1 μm and 1.0 μm or less. It is considered that the differential pore volume in the second range is based on the pores of the positive electrode active material. Then, in the Log differential pore volume distribution of the positive electrode active material layer, the total of the maximum value A of the differential pore volume in the first range and the maximum value B of the differential pore volume in the second range is 0. When it is 60 cm ³ / g or more, the dispersibility of the positive electrode active material and the conductive agent becomes good. As a result, even if the positive electrode active material layer expands with the charge / discharge cycle, the conductive path between the active materials is maintained. Can be suppressed.
Here, the "Log differential pore volume (dV / d (logD))" indicates the relationship between the size of the pores of the object to be measured and the volume thereof, and is the pore volume between the measurement points of the pore diameter. It is a value obtained by dividing the difference pore volume dV, which is the increase in the above, by the difference value d (logD) treated as a logarithm of the pore diameter. The log differential pore volume distribution is a plot of the log differential pore volume with respect to the average pore diameter of each section. The above-mentioned "current collecting resistance" can be evaluated by an AC resistance (Alternating Current Resistance: ACR) of 1 kHz.

It is preferable that A is 0.23 cm ³ / g or more and B is 0.33 cm ³ / g or more. In the Log differential pore volume distribution of the positive electrode active material layer, the maximum value A of the differential pore volume in the first range and the maximum value B of the differential pore volume in the second range are equal to or higher than the lower limit. The positive electrode for the power storage element can further improve the effect of suppressing an increase in the collection resistance due to the charge / discharge cycle of the power storage element.

It is preferable that the conductive agent is carbon black. When the conductive agent is carbon black, the electronic conductivity of the conductive agent and the coatability of the positive electrode mixture paste are improved.

The power storage element according to one aspect of the present invention includes the positive electrode. By providing the positive electrode, the power storage element can suppress an increase in current collection resistance due to a charge / discharge cycle.

A configuration of a positive electrode for a power storage element, a configuration of a power storage element, a configuration of a power storage device, a method for manufacturing a positive electrode for a power storage element, a method for manufacturing a power storage element, and other embodiments according to an embodiment of the present invention will be described in detail. The name of each component (each component) used in each embodiment may be different from the name of each component (each component) used in the background technique.

<Positive electrode for power storage element>
The positive electrode has a positive electrode base material and a positive electrode active material layer arranged directly on the positive electrode base material or via an intermediate layer.

(Positive electrode base material)
The positive electrode substrate has conductivity. Whether or not it has "conductivity" is determined with a volume resistivity of 107 Ω · cm measured in accordance with JIS-H-0505 (1975) as a threshold value. As the material of the positive electrode base material, metals such as aluminum, titanium, tantalum, and stainless steel, or alloys thereof are used. Among these, aluminum or an aluminum alloy is preferable from the viewpoint of potential resistance, high conductivity, and cost. Examples of the positive electrode base material include foils, thin-film deposition films, meshes, porous materials, and the like, and foils are preferable from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferable as the positive electrode base material. Examples of aluminum or aluminum alloy include A1085, A3003, and A1N30 specified in JIS-H-4000 (2014) or JIS-H4160 (2006).

The intermediate layer is a layer arranged between the positive electrode base material and the positive electrode active material layer. The intermediate layer contains a conductive agent such as carbon particles to reduce the contact resistance between the positive electrode base material and the positive electrode active material layer. The composition of the intermediate layer is not particularly limited and includes, for example, a binder and a conductive agent.

(Positive electrode active material layer)
The positive electrode active material layer contains a positive electrode active material and a conductive agent. The positive electrode active material layer contains optional components such as a binder, a thickener, and a filler, if necessary.

The positive electrode active material can be appropriately selected from known positive electrode active materials. As the positive electrode active material for a lithium ion secondary battery, a material capable of storing and releasing lithium ions is usually used. Examples of the positive electrode active material include a lithium transition metal composite oxide having an α-NaFeO type ₂ crystal structure, a lithium transition metal composite oxide having a spinel type crystal structure, a polyanionic compound, a chalcogen compound, sulfur and the like. Examples of the lithium transition metal composite oxide having an α-NaFeO type ₂ crystal structure include Li [Li _x Ni _(1-x) ] O ₂ (0 ≦ x <0.5) and Li [Li _x Ni _γ Co ₍ 0 ≦ x <0.5). _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 ( Examples thereof include 0 ≦ x <0.5, 0 <γ, 0 <β, 0.5 <γ + β <1). Examples of the lithium transition metal composite oxide having a spinel-type crystal structure include Li _x Mn ₂ O ₄ and Li _x Ni _γ Mn _(2-γ) O ₄ . Examples of the polyanionic 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 the chalcogen compound include titanium disulfide, molybdenum disulfide, molybdenum dioxide and the like. The atoms or polyanions in these materials may be partially substituted with atoms or anion species consisting of other elements. The surface of these materials may be coated with other materials. In the positive electrode active material layer, one of these materials may be used alone, or two or more of them may be mixed and used.

