JP6744319B2 - Positive electrode active material for lithium battery having porous structure and manufacturing method - Google Patents

Description

The present invention relates to a positive electrode active material for a lithium battery having a porous structure and a method for producing the same, and more particularly, to a positive electrode for a porous lithium battery having a large specific surface area and excellent efficiency characteristics due to the porous structure. The present invention relates to an active material and a method for producing the same.

Due to the expansion of the IT industry such as mobile phones and laptop computers and the popularization of mobile devices, the use of small secondary batteries, mainly lithium secondary batteries, is increasing, which satisfies the high demands of consumers. Therefore, there is an increasing need for batteries that have both high performance and light weight.

In addition, as a part of green energy, interest in environment-friendly automobiles is increasing, and research to preempt the medium and large-sized automobile market, which requires high output and high energy density, such as motor drive power supplies for electric vehicles. Is being promoted continuously.

The lithium secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separation film. Although the positive electrode is the core material that determines the capacity and performance of the battery, it has a large weight in the overall cost of the battery, so it is essential to improve the performance of the positive electrode in order to commercialize and improve the performance of the secondary battery. is there.

Cathode materials for secondary batteries are classified into lithium cobalt-based (LCO), lithium nickel-based (LNO), lithium manganese-based (LMO), and lithium iron phosphate-based (LFP) depending on the raw material, and are classified into LCO, LNO, and LMO. The specific gravity of use of lithium nickel-cobalt-manganese (NCM), which has both advantages, is increasing.

In recent years, the market of electric vehicles has been rapidly expanding centering on HEVs (hybrid electric vehicles) and PHEVs (plug-in hybrid electric vehicles). Since the instantaneous output characteristics of HEV and PHEV are important, the cathode active material is required to have high output characteristics. Conventionally, the improvement of output characteristics has been promoted in the direction of increasing the mobility of lithium ions to the electrolytic solution by increasing the contact specific surface area with the electrolytic solution by decreasing the particle size of the positive electrode active material, There is a problem that sufficient output cannot be obtained only by reducing the size, and that long-term performance characteristics are difficult to ensure because the ultrafine particles deteriorate in the process of repeating charge and discharge cycles.

In order to solve such a problem, attempts have been made to form a hollow structure inside the positive electrode active material particles to increase the surface area of the positive electrode active material in contact with the electrolytic solution.

Patent Document 1 presents a positive electrode active material having a hollow particle structure having a space in the center and an outer shell made of a composite oxide on the outside. However, the positive electrode active material is high-power charge/discharge. At times, the outer shell structure is likely to collapse, which reduces cycle performance.

Further, in Patent Document 2, the thickness of the outer shell part of the nickel-manganese composite hydroxide particles is set to 5 to the secondary particle diameter by advancing the initial nucleation step during the precursor production in an oxidizing atmosphere. Although a positive electrode active material set to 45% is presented, this also has large pores only inside the hollow structure, and cracks may occur due to rapid volume expansion during repeated charging and discharging. There is. If a crack occurs and the outer shell part peels off, the inside is exposed or it becomes difficult to maintain the shape of the spherical particles.

In this way, it is possible to improve the output characteristics to some extent by using the hollow structure, and it is possible to improve the deterioration of the long-life characteristics due to particle cracking due to the volume change in the charge and discharge process to some extent, There is a limit to improvement because it is difficult to secure a sufficient flow path with the electrolyte solution inside, there is a limit to the surface area of the hollow structure, and due to the characteristics of the hollow structure with the outer shell, it is There is a problem that particle damage is unavoidable.

Korean Patent Registration No. 10-1345509 Korean Patent Registration No. 10-1272411

The problem to be solved by the present invention is to provide a secondary battery positive electrode active material having high output characteristics and improved charge/discharge stability.

Another object of the present invention is to provide a method for producing the positive electrode active material for the lithium battery.

In order to solve the above problems, the present invention forms a secondary particle with an aggregate of primary particles, and has a porous structure in which pores are distributed over the entire inner region of the secondary particle, and the pores are Provided is a positive electrode active material for a lithium battery, which is radially distributed from the center of secondary particles.

According to one embodiment of the present invention, the primary particles may be aggregated radially from the central portion of the secondary particles toward the surface to form spherical secondary particles.

According to one embodiment of the present invention, the positive electrode active material may be composed of a composite oxide of lithium and a transition metal.

According to one embodiment of the present invention, the transition metal may be one or more transition metals selected from nickel, cobalt and manganese.

According to one embodiment of the present invention, the positive electrode active material for a lithium battery has a specific surface area of 1 to 5 m ² /g and an average particle diameter (D50) of secondary particles of 2 to 20 μm. possible.

According to an embodiment of the present invention, the lithium battery positive electrode active material may be a lithium battery positive electrode active material including a lithium-nickel composite oxide represented by the following chemical formula (I).

