JP2022073197A - Positive electrode active material mixture for power storage element, positive electrode for power storage element, and power storage element - Google Patents

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

The present invention relates to a positive electrode active material mixture for a power storage element, a positive electrode for a power storage element, and a power storage element.

Non-aqueous electrolyte secondary batteries typified by lithium ion secondary batteries are widely used in personal computers, electronic devices such as communication terminals, automobiles, etc. due to their high energy density. The non-aqueous electrolyte secondary battery generally has a pair of electrodes electrically separated by a separator and a non-aqueous electrolyte interposed between the electrodes, and transfers ions between the two electrodes. It is configured to charge and discharge. In addition, capacitors such as lithium ion capacitors and electric double layer capacitors are also widely used as power storage elements other than non-aqueous electrolyte secondary batteries.

In recent years, inexpensive and highly safe olivine-type lithium iron phosphate has been attracting attention as a positive electrode active material used in the power storage element. For example, a lithium secondary battery in which the active material in the active material layer in the positive electrode plate is lithium iron phosphate and the thickness of the active material layer is 40 μm or more and 200 μm or less has been proposed. (See Patent Document 1).

JP-A-2015-56318

However, the power storage element provided with the positive electrode active material layer as in Patent Document 1 may have a small discharge capacity in a low temperature environment such as 0 ° C. or lower.

An object of the present invention is to provide a positive electrode active material for a power storage element and a positive electrode for a power storage element capable of increasing the discharge capacity of the power storage element in a low temperature environment, and a power storage element having a large discharge capacity in a low temperature environment. Is.

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 of 10 m ² / g or more in a pore diameter range of 30 nm or more and 200 nm or less. Moreover, the pore specific surface area in the range of the pore diameter of 100 nm or more and 200 nm or less is 1 m ² / g or more.
LiFe _x Mn _(1-x) PO ₄ (0 ≦ x ≦ 1) ・ ・ ・ 1

The positive electrode for a power storage element according to another aspect of the present invention contains the positive electrode active material mixture for the power storage element.

The power storage element according to another aspect of the present invention includes a positive electrode for the power storage element.

The positive electrode active material mixture for a power storage element according to one aspect of the present invention can increase the discharge capacity of the power storage element in a low temperature environment.

The positive electrode for a power storage element according to another aspect of the present invention can increase the discharge capacity of the power storage element in a low temperature environment.

The power storage element according to another aspect of the present invention has a large discharge capacity in a low temperature environment.

FIG. 1 is a perspective perspective view showing an embodiment of a non-aqueous electrolyte power storage device. FIG. 2 is a schematic view showing an embodiment of a power storage device in which a plurality of non-aqueous electrolyte power storage elements are assembled.

First, the 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 in the present specification will be described.

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 of 10 m ² / g or more in a pore diameter range of 30 nm or more and 200 nm or less. Moreover, the pore specific surface area in the range of the pore diameter of 100 nm or more and 200 nm or less is 1 m ² / g or more.
LiFe _x Mn _(1-x) PO ₄ (0 ≦ x ≦ 1) ・ ・ ・ 1

According to this positive electrode active material mixture for a power storage element, the discharge capacity of the power storage element in a low temperature environment can be increased. The reason for this is not always clear, but it can be inferred as follows, for example. That is, the charge / discharge capacity can be increased by containing the compound of the above formula 1 containing iron, manganese, or a combination thereof as the transition metal in the positive electrode active material mixture for the power storage element. In addition, the pores having a pore diameter of 30 nm or more and 200 nm or less in the positive electrode active material mixture for a power storage element are in a range in which a non-aqueous electrolyte easily permeates, and the specific surface area of the pores in this pore diameter range is 10 m ³ . Pore structure that promotes permeation of non-aqueous electrolyte by setting / g or more and further setting the pore specific surface area in the relatively large pore diameter range of 100 nm or more and 200 nm or less to 1 m ² / g or more. Is obtained. As a result, the lithium ion diffusivity in the pores of the positive electrode active material mixture for the power storage element is improved. It is presumed that due to this improvement in lithium ion diffusivity, the positive electrode active material mixture for the power storage element can increase the discharge capacity of the power storage element in a low temperature environment.

Here, the positive electrode active material mixture for the power storage element may further contain porous carbon.

As described above, when the positive electrode active material mixture for a power storage element contains porous carbon, the pore ratio in the relatively large pore diameter of 100 nm or more and 200 nm or less of the positive electrode active material mixture for a power storage element is particularly high. The surface area can be easily adjusted to 1 m ² / g or more, that is, can be adjusted more reliably. Therefore, the positive electrode active material mixture for the power storage element can more reliably increase the discharge capacity of the power storage element in a low temperature environment.

The positive electrode for a power storage element according to another aspect of the present invention contains the positive electrode active material mixture for the power storage element.

As described above, since the positive electrode for the power storage element contains the above-mentioned positive electrode active material mixture for the power storage element, the discharge capacity of the power storage element in a low temperature environment can be increased.

The power storage element according to another aspect of the present invention includes a positive electrode for the power storage element.

As described above, since the power storage element includes the positive electrode for the power storage element described above, the discharge capacity in a low temperature environment is large.

A positive electrode active material mixture for a power storage element, a positive electrode for a power storage element, a configuration of a power storage element, a configuration of a power storage device, a method for manufacturing the power storage element, and other embodiments according to an embodiment of the present invention will be described in detail. The name of each component (each component) used in each embodiment may be different from the name of each component (each component) used in the background technique.

<Positive electrode active material mixture for power storage elements>
The positive electrode active material mixture for the power storage element (hereinafter, also simply referred to as a positive electrode active material mixture) contains a compound represented by the following formula 1 (hereinafter, also referred to as a first compound). Specifically, the positive electrode active material mixture contains a positive electrode active material, and the 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 contains optional components such as a conductive agent other than porous carbon, a binder (binder), a thickener, and a filler, if necessary.
LiFe _x Mn _(1-x) PO ₄ (0 ≦ x ≦ 1) ・ ・ ・ 1

(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. The compound having an olivine type crystal structure has a crystal structure that can be attributed to the space group Pnma. The crystal structure that can be attributed to the space group Pnma means that it has a peak 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 is highly safe and inexpensive.

As the first compound, as represented by the above formula 1, lithium iron phosphate (LiFePO ₄ ), lithium manganese phosphate (LiMnPO ₄ ), lithium iron manganese phosphate (LiFe _x Mn _1-x PO ₄ , 0 < It is composed of x <1) or a combination thereof. When the positive electrode active material contains iron, manganese, or a combination thereof as a transition metal, the charge / discharge capacity can be further increased.

