Positive electrode active material and nonaqueous electrolyte secondary battery comprising the same

Abstract

The present invention relates to a positive electrode active material and a nonaqueous electrolyte secondary battery containing the same. A positive electrode active material capable of improving the capacity and output of a nonaqueous electrolyte secondary battery is provided. The positive electrode active material disclosed herein contains particles of a lithium complex oxide having a layered structure. The tap density of the positive electrode active material is 2.8 g / cm 3 ~ 3.0 g / cm 3 and the dibutyl phthalate oil absorption of the positive electrode active material is 14.5 mL / 100 g ~ 18.5 mL / 100 g.

Description

Technical Field

[0001] This invention relates to positive electrode active materials. This invention also relates to non-aqueous electrolyte secondary batteries comprising the positive electrode active material. Background Technology

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

[0003] With the increasing prevalence of non-aqueous electrolyte secondary batteries, there is a demand for further performance improvements. In the positive electrode of non-aqueous electrolyte secondary batteries, particulate lithium composite oxides are generally used as the positive electrode active material. The particle characteristics of the positive electrode active material (in other words, the particle characteristics of the lithium composite oxide) affect the performance of the non-aqueous electrolyte secondary battery, but using only a single type of lithium composite oxide particle is limiting. Therefore, techniques are known to adjust the particle characteristics of the positive electrode active material by mixing particles of two lithium composite oxides with different particle characteristics (for example, see Patent Documents 1 and 2).

[0004] Existing technical documents

[0005] Patent documents

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

[0007] Patent Document 1: Japanese Patent No. 6859888 Summary of the Invention

[0008] However, the inventors conducted in-depth research and found that in the aforementioned prior art, the means for increasing the capacity of non-aqueous electrolyte secondary batteries is based on a specific composition of lithium composite oxides, and there is room for improvement in increasing the capacity of non-aqueous electrolyte secondary batteries. Furthermore, it was found that in the aforementioned prior art, there is room for improvement in increasing the output of non-aqueous electrolyte secondary batteries using the aforementioned positive electrode active material.

[0009] Therefore, the purpose of this invention is to provide a positive electrode active material that can improve the capacity and output of a non-aqueous electrolyte secondary battery.

[0010] The positive electrode active material disclosed herein contains lithium composite oxide particles with a layered structure. The tap density of the positive electrode active material is 2.8 g / cm³. 3 ~3.0g / cm 3Furthermore, the dibutyl phthalate in the positive electrode active material has an oil absorption capacity of 14.5 mL / 100g to 18.5 mL / 100g. Based on this configuration, a positive electrode active material capable of improving the capacity and output of a non-aqueous electrolyte secondary battery can be provided.

[0011] In a preferred embodiment of the positive electrode active material 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.

[0012] In a more preferred embodiment of the positive electrode active material disclosed herein, the nickel content in the 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.

[0013] In a preferred embodiment of the positive electrode active material disclosed herein, the tap density of the positive electrode active material is 2.9 g / cm³. 3 ~3.0g / cm 3 This configuration allows for the imparting of exceptionally high capacity to non-aqueous electrolyte secondary batteries.

[0014] In a preferred embodiment of the positive electrode active material disclosed herein, the dibutyl phthalate of the positive electrode active material has an oil absorption capacity of 16.2 mL / 100 g to 18.5 mL / 100 g. With this configuration, a particularly high output can be imparted to the non-aqueous electrolyte secondary battery.

[0015] From another perspective, the non-aqueous electrolyte secondary battery disclosed herein includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode comprises the aforementioned positive electrode active material. Based on this configuration, a non-aqueous electrolyte secondary battery with high capacity and high output can be provided. Attached Figure Description

[0016] Figure 1 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.

[0017] Figure 2 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.

[0018] Explanation of reference numerals in the attached figures

[0019] 20. Winded electrode body

[0020] 30 Battery casing

[0021] 36 Safety valve

[0022] 42 Positive extremes

[0023] 42a Positive Current Collector

[0024] 44 Negative extremes

[0025] 44a Negative Current Collector

[0026] 50 Positive electrode sheet (positive electrode)

[0027] 52 Positive current collector

[0028] 52a Non-forming portion of the positive electrode active material layer

[0029] 54 Positive electrode active material layer

[0030] 60 Negative electrode sheet (negative electrode)

[0031] 62 Negative current collector

[0032] 62a Non-forming portion of the negative electrode active material layer

[0033] 64 Negative Electrode Active Material Layer

[0034] 70. Separator sheet (separator body)

[0035] 80 Non-aqueous electrolytes

[0036] 100 Lithium-ion Secondary Battery Detailed Implementation

[0037] 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.