_{Li p Ni 1-x-y} -z Mn x Co y M z O 2 (I)
In the above formula,
M is at least one metal selected from Mg, Al, Ti, Zr, Mo, W, Y, Sr, V, Ca and Nb,
p is 0.90≦p≦1.2,
x is 0≦x≦0.80,
y is 0≦y≦0.50,
z is 0<z≦0.05.

According to one embodiment of the present invention, the positive electrode active material for a lithium battery may have a high rate property of 80% or more under the condition of 3C.

In order to solve the other problems of the present invention, in a method for producing a positive electrode active material for a lithium battery according to the present invention,
Producing a mixed metal salt aqueous solution containing nickel, cobalt and manganese;
Charging the reaction solution containing the metal salt mixed aqueous solution, the complex ion forming agent, and the crystal formation regulator into the reactor;
Adjusting the pH of the reaction solution by adding a pH adjuster to the reaction solution under an inert atmosphere;
Filtering the reaction solution to obtain a metal composite hydroxide,
Manufacturing a positive electrode active material precursor by mixing the metal composite hydroxide and a lithium raw material;
A method of manufacturing a positive electrode active material for a lithium battery, the method including the step of firing the positive electrode active material precursor.

According to an embodiment of the present invention, the concentration of the metal salt mixed aqueous solution containing nickel, cobalt and manganese may be 1.5 to 4.0M.

According to one embodiment of the present invention, the crystal formation regulator is an alcohol-based additive, an alcohol having 1 to 10 carbon atoms, and preferably a polyhydric alcohol having 2 to 10 carbon atoms.

According to one embodiment of the present invention, as the alcohol-based additive, methanol, ethanol, propanol, butanol, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, erythritol, pentaerythritol, butanediol, glycerin, or These mixtures may be selected from the group consisting of:

According to one embodiment of the present invention, the lithium raw material mixed with the composite metal hydroxide during the production of the precursor may be lithium carbonate or lithium hydroxide.

According to one embodiment of the present invention, the firing temperature of the positive electrode active material precursor may be 700 to 950°C.

The present invention also provides a lithium battery including the positive electrode active material.

The present invention relates to a positive electrode active material for a lithium secondary battery in which pores are uniformly distributed inside the particles, and pores are radially formed, and the shape of the secondary particle is a nearly spherical shape composed of a combination of primary particles. The pores are evenly distributed radially inside, and have a large specific surface area, which facilitates the inflow of electrolyte into the pores and reduces the migration resistance of lithium ions. It enables production of a secondary battery having output characteristics.

3 is an SEM image of a cross section of the active material for a lithium secondary battery manufactured by the manufacturing method of Example 1. 5 is a SEM image of a cross section of the active material for a lithium secondary battery manufactured by the manufacturing method of Comparative Example 1. 5 is an SEM image of a cross section of the active material for a lithium secondary battery manufactured by the manufacturing method of Comparative Example 2. 3 is a graph showing the output characteristics and life characteristics of the lithium secondary battery active materials according to Example 1, Comparative Example 1, and Comparative Example 2.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, it is understood that this is not intended to limit the present invention to specific embodiments, but includes any variations, equivalents or alternatives included in the technical idea of the present invention and the scope of the present invention. There must be.

The positive electrode active material for a lithium battery according to the present invention is a particle having a porous structure in which secondary particles are formed by agglomerates of primary particles, and pores are distributed over the entire inner region of the secondary particles, wherein the pores are The positive electrode active material is distributed radially from the center of the secondary particles.

The positive electrode active material according to the present invention provides porous secondary particles composed of primary particles. The primary particles have various shapes and are not particularly limited, but may be, for example, plate-shaped, needle-shaped, or amorphous particle shapes. The secondary particles may be particles in which the primary particles are aggregated to form spherical particles.

The inside of the secondary particles may include pores formed when the primary particles aggregate. The pores existing between the primary particles are radially formed based on the center of the secondary particles.

According to the present invention, the radial porous structure, the plate-shaped or needle-shaped primary particles radially aggregate from the center of the secondary particles inside the secondary particles, the radial area formed by the primary particles. By forming the pores on the basis, the positive electrode active material having a porous structure having a radial distribution according to the present invention may be formed.

The positive electrode active material particles of the present invention are formed by collecting plate-shaped or needle-shaped primary particles to form spherical secondary particles, and the primary particles are at least partially radially aggregated from the center inside the secondary particles. However, the pores may have a shape in which the pores are uniformly distributed among the primary particles that are radially aggregated. When the primary particles are radially aggregated and distributed from the center of the secondary particles, the pores may be radially distributed based on the center of the secondary particles. In addition, even when amorphous primary particles that are not needle-shaped or plate-shaped are present, the pores may have a form in which they are radially distributed.

The radial porous structure as described above realizes a large specific surface area due to the pores formed uniformly throughout the inside of the secondary particles, which is a structure capable of increasing the reaction area with the electrolytic solution. And contributes to the improvement of the output characteristics of the secondary battery.