As described above, the first compound is a phosphate compound containing iron, manganese or a combination thereof and lithium. The first compound may contain a transition metal element other than iron and manganese and a typical element such as aluminum as an unavoidable impurity. However, it is preferable that the first compound is substantially composed of iron, manganese or a combination thereof, lithium, phosphorus and oxygen.

In the above formula 1, the upper limit of x is 1, preferably 0.95. The lower limit of x is 0, preferably 0.25. When the value of x is not more than the above upper limit or more than the above lower limit, the first compound has more excellent lifetime characteristics. Note that x may be substantially 1.

The average particle size of the primary particles of the first compound is, for example, 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 in the above range, the diffusivity of lithium ions in 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 with a scanning electron microscope.

The average particle size of the secondary particles of the first compound is, for example, preferably 3 μm or more and 20 μm or less, and more preferably 5 μm or more and 15 μm or less. By setting the average particle of the secondary particles of the first compound in the above range, the production and handling are facilitated, and the diffusivity of lithium ions in 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.

A crusher, a classifier, or the like is used to obtain the first compound with a predetermined particle size. Examples of the crushing method include a method using a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling airflow type jet mill, a sieve, or the like. At the time of pulverization, wet pulverization in which water or an organic solvent such as hexane coexists can also be used. As a classification method, a sieve, a wind power classifier, or the like is used as needed for both dry type and wet type.

At least a part of the surface of the first compound may be coated with carbon. As described above, the positive electrode active material may be the first compound in which at least a part of the surface thereof is coated with carbon. The electron conductivity is improved by covering at least a part 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 in the above range, the electrical conductivity can be increased, and the electrode density and the capacity of the power storage element can be increased.

The positive electrode active material mixture may further contain a positive electrode active material other than the first compound. As such another positive electrode active material, a known positive electrode active material for a lithium ion secondary battery can be appropriately selected. However, the lower limit of the total content of the first compound in the total positive electrode active material contained in the positive electrode active material mixture is preferably 90% by mass, more preferably 99% by mass. The upper limit of the total content of the first compound in the total positive electrode active material may be 100% by mass. As described above, by using only the positive electrode active material having an olivine type crystal structure as the positive electrode active material, the effect of increasing the discharge capacity of the power storage element in a low temperature environment can be further enhanced.

As the positive electrode active material for the lithium ion secondary battery, a material capable of storing and releasing lithium ions is usually used. Examples of the positive electrode active material other than the first compound include a lithium transition metal composite oxide having an α-NaFeO type ₂ crystal structure, a lithium transition metal composite oxide having a spinel type crystal structure, a polyanion compound, a chalcogen compound, and sulfur. And so on. Examples of the lithium transition metal composite oxide having an α-NaFeO type ₂ crystal structure include Li [Li _x Ni _(1-x) ] O ₂ (0 ≦ x <0.5) and Li [Li _x Ni _γ Co ₍ 0 ≦ x <0.5). _1-x-γ) ] O ₂ (0 ≦ x <0.5, 0 <γ <1), Li [Li _x Co _(1-x) ] O ₂ (0 ≦ x <0.5), Li [ Li _x Ni _γ Mn _(1-x-γ) ] O ₂ (0 ≦ x <0.5, 0 <γ <1), Li [Li _x Ni _γ Mn _β Co _(1-x-γ-β) ] O ₂ (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) ] O ₂ ( Examples thereof include 0 ≦ x <0.5, 0 <γ, 0 <β, 0.5 <γ + β <1). Examples of the lithium transition metal composite oxide having a spinel-type crystal structure include Li _x Mn ₂ O ₄ and Li _x Ni _γ Mn _(2-γ) O ₄ . Examples of the polyanionic compound include LiNiPO ₄ , LiCoPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , Li ₂ MnSiO ₄ , Li ₂ CoPO ₄ F and the like. Examples of the chalcogen compound include titanium disulfide, molybdenum disulfide, molybdenum dioxide and the like. The atoms or polyanions in these materials may be partially substituted with atoms or anion species consisting of other elements. The surface 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 of them may be mixed and used.

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 further preferably 80% by mass or more and 95% by mass or less. .. By setting the content of the total positive electrode active material in the above range, it is possible to achieve both high energy density and improved conductivity of 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, preferably 99% by mass.

(Porous carbon)
Examples of the porous carbon include CNovell manufactured by Toyo Tanso and MSC-30 manufactured by Kansai Thermochemical. Since the positive electrode active material mixture contains porous carbon, the pore specific surface area of the positive electrode active material mixture in a relatively large pore diameter range of 100 nm or more and 200 nm or less is adjusted to 1 m ² / g or more. It can be facilitated, that is, it can be adjusted more reliably. In addition, the positive electrode active material mixture for the power storage element can more reliably increase the discharge capacity in a low temperature environment as described above while avoiding a decrease in the discharge capacity of the power storage element.

When 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 the relatively large pore diameter is set to 1 m mainly by the porous carbon as described above. It can be adjusted to ² / g or more. In addition to this, the pore specific surface area of the positive electrode active material mixture having a relatively small pore diameter of 30 nm or more and less than 100 nm can be adjusted mainly by the first compound. By these adjustments, the specific surface area of pores in the range of pore diameter of 30 nm or more and 200 nm or less can be adjusted to 10 m ² / g or more as a whole. As described above, by sharing the contribution to the adjustment of the pore specific surface area in the pore diameter between the porous carbon and the first compound, the positive electrode active material mixture can be more reliably and in detail described above in each pore diameter. The specific surface area of each pore can be adjusted to each of the above ranges.

The average particle size of the porous carbon is preferably 0.1 μm or more and 10 μm or less, and more preferably 0.5 μm or more and 5 μm or less. When the average particle size of the porous carbon is in the above range, the pore specific surface area in the range of the relatively large pore diameter of 100 nm or more and 200 nm or less of the positive electrode active material mixture can be easily adjusted to 1 m ² / g or more. be able to. For the pore size of the porous carbon, the binder such as PVDF is removed from the positive electrode active material mixture, dried to obtain a powder, and the porous carbon is extracted from the obtained powder by using wind power classification or the like. It is obtained by measuring the pore distribution of the extracted porous carbon.

The specific surface area of the porous carbon is preferably 10 m ² / g or more and 4000 m ² / g or less, and more preferably 100 m ² / g or more and 3000 m ² / g or less. When the specific surface area of the porous carbon is in the above range, it is easy to adjust the specific surface area of the pores of the positive electrode active material mixture in the range of the relatively large pore diameter of 100 nm or more and 200 nm or less to 1 m ² / g or more. Can be done. The specific surface area of the porous carbon is obtained by extracting the powder in the same manner as in the measurement of the pore diameter of the porous carbon and measuring the specific surface area of the extracted powder by the gas adsorption method.

