Nonaqueous electrolyte energy storage device and method for producing nonaqueous electrolyte energy storage device

Abstract

To provide a nonaqueous electrolyte element having low resistance and a high capacity retention rate after a charge / discharge cycle, and to provide a method of manufacturing such a nonaqueous electrolyte power storage element.SOLUTION: A nonaqueous electrolyte energy storage device according to one aspect of the present invention includes a positive electrode having a positive electrode active material and a negative electrode having a negative electrode active material, wherein the positive electrode active material contains at least one selected from the group consisting of a lithium transition metal compound having an olivine crystal structure and a lithium transition metal composite oxide having a spinel crystal structure, at least a part of a surface of the positive electrode active material is covered with a positive electrode covering layer, at least a part of a surface of the negative electrode active material is covered with a negative electrode covering layer, and the positive electrode covering layer and the negative electrode covering layer contain the same kind of element M.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a nonaqueous electrolyte electricity storage element and a method for manufacturing 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, as well as automobiles. Non-aqueous electrolyte secondary batteries generally have 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. Other non-aqueous electrolyte energy storage elements besides non-aqueous electrolyte secondary batteries include capacitors such as lithium ion capacitors and electric double layer capacitors.

[0003] As examples of non-aqueous electrolyte storage elements, Patent Document 1 describes a lithium secondary battery using lithium iron phosphate as the positive electrode active material, and Patent Document 2 describes a lithium ion battery using lithium manganese oxide as the positive electrode active material. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-215977 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-115610 Summary of the Invention [Problem to be solved by the invention]

[0005] In lithium iron phosphate, lithium manganese oxide, etc., transition metal elements are likely to leach into the non-aqueous electrolyte with repeated charge and discharge cycles, and therefore non-aqueous electrolyte storage elements using such positive electrode active materials have the disadvantage of being prone to an increase in resistance and a decrease in discharge capacity with repeated charge and discharge cycles.

[0006] An object of the present invention is to provide a nonaqueous electrolyte storage element that uses a predetermined positive electrode active material and has low resistance and a high capacity retention rate after charge / discharge cycling, and a method for producing such a nonaqueous electrolyte storage element. [Means for solving the problem]

[0007] A nonaqueous electrolyte storage element according to one embodiment of the present invention includes a positive electrode having a positive electrode active material and a negative electrode having a negative electrode active material, wherein the positive electrode active material contains at least one selected from the group consisting of lithium transition metal compounds having an olivine-type crystal structure and lithium transition metal composite oxides having a spinel-type crystal structure, at least a portion of the surface of the positive electrode active material is coated with a positive electrode coating layer, and at least a portion of the surface of the negative electrode active material layer is coated with a negative electrode coating layer, and the positive electrode coating layer and the negative electrode coating layer contain the same type of element M.

[0008] A method for producing a nonaqueous electrolyte storage element according to another embodiment of the present invention includes: preparing a positive electrode having a positive electrode active material, at least a portion of whose surface is coated with a positive electrode coating layer containing element M; preparing a negative electrode having a negative electrode active material; assembling an uncharged / discharged nonaqueous electrolyte storage element including the positive electrode and the negative electrode; and initially charging the uncharged / discharged nonaqueous electrolyte storage element to form a negative electrode coating layer that coats at least a portion of the surface of the negative electrode active material and contains element M, wherein the positive electrode active material comprises at least one selected from the group consisting of lithium transition metal compounds having an olivine-type crystal structure and lithium transition metal composite oxides having a spinel-type crystal structure. [Effects of the Invention]

[0009] According to any one aspect of the present invention, it is possible to provide a nonaqueous electrolyte storage element that uses a predetermined positive electrode active material and has low resistance and a high capacity retention rate after charge-discharge cycles, and a method for manufacturing such a nonaqueous electrolyte storage element. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a perspective view showing a nonaqueous electrolyte electricity storage element according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing an electricity storage device including a plurality of nonaqueous electrolyte electricity storage elements according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] First, an outline of the nonaqueous electrolyte storage element and the method for manufacturing the nonaqueous electrolyte storage element disclosed in this specification will be described.

[0012] [1] A nonaqueous electrolyte storage element according to one embodiment of the present invention includes a positive electrode having a positive electrode active material and a negative electrode having a negative electrode active material, wherein the positive electrode active material contains at least one selected from the group consisting of lithium transition metal compounds having an olivine-type crystal structure and lithium transition metal composite oxides having a spinel-type crystal structure, at least a portion of the surface of the positive electrode active material is coated with a positive electrode coating layer, and at least a portion of the surface of the negative electrode active material is coated with a negative electrode coating layer, and the positive electrode coating layer and the negative electrode coating layer contain the same element M.

[0013] The nonaqueous electrolyte storage element described in [1] above is a nonaqueous electrolyte storage element that uses a predetermined positive electrode active material and exhibits low resistance and high capacity retention after charge / discharge cycling. While the reason for this effect is unclear, the following reason is presumed. In conventional nonaqueous electrolyte storage elements that use at least one selected from the group consisting of lithium transition metal compounds having an olivine-type crystal structure and lithium transition metal composite oxides having a spinel-type crystal structure as the positive electrode active material, it is believed that transition metal elements leach from the positive electrode active material into the nonaqueous electrolyte with repeated charge / discharge cycles, and these leachable transition metal elements precipitate on the surface of the negative electrode active material layer, resulting in an increase in resistance and a decrease in capacity. In contrast, in the nonaqueous electrolyte storage element described in [1] above, at least a portion of the surface of the negative electrode active material is coated with a negative electrode coating layer, thereby suppressing the precipitation of transition metal elements leachable from the positive electrode active material into the nonaqueous electrolyte onto the surface of the negative electrode active material. In addition, because at least a portion of the surface of the positive electrode active material is coated with the positive electrode coating layer, the elution of transition metal elements in the positive electrode active material into the non-aqueous electrolyte can be suppressed. Furthermore, the negative electrode coating layer contains the same element M as the element M contained in the positive electrode coating layer. Such a negative electrode coating layer is efficiently formed during initial charging by element M eluting from the positive electrode coating layer into the non-aqueous electrolyte and depositing on the surface of the negative electrode active material. The negative electrode coating layer formed by such an electrochemical reaction has relatively high lithium ion conductivity, and therefore can suppress a decrease in lithium ion conductivity in the negative electrode due to the formation of the negative electrode coating layer. For these reasons, the non-aqueous electrolyte storage element described in [1] above is a non-aqueous electrolyte storage element using a predetermined positive electrode active material, and is presumed to have low resistance and high capacity retention after charge / discharge cycling.

[0014] The compositions of the lithium transition metal compound and lithium transition metal composite oxide in this specification refer to those before charge and discharge, or, if contained in the positive electrode of a nonaqueous electrolyte storage element, those after treatment according to the following procedure. First, the nonaqueous electrolyte storage element is charged at a constant current of 0.05 C until the charge end voltage in normal use is reached, and the element is fully charged. After a 10-minute rest, the element is discharged at a constant current of 0.05 C until the discharge end voltage in normal use is reached. The element is disassembled, the positive electrode is removed, and a test battery is assembled using the removed positive electrode as the working electrode and a metallic lithium electrode as the counter electrode. Pure metallic lithium is used for the metallic lithium electrode. The test battery is charged at a current of 10 mA per 1 g of positive electrode active material until the positive electrode potential reaches 2.0 V (vs. Li / Li + ) or 3.0V (vs. Li / Li + ) and adjust the positive electrode to a fully discharged state. When the positive electrode active material is a lithium transition metal compound having an olivine crystal structure, the positive electrode potential is adjusted to 2.0 V (vs. Li / Li + ), and when the positive electrode active material is a lithium transition metal composite oxide having a spinel crystal structure, the positive electrode potential is 3.0 V (vs. Li / Li + ) and discharge at a constant current until the positive electrode potential reaches 3.0 V (vs. Li / Li). + ), and then perform constant current discharge until the positive electrode potential reaches 2.0 V (vs. Li / Li) after processing according to the procedure described below. If the result confirms that the positive electrode active material is a lithium transition metal compound having an olivine crystal structure, reassemble the test battery and measure the positive electrode potential until the positive electrode potential reaches 2.0 V (vs. Li / Li) +), and the resulting battery is treated according to the procedure described below for measurement. After adjusting the positive electrode to a fully discharged state using the procedure described above, the test battery is disassembled and the positive electrode is removed. The removed positive electrode is washed with dimethyl carbonate. The positive electrode active material layer is then peeled from the positive electrode substrate, and the positive electrode active material layer is washed with a solvent capable of dissolving the binder to remove the binder. The battery is then washed with water and dried under reduced pressure at room temperature for 24 hours to obtain a lithium transition metal compound and a lithium transition metal composite oxide. The obtained lithium transition metal compound and lithium transition metal composite oxide are then subjected to measurement. The operations from disassembling the nonaqueous electrolyte storage element to obtaining the lithium transition metal compound and lithium transition metal composite oxide are carried out in an argon atmosphere with a dew point of -60°C or below. Here, "normal use" refers to the case where the nonaqueous electrolyte storage element is used under the charge / discharge conditions recommended or specified for the nonaqueous electrolyte storage element, and, if equipment for using the nonaqueous electrolyte storage element is available, the nonaqueous electrolyte storage element is used using that equipment.

