Non-aqueous secondary battery

Abstract

The present invention provides a nonaqueous secondary battery which, even when using a nonaqueous electrolyte containing acetonitrile and a polypropylene-based separator having a specific hole structure, has low volatility of the nonaqueous electrolyte and high ion conductivity.　Provided is a nonaqueous secondary battery comprising: a positive electrode containing at least one type of positive electrode active material capable of occluding and emitting lithium ions; a negative electrode containing a material capable of occluding and emitting lithium ions; a nonaqueous electrolyte; and a separator. The nonaqueous electrolyte contains a nonaqueous solvent, lithium salt, and an organic polymer, the nonaqueous solvent contains 10-90% by volume of acetonitrile, the lithium salt contains lithium-containing imide salt, the content thereof in the nonaqueous electrolyte is 0.5-2 mol / L inclusive, the viscosity average molecular weight of the organic polymer is 30,000-1,000,000 inclusive, the viscosity of the non- aqueous electrolyte at 25°C is 2-500 mPa•s inclusive, the ion conductivity thereof is 13 mS / cm or more, and a value Z represented by expression (1): Z = viscosity (mPa•s) of electrolyte × ion conductivity (mS / cm) of electrolyte is 70 or more.

Description

Technical Field

[0001] The present invention relates to a non-aqueous secondary battery.

Background Art

[0002] Non-aqueous secondary batteries such as lithium-ion batteries are characterized by being small, having a high capacity, and having a high output, and are widely used as power sources for various portable electronic devices.

[0003] In realizing such a small and high-capacity battery, the selection of the separator disposed between the electrodes is important. Conventionally, paper, woven fabric, non-woven fabric, glass mat, etc. have been used as the separator, but these have problems in terms of safety due to their structure. In recent years, separators having a small pore diameter such as polyolefin microporous membranes have been used, and the safety has been improved by a shutdown function and a function of suppressing short circuits between electrodes.

[0004] Further, conventionally, a non-aqueous electrolyte for a non-aqueous secondary battery has used a solvent of a cyclic carbonate or a cyclic ester, and there has been a problem that the impregnation property of the electrolyte with respect to the separator is poor.

[0005] However, in recent years, the impregnation property with respect to the separator has been improved by diluting a non-aqueous electrolyte using a solvent of a cyclic carbonate or a cyclic ester with a chain carbonate and further adding a surfactant.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] Compared with the non-aqueous electrolyte using an ester as the solvent as described above, the non-aqueous electrolyte containing acetonitrile has high ionic conductivity. Therefore, by applying it to a non-aqueous secondary battery, high output performance can be obtained. On the other hand, when using a non-aqueous electrolyte containing acetonitrile, which has a lower boiling point compared to the generally used ester solvent, it has been newly found that there is a problem with volatility in the process of manufacturing a non-aqueous secondary battery.

[0008] Patent Document 1 reports that by containing a polymer having a reactive functional group such as an acrylate ester and a methacrylate ester in a non-aqueous electrolyte, the reduction decomposition reaction on the surface of the negative electrode active material can be suppressed and the battery characteristics can be improved, but the problem regarding the volatility of the non-aqueous electrolyte is not mentioned. Patent Document 2 reports that by containing an organic polymer having a molecular weight of 20,000 or less in a non-aqueous electrolyte, the reduction decomposition reaction on the surface of the negative electrode active material can be suppressed and the battery characteristics can be improved, but the problem regarding the volatility of the non-aqueous electrolyte is not mentioned.

[0009] The present invention has been made in view of the above problems, and an object thereof is to provide a non-aqueous secondary battery that has low volatility of the non-aqueous electrolyte and high ionic conductivity even when using a non-aqueous electrolyte containing acetonitrile. Another object of the present invention is to provide a non-aqueous electrolyte containing acetonitrile that can realize such a non-aqueous secondary battery.

Means for Solving the Problems

[0010] One aspect of the present invention is as follows. [1] In a non-aqueous secondary battery including a positive electrode containing one or more positive electrode active materials capable of occluding and releasing lithium ions, a negative electrode containing a material capable of occluding and releasing lithium ions, a non-aqueous electrolyte, and a separator, the non-aqueous electrolyte includes a non-aqueous solvent, a lithium salt, and an organic polymer, The non-aqueous solvent contains 10% by volume or more and 90% by volume or less of acetonitrile, the lithium salt contains a lithium-containing imide salt and has a content of 0.5 mol / L or more and 2 mol / L or less with respect to the non-aqueous electrolyte, the organic polymer has a viscosity-average molecular weight of 30,000 or more and 1,000,000 or less, the non-aqueous electrolyte has a viscosity of 2 mPa·s or more and 500 mPa·s or less and an ionic conductivity of 13 mS / cm or more at 25°C, and the following formula (1): Z = viscosity of the electrolyte (mPa·s) × ionic conductivity of the electrolyte (mS / cm) ··· (1) a non-aqueous secondary battery in which Z represented by the formula is 70 or more. [2] The non-aqueous secondary battery according to item 1, wherein the organic polymer has at least one of a polyether structure and an ester structure. [3] The non-aqueous secondary battery according to item 1 or 2, wherein the organic polymer contains at least one of polyethylene oxide and poly(methyl methacrylate). [4] The non-aqueous secondary battery according to any one of items 1 to 3, wherein the organic polymer has a viscosity-average molecular weight of 90,000 or more and 650,000 or less. [5] The non-aqueous secondary battery according to any one of items 1 to 4, wherein the organic polymer has a content of 0.1% by mass or more and 10% by mass or less with respect to the total amount of the non-aqueous electrolyte. [6] The non-aqueous secondary battery according to any one of items 1 to 5, wherein the organic polymer has a content of 0.1% by mass or more and 3% by mass or less with respect to the total amount of the non-aqueous electrolyte. [7] The non-aqueous secondary battery according to any one of items 1 to 6, wherein the area of at least one of the positive electrode and the negative electrode is 100 cm 2 or more. [8] a wound body obtained by winding a laminate in which the separator is interposed between the positive electrode and the negative electrode; a laminate in which a positive electrode and a negative electrode sheet are alternately laminated via the separator; and A laminate in which a positive electrode and a negative electrode are alternately inserted between the alternately folded separators; The non-aqueous secondary battery according to any one of items 1 to 7, which houses any one of the structures in a battery casing. [9] The non-aqueous secondary battery according to any one of items 1 to 8, wherein the non-aqueous electrolyte has a viscosity at 25 ° C of 2.5 mPa·s or more and 150 mPa·s or less, and an ionic conductivity at 25 ° C of 10 mS / cm or more and 40 mS / cm or less.

[10] The lithium salt further contains lithium hexafluorophosphate (LiPF6), The non-aqueous secondary battery according to any one of items 1 to 9, which contains the lithium-containing imide salt and the LiPF6 at a molar concentration such that the LiPF6 < the lithium-containing imide salt.

[11] The non-aqueous secondary battery according to any one of items 1 to 10, wherein the non-aqueous solvent contains 20% by volume or more and 90% by volume or less of acetonitrile.

[12] The separator has a porosity of 20% or more and 90% or less, and an air permeability resistance of 20 seconds / 100 cm 3 or more and 500 seconds / 100 cm 3 or less. The non-aqueous secondary battery according to any one of items 1 to 11.

[13] The separator is provided with a porous layer containing an inorganic filler on one or both of its surfaces, The non-aqueous secondary battery according to any one of items 1 to 12, wherein the inorganic filler is at least one selected from the group consisting of aluminum oxide, aluminum hydroxide oxide, and aluminum silicate.

[14] The separator has a polypropylene-based microporous membrane, In the microporous membrane, a polymer matrix containing the polypropylene extends along a direction perpendicular to the membrane thickness, Fibrils containing the polypropylene are formed between the polymer matrices, and The non-aqueous secondary battery according to any one of items 1 to 13, wherein micropores are formed between the plurality of fibrils.

[15] The separator has a polypropylene-based microporous membrane, The non-aqueous secondary battery according to any one of items 1 to 14, wherein the pore size ratio a / b of the average major axis pore size a of the microporous membrane and the pore size b orthogonal to the average major axis pore size a is 0.5 or more and 30 or less.

[16] The non-aqueous electrolyte used in a non-aqueous secondary battery including a positive electrode containing one or more positive electrode active materials capable of occluding and releasing lithium ions, a negative electrode containing a material capable of occluding and releasing lithium ions, a non-aqueous electrolyte, and a separator, The non-aqueous electrolyte includes a non-aqueous solvent, a lithium salt, and an organic polymer, The non-aqueous solvent includes 10% by volume or more and 90% by volume or less of acetonitrile, The lithium salt includes a lithium-containing imide salt and has a content of 0.5 mol / L or more and 2 mol / L or less with respect to the non-aqueous electrolyte, The organic polymer has a viscosity-average molecular weight of 30,000 or more and 1,000,000 or less, The non-aqueous electrolyte has a viscosity of 2 mPa·s or more and 500 mPa·s or less at 25°C, an ionic conductivity of 13 mS / cm or more, and the following formula (1): Z = viscosity of the electrolyte (mPa·s) × ionic conductivity of the electrolyte (mS / cm) ··· (1) The non-aqueous electrolyte in which Z represented by the formula is 70 or more. Further, the present invention relates to the following aspects. [1A] In a non-aqueous secondary battery including a positive electrode containing one or more positive electrode active materials capable of occluding and releasing lithium ions, a negative electrode containing a material capable of occluding and releasing lithium ions, a non-aqueous electrolyte, and a separator, The non-aqueous electrolyte includes a non-aqueous solvent, a lithium salt, and an organic polymer, The non-aqueous solvent includes 5% by volume or more and 90% by volume or less of acetonitrile, The lithium salt includes a lithium-containing imide salt and has a content of 1 mol / L or more and 2 mol / L or less with respect to the non-aqueous electrolyte. The organic polymer has at least one of a polyether structure and a 5-membered lactam structure. The organic polymer has a viscosity-average molecular weight of 30,000 or more and 1,000,000 or less. The separator has a polypropylene-based microporous membrane. In the polypropylene-based microporous membrane, a polymer matrix containing polypropylene extends along a direction perpendicular to the membrane thickness, and fibrils containing polypropylene are present between the polymer matrices, and micropores are present between a plurality of the fibrils. A non-aqueous secondary battery. [2A] The organic polymer contains at least one of polyethylene oxide and polyvinylpyrrolidone. The non-aqueous secondary battery according to Item 1A. [3A] The organic polymer has a content of 0.1% by mass or more and 10% by mass or less with respect to the total amount of the non-aqueous electrolyte. The non-aqueous secondary battery according to Item 1A or 2A. [4A] The non-aqueous electrolyte has a viscosity at 25°C of 1.5 mPa·s or more and 40 mPa·s or less, and an ionic conductivity at 25°C of 10 mS / cm or more and 40 mS / cm or less. The non-aqueous secondary battery according to any one of Items 1A to 3A. [5A] The pore size ratio a / b of the average major pore diameter a of the polypropylene-based microporous membrane and the pore diameter b orthogonal to the average major pore diameter a is 0.5 or more and 30 or less. The non-aqueous secondary battery according to any one of Items 1A to 4A. [6A] The separator has a porosity of 30% or more and 80% or less, and an air permeability resistance of 100 seconds / 100 cm 3 or more and 500 seconds / 100 cm 3 or less. The non-aqueous secondary battery according to any one of Items 1A to 5A. [7A] The lithium salt further includes lithium hexafluorophosphate (LiPF6), and the non-aqueous secondary battery according to any one of Items 1A to 6A, which contains the lithium-containing imide salt and the LiPF6 at a molar concentration such that LiPF6 < the lithium-containing imide salt. The present invention is also related to the following aspects. [1B] In a non-aqueous secondary battery including a positive electrode containing one or more positive electrode active materials capable of occluding and releasing lithium ions, a negative electrode containing a material capable of occluding and releasing lithium ions, a non-aqueous electrolyte, and a separator, the non-aqueous electrolyte includes a non-aqueous solvent, a lithium salt, and an organic polymer, the non-aqueous solvent contains 5% by volume or more and 90% by volume or less of acetonitrile, the lithium salt includes a lithium-containing imide salt and has a content of 1 mol / L or more and 2 mol / L or less with respect to the non-aqueous electrolyte, the organic polymer has at least one of a polyether structure and a 5-membered lactam structure and the organic polymer has a viscosity average molecular weight of 30,000 or more and 1,000,000 or less, the separator is a microporous membrane containing at least one of polyethylene and polypropylene, and has a porous layer containing an inorganic filler on one or both sides of the microporous membrane, the non-aqueous secondary battery. [2B] The non-aqueous secondary battery according to Item 1B, wherein the organic polymer includes at least one of polyethylene oxide and polyvinylpyrrolidone. [3B] The non-aqueous secondary battery according to Item 1B or 2B, wherein the organic polymer has a content of 0.1% by mass or more and 10% by mass or less with respect to the total amount of the non-aqueous electrolyte. [4B] The non-aqueous secondary battery according to any one of Items 1B to 3B, wherein the non-aqueous electrolyte has a viscosity at 25°C of 1.5 mPa·s or more and 40 mPa·s or less, and an ionic conductivity at 25°C of 10 mS / cm or more and 40 mS / cm or less. [5B] The non-aqueous secondary battery according to any one of Items 1B to 4B, wherein the inorganic filler is at least one selected from the group consisting of aluminum oxide, aluminum oxyhydroxide, and aluminum silicate. [6B] The separator has a porosity of 20% or more and 90% or less, and an air permeability resistance of 20 seconds / 100 cm 3 or more and 500 seconds / 100 cm 3 or less. The non-aqueous secondary battery according to any one of Items 1B to 5B. [7B] The lithium salt further contains lithium hexafluorophosphate (LiPF6), and the non-aqueous secondary battery according to any one of Items 1B to 6B, which contains the lithium-containing imide salt and the LiPF6 at a molar concentration such that the LiPF6 < the lithium-containing imide salt. [Advantages of the Invention]

[0011] According to the present invention, even when a non-aqueous electrolyte containing acetonitrile is used, a non-aqueous secondary battery can be provided in which the volatility of the non-aqueous electrolyte is suppressed and which has high ionic conductivity. Further, according to the present invention, a non-aqueous electrolyte containing acetonitrile capable of realizing such a non-aqueous secondary battery can be provided. [Brief Description of the Drawings]

[0012]

Figure 1

Figure 2

Figure 3

[0013] Hereinafter, embodiments for implementing the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail. The present invention is not limited to the following embodiments, and various modifications are possible without departing from the gist thereof. In this specification, a numerical range described using "~" includes the numerical values described before and after it. In the present embodiment, the upper limit value or the lower limit value described in a numerical range of step-by-step description can be replaced with the upper limit value or the lower limit value of the numerical range in other step-by-step descriptions. In the present embodiment, the upper limit value or the lower limit value described in a certain numerical range can also be replaced with the value described in the examples. In the present embodiment, the configurations such as the scale, shape, and length of each part shown in the drawings may be exaggeratedly depicted for further clarity.

