Energy storage element

Abstract

To provide a power storage element capable of suppressing the dissolution of fine copper powder even when the fine copper powder is mixed between a positive electrode and a negative electrode.SOLUTION: A power storage element includes a positive electrode 11 having a conductive positive electrode base material 13, a positive electrode active material layer 14, and an insulating layer 15, a negative electrode 12 that is arranged so as to face the positive electrode and having a conductive negative electrode base material 16 and a negative electrode active material layer 17, and a separator 18 arranged between the positive electrode and the negative electrode, and in a region in which the positive electrode faces the negative electrode, the insulating layer covers a laminated structure including the positive electrode base material and the positive electrode active material layer, and the potential of the surface of the insulating layer is lower than 3.4 V vs. Li / Li+.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a power storage element.

Background Art

[0002] Secondary batteries represented by lithium ion secondary batteries are widely used in electronic devices such as personal computers and communication terminals, automobiles, etc. because of their high energy density. Generally, the secondary battery has a pair of electrodes composed of a sheet-like positive electrode and a negative electrode, and an electrolyte interposed between the electrodes, and is configured to charge and discharge by transferring ions between both electrodes. In addition, as power storage elements other than secondary batteries, capacitors such as lithium ion capacitors and electric double layer capacitors are also widely popular.

[0003] The pair of electrodes usually form an electrode body laminated or wound through a separator. As the separator, a porous resin membrane is widely used. A power storage element provided with an electrode having a porous insulating layer formed on the surface of a binder layer (active material layer) together with such a separator has been proposed. Patent Document 1 describes a secondary battery in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, and the positive electrode and the negative electrode each have a metal foil and a binder layer formed on the metal foil, and have a foil exposed portion where the metal foil is exposed on one side in the width direction, and the positive electrode or the negative electrode has an insulating layer covering the binder layer, etc.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In energy storage elements, copper components are sometimes used as negative electrode substrates, other conductive members, and containers. Therefore, during the manufacturing process of energy storage elements, fine copper powder generated, for example during the cutting or joining of copper negative electrode substrates, may be mixed into the energy storage element. If this mixed copper powder is interposed between the positive and negative electrodes and comes into contact with the positive electrode, it may oxidize when exposed to the high potential of the positive electrode during charging, dissolve into the electrolyte as copper ions, and affect the performance of the energy storage element.

[0006] The present invention has been made based on the circumstances described above, and its purpose is to provide an energy storage element that can suppress the dissolution of fine copper powder even when it is mixed between the positive and negative electrodes. [Means for solving the problem]

[0007] One aspect of the present invention comprises a positive electrode having a conductive positive electrode substrate, a positive electrode active material layer, and an insulating layer; a negative electrode disposed opposite to the positive electrode and having a conductive negative electrode substrate and a negative electrode active material layer; and a separator disposed between the positive electrode and the negative electrode, wherein in the region of the positive electrode opposite the negative electrode, the insulating layer covers a laminated structure including the positive electrode substrate and the positive electrode active material layer, and the surface potential of the insulating layer is 3.4V vs. Li / Li + It is a lower-power energy storage element. [Effects of the Invention]

[0008] The energy storage element according to one aspect of the present invention and the energy storage element according to another aspect of the present invention can suppress the dissolution of fine copper powder even when it is mixed between the positive electrode and the negative electrode. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a schematic cross-sectional view of a secondary battery according to one embodiment of the present invention. [Figure 2] Figure 2 is an explanatory diagram showing the relationship between the structure of a conventional energy storage element and its electric potential. [Figure 3]Figure 3 is an explanatory diagram showing the relationship between the structure of an energy storage element and its electric potential. [Figure 4] Figure 4 is an explanatory diagram showing the relationship between the structure of an energy storage element according to one aspect of the present invention and its potential. [Figure 5] Figure 5 is an explanatory diagram showing the relationship between the structure of an energy storage element according to one aspect of the present invention and its potential. [Figure 6] Figure 6 is an explanatory diagram showing the relationship between the structure of an energy storage element and its electric potential. [Figure 7] Figure 7 is an external perspective view showing one embodiment of an energy storage element. [Figure 8] Figure 8 is a schematic diagram showing one embodiment of an energy storage device configured by assembling multiple energy storage elements. [Modes for carrying out the invention]

[0010] First, an overview of the energy storage elements disclosed herein will be provided.

[0011] A storage element (A) according to one aspect of the present invention comprises a positive electrode having a conductive positive electrode substrate, a positive electrode active material layer, and an insulating layer; a negative electrode disposed opposite to the positive electrode and having a conductive negative electrode substrate and a negative electrode active material layer; and a separator disposed between the positive electrode and the negative electrode, wherein in the region of the positive electrode opposite to the negative electrode, the insulating layer covers a laminated structure including the positive electrode substrate and the positive electrode active material layer, and the potential of the surface of the insulating layer is 3.4V vs. Li / Li + It is a lower-power energy storage element.

[0012] With such an energy storage element (A), even if fine copper powder is mixed between the positive and negative electrodes, the dissolution of that fine copper powder can be suppressed. The reason for this effect is not entirely clear, but the following reasons are speculated: The oxidation-reduction potential of copper is approximately 3.38V vs. Li / Li + Therefore, in solid copper, typically 3.4V vs. Li / Li +At the above potentials, oxidation occurs, and copper ions dissolve into the electrolyte. Therefore, the surface of the positive electrode, for example, during charging at 3.4V vs. Li / Li + At the above potential, the fine copper powder adhering to the surface of the positive electrode can dissolve. Figure 2 shows a conventional energy storage element 20 in which a positive electrode 23 having a positive electrode active material layer 21 and an insulating layer 22, a separator 26, and a negative electrode 25 having a negative electrode active material layer 24 are stacked in this order. Figure 2 also schematically shows the potential from the positive electrode active material layer 21 to the negative electrode active material layer 24 in the charged state of the conventional energy storage element 20. Here in Figure 2, as an example, a common lithium transition metal composite oxide is used as the positive electrode active material and a common graphite is used as the negative electrode active material, and the potential of the positive electrode active material layer 21 in the charged state is 4.3V vs. Li / Li + The potential of the negative electrode active material layer 24 is set to 0.1V vs. Li / Li + Generally, the separator 26 is made of resin, and its volume resistivity is generally higher than that of the insulating layer 22, which is mainly composed of inorganic particles. Also, in terms of thickness, a typical separator is thicker than a typical insulating layer laminated on the surface of the active material layer. For this reason, the potential drop due to the insulating layer 22 is very small compared to the potential drop due to the separator 26, and the potential of the surface of the insulating layer 22, i.e., the surface of the positive electrode 23, is almost the same as the potential of the surface of the positive electrode active material layer 21. For this reason, in the charged state, the potential of the surface of the insulating layer 22 is 3.4V vs. Li / Li, which is the dissolution potential of copper. + As a result, the fine copper powder A present on the surface of the insulating layer 22 (the surface of the positive electrode 23) is more likely to dissolve. Furthermore, if the positive electrode does not have an insulating layer and is laminated to the negative electrode via a separator, the potential of the positive electrode surface is the same as the potential of the positive electrode active material layer, so the dissolution of the fine copper powder is even more likely to occur. In addition, regardless of the material and thickness of the insulating layer and separator, in the energy storage element with the configuration shown in Figure 2, the potential of the surface of the positive electrode (insulating layer) during charging is higher than the potential of the negative electrode active material layer, so the possibility of copper dissolution is high.

