Non-aqueous electrolyte secondary battery and method for manufacturing the same

Abstract

To provide a nonaqueous electrolyte secondary battery having large capacity and excellent thermal stability, and a method for manufacturing the same.SOLUTION: In a nonaqueous electrolyte secondary battery, a positive electrode active material layer includes a nickel-based positive electrode active material and lithium phosphate. A molar ratio of nickel with respect to a metal element other than lithium in the nickel-based positive electrode active material is 0.80 to 1.0. A content of the lithium phosphate in the positive electrode active material layer is 0.1 to 2 mass% with respect to a total mass of the Ni-based positive electrode active material and the lithium phosphate. A nonaqueous electrolyte solution includes lithium difluorophosphate, and a content of the lithium difluorophosphate in the nonaqueous electrolyte solution is 0.1 to 2 mass%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] International Publication No. 2021 / 124971 (Patent Document 1) proposes a positive electrode for a non-aqueous electrolyte secondary battery, which includes a first positive electrode active material having a nickel (Ni) content of 50 to 65 mol%, a second positive electrode active material having a Ni content of 45 mol% or less, and lithium phosphate (Li3PO4). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2021 / 124971 Summary of the Invention [Problem to be solved by the invention]

[0004] If a positive electrode active material with a high Ni content (e.g., 80% or more) is used to further increase the capacity of a nonaqueous electrolyte secondary battery, the thermal stability of the nonaqueous electrolyte secondary battery may decrease. On the other hand, although the addition of lithium phosphate to the positive electrode active material layer tends to improve the thermal stability of a nonaqueous electrolyte secondary battery, it may become difficult to increase the capacity of the nonaqueous electrolyte secondary battery.

[0005] An object of the present disclosure is to provide a non-aqueous electrolyte secondary battery having high capacity and excellent thermal stability, and a method for producing the same. [Means for solving the problem]

[0006] The present disclosure provides the following nonaqueous electrolyte secondary battery and method for producing the same. [1] A battery comprising an electrode assembly and a non-aqueous electrolyte solution, The electrode assembly includes a positive electrode plate, the positive electrode plate includes a positive electrode active material layer, the positive electrode active material layer contains a nickel-based positive electrode active material and lithium phosphate, The nickel-based positive electrode active material has a molar ratio of nickel to metal elements other than lithium of 0.80 to 1.0, the content of lithium phosphate in the positive electrode active material layer is 0.1 to 2 mass% with respect to the total mass of the Ni-based positive electrode active material and lithium phosphate, the nonaqueous electrolyte solution contains lithium difluorophosphate, The non-aqueous electrolyte secondary battery has a lithium difluorophosphate content of 0.1 to 2 mass % in the non-aqueous electrolyte solution. [2] The nonaqueous electrolyte secondary battery according to [1], wherein the positive electrode active material layer contains large particles and small particles, and the mass ratio of the large particles to the small particles is 5:5 to 8:2. [3] The nonaqueous electrolyte secondary battery according to [2], wherein the large particles have a particle diameter (D50) of 12 to 20 μm, and the small particles have a particle diameter (D50) of 2 to 6 μm. [4] The nonaqueous electrolyte secondary battery according to any one of [1] to [3], wherein the lithium phosphate has a particle size (D50) of 2 to 5 μm. [5] A method for manufacturing a nonaqueous electrolyte secondary battery, comprising: Inserting the electrode body into the outer casing; A step of injecting a non-aqueous electrolyte; and an activation step, The electrode assembly includes a positive electrode plate, the positive electrode plate includes a positive electrode active material layer, the positive electrode active material layer contains a nickel-based positive electrode active material and lithium phosphate, The nickel-based positive electrode active material has a molar ratio of nickel to metal elements other than lithium of 0.80 to 1.0, the content of lithium phosphate in the positive electrode active material layer is 0.1 to 2 mass% with respect to the total mass of the Ni-based positive electrode active material and lithium phosphate, the nonaqueous electrolyte solution contains lithium difluorophosphate, The method for producing a non-aqueous electrolyte secondary battery, wherein the content of lithium difluorophosphate in the non-aqueous electrolyte solution is 0.1 to 2 mass %. [6] The method for producing a nonaqueous electrolyte secondary battery according to [5], wherein the positive electrode active material layer contains large particles and small particles, and the mass ratio of the large particles to the small particles is 5:5 to 8:2. [7] The method for producing a non-aqueous electrolyte secondary battery according to [6], wherein the large particles have a particle diameter (D50) of 12 to 20 μm, and the small particles have a particle diameter (D50) of 2 to 6 μm. [8] The method for producing a non-aqueous electrolyte secondary battery according to any one of [5] to [7], wherein the lithium phosphate has a particle size (D50) of 2 to 5 μm. [Effects of the Invention]

