Positive active material, preparation method thereof, positive electrode, rechargeable lithium batteries, and all-solid rechargeable batteries

Abstract

The present invention relates to a positive active material, a preparation method therefor, and a positive electrode, a rechargeable lithium battery, and an all-solid rechargeable battery, comprising same, the positive active material comprising: a first positive active material including a secondary particle which includes a lithium nickel-cobalt-aluminum-based composite oxide and is formed by aggregating a plurality of primary particles, and in which at least a portion of the primary particles is radially arranged, and a coating layer located on the surface of the secondary particle and containing ZrO2 and Li6Zr2O7; and a second positive active material including a secondary particle which includes a lithium nickel-cobalt-aluminum-manganese-based composite oxide and is formed by aggregating a plurality of primary particles, and a coating layer located on the surface of the secondary particle and containing ZrO2 and Li6Zr2O7, wherein the average particle diameter of the secondary particles of the first positive active material is larger than the average particle diameter of the secondary particles of the second positive active material.

Description

Cathode active material and its manufacturing method, cathode, lithium secondary battery, and all-solid-state secondary battery

[0001] It relates to a cathode active material and a method for manufacturing the same, a cathode, a lithium secondary battery, and an all-solid-state secondary battery.

[0002] Lithium secondary batteries, which boast high energy density and portability, are primarily used as power sources for mobile information terminals such as mobile phones, laptops, and smartphones. Recently, active research is underway to utilize high-energy-density lithium secondary batteries as power sources for hybrid and electric vehicles, or as power storage devices.

[0003] To develop lithium secondary batteries suitable for these applications, various cathode active materials are being studied. Among them, lithium nickel oxide, lithium nickel manganese cobalt composite oxide, lithium nickel cobalt aluminum composite oxide, and lithium cobalt oxide are primarily used as cathode active materials.

[0004] Recently, high-nickel cathode active materials have been widely applied to achieve high capacity. Furthermore, to increase energy density, many cathode active materials are being developed that mix large and small particles of different sizes in appropriate ratios. However, these materials pose a problem: cracks form within the particles during long-term charge / discharge cycling. These cracks trigger side reactions between the cathode active material and the electrolyte, resulting in gas generation and reduced safety. Furthermore, electrolyte depletion degrades battery performance. Therefore, the development of cathode active materials that exhibit both high capacity and long cycle life is essential.

[0005] Furthermore, development of all-solid-state secondary batteries that use solid electrolytes instead of liquid electrolytes has been actively underway recently. However, solid electrolytes have problems such as lower ionic conductivity than liquid electrolytes, resistance occurring at the interface with solid particles such as positive electrode active materials within the battery, and depletion layers formed by the bonding of solids, which reduces ionic conductivity. There is a need for the development of positive electrode active materials that can be used with such solid electrolytes, and the development of positive electrode active materials that can improve the overall performance, such as capacity characteristics and long-life characteristics, of all-solid-state secondary batteries is also necessary.

[0006] Provided are a cathode active material having high initial charge / discharge capacity and efficiency and excellent life characteristics, a method for producing the same, and a cathode, a lithium secondary battery, and an all-solid-state secondary battery including the same.

[0007] In one embodiment, a first positive electrode active material is provided, which includes a lithium nickel-cobalt-aluminum composite oxide, a plurality of primary particles are aggregated, secondary particles are formed with at least a portion of the primary particles radially arranged, and a coating layer located on the surface of the secondary particles and containing ZrO2 and Li6Zr2O7; and a second positive electrode active material, which includes a lithium nickel-cobalt-aluminum-manganese composite oxide, a plurality of secondary particles are aggregated, and a coating layer located on the surface of the secondary particles and containing ZrO2 and Li6Zr2O7, wherein an average particle diameter of the secondary particles of the first positive electrode active material is larger than an average particle diameter of the secondary particles of the second positive electrode active material.

[0008] In another embodiment, a method for manufacturing a cathode active material is provided, comprising: (i) mixing a first cathode active material precursor comprising a nickel-cobalt-aluminum composite hydroxide and in the form of secondary particles formed by agglomeration of a plurality of primary particles and at least a portion of the primary particles being radially arranged; a second cathode active material precursor comprising a nickel-cobalt-manganese composite hydroxide and in the form of secondary particles formed by agglomeration of a plurality of primary particles; and a lithium raw material, and performing a first heat treatment to obtain a preliminary cathode active material, wherein the average particle diameter of the first cathode active material precursor is larger than the average particle diameter of the second cathode active material precursor; and (ii) dry mixing the preliminary cathode active material and a zirconium raw material and performing a second heat treatment to obtain a final cathode active material.

[0009] In one embodiment, a positive electrode including the positive electrode active material is provided.

[0010] In one embodiment, a lithium secondary battery is provided, including the positive electrode, the negative electrode, a separator positioned between the positive electrode and the negative electrode, and a non-aqueous electrolyte.

[0011] In one embodiment, an all-solid-state secondary battery is provided, comprising the positive electrode, the negative electrode, and a solid electrolyte layer positioned between the positive electrode and the negative electrode.

[0012] According to one embodiment, the cathode active material exhibits high capacity, high initial charge / discharge efficiency, and excellent life characteristics.

[0013] Figure 1 is a schematic diagram showing the shape of a plate-shaped primary particle according to one implementation example.

[0014] Figure 2 is a drawing for explaining the definition of radiality in secondary particles according to one implementation example.

[0015] Figure 3 is a schematic diagram showing the cross-sectional structure of a secondary particle according to one implementation example.

[0016] Figure 4 is a schematic diagram illustrating a lithium secondary battery according to one embodiment.

[0017] Figures 5 and 6 are cross-sectional views schematically showing an all-solid-state secondary battery according to one embodiment.

[0018] Figure 7 is a graph showing the initial charge capacity (left bar graph) and initial discharge capacity (right bar graph) for the all-solid-state secondary batteries of Example 1 and Comparative Examples 1 to 5.

[0019] Figure 8 is a graph showing the initial discharge capacity (bar graph, left vertical axis) and the capacity retention rate (dotted graph, right vertical axis), which is the ratio of the 100-cycle discharge capacity to the initial discharge capacity, for the all-solid-state secondary batteries of Example 1 and Comparative Examples 1 to 5.

[0020] Figure 9 is a life evaluation graph showing the capacity retention rate according to the number of cycles for the all-solid-state secondary batteries of Example 1 and Comparative Examples 1 to 5.

[0021] Figure 10 shows high-resolution transmission electron microscopy (HRTEM; left) and inverse-FFT (inverse-FFT; right) images of the cross-section of Example 1.

[0022] Figure 11 is an HRTEM image of a cross-section of a small particle of Example 1.

[0023] Figure 12 is an image of the inverse-FFT (left) and FFT rotation pattern (right) for the portion indicated by a square in Figure 11.

[0024] Below, specific implementation examples are described in detail to facilitate their implementation by those skilled in the art. However, the present invention may be implemented in various different forms and is not limited to the implementation examples described herein.

[0025] The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

[0026] Here, “combination of these” means a mixture, laminate, composite, copolymer, alloy, blend, reaction product, etc. of the components.

[0027] It should be understood that the terms "include," "comprising," or "having" herein are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0028] To clearly illustrate various layers and regions in the drawings, their thicknesses are enlarged, and similar parts are designated by the same drawing reference numerals throughout the specification. When an element such as a layer, film, region, or plate is said to be "over" or "on" another element, this includes not only the case where it is "directly over" the other element, but also the case where there are other elements in between. Conversely, when an element is said to be "directly over" another element, it means that there are no other elements in between.

[0029] Also, here, “layer” includes not only the shape formed on the entire surface when observed in a plan view, but also the shape formed on a portion of the surface.

[0030] The average particle size can be measured by methods well known to those skilled in the art, for example, by measuring with a particle size analyzer, or by measuring with transmission electron microscope images or scanning electron microscope images. Alternatively, the average particle size can be obtained by measuring using dynamic light scattering, performing data analysis, counting the number of particles for each particle size range, and calculating from the counted number. Unless otherwise defined, the average particle size is the diameter (D) of the particles in the particle size distribution that have a cumulative volume of 50% by volume. 50) can mean. In addition, unless otherwise defined, the average particle size is obtained by measuring the size (diameter or length of major axis) of about 20 particles randomly in a scanning electron microscope image to obtain a particle size distribution, and the diameter (D) of the particle having a cumulative volume of 50% by volume in the particle size distribution 50 ) may be taken as the average particle diameter.

[0031] Here, “or” is not interpreted in an exclusive sense, for example, “A or B” is interpreted to include A, B, A+B, etc.

[0032] “Metal” is interpreted as a concept that includes common metals, transition metals, and metalloids (semi-metals).

[0033] positive electrode active material

[0034] According to one embodiment, a cathode active material for a lithium secondary battery includes a first cathode active material and a second cathode active material. The first cathode active material includes a lithium nickel-cobalt-aluminum composite oxide, and is characterized in that it is formed by agglomeration of a plurality of primary particles, and has a secondary particle form in which at least a portion of the primary particles are radially arranged, and includes a coating layer located on the surface of the secondary particle and containing ZrO2 and Li6Zr2O7. The second cathode active material includes a lithium nickel-cobalt-aluminum-manganese composite oxide, and is characterized in that it is formed by agglomeration of a plurality of primary particles, and has a coating layer located on the surface of the secondary particle and containing ZrO2 and Li6Zr2O7.

[0035] The average particle size of the secondary particles of the first positive electrode active material is characterized by being larger than the average particle size of the secondary particles of the second positive electrode active material. The first positive electrode active material may be expressed as large particles or large particles, and the second positive electrode active material may be expressed as small particles or small particles. Here, the average particle size is measured through a scanning electron microscope and is the diameter (D) of particles having a cumulative volume of 50% by volume in the particle size distribution. 50) can mean.

[0036] In the first positive electrode active material, the lithium nickel-cobalt-aluminum composite oxide refers to an oxide that includes lithium, nickel, cobalt, and aluminum, and optionally further includes other elements, and may be expressed as Ni-Co-Al or NCA. In the second positive electrode active material, the lithium nickel-cobalt-aluminum-manganese composite oxide refers to an oxide that includes lithium, nickel, cobalt, aluminum, and manganese, and optionally further includes other elements, and may be expressed as Ni-Co-Al-Mn, or NCAM. In the method for manufacturing a positive electrode active material described below, the nickel-cobalt-manganese hydroxide, which is a precursor of the second positive electrode active material, refers to a hydroxide that includes nickel, cobalt, and manganese, and optionally further includes other elements, and may be expressed as a Ni-Co-Mn precursor, or an NCM precursor.

[0037] According to one embodiment, a cathode active material can be manufactured by a method of mixing an NCA precursor, which is a precursor of a first cathode active material, and an NCM precursor, which is a precursor of a second cathode active material, with a lithium raw material and then co-firing them. In the co-firing process, the Al component of the first cathode active material precursor, which is in the form of opposing and radial secondary particles, moves or diffuses into the precursor of the second cathode active material, which is in the form of small particles and secondary particles, thereby making the second cathode active material into NCAM, and conversely, the Mn component of the second cathode active material precursor does not diffuse into the first cathode active material precursor, so that the first cathode active material does not become NCAM but can be maintained as NCA.

[0038] In the cathode active material manufactured in this way, the second cathode active material is different in shape and composition distribution from the cathode active material manufactured simply using an NCAM composition precursor, or from the NCAM cathode active material manufactured and then post-treated with an Al raw material to coat or dope with Al, and it is confirmed that the capacity and life characteristics are also superior.

[0039] In addition, the cathode active material manufactured by the conventional method of firing the first cathode active material precursor and the second cathode active material precursor separately and then mixing them instead of firing them simultaneously is different from the cathode active material according to one embodiment in terms of shape and composition distribution, has a low pellet density, which reduces the volumetric capacity of the battery, and has low life characteristics due to different deterioration rates of large and small particles, and has been confirmed to have a problem of capacity decline due to the addition of Al raw material even if the structural stability is improved by separately doping or coating Al on the second cathode active material.

[0040] coating layer

[0041] Furthermore, the positive electrode active material according to one embodiment is characterized in that both large and small particles have a coating layer formed thereon. The coating layer may be characterized in that it is formed by a dry coating method. The coating layer includes a mixed phase of ZrO2 and Li6Zr2O7. It can be said that the coating layer includes ZrO2 having a relatively high crystallinity and Li6Zr2O7 having a lower crystallinity. The presence or absence of ZrO2 and Li6Zr2O7 can be determined, for example, through the inverse FFT or FFT rotation pattern of the HRTEM image. The coating layer containing ZrO2 and Li6Zr2O7 can facilitate the movement of lithium ions on the surfaces of each of the first positive electrode active material and the second positive electrode active material, improve the structural stability of the positive electrode active material, and, for example, improve the interfacial resistance by lowering the reactivity with the solid electrolyte. Here, the coating layer can be expressed as a buffer layer or a protective layer.

[0042] The coating layer may further include an amorphous region. For example, the coating layer may include a ZrO2 crystal phase, a Li6Zr2O7 crystal phase, and a Zr-containing amorphous region. Such a coating layer can have a thin and uniform thickness while improving lithium ion conductivity and enhancing the lifespan characteristics of the positive electrode active material.

[0043] The coating layer can be a continuous film or an island. The coating layer can be manufactured using the dry coating method described below, but can still be formed with a uniform thickness on the surface of the positive electrode active material without agglomeration or localization. For example, the coating layer can be formed as a continuous and uniform film on the surface of the secondary particle. In this case, the capacity and cycle life characteristics of the positive electrode active material can be further improved.

