Positive electrode active material mixture for non-aqueous electrolyte energy storage elements, positive electrode for non-aqueous electrolyte energy storage elements, and non-aqueous electrolyte energy storage elements

Abstract

To provide a positive electrode active material for a power storage element and a positive electrode for the power storage element capable of increasing the discharge capacity of the power storage element in a low temperature environment, and the power storage element having a large discharge capacity in the low temperature environment.SOLUTION: A positive electrode active material mixture for a power storage element contains a compound represented by the following formula (1), a pore specific surface area in a range of a pore diameter of 30 nm or more and 200 nm or less is 10 m2 / g or more, and the pore specific surface area in a range of the pore diameter of 100 nm or more and 200 nm or less is 1 m2 / g or more. LiFexMn(1-x)PO4(0≤x≤1) (1).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material mixture for energy storage elements, a positive electrode for energy storage elements, and an energy storage element. [Background technology]

[0002] Non-aqueous electrolyte secondary batteries, such as lithium-ion batteries, are widely used in electronic devices like personal computers and communication terminals, as well as automobiles, due to their high energy density. Generally, 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 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 energy storage elements.

[0003] In recent years, olivine-type lithium iron phosphate has attracted attention as a positive electrode active material used in the above-mentioned energy storage elements because it is inexpensive and highly safe. For example, a lithium secondary battery has been proposed in which the active material in the active material layer of the positive electrode plate is lithium iron phosphate, and the thickness of the active material layer is between 40 μm and 200 μm. (See Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2015-56318 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, energy storage elements equipped with a positive electrode active material layer, such as those described in Patent Document 1 above, may have a small discharge capacity in low-temperature environments, such as below 0°C.

[0006] The object of the present invention is to provide a positive electrode active material and a positive electrode for an energy storage element that can increase the discharge capacity of the energy storage element in a low-temperature environment, as well as an energy storage element with a large discharge capacity in a low-temperature environment. [Means for solving the problem]

[0007] A positive electrode active material mixture for an energy storage element according to one aspect of the present invention contains a compound represented by the following formula 1, and has a pore specific surface area of ​​10 m² in the range of pore diameter 30 nm to 200 nm. 2 The amount is 1 / g or more, and the pore specific surface area in the range of pore diameter 100 nm to 200 nm is 1 m². 2 It is 1 / g or more. LiFe x Mn (1-x) PO4(0≦x≦1) ···1

[0008] A positive electrode for an energy storage element according to another aspect of the present invention includes a positive electrode active material mixture for the energy storage element.

[0009] A power storage element according to another aspect of the present invention comprises a positive electrode for the power storage element. [Effects of the Invention]

[0010] A positive electrode active material mixture for an energy storage element according to one aspect of the present invention can increase the discharge capacity of the energy storage element in a low-temperature environment.

[0011] Another aspect of the present invention relates to a positive electrode for an energy storage element that can increase the discharge capacity of the energy storage element in a low-temperature environment.

[0012] Another aspect of the present invention is an energy storage element that has a large discharge capacity in low-temperature environments. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 is a perspective view showing one embodiment of a non-aqueous electrolyte energy storage element. [Figure 2]FIG. 2 is a schematic diagram showing an embodiment of a power storage device configured by aggregating a plurality of non-aqueous electrolyte power storage elements. MODE FOR CARRYING OUT THE INVENTION

[0014] First, an outline of the positive electrode active material mixture for a power storage element, the positive electrode for a power storage element, and the power storage element disclosed by this specification will be described.

[0015] The positive electrode active material mixture for a power storage element according to one aspect of the present invention contains a compound represented by the following formula 1, and has a pore specific surface area in the range of 30 nm or more and 200 nm or less of 10 m 2 / g or more, and the pore specific surface area in the range of 100 nm or more and 200 nm or less of the pore diameter is 1 m 2 / g or more. LiFe x Mn (1-x) PO4 (0≦x≦1) ···1

[0016] According to this positive electrode active material mixture for a power storage element, the discharge capacity in a low temperature environment of the power storage element can be increased. Although the reason for this is not necessarily clear, it is speculated as follows, for example. That is, since the positive electrode active material mixture for a power storage element contains the compound of formula 1 containing iron, manganese or a combination thereof as a transition metal, the charge and discharge capacity can be increased. In addition, the pores in the range of 30 nm or more and 200 nm or less of the pore diameter in the positive electrode active material mixture for a power storage element are in a range where the non-aqueous electrolyte easily penetrates, and the pore specific surface area in this pore diameter range is 10 m 3 / g or more, and further, the pore specific surface area in the range of 100 nm or more and 200 nm or less of the relatively large pore diameter in this pore diameter range is 1 m 2 / g or more, whereby a pore structure that promotes the penetration of the non-aqueous electrolyte is obtained. As a result, the lithium ion diffusibility in the pores of the positive electrode active material mixture for a power storage element is improved. It is speculated that the positive electrode active material mixture for a power storage element can increase the discharge capacity in a low temperature environment of the power storage element due to the improvement of this lithium ion diffusibility.

[0017] Here, the positive electrode active material mixture for the energy storage element may further contain porous carbon.

[0018] In the case where the positive electrode active material mixture for the energy storage element contains porous carbon, the specific surface area of ​​the pores in the range of 100 nm to 200 nm, which is relatively large, is set to 1 m². 2 It can be easily adjusted to a value of / g or higher, meaning it can be adjusted more reliably. Therefore, this positive electrode active material mixture for energy storage elements can more reliably increase the discharge capacity of the energy storage element in low-temperature environments.

[0019] A positive electrode for an energy storage element according to another aspect of the present invention includes a positive electrode active material mixture for the energy storage element.

[0020] Thus, because the positive electrode for the energy storage element contains the above-mentioned positive electrode active material mixture, the discharge capacity of the energy storage element in a low-temperature environment can be increased.

[0021] A power storage element according to another aspect of the present invention comprises a positive electrode for the power storage element.

