Nonaqueous electrolyte storage element and method for manufacturing same

Abstract

To provide a nonaqueous electrolyte power storage device which can suppress the occurrence of a short circuit accompanying the repetition of charge and discharge operations even in the case of a negative electrode having lithium metal.SOLUTION: A nonaqueous electrolyte power storage device 1 comprises: a negative electrode having lithium metal; a separator having a layer containing inorganic particles; and a nonaqueous electrolyte including an ionic liquid.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a non-aqueous electrolyte electricity storage element and a method for producing the same. [Background technology]

[0002] Due to their high energy density, non-aqueous electrolyte secondary batteries, such as lithium ion secondary batteries, are widely used in electronic devices such as personal computers and communication terminals, as well as automobiles. Non-aqueous electrolyte secondary batteries generally have 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. Metallic lithium is known as a negative electrode active material with high energy density that is used in non-aqueous electrolyte energy storage elements (see Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-100065 [Patent Document 2] Japanese Patent Application Publication No. 7-245099 Summary of the Invention [Problem to be solved by the invention]

[0004] A non-aqueous electrolyte storage element having a negative electrode containing metallic lithium as the negative electrode active material has the disadvantage that it is prone to short circuits due to repeated charge and discharge.

[0005] An object of the present invention is to provide a nonaqueous electrolyte electricity storage element in which the occurrence of short circuits due to repeated charge and discharge is suppressed when the negative electrode contains metallic lithium, and a method for producing such a nonaqueous electrolyte electricity storage element. [Means for solving the problem]

[0006] A nonaqueous electrolyte storage element according to one aspect of the present invention includes a negative electrode containing metallic lithium, a separator having a layer containing inorganic particles, and a nonaqueous electrolyte containing an ionic liquid.

[0007] A method for manufacturing a nonaqueous electrolyte storage element according to another aspect of the present invention includes preparing a combination of a positive electrode and metallic lithium or a negative electrode having a surface region on which metallic lithium can be deposited during charging, preparing a separator having a layer containing inorganic particles, and preparing a nonaqueous electrolyte containing an ionic liquid. [Effects of the Invention]

[0008] According to one aspect of the present invention, it is possible to provide a nonaqueous electrolyte electricity storage element in which the occurrence of short circuits due to repeated charge and discharge is suppressed when the negative electrode contains metallic lithium, and a method for manufacturing such a nonaqueous electrolyte electricity storage element. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is an external perspective view showing a nonaqueous electrolyte electricity storage element according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing an electricity storage device constructed by assembling a plurality of nonaqueous electrolyte electricity storage elements according to one embodiment of the present invention. [Figure 3A] FIG. 3A is a graph showing the capacity retention rate for each cycle in a charge-discharge test of each nonaqueous electrolyte storage element of Example 1. [Figure 3B] FIG. 3B is a graph showing the capacity retention rate for each cycle in a charge-discharge test of each nonaqueous electrolyte storage element of Comparative Example 1. [Figure 3C] FIG. 3C is a graph showing the capacity retention rate for each cycle in a charge-discharge test of each nonaqueous electrolyte storage element of Comparative Example 2. [Figure 3D] FIG. 3D is a graph showing the capacity retention rate for each cycle in a charge-discharge test of each nonaqueous electrolyte storage element of Comparative Example 3. [Figure 4A]FIG. 4A is a graph showing the capacity retention rate for each cycle in a charge-discharge test of each nonaqueous electrolyte storage element of Example 2. [Figure 4B] FIG. 4B is a graph showing the capacity retention rate for each cycle in the charge-discharge test of each nonaqueous electrolyte storage element of Example 3. DETAILED DESCRIPTION OF THE INVENTION

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

[0011] A nonaqueous electrolyte storage element according to one aspect of the present invention includes a negative electrode containing metallic lithium, a separator having a layer containing inorganic particles, and a nonaqueous electrolyte containing an ionic liquid.

[0012] In this nonaqueous electrolyte storage element, when the negative electrode contains metallic lithium, the occurrence of short circuits due to repeated charge and discharge is suppressed. While the reason for this is unclear, the following is presumed. In general, in nonaqueous electrolyte storage elements including a negative electrode containing metallic lithium as the negative electrode active material, metallic lithium may deposit in a dendritic form on the surface of the negative electrode during charging (hereinafter, dendritic metallic lithium is referred to as a "dendrite"). If these dendrites grow and penetrate the separator, contacting the positive electrode, causing a short circuit. In contrast, in this nonaqueous electrolyte storage element, the nonaqueous electrolyte contains an ionic liquid, which forms a high-quality coating (SEI) on the surface of the negative electrode. The presence of this coating, along with the separator having a layer containing inorganic particles, is presumed to make it difficult for dendrites to penetrate the separator, thereby suppressing the occurrence of short circuits. Therefore, with this nonaqueous electrolyte storage element, the occurrence of short circuits due to repeated charge and discharge is suppressed, and the number of charge and discharge cycles required before a short circuit occurs is large, allowing for multiple charge and discharge cycles to be performed successfully.

[0013] Furthermore, when a separator having a layer containing inorganic particles is applied to a nonaqueous electrolyte energy storage element having a negative electrode containing metallic lithium, metallic lithium that is not involved in the charge-discharge reaction is likely to be produced, and the capacity retention rate during repeated charge-discharge cycles tends to be low. However, the nonaqueous electrolyte energy storage element also has an improved capacity retention rate during repeated charge-discharge cycles. The reason for this is also unclear, but it is speculated that the inclusion of an ionic liquid in the nonaqueous electrolyte as described above allows a high-quality film to be formed on the surface of the negative electrode, suppressing the production of metallic lithium that is not involved in the charge-discharge reaction.

[0014] The negative electrode provided in the nonaqueous electrolyte storage element only needs to contain metallic lithium at least in a charged state, and need not contain metallic lithium in a discharged state. For example, the nonaqueous electrolyte storage element may be configured such that metallic lithium is deposited on at least a partial region of the negative electrode surface during charging, so that the negative electrode contains metallic lithium in a charged state, and substantially all of the metallic lithium on the negative electrode surface is eluted into the nonaqueous electrolyte during discharge, so that the negative electrode contains substantially no metallic lithium in a discharged state.

[0015] It is preferable that the surface of the negative electrode faces the surface of the layer containing inorganic particles. In such a case, the occurrence of short circuits due to repeated charge and discharge is further suppressed, and the capacity retention rate is further increased. Although the reason for this is unclear, it is speculated that when the surface of the negative electrode faces the surface of the layer containing inorganic particles, the film formed on the surface of the negative electrode is more easily maintained by the layer containing inorganic particles, and the growth of dendrites is further suppressed.

[0016] The ionic liquid preferably contains a quaternary ammonium cation. Quaternary ammonium cations are more likely to decompose due to a reduction reaction than, for example, phosphonium cations, and are therefore more likely to form a coating on the surface of the negative electrode. Therefore, when the ionic liquid contains a quaternary ammonium cation, the growth of dendrites is more suppressed, thereby further suppressing the occurrence of short circuits due to repeated charge and discharge.