[0013] In contrast, in the energy storage element (A), in the region of the positive electrode facing the negative electrode, the insulating layer covers a laminated structure including the positive electrode substrate and the positive electrode active material layer, and the potential of the surface of the insulating layer is 3.4 V vs. Li / Li + lower. Therefore, the copper powder mixed between the positive electrode and the negative electrode can contact the insulating layer but is difficult to contact the positive electrode substrate and the positive electrode active material layer with a high potential. And since the potential of the surface of the insulating layer is lower than the dissolution potential of copper, the dissolution of the fine copper powder present on the surface of the positive electrode, that is, the surface of the insulating layer, is suppressed.

[0014] "Conductivity" means that the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 7 Ω·cm or less. "Insulating layer" means a layer having insulating properties, that is, the property of insulating electricity. "Insulating (non-conductive)" means that the above volume resistivity is more than 10 7 Ω·cm.

[0015] "The potential of the surface of the insulating layer is lower than 3.4 V vs. Li / Li + " means that in all states from the discharge state to the charge state (SOC 0% to 100%) during the normal use of the energy storage element, the potential of the surface of the insulating layer is lower than 3.4 V vs. Li / Li + .

[0016] Note that making the potential of the surface of the insulating layer lower than 3.4 V vs. Li / Li + can be achieved by adjusting the volume resistivity and thickness of the insulating layer and the volume resistivity and thickness of the separator. Fig. 3 shows an energy storage element 30 in which a positive electrode 23 having a positive electrode active material layer 21 and an insulating layer 22, a separator 26, and a negative electrode 25 having a negative electrode active material layer 24 are laminated in this order. In addition, Fig. 3 schematically shows the potential from the positive electrode active material layer 21 to the negative electrode active material layer 24 in the charged state of the energy storage element 30. In the figure, α (vs. Li / Li + ) is the potential of the positive electrode active material layer 21, β (vs. Li / Li + ) is the potential of the negative electrode active material layer 24, γ (vs. Li / Li+ Δa(V) is the potential on the surface of the positive electrode 23 (the potential on the surface of the insulating layer 22), Δa(V) is the potential difference between the positive electrode active material layer 21 and the surface of the positive electrode 23 (i.e., the potential drop due to the insulating layer 22), and Δb(V) is the potential difference between the surface of the positive electrode 23 and the negative electrode active material layer 24 (i.e., the potential drop due to the separator 26). In the energy storage element 30, the potential drop Δa (V) due to the insulating layer 22, the potential drop Δb (V) due to the separator 26, and the resistance A (Ωcm) per unit area of ​​the insulating layer 22 in the region where the insulating layer 22 and the separator 26 face each other. -2 ), and the resistance B (Ωcm²) per unit area of ​​the separator 26 in the region where the insulating layer 22 and the separator 26 face each other. -2 In this case, Δa:Δb=A:B (i.e., A / Δa=B / Δb) holds true. The resistance per unit area of ​​the insulating layer 22 and the separator 26 is calculated by their respective volume resistivity and thickness. Therefore, by adjusting the volume resistivity and thickness of the insulating layer and the separator, Δa and Δb are adjusted, and the surface potential of the insulating layer is set to 3.4V vs. Li / Li + It can be made lower.

[0017] In the energy storage element (A), it is preferable that the average thickness of the insulating layer in the region of the positive electrode facing the negative electrode is greater than the thickness of the separator.

[0018] With such an energy storage element (A), the average thickness of the insulating layer is greater than the thickness of the separator, which allows for more effective suppression of the dissolution of fine copper powder. Figure 4 schematically shows such an energy storage element 30 and the potential from the positive electrode active material layer 21 to the negative electrode active material layer 24 in the charged state of such an energy storage element 30. The potentials of the positive electrode active material layer 21 and the negative electrode active material layer 24 (positive electrode active material and negative electrode active material) of the energy storage element 30 in Figure 4 are the same as those of the energy storage element 20 in Figure 2.

[0019] In the energy storage element (A), it is preferable that the resistivity of the insulating layer is greater than the resistivity of the separator.

[0020] With such an energy storage element (A), the resistivity of the insulating layer is greater than that of the separator, so the dissolution of the copper fine powder can be suppressed more effectively. Figure 5 schematically shows such an energy storage element 30 and the potential from the positive electrode active material layer 21 to the negative electrode active material layer 24 in the charged state of such an energy storage element 30. The potentials of the positive electrode active material layer 21 and the negative electrode active material layer 24 (positive electrode active material and negative electrode active material) of the energy storage element 30 in Figure 5 are the same as those of the energy storage element 20 in Figure 2.

[0021] The energy storage element (B) comprises a positive electrode having a conductive positive electrode substrate, a positive electrode active material layer, and an insulating layer, and a negative electrode disposed opposite to the positive electrode and having a conductive negative electrode substrate and a negative electrode active material layer. In the region of the positive electrode opposite the negative electrode, the insulating layer covers a laminated structure including the positive electrode substrate and the positive electrode active material layer, and the potential of the surface of the insulating layer is 3.4V vs. Li / Li + It is a lower-power energy storage element.

[0022] With such an energy storage element (B), even if fine copper powder is mixed between the positive and negative electrodes, the dissolution of that fine copper powder can be suppressed. The reason for this effect is not entirely clear, but the following reasons are speculated: The oxidation-reduction potential of copper is approximately 3.38V vs. Li / Li + Therefore, in solid copper, typically 3.4V vs. Li / Li + At the above potentials, oxidation occurs, and copper ions dissolve into the electrolyte. Therefore, the surface of the positive electrode, for example, during charging at 3.4V vs. Li / Li + When the potential is above this level, the fine copper powder adhering to the surface of the positive electrode can dissolve. In contrast, in the energy storage element (B), in the region of the positive electrode where the negative electrode faces, the insulating layer covers a laminated structure including the positive electrode substrate and the positive electrode active material layer, and the potential of the surface of the insulating layer is 3.4V vs. Li / Li +It is lower. Therefore, copper powder mixed between the positive and negative electrodes can come into contact with the insulating layer, but it is difficult for it to come into contact with the positive electrode substrate and positive electrode active material layer, which have higher potentials. Furthermore, since the potential of the surface of the insulating layer is lower than the dissolution potential of copper, the dissolution of the fine copper powder present on the positive electrode surface, i.e., the insulating layer surface, is suppressed.

[0023] The energy storage element (C) comprises a positive electrode having a conductive positive electrode substrate, a positive electrode active material layer, and an insulating layer, and a negative electrode disposed opposite to the positive electrode and having a conductive negative electrode substrate and a negative electrode active material layer, wherein in the region of the positive electrode opposite the negative electrode, the insulating layer covers a laminated structure including the positive electrode substrate and the positive electrode active material layer, and the surface of the insulating layer is in direct contact with the surface of the negative electrode.

