KR102195729B1 - Nickel-based active material for lithium secondary battery, preparing method thereof, and lithium secondary battery including a positive electrode including the same - Google Patents

Abstract

Nickel-based active material for lithium secondary batteries, which includes porous inside and outside including closed pores, and whose internal density is smaller than that of outside, and the true density of nickel-based active material is 4.7 g/cc or less, and its manufacturing method And a lithium secondary battery containing the positive electrode including the same is disclosed.

Description

Nickel-based active material for lithium secondary battery, preparing method thereof, and lithium secondary battery including a positive electrode including the same}

It relates to a nickel-based active material for a lithium secondary battery, a method of manufacturing the same, and a lithium secondary battery containing a positive electrode including the same.

With the development of portable electronic devices and communication devices, there is a high need to develop lithium secondary batteries with high energy density.

Lithium nickel manganese cobalt composite oxide, lithium cobalt oxide, and the like are used as the positive active material of the lithium secondary battery. However, in the case of using such a positive electrode active material, the long-term life of the lithium secondary battery decreases due to cracks generated in the unit of primary particles as charging and discharging is repeated, the resistance increases, and the capacity characteristics do not reach a satisfactory level. Required.

One aspect is to provide a nickel-based active material for lithium secondary batteries in which crack generation is suppressed by reducing the stress of volume change during charging and discharging.

Another aspect is to provide a method of manufacturing the above-described nickel-based active material.

Another aspect is to provide a lithium secondary battery having improved life characteristics by including a positive electrode including the above-described nickel-based active material.

According to one side

It includes a porous interior and an exterior including closed pores,

The density inside the porosity is smaller than the density outside,

A nickel-based active material for a lithium secondary battery having a true density of 4.7 g/cc or less of the nickel-based active material is provided.

In accordance with another aspect, there is provided a method of manufacturing a nickel-based active material for a lithium secondary battery, including the step of performing a primary heat treatment at 600 to 800° C. in an oxidizing gas atmosphere in a mixture of a lithium precursor and a metal hydroxide.

Prior to the step of performing the first heat treatment, it may further include pre-treating the mixture of the lithium precursor and the metal hydroxide at 400 to 700° C. for 1 to 3 hours in an oxidizing gas atmosphere.

According to another aspect, a lithium secondary battery containing a positive electrode including the above-described nickel-based active material for a lithium secondary battery is provided.

When the nickel-based active material for a lithium secondary battery according to an embodiment is used, the occurrence of cracks during charging and discharging is suppressed and the external density is increased, so that side reactions with the electrolyte at high temperatures are suppressed, and thus a lithium secondary battery with improved life can be manufactured.

1A is a schematic diagram showing the shape of plate particles.
1B is a view for explaining the definition of a radial type in secondary particles of a nickel-based active material according to an exemplary embodiment.
2 schematically shows the structure of a lithium secondary battery according to an embodiment.
3A to 3E show electron scanning microscope (SEM) analysis results of nickel-based active materials prepared according to Example 1, Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 3, respectively.
4A to 4C are electron scanning micrographs of a cross section of an anode in a coin cell manufactured according to Preparation Example 1 and Comparative Preparation Example 1-2, respectively.
5A is a SEM analysis photograph of the lengths in the plane direction and the thickness direction of the nickel-based active material primary particles having a plate shape on the surface of the secondary particles of Example 1. FIG.
5B is a SEM analysis photograph of the lengths in the plane direction and the thickness direction of the nickel-based active material primary particles having a plate shape in the cross-section of the secondary particles of Example 1. FIG.

Hereinafter, an exemplary nickel-based active material for a lithium secondary battery, a method of manufacturing the same, and a lithium secondary battery having a positive electrode including the same will be described in more detail below with reference to the accompanying drawings.

A nickel-based active material for lithium secondary batteries is provided that includes a porous interior and an exterior including closed pores, and the internal density of the porous material is smaller than that of the exterior, and the true density of the nickel-based active material is 4.7 g/cc or less. .

The nickel-based active material according to an embodiment has isolated pores, so that it is possible to suppress the occurrence of cracks due to volume expansion during charging and discharging. The isolated pores are closed pores and are closed pores that do not come into contact with the electrolytic solution and the secondary particle surface because all the walls of the pores are formed in a closed structure. When such closed pores are present, the contact area between the nickel-based active material and the electrolyte solution does not increase, and it can buffer a volume change occurring during charging and discharging. Since the density of the nickel-based active material from the outside is higher than that of the inside, side reactions with the electrolyte solution at high temperature can be effectively suppressed.

Closed pores and/or open pores may exist outside the nickel-based active material. The nickel-based active material has isolated pores therein, so that it is difficult to include an electrolyte, but when open pores are present outside the nickel-based active material, the electrolyte may contain the inside of the pores.

The true density of the nickel-based active material according to an embodiment is, for example, 4.50 g/cc to 4.7 g/cc, for example, 4.52 g/cc to 4.67 g/cc. When the true density of the nickel-based active material exceeds 4.7 g/cc, the void space in the particles is small, so the volume expansion stress increases during charging and discharging, and when charging and discharging is repeated, the resulting volume expansion stress accumulates and particle cracks occur. Lifespan characteristics may be deteriorated, or even if there are pores, the surface area of contact between the nickel-based active material and the electrolyte may increase because it contains open pores, which may reduce the life characteristics of a lithium secondary battery employing them.

