Positive electrode for non-aqueous electrolyte storage element, non-aqueous electrolyte storage element and storage device

Abstract

A positive electrode for a nonaqueous electrolyte power storage element according to one aspect of the present invention comprises a positive electrode mixture layer containing a composite positive electrode active material in which at least a part of the surface of a positive electrode active material is coated with carbon. The ratio of the pore specific surface area of the carbon to the pore specific surface area of the composite positive electrode active material is 20% to 50%, inclusive, and the density of the positive electrode mixture layer is 1.80g / cm3 to 2.10g / cm3, inclusive. The positive electrode active material is a compound represented by formula 1.　Formula 1: LiFexMn(1-x)PO4, where (0≤x≤1)

Description

[Technical Field]

[0001] The present invention relates to a positive electrode for a non-aqueous electrolyte electricity storage element, a non-aqueous electrolyte electricity storage element, and an electricity storage device. [Background technology]

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

[0003] In recent years, olivine-type positive electrode active materials have been attracting attention as inexpensive and safe positive electrode active materials for use in the nonaqueous electrolyte storage elements. Because of their low electronic conductivity, it has been difficult to obtain a discharge capacity close to the theoretical capacity. However, a technique for coating the surface of these olivine-type positive electrode active materials with carbon has been proposed to improve electronic conductivity (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-034306 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when applying the battery to a starting battery for an automobile, etc., output characteristics in a low-temperature environment are required, and since the output characteristics in a low-temperature environment are affected by factors other than electronic conductivity, further improvement is required even when using an olivine-type positive electrode active material with a carbon-coated surface.

[0006] The present invention has been made in light of the above circumstances, and an object of the present invention is to provide a positive electrode for a nonaqueous electrolyte storage element that can improve the initial output performance of the nonaqueous electrolyte storage element in a low-temperature environment. [Means for solving the problem]

[0007] A positive electrode for a non-aqueous electrolyte storage element according to one aspect of the present invention includes a positive electrode mixture layer containing a composite positive electrode active material in which at least a portion of the surface of the positive electrode active material is coated with carbon, the ratio of the specific surface area of ​​pores of the carbon to the specific surface area of ​​pores of the composite positive electrode active material being 20% ​​or more and 50% or less, and the density of the positive electrode mixture layer being 1.80 g / cm 3 More than 2.10g / cm 3 The positive electrode active material is a compound represented by the following formula 1. Life x Mn (1-x) PO4(0≦x≦1) 1 [Effects of the Invention]

[0008] A positive electrode for a nonaqueous electrolyte electricity storage element according to one aspect of the present invention can improve the initial output performance of a nonaqueous electrolyte electricity storage element and an electricity storage device in a low-temperature environment. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view showing one embodiment of a nonaqueous electrolyte electricity storage element. [Figure 2] FIG. 2 is a schematic diagram showing one embodiment of an electricity storage device configured by assembling a plurality of nonaqueous electrolyte electricity storage elements. DETAILED DESCRIPTION OF THE INVENTION

[0010] First, an outline of the positive electrode for a nonaqueous electrolyte electricity storage element, the nonaqueous electrolyte electricity storage element, and the electricity storage device disclosed in this specification will be described.

[0011] A positive electrode for a non-aqueous electrolyte storage element according to one aspect of the present invention includes a positive electrode mixture layer containing a composite positive electrode active material in which at least a portion of the surface of the positive electrode active material is coated with carbon, the ratio of the specific surface area of ​​pores of the carbon to the specific surface area of ​​pores of the composite positive electrode active material being 20% ​​or more and 50% or less, and the density of the positive electrode mixture layer being 1.80 g / cm 3 More than 2.10g / cm 3 The positive electrode active material is a compound represented by the following formula 1. Life x Mn (1-x) PO4(0≦x≦1) 1

[0012] The positive electrode for a nonaqueous electrolyte storage battery element includes a positive electrode mixture layer containing a composite positive electrode active material in which at least a portion of the surface of a positive electrode active material having an olivine crystal structure and made of a compound represented by Formula 1 is coated with carbon. The ratio of the specific pore surface area of ​​the carbon to the specific pore surface area of ​​the composite positive electrode active material and the density of the positive electrode mixture layer are within specific ranges, thereby improving the initial output performance of the nonaqueous electrolyte storage battery element in low-temperature environments. While the reason for this is unclear, it is presumed to be as follows. Because the composite positive electrode active material has good electronic conductivity due to at least a portion of its surface being coated with carbon, output in low-temperature environments tends to be dominated by the diffusivity of lithium ions in the pores of the positive electrode mixture layer. In the positive electrode for a nonaqueous electrolyte storage battery element, the ratio of the specific pore surface area of ​​the carbon to the specific pore surface area of ​​the composite positive electrode active material is 20% to 50%, thereby providing the carbon with appropriate density. Therefore, the positive electrode for a non-aqueous electrolyte storage element can maintain favorable diffusibility of lithium ions of the non-aqueous electrolyte in the pores between the carbon particles while reducing the contact resistance between the carbon particles. 3 More than 2.10g / cm 3or less, the positive electrode mixture layer has appropriate adhesion. Therefore, the positive electrode for a nonaqueous electrolyte storage element can maintain favorable diffusibility of lithium ions of the nonaqueous electrolyte in the pores of the positive electrode mixture layer while reducing resistance. As a result, it is presumed that the diffusibility of lithium ions in the pores of the positive electrode mixture layer is improved. Therefore, the positive electrode for a nonaqueous electrolyte storage element can improve the initial output performance of the nonaqueous electrolyte storage element in a low-temperature environment.

[0013] A positive electrode for a non-aqueous electrolyte storage element according to another aspect of the present invention includes a positive electrode mixture layer containing a composite positive electrode active material in which at least a portion of the surface of the positive electrode active material is coated with carbon, the ratio of the pore specific surface area of ​​the carbon to the pore specific surface area of ​​the composite positive electrode active material being 20% ​​or more and 50% or less, and the pore specific surface area of ​​the carbon being 1.0 m 2 / g or more 5.5m 2 / g or less, and the positive electrode active material is a compound represented by the following formula 1. Life x Mn (1-x) PO4(0≦x≦1) 1

[0014] In the positive electrode for a non-aqueous electrolyte storage element, the pore specific surface area of ​​the carbon is 1.0 m 2 / g or more 5.5m 2 / g or less, it is possible to suppress the elution of Fe ions from the composite positive electrode active material, thereby reducing the amount of eluted Fe ions that pass through the carbon coating the composite positive electrode active material, and improving the capacity retention rate after storage.

