Nonaqueous electrolyte secondary battery positive electrode and nonaqueous electrolyte secondary battery

Abstract

A nonaqueous electrolyte secondary battery positive electrode according to an embodiment of the present disclosure includes: a positive electrode current collector; and a positive electrode mixture layer disposed on the positive electrode current collector. The positive electrode mixture layer includes: a first positive electrode active material; a second positive electrode active material; a conductive member; and a binder. The first positive electrode active material is a lithium nickelate composite oxide. The second positive electrode active material is a lithium phosphate composite oxide represented by a general formula LiFexM11-xPO4 (in the formula, 0<x≤1 is satisfied and M1 represents at least one metal element selected from the group consisting of Mn, Fe, Co, and Ni). The binder is contained in an amount of not less than 0.6 but less than 2 parts by mass with respect to 100 parts by mass of the positive electrode mixture layer.

Description

Positive electrode for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery

[0001] The present invention relates to a positive electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery.

[0002] A non-aqueous electrolyte secondary battery includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. In such a non-aqueous electrolyte secondary battery, the positive electrode includes, for example, a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector, and the positive electrode mixture layer contains a positive electrode active material.

[0003] Patent Document 1 discloses a positive electrode for a lithium-ion secondary battery including a positive electrode current collector and a positive electrode composite material layer formed on one or both surfaces of the positive electrode current collector. The positive electrode composite material layer contains a positive electrode active material, a conductive auxiliary material, and a binder. The positive electrode active material is a mixture of a first positive electrode active material which is a lithium composite oxide having a layered structure (for example, lithium nickel composite oxide) and a second positive electrode active material which is a polyanion-based compound having an olivine structure (for example, lithium phosphate composite oxide). When the average secondary particle diameter of the first positive electrode active material is r1 and the average secondary particle diameter of the second positive electrode active material is r2, the relationship r1 > r2 is satisfied. The area occupancy rate of the second positive electrode active material on the surface of the positive electrode composite material layer is α in percentage, the weight ratio of the first positive electrode active material to the second positive electrode active material is 100 - β:β (0 < β < 100), and when the relationship between α and β is γ = β / α, a positive electrode for a lithium secondary battery in which γ is 0.33 or more and 0.84 or less is disclosed. Further, Patent Document 1 discloses a lithium secondary battery including the above positive electrode for a lithium-ion secondary battery.

[0004] Patent Document 2 discloses a positive electrode material constituting a positive electrode of a lithium secondary battery. The positive electrode material contains a first positive electrode active material and a second positive electrode active material. The first positive electrode active material is a lithium transition metal oxide containing nickel (for example, lithium nickel composite oxide), and the second positive electrode active material is an olivine-type active material having 50% or more of the total capacity in the potential range of 4.2 to 4.1 V when the counter electrode is lithium, LiVP ２ O ７A positive electrode material for a lithium-ion secondary battery is disclosed, which is (for example, a lithium phosphate composite oxide), and the ratio of the first positive electrode active material to the sum of the first and second positive electrode active materials is 50% by mass or more and 80% by mass or less. Patent Document 2 also discloses a positive electrode for a lithium-ion secondary battery containing the above-mentioned positive electrode material, and a lithium-ion secondary battery equipped with this positive electrode for a lithium-ion secondary battery.

[0005] As described above, non-aqueous electrolyte secondary batteries, such as lithium-ion secondary batteries containing lithium nickel composite oxide and lithium phosphate composite oxide as positive electrode active materials, aim to achieve both high capacity and safety. On the other hand, there is a demand for even higher capacity in such non-aqueous electrolyte secondary batteries.

[0006] Japanese Patent Publication No. 2023-10319, Japanese Patent Publication No. 7036701

[0007] Therefore, the object of this disclosure is to provide a positive electrode for a non-aqueous electrolyte secondary battery that can achieve high capacity, and a non-aqueous electrolyte secondary battery equipped with such a positive electrode for a non-aqueous electrolyte secondary battery.

[0008] One aspect of the present invention includes a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector, wherein the positive electrode mixture layer includes a first positive electrode active material, a second positive electrode active material, a conductive material, and a binder, wherein the first positive electrode active material is a lithium nickelate composite oxide, and the second positive electrode active material has the general formula: LiFe ｘ M1 １－ｘ PO ４ The present invention relates to a positive electrode for a non-aqueous electrolyte secondary battery, which is a lithium phosphate composite oxide represented by the formula (wherein 0 < x ≤ 1, and M1 is at least one metal element selected from the group consisting of Mn, Fe, Co, and Ni), and contains 0.6 parts by mass or more and less than 2 parts by mass of the binder per 100 parts by mass of the positive electrode composite layer.

[0009] Another aspect of this disclosure relates to a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode is a positive electrode for the above-mentioned non-aqueous electrolyte secondary battery.

[0010] According to this disclosure, it is possible to provide a positive electrode for a non-aqueous electrolyte secondary battery that can achieve high capacity. Furthermore, it is possible to provide a non-aqueous electrolyte secondary battery equipped with such a positive electrode for a non-aqueous electrolyte secondary battery.

[0011] This is a schematic perspective view showing a portion of a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure.

[0012] The embodiments of this disclosure will be described below with examples, but this disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be given as examples, but other numerical values, materials, etc. may be applied as long as the effects of this disclosure are obtained. Notwithstanding, known components may be applied to components of parts that are characteristic of this disclosure. In this specification, when "the range of numerical values ​​A to numerical values ​​B" is used, that range includes numerical values ​​A and B.

[0013] In the following explanation, when examples are given for the lower and upper limits of numerical values ​​related to specific physical properties or conditions, any combination of either of the given lower limits and any of the given upper limits is permitted, as long as the lower limit does not exceed the upper limit. When multiple materials are given as examples, unless otherwise specified, one type may be selected and used alone, or two or more types may be used in combination.

[0014] This disclosure includes any combination of two or more claims that can be arbitrarily selected from the claims set forth in the attached claims. In other words, any combination of two or more claims that can be arbitrarily selected from the claims set forth in the attached claims is possible, as long as it does not result in a technical inconsistency.

[0015] [Positive electrode for non-aqueous electrolyte secondary battery] A positive electrode for a non-aqueous electrolyte secondary battery according to an embodiment of the present disclosure includes a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector, the positive electrode mixture layer including a first positive electrode active material, a second positive electrode active material, a conductive material, and a binder.

[0016] In the positive electrode for a non-aqueous electrolyte secondary battery according to the embodiments of this disclosure, the first positive electrode active material is a lithium nickelate composite oxide, and the second positive electrode active material is a material with the general formula: LiFe ｘ M1１－ｘ PO ４ (where 0 < x ≤ 1, and M1 is at least one metal element selected from the group consisting of Mn, Fe, Co, and Ni.) is a lithium phosphate composite oxide represented by the formula.

