Non-aqueous electrolyte power storage element and method for manufacturing the same

Abstract

The nonaqueous electrolyte storage element of one aspect of the present application has: a positive electrode containing positive electrode active material particles including a compound having an olivine-type crystal structure, and a nonaqueous electrolyte containing a salt having oxalate complex anions; a D50 particle diameter of the positive electrode active material particles is 3 μm or less, and a BET specific surface area of the positive electrode active material particles is 10 m 2 / g or less.

Description

Technical Field

[0001] This invention relates to non-aqueous electrolyte energy storage devices and their manufacturing methods. Background Technology

[0002] Non-aqueous electrolyte secondary batteries, represented by lithium-ion batteries, are widely used in electronic devices such as personal computers and communication terminals, as well as automobiles, due to their high energy density. Generally, a non-aqueous electrolyte secondary battery consists of a pair of electrodes electrically isolated by a separator and a non-aqueous electrolyte between the electrodes, and is charged and discharged through the transfer of charge between the two electrodes via ion exchange. In addition, capacitors such as lithium-ion capacitors and double-layer capacitors, besides non-aqueous electrolyte secondary batteries, have also become widely used as non-aqueous electrolyte energy storage components.

[0003] As positive electrode active materials used in non-aqueous electrolyte energy storage devices, compounds with olivine-type crystal structures, such as lithium iron phosphate, are known. Patent Document 1 describes a non-aqueous electrolyte secondary battery that includes a positive electrode containing lithium iron phosphate as the positive electrode active material and a negative electrode containing graphite as the negative electrode active material.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2007-213961 Summary of the Invention

[0007] From the perspective of output performance, low resistance is desirable for non-aqueous electrolyte storage devices. In particular, non-aqueous electrolyte storage devices using lithium iron phosphate as the positive electrode active material and graphite as the negative electrode active material are sometimes used as replacements for lead-acid batteries in vehicles because their operating voltage is comparable to that of lead-acid batteries. In non-aqueous electrolyte storage devices used as replacements for automotive lead-acid batteries, a high CCA (Cold Cranking Ampere) value is important; therefore, reducing resistance is also desirable from this perspective.

[0008] The object of the present invention is to provide a non-aqueous electrolyte energy storage element with low resistance using a compound having an olivine-type crystal structure and a method for manufacturing such a non-aqueous electrolyte energy storage element.

[0009] One aspect of the present invention provides a non-aqueous electrolyte energy storage element comprising: a positive electrode containing positive electrode active material particles comprising a compound having an olivine-type crystal structure; and a non-aqueous electrolyte containing a salt having an oxalate complex anion; wherein the D50 particle size of the positive electrode active material particles is 3 μm or less, and the BET specific surface area of ​​the positive electrode active material particles is 10 m² / g. 2 / g or less.

[0010] Another aspect of the present invention describes a method for manufacturing a non-aqueous electrolyte energy storage element comprising the following steps: decomposing secondary particles of a positive electrode active material containing a compound having an olivine-type crystal structure to obtain a D50 particle size of 3 μm or less and a BET specific surface area of ​​10 m². 2 Positive electrode active material particles of less than / g; preparation of a positive electrode containing the above-mentioned positive electrode active material particles; and preparation of a non-aqueous electrolyte containing a salt with an oxalic acid complex anion.

[0011] According to any aspect of the present invention, it is possible to provide a low-resistance non-aqueous electrolyte storage element using a compound having an olivine-type crystal structure and a method for manufacturing such a non-aqueous electrolyte storage element. Attached Figure Description

[0012] Figure 1 This is a perspective view showing one embodiment of a non-aqueous electrolyte energy storage device.

[0013] Figure 2 This is a schematic diagram illustrating one embodiment of an energy storage device composed of multiple non-aqueous electrolyte energy storage elements. Detailed Implementation

[0014] First, a summary of the non-aqueous electrolyte energy storage element and its manufacturing method disclosed in this specification will be given.

[0015] [1] A non-aqueous electrolyte energy storage element of one aspect of the present invention comprises: a positive electrode containing positive electrode active material particles comprising a compound having an olivine-type crystal structure, and a non-aqueous electrolyte containing a salt having an oxalate complex anion; wherein the D50 particle size of the positive electrode active material particles is 3 μm or less, and the BET specific surface area of ​​the positive electrode active material particles is 10 m² / g or less.

[0016] The non-aqueous electrolyte storage element described above [1] is a non-aqueous electrolyte storage element using a compound with an olivine-type crystal structure and has low resistance. The reason is not yet clear, but it is speculated to be as follows. Generally, charge-transporting ions (such as lithium ions) in compounds with an olivine-type crystal structure only move along the crystal axis of the olivine-type crystal structure. Therefore, it is believed that when the positive electrode active material particles are in the form of secondary particles formed by the aggregation of multiple primary particles, the distance that charge-transporting ions can move in a straight line becomes shorter, and the ion transport resistance increases. Therefore, it is desirable to use compounds with an olivine-type crystal structure in a form that is as close as possible to the form of primary particles (each particle is formed by as few primary particles as possible). Here, it is believed that there is a negative correlation between the primary particle size and the BET specific surface area of ​​the positive electrode active material particles. Therefore, a small D50 particle size and a small BET specific surface area of ​​the positive electrode active material particles mean that the secondary particle size is small and the primary particle size is large, and each particle (usually a secondary particle) is formed by fewer primary particles. In the non-aqueous electrolyte energy storage device described above [1], the D50 particle size of the positive electrode active material particles is less than 3 μm, and the BET specific surface area of ​​the positive electrode active material particles is 10 m². 2 The concentration is below / g, therefore it is believed that each particle is formed from fewer primary particles, thus reducing the ion transport resistance.

[0017] Furthermore, in the non-aqueous electrolyte storage element described above [1], the non-aqueous electrolyte contains a salt having an oxalate complex anion. It is believed that in the non-aqueous electrolyte storage element described above [1], resistance is further reduced by forming a good coating from the salt on the surface of the positive electrode active material particles. In particular, positive electrode active material particles containing compounds with an olivine-type crystal structure are usually coated with carbon material to improve electronic conductivity. In addition, positive electrode active material particles formed from fewer primary particles can be well obtained by decomposition processing, as detailed below. However, when positive electrode active material particles are formed by decomposition, it is easy to produce a portion of the compound with an olivine-type crystal structure that is not coated with carbon material. Therefore, it is believed that the resistance is reduced by coating this exposed portion with a coating from the salt.

[0018] As described above, in the non-aqueous electrolyte energy storage element described above [1], it is speculated that the D50 particle size of the positive electrode active material particles is less than 3 μm and the BET specific surface area is 10 m². 2 The resistance is reduced by lowering the ion transport resistance of the positive electrode active material particles by reducing the ion transport resistance by lowering ...

[0019] Salts contained in non-aqueous electrolytes were qualitatively and quantitatively analyzed by ion chromatography. The apparatus used for IC analysis was a Thermo Fisher Scientific Dionex ICS-5000+. Water was used as the eluent. The specific steps are as follows. It should be noted that a series of determinations should be performed continuously under the same conditions.

[0020] First, disassemble the non-aqueous electrolyte storage element and remove the non-aqueous electrolyte. If removal is impossible, remove the non-aqueous electrolyte by centrifuging the storage element. If centrifugation also fails to remove it, inject a suitable solvent (e.g., acetonitrile) into the storage element and remove the non-aqueous electrolyte diluted with the extraction solvent. It should be noted that the non-aqueous electrolyte can be completely dissolved using a suitable solvent (e.g., acetonitrile).

[0021] (Qualitative Analysis)

[0022] The sample (non-aqueous electrolyte) is subjected to IC analysis. The components contained in the sample are predicted based on the peak positions of the obtained ion chromatogram. A known sample containing the predicted components is then subjected to IC analysis. The retention times of the peaks corresponding to the predicted components in the sample are compared with the retention times of the known samples. If they match, the prediction is presumed to be correct.