[0007] According to the present disclosure, it is possible to provide a non-aqueous electrolyte secondary battery having high capacity and excellent thermal stability, and a method for manufacturing the same. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing an example of the configuration of a battery according to this embodiment. [Figure 2] FIG. 2 is a schematic diagram showing an example of the configuration of the electrode body in this embodiment. [Figure 3] FIG. 3 is a schematic flowchart of the battery manufacturing method according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings, but the present disclosure is not limited to the following embodiments. In all of the following drawings, the scale has been adjusted appropriately to make each component easier to understand, and the scale of each component shown in the drawings does not necessarily match the scale of the actual component. In the following description of each embodiment, the same or equivalent parts in the drawings are designated by the same reference numerals, and their description will not be repeated.

[0010] <Nonaqueous electrolyte secondary battery> FIG. 1 is a schematic diagram showing an example of the configuration of a nonaqueous electrolyte secondary battery (hereinafter also referred to as a battery) according to this embodiment. The battery 100 can be used for any purpose. For example, the battery 100 may be used as a main power source or a power source for power assist in an electric vehicle. A plurality of batteries 100 may be connected to form a battery module or a battery pack.

[0011] The battery 100 includes an exterior body 90. The exterior body 90 is prismatic (flattened rectangular parallelepiped). However, the prismatic shape is just one example. The exterior body 90 may have any shape. The exterior body 90 may be, for example, cylindrical or pouch-shaped. The exterior body 90 may be made of, for example, an aluminum (Al) alloy. The exterior body 90 houses the electrode assembly 50 and a non-aqueous electrolyte (not shown). The exterior body 90 may include, for example, a sealing plate 91 and an exterior can 92. The sealing plate 91 closes the opening of the exterior can 92. The sealing plate 91 and the exterior can 92 may be joined by, for example, laser welding.

[0012] A positive electrode terminal 81 and a negative electrode terminal 82 are provided on the sealing plate 91. The sealing plate 91 may further be provided with an injection port and a gas exhaust valve. A non-aqueous electrolyte solution can be injected into the exterior body 90 through the injection port. The electrode body 50 is connected to the positive electrode terminal 81 by a positive electrode current collecting member 71. The positive electrode current collecting member 71 may be, for example, an Al plate or the like. The electrode body 50 is connected to the negative electrode terminal 82 by a negative electrode current collecting member 72. The negative electrode current collecting member 72 may be, for example, a copper (Cu) plate or the like.

[0013] FIG. 2 is a schematic diagram showing an example of the configuration of an electrode assembly in this embodiment. The electrode assembly 50 is a wound type. The electrode assembly 50 includes a positive electrode plate 10, a separator 30, and a negative electrode plate 20. That is, the battery 100 includes a positive electrode plate 10, a negative electrode plate 20, and a nonaqueous electrolyte. The positive electrode plate 10, the separator 30, and the negative electrode plate 20 are all strip-shaped sheets. The electrode assembly 50 may include multiple separators 30. The electrode assembly 50 is formed by stacking the positive electrode plate 10, the separator 30, and the negative electrode plate 20 in this order and winding them into a spiral shape. Either the positive electrode plate 10 or the negative electrode plate 20 may be sandwiched between separators 30. Both the positive electrode plate 10 and the negative electrode plate 20 may be sandwiched between separators 30. The electrode assembly 50 may be formed into a flat shape after winding. The wound type is just one example. The electrode body 50 may be, for example, a stack type.