[0015] The crystal structure of lithium transition metal compounds and lithium transition metal composite oxides is determined by X-ray diffraction measurement. X-ray diffraction measurements of lithium transition metal compounds and lithium transition metal composite oxides are performed before charging and discharging, or on samples obtained after processing using the above-mentioned composition measurement procedures. Specifically, X-ray diffraction measurements are performed by powder X-ray diffraction using an X-ray diffractometer (Rigaku's "MiniFlex II") with a CuKα radiation source, a tube voltage of 30 kV, and a tube current of 15 mA. The diffracted X-rays pass through a 30 μm-thick Kβ filter and are detected by a high-speed one-dimensional detector (D / teX Ultra 2). The sampling width is 0.02°, the scan speed is 5° / min, the divergence slit width is 0.625°, the receiving slit width is 13 mm (open), and the scattering slit width is 8 mm.

[0016] The presence or absence of the positive electrode coating layer and the negative electrode coating layer and the qualitative analysis of the element M in these layers are performed by mass spectrometry using time-of-flight secondary ion mass spectrometry (TOF-SIMS). The above analysis is performed on the positive electrode active material or the negative electrode active material that has not been exposed to the atmosphere, in an environment that has not been exposed to the atmosphere, using the IONTOF "TOF-SIMS TOFSIMS.5" as the equipment used.

[0017] [2] In the nonaqueous electrolyte storage element according to [1] above, the element M may be at least one element selected from the group consisting of boron, magnesium, aluminum, phosphorus, titanium, niobium, and tungsten.

[0018] Boron, magnesium, aluminum, phosphorus, titanium, niobium, and tungsten are elements whose oxides have low electronic conductivity and high ionic conductivity. In the nonaqueous electrolyte energy storage element described in [2] above, when the element M contained in the positive electrode coating layer and the negative electrode coating layer is one of these elements, the resistance after charge-discharge cycles can be further reduced and the capacity retention rate can be further increased.

[0019] [3] In the nonaqueous electrolyte storage element according to [1] or [2] above, at least a part of the element M in the negative electrode coating layer may be present as a constituent element of an oxide containing the element M.

[0020] The nonaqueous electrolyte storage element described in [3] above can reduce the resistance after charge / discharge cycles and increase the capacity retention rate. In addition, the negative electrode coating layer of the nonaqueous electrolyte storage element described in [3] above can be efficiently formed by an electrochemical reaction during initial charging.

[0021] [4] In the nonaqueous electrolyte storage element according to any one of [1] to [3] above, at least a part of the element M in the positive electrode coating layer may be present as a constituent element of an alkoxide of the element M or a component derived therefrom.

[0022] The nonaqueous electrolyte storage element described in [4] above can reduce the resistance after charge / discharge cycles and increase the capacity retention rate. In addition, the positive electrode coating layer of the nonaqueous electrolyte storage element described in [4] above can be efficiently formed by spraying a mixed solution containing an alkoxide of element M onto the positive electrode active material, followed by drying, for example.

[0023] [5] In the nonaqueous electrolyte storage element according to any one of [1] to [4] above, the negative electrode coating layer may have an average thickness of 500 nm or less.

[0024] According to the nonaqueous electrolyte storage element described in [5] above, the negative electrode coating layer is sufficiently thin, and a decrease in lithium ion conductivity in the negative electrode due to the formation of the negative electrode coating layer can be particularly sufficiently suppressed, so that the resistance after charge-discharge cycles can be further reduced and the capacity retention rate can be further increased.

[0025] The "average thickness" of the anode coating layer refers to the average thickness of any five locations on the layer that coats the surface of each particle of the anode active material. The average thickness of the anode coating layer is determined by depth profile analysis using TOF-SIMS. The above analysis is performed on anode active material that has not been exposed to the atmosphere, in an environment that has not been exposed to the atmosphere, using an IONTOF TOF-SIMS TOFSIMS.5.

[0026] [6] A method for producing a nonaqueous electrolyte storage element according to one embodiment of the present invention includes: preparing a positive electrode having a positive electrode active material, at least a portion of whose surface is coated with a positive electrode coating layer containing element M; preparing a negative electrode having a negative electrode active material; assembling an uncharged / discharged nonaqueous electrolyte storage element including the positive electrode and the negative electrode; and initially charging the uncharged / discharged nonaqueous electrolyte storage element to form a negative electrode coating layer that coats at least a portion of the surface of the negative electrode active material and contains element M, wherein the positive electrode active material comprises at least one selected from the group consisting of lithium transition metal compounds having an olivine-type crystal structure and lithium transition metal composite oxides having a spinel-type crystal structure.

[0027] According to the method for producing a nonaqueous electrolyte storage element described in [6] above, it is possible to produce a nonaqueous electrolyte storage element using a predetermined positive electrode active material, which has low resistance after charge-discharge cycles and a high capacity retention rate.

[0028] A nonaqueous electrolyte electricity storage element according to one embodiment of the present invention, a method for manufacturing a nonaqueous electrolyte electricity storage element, an electricity storage device, and other embodiments will be described in detail below.

[0029] <Non-aqueous electrolyte energy storage element> A nonaqueous electrolyte storage element according to one embodiment of the present invention comprises a positive electrode, a negative electrode, a nonaqueous electrolyte, and a container for accommodating these. The nonaqueous electrolyte storage element may further comprise a separator interposed between the positive electrode and the negative electrode to electrically insulate the positive electrode from the negative electrode. The positive electrode, the negative electrode, and any separator typically constitute an electrode assembly. At least a portion of the nonaqueous electrolyte typically exists in a state of being impregnated into the electrode assembly. The nonaqueous electrolyte storage element according to one embodiment of the present invention may further comprise other components.

[0030] For example, a nonaqueous electrolyte storage element 1 according to one embodiment of the present invention shown in FIG. 1 includes an electrode assembly 2, a nonaqueous electrolyte (not shown), and a rectangular parallelepiped container 3 that accommodates these. The nonaqueous electrolyte storage element 1 of FIG. 1 further includes a positive electrode lead 4, a positive electrode external terminal 5, a negative electrode lead 6, and a negative electrode external terminal 7. The positive electrode lead 4 and the negative electrode lead 6 are accommodated in the container 3 together with the electrode assembly 2 and the like. The positive electrode external terminal 5 and the negative electrode external terminal 7 are provided outside the container 3. The positive electrode constituting the electrode assembly 2 is electrically connected to the positive electrode external terminal 5 via the positive electrode lead 4. The negative electrode constituting the electrode assembly 2 is electrically connected to the negative electrode external terminal 7 via the negative electrode lead 6.

[0031] The nonaqueous electrolyte storage element of the present invention may be a nonaqueous electrolyte secondary battery. Below, the main components constituting the nonaqueous electrolyte storage element according to one embodiment of the present invention will be described in detail, mainly in the case where the nonaqueous electrolyte storage element is a nonaqueous electrolyte secondary battery (particularly a lithium ion secondary battery), but this is not intended to limit the application of the present invention.

[0032] The lower and upper limits of each numerical range described in the embodiments of the present invention can be combined in any manner.

[0033] (positive electrode) The positive electrode has a positive electrode substrate and a positive electrode active material layer laminated on the positive electrode substrate directly or via an intermediate layer.

[0034] Typically, the positive electrode has a portion where the positive electrode substrate is exposed. This exposed portion of the positive electrode substrate is typically connected to the above-described positive electrode lead. The positive electrode may have, for example, a sheet-like, plate-like, or strip-like shape.

[0035] The thickness of the positive electrode is appropriately set depending on the application of the nonaqueous electrolyte storage element, etc. The average thickness of the positive electrode may be, for example, 30 μm or more and 1,000 μm or less. The lower limit of the average thickness of the positive electrode may be 50 μm, 100 μm, or 200 μm. The upper limit of the average thickness of the positive electrode may be 500 μm, 400 μm, 300 μm, 200 μm, or 100 μm. The average thickness of the positive electrode is the average thickness of a portion where a positive electrode active material layer is laminated on a positive electrode substrate directly or via an intermediate layer. When there are portions where a positive electrode active material layer is laminated on both sides of the positive electrode substrate and portions where a positive electrode active material layer is laminated on only one side of the positive electrode substrate, the average thickness of the portion where a positive electrode active material layer is laminated on both sides of the positive electrode substrate is used.

[0036] The positive electrode substrate has electrical conductivity. In this specification, "having electrical conductivity" means that the volume resistivity is 10 -2 The volume resistivity is a value measured in accordance with JIS-H-0505 (1975). On the other hand, in this specification, "not having electrical conductivity" or "having (electrical) insulation" means that the volume resistivity is 107 This means that the resistance is Ω·cm or more.

[0037] Examples of materials for the positive electrode substrate include metals such as aluminum, titanium, iron, and alloys thereof (stainless steel, etc.). Among these, aluminum or an aluminum alloy is preferred from the viewpoints of potential resistance, high electronic conductivity, and cost.

