Non-aqueous electrolyte energy storage element

Abstract

To provide a non-aqueous electrolyte power storage element that uses a lithium-transition metal composite oxide with a high content of cobalt element for a positive electrode, and has a high capacity retention rate even when a positive electrode potential is repeatedly charged and discharged to a high potential.SOLUTION: A non-aqueous electrolyte power storage element according to the present invention includes a positive electrode containing positive electrode active material particles and a non-aqueous electrolyte containing a non-aqueous solvent, the positive electrode active material particles contain a lithium transition metal composite oxide in which the content ratio of the cobalt element to the transition metal element is 50 mol% or more, and an aluminum compound present on at least a part of the surface, and the non-aqueous solvent is mainly composed of fluorinated solvents.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 secondary batteries, are widely used in electronic devices such as personal computers and communication terminals, as well as in automobiles, due to their high energy density. Generally, these 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. In addition to 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] Lithium transition metal composite oxides having an α-NaFeO2 type crystal structure, such as lithium cobalt oxide, are known as positive electrode active materials for non-aqueous electrolyte energy storage elements. Patent Document 1 describes a non-aqueous electrolyte secondary battery comprising a positive electrode containing lithium cobalt oxide as the main positive electrode active material, a negative electrode containing a negative electrode active material other than metallic lithium, and a non-aqueous electrolyte containing a compound having an ether group. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2007-200821 [Overview of the project] [Problems that the invention aims to solve]

[0005] Non-aqueous electrolyte energy storage devices that use lithium transition metal composite oxides with a high cobalt content, such as lithium cobalt oxide, as the positive electrode have advantages such as a higher energy density per unit mass of the positive electrode active material compared to non-aqueous electrolyte energy storage devices using other lithium transition metal composite oxides, because the positive electrode potential reaches a high potential when charged to a high voltage. However, non-aqueous electrolyte energy storage devices using lithium transition metal composite oxides with a high cobalt content have advantages when repeatedly charging and discharging to high voltages, i.e., when the positive electrode potential reaches a high potential (for example, 4.5V vs. Li / Li + It has the disadvantage that the discharge capacity tends to decrease when repeated charging and discharging cycles are performed up to the above point.

[0006] The object of the present invention is to provide a non-aqueous electrolyte energy storage element in which a lithium transition metal composite oxide with a high cobalt content is used as the positive electrode, and which maintains high capacity even when repeated charging and discharging occurs to a high positive electrode potential. [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 containing positive electrode active material particles and a non-aqueous electrolyte containing a non-aqueous solvent, wherein the positive electrode active material particles include a lithium transition metal composite oxide having a cobalt element content of 50 mol% or more relative to a transition metal element, and an aluminum compound present on at least a portion of its surface, and the non-aqueous solvent mainly consists of a fluorinating solvent. [Effects of the Invention]

[0008] According to one aspect of the present invention, a non-aqueous electrolyte energy storage element is provided in which a lithium transition metal composite oxide with a high cobalt content is used as the positive electrode, and which maintains high capacity even when repeated charging and discharging occurs, causing the positive electrode potential to reach a high potential. [Brief explanation of the drawing]

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

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

[0011] A non-aqueous electrolyte power storage element according to one aspect of the present invention includes a positive electrode containing positive electrode active material particles, and a non-aqueous electrolyte containing a non-aqueous solvent, wherein the positive electrode active material particles include a lithium transition metal composite oxide in which a content ratio of cobalt element to transition metal elements is 50 mol% or more, and an aluminum compound present on at least a part of a surface of the positive electrode active material particles, and the non-aqueous solvent contains a fluorinated solvent as a main component.

[0012] A non-aqueous electrolyte energy storage element according to one aspect of the present invention is a non-aqueous electrolyte energy storage element in which a lithium transition metal composite oxide with a high cobalt content is used as the positive electrode, and the capacity retention rate is high even when repeated charging and discharging is performed until the positive electrode potential reaches a high potential. The reason for this effect is not clear, but the following reason is speculated. In conventional non-aqueous electrolyte energy storage elements using lithium transition metal composite oxides with a high cobalt content, when the positive electrode potential reaches a high potential, a change in the crystal structure of the lithium transition metal composite oxide occurs, making it easier for cobalt to dissolve from the lithium transition metal composite oxide into the non-aqueous electrolyte, which is thought to cause a significant decrease in the capacity retention rate. In contrast, in the non-aqueous electrolyte energy storage element according to one aspect of the present invention, an aluminum compound is present on at least a part of the surface of the particles containing the lithium transition metal composite oxide, in other words, at least a part of the surface of the lithium transition metal composite oxide particles is coated with an aluminum compound, so the contact area between the lithium transition metal composite oxide and the non-aqueous electrolyte is reduced, and it is difficult for cobalt to dissolve from the lithium transition metal composite oxide into the non-aqueous electrolyte. Furthermore, in a non-aqueous electrolyte energy storage element according to one aspect of the present invention, a non-aqueous solvent mainly composed of a fluorinated solvent is used. Since such a non-aqueous solvent has low solubility of cobalt ions, it is considered that cobalt elements are less likely to dissolve from the lithium transition metal composite oxide into the non-aqueous electrolyte. Thus, in a non-aqueous electrolyte energy storage element according to one aspect of the present invention, even when charging and discharging are repeated to a high positive electrode potential, the dissolution of cobalt elements from the lithium transition metal composite oxide into the non-aqueous electrolyte is less likely to occur, and therefore, it is presumed that the capacity retention rate is high.