Specifically, by forming a path that connects the inside and the outside of the particles between the primary particles, it is possible to infiltrate the electrolytic solution through the path between the primary particles, and not only on the surface of the secondary particles but also inside. A reaction interface is formed that reacts with the electrolyte. Thereby, the interfacial reaction between the Li ion active material and the electrolytic solution becomes smooth, the insertion and desorption of Li ions at the time of charging and discharging become smooth, and the output characteristics and capacity of the lithium battery are improved.

The positive electrode active material according to the present invention may be a positive electrode active material for a lithium battery having a specific surface area of 1 to 5 m ² /g and an average particle diameter of the particles of 2 to 20 μm. Specifically, if the average particle size of the particles is less than 2 μm, the charge density of the positive electrode is reduced and the battery capacity per volume is reduced. If the average particle size of the particles exceeds 20 μm, the specific surface area of the positive electrode active material decreases, the interface with the electrolytic solution decreases, the resistance of the positive electrode increases, and the output characteristics of the battery deteriorate.

The positive electrode active material is composed of a composite oxide of lithium and a transition metal, and the positive electrode active material may include two or more kinds of transitions even if the lithium transition metal oxide is used alone. You may mix and use a metal.

As a specific example,
Layered compounds such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), and compounds substituted with one or more transition metals;
Chemical formulas Li1+yMn2-yO4 (where y is 0 to 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2;
Lithium copper oxide (Li2CuO2);
Vanadium oxides such as LiV3O8, LiFe3O4, V2O5, Cu2V2O7;
Chemical formula LiNi1-yMyO2 (where M is one or more metals selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B and Ga, and y is 0.01 to 0.3). Ni site type lithium nickel oxide represented by
Chemical formula LiMn2-yMyO2 (where M is at least one metal selected from the group consisting of Co, Ni, Fe, Cr, Zn and Ta, and y is 0.01 to 0.1) or Li2Mn3MO8. (Where M is one or more metals selected from the group consisting of Fe, Co, Ni, Cu, Zn) and a lithium manganese composite oxide;
LiMn2O4 in which a part of Li in the chemical formula is replaced with an alkaline earth metal ion;
Disulfide compound;
Examples thereof include Fe2(MoO4)3, but are not limited thereto.

The transition metal according to the present invention is preferably a transition metal selected from nickel, cobalt and manganese, and more preferably a three-component positive electrode active material containing the above nickel, cobalt and manganese, but is not limited thereto.

The positive electrode active material according to the preferred embodiment of the present invention may be a lithium metal composite oxide represented by the following chemical formula (I).

_{Li p Ni 1-x-y} -z Mn x Co y M z O 2 (I)
In the above formula,
M is at least one metal selected from Mg, Al, Ti, Zr, Mo, W, Y, Sr, V, Ca and Nb,
p is 0.9≦p≦1.2,
x is 0≦x≦0.80,
y is 0≦y≦0.50,
z is 0<z≦0.05.

The positive electrode active material of the present invention may have a lithium molar ratio (p) of 0.9 to 1.2. When the molar ratio of lithium is less than 0.9, the capacity of the positive electrode active material decreases. When the molar ratio of lithium is more than 1.2, the content of residual lithium is increased, which may cause problems such as battery expansion due to gas generation.

The positive electrode active material of the present invention preferably contains an additive element in order to improve the output characteristics, structural stability, life characteristics and the like of the battery. It is desirable that the additive element is added in a small amount as compared with the content of the main element and is uniformly distributed on the surface or inside of the lithium nickel composite oxide particles.

When the molar ratio (z) of the additional element M exceeds 0.05, the amount of lithium that contributes to the redox reaction during charge/discharge decreases, so that the battery capacity decreases.

The positive electrode active material for a lithium secondary battery according to the present invention is obtained by optimizing the precursor production process of the positive electrode active material, and the specific surface area and morphology of the particles are appropriately controlled through the precursor process and the firing process. By doing so, it is possible to provide a method for producing a porous positive electrode active material for a lithium secondary battery having a large specific surface area.

The average particle size, particle size distribution, reaction area, particle internal structure, and composition of the precursor and active material are determined by the method for manufacturing a positive electrode active material for a lithium secondary battery as described above. Control of the conditions is not particularly limited as long as it is a method capable of producing a positive electrode active material, but by using the method for producing a positive electrode active material introduced below, the positive electrode active material of the present invention can be produced. The substance can be manufactured more reliably.

Hereinafter, a method for producing a positive electrode active material for a lithium secondary battery according to the present invention is provided.

The positive electrode active material for a lithium secondary battery of the present invention,
Producing a mixed metal salt aqueous solution containing nickel, cobalt and manganese;
Charging a reaction solution containing the metal salt mixed aqueous solution, a complex ion forming agent, and an alcohol-based additive into a reactor;
Adding a pH adjuster to the reaction solution under an inert atmosphere to adjust the pH,
Filtering the reaction solution to obtain a metal composite hydroxide,
Manufacturing a positive electrode active material precursor by mixing the metal composite hydroxide and a lithium raw material;
A method of manufacturing a positive electrode active material for a lithium battery, comprising: firing the positive electrode active material precursor.

