Non-aqueous electrolyte secondary battery

Abstract

A non-aqueous electrolyte secondary battery according to the present invention comprises: a positive electrode containing a positive electrode active material; a separator; a negative electrode opposing the positive electrode with the separator interposed therebetween; and a non-aqueous electrolytic solution. The non-aqueous electrolytic solution contains a non-aqueous solvent and 6-alkylthio-1,3,5-triazine-2,4-dithiol of which at least a portion is dissolved in the non-aqueous solvent, and the number of carbons of the alkyl group of the alkylthio group at the 6-position is preferably 1-8.

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, includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. In order to ensure excellent characteristics of the non-aqueous electrolyte secondary battery, attempts have been made to improve the components of the battery.

[0003] When metals such as copper and iron are present in a non-aqueous electrolyte secondary battery that utilizes an electrochemical oxidation-reduction reaction, dissolution and precipitation reactions of the metal occur, resulting in a drop in the battery voltage.

[0004] Meanwhile, in the field of metal surface treatment, it is known that dissolution and precipitation of metals can be suppressed by using a coating containing a metal complexing agent. The composition proposed in Patent Document 1 for application to a metal substrate includes a metal cation, a metal complexing agent, and an aqueous carrier, and the method for processing the substrate includes applying the composition to the substrate, drying the composition to form a conversion coating, and applying a coating onto the conversion coating.

[0005] Patent Document 2 proposes a lithium secondary battery that includes an electrode body formed by winding or stacking a positive electrode plate and a negative electrode plate with a separator interposed therebetween, and uses a non-aqueous electrolyte solution containing a lithium compound as an electrolyte, and is characterized in that an inhibitor that is an organic and / or inorganic Cu corrosion inhibitor, or an organic and / or inorganic Cu trapping agent is added to at least one of the positive electrode plate, the negative electrode plate, the separator, and the non-aqueous electrolyte solution.

[0006] Patent Document 3 proposes an electrolyte for a nonaqueous electrochemical device, which is characterized in that the nonaqueous electrolyte contains at least 6-substituted-1,3,5-triazine-2,4-dithiol and its derivatives, in a nonaqueous electrochemical device having at least two electrodes, a nonaqueous electrolyte in which a solute is dissolved in a nonaqueous solvent, and a separator interposed between the two electrodes. According to Patent Document 3, 6-substituted-1,3,5-triazine-2,4-dithiol is a coating known as organic plating, and has been used conventionally to provide mold releasability, to directly bond metals and polymers, and as a metal corrosion prevention technology. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Special Publication No. 2016-514770 [Patent Document 2] JP 2001-273927 A [Patent Document 3] JP 2001-110442 A Summary of the Invention

[0008] Complexing agents used in the field of metal surface treatment are difficult to use because they react with non-aqueous electrolytes or cause redox reactions on the electrode surface.

[0009] One aspect of the present disclosure is a method for producing a compound having a general formula:

[0010] [ka]

[0011] (wherein R is an alkyl group) and the non-aqueous electrolyte solution for a non-aqueous electrolyte secondary battery contains 6-alkylthio-1,3,5-triazine-2,4-dithiol.

[0012] Another aspect of the present disclosure is a battery comprising: a positive electrode; a separator; a negative electrode facing the positive electrode via the separator; and a nonaqueous electrolyte; The non-aqueous electrolyte solution includes a non-aqueous solvent and a cation exchange material having a general formula:

[0013] [ka]

[0014] (wherein R is an alkyl group) and the non-aqueous electrolyte secondary battery contains 6-alkylthio-1,3,5-triazine-2,4-dithiol.

[0015] According to the present disclosure, a decrease in voltage of a nonaqueous electrolyte secondary battery can be suppressed. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a partially cutaway perspective view of a nonaqueous electrolyte secondary battery according to one embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The nonaqueous electrolyte solution for a nonaqueous electrolyte secondary battery according to the present disclosure comprises a nonaqueous solvent and a compound having a general formula:

[0018] [ka]

[0019] (wherein R is an alkyl group) (hereinafter referred to as triazine dithiol derivative RS). The present disclosure also relates to a nonaqueous electrolyte secondary battery including a positive electrode, a separator, a negative electrode facing the positive electrode via the separator, and the nonaqueous electrolyte.