The positive electrode active material is usually particles (powder). The average particle size of the positive electrode active material is preferably 0.1 μm or more and 20 μm or less, for example. By setting the average particle size of the positive electrode active material to the above lower limit or more, the production or handling of the positive electrode active material becomes easy. By setting the average particle size of the positive electrode active material to the above upper limit or less, the electron conductivity of the positive electrode active material layer is improved. When a composite of a positive electrode active material and another material is used, the average particle size of the composite is taken as the average particle size of the positive electrode active material. The "average particle size" is based on JIS-Z-8825 (2013), and is based on the particle size distribution measured by the laser diffraction / scattering method for a diluted solution obtained by diluting the particles with a solvent. -2 (2001) means a value at which the volume-based integrated distribution calculated in accordance with (2001) is 50%.

A crusher, a classifier, or the like is used to obtain a powder having a predetermined particle size. Examples of the crushing method include a method using a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling airflow type jet mill, a sieve, or the like. At the time of pulverization, wet pulverization in which water or an organic solvent such as hexane coexists can also be used. As a classification method, a sieve, a wind power classifier, or the like is used as needed for both dry type and wet type.

The content of the positive electrode active material in the positive electrode active material layer is preferably 50% by mass or more and 99% by mass or less, more preferably 70% by mass or more and 98% by mass or less, and further preferably 80% by mass or more and 95% by mass or less. By setting the content of the positive electrode active material within the above range, it is possible to achieve both high energy density and manufacturability of the positive electrode active material layer.

The conductive agent is preferably carbon black. When the conductive agent is carbon black, the electronic conductivity of the conductive agent and the coatability of the positive electrode mixture paste are improved. Examples of the carbon black include furnace black, acetylene black, and ketjen black. Among these, acetylene black is preferable. Further, carbon black may be used alone or in combination of two or more.

The conductive agent may contain other conductive agents other than carbon black. The other 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 and the like. Examples of the carbonaceous material include graphite, other non-graphitic carbons other than carbon black, graphene-based carbon, and the like. Examples of other non-graphitic carbons include carbon nanofibers and pitch-based carbon fibers. Examples of graphene-based carbons include graphene, carbon nanotubes (CNTs), fullerenes and the like. Examples of the shape of the conductive agent include powder and fibrous. As the conductive agent, one of these materials may be used alone, or two or more of them may be mixed and used. Further, these materials may be combined and used.

The lower limit of the content of the conductive agent in the positive electrode active material layer is preferably 1% by mass, more preferably 2% by mass. On the other hand, the upper limit of the content of the conductive agent is preferably 8% by mass, more preferably 6% by mass. By setting the total content of the conductive agent in the above range, it is possible to enhance the effect of suppressing the increase in current collecting resistance and the energy density due to the charge / discharge cycle of the power storage element.

Examples of the binder include fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), thermoplastic resins such as polyethylene, polypropylene, polyacrylic, and polyimide; ethylene-propylene-diene rubber (EPDM), sulfone. Elastomers such as polyethylene chemicals, styrene-butadiene rubber (SBR), fluororubber; and polysaccharide polymers can be mentioned.

The binder content in the positive electrode active material layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 2% by mass or more and 9% by mass or less. By setting the binder content within the above range, the active substance can be stably retained.

Examples of the thickener include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. When the thickener has a functional group that reacts with lithium or the like, this functional group may be deactivated by methylation or the like in advance.

The filler is not particularly limited. Fillers include polyolefins such as polypropylene and polyethylene, silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, inorganic oxides such as aluminosilicate, magnesium hydroxide, calcium hydroxide, and hydroxide. Hydroxides such as aluminum, carbonates such as calcium carbonate, sparingly soluble ion crystals such as calcium fluoride, barium fluoride, barium sulfate, nitrides such as aluminum nitride and silicon nitride, talc, montmorillonite, boehmite, zeolite, etc. Examples thereof include mineral resource-derived substances such as apatite, kaolin, mulite, spinel, olivine, sericite, bentonite, and mica, or man-made products thereof.

The positive electrode active material layer includes typical non-metal elements such as B, N, P, F, Cl, Br, I, Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, Ba and the like. Typical metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, W and other transition metal elements are used as positive electrode active materials, conductive agents, binders, thickeners, fillers. It may be contained as a component other than.

