Non-aqueous electrolyte secondary battery

Abstract

A nonaqueous electrolyte secondary battery which is provided with a positive electrode, a negative electrode and a nonaqueous electrolyte, wherein: the positive electrode contains a positive electrode active material; the positive electrode active material contains a lithium transition metal composite oxide that contains Ni, Mn and Al; the content ratios of Ni, Mn and Al relative to the metal elements other than Li contained in the lithium transition metal composite oxide are 50% by atom or more, 10% by atom or less and 10% by atom or less, respectively; in cases where the lithium transition metal composite oxide contains Co, the content ratio of Co relative to the metal elements other than Li is 1.5% by atom or less; and the nonaqueous electrolyte contains a fluorosulfonic acid salt.

Description

[Technical Field]

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

[0002] A non-aqueous electrolyte secondary battery, such as a lithium ion secondary battery, comprises a positive electrode, a negative electrode, and a non-aqueous electrolyte. Attempts have been made to improve the components of the battery in order to ensure excellent characteristics of the non-aqueous electrolyte secondary battery.

[0003] Patent Document 1 proposes a non-aqueous electrolyte solution containing a compound (A) having an organic group having 1 to 20 carbon atoms, which may have a substituent on the nitrogen atom of isocyanuric acid, and a nitrile compound, an isocyanate compound, a difluorophosphate compound, a fluorosulfonate, or the like.

[0004] Patent Document 2 discloses a compound of Formula 1: Li x Ni 1-y-z-v-w Co y Al z M 1 v M 2 w The lithium-containing composite oxide is represented by O2, and the element M in formula 1 1 is at least one element selected from the group consisting of Mn, Ti, Y, Nb, Mo and W, and the element M 2 are at least two elements selected from the group consisting of Mg, Ca, Sr and Ba, and the element M 2 contains at least Mg and Ca, and Formula 1 satisfies 0.97≦x≦1.1, 0.05≦y≦0.35, 0.005≦z≦0.1, 0.0001≦v≦0.05, and 0.0001≦w≦0.05; the composite oxide is composed of primary particles that aggregate to form secondary particles, and the average particle size of the primary particles of the composite oxide is 0.1 μm or more and 3 μm or less, and the average particle size of the secondary particles of the composite oxide is 8 μm or more and 20 μm or less. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-194930 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-310181 Summary of the Invention [Problem to be solved by the invention]

[0006] The price of Co in lithium transition metal composite oxides has been rising in recent years. Reducing the Co content in lithium transition metal composite oxides is cost-effective, but it also reduces the cycle performance of non-aqueous electrolyte secondary batteries. This is thought to be because the lattice structure of the lithium transition metal composite oxide becomes unstable, accelerating degradation due to side reactions. [Means for solving the problem]

[0007] One aspect of the present disclosure relates to a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode includes a positive electrode active material, and the positive electrode active material includes a lithium transition metal composite oxide including Ni, Mn, and Al, and the proportions of Ni, Mn, and Al among metal elements other than Li contained in the lithium transition metal composite oxide are 50 atomic % or more of Ni, 10 atomic % or less of Mn, and 10 atomic % or less of Al, respectively, and when the lithium transition metal composite oxide contains Co, the proportion of Co among the metal elements other than Li is 1.5 atomic % or less, and the non-aqueous electrolyte includes a fluorosulfonate. [Effects of the Invention]

[0008] Even when using a lithium transition metal composite oxide that does not contain Co or a lithium transition metal composite oxide that has a low Co content, a non-aqueous electrolyte secondary battery with excellent cycle characteristics can be provided.

[0009] The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present application, will be better understood from the following detailed description taken in conjunction with the drawings. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a partially cutaway schematic perspective view of a nonaqueous electrolyte secondary battery according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0011] The non-aqueous electrolyte secondary battery according to the present disclosure includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode includes a positive electrode active material. The positive electrode active material includes a lithium transition metal composite oxide containing Ni, Mn, and Al.

[0012] If the Co content of a lithium-containing composite oxide can be reduced and the Ni content increased, it would be cost-effective and would ensure high capacity. Therefore, the Ni content is increased in the lithium transition metal composite oxide according to the present disclosure. On the other hand, the lithium transition metal composite oxide according to the present disclosure does not contain Co, or the proportion of Co in the metal elements other than Li is limited to 1.5 atomic % or less. Hereinafter, the lithium transition metal composite oxide according to the present disclosure will also be referred to as the "composite oxide NMA."

[0013] The proportions of Ni, Mn, and Al among the metal elements other than Li contained in the composite oxide NMA are Ni: 50 atomic % or more, Mn: 10 atomic % or less, and Al: 10 atomic % or less, respectively, and the composite oxide NMA does not contain Co, or the proportion of Co among the metal elements other than Li is 1.5 atomic % or less.

[0014] Mn and Al contribute to stabilizing the crystalline structure of the NMA composite oxide with a reduced Co content. However, because the Co content of the NMA composite oxide is limited to 1.5 atomic % or less and the Ni content is high, the crystalline structure is prone to instability, and metals such as Al and Ni can be eluted from the NMA composite oxide. The elution of metals reduces the positive electrode capacity and cycle characteristics (or capacity retention). In particular, in NMA composite oxides with a high Ni content, the eluted Ni forms an oxide coating on the particle surface of the NMA composite oxide that prevents the absorption and release of Li ions, which can lead to an increase in internal resistance. Furthermore, the eluted metals can precipitate on the negative electrode, affecting the durability of the secondary battery.

