Non-aqueous electrolyte energy storage element

Abstract

A nonaqueous electrolyte power storage element according to one aspect of the present invention comprises a cathode containing a polyanionic cathode active material and an anode containing non-graphitic carbon. The ratio A / B of the specific surface area A (m2 / g) of the polyanionic cathode active material and the average grain diameter B (µm) of the non-graphitic carbon is 4 or greater.

Description

[Technical Field]

[0001] The present invention relates to a non-aqueous electrolyte electricity storage element. [Background technology]

[0002] Non-aqueous electrolyte secondary batteries, typified by lithium-ion non-aqueous electrolyte secondary batteries, are widely used in electronic devices such as personal computers and communication terminals, automobiles, etc., due to their high energy density. The non-aqueous electrolyte secondary batteries generally include an electrode assembly having a pair of electrodes electrically isolated by a separator, and a non-aqueous electrolyte interposed between the electrodes, and are configured to charge and discharge by transferring ions between the electrodes. In addition to non-aqueous electrolyte secondary batteries, capacitors such as lithium-ion capacitors and electric double layer capacitors are also widely used as non-aqueous electrolyte energy storage elements.

[0003] Polyanion-based positive electrode active materials such as lithium iron phosphate are known as positive electrode active materials used in nonaqueous electrolyte storage elements. Patent Document 1 describes a nonaqueous electrolyte secondary battery including 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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2007-213961 Summary of the Invention [Problem to be solved by the invention]

[0005] Non-aqueous electrolyte energy storage elements that use a polyanion-based positive electrode active material and graphite as the negative electrode active material have the disadvantage that the charge-discharge curve (SOC-OCV curve) is relatively flat, i.e., the voltage remains relatively constant even when the SOC (State of Charge) changes, making it difficult to detect the SOC based on the voltage. Furthermore, in applications that require high input / output performance, such as power sources for mild hybrid vehicles, conventional non-aqueous electrolyte energy storage elements that use a polyanion-based positive electrode active material are desirably improved, particularly in terms of input performance.

[0006] The present invention has been made in light of the above circumstances, and an object of the present invention is to provide a nonaqueous electrolyte electricity storage element that allows easy detection of the SOC and has high input performance. [Means for solving the problem]

[0007] A non-aqueous electrolyte storage element according to one aspect of the present invention comprises a positive electrode containing a polyanionic positive electrode active material and a negative electrode containing non-graphitic carbon, and the specific surface area A (m 2 The ratio A / B of the particle size (µm) of the non-graphitic carbon to the average particle size B (µm) of the non-graphitic carbon is 4 or more. [Effects of the Invention]

[0008] According to one aspect of the present invention, a nonaqueous electrolyte electricity storage element is provided that allows easy detection of the SOC and has high input performance. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view showing one embodiment of a nonaqueous electrolyte electricity storage element. [Figure 2] FIG. 2 is a schematic diagram showing one embodiment of an electricity storage device configured by assembling a plurality of nonaqueous electrolyte electricity storage elements. [Figure 3] FIG. 3 shows the charging curves (SOC-OCV curves) of the nonaqueous electrolyte storage elements of Example 1 and Comparative Example 1. [Figure 4]FIG. 4 is a graph showing the relationship between the ratio A / B and input performance in each of the nonaqueous electrolyte electricity storage elements of Examples 1 to 3 and Comparative Examples 2 to 4. DETAILED DESCRIPTION OF THE INVENTION

[0010] First, an outline of the nonaqueous electrolyte electricity storage element disclosed in this specification will be described.

[0011] A non-aqueous electrolyte storage element according to one aspect of the present invention comprises a positive electrode containing a polyanionic positive electrode active material and a negative electrode containing non-graphitic carbon, and the specific surface area A (m 2 The ratio A / B of the particle size (µm) of the non-graphitic carbon to the average particle size B (µm) of the non-graphitic carbon is 4 or more.

[0012] The nonaqueous electrolyte energy storage element has easy SOC detection and high input performance. While the reasons for this are unclear, the following are presumed. The charge / discharge potential of a polyanionic positive electrode active material such as lithium iron phosphate remains relatively constant even when the SOC changes. The charge / discharge potential of graphite, the negative electrode active material, also remains relatively constant even when the SOC changes. Therefore, in the case of a nonaqueous electrolyte energy storage element that combines a polyanionic positive electrode active material and graphite as the positive and negative electrode active materials, the charge / discharge curve (SOC-OCV curve) is relatively flat. On the other hand, the charge / discharge potential of non-graphitic carbon changes depending on the SOC, and the charge / discharge potential decreases as the SOC decreases. Therefore, in the case of a nonaqueous electrolyte energy storage element that combines a polyanionic positive electrode active material and non-graphitic carbon as the positive and negative electrode active materials, the charge / discharge curve has a slope, making it easy to detect the SOC based on the voltage. Furthermore, it is believed that the input (reaction during charging) of a non-aqueous electrolyte storage element is rate-determined by the desorption reaction of charge carrier ions (lithium ions, etc.) from the positive electrode active material and the insertion reaction of charge carrier ions into the negative electrode active material. The reaction resistance of the desorption of charge carrier ions from the positive electrode active material is reduced by increasing the specific surface area A of the polyanionic positive electrode active material, which is the positive electrode active material, and the reaction resistance of the insertion of charge carrier ions into the negative electrode active material is reduced by decreasing the average particle size B of the non-graphitic carbon, which is the negative electrode active material. Therefore, the specific surface area A (m2 It is estimated that by increasing the ratio A / B of the average particle diameter B (μm) of the non-graphitic carbon to 4 or more, the reaction resistances of both the desorption reaction of charge carrier ions from the positive electrode active material and the insertion reaction of charge carrier ions into the negative electrode active material are reduced (and thus the input resistance of the non-aqueous electrolyte energy storage element is effectively reduced), resulting in a significant improvement in input performance.