[0017] In the positive electrode for a non-aqueous electrolyte secondary battery according to an embodiment of the present disclosure, the binder is contained in an amount of 0.6 parts by mass or more and less than 2 parts by mass with respect to 100 parts by mass of the positive electrode mixture layer.

[0018] In the positive electrode for a non-aqueous electrolyte secondary battery according to an embodiment of the present disclosure, (i) the positive electrode mixture layer contains a lithium nickelate composite oxide as a first positive electrode active material, and a general formula: LiFe ｘ M1 １－ｘ PO ４ (where 0 < x ≤ 1, and M1 is at least one metal element selected from the group consisting of Mn, Fe, Co, and Ni.), and (ii) the binder is contained in an amount of 0.6 parts by mass or more and less than 2 parts by mass with respect to 100 parts by mass of the positive electrode mixture layer are important. The reasons are explained below.

[0019] LiFe ｘ M1 １－ｘ PO ４ In the positive electrode active material represented by the formula, since the bond between the phosphorus atom (P) and the oxygen atom (O) is strong, even when the inside of the non-aqueous electrolyte secondary battery becomes high temperature during charge and discharge, the bond between the phosphorus atom (P) and the oxygen atom (O) is difficult to break, and oxygen (O ２ ) is difficult to generate. Therefore, even if the non-aqueous electrolyte vaporizes when the inside of the non-aqueous electrolyte secondary battery becomes high temperature, a combustion reaction between the vaporized non-aqueous electrolyte and oxygen (O ２ ) is difficult to occur. Therefore, by using the above positive electrode active material in the positive electrode for a non-aqueous electrolyte secondary battery, the safety of the non-aqueous electrolyte secondary battery can be improved. Incidentally, the above positive electrode active material has an olivine structure as a crystal structure.

[0020] On the other hand, the above-mentioned positive electrode active material contributes less to increasing the capacity of non-aqueous electrolyte secondary batteries, that is, contributes less to increasing the capacity of non-aqueous electrolyte secondary batteries, compared to lithium nickelate composite oxide having a layered rock salt structure. Therefore, in non-aqueous electrolyte secondary batteries, the above-mentioned positive electrode active material and lithium nickelate composite oxide are often used in combination to achieve high capacity while improving safety. In other words, the positive electrode for non-aqueous electrolyte secondary batteries often contains lithium nickelate composite oxide as the first positive electrode active material and the above-mentioned positive electrode active material as the second positive electrode active material.

[0021] A positive electrode for a non-aqueous electrolyte secondary battery typically includes a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector. The positive electrode mixture layer is formed by dispersing a positive electrode mixture containing a positive electrode active material, a conductive material, and a binder in a dispersion medium to obtain a positive electrode mixture slurry, applying this slurry to the surface of the positive electrode current collector to form a coating, and then drying and rolling the coating. To increase the capacity of a non-aqueous electrolyte secondary battery, it is preferable to make the positive electrode mixture layer thicker, and for this purpose, it is preferable to have a high solid content in the positive electrode mixture slurry. More specifically, it is preferable to increase the content of positive electrode active material by increasing the solid content in the positive electrode mixture slurry.

[0022] Furthermore, the second positive electrode active material described above has lower conductivity than the first positive electrode active material described above. Therefore, from the viewpoint of suppressing an increase in the internal resistance of the positive electrode for non-aqueous electrolyte secondary batteries, the second positive electrode active material described above is usually used after being pulverized. For example, the second positive electrode active material described above is used after being pulverized until the average particle size is 1 μm or less. The first positive electrode active material described above is usually used with an average particle size of 3 μm or more and 30 μm or less. By pulverizing the second positive electrode active material, its oil absorption capacity increases. Therefore, when the positive electrode mixture slurry contains the second positive electrode active material described above, it becomes necessary to include a large amount of dispersion medium in the positive electrode mixture slurry. In such cases, the solid content in the positive electrode mixture slurry decreases. That is, the content of the positive electrode active material in the positive electrode mixture slurry decreases.

[0023] To increase the content of positive electrode active material in the positive electrode mixture slurry, it is conceivable to reduce the content of conductive materials and binders. However, reducing the content of conductive materials makes it difficult to form a sufficient conductive network in the positive electrode mixture layer, thus increasing the internal resistance of the positive electrode mixture layer. Furthermore, if the content of binders is reduced, the specific surface area of ​​the second positive electrode active material increases due to miniaturization, which can lead to defects in the positive electrode mixture layer, such as poor bonding between the second positive electrode active material particles.

[0024] However, in the positive electrode for a non-aqueous electrolyte secondary battery according to the embodiment of this disclosure, the positive electrode mixture layer contains 0.6 parts by mass or more and less than 2 parts by mass of binder per 100 parts by mass of positive electrode mixture layer. That is, the positive electrode mixture layer contains an amount of binder that allows the positive electrode active material to maintain bonding between itself and the positive electrode active material. Therefore, the amount of positive electrode active material can be increased in the positive electrode mixture layer by the amount of binder that is reduced. As a result, by using the positive electrode for a non-aqueous electrolyte secondary battery according to the embodiment of this disclosure, it is possible to achieve a higher capacity for the non-aqueous electrolyte secondary battery.

[0025] The configuration of the positive electrode for a non-aqueous electrolyte secondary battery according to the embodiments of this disclosure will be described in more detail below. Hereinafter, the positive electrode for a non-aqueous electrolyte secondary battery will also be simply referred to as the positive electrode.

[0026] (Positive electrode active material) The first positive electrode active material is lithium nickelate composite oxide. The general formula for lithium nickelate composite oxide is: Li ａ [Ni ｙ M2 １－ｙ ]O ２ It is preferable that the compound is represented by the formula above. However, in the above formula, 0.9 < a ​​< 1.3, 0.85 ≤ y ≤ 1.0, and M2 is at least one metallic element selected from the group consisting of Co, Mn, and Al. Note that the value of a, which indicates the composition ratio of lithium in the above composition formula, increases or decreases with charging and discharging. A specific example of a lithium nickel composite oxide is lithium-nickel-cobalt-aluminum composite oxide (LiNi ０．９ Co ０．０５ Al ０．０５ O ２ Examples include:

[0027] Lithium nickelate composite oxides have a layered rock salt-type crystalline structure, and reversible insertion and removal of Li ions is possible between the layers of this structure. Furthermore, because lithium nickelate composite oxides contain Ni as described above, Li ions are more easily extracted during charging, thereby increasing the capacity of non-aqueous electrolyte secondary batteries. By using a high-Ni active material (a composite oxide with a high Ni content) as the lithium nickelate composite oxide, more Li ions can be extracted during charging, further increasing the capacity of non-aqueous electrolyte secondary batteries. In addition, Co, Mn, and Al contribute to stabilizing the layered rock salt-type crystalline structure. The contribution of Co, Mn, and Al to stabilizing the crystalline structure becomes more pronounced as the proportion of Ni in the lithium nickelate composite oxide increases. However, from the viewpoint of manufacturing costs, a low proportion of Co is preferable.

