Non-aqueous electrolyte energy storage element

Abstract

To provide a nonaqueous electrolyte power storage device with a positive electrode having a positive electrode active material containing at least one of the tungsten element and the boron element, where the nonaqueous electrolyte power storage device has a small irreversible capacity.SOLUTION: The nonaqueous electrolyte power storage device according to an aspect of the present invention comprises: a positive electrode having a positive electrode active material containing at least one of the tungsten element and the boron element; and a nonaqueous electrolyte containing a compound represented by the formula (1). In the formula (1), R1 to R3 are each independently a fluorine atom or a C1-10 organic group, provided that at least one of R1 to R3 is a fluorine atom; Mm+ is an alkali metal ion, alkaline earth metal ion or onium ion; and m is an integer equal to the valence of Mm+.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a non-aqueous electrolyte energy storage element. [Background technology]

[0002] Non-aqueous electrolyte secondary batteries, such as lithium-ion batteries, are widely used in electronic devices like personal computers and communication terminals, as well as automobiles, due to their high energy density. Generally, non-aqueous electrolyte secondary batteries consist of a pair of electrodes electrically isolated by a separator, and a non-aqueous electrolyte interposed between these electrodes. They are configured to charge and discharge by transferring charge-transporting ions between the two electrodes. Besides non-aqueous electrolyte secondary batteries, capacitors such as lithium-ion capacitors and electric double-layer capacitors are also widely used as non-aqueous electrolyte energy storage elements.

[0003] To improve the performance of non-aqueous electrolyte energy storage devices, the addition of various elements to the positive electrode active material is being investigated. Reference 1 describes that adding tungsten to the positive electrode active material improves the initial output performance of non-aqueous electrolyte energy storage devices. Reference 2 describes that adding boron to the positive electrode active material increases the capacity retention rate during the charge-discharge cycle of non-aqueous electrolyte energy storage devices. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2009-140787 [Patent Document 2] Japanese Patent Publication No. 2018-073481 [Overview of the project] [Problems that the invention aims to solve]

[0005] Non-aqueous electrolyte energy storage elements using positive electrode active materials doped with tungsten or boron have the advantages described above, but they also have the undesirable drawback of having a large irreversible capacity (the difference between the charging capacity and discharging capacity in one charge-discharge cycle).

[0006] The object of the present invention is to provide a non-aqueous electrolyte energy storage element having a positive electrode having a positive electrode active material containing at least one of tungsten and boron, and having a small irreversible capacity. [Means for solving the problem]

[0007] A non-aqueous electrolyte energy storage element according to one aspect of the present invention comprises a positive electrode having a positive electrode active material containing at least one of the elements tungsten and boron, and a non-aqueous electrolyte containing a compound represented by the following formula (1). [ka] (In formula (1), R 1 From R 3 Each of these is independently a fluorine atom or an organic group having 1 to 10 carbon atoms. However, R 1 From R 3 At least one of them is a fluorine atom. m+ m is an alkali metal ion, an alkaline earth metal ion, or an onium ion. m+ (These are integers equal to the valence of [the variable].) [Effects of the Invention]

[0008] According to one aspect of the present invention, it is possible to provide a non-aqueous electrolyte energy storage element having a positive electrode having a positive electrode active material containing at least one of tungsten and boron, wherein the non-aqueous electrolyte energy storage element has a small irreversible capacity. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a perspective view showing one embodiment of a non-aqueous electrolyte energy storage element. [Figure 2]FIG. 2 is a schematic diagram showing one embodiment of an electricity storage device configured by assembling a plurality of non-aqueous electrolyte electricity storage elements. MODE FOR CARRYING OUT THE INVENTION

[0010] First, an outline of the non-aqueous electrolyte electricity storage element disclosed in the present specification will be described.

[0011] [1] A non-aqueous electrolyte electricity storage element according to one aspect of the present invention includes: a positive electrode having a positive electrode active material containing at least one of a tungsten element and a boron element; and a non-aqueous electrolyte containing a compound represented by the following formula (1). [Chemical Formula] (In formula (1), R 1 to R 3 are each independently a fluorine atom or an organic group having 1 to 10 carbon atoms. Provided that at least one of R 1 to R 3 is a fluorine atom. M m+ is an alkali metal ion, an alkaline earth metal ion or an onium ion. m is an integer equal to the valence of M m+ .)

[0012] The non-aqueous electrolyte electricity storage element according to [1] above is a non-aqueous electrolyte electricity storage element including a positive electrode having a positive electrode active material containing at least one of a tungsten element and a boron element, and has small irreversible capacity. Although the reason for this is not clear, the following reasons are presumed. In general, the compound represented by formula (1) is considered to react mainly at the positive electrode and form a coating film on the surface of the positive electrode active material. However, when the positive electrode active material contains at least one of a tungsten element and a boron element, the reaction of the compound represented by formula (1) at the positive electrode is suppressed, so that the reaction of the compound represented by formula (1) at the negative electrode is promoted. In this case, a coating film derived from the compound represented by formula (1) is formed on the surface of the negative electrode active material, thereby suppressing the decomposition reaction of the non-aqueous electrolyte at the negative electrode. For this reason, it is presumed that the non-aqueous electrolyte electricity storage element described in [1] above has small irreversible capacity.

[0013] [2] In the non-aqueous electrolyte energy storage element described in [1] above, the non-aqueous electrolyte may further contain a compound having an anion containing the element boron.

[0014] The non-aqueous electrolyte energy storage element described in [2] above has a smaller irreversible capacity. The reason for this is not entirely clear, but it is speculated that the coating formed on the surface of the negative electrode active material contains components derived from compounds having anions containing boron, which further suppresses the decomposition reaction of the non-aqueous electrolyte at the negative electrode.

[0015] [3] In the non-aqueous electrolyte energy storage element described in [1] or [2] above, at least one of the tungsten element and the boron element may be present on at least the surface of the particles of the positive electrode active material.

[0016] The non-aqueous electrolyte energy storage element described in [3] above has a smaller irreversible capacity. The reason for this is not clear, but it is presumed that the presence of at least one of the tungsten and boron elements on the surface of the positive electrode active material particles suppresses the reaction of the compound represented by formula (1) at the positive electrode, and that a film derived from the compound represented by formula (1) is more easily formed on the surface of the negative electrode active material.

[0017] [4] In the non-aqueous electrolyte energy storage element described in any one of [1] to [3] above, the positive electrode active material may contain the tungsten element.

[0018] The non-aqueous electrolyte energy storage element described in [4] above can improve upon the fact that, in addition to having a small irreversible capacity, the resistance after the charge-discharge cycle is high when the positive electrode active material contains tungsten. The reason for this is not clear, but it is presumed that the film formed on the surface of the negative electrode active material, derived from the compound represented by formula (1) above, suppresses the deposition of tungsten dissolved from the positive electrode active material on the surface of the negative electrode active material.

[0019] [5] In the non-aqueous electrolyte energy storage element described in any one of [1] to [4] above, the positive electrode active material may contain the boron element.

[0020] The non-aqueous electrolyte energy storage element described in [5] above can improve upon the fact that, in addition to having a small irreversible capacity, the positive electrode active material contains boron, which results in high resistance after storage in a high-temperature environment. The reason for this is not clear, but it is presumed that when the positive electrode active material contains boron, the reaction of the compound represented by formula (1) at the positive electrode is further suppressed, and a film derived from the compound represented by formula (1) is more easily formed on the surface of the negative electrode active material.

