Positive electrode and non-aqueous electrolyte storage element

Abstract

To provide a positive electrode that enables a non-aqueous electrolyte power storage element to exhibit large electric capacity and excellent output performance when used for the non-aqueous electrolyte power storage element, and a non-aqueous electrolyte power storage element with such a positive electrode.SOLUTION: There is provided a positive electrode for a non-aqueous electrolyte power storage element that comprises a positive electrode base material including metal aluminum, an intermediate layer including a conductive agent and a positive electrode active material layer including lithium transition metal composite oxide in this order, wherein the lithium transition metal composite oxide contains nickel elements, and the positive electrode active material layer has a nickel element content of 1.1×10-4 mol / cm2 or more per unit area and also has a mass of 0.017 g / cm2 or less per unit area.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a positive electrode and a nonaqueous electrolyte electricity storage element. [Background technology]

[0002] Due to their high energy density, non-aqueous electrolyte secondary batteries, such as lithium ion secondary batteries, are widely used in electronic devices such as personal computers and communication terminals, automobiles, etc. The non-aqueous electrolyte secondary batteries generally include an electrode assembly having a pair of electrodes electrically isolated by a separator, and a non-aqueous electrolyte interposed between the electrodes, and are configured to charge and discharge by transferring charge-transporting ions between the electrodes. Furthermore, capacitors such as lithium ion capacitors and electric double layer capacitors are also widely used as non-aqueous electrolyte energy storage elements other than secondary batteries.

[0003] The positive electrode of such a nonaqueous electrolyte storage element is generally formed by laminating a positive electrode active material layer containing a positive electrode active material on a conductive positive electrode substrate such as metallic aluminum. Known positive electrode active materials include lithium transition metal composite oxides, and positive electrode active materials containing nickel, such as lithium nickel composite oxides, are also used (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2017-107827 Summary of the Invention [Problem to be solved by the invention]

[0005] In order to increase the electric capacity of a nonaqueous electrolyte energy storage element, the use of a positive electrode active material with a high nickel content has been investigated. However, the inventors have found that the use of a positive electrode active material containing nickel may deteriorate the metallic aluminum of the positive electrode substrate, resulting in a deterioration in the performance of the nonaqueous electrolyte energy storage element, such as output performance.

[0006] The present invention has been made in light of the above circumstances, and an object of the present invention is to provide a positive electrode that, when used in a nonaqueous electrolyte electricity storage element, enables the nonaqueous electrolyte electricity storage element to exhibit large electric capacity and good output performance, and a nonaqueous electrolyte electricity storage element including such a positive electrode. [Means for solving the problem]

[0007] A positive electrode according to one aspect of the present invention includes a positive electrode substrate containing metallic aluminum, an intermediate layer containing a conductive agent, and a positive electrode active material layer containing a lithium transition metal composite oxide, in this order. The lithium transition metal composite oxide contains nickel, and the nickel content per unit area of ​​the positive electrode active material layer is 1.1×10 -4 mol / cm 2 or more, and the mass per unit area of ​​the positive electrode active material layer is 0.017 g / cm 2 The following is a positive electrode for a non-aqueous electrolyte storage element.

[0008] A nonaqueous electrolyte storage element according to another aspect of the present invention includes the positive electrode according to the aspect of the present invention. [Effects of the Invention]

[0009] When the positive electrode according to one embodiment of the present invention is used in a nonaqueous electrolyte energy storage element, the nonaqueous electrolyte energy storage element can exhibit a large electric capacity and good output performance.

[0010] A nonaqueous electrolyte electricity storage element according to another aspect of the present invention can exhibit large electric capacity and good output performance. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a perspective view showing one embodiment of a nonaqueous electrolyte electricity storage element. [Figure 2] FIG. 2 is a schematic diagram showing one embodiment of an electricity storage device configured by assembling a plurality of nonaqueous electrolyte electricity storage elements. DETAILED DESCRIPTION OF THE INVENTION

[0012] First, an overview of the positive electrode and nonaqueous electrolyte electricity storage element disclosed in this specification will be described.

[0013] A positive electrode according to one aspect of the present invention includes a positive electrode substrate containing metallic aluminum, an intermediate layer containing a conductive agent, and a positive electrode active material layer containing a lithium transition metal composite oxide, in this order. The lithium transition metal composite oxide contains nickel, and the nickel content per unit area of ​​the positive electrode active material layer is 1.1×10 -4 mol / cm 2 or more, and the mass per unit area of ​​the positive electrode active material layer is 0.017 g / cm 2 The following is a positive electrode for a non-aqueous electrolyte storage element.

[0014] When this positive electrode is used in a nonaqueous electrolyte storage element, the nonaqueous electrolyte storage element can exhibit a large electric capacity and good output performance. The reason for this is unclear, but the following reason is presumed. In a conventional positive electrode for a nonaqueous electrolyte storage element, when a positive electrode active material with a high nickel content is used, the metallic aluminum of the positive electrode substrate deteriorates due to an increase in the alkaline component contained in the positive electrode active material. Specifically, it is presumed that the metallic aluminum on the surface of the positive electrode substrate reacts with the alkaline component to form aluminum hydroxide, reducing the conductivity and degrading the current collection performance of the positive electrode substrate. For this reason, in conventional positive electrodes, the nickel content per unit area of ​​the positive electrode active material layer is set to 1.1 × 10 -4 mol / cm 2 In contrast, in a positive electrode according to one embodiment of the present invention, an intermediate layer is provided between the positive electrode substrate and the positive electrode active material layer, which prevents the alkaline component from reaching the positive electrode substrate and reduces the mass per unit area of ​​the positive electrode active material layer to 0.017 g / cm. 2In addition, in the positive electrode according to one embodiment of the present invention, the nickel element content per unit area of ​​the positive electrode active material layer is 1.1 × 10 -4 mol / cm 2 For these reasons, it is presumed that the use of a positive electrode according to one embodiment of the present invention enables a nonaqueous electrolyte energy storage element to exhibit a large electric capacity and favorable output performance.

[0015] Nickel element content per unit area of ​​the positive electrode active material layer (mol / cm 2 ) can be determined by the following method. A test battery is assembled using a positive electrode to be measured, a metallic lithium negative electrode, a separator, and a non-aqueous electrolyte, and is fully discharged using the same method as in the measurement of the "discharge capacity per unit area of ​​the positive electrode active material layer" described below. The battery is disassembled again, and the positive electrode is removed. Components (non-aqueous electrolyte, etc.) adhering to the removed positive electrode are thoroughly washed using dimethyl carbonate, and the positive electrode is dried under reduced pressure at room temperature for 24 hours. A positive electrode active material layer of a predetermined area is then sampled, and the amount of nickel (mol) contained in this sample is measured using high-frequency inductively coupled plasma atomic emission spectroscopy (ICP). This measured amount of nickel (mol) is multiplied by the area (cm) of the positive electrode active material layer corresponding to the sample used for measurement. 2 ) is the nickel element content per unit area of ​​the positive electrode active material layer (mol / cm 2 In addition, when a positive electrode active material layer is provided on each side of the positive electrode substrate, the nickel element content per unit area of ​​the positive electrode active material layer (mol / cm 2 )" refers to the nickel element content of the positive electrode active material layer on one surface. When a positive electrode active material layer is provided on only one surface of the positive electrode substrate, "" refers to the nickel element content of that one positive electrode active material layer.

