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

Abstract

One aspect of the present invention is a non-aqueous electrolyte power storage element provided with: a positive electrode having a positive electrode active material layer having a per-unit-area capacitance density of 5 mAh / cm2 or more; a negative electrode containing lithium metal; and a non-aqueous electrolyte containing a fluorinated ether and an ionic liquid.

Description

[Technical Field]

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

[0002] 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, due to their high energy density. Generally, these non-aqueous electrolyte secondary batteries consist of a pair of electrodes electrically isolated by a separator and a non-aqueous electrolyte interposed between these electrodes. They are configured to charge and discharge by transferring ions between the two 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. Lithium metal is known as a high-energy-density negative electrode active material used in non-aqueous electrolyte energy storage elements (see Patent Documents 1 and 2).

[0003] Furthermore, in recent years, research has progressed on non-aqueous electrolyte energy storage elements using ionic liquids as non-aqueous electrolytes (see Patent Documents 3 and 4). Ionic liquids have advantages such as being liquid at room temperature, having virtually no volatility, and possessing high flame retardancy. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2016-100065 [Patent Document 2] Japanese Patent Application Publication No. 7-245099 [Patent Document 3] Japanese Patent Publication No. 2001-319688 [Patent Document 4] Japanese Patent Publication No. 2003-331918 [Overview of the project] [Problems that the invention aims to solve]

[0005] In non-aqueous electrolyte energy storage elements using metallic lithium as the negative electrode active material, the use of a non-aqueous electrolyte containing an ionic liquid is also being considered. Furthermore, from the standpoint of increasing the energy density of non-aqueous electrolyte energy storage elements, it is desirable to increase the capacity density of the positive electrode as well. However, according to the inventors' studies, in non-aqueous electrolyte energy storage elements using metallic lithium as the negative electrode active material and a non-aqueous electrolyte containing an ionic liquid, increasing the capacity density of the positive electrode has the disadvantage of making it easier for short circuits to occur with repeated charging and discharging.

[0006] The present invention was made based on the circumstances described above, and its purpose is to achieve a capacity density of 5 mAh / cm³ per unit area. 2 The objective is to provide a non-aqueous electrolyte energy storage element comprising a positive electrode having a positive electrode active material layer as described above, a negative electrode having metallic lithium, and a non-aqueous electrolyte containing an ionic liquid, wherein the occurrence of short circuits due to repeated charging and discharging is suppressed, and a method for manufacturing such a non-aqueous electrolyte energy storage element. [Means for solving the problem]

[0007] A non-aqueous electrolyte energy storage element according to one aspect of the present invention has a capacity density of 5 mAh / cm² per unit area. 2 This is a non-aqueous electrolyte energy storage element comprising a positive electrode having the positive electrode active material layer described above, a negative electrode having metallic lithium, and a non-aqueous electrolyte containing an ionic liquid and a fluorinated ether.

[0008] Another embodiment of the present invention provides a non-aqueous electrolyte energy storage element comprising a positive electrode, a negative electrode having metallic lithium, and a non-aqueous electrolyte containing an ionic liquid, wherein the positive electrode potential at the charging termination voltage during normal use is 4.2V (vs.Li / Li + The above ionic liquid is a non-aqueous electrolyte energy storage element whose main component is an ionic liquid that does not contain ether groups.

[0009] A method for manufacturing a non-aqueous electrolyte energy storage element according to another aspect of the present invention has a capacity density of 5 mAh / cm² per unit area. 2The method for manufacturing a non-aqueous electrolyte energy storage element comprises preparing a positive electrode having the positive electrode active material layer described above, preparing a negative electrode having metallic lithium or a surface region on which metallic lithium can be deposited during charging, and preparing a non-aqueous electrolyte containing an ionic liquid and a fluorinated ether. [Effects of the Invention]

[0010] According to one aspect of the present invention, the capacity density per unit area is 5 mAh / cm³. 2 A non-aqueous electrolyte energy storage element comprising a positive electrode having a positive electrode active material layer as described above, a negative electrode having metallic lithium, and a non-aqueous electrolyte containing an ionic liquid, wherein the occurrence of short circuits due to repeated charging and discharging is suppressed, and a method for manufacturing such a non-aqueous electrolyte energy storage element can be provided. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is an external perspective view showing a non-aqueous electrolyte energy storage element according to one embodiment of the present invention. [Figure 2] Figure 2 is a schematic diagram showing an energy storage device configured by assembling multiple non-aqueous electrolyte energy storage elements according to one embodiment of the present invention. [Modes for carrying out the invention]

[0012] First, an overview of the non-aqueous electrolyte energy storage element and the method for manufacturing the non-aqueous electrolyte energy storage element disclosed herein will be described.

[0013] A non-aqueous electrolyte energy storage element according to one aspect of the present invention has a capacity density of 5 mAh / cm² per unit area. 2 This is a non-aqueous electrolyte energy storage element comprising a positive electrode having the positive electrode active material layer described above, a negative electrode having metallic lithium, and a non-aqueous electrolyte containing an ionic liquid and a fluorinated ether.

[0014] A non-aqueous electrolyte energy storage element according to one aspect of the present invention has a capacity density of 5 mAh / cm² per unit area. 2The non-aqueous electrolyte energy storage element comprises a positive electrode having the positive electrode active material layer described above, a negative electrode having metallic lithium, and a non-aqueous electrolyte containing an ionic liquid, and the occurrence of short circuits associated with repeated charging and discharging is suppressed. The reason for this is not clear, but the following reasons are speculated. Generally, in non-aqueous electrolyte energy storage elements in which metallic lithium is used as the negative electrode active material, metallic lithium may deposit in a dendritic manner on the negative electrode surface during charging (hereinafter, metallic lithium in a dendritic form will be called "dendrites"). If these dendrites grow and penetrate the separator and come into contact with the positive electrode, it will cause a short circuit. In addition, the reductive decomposition of components constituting the non-aqueous electrolyte on the negative electrode may also be a factor that promotes the growth of dendrites. Furthermore, if the capacity density per unit area of ​​the positive electrode active material layer is high, the current density per unit area during charging will be high, so it is thought that the growth rate of dendrites on the negative electrode surface will be fast, and short circuits will be more likely to occur. In contrast, in a non-aqueous electrolyte energy storage element according to one aspect of the present invention, the inclusion of a fluorinated ether in the non-aqueous electrolyte containing an ionic liquid reduces the viscosity of the non-aqueous electrolyte, thereby suppressing the reductive decomposition of the ionic liquid itself. Furthermore, fluorinated ether is less susceptible to reductive decomposition in a fluorinated solvent. For these reasons, it is presumed that, according to a non-aqueous electrolyte energy storage element according to one aspect of the present invention, despite the high capacity density per unit area of ​​the positive electrode active material layer, the occurrence of short circuits associated with repeated charging and discharging is suppressed. Furthermore, this non-aqueous electrolyte energy storage element also exhibits high Coulomb efficiency. While the reason for this is not entirely clear, the following reasons are speculated: The presence of fluorinated ether in the non-aqueous electrolyte containing the ionic liquid reduces the viscosity of the non-aqueous electrolyte, as described above, thereby suppressing the reductive decomposition of the ionic liquid itself. Additionally, since fluorinated ether does not readily coordinate with ions in the non-aqueous electrolyte, it is thought not to interfere with the ionic liquid's characteristic of relatively increasing the Coulomb efficiency of non-aqueous electrolyte energy storage elements using metallic lithium as the negative electrode active material. It should be noted that, as shown in the comparative example described later, the decrease in Coulomb efficiency when a non-aqueous electrolyte containing an ionic liquid contains other fluorinated solvents besides fluorinated ether is presumed to be because the other fluorinated solvents coordinate with ions in the non-aqueous electrolyte, thereby inhibiting the characteristics of the ionic liquid. Thus, it is presumed that this non-aqueous electrolyte energy storage element achieves lower viscosity without inhibiting the characteristics of the ionic liquid by using a non-aqueous electrolyte mixture of ionic liquid and fluorinated ether, resulting in increased Coulomb efficiency. Furthermore, this non-aqueous electrolyte energy storage element can maintain high Coulomb efficiency even after repeated charging and discharging, resulting in a high capacity retention rate after the charge-discharge cycle. In addition, this non-aqueous electrolyte energy storage element has a capacity density of 5 mAh / cm² per unit area. 2 Because it comprises a positive electrode having the positive electrode active material layer described above and a negative electrode having metallic lithium, it has a high energy density.

[0015] The capacity density per unit area of the positive electrode active material layer is the value obtained by the following formula (a) when the design of the non-aqueous electrolyte storage element is clear, and the value obtained by the following capacity confirmation test and formula (b) when the design of the non-aqueous electrolyte storage element is unclear. In the following formulas (a) and (b), "capacity density" refers to the capacity density per unit area of the positive electrode active material layer. Also, in the following formula (a), "rated capacity" means the discharge capacity when the non-aqueous electrolyte storage element is fully charged and then discharged to a fully discharged state by adopting the charge and discharge conditions recommended or specified for the non-aqueous electrolyte storage element. When a charger for the non-aqueous electrolyte storage element is prepared, it means the case of charging by applying that charger. "Effective area" means the area where the positive electrode active material layer and the negative electrode active material layer face each other. (When the design of the non-aqueous electrolyte storage element is clear) Rated capacity (mAh) of non-aqueous electrolyte storage element / Effective area (cm 2 ) = Capacity density (mAh / cm 2 ) ···(a) (When the design of the non-aqueous electrolyte storage element is unclear) Disassemble the non-aqueous electrolyte storage element and conduct a capacity confirmation test on the positive electrode punched out to an arbitrary area. First, disassemble the non-aqueous electrolyte storage element, take out the positive electrode, and use dimethyl carbonate to thoroughly wash the non-aqueous electrolyte adhering to the taken-out positive electrode. After drying at room temperature for one day and night, assemble a test battery with a metal lithium electrode as the counter electrode. Here, pure metal lithium is used for the metal lithium electrode. Conduct a capacity confirmation test at a current value of 10 mA per 1 g of the positive electrode active material layer. Charge at a constant current until the charge termination voltage during normal use is reached to make it a fully charged state. After rest, discharge at a constant current until the lower limit voltage during normal use. From the discharge capacity (mAh) obtained in the capacity confirmation test and the area (cm 2 ) of the positive electrode active material layer in the test battery, the capacity density (mAh / cm 2) shall be determined. The work from disassembling the non-aqueous electrolyte energy storage element to assembling the test battery shall be carried out in an argon atmosphere with a dew point of -60°C or lower. "Normal use" refers to the case in which the non-aqueous electrolyte energy storage element is used under the charge and discharge conditions recommended or specified for the element, and if a charger for the non-aqueous electrolyte energy storage element is available, it refers to the case in which the charger is used. Discharge capacity (mAh) obtained in the capacity verification test / Area of ​​the positive electrode active material layer (cm²) in the test battery 2 )=capacity density(mAh / cm 2 ) ···(b)

[0016] Furthermore, the negative electrode of the non-aqueous electrolyte energy storage element only needs to have metallic lithium in the charged state, but does not need to have metallic lithium in the discharged state. For example, the negative electrode may have metallic lithium in the charged state because metallic lithium is deposited on at least a portion of the negative electrode surface during charging, and the negative electrode may be configured such that it substantially does not have metallic lithium in the discharged state because the metallic lithium on the negative electrode surface substantially dissolves into the non-aqueous electrolyte as lithium ions during discharge.