[0028] Lithium nickelate composite oxide may be secondary particles formed by the aggregation of multiple primary particles. The average particle diameter of lithium nickelate composite oxide may be 3 μm or more, or 5 μm or more. The average particle diameter of lithium nickelate composite oxide may be 30 μm or less, or 25 μm or less. The average particle diameter of lithium nickelate composite oxide is usually measured as the average particle diameter of secondary particles.

[0029] The average particle size of lithium nickelate composite oxide is the 50% particle size (median) of the cumulative volume-based particle size distribution measured using a laser diffraction / scattering particle size distribution analyzer. For example, the Microtrac series MT3300 manufactured by Nikkiso Co., Ltd. is used as the laser diffraction / scattering particle size distribution analyzer. Note that the measurement using the particle size distribution analyzer can be performed before incorporating the lithium nickelate composite oxide into the cathode mixture layer.

[0030] The average particle size of lithium nickelate composite oxide may be measured from a cross-section obtained by cutting the laminate of the positive electrode mixture layer and the positive electrode core (positive electrode current collector) in the thickness direction. The cross-section may be formed using a cross-section polisher (CP). In this case, the positive electrode mixture layer may be embedded with a thermosetting resin (such as epoxy resin). The average particle size from the cross-section can be measured using a scanning electron microscope (SEM) image of the cross-section. As the SEM image, an image taken so that 10 or more lithium nickelate composite oxides are observed can be used. Then, the equivalent circle diameter of the cross-sections of 10 or more lithium nickelate composite oxides is determined by image processing, and the average value of these is calculated as the average particle size. Here, the equivalent circle diameter means the diameter of a circle having the same area as the cross-section area of ​​the lithium nickelate composite oxide (the area of ​​the positive electrode active material observed in the cross-section of the positive electrode mixture layer). Note that the average particle size of lithium nickelate composite oxide obtained using a particle size distribution analyzer and the average particle size of lithium nickelate composite oxide obtained from the cross-section are equivalent values.

[0031] The second positive electrode active material has the general formula: LiFe ｘ M1 １－ｘ PO ４ This is a lithium phosphate composite oxide represented by the formula above. However, in the above formula, 0 < x ≤ 1, and M1 is at least one metallic element selected from the group consisting of Mn, Fe, Co, and Ni. A specific example of a lithium phosphate composite oxide represented by the above general formula is lithium iron manganese phosphate (LMFP).

[0032] The lithium phosphate complex oxide represented by the above general formula has an olivine structure. Furthermore, in the lithium phosphate complex oxide represented by the above general formula, the bond between the phosphorus (P) atom and the oxygen atom (O) is strong, so even when the inside of a non-aqueous electrolyte secondary battery becomes hot during charging and discharging, the bond between the phosphorus (P) atom and the oxygen atom (O) is less likely to break and oxygen (O) ２ ) is less likely to occur. Therefore, even if the non-aqueous electrolyte vaporizes when the inside of a non-aqueous electrolyte secondary battery becomes hot, the vaporized non-aqueous electrolyte and oxygen (O) are less likely to form. ２Combustion reactions between the two electrodes become less likely to occur. Therefore, by including a lithium phosphate composite oxide represented by the above general formula in the second positive electrode active material, the safety of the non-aqueous electrolyte secondary battery can be enhanced.

[0033] The second positive electrode active material has lower conductivity than the first positive electrode active material. Therefore, the second positive electrode active material is usually used in a granular form to suppress the increase in the internal resistance of non-aqueous electrolyte secondary batteries. When used in a granular form, the average particle diameter of the second positive electrode active material is preferably 1 μm or less. The lower limit of the average particle diameter of the second positive electrode active material is 0.01 μm. The second positive electrode active material may be secondary particles formed by the aggregation of multiple primary particles. The second positive electrode active material may also be used after granulating the granular particles. In that case, the average particle diameter of the second positive electrode active material may be, for example, 5 μm to 6 μm. The average particle diameter of the second positive electrode active material is usually measured as the average particle diameter of the secondary particles. The average particle diameter of the second positive electrode active material can be measured in the same manner as the first positive electrode active material.

[0034] When the mass ratio of the first positive electrode active material is W1 and the mass ratio of the second positive electrode active material is W2, it is preferable that W1:W2 = 40:60 to 90:10, and more preferably that W1:W2 = 50:50 to 60:40. In other words, it is preferable that the positive electrode mixture layer contains 50 parts by mass or less of the second positive electrode active material for every 100 parts by mass of the total of the first and second positive electrode active materials. This not only allows for higher capacity non-aqueous electrolyte secondary batteries but also enhances the safety of non-aqueous electrolyte secondary batteries.

[0035] In lithium nickelate composite oxides and lithium phosphate composite oxides represented by the above general formula, the content of the elements constituting these compounds can be measured by inductively coupled plasma atomic emission spectrometer (ICP-AES), electron probe microanalyzer (EPMA), or energy dispersive X-ray spectrometer (EDX).

[0036] The positive electrode active material may include other positive electrode active materials besides the first and second positive electrode active materials. Examples of other positive electrode active materials include lithium iron phosphate (LiFePO4). ４ (LFP), Lithium Cobalt Oxide (LiCoO) ２ ), and lithium manganese (LiMn ２ O ４ Examples include the following. Note that lithium manganate is a lithium transition metal composite oxide having a spinel structure. In the positive electrode active material, it is preferable that the proportion of the first positive electrode active material and the second positive electrode active material is high. The proportion of the first positive electrode active material and the second positive electrode active material in the positive electrode active material is, for example, 90% by mass or more, may be 95% by mass or more, or may be 100% by mass.

[0037] (Conductive Material) The conductive material includes a carbon material. Preferably, the carbon material includes carbon nanotubes (CNTs). By using carbon nanotubes (CNTs) as the conductive material, variations in potential within the positive electrode can be particularly suppressed, and gas generation can be particularly suppressed. Furthermore, by using carbon nanotubes (CNTs), the resistance of the positive electrode mixture layer can be reduced with a small amount of addition. The positive electrode mixture layer may also contain conductive materials other than carbon nanotubes (CNTs). Examples of such conductive materials include conductive carbon materials such as graphene, carbon black (e.g., acetylene black (AB), Ketjen black (KB), and furnace black (FB)), and other conductive carbon materials.

