Non-aqueous electrolyte storage element, method for manufacturing same, and non-aqueous electrolyte

Abstract

To provide a non-aqueous electrolyte power storage element in which the occurrence of micro-shorts due to repeated charging and discharging is suppressed when a negative electrode contains metallic lithium, a manufacturing method of the same, and a non-aqueous electrolyte for lithium batteries in which the occurrence of micro-shorts can be suppressed.SOLUTION: The non-aqueous electrolyte power storage element includes a negative electrode containing metallic lithium and a non-aqueous electrolyte containing imide salt and phosphate ester. The content of the imide salt in the nonaqueous electrolyte above is 2 mol / kg or more.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a non-aqueous electrolyte storage element, a method for manufacturing the same, and a non-aqueous electrolyte.

Background Art

[0002] Non-aqueous electrolyte secondary batteries typified by lithium-ion secondary batteries are widely used in electronic devices such as personal computers and communication terminals, and automobiles because of their high energy density. The non-aqueous electrolyte secondary battery generally has a pair of electrodes electrically isolated by a separator and a non-aqueous electrolyte interposed between the electrodes, and is configured to charge and discharge by transferring ions between both electrodes. In addition, as non-aqueous electrolyte storage elements other than non-aqueous electrolyte secondary batteries, capacitors such as lithium-ion capacitors and electric double layer capacitors have also become widespread. As a negative electrode active material having a high energy density used in non-aqueous electrolyte storage elements, metallic lithium is known (see Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In non-aqueous electrolyte storage elements in which metallic lithium is used as a negative electrode active material, such as lithium batteries, metallic lithium may be deposited dendritically on the surface of the negative electrode during charging (hereinafter, metallic lithium in a dendritic form is referred to as "dendrite"). When this dendrite grows and penetrates the separator and contacts the positive electrode, a micro short circuit is caused. For this reason, non-aqueous electrolyte storage elements containing metallic lithium as a negative electrode active material have the disadvantage that a micro short circuit is likely to occur due to repeated charge and discharge.

[0005] The present invention has been made based on the above circumstances, and an object thereof is to provide a non-aqueous electrolyte storage element in which the occurrence of micro short circuits accompanying repeated charge and discharge is suppressed when the negative electrode contains metallic lithium, a method for manufacturing such a non-aqueous electrolyte storage element, and a non-aqueous electrolyte for a lithium battery capable of suppressing the occurrence of micro short circuits.

Means for Solving the Problems

[0006] One aspect of the present invention is a non-aqueous electrolyte storage element including a negative electrode containing metallic lithium and a non-aqueous electrolyte containing an imide salt and a phosphate ester, wherein the content of the imide salt in the non-aqueous electrolyte is 2 mol / kg or more.

[0007] Another aspect of the present invention is a method for manufacturing a non-aqueous electrolyte storage element including preparing a negative electrode containing metallic lithium and preparing a non-aqueous electrolyte containing an imide salt and a phosphate ester.

[0008] Another aspect of the present invention is a non-aqueous electrolyte for a lithium battery containing an imide salt and a phosphate ester, wherein the content of the imide salt is 2 mol / kg or more.

Effects of the Invention

[0009] According to one aspect of the present invention, it is possible to provide a non-aqueous electrolyte storage element in which the occurrence of micro short circuits accompanying repeated charge and discharge is suppressed when the negative electrode contains metallic lithium, a method for manufacturing such a non-aqueous electrolyte storage element, and a non-aqueous electrolyte for a lithium battery capable of suppressing the occurrence of micro short circuits.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0011] First, an overview of the non-aqueous electrolyte storage element, the method for manufacturing the non-aqueous electrolyte storage element, and the non-aqueous electrolyte disclosed by this specification will be described.

[0012] A non-aqueous electrolyte storage element according to one aspect of the present invention includes a negative electrode containing metallic lithium and a non-aqueous electrolyte containing an imide salt and a phosphate ester, and is a non-aqueous electrolyte storage element in which the content of the imide salt in the non-aqueous electrolyte is 2 mol / kg or more.

[0013] Even though the negative electrode of the non-aqueous electrolyte storage element contains metallic lithium, the occurrence of minute short circuits accompanying repeated charge and discharge is suppressed. That is, in the non-aqueous electrolyte storage element, the occurrence of minute short circuits caused by repeated charge and discharge is delayed. The reason for this is not clear, but it is presumed that because the non-aqueous electrolyte contains a high concentration of imide salt and phosphate ester, the film formed on the surface of the negative electrode becomes of good quality that suppresses the growth of dendrites.

[0014] It is preferable that the phosphate ester is a fluorinated phosphate ester. When the phosphate ester is a fluorinated phosphate ester, the occurrence of minute short circuits accompanying repeated charge and discharge is more suppressed.

[0015] It is preferable that the non-aqueous electrolyte further contains at least one of carbonate and ether, and it is more preferable that the non-aqueous electrolyte further contains ether. When the non-aqueous electrolyte contains carbonate or ester, the occurrence of minute short circuits accompanying repeated charge and discharge is more suppressed. The reason for this is not clear, but it is presumed that when the non-aqueous electrolyte contains carbonate or ester, it affects the decrease in the viscosity of the non-aqueous electrolyte and the increase in ionic conductivity.

[0016] A method for manufacturing a non-aqueous electrolyte storage element according to one aspect of the present invention includes preparing a negative electrode containing metallic lithium and preparing a non-aqueous electrolyte containing an imide salt and a phosphate ester.

[0017] According to this manufacturing method, even though the negative electrode contains metallic lithium, it is possible to manufacture a non-aqueous electrolyte storage element in which the occurrence of micro short circuits associated with repeated charge and discharge is suppressed.

[0018] A non-aqueous electrolyte according to one aspect of the present invention contains an imide salt and a phosphate ester, and is a non-aqueous electrolyte for a lithium battery in which the content of the imide salt is 2 mol / kg or more.

[0019] According to this non-aqueous electrolyte, it is possible to suppress the occurrence of micro short circuits associated with repeated charge and discharge in a lithium battery.

[0020] Hereinafter, a non-aqueous electrolyte storage element, a method for manufacturing a non-aqueous electrolyte storage element, and a non-aqueous electrolyte according to one embodiment of the present invention will be described in order.

[0021] <Non-aqueous electrolyte storage element> A non-aqueous electrolyte storage element according to one embodiment of the present invention has a positive electrode, a negative electrode, and a non-aqueous electrolyte. Hereinafter, as an example of a non-aqueous electrolyte storage element, a non-aqueous electrolyte secondary battery (hereinafter, also simply referred to as a "secondary battery") will be described. The positive electrode and the negative electrode usually form an electrode body that is alternately stacked or wound via a separator. This electrode body is housed in a container, and the container is filled with a non-aqueous electrolyte. The non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. As the container, a known metal container, resin container, etc. that are usually used as a container for a secondary battery can be used.

[0022] (Positive electrode) The positive electrode has a positive electrode substrate and a positive electrode active material layer disposed directly or via an intermediate layer on the positive electrode substrate.

[0023] The positive electrode substrate has conductivity. Having "conductivity" means that the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 7 Ω·cm or less, and "non-conductive" means that the above volume resistivity is more than 10 7 Ω·cm. As the material of the positive electrode substrate, metals such as aluminum, titanium, tantalum, and stainless steel, or their alloys are used. Among these, aluminum and aluminum alloys are preferred in terms of the balance of potential resistance, high conductivity, and cost. Also, as the form of the positive electrode substrate, a foil, a vapor deposition film, etc. can be mentioned, and a foil is preferred in terms of cost. That is, an aluminum foil is preferred as the positive electrode substrate. Note that examples of aluminum or aluminum alloy include A1085P, A3003P, etc. defined in JIS-H-4000 (2014).

