JP2023168034A - Nonaqueous electrolyte storage device - Google Patents

Abstract

To provide nonaqueous electrolyte storage devices with low AC resistance increase rate and high capacity retention ratio after charge and discharge cycles at high temperature.SOLUTION: In one embodiment of the present invention, a nonaqueous electrolyte storage device includes a positive electrode, a negative electrode, and a nonaqueous electrolyte. The positive electrode above has a positive electrode active material layer containing positive electrode active material particles with a ratio of secondary particle size to primary particle size of 1 to 3. The nonaqueous electrolyte contains oxalate complex salt.SELECTED DRAWING: Figure 1

Description

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

Non-aqueous electrolyte secondary batteries, typified by lithium ion secondary batteries, are widely used in electronic devices such as personal computers and communication terminals, automobiles, etc. due to their high energy density. The nonaqueous electrolyte secondary battery generally has a pair of electrodes electrically isolated by a separator and a nonaqueous electrolyte interposed between the electrodes, and charge transport ions are exchanged between the two electrodes. The battery is configured to be charged and discharged by performing the following steps. In addition, capacitors such as lithium ion capacitors and electric double layer capacitors are also widely used as nonaqueous electrolyte storage devices other than nonaqueous electrolyte secondary batteries.

In recent years, there has been a need to reduce the amount of carbon dioxide in order to combat global warming, and progress has been made in the development of electric vehicles and plug-in hybrid vehicles that have less environmental impact. Therefore, non-aqueous electrolyte secondary batteries are being used in the power supplies of these next-generation eco-cars, and improvements in charge-discharge cycle characteristics are required. Patent Document 1 describes a positive electrode active material for a non-aqueous electrolyte secondary battery that uses lithium transition metal composite oxide particles with uniform particle sizes as a positive electrode active material.

Japanese Patent Application Publication No. 2017-188445

An example of a non-aqueous electrolyte storage device that can achieve both high output characteristics and high charge-discharge cycle characteristics is a non-aqueous electrolyte storage device that has a positive electrode active material layer containing single-particle positive electrode active material particles described below. However, the inventors found that although a non-aqueous electrolyte storage element having a cathode active material layer containing a single particle cathode active material has an improved capacity retention rate after charge/discharge cycles at high temperatures, It was found that the rate of increase in alternating current resistance (ACR), which is one type of resistance, was increased (see Comparative Examples 1 and 6). Continuing to use a non-aqueous electrolyte storage element that generally has high AC resistance may cause heat generation and a decrease in output.

The present invention was made based on the above-mentioned circumstances, and its purpose is to provide a non-aqueous electrolyte energy storage element with a low rate of increase in AC resistance after charge/discharge cycles at high temperatures and a high capacity retention rate. It is to provide.

One aspect of the present invention made to solve the above problems includes a positive electrode, a negative electrode, and a non-aqueous electrolyte, and the positive electrode has a ratio of secondary particle size to primary particle size of 1 or more and 3 or less. The present invention is a non-aqueous electrolyte storage element having a positive electrode active material layer containing positive electrode active material particles, and in which the non-aqueous electrolyte contains an oxalate complex salt.

According to the present invention, it is possible to provide a non-aqueous electrolyte storage element with a low rate of increase in AC resistance after charge/discharge cycles at high temperatures and a high capacity retention rate.

FIG. 1 is a transparent 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. FIG. 3 is an example of a scanning electron microscope image of positive electrode active material particles according to Example 1. FIG. 4 is an example of a scanning electron microscope image of positive electrode active material particles according to Comparative Example 2.

A non-aqueous electrolyte storage device according to an embodiment of the present invention includes a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode has a ratio of a secondary particle size to a primary particle size of 1 or more and 3 or less. The present invention is a non-aqueous electrolyte storage element having a positive electrode active material layer containing active material particles, and in which the non-aqueous electrolyte contains an oxalato complex salt.

In the present invention, the "primary particle diameter" is the arithmetic mean value of the particle diameters of ten arbitrary primary particles constituting the positive electrode active material particles observed with a scanning electron microscope (SEM). The particle diameter of the primary particles is determined as follows. First, a positive electrode to be measured is prepared according to the following procedure. If a positive electrode can be prepared before assembling the non-aqueous electrolyte storage element, it can be used as is. When preparing an assembled non-aqueous electrolyte storage element, the non-aqueous electrolyte storage element is first discharged at a constant current of 0.1 C to the final discharge voltage during normal use to bring it into a discharged state. This discharged nonaqueous electrolyte storage element is disassembled, the positive electrode is taken out, and components (electrolyte, etc.) attached to the positive electrode are thoroughly washed with dimethyl carbonate, and then dried under reduced pressure at room temperature for 24 hours. The work from disassembling the nonaqueous electrolyte storage element to preparing the positive electrode to be measured is performed in a dry air atmosphere with a dew point of -40°C or lower. The prepared positive electrode to be measured is fixed with thermosetting resin. A cross-section polisher is used to expose the cross section of the positive electrode fixed with resin, and a sample for measurement is prepared. To obtain the SEM image, JSM-7001F (manufactured by JEOL Ltd.) is used as a scanning electron microscope. The SEM image is assumed to be a secondary electron image. The accelerating voltage is 15 kV. The observation magnification is set at a magnification such that the number of positive electrode active material particles appearing in one field of view is 3 or more and 15 or less. The obtained SEM image is saved as an image file. The shortest diameter passing through the center of the minimum circumscribed circle of the primary particle observed in the acquired SEM image is defined as the short axis, and the diameter passing through the center and perpendicular to the short axis is defined as the long axis. Let the arithmetic mean value of the major axis and the minor axis be the particle diameter of the primary particle. However, if there are two or more shortest diameters, the longest orthogonal diameter is defined as the shortest diameter. "Secondary particle size" is based on the particle size distribution measured by laser diffraction/scattering method on a diluted solution of particles diluted with a solvent, in accordance with JIS-Z-8825 (2013). This is the median diameter (D50) at which the volume-based integrated distribution calculated in accordance with 8819-2 (2001) is 50%. The term "primary particle" refers to the smallest unit that can be identified as a granular material from its appearance among the morphological constituent elements constituting the positive electrode active material particles, and particularly refers to particles constituting the secondary particles described below. "Secondary particles" means particles formed by aggregation of a certain number of primary particles. The secondary particles may be composed of a single primary particle. The ratio of the secondary particle diameter to the primary particle diameter of the positive electrode active material particles is 1 or more and 3 or less, which means that the positive electrode active material particles are substantially composed of a single primary particle or a small number of primary particles. It means a particle (hereinafter also referred to as a "single particle").