[0022] Thus, because the energy storage element is equipped with the positive electrode for the energy storage element described above, it has a large discharge capacity in low-temperature environments.

[0023] This document describes in detail a positive electrode active material mixture for an energy storage element, a positive electrode for an energy storage element, the configuration of an energy storage element, the configuration of an energy storage device, a method for manufacturing an energy storage element, and other embodiments related to one embodiment of the present invention. Note that the names of the components (each element) used in each embodiment may differ from the names of the components (each element) used in the background art.

[0024] <Positive electrode active material mixture for energy storage elements> The positive electrode active material mixture for the energy storage element (hereinafter also simply referred to as the positive electrode active material mixture) contains a compound represented by the following formula 1 (hereinafter also referred to as the first compound). Specifically, the positive electrode active material mixture contains a positive electrode active material, and this positive electrode active material contains the first compound. The positive electrode active material mixture may further contain porous carbon. The positive electrode active material mixture may contain optional components such as a conductive agent other than porous carbon, a binder, a thickener, and a filler as necessary. LiFe x Mn (1-x) PO4(0≦x≦1) ···1

[0025] (Positive electrode active material) The positive electrode active material contains the first compound. The first compound is represented by the above formula 1 and 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 first compound 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.

[0026] As represented by the above formula 1, the first compound is composed of 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 the transition metal in the positive electrode active material, the charge and discharge capacity can be further increased.

[0027] Thus, the first compound is a phosphate compound containing iron, manganese or a combination thereof and lithium. The first compound may contain transition metal elements other than iron and manganese and typical elements such as aluminum as inevitable impurities. However, it is preferable that the first compound is substantially composed of iron, manganese or a combination thereof, lithium, phosphorus and oxygen.

[0028] In Formula 1 above, the upper limit of x is 1, and preferably 0.95. The lower limit of x is 0, and preferably 0.25. When the value of x is below the upper limit or above the lower limit, the first compound has better lifetime characteristics. Note that x may be substantially 1.

[0029] The average particle size of the primary particles of the first compound is preferably 0.01 μm or more and 0.2 μm or less, and more preferably 0.02 μm or more and 0.1 μm or less. By setting the average particle size of the primary particles of the first compound within the above range, the diffusivity of lithium ions within the pores of the positive electrode active material mixture is further improved. The average particle size of the primary particles is a value measured by observation using a scanning electron microscope.

[0030] The average particle size of the secondary particles of the first compound is preferably 3 μm to 20 μm, and more preferably 5 μm to 15 μm. By setting the average particle size of the secondary particles of the first compound within the above range, manufacturing and handling are facilitated, and the diffusivity of lithium ions within the pores of the positive electrode active material mixture is improved. The average particle size of the secondary particles is a value measured by particle size distribution measurement.

[0031] To obtain the first compound with a predetermined particle size, grinders, classifiers, etc., are used. Examples of grinding methods include using a mortar and pestle, ball mill, sand mill, vibrating ball mill, planetary ball mill, jet mill, counterjet mill, swirling airflow jet mill, or sieve. Wet grinding, which involves the coexistence of water or an organic solvent such as hexane, can also be used during grinding. For classification, sieves, wind classifiers, etc., can be used as needed, both dry and wet.

[0032] The first compound may have at least a portion of its surface coated with carbon. Thus, the positive electrode active material may be the first compound in which at least a portion of its surface is coated with carbon. The electron conductivity is improved by coating at least a portion of the surface of the first compound with carbon. The carbon content in the 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, the electrical conductivity can be increased, and the electrode density and, consequently, the capacity of the energy storage element can be increased.

[0033] The positive electrode active material mixture may further contain positive electrode active materials other than the first compound. Such other positive electrode active materials can be appropriately selected from known positive electrode active materials for lithium-ion secondary batteries. However, the lower limit of the total content of the first compound in the total positive electrode active materials contained in the positive electrode active material mixture is preferably 90% by mass, and more preferably 99% by mass. The upper limit of the total content of the first compound in the total positive electrode active materials may be 100% by mass. By using only the positive electrode active material having an olivine-type crystal structure as substantially the positive electrode active material in this way, the effect of increasing the discharge capacity of the energy storage element in low-temperature environments can be further enhanced.

[0034] As the positive electrode active material for the lithium-ion secondary battery described above, a material capable of intercalating and releasing lithium ions is usually used. Examples of positive electrode active materials other than the first compound described above include lithium transition metal composite oxides having an α-NaFeO2 type crystal structure, lithium transition metal composite oxides having a spinel type crystal structure, polyanionic compounds, chalcogen compounds, sulfur, etc. An example of a lithium transition metal composite oxide having an α-NaFeO2 type crystal structure is Li[Li x Ni (1-x) ]O2(0≦x<0.5), Li[Li x Ni γ Co (1-x-γ) ]O2(0≦x<0.5, 0<γ<1), Li[Li x Co (1-x) ]O2(0≦x<0.5), Li[Li x Ni γ Mn(1-x-γ) ]O2(0≦x<0.5, 0<γ<1), Li[Li x Ni γ Mn β Co (1-x-γ-β) ]O2(0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1), Li[Li x Ni γ Co β Al (1-x-γ-β) Examples include ]O2 (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1). As a lithium transition metal composite oxide having a spinel-type crystal structure, Li x Mn2O4, Li x Ni γ Mn (2-γ) Examples include O4. Examples of polyanion compounds include LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, Li2CoPO4F, etc. Examples of chalcogen compounds include titanium disulfide, molybdenum disulfide, molybdenum dioxide, etc. The atoms or polyanions in these materials may be partially substituted with atoms or anion species of other elements. The surfaces of these materials may be coated with other materials. In the positive electrode active material mixture, one of these materials may be used alone, or two or more may be used in mixture form.