[0013] Here, the "surface" of the positive electrode active material particle refers to the 1 μm thick surface layer from the outermost surface of the positive electrode active material particle to a depth of 1 μm. In other words, it is sufficient for the aluminum compound to be present within the surface layer of the positive electrode active material particle. The aluminum compound may also be present in parts of the positive electrode active material particle other than the surface layer. "A non-aqueous solvent whose main component is a fluorinated solvent" means that the fluorinated solvent content in the non-aqueous solvent is 50% by volume or more. "Fluorinated solvent" is a non-aqueous solvent containing fluorine atoms. The main component fluorinated solvent may consist of only one type of non-aqueous solvent, or it may consist of two or more types of non-aqueous solvents.

[0014] In one aspect of the present invention, a non-aqueous electrolyte energy storage element is preferably further comprising a negative electrode containing metallic lithium. In such a case, the discharge capacity and energy density per unit mass of the positive electrode active material particles of the non-aqueous electrolyte energy storage element can be increased. This is presumed to be because, when a non-aqueous electrolyte energy storage element is equipped with a negative electrode containing other negative electrode active materials such as graphite, lithium ions equivalent to the irreversible capacity of the negative electrode active material are trapped in the negative electrode active material, resulting in a smaller reversible discharge capacity. However, when the negative electrode is equipped with metallic lithium as the negative electrode active material, this phenomenon does not occur.

[0015] Furthermore, "a non-aqueous electrolyte energy storage element having a negative electrode containing metallic lithium" means that, at least in the charged state of the non-aqueous electrolyte energy storage element, the metallic lithium content in the negative electrode active material layer of the negative electrode is 50% by mass or more. In addition, this negative electrode only needs to contain metallic lithium at least in the charged state, and does not need to contain metallic lithium in the discharged state. For example, a non-aqueous electrolyte energy storage element may have a negative electrode configured such that metallic lithium is deposited on at least a portion of the negative electrode surface during charging, so that the negative electrode contains metallic lithium in the charged state, and the metallic lithium on the negative electrode surface substantially dissolves into the non-aqueous electrolyte as lithium ions during discharge, so that the negative electrode substantially does not contain metallic lithium in the discharged state.

[0016] The positive electrode potential at the charging termination voltage during normal use of a non-aqueous electrolyte energy storage element according to one aspect of the present invention is 4.5V vs. Li / Li + The above is preferable. In such cases, the discharge capacity and energy density per unit mass of the positive electrode active material particles can be increased.

[0017] Here, "under normal use" means using the non-aqueous electrolyte energy storage element under the charge and discharge conditions recommended or specified for that element, and, if a charger for the non-aqueous electrolyte energy storage element is available, using that charger when using the element.

[0018] 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.

[0019] <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.

[0020] (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.

[0021] 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 7The 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-H4160 (2006).

[0022] 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.

[0023] 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.

[0024] The positive electrode active material layer contains positive electrode active material particles. The positive electrode active material layer may optionally contain conductive agents, binders, thickeners, fillers, and other optional components.

[0025] (Cathode active material particles) The positive electrode active material particles consist of a lithium transition metal composite oxide in which the cobalt element content relative to the transition metal element is 50 mol% or more, and an aluminum compound present on at least a portion of the surface. Typically, the positive electrode active material particles are coated with the aluminum compound on at least a portion of the surface of the lithium transition metal composite oxide particles. The aluminum compound may also be present inside the positive electrode active material particles.

[0026] Lithium transition metal composite oxides typically have an α-NaFeO2 type crystal structure. The lower limit of the cobalt content relative to the transition metal elements in lithium transition metal composite oxides is 50 mol%, preferably 70 mol%, more preferably 90 mol%, and even more preferably 99 mol%. Lithium transition metal composite oxides may contain substantially only cobalt as the transition metal element.

[0027] The composition ratio (percentage of each element) of the lithium transition metal composite oxide refers to the composition ratio before charging and discharging or when fully discharged by the following method. First, the non-aqueous electrolyte energy storage element is charged with a constant current of 0.05C until it reaches the charging termination voltage for normal use, and is fully charged. After a 30-minute rest, it is discharged with a constant current of 0.05C until it reaches the lower limit voltage for normal use. It is then disassembled, the positive electrode is removed, and a test battery is assembled with a metallic lithium electrode as the counter electrode. With a current value of 10mA per gram of positive electrode active material, the positive electrode potential is 2.0V vs. Li / Li + Constant current discharge is performed until the positive electrode is fully discharged. The device is then disassembled again, and the positive electrode is removed. The non-aqueous electrolyte adhering to the removed positive electrode is thoroughly washed using dimethyl carbonate, and after drying at room temperature for 24 hours, the removed positive electrode is calcined at 600°C for 1 hour in an air atmosphere to thermally decompose and remove any optional components such as binder and conductive agent, and the lithium transition metal composite oxide of the positive electrode active material is collected. The collected lithium transition metal composite oxide is subjected to measurement. The content ratio of each element in the lithium transition metal composite oxide is measured by ICP (inductively coupled plasma) emission spectroscopy of the solution in which the lithium transition metal composite oxide is dissolved. The work from disassembly of the non-aqueous electrolyte energy storage element to drying of the positive electrode is performed in an argon atmosphere with a dew point of -60°C or lower. Here, the rated capacity of the non-aqueous electrolyte energy storage element is defined as the current discharged in 1 hour being 1C.

