Positive electrode and nonaqueous electrolyte secondary battery using the same

Abstract

The present application relates to a positive electrode and a nonaqueous electrolyte secondary battery using the same. A positive electrode capable of achieving high capacity and high output of a nonaqueous electrolyte secondary battery is provided. The positive electrode disclosed herein is provided with a positive electrode current collector and a positive electrode active material layer supported on the positive electrode current collector. The positive electrode active material layer contains particles of a lithium complex oxide having a layered structure as a positive electrode active material. The porosity of the positive electrode active material layer is 17% to 20%. The peak pore diameter in the pore distribution of the positive electrode active material layer measured by the mercury intrusion method is 0.400 μm to 0.550 μm.

Description

Technical Field

[0001] This invention relates to a positive electrode. It also relates to a non-aqueous electrolyte secondary battery using this positive electrode. Background Technology

[0002] In recent years, non-aqueous electrolyte secondary batteries such as lithium-ion batteries have become suitable for use in portable power supplies for personal computers, portable terminals, electric vehicles (BEVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and other vehicle power supplies.

[0003] The positive electrode of a non-aqueous electrolyte secondary battery typically comprises a positive electrode active material layer containing particulate lithium composite oxide as the positive electrode active material (see, for example, Patent Documents 1 and 2). With the increasing popularity of non-aqueous electrolyte secondary batteries, there is a demand for further performance improvements. It is known that the capacity of a non-aqueous electrolyte secondary battery can be increased by compressing the positive electrode active material layer to reduce its porosity, i.e., by increasing the density of the positive electrode active material layer (see, for example, Patent Document 3).

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2010-86693

[0007] Patent Document 2: Japanese Patent No. 6859888

[0008] Patent Document 3: International Publication No. 2014 / 118834 Summary of the Invention

[0009] However, when reducing the porosity of the positive electrode active material layer to achieve higher capacity, the contact area between the non-aqueous electrolyte and the positive electrode active material decreases, and the resistance increases, creating the aforementioned contradiction. Therefore, it is difficult to simultaneously achieve high capacity and high output in non-aqueous electrolyte secondary batteries.

[0010] Therefore, the object of the present invention is to provide a positive electrode that enables high capacity and high output of non-aqueous electrolyte secondary batteries.

[0011] The positive electrode disclosed herein comprises a positive current collector and a positive active material layer supported thereon. The positive active material layer contains lithium composite oxide particles with a layered structure as the positive active material. The porosity of the positive active material layer is 17% to 20%. The peak pore size in the pore distribution of the positive active material layer, measured using the mercury infiltration method, is 0.400 μm to 0.550 μm. Based on this configuration, a positive electrode capable of achieving high capacity and high output in non-aqueous electrolyte secondary batteries can be provided.

[0012] In a preferred embodiment of the positive electrode disclosed herein, the porosity of the aforementioned positive electrode active material layer is 17% to 19%. Based on this configuration, a particularly high capacity can be imparted to a non-aqueous electrolyte secondary battery.

[0013] In a preferred embodiment of the positive electrode disclosed herein, the peak pore size is 0.500 μm to 0.530 μm. This configuration enables the non-aqueous electrolyte secondary battery to achieve exceptionally high output.

[0014] In a preferred embodiment of the positive electrode disclosed herein, the lithium composite oxide is a nickel-cobalt-manganese composite oxide. With this configuration, superior battery characteristics, such as low initial resistance, can be imparted to non-aqueous electrolyte secondary batteries.

[0015] In a more preferred embodiment of the positive electrode disclosed herein, the nickel content in the aforementioned lithium-nickel-cobalt-manganese composite oxide is 55 mol% or more relative to the total content of metal elements other than lithium. With this configuration, a particularly high capacity can be imparted to a non-aqueous electrolyte secondary battery.

[0016] From another perspective, the non-aqueous electrolyte secondary battery disclosed herein includes the aforementioned positive electrode, negative electrode, and non-aqueous electrolyte. Based on this configuration, a non-aqueous electrolyte secondary battery with high capacity and high output can be provided. Attached Figure Description

[0017] Figure 1 This is a schematic cross-sectional view illustrating the positive electrode according to one embodiment of the present invention.

[0018] Figure 2 This is a schematic cross-sectional view illustrating the internal structure of a lithium-ion secondary battery according to one embodiment of the present invention.

[0019] Figure 3 This is a schematic exploded view showing the configuration of a wound electrode body of a lithium-ion secondary battery according to one embodiment of the present invention.

[0020] Explanation of reference numerals in the attached figures

[0021] 20. Winded electrode body

[0022] 30 Battery casing

[0023] 36 Safety valve

[0024] 42 Positive extremes

[0025] 42a Positive Current Collector

[0026] 44 Negative extremes

[0027] 44a Negative Current Collector

[0028] 50 Positive electrode sheet (positive electrode)

[0029] 52 Positive current collector

[0030] 52a Non-forming portion of the positive electrode active material layer

[0031] 54 Positive electrode active material layer

[0032] 60 Negative electrode sheet (negative electrode)

[0033] 62 Negative current collector

[0034] 62a Non-forming portion of the negative electrode active material layer

[0035] 64 Negative Electrode Active Material Layer

[0036] 70. Separator sheet (separator body)

[0037] 80 Non-aqueous electrolytes

[0038] 100 Lithium-ion Secondary Battery Detailed Implementation

[0039] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that any matters necessary for the implementation of the present invention not mentioned in this specification can be understood by those skilled in the art based on prior art. The present invention can be implemented based on the content disclosed in this specification and common technical knowledge in the field. Furthermore, in the following drawings, components and parts that perform the same function are labeled with the same reference numerals. Additionally, the dimensional relationships (length, width, thickness, etc.) in the drawings do not reflect actual dimensional relationships. It should be noted that the numerical range represented as "A to B" in this specification includes both A and B.