The lower limit of the content of porous carbon in the positive electrode active material mixture is preferably 0.1% by mass, more preferably 0.3% by mass. When the content of the porous carbon is not less than the above lower limit, it is easy to adjust the specific surface area of the pores of the positive electrode active material mixture in the range of the relatively large pore diameter of 100 nm or more and 200 nm or less to 1 m ² / g or more. can do. The upper limit of the content of the porous carbon is preferably 2% by mass, more preferably 1% by mass. When the content of the porous carbon is not more than the above upper limit, it is possible to reduce that the content of the first compound becomes relatively too small and the charge / discharge capacity of the power storage element decreases.

(Conducting agent)
The conductive agent is not particularly limited as long as it is a conductive material. Examples of such a conductive agent include carbonaceous materials other than the above-mentioned porous carbon, metals, conductive ceramics and the like. Examples of carbonaceous materials other than the porous carbon include graphitized carbon, non-graphitized carbon, and graphene-based carbon. Examples of the 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 (CNT), fullerenes and the like. Examples of the shape of the conductive agent include powder and fibrous. As the conductive agent, one of these materials may be used alone, or two or more of them may be mixed and used. Further, these materials may be combined and used. For example, a material in which carbon black and CNT are combined may be used. Among these, carbon black is preferable from the viewpoint of electron conductivity and coatability, and acetylene black is particularly preferable.

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 in the above range, the energy density of the power storage element can be increased.

(Binder)
Examples of the binder include fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), thermoplastic resins such as polyethylene, polypropylene, polyacrylic, and polyimide; ethylene-propylene-diene rubber (EPDM), sulfone. Examples thereof include elastomers such as polyethyleneized EPDM, styrene butadiene rubber (SBR), and fluororubber; and polysaccharide polymers.

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 setting the binder content within the above range, the active substance can be stably retained.

(Thickener)
Examples of the thickener include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. When the thickener has a functional group that reacts with lithium or the like, this functional group may be inactivated by methylation or the like in advance.

(Filler)
The filler is not particularly limited. Fillers include polyolefins such as polypropylene and polyethylene, silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, inorganic oxides such as aluminosilicate, magnesium hydroxide, calcium hydroxide, and hydroxide. Hydroxides such as aluminum, carbonates such as calcium carbonate, sparingly soluble ion crystals such as calcium fluoride, barium fluoride, barium sulfate, nitrides such as aluminum nitride and silicon nitride, talc, montmorillonite, boehmite, zeolite, etc. Examples thereof include mineral resource-derived substances such as apatite, kaolin, mulite, spinel, olivine, sericite, bentonite, and mica, or man-made products thereof.

The positive electrode active material mixture is a typical non-metal element such as B, N, P, F, Cl, Br, I, Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, Typical metal elements such as Ba, transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, and W are used as positive electrode active materials, conductive agents, binders, and thickeners. , May be contained as a component other than the filler.

The specific surface area of the pores of the positive electrode active material mixture in the range of 30 nm or more and 200 nm or less and the specific surface area of the pores in the range of 100 nm or more and 200 nm or less are determined by the desorption isotherm method using the nitrogen gas adsorption method. Is sought after. Specifically, the specific surface area of the pores of the positive electrode active material mixture in the range of 30 nm or more and 200 nm or less and the specific surface area of the pores in the range of 100 nm or more and 200 nm or less are obtained from the desorbed isotherm by the BJH method, respectively. can get. These pore specific surface areas are values measured for the remaining components of the positive electrode active material mixture excluding the binder.

The lower limit of the pore specific surface area in the range of the pore diameter of 30 nm or more and 200 nm or less of the positive electrode active material mixture is 10 m ² / g, preferably 12 m ² / g. The lower limit of the pore specific surface area in the range of the pore diameter of 100 nm or more and 200 nm or less of the positive electrode active material mixture is 1 m ² / g, preferably 2 m ² / g. When the lower limit of each pore specific surface area satisfies the above, the power storage element provided with the positive electrode containing the positive electrode active material mixture has an excellent discharge capacity in a low temperature environment. On the other hand, as the upper limit of the pore specific surface area in the range of the pore diameter of 30 nm or more and 200 nm or less of the positive electrode active material mixture, 40 m ² / g is preferable, and 30 m ² / g is more preferable. The upper limit of the pore specific surface area in the range of the pore diameter of 100 nm or more and 200 nm or less of the positive electrode active material mixture is preferably 7 m ² / g, more preferably 5 m ² / g. When the upper limit of each pore specific surface area satisfies the above, the power storage element provided with the positive electrode containing the positive electrode active material mixture is more reliably excellent in discharge capacity in a low temperature environment. The pore specific surface area in the pore diameter range of 30 nm or more and 200 nm or less of the positive electrode active material mixture satisfies the above specific range, that is, the pore specific surface area in each pore diameter measured in the pore diameter range of 30 nm or more and 200 nm. All of the above means that the specific pore specific surface area range is satisfied. Similarly, the pore specific surface area in the range of the pore diameter of 100 nm or more and 200 nm or less of the positive electrode active material mixture satisfies the above-mentioned specific range, that is, the pore ratio in each pore diameter measured in the range of 100 nm or more and 200 nm. It means that all of the surface areas satisfy the above-mentioned specific pore specific surface area range.

The pore specific surface area in the pore diameter range of 30 nm or more and 200 nm or less and the pore specific surface area in the pore diameter range of 100 nm or more and 200 nm or less of the positive electrode active material mixture are calculated based on the following procedure.
When measuring the pore specific surface area, "autosorbi iQ" manufactured by Quantachrome and control analysis software "ASiQwin" are used. 1.00 g of the positive electrode active material mixture (excluding the binder), which is the sample to be measured, is placed in a sample tube for measurement and dried under reduced pressure at 120 ° C. for 12 hours to sufficiently remove the water content in the measurement sample. To remove. Next, by the nitrogen gas adsorption method using liquid nitrogen, the isotherms on the adsorption side and the desorption side are measured within the range of relative pressure P / P0 (P0 = about 770 mmHg) from 0 to 1. Then, the specific surface area of the pores in the range of each pore diameter is calculated by the BJH method using the isotherm on the desorption side.