[0024] With such an energy storage element (C), even if fine copper powder is mixed between the positive and negative electrodes, the dissolution of the fine copper powder can be suppressed. The reason for this effect is not entirely clear, but the following reasons are speculated. Figure 2 shows a conventional energy storage element 20 in which a positive electrode 23 having a positive electrode active material layer 21 and an insulating layer 22, a separator 26, and a negative electrode 25 having a negative electrode active material layer 24 are stacked in this order. Figure 2 also schematically shows the potential from the positive electrode active material layer 21 to the negative electrode active material layer 24 in the charged state of the conventional energy storage element 20. Here in Figure 2, as an example, a common lithium transition metal composite oxide is used as the positive electrode active material and a common graphite is used as the negative electrode active material, and the potential of the positive electrode active material layer 21 in the charged state is 4.3V vs. Li / Li + The potential of the negative electrode active material layer 24 is set to 0.1V vs. Li / Li +Generally, the separator 26 is made of resin, and its volume resistivity is generally higher than that of the insulating layer 22, which is mainly composed of inorganic particles. Also, in terms of thickness, a typical separator is thicker than a typical insulating layer laminated on the surface of the active material layer. For this reason, the potential drop due to the insulating layer 22 is very small compared to the potential drop due to the separator 26, and the potential of the surface of the insulating layer 22, i.e., the surface of the positive electrode 23, is almost the same as the potential of the surface of the positive electrode active material layer 21. For this reason, in the charged state, the potential of the surface of the insulating layer 22 is 3.4V vs. Li / Li, which is the dissolution potential of copper. + As a result, the fine copper powder A present on the surface of the insulating layer 22 (the surface of the positive electrode 23) is more likely to dissolve. Furthermore, if the positive electrode does not have an insulating layer and is laminated to the negative electrode via a separator, the potential of the positive electrode surface is the same as the potential of the positive electrode active material layer, so the dissolution of the fine copper powder is even more likely to occur. In addition, regardless of the material and thickness of the insulating layer and separator, in the energy storage element with the configuration shown in Figure 2, the potential of the surface of the positive electrode (insulating layer) during charging is higher than the potential of the negative electrode active material layer, so the possibility of copper dissolution is high.

[0025] In contrast, Figure 6 shows a storage element 30 in which a positive electrode 23 having a positive electrode active material layer 21 and an insulating layer 22, and a negative electrode 25 having a negative electrode active material layer 24 are stacked in this order. Figure 6 also schematically shows the potential from the positive electrode active material layer 21 to the negative electrode active material layer 24 in the charged state of the storage element 30. The potentials of the positive electrode active material layer 21 and the negative electrode active material layer 24 (positive electrode active material and negative electrode active material) of the storage element 30 in Figure 6 are the same as those of the storage element 20 in Figure 2. Thus, in the storage element 30, the surface of the insulating layer 22 is in contact with the surface of the negative electrode 25. Therefore, the potential of the surface of the insulating layer 22, i.e., the surface of the positive electrode 23, is the same as the potential of the surface of the negative electrode 25, i.e., 0.1V vs. Li / Li in the configuration of Figure 6. +Therefore, the copper fine powder A present on the surface of the insulating layer 22 (the surface of the positive electrode 23) is difficult to dissolve. Furthermore, in the energy storage element (C), in the region of the positive electrode where the negative electrode faces, the insulating layer covers a laminated structure including the positive electrode substrate and the positive electrode active material layer. Therefore, the copper fine powder mixed between the positive and negative electrodes is unlikely to come into contact with the positive electrode substrate and positive electrode active material layer, which have a higher potential. For this reason, in the energy storage element (C), even if copper fine powder is mixed between the positive and negative electrodes, the dissolution of the copper fine powder can be suppressed.

[0026] In the energy storage element (C), the potential on the surface of the insulating layer is 3.4V vs. Li / Li + A lower value is preferable.

[0027] With such an energy storage element (C), the potential of the insulating layer surface is lower than the dissolution potential of copper, thus more effectively suppressing the dissolution of fine copper powder.

[0028] In the energy storage element (C), it is preferable that the surface of the insulating layer is in direct contact with the surface of the negative electrode active material layer.

[0029] With such an energy storage element (C), the potential of the surface of the insulating layer becomes the potential of the negative electrode active material layer, and the potential of the surface of the insulating layer can be sufficiently low, thereby more effectively suppressing the dissolution of the fine copper powder.

[0030] In energy storage elements (A), (B), and (C), it is preferable that the insulating layer contains insulating particles.

[0031] By including insulating particles in the insulating layer, the insulating layer can exhibit good insulating properties.

[0032] In energy storage elements (A), (B), and (C), it is preferable that the insulating layer contains inorganic particles.

[0033] By including insulating particles in the insulating layer, the insulating layer can exhibit good heat resistance, among other things.

[0034] In energy storage elements (A), (B), and (C), it is preferable that the negative electrode substrate contains copper.

[0035] By including copper, which has excellent conductivity, in the negative electrode substrate, the current collection performance of the negative electrode substrate can be improved. Furthermore, when the negative electrode substrate contains copper, the risk of fine copper powder contamination in the energy storage element during the manufacturing process increases. Therefore, when the negative electrode substrate contains copper, the advantages of the present invention can be enjoyed more effectively.

[0036] This document describes in detail an energy storage element, an energy storage device, a method for manufacturing an energy storage element, and other embodiments related to one embodiment of the present invention. Note that the names of the components (each element) used in each embodiment may differ from the names of the components (each element) used in the background art.

[0037] <Energy storage element> An energy storage element according to one embodiment of the present invention comprises an electrode body having a positive electrode, a negative electrode, and a separator, a non-aqueous electrolyte, and a container for housing the electrode body and the non-aqueous electrolyte. The electrode body is usually a stacked type in which a plurality of positive electrodes and a plurality of negative electrodes are stacked with a separator in between, or a wound type in which the positive electrode and negative electrode are wound in a stacked state with a separator in between. The non-aqueous electrolyte exists contained within the positive electrode, negative electrode, and separator. Below, as an example of an energy storage element, the configuration of a non-aqueous electrolyte secondary battery (hereinafter also simply referred to as a "secondary battery") will be described.

[0038] Figure 1 shows a schematic cross-sectional view of a secondary battery 10 according to one embodiment of the present invention. The secondary battery 10 in Figure 1 comprises a positive electrode 11, a negative electrode 12, and a separator 18. Note that in the secondary battery 10 of Figure 1, components other than the positive electrode 11 and negative electrode 12 (non-aqueous electrolyte, container, etc.) are omitted from the description. The positive electrode 11 and the negative electrode 12 are arranged facing each other, at least in part, via the separator 18.

[0039] The positive electrode 11 comprises a positive electrode substrate 13, a positive electrode active material layer 14, and an insulating layer 15. The positive electrode substrate 13 is a conductive film-like or plate-like substrate. The positive electrode active material layer 14 is laminated on both sides of the positive electrode substrate 13 (the upper and lower surfaces in Figure 1), leaving an uncoated portion P. The uncoated portion P is one end of the positive electrode substrate 13 (the right side in Figure 1). In other words, the positive electrode active material layer 14 is laminated on both sides of the positive electrode substrate 13 in the region X of the positive electrode 11 where the negative electrode 12 faces. The region X of the positive electrode 11 where the negative electrode 12 faces may be the region where the positive electrode 11 substantially overlaps with the negative electrode 12 when viewed in the thickness direction of the positive electrode (viewed in the vertical direction in Figure 1). Region X is the region other than the uncoated portion P. The uncoated portion P is the part that is electrically connected to a positive electrode terminal or the like (not shown).