[0028] Lithium transition metal composite oxides may contain other transition metal elements besides cobalt. Examples of other transition metal elements include nickel, manganese, iron, and niobium. Furthermore, lithium transition metal composite oxides may further contain metallic elements other than lithium and transition metal elements (such as aluminum and magnesium), and may further contain nonmetallic elements other than oxygen (such as fluorine and boron).

[0029] The molar ratio of lithium to other metal elements in a lithium transition metal composite oxide may be, for example, 0.9 to 1.1, or 0.95 to 1.05.

[0030] The lithium transition metal composite oxide may be represented, for example, by the following formula 1. Li x Co y M 1-y O2···1 In formula 1, x is a number between 0.9 and 1.1. y is a number between 0.5 and 1. M is one or more metallic elements other than Li and Co. x is preferably between 0.95 and 1.05, and may be 1. y is preferably 0.7 or higher, more preferably 0.9 or higher, and even more preferably 0.99 or higher.

[0031] The positive electrode active material particles may contain positive electrode active materials other than lithium transition metal composite oxides in which the cobalt element content ratio to the transition metal element is 50 mol% or more. The other positive electrode active materials can be appropriately selected from known positive electrode active materials commonly used in lithium-ion secondary batteries and the like. However, the content of lithium transition metal composite oxides in the total positive electrode active material contained in the positive electrode active material particles, in which the cobalt element content ratio to the transition metal element is 50 mol% or more, more preferably 90% or more, even more preferably 99% or more, and still more preferably 100% or even more preferably.

[0032] The aluminum compound is present on at least a portion of the surface of the positive electrode active material particles. The aluminum compound may be present across the entire surface of the positive electrode active material particles, or it may be present only on a portion of the surface, such that a portion of the lithium transition metal composite oxide is exposed. For example, the aluminum compound may be scattered as particulate matter on the surface of the positive electrode active material particles; that is, the aluminum compound may be dispersed as particulate matter on the surface of the positive electrode active material particles. In this case, multiple particles of the aluminum compound may aggregate together. Furthermore, as mentioned above, a portion of the aluminum compound may be present inside the positive electrode active material particles. The presence of the aluminum element on the surface of the positive electrode active material particles can be confirmed by SEM-EDX measurement using a scanning electron microscope (SEM) and its associated energy-dispersive X-ray spectroscopy (EDX) device.

[0033] When aluminum compounds are present as particles on the surface of the positive electrode active material particles, the average particle diameter of these aluminum compound particles may be, for example, between 0.1 nm and 1 μm, or between 1 nm and 100 nm. The average particle diameter of the aluminum compound particles is the average of the diameters of any 10 aluminum compound particles observed by SEM. Furthermore, the diameter of each aluminum compound particle is the equivalent diameter of a circle.

[0034] Examples of aluminum compounds include aluminum oxides, sulfides, halides, silicates, phosphorus oxides, sulfur oxides, nitrates, and alloys. Among these, aluminum oxides are preferred. Aluminum oxides may include aluminum oxide (Al2O3), as well as compounds such as LiAlO2 and other composite oxides containing elements other than aluminum and oxygen.

[0035] Methods for introducing an aluminum compound to the surface of positive electrode active material particles include adding the aluminum compound to a precursor of a lithium transition metal composite oxide and firing them simultaneously; mixing the aluminum compound and the lithium transition metal composite oxide and firing them; immersing lithium transition metal composite oxide particles in a liquid containing an aluminum compound and then drying the lithium transition metal composite oxide particles to which the aluminum compound has adhered; immersing lithium transition metal composite oxide particles in a solution containing an aluminum compound and then reacting the lithium transition metal composite oxide particles to which the aluminum compound has adhered by heating or other means; and spraying a solution or gas containing an aluminum compound onto lithium transition metal composite oxide particles while they are heated and then reacting them.

[0036] The aluminum compound content in the positive electrode active material particles is preferably 0.005% to 1% by mass, more preferably 0.01% to 0.5% by mass, and even more preferably 0.02% to 0.1% by mass. By setting the aluminum compound content above the lower limit, the effect of suppressing the elution of cobalt elements is enhanced, and the capacity retention rate when repeated charging and discharging leading to a high positive electrode potential can be further improved. On the other hand, by setting the aluminum compound content below the upper limit, the proportion of lithium transition metal composite oxides exposed increases, and the insertion and deinsertion of lithium ions is not inhibited, so the charge and discharge performance tends to improve. Furthermore, by setting the aluminum compound content below the upper limit, the content of aluminum compounds that do not contribute to the charge and discharge reaction is relatively small, so the energy density and other properties can be increased.