[0038] The positive electrode mixture layer may contain 0.01% by mass or more of conductive material, 0.1% by mass or more, or 0.2% by mass or more. The positive electrode mixture layer may contain 3% by mass or less of conductive material, 1% by mass or less, or 0.5% by mass or less. By having the conductive material within the above range, it is possible to increase the content of positive electrode active material in the positive electrode mixture layer while suppressing an increase in the internal resistance of the positive electrode mixture layer. In other words, in a non-aqueous electrolyte secondary battery, it is possible to achieve high capacity while suppressing an increase in internal resistance.

[0039] The average length of the carbon nanotubes may be 1 μm or more. Having an average length within this range allows the carbon nanotubes to easily make linear contact with the positive electrode active material and the current collector. Furthermore, carbon nanotubes have excellent conductivity. Therefore, by using carbon nanotubes, the DC resistance (DCR) of a non-aqueous electrolyte secondary battery can be significantly reduced.

[0040] The average length of the carbon nanotubes is preferably 1 μm or more from the viewpoint of improving conductivity in the positive electrode mixture layer. On the other hand, there is no particular upper limit to the length of the carbon nanotubes, but it is preferable that the length of the carbon nanotubes does not become too large compared to the particle size of the positive electrode active material. The average length of the carbon nanotubes may be 1 μm or more, or 5 μm or more. The average length of the carbon nanotubes may be 20 μm or less, or 10 μm or less. The carbon nanotubes present in the positive electrode mixture layer may exist as bundles of multiple carbon nanotubes. In calculating the average length as described above, the length of a single carbon nanotube present in a bundle of carbon nanotubes is used.

[0041] The average length of carbon nanotubes is determined by image analysis using a scanning electron microscope (SEM). This is done by randomly selecting 100 carbon nanotubes, measuring their lengths, and then taking the arithmetic mean. The length refers to the length of the carbon nanotube when it is stretched in a straight line.

[0042] The average diameter of the carbon nanotubes may be 20 nm or less, or 15 nm or less. The average diameter of the carbon nanotubes may also be 1 nm or more. By setting the average diameter to 20 nm or less, a high effect can be obtained with a small amount.

[0043] The average diameter of carbon nanotubes can be determined by image analysis using a transmission electron microscope (TEM). The average diameter of carbon nanotubes can be measured by the following method: First, 100 carbon nanotubes are randomly selected, and the diameter (outer diameter) of each nanotube at any one point is measured. Then, the average diameter is obtained by taking the arithmetic mean of the measured diameters.

[0044] The carbon nanotubes may be single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs). Examples of multi-walled carbon nanotubes include double-walled carbon nanotubes, triple-walled carbon nanotubes, and carbon nanotubes with four or more layers. The cathode mixture layer preferably contains at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes. The multi-walled carbon nanotubes contained in the cathode mixture layer may be one type of multi-walled carbon nanotube or multiple types of multi-walled carbon nanotubes with different numbers of layers.

[0045] The BET specific surface area of ​​carbon nanotubes is 200 m². ２ It may be more than / g, or 250m ２ It may be more than / g, or 300m ２ It may be 1000 m² or more. The upper limit of the BET specific surface area is not particularly limited, but 1000 m² is not limited. ２ It may be less than / g. BET specific surface area is 200 m². ２ By setting the amount to 1 / g or more, even small amounts of additive can suppress variations in the potential of the positive electrode active material in the positive electrode mixture layer. The BET specific surface area of ​​carbon nanotubes can be measured by the nitrogen adsorption method. However, generally, there is a correlation between the BET specific surface area of ​​carbon nanotubes and the fiber diameter and fiber length. Specifically, if the fiber diameter is 10 nm and the fiber length is 1 μm, the BET specific surface area is 200 m². ２ / g or more and 250m２ It is less than / g. Therefore, even when contained in the positive electrode mixture layer, the BET specific surface area of ​​carbon nanotubes can be calculated with high accuracy.

[0046] (Binding agent) It is preferable to use a fluorine-containing polymer as a binding agent. A fluorine-containing polymer is a polymer that contains fluorine. Examples of fluorine-containing polymers include vinylidene fluoride polymers. Examples of vinylidene fluoride polymers include polymers of monomers containing vinylidene fluoride. The fluorine-containing polymer may be a combination of a vinylidene fluoride polymer and other fluorine-containing polymers. The vinylidene fluoride polymer may be a copolymer of vinylidene fluoride and other monomers. Examples of vinylidene fluoride polymers include polyvinylidene fluoride (PVDF). In addition, other fluorine-containing polymers such as polytetrafluoroethylene (PTFE) exist and can obtain similar effects.

[0047] The positive electrode mixture layer contains 0.6 parts by mass or more and less than 2 parts by mass of binder per 100 parts by mass of the positive electrode mixture layer. By keeping the binder content in such a small amount as described above, the content of positive electrode active material in the positive electrode mixture layer can be increased. This makes it possible to achieve a higher capacity for non-aqueous electrolyte secondary batteries. Furthermore, according to the inventors' studies, the above range of binder content is the minimum amount that does not cause poor bonding between the positive electrode active materials.

[0048] The weight-average molecular weight of the fluorine-containing polymer (e.g., vinylidene fluoride polymer) may be 1 million or more, 1.1 million or more, or 1.2 million or more. The weight-average molecular weight of the fluorine-containing polymer may be 2 million or less, or 1.8 million or less. In other words, the fluorine-containing polymer is preferably a high-molecular-weight polymer. By setting the weight-average molecular weight to 1 million or more, it becomes easier to obtain a high binding effect with a smaller amount. This makes it easier to increase the content of the positive electrode active material in the positive electrode mixture layer. The weight-average molecular weight of the fluorine-containing polymer can be measured, for example, by ultra-high temperature gel permeation chromatography (GPC). Note that the weight-average molecular weight of the fluorine-containing polymer is measured as a polystyrene equivalent.

[0049] The measurement conditions for ultra-high temperature GPC are shown below. An ultra-high temperature GPC SSC-7110 is used as the measuring apparatus. One TSKguardcolumnHHR(S)HT column and two TSKgelGMHHR-H(S)HT (7.8 mm I.D. × 30 cm) columns are used. A differential refractometer (RI detector) is used as the detector. As a sample pretreatment, the fluorine-containing polymer sample is weighed, a predetermined amount of 1-chloronaphthalene (1-CN) is added as the solvent, and it is heated and dissolved at 250°C for 1 hour. After that, heating filtration is performed using a PTFE filter with a pore size of 0.5 μm. 500 μL of a solution with a sample concentration of 2 mg / mL is injected as the sample injection volume. The flow rate is 1.0 mL / min, the measurement temperature is set to the column temperature of 210°C, and the pre-oven temperature is set to 250°C. Polystyrene is used as the molecular weight standard.

[0050] The positive electrode mixture layer may contain components other than those mentioned above (e.g., thickeners) or compounds other than those mentioned above. For example, the positive electrode mixture layer may contain polyvinylpyrrolidone, cellulose derivatives (e.g., alkylcellulose, carboxyalkylcellulose, and salts thereof), etc. Polymer materials such as polyvinylpyrrolidone and cellulose derivatives may function as dispersants or binders.

