Non-aqueous electrolyte secondary batteries

Abstract

This nonaqueous electrolyte secondary battery is provided with a positive electrode, a negative electrode, a separator which is interposed between the positive electrode and the negative electrode, and an electrolyte solution. The electrolyte solution contains an organic sulfate that is represented by formula (1) (R-O-SO3)nX1, wherein R represents an organic group having 1 or more carbon atoms, X1 represents a cation and n represents an integer from 1 to 3; the electrolyte solution additionally 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 disclosure relates to a non-aqueous electrolyte secondary battery. [Background technology]

[0002] Non-aqueous electrolyte secondary batteries, especially lithium-ion secondary batteries, have high power output and high energy density, and are therefore expected to be used in small consumer applications, power storage devices, and power sources for electric vehicles. However, with the rapid spread of non-aqueous electrolyte secondary batteries, the importance of rapid charging performance has increased.

[0003] Patent Document 1 proposes a positive electrode active material that is particularly suitable for use in lithium-ion secondary batteries for driving vehicles, which have reduced internal resistance and require high-rate charging and discharging and high output. The positive electrode active material comprises a base made of a compound capable of absorbing and releasing charge carriers, a dielectric disposed on at least a portion of the surface of the base, and a carbonate compound disposed on at least a portion of the surface of the base. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-123500 A Summary of the Invention

[0005] When the positive electrode resistance decreases, the positive electrode active material is charged more deeply during charging, which makes it easier for the positive electrode potential to rise. This accelerates the oxidative decomposition of the electrolyte during the charge-discharge cycle, which increases the positive electrode resistance and can reduce durability (capacity retention rate).

[0006] In view of the above, one aspect of the present disclosure provides a battery including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte solution, The electrolyte solution has the formula (1): (RO-SO3) n X1 The organic sulfate is represented by wherein R is an organic group having one 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 the following relationship: The present invention relates to a non-aqueous electrolyte secondary battery that satisfies the requirement of 0.1≦Vec / Vfec≦15.

[0007] According to the present disclosure, it is possible to improve the durability of a non-aqueous electrolyte secondary battery while reducing the positive electrode resistance. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic perspective view of a secondary battery according to an embodiment of the present disclosure, with a portion cut away. DETAILED DESCRIPTION OF THE INVENTION

[0009] A nonaqueous electrolyte secondary battery according to an embodiment of the present disclosure includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. The positive electrode includes a positive electrode active material, such as a lithium-containing composite oxide, that includes a transition metal.

[0010] The electrolyte is a solution of the formula (1): (RO-SO3) n X1 where R is an organic group having one or more carbon atoms, X1 is a cation, and n is an integer of 1 or more and 3 or less.

[0011] The organic sulfate prevents the formation of a high-resistance coating on the surface of the positive electrode active material. This high-resistance coating is composed of oxidative decomposition components of the electrolyte and degradation components of the positive electrode active material. The mechanism behind this is the delocalization of the negative charge of the organic sulfate anion generated by the ionization of the organic sulfate in the electrolyte.

[0012] First, the negative charge is delocalized in the organic sulfate anion (RO-SO4 -) coordinates with the highly oxidized cathode active material (especially the highly oxidized transition metal ions). As a result, the surface of the cathode active material is converted into an organic sulfate anion (RO-SO4 - ), which suppresses side reactions between the positive electrode active material and the electrolyte. In other words, surface protection suppresses an increase in the positive electrode resistance, allowing the battery reaction to proceed preferentially. Therefore, even when rapid charging a non-aqueous electrolyte secondary battery, the charge acceptance of the positive electrode is improved (i.e., rapid charging performance is improved).

[0013] Also, RO-SO4 - Because the ions act effectively on the highly oxidized positive electrode active material, even when the positive electrode active material is charged to a deeper level as a result of the reduced positive electrode resistance, side reactions between the high-potential positive electrode (highly oxidized positive electrode active material) and the electrolyte are suppressed. This prevents the formation of a high-resistance coating on the positive electrode during charge-discharge cycles, improving the durability of the battery.

[0014] However, RO-SO4 - Even if ions act effectively, it may become difficult to suppress side reactions between the electrolyte and the positive electrode active material as the positive electrode active material is charged to a greater depth. For example, as the average potential of the positive electrode increases, the oxidation state of some of the positive electrode active material may become significantly higher than the average. Therefore, it is important to select electrolyte components that are less likely to be oxidized (highly oxidation-resistant) at a high-potential positive electrode. In other words, the presence or absence of organic sulfates in the electrolyte significantly affects the degree to which a highly oxidation-resistant electrolyte component improves the durability of the battery.