[0044] The thickness of the coating layer may be 5 nm to 300 nm, for example, 5 nm to 200 nm, 5 nm to 100 nm, 5 nm to 80 nm, or 10 nm to 50 nm. When the coating layer has the above thickness range, it can suppress an increase in resistance due to the coating, effectively protect the positive electrode active material, and improve ionic conductivity, thereby improving the electrochemical characteristics of the battery.

[0045] According to one embodiment, the coating layer may be formed with a uniform thickness without being locally present or aggregated on the surface of the positive electrode active material secondary particle. For example, the standard deviation of the thickness of the coating layer may be 10% or less, or 5% or less, and may be 100 nm or less, 50 nm or less, or 30 nm or less relative to the diameter of the positive electrode active material.

[0046] The total Zr content of the coating layer of the first positive electrode active material and the coating layer of the second positive electrode active material may be 0.1 mol part to 0.6 mol part with respect to 100 mol parts of the total metal excluding lithium in the lithium nickel-cobalt-aluminum composite oxide of the first positive electrode active material and the lithium nickel-cobalt-aluminum-manganese composite oxide of the second positive electrode active material, for example, 0.1 mol part to 0.5 mol part, or 0.1 mol part to 0.4 mol part.

[0047] Additionally, the total Zr content of the coating layer of the first positive electrode active material and the coating layer of the second positive electrode active material may be 0.1 wt% to 6 wt%, for example, 0.5 wt% to 6 wt%, or 1 wt% to 5.5 wt%, with respect to 100 wt% of the positive electrode active material. Alternatively, the total Zr content of the coating layer of the first positive electrode active material and the coating layer of the second positive electrode active material may be 0.1 at% to 10 at%, for example, 0.1 at% to 8 at%, 0.1 at% to 7 at%, 0.5 at% to 6.5 at%, or 1 at% to 6 at%, with respect to 100 at% of the positive electrode active material.

[0048] When the total Zr content of the coating layer satisfies the above range, the coating layer can sufficiently play a role in protecting the positive electrode active material, without acting as a resistor, and can exist well with a uniform thickness without agglomerating or existing locally on the surface of the secondary particles, thereby effectively improving the life characteristics without reducing the capacity of the positive electrode active material. For example, when the Zr content is excessive, the coating layer may act as a resistor as it becomes thick, thereby reducing the charge / discharge capacity of the battery, and conversely, when the Zr content is too low, it may not sufficiently perform the buffer function, which may reduce the life characteristics of the positive electrode active material.

[0049] Below, each of the first positive electrode active material and the second positive electrode active material is described in detail.

[0050] First positive electrode active material

[0051] The lithium nickel-cobalt-aluminum composite oxide of the first positive electrode active material can be represented by chemical formula 1.

[0052] [Chemical Formula 1]

[0053] Li a1 Ni x1 Co y1 Al z1 M 1 w1 O2-b1 X b1

[0054] In the above chemical formula 1, 0.9≤a1≤1.2, 0.7≤x1<1, 0 <y1<0.3, 0<z1<0.3, 0≤w1<0.3, 0.9≤x1+y1+z1+w1≤1.1, 및 0≤b1≤0.1이고, M 1 is one or more elements selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is one or more elements selected from F, P, and S.

[0055] In the above chemical formula 1, for example, 0.7≤x1≤0.98, 0.01≤y1≤0.29, 0.01≤z1≤0.29, 0≤w1≤0.28 may be present, 0.8≤x1≤0.98, 0.01≤y1≤0.19, 0.01≤z1≤0.19, 0≤w1≤0.18 may be present, or 0.9≤x1≤0.98, 0.01≤y1≤0.09, 0.01≤z1≤0.09, 0≤w1≤0.08 may be present.

[0056] The first positive electrode active material is in the form of secondary particles in which a plurality of primary particles are aggregated, and the secondary particles may be spherical, ellipsoidal, polygonal, amorphous, etc. The first positive electrode active material is a particle, and the average particle diameter of the secondary particles may be 9 ㎛ to 25 ㎛, for example, 9 ㎛ to 20 ㎛, or 10 ㎛ to 18 ㎛. Here, the average particle diameter of the secondary particles is obtained by selecting any 20 or so particles among the particles in the SEM image of the positive electrode active material, measuring the particle diameter (diameter, or major axis, or major axis length) thereof, and then obtaining a particle size distribution, and in the particle size distribution, the diameter (D) of the particles having a cumulative volume of 50% by volume 50 ) may be taken as the average particle diameter.

[0057] The average particle diameter of the primary particles forming the secondary particles of the first positive electrode active material may be less than 200 nm, for example, 50 nm or more and less than 200 nm, 100 nm or more and less than 200 nm, 50 nm or more and 190 nm or less, or 50 nm or more and 180 nm or less. When the average particle diameter of the primary particles satisfies the above range, the lithium diffusion path may be shortened, thereby reducing resistance and improving charge / discharge efficiency. Here, the average particle diameter of the primary particles refers to the size of the primary particles observed on the surface of the secondary particles, and may be obtained by selecting 20 or so primary particles randomly from the SEM image of the surface of the secondary particles, measuring their particle diameters (diameter, major axis, or major axis length), and then calculating the arithmetic mean thereof.

[0058] The first cathode active material is characterized in that at least a portion of the primary particles forming the secondary particles are radially arranged. In this case, the diffusion of lithium increases, thereby improving the initial charge / discharge efficiency and securing a high capacity. In addition, uniform expansion and contraction are possible during the insertion and de-insertion of lithium, thereby improving the problem of the cathode active material breaking during charge / discharge, thereby improving the life characteristics and safety of the battery. In addition, when the first cathode active material is in the form of secondary particles in which at least a portion of the primary particles are radially arranged, in the method for manufacturing a cathode active material according to one embodiment, the Al component in the precursor of the first cathode active material is advantageously diffused into the precursor of the second cathode active material, thereby manufacturing a cathode active material having improved capacity characteristics, initial charge / discharge efficiency, and life characteristics.

[0059] Below, the radial structure is described in detail.

[0060] At least some of the above primary particles may have a plate shape. Fig. 1 is a schematic diagram illustrating the plate shape of the primary particles. Referring to Fig. 1, the primary particles may have a basic plate structure but may also have various detailed shapes, such as (A) a polygonal nanoplate shape such as a hexagon, (B) a nanodisk shape, and (C) a rectangular parallelepiped shape.

[0061] In Fig. 1, "a" represents the length of the major axis of the primary particle, "b" represents the length of the minor axis, and "t" represents the thickness. Here, the length of the major axis (a) represents the maximum length based on the widest surface of the primary particle. The thickness (t) can be said to be the maximum length of the surface that is approximately perpendicular to the widest surface of the primary particle. The direction in which the length of the major axis (a) and the length of the minor axis (b) are contained is defined as the surface direction, and the direction in which the thickness (t) is defined is defined as the thickness direction.

[0062] The thickness (t) of the above primary particle may be smaller than the length of the major axis (a) and the length of the minor axis (b), which are lengths in the plane direction. Among the lengths in the plane direction, the length of the major axis (a) may be longer than or equal to the length of the minor axis (b).

[0063] The above-mentioned primary particles being arranged radially may mean, for example, that the long axes of the primary particles are arranged in a radial direction. Fig. 2 is a drawing for explaining the definition of radial. In one embodiment, the radial arrangement structure means that the thickness (t) direction of the primary particles is arranged perpendicular to the direction (R) from the center of the secondary particles toward the surface or at an angle of ±5° with the perpendicular direction, as shown in Fig. 2.

[0064] In this way, when at least some of the primary particles are arranged radially, the secondary particles can have relatively many lithium diffusion paths between the primary particles on the surface side, and many crystal planes capable of lithium transport are exposed to the outside, thereby improving lithium diffusion, thereby ensuring high initial efficiency and high capacity. In addition, when the primary particles are arranged radially, the pores exposed on the surface of the secondary particles are oriented toward the center of the secondary particles, which can further promote lithium diffusion. In addition, the radially arranged primary particles enable uniform expansion and contraction during lithium insertion and de-insertion, and the pores exist toward the Miller index (001) plane, which is the direction in which the particles expand during lithium de-insertion, and these act as a buffer. Accordingly, the probability of cracks occurring during shrinkage and expansion of the positive electrode active material is lowered, and the internal pores additionally alleviate volume changes, thereby reducing cracks occurring between the primary particles during charge and discharge, ultimately improving the life characteristics of lithium secondary batteries and reducing the increase in resistance.

[0065] For example, the secondary particle may include an interior having an irregular porous structure and an exterior having a radially oriented structure as a region surrounding the interior.

[0066] The above irregular porous structure means a structure having primary particles and pores, but the pore size, shape, location, etc. are not regular. That is, the primary particles arranged inside may be arranged without regularity, unlike the primary particles arranged outside. The above radial arrangement structure may mean a shape in which the primary particles are arranged radially. Here, “outside” may mean, for example, an area from 30% to 50% in length from the outermost surface among the total distance from the center of the secondary particle to the surface, for example, an area from 40% in length from the outermost surface, or may mean an area from the outermost edge of the secondary particle to a depth of approximately 3 ㎛. Additionally, the term "interior" may mean an area from 50% to 70% of the total distance from the center of the secondary particle to the surface, for example, an area from 60% of the total distance from the center, or may mean an area excluding an area from the outermost edge of the secondary particle to a depth of approximately 3 μm.

[0067] In addition, the pores present inside the secondary particle may be larger than the pores present outside. For example, the size of the pores present inside may be 150 nm to 1 ㎛, and the size of the pores present outside may be less than 150 nm. In this case, when the pore size inside is larger than that outside, compared to secondary particles having the same pore sizes inside and outside, there is an advantage in that the lithium diffusion distance inside the positive electrode active material is shortened, lithium insertion from the outside is facilitated, and the volume change that occurs during charge and discharge is alleviated. Here, the pore size refers to the diameter when the pore is spherical or circular, and refers to the length of the major axis when the pore is elliptical, etc. The pore size may be a value calculated by randomly measuring the sizes of about 20 pores in an SEM image of a cross-section of the secondary particle and then calculating the arithmetic mean thereof.

[0068] The secondary particle may have open pores on its surface. The size of the open pore may be less than about 150 nm, for example, 10 nm to 148 nm. The open pore is a pore in which a portion of the pore wall is not closed, and is formed by the space between the plate-shaped primary particles arranged radially, and is a pore deeply connected from the surface of the secondary particle toward the center. Such an open pore may be connected to the outside and serve as a passage through which substances can pass. The open pore may be formed to a depth of 150 nm or less on average, for example, 0.001 nm to 100 nm, for example, 1 nm to 50 nm from the surface of the secondary particle. The size and depth of the above open pores may be measured by the BJH (Barrett, Joyner and Halenda) method, which is a method of deriving the content of nitrogen adsorption or desorption.

[0069] Fig. 3 is a schematic diagram showing the cross-sectional structure of a positive electrode active material secondary particle. Referring to Fig. 3, the secondary particle (11) includes an outer portion (14) having a structure in which plate-shaped primary particles (13) are arranged radially, and an inner portion (12) in which the primary particles (13) are irregularly arranged. The inner portion (12) may have more empty spaces between the primary particles than the outer portion. In addition, the pore size and porosity in the inner portion may be larger than those in the outer portion, and the shape, etc. may be irregular. In Fig. 3, the arrow indicates the direction of movement of lithium ions.

[0070] The secondary particles have a porous structure on the inside, which reduces the diffusion distance of lithium ions to the inside, and the primary particles are arranged radially on the outside, which facilitates the insertion of lithium ions into the surface. In addition, the small size of the primary particles facilitates securing a lithium transfer path between the crystal grains. In addition, the small size of the primary particles and the pores between the primary particles alleviate the volume change that occurs during charge and discharge, thereby minimizing the stress due to the volume change during charge and discharge. Such a positive electrode active material can reduce the resistance of a lithium secondary battery and improve the capacity and life characteristics.

[0071] The first positive electrode active material may be included in an amount of 60 wt% to 95 wt%, for example, 70 wt% to 90 wt%, based on 100 wt% of the positive electrode active material for the lithium secondary battery. When the first positive electrode active material is included in the above content range, a positive electrode active material having an optimal composition can be manufactured while increasing the pellet density of the positive electrode active material and increasing the energy density of the positive electrode.

[0072] Second positive electrode active material

[0073] The second positive electrode active material is in the form of secondary particles in which a plurality of primary particles are aggregated, and is a small particle, and the average particle diameter of the secondary particles may be 2 ㎛ to 8 ㎛, for example, 2.5 ㎛ to 7 ㎛, or 3 ㎛ to 6 ㎛.

[0074] The lithium nickel-cobalt-aluminum-manganese composite oxide of the second positive electrode active material can be represented by chemical formula 2.

[0075] [Chemical Formula 2]

[0076] Li a2 Ni x2 Co y2 Al z2 Mn w2 M 2 v2 O 2-b2 X b2

[0077] In the above chemical formula 2, 0.9≤a2≤1.2, 0.7≤x2<1, 0 <y2<0.3, 0<z2<0.3, 0<w2<0.3, 0≤v2<0.3, 0.9≤x2+y2+z2+w2+v2≤1.1, 및 0≤b2≤0.1이고, M 2 is one or more elements selected from the group consisting of B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0078] In the above chemical formula 2, for example, 0.7≤x2≤0.979, 0.01≤y2≤0.289, 0.001≤z2≤0.289, 0.01≤w2≤0.289, 0≤v2≤0.279 may be present, 0.8≤x2≤0.979, 0.01≤y2≤0.189, 0.001≤z2≤0.189, 0.01≤w2≤0.189, 0≤v2≤0.179 may be present, and 0.9≤x2≤0.979, 0.01≤y2≤0.089, 0.001≤z2≤0.089, 0.01≤w2≤0.089, 0≤v2≤0.079 may be present.