[0023] (Quantitative analysis)

[0024] Quantitative analysis is performed using the calibration curve method. First, IC50 measurements are conducted on a known sample containing the predicted component with a known concentration to determine the peak area and construct a calibration curve. The coefficient of determination (r) is then used to calculate the peak area. 2 A calibration curve was prepared using a value ranging from 0.99 to 1. The content of the predicted component in the sample was determined based on the calibration curve and the peak area of ​​the predicted component. This process was repeated for all peaks detected in the IC analysis of the sample to determine the content of each predicted component.

[0025] The "D50 particle size" (and similarly for "D90 particle size" and "D10 particle size" described later) and "BET specific surface area" of the positive electrode active material particles refer to values ​​obtained by measuring the positive electrode active material particles after they have been removed from and processed from the non-aqueous electrolyte storage element through the following steps. First, the non-aqueous electrolyte storage element is subjected to constant current discharge at 0.1C until the discharge termination voltage under normal use is reached. Here, "under normal use" refers to the case where the non-aqueous electrolyte storage element is used under the recommended or specified charge and discharge conditions. The non-aqueous electrolyte storage element in this state is disassembled, the positive electrode is removed, and the components (non-aqueous electrolyte, etc.) adhering to the positive electrode are thoroughly cleaned with dimethyl carbonate. Then, the positive electrode is dried under reduced pressure at room temperature for 24 hours. Next, the powder of the positive electrode active material layer is taken from the positive electrode. After removing any conductive agents or other components mixed in the powder of the positive electrode active material layer using methods such as wind grading, the material is washed and filtered with a solvent that can dissolve binders and thickeners to remove them, thereby obtaining positive electrode active material particles. Finally, the obtained positive electrode active material particles are heated and dried, and a sample of the test object is taken. The heating temperature can be any temperature that can remove the solvent, for example, 60°C to 100°C. The process from disassembling the non-aqueous electrolyte storage element to taking the test object sample can be carried out in an argon atmosphere with a dew point below -60°C, as needed.

[0026] The "D50 particle size" of the positive electrode active material particles refers to the particle size distribution obtained by diluting the particles with a solvent according to JIS-Z-8825 (2013), measuring the particle size distribution of the diluted solution by laser diffraction / scattering, and calculating the cumulative distribution on a volume basis according to JIS-Z-8819-2 (2001), which is 50% of the total. The "D90 particle size" of the positive electrode active material particles is the same value calculated as the cumulative distribution on a volume basis, which is 90% of the total. The "D10 particle size" of the positive electrode active material particles is the same value calculated as the cumulative distribution on a volume basis, which is 10% of the total.

[0027] The "BET specific surface area" of the positive electrode active material particles is a value obtained by determination through the following steps. 1.00 g of positive electrode active material particles are placed in a sample tube for measurement and dried under reduced pressure at 120°C for 12 hours. Then, adsorption isotherms are measured using the nitrogen adsorption method with liquid nitrogen in the range of relative pressure P / P0 (P0 = approximately 770 mmHg) from 0 to 1. Five points are selected from the region of P / P0 = 0.05 to 0.3 of the obtained adsorption isotherms to plot a BET curve, and the BET specific surface area is calculated from the y-intercept and slope of the line.

[0028] [2] In the non-aqueous electrolyte storage element described in [1] above, the D90 particle size of the positive electrode active material particles can be less than 8 μm.

[0029] In the non-aqueous electrolyte storage element described above [2], there are fewer positive electrode active material particles with large secondary particle size formed by multiple primary particles, and therefore the resistance is lower.

[0030] [3] In the non-aqueous electrolyte storage element described in [1] or [2] above, the positive electrode active material particles may contain at least a portion of carbon material present on the surface.

[0031] In the non-aqueous electrolyte storage element described above[3], the electronic conductivity of the positive electrode active material particles is improved by carbon material, thus resulting in lower resistance.

[0032] [4] In any of the above-mentioned non-aqueous electrolyte storage elements [1] to [3], the compound having an olivine-type crystal structure may be lithium iron phosphate.

[0033] The non-aqueous electrolyte storage element described in [4] above is a preferred embodiment of the present invention.

[0034] [5] In any of the above-mentioned [1] to [4] non-aqueous electrolyte storage elements, the salt having oxalate complex anion can be lithium difluorobis(oxalate)phosphate.

[0035] The non-aqueous electrolyte storage element described in [5] above is a preferred embodiment of the present invention.

[0036] [6] In any of the above-mentioned [1] to [5] non-aqueous electrolyte storage elements, the above-mentioned positive electrode active material particles can be decomposition products.

[0037] [7] In any of the above-mentioned [1] to [6] non-aqueous electrolyte storage devices, the non-aqueous electrolyte may further include at least one selected from unsaturated cyclic carbonates and imide salts.

[0038] [8] In any of the above-mentioned [1] to [6] non-aqueous electrolyte storage elements, the non-aqueous electrolyte may further include at least one selected from vinylene carbonate and lithium difluorophosphonosulfonyl imide.

[0039] [9] In any of the above-mentioned [1] to [8] non-aqueous electrolyte storage elements, a negative electrode containing carbon material may be further provided.

[0040]

[10] In any of the above-mentioned [1] to [8] non-aqueous electrolyte storage elements, a negative electrode containing graphite may be further provided.

[0041] The non-aqueous electrolyte storage elements described in [6] to

[10] above are also preferred embodiments of the present invention.

[0042]

[11] Another aspect of the present invention describes a method for manufacturing a non-aqueous electrolyte energy storage element comprising the following steps: decomposing secondary particles of a positive electrode active material containing a compound having an olivine-type crystal structure to obtain a D50 particle size of 3 μm or less and a BET specific surface area of ​​10 m². 2 Positive electrode active material particles of less than / g; preparation of a positive electrode containing the above-mentioned positive electrode active material particles; and preparation of a non-aqueous electrolyte containing a salt having an oxalic acid complex anion.

[0043] According to the manufacturing method of the non-aqueous electrolyte storage element described above

[11] , a non-aqueous electrolyte storage element using a compound with an olivine-type crystal structure and low resistance can be obtained.

[0044] This invention provides a detailed description of one embodiment of a non-aqueous electrolyte energy storage element, an energy storage device, a method for manufacturing a non-aqueous electrolyte energy storage element, and other embodiments. It should be noted that the names of the components used in each embodiment sometimes differ from those used in the prior art.

[0045] <Non-aqueous electrolyte storage components>

[0046] One embodiment of the present invention comprises a non-aqueous electrolyte energy storage element (hereinafter also referred to as "energy storage element") having: an electrode body having a positive electrode, a negative electrode, and an separator; a non-aqueous electrolyte; and a container for housing the electrode body and the non-aqueous electrolyte. The electrode body is typically a stacked type consisting of multiple positive electrodes and multiple negative electrodes separated by a separator, or a wound type consisting of positive electrodes and negative electrodes stacked together separated by a separator. At least a portion of the non-aqueous electrolyte is present in a state of being immersed in the gaps between the positive electrode, the negative electrode, and the separator. As an example of the non-aqueous electrolyte energy storage element, a non-aqueous electrolyte secondary battery (hereinafter also referred to as "secondary battery") will be described.

[0047] (positive electrode)

[0048] The positive electrode has a positive electrode substrate and a layer of positive electrode active material disposed directly or through an intermediate layer on the positive electrode substrate.

[0049] The positive electrode substrate is conductive. Whether it is "conductive" will be determined according to the volume resistivity of 10⁻⁶ as measured by JIS-H-0505 (1975). -2 Ω cm is used as a threshold for determination. The material for the positive electrode substrate can be metals such as aluminum, titanium, tantalum, and stainless steel, or their alloys. Among these, aluminum or aluminum alloys are preferred from the viewpoints of high potential resistance, high conductivity, and cost. Examples of positive electrode substrates include foil, vapor-deposited film, mesh, and porous materials; from a cost perspective, foil is preferred. Therefore, aluminum foil or aluminum alloy foil is preferred as the positive electrode substrate. Examples of aluminum or aluminum alloys include A1085, A3003, and AlN30 as specified in JIS-H-4000 (2014) or JIS-H-4160 (2006).