[0040] It should be noted that in this specification, "secondary battery" refers to an energy storage device capable of repeated charging and discharging, and is a term that includes energy storage components such as batteries and double-layer capacitors. Furthermore, in this specification, "lithium-ion secondary battery" refers to a secondary battery that uses lithium ions as charge carriers and achieves charging and discharging through the movement of lithium ions' charge between the positive and negative electrodes.

[0041] The present invention will now be described in detail using the positive electrode of a lithium-ion secondary battery as an example, but it is not intended to limit the present invention to the contents described in this embodiment. Figure 1 This is a schematic cross-sectional view along the thickness direction of the positive electrode involved in this embodiment.

[0042] As shown in the figure, the positive electrode 50 includes a positive current collector 52 and a positive active material layer 54 supported on the positive current collector 52. In the example shown, the positive active material layer 54 is disposed on both sides of the positive current collector 52. However, the positive active material layer 54 may also be disposed on only one side of the positive current collector 52. Preferably, the positive active material layer 54 is disposed on both sides of the positive current collector 52.

[0043] As the positive current collector 52, a known positive current collector used in lithium-ion secondary batteries can be used, such as a sheet or foil made of a metal with good conductivity (e.g., aluminum, nickel, titanium, stainless steel, etc.). Aluminum foil is preferred as the positive current collector 52.

[0044] There is no particular limitation on the size of the positive current collector 52, which can be determined appropriately according to the battery design. When aluminum foil is used as the positive current collector 52, its thickness is not particularly limited, for example, it is 5μm or more and 35μm or less, preferably 7μm or more and 20μm or less.

[0045] In this embodiment, the porosity of the positive electrode active material layer 54 is 17% to 20%. Furthermore, in this embodiment, the peak pore size in the pore distribution of the positive electrode active material layer 54, measured using the mercury infiltration method, is 0.400 μm to 0.550 μm.

[0046] The positive electrode active material layer 54 contains lithium composite oxide particles with a layered structure as the positive electrode active material. Therefore, voids are created between these particles. Non-aqueous electrolytes can penetrate into these voids.

[0047] Generally, increasing the filling rate of the positive electrode active material in the positive electrode active material layer can increase the capacity of non-aqueous electrolyte secondary batteries. However, increasing the filling rate of the positive electrode active material in the positive electrode active material layer reduces the porosity of the positive electrode active material layer, decreasing the voids that the non-aqueous electrolyte can penetrate. Therefore, a contradiction exists: in the positive electrode active material layer, the contact area between the non-aqueous electrolyte and the positive electrode active material decreases, and the resistance increases. Thus, in non-aqueous electrolyte secondary batteries, it is difficult to simultaneously achieve high capacity and high output.

[0048] To address this, the inventors conducted in-depth research on the capacity and output of non-aqueous electrolyte secondary batteries by controlling the porosity and pore diameter of the positive electrode active material layer using lithium composite oxide particles with different particle characteristics. As a result, a novel positive electrode active material layer was obtained, achieving both lower porosity and larger peak pore size compared to conventional positive electrode active material layers. Furthermore, by using a positive electrode with this novel positive electrode active material layer, both high capacity and high output of non-aqueous electrolyte secondary batteries were simultaneously achieved.

[0049] That is, according to the positive electrode 50 of this embodiment, which appropriately controls the porosity and peak pore size of the positive electrode active material layer 54, the capacity of the non-aqueous electrolyte secondary battery can be improved, and the output of the non-aqueous electrolyte secondary battery can be improved.

[0050] Specifically, by making the porosity of the positive electrode active material layer 54 17% or more and the peak pore size 0.400 μm or more, the output of the non-aqueous electrolyte secondary battery can be improved. On the other hand, by making the porosity of the positive electrode active material layer 54 20% or less and the peak pore size 0.550 μm or less, the capacity of the non-aqueous electrolyte secondary battery can be improved.

[0051] Furthermore, in non-aqueous electrolyte secondary batteries, during repeated charge-discharge cycles, the positive electrode active material undergoes a side reaction with the non-aqueous electrolyte, leading to the decomposition of the non-aqueous electrolyte and the generation of gas. If this gas remains inside the electrode body, it can cause degradation of battery characteristics (especially capacity degradation). However, the positive electrode 50 according to this embodiment has a porosity and peak pore size within the aforementioned range, making it difficult for the positive electrode active material to undergo a side reaction with the non-aqueous electrolyte. Therefore, the positive electrode 50 according to this embodiment can also suppress the degradation of battery characteristics (especially capacity degradation) during repeated charge-discharge cycles of non-aqueous electrolyte secondary batteries.

[0052] The porosity of the positive electrode active material layer 54 is preferably 17% to 19%. The peak pore size of the positive electrode active material layer 54 is preferably 0.450 μm or more, more preferably 0.480 μm or more, and even more preferably 0.500 μm or more. The peak pore size of the positive electrode active material layer 54 is preferably 0.530 μm or less.

[0053] It should be noted that the porosity of the positive electrode active material layer 54 can be determined using the mercury infiltration method. Specifically, it can be determined using a mercury infiltration porosimeter according to known methods. Therefore, by using a mercury infiltration porosimeter and measuring according to known methods, the porosity of the positive electrode active material layer 54 and the peak pore size in the pore distribution can be determined. Specifically, for example, the pore distribution of the positive electrode active material layer can be measured within a pressure range of 4 psi to 60000 psi, and the peak pore size and porosity can be determined using a pore distribution curve in the range of 0.01 μm to 10 μm.

[0054] Examples of lithium composite oxides with layered structures include lithium-nickel composite oxides, lithium-cobalt composite oxides, lithium-manganese composite oxides, lithium-nickel-cobalt-manganese composite oxides, lithium-nickel-cobalt-aluminum composite oxides, and lithium-iron-nickel-manganese composite oxides. The layered structure (i.e., layered crystal structure) of lithium composite oxide particles can be confirmed using known methods (e.g., X-ray diffraction).