[0017] Preferably, the positive electrode contains a lithium transition metal composite oxide having an α-NaFeO2 type crystal structure or a spinel type crystal structure, or a polyanion compound containing nickel, cobalt, or manganese. By providing a positive electrode with such a high oxidation-reduction potential in the non-aqueous electrolyte energy storage element, the energy density can be increased. In conventional non-aqueous electrolyte energy storage elements equipped with a positive electrode with a high oxidation-reduction potential, when charging and discharging are repeated until the positive electrode potential reaches a high potential, it is thought that the amount of electricity used to decompose components with low oxidation resistance in the non-aqueous electrolyte at the positive electrode is used for dendrite growth at the negative electrode, making short circuits more likely to occur. In contrast, the non-aqueous electrolyte in the non-aqueous electrolyte energy storage element has good oxidation resistance, and even when such a positive electrode with a high oxidation-reduction potential is used, the occurrence of short circuits associated with repeated charging and discharging can be suppressed, and the Coulomb efficiency is also high.

[0018] In this non-aqueous electrolyte energy storage element, the positive electrode potential at the charging termination voltage during normal use is 3.5V (vs.Li / Li + It is preferable that the positive electrode potential is ) or higher. By increasing the positive electrode potential at the charging termination voltage during normal use, the energy density of the non-aqueous electrolyte energy storage element can be increased. Furthermore, the non-aqueous electrolyte in the non-aqueous electrolyte energy storage element has good oxidation resistance, and even if the positive electrode potential at the charging termination voltage during normal use is set high in this way, the occurrence of short circuits due to repeated charging and discharging can be suppressed, and the Coulomb efficiency is also high.

[0019] The above non-aqueous electrolyte preferably further contains lithium bis(fluorosulfonyl)imide (LiFSI). When the non-aqueous electrolyte contains LiFSI, LiFSI has relatively high ionic conductivity and forms a good film on the negative electrode surface, which further suppresses the occurrence of short circuits associated with repeated charging and discharging and can further improve Coulomb efficiency.

[0020] The above non-aqueous electrolyte further contains a lithium salt, and the lithium salt content in the above non-aqueous electrolyte is 1.5 mol / dm³ 3 Preferably, the lithium salt content in the non-aqueous electrolyte is 1.5 mol / dm³. 3 By doing so, the occurrence of short circuits associated with repeated charging and discharging can be further suppressed.

[0021] The fluorinated ether preferably contains 2 to 6 fluorine atoms. Using such a fluorinated ether can further suppress the occurrence of short circuits associated with repeated charging and discharging. The reason for this is not entirely clear, but it is presumed that such a fluorinated ether has moderate oxidation resistance and produces a high-quality coating on the negative electrode surface.

[0022] The ratio of the number of fluorine atoms to the total number of hydrogen atoms in the above-mentioned fluorinated ether is preferably 10% to 50%. By using such a fluorinated ether, the occurrence of short circuits associated with repeated charging and discharging can be further suppressed.

[0023] The above fluorinated ether is preferably represented by the following formula (1). R 1 -OR 2 ...(1) In formula (1), R 1 R is a fluorinated hydrocarbon group. 2 It is a hydrocarbon group. By using such fluorinated ethers, the occurrence of short circuits associated with repeated charging and discharging can be further suppressed.

[0024] It is preferable that the content of the fluorinated ether in all non-aqueous solvents included in the above non-aqueous electrolyte is 90% by volume or more. In such a case, the viscosity and resistance to reductive decomposition of the non-aqueous electrolyte are improved, which further suppresses the occurrence of short circuits associated with repeated charging and discharging. Note that ionic liquids are not included in the non-aqueous solvent.

[0025] The non-aqueous electrolyte energy storage element preferably includes a separator with an average thickness of 10 μm to 40 μm. By using a separator with an average thickness within the above range, the occurrence of short circuits associated with repeated charging and discharging can be further suppressed.

[0026] The above-mentioned ionic liquid preferably has as its main component an ionic liquid that does not contain ether groups. When an ionic liquid having as its main component an ionic liquid that does not contain ether groups is used, the decomposition of the ionic liquid is suppressed even when charging and discharging is repeated, and as a result, the occurrence of short circuits associated with repeated charging and discharging is further suppressed.

[0027] "An ionic liquid whose main component is an ionic liquid that does not contain an ether group" means that the content of an ionic liquid that does not contain an ether group relative to the total ionic liquid is more than 50% by volume.

[0028] Another embodiment of the present invention provides a non-aqueous electrolyte energy storage element comprising a positive electrode, a negative electrode having metallic lithium, and a non-aqueous electrolyte containing an ionic liquid, wherein the positive electrode potential at the charging termination voltage during normal use is 4.2V (vs.Li / Li + The ionic liquid is greater than ) and the above ionic liquid is a non-aqueous electrolyte energy storage element in which the ionic liquid mainly consists of an ionic liquid that does not have ether groups. According to another aspect of the present invention, a non-aqueous electrolyte energy storage element comprising a positive electrode, a negative electrode having metallic lithium and a non-aqueous electrolyte containing an ionic liquid, wherein the positive electrode potential is 4.2V (vs.Li / Li + This solves the problem of providing a non-aqueous electrolyte energy storage element in which the occurrence of short circuits is suppressed when charging and discharging is repeatedly performed to reach high potentials exceeding ).

[0029] A method for manufacturing a non-aqueous electrolyte energy storage element according to one aspect of the present invention has a capacity density of 5 mAh / cm² per unit area. 2 The method for manufacturing a non-aqueous electrolyte energy storage element comprises preparing a positive electrode having the positive electrode active material layer described above, preparing a negative electrode having metallic lithium or a surface region on which metallic lithium can be deposited during charging, and preparing a non-aqueous electrolyte containing an ionic liquid and a fluorinated ether.

[0030] According to this manufacturing method, the capacity density per unit area is 5 mAh / cm³. 2 A non-aqueous electrolyte energy storage element can be manufactured comprising a positive electrode having a positive electrode active material layer as described above, a negative electrode having metallic lithium, and a non-aqueous electrolyte containing an ionic liquid, wherein the occurrence of short circuits associated with repeated charging and discharging is suppressed. Furthermore, the non-aqueous electrolyte energy storage element obtained by this manufacturing method also exhibits high Coulomb efficiency, energy density, and capacity retention rate after charge-discharge cycles.

[0031] The following describes a non-aqueous electrolyte energy storage element according to one embodiment of the present invention, a method for manufacturing a non-aqueous electrolyte energy storage element, and other embodiments.

[0032] <Non-aqueous electrolyte energy storage element> A non-aqueous electrolyte energy storage element according to one embodiment of the present invention has a positive electrode, a negative electrode, and a non-aqueous electrolyte. Hereinafter, a non-aqueous electrolyte secondary battery (hereinafter also simply referred to as "secondary battery") will be described as an example of a non-aqueous electrolyte energy storage element. The positive electrode and the negative electrode usually form an electrode body that is alternately superimposed by lamination or winding with a separator in between. This electrode body is housed in a container, and the non-aqueous electrolyte is filled into this container. The non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. Furthermore, as the container, a known metal container, resin container, etc., which are normally used as containers for non-aqueous electrolyte energy storage elements, can be used.

[0033] (positive electrode) The positive electrode comprises a positive electrode substrate and a positive electrode active material layer disposed directly on the positive electrode substrate or via an intermediate layer.

[0034] The positive electrode substrate is conductive. "Conductive" means that the volume resistivity measured according to JIS-H-0505 (1975) is 10 7 This means that the above volume resistivity is 10 7 This means that the capacitance is greater than Ω·cm. As the material for the positive electrode substrate, metals such as aluminum, titanium, tantalum, and stainless steel, or alloys thereof, are used. Among these, aluminum and aluminum alloys are preferred due to the balance between high potential resistance, high conductivity, and cost. Furthermore, the positive electrode substrate can be formed in the form of foil or a vapor-deposited film, with foil being preferred from a cost standpoint. In other words, aluminum foil is preferred as the positive electrode substrate. Examples of aluminum or aluminum alloys include A1085P and A3003P as specified in JIS-H-4000 (2014).

[0035] 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 unit volume of the non-aqueous electrolyte energy storage element. The average thickness of the positive electrode substrate refers to the value obtained by dividing the punched mass when a predetermined area of ​​substrate is punched by the true density of the substrate and the punched area. The same applies to the average thickness of the negative electrode substrate, which will be described later.

[0036] The intermediate layer is a coating layer on the surface of the positive electrode substrate and reduces the contact resistance between the positive electrode substrate and the positive electrode active material layer by containing conductive particles such as carbon particles. The composition of the intermediate layer is not particularly limited and can be formed, for example, by a composition containing a resin binder and conductive particles.

[0037] The positive electrode active material layer is a layer formed from a so-called positive electrode mixture containing the positive electrode active material. The positive electrode mixture forming the positive electrode active material layer may contain optional components such as conductive agents, binders, thickeners, and fillers, as needed.

[0038] The positive electrode active material can be appropriately selected from known positive electrode active materials. For lithium secondary batteries, materials capable of intercalating and releasing lithium ions are typically used as positive electrode active materials. Examples of positive electrode active materials include lithium transition metal composite oxides having an α-NaFeO2 type crystal structure or a spinel type crystal structure, polyanion compounds, chalcogen compounds, sulfur, etc. Examples of 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[Lix 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 Examples include ]O2 (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1). As a lithium transition metal composite oxide having a spinel-type crystal structure, Li x Mn2O4, Li x Ni γ Mn 2-γ Examples include O4. Examples of polyanion compounds include LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, Li2CoPO4F, etc. Examples of chalcogen compounds include titanium disulfide, molybdenum disulfide, molybdenum dioxide, etc. Some atoms or polyanions in these materials may be substituted with atoms or anions 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 mixture form.

[0039] Preferred positive electrode active materials include lithium transition metal composite oxides having an α-NaFeO2 type crystal structure or a spinel type crystal structure, polyanion compounds, and chalcogen compounds. More preferably, lithium transition metal composite oxides having an α-NaFeO2 type crystal structure or a spinel type crystal structure, and polyanion compounds containing nickel, cobalt, or manganese (such as LiMnPO4, LiNiPO4, LiCoPO4, Li2MnSiO4, Li2CoPO4F, etc.) are used, and lithium transition metal composite oxides having an α-NaFeO2 type crystal structure are even more preferred. These positive electrode active materials have high oxidation-reduction potentials, and by using such positive electrode active materials, the energy density of the non-aqueous electrolyte energy storage element can be increased.