[0016] Mass per unit area of ​​the positive electrode active material layer (g / cm 2 ) is the mass (g) of the positive electrode active material layer multiplied by the area (cm 2When the positive electrode active material layer is formed by coating, the mass per unit area of ​​the positive electrode active material layer (g / cm 2 )" is the applied mass converted to solid content per unit area. When a positive electrode active material layer is provided on each side of the positive electrode substrate, the "mass per unit area of ​​the positive electrode active material layer (g / cm 2 When a positive electrode active material layer is provided on only one surface of the positive electrode substrate, the mass of one positive electrode active material layer is referred to as the mass of that single positive electrode active material layer.

[0017] In the positive electrode according to one embodiment of the present invention, the positive electrode potential in a fully charged state is 4.23 V vs. Li / Li + The positive electrode potential in a fully discharged state was 3.00 V vs. Li / Li + When the discharge capacity per unit area of ​​the positive electrode active material layer is 3.00 mAh / cm 2 It is preferable that this is equal to or greater than this.

[0018] This positive electrode allows the electric capacity of the non-aqueous electrolyte storage element to be increased. The discharge capacity measurement is performed as follows: A test battery is assembled using a positive electrode to be measured, a metallic lithium negative electrode, a separator, and a non-aqueous electrolyte. The non-aqueous electrolyte is a non-aqueous solvent mixture of EC (ethylene carbonate), EMC (ethyl methyl carbonate), and DMC (dimethyl carbonate) in a volume ratio of 30:35:35, to which LiPF6 is added at a concentration of 1.2 mol / dm 3 The assembled test battery was charged at 25°C with a charging current of 1.00 mA / cm 2 The battery was charged at a constant current for 5 hours with a charge cut-off voltage of 4.23 V, and then fully charged. After a 20-minute rest period, the discharge current was 1.00 mA / cm. 2The battery was then subjected to constant current discharge at a discharge cut-off voltage of 3.00 V to reach a fully discharged state. The quantity of electricity discharged at this time was taken as the discharge capacity. Note that, since the test battery uses a metallic lithium negative electrode as the negative electrode, the positive electrode potential relative to the oxidation-reduction potential of lithium at the charge cut-off voltage and discharge cut-off voltage was substantially equal to the charge cut-off voltage and discharge cut-off voltage of the test battery.

[0019] The mass per unit area of ​​the intermediate layer is 0.05 g / m 2 More than 1g / m 2 It is preferable that:

[0020] Such a positive electrode can exhibit a sufficient blocking function against alkaline components while preventing the positive electrode from becoming thick, and can further improve output performance. In addition, when a positive electrode active material layer and an intermediate layer are provided on both sides of the positive electrode substrate, the "mass per unit area of ​​the intermediate layer (g / cm 2 When a positive electrode active material layer and an intermediate layer are provided on only one surface of the positive electrode substrate, the mass of one intermediate layer is referred to as the mass of that single intermediate layer.

[0021] The content of nickel element in the transition metal elements in the lithium transition metal composite oxide is preferably 50 mol % or more.

[0022] Such a positive electrode uses a lithium transition metal composite oxide with a high content of nickel element, and therefore can further increase the electric capacity.

[0023] The conductive agent contained in the intermediate layer preferably has an average particle size of 40 nm or less.

[0024] Such a positive electrode improves the adhesion between conductive agents in the intermediate layer and reduces voids, thereby improving the conductivity of the intermediate layer and its blocking function against alkaline components.

[0025] A nonaqueous electrolyte storage element according to another aspect of the present invention includes the positive electrode according to the aspect of the present invention.

[0026] This non-aqueous electrolyte electricity storage element can exhibit a large electric capacity and good output performance.

[0027] A positive electrode and a nonaqueous electrolyte storage element according to one embodiment of the present invention will be described in detail. Note that the names of the components used in each embodiment may differ from the names of the components used in the background art.

[0028] <Positive electrode> A positive electrode according to one embodiment of the present invention includes a positive electrode substrate, an intermediate layer, and a positive electrode active material layer, in this order. The intermediate layer and the positive electrode active material layer may be laminated on both sides of the positive electrode substrate, respectively, or may be laminated on only one side of the positive electrode substrate. The positive electrode may typically be a multilayer sheet having these layers. The positive electrode is an electrode for a non-aqueous electrolyte storage element such as a non-aqueous electrolyte secondary battery.

[0029] (Positive electrode substrate) The positive electrode substrate has electrical conductivity. "Conductivity" means that the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 7 "Non-conductive" means that the volume resistivity is 10 Ω·cm or less. 7 This means that the resistance is greater than Ω·cm.

[0030] The positive electrode substrate contains metallic aluminum. The material of the positive electrode substrate is usually metallic aluminum alone or an aluminum alloy. The metallic aluminum content in the positive electrode substrate is preferably 90% by mass or more, more preferably 99% by mass or more, and may be substantially 100% by mass. The positive electrode substrate may contain components other than metallic aluminum.

[0031] The positive electrode substrate is in the form of a film or a plate. Examples of the positive electrode substrate include foils and vapor-deposited films, with foils being preferred from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferred as the positive electrode substrate. Examples of aluminum metal or aluminum alloys include A1085, A3003, and A1N30 as specified in JIS-H-4000 (2014) or JIS-H4160 (2006).

[0032] The average thickness of the positive electrode substrate is preferably 3 μm to 50 μm, more preferably 5 μm to 40 μm, even more preferably 8 μm to 30 μm, and particularly preferably 10 μm to 25 μm. By setting the average thickness of the positive electrode substrate within the above range, the strength of the positive electrode substrate can be increased while increasing the energy density per volume of the nonaqueous electrolyte storage element. The "average thickness" of the positive electrode substrate refers to the value obtained by dividing the punched mass when a positive electrode substrate of a predetermined area is punched out by the true density and punched area of ​​the positive electrode substrate. The average thickness of the "negative electrode substrate" described below is defined in the same way.

[0033] (middle class) The intermediate layer is a layer disposed between the positive electrode substrate and the positive electrode active material layer.

[0034] The intermediate layer contains a conductive agent. The conductive agent is a component having electrical conductivity, and is usually a particle having electrical conductivity. In this positive electrode, the presence of the intermediate layer prevents alkaline components from reaching the surface of the positive electrode substrate from the positive electrode active material layer, thereby suppressing deterioration of the positive electrode substrate, allowing the nonaqueous electrolyte storage element to exhibit good output performance. Furthermore, the presence of the conductive agent in the intermediate layer reduces contact resistance between the positive electrode substrate and the positive electrode active material layer.

[0035] The conductive agent is not particularly limited as long as it is a material having electrical conductivity. Examples of such conductive agents include carbonaceous materials, metals, and conductive ceramics. Examples of carbonaceous materials include graphite, non-graphitized carbon, and graphene-based carbon. Examples of non-graphitized carbon include carbon nanofibers, pitch-based carbon fibers, and carbon black. Examples of carbon black include furnace black, acetylene black, and ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNTs), and fullerenes. The conductive agent may be in the form of powder or fiber. As the conductive agent, one of these materials may be used alone, or two or more may be mixed and used. These materials may also be used in combination. For example, a composite material of carbon black and CNTs may be used. Among these, from the viewpoints of electrical conductivity and coatability, carbonaceous materials are preferred, carbon black is more preferred, and acetylene black is even more preferred.

