Positive electrode plate and nonaqueous electrolyte secondary battery

Abstract

To provide a positive electrode plate capable of obtaining a nonaqueous electrolyte secondary battery excellent in both quick charging property and cycle capacity maintenance rate.SOLUTION: A positive electrode current collector and a positive electrode active material layer, wherein the positive electrode active material layer includes a first layer including a first particle group and a second layer including a second particle group, the second layer is disposed between the first layer and the positive electrode current collector, the first particle group includes a plurality of first particles, the second particle group includes a plurality of second particles, and the first particles include secondary particles formed by aggregation of primary particles, An integrated intensity ratio (I003 / I004) of the secondary particles in an X-ray diffraction method is 1.05 to 1.19, a crystallite size L003 of the secondary particles is 1000 Å or more, and the second particles include particles having a void portion.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a positive electrode plate, and further to a non-aqueous electrolyte secondary battery. [Background technology]

[0002] Japanese Patent Laid-Open Publication No. 2013-93295 (Patent Document 1) discloses a positive electrode including a positive electrode mixture containing two types of positive electrode active material particles.

[0003] Japanese Patent Application Laid-Open No. 2022-63677 (Patent Document 2) discloses a nonaqueous electrolyte secondary battery including a positive electrode in which a first layer containing single particles and a second layer containing aggregated particles are disposed between the first layer and the positive electrode substrate. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-93295 [Patent Document 2] Japanese Patent Publication No. 2022-63677 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present disclosure is to provide a positive electrode plate that can provide a non-aqueous electrolyte secondary battery that is excellent in both rapid chargeability and capacity retention rate in charge / discharge cycles (hereinafter also referred to as cycle capacity retention rate). [Means for solving the problem]

[0006] [1] A positive electrode current collector and a positive electrode active material layer, the positive electrode active material layer includes a first layer including a first particle group and a second layer including a second particle group, the second layer is disposed between the first layer and the positive electrode current collector; the first particle group includes a plurality of first particles, The second particle group includes a plurality of second particles, The first particle includes secondary particles formed by aggregation of primary particles, The integrated intensity ratio (I 003 / I 104 ) of the diffraction peak in the X-ray diffraction method of the secondary particles is 1.05 to 1.19, The crystallite size L 003 of the secondary particles is 1000 Å or more, The second particle includes particles having voids, a positive electrode plate. [2] The thickness ratio (first layer: second layer) of the first layer and the second layer is 1:9 to 3:7, the positive electrode plate according to [1]. [3] The first particle includes a lithium transition metal composite oxide having a layered crystal structure, The lithium transition metal composite oxide is Li, Ni, Mn, Co, and M [M is one or more metal elements selected from the group consisting of Mg, Ca, Al, Ti, V, Cr, Fe, Cu, Zn, Zr, Nb, Mo, Ta, and W.], and The molar ratio of Li, Ni, Mn, Co, and M is Li:Ni:Mn:Co:M = a:x:y:z:t [a, x, y, z, and t are 1.0 ≦ a ≦ 1.3, x + y + z = 1, 0.25 ≦ x ≦ 0.9, 0 < y ≦ 0.6, 0 < z ≦ 0.6, and 0 < t ≦ 0.1.], the positive electrode plate according to [1] or [2]. [4] The average particle diameter of the first particle group is 3 to 20 μm, the positive electrode plate according to any one of [1] to [3]. [5] The second particle has a circularity of 0.92 or more, the positive electrode plate according to any one of [1] to [4]. [6] The second particle has a core part, the void part outside the core part, and an outer structure part outside the extended void part, the positive electrode plate according to any one of [1] to [5]. [7] The average particle diameter of the second particle group is 3 to 20 μm, the positive electrode plate according to any one of [1] to [6]. [8] The second layer further includes positive electrode active material particles of a type different from the second particles, the positive electrode plate according to any one of [1] to [7]. [9] A non-aqueous electrolyte secondary battery comprising the positive electrode plate according to any one of [1] to [8]. [Effects of the Invention]

[0007] According to the present disclosure, it is possible to provide a positive electrode plate that can provide a non-aqueous electrolyte secondary battery that is excellent in both rapid chargeability and cycle capacity retention rate. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic cross-sectional view of the positive electrode plate in the thickness direction. [Figure 2] FIG. 2 is a schematic cross-sectional view of a particle having voids. [Figure 3] FIG. 3 is a schematic cross-sectional view for explaining a reaction vessel that generates a Taylor vortex reaction field. DETAILED DESCRIPTION OF THE INVENTION

[0009] <Positive electrode> The positive electrode plate of the present disclosure includes a positive electrode current collector and a positive electrode active material layer. The positive electrode active material layer includes a first layer including a first particle group and a second layer including a second particle group. The second layer is disposed between the first layer and the positive electrode current collector. The first particle group includes a plurality of first particles. The second particle group includes a plurality of second particles. The first particles include secondary particles formed by aggregation of primary particles. The integrated intensity ratio (I 003 / I 104 ) is 1.05 to 1.19. The crystallite size L of the secondary particles 003 is 1000 Å or more. The second particles include particles having voids.

[0010] When the positive electrode active material layer has a single-layer structure, the reaction is concentrated near the surface of the positive electrode active material layer, which tends to accelerate degradation near the surface, leading to a decrease in cycle capacity retention due to particle cracking and a tendency for the reaction to not fully extend into the electrode. Furthermore, when the positive electrode active material layer has a two-layer structure consisting of an upper layer containing single particles (a layer located on the side of the positive electrode active material layer opposite the positive electrode current collector) and a lower layer containing agglomerated particles (a layer located on the side of the positive electrode active material layer facing the positive electrode current collector), the reaction is suppressed from being concentrated in the upper layer, but the single particles contained in the upper layer tend to have poorer lithium diffusibility than the agglomerated particles, which tends to reduce rapid charge performance. Furthermore, even when the lower layer contains agglomerated particles with relatively good lithium diffusibility, the reaction may still not fully extend into the electrode. The positive electrode plate of the present disclosure includes a positive electrode active material layer composed of a first layer (upper layer) containing first particles and a second layer (lower layer) containing second particles, thereby making it possible to obtain a nonaqueous electrolyte secondary battery (hereinafter also referred to as battery) that is excellent in both rapid chargeability and cycle capacity retention. The rapid chargeability and cycle capacity retention are evaluated according to the methods described in the Examples section below.

[0011] The positive electrode plate of the present disclosure will be described with reference to FIG. 1. FIG. 1 is a schematic cross-sectional view of the positive electrode plate in the thickness direction (stacking direction). The positive electrode plate 10 includes a positive electrode current collector 11 and a positive electrode active material layer 12. The positive electrode active material layer 12 includes a first layer 13 including a first particle group and a second layer 14 including a second particle group. The positive electrode active material layer is formed on one or both sides of the positive electrode current collector 11. The positive electrode current collector 11 is a metal foil made of an Al material such as Al or an Al alloy, and may be any metal foil that is stable within the potential range of the positive electrode plate 10.