[0040] Lithium transition metal composite oxides having an α-NaFeO2 type crystal structure preferably contain nickel or manganese as the transition metal, and more preferably contain both nickel and manganese. Lithium transition metal composite oxides may further contain other transition metals such as cobalt. In lithium transition metal composite oxides having an α-NaFeO2 type crystal structure, the molar ratio of lithium (Li) to the transition metal (Me) (Li / Me) is preferably greater than 1.0, more preferably 1.1 or greater, more preferably 1.2 or greater, and even more preferably 1.3 or greater. By using such lithium transition metal composite oxides, it is possible to increase the electrical capacity, etc. The upper limit of the molar ratio of lithium to the transition metal (Li / Me) is preferably 1.6, and more preferably 1.5.

[0041] As lithium transition metal composite oxides having an α-NaFeO2 type crystal structure, compounds represented by the following formula (2) are preferred. Li 1+α Me 1-α O2···(2) In equation (2), Me is a transition metal containing Ni or Mn. 0 < α < 1.

[0042] In formula (2), Me preferably contains Ni and Mn. Me is preferably composed of substantially two elements, Ni and Mn, or three elements, Ni, Mn and Co. Me may also contain other transition metals.

[0043] In equation (2), the lower limit of the molar ratio of Ni to Me (Ni / Me) is preferably 0.1, and more preferably 0.2. On the other hand, the upper limit of this molar ratio (Ni / Me) is preferably 0.5, and more preferably 0.45. By setting the molar ratio (Ni / Me) within the above range, the energy density and other properties of the non-aqueous electrolyte energy storage element are improved.

[0044] In equation (2), 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, and more preferably 0.7. By setting the molar ratio (Mn / Me) within the above range, the energy density and other properties of the non-aqueous electrolyte energy storage element are improved.

[0045] In equation (2), 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. This molar ratio (Co / Me) or the lower limit of this molar ratio (Co / Me) may be 0.

[0046] In equation (2), 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, and more preferably 1.5. By setting the molar ratio (Li / Me) within the above range, the capacitance increases.

[0047] Lithium transition metal composite oxides having a molar ratio of lithium (Li) to the transition metal (Me) (Li / Me) greater than 1.0 are preferably those in which no diffraction peaks are present in the range of 20° to 22° in the X-ray diffraction pattern using CuKα rays. Lithium transition metal composite oxides having a molar ratio of lithium (Li) to the transition metal (Me) (Li / Me) greater than 1.0 generally have a positive electrode potential of, for example, 4.5V (vs. Li / Li + The capacitance increases after undergoing initial charge-discharge cycles up to a certain point. Furthermore, due to the change in crystal structure during such initial charge-discharge cycles, the diffraction peaks in the range of 20° to 22° that existed before the initial charge-discharge cycle disappear. In other words, a lithium transition metal composite oxide in which the molar ratio (Li / Me) of lithium (Li) to the transition metal (Me) is greater than 1.0, and in which no diffraction peaks exist in the range of 20° to 22° in the above X-ray diffraction pattern, has a large capacitance.

[0048] In this specification, the composition ratio of lithium transition metal composite oxide refers to the composition ratio when the device is fully discharged by the following method. First, the non-aqueous electrolyte energy storage element is charged with a constant current of 0.05C until it reaches the charging termination voltage for normal use, and is fully charged. After a 30-minute rest, it is discharged with a constant current of 0.05C until it reaches the lower limit voltage for normal use. The device is disassembled, the positive electrode is removed, and a test battery is assembled with a metallic lithium electrode as the counter electrode. The positive electrode potential is set to 2.0V (vs. Li / Li) with a current of 10mA per gram of positive electrode mixture. + A constant current discharge is performed until the positive electrode is fully discharged. Pure metallic lithium, not a lithium alloy, is used for the metallic lithium electrode here. The device is disassembled again, and the positive electrode is removed. The non-aqueous electrolyte adhering to the removed positive electrode is thoroughly washed with dimethyl carbonate, and after drying at room temperature for 24 hours, the lithium transition metal composite oxide of the positive electrode active material is collected. The collected lithium transition metal composite oxide is subjected to measurement. The work from disassembling the non-aqueous electrolyte energy storage element to collecting the lithium transition metal composite oxide is performed in an argon atmosphere with a dew point of -60°C or lower.

[0049] X-ray diffraction measurements of lithium transition metal composite oxides are performed on lithium transition metal composite oxides that have been brought to a fully discharged state using the method described above. Specifically, the X-ray diffraction measurement is performed by powder X-ray diffraction using an X-ray diffractometer (Rigaku's "MiniFlex II"), with the radiation source being CuKα rays, the tube voltage being 30kV, and the tube current being 15mA. At this time, the diffracted X-rays pass through a 30μm 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 13mm (OPEN), and the scattering slit width is 8mm.

[0050] The average particle size of the positive electrode active material is preferably, for example, 0.1 μm or more and 20 μm or less. Setting the average particle size of the positive electrode active material above the lower limit makes it easier to manufacture or handle the positive electrode active material. Setting the average particle size of the positive electrode active material below the upper limit improves the electronic conductivity of the positive electrode active material layer. Here, "average particle size" refers to the value at which the volume-based integrated distribution calculated in accordance with JIS-Z-8819-2 (2001), based on the particle size distribution measured by laser diffraction / scattering method on a dilution of particles diluted with a solvent in accordance with JIS-Z-8825 (2013), becomes 50%.

[0051] To obtain positive electrode active material particles in a predetermined shape, grinders and classifiers are used. Examples of grinding methods include using mortars, ball mills, sand mills, vibrating ball mills, planetary ball mills, jet mills, counter-jet mills, swirling airflow jet mills, or sieves. Wet grinding, which involves the coexistence of water or organic solvents such as hexane, can also be used during grinding. For classification, sieves and air-powered classifiers are used as needed, both dry and wet.

[0052] The content of the positive electrode active material in the positive electrode active material layer is preferably 70% to 98% by mass, more preferably 80% to 97% by mass, and even more preferably 90% to 96% by mass. By setting the content of the positive electrode active material within the above range, the energy density of the non-aqueous electrolyte energy storage element can be increased.

[0053] The conductive agent is not particularly limited as long as it is a material that has conductivity. Examples of such conductive agents include carbonaceous materials, metals, and conductive ceramics. Examples of carbonaceous materials include graphite and carbon black. Examples of carbon black include furnace black, acetylene black, and Ketjen black. Among these, carbonaceous materials are preferred from the viewpoint of conductivity and coating properties. Acetylene black and Ketjen black are particularly preferred. The conductive agent can take the form of powder, sheet, or fiber.

[0054] 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, and 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 non-aqueous electrolyte energy storage element can be increased.

[0055] Examples of binders 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.

[0056] The binder content in the positive electrode active material layer is preferably 0.5% by mass or more and 10% by mass or less, and more preferably 1% by mass or more and 6% by mass or less. By keeping the binder content within the above range, the positive electrode active material can be stably maintained.

[0057] Examples of thickening agents include polysaccharide polymers such as carboxymethylcellulose (CMC) and methylcellulose. Furthermore, if the thickening agent has a functional group that reacts with lithium, it is preferable to deactivate this functional group beforehand by methylation or the like. In one embodiment of the present invention, it is preferable that the thickening agent is not contained in the positive electrode active material layer.

[0058] The filler is not particularly limited. Examples of fillers 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 aluminosilicates, hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide, carbonates such as calcium carbonate, sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate, nitrides such as aluminum nitride and silicon nitride, mineral resource-derived materials such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof. In one embodiment of the present invention, it is preferable that the filler is not contained in the positive electrode active material layer.

[0059] The positive electrode active material layer may contain typical nonmetallic 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.

[0060] 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 the thickness measured at any five locations in the positive electrode active material layer.

[0061] The lower limit of the capacity density per unit area of ​​the positive electrode active material layer is 5 mAh / cm². 2 Therefore, 6mAh / cm 2 This is preferable. By having a capacity density per unit area of ​​the positive electrode active material layer that is above the above lower limit, it is possible to increase the energy density of the non-aqueous electrolyte energy storage element. An upper limit for the capacity density per unit area of ​​the positive electrode active material layer is, for example, 20 mAh / cm³. 2 It may also be 15mAh / cm². 2 It may also be 10mAh / cm².2 This may also be the case. The capacity density per unit area of ​​the positive electrode active material layer can be adjusted by the content of the positive electrode active material in the positive electrode active material layer, the type of positive electrode active material, the thickness of the positive electrode active material layer, etc.

[0062] (Negative electrode) The negative electrode comprises a negative electrode substrate and a negative electrode active material layer disposed directly on the negative electrode substrate or via an intermediate layer. The intermediate layer of the negative electrode can have the same configuration as the intermediate layer of the positive electrode.

[0063] The negative electrode substrate can have the same configuration as the positive electrode substrate, but the material used can be a metal such as copper, nickel, stainless steel, nickel-plated steel or an alloy thereof, or a carbonaceous material, with copper or a copper alloy being preferred. In other words, copper foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0064] 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, it is possible to increase the strength of the negative electrode substrate while increasing the energy density per unit volume of the non-aqueous electrolyte energy storage element.

[0065] The negative electrode active material layer contains metallic lithium. The metallic lithium is a component that functions as the negative electrode active material. The metallic lithium may exist as pure metallic lithium, consisting substantially only of lithium, or as a lithium alloy containing other metallic components. Examples of lithium alloys include lithium silver alloy, lithium zinc alloy, lithium calcium alloy, lithium aluminum alloy, lithium magnesium alloy, and lithium indium alloy. The lithium alloy may also contain multiple metallic elements other than lithium.

[0066] The negative electrode active material layer may be a layer consisting substantially only of metallic lithium. The metallic lithium content in the negative electrode active material layer may be 90% by mass or more, 99% by mass or more, or 100% by mass.

[0067] The negative electrode active material layer may be pure metallic lithium foil or 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 having particles containing metallic lithium. A negative electrode active material layer that is a porous layer having particles containing metallic lithium may further contain, for example, resin particles, inorganic particles, etc.

[0068] The negative electrode active material layer, i.e., the layer containing metallic lithium, is preferably a layer that exists even in the discharge state, that is, a layer that exists in all states from the charge state to the discharge state. The average thickness of the negative electrode active material layer in the discharge state is preferably 5 μm to 1,000 μm, more preferably 10 μm to 500 μm, and even more preferably 30 μm to 300 μm. The average thickness of the negative electrode active material layer refers to the average value of the thickness measured at any five locations in the negative electrode active material layer. When a negative electrode active material containing metallic lithium exists even in the discharge state, and preferably its average thickness is above the lower limit mentioned above, there is an advantage such as the presence of a sufficient amount of metallic lithium, which suppresses the decrease in capacity retention rate associated with repeated charging and discharging.

