Non-aqueous secondary batteries

Abstract

To provide a nonaqueous secondary battery, which has no decrease in initial efficiency and has low bulk resistivity, even when a nonaqueous electrolytic solution containing acetonitrile and a separator having an inorganic filler layer are used therein.SOLUTION: Provided is a nonaqueous secondary battery including positive and negative electrodes, a nonaqueous electrolytic solution, and a separator. The nonaqueous electrolytic solution contains a nonaqueous solvent, a lithium salt, and a surfactant. The nonaqueous solvent contains 5-90 vol.% of acetonitrile. The lithium salt contains a lithium-containing imide salt, and is contained by 1-2 mol / L relative to the nonaqueous electrolytic solution. The surfactant contains a nonionic surfactant and does not contain a hydroxy group as a substituent. The nonionic surfactant contains at least one of a fatty acid ester compound, a phosphate ester compound, an ether compound, an ester ether compound, and an alkanol amide compound. The separator is a microporous film containing polyethylene or polypropylene, and includes an inorganic filler-containing porous layer on one side or both sides of the microporous film.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

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

[0003] To realize such a compact, high-capacity battery, the selection of the separator between the electrodes is important. Traditionally, separators have been made of paper, woven fabric, nonwoven fabric, glass mat, etc., but these have structural safety issues. Recently, inorganic fillers have been applied to separators with small pores, such as polyolefin microporous membranes, to suppress thermal shrinkage during shutdown, improving safety.

[0004] Furthermore, conventionally, a solvent of cyclic carbonate or cyclic ester has been used for the electrolyte, which has the problem of poor impregnation of the separator with the electrolyte.

[0005] However, in recent years, the impregnation of the separator has been improved by diluting a chain carbonate in a non-aqueous electrolyte solution using a cyclic carbonate or a cyclic ester solvent. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2-244565 [Patent Document 2] Japanese Patent Application Publication No. 7-263027 Summary of the Invention [Problem to be solved by the invention]

[0007] As described above, compared with non-aqueous electrolytes using esters as solvents, non-aqueous electrolytes containing acetonitrile have high ionic conductivity, and therefore, when applied to non-aqueous secondary batteries, high output performance can be obtained. However, problems have been found in cells using non-aqueous electrolytes containing acetonitrile and separators containing inorganic fillers, such as a decrease in initial efficiency or an increase in bulk resistance.

[0008] Patent Documents 1 and 2 report that the impregnation of the separator can be improved by adding a phosphorus-based compound or a fluorine-based surfactant to the non-aqueous electrolyte solution, but they do not mention the combination of a non-aqueous electrolyte solution containing acetonitrile with a separator containing an inorganic filler and the problems involved.

[0009] The present invention has been made in view of the above-mentioned problems, and aims to provide a nonaqueous secondary battery that does not reduce initial efficiency and has low bulk resistance even when using a nonaqueous electrolyte solution containing acetonitrile and a separator having an inorganic filler layer. [Means for solving the problem]

[0010] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have found that the above problems can be solved by using a nonaqueous electrolyte solution having the following composition in a specific nonaqueous secondary battery, thereby completing the present invention. [1] A non-aqueous secondary battery comprising a positive electrode containing one or more positive electrode active materials capable of absorbing and releasing lithium ions, a negative electrode containing a material capable of absorbing and releasing lithium ions, a non-aqueous electrolyte solution, and a separator, the non-aqueous electrolyte solution contains a non-aqueous solvent, a lithium salt, and a surfactant; 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 its content is 1 mol / L or more and 2 mol / L or less relative to the nonaqueous electrolyte solution; The surfactant includes a nonionic surfactant and does not include a hydroxy group as a substituent; the nonionic surfactant contains at least one compound selected from a fatty acid ester compound, a phosphate ester compound, an ether compound, an ester ether compound, and an alkanolamide compound; The separator is a microporous film containing at least one of polyethylene and polypropylene, and is provided with a porous layer containing an inorganic filler on one or both sides of the microporous film. A non-aqueous secondary battery characterized by: [2] 2. The non-aqueous secondary battery according to item 1, wherein the nonionic surfactant is the fatty acid ester compound or the phosphoric acid ester compound. [3] the fatty acid ester is ethyl laurate, or 3. The nonaqueous secondary battery according to item 1 or 2, wherein the phosphate ester compound is triamyl phosphate, triethyl phosphate, tris(2-butoxyethyl) phosphate, or tris(2-ethylhexyl) phosphate. [4] 4. The nonaqueous secondary battery according to any one of items 1 to 3, wherein the content of the nonionic surfactant is 0.1% by mass or more and 3% by mass or less with respect to the total amount of the nonaqueous electrolyte solution. [5] 5. The nonaqueous secondary battery according to any one of items 1 to 4, wherein the inorganic filler is at least one selected from the group consisting of aluminum oxide, aluminum oxide hydroxide, and aluminum silicate. [6] The separator has a porosity of 20% or more and 90% or less and an air permeability of 20 seconds / 100 cm 3 More than 500 seconds / 100cm 3 6. The nonaqueous secondary battery according to any one of items 1 to 5, wherein: [7] 7. The nonaqueous secondary battery according to any one of items 1 to 6, wherein the lithium salt further contains LiPF6, and the lithium-containing imide salt and LiPF6 are contained at molar concentrations such that LiPF6<the lithium-containing imide salt. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a nonaqueous secondary battery that does not decrease in initial efficiency and has low bulk resistance, and also to provide a nonaqueous secondary battery that has good impregnation of a nonaqueous electrolyte solution containing acetonitrile in the thickness direction of a separator having an inorganic filler layer and has high output performance. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a plan view schematically illustrating an example of a nonaqueous secondary battery according to an embodiment of the present invention. [Figure 2] 2 is a cross-sectional view of the nonaqueous secondary battery of FIG. 1 taken along line AA. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of 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 embodiment, and various modifications are possible without departing from the gist of the present invention. In this specification, a numerical range indicated using "to" includes the numerical values ​​before and after it.

[0014] [Non-aqueous secondary battery] The nonaqueous electrolyte solution according to this embodiment can be used to form a nonaqueous secondary battery.

[0015] The non-aqueous secondary battery according to this embodiment is configured by housing a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte solution in an appropriate battery exterior.

[0016] Specifically, the nonaqueous secondary battery according to this embodiment may be a nonaqueous secondary battery 100 shown in Figures 1 and 2. Here, Figure 1 is a plan view schematically showing the nonaqueous secondary battery, and Figure 2 is a cross-sectional view taken along line AA in Figure 1.

[0017] The nonaqueous secondary battery 100 shown in FIGS. 1 and 2 is a pouch-type cell. The nonaqueous secondary battery 100 accommodates a laminated electrode assembly formed by stacking a positive electrode 150 and a negative electrode 160 with a separator 170 interposed therebetween, and a nonaqueous electrolyte (not shown) within a space 120 of a battery exterior 110. The battery exterior 110 is made of, for example, an aluminum laminate film, and the outer periphery of the space formed by the two aluminum laminate films is sealed by heat-sealing the upper and lower films. The laminate, in which the positive electrode 150, the separator 170, and the negative electrode 160 are stacked in this order, is impregnated with a nonaqueous electrolyte. However, in FIG. 2, to avoid cluttering the drawing, the layers constituting the battery exterior 110 and the layers of the positive electrode 150 and the negative electrode 160 are not distinguished from one another.

[0018] The aluminum laminate film that constitutes the battery exterior 110 is preferably an aluminum foil coated on both sides with a polyolefin resin.

[0019] The positive electrode 150 is connected to the positive electrode lead body 130 within the nonaqueous secondary battery 100. Although not shown, the negative electrode 160 is also connected to the negative electrode lead body 140 within the nonaqueous secondary battery 100. One end of each of the positive electrode lead body 130 and the negative electrode lead body 140 is drawn out to the outside of the battery exterior 110 so that they can be connected to external devices, and the ionomer portions of these lead bodies are heat-sealed to one side of the battery exterior 110.

[0020] 1 and 2 has a laminated electrode body with one positive electrode 150 and one negative electrode 160, but the number of laminated positive electrodes 150 and negative electrodes 160 can be increased as needed depending on the capacity design. In the case of a laminated electrode body with multiple positive electrodes 150 and multiple negative electrodes 160, tabs of the same electrode may be joined together by welding or the like and then joined to a single lead body by welding or the like, and then taken out of the battery. The tabs of the same electrode may be formed from an exposed portion of a current collector, or may be formed by welding a metal piece to the exposed portion of a current collector, or the like.

[0021] The positive electrode 150 is composed of a positive electrode current collector and a positive electrode active material layer, and the negative electrode 160 is composed of a negative electrode current collector and a negative electrode active material layer.

[0022] 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.

[0023] The positive electrode 150 and the negative electrode 160 are arranged with the separator 170 interposed between them so that the positive electrode active material layer and the negative electrode active material layer face each other.

[0024] Hereinafter, each element constituting the nonaqueous secondary battery according to this embodiment will be described in order.

[0025] [Positive electrode] In the nonaqueous secondary battery according to this embodiment, the positive electrode contains one or more positive electrode active materials capable of absorbing 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.

[0026] [Positive electrode current collector] The positive electrode current collector is made of a metal foil such as aluminum foil, nickel foil, or stainless steel foil. The surface of the positive electrode current collector may be coated with carbon or processed into a mesh. The thickness of the positive electrode current collector is preferably 5 to 40 μm, more preferably 7 to 35 μm, and even more preferably 9 to 30 μm.

[0027] [Cathode 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.

[0028] (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.

[0029] 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; 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 the formula is preferable.

[0030] Also, examples of the positive electrode active material include Lithium cobalt oxide represented by LiCoO2; Lithium manganese oxides 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, LiNi0.8 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 Li-containing composite metal oxide represented by MO2 (where M contains 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); MnO2, FeO2, FeS2, V2O5, V6O 13 , metal oxides or metal chalcogenides having tunnel structures and layered structures, represented by TiO2, TiS2, MoS2, and NbSe2; sulfur; and conductive polymers such as polyaniline, polythiophene, polyacetylene, and polypyrrole; are exemplified.

[0031] In particular, when the Ni content ratio q of the Li-containing metal oxide represented by the general formula (a) is 0.5 < q < 1.2, it is preferable because both reduction of the usage amount of Co, which is a rare metal, and increase in the energy density are achieved.

[0032] Here, the higher the Ni content of the Li-containing metal oxide, the more likely degradation will occur at low voltages. The lithium-containing metal oxide positive electrode active material represented by general formula (a) has active sites that cause oxidative degradation of the non-aqueous electrolyte. These active sites can unintentionally consume compounds added to protect the negative electrode at the positive electrode. Acid anhydrides in particular tend to be susceptible to this effect. In particular, when the electrolyte contains acetonitrile as a non-aqueous solvent, the effect of adding an acid anhydride is significant, so the consumption of the acid anhydride at the positive electrode is a problem.

[0033] Furthermore, these additive decomposition products that are incorporated into and deposited on the positive electrode side not only increase the internal resistance of non-aqueous secondary batteries, but also accelerate the degradation of the lithium salt and result in insufficient protection of the negative electrode surface. To deactivate the active sites that essentially cause oxidative degradation of non-aqueous electrolytes, it is preferable to coexist with a component that controls Jahn-Teller distortion or acts as a neutralizer. Therefore, it is preferable that the positive electrode active material contain at least one metal selected from the group consisting of Al, Sn, In, Fe, V, Cu, Mg, Ti, Zn, Mo, Zr, Sr, and Ba.

[0034] For the same reasons 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. It is also 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. Furthermore, 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 this does not inhibit the permeation of lithium ions.

[0035] The positive electrode active material may be a lithium-containing compound other than the lithium-containing metal oxide represented by general formula (a). Examples of such lithium-containing compounds include composite oxides containing lithium and a transition metal element, metal chalcogenides containing lithium, metal phosphate compounds containing lithium and a transition metal element, and metal silicate compounds containing lithium and a transition metal element. From the viewpoint of obtaining a higher voltage, the lithium-containing compound is preferably 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.