[0079] The second cathode active material starts as an NCM precursor and receives the Al component from the first cathode active material during the sintering process, thereby forming an NCAM composition. As described above, the shape and composition distribution are different from those of the cathode active material manufactured using an NCAM precursor.

[0080] For example, the second positive electrode active material may have a higher aluminum content in the "surface layer of the secondary particle" than in the "interior of the secondary particle." The interior of the secondary particle may refer to a region from the center of the secondary particle to about 70 length% of the radius, and the surface layer of the secondary particle may refer to a region surrounding the interior, and may refer to a region from the outermost surface of the secondary particle to a depth corresponding to 30 length% of the radius. The outermost surface refers to the surface of the secondary particle excluding the coating layer, and may be understood as the boundary between the secondary particle and the coating layer. That is, the secondary particle of the second positive electrode active material may be said to include an interior, a surface layer surrounding the interior, and a coating layer positioned on the surface layer. Both the interior and the surface layer of the secondary particle are composed of a plurality of primary particles.

[0081] Below, the Al content in the interior or surface layer of the secondary particle can be measured through TEM-EELS (Transmission Electron Microscope - Electron Energy Loss Spectroscopy) analysis of a cross-section of the secondary particle cut by a focused ion beam (FIB), etc. In addition, the Al content can mean the at% content of aluminum with respect to 100 at% of the total metal excluding lithium in the lithium nickel-cobalt-aluminum-manganese composite oxide.

[0082] For example, the Al content in the surface layer of the secondary particle may be 0.2 at% to 2.0 at% with respect to 100 at% of the total metal excluding lithium in the second positive electrode active material, and the Al content in the interior of the secondary particle may be 0 at% to 0.6 at% with respect to 100 at% of the total metal excluding lithium in the second positive electrode active material, and the Al content in the surface layer may be higher than the Al content in the interior.

[0083] In addition, according to one embodiment, the second cathode active material may have a higher aluminum content in the surface layer of the secondary particle at a portion in contact with the first cathode active material during the first heat treatment than at a portion not in contact with the first cathode active material. This is understood to be because the second cathode active material received the Al component from the first cathode active material during the first heat treatment, and is also a distinguishing feature from cases where an NCAM precursor is used as a particle or where Al is coated or doped separately.

[0084] For example, in the surface layer of the secondary particles of the second positive electrode active material, the content of aluminum relative to the entire metal excluding lithium in the portion in contact with the first positive electrode active material may be 0.8 at% to 2.0 at%, for example, 0.8 at% to 1.8 at%, or 0.9 at% to 1.6 at%. The content of aluminum relative to the entire metal excluding lithium in the portion not in contact with the first positive electrode active material may be less than 0.8 at%, for example, 0 at% to 0.7 at%, or 0.1 at% to 0.6 at%.

[0085] In other words, the second cathode active material according to one embodiment may be said to include a high-concentration Al region and a low-concentration Al region in the surface layer of the secondary particle. The content of aluminum in the high-concentration Al region relative to the entire metal excluding lithium may be 0.8 at% to 2.0 at%, for example, 0.8 at% to 1.8 at%, or 0.9 at% to 1.6 at%. The content of aluminum in the low-concentration Al region relative to the entire metal excluding lithium may be less than 0.8 at%, for example, 0 at% to 0.7 at%, or 0.1 at% to 0.6 at%.

[0086] Additionally, the difference between the aluminum content in the high-concentration Al region and the aluminum content in the low-concentration Al region may be 0.3 at% to 2.0 at%, for example, 0.4 at% to 1.8 at%, or 0.5 at% to 1.5 at%.

[0087] It is well known that after manufacturing a lithium transition metal composite oxide, aluminum raw material is mixed and heat-treated to separately dope or coat Al. However, in this case, unreacted Al raw material, for example, aluminum oxide such as Al2O3, remains in the final positive electrode active material, and furthermore, since Al is unevenly doped on the particle surface, a high-concentration Al doping area exceeding 2 at% is generated on some part of the surface, which causes a problem of reduced capacity. In contrast, the positive electrode active material according to one embodiment does not add a separate Al raw material during the sintering process, and accordingly, in the final positive electrode active material, unreacted Al raw material such as aluminum oxide does not exist on the outermost surface of the secondary particles of each of the first positive electrode active material and the second positive electrode active material. In addition, even in a region with a high Al content in the surface layer of the second positive electrode active material, the Al content is 2 at% or less, and the difference in Al content between the high-concentration Al region and the low-concentration Al region is also small, at 2 at% or less. Accordingly, the second cathode active material according to one embodiment has structural stability and performance improvement effects due to Al doping, while problems such as capacity reduction that occur due to the addition of Al raw material during sintering can be effectively suppressed.

[0088] The second cathode active material, which is a small particle, may be included in an amount of 5 to 40 wt%, for example, 10 to 30 wt%, based on 100 wt% of the cathode active material for the lithium secondary battery. When the second cathode active material is included in the above content range, a cathode active material having an optimal composition can be manufactured while increasing the pellet density of the cathode active material and increasing the energy density of the cathode.

[0089] Below, the manufacturing method of the positive electrode active material is described in detail.

[0090] Method for manufacturing positive electrode active material

[0091] In one embodiment, a method for manufacturing a cathode active material is provided, comprising: (i) mixing a first cathode active material precursor comprising a nickel-cobalt-aluminum composite hydroxide and in the form of secondary particles formed by agglomeration of a plurality of primary particles and at least a portion of the primary particles being radially arranged; a second cathode active material precursor comprising a nickel-cobalt-manganese composite hydroxide and in the form of secondary particles formed by agglomeration of a plurality of primary particles; and a lithium raw material, and performing a first heat treatment to obtain a preliminary cathode active material, wherein the average particle diameter of the first cathode active material precursor is larger than the average particle diameter of the second cathode active material precursor; and (ii) dry mixing the preliminary cathode active material and a zirconium raw material and performing a second heat treatment to obtain a final cathode active material.

[0092] The above manufacturing method can be defined as a method of mixing a large NCA radial secondary particle precursor and a small NCM secondary particle precursor with a lithium raw material, co-firing them, and then dry-coating zirconium. During the co-firing process, the large Al component can diffuse or migrate to the small particles to form the NCAM composition in the small particles, and thus a cathode active material mixed with the large radial secondary particle NCA and the small particle secondary particle NCAM can be manufactured. This is understood to be possible because the large Al component has a faster diffusion rate than the small particle Mn within the co-firing temperature range, and also because the large Al component is more easily transferred to the small particles as the large precursor takes the form of radial secondary particles. The final cathode active material manufactured by this method can exhibit high capacity while realizing high initial charge / discharge efficiency and excellent cycle characteristics.

[0093] According to the above manufacturing method, compared to the existing method of manufacturing by separately firing large and small particles and then mixing them, the volumetric capacity can be significantly improved, and compared to the case where only the small particles are doped or coated with Al after the individual firing and then the large and small particles are mixed, the initial discharge capacity, volumetric capacity, energy density, etc. can be further improved. In addition, according to the method according to one embodiment, even if the simultaneous firing method is applied, the life characteristics can be improved compared to the case where large and small particles having the same components are used, and the initial discharge capacity and energy density can be improved compared to the case where Al is doped or coated separately after the simultaneous firing. In the method for manufacturing a cathode active material according to one embodiment, structural stability can be secured by introducing an appropriate amount of aluminum into large and small particles without mixing aluminum raw materials in the processes such as the first heat treatment and the second heat treatment, and the problem of capacity reduction due to the addition of aluminum raw materials can be improved.

[0094] The nickel-cobalt-aluminum composite hydroxide, which is the first positive electrode active material precursor, can be specifically represented by the following chemical formula 11.

[0095] [Chemical Formula 11]

[0096] Ni x11 Co y11 Al z11 M 11 w11 (OH)2

[0097] In the above chemical formula 11, 0.7≤x11<1, 0 <y11<0.3, 0<z11<0.3, 0≤w11<0.3, 0.9≤x11+y11+z11+w11≤1.1이고, M 11 is one or more elements selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Z.

[0098] The first positive electrode active material precursor may be formed by agglomerating a plurality of primary particles, and at least a portion of the primary particles may be in the form of secondary particles arranged radially. The average particle diameter of the secondary particles may be 9 ㎛ to 25 ㎛, for example, 9 ㎛ to 20 ㎛, or 10 ㎛ to 18 ㎛. Here, the average particle diameter of the secondary particles is obtained by selecting arbitrarily 20 or so particles from an SEM image of the first positive electrode active material precursor, measuring the particle diameter (diameter, or major axis, or major axis length) thereof, and then obtaining a particle size distribution, and in the particle size distribution, the diameter (D) of the particles having a cumulative volume of 50% by volume 50 ) may be taken as the average particle diameter.

[0099] The first cathode active material precursor can be prepared by a coprecipitation reaction. That is, a composite metal raw material is prepared by mixing metal raw materials such as nickel raw materials, and a complexing agent and a pH adjusting agent are added thereto to control the pH of the mixture while performing a coprecipitation reaction, thereby producing a nickel-based composite hydroxide of a desired composition. The complexing agent serves to control the reaction rate of precipitate formation in the coprecipitation reaction, and may be, for example, ammonium hydroxide (NH4OH) or citric acid. The pH adjusting agent may be, for example, sodium hydroxide (NaOH), sodium carbonate (Na2CO3), sodium oxalate (Na2C2O4), or the like. The pH of the mixture may be adjusted to, for example, a range of 10 to 13.

[0100] The above-described coprecipitation reaction can proceed in multiple stages, for example, in two, three, or four stages. In each stage, the concentration of the complexing agent, the rate of introduction of the metal raw material, the pH control range, the reaction temperature, the reaction time, or the stirring power can be adjusted differently. Through such adjustment, it is possible to manufacture a positive electrode active material precursor in the form of secondary particles in which at least a portion of the primary particles are radially arranged, and also to manufacture secondary particles with different internal and external shapes.

[0101] For example, a first positive electrode active material precursor having a radial structure can be manufactured, for example, by the following method. The method for manufacturing the first positive electrode active material precursor can include a first process, a second process, and a third process for forming a core, an intermediate layer, and a shell in that order. In the first process, a complexing agent, a pH adjusting agent, and a metal raw material are introduced into a reactor and reacted. At this time, the concentration of the complexing agent may be 0.1 M to 0.7 M, and the input amount may be 6 mL / min to 12 mL / min. The concentration of the metal raw material may be 0.1 M to 3.5 M, and the input amount may be 50 mL / min to 100 mL / min. Subsequently, in the second process, a complexing agent, a pH adjusting agent, and a metal raw material are further introduced, and at this time, the concentration of the complexing agent may be 0.3 M to 1.0 M, and the input amount may be 8 mL / min to 15 mL / min. The concentration of the metal raw material may be 0.1 M to 3.5 M and the input amount may be 60 mL / min to 120 mL / min. In the third process, the concentration and input amount of the complexing agent and the metal raw material may be further increased or maintained the same so as not to decrease the particle growth rate. At this time, the concentration of the complexing agent may be 0.35 M to 1.0 M and the input amount may be 12 mL / min to 20 mL / min. The concentration of the metal raw material may be 0.1 M to 3.5 M and the input amount may be 70 mL / min to 150 mL / min. In the first to third processes, the pH may be controlled between 10 and 12.

[0102] The nickel-cobalt-manganese composite hydroxide, which is the second cathode active material precursor, can be specifically represented by the following chemical formula 12.

[0103] [Chemical Formula 12]

[0104] Ni x12 Co y12 Mn w12 M 12 v12 (OH)2

[0105] In the above chemical formula 12, 0.7≤x12<1, 0 <y12<0.3, 0<w12<0.3, 0≤v12<0.3, 0.9≤x12+y12+w12+v12≤1.1이고, M 12 is one or more elements selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr.

[0106] The second positive electrode active material precursor may be in the form of secondary particles in which a plurality of primary particles are aggregated. The average particle diameter of the secondary particles may be 2 ㎛ to 8 ㎛, for example, 2.5 ㎛ to 7 ㎛, or 3 ㎛ to 6 ㎛. Here, the average particle diameter of the secondary particles is obtained by selecting 20 or so random particles from an SEM image of the second positive electrode active material precursor, measuring their particle diameters (diameter, or major axis, or major axis length), and then obtaining a particle size distribution, and in the particle size distribution, the diameter (D) of particles having a cumulative volume of 50% by volume 50 ) may be taken as the average particle diameter.

[0107] The second cathode active material precursor can be prepared by a general co-precipitation reaction.

[0108] The mixing weight ratio of the first positive electrode active material precursor and the second positive electrode active material precursor may be 60:40 to 95:5, or 70:30 to 90:10.

[0109] The lithium raw material may be, for example, Li2CO3, LiOH, a hydrate thereof, or a combination thereof. The lithium raw material may be mixed in an amount of 0.9 to 1.2 molar parts per 1 molar part of the total metal in the first cathode active material precursor and the second cathode active material precursor.

[0110] The first heat treatment may be performed at, for example, 600°C to 1000°C, or 700°C to 900°C. Within the above temperature range, a first positive electrode active material and a second positive electrode active material having an optimal composition can be manufactured.