[0014] (positive electrode plate) The positive electrode plate 10 includes a positive electrode substrate 11 and a positive electrode active material layer 12. The positive electrode substrate 11 is a conductive sheet. The positive electrode substrate 11 may be, for example, an Al alloy foil. The positive electrode substrate 11 may have a thickness of, for example, 10 μm to 30 μm. The positive electrode active material layer 12 is disposed on the surface of the positive electrode substrate 11. The positive electrode active material layer 12 may be disposed on only one surface of the positive electrode substrate 11, for example. The positive electrode active material layer 12 may be disposed on both the front and back surfaces of the positive electrode substrate 11, for example. The positive electrode substrate 11 may be exposed at one end in the width direction of the positive electrode plate 10 (the X-axis direction in FIG. 2 ). A positive electrode current collecting member 71 may be joined to the exposed portion of the positive electrode substrate 11.

[0015] For example, an intermediate layer (not shown) may be formed between the positive electrode active material layer 12 and the positive electrode substrate 11. In this embodiment, even when an intermediate layer is present, the positive electrode active material layer 12 is considered to be disposed on the surface of the positive electrode substrate 11. The intermediate layer may be thinner than the positive electrode active material layer 12. The intermediate layer may have a thickness of, for example, 0.1 μm to 10 μm. The intermediate layer may contain, for example, a conductive material, an insulating material, etc.

[0016] (Cathode active material layer) The positive electrode active material layer 12 contains a nickel-based positive electrode active material (hereinafter also referred to as a Ni-based positive electrode active material) and lithium phosphate. The Ni-based positive electrode active material has a molar ratio of Ni to a metal other than Li (hereinafter also referred to as the Ni content) of 0.80 to 1.0. When the Ni content in the Ni-based positive electrode active material is within the above range, the battery tends to have a higher capacity.

[0017] The Ni-based positive electrode active material is, for example, represented by the following formula (1): Li (1+x) Ni y Me (1-y) O2 [In formula (1), Me contains two or more selected from the group consisting of Mn, Co, and Al, and satisfies the relationships of 0 < x < 0.1, 0.8 < y < 0.8 and can include a layered metal oxide represented by

[0018] The layered metal oxide represented by formula (1) preferably satisfies the relationships of 0 < x < 0.1 and 0.8 < y < 0.84.

[0019] The layered metal oxide represented by formula (1) may contain at least one selected from the group consisting of Zr, B, Ti, Mg, Fe, Cu, Zn, Sn, Na, K, Ba, Sr, Ca, W, Mo, Nb, Si, V, Cr, and Ge.

[0020] The Ni-based positive electrode active material can be a particle group. The particle group can include a first positive electrode active material particle group and a second positive electrode active material particle group. The first positive electrode active material particle group consists of a plurality of large particles. The second positive electrode active material particle group consists of a plurality of small particles. The large particles have a larger particle diameter (D50) than the small particles. The large particles and the small particles can have any shape. The first positive electrode active material particles and the second positive electrode active material particles can be, for example, spherical, columnar, massive, etc. The particle diameter (D50) in this specification is the particle diameter at which the cumulative frequency from the smaller particle diameter in the volume-based particle size distribution reaches 50%. The volume-based particle size distribution is measured by a laser diffraction particle size distribution measuring device.

[0021] The mass ratio of the plurality of large particles (or the first positive electrode active material particle group) to the plurality of small particles (or the second positive electrode active material particle group) in the positive electrode active material layer 12 can be 5:5 to 8:2. This mass ratio can be the mass ratio (compounding ratio) when preparing a positive electrode slurry for forming the positive electrode active material layer 12.