[0013] "Non-graphitic carbon" refers to the carbon that has an average lattice spacing (d 002 ) is 0.34 nm or more and 0.42 nm or less. Here, "discharged state" refers to a state in which the carbon material, which is the negative electrode active material, is discharged so that lithium ions that can be absorbed and released during charging and discharging are sufficiently released. For example, in a single-electrode battery using a negative electrode containing a carbon material as the negative electrode active material as the working electrode and metallic Li as the counter electrode, this state is one in which the open circuit voltage is 1.3 V or more. "Specific surface area" refers to a value determined by measuring pore size distribution using the nitrogen adsorption method in accordance with JIS-Z-8830 (2013). This measurement can be performed using a specific surface area analyzer (product name: Flowsoap III2310) manufactured by Micromeritics, with 0.5±0.01 g of sample added, preheated to 110°C for 90 minutes, cooled using liquid nitrogen, and the amount of nitrogen gas adsorbed during the cooling process. "Average particle size" refers to the value at which the volume-based cumulative distribution calculated in accordance with JIS-Z-8819-2 (2001) is 50%, based on the particle size distribution measured by laser diffraction / scattering in accordance with JIS-Z-8825 (2013) for a diluted solution of particles diluted with a solvent.

[0014] The specific surface area A of the polyanion-based positive electrode active material is 14.0 m 2 In this case, the input performance of the nonaqueous electrolyte electricity storage element is further improved.

[0015] A nonaqueous electrolyte electricity storage element, an electricity storage device, a method for manufacturing a nonaqueous electrolyte electricity storage element according to one embodiment of the present invention, and other embodiments will be described in detail below. Note that the names of the components (elementary components) used in each embodiment may differ from the names of the components (elementary components) used in the background art.

[0016] <Non-aqueous electrolyte energy storage element> A nonaqueous electrolyte storage element (hereinafter also simply referred to as "storage element") according to one embodiment of the present invention comprises an electrode assembly having a positive electrode, a negative electrode, and a separator, a nonaqueous electrolyte, and a container that accommodates the electrode assembly and the nonaqueous electrolyte. The electrode assembly is typically a stacked type in which a plurality of positive electrodes and a plurality of negative electrodes are stacked with separators interposed therebetween, or a wound type in which a positive electrode and a negative electrode are stacked with separators interposed therebetween and wound. The nonaqueous electrolyte is present in a state contained in the positive electrode, the negative electrode, and the separator. As an example of a nonaqueous electrolyte storage element, a nonaqueous electrolyte secondary battery (hereinafter also simply referred to as "secondary battery") will be described.

[0017] (positive electrode) The positive electrode has a positive electrode substrate and a positive electrode active material layer disposed on the positive electrode substrate directly or via an intermediate layer.

[0018] The positive electrode substrate is electrically conductive. Whether or not it has "electrical conductivity" is determined by whether the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 7 The threshold value is Ω·cm. The positive electrode substrate may be made of metals such as aluminum, titanium, tantalum, or stainless steel, or alloys thereof. Among these, aluminum or aluminum alloys are preferred due to their high potential resistance, conductivity, and cost. Positive electrode substrates include foils, vapor-deposited films, meshes, and porous materials, with foils being preferred due to cost. Therefore, aluminum foil or aluminum alloy foil is preferred as the positive electrode substrate. Examples of aluminum or aluminum alloys include A1085, A3003, and A1N30, as specified in JIS-H-4000 (2014) or JIS-H4160 (2006). The positive electrode substrate may have a coating layer made of a carbon material or the like on its surface.

[0019] The average thickness of the positive electrode substrate is preferably 3 μm to 50 μm, more preferably 5 μm to 40 μm, even more preferably 8 μm to 30 μm, and particularly preferably 10 μm to 25 μm. By setting the average thickness of the positive electrode substrate within the above range, the strength of the positive electrode substrate can be increased while increasing the energy density per volume of the secondary battery.

[0020] The intermediate layer is a layer disposed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer contains a conductive agent such as carbon particles to reduce the contact resistance between the positive electrode substrate and the positive electrode active material layer. The configuration of the intermediate layer is not particularly limited, and may contain, for example, a binder and a conductive agent.

[0021] The positive electrode active material layer contains a polyanionic positive electrode active material as a positive electrode active material, and optionally contains other positive electrode active materials, a conductive agent, a binder, a thickener, a filler, and the like.