[0024] The average thickness of the positive electrode substrate is preferably 3 μm or more and 50 μm or less, more preferably 5 μm or more and 40 μm or less, still more preferably 8 μm or more and 30 μm or less, and particularly preferably 10 μm or more and 25 μm or less. By setting the average thickness of the positive electrode substrate within the above range, it is possible to increase the strength of the positive electrode substrate and at the same time increase the energy density per volume of the secondary battery. "Average thickness" refers to the value obtained by dividing the punching mass when punching out a substrate of a predetermined area by the true density and punching area of the substrate. Hereinafter, the same applies to the "average thickness" of the negative electrode substrate and the negative electrode active material layer described later.

[0025] The intermediate layer is a coating layer on the surface of the positive electrode substrate, and contains conductive particles 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 can be formed, for example, by a composition containing a resin binder and conductive particles.

[0026] The positive electrode active material layer is a layer formed from a so-called positive electrode mixture containing a positive electrode active material. The positive electrode mixture forming the positive electrode active material layer may contain optional components such as a conductive agent, a binder, a thickener, and a filler as necessary.

[0027] The positive electrode active material can be appropriately selected from known positive electrode active materials. As the positive electrode active material for a lithium secondary battery, a material that can occlude and release lithium ions is usually used. Examples of the positive electrode active material include lithium transition metal composite oxides having an α-NaFeO2-type crystal structure, lithium transition metal composite oxides having a spinel-type crystal structure, polyanion compounds, chalcogen compounds, sulfur, and the like. Examples of the lithium transition metal composite oxide having an α-NaFeO2-type crystal structure include Li[Li x Ni 1-x O2 (0 ≦ x < 0.5), Li[Li x Ni γ Co 1-x-γ O2 (0 ≦ x < 0.5, 0 < γ < 1), Li[Li x Co 1-x O2 (0 ≦ x < 0.5), Li[Li x Ni γ Mn 1-x-γ O2 (0 ≦ x < 0.5, 0 < γ < 1), Li[Li x Ni γ Mn β Co 1-x-γ-β O2 (0 ≦ x < 0.5, 0 < γ, 0 < β, 0.5 < γ + β < 1), Li[Li x Ni γ Co β Al 1-x-γ-β O2 (0 ≦ x < 0.5, 0 < γ, 0 < β, 0.5 < γ + β < 1), etc. Examples of the lithium transition metal composite oxide having a spinel-type crystal structure include Li x Mn2O4, Li x Ni γ Mn 2-γExamples include O4. Examples of the polyanion compound include LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, Li2CoPO4F, etc. Examples of the chalcogen compound include titanium disulfide, molybdenum disulfide, molybdenum dioxide, etc. Atoms or polyanions in these materials may be partially substituted with atoms or anion species composed of other elements. The surfaces of these materials may be coated with other materials. In the positive electrode active material layer, one of these materials may be used alone, or two or more of them may be mixed and used.

[0028] As the positive electrode active material, a lithium transition metal composite oxide is preferable, and a lithium transition metal composite oxide having an α-NaFeO2 type crystal structure is more preferable. The lithium transition metal composite oxide preferably contains nickel or manganese as the transition metal, and more preferably contains both nickel and manganese. The lithium transition metal composite oxide may further contain other transition metals such as cobalt. In the lithium transition metal composite oxide having an α-NaFeO2 type crystal structure, the molar ratio (Li / Me) of lithium (Li) to the transition metal (Me) is preferably greater than 1, more preferably 1.1 or more, still more preferably 1.2 or more, and most preferably 1.3 or more. By using such a lithium transition metal composite oxide, the capacitance can be increased. In the case of a non-aqueous electrolyte storage element using such a positive electrode active material, it tends to be used at a high current density, and usually, dendrites are likely to grow. Therefore, in the case of a non-aqueous electrolyte storage element including a positive electrode having the above lithium transition metal composite oxide, the effect of suppressing the occurrence of micro short circuits accompanying repeated charge and discharge can be more remarkably obtained. The upper limit of the molar ratio (Li / Me) of lithium to the transition metal is preferably 1.6, and more preferably 1.5.

[0029] As the lithium transition metal composite oxide having an α-NaFeO2 type crystal structure, a compound represented by the following formula (1) is preferable. Li 1+α Me 1-α O2···(1) In formula (1), Me is a transition metal containing Ni or Mn, and 0 < α < 1.

[0030] Me in formula (1) preferably contains Ni and Mn. Me is preferably composed substantially of two elements, Ni and Mn, or three elements, Ni, Mn, and Co. Me may contain other transition metals.

[0031] In formula (1), the lower limit of the molar ratio of Ni to Me (Ni / Me) is preferably 0.1, more preferably 0.2. On the other hand, the upper limit of this molar ratio (Ni / Me) is preferably 0.5, more preferably 0.45. By setting the molar ratio (Ni / Me) within the above range, the energy density is improved.

[0032] In formula (1), the lower limit of the molar ratio of Mn to Me (Mn / Me) is preferably 0.5, more preferably 0.55, still more preferably 0.6. On the other hand, the upper limit of this molar ratio (Mn / Me) is preferably 0.75, more preferably 0.7. By setting the molar ratio (Mn / Me) within the above range, the energy density is improved.

[0033] In formula (1), the upper limit of the molar ratio of Co to Me (Co / Me) is preferably 0.3, more preferably 0.2, still more preferably 0.1. The lower limit of this molar ratio (Co / Me) may be 0.

[0034] In formula (1), the molar ratio of Li to Me, i.e., (1 + α) / (1 - α), is preferably greater than 1.0 (α > 0), more preferably 1.1 or more, still more preferably 1.2 or more, even more preferably 1.3 or more. On the other hand, the upper limit of this molar ratio (Li / Me) is preferably 1.6, more preferably 1.5. By setting the molar ratio (Li / Me) within the above range, the capacitance increases.

[0035] It is preferable that the lithium transition metal composite oxide in which the molar ratio of lithium (Li) to the above transition metal (Me) (Li / Me) exceeds 1 has no diffraction peak in the range of 20° or more and 22° or less in the X-ray diffraction pattern using CuKα rays. The lithium transition metal composite oxide in which the molar ratio of lithium (Li) to the transition metal (Me) (Li / Me) exceeds 1 generally has an initial charge-discharge up to an initial charge-discharge until the positive electrode potential reaches, for example, 4.5V vs. Li / Li + The capacitance increases by undergoing the initial charge-discharge. Further, due to the change in the crystal structure during such initial charge-discharge, the diffraction peak that existed in the range of 20° or more and 22° or less before the initial charge-discharge disappears. That is, a lithium transition metal composite oxide in which the molar ratio of lithium (Li) to the transition metal (Me) (Li / Me) exceeds 1 and in which there is no diffraction peak in the range of 20° or more and 22° or less in the above X-ray diffraction pattern has a large capacitance as an active material.