[0015] A positive electrode for a non-aqueous electrolyte storage element according to another aspect of the present invention includes a positive electrode mixture layer containing a composite positive electrode active material in which at least a portion of the surface of the positive electrode active material is coated with carbon, the ratio of the pore specific surface area of ​​the carbon to the pore specific surface area of ​​the composite positive electrode active material being 20% ​​or more and 50% or less, and the pore specific surface area of ​​the carbon being 1.0 m 2 / g or more 5.5m 2 / g or less, and the density of the positive electrode mixture layer is 1.80 g / cm 3 More than 2.10g / cm 3The positive electrode active material is a compound represented by the following formula 1. Life x Mn (1-x) PO4(0≦x≦1) 1

[0016] The positive electrode for a non-aqueous electrolyte storage element can increase the initial output performance of the non-aqueous electrolyte storage element in a low-temperature environment, and can improve the capacity retention rate after storage.

[0017] A nonaqueous electrolyte storage element according to one aspect of the present invention includes the positive electrode. Because the nonaqueous electrolyte storage element includes a positive electrode containing the composite positive electrode active material, it exhibits excellent initial output performance in low-temperature environments.

[0018] An electricity storage device according to one aspect of the present invention includes two or more electricity storage elements, and includes one or more nonaqueous electrolyte electricity storage elements according to the above-described aspect of the present invention. Because the electricity storage device includes the nonaqueous electrolyte electricity storage element according to the above-described aspect of the present invention, the electricity storage device has excellent initial output performance in low-temperature environments.

[0019] The configuration of a positive electrode for a nonaqueous electrolyte energy storage element, the configuration of a nonaqueous electrolyte energy storage element, the configuration of an energy storage device, a method for manufacturing a positive electrode for a nonaqueous electrolyte energy storage element, and a method for manufacturing a nonaqueous electrolyte energy storage element according to one embodiment of the present invention will be described in detail below. Note that the names of the components (elements) used in each embodiment may differ from the names of the components (elements) used in the background art.

[0020] <Positive electrode for non-aqueous electrolyte energy storage element> The positive electrode for a non-aqueous electrolyte storage element (hereinafter also simply referred to as the positive electrode) has a positive electrode substrate and a positive electrode mixture layer disposed on the positive electrode substrate directly or via an intermediate layer.

[0021] [Positive electrode substrate] The positive electrode substrate is electrically conductive. Whether or not it has "electrical conductivity" is determined by whether the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 7The threshold value is Ω·cm. The material of the positive electrode substrate is a metal such as aluminum, titanium, tantalum, or stainless steel, or an alloy of these. Among these, aluminum or an aluminum alloy is preferred from the viewpoints of potential resistance, high conductivity, and cost. Positive electrode substrates include foils, vapor-deposited films, meshes, and porous materials, 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, the strength of the positive electrode substrate can be increased while increasing the energy density per volume of the secondary battery.

[0023] The intermediate layer is a layer disposed between the positive electrode substrate and the positive electrode mixture 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 mixture layer. The configuration of the intermediate layer is not particularly limited, and may contain, for example, a binder and a conductive agent.

[0024] [Positive electrode mixture layer] The positive electrode mixture layer contains a composite positive electrode active material in which at least a portion of the surface of a positive electrode active material is coated with carbon. The positive electrode mixture layer contains optional components such as a conductive agent, a binder, a thickener, and a filler as needed.

[0025] (Composite positive electrode active material) In the composite positive electrode active material, at least a portion of the surface of the positive electrode active material is coated with carbon.

[0026] The positive electrode active material is a compound represented by the following formula 1. Life x Mn (1-x) PO4(0≦x≦1) 1 The compound represented by the above formula 1 is a phosphate compound containing iron, manganese, or a combination thereof and lithium. The compound represented by the above formula 1 has an olivine-type crystal structure. A compound having an olivine-type crystal structure has a crystal structure that can be attributed to the space group Pnma. A crystal structure that can be attributed to the space group Pnma means having peaks that can be attributed to the space group Pnma in the X-ray diffraction pattern. Since the compound represented by the above formula 1 is a polyanion salt in which the oxygen desorption reaction from the crystal lattice does not easily proceed, it has high safety and is also inexpensive.

[0027] Examples of the above positive electrode active material include lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), lithium iron manganese phosphate (LiFe x Mn 1-x PO4, 0 < x < 1), or a combination thereof. By including iron, manganese, or a combination thereof as a transition metal in the above positive electrode active material, the charge-discharge capacity can be increased more.

[0028] The compound represented by the above formula 1 may contain transition metal elements other than iron and manganese and typical elements such as aluminum. However, it is preferable that the compound represented by the above formula 1 is substantially composed of iron, manganese, or a combination thereof, lithium, phosphorus, and oxygen.

[0029] In the above formula 1, the upper limit of x is 1, and 0.95 is preferable. Also, the lower limit of x is 0, and 0.25 is preferable. By the value of x being below the above upper limit or above the above lower limit, it has more excellent life characteristics. Note that x may be substantially 1.

[0030] As the average particle diameter of the primary particles of the above positive electrode active material, for example, it is preferably 0.01 μm or more and 0.20 μm or less, and more preferably 0.02 μm or more and 0.10 μm or less. By setting the average particle diameter of the primary particles of the compound represented by formula 1 within the above range, the diffusibility of lithium ions in the pores of the positive electrode mixture layer is improved.

[0031] The average particle size of the secondary particles of the positive electrode active material is, for example, preferably 3 μm to 20 μm, more preferably 5 μm to 15 μm. By setting the average particle size of the secondary particles of the compound represented by Formula 1 within this range, production and handling become easier and the diffusibility of lithium ions in the pores of the positive electrode mixture layer is improved.

[0032] "Average particle size of primary particles" is a value measured by observation with a scanning electron microscope. "Average particle size of secondary particles" means the value at which the volume-based cumulative distribution calculated in accordance with JIS-Z-8819-2 (2001) is 50% based on the particle size distribution measured by laser diffraction / scattering method for a diluted solution of particles diluted with a solvent in accordance with JIS-Z-8825 (2013).