[0022] The plurality of large particles may have a particle size (D50) of, for example, 12 μm to 20 μm, and the plurality of small particles may have a particle size (D50) of, for example, 2 μm to 6 μm.

[0023] The large particles and the small particles may each independently contain a Ni-based positive electrode active material represented by formula (1). The large particles and the small particles may each independently have any crystal structure. The large particles and the small particles may each independently have, for example, a layered structure, a spinel structure, an olivine structure, or the like. The large particles and the small particles may each have substantially the same chemical composition. The large particles and the small particles may each have different chemical compositions.

[0024] The content of lithium phosphate in the positive electrode active material layer 12 is 0.1% by mass to 2% by mass relative to the total mass of the Ni-based positive electrode active material and lithium phosphate. When the content of lithium phosphate is within this range, thermal stability tends to be improved even when a positive electrode active material layer containing a Ni-based positive electrode active material with a high Ni content is used. The above content can be the mass ratio (compounding ratio) when preparing the positive electrode slurry.

[0025] The lithium phosphate may be in the form of a particle group. The lithium phosphate particle group may include a plurality of lithium phosphate particles. The particle diameter (D50) of the plurality of lithium phosphate particles may be 2 to 5 μm.

[0026] The positive electrode active material layer 12 may further contain additional components. The positive electrode active material layer 12 may contain, for example, a conductive material and a binder. The conductive material may contain any component. The conductive material may contain, for example, at least one selected from the group consisting of carbon black, graphite, vapor-grown carbon fiber (VGCF), carbon nanotubes (CNT), and graphene flakes. The amount of the conductive material may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of the positive electrode active material. The binder may contain any component. The binder may include, for example, at least one selected from the group consisting of polyvinylidene fluoride (PVdF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP), polytetrafluoroethylene (PTFE), and polyacrylic acid (PAA). The amount of binder mixed may be, for example, 0.1 to 10 parts by mass relative to 100 parts by mass of the positive electrode active material. The positive electrode active material layer 12 may include, for example, in mass fraction, 80% to 99% of the total of the positive electrode active material and lithium phosphate, 0.1 to 10% of a conductive material, and the remainder being the binder.

[0027] The positive electrode active material layer 12 may have a thickness of, for example, 10 μm to 200 μm. The positive electrode active material layer 12 may have a thickness of, for example, 50 μm to 150 μm. The positive electrode active material layer 12 may have a thickness of, for example, 50 μm to 100 μm.

[0028] The positive electrode active material layer 12 may have a high density. For example, the positive electrode active material layer 12 may have a density of 3.3 g / cm 3 to 3.9 g / cm 3 The positive electrode active material layer 12 may have a density of, for example, 3.4 g / cm 3 to 3.7 g / cm 3 The positive electrode active material layer 12 may have a density of, for example, 3.4 g / cm 3 to 3.6 g / cm 3 In this specification, the density of the active material layer refers to the apparent density.

[0029] The positive electrode plate 10 is manufactured by applying a positive electrode slurry to the surface of a positive electrode substrate 11 to form a positive electrode active material layer 12, and then rolling the positive electrode active material layer 12 and the positive electrode substrate 11 to produce a raw sheet, which is then cut to a predetermined planar size according to the specifications of the battery 100. The positive electrode slurry is prepared by mixing the positive electrode active material with additional components.

[0030] (negative plate) The negative electrode plate 20 may include, for example, a negative electrode substrate 21 and a negative electrode active material layer 22. The negative electrode substrate 21 is a conductive sheet. The negative electrode substrate 21 may be, for example, a Cu alloy foil or the like. The negative electrode substrate 21 may have a thickness of, for example, 5 μm to 30 μm. The negative electrode active material layer 22 may be disposed on the surface of the negative electrode substrate 21. The negative electrode active material layer 22 may be disposed on only one surface of the negative electrode substrate 21, for example. The negative electrode active material layer 22 may be disposed on both the front and back surfaces of the negative electrode substrate 21, for example. The negative electrode substrate 21 may be exposed at one end in the width direction (X-axis direction in FIG. 2 ) of the negative electrode plate 20. A negative electrode current collecting member 72 may be joined to the exposed portion of the negative electrode substrate 21.