[0037] The content of elements such as aluminum in the positive electrode active material particles can be measured by ICP emission spectrometry on a solution obtained by dissolving the positive electrode active material particles using the method described above. Furthermore, the content of aluminum compounds contained in the positive electrode active material particles can be calculated based on the content of these elements such as aluminum.

[0038] In the positive electrode active material particles, the total content of lithium transition metal composite oxide and aluminum compound, where the cobalt element content ratio to the transition metal element is 50 mol% or more, is preferably 50% by mass or more, more preferably 90% by mass or more, even more preferably 99% by mass or more, and even more preferably 100% by mass. In this way, when the positive electrode active material particles are substantially composed of lithium transition metal composite oxide and aluminum compound, where the cobalt element content ratio to the transition metal element is 50 mol% or more, the capacity retention rate when the positive electrode potential is repeatedly increased to a high potential can be increased, and the discharge capacity and energy density per unit mass of the positive electrode active material particles can be increased.

[0039] The average particle size (D50) of the positive electrode active material particles is preferably, for example, 0.1 μm or more and 20 μm or less. Setting the average particle size (D50) of the positive electrode active material particles to be above the lower limit makes it easier to manufacture or handle the positive electrode active material particles. Setting the average particle size (D50) of the positive electrode active material particles to be below the upper limit improves the electronic conductivity of the positive electrode active material layer. "Average particle size (D50)" 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 positive electrode active material particles and the like 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 positive electrode active material particles 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 97% by mass. By setting the content of positive electrode active material particles 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 1.5% 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 1% by mass or more and 10% by mass or less, and more preferably 2% by mass or more and 9% by mass or less. By keeping the binder content within the above range, the positive electrode active material particles can be stably held.

[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 or the like, this functional group may be deactivated beforehand by methylation or the like.

[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.

[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 materials other than positive electrode active material particles, conductive agents, binders, thickeners, and fillers.

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

[0051] The average thickness of the negative electrode substrate is preferably 2 μm or more and 35 μm or less, more preferably 3 μm or more and 30 μm or less, still more preferably 4 μm or more and 25 μm or less, and particularly preferably 5 μm or more and 20 μm or less. By setting the average thickness of the negative electrode substrate within the above range, the energy density per volume of the non-aqueous electrolyte electricity storage element can be increased while increasing the strength of the negative electrode substrate.

[0052] 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 necessary. 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 described above.

[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 materials other than the negative electrode active material, the conductive agent, the binder, the thickener, and the filler.

[0054] The negative electrode active material can be appropriately selected from known negative electrode active materials. As the negative electrode active material for a lithium ion secondary battery, a material capable of intercalating and deintercalating lithium ions is generally used. Examples of the negative electrode active material include metallic lithium; metals or semimetals such as Si and Sn; metal oxides or semimetal oxides such as Si oxide, Ti oxide, and Sn oxide; Li4Ti5O 12 , LiTiO 2、Examples 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). 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 in the discharged state. 002 ) refers to carbon materials with a n-scale between 0.33 nm and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite. Artificial graphite is preferred from the standpoint of obtaining materials with stable physical properties.

[0056] "Non-graphite carbon" refers to the average lattice plane spacing (d) of the (002) plane, determined by X-ray diffraction before charging or after discharging. 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, in the context of carbon materials, "discharged 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 metallic lithium 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 between 0.36 nm and 0.42 nm.

[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] Preferably, the negative electrode active material is metallic lithium, Si oxide, or carbon material, with metallic lithium being more preferred. By using Si oxide or metallic lithium as the negative electrode active material, the discharge capacity and energy density per unit mass of positive electrode active material particles in the non-aqueous electrolyte energy storage element can be increased. On the other hand, by using a carbon material, particularly graphite, as the negative electrode active material, the capacity retention rate when repeated charging and discharging reaches a high positive electrode potential is further increased.

[0061] When the negative electrode active material contains metallic lithium, the metallic lithium content in the negative electrode active material layer of the negative electrode is 50% by mass, at least in a charged non-aqueous electrolyte energy storage element. In the negative electrode active material layer, metallic lithium may exist as pure metallic lithium consisting substantially only of lithium element, or as a lithium alloy containing other elements. Examples of lithium alloys include lithium silver alloy, lithium zinc alloy, lithium calcium alloy, lithium aluminum alloy, lithium magnesium alloy, and lithium indium alloy. The lithium alloy may contain multiple elements other than lithium. The lithium element content in the negative electrode active material layer may be 90% by mass or more, 99% by mass or more, or 100% by mass.

