Non-aqueous electrolyte secondary battery

Abstract

The non-aqueous electrolyte secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolytic solution. The electrolytic solution contains the organic sulfate shown by formula (1): (R-O-SO3) n X1, where R is an organic group having 1 or more carbon atoms, X1 is a cation, n is an integer of 1 to 3. The electrolytic solution further contains ethylene carbonate and fluoroethylene carbonate, and the volume Vec of the ethylene carbonate and the volume Vfec of the fluoroethylene carbonate satisfy: 0.1 ≤ Vec / Vfec ≤ 15.

Description

Technical Field

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

[0002] Non-aqueous electrolyte secondary batteries, particularly lithium-ion secondary batteries, are expected as power sources for small consumer applications, power storage devices, and electric vehicles because of their high output and high energy density. On the other hand, with the rapid spread of non-aqueous electrolyte secondary batteries, the importance of fast charging performance has been increasing.

[0003] In Patent Document 1, as a positive electrode active material particularly suitable for a lithium-ion secondary battery for vehicle drive that can reduce the internal resistance of a battery, pursue high-rate charge and discharge, and high output, the following positive electrode active material is proposed, which includes: a matrix portion composed of a compound capable of storing and releasing charge carriers, a dielectric disposed on at least a part of the surface of the matrix portion, and a carbonate compound disposed on at least a part of the surface of the matrix portion.

[0004] Prior Art Documents

[0005] Patent Document

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2020-123500 Summary of the Invention

[0007] When the positive electrode resistance is reduced, since the positive electrode active material is charged deeper during charging, the positive electrode potential tends to rise. Therefore, during the charge-discharge cycle, the oxidative decomposition of the electrolyte is promoted, the positive electrode resistance increases, and the durability (capacity retention rate) decreases.

[0008] In view of the above, one aspect of the present invention relates to a non-aqueous electrolyte secondary battery including: a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte.

[0009] The electrolyte includes the organic sulfate represented by the formula (1): (R-O-SO3) n shown by X1,

[0010] wherein, R is an organic group having 1 or more carbon atoms, X1 is a cation, n is an integer of 1 to 3, the electrolyte further includes ethylene carbonate and fluoroethylene carbonate, and the volume Vec of the ethylene carbonate and the volume Vfec of the fluoroethylene carbonate satisfy: 0.1 ≤ Vec / Vfec ≤ 15.

[0011] According to the present invention, it is possible to reduce the positive electrode resistance and improve the durability of the non-aqueous electrolyte secondary battery. Brief Description of the Drawings

[0012] Figure 1 Schematic perspective view of a cross-section of a secondary battery according to an embodiment of the present invention. Detailed Embodiment

[0013] The non-aqueous electrolyte secondary battery according to an embodiment of the present invention includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. The positive electrode contains a positive electrode active material. The positive electrode active material is, for example, a lithium-containing composite oxide and contains a transition metal.

[0014] The electrolyte contains formula (1): (R-O-SO3) n The organic sulfate shown by X1, where R is an organic group having 1 or more carbon atoms, X1 is a cation, and n is an integer of 1 or more and 3 or less.

[0015] The organic sulfate functions to prevent the formation of a high-resistance film on the surface of the positive electrode active material. The high-resistance film is composed of oxidation decomposition components of the electrolyte, deterioration components of the positive electrode active material, and the like. The mechanism is found to be that the negative charge of the organic sulfate anion generated by the ionization of the organic sulfate in the electrolyte is delocalized.

[0016] First, the organic sulfate anion (R-O-SO4 - ) in which the negative charge is delocalized coordinates to the positive electrode active material in a high oxidation state (especially transition metal ions in a high oxidation state). As a result, the surface of the positive electrode active material is protected by the organic sulfate anion (R-O-SO4 - ), and the side reaction between the positive electrode active material and the electrolyte is suppressed. That is, by surface protection, an increase in the positive electrode resistance is suppressed, and the battery reaction proceeds more preferentially. Therefore, even in the case of rapid charging of the non-aqueous electrolyte secondary battery, the charging acceptance of the positive electrode is improved (that is, the rapid charging performance is improved).