For the measurement of the specific surface area of the pores, if the powder is a pre-charge / discharge powder of the positive electrode active material mixture (excluding the binder) before the positive electrode is prepared, it is used as it is.
When a measurement sample is collected from the positive electrode taken out by disassembling the power storage element, the same electricity as the nominal capacity of the power storage element is obtained when the power storage element is energized with a constant current for 1 hour before the power storage element is disassembled. With a current value (0.1 C) that is one tenth of the current value that is a quantity, constant current discharge is performed up to a voltage that is the lower limit of the voltage specified in a 25 ° C environment. The power storage element is disassembled, the positive electrode is taken out, a battery with a metallic lithium electrode as the counter electrode is assembled, the current value is 10 mA per 1 g of the positive electrode active material mixture, and the voltage between the terminals of the positive electrode is 2.0 V ( Perform constant current discharge until vs. Li / Li ⁺ ), and adjust to a completely discharged state. After that, it is disassembled again and the positive electrode is taken out. The removed positive electrode is thoroughly washed with dimethyl carbonate to thoroughly wash the non-aqueous electrolyte adhering to the positive electrode, dried at room temperature for 24 hours, and then the positive electrode active material mixture on the positive electrode substrate is collected. The work up to the disassembly of the battery, the positive electrode cleaning, and the drying work are performed in an argon atmosphere having a dew point of −60 ° C. or lower. The obtained positive electrode active material mixture powder is dispersed in N-methylpyrrolidone (NMP), and the binder (for example, PVDF) in the positive electrode active material mixture is removed. Further, it is washed with dimethyl carbonate and then dried to obtain a powder. In the measurement of the pore specific surface area, the powder thus collected is used for the measurement.

<Manufacturing method of positive electrode active material mixture for power storage element>
The positive electrode active material mixture can be produced by mixing a positive electrode active material containing the first compound, porous carbon, and, if necessary, other components described above. The positive electrode active material mixture is formed into a paste together with a solvent as a dispersion medium, applied to a positive electrode base material, and dried to form a positive electrode active material mixture layer. The first compound can be produced, for example, based on the following procedure.

(Method for producing the first compound)
First, a mixed solution of FeSO ₄ and MnSO ₄ at an arbitrary ratio is added dropwise to the reaction vessel at a constant rate, and a NaOH aqueous solution, an NH ₃ aqueous solution, and an NH ₂ NH ₂ aqueous solution are added so that the pH between them remains constant. To prepare a Fe _x Mn _1-x (OH) ₂ precursor. Next, the prepared Fe _x Mn _(1-x) (OH) ₂ precursor is taken out from the reaction vessel and mixed with LiH ₂ PO ₄ and sucrose powder in a solid phase. Then, the obtained mixture is calcined in a nitrogen atmosphere at a calcining temperature of 550 ° C. or higher and 750 ° C. or lower to prepare a first compound having an olivine-type crystal structure and represented by the following formula 1. This first compound is coated with carbon. The first compound not coated with carbon can be produced by performing solid phase mixing and firing in the same manner as described above except that sucrose powder is not added.
LiFe _x Mn _(1-x) PO ₄ (0 ≦ x ≦ 1) ・ ・ ・ 1

(Method of adjusting pore specific surface area)
As described above, the range in which the pore diameter of the positive electrode active material mixture is 30 nm or more and 200 nm or less is a region in which the non-aqueous electrolyte easily permeates, and the positive electrode active material mixture has a pore ratio in this pore diameter range. By setting the surface area to 10 m ² / g or more and the pore specific surface area in the range of the pore diameter of 100 nm or more and 200 nm or less to 1 m ² / g or more, a pore structure that promotes the penetration of the non-aqueous electrolyte 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 for producing the first compound described above.

Examples of control of such a method for producing the first compound include pH adjustment when producing the precursor of the first compound, temperature adjustment when firing the precursor, and the like.

When the positive electrode active material mixture contains porous carbon, the specific surface area of the pores of the positive electrode active material mixture in the range of each of the pore diameters is porous in addition to controlling the method for producing the first compound. It can be obtained by adjusting the average particle size and specific surface area of carbon. In this case, for example, from porous carbons having various average particle diameters and specific surface areas, it is possible to select porous carbons having a pore specific surface area in the range of each pore diameter. In addition, the specific surface area of the pores in the range of each pore diameter can also be obtained by adjusting the compounding ratio of the porous carbon and the first compound.

According to the positive electrode active material mixture for the power storage element, the discharge capacity of the power storage element in a low temperature environment can be increased.

<Positive electrode for power storage element>
The positive electrode for a power storage element (hereinafter, also simply referred to as a positive electrode) contains the positive electrode active material mixture. The positive electrode has a positive electrode base material and a positive electrode active material mixture layer arranged directly on the positive electrode base material or via an intermediate layer.

(Positive electrode base material)
The positive electrode substrate has conductivity. Whether or not it has "conductivity" is determined with a volume resistivity of ¹⁰⁷ Ω · cm measured in accordance with JIS-H-0505 (1975) as a threshold value. As the material of the positive electrode base material, metals such as aluminum, titanium, tantalum, and stainless steel, or alloys thereof are used. Among these, aluminum or an aluminum alloy is preferable from the viewpoint of potential resistance, high conductivity, and cost. Examples of the positive electrode base material include foils, thin-film deposition films, meshes, porous materials, and the like, and foils are preferable from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferable as the positive electrode base material. Examples of aluminum or aluminum alloy include A1085, A3003, and A1N30 specified in JIS-H-4000 (2014) or JIS-H4160 (2006).

The average thickness of the positive electrode substrate is preferably 3 μm or more and 50 μm or less, more preferably 5 μm or more and 40 μm or less, further preferably 8 μm or more and 30 μm or less, and particularly preferably 10 μm or more and 25 μm or less. By setting the average thickness of the positive electrode base material in the above range, it is possible to increase the energy density per volume of the secondary battery while increasing the strength of the positive electrode base material. The "average thickness of the base material" refers to a value obtained by dividing the punched mass when punching a base material having a predetermined area by the true density of the base material and the punched area, and the same applies to the negative electrode base material.

(Middle layer)
The intermediate layer is a layer arranged between the positive electrode base material 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 base material and the positive electrode active material mixture layer. The composition of the intermediate layer is not particularly limited and includes, for example, a binder and a conductive agent.

(Positive electrode active material mixture layer)
The positive electrode active material mixture layer is a layer formed by the above-mentioned positive electrode active material mixture.