[0031] (Negative electrode active material layer) The negative electrode active material layer 22 contains a negative electrode active material. The negative electrode active material may contain any component. The negative electrode active material may contain, for example, at least one selected from the group consisting of graphite, soft carbon, hard carbon, silicon, silicon oxide, a silicon-based alloy, tin, tin oxide, a tin-based alloy, and a lithium-titanium composite oxide. The graphite may be natural graphite or artificial graphite.

[0032] The negative electrode active material layer 22 may have a thickness of, for example, 10 μm to 200 μm.

[0033] The negative electrode active material layer 22 may have a high density. For example, the negative electrode active material layer 22 may have a density of 1.0 g / cm 3 to 2.0 g / cm 3 The negative electrode active material layer 22 may have a density of, for example, 1.2 g / cm 3 to 1.7 g / cm 3The negative electrode active material layer 22 may have a density of, for example, 1.3 g / cm 3 to 1.6 g / cm 3 The density may be

[0034] The negative electrode plate 20 is manufactured by applying the negative electrode slurry to the surface of the negative electrode substrate 21 to form the negative electrode active material layer 22, and then rolling the negative electrode active material layer 22 and the negative electrode substrate 21 to produce a raw sheet, which is then cut to a predetermined planar size according to the specifications of the battery 100. The negative electrode slurry is prepared by mixing the negative electrode active material with other components.

[0035] (separator) At least a portion of the separator 30 is interposed between the positive electrode plate 10 and the negative electrode plate 20. The separator 30 separates the positive electrode plate 10 from the negative electrode plate 20. The separator 30 may have a thickness of, for example, 10 μm to 30 μm.

[0036] The separator 30 is a porous sheet. The separator 30 is permeable to a non-aqueous electrolyte. The separator 30 may have an air permeability of, for example, 100 s / 100 mL to 400 s / 100 mL. In this specification, "air permeability" refers to "air resistance" as defined in "JIS P 8117:2009." The air permeability is measured by the Gurley test method.

[0037] The separator 30 is electrically insulating. The separator 30 may contain, for example, a polyolefin resin. The separator 30 may, for example, be substantially made of a polyolefin resin. The polyolefin resin may, for example, contain at least one selected from the group consisting of polyethylene (PE) and polypropylene (PP). The separator 30 may, for example, have a single-layer structure. The separator 30 may, for example, be substantially made of a PE layer. The separator 30 may, for example, have a multi-layer structure. The separator 30 may, for example, be formed by laminating a PP layer, a PE layer, and a PP layer in this order. A heat-resistant layer, for example, may be formed on the surface of the separator 30.

[0038] (Non-aqueous electrolyte) The non-aqueous electrolyte solution contains a solvent. The solvent is aprotic. The solvent may contain any component. For example, the solvent may contain at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), 1,2-dimethoxyethane (DME), methyl formate (MF), methyl acetate (MA), methyl propionate (MP), and γ-butyrolactone (GBL).

[0039] The nonaqueous electrolyte may include a supporting electrolyte. The supporting electrolyte is dissolved in a solvent. The supporting electrolyte may include, for example, at least one selected from the group consisting of LiPF6, LiBF4, and LiN(FSO2)2. The supporting electrolyte may have a molar concentration of, for example, 0.5 mol / L to 2.0 mol / L. The supporting electrolyte may have a molar concentration of, for example, 0.8 mol / L to 1.2 mol / L.