[0036] More specifically, the lithium-containing compound is represented by the following formula (XXa): Li v M I D2(XXa) {wherein D represents a chalcogen element, and M I represents one or more transition metal elements including at least one transition metal element, and the value of v is determined by the charge / 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 formula, M II represents one or more transition metal elements, and the value of w is determined depending on the charge / discharge state of the battery and represents a number between 0.05 and 1.10.}, and The following formula (XXc): Li t M III u SiO4(XXc) {In formula, M III represents one or more transition metal elements, the value of t is determined depending on the charge / discharge state of the battery and represents a number from 0.05 to 1.10, and u represents a number from 0 to 2.} Examples of compounds include compounds represented by the following formulae:

[0037] The lithium-containing compound represented by the formula (XXa) has a layered structure, and the compounds represented by the formulas (XXb) and (XXc) have an olivine structure. These lithium-containing compounds may be those in which, for the purpose of stabilizing the structure, a part of the transition metal element is substituted with Al, Mg, or another transition metal element, those in which these metal elements are contained in the crystal grain boundaries, those in which a part of the oxygen atoms is substituted with fluorine atoms, 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, or the like.

[0038] The positive electrode active material may be used alone or in combination of two or more. The positive electrode active material layer preferably contains at least one transition metal element selected from Ni, Mn, and Co, because this allows for reversible and stable absorption and desorption of lithium ions and a high energy density.

[0039] When a lithium-containing compound and another positive electrode active material are used in combination as the positive electrode active material, the ratio of the lithium-containing compound to the total positive electrode active material is preferably 80 mass% or more, and more preferably 85 mass% or more.

[0040] (Conductive additive) Examples of the conductive additive include graphite, carbon black such as acetylene black and ketjen black, and carbon fiber. The content of the conductive additive is preferably 10 parts by mass or less, more preferably 1 to 5 parts by mass, per 100 parts by mass of the positive electrode active material.

[0041] (binder) Examples of binders include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid, 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, per 100 parts by mass of the positive electrode active material.

[0042] [Formation of positive electrode active material layer] The positive electrode active material layer is formed by dispersing a positive electrode mixture, which is a mixture of a positive electrode active material and, if necessary, a conductive additive and a binder, in a solvent to form a positive electrode mixture-containing slurry, which is applied to a positive electrode current collector, dried (solvent removal), and, if necessary, pressed. Known solvents can be used. Examples of such solvents include N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, and water.

[0043] [Negative electrode] The negative electrode in the nonaqueous secondary battery according to this embodiment contains a material capable of absorbing and releasing lithium ions, and may have a negative electrode active material layer on one or both sides of the negative electrode current collector, as desired.

[0044] [Negative electrode current collector] The negative electrode current collector is made of a metal foil such as copper foil, nickel foil, or stainless steel foil. The surface of the negative electrode current collector may be coated with carbon or may be processed into a mesh. 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.

[0045] [Negative electrode active material layer] The negative electrode active material layer contains a negative electrode active material, and may further contain a conductive additive and / or a binder as necessary.

[0046] (Negative electrode active material) Examples of negative electrode active materials include graphites such as amorphous carbon (hard carbon), artificial graphite, and natural graphite; carbon materials such as pyrolytic carbon, coke, glassy carbon, fired bodies of organic polymer compounds, mesocarbon microbeads, carbon fiber, activated carbon, carbon colloids, and carbon black; and metal lithium, metal oxides, metal nitrides, lithium alloys, tin alloys, Si materials, intermetallic compounds, organic compounds, inorganic compounds, metal complexes, and organic polymer compounds. The negative electrode active materials may be used alone or in combination of two or more. Examples of the Si materials include silicon, Si alloys, and Si oxides.

[0047] The negative electrode active material layer uses lithium ions as the negative electrode active material to increase the battery voltage. + It is preferable that the material contains a material capable of occluding at a potential lower than the potential of the material.

[0048] The nonaqueous electrolyte solution according to this embodiment has the advantage of being able to suppress various deterioration phenomena that accompany volume changes in the negative electrode during repeated charge-discharge cycles, even when a Si material is used as the negative electrode active material. Therefore, in the nonaqueous secondary battery according to this embodiment, using a Si material, such as a silicon alloy, as the negative electrode active material is also a preferred embodiment, since it provides the battery with high capacity derived from the Si material and excellent charge-discharge cycle characteristics.

[0049] In this embodiment, a Si material, particularly SiO x (wherein 0.5≦x≦1.5). The Si material may be in any form of crystalline, low-crystalline, or amorphous. When a Si material is used as the negative electrode active material, it is preferable to coat the surface of the active material with a conductive material, since this improves the conductivity between the active material particles.

[0050] Silicon has an operating potential of approximately 0.5V (vsLi / Li + ), which is about 0.05 V (vs Li / Li) of the operating potential of graphite. + ) is slightly higher than that of the non-aqueous electrolyte solution containing acetonitrile. Therefore, the risk of lithium electrodeposition is reduced when a Si material is used. Acetonitrile, which is used as the non-aqueous solvent in this embodiment, may undergo a reduction reaction with lithium metal, potentially causing gas generation. Therefore, a negative electrode active material that is difficult to electrodeposit lithium is preferably used in combination with a non-aqueous electrolyte solution containing acetonitrile.

[0051] 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, the negative electrode active material should be 0.4V vs. Li / Li. +It is preferable to operate at a more noble potential than

[0052] The content of the Si material, expressed as the amount relative to the total amount of the negative electrode active material layer, is preferably in the range of 0.1% by mass to 100% by mass, more preferably in the range of 1% by mass to 80% by mass, and even more preferably in the range of 3% by mass to 60% by mass. By adjusting the content of the Si material within the above range, a balance can be secured between the high capacity and the charge / discharge cycle performance of the nonaqueous secondary battery.

[0053] (Conductive additive) Examples of conductive additives include graphite, carbon black such as acetylene black and ketjen black, and carbon fiber. The content of the conductive additive is preferably 20 parts by mass or less, more preferably 0.1 to 10 parts by mass, per 100 parts by mass of the negative electrode active material.

[0054] (binder) Examples of binders include carboxymethyl cellulose, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid, and fluororubber. Also included are diene rubbers such as styrene-butadiene rubber. The binder content is preferably 10 parts by mass or less, more preferably 0.5 to 6 parts by mass, per 100 parts by mass of the negative electrode active material.

[0055] [Formation of negative electrode active material layer] The negative electrode active material layer is formed by dispersing a negative electrode mixture, which is a mixture of a negative electrode active material and, optionally, a conductive additive and / or a binder, in a solvent to form a negative electrode mixture-containing slurry, which is applied to a negative electrode current collector, dried (solvent removal), and, if necessary, pressed. Known solvents can be used. Examples of such solvents include N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, and water.

[0056] [Non-aqueous electrolyte] In this specification, the term "nonaqueous electrolyte solution" (hereinafter simply referred to as "electrolyte solution") refers to an electrolyte solution in which the water content is 1 mass % or less relative to the total amount of the electrolyte solution.

[0057] The electrolyte solution according to this embodiment preferably contains as little water as possible, but may contain a very small amount of water as long as it does not impede the solution of the problems of the present invention. The water content is 300 mass ppm or less, more preferably 200 mass ppm or less, based on the total amount of the nonaqueous electrolyte solution. As long as the nonaqueous electrolyte solution has a configuration that achieves the solution of the problems of the present invention, the other components can be appropriately selected and applied from the constituent materials of known nonaqueous electrolyte solutions used in lithium-ion batteries.

[0058] The non-aqueous electrolyte solution according to this embodiment contains acetonitrile, a non-aqueous solvent, a lithium salt, and a surfactant, and may further contain an additive for protecting an electrode, if desired.

[0059] <Non-aqueous solvent> In this embodiment, the term "non-aqueous solvent" refers to the elements remaining in the non-aqueous electrolyte solution excluding the lithium salt and various additives. When the non-aqueous electrolyte solution contains an electrode protection additive, the term "non-aqueous solvent" refers to the elements remaining in the non-aqueous electrolyte solution excluding the lithium salt and additives other than the electrode protection additive. Examples of non-aqueous solvents include alcohols such as methanol and ethanol; and aprotic solvents. Among these, aprotic solvents are preferred as non-aqueous solvents. The non-aqueous solvent may contain a solvent other than an aprotic solvent, as long as it does not impede the solution of the problems of the present invention.

[0060] For example, the nonaqueous solvent for the nonaqueous electrolyte solution can contain acetonitrile as an aprotic solvent. The inclusion of acetonitrile in the nonaqueous solvent improves the ionic conductivity of the nonaqueous electrolyte solution, thereby increasing the diffusibility of lithium ions within the battery. Therefore, when the nonaqueous electrolyte solution contains acetonitrile, lithium ions can be effectively diffused even to the region near the current collector, which is difficult for lithium ions to reach during high-load discharge, especially in a positive electrode in which the positive electrode active material layer is thickened to increase the loading amount of the positive electrode active material. Therefore, it is possible to extract sufficient capacity even during high-load discharge, and a nonaqueous secondary battery with excellent load characteristics can be obtained.

[0061] Furthermore, the inclusion of acetonitrile in the nonaqueous solvent can improve the rapid charging characteristics of nonaqueous secondary batteries. In constant current (CC)-constant voltage (CV) charging of nonaqueous secondary batteries, the charge capacity per unit time during the CC charging period is greater than the charge capacity per unit time during the CV charging period. When acetonitrile is used as the nonaqueous solvent in a nonaqueous electrolyte, the range in which CC charging is possible can be expanded (CC charging time can be extended), and the charging current can also be increased, significantly shortening the time from the start of charging to fully charging a nonaqueous secondary battery.

[0062] Acetonitrile is easily electrochemically reductively decomposed, and therefore, when acetonitrile is used, it is preferable to use another solvent (e.g., an aprotic solvent other than acetonitrile) in combination with acetonitrile as a non-aqueous solvent, and / or to add an electrode protection additive for forming a protective film on the electrode.

[0063] The acetonitrile content is preferably 5% by volume or more and 90% by volume or less, based on the total amount of the non-aqueous solvent. The acetonitrile content is more preferably 10% by volume or more, more preferably 15% by volume or more, more preferably 20% by volume or more, more preferably 30% by volume or more, and even more preferably 40% by volume or more, based on the total amount of the non-aqueous solvent. This value is more preferably 85% by volume or less, and even more preferably 66% by volume or less. When the acetonitrile content is 5% by volume or more, based on the total amount of the non-aqueous solvent, the ionic conductivity tends to increase, resulting in high-power performance, and the dissolution of the lithium salt can be promoted. Since the additives described below suppress an increase in the internal resistance of the battery, when the acetonitrile content 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.

[0064] Examples of aprotic solvents other than acetonitrile include cyclic carbonates, fluoroethylene carbonate, lactones, organic compounds having sulfur atoms other than those represented by general formula (1), chain fluorinated carbonates, cyclic ethers, mononitriles other than acetonitrile, alkoxy group-substituted nitriles, dinitriles, cyclic nitriles, short-chain fatty acid esters, chain ethers, fluorinated ethers, ketones, and compounds in which some or all of the H atoms of the aprotic solvents have been substituted with halogen atoms.