In the Log differential pore volume distribution of the positive electrode active material layer, the maximum value A of the differential pore volume in the first range of the pore diameter of 0.04 μm or more and 0.1 μm or less and the pore diameter of more than 0.1 μm and 1.0 μm or less. The lower limit of the total with the maximum value B of the differential pore volume in the second range is 0.60 cm ³ / g, more preferably 0.63 cm ³ / g. When the lower limit of the total with the maximum value of the differential pore volume is within the above range, the dispersibility of the positive electrode active material and the conductive material is good, so that the positive electrode active material layer expands with the charge / discharge cycle. Also, the conductive path between the active materials is maintained. As a result, the positive electrode for the power storage element can suppress an increase in current collection resistance due to the charge / discharge cycle of the power storage element.

As the lower limit of the maximum value A of the differential pore volume in the first range, 0.05 cm ³ / g is preferable, 0.23 cm ³ / g is more preferable, and 0.30 cm ³ / g is further preferable. The lower limit of the maximum value B of the differential pore volume in the second range is preferably 0.05 cm ³ / g, more preferably 0.33 cm ³ / g, and even more preferably 0.38 cm ³ / g. When the lower limit of the maximum value A of the differential pore volume in the first range and the maximum value B of the differential pore volume in the second range is in the above range, the positive electrode for the power storage element is the charge / discharge cycle of the power storage element. It is possible to further improve the effect of suppressing the increase in the current collecting resistance accompanying the increase. On the other hand, the upper limit of the maximum value A of the differential pore volume in the first range is preferably 1.0 cm ³ / g. Further, the upper limit of the maximum value B of the differential pore volume in the second range is preferably 1.6 cm ³ / g. By setting the maximum value A and the maximum value B to the upper limit or less, the pore volume of the positive electrode active material layer does not become excessively large, so that the adhesion of the positive electrode active material layer is lowered and the electrode plate is peeled off. It can be suppressed.

The Log differential pore volume of the positive electrode active material layer is measured by a mercury intrusion method based on the following procedure.
Using AutoPore 9400 (Micrometritics), the pore volume distribution is measured by the mercury intrusion method. The contact angle of mercury is set to 130 ° and the surface tension is set to 484 days / cm. The pore diameter range to be measured is 6 nm to 20 μm. The cumulative pore volume curve is obtained by plotting the pore diameter on the horizontal axis and the pore volume on the vertical axis. Next, the difference volume dV between the measurement points is divided by the difference value d (logD) treated as a logarithm of the pore diameter, and this is plotted against the average pore diameter of each section to obtain the Log differential fine. Find the hole volume curve. The "maximum value of the differential pore volume in the range of the pore diameter of 0.04 μm or more and 0.1 μm or less" is the maximum value of the Log differential pore volume in the range of the average pore diameter of 0.04 μm or more and 0.1 μm or less. The "maximum value of the differential pore volume in the range of more than 0.1 μm and 1.0 μm or less" is the maximum value of the Log differential pore volume in the range of the average pore diameter of more than 0.1 μm and 1.0 μm or less. A sample of the positive electrode active material layer to be used for measuring the pore volume distribution is prepared by the following method. The power storage element is constantly discharged with a current of 0.1 C to the discharge end voltage during normal use. Here, "during normal use" means a case where the power storage element is used by adopting the discharge conditions recommended or specified for the power storage element. The power storage element is disassembled, the positive electrode is taken out and used as the working electrode, the metal Li is used as the counter electrode to assemble a unipolar battery, and the battery is discharged with a current of 0.1 C until the positive electrode potential reaches 3.0 V (vs. Li / Li ⁺ ). .. The unipolar battery is disassembled, the positive electrode taken out is thoroughly washed with dimethyl carbonate, and then dried under reduced pressure at room temperature. The dried positive electrode is cut into a predetermined size (for example, 2 × 2 cm) and used as a sample for measuring the pore volume distribution. The work from disassembling the power storage element to cutting out the positive electrode to a predetermined size is performed in a dry air atmosphere with a dew point of −40 ° C. or lower.

The porosity of the positive electrode active material layer may be, for example, 30% or more and 50% or less, preferably 35% or more and 47% or less, and more preferably 37% or more and 45% or less. By setting the porosity of the positive electrode active material layer to the above range, it is possible to increase the maximum value A of the differential pore volume in the first range and the maximum value B of the differential pore volume in the second range. It is possible to further suppress an increase in the current collecting resistance due to the charge / discharge cycle of the power storage element.

According to the positive electrode for the power storage element, it is possible to suppress an increase in the current collecting resistance due to the charge / discharge cycle of the power storage element.

<Power storage element>
The power storage element according to an embodiment of the present invention includes an electrode body having a positive electrode, a negative electrode, and a separator, a non-aqueous electrolyte, and a case for accommodating the electrode body and the non-aqueous electrolyte. The electrode body is usually a laminated type in which a plurality of positive electrodes and a plurality of negative electrodes are laminated via a separator, or a wound type in which a positive electrode and a negative electrode are laminated via a separator. The non-aqueous electrolyte exists in a state of being impregnated in the positive electrode, the negative electrode and the separator. As an example of the power storage element, a non-aqueous electrolyte secondary battery (hereinafter, also simply referred to as “secondary battery”) will be described.