[0050] 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 making the average thickness of the positive electrode substrate within the above range, the strength of the positive electrode substrate can be improved, and the energy density of the non-aqueous electrolyte energy storage device can be increased.

[0051] The interlayer is a layer disposed between the positive electrode substrate and the positive electrode active material layer. The interlayer reduces the contact resistance between the positive electrode substrate and the positive electrode active material layer by including conductive agents such as carbon particles. The composition of the interlayer is not particularly limited; for example, it may include a binder and a conductive agent.

[0052] The positive electrode active material layer contains positive electrode active material particles. The positive electrode active material layer may contain any components such as conductive agents, binders, thickeners, and fillers, as needed.

[0053] The positive electrode active material particles include compounds with an olivine-type crystal structure. Compounds with an olivine-type crystal structure have a crystal structure that can be attributed to space group Pnma. "A crystal structure that can be attributed to space group Pnma" refers to a crystal structure that has peaks in an X-ray diffraction pattern that can be attributed to space group Pnma.

[0054] Compounds with an olivine-type crystal structure can be compounds containing lithium and transition metal elements. Examples of compounds with an olivine-type crystal structure include those containing oxyacid anions (PO4). 3- SO4 2- SiO4 4- BO3 3- VO4 3- Compounds containing lithium ions and transition metal ions, etc. Compounds with an olivine-type crystal structure may further contain other elements (e.g., halogens). Among the transition metal elements present in compounds with an olivine-type crystal structure, iron, manganese, nickel, and cobalt are preferred, with iron being more preferred. Among the oxyacid anions present in compounds with an olivine-type crystal structure, phosphate anion (PO4) is preferred. 3- ).

[0055] Compounds with an olivine-type crystal structure are preferably those represented by formula (1).

[0056] Li a M b (AO c ) d X e (1)

[0057] In equation (1), M is at least one transition metal element. A is at least one element selected from B, Al, Si, P, S, Cl, Ti, V, Cr, Mo, and W. X is at least one halogen element. a, b, c, d, and e are numbers that satisfy 0 < a ≤ 3, 0 < b ≤ 2, 2 ≤ c ≤ 4, 1 ≤ d ≤ 3, and 0 ≤ e ≤ 1. a, b, c, d, and e can all be integers or decimals.

[0058] As M in formula (1), it is preferably any one of Fe, Mn, Ni, and Co, or a combination of any two of them. As M, it is further preferably Fe, Mn, or a combination thereof, and more preferably Fe. In addition, the content of Fe in M ​​is preferably 50 mol% or more, more preferably 70 mol% or more, 90 mol% or more, or 99 mol% or more. As A, P is preferred. As X, F is preferred. As one embodiment, it is also sometimes preferred that a=1, b=1, c=4, d=1, e=0.

[0059] Specific examples of compounds with an olivine-type crystal structure include LiFePO4, LiCoPO4, and LiFe x Co 1-x PO4(0<x<1), LiMnPO4, LiNiPO4, LiFe x Mn 1-x PO4(0<x<1), LiCrPO4, LiFeVO4, Li2FeSiO4, Li2Fe2(SO4)3, LiFeBO3, LiFePO 3.9 F 0.2 Examples of compounds with an olivine-type crystal structure include Li₂MnSiO₄ and Li₂CoPO₄F. In these compounds, atoms or polyanions can be partially replaced by other atoms or anions. Lithium iron phosphate (LiFePO₄) is preferred as a compound with an olivine-type crystal structure. Lithium iron phosphate can be a compound in which some of the atoms or polyanions constituting lithium iron phosphate are replaced by other atoms or anions. Compounds with an olivine-type crystal structure can be used alone or in combination of two or more.

[0060] The content of compounds with olivine-type crystal structures in the positive electrode active material particles is preferably 80% to 99.9% by mass, and more preferably 90% to 99% by mass.

[0061] Positive electrode active material particles containing compounds with olivine-type crystal structures are typically secondary particles formed by the aggregation of primary particles of the compounds with olivine-type crystal structures. Positive electrode active material particles can be multiple primary particles existing independently without aggregation (single particles), or they can be a mixture of single particles and secondary particles. It should be noted that "primary particles" refer to particles whose grain boundaries are not visible under a scanning electron microscope. "Secondary particles" refer to particles formed by the aggregation of multiple primary particles.

[0062] The positive electrode active material particles preferably contain carbon material present in at least a portion of their surface. A portion of the carbon material may be present within the secondary particles (inter-particle space) of a compound having an olivine-type crystal structure. Within the positive electrode active material particles, there may be portions uncoated by the carbon material (typically, portions of compounds with polyanionic structures exposed). By having carbon material present in at least a portion of the surface of the positive electrode active material particles containing compounds with polyanionic structures, the positive electrode active material particles can exhibit sufficient inter-particle electronic conductivity.

[0063] Carbon materials refer to materials whose main constituent element is carbon. The main constituent element is the element with the highest content by mass. For example, the carbon content in a carbon material can be 80% or more by mass, 90% or more by mass, 95% or more by mass, 99% or more by mass, or 99.9% or more by mass. Preferably, carbon materials are those other than uncarbonized polymers. Examples of elements other than carbon that can be present in carbon materials include oxygen, hydrogen, and nitrogen. Examples of carbon materials include graphite and non-graphitic carbon.

[0064] The content of carbon material in the positive electrode active material particles is preferably 0.1% to 20% by mass, more preferably 0.2% to 10% by mass, and even more preferably 0.3% to 5% by mass. When the content of carbon material in the positive electrode active material particles is at or above the lower limit mentioned above, electronic conductivity and the like can be improved. When the content of carbon material in the positive electrode active material particles is at or below the upper limit mentioned above, the content of compounds with polyanionic structures can be increased, for example, the discharge capacity per unit volume of the positive electrode active material layer can be increased.

[0065] The total content of compounds with polyanionic structures and carbon materials in the positive electrode active material particles is preferably 90% to 100% by mass, or may be 95% or more by mass, 98% or more by mass, 99% or more by mass, or 99.9% or more by mass.

[0066] The upper limit of the D50 particle size of the positive electrode active material particles is 3 μm, preferably 2.5 μm, more preferably 2.0 μm, and even more preferably 1.5 μm. By having the D50 particle size of the positive electrode active material particles below the aforementioned upper limit, the resistance can be reduced. As the lower limit of the aforementioned D50 particle size, 0.1 μm is preferred, more preferably 0.3 μm, and even more preferably 0.7 μm. By having the D50 particle size of the positive electrode active material particles above the aforementioned lower limit, the manufacture or processing of the positive electrode active material particles becomes easier. The D50 particle size of the positive electrode active material particles can be within a range obtained by combining any of the aforementioned lower limits with any of the aforementioned upper limits.

[0067] The upper limit of the D90 particle size of the positive electrode active material particles is preferably 8 μm, more preferably 6 μm, and even more preferably 4 μm. By having the D90 particle size of the positive electrode active material particles below the above-mentioned upper limit, the resistance can be further reduced. The lower limit of the above-mentioned D90 particle size is preferably 0.5 μm, more preferably 1 μm, and even more preferably 2 μm. By having the D90 particle size of the positive electrode active material particles above the above-mentioned lower limit, the manufacture or processing of the positive electrode active material particles becomes easier. The D90 particle size of the positive electrode active material particles can be within a range obtained by combining any of the above-mentioned lower limits and any of the above-mentioned upper limits.

[0068] The upper limit of the D10 particle size of the positive electrode active material particles is preferably 2 μm, more preferably 1.5 μm, and even more preferably 1.0 μm. By having the D10 particle size of the positive electrode active material particles below the aforementioned upper limit, the resistance can be further reduced. The lower limit of the aforementioned D10 particle size is preferably 0.05 μm, more preferably 0.1 μm, and even more preferably 0.2 μm. By having the D10 particle size of the positive electrode active material particles above the aforementioned lower limit, the manufacture or processing of the positive electrode active material particles becomes easier. The D10 particle size of the positive electrode active material particles can be within a range obtained by combining any of the aforementioned lower limits with any of the aforementioned upper limits.