[0014] [Non-aqueous secondary battery] The non-aqueous secondary battery according to the present embodiment includes a positive electrode containing one or more positive electrode active materials capable of occluding and releasing lithium ions, a negative electrode containing a material capable of occluding and releasing lithium ions, a non-aqueous electrolyte, and a separator. And the non-aqueous electrolyte includes a non-aqueous solvent, a lithium salt, and an organic polymer. In a non-aqueous secondary battery including a positive electrode containing one or more positive electrode active materials capable of occluding and releasing lithium ions, a negative electrode containing a material capable of occluding and releasing lithium ions, a non-aqueous electrolyte, and a separator, the non-aqueous electrolyte includes a non-aqueous solvent, a lithium salt, and an organic polymer. The non-aqueous solvent contains 10% by volume or more and 90% by volume or less of acetonitrile. The lithium salt includes a lithium-containing imide salt and has a content of 0.5 mol / L or more and 2 mol / L or less with respect to the non-aqueous electrolyte. The organic polymer has a viscosity average molecular weight of 30,000 or more and 1,000,000 or less. The non-aqueous electrolyte has a viscosity at 25°C of 2 mPa·s or more and 500 mPa·s or less, an ionic conductivity of 13 mS / cm or more, and the following formula (1): Z = Viscosity of the electrolytic solution (mPa·s) × Ionic conductivity of the electrolytic solution (mS / cm) ··· (1) The value Z represented by the following formula is 70 or more. According to such an aspect, even when a non-aqueous electrolytic solution containing acetonitrile is used, a non-aqueous secondary battery having low volatility of the non-aqueous electrolytic solution and high ionic conductivity can be provided.

[0015] The non-aqueous electrolytic solution according to the present embodiment can be used to configure a non-aqueous secondary battery.

[0016] The non-aqueous secondary battery according to the present embodiment is configured by housing a positive electrode, a negative electrode, a separator, and a non-aqueous electrolytic solution in a suitable battery exterior.

[0017] Specifically, the non-aqueous secondary battery according to the present embodiment may be the non-aqueous secondary battery 100 illustrated in FIGS. 1 and 2. Here, FIG. 1 is a plan view schematically showing the non-aqueous secondary battery, and FIG. 2 is a cross-sectional view taken along line A-A of FIG. 1.

[0018] The non-aqueous secondary battery 100 shown in FIGS. 1 and 2 is composed of a pouch-type cell. The non-aqueous secondary battery 100 houses a laminated electrode body in which a positive electrode 150 and a negative electrode 160 are laminated via a separator 170 in a space 120 of a battery exterior 110, and a non-aqueous electrolytic solution (not shown). The battery exterior 110 is made of, for example, an aluminum laminate film, and is sealed by heat-sealing the upper and lower films at the outer peripheral portion of the space formed by two aluminum laminate films. The laminated body in which the positive electrode 150, the separator 170, and the negative electrode 160 are laminated in this order is impregnated with a non-aqueous electrolytic solution. However, in FIG. 2, in order to avoid complication of the drawing, each layer constituting the battery exterior 110 and each layer of the positive electrode 150 and the negative electrode 160 are not shown separately.

[0019] The aluminum laminate film constituting the battery exterior 110 is preferably one in which both surfaces of an aluminum foil are coated with a polyolefin-based resin.

[0020] The positive electrode 150 is connected to the positive electrode lead 130 inside the non-aqueous secondary battery 100. Although not shown, the negative electrode 160 is also connected to the negative electrode lead 140 inside the non-aqueous secondary battery 100. Then, one end sides of the positive electrode lead 130 and the negative electrode lead 140 are drawn out to the outside of the battery enclosure 110 so that they can be connected to external devices or the like, and their ionomer portions are heat-sealed together with one side of the battery enclosure 110.

[0021] In the non-aqueous secondary battery 100 shown in FIGS. 1 and 2, the positive electrode 150 and the negative electrode 160 each have a single-layer laminated electrode body, but the number of laminated sheets of the positive electrode 150 and the negative electrode 160 can be appropriately increased according to the capacity design. In the case of a laminated electrode body having a plurality of positive electrodes 150 and negative electrodes 160, tabs of the same pole can be joined by welding or the like and then joined to one lead body by welding or the like and taken out to the outside of the battery. As the tabs of the same pole, modes composed of exposed portions of the current collector, modes formed by welding a metal piece to the exposed portion of the current collector, etc. are possible.

[0022] The positive electrode 150 is composed of a positive electrode current collector and a positive electrode active material layer. The negative electrode 160 is composed of a negative electrode current collector and a negative electrode active material layer.

[0023] The positive electrode active material layer contains a positive electrode active material, and the negative electrode active material layer contains a negative electrode active material.

[0024] The positive electrode 150 and the negative electrode 160 are arranged such that the positive electrode active material layer and the negative electrode active material layer face each other with the separator 170 interposed therebetween.

[0025] Hereinafter, each element constituting the non-aqueous secondary battery according to the present embodiment will be described in order.

[0026] [Positive Electrode] In the non-aqueous secondary battery according to the present embodiment, the positive electrode contains one or more positive electrode active materials capable of occluding and releasing lithium ions, and may have a positive electrode active material layer on one or both sides of the positive electrode current collector as desired.

[0027] [Positive current collector] The positive current collector is composed of, for example, a metal foil such as aluminum foil, nickel foil, or stainless steel foil. The positive current collector may have a carbon coating on its surface and may be processed into a mesh shape. The thickness of the positive current collector is preferably 5 to 40 μm, more preferably 7 to 35 μm, and even more preferably 9 to 30 μm.

[0028] [Positive electrode active material layer] The positive electrode active material layer contains a positive electrode active material and may further contain a conductive assistant and / or a binder as required.

[0029] (Positive electrode active material) The positive electrode active material layer preferably contains, as the positive electrode active material, a material capable of occluding and releasing lithium ions. When such a material is used, it is preferable because there is a tendency to obtain a high voltage and a high energy density.

[0030] Examples of the positive electrode active material include A positive electrode active material containing at least one transition metal element selected from the group consisting of Ni, Mn, and Co; are mentioned, and the following general formula (a): Li p Ni q Co r Mn s M t O u ·····(a) {In the formula, M is at least one metal selected from the group consisting of Al, Sn, In, Fe, V, Cu, Mg, Ti, Zn, Mo, Zr, Sr, and Ba, and 0 < p < 1.3, 0 < q < 1.2, 0 < r < 1.2, 0 ≤ s < 0.5, 0 ≤ t < 0.3, 0.7 ≤ q + r + s + t ≤ 1.2, 1.8 < u < 2.2, and p is a value determined by the charge and discharge state of the battery.} At least one selected from lithium-containing metal oxides represented by is preferable.

[0031] In addition, examples of the positive electrode active material include Lithium cobalt oxide represented by LiCoO2; Lithium manganese oxide represented by LiMnO2, LiMn2O4, and Li2Mn2O4; Lithium nickel oxide represented by LiNiO2; LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.8 Co 0.2 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.75 Co 0.15 Mn 0.15 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.85 Co 0.075 Mn 0.075 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.81 Co 0.1 Al 0.09 O2, and LiNi 0.85 Co 0.1 Al 0.05 Li represented by O2 z A lithium-containing composite metal oxide represented by LiMO2 (wherein M represents at least one transition metal element selected from the group consisting of Ni, Mn, and Co, and represents two or more metal elements selected from the group consisting of Ni, Mn, Co, Al, and Mg, and z represents a number greater than 0.9 and less than 1.2); Metal oxides or metal chalcogenides having a tunnel structure and a layered structure, represented by MnO2, FeO2, FeS2, V2O5, V6O 13 , TiO2, TiS2, MoS2, and NbSe2; Sulfur; and Conductive polymers represented by polyaniline, polythiophene, polyacetylene, and polypyrrole; And the like.

[0032] In particular, when the Ni content ratio q of the Li-containing metal oxide represented by the general formula (a) satisfies 0.5 < q < 1.2, it is preferable because both the reduction in the amount of Co, which is a rare metal, and the increase in the energy density can be achieved.

[0033] Here, as the Ni content ratio of the Li-containing metal oxide increases, deterioration tends to progress at a low voltage. In the positive electrode active material of the lithium-containing metal oxide represented by the general formula (a), there are active sites that oxidatively deteriorate the non-aqueous electrolyte, and these active sites may unintentionally consume the compound added to protect the negative electrode on the positive electrode side.

[0034] In addition, these additive decomposition products incorporated and deposited on the positive electrode side not only increase the internal resistance of the non-aqueous secondary battery, but also accelerate the deterioration of the lithium salt, and furthermore, the protection of the negative electrode surface becomes insufficient. To deactivate the active sites that essentially oxidatively deteriorate the non-aqueous electrolyte, it is preferable to control the Jahn-Teller distortion or coexist with components that play a role as a neutralizing agent. Therefore, the positive electrode active material preferably contains at least one metal selected from the group consisting of Al, Sn, In, Fe, V, Cu, Mg, Ti, Zn, Mo, Zr, Sr, and Ba.

[0035] For the same reason as above, it is preferable that the surface of the positive electrode active material is coated with a compound containing at least one metal element selected from the group consisting of Zr, Ti, Al, and Nb. Moreover, it is more preferable that the surface of the positive electrode active material is coated with an oxide containing at least one metal element selected from the group consisting of Zr, Ti, Al, and Nb. It is even more preferable that the surface of the positive electrode active material is coated with at least one oxide selected from the group consisting of ZrO2, TiO2, Al2O3, NbO3, and LiNbO2 because it does not inhibit the permeation of lithium ions.

[0036] Note that the positive electrode active material may be a lithium-containing compound other than the lithium-containing metal oxide represented by the general formula (a). Examples of such lithium-containing compounds include composite oxides containing lithium and transition metal elements, metal chalcogenides having lithium, metal phosphate compounds containing lithium and transition metal elements, and metal silicate compounds containing lithium and transition metal elements. From the viewpoint of obtaining a higher voltage, as the lithium-containing compound, particularly, a metal phosphate compound containing lithium and at least one transition metal element selected from the group consisting of Co, Ni, Mn, Fe, Cu, Zn, Cr, V, and Ti is preferable.

[0037] As the lithium-containing compound, more specifically, the following formula (XXa): Li v M I D2(XXa) {In the formula, D represents a chalcogen element, M I represents one or more transition metal elements containing at least one transition metal element, and the value of v is determined by the charge and discharge state of the battery and represents a number from 0.05 to 1.10.}, The following formula (XXb): Li w M II PO4(XXb) {In the formula, M II represents one or more transition metal elements, and the value of w is determined by the charge and discharge state of the battery and represents a number from 0.05 to 1.10.}, and The following formula (XXc): Li t M III u SiO4(XXc) {In the formula, M III represents one or more transition metal elements, the value of t is determined by the charge and discharge state of the battery and represents a number from 0.05 to 1.10, and u represents a number from 0 to 2.} Compounds represented by each of the above are included.

[0038] The lithium-containing compound represented by the above formula (XXa) has a layered structure, and the compounds represented by the above formulas (XXb) and (XXc) have an olivine structure. These lithium-containing compounds may be those in which a part of the transition metal elements are substituted with Al, Mg, or other transition metal elements for the purpose of stabilizing the structure, those containing these metal elements at the grain boundaries, those in which a part of the oxygen atoms are substituted with fluorine atoms, etc., or those in which at least a part of the surface of the positive electrode active material is coated with another positive electrode active material.

[0039] The positive electrode active material is used alone or in combination of two or more. Since it is possible to reversibly and stably occlude and release lithium ions and achieve a high energy density, it is preferable that the positive electrode active material layer contains at least one transition metal element selected from Ni, Mn, and Co.

[0040] When using a lithium-containing compound and other positive electrode active materials in combination as the positive electrode active material, regarding the usage ratio of both, the usage ratio of the lithium-containing compound with respect to all of the positive electrode active material is preferably 80% by mass or more, more preferably 85% by mass or more.

[0041] (Conductive aid) Examples of the conductive aid include graphite; carbon black typified by acetylene black and ketjen black; and carbon fibers. The content of the conductive aid is preferably 1 to 20 parts by mass, more preferably 2 to 15 parts by mass, per 100 parts by mass of the positive electrode active material. If the content of the conductive aid is too much, the volume energy density will decrease, but if it is too little, the formation of the electron conduction path will be insufficient. In particular, since the positive electrode active material layer has lower electron conductivity than the negative electrode active material layer, when the amount of the conductive aid is insufficient, it becomes impossible to extract a predetermined battery capacity when discharging or charging the non-aqueous secondary battery at a high current value. Therefore, in applications that require high output and / or rapid charging, it is preferable to increase the content of the conductive aid within a range where the reaction based on the movement of electrons does not become rate-determining.

[0042] (Binder) Examples of the binder include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid, carboxymethyl cellulose, styrene-butadiene rubber, and fluororubber. The content of the binder is preferably 6 parts by mass or less, more preferably 0.5 to 4 parts by mass, based on 100 parts by mass of the positive electrode active material.

[0043] [Formation of Positive Electrode Active Material Layer] The positive electrode active material layer is formed by applying and drying (removing the solvent), and if necessary, pressing a positive electrode mixture-containing slurry in which a positive electrode mixture obtained by mixing a positive electrode active material, a conductive assistant and / or a binder as necessary is dispersed in a solvent, onto a positive electrode current collector. As such a solvent, known ones can be used. For example, N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, water, etc. can be mentioned.

[0044] [Negative Electrode] The negative electrode in the non-aqueous secondary battery according to this embodiment contains a material capable of occluding and releasing lithium ions, and may have a negative electrode active material layer on one or both sides of the negative electrode current collector, if desired.

[0045] [Negative Electrode Current Collector] The negative electrode current collector is composed of, for example, a metal foil such as a copper foil, a nickel foil, or a stainless steel foil. Also, the negative electrode current collector may be carbon-coated on the surface or may be processed into a mesh shape. The thickness of the negative electrode current collector is preferably 5 to 40 μm, more preferably 6 to 35 μm, and even more preferably 7 to 30 μm.

[0046] [Negative Electrode Active Material Layer] The negative electrode active material layer contains a negative electrode active material, and may further contain a conductive assistant and / or a binder as necessary.

[0047] (Negative Electrode Active Material) The negative electrode active material includes, for example, amorphous carbon (hard carbon, soft carbon); graphite such as artificial graphite and natural graphite; pyrolytic carbon, coke, vitreous carbon, fired bodies of organic polymer compounds, mesocarbon microbeads, carbon fibers, activated carbon, carbon colloids, and carbon black, and other carbon materials. In addition, metallic lithium, metal oxides, metal nitrides, lithium alloys, tin alloys, Si materials, intermetallic compounds, organic compounds, inorganic compounds, metal complexes, organic polymer compounds, etc. may be mentioned. The negative electrode active material is used alone or in combination of two or more. Examples of the above Si material include silicon, Si alloys, Si oxides, etc.