[0062] When the negative electrode active material contains metallic lithium, the negative electrode active material layer may be pure metallic lithium foil or lithium alloy foil. The negative electrode active material layer may be a non-porous layer (solid layer). Alternatively, the negative electrode active material layer may be a porous layer having particles containing metallic lithium. A negative electrode active material layer that is a porous layer having particles containing metallic lithium may further contain, for example, resin particles, inorganic particles, etc.

[0063] It is preferable that the negative electrode active material layer containing metallic lithium is present even in the discharge state, that is, that it is present in all states from the charge state to the discharge state. The average thickness of the negative electrode active material layer containing metallic lithium in the discharge state is preferably 5 μm to 1,000 μm, more preferably 10 μm to 500 μm, and even more preferably 30 μm to 300 μm. The average thickness of the negative electrode active material layer is the average of the thicknesses measured at any five locations. When the negative electrode active material containing metallic lithium is present even in the discharge state, and preferably its average thickness is above the lower limit above, a sufficient amount of metallic lithium is present, so the discharge capacity and energy density per unit mass of the positive electrode active material particles of the non-aqueous electrolyte energy storage element become higher.

[0064] Furthermore, in the case of a non-aqueous electrolyte energy storage element configured such that metallic lithium is deposited on at least a portion of the surface area of ​​the negative electrode during charging, and the metallic lithium of the negative electrode substantially dissolves into the non-aqueous electrolyte as lithium ions during discharge, the negative electrode does not need to substantially have a negative electrode active material layer in the discharge state.

[0065] The negative electrode active material, such as carbon material, is usually in the form of particles (powder). The average particle size (D50) of the negative electrode active material can be, for example, between 1 nm and 100 μm. If the negative electrode active material is a carbon material, titanium-containing oxide, or polyphosphate compound, its average particle size (D50) may be between 1 μm and 100 μm. If the negative electrode active material is Si, Sn, Si oxide, or Sn oxide, its average particle size may be between 1 nm and 10 μm. Setting the average particle size (D50) of the negative electrode active material above the lower limit makes it easier to manufacture or handle the negative electrode active material. Setting the average particle size (D50) 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 powder grading method can be selected from, for example, the methods exemplified above for the positive electrode.

[0066] When the negative electrode active material contains metallic lithium, the negative electrode active material layer may consist substantially of metallic lithium only. The metallic lithium content in the negative electrode active material layer may be 90% by mass or more, 99% by mass or more, or 100% by mass. Furthermore, when the negative electrode active material contains carbon material, etc., the content of carbon material, etc., in the negative electrode active material layer may preferably be 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 negative electrode active material content within the above range, it is possible to achieve both high energy density and manufacturability of the negative electrode active material layer.

[0067] (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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] (Non-aqueous electrolytes) Non-aqueous electrolytes are typically non-aqueous electrolyte solutions. A non-aqueous electrolyte solution contains a non-aqueous solvent and an electrolyte salt dissolved in this non-aqueous solvent.

[0072] The non-aqueous solvent mainly consists of a fluorinated solvent. The fluorinated solvent may be a non-aqueous solvent having a hydrocarbon group in which some or all of the hydrogen atoms in the hydrocarbon group are replaced with fluorine atoms. Examples of fluorinated solvents include fluorinated carbonates (fluorinated cyclic carbonates and fluorinated linear carbonates), fluorinated carboxylic acid esters, fluorinated phosphate esters, and fluorinated ethers.

[0073] Examples of fluorinated cyclic carbonates include fluorinated ethylene carbonates such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate, fluorinated propylene carbonate, and fluorinated butylene carbonate. Among these, fluorinated ethylene carbonate is preferred, and FEC is more preferred.

[0074] Examples of fluorinated chain carbonates include 2,2,2-trifluoroethylmethyl carbonate and bis(2,2,2-trifluoroethyl) carbonate.

[0075] Examples of fluorinated carboxylic acid esters include methyl 3,3,3-trifluoropropionate and 2,2,2-trifluoroethyl acetate.

[0076] Examples of fluorinated phosphate esters include tris(2,2-difluoroethyl) phosphate and tris(2,2,2-trifluoroethyl) phosphate.

[0077] Examples of fluorinated ethers include 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, methylheptafluoropropyl ether, and methyl nonafluorobutyl ether.

[0078] The fluorinating solvent preferably contains a fluorinated carbonate, and more preferably contains a fluorinated cyclic carbonate. The fluorinating solvent is even more preferably contains a fluorinated cyclic carbonate and at least one of a fluorinated linear carbonate and a fluorinated carboxylic acid ester, and even more preferably contains a fluorinated cyclic carbonate and a fluorinated linear carbonate. The volume ratio of the fluorinated cyclic carbonate to at least one of the fluorinated linear carbonate and the fluorinated carboxylic acid ester (fluorinated cyclic carbonate: at least one of the fluorinated linear carbonate and the fluorinated carboxylic acid ester) is preferably in the range of 5:95 to 70:30, for example.

[0079] The non-aqueous solvent may contain non-aqueous solvents other than fluorinated solvents. Examples of such non-aqueous solvents include carbonates, carboxylic acid esters, phosphate esters, ethers, and the like, other than fluorinated solvents.