[0038] 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.

[0039] The positive electrode active material involved in this embodiment contains lithium composite oxide particles with a layered structure. The tap density of this positive electrode active material is 2.8 g / cm³. 3 ~3.0g / cm 3 The oil absorption capacity of the dibutyl phthalate (DBP) in this positive electrode active material is 14.5 mL / 100g to 18.5 mL / 100g.

[0040] Generally, high capacity can be achieved in non-aqueous electrolyte secondary batteries by highly filling the positive electrode active material particles. However, highly filling the positive electrode active material particles reduces the gaps between the particles into which the non-aqueous electrolyte can penetrate. Therefore, the contact area between the positive electrode active material particles and the non-aqueous electrolyte decreases, leading to a reduction in the output of the non-aqueous electrolyte secondary battery. Thus, there is a trade-off between the capacity and output of non-aqueous electrolyte secondary batteries.

[0041] However, the inventors conducted in-depth research focusing on the particle characteristics of the positive electrode active material, resulting in a novel positive electrode active material in which the interparticle gaps are sufficiently retained even at high fill levels, allowing the non-aqueous electrolyte to penetrate. This novel positive electrode active material enables high capacity and high output in non-aqueous electrolyte secondary batteries. Furthermore, they discovered that the particle characteristics of this positive electrode active material can be characterized using tap density and DBP oil absorption, thus completing the positive electrode active material disclosed herein.

[0042] When the positive electrode active material is a typical lithium composite oxide with a layered structure, its tap density is 1.5 g / cm³. 3 ~2.5g / cm 3 Approximately. In contrast, the tap density of the positive electrode active material involved in this embodiment is 2.8 g / cm³. 3 ~3.0g / cm 3 That is, the tap density of the positive electrode active material involved in this embodiment is greater than that of a typical positive electrode active material. This large tap density, specifically a tap density of 2.8 g / cm³, results in a positive electrode active material with a tap density of 2.8 g / cm³. 3 The above enables the high-capacity development of non-aqueous electrolyte secondary batteries. On the other hand, the tap density exceeds 3.0 g / cm³. 3 When the interparticle gaps are not sufficiently large to ensure that the non-aqueous electrolyte can penetrate, the high output of the non-aqueous electrolyte secondary battery becomes insufficient. Since a particularly high capacity can be imparted to the non-aqueous electrolyte secondary battery, the tap density of the positive electrode active material is preferably 2.9 g / cm³. 3 ~3.0g / cm 3 .

[0043] It should be noted that the tap density of the positive electrode active material 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" (made by Kuramochi Scientific Instruments Manufacturing Co., Ltd.)). The average value of the two measurements of the powder filling density can then be calculated.

[0044] Furthermore, the positive electrode active material involved in this embodiment has such a high tap density, and the DBP oil absorption is 14.5 mL / 100g to 18.5 mL / 100g. DBP oil absorption is an indicator of how much liquid (especially a non-aqueous electrolyte) can enter the gaps between particles and the internal voids of the particles. Generally, the higher the tap density of the positive electrode active material, the smaller the gaps between particles, and therefore the lower the DBP oil absorption. However, the positive electrode active material involved in this embodiment has the high tap density described above, while simultaneously increasing the DBP oil absorption. Specifically, in the positive electrode active material involved in this embodiment, the DBP oil absorption is increased to 14.5 mL / 100g or more, thereby enabling sufficiently high output of the non-aqueous electrolyte secondary battery. However, when the DBP oil absorption exceeds 18.5 mL / 100g, the high capacity of the non-aqueous electrolyte secondary battery becomes insufficient.

[0045] 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, with respect to the positive electrode active material according to this embodiment, since the DBP oil absorption is within the aforementioned range, the side reaction between the positive electrode active material and the non-aqueous electrolyte is unlikely to occur. Therefore, according to the positive electrode active material according to this embodiment, the degradation of battery characteristics (especially capacity degradation) during repeated charge-discharge cycles of non-aqueous electrolyte secondary batteries can be suppressed.

[0046] From the perspective of being able to impart particularly high output to non-aqueous electrolyte secondary batteries, the oil absorption capacity of DBP is preferably 16.2 mL / 100g or more, more preferably 17.0 mL / 100g or more, and even more preferably 17.5 mL / 100g or more. On the other hand, the oil absorption capacity of DBP can be 18.2 mL / 100g or less, or 18.0 mL / 100g or less.