[0069] Furthermore, in the case of a non-aqueous electrolyte energy storage element configured such 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 dissolves into the non-aqueous electrolyte as lithium ions during discharge, the negative electrode does not need to have a negative electrode active material layer in the discharge state.

[0070] (Separator) The separator can be appropriately selected from known separators. As the separator, for example, a separator consisting only of a base layer, or a separator in which a heat-resistant layer containing heat-resistant particles and a binder is formed on one or both sides of the base layer, can be used. The base layer of the separator may also contain heat-resistant particles. Examples of materials for the base layer of the separator include woven fabric, nonwoven fabric, and porous resin film. Among these materials, porous resin film is preferred from the viewpoint of strength, and nonwoven fabric is preferred from the viewpoint of liquid retention of non-aqueous electrolytes. As the material for the base layer of the separator, 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 degradation resistance. A composite material of these resins may also be used as the base layer of the separator.

[0071] The heat-resistant particles contained in the heat-resistant layer and the base layer are preferably those whose mass loss when heated from room temperature to 500°C in air is 5% or less, and more preferably those whose mass loss when heated from room temperature to 800°C in air is 5% or less. Inorganic compounds are examples of materials whose mass loss when heated is below a predetermined level. Examples of inorganic compounds include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates; hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium titanate; covalent crystals such as silicon and diamond; mineral resource-derived materials or artificial products thereof such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica. These inorganic compounds may be used individually or in combination, or two or more may be used in mixtures. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicates are preferred from the viewpoint of safety for non-aqueous electrolyte energy storage elements.

[0072] The porosity of the separator is preferably 80 volume% or less from the viewpoint of strength, and preferably 20 volume% or more from the viewpoint of discharge performance. Here, "porosity" refers to a volume-based value and means the measurement value obtained using a mercury porosimeter.

[0073] The average thickness of the separator is preferably 10 μm or more and 40 μm or less. The lower limit of the average thickness of the separator is more preferably 15 μm, and may be even more preferably 20 μm or 25 μm. On the other hand, the upper limit of the average thickness of the separator is preferably 30 μm, and may be 25 μm. By having an average thickness of the separator above the lower limit, the occurrence of short circuits associated with repeated charging and discharging can be further suppressed. On the other hand, by having an average thickness of the separator below the upper limit, it is possible to increase the energy density per unit volume of the non-aqueous electrolyte energy storage element. The average thickness of the separator refers to the average value of the thickness measured at any five locations on the separator.

[0074] The separator preferably has a resin coating layer on one or both of its outermost layers. Examples of the resin include those exemplified as binders for the positive electrode active material layer, and fluororesins such as PVDF are preferred. The average thickness of one layer of the coating layer may be, for example, 0.1 μm or more and 3 μm or less. The average thickness of the coating layer is the average thickness of the separator minus the average thickness measured at any five locations on the separator with the coating layer removed. By providing such a coating layer, the oxidation resistance of the separator is increased, and the Coulomb efficiency and capacity retention rate of the non-aqueous electrolyte energy storage element are improved.

[0075] A polymer gel composed of a polymer and a non-aqueous electrolyte may be used as a separator. Examples of polymers include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polyethylene carbonate, polypropylene carbonate, polyvinyl carbonate, polyalkyl methacrylates such as polymethyl methacrylate, polyalkyl acrylates such as polymethyl acrylate, polyvinylethylene carbonate, polyvinyl acetate, polyvinylpyrrolidone, polymaleic acid and its derivatives, polyvinylidene fluoride, poly(vinylidene fluoride-co-hexafluoropropylene), polytetrafluoroethylene, copolymers of monomers constituting these polymers, and mixtures of these polymers. These polymers may also be compounded with inorganic salts or ionic liquids. Using a polymer gel has the effect of suppressing leakage. A polymer gel may also be used in combination with a porous resin film or nonwoven fabric as described above as a separator.

[0076] (Non-aqueous electrolytes) Non-aqueous electrolytes contain an ionic liquid and a fluorinated ether, which is a non-aqueous solvent. Non-aqueous electrolytes typically further contain a lithium salt. Note that the ionic liquid is not included in the non-aqueous solvent. In other words, non-aqueous electrolytes typically contain an ionic liquid, a non-aqueous solvent, and a lithium salt, with at least a fluorinated ether as the non-aqueous solvent. The non-aqueous solvent may consist solely of a fluorinated ether, or it may further contain other non-aqueous solvents other than the fluorinated ether. Non-aqueous electrolytes may further contain other components besides the ionic liquid, non-aqueous solvent, and lithium salt. Examples of other components include additives.

[0077] (Ionic liquid) An ionic liquid is an ionic compound that is at least partially liquid at room temperature (20°C). It is preferable that the ionic liquid mainly consists of an ionic liquid that does not contain an ether group. An ether group is defined as -R a -OR b (R a R is a divalent hydrocarbon group. bThis refers to a monovalent hydrocarbon group. Some or all of the hydrogen atoms in the above-mentioned divalent hydrocarbon group, and some or all of the hydrogen atoms in the above-mentioned monovalent hydrocarbon group, may be substituted with other groups or atoms.

[0078] The content of ionic liquids without ether groups relative to all ionic liquids in the non-aqueous electrolyte is preferably 70% by volume or more, preferably 80% 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 ionic liquid is mainly composed of ionic liquids without ether groups, and especially when it consists substantially only of ionic liquids without ether groups, the oxidation resistance of the non-aqueous electrolyte is particularly increased, and the occurrence of short circuits when charging and discharging is repeated is further suppressed.

[0079] Examples of cations that constitute ionic liquids include ammonium cations (quaternary ammonium cations), phosphonium cations (quaternary phosphonium cations), and sulfonium cations (tertiary sulfonium cations).

[0080] Examples of ammonium cations include imidazolium cation, tetraalkylammonium cation, pyridinium cation, pyrrolium cation, pyrazolium cation, pyrrolidinium cation, and piperidinium cation.

[0081] Examples of imidazolium cations include 1,3-dimethylimidazolium ion, 1-ethyl-3-methylimidazolium ion, 1,3-diethylimidazolium ion, 1-butyl-3-methylimidazolium ion, 1,2,3-trimethylimidazolium ion, 1,2-dimethyl-3-ethylimidazolium ion, 1,2-dimethyl-3-propylimidazolium ion, 1-butyl-2,3-dimethylimidazolium ion, 1-methoxymethyl-3-methylimidazolium ion, 1-(2-methoxyethyl)-3-methylimidazolium ion, 1-(3-methoxypropyl)-3-methylimidazolium ion, 1-methoxymethyl-3-ethylimidazolium ion, 1-(2-methoxyethyl)-3-ethylimidazolium ion, and 1-(3-methoxypropyl)-3-ethylimidazolium ion. Among these, 1,3-dimethylimidazolium ion, 1-ethyl-3-methylimidazolium ion, 1,3-diethylimidazolium ion, 1-butyl-3-methylimidazolium ion, 1,2,3-trimethylimidazolium ion, 1,2-dimethyl-3-ethylimidazolium ion, 1,2-dimethyl-3-propylimidazolium ion, and 1-butyl-2,3-dimethylimidazolium ion are preferred from the viewpoint of further suppressing the occurrence of short circuits.

[0082] Examples of tetraalkylammonium cations include trimethylethylammonium ion, trimethylpropylammonium ion, trimethylhexylammonium ion, tetrapentylammonium ion, trimethyl(methoxymethyl)ammonium ion, trimethyl(2-methoxyethyl)ammonium ion, trimethyl(3-methoxypropyl)ammonium ion, diethyl(methoxymethyl)methylammonium ion, diethyl(2-methoxyethyl)methylammonium ion, and diethyl(3-methoxypropyl)methylammonium ion. Among these, trimethylethylammonium ion, trimethylpropylammonium ion, trimethylhexylammonium ion, and tetrapentylammonium ion are preferred from the viewpoint of further suppressing the occurrence of short circuits.

[0083] 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, 1-butyl-2,4-dimethylpyridinium ion, N-methoxymethylpyridinium ion, N-(2-methoxyethyl)pyridinium ion, and N-(3-methoxypropyl)pyridinium ion. Among these, 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 are preferred from the viewpoint of further suppressing the occurrence of short circuits.

[0084] Examples of pyrrolium cations include 1,1-dimethylpyrrolium ion, 1-ethyl-1-methylpyrrolium ion, 1-methyl-1-propylpyrrolium ion, 1-butyl-1-methylpyrrolium ion, 1-methoxymethyl-1-methylpyrrolium ion, 1-(2-methoxyethyl)-1-methylpyrrolium ion, 1-(3-methoxypropyl)-1-methylpyrrolium ion, 1-methoxymethyl-2-methylpyrazolium ion, 1-(2-methoxyethyl)-2-methylpyrazolium ion, and 1-(3-methoxypropyl)-2-methylpyrazolium ion. Among these, 1,1-dimethylpyrrolium ion, 1-ethyl-1-methylpyrrolium ion, 1-methyl-1-propylpyrrolium ion, and 1-butyl-1-methylpyrrolium ion are preferred from the viewpoint of further suppressing the occurrence of short circuits.

[0085] Examples of pyrazolium cations include 1,2-dimethylpyrazolium ions, 1-ethyl-2-methylpyrazolium ions, 1-propyl-2-methylpyrazolium ions, and 1-butyl-2-methylpyrazolium ions.

[0086] Examples of pyrrolinium cations include 1,2-dimethylpyrrolinium ion, 1-ethyl-2-methylpyrrolinium ion, 1-propyl-2-methylpyrrolinium ion, 1-butyl-2-methylpyrrolinium ion, 1-methoxymethyl-2-methylpyrrolinium ion, 1-(2-methoxyethyl)-2-methylpyrrolinium ion, and 1-(3-methoxypropyl)-2-methylpyrrolinium ion. Among these, 1,2-dimethylpyrrolinium ion, 1-ethyl-2-methylpyrrolinium ion, 1-propyl-2-methylpyrrolinium ion, and 1-butyl-2-methylpyrrolinium ion are preferred from the viewpoint of further suppressing the occurrence of short circuits.

[0087] Examples of pyrrolidinium cations include 1,1-dimethylpyrrolidinium ion, 1-ethyl-1-methylpyrrolidinium ion, 1-methyl-1-propylpyrrolidinium ion, 1-butyl-1-methylpyrrolidinium ion, 1-methoxymethyl-1-methylpyrrolidinium ion, 1-(2-methoxyethyl)-1-methylpyrrolidinium ion, and 1-(3-methoxypropyl)-1-methylpyrrolidinium ion. Among these, 1,1-dimethylpyrrolidinium ion, 1-ethyl-1-methylpyrrolidinium ion, 1-methyl-1-propylpyrrolidinium ion, and 1-butyl-1-methylpyrrolidinium ion are preferred from the viewpoint of further suppressing the occurrence of short circuits.