[0012] The first layer 13 includes a first particle group. The first particle group includes a plurality of first particles 15. The content of the first particles 15 in the first particle group is, for example, 70 to 100 mass %, or may be 85 to 98 mass %, or may be 90 to 95 mass %, when the total amount of the first particle group is 100 mass %. The first particle group may include only a plurality of first particles 15.

[0013] The average particle diameter of the first particle group may be, for example, 3 to 20 μm. When the average particle diameter of the first particle group is within the above range, a battery with excellent cycle capacity retention rate is easily obtained. In this specification, the average particle diameter is the particle diameter (D50) at which the cumulative frequency from the smaller particle diameters in the volume-based particle size distribution reaches 50%. The volume-based particle size distribution can be measured by a laser diffraction particle size distribution measuring device. The average particle diameter of the first particle group can be controlled, for example, by adjusting manufacturing conditions such as precursor synthesis conditions (reaction time, pH, etc.) and firing conditions (firing temperature, firing time, etc.).

[0014] The first particles 15 include secondary particles in which primary particles are aggregated (hereinafter, also referred to as the first secondary particles). The first secondary particles are a lithium transition metal composite oxide having a layered crystal structure (hereinafter, also referred to as the first composite oxide). The first composite oxide contains Li, Ni, Mn, Co, and M [M is one or more metal elements selected from the group consisting of Mg, Ca, Al, Ti, V, Cr, Fe, Cu, Zn, Zr, Nb, Mo, Ta, and W.], and the molar ratio of Li, Ni, Mn, Co, and M is Li:Ni:Mn:Co:M = a:x:y:z:t (a, x, y, z, and t are 1.0≦a≦1.3, x + y + z = 1, 0.25≦x≦0.9, 0<y≦0.6, 0<z≦0.6, and 0<t≦0.1). That the first composite oxide contains Li, Ni, Mn, and Co means that it contains a lithium element, a nickel element, a manganese element, and a cobalt element. The composition of the first composite oxide can be determined by ICP (inductively coupled plasma) emission spectroscopic analysis (ICP-AES). More specifically, it can be measured in accordance with the general rules for emission spectroscopic analysis of JIS K 0116:2014. For example, using a high-resolution ICP emission spectroscopic analyzer ("PS3500DDII" manufactured by Hitachi High-Technologies Corporation), the first composite oxide is dissolved by an alkali fusion method and diluted to a predetermined amount with ultrapure water, tartaric acid, or hydrochloric acid for analysis. The measurement wavelengths of each element in ICP-AES can be Li: 670.784 nm, Co: 238.892 nm, Mn: 257.61 nm, Ni: 231.604 nm.

[0015] In the first particle 15, the integrated intensity ratio (I 003 / I 104 ) is 1.05 to 1.19, and the crystallite size L of the first secondary particles 003 The first secondary particle has an integrated intensity ratio (I 003 / I 104 ) and crystallite size L 003 By having this, the cycle capacity retention rate tends to be easily improved.

[0016] The first secondary particles are aggregated particles formed by aggregation of primary particles. The aggregation number of the primary particles in the first secondary particles is preferably 50 or more, may be 100 or more, or may be 1000 or more, and is usually 5 × 10 6 5 x 10 or less 5 The agglomeration number of the first secondary particles can be adjusted by adjusting the manufacturing conditions, such as the firing conditions (firing temperature, number of firings, firing time, etc.) when manufacturing the first secondary particles. The agglomeration number of the primary particles contained in the first secondary particles can be confirmed, for example, by a scanning electron microscope (hereinafter also referred to as "SEM") image obtained by SEM. The first secondary particles can be agglomerated particles with a solid structure that does not have voids inside.

[0017] The first secondary particles are a first composite oxide, and it can be confirmed, for example, by X-ray diffraction measurement that the first composite oxide has a layered crystal structure. Examples of the layered crystal structure of the first composite oxide include a hexagonal crystal structure (layered rock salt type) and a monoclinic crystal structure. The first composite oxide with a layered crystal structure can easily insert and extract lithium ions smoothly.

[0018] The metal element M contained in the first composite oxide may contain one or more of the above-mentioned metal elements, but preferably contains at least W (tungsten). When the metal element M contains W, the integrated intensity ratio (I 003 / I 104 ) and crystallite size L 003 It becomes easier to obtain a composite oxide having the above structure.

[0019] The molar ratio of Li is 1.0 ≤ a ≤ 1.3, and it may be 1.0 ≤ a ≤ 1.25, 1.01 ≤ a ≤ 1.2, 1.03 ≤ a ≤ 1.15, or 1.04 ≤ a ≤ 1.1. The molar ratio of Ni is 0.25 ≤ x ≤ 0.9, and it may be 0.3 ≤ x ≤ 0.9, 0.4 ≤ x ≤ 0.88, or 0.5 ≤ x ≤ 0.85. The molar ratio of Mn is 0 < y ≤ 0.6, and it may be 0.05 ≤ y ≤ 0.5, 0.08 ≤ y ≤ 0.3, or 0.10 ≤ y ≤ 0.2. The molar ratio of Co is 0 < z ≤ 0.6, and it may be 0 < z ≤ 0.5, 0.01 ≤ z ≤ 0.3, or 0.02 ≤ z ≤ 0.1. The molar ratio of M is 0 < t ≤ 0.1, and it may be 0 < t ≤ 0.08, 0.001 ≤ t ≤ 0.05, or 0.002 ≤ t ≤ 0.01. When the first composite oxide contains two or more metal elements M, the molar ratio of M refers to the total amount of the two or more metal elements.

[0020] The integrated intensity ratio (I 003 / I 104 ) of the diffraction peak of the first secondary particles is 1.05 to 1.19, and it may be 1.06 to 1.18, 1.08 to 1.17, or 1.10 to 1.15. The integrated intensity ratio (I 003 / I 104 ) is preferably 1.05 to 1.16, and more preferably 1.06 to 1.15. When the integrated intensity ratio (I 003 / I 104 ) exceeds the above range, the crystal growth of the primary particles is promoted during the process of manufacturing the secondary particles, and the secondary particles are likely to crack, so the cycle capacity retention rate is likely to decrease. The first secondary particles are difficult to crack because the integrated intensity ratio (I 003 / I 104 ) is within the above range. Therefore, by using the first secondary particles, it is easier to obtain a battery with excellent cycle retention rate.

[0021] The integrated intensity I 003 and I104 are the integrated intensities of the diffraction peaks on the (003) and (104) planes of the secondary particles measured by XRD, respectively, and can be measured by the method described in the Examples below. 003 / I 104 ) can be adjusted by, for example, the amount of lithium added (compounding ratio) when producing the first secondary particles, the raw material composition, and production conditions such as firing conditions (firing temperature, number of firings, firing time, etc.).