In the present specification, the term "net density" refers to the inherent density of an electrode active material, and more specifically describes the density of only a portion completely filled with the material except for the gap between the particles and the particles. True density is measured as the same value as solid density (theoretical density) if there are no isolated pores. However, in the case of a nickel-based active material containing isolated pores, the density decreases due to the creation of empty spaces in the interior, so this is the density value of the solid containing the isolated pores. Open pores connected to surfaces other than isolated pores are not reflected in the true density value. Density is a value obtained by dividing the weight by volume or various density values are measured according to the method of measuring the volume, and the true density is a method of calculating the density value by measuring the volume (solid + isolated pores) excluding open pores. to be. True density is measured using a method that applies Archimedes' principle or a gas pycnometer.

In the present specification, the definitions of the terms "inside" and "outside" of the active material will be described. The terms "inside" and "outside" mean the inner side and the inner side, respectively, based on an area in which the volume becomes the same when divided by the same ratio in all directions from the center of the active material to the surface. The interior is, for example, 10 to 90% by volume, for example, 50% by volume, based on the total volume of the active material, and the outside refers to the remaining area. The term "outer" refers to the area of 30 to 50% by volume, for example 40% by volume from the outermost surface of the total volume from the center to the surface of the nickel-based compound, or of the total distance from the center to the surface of the nickel-based compound, nickel It refers to the area within 2㎛ from the outermost part of the system. The term "inside" refers to the area of 50 to 70% by volume, for example 60% by volume from the center, of the total volume from the center to the surface of the nickel-based compound, or of the total distance from the center to the surface of the nickel-based compound. Refers to the rest of the active material except the area within 2㎛ from the outermost.

The size of the isolated pores in the nickel-based active material according to an embodiment is 150 nm to 1 μm, for example, 200 to 500 nm, and the porosity in the inside is 3 to 30%. The external pore size is less than 150 nm, such as 100 nm or less, such as 20 to 90 nm, and the external porosity is, for example, 0.1 to 2.5%. In this specification, the porosity inside and outside refers to the closed porosity inside and outside. The porosity inside is about 1.2 times or more, for example, 2 times or more compared to the porosity outside. The pore size and porosity inside are larger and irregular compared to the pore size and porosity outside. When the porosity inside and outside of the nickel-based active material satisfies the above-described range, the density of the outside becomes higher than that of the inside, so that side reactions with the electrolyte solution at a high temperature can be effectively suppressed. In addition, the internal pore size is larger than that of the external case, so that the lithium diffusion distance is shortened in secondary particles of the same size, and in terms of mitigating the volume change that occurs during charging and discharging without the pores being exposed to the electrolyte. It is advantageous. The term “pore size” refers to the average pore diameter or the opening width of the pores when the pores are spherical or circular. If the pores are elliptical, the pore size indicates the length of the major axis.

The nickel-based active material includes plate particles, and the major axes of the plate particles are arranged in a radial direction. At this time, the surface through which lithium can enter and exit (the surface perpendicular to the (001) surface) is exposed on the surface of the secondary particle. The nickel-based active material has exposed pores directed from the surface toward the inside on the outside and irregular porous pores on the inside. The pores exposed on the surface are exposed pores through which the electrolyte can enter and exit. "Irregular porous structure" means a structure having pores that are not regular and have no uniformity in pore size and shape. The inside including the irregular porous structure includes plate-shaped particles, and the outside also includes plate-shaped particles. Inside, the plate-like particles are arranged without regularity unlike the outside.

1A is a schematic diagram showing the shape of plate particles according to an embodiment. With reference to this, the plate particles may have a polygonal nanoplate shape such as a hexagon like A, a nanodisk shape like B, and a rectangular parallelepiped shape like C.

In Fig. 1a, the thickness t of the plate particles is smaller than the surface thickness t is the length a and/or b in the plane direction. The length a in the plane direction may be longer than or equal to b. In the plate particle, the direction in which the thickness t is defined is defined as the thickness direction, and the direction containing the lengths a and b is defined as the surface direction (length direction).

In the present specification, "radial" is aligned so that the thickness (t) direction ((001) direction) of the plate forms an angle perpendicular and perpendicular to the direction (R) toward the center of the secondary particle as shown in FIG. 1B. Means that.

The average thickness of the plate-shaped particles forming the outside and the inside is 100 to 200 nm, for example, 120 to 180 nm, specifically 130 to 150 nm, and the average length is 150 to 500 nm, for example 200 to 380 nm, specifically 290 To 360 nm. The average length refers to the average length of the average major axis length and the average minor axis length in the plane direction of the plate particles.

The ratio of the average thickness to the average length is 1:2 to 1:10, for example 1:2.0 to 1:5, specifically 1:2.3 to 1:2.9. As such, when the average length and average thickness of the plate-shaped particles are the ratio, and when the size of the plate-shaped particles is small and the primary particles are arranged radially from the outside, the lithium diffusion path between the relatively large number of grain boundaries on the surface side and the outside Since a large number of crystal planes capable of transferring lithium are exposed, the diffusion of lithium is improved, so that high initial efficiency and capacity can be secured. In addition, when the plate-shaped particles are arranged in a radial manner, the pores exposed from the surface between them are also directed toward the center, thereby promoting lithium diffusion from the surface. By the radially arranged primary particles, uniform contraction and expansion are possible when lithium is removed, and pores exist in the direction 001, which is the direction in which the particles expand when lithium is removed, providing a buffering function, and the size of the plate-shaped primary particles. Because is small, the probability of cracking during contraction and expansion decreases, and internal pores further mitigate volume change, thereby reducing cracks generated between primary particles during charging and discharging, improving lifespan characteristics and reducing resistance increase. In other words, it includes radial plate-shaped particles to help lithium diffusion, suppresses the occurrence of cracks by suppressing the stress caused by volume changes during lithium charging and discharging, and reduces the surface resistance layer during manufacture, and increases the lithium diffusion direction on the surface. By exposure, the active surface area required for lithium diffusion can be made large.

The nickel-based active material is an active material represented by Formula 1 below.