[0017] In addition, since the R-O-SO4 - ion effectively acts on the positive electrode active material in a high oxidation state, even when the positive electrode resistance decreases and the positive electrode active material is charged to a deeper level, the side reaction between the high-potential positive electrode (positive electrode active material in a high oxidation state) and the electrolyte can be suppressed. Therefore, even during the charge-discharge cycle, the formation of a high-resistance film at the positive electrode can be suppressed, and the durability of the battery can be improved.

[0018] However, even in the case of R-O-SO4 -When ions function effectively, when the positive electrode active material is charged deeper, it is sometimes difficult to suppress the side reaction between the electrolyte and the positive electrode active material. For example, when the average potential of the positive electrode becomes higher, in a part of the positive electrode active material, the oxidation state sometimes becomes considerably higher than the average value. Therefore, the importance of selecting an electrolyte component that is not easily oxidized (high oxidation resistance) at a high potential positive electrode increases. In other words, when organic sulfate is present in the electrolyte and when it is not present, there is a large difference in the degree of improvement in the durability of the battery caused by an electrolyte component with high oxidation resistance.

[0019] The electrolyte contains ethylene carbonate (EC) and fluoroethylene carbonate (FEC). EC is a component that forms a solid electrolyte interface (SEI) with low resistance at the negative electrode and is considered to play an important role in reducing the internal resistance of the battery. On the other hand, EC has slightly lower oxidation resistance to a high potential positive electrode. When the positive electrode is repeatedly charged and discharged to a high potential, it gradually oxidizes and decomposes, and a high resistance film can be formed on the positive electrode. FEC has a structure in which one hydrogen of EC is replaced by fluorine, has excellent oxidation resistance compared to EC, and is expected to form a low resistance inorganic film containing a fluoride salt (such as LiF) at the negative electrode. By including FEC in the electrolyte at a specified ratio, even when the positive electrode becomes a high potential, the oxidative decomposition of EC can be significantly suppressed. Moreover, when organic sulfate is present in the electrolyte, the effect of suppressing the decomposition of EC and improving the durability of the battery is significantly enhanced.

[0020] In order to significantly improve the durability of the battery, the volume Vec of EC and the volume Vfec of FEC contained in the electrolyte need to satisfy: 0.1 ≤ Vec / Vfec ≤ 15. Additionally, in the case of more significantly improving the durability of the battery, it is preferably satisfied: 0.1 ≤ Vec / Vfec ≤ 12 or 0.1 ≤ Vec / Vfec ≤ 5, it can be satisfied: 0.1 ≤ Vec / Vfec ≤ 4, and it can also be satisfied: 0.1 ≤ Vec / Vfec ≤ 2.

[0021] In the organic sulfate shown in formula (1), the cation X1 only needs to form a salt that can be ionized in the electrolyte and is not particularly limited. The valence of the cation X1 can be 1 to 3, preferably a cation with a valence of 2 or less (n = 2), and more preferably a monovalent cation (n = 1). For example, as the cation X1, an alkali metal ion or NH4 can be used. + Among them, from the viewpoints of being easily ionized, easily obtained, and having little influence on increasing the viscosity of the electrolyte, sodium ions, lithium ions, etc. are preferred.

[0022] In the organic sulfate represented by the formula (1), R may be, for example, an alkyl group having 1 or more and 6 or less carbon atoms. If R is too large, in addition to the function of protecting the positive electrode active material in a highly oxidized state and suppressing side reactions, it may also hinder the battery reaction itself. From the viewpoint of effectively suppressing side reactions and promoting the battery reaction, the carbon number of R is preferably 1 to 3, particularly preferably 1 or 2. Specific examples of the organic sulfate that satisfies such conditions include lithium methyl sulfate, sodium methyl sulfate, lithium ethyl sulfate, sodium ethyl sulfate, etc. Among them, lithium ethyl sulfate and sodium ethyl sulfate are preferred. The organic sulfate may be used alone or in combination of two or more.

[0023] Regarding the content C1 of the organic sulfate contained in the electrolyte, for example, it may be 0.1% by mass or more and 5% by mass or less, may be 0.5% by mass or more and 5% by mass or less, or may be 0.5% by mass or more and 3% by mass or less.