[0111] For example, the first heat treatment includes a temperature raising step and a temperature holding step, and the temperature raising time may be set to be longer than the temperature holding time. For example, the temperature raising time may be 6 hours to 16 hours and the temperature holding time may be 1 hour to 9 hours, and the temperature raising time may be longer than the temperature holding time. In the first heat treatment, the temperature raising time may be, for example, 6 hours to 15 hours, 6 hours to 14 hours, 6 hours to 13 hours, or 7 hours to 12 hours, and the temperature holding time may be 2 hours to 9 hours, or 3 hours to 8 hours. In addition, the ratio of (temperature raising time):(temperature holding time) may be 1.1:1 to 10:1, for example, 1.1:1 to 8:1, 1.1:1 to 6:1, 1.1:1 to 5:1, or 1.1:1 to 4:1.

[0112] The preliminary positive electrode active material obtained through the first heat treatment may be a mixture of a first preliminary positive electrode active material in the form of secondary particles, which include a lithium nickel-cobalt-aluminum composite oxide represented by the chemical formula 1 and are formed by agglomeration of a plurality of primary particles, and at least a portion of the primary particles are arranged radially, and a second preliminary positive electrode active material in the form of secondary particles, which include a lithium nickel-cobalt-aluminum-manganese composite oxide represented by the chemical formula 2 and are formed by agglomeration of a plurality of primary particles.

[0113] In one embodiment, a method is provided for forming a zirconium-containing coating layer on both large and small particles by dry-mixing a preliminary positive electrode active material and a zirconium raw material and performing a second heat treatment. The method applies a dry coating method, does not use an organic solvent and expensive coating raw materials, and can use existing equipment, making it economical and environmentally friendly, and enabling mass production. According to the method, a positive electrode active material having a coating layer containing ZrO2 and Li6Zr2O7 formed on both large and small particles can be synthesized, and a coating layer having an appropriate content and thickness can be synthesized in a good form, thereby manufacturing a positive electrode active material having both improved capacity characteristics and cycle life characteristics. For example, such a positive electrode active material has low reactivity with sulfide-based solid electrolyte particles and low interfacial resistance, and thus can be applied to all-solid-state secondary batteries, etc., to improve capacity characteristics, rate characteristics, cycle life characteristics, etc.

[0114] Zirconium raw materials are compounds containing the element zirconium, and any compound capable of dry mixing can be applied without limitation. Zirconium raw materials may be, for example, zirconium-containing oxides, zirconium-containing sulfides, zirconium-containing carbonates, zirconium-containing hydroxides, etc., and may be, for example, zirconium oxide, zirconium sulfide, zirconium carbonate, zirconium hydroxide, or combinations thereof.

[0115] The zirconium raw material can be mixed in an amount of 0.1 to 0.6 mol parts based on 100 mol parts of the total metal excluding lithium in the preliminary active material, for example, 0.1 to 0.5 mol parts, or 0.1 to 0.4 mol parts. When the zirconium raw material is added in the above range, a coating layer having an appropriate content and thickness can be formed, so that it can sufficiently play a role in protecting the positive electrode active material, and can exist in a uniform thickness without being aggregated or locally present on the surface of the secondary particles. For example, when the content of the zirconium raw material is excessive, the coating layer may become thicker and act as a resistive layer, thereby reducing the charge / discharge capacity of the positive electrode active material. On the other hand, when the content of the zirconium raw material is too small, it cannot sufficiently play a buffer role, so that the life characteristics of the positive electrode active material may deteriorate.

[0116] The zirconium raw material may be in the form of nanoparticles, for example. The zirconium raw material is in the form of particles, and the average particle diameter (D) of the particles 50 ) may be, for example, 10 nm to 500 nm, 10 nm to 500 nm, or 50 nm to 500 nm. As an example, the zirconium raw material is a particle containing zirconium oxide, and the average particle diameter (D of the particles 50 ) may be from 10 nm to 500 nm. In this case, it may be advantageous for synthesizing a coating layer of an appropriate thickness.

[0117] In the method for manufacturing a cathode active material according to one embodiment, dry mixing means mixing without a solvent and can be understood as a solid-state coating method. This is distinguished from wet coating or liquid coating.

[0118] In a method for manufacturing a positive electrode active material according to one embodiment, a second heat treatment is performed after dry mixing to form a coating layer containing a mixed phase of ZrO2 and Li6Zr2O7 and having a uniform thickness. The heat treatment temperature may be 420°C to 580°C, for example, 430°C to 570°C, 440°C to 560°C, 450°C to 550°C, or 460°C to 530°C. By performing heat treatment in the above temperature range, it is possible to synthesize a coating layer having an appropriate crystal phase, and the coating layer does not act as a resistor but sufficiently functions as a buffer, thereby improving the capacity characteristics and life characteristics of the positive electrode active material. For example, when the second heat treatment temperature is lower than 420°C, the coating layer may not form an appropriate crystal phase and only act as a resistor, thereby deteriorating the capacity characteristics of the positive electrode active material. If the second heat treatment temperature exceeds 580℃, the coating materials may coagulate or be coated only locally, reducing the buffer effect. In addition, zirconium may be absorbed into the positive electrode active material, failing to function as a buffer and causing deterioration in capacity characteristics and life characteristics.

[0119] The second heat treatment can be performed in an oxygen atmosphere, for example, for 5 to 25 hours, or 10 to 20 hours. A good coating layer can be formed under these conditions.

[0120] In one embodiment, when dry mixing the preliminary positive electrode active material and the zirconium raw material, a lithium raw material may be mixed together. The lithium raw material is a lithium-containing compound that can be dry mixed, and can be applied without limitation. The lithium raw material may be, for example, Li2CO3, LiOH, a hydrate thereof, or a combination thereof. In one embodiment, anhydrous lithium hydroxide may be used as the lithium raw material. The lithium raw material may be mixed in an amount of more than 1 mol part to less than 4 mol parts with respect to 1 mol part of the zirconium raw material, for example, more than 1 mol part to less than 3 mol parts, or more than 2 mol parts to less than 4 mol parts. When the lithium raw material is mixed together and heat-treated, it is advantageous for forming a lithium zirconium oxide, for example, a Li6Zr2O7 crystal phase, in the coating layer, and it is advantageous for increasing lithium ion conductivity and obtaining a coating layer of an appropriate thickness in a good shape.

[0121] anode

[0122] In one embodiment, a positive electrode comprising the positive electrode active material described above is provided. The positive electrode comprises a current collector and a positive electrode active material layer positioned on the current collector, wherein the positive electrode active material layer comprises the positive electrode active material described above and may further comprise a binder and / or a conductive material.

[0123] The above binder serves to adhere the positive electrode active material particles well to each other and also to adhere the positive electrode active material well to the current collector, and representative examples thereof include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0124] The content of the binder may be approximately 0.1 wt% to 5 wt%, or 0.1 wt% to 3 wt%, based on 100 wt% of the entire positive electrode active material layer.

[0125] The conductive material is used to provide conductivity to the electrode, and any material that does not cause a chemical change and is electronically conductive can be used in the battery to be constructed. Examples of conductive materials that can be used include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc.; metal-based materials containing copper, nickel, aluminum, silver, etc. in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; or conductive materials containing mixtures thereof.

[0126] The content of the conductive agent may be 0.1 wt% to 5 wt%, or 0.1 wt% to 3 wt%, based on 100 wt% of the total positive electrode active material layer.

[0127] Aluminum foil may be used as the positive electrode current collector, but is not limited thereto.

[0128] lithium secondary battery

[0129] In one embodiment, a lithium secondary battery comprising the aforementioned positive electrode active material is provided. Here, the lithium secondary battery may be understood as a superordinate concept of a lithium ion battery using a non-aqueous electrolyte, a lithium metal battery using lithium metal as an anode, and an all-solid-state secondary battery having a solid electrolyte layer interposed between the positive electrode and the negative electrode.

[0130] In one example, a lithium secondary battery is provided, which includes a positive electrode including the positive active material described above, a negative electrode, a separator positioned between the positive electrode and the negative electrode, and a non-aqueous electrolyte.

[0131] In another embodiment, an all-solid-state secondary battery is provided, comprising a positive electrode including the positive active material described above, a negative electrode, and a solid electrolyte layer positioned between the positive electrode and the negative electrode.

[0132] lithium ion battery

[0133] In one example, a lithium ion battery using a non-aqueous electrolyte as an electrolyte while applying the aforementioned positive electrode active material is described.

[0134] Fig. 4 is a schematic diagram illustrating a lithium secondary battery according to one embodiment. Referring to Fig. 4, a lithium secondary battery (100) according to one embodiment includes a battery cell including a positive electrode (114), a negative electrode (112) positioned opposite the positive electrode (114), a separator (113) positioned between the positive electrode (114) and the negative electrode (112), and an electrolyte for a lithium secondary battery that impregnates the positive electrode (114), the negative electrode (112), and the separator (113), a battery container (120) containing the battery cell, and a sealing member (140) that seals the battery container (120).

[0135] cathode

[0136] A negative electrode for a lithium secondary battery includes a current collector and a negative electrode active material layer positioned on the current collector. The negative electrode active material layer includes a negative electrode active material and may further include a binder and / or a conductive material.

[0137] The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0138] The material capable of reversibly intercalating / deintercalating the lithium ions may include a carbon-based negative electrode active material, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as natural graphite or artificial graphite in an amorphous, plate-like, flake-like, spherical, or fibrous form, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0139] As the above lithium metal alloy, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0140] As the material capable of doping and dedoping the lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material is silicon, a silicon-carbon composite, SiOx(0 <x<2), Si-Q 합금(상기 Q는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소(Si를 제외함), 15족 원소, 16족 원소, 전이금속, 희토류 원소 및 이들의 조합에서 선택됨), 또는 이들의 조합일 수 있다. 상기 Sn계 음극 활물질로는 Sn, SnO2, Sn계 합금 또는 이들의 조합일 수 있다.

[0141] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, the composite may include secondary particles (cores) in which silicon primary particles are assembled and an amorphous carbon coating layer (shell) positioned on the surface of the secondary particles. The amorphous carbon may also be positioned between the silicon primary particles, such that, for example, the silicon primary particles may be coated with amorphous carbon. The secondary particles may be dispersed and present in an amorphous carbon matrix.

[0142] The silicon-carbon composite may further comprise crystalline carbon. For example, the silicon-carbon composite may comprise a core comprising crystalline carbon and silicon particles and an amorphous carbon coating layer positioned on the surface of the core.

[0143] The above Si-based negative electrode active material or Sn-based negative electrode active material can be used in a mixture with a carbon-based negative electrode active material.

[0144] The content of the negative active material in the above negative active material layer may be 95 wt% to 99 wt% with respect to the total weight of the negative active material layer.

[0145] In one embodiment, the negative electrode active material layer further includes a binder and may optionally further include a conductive material. The content of the binder in the negative electrode active material layer may be 1 wt% to 5 wt% based on the total weight of the negative electrode active material layer. In addition, when the negative electrode active material layer further includes a conductive material, the negative electrode active material layer may include 90 wt% to 98 wt% of the negative electrode active material, 1 wt% to 5 wt% of the binder, and 1 wt% to 5 wt% of the conductive material.

[0146] The above binder serves to adhere the negative electrode active material particles well to each other and also to adhere the negative electrode active material well to the current collector. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0147] Examples of the non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0148] The above-mentioned aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluoroelastomer, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0149] When using an aqueous binder as the above-mentioned negative electrode binder, a cellulose-based compound capable of imparting viscosity may be further included. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or an alkali metal salt thereof. The alkali metal may be Na, K, or Li.

[0150] The above dry binder is a polymeric material capable of being fiberized, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0151] The conductive material is used to provide conductivity to the electrode, and any material that does not cause chemical changes and is electronically conductive can be used in the battery. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes; metal-based materials in the form of metal powder or metal fibers, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0152] The negative electrode current collector may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and a combination thereof.

[0153] electrolyte

[0154] An electrolyte for a lithium secondary battery contains a non-aqueous organic solvent and a lithium salt.

[0155] The non-aqueous organic solvent acts as a medium through which ions involved in the electrochemical reaction of the battery can move. The non-aqueous organic solvent may be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0156] Examples of the carbonate solvent that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. Examples of the ester solvent that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methylpropionate, ethylpropionate, decanolide, mevalonolactone, valerolactone, caprolactone, etc. Examples of ether solvents that can be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. In addition, examples of ketone solvents that can be used include cyclohexanone. Examples of alcohol solvents that can be used include ethyl alcohol and isopropyl alcohol, and examples of aprotic solvents that can be used include nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane; and sulfolanes.

[0157] The above non-aqueous organic solvents can be used alone or in combination of two or more.

[0158] In addition, when using a carbonate solvent, a cyclic carbonate and a chain carbonate can be mixed and used, and the cyclic carbonate and the chain carbonate can be mixed in a volume ratio of 1:1 to 1:9.

[0159] The above lithium salt is a substance that dissolves in an organic solvent and acts as a source of lithium ions in the battery, enabling the basic operation of a lithium secondary battery and promoting the movement of lithium ions between the positive and negative electrodes. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFOB), lithium bis(oxalato)borate (LiBOB).

[0160] separator

[0161] Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such separators may include polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films comprising two or more layers thereof. Furthermore, mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may also be used.

[0162] The above separator may include a porous substrate and a coating layer comprising an organic material, an inorganic material, or a combination thereof, positioned on one or both sides of the porous substrate.