[0048] From the viewpoint of increasing the battery voltage, the negative electrode active material layer preferably contains a material capable of occluding lithium ions at a potential lower than 0.4V vs. Li / Li + more negative.

[0049] The non-aqueous electrolyte according to this embodiment has the advantage of being able to suppress various deterioration phenomena associated with the volume change of the negative electrode when repeating charge and discharge cycles even when a Si material is applied to the negative electrode active material. Therefore, in the non-aqueous secondary battery according to this embodiment, using a Si material represented by a silicon alloy or the like as the negative electrode active material is also a preferred embodiment in that it has a high capacity derived from the Si material and excellent charge and discharge cycle characteristics.

[0050] In this embodiment, as the negative electrode active material, a Si material, particularly SiO x (where 0.5 ≦ x ≦ 1.5) may be included. The Si material may be in any form of crystal, low crystal, and amorphous. Further, when using a Si material as the negative electrode active material, it is preferable to coat the surface of the active material with a conductive material because the conductivity between the active material particles is improved.

[0051] Silicon has an operating potential of about 0.5V (vsLi / Li + ), and the operating potential of graphite (graphite) is about 0.05V (vsLi / Li +) is slightly higher than that. Therefore, when using Si material, the risk of lithium deposition is reduced. Acetonitrile used in the non-aqueous solvent in this embodiment may react with lithium metal by a reduction reaction, causing gas generation. Therefore, a negative electrode active material that is difficult to deposit lithium is preferable when used in combination with a non-aqueous electrolyte containing acetonitrile.

[0052] On the other hand, if the operating potential of the negative electrode active material is too high, the energy density of the battery will decrease. Therefore, from the viewpoint of improving the energy density, it is preferable that the negative electrode active material operates at a potential lower than 0.4V vs. Li / Li + more preferably.

[0053] The content of the Si material is preferably in the range of 0.1% by mass or more and 100% by mass or less, more preferably in the range of 1% by mass or more and 80% by mass or less, and still more preferably in the range of 3% by mass or more and 60% by mass or less, as the amount per total amount of the negative electrode active material layer. By adjusting the content of the Si material within the above range, it is possible to ensure the balance between the high capacity of the non-aqueous secondary battery and the charge-discharge cycle performance.

[0054] (Conductive aid) Examples of the conductive aid include graphite; carbon black typified by acetylene black and ketjen black; and carbon fiber. The content of the conductive aid is preferably 20 parts by mass or less, more preferably 0.1 to 10 parts by mass, as the amount per 100 parts by mass of the negative electrode active material.

[0055] (Binder) Examples of the binder include carboxymethyl cellulose, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid, and fluororubber. Also, diene-based rubbers such as styrene-butadiene rubber are included. The content of the binder is preferably 10 parts by mass or less, more preferably 0.5 to 6 parts by mass, as the amount per 100 parts by mass of the negative electrode active material.

[0056] [Formation of Negative Electrode Active Material Layer] The negative electrode active material layer is formed by applying and drying (removing the solvent), and if necessary, pressing a negative electrode active material-containing slurry in which a negative electrode active material and a conductive assistant and / or a binder contained as necessary are dispersed in a solvent onto a negative electrode current collector. As such a solvent, known ones can be used. For example, N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, water, etc. can be mentioned.

[0057] [Non-aqueous Electrolyte] In this specification, the "non-aqueous electrolyte" (hereinafter, also simply referred to as "electrolyte") refers to an electrolyte in which water is 1 mass% or less with respect to the total amount of the electrolyte.

[0058] The electrolyte according to this embodiment is used in a non-aqueous secondary battery including a positive electrode containing one or more positive electrode active materials capable of occluding and releasing lithium ions, a negative electrode containing a material capable of occluding and releasing lithium ions, a non-aqueous electrolyte, and a separator. And such a non-aqueous electrolyte contains a non-aqueous solvent, a lithium salt, and an organic polymer, the non-aqueous solvent contains 10% by volume or more and 90% by volume or less of acetonitrile, the lithium salt contains a lithium-containing imide salt and has a content of 0.5 mol / L or more and 2 mol / L or less with respect to the non-aqueous electrolyte, the organic polymer has a viscosity average molecular weight of 30,000 or more and 1,000,000 or less, the non-aqueous electrolyte has a viscosity at 25°C of 2 mPa·s or more and 500 mPa·s or less, an ionic conductivity of 13 mS / cm or more, and the following formula (1): Z = viscosity of the electrolyte (mPa·s) × ionic conductivity of the electrolyte (mS / cm) ··· (1) and Z represented by this is 70 or more. According to this, a non-aqueous electrolyte containing acetonitrile that can realize the above non-aqueous secondary battery can be provided.

[0059] Here, the fact that Z represented by formula (1) is 70 or more means that within the ranges of the viscosity at 25°C and the ionic conductivity at 25°C respectively being within the above ranges, a suitable value can be obtained as the viscosity, and a sufficiently high value can be obtained as the ionic conductivity. Such an electrolytic solution contributes to the realization of the non-aqueous secondary battery according to the present embodiment. Z represented by formula (1) can be derived from the product of the value of "viscosity (mPa·s)" obtained by the method described in the examples and the value of "ionic conductivity (mS / cm)" obtained by the method described in the examples.

[0060] The electrolytic solution according to the present embodiment preferably contains as little water as possible, but may contain a very small amount of water as long as it does not inhibit the solution of the problems of the present invention. The content of such water is 300 mass ppm or less, more preferably 200 mass ppm or less, based on the total amount of the electrolytic solution. For the electrolytic solution, as long as it has a configuration for achieving the solution of the problems of the present invention, for other constituent elements, the constituent materials in known electrolytic solutions used in lithium-ion batteries can be appropriately selected and applied.

[0061] The electrolytic solution according to the present embodiment can contain acetonitrile, a non-aqueous solvent, a lithium salt, an additive for electrode protection, a surfactant, and an organic polymer.

[0062] <Non-aqueous solvent> The "non-aqueous solvent" referred to in the present embodiment means the elements excluding the lithium salt and various additives from the electrolytic solution. When the electrolytic solution contains an additive for electrode protection, the "non-aqueous solvent" means the elements excluding the lithium salt and the additives other than the additive for electrode protection from the electrolytic solution. Examples of the non-aqueous solvent include alcohols such as methanol and ethanol; aprotic solvents and the like. Among them, as the non-aqueous solvent, an aprotic solvent is preferable. As long as it does not inhibit the solution of the problems of the present invention, the non-aqueous solvent may contain solvents other than aprotic solvents.

[0063] For example, the non-aqueous solvent for the electrolytic solution can contain acetonitrile as an aprotic solvent. Since the ionic conductivity of the electrolytic solution is improved by the non-aqueous solvent containing acetonitrile, the diffusibility of lithium ions in the battery can be enhanced. Therefore, when the electrolytic solution contains acetonitrile, even in the case of a positive electrode in which the positive electrode active material layer is thickened and the filling amount of the positive electrode active material is increased, lithium ions can diffuse well to the region near the current collector where it is difficult for lithium ions to reach during high-load discharge. Thus, it becomes possible to draw out a sufficient capacity even during high-load discharge, and a non-aqueous secondary battery with excellent load characteristics can be obtained.

[0064] In addition, since the non-aqueous solvent contains acetonitrile, the rapid charging characteristics of the non-aqueous secondary battery can be enhanced. In the constant current (CC)-constant voltage (CV) charging of the non-aqueous secondary battery, the capacity per unit time during the CC charging period is larger than the charging capacity per unit time during the CV charging period. When acetonitrile is used as the non-aqueous solvent of the electrolytic solution, the region where CC charging can be performed can be enlarged (the time for CC charging can be lengthened), and the charging current can also be increased. Therefore, the time from the start of charging to the fully charged state of the non-aqueous secondary battery can be significantly shortened.

[0065] Note that acetonitrile is liable to be electrochemically reductively decomposed. Therefore, when using acetonitrile, it is preferable to use it in combination with another solvent (for example, an aprotic solvent other than acetonitrile) as the non-aqueous solvent, and / or to add an electrode protection additive for forming a protective film on the electrode.

[0066] The content of acetonitrile may be 10% by volume or more and 90% by volume or less as the amount per total amount of the non-aqueous solvent. The content of acetonitrile is preferably 10% by volume or more, more preferably 15% by volume or more, still more preferably 20% by volume or more, even more preferably 30% by volume or more, and still even more preferably 40% by volume or more as the amount per total amount of the non-aqueous solvent. This value is more preferably 85% by volume or less, and still more preferably 66% by volume or less. When the content of acetonitrile is 10% by volume or more as the amount per total amount of the non-aqueous solvent, the ionic conductivity tends to increase and high output characteristics can be exhibited, and furthermore, the dissolution of the lithium salt can be promoted. Since the additives described later suppress the increase in the internal resistance of the battery, when the content of acetonitrile in the non-aqueous solvent is within the above range, the high-temperature cycle characteristics and other battery characteristics tend to be further improved while maintaining the excellent performance of acetonitrile. On the other hand, as the content of acetonitrile increases, the electrolyte solution becomes more volatile, so the amount of the electrolyte solution may be insufficient in the process of manufacturing the non-aqueous secondary battery, which may have an adverse effect on the battery characteristics. Adding the organic polymer described later is advantageous for improving the problem of volatility.

[0067] Examples of the aprotic solvent other than acetonitrile include cyclic carbonate, fluoroethylene carbonate, lactone, organic compounds having a sulfur atom, chain fluorinated carbonate, cyclic ether, mononitrile other than acetonitrile, alkoxy group-substituted nitrile, dinitrile, cyclic nitrile, short-chain fatty acid ester, chain ether, fluorinated ether, ketone, and compounds in which some or all of the H atoms of the aprotic solvent are substituted with halogen atoms.

[0068] Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, trans-2,3-butylene carbonate, cis-2,3-butylene carbonate, 1,2-pentylene carbonate, trans-2,3-pentylene carbonate, cis-2,3-pentylene carbonate, vinylene carbonate, 4,5-dimethylvinylene carbonate, and vinyl ethylene carbonate;

[0069] Examples of fluoroethylene carbonates include 4-fluoro-1,3-dioxolan-2-one, 4,4-difluoro-1,3-dioxolan-2-one, cis-4,5-difluoro-1,3-dioxolan-2-one, trans-4,5-difluoro-1,3-dioxolan-2-one, 4,4,5-trifluoro-1,3-dioxolan-2-one, 4,4,5,5-tetrafluoro-1,3-dioxolan-2-one, and 4,4,5-trifluoro-5-methyl-1,3-dioxolan-2-one;

[0070] Examples of lactones include γ-butyrolactone, α-methyl-γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε-caprolactone;

[0071] Examples of organic compounds having a sulfur atom include ethylene sulfite, propylene sulfite, butylene sulfite, pentene sulfite, sulfolane, 3-sulfolene, 3-methylsulfolane, 1,3-propanesultone, 1,4-butanesultone, 1-propene 1,3-sultone, dimethyl sulfoxide, tetramethylene sulfoxide, and ethylene glycol sulfite;

[0072] Examples of chain carbonates include ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, methyl butyl carbonate, dibutyl carbonate, and ethyl propyl carbonate;

[0073] Examples of the cyclic ether include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, and 1,3-dioxane;

[0074] Examples of the mononitrile other than acetonitrile include propionitrile, butyronitrile, valeronitrile, benzonitrile, and acrylonitrile;

[0075] Examples of the alkoxy group-substituted nitrile include methoxyacetonitrile and 3-methoxypropionitrile;

[0076] Examples of the dinitrile include malononitrile, succinonitrile, glutaronitrile, adiponitrile, 1,4-dicyanoheptane, 1,5-dicyanopentane, 1,6-dicyanohexane, 1,7-dicyanoheptane, 2,6-dicyanoheptane, 1,8-dicyanooctane, 2,7-dicyanooctane, 1,9-dicyanononane, 2,8-dicyanononane, 1,10-dicyanodecane, 1,6-dicyanodecane, and 2,4-dimethylglutaronitrile;

[0077] Examples of the cyclic nitrile include benzonitrile;

[0078] Examples of short-chain fatty acid esters include methyl acetate, methyl propionate, methyl isobutyrate, methyl butyrate, methyl isovalerate, methyl valerate, methyl pivalate, methyl hydroangelate, methyl caproate, ethyl acetate, ethyl propionate, ethyl isobutyrate, ethyl butyrate, ethyl isovalerate, ethyl valerate, ethyl pivalate, ethyl hydroangelate, ethyl caproate, propyl acetate, propyl propionate, propyl isobutyrate, propyl butyrate, propyl isovalerate, propyl valerate, propyl pivalate, propyl hydroangelate, propyl caproate, isopropyl acetate, isopropyl propionate, isopropyl isobutyrate, isopropyl butyrate, isopropyl isovalerate, isopropyl valerate, isopropyl pivalate, isopropyl hydroangelate, isopropyl caproate, butyl acetate, butyl propionate, butyl isobutyrate, butyl butyrate, butyl isovalerate, butyl valerate, butyl pivalate, butyl hydroangelate, butyl caproate, isobutyl acetate, isobutyl propionate, isobutyl isobutyrate, isobutyl butyrate, isobutyl isovalerate, isobutyl valerate, isobutyl pivalate, isobutyl hydroangelate, isobutyl caproate, tert-butyl acetate, tert-butyl propionate, tert-butyl isobutyrate, tert-butyl butyrate, tert-butyl isovalerate, tert-butyl valerate, tert-butyl pivalate, tert-butyl hydroangelate, and tert-butyl caproate;

[0079] Examples of chain ethers include dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme, and tetraglyme;

[0080] Examples of fluorinated ethers include Rf aa -OR bb (wherein Rf aa represents an alkyl group containing a fluorine atom, and R bb represents an organic group which may contain a fluorine atom);

[0081] Examples of the ketone include acetone, methyl ethyl ketone, and methyl isobutyl ketone;

[0082] Examples of the compound in which some or all of the H atoms of the aprotic solvent are substituted with halogen atoms include a compound in which the halogen atom is fluorine; and the like can be mentioned.

[0083] Here, examples of the fluoride of the chain carbonate include methyl trifluoroethyl carbonate, trifluorodimethyl carbonate, trifluorodiethyl carbonate, trifluoroethyl methyl carbonate, methyl 2,2-difluoroethyl carbonate, methyl 2,2,2-trifluoroethyl carbonate, and methyl 2,2,3,3-tetrafluoropropyl carbonate. The above-mentioned fluorinated chain carbonates have the following general formula: R cc -O-C(O)O-R dd (In the formula, R cc and R dd are at least one selected from the group consisting of CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, and CH2Rf ee , where Rf ee is an alkyl group having 1 to 3 carbon atoms in which at least one hydrogen atom is substituted with a fluorine atom, and R cc and / or R dd contain at least one fluorine atom) and can be represented by.