[Positive electrode]
The positive electrode provided in the power storage element is as described above.

[Negative electrode]
The negative electrode has a negative electrode base material and a negative electrode active material layer arranged directly on the negative electrode base material or via an intermediate layer. The configuration of the intermediate layer is not particularly limited, and can be selected from, for example, the configurations exemplified by the positive electrode.

(Negative electrode base material)
The negative electrode substrate has conductivity. As the material of the negative electrode base material, metals such as copper, nickel, stainless steel, nickel-plated steel and aluminum, alloys thereof, carbonaceous materials and the like are used. Among these, copper or a copper alloy is preferable. Examples of the negative electrode base material include foils, thin-film deposition films, meshes, porous materials, and the like, and foils are preferable from the viewpoint of cost. Therefore, a copper foil or a copper alloy foil is preferable as the negative electrode base material. Examples of the copper foil include rolled copper foil, electrolytic copper foil and the like.

The average thickness of the negative electrode substrate is preferably 2 μm or more and 35 μm or less, more preferably 3 μm or more and 30 μm or less, further preferably 4 μm or more and 25 μm or less, and particularly preferably 5 μm or more and 20 μm or less. By setting the average thickness of the negative electrode base material in the above range, it is possible to increase the energy density per volume of the secondary battery while increasing the strength of the negative electrode base material.

(Negative electrode active material layer)
The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer contains optional components such as a conductive agent, a binder, a thickener, and a filler, if necessary. Optional components such as a conductive agent, a binder, a thickener, and a filler can be selected from the materials exemplified by the positive electrode.

The negative electrode active material layer is a typical non-metal element such as B, N, P, F, Cl, Br, I, Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, Ba, etc. Typical metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, W and other transition metal elements are used as negative electrode active materials, conductive agents, binders, etc. It may be contained as a component other than a thickener and a filler.

The negative electrode active material can be appropriately selected from known negative electrode active materials. As the negative electrode active material for a lithium ion secondary battery, a material capable of storing and releasing lithium ions is usually used. Examples of the negative electrode active material include metal Li; metal or semi-metal such as Si and Sn; metal oxide or semi-metal oxide such as Si oxide, Ti oxide and Sn oxide; Li ₄ Ti ₅ O ₁₂ ; Titanium-containing oxides such as LiTIO _{2 and} TiNb _{2O 7} ; polyphosphate compounds; silicon carbide; carbon materials such as graphite (graphite) and non-graphitric carbon (easy graphitable carbon or non-graphitizable carbon) can be mentioned. Be done. Among these materials, graphite and non-graphitic carbon are preferable. In the negative electrode active material layer, one of these materials may be used alone, or two or more thereof may be mixed and used.

“Graphite” refers to a carbon material having an average lattice spacing (d ₀₀₂ ) of (002) planes determined by X-ray diffraction before charging / discharging or in a discharged state of 0.33 nm or more and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite. Artificial graphite is preferable from the viewpoint that a material having stable physical properties can be obtained.

"Non-graphitic carbon" refers to a carbon material having an average lattice spacing (d ₀₀₂ ) of the (002) plane determined by X-ray diffraction before charging / discharging or in a discharged state of 0.34 nm or more and 0.42 nm or less. say. Examples of non-graphitizable carbon include non-graphitizable carbon and easily graphitizable carbon. Examples of the non-planar carbon include a resin-derived material, a petroleum pitch or a petroleum pitch-derived material, a petroleum coke or a petroleum coke-derived material, a plant-derived material, an alcohol-derived material, and the like.

Here, the "discharged state" means a state in which the carbon material, which is the negative electrode active material, is discharged so as to sufficiently release lithium ions that can be occluded and discharged by charging and discharging. For example, in a unipolar battery in which a negative electrode containing a carbon material as a negative electrode active material is used as a working electrode and metallic Li is used as a counter electrode, the open circuit voltage is 0.7 V or more.

The “non-graphitizable carbon” refers to a carbon material having d ₀₀₂ of 0.36 nm or more and 0.42 nm or less.

The “graphitizable carbon” refers to a carbon material having d ₀₀₂ of 0.34 nm or more and less than 0.36 nm.

The negative electrode active material is usually particles (powder). The average particle size of the negative electrode active material can be, for example, 1 nm or more and 100 μm or less. When the negative electrode active material is a carbon material, a titanium-containing oxide or a polyphosphate compound, the average particle size thereof may be 1 μm or more and 100 μm or less. When the negative electrode active material is Si, Sn, Si oxide, Sn oxide or the like, the average particle size thereof may be 1 nm or more and 1 μm or less. By setting the average particle size of the negative electrode active material to be equal to or higher than the above lower limit, the production or handling of the negative electrode active material becomes easy. By setting the average particle size of the negative electrode active material to the above upper limit or less, the electron conductivity of the active material layer is improved. A crusher, a classifier, or the like is used to obtain a powder having a predetermined particle size. The pulverization method and the powder grade method can be selected from, for example, the methods exemplified for the positive electrode. When the negative electrode active material is a metal such as metal Li, the negative electrode active material may be in the form of a foil.