[0022] First secondary particle crystallite size L 003 is 1000 Å or more, may be 1010 Å or more, may be 1020 Å or more, may be 1000 to 3000 Å, may be 1010 to 2500 Å, may be 1020 to 2000 Å, or may be 1020 to 1500 Å. 003 / I 104 When the crystallite size L of the first secondary particles is within the above range, the Li site occupancy rate in the transition metal layer of the first secondary particles tends to be large, and the discharge capacity of the secondary battery tends to decrease. 003 By setting the value within the above range, the Li site occupancy rate can be reduced, and therefore, the decrease in the discharge capacity of the battery can be suppressed.

[0023] First secondary particle crystallite size L 003 The crystallite size L of the first secondary particles can be calculated from the half-width of the diffraction peak of the (003) plane measured by the XRD method, and can be calculated by the method described in the examples below. 003 can be adjusted by the manufacturing conditions such as the amount of lithium added (compounding ratio) when manufacturing the first secondary particles, the raw material composition, and the firing conditions (firing temperature, number of firings, firing time, etc.).

[0024] The first secondary particles can be obtained, for example, by mixing a compound containing Ni, Mn, and Co (hereinafter also referred to as a "NiMnCo-containing precursor"), a lithium compound, and, if necessary, an M-containing compound containing the metal element M to obtain a mixture, and then firing this mixture. Alternatively, the first secondary particles may be obtained by mixing a Ni-containing compound containing Ni, a Mn-containing compound containing Mn, a Co-containing compound containing Co, a lithium compound, and an M-containing compound containing the metal element M to obtain a mixture, and then firing this mixture. The Ni-containing compound, the Mn-containing compound, and the Co-containing compound may contain the metal element M.

[0025] Examples of NiMnCo precursors include composite oxides or composite hydroxides containing Ni, Mn, and Co. Examples of lithium compounds include lithium hydroxide and lithium carbonate. Examples of M-containing compounds include ammonium compounds containing the metal element M.

[0026] The second layer 14 includes a second particle group. The second particle group includes a plurality of second particles 16. The content of the second particles 16 in the second particle group is, for example, 70 to 100 mass %, or may be 85 to 98 mass %, or may be 90 to 95 mass %, when the total amount of the second particle group is 100 mass %. The second particle group may include only a plurality of second particles 16.

[0027] The average particle diameter of the second particle group may be, for example, 3 to 20 μm. The average particle diameters of the first particle group and the second particle group may be different or the same. The average particle diameter of the first particle group may be larger or smaller than that of the second particle group. The average particle diameter of the second particle group can be controlled, for example, by adjusting the raw material composition and firing conditions (firing temperature, firing time, etc.), and by selecting the type and particle diameter of precursor particles used to produce the second particles 16.

[0028] The second particle 16 includes particles having voids. The second particle 16 may include only particles having voids. Particles having voids will be described with reference to FIG. 2. FIG. 2 is a schematic cross-sectional view of a particle 20 having voids. The particle 20 having voids has a core 21, a void 22, and an outer structure 23. The particle 20 having voids may be a secondary particle (hereinafter also referred to as a second secondary particle) formed by aggregation of primary particles. The second secondary particle is a particle different from the first secondary particle contained in the first particle. The particle 20 having voids has one core and one layer of outer structure. The particle 20 having voids has improved Li diffusibility within the particle, and tends to be more likely to have excellent rapid charging properties due to the presence of voids.

[0029] The void portion 22 can be a space between the core portion 21 and the outer structure portion 23. The core portion 21 may be an aggregate of primary particles 24. The core portion 21 may have a solid structure or a hollow structure. When the core portion 21 is hollow, the hollow portion of the core portion 21 is not considered to be a void portion 22. The outer structure portion 23 may be an aggregate of primary particles 25. The core portion 21 and the outer structure portion 23 may be completely separated by the void portion 22, or in a particle 20 having a void portion, the primary particles 24 and the primary particles 25 may be in contact with each other at some points, so that the core portion 21 and the outer structure portion 23 are in contact with each other. In FIG. 2, only a portion of the primary particles 24 and the primary particles 25 are shown.

[0030] The particle 20 having voids may further have one or more layers of additional outer structure outside the outer structure 23. When the particle 20 having voids has two or more layers of outer structure, the particle 20 having voids may have two layers of voids. The outer structure 23 may be formed so as to completely cover the core 21, or may be formed so as to partially cover it.

[0031] The circularity of the void-containing particles 20 may be, for example, 0.92 or more, preferably 0.93 or more, more preferably 0.94 or more, and may be, for example, 1.00 or less. The circularity of the void-containing particles 20 is the average of 50 void-containing particles 20. When the circularity of the void-containing particles 20 is 0.92 or more, the packing property tends to be easily improved. In this specification, the circularity is calculated by the following formula: Circularity = (perimeter of a circle equal to the projected area of ​​the particle) / (perimeter of the particle) The circularity of a voided particle is the average of 50 voided particles.

[0032] The particle 20 having voids may have an average ratio (%) of the width (thickness) of the voids 22 to the particle size (diameter) (hereinafter also referred to as a first ratio) of, for example, 10% or more or 40% or more, or 80% or less or 70% or less. The particle size of the particle 20 having voids may be the diameter of the cross section of the particle 20 having voids when the particle 20 having voids is considered to be a circle. For example, in FIG. 2, the particle size of the particle 20 having voids is indicated by a line 26. The width (thickness) of the voids 22 may be the dimension of the voids 22 at the radius (line 26) of the particle 20 having voids.

[0033] The particle 20 having voids may have an average ratio (%) of the thickness of the outer structure 23 to the particle size (diameter) of 3% to 50% (hereinafter also referred to as the second ratio). The thickness of the outer structure 23 may be the dimension of the outer structure 23 at the diameter (straight line 26) of the particle 20 having voids. The first ratio and the second ratio are averages for 50 particles 20 having voids. The first ratio and the second ratio are measured according to the method described in the Examples section below.

[0034] The proportion of voids 22 to the total volume of void-containing particle 20 may be, for example, 10% or more, 40% or more, or 60% or more, or 30% or less, 60% or less, or 80% or less. In this specification, the proportion of voids 22 to the total volume of void-containing particle 20 is a value determined by processing a cross-sectional SEM image of void-containing particle 20, distinguishing between the portions containing primary particles 24 and 25 and voids 22, and calculating the proportion of the total area of ​​voids 22 to the area of ​​void-containing particle 20.

[0035] The BET specific surface area of ​​the particles 20 having voids is, for example, 0.5 to 2.8 m 2 The BET specific surface area may be measured according to the method described in the Examples section below.

[0036] The primary particle diameter of the void-containing particles 20 may be, for example, 0.1 to 1.0 μm. The primary particle diameter of the void-containing particles 20 is measured according to the method described in the Examples section below.