[0163] The above porous substrate may be a polymer film formed of any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyarylether ketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon, and polytetrafluoroethylene, or a copolymer or mixture of two or more thereof.

[0164] The above organic material may include a polyvinylidene fluoride-based antibody or a (meth)acrylic polymer.

[0165] The above inorganic materials are Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, It may include inorganic particles selected from, but not limited to, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0166] The organic and inorganic substances may be mixed and present in one coating layer, or a coating layer including an organic substance and a coating layer including an inorganic substance may be present in a laminated form.

[0167] All-solid-state secondary battery

[0168] In one example, an all-solid-state secondary battery is described in which the aforementioned positive electrode active material is applied, a solid electrolyte is used as an electrolyte, and a solid electrolyte layer is interposed between the positive electrode and the negative electrode.

[0169] Fig. 5 is a cross-sectional view of an all-solid-state secondary battery according to an embodiment. Referring to Fig. 5, the all-solid-state secondary battery (100') may have a structure in which an electrode assembly in which a negative electrode (400) including a negative electrode collector (401) and a negative electrode active material layer (403), a solid electrolyte layer (300), and a positive electrode (200) including a positive electrode active material layer (203) and a positive electrode collector (201) are laminated is housed in a battery case. The all-solid-state secondary battery (100') may further include an elastic layer (500) on the outer side of at least one of the positive electrode (200) and the negative electrode (400). Although Fig. 5 illustrates one electrode assembly including the negative electrode (400), the solid electrolyte layer (300), and the positive electrode (200), an all-solid-state secondary battery may be manufactured by laminating two or more electrode assemblies.

[0170] anode

[0171] The positive electrode for an all-solid-state secondary battery includes the positive electrode active material described above and may optionally include a binder, a conductive material, and / or a solid electrolyte.

[0172] solid electrolyte

[0173] The above solid electrolyte may be an inorganic solid electrolyte such as a sulfide-based solid electrolyte, an oxide-based solid electrolyte, or a halide-based solid electrolyte.

[0174] In one embodiment, the solid electrolyte may be a sulfide-based solid electrolyte having excellent ion conductivity. The sulfide-based solid electrolyte particles include, for example, Li2S-P2S5, Li2S-P2S5-LiX (wherein X is a halogen element, for example, I or Cl), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z. m S n(m, n are integers, Z is Ge, Zn or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (p, q are integers, and M is P, Si, Ge, B, Al, Ga or In), or a combination thereof.

[0175] Such sulfide-based solid electrolytes can be obtained, for example, by mixing Li2S and P2S5 in a molar ratio of 50:50 to 90:10, or 50:50 to 80:20, and optionally heat-treating them. Within the above mixing ratio range, a sulfide-based solid electrolyte having excellent ionic conductivity can be produced. Here, the ionic conductivity can be further improved by further including other components such as SiS2, GeS2, and B2S3.

[0176] Methods for mixing sulfur-containing raw materials for manufacturing sulfide-based solid electrolytes can be either mechanical milling or solution milling. Mechanical milling involves placing starting materials in a ball mill reactor and vigorously stirring them to finely atomize and mix them. Using the solution milling method, the starting materials are mixed in a solvent to obtain a solid electrolyte as a precipitate. Furthermore, heat treatment after mixing can solidify the crystals of the solid electrolyte and improve ionic conductivity. The heat treatment can be performed at a temperature ranging from 400°C to 600°C, for example, from 450°C to 500°C, or from 460°C to 490°C, for 5 to 30 hours, 10 to 24 hours, or 15 to 20 hours. Heat treatment under the above conditions can maximize ionic conductivity. For example, a sulfide-based solid electrolyte can be manufactured by mixing sulfur-containing raw materials and heat-treating them twice or more, in which case a sulfide-based solid electrolyte with high ionic conductivity and strength can be manufactured.

[0177] According to one embodiment, sulfide-based solid electrolyte particles can be manufactured through, for example, a first heat treatment in which sulfur-containing raw materials are mixed and calcined at 120°C to 350°C, and a second heat treatment in which the first heat treatment result is mixed and calcined at 350°C to 800°C. The first heat treatment and the second heat treatment can each be performed in an inert gas or nitrogen atmosphere. The first heat treatment can be performed for 1 to 10 hours, and the second heat treatment can be performed for 5 to 20 hours. The first heat treatment can have the effect of milling small raw materials, and the second heat treatment can synthesize the final solid electrolyte. Through two or more such heat treatments, a high-performance sulfide-based solid electrolyte with high ionic conductivity and robustness can be obtained, and such a solid electrolyte can be said to be suitable for mass production. The temperature of the first heat treatment may be, for example, 150°C to 330°C, or 200°C to 300°C, and the temperature of the second heat treatment may be, for example, 380°C to 700°C, or 400°C to 600°C.

[0178] For example, the sulfide-based solid electrolyte particles may include argyrodite-type sulfides. The argyrodite-type sulfide-based solid electrolyte particles may have an ionic conductivity of 10, which is the ionic conductivity of a typical liquid electrolyte at room temperature. -4 10 inland -2 It has a high ionic conductivity approaching the S / cm range, can form a close bond between a positive electrode active material and a solid electrolyte without causing a decrease in ionic conductivity, and can further form a close interface between an electrode layer and a solid electrolyte layer. An all-solid-state secondary battery including the same can have improved battery performance, such as rate characteristics, Coulombic efficiency, and cycle life characteristics.

[0179] The argyrodite-type sulfide-based solid electrolyte particles may include, for example, a compound represented by the chemical formula 21 below.

[0180] [Chemical Formula 21]

[0181] (Li a M 1 b M 2 c )(P d M 3 e )(S f M 4 g )X h

[0182] In the above chemical formula 21, 4≤a≤8, and M 1 is Mg, Ca, Cu, Ag, or a combination thereof, and 0≤b<0.5, and M 2 is Na, K, or a combination thereof, 0≤c<0.5, and M 3 is Sn, Zn, Si, Sb, Ge, or a combination thereof, and 0 <d<4, 0≤e<1 이고, M 4 is N,O,SO n , or a combination thereof, and 1.5≤n≤5, 3≤f≤12, 0≤g<2, and X is F, Cl, Br, I, or a combination thereof, and 0≤h≤2.

[0183] For example, in chemical formula 21, a halide element (X) may be included as an essential element, in which case 0 <h≤2로 표시될 수 있다. 일 예로 화학식 21에 M 1 Elements may be required, in which case 0 <b<0.5로 표시될 수 있다. 화학식 21에서 M 3 can be understood as an element substituted in place of P and 0 <e<1일 수 있다. 화학식 21에서 M 4 is substituted in the S position, for example, 0 <g<2일 수 있으며 S의 비율인 f는 예를 들어 3≤f≤7일 수 있다. M 4 Go SO n If SO n It can be, for example, S4O6, S3O6, S2O3, S2O4, S2O5, S2O6, S2O7, S2O8, SO4, or SO5, and can be, for example, SO4.

[0184] For example, in chemical formula 21, a+b+c+h=7, d+e=1, and f+g+h=6.

[0185] As a specific example, argyrodite-type sulfide-based solid electrolyte particles include Li3PS4 and Li7P3S. 11 , Li7PS6, Li6PS5Cl, Li6PS5Br, Li 5.8 PS 4.8 Cl 1.2 , Li 6.2 PS 5.2 Br 0.8 , Li 5.75 PS 4.75 Cl 1.25 , (Li 5.69 Cu 0.06 )PS 4.75 Cl 1.25 , (Li 5.72 Cu 0.03 )PS 4.75 Cl 1.25 , (Li 5.69 Cu 0.06 )P(S 4.70 (SO4) 0.05 )Cl 1.25 , (Li 5.69 Cu 0.06 )P(S 4.60 (SO4) 0.15 )Cl 1.25 , (Li 5.72 Cu 0.03 )P(S 4.725 (SO4) 0.025 )Cl 1.25 , (Li 5.72 Na 0.03 )P(S 4.725 (SO4) 0.025 )Cl 1.25 , Li 5.75 P(S 4.725 (SO4) 0.025 )Cl 1.25 , or combinations thereof, but are not limited thereto.

[0186] An argyrodite-type sulfide-based solid electrolyte can be manufactured, for example, by mixing lithium sulfide and phosphorus sulfide, optionally a lithium halide. After mixing these, a heat treatment may be performed. The heat treatment may include, for example, two or more heat treatment steps. Here, manufacturing an argyrodite-type sulfide-based solid electrolyte may include, for example, a first heat treatment of mixing raw materials and calcining at 120°C to 350°C, and a second heat treatment of mixing the resultant of the first heat treatment again and calcining at 350°C to 800°C.

[0187] The average particle diameter (D) of the above sulfide-based solid electrolyte particles 50 ) may be, for example, 0.1 ㎛ to 5.0 ㎛, may be small particles of 0.1 ㎛ to 1.9 ㎛, or may be large particles of 2.0 ㎛ to 5.0 ㎛. The average particle diameter of the sulfide-based solid electrolyte particles may be measured by an electron microscope image, and for example, a particle size distribution is obtained by measuring the size (diameter or length of major axis) of about 20 particles in a scanning electron microscope image, where D 50 It may have been calculated.

[0188] The above solid electrolyte may include an oxide-based inorganic solid electrolyte in addition to a sulfide-based material. The above oxide-based inorganic solid electrolyte may include, for example, Li 1+x Ti 2-x Al(PO4)3(LTAP)(0≤x≤4), Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 (0 <x<2, 0≤y<3), BaTiO3, Pb(Zr,Ti)O3(PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT)(0≤x<1, 0≤y<1), PB(Mg3Nb 2 / 3)O3-PbTiO3(PMN-PT), HfO2, SrTiO3, SnO2, CeO2, Na2O, MgO, NiO, CaO, BaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiO2, lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 <x<2, 0<y<3), Li 1+x+y (Al, Ga) x (Ti, Ge) 2-x Si y P 3-y O 12 (0≤x≤1, 0≤y≤1), lithium lanthanum titanate (Li x La y TiO3, 0 <x<2, 0<y<3), Li2O, LiAlO2, Li2O-Al2O3-SiO2-P2O5-TiO2-GeO2계 세라믹스, 가넷(Garnet)계 세라믹스 Li 3+x La3M2O 12 (M= Te, Nb, or Zr; x is an integer from 1 to 10), or mixtures thereof.

[0189] The solid electrolyte may further include, for example, a halide-based solid electrolyte. The halide-based solid electrolyte contains a halogen element as a main component, and may mean that the ratio of the halide element to all elements constituting the solid electrolyte is 50 mol% or more, 70 mol% or more, 90 mol% or more, or 100 mol%. For example, the halide-based solid electrolyte may not contain a sulfur element.

[0190] The halide-based solid electrolyte may contain lithium element, a metal element other than lithium, and a halogen element. The metal element other than lithium may be Al, As, B, Bi, Ca, Cd, Co, Cr, Fe, Ga, Hf, In, Mg, Mn, Ni, Sb, Sc, Sn, Ta, Ti, Y, Zn, Zr, or a combination thereof. The halogen element may be F, Cl, Br, I, or a combination thereof, and may be Cl, Br, or a combination thereof. The halide-based solid electrolyte may contain, for example, Li a M1X6 (M is Al, As, B, Bi, Ca, Cd, Co, Cr, Fe, Ga, Hf, In, Mg, Mn, Ni, Sb, Sc, Sn, Ta, Ti, Y, Zn, Zr, or a combination thereof, X is F, Cl, Br, I, or a combination thereof, and 2≤a≤3) can be represented. The halide-based solid electrolyte is, for example, Li2ZrCl6, Li 2.7 Y 0.7 Zr 0.3 Cl6, Li 2.5 Y 0.5 Zr 0.5 Cl6, Li 2.5 In 0.5 Zr 0.5 Cl6, Li2In 0.5 Zr 0.5 Cl6, Li3YBr6, Li3YCl6, Li3YBr2Cl4, Li3YbCl6, Li 2.6 Hf 0.4 Yb 0.6 Cl6, or combinations thereof, but is not limited thereto.

[0191] The above solid electrolyte is in particle form and has an average particle diameter (D 50) may be 5.0 μm or less, for example, 0.1 μm to 5.0 μm, 0.5 μm to 5.0 μm, 0.5 μm to 4.0 μm, 0.5 μm to 3.0 μm, 0.5 μm to 2.0 μm, or 0.5 μm to 1.0 μm. Such a solid electrolyte can effectively penetrate between positive electrode active materials, and has excellent contact with the positive electrode active material and connectivity between solid electrolyte particles.

[0192] With respect to the total 100 wt% of the positive electrode active material layer, the solid electrolyte may be included in an amount of 0.1 wt% to 35 wt%, for example, 1 wt% to 35 wt%, 5 wt% to 30 wt%, 8 wt% to 25 wt%, or 10 wt% to 20 wt%. In addition, with respect to the total weight of the positive electrode active material and the solid electrolyte in the positive electrode active material layer, 65 wt% to 99 wt% of the positive electrode active material and 1 wt% to 35 wt% of the solid electrolyte may be included, for example, 80 wt% to 90 wt% of the positive electrode active material and 10 wt% to 20 wt% of the solid electrolyte may be included. When the solid electrolyte is included in the positive electrode in such an amount, the efficiency and life characteristics of the all-solid-state battery can be improved without reducing the capacity.

[0193] cathode

[0194] The negative electrode for the all-solid-state secondary battery may be, for example, the same negative electrode as described for the lithium-ion battery.