[0065] 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 vinylethylene carbonate;

[0066] Fluoroethylene carbonates include, for example, 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;

[0067] Lactones include γ-butyrolactone, α-methyl-γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε-caprolactone;

[0068] Examples of organic compounds having a sulfur atom include ethylene sulfite, propylene sulfite, butylene sulfite, pentene sulfite, sulfolane, 3-sulfolene, 3-methyl sulfolane, 1,3-propane sultone, 1,4-butane sultone, 1-propene 1,3-sultone, dimethyl sulfoxide, tetramethylene sulfoxide, and ethylene glycol sulfite;

[0069] 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;

[0070] Cyclic ethers include, for example, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, and 1,3-dioxane;

[0071] Examples of mononitriles other than acetonitrile include propionitrile, butyronitrile, valeronitrile, benzonitrile, and acrylonitrile;

[0072] Alkoxy-substituted nitriles include, for example, methoxyacetonitrile and 3-methoxypropionitrile;

[0073] Dinitriles include, for example, malononitrile, succinonitrile, glutaronitrile, adiponitrile, 1,4-dicyanoheptane, 1,5-dicyanopentane, 1,6-dicyanohexane, 1,7-dicyanoheptane, 2,6-dicyanoheptane, 1,8-dicyanoctane, 2,7-dicyanoctane, 1,9-dicyanononane, 2,8-dicyanononane, 1,10-dicyanodecane, 1,6-dicyanodecane, and 2,4-dimethylglutaronitrile;

[0074] Cyclic nitriles include, for example, benzonitrile;

[0075] 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, and iso pivalate. propyl, 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;

[0076] Chain ethers include, for example, dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme, and tetraglyme;

[0077] Examples of fluorinated ethers include Rf aa -OR bb (In the formula, Rf aa represents an alkyl group containing a fluorine atom, and R bb represents an organic group which may contain a fluorine atom);

[0078] Ketones, for example, acetone, methyl ethyl ketone, and methyl isobutyl ketone;

[0079] Examples of the compound in which some or all of the H atoms of the aprotic solvent have been substituted with halogen atoms include compounds in which the halogen atoms are fluorine; Examples include:

[0080] Examples of fluorinated chain carbonates include methyl trifluoroethyl carbonate, trifluorodimethyl carbonate, trifluorodiethyl carbonate, trifluoroethylmethyl carbonate, methyl 2,2-difluoroethyl carbonate, methyl 2,2,2-trifluoroethyl carbonate, and methyl 2,2,3,3-tetrafluoropropyl carbonate. The fluorinated chain carbonates are represented by the following general formula: R cc -OC(O)OR dd (In the formula, R cc and R dd are CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, and CH2Rf ee and Rf ee is an alkyl group having 1 to 3 carbon atoms in which a hydrogen atom is substituted with at least one fluorine atom, and R cc and / or R dd contains at least one fluorine atom).

[0081] In addition, examples of fluorinated short-chain fatty acid esters include fluorinated short-chain fatty acid esters such as 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, and 2,2,3,3-tetrafluoropropyl acetate. Fluorinated short-chain fatty acid esters are represented by the following general formula: R ff -C(O)OR gg (In the formula, R ffis CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, CF3CF2H, CFH2, CF2Rf hh , CFHRf hh , and CH2Rf ii and R is at least one selected from the group consisting of gg are CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, and CH2Rf ii and Rf hh is an alkyl group having 1 to 3 carbon atoms in which a hydrogen atom may be substituted with at least one fluorine atom, and Rf ii is an alkyl group having 1 to 3 carbon atoms in which a hydrogen atom is substituted with at least one fluorine atom, and R ff and / or R gg contains at least one fluorine atom, and R ff If is CF2H, R gg can be expressed as (not CH3).

[0082] In the present embodiment, the aprotic solvent other than acetonitrile may be used alone or in combination of two or more.

[0083] In the present embodiment, the non-aqueous solvent is preferably one or more of cyclic carbonates and chain carbonates in combination with acetonitrile from the viewpoint of improving the stability of the non-aqueous electrolyte solution. From this viewpoint, the non-aqueous solvent in the present embodiment is more preferably one of cyclic carbonates in combination with acetonitrile, and further preferably one of cyclic carbonates and chain carbonates in combination with acetonitrile.

[0084] When a cyclic carbonate is used with acetonitrile, it is particularly preferred that the cyclic carbonate comprises ethylene carbonate, vinylene carbonate and / or fluoroethylene carbonate.

[0085] <Lithium salt> The non-aqueous electrolyte solution according to this embodiment contains a lithium salt, which includes a lithium-containing imide salt, and the content of the lithium salt in the non-aqueous electrolyte solution is 1 mol / L or more and 2 mol / L or less.

[0086] The lithium-containing imide salt in this embodiment is LiN(SO2C m F 2m+1 )2 {wherein m is an integer of 0 to 8}.

[0087] The lithium salt in this embodiment may further include, in addition to the imide salt, one or more selected from fluorine-containing inorganic lithium salts, organic lithium salts, and other lithium salts.

[0088] (Lithium-containing imide salt) Specifically, the lithium-containing imide salt preferably contains at least one of LiN(SO2F)2 and LiN(SO2CF3)2.

[0089] When acetonitrile is contained in the non-aqueous solvent, the lithium salt preferably contains LiPF6. Since the saturation concentration of the imide salt relative to acetonitrile is higher than that of LiPF6, it is preferable to contain LiPF6 and the imide salt at a molar concentration such that LiPF6 < lithium-containing imide salt, since this can suppress association and precipitation of the lithium salt and acetonitrile at low temperatures. Furthermore, it is preferable that the content of the imide salt is 0.5 mol or more and 3.0 mol or less per liter of non-aqueous solvent from the viewpoint of ensuring the supply of ions to the non-aqueous electrolyte solution according to this embodiment.

[0090] A non-aqueous electrolyte solution containing acetonitrile containing at least one of LiN(SO2F)2 and LiN(SO2CF3)2 can effectively suppress the decrease in ionic conductivity at low temperatures such as -10°C or -30°C, thereby achieving excellent low-temperature properties.

[0091] Furthermore, by limiting the contents of the imide salt and LiPF6 as described above, it is possible to more effectively suppress the increase in resistance when heated to high temperatures.

[0092] (Fluorine-containing inorganic lithium salt) The lithium salt in this embodiment may include a fluorine-containing inorganic lithium salt. Here, the term "fluorine-containing inorganic lithium salt" refers to a lithium salt that does not contain a carbon atom in the anion but 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 inhibits corrosion of the positive electrode current collector.

[0093] Examples of fluorine-containing inorganic lithium salts include LiPF6, LiBF4, LiAsF6, Li2SiF6, LiSbF6, and Li2B 12 F b H 12-b {wherein b represents an integer of 0 to 3}, and one or more selected from these can be used.

[0094] As the fluorine-containing inorganic lithium salt, a compound that is a double salt of LiF and a Lewis acid is desirable, and among them, a fluorine-containing inorganic lithium salt having a phosphorus atom is more preferred because it easily releases free fluorine atoms. A typical fluorine-containing inorganic lithium salt is LiPF6, which dissolves and releases PF6 anions. When a fluorine-containing inorganic lithium salt having a boron atom is used as the fluorine-containing inorganic lithium salt, it is preferred because it easily captures excess free acid components that may cause battery degradation, and from this viewpoint, LiBF4 is preferred.

[0095] The content of the fluorine-containing inorganic lithium salt in the non-aqueous electrolyte solution according to this embodiment is preferably 0.01 mol or more, more preferably 0.1 mol or more, and even more preferably 0.25 mol or more, per 1 L of 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-power characteristics tend to be realized. Furthermore, the amount per 1 L of non-aqueous solvent is preferably 2.8 mol or less, more preferably 1.5 mol or less, and even 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-power characteristics can be realized, and the decrease in ionic conductivity due to an increase in viscosity at low temperatures tends to be suppressed. Therefore, the high-temperature cycle characteristics and other battery characteristics tend to be further improved while maintaining the excellent performance of the non-aqueous electrolyte solution.

[0096] The content of the fluorine-containing inorganic lithium salt in the nonaqueous electrolyte solution according to this embodiment may be, for example, 0.05 mol or more and 1.0 mol or less per 1 L of the nonaqueous solvent.

[0097] (organic lithium salts) The lithium salt in this embodiment may include an organic lithium salt. The term "organic lithium salt" refers to a lithium salt other than an imide salt that contains a carbon atom in the anion and is soluble in acetonitrile.

[0098] Examples of organic lithium salts include organic lithium salts having an oxalic acid group. Specific examples of organic lithium salts having an oxalic acid group include organic lithium salts represented by LiB(C2O4)2, LiBF2(C2O4), LiPF4(C2O4), and LiPF2(C2O4)2. Among these, at least one lithium salt selected from the group consisting of LiB(C2O4)2 and LiBF2(C2O4) is preferred. It is more preferred to use one or more of these together with a fluorine-containing inorganic lithium salt. This organic lithium salt having an oxalic acid group may be added to a nonaqueous electrolyte solution or incorporated into the negative electrode (negative electrode active material layer).

[0099] In this embodiment, the amount of the organic lithium salt added to the non-aqueous electrolyte solution is preferably 0.005 mol or more, more preferably 0.01 mol or more, even more preferably 0.02 mol or more, and particularly preferably 0.05 mol or more, per 1 L of non-aqueous solvent, in order to better ensure the effects of its use. However, if the amount of the organic lithium salt having an oxalic acid group in the non-aqueous electrolyte solution is too large, precipitation may occur. Therefore, the amount of the organic lithium salt having an oxalic acid group added to the non-aqueous electrolyte solution is preferably less than 1.0 mol, more preferably less than 0.5 mol, and even more preferably less than 0.2 mol, per 1 L of non-aqueous solvent.

[0100] It is known that organic lithium salts having an oxalic acid group are poorly soluble in organic solvents with low polarity, particularly in chain carbonates. The content of the organic lithium salt in the nonaqueous electrolyte solution according to this embodiment may be, for example, 0.01 mol or more and 0.5 mol or less per 1 L of the nonaqueous solvent.

[0101] In addition, the organic lithium salt having an oxalic acid group may contain a small amount of lithium oxalate, and when mixed to form a non-aqueous electrolyte solution, it may react with a small amount of water contained in other raw materials to generate a new white precipitate of lithium oxalate. Therefore, it is preferable that the content of lithium oxalate in the non-aqueous electrolyte solution according to this embodiment be limited to a range of 500 ppm or less.

[0102] (Other lithium salts) The lithium salt in this embodiment may include other lithium salts in addition to those mentioned above.

[0103] Other specific examples of lithium salts include: LiClO4, LiAlO4, LiAlCl4, LiB 10 Cl 10 inorganic lithium salts that do not contain fluorine atoms in the anion, such as chloroborane Li; LiCF3SO3, LiCF3CO2, Li2C2F4(SO3)2, LiC(CF3SO2)3, LiC n F (2n+1) SO3 (wherein n≧2), organic lithium salts such as lower aliphatic carboxylic acids Li, tetraphenylborate Li, and LiB(C3O4H2)2; LiPF such as LiPF5(CF3) n (C p F 2p+1 ) 6-n an organic lithium salt represented by the formula (wherein n is an integer of 1 to 5, and p is an integer of 1 to 8); LiBF such as LiBF3(CF3) q (C s F 2s+1 ) 4-q an organic lithium salt represented by the formula (wherein q is an integer of 1 to 3, and s is an integer of 1 to 8); Lithium salts combined with polyvalent anions; The following formula (YYa): LiC(SO2R jj )(SO2R kk )(SO2R ll ) (YYa) {where, R jj , R kk , and R ll may be the same or different and represent a perfluoroalkyl group having 1 to 8 carbon atoms. The following formula (YYb) LiN(SO2OR mm )(SO2OR nn ) (YYb) {where, R mm , and R nn may be the same or different and represent a perfluoroalkyl group having 1 to 8 carbon atoms.}, and The following formula (YYc) LiN(SO2R oo )(SO2OR pp ) (YYc) {where, R oo , and R pp may be the same or different and represent a perfluoroalkyl group having 1 to 8 carbon atoms.} One or more of these can be used together with the fluorine-containing inorganic lithium salt.

[0104] The amount of the other lithium salt added to the non-aqueous electrolyte solution may be appropriately set within the range of, for example, 0.01 mol or more and 0.5 mol or less per liter of non-aqueous solvent.