[0020] The nonaqueous electrolyte may be not only a liquid nonaqueous electrolyte, but may also be a composite with a gelling agent or a matrix material to form a gel electrolyte or solid electrolyte with no fluidity. The term "nonaqueous electrolyte" refers to a concept that includes nonaqueous electrolytes, gel electrolytes, and solid electrolytes, but excludes electrolytes in aqueous solutions.

[0021] The triazine dithiol derivative RS can form a coating on a metal surface or form a complex with a metal ion. The two thiol groups (SH groups) directly bonded to the carbon atoms of the triazine ring contribute to the reaction with the metal surface or metal ions. On the other hand, the alkylthio group (RS group) at the 6th position contributes to the functioning of the coating. For example, when the triazine dithiol derivative RS forms a complex with a metal ion, the alkylthio group at the 6th position suppresses the excessive generation of precipitation due to the aggregation of the complex. In addition, the alkylthio group at the 6th position is thought to have the effect of suppressing the decomposition of the triazine dithiol derivative RS in a battery. In addition, compared to conventional triazine dithiol derivatives having an alkylamino group at the 6th position, the triazine dithiol derivative RS has high solubility in nonaqueous solvents (especially carbonate esters) used in nonaqueous electrolytes and has excellent affinity with nonaqueous electrolytes.

[0022] When impurity metals are mixed into the battery, metal ions may be dissolved from the impurity metals exposed to the positive electrode potential into the non-aqueous electrolyte. In addition, transition metals may be dissolved from the positive electrode active material contained in the positive electrode into the non-aqueous electrolyte. Metal ions in the non-aqueous electrolyte are precipitated on the surface of the negative electrode. When metal dissolution and precipitation reactions occur, the battery voltage drops.

[0023] The triazine dithiol derivative RS contained in the non-aqueous electrolyte has a property of forming a coating on the metal surface, so that the elution of metal ions into the non-aqueous electrolyte is suppressed. In addition, the triazine dithiol derivative RS has a property of forming a complex with the metal ion, so that the metal ion eluted into the non-aqueous electrolyte is complexed and the degree of freedom of movement is restricted. The elution of the metal ion is suppressed, and the metal ion is complexed, so that the deposition of the metal is significantly suppressed. Therefore, even if impurity metals are mixed into the battery or transition metal ions are easily eluted from the positive electrode active material, the decrease in the battery voltage is suppressed.

[0024] The number of carbon atoms in the alkyl group (R group) of the alkylthio group (RS group) at the 6-position of the triazine dithiol derivative RS may be, for example, 1 to 8. By setting the number of carbon atoms in the alkyl group to 8 or less, the diffusibility of the triazine dithiol derivative RS is improved, and it becomes easier to coat the metal surface or the positive electrode active material surface. In particular, in terms of easy availability of the triazine dithiol derivative RS, the number of carbon atoms in the alkyl group (R group) is preferably 1 to 4. Specific examples of the alkylthio group include a methylthio group and a butylthio group.

[0025] The content of the triazine dithiol derivative RS in the nonaqueous electrolyte may be, for example, 0.001% by mass or more and 5% by mass or less, 0.01% by mass or more and 5% by mass or less, 0.01% by mass or more and 3% by mass or less, or 0.1% by mass or more and 1.5% by mass or less. When the triazine dithiol derivative RS is used in an amount within the above range, the effect of suppressing metal deposition and a decrease in battery voltage is increased.

[0026] However, in a battery, the triazine dithiol derivative RS is used to adhere to metal surfaces such as an electrode current collector and the surface of a positive electrode active material to form a coating. Therefore, when analyzing a nonaqueous electrolyte solution collected from inside a battery, the content of the triazine dithiol derivative RS may be less than 0.01% by mass. Meanwhile, it is rare for the triazine dithiol derivative RS to be completely consumed. From the viewpoint of obtaining the effects of the present disclosure, it is sufficient that the nonaqueous electrolyte solution collected from inside a battery contains the triazine dithiol derivative RS at a detection limit or more (for example, 0.0001% by mass or more).