[0038] The positive electrode substrate has a shape such as a sheet, plate, or strip. Examples of the positive electrode substrate include foil, vapor-deposited film, mesh, and porous material, and foil is preferred. The positive electrode substrate may be, for example, aluminum foil or aluminum alloy foil.

[0039] The average thickness of the positive electrode substrate may be, for example, 3 μm or more and 50 μm or less. The lower limit of the average thickness of the positive electrode substrate may be 5 μm, 8 μm, 10 μm, or 15 μm. The upper limit of the average thickness of the positive electrode substrate may be 40 μm, 30 μm, 20 μm, or 15 μm.

[0040] The intermediate layer is a layer disposed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer contains, for example, a conductive agent and a binder. When the intermediate layer contains a conductive agent, the contact resistance between the positive electrode substrate and the positive electrode active material layer can be reduced. Examples of the conductive agent and binder used in the intermediate layer include the same conductive agent and binder used in the positive electrode active material layer described below.

[0041] The positive electrode active material layer contains a positive electrode active material. The positive electrode active material layer contains optional components such as a conductive agent, a binder, a thickener, and a filler as needed. The positive electrode active material layer may be formed from a positive electrode mixture containing the positive electrode active material and other optional components. The positive electrode active material layer may be provided on only one side or on both sides of a positive electrode substrate having a shape such as a sheet.

[0042] The positive electrode active material contains at least one material selected from the group consisting of lithium transition metal compounds having an olivine-type crystal structure and lithium transition metal composite oxides having a spinel-type crystal structure.

[0043] A lithium transition metal compound having an olivine-type crystal structure may be an ionic compound (polyanion compound) containing, for example, a lithium cation and a transition metal cation as cations and a polyanion (i.e., a polyvalent oxoacid ion). Examples of the polyanion include oxoacid anions such as PO4 3- , SO4 2- , SiO4 4- , BO3 3- , VO4 3- , etc., and phosphate ions (PO4 3- ) are preferred. Examples of the transition metal element contained in the lithium transition metal compound include an iron element, a manganese element, a nickel element, a cobalt element, a vanadium element, etc. The lithium transition metal compound preferably contains an iron element as the transition metal element. The lithium transition metal compound may further contain other elements (e.g., a halogen element, etc.).

[0044] The lithium transition metal compound is preferably a compound represented by the following formula (1). Li a M 1 b (AO c ) d X e ···(1) In formula (1), M 1 is at least one transition metal element. A is at least one selected from B, Al, Si, P, S, Cl, Ti, V, Cr, Mo, and W. X is at least one halogen element. a, b, c, d, and e are numbers satisfying 0 < a ≤ 3, 0 < b ≤ 2, 2 ≤ c ≤ 4, 1 ≤ d ≤ 3, and 0 ≤ e ≤ 1. a, b, c, d, and e may all be integers or may be decimals.

[0045] M 1 in formula (1) preferably contains Fe. The content of Fe in M 1 in formula (1) is preferably 50 mol% or more, more preferably 70 mol% or more, 90 mol% or more, or 99 mol% or more. M1 It may be Fe. As A, P is preferable. As X, F is preferable. In one embodiment, a = 1, b = 1, c = 4, d = 1, and e = 0 may be preferable in some cases.

[0046] Examples of the lithium transition metal compound include LiFePO4, LiMnPO4, LiNiPO4, LiMn x Fe 1-x PO4 (0 < x < 1), LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, Li2FePO4F, Li2CoPO4F, Li2NiPO4F, etc.

[0047] Among the above lithium transition metal compounds, lithium iron phosphate (typically, LiFePO4) is particularly preferable. Lithium iron phosphate is not limited to LiFePO4, and a part of the constituent atoms or polyanions may be substituted with other atoms or other anion species.

[0048] The lithium transition metal composite oxide having a spinel-type crystal structure contains a lithium element, a transition metal element, and an oxygen element. Examples of the transition metal element contained in the lithium transition metal composite oxide include a manganese element, a nickel element, etc. It is preferable that the lithium transition metal composite oxide contains a manganese element as the transition metal element. The lithium transition metal composite oxide may further contain other elements other than the lithium element, the transition metal element, and the oxygen element.

[0049] The lithium transition metal composite oxide is preferably a compound represented by the following formula (2). Li f M 2 2O4···(2) In formula (2), M 2 is a metal element other than the lithium element, containing at least one kind of transition metal element. 0 < f ≦ 1.2. [[ID=~]]

[0050] [[ID=~]] M in formula (2) 2 preferably contains Mn. M in formula (2) 2The Mn content in the Mn alloy is preferably 50 mol % or more, more preferably 70 mol % or more, 90 mol % or more, or 99 mol % or more. 2 may be Mn. In one embodiment, 0.9≦f≦1.1 may be satisfied, and f=1.

[0051] As the lithium transition metal composite oxide, lithium manganese oxide (typically, LiMn2O4) is particularly preferable. The lithium manganese oxide is not limited to LiMn2O4, and may be one in which some of the constituent atoms are substituted with other atoms.

[0052] The surface of these materials serving as positive electrode active materials may be coated with a carbon material or the like. The carbon material refers to a material containing carbon as the main constituent element. The main constituent element refers to the element that is most abundant on a mass basis. For example, the carbon content in the carbon material may be 80 mass% or more, 90 mass% or more, 95 mass%, 99 mass% or more, or 99.9 mass% or more. The carbon material is preferably a carbon material other than an uncarbonized polymer compound.

[0053] The positive electrode active material is preferably a lithium transition metal compound having an olivine crystal structure, and more preferably lithium iron phosphate. The positive electrode active material may contain other positive electrode active materials in addition to the lithium transition metal compound having an olivine crystal structure and the lithium transition metal composite oxide having a spinel crystal structure. However, the content of the lithium transition metal compound having an olivine crystal structure and the lithium transition metal composite oxide having a spinel crystal structure in the total positive electrode active material contained in the positive electrode active material layer is preferably 90% by mass or more and 100% by mass or less, more preferably 99% by mass or more and 100% by mass or less.

[0054] At least a portion of the surface of the positive electrode active material is coated with a positive electrode coating layer. The positive electrode active material is usually in a particulate form. The positive electrode active material may be coated particles having at least a portion of the surface coated with a positive electrode coating layer. The positive electrode active material may also include particles that are not covered with a positive electrode coating layer. Even in each particle of the positive electrode active material coated with a positive electrode coating layer, there may be a portion where the positive electrode active material is exposed on the surface.

[0055] The positive electrode coating layer contains the element M. The element M is preferably at least one selected from the group consisting of boron, magnesium, aluminum, phosphorus, titanium, niobium, and tungsten, more preferably at least one selected from the group consisting of titanium and niobium, and even more preferably titanium. When the positive electrode coating layer and the negative electrode coating layer described below contain the element M, the resistance after charge-discharge cycling of the nonaqueous electrolyte storage element can be reduced and the capacity retention rate can be increased. The positive electrode coating layer may contain one or more elements M.

[0056] In one embodiment, at least a portion of element M in the positive electrode coating layer is preferably present as a constituent element of an alkoxide of element M or a component derived therefrom. In other words, the positive electrode coating layer is preferably a layer containing an alkoxide of element M or a component derived therefrom. Examples of components derived from the alkoxide of element M include hydrolysis and condensation reaction products of the alkoxide of element M. The positive electrode coating layer is preferably formed using an alkoxide of element M. Examples of alkoxides include methoxides (titanium methoxide, niobium methoxide, etc.), ethoxides (titanium ethoxide, niobium ethoxide, etc.), and propoxides (titanium propoxide, niobium propoxide, etc.).

[0057] The positive electrode coating layer may contain components other than the alkoxide of element M and components derived therefrom. For example, the positive electrode coating layer may contain elemental lithium. The positive electrode active material layer may be formed from a compound containing elemental lithium and element M, or may be a layer of a compound containing elemental lithium and element M. The positive electrode coating layer may be a layer formed from a hydrolysis-condensation reaction product of an alkoxide of element M and an alkoxide of elemental lithium. Examples of alkoxides of elemental lithium include lithium methoxide, lithium ethoxide, and lithium propoxide.

[0058] The average thickness of the positive electrode coating layer is preferably 1 nm or more and 5,000 nm or less, and may be 100 nm or more and 2,000 nm or less. When the average thickness of the positive electrode coating layer is in this range, the resistance after charge-discharge cycling of the nonaqueous electrolyte storage element can be further reduced and the capacity retention rate can be further increased.

[0059] The average particle size of the positive electrode active material is preferably, for example, 0.1 μm to 20 μm. Setting the average particle size of the positive electrode active material above the lower limit facilitates the production and handling of 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. The average particle size of the positive electrode active material includes the size of the positive electrode coating layer and the coating of the carbon material or the like. That is, the average particle size of the positive electrode active material is the average particle size of coated particles, at least a portion of whose surface is coated with the positive electrode coating layer. The term "average particle size" refers to the value at which the volume-based cumulative distribution (D50) reaches 50% as calculated in accordance with JIS-Z-8819-2 (2001) based on the particle size distribution measured by laser diffraction / scattering in a diluted solution obtained by diluting particles with a solvent in accordance with JIS-Z-8825 (2013). As a method for obtaining particles of the positive electrode active material and the negative electrode active material described below with a predetermined particle size, a known method using, for example, a pulverizer, a classifier, or the like can be employed.