[0021] This document describes in detail a non-aqueous electrolyte energy storage element, an energy storage device, a method for manufacturing a non-aqueous electrolyte energy storage element, and other embodiments according to one embodiment of the present invention. Note that the names of the components (parts) used in each embodiment may differ from the names of the components (parts) used in the background art.

[0022] <Non-aqueous electrolyte energy storage element> A non-aqueous electrolyte energy storage element (hereinafter also simply referred to as "energy storage element") according to one embodiment of the present invention comprises an electrode body having a positive electrode, a negative electrode, and a separator, a non-aqueous electrolyte, and a container for housing the electrode body and the non-aqueous electrolyte. The electrode body is usually a stacked type in which a plurality of positive electrodes and a plurality of negative electrodes are stacked with a separator in between, or a wound type in which the positive electrode and negative electrode are wound in a stacked state with a separator in between. The non-aqueous electrolyte exists in a state impregnated with the positive electrode, negative electrode, and separator. As an example of a non-aqueous electrolyte energy storage element, a non-aqueous electrolyte secondary battery (hereinafter also simply referred to as "secondary battery") will be described.

[0023] (positive electrode) The positive electrode comprises a positive electrode substrate and a positive electrode active material layer disposed directly on the positive electrode substrate or via an intermediate layer.

[0024] The positive electrode substrate is conductive. Whether or not it is conductive is determined by the volume resistivity measured in accordance with JIS-H-0505 (1975), which is 10 -2The determination is made using Ω·cm as the threshold. The positive electrode substrate material can be a metal such as aluminum, titanium, tantalum, or stainless steel, or an alloy thereof. Among these, aluminum or an aluminum alloy is preferred from the viewpoint of high potential resistance, high conductivity, and cost. Examples of positive electrode substrates include foil, vapor-deposited film, mesh, and porous material, with foil being preferred from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferred as the positive electrode substrate. Examples of aluminum or aluminum alloys include A1085, A3003, and A1N30 as specified in JIS-H-4000 (2014) or JIS-H-4160 (2006).

[0025] The average thickness of the positive electrode substrate is preferably 3 μm to 50 μm, more preferably 5 μm to 40 μm, even more preferably 8 μm to 30 μm, and particularly preferably 10 μm to 25 μm. By setting the average thickness of the positive electrode substrate within the above range, it is possible to increase the strength of the positive electrode substrate while increasing the energy density per unit volume of the non-aqueous electrolyte energy storage element.

[0026] The intermediate layer is a layer placed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer contains a conductive agent such as carbon particles to reduce the contact resistance between the positive electrode substrate and the positive electrode active material layer. The composition of the intermediate layer is not particularly limited and may include, for example, a binder and a conductive agent.

[0027] The positive electrode active material layer contains a positive electrode active material. The positive electrode active material layer may optionally contain conductive agents, binders, thickeners, fillers, and other optional components.

[0028] The positive electrode active material contains at least one of tungsten and boron. The positive electrode active material is usually in the form of particles (powder). At least one of tungsten and boron may be present on at least the surface of the particles of the positive electrode active material. At least one of tungsten and boron may be scattered on the surface of the particles of the positive electrode active material, or may form a coating layer. In addition, at least one of tungsten and boron may be present inside the particles of the positive electrode active material. If the positive electrode active material is a secondary particle, at least one of tungsten and boron may be present at the grain boundaries of the primary particles of the positive electrode active material.

[0029] At least one of the tungsten and boron elements contained in the positive electrode active material may exist in the form of a compound, such as an oxide (tungsten oxide, boron oxide, etc.). The oxide may further contain other elements other than at least one of the tungsten and boron elements and oxygen. The compound containing at least one of the tungsten and boron elements may be, for example, scattered on the surface of the particles of the positive electrode active material, forming a coating layer, or, if the positive electrode active material is a secondary particle, present at the grain boundaries of the primary particles of the positive electrode active material.

[0030] In one embodiment of the present invention, a compound containing at least one of tungsten and boron may coat at least a portion of the surface of particles of a substance capable of intercepting and releasing charge transport ions such as lithium ions. In this embodiment, the positive electrode active material comprises a substance capable of intercepting and releasing charge transport ions and a compound containing at least one of tungsten and boron. The positive electrode active material may substantially consist only of a substance capable of intercepting and releasing charge transport ions and a compound containing at least one of tungsten and boron. Alternatively, the substance capable of intercepting and releasing charge transport ions itself may contain at least one of tungsten and boron.

[0031] One method for incorporating at least one of tungsten and boron into the positive electrode active material is to coat the particle surface of a material capable of intercepting and releasing charge transport ions with a compound containing at least one of tungsten and boron. After coating with the compound containing at least one of tungsten and boron, heat treatment or the like may be performed. Another method involves adding a material containing at least one of tungsten and boron during the synthesis of a material capable of intercepting and releasing charge transport ions, and then calcining it to incorporate at least one of tungsten and boron into the particles of the positive electrode active material. Commercially available products may be used as the positive electrode active material containing at least one of tungsten and boron.

[0032] In one embodiment of the present invention, the positive electrode active material may contain tungsten. This type of non-aqueous electrolyte energy storage element can improve upon the fact that, in addition to having a small irreversible capacity, the positive electrode active material contains tungsten, which results in high resistance after charge-discharge cycles.

[0033] In one embodiment of the present invention, the positive electrode active material may contain the element boron. This type of non-aqueous electrolyte energy storage element can improve upon the fact that, in addition to having a small irreversible capacity, the positive electrode active material contains the element boron, which results in high resistance after storage in a high-temperature environment.

[0034] In one embodiment of the present invention, the positive electrode active material may contain both tungsten and boron.

[0035] The content of at least one of tungsten and boron in the positive electrode active material (or the total content of both if both are included) is preferably 0.05 mol% to 3 mol%, and more preferably 0.2 mol% to 2 mol%, relative to the total content of all metal elements other than lithium in the positive electrode active material. The advantages of including these elements are fully realized when the content of at least one of tungsten and boron is within the above range. All metal elements other than lithium in the positive electrode active material include tungsten and boron.

[0036] The content of tungsten, boron, and all metallic elements in the positive electrode active material can be determined by inductively coupled plasma atomic emission spectroscopy (ICP). Specifically, the procedure is as follows: First, the non-aqueous electrolyte energy storage element is discharged at a constant current of 0.05C to the lower limit voltage for normal use. Here, "normal use" refers to using the non-aqueous electrolyte energy storage element under the charge and discharge conditions recommended or specified for the element. Next, the non-aqueous electrolyte energy storage element is disassembled, the positive electrode is removed, and a test battery is assembled with a metallic Li electrode as the counter electrode. The positive electrode potential is then measured at a current of 10mA per gram of positive electrode mixture, resulting in a positive electrode potential of 2.0V vs. Li / Li +Constant current discharge is performed until the positive electrode is fully discharged. The positive electrode active material is collected from the fully discharged positive electrode. The collected positive electrode active material is then completely dissolved using an acid capable of dissolving tungsten, boron, and other metallic elements contained in the positive electrode active material by microwave decomposition. Next, this solution is diluted to a certain volume with pure water to prepare the measurement solution. Then, the concentrations of tungsten, boron, and other metallic elements in the measurement solution are measured by ICP emission spectroscopy using a multi-type ICP emission spectrometer ICPE-9820 (manufactured by Shimadzu Corporation). The element content in the positive electrode active material is quantified from the obtained concentrations of each element. Note that in calculating the concentration of each element in the measurement solution, a calibration curve method can be used to create a calibration curve from solutions of known concentrations of tungsten, boron, and other metallic elements, and to determine the concentrations of tungsten, boron, and other metallic elements in the measurement solution. Furthermore, the presence of at least one of tungsten and boron on the surface of the positive electrode active material can be confirmed by observing the distribution of tungsten, boron, and other metallic elements on the surface of the positive electrode active material using a scanning electron microscope-energy dispersive X-ray analyzer (SEM-EDX), electron probe microanalyzer (EPMA), etc.