[0035] The content of the total positive electrode active material in the positive electrode active material mixture is preferably 50% by mass or more and 99% by mass or less, more preferably 70% by mass or more and 98% by mass or less, and even more preferably 80% by mass or more and 95% by mass or less. By setting the content of the total positive electrode active material within the above range, it is possible to achieve both high energy density and improved conductivity in the positive electrode active material mixture. The lower limit of the content of the first compound in the positive electrode active material mixture is preferably 90% by mass and preferably 99% by mass.

[0036] (Porous carbon) Examples of porous carbon include CNovel manufactured by Toyo Tanso and MSC-30 manufactured by Kansai Thermal Chemical. The inclusion of porous carbon in the cathode active material mixture increases the pore specific surface area, particularly in the range of relatively large pore diameters between 100 nm and 200 nm, to 1 m². 2It can be easily adjusted to a value of / g or higher, meaning it can be adjusted more reliably. In addition, the positive electrode active material mixture for the energy storage element can more reliably increase the discharge capacity in low-temperature environments, as described above, while avoiding a decrease in the discharge capacity of the energy storage element.

[0037] Furthermore, if the positive electrode active material mixture contains porous carbon, the pore specific surface area of ​​the positive electrode active material mixture in the range of relatively large pore diameters is increased to 1 m², primarily due to the porous carbon as described above. 2 The concentration can be adjusted to 10 m² or higher. In addition, the pore specific surface area of ​​the positive electrode active material mixture can be adjusted primarily by the first compound, resulting in a relatively small pore diameter of 30 nm to less than 100 nm. Through these adjustments, the overall pore specific surface area in the pore diameter range of 30 nm to 200 nm can be increased to 10 m². 2 It can be adjusted to a value of / g or higher. In this way, by sharing the contribution of porous carbon and the first compound to adjusting the pore specific surface area at the above pore diameters, the pore specific surface area at each of the above pore diameters of the positive electrode active material mixture can be adjusted to the above ranges more reliably and precisely.

[0038] The average particle size of the porous carbon is preferably 0.1 μm to 10 μm, and more preferably 0.5 μm to 5 μm. If the average particle size of the porous carbon is within the above range, the specific surface area of ​​the pores in the relatively large pore diameter range of 100 nm to 200 nm of the positive electrode active material mixture is set to 1 m². 2 It can be easily adjusted to a value of 1 / g or higher. The pore size of porous carbon is obtained by removing a binder such as PVDF from the positive electrode active material mixture, drying it to obtain a powder, extracting porous carbon from the obtained powder using wind classification or the like, and then performing pore distribution measurement on the extracted porous carbon.

[0039] The specific surface area of ​​porous carbon is 10 m². 2 / g or more 4000m 2 Preferably less than / g, 100m 2 / g or more 3000m 2It is more preferable that the amount is less than / g. If the specific surface area of ​​the porous carbon is within the above range, the specific surface area of ​​the pores in the range of relatively large pore diameters of 100 nm to 200 nm of the positive electrode active material mixture is 1 m 2 It can be easily adjusted to a value of / g or higher. The specific surface area of ​​porous carbon is obtained by extracting the powder in the same manner as the measurement of the pore diameter of porous carbon described above, and then measuring the specific surface area of ​​the extracted powder by gas adsorption.

[0040] The lower limit of the porous carbon content in the positive electrode active material mixture is preferably 0.1% by mass, and more preferably 0.3% by mass. If the porous carbon content is above the lower limit, the pore specific surface area of ​​the positive electrode active material mixture in the range of relatively large pore diameters of 100 nm to 200 nm is set to 1 m 2 It can be easily adjusted to a value of 1g or more. The upper limit for the porous carbon content is preferably 2% by mass, and more preferably 1% by mass. If the porous carbon content is below the above upper limit, it is possible to reduce the decrease in the charge / discharge capacity of the energy storage element due to the relatively low content of the first compound.

[0041] (Conductive agent) The conductive agent is not particularly limited as long as it is a conductive material. Examples of such conductive agents include carbonaceous materials other than the porous carbon mentioned above, metals, conductive ceramics, etc. Examples of carbonaceous materials other than the porous carbon mentioned above include graphitized carbon, non-graphitized carbon, graphene-based carbon, etc. Examples of non-graphitized carbon include carbon nanofibers, pitch-based carbon fibers, and carbon black. Examples of carbon black include furnace black, acetylene black, and Ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNTs), and fullerenes. The conductive agent can take the form of powder, fibers, etc. One of these materials may be used alone as the conductive agent, or two or more may be used in mixture form. Alternatively, these materials may be used in composite form. For example, a material composite 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.

[0042] The content of the conductive agent in the positive electrode active material mixture is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. By setting the content of the conductive agent within the above range, the energy density of the energy storage element can be increased.

[0043] (Binder) 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.

[0044] The binder content in the positive electrode active material mixture is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. By keeping the binder content within the above range, the active material can be stably maintained.

[0045] (Thickening agent) 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.

[0046] (Filler) 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.

[0047] The positive electrode active material mixture 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, Nb, and W as components other than the positive electrode active material, conductive agent, binder, thickener, and filler.

[0048] The specific surface area of ​​the pores in the range of 30 nm to 200 nm and the pores in the range of 100 nm to 200 nm of the positive electrode active material mixture are determined by the BJH method from desorption isotherms obtained using the nitrogen gas adsorption method. Specifically, the specific surface area of ​​the pores in the range of 30 nm to 200 nm and the pores in the range of 100 nm to 200 nm of the positive electrode active material mixture are obtained by the BJH method from the above desorption isotherms. These specific surface areas of the pores are measured for the components remaining after excluding the binder of the positive electrode active material mixture.