The non-aqueous electrolyte electricity storage element has a positive electrode having a positive electrode active material layer containing positive electrode active material particles having a ratio of secondary particle size to primary particle size of 1 or more and 3 or less, and wherein the non-aqueous electrolyte contains an oxalato complex salt. By containing it, the rate of increase in AC resistance after charge/discharge cycles at high temperatures is low and the capacity retention rate is high. Although the reason for this is not certain, it is thought to be as follows. When the positive electrode active material layer of the positive electrode of a non-aqueous electrolyte storage element contains a single particle positive electrode active material, the capacity decreases due to disruption of the lithium ion conduction path due to grain boundary dissociation between primary particles that may occur during charge/discharge cycles. Decrease in retention rate can be suppressed. On the other hand, secondary particles are a state in which primary particles are aggregated by forming physical or chemical bonds between particles, whereas single particles are primary particles that are not bonded physically or chemically. Or it is in a state where there is little bonding. Since the contact area between single particles is smaller than that of secondary particles, the contact resistance between particles is larger than that of secondary particles. Therefore, when the positive electrode active material layer of the positive electrode of a non-aqueous electrolyte storage element contains a single particle positive electrode active material, the conductive path between the positive electrode active material particles is no longer maintained due to repeated charging and discharging in a high temperature environment. , it is thought that the AC resistance increases. In the non-aqueous electrolyte storage element, since the non-aqueous electrolyte contains an oxalato complex salt, the decomposition products derived from the oxalato complex decomposed on the negative electrode during charging and discharging move to the positive electrode side, thereby causing the positive electrode active material particles to It is assumed that a low-resistance lithium ion conductive film is formed on the surface. By forming a film on the surface of the positive electrode active material particles that exist as single particles, it is possible to reduce the increase in contact resistance due to expansion and contraction of the positive electrode active material layer during charging and discharging. It is thought that a water electrolyte storage element has a low rate of increase in AC resistance after charge/discharge cycles at high temperatures and a high capacity retention rate.

In the non-aqueous electrolyte storage element, the positive electrode active material particles preferably have no grain boundaries in appearance. "Grain boundary" refers to the interface between each crystal grain in a polycrystalline body, and "no grain boundary exists in appearance" means that it exists as a substantially single grain. means. Such a nonaqueous electrolyte storage element can further suppress a decrease in capacity retention rate after charge/discharge cycles at high temperatures. On the other hand, it is thought that the contact resistance between particles and the interfacial resistance with the electrolyte become larger, and the rate of increase in AC resistance after charge/discharge cycles at high temperatures becomes larger. The non-aqueous electrolyte storage element fully enjoys the advantages of the present invention, has a low rate of increase in AC resistance, and has a higher capacity retention rate.

In the non-aqueous electrolyte storage device, the oxalato complex salt is preferably at least one of a boron-containing oxalato complex salt and a phosphorus-containing oxalato complex salt. Such a non-aqueous electrolyte storage element can lower the rate of increase in AC resistance after charge/discharge cycles at high temperatures. When the above-mentioned oxalato complex salt is a boron-containing oxalato complex salt or a phosphorus-containing oxalato complex salt, the presence of a polarized B-O bond or P-O bond in the molecule causes the decomposition product generated at the negative electrode to be transferred to the positive electrode side. It is thought that it will be easier to move. This is thought to efficiently form a stable lithium ion conductive film with low interfacial resistance on the surface of the positive electrode active material particles existing as single particles.

Hereinafter, the configuration of a non-aqueous electrolyte power storage element, the configuration of a non-aqueous electrolyte power storage device, and the method for manufacturing a non-aqueous electrolyte power storage element according to an embodiment of the present invention will be described in detail. Note that the name of each component used in each embodiment may be different from the name of each component used in the background art. Embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

<Configuration of non-aqueous electrolyte storage element>
A nonaqueous electrolyte storage device (hereinafter also simply referred to as a “power storage device”) according to an embodiment of the present invention includes a positive electrode, a negative electrode, and a nonaqueous electrolyte. The above-mentioned positive electrode and the above-mentioned negative electrode usually form an electrode body that is laminated or wound with a separator interposed in between. This electrode body is housed in a case, and the case is filled with a nonaqueous electrolyte. 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. A non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. As an example of a non-aqueous electrolyte storage element, a non-aqueous electrolyte secondary battery (hereinafter also simply referred to as a "secondary battery") will be described.

(positive electrode)
The positive electrode has a positive electrode base material and a positive electrode active material layer. The positive electrode active material layer is laminated along at least one surface of the positive electrode base material directly or via an intermediate layer.