[0037] As a substance capable of intercepting and releasing charge transport ions, a substance capable of intercepting and releasing lithium ions is preferred, and conventionally known materials can be used for this purpose. Examples of such substances include lithium transition metal composite oxides having an α-NaFeO2 type crystal structure, lithium transition metal composite oxides having a spinel type crystal structure, polyanion compounds, chalcogen compounds, sulfur, etc. As an example of a lithium transition metal composite oxide having an α-NaFeO2 type crystal structure, Li[Li x Ni (1-x) ]O2(0≦x<0.5), Li[Li x Ni γ Co (1-x-γ) ]O2(0≦x<0.5, 0<γ<1, 0<1-x-γ), Li[Li x Co (1-x)]O2(0≦x<0.5), Li[Li x Ni γ Mn (1-x-γ) ]O2(0≦x<0.5, 0<γ<1, 0<1-x-γ), Li[Li x Ni γ Mn β Co (1-x-γ-β) ]O2(0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1, 0<1-x-γ-β), Li[Li x Ni γ Co β Al (1-x-γ-β) Examples include ]O2 (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1, 0<1-x-γ-β), etc. As a lithium transition metal composite oxide having a spinel-type crystal structure, Li x Mn2O4, Li x Ni γ Mn (2-γ) Examples include O4. Examples of polyanion compounds include LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, Li2CoPO4F, etc. Examples of chalcogen compounds include titanium disulfide, molybdenum disulfide, molybdenum dioxide, etc. The atoms or polyanions in these materials may be partially substituted with atoms or anion species of other elements. These materials may be compounded with other materials. In the positive electrode active material layer, these materials may be used individually or as a mixture of two or more.

[0038] As a substance capable of intercalating and releasing charge transport ions, lithium transition metal composite oxides are preferred, and lithium transition metal composite oxides having an α-NaFeO2 type crystal structure are more preferred. Among lithium transition metal composite oxides having an α-NaFeO2 type crystal structure, those containing at least one of nickel, cobalt, and manganese are preferred, and those containing nickel, cobalt, and manganese are more preferred.

[0039] As described above, the positive electrode active material is usually in the form of particles (powder). The average particle size of the positive electrode active material is preferably, for example, 0.1 μm or more and 20 μm or less. Setting the average particle size of the positive electrode active material above the lower limit makes it easier to manufacture or handle the positive electrode active material. Setting the average particle size of the positive electrode active material below the upper limit improves the electronic conductivity of the positive electrode active material layer. When a composite material of the positive electrode active material and other materials is used, the average particle size of the composite material is used as the average particle size of the positive electrode active material. "Average particle size" refers to the value at which the volume-based integrated distribution calculated in accordance with JIS-Z-8819-2 (2001), based on the particle size distribution measured by laser diffraction / scattering method on a dilution of particles diluted with a solvent, in accordance with JIS-Z-8825 (2013), becomes 50%.

[0040] To obtain powder with a predetermined particle size, grinders and classifiers are used. Examples of grinding methods include using mortars, ball mills, sand mills, vibrating ball mills, planetary ball mills, jet mills, counter-jet mills, swirling airflow jet mills, or sieves. Wet grinding, which involves the coexistence of water or organic solvents such as hexane, can also be used during grinding. For classification, sieves and wind classifiers are used as needed, both dry and wet.

[0041] The content of the positive electrode active material in the positive electrode active material layer is preferably 50% to 99% by mass, more preferably 70% to 98% by mass, and even more preferably 80% to 95% by mass. By setting the content of the positive electrode active material within the above range, it is possible to achieve both high energy density and manufacturability in the positive electrode active material layer.

[0042] The conductive agent is not particularly limited as long as it is a conductive material. Examples of such conductive agents include carbonaceous materials, metals, and conductive ceramics. Examples of carbonaceous materials include graphite, non-graphitic carbon, and graphene-based carbon. Examples of non-graphitic carbon include carbon nanofibers, pitch-based carbon fibers, and carbon black. Examples of carbon black include furnace black, acetylene black, and Ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNTs), and fullerenes. The conductive agent can take the form of powder or fiber. One of these materials may be used alone as the conductive agent, or two or more may be used in mixture form. These materials may also be used in composite form. For example, a composite material of carbon black and CNTs may be used. Among these, carbon black is preferred from the viewpoint of electronic conductivity and coating properties, and acetylene black is particularly preferred.

[0043] The content of the conductive agent in the positive electrode active material layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. By setting the content of the conductive agent within the above range, the energy density of the non-aqueous electrolyte energy storage element can be increased.

[0044] Examples of binders include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylic, and polyimide; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers.

[0045] The binder content in the positive electrode active material layer is preferably 0.5% by mass or more and 10% by mass or less, and more preferably 1% by mass or more and 5% by mass or less. By keeping the binder content within the above range, the positive electrode active material can be stably maintained.

[0046] Examples of thickening agents include polysaccharide polymers such as carboxymethylcellulose (CMC) and methylcellulose. If the thickening agent has a functional group that reacts with lithium, etc., this functional group may be deactivated beforehand by methylation or the like. When a thickening agent is used in the positive electrode active material layer, the content of the thickening agent in the positive electrode active material layer can be 0.1% by mass or more and 8% by mass or less, usually preferably 5% by mass or less, and more preferably 2% by mass or less. The technology disclosed herein can preferably be carried out in a manner in which the positive electrode active material layer does not contain a thickening agent.

[0047] The filler is not particularly limited. Examples of fillers include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates, hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide, carbonates such as calcium carbonate, sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate, nitrides such as aluminum nitride and silicon nitride, mineral resource-derived materials such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof. When a filler is used in the positive electrode active material layer, the filler content in the positive electrode active material layer can be 0.1% by mass or more and 8% by mass or less, usually preferably 5% by mass or less, and more preferably 2% by mass or less. The technology disclosed herein can preferably be implemented in a manner in which the positive electrode active material layer does not contain a filler.

[0048] The positive electrode active material layer may contain typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba, and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, and W as components other than the positive electrode active material, conductive agent, binder, thickener, and filler.

[0049] (Negative electrode) The negative electrode comprises a negative electrode substrate and a negative electrode active material layer disposed directly on the negative electrode substrate or via an intermediate layer. The configuration of the intermediate layer is not particularly limited and can be selected from, for example, the configurations exemplified in the positive electrode.

[0050] The negative electrode substrate is electrically conductive. Suitable materials for the negative electrode substrate include metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, or alloys thereof, as well as carbonaceous materials. Among these, copper or copper alloys are preferred. Examples of negative electrode substrates include foil, vapor-deposited film, mesh, and porous materials, with foil being preferred from a cost perspective. Therefore, copper foil or copper alloy foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0051] The average thickness of the negative electrode substrate is preferably 2 μm to 35 μm, more preferably 3 μm to 30 μm, even more preferably 4 μm to 25 μm, and particularly preferably 5 μm to 20 μm. By setting the average thickness of the negative electrode substrate within the above range, it is possible to increase the strength of the negative electrode substrate while increasing the energy density per unit volume of the non-aqueous electrolyte energy storage element.