[Formula 1]

Li _a (Ni _1-xyz Co _x Mn _y M _z ) O ₂

In Formula 1, M is boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe ), copper (Cu), zirconium (Zr), and aluminum (Al), and 0.95≤a≤1.3, x≤(1-xyz), y≤(1-xyz), z≤( 1-xyz), 0<x<0.5, 0<y<0.5, 0≤z<0.5. As described above, in the nickel-based active material of Formula 1, the content of nickel is larger than that of cobalt and the content of nickel is larger than that of manganese. In Formula 1, 0.95≤a≤1.3, 0<x≤0.3, and 0<y<0.5, 0≤z≤0.05, 0.5≤(1-x-y-z)≤0.95. In Formula 1, a is, for example, 1 to 1.1, x is 0.1 to 0.3, and y is 0.05 to 0.3. According to an embodiment, in Chemical Formula 1, z is 0. According to another embodiment, when 0<z≤0.05 in Formula 1, M may be aluminum.

The content of nickel in the nickel-based active material is larger than that of each of the other transition metals, based on a total of 1 mol of the transition metal. When using a nickel-based active material with a large amount of nickel as described above, lithium diffusivity is high, conductivity is good, and a higher capacity can be obtained at the same voltage when using a lithium secondary battery employing a positive electrode including the same. There is a problem that a crack occurs and life characteristics are deteriorated.

The nickel-based active material is LiNi _{0 . 6} Co _{0 . 2} Mn _{0 . 2} O ₂ , LiNi _{0 . 5} Co _{0 . 2} Mn _{0 . 3} O ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _{0 . 8} Co _{0 . 1} Mn _{0 . 1} O ₂ , or LiNi _{0 . 85} Co _{0 . 1} Al _{0 . 05} O ₂

The overall porosity of the nickel-based active material is 1 to 8%, for example, 1.5 to 7.3%. In the nickel-based active material, the external porosity is smaller than the internal porosity. The outer closed porosity is 0.1 to 2.5%, for example 0.1 to 2%, and the inner closed porosity is 3 to 30%. The term "closed porosity" means the fraction of closed pores (pores through which an electrolyte cannot penetrate) relative to the volume of total pores.

Hereinafter, a method of manufacturing a nickel-based active material according to an embodiment will be described.

A nickel-based active material may be prepared by mixing a lithium precursor and a metal hydroxide at a predetermined molar ratio and performing a first heat treatment at 600 to 800°C.

It is possible to obtain a nickel-based active material having the desired true density and density characteristics by performing a pretreatment process at 400 to 700°C for 1 to 3 hours in an oxidizing gas atmosphere before performing the first heat treatment. The pretreatment process can be carried out, for example, at 650° C. for 2 hours.

The metal hydroxide may be a compound represented by Formula 2 below.

[Formula 2]

(Ni _{1 -xy- z} Co _x Mn _y M _z ) OH ₂

In Formula 2, M is boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe ), copper (Cu), zirconium (Zr), and aluminum (Al), and x≤(1-xyz), y≤(1-xyz), z≤(1-xyz), 0 <x<1, 0≤y<1, and 0≤z<1. In Formula 2, 0<x≤0.3, 0≤y≤0.5, 0≤z≤0.05, 0.5≤(1-xyz) ≤0.95. The metal hydroxide of Formula 2 is, for example, Ni _{0 . 6} Co _{0 . 2} Mn _{0 . 2} O _H2 , Ni _{0 . 5} Co _{0 . 2} Mn _{0 . 3 OH 2, Ni 1/3} Co 1/3 Mn 1/3 OH 2, Ni 0. ₈ Co _{0 . 1} Mn _{0 . 1} OH ₂ and so on.

The lithium precursor is, for example, lithium hydroxide, lithium fluoride, lithium carbonate, or a mixture thereof. The mixing ratio of the lithium precursor and the metal hydroxide is controlled stoichiometrically so that the metal hydroxide of Formula 2 can be prepared.

The mixing may be dry mixing, and may be performed using a mixer or the like.

The first heat treatment is carried out in an oxidizing gas atmosphere. The oxidizing gas atmosphere uses an oxidizing gas such as oxygen or air. For example, the oxidizing gas is composed of 10 to 20% by volume of oxygen or air and 80-90% by volume of an inert gas.

It is appropriate to perform the first heat treatment in a range below the densification temperature while the reaction between the lithium precursor and the metal hydroxide proceeds. Here, the densification temperature refers to a temperature at which crystallization is sufficiently achieved so that the active material can realize a charging capacity. The primary heat treatment is performed at, for example, 600 to 800°C, specifically 700 to 800°C.

The heat treatment time varies depending on the low temperature heat treatment temperature, but is performed for 3 to 10 hours, for example.

When the heat treatment is performed under the above-described conditions, nickel-based active material particles having a radially arranged outer structure and an irregular porous structure may be manufactured. The average thickness of the nickel-based active material particles is 100 to 250 nm. By having such an average thickness, it is possible to suppress stress due to volume change during charging and discharging.

The nickel-based active material particles undergo a secondary heat treatment (high temperature heat treatment) in an oxidizing gas atmosphere. When producing nickel-based active material particles, the oxygen atmosphere inside the reactor is maintained as much as possible during the secondary heat treatment, thereby suppressing the formation of the resistive layer as much as possible and performing particle densification.

The secondary heat treatment is performed at a higher temperature than the first heat treatment, for example, at 700 to 900°C. The high-temperature heat treatment time varies depending on the high-temperature heat treatment temperature and the like, but is performed for 3 to 10 hours, for example. The nickel-based active material secondary particles have an average particle diameter of 2 to 18 μm, for example 3 to 15 μm.