[0033] To obtain powders with a predetermined particle size, grinders, classifiers, etc. are used. Grinding methods include, for example, methods using a mortar, ball mill, sand mill, vibration ball mill, planetary ball mill, jet mill, counter jet mill, swirling airflow jet mill, or sieves. Wet grinding in the presence of water or an organic solvent such as hexane can also be used during grinding. As classification methods, sieves, air classifiers, etc. are used as needed for both dry and wet methods.

[0034] In the composite positive electrode active material, at least a portion of the surface of the positive electrode active material is coated with carbon, thereby improving electronic conductivity. The carbon content in the composite positive electrode active material is preferably 0.5% by mass or more and 5% by mass or less. By setting the carbon content within this range, it is possible to increase electrical conductivity, the density of the positive electrode mixture layer, and ultimately the capacity of the nonaqueous electrolyte storage element.

[0035] The lower limit of the pore specific surface area of ​​the carbon is 0.1 m 2 / g is preferred, and 0.5m 2 / g is more preferred, and 1.0m 2 The upper limit of the pore specific surface area of ​​the carbon is 5.7 m / g. 2 / g is preferred, 5.6m2 / g is more preferable, and 5.5m 2 / g is more preferred.

[0036] The lower limit of the ratio of the pore specific surface area of ​​the carbon to the pore specific surface area of ​​the composite positive electrode active material is 20%, preferably 25%. When the pore specific surface area ratio of the carbon is equal to or greater than the lower limit, the diffusibility of the non-aqueous electrolyte can be maintained favorably, thereby improving the lithium ion diffusibility in the positive electrode mixture layer. Therefore, the initial output performance of the non-aqueous electrolyte storage element in a low-temperature environment can be improved. Meanwhile, the upper limit of the pore specific surface area ratio of the carbon is 50%, preferably 45%. When the pore specific surface area ratio of the carbon is equal to or less than the upper limit, the contact resistance between carbon particles can be reduced. Therefore, the initial output performance of the non-aqueous electrolyte storage element in a low-temperature environment can be improved.

[0037] The pore specific surface areas of the composite positive electrode active material and the carbon are calculated using a nitrogen gas adsorption method according to the following procedure. The pore specific surface area was measured using Quantachrome's "autosorb iQ" and control analysis software "ASiQwin." 1.00 g of the sample to be measured was placed in a sample tube and dried under reduced pressure at 120°C for 12 hours to thoroughly remove moisture. Next, adsorption and desorption isotherms were measured using liquid nitrogen gas adsorption at relative pressures P / P0 (P0 = approximately 770 mmHg) ranging from 0 to 1. The desorption isotherm was then used to calculate the pore specific surface area using the BJH method. Furthermore, carbon-coated active materials were heat-treated in air at 400°C for 2 hours to remove only the surface-coated carbon. Therefore, the specific surface area of ​​the active material alone could be measured after heat treatment, and the specific surface area ratio of the surface-coated carbon could be calculated from the difference in specific surface area before and after heat treatment.

[0038] For the measurement of the pore specific surface area, if the powder is a pre-charge / discharge powder of the composite positive electrode active material before the positive electrode is fabricated, it is used for the measurement as is. On the other hand, when a measurement sample is taken from a positive electrode taken out by disassembling a nonaqueous electrolyte storage element, before disassembling the nonaqueous electrolyte storage element, the nonaqueous electrolyte storage element is discharged at a constant current value (0.1 C) that is one-tenth of the current value that produces the same amount of electricity as the nominal capacity of the nonaqueous electrolyte storage element when a constant current is applied to the nonaqueous electrolyte storage element for one hour, until the voltage reaches the lower limit of the specified voltage in a 25°C environment. The nonaqueous electrolyte storage element is disassembled, the positive electrode is removed, and a battery is assembled using a metallic lithium electrode as the counter electrode. The terminal voltage of the positive electrode is measured at a current value of 10 mA per 1 g of positive electrode mixture in a 25°C environment, and the terminal voltage of the positive electrode is measured at a current value of 2.0 V (vs. Li / Li). + ) and adjust to a fully discharged state. The battery is then disassembled again, and the positive electrode is removed. The removed positive electrode is thoroughly washed with dimethyl carbonate to remove any nonaqueous electrolyte adhering to the positive electrode, and then dried at room temperature for a day and night, after which the positive electrode mixture on the positive electrode substrate is collected. The above-mentioned battery disassembly, as well as the positive electrode washing and drying, are carried out in an argon atmosphere with a dew point of -60°C or less. The obtained positive electrode mixture is dispersed in N-methylpyrrolidone (NMP) to remove the binder (PVdF) from the positive electrode mixture. The powder obtained after washing with dimethyl carbonate and drying is then subjected to air classification or other methods to remove the conductive agent. The positive electrode mixture collected in this manner can be used to measure the pore specific surface area.

[0039] The lower limit of the density of the positive electrode mixture layer is 1.80 g / cm 3 and 1.85 g / cm 3 When the density of the positive electrode mixture layer is equal to or greater than the lower limit, the adhesion of the positive electrode active material can be improved, thereby reducing the resistance of the positive electrode for the nonaqueous electrolyte storage element. Therefore, the initial output performance of the nonaqueous electrolyte storage element in a low-temperature environment can be improved. On the other hand, the upper limit of the density of the positive electrode mixture layer is 2.10 g / cm. 3 and 2.05 g / cm 3When the density of the positive electrode mixture layer is equal to or less than the lower limit, the diffusibility of the non-aqueous electrolyte can be maintained favorably, thereby improving the diffusibility of lithium ions in the pores of the positive electrode mixture layer, thereby improving the initial output performance of the non-aqueous electrolyte storage element in a low-temperature environment.

[0040] The density of the positive electrode mixture layer is calculated by measuring the mass per unit area of ​​the positive electrode mixture layer, measuring the average thickness of the positive electrode mixture layer, and dividing the obtained mass per unit area by the average thickness. If the nonaqueous electrolyte storage element is assembled before, the density of the positive electrode mixture layer is measured as is. If the nonaqueous electrolyte storage element is assembled after, the density of the positive electrode mixture layer of the positive electrode adjusted to a fully discharged state using the method described above is measured. The average thickness of the positive electrode mixture layer is obtained by measuring the thickness at 10 random locations and calculating the average of the measurement results.