[0052] The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer optionally contains conductive agents, binders, thickeners, fillers, and other optional components. These optional components can be selected from the materials exemplified above for the positive electrode.

[0053] The negative electrode active material layer may contain typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba, and transition metallic elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W as components other than the negative electrode active material, conductive agent, binder, thickener, and filler.

[0054] The negative electrode active material can be appropriately selected from known negative electrode active materials. For lithium-ion secondary batteries, materials capable of intercalating and releasing lithium ions are typically used as negative electrode active materials. Examples of negative electrode active materials include: metallic Li; metals or metalloids such as Si and Sn; metal oxides or metalloid oxides such as Si oxide, Ti oxide, and Sn oxide; and Li4Ti5O 12 LiTiO 2、 Examples of materials include titanium-containing oxides such as TiNb2O7; polyphosphate compounds; silicon carbide; and carbon materials such as graphite and non-graphitizable carbon (easily graphitizable carbon or poorly graphitizable carbon). Among these materials, graphite and non-graphitizable carbon are preferred, with graphite being more preferred. In the negative electrode active material layer, one of these materials may be used alone, or two or more may be used in mixture form.

[0055] "Graphite" refers to the average lattice plane spacing (d) of the (002) plane, determined by X-ray diffraction before charging or discharging, or during the discharge state. 002 ) refers to carbon materials with a n-scale of 0.33 nm or more and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite. From the viewpoint of obtaining materials with stable physical properties, artificial graphite is preferred, while natural graphite is preferred from the viewpoint of high crystallinity which improves the input performance of non-aqueous electrolyte energy storage elements.

[0056] "Non-graphite carbon" refers to the average lattice plane spacing (d) of the (002) plane, which is determined by X-ray diffraction before charging or during the discharge state. 002 This refers to carbon materials with a nautical radius of 0.34 nm or more and 0.42 nm or less. Non-graphitized carbons include poorly graphitizable carbons and easily graphitizable carbons. Examples of non-graphitized carbons include resin-derived materials, petroleum pitch or materials derived from petroleum pitch, petroleum coke or materials derived from petroleum coke, plant-derived materials, and alcohol-derived materials.

[0057] Here, "discharge state" refers to a state in which sufficient lithium ions capable of being absorbed and released during charging and discharging are released from the carbon material, which is the negative electrode active material. For example, in a half-cell using a negative electrode containing a carbon material as the negative electrode active material as the working electrode and a metallic Li electrode as the counter electrode, this is a state in which the open-circuit voltage is 0.7V or higher.

[0058] "Non-graphitizable carbon" refers to the above d 002 This refers to carbon materials with a wavelength of 0.36 nm or more and 0.42 nm or less.

[0059] "Easily graphitizable carbon" refers to the above d 002 This refers to carbon materials with a wavelength of 0.34 nm or more and less than 0.36 nm.

[0060] The negative electrode active material is usually in the form of particles (powder). The average particle size of the negative electrode active material can be, for example, 1 nm to 100 μm. If the negative electrode active material is a carbon material, titanium-containing oxide, or polyphosphate compound, its average particle size may be 1 μm to 100 μm, or 5 μm to 20 μm. If the negative electrode active material is Si, Sn, Si oxide, or Sn oxide, its average particle size may be 1 nm to 1 μm. Setting the average particle size of the negative electrode active material above the lower limit makes it easier to manufacture or handle. Setting the average particle size of the negative electrode active material below the upper limit improves the electronic conductivity of the negative electrode active material layer. To obtain powder with a predetermined particle size, a pulverizer or classifier is used. The pulverizing method and classification method can be selected from, for example, the methods exemplified above for the positive electrode. If the negative electrode active material is a metal such as metallic Li, the negative electrode active material layer may be in the form of foil.

[0061] The BET specific surface area of ​​the negative electrode active material is 3m². 2 / g or more 12m 2 It may be less than / g, 4m 2 / g or more 8m 2It may be less than or equal to / g. When one embodiment of the present invention is applied to a non-aqueous electrolyte energy storage element using a negative electrode active material having a BET specific surface area in such a range, the amount of film formed on the surface of the negative electrode active material becomes appropriate, and effects such as a reduction in irreversible capacity may occur particularly significantly.

[0062] The "BET specific surface area" of the negative electrode active material is determined by the following method. First, the non-aqueous electrolyte energy storage element is discharged with a constant current of 0.05C to the lower limit voltage during normal use, and then discharged. Next, the discharged non-aqueous electrolyte energy storage element is disassembled, the negative electrode is removed, the attached components (non-aqueous electrolyte, etc.) are thoroughly washed, and the negative electrode active material obtained by drying under reduced pressure at room temperature for 24 hours is subjected to pore size distribution measurement using the nitrogen adsorption method. This measurement can be performed using Quantachrome's "autosorb iQ". Five points are extracted from the region P / P0 = 0.06 to 0.3 of the obtained adsorption isotherm and a BET plot is performed, and the BET specific surface area is calculated from the y-intercept and slope of the line.

[0063] The content of the negative electrode active material in the negative electrode active material layer is preferably 60% by mass or more and 99% by mass or less, and more preferably 90% by mass or more and 98% by mass or less. By setting the content of the negative electrode active material within the above range, it is possible to achieve both high energy density and manufacturability in the negative electrode active material layer.

[0064] When a conductive agent is used in the negative electrode active material layer, the content of the conductive agent in the negative electrode active material layer may be 1% by mass or more and 10% by mass or less, or 3% by mass or more and 9% by mass or less. When the negative electrode active material is a carbon material or the like, the negative electrode active material layer does not need to contain a conductive agent.

[0065] The binder content in the negative electrode active material layer is preferably 0.5% by mass or more and 10% by mass or less, and more preferably 1% by mass or more and 5% by mass or less. By keeping the binder content within the above range, the negative electrode active material can be stably maintained.

[0066] The content of the thickener in the negative electrode active material layer is preferably 0.1% by mass or more and 8% by mass or less, and more preferably 0.3% by mass or more and 5% by mass or less.

[0067] When a filler is used in the negative electrode active material layer, the filler content in the negative electrode active material layer can be 0.1% by mass or more and 8% by mass or less, and is generally preferably 5% by mass or less, and more preferably 2% by mass or less. The technology disclosed herein can preferably be carried out in a manner in which the negative electrode active material layer does not contain a filler.

[0068] (Separator) The separator can be appropriately selected from known separators. Examples of separators include a separator consisting only of a base layer, or a separator in which a heat-resistant layer containing heat-resistant particles and a binder is formed on one or both sides of the base layer. Examples of the base layer shape of the separator include woven fabric, nonwoven fabric, and porous resin film. Among these shapes, porous resin film is preferred from the viewpoint of strength, and nonwoven fabric is preferred from the viewpoint of liquid retention of non-aqueous electrolytes. As for the material of the base layer of the separator, polyolefins such as polyethylene and polypropylene are preferred from the viewpoint of shutdown function, and polyimide and aramid are preferred from the viewpoint of oxidative degradation resistance. A composite material of these resins may also be used as the base layer of the separator.