[0017] The battery further comprises a positive electrode having a lithium transition metal composite oxide, the non-aqueous electrolyte further contains a lithium salt, and the content of the lithium salt in the non-aqueous electrolyte is 1.5 mol / dm 3 When the positive electrode contains a lithium transition metal composite oxide as a positive electrode active material, it has advantages such as an increased capacity density, but it may be prone to short circuits. Therefore, when the nonaqueous electrolyte storage element has a positive electrode containing a lithium transition metal composite oxide, the content of the lithium salt in the nonaqueous electrolyte is preferably 1.5 mol / dm or more. 3 By doing so, the occurrence of a short circuit can be more sufficiently suppressed.

[0018] A method for manufacturing a nonaqueous electrolyte storage element according to another aspect of the present invention includes preparing a combination of a positive electrode and metallic lithium or a negative electrode having a surface region on which metallic lithium can be deposited during charging, preparing a separator having a layer containing inorganic particles, and preparing a nonaqueous electrolyte containing an ionic liquid.

[0019] According to this manufacturing method, a nonaqueous electrolyte energy storage element can be manufactured in which the occurrence of short circuits due to repeated charge and discharge is suppressed when the negative electrode contains metallic lithium. Furthermore, the nonaqueous electrolyte energy storage element obtained by this manufacturing method also has a high capacity retention rate during repeated charge and discharge.

[0020] 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.

[0021] <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 of being impregnated 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.

[0022] (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.

[0023] 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 material of the positive electrode substrate is a metal such as aluminum, titanium, tantalum, or stainless steel, or an alloy of these. Among these, aluminum or an aluminum alloy is preferred from the viewpoints of potential resistance, high conductivity, and cost. Positive electrode substrates include foils, vapor-deposited films, meshes, and porous materials, with foil being preferred from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferred as the positive electrode substrate. Examples of aluminum or aluminum alloys include A1085, A3003, and A1N30, as specified in JIS-H-4000 (2014) or JIS-H4160 (2006).

[0024] 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. The "average thickness" refers to the value obtained by dividing the punched mass when a substrate of a predetermined area is punched out by the true density and punched area of ​​the substrate. The same applies to the "average thickness" of the negative electrode substrate described below.

[0025] 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.

[0026] The positive electrode active material layer contains a positive electrode active material. The positive electrode active material layer contains optional components such as a conductive agent, a binder, a thickener, and a filler, as needed. The positive electrode active material layer may be formed from a positive electrode mixture containing the positive electrode active material and other optional components.

[0027] The positive electrode active material can be appropriately selected from known positive electrode active materials. As the positive electrode active material, a material capable of absorbing and releasing 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, Li2O, etc. Examples of the lithium transition metal composite oxides 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). Lithium transition metal composite oxides with spinel crystal structure include Li x Mn2O4, Li x Ni γ Mn (2-γ) Examples of polyanion compounds include LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, and Li2CoPO4F. Examples of chalcogen compounds include titanium disulfide, molybdenum disulfide, and molybdenum dioxide. Atoms or polyanions in these materials may be partially substituted with atoms or anion species of other elements. The surfaces of these materials may be coated with other materials. In the positive electrode active material layer, one of these materials may be used alone, or two or more may be used in combination.

[0028] The positive electrode active material is preferably a lithium transition metal composite oxide (such as a lithium transition metal composite oxide having an α-NaFeO2 crystal structure or a spinel crystal structure), and more preferably a lithium transition metal composite oxide having an α-NaFeO2 crystal structure. By using such a positive electrode active material, the capacity density, energy density, etc. of the secondary battery can be increased.

[0029] The lithium transition metal composite oxide having an α-NaFeO2-type crystal structure 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 another transition metal such as cobalt. In the lithium transition metal composite oxide having an α-NaFeO2-type crystal structure, the molar ratio of lithium (Li) to the transition metal (Me) (Li / Me) is preferably greater than 1, more preferably 1.1 or greater, even more preferably 1.2 or greater, and even more preferably 1.3 or greater. The use of such a lithium transition metal composite oxide can increase the electrical capacity, for example. The upper limit of the molar ratio of lithium to the transition metal (Li / Me) is preferably 1.6, more preferably 1.5.

[0030] The lithium transition metal composite oxide having an α-NaFeO2 type crystal structure is preferably a compound represented by the following formula (1). Li 1+α Me 1-α O2···(1) In formula (1), Me is a transition metal including Ni or Mn, and 0<α<1.

[0031] In formula (1), Me preferably contains Ni and Mn. Me preferably consists essentially of two elements, Ni and Mn, or three elements, Ni, Mn, and Co. Me may contain other transition metals.

[0032] 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 and other properties are improved.

[0033] In formula (1), the lower limit of the molar ratio of Mn to Me (Mn / Me) is preferably 0.5, more preferably 0.55, and even 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 and other properties are improved.

[0034] In formula (1), the upper limit of the molar ratio of Co to Me (Co / Me) is preferably 0.3, more preferably 0.2, and even more preferably 0.1. The molar ratio (Co / Me) or the lower limit of the molar ratio (Co / Me) may be 0.

[0035] In formula (1), the molar ratio of Li to Me (Li / Me), i.e., (1+α) / (1-α), is preferably greater than 1.0 (α>0), more preferably 1.1 or greater, even more preferably 1.2 or greater, and even more preferably 1.3 or greater. On the other hand, the upper limit of this molar ratio (Li / Me) is preferably 1.6, more preferably 1.5. By keeping the molar ratio (Li / Me) within the above range, the discharge capacity increases.

[0036] The lithium transition metal composite oxide having a molar ratio (Li / Me) of lithium (Li) to the transition metal (Me) of more than 1 is preferably one in which no diffraction peak exists in the range of 20° to 22° in an X-ray diffraction pattern using CuKα radiation. The lithium transition metal composite oxide having a molar ratio (Li / Me) of lithium (Li) to the transition metal (Me) of more than 1 generally exhibits a high solubility in water when the positive electrode potential is, for example, 4.5 V (vs. Li / Li + ) or more, the electric capacity increases. Furthermore, due to such a change in the crystal structure during the initial charge, the diffraction peak in the range of 20° to 22° that existed before the initial charge disappears. In other words, an active material that is a lithium transition metal composite oxide in which the molar ratio (Li / Me) of lithium (Li) to transition metal (Me) is greater than 1 and that does not have a diffraction peak in the range of 20° to 22° in the X-ray diffraction pattern has a large electric capacity.