[0060] The content of the positive electrode active material in the positive electrode active material layer is preferably 50% by mass to 99% by mass, more preferably 70% by mass to 98% by mass, and may be 80% by mass to 95% by mass. By setting the content of the positive electrode active material within the above range, both high energy density and manufacturability of the positive electrode active material layer can be achieved. Furthermore, the content of at least one selected from the group consisting of lithium transition metal compounds having an olivine crystal structure and lithium transition metal composite oxides having a spinel crystal structure in the positive electrode active material layer is preferably 50% by mass to 99% by mass, more preferably 70% by mass to 98% by mass, and may be 80% by mass to 95% by mass. The content of the positive electrode active material also includes the content of the positive electrode coating layer and the coating such as the carbon material. That is, the content of the positive electrode active material may be the content of coated particles in which at least a portion of the surface of a particle of the positive electrode active material is coated with a positive electrode coating layer.

[0061] Conductive agents are usually components made of materials that have electrical conductivity. Even if the volume resistivity of a conductive agent cannot be measured directly, it is possible to measure the volume resistivity by measuring the volume resistivity of the conductive agent when the volume resistivity is 10 -2 Conductive agents are materials known to have a resistivity of Ω·cm or less. Examples of conductive agents include carbon materials, metals, and conductive ceramics. Examples of carbon materials include graphite, non-graphitic carbon, and graphene-based carbon. Examples of non-graphitic carbon include carbon nanofiber, pitch-based carbon fiber, and carbon black. Examples of carbon black include furnace black, acetylene black, and ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNT), and fullerene. Conductive agents may be in the form of powder or fiber. One or more conductive agents may be used. These materials may be combined to form a conductive agent. For example, a composite of carbon black and CNT may be used.

[0062] The content of the conductive agent in the positive electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less, more preferably 1% by mass or more and 9% by mass or less, and even more preferably 3% by mass or more and 8% by mass or less. The upper limit of the content of the conductive agent may be 5%, 4%, or 3% by mass. By setting the content of the conductive agent within the above range, it is possible to increase the energy density of the nonaqueous electrolyte storage element. Note that the carbon material and the like that coat the positive electrode active material are not included in the conductive agent.

[0063] Examples of the binder include a water-based binder and an organic solvent-based binder.

[0064] The aqueous binder is a binder that dissolves or disperses in water. The aqueous binder may be a binder that dissolves or disperses at 1 part by mass or more in 100 parts by mass of water at 20°C. When a positive electrode active material layer is formed using a positive electrode mixture paste whose dispersion medium is water or a mixed solvent mainly composed of water, an aqueous binder (a water-soluble or water-dispersible polymer material) can be used. Examples of aqueous binders include polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyacrylic acid, polymethacrylic acid, polytetrafluoroethylene, styrene-butadiene rubber, polyethylene, polypropylene, nitrile-butadiene rubber, and cellulose.

[0065] The organic solvent-based binder is a binder that dissolves or disperses in an organic solvent (e.g., N-methylpyrrolidone). The organic solvent-based binder may be a binder that dissolves or disperses at 1 part by mass or more in 100 parts by mass of an organic solvent (e.g., N-methylpyrrolidone) at 20°C. When a positive electrode active material layer is formed using a positive electrode mixture paste whose dispersion medium is an organic solvent or a mixed solvent mainly containing an organic solvent, an organic solvent-based binder (a polymer material that is soluble or dispersible in an organic solvent) can be used. Examples of organic solvent-based binders include polyvinylidene fluoride, copolymers of vinylidene fluoride and hexafluoropropylene, copolymers of ethylene and vinyl alcohol, polyacrylonitrile, polyphosphazene, polysiloxane, polyvinyl acetate, polymethyl methacrylate, polystyrene, polycarbonate, polyamide, polyimide, polyamideimide, crosslinked polymers of cellulose and chitosan pyrrolidone carboxylate, chitosan derivatives, and the like.

[0066] The binder may be a fluororesin (polytetrafluoroethylene, polyvinylidene fluoride, etc.), a polyolefin (polyethylene, polypropylene, etc.), an elastomer (ethylene propylene diene rubber, styrene butadiene rubber, fluororubber, etc.), a polysaccharide polymer (cellulose, chitosan derivatives, etc.), etc. One or more types of binders may be used.

[0067] The content of the binder in the positive electrode active material layer is preferably 0.1% by mass to 10% by mass, more preferably 1% by mass to 9% by mass, and even more preferably 3% by mass to 8% by mass. The upper limit of the binder content may be 5%, 4%, or 3% by mass. By setting the binder content within the above range, it is possible to stably hold the positive electrode active material. The technology disclosed herein can also be implemented in an embodiment in which the positive electrode active material layer does not contain a binder.

[0068] Examples of thickeners include polysaccharide polymers such as carboxymethyl cellulose and methyl cellulose. When the thickener has a functional group that reacts with lithium or the like, the functional group may be deactivated in advance by methylation or the like. The thickener may also function as a binder. One or more types of thickeners may be used. When the positive electrode active material layer contains a thickener, the content of the thickener in the positive electrode active material layer is preferably 0.1% by mass or more and 8% by mass or less, more preferably 5% by mass or less, and even more preferably 2% by mass or less. The technology disclosed herein may also be implemented in an embodiment in which the positive electrode active material layer does not contain a thickener.

[0069] The filler is not particularly limited. The filler may be a component other than the positive electrode active material, conductive agent, binder, and thickener, and may be intentionally added. The filler may be added to fill gaps in the positive electrode active material layer, or may be added for other purposes. The filler may be an organic substance such as polyolefin, or an inorganic substance such as an inorganic oxide, hydroxide, or carbonate. One or more fillers may be used. When the positive electrode active material layer contains a filler, the content of the filler in the positive electrode active material layer may be 0.1% by mass or more and 8% by mass or less, typically preferably 5% by mass or less, and more preferably 2% by mass or less. The technology disclosed herein may also be implemented in an embodiment in which the positive electrode active material layer does not contain a filler.

[0070] The positive electrode active material layer may further contain other components in addition to the positive electrode active material, conductive agent, binder, thickener, and filler. The other components include those unintentionally present in the positive electrode active material layer. The positive electrode active material layer may also contain unintentionally contained impurities as the other components, as long as the effects of the present invention are achieved. The upper limit of the content of the other components in the positive electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of the unintentionally contained components in the positive electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of the unintentionally contained impurities in the positive electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass.

[0071] The thickness of the positive electrode active material layer is appropriately set depending on the type of positive electrode active material, the application of the nonaqueous electrolyte storage element, and the like. The average thickness of one positive electrode active material layer may be, for example, 5 μm or more and 1,000 μm or less. The lower limit of the average thickness of one positive electrode active material layer may be 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, or 100 μm. The upper limit of the average thickness of one positive electrode active material layer may be 800 μm, 500 μm, 200 μm, 100 μm, 80 μm, 60 μm, or 40 μm. The mass per unit area of ​​one positive electrode active material layer is, for example, 4 mg / cm. 2 More than 100mg / cm 2 The lower limit of the mass per unit area of ​​one positive electrode active material layer may be 6 mg / cm or less. 2 , 8 mg / cm 2 or 10 mg / cm 2 The upper limit of the mass per unit area of ​​one positive electrode active material layer is 50 mg / cm. 2 , 20 mg / cm 2 , 15 mg / cm 2 , 12 mg / cm 2 or 10 mg / cm 2 may be.

[0072] The porosity of the positive electrode active material layer may be, for example, 20% or more and 50% or less. The lower limit of the porosity of the positive electrode active material layer may be 25%, 30%, or 35%. The upper limit of the porosity of the positive electrode active material layer may be 45%, 40%, or 35%. The "porosity (%)" of the positive electrode active material layer and the negative electrode active material layer described below is calculated by the formula (1-V2 / V1) × 100, where V1 is the apparent volume (volume including voids) of the positive (negative) electrode active material layer and V2 is the sum of the actual volumes of the materials constituting the positive (negative) electrode active material layer. The sum V2 of the actual volumes of the materials constituting the positive (negative) electrode active material layer can be calculated from the content of each material in the positive (negative) electrode active material layer and the true density of each material.

[0073] (Negative electrode) The negative electrode has a negative electrode substrate and a negative electrode active material layer laminated on the negative electrode substrate directly or via an intermediate layer.

[0074] The negative electrode usually has a portion where the negative electrode substrate is exposed. This exposed portion of the negative electrode substrate is usually connected to the above-mentioned negative electrode lead. The negative electrode may have a shape such as a sheet, plate, or strip.