[0036] The conductive agent, such as a carbonaceous material, preferably has its surface not coated with other components, such as inorganic oxides (e.g., metal oxides), and more preferably is substantially composed of only the carbonaceous material. Carbonaceous materials are generally hydrophobic, while metal oxides and the like are generally hydrophilic. By using a hydrophobic conductive agent, it is possible to more effectively prevent alkaline components (e.g., moisture containing alkaline components) from penetrating the intermediate layer from the positive electrode active material layer and reaching the positive electrode substrate surface. This allows the conductive agent to more reliably exhibit a sufficient blocking function against alkaline components.

[0037] The average particle size of the conductive agent is preferably, for example, 1 nm or more and 200 nm or less, more preferably 10 nm or more and 100 nm or less, with an upper limit of 40 nm being even more preferable. By setting the average particle size of the conductive agent within the above range, it is possible to further improve conductivity and blocking properties against alkaline components. "Average particle size" refers to the value at which the volume-based cumulative distribution calculated in accordance with JIS-Z-8819-2 (2001) is 50% based on the particle size distribution measured by laser diffraction / scattering method for a diluted solution of particles diluted with a solvent in accordance with JIS-Z-8825 (2013). Hereinafter, the average particle size of other materials will be defined similarly.

[0038] The content of the conductive agent in the intermediate layer is preferably 10% by mass to 80% by mass, more preferably 20% by mass to 60% by mass, and even more preferably 25% by mass to 40% by mass. By setting the content of the conductive agent in the intermediate layer within the above range, it is possible to achieve a good balance between the adhesion between the conductive agents themselves or with other layers, and the conductivity, thereby improving the output performance of the nonaqueous electrolyte storage element. In addition, it is possible to prevent alkaline components (e.g., moisture containing alkaline components) from penetrating into the intermediate layer from the positive electrode active material layer and reaching the surface of the positive electrode substrate, thereby providing a sufficient blocking function against alkaline components.

[0039] The intermediate layer preferably further contains a binder in addition to the conductive agent. Examples of binders include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylic, and polyimide; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers. Polysaccharide polymers are preferred as binders in the intermediate layer. Examples of polysaccharide polymers include chitosan, chitin, cellulose, and derivatives thereof. Among these, chitosan, chitin, and derivatives thereof are preferred, and chitosan and its derivatives are more preferred. Examples of chitosan derivatives include hydroxyalkyl chitosans such as hydroxyethyl chitosan and hydroxypropyl chitosan. Furthermore, from the viewpoint of durability, derivatives of chitosan and the like having a crosslinked structure obtained by reacting them with organic acids such as salicylic acid, pyromellitic acid, citric acid, and trimellitic acid can also be used.

[0040] The binder content in the intermediate layer is preferably 20% by mass to 80% by mass, more preferably 50% by mass to 75% by mass. By setting the binder content within this range, the conductive agent can be stably held and good conductivity can be maintained and exhibited.

[0041] The intermediate layer may further contain components other than the conductive agent and binder. Examples of such components include non-conductive fillers (e.g., metal oxides). However, the total content of the conductive agent and binder in the intermediate layer is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 99% by mass or more. The intermediate layer may be composed essentially of only the conductive agent and binder. The technology disclosed herein can be preferably implemented in an embodiment in which the intermediate layer contains no components other than the conductive agent and binder. Such a configuration of the intermediate layer allows the intermediate layer to exhibit good conductivity while becoming hydrophobic, thereby sufficiently reducing the reach of alkaline components from the positive electrode active material layer to the positive electrode substrate. Therefore, this configuration can further increase the electrical capacity and improve the output performance of the non-aqueous electrolyte storage element.

[0042] The mass per unit area of ​​the intermediate layer is 0.05 g / m 2 More than 1g / m 2 Less than 0.1 g / m is preferred 2 More than 0.5g / m 2 The following is more preferable: By setting the mass per unit area of ​​the intermediate layer within the above range, it is possible to suppress an increase in thickness of the positive electrode while allowing the intermediate layer to exhibit a sufficient blocking function against alkaline components.

[0043] (Cathode active material layer) The positive electrode active material layer contains a positive electrode active material and, if necessary, optional components such as a conductive agent, a binder, a thickener, and a filler.

[0044] The positive electrode active material includes a lithium transition metal composite oxide containing nickel. The lower limit of the content ratio of nickel (Ni) to the transition metal element (Me) in the lithium transition metal composite oxide containing nickel (Ni / Me) may be, for example, 30 mol%, but is preferably 50 mol%, more preferably 70 mol%, and even more preferably 80 mol%. By using such a lithium transition metal composite oxide with a high content ratio of nickel, the electric capacity can be increased. On the other hand, the upper limit of the content ratio of nickel (Ni / Me) may be, for example, 100 mol% or 90 mol%. The content ratio of nickel (Ni / Me) may be equal to or greater than any of the above lower limits and equal to or less than any of the above upper limits.

[0045] The lithium transition metal composite oxide containing nickel preferably further contains at least one of manganese and cobalt, and more preferably both manganese and cobalt. The content ratio of manganese (Mn) to the transition metal element (Me) in the lithium transition metal composite oxide containing nickel (Mn / Me) is preferably 1 mol% to 30 mol%, more preferably 5 mol% to 15 mol%. The content ratio of cobalt (Co) to the transition metal element (Me) in the lithium transition metal composite oxide containing nickel (Co / Me) is preferably 1 mol% to 30 mol%, more preferably 5 mol% to 15 mol%.

[0046] The content ratio (Li / Me) of lithium element (Li) to transition metal element (Me) in the lithium transition metal composite oxide containing nickel element is preferably 1 or more and less than 1.5, and may be 1.

[0047] As an example of a lithium transition metal composite oxide containing nickel, there is Li[Li x Ni (1-x) ]O2(0≦x≦0.5), Li[Li x Ni α Co (1-x-α)O2 (0 ≦ x ≦ 0.5, 0 < α < 1, 0 < x + α < 1), Li[Li x Ni α Mn β Co (1-x-α-β) O2 (0 ≦ x < 0.5, 0 < α < 1, 0 < β < 1, 0 < x + α + β < 1), etc., Li having a spinel crystal structure x Ni γ Mn (2-γ) O4, etc. can be mentioned. These materials may have their surfaces coated with other materials. Also, these materials may be used alone or two or more of them may be used in combination.

[0048] Among these, compounds having a layered α-NaFeO2-type crystal structure are preferred, Li[Li x Ni α Mn β Co (1-x-α-β) O2 (0 ≦ x < 0.5, 0 < α < 1, 0 < β < 1, 0 < x + α + β < 1) is more preferred. At this time, it is more preferred that 0.7 < α < 0.9, 0.05 < β < 0.2, and 0.05 < 1 - x - α - β < 0.2.