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

[0042] (optional ingredient) Although the carbon contained in the composite positive electrode active material is also conductive, the positive electrode mixture layer may contain a conductive agent in addition to the carbon contained in the composite positive electrode active material, as necessary. 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. Examples of the conductive agent include powder and fiber. As the conductive agent, one of these materials may be used alone, or two or more may be mixed and used. Furthermore, these materials may be used in combination. For example, a composite material of carbon black and CNTs may be used. Of these, carbon black is preferred from the viewpoint of electron conductivity and coatability, and acetylene black is particularly preferred.

[0043] The content of the conductive agent in the positive electrode mixture layer is preferably 1% by mass to 10% by mass, more preferably 3% by mass to 9% by mass. By setting the content of the conductive agent within this range, the energy density of the nonaqueous electrolyte 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 mixture layer is preferably 1% by mass to 10% by mass, more preferably 3% by mass to 9% by mass. By setting the binder content within this range, the active material can be stably maintained.

[0046] Examples of thickeners include polysaccharide polymers such as carboxymethyl cellulose (CMC), methyl cellulose, etc. When the thickener has a functional group that reacts with lithium or the like, this functional group may be deactivated in advance by methylation or the like.

[0047] The filler is not particularly limited, and examples of the filler 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, substances derived from mineral resources such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, and artificial products thereof.

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

[0049] [Method of manufacturing a positive electrode for a non-aqueous electrolyte storage element] A method for producing a positive electrode according to one embodiment of the present invention includes producing a positive electrode using the above-described composite positive electrode active material in which at least a portion of the surface of the positive electrode active material is coated with carbon. The positive electrode for a non-aqueous electrolyte storage element can be produced, for example, by the following method, although not particularly limited thereto.

[0050] The positive electrode can be fabricated by, for example, applying a positive electrode mixture paste to a positive electrode substrate directly or via an intermediate layer, followed by drying. The positive electrode mixture paste includes a composite positive electrode active material in which at least a portion of the surface of the positive electrode active material is coated with carbon, and optional components such as a conductive agent and a binder, which constitute the positive electrode mixture layer. The positive electrode mixture paste may further include a dispersion medium.

[0051] The composite positive electrode active material can be produced, for example, by the following procedure. First, a mixed solution of FeSO4 and MnSO4 at an arbitrary ratio was dropped at a constant rate into a reaction vessel containing ion-exchanged water, while an aqueous NaOH solution, an aqueous NH3 solution, and an aqueous NH2NH2 solution were dropped so that the pH was kept constant. x Mn 1-x (OH) precursor is prepared. x Mn (1-x) The (OH) precursor is mixed with LiHPO and sucrose powder in a solid phase, and then fired at a temperature of 550°C to 750°C in a nitrogen atmosphere to produce a composite positive electrode active material having an olivine crystal structure and represented by the following formula 1, at least a portion of whose surface is coated with carbon: Life x Mn (1-x) PO4(0≦x≦1) 1

[0052] The pore specific surface area of ​​the positive electrode active material can be adjusted to a favorable range by using NH3 as a complexing agent and NH2NH2 as an antioxidant in the manufacturing method of the composite positive electrode active material. Without using NH3 and NH2NH2, the pore specific surface area of ​​the positive electrode active material may be too small, resulting in insufficient initial output in a low-temperature environment. Thus, in the manufacturing method of the composite positive electrode active material, the use of NH3 and NH2NH2 and pH control can result in a pore structure that promotes penetration of the nonaqueous electrolyte.

[0053] The pore specific surface area of ​​the carbon can be adjusted by controlling the firing temperature and firing time in the method for producing the composite positive electrode active material.

[0054] The density of the positive electrode mixture layer can be adjusted by controlling the pressing pressure during compression molding using a roll press or the like.

[0055] The positive electrode for a nonaqueous electrolyte electricity storage element can improve the initial output performance of the nonaqueous electrolyte electricity storage element in a low-temperature environment.

[0056] <Non-aqueous electrolyte energy storage element> A nonaqueous electrolyte storage element according to one embodiment of the present invention comprises an electrode assembly having the positive electrode, negative electrode, and separator, a nonaqueous electrolyte, and a container for accommodating the electrode assembly and nonaqueous electrolyte. The electrode assembly is typically a stacked type in which a plurality of positive electrodes and a plurality of negative electrodes are stacked with separators interposed therebetween, or a wound type in which a positive electrode and a negative electrode are stacked with separators interposed therebetween and wound. The nonaqueous electrolyte is present in a state of being impregnated in the positive electrode, negative electrode, and separator. As an example of a nonaqueous electrolyte storage element, a nonaqueous electrolyte secondary battery (hereinafter also simply referred to as a "secondary battery") will be described.

[0057] [Positive electrode] The positive electrode of the nonaqueous electrolyte storage element is as described above. The nonaqueous electrolyte storage element has a positive electrode containing the composite positive electrode active material, and therefore has excellent initial output performance in low-temperature environments.

[0058] [Negative electrode] The negative electrode has a negative electrode substrate and a negative electrode mixture layer disposed on the negative electrode substrate directly or via an intermediate layer. The configuration of the intermediate layer is not particularly limited and can be selected from the configurations exemplified for the positive electrode above.

[0059] The negative electrode substrate is conductive. Metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, alloys thereof, and carbonaceous materials are used as the material for the negative electrode substrate. Among these, copper or copper alloys are preferred. Examples of the negative electrode substrate include foils, vapor-deposited films, meshes, and porous materials, with foils being preferred from the viewpoint of cost. 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.

[0060] The average thickness of the negative electrode substrate is preferably 2 μm to 35 μm, more preferably 3 μm to 30 μm, even more preferably 4 μm to 25 μm, and particularly preferably 5 μm to 20 μm. By setting the average thickness of the negative electrode substrate within the above range, the strength of the negative electrode substrate can be increased while increasing the energy density per volume of the secondary battery.