[0055] It should be noted that in this specification, "lithium-nickel-cobalt-manganese composite oxide" is a term encompassing oxides containing one or more additive elements besides Li, Ni, Co, Mn, and O. Examples of such additive elements include transition metals and typical metallic elements such as Mg, Ca, Al, Ti, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, W, Na, Fe, Zn, and Sn. Additionally, additive elements can also be half-metals such as B, C, Si, and P, and non-metals such as S, F, Cl, Br, and I. This also applies to the aforementioned lithium-nickel composite oxides, lithium-cobalt composite oxides, lithium-manganese composite oxides, lithium-nickel-cobalt-aluminum composite oxides, and lithium-iron-nickel-manganese composite oxides.

[0056] Due to its excellent properties such as low initial resistance, lithium nickel cobalt manganese composite oxides with a layered structure are preferred. From the viewpoint of further increasing the capacity of non-aqueous electrolyte secondary batteries, the content of nickel in the lithium nickel cobalt manganese composite oxide relative to the total content of metal elements other than lithium is preferably more than 50 mol%, and more preferably more than 55 mol%.

[0057] As a lithium nickel cobalt manganese composite oxide, specifically, a lithium nickel cobalt manganese composite oxide having the composition shown in formula (I) is preferred.

[0058] Li 1+x Ni y Co z Mn (1-y-z) M α O 2-β Q β (I)

[0059] In equation (I), x, y, z, α, and β satisfy -0.3 ≤ x ≤ 0.3, 0.1 < y < 0.9, 0.1 < z < 0.5, 0 ≤ α ≤ 0.1, and 0 ≤ β ≤ 0.5, respectively. M is at least one element selected from Zr, Mo, W, Mg, Ca, Na, Fe, Cr, Zn, Sn, and Al. Q is at least one element selected from F, Cl, and Br.

[0060] In equation (I), x, y, z, α, and β satisfy -0.3 ≤ x ≤ 0.3, 0.1 < y < 0.9, 0 < z < 0.5, 0 ≤ α ≤ 0.1, and 0 ≤ β ≤ 0.5, respectively. M is at least one element selected from Zr, Mo, W, Mg, Ca, Na, Fe, Cr, Zn, Sn, B, and Al. Q is at least one element selected from F, Cl, and Br.

[0061] From the perspective of further increasing the capacity of non-aqueous electrolyte secondary batteries, y and z preferably satisfy 0.50<y≤0.95 and 0.02≤z<0.48, respectively; more preferably, they satisfy 0.55≤y≤0.95 and 0.02≤z≤0.43; and even more preferably, they satisfy 0.60≤y≤0.95 and 0.02≤z≤0.38.

[0062] The positive electrode active material layer 54 may contain components other than the positive electrode active material, such as lithium triphosphate, conductive materials, and binders. As the conductive material, carbon black such as acetylene black (AB) or other carbon materials (such as graphite) are preferred. As the binder, polyvinylidene fluoride (PVDF) can be used, for example.

[0063] The content of the positive electrode active material in the positive electrode active material layer 54 (i.e., the content of the positive electrode active material relative to the total mass of the positive electrode active material layer 54) is not particularly limited, but is preferably 70% by mass or more, more preferably 80% by mass or more and 97% by mass or less, and even more preferably 85% by mass or more and 96% by mass or less. The content of trilithium phosphate in the positive electrode active material layer 54 is not particularly limited, but is preferably 1% by mass or more and 15% by mass or less, more preferably 2% by mass or more and 12% by mass or less. The content of conductive material in the positive electrode active material layer 54 is not particularly limited, but is preferably 1% by mass or more and 15% by mass or less, more preferably 3% by mass or more and 13% by mass or less. The content of binder in the positive electrode active material layer 54 is not particularly limited, but is preferably 1% by mass or more and 15% by mass or less, more preferably 1.5% by mass or more and 10% by mass or less.

[0064] The thickness of the positive electrode active material layer 54 is not particularly limited, for example, it is 10 μm or more and 300 μm or less, preferably 20 μm or more and 200 μm or less.

[0065] In the non-positive electrode active material layer non-forming portion 52a of the positive electrode sheet 50, an insulating protective layer (not shown) containing insulating particles can be provided at a position adjacent to the positive electrode active material layer 54. This protective layer can prevent short circuits between the non-positive electrode active material layer non-forming portion 52a and the negative electrode active material layer 64.

[0066] The method for obtaining the positive electrode active material layer 54 having a porosity and peak pore size within the aforementioned range is not particularly limited. As a preferred method, a method using two types of positive electrode active material particles with different particle properties can be cited.

[0067] (1) The first lithium composite oxide particles have a layered structure, an average particle size of 3.0 μm to 6.0 μm, and a DBP oil absorption capacity of 15 mL / 100g to 27 mL / 100g;

[0068] (2) The second lithium composite oxide particles have a layered structure, with an average particle size of 10.0 μm to 22.0 μm and a DBP oil absorption capacity of 14 mL / 100g to 22 mL / 100g.

[0069] The first lithium composite oxide particles and the second lithium composite oxide particles are described in detail below. Both the first and second lithium composite oxide particles are lithium composite oxide particles with a layered structure, and their compositions may be the same or different. Preferably, the first and second lithium composite oxide particles are lithium-nickel-cobalt-manganese composite oxide particles.

[0070] From the viewpoint of high capacity, regarding the first lithium composite oxide particles, the nickel content is preferably 55 mol% or more, more preferably 60 mol% or more, relative to the total amount of metal elements other than lithium in the lithium-nickel-cobalt-manganese composite oxide. Furthermore, from the viewpoint of high capacity, regarding the second lithium composite oxide particles, the nickel content is preferably more than 50 mol%, more preferably 55 mol% or more, relative to the total amount of metal elements other than lithium in the lithium-nickel-cobalt-manganese composite oxide.

[0071] From the viewpoint of energy density, regarding the first lithium composite oxide particle, in the above formula (I), y and z preferably satisfy 0.55≤y≤0.95 and 0.02≤z≤0.43, respectively, and more preferably satisfy 0.60≤y≤0.95 and 0.02≤z≤0.38. From the viewpoint of energy density, in the above formula (I), regarding the second lithium composite oxide particle, y and z preferably satisfy 0.50<y≤0.95 and 0.02≤z<0.48, respectively, and more preferably satisfy 0.55≤y≤0.95 and 0.02≤z≤0.43.