[0036] In addition, the composition ratio of the lithium transition metal composite oxide in this specification refers to the composition ratio when it is in a fully discharged state by the following method. First, the non-aqueous electrolyte storage element is charged at a constant current with a current of 0.05C until it reaches the charge termination voltage during normal use to make it in a fully charged state. After a 30-minute rest, it is discharged at a constant current with a current of 0.05C to the lower limit voltage during normal use. It is disassembled, the positive electrode is taken out, a test cell is assembled with a metal lithium electrode as the counter electrode, and at a current value of 10 mA per 1 g of the positive electrode mixture, the positive electrode potential is 2.0V vs. Li / Li +Constant current discharge is performed until it reaches a certain state, and the positive electrode is adjusted to a fully discharged state. Here, for the metallic lithium electrode, pure metallic lithium is used instead of a lithium alloy. It is disassembled again, and the positive electrode is taken out. Using dimethyl carbonate, the non-aqueous electrolyte adhering to the taken-out positive electrode is thoroughly washed, dried at room temperature for a whole day and night, and then the lithium transition metal composite oxide of the positive electrode active material is collected. The collected lithium transition metal composite oxide is used for measurement. The operations from the disassembly to the measurement of the non-aqueous electrolyte storage element are carried out in an argon atmosphere with a dew point of -60°C or lower. Here, normal use means the case where the non-aqueous electrolyte storage element is used by adopting the charge-discharge conditions recommended or specified for the non-aqueous electrolyte storage element, and when a charger for the non-aqueous electrolyte storage element is prepared, it means the case where the non-aqueous electrolyte storage element is used by applying that charger.

[0037] X-ray diffraction measurement of the lithium transition metal composite oxide is performed on the lithium transition metal composite oxide in a fully discharged state by the above method. Specifically, the X-ray diffraction measurement is carried out by powder X-ray diffraction measurement using an X-ray diffractometer (Rigaku's "MiniFlex II"), with the radiation source being CuKα ray, the tube voltage being 30 kV, and the tube current being 15 mA. At this time, the diffracted X-ray passes through a Kβ filter with a thickness of 30 μm and is detected by a high-speed one-dimensional detector (D / teX Ultra 2). Also, the sampling width is 0.02°, the scan speed is 5° / min, the divergence slit width is 0.625°, the receiving slit width is 13 mm (OPEN), and the scattering slit width is 8 mm.

[0038] The lower limit of the content of the above lithium transition metal composite oxide with respect to all the positive electrode active materials is preferably 50% by mass, more preferably 80% by mass, and even more preferably 95% by mass. The content of the above lithium transition metal composite oxide with respect to all the positive electrode active materials may be 100% by mass.

[0039] The average particle size of the 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 positive electrode active material to be not less than the above lower limit, the production or handling of the positive electrode active material becomes easy. By setting the average particle size of the positive electrode active material to be not more than the above upper limit, the electron conductivity of the positive electrode active material layer is improved. Here, the "average particle size" is based on the particle size distribution measured by the laser diffraction / scattering method for a dilution obtained by diluting particles with a solvent in accordance with JIS-Z-8825 (2013), and is calculated in accordance with JIS-Z-8819-2 (2001). It means the value at which the volume-based integrated distribution becomes 50%.

[0040] In order to obtain the particles of the positive electrode active material in a predetermined shape, a pulverizer, a classifier, etc. are used. As the pulverization method, for example, methods using a mortar, a ball mill, a sand mill, a vibration ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling air flow type jet mill, a sieve, etc. can be mentioned. At the time of pulverization, wet pulverization in which water or an organic solvent such as hexane coexists can also be used. As the classification method, a sieve, an air classifier, etc. are used as needed for both dry and wet methods.

[0041] The content of the positive electrode active material in the positive electrode active material layer is preferably 70% by mass or more and 98% by mass or less, more preferably 80% by mass or more and 97% by mass or less, and even more preferably 90% by mass or more and 96% by mass or less. By setting the content of the positive electrode active material within the above range, the electric capacity of the secondary battery can be increased.

[0042] The conductive agent is not particularly limited as long as it is a material having conductivity. Examples of such a conductive agent include carbonaceous materials; metals; conductive ceramics, etc. Examples of the carbonaceous materials include graphite and carbon black. Examples of the types of carbon black include furnace black, acetylene black, ketjen black, etc. Among these, from the viewpoints of conductivity and coatability, carbonaceous materials are preferred. Among them, acetylene black and ketjen black are preferred. Examples of the shape of the conductive agent include powder, sheet, fiber, etc.

[0043] The content of the conductive agent in the positive electrode active material layer is preferably 1% by mass or more and 40% by mass or less, more preferably 2% by mass or more and 10% 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.

[0044] Examples of the binder include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, and polyimide; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers.

[0045] The content of the binder in the positive electrode active material layer is preferably 0.5% by mass or more and 10% by mass or less, more preferably 1% by mass or more and 6% by mass or less. By setting the content of the binder within the above range, the active material can be stably held.

[0046] Examples of the thickener include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. When the thickener has a functional group that reacts with lithium, it is preferably deactivated in advance by methylation or the like. In one aspect of the present invention, it may be preferable that the thickener is not contained in the positive electrode active material layer.

[0047] The filler is not particularly limited. Examples of the filler include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silicon dioxide, aluminum oxide, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicate, hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide, carbonates such as calcium carbonate, sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate, nitrides such as aluminum nitride and silicon nitride, mineral resource-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof. In one aspect of the present invention, it may be preferable that the filler is not contained in the positive electrode active material layer.

[0048] The positive electrode active material layer may contain typical non-metal elements such as B, N, P, F, Cl, Br, and I, typical metal 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, and Nb as components other than the positive electrode active material, conductive agent, binder, thickener, and filler.

[0049] (Negative electrode) The negative electrode has a negative electrode substrate and a negative electrode active material layer disposed directly or via an intermediate layer on the negative electrode substrate. The intermediate layer of the negative electrode can have the same configuration as the intermediate layer of the positive electrode.

[0050] The negative electrode substrate can have the same configuration as the positive electrode substrate. As the material, metals such as copper, nickel, stainless steel, and nickel-plated steel or their alloys, carbonaceous materials, etc. are used, and copper or a copper alloy is preferable. That is, a copper foil is preferable as the negative electrode substrate. Examples of the copper foil include rolled copper foil and electrolytic copper foil.

[0051] The average thickness of the negative electrode substrate is preferably 2 μm or more and 35 μm or less, more preferably 3 μm or more and 30 μm or less, still more preferably 4 μm or more and 25 μm or less, and particularly preferably 5 μm or more and 20 μm or less. By setting the average thickness of the negative electrode substrate within the above range, it is possible to increase the strength of the negative electrode substrate while increasing the energy density per unit volume of the secondary battery.

[0052] The negative electrode active material layer contains metallic lithium. That is, the secondary battery of the present embodiment is a lithium battery. Metallic lithium is a component that functions as a negative electrode active material. Metallic lithium may exist as pure metallic lithium consisting essentially of only lithium element, or may exist as a lithium alloy containing other metal elements. Examples of the lithium alloy include lithium-silver alloy, lithium-zinc alloy, lithium-calcium alloy, lithium-aluminum alloy, lithium-magnesium alloy, lithium-indium alloy, and the like. The lithium alloy may contain a plurality of metal elements other than lithium.

[0053] The negative electrode active material layer may be a layer consisting essentially of only metallic lithium. The content of metallic lithium in the negative electrode active material layer may be 90% by mass or more, may be 99% by mass or more, or may be 100% by mass.

[0054] The negative electrode active material layer may be a metallic lithium foil or a lithium alloy foil. The negative electrode active material layer may be a non-porous layer (solid layer). The average thickness of the negative electrode active material layer is preferably 5 μm or more and 1,000 μm or less, more preferably 10 μm or more and 500 μm or less, and still more preferably 30 μm or more and 300 μm or less.

[0055] (Separator) The separator can be appropriately selected from known separators. As the separator, for example, a separator composed only of a base material layer, a separator having a heat-resistant layer containing heat-resistant particles and a binder formed on one or both surfaces of the base material layer, etc. can be used. The base material layer of the separator may contain heat-resistant particles. Examples of the material of the base material layer of the separator include woven fabric, non-woven fabric, porous resin film, etc. Among these materials, a porous resin film is preferable from the viewpoint of strength, and a non-woven fabric is preferable from the viewpoint of the liquid retention property of the non-aqueous electrolyte. As the material of the base material layer of the separator, polyolefins such as polyethylene and polypropylene are preferable from the viewpoint of the shutdown function, and polyimides and aramids, etc. are preferable from the viewpoint of oxidation decomposition resistance. As the base material layer of the separator, a material obtained by compounding these resins may be used.