[0027] The non-aqueous electrolyte contains the triazine dithiol derivative RS together with a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The triazine dithiol derivative RS is used as an additive, not as a main component of the non-aqueous electrolyte. The additive refers to a component other than the electrolyte salt, the content of which in the non-aqueous electrolyte is, for example, 20 mass % or less (or 10 mass % or less (particularly 5 mass % or less)).

[0028] The non-aqueous electrolyte may further contain, as an additive, vinyl ethylene carbonate (VEC), vinylene carbonate (VC), fluoroethylene carbonate (FEC), etc. Among them, VC forms a thin coating on the negative electrode surface, suppressing the decomposition of the non-aqueous solvent and suppressing the deposition of metals.

[0029] The non-aqueous electrolyte may further contain an oxalate complex salt as an additive. As the oxalate complex salt, a salt of an oxalate complex anion and a lithium ion is preferable because it has excellent compatibility with the non-aqueous electrolyte. As the oxalate complex anion, bisoxalate borate anion (BOB anion), difluorooxalate borate anion (FOB anion), etc. are preferable, and among them, lithium bisoxalate borate (LiBOB) forms a thin coating on the negative electrode surface that is stable even at relatively high temperatures, suppresses the decomposition of the non-aqueous solvent, and suppresses the deposition of metals.

[0030] The content of each component in the non-aqueous electrolyte solution can be determined, for example, by using high performance liquid chromatography.

[0031] Hereinafter, each component of the nonaqueous electrolyte secondary battery according to the present disclosure will be described in more detail.

[0032] (positive electrode) The positive electrode includes a positive electrode active material. The positive electrode usually includes a positive electrode current collector and a positive electrode mixture held by the positive electrode current collector. The positive electrode usually includes a layer of positive electrode mixture (hereinafter referred to as a positive electrode mixture layer) held by 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 positive electrode mixture layer. The coating film after drying may be rolled as necessary. The positive electrode mixture layer may be formed on one surface or both surfaces of the positive electrode current collector.

[0033] 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.

[0034] As the positive electrode active material, for example, a lithium transition metal composite oxide having a layered rock salt structure is used. Among them, a lithium transition metal composite oxide containing Ni, Co, and at least one of Al and Mn (hereinafter also referred to as composite oxide NC) is promising because it exhibits high capacity and high voltage. Here, if the Ni content of the composite oxide NC can be increased, it is cost-effective and a higher capacity can be secured. However, when the Ni content is high, the crystal structure of the composite oxide NC tends to become unstable, and transition metals such as Ni tend to be easily eluted. In addition, when Ni is eluted from a composite oxide NC with a high Ni content, a nickel oxide (NiO) layer is formed on the particle surface, which causes an increase in the resistance of the positive electrode. On the other hand, the triazine dithiol derivative RS is expected to adsorb to the surface of the composite oxide NC to form a coating, thereby suppressing the elution of transition metals (especially Ni).

[0035] The composition of the composite oxide NC is, for example, Li α Ni (1-x1-x2-x3-y) Co x1 Mn x2 Al x3 M yO 2+β (0.95 ≤ α ≤ 1.05, 0.5 ≤ 1 - x1 - x2 - x3 - y ≤ 0.95, 0 < x1 ≤ 0.4, 0 ≤ x2 ≤ 0.2, 0 ≤ x3 ≤ 0.2, 0 < x2 + x3 ≤ 0.4, 0 ≤ y ≤ 0.1, -0.05 ≤ β ≤ 0.05), although it is not particularly limited. However, M is at least one selected from the group consisting of Ti, Zr, Nb, Mo, W, Fe, Zn, B, Si, Mg, Ca, Sr, and Y.

[0036] The ratio (atomic ratio) of Ni, represented by (1 - x1 - x2 - x3 - z), preferably satisfies 0.8 ≤ 1 - x1 - x2 - x3 - z ≤ 0.95, and more preferably satisfies 0.9 ≤ 1 - x1 - x2 - x3 - z ≤ 0.95, from the viewpoint of increasing the capacity.