[0084] In addition, examples of the fluoride of the short-chain fatty acid ester include fluorinated short-chain fatty acid esters typified by 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, and 2,2,3,3-tetrafluoropropyl acetate. The fluorinated short-chain fatty acid esters have the following general formula: R ff -C(O)O-R gg (In the formula, R ffis at least one selected from the group consisting of CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, CF3CF2H, CFH2, CF2Rf hh , CFHRf hh , and CH2Rf ii wherein R gg is at least one selected from the group consisting of CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, and CH2Rf ii wherein Rf hh is an alkyl group having 1 to 3 carbon atoms in which at least one hydrogen atom is substituted with a fluorine atom, and Rf ii is an alkyl group having 1 to 3 carbon atoms in which at least one hydrogen atom is substituted with a fluorine atom, and R ff and / or R gg contains at least one fluorine atom, and when R ff is CF2H, R gg is not CH3).

[0085] The aprotic solvent other than acetonitrile in this embodiment can be used alone or in combination of two or more.

[0086] In this embodiment, from the viewpoint of improving the stability of the non-aqueous electrolyte, it is preferable to use, together with acetonitrile, one or more of cyclic carbonates and chain carbonates. From this viewpoint, in this embodiment, it is more preferable to use a cyclic carbonate together with acetonitrile, and it is even more preferable to use both a cyclic carbonate and a chain carbonate together with acetonitrile.

[0087] When using a cyclic carbonate together with acetonitrile, it is particularly preferable that such a cyclic carbonate contains ethylene carbonate, vinylene carbonate and / or fluoroethylene carbonate.

[0088] <Lithium salt> The electrolytic solution according to this embodiment contains a lithium salt. The content of the lithium salt may be 0.5 mol / L or more and 2 mol / L or less with respect to the electrolytic solution.

[0089] The lithium salt in this embodiment, as an imide salt, includes a lithium-containing imide salt, and the lithium-containing imide salt is preferably an imide salt represented by LiN(SO2C m F 2m+1 )2 {wherein m is an integer from 0 to 8}.

[0090] The lithium salt in this embodiment may further contain one or more selected from a fluorine-containing inorganic lithium salt, an organic lithium salt, and other lithium salts together with the imide salt.

[0091] (Imide salt) Specifically, as the imide salt, it is preferable to contain at least one of LiN(SO2F)2 and LiN(SO2CF3)2.

[0092] When acetonitrile is contained in the non-aqueous solvent, the lithium salt preferably contains LiPF6. Since the saturation concentration of the imide salt with respect to acetonitrile is higher than the saturation concentration of LiPF6, it is preferable to contain LiPF6 and the imide salt at a molar concentration such that LiPF6 ≤ imide salt, because it can suppress the association and precipitation of the lithium salt and acetonitrile at low temperatures. In particular, it is preferable to contain the imide salt and LiPF6 at a molar concentration such that LiPF6 < imide salt. Also, the content of the imide salt is preferably 0.5 mol or more and 2.0 mol or less as the amount per liter of the non-aqueous solvent, and particularly preferably 0.8 mol or more and 1.5 mol or less from the viewpoint of ensuring the ion supply amount to the electrolytic solution according to this embodiment. When the content of the lithium salt is within the above range, high ionic conductivity can be maintained. The ionic conductivity is preferably 13 mS / cm or more, more preferably 15 mS / cm or more, and preferably 18 mS / cm or more from the viewpoint of maintaining the output performance of the non-aqueous secondary battery according to the present embodiment. The ionic conductivity may be, for example, 300 mS / cm or less, 150 mS / cm or less, or 75 mS / cm or less.

[0093] According to an acetonitrile-containing electrolyte solution containing at least one of LiN(SO2F)2 and LiN(SO2CF3)2, a reduction in ionic conductivity in a low temperature range such as -10°C or -30°C can be effectively suppressed, and excellent low temperature characteristics can be obtained.

[0094] And as described above, by limiting the content of the imide salt and / or LiPF6, it is also possible to more effectively suppress an increase in resistance during high temperature heating.

[0095] (Fluorine-containing inorganic lithium salt) The lithium salt in the present embodiment may include a fluorine-containing inorganic lithium salt. Here, the "fluorine-containing inorganic lithium salt" refers to a lithium salt that does not contain a carbon atom in the anion, contains a fluorine atom in the anion, and is soluble in acetonitrile. The fluorine-containing inorganic lithium salt is excellent in that it forms a passive film on the surface of the positive electrode current collector and suppresses corrosion of the positive electrode current collector.

[0096] Examples of the fluorine-containing inorganic lithium salt include LiPF6, LiBF4, LiAsF6, Li2SiF6, LiSbF6, Li2B 12 F b H 12-b {wherein b represents an integer from 0 to 3} etc. can be mentioned, and one or more selected from these can be used.

[0097] As the fluorine-containing inorganic lithium salt, a compound which is a double salt of LiF and a Lewis acid is desirable. Among them, when a fluorine-containing inorganic lithium salt having a phosphorus atom is used, it is more preferable because it is easier to release free fluorine atoms. A typical fluorine-containing inorganic lithium salt is LiPF6 which dissolves to release PF6 anions. When a fluorine-containing inorganic lithium salt having a boron atom is used as the fluorine-containing inorganic lithium salt, it is preferable because it is easier to capture an excessive free acid component which may cause battery deterioration. From this point of view, LiBF4 is preferable.

[0098] The content of the fluorine-containing inorganic lithium salt in the electrolytic solution according to this embodiment is preferably 0.01 mol or more, more preferably 0.1 mol or more, and still more preferably 0.25 mol or more, as the amount per 1 L of the non-aqueous solvent. When the content of the fluorine-containing inorganic lithium salt is within the above range, the ionic conductivity tends to increase and high output characteristics can be exhibited. Also, the amount per 1 L of the non-aqueous solvent is preferably 2.8 mol or less, more preferably 1.5 mol or less, and still more preferably 1.0 mol or less. When the content of the fluorine-containing inorganic lithium salt is within the above range, the ionic conductivity tends to increase and high output characteristics can be exhibited, and at the same time, a decrease in ionic conductivity due to an increase in viscosity at low temperature can be suppressed, and while maintaining excellent performance of the electrolytic solution, the high temperature cycle characteristics and other battery characteristics tend to be further improved.

[0099] The content of the fluorine-containing inorganic lithium salt in the electrolytic solution according to this embodiment may be, for example, 0.05 mol or more and 1.0 mol or less as the amount per 1 L of the non-aqueous solvent.

[0100] (Organic lithium salt) The lithium salt in this embodiment may contain an organic lithium salt. The "organic lithium salt" refers to a lithium salt other than an imide salt which contains a carbon atom in the anion and is soluble in acetonitrile.

[0101] Examples of the organic lithium salt include organic lithium salts having an oxalate group. Specific examples of the organic lithium salt having an oxalate group include, for example, organic lithium salts represented by each of LiB(C2O4)2, LiBF2(C2O4), LiPF4(C2O4), and LiPF2(C2O4)2. Among them, at least one lithium salt selected from the lithium salts represented by LiB(C2O4)2 and LiBF2(C2O4) is preferable. Further, it is more preferable to use one or more of these together with a fluorine-containing inorganic lithium salt. This organic lithium salt having an oxalate group may be contained in the negative electrode (negative electrode active material layer) in addition to being added to the electrolytic solution.

[0102] From the viewpoint of ensuring better effects by its use, the addition amount of the organic lithium salt to the electrolytic solution in this embodiment is preferably 0.005 mol or more, more preferably 0.01 mol or more, still more preferably 0.02 mol or more, and particularly preferably 0.05 mol or more, as the amount per 1 L of the non-aqueous solvent. However, if the amount of the organic lithium salt having an oxalate group in the electrolytic solution is too large, there is a risk of precipitation. Therefore, the addition amount of the organic lithium salt having an oxalate group to the electrolytic solution is preferably less than 1.0 mol, more preferably less than 0.5 mol, and still more preferably less than 0.2 mol, as the amount per 1 L of the non-aqueous solvent.

[0103] The organic lithium salt having an oxalate group is known to be hardly soluble in a low-polarity organic solvent, particularly a chain carbonate. The content of the organic lithium salt in the electrolytic solution according to this embodiment may be, for example, 0.01 mol or more and 0.5 mol or less as the amount per 1 L of the non-aqueous solvent.

[0104] Incidentally, an organic lithium salt having an oxalic acid group may contain a trace amount of lithium oxalate. Further, when it is mixed as an electrolytic solution, it may react with a trace amount of moisture contained in other raw materials to newly generate a white precipitate of lithium oxalate. Therefore, the content of lithium oxalate in the electrolytic solution according to the present embodiment is preferably suppressed to a range of 500 ppm or less.

[0105] (Other lithium salts) The lithium salt in the present embodiment may contain other lithium salts in addition to the above.

[0106] Specific examples of other lithium salts include, for example, LiClO4, LiAlO4, LiAlCl4, LiB 10 Cl 10 , inorganic lithium salts that do not contain fluorine atoms in the anion such as chloro borane Li; LiCF3SO3, LiCF3CO2, Li2C2F4(SO3)2, LiC(CF3SO2)3, LiC n F (2n+1) SO3 (where n ≥ 2), organic lithium salts such as lower aliphatic carboxylic acid Li, lithium tetraphenylborate, LiB(C3O4H2)2; LiPF5(CF3) and other LiPF n (C p F 2p+1 ) 6-n [wherein, n is an integer from 1 to 5 and p is an integer from 1 to 8] represented by an organic lithium salt; LiBF3(CF3) and other LiBF q (C s F 2s+1 ) 4-q [wherein, q is an integer from 1 to 3 and s is an integer from 1 to 8] represented by an organic lithium salt; Lithium salts bonded to polyvalent anions; The following formula (YYa): LiC(SO2R jj )(SO2R kk )(SO2R ll ) (YYa) {wherein, R jj , Rkk and R ll may be the same as or different from each other and each represents a perfluoroalkyl group having 1 to 8 carbon atoms.}, The following formula (YYb): LiN(SO2OR mm )(SO2OR nn )(YYb) {In the formula, R mm and R nn may be the same as or different from each other and each represents a perfluoroalkyl group having 1 to 8 carbon atoms.}, and the following formula (YYc): LiN(SO2R oo )(SO2OR pp )(YYc) {In the formula, R oo and R pp may be the same as or different from each other and each represents a perfluoroalkyl group having 1 to 8 carbon atoms.} Examples thereof include organolithium salts represented by each of the above, and one or more of these can be used together with a fluorine-containing inorganic lithium salt.

[0107] The addition amount of other lithium salts to the electrolytic solution may be appropriately set, for example, in the range of 0.01 mol or more and 0.5 mol or less per liter of the non-aqueous solvent.

[0108] <Additive for electrode protection> The electrolytic solution according to the present embodiment may contain an additive for protecting the electrode (additive for electrode protection). The additive for electrode protection may substantially overlap with a substance that serves as a solvent for dissolving the lithium salt (i.e., the above non-aqueous solvent). The additive for electrode protection is preferably a substance that contributes to improving the performance of the electrolytic solution and the non-aqueous secondary battery, but also includes substances that are not directly involved in the electrochemical reaction.

[0109] Specific examples of the additive for electrode protection include, for example, Fluoroethylene carbonates represented by 4-fluoro-1,3-dioxolan-2-one, 4,4-difluoro-1,3-dioxolan-2-one, cis-4,5-difluoro-1,3-dioxolan-2-one, trans-4,5-difluoro-1,3-dioxolan-2-one, 4,4,5-trifluoro-1,3-dioxolan-2-one, 4,4,5,5-tetrafluoro-1,3-dioxolan-2-one, and 4,4,5-trifluoro-5-methyl-1,3-dioxolan-2-one; Unsaturated bond-containing cyclic carbonates represented by vinylene carbonate, 4,5-dimethylvinylene carbonate, and vinyl ethylene carbonate; Lactones represented by γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε-caprolactone; Cyclic ethers represented by 1,4-dioxane; Cyclic sulfur compounds represented by ethylene sulfite, propylene sulfite, butylene sulfite, pentene sulfite, sulfolane, 3-sulfolene, 3-methylsulfolane, 1,3-propane sultone, 1,4-butane sultone, 1-propene 1,3-sultone, and tetramethylene sulfoxide; These are mentioned, and they can be used alone or in combination of two or more.

[0110] The content of the additive for electrode protection in the electrolytic solution is preferably 0.1 to 30% by volume, more preferably 0.3 to 15% by volume, and particularly preferably 0.4 to 10% by volume, based on the total amount of the non-aqueous solvent.

[0111] In this embodiment, the higher the content of the additive for electrode protection, the more the deterioration of the electrolytic solution is suppressed. However, the lower the content of the additive for electrode protection, the more the high-power characteristics of the non-aqueous secondary battery in a low-temperature environment are improved. Therefore, by adjusting the content of the additive for electrode protection within the above range, it is possible to exhibit excellent performance based on the high ionic conductivity of the electrolytic solution without impairing the basic functions of the non-aqueous secondary battery. And by preparing the electrolytic solution with such a composition, the cycle performance, high-power performance in a low-temperature environment, and other battery characteristics of the non-aqueous secondary battery tend to be further improved.

[0112] Acetonitrile is easily electrochemically reductively decomposed. Therefore, the non-aqueous solvent containing acetonitrile preferably contains one or more cyclic aprotic polar solvents as an additive for electrode protection for forming a protective film on the negative electrode, and more preferably contains one or more unsaturated bond-containing cyclic carbonates.

[0113] Vinylene carbonate is preferable as the unsaturated bond-containing cyclic carbonate, and the content of vinylene carbonate is preferably 0.1% by volume or more and 10% by volume or less, more preferably 0.2% by volume or more and less than 8% by volume, and still more preferably 0.5% by volume or more and less than 6% by volume in the electrolytic solution. Thereby, the low-temperature durability can be more effectively improved, and it becomes possible to provide a secondary battery excellent in low-temperature performance.

[0114] Vinylene carbonate as an additive for electrode protection suppresses the reductive decomposition reaction of acetonitrile on the negative electrode surface. On the other hand, excessive film formation causes a decrease in low-temperature performance. Therefore, by adjusting the addition amount of vinylene carbonate within the above range, the interfacial (film) resistance can be kept low, and the cycle deterioration at low temperature can be suppressed.

[0115] <Acid anhydride> The non-aqueous secondary battery according to this embodiment is stabilized by having a part of the electrolytic solution decomposed during the first charging to form an SEI on the surface of the negative electrode. In order to more effectively strengthen this SEI, an acid anhydride can be added. When acetonitrile is included as the non-aqueous solvent, the strength of the SEI tends to decrease as the temperature rises, but the addition of the acid anhydride promotes the strengthening of the SEI. Therefore, by using such an acid anhydride, it is possible to effectively suppress the increase in internal resistance over time due to the thermal history.

[0116] Specific examples of the acid anhydride include, for example, chain acid anhydrides typified by acetic anhydride, propionic anhydride, and benzoic anhydride; cyclic acid anhydrides typified by malonic anhydride, succinic anhydride, glutaric anhydride, maleic anhydride, phthalic anhydride, 1,2-cyclohexanedicarboxylic anhydride, 2,3-naphthalenedicarboxylic anhydride, or naphthalene-1,4,5,8-tetracarboxylic dianhydride; and mixed acid anhydrides having a structure in which two different types of carboxylic acids or different types of acids such as carboxylic acids and sulfonic acids are dehydrated and condensed. These can be used alone or in combination of two or more.