[0049] Specific examples of lithium transition metal composite oxides containing nickel include, for example, LiNi 3 / 5 Co 1 / 5 Mn 1 / 5 O2, LiNi 1 / 2 Co 1 / 5 Mn 3 / 10 O2, LiNi 1 / 2 Co 3 / 10 Mn 1 / 5 O2, LiNi 8 / 10 Co 1 / 10 Mn 1 / 10 O2, etc. can be mentioned. Note that the chemical formulas indicating the above lithium transition metal composite oxides represent the composition in the state before the first charge treatment (that is, the charge treatment performed for the first time after assembling battery components such as the positive electrode, negative electrode, and electrolyte) or the composition in the state of being fully discharged by the method described above.

[0050] The content of the nickel-containing lithium transition metal composite oxide in the positive electrode active material layer is preferably 70% by mass or more and 99% by mass or less, more preferably 80% by mass or more and 99% by mass or less, and even more preferably 90% by mass or more and 98.5% by mass or less. By setting the content of the nickel-containing lithium transition metal composite oxide within the above range, both high energy density and manufacturability of the positive electrode active material layer can be achieved. Furthermore, when the content of the nickel-containing lithium transition metal composite oxide in the positive electrode active material layer is high, the alkaline component increases and the binder content relatively decreases, which tends to cause peeling of the positive electrode active material layer and reduce output performance in conventional positive electrodes. Therefore, the advantages of the present invention are more effectively achieved when the content of the nickel-containing lithium transition metal composite oxide in the positive electrode active material layer is, for example, 92% by mass or more, or even 94% by mass or more. In some embodiments, the content of the lithium transition metal composite oxide may be 95% by mass or more, or even 98% by mass or more.

[0051] The positive electrode active material layer may further contain a positive electrode active material other than the lithium transition metal composite oxide containing nickel. Examples of such other positive electrode active materials include conventionally known positive electrode active materials such as lithium transition metal composite oxides not containing nickel, polyanion compounds, chalcogen compounds, and sulfur. The surfaces of these materials may be coated with other materials. These materials may be used alone or in combination of two or more.

[0052] The lower limit of the content of the lithium transition metal composite oxide containing nickel in the positive electrode active material is preferably 80 mass %, more preferably 90 mass %, even more preferably 95 mass %, and even more preferably 99 mass %. The positive electrode active material may essentially consist of only the lithium transition metal composite oxide containing nickel. In this way, by increasing the content of the lithium transition metal composite oxide containing nickel in the positive electrode active material, the electrical capacity of the nonaqueous electrolyte storage element can be further increased.

[0053] The positive electrode active material is usually particulate. The average particle size of the positive electrode active material is preferably, for example, 0.1 μm or more and 20 μm or less. By setting the average particle size of the positive electrode active material to the above lower limit or more, the positive electrode active material becomes easy to manufacture or handle. By setting the average particle size of the positive electrode active material to the above upper limit or less, the conductivity of the positive electrode active material layer is improved. Note that when a composite of the 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.

[0054] To obtain particles with a predetermined particle size, a pulverizer, a classifier, or the like is used. Examples of pulverization methods include methods using a mortar, a ball mill, a sand mill, a vibration ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling airflow jet mill, or a sieve. Wet pulverization in the presence of water or an organic solvent such as hexane can also be used. As a classification method, a sieve, an air classifier, or the like is used as needed for both dry and wet methods.

[0055] The content of the positive electrode active material in the positive electrode active material layer is preferably 70% by mass to 99% by mass, more preferably 80% by mass to 99% by mass, and even more preferably 90% by mass to 98% by mass. By setting the content of the positive electrode active material within this range, both high energy density and manufacturability of the positive electrode active material layer can be achieved.

[0056] Examples of the conductive agent in the positive electrode active material layer include the same conductive agents as those exemplified for the intermediate layer. The content of the conductive agent in the positive electrode active material layer is preferably 0.2% by mass to 10% by mass, more preferably 0.5% by mass to 8% by mass, and even more preferably 1% by mass to 5% by mass. By setting the content of the conductive agent in the positive electrode active material layer within the above range, the energy density of the nonaqueous electrolyte storage element can be increased.

[0057] Examples of binders in the positive electrode active material layer include those exemplified as binders in the intermediate layer. The binder content in the positive electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.3% by mass or more and 5% by mass or less. By setting the binder content in the positive electrode active material layer within the above range, the positive electrode active material can be stably maintained. In particular, when the content of nickel-containing lithium transition metal composite oxide in the positive electrode active material layer is high and the content of binder is relatively low, in a conventional positive electrode, peeling of the positive electrode active material layer tends to occur, and output performance tends to decrease. Therefore, when the binder content in the positive electrode active material layer is, for example, 2% by mass or less, or even 1% by mass or less, the advantages of the present invention are more effectively achieved.

[0058] Examples of thickeners include polysaccharide polymers such as carboxymethyl cellulose (CMC), methyl cellulose, etc. 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.

[0059] Examples of 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; hydroxides such as magnesium hydroxide, calcium hydroxide and aluminum hydroxide; carbonates such as calcium carbonate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride and barium sulfate; nitrides such as aluminum nitride and silicon nitride; substances derived from mineral resources such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite and mica; and artificial products thereof.

[0060] The positive electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I; typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, and W as components other than the positive electrode active material, conductive agent, binder, thickener, and filler.

[0061] The positive electrode active material layer preferably does not substantially contain a neutralizing agent. In this case, the positive electrode active material layer in the positive electrode is usually alkaline. To prevent alkaline components from reaching the surface of the positive electrode substrate from the positive electrode active material layer, it is possible to incorporate a neutralizing agent into the positive electrode active material layer and reduce the alkaline component content in the positive electrode active material layer. However, if a neutralizing agent is incorporated into the positive electrode active material, the neutralizing agent may become an impurity and affect the performance of the nonaqueous electrolyte storage element. In other words, by substantially not incorporating a neutralizing agent into the positive electrode active material layer, the output performance of the nonaqueous electrolyte storage element can be further improved. The content of the neutralizing agent in the positive electrode active material layer is preferably 1% by mass or less, more preferably 0.1% by mass or less, and even more preferably 0.01% by mass or less (e.g., 0.001% by mass or less). Examples of neutralizing agents include organic acids such as citric acid and maleic acid.

[0062] The lower limit of the nickel element content per unit area of ​​the positive electrode active material layer is 1.1 × 10 -4 mol / cm 2 is 1.2 × 10 -4 mol / cm 2 is preferred, and 1.25 × 10 -4 mol / cm 2 In some cases, it is more preferable that the nickel content per unit area of ​​the positive electrode active material layer is equal to or greater than the lower limit. The electric capacity of the nonaqueous electrolyte storage element can be increased by setting the nickel content per unit area of ​​the positive electrode active material layer to the lower limit. The upper limit of the nickel content per unit area of ​​the positive electrode active material layer is, for example, 2 × 10 -4 mol / cm 2 is 1.6 × 10 -4 mol / cm 2 may be 1.4 x 10 -4 mol / cm2 may be 1.3 x 10 -4 mol / cm 2 The nickel element content per unit area of ​​the positive electrode active material layer may be equal to or greater than any one of the above lower limits and equal to or less than any one of the above upper limits.