[0061] The negative electrode mixture layer contains a negative electrode active material. The negative electrode mixture layer contains optional components such as a conductive agent, a binder, a thickener, and a filler, as needed. The optional components such as the conductive agent, the binder, the thickener, and the filler can be selected from the materials exemplified for the positive electrode above.

[0062] The negative electrode mixture layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I; typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W as components other than the negative electrode active material, conductive agent, binder, thickener, and filler.

[0063] The negative electrode active material can be appropriately selected from known negative electrode active materials. A material capable of absorbing and releasing lithium ions is usually used as the negative electrode active material for lithium ion secondary batteries. Examples of the negative electrode active material include metallic Li; metals or semimetals such as Si and Sn; metal oxides or semimetal oxides such as Si oxide, Ti oxide, and Sn oxide; and Li4Ti5O 12 , LiTiO 2、Examples of the material include titanium-containing oxides such as TiNbO; polyphosphate compounds; silicon carbide; and carbon materials such as graphite and non-graphitic carbon (easily graphitized carbon or non-graphitizable carbon). Among these materials, graphite and non-graphitic carbon are preferred. In the negative electrode mixture layer, one of these materials may be used alone, or two or more may be used in combination.

[0064] "Graphite" refers to a graphite material that has an average lattice spacing (d 002 ) is 0.33 nm or more and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite. Artificial graphite is preferred from the viewpoint of being able to obtain a material with stable physical properties.

[0065] "Non-graphitic carbon" refers to carbon that has an average lattice spacing (d 002 ) is 0.34 nm or more and 0.42 nm or less. Non-graphitic carbon includes non-graphitizable carbon and graphitizable carbon. Examples of non-graphitic carbon include resin-derived materials, petroleum pitch or petroleum pitch-derived materials, petroleum coke or petroleum coke-derived materials, plant-derived materials, and alcohol-derived materials.

[0066] Here, the "discharged state" refers to a state in which the negative electrode active material, a carbonaceous material, is discharged so that lithium ions capable of being absorbed and desorbed during charging and discharging are sufficiently released. For example, in a single-electrode battery using a negative electrode containing a carbonaceous material as a negative electrode active material as a working electrode and metallic Li as a counter electrode, this refers to a state in which the open circuit voltage is 0.7 V or higher.

[0067] "Non-graphitizable carbon" means the above d 002 This refers to carbon materials with a particle size of 0.36 nm or more and 0.42 nm or less.

[0068] "Graphitizable carbon" means the above d 002 This refers to carbon materials with a particle size of 0.34 nm or more and less than 0.36 nm.

[0069] 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 or more and 100 μm or less. When the negative electrode active material is a carbon material, a titanium-containing oxide, or a polyphosphate compound, the average particle size may be 1 μm or more and 100 μm or less. When the negative electrode active material is Si, Sn, Si oxide, Sn oxide, or the like, the average particle size may be 1 nm or more and 1 μm or less. By setting the average particle size of the negative electrode active material to be equal to or greater than the above-mentioned lower limit, the negative electrode active material can be easily produced or handled. By setting the average particle size of the negative electrode active material to be equal to or less than the above-mentioned upper limit, the electronic conductivity of the negative electrode mixture layer is improved. To obtain powder with a predetermined particle size, a pulverizer, a classifier, or the like is used. The pulverization method and the powder classification method can be selected, for example, from the methods exemplified for the positive electrode. When the negative electrode active material is a metal such as metallic Li, the negative electrode active material may be in the form of a foil.

[0070] The content of the negative electrode active material in the negative electrode mixture 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 this range, both high energy density and manufacturability of the negative electrode mixture layer can be achieved.

[0071] [Separator] The separator can be appropriately selected from known separators. Examples of separators that can be used include separators consisting of only a substrate layer and separators in which a heat-resistant layer containing heat-resistant particles and a binder is formed on one or both surfaces of the substrate layer. Examples of the shape of the substrate layer of the separator include woven fabric, nonwoven fabric, and porous resin film. Among these shapes, porous resin films are preferred from the viewpoint of strength, and nonwoven fabrics are preferred from the viewpoint of non-aqueous electrolyte retention. Materials for the substrate layer of the separator are preferably polyolefins such as polyethylene and polypropylene from the viewpoint of shutdown function, and polyimide and aramid from the viewpoint of oxidative decomposition resistance. A composite material of these resins may also be used for the substrate layer of the separator.

[0072] The heat-resistant particles contained in the heat-resistant layer preferably exhibit a mass loss of 5% or less when heated from room temperature to 500°C in an air atmosphere at 1 atmosphere pressure, and more preferably exhibit a mass loss of 5% or less when heated from room temperature to 800°C. Examples of materials exhibiting a mass loss of a predetermined value or less include inorganic compounds. Examples of inorganic compounds include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicate; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium titanate; covalently bonded crystals such as silicon and diamond; mineral-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, as well as artificial products thereof. As the inorganic compound, these substances may be used alone or in the form of a complex, or two or more of them may be used in combination. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicate is preferred from the viewpoint of safety of the nonaqueous electrolyte electricity storage element.

[0073] The porosity of the separator is preferably 80% by volume or less from the viewpoint of strength, and 20% by volume or more from the viewpoint of discharge performance. Here, "porosity" refers to a volume-based value measured with a mercury porosimeter.

[0074] The separator may be a polymer gel composed of a polymer and a non-aqueous electrolyte. Examples of polymers include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, and polyvinylidene fluoride. The use of a polymer gel has the effect of suppressing leakage. The separator may be a combination of the porous resin film or nonwoven fabric described above and a polymer gel.

[0075] [Non-aqueous electrolyte] The nonaqueous electrolyte can be appropriately selected from known nonaqueous electrolytes. The nonaqueous electrolyte may be a nonaqueous electrolytic solution. The nonaqueous electrolytic solution contains a nonaqueous solvent and an electrolyte salt dissolved in the nonaqueous solvent.

[0076] The non-aqueous solvent can be appropriately selected from known non-aqueous solvents. Examples of non-aqueous solvents include cyclic carbonates, chain carbonates, carboxylic acid esters, phosphate esters, sulfonic acid esters, ethers, amides, and nitriles. Non-aqueous solvents in which some of the hydrogen atoms contained in these compounds have been substituted with halogens may also be used.

[0077] Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinylethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), styrene carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate, etc. Among these, EC is preferred.