[0051] The proportion of positive electrode active material in the positive electrode mixture layer can be determined using a positive electrode mixture sample. A positive electrode mixture sample is obtained by the following procedure. First, a discharged non-aqueous electrolyte secondary battery is disassembled and the positive electrode is removed. Next, this positive electrode is washed with an organic solvent and then vacuum-dried. After that, only the positive electrode mixture layer is removed and used as the positive electrode mixture sample. By performing analysis on the positive electrode mixture sample using TG-DTA, NMR, or pyrolysis GC-MS, the ratio of binders and conductive materials other than the positive electrode active material can be calculated. If the conductive material contains multiple types of carbon materials, the proportion of carbon nanotubes in the conductive material can be calculated by using thermal analysis such as TG-DTA and micro-Raman spectroscopy on a cross-section of the positive electrode mixture layer.

[0052] 1 m of positive electrode mixture layer (1 layer) ２ The mass per unit is preferably 250 g or more. That is, the basis weight of the positive electrode mixture layer in the positive electrode current collector is 250 g / m². ２ The above is preferable. The basis weight of the positive electrode mixture layer is 250 g / m². ２ As a result of the above, the capacity of non-aqueous electrolyte secondary batteries can be further increased. The basis weight of the positive electrode mixture layer can be increased by making the positive electrode mixture layer thicker or increasing the density of the positive electrode mixture layer.

[0053] There are no particular limitations on the thickness of the positive electrode mixture layer, but it may be in the range of 50 μm to 250 μm.

[0054] The positive electrode mixture layer can be obtained by coating the surface of the positive electrode current collector with a slurry of positive electrode mixture containing the above-mentioned components dispersed in a liquid medium (dispersion medium), and then drying the coating. The dried coating may be rolled if necessary. The positive electrode mixture layer may be placed on one surface of the positive electrode current collector or on both surfaces. The liquid medium (dispersion medium) is not particularly limited and can be water, organic solvents, or mixed solvents thereof. Examples of organic solvents include alcohols (such as ethanol), ethers (such as tetrahydrofuran), amides (such as dimethylformamide), and N-methyl-2-pyrrolidone (NMP).

[0055] The ratio of each component in the positive electrode mixture slurry is, in principle, reflected in the ratio of each component in the positive electrode mixture layer. Therefore, by changing the ratio of each component in the positive electrode mixture slurry, the ratio of each component in the positive electrode mixture layer can be changed.

[0056] In a positive electrode mixture slurry, the mass ratio of solids may be, for example, 60% by mass or more. By keeping the mass ratio of solids within the above range, the content of positive electrode active material in the positive electrode mixture slurry can be increased. Note that "solids" refers to the solid components contained in the positive electrode mixture slurry; that is, components other than the liquid medium. Therefore, the solids include positive electrode active material, conductive material, and binders. The mass ratio of solids in a positive electrode mixture slurry can be measured using a Kett moisture meter. Specifically, the mass ratio of liquids in the positive electrode mixture slurry can be measured with a Kett moisture meter, and the mass ratio of solids can be determined using the measurement results.

[0057] [Non-aqueous electrolyte secondary battery] A non-aqueous electrolyte secondary battery according to the embodiments of this disclosure comprises a positive electrode, a negative electrode, and a non-aqueous electrolyte. In addition to the positive electrode, negative electrode, and non-aqueous electrolyte, the non-aqueous electrolyte secondary battery according to the embodiments of this disclosure may also include a separator and an outer casing. Examples of non-aqueous electrolyte secondary batteries include lithium-ion secondary batteries and lithium metal secondary batteries. The components other than the positive electrode mixture layer are not particularly limited, and various known components may be used. Examples of components of the non-aqueous electrolyte secondary battery according to this disclosure are described below.

[0058] (Positive electrode) A positive electrode for a non-aqueous electrolyte secondary battery according to the embodiment of this disclosure is used as the positive electrode.

[0059] The shape and thickness of the positive electrode current collector can be selected according to the application and can be selected to correspond to the shape and thickness of the negative electrode current collector. Examples of materials for the positive electrode current collector include stainless steel, aluminum, aluminum alloy, and titanium. The positive electrode mixture layer may be formed on only one side of the positive electrode current collector or on both sides.

[0060] (Negative electrode) The negative electrode typically includes a negative electrode mixture layer containing a negative electrode active material. The negative electrode may also include a negative electrode current collector and a negative electrode mixture layer disposed on the negative electrode current collector. In the case of a non-aqueous electrolyte secondary battery that is a lithium metal secondary battery, a negative electrode current collector capable of depositing lithium metal or a lithium alloy is used for the negative electrode.

[0061] The negative electrode mixture layer contains a negative electrode active material as an essential component. The negative electrode mixture layer may also contain optional components such as binders, thickeners, and conductive materials. These optional components may be those listed as examples of positive electrode components.

[0062] The negative electrode mixture layer may be formed by dispersing the components of the negative electrode mixture layer in a liquid medium (dispersion medium), applying a negative electrode mixture slurry to the surface of the negative electrode current collector to form a coating film, and then drying this coating film. The dried coating film may be rolled as needed. The liquid medium may be one of the liquid mediums exemplified for the positive electrode mixture slurry. The negative electrode mixture layer may be formed on only one side of the negative electrode current collector, or on both sides of the negative electrode current collector.

[0063] <Negative Electrode Active Material> The negative electrode active material is selected according to the type of non-aqueous electrolyte secondary battery. An example of a negative electrode active material is a material capable of intercalating and releasing lithium ions. Examples of such materials include carbonaceous materials and silicon (Si)-containing materials. It is preferable that the negative electrode active material contains silicon (Si)-containing material. That is, it is preferable that the negative electrode mixture layer contains silicon (Si)-containing material as the negative electrode active material. Since silicon (Si)-containing material has a high lithium ion intercalation capacity, the inclusion of silicon (Si)-containing material in the negative electrode mixture layer makes it easier to increase the capacity of the non-aqueous electrolyte secondary battery. The mass ratio of silicon (Si)-containing material in the negative electrode active material may be 100% by mass. In addition, silicon (Si)-containing material may be used in combination with carbonaceous material. In this case, it is preferable that the mass ratio of silicon (Si)-containing material in the negative electrode active material be 5% by mass or more. Metallic lithium, lithium alloys, etc., may be used as the negative electrode active material. The negative electrode may contain one type of negative electrode active material, or it may contain a combination of two or more types.

[0064] Examples of carbonaceous materials include graphite, easily graphitizable carbon (soft carbon), and difficult-to-graphitize carbon (hard carbon). A single carbonaceous material may be used, or two or more may be used in combination. Graphite is preferred as the carbonaceous material due to its excellent charge-discharge stability and low irreversible capacity. Examples of graphite include natural graphite, artificial graphite, and graphitized mesophase carbon particles.