[0072] It should be noted that in this specification, the average particle size (D50) of lithium composite oxide particles refers to the median particle size (D50), which is the particle size that corresponds to 50% of the cumulative frequency from the smallest particle side in a volume-based particle size distribution based on laser diffraction and scattering. Therefore, the average particle size (D50) can be determined using a laser diffraction and scattering particle size distribution measuring device or the like.

[0073] The average particle size of the first and second lithium composite oxide particles can be adjusted by known methods (e.g., crushing, grading, etc.).

[0074] The DBP oil absorption of the first and second lithium composite oxide particles can be adjusted, for example, by using secondary particles formed from the aggregation of primary particles as lithium composite oxide particles, thereby changing the primary particle size. Alternatively, the DBP oil absorption of the first and second lithium composite oxide particles can be adjusted by changing the amount of internal porosity of the lithium composite oxide particles.

[0075] For example, when using secondary particles formed by the aggregation of primary particles as the first lithium composite oxide particles, and setting the average primary particle size to approximately 1.4 μm to 2.5 μm, it is easy to adjust the oil absorption of the DBP to a range of 15 mL / 100g to 27 mL / 100g. In particular, single particles can form secondary particles formed by the aggregation of multiple particles. Therefore, as the first lithium composite oxide particles, single particles, especially single particles with an average primary particle size of approximately 1.4 μm to 2.5 μm, are preferred. Here, "single particle" refers to a particle generated by the growth of a single crystal nucleus, and therefore a single crystal particle that does not contain grain boundaries. The fact that the particle is a single crystal can be confirmed, for example, by analyzing the electron beam diffraction image using a transmission electron microscope (TEM).

[0076] For example, when using secondary particles formed by the aggregation of primary particles as the second lithium composite oxide particles, and setting the average primary particle size to about 0.1μm to 0.3μm, it is easy to adjust the oil absorption of the DBP to the range of 14mL / 100g to 22mL / 100g.

[0077] In a preferred embodiment of the positive electrode active material involved in this embodiment, the first lithium composite oxide particles are single particles and aggregated particles with an average primary particle size of 1.4 μm to 2.5 μm, and the second lithium composite oxide particles are secondary particles formed by the aggregation of primary particles with an average primary particle size of 0.1 to 0.3 μm.

[0078] It should be noted that the average primary particle size refers to the average of the major diameters of any 50 or more randomly selected primary particles obtained from an electron microscope image of lithium composite oxide particles. Therefore, the average primary particle size can be calculated, for example, by obtaining SEM images of lithium composite oxide particles using a scanning electron microscope (SEM), determining the major diameters of any 50 or more randomly selected primary particles using image-resolution particle size distribution measurement software (such as "Mac-View"), and then calculating their average value.

[0079] Because it imparts excellent output characteristics to non-aqueous electrolyte secondary batteries, the dibutyl phthalate oil absorption capacity of the first lithium composite oxide particles is preferably 18 mL / 100g to 27 mL / 100g, more preferably 18 mL / 100g to 25 mL / 100g. Because it imparts excellent output characteristics to non-aqueous electrolyte secondary batteries, the dibutyl phthalate oil absorption capacity of the second lithium composite oxide particles is preferably 16 mL / 100g to 22 mL / 100g, more preferably 16.5 mL / 100g to 21.5 mL / 100g.

[0080] The average particle size (D50) of the first lithium composite oxide particles is preferably 3.0 μm to 5.5 μm, more preferably 3.0 μm to 5.0 μm. The average particle size (D50) of the second lithium composite oxide particles is preferably 10.0 μm to 21.0 μm, more preferably 10.0 μm to 20.0 μm.

[0081] Because it can impart excellent output characteristics to non-aqueous electrolyte secondary batteries, the BET specific surface area of ​​the first lithium composite oxide particles is preferably 0.54 m². 2 / g or more, preferably 0.54m 2 / g~0.69m 2 / g. Because it can impart excellent output characteristics to non-aqueous electrolyte secondary batteries, the BET specific surface area of ​​the second lithium composite oxide particles is preferably 0.18 m² / g. 2 / g or more, preferably 0.18m 2 / g~0.36m 2 / g.

[0082] It should be noted that the BET specific surface area of ​​the first lithium composite oxide particles and the second lithium composite oxide particles can be determined using a commercially available specific surface area measuring device (such as "Macsorb Model-1208" (manufactured by Mountech)) by nitrogen adsorption method.

[0083] Because it can significantly improve the capacity of non-aqueous electrolyte secondary batteries, the tap density of the first lithium composite oxide particles is preferably 2.0 g / cm³. 3 The above, more preferably 2.0 g / cm³ 3 ~2.2g / cm 3 Because it can significantly improve the capacity of non-aqueous electrolyte secondary batteries, the tap density of the second lithium composite oxide particles is preferably 2.4 g / cm³. 3 The above, more preferably 2.4 g / cm³ 3 ~2.5g / cm 3 .

[0084] It should be noted that the tap density of the first lithium composite oxide particles and the second lithium composite oxide particles can be obtained by measuring the powder filling density after 2000 taps with an amplitude of 8mm using a commercially available tapping instrument (such as the "KRS-409 type" (manufactured by Kurashiki Science Machines Co., Ltd.)), and calculating the average of the two measurement results of the powder filling density.

[0085] The content ratio of the first lithium composite oxide particles to the second lithium composite oxide particles is not particularly limited. Their mass ratio (first lithium composite oxide particles: second lithium composite oxide particles) is, for example, 10:90 to 90:10, preferably 20:80 to 80:20, more preferably 30:70 to 70:30, and even more preferably 30:70 to 60:40.