[0105] <Surfactant> The surfactant of this embodiment includes a nonionic surfactant and does not include a hydroxy group as a substituent.

[0106] The nonionic surfactant contains at least one compound selected from a fatty acid ester compound, a phosphate ester compound, an ether compound, an ester ether compound, and an alkanolamide compound.

[0107] 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 surfactants include anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants. Ionizable surfactants are limited to those that do not inhibit the insertion and desorption of lithium ions into the negative electrode. Therefore, nonionic surfactants are preferred as surfactants. Furthermore, from the viewpoint of solubility in nonaqueous electrolytes, nonionic surfactants are preferred as surfactants.

[0108] 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; ethyl diethylphosphonoacetate {EDPA: (C2H5O)2(P=O)-CH2(C=O)OC2H5}, tris(trifluoroethyl) phosphate {TFEP: (CF3CHO)3P=O}, triphenyl phosphate {TPP: (C6H5O)3P=O}, triallyl phosphate {CH2=CHCHO)3P=O}, triamyl phosphate, triethyl phosphate, tris(2-butoxyethyl) phosphate, Examples of suitable phosphate ester compounds include tris(2-ethylhexyl) phosphate; ether compounds such as polyoxyethylene alkyl ethers, polyoxyalkylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene polycyclic phenyl ethers, polyoxyethylene distyrenated phenyl ethers, and polyoxyethylene polyoxypropylene glycol; 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 viewpoint of improving the stability of nonaqueous electrolytes, fatty acid ester compounds, phosphate ester compounds, ether compounds, ester ether compounds, and alkanolamide compounds are preferred, with fatty acid ester compounds or phosphate ester compounds being more preferred. Among these, ethyl laurate is more preferred as the fatty acid ester, and triamyl phosphate, triethyl phosphate, tris(2-butoxyethyl) phosphate, or tris(2-ethylhexyl) phosphate is more preferred as the phosphate ester compound.

[0109] In this embodiment, the content of the surfactant is 0.1% by mass or more and 3% by mass or less, based on the total amount of the non-aqueous electrolyte solution. The content of the surfactant is more preferably 0.3% by mass or more, based on the total amount of the non-aqueous electrolyte solution, from the viewpoint of improving impregnation, and more preferably 1.5% by mass or less, based on the total amount of the non-aqueous electrolyte solution, from the viewpoint of maintaining high ionic conductivity. Similarly, the content of the nonionic surfactant is preferably 0.1% by mass or more and 3% by mass or less, based on the total amount of the non-aqueous electrolyte solution, and more preferably 0.3% by mass or more and 1.5% by mass or less. When the content of the surfactant or nonionic surfactant is 0.1% by mass or more, the effect of improving impregnation can be more effectively obtained, and when the content is 3% by mass or less, the decrease in ionic conductivity is small, resulting in less impact on battery characteristics such as input / output characteristics and battery life.

[0110] Here, the surfactant content can be determined by H-NMR measurement of the non-aqueous electrolyte solution at room temperature (normalization is performed using a standard substance (C6F4H2), and the surfactant content is calculated from the integrated value of the signal of each detected component).

[0111] As a result of extensive research, the inventors found that while the presence of hydroxyl groups in surfactants improves separator impregnation, they also facilitate reductive decomposition at the negative electrode, resulting in deterioration of battery performance. Furthermore, it was newly discovered that when surfactants contain hydroxyl groups, bubbles are more likely to form during the decompression process after the injection of the nonaqueous electrolyte solution. If bubbles are not completely removed from the negative electrode surface, the initial charge is performed with insufficient solid electrolyte interface (SEI) formation. Nonaqueous electrolytes containing acetonitrile form a uniform SEI during the initial charge, enabling subsequent charge / discharge operations. Therefore, if there are areas where SEI formation is insufficient due to the generation of bubbles, the battery life of nonaqueous electrolytes containing acetonitrile is significantly reduced compared to nonaqueous electrolytes that do not contain acetonitrile. Therefore, it is important that the surfactant of this embodiment does not contain hydroxyl groups as a substituent, more specifically, as a terminal substituent.

[0112] <Electrode protection additive> The non-aqueous electrolyte solution according to this embodiment may contain an additive for protecting the electrodes (electrode protection additive). The electrode protection additive may substantially overlap with the substance that serves as a solvent for dissolving the lithium salt (i.e., the non-aqueous solvent described above). The electrode protection additive is preferably a substance that contributes to improving the performance of the non-aqueous electrolyte solution and the non-aqueous secondary battery, but also includes substances that are not directly involved in the electrochemical reaction.

[0113] Specific examples of the electrode protection additive include: 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, such as vinylene carbonate, 4,5-dimethylvinylene carbonate, and vinylethylene carbonate; Lactones represented by γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε-caprolactone; cyclic ethers, such as 1,4-dioxane; cyclic sulfur compounds represented by ethylene sulfite, propylene sulfite, butylene sulfite, pentene sulfite, sulfolane, 3-sulfolene, 3-methyl sulfolane, 1,3-propane sultone, 1,4-butane sultone, 1-propene 1,3-sultone, and tetramethylene sulfoxide; These may be used alone or in combination of two or more.

[0114] The content of the electrode protection additive in the non-aqueous electrolyte solution is preferably 0.1 to 30% by volume, more preferably 0.3 to 15% by volume, even more preferably 0.4 to 8% by volume, and particularly preferably 0.5 to 4% by volume, relative to the total amount of the non-aqueous solvent.

[0115] In this embodiment, the higher the content of the electrode protection additive, the more the deterioration of the nonaqueous electrolyte solution is suppressed. However, the lower the content of the electrode protection additive, the more the high-power performance of the nonaqueous secondary battery in a low-temperature environment is improved. Therefore, by adjusting the content of the electrode protection additive within the above range, it is possible to exhibit excellent performance based on the high ionic conductivity of the electrolyte solution without impairing the basic functions of the nonaqueous secondary battery. Furthermore, by preparing a nonaqueous electrolyte solution with such a composition, it is possible to further improve the cycle performance of the nonaqueous secondary battery, the high-power performance in a low-temperature environment, and other battery characteristics.

[0116] Acetonitrile is easily electrochemically reductively decomposed, and therefore, the nonaqueous solvent containing acetonitrile preferably contains one or more cyclic aprotic polar solvents, more preferably one or more unsaturated bond-containing cyclic carbonates, as an electrode protection additive for forming a protective coating on the negative electrode.

[0117] The unsaturated bond-containing cyclic carbonate is preferably vinylene carbonate, and the content of vinylene carbonate in the nonaqueous electrolyte is preferably 0.1% by volume or more and 4% by volume or less, more preferably 0.2% by volume or more and less than 3% by volume, and even more preferably 0.5% by volume or more and less than 2.5% by volume. This makes it possible to more effectively improve low-temperature durability and provide a secondary battery with excellent low-temperature performance.

[0118] Vinylene carbonate, an additive for electrode protection, suppresses the reductive decomposition reaction of acetonitrile on the negative electrode surface. On the other hand, excessive film formation leads to a decrease in low-temperature performance. Therefore, by adjusting the amount of vinylene carbonate added within the above range, it is possible to keep the interfacial (film) resistance low and suppress cycle degradation at low temperatures.

[0119] <Acid anhydride> The nonaqueous secondary battery according to this embodiment is stabilized by the formation of an SEI on the negative electrode surface due to partial decomposition of the nonaqueous electrolyte during initial charging. To more effectively strengthen this SEI, an acid anhydride can be added. When acetonitrile is included as the nonaqueous solvent, the strength of the SEI tends to decrease with increasing temperature, but the addition of an acid anhydride promotes 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 thermal history.

[0120] Specific examples of acid anhydrides include chain acid anhydrides such as acetic anhydride, propionic anhydride, and benzoic anhydride; cyclic acid anhydrides such as malonic anhydride, succinic anhydride, glutaric anhydride, maleic anhydride, phthalic anhydride, 1,2-cyclohexanedicarboxylic anhydride, 2,3-naphthalenedicarboxylic anhydride, and naphthalene-1,4,5,8-tetracarboxylic dianhydride; and mixed acid anhydrides having a structure formed by dehydration condensation of different types of acids, such as two different types of carboxylic acids or a carboxylic acid and a sulfonic acid. These may be used alone or in combination of two or more types.

[0121] Since the nonaqueous secondary battery according to this embodiment preferably strengthens the SEI before the reductive decomposition of the nonaqueous solvent, it is preferable that the acid anhydride contains at least one cyclic acid anhydride that acts early during the first charge. These cyclic acid anhydrides may be contained alone or in combination. Alternatively, a cyclic acid anhydride other than these cyclic acid anhydrides may be contained. Furthermore, the cyclic acid anhydride preferably contains at least one of succinic anhydride, maleic anhydride, and phthalic anhydride.

[0122] A nonaqueous electrolyte solution containing at least one of succinic anhydride, maleic anhydride, and phthalic anhydride can form a strong SEI on the negative electrode and more effectively suppress an increase in resistance during high-temperature heating. It is particularly preferable to include succinic anhydride. This allows for more effective formation of a strong SEI on the negative electrode while suppressing side reactions.

[0123] When the non-aqueous electrolytic solution according to the present embodiment contains an acid anhydride, the content thereof 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 even more preferably 0.1 parts by mass or more and 0.5 parts by mass or less, per 100 parts by mass of the non-aqueous electrolytic solution.

[0124] The acid anhydride is preferably contained in the non-aqueous electrolyte solution. On the other hand, as long as the acid anhydride can function in a non-aqueous secondary battery, at least one battery component selected from the group consisting of a positive electrode, a negative electrode, and a separator may contain the acid anhydride. The acid anhydride may be contained in the battery component during production of the battery component, or may be impregnated into the battery component by post-treatment such as coating, immersion, or spray drying.

[0125] Optional Additives In this embodiment, for the purpose of improving the charge / discharge cycle characteristics, high-temperature storage properties, and safety (for example, prevention of overcharging) of the nonaqueous secondary battery, optional additives (additives other than acid anhydrides and electrode protection additives) may be appropriately contained in the nonaqueous electrolyte solution.

[0126] Examples of optional additives include sulfonic acid esters, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, tert-butylbenzene, nitrogen-containing cyclic compounds with no steric hindrance around the unshared electron pair (pyridine, 1-methyl-1H-benzotriazole, 1-methylpyrazole, etc.), etc. In particular, phosphate esters have the effect of suppressing side reactions during storage and are effective as optional additives.

[0127] When the non-aqueous electrolyte solution according to this embodiment contains other optional additives, the content thereof is preferably in the range of 0.01% by mass to 10% by mass, more preferably 0.02% by mass to 5% by mass, and even more preferably 0.05 to 3% by mass, relative to the total amount of the non-aqueous electrolyte solution. By adjusting the content of the other optional additives within the above ranges, it tends to be possible to impart even better battery characteristics without impairing the basic functions of a non-aqueous secondary battery.

[0128] <separator> A separator is a member that is disposed between a plurality of electrodes in an electricity storage device and has ion permeability and, if necessary, a shutdown property.

[0129] Because separators require insulation and ion permeability, they are generally formed from insulating materials with a porous structure, such as paper, polyolefin nonwoven fabric, or resin microporous membrane. In particular, when a separator is used in a nonaqueous electrolyte secondary battery comprising a positive electrode and a negative electrode capable of absorbing and releasing lithium and a nonaqueous electrolyte solution prepared by dissolving an electrolyte in a nonaqueous solvent, a polyolefin microporous membrane is an excellent separator substrate, because it can provide resistance to oxidation-reduction degradation of the separator and a dense, uniform porous structure. Therefore, the separator according to this embodiment can include a polyolefin microporous membrane.