[0049] The lower limit of the pore specific surface area in the pore diameter range of 30 nm to 200 nm for the positive electrode active material mixture is 10 m 2 / g is 12m 2 / g is preferred. The lower limit of the pore specific surface area in the pore diameter range of 100 nm to 200 nm of the positive electrode active material mixture is 1 m 2 / g is 2m 2 / g is preferred. By satisfying the above lower limits for each pore specific surface area, the energy storage element equipped with a positive electrode containing the positive electrode active material mixture has excellent discharge capacity in low-temperature environments. On the other hand, the upper limit for the pore specific surface area of ​​the positive electrode active material mixture in the range of pore diameter 30 nm to 200 nm is 40 m 2 / g is preferred, 30m 2 / g is more preferable. The upper limit of the pore specific surface area of ​​the positive electrode active material mixture in the range of pore diameter 100 nm to 200 nm is 7 m 2 / g is preferred, 5m 2 / g is more preferable. When the upper limit of each of the above pore specific surface areas satisfies the above, the energy storage element equipped with a positive electrode containing the positive electrode active material mixture will more reliably have superior discharge capacity in low-temperature environments. Note that when the pore specific surface area of ​​the positive electrode active material mixture in the range of pore diameters from 30 nm to 200 nm satisfies the above specific range, it means that all of the pore specific surface areas measured in the range of 30 nm to 200 nm for each pore diameter satisfy the above specific range. Similarly, when the pore specific surface area of ​​the positive electrode active material mixture in the range of pore diameters from 100 nm to 200 nm satisfies the above specific range, it means that all of the pore specific surface areas measured in the range of 100 nm to 200 nm for each pore diameter satisfy the above specific range.

[0050] The specific surface area of ​​the pores in the range of 30 nm to 200 nm in pore diameter of the positive electrode active material mixture, and the specific surface area of ​​the pores in the range of 100 nm to 200 nm in pore diameter, are calculated based on the following procedure. For the measurement of the pore specific surface area described above, Quantachrome's "autosorb iQ" and control and analysis software "ASiQwin" are used. 1.00 g of the cathode active material mixture (excluding the binder), which is the sample to be measured, is placed in a sample tube for measurement, and moisture is thoroughly removed from the sample by drying under reduced pressure at 120°C for 12 hours. Next, isotherms on the adsorption and desorption sides are measured using the nitrogen gas adsorption method with liquid nitrogen, within the range of relative pressure P / P0 (P0 = approximately 770 mmHg) from 0 to 1. Then, the pore specific surface area for each pore diameter range is calculated by using the BJH method with the isotherm on the desorption side.

[0051] For measuring the pore specific surface area as described above, the pre-charge / pre-discharge powder of the positive electrode active material mixture (excluding the binder) before positive electrode fabrication can be used directly for measurement. When taking a sample from the positive electrode extracted after disassembling an energy storage element, before disassembling the element, discharge it at a constant current value (0.1C) that is one-tenth of the current value that would produce the same amount of electricity as the nominal capacity of the energy storage element when a constant current is applied to the element for one hour, at a 25°C environment until the voltage reaches the lower limit of the specified voltage. Disassemble the energy storage element, extract the positive electrode, assemble a battery with a metallic lithium electrode as the counter electrode, and at a current value of 10mA per gram of positive electrode active material mixture, the terminal voltage of the positive electrode is measured at a 25°C environment until it reaches 2.0V (vs.Li / Li + Constant current discharge is performed until the battery reaches a fully discharged state. After that, the battery is disassembled again and the positive electrode is removed. The removed positive electrode is thoroughly washed with dimethyl carbonate to remove any non-aqueous electrolyte adhering to it, and after drying at room temperature for 24 hours, the positive electrode active material mixture is collected from the positive electrode substrate. The above battery disassembly work, as well as the positive electrode washing and drying work, is performed in an argon atmosphere with a dew point of -60°C or lower. The obtained positive electrode active material mixture powder is dispersed in N-methylpyrrolidone (NMP) to remove the binder (e.g., PVDF) from the positive electrode active material mixture. After further washing with dimethyl carbonate and drying, a powder is obtained. In the measurement of the pore specific surface area described above, the powder collected in this manner is used for measurement.

[0052] <Method for manufacturing a positive electrode active material mixture for energy storage elements> The positive electrode active material mixture can be manufactured by mixing a positive electrode active material containing the first compound, porous carbon, and other components as described above, if necessary. The positive electrode active material mixture is made into a paste with a solvent acting as a dispersion medium, applied to a positive electrode substrate, and dried to form a positive electrode active material mixture layer. The first compound can be manufactured, for example, according to the following procedure.

[0053] (Method for producing the first compound) First, a mixed solution of FeSO4 and MnSO4 in any ratio is added dropwise to the reaction vessel at a constant rate, while simultaneously adding NaOH aqueous solution, NH3 aqueous solution, and NH2NH2 aqueous solution to maintain a constant pH. x Mn 1-x (OH)2 precursor is prepared. Next, the prepared Fe xMn (1-x) The (OH)2 precursor is removed from the reaction vessel and solid-phase mixed with LiH2PO4 and sucrose powder. The resulting mixture is then calcined under a nitrogen atmosphere at a calcination temperature of 550°C to 750°C to produce a first compound having an olivine-type crystalline structure and represented by formula 1 below. This first compound is coated with carbon. Note that a first compound without carbon coating can be produced by performing solid-phase mixing and calcination in the same manner as above, except that sucrose powder is not added. LiFe x Mn (1-x) PO4(0≦x≦1) ···1

[0054] (Method for adjusting the pore specific surface area) As described above, the pore diameter range of the positive electrode active material mixture from 30 nm to 200 nm is a region where non-aqueous electrolytes can easily penetrate, and the specific surface area of ​​the pores in this pore diameter range of the positive electrode active material mixture is 10 m². 2 The amount shall be 1 / g or more, and the pore specific surface area in the range of pore diameter 100 nm to 200 nm shall be 1 m². 2 By setting the value to 1 / g or higher, a pore structure that promotes the penetration of non-aqueous electrolytes can be obtained. The specific surface area of ​​the pores in each of the above ranges can be adjusted, for example, by controlling the method of producing the first compound as described above.