[0040] In the region X where the negative electrode 12 of the positive electrode 11 faces, the insulating layer 15 covers a laminated structure Y including the positive electrode substrate 13 and the positive electrode active material layer 14. In this embodiment, the laminated structure Y including the positive electrode substrate 13 and the positive electrode active material layer 14 is a three-layer structure composed of the positive electrode substrate 13 and the positive electrode active material layers 14 laminated on both sides of the positive electrode substrate 13. In this embodiment, the portion of the three-layer structure (laminated structure Y) composed of the positive electrode substrate 13 and the two positive electrode active material layers 14 is the region where the negative electrode 12 of the positive electrode faces. This laminated structure Y is covered by the insulating layer 15, including its sides. That is, the left end face of the positive electrode substrate 13 in Figure 1 is also covered by the insulating layer 15, and the left and right end faces of the positive electrode active material layer 14 in Figure 1 are also covered by the insulating layer 15. Thus, in the region X where the negative electrode 12 of the positive electrode 11 faces, the insulating layer 15 is the outermost layer. In other words, in the region X of the positive electrode 11 facing the negative electrode 12, the positive electrode substrate 13 and the positive electrode active material layer 14 are not exposed. Furthermore, all surfaces of the positive electrode substrate 13 are not exposed except for the uncoated portion P that does not face the negative electrode 12. Also, all surfaces of the positive electrode active material layer 14 are not exposed.

[0041] In other embodiments of the present invention, an insulating layer may be provided in the region of the positive electrode that does not face the negative electrode. Alternatively, a positive electrode active material layer may be provided in the region of the positive electrode that does not face the negative electrode, and the positive electrode active material layer provided in the region of the positive electrode that does not face the negative electrode may or may not be covered by an insulating layer.

[0042] The negative electrode 12 comprises a negative electrode substrate 16 and a negative electrode active material layer 17. The negative electrode substrate 16 is a conductive film-like or plate-like substrate. The negative electrode active material layer 17 is laminated on both sides of the negative electrode substrate 16 (the upper and lower surfaces in Figure 1), leaving an uncoated area Q. The uncoated area Q is one end of the negative electrode substrate 16 (the left side in Figure 1) and is a region that does not face the positive electrode 11. In other words, the negative electrode active material layer 17 is laminated on both sides of the negative electrode substrate 16 in the region of the negative electrode 12 that faces the positive electrode 11. The uncoated area Q is a portion that is electrically connected to a negative electrode terminal or the like (not shown).

[0043] In one embodiment of the present invention, the surface potential of the insulating layer 15 of the secondary battery 10 is 3.4V vs. Li / Li + Lower. The potential on the surface of the insulating layer 15 is 3V vs. Li / Li + A lower voltage is preferable, 2.5V vs. Li / Li + A lower value is preferable. The potential on the surface of the insulating layer 15 is 0V vs. Li / Li + That's all.

[0044] The following describes in detail the various components of a secondary battery according to one embodiment of the energy storage element of the present invention.

[0045] (positive electrode) The positive electrode comprises a positive electrode substrate, a positive electrode active material layer disposed directly on the positive electrode substrate or via an intermediate layer, and an insulating layer.

[0046] As the material for the positive electrode substrate, metals such as aluminum, titanium, tantalum, and stainless steel, or alloys thereof, can be used. Among these, aluminum or aluminum alloys are preferred from the viewpoint of high potential resistance, high conductivity, and cost. Examples of positive electrode substrates include foil and vapor-deposited film, with foil being preferred from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferred as the positive electrode substrate. Examples of aluminum or aluminum alloys include A1085 and A3003 as specified in JIS-H-4000 (2014).

[0047] 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 unit volume of the secondary battery. "Average thickness" refers to the value obtained by dividing the punched mass when punching out a predetermined area of ​​substrate by the true density of the substrate and the punched area. The "average thickness" of the negative electrode substrate is defined similarly.

[0048] The intermediate layer is a layer placed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer reduces the contact resistance between the positive electrode substrate and the positive electrode active material layer by containing conductive particles such as carbon particles. The composition of the intermediate layer is not particularly limited and may include, for example, a resin binder and conductive particles.

[0049] The positive electrode active material layer contains the positive electrode active material. The positive electrode active material layer may optionally contain conductive agents, binders, thickeners, fillers, and other optional components.

[0050] The positive electrode active material can be appropriately selected from known positive electrode active materials. For lithium-ion secondary batteries, a material capable of intercalating and releasing lithium ions is usually used as the positive electrode active material. As for the positive electrode active material, a potential of 3.4V vs. Li / Li in the charged state (SOC 100%) is used. + Furthermore, 4.0V vs. Li / Li +The above is preferable from the viewpoint of achieving high energy density. Examples of 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, etc. Examples of lithium transition metal composite oxides having an α-NaFeO2 type crystal structure include Li[Li x Ni 1-x ]O2(0≦x<0.5), Li[Li x Ni γ Co 1-x-γ ]O2(0≦x<0.5, 0<γ<1), Li[Li x Co 1-x ]O2(0≦x<0.5), Li[Li x Ni γ Mn 1-x-γ ]O2(0≦x<0.5, 0<γ<1), Li[Li x Ni γ Mn β Co 1-x-γ-β ]O2(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 Examples include ]O2 (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1). As a lithium transition metal oxide having a spinel-type crystal structure, Li x Mn2O4,Li x Ni γ Mn 2-γ Examples include O4. Examples of polyanion compounds include LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, Li2CoPO4F, etc. Examples of chalcogen compounds include titanium disulfide, molybdenum disulfide, molybdenum dioxide, etc. Some atoms or polyanions in these materials may be substituted with atoms or anions of other elements. The surfaces of these materials may be coated with other materials. In the positive electrode active material layer, one of these materials may be used alone, or two or more may be used in mixture form.

[0051] The positive electrode active material is usually in the form of particles (powder). The average particle size of the positive electrode active material is preferably, for example, 0.1 μm or more and 20 μm or less. Setting the average particle size of the positive electrode active material above the lower limit makes it easier to manufacture or handle the positive electrode active material. Setting the average particle size of the positive electrode active material below the upper limit improves the electronic conductivity of the positive electrode active material layer. When a composite material of the positive electrode active material and other materials is used, the average particle size of the composite material is used as the average particle size of the positive electrode active material. "Average particle size" refers to the value at which the volume-based integrated distribution calculated in accordance with JIS-Z-8819-2 (2001), based on the particle size distribution measured by laser diffraction / scattering method on a dilution of particles diluted with a solvent, in accordance with JIS-Z-8825 (2013), becomes 50%.

[0052] To obtain powder with a predetermined particle size, grinders and classifiers are used. Examples of grinding methods include using mortars, ball mills, sand mills, vibrating ball mills, planetary ball mills, jet mills, counterjet mills, swirling airflow jet mills, or sieves. Wet grinding, which involves the coexistence of water or organic solvents such as hexane, can also be used during grinding. For classification, sieves and wind classifiers are used as needed, both dry and wet.