In the high-temperature heat treatment process of the nickel-based active material particles, a compound containing at least one selected from titanium, zirconium, magnesium, barium, boron, and aluminum may be further added.

Examples of the compound containing at least one selected from titanium, zirconium, magnesium, barium, boron, and aluminum include titanium oxide, zirconium oxide, magnesium oxide, barium carbonate, boric acid, and aluminum oxide.

The content of the compound containing at least one selected from titanium, zirconium, magnesium, barium, boron, and aluminum is 0.0001 to 10 parts by weight, specifically 0.0001 to 1 part by weight, based on 100 parts by weight of the nickel-based active material secondary particles. Specifically, it is 0.0005 to 0.01 parts by weight.

The presence and distribution of one or more oxides selected from titanium, zirconium, magnesium, barium, boron, and aluminum can be confirmed through Electron Probe Micro-Analysis (EPMA).

When the active material is discharged, the diffusion rate of lithium decreases at the end of the discharge, and if the size of the nickel-based active material secondary particles is large, the discharge capacity is small compared to the charging capacity due to resistance to penetration of lithium into the nickel-based active material secondary particles. This can be degraded. However, the nickel-based active material secondary particles according to an embodiment have a porous structure inside, so that the diffusion distance to the inside is reduced, and the outside is arranged in a radial direction toward the surface, so that lithium can be easily inserted into the surface. In addition, the size of the primary particles of the nickel-based active material is small, making it easier to secure a lithium transfer path between crystal grains. In addition, the size of the primary particles is small, and the pores between the primary particles alleviate the volume change occurring during charging and discharging, thereby minimizing the stress received during the volume change during charging and discharging.

When the nickel-based positive electrode active material according to an embodiment is cut in cross section, the internal and external volume ratios and area ratios are examined. If the interior is defined as an area within about 60% from the center, the interior is based on the total volume of the nickel-based active material. By 20 to 35% by volume. For example, it can occupy about 22% of the volume.

The c-plane of the primary particles of the nickel-based active material according to an embodiment is arranged in a radial direction.

According to an embodiment, a method of manufacturing a metal hydroxide having a porous and plate particle shape is as follows.

The method of preparing the metal hydroxide is not particularly limited, but, for example, a coprecipitation method or a solid phase method may be used. Hereinafter, a method of preparing a compound of Formula 2 as an example of a metal hydroxide according to a coprecipitation method will be described.

A nickel precursor, a cobalt precursor, a manganese precursor, and a metal (M) precursor, which are nickel-based active material raw materials, are mixed with a solvent to obtain a precursor mixture.

The amounts of the nickel precursor, cobalt precursor, manganese precursor, and metal precursor are stoichiometrically controlled to obtain the compound of Formula 2.

Water, ethanol, propanol, butanol, etc. are used as the solvent. And the content of the solvent is 100 to 2000 parts by weight based on 100 parts by weight of the total weight of the nickel precursor, cobalt precursor, manganese precursor, and metal precursor.

A precipitate is obtained through the step of performing a coprecipitation reaction by controlling the pH of the mixture by adding a precipitating agent and a pH adjusting agent to the precursor mixture. The pH of the mixture is adjusted to, for example, 11 to 13. The precipitate thus obtained is filtered and heat treated. Heat treatment is carried out at 20 to 160°C to dry the product.

Precipitants play a role in controlling the reaction rate of formation of precipitates in the co-precipitation reaction, and include ammonium hydroxide (NH ₄ OH) and citric acid. The content of the precipitant is used at the usual level.

The pH adjuster plays a role of adjusting 6 to 12 of the reaction mixture, and examples include ammonium hydroxide, sodium hydroxide (NaOH), sodium carbonate (Na ₂ CO ₃ ), sodium oxalate (Na ₂ C ₂ O ₄ ), etc. do.

The nickel precursor is, for example, nickel sulfate, nickel chloride, or nickel nitrate, the cobalt precursor is, for example, cobalt sulfate, cobalt chloride or cobalt nitrate, and the manganese precursor is, for example, manganese sulfate, manganese nitrate, manganese chloride, etc. Can be lifted. And the metal (M) precursor may be, for example, metal carbonate, metal sulfate, metal nitrate, metal chloride, and the like.

Hereinafter, a method of manufacturing a lithium secondary battery having a positive electrode, a negative electrode, a non-aqueous electrolyte containing a lithium salt, and a separator including a nickel-based active material according to an exemplary embodiment will be described.

The positive electrode and the negative electrode are prepared by coating and drying a composition for forming a positive active material layer and a composition for forming a negative active material layer on a current collector, respectively.

The composition for forming a positive electrode active material is prepared by mixing a positive electrode active material, a conductive agent, a binder, and a solvent, and the positive electrode active material according to the embodiment is used as the positive electrode active material.

The binder is a component that aids in bonding of an active material and a conductive agent, and bonding to a current collector, and is added in an amount of 1 to 50 parts by weight based on 100 parts by weight of the total weight of the positive electrode active material. Non-limiting examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, recycled cellulose, polyvinylpyrrolidone, tetrafluoro Ethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluorine rubber, and various copolymers. The content is 2 to 5 parts by weight based on 100 parts by weight of the total weight of the positive electrode active material. When the content of the binder is within the above range, the binding strength of the active material layer to the current collector is good.

The conductive agent is not particularly limited as long as it does not cause chemical change in the battery and has conductivity, and examples thereof include graphite such as natural graphite or artificial graphite; Carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fibers and metal fibers; Carbon fluoride; Metal powders such as aluminum and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

The content of the conductive agent is 2 to 5 parts by weight based on 100 parts by weight of the total weight of the positive electrode active material. When the content of the conductive agent is within the above range, the finally obtained electrode has excellent conductivity properties.