<Structure of power storage element>
The power storage element according to an embodiment of the present invention includes an electrode body having a positive electrode, a negative electrode, and a separator, a non-aqueous electrolyte, and a container for accommodating the electrode body and the non-aqueous electrolyte. The electrode body is usually a laminated type in which a plurality of positive electrodes and a plurality of negative electrodes are laminated via a separator, or a wound type in which a positive electrode and a negative electrode are laminated in a laminated state via a separator. The non-aqueous electrolyte exists in the positive electrode, the negative electrode and the separator. As an example of the power storage element, a non-aqueous electrolyte secondary battery (hereinafter, also simply referred to as “secondary battery”) will be described.

[Positive electrode]
The positive electrode included in the power storage element is the above-mentioned positive electrode for the power storage element.

[Negative electrode]
The negative electrode has a negative electrode base material and a negative electrode active material mixture layer arranged directly on the negative electrode base material 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 by the positive electrode for the power storage element.

(Negative electrode base material)
The negative electrode substrate has conductivity. As the material of the negative electrode base material, metals such as copper, nickel, stainless steel, nickel-plated steel and aluminum, alloys thereof, carbonaceous materials and the like are used. Among these, copper or a copper alloy is preferable. Examples of the negative electrode base material include foils, thin-film deposition films, meshes, porous materials, and the like, and foils are preferable from the viewpoint of cost. Therefore, a copper foil or a copper alloy foil is preferable as the negative electrode base material. Examples of the copper foil include rolled copper foil, electrolytic copper foil and the like.

The average thickness of the negative electrode substrate is preferably 2 μm or more and 35 μm or less, more preferably 3 μm or more and 30 μm or less, further preferably 4 μm or more and 25 μm or less, and particularly preferably 5 μm or more and 20 μm or less. By setting the average thickness of the negative electrode base material in the above range, it is possible to increase the energy density per volume of the secondary battery while increasing the strength of the negative electrode base material.

(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 contains optional components such as a conductive agent, a binder, a thickener, and a filler, if necessary. Optional components such as a conductive agent, a binder, a thickener, and a filler can be selected from the materials exemplified for the positive electrode.

The negative electrode active material mixture layer is a typical non-metal element such as B, N, P, F, Cl, Br, I, Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, Typical metal elements such as Ba, and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W are used as negative electrode active materials, conductive agents, and the like. It may be contained as an ingredient other than a binder, a thickener, and a filler.

The negative electrode active material can be appropriately selected from known negative electrode active materials. As the negative electrode active material for a lithium ion secondary battery, a material capable of storing and releasing lithium ions is usually used. Examples of the negative electrode active material include metal Li; metal or semi-metal such as Si and Sn; metal oxide or semi-metal oxide such as Si oxide, Ti oxide and Sn oxide; Li ₄ Ti ₅ O ₁₂ ; Titanium-containing oxides such as LiTIO _{2 and} TiNb ₂ O ₇ ; polyphosphate compounds; silicon carbide; carbon materials such as graphite (graphite) and non-graphitable carbon (easy graphitable carbon or non-graphitizable carbon). Be done. Among these materials, graphite and non-graphitic carbon are preferable. In the negative electrode active material layer, one of these materials may be used alone, or two or more thereof may be mixed and used.

“Graphite” refers to a carbon material having an average lattice spacing (d ₀₀₂ ) of (002) planes determined by X-ray diffraction method before charging / discharging or in a discharged state of 0.33 nm or more and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite. Artificial graphite is preferable from the viewpoint that a material having stable physical properties can be obtained.

"Non-graphitic carbon" refers to a carbon material having an average lattice spacing (d ₀₀₂ ) of the (002) plane determined by the X-ray diffraction method before charging / discharging or in a discharged state of 0.34 nm or more and 0.42 nm or less. .. Examples of non-graphitizable carbon include non-graphitizable carbon and easily graphitizable carbon. Examples of the non-planar carbon include a resin-derived material, a petroleum pitch or a petroleum pitch-derived material, a petroleum coke or a petroleum coke-derived material, a plant-derived material, an alcohol-derived material, and the like.

Here, the "discharged state" means a state in which the carbon material, which is the negative electrode active material, is discharged so as to sufficiently release lithium ions that can be occluded and discharged by charging and discharging. For example, in a unipolar battery in which a negative electrode containing a carbon material as a negative electrode active material is used as a working electrode and metallic Li is used as a counter electrode, the open circuit voltage is 0.7 V or more.

The “non-graphitizable carbon” refers to a carbon material having d ₀₀₂ of 0.36 nm or more and 0.42 nm or less.

The “graphitizable carbon” refers to a carbon material having d ₀₀₂ of 0.34 nm or more and less than 0.36 nm.

The negative electrode active material is usually 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 thereof 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 thereof may be 1 nm or more and 1 μm or less. By setting the average particle size of the negative electrode active material to the above lower limit or more, the production or handling of the negative electrode active material becomes easy. By setting the average particle size of the negative electrode active material to the above upper limit or less, the electron conductivity of the active material layer is improved. A crusher, a classifier, or the like is used to obtain a powder having a predetermined particle size. The pulverization method and the powder grade method can be selected from, for example, the methods exemplified for the positive electrode. When the negative electrode active material is a metal such as metal Li, the negative electrode active material may be in the form of a foil.

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 of the negative electrode active material layer.

[Separator]
The separator can be appropriately selected from known separators. As the separator, for example, a separator composed of only a base material layer, a separator having a heat-resistant layer containing heat-resistant particles and a binder formed on one surface or both surfaces of the base material layer can be used. Examples of the shape of the base material layer of the separator include woven fabrics, non-woven fabrics, and porous resin films. Among these shapes, a porous resin film is preferable from the viewpoint of strength, and a non-woven fabric is preferable from the viewpoint of liquid retention of a non-aqueous electrolyte. As the material of the base material layer of the separator, polyolefins such as polyethylene and polypropylene are preferable from the viewpoint of shutdown function, and polyimide and aramid are preferable from the viewpoint of oxidative decomposition resistance. As the base material layer of the separator, a material in which these resins are combined may be used.

The heat-resistant particles contained in the heat-resistant layer preferably have a mass reduction of 5% or less when the temperature is raised from room temperature to 500 ° C. in an air atmosphere of 1 atm, and the mass reduction when the temperature is raised from room temperature to 800 ° C. Is more preferably 5% or less. Inorganic compounds can be mentioned as materials whose mass reduction is less than or equal to a predetermined value. Examples of the inorganic compound 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 aluminosilicate; aluminum nitride and silicon nitride. Nitrides such as; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ion crystals such as calcium fluoride and barium fluoride; covalent crystals such as silicon and diamond; talc, montmorillonite, boehmite, etc. Examples thereof include substances derived from mineral resources such as zeolite, apatite, kaolin, mulite, spinel, olivine, sericite, bentonite, and mica, or man-made products thereof. As the inorganic compound, a simple substance or a complex of these substances may be used alone, or two or more kinds thereof may be mixed and used. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicate is preferable from the viewpoint of safety of the power storage element.