[0022] The polyanion-based positive electrode active material is a polyanion compound that can absorb and release ions such as lithium ions. The polyanion compound includes oxoacid anions (PO4 3- , SO4 2- , SiO4 4- , BO3 3- , VO4 3- Oxo acid anions include compounds containing condensed anions (P2O7 4- , P3O 10 5-It may be (etc.). The polyanion-based positive electrode active material is preferably a polyanion compound containing an alkali metal element or an alkaline earth metal element and a transition metal element. The polyanion-based positive electrode active material may further contain other elements (such as halogen elements, etc.). As the alkali metal element or alkaline earth metal element contained in the polyanion-based positive electrode active material, a lithium element is preferable. As the transition metal element contained in the polyanion-based positive electrode active material, an iron element, a manganese element, a nickel element, and a cobalt element are preferable, and an iron element is more preferable. As the oxoacid anion contained in the polyanion-based positive electrode active material, a phosphate anion (PO4 3- ) is preferable.

[0023] The polyanion-based positive electrode active material is preferably a compound represented by the following formula 1. Li a M b (AO c ) d X e ···1 In formula 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 satisfying 0 < a ≤ 3, 0 < b ≤ 2, 2 ≤ c ≤ 4, 1 ≤ d ≤ 3, and 0 ≤ e ≤ 1. a, b, c, d, and e may all be integers or may be decimals.

[0024] M in Formula 1 is preferably any one of Fe, Mn, Ni, and Co, or a combination of any two of these, and is preferably one with a high content of such an element (for example, M containing 50 mol% or more of Fe or Mn). Of these, Fe or Mn, or a combination of two of Fe and Mn, is preferred, and it is particularly preferred that M is Fe only or has a high content of Fe. A is preferably P. X is preferably F. In one embodiment, a = 1, b = 1, c = 4, d = 1, and e = 0 may be preferred. The technology disclosed herein can be preferably implemented in an embodiment in which the polyanion-based positive electrode active material contains at least one of Fe, Mn, Ni, and Co.

[0025] Specific examples of polyanion-based positive electrode active materials include LiFePO4, LiCoPO4, and LiFe 0.5 Co 0.5 PO4, LiMnPO4, LiNiPO4, LiMn 0.5 Fe 0.5 PO4, LiCrPO4, LiFeVO4, Li2FeSiO4, Li2Fe2(SO4)3, LiFeBO3, LiFePO 3.9 F 0.2 , Li3V2(PO4)3, Li2MnSiO4, Li2CoPO4F, etc. The atoms or polyanions in these polyanionic positive electrode active materials may be partially substituted with other atoms or anionic species. The surface of the polyanionic positive electrode active material may be coated with other materials. One type of polyanionic positive electrode active material may be used alone, or two or more types may be used in combination.

[0026] The polyanionic positive electrode active material is usually in the form of particles (powder). The average particle size of the polyanionic positive electrode active material is preferably, for example, 0.1 μm or more and 20 μm or less. By setting the average particle size of the polyanionic positive electrode active material to the above lower limit or more, the polyanionic positive electrode active material becomes easy to manufacture or handle. By setting the average particle size of the polyanionic positive electrode active material to the above upper limit or less, the electronic conductivity of the positive electrode active material layer is improved.

[0027] To obtain powders with a predetermined particle size, grinders, classifiers, etc. are used. Grinding methods include, for example, methods using a mortar, ball mill, sand mill, vibration ball mill, planetary ball mill, jet mill, counter jet mill, swirling airflow jet mill, or sieves. Wet grinding in the presence of water or an organic solvent such as hexane can also be used during grinding. As classification methods, sieves, air classifiers, etc. are used as needed for both dry and wet methods.

[0028] The specific surface area A of the polyanion-based positive electrode active material is not particularly limited as long as the ratio (A / B) of the specific surface area A to the average particle size B of the non-graphitic carbon is 4 or more. 2 / g or more is preferable, and 12m 2 / g or more is more preferable, and 14.0m 2 By setting the specific surface area A of the polyanionic positive electrode active material to the above lower limit or more, the input performance of the secondary battery is further improved. The specific surface area A of the polyanionic positive electrode active material is 30 m 2 / g or less is preferable, and 20m 2 / g or less is more preferable. By setting the specific surface area A of the polyanionic positive electrode active material to the above upper limit or less, adsorption of water to the polyanionic positive electrode active material is suppressed, and thereby the productivity of the positive electrode mixture paste used to form the positive electrode active material layer is stabilized. The technology disclosed herein is a method for producing a polyanionic positive electrode active material having a specific surface area A of 10 m 2 / g or more 30m 2 / g or less (e.g., 12m 2 / g or more 25m 2 / g or less, 14.0m 2 / g super 20m 2 / g or less).

[0029] The surface of the polyanionic positive electrode active material may be coated with a carbonaceous material (graphite, non-graphitic carbon, etc.). However, when the polyanionic positive electrode active material is lithium iron phosphate (LiFePO4) coated with non-graphitic carbon, the Raman spectrum of the coated positive electrode active material has a wave number of 965 cm. -1 From 1790cm -1The intensity area (C) of the carbon Raman peak appearing at the wavenumber 935 cm -1 From 965cm -1 It may be preferable that the ratio (C / L) of the intensity area (L) of the Raman peak of lithium iron phosphate appearing in the sample (C) is not 400 or more. The Raman spectrum is a Raman spectrum obtained by Raman spectroscopy at a laser wavelength of 532 nm. When the surface of the polyanionic positive electrode active material is coated with a carbonaceous material (graphite, non-graphitic carbon, etc.), the specific surface area A of the polyanionic positive electrode active material is the specific surface area in a state coated with the carbonaceous material, etc.