[0075] The thickness of the negative electrode is appropriately set depending on the application of the nonaqueous electrolyte storage element, etc. The average thickness of the negative electrode may be, for example, 30 μm or more and 1,000 μm or less. The lower limit of the average thickness of the negative electrode may be 50 μm, 100 μm, or 200 μm. The upper limit of the average thickness of the negative electrode may be 500 μm, 400 μm, 300 μm, 200 μm, or 100 μm. The average thickness of the negative electrode is the average thickness of a portion where the negative electrode active material layer is laminated on the negative electrode substrate directly or via an intermediate layer. When the negative electrode substrate has both a portion where the negative electrode active material layer is laminated on both sides and a portion where the negative electrode active material layer is laminated on only one side, the average thickness of the portion where the negative electrode active material layer is laminated on both sides of the negative electrode substrate is taken as the average thickness.

[0076] The negative electrode substrate is conductive. Examples of materials for the negative electrode substrate include metals such as copper, nickel, iron, and alloys thereof (such as stainless steel), and carbon materials. Among these, copper or copper alloys are preferred.

[0077] The negative electrode substrate has a shape such as a sheet, plate, or strip. Examples of the form of the negative electrode substrate include foil, vapor-deposited film, mesh, and porous material, and foil is preferred. The negative electrode substrate may be, for example, copper foil or copper alloy foil.

[0078] The average thickness of the negative electrode substrate may be, for example, 2 μm or more and 35 μm or less. The lower limit of the average thickness of the negative electrode substrate may be 3 μm, 4 μm, 5 μm, or 10 μm. The upper limit of the average thickness of the negative electrode substrate may be 30 μm, 20 μm, 15 μm, or 10 μm.

[0079] The structure of the intermediate layer of the negative electrode is not particularly limited, and can be selected from the structures exemplified for the intermediate layer of the positive electrode, for example.

[0080] 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. The negative electrode active material layer may be formed from a negative electrode mixture containing a negative electrode active material and other optional components. The negative electrode active material layer may be provided on only one side or on both sides of a negative electrode substrate having a shape such as a sheet.

[0081] The negative electrode active material can be a known negative electrode active material. A material capable of absorbing and releasing lithium ions is typically used as the negative electrode active material for lithium ion secondary batteries. Examples of the negative electrode active material include metallic lithium; metals or semimetals such as silicon and tin; metal oxides or semimetal oxides such as silicon oxide, titanium oxide, and tin oxide; and Li4Ti5O. 12 , LiTiO 2、Examples of the negative electrode active material include titanium-containing oxides such as TiNbO; polyphosphate compounds; silicon carbide; and carbon materials such as graphite and non-graphitic carbon. Among these materials, carbon materials are preferred, and graphite or non-graphitic carbon is more preferred. The surface of graphite may be coated with other materials such as non-graphitic carbon. One or more negative electrode active materials can be used.

[0082] "Graphite" refers to a graphite material that has an average lattice spacing (d 002 ) is a carbon material with a particle size of 0.33 nm or more and less than 0.34 nm. Graphite includes natural graphite and artificial graphite.

[0083] "Non-graphitic carbon" refers to carbon that has an average lattice spacing (d 002 ) refers to a carbon material in which the particle size is 0.34 nm or more and 0.42 nm or less. Non-graphitizable carbon includes non-graphitizable carbon and graphitizable carbon. "Non-graphitizable carbon" refers to a carbon material in which the particle size is 0.34 nm or more and 0.42 nm or less. 002 The term "easily graphitizable carbon" refers to a carbon material having a particle size of 0.36 nm or more and 0.42 nm or less. 002 This refers to carbon materials with a particle size of 0.34 nm or more and less than 0.36 nm.

[0084] 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, this refers to a state in which the open circuit voltage of a half cell 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 is 0.7 V or higher.

[0085] At least a portion of the surface of the negative electrode active material is coated with a negative electrode coating layer. When the negative electrode active material is particulate, the negative electrode active material may be coated particles at least a portion of the surface of which is coated with a negative electrode coating layer. The negative electrode active material may also include particles that are not covered with a negative electrode coating layer. Even in each particle of the negative electrode active material coated with a negative electrode coating layer, there may be a portion where the negative electrode active material is exposed on the surface.

[0086] The negative electrode coating layer contains an element M. The element M contained in the negative electrode coating layer is the same element as the element M contained in the positive electrode coating layer. A preferred embodiment of the element M contained in the negative electrode coating layer is the same as the preferred embodiment of the element M contained in the positive electrode coating layer. That is, the element M contained in the negative electrode coating layer is preferably at least one element selected from the group consisting of boron, magnesium, aluminum, phosphorus, titanium, niobium, and tungsten, more preferably at least one element selected from the group consisting of titanium and niobium, and even more preferably titanium. The negative electrode coating layer may contain one or more elements M.

[0087] In one embodiment, at least a portion of the element M in the negative electrode coating layer is preferably present as a constituent element of an oxide containing the element M. In other words, the negative electrode coating layer is preferably a layer containing an oxide containing the element M, and more preferably a layer of an oxide containing the element M.

[0088] The negative electrode coating layer may contain an element other than element M and oxygen. For example, the negative electrode coating layer may contain lithium. The negative electrode active material layer may be a layer of an oxide containing lithium and element M.

[0089] The upper limit of the average thickness of the negative electrode coating layer is preferably 500 nm, more preferably 200 nm, even more preferably 100 nm, and may be 50 nm. By setting the average thickness of the negative electrode coating layer to the above upper limit or less, it is possible to particularly sufficiently suppress a decrease in lithium ion conductivity in the negative electrode due to the formation of the negative electrode coating layer, thereby further reducing the resistance after charge / discharge cycling of the non-aqueous electrolyte storage element and further increasing the capacity retention rate. The lower limit of the average thickness of the negative electrode coating layer may be 1 nm or 5 nm. The negative electrode coating layer is gradually formed on the surface of the negative electrode active material by electrochemical reactions during initial charging and subsequent charging. It is believed that if the negative electrode coating layer has an average thickness equal to or greater than the above lower limit in a state after initial charging, for example, it can sufficiently suppress the deposition of transition metal elements eluted from the positive electrode active material into the non-aqueous electrolyte on the surface of the negative electrode active material.

[0090] The negative electrode active material may be particulate. The average particle size of the negative electrode active material may be, for example, 1 nm or more and 100 μm or less. When the negative electrode active material is a carbon material, a titanium-containing oxide, a polyphosphate compound, or the like, 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-mentioned lower limit, the negative electrode active material can be easily manufactured or handled. By setting the average particle size of the negative electrode active material to be equal to or less than the above-mentioned upper limit, the electronic conductivity of the negative electrode active material layer is improved. Note that the average particle size of the negative electrode active material is the size including the negative electrode coating layer. That is, the average particle size of the negative electrode active material is the average particle size of coated particles in which at least a portion of the surface of the negative electrode active material particles is coated with a negative electrode coating layer.

[0091] The content of the negative electrode active material in the negative electrode active material layer is, for example, preferably 60% by mass or more and 99% by mass or less, and more preferably 90% by mass or more and 98% by mass or less. By setting the content of the negative electrode active material within the above range, it is possible to achieve both high energy density and manufacturability of the negative electrode active material layer. Note that the content of the negative electrode active material also includes the content of the negative electrode coating layer. That is, the content of the negative electrode active material may be the content of coated particles in which at least a portion of the surface of particles of the negative electrode active material is coated with a negative electrode coating layer.

[0092] When the negative electrode active material is a metal such as metallic lithium, the negative electrode active material layer may be in the form of a foil. The metallic lithium may exist as pure metallic lithium consisting essentially of elemental lithium, or may exist as a lithium alloy containing other metal elements. When the negative electrode active material is a metal such as metallic lithium, the content of elemental lithium in the negative electrode active material layer may be 90% by mass or more, or may be 99% by mass or more.

[0093] When the negative electrode active material layer contains a conductive agent, the content of the conductive agent in the negative 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. The content of the conductive agent in the negative electrode active material layer may be 5% by mass or less, or may be 2% by mass or less. The technology disclosed herein may also be implemented in an embodiment in which the negative electrode active material layer does not contain a conductive agent.

[0094] When the negative electrode active material layer contains a binder, the content of the binder in the negative electrode active material layer is preferably 0.1% by mass to 10% by mass, more preferably 0.5% by mass to 8% by mass. The content of the binder in the negative electrode active material layer may be 5% by mass or less, or may be 2% by mass or less. The technology disclosed herein may also be implemented in an embodiment in which the negative electrode active material layer does not contain a binder.

[0095] When the negative electrode active material layer contains a thickener, the content of the thickener in the negative electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 0.5% by mass or more and 8% by mass or less. The content of the thickener in the negative electrode active material layer may be 5% by mass or less, or may be 2% by mass or less. The technology disclosed herein may also be implemented in an embodiment in which the negative electrode active material layer does not contain a thickener.

[0096] The filler in the negative electrode active material layer may be a component other than the negative electrode active material, conductive agent, binder, and thickener, and may be an intentionally contained component. The filler may be contained as a component to fill gaps in the negative electrode active material layer, or may be contained for other purposes. When the negative electrode active material layer contains a filler, the content of the filler in the negative electrode active material layer can be 0.1% by mass or more and 8% by mass or less, and typically 5% by mass or less is preferred, and 2% by mass or less is more preferred. The technology disclosed herein may also be implemented in an embodiment in which the negative electrode active material layer does not contain a filler.