[0088] Examples of piperidinium cations include 1,1-dimethylpiperidinium ion, 1-ethyl-1-methylpiperidinium ion, 1-methyl-1-propylpiperidinium ion, 1-butyl-1-methylpiperidinium ion, 1-methoxymethyl-1-methylpiperidinium ion, 1-(2-methoxyethyl)-1-methylpiperidinium ion, and 1-(3-methoxypropyl)-1-methylpiperidinium ion. Among these, 1,1-dimethylpiperidinium ion, 1-ethyl-1-methylpiperidinium ion, 1-methyl-1-propylpiperidinium ion, and 1-butyl-1-methylpiperidinium ion are preferred from the viewpoint of further suppressing the occurrence of short circuits.

[0089] An example of a phosphonium cation is the cation represented by the following formula (3), which does not have an ether group. PR4 + ...(3) In formula (3), R is independently a monovalent hydrocarbon group.

[0090] The above R is preferably an aliphatic hydrocarbon group, and more preferably an alkyl group. The number of carbon atoms in R is preferably 1 to 8, and more preferably 1 to 4.

[0091] Examples of phosphonium cations include tetramethylphosphonium ions, tetraethylphosphonium ions, trimethylethylphosphonium ions, trimethylpropylphosphonium ions, tetraphenylphosphonium ions, and trimethylmethoxymethylphosphonium ions. Among these, tetramethylphosphonium ions, tetraethylphosphonium ions, trimethylethylphosphonium ions, trimethylpropylphosphonium ions, and tetraphenylphosphonium ions are preferred from the viewpoint of further suppressing the occurrence of short circuits.

[0092] Examples of sulfonium cations include trimethylsulfonium ions, triethylsulfonium ions, and tributylsulfonium ions.

[0093] Preferred cations for the ionic liquid are ammonium cations and phosphonium cations. Furthermore, cations constituting the ionic liquid are preferably those that do not have an ether group. Preferred cations constituting the ionic liquid without an ether group are those composed of at least one of phosphorus, nitrogen, and sulfur atoms, along with carbon and hydrogen atoms; those composed of phosphorus, carbon, and hydrogen atoms are more preferred. Among ammonium cations, pyrrolidinium cations are more preferred. Among phosphonium cations, the cation represented by formula (3) above is more preferred. These cations may be present in one or more forms.

[0094] 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)imido anion), N(CF3SO2)2 - (Bis(trifluoromethanesulfonyl)imide anion), N(C2F5SO2)2 - (Bis(pentafluoroethanesulfonyl)imido anion), N(C4F9SO2)2 - (Bis(nonafluorobutanesulfonyl)imide anion), N(POF2)2 - (Bis(difluorophosphonyl)imido anion), N(CF3SO2)(CF3CO) - ((trifluoromethanesulfonyl)(trifluoromethanecarbonyl)imido 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- These are some examples.

[0095] The anion that constitutes the ionic liquid is preferably an imide anion, N(SO2F)2 - (Bis(fluorosulfonyl)imide anion) is more preferred. When the anion constituting the ionic liquid is such an anion, the ionic conductivity of the non-aqueous electrolyte is increased, and the Coulomb efficiency of the non-aqueous electrolyte energy storage element can be further increased. Furthermore, it is preferable that the anion constituting the ionic liquid has a fluorine atom. Furthermore, it is preferable that the anion constituting the ionic liquid does not have an ether group. One or more of these anions may be included.

[0096] (Fluorinated ether) Fluorinated ethers are compounds in which some or all of the hydrogen atoms in an ether are replaced with fluorine atoms. Fluorinated ethers preferably have one or two ether groups, and more preferably have only one ether group. One or more types of fluorinated ethers can be used.

[0097] The number of fluorine atoms in the fluorinated ether is preferably 1 to 10, more preferably 2 to 6, and even more preferably 3 to 5. When the number of fluorine atoms in the fluorinated ether is within the above range, the occurrence of short circuits associated with repeated charging and discharging can be further suppressed. Furthermore, from the viewpoint of improving the capacity retention rate of the non-aqueous electrolyte energy storage element, the number of fluorine atoms in the fluorinated ether may be preferably 4 to 10, and more preferably 6 to 8. The number of carbon atoms in the fluorinated ether may be, for example, 2 to 12, but preferably 2 to 8, and more preferably 4 to 6.

[0098] The ratio of the number of fluorine atoms to the total number of hydrogen atoms and fluorine atoms in the fluorinated ether (F / (H+F)) may be, for example, 5% or more and 95% or less, preferably 10% or more and 50% or less, and more preferably 20% or more and 45% or less. When the ratio of the number of fluorine atoms to the total number of hydrogen atoms and fluorine atoms in the fluorinated ether (F / (H+F)) is within the above range, the occurrence of short circuits accompanying repeated charge and discharge can be more suppressed. Further, from the viewpoint of increasing the capacity retention rate of the non-aqueous electrolyte storage element, etc., the ratio of the number of fluorine atoms to the total number of hydrogen atoms and fluorine atoms in the fluorinated ether (F / (H+F)) may be preferably 40% or more and 90% or less, and may be more preferably 50% or more and 80% or less.

[0099] The fluorinated ether may be a cyclic fluorinated ether or a chain fluorinated ether, but a chain fluorinated ether is preferred. Examples of the fluorinated ether include compounds represented by the following formula (1). R 1 -O-R 2 ···(1) In formula (1), R 1 is a fluorinated hydrocarbon group. R 2 is a hydrocarbon group or a fluorinated hydrocarbon group. Or, R 1 and R 2 may be a divalent fluorinated hydrocarbon group bonded to each other.

[0100] As the above R 1 , a fluorinated alkyl group is preferred. The upper limit of the carbon number of R 1 is preferably 8, more preferably 5, still more preferably 3, and even more preferably 2. The lower limit of the carbon number of R 1 may be 1, but 2 is preferred.

[0101] As the above R 2 , a hydrocarbon group is preferred, and an alkyl group is more preferred. Also, as R 2 , an alkyl group or a fluorinated alkyl group may be preferred. R 2The upper limit of the number of carbon atoms is preferably 8, more preferably 5, even more preferably 3, and even more preferably 2. 2 The lower limit of the number of carbon atoms may be 1, but 2 is preferred.

[0102] The above R 1 and R 2 The upper limit of the total number of carbon atoms is preferably 16, more preferably 8, even more preferably 6, even more preferably 5, and even more preferably 4. On the other hand, the lower limit of this total number of carbon atoms may be 2, but is preferably 3, and more preferably 4. The above R 1 and R 2 The upper limit for the total number of fluorine atoms is preferably 15, more preferably 10, even more preferably 6, and even more preferably 5. On the other hand, the lower limit for the total number of fluorine atoms is preferably 2, more preferably 4, and may also be 6. By using fluorinated ethers with such a number of carbon atoms and fluorine atoms, the viscosity, oxidation resistance, ionic conductivity, etc., of the non-aqueous electrolyte can be optimized, further suppressing the occurrence of short circuits associated with repeated charging and discharging of the non-aqueous electrolyte energy storage element, and further increasing the Coulomb efficiency.

[0103] F(CF2)2OCH3、F(CF) 2)2OC2H5、CF3(CF2)CH2O(CF2)CF3、F(CF2)3OCH3、F(CF2)3OC2H 5、F(CF2)4OCH3、F(CF2)4OC2H5、F(CF2)5OCH3、F(CF2)5OC2H5、F(CF2)8OCH3、F(CF2)8OC2H5、F(CF2)9OCH3、CF3CH2OCH3、CF3CH2 OCHF2, CF3CF2CH2OCH3, CF3CF2CH2OCHF2, CF3CF2CH2O(CF2)2H, CF3CF2CH2O(CF2)2F, HCF2CH2OCH3, (CF3)(CF2)CH2O(CF2)2H, H(CF2)2OCH2CH3, 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)2F, CF3CHFCF2OCH2CF2CF2H, H(CF2)4CH2O(CF2)2H, CH3CH2O(CF2)4F, F(CF2)4CH2O(CF2)2H, H(CF2)2CH2OCF2CHFCF3, F(CF2 )2CH2OCF2CHFCF3, 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

[0104] The molar ratio (amount of substance) of the ionic liquid to the fluorinated ether (ionic liquid:fluorinated ether) 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 ratio of the ionic liquid to the fluorinated ether within the above range, it is possible to further suppress the occurrence of short circuits associated with repeated charging and discharging, and to further improve Coulomb efficiency.

[0105] (Other non-aqueous solvents besides fluorinated ethers) Other non-aqueous solvents besides fluorinated ethers include cyclic carbonates, linear carbonates, esters, amides, sulfones, lactones, and nitriles. Some or all of the hydrogen atoms in these non-aqueous solvents may be substituted with other groups or atoms (e.g., fluorine atoms). However, the content of fluorinated ether in all non-aqueous solvents contained in the non-aqueous electrolyte is preferably 90% by volume or more, and more preferably 99% by volume or more. Alternatively, the content of other non-aqueous solvents other than fluorinated ether is preferably 10% by volume or less, more preferably 1% by volume or less, relative to the fluorinated ether, and it is particularly preferable that substantially only fluorinated ether is used as the non-aqueous solvent. In such cases, it is possible to further suppress the occurrence of short circuits associated with repeated charging and discharging, and to further increase the Coulomb efficiency.

[0106] (Lithium salt) Examples of lithium salts include salts of anions and lithium ions that constitute the ionic liquids mentioned above. Among lithium salts, lithium imide salts are preferred, and LiN(SO2F)2 (lithium bis(fluorosulfonyl)imide: LiFSI) is more preferred. By using such lithium salts, it is possible to further suppress the occurrence of short circuits associated with repeated charging and discharging, and to further improve Coulomb efficiency.

[0107] Furthermore, it is preferable that the anions present in the non-aqueous electrolyte consist substantially only of imide anions, and more preferably substantially only of bis(fluorosulfonyl)imide anions. For example, the content ratio of imide anions or bis(fluorosulfonyl)imide anions to the total 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 having the anions in the non-aqueous electrolyte in this configuration, it is possible to further suppress the occurrence of short circuits associated with repeated charging and discharging, and to further improve Coulomb efficiency.