[0037] The particles 20 having voids have voids that are relatively uniform in cross section, and therefore when used in a positive electrode plate, can easily improve the rapid charging performance of the battery.

[0038] The void-containing particles 20 may be particles made of a composite oxide containing Li and Ni, particles made of a transition metal composite oxide containing Li, Ni, and Mn, or particles made of a transition metal composite oxide containing Li, Ni, Co, and Mn.

[0039] The particle 20 having a void portion may be, for example, a particle having a void portion represented by the following formula (i): Li 1+a1 Ni 1-x-y-z Co x Mn y M z O2(i) [In formula (i), -0.1≦a1<0.3, 0≦x<0.5, 0≦y<0.5, 0≦z<0.05, M is one or more elements selected from the group consisting of Al, Ti, Zr, B, Mg, Fe, Cu, Zn, Sn, Na, K, Ba, Sr, Ca, W, Mo, Nb, Si, V, Cr and Ge. The composition of the second composite oxide can be adjusted by the amount of lithium added (compounding ratio) used in producing the second composite oxide, and the types and amounts of raw materials used. The composition of the second composite oxide can be determined by inductively coupled plasma (ICP) atomic emission spectroscopy (ICP-AES).

[0040] The particles 20 having voids can be produced by a production method including, for example, a mixing step of mixing precursor particles with Li to obtain a mixture, and a firing step of firing the mixture.

[0041] The precursor particles may be particles that have, for example, a core portion, a void portion outside the core portion, and an outer structure portion outside the void portion, and are made of a transition metal composite hydroxide that contains Ni.

[0042] The precursor particles can be produced by a production method including a crystallization step of generating a Taylor vortex reaction field, adding an aqueous solution containing a compound containing a transition metal (hereinafter also referred to as a raw metal aqueous solution), an ammonium donor, and an alkaline aqueous solution to the Taylor vortex reaction field, and crystallizing a transition metal composite hydroxide containing nickel (hereinafter also referred to as a first metal hydroxide).

[0043] The transition metal composite hydroxide containing Ni may be a composite hydroxide further containing Mn, or may be a nickel-cobalt-manganese composite hydroxide further containing Mn and Co. The transition metal composite hydroxide containing Ni is preferably a nickel-cobalt-manganese composite hydroxide (hereinafter also referred to as an NCM composite hydroxide).

[0044] The NCM composite hydroxide may be, for example, a compound represented by the following formula (i): Ni 1-x-y-z Co x Mny M z (OH)2(i) (In formula (i), 0≦x<0.5, 0≦y<0.5, 0≦z<0.05, M is one or more elements selected from the group consisting of Al, Ti, Zr, B, Mg, Fe, Cu, Zn, Sn, Na, K, Ba, Sr, Ca, W, Mo, Nb, Si, V, Cr, and Ge. The composition of the first metal hydroxide can be determined by, for example, ICP (inductively coupled plasma) emission spectrometry.

[0045] The transition metal-containing compound contained in the raw metal aqueous solution can be, for example, a transition metal sulfate, nitrate, or carbonate. The transition metal-containing compound includes a Ni-containing compound. Examples of Ni-containing compounds include nickel sulfate (NiSO4), nickel nitrate [Ni(NO3)2], and nickel carbonate (NiCO3).

[0046] When the first metal hydroxide is a composite hydroxide further containing Mn, the raw metal aqueous solution may further contain a compound containing Mn. Examples of the compound containing Mn include manganese sulfate (MnSO), manganese nitrate [Mn(NO)], and manganese carbonate (MnCO). When the void-containing particles 20 are a transition metal composite oxide containing Li, Ni, Co, and Mn, the raw metal aqueous solution may further contain a compound containing Mn and a compound containing Co. Examples of the compound containing Co include cobalt sulfate (CoSO), cobalt nitrate [Co(NO)], and cobalt carbonate (CoCO).

[0047] The aqueous raw metal solution may further contain at least one element (hereinafter also referred to as an additive element) selected from the group consisting of Al, Ti, Zr, B, Mg, Fe, Cu, Zn, Sn, Na, K, Ba, Sr, Ca, W, Mo, Nb, Si, V, Cr, and Ge. The additive element may be added to the aqueous raw metal solution as the element itself or in the form of a salt (for example, in the form of a sulfate, nitrate, or carbonate).

[0048] The molar ratio of the transition metal-containing compound in the raw metal aqueous solution can be the molar ratio of the transition metal contained in the first metal hydroxide. The metal content in the raw metal aqueous solution can be, for example, 1.0 to 3.0 mol / L.

[0049] When the raw metal aqueous solution contains Mn, the molar ratio of Ni to Mn (Ni:Mn) in the raw metal aqueous solution is, for example, 1-x:0. <x<0.5であってよく、1-x:0.1<x<0.5または1-x:0.2<x<0.4であってもよい。

[0050] When the raw metal aqueous solution contains Mn and Co, the molar ratio of Ni, Mn, and Co in the raw metal aqueous solution (Ni:Mn:Co) is, for example, 1-xy:0 <x<0.5:0<y<0.5であってよく、1-x-y:0.05<x<0.25:0.05<y<0.25または1-x-y:0.1<x<0.2:0.1<y<0.2であってもよい。

[0051] When the raw metal aqueous solution contains Mn, Co, and other additive elements, the molar ratio of Ni, Mn, Co, and other additive elements in the raw metal aqueous solution (Ni:Co:Mn:other additive elements) is, for example, 1-xyz:0 <x<0.5:0<y<0.5:0<z<0.05であってよく、1-x-y-z:0.05<x<0.25:0.05<y<0.25:0.001<z<0.01または1-x-y-z:0.1<x<0.2:0.1<y<0.2:0.001<z<0.005であってもよい。

[0052] The ammonium donor may be, for example, an aqueous ammonia solution, the ammonia concentration of which may be, for example, 5 to 20 wt %.

[0053] The alkaline aqueous solution may be, for example, an aqueous sodium hydroxide solution, the sodium hydroxide concentration of which may be, for example, 10 to 40 wt %.

[0054] The Taylor vortex reaction field can be a fluid in which a Taylor vortex flow is generated. A Taylor vortex flow is a row of two donut-shaped vortices rotating in opposite directions. For example, by filling the interior of two concentric cylinders, the difference between their radii being small compared to their diameters, with a fluid, and rotating the inner cylinder (hereinafter also referred to as the inner cylinder) while keeping the outer cylinder (hereinafter also referred to as the outer cylinder) stationary, two rows of vortices can be generated in a ring shape along the circumference between the outer and inner cylinders. Multiple rows of two vortices can be generated along the length direction of the two concentric cylinders (direction perpendicular to the diameter).