[0015] In view of the above, the present disclosure uses a composite oxide NMA and a nonaqueous electrolyte containing fluorosulfonate. It is believed that the anions generated by the fluorosulfonate form a strong coating with Al on the surface of the composite oxide NMA particles, suppressing metal elution. This ensures excellent cycle performance and also suppresses the increase in internal resistance during repeated charge / discharge cycles. Furthermore, because the coating derived from the fluorosulfonate has excellent ionic conductivity, it is believed that while it is strong, it only has a minor effect on inhibiting electrode reactions.

[0016] The nonaqueous electrolyte may further contain an isocyanurate ester component having at least one unsaturated organic group having an unsaturated carbon-carbon bond. The isocyanurate ester component forms a coating on the particle surface of the composite oxide NMA that suppresses side reactions. This ensures better cycle characteristics and further suppresses increases in internal resistance. However, if the isocyanurate ester component is used alone, the coating may be formed too thick, which may increase resistance to ion conduction. In contrast, a coating derived from a combination of a fluorosulfonate and an isocyanurate ester component has excellent ionic conductivity. In other words, the fluorosulfonate also has the effect of improving the ionic conductivity of the coating derived from the isocyanurate ester component.

[0017] However, even when fluorosulfonates are combined with lithium transition metal composite oxides with a higher Co content than the composite oxide NMA, the effects of improving cycle characteristics and suppressing increases in internal resistance are not significantly achieved. Fluorosulfonates are most pronounced when combined with the composite oxide NMA. The reason for the significant effect in the composite oxide NMA is thought to be that the composite oxide NMA has a higher resistance and relatively fragile particles compared to lithium transition metal composite oxides with a higher Co content. Particles of the composite oxide NMA are prone to cracking and significant metal elution, which can significantly increase resistance during charge and discharge. Therefore, the coating derived from fluorosulfonates significantly improves the properties of the composite oxide NMA. On the other hand, lithium transition metal composite oxides with a higher Co content are superior in this respect, so the need for fluorosulfonates is reduced.

[0018] Each component of the nonaqueous electrolyte secondary battery of the present disclosure will be described in more detail below.

[0019] [Positive electrode] The positive electrode contains a positive electrode active material. The positive electrode typically includes a positive electrode current collector and a layer of positive electrode mixture (hereinafter referred to as a positive electrode mixture layer) held on the positive electrode current collector. The positive electrode mixture layer can be formed by applying a positive electrode slurry, in which the components of the positive electrode mixture are dispersed in a dispersion medium, to the surface of the positive electrode current collector and drying the applied layer. The dried coating may be rolled if necessary.

[0020] The positive electrode mixture contains a positive electrode active material as an essential component, and may contain a binder, a thickener, a conductive agent, and the like as optional components.

[0021] (Cathode active material) The positive electrode active material includes a composite oxide NMA. The composite oxide NMA contains Ni, Mn, and Al, and may contain a trace amount of Co or may be Co-free. From the perspective of reducing production costs, a lower Co content is desirable, and the proportion of Co in the metal elements other than Li is 1.5 atomic % or less, preferably 1.0 atomic % or less, more preferably 0.5 atomic % or less, and most preferably no Co. On the other hand, from the perspective of increasing capacity, the proportions of Ni, Mn, and Al in the metal elements other than Li in the composite oxide NMA are Ni: 50 atomic % or more, Mn: 10 atomic % or less, and Al: 10 atomic % or less, respectively. The Ni content in the metal elements other than Li is preferably 80 atomic % or more, more preferably 90 atomic % or more, and may be 92 atomic % or more. The Mn content may be 7 atomic % or less, 5 atomic % or less, or 3 atomic % or less. The Al content may be 9 atomic % or less, 7 atomic % or less, or 5 atomic % or less. The composite oxide NMA has, for example, a layered crystal structure (for example, a rock salt type crystal structure).

[0022] The composite oxide NMA is, for example, a compound represented by the formula: Li α Ni (1-x1-x2-y-z) Co x1 Mn x2 Al y M z O 2+β The element M is an element other than Li, Ni, Mn, Al, Co, and oxygen.

[0023] In the above formula, α, which represents the atomic ratio of lithium, is, for example, 0.95≦α≦1.05. α increases or decreases with charge and discharge. In (2+β), which represents the atomic ratio of oxygen, β satisfies −0.05≦β≦0.05.

[0024] The atomic ratio of Ni, 1 - x1 - x2 - y - z(=v), is, for example, 0.5 or more, may be 0.8 or more, may be 0.90 or more, and may be 0.92 or more. Also, v representing the atomic ratio of Ni may be 0.95 or less. v may be 0.5 or more and 0.95 or less (0.5 ≤ v ≤ 0.95), may be 0.80 or more and 0.95 or less, may be 0.90 or more and 0.95 or less, and may be 0.92 or more and 0.95 or less.