The positive electrode base material is a conductive base material. "Conductive" means that the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 ⁷ Ω・cm or less, and "non-conductive" means that This means that the volume resistivity is more than 10 ⁷ Ω·cm. 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 or aluminum alloy is preferred from the viewpoint of potential resistance, high conductivity, and cost. Examples of the shape of the positive electrode base material include foil, vapor deposited film, mesh, porous material, etc. Foil is preferable from the viewpoint of cost. Therefore, the positive electrode base material is preferably aluminum foil or aluminum alloy foil. Examples of aluminum or aluminum alloy include A1085, A3003, A1N30, etc. specified in JIS-H-4000 (2014) or JIS-H-4160 (2006).

The average thickness of the positive electrode base material is preferably 3 μm or more and 50 μm or less, more preferably 5 μm or more and 40 μm or less, even more preferably 8 μm or more and 30 μm or less, and particularly preferably 10 μm or more and 25 μm or less. By setting the average thickness of the positive electrode base material within the above range, it is possible to increase the energy density per volume of the secondary battery while increasing the strength of the positive electrode base material. "Average thickness" refers to the value obtained by dividing the punching mass when punching a base material of a predetermined area by the true density and punching area of the base material. The "average thickness" of the negative electrode base material, which will be described later, is defined similarly.

The intermediate layer is a layer disposed between the positive electrode base material and the positive electrode active material layer. The intermediate layer reduces contact resistance between the positive electrode base material and the positive electrode active material layer by containing a conductive agent such as carbon particles. The structure of the intermediate layer is not particularly limited, and includes, for example, a binder and a conductive agent.

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 layer contains optional components such as a conductive agent, a binder, a thickener, and a filler, as necessary.

The positive electrode active material can be appropriately selected from known positive electrode active materials. 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 such positive electrode active materials include lithium transition metal composite oxides having an α- _NaFeO2 type crystal structure, lithium transition metal oxides having a spinel type crystal structure, polyanion compounds, chalcogen compounds, sulfur, and the like. It will be done. Examples of lithium transition metal composite oxides having α-NaFeO type ₂ 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≦x<0.5, 0<γ, Examples include 0<β, 0.5<γ+β<1). Examples of lithium transition metal oxides having a spinel crystal structure include Li _x Mn ₂ O ₄ and Li _x Ni _γ Mn _2-γ O ₄ . 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. The surfaces of these materials may be coated with other materials. 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.

As the positive electrode active material, a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure is preferable, and a compound represented by the following formula 1 is more preferable.
Li _1+α Me _1-α O ₂ ...1
However, in the above formula 1, Me is a transition metal element such as a nickel element, a cobalt element, or a manganese element, or an aluminum element. Me may be one or more metal elements. Further, 0≦α<1. By using such a positive electrode active material, energy density can be further increased.

In the above formula 1, it is more preferable that Me contains a nickel element, a cobalt element, and a manganese element. That is, the positive electrode active material is preferably a lithium-transition metal composite oxide represented by the above formula 1 and containing a nickel element, a cobalt element, and a manganese element. As such a positive electrode active material, for example, 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) etc. A nonaqueous electrolyte storage device using such a positive electrode active material can have both high energy density and low cost. On the other hand, when the positive electrode active material layer contains single particles of the lithium transition metal composite oxide as described above, the conductive path between the positive electrode active material particles is no longer maintained, and the AC resistance of the nonaqueous electrolyte storage element becomes larger. Conceivable. By using the above-mentioned lithium transition metal composite oxide in the present invention, it is possible to eliminate such a disadvantage of increased AC resistance.

From the viewpoint of easily making the positive electrode active material particles described later into single particles, it is also preferable that Me in the above formula 1 is substantially composed only of the cobalt element. That is, it is also preferable that the positive electrode active material is a lithium transition metal composite oxide represented by the above formula 1 and containing substantially only the cobalt element. Examples of such positive electrode active materials include Li[Li _x Co _1-x ]O ₂ (0≦x<0.5).

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 even more 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 positive electrode active material in the positive electrode active material layer is in the form of particles. That is, the positive electrode active material layer contains positive electrode active material particles. The ratio of the secondary particle diameter to the primary particle diameter of the positive electrode active material particles is 1 or more and 3 or less. By setting the ratio of the secondary particle diameter to the primary particle diameter of the positive electrode active material particles within the above range, the lithium ion conduction path associated with grain boundary dissociation of particles that may occur during charge/discharge cycles of the nonaqueous electrolyte storage element is interrupted. etc., and a decrease in capacity retention rate after charge/discharge cycles can be suppressed. Further, from the viewpoint of further suppressing a decrease in capacity retention rate, the ratio of the secondary particle size to the primary particle size is more preferably 1 or more and 2.5 or less, further preferably 1 or more and 2 or less, and 1 More preferably, it is 1.5 or less.

The positive electrode active material particles preferably have no grain boundaries in appearance. A non-aqueous electrolyte storage element using such positive electrode active material particles can further suppress a decrease in capacity retention rate after charge/discharge cycles. For example, when the ratio of the secondary particle size to the primary particle size is 1 or more and 2 or less, it is visually confirmed that no grain boundaries exist in the positive electrode active material particles. On the other hand, since the contact resistance between the particles and the interfacial resistance with the electrolyte become larger, it is possible to fully enjoy the advantages of the present invention which eliminates such disadvantages.

The lower limit of the primary particle size of the positive electrode active material particles is preferably 0.1 μm, more preferably 0.5 μm. On the other hand, the upper limit of the primary particle diameter of the positive electrode active material particles is preferably 20 μm, more preferably 10 μm. By setting the primary particle diameter of the positive electrode active material particles to be equal to or larger than the above lower limit, the manufacturing or handling of the positive electrode active material layer becomes easy. Furthermore, by setting the primary particle diameter of the positive electrode active material particles to be equal to or less than the above upper limit, the electronic conductivity of the positive electrode active material layer is improved.