The content of the negative electrode active material in the negative electrode active material layer is preferably 60% by mass or more and 99% by mass or less, and more preferably 90% by mass or more and 98% by mass or less. By setting the content of the negative electrode active material within the above range, it is possible to achieve both high energy density and manufacturability of the negative electrode active material layer.

[Separator]
The separator can be appropriately selected from known separators. As the separator, for example, a separator composed of only a base material layer, a separator having a heat-resistant layer containing heat-resistant particles and a binder formed on one surface or both surfaces of the base material layer can be used. Examples of the material of the base material layer of the separator include woven fabrics, non-woven fabrics, and porous resin films. Among these materials, a porous resin film is preferable from the viewpoint of strength, and a non-woven fabric is preferable from the viewpoint of liquid retention of a non-aqueous electrolyte. As the material of the base material layer of the separator, polyolefins such as polyethylene and polypropylene are preferable from the viewpoint of shutdown function, and polyimide and aramid are preferable from the viewpoint of oxidative decomposition resistance. As the base material layer of the separator, a material in which these resins are combined may be used.

The heat-resistant particles contained in the heat-resistant layer preferably have a mass reduction of 5% or less when the temperature is raised from room temperature to 500 ° C. in an air atmosphere of 1 atm, and the mass reduction when the temperature is raised from room temperature to 800 ° C. Is more preferably 5% or less. Inorganic compounds can be mentioned as materials whose mass reduction is less than or equal to a predetermined value. Examples of the inorganic compound include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, barium titanate, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide and aluminosilicate; aluminum nitride and silicon nitride. Nitridees such as; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ion crystals such as calcium fluoride and barium fluoride; covalent crystals such as silicon and diamond; talc, montmorillonite, boehmite, etc. Examples thereof include substances derived from mineral resources such as zeolite, apatite, kaolin, mulite, spinel, olivine, sericite, bentonite, and mica, or man-made products thereof. As the inorganic compound, a simple substance or a complex of these substances may be used alone, or two or more kinds thereof may be mixed and used. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicate is preferable from the viewpoint of safety of the power storage device.

The porosity of the separator is preferably 80% by volume or less from the viewpoint of strength, and preferably 20% by volume or more from the viewpoint of discharge performance. Here, the "porosity" is a volume-based value and means a measured value with a mercury porosity meter.

As the separator, a polymer gel composed of a polymer and a non-aqueous electrolyte may be used. Examples of the polymer include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, polyvinylidene fluoride and the like. The use of polymer gel has the effect of suppressing liquid leakage. As the separator, a polymer gel may be used in combination with a porous resin film or a non-woven fabric as described above.

[Non-water electrolyte]
As the non-aqueous electrolyte, a known non-aqueous electrolyte can be appropriately selected. A non-aqueous electrolyte solution may be used as the non-aqueous electrolyte. The non-aqueous electrolyte solution contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.

As the non-aqueous solvent, a known non-aqueous solvent can be appropriately selected. Examples of the non-aqueous solvent include cyclic carbonates, chain carbonates, carboxylic acid esters, phosphoric acid esters, sulfonic acid esters, ethers, amides, nitriles and the like. As the non-aqueous solvent, a solvent in which some of the hydrogen atoms contained in these compounds are replaced with halogen may be used.

Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), and difluoroethylene carbonate. (DFEC), styrene carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate and the like can be mentioned. Among these, EC is preferable.

Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), diphenyl carbonate, trifluoroethylmethyl carbonate, bis (trifluoroethyl) carbonate and the like. Among these, EMC is preferable.

As the non-aqueous solvent, it is preferable to use cyclic carbonate or chain carbonate, and it is more preferable to use cyclic carbonate and chain carbonate in combination. By using the cyclic carbonate, the dissociation of the electrolyte salt can be promoted and the ionic conductivity of the non-aqueous electrolyte solution can be improved. By using the chain carbonate, the viscosity of the non-aqueous electrolytic solution can be kept low. When the cyclic carbonate and the chain carbonate are used in combination, the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate: chain carbonate) is preferably in the range of, for example, 5:95 to 50:50.