Since the composition ratio (Ni:Co:Mn) of the metal composite hydroxide particles is retained in the positive electrode active material, the composition ratio of the metal composite hydroxide should be the same as that of the positive electrode active material to be obtained. It is desirable to adjust to.

The metal composite hydroxide reflects the molar ratio of the metal elements in order to produce a metal composite compound corresponding to the molar ratio of metal atoms in the particles of the metal composite hydroxide represented by the chemical formula (I). The metal salt mixed aqueous solution can be prepared by dissolving a quantity of each metal salt compound in water.

On the other hand, the reaction solution charged into the reactor contains the metal salt mixed aqueous solution and the complex ion forming agent. According to a preferred embodiment of the present invention, the reaction solution may further include an alcohol-based additive. Further, the pH of the reaction solution can be adjusted by adjusting the supply amount of the alkaline aqueous solution.

Further, in the reaction solution, the pH of the solution changes with particle growth, so that the reaction solution is supplied with the mixed aqueous solution and the alkaline aqueous solution in order to keep the pH of the reaction solution at a predetermined value.

<Metal compound>
As the metal salt compound, a metal compound having a metal molar ratio corresponding to the metal molar ratio in the particles of the metal composite hydroxide represented by the chemical formula (I) is used. The metal compound is composed of a metal salt compound corresponding to the metal in order to contain the metal in a molar ratio corresponding to the metal in the nickel composite hydroxide represented by the chemical formula (I).

In order to facilitate the supply to the metal salt mixed aqueous solution and to mix it well, the metal salt compound is usually preferably water-soluble, and can be dissolved in the aqueous solution and reacted. Therefore, it is desirable that the metal salt compound has water solubility.

Specific examples of the metal salt compound include inorganic acid salts. Specific examples thereof include, but are not limited to, nitrates, sulfates and hydrochlorides. These inorganic acid salts may be used alone or in combination of two or more kinds. According to a preferred embodiment of the present invention, examples of the metal salt compound include nickel sulfate, cobalt sulfate, and manganese sulfate.

<Concentration of metal salt mixed aqueous solution>
The concentration of the metal salt compound in the metal salt mixed aqueous solution is preferably 1.5 to 4M. When the concentration of the metal compound in the aqueous metal complex solution is less than 1.5 M, the amount of particles produced is small and the productivity is low. On the other hand, when the concentration of the metal composite aqueous solution exceeds 4 M, crystals of the metal salt may be deposited and the piping of the equipment may be clogged. When two or more kinds of metal compounds are used, the mixed aqueous solution of each metal salt compound may be adjusted so that the concentration of the metal salt compound falls within the above range. The metal salt mixed aqueous solution may be charged into the reactor at a flow rate of 0.1 to 0.8 L/hour.

<Crystal formation regulator>
During the precursor synthesis, alcohol can be added as a crystal formation regulator (habit modifier) to control the particle properties. The hydroxyl group of alcohol is adsorbed to the surface hydroxyl group of the specific surface of the particle in the aqueous solution, and the particle growth on the adsorbed surface is suppressed. This manifests itself as a morphological change. It was confirmed that when a precursor was produced using a crystal formation regulator, the primary particles aggregated during firing to form secondary particles, and that it is possible to produce a positive electrode material having a uniform void distribution. did. The crystal formation modifier has properties that vary depending on the composition and morphology, and can be optimized through adjustment of reaction conditions and content.

As the crystal formation regulator, an alcohol compound having 1 to 10 carbon atoms, preferably an alcohol additive having 2 to 10 carbon atoms can be used. The alcohol-based additive may be added to the reaction vessel together with the aqueous metal complex solution and the complex ion-forming agent, and may contain 1 to 10, preferably 2 or more, more preferably 2 to 5 hydroxyl groups. ..

For example, it is selected from the group consisting of methanol, ethanol, propanol, butanol, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, erythritol, pentaerythritol, butanediol, glycerin, or a mixture thereof, The additive can be added to the aqueous metal complex solution using an aqueous solvent to control the crystal formation of particles of the produced metal complex hydroxide.

The amount of the crystal formation regulator added is in the range of 0.01 to 5 parts by weight, preferably 0.01 to 3 parts by weight, and more preferably 0.05 to 2 parts by weight, based on 100 parts by weight of the transition metal. It can be adjusted.

<pH adjuster>
The pH of the reaction solution can be adjusted using a pH adjuster. Examples of the pH adjuster include, but are not limited to, alkaline aqueous solutions such as aqueous solutions of alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. It is preferable to use sodium hydroxide as the pH adjusting agent according to the present invention. The pH of the reaction solution can be measured by a commonly used pH meter.