[0065] Si-containing materials include, for example, elemental Si, silicon alloys, silicon compounds (such as silicon oxides), and composite materials in which a silicon phase is dispersed within a lithium-ion conductive phase (matrix). Examples of silicon oxides include SiO ｘ Particles are an example. x may be, for example, 0.5 ≤ x < 2, and 0.8 ≤ x ≤ 1.6. The lithium ion conducting phase is SiO ２ At least one selected from the group consisting of phases, silicate phase, and carbon phase can be used.

[0066] Metal foil may be used for the negative electrode current collector. The negative electrode current collector may also be porous. Examples of materials for the negative electrode current collector include stainless steel, nickel, nickel alloys, copper, and copper alloys.

[0067] <Non-aqueous electrolytes> Non-aqueous electrolytes (non-aqueous electrolyte solutions) contain a solvent (non-aqueous solvent) and a solute dissolved in the solvent. Examples of solutes include lithium salts. Various additives may be added to the electrolyte solution.

[0068] Various known materials can be used as solvents. Examples of solvents include cyclic carbonate esters, linear carbonate esters, cyclic carboxylic acid esters, and linear carboxylic acid esters. Examples of cyclic carbonate esters include propylene carbonate (PC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC). Examples of linear carbonate esters 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 linear carboxylic acid esters include non-aqueous solvents such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate (EP). Non-aqueous solvents may be used individually or in combination of two or more.

[0069] Examples of lithium salts include lithium salts of chlorine-containing acids (LiClO2). ４ LiAlCl ４ LiB １０ Cl １０ (e.g.), lithium salts of fluorine-containing acids (LiPF) ６ LiPF ２ O ２ LiBF ４ LiSbF ６ LiAsF ６ LiCF ３ SO ３ LiCF ３ CO ２ (etc.), lithium salts of fluorine-containing acidimides (LiN(FSO) ２ ) ２ ,LiN(CF ３ SO ２ ) ２ ,LiN(CF ３ SO ２ ) (C ４ F ９ SO ２ ), LiN(C ２ F ５ SO ２ ) ２Examples include lithium halides (LiCl, LiBr, LiI, etc.). Lithium salts may be used individually or in combination of two or more types.

[0070] The concentration of lithium salt in the electrolyte may be 1 mol / L or more and 2 mol / L or less, or 1 mol / L or more and 1.5 mol / L or less. By setting the lithium salt concentration within the above range, an electrolyte with excellent ionic conductivity and appropriate viscosity can be obtained.

[0071] The electrolyte may contain various known additives. Examples of additives include 1,3-propanesaltone, methylbenzenesulfonate, cyclohexylbenzene, biphenyl, diphenyl ether, and fluorobenzene.

[0072] <Separator> The separator is placed between the positive electrode and the negative electrode. The separator preferably has high ion permeability and appropriate mechanical strength and insulating properties. As the separator, a microporous thin film, woven fabric, nonwoven fabric, etc., can be used. Examples of separator materials include polyolefins (polypropylene, polyethylene, etc.) and other resins.

[0073] <Outer casing> The outer casing (battery case) houses the electrode group and the non-aqueous electrolyte. The outer casing is not particularly limited, and known outer casings may be used. The electrode group consists of a positive electrode, a negative electrode, and a separator. The configuration of the electrode group is not particularly limited, and may be a wound type or a laminated type. A wound type electrode group is formed by winding the positive electrode and negative electrode with a separator in between. A laminated type electrode group is formed by stacking the positive electrode and negative electrode with a separator in between. The form of the non-aqueous electrolyte secondary battery is not particularly limited, and may be cylindrical, prismatic, coin-shaped, button-shaped, laminated, etc. The form of the non-aqueous electrolyte secondary battery is preferably cylindrical. In such a case, even if the electrode group is configured as a wound type and the positive electrode mixture layer is formed thickly, peeling of the positive electrode mixture layer from the positive electrode current collector can be sufficiently suppressed.

[0074] Figure 1 is a schematic perspective view showing a portion of a non-aqueous electrolyte secondary battery 10 according to one embodiment of the present disclosure. Figure 1 shows a rectangular non-aqueous electrolyte secondary battery as an example. The non-aqueous electrolyte secondary battery 10 shown in Figure 1 includes a bottomed rectangular tubular battery case 4, and an electrode group 1 and a non-aqueous electrolyte (not shown) housed within the battery case 4.

[0075] The electrode group 1 includes a long, strip-shaped negative electrode, a long, strip-shaped positive electrode, and a separator placed between them. The negative electrode current collector of the negative electrode is electrically connected to a negative electrode terminal 6 provided on the 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 of the positive electrode is electrically connected to the back surface of the sealing plate 5 via a positive electrode lead 2. That is, the positive electrode is electrically connected to the battery case 4, which also serves as the positive electrode terminal. The periphery of the sealing plate 5 is fitted to the open end of the battery case 4, and the fitting portion is laser-welded. The sealing plate 5 has an injection hole for a non-aqueous electrolyte. The injection hole is sealed by a seal 8 after the non-aqueous electrolyte is injected.

[0076] The positive electrode includes a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector. The positive electrode mixture layer used is the positive electrode mixture layer described above. That is, as the positive electrode, the positive electrode for a non-aqueous electrolyte secondary battery according to the embodiment of this disclosure is used.

[0077] (Note) The following technologies are disclosed in accordance with the above description. (Technology 1) A positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector, wherein the positive electrode mixture layer comprises a first positive electrode active material, a second positive electrode active material, a conductive material, and a binder, wherein the first positive electrode active material is a lithium nickelate composite oxide, and the second positive electrode active material has a general formula: LiFe ｘ M1 １－ｘ PO ４A lithium phosphate composite oxide represented by the formula (wherein 0 < x ≤ 1, and M1 is at least one metal element selected from the group consisting of Mn, Fe, Co, and Ni), wherein the binder is present in an amount of 0.6 parts by mass or more and less than 2 parts by mass per 100 parts by mass of the positive electrode composite layer, for a positive electrode for a non-aqueous electrolyte secondary battery. (Technology 2) A positive electrode for a non-aqueous electrolyte secondary battery according to Technology 1, wherein the binder is present in an amount of 0.6 parts by mass or more and 1 part by mass per 100 parts by mass of the positive electrode composite layer. (Technology 3) A positive electrode for a non-aqueous electrolyte secondary battery according to Technology 1 or 2, wherein the positive electrode composite layer contains 50 parts by mass or less of the second positive electrode active material in a total of 100 parts by mass of the first positive electrode active material and the second positive electrode active material. (Technology 4) A positive electrode for a non-aqueous electrolyte secondary battery according to any one of Technology 1 to 3, wherein the conductive material includes carbon nanotubes. (Technical 5) The basis weight of the positive electrode mixture layer in the positive electrode current collector is 250 g / m². ２ The above is a positive electrode for a non-aqueous electrolyte secondary battery as described in any one of the technologies 1 to 4. (Technology 6) The lithium nickelate composite oxide has the general formula: Li ａ [Ni ｙ M2 １－ｙ ]O ２ (Technology 7) A positive electrode for a non-aqueous electrolyte secondary battery according to any one of Technology 1 to 5, which is a compound represented by the formula (wherein 0.9 < a ​​< 1.3, 0.85 ≤ y ≤ 1.0, and M2 is at least one metallic element selected from the group consisting of Co, Mn, and Al). (Technology 8) A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode is the positive electrode for a non-aqueous electrolyte secondary battery according to any one of Technology 1 to 6.