[0130] The separator of this embodiment is a microporous membrane containing at least one of polyethylene and polypropylene, and is provided with a porous layer containing an inorganic filler on one or both sides of the microporous membrane. In this embodiment, if a nonaqueous electrolyte solution containing acetonitrile is retained in the porous layer containing the inorganic filler in the separator, the nonaqueous electrolyte solution does not spread to the electrode side. As a result, charge and discharge are performed only in the electrode part where the electrolyte solution has penetrated, which is thought to be the cause of a decrease in initial efficiency.

[0131] In this embodiment, examples of polyolefin resins used as the substrate material include homopolymers such as polyethylene and polypropylene, copolymers of multiple monomers constituting each homopolymer, and mixtures of these polymers. Examples of polyethylene include low-, medium-, and high-density polyethylenes, with high-density polyethylene being preferred from the standpoint of puncture resistance or mechanical strength. Two or more of these polyethylenes may be mixed to provide flexibility. The polymerization catalyst used in producing these polyethylenes is also not particularly limited, and examples include Ziegler-Natta catalysts, Phillips catalysts, and metallocene catalysts. To achieve both high mechanical strength and high permeability, the viscosity-average molecular weight of the polyethylene is preferably 100,000 to 12,000,000, and more preferably 200,000 to 3,000,000.

[0132] The microporous membrane according to this embodiment may be a microporous laminate membrane, if desired. A microporous laminate membrane refers to a multilayer membrane in which multiple polyolefin-based microporous layers are laminated, or a composite microporous membrane in which a polyolefin-based microporous membrane is laminated with a microporous membrane containing another resin, and may hereinafter be simply referred to as a laminate.

[0133] Examples of polypropylene include homopolymers, random copolymers, and block copolymers, and these can be used alone or in combination. The polymerization catalyst for polypropylene is also not particularly limited, and examples include Ziegler-Natta catalysts and metallocene catalysts. The stereoregularity of polypropylene is also not particularly limited, and it may be isotactic, syndiotactic, or atactic. However, from the perspective of cost, isotactic polypropylene is preferably used. Furthermore, to the extent that the effects of the present invention are not impaired, the microporous membrane used as the separator substrate may contain appropriate amounts of polyolefins other than polyethylene and polypropylene, as well as additives such as antioxidants and nucleating agents.

[0134] The method for producing the substrate containing a polyolefin resin as a main component may be a known method, for example, a dry production method or a wet production method.

[0135] In a dry production method, for example, a polyolefin resin such as polypropylene or polyethylene is first melt-extruded to form a film, which is then annealed at a low temperature to grow crystalline domains, and stretched in this state to elongate the amorphous regions to form a microporous membrane as a substrate.

[0136] In a wet production method, for example, a hydrocarbon solvent or other low-molecular-weight material is first mixed with a polyolefin resin such as polypropylene or polyethylene, and then formed into a film. Next, the solvent and low-molecular-weight material are collected in the amorphous phase to form island phases, and the solvent and low-molecular-weight material are then removed using another easily volatile solvent to form a microporous membrane as a substrate.

[0137] A porous layer containing an inorganic filler is disposed on at least one surface of the substrate used in this embodiment for the purpose of controlling strength, hardness, and thermal shrinkage. The porous layer may further contain an organic filler or a fibrous compound.

[0138] The inorganic filler is not particularly limited, but is preferably one that has high heat resistance and electrical insulation properties and is electrochemically stable within the range of use of lithium-ion secondary batteries. Examples of inorganic fillers include aluminum compounds, magnesium compounds, and other compounds. Examples of aluminum compounds include aluminum oxide, aluminum silicate, aluminum hydroxide, aluminum oxide hydroxide, sodium aluminate, aluminum sulfate, aluminum phosphate, and hydrotalcite. Examples of magnesium compounds include magnesium sulfate and magnesium hydroxide. Examples of other compounds include oxide ceramics, nitride ceramics, clay minerals, silicon carbide, calcium carbonate, barium titanate, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, silica sand, and glass fiber. Examples of oxide ceramics include silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide. Examples of nitride ceramics include silicon nitride, titanium nitride, and boron nitride. Examples of clay minerals include talc, montmorillonite, sericite, mica, amesite, bentonite, etc. These may be used alone or in combination.

[0139] Among the above, from the viewpoint of electrochemical stability and heat resistance, at least one selected from the group consisting of aluminum oxide, aluminum oxide hydroxide, and aluminum silicate is preferred. Specific examples of aluminum oxide include alumina. Specific examples of aluminum oxide hydroxide include boehmite. Specific examples of aluminum silicate include kaolinite, dickite, nacrite, halloysite, and pyrophyllite.

[0140] The substrate used in this embodiment may have a multilayer structure in which the above-mentioned substrates are laminated together for the purpose of increasing tear strength and puncture strength. Specific examples include a laminate of a polyethylene microporous membrane and a polypropylene microporous membrane, and a laminate of a nonwoven fabric and a polyolefin microporous membrane.

[0141] From the viewpoint of improving the performance and mechanical strength of the electricity storage device, the porosity of the substrate or separator is preferably 20% or more as a lower limit, more preferably 35% or more, and preferably 90% or less as an upper limit, more preferably 80% or less. A porosity of 20% or more is preferred from the viewpoint of ensuring even better separator permeability. On the other hand, a porosity of 90% or less is preferred from the viewpoint of ensuring even better pin puncture strength.

[0142] From the same viewpoint, the air permeability (hereinafter also referred to as "air permeability resistance") of the substrate or separator is not particularly limited, but from the viewpoint of improving the performance of the non-aqueous secondary battery, the lower limit is preferably 20 sec / 100 cm 3 More than 50sec / 100cm, preferably 3 The upper limit is preferably 500 sec / 100 cm 3 Less than 300sec / 100cm, preferably less than 300sec / 100cm 3 The air permeability is 10sec / 100cm 3 On the other hand, it is preferable to set the air permeability to 1000 sec / 100 cm or more from the viewpoint of further suppressing self-discharge of the non-aqueous secondary battery. 3 The following is preferable from the viewpoint of obtaining even better charge / discharge characteristics. The air permeability and porosity are measured in accordance with the method described in the examples.

[0143] Furthermore, from the viewpoint of improving the reliability of the separator and suppressing thermal shrinkage, the pin puncture strength of the substrate is preferably 200 g / 20 μm or more as a lower limit, more preferably 300 g / 20 μm or more, and preferably 2000 g / 20 μm or less as an upper limit, more preferably 1000 g / 20 μm or less. A pin puncture strength of 200 g / 20 μm or more is preferable from the viewpoint of further suppressing film rupture due to active material that falls off during battery winding, and is also preferable from the viewpoint of further suppressing the risk of short circuit due to expansion and contraction of the electrodes during charge and discharge. On the other hand, a pin puncture strength of 2000 g / 20 μm or less is preferable from the viewpoint of further reducing width shrinkage due to orientation relaxation during heating.

[0144] The separator comprises a microporous membrane and / or a microporous laminate membrane, and may further comprise any functional layer, if desired.

[0145] <Battery exterior> The battery exterior of the nonaqueous secondary battery of this embodiment may have a known structure, for example, a battery can or a laminate film exterior.

[0146] The battery can may be a metal can made of, for example, steel, stainless steel, aluminum, or a clad material.

[0147] The laminate film exterior can be used as an exterior by stacking two sheets with the heat-melt resin side facing inward, or by folding the laminate film exterior so that the heat-melt resin side faces inward and sealing the edges with heat sealing. When using a laminate film exterior, a positive electrode lead (or a positive electrode terminal and a lead tab connected to the positive electrode terminal) may be connected to the positive electrode current collector, and a negative electrode lead (or a negative electrode terminal and a lead tab connected to the negative electrode terminal) may be connected to the negative electrode current collector. In this case, the laminate film exterior may be sealed with the ends of the positive electrode lead and the negative electrode lead (or the lead tabs connected to the positive electrode terminal and the negative electrode terminal, respectively) extended outside the exterior.

[0148] As the laminate film exterior body, for example, a laminate film having a three-layer structure of heat-melting resin / metal film / resin can be used.

[0149] The aluminum laminate film constituting the battery exterior is preferably an aluminum foil coated on both sides with a polyolefin resin.

[0150] <Shape of non-aqueous secondary battery> The shape of the nonaqueous secondary battery according to this embodiment can be, for example, a square, rectangular tube, cylindrical, elliptical, button, coin, flat, laminate, or the like.

[0151] The nonaqueous secondary battery according to this embodiment can be particularly preferably applied to a prismatic, rectangular tube, and laminate type battery.

[0152] <Method of manufacturing non-aqueous secondary battery> The nonaqueous secondary battery of this embodiment can be manufactured using the above-mentioned nonaqueous electrolyte, a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, a separator, and, if necessary, a battery exterior.

[0153] First, a laminate consisting of a positive electrode, a negative electrode, and a separator can be formed. For example, possible methods include a method of preparing a laminate of long positive electrodes and negative electrodes with a long separator interposed between them, and then winding the laminate to form a wound laminate; a method of cutting the positive electrodes and negative electrodes into multiple sheets having a certain area and shape, and alternately stacking the resulting positive electrode sheets and negative electrode sheets with a separator sheet interposed therebetween to form a laminate with a layered structure; or a method of folding a long separator zigzag, and alternately inserting positive electrode sheets and negative electrode sheets between the zigzag folded separators to form a laminate with a layered structure.

[0154] Next, the above-mentioned laminate is housed in a battery exterior (battery case), an electrolyte solution is poured into the battery case, and the laminate is immersed in the electrolyte solution and sealed, thereby producing a nonaqueous secondary battery of this embodiment. Alternatively, a gel-state electrolyte membrane may be produced in advance by impregnating a substrate made of a polymer material with the electrolyte solution, and a laminate having a laminate structure may be formed using sheet-like positive electrodes, negative electrodes, and electrolyte membranes, as well as a separator, and then housed in the battery exterior to produce a nonaqueous secondary battery.

[0155] If the electrodes are arranged so that there is a portion where the outer peripheral edge of the negative electrode active material layer overlaps with that of the positive electrode active material layer, or there is a portion where the width is too small in the non-facing portion of the negative electrode active material layer, misalignment of the electrodes may occur during battery assembly, which may result in a deterioration in the charge-discharge cycle characteristics of the non-aqueous secondary battery. Therefore, it is preferable to fix the positions of the electrodes of the electrode body used in the non-aqueous secondary battery in advance using tapes such as polyimide tape, polyphenylene sulfide tape, and polypropylene (PP) tape, adhesives, etc.

[0156] In this embodiment, when a nonaqueous electrolyte containing acetonitrile is used, its high ionic conductivity may cause lithium ions released from the positive electrode during the initial charge of the nonaqueous secondary battery to diffuse throughout the negative electrode. In nonaqueous secondary batteries, the area of ​​the negative electrode active material layer is generally larger than that of the positive electrode active material layer. However, if lithium ions diffuse and are absorbed in a portion of the negative electrode active material layer that does not face the positive electrode active material layer, these lithium ions will not be released during the initial discharge and will remain in the negative electrode. Therefore, the contribution of these unreleased lithium ions will be the irreversible capacity. For these reasons, nonaqueous secondary batteries using a nonaqueous electrolyte containing acetonitrile may have low initial charge / discharge efficiency.

[0157] On the other hand, if the area of ​​the positive electrode active material layer is larger than that of the negative electrode active material layer or if the two are the same, current tends to concentrate at the edge portions of the negative electrode active material layer during charging, making it easier for lithium dendrites to form.

[0158] Although there are no particular limitations 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, 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, even 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 nonaqueous secondary battery using a nonaqueous electrolyte solution containing acetonitrile, the initial 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.

[0159] 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 limiting the area of ​​the portion of the negative electrode active material layer that does not face the positive electrode active material layer. This makes it possible to minimize the amount of lithium ions released from the positive electrode during the initial charge that are absorbed 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 are not released from the negative electrode during the initial discharge and result in irreversible capacity). 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, it is possible to improve the load characteristics of the battery by using acetonitrile, increase the initial charge / discharge efficiency of the battery, and further suppress the formation of lithium dendrites.