[0040] The non-aqueous electrolyte contains lithium difluorophosphate (LiPO2F2) as an additive. The content of lithium difluorophosphate in the non-aqueous electrolyte can be 0.1 to 2 mass% relative to the mass of the non-aqueous electrolyte. When the non-aqueous electrolyte contains lithium difluorophosphate in the above range, thermal stability tends to be easily improved even when a positive electrode active material layer containing a Ni-based positive electrode active material with a high Ni content is used, and thermal stability tends to be easily improved particularly when the positive electrode active material layer containing a Ni-based positive electrode active material with a high Ni content contains lithium phosphate.

[0041] The non-aqueous electrolyte may further contain other additives. For example, the non-aqueous electrolyte may contain 0.01% to 5% by mass of the additive. The additive may include, for example, at least one selected from the group consisting of LiPF6, vinylene carbonate (VC), lithium fluorosulfonate (LiFSO3), and lithium bis(oxalato)borate (LiBOB).

[0042] <Battery manufacturing method> As shown in FIG. 3, the method for manufacturing a battery in this embodiment includes a step (A) of inserting an electrode assembly into an outer casing, a step (B) of injecting a non-aqueous electrolyte, and an initial charge / discharge step (C).

[0043] In step (A) of inserting the electrode body into the exterior body, the electrode body 50 is housed in the exterior body 90. The electrode body 50 can be connected to a positive electrode terminal 81 by a positive electrode current collecting member 71. The electrode body 50 can be connected to a negative electrode terminal 82 by, for example, a negative electrode current collecting member 72.

[0044] In step (B) of injecting a non-aqueous electrolyte, the non-aqueous electrolyte is injected into the exterior body 90. The non-aqueous electrolyte is impregnated into the electrode assembly 50. After the injection of the non-aqueous electrolyte, the exterior body 90 is sealed.

[0045] In the initial charge / discharge step (C), the battery 100 is charged and discharged. For example, the battery 100 is charged by a constant current-constant voltage (CC-CV) method, and after a predetermined time has elapsed, it is discharged by a constant current (CC-CV) method. More specifically, in a temperature environment of 25°C, a current of 2.6 mA / cm is used. 2 The battery was charged at a constant current until the battery voltage reached 4.2 V, and then the current was increased to 0.4 mA / cm 2 The battery is charged at a constant voltage until it reaches 0.2mA / cm. After that, there is a 10-minute break, and then the battery is charged at 0.2mA / cm. 2 The battery is discharged at a constant current until the battery voltage reaches 2.5V.

[0046] This completes the manufacture of the battery 100. The battery 100 has excellent thermal stability and can be a high-capacity battery.

[0047] The present invention will be described in more detail below with reference to examples. [Example]

[0048] Example 1 [Preparation of positive electrode plate] Lithium nickel cobalt manganese composite oxide (Li 1.03 Ni 0.815 Co 0.05 Mn 0.115 O2, D50=17μm), and lithium nickel cobalt manganese composite oxide (Li 1.03 Ni 0.83 Co 0.125 Mn 0.045A positive electrode slurry was prepared by kneading a mixture of Ni-based positive electrode active material (large and small particles) and lithium phosphate (LiPO, D50=4μm), lithium phosphate (LiPO, D50=4μm) as an additive, carbon black as a conductive material, polyvinylidene fluoride (PVdF) as a binder, and N-methyl-2-pyrrolidone as a dispersion medium. The mass ratio of large particles to small particles was 7:3. The lithium phosphate content relative to the total mass of the Ni-based positive electrode active material (large and small particles) and lithium phosphate was 1% by mass. The mass ratio of the total mass of the Ni-based positive electrode active material (large and small particles) and lithium phosphate to acetylene black and polyvinylidene fluoride was 97.6:1.5:0.9. The prepared positive electrode slurry was uniformly applied to one side of a positive electrode current collector made of aluminum foil, dried, and then rolled using a rolling roller. The packing density of the positive electrode mixture layer formed on one side of the positive electrode current collector was 3.5 g / cm. 3 Furthermore, a positive electrode current collecting tab was attached to the surface of the positive electrode current collector to prepare a positive electrode plate in which a positive electrode active material layer was formed on one surface of the positive electrode current collector.