[0097] The negative electrode active material layer may further contain components other than the negative electrode active material, conductive agent, binder, thickener, and filler. These other components include those unintentionally present in the negative electrode active material layer. The negative electrode active material layer may also contain unintentionally present impurities as the other components, as long as the effects of the present invention are achieved. The upper limit of the content of the other components in the negative electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of the unintentionally present components in the negative electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of the unintentionally present impurities in the negative electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass.

[0098] The thickness of the negative electrode active material layer is appropriately set depending on the type of negative electrode active material, the application of the nonaqueous electrolyte storage element, and the like. The average thickness of one negative electrode active material layer may be, for example, 5 μm or more and 1,000 μm or less. The lower limit of the average thickness of one negative electrode active material layer may be 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, or 100 μm. The upper limit of the average thickness of one positive electrode active material layer may be 800 μm, 500 μm, 200 μm, 100 μm, 80 μm, 60 μm, or 40 μm. The mass per unit area of ​​one negative electrode active material layer is, for example, 2 mg / cm. 2 More than 50mg / cm 2 The lower limit of the mass per unit area of ​​one negative electrode active material layer may be 3 mg / cm or less. 2 , 4 mg / cm 2 , 5 mg / cm 2 or 6 mg / cm 2 The upper limit of the mass per unit area of ​​one negative electrode active material layer is 30 mg / cm. 2 , 20 mg / cm 2 , 15 mg / cm 2 , 12 mg / cm 2 or 10 mg / cm 2 may be.

[0099] The porosity of the negative electrode active material layer may be, for example, 30% or more and 70% or less. The lower limit of the porosity of the negative electrode active material layer may be 35%, 40%, or 45%. The upper limit of the porosity of the negative electrode active material layer may be 60%, 50%, or 40%. When the negative electrode active material layer is in a foil shape, for example, the porosity of the negative electrode active material layer may be 0%.

[0100] A layer covering the negative electrode active material layer may be formed on the surface of the negative electrode active material layer. The components of this layer covering the negative electrode active material layer may be the same as those of the above-mentioned negative electrode coating layer. The thickness of this layer covering the negative electrode active material layer may be, for example, about 1 μm or more and 100 μm or less.

[0101] (separator) The separator may be a known separator, such as a separator consisting of only a base layer, or a separator having an inorganic layer containing inorganic particles and a binder formed on one or both surfaces of a base layer.

[0102] Examples of the form of the substrate layer of the separator include woven fabric, nonwoven fabric, porous resin film, etc. Among these forms, porous resin film is preferred from the viewpoint of strength, etc., and nonwoven fabric is preferred from the viewpoint of non-aqueous electrolyte retention, etc. The material of the substrate layer of the separator is not particularly limited as long as it has insulating properties, but resins such as polyolefin (polyethylene, polypropylene, etc.), polyimide, aramid, etc. are preferred.

[0103] Examples of inorganic compounds constituting the inorganic particles include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, and magnesium oxide; 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; mineral-derived substances such as talc, zeolite, kaolin, bentonite, and mica, or artificial products thereof. One or more types of inorganic particles can be used. The average particle size of the inorganic particles is preferably, for example, from 0.5 μm to 10 μm. The content of the inorganic particles in the inorganic layer is preferably from 50% to 99% by mass, and more preferably from 80% to 98% by mass.

[0104] Examples of binders used in the inorganic layer include the same binders as those exemplified for the positive electrode active material layer.

[0105] The porosity of the separator may be, for example, 20% or more and 80% or less. The lower limit of the porosity of the separator may be 30%, 40%, or 50% from the viewpoint of discharge performance, etc. The upper limit of the porosity of the separator may be 70%, 60%, or 50% from the viewpoint of strength, etc. In this specification, "porosity" refers to a volume-based value measured with a mercury porosimeter.

[0106] The average thickness of the separator may be, for example, 10 μm or more and 40 μm or less, or 15 μm or more and 30 μm or less.

[0107] The separator may be a polymer gel composed of a polymer and a non-aqueous electrolyte, or may be a combination of the porous resin film, nonwoven fabric, or the like described above and a polymer gel.

[0108] (electrode body) As the electrode body, for example, a wound type electrode body, a laminated type electrode body, or other electrode body having a known structure can be used.

[0109] A wound electrode body has a structure in which a positive electrode and a negative electrode are wound in an insulated state. The wound electrode body may be cylindrical (columnar) or flat. The electrode body 2 provided in the nonaqueous electrolyte storage element 1 of FIG. 1 is a flat wound electrode body. The wound electrode body can be produced, for example, by the following procedure. First, a positive electrode, a separator, and a negative electrode, each formed in a strip shape, are stacked in this order to obtain a laminate. The wound electrode body is obtained by rolling this laminate.

[0110] A laminated electrode body has a structure in which one or more positive electrodes and one or more negative electrodes are stacked in an insulated state. For example, a laminated electrode body can be obtained by stacking a positive electrode, a separator, and a negative electrode, each of which is formed into a rectangular shape, in this order.

[0111] As the electrode body, for example, one having a structure in which at least one of the positive electrode and the negative electrode is folded in an accordion-like manner and stacked can also be used.

[0112] (non-aqueous electrolyte) As the non-aqueous electrolyte, a known non-aqueous electrolyte can be used. The non-aqueous electrolyte is a medium responsible for transporting charge-transporting ions (lithium ions) between a positive electrode and a negative electrode, and is substantially free of water. The water content in the non-aqueous electrolyte may be, for example, 10,000 ppm or less, or 5,000 ppm or less. Examples of the non-aqueous electrolyte include a non-aqueous electrolyte solution and a solid electrolyte. A non-aqueous electrolyte solution and a solid electrolyte may be used in combination. As the non-aqueous electrolyte, it is preferable to use a non-aqueous electrolyte solution, and it is more preferable to use only a non-aqueous electrolyte solution.

[0113] (Non-aqueous electrolyte) The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.

[0114] As the non-aqueous solvent, known non-aqueous solvents can be used. Examples of non-aqueous solvents include carbonates, esters, ethers, amides, and nitriles. Examples of carbonates include cyclic carbonates and chain carbonates. Examples of esters include carboxylic acid esters, phosphate esters, and sulfonic acid esters. Non-aqueous solvents in which some of the hydrogen atoms contained in these compounds have been substituted with halogen atoms may also be used. One or more non-aqueous solvents can be used.

[0115] The term "cyclic carbonate" refers to a carbonate having a ring structure containing a carbonate group (-OC(=O)-O-). Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, vinylethylene carbonate, chloroethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, styrene carbonate, 1-phenylvinylene carbonate, and 1,2-diphenylvinylene carbonate. The cyclic carbonate may be a saturated cyclic carbonate such as ethylene carbonate, or an unsaturated cyclic carbonate such as vinylene carbonate. "Saturated" refers to the absence of a carbon-carbon unsaturated bond (a carbon-carbon double bond or a carbon-carbon triple bond). "Unsaturated" refers to the presence of a carbon-carbon unsaturated bond. As the cyclic carbonate, a saturated cyclic carbonate is preferred, and ethylene carbonate is more preferred.

[0116] The chain carbonate means a carbonate that does not have a ring structure containing a carbonate group. Examples of the chain carbonate include diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, diphenyl carbonate, trifluoroethyl methyl carbonate, and bis(trifluoroethyl) carbonate. The chain carbonate may be a saturated chain carbonate such as dimethyl carbonate, or an unsaturated chain carbonate such as diphenyl carbonate. The chain carbonate is preferably a saturated chain carbonate, and more preferably ethyl methyl carbonate.

[0117] The non-aqueous solvent preferably contains a carbonate, and more preferably contains a cyclic carbonate and a chain carbonate. The content of the carbonate in the non-aqueous solvent is preferably 80% by volume or more and 100% by volume or less, and may be 99% by volume or more and 100% by volume or less, or even 100% by volume. The use of a cyclic carbonate can promote dissociation of the electrolyte salt and increase 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, for example, in the range of 5:95 to 50:50.

[0118] The electrolyte salt may be a known electrolyte salt. Lithium salt is usually used as the electrolyte salt. One or more kinds of electrolyte salts may be used.

[0119] Examples of lithium salts include inorganic lithium salts such as LiPF6, LiPO2F2, LiBF4, and LiClO4; imide salts such as LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2C2F5)2, and LiN(SO2CF3)(SO2C4F9); and lithium oxalates such as LiB(C2O4)2, LiBF2(C2O4), and LiPF2(C2O4)2. LiN(SO2F)2 also falls under the category of inorganic lithium salts. Among these, inorganic lithium salts are preferred, with LiPF6 being more preferred. In some cases, imide salts are also preferred.

[0120] 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 3 Less 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 3The 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.

[0121] The non-aqueous electrolyte may contain an additive in addition to the non-aqueous solvent and the electrolyte salt. One or more additives may be used. When an additive is used in the non-aqueous electrolyte, the content of the additive 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.