[0015] The electrolyte contains ethylene carbonate (EC) and fluoroethylene carbonate (FEC). EC forms a low-resistance solid electrolyte interface (SEI) on the negative electrode and is thought to play an important role in reducing the internal resistance of the battery. However, EC has relatively low oxidation resistance against high-potential positive electrodes. Repeated charge-discharge cycles in which the positive electrode is charged to a high potential gradually cause oxidative decomposition, resulting in the formation of a highly resistive coating on the positive electrode. FEC, which has a structure in which one hydrogen atom in EC is replaced by fluorine, is expected to have better oxidation resistance than EC and to form a low-resistance inorganic coating containing fluoride salts (e.g., LiF) on the negative electrode. By incorporating FEC into the electrolyte at a specified ratio, the oxidative decomposition of EC is significantly suppressed, even when the positive electrode is at a high potential. Furthermore, the effect of suppressing EC decomposition and improving battery durability is more pronounced when organic sulfates are present in the electrolyte.

[0016] To significantly improve the durability of the battery, the volume Vec of EC and the volume Vfec of FEC contained in the electrolyte solution must satisfy 0.1≦Vec / Vfec≦15. To further significantly improve the durability of the battery, it is desirable to satisfy 0.1≦Vec / Vfec≦12 or 0.1≦Vec / Vfec≦5, and it is also acceptable to satisfy 0.1≦Vec / Vfec≦4 or 0.1≦Vec / Vfec≦2.

[0017] In the organic sulfate salt represented by formula (1), the cation X1 is not particularly limited as long as it forms a salt that can be ionized in the electrolyte. The valence of the cation X1 may be 1 to 3, but a divalent or lower cation (n=2) is preferred, and a monovalent cation (n=1) is more preferred. For example, the cation X1 may be an alkali metal ion or NH4 + Among these, sodium ions and lithium ions are preferred because they are easily ionized, readily available, and have little effect on increasing the viscosity of the electrolyte.

[0018] In the organic sulfate represented by formula (1), R may be, for example, an alkyl group having 1 to 6 carbon atoms. However, if R is too large, it may not only protect the highly oxidized cathode active material and suppress side reactions, but may also inhibit the battery reaction itself. From the viewpoint of efficiently suppressing side reactions and promoting the battery reaction, R preferably has 1 to 3 carbon atoms, and particularly preferably 1 or 2 carbon atoms. Specific examples of organic sulfates that satisfy these conditions include lithium methyl sulfate, sodium methyl sulfate, lithium ethyl sulfate, and sodium ethyl sulfate. Of these, lithium ethyl sulfate and sodium ethyl sulfate are preferred. One type of organic sulfate may be used alone, or two or more types may be used in combination.

[0019] The content C1 of the organic sulfate contained in the electrolytic solution may be, for example, 0.1 mass % or more and 5 mass % or less, 0.5 mass % or more and 5 mass % or less, or 0.5 mass % or more and 3 mass % or less.

[0020] The electrolyte further comprises a compound represented by the formula (2): (F-SO3) m X2 where X2 is a cation and m is an integer of 1 to 3. Fluorosulfonates ionize in the electrolyte to form F-SO3 where the negative charge is delocalized. - Since fluorosulfonates generate ions, they are thought to protect the surface of the highly oxidized positive electrode active material and suppress side reactions between the high-potential positive electrode and the electrolyte, similar to organic sulfates. However, fluorosulfonates alone cannot sufficiently protect the surface of the positive electrode active material, and the effect of suppressing an increase in positive electrode resistance is not apparent. On the other hand, when organic sulfates and fluorosulfonates are used in combination, the parts that cannot be protected by organic sulfate anions are protected by fluorosulfonate anions, and the increase in positive electrode resistance is more significantly suppressed.

[0021] In the fluorosulfonate represented by formula (2), the cation X2 is not particularly limited as long as it forms a salt that can be ionized in the electrolytic solution. The valence of the cation X2 may be 1 to 3, but a divalent or lower cation (m = 2) is preferred, and a monovalent cation (m = 1) is more preferred. For example, as the cation X2, an alkali metal ion or NH4 + can be used. Among them, lithium ions are preferred because they are easily ionized and have little effect on increasing the viscosity of the electrolytic solution. The fluorosulfonate may be used alone or in combination of two or more.