In order to control the primary particle size or the ratio of the secondary particle size to the primary particle size of the positive electrode active material particles, it is possible to increase the firing temperature or increase the firing time in the manufacturing process of the positive electrode active material particles. It is possible to increase the primary particle diameter by growing a plurality of primary particles. Alternatively, it is possible to obtain primary particles by crushing secondary particles. A crusher, a classifier, etc. are used for the crushing. Examples of the pulverization method include methods 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 jet mill, a sieve, and the like. At the time of pulverization, wet pulverization in which water or an organic solvent such as hexane is present can also be used. As for the classification method, a sieve, a wind classifier, etc. are used in both dry and wet methods as necessary. Moreover, a commercially available product may be used as the positive electrode active material particle which is a single particle.

The conductive agent is not particularly limited as long as it is a conductive material. Examples of such conductive agents include carbonaceous materials, metals, conductive ceramics, and the like. Examples of the carbonaceous material include graphite, non-graphitic carbon, graphene-based carbon, and the like. Examples of non-graphitic 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 above-mentioned 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 among carbon blacks, acetylene black is preferred.

The content of the conductive agent in the positive electrode active material layer is preferably 1% by mass or more and 10% by mass or less, more preferably 3% by mass or more and 9% by mass or less. By setting the content of the conductive agent within the above range, the energy density of the secondary battery can be increased.

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

The content of the binder in the positive electrode active material layer is preferably 1% by mass or more and 10% by mass or less, more preferably 3% by mass or more and 9% by mass or less. By setting the content of the binder within the above range, the active material can be stably held.

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

The above filler is not particularly limited. The above fillers include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicate, magnesium hydroxide, calcium hydroxide, and water. Hydroxides such as aluminum oxide, carbonates such as calcium carbonate, poorly soluble ionic crystals such as calcium fluoride, barium fluoride, barium sulfate, nitrides such as aluminum nitride and silicon nitride, talc, montmorillonite, boehmite, zeolite , apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, mica, and other materials derived from mineral resources, or artificial products thereof.

The positive electrode active material layer includes typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba. 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, It may be contained as a component other than filler.

(Negative electrode)
The negative electrode has 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 along at least one surface of the negative electrode base material directly 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 for the positive electrode.

The negative electrode base material has electrical conductivity. As the material of the negative electrode base material, metals such as copper, nickel, stainless steel, nickel-plated steel, aluminum, or alloys thereof are used. Among these, copper or copper alloy is preferred. Examples of the negative electrode base material include foil, vapor deposited film, mesh, porous material, etc. Foil is preferred from the viewpoint of cost. Therefore, copper foil or copper alloy foil is preferable as the negative electrode base material. Examples of copper foil include rolled copper foil, electrolytic copper foil, and the like.

The average thickness of the negative electrode base material is preferably 2 μm or more and 35 μm or less, more preferably 3 μm or more and 30 μm or less, even more 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 within 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.

The negative electrode active material layer includes 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, 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 positive electrode.

The negative electrode active material layer contains typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba. 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, It may be contained as a component other than the thickener and filler.

The negative electrode active material can be appropriately selected from known negative electrode active materials. As a negative electrode active material for a lithium ion secondary battery, a material that can insert and release lithium ions is usually used. Examples of the negative electrode active material include metal Li; metals or semimetals such as Si and Sn; metal oxides or semimetal oxides such as Si oxide, Ti oxide, and Sn oxide; Li ₄ Ti ₅ O ₁₂ , LiTiO ₂ , TiNb ₂ O ₇ and other titanium-containing oxides; polyphosphoric acid compounds; silicon carbide; carbon materials such as graphite, non-graphitizable carbon (easily graphitizable carbon or non-graphitizable carbon), etc. Can be mentioned. Among these materials, it is preferable to use a negative electrode active material containing graphite or non-graphitic carbon. In addition, in the negative electrode active material layer, one type of these materials may be used alone, or two or more types may be used in combination.

"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.

Here, the term "discharged state" refers to a state in which the carbon material, which is the negative electrode active material, is discharged such that lithium ions that can be intercalated and released are sufficiently released during charging and discharging. For example, in a monopolar battery using a negative electrode containing a carbon material as a negative electrode active material as a working electrode and metal Li as a counter electrode, the open circuit voltage is 0.7 V or more.

"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.

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, for example, a carbon material, a titanium-containing oxide, or a polyphosphoric acid compound, the average particle size may preferably 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 may preferably 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 larger than the lower limit, the negative electrode active material can be manufactured or handled easily. By setting the average particle size of the negative electrode active material to be equal to or less than the above upper limit, the electronic conductivity of the negative electrode active material layer is improved. A pulverizer, classifier, etc. are used to obtain powder with a predetermined particle size. The pulverization method and classification 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, 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 consisting of only a base material layer, a separator in which a heat resistant layer containing heat resistant particles and a binder is formed on one or both surfaces of the base material layer, etc. can be used. Examples of the shape of the base material layer of the separator include woven fabric, nonwoven fabric, porous resin film, and the like. Among these shapes, a porous resin film is preferred from the viewpoint of strength, and a nonwoven fabric is preferred from the viewpoint of liquid retention of the nonaqueous electrolyte. As the material for the base layer of the separator, polyolefins such as polyethylene and polypropylene are preferred from the viewpoint of shutdown function, and polyimide, aramid, etc. are preferred from the viewpoint of oxidative decomposition resistance. A composite material of these resins may be used as the base material layer of the separator.