[0069] To obtain positive electrode active material particles with a specified particle size (D50 particle size, etc.), a decomposition machine (pulverizer), a classifier, etc., can be used. In particular, as detailed later, positive electrode active material particles with a D50 particle size of less than 3 μm can be effectively obtained by decomposing secondary particles of positive electrode active material containing compounds with an olivine-type crystal structure. That is, the positive electrode active material particles are preferably the decomposed product.

[0070] The upper limit of the BET specific surface area of ​​the positive electrode active material particles is 10m².2 / g, preferably 9m 2 / g, more preferably 8m 2 / g. When the BET specific surface area of ​​the positive electrode active material particles is below the aforementioned upper limit and the D50 particle size of the positive electrode active material particles is below the aforementioned upper limit, each positive electrode active material particle becomes a state composed of fewer primary particles, thus reducing ion transport resistance. The preferred lower limit for the aforementioned BET specific surface area is 3m. 2 / g, more preferably 5m 2 / g, further preferably 7m 2 / g. When the BET specific surface area of ​​the positive electrode active material particles is above the lower limit mentioned above, the contact area between the positive electrode active material particles and the non-aqueous electrolyte increases, and the output performance tends to improve. The BET specific surface area of ​​the positive electrode active material particles can be within the range obtained by combining any of the above lower limits and any of the above upper limits.

[0071] Positive electrode active material particles containing compounds with an olivine-type crystal structure can be manufactured, for example, by the following method: A compound (precursor) containing a transition metal element constituting the compound with an olivine-type crystal structure is mixed with a lithium salt of phosphoric acid such as LiH₂PO₄, and heated to obtain a compound with an olivine-type crystal structure. Examples of such precursors include hydroxides of transition metal elements (hydroxide precursors), sulfate compounds of transition metal elements, and phosphoric acid compounds of transition metal elements. Hydroxide precursors can be obtained, for example, by a precipitation reaction of transition metal ions with hydroxide ions in water.

[0072] The obtained compound with an olivine-type crystal structure is mixed with a carbon source in water and slurried. The slurry is then pulverized using a bead mill or similar device and dried. The primary particle size of the resulting positive electrode active material particles can be adjusted by varying the pulverization conditions. For example, decreasing the bead size used in the bead mill or extending the processing time tends to reduce the primary particle size of the positive electrode active material particles. The dried mixture of the compound with the olivine-type crystal structure and the carbon source is calcined in a reducing or inactive atmosphere to obtain particles containing secondary particles of the positive electrode active material with an olivine-type crystal structure coated with carbon material. Alternatively, a precursor, a lithium salt of phosphate such as LiH2PO4, and a carbon source can be mixed and calcined in a reducing or inactive atmosphere to also obtain particles containing secondary particles of the positive electrode active material with an olivine-type crystal structure coated with carbon material. Organic materials such as sucrose, lactose, maltose, polyvinyl alcohol, and ascorbic acid can be used as the carbon source. The calcination temperature is preferably in the range of 500°C to 1000°C. By setting the firing temperature above 500°C, the carbonization of the carbon source becomes particularly thorough, resulting in positive electrode active material particles with excellent electronic conductivity. By setting the firing temperature below 1000°C, the sublimation of lithium and other materials in compounds with olivine-type crystal structures is suppressed, thereby suppressing deviations in elemental composition ratios and inhibiting particle growth, thus improving charge-discharge performance. Furthermore, in the case of manufacturing positive electrode active materials that do not contain carbon materials, mixing with the carbon source can be omitted.

[0073] By decomposing the obtained particles using a jet mill or similar method, positive electrode active material particles containing compounds with an olivine-type crystal structure can be obtained. The degree of decomposition at this stage can adjust the D50 particle size and other properties of the obtained positive electrode active material particles. Furthermore, the BET specific surface area of ​​the obtained positive electrode active material particles can be adjusted by changing the firing temperature and firing time. For example, increasing the firing temperature or extending the firing time tends to increase the primary particle size and decrease the BET specific surface area of ​​the obtained positive electrode active material particles. Additionally, the BET specific surface area and other properties of the obtained positive electrode active material particles can also be adjusted by changing the manufacturing conditions of the precursor (e.g., pH during the precipitation reaction).

[0074] The content of positive electrode active material particles in the positive electrode active material layer is preferably 50% to 99% by mass, more preferably 70% to 98% by mass, and even more preferably 80% to 95% by mass. By setting the content of positive electrode active material particles within the above range, both high energy density and manufacturability of the positive electrode active material layer can be achieved.

[0075] There are no particular limitations on conductive agents as long as they are conductive materials. Examples of such conductive agents include carbon materials, metals, and conductive ceramics. Examples of carbon materials include graphite, non-graphite carbon, and graphene-based carbon. Examples of non-graphite 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, and fullerenes. Examples of conductive agents include powder and fibrous forms. One of these materials can be used alone, or two or more can be used in combination. Furthermore, these materials can be combined. For example, a material combining carbon black and carbon nanotubes can be used. From the viewpoint of electronic conductivity and coatability, carbon black is preferred, and acetylene black is preferred.

[0076] The content of the conductive agent in the positive electrode active material layer is preferably 1% to 10% by mass, more preferably 3% to 9% by mass. By setting the content of the conductive agent within the above range, the energy density of the non-aqueous electrolyte energy storage element can be improved. It should be noted that the carbon material contained in the positive electrode active material particles is not included in this conductive agent.

[0077] Examples of adhesives include fluoropolymers (such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF)), thermoplastic resins such as polyethylene, polypropylene, polyacrylic acid, and polyimide; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers.

[0078] The binder content in the positive electrode active material layer is preferably 1% to 10% by mass, more preferably 2% to 9% by mass. By keeping the binder content within the above range, the positive electrode active material particles can be stably maintained.

[0079] Examples of thickeners include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. When the thickener has functional groups that react with lithium, these functional groups can be deactivated beforehand by methylation or the like. In one embodiment of the present invention, the positive electrode active material layer may not contain a thickener.

[0080] The filler is not particularly limited. Examples of fillers include polyolefins such as polypropylene and polyethylene; inorganic oxides such as silica, 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; and substances derived from mineral resources or their synthetic forms, such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica. In one embodiment of the present invention, the positive electrode active material layer may not contain any filler.

[0081] The positive electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, I, typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, Ba, and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, W as components other than positive electrode active material particles, conductive agents, binders, thickeners, and fillers.

[0082] (negative electrode)

[0083] The negative electrode has a negative electrode substrate and a layer of negative electrode active material disposed directly on or separated from the negative electrode substrate by an intermediate layer. The composition of the intermediate layer is not particularly limited, and may be selected from the composition exemplified in the positive electrode described above.

[0084] The negative electrode substrate is conductive. Materials used for the negative electrode substrate include metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, or their alloys, and carbonaceous materials. Copper or copper alloys are preferred. Examples of negative electrode substrates include foil, vapor-deposited film, mesh, and porous materials; from a cost perspective, foil is preferred. 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.

[0085] 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 making the average thickness of the negative electrode substrate within the above range, the strength of the negative electrode substrate can be improved, and the energy density of the non-aqueous electrolyte energy storage device can be increased.

[0086] The negative electrode active material layer contains negative electrode active material. This layer may contain any components such as conductive agents, binders, thickeners, and fillers, as needed. These components can be selected from the materials exemplified in the positive electrode description above.

[0087] The negative electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, I, typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, Ba, and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, W as components other than the negative electrode active material, conductive agent, binder, thickener, and filler.