[0160] The nonaqueous secondary battery of this embodiment can function as a battery after initial charging, but is stabilized by partial decomposition of the electrolyte during initial charging. While there are no particular limitations on the initial charging method, the initial charging 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. Performing the initial charging via a constant voltage charge during the initial charging also produces favorable results. By setting the voltage range in which the lithium salt participates in the electrochemical reaction to a long range, a stable and strong SEI is uniformly formed on the electrode surface, suppressing an increase in internal resistance. Furthermore, the reaction product is not firmly fixed only to the negative electrode, and in some way, it also has a favorable effect on components other than the negative electrode, such as the positive electrode and separator. Therefore, it is very effective to perform the initial charging while taking into account the electrochemical reaction of the lithium salt dissolved in the nonaqueous electrolyte.

[0161] The nonaqueous secondary battery of this embodiment can also be used as a battery pack in which a plurality of nonaqueous 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 2.5 to 5 V, and particularly preferably 2.75 V to 5 V.

[0162] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and can be modified in various ways without departing from the spirit and scope of the present invention. [Example]

[0163] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, experiments and measurements in the examples were carried out at room temperature.

[0164] (1) Preparation of non-aqueous electrolyte Various non-aqueous solvents were mixed in an inert atmosphere to achieve the predetermined concentrations shown in Table 1. A surfactant was added to the resulting non-aqueous solvent in the proportions shown in Table 1. Furthermore, various lithium salts were added to achieve the predetermined concentrations, thereby preparing non-aqueous electrolyte solutions (S01) to (S10). The compositions of these non-aqueous electrolyte solutions are shown in Table 1.

[0165] The abbreviations for the non-aqueous solvent, lithium salt, and surfactant in Table 1 have the following meanings. Furthermore, the mass % of the surfactant in Table 1 indicates the mass parts relative to 100 mass parts of the non-aqueous electrolyte solution. The mass % can be converted to volume % using the following formula 1: (Formula 1) Mass of surfactant divided by specific gravity / (100 + mass of surfactant divided by specific gravity) x 100

[0166] (lithium salts) LiPF6: Lithium hexafluorophosphate LiFSI: Lithium bis(fluorosulfonyl)imide (LiN(SO2F)2) (non-aqueous solvent) AcN: acetonitrile EMC: Ethyl methyl carbonate EC: Ethylene carbonate VC: vinylene carbonate ES: Ethylene sulfite (surfactant) L0013: Ethyl laurate P0265: Triamyl phosphate P0270: Triethyl phosphate P0683: Tris(2-butoxyethyl) phosphate P1022: Tris(2-ethylhexyl) phosphate

[0167] [Table 1]

[0168] (2) Fabrication of small non-aqueous secondary batteries

[0169] (2-1) Preparation of the positive electrode

[0170] (2-1-1) Preparation of the positive electrode (P1) (A) Lithium iron phosphate (LiFePO4) having an olivine structure as the positive electrode active material, (B) carbon black powder (Super-P) as the conductive additive, and (C) polyvinylidene fluoride (PVDF) as the binder were mixed in a mass ratio of 89:3:8 to obtain a positive electrode mixture.

[0171] N-methyl-2-pyrrolidone was added as a solvent to the resulting positive electrode mixture to a solids content of 68% by mass, and the mixture was further mixed to prepare a positive electrode mixture-containing slurry. The positive electrode mixture-containing slurry was applied to one side of a 15 μm-thick, 280 mm-wide aluminum foil serving as a positive electrode current collector, adjusting the basis weight of the slurry, using a three-roll transfer coater to create a coating pattern with a coating width of 240-250 mm, a coating length of 125 mm, and an uncoated length of 20 mm. The solvent was then dried and removed in a hot air drying oven. The resulting electrode roll was trimmed on both sides and dried under reduced pressure at 130°C for 8 hours. The density of the positive electrode active material layer was then adjusted to 1.8 g / cm using a roll press. 3 The positive electrode (P1) was obtained by rolling the positive electrode active material layer and the positive electrode current collector so that the weight per unit area excluding the positive electrode current collector was 11.0 mg / cm. 2 It was.

[0172] (2-1-2) Preparation of the positive electrode (P2) (A) A composite oxide of lithium, nickel, manganese, and cobalt (LiNi 0.8 Mn 0.1 Co 0.1 O2), (B) carbon black powder (Super-P) as a conductive additive, and (C) polyvinylidene fluoride (PVDF) as a binder were mixed in a mass ratio of 94:3:3 to obtain a positive electrode mixture.

[0173] N-methyl-2-pyrrolidone was added as a solvent to the resulting positive electrode mixture to a solids content of 68% by mass, and the mixture was further mixed to prepare a positive electrode mixture-containing slurry. The positive electrode mixture-containing slurry was applied to one side of a 15 μm-thick, 280 mm-wide aluminum foil serving as a positive electrode current collector, adjusting the basis weight of the slurry, using a three-roll transfer coater to create a coating pattern with a coating width of 240-250 mm, a coating length of 125 mm, and an uncoated length of 20 mm. The solvent was then dried and removed in a hot air drying oven. The resulting electrode roll was trimmed on both sides and dried under reduced pressure at 130°C for 8 hours. The density of the positive electrode active material layer was then adjusted to 2.9 g / cm using a roll press. 3 The positive electrode (P2) was obtained by rolling the positive electrode active material layer and the positive electrode current collector so that the weight per unit area excluding the positive electrode current collector was 16.6 mg / cm. 2 It was.

[0174] (2-1-3) Preparation of positive electrode (P3) (A) A composite oxide of lithium, nickel, manganese, and cobalt (LiNi 0.8 Mn 0.1 Co 0.1 O2), (B) carbon black powder (Super-P) as a conductive additive, and (C) polyvinylidene fluoride (PVDF) as a binder were mixed in a mass ratio of 94:3:3 to obtain a positive electrode mixture.

[0175] N-methyl-2-pyrrolidone was added as a solvent to the resulting positive electrode mixture to a solids content of 68% by mass, and the mixture was further mixed to prepare a positive electrode mixture-containing slurry. The positive electrode mixture-containing slurry was applied to one side of a 15 μm-thick, 280 mm-wide aluminum foil serving as a positive electrode current collector, adjusting the basis weight of the slurry, using a three-roll transfer coater to create a coating pattern with a coating width of 240-250 mm, a coating length of 125 mm, and an uncoated length of 20 mm. The solvent was then dried and removed in a hot air drying oven. The resulting electrode roll was trimmed on both sides and dried under reduced pressure at 130°C for 8 hours. The density of the positive electrode active material layer was then adjusted to 2.7 g / cm using a roll press. 3The positive electrode (P3) was obtained by rolling the positive electrode active material layer and the positive electrode current collector so that the weight per unit area excluding the positive electrode current collector was 11.4 mg / cm. 2 It was.

[0176] (2-2) Preparation of negative electrode

[0177] (2-2-1) Preparation of negative electrode (N1) (a) Graphite powder as the negative electrode active material, (b) carbon black powder (Super-P) as a conductive additive, and (c) polyvinylidene fluoride (PVDF) as a binder were mixed in a solid mass ratio of 90:3:7 to obtain a negative electrode mixture. Water was added as a solvent to the resulting negative electrode mixture to a solids content of 45% by mass, and the mixture was further mixed to prepare a negative electrode mixture-containing slurry. The negative electrode mixture-containing slurry was applied to one side of a copper foil with a thickness of 8 μm and a width of 280 mm, which served as a negative electrode current collector, while adjusting the basis weight, using a three-roll transfer coater to obtain a coating pattern with a coating width of 240 to 250 mm, a coating length of 125 mm, and an uncoated length of 20 mm. The solvent was then dried and removed in a hot air drying oven. The resulting electrode roll was trimmed on both sides and dried under reduced pressure at 80°C for 12 hours. The density of the negative electrode active material layer was then adjusted to 1.3 g / cm using a roll press. 3 The negative electrode (N1) was obtained by rolling the negative electrode active material layer and the negative electrode current collector so that the coating weight excluding the negative electrode current collector was 5.4 mg / cm. 2 It was.

[0178] (2-2-2) Preparation of negative electrode (N2) (a) Graphite powder as the negative electrode active material, (b) carbon black powder (Super-P) as the conductive additive, and (c) polyvinylidene fluoride (PVDF) as the binder were mixed in a mass ratio of 90.0:3.0:7.0 to obtain a negative electrode mixture. Water was added as a solvent to the resulting negative electrode mixture to a solids content of 45% by mass, and the mixture was further mixed to prepare a negative electrode mixture-containing slurry. The negative electrode mixture-containing slurry was applied to one side of a copper foil with a thickness of 8 μm and a width of 280 mm, which served as a negative electrode current collector, while adjusting the basis weight, using a three-roll transfer coater to obtain a coating pattern with a coating width of 240 to 250 mm, a coating length of 125 mm, and an uncoated length of 20 mm. The solvent was then dried and removed in a hot air drying oven. The resulting electrode roll was trimmed on both sides and dried under reduced pressure at 80°C for 12 hours. The density of the negative electrode active material layer was then adjusted to 1.4 g / cm using a roll press. 3 The negative electrode (N2) was obtained by rolling the negative electrode active material layer and the negative electrode current collector so that the weight per unit area excluding the negative electrode current collector was 11.9 mg / cm. 2 It was.

[0179] (2-3) Preparation of separator

[0180] (2-3-1) Preparation of separator (F1)

[0181] [Preparation of microporous membrane (single layer)] A mixed resin raw material consisting of polyethylene with a viscosity average molecular weight of 770,000 and polypropylene with a viscosity average molecular weight of 850,000 in a weight ratio of 95:5 was fed into a twin-screw extruder equipped with a manifold (T-die) with a die lip spacing of 1800 μm and melt-mixed. During melt-mixing, liquid paraffin (kinematic viscosity at 37.88 °C: 7.59 × 10 -5 m 2 The mixture (100g / s) was fed to a twin-screw extruder through an injection nozzle, and further kneaded to extrude a resin composition. Liquid paraffin was further injected from the middle stage of the extrusion (the middle feed port of the twin-screw extruder) so that the liquid paraffin content of the resin composition extruded from the twin-screw extruder was 68% by mass and the temperature of the resin composition was 200°C. The extruded resin composition was then extruded onto a cooling roll whose surface temperature was controlled to 68°C, and cast to obtain a sheet-like molded product.

[0182] Next, the sheet-like molded product was introduced into a simultaneous biaxial tenter stretching machine and biaxially stretched to obtain a stretched product. The stretching conditions were MD magnification of 7.0 times and TD magnification of 6.5 times (i.e., 7 x 6.5 times), and the porosity, air permeability, thickness, etc. were adjusted by appropriately adjusting the stretching temperature, heating air volume, etc. The biaxial stretching temperature was set to 124°C.

[0183] Next, the stretched product was immersed in dichloromethane to extract the liquid paraffin from the stretched product, thereby forming a porous body.

[0184] Next, the porous body was introduced into a TD tenter to be heat-set, where heat setting (HS) was performed at 127.5°C, and the porous body was stretched to a TD stretch ratio of 1.75 times based on the inlet, and then relaxed to 1.6 times TD to obtain a microporous membrane (single layer).

[0185] [Method of synthesizing resin binder] The acrylic latex used as the resin binder is produced by the following method. A reaction vessel equipped with a stirrer, reflux condenser, dropping tank, and thermometer was charged with 70.4 parts by mass of ion-exchanged water, 0.5 parts by mass of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as an emulsifier, and 0.5 parts by mass of "ADEKA REASOAP SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation). The temperature inside the reaction vessel was then raised to 80°C, and while maintaining the temperature at 80°C, 7.5 parts by mass of a 2% aqueous solution of ammonium persulfate was added to obtain an initial mixture. Five minutes after the addition of the ammonium persulfate aqueous solution was completed, the emulsion was added dropwise from the dropping tank to the reaction vessel over 150 minutes.