[0117] Since it is preferable to strengthen the SEI before the reduction decomposition of the non-aqueous solvent in the non-aqueous secondary battery according to this embodiment, it is preferable that the acid anhydride contains at least one cyclic acid anhydride that acts early during the first charging. These cyclic acid anhydrides may contain only one type or a plurality of types. Or, it may contain cyclic acid anhydrides other than these cyclic acid anhydrides. Further, it is preferable that the cyclic acid anhydride contains at least one of succinic anhydride, maleic anhydride, and phthalic anhydride.

[0118] According to an electrolytic solution containing at least one of succinic anhydride, maleic anhydride, and phthalic anhydride, a strong SEI can be formed on the negative electrode, and the increase in resistance during high-temperature heating can be more effectively suppressed. In particular, it is preferable to contain succinic anhydride. Thereby, while suppressing side reactions, a strong SEI can be more effectively formed on the negative electrode.

[0119] When the electrolytic solution according to this embodiment contains an acid anhydride, its content is preferably in the range of 0.01 parts by mass or more and 10 parts by mass or less, more preferably 0.05 parts by mass or more and 1 part by mass or less, and still more preferably 0.1 parts by mass or more and 0.5 parts by mass or less, based on 100 parts by mass of the electrolytic solution.

[0120] <Optional additive> In this embodiment, for the purposes of improving the charge-discharge cycle characteristics of the non-aqueous secondary battery, enhancing high-temperature storage performance, and improving safety (such as preventing overcharging), etc., the electrolytic solution may appropriately contain optional additives (additives other than acid anhydrides and electrode protection additives).

[0121] Examples of optional additives include sulfonic acid esters, diphenyldisulfide, cyclohexylbenzene, biphenyl, fluorobenzene, tert-butylbenzene, nitrogen-containing cyclic compounds without steric hindrance around the lone pair of electrons [pyridine, 1-methyl-1H-benzotriazole, 1-methylpyrazole, etc.]. In particular, phosphate esters have the effect of suppressing side reactions during storage and are effective as optional additives.

[0122] When the electrolytic solution according to this embodiment contains other optional additives, its content is preferably in the range of 0.01% by mass or more and 10% by mass or less, more preferably 0.02% by mass or more and 5% by mass or less, and still more preferably 0.05 to 3% by mass, based on the total amount of the electrolytic solution. By adjusting the content of other optional additives within the above range, it is possible to add better battery characteristics without impairing the basic functions of the non-aqueous secondary battery.

[0123] <Surfactant> The electrolyte of this embodiment can contain a surfactant. In this embodiment, the surfactant is a compound having one or more hydrophilic groups and one or more lipophilic groups in one molecule. Examples of the surfactant include anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants. The surfactant that ionizes is limited to those that do not inhibit the insertion and desorption of lithium ions into the negative electrode. Also, from the perspective of the solubility of the electrolyte, nonionic surfactants are preferred as the surfactant.

[0124] Nonionic surfactants include fatty acid ester compounds such as glycerin fatty acid esters, sorbitan fatty acid esters, sucrose fatty acid esters, and saturated fatty acid esters; phosphoric acid ester compounds such as ethyldiethylphosphonoacetate {EDPA; (C2H5O)2(P=O)-CH2(C=O)OC2H5}, tris(trifluoroethyl) phosphate {TFEP; (CF3CH2O)3P=O}, triphenyl phosphate {TPP; (C6H5O)3P=O}, triallyl phosphate {CH2=CHCH2O)3P=O}, triamyl phosphate, tris(2-butoxyethyl) phosphate, and tris(2-ethylhexyl) phosphate; ether compounds such as polyoxyethylene alkyl ethers, polyoxyalkylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene polycyclic phenyl ethers, polyoxyethylene distyrenated phenyl ethers, and polyoxyethylene polyoxypropylene glycols; ester ether compounds such as fatty acid polyethylene glycols and polyoxyethylene sorbitan fatty acid esters; and alkanolamide compounds such as fatty acid alkanolamides. From the perspective of improving the stability of the electrolyte, fatty acid ester compounds or phosphoric acid ester compounds are preferred. As the fatty acid ester compound, ethyl laurate is preferred. In particular, phosphoric acid ester compounds are preferred, and among them, at least one selected from the group consisting of triamyl phosphate, tris(2-butoxyethyl) phosphate, and tris(2-ethylhexyl) phosphate is more preferred, and tris(2-ethylhexyl) phosphate is particularly preferred.

[0125] The number of carbon atoms contained in at least one substituent constituting the hydrophobic part of the nonionic surfactant is preferably 3 or more, more preferably 5 or more, and still more preferably 8 or more from the viewpoint of reducing the surface tension of the electrolytic solution. Further, from the viewpoint that a larger number of carbon atoms in the substituent increases the boiling point of the compound and makes purification difficult, the number of carbon atoms contained in the substituent is preferably 25 or less, and still more preferably 20 or less. When the hydrocarbon chain of the substituent is branched, the total number of carbon atoms contained in the substituent is used. Specific examples of the substituent having 3 or more carbon atoms include a propyl group, an isopropyl group, a butyl group, an isobutyl group, an s-butyl group, a t-butyl group, an amyl group, an isoamyl group, an s-amyl group, a t-amyl group, a 2-butoxyethyl group, a 2-ethylhexyl group, a phenyl group, and the like.

[0126] In the present embodiment, the content of the surfactant is 0.1% by mass or more and 3% by mass or less with respect to the total amount of the electrolytic solution. From the viewpoint of improving impregnation properties, the content of the surfactant is more preferably 0.3% by mass or more with respect to the total amount of the electrolytic solution, and from the viewpoint of maintaining high ionic conductivity, it is more preferably 2% by mass or less. Similarly, the content of the nonionic surfactant is preferably 0.1% by mass or more and 3% by mass or less with respect to the total amount of the electrolytic solution, and more preferably 0.3% by mass or more and 2% by mass or less. If the content of the surfactant or the nonionic surfactant is 0.1% by mass or more, the effect of suppressing output reduction can be obtained more effectively, and if the content is 3% by mass or less, the decrease in ionic conductivity is small and the influence on battery characteristics such as input / output characteristics and battery life is less.

[0127] Here, the content of the surfactant is that of the electrolytic solution at room temperature 1 It can be determined by 1H-NMR measurement (normalized with a standard substance (C6F4H2) and calculating the content of the surfactant from the integral value of the signal of each detected component).

[0128] As a result of the inventors' intensive studies, it has been found that when a surfactant contains a hydroxy group, the impregnation property into the separator is improved, but it is easily reductively decomposed at the negative electrode during charging, which causes deterioration of battery performance. Furthermore, it has newly been found that when a surfactant contains a hydroxy group, bubbles are likely to be generated in the decompression step after injecting the electrolytic solution. If the first charge is performed with the bubbles not completely removed, the SEI is not uniformly formed on the surface of the negative electrode, leading to poor first charge and discharge. The electrolytic solution containing acetonitrile enables subsequent charge and discharge operations by uniformly forming the SEI during the first charge. Therefore, when there is a portion where the SEI formation during the first charge is insufficient due to bubble generation, the electrolytic solution containing acetonitrile directly leads to poor first charge or a decrease in battery life compared to the electrolytic solution not containing acetonitrile. Therefore, it is important that the surfactant of the present embodiment does not contain a hydroxy group as a substituent, more specifically, as a terminal substituent.

[0129] <organic polymer> From the viewpoint of preventing volatilization of the electrolytic solution, the electrolytic solution according to the present embodiment can contain an organic polymer. The organic polymer is limited to those that do not excessively inhibit the insertion and desorption of lithium ions into the negative electrode. Further, from the viewpoint of the solubility of the electrolytic solution, the organic polymer preferably has at least one of a polyether structure and an ester structure.

[0130] Examples of the organic polymer having a polyether structure include polyethylene oxide, polypropylene oxide, polyethylene glycol monododecyl ether, polyethylene glycol mono-4-nonylphenyl ether, polyethylene glycol monooleyl ether, polyethylene glycol monocetyl ether, poly(ethylene glycol) methacrylate, poly(ethylene glycol) diacrylate, poly(ethylene glycol) distearate, O-[(N-succinimidyl) succinyl-aminoethyl]-O'-methyl polyethylene glycol, O-[2-(3-mercaptopropionylamino)ethyl]-O'-methyl polyethylene glycol, poly(ethylene glycol) bis(3-aminopropyl), poly(ethylene glycol) methyl ether, methoxypolyethylene glycol amine, methoxypolyethylene oxide, poly(ethylene glycol) bis(carboxymethyl) ether, poly(ethylene glycol) dimethyl ether, poly(ethylene glycol) bis(amine), poly(ethylene glycol) methyl ether acetylene, and the like. Examples of the organic polymer having an ester structure include poly(methyl methacrylate), poly(ethyl methacrylate), poly(isopropyl methacrylate), poly(tert-butyl acrylate), isobutyl methacrylate (polymer), poly(ethylene glycol) monomethyl ether monomethacrylate, and the like. These may be used alone or in combination of two or more. For example, the organic polymer may contain at least one of polyethylene oxide and poly(methyl methacrylate). Further, the organic polymer may have a branched structure such as a multi-branched structure, and a copolymer such as a block copolymer or a random copolymer may be used.

[0131] The content of the organic polymer can be 0.1% by mass or more and 10% by mass or less based on the total amount of the electrolytic solution. From the viewpoint of improving volatility, 0.3% by mass or more is preferable, and 0.5% by mass or more is more preferable. Further, from the viewpoint of suppressing a decrease in impregnation property, 6% by mass or less is preferable, and 3% by mass or less is more preferable.

[0132] The viscosity-average molecular weight of the organic polymer is 30,000 or more and 1,000,000 or less. The viscosity-average molecular weight may be 40,000 or more, may be 70,000 or more, or may be 90,000 or more. Further, from the viewpoint of suppressing a decrease in impregnation property, it is preferably 800,000 or less, more preferably 650,000 or less. When the content and the viscosity-average molecular weight of the organic polymer are within the above ranges, the viscosity of the electrolytic solution can be increased and it is easy to maintain a high ionic conductivity. By increasing the viscosity of the electrolytic solution, the fluidity of the electrolytic solution is likely to decrease, and thus the heat transfer rate and the diffusion rate in the liquid phase are likely to be suppressed. From the viewpoint of suppressing volatility during the process of manufacturing the non-aqueous secondary battery, the viscosity at 25 °C is preferably 2 mPa·s or more, more preferably 3 mPa·s or more, and still more preferably 4 mPa·s or more. Further, from the viewpoint of suppressing a decrease in the impregnation property into the electrode and the separator, etc., it is preferably 500 mPa·s or less, preferably 200 mPa·s or less, and still more preferably 100 mPa·s or less. From the viewpoint of maintaining the output performance of the non-aqueous secondary battery, the ionic conductivity at 25 °C is preferably 13 mS / cm or more, more preferably 15 mS / cm or more, and still more preferably 18 mS / cm or more.

[0133] <Separator> The separator of the present embodiment refers to a member that is disposed between a plurality of electrodes in a power storage device and has ion permeability and, if necessary, shutdown characteristics. The separator includes a microporous membrane and / or a microporous laminated membrane, and may further include any functional layer as desired.

[0134] Since the separator requires insulation and ion permeability, it is generally formed from paper, a polyolefin nonwoven fabric, a microporous resin film, or the like, which are insulating materials having a porous structure. In particular, when the separator is used in an electrolytic solution secondary battery including a positive electrode and a negative electrode capable of occluding and releasing lithium and an electrolytic solution formed by dissolving an electrolyte in a non-aqueous solvent, a microporous polyolefin film capable of constructing a redox degradation-resistant and dense and uniform porous structure is excellent as a separator substrate. Therefore, the separator according to the present embodiment can include a microporous polyolefin film. The separator of the present embodiment is a microporous film including at least one of polyethylene and polypropylene, and may include a porous layer containing an inorganic filler on one or both surfaces of the microporous film.

[0135] In the present embodiment, examples of the polyolefin resin used as the material of the substrate include homopolymers such as polyethylene and polypropylene, copolymers of a plurality of monomers constituting each homopolymer, and further mixtures of these polymers. Examples of polyethylene include low-density, medium-density, and high-density polyethylene, and high-density polyethylene is preferable from the viewpoint of puncture strength or mechanical strength. Further, two or more of these polyethylenes may be mixed for the purpose of imparting flexibility. The polymerization catalyst used in the production of these polyethylenes is not particularly limited, and examples thereof include Ziegler-Natta catalysts, Phillips catalysts, and metallocene catalysts. From the viewpoint of achieving both high mechanical strength and high permeability, the viscosity average molecular weight of polyethylene is preferably 100,000 or more and 12,000,000 or less, and more preferably 200,000 or more and 3,000,000 or less.

[0136] The microporous film according to the present embodiment may be a microporous laminated film, if desired. The microporous laminated film means a multilayer film in which a plurality of polyolefin-based microporous layers are laminated, or a composite microporous film in which a polyolefin-based microporous film and a microporous film containing another resin are laminated, and may hereinafter be simply referred to as a laminate. A method for producing a substrate containing a polyolefin-based resin as a main component may be a known one. Examples of the production method include a dry production method and a wet production method.

[0137] In the dry production method, for example, first, a film is formed from a polyolefin-based resin such as polypropylene or polyethylene by melt extrusion. Then, the film is annealed at a low temperature to grow crystal domains, and in this state, it is stretched to extend the amorphous region to form a microporous membrane as a substrate.

[0138] Also, in the wet production method, for example, first, a hydrocarbon solvent and other low-molecular materials are mixed with a polyolefin-based resin such as polypropylene or polyethylene, and then formed into a film shape. Next, a microporous membrane as a substrate is formed by removing these solvents and low-molecular materials from the film in which the solvent and low-molecular materials have gathered in the amorphous phase to start forming an island phase, using another easily volatile solvent.

[0139] On at least one side of the substrate used in this embodiment, a porous layer provided with an inorganic filler may be arranged for the purpose of controlling strength, hardness, and thermal shrinkage rate. Further, the porous layer may further contain an organic filler and a fiber compound.

[0140] The inorganic filler is not particularly limited, but those having high heat resistance and electrical insulation properties and being electrochemically stable within the usage range of the lithium ion secondary battery are preferred. Examples of the inorganic filler include aluminum compounds, magnesium compounds, and other compounds. Examples of the aluminum compounds include aluminum oxide, aluminum silicate, aluminum hydroxide, aluminum oxide hydroxide, sodium aluminate, aluminum sulfate, aluminum phosphate, hydrotalcite, and the like. Examples of the magnesium compounds include magnesium sulfate, magnesium hydroxide, and the like. Examples of the other compounds include oxide-based ceramics, nitride-based ceramics, clay minerals, silicon carbide, calcium carbonate, barium titanate, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, silica sand, glass fiber, and the like. Examples of the oxide-based ceramics include silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, iron oxide, and the like. Examples of the nitride-based ceramics include silicon nitride, titanium nitride, boron nitride, and the like. Examples of the clay minerals include talc, montmorillonite, sericite, mica, amesite, bentonite, and the like. These may be used alone or in combination of two or more.