[0037] The composition ratio of the lithium transition metal composite oxide in this specification refers to the composition ratio when the battery is fully discharged by the following method. First, the nonaqueous electrolyte storage element (secondary battery) is charged at a constant current of 0.05 C until the end-of-charge voltage in normal use is reached, and the battery is fully charged. After a 30-minute rest, the battery is discharged at a constant current of 0.05 C until the lower limit voltage in normal use is reached. The battery is then disassembled, the positive electrode is removed, and a test battery is assembled using a metallic lithium electrode as the counter electrode. The positive electrode potential is measured at a current of 10 mA per 1 g of positive electrode mixture until the positive electrode potential reaches 2.0 V (vs. Li / Li). + ) to adjust the positive electrode to a fully discharged state. Pure metallic lithium is used for the metallic lithium electrode here. The device is disassembled again, and the positive electrode is removed. The nonaqueous electrolyte adhering to the removed positive electrode is thoroughly washed with dimethyl carbonate, and after drying at room temperature for one day, the lithium transition metal composite oxide, the positive electrode active material, is extracted. The extracted lithium transition metal composite oxide is subjected to measurement. The operations from disassembly of the nonaqueous electrolyte storage element to extraction of the lithium transition metal composite oxide are carried out in an argon atmosphere with a dew point of -60°C or lower. Note that "normal use" refers to the case where the nonaqueous electrolyte storage element is used under the charge / discharge conditions recommended or specified for the nonaqueous electrolyte storage element, and, if a charger for the nonaqueous electrolyte storage element is provided, the nonaqueous electrolyte storage element is used with the charger.

[0038] X-ray diffraction measurements of lithium transition metal composite oxides are performed on lithium transition metal composite oxides that have been fully discharged using the method described above. Specifically, X-ray diffraction measurements are performed by powder X-ray diffraction using an X-ray diffractometer (Rigaku's "MiniFlex II") with a CuKα radiation source, a tube voltage of 30 kV, and a tube current of 15 mA. The diffracted X-rays pass through a 30 μm-thick Kβ filter and are detected by a high-speed one-dimensional detector (D / teX Ultra 2). 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.

[0039] The positive electrode active material is usually in the form of particles (powder). 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 the above lower limit or more, the positive electrode active material becomes easier to manufacture and handle. By setting the average particle size of the positive electrode active material to the above upper limit or less, the electronic conductivity of the positive electrode active material layer is improved. Note that when a composite of the positive electrode active material and another material is used, the average particle size of the composite is taken as the average particle size of the positive electrode active material. The "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 a diluted solution obtained by diluting particles with a solvent in accordance with JIS-Z-8825 (2013).

[0040] 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.

[0041] The content of the 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 positive electrode active material within this range, both high energy density and manufacturability of the positive electrode active material layer can be achieved.

[0042] 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.

[0043] The content of the conductive agent 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 content of the conductive agent within this range, the energy density of the secondary battery can be increased.

[0044] 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; polysaccharide polymers; and aramid.

[0045] 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.

[0046] Examples of thickeners include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. When the thickener has a functional group that reacts with lithium or the like, the functional group may be deactivated in advance by methylation or the like. In one embodiment 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, alumina, 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-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, and artificial products thereof. In one embodiment of the present invention, it may be preferable that the positive electrode active material layer does not contain a filler.

[0048] 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.

[0049] The average thickness of the positive electrode active material layer is preferably 5 μm to 1,000 μm, more preferably 10 μm to 500 μm, and even more preferably 50 μm to 300 μm. The average thickness of the positive electrode active material layer refers to the average value of thicknesses measured at any five points in the positive electrode active material layer. The same applies to the average thicknesses of the negative electrode active material layer, separator substrate layer, and inorganic particle-containing layer, which will be described later.

[0050] (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.

[0051] The negative electrode substrate is conductive. Metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, alloys thereof, and carbonaceous materials are used as the material for the negative electrode substrate. Among these, copper or copper alloys are preferred. Examples of the negative electrode substrate include foils, vapor-deposited films, meshes, and porous materials, with foils 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.

[0052] 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.

[0053] The negative electrode active material layer contains metallic lithium. That is, the secondary battery of this 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 lithium alone, or may exist as a lithium alloy containing other metal components. Examples of lithium alloys include lithium-silver alloys, lithium-zinc alloys, lithium-calcium alloys, lithium-aluminum alloys, lithium-magnesium alloys, and lithium-indium alloys. The lithium alloy may contain multiple metal elements other than lithium.

[0054] The negative electrode active material layer may be a layer consisting essentially of lithium. The lithium content in the negative electrode active material layer may be 90% by mass or more, 99% by mass or more, or even 100% by mass.

[0055] The negative electrode active material layer may be a lithium foil or a lithium alloy foil. The negative electrode active material layer may be a non-porous layer (solid layer). Alternatively, the negative electrode active material layer may be a porous layer containing particles containing metallic lithium. A negative electrode active material layer that is a porous layer containing particles containing metallic lithium may further contain, for example, resin particles, inorganic particles, etc. The average thickness of the negative electrode active material layer is preferably 5 μm to 1,000 μm, more preferably 10 μm to 500 μm, and even more preferably 30 μm to 300 μm.

[0056] In the case of a nonaqueous electrolyte storage element configured so that metallic lithium is deposited on at least a portion of the negative electrode surface during charging and substantially all of the metallic lithium on the negative electrode surface is eluted into the nonaqueous electrolyte during discharging, the negative electrode may not have a negative electrode active material layer in a discharged state.

[0057] (separator) The separator has a layer containing inorganic particles. Examples of the separator include a separator consisting of only a substrate layer, and a separator having a substrate layer and a layer containing inorganic particles laminated on one or both surfaces of the substrate layer. In the case of a separator consisting of only a substrate layer, the substrate layer is a layer containing inorganic particles. In the case of a separator having a substrate layer and a layer containing inorganic particles laminated on one or both surfaces of the substrate layer, the substrate layer may or may not contain inorganic particles. A separator having a substrate layer and a layer containing inorganic particles laminated on one or both surfaces of the substrate layer is preferred. In this way, when a layer containing inorganic particles is provided in addition to the substrate layer, the content of inorganic particles in the layer containing inorganic particles can be increased, and the layer containing inorganic particles can fully exhibit the effect of inhibiting dendrite growth, etc.

[0058] In a secondary battery according to one embodiment of the present invention, the surface of the negative electrode is preferably configured to face the surface of the layer containing inorganic particles. For example, when the separator is composed of only a substrate layer, or when the separator has a substrate layer and a layer containing inorganic particles laminated on both surfaces of the substrate layer, the above configuration is necessarily satisfied. Furthermore, when the separator has a substrate layer and a layer containing inorganic particles laminated on only one surface of the substrate layer, the above configuration is satisfied by arranging the layer containing inorganic particles of the separator on the negative electrode side and the substrate layer side of the separator on the positive electrode side. In this configuration, the occurrence of short circuits due to repeated charge and discharge is further suppressed, and the capacity retention rate is further improved.

[0059] Examples of the shape of the separator substrate layer include woven fabric, nonwoven fabric, and porous resin film. Among these shapes, porous resin film is preferred from the viewpoint of strength, and nonwoven fabric is preferred from the viewpoint of nonaqueous electrolyte retention. As the material for the separator substrate layer, polyolefins such as polyethylene and polypropylene are preferred from the viewpoint of shutdown function, and polyimide and aramid are preferred from the viewpoint of oxidative decomposition resistance. A composite material of these resins may also be used for the separator substrate layer.