[0055] Controls for the manufacturing method of such a first compound include adjusting the pH when preparing the precursor of the first compound, and adjusting the temperature when calcining the precursor.

[0056] If the positive electrode active material mixture contains porous carbon, the specific surface area of ​​the pores within each of the above-mentioned pore diameter ranges of the positive electrode active material mixture can be obtained by adjusting the average particle size and specific surface area of ​​the porous carbon, in addition to controlling the manufacturing method of the first compound. In this case, for example, one could select porous carbon having various average particle sizes and specific surface areas such as the porous carbon that yields the specific surface area within each of the above-mentioned pore diameter ranges. Alternatively, the specific surface area of ​​the pores within each of the above-mentioned pore diameter ranges can also be obtained by adjusting the mixing ratio of the porous carbon and the first compound.

[0057] This positive electrode active material mixture for energy storage elements can increase the discharge capacity of the energy storage element in low-temperature environments.

[0058] <Positive electrode for energy storage element> The positive electrode for the energy storage element (hereinafter also simply referred to as the positive electrode) contains the positive electrode active material mixture. The positive electrode has a positive electrode substrate and a positive electrode active material mixture layer disposed directly on the positive electrode substrate or via an intermediate layer.

[0059] (Positive electrode substrate) 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 7 The 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).

[0060] The average thickness of the positive electrode substrate is preferably 3 μm to 50 μm, more preferably 5 μm to 40 μm, even more preferably 8 μm to 30 μm, and particularly preferably 10 μm to 25 μm. By setting the average thickness of the positive electrode substrate within the above range, the strength of the positive electrode substrate can be increased while increasing the energy density per unit volume of the secondary battery. "Average thickness of the substrate" refers to the value obtained by dividing the punched mass when punching out a predetermined area of ​​the substrate by the true density of the substrate and the punched area, and the same applies to the negative electrode substrate.

[0061] (Middle class) The intermediate layer is a layer placed between the positive electrode substrate and the positive electrode active material 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 active material mixture layer. The composition of the intermediate layer is not particularly limited and may include, for example, a binder and a conductive agent.

[0062] (Positive electrode active material mixture layer) The positive electrode active material mixture layer is a layer formed by the positive electrode active material mixture described above.

[0063] <Configuration of energy storage element> An energy storage element according to one embodiment of the present invention comprises an electrode body having a positive electrode, a negative electrode, and a separator; a non-aqueous electrolyte; and a container for housing the electrode body and the non-aqueous electrolyte. The electrode body is usually a stacked type in which a plurality of positive electrodes and a plurality of negative electrodes are stacked with a separator in between, or a wound type in which the positive electrode and negative electrode are wound in a stacked state with a separator in between. The non-aqueous electrolyte exists contained within the positive electrode, negative electrode, and separator. As an example of an energy storage element, a non-aqueous electrolyte secondary battery (hereinafter also simply referred to as a "secondary battery") will be described.

[0064] [Positive electrode] The positive electrode of the energy storage element is the positive electrode for the energy storage element described above.

[0065] [Negative electrode] The negative electrode comprises a negative electrode substrate and a negative electrode active material mixture 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 for the energy storage element described above.

[0066] (Negative electrode substrate) The negative electrode substrate is electrically conductive. Suitable materials for the negative electrode substrate include metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, or alloys thereof, as well as carbonaceous materials. Among these, copper or copper alloys are preferred. Examples of negative electrode substrates include foil, vapor-deposited film, mesh, and porous materials, with foil being preferred from a cost perspective. Therefore, copper foil or copper alloy foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0067] The average thickness of the negative electrode substrate is preferably 2 μm to 35 μm, more preferably 3 μm to 30 μm, even more preferably 4 μm to 25 μm, and particularly preferably 5 μm to 20 μm. By setting the average thickness of the negative electrode substrate within the above range, it is possible to increase the strength of the negative electrode substrate while increasing the energy density per unit volume of the secondary battery.

[0068] (Negative electrode active material mixture layer) The negative electrode active material mixture layer contains a negative electrode active material. The negative electrode active material mixture layer optionally contains conductive agents, binders, thickeners, fillers, and other optional components. These optional components can be selected from the materials exemplified above for the positive electrode.

[0069] The negative electrode active material mixture layer may contain typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba, and transition metallic elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W as components other than the negative electrode active material, conductive agent, binder, thickener, and filler.

[0070] The negative electrode active material can be appropriately selected from known negative electrode active materials. For lithium-ion secondary batteries, materials capable of intercalating and releasing lithium ions are typically used as negative electrode active materials. Examples of negative electrode active materials include: metallic Li; metals or metalloids such as Si and Sn; metal oxides or metalloid oxides such as Si oxide, Ti oxide, and Sn oxide; and Li4Ti5O 12 LiTiO 2、 Examples of materials include titanium-containing oxides such as TiNb2O7; polyphosphate compounds; silicon carbide; and carbon materials such as graphite and non-graphitizable carbon (easily graphitizable carbon or poorly graphitizable carbon). Among these materials, graphite and non-graphitizable carbon are preferred. 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.

[0071] "Graphite" refers to the average lattice plane spacing (d) of the (002) plane, determined by X-ray diffraction before charging or discharging, or during the discharge state. 002 ) refers to carbon materials with a n-scale between 0.33 nm and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite. Artificial graphite is preferred from the standpoint of obtaining materials with stable physical properties.

[0072] "Non-graphite carbon" refers to the average lattice plane spacing (d) of the (002) plane, which is determined by X-ray diffraction before charging / discharging or during the discharge state. 002 This refers to carbon materials with a nautical radius of 0.34 nm or more and 0.42 nm or less. Non-graphitized carbons include poorly graphitizable carbons and easily graphitizable carbons. Examples of non-graphitized carbons include resin-derived materials, petroleum pitch or materials derived from petroleum pitch, petroleum coke or materials derived from petroleum coke, plant-derived materials, and alcohol-derived materials.