As a non-limiting example of the solvent, N-methylpyrrolidone or the like is used.

The content of the solvent is 100 to 3000 parts by weight based on 100 parts by weight of the positive electrode active material. When the content of the solvent is in the above range, the operation for forming the active material layer is easy.

The positive electrode current collector has a thickness of 3 to 500 μm, and is not particularly limited as long as it has high conductivity without causing chemical changes to the battery. For example, stainless steel, aluminum, nickel, titanium, heat-treated carbon, Alternatively, a surface-treated aluminum or stainless steel surface with carbon, nickel, titanium, silver, or the like may be used. The current collector may increase the adhesion of the positive electrode active material by forming fine irregularities on its surface, and various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics are possible.

Separately, a negative active material, a binder, a conductive agent, and a solvent are mixed to prepare a composition for forming a negative active material layer.

The negative active material is a material capable of storing and releasing lithium ions. As a non-limiting example of the negative active material, a carbon-based material such as graphite and carbon, lithium metal, an alloy thereof, and a silicon oxide-based material may be used. According to an embodiment of the present invention, silicon oxide is used.

The binder is added in an amount of 1 to 50 parts by weight based on 100 parts by weight of the total weight of the negative active material. As a non-limiting example of such a binder, the same type as the positive electrode may be used.

The conductive agent is used in an amount of 1 to 5 parts by weight based on 100 parts by weight of the negative active material. When the content of the conductive agent is within the above range, the finally obtained electrode has excellent conductivity properties.

The content of the solvent is 100 to 3000 parts by weight based on 100 parts by weight of the negative active material. When the content of the solvent is within the above range, the operation for forming the negative active material layer is easy.

The conductive agent and the solvent may be made of the same type of material as in manufacturing the positive electrode.

The negative electrode current collector is generally made to have a thickness of 3 to 500 μm. Such a negative electrode current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery, for example, copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, copper or stainless steel. For the surface treatment with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloys, etc. may be used. In addition, like the positive electrode current collector, it is possible to enhance the bonding strength of the negative electrode active material by forming fine irregularities on the surface thereof, and may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

A separator is interposed between the positive electrode and the negative electrode manufactured according to the above process.

The separator has a pore diameter of 0.01 to 10 µm and a thickness of 5 to 300 µm. As specific examples, olefin-based polymers such as polypropylene and polyethylene; Alternatively, a sheet made of fiberglass or a nonwoven fabric is used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

The lithium salt-containing nonaqueous electrolyte is composed of a nonaqueous electrolyte and a lithium salt. As the nonaqueous electrolyte, a nonaqueous electrolyte, an organic solid electrolyte, an inorganic solid electrolyte, or the like is used.

Examples of the non-aqueous electrolyte include, but are not limited to, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2- Dimethoxyethane, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, N,N-formamide, N,N-dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate , Methyl acetate, phosphoric acid tryester, trimethoxy methane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, pyro An aprotic organic solvent such as methyl pionate and ethyl propionate may be used.

Examples of the organic solid electrolyte include, but are not limited to, polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, polyester sulfides, polyvinyl alcohol, polyvinylidene fluoride, and the like.

Examples of the inorganic solid electrolyte include, but are not limited to, Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , Li ₂ SiS ₃ , Li ₄ SiO ₄ , Li ₄ SiO ₄ Nitrides, halides, and sulfates of Li such as -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ may be used.

The lithium salt is a material that is soluble in the non-aqueous electrolyte, and is not limited to, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO _{2, LiAsF 6, LiSbF 6,} LiAlCl 4, CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) ₂ NLi, (FSO ₂ ) ₂ NLi, lithium chloroborate, lower aliphatic lithium carboxylate, tetraphenyl borate lithium imide, and the like can be used.

2 is a schematic cross-sectional view showing a typical structure of a lithium secondary battery according to an embodiment.

Referring to FIG. 2, the lithium secondary battery 20 includes a positive electrode 23, a negative electrode 22, and a separator 24. The positive electrode 23, the negative electrode 22, and the separator 24 described above are wound or folded to be accommodated in the battery case 25. Subsequently, an organic electrolyte is injected into the battery case 25 and sealed with a cap assembly 26 to complete the lithium secondary battery 20. The battery case 25 may be cylindrical, rectangular, thin-film, or the like. For example, the lithium secondary battery 20 may be a large thin film type battery. The lithium secondary battery may be a lithium ion battery. A separator may be disposed between the positive electrode and the negative electrode to form a battery structure. After the battery structure is stacked in a bi-cell structure, it is impregnated with an organic electrolyte, and the resulting product is accommodated in a pouch and sealed to complete a lithium ion polymer battery. In addition, a plurality of the battery structures are stacked to form a battery pack, and such a battery pack can be used in all devices requiring high capacity and high output. For example, it can be used for laptop computers, smart phones, electric vehicles, and the like.

In addition, since the lithium secondary battery has excellent storage stability, life characteristics, and high rate characteristics at high temperatures, it can be used in an electric vehicle (EV). For example, it may be used in hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs).

It will be described in more detail through the following Examples and Comparative Examples. However, the examples are for illustrative purposes and are not limited thereto.

Manufacturing example 1: composite metal Hydroxide Produce

It was carried out according to the co-precipitation method described later to obtain a composite metal hydroxide (Ni _0.6 Co _0.2 Mn _0.2 (OH) ₂ ) which is a radial, porous plate particle.

Ammonia water was added to the reactor, and the pH of the mixture of the reactor was adjusted using the added sodium hydroxide while controlling stoichiometrically so as to obtain a composition of the final product to be prepared as a raw material of the nickel-based active material. Next, stirring until the desired size was reached, the addition of the raw material solution was stopped, followed by drying to obtain the target product. This manufacturing process is described in detail as follows.