[0047] The 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.

[0048] There are no particular limitations on the positive electrode filling density, but 3.61 g / cm³ is preferred.3 ~3.65g / cm 3 .

[0049] 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).

[0050] It should be noted that in this specification, "lithium-nickel-cobalt-manganese composite oxide" refers to an oxide that, in addition to oxides with Li, Ni, Co, Mn, and O as constituent elements, also contains one or more additive elements. 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. Furthermore, additive elements can also be half-metallic elements such as B, C, Si, and P, and non-metallic elements 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.

[0051] Considering its superior properties such as low initial resistance, lithium nickel cobalt manganese composite oxides with a layered structure are preferred as lithium composite oxides. 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%.

[0052] 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.

[0053] Li 1+x Ni y Co z Mn (1-y-z) M α O 2-β Q β (I)

[0054] 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.

[0055] x preferably satisfies 0 ≤ x ≤ 0.3, more preferably 0 ≤ x ≤ 0.15, and even more preferably 0. α preferably satisfies 0 ≤ α ≤ 0.01, and more preferably 0.005. β preferably satisfies 0 ≤ β ≤ 0.1, and more preferably 0.

[0056] 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.

[0057] For adjusting the tap density of the positive electrode active material to 2.8–3.0 g / cm³ 3 There are no particular limitations on the method for adjusting the DBP oil absorption within the range of 14.5 mL / 100g to 18.5 mL / 100g. The tap density of the positive electrode active material and the DBP oil absorption can be easily adjusted by mixing the following two types of lithium composite oxide particles.

[0058] (1) The first lithium composite oxide particles have a layered structure, with 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.

[0059] (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.

[0060] Therefore, the positive electrode active material according to this embodiment preferably comprises first lithium composite oxide particles having a layered structure and having an average particle size and DBP oil absorption capacity within the above-mentioned range, and second lithium composite oxide particles having a layered structure and having an average particle size and DBP oil absorption capacity within the above-mentioned range. Hereinafter, the first lithium composite oxide particles and the second lithium composite oxide particles will be described in detail.

[0061] Both the first lithium composite oxide particles and the 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 lithium composite oxide particles and the second lithium composite oxide particles are lithium nickel cobalt manganese composite oxide particles.

[0062] From the viewpoint of further increasing the capacity of non-aqueous electrolyte secondary batteries, regarding the first lithium composite oxide particles, 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 55 mol% or more, more preferably 60 mol% or more. Furthermore, from the viewpoint of further increasing the capacity of non-aqueous electrolyte secondary batteries, regarding the second lithium composite oxide particles, 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%, more preferably 55 mol% or more.

[0063] From the viewpoint of further increasing the capacity of non-aqueous electrolyte secondary batteries, regarding the first lithium composite oxide particles, 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 further increasing the capacity of non-aqueous electrolyte secondary batteries, regarding the second lithium composite oxide particles, in the above formula (I), 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.

[0064] 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 corresponding 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.

[0065] The average particle size of the first and second lithium composite oxide particles can be adjusted by known methods (e.g., crushing, grading, etc.).

[0066] 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.

[0067] 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 DBP oil absorption 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).

[0068] For example, when using secondary particle size formed by primary particle aggregation as the second lithium composite oxide particle, and setting the average primary particle size to about 0.1μm to 0.3μm, it is easy to adjust its DBP oil absorption to the range of 14mL / 100g to 22mL / 100g.

[0069] 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.

[0070] It should be noted that the average primary particle size refers to the average of the major diameters of any 50 or more primary particles selected from an electron microscope image of lithium composite oxide particles. Therefore, the average primary particle size can be obtained, for example, by obtaining an SEM image of lithium composite oxide particles using a scanning electron microscope (SEM), calculating the major diameter of any 50 or more primary particles selected individually using image-resolution particle size distribution measurement software (such as "Mac-View"), and then calculating the average of these values.

[0071] Based on the goal of imparting 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. Based on the goal of imparting 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.

[0072] 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.

[0073] Based on the goal of imparting excellent output characteristics to non-aqueous electrolyte secondary batteries, the preferred BET specific surface area of ​​the first lithium composite oxide particles is 0.54 m². 2 / g or more, preferably 0.54m 2 / g~0.69m 2 / g. Based on the goal of imparting 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. 2 / g or more, preferably 0.18m 2 / g~0.36m 2 / g.