[0086] The positive electrode active material may consist solely of first lithium composite oxide particles and second lithium composite oxide particles. In addition to the first and second lithium composite oxide particles, the positive electrode active material may further contain particles that function as the positive electrode active material.

[0087] There is no particular limitation on the overall tap density of the positive electrode active material. However, since it can significantly improve the capacity and output of non-aqueous electrolyte secondary batteries, the overall tap density of the positive electrode active material is preferably 2.7 g / cm³. 3 ~3.0g / cm 3 More preferably 2.8 g / cm³ 3 ~3.0g / cm 3 Further optimized to 2.9 g / cm³ 3 ~3.0g / cm 3 .

[0088] The overall tap density of the positive electrode active material can be determined by measuring the powder filling density after 2000 taps with an amplitude of 8mm using a commercially available tapping instrument (such as the "KRS-409 type" (manufactured by Kurashiki Science Machines Co., Ltd.)). The average value of the two measurements of the powder filling density can then be calculated.

[0089] There is no particular limitation on the overall DBP oil absorption of the positive electrode active material. Since it can particularly improve the capacity and output of non-aqueous electrolyte secondary batteries, the overall DBP oil absorption of the positive electrode active material is preferably 14.5 mL / 100g to 18.5 mL / 100g, more preferably 16.2 mL / 100g to 18.2 mL / 100g, and even more preferably 17.0 mL / 100g to 18.0 mL / 100g.

[0090] The overall DBP absorption of the positive electrode active material can be determined using dibutyl phthalate (DBP) as a reagent liquid, according to the method described in JIS K6217-4:2008, and can be calculated as the average of three measurement results.

[0091] The positive electrode 50 in this embodiment can be manufactured by preparing a paste for forming a positive electrode active material layer containing a first lithium composite oxide particle, a second lithium composite oxide particle, a solvent (dispersion medium), a binder as needed, a conductive material, etc., coating the paste onto the positive electrode current collector 52 and drying it, and then pressing it as needed.

[0092] According to the positive electrode of this embodiment, the capacity of a non-aqueous electrolyte secondary battery can be improved, and the output of the non-aqueous electrolyte secondary battery can also be improved. Furthermore, according to the positive electrode of this embodiment, the non-aqueous electrolyte secondary battery can be endowed with excellent capacity degradation resistance during repeated charge-discharge cycles. The positive electrode of this embodiment is typically used for non-aqueous electrolyte secondary batteries, and is preferably used for non-aqueous lithium-ion secondary batteries. The positive electrode of this embodiment can also be used as the positive electrode of an all-solid-state secondary battery.

[0093] Therefore, from another perspective, the non-aqueous electrolyte secondary battery according to this embodiment has a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode is the positive electrode according to the above embodiment.

[0094] Hereinafter, the non-aqueous electrolyte secondary battery according to this embodiment will be described in detail using a flat square lithium-ion secondary battery having a flat wound electrode body and a flat battery casing as an example. However, the non-aqueous electrolyte secondary battery according to this embodiment is not limited to the example described below.

[0095] Figure 2 The lithium-ion secondary battery 100 shown is a sealed battery constructed by housing a flat, wound electrode body 20 and a non-aqueous electrolyte (not shown) within a flat, square battery casing (i.e., outer container) 30. The battery casing 30 is provided with a positive terminal 42 and a negative terminal 44 for external connection, and a thin-walled safety valve 36 configured to release internal pressure if the internal pressure of the battery casing 30 rises above a predetermined level. The positive and negative terminals 42 and 44 are electrically connected to positive and negative current collectors 42a and 44a, respectively. The battery casing 30 is made of a lightweight and thermally conductive metal material, such as aluminum. Furthermore, a current blocking mechanism (CID) may be provided between the positive terminal 42 and the positive current collector 42a, or between the negative terminal 44 and the negative current collector 44a.

[0096] like Figure 2 and Figure 3As shown, the wound electrode body 20 has a configuration in which a positive electrode sheet 50 and a negative electrode sheet 60 are overlapped and wound along the length direction, separated by two elongated separator sheets 70. The positive electrode sheet 50 has a configuration in which a positive electrode active material layer 54 is formed along the length direction on one or both sides (in this case, both sides) of the elongated positive electrode current collector 52. The negative electrode sheet 60 has a configuration in which a negative electrode active material layer 64 is formed along the length direction on one or both sides (in this case, both sides) of the elongated negative electrode current collector 62.

[0097] The non-formed portion 52a of the positive active material layer (i.e., the portion where the positive current collector 52 is exposed without the formation of the positive active material layer 54) and the non-formed portion 62a of the negative active material layer (i.e., the portion where the negative current collector 62 is exposed without the formation of the negative active material layer 64) are formed to extend outward from both ends in the winding axis direction of the wound electrode body 20 (i.e., the sheet width direction orthogonal to the aforementioned length direction). The non-formed portion 52a of the positive active material layer and the non-formed portion 62a of the negative active material layer each function as current collectors. A positive current collector plate 42a and a negative current collector plate 44a are respectively bonded to the non-formed portion 52a of the positive active material layer and the non-formed portion 62a of the negative active material layer. Furthermore, the shapes of the non-formed portion 52a of the positive active material layer and the non-formed portion 62a of the negative active material layer are not limited to the example shown in the figure. The non-forming portion 52a of the positive electrode active material layer and the non-forming portion 62a of the negative electrode active material layer can be formed into a current collector sheet processed into a specified shape.

[0098] The positive electrode 50 described in this embodiment is used as the positive electrode sheet 50. It should be noted that in this configuration example, the positive electrode sheet 50 has positive electrode active material layers 54 formed on both sides of the positive electrode current collector 52.

[0099] As the negative electrode current collector 62 constituting the negative electrode sheet 60, a known negative electrode current collector used in lithium-ion secondary batteries can be used. Examples of such current collectors include sheets or foils made of metals with good conductivity (such as copper, nickel, titanium, stainless steel, etc.). Copper foil is preferred as the negative electrode current collector 52.