[0024] The electrolyte may further contain the fluorosulfonate represented by the formula (2): (F-SO3) m X2, where X2 is a cation and m is an integer of 1 to 3. The fluorosulfonate ionizes in the electrolyte to generate a non-localized F-SO3 - ion. Therefore, it is considered that, like the organic sulfate, it protects the surface of the positive electrode active material in a highly oxidized state and suppresses side reactions between the high-potential positive electrode and the electrolyte. However, using only the fluorosulfonate cannot sufficiently protect the surface of the positive electrode active material, and the effect of suppressing the increase in the positive electrode resistance is not significant. On the other hand, when the organic sulfate and the fluorosulfonate are used in combination, the portion that cannot be protected by the organic sulfate anion is protected by the fluorosulfonate anion, and the increase in the positive electrode resistance is more significantly suppressed.

[0025] In the fluorosulfonate represented by the formula (2), the cation X2 only needs to form a salt that can be ionized in the electrolyte, and there is no particular limitation. The valence of the cation X2 is 1 to 3, preferably a cation with a valence of 2 or less (m = 2), and more preferably a monovalent cation (m = 1). For example, an alkali metal ion or NH4 + can be used as the cation X2. Among them, from the viewpoint of easy ionization and little influence on the increase in the viscosity of the electrolyte, lithium ion is preferred. The fluorosulfonate may be used alone or in combination of two or more.

[0026] Regarding the content C2 of the fluorosulfonate contained in the electrolyte, for example, it may be 0.5% by mass or more and 5% by mass or less, or may be 0.5% by mass or more and 3% by mass or less.

[0027] Regarding the mass ratio of the content C2 of fluorosulfonate to the content C1 of organic sulfate in the electrolyte: C2 / C1, for example, it can satisfy: 0 ≤ C2 / C1 ≤ 3, it can satisfy: 0 < C2 / C1 ≤ 2, it can satisfy: 0.05 ≤ C2 / C1 ≤ 1.5, and it can also satisfy: 0.5 ≤ C2 / C1 ≤ 1.5.

[0028] For the positive electrode active material, for example, it can include: a lithium-containing composite oxide having a layered rock-salt type crystal structure and with more than 80 atomic% of a metal other than lithium being nickel. Generally, a positive electrode active material containing nickel in a high content has a high capacity, but the greater the nickel content, the more easily the composite oxide deteriorates and the more easily the durability of the battery decreases. In the composite oxide, nickel exists in a trivalent or tetravalent state, which is helpful for charge and discharge, but the stable state of the element is divalent. The reaction to become divalent is an irreversible reaction. The tetravalent nickel contained in the composite oxide in a high oxidation state is strongly reduced by side reactions and easily becomes divalent. When a nickel oxide (NiO) layer is formed on the surface of the positive electrode active material, the resistance of the positive electrode increases and the durability of the battery decreases. In contrast, when organic sulfate is included in the electrolyte, the R-O-SO4 - ion (organic sulfate anion) coordinates on the tetravalent nickel to protect the tetravalent nickel. Therefore, for the effect of reducing the positive electrode resistance and improving the durability of the battery caused by organic sulfate, it becomes most significant when using a positive electrode active material containing a high content of nickel.

[0029] For the lithium-containing composite oxide, for example, it can be a chemical formula Li a Ni x M 1-x O 2-δ (where 0 < a ≤ 1.2, 0.8 ≤ x < 1, 0 ≤ δ ≤ 0.05, and M can include at least one selected from the group consisting of Mn, Fe, Ti, Si, Nb, Zr, Mo, Co, Al, Zn, W, Sr, and Ca.) The lithium-nickel composite oxide shown above. The Ni ratio x in the above chemical formula can be 0.85 or more (0.85 ≤ x), or can be 0.90 or more (0.90 ≤ x).

[0030] In the lithium-nickel composite oxide, M can include: at least one element selected from the group consisting of Mn, Fe, Ti, Si, Nb, Zr, Mo, Co, Al, and Zn; and at least one element selected from the group consisting of W, Sr, and Ca. By including at least one of W, Sr, and Ca in the composite oxide, the surface structure of the composite oxide is stabilized, and the deterioration of the positive electrode active material can be more effectively suppressed. When W, Sr, and Ca are unevenly present near the surface of the composite oxide as the positive electrode active material, it is effective.