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

As the separator, a polymer gel composed of a polymer and a non-aqueous electrolyte may be used. Examples of the polymer include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, polyvinylidene fluoride and the like. The use of polymer gel has the effect of suppressing liquid leakage. As the separator, a polymer gel may be used in combination with a porous resin film or a non-woven fabric as described above.

[Non-water electrolyte]
As the non-aqueous electrolyte, a known non-aqueous electrolyte can be appropriately selected. 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 the non-aqueous solvent.

As the non-aqueous solvent, a known non-aqueous solvent can be appropriately selected. Examples of the non-aqueous solvent include cyclic carbonates, chain carbonates, carboxylic acid esters, phosphoric acid esters, sulfonic acid esters, ethers, amides, nitriles and the like. As the non-aqueous solvent, a solvent in which some of the hydrogen atoms contained in these compounds are replaced with halogen may be used.

Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), and difluoroethylene carbonate. (DFEC), styrene carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate and the like can be mentioned. Among these, EC is preferable.

Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), diphenyl carbonate, trifluoroethylmethyl carbonate, bis (trifluoroethyl) carbonate and the like. Among these, EMC is preferable.

As the non-aqueous solvent, it is preferable to use cyclic carbonate or chain carbonate, and it is more preferable to use cyclic carbonate and chain carbonate in combination. By using the cyclic carbonate, the dissociation of the electrolyte salt can be promoted and the ionic conductivity of the non-aqueous electrolyte solution can be improved. By using the chain carbonate, the viscosity of the non-aqueous electrolytic solution can be kept low. When the cyclic carbonate and the 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.

The electrolyte salt can be appropriately selected from known electrolyte salts. Examples of the electrolyte salt include lithium salt, sodium salt, potassium salt, magnesium salt, onium salt and the like. Of these, lithium salts are preferred.

Examples of the lithium salt include inorganic lithium salts such as LiPF ₆ , LiPO ₂ F ₂ , LiBF ₄ , LiClO ₄ , LiN (SO ₂ F) ₂ , lithium bis (oxalate) borate (LiBOB), and lithium difluorooxalate borate (LiFOB). , Lithium oxalate salts such as lithium bis (oxalate) difluorophosphate (LiFOP), LiSO ₃ CF ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) Examples thereof include lithium salts having a halogenated hydrocarbon group such as (SO ₂ C ₄ F ₉ ), LiC (SO ₂ CF ₃ ) ₃ , and LiC (SO ₂ C ₂ F ₅ ) ₃ . Among these, an inorganic lithium salt is preferable, and LiPF ₆ is more preferable.

The content of the electrolyte salt in the non-aqueous electrolyte solution is preferably 0.1 mol / dm ³ or more and 2.5 mol / dm ³ or less at 20 ° C. and 1 atm, and 0.3 mol / dm ³ or more and 2.0 mol / dm. It is more preferably ³ or less, more preferably 0.5 mol / dm ³ or more and 1.7 mol / dm ³ or less, and particularly preferably 0.7 mol / dm ³ or more and 1.5 mol / dm ³ or less. By setting the content of the electrolyte salt in the above range, the ionic conductivity of the non-aqueous electrolyte solution can be increased.

The non-aqueous electrolyte solution may contain additives in addition to the non-aqueous solvent and the electrolyte salt. Examples of the additive include halogenated carbonate esters such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC); lithium bis (oxalate) borate (LiBOB), lithium difluorooxalate borate (LiFOB), and lithium bis (oxalate). ) Difluorophosphate (LiFOP) and other oxalates; Lithiumbis (fluorosulfonyl) imide (LiFSI) and other imide salts; Biphenyl, alkylbiphenyl, terphenyl, partially hydride of terphenyl, cyclohexylbenzene, t-butylbenzene , T-Amilbenzene, diphenyl ether, dibenzofuran and other aromatic compounds; partial halides of the aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene; 2,4-difluoroanisole, 2 , 5-Difluoroanisole, 2,6-difluoroanisole, 3,5-difluoroanisole and other halogenated anisole compounds; vinylene carbonate, methylvinylene carbonate, ethylvinylene carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, anhydrous. Citraconic acid, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic acid anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, propane sulton, propensulton, butane sulton, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, sulfate. Ethylene, sulfolane, dimethylsulfone, diethylsulfone, dimethylsulfoxide, diethylsulfoxide, tetramethylenesulfoxide, diphenylsulfide, 4,4'-bis (2,2-dioxo-1,3,2-dioxathiolane), 4-methylsulfonyloxy Methyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisol, diphenyldisulfide, dipyridinium disulfide, 1,3-propensulton, 1,3-propanesulton, 1,4-butanesulton, 1,4- Examples thereof include buten sulton, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakistrimethylsilyl titanate, lithium monofluorophosphate, lithium difluorophosphate and the like. These additives may be used alone or in combination of two or more.

The content of the additive contained in the non-aqueous electrolytic solution is preferably 0.01% by mass or more and 10% by mass or less, and is 0.1% by mass or more and 7% by mass or less with respect to the total mass of the non-aqueous electrolytic solution. It is more preferable to have it, more preferably 0.2% by mass or more and 5% by mass or less, and particularly preferably 0.3% by mass or more and 3% by mass or less. By setting the content of the additive in the above range, it is possible to improve the capacity maintenance performance or the cycle performance after high temperature storage, and further improve the safety.

As the non-aqueous electrolyte, a solid electrolyte may be used, or a non-aqueous electrolyte solution and a solid electrolyte may be used in combination.

The solid electrolyte can be selected from any material having ionic conductivity such as lithium, sodium and calcium and being solid at room temperature (for example, 15 ° C to 25 ° C). Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, oxynitride solid electrolytes, polymer solid electrolytes and the like.

Examples of the lithium ion secondary battery include Li ₂ SP ₂ S ₅ , LiI-Li ₂ SP ₂ S ₅ , Li ₁₀ Ge-P ₂ S ₁₂ , and the like as the sulfide solid electrolyte. ..

<Specific configuration of power storage element>
The shape of the power storage element of the present embodiment is not particularly limited, and examples thereof include a cylindrical battery, a square battery, a flat battery, a coin battery, and a button battery.
FIG. 1 shows a power storage element 1 as an example of a square battery. The figure is a perspective view of the inside of the container. The electrode body 2 having the positive electrode and the negative electrode wound around the separator is housed in the square container 3. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 41. The negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 51. A non-aqueous electrolyte is injected into the container 3.