As a raw material for a nickel-based active material, distilled water as a solvent to make a 6:2:2 molar ratio of nickel sulfate (NiSO ₄ ·6H ₂ O), cobalt sulfate (CoSO ₄ ·7H ₂ O) and manganese sulfate (MnSO ₄ ·H ₂ O) Dissolved in to prepare a mixed solution. To form a complex compound, a dilute solution of aqueous ammonia (NH ₄ OH) and sodium hydroxide (NaOH) as a precipitant were prepared. Thereafter, a mixed solution of metal raw materials, aqueous ammonia, and sodium hydroxide were added into the reactor, respectively. Sodium hydroxide was added to maintain the pH inside the reactor. Next, the reaction was carried out for about 20 hours while stirring, and the addition of the raw material solution was stopped.

The slurry solution in the reactor was filtered and washed with high-purity distilled water, and then dried in a hot air oven for 24 hours to obtain a composite metal hydroxide (Ni _0.6 Co _0.2 Mn _0.2 (OH) ₂ ) powder.

Manufacturing example 2: composite metal Hydroxide Produce

In the same method as in Preparation Example 1, except that the contents of nickel sulfate, cobalt sulfate and manganese sulfate were changed and reacted for 25 hours to obtain a composite metal hydroxide (Ni _0.5 Co _0.2 Mn _0.3 (OH) ₂ ). Then, a composite metal hydroxide (Ni _0.5 Co _0.2 Mn _0.3 (OH) ₂ ) was obtained.

Manufacturing example 3: composite metal Hydroxide Produce

Except for changing the content of nickel sulfate, cobalt sulfate and manganese sulfate to obtain a porous composite metal hydroxide (LiNi _0.8 Co _0.1 Mn _0.1 (OH) ₂ ) and reacting for 25 hours, Preparation Example 1 and By carrying out according to the same method, a radial and porous composite metal hydroxide (Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ ) was obtained.

Manufacturing example 4: composite metal Hydroxide Produce

As a nickel-based active material raw material, 85:10:5 molar ratio of nickel sulfate (NiSO ₄ 6H ₂ O), cobalt sulfate (CoSO ₄ 7H ₂ O) and aluminum nitrate (Al(NO ₃ ) ₃ 9H ₂ O) A mixture was used, and the reaction was carried out in the same manner as in Preparation Example 1, except that the reaction was performed for 18 hours to obtain a radial, porous composite metal hydroxide (Ni _0.85 Co _0.1 Al _0.05 (OH) ₂ ).

Manufacturing example 5: composite metal Hydroxide Produce

_Except for changing the contents of nickel sulfate, cobalt sulfate and manganese sulfate to obtain a porous composite metal hydroxide (Ni _1/3 Co _1/3 Mn _1/33 (OH) ₂ ) and reacting for 28 hours _Was carried out in the same manner as in Preparation Example 1 to obtain a composite metal hydroxide (Ni _1/3 Co _1/3 Mn _1/33 (OH) ₂ ) having a radial and porous plate particle shape.

Example 1: Preparation of nickel-based active material secondary particles

The radial and porous composite metal hydroxide (Ni _0.6 Co _0.2 Mn _0.2 (OH) ₂ ) obtained according to Preparation Example 1 and lithium hydroxide (LiOH) were mixed dry in a 1:1 molar ratio, and this was mixed at 650°C for about 2 Pretreatment was carried out for hours. Then, by performing a primary heat treatment at about 780 ℃ for 8 hours in an air atmosphere, the nickel-based active material _{(. LiNi 0 6 Co 0.} 2 Mn 0. 2 O 2) to obtain a particle.

Then, the resultant subjected to secondary heat treatment for 6 hours at about 830 ℃ in an oxygen atmosphere, a nickel-based active material _{(LiNi 0. 6 Co 0.} 2 Mn 0. 2 O 2) to obtain a secondary particle. In the nickel-based active material particles thus obtained, there were isolated pores inside.

Example 2

Nickel-based active material particles were obtained in the same manner as in Example 1, except that the first heat treatment conditions were performed at 750°C for 10 hours, and the second heat treatment conditions were changed to 850°C for 6 hours.

Comparative example One

The complex metal hydroxide (Ni0.6Co0.2Mn0.2(OH)2) and lithium hydroxide (LiO·H ₂ O), which have no pores inside and are arranged without orientation, are dryly mixed in a 1:1 molar ratio. This was heat-treated at about 870° C. for 15 hours in an air atmosphere. A primary heat-treated product at about 500 ℃ in an oxygen atmosphere for 6 hours to conduct a secondary heat treatment to nickel-based active material _{(LiNi 0. 6 Co 0.} 2 Mn 0. 2 O 2) to obtain a secondary particle.

Comparative example 2

The complex metal hydroxide (Ni0.6Co0.2Mn0.2(OH)2) and lithium hydroxide (LiO·H ₂ O), which have no pores inside and are arranged without orientation, are dryly mixed in a 1:1 molar ratio. This was heat-treated at about 890°C for 15 hours in an air atmosphere to obtain a nickel-based active material (LiNi _0.6 Co _0.2 Mn _0.2 O ₂ ) secondary particles.

Comparative example 3

A complex metal hydroxide (Ni _0.6 Co _0.2 Mn _0.2 (OH) ₂ ) and lithium hydroxide (LiO·H ₂ O) with a directionality, a dense central part and a porous exterior are mixed dry in a 1:1 molar ratio and air A nickel-based active material (LiNi _0.6 Co _0.2 Mn _0.2 O ₂ ) particles were obtained by performing heat treatment at about 800°C for 6 hours in an atmosphere. In the nickel-based active material particles thus obtained, there were isolated pores inside. In the nickel-based active material particles thus obtained, non-isolated pores existed outside.