[0069] The heat-resistant particles contained in the heat-resistant layer preferably have a mass loss of 5% or less when heated from room temperature to 500°C in an air atmosphere of 1 atmosphere, and more preferably have a mass loss of 5% or less when heated from room temperature to 800°C. Inorganic compounds are examples of materials with a mass loss of less than the specified amount. Examples of inorganic compounds include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates; 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; covalent crystals such as silicon and diamond; mineral resource-derived materials such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof. These inorganic compounds may be used individually or in combination, or two or more may be used as a mixture. Among these inorganic compounds, silicon dioxide, aluminum oxide, or aluminosilicates are preferred from the viewpoint of safety for energy storage elements.

[0070] The porosity of the separator is preferably 80 volume% or less from the viewpoint of strength, and preferably 20 volume% or more from the viewpoint of discharge performance. Here, "porosity" refers to a volume-based value and means the measurement value obtained using a mercury porosimeter.

[0071] A polymer gel composed of a polymer and a non-aqueous electrolyte may be used as a separator. Examples of polymers include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, and polyvinylidene fluoride. Using a polymer gel has the effect of suppressing leakage. A polymer gel may also be used in combination with a porous resin film or nonwoven fabric as described above as a separator.

[0072] (Non-aqueous electrolytes) The non-aqueous electrolyte contains a compound represented by the following formula (1) (hereinafter also referred to as the "first compound"). By including the first compound in the non-aqueous electrolyte, the irreversible capacity of a non-aqueous electrolyte energy storage element equipped with a positive electrode having a positive electrode active material containing at least one of tungsten and boron can be reduced. Furthermore, by including the first compound in the non-aqueous electrolyte, the high resistance after charge-discharge cycles in a non-aqueous electrolyte energy storage element equipped with a positive electrode having a positive electrode active material containing tungsten can be improved, and the high resistance after storage in a high-temperature environment in a non-aqueous electrolyte energy storage element equipped with a positive electrode having a positive electrode active material containing boron can be improved. [ka]

[0073] In formula (1), R 1 From R 3 Each of these is independently a fluorine atom or an organic group having 1 to 10 carbon atoms. However, R 1 From R 3 At least one of them is a fluorine atom. m+ m is an alkali metal ion, an alkaline earth metal ion, or an onium ion. m+ These are integers equal to the valence of [the variable].

[0074] An organic group is a group containing at least one carbon atom. Examples of organic groups include hydrocarbon groups, groups in which an oxygen atom (-O-), a carbonyl group (-CO-), or a combination thereof is bonded between or at the end of a hydrocarbon group's carbon atoms, and groups in which at least one hydrogen atom of these groups is substituted with another atom (e.g., a halogen atom such as a fluorine atom) or another group (e.g., a carboxyl group, an amino group, etc.). Preferred organic groups are hydrocarbon groups, groups in which an oxygen atom is bonded to the end of a hydrocarbon group, or groups in which at least one hydrogen atom of these groups is substituted with a fluorine atom.

[0075] The hydrocarbon group may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group. Examples of aliphatic hydrocarbon groups include alkyl groups, alkenyl groups, alkynyl groups, cycloalkyl groups, and cycloalkenyl groups. Examples of aromatic hydrocarbon groups include phenyl groups and benzyl groups.

[0076] R 1 From R 3 As such, a fluorine atom or an organic group having 1 to 6 carbon atoms is preferred, a fluorine atom or an organic group having 1 to 3 carbon atoms is more preferred, and a fluorine atom is even more preferred. That is, R 1 , R 2 and R 3 It is most preferable that each of these atoms is a fluorine atom.

[0077] Examples of alkali metal ions include lithium ions (Li + ), sodium ions (Na + ), potassium ions (K + Examples include magnesium ions (Mg 2+ ), calcium ions (Ca 2+ Examples include the onium ion (onium cation), and the ammonium ion (NH4). + ), phosphonium ion (PH4 + ), sulfonium ion (SH3 + Examples include ions in which at least one hydrogen atom of these ions is substituted with another atom (e.g., a halogen atom such as a fluorine atom) or group (e.g., an alkyl group, a carboxyl group, an amino group, etc.).

[0078] M m+ As such, alkali metal ions are preferred, and lithium ions (Li + ) is preferable.

[0079] M m+ If it is a monovalent ion, then m is 1. m+ If it is a divalent ion, then m is 2.

[0080] The first compound can be one or more types. The first compound is composed of an anion and a cation (M) in a non-aqueous electrolyte. m+ ) may exist in a dissociated state as an anion and a cation (M m+ ) may exist in a bonded state with cation (M m+ ) If it is a divalent or greater ion, it consists of an anion and a number of cations (M) between 1 and 1. m+ ) may exist in a combined state.

[0081] The content of the first compound in the non-aqueous electrolyte is preferably greater than 0% by mass and 5% by mass or less, more preferably 0.01% by mass or more and 4% by mass or less, even more preferably 0.05% by mass or more and 3% by mass or less, and even more preferably 0.1% by mass or more and 2% by mass or less. By setting the content of the first compound within the above range, the effects of the first compound, such as reducing irreversible capacity, are more fully realized. At least a portion of the first compound contained in the non-aqueous electrolyte is decomposed during initial charging and discharging, mainly forming a film that covers the surface of the negative electrode active material. Therefore, if it can be confirmed that even a small amount of the first compound remains in the non-aqueous electrolyte of the non-aqueous electrolyte energy storage element, it can be said that a sufficient film has already been formed on the surface of the negative electrode active material, and thus the effects of the first compound are realized.

[0082] The non-aqueous electrolyte preferably further contains a compound having an anion containing the element boron (hereinafter also referred to as the "second compound"). The further inclusion of the second compound in the non-aqueous electrolyte reduces the irreversible capacity of the non-aqueous electrolyte energy storage element.

[0083] Anions containing the element boron include the tetrafluoroborate anion (BF4). - ), difluorooxalatoborate anion (BF2(C2O4) - ), bis(oxalato)borate anion (B(C2O4)2 - Examples include the following. Among these, oxalate complex anions having a boron element, such as difluorooxalatoborate anions and bisoxalatoborate anions, are preferred.

[0084] The second compound is usually a salt consisting of a boron-containing anion and a cation. The cation constituting the second compound is M in formula (1) above. m+ Examples of alkali metal ions, alkaline earth metal ions, or onium ions represented by the same as those exemplified are shown, with alkali metal ions being preferred, and lithium ions (Li + ) is preferable.

[0085] The second compound may be one or more types. The second compound may exist in a non-aqueous electrolyte in a dissociated state as an anion and a cation, or in a state in which the anion and cation are bonded. If the cation is a divalent or higher ion, it may exist in a state in which the anion is bonded to 1 or more cations but less than m.

[0086] The content of the second compound in the non-aqueous electrolyte is preferably greater than 0% by mass and 3% by mass or less, more preferably 0.01% by mass or more and 2% by mass or less, even more preferably 0.05% by mass or more and 1% by mass or less, and even more preferably 0.1% by mass or more and 0.5% by mass or less. By setting the content of the second compound within the above range, the effect of the second compound, such as reducing irreversible capacity, is more fully realized. At least a portion of the second compound contained in the non-aqueous electrolyte is decomposed during initial charging and discharging, forming a film on the surface of the negative electrode active material. Therefore, if it can be confirmed that even a small amount of the second compound remains in the non-aqueous electrolyte of the non-aqueous electrolyte energy storage element, it can be said that a sufficient film has already been formed on the surface of the negative electrode active material, and thus the effect of the second compound is realized.