[0088] The negative electrode active material can be appropriately selected from known negative electrode active materials. For lithium-ion secondary batteries, materials capable of both attracting and releasing lithium ions are typically used as negative electrode active materials. Examples of negative electrode active materials include metallic lithium; metals or half-metals such as Si and Sn; metal oxides or half-metal oxides such as Si oxide, Ti oxide, and Sn oxide; and Li₄Ti₅O₅. 12 Titanium oxides such as LiTiO2 and TiNb2O7; polyphosphate compounds; silicon carbide; and carbon materials such as graphite and non-graphite carbon (easily graphitized or difficult-to-graphitize carbon). Among these materials, carbon materials are preferred, graphite or non-graphite carbon are more preferred, and graphite is even more preferred. In the negative electrode active material layer, one of these materials can be used alone, or two or more can be used in combination.

[0089] "Graphite" refers to the average lattice spacing (d) of the (002) surface determined by X-ray diffraction before or during charging and discharging. 002 Carbon materials with a wavelength greater than 0.33 nm and less than 0.34 nm are preferred. Examples of graphite include natural graphite and synthetic graphite. From the perspective of obtaining materials with stable physical properties, synthetic graphite is preferred.

[0090] "Non-graphitic carbon" refers to the average lattice spacing (d) of the (002) plane determined by X-ray diffraction before or during charging and discharging. 002 Carbon materials with a wavelength of 0.34 nm to 0.42 nm can be categorized as non-graphitic carbon, including difficult-to-graphitize carbon and easily-graphitize carbon. Examples of non-graphitic carbon include materials derived from resins, petroleum asphalt or materials derived from petroleum asphalt, petroleum coke or materials derived from petroleum coke, plant-derived materials, and materials derived from alcohols.

[0091] Here, the "discharge state" of carbon materials refers to the state in which lithium ions that can be adsorbed and released during charging and discharging are fully released from the carbon material, which serves as the negative electrode active material. For example, it is the state in which the open circuit voltage is 0.7V or higher in a half-cell that uses a negative electrode containing carbon material as the negative electrode active material as the working electrode and lithium metal as the counter electrode.

[0092] "Difficult-to-graphitize carbon" refers to the above-mentioned d002 It is a carbon material with a wavelength of 0.36 nm to 0.42 nm.

[0093] "Easily graphitized carbon" refers to the above-mentioned d 002 It is a carbon material with a wavelength greater than 0.34 nm and less than 0.36 nm.

[0094] The negative electrode active material is typically a particle (powder). The average particle size of the negative electrode active material can be, for example, 1 nm to 100 μm. When the negative electrode active material is a carbon material, a titanium oxide, or a polyphosphate compound, its average particle size can be 1 μm to 100 μm. When the negative electrode active material is Si, Sn, Si oxide, or Sn oxide, its average particle size can be 1 nm to 1 μm. By making the average particle size of the negative electrode active material above or below the aforementioned lower limit, the manufacturing or processing of the negative electrode active material becomes easier. By making the average particle size of the negative electrode active material below or below the aforementioned upper limit, the electronic conductivity of the negative electrode active material layer is improved. To obtain powder with a specified particle size, a pulverizer, classifier, etc., can be used. The pulverizing method and classification method can be, for example, selected from the methods exemplified in the positive electrode described above. When the negative electrode active material is a metal such as lithium, the negative electrode active material layer can be in foil form.

[0095] The content of the negative electrode active material in the negative electrode active material layer is preferably 60% to 99% by mass, more preferably 90% to 98% by mass. By setting the content of the negative electrode active material within the above range, both high energy density and manufacturability of the negative electrode active material layer can be achieved.

[0096] When the negative electrode active material layer contains a conductive agent, the content of the conductive agent in the negative electrode active material layer is preferably 1% to 10% by mass, more preferably 3% to 9% by mass. The content of the conductive agent in the negative electrode active material layer can be less than 5% by mass, or less than 2% by mass. In one embodiment of the present invention, the negative electrode active material layer may not contain a conductive agent.

[0097] When the negative electrode active material layer contains a binder, the content of the binder in the negative electrode active material layer is preferably 1% to 10% by mass, more preferably 2% to 8% by mass.

[0098] When the negative electrode active material layer contains a thickener, the content of the thickener in the negative electrode active material layer is preferably 0.1% to 10% by mass, more preferably 0.5% to 8% by mass. The content of the thickener in the negative electrode active material layer can be less than 5% by mass or less than 2% by mass.

[0099] When the negative electrode active material layer contains filler, the filler content in the negative electrode active material layer can be from 0.1% to 8% by mass, preferably 5% by mass or less, and more preferably 2% by mass or less. In one embodiment of the present invention, the negative electrode active material layer may not contain filler.

[0100] (Isolation component)

[0101] The insulating element can be appropriately selected from known insulating elements. Examples of insulating elements include those consisting solely of a substrate layer, or those with a heat-resistant layer comprising heat-resistant particles and an adhesive formed on one or both sides of the substrate layer. Examples of the shape of the substrate layer for the insulating element include fabrics, nonwoven fabrics, and porous resin membranes. Among these shapes, porous resin membranes are preferred from the viewpoint of strength, while nonwoven fabrics are preferred from the viewpoint of retaining non-aqueous electrolytes. For the material of the substrate layer for the insulating element, polyolefins such as polyethylene and polypropylene are preferred from the viewpoint of shut-down function, while polyimide and aramid are preferred from the viewpoint of resistance to oxidative decomposition. Materials composed of these resins can also be used as the substrate layer for the insulating element.

[0102] The heat-resistant particles contained in the heat-resistant layer are preferably materials whose mass decreases by less than 5% when heated from room temperature to 500°C in an air atmosphere at 1 atmosphere, and more preferably materials whose mass decreases by less than 5% when heated from room temperature to 800°C. Inorganic compounds can be cited as materials whose mass decreases to the specified level. Examples of inorganic compounds include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium titanate; covalently bonded crystals such as silicon and diamond; and substances derived from mineral resources or their synthetic forms, such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica. These substances can be used alone as monomers or in combination, or in mixtures of two or more. Among these inorganic compounds, from the viewpoint of the safety of non-aqueous electrolyte storage elements, silicon oxide, aluminum oxide, or aluminosilicates are preferred.

[0103] From a strength point of view, the porosity of the separator is preferably 80% by volume or less, and from a discharge performance point of view, preferably 20% by volume or more. Here, "porosity" is a volume-based value, referring to the value measured using a mercury porosimeter.

[0104] As a separator, a polymer gel composed of a polymer and a non-aqueous electrolyte can be used. 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. As a separator, a porous resin membrane or nonwoven fabric, as described above, can also be used in combination with the polymer gel.

[0105] (Non-aqueous electrolyte)

[0106] Non-aqueous electrolytes contain a salt with an oxalate complex anion (hereinafter also referred to as "salt X"). Non-aqueous electrolytes typically further contain other salts besides salt X as electrolyte salts. Salt X can function as an electrolyte salt. Non-aqueous electrolytes can be used with non-aqueous electrolyte solutions. A non-aqueous electrolyte solution contains a non-aqueous solvent, in which salt X and the electrolyte salt are dissolved.

[0107] Salt X consists of an oxalate complex anion and a counter cation. The oxalate complex anion is at least one oxalate ion (C₂O₄⁻). 2- The anion of a complex formed by coordination bonding with a central element. Examples of central elements include nonmetallic elements such as boron, phosphorus, and silicon, with phosphorus being preferred. Examples of counter cations include alkali metal ions such as lithium, sodium, and potassium, with lithium being preferred. That is, salt X is preferably a lithium salt. Salt X can be used alone or in combination with two or more types.

[0108] As salt X, examples include those having at least one oxalate ion (C2O4). 2- Salts of tetracoordinated oxalate complex anions formed by coordination of lithium bis(oxalate)borate (Li[B(C2O4)2]; LiBOB), lithium difluorooxalateborate (Li[BF2(C2O4)]; LiFOB), and lithium bis(trifluoroethoxy)oxalateborate (Li[B(CF3CH2O)2(C2O4)]) have at least one oxalate ion (C2O4). 2- Salts of hexacoordinate oxalate complex anions formed by coordination of lithium tri(oxalate)phosphate with phosphorus (P) as the central element, such as lithium tri(oxalate)phosphate (Li[P(C2O4)3]), lithium difluorobis(oxalate)phosphate (Li[PF2(C2O4)2]; LiFOP), and lithium tetrafluorooxalate phosphate (Li[PF4(C2O4)]). Among these, from the viewpoint of forming a better film, salts containing at least one oxalate ion (C2O4) are preferred. 2- LiFOP is a salt of a six-coordinate oxalate complex anion formed by coordination of phosphorus (P) as the central element.