[0022] The content C2 of the fluorosulfonate contained in the electrolytic solution may be, for example, 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.

[0023] The mass ratio C2 / C1 of the content C2 of the fluorosulfonate contained in the electrolytic solution to the content C1 of the organic sulfate may satisfy, for example, 0 ≦ C2 / C1 ≦ 3, or may satisfy 0 < C2 / C1 ≦ 2, or may satisfy 0.05 ≦ C2 / C1 ≦ 1.5, or may satisfy 0.5 ≦ C2 / C1 ≦ 1.5.

[0024] The positive electrode active material may include, for example, a lithium-containing composite oxide having a layered rock salt-type crystal structure and in which 80 atomic% or more of a metal other than lithium is nickel. Generally, a positive electrode active material containing a high content of nickel has a high capacity, but as the nickel content increases, the composite oxide is more likely to deteriorate and the durability of the battery is likely to decrease. In the composite oxide, nickel exists in a trivalent or tetravalent state and contributes to charge and discharge, but the stable state as an 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 a side reaction and is likely to become 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. On the other hand, when the electrolytic solution contains an organic sulfate, R-O-SO4 is added to the tetravalent nickel -Ions (organic sulfate anions) coordinate to protect tetravalent nickel. Therefore, the effect of reducing the anode resistance by the organic sulfate and the effect of improving the battery durability are most prominent when using an anode active material containing nickel in a high content.

[0025] The lithium-containing composite oxide may be, for example, a lithium-nickel composite oxide represented by the chemical formula Li a Ni x M 1-x O 2-δ (However, 0 < a ≤ 1.2, 0.8 ≤ x < 1, 0 ≤ δ ≤ 0.05, and M contains at least one selected from the group consisting of Mn, Fe, Ti, Si, Nb, Zr, Mo, Co, Al, Zn, W, Sr, and Ca.) The Ni ratio x in the above chemical formula may be 0.85 or more (0.85 ≤ x), or may be 0.90 or more (0.90 ≤ x).

[0026] In the lithium-nickel composite oxide, M may contain 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. When at least one of W, Sr, and Ca is contained in the composite oxide, the surface structure of the composite oxide is stabilized, and the deterioration of the anode active material can be more effectively suppressed. In the composite oxide, it is effective that W, Sr, and Ca are unevenly distributed near the surface of the composite oxide which is the anode active material.

[0027] Next, the non-aqueous electrolyte secondary battery according to the embodiment of the present disclosure will be described in detail.

[0028] [Anode] The positive electrode comprises 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. The positive electrode mixture layer can be formed by applying a positive electrode slurry to the surface of the positive electrode current collector and drying the slurry. The positive electrode mixture contains a positive electrode active material as an essential component and optional components such as a binder, a thickener, and a conductive agent. The dried coating film may be rolled as necessary. Known materials can be used as the positive electrode active material, the binder, the thickener, the conductive agent, and the like.

[0029] The lithium-containing composite oxide used as the positive electrode active material is, for example, a secondary particle formed by aggregation of a plurality of primary particles. The particle size of the primary particles is generally 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 means the median diameter (D50) at which the cumulative frequency is 50% in the volume-based particle size distribution, and is measured using a laser diffraction particle size distribution measuring device.

[0030] The content of elements constituting the composite oxide can be measured by an inductively coupled plasma atomic emission spectrometer (ICP-AES), an electron probe microanalyzer (EPMA), an energy dispersive X-ray analyzer (EDX), or the like.

[0031] The positive electrode current collector may be a non-porous conductive substrate (such as a metal foil) or a porous conductive substrate (such as a mesh, net, or punched sheet). Examples of the material for the positive electrode current collector include stainless steel, aluminum, aluminum alloy, and titanium.

[0032] [Negative electrode] The negative electrode includes, for example, a negative electrode current collector and a negative electrode active material layer formed on the surface of the negative electrode current collector. The negative electrode active material layer can be formed, for example, by applying a positive electrode slurry to the surface of the negative electrode current collector, in which a negative electrode mixture containing a negative electrode active material as an essential component and optional components such as a binder, a thickener, and a conductive agent is dispersed in a dispersion medium, and then drying the slurry. The dried coating film may be rolled as necessary. In other words, the negative electrode active material may be a mixture layer. Alternatively, a lithium metal foil or a lithium alloy foil may be attached to the negative electrode current collector. Known materials may be used as the negative electrode active material, the binder, the conductive agent, and the thickener.