<Additive element>
In the chemical formula (I), M represents an additive element, and at least selected from the group consisting of Mg, Al, Ca, Ti, V, Cr, Mn, Zr, Nb, Mo, and W excluding Ni, Co, and Mn. It is desirable to use a water-soluble compound as the compound containing one kind of the additional element. Examples of the compound containing the additional element include magnesium sulfate, aluminum sulfate, sodium aluminate, titanium sulfate, ammonium peroxotitanate, potassium titanium oxalate, vanadium sulfate, ammonium vanadate, chromium sulfate, potassium chromate, and sulfuric acid. Examples thereof include, but are not limited to, manganese, zirconium sulfate, zirconium nitrate, niobium oxalate, ammonium molybdate, sodium tungstate, ammonium tungstate, and the like.

In order to uniformly disperse the additive element inside the composite hydroxide particles, a compound containing the additive element, preferably a water-soluble compound containing the additive element, may be added to the mixed aqueous solution. This makes it possible to uniformly disperse the additional element inside the composite hydroxide particles.

When the surface of the composite hydroxide particles is coated with the additional element, the composite metal hydroxide particles are slurried with an aqueous solution having the additional element, and the additional element is added to the surface of the composite hydroxide particles by the crystallization reaction. By precipitating, the surface can be coated with the additional element. In this case, an alkoxide solution of the compound containing the additional element may be used instead of the aqueous solution containing the compound containing the additional element. The surface of the composite hydroxide particles can be coated with the additive element by spraying an aqueous solution or a slurry containing a compound containing the additive element onto the metal composite hydroxide particles and drying.

<Complex ion forming agent>
The metal complex hydroxide reaction according to the present invention may use a complex ion-forming agent that forms a complex salt with the metal salt complex aqueous solution. The complex ion forming agent can increase the solubility of the metal salt. Typical complex ion formers include ammonium ion donors. Examples of the ammonium ion supplier include, but are not limited to, ammonia, ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride and the like.

Ammonia is added at a concentration within a range where the solubility of metal ions can be kept constant. The metal mixed solution may be supplied at a ratio of 0.01 to 0.2, preferably 0.05 to 0.1 with respect to the flow rate. Further, when the ammonia concentration changes, the solubility of the metal ions also changes and uniform hydroxide particles are not formed, so it is desirable to maintain the ammonia concentration at a constant value.

<pH and reaction temperature of reaction solution>
The temperature of the reaction solution in the reaction tank is preferably maintained at 30 to 80°C. Further, at the temperature of the reaction solution, it is desirable to adjust the pH to 10 to 13 by adding a pH adjusting agent. If the pH is higher than 13.0, the particle size becomes excessively small. If the pH is less than 10, large particles may be formed or impurities may be mixed in, and the particle size distribution of the produced particles themselves may become inhomogeneous. Therefore, by adjusting the pH to a constant value within the above pH range, the size of the primary particles and secondary particles produced can be adjusted, and a uniform particle size distribution can be obtained.

<Atmosphere of reaction process>
The atmosphere of the reaction tank in the present invention is defined as an atmosphere in which the oxygen concentration in the reaction tank is 1 vol% or less. The oxygen concentration in the mixed atmosphere of oxygen and the inert gas is controlled to be preferably 0.5% by volume or less, more preferably 0.2% by volume or less. By controlling the oxygen concentration in the space in the reaction tank to 1% by volume or less to grow the particles, it is possible to suppress undesired oxidation of the particles and promote the growth of the primary particles. As a means for maintaining the space in the reaction tank in such an atmosphere, an inert gas such as nitrogen is circulated in the space in the reaction tank, and further, an inert gas is bubbled in the reaction solution. Is mentioned.

The oxygen concentration in the atmosphere can be adjusted using, for example, an inert gas such as nitrogen. Examples of means for adjusting the oxygen concentration in the atmosphere to a predetermined concentration include, for example, constantly circulating the oxygen in the atmosphere.

<Control of particle size of composite hydroxide particles>
The particle size of the metal composite hydroxide particles can be controlled by the time of the particle growth step. By adjusting the reaction time so as to grow to a desired particle size, composite hydroxide particles having a desired particle size can be obtained.

The particle size of the metal composite hydroxide particles can also be controlled by the pH value and the ratio of the raw materials to be added.

<Production reactor>
As the apparatus, a reactor used for a reaction for producing a secondary battery positive electrode active material using a coprecipitation reaction may be used. For example, a continuous reactor (CSTR, Continuous Stirring Tank Reactor) or a batch A Batch Type Tank Reactor can be used. The continuous reactor has an advantage in productivity. The batch reactor has advantages in that there is no reactor stabilization time and that mold replacement is unnecessary.

In the reaction for producing the metal composite hydroxide according to the present invention, the substance in the reactor is reacted with stirring at a rotation speed of 10 to 1000 rpm, and the reaction time for staying in the reaction tank is 3 to 24 hours, preferably 5 to 12 hours.

<Heat treatment process>
The metal complex hydroxide slurry recovered in the reaction tank is filtered from the overflow solution and washed with distilled water, and then the water remaining in the metal complex hydroxide particles is removed in a step of heating the particles to heat-treat them. Can be performed.