[0109] The content of salt X in the non-aqueous electrolyte is preferably 0.01% to 5% by mass, more preferably 0.05% to 3% by mass, even more preferably 0.1% to 2% by mass, and even more preferably 0.2% to 1% by mass. By setting the content of salt X within the above range, the resistance of the non-aqueous electrolyte energy storage element can be further reduced.

[0110] As electrolyte salts (salts other than salt X), appropriate selections can be made from known electrolyte salts. Examples of electrolyte salts include lithium salts, sodium salts, potassium salts, and magnesium salts. Salts, etc. Among them, lithium salts are preferred.

[0111] Examples of lithium salts include inorganic lithium salts such as LiPF6, LiPO2F2, LiBF4, LiClO4, and LiN(SO2F)2, as well as lithium salts with 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.

[0112] The electrolyte salt content in non-aqueous electrolytes or non-aqueous electrolyte solutions is preferably 0.1 mol / dm³ at 20°C and 1 atmosphere. 3 ~2.5mol / dm 3 More preferably 0.3 mol / dm 3 ~2.0 mol / dm 3 Further preferably 0.5 mol / dm 3 ~1.7mol / dm 3 The preferred value is 0.7 mol / dm³. 3 ~1.5mol / dm 3 By ensuring the electrolyte salt content falls within the aforementioned range, the ionic conductivity of non-aqueous electrolytes or non-aqueous electrolyte solutions can be improved. It should be noted that the electrolyte salt content in a non-aqueous electrolyte or non-aqueous electrolyte solution is the sum of the content of salt X and the content of all other salts except salt X.

[0113] As a non-aqueous solvent, a suitable selection can be made from known non-aqueous solvents. Examples of non-aqueous solvents include cyclic carbonates, chain carbonates, carboxylic acid esters, phosphate esters, sulfonates, ethers, amides, and nitriles. Solvents in which some of the hydrogen atoms in these compounds are replaced by halogens can also be used as non-aqueous solvents.

[0114] Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), chloroethylene carbonate, fluoroethylene carbonate (FEC), and difluoroethylene carbonate (DFEC). Saturated cyclic carbonates are preferred, and EC is more preferred.

[0115] Examples of chain carbonates include diethyl carbonate (DEC), dimethyl carbonate (DMC), methyl ethyl carbonate (EMC), diphenyl carbonate, methyl ethyl trifluorocarbonate, and bis(trifluoroethyl) carbonate. Among these, EMC is preferred.

[0116] As a non-aqueous solvent, at least one of cyclic carbonates and linear carbonates is preferred, and more preferably, both cyclic carbonates and linear carbonates are used in combination. Using cyclic carbonates can promote the dissociation of electrolyte salts and improve the ionic conductivity of the non-aqueous electrolyte. Using linear carbonates can keep the viscosity of the non-aqueous electrolyte low. When cyclic carbonates and linear carbonates are used in combination, the volume ratio of cyclic carbonates to linear carbonates (cyclic carbonate: linear carbonate) is preferably in the range of, for example, 5:95 to 50:50.

[0117] In addition to salt X, electrolyte salt, and non-aqueous solvent, non-aqueous electrolytes or non-aqueous electrolyte solutions may also contain additives. Examples of additives include halogenated carbonates such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC); unsaturated cyclic carbonates such as vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, 1-phenylethyleneene carbonate, 1,2-diphenylethyleneene carbonate, and vinylethylene carbonate; imide salts such as lithium bis(fluorosulfonyl)imide and lithium difluorophosphonofluorosulfonylimide; aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrides of terphenyl, cyclohexylbenzene, tert-butylbenzene, diphenyl ether, and dibenzofuran; partially halides of the above aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; and 2,4-difluoroanisole, 2,5-difluoroanisole, etc. - Difluoroanisole, 2,6-difluoroanisole, 3,5-difluoroanisole and other halogenated anisole compounds; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, pentenic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride; vinyl sulfite, propylene sulfite, dimethyl sulfite, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, vinyl sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethyl sulfoxide, diphenyl sulfide, 4,4'-bis(2,2-dioxo-1,3,2-dioxothiacyclopentane), 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxothiacyclopentane, thioanisole, diphenyl disulfide, dipyridine Disulfide, 1,3-propenesulfonyl lactone, 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, 1,4-butenesulfonyl lactone, perfluorooctane, tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate, tetra(trimethylsilyl)titanate, lithium monofluorophosphate, lithium difluorophosphate, etc. Preferably, it contains at least one selected from unsaturated cyclic carbonates and imide salts, more preferably, it contains both unsaturated cyclic carbonates and imide salts. As an unsaturated cyclic carbonate, vinylene carbonate is preferred. As an imide salt, lithium difluorophosphonofluorine sulfonyl imide is preferred. These additives can be used alone or in combination of two or more.

[0118] The content of additives contained in the non-aqueous electrolyte or non-aqueous electrolyte, relative to the overall mass of the non-aqueous electrolyte or non-aqueous electrolyte, is preferably 0.01% to 10% by mass, more preferably 0.1% to 7% by mass, even more preferably 0.2% to 5% by mass, and particularly preferably 0.3% to 3% by mass. By setting the content of additives within the above range, the capacity maintenance performance or cycling performance after high-temperature storage can be improved, or safety can be further improved.

[0119] Non-aqueous electrolytes can use solid electrolytes, or a combination of non-aqueous electrolytes and solid electrolytes.

[0120] As a solid electrolyte, any material that has ionic conductivity and is solid at room temperature (e.g., 15°C to 25°C), such as lithium, sodium, and calcium, can be selected. Examples of solid electrolytes include sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and polymer solid electrolytes.

[0121] Examples of sulfide solid electrolytes include Li₂S-P₂S₅, LiI-Li₂S-P₂S₅, and Li 10 Ge-P2S 12 wait.

[0122] The shape of the non-aqueous electrolyte storage element in this embodiment is not particularly limited. Examples include cylindrical batteries, square batteries, flat batteries, coin-shaped batteries, and button batteries.

[0123] Figure 1 This diagram shows a non-aqueous electrolyte storage element 1, an example of a square battery. It should be noted that this diagram is a perspective view of the interior of the container. Electrode bodies 2, having positive and negative electrodes wound together with a separator, are housed within a square container 3. The positive electrode is electrically connected to the positive terminal 4 via a positive electrode wire 41. The negative electrode is electrically connected to the negative terminal 5 via a negative electrode wire 51.

[0124] <Electronic Storage Devices>

[0125] The non-aqueous electrolyte energy storage element of this embodiment can be used as an energy storage unit (battery module) composed of multiple non-aqueous electrolyte energy storage elements in power supplies for automobiles such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), as well as power supplies for electronic devices such as personal computers and communication terminals, or power storage devices. In this case, it is sufficient to apply the technology of this invention to at least one non-aqueous electrolyte energy storage element included in the energy storage unit.

[0126] Figure 2 This illustrates an example of an energy storage device 30 formed by further assembling energy storage units 20, which are electrically connected to each other, into a single energy storage unit. The energy storage device 30 may include a busbar (not shown) electrically connecting two or more non-aqueous electrolyte energy storage elements 1, and a busbar (not shown) electrically connecting two or more energy storage units 20. The energy storage unit 20 or the energy storage device 30 may include a status monitoring device (not shown) for monitoring the status of one or more non-aqueous electrolyte energy storage elements.