[0053] The content of the positive electrode active material in the positive electrode active material layer is preferably 50% to 99% by mass, more preferably 70% to 98% by mass, and even more preferably 80% to 95% by mass. 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 in the positive electrode active material layer.

[0054] The conductive agent is not particularly limited as long as it is a material that has electrical conductivity. Examples of such conductive agents include carbonaceous materials, metals, and conductive ceramics. Examples of carbonaceous materials include graphitized carbon, 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 can take the form of powder or fiber. One of these materials may be used alone as the conductive agent, or two or more may be used in mixture form. These materials may also be used in composite form. For example, a composite material of carbon black and CNTs may be used. Among these, carbon black is preferred from the viewpoint of electronic conductivity and coating properties, and acetylene black is particularly preferred.

[0055] 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, and 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.

[0056] 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.

[0057] The binder content in the positive electrode active material layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. By keeping the binder content within the above range, the active material can be stably maintained.

[0058] Examples of thickening agents include polysaccharide polymers such as carboxymethylcellulose (CMC) and methylcellulose. If the thickening agent has a functional group that reacts with lithium or the like, this functional group may be deactivated beforehand by methylation or the like.

[0059] The filler is not particularly limited. Examples of fillers include polyolefins such as polypropylene and polyethylene; inorganic oxides such as silicon dioxide, aluminum oxide, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates; 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; mineral resource-derived materials such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof.

[0060] The positive electrode active material layer may contain typical nonmetallic 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] (Insulating layer) The insulating layer covers the laminated structure, which includes the positive electrode substrate and the positive electrode active material layer, in the region of the positive electrode where the negative electrode faces. The insulating layer is usually porous.

[0062] The insulating layer typically contains particles and a binder.

[0063] The above particles are preferably insulating particles. Examples of insulating particles include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, barium titanate, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and 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 and barium fluoride; and particles of mineral resources or artificial products thereof such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica. In addition, resin particles may also be used as insulating particles.

[0064] The above-mentioned particles are preferably inorganic particles. Examples of inorganic particles include the oxides, hydroxides, nitrides, carbonates, sulfates, flame-retardant ionic crystals, mineral resource-derived materials, or artificial products thereof.

[0065] As the above particles, insulating inorganic particles are more preferred, and silicon dioxide, aluminum oxide, and aluminosilicates are even more preferred.

[0066] The particle content in the insulating layer is preferably 50% to 99% by mass, more preferably 60% to 98% by mass, and even more preferably 65% ​​to 97% by mass. By setting the particle content within the above range, sufficient insulating properties can be achieved.

[0067] As the binder for the insulating layer, those exemplified as the binder for the positive electrode active material layer can be used. The binder content in the insulating layer is preferably 1% by mass or more and 50% by mass or less, more preferably 2% by mass or more and 40% by mass or less, and even more preferably 3% by mass or more and 35% by mass or less. By setting the binder content within the above range, it is possible to stably hold particles while maintaining a good porous state.

[0068] The average thickness of the insulating layer is preferably greater than the thickness of the separator. This allows for a more effective suppression of the dissolution of fine copper powder. The average thickness of the insulating layer is preferably 3 μm to 50 μm, and more preferably 6 μm to 30 μm. By setting the average thickness of the insulating layer within the above range, sufficient insulation and thinness can be achieved simultaneously. Furthermore, by giving the insulating layer an appropriate thickness, the amount of fine copper powder mixed in that reaches the surface of the positive electrode active material layer can be sufficiently reduced. Note that the "average thickness of the insulating layer" is the average value of any three points observed in the cross-section using an electron microscope image.

[0069] The resistivity of the insulating layer is preferably greater than that of the separator. This allows for a more effective suppression of the dissolution of the fine copper powder. The resistance of the insulating layer is 1 × 10¹³ Ωcm. 2 The above is preferable, and 1 × 10¹⁴ Ωcm 2 The above is more preferable. By setting the resistance of the insulating layer to above the lower limit, sufficient insulation can be obtained. A higher resistance of the insulating layer is preferable, and there is no particular upper limit, but for example, 1 × 10¹⁶ Ωcm 2 The following is also acceptable. Note that "resistance" refers to the DC resistance value obtained by multiplying the DC resistance value when the object being measured is sandwiched between metal plates by the area of ​​the region where the DC resistance value was measured. The same definition applies when using "resistivity" for other materials, etc.

[0070] (Separator) The separator can be appropriately selected from known separators. Examples of separators include a separator consisting only of a base layer, or a separator in which a heat-resistant layer containing heat-resistant particles and a binder is formed on one or both sides of the base layer. Examples of the base layer shape of the separator include woven fabric, nonwoven fabric, and porous resin film. Among these shapes, porous resin film is preferred from the viewpoint of strength, and nonwoven fabric is preferred from the viewpoint of liquid retention of non-aqueous electrolytes. As for the material of the base layer of the separator, polyolefins such as polyethylene and polypropylene are preferred from the viewpoint of shutdown function, and polyimide and aramid are preferred from the viewpoint of oxidative degradation resistance. A composite material of these resins may also be used as the base layer of the separator.

[0071] The heat-resistant particles contained in the heat-resistant layer preferably have a mass reduction of 5% or less when heated from room temperature to 500°C in an air atmosphere of 1 atmosphere, and more preferably have a mass reduction of 5% or less when heated from room temperature to 800°C. Inorganic compounds are examples of materials with a mass reduction of less than or equal to the specified amount. Examples of inorganic compounds include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, barium titanate, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates; 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 and barium fluoride; covalent crystals such as silicon and diamond; mineral resource-derived materials such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof. These inorganic compounds may be used individually or in combination, or two or more may be used as a mixture. Among these inorganic compounds, silicon dioxide, aluminum oxide, or aluminosilicates are preferred from the viewpoint of safety for energy storage elements.

[0072] The porosity of the separator is preferably 80 volume% or less from the viewpoint of strength, and preferably 20 volume% or more from the viewpoint of discharge performance. Here, "porosity" refers to a volume-based value and means the measurement value obtained using a mercury porosimeter.

[0073] A polymer gel composed of a polymer and a non-aqueous electrolyte may be used as a separator. Examples of polymers include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, and polyvinylidene fluoride. Using a polymer gel has the effect of suppressing leakage. A polymer gel may also be used in combination with a porous resin film or nonwoven fabric as described above as a separator.

[0074] The thickness of the separator is preferably less than the average thickness of the insulating layer. The separator thickness is preferably 1 μm to 40 μm, and more preferably 3 μm to 20 μm. By setting the separator thickness within the above range, it is possible to achieve both sufficient insulation and a thin profile.

[0075] The resistivity of the separator is preferably lower than that of the insulating layer. This allows for more effective suppression of the dissolution of the fine copper powder. The separator's resistance is 1 × 10¹² Ωcm. 2 The above is preferable, and 1 × 10¹³ Ωcm 2 The above is more preferable. By setting the resistivity of the separator to above the lower limit, sufficient insulation can be obtained. The resistance of the separator is preferably as large as possible, as long as it does not exceed the resistivity of the insulating layer. There is no particular upper limit, but for example, 1 × 10¹⁵ Ωcm 2 The following may also be true: 1 × 10¹⁴ Ωcm 2 The following limits may also be applied. By keeping the resistivity of the separator below the above upper limit, it becomes easier to maintain the effect of suppressing the dissolution of the copper fine powder even if the insulating layer deteriorates and its resistivity decreases.