[0033] The negative electrode active material includes a material that electrochemically absorbs and releases lithium ions, lithium metal, lithium alloys, etc. Examples of the material that electrochemically absorbs and releases lithium ions include carbon materials and alloy-based materials. Examples of carbon materials include graphite, easily graphitized carbon (soft carbon), and hardly graphitized carbon (hard carbon). Examples of alloy-based materials include silicon, tin, silicon alloys, tin alloys, and silicon compounds.

[0034] The negative electrode current collector may be a non-porous conductive substrate (such as a metal foil) or a porous conductive substrate (such as a mesh, net, or punched sheet). Examples of the material for the negative electrode current collector include stainless steel, nickel, nickel alloys, copper, and copper alloys.

[0035] [Electrolyte] An electrolyte solution contains a solvent and a solute dissolved in the solvent. The solute is an electrolyte salt that ionically dissociates in the electrolyte solution. The solute includes organic sulfates and fluorosulfonates, which are usually treated as additives. The main component of the solute is a lithium salt.

[0036] Known materials can be used as the solvent. Examples of the solvent that can be used include cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, and chain carboxylic acid esters. Examples of cyclic carbonates include propylene carbonate (PC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC). Examples of chain carbonates include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). Examples of cyclic carboxylic acid esters include γ-butyrolactone (GBL) and γ-valerolactone (GVL). Examples of chain carboxylic acid esters include non-aqueous solvents such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate (EP). One type of non-aqueous solvent may be used alone, or two or more types may be used in combination.

[0037] 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, and more preferably 15% by volume or more and 25% by volume or less. Furthermore, a chain carbonate ester is preferred as a solvent to be used in combination with EC and FEC, as it facilitates optimizing the viscosity of the electrolyte. The total volume of EC, FEC, and the chain carbonate ester in the entire solvent is preferably 80% by volume or more, and may be 100% by volume.

[0038] Examples of lithium salts other than organic sulfates and fluorosulfonates include lithium salts of chlorine-containing acids (LiClO4, LiAlCl4, LiB 10 Cl 10 etc.), lithium salts of fluorine-containing acids (LiPF6, LiPF2O2, LiBF4, LiSbF6, LiAsF6, LiCF3SO3, LiCF3CO2, etc.), lithium salts of fluorine-containing acid imides (LiN(FSO2)2, LiN(CF3SO2)2, LiN(CF3SO2)(C4F9SO2), LiN(C2F5SO2)2, etc.), lithium halides (LiCl, LiBr, LiI, etc.), etc., can be used. One type of lithium salt may be used alone, or two or more types may be used in combination.

[0039] The concentration of the lithium salt (other than organic sulfates and fluorosulfonates) in the electrolyte may be 1 mol / L or more and 2 mol / L or less, or 1 mol / L or more and 1.5 mol / L or less. By controlling the lithium salt concentration within the above range, an electrolyte having excellent ionic conductivity and appropriate viscosity can be obtained. However, the lithium salt concentration is not limited to the above.

[0040] The electrolyte may contain other known additives, such as vinylene carbonate, 1,3-propane sultone, methylbenzenesulfonate, cyclohexylbenzene, biphenyl, diphenyl ether, and fluorobenzene.

[0041] The content of each component in the electrolyte can be determined using, for example, high performance liquid chromatography, gas chromatography-mass spectrometry (GC-MS), NMR, inductively coupled plasma mass spectrometry (ICP-MS), elemental analysis, or the like.

[0042] [Separator] A separator is interposed between the positive electrode and the negative electrode. The separator has high ion permeability and adequate mechanical strength and insulation. The separator can be made of a microporous thin film, woven fabric, nonwoven fabric, or the like. The separator is preferably made of polyolefin such as polypropylene or polyethylene.

[0043] An example of the structure of a nonaqueous electrolyte secondary battery is a structure in which an electrode group formed by winding a positive electrode and a negative electrode with a separator interposed therebetween is housed in an outer casing together with a nonaqueous electrolyte. However, this is not limited thereto, and other forms of electrode groups may also be applied. For example, a stacked electrode group in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween may also be used. The shape of the nonaqueous electrolyte secondary battery is also not limited, and may be, for example, a cylindrical type, a prismatic type, a coin type, a button type, a laminate type, or the like.