[0108] The lithium salt content in the non-aqueous electrolyte is 0.1 mol / dm³. 3 More than 3.0mol / dm 3 The following is preferable: 0.1 mol / dm 3 More than 2.6mol / dm 3 Less than 0.3 mol / dm³ is more preferable. 3 More than 2.5mol / dm 3 The following is even more preferable: The lower limit of the lithium salt content in the non-aqueous electrolyte is 0.5 mol / dm³. 3 More preferably, 1.0 mol / dm 3 A more preferable option is 1.5 mol / dm 3 A more preferable option is 2.0 mol / dm 3 In some cases, this may be even more preferable. The upper limit for the lithium salt content in non-aqueous electrolytes is 2.2 mol / dm³. 3 or 2.0 mol / dm³ 3 In some cases, this is preferable. By setting the lithium salt content within the above range, it is possible to increase the ionic conductivity of the non-aqueous electrolyte. In particular, by setting the lithium salt content in the non-aqueous electrolyte above the lower limit, it is possible to further suppress the occurrence of short circuits associated with repeated charging and discharging, and to improve various performances related to the charge-discharge cycle.

[0109] The total content of ionic liquid, fluorinated ether, and lithium salt in the non-aqueous electrolyte is preferably 90% by mass or more, more preferably 99% by mass or more, and even more preferably 99.9% by mass or more. In such cases, the occurrence of short circuits associated with repeated charging and discharging tends to be further suppressed.

[0110] (Additives) Additives that may be included in non-aqueous electrolytes include, for example, aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, and dibenzofuran; partially halogenated compounds of the above aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, and cyclohexanedicarboxylic acid anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, and dimethyl sulfate. Examples of additives include 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, perfluorooctane, tristrimethylsilyl borate, tris(trimethylsilyl) phosphite, tris(trimethylsilyl) phosphate, and tetrakithtrimethylsilyl titanate. These additives may be used individually or in combination of two or more.

[0111] The additive content in the non-aqueous electrolyte is preferably 0.01% to 10% by mass relative to the total non-aqueous electrolyte, more preferably 0.1% to 7% by mass, even more preferably 0.2% to 5% by mass, and particularly preferably 0.3% to 3% by mass. By setting the additive content within the above range, it is possible to improve the capacity retention performance or charge / discharge cycle performance after high-temperature storage, or to further improve safety.

[0112] In this non-aqueous electrolyte energy storage element, the positive electrode potential at the charging termination voltage during normal use is 3.5V (vs.Li / Li + It is preferable that the voltage is 4.0V (vs. Li / Li + It is more preferable that the voltage be 4.2V (vs. Li / Li + ) or above, 4.3V (vs.Li / Li + ) or above, 4.4V (vs.Li / Li + ) or above or 4.5V (vs. Li / Li + In some cases, it is even more preferable that the value be above this limit. By setting the positive electrode potential at the charging termination voltage during normal use to be above the above lower limit, the discharge capacity can be increased and the energy density can be improved.

[0113] The upper limit of the positive electrode potential at the charging termination voltage during normal use of the non-aqueous electrolyte energy storage element is, for example, 5.0V (vs. Li / Li + ) and 4.8V (vs.Li / Li + ) may also be 4.7V (vs.Li / Li + ) may also be 4.6V (vs.Li / Li + ) is also acceptable.

[0114] In the non-aqueous electrolyte energy storage element of this embodiment, the electrode body may be subjected to a load in the thickness direction. When a load is applied to the electrode body, the charge and discharge performance generally tends to improve, but the distance between electrodes becomes shorter, which can make short circuits more likely to occur with repeated charging and discharging. Therefore, by applying one embodiment of the present invention to a non-aqueous electrolyte energy storage element in which the electrode body is subjected to a load in the thickness direction, the advantage of suppressing the occurrence of short circuits with repeated charging and discharging can be particularly effectively enjoyed. The load on the electrode body (pressure on the electrode body) can be applied, for example, by a pressurizing member that pressurizes the container from the outside. The pressurizing member may be a restraining member that restrains the shape of the container. The pressurizing member (restraining member) is provided, for example, to pressurize the electrode body by sandwiching it from both sides in the thickness direction through the container. The surface of the electrode body that is pressed is in contact with the inner surface of the container, either directly or through another member. Therefore, the electrode body is pressed when the container is pressed. Examples of pressurizing members include restraining bands and metal frames. For example, in the case of a metal frame, the load may be adjustable by bolts or the like. Alternatively, multiple non-aqueous electrolyte energy storage elements may be arranged in the thickness direction of the electrode body, and these elements may be fixed to each other using a frame or the like while under pressure from both ends in the thickness direction.

[0115] The shape of the non-aqueous electrolyte energy storage element in this embodiment is not particularly limited, and examples include cylindrical batteries, prismatic batteries, flat batteries, coin-type batteries, button-type batteries, and the like.

[0116] Figure 1 shows a non-aqueous electrolyte energy storage element 1 as an example of a rectangular battery. Note that the figure is a transparent view of the inside of the container. An electrode body 2 having a positive electrode and a negative electrode wound around a separator is housed in a rectangular container 3. The positive electrode is electrically connected to the positive electrode terminal 4 via a positive electrode lead 41. The negative electrode is electrically connected to the negative electrode terminal 5 via a negative electrode lead 51.

[0117] Another embodiment of the present invention provides a non-aqueous electrolyte energy storage element comprising a positive electrode, a negative electrode having metallic lithium, and a non-aqueous electrolyte containing an ionic liquid, wherein the positive electrode potential at the charging termination voltage during normal use is 4.2V (vs.Li / Li + The above ionic liquid is a non-aqueous electrolyte energy storage element in which the ionic liquid mainly consists of an ionic liquid that does not have ether groups. The specific and preferred forms of the non-aqueous electrolyte energy storage element of this embodiment are the same as the specific and preferred forms of the non-aqueous electrolyte energy storage element according to the above embodiment of the present invention. In the non-aqueous electrolyte energy storage element of this embodiment, the positive electrode has a capacity density of 5 mAh / cm³ per unit area. 2 The positive electrode does not necessarily have a positive electrode active material layer as described above. However, the positive electrode must have a capacity density of 5 mAh / cm³ per unit area. 2 It is preferable to have a positive electrode active material layer as described above. Furthermore, the non-aqueous electrolyte does not have to contain fluorinated ether. However, it is preferable that the non-aqueous electrolyte contains a fluorinated solvent (fluorinated ether, fluorinated ester, fluorinated carbonate, etc.), and it is more preferable that it contains fluorinated ether.

[0118] In the non-aqueous electrolyte energy storage elements of each embodiment of the present invention, it is preferable that the non-aqueous electrolyte is not the following electrolyte A. The above electrolyte A comprises a lithium salt, an ionic liquid, and a phosphate ester derivative, and the concentration of the lithium salt is 2.6 mol / dm³. 3 The above ionic liquid contains a cationic component and an anionic component, and the cationic component contains at least one of the pyrrolidinium cation represented by the following formula (i) and the piperidinium cation represented by the following formula (ii), and the proportion of the phosphate ester derivative in the electrolyte A is 15% by volume or more and 90% by volume or less. By using a non-aqueous electrolyte other than the above electrolyte A, the occurrence of short circuits associated with repeated charging and discharging is further suppressed.

[0119] [ka] In equations (i) and (ii), R 3 and R 4Each of these is independently a linear or branched alkyl group, alkenyl group, alkynyl group, or alkylene alkoxy group having 1 to 5 carbon atoms.

[0120] <How to use non-aqueous electrolyte energy storage elements> A method of using a non-aqueous electrolyte energy storage element according to one embodiment of the present invention involves setting the positive electrode potential of the non-aqueous electrolyte energy storage element to 4.2V (vs.Li / Li + The non-aqueous electrolyte energy storage element is equipped with a positive electrode, a negative electrode having metallic lithium, and a non-aqueous electrolyte containing an ionic liquid, wherein the ionic liquid mainly consists of an ionic liquid that does not have ether groups.

[0121] Specific examples of the non-aqueous electrolyte energy storage element used in this method of use include the non-aqueous electrolyte energy storage elements according to each embodiment of the present invention described above. In this method of use, the positive electrode potential of a predetermined non-aqueous electrolyte energy storage element is set to 4.2V (vs.Li / Li + Except for performing charging to the point of exceeding ) the conventional method of using a non-aqueous electrolyte energy storage element may be the same as conventionally known methods.

[0122] The positive electrode potential at the charging termination voltage during the above charging process is 4.2V (vs.Li / Li + ) is greater than 4.3V (vs.Li / Li + It is preferable that the voltage is 4.4V (vs. Li / Li + It is more preferable that the voltage be 4.5V (vs. Li / Li + It is even more preferable that the voltage be 4.6V (vs. Li / Li + It is even more preferable that it be ) or higher. The upper limit of the positive electrode potential is, for example, 5.0V (vs.Li / Li + ) and 4.8V (vs.Li / Li + ) may also be 4.7V (vs.Li / Li + ) is also acceptable.

[0123] <Non-aqueous electrolyte energy storage device> The non-aqueous electrolyte energy storage element of this embodiment can be mounted as an energy storage unit (battery module) composed of multiple non-aqueous electrolyte energy storage elements in power supplies for vehicles such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), power supplies for electronic devices such as personal computers and communication terminals, or power storage power supplies. In this case, it is sufficient that the technology according to one embodiment of the present invention is applied to at least one non-aqueous electrolyte energy storage element included in the energy storage unit.

[0124] Figure 2 shows an example of an energy storage device 30 which is formed by further assembling energy storage units 20, each of which is an assembly of two or more electrically connected non-aqueous electrolyte energy storage elements 1. The energy storage device 30 may include busbars (not shown) that electrically connect two or more non-aqueous electrolyte energy storage elements 1, busbars (not shown) that electrically connect two or more energy storage units 20, etc. The energy storage unit 20 or the energy storage device 30 may include a condition monitoring device (not shown) that monitors the state of one or more non-aqueous electrolyte energy storage elements.

[0125] <Method for manufacturing a non-aqueous electrolyte energy storage element> A method for manufacturing a non-aqueous electrolyte energy storage element according to one embodiment of the present invention has a capacity density of 5 mAh / cm² per unit area. 2 The method comprises preparing a positive electrode having the positive electrode active material layer described above, preparing a negative electrode having metallic lithium or a surface region on which metallic lithium can be deposited during charging, and preparing a non-aqueous electrolyte containing an ionic liquid and a fluorinated ether.

[0126] A method for manufacturing a non-aqueous electrolyte energy storage element according to another embodiment of the present invention comprises preparing a positive electrode, preparing a negative electrode having metallic lithium or a surface region on which metallic lithium can be deposited during charging, and preparing a non-aqueous electrolyte containing an ionic liquid, wherein the ionic liquid mainly consists of an ionic liquid without ether groups, and the positive electrode potential at the charging termination voltage during normal use is 4.2V (vs.Li / Li + This is a method for manufacturing a non-aqueous electrolyte energy storage element that is superior to ).