In the heat treatment step, the composite hydroxide particles may be heated to a temperature at which residual water is removed. The heat treatment temperature is not particularly limited, but may be 100 to 400°C, and preferably 105 to 200°C. When the heat treatment temperature is lower than 105°C, it takes a long time to remove the residual moisture.

Further, the heat treatment time of the metal composite hydroxide particles cannot be uniformly determined because it depends on the heat treatment temperature. However, if less than 1 hour, the residual water content in the composite hydroxide particles may not be sufficiently removed. Therefore, it is preferably 1 hour or more, more preferably 5 to 24 hours. The equipment used for the heat treatment of the composite hydroxide particles is not particularly limited, as long as it can heat the composite hydroxide particles in an air stream, for example, a blast dryer, an electric furnace without gas generation. , And so on.

The atmosphere in which the heat treatment of the metal composite hydroxide particles is performed is not particularly limited, and it is desirable that the atmosphere is such that it can be performed easily.

<Metal composite hydroxide particles>
The metal composite hydroxide according to the present invention may be represented by the following chemical formula (II).

_{Ni 1-x-y-z} Co x Mn y M z (OH) 2 + α (II)
In the above formula,
M is at least one metal selected from Mg, Al, Ti, Zr, Mo, W, Y, Sr, V, Ca and Nb,
x is 0≦x≦0.8,
y is 0≦y≦0.5, and
z is 0≦z≦0.05,
α is 0≦α≦0.5.

The composite hydroxide particles of the present invention are spherical secondary particles formed by aggregating a plurality of primary particles.

The composite hydroxide particles of the present invention are particularly suitable as a raw material for the positive electrode active material of the present invention described above. Therefore, the metal composite hydroxide particles of the present invention will be described later on the assumption that they are used for the positive electrode active material of the present invention.

<Average particle size>
The metal composite hydroxide particles of the present invention have an average particle size of about 2 to 21 μm. The positive electrode active material prepared from the metal composite hydroxide having the above average particle diameter has an average particle diameter of about 2 to 20 μm. When the average particle size of the metal composite hydroxide particles of the present invention is less than 2 μm, the average particle size of the positive electrode active material decreases, the charge density of the positive electrode decreases, and the battery capacity per volume decreases. When the average particle size of the composite hydroxide particles of the present invention exceeds 21 μm, the specific surface area of the obtained positive electrode active material decreases and the contact area between the positive electrode active material and the electrolytic solution decreases, so that the resistance of the positive electrode increases. Rises and the output characteristics of the battery deteriorate.

<Mixing process>
The mixing step is a step of mixing the dried metal composite hydroxide after the heat treatment step with a lithium compound to obtain a lithium composite metal mixture and manufacturing a precursor of the positive electrode active material.

The ratio Li/Me of the molar ratio (Li) of lithium and the molar ratio (Me) of metals other than lithium in the lithium mixture is mixed so as to be the same as Li/Me in the positive electrode active material. That is, it is desirable that the ratio Li/Me of lithium (Li) and the sum (Me) of the number of atoms of nickel, cobalt, manganese, and other additive elements be 0.90/1 to 1.2/1. Are mixed so as to be 1/1 to 1.15/1.

The lithium compound used to form the lithium mixture is preferably lithium hydroxide, lithium nitrate, lithium carbonate, or a mixture thereof because it is easily available. In order to form the porous secondary particles according to the present invention, lithium carbonate or lithium hydroxide is more preferable.

In addition, when the mixture of the lithium compound and the heat-treated metal composite compound is not sufficient, the distribution of lithium becomes uneven among particles, and Li/Me of each particle varies. That is, not only the target composition of the active material cannot be obtained, but also sufficient battery characteristics may not be obtained.

In addition, a general mixer can be used in the mixing step. For example, a shaker mixer, a Loedige mixer, a Julia mixer, a V blender, etc. are mentioned. The metal composite hydroxide particles can be mixed to such an extent that the lithium compound is not destroyed and the lithium compound is sufficiently mixed.

<Firing process>
The firing step is a step of firing the lithium-metal mixture produced in the mixing step to form a lithium-metal oxide. If the lithium-metal mixture is fired in the firing step, lithium in the lithium compound may diffuse into the heat-treated particles to form a lithium-metal composite oxide.

In the firing step, the firing temperature of the lithium mixture is 700 to 950°C, preferably 800 to 950°C, and the temperature can be raised at a rate of 2 to 10°C/min.

If the firing temperature is lower than 700° C., the lithium is not sufficiently diffused into the heat-treated particles and surplus lithium and unreacted particles remain, or the crystal structure is not sufficiently aligned, resulting in sufficient battery characteristics. Will not be obtained. If the firing temperature exceeds 950° C., violent sintering may occur between the heat-treated particles and abnormal particles may occur. Therefore, the particles after firing may become coarse and may not be able to maintain the particle morphology (morphology of spherical secondary particles described later), that is, the specific surface area decreases when the positive electrode active material is formed. The resistance of the positive electrode increases and the capacity of the battery decreases.