[0078] Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, trifluoroethyl methyl carbonate, bis(trifluoroethyl) carbonate, etc. Among these, EMC is preferred.

[0079] It is preferable to use a cyclic carbonate or a chain carbonate as the non-aqueous solvent, and it is more preferable to use a combination of a cyclic carbonate and a chain carbonate. The use of a cyclic carbonate can promote dissociation of the electrolyte salt and improve the ionic conductivity of the non-aqueous electrolyte. The use of a chain carbonate can reduce the viscosity of the non-aqueous electrolyte. When a cyclic carbonate and a chain carbonate are used in combination, the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate:chain carbonate) is preferably in the range of, for example, 5:95 to 50:50.

[0080] The electrolyte salt can be appropriately selected from known electrolyte salts, such as lithium salts, sodium salts, potassium salts, magnesium salts, and onium salts. Of these, lithium salts are preferred.

[0081] Examples of lithium salts include inorganic lithium salts such as LiPF6, LiPO2F2, LiBF4, LiClO4, and LiN(SO2F)2, lithium oxalates such as lithium bis(oxalate)borate (LiBOB), lithium difluorooxalateborate (LiFOB), and lithium bis(oxalate)difluorophosphate (LiFOP), and lithium salts having a halogenated hydrocarbon group such as LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), LiC(SO2CF3)3, and LiC(SO2C2F5)3. Among these, inorganic lithium salts are preferred, and LiPF6 is more preferred.

[0082] The content of electrolyte salt in the non-aqueous electrolyte is 0.1 mol / dm at 20°C and 1 atmosphere. 3 More than 2.5mol / dm 3 It is preferable that the value is 0.3 mol / dm or less. 3 More than 2.0mol / dm 3 It is more preferable that it is 0.5 mol / dm or less. 3 More than 1.7mol / dm 3 It is more preferable that it is 0.7 mol / dm or less. 3More than 1.5mol / dm 3 By setting the content of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

[0083] The non-aqueous electrolyte may contain additives in addition to the non-aqueous solvent and the electrolyte salt. Examples of additives include halogenated carbonates such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC); oxalates such as lithium bis(oxalate)borate (LiBOB), lithium difluorooxalateborate (LiFOB), and lithium bis(oxalate)difluorophosphate (LiFOP); imide salts such as lithium bis(fluorosulfonyl)imide (LiFSI); aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partial halides of the above 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, and the like. Carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, 4,4'-bis(2,2-dioxo-1 ,3,2-dioxathiolane), 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, 1,3-propene sultone, 1,3-propane sultone, 1,4-butane sultone, 1,4-butene sultone, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakistrimethylsilyl titanate, lithium monofluorophosphate, lithium difluorophosphate, etc. These additives may be used alone or in combination of two or more.

[0084] The content of the additive contained in the non-aqueous electrolyte is preferably 0.01% by mass to 10% by mass, more preferably 0.1% by mass to 7% by mass, even more preferably 0.2% by mass to 5% by mass, and particularly preferably 0.3% by mass to 3% by mass. By setting the content of the additive within the above range, it is possible to improve the capacity retention performance or cycle performance after high-temperature storage, and further improve safety.

[0085] The non-aqueous electrolyte may be a solid electrolyte, or a non-aqueous electrolytic solution and a solid electrolyte may be used in combination.

[0086] The solid electrolyte can be selected from any material that has ionic conductivity of lithium, sodium, calcium, etc. and is solid at room temperature (e.g., 15° C. to 25° C.) Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, oxynitride solid electrolytes, and polymer solid electrolytes.

[0087] Examples of sulfide solid electrolytes include Li2S-P2S5, LiI-Li2S-P2S5, and Li 10 Ge-P2S 12 etc.

[0088] The shape of the nonaqueous electrolyte storage element of this embodiment is not particularly limited, and examples thereof include cylindrical batteries, prismatic batteries, flat batteries, coin batteries, and button batteries.

[0089] FIG. 1 shows a nonaqueous electrolyte storage element 1 as an example of a prismatic battery. The figure is a see-through view of the inside of the container. An electrode assembly 2 having a positive electrode and a negative electrode wound with a separator sandwiched between them is housed in a prismatic container 3. The positive electrode is electrically connected to a positive electrode terminal 4 via a positive electrode lead 41. The negative electrode is electrically connected to a negative electrode terminal 5 via a negative electrode lead 51.

[0090] [Configuration of Nonaqueous Electrolyte Energy Storage Device] The nonaqueous electrolyte energy storage element of this embodiment can be mounted as an energy storage device comprising a plurality of nonaqueous electrolyte energy storage elements 1 in an automobile power source such as an electric vehicle (EV), a hybrid electric vehicle (HEV), or a plug-in hybrid electric vehicle (PHEV), a power source for electronic devices such as a personal computer or a communication terminal, or a power storage power source, etc. In this case, the technology of the present invention may be applied to at least one nonaqueous electrolyte energy storage element included in the energy storage device.

[0091] An electricity storage device according to one embodiment of the present invention is an electricity storage device that includes two or more electricity storage elements and one or more nonaqueous electrolyte electricity storage elements according to one embodiment of the present invention. Fig. 2 shows an example of an electricity storage device 30 in which electricity storage units 20, each of which is an assembly of two or more electrically connected nonaqueous electrolyte electricity storage elements 1, are further assembled. The electricity storage device 30 may include a bus bar (not shown) that electrically connects two or more nonaqueous electrolyte electricity storage elements 1, a bus bar (not shown) that electrically connects two or more electricity storage units 20, and the like. The electricity storage unit 20 or the electricity storage device 30 may include a status monitoring device (not shown) that monitors the status of one or more nonaqueous electrolyte electricity storage elements.

[0092] [Method of manufacturing nonaqueous electrolyte energy storage element] The nonaqueous electrolyte storage element can be manufactured by a known method except for using the above-described positive electrode as the positive electrode. The manufacturing method of the nonaqueous electrolyte storage element of this embodiment can be appropriately selected from known methods. The manufacturing method of the nonaqueous electrolyte storage element includes, for example, preparing an electrode assembly, preparing a nonaqueous electrolyte, and housing the electrode assembly and the nonaqueous electrolyte in a container. Preparing the electrode assembly includes preparing the positive electrode and negative electrode, and forming the electrode assembly by stacking or winding the positive electrode and negative electrode with a separator interposed therebetween.