[0127] <Manufacturing Method of Non-Aqueous Electrolyte Storage Components>

[0128] The manufacturing method of the non-aqueous electrolyte energy storage element of this embodiment can be appropriately selected from known methods, but the following method is preferred. Specifically, the manufacturing method of the non-aqueous electrolyte energy storage element according to one embodiment of the present invention includes the following steps: by decomposing secondary particles of a positive electrode active material containing a compound having an olivine-type crystal structure, a D50 particle size of 3 μm or less and a BET specific surface area of ​​10 m² is obtained. 2 The method for manufacturing a non-aqueous electrolyte storage element according to this embodiment may further include: preparing an electrode body, storing the electrode body and the non-aqueous electrolyte in a container, etc.

[0129] Secondary particles of the positive electrode active material, which contain compounds with an olivine-type crystal structure and are used for decomposition, may contain at least a portion of carbon material present on their surface. These secondary particles can be obtained, for example, by calcining various compounds used as raw materials, as described above. The decomposition of these secondary particles can be performed using a mortar and pestle, ball mill, sand mill, vibratory ball mill, planetary ball mill, jet mill, reverse jet mill, or swirling airflow jet mill. Decomposition can be carried out using either dry or wet methods. The decomposed secondary particles of the positive electrode active material can be classified. Classification methods include using sieves or air classifiers.

[0130] The positive electrode can be fabricated, for example, by coating a positive electrode slurry directly or through an intermediate layer onto a positive electrode substrate and then drying it. The positive electrode slurry contains various components constituting the positive electrode active material layer, such as positive electrode active material particles, and a dispersion medium. Alternatively, the coated positive electrode slurry can be dried and then pressed. The specific and preferred form of the fabricated positive electrode is the same as the specific and preferred form of the positive electrode in a non-aqueous electrolyte energy storage device according to one embodiment of the present invention.

[0131] Preparing a non-aqueous electrolyte can be achieved by manufacturing a non-aqueous electrolyte. For example, the preparation of a non-aqueous electrolyte can be carried out by mixing its components. The specific and preferred form of the prepared non-aqueous electrolyte is the same as the specific and preferred form of the non-aqueous electrolyte in the non-aqueous electrolyte energy storage element of one embodiment of the present invention.

[0132] The manufacturing method may also include: preparing a negative electrode, preparing an electrode body, and storing the electrode body and non-aqueous electrolyte in a container.

[0133] Preparing the negative electrode can be achieved by fabricating the negative electrode. For example, the negative electrode can be fabricated by coating a negative electrode slurry directly or through an intermediate layer onto a negative electrode substrate and then drying it. The negative electrode slurry contains various components constituting the negative electrode active material layer, such as the negative electrode active material, and a dispersion medium. Alternatively, the coated negative electrode slurry can be dried and then pressed. Instead of coating the negative electrode slurry, the negative electrode active material layer can be formed by stacking metal foils. The specific and preferred form of the prepared negative electrode is the same as the specific and preferred form of the negative electrode in a non-aqueous electrolyte energy storage device according to one embodiment of the present invention.

[0134] Preparing the electrode body can be done by fabricating the electrode body. The electrode body can be fabricated, for example, by stacking or winding the positive and negative electrodes with a separator in between. The non-aqueous electrolyte can be stored in a container using a suitable known method. For example, when a non-aqueous electrolyte solution is used, it can be simply injected into the non-aqueous electrolyte solution through an inlet formed on the container and then the inlet is sealed.

[0135] <Other Implementation Methods>

[0136] It should be noted that the non-aqueous electrolyte energy storage element of the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, the configuration of other embodiments can be added to the configuration of one embodiment, and a part of the configuration of one embodiment can be replaced with the configuration of other embodiments or known technology. Furthermore, a part of the configuration of one embodiment can be deleted. In addition, known technology can be added to the configuration of one embodiment.

[0137] In the above embodiments, the use of non-aqueous electrolyte storage elements as rechargeable non-aqueous electrolyte secondary batteries (e.g., lithium-ion secondary batteries) has been described, but the type, shape, size, capacity, etc., of the non-aqueous electrolyte storage elements are arbitrary. This invention can also be applied to various secondary batteries.

[0138] In the above embodiments, an electrode body formed by stacking positive and negative electrodes with an insulating member in between has been described. However, the electrode body may also lack an insulating member. For example, the positive and negative electrodes may be in direct contact with each other while a non-conductive layer is formed on the active material layer of either the positive or negative electrode.

[0139] Example

[0140] The present invention will be further described in detail below through embodiments, but the present invention is not limited to the following embodiments.

[0141] [Example 1]

[0142] (Preparation of positive electrode active material particles)

[0143] Through the following steps, positive electrode active material particles are obtained by coating secondary particles of lithium iron phosphate with carbon material.

[0144] Lithium hydroxide monohydrate, diammonium hydrogen phosphate, and ferric sulfate heptahydrate were weighed in a Li:Fe:P molar ratio of 3:1:1 and mixed in ion-exchanged water to prepare a solution. The solution was then transferred to a polytetrafluoroethylene (PTFE) container and placed in a pressure-resistant hydrothermal reaction vessel. After the hydrothermal reaction vessel was fully purged with nitrogen and sealed, it was heated at 170°C for 15 hours to carry out hydrothermal synthesis. After the hydrothermal synthesis reaction was completed, the mixture was allowed to cool naturally to room temperature. The resulting product was then thoroughly washed with ion-exchanged water and dried under reduced pressure at 120°C for 6 hours to obtain lithium iron phosphate (LFP).

[0145] The obtained LFP was mixed with sucrose powder as a carbon source in water to obtain a slurry. The slurry was pulverized using a zirconia bead mill and dried by spray drying. The dried LFP-sucrose mixture was calcined at 650°C under a nitrogen atmosphere to obtain particles of secondary active material containing LFP coated with carbon material. The obtained particles were decomposed using a jet mill to obtain active material particles as decomposed products. To obtain the specified physical properties, the bead mill conditions (bead diameter and processing time), calcination conditions (calcination temperature and calcination time), and decomposition conditions (decomposition time) were adjusted.

[0146] The BET specific surface area, D10 particle size, D50 particle size, and D90 particle size of the obtained positive electrode active material particles were measured. The results are shown in Table 1.

[0147] (The production of the positive electrode)

[0148] A positive electrode slurry was prepared using the obtained positive electrode active material particles, acetylene black (AB) as a conductive agent, polyvinylidene fluoride (PVDF) as a binder, and N-methylpyrrolidone (NMP) as a dispersion medium. The mass ratio of the positive electrode active material particles, AB, and PVDF, converted from solid components, was 90:5:5. This positive electrode slurry was coated onto an aluminum foil serving as the positive electrode substrate, dried, and then rolled to form a positive electrode active material layer, thus obtaining the positive electrode.

[0149] (Making the negative electrode)

[0150] A negative electrode slurry was prepared by mixing graphite (as the negative electrode active material), styrene-butadiene rubber (SBR) (as a binder), carboxymethyl cellulose (CMC) (as a thickener), and water (as a dispersion medium). The mass ratio of graphite, SBR, and CMC, converted from solid components, was 98.0:1.0:1.0. This negative electrode slurry was coated onto copper foil (as the negative electrode substrate), dried, and then rolled to form a negative electrode active material layer, thus obtaining the negative electrode.

[0151] (Preparation of non-aqueous electrolytes)

[0152] In a solvent prepared by mixing ethylene carbonate, diethyl carbonate, and methyl ethyl carbonate in a volume ratio of 30:35:35, a concentration of 1.0 mol / dm³ was used. 3 LiPF6 was dissolved at a concentration of [missing value] to obtain a solution. In this solution, 0.7% by mass of vinylene carbonate, 2.5% by mass of lithium difluorophosphonosulfonyl imide, and 0.5% by mass of lithium difluorobis(oxalate)phosphate (LiFOP) were dissolved to obtain a non-aqueous electrolyte.

[0153] (Isolation component)

[0154] The separator uses a polyethylene microporous membrane.