The firing time of the lithium mixture, that is, the holding time at the firing temperature is preferably 3 hours or more, more preferably 6 to 24 hours. If it is less than 3 hours, the lithium nickel composite oxide may not be sufficiently formed.

The firing furnace is not particularly limited as long as it can heat the lithium-metal mixture in the atmosphere, oxygen and, in some cases, nitrogen atmosphere. For example, an electric furnace that does not generate gas is desirable, and a firing furnace in the form of a box furnace, a rotary kiln, or the like can be used.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

(Example 1)
A 4 L continuous overflow reactor (CSTR) was filled with water and stirred at a stirring speed of 700 rpm to adjust the temperature to a set temperature (30 to 50° C.), and nitrogen gas was introduced into the reaction tank to create an inert atmosphere. Adjusted to.
A 2.5M concentration metal sulfate aqueous solution prepared by mixing nickel sulfate, cobalt sulfate and manganese sulfate in a molar ratio of 0.33:0.33:0.33, 25% sodium hydroxide and 10% ammonia water were prepared. ..
The flow rate of the metal sulfate aqueous solution was adjusted to 0.4 L/hour, and the flow rate of the ammonia water was adjusted to a ratio of 0.08 to the flow rate of the metal aqueous solution and supplied to the reactor. The amount of sodium hydroxide solution added was adjusted so that the pH in the reactor was about 11.0 to 12.0. At this time, 0.2 part by weight of glycerin was added to the reactor with respect to 100 parts by weight of the transition metal. The reaction product was charged so that the stirring rate was 700 rpm and the average residence time of the entire solution was 6 hours, the reaction temperature was maintained at 30°C to 50°C, and nitrogen gas was introduced to maintain the inert atmosphere.
After the reaction was stabilized, the recovered overflow solution was filtered, washed, and then dried in an oven at 120° C. to obtain composite metal hydroxide precursor particles.
Lithium carbonate was mixed with the hydroxide particles obtained as described above so that the equivalent ratio to the hydroxide was 1.02, and then the temperature was raised at a rate of 3° C./min to obtain 910° C. By firing for 9 hours, a lithium mixed metal oxide having a uniform radial pore structure was produced.

Comparative Example 1
Using a 4 L continuous overflow reactor (CSTR), an aqueous solution of metal sulfate having a concentration of 2.5 M in which nickel sulfate, cobalt sulfate and manganese sulfate were mixed at a molar ratio of 0.33:0.33:0.33. A composite metal hydroxide was produced.
The flow rate of the aqueous solution of metal sulfate was adjusted to 0.4 L/hour, and the flow rate of ammonia was adjusted to a ratio of 0.08 to the flow rate of the aqueous solution of metal to be supplied to the reactor. The amount of sodium hydroxide solution added was adjusted so that the pH in the reactor was about 11.0 to 12.0. The reaction product was charged so that the stirring rate was 700 rpm and the average residence time of the entire solution was 6 hours, the reaction temperature was maintained at 30°C to 50°C, and nitrogen gas was introduced to maintain the inert atmosphere.
After the reaction was stabilized, the recovered overflow solution was filtered, washed, and then dried in an oven at 120° C. to obtain composite metal hydroxide precursor particles.
Lithium carbonate was mixed with the hydroxide particles obtained as described above so that the equivalent ratio to the hydroxide was 1.02, and then the temperature was raised at a rate of 3° C./min to obtain 910° C. By firing for 9 hours, a lithium composite metal oxide having few pores was produced.

Comparative example 2
30% of water was put in a reaction tank (4 L), the temperature was adjusted to a preset temperature (30 to 50° C.) while stirring at a stirring speed of 700 rpm, and nitrogen gas was introduced into the reaction tank to adjust to an inert atmosphere.
100 g of ammonia water was further added to the reaction tank, and sodium hydroxide was added so that the pH became 12.5.
Then, a metal sulfate aqueous solution having a concentration of 2.5M in which nickel sulfate, cobalt sulfate, and manganese sulfate were mixed at a molar ratio of 0.33:0.33:0.33 and ammonia water were respectively added to the reaction tank in an amount of 0. It was charged at 1 L/hour and 0.01 L/hour. Ten minutes after starting the introduction of the aqueous metal sulfate solution and the aqueous ammonia, sodium hydroxide was introduced to allow the initial particles to grow. Thereafter, an aqueous sodium hydroxide solution was added at a flow rate of 0.063 to 0.065 L/hour.
When the inside of the reaction tank became full, the supply of the aqueous metal sulfate solution, the sodium hydroxide solution, and the aqueous ammonia was stopped to terminate the reaction. Then, the entire amount of the obtained product was discharged, filtered, washed, and then dried in an oven at 120° C. to obtain precursor particles in the form of a composite metal hydroxide.
Lithium carbonate was mixed with the hydroxide particles obtained as described above so that the equivalent ratio to the hydroxide was 1.02, and then the temperature was raised at a rate of 3° C./min, and the temperature was adjusted to 9 at 910° C. By firing for a period of time, a lithium composite metal oxide having a hollow structure having an internal hollow space and an outer shell was produced.