The heat-resistant particles contained in the heat-resistant layer are preferably those whose mass decreases by 5% or less when the temperature is raised from room temperature to 500°C in an air atmosphere of 1 atm, and when heated from room temperature to 800°C in an air atmosphere of 1 atm. It is more preferable that the mass decrease when the temperature is increased to 5% or less. Inorganic compounds are examples of materials whose mass loss is less than a predetermined value. Such inorganic compounds include, for example, oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, aluminosilicate; magnesium hydroxide, hydroxide; Hydroxides such as calcium and aluminum hydroxide; Nitrides such as aluminum nitride and silicon nitride; Carbonates such as calcium carbonate; Sulfates such as barium sulfate; Hardly soluble such as calcium fluoride, barium fluoride, and barium titanate. ionic crystals; 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, mica, etc., or artificial products thereof, etc. can be mentioned. As such inorganic compounds, 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, or aluminosilicate is preferred from the viewpoint of safety of the nonaqueous electrolyte 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, "porosity" is a value based on volume, and means a value measured with a mercury porosimeter.

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

(Nonaqueous electrolyte)
The nonaqueous electrolyte includes a nonaqueous solvent, an electrolyte salt dissolved in the nonaqueous solvent, and an additive. The non-aqueous electrolyte contains an oxalate complex salt as the additive.

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

Examples of 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, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate, and the like. Among these, EC or PC is preferred.

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

As the non-aqueous solvent, it is preferable to use a cyclic carbonate or a chain carbonate, and it is more preferable to use a cyclic carbonate and a chain carbonate together. By using a cyclic carbonate, it is possible to promote the dissociation of the electrolyte salt and improve the ionic conductivity of the nonaqueous electrolyte. By using chain carbonate, the viscosity of the nonaqueous electrolyte can be kept low. When a cyclic carbonate and a chain carbonate are used together, 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 salts include lithium salts, sodium salts, potassium salts, magnesium salts, onium salts, and the like. Among these, lithium salts are preferred.

Examples of lithium salts 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 Halogenated} hydrocarbon _groups such _{as C2F5 ) 2} , LiN( _SO2CF3 )( _SO2C4F9 ), _LiC ( _{SO2CF3 ) 3} , LiC( _{SO2C2F5 ) 3,} etc. Examples include lithium salts with Among these, inorganic lithium salts are preferred, and LiPF ₆ is more preferred.

The content of the electrolyte salt in the nonaqueous electrolyte is preferably 0.1 mol/dm ³ or more and 2.5 mol/dm ³ or less, more preferably 0.3 mol/dm ³ or more and 2.0 mol/dm ³ or less. , more preferably 0.5 mol/dm ³ or more and 1.7 mol/dm ³ or less, 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 within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased. Note that the content of electrolyte salt in the non-aqueous electrolyte does not include the content of oxalate complex salt, which will be described later.

(Oxalate complex salt)
The non-aqueous electrolyte contains an oxalate complex salt. The oxalato complex salt refers to a salt of an oxalato complex formed by coordinate bonding of at least one oxalate ion (C ₂ O ₄ ^2- ) with a central element. Examples of the central element include nonmetallic elements or metalloid elements such as boron, phosphorus, and silicon, and metallic elements such as iron, cobalt, manganese, aluminum, and chromium. Since the non-aqueous electrolyte contains the oxalate complex salt, the non-aqueous electrolyte storage element can reduce the rate of increase in AC resistance after charge/discharge cycles at high temperatures. After the oxalate complex salt decomposes on the negative electrode during charging and discharging, the decomposed products migrate to the positive electrode side, forming a stable lithium ion conductive coating with low interfacial resistance on the surface of the positive electrode active material particles existing as single particles. It is thought that the formation of By forming a film on the particle surface, it is possible to reduce the increase in contact resistance due to expansion and contraction of the positive electrode active material layer during charging and discharging, and the non-aqueous electrolyte storage element can be It is considered that the rate of increase in AC resistance can be lowered.

The counter cation of the oxalato complex forming the complex salt in the above oxalato complex salt is not particularly limited, and examples include lithium cation, sodium cation, potassium cation, rubidium cation, cesium cation, magnesium cation, calcium cation, barium cation, silver cation. metal cations such as, tetraalkylammonium cations, tetraalkylphosphonium cations, and onium cations such as imidazolium derivative cations. Among these, lithium cations, sodium cations, and potassium cations are preferred, and lithium cations are more preferred. The counter cation of the oxalato complex may be used alone or in combination of two or more.

Specific examples of the above-mentioned oxalato complex salts include boron-containing oxalato complex salts, phosphorus-containing oxalato complex salts, ferric oxalate salts, tris(oxalato) acid cobalt (III) salts, and the like. The above-mentioned oxalate complex salts may be used alone or in combination of two or more.

The oxalato complex salt is preferably at least one of a boron-containing oxalato complex salt and a phosphorus-containing oxalato complex salt. The boron-containing oxalato complex salt is one of the above-mentioned oxalato complex salts, in which the central element of the oxalato complex is boron element. The phosphorus-containing oxalato complex salt is an oxalato complex salt among the above-mentioned oxalato complex salts, in which the central element of the oxalato complex is a phosphorus element. When the non-aqueous electrolyte contains at least one of a boron-containing oxalato complex salt and a phosphorus-containing oxalato complex salt, it is possible to further reduce the rate of increase in AC resistance of the non-aqueous electrolyte storage element after charge/discharge cycles at high temperatures. can. When the above-mentioned oxalato complex salt is a boron-containing oxalato complex salt or a phosphorus-containing oxalato complex salt, a stable lithium ion conductive coating with low interfacial resistance is efficiently applied to the surface of the positive electrode active material particles existing as single particles in the positive electrode active material layer. It is thought that the formation of