[0031] Next, the non-aqueous electrolyte secondary battery of the embodiment of the present invention will be described in detail.

[0032] [Positive electrode]

[0033] The positive electrode includes: a positive electrode current collector; and a positive electrode mixture layer formed on the surface of the positive electrode current collector and containing a positive electrode active material. For the positive electrode mixture layer, it can be formed by coating a positive electrode paste obtained by dispersing a positive electrode mixture in a dispersion medium on the surface of the positive electrode current collector and drying it. The positive electrode mixture contains a positive electrode active material as an essential component, and contains a binder, a thickener, a conductive agent, etc. as optional components. The dried coating film can be calendered as needed. As the positive electrode active material, binder, thickener, conductive agent, etc., known materials can be used.

[0034] The lithium-containing composite oxide used as the positive electrode active material is, for example, a secondary particle aggregated from a plurality of primary particles. The particle size of the primary particle is usually 0.05 μm to 1 μm. The average particle size of the composite oxide is, for example, 3 μm to 30 μm, preferably 5 μm to 25 μm. Here, the average particle size of the composite oxide refers to the median particle size (D50) at which the cumulative frequency in the volume-based particle size distribution becomes 50%, and is measured by a laser diffraction type particle size distribution measuring device.

[0035] The content of the elements constituting the composite oxide can be measured by an inductively coupled plasma emission spectrometer (ICP-AES), an electron probe microanalyzer (EPMA), an energy dispersive X-ray analyzer (EDX), etc.

[0036] As the positive electrode current collector, a non-porous conductive substrate (such as a metal foil) or a porous conductive substrate (such as a mesh body, a net-like body, a punched sheet) is used. As the material of the positive electrode current collector, for example, stainless steel, aluminum, aluminum alloy, titanium, etc. can be exemplified.

[0037] [Negative electrode]

[0038] The negative electrode, for example, includes: a negative electrode current collector and a negative electrode active material layer formed on the surface of the negative electrode current collector. For the negative electrode active material layer, it can be formed by coating a negative electrode paste obtained by dispersing a negative electrode mixture in a dispersion medium on the surface of the negative electrode current collector and drying it. The negative electrode mixture contains a negative electrode active material as an essential component, and contains a binder, a thickener, a conductive agent, etc. as optional components. The dried coating film can be calendered as needed. That is, the negative electrode active material can also be a mixture layer. In addition, a lithium metal foil or a lithium alloy foil can be adhered to the negative electrode current collector. As the negative electrode active material, binder, conductive agent, thickener, known materials can be used.

[0039] The negative electrode active material includes materials that electrochemically store and release lithium ions, lithium metal, lithium alloys, etc. As materials that electrochemically store and release lithium ions, carbon materials, alloy-based materials, etc. can be used. As carbon materials, for example, graphite, easily graphitizable carbon (soft carbon), hardly graphitizable carbon (hard carbon), etc. can be exemplified. As alloy-based materials, silicon, tin, silicon alloys, tin alloys, silicon compounds, etc. can be cited.

[0040] As the negative electrode current collector, a non-porous conductive substrate (such as a metal foil) or a porous conductive substrate (such as a mesh body, a net-like body, a punched sheet, etc.) can be used. As the material of the negative electrode current collector, stainless steel, nickel, nickel alloy, copper, copper alloy, etc. can be exemplified.

[0041] [Electrolyte]

[0042] The electrolyte contains a solvent and a solute dissolved in the solvent. The solute is an electrolyte salt that dissociates ions in the electrolyte. Organic sulfates and fluorosulfonates are included in the solute, but organic sulfates and fluorosulfonates are generally regarded as additives. The main component of the solute is a lithium salt.

[0043] As the solvent, known materials can be used. As the solvent, for example, cyclic carbonates, chain carbonates, cyclic carboxylates, chain carboxylates, etc. can be used. As cyclic carbonates, propylene carbonate (PC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), etc. can be cited. As chain carbonates, diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), etc. can be cited. As cyclic carboxylates, γ-butyrolactone (GBL), γ-valerolactone (GVL), etc. can be cited. As chain carboxylates, methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), ethyl propionate (EP), etc. can be cited as non-aqueous solvents. The non-aqueous solvents can be used alone or in combination of two or more.