[0030] The content of the polyanionic positive electrode active material in the positive electrode active material layer is preferably 50% by mass to 99% by mass, more preferably 70% by mass to 98% by mass, and even more preferably 80% by mass to 95% by mass. By setting the content of the polyanionic positive electrode active material within this range, both high energy density and manufacturability of the positive electrode active material layer can be achieved.

[0031] The positive electrode active material layer may further contain a positive electrode active material other than the polyanionic positive electrode active material. As the other positive electrode active material, various conventionally known positive electrode active materials can be used. However, the content of the polyanionic positive electrode active material relative to all the positive electrode active materials contained in the positive electrode active material layer (the total of the polyanionic positive electrode active material and other positive electrode active materials) is preferably 90% by mass or more, more preferably 99% by mass or more, and even more preferably 100% by mass. By thus constructing the positive electrode active material substantially only from the polyanionic positive electrode active material, detection of the SOC becomes easier.

[0032] The conductive agent is not particularly limited as long as it is a material having electrical conductivity. Examples of such conductive agents include carbonaceous materials, metals, and conductive ceramics. Examples of carbonaceous materials include graphite, non-graphitic carbon, and graphene-based carbon. Examples of non-graphitic carbon include carbon nanofibers, pitch-based carbon fibers, and carbon black. Examples of carbon black include furnace black, acetylene black, and ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNTs), and fullerenes. The conductive agent may be in the form of powder or fiber. As the conductive agent, one of these materials may be used alone, or two or more may be mixed. These materials may also be used in combination. For example, a composite of carbon black and CNTs may be used. Among these, carbon black is preferred from the viewpoints of electronic conductivity and coatability, and acetylene black is particularly preferred.

[0033] The content of the conductive agent in the positive electrode active material layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. By setting the content of the conductive agent within the above range, the energy density of the secondary battery can be increased. Note that the content of the conductive agent does not include the carbonaceous material, etc., that coats the surface of the polyanion-based positive electrode active material.

[0034] Examples of binders include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylic, and polyimide; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers.

[0035] The binder content in the positive electrode active material layer is preferably 1% by mass to 10% by mass, more preferably 3% by mass to 9% by mass. By setting the binder content within this range, the active material can be stably held.

[0036] Examples of thickeners include polysaccharide polymers such as carboxymethyl cellulose (CMC), methyl cellulose, etc. When the thickener has a functional group that reacts with lithium or the like, this functional group may be deactivated in advance by methylation or the like.

[0037] The filler is not particularly limited, and examples of the filler include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates, hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide, carbonates such as calcium carbonate, sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate, nitrides such as aluminum nitride and silicon nitride, substances derived from mineral resources such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, and artificial products thereof.

[0038] The positive electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I; typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, and W as components other than the positive electrode active material, conductive agent, binder, thickener, and filler.

[0039] (Negative electrode) The negative electrode has a negative electrode substrate and a negative electrode active material layer disposed on the negative electrode substrate directly or via an intermediate layer. The configuration of the intermediate layer is not particularly limited and can be selected from the configurations exemplified for the positive electrode above, for example.

[0040] The negative electrode substrate is conductive. Metals such as copper, nickel, stainless steel, and nickel-plated steel, alloys thereof, and carbonaceous materials are used as the material of the negative electrode substrate. Among these, copper or copper alloys are preferred. Examples of the negative electrode substrate include foil, vapor-deposited film, mesh, and porous material, with foil being preferred from the viewpoint of cost. Therefore, copper foil or copper alloy foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0041] The average thickness of the negative electrode substrate is preferably 2 μm to 35 μm, more preferably 3 μm to 30 μm, even more preferably 4 μm to 25 μm, and particularly preferably 5 μm to 20 μm. By setting the average thickness of the negative electrode substrate within the above range, the strength of the negative electrode substrate can be increased while increasing the energy density per volume of the secondary battery.

[0042] The negative electrode active material layer contains non-graphitic carbon as a negative electrode active material. The negative electrode active material layer contains optional components such as other negative electrode active materials, conductive agents, binders, thickeners, and fillers as necessary. The optional components such as conductive agents, binders, thickeners, and fillers can be selected from the materials exemplified for the positive electrode above. In a preferred embodiment, the negative electrode active material layer contains an aqueous binder (a water-soluble or water-dispersible binder) as a binder. Examples of aqueous binders include SBR and PTFE. When the negative electrode active material layer contains an aqueous binder, the above-mentioned effects can be more suitably exhibited. In a preferred embodiment, the negative electrode active material layer does not contain the above-mentioned conductive agent.

[0043] The negative electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I; typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W as components other than the negative electrode active material, conductive agent, binder, thickener, and filler.

[0044] Examples of non-graphitizable carbon include non-graphitizable carbon and graphitizable carbon, with non-graphitizable carbon being preferred. Examples of non-graphitizable carbon include resin-derived materials, petroleum pitch or petroleum pitch-derived materials, petroleum coke or petroleum coke-derived materials, plant-derived materials, and alcohol-derived materials.