[0060] The average thickness of the separator substrate layer is preferably 1 μm or more and 30 μm or less, and more preferably 3 μm or more and 15 μm or less. When the average thickness of the separator substrate layer is within the above range, it is possible to achieve both sufficient strength and high energy density.

[0061] Inorganic particles are particles composed of inorganic compounds. Examples of inorganic compounds include oxides such as aluminum oxide and magnesium oxide; nitrides such as aluminum nitride and silicon nitride; and sulfates such as barium sulfate. As the inorganic compound, these substances may be used alone or in the form of a complex, or two or more may be mixed together. Among these inorganic compounds, aluminum oxide, magnesium oxide, barium sulfate, aluminum nitride, and silicon nitride are preferred because of their excellent resistance to reduction. The inorganic particles 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.

[0062] The inorganic particles are preferably the main component of the layer containing inorganic particles. The main component refers to the component with the largest content by mass (the same applies hereinafter). The layer containing inorganic particles may be a layer containing inorganic particles and a binder. The content of the inorganic particles in the layer containing inorganic particles is preferably 50% by mass or more and 99% by mass or less, and more preferably 70% by mass or more and 97% by mass or less. When the content of the inorganic particles in the layer containing inorganic particles is equal to or greater than the above lower limit, the layer containing inorganic particles can sufficiently exhibit the effect of inhibiting dendrite growth. Furthermore, when the content of the inorganic particles in the layer containing inorganic particles is equal to or less than the above upper limit, the inorganic particles can be sufficiently fixed to the layer containing inorganic particles, for example, by the presence of a sufficient binder.

[0063] The binder in the layer containing inorganic particles can be the same as those exemplified as the binder in the positive electrode active material layer, etc. The content of the binder in the layer containing inorganic particles is, for example, preferably 1% by mass or more and 50% by mass or less, and more preferably 3% by mass or more and 30% by mass or less.

[0064] The average thickness of one layer containing inorganic particles is preferably from 1 μm to 20 μm, more preferably from 2 μm to 15 μm, and even more preferably from 3 μm to 10 μm. When the average thickness of the layer containing inorganic particles is within the above range, the occurrence of short circuits due to repeated charge and discharge is further suppressed, and the capacity retention rate is further improved.

[0065] The porosity of the separator is preferably 80% by volume or less from the viewpoint of strength, and is preferably 20% by volume or more from the viewpoint of discharge performance. Here, "porosity" refers to a volume-based value measured with a mercury porosimeter.

[0066] (non-aqueous electrolyte) The non-aqueous electrolyte includes an ionic liquid. The non-aqueous electrolyte preferably includes lithium cations. The non-aqueous electrolyte may include a lithium salt as a form containing lithium cations. The non-aqueous electrolyte preferably further includes a non-aqueous solvent. The non-aqueous electrolyte may include, for example, an ionic liquid, a lithium salt, and a non-aqueous solvent.

[0067] [Ionic liquid] An ionic liquid is an ionic compound that is at least partially liquid at room temperature (20°C) under 1 atmosphere. The ionic liquid is preferably the main component of the non-aqueous electrolyte. The content of the ionic liquid in the non-aqueous electrolyte may be, for example, 50% by mass to 99% by mass, or 60% by mass to 95% by mass.

[0068] Examples of cations constituting the ionic liquid include quaternary ammonium cations, quaternary phosphonium cations, and tertiary sulfonium cations.

[0069] Examples of the quaternary ammonium cation include an imidazolium cation, a tetraalkylammonium cation, a pyridinium cation, a pyrrolium cation, a pyrazolium cation, a pyrrolinium cation, a pyrrolidinium cation, and a piperidinium cation.

[0070] Examples of imidazolium cations include a 1,3-dimethylimidazolium ion, a 1-ethyl-3-methylimidazolium ion, a 1,3-diethylimidazolium ion, a 1-butyl-3-methylimidazolium ion, a 1,2,3-trimethylimidazolium ion, a 1,2-dimethyl-3-ethylimidazolium ion, a 1,2-dimethyl-3-propylimidazolium ion, and a 1-butyl-2,3-dimethylimidazolium ion.

[0071] Examples of the tetraalkylammonium cation include a trimethylethylammonium ion, a trimethylpropylammonium ion, a trimethylbutylammonium ion, a trimethylhexylammonium ion, and a tetrapentylammonium ion.

[0072] Examples of pyridinium cations include N-methylpyridinium ion, N-ethylpyridinium ion, N-propylpyridinium ion, N-butylpyridinium ion, 1-ethyl-2-methylpyridinium ion, 1-butyl-4-methylpyridinium ion, and 1-butyl-2,4-dimethylpyridinium ion.

[0073] Examples of pyrrolium cations include 1,1-dimethylpyrrolium ion, 1-ethyl-1-methylpyrrolium ion, 1-methyl-1-propylpyrrolium ion, and 1-butyl-1-methylpyrrolium ion.

[0074] Examples of the pyrazolium cation include a 1,2-dimethylpyrazolium ion, a 1-ethyl-2-methylpyrazolium ion, a 1-propyl-2-methylpyrazolium ion, and a 1-butyl-2-methylpyrazolium ion.

[0075] Examples of the pyrrolinium cation include a 1,2-dimethylpyrrolinium ion, a 1-ethyl-2-methylpyrrolinium ion, a 1-propyl-2-methylpyrrolinium ion, and a 1-butyl-2-methylpyrrolinium ion.

[0076] Examples of the pyrrolidinium cation include a 1,1-dimethylpyrrolidinium ion, a 1-ethyl-1-methylpyrrolidinium ion, a 1-methyl-1-propylpyrrolidinium ion, and a 1-butyl-1-methylpyrrolidinium ion.

[0077] Examples of the piperidinium cation include a 1,1-dimethylpiperidinium ion, a 1-ethyl-1-methylpiperidinium ion, a 1-methyl-1-propylpiperidinium ion, and a 1-butyl-1-methylpiperidinium ion.

[0078] Examples of the quaternary phosphonium cation include a tetramethylphosphonium ion, a tetraethylphosphonium ion, a trimethylethylphosphonium ion, a trimethylpropylphosphonium ion, a trimethylbutylphosphonium ion, and a tetraphenylphosphonium ion.

[0079] Examples of the tertiary sulfonium cation include a trimethyl sulfonium ion, a triethyl sulfonium ion, and a tributyl sulfonium ion.

[0080] As the cation constituting the ionic liquid, from the viewpoints of being appropriately reductively decomposed and forming a better coating on the negative electrode surface, a quaternary ammonium cation is preferred, an aliphatic quaternary ammonium cation such as a pyrrolium cation, a pyrazolium cation, a pyrrolinium cation, a pyrrolidinium cation, a piperidinium cation, or a tetraalkylammonium cation is more preferred, a cyclic aliphatic quaternary ammonium cation such as a pyrrolium cation, a pyrazolium cation, a pyrrolinium cation, a pyrrolidinium cation, or a piperidinium cation is even more preferred, and a pyrrolidinium cation is even more preferred. One or more of these cations may be contained.