[0044] The solvent contains EC and FEC as essential components. The total volume of EC and FEC in the entire solvent is preferably 10% by volume or more and 30% by volume or less, more preferably 15% by volume or more and 25% by volume or less. In addition, as the solvent used in combination with EC and FEC, from the viewpoint of easily making the viscosity of the electrolyte appropriate, chain carbonates are preferred. The total volume of EC, FEC, and chain carbonates in the entire solvent is selected to be 80% by volume or more, and can also be 100% by volume.

[0045] As lithium salts other than organic sulfates and fluorosulfonates, for example, lithium salts containing perchloric acid (LiClO4, LiAlCl4, LiB 10 Cl 10etc.), lithium salts containing fluorinated acids (LiPF6, LiPF2O2, LiBF4, LiSbF6, LiAsF6, LiCF3SO3, LiCF3CO2, etc.), lithium salts containing fluorinated acid imides (LiN(FSO2)2, LiN(CF3SO2)2, LiN(CF3SO2)(CF9SO2), LiN(C2F5SO2)2, etc.), lithium halides (LiCl, LiBr, LiI, etc.). The lithium salt can be used alone or in combination of two or more kinds.

[0046] The concentration of the lithium salt (except for organic sulfates and fluorosulfonates) in the electrolytic solution can be 1 mol / L or more and 2 mol / L or less, or can be 1 mol / L or more and 1.5 mol / L or less. By controlling the lithium salt concentration within the above range, an electrolytic solution with excellent ion conductivity and moderate viscosity can be obtained. However, the lithium salt concentration is not limited to the above.

[0047] The electrolytic solution can contain other known additives. Examples of the additives include vinylene carbonate, 1,3 - propane sultone, methyl benzenesulfonate, cyclohexylbenzene, biphenyl, diphenyl ether, fluorobenzene, etc.

[0048] The content of each component in the electrolytic solution is determined, for example, by using high - performance liquid chromatography, gas chromatography - mass spectrometry (GC - MS), NMR, inductively coupled plasma mass spectrometry (ICP - MS), and elemental analysis.

[0049] [Separator]

[0050] A separator is interposed between the positive electrode and the negative electrode. The separator has a high ion permeability, appropriate mechanical strength, and insulation. As the separator, microporous membranes, woven fabrics, non - woven fabrics, etc. can be used. As the material of the separator, polyolefins such as polypropylene and polyethylene are preferred.

[0051] As an example of the structure of a non - aqueous electrolyte secondary battery, a structure in which an electrode group formed by winding a positive electrode and a negative electrode with a separator in between is housed together with a non - aqueous electrolyte in an outer package can be cited. However, it is not limited thereto, and other types of electrode groups can also be applied. For example, it can also be a laminated electrode group in which a positive electrode and a negative electrode are laminated with a separator in between. The form of the non - aqueous electrolyte secondary battery is not limited either. For example, it can be cylindrical, square, coin - type, button - type, laminated - type, etc.

[0052] Figure 1Fig. 0 is a schematic perspective view showing a cut-away part of a square non-aqueous electrolyte secondary battery according to an embodiment of the present invention. The battery includes: a bottomed square battery case 4, an electrode group 1 housed in the battery case 4, and a non-aqueous electrolyte. The electrode group 1 has: a long strip-shaped negative electrode, a long strip-shaped positive electrode, and a separator interposed therebetween. The negative electrode current collector of the negative electrode is electrically connected via a negative electrode lead 3 to a negative electrode terminal 6 provided on a sealing plate 5. The negative electrode terminal 6 is insulated from the sealing plate 5 by a resin gasket 7. The positive electrode current collector of the positive electrode is electrically connected to the back surface of the sealing plate 5 via a positive electrode lead 2. That is, the positive electrode is electrically connected to the battery case 4 which also serves as a positive electrode terminal. The periphery of the sealing plate 5 is fitted into the opening end portion of the battery case 4, and the fitting portion is laser welded. There is an injection hole for the non-aqueous electrolyte on the sealing plate 5, which is blocked by a seal plug 8 after the injection of the liquid.

[0053] Hereinafter, the present invention will be specifically described based on examples and comparative examples, but the present invention is not limited to the following examples.