[0055] The reaction layer that generates a Taylor vortex reaction field will be described with reference to Fig. 3. The reaction vessel 100 shown in Fig. 3 includes an outer cylinder 111 and an inner cylinder 112. The outer cylinder 111 is fixed. The inner cylinder 112 can be rotated by a motor 118. The outer cylinder 111 includes a first supply port 113 for supplying a raw metal aqueous solution, a second supply port 114 for supplying an ammonium supply, and a third supply port 115 for supplying an alkaline aqueous solution. The outer cylinder 111 further includes an outlet 116.

[0056] In the reaction tank 100, crystallization can be carried out, for example, by the following procedure. First, water is filled between the outer cylinder 111 and the inner cylinder 112 through the first supply port 113, and the inner cylinder 112 is rotated to generate a Taylor vortex flow between the outer cylinder 111 and the inner cylinder 112, thereby generating a Taylor vortex reaction field. The rotation speed of the inner cylinder 112 can be, for example, 500 to 2000 rpm.

[0057] Aqueous sodium hydroxide solution is supplied to the fluid from the third supply port 115, and the pH of the Taylor vortex reaction field at a liquid temperature of 25°C can be adjusted to 12.5 or less. The pH at a liquid temperature of 25°C can be controlled, for example, by adjusting the flow rate of the aqueous sodium hydroxide solution using a pH controller. The pH of the Taylor vortex reaction field at a liquid temperature of 25°C may be, for example, 10.7 or more. From the viewpoint of the circularity of the particles 20 having voids, the pH of the Taylor vortex reaction field at a liquid temperature of 25°C is preferably 11.0 or more and 12.5 or less.

[0058] The crystallization process can include, for example, first and second crystallizations. The first crystallization can be initiated by supplying the raw metal aqueous solution through the first supply port 113 and the ammonium supply through the second supply port 114. The raw metal aqueous solution and the ammonium supply can be supplied to the Taylor vortex reaction field at a molar ratio of 1:1. In the first crystallization, the oxygen concentration in the Taylor vortex reaction field can be maintained at 3.5 vol% or less. One method for maintaining the oxygen concentration in the Taylor vortex reaction field at 3.5 vol% or less is to inject nitrogen gas into the raw metal aqueous solution and the ammonium supply supplied to the Taylor vortex reaction field and bubble the gas. Hereinafter, the oxygen concentration in the Taylor vortex reaction field from the start of crystallization until the oxygen concentration in the Taylor vortex reaction field is changed as described below is also referred to as the "first oxygen concentration." The oxygen concentration in the Taylor vortex reaction field can be confirmed using a dissolved oxygen meter.

[0059] The time for which the first crystallization is performed (hereinafter also referred to as the first crystallization time) can be set so that the ratio of the time for which crystallization is performed to the total time for which crystallization is performed in the crystallization step (hereinafter also referred to as the first crystallization ratio) is, for example, 40% to 90%. When the first crystallization ratio is within the above range, it tends to be easier to produce precursor particles. When the first crystallization ratio is less than 40%, it tends to be difficult to form the core portion. When the first crystallization ratio is more than 90%, it tends to be difficult to form the outer structure portion.

[0060] Next, the oxygen concentration in the Taylor vortex reaction field can be changed to 5 vol% or more and 65 vol% or less, and the second crystallization can be performed while maintaining the oxygen concentration. The oxygen concentration in the Taylor vortex reaction field can be changed, for example, by changing the type of gas bubbled into the raw metal aqueous solution and the ammonium supplier. In the second crystallization, the type of gas used to maintain the oxygen concentration in the Taylor vortex reaction field from 5 vol% to 65 vol% or less can be, for example, a mixed gas of oxygen and nitrogen. To change the oxygen concentration in the Taylor vortex reaction field, the supply of the raw metal aqueous solution and the ammonium supplier is stopped, the oxygen concentration in the Taylor vortex reaction field is changed to 5 vol% to 65 vol% or less, and then the supply of the raw metal aqueous solution and the ammonium supplier is resumed, and crystallization can be performed. The time during which the supply of the raw metal aqueous solution and the ammonium supplier is stopped is not included in the overall crystallization time. Hereinafter, the oxygen concentration in the Taylor vortex reaction field in the second crystallization is also referred to as the second oxygen concentration. If the second oxygen concentration is less than 5 vol%, the formation of an external structure tends to be difficult. If the second oxygen concentration exceeds 65 vol %, the circularity of the first particles tends to be difficult to improve.

[0061] The time for which the second crystallization is performed (hereinafter also referred to as the second crystallization time) may be such that the proportion of the time for which the second crystallization is performed to the total time for which crystallization is performed in the crystallization step (hereinafter also referred to as the second crystallization proportion) is, for example, 10% to 60%. When the second crystallization proportion is within the above range, the first particles tend to be easily produced and the circularity tends to be easily improved. When the second crystallization proportion is less than 10%, the outer structure tends to be less easily formed. When the first crystallization proportion is more than 60%, the circularity tends to be less easily improved. From the viewpoints of the production and circularity of precursor particles, the second crystallization proportion is preferably 15% to 55%, more preferably 20% to 50%. The second crystallization time may be, for example, 3 to 30 minutes. During crystallization, the pH of the Taylor vortex reaction field at a liquid temperature of 25°C may be maintained at the pH adjusted before the start of crystallization. As a result, the precursor particles can be easily produced. The pH at a liquid temperature of 25°C in the Taylor vortex reaction field during crystallization is maintained at 12.5 or less, preferably 11.0 or more and 12.5 or less.

[0062] In the crystallization step, after the second crystallization, the oxygen concentration in the Taylor vortex reaction field may be changed from 5 vol% to 65 vol% to 3.5 vol% or less and a further crystallization (hereinafter referred to as third crystallization a) may be performed. Alternatively, the oxygen concentration in the Taylor vortex reaction field may be changed from 3.5 vol% or less to 5 vol% to 65 vol% or less and a further crystallization (hereinafter referred to as third crystallization b) may be performed. Third crystallization a and third crystallization b may each be performed one or more times. Performing third crystallization a and third crystallization b one or more times each makes it easier to produce precursor particles having two or more layers of voids.

[0063] The first ratio and the second ratio can be controlled, for example, by adjusting the pH, oxygen concentration, and timing of switching the oxygen concentration in the crystallization step, adjusting the rotation of the inner cylinder, and the like.

[0064] The ratio of the core portion 21 to the particle size (diameter) of the particle 20 having a void portion can be controlled, for example, by adjusting the pH, oxygen concentration, and the time from the start of crystallization to the first change in oxygen concentration during the crystallization process, or by adjusting the rotation speed of the inner cylinder.

[0065] After the crystallization step is completed, the solution containing the precursor particles can be taken out from the outlet 116 and collected in the container 17. The collected solution containing the precursor particles can be filtered, washed with water, and then dried to obtain the precursor particles.