[0093] The method for placing the non-aqueous electrolyte in the container can be appropriately selected from known methods. For example, when a non-aqueous electrolyte solution is used as the non-aqueous electrolyte, the non-aqueous electrolyte solution may be poured into the container through an inlet formed in the container, and then the inlet may be sealed.

[0094] <Other embodiments> The nonaqueous electrolyte storage element of the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the spirit of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, or part of the configuration of one embodiment can be replaced with the configuration of another embodiment or well-known technology. Furthermore, part of the configuration of one embodiment can be deleted. Also, well-known technology can be added to the configuration of one embodiment.

[0095] In the above embodiment, the nonaqueous electrolyte storage element is used as a chargeable and dischargeable nonaqueous electrolyte secondary battery (e.g., a lithium ion secondary battery), but the type, shape, size, capacity, etc. of the nonaqueous electrolyte storage element are arbitrary. The present invention can also be applied to various secondary batteries, electric double layer capacitors, lithium ion capacitors, and other capacitors.

[0096] In the above embodiment, the electrode assembly in which the positive electrode and the negative electrode are stacked with a separator interposed therebetween has been described, but the electrode assembly may not include a separator. For example, the positive electrode and the negative electrode may be in direct contact with each other in a state in which a non-conductive layer is formed on the mixture layer of the positive electrode or the negative electrode. [Example]

[0097] 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.

[0098] [Examples 1 to 8 and Comparative Examples 1 to 7] (Preparation of composite positive electrode active material) First, 750cm 3 2 dm containing ion-exchanged water 3 In a reaction vessel, 1 mol / dm 3 The solution was added dropwise at a constant rate while maintaining the pH as shown in Table 1. 3 NaOH solution and 0.5 mol / dm 3 NH3 aqueous solution and 0.5 mol / dm 3The NH2NH2 aqueous solution was added dropwise to prepare an Fe(OH)2 precursor. The temperature of the reaction vessel was set to 50°C (±2°C). Next, the prepared Fe(OH)2 precursor was solid-phase mixed with LiH2PO4 and sucrose powder. Then, by firing in a nitrogen atmosphere, composite positive electrode active materials of Examples 1 to 8 and Comparative Examples 1 to 7 were prepared in which the entire surface of the positive electrode active material LiFePO4 represented by the above formula 1 was coated with carbon.

[0099] In these composite positive electrode active materials, the ratio of the pore specific surface area of ​​the carbon to the pore specific surface area of ​​the composite positive electrode active material was adjusted by the pH, baking temperature, and baking time during precursor preparation. The pH, baking temperature, and baking time during precursor preparation for Examples 1 to 8 and Comparative Examples 1 to 7 are shown in Table 1.

[0100] Table 1 shows the specific pore surface area of ​​the carbon, the total specific pore surface area, and the ratio of the specific pore surface area of ​​the carbon to the specific pore surface area of ​​the composite positive electrode active material for Examples 1 to 8 and Comparative Examples 1 to 7. The specific pore surface areas were measured according to the method described above.

[0101] Furthermore, the composite positive electrode active materials of Examples 9 to 13 and Comparative Examples 8 to 10 were prepared in the same manner as in Example 1, except that the pore specific surface area of ​​the carbon was adjusted by adjusting the firing temperature and the amount of sucrose powder mixed relative to the amount of the composite positive electrode active material. The firing temperatures and the amounts of sucrose powder mixed relative to the amount of the composite positive electrode active material for Examples 9 to 13 and Comparative Examples 8 to 10 are shown in Table 2.

[0102] Table 2 shows the specific pore surface areas of the carbon and the ratios of the specific pore surface area of ​​the carbon to the specific pore surface area of ​​the composite positive electrode active material for Examples 9 to 13 and Comparative Examples 8 to 10. The specific pore surface areas were measured according to the method described above.

[0103] The composite positive electrode active material used in Examples 1 to 13 and Comparative Examples 1 to 10 had the value of x in the above formula 1 set to 1, that is, LiFePO4.

[0104] (Preparation of positive electrode) N-methylpyrrolidone (NMP) was used as the dispersion medium, the composite positive electrode active material as the positive electrode active material, acetylene black as the conductive agent, and PVdF as the binder. The composite positive electrode active material, conductive agent, binder, and dispersion medium were mixed. At this time, the solid mass ratio of the positive electrode active material:conductive agent:binder was set to 90:5:5. An appropriate amount of NMP was added to the resulting mixture to adjust the viscosity, and a positive electrode mixture paste was prepared. Next, the positive electrode mixture paste was applied to both sides of an aluminum foil serving as a positive electrode substrate, leaving uncoated areas (areas where the positive electrode mixture layer was not formed), and the mixture was dried at 120°C and roll-pressed to form a positive electrode mixture layer on the positive electrode substrate. The amount of the positive electrode mixture paste applied was 10 mg / cm in solid content. 2 The density of the positive electrode mixture layer was adjusted by roll press molding. The densities of the positive electrode mixture layers of Examples 1 to 8 and Comparative Examples 1 to 7 were measured according to the above method. The results are shown in Table 1. In this way, the positive electrodes of Examples 1 to 13 and Comparative Examples 1 to 10 were obtained.

[0105] (Preparation of negative electrode) Graphite was used as the negative electrode active material, SBR as the binder, and CMC as the thickener. The negative electrode active material, binder, thickener, and water as the dispersion medium were mixed. The solid mass ratio of negative electrode active material:binder:thickener was 97:2:1. An appropriate amount of water was added to the resulting mixture to adjust the viscosity, and a negative electrode mixture paste was prepared. This negative electrode mixture paste was applied to both sides of copper foil, leaving uncoated areas (areas where the negative electrode mixture layer was not formed), and then dried to prepare a negative electrode mixture layer. Then, a roll press was performed to prepare a negative electrode.

[0106] (Preparation of non-aqueous electrolyte) EC and EMC were mixed in a volume ratio of 3:7, and LiPF6 was added at 1 mol / dm 3 A non-aqueous electrolyte was prepared by dissolving the solution at a concentration of 100 ppm.