[0073] Here, "discharge state" refers to a state in which sufficient lithium ions capable of being absorbed and released during charging and discharging are released from the carbon material, which is the negative electrode active material. For example, in a monoelectrode battery using a negative electrode containing a carbon material as the negative electrode active material as the working electrode and metallic Li as the counter electrode, this is the state in which the open-circuit voltage is 0.7V or higher.

[0074] "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.

[0075] "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.

[0076] The negative electrode active material is usually in the form of particles (powder). The average particle size of the negative electrode active material can be, for example, between 1 nm and 100 μm. If the negative electrode active material is a carbon material, titanium-containing oxide, or polyphosphate compound, its average particle size 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 1 μm. Setting the average particle size of the negative electrode active material above the lower limit makes it easier to manufacture or handle. Setting the average particle size of the negative electrode active material below the upper limit improves the electronic conductivity of the active material layer. To obtain powder with a predetermined particle size, a pulverizer or classifier is used. The pulverization method and powder grading method can be selected from, for example, the methods exemplified above for the positive electrode. If the negative electrode active material is a metal such as metallic Li, the negative electrode active material may be in the form of foil.

[0077] The content of the negative electrode active material in the negative electrode active material 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 the above range, it is possible to achieve both high energy density and manufacturability in the negative electrode active material layer.

[0078] [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.

[0079] The heat-resistant particles contained in the heat-resistant layer preferably have a mass reduction of 5% or less when heated from room temperature to 500°C in an air atmosphere of 1 atmosphere, and more preferably have a mass reduction of 5% or less when heated from room temperature to 800°C. Inorganic compounds are examples of materials with a mass reduction of less than or equal to the specified amount. Examples of inorganic compounds include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, barium titanate, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ionic crystals such as calcium fluoride and barium fluoride; covalent crystals such as silicon and diamond; mineral resource-derived materials such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof. These inorganic compounds may be used individually or in combination, or two or more may be used as a mixture. Among these inorganic compounds, silicon dioxide, aluminum oxide, or aluminosilicates are preferred from the viewpoint of safety for energy storage elements.

[0080] 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.

[0081] 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.

[0082] [Non-aqueous electrolytes] As the non-aqueous electrolyte, it can be appropriately selected from known non-aqueous electrolytes. A non-aqueous electrolyte solution may be used as the non-aqueous electrolyte. The non-aqueous electrolyte solution contains a non-aqueous solvent and an electrolyte salt dissolved in this non-aqueous solvent.

[0083] As the non-aqueous solvent, it can be appropriately selected from known non-aqueous solvents. Examples of non-aqueous solvents include cyclic carbonates, linear carbonates, carboxylic acid esters, phosphate esters, sulfonic acid esters, ethers, amides, and nitriles. As the non-aqueous solvent, compounds in which some of the hydrogen atoms contained in these compounds are substituted with halogens may also be used.

[0084] Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinylethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), styrene carbonate, 1-phenylvinylene carbonate, and 1,2-diphenylvinylene carbonate. Among these, EC is preferred.

[0085] Examples of linear carbonates include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, trifluoroethyl methyl carbonate, and bis(trifluoroethyl) carbonate. Among these, EMC is preferred.

[0086] It is preferable to use a cyclic carbonate or a linear carbonate as the non-aqueous solvent, and it is more preferable to use a cyclic carbonate and a linear carbonate in combination. Using a cyclic carbonate can promote the dissociation of the electrolyte salt and improve the ionic conductivity of the non-aqueous electrolyte. Using a linear carbonate can keep the viscosity of the non-aqueous electrolyte low. When using a cyclic carbonate and a linear carbonate in combination, the volume ratio of the cyclic carbonate to the linear carbonate (cyclic carbonate:linear carbonate) is preferably in the range of 5:95 to 50:50.

[0087] 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.

[0088] 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.

[0089] The electrolyte salt content in the non-aqueous electrolyte is 0.1 mol / dm³ at 20°C and 1 atm. 3More 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.

[0090] Non-aqueous electrolytes may contain additives in addition to the non-aqueous solvent and 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 difluorooxalate borate (LiFOB), and lithium bis(oxalate) difluorophosphate (LiFOP); imide salts such as lithium bis(fluorosulfonyl)imide (LiFSI); biphenyls, alkylbiphenyls, terphenyls, partially hydrogenated terphenyls, and cyclohexyls. Aromatic compounds such as benzene, 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, succinic anhydride, Glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic acid anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, propanesultone, propensultone, butanesultone, 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- Examples include 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.

[0091] The additive content in the non-aqueous electrolyte is preferably 0.01% to 10% by mass relative to the total mass of the non-aqueous electrolyte, more preferably 0.1% to 7% by mass, even more preferably 0.2% to 5% by mass, and particularly preferably 0.3% to 3% by mass. By setting the additive content within the above range, it is possible to improve the capacity retention performance or cycle performance after high-temperature storage, and to further improve safety.

[0092] For the non-aqueous electrolyte, a solid electrolyte may be used, or a non-aqueous electrolyte and a solid electrolyte may be used in combination.

[0093] 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.

[0094] Examples of sulfide solid electrolytes in lithium-ion secondary batteries include Li2S-P2S5, LiI-Li2S-P2S5, and Li 10 Ge-P2S 12 Examples include, etc.

[0095] <Specific configuration of the energy storage element> The shape of the energy storage element in this embodiment is not particularly limited, and examples include cylindrical batteries, prismatic batteries, flat batteries, coin-type batteries, button-type batteries, and the like. Figure 1 shows an example of a rectangular battery, specifically an energy storage element 1. 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. A non-aqueous electrolyte is injected into the container 3.