[0066] In the mixing step, the precursor particles and Li can be mixed so that the ratio of the number of Li atoms to the total number of metal elements other than Li in the positive electrode active material particles (Li / Me ratio) is, for example, 1.0 to 1.3.

[0067] In the firing step, the temperature at which the mixture is fired may be, for example, 700 to 1000° C., preferably 700 to 850° C., and more preferably 710 to 850° C. The time for firing the mixture may be, for example, 3 to 10 hours. The firing step can be carried out in an oxidizing atmosphere.

[0068] The thickness ratio of the first layer 13 to the second layer 14 (first layer:second layer) may be, for example, 1:9 to 5:5, and preferably 1:9 to 3:7. When the thickness ratio of the first layer 13 to the second layer 14 is within the above range, both the rapid chargeability and the cycle capacity retention rate tend to be excellent.

[0069] The second layer 14 may contain positive electrode active material particles of a different type from the second particles. The positive electrode active material particles of a different type from the second particles that the second layer 14 may contain may be single particles or may be secondary particles other than the second particles (hereinafter also referred to as other secondary particles). The single particles may be a lithium transition metal composite oxide having a layered crystal structure, and the composition thereof may be within the range of the composition described for the first particle group and the second particle group, or may be outside this range of composition. The other secondary particles may be the first secondary particles, or may be secondary particles having a composition outside the range of the composition described for the first secondary particles, and may be those having a composition that is different from the integrated intensity ratio (I 003 / I 104 ) may be secondary particles outside the range of the crystallite size L 003 Other secondary particles may have a solid structure without voids, or may have a structure with voids.

[0070] The positive electrode active material layer 12 can be formed, for example, by applying a second positive electrode mixture slurry for forming the second layer 14 to one or both surfaces of the positive electrode current collector 11 and drying it, and then applying a first positive electrode mixture slurry for forming the first layer 13 onto the coating film derived from the second positive electrode mixture slurry, drying it, and then compressing it. The thickness ratio of the first layer 13 to the second layer 14 can be controlled by adjusting the coating thickness ratio of the first positive electrode mixture slurry and the second positive electrode mixture slurry. The first positive electrode mixture slurry and the second positive electrode mixture slurry can be prepared by adding a solvent such as N-methyl-2-pyrrolidone (NMP) to materials for forming the active material layer, such as a positive electrode active material, a binder, and a conductive material, and kneading the mixture. The positive electrode active material contained in the first positive electrode mixture slurry and the second positive electrode mixture slurry each includes first particles and second particles.

[0071] The positive electrode active material layer 12 may contain, in addition to the positive electrode active material described above, a binder, a conductive material, and the like. Examples of binders include known materials such as fluororesins such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE), and cellulose-based resins such as carboxymethyl cellulose (CMC). Examples of conductive materials include carbon materials. Examples of carbon materials include one or more selected from the group consisting of fibrous carbon, carbon black, coke, and activated carbon. Examples of fibrous carbon include carbon nanotubes (CNTs).

[0072] The positive electrode active material layer 12 may have a thickness of, for example, 10 to 200 μm. The positive electrode active material layer 12 may have a high density. The density of the positive electrode active material layer 12 is, for example, 3.5 g / cm 3 or more, for example, 4.0 g / cm 3 It may have the following densities:

[0073] <Nonaqueous electrolyte secondary battery> The battery of the present disclosure has the above-described positive electrode plate, and therefore tends to be excellent in both rapid chargeability and cycle capacity retention rate.

[0074] A battery typically includes an electrode assembly including a positive electrode plate and a non-aqueous electrolyte. The battery may have a battery case that houses the electrode assembly and the non-aqueous electrolyte. The battery case may include an exterior body having an opening and a sealing plate that seals the opening. The exterior body and the sealing plate may be formed using a metal such as Al, an Al alloy, iron, or an iron alloy, and may be formed using, for example, an Al laminate film. A resin sheet serving as an electrode holder may be disposed between the electrode assembly and the exterior body.

[0075] The electrode assembly may include a positive electrode plate, a negative electrode plate, and a separator. In the electrode assembly, the active material layer of the positive electrode plate and the negative electrode active material layer of the negative electrode plate face each other via the separator. The electrode assembly may be a laminated type in which the positive electrode plate, the negative electrode plate, and the separator are stacked, or a wound type in which a laminate in which the positive electrode plate, the negative electrode plate, and the separator are stacked is wound.

[0076] A negative electrode plate typically includes a negative electrode current collector and a negative electrode active material layer formed on one or both sides of the negative electrode current collector. The negative electrode current collector is a metal foil made of a copper material such as copper or a copper alloy. The negative electrode active material layer contains a negative electrode active material and may further contain a conductive material, a binder, and the like.

[0077] Examples of the negative electrode active material include known materials, such as carbon-based active material particles such as graphite, and metal-based active material particles containing an element selected from the group consisting of Si, Sn, Sb, Bi, Ti, and Ge. Examples of the conductive material include those described above. Examples of the binder include cellulose-based resins such as CMC, methyl cellulose (MC), and hydroxypropyl cellulose; polyacrylic acid; and styrene-butadiene rubber (SBR). CMC can also be used as a thickener.

[0078] The separator may have a substrate with a single-layer or multi-layer structure and a functional layer on at least one side of the substrate. The substrate may be a film made of a resin such as a polyolefin (e.g., polyethylene or polypropylene), polyester, cellulose, or polyamide, or a porous sheet such as a nonwoven fabric. The functional layer may be, for example, an adhesive layer and / or a heat-resistant layer. The adhesive layer may be formed, for example, with an adhesive. The heat-resistant layer may contain, for example, a filler and a binder.

[0079] The non-aqueous electrolyte preferably contains an electrolyte in a non-aqueous solvent such as an organic solvent. Examples of the electrolyte include one or more of LiPF6, LiBF4, LiClO4, LiFSO3, and LiBOB. Examples of the non-aqueous solvent include one or more of ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate (PC), butylene carbonate (BC), and diethyl carbonate (DEC). The non-aqueous electrolyte may further contain additives such as vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and fluoroethylene carbonate.

[0080] The present invention will be described in more detail below with reference to examples. [Example]

[0081] [Measuring average particle size] The average particle diameter (D50) of the first particles A and the second particles A used in the examples and comparative examples was measured in accordance with JIS Z 8825:2022 Particle size analysis - Laser diffraction and scattering method. The laser diffraction particle size distribution measuring device used was the "MT3000II" manufactured by Microtrac. Isopropyl alcohol (IPA) was used as the solvent for wet dispersion.

[0082] [BET specific surface area measurement] The BET specific surface areas of the first particles A and the second particles A used in the examples and comparative examples were measured using a commercially available flow type gas adsorption specific surface area measuring device.

[0083] [Circularity measurement] The circularity of the second particles A used in the examples and comparative examples was measured using a commercially available particle shape image analyzer.