[0100] There is no particular limitation on the size of the negative electrode current collector 62, which can be appropriately determined according to the battery design. When copper foil is used as the negative electrode current collector 62, its thickness is not particularly limited, for example, it is 5 μm or more and 35 μm or less, preferably 7 μm or more and 20 μm or less.

[0101] The negative electrode active material layer 64 contains a negative electrode active material. This negative electrode active material can be a carbon material such as graphite, hard carbon, or soft carbon. The graphite can be natural graphite or artificial graphite, or it can be graphite coated with an amorphous carbon material, in the form of amorphous carbon-coated graphite.

[0102] The average particle size (median particle size: D50) of the negative electrode active material is not particularly limited, but is, for example, 0.1 μm or more and 50 μm or less, preferably 1 μm or more and 25 μm or less, and more preferably 5 μm or more and 20 μm or less. It should be noted that the average particle size (D50) of the negative electrode active material can be determined, for example, by laser diffraction scattering.

[0103] The negative electrode active material layer 64 may contain components other than the active material, such as adhesives and thickeners. Examples of adhesives include styrene-butadiene rubber (SBR) and polyvinylidene fluoride (PVDF). Examples of thickeners include carboxymethyl cellulose (CMC).

[0104] The content of the negative electrode active material in the negative electrode active material layer is preferably 90% by mass or more, more preferably 95% by mass or more and 99% by mass or less. The content of the binder in the negative electrode active material layer is preferably 0.1% by mass or more and 8% by mass or less, more preferably 0.5% by mass or more and 3% by mass or less. The content of the thickener in the negative electrode active material layer is preferably 0.3% by mass or more and 3% by mass or less, more preferably 0.5% by mass or more and 2% by mass or less.

[0105] There is no particular limitation on the thickness of the negative electrode active material layer 64, for example, it is 10 μm or more and 300 μm or less, preferably 20 μm or more and 200 μm or less.

[0106] Examples of separators 70 include porous sheets (membranes) made of resins such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. The porous sheet can be a single-layer structure or a multi-layered structure (e.g., a three-layer structure with PP layers laminated on both sides of a PE layer). A heat-resistant layer (HRL) can also be provided on the surface of the separator 70.

[0107] Non-aqueous electrolytes typically contain a non-aqueous solvent and a supporting salt (electrolyte salt). As the non-aqueous solvent, various organic solvents commonly used in lithium-ion secondary battery electrolytes, such as carbonates, ethers, esters, nitriles, sulfones, and lactones, can be used without particular limitation. Specific examples include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), monofluoromethyl difluoromethyl carbonate (F-DMC), and dimethyl trifluorocarbonate (TFDMC). Such non-aqueous solvents can be used alone or in appropriate combinations of two or more.

[0108] As the supporting salt, lithium salts such as LiPF6, LiBF4, and lithium bis(fluorosulfonyl)imide (LiFSI) (LiPF6 is preferred) can be used. The concentration of the supporting salt is preferably 0.7 mol / L or more and 1.3 mol / L or less.

[0109] It should be noted that the non-aqueous electrolyte 80 may contain components other than those mentioned above, as long as it does not significantly impair the effect of the present invention. These components may include film-forming agents such as oxalic acid complexes, gas generators such as biphenyl (BP) and cyclohexylbenzene (CHB), and various additives such as tackifiers.

[0110] The lithium-ion secondary battery 100 configured as described above has high capacity and excellent resistance to capacity degradation during repeated charge and discharge cycles. The lithium-ion secondary battery 100 can be used for various applications. Specific applications include portable power supplies for personal computers, portable electronic devices, portable terminals, etc.; vehicle power supplies for electric vehicles (BEVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), etc.; and batteries for small energy storage devices, etc., with vehicle power supplies being the preferred option. The lithium-ion secondary battery 100 can typically be used in the form of a battery pack consisting of multiple batteries connected in series and / or in parallel.

[0111] Furthermore, as an example, a square lithium-ion secondary battery 100 having a flat, wound electrode body 20 has been described. However, the non-aqueous electrolyte secondary battery disclosed herein can also be configured as a lithium-ion secondary battery having a stacked electrode body (i.e., an electrode body in which multiple positive electrodes and multiple negative electrodes are alternately stacked). The stacked electrode body may include multiple separators in such a way that a separator is sandwiched between each of the positive and negative electrodes, or it may be an electrode body in which positive and negative electrodes are alternately stacked while folding back one separator.

[0112] Furthermore, the non-aqueous electrolyte secondary battery disclosed herein can also be configured as a coin-type lithium-ion secondary battery, a button-type lithium-ion secondary battery, a cylindrical lithium-ion secondary battery, or a stacked-casing lithium-ion secondary battery. Additionally, the non-aqueous electrolyte secondary battery disclosed herein can also be configured as a non-aqueous electrolyte secondary battery other than a lithium-ion secondary battery using known methods.

[0113] On the other hand, the positive electrode active material involved in this embodiment can also be used to construct an all-solid-state secondary battery (especially an all-solid-state lithium-ion secondary battery) by using a solid electrolyte instead of a non-aqueous electrolyte 80, according to known methods.

[0114] The following describes embodiments of the present invention, but it is not intended to limit the present invention to the contents shown in these embodiments.

[0115] <Examples 1-4 and Comparative Examples 1-8>

[0116] LiNi was prepared as the first lithium composite oxide particle as the positive electrode active material according to the mass ratio shown in Table 1. 0.6 Co 0.2 Mn 0.2 O2, and LiNi as the second lithium composite oxide particle 0.55 Co 0.2 Mn 0.25 O2. Particles having the particle characteristics shown in Table 1 were used as both the first and second lithium composite oxide particles. However, in Comparative Examples 3 and 4, LiNi was used alone as the first lithium composite oxide particle. 0.6 Co 0.2 Mn 0.2 In Comparative Examples 5 and 6, O2 was used as the positive electrode active material, and LiNi was used alone as the second lithium composite oxide particle. 0.55 Co 0.2 Mn 0.25 O2 was used as the positive electrode active material. The positive electrode active material, acetylene black (AB) as the conductive material, and polyvinylidene fluoride (PVDF) as the binder were mixed at a mass ratio of positive electrode active material:AB:PVDF = 97.5:1.5:1.0. An appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to the resulting mixture to prepare a slurry for forming the positive electrode active material layer.