[0037] The ratio (atomic ratio) of Co, represented by x1, is greater than 0 and may be 0.04 or less, preferably 0.02 or less, and more preferably 0.015 or less.

[0038] The ratio (atomic ratio) of Mn, represented by x2, may be 0 ≤ x2 ≤ 0.1, and preferably 0 < x2 ≤ 0.1. The composite oxide NC containing Mn is relatively inexpensive and has a high capacity.

[0039] The ratio (atomic ratio) of Al, represented by x3, may be 0 ≤ x3 ≤ 0.1, preferably 0.03 ≤ x3 ≤ 0.1, and may also be 0.05 ≤ x3 ≤ 0.1. When the composite oxide NC contains Al, the crystal structure is stabilized, and it is easier to ensure high cycle characteristics.

[0040] The element M contained in the composite oxide NC is preferably at least one selected from the group consisting of Nb, Sr, and Ca. It is considered that the surface structure of the composite oxide NC is stabilized and metal elution is easily suppressed. In the particles of the composite oxide NC, Nb, Sr, and Ca are more effective when they are unevenly distributed near the surface of the particles. The ratio of the element M, represented by y, is 0 or more and 0.1 or less, and may also be 0 or more and 0.05 or less.

[0041] The contents of the elements constituting the complex oxide NC can be measured using an inductively coupled plasma atomic emission spectroscopy (ICP-AES), an electron probe micro analyzer (EPMA), an energy dispersive X-ray spectroscopy (EDX), or the like.

[0042] The composite oxide NC is, for example, a secondary particle formed by agglomeration of a plurality of primary particles. 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 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.

[0043] In this specification, the average particle size means a particle size (volume average particle size) at which the volume cumulative value is 50% in the particle size distribution measured by the laser diffraction scattering method. Such an average particle size may be referred to as D50. For example, the "LA-750" manufactured by HORIBA Co., Ltd. can be used as the measuring device.

[0044] The positive electrode active material may contain a lithium transition metal composite oxide other than the composite oxide NC, but it is preferable that the ratio of the composite oxide NC is high. The ratio of the composite oxide NC in the positive electrode active material is, for example, 90 mass% or more, and may be 95 mass% or more. The ratio of the composite oxide NC in the positive electrode active material is 100 mass% or less. The positive electrode active material may be composed of only the composite oxide NC.

[0045] As the binder, for example, a resin material is used. As the binder, for example, fluororesin (for example, polytetrafluoroethylene, polyvinylidene fluoride), polyolefin resin (for example, polyethylene, polypropylene), polyamide resin (for example, aramid resin), polyimide resin (for example, polyimide, polyamideimide), acrylic resin (for example, polyacrylic acid, polymethacrylic acid, acrylic acid-methacrylic acid copolymer, ethylene-acrylic acid copolymer, or salts thereof), vinyl resin (for example, polyvinyl acetate), rubber-like material (for example, styrene-butadiene copolymer rubber (SBR)) can be mentioned. As the binder, one kind may be used alone, or two or more kinds may be used in combination.

[0046] Examples of thickeners include cellulose derivatives such as cellulose ether. Examples of cellulose derivatives include CMC and its modified products, methylcellulose, and the like. Modified CMC also includes salts of CMC. Examples of salts include alkali metal salts (e.g., sodium salts), ammonium salts, and the like. The thickeners may be used alone or in combination of two or more.

[0047] Examples of the conductive agent include conductive fibers and conductive particles. Examples of the conductive fibers include carbon fibers, carbon nanotubes, and metal fibers. Examples of the conductive particles include conductive carbon (carbon black, graphite, and the like), and metal powders. The conductive agent may be used alone or in combination of two or more.

[0048] The dispersion medium used in the positive electrode slurry is not particularly limited, but examples thereof include water, alcohol (e.g., ethanol), ether (e.g., tetrahydrofuran), amide (e.g., dimethylformamide), N-methyl-2-pyrrolidone (NMP), or a mixed solvent thereof.

[0049] The positive electrode current collector is selected according to the type of the nonaqueous electrolyte secondary battery. For example, the positive electrode current collector may be in the form of a sheet. For example, a metal foil may be used as the current collector. For example, the material of the positive electrode current collector may be stainless steel, aluminum, aluminum alloy, titanium, or the like.