[0141] Among these, from the viewpoints of electrochemical stability and heat resistance characteristics, at least one selected from the group consisting of aluminum oxide, aluminum oxide hydroxide, and aluminum silicate is preferred. Specific examples of the aluminum oxide include alumina. Specific examples of the aluminum oxide hydroxide include boehmite. Specific examples of the aluminum silicate include kaolinite, dickite, nacrite, halloysite, and pyrophyllite. For the purpose of enhancing the tear strength and puncture strength, the base material used in this embodiment may have a multilayer structure in which the above-mentioned base materials are stacked. Specifically, examples include a laminate of a polyethylene microporous membrane and a polypropylene microporous membrane, and a laminate of a nonwoven fabric and a polyolefin-based microporous membrane. From the perspective of enhancing the performance of the power storage device and improving the mechanical strength, the porosity of the base material or separator is preferably at least 20%, more preferably at least 35% as the lower limit, and preferably at most 90%, more preferably at most 80% as the upper limit. Setting the porosity to 20% or more is preferable from the perspective of ensuring better permeability of the separator. On the other hand, setting the porosity to 90% or less is preferable from the perspective of ensuring better puncture strength.

[0142] Also, from the same perspective, the air permeability (hereinafter also referred to as "air resistance") of the base material or separator is not particularly limited, but from the perspective of enhancing the performance of the non-aqueous secondary battery, the lower limit is preferably 20 sec / 100 cm 3 or more, more preferably 50 sec / 100 cm 3 or more, and the upper limit is preferably 500 sec / 100 cm 3 or less, more preferably 300 sec / 100 cm 3 or less. Setting the air permeability to 10 sec / 100 cm 3 or more is preferable from the perspective of further suppressing self-discharge of the non-aqueous secondary battery. On the other hand, setting the air permeability to 1000 sec / 100 cm 3 or less is preferable from the perspective of obtaining better charge-discharge characteristics. These air permeabilities and porosities are measured according to the methods described in the examples.

[0143] Furthermore, the puncture strength of the base material is preferably at least 200 g / 20 μm, more preferably at least 300 g / 20 μm as the lower limit, and preferably at most 2000 g / 20 μm, more preferably at most 1000 g / 20 μm as the upper limit, from the perspectives of improving the reliability as a separator and suppressing heat shrinkage. The fact that the puncture strength is 200 g / 20 μm or more is preferable from the perspective of further suppressing film breakage caused by fallen active materials or the like during battery winding, and also from the perspective of further suppressing the risk of short circuit due to the expansion and contraction of the electrodes during charge and discharge. On the other hand, setting the puncture strength to 2000 g / 20 μm or less is preferable from the perspective of being able to further reduce the width shrinkage due to the relaxation of orientation during heating.

[0144] The polypropylene-based microporous membrane according to this embodiment has a polymer matrix containing polypropylene extending along a direction perpendicular to the film thickness, and fibrils containing polypropylene between the polymer matrices, and micropores between a plurality of the fibrils. The above-mentioned "direction perpendicular to the film thickness" means the machine direction (hereinafter sometimes abbreviated as MD) of continuous forming of the microporous membrane. The structure of the polypropylene-based microporous membrane can be obtained by manufacturing by a dry process, and more specifically, can be obtained by a dry process including a step of dry-poring a polypropylene-containing resin molded body. FIG. 3 shows an example of an SEM image of a microporous membrane made of polypropylene. For example, from FIG. 3, a polypropylene-containing polymer matrix structure extending along the above-mentioned "direction perpendicular to the film thickness" can be observed.

[0145] The microporous membrane is a single-layer membrane composed of a single polyolefin-based microporous layer, or a microporous single-layer membrane composed of a resin layer other than the polyolefin-based microporous layer, or a composite microporous single-layer membrane having a polyolefin-based resin and other resins, and may also be called a microporous layer.

[0146] The polyolefin-based microporous membrane is formed from a polyolefin resin composition containing a polyolefin resin as a main component.

[0147] The polypropylene-based microporous membrane is formed from a polypropylene resin composition containing polypropylene as a main component.

[0148] In this specification, that a film contains a specific material as a main component means that the material is contained in an amount of 50% or more based on the mass of the film.

[0149] In this specification, that a microporous membrane contains a polyolefin resin as a main component means that the proportion of the polyolefin resin in the microporous membrane is 50% by mass or more based on the mass of the microporous membrane. Therefore, the polyolefin resin can form a polymer network in the microporous membrane.

[0150] That the polypropylene resin composition contains polypropylene as a main component means that the proportion of polypropylene in the polypropylene resin composition is 50% by mass or more based on the mass of the polypropylene resin composition.

[0151] The inventors of the present invention have found that there are particularly problems with the volatility of the electrolytic solution when a polypropylene-based microporous membrane and an electrolytic solution containing acetonitrile are combined. As a result of intensive studies on this problem, among polypropylene-based separators having a small pore diameter, when a separator manufactured by a dry method and having a pore structure parallel to the thickness direction is used, it has been found that the impregnability of the electrolytic solution containing acetonitrile becomes extremely low. For this reason, the electrolytic solution volatilizes before it can penetrate into the separator. In particular, during battery manufacturing, it is necessary to extend the time of the decompression process to sufficiently impregnate the electrolytic solution into the separator. As a result, it has been newly found that low-boiling solvents in the electrolytic solution volatilize, causing initial defects.

[0152] In terms of enhancing strength, it is preferable that the pore size ratio a / b of the average major axis pore diameter a of the microporous membrane and the pore diameter b orthogonal to the average major axis pore diameter a of the polypropylene-based microporous membrane is 0.5 or more and 30 or less. From the viewpoint of enhancing strength, the pore size ratio a / b is more preferably 1 or more and 20 or less, and still more preferably 1.5 or more and 15 or less.

[0153] The separator preferably has a porosity of 30% or more and 80% or less, and / or a gas permeability (hereinafter, also referred to as "air permeability resistance") of 100 seconds / 100 cm 3 or more and 500 seconds / 100 cm 3 or less.

[0154] When the porosity is lower than 30%, it becomes difficult to ensure sufficient ion permeability when the microporous membrane is used for battery applications. Also, when the porosity is higher than 80%, the microporous membrane may not be able to maintain sufficient strength. From such a perspective, the porosity of the separator is more preferably 33% or more and 77% or less, and even more preferably 37% or more and 73% or less. Also, adjusting the air permeability resistance of the separator to 100 seconds / 100 cm 3 or more is suitable from the perspective of obtaining a separator including a homogeneous microporous membrane without defects. Also, adjusting the air permeability resistance of the separator to 500 seconds / 100 cm 3 or less is preferable because it can contribute to ensuring sufficient ion permeability. From such a perspective, the air permeability resistance of the separator is more preferably 120 seconds / 100 cm 3 or more and 450 seconds / 100 cm 3 or less, and even more preferably 150 seconds / 100 cm 3 or more and 400 seconds / 100 cm 3 or less.

[0155] <Battery exterior> The configuration of the battery exterior of the non-aqueous secondary battery in this embodiment can adopt a known configuration. For example, as the battery exterior, a battery can or a laminated film exterior body may be used.

[0156] As the battery can, for example, a metal can made of steel, stainless steel, aluminum, or a clad material, etc. can be used.

[0157] The laminated film exterior can be used as an exterior by stacking two sheets with the heat-melt resin side facing inward, or by folding it so that the heat-melt resin side faces inward, and sealing the ends by heat-sealing. When using the laminated film exterior, a positive electrode lead body (or a positive electrode terminal and a lead tab connected to the positive electrode terminal) can be connected to the positive electrode current collector, and a negative electrode lead body (or a negative electrode terminal and a lead tab connected to the negative electrode terminal) can be connected to the negative electrode current collector. In this case, the laminated film exterior may be sealed with the ends of the positive electrode lead body and the negative electrode lead body (or the lead tabs connected to the positive electrode terminal and the negative electrode terminal respectively) drawn out to the outside of the exterior.

[0158] As the laminated film exterior, for example, a laminated film having a three-layer structure of heat-melt resin / metal film / resin can be used.

[0159] The aluminum laminated film constituting the battery exterior is preferably one in which both sides of the aluminum foil are coated with a polyolefin-based resin.

[0160] <Shape of Non-aqueous Secondary Battery> The shape of the non-aqueous secondary battery according to this embodiment can be applied, for example, to a square shape, a square tube shape, a cylindrical shape, an elliptical shape, a button shape, a coin shape, a flat shape, a laminated shape, etc.

[0161] The non-aqueous secondary battery according to this embodiment can be preferably applied particularly to a square shape, a square tube shape, and a laminated shape.

[0162] <Manufacturing Method of Non-aqueous Secondary Battery> The non-aqueous secondary battery in this embodiment can be manufactured using the above-described electrolytic solution, a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, a separator, and a battery exterior as required.

[0163] First, a laminate composed of a positive electrode, a negative electrode, and a separator can be formed. For example, a method of manufacturing a laminate in which a long positive electrode and a negative electrode are laminated with the long separator interposed therebetween, and then winding this to form a laminate with a wound structure; a method of forming a laminate with a laminated structure in which a positive electrode sheet and a negative electrode sheet obtained by cutting the positive electrode and the negative electrode into a plurality of sheets having a certain area and shape are alternately laminated via a separator sheet; a method of forming a laminate with a laminated structure in which a long separator is folded in a zigzag pattern and a positive electrode body sheet and a negative electrode body sheet are alternately inserted between the folded separators; etc. are possible.

[0164] Next, by housing the above-described laminate in a battery exterior (battery case), injecting an electrolytic solution into the battery case, immersing the laminate in the electrolytic solution, and sealing it, the non-aqueous secondary battery in the present embodiment can be manufactured.

[0165] In addition, when the electrode arrangement is designed such that there is a portion where the outer peripheral ends of the negative electrode active material layer and the positive electrode active material layer overlap, or there is a portion where the width is too small in the non-opposing portion of the negative electrode active material layer, electrode misalignment may occur during battery assembly, which may reduce the charge-discharge cycle characteristics of the non-aqueous secondary battery. Therefore, it is preferable to fix the position of the electrodes in advance with tapes such as polyimide tape, polyphenylene sulfide tape, polypropylene (PP) tape, adhesives, etc.

[0166] In this embodiment, when an electrolytic solution using acetonitrile is used, due to its high ionic conductivity, lithium ions released from the positive electrode during the first charge of the non-aqueous secondary battery may diffuse throughout the negative electrode. In a non-aqueous secondary battery, it is common to make the area of the negative electrode active material layer larger than that of the positive electrode active material layer. However, if lithium ions diffuse and are occluded even in the portion of the negative electrode active material layer that does not face the positive electrode active material layer, these lithium ions will remain in the negative electrode without being released during the first discharge. Therefore, the contribution of the lithium ions that are not released becomes an irreversible capacity. For these reasons, in a non-aqueous secondary battery using an electrolytic solution containing acetonitrile, the first charge-discharge efficiency may be low.

[0167] On the other hand, when the area of the positive electrode active material layer is larger than that of the negative electrode active material layer, or when both are the same, current concentration is likely to occur at the edge portion of the negative electrode active material layer during charging, and lithium dendrites are likely to be generated.

[0168] There is no particular limitation on the ratio of the area of the entire negative electrode active material layer to the area of the portion where the positive electrode active material layer and the negative electrode active material layer face each other. However, for the reasons described above, it is preferably greater than 1.0 and less than 1.1, more preferably greater than 1.002 and less than 1.09, still more preferably greater than 1.005 and less than 1.08, and particularly preferably greater than 1.01 and less than 1.08. In a non-aqueous secondary battery using an electrolytic solution containing acetonitrile, the first charge-discharge efficiency can be improved by reducing the ratio of the area of the entire negative electrode active material layer to the area of the portion where the positive electrode active material layer and the negative electrode active material layer face each other.

[0169] Reducing the ratio of the area of the entire negative electrode active material layer to the area of the portion where the positive electrode active material layer and the negative electrode active material layer face each other means restricting the ratio of the area of the portion of the negative electrode active material layer that does not face the positive electrode active material layer. As a result, among the lithium ions released from the positive electrode during the first charge, the amount of lithium ions occluded in the portion of the negative electrode active material layer that does not face the positive electrode active material layer (i.e., the amount of lithium ions that become irreversible capacity without being released from the negative electrode during the first discharge) can be reduced as much as possible. Therefore, by designing the ratio of the area of the entire negative electrode active material layer to the area of the portion where the positive electrode active material layer and the negative electrode active material layer face each other within the above range, while improving the load characteristics of the battery by using acetonitrile, the first charge-discharge efficiency of the battery can be increased, and furthermore, the generation of lithium dendrites can be suppressed.

[0170] The non-aqueous secondary battery in this embodiment can function as a battery by the first charge, but is stabilized by the decomposition of a part of the electrolyte during the first charge. There is no particular limitation on the method of the first charge, but the first charge is preferably performed at 0.001 to 0.3 C, more preferably at 0.002 to 0.25 C, and even more preferably at 0.003 to 0.2 C. It is also preferable that the first charge is performed via constant voltage charging in the middle. By setting a long voltage range in which the lithium salt participates in the electrochemical reaction, a stable and strong SEI is uniformly formed on the electrode surface, and in addition to the effect of suppressing the increase in the internal resistance, the reaction products are not firmly fixed only to the negative electrode, but in some form, also have a good effect on members other than the negative electrode, such as the positive electrode and the separator. Therefore, it is very effective to perform the first charge in consideration of the electrochemical reaction of the lithium salt dissolved in the electrolyte.

[0171] The non-aqueous secondary battery in this embodiment can also be used as a battery pack in which a plurality of non-aqueous secondary batteries are connected in series or in parallel. From the viewpoint of managing the charge-discharge state of the battery pack, the operating voltage range per battery is preferably 2 to 5 V, more preferably 2 to 4.5 V, and particularly preferably 2 V to 4.3 V.