[0025] The higher the atomic ratio v of Ni, the more lithium ions can be extracted from the composite oxide NMA during charging, and the higher the capacity can be increased. However, Ni in the composite oxide NMA with increased capacity in this way tends to have a higher valence. Also, when the atomic ratio of Ni increases, the atomic ratios of other elements relatively decrease. In this case, particularly in the fully charged state, the crystal structure tends to become unstable, and it easily inactivates by changing to a crystal structure where reversible intercalation and deintercalation of lithium ions are difficult due to repeated charge and discharge. As a result, the cycle characteristics tend to deteriorate. In the non-aqueous electrolyte secondary battery according to the present disclosure, excellent cycle characteristics can be ensured by using a non-aqueous electrolyte containing a fluorosulfonic acid component, even when using a composite oxide NMA with a high Ni content like this.

[0026] x1 representing the atomic ratio of Co is, for example, 0.015 or less (0 ≤ x1 ≤ 0.015), may be 0.01 or less, and may be 0.005 or less. When x1 is 0, the case where Co is below the detection limit is included.

[0027] x2 representing the atomic ratio of Mn is, for example, 0.1 or less (0 < x2 ≤ 0.1), may be 0.07 or less, may be 0.05 or less, and may be 0.03 or less. x2 may be 0.01 or more and may be 0.02 or more. Mn contributes to the stabilization of the crystal structure of the composite oxide NMA, and it is advantageous for cost reduction because the composite oxide NMA contains inexpensive Mn.

[0028] The y representing the atomic ratio of Al is, for example, 0.1 or less (0 < y ≤ 0.1), and may be 0.09 or less, may be 0.07 or less, or may be 0.05 or less. y may also be 0.01 or more, or may be 0.02 or more. Al contributes to the stabilization of the crystal structure of the composite oxide NMA. Also, it is preferable to satisfy 0.05 ≤ x2 + y ≤ 0.1. In this case, the effect of the fluorosulfonate and the effect of suppressing the increase in internal resistance after repeated charge and discharge are further manifested.

[0029] The z representing the atomic ratio of element M is, for example, 0 ≤ z ≤ 0.10, and may be 0 < z ≤ 0.05, or may be 0.001 ≤ z ≤ 0.005.

[0030] Element M may be at least one selected from the group consisting of Ti, Zr, Nb, Mo, W, Fe, Zn, B, Si, Mg, Ca, Sr, Sc, and Y. Among them, when at least one selected from the group consisting of Nb, Sr, and Ca is contained in the composite oxide MNA, it is considered that the surface structure of the composite oxide NMA is stabilized, the resistance is reduced, and the elution of the metal is further suppressed. It is more effective that element M is unevenly distributed in the vicinity of the particle surface of the composite oxide NMA.

[0031] The content of the elements constituting the composite oxide NMA can be measured by an inductively coupled plasma atomic emission spectrometer (ICP - AES), an electron probe micro analyzer (EPMA), an energy dispersive X - ray spectrometer (EDX), or the like.

[0032] The composite oxide NMA is, for example, secondary particles in which a plurality of primary particles are aggregated. The particle size of the primary particles is generally 0.05 μm or more and 1 μm or less. The average particle size of the secondary particles of the composite oxide is, for example, 3 μm or more and 30 μm or less, and may be 5 μm or more and 25 μm or less.

[0033] In this specification, the average particle size of secondary particles refers to the particle size (volume average particle size) at which the volume cumulative value is 50% in the particle size distribution measured by laser diffraction scattering. This particle size is sometimes referred to as D50. For example, an "LA-750" manufactured by HORIBA Ltd. can be used as a measuring device.

[0034] The composite oxide NMA can be obtained, for example, by the following procedure. First, a solution containing an alkali such as sodium hydroxide is added dropwise to a stirred solution of salts containing the metal elements that constitute the composite oxide NMA, and the pH is adjusted to the alkaline side (e.g., 8.5 to 12.5), thereby precipitating a composite hydroxide containing metal elements (Ni, Mn, Al, and optionally Co, and optionally element M). Next, the composite hydroxide is calcined to obtain a composite oxide containing the metal elements (hereinafter also referred to as the "raw composite oxide"). The calcination temperature is not particularly limited, but is, for example, 300°C to 600°C.

[0035] Next, the raw composite oxide, a lithium compound, and optionally a compound containing element M are mixed, and the mixture is calcined under an oxygen stream to obtain the composite oxide NMA. The calcination temperature is not particularly limited, but is, for example, 450° C. or higher and 800° C. or lower. Each calcination may be carried out in one step, in multiple steps, or while increasing the temperature.

[0036] When mixing the raw composite oxide with the lithium compound, by mixing a compound containing element M, it is possible to cause element M to be unevenly distributed in the vicinity of the particle surfaces of the composite oxide NMA.

[0037] As the lithium compound, lithium oxide, lithium hydroxide, lithium carbonate, lithium halide, lithium hydrate, etc. may be used.

[0038] The positive electrode active material may contain a lithium transition metal composite oxide other than the composite oxide NMA, but preferably contains a higher proportion of the composite oxide NMA. The proportion of the composite oxide NMA in the positive electrode active material is, for example, 90% by mass or more, and may be 95% by mass or more. The proportion of the composite oxide in the positive electrode active material is 100% by mass or less.

[0039] (others) As the binder, for example, a resin material is used. Examples of the binder include fluororesin, polyolefin resin, polyamide resin, polyimide resin, acrylic resin, vinyl resin, and rubber-like material (for example, styrene butadiene copolymer (SBR)). One type of binder may be used alone, or two or more types may be used in combination.