[0045] "Non-graphitizable carbon" means the above d 002 This refers to carbon materials with a particle size of 0.36 nm or more and 0.42 nm or less.

[0046] "Graphitizable carbon" means the above d 002 This refers to carbon materials with a particle size of 0.34 nm or more and less than 0.36 nm.

[0047] The average particle size B of the non-graphitic carbon is not particularly limited as long as the ratio (A / B) of the average particle size B to the specific surface area A of the polyanionic positive electrode active material is 4 or more, but is preferably 4 μm or less, more preferably 3 μm or less. Setting the average particle size B of the non-graphitic carbon to the above upper limit or less further improves the input performance of the secondary battery. The average particle size B of the non-graphitic carbon is preferably 0.5 μm or more, more preferably 1 μm or more, and even more preferably 2 μm or more. Setting the average particle size B of the non-graphitic carbon to the above lower limit or more facilitates the production and handling of a negative electrode active material layer containing non-graphitic carbon. Specifically, aggregation of the non-graphitic carbon in the negative electrode mixture paste used to form the negative electrode active material layer is suppressed, thereby improving stability when forming the negative electrode active material layer by coating. A pulverizer, classifier, or the like is used to obtain non-graphitic carbon with a predetermined particle size. The pulverization method and powder classification method can be selected, for example, from the methods exemplified for the positive electrode above. The technology disclosed herein can be preferably implemented in an embodiment in which the average particle size B of the non-graphitic carbon is 0.5 μm or more and 4 μm or less (for example, 1 μm or more and 3.5 μm or less, 1.5 μm or more and 3 μm or less, 2 μm or more and 2.8 μm or less).

[0048] The content of non-graphitic carbon in the negative electrode active material layer is preferably 60% by mass to 99% by mass, more preferably 90% by mass to 98% by mass. By setting the content of non-graphitic carbon within this range, both high energy density and manufacturability of the negative electrode active material layer can be achieved.

[0049] The negative electrode active material layer may further contain other negative electrode active materials besides non-graphitic carbon. As the other negative electrode active materials, various conventionally known negative electrode active materials can be used. However, the content of non-graphitic carbon relative to all negative electrode active materials (total of non-graphitic carbon and other negative electrode active materials) contained in the negative electrode active material layer is preferably 90 mass% or more, more preferably 99 mass% or more, and even more preferably 100 mass%. By constructing the negative electrode active material substantially solely from non-graphitic carbon in this manner, SOC detection becomes easier and input performance is further improved. In a preferred embodiment, the negative electrode active material layer does not contain amorphous carbon or activated carbon.

[0050] (ratio A / B) The specific surface area A (m 2 The lower limit of the ratio A / B of the carbon content (µm) of the positive electrode active material layer to the average particle size B (µm) of the non-graphitic carbon contained in the negative electrode active material layer is 4, preferably 4.5. In some embodiments, the ratio A / B may be 5 or more, or 6 or more. By setting the ratio A / B to the lower limit or more, input performance is improved. On the other hand, the upper limit of the ratio A / B is not particularly limited, but is preferably 20, more preferably 10, and even more preferably 8. In some embodiments, the ratio A / B may be 6 or less (e.g., less than 6) or 5.5 or less (e.g., 5 or less). If the ratio A / B is too large, the aforementioned effect of improving input performance tends to be weaker, and the durability of an energy storage device fabricated using the positive electrode and the negative electrode may tend to decrease. Furthermore, by setting the ratio A / B to the upper limit or less, the energy storage device disclosed herein can be fabricated with good manufacturing stability. The technology disclosed herein can be preferably implemented in an embodiment in which the ratio A / B is 4 or more and 20 or less (preferably 4.5 or more and 15 or less, more preferably 5 or more and 10 or less, for example 6 or more and 8 or less).

[0051] (separator) The separator can be appropriately selected from known separators. Examples of separators that can be used include separators consisting of only a substrate layer and separators in which a heat-resistant layer containing heat-resistant particles and a binder is formed on one or both surfaces of the substrate layer. Examples of the shape of the substrate layer of the separator include woven fabric, nonwoven fabric, and porous resin film. Among these shapes, porous resin films are preferred from the viewpoint of strength, and nonwoven fabrics are preferred from the viewpoint of non-aqueous electrolyte retention. Materials for the substrate layer of the separator are preferably polyolefins such as polyethylene and polypropylene from the viewpoint of shutdown function, and polyimide and aramid from the viewpoint of oxidative decomposition resistance. A composite material of these resins may also be used for the substrate layer of the separator.

[0052] The heat-resistant particles contained in the heat-resistant layer preferably exhibit a mass loss of 5% or less when heated from room temperature to 500°C in an air atmosphere at 1 atmosphere pressure, and more preferably exhibit a mass loss of 5% or less when heated from room temperature to 800°C. Examples of materials exhibiting a mass loss of a predetermined value or less include inorganic compounds. Examples of inorganic compounds include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicate; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium titanate; covalently bonded crystals such as silicon and diamond; mineral-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, as well as artificial products thereof. As the inorganic compound, these substances may be used alone or in the form of a complex, or two or more of them may be used in combination. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicate is preferred from the viewpoint of the safety of the energy storage device.