[0172] When the size of the non-aqueous secondary battery increases, it becomes difficult for the electrolytic solution to penetrate the entire separator. Therefore, after injecting the electrolytic solution, it is preferable to leave it standing for 12 hours or more. Further, from the viewpoint of improving the efficiency of the manufacturing process of the non-aqueous secondary battery, after injecting the electrolytic solution, it is preferable to leave it standing under reduced pressure conditions and then seal the release part. Furthermore, from the viewpoint of simplifying the process of removing the gas generated during the formation of the film during the first charge (degassing process), it is preferable to perform the first charge and discharge under reduced pressure conditions without sealing the release part. However, by applying the above manufacturing process, in the electrolytic solution containing highly volatile acetonitrile, the amount of the electrolytic solution is likely to decrease. Therefore, there is a possibility that the first charge and discharge may be performed in a state where a part of the electrode and the separator is not immersed in the electrolytic solution. In that case, since the charge and discharge reaction does not proceed satisfactorily in the part where the electrolytic solution has not penetrated, it is expected that the battery capacity will decrease. Also, when the non-penetrated part penetrates into the electrolytic solution by adding the electrolytic solution during the first charge and discharge process, since the film formation during the first charge is not performed well in the non-penetrated part, the reduction decomposition reaction of the non-aqueous solvent easily proceeds, and therefore, it is expected to lead to a decrease in the battery capacity. The larger the area of the positive electrode or the negative electrode of the battery, the more difficult it is for the electrolytic solution to penetrate, and the more gas is likely to be generated. Therefore, the above manufacturing process is often used. From the viewpoint of improving the efficiency of the manufacturing process, this embodiment is preferably applied to a non-aqueous secondary battery having an area of at least one of the positive electrode and the negative electrode of 100 cm 2 or more, more preferably applied to a non-aqueous secondary battery having an area of 150 cm 2 or more, and even more preferably applied to a non-aqueous secondary battery having an area of 200 cm 2 or more. In addition, when the positive electrode and the negative electrode constitute a laminate, the "area of the positive electrode" refers to the area obtained by adding the areas of each surface of the positive electrode. Similarly, the "area of the negative electrode" refers to the area obtained by adding the areas of each surface of the negative electrode. The above matters are preferable from the viewpoint of improving the performance of the non-aqueous secondary battery according to this embodiment to which the above manufacturing process is applied.

[0173] The embodiments for carrying out the present invention have been described above. However, the present invention is not limited to the above-described embodiments. The present invention can be variously modified without departing from its gist.

Examples

[0174] Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited only to these examples. Unless otherwise specified, the experiments and measurements in the examples were carried out under room temperature conditions.

[0175] [Examples 1 to 6, Comparative Examples 1 to 11] Preparation of non-aqueous electrolyte Under an inert atmosphere, various non-aqueous solvents were mixed so that each had a predetermined concentration shown in Table 1. An organic polymer was added to the obtained non-aqueous solvent at the ratio shown in Table 1. Further, various lithium salts were added so as to have predetermined concentrations, thereby preparing electrolytes (S01) to (S12). These electrolyte compositions are shown in Table 1.

[0176] The abbreviations of the non-aqueous solvent, lithium salt, organic polymer, and additive in each table have the following meanings respectively. Also, the mass % of the organic polymer and the additive indicates the number of parts by mass with respect to 100 parts by mass of the electrolyte. Note that the mass % can be converted to volume % from the following formula (2): {Value obtained by dividing the mass of the organic polymer by its specific gravity / (100 + value obtained by dividing the mass of the organic polymer by its specific gravity)} × 100 ··· (2) And the following formula (3): {Value obtained by dividing the mass of the additive by its specific gravity / (100 + value obtained by dividing the mass of the additive by its specific gravity)} × 100 ··· (3) can be converted to volume %.

[0177] (Lithium salt) LiPF6: Lithium hexafluorophosphate LiFSI: Lithium bis(fluorosulfonyl)imide (LiN(SO2F)2) (Non-aqueous solvent) AcN: Acetonitrile EMC: Ethyl methyl carbonate EC: Ethylene carbonate PC: Propylene carbonate GBL: γ-Butyrolactone VC: Vinylene carbonate ES: Ethylene sulfite (Organic polymer) P0903: Polyethylene oxide (viscosity-average molecular weight 6000) P2830: Polyethylene oxide (viscosity-average molecular weight 20000) SE-8: Polyethylene oxide (viscosity-average molecular weight 93000) P1819: Polyethylene oxide (viscosity-average molecular weight 100000) P1820: Polyethylene oxide (viscosity-average molecular weight 600000) SE-70: Polyethylene oxide (viscosity-average molecular weight 63000) P3727: Polyethylene oxide (viscosity-average molecular weight 1000000) P3728: Polyethylene oxide (viscosity-average molecular weight 2000000) P1822: Poly(methyl methacrylate) (viscosity-average molecular weight 120000) P4457: Poly(methyl methacrylate) (viscosity-average molecular weight 350000) (Additive) P1022: Tris(2-ethylhexyl) phosphate

[0178] The viscosity-average molecular weight of the organic polymer was measured by the following method.

[0179] (1) Viscosity-average molecular weight The viscosity-average molecular weight was evaluated by the viscosity method. The viscosity-average molecular weight of the organic polymer was calculated from the intrinsic viscosity [η] measured based on JIS K 7367-2:1999.

[0180]

Table 1

[0181] The ionic conductivity and viscosity of the electrolytic solution prepared as described in (1) above were measured by the following methods. For electrolytic solutions in which undissolved substances or re-precipitation of organic polymers were observed after the preparation of the electrolytic solution, they were described as “-”, and subsequent measurements and battery evaluations were not carried out.

[0182] (2) Measurement of Ionic Conductivity The electrolytic solution was prepared as described in (1) above, and a cell for measuring ionic conductivity “CT-58101B” (trade name) manufactured by Toa DKK Corporation, which was connected to an ionic conductivity meter “CM-41X” (trade name) manufactured by Toa DKK Corporation, was inserted into a container containing the electrolytic solution, and the ionic conductivity of the electrolytic solution at 25 °C was measured.

[0183] (3) Viscosity Measurement The electrolytic solution was prepared as described in (1) above, and the detection terminal of a vibrating viscometer “VM-10A” (trade name) manufactured by Sekonic Corporation was inserted into a container containing the electrolytic solution, and the viscosity of the electrolytic solution at 25 °C was measured.

[0184] Table 2 below shows the results of measuring the ionic conductivity, viscosity, and the value Z obtained from Equation (1) at 25 °C for electrolytic solutions S01 to S12.

[0185]

Table 2

[0186] As shown in the above table, the electrolytic solutions (Examples 1 to 4) according to this embodiment had a viscosity of 4.1 mPa·s or more and an ionic conductivity of 18.5 mS / cm or more, and Z was 75 or more. On the other hand, Comparative Examples 1 to 3 had a low viscosity of 3.5 mPa·s or less, and Z was 65 or less. For Comparative Examples 4 to 6, since undissolved substances were observed after adding the organic polymer after adjusting the electrolytic solution, measurements were not carried out. For Comparative Example 7, the ionic conductivity was 11.3 mS / cm, and for Comparative Example 8, the ionic conductivity was 5.0 mS / cm, both of which were 13.0 mS / cm or less.

[0187] (4) Volatility Test An aluminum dish was placed on a weighing scale, and 20 μl of the adjusted electrolytic solution was dropped onto it. The weight A immediately after dropping was measured. The weight B was measured 2 minutes after dropping, and the volatility of the electrolytic solution was evaluated from the weight change using the following formula: {(Weight B - Weight A) / Weight A} × 100

[0188] (5) Fabrication of non-aqueous secondary battery (5-1) Fabrication of positive electrode LiFePO4 as the positive electrode active material, acetylene black powder as the conductive assistant, and polyvinylidene fluoride (PVDF) as the binder were mixed at a mass ratio of 87:8:5 to obtain a positive electrode mixture. N-Methyl-2-pyrrolidone was added as a solvent to the obtained positive electrode mixture and further mixed to prepare a positive electrode mixture-containing slurry. The slurry was applied onto one or both sides of a 15-μm-thick aluminum foil serving as the positive electrode current collector while adjusting the coating weight per side to 20.7 mg / cm 2 , and the solvent was removed by drying in a hot air drying oven. Thereafter, the positive electrode active material layer was rolled by a roll press to a density of 1.9 g / cm 3 to obtain a positive electrode composed of a positive electrode active material layer and a positive electrode current collector. Thereafter, vacuum drying was performed at 120 °C for 12 hours or more to obtain a positive electrode.

[0189] (5-2) Fabrication of negative electrode Graphite as the negative electrode active material, carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) as the binder were mixed at a mass ratio of 97.4:1.1:1.5 to obtain a negative electrode mixture. Water was added as a solvent to the obtained negative electrode mixture and further mixed to prepare a negative electrode mixture-containing slurry. The slurry was applied onto one or both sides of a 10-μm-thick copper foil serving as the negative electrode current collector while adjusting the coating weight per side to 8.8 mg / cm 2 , and the solvent was removed by drying in a hot air drying oven. Thereafter, the negative electrode active material layer was rolled by a roll press to a density of 1.4 g / cm 3 to obtain a negative electrode composed of a negative electrode active material layer and a negative electrode current collector. Thereafter, vacuum drying was performed at 80 °C for 12 hours or more to obtain a negative electrode.​

[0190] (5-3) Preparation of separator <Preparation of polypropylene resin composition> Ultra-high molecular weight polypropylene resin (PP, MFR = 0.25) and ethylene / 1-butene copolymer (C2 / C4: density = 0.893 g / cm 2 , melting point = 80 °C, MFR = 6.7) pellets were dry blended at a mass ratio of PP:C2 / C4 = 50:50 (mass %), and then melt kneaded using a ZSK40 (manufactured by Coperion, L / D = 46). In order to suppress resin decomposition and modification as much as possible, from the resin input hopper opening to the raw material tank was made completely airtight, and nitrogen was continuously flowed from the lower part of the hopper to control the oxygen concentration near the raw material input port to 50 ppm or less. Also, all vent parts were completely sealed to eliminate air leakage into the cylinder. Due to this oxygen concentration reduction effect, polymer decomposition and modification were significantly suppressed even under high temperature conditions, and furthermore, fine dispersion of the ethylene / 1-butene copolymer became possible. After melt kneading, strands were drawn from a die (8 holes) and the melt kneaded product was cooled in a water cooling bath, and then cut using a pelletizer to obtain pellets.

[0191] <Preparation of microporous membrane (separator having a three-layer microporous membrane)> Ultra-high molecular weight polypropylene resin (PP, MFR = 0.25) and the above pellets were dry blended at a mass ratio of PP:pellets = 90:10 (mass %), then melted using a 2.5-inch extruder and supplied to an annular die using a gear pump. As a result, the charging ratio of the resin input was PP:C2 / C4 = 95:5 (mass %).

[0192] The temperature of the die was set to 240 °C, and the melted polymer was cooled by blown air and then wound onto a roll. The extruded PP precursor (original film) had a thickness of 6 μm.

[0193] High molecular weight polyethylene resin (PE, MFR = 0.38) was melted using a 2.5-inch extruder and supplied to an annular die using a gear pump.

[0194] The temperature of the die was set at 210 °C, and the molten polymer was cooled by blowing air and then wound onto a roll. The extruded PE precursor (raw film) had a thickness of 6 μm.

[0195] The obtained PP precursor and the obtained PE precursor were overlapped in three layers of PP precursor / PE precursor / PP precursor and laminated at 120 °C to obtain a raw film of a three-layer laminate. This raw film was annealed at 125 °C for 20 minutes. Then, the annealed film was cold-stretched to 15% at room temperature, then hot-stretched to 150% at 115 °C, and relaxed to 103% at 125 °C to form a separator having a structure with a three-layer microporous membrane. After the above stretching and pore formation, the physical properties of the separator were measured. The physical properties of the separator prepared above were measured by the following method.

[0196] [Average major pore diameter (nm), pore diameter ratio] The average major pore diameter of the microporous membrane was obtained by observing the surface of the microporous membrane with SEM and measuring the pore diameter of the SEM image. Specifically, from six images of the surface of the microporous membrane observed by SEM at 30,000 times magnification, the major pore diameters of the micropores within an image range of 4.0 μm × 2.8 μm were all measured, and the average was calculated to obtain the average major pore diameter a. Also, the pore diameters in the direction perpendicular to the major pore diameter direction of each pore were measured, and the average was calculated to obtain the average pore diameter b. The pore diameter ratio (a / b) was calculated by dividing the average major pore diameter by the average pore diameter. FIG. 3 shows an example of an SEM image of a microporous membrane made of polypropylene as a separator. For example, the pore diameter and pore diameter ratio can be calculated from the observation in FIG. 3.

[0197] [Measurement of thickness (μm)] The thickness of the separator including the microporous membrane was measured at room temperature of 23 ± 2 °C using a Mitutoyo Digimatic Indicator IDC112.

[0198] [Porosity (%)] A 5 cm × 5 cm square sample was cut out from the separator including the microporous membrane, and from the volume and mass of the sample, the following formula: Porosity (%) = { (Volume (cm 3 ³) - Mass (g) / Density of resin composition (g / cm 3 ³)) / Volume (cm 3 ³)} × 100 The porosity was calculated using the above formula.

[0199] [Air permeability resistance (seconds / 100 cm 3 )] The air permeability resistance of the separator including the microporous membrane was measured with a Gurley-type air permeability meter conforming to JIS P-8117. The physical property values of the separator measured according to the above method were a pore size ratio of 8.1, a film thickness of 25 μm, an air permeability resistance of 217 seconds / 100 cm 3 , and a porosity of 55%.

[0200] (5-4) Assembly of non-aqueous secondary battery In a dry room with a dew point temperature of -80°C to -20°C, the cut leaded positive electrode and the leaded negative electrode were overlapped through the separator to form a laminated electrode body, and this laminated electrode body was housed in an aluminum laminate sheet exterior body. Subsequently, 7.0 g of electrolyte was injected into the exterior body, and then a pressure reduction process was performed to impregnate the electrolyte into the separator. The pressure reduction process was to perform vacuum pumping from normal pressure to 60 kPa and immediately return to normal pressure after reaching 60 kPa, and this operation was repeated 3 times. Next, vacuum pumping was performed from normal pressure to 60 kPa, and then it was left standing in that state for 30 seconds and then returned to normal pressure. Finally, vacuum pumping was performed from normal pressure to 60 kPa and immediately returned to normal pressure after reaching 60 kPa, and this operation was repeated 3 times. After the pressure reduction process was completed, the exterior body was sealed to obtain a non-aqueous secondary battery. Here, the area of the electrodes was such that the positive electrode was 56 mm wide × 378 mm long and 56 mm wide × 304 mm long, and the negative electrode was 58 mm wide × 401 mm long and 58 mm wide × 342 mm long, and they were laminated alternately with the separator in between and wound.

[0201] (6) Evaluation of non-aqueous secondary battery Regarding the non-aqueous secondary battery obtained as described above, first, the first charge treatment and the measurement of the first charge-discharge capacity were performed according to the following procedures (6-1) and (6-2). Next, the non-aqueous secondary battery was evaluated according to the procedure of (6-2). Note that for charge and discharge, TOSCAT-300 (trade name) manufactured by Toyo System Co., Ltd. and LU-123 (trade name) or BTS-408C (trade name) manufactured by ESPEC were used. Here, 1C means the current value at which it is expected that a fully charged battery will be discharged at a constant current and the discharge will end in 1 hour.