[0056] The heat-resistant particles contained in the heat-resistant layer and the base material layer preferably have a mass loss of 5% or less when heated from room temperature to 500 °C in air, and more preferably have a mass loss of 5% or less when heated from room temperature to 800 °C in air. Inorganic compounds are mentioned as materials having a mass loss of a predetermined value or less when heated. Examples of inorganic compounds include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, barium titanate, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, aluminosilicate; hydroxides such as magnesium hydroxide, calcium hydroxide, aluminum hydroxide; nitrides such as aluminum nitride, silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride; covalent crystals such as silicon, diamond; mineral resource-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, mica, or artificial products thereof, etc. As inorganic compounds, these substances may be used alone as a simple substance or a composite, or two or more kinds may be mixed and used. Among these inorganic compounds, from the viewpoint of the safety of the electrical storage element, silicon oxide, aluminum oxide, or aluminosilicate is preferable.

[0057] From the viewpoint of strength, the porosity of the separator is preferably 80% by volume or less, and from the viewpoint of discharge performance, it is preferably 20% by volume or more. Here, the "porosity" is a value based on volume and means the measured value by a mercury porosimeter.

[0058] As the separator, a polymer gel composed of a polymer and a non-aqueous electrolyte may be used. Examples of the polymer include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polyethylene carbonate, polypropylene carbonate, polyvinyl carbonate, polyalkyl methacrylates such as polymethyl methacrylate, polyalkyl acrylates such as polymethyl acrylate, polyvinyl ethylene carbonate, polyvinyl acetate, polyvinyl pyrrolidone, polymaleic acid and its derivatives, polyvinylidene fluoride, vinylidene fluoride - hexafluoropropylene copolymer, polytetrafluoroethylene, etc., and copolymers of monomers constituting these polymers, and mixtures of these polymers. These polymers may also be combined with inorganic salts or ionic liquids. Using a polymer gel has the effect of suppressing liquid leakage. As the separator, a porous resin film or non-woven fabric as described above and a polymer gel may be used in combination.

[0059] (Non-aqueous electrolyte) The non-aqueous electrolyte contains an imide salt and a phosphate ester. The non-aqueous electrolyte usually contains a non-aqueous solvent and an electrolyte salt dissolved in this non-aqueous solvent. The imide salt may be contained in the non-aqueous electrolyte as an electrolyte salt. The phosphate ester is usually contained in the non-aqueous electrolyte as a non-aqueous solvent. The non-aqueous electrolyte may further contain an electrolyte salt other than the imide salt, a non-aqueous solvent other than the phosphate ester, and additives, etc.

[0060] (Imide salt and other electrolyte salts) Examples of the imide salt include lithium imide salt, sodium imide salt, potassium imide salt, magnesium imide salt, imide salt having an onium ion, etc., and the lithium imide salt is preferred.

[0061] Examples of the lithium imide salts include symmetric lithium sulfonyl imide salts such as LiN(SO2F)2 (lithium bis(fluorosulfonyl)imide: LiFSI), LiN(CF3SO2)2 (lithium bis(trifluoromethanesulfonyl)imide: LiTFSI), LiN(C2F5SO2)2 (lithium bis(pentafluoroethanesulfonyl)imide: LiBETI), LiN(C4F9SO2)2 (lithium bis(nonafluorobutanesulfonyl)imide), CF3-SO2-N-SO2-N-SO2-CF3Li, CF3-SO2-N-SO2-CF2-SO2-N-SO2-CF3Li2, etc.; and asymmetric lithium sulfonyl imide salts such as LiN(SO2F)(SO2CF3) (lithium (fluorosulfonyl)(trifluoromethanesulfonyl)imide), LiN(SO2F)(SO2C2F5) (lithium (fluorosulfonyl)(pentafluoroethanesulfonyl)imide), LiN(SO2F)(SO2C4F9) (lithium (fluorosulfonyl)(nonafluorobutanesulfonyl)imide), LiN(SO2CF3)(SO2C4F9) (lithium (trifluoromethanesulfonyl)(nonafluorobutanesulfonyl)imide), FSO2-N-SO2-C4F9Li, CF3-SO2-N-SO2-C4F9Li, CF3-SO2-N-SO2-CF2-SO3Li2, CF3-SO2-N-SO2-CF2-SO2-C(-SO2CF3)2Li2, etc.; and lithium phosphonyl imide salts such as LiN(POF2)2 (lithium bis(difluorophosphonyl)imide: LiDFPI), etc. Lithium sulfonyl imide salts (symmetric lithium sulfonyl imide salts and asymmetric lithium sulfonyl imide salts) are preferred. One or more lithium imide salts can be used.

[0062] The imide salt preferably has a fluorine atom, and specifically, for example, preferably has a fluorosulfonyl group, a difluorophosphonyl group, a fluoroalkyl group, etc. As the imide salt, a bis(fluorosulfonyl)imide salt such as LiFSI is preferable. By using such an imide salt, the generation of micro short circuits accompanying repeated charge and discharge can be more suppressed due to, for example, the formed film becoming of better quality.

[0063] The content of the imide salt in the non-aqueous electrolyte (the molality of the imide salt in the non-aqueous electrolyte) is 2 mol / kg or more. The content (molality) of this imide salt may be 2 mol / kg or more and 5 mol / kg or less, may preferably be 2.5 mol / kg or more and 4.5 mol / kg or less, and may more preferably be 3 mol / kg or more and 4 mol / kg or less. By setting the content of the imide salt to be equal to or higher than the above lower limit, a good-quality film can be sufficiently formed, etc., so that the generation of micro short circuits accompanying repeated charge and discharge can be suppressed. On the other hand, by setting the content of the imide salt to be equal to or lower than the above upper limit, the ionic conductivity of the non-aqueous electrolyte can be increased, and the generation of micro short circuits accompanying repeated charge and discharge can be more suppressed.

[0064] The non-aqueous electrolyte may further contain other conventionally known electrolyte salts other than the imide salt. Examples of other electrolyte salts include lithium salts such as LiPF6, LiPO2F2, LiBF4, and LiClO4. However, the content ratio of the imide salt to all the electrolyte salts may preferably be 50 mol% or more, may more preferably be 90 mol%, and may further preferably be 99 mol% or more or 100 mol%. By using the imide salt as the main electrolyte salt, the effect of suppressing the generation of micro short circuits accompanying repeated charge and discharge can be further enhanced.

[0065] (Phosphate ester) The phosphate ester is a compound in which some or all of the three hydrogen atoms of phosphoric acid (O=P(OH)3) are substituted with organic groups. Examples of the above organic groups include hydrocarbon groups and halogenated hydrocarbon groups. The above organic group is an alkoxyalkyl group (Ra -O-R b -:R a where R is a monovalent hydrocarbon group and R is a divalent hydrocarbon group. A group other than a group containing an ether bond such as ()) may be preferred. b Groups other than those containing an ether bond such as ()) may be preferred.

[0066] As the phosphate ester, a halogenated phosphate ester is preferably used, and a fluorinated phosphate ester is more preferably used. By using such a phosphate ester, the occurrence of micro short circuits associated with repeated charge and discharge is further suppressed. A halogenated phosphate ester is a phosphate ester containing a halogen, and a fluorinated phosphate ester is a phosphate ester containing a fluorine atom.