[0049] [Preparation of negative electrode plate] 98 parts by mass of negative electrode active material (graphite, D50 = 17 μm, specific surface area = 1.2 m 2 A negative electrode slurry was prepared by mixing 225 (g / m2) of cellulose acetate, 1 part by mass of CMC, 1 part by mass of SBR, and a predetermined amount of dispersion medium (water). The negative electrode slurry was applied to the surface of a negative electrode substrate (Cu foil) in an amount of 225 (g / m2). 2 ) and dried, the specific surface area S becomes 2 (m 2 A negative electrode active material layer with a density of 1.5 (g / cc) was formed. The negative electrode active material layer was compressed using a rolling mill to produce a negative electrode blank with a density of 1.5 (g / cc). The negative electrode blank was cut to a predetermined size to produce a negative electrode plate. A tab terminal (Ni thin plate) was joined to the negative electrode plate.

[0050] [Preparation of non-aqueous electrolyte] A mixed solvent was prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 30:30:40. The nonaqueous electrolyte contained lithium difluorophosphate (LiPO2F2) as an additive. The concentration of lithium difluorophosphate in the nonaqueous electrolyte was 0.1% by mass relative to the mass of the nonaqueous electrolyte.

[0051] [assembly] A porous polyolefin sheet was prepared as the separator. A wound electrode assembly was fabricated by stacking and winding a positive electrode plate, a separator, and a negative electrode plate so that the separator was interposed between the positive electrode plate and the negative electrode plate. A pouch made of an Al laminate film was prepared as the exterior body. The electrode assembly was housed in the exterior body, and a nonaqueous electrolyte was poured into it to fabricate a test cell.

[0052] [Initial charge / discharge] The test cell was initially charged and discharged at a temperature of 25°C. 2 The battery voltage was charged to 4.2V at a constant current of 0.4mA / cm. After the battery voltage reached 4.2V, the battery was charged at a constant voltage of 4.2V at a constant current of 0.4mA / cm. 2 The battery was then charged at a constant voltage of 2.6 mA / cm 2 The battery was discharged at a constant current until the battery voltage reached 2.5 V (vs. Li / Li+). The rest interval between the charge and discharge was 10 minutes.

[0053] [Thermal stability] 2.6mA / cm at 25℃ 2 After charging at a constant current / constant voltage up to 4.2 V at a current density of 1000 kJ / s, the positive electrode plate was removed from the test cell and washed with DMC. The positive electrode active material layer was then peeled off from the positive electrode plate and placed in a sample pan. 2 μL (microliter) of non-aqueous electrolyte was added and sealed. The sample was heated from room temperature to 350°C at a rate of 5°C / min, and the calorific value (J / g) was measured. The ratio of this value to the calorific value of Comparative Example 1 described below was calculated. A ratio of 0.80 or less to Comparative Example 1 was considered to have excellent thermal stability. The results are shown in Table 1.

[0054] <Capacity> The volumetric charge capacity density was measured as the capacity of the battery. The large particles and small particles used to prepare the positive electrode active material layer were mixed in a mass ratio of 7:3 and formed into a cylindrical sample with a diameter of 19 mm. The sample was pressed for 30 seconds with a load of 70 kN. The density of the mixture after pressing was measured. The volumetric charge capacity density (mAh / cc) was calculated by multiplying this density (g / cc) by the charge capacity (mAh / g). The ratio to the volumetric charge capacity density of Comparative Example 1 described below was determined. A ratio of 0.97 or more to the volumetric charge capacity density of Comparative Example 1 was considered to have a high capacity. The results are shown in Table 1.

[0055] <Examples 2 to 8 and Comparative Examples 1 to 15> Test cells were prepared in the same manner as in Example 1, except that the Ni content in the positive electrode active material (large particles, small particles), the mixing ratio of large particles to small particles, the lithium phosphate content, and the content of additives in the non-aqueous electrolyte were changed as shown in Table 1, and further, in Comparative Examples 14 and 15, the type of additive in the non-aqueous electrolyte was changed to LiPF6. The results are shown in Table 1.