[0040] Examples of thickeners include cellulose derivatives such as cellulose ether. Examples of cellulose derivatives include carboxymethyl cellulose (CMC) and its modified forms, methyl cellulose, etc. One type of thickener may be used alone, or two or more types may be used in combination.

[0041] Examples of conductive agents include conductive fibers and conductive particles. Examples of conductive fibers include carbon fibers, carbon nanotubes, and metal fibers. Examples of conductive particles include conductive carbon (carbon black, graphite, etc.) and metal powder. One type of conductive agent may be used alone, or two or more types may be used in combination.

[0042] The dispersion medium used in the positive electrode slurry is not particularly limited, but examples thereof include water, alcohol, N-methyl-2-pyrrolidone (NMP), and mixed solvents thereof.

[0043] The positive electrode current collector may be, for example, a metal foil. The positive electrode current collector may be porous. Examples of porous current collectors include nets, punched sheets, and expanded metals. Examples of materials for the positive electrode current collector include stainless steel, aluminum, aluminum alloys, and titanium. The thickness of the positive electrode current collector is not particularly limited, but may be, for example, 1 to 50 μm, or 5 to 30 μm.

[0044] [Negative electrode] The negative electrode contains a negative electrode active material. The negative electrode typically includes a negative electrode current collector and a layer of a negative electrode mixture (hereinafter referred to as a negative electrode mixture layer) held on the negative electrode current collector. The negative electrode mixture layer can be formed by applying a negative electrode slurry, in which the components of the negative electrode mixture are dispersed in a dispersion medium, to the surface of the negative electrode current collector and drying the slurry. The dried coating may be rolled, if necessary.

[0045] The negative electrode mixture contains a negative electrode active material as an essential component, and may contain a binder, a thickener, a conductive agent, and the like as optional components.

[0046] (Negative electrode active material) The negative electrode active material may be metallic lithium, a lithium alloy, or the like, but is preferably a material capable of electrochemically absorbing and releasing lithium ions. Examples of such materials include carbonaceous materials and Si-containing materials. The negative electrode may contain one type of negative electrode active material or a combination of two or more types.

[0047] Examples of carbonaceous materials include graphite, easily graphitizable carbon (soft carbon), and non-graphitizable carbon (hard carbon). One type of carbonaceous material may be used alone, or two or more types may be used in combination.

[0048] Among these, graphite is preferred as the carbonaceous material because of its excellent charge / discharge stability and low irreversible capacity. Examples of graphite include natural graphite, artificial graphite, and graphitized mesophase carbon particles.

[0049] Examples of Si-containing materials include elemental Si, silicon alloys, silicon compounds (such as silicon oxides), and composite materials in which silicon phases are dispersed within a lithium ion conductive phase (matrix). Examples of silicon oxides include SiO x The lithium ion conductive phase may be at least one selected from the group consisting of an SiO2 phase, a silicate phase, and a carbon phase.

[0050] As the binder, thickener, conductive agent and dispersion medium used in the negative electrode slurry, for example, the materials exemplified for the positive electrode can be used.

[0051] The negative electrode current collector may be, for example, a metal foil. The negative electrode current collector may be porous. Examples of the material for the negative electrode current collector include stainless steel, nickel, nickel alloy, copper, and copper alloy. The thickness of the negative electrode current collector is not particularly limited, but may be, for example, 1 to 50 μm, or 5 to 30 μm.

[0052] [Non-aqueous electrolyte] The non-aqueous electrolyte usually contains a non-aqueous solvent and a lithium salt.

[0053] (fluorosulfonate) The non-aqueous electrolyte is represented by the formula (1):

[0054] [ka]

[0055] In formula (1), X is a cation.

[0056] The fluorosulfonate may be at least one selected from the group consisting of FSO3Li (lithium fluorosulfonate) and FSO3Na (sodium fluorosulfonate). Among these, FSO3Li (lithium fluorosulfonate), which is a lithium salt, is preferred. Note that the fluorosulfonate may generate a fluorosulfonate anion in the non-aqueous electrolyte. Therefore, the fluorosulfonate anion is counted as a fluorosulfonate.

[0057] The content of fluorosulfonate in the non-aqueous electrolyte may be 3% by mass or less, 1.5% by mass or less, 1% by mass or less, or 0.5% by mass or less. When the content of fluorosulfonate is within this range, excessive film formation on the positive electrode surface is suppressed, and the effect of suppressing an increase in internal resistance during repeated charge and discharge can be enhanced. In a non-aqueous electrolyte secondary battery, the content of fluorosulfonate in the non-aqueous electrolyte changes during storage or charge and discharge. Therefore, it is sufficient that the fluorosulfonate remains in the non-aqueous electrolyte sampled from the non-aqueous electrolyte secondary battery at a concentration above the detection limit. The content of fluorosulfonate in the non-aqueous electrolyte may be 0.01% by mass or more.

[0058] The content of fluorosulfonate in the non-aqueous electrolyte used in the manufacture of a non-aqueous electrolyte secondary battery may be 0.01% by mass or more, 0.1% by mass or more, or 0.3% by mass or more. The content of fluorosulfonate in the non-aqueous electrolyte used in the manufacture of a non-aqueous electrolyte secondary battery may be, for example, 1.5% by mass or less, 1% by mass or less, or 0.5% by mass or less. These lower and upper limits can be combined in any manner.