[0050] The thickness of the positive electrode current collector is not particularly limited, but may be, for example, 1 to 50 μm, and may be 5 to 30 μm.

[0051] (Negative electrode) The negative electrode includes a negative electrode active material. The negative electrode usually includes a negative electrode mixture including the negative electrode active material and a negative electrode current collector that holds the negative electrode mixture. The negative electrode usually includes a layered negative electrode mixture (hereinafter, referred to as a negative electrode mixture layer). The negative electrode mixture may further include at least one selected from the group consisting of a binder, a thickener, and a conductive agent.

[0052] As the negative electrode active material, metallic lithium, lithium alloys, etc. may be used, but materials capable of electrochemically absorbing and releasing lithium ions are preferably used. Such materials include carbonaceous materials, Si-containing materials, Sn-containing materials, etc. The negative electrode may contain one type of negative electrode active material, or may contain two or more types in combination. Among the negative electrode active materials, carbonaceous materials and Si-containing materials are preferred. A carbonaceous material and a Si-containing material may be combined.

[0053] Examples of the carbonaceous material include graphite, easily graphitized carbon (soft carbon), and non-graphitizable carbon (hard carbon). The carbonaceous material may be used alone or in combination of two or more.

[0054] Graphite is preferred as the carbonaceous material because it has excellent charge / discharge stability and a small irreversible capacity. Examples of graphite include natural graphite, artificial graphite, and graphitized mesophase carbon particles. The graphite particles may partially contain amorphous carbon, graphitizable carbon, and non-graphitizable carbon.

[0055] Graphite is a carbonaceous material with a developed graphite crystal structure. The interplanar spacing d002 of the (002) plane of graphite measured by X-ray diffraction may be, for example, 0.340 nm or less, or 0.3354 nm or more and 0.340 nm or less. The crystallite size Lc(002) of graphite may be, for example, 5 nm or more, or 5 nm or more and 200 nm or less. The crystallite size Lc(002) is measured, for example, by the Scherrer method. When the interplanar spacing d002 of the (002) plane of graphite and the crystallite size Lc(002) are within the above ranges, a high capacity is easily obtained.

[0056] Examples of the Si-containing material include simple Si, silicon alloys, and silicon compounds (silicon oxides, silicates, etc.). Examples of silicon oxides include SiO x Examples of the Si-containing material include particles. x is, for example, 0.5≦x<2, and may be 0.8≦x≦1.6. The Si-containing material may be used alone or in combination of two or more. The Si-containing material is, for example, a particulate material. The average particle size (D50) of the Si-containing material may be, for example, 1 μm or more and 25 μm or less, and may be 4 μm or more and 15 μm or less.

[0057] The binder may be a resin material exemplified for the positive electrode. The conductive agent may be selected from those exemplified for the positive electrode. The shape and thickness of the negative electrode current collector may be selected from the shapes and ranges described for the positive electrode current collector. Examples of the material of the negative electrode current collector include stainless steel, nickel, nickel alloy, copper, and copper alloy. The dispersion medium used in the negative electrode slurry may be selected from those exemplified for the positive electrode.

[0058] (Non-aqueous electrolyte) Examples of non-aqueous solvents constituting the non-aqueous electrolyte include cyclic carbonates, chain carbonates, cyclic carboxylates, and chain carboxylates. Examples of cyclic carbonates include propylene carbonate (PC), ethylene carbonate (EC), and the like. Examples of chain carbonates include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and the like. Examples of cyclic carboxylates include γ-butyrolactone (GBL), γ-valerolactone (GVL), and the like. Examples of chain carboxylates include methyl formate, ethyl formate, propyl formate, methyl acetate (MA), ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and the like. The non-aqueous electrolyte may include one type of non-aqueous solvent, or may include a combination of two or more types.