[0195] Alternatively, as another example, the negative electrode for an all-solid-state secondary battery may be a precipitation-type negative electrode, unlike the above-mentioned one. The precipitation-type negative electrode may refer to a negative electrode that does not include a negative electrode active material when the battery is assembled, but in which lithium metal or the like is precipitated or deposited on the negative electrode when the battery is charged, and this acts as a negative electrode active material.

[0196] Fig. 6 is a schematic cross-sectional view of an all-solid-state secondary battery including a precipitation-type negative electrode. Referring to Fig. 6, the precipitation-type negative electrode (400') may include a current collector (401) and a negative electrode coating layer (405) positioned on the current collector. An all-solid-state secondary battery including such a precipitation-type negative electrode (400') starts initial charging in a state in which no negative electrode active material is present, and during charging, a high-density lithium metal is precipitated or deposited between the current collector (401) and the negative electrode coating layer (405) or on the negative electrode coating layer (405) to form a lithium metal layer (404), which may function as a negative electrode active material. Accordingly, in an all-solid-state secondary battery that has been charged more than once, the precipitation-type negative electrode (400') may include, for example, a current collector (401), a lithium metal layer (404) positioned on the current collector, and a negative electrode coating layer (405) positioned on the metal layer. The lithium metal layer (404) refers to a layer in which lithium metal or the like is precipitated during the charging process of the battery, and may be referred to as a metal layer, a lithium layer, a lithium deposition layer, or a negative electrode active material layer.

[0197] The cathode coating layer (405) may be referred to as a lithium electrodeposition induction layer or a cathode catalyst layer, and may include a lithium-philic metal, a carbon material, or a combination thereof.

[0198] The above-mentioned lithium-philic metal may include, for example, gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, zinc, or a combination thereof, and may be composed of one type of these or may be composed of several types of alloys. When the lithium-philic metal is present in the form of particles, its average particle diameter (D 50 ) may be about 4 ㎛ or less, for example, 10 nm to 4 ㎛, 10 nm to 1 ㎛, 10 nm to 600 nm. As an example, the lithium-philic metal may be in the form of nanoparticles having an average particle size of several to several hundred nanometers.

[0199] The carbon material may be, for example, crystalline carbon, amorphous carbon, or a combination thereof. The crystalline carbon may be, for example, natural graphite, artificial graphite, mesophase carbon microbeads, or a combination thereof. The amorphous carbon may be, for example, carbon black, activated carbon, acetylene black, Denka black, Ketjen black, or a combination thereof.

[0200] When the negative electrode coating layer (405) includes both a lithium-philic metal and a carbon material, the mixing ratio of the metal and the carbon material may be, for example, a weight ratio of 1:10 to 2:1. In this case, the precipitation of lithium metal can be effectively promoted and the characteristics of the all-solid-state secondary battery can be improved. The negative electrode coating layer (405) may include, for example, a carbon material loaded with a lithium-philic metal, or may include a mixture of lithium-philic metal particles and carbon material particles.

[0201] The cathode coating layer (405) may include, for example, a lithium-philic metal and amorphous carbon, in which case the precipitation of lithium metal can be effectively promoted.

[0202] The cathode coating layer (405) may further include a binder, which may be, for example, a conductive binder. In addition, the cathode coating layer (405) may further include general additives such as fillers, dispersants, and ionic conductive agents.

[0203] The thickness of the cathode coating layer (405) may be, for example, 100 nm to 20 μm, or 500 nm to 10 μm, or 1 μm to 5 μm.

[0204] The precipitation-type negative electrode (400') may further include, for example, a thin film on the surface of the current collector, i.e., between the current collector and the negative electrode coating layer. The thin film may include an element capable of forming an alloy with lithium. The element capable of forming an alloy with lithium may be, for example, gold, silver, zinc, tin, indium, silicon, aluminum, bismuth, etc., and may be composed of one type thereof or may be composed of multiple types of alloys. The thin film may further planarize the precipitation pattern of the lithium metal layer (404) and further improve the characteristics of the all-solid-state secondary battery. The thin film may be formed by, for example, a vacuum deposition method, a sputtering method, a plating method, etc. The thickness of the thin film may be, for example, 1 nm to 500 nm.

[0205] The lithium metal layer (404) may include lithium metal or a lithium alloy. The lithium alloy may be, for example, a Li-Al alloy, a Li-Sn alloy, a Li-In alloy, a Li-Ag alloy, a Li-Au alloy, a Li-Zn alloy, a Li-Ge alloy, or a Li-Si alloy.

[0206] The thickness of the lithium metal layer (404) may be 1 μm to 500 μm, 1 μm to 200 μm, 1 μm to 100 μm, or 1 μm to 50 μm. If the thickness of the lithium metal layer (404) is too thin, it may be difficult to perform the role of a lithium storage, and if it is too thick, the battery volume may increase and performance may deteriorate.

[0207] When such a precipitation-type cathode is applied, the cathode coating layer (405) can play a role in protecting the lithium metal layer (404) and suppressing the precipitation growth of lithium deadlight. Accordingly, short-circuiting and capacity reduction of the all-solid-state battery can be suppressed, and the life characteristics can be improved.

[0208] solid electrolyte layer

[0209] The solid electrolyte layer (300) may include a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a halide-based solid electrolyte, etc. Details on this are omitted as they are the same as those described in the anode section.

[0210] Meanwhile, the average particle diameter (D) of the solid electrolyte included in the solid electrolyte layer (300) 50 ) is the average particle diameter (D) of the solid electrolyte contained in the positive electrode (200). 50 ) may be larger than the average particle size of the solid electrolyte (200). In this case, the overall performance can be improved by increasing the mobility of lithium ions while maximizing the energy density of the all-solid-state secondary battery. For example, the average particle size (D) of the solid electrolyte included in the positive electrode (200) 50 ) may be 0.1 ㎛ to 1.9 ㎛, or 0.1 ㎛ to 1.0 ㎛, and the average particle diameter (D) of the solid electrolyte included in the solid electrolyte layer (300) 50 ) may be 2.0 ㎛ to 5.0 ㎛, or 2.0 ㎛ to 4.0 ㎛, or 2.5 ㎛ to 3.5 ㎛. When this particle size range is satisfied, the energy density of the all-solid-state secondary battery can be maximized while the transfer of lithium ions is facilitated, thereby suppressing the resistance and improving the overall performance of the all-solid-state secondary battery. Here, the average particle diameter (D of the solid electrolyte 50 ) may be measured using a particle size analyzer using laser diffraction.

[0211] The solid electrolyte layer (300) may further include a binder in addition to the solid electrolyte. At this time, the binder may be styrene butadiene rubber, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, an acrylate polymer, or a combination thereof, but is not limited thereto, and any binder used in the relevant technical field may be used. The acrylate polymer may be, for example, butyl acrylate, polyacrylate, polymethacrylate, or a combination thereof.

[0212] The solid electrolyte layer (300) can be formed by adding a solid electrolyte to a binder solution, coating the same on a substrate film, and drying the same. The solvent of the binder solution may be isobutyryl isobutyrate, xylene, toluene, benzene, hexane, or a combination thereof. Since the solid electrolyte layer formation process is widely known in the art, a detailed description thereof will be omitted.

[0213] The thickness of the solid electrolyte layer (300) may be, for example, 10 μm to 300 μm.

[0214] The solid electrolyte layer may further include an alkali metal salt, and / or an ionic liquid, and / or a conductive polymer.

[0215] The above alkali metal salt may be, for example, a lithium salt. The content of the lithium salt in the solid electrolyte layer may be 1 M or more, for example, 1 M to 4 M. In this case, the lithium salt may improve ion conductivity by enhancing the lithium ion mobility of the solid electrolyte layer.

[0216] The lithium salt may be applied without limitation on type, and may include, for example, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiSCN, LiN(CN)2, lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium difluorobis(oxalato)phosphate (LiDFBP), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, or a combination thereof.

[0217] For example, the lithium salt may be an imide-based lithium salt such as LiTFSI, LiFSI, LiBETI, or a combination thereof. The imide-based lithium salt can maintain or improve ionic conductivity by appropriately maintaining chemical reactivity with the ionic liquid.

[0218] Ionic liquids are salts or molten salts that are composed only of ions and are liquid at room temperature, with a melting point below room temperature.

[0219] The ionic liquid comprises a) one or more cations selected from ammonium, pyrrolidinium, pyridinium, pyrimidinium, imidazolium, piperidinium, pyrazolium, oxazolium, pyridazinium, phosphonium, sulfonium, trizolium, and mixtures thereof, and b) BF4. - , PF6 - , AsF6 - , SbF6 - , AlCl4 - , HSO4 - , ClO4 - , CH3SO3 - , CF3CO2 - , Cl - , Br - , I - , BF4 - , SO4 - , CF3SO3 - , (FSO2)2N - , (C2F5SO2)2N - , (C2F5SO2)(CF3SO2)N - , and (CF3SO2)2N - It may be a compound containing one or more anions selected from among.

[0220] The ionic liquid may be, for example, one or more selected from the group consisting of N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide, N-butyl-N-methylpyrrolidinium bis(3-trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide, and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide.

[0221] In the solid electrolyte layer, the weight ratio of the solid electrolyte to the ionic liquid may be 0.1:99.9 to 90:10, for example, 10:90 to 90:10, 20:80 to 90:10, 30:70 to 90:10, 40:60 to 90:10, or 50:50 to 90:10. A solid electrolyte layer satisfying the above range can maintain or improve ionic conductivity by improving the electrochemical contact area with the electrode. Accordingly, the energy density, discharge capacity, rate characteristics, etc. of the all-solid-state secondary battery can be improved.

[0222] The all-solid-state secondary battery may be a unit cell having a structure of positive electrode / solid electrolyte layer / negative electrode, a bi-cell having a structure of negative electrode / solid electrolyte layer / positive electrode / solid electrolyte layer / negative electrode, or a laminated battery in which the structure of the unit cell is repeated.

[0223] The shape of the above-mentioned all-solid-state secondary battery is not particularly limited, and may be, for example, coin-shaped, button-shaped, sheet-shaped, stacked, cylindrical, flat, etc. In addition, the above-mentioned all-solid-state secondary battery can be applied to large-sized batteries used in electric vehicles, etc. For example, the above-mentioned all-solid-state secondary battery can be used in hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs). In addition, it can be used in fields requiring a large amount of power storage, and for example, it can be used in electric bicycles or power tools, etc. In addition, the above-mentioned all-solid-state secondary battery can be used in various fields such as portable electronic devices.

[0224] Hereinafter, examples and comparative examples of the present invention are described. The following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0225] Example 1 (NCA Large (radiation) + NCAM Small, dry)

[0226] 1. Manufacturing of the first nickel-based composite hydroxide

[0227] Through the coprecipitation method described below, the first nickel-based composite hydroxide (Ni), which is a precursor of the first positive electrode active material, 0.945 Co 0.04 Al 0.015 (OH)2) was synthesized. Nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and sodium aluminum sulfate (NaAl(SO4)2·12H2O) were dissolved in distilled water as a solvent at a molar ratio of 94.5:4:1.5 to prepare a mixed solution of metal raw materials. In addition, ammonia water (NH4OH) and sodium hydroxide (NaOH) were prepared as a precipitant to form a complex compound.

[0228] [Step 1: 2.5 kW / ㎥, NH4OH 0.40 M, pH 10.5~11.5, reaction time 6 hours]

[0229] First, ammonia water with a concentration of 0.40 M was added to the reactor. The reaction was initiated by adding a mixed solution of metal raw materials and a complexing agent (NH4OH) at a rate of 85 ml / min and 10 ml / min, respectively, at a stirring power of 2.5 kW / ㎥ and a reaction temperature of 50℃. The reaction was carried out for 6 hours while adding NaOH to maintain the pH. As a result of the reaction, it was confirmed that the average size of the obtained core particles was in the range of approximately 6.5 ㎛ to 7.5 ㎛, and the second step was carried out as follows.

[0230] [Step 2: 2.0 kW / ㎥, NH4OH 0.45 M, pH 10.5~11.5, reaction time 18 hours]

[0231] While maintaining the reaction temperature at 50℃, the metal raw material mixture solution and complexing agent were introduced at a rate of 85 ml / min and 12 ml / min, respectively, so that the concentration of the complexing agent became 0.45 M. The reaction was continued for 18 hours while adding NaOH to maintain the pH. At this time, the stirring power was lowered to 2.0 kW / ㎥, which was lower than in step 1, and the reaction was conducted. By conducting this reaction, it was confirmed that the average size of the product particles containing the core and intermediate layer was 13.5 ㎛ to 14 ㎛, and the following 3 steps were performed.

[0232] [Step 3: 1.5 kW / ㎥, NH4OH 0.45 M, pH 10.5~11.5, reaction time 14 hours]

[0233] While maintaining the reaction temperature at 50℃, the injection speed of the metal raw material mixture solution and the complexing agent and the concentration of the complexing agent were the same as in the second step. The reaction was conducted for 14 hours while adding NaOH to maintain the pH. At this time, the stirring power was lowered to 1.5 kW / ㎥, which was lower than in the second step, to proceed with the reaction. After washing the obtained result, it was dried with hot air at about 150℃ for 24 hours to obtain the first nickel-based composite hydroxide (Ni 0.945 Co 0.04 Al 0.015 (OH)2) was obtained.