[0078] The present disclosure will be described below in detail based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0079] [Example 1] (1) Preparation of the negative electrode A mixture of graphite and silicon composite material was used as the negative electrode active material. In the negative electrode active material, the mass ratio of silicon composite material to graphite was set to silicon composite material:graphite = 5:95. The silicon composite material is a composite material in which a silicon phase is dispersed in the lithium ion conducting phase (matrix phase). The negative electrode active material, carboxymethylcellulose sodium (CMC-Na), styrene-butadiene rubber (SBR), and water were mixed in a predetermined mass ratio to prepare a negative electrode mixture slurry. Next, the negative electrode mixture slurry was applied to both main surfaces (both sides) of the copper foil (negative electrode core) to form a coating film. After drying the coating film, the laminate of the coating film and the copper foil was rolled. This produced a negative electrode comprising copper foil and negative electrode mixture layers arranged on both main surfaces of the copper foil.

[0080] (2) Preparation of the positive electrode A positive electrode slurry was prepared by mixing a positive electrode active material, a conductive material, a positive electrode mixture containing polyvinylidene fluoride (fluorine-containing polymer, PVDF) as a binder, and N-methyl-2-pyrrolidone (liquid medium) in a predetermined mass ratio.

[0081] The positive electrode active material is lithium-nickel-cobalt-aluminum composite oxide (LiNi ０．９ Co ０．０５ Al ０．０５ O ２ First positive electrode active material), and lithium phosphate composite oxide (LiFe ０．４ Mn ０．６ PO ４ A second positive electrode active material was used. The mass ratio of the first positive electrode active material was 60 parts by mass per 100 parts by mass of the total of the first and second positive electrode active materials, and the mass ratio of the second positive electrode active material was 40 parts by mass per 100 parts by mass of the total of the first and second positive electrode active materials.

[0082] As the conductive material, multi-wall carbon nanotubes (MWCNT) were used. The average length of the MWCNT was 1 μm, and the average diameter of the MWCNT was 10 nm. The addition amount of the conductive material was 0.5 parts by mass with respect to 100 parts by mass of the positive electrode mixture layer (positive electrode mixture). The addition amount of PVDF as the binder was 0.6 parts by mass with respect to 100 parts by mass of the positive electrode mixture layer (positive electrode mixture). Note that as the PVDF, one having a weight average molecular weight of 1.2 million was used. That is, as the PVDF, a high molecular polymer was used. The weight average molecular weight of the PVDF was measured according to the method described in the section of the above embodiment.

[0083] Next, the positive electrode mixture slurry was applied to both surfaces (both sides) of the aluminum foil (positive electrode current collector) to form a coating film, and a laminate of the aluminum foil and the coating film was obtained. Note that the positive electrode mixture slurry was applied so that the basis weight (basis weight of one side) of the positive electrode mixture layer on the positive electrode current collector was 300 g / m ２ Then, after drying the coating film, the laminate was rolled. In this way, a positive electrode including the aluminum foil and the positive electrode mixture layers disposed on both sides of the aluminum foil was produced.

[0084] (3) Preparation of non-aqueous electrolyte (non-aqueous electrolyte solution) A non-aqueous electrolyte (non-aqueous electrolyte solution) was prepared by adding LiPF ６ (lithium salt) to a non-aqueous solvent. In the non-aqueous electrolyte, the concentration of LiPF ６ was set to 1.0 mol / L. As the non-aqueous solvent, a mixed solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of EC:EMC = 3:7 was used.

[0085] (4) Fabrication of a non-aqueous electrolyte secondary battery Leads were attached to the positive electrode and negative electrode fabricated as described above. Next, an electrode stack was obtained by interposing a separator between the positive electrode and the negative electrode, and then this electrode stack was wound in a spiral shape to fabricate an electrode group (wound electrode group). Next, this electrode group was placed inside an outer casing. An outer casing made of laminate film containing aluminum foil (barrier layer) was used. Next, the outer casing in which the electrode group was placed was vacuum dried at 105°C for 2 hours, then a non-aqueous electrolyte (non-aqueous electrolyte solution) was injected into the inside of the outer casing, and the opening of the outer casing was sealed. In this way, a non-aqueous electrolyte secondary battery according to Example 1 was fabricated.

[0086] [Example 2] A non-aqueous electrolyte secondary battery according to Example 2 was prepared in the same manner as in Example 1, except that the amount of PVDF added to the positive electrode was changed to 0.8 parts by mass per 100 parts by mass of the positive electrode mixture layer (positive electrode mixture).

[0087] [Example 3] A non-aqueous electrolyte secondary battery according to Example 3 was prepared in the same manner as in Example 2, except that the conductive material in the positive electrode was changed from carbon nanotubes (CNTs) to acetylene black (AB), and the amount of acetylene black (AB) added was changed to 1.0 part by mass per 100 parts by mass of the positive electrode mixture layer (positive electrode mixture).

[0088] [Example 4] A non-aqueous electrolyte secondary battery according to Example 4 was prepared in the same manner as in Example 1, except that the amount of PVDF added to the positive electrode was changed to 1.0 part by mass per 100 parts by mass of the positive electrode mixture layer (positive electrode mixture).

[0089] [Example 5] In the positive electrode, the positive electrode mixture slurry was applied to the positive electrode current collector so that the basis weight of the positive electrode mixture layer (basis weight on one side) was 150 g / m². ２ A non-aqueous electrolyte secondary battery according to Example 5 was prepared in the same manner as in Example 4, except that the coating was applied in the manner described above.

[0090] [Example 6] A non-aqueous electrolyte secondary battery according to Example 6 was prepared in the same manner as in Example 1, except that the amount of PVDF added to the positive electrode was changed to 1.5 parts by mass per 100 parts by mass of the positive electrode mixture layer (positive electrode mixture).