[0067] As one form of a suitable phosphate ester, a compound represented by O=P(OR 1 )(OR 2 )(OR 3 )(R 1 where R, R 2 and R 3 are each independently a hydrocarbon group or a halogenated hydrocarbon group.

[0068] R 1 R 2 and R 3 The hydrocarbon group represented by may be either an aliphatic hydrocarbon group or an aromatic hydrocarbon group. Examples of the aliphatic hydrocarbon group include alkyl groups such as methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, n-pentyl group, alkenyl groups such as ethenyl group (vinyl group), 1-propenyl group, 2-propenyl group (allyl group), alkynyl groups such as ethynyl group, propynyl group, and cycloalkyl groups such as cyclohexyl group. Examples of the aromatic hydrocarbon group include phenyl group, tolyl group.

[0069] R 1 R 2 and R 3Examples of the halogenated hydrocarbon group represented by the formula (I) include the above-mentioned hydrocarbon groups in which some or all of the hydrogen atoms have been substituted with halogen atoms such as fluorine atoms, chlorine atoms, bromine atoms, etc. As the halogen atom, fluorine atoms are preferred.

[0070] R 1 , R 2 and R 3 As the group, an aliphatic hydrocarbon group and a fluorinated aliphatic hydrocarbon group are preferable, an alkyl group, an alkenyl group, a fluoroalkyl group and a fluoroalkenyl group are more preferable, a fluoroalkyl group and a fluoroalkenyl group are further preferable, and a fluoroalkyl group is particularly preferable.

[0071] R 1 , R 2 and R 3 The number of carbon atoms may be, for example, 1 or more and 12 or less, preferably 1 or more and 6 or less, and more preferably 2 or more and 4 or less.

[0072] R 1 , R 2 and R 3 When R is a halogenated hydrocarbon group, 1 , R 2 and R 3 The number of halogen atoms contained in is preferably 1 or more and 12 or less, and more preferably 2 or more and 8 or less.

[0073] Examples of phosphate esters include O=P(OCH3)3, O=P(OCH2CH3)3, O=P(OCH2CFH2)3, O=P(OCH2CF2H)3, O=P(OCH2CF3)3, O=P(OCH3)2(OCH2CF3), O=P(OCH3)(OCH2CF3)2, O=P(OCH2CH3)2(OCH2CF3), O=P(OCH2CH3)(OCH2CF3)2, O=P(OCH2CH2CH3)3, O=P(OCH2CF2CF2H)3, O=P(OCH2CF2CF3)3, O=P(OCH2CH=CH2)3, O=P(OCH(CH3)2), O=P(OCH(CF3)2), and O=P(OC(CH3)3).

[0074] The content of the phosphate ester in the entirely non-aqueous solvent (phosphate ester and other non-aqueous solvents) is preferably 1% by volume or more and 80% by volume or less, more preferably 3% by volume or more and 60% by volume or less, still more preferably 5% by volume or more and 40% by volume or less, and even more preferably 10% by volume or more and 30% by volume or less. By setting the content of the phosphate ester to be not less than the above lower limit, a coating film with sufficient quantity and quality is formed, and the occurrence of micro short circuits accompanying repeated charge and discharge is more suppressed. On the other hand, by setting the content of the phosphate ester with relatively high viscosity to be not more than the above upper limit, the increase in the viscosity of the non-aqueous electrolyte is suppressed, and as a result, the ionic conductivity increases, and the occurrence of micro short circuits accompanying repeated charge and discharge is more suppressed.

[0075] (Other non-aqueous solvents) The non-aqueous electrolyte preferably contains other non-aqueous solvents other than the phosphate ester. Examples of other non-aqueous solvents include carbonates (linear carbonates and cyclic carbonates), esters (excluding phosphate esters), ethers, amides, sulfones, lactones, nitriles, etc. These may have substituents. Among these, carbonates and ethers are preferred. That is, the non-aqueous electrolyte preferably contains at least one of carbonate and ether, more preferably contains ether, and still more preferably contains both carbonate and ether. By using such a non-aqueous solvent together with the phosphate ester, the increase in viscosity caused by the phosphate ester is suppressed, and as a result, the ionic conductivity increases, and the occurrence of micro short circuits accompanying repeated charge and discharge is more suppressed.

[0076] Examples of linear carbonates include diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, diphenyl carbonate, 2,2,2-trifluoroethyl methyl carbonate, bis(2,2,2-trifluoroethyl) carbonate, ethyl-2,2,2-trifluoroethyl carbonate, etc. The number of carbon atoms of the linear carbonate may be, for example, 3 or more and 13 or less, and may also be 7 or less or 5 or less.

[0077] As the chain carbonate, from the viewpoint of oxidation resistance and the like, fluorinated chain carbonates such as 2,2,2-trifluoroethyl methyl carbonate, bis(2,2,2-trifluoroethyl) carbonate, and ethyl-2,2,2-trifluoroethyl carbonate are preferred.

[0078] Examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, vinyl ethylene carbonate, chloroethylene carbonate, fluoroethylene carbonate (FEC), difluoroethylene carbonate (including trans form, cis form, and mixtures thereof), 4-(fluoromethyl)-1,3-dioxolan-2-one, 4-(difluoromethyl)-1,3-dioxolan-2-one, trifluoropropyl carbonate, 4-(trifluoroethyl)-1,3-dioxolan-2-one, styrene carbonate, catechol carbonate, phenylvinylene carbonate, 1,2-diphenylvinylene carbonate, and the like. The number of carbon atoms of the cyclic carbonate may be, for example, 3 or more and 13 or less, and may also be 7 or less or 5 or less.

[0079] As the cyclic carbonate, from the viewpoint of oxidation resistance and the like, fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), difluoroethylene carbonate, 4-(fluoromethyl)-1,3-dioxolan-2-one, 4-(difluoromethyl)-1,3-dioxolan-2-one, trifluoropropyl carbonate, 4-(trifluoroethyl)-1,3-dioxolan-2-one are preferred.

[0080] The content of carbonate in the total non-aqueous solvent is preferably 20% by volume or more and 95% by volume or less, more preferably 40% by volume or more and 90% by volume or less, and even more preferably 60% by volume or more and 85% by volume or less. Also, the content of linear carbonate in the total non-aqueous solvent is preferably 30% by volume or more and 80% by volume or less, and more preferably 50% by volume or more and 75% by volume or less. The content of cyclic carbonate in the total non-aqueous solvent is preferably 3% by volume or more and 40% by volume or less, and more preferably 5% by volume or more and 20% by volume or less. When the content of carbonate (linear carbonate and cyclic carbonate) is within the above range, the viscosity and ionic conductivity are optimized, and the occurrence of micro short circuits during repeated charge and discharge is more suppressed.

[0081] The non-aqueous solvent preferably contains a linear carbonate and a cyclic carbonate. The volume ratio of the linear carbonate to the cyclic carbonate (linear carbonate: cyclic carbonate) is preferably, for example, 50:50 or more and 90:10 or less.

[0082] Examples of the ether include dimethyl ether, ethyl methyl ether, diethyl ether, methyl propyl ether, methyl butyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TFEE), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE), methyl heptafluoropropyl ether, methyl nonafluorobutyl ether, 1,2-dimethoxyethane (DME), diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran (THF), 1,4-dioxane (DOL), etc. The ether is preferably a dialkyl ether and a bisfluoroalkyl ether. From the viewpoint of viscosity and the like, the number of carbon atoms of the ether may be, for example, 2 or more and 8 or less, and preferably 3 or more and 6 or less.

[0083] As the ether, from the viewpoint of oxidation resistance and the like, fluorinated ethers such as 1,1,2,2 - tetrafluoroethyl - 2,2,2 - trifluoroethyl ether, methylheptafluoropropyl ether, and methylnonafluorobutyl ether are preferred.