[0059] Examples of electrolyte salts or additives constituting the non-aqueous electrolyte include LiClO4, LiBF4, LiPF6, LiAlCl4, LiSbF6, LiSCN, LiCF3SO3, LiCF3CO2, LiAsF6, LiB 10 Cl 10 , lower aliphatic carboxylate lithium, LiCl, LiBr, LiI, borate salts, imide salts. Examples of borates include lithium bis(1,2-benzenedioleate(2-)-O,O')borate, lithium bis(2,3-naphthalenediolate(2-)-O,O')borate, lithium bis(2,2'-biphenyldioleate(2-)-O,O')borate, lithium bis(5-fluoro-2-oleate-1-benzenesulfonic acid-O,O')borate, and the like. Examples of imide salts include lithium bisfluorosulfonylimide (LiN(FSO2)2), lithium bistrifluoromethanesulfonyl imide (LiN(CF3SO2)2), lithium trifluoromethanesulfonate nonafluorobutanesulfonate imide (LiN(CF3SO2)(C4F9SO2)), lithium bispentafluoroethanesulfonate imide (LiN(C2F5SO2)2), and the like. The non-aqueous electrolyte may contain one type of lithium salt or a combination of two or more types of lithium salts.

[0060] The concentration of the electrolyte salt in the nonaqueous electrolyte is, for example, 0.5 mol / L or more and 2 mol / L or less.

[0061] (Separator) Usually, it is desirable to interpose a separator between the positive electrode and the negative electrode. The separator has high ion permeability and has appropriate mechanical strength and insulating properties. For example, a microporous thin film, a woven fabric, or a nonwoven fabric, or a laminate of at least two of these materials can be used as the separator. The material of the separator is preferably polyolefin (e.g., polypropylene, polyethylene).

[0062] (others) An example of the structure of the non-aqueous electrolyte secondary battery is a structure in which an electrode group in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, and a non-aqueous electrolyte are housed in an exterior body. Alternatively, instead of a wound type electrode group, an electrode group of another form, such as a stacked type electrode group in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween, may be applied. The non-aqueous electrolyte secondary battery may be in any form, such as a cylindrical type, a square type, a coin type, a button type, a laminate type, or the like.

[0063] Hereinafter, as an example of the nonaqueous electrolyte secondary battery according to the present disclosure, the structure of a prismatic nonaqueous electrolyte secondary battery will be described with reference to Fig. 1. Fig. 1 is a schematic perspective view of a nonaqueous electrolyte secondary battery according to an embodiment of the present disclosure, with a portion cut away.

[0064] The battery includes a bottomed prismatic battery case 4, and an electrode group 1 and a non-aqueous 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 between them to prevent direct contact. The electrode group 1 is formed by winding the negative electrode, positive electrode, and separator around a flat plate-shaped winding core and then removing the winding core.

[0065] One end of the negative electrode lead 3 is attached to the negative electrode collector of the negative electrode by welding or the like. The other end of the negative electrode lead 3 is electrically connected to a negative electrode terminal 6 provided on the sealing plate 5 via a resin insulating plate. The negative electrode terminal 6 is insulated from the sealing plate 5 by a resin gasket 7. One end of the positive electrode lead 2 is attached to the positive electrode collector of the positive electrode by welding or the like. The other end of the positive electrode lead 2 is connected to the back surface of the sealing plate 5 via an insulating plate. That is, the positive electrode lead 2 is electrically connected to the battery case 4 which also serves as the positive electrode terminal. The insulating plate separates the electrode group 1 and the sealing plate 5, and separates the negative electrode lead 3 and the battery case 4. The periphery of the sealing plate 5 is fitted into the open end of the battery case 4, and the fitting portion is laser welded. In this way, the opening of the battery case 4 is sealed with the sealing plate 5. The electrolyte injection hole provided in sealing plate 5 is closed with a sealing plug 8 .

[0066] [Example] The present disclosure will be specifically described below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0067] Examples 1 to 12, Reference Examples 1 to 2, and Comparative Examples 1 to 4 A non-aqueous electrolyte secondary battery was produced and evaluated according to the following procedure.

[0068] (1) Preparation of the positive electrode 100 parts by mass of the positive electrode active material particles shown in Table 1, 1 part by mass of acetylene black, 1 part by mass of polyvinylidene fluoride, and an appropriate amount of NMP were mixed to obtain a positive electrode slurry. Next, the positive electrode slurry was applied to one side 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.