<Configuration of power storage device>
The power storage element of the present embodiment is a power source for automobiles such as an electric vehicle (EV), a hybrid vehicle (HEV), and a plug-in hybrid vehicle (PHEV), a power source for electronic devices such as a personal computer and a communication terminal, or a power source for power storage. For example, it can be mounted as a power storage unit (battery module) configured by assembling a plurality of power storage elements 1. In this case, the technique of the present invention may be applied to at least one power storage element included in the power storage device.
FIG. 2 shows an example of a power storage device 30 in which a power storage unit 20 in which two or more electrically connected power storage elements 1 are assembled is further assembled. The power storage device 30 may include a bus bar (not shown) that electrically connects two or more power storage elements 1, a bus bar (not shown) that electrically connects two or more power storage units 20 and the like. The power storage unit 20 or the power storage device 30 may include a state monitoring device (not shown) for monitoring the state of one or more power storage elements.

<Manufacturing method of power storage element>
The method for manufacturing the power storage element of the present embodiment can be appropriately selected from known methods except that the positive electrode for the power storage element is used as the positive electrode. The manufacturing method includes, for example, preparing an electrode body, preparing a non-aqueous electrolyte, and accommodating the electrode body and the non-aqueous electrolyte in a container. Preparing the electrode body includes preparing the positive electrode body and the negative electrode body, and forming the electrode body by laminating or winding the positive electrode body and the negative electrode body via the separator.

The storage of 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 solution, the non-aqueous electrolyte solution may be injected from the injection port formed in the container, and then the injection port may be sealed.

<Other embodiments>
The power storage element of the present invention is not limited to the above embodiment, and various modifications may be made without departing from the gist of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, and a part of the configuration of one embodiment can be replaced with the configuration of another embodiment or a well-known technique. In addition, some of the configurations of certain embodiments can be deleted. Further, a well-known technique can be added to the configuration of a certain embodiment.

In the above embodiment, the case where the power storage element is used as a non-aqueous electrolyte secondary battery (for example, a lithium ion secondary battery) capable of charging and discharging has been described, but the type, shape, size, capacity, etc. of the power storage element are arbitrary. .. The present invention can also be applied to capacitors such as various secondary batteries, electric double layer capacitors and lithium ion capacitors.

In the above embodiment, the electrode body in which the positive electrode and the negative electrode are laminated via the separator has been described, but the electrode body may not include the separator. For example, the positive electrode and the negative electrode may be in direct contact with each other in a state where a non-conductive layer is formed on the active material layer of the positive electrode or the negative electrode.

Hereinafter, the present invention will be described in more detail by way of examples. The present invention is not limited to the following examples.

[Preparation of positive electrode active material]
(1) Preparation of LiFePO ₄ First, a 1 mol / dm ³ FeSO ₄ aqueous solution was dropped into a 2 dm ³ reaction vessel containing 750 cm ³ ion-exchanged water at a constant rate, and the pH during that period was a constant value of 10.0. A 4 mol / dm ³ NaOH aqueous solution, a 0.5 mol / dm ³ NH ₃ aqueous solution, and a 0.5 mol / dm ³ NH ₂ NH ₂ aqueous solution were added dropwise so as to maintain ± 0.1, and Fe (OH) ₂ was added. A precursor was prepared. The temperature of the reaction vessel was set to 50 ° C. (± 2 ° C.). Next, the prepared Fe (OH) ₂ precursor was taken out from the reaction vessel and mixed with LiH ₂ PO ₄ and sucrose powder in a solid phase. Then, the obtained mixture was calcined at a calcining temperature of 650 ° C. under a nitrogen atmosphere to prepare LiFePO ₄ , a positive electrode active material having an olivine-type crystal structure.
(2) Preparation of LiFe _0.25 Mn _0.75 PO ₄ First, adjust the molar ratio of FeSO ₄ and MnSO ₄ to 1: 3 in a 2 dm ³ reaction vessel containing 750 cm ³ ion-exchanged water. While dropping the 1 mol / dm ³ aqueous solution at a constant rate, a 4 mol / dm ³ NaOH aqueous solution and a 0.5 mol / dm ³ NH ₃ so that the pH during that period is maintained at a constant value of 10.0 ± 0.1. An aqueous solution and a 0.5 mol / dm ³ NH ₂ NH ₂ aqueous solution were added dropwise to prepare a Fe _0.25 Mn _0.75 (OH) ₂ precursor. The temperature of the reaction vessel was set to 50 ° C. (± 2 ° C.). Next, the prepared Fe _0.25 Mn _0.75 (OH) ₂ precursor was taken out from the reaction vessel and mixed with LiH ₂ PO ₄ and sucrose powder in a solid phase. Then, the obtained mixture was fired in a nitrogen atmosphere at a firing temperature of 650 ° C. to prepare a positive electrode active material LiFe _0.25 Mn _0.75 PO ₄ having an olivine type crystal structure.

Table 1 shows the values of x in the following formula 1 of the positive electrode active materials of Examples 1 to 15 and Comparative Examples 1 to 3.
LiFe _x Mn _(1-x) PO ₄ (0 ≦ x ≦ 1) ・ ・ ・ 1

[Preparation of positive electrode]
(Examples 1 to 12, and comparative example 3)
LiFePO ₄ 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 was used as the conductive agent, and PVDF was used as the binder. The positive electrode active material, porous carbon, a conductive agent, a binder and a dispersion medium were mixed. At that time, the solid content mass ratio of the positive electrode active material: conductive agent: binder was set to 90: 5: 5, and the total solid content mass was 100, and the porosity was set to the content (mass%) in Table 1. Further carbon was added. An appropriate amount of a dispersion medium was added to the obtained mixture to adjust the viscosity, and a positive electrode active material mixture paste was prepared. Next, the positive electrode active material mixture paste is applied to both sides of the aluminum foil as the positive electrode base material, leaving an uncoated portion (positive electrode active material mixture layer non-forming portion), dried at 120 ° C., and rolled. By pressing, a positive electrode active material mixture layer was formed on the positive electrode base material. The amount of the positive electrode active material mixture paste applied was 10 mg / cm ² in terms of solid content. In this way, positive electrodes of Examples 1 to 12 and Comparative Example 3 were obtained. The specific surface area of the pores of the positive electrode active material mixture in the obtained positive electrode in the range of 30 nm or more and 100 nm or less, the specific surface area of the pores in the range of 100 nm or more and 200 nm or less, and the fine surface area in the range of 30 nm or more and 200 nm or less. The pore specific surface area was measured based on the above method. The results are shown in Table 1.