[0044] FIG. 1 is a schematic perspective view, partially cut away, of a prismatic nonaqueous electrolyte secondary battery according to an embodiment of the present disclosure. The battery includes a bottomed prismatic battery case 4, an electrode group 1, and a nonaqueous electrolyte housed within the battery case 4. The electrode group 1 includes a long, strip-shaped negative electrode, a long, strip-shaped positive electrode, and a separator interposed therebetween. The negative electrode current collector is electrically connected to a negative electrode terminal 6 provided on a sealing plate 5 via a negative electrode lead 3. The negative electrode terminal 6 is insulated from the sealing plate 5 by a resin gasket 7. The positive electrode current collector is electrically connected to the back surface of the sealing plate 5 via a positive electrode lead 2. In other words, the positive electrode is electrically connected to the battery case 4, which also serves as the positive electrode terminal. The periphery of the sealing plate 5 fits into the open end of the battery case 4, and the fitting is laser-welded. The sealing plate 5 has an injection hole for the nonaqueous electrolyte, which is closed with a seal plug 8 after injection.

[0045] Hereinafter, the present disclosure will be specifically described based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0046] <Examples 1 to 3> [Preparation of negative electrode] SiO and graphite were mixed in a mass ratio of 5:95 and used as the negative electrode active material. The negative electrode active material, carboxymethyl cellulose sodium (CMC-Na), styrene-butadiene rubber (SBR), and water were mixed in a predetermined mass ratio to prepare a negative electrode slurry. Next, the negative electrode slurry was applied to the surface of copper foil, which served as a negative electrode current collector. The coating was dried and then rolled to form a negative electrode mixture layer on both sides of the copper foil.

[0047] [Preparation of positive electrode] As a lithium-containing composite oxide, LiNi, a rock-salt type lithium-containing transition metal oxide with a layered structure, 0.8 Co 0.18 Al 0.02O2 (NCA: cathode active material), acetylene black (AB: conductive material), and polyvinylidene fluoride (PVdF: binder) were mixed in a mass ratio of NCA:AB:PVdF = 95:2.5:2.5, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added and stirred to prepare a cathode slurry. The cathode slurry was applied to both sides of an Al foil serving as a cathode current collector, and the coating was dried and then rolled to form a cathode mixture layer on both sides of the Al foil.

[0048] [Preparation of electrolyte] An electrolyte solution was prepared by adding LiPF6 as a lithium salt to 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, and further adding sodium ethyl sulfate (NaES) as an additive. The concentration of LiPF6 in the nonaqueous electrolyte was 1.0 mol / L, and the concentration of NaES was 1 mass%.

[0049] The total volume of EC and FEC in the mixed solvent was kept constant, and the ratio of the volume of EC Vec to the volume of FEC Vfec: Vec / Vfec was changed as shown in Table 1.

[0050] [Secondary battery production] A lead tab was attached to each electrode, and the positive and negative electrodes were spirally wound with a separator between them so that the leads were positioned at the outermost periphery to produce an electrode assembly. The electrode assembly was inserted into an exterior case made of a laminate film with an aluminum foil barrier layer, and vacuum dried at 105°C for 2 hours. After that, a nonaqueous electrolyte was poured into the exterior case, and the opening of the exterior case was sealed to produce secondary batteries A1 to A3.

[0051] <Examples 4 to 7> Secondary batteries A4 to A7 were fabricated in the same manner as in Examples 1 to 3, except that lithium fluorosulfonate (FSO3Li) was further added to the electrolyte solution as an additive, the concentration of FSO3Li in the non-aqueous electrolyte solution was 1 mass %, and the Vec / Vfec ratio was changed as shown in Table 1.

[0052] <Comparative Examples 1 to 5> Secondary batteries B1 to B5 were fabricated 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.

[0053] <Comparative Example 6> A 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 1 mass %.

[0054] <Comparative Example 7> A secondary battery B7 was fabricated 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.

[0055] [evaluation] (Capacity maintenance rate) Each completed battery was placed in a 25°C environment and subjected to constant current charging at a current of 0.3 It until the voltage reached 4.2 V, and then constant voltage charging at a constant voltage of 4.2 V until the current reached 0.02 It. Subsequently, constant current discharging was performed at a current of 0.5 It until the voltage reached 2.5 V, and the initial capacity C0 was calculated. Charging and discharging were performed in a 25°C environment.