[0069] The composition of the positive electrode active material shown in Table 1 is as follows.

[0070] LNCM:LiNi 0.35 Co 0.35 Mn 0.30 O2 LNCA:LiNi 0.88 Co 0.09 Al 0.03 O2 (2) Preparation of the negative electrode A negative electrode slurry was prepared by mixing 98 parts by mass of a negative electrode active material (graphite), 1 part by mass of sodium salt of carboxymethylcellulose (CMC-Na), 1 part by mass of SBR, and an appropriate amount of water. The negative electrode slurry was then applied to one side of a copper foil serving as a negative electrode current collector, and the coating was dried and then rolled to form a negative electrode mixture layer on both sides of the copper foil.

[0071] (3) Preparation of non-aqueous electrolyte A non-aqueous electrolyte was prepared by dissolving LiPF6 and 6-methylthio-1,3,5-triazine-2,4-dithiol as a triazine dithiol derivative RS (shown as RS in Table 1) in a mixed solvent of EC and EMC (EC:EMC = 3:7 (volume ratio)). The concentration of LiPF6 in the non-aqueous electrolyte was 1.0 mol / L. The concentration (initial concentration) of 6-methylthio-1,3,5-triazine-2,4-dithiol in the prepared non-aqueous electrolyte was the value (mass%) shown in Table 1.

[0072] (4) Fabrication of non-aqueous electrolyte secondary battery The positive electrode was cut into a predetermined shape to obtain a positive electrode for evaluation. The positive electrode was provided with a region of 20 mm x 20 mm to function as a positive electrode and a connection region with a tab lead of 5 mm x 5 mm. Then, the positive electrode mixture layer formed on the connection region was scraped off to expose the positive electrode current collector. Then, the exposed portion of the positive electrode current collector was connected to the positive electrode tab lead, and a predetermined region on the periphery of the positive electrode tab lead was covered with an insulating tab film. In Examples 1 to 12 and Comparative Examples 1 to 4, metal powder of the elements shown in Table 1 with a diameter of about 100 μm was intentionally embedded near the center of the positive electrode mixture layer.

[0073] The negative electrode was cut into the same shape as the positive electrode to obtain a negative electrode for evaluation. The negative electrode mixture layer formed on the connection area formed in the same manner as the positive electrode was peeled off to expose the negative electrode current collector. Thereafter, the exposed portion of the negative electrode current collector was connected to a negative electrode tab lead in the same manner as the positive electrode, and a predetermined area on the periphery of the negative electrode tab lead was covered with an insulating tab film.

[0074] A cell was prepared using the positive and negative electrodes for evaluation. First, the positive and negative electrodes were placed opposite each other with a polypropylene separator (thickness 30 μm) between them so that the positive electrode mixture layer and the negative electrode mixture layer overlapped to obtain an electrode plate group. Next, an Al laminate film (thickness 100 μm) cut into a rectangle of 60 × 90 mm was folded in half, and the end of the 60 mm long side was heat sealed at 230 ° C. to form a 60 × 45 mm cylindrical shape. Thereafter, the electrode plate group prepared was placed in the cylinder, and the end face of the Al laminate film was aligned with the position of the heat-sealed resin of each tab lead and heat-sealed at 230 ° C. Next, nonaqueous electrolyte was poured 0.3 cm from the short side of the Al laminate film that was not heat-sealed. 3 After the injection, the cells were left to stand for 5 minutes under a reduced pressure of 0.06 MPa to impregnate each mixture layer with the nonaqueous electrolyte. Finally, the end face of the Al laminate film on the injected side was heat sealed at 230°C to obtain evaluation cells A1 to A12 of Examples 1 to 12, evaluation cells R1 to R2 of Reference Examples 1 to 2, and evaluation cells B1 to B4 of Comparative Examples 1 to 4. The evaluation cells were prepared in a dry environment with a dew point of -50°C or less.

[0075] (5) Battery evaluation The evaluation cell was clamped between a pair of 80×80 cm stainless steel clamps (thickness: 2 mm) and pressurized and fixed at 0.2 MPa.