[0080] The lower limit of the fluorinated solvent content relative to the total non-aqueous solvent is preferably 70% by volume, more preferably 90% by volume, and even more preferably 99% by volume. A fluorinated solvent content of 100% by volume relative to the total non-aqueous solvent is particularly preferable. By substantially composing the non-aqueous solvent solely from the fluorinated solvent, it is possible to further improve the capacity retention rate when repeated charging and discharging reaches a high positive electrode potential.

[0081] 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.

[0082] Examples of lithium salts include inorganic lithium salts such as LiPF6, LiPO2F2, LiBF4, LiClO4, and LiN(SO2F)2; lithium oxalate salts such as lithium bis(oxalate)borate (LiBOB), lithium difluorooxalate borate (LiFOB), and 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.

[0083] The electrolyte salt content in a non-aqueous electrolyte solution 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.

[0084] Non-aqueous electrolytes may contain additives in addition to a non-aqueous solvent and electrolyte salt. Examples of additives include aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partially halides of the aforementioned aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; halogenated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole; vinylene carbonate, methylvinylene carbonate, ethylvinylene carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, and cyclohexanedicarboxylic acid anhydride; ethylene sulfite, propylene sulfite, and sulfurous acid. Examples include dimethyl acid, 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. These additives may be used individually or in combination of two or more.

[0085] The additive content in the non-aqueous electrolyte is preferably 0.01% to 10% by mass relative to the total mass of the non-aqueous electrolyte, more preferably 0.1% to 7% by mass, even more preferably 0.2% to 6% by mass, and particularly preferably 0.3% to 5% by mass. By setting the additive content within the above range, it is possible to improve the capacity retention performance or cycle performance after high-temperature storage, and to further improve safety.

[0086] Non-aqueous electrolytes may be a combination of non-aqueous electrolyte solution and solid electrolyte. The solid electrolyte can be selected from any material that has ionic conductivity, such as lithium, sodium, and calcium, and is solid at room temperature (e.g., 15°C to 25°C). Examples of solid electrolytes include sulfide solid electrolytes, oxide solid electrolytes, oxynitride solid electrolytes, and polymer solid electrolytes.

[0087] (Positive electrode potential at the charging termination voltage during normal use) In the non-aqueous electrolyte energy storage element, the positive electrode potential (positive electrode reach potential) at the charging termination voltage during normal use is not particularly limited, but its lower limit is 4.3V vs. Li / Li + This is preferable, 4.4V vs. Li / Li + More preferable, 4.5V vs. Li / Li + More preferably, 4.55V vs. Li / Li + Or 4.6V vs. Li / Li + In some cases, this is even more preferable. By having the positive electrode potential at the charging termination voltage during normal use be above the above lower limit, the discharge capacity and energy density per unit mass of the positive electrode active material particles of the non-aqueous electrolyte energy storage element can be increased. Furthermore, in such a non-aqueous electrolyte energy storage element, even if the positive electrode potential at the charging termination voltage during normal use is high, the capacity retention rate after the charge-discharge cycle is high.

[0088] In the non-aqueous electrolyte energy storage element, the upper limit of the positive electrode potential at the charging termination voltage during normal use is 5.0V vs. Li / Li + This is preferable, 4.9V vs. Li / Li+ More preferable, 4.8V vs. Li / Li + This is even more preferable, 4.7V vs. Li / Li + More preferably, 4.6V vs. Li / Li + This is even more preferable. The positive electrode potential at the charging termination voltage during normal use of the non-aqueous electrolyte energy storage element may be within the range of either the lower limit or the upper limit of the above-mentioned limits.

[0089] 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.

[0090] 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.

[0091] <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 1 in power supplies for automobiles 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 non-aqueous electrolyte energy storage element included in the energy storage unit.

[0092] 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.

[0093] <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 includes, for example, preparing an electrode body, preparing a non-aqueous electrolyte, and housing the electrode body and the non-aqueous electrolyte in a container. Preparing the electrode body includes preparing a positive electrode and a negative electrode, and forming the electrode body by stacking or winding the positive electrode and the negative electrode via a separator.

[0094] 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.

[0095] <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.

[0096] In the above embodiment, a case in which a non-aqueous electrolyte energy storage element is used as a rechargeable non-aqueous electrolyte 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, lithium-ion capacitors, and other capacitors.

[0097] 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]

[0098] 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.

[0099] [Manufacturing Example 1] Manufacturing of positive electrode active material particles A in which an aluminum compound is present on at least a portion of the surface. LiCoO2 (LCO), a lithium transition metal composite oxide having an α-NaFeO2 type crystal structure, was used as the positive electrode active material. An Al2O3 layer was coated onto these LiCoO2 particles using atomic layer deposition. This yielded positive electrode active material particles A in which an aluminum compound (Al2O3) was present on at least a portion of the surface. The aluminum compound content in positive electrode active material particles A was 0.02 mass%. The aluminum element content in positive electrode active material particles A was measured by the ICP emission spectrometry method described above, and the aluminum compound (Al2O3) content was determined by assuming that all the aluminum elements in positive electrode active material particles A constituted Al2O3. The average particle size (D50) of positive electrode active material particles A was 8 μm.