[0084] The content of the ether in the total non - aqueous solvent is preferably 3% by volume or more and 40% by volume or less, more preferably 5% by volume or more and 20% by volume or less, and even more preferably 7% by volume or more and 15% by volume or less. When the content of the ether is within the above range, the viscosity and ionic conductivity are optimized, and the occurrence of micro - short - circuits accompanying repeated charge and discharge is more suppressed.

[0085] The total content of the fluorinated solvents in the total non - aqueous solvent is preferably 60% by volume or more, more preferably 90% by volume or more, even more preferably 99% by volume or more, and particularly preferably 100% by volume. The fluorinated solvent refers to a solvent (non - aqueous solvent) having a fluorine atom in the molecule, such as fluorinated phosphate ester, fluorinated carbonate (fluorinated linear carbonate and fluorinated cyclic carbonate), and fluorinated ether. By setting the total content of the fluorinated solvent to be not less than the above lower limit, the suppression of micro - short - circuits accompanying repeated charge and discharge, oxidation resistance, etc. can be further enhanced.

[0086] In addition, the content of other non - aqueous solvents other than phosphate ester in the total non - aqueous solvent is preferably 20% by volume or more and 99% by volume or less, more preferably 40% by volume or more and 97% by volume or less, even more preferably 60% by volume or more and 95% by volume or less, and even more preferably 70% by volume or more and 90% by volume or less. By setting the content of other non - aqueous solvents within the above range, the action of forming a high - quality film due to the presence of phosphate ester and the action of optimizing the viscosity, etc. of the non - aqueous solvent occur in a well - balanced manner, and the occurrence of micro - short - circuits accompanying repeated charge and discharge is more suppressed.

[0087] The non-aqueous electrolyte may contain an additive. Examples of the additive include aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, dibenzofuran; partial halides of the above aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, 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-propenesultone, 1,3-propanesultone, 1,4-butanesultone, 1,4-butenesultone, perfluorooctane, tris(trimethylsilyl) borate, tris(trimethylsilyl) phosphite, tris(trimethylsilyl) phosphate, tetrakis(trimethylsilyl) titanate, etc. These additives may be used alone or in combination of two or more.

[0088] The content of the additive contained in the non-aqueous electrolyte is preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.1% by mass or more and 7% by mass or less, still more preferably 0.2% by mass or more and 5% by mass or less, and particularly preferably 0.3% by mass or more and 3% by mass or less with respect to the whole non-aqueous electrolyte. By setting the content of the additive within the above range, the capacity retention performance or charge-discharge cycle performance after high-temperature storage can be improved, or the safety can be further improved.

[0089] As the lower limit of the ionic conductivity of the non-aqueous electrolyte, 9.0×10 -4 S / cm is preferable, and 1.0×10 -3S / cm is more preferable. The upper limit of this ionic conductivity may be, for example, 1.0×10 -2 S / cm.

[0090] In the secondary battery (non-aqueous electrolyte storage element), the positive electrode potential at the end-of-charge voltage during normal use is preferably 4.30 V vs. Li / Li + or higher, more preferably 4.35 V vs. Li / Li + or higher, and even more preferably 4.40 V vs. Li / Li + in some cases. By setting the positive electrode potential at the end-of-charge voltage during normal use to be not less than the above lower limit, the discharge capacity can be increased and the energy density can be enhanced.

[0091] Note that "during normal use" refers to the case where the non-aqueous electrolyte storage element is used under the charging conditions recommended or specified for the non-aqueous electrolyte storage element. For example, when a charger for the non-aqueous electrolyte storage element is available, it refers to the case where the non-aqueous electrolyte storage element is used by applying the charger.

[0092] The upper limit of the positive electrode potential at the end-of-charge voltage during normal use of the secondary battery is, for example, 5.0 V vs. Li / Li + and may be 4.8 V vs. Li / Li + or may be 4.7 V vs. Li / Li + or may be 4.6 V vs. Li / Li + or may be.

[0093] Dendrites tend to grow when the current density during charging is high. Therefore, the non-aqueous electrolyte storage element according to an embodiment of the present invention can be suitably applied to applications where charging with a high current density is performed. Such applications include power sources for automobiles such as electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and power sources for regenerative power charging.

[0094] The shape of the non-aqueous electrolyte storage element of the present embodiment is not particularly limited, and examples thereof include a cylindrical battery, a prismatic battery, a flat battery, a coin-shaped battery, a button-shaped battery, and the like.

[0095] FIG. 1 shows a non-aqueous electrolyte storage element 1 as an example of a prismatic battery. Note that this figure is a perspective view of the inside of the container. An electrode body 2 having a positive electrode and a negative electrode wound with a separator interposed therebetween is housed in a prismatic container 3. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 41. The negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 51.

[0096] <Configuration of Non-aqueous Electrolyte Storage Device> The non-aqueous electrolyte storage element of the present embodiment can be mounted as a power storage unit (battery module) configured by aggregating a plurality of non-aqueous electrolyte storage elements for power sources for automobiles such as electric vehicles (EVs), hybrid vehicles (HEVs), plug-in hybrid vehicles (PHEVs), power sources for electronic devices such as personal computers and communication terminals, or power sources for power storage. In this case, the technology according to one embodiment of the present invention may be applied to at least one non-aqueous electrolyte storage element included in the power storage unit.

[0097] FIG. 2 shows an example of a power storage device 30 in which power storage units 20 in which two or more non-aqueous electrolyte storage elements 1 are electrically connected are further aggregated. The power storage device 30 may include a bus bar (not shown) for electrically connecting two or more non-aqueous electrolyte storage elements 1, a bus bar (not shown) for electrically connecting two or more power storage units 20, and the like. The power storage unit 20 or the power storage device 30 may include a state monitoring device (not shown) for monitoring the state of one or more non-aqueous electrolyte storage elements.

[0098] <Manufacturing Method of Non-aqueous Electrolyte Storage Element> The manufacturing method of the non-aqueous electrolyte storage element according to one embodiment of the present invention includes preparing a negative electrode containing metallic lithium and preparing a non-aqueous electrolyte containing an imide salt and a phosphate ester.

[0099] Preparing a negative electrode containing metallic lithium may involve fabricating a negative electrode containing metallic lithium. The fabrication of the negative electrode can be carried out by laminating a negative electrode active material layer containing metallic lithium directly on the negative electrode substrate or via an intermediate layer, and then pressing or the like. The negative electrode active material layer containing metallic lithium may be a metallic lithium foil or a lithium alloy foil. The specific form and preferred form of the prepared negative electrode can apply the forms described above as the negative electrode provided in the non-aqueous electrolyte storage element.

[0100] Preparing a non-aqueous electrolyte containing an imide salt and a phosphate ester may involve preparing a non-aqueous electrolyte containing an imide salt and a phosphate ester. The preparation of the non-aqueous electrolyte can be carried out by mixing each component constituting the non-aqueous electrolyte, such as an imide salt, a phosphate ester, and other components. The specific form and preferred form of the prepared non-aqueous electrolyte can apply the forms described above as the non-aqueous electrolyte provided in the non-aqueous electrolyte storage element.

[0101] For example, the manufacturing method of the non-aqueous electrolyte storage element includes preparing or fabricating a positive electrode, preparing or fabricating a negative electrode, preparing or preparing a non-aqueous electrolyte, preparing or fabricating a separator, forming an electrode body in which the positive electrode and the negative electrode are alternately stacked by laminating or winding them with a separator in between, accommodating the positive electrode and the negative electrode (electrode body) in a container, and injecting the non-aqueous electrolyte into the container. After injection, the non-aqueous electrolyte storage element can be obtained by sealing the injection port.