The boron-containing oxalato complex salt is a compound having a four-coordinated structural moiety in which at least one oxalate ion (C ₂ O ₄ ^2- ) is coordinated to the boron (B) atom as the central atom, such as lithium bis (oxalato)borate (Li[B(C ₂ O ₄ ) ₂ ]; LiBOB), lithium difluorooxalatoborate (Li[BF ₂ (C ₂ O ₄ )]; LiFOB), lithium bis(trifluoroethoxy)oxalato Examples include borate (Li[B(C ₂ H ₂ F ₃ O) ₂ (C ₂ O ₄ )]). The above-mentioned phosphorus-containing oxalato complex salt is a compound having a six-coordinated structural moiety in which at least one oxalate ion (C ₂ O ₄ ^2- ) is coordinated to a phosphorus (P) atom as a central atom, such as lithium tris. (oxalato)phosphate (Li[P( _C2O4 ) ₃ ]) _, lithium difluorobis(oxalato)phosphate (Li[ _PF2 ( _C2O4 ) ₂ ]; LiFOP), lithium tetrafluorooxalatophosphate (Li[ BF ₄ (C ₂ O ₄ )]) and the like. Note that among the above-mentioned oxalato complex salts, boron-containing oxalato complex salts are preferred, and LiBOB and LiFOB are more preferred, from the viewpoint of being able to form a more durable film on the surface of the positive electrode active material particles.

The lower limit of the content of the oxalate complex salt in the nonaqueous electrolyte is preferably 0.01% by mass, more preferably 0.02% by mass, and even more preferably 0.1% by mass. On the other hand, the upper limit of this content is preferably 5.0% by mass, more preferably 3.0% by mass, and even more preferably 2.0% by mass. When the content of the oxalato complex salt is within the above range, the effect of reducing the rate of increase in AC resistance of the nonaqueous electrolyte storage element after charge/discharge cycles at high temperatures can be further improved. Here, the content of the oxalato complex compound means the mass of the oxalato complex salt relative to the total mass of the nonaqueous solvent and electrolyte salt that constitute the nonaqueous electrolyte. When a plurality of types of the oxalato complex salts are included, the content of the oxalato complex salts means the total mass of the plurality of oxalato complex salts relative to the total mass of the nonaqueous solvent and electrolyte salt that constitute the nonaqueous electrolyte.

(Other additives)
The non-aqueous electrolyte may contain other additives in addition to the above-mentioned oxalate complex salt. Examples of such other additives include aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated products of terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; - Partial halides of the above aromatic compounds such as fluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene; 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, 3,5 - Halogenated anisole compounds such as difluoroanisole; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, sulfuric acid Dimethyl, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane), 4- Methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakistrimethylsilyl titanate, etc. It will be done. The other additives mentioned above may be used alone or in combination of two or more. The content of these other additives is preferably 5% by mass or less, more preferably 1% by mass or less.

The shape of the nonaqueous electrolyte storage element of this embodiment is not particularly limited, and examples include a cylindrical battery, a square battery, a flat battery, a coin battery, a button battery, and the like. FIG. 1 shows a non-aqueous electrolyte storage element 1 as an example of a square battery. 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.

<Configuration of non-aqueous electrolyte power storage device>
The non-aqueous electrolyte storage element of this embodiment can be used as a power source for automobiles such as electric vehicles (EVs), hybrid vehicles (HEVs), and plug-in hybrid vehicles (PHEVs), power sources for electronic devices such as personal computers and communication terminals, or electric power sources. It can be installed in a storage power source or the like as a power storage unit (battery module) configured by collecting a plurality of non-aqueous electrolyte power storage elements 1. 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. 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 includes a bus bar (not shown) that electrically connects two or more non-aqueous electrolyte power storage elements 1, a bus bar (not shown) that electrically connects two or more power storage units 20, and the like. Good too. 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 non-aqueous electrolyte power storage elements.

<Method for manufacturing non-aqueous electrolyte storage element>
A method for manufacturing the non-aqueous electrolyte storage element of this embodiment can be appropriately selected from known methods. The above manufacturing method includes, for example, preparing a positive electrode containing positive electrode active material particles having a ratio of secondary particle size to primary particle size of 1 or more and 3 or less, preparing a negative electrode, and non-alcoholic material containing an oxalate complex salt. and preparing a water electrolyte. Each step will be explained in detail below.

In preparing the positive electrode, the positive electrode can be prepared by a known method using a positive electrode mixture paste containing the positive electrode active material particles. The above-mentioned positive electrode can be obtained by laminating a positive electrode active material layer on a positive electrode base material directly or via an intermediate layer. Lamination of the positive electrode active material layer is performed, for example, by applying the positive electrode mixture paste to the positive electrode base material. The positive electrode mixture paste may contain a dispersion medium. As this dispersion medium, for example, organic solvents such as N-methylpyrrolidone, acetone, ethanol, and toluene can be used. The method for applying the positive electrode mixture paste is not particularly limited, and can be performed by any known method such as roller coating, screen coating, or spin coating.

In preparing the negative electrode, the negative electrode can be prepared by a known method using a negative electrode mixture paste containing a negative electrode active material. The above negative electrode can be obtained by laminating a negative electrode mixture layer on a negative electrode base material directly or via an intermediate layer. Lamination of the negative electrode mixture layer is performed, for example, by applying the negative electrode mixture paste to the negative electrode base material. The negative electrode mixture paste may contain a dispersion medium. As the dispersion medium, for example, an aqueous solvent such as water or a mixed solvent mainly composed of water, or an organic solvent such as N-methylpyrrolidone, acetone, ethanol, or toluene can be used.