[0084] [Measurement of primary particle size, first ratio, and second ratio] The second particles A used in the examples and comparative examples were cross-sectionally processed by ion milling. The cross-sections were observed using a commercially available scanning electron microscope (SEM) to obtain SEM images. Regarding the primary particle diameter, 50 or more primary particles were extracted using image analysis software, and the average particle diameter was calculated. The void and outer structure regions were identified in the obtained images using image analysis software, and the first ratio (void width / particle diameter) and the second ratio (outer structure thickness / particle diameter) were calculated from the scale ratio.

[0085] [integrated intensity ratio (I 003 / I 104 ) and crystallite size L 003 Measurement of The first particles A used in the examples and comparative examples were crushed in an agate mortar to an average particle size (D50) of 43 μm or less, and then subjected to X-ray diffraction measurement using an X-ray diffractometer (Rigaku "SmartLab"). The XRD profile obtained by the X-ray diffraction measurement confirmed that the lithium transition metal composite oxide had a layered crystal structure.

[0086] The integrated intensity ratio (I 003 / I 104 ) was calculated.

[0087] Intensity of the diffraction peak on the (003) plane in the XRD profile I 003 The value of the half-width of the diffraction peak is used as the broadening B of the diffraction peak in the Scherrer formula below, and the crystallite size L on the (003) plane is calculated. 003 was calculated. L 003 =Kλ / Bcosθ [In the formula, K is the Scherrer constant, λ is the wavelength of the X-ray [nm], B is the broadening of the diffraction peak [rad], and θ is the Flag angle [rad].]

[0088] [Battery construction] A negative electrode active material was prepared as a mixture of graphite and SiO. Styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) were used as binders. The negative electrode active material, SBR, and CMC were mixed in a mass ratio of 100:1:1 (negative electrode active material:SBR:CMC) and water to prepare a negative electrode slurry. The negative electrode slurry was applied to copper foil as a negative electrode current collector foil, dried, compressed, and then cut to the specified size to obtain a negative electrode plate. A separator having a three-layer structure of polypropylene / polyethylene / polypropylene was prepared. The positive electrode plate prepared in each of the examples and comparative examples was laminated with the negative electrode plate via a separator to obtain an electrode assembly. A positive electrode tab formed of aluminum foil in the region where the positive electrode active material layer of the positive electrode current collector foil was not formed, and a negative electrode tab formed of copper foil in the region where the negative electrode active material layer of the negative electrode current collector foil was not formed were exposed at both ends of the electrode assembly. The positive electrode tab was welded to the external positive electrode current collector, and the negative electrode tab was welded to the external negative electrode current collector, and then the electrode assembly was inserted into an exterior body made of aluminum laminate film, and the film was welded to form a liquid injection port. After pouring nonaqueous electrolyte through the liquid injection port, the liquid injection port was sealed to obtain a battery.

[0089] [Evaluation of fast charging] The state of charge of the fabricated battery was set to SOC = 0% (3.0V). CC charging was performed at a current value of 2C rate, and charging was performed until SOC = 100% (4.2V). After the cutoff voltage was reached and charging was completed, a sufficient rest time (30 minutes) was allowed to pass, and the voltage of the test battery was measured. The SOC value corresponding to the battery voltage was calculated, and this value was used as the SOC reached at 2C charging. The higher the SOC reached at 2C charging, the better the rapid charging ability is judged to be.

[0090] [Evaluation of cycle capacity retention rate] The fabricated battery was subjected to 300 cycles of 0.5C charge / discharge in a voltage range of 4.2V-3.0V at a temperature of 25°C. A 0.1C charge / discharge process was performed in a voltage range of 4.2V-3.0V at a temperature of 25°C, and the capacity obtained during discharge was defined as the post-cycle battery capacity. The cycle capacity retention rate was calculated using the following formula: Cycle capacity retention rate = Battery capacity after cycling / Initial battery capacity The higher the cycle capacity retention rate, the better the cycle capacity retention rate is judged to be.

[0091] Example 1 [Preparation of positive electrode]

[0092] First particles A were prepared as first particles. SEM observation confirmed that first particles A were secondary particles formed by aggregation of 50 or more primary particles, and that they had a solid structure with no voids inside the particles. The composition, average particle diameter (D50), BET specific surface area, and integrated intensity ratio (I 003 / I 104 ) and crystallite size L 003 is shown in Table 1.

[0093] 100 parts by mass of the first particles A, 1 part by mass of graphite as a conductive material, and 1 part by mass of polyvinylidene fluoride powder as a binder were mixed, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was further added to prepare a first positive electrode mixture slurry.

[0094] Second particles A were prepared as second particles. SEM observation confirmed that second particles A were secondary particles formed by agglomeration of 50 or more primary particles, and that they had a core, a void outside the core, and an outer structure outside the void. The composition, average particle diameter (D50), BET specific surface area, primary particle diameter, circularity, first ratio, and second ratio of second particles A are shown in Table 2.

[0095] A second positive electrode mixture slurry was prepared by mixing 100 parts by mass of second particles A, 1 part by mass of graphite as a conductive material, and 1 part by mass of polyvinylidene fluoride powder as a binder, and then adding an appropriate amount of N-methyl-2-pyrrolidone (NMP).

[0096] The second positive electrode composite slurry was applied to both sides of a positive electrode current collector made of aluminum foil and dried. Next, the first positive electrode composite slurry was applied to the coating film derived from the second positive electrode composite slurry and dried. The coating thickness ratio of the first positive electrode composite slurry to the second positive electrode composite slurry was set to 2:8. The coating film was then rolled using a rolling roller. This resulted in a positive electrode plate having a positive electrode active material layer formed on both sides of the positive electrode current collector, with a second layer containing second particles A on the positive electrode current collector side and a first layer containing first particles A on the side opposite the second layer from the positive electrode current collector. SEM observation of the cross section of the obtained positive electrode plate confirmed that the thickness ratio (first layer:second layer) of the first layer (upper layer) to the second layer (lower layer) was 2:8. The results are shown in Table 3. The lower layer is on the positive electrode current collector side, and the upper layer is on the negative electrode plate side.

[0097] <Examples 2 and 3> A positive electrode plate was produced in the same manner as in Example 1, except that the thickness ratios were as shown in Table 3. The results are shown in Table 3.

[0098] Example 4 A third positive electrode composite slurry was prepared by mixing 100 parts by mass of a positive electrode active material mixture in which the first particles A and the second particles A were mixed in a weight ratio of 2:8, 1 part by mass of graphite as a conductive material, and 1 part by mass of polyvinylidene fluoride powder as a binder, and then adding an appropriate amount of N-methyl-2-pyrrolidone (NMP).

[0099] 100 parts by mass of the first particles A, 1 part by mass of graphite as a conductive material, and 1 part by mass of polyvinylidene fluoride powder as a binder were mixed, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was further added to prepare a first positive electrode mixture slurry.