[0102] The method for manufacturing the non-aqueous electrolyte storage element may further include performing initial charge and discharge on the assembled non-charged and discharged storage element. For example, when a lithium transition metal composite oxide in which the molar ratio of lithium (Li) to transition metal (Me) (Li / Me) in the positive electrode active material of the non-aqueous electrolyte storage element is greater than 1 is used, the capacity increases through the initial charge and discharge. The number of charge and discharge cycles in the initial charge and discharge may be 1 or 2, or may be 3 or more. When a lithium transition metal composite oxide in which the molar ratio of lithium (Li) to transition metal (Me) (Li / Me) in the positive electrode active material of the non-aqueous electrolyte storage element is greater than 1 is used, the positive electrode potential (positive electrode reaching potential) at the charge cut-off voltage in the initial charge and discharge is 4.5V vs. Li / Li + to 4.7V vs. Li / Li + or less is preferable.

[0103] <Non-aqueous electrolyte> The non-aqueous electrolyte according to one embodiment of the present invention is a non-aqueous electrolyte for a lithium battery that contains an imide salt and a phosphate ester, and the content of the imide salt is 2 mol / kg or more. A lithium battery is a secondary battery in which metallic lithium (pure metallic lithium or a lithium alloy) is used as the negative electrode active material. Specific forms and preferred forms of the non-aqueous electrolyte are those described above as the non-aqueous electrolyte constituting the non-aqueous electrolyte storage element according to one embodiment of the present invention.

[0104] <Other embodiments> The present invention is not limited to the above embodiments, and various modifications may be made without departing from the gist of the present invention. For example, the configuration of another embodiment 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 another embodiment or well-known technology. Furthermore, a part of the configuration of one embodiment can be deleted. Also, well-known technology can be added to the configuration of one embodiment.

[0105] In the above embodiment, the case where the non-aqueous electrolyte storage element is used as a rechargeable non-aqueous electrolyte secondary battery (lithium battery) has been described. However, the type, shape, dimensions, capacity, etc. of the non-aqueous electrolyte storage element are arbitrary. The non-aqueous electrolyte storage element of the present invention can also be applied to various non-aqueous electrolyte secondary batteries, electric double layer capacitors or capacitors such as lithium ion capacitors.

Examples

[0106] Hereinafter, the present invention will be described more specifically by way of examples. However, the present invention is not limited to the following examples.

[0107] [Example 1] (Fabrication of positive electrode) As the positive electrode active material, a lithium transition metal composite oxide having an α-NaFeO2 type crystal structure and represented by Li 1+α Me 1-α O2 (Me is a transition metal) was used. Here, the molar ratio Li / Me of Li and Me was 1.33, and Me consisted of Ni and Mn and contained them in a molar ratio of Ni:Mn = 1:2.

[0108] Using N-methylpyrrolidone (NMP) as a dispersion medium, a positive electrode mixture paste containing the above positive electrode active material, acetylene black (AB) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder in a mass ratio of 94:4.5:1.5 was prepared. The positive electrode mixture paste was applied to one side of an aluminum foil which is a positive electrode substrate, dried and then pressed to produce a positive electrode in which a positive electrode active material layer was disposed on one side of the positive electrode substrate.

[0109] (Fabrication of negative electrode) A metal lithium foil (pure metal lithium of 100% by mass of metallic lithium) was laminated on one side of a copper foil which is a negative electrode substrate and then pressed to produce a negative electrode. Note that the positive electrode and the negative electrode were designed and fabricated so that the current density at 1C was 5.0 mA / cm 2 to be.

[0110] (Preparation of non-aqueous electrolyte) Tris(2,2,2-trifluoroethyl) phosphate (O=P(OCH2CF3)3: TFEP), fluoroethylene carbonate (FEC), 2,2,2-trifluoroethyl methyl carbonate (TFEMC) and 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TFEE) were mixed in a volume ratio of 20:10:60:10, and lithium bis(fluorosulfonyl)imide (LiFSI) was dissolved in the mixed solvent at a concentration of 3 mol / kg to obtain a non-aqueous electrolyte.

[0111] (Fabrication of non-aqueous electrolyte energy storage device) An electrode body was fabricated by laminating the above positive electrode and the above negative electrode through a microporous polyolefin membrane as a separator. This electrode body was housed in a container made of a metal-resin composite film, the above non-aqueous electrolyte was injected therein, and then sealed by heat welding to obtain the non-aqueous electrolyte energy storage device of Example 1.

[0112] [Examples 2 to 4 and Comparative Examples 1 to 8] Except that the composition of the non-aqueous electrolyte was as shown in Tables 1 and 2, each non-aqueous electrolyte energy storage device of Examples 2 to 4 and Comparative Examples 1 to 8 was obtained in the same manner as in Example 1. In Table 2, TEP represents triethyl phosphate (O=P(OCH2CH3)3).

[0113] (Initial charge and discharge) For each of the obtained non-aqueous electrolyte energy storage devices, initial charge and discharge were performed under the following conditions. At 25°C, constant current and constant voltage charging was performed with a charging current of 0.1C and a charging cut-off voltage of 4.6V. The end condition of charging was until the charging current became 0.05C. Thereafter, a rest period of 10 minutes was provided. Thereafter, constant current discharge was performed with a discharge current of 0.1C and a discharge cut-off voltage of 2.0V, and then a rest period of 10 minutes was provided. This charge and discharge cycle was performed 2 cycles.

[0114] (Charge and discharge cycle test) Next, the following charge-discharge cycle test was conducted. At 25°C, constant current constant voltage charging was performed with a charging current of 0.2C and a charging cut-off voltage of 4.6V. The end condition of charging was until the charging current reached 0.05C. Thereafter, a 10-minute rest period was provided. Then, constant current discharging was performed with a discharging current of 0.1C and a discharging cut-off voltage of 2.0V, and thereafter, a 10-minute rest period was provided. This charge-discharge cycle was repeated, and the number of cycles until a micro short circuit occurred was recorded. The results (number of cycles until a micro short circuit occurred) of Examples 1 to 3 and Comparative Examples 1 to 6 are shown in Table 1. For Example 4 and Comparative Examples 7 and 8, Table 2 shows the increase rate of the number of cycles until a micro short circuit occurred, based on the number of cycles until a micro short circuit occurred in Comparative Example 7, as the result.

[0115]

Table 1

[0116]

Table 2

[0117] The following can be considered from Table 1. When a non-aqueous electrolyte with a low electrolyte salt concentration and no phosphate ester was used as in Comparative Examples 1 and 2, the number of cycles until a micro short circuit occurred was about 75 times. When taking these as a reference, when the concentration of LiFSI, which is the electrolyte salt of the non-aqueous electrolyte without phosphate ester, was increased as in Comparative Example 3, the number of cycles until a micro short circuit occurred decreased. This is presumably because the ionic conductivity decreased due to the increase in the viscosity of the non-aqueous electrolyte. Also, when the non-aqueous electrolyte contained phosphate ester (TFEP) without increasing the concentration of the electrolyte salt LiFSI as in Comparative Examples 4 and 5, the number of cycles until a micro short circuit occurred also decreased. This is also presumably because the ionic conductivity decreased due to the increase in the viscosity of the non-aqueous electrolyte by the phosphate ester. Even when the non-aqueous electrolyte contained phosphate ester without increasing the concentration of the electrolyte salt LiPF6 as in Comparative Example 6, the effect of suppressing the occurrence of micro short circuits was not shown.