[0202] (6-1) First charge-discharge treatment of non-aqueous secondary battery The ambient temperature of the fabricated non-aqueous secondary battery was set to 25°C, and it was charged at a constant current corresponding to 0.025C until the battery voltage reached 3.5V. Then, while maintaining the battery voltage at 3.5V, the current was decayed for 2 hours, or constant voltage charging was continued until the charge capacity reached 90% of the designed capacity. After charging, a rest period of 20 minutes was taken, and then it was discharged at a constant current of 0.1C until 2.0V.

[0203] (6-2) Finishing charge-discharge treatment After the treatment of (6-1), the ambient temperature of the non-aqueous secondary battery was set to 25°C, and it was charged at a constant current of 0.2C until 3.5V. Then, while maintaining the voltage at 3.5V, the current was decayed for 2 hours, or constant voltage charging was continued until the current value decayed to 0.05C. After charging, a rest period of 20 minutes was taken. Then, it was discharged at a constant current of 0.2C until 2.0V.

[0204] (6-3) 45°C cycle test of non-aqueous secondary battery For the non-aqueous secondary battery that was charged and discharged by the method described in (6-1) and (6-2) above, the ambient temperature was set to 45°C. First, the battery was charged at a constant current of 1C until it reached 3.5V, and then charged at a constant voltage of 3.5V until the current decayed to 0.05C. After charging, a rest period of 10 minutes was taken. Then, the battery was discharged at 1C to 2.5V. This process of charging and discharging once each was defined as one cycle, and 300 cycles of charge and discharge were performed. The discharge capacity retention rate of the 300th cycle when the discharge capacity of the first cycle was set to 100% was defined as the discharge capacity retention rate of the 45°C cycle test.

[0205] Using the electrolytes in Table 1, the volatility of the electrolytes was evaluated according to the method described in (4) above. Also, the cycle performance of the non-aqueous secondary battery was evaluated according to the method described in (6) above. The test results are shown in Table 3.

[0206]

Table 3

[0207] As shown in Table 3, for the non-aqueous secondary batteries (Comparative Examples 9 to 11), the weight change 2 minutes after dropping the electrolyte was as large as 12.7% or more, indicating high volatility. Therefore, even when the battery was fabricated, acetonitrile volatilized during the depressurization process, and the discharge capacity retention rate was 59% or less. On the other hand, for the non-aqueous secondary batteries according to this embodiment (Examples 5 and 6), the weight change 2 minutes after dropping the electrolyte was as small as 10.5% or less, indicating that the volatility was suppressed. Therefore, the discharge capacity retention rate after 300 cycles was 78.5% for both Examples 5 and 6.

[0208] [Examples 7 to 10 and Comparative Examples 12 to 17] Under an inert atmosphere, various non-aqueous solvents were mixed so that each had a predetermined concentration shown in Table 4. An organic polymer was added to the obtained non-aqueous solvent at the ratio shown in Table 4. Further, various lithium salts were added so that each had a predetermined concentration, thereby preparing electrolytes (S13) to (S19). These electrolyte compositions are shown in Table 4.

[0209]

Table 4

[0210] Table 5 shows the results of measuring the ionic conductivity and viscosity at 25°C of electrolytes S13 to S19, and the value Z obtained from Equation (1).

[0211]

Table 5

[0212] As shown in Table 5, the electrolyte (Example 7) according to this embodiment had a viscosity of 4.9 mPa·s and an ionic conductivity of 22.0 mS / cm, and Z was 108. The electrolyte (Example 8) according to this embodiment had a viscosity of 22.8 mPa·s and an ionic conductivity of 21.9 mS / cm, and Z was 499. On the other hand, the electrolytes (Comparative Examples 12 to 14) had a low viscosity of 2.2 mPa·s or less, and Z was 49 or less. In particular, Comparative Example 14 had a viscosity below 2.0 mS / cm and was presumed to have high volatility. For Comparative Examples 15 and 16, since undissolved substances were observed after adding the organic polymer after preparing the electrolyte, the measurement was not carried out.

[0213] Using the electrolytes in Table 4, the volatility of the electrolytes was evaluated according to the method described in (4) above. Also, the cycle performance of the non-aqueous secondary battery was evaluated according to the method described in (6) above. The results of this test are shown in Table 6.

[0214]

Table 6

[0215] As shown in Table 6, the non-aqueous secondary battery (Comparative Example 17) had a large weight change of 13.3% or more 2 minutes after dropping the electrolyte, indicating high volatility. Therefore, even when the battery was fabricated, acetonitrile volatilized during the decompression process, resulting in a discharge capacity retention rate of 41.5%. On the other hand, for the non-aqueous secondary batteries according to this embodiment (Examples 9 and 10), the weight change until 2 minutes after dropping the electrolyte was as small as 11.6% or less, indicating that the volatility was suppressed. And the discharge capacity retention rate after 300 cycles was 69.0% or more.

[0216] [Examples 11 to 23 and Comparative Examples 18 to 27] Under an inert atmosphere, various non-aqueous solvents were mixed so that each had a predetermined concentration shown in Table 7. An organic polymer was added to the obtained non-aqueous solvent at the ratio shown in Table 7. Further, by adding various lithium salts so as to have predetermined concentrations, electrolytes (S20) to (S36) were prepared. These electrolyte compositions are shown in Table 7.

[0217]

Table 7

[0218] The following Table 8 shows the results of measuring the ionic conductivity and viscosity at 25°C of electrolytes S20 to S36, and the value Z obtained from Equation (1).

[0219]

Table 8

[0220] As shown in Table 8, the electrolytes according to this embodiment (Examples 11 to 18) had a viscosity of 3.3 mPa·s or more and an ionic conductivity of 24.1 mS / cm or more, and Z was 87 or more. On the other hand, looking at the electrolytes (Comparative Examples 18 to 16), Comparative Example 18 had a viscosity of less than 2.0 mPa·s. Comparative Examples 19 and 21 had a low viscosity of 2.5 mPa·s or less, and Z was 67 or less. For Comparative Example 20 and Comparative Examples 22 to 26, since undissolved substances were observed after adding the organic polymer after adjusting the electrolyte, the measurement was not carried out.

[0221] Using the electrolytic solution of Table 7, the volatility of the electrolytic solution was evaluated according to the method described in (4) above. Also, the cycle performance of the non-aqueous secondary battery was evaluated according to the method described in (6) above. The test results are shown in Table 9.

[0222]

Table 9

[0223] As shown in Table 9, the non-aqueous secondary battery (Comparative Example 27) shows a large weight change of 15.1% 2 minutes after dropping the electrolytic solution, indicating high volatility. Therefore, even when the battery was fabricated, acetonitrile volatilized during the depressurization process, resulting in a discharge capacity retention rate of 24.0% after 300 cycles. On the other hand, for the non-aqueous secondary batteries (Examples 19 to 23) according to the present embodiment, the weight change within 2 minutes after dropping the electrolytic solution was as small as 13.1% or less, indicating that the volatility was suppressed. Therefore, the discharge capacity retention rate after 300 cycles was 52.0% or more. Among them, Example 22 had a weight change of 11.4%, indicating particularly suppressed volatility. And the discharge capacity retention rate after 300 cycles was 70.0%.

[0224] [Examples 24 to 29 and Comparative Examples 28 to 29] Under an inert atmosphere, various non-aqueous solvents were mixed so that each had a predetermined concentration shown in Table 10. An organic polymer was added to the obtained non-aqueous solvent at the ratio shown in Table 10. Further, by adding various lithium salts so as to have respective predetermined concentrations, electrolytic solutions (S40) to (S43) were prepared. These electrolytic solution compositions are shown in Table 10.

[0225]

Table 10

[0226]

Table 11

[0227] Using the electrolytes in Table 7, the volatility of the electrolytes was evaluated according to the method described in (4) above. Also, the cycle performance of the non-aqueous secondary battery was evaluated according to the method described in (6) above. The test results are shown in Table 9.

[0228]

Table 12

[0229] As shown in Table 12, the non-aqueous secondary battery (Comparative Example 29) showed a large weight change of 12.4% two minutes after dropping the electrolyte, indicating high volatility. Therefore, even when the battery was fabricated, acetonitrile volatilized during the depressurization process, and the discharge capacity retention rate after 300 cycles was 60.5%. On the other hand, the non-aqueous secondary batteries (Examples 27 to 29) according to this embodiment had a small weight change of 11.5% or less two minutes after dropping the electrolyte, and the volatility was suppressed. Therefore, the discharge capacity retention rate after 300 cycles was 70.0% or more. Among them, in Example 28, the weight change was 10.2%, and the volatility was particularly suppressed. And the discharge capacity retention rate after 300 cycles was 81.9%.

[0230] As shown by these results, by using the electrolyte and the non-aqueous secondary battery within the scope of the constituent requirements according to the present invention, even when using an electrolyte containing acetonitrile, it has become clear that a non-aqueous secondary battery can be provided in which the volatility of the electrolyte is suppressed and which has high ionic conductivity.

Industrial Applicability

[0231] Since the electrolytic solution within the scope of the constituent elements according to the present invention can be used in batteries that require suppression of volatility, in particular, the non-aqueous secondary battery using the non-aqueous solvent of the present invention can be used, for example, as a rechargeable battery for portable devices such as mobile phones, portable audio devices, personal computers, IC (Integrated Circuit) tags, etc.; rechargeable batteries for automobiles such as hybrid vehicles, plug-in hybrid vehicles, electric vehicles, etc.; low-voltage power supplies such as 12V-class power supplies, 24V-class power supplies, 48V-class power supplies, etc.; and is expected to be used as a residential energy storage system, IoT devices, etc. Further, the non-aqueous secondary battery using the non-aqueous solvent of the present invention can also be applied to uses in cold regions and outdoor uses in summer, etc.

Explanation of Symbols

[0232] 100 Non-aqueous secondary battery 110 Battery exterior 120 Space of battery exterior 130 Positive electrode lead body 140 Negative electrode lead body 150 Positive electrode 160 Negative electrode 170 Separator

Claims

1. In a non-aqueous secondary battery comprising a positive electrode containing one or more positive electrode active materials capable of occluding and releasing lithium ions, a negative electrode containing a material capable of occluding and releasing lithium ions, a non-aqueous electrolyte, and a separator, the non-aqueous electrolyte contains a non-aqueous solvent, a lithium salt, and an organic polymer, the non-aqueous solvent contains 10% by volume or more and 90% by volume or less of acetonitrile, the lithium salt contains a lithium-containing imide salt and has a content of 0.5 mol / L or more and 2 mol / L or less with respect to the non-aqueous electrolyte, the organic polymer has a viscosity-average molecular weight of 30,000 or more and 1,000,000 or less, the non-aqueous electrolyte has a viscosity of 2 mPa·s or more and 500 mPa·s or less and an ionic conductivity of 13 mS / cm or more at 25°C, and the following formula (1): Z = viscosity of the electrolyte (mPa·s) × ionic conductivity of the electrolyte (mS / cm) ··· (1) A non-aqueous secondary battery in which the value Z represented by is 70 or more.

2. The non-aqueous secondary battery according to claim 1, wherein the organic polymer has at least one of a polyether structure and an ester structure.

3. The non-aqueous secondary battery according to claim 1 or 2, wherein the organic polymer contains at least one of polyethylene oxide and poly(methyl methacrylate).

4. The non-aqueous secondary battery according to claim 1 or 2, wherein the organic polymer has a viscosity-average molecular weight of 90,000 or more and 650,000 or less.

5. The non-aqueous secondary battery according to claim 1 or 2, wherein the organic polymer has a content of 0.1% by mass or more and 10% by mass or less with respect to the total amount of the non-aqueous electrolyte.

6. The non-aqueous secondary battery according to claim 1 or 2, wherein the organic polymer has a content of 0.1% by mass or more and 3% by mass or less with respect to the total amount of the non-aqueous electrolyte.

7. The area of at least one of the positive electrode and the negative electrode is 100 cm ２ or more. The non-aqueous secondary battery according to claim 1 or 2.

8. A wound body obtained by winding a laminate in which the separator is interposed between the positive electrode and the negative electrode; A laminate in which a positive electrode and a negative electrode sheet are alternately laminated with the separator interposed therebetween; and A laminate in which a positive electrode and a negative electrode are alternately inserted between alternately folded separators; The non-aqueous secondary battery according to claim 1 or 2, wherein any of the above structures is housed in a battery exterior.

9. The non-aqueous electrolyte has a viscosity at 25 °C of 2.5 mPa·s or more and 150 mPa·s or less, and an ionic conductivity at 25 °C of 10 mS / cm or more and 40 mS / cm or less. The non-aqueous secondary battery according to claim 1 or 2.

10. The lithium salt further includes lithium hexafluorophosphate (LiPF ６ ), The above LiPF ６ <The lithium-containing imide salt and the LiPF in the molar concentration to be the lithium-containing imide salt> ６ The non-aqueous secondary battery according to claim 1 or 2, comprising the same.

11. The non-aqueous solvent contains 20% by volume or more and 90% by volume or less of acetonitrile. The non-aqueous secondary battery according to claim 1 or 2.

12. The separator has a porosity of 20% or more and 90% or less, and an air permeability resistance of 20 seconds / 100 cm ３ or more and 500 seconds / 100 cm ３ or less. The non-aqueous secondary battery according to claim 1 or 2.

13. The separator is provided with a porous layer containing an inorganic filler on one or both of its sides, The inorganic filler is at least one selected from the group consisting of aluminum oxide, aluminum hydroxide oxide, and aluminum silicate. The non-aqueous secondary battery according to claim 1 or 2.

14. The separator has a polypropylene-based microporous membrane, In the microporous membrane, a polymer matrix containing the polypropylene extends along a direction perpendicular to the membrane thickness, Fibrils containing the polypropylene are formed between the polymer matrices, and Micropores are formed between a plurality of the fibrils. The non-aqueous secondary battery according to claim 1 or 2.

15. The separator has a polypropylene-based microporous membrane, The pore size ratio a / b of the average major pore diameter a of the microporous membrane and the pore diameter b perpendicular to the average major pore diameter a is 0.5 or more and 30 or less. The non-aqueous secondary battery according to claim 1 or 2.

16. A non-aqueous electrolyte used in a non-aqueous secondary battery comprising a positive electrode containing one or more positive electrode active materials capable of occluding and releasing lithium ions, a negative electrode containing a material capable of occluding and releasing lithium ions, a non-aqueous electrolyte, and a separator, The non-aqueous electrolyte contains a non-aqueous solvent, a lithium salt, and an organic polymer, The non-aqueous solvent contains 10% by volume or more and 90% by volume or less of acetonitrile, The lithium salt contains a lithium-containing imide salt and has a content of 0.5 mol / L or more and 2 mol / L or less with respect to the non-aqueous electrolyte, The organic polymer has a viscosity-average molecular weight of 30,000 or more and 1,000,000 or less, The non-aqueous electrolyte has a viscosity at 25 °C of 2 mPa·s or more and 500 mPa·s or less, an ionic conductivity of 13 mS / cm or more, and the following formula (1): Z = viscosity of the electrolyte (mPa·s) × ionic conductivity of the electrolyte (mS / cm) ··· (1) The non-aqueous electrolyte in which Z represented by is 70 or more.

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