[0076] First, five cycles of charging and discharging were repeated at a constant current of 0.05 C (1 C is the current value at which the designed capacity is discharged in one hour) in a thermostatic bath at 25° C. Charging was terminated at a battery voltage of 4.2 V, and discharging was terminated at a battery voltage of 2.5 V. Between charging and discharging, the battery was left to stand in an open circuit for 20 minutes.

[0077] (6) Evaluation The non-aqueous electrolyte secondary batteries obtained in the Examples, Reference Examples, and Comparative Examples were evaluated as follows. 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. The battery was then stored in a temperature environment of 25°C, and the voltage drop after 100 hours was determined. If the voltage drop was 20 mV or more, it was determined that a metal dissolution reaction and a precipitation reaction had occurred. The results are shown in Table 1.

[0078] [Table 1]

[0079] As shown by the cells B1 to B4 of the comparative examples 1 to 4, when impurity metals are mixed into a battery, a voltage drop usually occurs due to the mechanism already described. On the other hand, in the cells A1 to A12 of the examples 1 to 12 in which the triazine dithiol derivative RS is contained in the non-aqueous electrolyte, there is almost no voltage drop, and it can be seen that the influence of the impurity metal is greatly alleviated. It can also be seen that the content of the triazine dithiol derivative RS in the non-aqueous electrolyte is sufficient even at 0.01 mass %, and does not change significantly up to at least 5 mass %. The voltage drop of the cells A1 to A12 of the examples 1 to 12 is at the same level as that of the cells R1 to R2 of the reference examples 1 to 2 that do not contain metal powder.

[0080] A slight voltage drop is also observed in the cells R1 and R2 of Reference Examples 1 and 2. However, the cells R1 and R2 of Reference Examples 1 and 2 do not contain the triazine dithiol derivative RS. It is considered that when the triazine dithiol derivative RS is contained in a normal battery without impurities, the voltage drop can be further reduced compared to the cells R1 and R2 of Reference Examples 1 and 2. [Industrial Applicability]

[0081] The nonaqueous electrolyte secondary battery of the present disclosure is suitable for use as a main power source for mobile communication devices, portable electronic devices, and the like, and as an in-vehicle power source, but is not limited to these uses. [Explanation of symbols]

[0082] 1 electrode group 2 Positive Lead 3 Negative lead 4 Battery case 5 Sealing plate 6 Negative terminal 7 Gasket 8. Sealing

Claims

1. a non-aqueous solvent and a compound of the general formula: 【Chemistry 1】 (wherein R is an alkyl group) and a difluorooxalatoborate anion.

2. 2. The nonaqueous electrolyte for a nonaqueous electrolyte secondary battery according to claim 1, wherein the alkyl group of the alkylthio group at the 6-position has 1 to 8 carbon atoms.

3. 3. The nonaqueous electrolyte for a nonaqueous electrolyte secondary battery according to claim 1, wherein the content of the 6-alkylthio-1,3,5-triazine-2,4-dithiol in the nonaqueous electrolyte is 0.01% by mass or more and 5% by mass or less.

4. The nonaqueous electrolyte for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the nonaqueous electrolyte contains vinylene carbonate.

5. A battery comprising: a positive electrode including a positive electrode active material; a separator; a negative electrode facing the positive electrode via the separator; and a non-aqueous electrolyte; The non-aqueous electrolyte solution includes a non-aqueous solvent and a cation exchange material having a general formula: 【Chemistry 2】 (wherein R is an alkyl group) and a difluorooxalatoborate anion.

6. 6. The nonaqueous electrolyte secondary battery in accordance with claim 5, wherein the alkyl group of the alkylthio group at the 6-position has 1 to 8 carbon atoms.

7. 7. The nonaqueous electrolyte secondary battery according to claim 5, wherein the content of the 6-alkylthio-1,3,5-triazine-2,4-dithiol in the nonaqueous electrolyte is 5 mass % or less.

8. The nonaqueous electrolyte secondary battery according to any one of claims 5 to 7, wherein the positive electrode active material includes a lithium transition metal composite oxide having a layered rock salt structure and including Ni, Co, and at least one of Al and Mn.

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