[0107] (Fabrication of non-aqueous electrolyte energy storage element) Next, the positive electrode and the negative electrode were stacked via a separator consisting of a polyethylene microporous membrane substrate and an inorganic layer formed on the polyethylene microporous membrane substrate to prepare an electrode assembly. The inorganic layer was disposed on the surface facing the positive electrode. The electrode assembly was placed in an aluminum prismatic container, and a positive electrode terminal and a negative electrode terminal were attached. The nonaqueous electrolyte was poured into the container, which was then sealed to obtain nonaqueous electrolyte storage elements of Examples and Comparative Examples.

[0108] (Initial output performance test in a low temperature environment) The initial output performance [W] in a low-temperature environment was evaluated using the following procedure. Each of the nonaqueous electrolyte storage elements of Examples 1 to 8 and Comparative Examples 1 to 7 was subjected to constant-current charging at a charging current of 0.1 C up to 3.6 V in a 25°C environment, followed by constant-voltage charging at 3.6 V. The charging was terminated when the charging current reached 0.02 C. After a 10-minute rest period, the element was discharged at a constant current of 0.1 C down to 2.0 V in a 25°C environment, and the "0.1 C discharge capacity in a 25°C environment" was measured. Next, half the electrical quantity of this "0.1 C discharge capacity in a 25°C environment" was set as SOC 50%, and constant-current charging was performed from a fully discharged state at a charging current of 0.1 C up to SOC 50%. After storage for 3 hours in a 0°C environment, the element was discharged at a discharging current of 0.1 C for 30 seconds, followed by a 10-minute rest period and then supplementary charging at a charging current of 0.1 C for 30 seconds. Similarly, the discharge current was adjusted to 0.3 C and 0.5 C, and the battery was discharged for 30 seconds each, followed by a 10-minute rest period, followed by supplementary charging at a charge current of 0.1 C until the SOC reached 50%. The "initial 0°C output" (shown as "initial output 0°C" in Table 1) was calculated from the current during each discharge and the battery voltage 10 seconds after the start of discharge.

[0109] Table 1 shows the results of the initial output performance test in a low temperature environment (0°C).

[0110] (Capacity retention rate after storage) The capacity retention rate [%] after storage was evaluated according to the following procedure. Each of the nonaqueous electrolyte storage elements of Examples 9 to 13 and Comparative Examples 8 to 10 was subjected to constant current charging at a current of 0.1 C up to 3.6 V in a 25°C environment, followed by constant voltage charging at 3.6 V. The charge was terminated when the charging current reached 0.02 C. After a 10-minute rest period following charge, the element was discharged at a constant current of 0.1 C down to 2.0 V. The discharge capacity at this time was designated the "discharge capacity before storage." The nonaqueous electrolyte storage element was then charged at a constant current of 0.1 C to 3.6 V in a 25°C environment, followed by constant voltage charging at 3.6 V. The charging termination condition was until the charging current reached 0.02 C. The element was then stored in an 85°C environment for 10 days. The element was then discharged at a constant current of 0.1 C to 2.0 V in a 25°C environment, and further charged at a constant current of 0.1 C to 3.6 V, followed by constant voltage charging at 3.6 V. The charging termination condition was until the charging current reached 0.02 C. The element was then discharged at a constant current of 0.1 C to 2.0 V. A 10-minute rest period was provided after each charge and discharge. The discharge capacity at this time was designated the "discharge capacity after storage." The percentage of the "discharge capacity after storage" to the "discharge capacity before storage" was calculated using the formula "discharge capacity after storage" / "discharge capacity before storage"×100, and this was taken as the "capacity retention rate after storage."

[0111] Table 2 shows the test results for capacity retention after storage.

[0112] [Table 1]

[0113] [Table 2]

[0114] As shown in Table 1 above, the positive electrode active material contains a composite positive electrode active material in which at least a portion of the surface of the positive electrode active material represented by Formula 1 above is coated with carbon, the ratio of the pore specific surface area of ​​the carbon to the pore specific surface area of ​​the composite positive electrode active material is 20% or more and 50% or less, and the density of the positive electrode mixture layer is 1.80 g / cm 3 More than 2.10g / cm3 It can be seen that Examples 1 to 8 below are superior in initial output performance in a low temperature environment compared to Comparative Examples 1 to 7.

[0115] As shown in Table 2 above, the composite positive electrode active material is comprised of a positive electrode active material represented by Formula 1, in which at least a portion of the surface thereof is covered with carbon, and the ratio of the pore specific surface area of ​​the carbon to the pore specific surface area of ​​the composite positive electrode active material is 20% or more and 50% or less, and the pore specific surface area of ​​the carbon is 1.0 m 2 / g or more 5.5m 2 It can be seen that Examples 9 to 13, in which the capacitance is less than 1 / g, have superior capacity retention rates after storage compared to Comparative Examples 8 to 10.

[0116] The above results demonstrate that the composite positive electrode active material can improve the initial output performance of nonaqueous electrolyte energy storage elements in low-temperature environments. The positive electrode is suitable for use as a positive electrode for nonaqueous electrolyte energy storage elements used as power sources for electronic devices such as personal computers and communication terminals, and automobiles. [Explanation of symbols]

[0117] 1. Non-aqueous electrolyte energy storage element 2 Electrode body 3 containers 4 Positive terminal 41 Positive lead 5 Negative terminal 51 Negative lead 20 Energy storage unit 30 Electricity storage device

Claims

1. a positive electrode mixture layer containing a composite positive electrode active material in which at least a portion of the surface of the positive electrode active material is coated with carbon; a ratio of the pore specific surface area of ​​the carbon to the pore specific surface area of ​​the composite positive electrode active material is 20% or more and 50% or less; The density of the positive electrode mixture layer is 1.80 g / cm 3 2.10g / cm or more 3 is as follows: the carbon has a pore specific surface area of ​​1.0 m 2 / g or more and 5.5 m 2 / g or less; The positive electrode for a non-aqueous electrolyte storage element, wherein the positive electrode active material is a compound represented by the following formula 1: LiFe x Mn (1-x) PO 4 (0≦x≦1) ・・・1

2. A non-aqueous electrolyte electricity storage element comprising the positive electrode according to claim 1 .

3. An electricity storage device comprising two or more electricity storage elements and one or more nonaqueous electrolyte electricity storage elements according to claim 2 .

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