In preparing the above non-aqueous electrolyte, for example, a non-aqueous electrolyte containing an oxalato complex salt can be prepared by dissolving the oxalato complex salt in a non-aqueous solvent. In preparing this non-aqueous electrolyte, other components such as an electrolyte salt may be further dissolved. This dissolution can be performed by a known method.

In addition to preparing the positive electrode, the negative electrode, and the nonaqueous electrolyte, the manufacturing method may include the following steps. That is, the method for manufacturing the non-aqueous electrolyte energy storage device includes, for example, forming an electrode body in which the positive electrode and the negative electrode are stacked or wound alternately with a separator interposed therebetween; The nonaqueous electrolyte may be placed in a case, and the nonaqueous electrolyte may be injected into the case. After these steps, a non-aqueous electrolyte storage element can be obtained by sealing the injection port. Further, after the injection port is sealed, the first charging and discharging may be performed.

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 above manufacturing method, it is possible to manufacture a non-aqueous electrolyte storage element that has a low rate of increase in AC resistance after charge/discharge cycles at high temperatures and a high capacity retention rate.

<Other embodiments>
The non-aqueous electrolyte storage device according to the present invention is not limited to the above embodiments, and various changes 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 known technique. Additionally, some of the configurations of certain embodiments may be deleted. Furthermore, well-known techniques can be added to the configuration of a certain embodiment.

In the above embodiment, the case where the non-aqueous electrolyte storage element is a chargeable/dischargeable non-aqueous electrolyte secondary battery (for example, a lithium ion secondary battery) has been described. etc. are optional. The present invention can also be applied to capacitors such as various secondary batteries, electric double layer capacitors, and lithium ion capacitors.

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]
(Cathode active material)
As the positive electrode active material, a lithium transition metal composite compound having an α-NaFeO ₂ type crystal structure and represented by LiNi _0.5 Mn _0.3 Co _0.2 O ₂ was used. The primary particle size of the positive electrode active material particles was 4.0 μm, the secondary particle size was 4.0 μm, and the ratio of the secondary particle size to the primary particle size was 1. (also called “single particle form”). A scanning electron microscope (SEM) image of the positive electrode active material particles of Example 1 is shown in FIG. The primary particles existed without agglomeration, and no grain boundaries were observed in the appearance of the positive electrode active material particles.

(positive electrode)
Using N-methylpyrrolidone (NMP) as a dispersion medium, the positive electrode active material, acetylene black (AB) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder were mixed in a mass ratio of 94:3:3 (solid content equivalent). A positive electrode mixture paste containing the following ratios was prepared. The positive electrode mixture paste was applied to both sides of an aluminum foil serving as a positive electrode base material, dried, and then pressed. Thereby, a positive electrode was obtained in which positive electrode active material layers were laminated on both sides of the positive electrode base material.

(Negative electrode)
A negative electrode mixture paste was prepared by mixing graphite (Gr) as a negative electrode active material, styrene-butadiene rubber (SBR) as a binder, carboxymethyl cellulose (CMC) as a thickener, and water as a dispersion medium. Note that the mass ratio of Gr, SBR, and CMC was 98:1:1 (in terms of solid content). A negative electrode mixture paste was applied to both sides of a copper foil serving as a negative electrode base material, dried, and then pressed. In this way, a negative electrode was obtained.

(Nonaqueous electrolyte)
LiPF ₆ was dissolved at a concentration of 1.0 mol/dm ³ in a mixed solvent of ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) in a volume ratio of 25:5:70 to form a base electrolyte. was created. Furthermore, with respect to 100% by mass of the base electrolyte, the content of lithium difluorooxalatoborate (LiFOB) as an oxalate complex salt is 0.3% by mass, the content of vinylene carbonate (VC) is 0.3% by mass, and the content of lithium bis( A non-aqueous electrolyte is created by dissolving fluorosulfonyl)imide (LiFSI) in a content of 2.0% by mass and 1,3,2-dioxathiolane-2,2-dioxide (DTD) in a content of 1.0% by mass. was prepared.

(Production of non-aqueous electrolyte storage element)
An electrode body was produced by laminating the above positive electrode and the above negative electrode with a polyolefin separator interposed therebetween. This electrode body was housed in a case, and the nonaqueous electrolyte was injected into the case. Thereafter, it was sealed to obtain the non-aqueous electrolyte storage element of Example 1.

[Examples 2 to 4]
Non-aqueous electrolyte storage elements of Examples 2 to 4 were obtained in the same manner as in Example 1, except that the content of LiFOB in the non-aqueous electrolyte was as shown in Table 1.

[Comparative example 2]
Except that positive electrode active material particles were used in which the primary particle size of the positive electrode active material particles was 0.535 μm, the secondary particle size was 7.9 μm, and the ratio of the secondary particle size to the primary particle size was 14.8. A nonaqueous electrolyte storage element of Comparative Example 2 was obtained in the same manner as Example 1. (Hereinafter, such a form of positive electrode active material particles is also referred to as a "secondary particle form"). A scanning electron microscope (SEM) image of the positive electrode active material particles of Comparative Example 2 is shown in FIG. Primary particles aggregated to form secondary particles, and grain boundaries were confirmed on the appearance of the positive electrode active material particles.

[Comparative example 1]
A nonaqueous electrolyte storage element of Comparative Example 1 was obtained in the same manner as Comparative Example 2, except that the nonaqueous electrolyte was prepared without containing LiFOB.

[Comparative Examples 3 to 5]
Nonaqueous electrolyte storage elements of Comparative Examples 3 to 5 were obtained in the same manner as Comparative Example 2, except that the content of LiFOB in the nonaqueous electrolyte was as shown in Table 2.

[Comparative example 6]
A non-aqueous electrolyte storage element of Comparative Example 6 was obtained in the same manner as in Example 1, except that the non-aqueous electrolyte was prepared without containing LiFOB.