[0063] The upper limit of the mass per unit area of ​​the positive electrode active material layer is 0.017 g / cm 2 and 0.0165 g / cm 2 By setting the mass per unit area of ​​the positive electrode active material layer to the above upper limit or less, the amount of alkaline component contained in the positive electrode active material layer that reaches the positive electrode substrate can be reduced, and the output performance of the nonaqueous electrolyte storage element can be improved. In some embodiments, the mass per unit area of ​​the positive electrode active material layer is 0.0161 g / cm or less. 2 It may be less than 0.0158 g / cm 2 The lower limit of the mass per unit area of ​​the positive electrode active material layer is 0.014 g / cm. 2 is preferred, and 0.015 g / cm 2 More preferably, 0.0155 g / cm 2 It is more preferable that the mass per unit area of ​​the positive electrode active material layer is equal to or greater than the above lower limits, thereby making it possible to further increase the electrical capacity of the nonaqueous electrolyte storage element. The mass per unit area of ​​the positive electrode active material layer can be equal to or greater than any of the above lower limits and equal to or less than any of the above upper limits.

[0064] The positive electrode potential in the fully charged state of the positive electrode is 4.23 V vs. Li / Li + The positive electrode potential in a fully discharged state was 3.00 V vs. Li / Li + The discharge capacity per unit area of ​​the positive electrode active material layer when 2 It may be more than 3.00mAh / cm 2 It is preferable that the value is equal to or greater than 3.05 mAh / cm 2 In this case, the electric capacity of the nonaqueous electrolyte storage element can be increased. On the other hand, the discharge capacity per unit area of ​​the positive electrode active material layer is preferably 3.5 mAh / cm or more, for example.2 may be less than or equal to 3.3 mAh / cm 2 may be less than 3.2mAh / cm 2 The discharge capacity per unit area of ​​the positive electrode active material layer may be equal to or greater than any of the above lower limits and equal to or less than any of the above upper limits.

[0065] <Positive electrode manufacturing method> A positive electrode according to one embodiment of the present invention can be obtained, for example, by a manufacturing method including forming an intermediate layer on the surface of a positive electrode substrate and forming a positive electrode active material layer on the surface of the intermediate layer.

[0066] The intermediate layer can be formed by applying and drying an intermediate layer-forming paste containing the components constituting the intermediate layer and a dispersion medium. The positive electrode active material layer can be formed by applying and drying a positive electrode active material layer-forming paste (positive electrode mixture paste) containing the components constituting the positive electrode active material layer and a dispersion medium.

[0067] The method for applying the intermediate layer-forming paste and the positive electrode active material layer-forming paste is not particularly limited, and can be performed by a known method such as roller coating, screen coating, spin coating, etc. After application and drying, the intermediate layer and the positive electrode active material layer may be pressed in the thickness direction by a known method.

[0068] <Non-aqueous electrolyte energy storage element> A nonaqueous electrolyte storage element (hereinafter also simply referred to as "storage element") according to one embodiment of the present invention comprises a positive electrode, a negative electrode, and a nonaqueous electrolyte. The positive electrode and negative electrode are usually stacked or wound with a separator interposed therebetween to form an electrode assembly. This electrode assembly is housed in a container, and the container is filled with a nonaqueous electrolyte. The nonaqueous electrolyte is interposed between the positive electrode and the negative electrode. As an example of a nonaqueous electrolyte storage element, a nonaqueous electrolyte secondary battery (hereinafter also simply referred to as "secondary battery") will be described.

[0069] (positive electrode) The positive electrode is the positive electrode according to one embodiment of the present invention described above.

[0070] (Negative electrode) The negative electrode has a negative electrode substrate and a negative electrode active material layer disposed on the negative electrode substrate directly or via an intermediate layer. The configuration of the intermediate layer is not particularly limited and can be selected from the configurations exemplified for the positive electrode above. The negative electrode may usually be a multilayer sheet having these layers.

[0071] The negative electrode substrate is conductive. Metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, or alloys thereof, are used as the material for the negative electrode substrate. Among these, copper or a copper alloy is preferred. Examples of the negative electrode substrate include foils and vapor-deposited films, with foils being preferred from the viewpoint of cost. Therefore, copper foil or a copper alloy foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0072] The average thickness of the negative electrode substrate is preferably 2 μm to 35 μm, more preferably 3 μm to 30 μm, even more preferably 4 μm to 25 μm, and particularly preferably 5 μm to 20 μm. By setting the average thickness of the negative electrode substrate within the above range, the strength of the negative electrode substrate can be increased while increasing the energy density per volume of the secondary battery.

[0073] 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, as needed. The optional components such as the conductive agent, the binder, the thickener, and the filler can be selected from the materials exemplified for the positive electrode above.

[0074] The negative electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I; typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W as components other than the negative electrode active material, conductive agent, binder, thickener, and filler.

[0075] The negative electrode active material can be appropriately selected from known negative electrode active materials. A material capable of absorbing and releasing lithium ions is usually used as the negative electrode active material for lithium ion secondary batteries. Examples of the negative electrode active material include metallic Li; metals or semimetals such as Si and Sn; metal oxides or semimetal oxides such as Si oxide, Ti oxide, and Sn oxide; and Li4Ti5O 12 , LiTiO 2、 Examples of the material include titanium-containing oxides such as TiNbO; polyphosphate compounds; silicon carbide; and carbon materials such as graphite and non-graphitic carbon (easily graphitizable carbon or non-graphitizable carbon). Among these materials, graphite and non-graphitic carbon are preferred. In the negative electrode active material layer, one of these materials may be used alone, or two or more may be used in combination.

[0076] "Graphite" refers to graphite that has an average lattice spacing (d 002 ) is 0.33 nm or more and less than 0.34 nm. 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.

[0077] "Non-graphitic carbon" refers to the carbon that has an average lattice spacing (d 002 ) is 0.34 nm or more and 0.42 nm or less. Non-graphitic carbon includes non-graphitizable carbon and graphitizable carbon. Examples of non-graphitic carbon include resin-derived materials, petroleum pitch or petroleum pitch-derived materials, petroleum coke or petroleum coke-derived materials, plant-derived materials, and alcohol-derived materials.

[0078] Here, the "discharged state" of a carbon material refers to a state in which the carbon material, which is a negative electrode active material, is discharged so that lithium ions that can be absorbed and released during charging and discharging are sufficiently released from the carbon material. For example, in a single-electrode battery using a negative electrode containing a carbon material as a negative electrode active material as a working electrode and metallic lithium as a counter electrode, this state refers to a state in which the open circuit voltage is 0.7 V or higher.

[0079] "Non-graphitizable carbon" means the above d 002 This refers to carbon materials with a particle size of 0.36 nm or more and 0.42 nm or less.

[0080] "Graphitizable carbon" means the above d 002 This refers to carbon materials with a particle size of 0.34 nm or more and less than 0.36 nm.

[0081] The negative electrode active material is usually particulate. The average particle size of the negative electrode active material can be, for example, 1 μm 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 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 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 greater than the above lower limit, the production and handling of the negative electrode active material becomes easy. By setting the average particle size of the negative electrode active material to be equal to or less than the above upper limit, the conductivity of the negative electrode active material layer is improved. A pulverizer, a classifier, or the like is used to obtain particles with a predetermined particle size. The pulverization method and the powder classification method can be selected, for example, from the methods exemplified for the positive electrode above.