[0127] Preparing a positive electrode may also mean manufacturing a positive electrode. A positive electrode can be manufactured, for example, by applying a paste-like positive electrode mixture (positive electrode mixture paste) directly to a positive electrode substrate or via an intermediate layer, and then drying it to form a positive electrode active material layer. The capacity density per unit area of ​​the positive electrode active material layer can be adjusted by the content of the positive electrode active material in the positive electrode active material layer, the type of positive electrode active material, the thickness of the positive electrode active material layer (amount of positive electrode mixture paste applied), etc.

[0128] Preparing a negative electrode may be equivalent to manufacturing a negative electrode. The negative electrode to be prepared is a negative electrode having metallic lithium, or a negative electrode having a surface region on which metallic lithium can be deposited during charging. A negative electrode having metallic lithium can be manufactured by laminating a negative electrode active material layer containing metallic lithium directly onto a negative electrode substrate or via an intermediate layer, and then pressing or otherwise processing it. The negative electrode active material layer containing metallic lithium may be pure metallic lithium foil or lithium alloy foil. A 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 for the positive electrode.

[0129] Preparing a non-aqueous electrolyte may be equivalent to preparing a non-aqueous electrolyte. The preparation of a non-aqueous electrolyte can be carried out by mixing the various components that make up the non-aqueous electrolyte. The specific and preferred forms of the prepared non-aqueous electrolyte can be those described above, applicable to a non-aqueous electrolyte in a non-aqueous electrolyte energy storage element.

[0130] For example, the method for manufacturing the non-aqueous electrolyte energy storage element also includes preparing a separator, forming an electrode body in which positive and negative electrodes are alternately superimposed by stacking or winding them via the separator, housing the positive and negative electrodes (electrode body) in a container, and injecting the non-aqueous electrolyte into the container. After injection, the non-aqueous electrolyte energy storage element can be obtained by sealing the injection port.

[0131] The manufacturing method for the non-aqueous electrolyte energy storage element may further include initial charging and discharging of the assembled uncharged energy storage element. For example, if the positive electrode active material of the non-aqueous electrolyte energy storage element is a lithium transition metal composite oxide in which the molar ratio of lithium (Li) to the transition metal (Me) (Li / Me) is greater than 1.0, the capacity will increase after undergoing initial charging and discharging. The number of charge and discharge cycles in the initial charging and discharging may be one, two, or three or more. If the positive electrode active material of the non-aqueous electrolyte energy storage element is a lithium transition metal composite oxide in which the molar ratio of lithium (Li) to the transition metal (Me) (Li / Me) is greater than 1.0, the positive electrode potential (positive electrode attainment potential) at the charging termination voltage during initial charging and discharging is 4.5V (vs. Li / Li + ) Above 4.7V (vs. Li / Li + It is preferable that it be less than or equal to the following:

[0132] <Other Embodiments> The present invention is not limited to the embodiments described above, and various modifications may be made without departing from the spirit of the invention. For example, the configuration of one embodiment may be added to the configuration of another embodiment, and a part of the configuration of one embodiment may be replaced with the configuration of another embodiment or with well-known technology. Furthermore, a part of the configuration of one embodiment may be deleted. Also, well-known technology may be added to the configuration of one embodiment.

[0133] In the above embodiment, the case in which the non-aqueous electrolyte energy storage element is used as a rechargeable non-aqueous electrolyte secondary battery (lithium secondary battery) was described, but the type, shape, dimensions, capacity, etc. of the non-aqueous electrolyte energy storage element are arbitrary. The non-aqueous electrolyte energy 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]

[0134] 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.

[0135] [Example 1] As an alternative, we prepared lithium foil (100% pure metallic lithium by mass: average thickness 300 μm). A copper foil (average thickness 20 μm) was prepared as the working electrode. As a separator, we prepared a separator (average thickness 28 μm) made by coating both sides of a polyolefin microporous membrane (average thickness 27 μm) with polyvinylidene fluoride (PVDF). 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide (Py 13 A mixture of FSI and the fluorinated ether 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TFEE) (molar ratio 70:30) contains 2.0 mol / dm³ 3 A non-aqueous electrolyte was prepared by mixing LiFSI with the specified content. An electrochemical measurement cell (manufactured by Nippon Tomcell Co., Ltd.) was used as the container, along with the counter electrode, working electrode, separator, and non-aqueous electrolyte described above, to fabricate the non-aqueous electrolyte energy storage element (test cell) of Example 1.

[0136] [Comparative Example 1] Py 13 Replace the mixture of FSI and TFEE with Py 13 A non-aqueous electrolyte energy storage element of Comparative Example 1 was obtained in the same manner as in Example 1, except that only FSI was used.

[0137] [Reference example 1] A non-aqueous electrolyte energy storage element for Reference Example 1 was obtained in the same manner as in Comparative Example 1.

[0138] [Example 2] The LiFSI content in non-aqueous electrolytes should be 1.0 mol / dm³ 3 A non-aqueous electrolyte energy storage element of Example 2 was obtained in the same manner as in Example 1, except for the difference described above.

[0139] [Comparative Example 2] Py 13 Replace the mixture of FSI and TFEE with Py 13A non-aqueous electrolyte energy storage element of Comparative Example 2 was obtained in the same manner as in Example 2, except that only FSI was used.

[0140] [Comparative Example 3] A non-aqueous electrolyte energy storage element of Comparative Example 3 was obtained in the same manner as in Example 2, except that 2,2,2-trifluoroethylmethyl carbonate (TFEMC), a fluorinated carbonate, was used instead of TFEE.

[0141] [Comparative Example 4] A non-aqueous electrolyte energy storage element of Comparative Example 4 was obtained in the same manner as in Example 2, except that 2,2,2-trifluoroethyl acetate (FEA), a fluorinated ester, was used instead of TFEE.

[0142] [Reference example 2] As a non-aqueous electrolyte, a mixture of fluoroethylene carbonate (FEC) and 2,2,2-trifluoroethylmethyl carbonate (TFEMC) (volume ratio 30:70) is used, with 1.0 mol / dm³ added. 3 A non-aqueous electrolyte energy storage element of Reference Example 2 was obtained in the same manner as in Example 2, except that a non-aqueous electrolyte prepared by mixing LiPF6 with the specified content was used.

[0143] (Evaluation: Short-circuit occurrence confirmation test) The following charging and discharging procedures were performed on each non-aqueous electrolyte energy storage element in Examples 1 and 2, Comparative Examples 1 to 4, and Reference Examples 1 and 2. Constant current charging was performed at 25°C with a charging current of 0.2C. The charging termination condition was when the charging voltage reached 3.0V or when the charging time reached 5 hours. In each non-aqueous electrolyte energy storage element in Examples 1 and 2, Comparative Examples 1 to 4, and Reference Example 2, the current density per unit area of ​​the working electrode at 1C was 6mA / cm². 2 In addition, in the non-aqueous electrolyte energy storage element of Reference Example 1, the current density per unit area of ​​the working electrode at 1C was set to 1 mA / cm². 2 In the short-circuit detection test, "charging" refers to the movement of lithium ions and electrons from the counter electrode to the working electrode. In the short-circuit detection test, "discharging" refers to the movement of lithium ions and electrons from the working electrode to the counter electrode. For each non-aqueous electrolyte energy storage element in Example 1, Comparative Example 1, and Reference Example 1, the above charge-discharge cycle was repeated until a short circuit occurred. For each non-aqueous electrolyte energy storage element in Example 2, Comparative Examples 2 to 4, and Reference Example 2, the above charge-discharge cycle was repeated for approximately 10 cycles. Table 1 shows the number of charge-discharge cycles until a short circuit occurs in each non-aqueous electrolyte energy storage element of Example 1, Comparative Example 1, and Reference Example 1. Table 2 shows the number of cycles until a short circuit occurs and the Coulomb efficiency at the 10th cycle for each non-aqueous electrolyte energy storage element of Example 2, Comparative Examples 2 to 4, and Reference Example 2. Note that for the non-aqueous electrolyte energy storage element of Comparative Example 3, a short circuit occurred at the 9th cycle, so the Coulomb efficiency at the 8th cycle is shown. Also, for the non-aqueous electrolyte energy storage element of Comparative Example 4, a short circuit occurred at the 3rd cycle, so the Coulomb efficiency at the 2nd cycle is shown.

[0144] [Table 1]

[0145] [Table 2]

[0146] The results shown in Table 1 reveal the following: First, as in the non-aqueous electrolyte energy storage element of Reference Example 1, the non-aqueous electrolyte contains an ionic liquid, and the capacity density per unit area of ​​the working electrode is 5 mAh / cm². 2 If the value was less than 5 mAh / cm², no short circuit occurred even after 100 charge-discharge cycles. Similar to the non-aqueous electrolyte energy storage element in Comparative Example 1, the capacity density per unit area of ​​the working electrode was 5 mAh / cm². 2 At this point, short circuits associated with charge-discharge cycles became significantly more likely. In contrast, the non-aqueous electrolyte energy storage element of Example 1, by containing a fluorinated ether along with the ionic liquid in the non-aqueous electrolyte, has a capacity density of 5 mAh / cm² per unit area of ​​the working electrode. 2 Despite the above, no short circuit occurred even after 60 charge-discharge cycles, indicating that the occurrence of short circuits was suppressed.

[0147] Furthermore, the results shown in Table 2 reveal the following: When a non-aqueous electrolyte containing a fluorinated solvent other than an ionic liquid and fluorinated ether was used, as in the non-aqueous electrolyte energy storage elements of Comparative Examples 3 and 4, short circuits were more likely to occur and the Coulomb efficiency was low. In addition, the non-aqueous electrolyte energy storage element of Example 2 showed higher Coulomb efficiency compared to the non-aqueous electrolyte energy storage element of Comparative Example 2, which consisted only of a lithium salt and an ionic liquid, and the non-aqueous electrolyte energy storage element of Reference Example 2, which did not contain an ionic liquid.

[0148] [Example 3] (Fabrication of the positive electrode) As the positive electrode active material, it has an α-NaFeO2 type crystal structure, Li 1+α Me 1-α A lithium transition metal composite oxide (Li-rich) represented as O2 (where Me is a transition metal) was used. Here, the molar ratio of Li to Me (Li / Me) was 1.33, and Me consisted of Ni and Mn, with Ni:Mn present in a molar ratio of 1:2.

[0149] A positive electrode mixture paste was prepared using N-methylpyrrolidone (NMP) as the dispersion medium, containing the above-mentioned positive electrode active material, acetylene black (AB) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder in a solid content mass ratio of 94:4.5:1.5. The positive electrode mixture paste was applied to one side of an aluminum foil substrate (average thickness 15 μm), and dried to produce a positive electrode with a positive electrode active material layer (average thickness 135 μm). The capacity density per unit area of ​​the positive electrode active material layer was 5 mAh / cm³. 2 It was designed to be that way.

[0150] (Fabrication of the negative electrode) A negative electrode was fabricated by laminating a lithium foil made of pure metallic lithium onto one side of a copper foil (average thickness 10 μm), which served as the negative electrode substrate, and then pressing it to create a negative electrode active material layer (average thickness 60 μm).