[0059] (Isocyanuric acid ester component) The non-aqueous electrolyte may further include an isocyanurate ester component having at least one unsaturated organic group having an unsaturated carbon-carbon bond. The unsaturated organic group is bonded to, for example, at least one of the three nitrogen atoms constituting the isocyanuric acid ring. The isocyanurate ester component may have the unsaturated organic group on two or three of the three nitrogen atoms constituting the isocyanuric acid ring.

[0060] The isocyanurate component may be, for example, a compound represented by formula (2):

[0061] [ka] It is shown as follows.

[0062] where R 1 ~R 3 are each a hydrogen atom, a halogen atom, or an organic group, and R 1 ~R 3 At least one of R is an unsaturated organic group having an unsaturated carbon-carbon bond. 1 ~R 3 At least two of them may be the same, or all of them may be different.

[0063] R 1 ~R 3 Examples of the halogen atom represented by the formula (I) include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. Examples of the organic group include an organic group having 1 to 20 carbon atoms. Examples of the organic group include a hydrocarbon group, an alkoxy group, an alkoxycarbonyl group, an acyl group, and a nitrile group, which may have a substituent. The alkoxy group is represented by the formula (I) a -O-, and the alkoxycarbonyl group is represented by R a -OC(=O)-, and the acyl group is R a In these groups, R a is a hydrocarbon group which may have a substituent.

[0064] R 1 ~R 3and R a The hydrocarbon group represented by the formula (I) may be an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, or an aromatic hydrocarbon group. Examples of the aliphatic hydrocarbon group include an alkyl group, an alkenyl group, an alkynyl group, and a dienyl group. The aliphatic hydrocarbon group may be either linear or branched. The number of carbon atoms in the aliphatic hydrocarbon group is, for example, 1 to 20, or may be 1 to 10, 1 to 6, or 1 to 4. Examples of the alicyclic hydrocarbon group include a cycloalkyl group, a cycloalkenyl group, and a cycloalkadienyl group. The number of carbon atoms in the alicyclic hydrocarbon group is, for example, 4 to 20, or may be 5 to 10, 5 to 8, or 5 to 6. Alicyclic hydrocarbon groups also include fused rings in which aromatic rings such as a benzene ring and a pyridine ring are fused. Examples of the aromatic hydrocarbon group include an aryl group. Examples of the aryl group include a phenyl group, a naphthyl group, and a biphenyl group. The number of carbon atoms in the aromatic hydrocarbon group is, for example, 6 to 20, and may be 6 to 14 or 6 to 10. The aromatic hydrocarbon group also encompasses a fused ring in which a non-aromatic hydrocarbon ring or a non-aromatic heterocyclic ring is fused. The hydrocarbon ring or heterocyclic ring may be 4 to 8 members, 5 to 8 members, or 5 or 6 members.

[0065] Examples of alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, hexyl, 2-ethylhexyl, decyl, tetradecyl, and stearyl. Examples of alkenyl groups include vinyl, allyl, prop-2-en-1-yl, 4-hexenyl, and 5-hexenyl. Examples of alkynyl groups include ethynyl and propargyl. Examples of dienyl groups include 1,3-butadien-1-yl. Examples of cycloalkyl groups include cyclopentyl, cyclohexyl, and cyclooctyl. Examples of cycloalkenyl groups include cyclohexenyl and cyclooctenyl. Examples of cycloalkadienyl groups include cyclopentadienyl.

[0066] Examples of substituents that the hydrocarbon group may have include a halogen atom, a hydroxy group, an alkyl group, an alkenyl group, a dienyl group, an aryl group, an aralkyl group, an alkoxy group, an alkoxycarbonyl group, an acyl group, an acyloxy group, a nitrile group, and an oxo group (═O). Examples of halogen atoms include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. The alkyl group and the alkoxy group have, for example, 1 to 6 carbon atoms, and may have 1 to 4 carbon atoms. The alkenyl group, the alkoxycarbonyl group, the acyl group, and the acyloxy group have, for example, 2 to 6 carbon atoms, and may have 2 to 4 carbon atoms. The dienyl group has, for example, 4 to 8 carbon atoms. Examples of aryl groups include aryl groups having 6 to 10 carbon atoms, such as a phenyl group. Examples of aralkyl groups include aralkyl groups having 7 to 12 carbon atoms, such as a benzyl group and a phenethyl group. The hydrocarbon group may have one or more of these substituents. When the hydrocarbon group has two or more substituents, at least two of the substituents may be the same, or all of the substituents may be different.

[0067] The unsaturated organic group may have an unsaturated carbon-carbon bond. Examples of unsaturated carbon-carbon bonds include carbon-carbon double bonds and carbon-carbon triple bonds. Examples of unsaturated organic groups include, among the organic groups exemplified above, alkenyl groups, alkynyl groups, dienyl groups, cycloalkenyl groups, cycloalkadienyl groups, and aryl groups. From the viewpoint of excellent film-forming properties on the positive electrode, alkenyl groups, alkynyl groups, and aryl groups are preferred, with alkenyl groups and alkynyl groups being more preferred. Preferred alkenyl groups include vinyl groups and allyl groups. Preferred alkynyl groups include propargyl groups. The alkenyl groups, alkynyl groups, and aryl groups also include those having the above-mentioned substituents. Examples of the substituents that the alkenyl groups and alkynyl groups may have include, among the above-mentioned substituents, halogen atoms, hydroxy groups, aryl groups, aralkyl groups, alkoxy groups, alkoxycarbonyl groups, acyl groups, acyloxy groups, and nitrile groups. Among these, an isocyanurate component having two or three groups selected from the group consisting of alkenyl groups and alkynyl groups is preferred, and triallyl isocyanurate and diallyl isocyanurate are preferred. Triallyl isocyanurate (TIC) and diallyl isocyanurate (DIC) are respectively represented by the following formulas:

[0068] [ka]

[0069] The content of the isocyanuric acid ester component in the non-aqueous electrolyte is preferably 1.5% by mass or less, and may be 1% by mass or less, or 0.5% by mass or less. When the content of the isocyanuric acid ester component is within this range, excessive film formation on the positive electrode surface is suppressed, and the effect of suppressing an increase in internal resistance during repeated charge and discharge can be enhanced. In a non-aqueous electrolyte secondary battery, the content of the isocyanuric acid ester component in the non-aqueous electrolyte changes during storage or charge and discharge. Therefore, it is sufficient that the isocyanuric acid ester component remains in the non-aqueous electrolyte sampled from the non-aqueous electrolyte secondary battery at a concentration equal to or greater than the detection limit. The content of the isocyanuric acid ester component in the non-aqueous electrolyte may be 0.01% by mass or more.

[0070] The content of the isocyanuric acid ester component in the non-aqueous electrolyte used in the production of a non-aqueous electrolyte secondary battery may be 0.01% by mass or more, 0.1% by mass or more, or 0.3% by mass or more. The content of the isocyanuric acid ester component in the non-aqueous electrolyte used in the production of a non-aqueous electrolyte secondary battery may be, for example, 1.5% by mass or less, 1% by mass or less, or 0.5% by mass or less. These lower and upper limits can be combined in any desired manner.

[0071] The contents of the fluorosulfonate and isocyanurate components in the non-aqueous electrolyte can be determined, for example, using gas chromatography under the following conditions. Equipment used: Manufactured by Shimadzu Corporation, GC-2010 Plus Column: J&W HP-1 (film thickness 1 μm, inner diameter 0.32 mm, length 60 m) Column temperature: Raise from 50°C to 90°C at a rate of 5°C / min, maintain at 90°C for 15 minutes, then raise from 90°C to 250°C at a rate of 10°C / min, maintain at 250°C for 15 minutes Split ratio: 1 / 50 Linear speed: 30.0cm / sec Inlet temperature: 270℃ Injection volume: 1μL Detector: FID 290℃ (sens.10 1 )

[0072] In the non-aqueous electrolyte, the mass ratio of the isocyanurate component to the fluorosulfonate (=isocyanurate component / fluorosulfonate) is, for example, preferably 0.5 to 1.5, and may be 0.8 to 1.2. When the mass ratio of both components is within this range, the composition of the coating film formed on the particle surface of the composite oxide NMA is well balanced. That is, a coating film is formed that has excellent ionic conductivity and is effective in suppressing metal elution and suppressing an increase in internal resistance during repeated charge and discharge.

[0073] (non-aqueous solvent) Examples of non-aqueous solvents include cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, and chain carboxylic acid esters. Examples of cyclic carbonates include propylene carbonate (PC) and ethylene carbonate (EC). 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 methyl formate, ethyl formate, propyl formate, methyl acetate (MA), ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate. The non-aqueous electrolyte may contain one type of non-aqueous solvent or a combination of two or more types.

[0074] (lithium salts) Examples of lithium salts include LiClO4, LiBF4, LiPF6, LiAlCl4, LiSbF6, LiSCN, LiCF3SO3, LiCF3CO2, LiAsF6, and LiB 10 Cl 10Examples of the borate include lithium bis(oxalato)borate, lithium difluorooxalatoborate, lithium bis(1,2-benzenediolate(2-)-O,O')borate, lithium bis(2,3-naphthalenediolate(2-)-O,O')borate, lithium bis(2,2'-biphenyldiolate(2-)-O,O')borate, and lithium bis(5-fluoro-2-oleate-1-benzenesulfonic acid-O,O')borate. Examples of imide salts include lithium bisfluorosulfonylimide (LiN(FSO2)2), lithium bistrifluoromethanesulfonyl imide (LiN(CF3SO2)2), lithium trifluoromethanesulfonyl nonafluorobutanesulfonyl imide (LiN(CF3SO2)(C4F9SO2)), lithium bispentafluoroethanesulfonyl imide (LiN(C2F5SO2)2), etc. The nonaqueous electrolyte may contain one type of lithium salt or a combination of two or more types.

[0075] The concentration of the lithium salt in the non-aqueous electrolyte (when the fluorosulfonate is lithium fluorosulfonate, the lithium salt other than lithium fluorosulfonate) is, for example, 0.5 mol / L or more and 2 mol / L or less.

[0076] The non-aqueous electrolyte may contain other additives. The other additives are referred to as the second component. Examples of the second component include at least one selected from the group consisting of vinylene carbonate, fluoroethylene carbonate, and vinylethylene carbonate.

[0077] [Separator] It is desirable to interpose a separator between the positive electrode and the negative electrode. The separator has high ion permeability and adequate mechanical strength and insulating properties. The separator may 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.

[0078] 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 laminated 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.

[0079] Hereinafter, the structure of a prismatic nonaqueous electrolyte secondary battery will be described as an example of the nonaqueous electrolyte secondary battery according to the present invention with reference to FIG.