[0100] Furthermore, LiCoO2 (LCO) particles that do not have an aluminum compound attached to at least a portion of their surface were designated as positive electrode active material particles B.

[0101] Furthermore, it has an α-NaFeO2 type crystal structure, Li 1+αMe 1-α Particles of lithium transition metal composite oxide (LR), represented as O2 (where Me is a transition metal element), were prepared as positive electrode active material particles C. Here, the molar ratio of Li to Me (Li / Me) was 1.33, and Me consisted of Ni and Mn, with Ni:Mn present in a molar ratio of 1:2.

[0102] [Example 1] (Fabrication of the positive electrode) A positive electrode mixture paste was prepared containing positive electrode active material particles A, acetylene black (AB), and polyvinylidene fluoride (PVDF) in a mass ratio of 93:3:4 (on a solid basis), with N-methylpyrrolidone (NMP) as the dispersion medium. After drying the dispersion medium on aluminum foil as the positive electrode substrate, the mass per unit area of ​​the positive electrode active material layer was 2.5 g / 100 cm². 2 The material was applied, dried, and pressed to obtain a positive electrode having a positive electrode active material layer.

[0103] (Fabrication of the negative electrode) A negative electrode having a negative electrode active material layer was obtained by laminating a lithium foil with an average thickness of 100 μm, which is made of pure metallic lithium (metallic Li) as the negative electrode active material, onto a copper foil with an average thickness of 8 μm as the negative electrode substrate, and then pressing the layers.

[0104] (Preparation of non-aqueous electrolytes) A non-aqueous solvent prepared by mixing fluoroethylene carbonate (FEC) and 2,2,2-trifluoroethylmethyl carbonate (TFEMC) in a volume ratio of 30:70, to which the lithium salt LiPF6 was added at a concentration of 1.0 mol / dm³. 3 A solution was obtained by dissolving the substance in the given concentration. To the obtained solution, 1,3-propensultone was further dissolved as an additive at a concentration of 2% by mass to prepare a non-aqueous electrolyte.

[0105] (Preparing the separator) A 21 μm thick microporous polyolefin membrane was prepared as a separator.

[0106] (Fabrication of non-aqueous electrolyte energy storage elements) An electrode body was fabricated by stacking the positive electrode and the negative electrode via the above separator. The electrode body was placed in a container made of a metal-resin composite film, the above non-aqueous electrolyte was injected into the container, and then the container was sealed by heat welding to obtain the non-aqueous electrolyte energy storage element of Example 1.

[0107] [Examples 2 to 6, Comparative Examples 1 to 4, and Reference Examples 1 to 7] Except for the type of positive electrode active material particles, the type of negative electrode active material, and the composition of the non-aqueous solvent being as shown in Table 1, non-aqueous electrolyte energy storage elements for Examples 2 to 6, Comparative Examples 1 to 4, and Reference Examples 1 to 7 were obtained in the same manner as in Example 1. In Table 1, FMP represents methyl 3,3,3-trifluoropropionate, and FEA represents 2,2,2-trifluoroethyl acetate.

[0108] Furthermore, in Example 4, where the negative electrode active material was graphite (Gr), metallic lithium was used as the negative electrode and reference electrode, which were prepared using the following procedure. (Fabrication of the negative electrode) A negative electrode mixture paste was prepared containing graphite (Gr), styrene-butadiene rubber (SBR), and carboxymethylcellulose (CMC) as negative electrode active materials in a mass ratio (solid content basis) of 96.7:2.1:1.2, with water as the dispersion medium. After drying the dispersion medium on copper foil, which served as the negative electrode substrate, the mass per unit area of ​​the negative electrode active material layer was 1.3 g / 100 cm². 2 The material was applied, dried, and pressed to obtain a negative electrode having a negative electrode active material layer.

[0109] (Initial charge / discharge) For each of the non-aqueous electrolyte energy storage elements obtained in Examples 1 to 6, Comparative Examples 1 to 4, and Reference Examples 1 to 7, initial charging and discharging were performed at 25°C according to the following procedure. Constant current and constant voltage charging was performed with a charging current of 20 mA / g and the charging termination voltage listed in Table 1. The charging termination condition was when the charging current became 10 mA / g. After that, a 10-minute rest period was provided. Subsequently, constant current discharging was performed with a discharge current of 20 mA / g and a discharge termination voltage of 2.7 V (Examples 1 to 6, Comparative Examples 1 to 4, and Reference Examples 1 and 2) or 2.0 V (Reference Examples 3 to 7). The charging current and discharge current were defined as the current per unit mass of positive electrode active material particles. This charging and discharging was performed for two cycles, and the discharge capacity per unit mass of positive electrode active material particles and energy density were determined based on the discharge amount of the second cycle. Energy density was determined by the product of the discharge capacity per unit mass of positive electrode active material particles and the average discharge potential during discharge. The results are shown in Table 1. Table 1 also shows the positive electrode potential at the charging termination voltage for each non-aqueous electrolyte energy storage element. In each non-aqueous electrolyte energy storage element using metallic lithium as the negative electrode, the potential of the negative electrode in the open circuit state is approximately equal to the oxidation-reduction potential of lithium, so the voltage in the non-aqueous electrolyte energy storage element was considered as the positive electrode potential relative to the oxidation-reduction potential of lithium. In addition, in the non-aqueous electrolyte energy storage element of Example 4, which uses graphite as the negative electrode, the positive electrode potential was confirmed with reference to the reference electrode.