[0082] The content of the negative electrode active material in the negative electrode active material layer is preferably 60% by mass to 99% by mass, more preferably 90% by mass to 98% by mass. By setting the content of the negative electrode active material within this range, both high energy density and manufacturability of the negative electrode active material layer can be achieved.

[0083] (separator) The separator can be appropriately selected from known separators. Examples of separators that can be used include separators consisting of only a substrate layer and separators in which a heat-resistant layer containing heat-resistant particles and a binder is formed on one or both surfaces of the substrate layer. Examples of the shape of the substrate layer of the separator include woven fabric, nonwoven fabric, and porous resin film. Among these shapes, porous resin films are preferred from the viewpoint of strength, and nonwoven fabrics are preferred from the viewpoint of non-aqueous electrolyte retention. Materials for the substrate layer of the separator are preferably polyolefins such as polyethylene and polypropylene from the viewpoint of shutdown function, and polyimide and aramid from the viewpoint of oxidative decomposition resistance. A composite material of these resins may also be used for the substrate layer of the separator.

[0084] The heat-resistant particles contained in the heat-resistant layer preferably exhibit a mass loss of 5% or less when heated from room temperature to 500°C under an air atmosphere at 1 atmosphere pressure, and more preferably exhibit a mass loss of 5% or less when heated from room temperature to 800°C. Examples of materials exhibiting a mass loss of a predetermined value or less include inorganic compounds. Examples of inorganic compounds include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates; hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium titanate; covalently bonded crystals such as silicon and diamond; mineral-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, as well as artificial products thereof. As the inorganic compound, these substances may be used alone or in the form of a complex, or two or more of them 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 electricity storage element.

[0085] The porosity of the separator is preferably 80% by volume or less from the viewpoint of strength, and 20% by volume or more from the viewpoint of discharge performance. Here, "porosity" refers to a volume-based value measured with a mercury porosimeter.

[0086] The separator may be a polymer gel composed of a polymer and a non-aqueous electrolyte. Examples of polymers include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, and polyvinylidene fluoride. The use of a polymer gel has the effect of suppressing leakage. The separator may be a combination of the porous resin film or nonwoven fabric described above and a polymer gel.

[0087] (non-aqueous electrolyte) The nonaqueous electrolyte can be appropriately selected from known nonaqueous electrolytes. The nonaqueous electrolyte may be a nonaqueous electrolytic solution. The nonaqueous electrolytic solution contains a nonaqueous solvent and an electrolyte salt dissolved in the nonaqueous solvent.

[0088] The non-aqueous solvent can be appropriately selected from known non-aqueous solvents. Examples of non-aqueous solvents include cyclic carbonates, chain carbonates, carboxylic acid esters, phosphate esters, sulfonic acid esters, ethers, amides, and nitriles. Non-aqueous solvents in which some of the hydrogen atoms contained in these compounds have been substituted with halogens may also be used.

[0089] 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), difluoroethylene carbonate (DFEC), styrene carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate, etc. Among these, EC is preferred.

[0090] Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, trifluoroethyl methyl carbonate, bis(trifluoroethyl) carbonate, etc. Among these, EMC is preferred.

[0091] It is preferable to use a cyclic carbonate or a chain carbonate as the non-aqueous solvent, and it is more preferable to use a combination of a cyclic carbonate and a chain carbonate. The use of a cyclic carbonate can promote dissociation of the electrolyte salt and improve the ionic conductivity of the non-aqueous electrolyte. The use of a chain carbonate can reduce the viscosity of the non-aqueous electrolyte. When a cyclic carbonate and a 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.

[0092] The electrolyte salt can be appropriately selected from known electrolyte salts, such as lithium salts, sodium salts, potassium salts, magnesium salts, and onium salts. Of these, lithium salts are preferred.

[0093] Examples of lithium salts include inorganic lithium salts such as LiPF6, LiPO2F2, LiBF4, LiClO4, and LiN(SO2F)2, and lithium salts having a halogenated hydrocarbon group such as LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), LiC(SO2CF3)3, and LiC(SO2C2F5)3. Among these, inorganic lithium salts are preferred, and LiPF6 is more preferred.

[0094] The content of electrolyte salt in the non-aqueous electrolyte is 0.1 mol / dm at 20°C and 1 atmosphere. 3 More than 2.5mol / dm 3 Preferably less than 0.3 mol / dm 3 More than 2.0mol / dm 3Less than 0.5 mol / dm is more preferable. 3 More than 1.7mol / dm 3 More preferably, 0.7 mol / dm 3 More than 1.5mol / dm 3 The following is particularly preferred: By setting the content of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

[0095] The non-aqueous electrolyte may contain an additive, such as aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partial halides of the aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; halogenated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole; vinylene carbonate, methylvinylene carbonate, ethylvinylene carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, and cyclohexane. Examples of the additives include dicarboxylic anhydrides, ethylene sulfite, propylene sulfite, dimethyl sulfite, dimethyl sulfate, 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, 1,3-propene sultone, 1,3-propane sultone, 1,4-butane sultone, 1,4-butene sultone, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, and tetrakistrimethylsilyl titanate. These additives may be used alone or in combination of two or more.

[0096] The content of the additive contained in the non-aqueous electrolyte is preferably 0.01% by mass to 10% by mass, more preferably 0.1% by mass to 7% by mass, even more preferably 0.2% by mass to 5% by mass, and particularly preferably 0.3% by mass to 3% by mass. By setting the content of the additive within the above range, it is possible to improve the capacity retention performance or cycle performance after high-temperature storage, and further improve safety.

[0097] The non-aqueous electrolyte may be a solid electrolyte, or a non-aqueous electrolytic solution and a solid electrolyte may be used in combination.

[0098] The solid electrolyte can be selected from any material that has ion conductivity for lithium, sodium, calcium, etc. and is solid at room temperature (e.g., 15° C. to 25° C.) Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, oxynitride solid electrolytes, and polymer solid electrolytes.

[0099] Examples of sulfide solid electrolytes include Li2S-P2S5, LiI-Li2S-P2S5, and Li 10 Ge-P2S 12 etc.

[0100] The shape of the nonaqueous electrolyte storage element of this embodiment is not particularly limited, and examples thereof include cylindrical batteries, prismatic batteries, flat batteries, coin batteries, and button batteries.

[0101] FIG. 1 shows a nonaqueous electrolyte storage element 1 as an example of a prismatic battery. The figure is a see-through view of the inside of the container. An electrode assembly 2 having a positive electrode and a negative electrode wound with a separator sandwiched between them is housed in a prismatic container 3. The positive electrode is electrically connected to a positive electrode terminal 4 via a positive electrode lead 41. The negative electrode is electrically connected to a negative electrode terminal 5 via a negative electrode lead 51.