[0054] <Examples 1 to 3>

[0055] [Fabrication of Negative Electrode]

[0056] SiO and graphite were mixed at a mass ratio of 5:95 and used as the negative electrode active material. The negative electrode active material, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber (SBR), and water were mixed at a specified mass ratio to prepare a negative electrode slurry. Then, the negative electrode slurry was coated on the surface of a copper foil serving as the negative electrode current collector, and after the coating film was dried, rolling was performed to form a negative electrode mixture layer on both sides of the copper foil.

[0057] [Fabrication of Positive Electrode]

[0058] As the lithium-containing composite oxide, a layered rock salt-type lithium-containing transition metal oxide LiNi 0.8 Co 0.18 Al 0.02 O2 (NCA: positive electrode active material), acetylene black (AB: conductive material), and polyvinylidene fluoride (PVdF: binder material) were mixed at a mass ratio of NCA:AB:PVdF = 95:2.5:2.5, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was further added and stirred to prepare a positive electrode slurry. The positive electrode slurry was coated on both sides of an Al foil serving as the positive electrode current collector, and after the coating film was dried, rolling was performed to form a positive electrode mixture layer on both sides of the Al foil.

[0059] [Preparation of Electrolyte Solution]

[0060] In a mixed solvent containing ethylene carbonate (EC), fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) in a volume ratio of (EC+FEC):EMC:DMC=20:10:70, LiPF6 was added as a lithium salt, and further, sodium ethyl sulfate (NaES) was added as an additive to prepare an electrolyte. The concentration of LiPF6 in the non-aqueous electrolyte was 1.0 mol / liter, and the concentration of NaES was 1% by mass.

[0061] The total volume of EC and FEC in the mixed solvent was kept constant, and the ratio of the volume Vec of EC to the volume Vfec of FEC was changed as shown in Table 1: Vec / Vfec.

[0062] [Manufacturing of Secondary Batteries]

[0063] Lead tabs were installed on each electrode, and the positive and negative electrodes were wound in a spiral shape with the tabs located at the outermost periphery through a separator to produce an electrode group. The electrode group was inserted into an outer casing made of a laminated film with an aluminum foil as a barrier layer, and after vacuum drying at 105°C for 2 hours, a non-aqueous electrolyte was injected, and the opening of the outer casing was sealed to produce secondary batteries A1 to A3.

[0064] <Examples 4 to 7>

[0065] Secondary batteries A4 to A7 were prepared in the same manner as in Examples 1 to 3 except that lithium fluorosulfonate (FSO3Li) was further added to the electrolyte as an additive and the concentration of FSO3Li in the nonaqueous electrolyte was set to 1 mass % and the Vec / Vfec ratio was changed as shown in Table 1.

[0066] <Comparative Examples 1 to 5>

[0067] Secondary batteries B1 to B5 were prepared in the same manner as in Examples 1 to 3 except that NaES was not added to the electrolyte solution and the Vec / Vfec ratio was changed as shown in Table 1.

[0068] <Comparative Example 6>

[0069] Secondary battery B6 was produced in the same manner as in Example 3 except that NaES was not added to the electrolyte solution and the concentration of FSO3Li in the electrolyte solution was set to 1 mass %.

[0070] <Comparative Example 7>

[0071] A secondary battery B7 was produced in the same manner as in Examples 1 to 3 except that the Vec / Vfec ratio was set to 20 as shown in Table 1.

[0072] [evaluate]

[0073] (Capacity maintenance rate)

[0074] For each of the completed batteries, they are placed in an environment at 25 °C and charged at a constant current of 0.3It until the voltage reaches 4.2V. Then, they are charged at a constant voltage of 4.2V until the current reaches 0.02It. Then, they are discharged at a constant current of 0.5It until the voltage reaches 2.5V, and the initial capacity C0 is obtained. The charge and discharge are carried out in an environment at 25 °C.

[0075] The pause period between charging and discharging is 10 minutes. In an environment at 25 °C, 200 charge-discharge cycles are repeatedly carried out under the above charge-discharge conditions, and the discharge capacity C1 of the 200th cycle is obtained. The percentage value of the ratio R1 = C1 / C0 of the discharge capacity C1 to the initial capacity C0 is obtained as the capacity retention rate. The results are shown in Table 1.