[evaluation]
(Initial charge/discharge)
Each of the obtained non-aqueous electrolyte storage devices was subjected to initial charging and discharging at 25° C. in the following manner.
Constant current and constant voltage charging was performed with a charging current of 0.1 C and a charge end voltage of 4.25 V. The charging termination condition was until the charging current reached 0.05C. After a 10-minute break, constant current discharge was performed at a discharge current of 0.2C and a discharge end voltage of 2.75V.
(Initial AC resistance)
After the initial charging and discharging, the AC resistance (ACR) at 1 kHz was measured at 25° C. for each nonaqueous electrolyte storage element, and the result was defined as "initial ACR." AC resistance was measured by a known method.

(Initial discharge capacity)
Next, the initial discharge capacity of each nonaqueous electrolyte storage element was confirmed at 25° C. in the following manner.
Constant current and constant voltage charging was performed with a charging current of 0.1 C and a charge end voltage of 4.25 V. The charging termination condition was until the charging current reached 0.05C. After a 10-minute break, constant current discharge was performed at a discharge current of 0.2C and a discharge end voltage of 2.75V. The discharge capacity at this time was defined as the "initial discharge capacity".

(45℃ charge/discharge cycle test)
After confirming the initial discharge capacity, each non-aqueous electrolyte storage element was subjected to a charge/discharge cycle test in a constant temperature bath at 45° C. as follows.
Constant current and constant voltage charging was performed with a charging current of 1.0 C and a charging end voltage of 4.25 V. The charging termination condition was until the charging current reached 0.05C. Thereafter, a rest period of 10 minutes was provided. Furthermore, constant current discharge was performed with a discharge current of 1.0 C and a discharge end voltage of 2.75 V, followed by a rest period of 10 minutes. This charging and discharging was performed for 500 cycles.

(ACR increase rate after 45°C charge/discharge cycle test)
After the 45° C. charge/discharge cycle test, the alternating current resistance (ACR) at 1 kHz was measured at 25° C. for each nonaqueous electrolyte storage element, and the result was defined as “ACR after 45° C. charge/discharge cycle test.” AC resistance was measured by a known method.
The ratio of ACR of "ACR after 45°C charge/discharge cycle test" to "initial ACR" expressed as a percentage was determined as "ACR increase rate after 45°C charge/discharge cycle test". Tables 1 and 2 show the ACR increase rate (hereinafter also referred to as "ACR increase rate") after the 45°C charge/discharge cycle test in each of the non-aqueous electrolyte storage elements of Examples 1 to 4 and Comparative Examples 1 to 6. Shown below.

(Capacity maintenance rate)
After measuring the ACR after the 45°C charge/discharge cycle test, each nonaqueous electrolyte storage element was charged and discharged under the same conditions as the initial discharge capacity. The discharge capacity at this time was defined as "discharge capacity after 45°C charge/discharge cycle test."
The value expressed as a percentage of the "discharge capacity after 45°C charge/discharge cycle test" to "initial discharge capacity" was defined as "capacity retention rate after 45°C charge/discharge cycle test". Table 1 and Table 1 show the values of capacity retention rates after 45°C charge/discharge cycle tests (hereinafter also referred to as "capacity retention rates") for each of the non-aqueous electrolyte storage elements of Examples 1 to 4 and Comparative Examples 1 to 6. It is shown in Table 2.

The non-aqueous electrolyte energy storage element of Comparative Example 6 in which the positive electrode active material particles contained in the positive electrode active material layer are in the form of single particles and the non-aqueous electrolyte does not contain an oxalato complex salt is characterized in that the positive electrode active material particles contained in the positive electrode active material layer are Compared to the nonaqueous electrolyte storage element of Comparative Example 1 in which the nonaqueous electrolyte was in the form of secondary particles and the nonaqueous electrolyte did not contain an oxalate complex salt, the capacity retention rate was high and the ACR increase rate was high. On the other hand, the non-aqueous electrolyte energy storage elements of Examples 1 to 4 in which the positive electrode active material particles contained in the positive electrode active material layer are in the form of single particles and the non-aqueous electrolyte contains an oxalato complex salt are It exhibited a high capacity retention rate equivalent to that of the electrolyte storage element, and had a lower ACR increase rate than the non-aqueous electrolyte storage element of Comparative Example 6. The reduction in ACR increase rate due to the non-aqueous electrolyte containing an oxalato complex salt was compared with Comparative Example 2 in which the positive electrode active material particles contained in the positive electrode active material layer were in the form of secondary particles and the non-aqueous electrolyte contained an oxalato complex salt. This was not confirmed in the non-aqueous electrolyte storage device of Example 5.

As described above, the non-aqueous electrolyte storage element was shown to have a low rate of increase in AC resistance after charge/discharge cycles at high temperatures and a high capacity retention rate after charge/discharge cycles.

INDUSTRIAL APPLICATION This invention is suitably used as a non-aqueous electrolyte storage element including the non-aqueous electrolyte secondary battery used as a power supply of electronic devices, such as a personal computer and a communication terminal, and an automobile.

1 Nonaqueous electrolyte 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 (3)

Comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte,
The positive electrode has a positive electrode active material layer containing positive electrode active material particles having a ratio of secondary particle size to primary particle size of 1 or more and 3 or less,
A non-aqueous electrolyte storage device, wherein the non-aqueous electrolyte contains an oxalate complex salt. The non-aqueous electrolyte storage element according to claim 1, wherein the positive electrode active material particles have no grain boundaries in their appearance. 3. The non-aqueous electrolyte storage device according to claim 1, wherein the oxalato complex salt is at least one of a boron-containing oxalato complex salt and a phosphorus-containing oxalato complex salt.

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