[0102] <Electricity storage device> The nonaqueous electrolyte energy storage element of this embodiment can be mounted as an energy storage unit (battery module) comprising a plurality of nonaqueous electrolyte energy storage elements 1 in an automobile power source such as an electric vehicle (EV), a hybrid electric vehicle (HEV), or a plug-in hybrid electric vehicle (PHEV), a power source for electronic devices such as a personal computer or a communication terminal, or a power storage power source, etc. In this case, the technology of the present invention may be applied to at least one nonaqueous electrolyte energy storage element included in the energy storage unit.

[0103] 2 shows an example of an electricity storage device 30 in which electricity storage units 20, each of which is an assembly of two or more electrically connected nonaqueous electrolyte electricity storage elements 1, are further assembled. The electricity storage device 30 may include a bus bar (not shown) that electrically connects two or more nonaqueous electrolyte electricity storage elements 1, and a bus bar (not shown) that electrically connects two or more electricity storage units 20. The electricity storage unit 20 or the electricity storage device 30 may include a status monitoring device (not shown) that monitors the status of one or more nonaqueous electrolyte electricity storage elements.

[0104] <Method of manufacturing nonaqueous electrolyte energy storage element> The method for manufacturing the nonaqueous electrolyte storage element of this embodiment can be appropriately selected from known methods. The manufacturing method includes, for example, preparing an electrode assembly, preparing a nonaqueous electrolyte, and housing the electrode assembly and the nonaqueous electrolyte in a container. Preparing the electrode assembly includes preparing a positive electrode and a negative electrode, and forming the electrode assembly by stacking or winding the positive electrode and the negative electrode with a separator interposed therebetween. Housing the nonaqueous electrolyte in the container can be appropriately selected from known methods. For example, when a nonaqueous electrolyte solution is used as the nonaqueous electrolyte, the nonaqueous electrolyte solution may be injected through an injection port formed in the container, and the injection port may then be sealed.

[0105] <Other embodiments> The nonaqueous electrolyte storage element of the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the spirit of the present invention. For example, the configuration of one embodiment may be added to the configuration of another embodiment, or part of the configuration of one embodiment may be replaced with the configuration of another embodiment or well-known technology. Furthermore, part of the configuration of one embodiment may be deleted. Also, well-known technology may be added to the configuration of one embodiment.

[0106] In the above embodiment, the nonaqueous electrolyte storage element is used as a chargeable and dischargeable nonaqueous electrolyte secondary battery (e.g., a lithium ion secondary battery), but the type, shape, size, capacity, etc. of the nonaqueous electrolyte storage element are arbitrary. The present invention can also be applied to various secondary batteries, electric double layer capacitors, lithium ion capacitors, and other capacitors. [Example]

[0107] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0108] (Preparation of positive electrode) [Example 1] An intermediate layer was formed on the surface of aluminum foil (average thickness 15 μm) as a positive electrode substrate in the following manner. Acetylene black, a conductive agent, and chitosan, a binder, were weighed out in a mass ratio (solid content equivalent) of 30:70. These were mixed with water as a dispersion medium to prepare a paste for forming the intermediate layer. This paste for forming the intermediate layer was applied to one side of the aluminum foil. After that, the mixture was dried to obtain an intermediate layer.

[0109] Positive electrode active material LiNi 8 / 10 Co 1 / 10 Mn 1 / 10O2, acetylene black as a conductive agent, and PVDF as a binder were weighed in a mass ratio (solid content equivalent) of 96:3:1. These were mixed with NMP (N-methylpyrrolidone) as a dispersion medium to prepare a paste for forming a positive electrode active material layer. This paste for forming a positive electrode active material layer was applied to the surface of the intermediate layer and dried to remove the dispersion medium. Thereafter, pressure molding was performed using a roller press to obtain the positive electrode of Example 1. The mass per unit area of ​​the intermediate layer in the obtained positive electrode was 0.5 g / m 2 The mass per unit area of ​​the positive electrode active material layer in the obtained positive electrode was 0.01617 g / cm 2 The nickel element content per unit area of ​​the positive electrode active material layer is 1.274 × 10 -4 mol / cm 2 It was.

[0110] [Example 2] A positive electrode of Example 2 was obtained in the same manner as in Example 1, except that the mass ratio (in terms of solid content) of the positive electrode active material, the conductive agent, and the binder was set to 94:4:2, the amount of the paste for forming the positive electrode active material layer was changed, and the mass per unit area of ​​the positive electrode active material layer was set as shown in Table 1.

[0111] [Example 3] A positive electrode of Example 3 was obtained in the same manner as in Example 1, except that the mass ratio (in terms of solid content) of the positive electrode active material, the conductive agent, and the binder was set to 98:1:1, the amount of the paste for forming the positive electrode active material layer was changed, and the mass per unit area of ​​the positive electrode active material layer was set as shown in Table 1.

[0112] [Comparative Example 1] A positive electrode of Comparative Example 1 was obtained in the same manner as in Example 1, except that no intermediate layer was provided and the positive electrode active material layer was formed directly on aluminum foil as the positive electrode substrate.

[0113] Comparative Example 2 A positive electrode of Comparative Example 2 was obtained in the same manner as in Comparative Example 1, except that citric acid as a neutralizing agent was further added when preparing the paste for forming a positive electrode active material layer.

[0114] Comparative Example 3 A positive electrode of Comparative Example 3 was obtained in the same manner as in Comparative Example 1, except that the amount of the paste for forming the positive electrode active material layer was changed to give a mass per unit area of ​​the positive electrode active material layer as shown in Table 1.

[0115] Comparative Example 4 A positive electrode of Comparative Example 4 was obtained in the same manner as in Example 1, except that the amount of the paste for forming the positive electrode active material layer was changed to give a mass per unit area of ​​the positive electrode active material layer as shown in Table 1.

[0116] Comparative Example 5 LiNi as the positive electrode active material 3 / 5 Co 1 / 5 Mn 1 / 5 A positive electrode of Comparative Example 5 was obtained in the same manner as in Example 1 except that O2 was used.

[0117] Comparative Example 6 A positive electrode of Comparative Example 6 was obtained in the same manner as in Comparative Example 5, except that the amount of the paste for forming the positive electrode active material layer was changed to give a mass per unit area of ​​the positive electrode active material layer as shown in Table 1.

[0118] Comparative Example 7 A positive electrode of Comparative Example 7 was obtained in the same manner as in Comparative Example 5, except that no intermediate layer was provided and the positive electrode active material layer was formed directly on the aluminum foil serving as the positive electrode substrate.

[0119] The nickel element content per unit area of ​​the positive electrode active material layer of each of the positive electrodes of Examples 2 and 3 and Comparative Examples 1 to 7 was as shown in Table 1.

[0120] (Discharge capacity per unit area of ​​positive electrode active material layer) For each positive electrode obtained in the examples and comparative examples, the potential in a fully charged state was 4.23 V vs. Li / Li + The positive electrode potential in a fully discharged state was 3.00 V vs. Li / Li + The discharge capacity per unit area of ​​the positive electrode active material layer was measured by the method described above. The measurement results are shown in Table 1.