[0234] 2. Manufacturing of secondary nickel-based composite hydroxides

[0235] Through the coprecipitation method described below, a second nickel-based composite hydroxide (Ni), which is a precursor of the second positive electrode active material, is prepared. 0.94 Co 0.04 Mn 0.02 (OH)2) was synthesized. Nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and manganese sulfate (MnSO4·H2O) were dissolved in distilled water as a solvent in a molar ratio of 94:4:2 to prepare a mixed solution of metal raw materials. Ammonia water (NH4OH) and sodium hydroxide (NaOH) were prepared as a precipitant to form a complex compound.

[0236] First, ammonia water with a concentration of 0.25 M was placed in the reactor, and the reaction was started by adding a mixed solution of metal raw materials and a complexing agent at a rate of 142 ml / min and 34 ml / min, respectively, at a stirring power of 3.0 kW / ㎥ and a reaction temperature of 50°C. The reaction was carried out for 30 hours while adding NaOH to maintain the pH. The reaction was terminated when the average size of the obtained particles reached about 4 μm. After washing the obtained result, it was dried with hot air at about 150°C for 24 hours to obtain a second nickel-based composite hydroxide (Ni 0.94 Co 0.04 Mn 0.02 (OH)2) was prepared.

[0237] 3. Manufacturing of positive electrode active material

[0238] First nickel-based composite hydroxide (Ni 0.945 Co 0.04 Al 0.015 (OH)2) 80 wt% and a second nickel-based composite hydroxide (Ni 0.94 Co 0.04 Mn 0.02 (OH)2) 20 wt% was mixed, and LiOH was mixed so that 100 molar parts of lithium were mixed for 100 molar parts of the total metal. A preliminary positive electrode active material was manufactured by performing a first heat treatment in which the temperature was raised to 700°C for 8 hours in an oxygen atmosphere and the temperature was maintained for 7 hours.

[0239] The method for forming a buffer layer on the preliminary positive electrode active material is a dry coating method as follows. The manufactured preliminary positive electrode active material, zirconium oxide (ZrO2), and anhydrous lithium hydroxide (LiOH) are mixed in a Henschel Mixer to perform coating. At this time, zirconium oxide is added so that 0.25 mol parts of zirconium are added based on 100 mol parts of metal excluding lithium in the preliminary positive electrode active material, and anhydrous lithium hydroxide is added so that 0.5 mol parts of lithium are added. During coating, the mixer is operated at low, medium, and high speeds to ensure even coating without layer separation, and heat treatment is performed at 460°C for 15 hours in an oxygen atmosphere to obtain the final positive electrode active material (LiNi) coated with a buffer layer. 0.944 Co 0.04 Al 0.012 Mn 0.004 O2) was manufactured.

[0240] In the final positive electrode active material, the first positive electrode active material is confirmed to be in the form of secondary particles including an inner part having an irregular porous structure and an outer part having a radial array structure as a result of SEM analysis of the cross section, and the average particle diameter (D) of the secondary particles measured through the SEM image 50 ) is confirmed to be about 14 ㎛. The second positive electrode active material is confirmed to be in the form of secondary particles in which multiple primary particles are aggregated, and the average particle diameter (D) of the secondary particles measured through the SEM image 50 ) is confirmed to be approximately 3.5㎛.

[0241] The composition analysis for the second positive electrode active material is described in Evaluation Example 3 below, and the analysis of the crystal phase of the coating layer of each of the first positive electrode active material and the second positive electrode active material is described in Evaluation Example 4 below.

[0242] 4. Manufacturing of the anode

[0243] 84.9 wt% of positive electrode active material coated with a buffer layer, argyrodite-type solid electrolyte of Li6PS5Cl (D 50=1㎛) 13.61 wt%, PVdF binder 1 wt%, carbon nanotube conductive material 0.35 wt%, and hydrogenated nitrile butadiene rubber (HNBR) 0.14 wt% as a dispersant were mixed in an isobutyryl isobutyrate (IBIB) solvent to prepare a positive electrode composition. This was applied to a positive electrode current collector, dried, and then rolled (hydrostatic pressing (WIP), 500 Mpa, 85°C, 30 min) to prepare a positive electrode.

[0244] 5. Manufacturing of all-solid-state secondary batteries

[0245] Carbon black with a primary particle size of about 30 nm and an average particle size (D 50 ) was prepared by mixing silver (Ag) having a diameter of approximately 60 nm in a weight ratio of 3:1, and 0.25 g of the above complex was added to 2 g of an NMP solution containing 7 wt% of polyvinylidene fluoride binder and mixed to prepare a negative electrode coating layer composition. This was applied onto a negative electrode current collector and then dried, thereby preparing a deposition-type negative electrode in which a negative electrode coating layer was formed on the current collector.

[0246] Argyrodite-type solid electrolyte of Li6PS5Cl (D 50 =3㎛) was added to an IBIB solvent containing an acrylic binder and mixed to prepare a composition for forming a solid electrolyte layer. The composition includes 98.5 wt% of the solid electrolyte and 1.5 wt% of the binder. The composition was cast on a release film and dried at room temperature to prepare a solid electrolyte layer.

[0247] The prepared positive electrode, negative electrode, and solid electrolyte layers were cut, a solid electrolyte layer was laminated on the positive electrode, and then a negative electrode was laminated on top of that. This was sealed in a pouch shape and subjected to high-temperature hydrostatic pressing at 80°C and 500 MPa for 30 minutes to manufacture an all-solid-state secondary battery.

[0248] Comparative Example 1 (NCA Large (radiation) + NCM Small, dry)

[0249] 1. Preparation of the first lithium nickel-based composite oxide

[0250] The first nickel-based composite hydroxide manufactured in Example 1 and LiOH were mixed so that lithium was 100 molar parts based on 100 molar parts of the total metal of the first nickel-based composite hydroxide, and heat treatment was performed by raising the temperature to 700°C for 8 hours in an oxygen atmosphere and maintaining the temperature for 7 hours, thereby producing the first lithium nickel-based composite oxide (LiNi 0.945 Co 0.04 Al 0.015 O2) was manufactured.

[0251] The first lithium nickel-based composite oxide thus manufactured is confirmed to have a secondary particle form including an interior having an irregular porous structure and an exterior having a radial array structure, and the average particle diameter (D) of the secondary particles measured using a particle size distribution measuring device using laser diffraction 50 ) is confirmed to be approximately 14 ㎛.

[0252] 2. Preparation of a second lithium nickel-based composite oxide

[0253] The second nickel-based composite hydroxide manufactured in Example 1 was mixed with LiOH, and LiOH was mixed so that lithium was 100 molar parts for 100 molar parts of the total metal of the second nickel-based composite hydroxide, and heat-treated at 700°C in an oxygen atmosphere for 10 hours to obtain the second lithium nickel-based composite oxide (LiNi 0.94 Co 0.04 Mn 0.02 O2) was obtained.

[0254] The second lithium nickel-based composite oxide manufactured in this way is confirmed to be in the form of secondary particles in which multiple primary particles are aggregated, and the average particle diameter (D) of the secondary particles measured using a particle size distribution measuring device using laser diffraction 50 ) is confirmed to be approximately 3.5㎛.

[0255] 3. Positive electrode active material buffer layer coating

[0256] The method for forming a buffer layer on the positive electrode active material is a dry coating method as follows. The first lithium nickel-based composite oxide and the second lithium nickel-based composite oxide prepared are mixed in a weight ratio of 8:2 in a Hansel mixer. At this time, zirconium oxide (ZrO2) is added so that zirconium is 0.25 molar parts per 100 molar parts of metals excluding lithium in the first lithium nickel-based composite oxide and the second lithium nickel-based composite oxide, and anhydrous lithium hydroxide is added so that lithium is 0.5 molar parts. During coating, the mixer is operated at low, medium, and high speeds to ensure even coating without layer separation, and heat treatment is performed at 500°C for 15 hours in an oxygen atmosphere to obtain the final positive electrode active material (LiNi) coated with a buffer layer. 0.944 Co 0.04 Al 0.012 Mn 0.004 O2) was manufactured.

[0257] Other than that, the positive electrode and the all-solid-state secondary battery were manufactured in substantially the same manner as in Example 1.

[0258] Comparative Example 2 (NCA Large (radiation) + NCA Small, dry)

[0259] The mixed solution of metal raw materials used in the method for producing the first nickel-based composite hydroxide of Example 1 was used, but the co-precipitation reaction was carried out in substantially the same manner as the method for producing the second nickel-based composite hydroxide, so that a plurality of primary particles were aggregated into secondary particles, and the average particle diameter (D) of the secondary particles was 50 ) is a third nickel-based composite hydroxide (Ni) with a diameter of about 4 μm 0.945 Co 0.04 Al 0.015 (OH)2) was prepared.

[0260] A cathode active material, a cathode, and an all-solid-state secondary battery were manufactured in substantially the same manner as in Comparative Example 1, except that a third nickel-based composite hydroxide was used instead of the second nickel-based composite hydroxide.

[0261] Comparative Example 3 (NCA Large (non-radioactive) + NCA Small, dry)

[0262] While introducing ammonia water dilution into a continuous reactor, the mixed solution of metal raw materials used in the method for producing the first nickel-based composite hydroxide of Example 1 was continuously introduced, and sodium hydroxide aqueous solution was introduced to maintain the pH inside the reactor. The reaction was carried out slowly for approximately 80 hours, and when the reaction stabilized, the overflowing product was collected. After washing the obtained product, it was dried with hot air at approximately 150°C for 24 hours, and the primary particles were in the form of secondary particles in which the primary particles were not arranged radially, and the average particle diameter (D) of the secondary particles was 50 ) is about 15 ㎛ of the fourth nickel-based composite hydroxide (Ni 0.945 Co 0.04 Al 0.015 (OH)2) was prepared.

[0263] A cathode active material, a cathode, and an all-solid-state secondary battery were manufactured in substantially the same manner as in Comparative Example 1, except that a fourth nickel-based composite hydroxide was used instead of the first nickel-based composite hydroxide.

[0264] Comparative Example 4 (NCA Large (radiation) + NCM Small, no buffer layer coating)

[0265] A cathode active material, a cathode, and an all-solid-state secondary battery were manufactured in substantially the same manner as in Comparative Example 1, except that the cathode active material buffer layer was not coated.

[0266] Comparative Example 5 (NCA Large (radiation) + NCM Small, wet buffer layer coating)

[0267] A positive electrode active material, a positive electrode, and an all-solid-state secondary battery were manufactured in substantially the same manner as in Comparative Example 1, except that a buffer layer was coated on the positive electrode active material using a wet coating method as follows.

[0268] Dehydrated 2-propanol, a methanol solution containing 10% lithium methoxide, and zirconium isopropoxide were mixed in a molar ratio of 200:2:1, and the first lithium nickel-based composite oxide and the second lithium nickel-based composite oxide were dispersed in a weight ratio of 8:2. The zirconium content was designed to be 0.25 molar parts per 100 molar parts of metals other than lithium in the composite oxides. The solvent was evaporated in a vacuum at 50°C while irradiating ultrasonic waves to prevent agglomeration of the positive electrode active material particles. The resultant was filtered and heat-treated at 350°C for 1 hour in an air atmosphere to obtain a positive electrode active material coated with a buffer layer containing Li2CO3, LiOH, and ZrO2.

[0269] To aid understanding, the design details of the positive electrode active materials of Example 1 and Comparative Examples 1 to 5 are briefly shown in Table 1 below.

[0270] Anti-grain coating method Example 1 NCA large (radiation) NCAM small dry Comparative example 1 NCM small Comparative example 2 NCA small Comparative example 3 NCA large (non-radiation) Comparative example 4 NCA large (radiation) NCM small Buffer layer no Comparative example 5 NCA large (radiation) wet

[0271] Evaluation Example 1: Evaluation of the initial charge / discharge capacity of an all-solid-state secondary battery.

[0272] The all-solid-state secondary batteries manufactured in Example 1 and Comparative Examples 1 to 5 were charged at 45°C with a constant current of 0.1 C to 4.25 V and a constant voltage of 0.05 C to measure the charge capacity, and discharged at 0.1 C to 2.5 V to measure the initial discharge capacity. The ratio of the discharge capacity to the charge capacity was calculated as efficiency, and the results are shown in Fig. 7 and Table 2.

[0273] Charge capacity (mAh / g)Discharge capacity (mAh / g)Efficiency (%)Example 1242.3207.285.5%Comparative example 1244.2205.984.3%Comparative example 2239.4204.285.3%Comparative example 3231.5184.279.6%Comparative example 4226.7198.087.3%Comparative example 5239.2204.285.4%

[0274] Referring to Fig. 7 and Table 2, it can be seen that Example 1 and Comparative Examples 1 to 2 secure equivalent or higher charge / discharge capacities even though they apply dry coating, which is easy to mass-produce, compared to Comparative Example 5, which wet-coates a buffer layer using an expensive metal alkoxide raw material in an organic solvent, which is a conventional technology.

[0275] In the case of Example 1, it was confirmed in Evaluation Example 3 below that Al of the large particles moved to the small particles and was doped by simultaneously firing the large and small particles, and through this, it was found that the performance of the all-solid-state battery was improved and the mass production of the positive electrode active material became easier.

[0276] When a non-radial NCA was used as in Comparative Example 3, the resistance inside the active material became very large, resulting in a lower capacity than in Comparative Example 4, which did not separately coat the buffer layer.

[0277] Evaluation Example 2: Evaluation of the Lifetime Characteristics of All-Solid-State Secondary Batteries

[0278] For the all-solid-state secondary batteries of Example 1 and Comparative Examples 1 to 5, the initial charge and discharge were performed as in Evaluation Example 1, and then the charging at 0.33C and discharging at 0.33C in the voltage range of 2.5 V to 4.25 V at 45°C were repeated 100 times to evaluate the life characteristics. Table 3 below and Fig. 8 show the capacity retention rate, which is the ratio of the initial discharge capacity to the 100-cycle discharge capacity, and Fig. 9 shows a graph of the capacity change with respect to the number of cycles.