[0081] The anions that make up the ionic liquid are PF6 - , PO2F2 - , BF4- , ClO4 - , NO2 - , NO3 - , I - , SO3CF3 - , C(SO2CF3)3 - , C(SO2C2F5)3 - , N(SO2F)2 - (Bis(fluorosulfonyl)imide anion: FSI - ), N(CF3SO2)2 - (bis(trifluoromethanesulfonyl)imide anion), N(C2F5SO2)2 - (bis(pentafluoroethanesulfonyl)imide anion), N(C4F9SO2)2 - (bis(nonafluorobutanesulfonyl)imide anion), N(POF2)2 - (bis(difluorophosphonyl)imide anion), N(CF3SO2)(CF3CO) - ((Trifluoromethanesulfonyl)(trifluoromethanecarbonyl)imide anion), N(CN)2 - (dicyanoimide anion), CF3-SO2-N-SO2-N-SO2CF3 - , FSO2-N-SO2-C4F9 - , CF3-SO2-N-SO2-C4F9 - , CF3-SO2-N-SO2-CF2-SO2-N-SO2-CF3 2- , CF3-SO2-N-SO2-CF2-SO3 2- , CF3-SO2-N-SO2-CF2-SO2-C(-SO2CF3)2 2- etc.

[0082] The anion constituting the ionic liquid is preferably an imide anion, such as N(SO2F)2 - (Bis(fluorosulfonyl)imide anion: FSI -) is more preferable. Furthermore, the anion constituting the ionic liquid preferably contains a fluorine atom. When the anion constituting the ionic liquid is such an anion, the ionic conductivity of the non-aqueous electrolyte is increased, and the occurrence of short circuits due to repeated charge and discharge is sufficiently suppressed. One or more of these anions may be contained.

[0083] [Lithium salt] Examples of lithium salts include salts of lithium ions and anions constituting the ionic liquid described above. Among lithium salts, lithium imide salts are preferred, and LiN(SO2F2)2 (lithium bis(fluorosulfonyl)imide: LiFSI) is more preferred. The use of such lithium salts increases the ionic conductivity of the non-aqueous electrolyte, and sufficiently suppresses the occurrence of short circuits due to repeated charge and discharge.

[0084] Furthermore, it is preferable that the anions present in the non-aqueous electrolyte are substantially only imide anions, and it is preferable that the anions are substantially only bis(fluorosulfonyl)imide anions. For example, the content of imide anions or bis(fluorosulfonyl)imide anions relative to all anions in the non-aqueous electrolyte is preferably 90 mol% or more, more preferably 99 mol% or more, and even more preferably 99.9 mol% or more. By configuring the anions in the non-aqueous electrolyte in this way, the ionic conductivity of the non-aqueous electrolyte is increased, and the occurrence of short circuits due to repeated charge and discharge is sufficiently suppressed.

[0085] The content of lithium salt in the non-aqueous electrolyte is 0.1 mol / dm 3 More than 3.0mol / dm 3 Preferably, 1.0 mol / dm or less 3 More than 2.5mol / dm 3 Less than 1.5 mol / dm is more preferable. 3 or more, and even 1.8 mol / dm 3 The above is even more preferable. By setting the content of the lithium salt in the above range, the ionic conductivity of the non-aqueous electrolyte can be increased, and various performances relating to the charge-discharge cycle can be improved. In particular, when the content of the lithium salt in the non-aqueous electrolyte is 1.5 mol / dm3 By setting the content to the upper limit or less, it is possible to effectively suppress the occurrence of short circuits, which tend to occur when a positive electrode active material with high capacity density, such as a lithium transition metal composite oxide, sulfur, LiO, etc. is used. Furthermore, by setting the content of the lithium salt to the upper limit or less, the viscosity and other properties of the non-aqueous electrolyte are optimized.

[0086] [Non-aqueous solvent] By including a nonaqueous solvent in the nonaqueous electrolyte, the viscosity of the nonaqueous electrolyte can be reduced, and the charge / discharge performance of the secondary battery can be improved, etc. Examples of the nonaqueous solvent include ethers, cyclic carbonates, chain carbonates, esters, amides, sulfones, lactones, and nitriles.

[0087] Some or all of the hydrogen atoms of the non-aqueous solvent may be substituted with other groups or atoms (e.g., fluorine atoms), and are preferably substituted with fluorine atoms. That is, the non-aqueous solvent is preferably a fluorinated solvent or contains a fluorinated solvent. The content of the fluorinated solvent relative to the non-aqueous solvent is preferably 50% by volume or more, preferably 70% 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. When the non-aqueous solvent consists essentially of a fluorinated solvent, oxidation resistance is particularly enhanced, and the occurrence of short circuits due to repeated charge and discharge is further suppressed.

[0088] Examples of the fluorinated solvent include fluorinated ethers, fluorinated cyclic carbonates, fluorinated chain carbonates, fluorinated carboxylic acid esters, fluorinated phosphate esters, etc. One or more types of fluorinated solvents can be used.

[0089] The fluorinated ether may be a fluorinated cyclic ether or a fluorinated chain ether, but is preferably a fluorinated chain ether. Examples of the fluorinated chain ether include compounds represented by the following formula (2): R 1 -OR 2 ···(2) In formula (2), R 1is a fluorinated hydrocarbon group having 1 to 8 carbon atoms. 2 is a hydrocarbon group having 1 to 8 carbon atoms or a fluorinated hydrocarbon group having 1 to 8 carbon atoms.

[0090] Above R 1 R is preferably a fluorinated alkyl group. 1 The upper limit of the number of carbon atoms in R is preferably 5, more preferably 3, and even more preferably 2. 1 The lower limit of the number of carbon atoms is preferably 2.

[0091] Above R 2 R is preferably a fluorinated hydrocarbon group, more preferably a fluorinated alkyl group. 2 The upper limit of the number of carbon atoms in R is preferably 5, more preferably 3, and even more preferably 2. 2 The lower limit of the number of carbon atoms is preferably 2.

[0092] Above R 1 and R 2 The upper limit of the total number of carbon atoms is preferably 6, more preferably 5, and even more preferably 4. On the other hand, the lower limit of the total number of carbon atoms is preferably 3, and more preferably 4. 1 and R 2 The upper limit of the total number of fluorines is preferably 15, more preferably 10. On the other hand, the lower limit of the total number of fluorines is preferably 2, more preferably 4. By using a fluorinated ether having such a carbon number and fluorine number, the viscosity and ionic conductivity are optimized, and the occurrence of short circuits due to repeated charge and discharge is further suppressed.