[0096] <Configuration of the energy storage device> The energy storage element of this embodiment can be mounted as an energy storage unit (battery module) composed of multiple energy storage elements 1 in power supplies for vehicles such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), power supplies for electronic devices such as personal computers and communication terminals, or power storage devices. In this case, it is sufficient that the technology of the present invention is applied to at least one of the energy storage elements included in the energy storage device. 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 power storage elements 1. The power storage device 30 may include busbars (not shown) that electrically connect two or more power 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 power storage elements.

[0097] <Manufacturing method for energy storage elements> The method for manufacturing the energy storage element of this embodiment can be appropriately selected from known methods, except that a positive electrode for the energy storage element is used as the positive electrode. The manufacturing method comprises, 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 comprises 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.

[0098] 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.

[0099] <Other Embodiments> Furthermore, the energy storage element of the present invention is not limited to the embodiments described above, and various modifications may be made without departing from the spirit of the 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 with well-known technology. In addition, a part of the configuration of one embodiment may be deleted. Also, well-known technology may be added to the configuration of one embodiment.

[0100] In the above embodiment, the case in which the energy storage element is used as a rechargeable non-aqueous electrolyte secondary battery (e.g., a lithium-ion secondary battery) has been described, but the type, shape, dimensions, capacity, etc. of the energy storage element are arbitrary. The present invention can also be applied to various secondary batteries, electric double-layer capacitors, or capacitors such as lithium-ion capacitors.

[0101] 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]

[0102] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples.

[0103] [Fabrication of positive electrode active material] (1) Preparation of LiFePO4 First, 750cm 3 2dm 3 Add 1 mol / dm³ to the reaction vessel. 3 While adding an aqueous FeSO4 solution dropwise at a constant rate, maintain a pH of 10.0 ± 0.1 during the process at a rate of 4 mol / dm³ 3 NaOH aqueous solution and 0.5 mol / dm 3 NH3 aqueous solution and 0.5 mol / dm 3An aqueous solution of NH2NH2 was added dropwise to prepare a Fe(OH)2 precursor. The temperature of the reaction vessel was set at 50 °C (±2 °C). Next, the prepared Fe(OH)2 precursor was taken out of the reaction vessel and mixed solid-phase with LiH2PO4 and sucrose powder. Then, the obtained mixture was calcined at a firing temperature of 650 °C in a nitrogen atmosphere to prepare a cathode active material LiFePO4 having an olivine-type crystal structure. (2)LiFe 0.25 Mn 0.75 Preparation of PO4 First, 750 cm 3 of deionized water was placed in a 2 dm 3 reaction vessel, and an aqueous solution of 1 mol / dm 3 prepared by adjusting FeSO4 and MnSO4 to a molar ratio of 1:3 was added dropwise at a constant rate while maintaining the pH during that time at a constant value of 10.0 ± 0.1 with a 4 mol / dm 3 aqueous NaOH solution, a 0.5 mol / dm 3 aqueous NH3 solution, and a 0.5 mol / dm 3 aqueous NH2NH2 solution were added dropwise to prepare a Fe 0.25 Mn 0.75 (OH)2 precursor. The temperature of the reaction vessel was set at 50 °C (±2 °C). Next, the prepared Fe 0.25 Mn 0.75 (OH)2 precursor was taken out of the reaction vessel and mixed solid-phase with LiH2PO4 and sucrose powder. Then, the obtained mixture was calcined at a firing temperature of 650 °C in a nitrogen atmosphere to prepare a cathode active material LiFe 0.25 Mn 0.75 PO4.

[0104] Table 1 shows the values of x in the following formula 1 of the cathode active materials of Examples 1 to 15 and Comparative Examples 1 to 3. LiFe x Mn (1-x) PO4(0 ≦ x ≦ 1) ···1

[0105] [Preparation of Cathode] (Examples 1 to 12, and Comparative Example 3) LiFePO4 was used as the positive electrode active material. Porous carbon having the average particle size and specific surface area shown in Table 1 was used. N-methylpyrrolidone (NMP) was used as the dispersion medium, acetylene black as the conductive agent, and PVDF as the binder. The above positive electrode active material, porous carbon, conductive agent, binder, and dispersion medium were mixed. At that time, the solid content mass ratio of positive electrode active material:conductive agent:binder was set to 90:5:5, and porous carbon was further added to this total solid content mass of 100 so that the content (mass%) shown in Table 1 was obtained. An appropriate amount of dispersion medium was added to the obtained mixture to adjust the viscosity and prepare a positive electrode active material mixture paste. Next, the above positive electrode active material mixture paste was applied to both sides of the aluminum foil, which was the positive electrode substrate, leaving uncoated areas (areas where the positive electrode active material mixture layer was not formed), dried at 120°C, and roll-pressed to form a positive electrode active material mixture layer on the positive electrode substrate. The application amount of the positive electrode active material mixture paste is 10 mg / cm³ in terms of solid content. 2 This was done. In this way, the positive electrodes of Examples 1 to 12 and Comparative Example 3 were obtained. The specific surface area of ​​the pores in the positive electrode active material mixture in the range of pore diameters from 30 nm to 100 nm, the specific surface area of ​​the pores in the range of pore diameters from 100 nm to 200 nm, and the specific surface area of ​​the pores in the range of pore diameters from 30 nm to 200 nm were measured in the positive electrodes based on the method described above. The results are shown in Table 1.

[0106] (Examples 13 to 15) LiFe 0.25 Mn 0.75 The cathodes of Examples 13 to 15 were obtained in the same manner as in Examples 7 to 9, except that PO4 was used and porous carbon having the average particle size and specific surface area shown in Table 1 was added in the amount shown in Table 1. The specific surface area of ​​the pores in the cathode active material mixture in the range of pore diameters from 30 nm to 100 nm, the pores in the range of pore diameters from 100 nm to 200 nm, and the pores in the range of pore diameters from 30 nm to 200 nm in the obtained cathodes were measured based on the method described above. The results are shown in Table 1.