(Examples 13 to 15)
Examples from Example 7 except that LiFe _0.25 Mn _0.75 PO ₄ is used as the positive electrode active material and porous carbon having the average particle size and specific surface area shown in Table 1 is used in the addition amount shown in Table 1. In the same manner as in 9, the positive electrodes of Example 15 were obtained from Example 13. The specific surface area of the pores of the positive electrode active material mixture in the obtained positive electrode in the range of 30 nm or more and 100 nm or less, the specific surface area of the pores in the range of 100 nm or more and 200 nm or less, and the fine surface area in the range of 30 nm or more and 200 nm or less. The pore specific surface area was measured based on the above method. The results are shown in Table 1.

(Comparative Example 1)
A positive electrode of 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 of the positive electrode active material mixture in the obtained positive electrode in the range of 30 nm or more and 100 nm or less, the specific surface area of the pores in the range of 100 nm or more and 200 nm or less, and the fine surface area in the range of 30 nm or more and 200 nm or less. The pore specific surface area was measured based on the above method. The results are shown in Table 1.

(Comparative Example 2)
A positive electrode of Comparative Example 2 was obtained in the same manner as in Example 1 except that porous carbon was not added and the firing temperature at the time of producing the positive electrode active material was 550 ° C. The specific surface area of the pores of the positive electrode active material mixture in the obtained positive electrode in the range of 30 nm or more and 100 nm or less, the specific surface area of the pores in the range of 100 nm or more and 200 nm or less, and the fine surface area in the range of 30 nm or more and 200 nm or less. The pore specific surface area was measured based on the above method. The results are shown in Table 1.

[Manufacturing of negative electrode]
Graphite was used as the negative electrode active material, SBR was used as the binder, and CMC was used as the thickener. Water as a negative electrode active material, binder, thickener and dispersant was mixed. At that time, the solid content mass ratio of the negative electrode active material: binder: thickener was set to a ratio of 97: 2: 1. An appropriate amount of water was added to the obtained mixture to adjust the viscosity, and a negative electrode mixture paste was prepared. This negative electrode mixture paste was applied to both sides of the copper foil, leaving an uncoated portion (negative electrode active material layer non-forming portion), and dried to prepare a negative electrode active material layer. Then, a roll press was performed to prepare a negative electrode.

[Preparation of non-aqueous electrolyte]
A non-aqueous electrolyte was prepared by dissolving LiPF ₆ at a concentration of 1 mol / dm ³ in a mixed solvent in which EC and EMC were mixed at a volume ratio of 3: 7.

[Manufacturing of power storage element]
Next, the positive electrode and the negative electrode were laminated via a separator made of a polyethylene microporous membrane substrate and a heat-resistant layer formed on the polyethylene microporous membrane substrate to prepare an electrode body. The heat-resistant layer was arranged on the surface facing the positive electrode. This electrode body was housed in a square container made of aluminum, and a positive electrode terminal and a negative electrode terminal were attached. After injecting the non-aqueous electrolyte into the inside of this square container, the container was sealed to obtain a power storage element of Examples and Comparative Examples.

[Capacity confirmation test]
Each of the above-mentioned power storage elements was charged with a constant current of 0.1 C to 3.6 V in an environment of 25 ° C., and then charged with a constant voltage of 3.6 V. The charging end condition was until the charging current reached 0.02C. After a 10-minute pause after charging, constant current discharge was performed at a discharge current of 0.1 C up to 2.0 V in an environment of 25 ° C. A 10-minute rest was provided after discharge. The above cycle was repeated twice, and the second discharge capacity was set to 0.1 C capacity.

[Discharge capacity ratio in low temperature environment]
Each of the above-mentioned power storage elements was charged with a constant current of 0.1 C to 3.6 V in an environment of 25 ° C., and then charged with a constant voltage of 3.6 V. The charging end condition was until the charging current reached 0.02C. After a 10-minute pause after charging, constant current discharge was performed up to 2.0 V at a discharge current of 2 C in a 25 ° C environment, and "2C discharge capacity at 25 ° C" was measured. Next, in a 25 ° C. environment, constant current charging was performed up to 3.6 V with a charging current of 0.1 C, and then constant voltage charging was performed at 3.6 V. The charging end condition was until the charging current reached 0.02C. After that, a rest period of 10 minutes was provided. Then, after storing for 3 hours in the environment of −30 ° C., constant current discharge was performed with a discharge current of 2C up to 2.0V, and “2C discharge capacity at −30 ° C.” was measured.
From the 2C discharge capacity at 25 ° C and the 2C discharge capacity at -30 ° C, these "capacity ratios", that is, the 2C discharge capacity at -30 ° C to the 2C discharge capacity at 25 ° C, are used as indicators of low-temperature high-rate discharge performance. Was calculated. The results are shown in Table 1.

As shown in Table 1 above, the positive electrode active material contains a first compound having an olivine-type crystal structure as represented by the above formula 1, and the pore diameter of the positive electrode active material mixture is in the range of 30 nm or more and 200 nm or less. Examples 1 to 15 have a pore specific surface area of 10 m ² / g or more and a pore specific surface area of 1 m ² / g or more in the range of a pore diameter of 100 nm or more and 200 nm or less. It can be seen that the discharge capacity in a low temperature environment is larger than that in 3.

As a result of the above, it was shown that the positive electrode active material mixture can increase the discharge capacity of the power storage element in a low temperature environment.

The present invention can be applied to a power storage element used as a power source for personal computers, electronic devices such as communication terminals, automobiles and the like.

1 Power storage element 2 Electrode body 3 Container 4 Positive terminal 41 Positive lead 5 Negative terminal 51 Negative lead 20 Power storage unit 30 Power storage device

Claims (4)

It contains a compound represented by the following formula 1 and contains
Positive electrode activity for power storage elements having a pore specific surface area of 10 m ² / g or more in the range of pore diameter of 30 nm or more and 200 nm or less, and a pore specific surface area of 1 m ² / g or more in the range of pore diameter of 100 nm or more and 200 nm or less. Material mixture.
LiFe _x Mn _(1-x) PO ₄ (0 ≦ x ≦ 1) ・ ・ ・ 1 The positive electrode active material mixture for a power storage element according to claim 1, further containing porous carbon. A positive electrode for a power storage element containing the positive electrode active material mixture for a power storage element according to claim 1 or 2. A power storage element including the positive electrode for the power storage element according to claim 3.

Images