[0093] Specific examples of fluorinated ethers include CF3OCH3, CF3OC2H5, F(CF2)2OCH3, F(CF2)2OC2H5, CF3(CF2)CH2O(CF2)CF3, F(CF2)3OCH3, F(CF2)3OC2H5, F(CF2)4OCH3, F(CF2)4OC2H5, F(CF2)5OCH3, F(CF2)5OC2H5, F(CF2)8OCH3, F(CF2)8OC2H5, CF3CH2OCH3, CF3CH2OCHF2, CF3 CF2CH2OCH3, CF3CF2CH2OCHF2, CF3CF2CH2O(CF2)2H, CF3CF2CH2O(CF2)2F, HCF2CH2OCH3, (CF3)(CF2)CH2O(CF2)2H, H(CF2)2OC H2CH3, H(CF2)2OCH2CF3, H(CF2)2CH2OCHF2, H(CF2)2CH2O(CF2)2H, H(CF2)2CH2O(CF2)3H, H(CF2)3CH2O(CF2)2H, H(CHF)2CH2O (CF2)2H, (CF3)2CHOCH3, (CF3)2CHCF2OCH3, CF3CHFCF2OCH3, CF3CHFCF2OCH2CH3, CF3CHFCF2CH2OCHF2, CF3CHFCF2OCH2(CF2)2 F, CF3CHFCF2OCH2CF2CF2H, H(CF2)4CH2O(CF2)2H, CH3CH2O(CF2)4F, F(CF2)4CH2O(CF2)2H, H(CF2)2CH2OCF2CHFCF3, F(CF2)2C Examples include H2OCF2CHFCF3, H(CF2)4CH2O(CF2)H, CF3OCH2(CF2)2F, CF3CHFCF2OCH2(CF2)3F, CH3CF2OCH2(CF2)2F, CH3CF2OCH2(CF2)3F, CH3O(CF2)5F, F(CF2)3CH2OCH2(CF2)3F, F(CF2)2CH2OCH2(CF2)2F, H(CF2)2CH2OCH2(CF2)2H, CH3CF2OCH2(CF2)2H, etc.

[0094] Examples of the fluorinated cyclic carbonate include fluorinated ethylene carbonates such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate, fluorinated propylene carbonate, and fluorinated butylene carbonate.

[0095] Examples of the fluorinated chain carbonate include 2,2,2-trifluoroethyl methyl carbonate, bis(2,2,2-trifluoroethyl) carbonate, and ethyl-2,2,2-trifluoroethyl carbonate.

[0096] Examples of the fluorinated carboxylic acid ester include methyl 3,3,3-trifluoropropionate and 2,2,2-trifluoroethyl acetate.

[0097] Examples of the fluorinated phosphate ester include tris(2,2-difluoroethyl) phosphate and tris(2,2,2-trifluoroethyl) phosphate.

[0098] Among fluorinated solvents, fluorinated ethers are more preferred. The use of fluorinated ethers can further reduce the viscosity of the non-aqueous electrolyte, thereby further suppressing the occurrence of short circuits due to repeated charge and discharge. Furthermore, since fluorinated ethers are unlikely to coordinate with ions in the non-aqueous electrolyte, it is believed that they do not impair the properties of the ionic liquid. Therefore, by using a non-aqueous electrolyte in which an ionic liquid and a fluorinated ether are mixed, the viscosity is reduced without impairing the properties of the ionic liquid, and the charge and discharge performance of the secondary battery is improved. From the viewpoint of further enhancing the above-mentioned effects, the content of the fluorinated ether relative to the non-aqueous solvent or the fluorinated solvent is preferably 50% by volume or more, more preferably 70% 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.

[0099] The molar ratio of the ionic liquid to the non-aqueous solvent (ionic liquid:non-aqueous solvent) is preferably in the range of 50:50 to 90:10, and more preferably in the range of 60:40 to 80:20. By setting the molar ratio of the ionic liquid to the non-aqueous solvent in this range, the viscosity and other properties of the non-aqueous electrolyte can be optimized.

[0100] [Other ingredients] The non-aqueous electrolyte may further contain other components as additives in addition to the ionic liquid, lithium salt, and non-aqueous solvent.

[0101] Examples of additives include 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, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, and cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, and propane sulfite. sultone, propene sultone, butane sultone, 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, and lithium difluorophosphate. These additives may be used alone or in combination of two or more.

[0102] The content of the additive 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, based on the total mass of the non-aqueous electrolyte. By setting the content of the additive within the above range, it is possible to improve the capacity retention or cycle performance after high-temperature storage, and to further improve safety.

[0103] In non-aqueous electrolyte storage elements, the lower limit of the positive electrode potential at the end-of-charge voltage during normal use is 4.2 V (vs. Li / Li + ), and 4.3V (vs. Li / Li + ) is more preferable, and 4.4V (vs. Li / Li + ), and 4.5V (vs. Li / Li + ), and 4.6V (vs. Li / Li + ) is even more preferable. By setting the positive electrode potential at the end-of-charge voltage during normal use to be equal to or higher than the above lower limit, it is possible to increase the energy density and voltage, and also to increase the discharge capacity. Furthermore, the nonaqueous electrolyte provided in the nonaqueous electrolyte storage element has good oxidation resistance, and even if the positive electrode potential at the end-of-charge voltage during normal use is set high in this way, the occurrence of short circuits due to repeated charge and discharge is sufficiently suppressed, and the capacity retention rate is also high.

[0104] The upper limit of the positive electrode potential at the end-of-charge voltage during normal use of the nonaqueous electrolyte storage element is, for example, 5.0 V (vs. Li / Li + ) and 4.8V (vs. Li / Li + ) and 4.7V (vs. Li / Li + ) may also be used.

[0105] In the nonaqueous electrolyte storage element, it is preferable that at least a portion of the electrode assembly composed of a positive electrode, a negative electrode, and a separator is in a pressurized state. Such pressurization tends to increase the capacity retention rate during repeated charge and discharge. For example, the electrode assembly housed in a container may be pressurized from the outside of the container, i.e., via the container. The electrode assembly is preferably pressurized in the direction in which the positive electrode, negative electrode, and separator are stacked (thickness direction of each layer). That is, it is preferable that the positive electrode active material layer and the negative electrode active material layer are pressurized in a direction in which they are crushed in the thickness direction. However, a portion of the electrode assembly (e.g., a pair of curved portions in a flat, wound electrode assembly) may not be pressurized. Furthermore, only a portion of the flat portion of a laminated electrode assembly or a flat, wound electrode assembly may be pressurized. The pressure applied to at least a portion of the electrode assembly in the pressurized state or the pressure applied externally to the container is preferably 0.01 MPa to 2 MPa, more preferably 0.1 MPa to 1.5 MPa, and even more preferably 0.2 MPa to 1 MPa. By setting the pressure to the lower limit or more, the capacity retention rate can be increased more sufficiently, whereas by setting the pressure to the upper limit or less, the occurrence of short circuits during repeated charge and discharge is further suppressed.

[0106] The electrode assembly can be pressurized, for example, by a pressure member that pressurizes the container from the outside. The pressure member may be a restraining member that restrains the shape of the container. The pressure member (restraining member) is arranged to sandwich and pressurize the electrode assembly from both sides in the thickness direction, for example, via the container. The surface of the electrode assembly to be pressed is in contact with the inner surface of the container directly or via another member. Therefore, the electrode assembly is pressurized by pressurizing the container. Examples of pressure members include restraining bands and metal frames. For example, the metal frame may be configured so that the load can be adjusted using bolts or the like. Alternatively, a plurality of nonaqueous electrolyte storage elements may be arranged in the thickness direction of the electrode assembly, and fixed using a frame or the like while being pressed from both ends in the thickness direction.