[0110] (Charge-discharge cycle test) After initial charging and discharging, charge-discharge cycle tests were performed on each non-aqueous electrolyte energy storage element in Examples 1 to 6, Comparative Examples 1 to 4, and Reference Examples 1 to 7 at 25°C according to the following procedure. Constant current and constant voltage charging was performed with a charging current of 40 mA / g and the charging termination voltage listed in Table 1. The charging termination condition was when the charging current became 10 mA / g. Subsequently, constant current discharge was performed with a discharge current of 20 mA / g and a discharge termination voltage of 2.7 V (Examples 1 to 6, Comparative Examples 1 to 4, and Reference Examples 1 and 2) or 2.0 V (Reference Examples 3 to 7). A 10-minute rest period was provided after both charging and discharging. This charge-discharge cycle was performed 100 times. The capacity retention rate (%) was calculated as the percentage of the discharge capacity at cycle 100 relative to the discharge capacity at cycle 1. The results are shown in Table 1.

[0111] [Table 1]

[0112] As shown in Table 1, in each of the non-aqueous electrolyte energy storage elements in Comparative Examples 1 to 4, where no aluminum compound is present on the surface of the positive electrode active material particles, or where the non-aqueous solvent is not mainly composed of a fluorinated solvent, the positive electrode potential is 4.5V vs. Li / Li + The capacity retention rate after the charge-discharge cycle tests described above was 80% or less. In contrast, in each of the non-aqueous electrolyte energy storage elements in Examples 1 to 6, in which an aluminum compound is present on at least a portion of the surface of the positive electrode active material particles and the non-aqueous solvent is mainly composed of a fluorinated solvent, the positive electrode potential was 4.5V vs. Li / Li + The capacity retention rate after the charge-discharge cycle tests described above exceeded 80%.

[0113] Among Examples 1 to 6, the non-aqueous electrolyte energy storage elements in Examples 1 to 3, 5, and 6, where the negative electrode active material is metallic lithium, showed higher discharge capacity and energy density per unit mass of positive electrode active material particles. The non-aqueous electrolyte energy storage element in Example 4, where the negative electrode active material is graphite, showed particularly high capacity retention. Furthermore, a comparison of Examples 2, 5, and 6, which differ only in the composition of the non-aqueous solvent, shows that when the non-aqueous solvent contains fluorinated cyclic carbonates and fluorinated chain carbonates, the capacity retention tends to be higher, and the discharge capacity and energy density per unit mass of positive electrode active material particles tend to be higher.

[0114] Furthermore, in Reference Examples 1 and 2, where charge-discharge cycle tests reaching high potentials were not performed, and in Reference Examples 3 to 7, where the positive electrode active material was not a lithium transition metal composite oxide with a high cobalt content, the capacity retention rate after the charge-discharge cycle tests was high, and there was no problem of improving the capacity retention rate. In other words, the problem of improving the capacity retention rate after charge-discharge cycle tests is a problem specific to non-aqueous electrolyte energy storage elements using lithium transition metal composite oxides with a high cobalt content as the positive electrode, when repeated charge-discharges reach high potentials. It should be noted that, for example, a comparison between Reference Example 2 and Example 1, where only the positive electrode potential at the charge termination voltage differs, shows that increasing the positive electrode potential at the charge termination voltage increases the discharge capacity and energy density per unit mass of positive electrode active material particles. Furthermore, a comparison between Reference Example 3, which differs only in the positive electrode active material particles, and Example 1 reveals that using a lithium transition metal composite oxide with a high cobalt content as the positive electrode active material increases the energy density per unit mass of the positive electrode active material particles. [Industrial applicability]

[0115] 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 for automobiles and industrial applications. [Explanation of Symbols]

[0116] 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 containing positive electrode active material particles, and Non-aqueous electrolytes containing non-aqueous solvents Equipped with, The above positive electrode active material particles, A lithium transition metal composite oxide having a cobalt content of 50 mol% or more relative to the transition metal element, Aluminum compounds present in at least a portion of the surface and Includes, The above non-aqueous electrolyte contains a fluorinated solvent with a content ratio of 50% by volume or more relative to the total non-aqueous solvent. The above non-aqueous electrolyte is a non-aqueous electrolyte energy storage element containing LiPF6 as the electrolyte salt.

2. The non-aqueous electrolyte energy storage element according to claim 1, further comprising a negative electrode containing metallic lithium.

3. The positive electrode potential at the charging termination voltage during normal use is 4.5V vs. Li / Li ＋ The non-aqueous electrolyte energy storage element according to claim 1 or claim 2.

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