The electrolyte salt can be appropriately selected from known electrolyte salts. Examples of the electrolyte salt include lithium salt, sodium salt, potassium salt, magnesium salt, onium salt and the like. Of these, lithium salts are 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 , lithium bis (oxalate) borate (LiBOB), and lithium difluorooxalate borate (LiFOB). , Lithium oxalate salts such as lithium bis (oxalate) difluorophosphate (LiFOP), LiSO ₃ CF ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) Examples thereof include lithium salts having a halogenated hydrocarbon group such as (SO ₂ C ₄ F ₉ ), LiC (SO ₂ CF ₃ ) ₃ , and LiC (SO ₂ C ₂ F ₅ ) ₃ . Among these, an inorganic lithium salt is preferable, and LiPF ₆ is more preferable.

The content of the electrolyte salt in the non-aqueous electrolyte solution is preferably 0.1 mol / dm ³ or more and 2.5 mol / dm ³ or less at 20 ° C. and 1 atm, and 0.3 mol / dm ³ or more and 2.0 mol / dm. It is more preferably ³ or less, more preferably 0.5 mol / dm ³ or more and 1.7 mol / dm ³ or less, and particularly preferably 0.7 mol / dm ³ or more and 1.5 mol / dm ³ or less. By setting the content of the electrolyte salt in the above range, the ionic conductivity of the non-aqueous electrolyte solution can be increased.

The non-aqueous electrolyte solution may contain additives in addition to the non-aqueous solvent and the electrolyte salt. Examples of the additive include halogenated carbonate esters such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC); lithium bis (oxalate) borate (LiBOB), lithium difluorooxalate borate (LiFOB), and lithium bis (oxalate). ) Difluorophosphate (LiFOP) and other oxalates; Lithiumbis (fluorosulfonyl) imide (LiFSI) and other imide salts; Biphenyl, alkylbiphenyl, terphenyl, partially hydride of terphenyl, cyclohexylbenzene, t-butylbenzene , T-Amilbenzene, diphenyl ether, dibenzofuran and other aromatic compounds; partial halides of the aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene; 2,4-difluoroanisole, 2 , 5-Difluoroanisol, 2,6-difluoroanisol, 3,5-difluoroanisol and other halogenated anisole compounds; vinylene carbonate, methylvinylene carbonate, ethylvinylene carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, anhydrous. Citraconic acid, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic acid anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, propane sulton, propensulton, butane sulton, methyl methanesulphonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, sulfate Ethylene, Sulfonide, Dimethyl Sulfonide, Diethyl Sulfonide, Dimethyl Sulfoxide, Diethyl Sulfoxide, Tetramethylene Sulfoxide, Diphenyl Sulfate, 4,4'-Bis (2,2-Dioxo-1,3,2-Dioxathiolane), 4-Methylsulfonyloxy Methyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisol, diphenyldisulfide, dipyridinium disulfide, 1,3-propensulton, 1,3-propanesulfon, 1,4-butansulton, 1,4- Examples thereof include butensulton, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakistrimethylsilyl titanate, lithium monofluorophosphate, lithium difluorophosphate and the like. These additives may be used alone or in combination of two or more.

The content of the additive contained in the non-aqueous electrolytic solution is preferably 0.01% by mass or more and 10% by mass or less, and is 0.1% by mass or more and 7% by mass or less with respect to the total mass of the non-aqueous electrolytic solution. It is more preferable to have it, more preferably 0.2% by mass or more and 5% by mass or less, and particularly preferably 0.3% by mass or more and 3% by mass or less. By setting the content of the additive in the above range, it is possible to improve the capacity maintenance performance or the cycle performance after high temperature storage, and further improve the safety.

As the non-aqueous electrolyte, a solid electrolyte may be used, or a non-aqueous electrolyte solution and a solid electrolyte may be used in combination.

The solid electrolyte can be selected from any material having ionic conductivity such as lithium, sodium and calcium and being solid at room temperature (for example, 15 ° C to 25 ° C). Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, oxynitride solid electrolytes, polymer solid electrolytes and the like.

Examples of the sulfide solid electrolyte include Li ₂ SP ₂ S ₅ , LiI-Li ₂ SP ₂ S ₅ , Li ₁₀ Ge-P ₂ S ₁₂ and the like.

[Specific configuration of power storage element]
The shape of the power storage element of the present embodiment is not particularly limited, and examples thereof include a cylindrical battery, a square battery, a flat battery, a coin battery, and a button battery.

FIG. 1 shows a power storage element 1 as an example of a square battery. The figure is a perspective view of the inside of the case. The electrode body 2 having the positive electrode and the negative electrode wound around the separator is housed in the square case 3. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 41. The negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 51.

[Configuration of power storage device]
The power storage element of the present embodiment is a power source for automobiles such as an electric vehicle (EV), a hybrid vehicle (HEV), and a plug-in hybrid vehicle (PHEV), a power source for electronic devices such as a personal computer and a communication terminal, or a power source for power storage. For example, it can be mounted as a power storage device configured by assembling a plurality of power storage elements 1. In this case, the technique of the present invention may be applied to at least one power storage element included in the power storage device.
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 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 power storage elements 1, a bus bar (not shown) that electrically connects two or more power storage units 20 and the like. The power storage unit 20 or the power storage device 30 may include a state monitoring device (not shown) for monitoring the state of one or more power storage elements.