[0087] The non-aqueous electrolyte may also be a non-aqueous electrolyte solution. The non-aqueous electrolyte solution comprises a non-aqueous solvent, an electrolyte salt dissolved in the non-aqueous solvent, and the first compound. Preferably, the non-aqueous electrolyte solution further contains a second compound as a component dissolved in the non-aqueous solvent. The first compound or the second compound may function as an electrolyte salt.

[0088] As the non-aqueous solvent, any known non-aqueous solvent can be appropriately selected. Examples of non-aqueous solvents include cyclic carbonates, linear carbonates, carboxylic acid esters, phosphate esters, ethers, amides, and nitriles. As the non-aqueous solvent, compounds in which some of the hydrogen atoms contained in these compounds are substituted with halogen atoms may also be used.

[0089] Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), chloroethylene carbonate, fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), styrene carbonate, 1-phenylvinylene carbonate, and 1,2-diphenylvinylene carbonate. Among these, EC and PC are preferred.

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

[0091] It is preferable to use a cyclic carbonate or a linear carbonate as the non-aqueous solvent, and it is more preferable to use a cyclic carbonate and a linear carbonate in combination. Using a cyclic carbonate can promote the dissociation of the electrolyte salt and improve the ionic conductivity of the non-aqueous electrolyte. Using a linear carbonate can keep the viscosity of the non-aqueous electrolyte low. When using a cyclic carbonate and a linear carbonate in combination, the volume ratio of the cyclic carbonate to the linear carbonate (cyclic carbonate:linear carbonate) is preferably in the range of 5:95 to 50:50.

[0092] The electrolyte salt can be appropriately selected from known electrolyte salts. Examples of electrolyte salts include lithium salts, sodium salts, potassium salts, magnesium salts, and onium salts. Among these, lithium salts are preferred.

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

[0094] The electrolyte salt content in the non-aqueous electrolyte is 0.1 mol / dm³ at 20°C and 1 atm. 3 More than 2.5mol / dm 3 Preferably, it is 0.3 mol / dm³ 3 More than 2.0mol / dm 3 It is more preferable that it be less than or equal to 0.5 mol / dm 3 More than 1.7mol / dm 3 It is even more preferable that the following is the case: 0.7 mol / dm 3 More than 1.5mol / dm 3 The following is particularly preferable. By setting the electrolyte salt content within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

[0095] The non-aqueous electrolyte may contain other components besides the first compound, the second compound, the non-aqueous solvent, and the electrolyte salt. Other components may include, for example, unsaturated cyclic carbonates such as vinylene carbonate (VC), methylvinylene carbonate, and ethylvinylene carbonate; aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partially halides of the aforementioned aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; halogenated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, and cyclohexanedicarboxylic acid anhydride; ethylene sulfite, sulfurous acid Examples include propylene sulfate, dimethyl sulfite, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethylsulfone, dimethyl sulfoxide, diethylsulfoxide, tetramethylene sulfoxide, diphenyl sulfide, 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane), 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, 1,3-propensultone, 1,3-propanesultone, 1,4-butanesultone, 1,4-butensultone, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakithtrimethylsilyl titanate, lithium monofluorophosphate, and lithium difluorophosphate. Among these, the use of unsaturated cyclic carbonates is preferred. These other components may be used individually or in combination of two or more.

[0096] The content of the above-mentioned other components in the non-aqueous electrolyte is preferably 0.01% to 10% by mass, more preferably 0.1% to 7% by mass, even more preferably 0.2% to 5% by mass, and particularly preferably 0.3% to 3% by mass, relative to the total mass of the non-aqueous electrolyte. By setting the content of the above-mentioned other components within the above range, it is possible to improve the capacity retention performance or cycle performance after high-temperature storage, or to further improve safety. The upper limit of the content of the above-mentioned other components may be 2% by mass or 1% by mass.

[0097] As the non-aqueous electrolyte, a non-aqueous electrolyte and a solid electrolyte may be used in combination. The solid electrolyte can be selected from any material that has ionic conductivity, such as lithium, sodium, and calcium, and is solid at room temperature (e.g., 15°C to 25°C). Examples of solid electrolytes include sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and polymer solid electrolytes.

[0098] The shape of the non-aqueous electrolyte energy storage element in this embodiment is not particularly limited, and examples include cylindrical batteries, prismatic batteries, flat batteries, coin-type batteries, button-type batteries, and the like.

[0099] Figure 1 shows a non-aqueous electrolyte energy storage element 1 as an example of a rectangular battery. Note that the figure is a transparent view of the inside of the container. An electrode body 2 having a positive electrode and a negative electrode wound around a separator is housed in a rectangular container 3. The positive electrode is electrically connected to the positive electrode terminal 4 via a positive electrode lead 41. The negative electrode is electrically connected to the negative electrode terminal 5 via a negative electrode lead 51.

[0100] <Energy storage device> The non-aqueous electrolyte energy storage element of this embodiment can be mounted as an energy storage unit (battery module) composed of multiple non-aqueous electrolyte energy storage elements in power supplies for vehicles such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), power supplies for electronic devices such as personal computers and communication terminals, or power storage power supplies. In this case, it is sufficient that the technology of the present invention is applied to at least one of the non-aqueous electrolyte energy storage elements included in the energy storage unit.

[0101] Figure 2 shows an example of a power storage device 30 which is formed by further assembling power storage units 20, each of which is an assembly of two or more electrically connected non-aqueous electrolyte energy storage elements 1. The power storage device 30 may include busbars (not shown) that electrically connect two or more non-aqueous electrolyte energy storage elements 1, busbars (not shown) that electrically connect two or more power storage units 20, etc. The power storage unit 20 or the power storage device 30 may include a condition monitoring device (not shown) that monitors the state of one or more non-aqueous electrolyte energy storage elements 1.

[0102] <Method for manufacturing a non-aqueous electrolyte energy storage element> The method for manufacturing the non-aqueous electrolyte energy storage element of this embodiment can be appropriately selected from known methods. The manufacturing method comprises, for example, preparing an electrode body, preparing a non-aqueous electrolyte containing a first compound, and housing the electrode body and the non-aqueous electrolyte in a container. Preparing the electrode body comprises preparing a positive electrode and a negative electrode having a positive electrode active material containing at least one of tungsten and boron, and forming the electrode body by stacking or winding the positive electrode and the negative electrode via a separator.

[0103] The method for housing the non-aqueous electrolyte in a container can be appropriately selected from known methods. For example, when using a non-aqueous electrolyte solution, the non-aqueous electrolyte solution can be injected through an inlet formed in the container, and then the inlet can be sealed.

[0104] <Other Embodiments> Furthermore, the non-aqueous electrolyte energy storage element of the present invention is not limited to the above 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, and a part of the configuration of one embodiment may be replaced with the configuration of another embodiment or known technology. In addition, a part of the configuration of one embodiment may be deleted. Also, known technology may be added to the configuration of one embodiment.

[0105] In the above embodiment, the case in which the non-aqueous electrolyte energy storage element is used as a rechargeable non-aqueous electrolyte secondary battery (e.g., a lithium-ion secondary battery) was described, but the type, shape, dimensions, capacity, etc. of the non-aqueous electrolyte energy storage element are arbitrary. The present invention can also be applied to various secondary batteries, electric double-layer capacitors, or capacitors such as lithium-ion capacitors.