[0080] The battery includes a bottomed, rectangular battery case 4, and an electrode group 1 and a nonaqueous electrolyte (not shown) 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 edge 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.

[0081] The present invention will be specifically described below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0082] [Example]

[0083] Examples 1 to 4 and Comparative Examples 1 to 5 A non-aqueous electrolyte secondary battery was fabricated and evaluated according to the following procedure. (1) Preparation of the positive electrode 95 parts by mass of the positive electrode active material particles were mixed with 2.5 parts by mass of acetylene black, 2.5 parts by mass of polyvinylidene fluoride, and an appropriate amount of NMP to obtain a positive electrode slurry. Next, the positive electrode slurry was applied to the surface of an aluminum foil, the coating was dried, and then rolled to form a positive electrode mixture layer (thickness 95 μm, density 3.6 g / cm) on both sides of the aluminum foil. 3 ) was formed to obtain a positive electrode.

[0084] The positive electrode active material particles were prepared by the following procedure. An aqueous solution was prepared by dissolving nickel sulfate, aluminum sulfate, and, if necessary, cobalt sulfate or manganese sulfate. The concentration of nickel sulfate in the aqueous solution was set to 1 mol / L, and the concentrations of the other sulfates were adjusted so that the relationship between the ratio of Ni and each metal element was the value shown in Table 1.

[0085] At 50°C, while stirring the aqueous solution, an aqueous solution containing 30% by mass of sodium hydroxide was added dropwise until the pH of the mixture reached 12, thereby precipitating hydroxide. The hydroxide was recovered by filtration, washed with water, and dried. The dried product was calcined at 500°C for 8 hours in a nitrogen atmosphere to obtain a composite oxide.

[0086] The obtained composite oxide, lithium hydroxide, and an oxide containing element M (specifically, niobium oxide or strontium oxide) as needed were mixed so that the atomic ratio of the sum of Li, Ni, Co, Mn, and Al to element M was 1:1:z (specifically, the value of z shown in Table 1). The mixture was fired in an oxygen atmosphere using an electric furnace by heating from room temperature to 650°C at a heating rate of 2.0°C / min. Thereafter, the mixture was fired by heating from 650°C to 715°C at a heating rate of 0.5°C / min. The fired product was washed with water and dried to obtain composite oxide NMA (positive electrode active material particles).

[0087] (2) Preparation of the negative electrode A silicon composite material and graphite were mixed in a mass ratio of 5:95 and used as the negative electrode active material. The negative electrode active material, a sodium salt of CMC (CMC-Na), SBR, and water were mixed in a predetermined mass ratio to prepare a negative electrode slurry. The negative electrode slurry was then 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.

[0088] (3) Preparation of non-aqueous electrolyte A nonaqueous electrolyte (electrolyte solution) was prepared by dissolving LiPF6 and, if necessary, a fluorosulfonate salt (first component) and an isocyanurate ester component (second component) shown in Table 1 in a mixed solvent of EC and EMC (EC:EMC = 3:7 (volume ratio)). The concentration of LiPF6 in the electrolyte solution was 1.0 mol / L. The concentrations (initial concentrations) of the first and second components in the prepared nonaqueous electrolyte were the values ​​(mass%) shown in Table 1.

[0089] (4) Fabrication of non-aqueous electrolyte secondary battery An Al positive electrode lead was attached to the positive electrode obtained above, and a Ni negative electrode lead was attached to the negative electrode obtained above. The positive electrode and negative electrode were spirally wound with a polyethylene thin film (separator) interposed therebetween in an inert gas atmosphere to produce a wound electrode assembly. The electrode assembly was housed in a bag-shaped exterior body formed of a laminate sheet having an Al layer, and the nonaqueous electrolyte was injected thereinto. The exterior body was then sealed to produce a nonaqueous electrolyte secondary battery. When the electrode assembly was housed in the exterior body, a portion of the positive electrode lead and the negative electrode lead were each exposed to the outside from the exterior body.

[0090] (5) Evaluation The nonaqueous electrolyte secondary batteries obtained in the examples and comparative examples were evaluated as follows. (a) Initial DC resistance (DCIR) In a temperature environment of 25°C, the battery was charged at a constant current of 0.3 It until the voltage reached 4.1 V, and then charged at a constant voltage of 4.1 V until the current reached 0.05 It. It was then discharged at a constant current of 0.3 It for 100 minutes to bring the state of charge (SOC) to 50%.

[0091] The voltage value was measured when a battery with an SOC of 50% was discharged for 10 seconds at current values ​​of 0 A, 0.1 A, 0.5 A, and 1.0 A. The relationship between the discharge current value and the voltage value after 10 seconds was approximated to a straight line using the least squares method, and the DCIR (initial DCIR) was calculated from the absolute value of the slope.

[0092] (b) Charge / discharge cycle test At an ambient temperature of 45°C, the battery was charged at a constant current of 0.5 It until the voltage reached 4.1 V, and then charged at a constant voltage of 4.1 V until the current reached 0.02 It. It was then discharged at a constant current of 0.5 It until the voltage reached 3.0 V. This cycle of charging and discharging was repeated 100 times.