[0117] A slurry for forming a positive electrode active material layer is coated on both sides of a 15μm thick aluminum foil current collector and then dried. The coating is then rolled using calendering rollers to produce a positive electrode sheet.

[0118] In addition, graphite (C) as the negative electrode active material, styrene-butadiene rubber (SBR) as the binder, and carboxymethyl cellulose (CMC) as the tackifier were mixed in ion-exchanged water at a mass ratio of C:SBR:CMC = 98:1:1 to prepare a slurry for forming the negative electrode active material layer. This slurry was then coated onto a copper foil with a thickness of 8 μm. After drying, the foil was rolled to a specified thickness to produce a negative electrode sheet.

[0119] As a separator, a porous polyolefin sheet with a thickness of 24 μm and a three-layer structure of PP / PE / PE is prepared. The positive electrode sheet and the negative electrode sheet are overlapped with the separator sandwiched between them to obtain a laminate. Next, the laminate is wound to obtain a wound body, which is then pressed into a flat shape to obtain a flat wound electrode body.

[0120] The electrode terminals were installed on the electrode body, inserted into the battery casing, and fused together. A non-aqueous electrolyte was then injected. It should be noted that the non-aqueous electrolyte was a non-aqueous electrolyte containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) at a concentration of 1.2 mol / L, dissolved as a supporting salt, in a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of EC:EMC:DMC = 30:30:40. The battery casing was then sealed, thus obtaining the evaluation lithium-ion secondary batteries of Examples 1-4 and Comparative Examples 1-8.

[0121] <Examples 5, 6 and Comparative Examples 9, 10>

[0122] LiNi was prepared as the first lithium composite oxide particle as the positive electrode active material according to the mass ratio shown in Table 2. 0.35 Co 0.30 Mn 0.35 O2, and LiNi as the second lithium composite oxide particle 0.55 Co 0.2 Mn 0.25 O2. Particles with the particle characteristics shown in Table 2 were used as the first and second lithium composite oxide particles. The positive electrode active material, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVDF) as a binder were mixed at a mass ratio of positive electrode active material:AB:PVDF = 97.5:1.5:1.0. An appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to the resulting mixture to prepare a slurry for forming the positive electrode active material layer.

[0123] Alumina powder, carbon material as a conductive material, and polyvinylidene fluoride (PVDF) as a binder are mixed in a mass ratio of alumina powder:carbon material:PVDF = 83:3:14. An appropriate amount of N-methyl-2-pyrrolidone (NMP) is added to the resulting mixture to prepare a slurry for forming a protective layer.

[0124] A slurry for forming a positive electrode active material layer and a slurry for forming a protective layer are coated on both sides of a 15 μm thick aluminum foil positive electrode current collector, and then dried. The slurry for forming the positive electrode active material layer is applied in a wide width along one end of the positive electrode current collector, while the slurry for forming the protective layer is applied adjacent to the slurry in a narrow width. The coating is then rolled using calendering rollers to create a master sheet for the positive electrode sheet. This master sheet is cut to specified dimensions to obtain multiple positive electrode sheets.

[0125] In addition, graphite (C) as the negative electrode active material, styrene-butadiene rubber (SBR) as the binder, and carboxymethyl cellulose (CMC) as the tackifier were mixed in ion-exchanged water at a mass ratio of C:SBR:CMC = 98:1:1 to prepare a slurry for forming the negative electrode active material layer. This slurry was then coated onto an 8 μm thick copper foil. After drying, it was rolled to a specified thickness to create a master sheet for the negative electrode sheet. The master sheet was then cut to specified dimensions to obtain multiple negative electrode sheets.

[0126] The above-prepared positive and negative electrode sheets are alternately stacked while sandwiching a 24 μm thick porous polyolefin sheet with a three-layer structure of PP / PE / PE as a separator. This results in a stacked electrode body.

[0127] The electrode terminals were installed on the electrode body, inserted into the battery casing, and fused together. A non-aqueous electrolyte was then injected. It should be noted that the non-aqueous electrolyte was a non-aqueous electrolyte containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) at a concentration of 1.2 mol / L, with LiPF6 dissolved as a supporting salt in a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) at a volume ratio of EC:EMC:DMC = 30:30:40. The battery casing was then sealed, thus obtaining the evaluation lithium-ion secondary batteries of Examples 5, 6, and Comparative Examples 9, 10.

[0128] <Determination of porosity and peak pore size of positive electrode active material layer>

[0129] Test pieces of the positive electrodes prepared in each example and comparative example were prepared and placed in the cell of a mercury porosimeter "AutoporeIII 9410" (manufactured by Shimadzu Corporation). The pore distribution of the positive electrode active material layer was measured within a pressure range of 4 psi to 60,000 psi. The peak pore size and porosity were determined using pore distribution curves in the range of 0.01 μm to 10 μm.

[0130] <Determination of DBP oil absorption of lithium composite oxide particles>

[0131] The DBP oil absorption of lithium composite oxide particles was determined according to the method described in JIS K6217-4:2008. Specifically, 60 g of lithium composite oxide particles were measured as a sample and placed in the oil absorption measuring apparatus "S-500" (manufactured by Asahi Soken Kaisha). While stirring the sample with a stirring blade, DBP was added dropwise, and the torque curve was recorded. The amount of DBP added at 70% of the maximum torque was read, and the DBP oil absorption (mL / 100g) was calculated based on this. This measurement was performed three times, and the average value of the obtained DBP oil absorption was taken as the DBP oil absorption of the lithium composite oxide particles used in the sample. The results are shown in Tables 1 and 2.