[0186] The above emulsion was prepared by mixing a mixture of: 69 parts by mass of butyl acrylate; 30 parts by mass of methyl methacrylate; 1 part by mass of methacrylic acid; 3 parts by mass of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) and 3 parts by mass of "Adeka Reasoap SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation) as emulsifiers; 7.5 parts by mass of a 2% aqueous solution of ammonium persulfate; and 52 parts by mass of ion-exchanged water using a homomixer for 5 minutes.

[0187] After the emulsion was added dropwise, the temperature inside the reaction vessel was maintained at 76°C for 90 minutes, and then cooled to room temperature. The resulting emulsion was adjusted to pH 8.0 with a 25% aqueous ammonium hydroxide solution, and a small amount of water was added to obtain an acrylic latex with a solids content of 40%. The resulting acrylic latex had a number average particle size of 145 nm and a glass transition temperature of -33°C.

[0188] [Inorganic coating layer paint preparation method and coating method] A dispersion was prepared by uniformly dispersing 95 parts by mass of aluminum hydroxide oxide (average particle size 1.4 μm) as inorganic particles and 0.4 parts by mass (solid content equivalent) of an aqueous solution of ammonium polycarboxylate (SN Dispersant 5468, manufactured by San Nopco, solid content concentration 40%) as an ionic dispersant in 100 parts by mass of water. The resulting dispersion was milled in a bead mill (cell volume 200 cm). 3 The inorganic particles were crushed using zirconia beads (0.1 mm diameter, 80% loading) to adjust the particle size distribution of the inorganic particles to D50 = 1.0 μm, producing an inorganic particle-containing slurry. 2.0 parts by mass (solids equivalent) of the acrylic latex produced above as a resin binder was added to the dispersion with the adjusted particle size distribution.

[0189] Next, a microporous membrane was continuously unwound from the microporous membrane mother roll, and one side of the microporous membrane was coated with the inorganic particle-containing slurry using a gravure reverse coater. The microporous membrane was then dried in a dryer at 60°C to remove water, and taken up to obtain a separator mother roll.

[0190] At the time of evaluation, the separator unwound from the mother roll was slit as necessary and used as the separator for evaluation.

[0191] (2-3-2) Preparation of separator (F2) The separator (F1) was produced under the same conditions as those for (2-3-1) Separator (F1), except that no inorganic filler layer was formed on one surface of the separator (F1).

[0192] (2-3-3) Preparation of separator (F3)

[0193] <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 Pellets of PP (C2 / C4) with a melting point of 80°C and a molecular weight of 6.7 were dry-blended in a 50:50 (mass%) ratio of PP to C2 / C4, and then melt-mixed using a ZSK40 (Coperion, L / D = 46). To minimize resin decomposition and denaturation, the resin inlet hopper and raw material tank were completely sealed, and nitrogen was continuously flowed from the bottom of the hopper to maintain the oxygen concentration near the raw material inlet at 50 ppm or less. All vents were also completely sealed to prevent air leakage into the cylinder. This oxygen concentration reduction significantly suppressed polymer decomposition and denaturation even under high-temperature conditions, further enabling the fine dispersion of the ethylene / 1-butene copolymer. After melt-mixing, the strand was pulled from an 8-hole die and cooled in a water-cooled bath. The molten mixture was then cut into pellets using a pelletizer.

[0194] <Preparation of microporous membrane (separator with three-layer microporous membrane)> The pellets were dry-blended with ultra-high molecular weight polypropylene resin (PP, MFR = 0.25) at a mass ratio of PP:pellets = 90:10 (mass%), then melted in a 2.5-inch extruder and fed into an annular die using a gear pump. This resulted in a resin ratio of PP:C2 / C4 = 95:5 (mass%).

[0195] The die temperature was set at 240°C, and the molten polymer was cooled by blown air and then wound up on a roll. The extruded PP precursor (raw film) had a thickness of 6 µm.

[0196] High molecular weight polyethylene resin (PE, MFR=0.38) was melted in a 2.5-inch extruder and fed to an annular die using a gear pump.

[0197] The die temperature was set at 210°C, and the molten polymer was cooled by blown air and then wound up on a roll. The extruded PE precursor (raw film) had a thickness of 6 µm.

[0198] The resulting PP precursor and the resulting PE precursor were stacked together in a PP precursor / PE precursor / PP precursor triple layer configuration and laminated at 120°C to obtain a three-layer laminated raw film. This raw film was annealed at 125°C for 20 minutes. The annealed film was then 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 with a three-layer microporous membrane structure.

[0199] <Preparation of inorganic filler layer> An inorganic filler layer was formed on one surface of the three-layered microporous membrane prepared above under the same conditions as for the separator (F1).

[0200] [Thickness measurement (μm)] The thickness of the separator including the microporous membrane was measured at room temperature of 23±2°C using a Digimatic Indicator IDC112 manufactured by Mitutoyo Corporation.

[0201] [Porosity (%)] A 5 cm x 5 cm square sample was cut out from the separator including the microporous membrane, and the porosity was calculated from the volume and mass of the sample using the following formula. Porosity (%) = (Volume (cm 3 ) - mass (g) / density of resin composition (g / cm 3 )) / volume(cm 3 ) x 100

[0202] [Air resistance (sec / 100cm) 3 )] The air resistance of the separator including the microporous membrane was measured using a Gurley air permeability meter in accordance with JIS P-8117.

[0203] (2-4) Assembly of small non-aqueous secondary batteries The positive electrode (P1) obtained as described above was punched into a disk shape with a diameter of 15.958 mm, and the negative electrode (N1) obtained as described above was punched into a disk shape with a diameter of 16.156 mm. These were then used to form the separator (F1) obtained as described above (film thickness 20 μm, air permeability 172 sec / 100 cm 3 A laminate was obtained by stacking two sheets of aluminum foil on both sides of a sheet with a porosity of 43%. The laminate was inserted into a disk-shaped battery case made of SUS. Next, 100 μL of non-aqueous electrolyte (S03 to S05, S07 to S10) was poured into the battery case, and the laminate was immersed in the non-aqueous electrolyte. After that, the battery case was sealed and the non-aqueous electrolyte was allowed to fully penetrate the laminate, thereby obtaining a small non-aqueous secondary battery (P1 / F1 / N1).

[0204] Using the same procedure, P1 was used as the positive electrode, N1 as the negative electrode, and separator F2 (film thickness 16 μm, air permeability 165 s / 100 cm 3 , porosity 40%), small non-aqueous secondary battery (P1 / F2 / N1) using S03 as non-aqueous electrolyte, P1 as positive electrode, N1 as negative electrode, separator F3 (film thickness 22 μm, air permeability 237 s / 100 cm 3 The following small nonaqueous secondary batteries were obtained: a small nonaqueous secondary battery (P1 / F3 / N1) with a porosity of 45%) and S05-S06 as the nonaqueous electrolyte; a small nonaqueous secondary battery (P2 / F1 / N2) with P2 as the positive electrode, N2 as the negative electrode, separator F1, and S01-S02 as the nonaqueous electrolyte; and a small nonaqueous secondary battery (P3 / F1 / N1) with P3 as the positive electrode, N1 as the negative electrode, separator F1, and S01-S02 as the nonaqueous electrolyte.

[0205] (3) Evaluation of small non-aqueous secondary batteries The small nonaqueous secondary batteries obtained as described above were first subjected to an initial charge treatment and initial charge / discharge capacity measurement according to the procedure in (3-1) below. Next, each small nonaqueous secondary battery was evaluated according to the procedure in (3-2). Charge / discharge was performed using a charge / discharge device ACD-M01A (product name) manufactured by Asuka Electronics Co., Ltd. and a programmable thermostatic bath IN804 (product name) manufactured by Yamato Scientific Co., Ltd.

[0206] In this specification, 1 C means the current value at which a fully charged battery is expected to be discharged completely in one hour when discharged at a constant current.

[0207] Specifically, for the small nonaqueous secondary batteries (P1 / F1 / N1), (P1 / F2 / N1), and (P1 / F3 / N1), 1C refers to the current value expected to be discharged from a fully charged state of 3.5 V to 2.0 V at a constant current, with the discharge expected to be completed in one hour. For the small nonaqueous secondary batteries (P2 / F1 / N2) and (P3 / F1 / N1), 1C refers to the current value expected to be discharged from a fully charged state of 4.2 V to 3.0 V at a constant current, with the discharge expected to be completed in one hour.

[0208] The small nonaqueous secondary batteries (P1 / F1 / N1), (P1 / F2 / N1), (P1 / F3 / N1), and (P3 / F1 / N1) assembled according to the procedures in (2-4) and (3) above are 3 mAh-class cells, with a current value of 3 mA at 1 C. Similarly, the small nonaqueous secondary battery (P2 / F1 / N2) is a 6 mAh-class cell, with a current value of 6 mA at 1 C. Hereinafter, unless otherwise specified, current values ​​and voltages will be omitted for convenience. Furthermore, because the processing method remains the same even if the separators are different as long as the positive and negative electrode combinations are the same, separator notation will be omitted.

[0209] (3-1) Initial charge / discharge treatment of small non-aqueous secondary batteries The ambient temperature of the small nonaqueous secondary battery (P1 / N1) was set to 25°C, and it was charged at a constant current equivalent to 0.1C until it reached a fully charged state, after which it was charged at a constant voltage for 1.5 hours. The battery was then discharged to a predetermined voltage at a constant current equivalent to 0.1C. The initial efficiency was calculated by dividing the discharge capacity by the charge capacity. The initial charge-discharge process for the small nonaqueous secondary batteries (P2 / N2) and (P3 / N1) was carried out using the same procedure.

[0210] (3-2) AC impedance measurement of small non-aqueous secondary battery (P1 / N1) The small nonaqueous secondary battery (P1 / N1) that had been subjected to the initial charge-discharge treatment by the method described in (3-1) above was charged at a constant current of 1 C at an ambient temperature of 25°C until it reached 3.5 V, and then charged at a constant voltage of 3.5 V until the current value decayed to 0.025 C. Then, AC impedance measurements were performed.

[0211] The AC impedance measurements were performed using a Solartron Frequency Response Analyzer 1400 (trade name) and a Solartron Potentio-Galvanostat 1470E (trade name). An AC signal was applied while varying the frequency from 1000 kHz to 0.01 Hz, and the impedance was measured from the voltage-current response signal. The value where the signal intersected the horizontal axis of a complex impedance plane plot (Cole-Cole plot) was calculated as the bulk resistance. The resistance value was the real part (horizontal axis). The amplitude of the applied AC voltage was ±5 mV. The ambient temperature of the battery during AC impedance measurements was 25°C.

[0212] The bulk resistance after the initial charge is an indicator of the separator and electrode electrolyte impregnation, with higher bulk resistance indicating poorer separator and electrode electrolyte impregnation, and lower bulk resistance indicating better separator and electrode electrolyte impregnation. From this perspective, the bulk resistance is preferably less than 0.8 Ω, more preferably 0.7 Ω or less, and even more preferably 0.6 Ω or less. Furthermore, poor separator and electrode electrolyte impregnation reduces the initial efficiency, so the initial efficiency is preferably 83.5% or more, more preferably 85% or more, and even more preferably 86.5% or more.

[0213] [Examples 1 to 6, Comparative Examples 1 to 4] Here, we will explain the interpretation of the test results for the small nonaqueous secondary battery (P1 / N1). The small nonaqueous secondary battery (P1 / N1) was fabricated according to the method described in (2) above. Next, each small nonaqueous secondary battery (P1 / N1) was evaluated according to the procedures described in (3-1) and (3-2) above. The test results are shown in Table 2.