[0053] The porosity of the separator is preferably 80% by volume or less from the viewpoint of strength, and 20% by volume or more from the viewpoint of discharge performance. Here, "porosity" refers to a volume-based value measured with a mercury porosimeter.

[0054] The separator may be a polymer gel composed of a polymer and a non-aqueous electrolyte. Examples of polymers include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, and polyvinylidene fluoride. The use of a polymer gel has the effect of suppressing leakage. The separator may be a combination of the porous resin film or nonwoven fabric described above and a polymer gel.

[0055] (non-aqueous electrolyte) The nonaqueous electrolyte can be appropriately selected from known nonaqueous electrolytes. The nonaqueous electrolyte may be a nonaqueous electrolytic solution. The nonaqueous electrolytic solution contains a nonaqueous solvent and an electrolyte salt dissolved in the nonaqueous solvent.

[0056] The non-aqueous solvent can be appropriately selected from known non-aqueous solvents. Examples of non-aqueous solvents include cyclic carbonates, chain carbonates, carboxylic acid esters, phosphate esters, sulfonic acid esters, ethers, amides, and nitriles. Non-aqueous solvents in which some of the hydrogen atoms contained in these compounds have been substituted with halogens may also be used.

[0057] Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinylethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), styrene carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate, etc. Among these, EC is preferred.

[0058] Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, trifluoroethyl methyl carbonate, bis(trifluoroethyl) carbonate, etc. Among these, EMC is preferred.

[0059] It is preferable to use a cyclic carbonate or a chain carbonate as the non-aqueous solvent, and it is more preferable to use a combination of a cyclic carbonate and a chain carbonate. The use of a cyclic carbonate can promote dissociation of the electrolyte salt and improve the ionic conductivity of the non-aqueous electrolyte. The use of a chain carbonate can reduce the viscosity of the non-aqueous electrolyte. When a cyclic carbonate and a chain carbonate are used in combination, the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate:chain carbonate) is preferably in the range of, for example, 5:95 to 50:50.

[0060] The electrolyte salt can be appropriately selected from known electrolyte salts, such as lithium salts, sodium salts, potassium salts, magnesium salts, and onium salts. Of these, lithium salts are preferred.

[0061] Examples of lithium salts include inorganic lithium salts such as LiPF6, LiPO2F2, LiBF4, LiClO4, and LiN(SO2F)2, lithium oxalates such as lithium bis(oxalate)borate (LiBOB), lithium difluorooxalateborate (LiFOB), and lithium bis(oxalate)difluorophosphate (LiFOP), and lithium salts having a halogenated hydrocarbon group such as LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), LiC(SO2CF3)3, and LiC(SO2C2F5)3. Among these, inorganic lithium salts are preferred, and LiPF6 is more preferred.

[0062] The content of electrolyte salt in the non-aqueous electrolyte is 0.1 mol / dm at 20°C and 1 atmosphere. 3More than 2.5mol / dm 3 It is preferable that the value is 0.3 mol / dm or less. 3 More than 2.0mol / dm 3 It is more preferable that it is 0.5 mol / dm or less. 3 More than 1.7mol / dm 3 It is more preferable that it is 0.7 mol / dm or less. 3 More than 1.5mol / dm 3 By setting the content of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

[0063] The non-aqueous electrolyte may contain additives in addition to the non-aqueous solvent and the electrolyte salt. Examples of additives include halogenated carbonates such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC); oxalates such as lithium bis(oxalate)borate (LiBOB), lithium difluorooxalateborate (LiFOB), and lithium bis(oxalate)difluorophosphate (LiFOP); imide salts such as lithium bis(fluorosulfonyl)imide (LiFSI); aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partial halides of the above aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; halogenated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole; vinylene carbonate, methylvinylene carbonate, ethylvinylene carbonate, and the like. Carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, 4,4'-bis(2,2-dioxo-1 ,3,2-dioxathiolane), 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, 1,3-propene sultone, 1,3-propane sultone, 1,4-butane sultone, 1,4-butene sultone, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakistrimethylsilyl titanate, lithium monofluorophosphate, lithium difluorophosphate, etc. These additives may be used alone or in combination of two or more.

[0064] The content of the additive contained in the non-aqueous electrolyte is preferably 0.01% by mass to 10% by mass, more preferably 0.1% by mass to 7% by mass, even more preferably 0.2% by mass to 5% by mass, and particularly preferably 0.3% by mass to 3% by mass. By setting the content of the additive within the above range, it is possible to improve the capacity retention performance or cycle performance after high-temperature storage, and further improve safety.

[0065] The non-aqueous electrolyte may be a solid electrolyte, or a non-aqueous electrolytic solution and a solid electrolyte may be used in combination.

[0066] The solid electrolyte can be selected from any material that has ionic conductivity of lithium, sodium, calcium, etc. and is solid at room temperature (e.g., 15° C. to 25° C.) Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, oxynitride solid electrolytes, and polymer solid electrolytes.

[0067] As the sulfide solid electrolyte, for example, Li2S-P2S5, LiI-Li2S-P2S5, Li 10 Ge-P2S 12 etc.