[0121] (Fabrication of non-aqueous electrolyte energy storage element) [Fabrication of positive electrodes for non-aqueous electrolyte storage elements] In the same manner as the positive electrodes obtained in the above-described Examples and Comparative Examples, positive electrodes for nonaqueous electrolyte storage elements in the Examples and Comparative Examples were obtained in which an intermediate layer and a positive electrode active material layer were formed on both sides of an aluminum foil serving as a positive electrode substrate. [Fabrication of negative electrode for non-aqueous electrolyte energy storage element] Graphite as the negative electrode active material, SBR as the binder, and CMC as the thickener were weighed out in a mass ratio (solid content equivalent) of 98:1:1. These were mixed with water as the dispersion medium to prepare a paste for forming a negative electrode active material layer. This paste for forming a negative electrode active material layer was applied to both sides of copper foil as the negative electrode substrate and dried to remove the dispersion medium. The paste was then pressure-molded using a roller press to obtain a negative electrode for a nonaqueous electrolyte storage element.

[0122] [Assembly of non-aqueous electrolyte energy storage element] The positive electrode for the nonaqueous electrolyte storage element of each of the Examples and Comparative Examples and the negative electrode for the nonaqueous electrolyte storage element were wound with a polyethylene separator interposed therebetween to obtain an electrode assembly in which the positive electrode and the negative electrode were wound. In addition, 1.4 mol / dm LiPF6 as an electrolyte salt was added to a nonaqueous solvent in which EC and EMC were mixed at a volume ratio of 30:70. 3 A non-aqueous electrolyte was prepared by dissolving the electrode body and the non-aqueous electrolyte at a concentration of 1000 kJ / cm2. Each of the non-aqueous electrolyte storage elements of Examples and Comparative Examples was fabricated using the electrode body and the non-aqueous electrolyte.

[0123] [Initial capacity] The initial capacity of each of the nonaqueous electrolyte storage elements of the Examples and Comparative Examples was measured by the following method. The following test was carried out in a thermostatic chamber at 25°C. The upper limit voltage was 4.15V and the charging current was 1mA / cm. 2 After constant current charging at 4.15 V, constant voltage charging was performed at 4.15 V. The charging termination condition was 5 hours from the start of charging. After a 10-minute rest period, the discharge current was 1 mA / cm at a lower limit voltage of 2.75 V. 2 The amount of electricity during this discharge was taken as the initial capacity. The measurement results of the initial capacity are shown in Table 1. The measurement results of the initial capacity shown in Table 1 are relative values ​​with Example 1 being 100%.

[0124] (Whether or not the surface of the positive electrode substrate has turned white) For each of the positive electrodes of the examples and comparative examples prepared separately using the same procedure, the positive electrode active material layer and intermediate layer were peeled off, and the presence or absence of whitening of the positive electrode substrate surface was visually confirmed. Note that whitening of the positive electrode substrate surface is thought to occur due to the reaction of metallic aluminum with an alkaline component to produce aluminum hydroxide. The results of the confirmation of the presence or absence of whitening are shown in Table 1.

[0125] (output performance) The output performance of each nonaqueous electrolyte storage element in the Examples and Comparative Examples was measured using the following method. The initial capacity test described above determined a capacity of 1 C. From the discharged state, the element was charged at a constant current of 0.5 C for 1 hour at 25°C, adjusting the SOC (State of Charge) to 50%. Then, at 25°C, a constant current discharge was performed for 10 seconds at discharge currents of 0.2 C, 0.5 C, and 1.0 C. After each discharge, the element was charged at a constant current of 0.5 C and supplemented with a supplementary charge equivalent to the discharged amount of electricity to ensure that the SOC did not deviate from 50%. The voltage at 1 second at each current was plotted to obtain a straight line. The slope of the line was taken as the DC resistance (DCR), and the intercept was taken as the pre-energization voltage (Vo). The output power was calculated using the formula {(Vo-2.5) / DCR} × 2.5. The output power measurement results are shown in Table 1. The output measurement results shown in Table 1 are relative values ​​with the output of Example 1 taken as 100%.

[0126] [Table 1]

[0127] As shown in Table 1, Comparative Example 1, which uses a positive electrode having no intermediate layer and a high nickel content per unit area of ​​the positive electrode active material layer, exhibits whitening of the aluminum-containing positive electrode substrate and low output. In contrast to Comparative Example 1, Comparative Example 2, which uses a positive electrode with a neutralizing agent added to the positive electrode active material layer, suppresses whitening of the positive electrode substrate but exhibits low output. Comparative Example 3, which uses a positive electrode having no intermediate layer and a high mass per unit area of ​​the positive electrode active material layer, and Comparative Examples 4 and 6, which use positive electrodes having an intermediate layer but a high mass per unit area of ​​the positive electrode active material layer, all exhibit high initial capacity but low output. Comparative Examples 5 and 7, which use positive electrodes having a low nickel content per unit area of ​​the positive electrode active material layer, exhibit low initial capacity.

[0128] In comparison with the above comparative examples, the positive electrode active material layer had an intermediate layer and a nickel element content per unit area of ​​1.1 × 10 -4 mol / cm 2 or more, and the mass per unit area of ​​the positive electrode active material layer is 0.017 g / cm 2 Examples 1 to 3 using the positive electrodes described below all had large initial capacities of 97% or more, suppressed whitening of the positive electrode substrate, and achieved outputs of 100% or more. These results demonstrate that when the positive electrodes are used in nonaqueous electrolyte energy storage elements, the nonaqueous electrolyte energy storage elements can exhibit large electrical capacity and good output performance. Comparisons between Example 1 and Comparative Examples 5 and 6, for example, reveal that the presence or absence of whitening of the positive electrode substrate and the level of output are influenced by both the nickel element content per unit area of ​​the positive electrode active material layer and the mass per unit area of ​​the positive electrode active material layer. [Explanation of symbols]

[0129] 1. Non-aqueous electrolyte energy storage element 2 Electrode body 3 containers 4 Positive terminal 41 Positive lead 5 Negative terminal 51 Negative lead 20 Energy storage unit 30 Electricity storage device

Claims

1. a positive electrode substrate containing metallic aluminum, an intermediate layer containing a conductive agent, and a positive electrode active material layer containing a lithium transition metal composite oxide, in this order; the lithium transition metal composite oxide contains nickel; The nickel element content per unit area of ​​the positive electrode active material layer is 1.1×10 -4 mol / cm 2 2 x 10 or more -4 mol / cm 2 is as follows: The mass per unit area of ​​the positive electrode active material layer is 0.014 g / cm 2 0.017g / cm or more 2 A positive electrode for a non-aqueous electrolyte storage element, which is as follows:

2. The positive electrode potential in a fully charged state was 4.23 V vs. Li / Li + The positive electrode potential in a fully discharged state was 3.00 V vs. Li / Li + When the discharge capacity per unit area of ​​the positive electrode active material layer is 3.00 mAh / cm 2 The positive electrode of claim 1 .

3. The mass per unit area of ​​the intermediate layer is 0.05 g / m 2 1g / m or more 2 3. The positive electrode of claim 1 or claim 2, wherein:

4. 4. The positive electrode according to claim 1, wherein the lithium transition metal composite oxide contains nickel at a content of 50 mol % or more of the transition metal elements.

5. The positive electrode according to claim 1 , wherein the conductive agent contained in the intermediate layer has an average particle size of 1 nm or more and 40 nm or less.

6. A nonaqueous electrolyte electricity storage element comprising the positive electrode of claim 1 .

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