[0118] In contrast, in Examples 1 to 3 in which the electrolyte salt LiFSI was highly concentrated and the non-aqueous electrolyte contained a phosphate ester, the number of cycles until a micro-short circuit occurred was significantly increased, and a high effect of suppressing the occurrence of a micro-short circuit was confirmed. Inferred from the results of Comparative Examples 3 to 5, etc., when the electrolyte salt LiFSI was highly concentrated and the non-aqueous electrolyte contained a phosphate ester, it is considered that the ionic conductivity of the non-aqueous electrolyte is synergistically lowered, further decreasing the number of cycles until a micro-short circuit occurs. However, it is presumed that such a high effect of suppressing the occurrence of a micro-short circuit was achieved because the coating formed on the negative electrode surface by the high concentration of imide salt and phosphate ester was of good quality.

[0119] Furthermore, as shown in Table 2, the effect of suppressing the occurrence of micro-short circuits was confirmed even when TEP, a non-fluorinated phosphate ester, was used as the phosphate ester and the imide salt was made highly concentrated. However, the effect of suppressing the occurrence of micro-short circuits in Example 4 was lower than in Examples 1 to 3, and it can be seen that the effect of suppressing the occurrence of micro-short circuits is remarkable when a fluorinated phosphate ester is used as the phosphate ester or when the content of the fluorinated solvent in the nonaqueous solvent is increased. [Industrial Applicability]

[0120] The present invention can be applied to nonaqueous electrolyte electricity storage elements used as power sources for electronic devices such as personal computers and communication terminals, and automobiles. [Explanation of symbols]

[0121] 1. Non-aqueous electrolyte storage element 2 Electrode body 3 containers 4 Positive terminal 41 Positive lead 5 Negative terminal 51 Negative lead 20 Energy Storage Unit 30 Energy storage device

Claims

1. A negative electrode containing metallic lithium, a non-aqueous electrolyte containing an imide salt and a non-aqueous solvent, and the content of the imide salt in the non-aqueous electrolyte is 2 mol / kg or more, the non-aqueous solvent is a phosphate ester, and at least one selected from the group consisting of carbonate, ester (excluding the phosphate ester), ether, amide, sulfone, lactone, and nitrile and another non-aqueous solvent containing the carbonate, and the content of the other non-aqueous solvent in the non-aqueous solvent is 60% by volume or more and 97% by volume or less, a non-aqueous electrolyte storage element.

2. A negative electrode containing metallic lithium, a non-aqueous electrolyte containing an imide salt and a non-aqueous solvent, and the content of the imide salt in the non-aqueous electrolyte is 2 mol / kg or more, the non-aqueous solvent is a phosphate ester, and at least one selected from the group consisting of carbonate, ester (excluding the phosphate ester), ether, amide, sulfone, lactone, and nitrile and another non-aqueous solvent containing the carbonate, and the content of the other non-aqueous solvent in the non-aqueous solvent is 40% by volume or more and 97% by volume or less, the content of the carbonate in the non-aqueous solvent is 40% by volume or more and 95% by volume or less, a non-aqueous electrolyte storage element.

3. A negative electrode containing metallic lithium, a non-aqueous electrolyte containing an imide salt and a non-aqueous solvent, and the content of the imide salt in the non-aqueous electrolyte is 2 mol / kg or more, the non-aqueous solvent contains a phosphate ester, an ether, a fluorinated cyclic carbonate, and a fluorinated chain carbonate, a non-aqueous electrolyte storage element.

4. A negative electrode containing metallic lithium, a non-aqueous electrolyte containing an imide salt and a non-aqueous solvent, and the content of the imide salt in the non-aqueous electrolyte is 2 mol / kg or more, the non-aqueous solvent contains a phosphate ester, an ether, and a carbonate, the content of the carbonate in the non-aqueous solvent is 40% by volume or more and 95% by volume or less, a non-aqueous electrolyte storage element.

5. Preparing a negative electrode containing metallic lithium, and preparing a non-aqueous electrolyte containing an imide salt and a non-aqueous solvent, and the content of the imide salt in the non-aqueous electrolyte is 2 mol / kg or more, the non-aqueous solvent is a phosphate ester, At least one selected from the group consisting of carbonate, ester (excluding the above-mentioned phosphate ester), ether, amide, sulfone, lactone and nitrile and containing the above-mentioned carbonate and other non-aqueous solvents comprising A method for manufacturing a non-aqueous electrolyte storage element, wherein the content of the other non-aqueous solvent in the non-aqueous solvent is 60% by volume or more and 97% by volume or less.

6. Preparing a negative electrode containing metallic lithium, and preparing a non-aqueous electrolyte containing an imide salt and a non-aqueous solvent comprising the content of the imide salt in the non-aqueous electrolyte is 2 mol / kg or more, the non-aqueous solvent is phosphate ester, and at least one selected from the group consisting of carbonate, ester (excluding the above-mentioned phosphate ester), ether, amide, sulfone, lactone and nitrile and containing the above-mentioned carbonate and other non-aqueous solvents comprising the content of the other non-aqueous solvent in the non-aqueous solvent is 40% by volume or more and 97% by volume or less, A method for manufacturing a non-aqueous electrolyte storage element, wherein the content of the carbonate in the non-aqueous solvent is 40% by volume or more and 95% by volume or less.

7. Preparing a negative electrode containing metallic lithium, and preparing a non-aqueous electrolyte containing an imide salt and a non-aqueous solvent comprising the content of the imide salt in the non-aqueous electrolyte is 2 mol / kg or more, A method for manufacturing a non-aqueous electrolyte storage element, wherein the non-aqueous solvent contains phosphate ester, ether, fluorinated cyclic carbonate and fluorinated chain carbonate.

8. Preparing a negative electrode containing metallic lithium, and preparing a non-aqueous electrolyte containing an imide salt and a non-aqueous solvent comprising the content of the imide salt in the non-aqueous electrolyte is 2 mol / kg or more, the non-aqueous solvent contains phosphate ester, ether and carbonate, A method for manufacturing a non-aqueous electrolyte storage element, wherein the content of the carbonate in the non-aqueous solvent is 40% by volume or more and 95% by volume or less.

9. comprising an imide salt and a non-aqueous solvent, the content of the imide salt is 2 mol / kg or more, the non-aqueous solvent is phosphate ester, and at least one selected from the group consisting of carbonate, ester (excluding the above-mentioned phosphate ester), ether, amide, sulfone, lactone and nitrile and containing the above-mentioned carbonate and other non-aqueous solvents comprising A non-aqueous electrolyte for a lithium battery, wherein the content of the other non-aqueous solvent in the non-aqueous solvent is 60% by volume or more and 97% by volume or less.

10. Comprising an imide salt and a non-aqueous solvent, wherein the content of the imide salt is 2 mol / kg or more, the non-aqueous solvent is a phosphate ester, and at least one selected from the group consisting of carbonate, ester (excluding the phosphate ester), ether, amide, sulfone, lactone and nitrile and another non-aqueous solvent containing the carbonate and the content of the other non-aqueous solvent in the non-aqueous solvent is 40% by volume or more and 97% by volume or less, a non-aqueous electrolyte for a lithium battery, wherein the content of the carbonate in the non-aqueous solvent is 40% by volume or more and 95% by volume or less.

11. Comprising an imide salt and a non-aqueous solvent, wherein the content of the imide salt is 2 mol / kg or more, a non-aqueous electrolyte for a lithium battery, wherein the non-aqueous solvent contains a phosphate ester, an ether, a fluorinated cyclic carbonate and a fluorinated chain carbonate.

12. Comprising an imide salt and a non-aqueous solvent, wherein the content of the imide salt is 2 mol / kg or more, the non-aqueous solvent contains a phosphate ester, an ether and a carbonate, a non-aqueous electrolyte for a lithium battery, wherein the content of the carbonate in the non-aqueous solvent is 40% by volume or more and 95% by volume or less.

Images