[0279] Initial discharge capacity (mAh / g) 100 times capacity retention rate (%) Example 1207.29 0.4% Comparative example 1205.98 8.7% Comparative example 2204.28 6.9% Comparative example 3184.28 3.0% Comparative example 4198.0- Comparative example 5204.28 4.3%

[0280] Comparing Comparative Example 1 and Comparative Example 5, which have different coating methods for the same positive electrode active material, it can be seen that Comparative Example 1, which applies the dry coating proposed in the present invention, can secure superior initial discharge capacity and capacity retention rate during life.

[0281] In addition, it can be seen that Example 1, in which a radial opposing NCA precursor and a small-grain NCM precursor are simultaneously fired to dope the small grains with NCAM, secures a better initial discharge capacity and capacity retention rate during life than Comparative Examples 1 to 5.

[0282] Evaluation Example 3: Evaluation of small particle composition

[0283] The final positive electrode active materials manufactured in Example 1 and Comparative Example 1 were prepared by separating large and small particles. The separation of the active materials was performed using a turbo classifier (Nisshin Engineering Inc.) and nitrogen as a transport gas. The separated small particles of Example 1 and Comparative Example 1 were subjected to ICP (Inductively Coupled Plasma) emission spectroscopic analysis to measure the contents of cobalt, aluminum, and manganese, and the results are shown in Table 4.

[0284] Mol % Example 1 Comparative Example 1 Ni93.994.0 Co3.94.1 Al0.6-Mn1.61.9

[0285] Referring to Table 4, Example 1 confirms that 20 wt% of small-grain NCM receives Al from 80 wt% of large-grain NCA and is doped with Al at a level of 0.6 mol%. It is understood that the small-grain NCM of Example 1 exists as NCAM doped with Al in the NCM structure, and thus, compared to the NCM small-grain NCM of Comparative Example 1 and the NCA small-grain NCA of Comparative Example 2, other volume expansions during charge and discharge are effectively suppressed, and the structural stability of the positive electrode active material is improved, thereby improving the capacity retention rate.

[0286] Evaluation Example 4: TEM Evaluation of the Coating Layer

[0287] To analyze the crystal phase of the coating layer, HRTEM and inverse-FFT analyses were performed on the cross-section of Example 1. As shown in the left drawing of Fig. 10, a relatively thick coating layer region was selected to confirm the atomic arrangement, and as shown in the right drawing of Fig. 10, it was confirmed that a Li6ZrO7 crystal phase exists.

[0288] In addition, HRTEM and inverse-FFT analyses were performed on the cross-section of the small particles of Example 1. As shown in Fig. 11, the crystal structure was analyzed by selecting a relatively thick coating layer region, and as a result, it was confirmed that there were ZrO2 crystal phases, Li2ZrO6 crystal phases, and an amorphous part containing Zr, as shown in the left drawing of Fig. 12. As a result of analyzing the rotation pattern, as shown in the right drawing of Fig. 12, it was confirmed that two crystal phases of ZrO2 and Li2ZrO6 were present together.

[0289] Although the preferred embodiments have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concepts defined in the following claims also fall within the scope of the present invention.

[0290] [Explanation of symbols]

[0291] 11: Secondary particle 12: Inside the secondary particle

[0292] 13: Primary particle 14: External of secondary particle

[0293] 100: Lithium secondary battery 112: Cathode

[0294] 113: Separator 114: Anode

[0295] 120: Battery container 140: Encapsulating member

[0296] 100': All-solid-state battery 200: Anode

[0297] 201: Cathode current collector 203: Cathode active material layer

[0298] 300: Solid electrolyte layer 400: Cathode

[0299] 401: Negative current collector 403: Negative active material layer

[0300] 400': Precipitation type cathode 404: Lithium metal layer

[0301] 405: Cathode coating layer 500: Elastic layer

Claims

1. A first cathode active material comprising a lithium nickel-cobalt-aluminum composite oxide, a plurality of primary particles agglomerated, secondary particles in which at least a portion of the primary particles are radially arranged, and a coating layer located on the surface of the secondary particles and containing ZrO2 and Li6Zr2O7; and A second cathode active material comprising a lithium nickel-cobalt-aluminum-manganese composite oxide, a secondary particle in which a plurality of primary particles are aggregated, and a coating layer located on the surface of the secondary particle and containing ZrO2 and Li6Zr2O7, A cathode active material wherein the average particle diameter of the secondary particles of the first cathode active material is larger than the average particle diameter of the secondary particles of the second cathode active material.

2. In paragraph 1, The average particle size of the secondary particles of the first positive electrode active material is 9 ㎛ to 25 ㎛, A cathode active material, wherein the average particle size of the secondary particles of the second cathode active material is 2 ㎛ to 8 ㎛.

3. In paragraph 1, For a total of 100 wt% of the first positive electrode active material and the second positive electrode active material, A positive electrode active material comprising 60 to 95 wt% of the first positive electrode active material and 5 to 40 wt% of the second positive electrode active material.

4. In paragraph 1, A positive electrode active material, wherein the coating layer of the first positive electrode active material and the coating layer of the second positive electrode active material each include a ZrO2 crystal phase, a Li6Zr2O7 crystal phase, and a Zr-containing amorphous region.

5. In paragraph 1, A positive electrode active material in which the coating layer of the first positive electrode active material and the coating layer of the second positive electrode active material are each in the form of a continuous film or an island.

6. In paragraph 1, A positive electrode active material, wherein the thickness of each of the coating layer of the first positive electrode active material and the coating layer of the second positive electrode active material is 5 nm to 300 nm.

7. In paragraph 1, A positive electrode active material in which the total content of Zr in the coating layer of the first positive electrode active material and the coating layer of the second positive electrode active material is 0.1 mol part to 0.6 mol part based on 100 mol parts of the total metal excluding lithium in the lithium nickel-cobalt-aluminum composite oxide of the first positive electrode active material and the lithium nickel-cobalt-aluminum-manganese composite oxide of the second positive electrode active material.

8. In paragraph 1, A positive electrode active material in which the total content of Zr in the coating layer of the first positive electrode active material and the coating layer of the second positive electrode active material is 0.1 wt% to 6 wt% with respect to 100 wt% of the positive electrode active material.

9. In paragraph 1, The lithium nickel-cobalt-aluminum composite oxide of the first positive electrode active material is a positive electrode active material represented by the following chemical formula 1: [Chemical Formula 1] Li a1 Ni x1 Co y1 Al z1 M 1 w1 O 2-b1 X b1 In the above chemical formula 1, 0.9≤a1≤1.2, 0.7≤x1<1, 0 <y1<0.3, 0<z1<0.3, 0≤w1<0.3, 0.9≤x1+y1+z1+w1≤1.1, 및 0≤b1≤0.1이고, M 1 is one or more elements selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sr, Sn, Ti, V, W, and Zr, and X is one or more elements selected from F, P, and S.

10. In paragraph 1, A cathode active material in which the average particle diameter of the primary particles forming the secondary particles in the first cathode active material is less than 200 nm.

11. In paragraph 1, A positive electrode active material comprising a secondary particle of a first positive electrode active material having an interior having an irregular porous structure and an exterior having a radial array structure as a region surrounding the interior.

12. In paragraph 1, At least some of the primary particles forming the secondary particles in the first positive electrode active material have a plate shape, The above secondary particles include open pores on the surface, and the open pores are formed by spaces between the plate-shaped primary particles arranged radially, and are pores connected in a central direction from the surface of the secondary particles, which is a positive electrode active material.

13. In paragraph 1, The lithium nickel-cobalt-aluminum-manganese composite oxide of the second positive electrode active material is a positive electrode active material represented by the following chemical formula 2: [Chemical Formula 2] Li a2 Ni x2 Co y2 Al z2 Mr w2 M 2 v2 O 2-b2 X b2 In the above chemical formula 2, 0.9≤a2≤1.2, 0.7≤x2<1, 0 <y2<0.3, 0<z2<0.3, 0<w2<0.3, 0≤v2<0.3, 0.9≤x2+y2+z2+w2+v2≤1.1, 및 0≤b2≤0.1이고, M 2 is one or more elements selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sr, Sn, Ti, V, W, and Zr, and X is one or more elements selected from F, P, and S.

14. In paragraph 1, The second cathode active material has a higher aluminum content in the surface layer of the secondary particle than in the interior of the secondary particle. The above-mentioned interior refers to an area from the center of the secondary particle to about 70% of the radius in length, and the above-mentioned surface layer refers to an area surrounding the interior, and is an area from the outermost surface of the secondary particle to a depth corresponding to 30% of the radius in length.

15. In paragraph 14, The Al content in the surface layer of the secondary particles of the second positive electrode active material is 0.2 at% to 2.0 at% with respect to 100 at% of the total metal excluding lithium in the second positive electrode active material, A cathode active material in which the Al content inside the secondary particles of the second cathode active material is 0 at% to 0.6 at% with respect to 100 at% of the total metal excluding lithium in the second cathode active material.

16. In paragraph 14, The surface layer of the secondary particles of the second positive electrode active material includes a high-concentration Al region and a low-concentration Al region, The Al content in the above high-concentration Al region is 0.8 at% to 2.0 at% with respect to 100 at% of the total metal excluding lithium in the second positive electrode active material, A cathode active material in which the Al content in the above low-concentration Al region is less than 0.8 at% with respect to 100 at% of the total metal excluding lithium in the second cathode active material.

17. In paragraph 16, A cathode active material in which the difference between the Al content in the high-concentration Al region and the Al content in the low-concentration Al region is 0.3 at% to 2.0 at%. 18.(i) A first cathode active material precursor comprising a nickel-cobalt-aluminum composite hydroxide, wherein a plurality of primary particles are aggregated and at least a portion of the primary particles are arranged radially in the form of secondary particles; A second cathode active material precursor comprising a nickel-cobalt-manganese composite hydroxide and having a secondary particle form in which a plurality of primary particles are aggregated; and A preliminary positive electrode active material is obtained by mixing lithium raw materials and performing a first heat treatment, wherein the average particle diameter of the first positive electrode active material precursor is larger than the average particle diameter of the second positive electrode active material precursor. (ii) A method for producing a positive electrode active material, comprising dry mixing the above-mentioned preliminary positive electrode active material and a zirconium raw material and performing a second heat treatment to obtain a final positive electrode active material.

19. In paragraph 18, The nickel-cobalt-aluminum composite hydroxide of the first cathode active material precursor is represented by the following chemical formula 11: The nickel-cobalt-manganese composite hydroxide of the second cathode active material precursor is a method for producing a cathode active material represented by the following chemical formula 12: [Chemical Formula 11] Ni x11 Co y11 Al z11 M 11 w11 (OH)2 In the above chemical formula 11, 0.7≤x11<1, 0 <y11<0.3, 0<z11<0.3, 0≤w11<0.3, 0.9≤x11+y11+z11+w11≤1.1이고, M 11 is one or more elements selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sr, Sn, Ti, V, W, and Zr, [Chemical Formula 12] Ni x12 What y12 Mn w12 M 12 v12 (OH)2 In the above chemical formula 12, 0.7≤x12<1, 0 <y12<0.3, 0<w12<0.3, 0≤v12<0.3, 0.9≤x12+y12+w12+v12≤1.1이고, M 12 is one or more elements selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sr, Sn, Ti, V, W, and Zr.

20. In paragraph 18, The average particle size of the secondary particles of the first cathode active material precursor is 9 ㎛ to 25 ㎛, A method for producing a cathode active material, wherein the average particle size of the secondary particles of the second cathode active material precursor is 2 µm to 8 µm.

21. In paragraph 18, A method for producing a positive electrode active material, wherein the mixing weight ratio of the first positive electrode active material precursor and the second positive electrode active material precursor is 60:40 to 95:

5.

22. In paragraph 18, A method for manufacturing a positive electrode active material, wherein the first heat treatment is performed at a temperature range of 600°C to 1000°C.

23. In paragraph 18, A method for producing a positive electrode active material, wherein the zirconium raw material is mixed in an amount of 0.1 to 0.6 molar parts relative to 100 molar parts of the total metal excluding lithium in the preliminary active material.

24. In paragraph 18, The above zirconium raw material is a particle containing zirconium oxide, and the average particle diameter (D) of the particles 50 ) is a method for producing a positive electrode active material having a diameter of 10 nm to 500 nm.

25. In paragraph 18, A method for manufacturing a positive electrode active material, wherein the second heat treatment is performed in an oxygen atmosphere at a temperature range of 420°C to 580°C for 5 to 25 hours.

26. In paragraph 18, When mixing the above preliminary positive electrode active material and zirconium raw material in a dry manner, the lithium raw material is mixed together, A method for producing a positive electrode active material, wherein the content of the lithium raw material is more than 1 mol part and less than 4 mol parts with respect to 1 mol part of the zirconium raw material.

27. A positive electrode comprising a positive electrode active material according to any one of claims 1 to 17.

28. In paragraph 27, The above positive electrode further comprises a sulfide-based solid electrolyte.

29. The anode according to Article 27, cathode, A separator positioned between the anode and the cathode, and A lithium secondary battery containing a non-aqueous electrolyte.

30. The anode according to Article 27, cathode, An all-solid-state secondary battery comprising a solid electrolyte layer positioned between the positive electrode and the negative electrode.

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