[0074] 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" (made by Mountech)) and the nitrogen adsorption method.

[0075] To 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 To 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 .

[0076] 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 Kuramochi Scientific Instruments Manufacturing Co., Ltd.)). The average value of the two measurements of the powder filling density can then be calculated.

[0077] There is no particular limitation on the content ratio of the first lithium composite oxide particles and the second lithium composite oxide particles. 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.

[0078] In one embodiment of the positive electrode active material, the positive electrode active material consists only of first lithium composite oxide particles and second lithium composite oxide particles. In another embodiment of the positive electrode active material, in addition to the first lithium composite oxide particles and second lithium composite oxide particles, the positive electrode active material may further contain particles other than these particles that function as a positive electrode active material.

[0079] According to the positive electrode active material of this embodiment, the capacity of non-aqueous electrolyte secondary batteries can be improved, and the output of non-aqueous electrolyte secondary batteries can also be improved. Furthermore, the positive electrode active material of this embodiment imparts excellent capacity degradation resistance to non-aqueous electrolyte secondary batteries during repeated charge-discharge cycles. The positive electrode active material 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 active material of this embodiment can also be used as a positive electrode active material for all-solid-state secondary batteries.

[0080] Therefore, from another perspective, the positive electrode involved in this embodiment is a positive electrode containing the aforementioned positive electrode active material. This positive electrode, for example, has a positive electrode current collector and a layer of positive electrode active material supported on the positive electrode current collector, the positive electrode active material layer containing the aforementioned positive electrode active material.

[0081] Furthermore, from another perspective, the non-aqueous electrolyte secondary battery according to this embodiment includes a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode contains the aforementioned positive electrode active material. The non-aqueous electrolyte secondary battery according to this embodiment typically has a positive electrode current collector and a positive electrode active material layer supported on the positive electrode current collector, wherein the positive electrode active material layer contains the aforementioned positive electrode active material.

[0082] 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.

[0083] Figure 1The 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 packaging 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. It should be noted that a current cut-off 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.

[0084] like Figure 1 and Figure 2 As 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.

[0085] The non-formed portions 52a of the positive active material layer (i.e., the portion where the positive active material layer 54 is not formed and the positive current collector 52 is exposed) and 62a of the non-formed portions 64 of the negative active material layer (i.e., the portion where the negative active material layer 64 is not formed and the negative current collector 62 is exposed) 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 portions 52a and 62a of the positive and negative active material layers respectively function as current collectors. A positive current collector plate 42a and a negative current collector plate 44a are respectively bonded to the non-formed portions 52a and 62a of the positive and negative active material layers. It should be noted that the shapes of the non-formed portions 52a and 62a of the positive and negative active material layers are not limited to the examples 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 also be formed into a current collector tab processed into a specified shape.

[0086] As the positive current collector 52, a known positive current collector used in lithium-ion secondary batteries can be used, such as sheets or foils made of metals with good conductivity (e.g., aluminum, nickel, titanium, stainless steel, etc.). Aluminum foil is preferred as the positive current collector 52.

[0087] There are no particular limitations on the size of the positive current collector 52; it can be determined appropriately according to the battery design. When using aluminum foil as the positive current collector 52, there are no particular limitations on its thickness; for example, it can be 5 μm or more and 35 μm or less, preferably 7 μm or more and 20 μm or less.

[0088] The positive electrode active material layer 54 contains a positive electrode active material. The positive electrode active material used is the one described in this embodiment. Without hindering the effects of the present invention, the positive electrode active material layer 54 may contain other positive electrode active materials besides the one described in this embodiment.

[0089] 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.

[0090] 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.

[0091] There is no particular limitation on the thickness of the positive electrode active material layer 54, for example, it is 10 μm or more and 300 μm or less, preferably 20 μm or more and 200 μm or less.

[0092] 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.

[0093] As the negative electrode current collector 62, 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 (e.g., copper, nickel, titanium, stainless steel, etc.). Copper foil is preferred as the negative electrode current collector 62.

[0094] There are no particular limitations on the size of the negative electrode current collector 62; it can be determined appropriately according to the battery design. When using copper foil as the negative electrode current collector 62, there are no particular limitations on its thickness; for example, it can be 5 μm or more and 35 μm or less, preferably 7 μm or more and 20 μm or less.

[0095] 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.