[0106] In the above embodiment, an electrode body in which a positive electrode and a negative electrode are stacked with a separator in between has been described, but the electrode body does not need to have a separator. For example, the positive electrode and the negative electrode may be in direct contact with each other, with a non-conductive layer formed on the active material layer of either the positive electrode or the negative electrode. [Examples]

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

[0108] [Example 1] (Fabrication of the positive electrode) LiRing 1 / 3 Mn 1 / 3 Co 1 / 3 A positive electrode active material (hereinafter also referred to as "active material W") was prepared by attaching tungsten oxide to the surface of O2 particles. The tungsten content in this active material W relative to all metal elements other than lithium was 0.5 mol%. A positive electrode mixture paste containing the above positive electrode active material, polyvinylidene fluoride (PVDF) as a binder, and acetylene black (AB) as a conductive agent, with N-methylpyrrolidone (NMP) as a dispersion medium was prepared. The mass ratio of the positive electrode active material, the binder, and the conductive agent was set to 94.5:1.5:4.0 in terms of solid content. The positive electrode mixture paste was applied onto an aluminum foil serving as a positive electrode current collector, dried, and pressed to form a positive electrode active material layer. Thus, a positive electrode in which a positive electrode active material layer was laminated on a positive electrode current collector was obtained.

[0109] (Production of Negative Electrode) Graphite as a negative electrode active material (average particle diameter: 10.0 µm, BET specific surface area: 6.12 m 2 / g), styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener, with water as a dispersion medium, was used to prepare a negative electrode mixture paste. The mass ratio of the negative electrode active material, the binder, and the thickener was 97.8:1.0:1.2 in terms of solid content. The negative electrode mixture paste was applied onto a copper foil serving as a negative electrode current collector, dried, and pressed to form a negative electrode active material layer. Thus, a negative electrode in which a negative electrode active material layer was laminated on a negative electrode current collector was obtained.

[0110] (Preparation of Nonaqueous Electrolyte) Lithium hexafluorophosphate (LiPF6) as an electrolyte salt was added at 1.0 mol / dm 3 to a nonaqueous solvent obtained by mixing ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) at a volume ratio of 25:5:70, and mixed at this concentration. To this mixed solution, lithium difluorophosphonyl fluorosulfonyl imide (in the above formula (1), R 1 to R 3 are each a fluorine atom, M m+ is Li + , m is 1; hereinafter also referred to as "compound A") was mixed at a content of 2.0% by mass, and vinylene carbonate (VC) was mixed at a content of 0.5% by mass, to prepare a nonaqueous electrolyte. Note that, in the present examples (including comparative examples and reference examples), components other than the nonaqueous solvent and the electrolyte salt contained in the nonaqueous electrolyte are referred to as additives.

[0111] (Assembly of Nonaqueous Electrolyte Electricity Storage Element) The above positive electrode and negative electrode were laminated with a polyethylene microporous membrane separator interposed therebetween to prepare an electrode assembly. The electrode assembly was housed in a container, and the above nonaqueous electrolyte was injected into the container, whereby the nonaqueous electrolyte electricity storage element of Example 1 was obtained.

[0112] [Examples 2 to 5, Comparative Examples 1 to 3, Reference Examples 1 to 5] Each of the nonaqueous electrolyte electricity storage elements of Examples 2 to 5, Comparative Examples 1 to 3, and Reference Examples 1 to 5 was obtained in the same manner as in Example 1, except that the type of positive electrode active material, and the type and content of the additive contained in the nonaqueous electrolyte were as described in Table 1. In Table 1, for "Active Material B", LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 A positive electrode active material obtained by adhering boron oxide to the particle surface of O2 was used. This active material B was obtained by mixing LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 particles of O2 to prepare a suspension, then drying the suspension and performing heat treatment. The content of boron element relative to all metal elements other than lithium element in this active material B was 0.5 mol%. For "Active Material X", LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 particles of O2 were used. Further, the additives used are as follows. • Compound A: lithium difluorophosphonyl fluorosulfonyl imide • LiBOB: lithium bis(oxalato)borate • LiFOB: lithium difluoro(oxalato)borate • VC: vinylene carbonate • LiFSI: lithium bis(fluorosulfonyl)imide Further, in Table 1 and Tables 2 and 3 described later, the numerical values in parentheses in each column for additives represent the content (mass%) of each additive.

[0113] [evaluation] (Initial charge / discharge) Each obtained non-aqueous electrolyte energy storage element was subjected to constant current and constant voltage charging in a constant temperature bath at 25°C with a charging current of 1.0C and a charging termination voltage of 4.10V. The charging termination condition was defined as when the charging current decreased to 0.01C. After a 10-minute rest period, constant current discharge was performed with a discharge current of 1.0C and a discharge termination voltage of 2.50V, followed by another 10-minute rest period. These charging and discharging cycles constituted one cycle, and two initial charge-discharge cycles were performed.

[0114] (1) Measurement of irreversible capacity For each non-aqueous electrolyte energy storage element that underwent initial charging and discharging, the irreversible capacity was determined by charging and discharging according to the following procedure. Constant current and constant voltage charging was performed in a constant temperature bath at 25°C with a charging current of 1.0C and a charging termination voltage of 4.10V. The charging termination condition was defined as when the charging current decreased to 0.01C. Subsequently, constant current discharging was performed with a discharge current of 1.0C and a discharge termination voltage of 2.50V. A 10-minute rest period was provided after both charging and discharging. This charging and discharging was performed for two cycles, and the sum of the irreversible capacity per unit mass of negative electrode active material (difference between charging capacity and discharging capacity) for each cycle was defined as the irreversible capacity. The values ​​of the irreversible capacity are shown in Table 1. Furthermore, Table 1 shows the relative irreversible capacities of each non-aqueous electrolyte energy storage element using the same positive electrode active material, with a non-aqueous electrolyte energy storage element containing LiBOB (0.5 mass%) and VC (0.5 mass%) as additives set as the baseline (100.0%). Specifically, in Reference Examples 1 to 5, the relative values ​​are based on Reference Example 1; in Comparative Examples 1 and 2 and Examples 1 to 3, the relative values ​​are based on Comparative Example 1; and in Comparative Example 3 and Examples 4 and 5, the relative values ​​are based on Comparative Example 3.

[0115] [Table 1]

[0116] As can be seen from the comparison between Reference Example 1 and Comparative Examples 1 and 3, a non-aqueous electrolyte energy storage element having a positive electrode with a positive electrode active material containing at least one of tungsten and boron exhibited a larger irreversible capacity compared to a non-aqueous electrolyte energy storage element having a positive electrode with a positive electrode active material that did not contain these elements. Furthermore, as can be seen from the comparison between Comparative Example 1 and Examples 1 to 3, and between Comparative Example 3 and Examples 4 and 5, in a non-aqueous electrolyte energy storage element having a positive electrode with a positive electrode active material containing at least one of tungsten and boron, the irreversible capacity was reduced by including the first compound in the non-aqueous electrolyte. As can be seen from the relative values ​​of the irreversible capacity, the effect of reducing the irreversible capacity by this first compound was particularly pronounced in the case of a non-aqueous electrolyte energy storage element having a positive electrode with a positive electrode active material containing at least one of tungsten and boron. In addition, as can be seen from the comparison between Example 1 and Examples 2 and 3, and between Example 4 and Example 5, when the non-aqueous electrolyte contained the second compound in addition to the first compound, the irreversible capacity was further reduced.