[0155] (Assembly of non-aqueous electrolyte storage components)

[0156] The above-mentioned positive electrode, negative electrode, and separator are stacked to form an electrode body. The obtained electrode body is placed in a container, and then the above-mentioned non-aqueous electrolyte is injected into the container and sealed, thereby obtaining the non-aqueous electrolyte energy storage device of Example 1.

[0157] [Comparative Examples 1-7]

[0158] As positive electrode active material particles, positive electrode active material particles containing LFP and having secondary particles of positive electrode active material with BET specific surface area and particle size (D10 particle size, D50 particle size and D90 particle size) as shown in Table 1 were coated with carbon material, and the content of lithium difluorobis(oxalate) phosphate (LiFOP) in the non-aqueous electrolyte was set as shown in Table 1. Otherwise, the non-aqueous electrolyte energy storage elements of Comparative Examples 1 to 7 were obtained in the same manner as in Example 1.

[0159] It should be noted that for the positive electrode active material particles of Comparative Examples 4 to 6, the above-mentioned firing conditions were changed, and the secondary particles of the positive electrode active material containing LFP were screened instead of being decomposed by a jet mill. As a result, the BET specific surface area and particle size of the positive electrode active material particles of Example 1 are different.

[0160] Furthermore, the positive electrode active material particles of Comparative Examples 1-3 were obtained through the following steps. Ferric phosphate hydrate and lithium hydroxide monohydrate were weighed in a Li:Fe:P molar ratio of 2:1:1, and a solution was prepared by mixing them in ion-exchanged water containing polyvinylpyrrolidone and fructose. The resulting solution was dried by spray drying to prepare a powdered precursor. The prepared precursor was calcined under a nitrogen atmosphere to obtain particles containing LFP positive electrode active material secondary particles coated with carbon material. The obtained particles were decomposed using a jet mill to obtain positive electrode active material particles as decomposition products. To obtain the specified physical properties, the spray drying conditions (method, solution concentration, nozzle diameter, disk shape and rotation speed, etc.), calcination conditions (calcination temperature and calcination time), and decomposition conditions (decomposition time) were adjusted.

[0161] Furthermore, the positive electrode active material particles of Comparative Examples 5-7 were obtained through the following steps: Phosphoric acid and iron powder were reacted in ion-exchanged water. The resulting solution was dried by spray drying to prepare a powdered precursor. The prepared precursor was calcined under a nitrogen atmosphere to obtain Fe7(PO4)6. The obtained Fe7(PO4)6, phosphoric acid, lithium carbonate, and fructose were mixed in ion-exchanged water to prepare a solution. The resulting solution was dried by spray drying to prepare a powdered precursor. The prepared precursor was calcined under a nitrogen atmosphere to obtain particles containing LFP positive electrode active material secondary particles coated with carbon material. In order to obtain the specified physical property values, the spray drying conditions (method, solution concentration, nozzle diameter, disk shape, and rotation speed, etc.) and calcination conditions (calcination temperature and calcination time) were adjusted, and sieving was performed.

[0162] In addition, "-" in Table 1 indicates that it does not contain LiFOP.

[0163] [evaluate]

[0164] (Initial charge and discharge)

[0165] For each non-aqueous electrolyte energy storage element in the embodiments and comparative examples, initial charge and discharge were performed under the following conditions: Constant current charging was performed in a constant temperature bath at 25°C with a charging current of 0.2C and a charging termination voltage of 3.5V, followed by constant voltage charging at 3.5V. The charging termination condition was set at the moment the charging current decayed to 0.01C. Then, a 10-minute rest period was set. Then, constant current discharging was performed with a discharge current of 0.2C and a discharge termination voltage of 2.0V.

[0166] (Initial capacity validation test)

[0167] Next, for each non-aqueous electrolyte storage element, an initial capacity verification test was conducted at 25°C according to the following procedure: After constant current charging at a charging current of 1.0C and a charging termination voltage of 3.5V, constant voltage charging was performed at 3.5V. The charging termination condition was set at the moment the charging current decayed to 0.01C. Then, a 10-minute rest period was set. Then, constant current discharging was performed at a discharging current of 1.0C and a discharging termination voltage of 2.0V. The discharge capacity at this point was taken as the "initial discharge capacity". The state of full charge based on the initial discharge capacity was set as SOC (state of charge) 100%.

[0168] (DC resistance measurement)

[0169] After the initial charge and discharge as described above, measure the DC resistance (DCR) according to the following procedure. Charge at a constant current of 1.0C at 25°C until reaching a state of charge (SOC) equivalent to 50%. After storing in a constant temperature bath at -10°C for 4 hours, discharge for 30 seconds each at currents of 0.2C, 0.5C, or 1.0C. After each discharge, charge at a constant current of 1.0C until the SOC reaches 50%. Plot the relationship between the current during each discharge and the voltage 10 seconds after the start of discharge. Calculate the DC resistance (DCR) based on the slope of the straight line obtained from the curves at the three points. The calculated DC resistance (DCR) is shown in Table 1.

[0170]

[0171] As shown in Table 1, D50 particles with a diameter of less than 3 μm and a BET specific surface area of ​​10 m² were used. 2 The DC resistance (DCR) of the non-aqueous electrolyte storage element in Example 1, which contains positive electrode active material particles of less than / g and LiFOP as a salt with oxalic acid complex anion, is less than 300mΩ, indicating low resistance.

[0172] On the other hand, it does not meet the requirements that the D50 particle size of the positive electrode active material particles is less than 3 μm and the BET specific surface area of ​​the positive electrode active material particles is 10 m².2 The DC resistance (DCR) of each non-aqueous electrolyte storage element in Comparative Examples 1 to 7, which are below / g and contain one or more salts with oxalate complex anions in their non-aqueous electrolytes, exceeds 300mΩ.

[0173] It should be noted that, as with the positive electrode active material particles used in Comparative Examples 4-7, when the secondary particles of the positive electrode active material containing LFP are sieved with carbon-coated particles, the particle size (D10, D50, and D90) of the resulting positive electrode active material particles increases. This is believed to be because, after sieving, the secondary particles of the positive electrode active material containing LFP coated with carbon-coated particles aggregate with each other.

[0174] Industrial availability

[0175] This invention can be applied to non-aqueous electrolyte storage components used as power sources for personal computers, communication terminals and other electronic devices, automobiles and the like.

[0176] Symbol Explanation

[0177] 1. Non-aqueous electrolyte storage element

[0178] 2 Electrode body

[0179] 3 containers

[0180] 4 Positive extremes

[0181] 41 Positive wire

[0182] 5 Negative extremes

[0183] 51 Negative conductor

[0184] 20 energy storage units

[0185] 30. Energy storage device

Claims

1. A non-aqueous electrolyte energy storage element, comprising: The positive electrode contains positive electrode active material particles comprising compounds with an olivine-type crystal structure, and Non-aqueous electrolyte, containing salts with oxalate complex anions; The D50 particle size of the positive electrode active material particles is less than 3 μm. The BET specific surface area of ​​the positive electrode active material particles is less than 10 m² / g.

2. The non-aqueous electrolyte energy storage element according to claim 1, wherein, The D90 particle size of the positive electrode active material particles is less than 8 μm.

3. The non-aqueous electrolyte energy storage element according to claim 1 or 2, wherein, The positive electrode active material particles contain at least a portion of carbon material present on the surface.

4. The non-aqueous electrolyte energy storage element according to claim 1 or 2, wherein, The compound with the olivine-type crystal structure is lithium iron phosphate.

5. The non-aqueous electrolyte energy storage element according to claim 1 or 2, wherein, The salt containing the oxalic acid complex anion is lithium difluorobis(oxalic acid)phosphate.

6. A method for manufacturing a non-aqueous electrolyte energy storage element, comprising the following steps: By decomposing secondary particles of positive electrode active material containing compounds with olivine-type crystal structures, positive electrode active material particles with a D50 particle size of less than 3 μm and a BET specific surface area of ​​less than 10 m² / g are obtained. To fabricate a positive electrode containing the aforementioned positive electrode active material particles; and Prepare a non-aqueous electrolyte containing a salt with an oxalic acid complex anion.

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