[0107] 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.

[0108] 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.

[0109] <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 energy storage element included in the energy storage unit.

[0110] 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.

[0111] <Method of manufacturing nonaqueous electrolyte energy storage element> A method for producing a nonaqueous electrolyte storage element according to one embodiment of the present invention includes preparing a combination of a positive electrode and metallic lithium or a negative electrode having a surface region on which metallic lithium can be deposited during charging (Step 1), preparing a separator having a layer containing inorganic particles (Step 2), and preparing a nonaqueous electrolyte containing an ionic liquid (Step 3). The order of Steps 1, 2, and 3 is not particularly limited.

[0112] Step 1 may be to provide a positive electrode and a negative electrode having metallic lithium, or to provide a positive electrode and a negative electrode having a surface region onto which metallic lithium can be deposited during charging.

[0113] Preparing a negative electrode containing metallic lithium may mean fabricating a negative electrode containing metallic lithium. The negative electrode can be fabricated by laminating a negative electrode active material layer containing metallic lithium directly or via an intermediate layer on a negative electrode substrate, and then pressing the layer. The negative electrode active material layer containing metallic lithium may be a lithium foil or a lithium alloy foil.

[0114] The negative electrode having a surface region on which metallic lithium can be deposited during charging may be, for example, a negative electrode consisting only of a negative electrode substrate. When preparing a negative electrode having a surface region on which metallic lithium can be deposited during charging, a positive electrode having a positive electrode active material containing lithium ions is prepared in advance.

[0115] The positive electrode may be prepared by, for example, applying a paste-like positive electrode mixture (positive electrode mixture paste) to a positive electrode substrate directly or via an intermediate layer, and then drying the mixture to form a positive electrode active material layer.

[0116] Step 2 may be to prepare a separator having a layer containing inorganic particles, or may be to prepare a commercially available separator having a layer containing inorganic particles.

[0117] Step 3 may be preparing a non-aqueous electrolyte containing an ionic liquid. The non-aqueous electrolyte can be prepared by mixing the components that make up the non-aqueous electrolyte.

[0118] For example, a specific method for producing the nonaqueous electrolyte storage element includes preparing or fabricating a positive electrode, preparing or fabricating a negative electrode, preparing or preparing a nonaqueous electrolyte, preparing or fabricating a separator, stacking or winding the positive electrode and negative electrode with the separator interposed therebetween to form an alternately stacked electrode assembly, housing the positive electrode and negative electrode (electrode assembly) in a container, and injecting the nonaqueous electrolyte into the container. After injection, the nonaqueous electrolyte storage element can be obtained by sealing the inlet.

[0119] The method for producing the nonaqueous electrolyte storage element may further include initially charging and discharging the assembled, uncharged storage element. For example, when a lithium transition metal composite oxide in which the molar ratio (Li / Me) of lithium (Li) to the transition metal (Me) is greater than 1 is used as the positive electrode active material of the nonaqueous electrolyte storage element, the capacity increases through the initial charging and discharging. The number of charging and discharging in the initial charging and discharging may be one or two, or may be three or more. When a lithium transition metal composite oxide in which the molar ratio (Li / Me) of lithium (Li) to the transition metal (Me) is greater than 1 is used as the positive electrode active material of the nonaqueous electrolyte storage element, the positive electrode potential (positive electrode potential) at the end-of-charge voltage in the initial charging and discharging is 4.5 V (vs. Li / Li + ) or more than 4.7V (vs. Li / Li + ) or less.

[0120] <Other embodiments> The energy storage device 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 can be added to the configuration of another embodiment, and part of the configuration of one embodiment can be replaced with the configuration of another embodiment or well-known technology. Furthermore, part of the configuration of one embodiment can be deleted. Also, well-known technology can be added to the configuration of one embodiment.

[0121] In the above embodiment, the nonaqueous electrolyte storage element is described as being 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 and capacitors such as electric double layer capacitors and lithium ion capacitors. The nonaqueous electrolyte storage element of the present invention can also be applied to lithium-air batteries. [Example]

[0122] 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.

[0123] [Example 1] (Preparation of positive electrode) The positive electrode active material has an α-NaFeO2 type crystal structure and Li 1+α Me 1-α A lithium transition metal composite oxide represented by O2 (Me is a transition metal) was used. Here, the molar ratio of Li to Me, Li / Me, was 1.33, and Me was composed of Ni and Mn, with a molar ratio of Ni:Mn=1:2. A positive electrode mixture paste containing the 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 (solid content) was prepared using N-methylpyrrolidone (NMP) as a dispersion medium. The positive electrode mixture paste was applied to one side of an aluminum foil (average thickness 15 μm) as a positive electrode substrate and dried to prepare a positive electrode with a positive electrode active material layer (average thickness 135 μm) disposed thereon.

[0124] (Preparation of negative electrode) A lithium foil made of pure metallic lithium was laminated on one side of the copper foil (average thickness 10 μm) serving as the negative electrode substrate, and then pressed to produce a negative electrode with a negative electrode active material layer (average thickness 60 μm) disposed thereon.

[0125] (Preparation of non-aqueous electrolyte) The ionic liquid 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide (Py 13 FSI) and 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TFEE), a fluorinated ether, were mixed in a molar ratio of 70:30. 3 A non-aqueous electrolyte was prepared by mixing LiFSI at a concentration of 1000 ppm.

[0126] (Preparing the separator) A separator with an average thickness of 20 μm was prepared, in which a layer containing 70 mass % or more of inorganic particles (average thickness 6 μm) was laminated on each side of a substrate layer (average thickness 8 μm) which was a porous resin film.

[0127] (Fabrication of non-aqueous electrolyte energy storage element) The positive electrode and the negative electrode were stacked with the separator interposed therebetween to produce an electrode assembly, which was then housed in a container made of a metal resin composite film, the nonaqueous electrolyte was poured into the container, the container was sealed by heat welding, and the container was externally pressurized at 0.3 MPa to produce the nonaqueous electrolyte storage element of Example 1.

[0128] [Comparative Example 1] A nonaqueous electrolyte storage element of Comparative Example 1 was obtained in the same manner as in Example 1, except that a separator in which polyvinylidene fluoride (PVDF) layers were laminated on both sides of a polyolefin microporous membrane was used as the separator.

[0129] Comparative Example 2 The non-aqueous electrolyte was a mixture of fluoroethylene carbonate (FEC) and 2,2,2-trifluoroethyl methyl carbonate (TFEMC) (volume ratio 30:70) with 1.0 mol / dm 3 A nonaqueous electrolyte storage element of Comparative Example 2 was obtained in the same manner as in Example 1, except that a nonaqueous electrolyte prepared by mixing LiPF6 at a concentration of 1000 ppm was used.