[0096] There is no particular limitation on the average particle size (median particle size: D50) of the negative electrode active material, for example, it is 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.

[0097] The negative electrode active material layer 64 may contain components other than the active material, such as adhesives and tackifiers. Examples of adhesives include styrene-butadiene rubber (SBR) and polyvinylidene fluoride (PVDF). Examples of tackifiers include carboxymethyl cellulose (CMC).

[0098] 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 tackifier 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.

[0099] 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.

[0100] As the separator 70, examples include porous sheets (membranes) made of resins such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. This porous sheet can be a single-layer structure or a laminated structure with two or more layers (for example, 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.

[0101] Non-aqueous electrolytes typically contain a non-aqueous solvent and a supporting salt (electrolyte salt). As the non-aqueous solvent, various organic solvents such as carbonates, ethers, esters, nitriles, sulfones, and lactones commonly used in electrolytes for lithium-ion secondary batteries 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), ethylene monofluorocarbonate (MFEC), ethylene difluorocarbonate (DFEC), methyl monofluorodifluoromethyl carbonate (F-DMC), and dimethyl trifluorocarbonate (TFDMC). Such non-aqueous solvents can be used alone or in appropriate combinations of two or more.

[0102] 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.

[0103] It should be noted that, as long as it does not significantly impair the effect of the present invention, the above-mentioned non-aqueous electrolyte 80 may also contain components other than those mentioned above, such as film-forming agents such as oxalic acid complexes, gas generators such as biphenyl (BP) and cyclohexylbenzene (CHB), thickeners, and various additives.

[0104] The lithium-ion secondary battery 100 constructed 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 driving power supplies for battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), etc.; and batteries for small energy storage devices, etc., with vehicle driving 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.

[0105] 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.

[0106] 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 laminated shell type 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.

[0107] 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.

[0108] 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.

[0109] <Examples 1-5 and Comparative Examples 1-7>

[0110] LiNi was prepared as the first lithium composite oxide particle at a mass ratio of 50:50 as the positive electrode active material. 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 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.

[0111] 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.

[0112] 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 produce a negative electrode sheet.

[0113] 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 in between to obtain a laminate. Then, the laminate is wound to obtain a wound body, which is pressed into a flat shape to obtain a flat wound electrode body.

[0114] The electrode terminals were installed on the electrode body, inserted into the battery casing, and fused together before injecting a non-aqueous electrolyte. It should be noted that the non-aqueous electrolyte was prepared by dissolving LiPF6, the supporting salt, at a concentration of 1.2 mol / L 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, thereby obtaining the evaluation lithium-ion secondary batteries of Examples 1-5 and Comparative Examples 1-7.

[0115] <Examples 6-10 and Comparative Examples 8-14>

[0116] LiNi was prepared as the first lithium composite oxide particle at a mass ratio of 50:50 as the positive electrode active material. 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 having 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.

[0117] 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.

[0118] 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.

[0119] 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.

[0120] The aforementioned positive and negative electrode sheets are alternately stacked while separated by a 24 μm thick porous polyolefin sheet with a three-layer PP / PE / PE structure, which serves as a separator. This results in a stacked electrode body.

[0121] The electrode terminals were installed on the electrode body, inserted into the battery casing, and fused together before injecting a non-aqueous electrolyte. It should be noted that the non-aqueous electrolyte was prepared by dissolving LiPF6, the supporting salt, at a concentration of 1.2 mol / L 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, thereby obtaining the evaluation lithium-ion secondary batteries of Examples 6-10 and Comparative Examples 8-14.

[0122] <Determination of tap density of positive electrode active material>

[0123] The tap density of the positive electrode active material was determined according to the method specified in JIS K1469:2003. Specifically, 50g of a sample filled with lithium composite oxide particles was placed in a glass cylindrical container of a commercially available "KRS-409" tapping instrument (manufactured by Kuramochi Scientific Equipment Manufacturing Co., Ltd.), and subjected to 2000 taps at an amplitude of 8mm. The volume was then measured. The powder filling density (apparent density) was calculated from the measurement results, and the average of two measurement results was used as the tap density of the lithium composite oxide particles. The results are shown in Tables 1 and 2.

[0124] <Determination of Positive Electrode Filling Density>

[0125] For the positive electrode sheets produced in each embodiment and comparative example, the positive electrode packing density is calculated according to the following formula. It should be noted that the positive electrode packing density refers to the mass of the constituent components of the positive electrode active material layer (i.e., the positive electrode active material and any components such as conductive materials and adhesives) contained per unit volume of the positive electrode active material layer containing void portions in the positive electrode sheet.