Production example One

Nickel-based active material obtained according to Example 1 as a positive electrode active material _{(LiNi 0. 6 Co 0.} 2 Mn 0. 2 O 2) was prepared as follows: a lithium secondary battery using the secondary particle.

Exemplary nickel-based active material obtained according to Example _{1 (LiNi 0. 6 Co 0} . 2 Mn 0. 2 O 2) A mixture of 96 g of secondary particles, 2 g of polyvinylidene fluoride, and 47 g of N-methylpyrrolidone as a solvent and 2 g of carbon black as a conductive agent was removed by using a mixer to prepare a uniformly dispersed slurry for forming a positive electrode active material layer. .

The slurry prepared according to the above process was coated on an aluminum foil using a doctor blade to form a thin electrode plate, dried at 135° C. for 3 hours or more, and then subjected to rolling and vacuum drying processes to produce a positive electrode.

A 2032 type coin cell was manufactured using a lithium metal counter electrode as the positive electrode and a counter electrode. A separator (thickness: about 16 μm) made of a porous polyethylene (PE) film was interposed between the positive electrode and the lithium metal counter electrode, and an electrolyte was injected to prepare a 2032 type coin cell. At this time, the electrolyte was a solution containing 1.1M LiPF ₆ dissolved in a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3:5.

Production example 2

A lithium secondary battery was manufactured in the same manner as in Preparation Example 1, except that the nickel-based active material prepared according to Example 2 was used instead of the nickel-based active material prepared according to Example 1.

Comparative Production Example 1-3

A lithium secondary battery was manufactured in the same manner as in Preparation Example 1, except that nickel-based active materials prepared according to Comparative Preparation Examples 1 to 3 were respectively used instead of the nickel-based active material prepared according to Example 1.

Evaluation example One: Electron scanning microscope analysis

Electron scanning microscopy analysis was performed on the nickel-based active material particles prepared according to Example 1-2 and Comparative Example 1-3. Magellan 400L (FEI company) was used as an electron scanning microscope. The sample cross section was pretreated by milling for 6kV, 150uA, 4hr using JEOL's CP2. And the electron scanning microscope analysis was carried out under 350V, 3.1pA SE conditions.

The electron scanning microscope analysis results are shown in FIGS. 3A to 3E. 3A to 3E show nickel-based active materials prepared according to Example 1, Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 3, respectively.

Referring to this, it was found that the nickel-based active material prepared according to Examples 1 and 2 had a denser structure on the outside compared to the inside.

In contrast, the nickel-based active material prepared according to Comparative Examples 1 and 2 showed almost the same density inside and outside, and it was found that the nickel-based active material had almost no pores inside compared to the cases of Examples 1 and 2. In addition, it was found that the nickel crab active material prepared according to Comparative Example 3 had a dense inside but a porous structure outside.

Evaluation example 2: Measurement of porosity and pore size inside and outside the active material

In the nickel-based active material particles prepared according to Examples 1-2 and Comparative Examples 1 and 3, the porosity and pore size inside and outside were measured. Here, porosity and pore size were evaluated using an electron scanning microscope image taken of a cross section of the active material. Magellan 400L (FEI company) was used as an electron scanning microscope. The sample cross section was pretreated by milling for 6kV, 150uA, 4hr using JEOL's CP2. And the electron scanning microscope analysis was carried out under 350V, 3.1pA SE conditions.

The analysis results are shown in Table 1 below.

division Internal porosity Out
Porosity Internal pore size (nm) External pore size (nm) Example 1 30 2 500 30 Comparative Example 1 2 2 30 30 Comparative Example 3 2 20 30 30

From Table 1 above, it can be seen that the nickel-based active material prepared according to Example 1 has irregular isolated pores distributed inside, and that the outside has fewer pores than the inside and is formed more densely than the nickel-based active material of Comparative Example 3. there was. On the other hand, it was found that the nickel-based active material of Comparative Example 3 had low porosity inside and the pores were mainly distributed outside the particles.

Further, an electron scanning microscope analysis was performed on the secondary particles of the nickel-based active material obtained according to Example 1. The sample cross section was pretreated by milling for 6kV, 150uA, 4hr using JEOL's CP2. And the electron scanning microscope analysis was carried out under 350V, 3.1pA SE conditions.

An SEM analysis picture of the surface of the nickel-based active material secondary particle is shown in FIG. 5A, and an SEM analysis picture of the cross section is shown in FIG. 5B.

Referring to FIGS. 5A and 5B, most of the primary particles of the nickel-based active material are radially arranged in a plate shape, and plate particles partially arranged in a non-radiative manner as shown in a circled area were observed. At this time, the content of the non-radiative plate particles was about 3% by weight based on 100 parts by weight of the total weight of the radial plate particles and the non-radiative plate particles. The term “non-radiative plate particles” refers to plate particles that are not arranged radially.

The average length, average thickness, and average ratio (average length/average thickness) were calculated with reference to the state of the plate particles shown in the scanning electron microscope of FIGS. 5A and 5B, and are shown in Table 1 below.

division surface division section Average length (nm) 290 Average length (nm) 360 Average thickness (nm) 130 Average thickness (nm) 150 Average ratio 2.3 Average ratio 2.9

Evaluation example 3: of the active material True density

In the nickel-based active material prepared according to Example 1-2 and Comparative Example 1-4, the true density was evaluated using a gas pycnometer.