[0107] (Comparative Example 1) A positive electrode for Comparative Example 1 was obtained in the same manner as in Example 1, except that porous carbon was not added. The specific surface area of ​​the pores in the positive electrode active material mixture in the range of pore diameters from 30 nm to 100 nm, the specific surface area of ​​the pores in the range of pore diameters from 100 nm to 200 nm, and the specific surface area of ​​the pores in the range of pore diameters from 30 nm to 200 nm were measured in the positive electrode active material mixture in the obtained positive electrode based on the method described above. The results are shown in Table 1.

[0108] (Comparative Example 2) A positive electrode for Comparative Example 2 was obtained in the same manner as in Example 1, except that porous carbon was not added and the firing temperature during the production of the positive electrode active material was set to 550°C. The specific surface area of ​​the pores in the positive electrode active material mixture in the range of pore diameters from 30 nm to 100 nm, the specific surface area of ​​the pores in the range of pore diameters from 100 nm to 200 nm, and the specific surface area of ​​the pores in the range of pore diameters from 30 nm to 200 nm were measured in the obtained positive electrode based on the method described above. The results are shown in Table 1.

[0109] [Fabrication of the 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 a dispersant were mixed. The solid content mass ratio of negative electrode active material:binder:thickener was set to 97:2:1. An appropriate amount of water was added to the resulting mixture to adjust the viscosity and prepare a negative electrode mixture paste. This negative electrode mixture paste was applied to both sides of a copper foil, leaving uncoated areas (areas where the negative electrode active material layer was not formed), and dried to prepare the negative electrode active material layer. Subsequently, a roll press was performed to produce the negative electrode.

[0110] [Preparation of non-aqueous electrolytes] A mixed solvent of EC and EMC in a volume ratio of 3:7 is mixed with 1 mol / dm³ of LiPF6. 3 A non-aqueous electrolyte was prepared by dissolving it at the specified concentration.

[0111] [Fabrication of energy storage elements] Next, the positive electrode and the negative electrode were laminated together via a separator consisting of a polyethylene microporous membrane substrate and a heat-resistant layer formed on the polyethylene microporous membrane substrate to create an electrode body. The heat-resistant layer was positioned on the surface facing the positive electrode. This electrode body was placed in a rectangular aluminum container, and the positive electrode terminals and negative electrode terminals were attached. After injecting the non-aqueous electrolyte into the rectangular container, it was sealed to obtain the energy storage elements of the example and comparative example.

[0112] [Capacity verification test] Each of the above energy storage elements was charged with a constant current of 0.1C at a charging current of 0.1C to 3.6V in a 25°C environment, and then charged with a constant voltage at 3.6V. The charging termination condition was when the charging current became 0.02C. After a 10-minute rest period following charging, the elements were discharged with a constant current of 0.1C at a discharge current of 0.1C to 2.0V in a 25°C environment. A 10-minute rest period was followed after discharge. The above cycle was repeated twice, and the discharge capacity of the second discharge was set to a capacity of 0.1C.

[0113] [Discharge capacity ratio under low-temperature conditions] Each of the above energy storage elements was charged with a constant current of 0.1C to 3.6V in a 25°C environment, and then charged with a constant voltage at 3.6V. The charging termination condition was when the charging current became 0.02C. After a 10-minute rest period following charging, a constant current discharge was performed with a discharge current of 2C to 2.0V in a 25°C environment, and the "2C discharge capacity at 25°C" was measured. Next, a constant current charge was performed with a charging current of 0.1C to 3.6V in a 25°C environment, and then charged with a constant voltage at 3.6V. The charging termination condition was when the charging current became 0.02C. After that, a 10-minute rest period was observed. After that, the elements were stored in a -30°C environment for 3 hours, and then a constant current discharge was performed with a discharge current of 2C to 2.0V, and the "2C discharge capacity at -30°C" was measured. From the 2C discharge capacity at 25°C and the 2C discharge capacity at -30°C, the "capacity ratio," i.e., the percentage of the 2C discharge capacity at -30°C to the 2C discharge capacity at 25°C, was calculated as an indicator of low-temperature high-rate discharge performance. The results are shown in Table 1.

[0114] [Table 1]

[0115] As shown in Table 1 above, the positive electrode active material contains a first compound having an olivine-type crystal structure as represented by Formula 1, and the pore specific surface area of ​​the positive electrode active material mixture in the range of pore diameter 30 nm to 200 nm is 10 m². 2 The concentration is 1 / g or more, and the specific surface area of ​​the pores in the range of pore diameter 100 nm to 200 nm is 1 m². 2 Examples 1 to 15, which have a discharge capacity of 1 / g or more, show that they have a larger discharge capacity in low-temperature environments compared to Comparative Examples 1 to 3.

[0116] The results above demonstrate that the positive electrode active material mixture can increase the discharge capacity of the energy storage element under low-temperature conditions. [Industrial applicability]

[0117] This invention can be applied to energy storage elements used as power sources for electronic devices such as personal computers and communication terminals, as well as automobiles. [Explanation of symbols]

[0118] 1. 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. It contains a compound represented by the following formula 1, The pore specific surface area in the range of pore diameter 30 nm to 200 nm is 10 m². ２ The amount is 1 / g or more, and the pore specific surface area in the range of pore diameter 100 nm to 200 nm is 1 m². ２ / g or more, A positive electrode active material mixture for a non-aqueous electrolyte energy storage element, wherein at least a portion of the surface of the above compound is coated with carbon. LiFe ｘ Mn （１－ｘ） PO ４ (0≦x≦1) ・・・1

2. The positive electrode active material mixture for a non-aqueous electrolyte energy storage element according to claim 1, further containing porous carbon.

3. A positive electrode for a non-aqueous electrolyte energy storage element, comprising the positive electrode active material mixture for energy storage elements described in claim 1 or claim 2.

4. A non-aqueous electrolyte energy storage element comprising a positive electrode for a non-aqueous electrolyte energy storage element according to claim 3.

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