[0126] (Formula) Positive electrode packing density (g / cm³) 3 = Mass of the positive electrode active material layer / Volume of the positive electrode active material layer

[0127] <Determination of DBP oil absorption of positive electrode active material and various lithium composite oxide particles>

[0128] The DBP oil absorption of the positive electrode active material and lithium composite oxide particles was determined according to the method described in JIS K6217-4:2008. Specifically, 60g of the test sample of the positive electrode active material and each lithium composite oxide particle was measured and installed in the oil absorption measuring device "S-500" (manufactured by Asahi Sokensha). While stirring the sample with the 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 positive electrode active material and each lithium composite oxide particle. The results are shown in Tables 1 and 2.

[0129] <Determination of the average particle size of lithium composite oxide particles>

[0130] 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.

[0131] <Mean primary particle size determination of lithium composite oxide particles>

[0132] 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.

[0133] Initial capacity and cycling characteristics evaluation

[0134] 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 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.

[0135] Each evaluation lithium-ion secondary battery was placed at 25°C. One charge-discharge cycle consisted of charging at 2C constant current to 4.2V, pausing for 10 minutes, discharging at 2C constant current to 3.0V, and pausing for 10 minutes. This cycle 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 (discharge capacity after 500 charge-discharge cycles / initial capacity) × 100, serving as an indicator of cycle characteristics. The results are shown in Tables 1 and 2.

[0136] <Output Characteristics>

[0137] The initial resistance was evaluated as an indicator of output characteristics. The lithium-ion secondary batteries prepared above were adjusted to 50% SOC 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.

[0138] [Table 1]

[0139]

[0140] [Table 2]

[0141]

[0142] As shown in Tables 1 and 2, in a comparison of cathode active materials using lithium composite oxide particles with the same composition, the tap density of the cathode active material containing lithium composite oxide particles with a layered structure is 2.8 g / cm³. 3 ~3.0g / cm 3Furthermore, when the DBP oil absorption is between 14.5 mL / 100g and 18.5 mL / 100g, the initial capacity is high and the initial resistance is low (i.e., high output). It is also known that under these conditions, the capacity retention rate after charge-discharge cycles is high. Therefore, it is evident that the positive electrode active material disclosed herein can improve the capacity and output of non-aqueous electrolyte secondary batteries. Additionally, it is evident that the positive electrode active material disclosed herein can impart excellent capacity degradation tolerance to non-aqueous electrolyte secondary batteries during repeated charge-discharge cycles.

[0143] Furthermore, as shown in Tables 1 and 2, from the perspective of achieving high-level, high-capacity non-aqueous electrolyte secondary batteries, the tap density of the positive electrode active material is 2.9 g / cm³. 3 ~3.0g / cm 3 This is advantageous. Furthermore, from the perspective of high output at a high level in non-aqueous electrolyte secondary batteries, it is advantageous for the dibutyl phthalate of the positive electrode active material to have an oil absorption capacity of 16.2 mL / 100g to 18.5 mL / 100g.

[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 active material, which is a positive electrode active material containing particles of a lithium complex oxide having a layered structure, wherein, The tap density of the positive electrode active material is 2.8 g / cm 3 ~ 3.0 g / cm 3 and the dibutyl phthalate oil absorption of the positive electrode active material is 16.0 mL / 100 g ~ 18.5 mL / 100 g, The positive electrode active material comprises first lithium composite oxide particles and second lithium composite oxide particles. 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 first lithium composite oxide particles have a layered structure with 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. 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.

2. The positive electrode active material according to claim 1, wherein The lithium composite oxide is a lithium-nickel-cobalt-manganese composite oxide.

3. The positive electrode active material according to claim 2, wherein, The nickel content in the lithium-nickel-cobalt-manganese composite oxide is 55 mol% or more relative to the total content of metal elements other than lithium.

4. The positive electrode active material according to any one of claims 1 to 3, wherein, The tap density of the positive electrode active material is 2.9 g / cm 3 ~ 3.0 g / cm 3 .

5. A nonaqueous electrolyte secondary battery which is a nonaqueous electrolyte secondary battery provided with a positive electrode, a negative electrode, and a nonaqueous electrolyte, wherein The positive electrode comprises the positive electrode active material according to any one of claims 1 to 4.

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