<Cathode active material cross-section measurement>
The positive electrode active material particles fired from Example 1, Comparative Example 1 and Comparative Example 2 were sampled, and the cross section of the particles was multiplied by 5,000 times using an ion beam cross section processing machine (JEOL, SM-09010). Was measured at a magnification of. The observation results are shown in FIGS. 1, 2 and 3, respectively.

<Specific surface area measurement>
The specific surface area was measured by a gas adsorption method specific surface area measuring apparatus (BELSORP-mini II, manufactured by Microtrac Bell Co., Ltd.).

<Particle size measurement>
The average particle diameters of the composite hydroxide and the positive electrode active material were calculated from the integrated volume values measured using a laser diffraction/scattering particle size distribution measuring device (Microtrac S3500, manufactured by Microtrac Inc.).

The lithium mixed metal oxides of the examples and the comparative examples were each manufactured to have a particle size of 5 μm or less. As shown in FIGS. 1 to 3, the positive electrode active material manufactured by the manufacturing method according to the present invention. It can be seen that has uniform pores throughout and has a relatively large specific surface area.

Test Example 2: Electrochemical property evaluation <Coin cell evaluation>
The positive electrode active material obtained from Example 1, Comparative Example 1 and Comparative Example 2, the conductive agent (Super P), and polyvinylidene fluoride (binder) were used in a weight ratio of 90%, 5%, Mixed at 5% and mixed with NMP to obtain a uniform slurry. This slurry was applied on an aluminum plate to a thickness of 80 μm, and then dried at 120° C. for 30 minutes until NMP was completely evaporated.
The electrolytic solution used was one in which 1 mol of LiPF ₆ was dissolved in ethylene carbonate/dimethyl carbonate (EC/DMC) (1/1% by volume). As an initial formation condition, charging and discharging were performed once at 0.1C.
The high rate characteristic evaluation was performed under each condition of 0.1C, 0.2C, 0.5C, 1.0C, 2.0C and 3.0C. The charging voltage was 4.3V and the final discharge voltage was 3.0V.

From Table 2, it can be seen that Example 1 exhibited improved high rate characteristics as compared with Comparative Examples 1 and 2. This is because the positive electrode active material of Example 1 has a more uniform distribution of pores inside and a larger contact area with the electrolyte, as compared with Comparative Example 1 in which pores are not relatively present inside. It is considered that the high-rate characteristics were improved by smooth movement of the electrolyte to the electrolytic solution. On the other hand, even if it has pores, in the case where the outer shell is formed in the form of a hollow structure (Comparative Example 2), there is a limit to the increase in surface area, and it is difficult for the electrolyte to flow into the hollow interior and Because of the limited movement path, the output characteristics were relatively low at high rate evaluation.

The positive electrode active material for a lithium battery according to the present invention is a particle having a porous structure in which pores are distributed over the entire inner region of the secondary particles formed of an aggregate of primary particles, and the pores are the secondary particles. It has a large specific surface area due to the radial distribution from the center, which facilitates the inflow of the electrolyte into the pores and reduces the migration resistance of lithium ions, resulting in high output characteristics. Enables the manufacture of secondary batteries.

Claims (6)

Aggregates of primary particles form secondary particles,
A particle having a porous structure in which pores are distributed over the entire inner region of the secondary particle,
A method for producing a positive electrode active material for a lithium battery, wherein the pores are radially distributed from the center of the secondary particles,
Producing a mixed metal salt aqueous solution containing nickel, cobalt and manganese;
Charging the reaction solution containing the metal salt mixed aqueous solution, the complex ion forming agent, and the crystal formation regulator into the reactor;
Adding a pH adjuster to the reaction solution under an inert atmosphere to adjust the pH of the reaction solution;
Filtering the reaction solution to obtain a metal composite hydroxide,
Producing a positive electrode active material precursor by mixing the metal composite hydroxide and a lithium raw material;
Firing the positive electrode active material precursor,
The method for producing a positive electrode active material for a lithium battery, wherein the crystal formation regulator is an alcohol-based additive and is an alcohol having 1 to 10 carbon atoms. The method for producing a positive electrode active material for a lithium battery according to claim 1, wherein the concentration of the metal salt mixed aqueous solution is 1.0 to 4.0M. The method for producing a positive electrode active material for a lithium battery according to claim 1, wherein the crystal formation regulator is a polyhydric alcohol having 2 to 10 carbon atoms and two or more hydroxyl groups. The alcohol additive is selected from the group consisting of methanol, ethanol, propanol, butanol, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, erythritol, pentaerythritol, butanediol, glycerin, or a mixture thereof. The method for producing a positive electrode active material for a lithium battery according to claim 1. The method for producing a positive electrode active material for a lithium battery according to claim 1, wherein the pH in the step of adjusting the pH is 10 to 13. The method for producing a positive electrode active material for a lithium battery according to claim 1, wherein a firing temperature of the positive electrode active material precursor is 700 to 950°C.

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