[0122] (solid electrolyte) The solid electrolyte can be selected from any material that has lithium ion conductivity and is solid at room temperature (e.g., 20°C). Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, halide solid electrolytes, and polymer solid electrolytes. One or more types of solid electrolytes can be used.

[0123] (container) The container accommodates the electrode assembly and the non-aqueous electrolyte in its internal space. The container may be made of a metal material such as aluminum or stainless steel, or a resin material. Metal materials are preferred from the viewpoint of strength, etc. Composite materials of metal and resin may also be used.

[0124] The shape of the container is not particularly limited, and may be cylindrical, rectangular (square), disk-like, etc. The container may also be in the shape of a sheet formed from a metal resin composite film.

[0125] (shape, use, etc. of non-aqueous electrolyte storage element) The shape of the nonaqueous electrolyte storage element according to one embodiment of the present invention is not particularly limited, and may be, for example, a cylindrical battery, a prismatic battery, a flat battery, a coin battery, a button battery, or the like.

[0126] The use of the nonaqueous electrolyte electricity storage element according to one embodiment of the present invention is not particularly limited, and the nonaqueous electrolyte electricity storage element can be used, for example, as a power source for automobiles such as electric vehicles, hybrid vehicles, and plug-in hybrid vehicles, a power source for electronic devices such as personal computers and communication terminals, a power source for power storage, etc.

[0127] The nonaqueous electrolyte electricity storage element of the present invention may be used singly or in plural. When the required output and required voltage are small, the nonaqueous electrolyte electricity storage element may be used singly. On the other hand, when at least one of the required output and required voltage is large, the nonaqueous electrolyte electricity storage element may be used as an electricity storage device in combination with other nonaqueous electrolyte electricity storage elements. In an electricity storage device in which a plurality of nonaqueous electrolyte electricity storage elements are combined, at least one nonaqueous electrolyte electricity storage element included in the electricity storage device may be the nonaqueous electrolyte electricity storage element according to one embodiment of the present invention. The electricity storage device will be described in detail later.

[0128] In a nonaqueous electrolyte energy storage element according to one embodiment of the present invention, for example, the container may be constrained so as to maintain a constant thickness, or may not be constrained in this manner. Alternatively, the container may be constrained so as to apply a constant load to it. When the container is constrained, expansion of the container due to charge / discharge cycles, etc., may be suppressed, and deterioration of charge / discharge performance may be suppressed. When the container is constrained, a load may or may not be applied to the electrode assembly within the container. For example, a constraining member that performs such constraining may be provided in the nonaqueous electrolyte energy storage element or the energy storage device.

[0129] <Method of manufacturing nonaqueous electrolyte energy storage element> A method for producing a nonaqueous electrolyte storage element according to one embodiment of the present invention includes: preparing a positive electrode having a positive electrode active material, at least a portion of whose surface is coated with a positive electrode coating layer containing element M; preparing a negative electrode having a negative electrode active material; assembling an uncharged / discharged nonaqueous electrolyte storage element including the positive electrode and the negative electrode; and initially charging the uncharged / discharged nonaqueous electrolyte storage element to form a negative electrode coating layer that coats at least a portion of the surface of the negative electrode active material and contains element M. The positive electrode active material includes at least one selected from the group consisting of lithium transition metal compounds having an olivine-type crystal structure and lithium transition metal composite oxides having a spinel-type crystal structure. The method for producing a nonaqueous electrolyte storage element may also include preparing a separator, producing an electrode assembly using the positive electrode, the negative electrode, and the separator, and preparing a nonaqueous electrolyte.

[0130] The preparation of the positive electrode may be the manufacture of a positive electrode. The manufacture of a positive electrode can be carried out, for example, by applying a paste-like positive electrode mixture (positive electrode mixture paste) to a positive electrode substrate directly or via an intermediate layer, and drying the mixture to form a positive electrode active material layer. The positive electrode mixture paste typically contains a positive electrode active material, at least a portion of whose surface is coated with a positive electrode coating layer containing element M, other optional components, and a dispersion medium. After drying, the positive electrode active material layer and the positive electrode coating layer may be pressed, for example.

[0131] A cathode active material at least partially coated with a cathode coating layer containing element M can be obtained by spraying a cathode active material with a cathode coating layer-forming material and drying the material. The cathode coating layer-forming material may be attached to the surface of the cathode active material by means other than spraying. The cathode coating layer-forming material may be, for example, a solution containing an alkoxide of element M. The cathode coating layer-forming material may further contain a solute such as an alkoxide of lithium. The cathode coating layer-forming material may contain a catalyst or the like. Examples of solvents for the cathode coating layer-forming material include alcohol. After spraying the cathode coating layer-forming material onto the cathode active material and drying, the material may be fired. The firing may be performed, for example, in a nitrogen gas atmosphere at a firing temperature of 300°C to 900°C.

[0132] The preparation of the negative electrode may also mean the manufacture of a negative electrode. The manufacture of a negative electrode can be carried out, for example, by applying a paste-like negative electrode mixture (negative electrode mixture paste) to a negative electrode substrate directly or via an intermediate layer, and drying the mixture to form a negative electrode active material layer. After drying, the negative electrode active material layer may be pressed, etc. When the negative electrode active material is a metal such as metallic lithium, the negative electrode can also be manufactured by laminating a metal foil on the negative electrode substrate directly or via an intermediate layer, and then pressing, etc. In one embodiment of the present invention, the negative electrode active material included in the prepared negative electrode (negative electrode to be used in assembling an uncharged nonaqueous electrolyte storage element) is not covered with a negative electrode coating layer.

[0133] The term "preparing a non-aqueous electrolyte" may refer to preparing a non-aqueous electrolyte. The non-aqueous electrolyte can be prepared, for example, by dissolving an electrolyte salt in a non-aqueous solvent. The positive electrode, negative electrode, separator, non-aqueous electrolyte, etc. may be prepared by purchasing them.

[0134] The uncharged / discharged nonaqueous electrolyte storage element including the positive electrode and negative electrode can be assembled by, for example, placing the electrode body manufactured using the positive electrode, the negative electrode, and the separator, and the nonaqueous electrolyte in a container.

[0135] The thus-obtained non-charged / discharged non-aqueous electrolyte storage element is subjected to initial charging. An electrochemical reaction during this initial charging results in the formation of a negative electrode coating layer on the negative electrode. Specifically, the initial charging causes a portion of element M in the positive electrode coating layer to dissolve into the non-aqueous electrolyte and deposit on the surface of the negative electrode active material, thereby forming the negative electrode coating layer. Because the positive electrode coating layer is formed on the surface of the positive electrode active material, it is believed that element M in the positive electrode coating layer dissolves into the non-aqueous electrolyte and deposits on the surface of the negative electrode active material layer in preference to a transition metal element contained in the positive electrode active material dissolving into the non-aqueous electrolyte and depositing on the surface of the negative electrode active material layer, resulting in the formation of the negative electrode coating layer.

[0136] <Electricity storage device> 2 includes a plurality of energy storage units 20. Each energy storage unit 20 includes a plurality of electrically connected nonaqueous electrolyte energy storage elements 1. The energy storage device 30 may include a bus bar (not shown) that electrically connects the plurality of nonaqueous electrolyte energy storage elements 1, a bus bar (not shown) that electrically connects the plurality of energy storage units 20, and the like. The energy storage unit 20 or the energy storage device 30 may include a state monitoring device (not shown) that monitors the state of one or more nonaqueous electrolyte energy storage elements 1.

[0137] <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.

[0138] In the above embodiment, the nonaqueous electrolyte storage element is used as a chargeable and dischargeable nonaqueous electrolyte secondary battery, but the nonaqueous electrolyte storage element may be of any type, shape, size, capacity, etc. The present invention can also be applied to various secondary batteries, electric double layer capacitors, lithium ion capacitors, and other capacitors.

[0139] In the above embodiment, the electrode assembly has been described in which a separator is interposed between the positive electrode and the negative electrode, but the electrode assembly does not necessarily have to include a separator. [Example]

[0140] 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.

[0141] [Example 1] Lithium iron phosphate (LFP: LiFePO4) was prepared as the positive electrode active material, and a positive electrode coating layer was formed using a tumbling fluidization device manufactured by Powrex. Specifically, the process was carried out as follows: A material for forming a positive electrode coating layer was prepared by mixing lithium ethoxide and titanium ethoxide and dissolving the mixture in anhydrous ethanol. This material for forming a positive electrode coating layer was sprayed onto the LFP. The LFP used was secondary particles whose surfaces were coated with a carbon material. Next, the LFP was dried at 100°C and then calcined at 700°C in a nitrogen atmosphere, yielding coated particles in which at least a portion of the LFP surface was coated with a positive electrode coating layer with an average thickness of approximately 1 μm. The formed positive electrode coating layer is presumed to be a layer containing lithium titanate. A positive electrode mixture paste was prepared using the coated particles (LFP with at least a portion of its surface coated with a positive electrode coating layer), acetylene black (AB) as a conductive agent, polyvinylidene fluoride (PVDF) as a binder, and N-methylpyrrolidone (NMP) as a dispersion medium. The mass ratio of the coated particles, AB, and PVDF was 90:5:5 in terms of solid content. This positive electrode mixture paste was applied to aluminum foil as a positive electrode substrate, dried, and roll-pressed to form a positive electrode active material layer.