[0151] (Preparation of non-aqueous electrolytes) 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide (Py 13 A mixture of FSI and the fluorinated ether 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TFEE) (molar ratio 70:30) contains 2.0 mol / dm³ 3 A non-aqueous electrolyte was prepared by mixing LiFSI with the specified content.

[0152] (Preparing the separator) As a separator, we prepared one in which polyvinylidene fluoride (PVDF) was coated on both sides of a microporous membrane made of polyolefin.

[0153] (Fabrication of non-aqueous electrolyte energy storage elements) An electrode body was fabricated by stacking the positive electrode and the negative electrode via the above separator. This electrode body was placed in a container made of a metal-resin composite film, the above non-aqueous electrolyte was injected into it, and then the container was sealed by heat welding. The container was then compressed from the outside at 0.3 MPa to obtain the non-aqueous electrolyte energy storage element of Example 3.

[0154] [Reference example 3] As a non-aqueous electrolyte, a mixture of fluoroethylene carbonate (FEC) and 2,2,2-trifluoroethylmethyl carbonate (TFEMC) (volume ratio 30:70) is used, with 1.0 mol / dm³ added. 3 A non-aqueous electrolyte energy storage element of Reference Example 3 was obtained in the same manner as in Example 3, except that a non-aqueous electrolyte prepared by mixing LiPF6 with the specified content was used, and a microporous polyolefin membrane without polyvinylidene fluoride (PVDF) coating on both sides was used as the separator.

[0155] (Initial charge / discharge) Initial charging and discharging were performed on each non-aqueous electrolyte energy storage element in Example 3 and Reference Example 3 under the following conditions: Constant current and constant voltage charging was performed at 25°C with a charging current of 0.1C and a charging termination voltage of 4.6V. The charging termination condition was when the charging current became 0.02C. A 10-minute rest period was then observed. Subsequently, constant current discharge was performed with a discharge current of 0.1C and a discharge termination voltage of 2.0V, followed by a 10-minute rest period. This charge-discharge cycle was repeated twice.

[0156] (Charge-discharge cycle test) Next, the following charge-discharge cycle test was performed. Constant current and constant voltage charging was performed at 25°C with a charging current of 0.2C and a charging termination voltage of 4.6V. The charging termination condition was when the charging current became 0.05C. After that, a 10-minute rest period was observed. Then, constant current discharge was performed with a discharge current of 0.1C and a discharge termination voltage of 2.0V, followed by a 10-minute rest period. This charge-discharge cycle was repeated 50 times. The capacity retention rate was calculated as the percentage of the discharge capacity at the 50th cycle relative to the discharge capacity at the 1st cycle. The results are shown in Table 3.

[0157] [Table 3]

[0158] As shown in Table 3, the non-aqueous electrolyte energy storage element of Example 3, which includes an ionic liquid and a fluorinated ether, was confirmed to have a high capacity retention rate during charge-discharge cycles. Furthermore, the Coulomb efficiency of the non-aqueous electrolyte energy storage element of Example 3 at 50 cycles was high, exceeding 99.9%. Furthermore, the ionic liquid is 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide (Py 13 FSI) trimethylpropylphosphonium bis(fluorosulfonyl)imide (P 1113A non-aqueous electrolyte energy storage element obtained in the same manner as in Example 3, except for the change to FSI, was subjected to a similar charge-discharge cycle test. It was confirmed that it had a Coulomb efficiency and capacity retention rate at 50 cycles that were as high as those of the non-aqueous electrolyte energy storage element in Example 3.

[0159] [Example 4] A non-aqueous electrolyte energy storage element of Example 4 was obtained in the same manner as in Example 3 described above. Specifically, in Example 4, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TFEE) was used as the fluorinated ether.

[0160] [Example 5] A non-aqueous electrolyte energy storage element of Example 5 was obtained in the same manner as in Example 4, except that the fluorinated ether was replaced with ethyl-1,1,2,2-tetrafluoroethyl ether (ETFEE).

[0161] [Example 6] A non-aqueous electrolyte energy storage element of Example 6 was obtained in the same manner as in Example 4, except that the fluorinated ether was replaced with 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TFETFPE).

[0162] [Example 7] Ionic liquid trimethylpropylphosphonium bis(fluorosulfonyl)imide (P 1113 A non-aqueous electrolyte energy storage element of Example 7 was obtained in the same manner as in Example 4, except that it was replaced with FSI.

[0163] [Example 8] Ionic liquid trimethylmethoxymethylphosphonium bis(fluorosulfonyl)imide (P 111(1O1) A non-aqueous electrolyte energy storage element of Example 8 was obtained in the same manner as in Example 4, except that it was replaced with FSI.

[0164] (Initial charge / discharge) Initial charging and discharging were performed on each of the non-aqueous electrolyte energy storage elements in Examples 4 to 8 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 termination voltage of 4.6V. The charging termination condition was defined as the charging current becoming 0.02C. After that, a 10-minute rest period was observed. Subsequently, constant current discharge was performed with a discharge current of 0.1C and a discharge termination voltage of 2.0V, followed by a 10-minute rest period. Next, constant current and constant voltage charging was performed with a charging current of 0.2C and a charging termination voltage of 4.6V. The charging termination condition was set to when the charging current became 0.05C. After that, a 10-minute rest period was observed. Subsequently, constant current discharge was performed with a discharge current of 0.1C and a discharge termination voltage of 2.0V.

[0165] (Charge-discharge cycle test) Next, the following charge-discharge cycle tests were performed on each of the non-aqueous electrolyte energy storage elements in Examples 4 to 8. Constant current and constant voltage charging was performed at 25°C with a charging current of 0.2C and a charging termination voltage of 4.6V. The charging termination condition was set to when the charging current became 0.05C. After that, a 10-minute rest period was observed. Then, constant current discharge was performed with a discharge current of 0.1C and a discharge termination voltage of 2.0V, followed by a 10-minute rest period. This charge-discharge cycle was repeated until a short circuit occurred.

[0166] For each non-aqueous electrolyte energy storage element in Examples 7 and 8, two samples were prepared and the initial charge-discharge and charge-discharge cycle tests described above were performed. The number of charge-discharge cycles until a short circuit occurred is shown in Table 4. In addition, the capacity retention rate was calculated as the percentage of the discharge capacity at cycle 80 to the discharge capacity at cycle 1 for each non-aqueous electrolyte energy storage element in Examples 4 to 6. The results are shown in Table 4.

[0167] [Table 4]

[0168] The results shown in Table 4 reveal the following: A comparison of the non-aqueous electrolyte energy storage elements in Examples 4 to 6 shows that using a fluorinated ether with a small number of fluorine atoms increases the number of charge-discharge cycles before a short circuit occurs, and tends to further suppress short circuits. On the other hand, using a fluorinated ether with a large number of fluorine atoms tends to increase the capacity retention rate after charge-discharge cycles. Furthermore, a comparison of the non-aqueous electrolyte energy storage element in Example 8 with the non-aqueous electrolyte energy storage elements in the other examples shows that the ionic liquid is an ionic liquid (Py) that does not have an ether group. 13 FSI or P 1113 When FSI is the main component, it was confirmed that the number of cycles until a short circuit occurs is particularly high, and the occurrence of short circuits is particularly well suppressed. [Industrial applicability]

[0169] This invention can be applied to non-aqueous electrolyte energy storage elements used as power sources for electronic devices such as personal computers and communication terminals, and for automobiles, etc. [Explanation of symbols]

[0170] 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 units 30 Energy storage devices

Claims

1. Capacity density per unit area is 5 mAh / cm³ ２ A positive electrode having the positive electrode active material layer described above, A negative electrode having metallic lithium, Non-aqueous electrolytes including ionic liquids and fluorinated ethers Equipped with, The above ionic liquid contains at least one cation selected from the group consisting of imidazolium cation, tetraalkylammonium cation, pyridinium cation, pyrrolium cation, pyrazolium cation, pyrrolidinium cation, piperidinium cation, phosphonium cation, and sulfonium cation. A non-aqueous electrolyte energy storage element in which the above-mentioned ionic liquid contains 70% or more by volume of an ionic liquid that does not have an ether group.

2. The above positive electrode is α-NaFeO ２ A non-aqueous electrolyte energy storage element according to claim 1, comprising a lithium transition metal composite oxide having a type crystal structure or a spinel type crystal structure, or a polyanion compound containing nickel, cobalt, or manganese.

3. The positive electrode potential at the charging termination voltage during normal use is 3.5V (vs. Li / Li ＋ ) The non-aqueous electrolyte energy storage element according to claim 1 or claim 2, wherein the above conditions apply.

4. The non-aqueous electrolyte energy storage element according to claim 1, claim 2, or claim 3, further comprising lithium bis(fluorosulfonyl)imide as the non-aqueous electrolyte.

5. The above non-aqueous electrolyte further contains a lithium salt, and the lithium salt content in the above non-aqueous electrolyte is 1.5 mol / dm³ ３ The non-aqueous electrolyte energy storage element according to claim 1, claim 2, or claim 3.

6. The non-aqueous electrolyte energy storage element according to any one of claims 1 to 5, wherein the number of fluorine atoms in the fluorinated ether is 2 or more and 6 or less.

7. A non-aqueous electrolyte energy storage element according to any one of claims 1 to 6, wherein the ratio of the number of fluorine atoms to the total number of hydrogen atoms and fluorine atoms of the fluorinated ether is 10% or more and 50% or less.

8. The non-aqueous electrolyte energy storage element according to any one of claims 1 to 7, wherein the fluorinated ether is represented by the following formula (1). R １ -O-R ２ ・・・(1) In formula (1), R １ R is a fluorinated hydrocarbon group. ２ It is a hydrocarbon group.

9. A non-aqueous electrolyte energy storage element according to any one of claims 1 to 8, wherein the content of the fluorinated ether in all non-aqueous solvents contained in the non-aqueous electrolyte is 90% by volume or more.

10. A non-aqueous electrolyte energy storage element according to any one of claims 1 to 9, comprising a separator having an average thickness of 10 μm or more and 40 μm or less.

11. A positive electrode having a positive electrode active material layer with a capacity density per unit area of 5 mAh / cm ２ or more is prepared, and Prepare a negative electrode that has metallic lithium or a surface region on which metallic lithium can be deposited during charging, Prepare an ionic liquid and a non-aqueous electrolyte containing a fluorinated ether. Equipped with, The above ionic liquid contains at least one cation selected from the group consisting of imidazolium cation, tetraalkylammonium cation, pyridinium cation, pyrrolium cation, pyrazolium cation, pyrrolidinium cation, piperidinium cation, phosphonium cation, and sulfonium cation. A method for manufacturing a non-aqueous electrolyte energy storage element, wherein the above-mentioned ionic liquid contains 70% or more by volume of an ionic liquid that does not have an ether group.

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