[0076] (Negative electrode) The negative electrode comprises a negative electrode substrate and a negative electrode active material layer disposed directly on the negative electrode substrate 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 in the positive electrode.

[0077] The negative electrode substrate is electrically conductive. The negative electrode substrate can be made from metals such as copper, nickel, stainless steel, nickel-plated steel, or aluminum, or alloys thereof. It is preferable that the negative electrode substrate contains copper. For example, the copper content in the negative electrode substrate is preferably 50% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and even more preferably 99% by mass or more. The copper content in the negative electrode substrate may be 100% by mass or less. In other words, copper or copper alloys are preferred as the material of the negative electrode substrate. Examples of negative electrode substrates include foil and vapor-deposited films, with foil being preferred from a cost viewpoint. Therefore, copper foil or copper alloy foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0078] 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, it is possible to increase the strength of the negative electrode substrate while increasing the energy density per unit volume of the secondary battery.

[0079] The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer optionally contains conductive agents, binders, thickeners, fillers, and other optional components. These optional components can be selected from the materials exemplified above for the positive electrode.

[0080] The negative electrode active material layer may contain typical nonmetallic 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 metallic 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.

[0081] The negative electrode active material can be appropriately selected from known negative electrode active materials. For lithium-ion secondary batteries, materials that can intercept and release lithium ions are usually used as negative electrode active materials. As for the negative electrode active material, a potential of 3.4V vs. Li / Li in the discharge state (SOC 0%) is used. + A lower value is preferable in terms of achieving higher energy density and suppressing the dissolution of fine copper powder. Examples of negative electrode active materials include metallic Li; metals or metalloids such as Si and Sn; metal oxides or metalloid oxides such as Si oxide, Ti oxide, and Sn oxide; and Li4Ti5O 12 LiTiO 2、 Examples of materials include titanium-containing oxides such as TiNb2O7; polyphosphate compounds; silicon carbide; and carbon materials such as graphite and non-graphitizable carbon (easily graphitizable carbon or poorly graphitizable carbon). Among these materials, graphite and non-graphitizable 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 mixture form.

[0082] "Graphite" refers to the average lattice plane spacing (d) of the (002) plane, determined by X-ray diffraction before charging or discharging, or during the discharge state. 002 ) refers to carbon materials with a n-scale between 0.33 nm and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite. Artificial graphite is preferred from the standpoint of obtaining materials with stable physical properties.

[0083] "Non-graphite carbon" refers to the average lattice plane spacing (d) of the (002) plane, which is determined by X-ray diffraction before charging or during the discharge state. 002 This refers to carbon materials with a nautical radius of 0.34 nm or more and 0.42 nm or less. Non-graphitized carbons include poorly graphitizable carbons and easily graphitizable carbons. Examples of non-graphitized carbons include resin-derived materials, petroleum pitch or materials derived from petroleum pitch, petroleum coke or materials derived from petroleum coke, plant-derived materials, and alcohol-derived materials.

[0084] Here, the "discharge state" in the definition of graphite and non-graphite carbon refers to a state in a monoelectrode battery where the open-circuit voltage is 0.7V or higher, using a carbon material as the negative electrode active material as the working electrode and metallic Li as the counter electrode. Since the potential of the metallic Li counter electrode in the open-circuit state is approximately equal to the oxidation-reduction potential of Li, the open-circuit voltage in the above monoelectrode battery is approximately equivalent to the potential of the carbon material-containing negative electrode relative to the oxidation-reduction potential of Li. In other words, an open-circuit voltage of 0.7V or higher in the above monoelectrode battery means that sufficient lithium ions that can be intercepted and released during charging and discharging are being released from the carbon material, which is the negative electrode active material.

[0085] "Non-graphitizable carbon" refers to the above d 002 This refers to carbon materials with a wavelength between 0.36 nm and 0.42 nm.

[0086] "Easily graphitizable carbon" refers to the above d 002 This refers to carbon materials with a wavelength of 0.34 nm or more and less than 0.36 nm.

[0087] The negative electrode active material is usually in the form of particles (powder). The average particle size of the negative electrode active material can be, for example, between 1 nm and 100 μm. If the negative electrode active material is, for example, a carbon material, an average particle size of 1 μm or more and 100 μm may be preferable. If the negative electrode active material is a metal, metalloid, metal oxide, metalloid oxide, titanium-containing oxide, polyphosphate compound, etc., an average particle size of 1 nm or more and 1 μm may be preferable. Setting the average particle size of the negative electrode active material above the lower limit above makes the manufacturing or handling of the negative electrode active material easier. Setting the average particle size of the negative electrode active material below the upper limit above improves the electronic conductivity of the active material layer. To obtain powder with a predetermined particle size, a pulverizer or classifier is used. The pulverizing method and powder grading method can be selected from, for example, the methods exemplified above for the positive electrode.

[0088] The content of the negative electrode active material in the negative electrode active material layer is preferably 60% by mass or more and 99% by mass or less, and more preferably 90% by mass or more and 98% by mass or less. By setting the content of the negative electrode active material within the above range, it is possible to achieve both high energy density and manufacturability in the negative electrode active material layer.

[0089] (Non-aqueous electrolytes) As the non-aqueous electrolyte, it can be appropriately selected from known non-aqueous electrolytes. A non-aqueous electrolyte solution may be used as the non-aqueous electrolyte. The non-aqueous electrolyte solution contains a non-aqueous solvent and an electrolyte salt dissolved in this non-aqueous solvent.

[0090] As the non-aqueous solvent, it can be appropriately selected from known non-aqueous solvents. Examples of non-aqueous solvents include cyclic carbonates, linear carbonates, carboxylic acid esters, phosphate esters, sulfonic acid esters, ethers, amides, and nitriles. As the non-aqueous solvent, compounds in which some of the hydrogen atoms contained in these compounds are substituted with halogens may also be used.

[0091] 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, and 1,2-diphenylvinylene carbonate. Among these, EC is preferred.

[0092] Examples of linear carbonates include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, trifluoroethyl methyl carbonate, and bis(trifluoroethyl) carbonate. Among these, EMC is preferred.

[0093] It is preferable to use a cyclic carbonate or a linear carbonate as the non-aqueous solvent, and it is more preferable to use a cyclic carbonate and a linear carbonate in combination. Using a cyclic carbonate can promote the dissociation of the electrolyte salt and improve the ionic conductivity of the non-aqueous electrolyte. Using a linear carbonate can keep the viscosity of the non-aqueous electrolyte low. When using a cyclic carbonate and a linear carbonate in combination, the volume ratio of the cyclic carbonate to the linear carbonate (cyclic carbonate:linear carbonate) is preferably in the range of 5:95 to 50:50.

[0094] The electrolyte salt can be appropriately selected from known electrolyte salts. Examples of electrolyte salts include lithium salts, sodium salts, potassium salts, magnesium salts, and onium salts. Among these, lithium salts are preferred.