[0142] (Preparation of negative electrode) A negative electrode mixture paste was prepared by mixing graphite (negative electrode active material), acetylene black (conductive agent), styrene-butadiene rubber (SBR) (binder), carboxymethyl cellulose (CMC) (thickener), and water (dispersion medium). The mass ratio of graphite to conductive agent, SBR to CMC was 95.7:1.0:2.1:1.2 (solids equivalent). This negative electrode mixture paste was applied to copper foil (negative electrode substrate), dried, and roll-pressed to form a negative electrode active material layer, resulting in a negative electrode.

[0143] (Preparation of non-aqueous electrolyte) A non-aqueous solvent was prepared by mixing ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate in a volume ratio of 20:35:45, and LiPF6 was added as an electrolyte salt at a concentration of 0.9 mol / dm 3 The non-aqueous electrolyte was obtained by dissolving the solution at a concentration of 100 ppm.

[0144] (separator) A microporous polyethylene film was used as the separator.

[0145] (Assembly of uncharged non-aqueous electrolyte storage element) The positive electrode, the negative electrode, and the separator were stacked to prepare an electrode assembly, which was then placed in a container, and the non-aqueous electrolyte was poured into the container, which was then sealed.

[0146] (Initial charge / discharge) The uncharged nonaqueous electrolyte storage element was subjected to initial charge and discharge (initial charge and initial discharge) under the following conditions. In a thermostatic chamber at 25°C, constant-current charging was performed with a charging current of 0.2 C and a cut-off voltage of 3.5 V, followed by constant-voltage charging at 3.5 V. The charge was terminated when the current decayed to 0.01 C. A 10-minute rest period was then provided. Constant-current discharging was performed with a discharging current of 0.2 C and a cut-off voltage of 2.0 V. The discharged quantity of electricity was defined as the initial discharge capacity. The nonaqueous electrolyte storage element of Example 1 was thus obtained. It is presumed that, after the initial charge, a negative electrode coating layer containing titanium, the element M contained in the positive electrode coating layer, was formed on the surface of the negative electrode active material. It is also presumed that the formed negative electrode coating layer contains at least one of titanium oxide and lithium titanate.

[0147] [Example 2] A nonaqueous electrolyte storage element of Example 2 was obtained in the same manner as in Example 1, except that a mixture of lithium ethoxide and niobium ethoxide dissolved in absolute ethanol was used as the material for forming the positive electrode coating layer. In the nonaqueous electrolyte storage element of Example 2, the formed positive electrode coating layer is presumed to be a layer containing lithium niobate, and the formed negative electrode coating layer is presumed to be a layer containing at least one of niobium oxide and lithium niobate.

[0148] [Comparative Example 1] A nonaqueous electrolyte electricity storage element of Comparative Example 1 was obtained in the same manner as in Example 1, except that the LFP was not covered with a positive electrode covering layer.

[0149] Comparative Example 2 A nonaqueous electrolyte storage element of Comparative Example 2 was obtained in the same manner as in Example 1, except that the LFP was not coated with a positive electrode coating layer, and a negative electrode coating layer was formed by applying and drying a material for forming a negative electrode coating layer to the surface of the negative electrode active material layer of the negative electrode. The material for forming a negative electrode coating layer of Comparative Example 2 was prepared by mixing titanium oxide (IV), acetylene black (AB) as a conductive agent, polyvinylidene fluoride (PVDF) as a binder, and N-methylpyrrolidone (NMP) as a dispersion medium.

[0150] (1) Charge / discharge cycle test A charge-discharge cycle test was conducted on each of the nonaqueous electrolyte storage elements of the Examples and Comparative Examples as follows. Constant-current, constant-voltage charging was performed in a thermostatic chamber at 60°C, with a charging current of 1.0 C and a cut-off voltage of 3.5 V. The charge cut-off condition was when the current decayed to 0.01 C. Subsequently, constant-current discharging was performed with a discharging current of 1.0 C and a cut-off voltage of 2.0 V. A 10-minute rest period was provided after each charge and discharge. 500 cycles of this charge-discharge cycle were performed.

[0151] (2) Measurement of DC resistance (DCR) after charge / discharge cycles Next, each nonaqueous electrolyte storage element was subjected to constant current charging at a charging current of 1.0 C in a temperature environment of 25°C, and the state of charge (SOC) was adjusted to 50%. Each nonaqueous electrolyte storage element was charged for 10 seconds at a constant current of 0.2 C, 0.5 C, or 1.0 C. After each charge, a constant current discharge was performed at a current of 0.2 C to adjust the SOC to 50%. The relationship between the current and the voltage 1 second after the start of each charge was plotted, and the direct current resistance (DCR) was calculated from the slope of the straight line obtained from the three plots. The results are shown in Table 1.

[0152] (3) Measurement of capacity retention after charge / discharge cycles Next, each nonaqueous electrolyte storage element was subjected to one cycle of charge and discharge under the same conditions as the initial charge and discharge described above, and the discharged amount of electricity was defined as the discharge capacity after the charge and discharge cycle. The percentage of the discharge capacity after the charge and discharge cycle to the initial discharge capacity was calculated as the capacity retention rate. The results are shown in Table 1.

[0153] (4) Measurement of the average thickness of the negative electrode coating layer after charge-discharge cycles Thereafter, each nonaqueous electrolyte storage element was disassembled, and the average thickness of the negative electrode coating layer was measured by the method described above. The results are shown in Table 1. Note that the positive electrode coating layer remained on at least a portion of the surface of the disassembled positive electrode active material.

[0154] [Table 1]

[0155] As shown in Table 1, in each of the nonaqueous electrolyte storage elements of Examples 1 and 2, in which at least a portion of the surface of the positive electrode active material was coated with a positive electrode coating layer and at least a portion of the surface of the negative electrode active material was coated with a negative electrode coating layer, the DCR after charge-discharge cycles was less than 5.70 Ω and the capacity retention rate was 65% or more, resulting in low resistance after charge-discharge cycles and high capacity retention rate. On the other hand, in each of the nonaqueous electrolyte storage elements of Comparative Example 1, in which the positive electrode active material was not coated with a positive electrode coating layer, and Comparative Example 2, in which the positive electrode active material was not coated with a positive electrode coating layer but a negative electrode coating layer was provided by coating on the surface of the negative electrode active material layer, the resistance after charge-discharge cycles was high and the capacity retention rate was low. [Industrial Applicability]

[0156] The present invention can be applied to nonaqueous electrolyte storage elements used as power sources for electronic devices such as personal computers and communication terminals, automobiles, industrial equipment, and the like. [Explanation of symbols]

[0157] 1. Non-aqueous electrolyte energy storage element 2 Electrode body 3 containers 4 Positive lead 5 Positive external terminal 6 Negative lead 7 Negative external terminal 20 Energy storage unit 30 Electricity storage device

Claims

1. a positive electrode having a positive electrode active material; a negative electrode having a negative electrode active material; Equipped with the positive electrode active material comprises at least one selected from the group consisting of a lithium transition metal compound having an olivine-type crystal structure and a lithium transition metal composite oxide having a spinel-type crystal structure, At least a portion of the surface of the positive electrode active material is coated with a positive electrode coating layer, At least a portion of the surface of the negative electrode active material is coated with a negative electrode coating layer, The positive electrode coating layer and the negative electrode coating layer contain the same element M.

2. 2. The nonaqueous electrolyte electricity storage element according to claim 1, wherein the element M is at least one element selected from the group consisting of boron, magnesium, aluminum, phosphorus, titanium, niobium, and tungsten.

3. 3. The nonaqueous electrolyte storage element according to claim 1, wherein at least a portion of the element M in the negative electrode coating layer is present as a constituent element of an oxide containing the element M.

4. 3. The nonaqueous electrolyte storage element according to claim 1, wherein at least a portion of the element M in the positive electrode coating layer is present as a constituent element of an alkoxide of the element M or a component derived therefrom.

5. 3. The nonaqueous electrolyte storage element according to claim 1, wherein the negative electrode coating layer has an average thickness of 500 nm or less.

6. preparing a positive electrode having a positive electrode active material, at least a portion of the surface of which is coated with a positive electrode coating layer containing element M; providing a negative electrode having a negative electrode active material; assembling an uncharged / discharged nonaqueous electrolyte electricity storage element including the positive electrode and the negative electrode; performing initial charging on the uncharged / discharged nonaqueous electrolyte storage element to form a negative electrode coating layer that coats at least a portion of the surface of the negative electrode active material and contains the element M; Equipped with The method for producing a nonaqueous electrolyte storage element includes the positive electrode active material comprising at least one selected from the group consisting of lithium transition metal compounds having an olivine crystal structure and lithium transition metal composite oxides having a spinel crystal structure.

Images