[Manufacturing method of power storage element]
The method for manufacturing the power storage element of the present embodiment can be appropriately selected from known methods except that the positive electrode described above is used as the positive electrode. The manufacturing method includes, for example, preparing an electrode body, preparing a non-aqueous electrolyte, and accommodating the electrode body and the non-aqueous electrolyte in a case. Preparing the electrode body includes preparing the positive electrode body and the negative electrode body, and forming the electrode body by laminating or winding the positive electrode body and the negative electrode body via the separator. The positive electrode can be produced, for example, by applying the positive electrode mixture paste directly to the positive electrode substrate or via an intermediate layer and drying it. After drying, pressing or the like may be performed if necessary. The positive electrode mixture paste contains each component constituting the positive electrode active material layer, such as a positive electrode active material, a conductive agent, and a binder which is an optional component. The positive electrode mixture paste usually further contains a dispersion medium. In the Log differential pore volume distribution of the positive electrode active material layer, the maximum value A of the differential pore volume in the first range and the maximum value B of the differential pore volume in the second range are the particle size and specific surface area of the positive electrode active material. It can be adjusted by the particle size and specific surface area of the conductive agent, the composition, thickness and area of the positive electrode active material layer, the kneading conditions of the positive electrode mixture paste at the time of manufacture, the press strength of the positive electrode active material layer, and the like.

The inclusion of the non-aqueous electrolyte in the case can be appropriately selected from known methods. For example, when a non-aqueous electrolyte solution is used as the non-aqueous electrolyte solution, the non-aqueous electrolyte solution may be injected from the injection port formed in the case, and then the injection port may be sealed.

According to the power storage element, by providing the positive electrode, it is possible to suppress an increase in current collection resistance due to a charge / discharge cycle.

<Other embodiments>
The power storage element of the present invention is not limited to the above embodiment, and various modifications may be made without departing from the gist of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, and a part of the configuration of one embodiment can be replaced with the configuration of another embodiment or a well-known technique. In addition, some of the configurations of certain embodiments can be deleted. Further, a well-known technique can be added to the configuration of a certain embodiment.

In the above embodiment, the case where the power storage element is used as a non-aqueous electrolyte secondary battery (for example, a lithium ion secondary battery) capable of charging and discharging has been described, but the type, shape, size, capacity, etc. of the power storage element are arbitrary. .. The present invention can also be applied to capacitors such as various secondary batteries, electric double layer capacitors and lithium ion capacitors.

In the above embodiment, the electrode body in which the positive electrode and the negative electrode are laminated via the separator has been described, but the electrode body may not include the separator. For example, the positive electrode and the negative electrode may be in direct contact with each other in a state where a non-conductive layer is formed on the active material layer of the positive electrode or the negative electrode.

Hereinafter, the present invention will be described in more detail by way of examples. The present invention is not limited to the following examples.

[Examples 1 to 4 and Comparative Examples 1 to 6]
(Preparation of positive electrode)
As the positive electrode active material, a lithium transition metal composite oxide composed of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (NCM111) having a particle size of 4 μm was used. The types of carbon black shown in Table 1 were used as the conductive agent. Polyvinylidene fluoride was used as a binder.

N-Methylpyrrolidone (NMP) is used as the dispersion medium, and a high-speed mixer is used so that the mass ratio (solid content conversion) of the positive electrode active material, the conductive agent and the binder in the positive electrode active material layer is 93.5: 4.5: 2. The mixture was kneaded under the conditions shown in Table 1 using "Fillmix" manufactured by Primix Co., Ltd. to obtain a positive electrode mixture paste. Next, the positive electrode mixture paste is applied to both sides of the aluminum foil, which is the positive electrode base material, leaving a non-coated portion (positive electrode active material layer non-forming portion), dried at 100 ° C., and roll-pressed. , A positive electrode active material layer was formed on the positive electrode substrate. The amount of the positive electrode mixture paste applied was 10 mg / cm ² in terms of solid content. In this way, positive electrodes of Example 1 to Example 4 and Comparative Example 1 to Comparative Example 6 were obtained.

(Manufacturing of negative electrode)
Graphite was used as the negative electrode active material, styrene-butadiene rubber (SBR) was used as the binder, and carboxymethyl cellulose (CMC) was used as the thickener. An appropriate amount of water was added as a dispersion medium to a mixture of a negative electrode active material, a binder and a thickener at a mass ratio of 98: 1: 1 (in terms of solid content) to adjust the viscosity, and a negative electrode mixture paste was prepared. This negative electrode mixture paste was applied to both sides of a copper foil as a negative electrode base material, leaving a non-coated portion (negative electrode active material layer non-forming portion), and dried to form a negative electrode active material layer. Then, a roll press was performed to obtain a negative electrode.