[0068] The shape of the nonaqueous electrolyte storage element of this embodiment is not particularly limited, and examples thereof include cylindrical batteries, prismatic batteries, flat batteries, coin batteries, and button batteries.

[0069] FIG. 1 shows a nonaqueous electrolyte storage element 1 as an example of a prismatic battery. The figure is a see-through view of the inside of the container. An electrode assembly 2 having a positive electrode and a negative electrode wound with a separator sandwiched between them is housed in a prismatic container 3. The positive electrode is electrically connected to a positive electrode terminal 4 via a positive electrode lead 41. The negative electrode is electrically connected to a negative electrode terminal 5 via a negative electrode lead 51.

[0070] <Electricity storage device> The nonaqueous electrolyte energy storage element of this embodiment can be mounted as an energy storage unit (battery module) comprising a plurality of nonaqueous electrolyte energy storage elements 1 in an automobile power source such as an electric vehicle (EV), a hybrid electric vehicle (HEV), or a plug-in hybrid electric vehicle (PHEV), a power source for electronic devices such as a personal computer or a communication terminal, or a power storage power source, etc. In this case, the technology of the present invention may be applied to at least one nonaqueous electrolyte energy storage element included in the energy storage unit.

[0071] 2 shows an example of an electricity storage device 30 in which electricity storage units 20, each of which is an assembly of two or more electrically connected nonaqueous electrolyte electricity storage elements 1, are further assembled. The electricity storage device 30 may include a bus bar (not shown) that electrically connects two or more nonaqueous electrolyte electricity storage elements 1, a bus bar (not shown) that electrically connects two or more electricity storage units 20, etc. The electricity storage unit 20 or the electricity storage device 30 may include a status monitoring device (not shown) that monitors the status of one or more nonaqueous electrolyte electricity storage elements.

[0072] <Method of manufacturing nonaqueous electrolyte energy storage element> The method for manufacturing the nonaqueous electrolyte storage element of this embodiment can be appropriately selected from known methods. The manufacturing method includes, for example, preparing an electrode assembly, preparing a nonaqueous electrolyte, and housing the electrode assembly and the nonaqueous electrolyte in a container. Preparing the electrode assembly includes preparing a positive electrode and a negative electrode, and forming the electrode assembly by stacking or winding the positive electrode and the negative electrode with a separator interposed therebetween.

[0073] The method for placing the non-aqueous electrolyte in the container can be appropriately selected from known methods. For example, when a non-aqueous electrolyte solution is used as the non-aqueous electrolyte, the non-aqueous electrolyte solution may be poured into the container through an inlet formed in the container, and then the inlet may be sealed.

[0074] <Other embodiments> The nonaqueous electrolyte storage element of the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the spirit of the present invention. For example, the configuration of one embodiment may be added to the configuration of another embodiment, or part of the configuration of one embodiment may be replaced with the configuration of another embodiment or well-known technology. Furthermore, part of the configuration of one embodiment may be deleted. Also, well-known technology may be added to the configuration of one embodiment.

[0075] In the above embodiment, the nonaqueous electrolyte storage element is used as a chargeable and dischargeable nonaqueous electrolyte secondary battery (e.g., a lithium ion secondary battery), but the type, shape, size, capacity, etc. of the nonaqueous electrolyte storage element are arbitrary. The present invention can also be applied to various secondary batteries, electric double layer capacitors, lithium ion capacitors, and other capacitors.

[0076] In the above embodiment, the electrode assembly in which the positive electrode and the negative electrode are stacked with a separator interposed therebetween has been described, but the electrode assembly may not include a separator. For example, the positive electrode and the negative electrode may be in direct contact with each other in a state in which a non-conductive layer is formed on the active material layer of the positive electrode or the negative electrode. [Example]

[0077] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0078] [Example 1] (Preparation of positive electrode) The polyanion-based positive electrode active material is lithium iron phosphate (specific surface area A 10 m 2 A positive electrode mixture paste was prepared using lithium iron phosphate (LiFePO4 / g), acetylene black (AB) as a conductive agent, polyvinylidene fluoride (PVDF) as a binder, and N-methylpyrrolidone (NMP) as a non-aqueous dispersion medium. The mass ratio of lithium iron phosphate, AB, and PVDF was 90:5:5 in terms of solid content. This positive electrode mixture paste was applied to a carbon-coated aluminum foil as a positive electrode substrate, dried, and roll-pressed to form a positive electrode active material layer, resulting in a positive electrode.

[0079] (Preparation of negative electrode) A negative electrode mixture paste was prepared by mixing non-graphitizable carbon (HC: average particle size B 2.5 μm), styrene-butadiene rubber (SBR) as a binder, carboxymethyl cellulose (CMC) as a thickener, and water as a dispersion medium. The mass ratio of HC to SBR to CMC was 96:3.3:0.7 in terms of solid content. This negative electrode mixture paste was applied to copper foil as a negative electrode substrate, dried, and roll-pressed to form a negative electrode active material layer, resulting in a negative electrode.

[0080] (non-aqueous electrolyte) The non-aqueous electrolyte was a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 30:35:35, with a concentration of 1.1 mol / dm 3 It was prepared by dissolving LiPF6 at a concentration of

[0081] (separator) A microporous polyethylene film was used as the separator.