[0091] [Example 7] In the positive electrode, the mass ratio of the first positive electrode active material was set to 40 parts by mass per 100 parts by mass of the total of the first and second positive electrode active materials, and the mass ratio of the second positive electrode active material was set to 60 parts by mass per 100 parts by mass of the total of the first and second positive electrode active materials, and the positive electrode mixture slurry was prepared so that the basis weight of the positive electrode mixture layer (basis weight on one side) in the positive electrode current collector was 150 g / m². ２ A non-aqueous electrolyte secondary battery according to Example 7 was prepared in the same manner as in Example 3, except that the coating was applied in the manner described above.

[0092] [Comparative Example 1] An attempt was made to produce a non-aqueous electrolyte secondary battery according to Comparative Example 1, in the same manner as in Example 1, except that the amount of PVDF added to the positive electrode was changed to 0.4 parts by mass per 100 parts by mass of the positive electrode mixture layer (positive electrode mixture). However, in Comparative Example 1, it was visually observed that the positive electrode mixture layer had peeled off from the positive electrode current collector, so it was not possible to assemble the non-aqueous electrolyte secondary battery.

[0093] [Comparative Example 2] An attempt was made to produce a non-aqueous electrolyte secondary battery according to Comparative Example 2, in the same manner as in Example 1, except that the amount of PVDF added to the positive electrode was changed to 2.0 parts by mass per 100 parts by mass of the positive electrode mixture layer (positive electrode mixture). However, in Comparative Example 2, the viscosity of the positive electrode mixture slurry was high, making it difficult to apply the positive electrode mixture slurry to the positive electrode current collector. Therefore, it was not possible to assemble a non-aqueous electrolyte secondary battery in Comparative Example 2 either.

[0094] For the positive electrode of the non-aqueous electrolyte secondary battery in each example, the mass ratio of the first positive electrode active material and the second positive electrode active material, the amount of conductive material added, the amount of binder (PVDF) added, and the amount of positive electrode mixture slurry applied are shown in Table 1 below.

[0095]

[0096] [Evaluation] (Initial Capacity) The non-aqueous electrolyte secondary batteries according to each example (Examples 1 to 7) were left in an environment of 25°C, and constant current charging was performed with a current of 0.2 It until the voltage reached 4.2 V. Then, constant voltage charging was performed with a constant voltage of 4.2 V until the current reached 0.02 It. Next, constant current discharge was performed with a current of 0.2 It until the voltage reached 2.5 V in an environment of 25°C, and the discharge capacity C1 was determined. The discharge capacity C0 was determined in the same manner as above, except that the current value was changed to 0.05 It. Then, for the non-aqueous electrolyte secondary batteries according to each example, the ratio of C1 / C0 was evaluated as the initial capacity.

[0097] (Initial DC Resistance (DCIR)) For each example of the non-aqueous electrolyte secondary battery, the battery was charged with a constant current of 0.3 It at a temperature of 25°C until the voltage reached 4.1 V, and then charged with a constant voltage of 4.1 V until the current reached 0.05 It. Next, it was discharged with a constant current of 0.3 It for 100 minutes to bring the State of Charge (SOC) to 50%.

[0098] Then, for a battery with a state of charge (SOC) of 50%, ΔV / I was calculated as DCIR when discharged at a constant current (0.5It) for a predetermined time (10s).

[0099] (Solid Content) In each example (Examples 1 to 7, Comparative Example 1, and Comparative Example 2), the mass ratio of solid content in the positive electrode mixture slurry before application to the positive electrode current collector was determined. Specifically, the mass ratio of liquid content in the positive electrode mixture slurry was measured using a Kett moisture meter, and the mass ratio of solid content was determined using the measurement results.

[0100] The evaluation results for initial volume and DCIR for Examples 1 to 7 are shown in Table 2 below. The evaluation results for solid content for each example (Examples 1 to 7, Comparative Example 1, and Comparative Example 2) are also shown in Table 2 below. Note that the evaluation results for initial volume, DCIR, and solid content are shown as relative values ​​with Example 1 set to 1. For initial volume, a value closer to 1 indicates a better result; for DCIR, a value less than 1 indicates a better result; and for solid content, a value greater than 1 indicates a good result, while a value less than 1 indicates a better result the closer to 1.

[0101]

[0102] Table 2 shows that the non-aqueous electrolyte secondary batteries in each example show good results in the evaluation items of initial capacity, DCIR, and solid content. In particular, Examples 4 and 5 show good results in DCIR. In contrast, in Comparative Example 1, although the evaluation of solid content was good, it was not possible to assemble the non-aqueous electrolyte secondary battery, so the evaluation of initial capacity and DCIR could not be performed. In other words, measurement was not possible. Similarly, in Comparative Example 2, the evaluation of solid content was poor, and it was not possible to assemble the non-aqueous electrolyte secondary battery, so the evaluation of initial capacity and DCIR could not be performed. In other words, measurement was not possible.

[0103] The positive electrode for non-aqueous electrolyte secondary batteries relating to this disclosure can be used in applications where high capacity of non-aqueous electrolyte secondary batteries is required.

[0104] 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, 10: Non-aqueous electrolyte secondary battery

Claims

1. The device comprises a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector, wherein the positive electrode mixture layer comprises a first positive electrode active material, a second positive electrode active material, a conductive material, and a binder, wherein the first positive electrode active material is a lithium nickelate composite oxide, and the second positive electrode active material has the general formula: LiFe ｘ M1 １－ｘ PO ４ A lithium phosphate composite oxide represented by the formula (wherein 0 < x ≤ 1, and M1 is at least one metal element selected from the group consisting of Mn, Fe, Co, and Ni), wherein the positive electrode for a non-aqueous electrolyte secondary battery contains 0.6 parts by mass or more and less than 2 parts by mass of the binder per 100 parts by mass of the positive electrode mixture layer.

2. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, comprising 0.6 parts by mass or more and 1 part by mass of the binder per 100 parts by mass of the positive electrode mixture layer.

3. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode mixture layer contains 50 parts by mass or less of the second positive electrode active material with respect to 100 parts by mass of the total of the first positive electrode active material and the second positive electrode active material.

4. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the conductive material comprises carbon nanotubes.

5. The basis weight of the positive electrode mixture layer in the positive electrode current collector is 250 g / m². ２ The above is the positive electrode for a non-aqueous electrolyte secondary battery according to claim 1.

6. The lithium nickelate composite oxide has the general formula: Li ａ [Ni ｙ M2 １－ｙ ]O ２ A positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, which is a compound represented by the formula (wherein 0.9 < a ​​< 1.3, 0.85 ≤ y ≤ 1.0, and M2 is at least one metallic element selected from the group consisting of Co, Mn, and Al).

7. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode is a positive electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 6.

8. The non-aqueous electrolyte secondary battery according to claim 7, wherein the negative electrode comprises a negative electrode current collector and a negative electrode mixture layer disposed on the negative electrode current collector, and the negative electrode mixture layer contains a silicon-containing material as a negative electrode active material.

Images