[0056] The rest period between charges and discharges was 10 minutes, and the charge-discharge cycle was repeated 200 times under the above conditions at 25°C. The discharge capacity C1 at the 200th cycle was calculated. The percentage value of the ratio R1 = C1 / C0 of the discharge capacity C1 to the initial capacity C0 was calculated as the capacity retention rate. The results are shown in Table 1.

[0057] (Quick charging index (reaction resistance component)) The reaction resistance of the battery at 100% charge (SOC 100%) in a 25°C environment was determined by AC impedance measurement.

[0058] [Table 1]

[0059] In Table 1, for batteries B1 to B6 that do not contain NaES, the R1 value (79.8 to 81 (fluctuation range: 1.2)) hardly changes even when the Vec / Vfec ratio is changed. As the Vec / Vfec ratio decreases (i.e., as the proportion of FEC increases), only a slight improvement is observed. On the other hand, for batteries B7 and A1 to A3 that contain NaES, as the Vec / Vfec ratio decreases, the R1 value improves from 79.9 to 84.1 (fluctuation range: 4.2). Furthermore, for batteries A4 to A7 that also contain lithium fluorosulfonate, the R1 value improves even more significantly, to 85.0.

[0060] Comparing batteries B1 to B7 in Table 1, battery B7 containing NaES has a rapid charge index of 1.00, which is significantly improved compared to batteries B1 to B6 not containing NaES. It can also be seen that batteries B1 to B6 not containing NaES show almost no change in their rapid charge index even when the Vec / Vfec ratio is changed. On the other hand, batteries A1 to A3 containing NaES maintain the rapid charge index at the same level as battery B7. In other words, batteries A1 to A3 have improved durability while reducing the positive electrode resistance, similar to battery B7. Furthermore, batteries A4 to A7 have further improved durability despite further reduced positive electrode resistance.

[0061] A comparison of batteries B5 and B6 shows that adding lithium fluorosulfonate (FSO3Li) alone as an additive has almost no effect on the R1 value or fast charge index, whereas a comparison of batteries A3 and A7 shows that using NaES and lithium fluorosulfonate together significantly increases the R1 value and improves the fast charge index. [Industrial Applicability]

[0062] The nonaqueous electrolyte secondary battery according to the present disclosure is useful for applications requiring high-speed charging performance and durability, such as the main power source for mobile communication devices, portable electronic devices, electric vehicles, hybrid vehicles, and the like. [Explanation of symbols]

[0063] 1 electrode group 2 positive leads 3 Negative lead 4 Battery case 5 Sealing plate 6 Negative terminal 7 Gasket 8. Seal

Claims

1. a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte; The electrolyte solution contains a compound of formula (1): (R—O—SO 3 ) n X1 The organic sulfate is represented by where R is an organic group having one or more carbon atoms, X1 is a cation, and n is an integer of 1 to 3. The content of the organic sulfate contained in the electrolytic solution is 0.1% by mass or more and 5% by mass or less, The electrolyte solution further contains ethylene carbonate and fluoroethylene carbonate, The volume V of the ethylene carbonate and the volume V of the fluoroethylene carbonate are A non-aqueous electrolyte secondary battery that satisfies 0.1≦Vec / Vfec≦4.

2. 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein 0.1≦Vec / Vfec≦2 is satisfied.

3. The X1 is an alkali metal ion or NH 4 ＋ 3. The nonaqueous electrolyte secondary battery according to claim 1, wherein

4. 4. The nonaqueous electrolyte secondary battery according to claim 1, wherein R is an alkyl group having 1 to 6 carbon atoms.

5. 5. The nonaqueous electrolyte secondary battery according to claim 4, wherein R is a methyl group or an ethyl group.

6. The electrolyte solution further comprises a compound represented by the formula (2): (F-SO 3 ) ｍ X2 and a fluorosulfonate salt represented by wherein X2 is a cation and m is an integer of 1 to 3; 6. The nonaqueous electrolyte secondary battery according to claim 1, wherein the content of the fluorosulfonate in the electrolyte is 0.5% by mass or more and 5% by mass or less.

7. The X2 is an alkali metal ion or NH 4 ＋ 7. The nonaqueous electrolyte secondary battery according to claim 6, wherein

8. 8. The nonaqueous electrolyte secondary battery according to claim 1, wherein the positive electrode contains a lithium-containing composite oxide having a layered rock salt crystal structure and in which 80 atomic % or more of the metals other than lithium is nickel.

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