[0117] (2) Measurement of resistance after charge-discharge cycle (Charge-discharge cycle test) For each of the non-aqueous electrolyte energy storage elements in Examples 3 and 5, Comparative Examples 1 and 3, and Reference Examples 1 and 5, the initial charge and discharge described above were prepared separately, and charge and discharge cycle tests were performed according to the following procedure. Constant current and constant voltage charging was performed in a constant temperature bath at 45°C with a charging current of 1.0C and a charging termination voltage of 4.10V. The charging termination condition was set to when the charging current decreased to 0.01C. Subsequently, constant current discharge was performed with a discharge current of 1.0C and a discharge termination voltage of 2.50V. A 10-minute rest period was provided after both charging and discharging. This charge and discharge cycle was performed 4290 times.

[0118] (Measurement of DC resistance after charge-discharge cycle test) For each non-aqueous electrolyte energy storage element after the above charge-discharge cycle test, the DC resistance at input after the charge-discharge cycle test was measured in the following manner. Constant current charging was performed with a charging current of 1.0C in a constant temperature bath at 25°C to bring the SOC to 50%. Subsequently, charging was performed for 30 seconds each at charging currents of 0.2C, 0.5C, and 1.0C in that order, also in a constant temperature bath at 25°C. After each charging cycle, constant current discharge was performed with a discharge current of 0.05C to bring the SOC to 50%. The relationship between the charging current and the voltage at 10 seconds after the start of charging was plotted for each charging current, and the DC resistance at input was determined from the slope of the straight line obtained from the three plots. The results are shown in Table 2. Furthermore, Table 2 shows the relative values ​​of the DC resistance at input for each non-aqueous electrolyte energy storage element using the same positive electrode active material, with a non-aqueous electrolyte energy storage element containing only LiBOB (0.5 mass%) and VC (0.5 mass%) as additives as the baseline (100.0%). Specifically, in Reference Examples 1 and 5, the relative values ​​are based on Reference Example 1; in Comparative Example 1 and Example 3, the relative values ​​are based on Comparative Example 1; and in Comparative Example 3 and Example 5, the relative values ​​are based on Comparative Example 3.

[0119] [Table 2]

[0120] As can be seen from the comparison of Reference Example 1, Comparative Example 1, and Comparative Example 3, the non-aqueous electrolyte energy storage element having a positive electrode with a positive electrode active material containing tungsten had a higher resistance after the charge-discharge cycle compared to the non-aqueous electrolyte energy storage element having a positive electrode with a positive electrode active material that does not contain tungsten. Furthermore, as can be seen from the comparison of Comparative Example 1 and Example 3, in the non-aqueous electrolyte energy storage element having a positive electrode with a positive electrode active material containing tungsten, the resistance after the charge-discharge cycle was reduced by including the first compound in the non-aqueous electrolyte.

[0121] (3) Measurement of resistance after storage in a high-temperature environment (High-temperature storage test) For each of the non-aqueous electrolyte energy storage elements in Examples 3 and 5, Comparative Examples 1 and 3, and Reference Examples 1 and 5, the initial charge and discharge described above were prepared separately, and a high-temperature storage test was conducted as follows: Constant current and constant voltage charging was performed at a charging current of 1.0C in a constant temperature bath at 25°C until the State of Charge (SOC) reached 85%. Each non-aqueous electrolyte energy storage element was then stored in a constant temperature bath at 80°C for 60 days in this SOC state.

[0122] (Measurement of DC resistance after high-temperature storage test) For each non-aqueous electrolyte energy storage element after the high-temperature storage test described above, the DC resistance at output after the test was measured according to the following procedure. First, after being stored in a constant temperature bath at 25°C for more than 3 hours, constant current discharge was performed with a discharge current of 1.0C and a discharge termination voltage of 2.50V. Then, constant current charging was performed in a constant temperature bath at 25°C with a charging current of 1.0C to bring the SOC to 15%. Next, in a constant temperature bath at 25°C, discharge currents of 0.2C, 0.5C, and 1.0C were performed for 30 seconds each. After each discharge, constant current charging was performed with a charging current of 0.05C to bring the SOC to 15%. The relationship between the discharge current and the voltage at 10 seconds after the start of discharge was plotted for each discharge current, and the DC resistance at output was determined from the slope of the straight line obtained from the three plots. The results are shown in Table 3. Furthermore, Table 3 shows the relative values ​​of the DC resistance at output for each non-aqueous electrolyte energy storage element using the same positive electrode active material, with a non-aqueous electrolyte energy storage element containing only LiBOB (0.5 mass%) and VC (0.5 mass%) as additives as the baseline (100.0%). Specifically, in Reference Examples 1 and 5, the relative values ​​are based on Reference Example 1; in Comparative Example 1 and Example 3, the relative values ​​are based on Comparative Example 1; and in Comparative Example 3 and Example 5, the relative values ​​are based on Comparative Example 3.

[0123] [Table 3]

[0124] As can be seen from the comparison of Reference Example 1, Comparative Example 1, and Comparative Example 3, the non-aqueous electrolyte energy storage element having a positive electrode with a positive electrode active material containing boron had higher resistance after high-temperature storage compared to the non-aqueous electrolyte energy storage element having a positive electrode active material that does not contain boron. Furthermore, as can be seen from the comparison of Comparative Example 3 and Example 5, in the non-aqueous electrolyte energy storage element having a positive electrode active material containing boron, the resistance after high-temperature storage was reduced by including the first compound in the non-aqueous electrolyte.

[0125] Furthermore, similar to the non-aqueous electrolyte energy storage element in Reference Example 1, the positive electrode active material is LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 In a non-aqueous electrolyte energy storage element where the non-aqueous electrolyte contains LiBOB, the boron content in the positive electrode active material was measured by ICP emission spectroscopy after initial charging and discharging. The boron content was below the detection limit (0.02 mol%). From this, it can be concluded that when the non-aqueous electrolyte contains LiBOB, there is virtually no boron element derived from LiBOB on the surface of the positive electrode active material. [Industrial applicability]

[0126] This invention can be applied to non-aqueous electrolyte energy storage elements used as power sources for electronic devices such as personal computers and communication terminals, as well as automobiles. [Explanation of symbols]

[0127] 1. Non-aqueous electrolyte energy storage element 2 Electrode body 3 containers 4 Positive terminal 41 Positive lead 5 Negative terminal 51 Negative lead 20 Energy storage units 30 Energy storage devices

Claims

1. A positive electrode having a positive electrode active material containing at least one of the elements tungsten and boron, A non-aqueous electrolyte containing a compound represented by the following formula (1) and A non-aqueous electrolyte energy storage element equipped with the above features. 【Chemistry 1】 (In formula (1), R １ From R ３ Each of these is independently a fluorine atom or an organic group having 1 to 10 carbon atoms. However, R １ From R ３ At least one of them is a fluorine atom. ｍ＋ m is an alkali metal ion, an alkaline earth metal ion, or an onium ion. ｍ＋ (It is an integer equal to the valence of [the variable].)

2. The non-aqueous electrolyte energy storage element according to claim 1, wherein the non-aqueous electrolyte further comprises a compound having an anion containing the element boron.

3. The non-aqueous electrolyte energy storage element according to claim 1 or claim 2, wherein at least one of the tungsten element and the boron element is present on at least the surface of the particles of the positive electrode active material.

4. The non-aqueous electrolyte energy storage element according to claim 1 or claim 2, wherein the positive electrode active material contains the tungsten element.

5. The non-aqueous electrolyte energy storage element according to claim 1 or claim 2, wherein the positive electrode active material contains the boron element.

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