[0100] The third positive electrode composite slurry was applied to both sides of a positive electrode current collector made of aluminum foil and dried. Next, the first positive electrode composite slurry was applied to the coating film derived from the third positive electrode composite slurry and dried. The coating thickness ratio of the first positive electrode composite slurry to the third positive electrode composite slurry was set to 2:8. The coating film was then rolled using a rolling roller. This resulted in a positive electrode plate having a positive electrode active material layer formed on both sides of the positive electrode current collector, with a second layer containing first particles A and second particles A on the positive electrode current collector side and a first layer containing first particles A on the side opposite the second layer from the positive electrode current collector. SEM observation of the cross section of the obtained positive electrode plate confirmed that the thickness ratio (first layer:second layer) of the first layer (upper layer) to the second layer (lower layer) was 2:8. The results are shown in Table 3.

[0101] <Comparative Example 1> A positive electrode plate was produced in the same manner as in Example 1, except that instead of producing a positive electrode active material layer having a first layer and a second layer using the first particles A and the second particles A, respectively, a positive electrode active material layer having a single layer structure including a layer containing the second particles A was produced. The results are shown in Table 3.

[0102] <Comparative Example 2> A positive electrode plate was produced in the same manner as in Example 1, except that a positive electrode active material layer having a first layer and a second layer, respectively, was produced using second particles A and first particles A, instead of using first particles A and second particles A to produce a positive electrode active material layer having a first layer and a second layer, respectively, in Example 1. The results are shown in Table 3.

[0103] <Comparative Example 3> A positive electrode plate was produced in the same manner as in Example 1, except that a positive electrode active material layer having a single layer structure including a layer containing the first particle A was produced instead of producing a positive electrode active material layer having a first layer and a second layer using the first particle A and the second particle A in Example 1. The results are shown in Table 3.

[0104] <Comparative Example 4> A positive electrode mixture slurry was prepared by mixing 100 parts by weight of a positive electrode active material mixture (a mixture of first particles and second particles in a weight ratio of 2:8), 1 part by weight of graphite as a conductive material, and 1 part by weight of polyvinylidene fluoride powder as a binder, followed by the addition of an appropriate amount of N-methyl-2-pyrrolidone (NMP). The positive electrode mixture slurry was applied to both sides of a positive electrode current collector made of aluminum foil and dried. The coating was then rolled using a rolling roller to produce a positive electrode with a positive electrode active material layer formed on both sides of the positive electrode current collector. The results are shown in Table 3.

[0105] [Table 1]

[0106] [Table 2]

[0107] [Table 3]

[0108] In Example 1, first particles with relatively low Li diffusivity and thus less prone to degradation were arranged in the upper layer (negative electrode plate side) of the positive electrode plate, and first particles with relatively high Li diffusivity were arranged in the lower layer (positive electrode current collector side). This suppressed degradation due to reactions in the upper layer and facilitated reactions within the electrode (lower layer). As a result, a decrease in cycle capacity retention was suppressed and fast chargeability was excellent. On the other hand, in Comparative Examples 1 and 3, the positive electrode active material layer had a single composition, and in Comparative Example 2, second particles with relatively high Li diffusivity were arranged in the upper layer (negative electrode side) and first particles with relatively low Li diffusivity were arranged in the lower layer (positive electrode current collector side). During fast charge, the reaction occurred intensively in the upper layer (negative electrode side) of the positive electrode plate, and the reaction did not occur sufficiently within the electrode (near the positive electrode current collector side). As a result, the SOC achieved after charge was low and good fast chargeability was not obtained.

[0109] In Example 2, the thickness of the first layer (negative electrode plate side) containing the first particles was thicker than in Examples 1 and 3, and the relatively low Li diffusibility of the first particles had a greater effect, resulting in a slightly lower improvement in rapid charging performance than in Examples 1 and 3, but better results than in Comparative Examples 1 to 3.

[0110] In Example 4, although the lower layer (current collecting foil side) contains the first particles and the second particles, there is a difference in Li diffusibility compared to the upper layer (negative electrode side), and therefore good rapid chargeability was obtained.

[0111] In Comparative Example 4, the reaction concentrated near the surface layer (negative electrode side), and good rapid chargeability was not obtained. [Explanation of symbols]

[0112] 10 positive electrode plate, 11 positive electrode current collector, 12 positive electrode active material layer, 13 first layer, 14 second layer, 15 first particle, 16 second particle, 20 particle having void portion, 21 core portion, 22 void portion, 23 outer structure portion, 24, 25 primary particle, 26 straight line, 100 reaction vessel, 111 outer cylinder, 112 inner cylinder, 113 first supply port, 114 second supply port, 115 third supply port, 116 discharge port, 117 container, 118 motor.

Claims

1. a positive electrode current collector and a positive electrode active material layer, the positive electrode active material layer includes a first layer including a first particle group and a second layer including a second particle group, the second layer is disposed between the first layer and the positive electrode current collector; the first particle group includes a plurality of first particles, the second particle group includes a plurality of second particles, the first particles include secondary particles formed by aggregation of primary particles, The integrated intensity ratio (I ００３ / I １０４ ) is 1.05 to 1.19, The crystallite size L of the secondary particles ００３ is 1000 Å or more, The positive electrode plate, wherein the second particles include particles having voids.

2. The positive electrode plate according to claim 1, wherein a thickness ratio of the first layer to the second layer (first layer:second layer) is 1:9 to 3:

7.

3. the first particles contain a lithium transition metal composite oxide having a layered crystal structure, The lithium transition metal composite oxide is Li, Ni, Mn, Co, and M (M is one or more metal elements selected from the group consisting of Mg, Ca, Al, Ti, V, Cr, Fe, Cu, Zn, Zr, Nb, Mo, Ta, and W), and 3. The positive electrode plate according to claim 1 or 2, wherein the molar ratio of Li, Ni, Mn, Co, and M is Li:Ni:Mn:Co:M=a:x:y:z:t, where a, x, y, z, and t are 1.0≦a≦1.3, x+y+z=1, 0.25≦x≦0.9, 0<y≦0.6, 0<z≦0.6, and 0<t≦0.

1.

4. The positive electrode plate according to claim 1 or 2, wherein the first particle group has an average particle diameter of 3 to 20 μm.

5. The positive electrode plate according to claim 1 , wherein the second particles have a circularity of 0.92 or more.

6. The positive electrode plate according to claim 1 or 2, wherein the second particle has a core portion, the void portion outside the core portion, and an outer portion outside the void portion.

7. The positive electrode plate according to claim 1 or 2, wherein the average particle diameter of the second particle group is 3 to 20 μm.

8. The positive electrode plate according to claim 1 or 2, wherein the second layer further contains positive electrode active material particles of a different type from the second particles.

9. A non-aqueous electrolyte secondary battery comprising the positive electrode plate according to claim 1 or 2.

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