[0132] <Determination of the average particle size of lithium composite oxide particles>

[0133] Using a commercially available laser diffraction-scattering particle size distribution measuring device, the volume-based particle size distribution of lithium composite oxide particles was measured, and the particle size corresponding to the cumulative frequency of 50% by volume from the smallest particle side was determined as the average particle size (D50) of the lithium composite oxide particles. The results are shown in Tables 1 and 2.

[0134] <Mean primary particle size determination of lithium composite oxide particles>

[0135] Microscopic images of lithium composite oxide particles were obtained using a scanning electron microscope. The major diameter of more than 50 randomly selected primary particles was determined using the image-resolving particle size distribution measurement software "Mac-View". The average value was calculated and used as the average primary particle size of the lithium composite oxide particles. The results are shown in Tables 1 and 2.

[0136] Initial capacity and cycling characteristics evaluation

[0137] Each evaluation lithium-ion secondary battery was charged at a constant current of 0.1C to 4.2V at room temperature, and then discharged at a constant current of 0.1C to 2.5V. The discharge capacity at this point was determined and used as the initial capacity. The ratio of the initial capacity of each embodiment and the other comparative examples was calculated when the initial capacity of Comparative Example 1 was set to 100. The results are shown in Tables 1 and 2.

[0138] Each evaluation lithium-ion secondary battery was placed at 25°C and charged at a constant current of 2C to 4.2V, stopped for 10 minutes, and then discharged at a constant current of 2C to 3.0V, stopped for 10 minutes, constituting one charge-discharge cycle. This process was repeated 500 times. The discharge capacity after 500 cycles was calculated using the same method as for the initial capacity. The capacity retention rate (%) was calculated as an indicator of cycle characteristics by multiplying (discharge capacity after 500 charge-discharge cycles / initial capacity) by 100. The results are shown in Tables 1 and 2.

[0139] <Output Characteristics>

[0140] The initial resistance was evaluated as an indicator of output characteristics. The lithium-ion secondary batteries prepared above were adjusted to a SOC of 50% and placed in an environment of 25°C. They were discharged for 2 seconds at various current values, and the battery voltage after discharge at each current value was measured. The current values ​​and battery voltages were plotted to determine the IV characteristic during discharge. The IV resistance (Ω) during discharge was calculated from the slope of the resulting straight line and used as the initial resistance.

[0141]

[0142]

[0143] As shown in Tables 1 and 2, in a comparison of batteries using positive electrode active materials with the same composition of lithium composite oxide particles, the positive electrode active material layer containing lithium composite oxide particles with a layered structure, having a porosity of 16.5%–20.5%, and a peak pore size of 0.400 μm–0.550 μm in the pore distribution of the positive electrode active material layer as measured by mercury infiltration, exhibits high initial capacity and low initial resistance (i.e., high output). Furthermore, it is evident that under these conditions, the capacity retention rate after charge-discharge cycles is also high. Therefore, it is clear that the positive electrode disclosed herein can improve the capacity and output of non-aqueous electrolyte secondary batteries. Additionally, it is evident that the positive electrode disclosed herein can impart excellent capacity degradation tolerance to non-aqueous electrolyte secondary batteries during repeated charge-discharge cycles.

[0144] The specific examples of the present invention have been described in detail above, but these are merely illustrative and do not limit the scope of the claims. The technology described in the claims includes technologies obtained by various modifications and alterations to the specific examples described above.

Claims

1. A positive electrode, comprising a positive current collector and a layer of positive active material supported on the positive current collector, wherein, The positive electrode active material layer contains lithium composite oxide particles with a layered structure as the positive electrode active material. The porosity of the positive electrode active material layer is 17% to 20%, and the peak pore size in the pore distribution of the positive electrode active material layer, measured by mercury infiltration method, is 0.400 μm to 0.550 μm. The lithium composite oxide is a lithium-nickel-cobalt-manganese composite oxide, wherein the nickel content in the lithium-nickel-cobalt-manganese composite oxide, relative to the total content of metal elements other than lithium, is 55 mol% or more. The layered lithium composite oxide particles comprise first lithium composite oxide particles and second lithium composite oxide particles. The first lithium composite oxide particles have a layered structure with an average particle size D50 of 3.0 μm to 6.0 μm and a DBP oil absorption capacity of 15 mL / 100g to 27 mL / 100g. The second lithium composite oxide particles have a layered structure with an average particle size D50 of 10.0 μm to 22.0 μm and a DBP oil absorption capacity of 14 mL / 100g to 22 mL / 100g. The first lithium composite oxide particles are secondary particles formed by the aggregation of primary particles, with an average primary particle size of 1.4 μm to 2.5 μm. The second lithium composite oxide particles are secondary particles formed by the aggregation of primary particles, with an average primary particle size of 0.1 μm to 0.3 μm. The mass ratio of the first lithium composite oxide particles to the second lithium composite oxide particles is 10:90 to 90:

10. The lithium-nickel-cobalt-manganese composite oxide has the composition shown in formula (I): Li 1+x Ni y Co z Mr (1-y-z) M α O 2-β Q β (I) In equation (I), x, α, and β satisfy -0.3≤x≤0.3, 0≤α≤0.1, and 0≤β≤0.5, respectively; M is at least one element selected from Zr, Mo, W, Mg, Ca, Na, Fe, Cr, Zn, Sn, and Al; and Q is at least one element selected from F, Cl, and Br. Regarding the first lithium composite oxide particles, in the above equation (I), y and z satisfy 0.55≤y≤0.95 and 0.02≤z≤0.43, respectively. Regarding the second lithium composite oxide particles, in the above formula (I), y and z satisfy 0.50<y≤0.95 and 0.02≤z<0.48, respectively.

2. The positive electrode according to claim 1, wherein, The porosity of the positive electrode active material layer is 17% to 19%.

3. The positive electrode according to claim 1 or 2, wherein, The peak pore size is 0.500 μm to 0.530 μm.

4. A non-aqueous electrolyte secondary battery, comprising: a positive electrode, a negative electrode, and a non-aqueous electrolyte according to any one of claims 1 to 3.

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