[0076] (Fast charging index (reactance component))

[0077] In an environment at 25 °C, the reactance of the battery in a 100% charged state (SOC100%) is obtained by AC impedance measurement.

[0078] [Table 1]

[0079]

[0080] In Table 1, among batteries B1 - B6 without NaES, even when changing the Vec / Vfec ratio, the R1 values (79.8 - 81 (deviation range 1.2)) hardly change. When the Vec / Vfec ratio becomes smaller (i.e., when the proportion of FEC increases), a slight improvement can be seen. On the other hand, among batteries B7, A1 - A3 containing NaES, when the Vec / Vfec ratio becomes smaller, the R1 value improves from 79.9 to 84.1 (deviation range 4.2). In addition, among batteries A4 - A7 using lithium fluorosulfonate in combination, the R1 value further improves significantly to 85.0.

[0081] In Table 1, when comparing batteries B1 - B7, in battery B7 containing NaES, the fast charging index is 1.00, showing a great improvement compared to batteries B1 - B6 without NaES. In addition, it can be understood that in batteries B1 - B6 without NaES, even when changing the Vec / Vfec ratio, the fast charging index hardly changes. On the other hand, looking at batteries A1 - A3 containing NaES, the fast charging index maintains the same level as that of battery B7. That is, in batteries A1 - A3, like battery B7, the positive electrode resistance is reduced while the durability of the battery is improved. In addition, in batteries A4 - A7, although the positive electrode resistance is further reduced, the durability of the battery is further improved.

[0082] Note that, by comparing batteries B5 and B6, it can be seen that even when lithium fluorosulfonate (FSO3Li) is added alone as an additive, it has almost no effect on the R1 value and the fast charging index. On the other hand, by comparing batteries A3 and A7, by using NaES and lithium fluorosulfonate in combination, the R1 value increases significantly and the fast charging index is significantly improved.

[0083] Industrial applicability

[0084] The non-aqueous electrolyte secondary battery of the present invention is useful as a main power source for applications requiring high-speed charging performance and durability, such as mobile communication devices, portable electronic devices, electric vehicles, hybrid vehicles, etc.

[0085] Explanation of reference numerals

[0086] 1 Electrode assembly

[0087] 2 Positive electrode lead

[0088] 3 Negative electrode lead

[0089] 4 Battery case

[0090] 5 Sealing plate

[0091] 6 Negative terminal

[0092] 7 Gasket

[0093] 8 Plug

Claims

1. A non-aqueous electrolyte secondary battery, comprising: a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte solution, The electrolyte contains the organic sulfate shown by formula (1): (R-O-SO3) n X1 Among them, R is an organic group having 1 or more carbon atoms, X1 is a cation, and n is an integer of 1 to 3, The electrolyte solution further contains ethylene carbonate and fluoroethylene carbonate, The volume Vec of the ethylene carbonate and the volume Vfec of the fluoroethylene carbonate satisfy: 0.1 ≤ Vec / Vfec ≤ 4; The electrolyte further contains the compound of formula (2): (F-SO3) m fluorosulfonate represented by X2, wherein, X2 is a cation and m is an integer of 1 to 3.

2. The non-aqueous electrolyte secondary battery according to claim 1, which satisfies: 0.1 ≤ Vec / Vfec ≤ 2.

3. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein, The X1 is an alkali metal ion or NH4 + .

4. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein, The R is an alkyl group having 1 or more and 6 or less carbon atoms.

5. The non-aqueous electrolyte secondary battery according to claim 4, wherein The R is methyl or ethyl.

6. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein, The content of the organic sulfate contained in the electrolyte solution is 0.1% by mass or more and 5% by mass or less.

7. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein The content of the fluorosulfonate contained in the electrolyte solution is 0.5% by mass or more and 5% by mass or less.

8. The non-aqueous electrolyte secondary battery according to claim 1, wherein, The X2 is an alkali metal ion or NH4 + .

9. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein, The positive electrode includes: a lithium-containing composite oxide having a layered rock salt-type crystal structure and 80 atomic% or more of a metal other than lithium being nickel.

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