[0056] [Table 1]

[0057] As can be seen from Table 1, the test cells of Examples 1 to 8 had high capacity and excellent thermal stability. Therefore, it is understood that in a battery having a positive electrode active material layer containing a Ni-based positive electrode active material with a high Ni content, by setting the lithium phosphate in the positive electrode active material layer and the lithium difluorophosphate in the non-aqueous electrolyte to specific contents, it is possible to provide a non-aqueous electrolyte secondary battery having high capacity and excellent thermal stability, and a method for producing the same. [Explanation of symbols]

[0058] 10 positive electrode plate, 11 positive electrode substrate, 12 positive electrode active material layer, 13, 23 tab, 20 negative electrode plate, 21 negative electrode substrate, 22 negative electrode active material layer, 30 separator, 50 electrode body, 71 positive electrode current collecting member, 72 negative electrode current collecting member, 81 positive electrode terminal, 82 negative electrode terminal, 90 exterior body, 91 sealing plate, 92 exterior can, 100 battery.

Claims

1. The battery includes an electrode assembly and a non-aqueous electrolyte solution, The electrode assembly includes a positive electrode plate, the positive electrode plate includes a positive electrode active material layer, the positive electrode active material layer contains a nickel-based positive electrode active material and lithium phosphate, The nickel-based positive electrode active material has a molar ratio of nickel to metal elements other than lithium of 0.80 to 1.0, the content of lithium phosphate in the positive electrode active material layer is 0.1 to 2 mass% with respect to the total mass of the Ni-based positive electrode active material and the lithium phosphate, the nonaqueous electrolyte solution contains lithium difluorophosphate, The nonaqueous electrolyte secondary battery has a lithium difluorophosphate content of 0.1 to 2 mass % in the nonaqueous electrolyte solution.

2. 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material layer contains large particles and small particles, and the mass ratio of the large particles to the small particles is 5:5 to 8:

2.

3. 3. The nonaqueous electrolyte secondary battery according to claim 2, wherein the large particles have a particle diameter (D50) of 12 to 20 μm, and the small particles have a particle diameter (D50) of 2 to 6 μm.

4. 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the lithium phosphate has a particle diameter (D50) of 2 to 5 μm.

5. A method for manufacturing a non-aqueous electrolyte secondary battery, Inserting the electrode body into the outer casing; A step of injecting a non-aqueous electrolyte; and an activation step, The electrode assembly includes a positive electrode plate, the positive electrode plate includes a positive electrode active material layer, the positive electrode active material layer contains a nickel-based positive electrode active material and lithium phosphate, The nickel-based positive electrode active material has a molar ratio of nickel to metal elements other than lithium of 0.80 to 1.0, the content of lithium phosphate in the positive electrode active material layer is 0.1 to 2 mass% with respect to the total mass of the Ni-based positive electrode active material and the lithium phosphate, the nonaqueous electrolyte solution contains lithium difluorophosphate, The method for producing a non-aqueous electrolyte secondary battery, wherein the content of lithium difluorophosphate in the non-aqueous electrolyte solution is 0.1 to 2 mass %.

6. 6. The method for producing a nonaqueous electrolyte secondary battery according to claim 5, wherein the positive electrode active material layer contains large particles and small particles, and the mass ratio of the large particles to the small particles is 5:5 to 8:

2.

7. 7. The method for producing a non-aqueous electrolyte secondary battery according to claim 6, wherein the large particles have a particle diameter (D50) of 12 to 20 μm, and the small particles have a particle diameter (D50) of 2 to 6 μm.

8. 6. The method for producing a non-aqueous electrolyte secondary battery according to claim 5, wherein the lithium phosphate has a particle diameter (D50) of 2 to 5 μm.

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