Table 3 shows the overall true density evaluation results of the nickel-based active material.

division True density (g/cc) Example 1 4.5165 Example 2 4.6657 Comparative Example 1 4.7613 Comparative Example 2 4.7706 Comparative Example 3 4.7501

Referring to Table 3, the nickel-based active material of Examples 1 and 2 has isolated pores therein, and the true density is lower to 4.7 g/cc or less compared to the nickel-based active material of Comparative Examples 1 and 2 without pores as a whole. I was able to confirm the loss. It was found that the nickel-based active material of Comparative Example 3 had pores, but had pores open to the outside, and in this case, when present outside, the open pores hardly affect the true density.

Evaluation example 4: life characteristics

In the coin cell manufactured according to Production Example 1 and Comparative Production Example 1-4, first charge/discharge at 0.1C to proceed with formation and then check initial charge/discharge characteristics with 0.2C charge/discharge once. And the cycle characteristics were examined by repeating charging and discharging 50 times at 45°C and 1C. When charging, it started in CC (constant current) mode and then changed to CV (constant voltage) to cut off at 4.3V and 0.05C, and when discharging, it was set to cutoff at 3.0V in CC (constant current) mode.

Life characteristics are shown in Table 4 and FIGS. 4A to 4C. 4A to 4C are electron scanning micrographs of a cross section of an anode in a coin cell manufactured according to Preparation Example 1 and Comparative Preparation Example 1-2, respectively.

division Life (@50 times)(%) Production example 1 98.7 Production Example 2 98.4 Comparative Production Example 1 90.1 Comparative Production Example 2 92.4 Comparative Production Example 3 95.1

Referring to Table 4, it was found that the lifespan characteristics of the coin cell manufactured according to Preparation Example 1-2 were improved compared to the case of Comparative Preparation Example 1-3. From this, it was found that when the positive electrode containing the nickel-based active material of Example 1-2 having isolated pores only inside the nickel-based active material was employed, the occurrence of cracks was suppressed and the high-temperature life characteristics were improved compared to the case where it was not.

With reference to FIGS. 4A to 4C, it was confirmed that in the coin cell of Production Example 1, cracks were suppressed after evaluation of the life characteristics of the anode compared to the case of Comparative Production Example 1-2.

In the above, one embodiment has been described with reference to the drawings and embodiments, but this is only illustrative, and those of ordinary skill in the art can understand that various modifications and other equivalent embodiments are possible therefrom. will be. Therefore, the scope of protection of the present invention should be determined by the appended claims.

20.. Lithium secondary battery 22.. Anode
23.. anode 24.. separator
25.. battery case 26.. cap assembly

Claims (15)

It includes a porous interior and an exterior including closed pores,
The density inside the porosity is smaller than the density outside,
Nickel-based active material for a lithium secondary battery having a true density of 4.7 g/cc or less of a nickel-based active material, and a size of isolated pores in the interior of 150 nm to 1 um. delete The method of claim 1,
The porosity in the interior is 3 to 30%, and the porosity in the interior is 1.2 times greater than the porosity in the outside. The method of claim 1,
The outside is a nickel-based active material for a lithium secondary battery having a radial arrangement structure. The method of claim 1,
A nickel-based active material for a lithium secondary battery having an external pore size of less than 150 nm. The method of claim 1,
The nickel-based active material includes plate particles,
Nickel-based active material for lithium secondary batteries in which the long axes of the plate-shaped particles are arranged in a radial direction. The method of claim 1,
The nickel-based active material is a nickel-based active material for a lithium secondary battery, which is a compound represented by the following Formula 1:
[Formula 1]
Li _a (Ni _1-xyz Co _x Mn _y M _z ) O ₂
In Formula 1, M is boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe ), copper (Cu), zirconium (Zr), and an element selected from the group consisting of aluminum (Al),
0.95≤a≤1.3, x≤(1-xyz), y≤(1-xyz), z≤(1-xyz), 0<x<0.5, 0<y<0.5, 0≤z<0.5. The method of claim 7,
In Formula 1, 1.0≤a≤1.3, 0<x≤1/3, 0<y<0.5, 0≤z≤0.05, 1/3≤(1-xyz)≤0.95 nickel-based active material for a lithium secondary battery. The method of claim 7,
The nickel-based active material is LiNi _{0 . 6} Co _{0 . 2} Mn _{0 . 2} O ₂ , LiNi _{0 . 5} Co _{0 . 2} Mn _{0 . 3} O ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _{0 . 8} Co _{0 . 1} Mn _{0 . 1} O ₂ , or LiNi _{0 . 85} Co _{0 . 1} Al _{0 . 05} Nickel-based active material for lithium secondary batteries that are O ₂ . Nickel for lithium secondary batteries to prepare the nickel-based active material of any one of claims 1, 3 to 9, including the step of first heat treating a mixture of a lithium precursor and a metal hydroxide at 600 to 800°C in an oxidizing gas atmosphere Method of manufacturing an active material. The method of claim 10,
After the step of the first heat treatment, further comprising the step of performing a second heat treatment at 700 to 900 °C in an oxidizing gas atmosphere,
The secondary heat treatment is a method for producing a nickel-based active material for a lithium secondary battery performed at a higher temperature than the first heat treatment. The method of claim 10,
Before the step of performing the primary heat treatment, a method of preparing a nickel-based active material for a lithium secondary battery further comprising pre-treating a mixture of a lithium precursor and a metal hydroxide at 400 to 700° C. for 1 to 3 hours in an oxidizing gas atmosphere. A lithium secondary battery containing a positive electrode, a negative electrode, and an electrolyte interposed therebetween comprising the nickel-based active material of any one of claims 1, 3 to 9. The nickel-based active material for a lithium secondary battery according to claim 1, wherein the nickel-based active material has a true density of 4.5 to 4.7 g/cc. The method of claim 6,
A nickel-based active material for a lithium secondary battery in which the ratio of the average thickness and the average length of the plate particles is 1:2 to 1:10.

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