(Preparation of non-aqueous electrolyte)
LiPF ₆ was dissolved at a concentration of 1.2 mol / dm ³ in a mixed solvent in which EC, DMC and EMC were mixed at a volume ratio of 30:35:35 to prepare a non-aqueous electrolyte.

(Manufacturing of power storage element)
Next, the positive electrode and the negative electrode were laminated via a separator made of a polyethylene base material and an inorganic layer formed on the polyethylene base material to prepare an electrode body. This electrode body was housed in an aluminum case (square electric tank can), and a positive electrode terminal and a negative electrode terminal were attached. After injecting the non-aqueous electrolyte into the inside of this case (square electric tank can), the non-aqueous electrolyte was sealed, and storage elements of Examples and Comparative Examples were obtained.

(Initial charge / discharge)
Each of the above storage elements was constantly charged with a current of 0.2 C up to 4.1 V at 25 ° C., and then charged with a constant voltage at 4.1 V. The charging end condition was until the total charging time reached 7 hours. After a 10-minute pause after charging, constant current discharge was performed at 25 ° C. up to 2.5 V with a current of 0.2 C. A 10-minute rest was provided after discharge. The above cycle was repeated twice. For each power storage element after the initial charge / discharge, the AC resistance of 1 kHz was measured using a 1 kHz AC impedance meter in a state where 10 minutes or more had passed after the end of the discharge.

(Measurement of Log differential pore volume)
For each storage element after the initial charge and discharge, the Log differential pore volume distribution of the positive electrode active material layer is measured by the above method, and the differential pores in the first range having a pore diameter of 0.04 μm or more and 0.1 μm or less are measured. The sum of the maximum value A of the volume and the maximum value B of the differential pore volume in the second range having a pore diameter of more than 0.1 μm and 1.0 μm or less was calculated. The results are shown in Table 1.

(Charge / discharge cycle test)
After each storage element after the initial charge and discharge is stored in a constant temperature bath at 55 ° C. for 3 hours, each is charged with a constant current of 4C to 4.1V, and then a current of 4C is not provided without a pause period. A constant current discharge was performed up to 2.5 V. These charging and discharging steps were set as one cycle, and this cycle was repeated for 1500 cycles. Both charging and discharging were performed in a constant temperature bath at 55 ° C.

(AC resistance (ACR) increase rate after charge / discharge cycle test)
The rate of increase in AC resistance of the power storage element after the charge / discharge cycle test was evaluated. For each power storage element after the charge / discharge cycle test, the AC resistance of 1 kHz was measured by the above method. The rate of increase (%) of the 1 kHz AC resistance after the charge / discharge cycle test with respect to the 1 kHz AC resistance after the initial charge / discharge was calculated by the following formula. Table 1 shows the obtained AC resistance increase rate.
AC resistance increase rate (%) = (ACR after charge / discharge cycle test / ACR after initial charge / discharge) x 100

The evaluation results are shown in Table 1 below.

As shown in Table 1 and FIG. 3, in the Log differential pore volume distribution of the positive electrode active material layer, the maximum value A of the differential pore volume in the range of the pore diameter of 0.04 μm or more and 0.1 μm or less is fine. In Examples 1 to 4, the maximum value of the differential pore volume in the range of more than 0.1 μm and 1.0 μm or less is 0.60 cm ³ / g or more in total with the maximum value B of the differential pore volume. Compared with Comparative Example 1 to Comparative Example 6 in which the total of the above is out of the above range, the rate of increase in AC resistance after the charge / discharge cycle test was reduced.

As a result of the above, it was shown that the positive electrode for the power storage element can suppress an increase in the current collection resistance due to the charge / discharge cycle of the power storage element.

The positive electrode for a power storage element can be applied to a personal computer, an electronic device such as a communication terminal, a power storage element used as a power source for an automobile or the like.

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

Claims (4)

A positive electrode active material layer containing a positive electrode active material and a conductive agent is provided.
In the Log differential pore volume distribution of the positive electrode active material layer, the maximum value of the differential pore volume in the range of pore diameter 0.04 μm or more and 0.1 μm or less is defined as A.
When B is the maximum value of the differential pore volume in the range of more than 0.1 μm and 1.0 μm or less in pore diameter,
A positive electrode for a power storage element in which the total of A and B is 0.60 cm ³ / g or more. The above A is 0.23 cm ³ / g or more, and
The positive electrode for a power storage element according to claim 1, wherein B is 0.33 cm ³ / g or more. The positive electrode for a power storage element according to claim 1 or 2, wherein the conductive agent is carbon black. A power storage element comprising the positive electrode according to claim 1, claim 2 or claim 3.

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