[0214] [Table 2]

[0215] As shown in Table 2, the bulk resistance after the initial charge-discharge treatment was less than 0.8Ω and the initial efficiency was 83.5% or more in Examples 1 to 6. On the other hand, the bulk resistance after the initial charge-discharge treatment was 0.8Ω or more and the initial efficiency was less than 83.5% in Comparative Examples 1 to 4.

[0216] The examples had an initial efficiency of 83.9% or more. On the other hand, the comparative examples had an initial efficiency of 83.4% or less. These results demonstrate that adding a specific surfactant to the non-aqueous electrolyte solution improves the electrolyte impregnation into the separator and electrodes, thereby improving the initial efficiency.

[0217] (3-3) 50℃ cycle test of small non-aqueous secondary battery (P1 / N1) The ambient temperature of a small nonaqueous secondary battery (P1 / N1) that had undergone an initial charge-discharge treatment according to the method described in (3-1) above was set to 50°C. First, the battery was charged at a constant current of 3 mA, equivalent to 1 C, until it reached 3.5 V. It was then charged at a constant voltage of 3.5 V until the current decayed to 0.025 C. The battery was then discharged to 2.5 V at a constant current of 3 mA. This cycle, consisting of one charge and one discharge, was counted as one cycle, and 100 charge-discharge cycles were performed. The discharge capacity at the 100th cycle, when the discharge capacity at the first cycle was taken as 100%, was taken as the capacity retention rate in the 50°C cycle test.

[0218] The capacity retention rate in a 50°C cycle test indicates the ratio of the discharge capacity at the 100th cycle to the discharge capacity at the first cycle; the higher the value, the less the battery capacity deteriorates when repeatedly charged and discharged in a high-temperature environment. The absolute value of the capacity retention rate varies depending on the combination of components in the nonaqueous secondary battery. When using a small nonaqueous secondary battery (P1 / F1 / N1), the capacity retention rate is preferably 88% or more, more preferably 89% or more, and even more preferably 90% or more. When using a small nonaqueous secondary battery (P1 / F3 / N1), the capacity retention rate is preferably 78% or more, more preferably 80% or more, and even more preferably 82% or more.

[0219] [Examples 7 to 12, Comparative Examples 5 to 6] Here, we will explain the interpretation of the test results for the small nonaqueous secondary battery (P1 / N1). The small nonaqueous secondary battery (P1 / N1) was fabricated according to the method described in (2) above. Next, each small nonaqueous secondary battery (P1 / N1) was evaluated according to the procedures described in (3-1) and (3-3) above. The test results are shown in Table 3.

[0220] [Table 3]

[0221] As shown in Table 3, Examples 7 to 11, which used a small nonaqueous secondary battery (P1 / F1 / N1), had a capacity retention rate of 88% or more. On the other hand, Comparative Example 5 had a capacity retention rate of 86%. Example 12, which used a small nonaqueous secondary battery (P1 / F3 / N1), had a capacity retention rate of 82% or more. On the other hand, Comparative Example 6 had a capacity retention rate of 76.7%. From these results, it was confirmed that the Examples showed little decrease in capacity retention rate when cycled in a 50°C environment, and that cycle performance in a high-temperature environment was improved.

[0222] (3-4) AC impedance measurement of small non-aqueous secondary battery (P2 / N2) The small nonaqueous secondary battery (P2 / N2) that had been subjected to the initial charge-discharge treatment by the method described in (3-1) above was charged at a constant current of 1 C at an ambient temperature of 25°C until it reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current value decayed to 0.025 C. Then, AC impedance measurements were performed.

[0223] The AC impedance measurements were performed using a Solartron Frequency Response Analyzer 1400 (trade name) and a Solartron Potentio-Galvanostat 1470E (trade name). An AC signal was applied while varying the frequency from 1000 kHz to 0.01 Hz, and the impedance was measured from the voltage-current response signal. The value where the signal intersected the horizontal axis of a complex impedance plane plot (Cole-Cole plot) was calculated as the bulk resistance. The resistance value was the real part (horizontal axis). The amplitude of the applied AC voltage was ±5 mV. The ambient temperature of the battery during AC impedance measurements was 25°C.

[0224] The bulk resistance after the initial charge is an indicator of the impregnation of the separator and electrodes with electrolyte, and a battery with a higher bulk resistance indicates poorer impregnation of the separator and electrodes with electrolyte, while a battery with a lower bulk resistance indicates better impregnation of the separator and electrodes with electrolyte. From this perspective, the bulk resistance is preferably less than 1.3 Ω, more preferably 1.2 Ω or less, and even more preferably 1.0 Ω or less.

[0225] [Example 13, Comparative Example 7] Here, we will explain the interpretation of the test results for the small nonaqueous secondary battery (P2 / N2). The small nonaqueous secondary battery (P2 / N2) was fabricated according to the method described in (2) above. Next, each small nonaqueous secondary battery (P2 / N2) was evaluated according to the procedures described in (3-1) and (3-4) above. The test results are shown in Table 4.

[0226] [Table 4]

[0227] As shown in Table 3, Example 13 exhibited a bulk resistance of 1.0 Ω after the initial charge-discharge treatment, while Comparative Example 7 exhibited a resistance of 1.3 Ω. These results demonstrate that the addition of tris(2-ethylhexyl) phosphate to the nonaqueous electrolyte improves the impregnation of the separator and electrodes with the electrolyte.

[0228] (3-5) Output test of small non-aqueous secondary batteries The small nonaqueous secondary battery (P3 / N1) that had been subjected to the initial charge-discharge treatment by the method described in (3-1) above was charged at a constant current of 1 C at an ambient temperature of 25°C until it reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current value decayed to 0.025 C. It was then discharged at 0.1 C to 2.7 V.

[0229] Next, the battery was charged at a constant current of 1 C until it reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current value decayed to 0.025 C. It was then discharged at 0.5 C to 2.7 V. Next, the battery was charged at a constant current of 1 C until it reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current value decayed to 0.025 C. It was then discharged at 1 C to 2.7 V. Next, the battery was charged at a constant current of 1 C until it reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current value decayed to 0.025 C. It was then discharged at 5 C to 2.7 V. Next, the battery was charged at a constant current of 1 C until it reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current value decayed to 0.025 C. It was then discharged at 10 C to 2.7 V. Next, the battery was charged at a constant current of 1 C until it reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current value decayed to 0.025 C. It was then discharged at 20 C to 2.7 V. The 20 C discharge capacity was calculated as the 20 C capacity retention rate, assuming the 0.1 C discharge capacity in the first cycle as 100%.

[0230] The 20C capacity retention rate is an index of output performance at 25°C, and is preferably 15% or more, more preferably 20% or more, and even more preferably 25% or more.

[0231] [Example 14, Comparative Example 8] Here, we will explain the interpretation of the test results for the small nonaqueous secondary battery (P3 / N1). The small nonaqueous secondary battery (P3 / N1) was fabricated according to the method described in (2) above. Next, each small nonaqueous secondary battery (P3 / N1) was evaluated according to the procedures described in (3-1) and (3-5) above. The test results are shown in Table 5.

[0232] [Table 5]

[0233] As shown in Table 5, Example 14 exhibited a 20C capacity retention rate of 25% or more. On the other hand, Comparative Example 8 exhibited an initial efficiency of less than 75%, which did not satisfy the predetermined battery capacity and made it difficult to obtain accurate evaluation results, so subsequent output tests could not be carried out.

[0234] As shown by these results, it has become clear that by using a nonaqueous electrolyte solution within the range of the constituent requirements of the present invention, impregnation into the separator and electrodes is good, so that a nonaqueous secondary battery can be provided which does not decrease the initial efficiency, has small bulk resistance, and ultimately has high output performance. [Industrial Applicability]

[0235] The nonaqueous secondary battery using the nonaqueous solvent of the present invention is expected to be used, for example, as a rechargeable battery for portable devices such as mobile phones, portable audio devices, personal computers, and IC (Integrated Circuit) tags; a rechargeable battery for automobiles such as hybrid vehicles, plug-in hybrid vehicles, and electric vehicles; a low-voltage power supply such as a 12V-class power supply, a 24V-class power supply, or a 48V-class power supply; a residential power storage system; an IoT device; etc. Furthermore, the nonaqueous secondary battery using the nonaqueous solvent of the present invention can also be used in cold regions and outdoors in summer. [Explanation of symbols]

[0236] 100 Nonaqueous secondary battery 110 Battery casing 120 Battery enclosure space 130 Positive electrode lead body 140 Negative electrode lead body 150 positive electrode 160 negative electrode 170 Separator

Claims

1. A non-aqueous secondary battery comprising a positive electrode containing one or more positive electrode active materials capable of absorbing and releasing lithium ions, a negative electrode containing a material capable of absorbing and releasing lithium ions, a non-aqueous electrolyte solution, and a separator, the non-aqueous electrolyte solution contains a non-aqueous solvent other than γ-butyrolactone, a lithium salt, and a surfactant; 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 the content of the lithium salt relative to the nonaqueous electrolyte solution is 1 mol / L or more and 2 mol / L or less; The surfactant includes a nonionic surfactant and does not include a hydroxy group as a substituent; the nonionic surfactant contains at least one compound selected from a fatty acid ester compound excluding a fluorinated alkyl ester, a phosphate ester compound, an ether compound excluding polyethylene glycol dimethyl ether, an ester ether compound, and an alkanolamide compound; The separator is a microporous film containing at least one of polyethylene and polypropylene, and is provided with a porous layer containing an inorganic filler on one or both sides of the microporous film. A non-aqueous secondary battery characterized by:

2. 2. The non-aqueous secondary battery according to claim 1, wherein the nonionic surfactant is the fatty acid ester compound or the phosphoric acid ester compound.

3. the fatty acid ester is ethyl laurate, or 3. The nonaqueous secondary battery according to claim 1, wherein the phosphate ester compound is triamyl phosphate, triethyl phosphate, tris(2-butoxyethyl) phosphate, or tris(2-ethylhexyl) phosphate.

4. The non-aqueous secondary battery of claim 1, wherein the nonionic surfactant is at least one selected from the group consisting of ethyl laurate, triethyl phosphate, and tris(2-butoxyethyl) phosphate.

5. A non-aqueous secondary battery comprising a positive electrode containing one or more positive electrode active materials capable of absorbing and releasing lithium ions, a negative electrode containing a material capable of absorbing and releasing lithium ions, a non-aqueous electrolyte solution, and a separator, the non-aqueous electrolyte solution contains a non-aqueous solvent, a lithium salt, and a surfactant; 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 the content of the lithium salt relative to the nonaqueous electrolyte solution is 1 mol / L or more and 2 mol / L or less; The surfactant includes a nonionic surfactant and does not include a hydroxy group as a substituent; the nonionic surfactant is at least one selected from the group consisting of ethyl laurate, triethyl phosphate, and tris(2-butoxyethyl) phosphate; The separator is a microporous film containing at least one of polyethylene and polypropylene, and is provided with a porous layer containing an inorganic filler on one or both sides of the microporous film. A non-aqueous secondary battery characterized by:

6. 6. The non-aqueous secondary battery according to claim 1, wherein the nonionic surfactant is contained in an amount of 0.1 mass % or more and 3 mass % or less with respect to the total amount of the non-aqueous electrolyte solution.

7. 7. The nonaqueous secondary battery according to claim 1, wherein the inorganic filler is at least one selected from the group consisting of aluminum oxide, aluminum oxide hydroxide, and aluminum silicate.

8. The separator has a porosity of 20% or more and 90% or less and an air permeability of 20 seconds / 100 cm ３ More than 500 seconds / 100cm ３ The nonaqueous secondary battery according to any one of claims 1 to 7, wherein:

9. The lithium salt is LiPF ６ and further comprising LiPF ６ <The lithium-containing imide salt and LiPF at a molar concentration that forms the lithium-containing imide salt. ６ The non-aqueous secondary battery according to any one of claims 1 to 8, comprising:

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