[0095] Examples of lithium salts include inorganic lithium salts such as LiPF6, LiPO2F2, LiBF4, LiClO4, and LiN(SO2F)2, and lithium salts having halogenated hydrocarbon groups 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.

[0096] The electrolyte salt content in the non-aqueous electrolyte is 0.1 mol / dm³. 3 More than 2.5mol / dm 3 Preferably, it is 0.3 mol / dm³ 3 More than 2.0mol / dm 3 It is more preferable that it be less than or equal to 0.5 mol / dm 3 More than 1.7mol / dm 3 It is even more preferable that the following is the case: 0.7 mol / dm 3 More than 1.5mol / dm 3 The following is particularly preferable. By setting the electrolyte salt content within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

[0097] Non-aqueous electrolytes may contain additives. Examples of additives include aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partially halides of the aforementioned 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; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, and cyclo Examples include hexahexanedicarboxylic acid anhydride; 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, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakithrimethylsilyl titanate, etc. These additives may be used individually or in combination of two or more.

[0098] The additive content in the non-aqueous electrolyte is preferably 0.01% to 10% by mass relative to the total mass of the non-aqueous electrolyte, more preferably 0.1% to 7% by mass, even more preferably 0.2% to 5% by mass, and particularly preferably 0.3% to 3% by mass. By setting the additive content within the above range, it is possible to improve the capacity retention performance or cycle performance after high-temperature storage, and to further improve safety.

[0099] For the non-aqueous electrolyte, a solid electrolyte may be used, or a non-aqueous electrolyte and a solid electrolyte may be used in combination.

[0100] The solid electrolyte can be selected from any material that has ionic conductivity, such as lithium, sodium, and calcium, and is solid at room temperature (e.g., 15°C to 25°C). Examples of solid electrolytes include sulfide solid electrolytes, oxide solid electrolytes, oxynitride solid electrolytes, and polymer solid electrolytes.

[0101] Examples of sulfide solid electrolytes in lithium-ion secondary batteries include Li2S-P2S5, LiI-Li2S-P2S5, and Li 10 Ge-P2S 12 These are some examples.

[0102] The shape of the energy storage element in this embodiment is not particularly limited, and examples include cylindrical batteries, prismatic batteries, flat batteries, coin-type batteries, button-type batteries, and the like.

[0103] Figure 7 shows an example of a rectangular battery, specifically an energy storage element 40. Note that this figure is a transparent view of the inside of the container. An electrode body 41, having a wound positive and negative electrode, is housed in a rectangular container 42. The positive electrode is electrically connected to the positive electrode terminal 44 via a positive electrode lead 43. The negative electrode is electrically connected to the negative electrode terminal 46 via a negative electrode lead 45.

[0104] <Energy storage device> The energy storage element of this embodiment can be mounted as an energy storage unit (battery module) composed of multiple energy storage elements 40 in power supplies for vehicles such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), power supplies for electronic devices such as personal computers and communication terminals, or power storage devices. In this case, it is sufficient that the technology of the present invention is applied to at least one of the energy storage elements included in the energy storage device.

[0105] Figure 8 shows an example of a power storage device 60 which is formed by further assembling power storage units 50, each of which is a collection of two or more electrically connected power storage elements 40. The power storage device 60 may include busbars (not shown) for electrically connecting two or more power storage elements 40, busbars (not shown) for electrically connecting two or more power storage units 50, etc. The power storage unit 50 or the power storage device 60 may include a condition monitoring device (not shown) for monitoring the state of one or more power storage elements.

[0106] <Manufacturing method for energy storage elements> The method for manufacturing the energy storage element of this embodiment can be appropriately selected from known methods. The manufacturing method includes, for example, preparing an electrode body, preparing a non-aqueous electrolyte, and housing the electrode body and the non-aqueous electrolyte in a container. Preparing the electrode body includes, for example, preparing a positive electrode and a negative electrode, and forming the electrode body by stacking or winding the positive electrode and the negative electrode.

[0107] The method for housing the non-aqueous electrolyte in a container can be appropriately selected from known methods. For example, when using a non-aqueous electrolyte solution, the non-aqueous electrolyte solution can be injected through an inlet formed in the container, and then the inlet can be sealed.

[0108] <Other Embodiments> The energy storage element of the present invention is not limited to the embodiments described above, and various modifications may be made without departing from the spirit of the invention. For example, the configuration of one embodiment may be added to the configuration of another embodiment, and a part of the configuration of one embodiment may be replaced with the configuration of another embodiment or with well-known technology. Furthermore, a part of the configuration of one embodiment may be deleted. Also, well-known technology may be added to the configuration of one embodiment.

[0109] In the embodiments described above, the focus was on cases where the energy storage element is used as a rechargeable non-aqueous electrolyte secondary battery (e.g., a lithium-ion secondary battery), but the type, shape, dimensions, and capacity of the energy storage element are arbitrary. The present invention can also be applied to various secondary batteries, electric double-layer capacitors, or capacitors such as lithium-ion capacitors.

[0110] In one embodiment of the present invention, the negative electrode may further have an insulating layer covering the negative electrode active material layer. Also, in one embodiment of the present invention, the potential of the surface of the insulating layer of the positive electrode is 3.4V vs. Li / Li + If the potential is lower, a separator may be provided between the positive and negative electrodes, and the surface of the insulating layer of the positive electrode may not be in direct contact with the surface of the negative electrode. When a separator is provided, it is preferable to use a separator with relatively low volume resistivity and relatively thin thickness, as this can lower the potential of the surface of the insulating layer of the positive electrode. Alternatively, when a separator is provided, it is also preferable to use an insulating layer with relatively high volume resistivity and relatively thick thickness, as this can lower the potential of the surface of the insulating layer of the positive electrode.

[0111] Furthermore, the positive electrode active material layer may be laminated on only one side of the positive electrode substrate, and the negative electrode active material layer may be laminated on only one side of the negative electrode substrate. Also, the laminated structure including the positive electrode substrate and the positive electrode active material layer that is covered by the insulating layer is not limited to being composed only of the positive electrode substrate and the positive electrode active material layer. The above laminated structure may have, for example, an intermediate layer provided between the positive electrode substrate and the positive electrode active material layer.

[0112] In one embodiment of the present invention, the insulating layer of the positive electrode is insulating, and the potential of the insulating layer of the positive electrode is 3.4 vs. Li / Li + If the voltage is low enough, the insulating layer of the positive electrode may be a layer made of a solid electrolyte. In other words, the insulating layer of the positive electrode may be ionic conductive as long as it has the property of insulating electricity. Also, if the insulating layer of the positive electrode is a layer made of a solid electrolyte, the energy storage element may be an all-solid-state battery. [Explanation of symbols]

[0113] 10. Secondary batteries (energy storage elements) 11 Positive electrode 12 Negative electrode 13 Positive electrode substrate 14 Cathode active material layer 15. Insulating layer 16. Negative electrode substrate 17 Negative electrode active material layer 18 Separator 20, 30 energy storage elements 21, 31 Cathode active material layer 22, 32 Insulating layer 23, 33 positive electrode 24, 34 Negative electrode active material layer 25, 35 negative electrode 26 Separators A. Fine copper powder P, Q Uncovered parts X Region of the positive electrode where the negative electrode faces the positive electrode. Y Laminated structure including positive electrode substrate and positive electrode active material layer 40 Energy storage elements 41 Electrode body 42 Container 43 Positive lead 44 Positive terminal 45 Negative lead 46 Negative terminal 50 Energy Storage Units 60 Energy storage devices