[0093] (c) DCIR increase rate (ΔDCIR) The DCIR (DCIR at the 100th cycle) was calculated in the same manner as in (a) above, except that the battery after 100 cycles of charge / discharge in the charge / discharge cycle test (b) above was used. The ratio of the DCIR after 100 cycles to the initial DCIR was taken as the DCIR increase rate and calculated using the following formula. DCIR increase rate (%) = {(DCIR at 100th cycle - initial DCIR)} / initial DCIR × 100

[0094] (d) Capacity retention rate (MR) In the charge-discharge cycle test (b) above, the discharge capacity at the first cycle and the discharge capacity at the 100th cycle were measured, and the capacity retention rate was calculated using the following formula and used as an index of cycle characteristics. Capacity retention rate (%) = (discharge capacity at 100th cycle / discharge capacity at 1st cycle) x 100

[0095] The evaluation results are shown in Table 1. In Table 1, E1 to E4 are Examples 1 to 4, and C1 to C5 are Comparative Examples 1 to 5.

[0096] [Table 1]

[0097] First, a comparison of C1 and C4 shows that when using the composite oxide NMA, which does not contain Co (C1), and when using a composite oxide with a relatively high Co content (C4), the capacity retention rate (MR) decreases by 2.1% (85.5% to 83.4%) and the DCIR increase rate (ΔDCIR) increases significantly by 4.6% (29.8% to 34.4%).

[0098] Next, comparing C1 and E1, E1, which uses a non-aqueous electrolyte containing the first component, shows a significant increase in capacity retention (MR) of 5.7% (83.4% → 89.1%) and a reduction in DCIR increase rate (ΔDCIR) of 16.1% (34.4% → 18.3%). Similarly, E2 to E4 also show a significant increase in capacity retention (MR) and a significant reduction in DCIR increase rate (ΔDCIR). Furthermore, E1 to E4 also show an excellent balance between capacity retention rate (MR) and DCIR increase rate (ΔDCIR).

[0099] On the other hand, a comparison between C4 and C5 shows that in C5, which uses a non-aqueous electrolyte containing the first component, the capacity retention rate (MR) increases by only 1.5% (85.5% → 87.0%) and the DCIR increase rate (ΔDCIR) decreases by only 4.7% (29.8% → 25.1%) compared to C4.

[0100] In other words, when using the composite oxide NMA that does not contain Co, using a non-aqueous electrolyte containing the first component makes the effect of the first component more pronounced than when using a composite oxide that contains a relatively large amount of Co. Compared with C1 to C3, using the element M (Nb, Sr) improves the capacity retention (MR) by 1.7% to 2.5% and reduces the DCIR increase rate (ΔDCIR) by 5.3% to 6.2%. [Industrial Applicability]

[0101] The nonaqueous electrolyte secondary battery of the present disclosure is useful as a main power source for mobile communication devices, portable electronic devices, etc. Furthermore, the nonaqueous electrolyte secondary battery has high capacity and excellent cycle characteristics, making it suitable for in-vehicle use. However, the uses of the nonaqueous electrolyte secondary battery are not limited to these.

[0102] While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention. [Explanation of symbols]

[0103] 1: electrode group, 2: positive electrode lead, 3: negative electrode lead, 4: battery case, 5: sealing plate, 6: negative electrode terminal, 7: gasket, 8: sealing plug

Claims

1. A positive electrode, a negative electrode, and a non-aqueous electrolyte, the positive electrode includes a positive electrode active material, the positive electrode active material includes a lithium transition metal composite oxide including Ni, Mn, and Al; The proportions of Ni, Mn, and Al in the metal elements other than Li contained in the lithium transition metal composite oxide are Ni: 50 atomic% or more, Mn: 10 atomic % or less, and Al: 10 atomic% or less and When the lithium transition metal composite oxide contains Co, the ratio of Co to the metal elements other than Li is 1.5 atomic % or less, the non-aqueous electrolyte contains a fluorosulfonate and an isocyanurate component having at least one unsaturated organic group having an unsaturated carbon-carbon bond; In the non-aqueous electrolyte, the mass ratio of the isocyanurate component to the fluorosulfonate is 0.5 to 1.

5.

2. The lithium transition metal composite oxide has the following formula: Li α Ni （１－ｘ１－ｘ２－ｙ－ｚ） Co ｘ１ Mn ｘ２ Al ｙ M ｚ O ２＋β wherein: ０．９５≦α≦１．０５、 0.5≦1-x1-x2-y-z≦0.95, 0≦x1≦0.015, 0<x2≦0.1, 0<y≦0.1, 0≦z≦0.1, and －０．０５≦β≦０．０５ Fulfilling 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein M is an element other than Li, Ni, Mn, Al, Co, and oxygen.

3. 3. The nonaqueous electrolyte secondary battery according to claim 2, wherein the element M is at least one selected from the group consisting of Ti, Zr, Nb, Mo, W, Fe, Zn, B, Si, Mg, Ca, Sr, Sc, and Y.

4. The fluorosulfonate is FSO 3 Li and FSO 3 4. The nonaqueous electrolyte secondary battery according to claim 1, wherein the nonaqueous electrolyte is at least one selected from the group consisting of Na.

5. 5. The non-aqueous electrolyte secondary battery according to claim 1, wherein the content of the fluorosulfonate in the non-aqueous electrolyte is 3 mass % or less.

6. 6. The nonaqueous electrolyte secondary battery according to claim 1, wherein the isocyanurate component includes at least one selected from the group consisting of triallyl isocyanurate and diallyl isocyanurate.

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