[0082] (Assembly of non-aqueous electrolyte energy storage element) The positive electrode, negative electrode, and separator were stacked to prepare an electrode assembly, which was then placed in a container. The nonaqueous electrolyte was then poured into the container, which was then sealed, to obtain the nonaqueous electrolyte storage element of Example 1.

[0083] [Comparative Example 1] A nonaqueous electrolyte storage element of Comparative Example 1 was obtained in the same manner as in Example 1, except that graphite (Gr) was used instead of HC as the negative electrode active material.

[0084] [Examples 2 and 3, Comparative Examples 2 to 4] The nonaqueous electrolyte storage elements of Examples 2 and 3 and Comparative Examples 2 to 4 were obtained in the same manner as in Example 1, except that the specific surface area A of the lithium iron phosphate, which was the polyanion-based positive electrode active material, and the average particle size B of the HC, which was the non-graphitic carbon, were set as shown in Table 1.

[0085] [evaluation] (charging curve) For each of the nonaqueous electrolyte storage elements of Example 1 and Comparative Example 1, predetermined initial charge and discharge cycles were carried out, and then a charge curve (SOC-OCV curve) was obtained by the following procedure. Constant-current, constant-voltage charging was performed with a charging current of 1C and a cut-off voltage of 3.6V. The charging was terminated after a total charging time of 2 hours. Subsequently, a constant-current discharge was performed with a discharge current of 1C and a cut-off voltage of 2V, and the capacity at this time was recorded as the discharge capacity. The battery was then charged with 10% of the discharge capacity at a charging current of 1C, and then rested for 2 hours with the SOC at 10%. The average OCV (open circuit voltage) between 1.5 hours and 2 hours after the start of the rest period was recorded as the OCV at the corresponding SOC. The above charging with 10% of the discharge capacity and resting were repeated until the SOC reached 100%. The resulting charging curve (SOC-OCV curve) is shown in Figure 3. 3, the charge curve of the nonaqueous electrolyte energy storage element of Comparative Example 1, which is a combination of lithium iron phosphate and Gr, is relatively flat. In contrast, the charge curve of the nonaqueous electrolyte energy storage element of Example 1, which is a combination of lithium iron phosphate and HC, is inclined over a wide range of SOC, indicating that the SOC can be easily detected based on the voltage.

[0086] (Input performance) The input performance of each of the nonaqueous electrolyte energy storage elements of Examples 1 to 3 and Comparative Examples 2 to 4 was evaluated according to the following procedure. The elements were charged at a charging current of 1 C until the SOC reached 50%, discharged for 10 seconds at a discharging current of 15 C, and after a 10-minute rest period, charged at a charging current of 15 C for 10 seconds. Similarly, the discharging and charging currents were adjusted to 30 C and 45 C, and the input performance was determined from the battery voltage 10 seconds after the start of charging at each charging current. The results are shown in Table 1. Furthermore, FIG. 4 shows the specific surface area A (m ) of the polyanion-based positive electrode active material in each of the nonaqueous electrolyte energy storage elements of Examples 1 to 3 and Comparative Examples 2 to 4. 2 1 shows a graph in which the horizontal axis plots the ratio A / B of the average particle size B (μm) of the non-graphitic carbon and the input performance on the vertical axis.

[0087] [Table 1]

[0088] As shown in Table 1, the specific surface area A (m 2 The nonaqueous electrolyte energy storage elements of Examples 1 to 3, in which the ratio A / B of the carbon content (A / g) to the average particle size B (μm) of the non-graphitic carbon was 4 or more, exhibited high input performance, exceeding 1400 W. Also, Figure 4 shows that the ratio A / B is highly correlated with input performance. [Industrial Applicability]

[0089] The present invention is suitably used as a nonaqueous electrolyte storage element, including a nonaqueous electrolyte secondary battery used as a power source for electronic devices such as personal computers and communication terminals, automobiles, and the like. [Explanation of symbols]

[0090] 1. Non-aqueous electrolyte energy storage element 2 Electrode body 3 containers 4 Positive terminal 41 Positive lead 5 Negative terminal 51 Negative lead 20 Energy storage unit 30 Electricity storage device

Claims

1. A battery is provided with a positive electrode containing a polyanion-based positive electrode active material and a negative electrode containing non-graphitizable carbon as non-graphitic carbon, The specific surface area A (m 2 a ratio A / B of the particle size (A / g) of the non-graphitic carbon to the average particle size B (μm) of the non-graphitic carbon is 4 or more; the specific surface area A of the polyanionic positive electrode active material is 10 m 2 / g or more and 30 m 2 / g or less; The non-aqueous electrolyte electricity storage element has an average particle size B of the non-graphitic carbon of 0.5 μm or more and 4 μm or less.

2. The specific surface area A of the polyanion-based positive electrode active material is 14.0 m 2 The nonaqueous electrolyte electricity storage element according to claim 1 , wherein the nonaqueous electrolyte has a molecular weight of more than 1 / g.

3. 3. The nonaqueous electrolyte storage element according to claim 1, wherein the ratio A / B is 10 or less.

4. 4. The nonaqueous electrolyte electricity storage element according to claim 1, wherein the average particle size B of the non-graphitic carbon is 2.8 μm or less.

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