[0130] Comparative Example 3 The separator used was a polyolefin microporous membrane with PVDF layers laminated on both sides. The non-aqueous electrolyte was a mixture of FEC and TFEMC (volume ratio 30:70) at 1.0 mol / dm 3 A nonaqueous electrolyte storage element of Comparative Example 3 was obtained in the same manner as in Example 1, except that a nonaqueous electrolyte prepared by mixing LiPF6 at a concentration of 1000 ppm was used.

[0131] (Initial charge / discharge) Two samples were prepared for each of the nonaqueous electrolyte storage elements of Example 1 and Comparative Examples 1 to 3, and initial charge / discharge was carried out under the following conditions. At 25°C, the battery was charged at a constant current and constant voltage with a charge current of 0.1 C and a cut-off voltage of 4.6 V. The charge was terminated when the charge current reached 0.02 C. A 10-minute rest period was then allowed. Subsequently, a constant current discharge was performed with a discharge current of 0.1 C and a cut-off voltage of 2.0 V, followed by another 10-minute rest period. Next, the battery was charged at a constant current and constant voltage with a charging current of 0.2 C and a cut-off voltage of 4.6 V. The charge was terminated when the charging current reached 0.05 C. After that, a 10-minute rest period was allowed. After that, the battery was discharged at a constant current of 0.1 C and a cut-off voltage of 2.0 V.

[0132] (Charge-discharge cycle test) Next, the following charge-discharge cycle test was performed on two samples of each of the nonaqueous electrolyte storage elements of Example 1 and Comparative Examples 1 to 3. Constant-current, constant-voltage charging was performed at 25°C with a charging current of 0.2 C and a cut-off voltage of 4.6 V. The charge was terminated until the charging current reached 0.05 C. A 10-minute rest period was then provided. Subsequently, constant-current discharging was performed with a discharging current of 0.1 C and a cut-off voltage of 2.0 V, followed by a 10-minute rest period. This charge-discharge cycle was repeated until a short circuit occurred, or for a maximum of approximately 150 cycles.

[0133] Table 1 shows the number of charge-discharge cycles required until a short circuit occurred for two samples of each of the nonaqueous electrolyte storage elements of Example 1 and Comparative Examples 1 to 3. Fig. 3A shows a graph representing the capacity retention rate per cycle for each nonaqueous electrolyte storage element of Example 1, Fig. 3B shows a graph representing the capacity retention rate per cycle for each nonaqueous electrolyte storage element of Comparative Example 1, Fig. 3C shows a graph representing the capacity retention rate per cycle for each nonaqueous electrolyte storage element of Comparative Example 2, and Fig. 3D shows a graph representing the capacity retention rate per cycle for each nonaqueous electrolyte storage element of Comparative Example 3.

[0134] [Table 1]

[0135] As shown in Table 1 above and FIG. 3A, the nonaqueous electrolyte energy storage element of Example 1, which includes a nonaqueous electrolyte containing an ionic liquid and a separator having a layer containing inorganic particles, does not short-circuit even after at least 145 charge-discharge cycles, confirming that the occurrence of short circuits is suppressed. Furthermore, it can be seen that when a separator having a layer containing inorganic particles is used in a nonaqueous electrolyte storage element having a nonaqueous electrolyte that does not contain an ionic liquid, as in Comparative Example 2 (FIG. 3C), the capacity retention rate tends to be lower than when a separator not having a layer containing inorganic particles is used, as in Comparative Example 3 (FIG. 3D). However, a comparison between Example 1 (FIG. 3A) and Comparative Example 2 (FIG. 3B) shows that the nonaqueous electrolyte storage element having a nonaqueous electrolyte containing an ionic liquid of Example 1 has a capacity retention rate that is equal to or higher than that of the nonaqueous electrolyte storage element of Comparative Example 1, despite using a separator having a layer containing inorganic particles.

[0136] [Example 2] A nonaqueous electrolyte electricity storage element of Example 2 was obtained in the same manner as in Example 1, except that the container was pressurized from the outside at 0.6 MPa.

[0137] [Example 3] As an ionic liquid, Py 13 Instead of FSI, trimethylpropylphosphonium bis(fluorosulfonyl)imide (P 1113 A nonaqueous electrolyte electricity storage element of Example 3 was obtained in the same manner as in Example 2, except that FSI was used.

[0138] (Initial charge / discharge and charge / discharge cycle test) The initial charge-discharge and charge-discharge cycle tests were carried out using the above-described methods for each of the nonaqueous electrolyte storage elements of Examples 2 and 3. The number of charge-discharge cycles required until a short circuit occurred is shown in Table 2. FIG. 4A is a graph showing the capacity retention rate per cycle for each of the nonaqueous electrolyte storage elements of Example 2, and FIG. 4B is a graph showing the capacity retention rate per cycle for each of the nonaqueous electrolyte storage elements of Example 3.

[0139] [Table 2]

[0140] As shown in Table 2 above and Figures 4A and 4B, the ionic liquid having a quaternary ammonium cation (Py 13The nonaqueous electrolyte energy storage element of Example 2 (FIG. 4A) having a nonaqueous electrolyte containing an ionic liquid having a quaternary phosphonium cation (P FSI) was subjected to a relatively high pressure, which is a condition that makes a short circuit likely to occur. 1113 It can be seen that the occurrence of short circuits is sufficiently suppressed compared to the nonaqueous electrolyte energy storage element of Example 3 (FIG. 4B) which has a nonaqueous electrolyte containing FSI). Furthermore, a comparison between Example 1 (FIG. 3A) in which a pressure was applied at 0.3 MPa and Example 2 (FIG. 4A) in which a pressure was applied at 0.6 MPa reveals that the capacity retention rate after, for example, approximately 150 charge-discharge cycles is improved by applying a relatively high pressure. [Industrial Applicability]

[0141] 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]

[0142] 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 Energy storage device

Claims

1. a negative electrode having metallic lithium; a separator having a layer containing inorganic particles; a non-aqueous electrolyte containing an ionic liquid and a fluorinated solvent; A non-aqueous electrolyte electricity storage element comprising:

2. a negative electrode having metallic lithium; a separator having a substrate layer and a layer containing inorganic particles laminated on one or both surfaces of the substrate layer; a non-aqueous electrolyte containing an ionic liquid and a lithium salt; Equipped with The content of the lithium salt in the non-aqueous electrolyte is 1.0 mol / dm ３ 2.0mol / dm or more ３ A non-aqueous electrolyte electricity storage element as follows:

3. 3. The nonaqueous electrolyte storage element according to claim 1, wherein a surface of the negative electrode faces a surface of the layer containing inorganic particles.

4. preparing a combination of a positive electrode and a negative electrode having metallic lithium or a surface area on which metallic lithium can be deposited upon charging; providing a separator having a layer including inorganic particles; and Preparing a non-aqueous electrolyte containing an ionic liquid The method for manufacturing the nonaqueous electrolyte storage element according to claim 1 , comprising:

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