Claims

1. A positive electrode having a conductive positive electrode substrate, a positive electrode active material layer, and an insulating layer, A negative electrode is disposed opposite the positive electrode and has a conductive negative electrode substrate and a negative electrode active material layer. A separator is placed between the positive electrode and the negative electrode. Non-aqueous electrolytes and Equipped with, In the region of the positive electrode where the negative electrode faces, the insulating layer covers a laminated structure including the positive electrode substrate and the positive electrode active material layer. All surfaces of the positive electrode active material layer are covered by the insulating layer. The above negative electrode substrate contains copper, The positive electrode active material layer comprises a lithium transition metal composite oxide having an α-NaFeO2 type crystal structure, or a lithium transition metal oxide having a spinel type crystal structure. The potential on the surface of the above insulating layer is 3.4V vs. Li / Li ＋ A lower energy storage element (except in cases where the lithium difluorobisoxalate phosphate content in the above non-aqueous electrolyte is 0.2% by mass or more and 1% by mass or less).

2. A positive electrode having a conductive positive electrode substrate, a positive electrode active material layer, and an insulating layer, A negative electrode is disposed opposite the positive electrode and has a conductive negative electrode substrate and a negative electrode active material layer. A separator is placed between the positive electrode and the negative electrode. Non-aqueous electrolytes and Equipped with, In the region of the positive electrode where the negative electrode faces, the insulating layer covers a laminated structure including the positive electrode substrate and the positive electrode active material layer. All surfaces of the positive electrode active material layer are covered by the insulating layer. The above negative electrode substrate contains copper, The potential on the surface of the above insulating layer is 3.4V vs. Li / Li ＋ A lower energy storage element (except when the positive electrode active material layer contains a phosphorylated compound with an olivine structure represented by the general formula Li z Fe 1-y X y PO 4 (0 ≤ y ≤ 0.3, 0 < z ≤ 1) (X = one of the metals Nb, Mg, Ti, Zr, Ta, W, Mn, Ni, and Co), and when the lithium difluorobisoxalate phosphate content in the non-aqueous electrolyte is 0.2% by mass or more and 1% by mass or less).

3. A positive electrode having a conductive positive electrode substrate, a positive electrode active material layer, and an insulating layer, A negative electrode is disposed opposite the positive electrode and has a conductive negative electrode substrate and a negative electrode active material layer. A separator is placed between the positive electrode and the negative electrode. Non-aqueous electrolytes and Equipped with, In the region of the positive electrode where the negative electrode faces, the insulating layer covers a laminated structure including the positive electrode substrate and the positive electrode active material layer. All surfaces of the positive electrode active material layer are covered by the insulating layer. The porosity of the above separator is 80% by volume or less. The positive electrode active material layer comprises a lithium transition metal composite oxide having an α-NaFeO2 type crystal structure, or a lithium transition metal oxide having a spinel type crystal structure. The potential on the surface of the above insulating layer is 3.4V vs. Li / Li ＋ A lower energy storage element (except in cases where the lithium difluorobisoxalate phosphate content in the non-aqueous electrolyte is 0.2% by mass or more and 1% by mass or less).

4. A positive electrode having a conductive positive electrode substrate, a positive electrode active material layer, and an insulating layer, A negative electrode is disposed opposite the positive electrode and has a conductive negative electrode substrate and a negative electrode active material layer. A separator is placed between the positive electrode and the negative electrode. Non-aqueous electrolytes and Equipped with, In the region of the positive electrode where the negative electrode faces, the insulating layer covers a laminated structure including the positive electrode substrate and the positive electrode active material layer. All surfaces of the positive electrode active material layer are covered by the insulating layer. The porosity of the above separator is 80% by volume or less. The potential on the surface of the above insulating layer is 3.4V vs. Li / Li ＋ A lower energy storage element (except when the positive electrode active material layer contains a phosphorylated compound with an olivine structure represented by the general formula Li z Fe 1-y X y PO 4 (0 ≤ y ≤ 0.3, 0 < z ≤ 1) (X = one of the metals Nb, Mg, Ti, Zr, Ta, W, Mn, Ni, and Co), and when the lithium difluorobisoxalate phosphate content in the non-aqueous electrolyte is 0.2% by mass or more and 1% by mass or less).

5. A positive electrode having a conductive positive electrode substrate, a positive electrode active material layer, and an insulating layer, A negative electrode is disposed opposite the positive electrode and has a conductive negative electrode substrate and a negative electrode active material layer. A separator is placed between the positive electrode and the negative electrode. Non-aqueous electrolytes and Equipped with, In the region of the positive electrode where the negative electrode faces, the insulating layer covers a laminated structure including the positive electrode substrate and the positive electrode active material layer. The above negative electrode substrate contains copper, The potential on the surface of the above insulating layer is 3.4V vs. Li / Li ＋ Lower, energy storage element (However, this excludes cases where the insulating layer contains a bicarbonate, the average particle size of the bicarbonate is 2 μm or more and 20 μm or less, the content of the bicarbonate is 5% by volume or more and 80% by volume or less relative to the total volume of the insulating layer, and the thickness of the insulating layer is 4 μm or more and 40 μm or less; cases where the positive electrode active material layer contains a phosphorylated compound with an olivine structure represented by the general formula Li z Fe 1-y X y PO 4 (0 ≤ y ≤ 0.3, 0 < z ≤ 1) (X = one of the metals Nb, Mg, Ti, Zr, Ta, W, Mn, Ni, and Co); and cases where the content of lithium difluorobisoxalate phosphate in the non-aqueous electrolyte is 0.2% by mass or more and 1% by mass or less).

6. A positive electrode having a conductive positive electrode substrate, a positive electrode active material layer, and an insulating layer, A negative electrode is disposed opposite the positive electrode and has a conductive negative electrode substrate and a negative electrode active material layer. A separator is placed between the positive electrode and the negative electrode. Non-aqueous electrolytes and Equipped with, In the region of the positive electrode where the negative electrode faces, the insulating layer covers a laminated structure including the positive electrode substrate and the positive electrode active material layer. The above negative electrode active material layer contains a carbon material which is the negative electrode active material. The porosity of the above separator is 80% by volume or less. The potential on the surface of the above insulating layer is 3.4V vs. Li / Li ＋ Lower, energy storage element (However, this excludes cases where the insulating layer contains a bicarbonate, the average particle size of the bicarbonate is 2 μm or more and 20 μm or less, the content of the bicarbonate is 5% by volume or more and 80% by volume or less relative to the total volume of the insulating layer, and the thickness of the insulating layer is 4 μm or more and 40 μm or less; cases where the positive electrode active material layer contains a phosphorylated compound with an olivine structure represented by the general formula Li z Fe 1-y X y PO 4 (0 ≤ y ≤ 0.3, 0 < z ≤ 1) (X = one of the metals Nb, Mg, Ti, Zr, Ta, W, Mn, Ni, and Co); and cases where the content of lithium difluorobisoxalate phosphate in the non-aqueous electrolyte is 0.2% by mass or more and 1% by mass or less).

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