JP7185838B2 - Method for producing positive electrode active material for high-strength lithium-ion secondary battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a positive electrode active material for high-strength lithium-ion secondary batteries.

In recent years, the spread of portable electronic devices such as smartphones, tablets, and mini-notebook computers, as well as hybrid and electric vehicles, has led to the development of compact, lightweight lithium-ion secondary batteries with high energy density, as well as medium-sized and large-sized high-performance batteries. Development needs for output lithium-ion secondary batteries are rapidly expanding.
These lithium-ion secondary batteries are composed of a positive electrode, a negative electrode, a separator, an electrolytic solution, etc., and the active material of the positive electrode and the negative electrode is a material that can desorb and insert lithium ions. there is Lithium-ion secondary batteries are still being actively researched and developed. Since a high voltage can be obtained, it is being put to practical use as a battery with a high energy density.

Positive electrode materials mainly proposed so far include lithium-cobalt composite oxide (LiCoO ₂ ), which is relatively easy to synthesize, and lithium-nickel composite oxide (LiNiO ₂ ), which uses nickel, which is cheaper than cobalt. Lithium-nickel-manganese-cobalt composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) and lithium-manganese composite oxide (LiMn ₂ O ₄ ) using manganese can be mentioned.
Among these, lithium-nickel-manganese-cobalt composite oxides (hereinafter also referred to as “NMC” for lithium metal composite oxides containing lithium, nickel, manganese, and cobalt as main components) have good battery cycle characteristics and low resistance. It is attracting attention as a material that can provide high output. .
For example, Patent Document 1 describes the properties of NMC, such as having an α-NaFeO ₂ type crystal structure, and Patent Document 2 describes a sulfate group present in the form of lithium sodium sulfate (LiNaSO ₄ ). NMC that has been washed with water to a concentration of less than 0.1% is said to be preferred.
In Patent Document 3, with a specific surface area of 0.1 to 3 m ² /g when measured by the BET method, with an agglomerate size of greater than 6 μm when determined from the D50 value by the laser diffraction/scattering method, the D90 value Internal pores with a diameter as determined of 100 μm or less and a size of 0.3 μm<Dintra<D50 value/4 μm and an internal pore volume of at least 0.08 ml/g NMC is said to be preferred.
Further, Patent Document 4 describes a method for producing NMC in which at least a portion thereof has a single crystal structure by hydrothermally reacting lithium ions and other metal ions in supercritical or subcritical water. , Patent Literature 5 describes a manufacturing method for obtaining NMC with high capacity and high durability by performing long-time sintering of up to 50 hours.
Furthermore, Patent Document 6 describes an NMC composed of particles having a minimum value of crushing strength when the NMC is crushed is greater than 70 MPa for the purpose of improving initial charge-discharge efficiency and cycle characteristics. In 7, while continuously introducing the raw material solution into the reaction vessel at 40 to 90 ° C., the pH is maintained at 9 to 11, nickel manganese cobalt composite hydroxide (hereinafter, nickel, manganese, cobalt as main components A metal complex hydroxide is also referred to as "NMC precursor") is coprecipitated, the NMC precursor is oxidized and roasted at a temperature of 300 to 700 ° C., washed with water, and dried to obtain NMC. there is

JP 2003-007298 Japanese Patent Laid-Open No. 13-273898 Japanese Patent Application Laid-Open No. 2003-505326 Japanese Patent Laid-Open No. 13-163700 JP 2007-179917 JP 2013-232318 JP 2008-251191

In general, it is known to increase the filling density of the positive electrode active material in the electrode in order to use a positive electrode active material with a high energy density and an electrode with a high density in order to increase the capacity of the battery. However, when the packing density is increased, a high pressure is applied to the positive electrode active material, so if the particle strength is weak, cracks occur in the secondary particles, resulting in a decrease in electrical conductivity. In addition, although the positive electrode active material repeatedly expands and contracts due to charging and discharging, an irreversible reaction occurs in a part of the positive electrode active material, causing expansion. For this reason, if the particle strength is weak, the secondary particles are broken, the electrical conductivity is lowered, and the positive electrode plate itself expands, thereby degrading the battery performance.
Also, in the positive electrode film coating process, high pressure is applied to the positive electrode active material, so if the particle strength is weak, the secondary particles will collapse, and the collapsed particles will adhere to the rolls during roll pressing, resulting in a decrease in yield. do. Furthermore, the collapsed particles that do not adhere to the roll also cause deterioration of the battery performance due to interruption of the lithium conductivity between the primary particles.
As described above, the particle strength of the positive electrode active material is a very important factor in order to improve battery performance such as high capacity and high durability of the battery and to prevent a decrease in yield rate.
On the other hand, the NMCs described in Patent Documents 1 to 3 do not mention particle strength at all, and the capacity and durability are not sufficient. Both of the NMC production methods described in Patent Documents 4 and 5 require a large amount of energy, which is industrially undesirable. In addition, according to the example shown in Patent Document 6, the crushing strength of the produced particles is about 75 to 85 MPa, and the particle strength is still low, so the initial charge-discharge efficiency and cycle characteristics are not sufficient. do not have. Furthermore, in US Pat. No. 6,200,000, the pH control values disclosed increase the residual sulfate in the NMC and degrade the battery performance. Moreover, although heat treatment of the NMC precursor improves the particle strength of NMC, no attention is paid to the effect. In addition, the NMC precursor after oxidizing roasting is washed with water, which reduces impurities such as sulfates, but on the other hand, the impurities present at the grain boundaries are washed away, weakening the cohesion between the primary particles, which leads to secondary The particle strength of the particles is lowered, and the battery performance is deteriorated.
Thus, the NMC described in Patent Documents 1 to 7 cannot be said to be a positive electrode active material that meets the needs for environmentally friendly automobiles, and has a higher capacity and higher durability. is required.
In view of such problems, in order to obtain an excellent lithium ion secondary battery with improved safety in addition to discharge capacity and durability, while maintaining high particle strength, the primary particle average particle size and An object of the present invention is to provide a lithium-nickel-manganese-cobalt-aluminum composite oxide in which the concentration of sulfate radicals is suppressed while controlling the average particle diameter of secondary particles within an optimum range, and a method for producing the same.

The present inventors have made intensive studies in order to solve the above problems. As a result, in order to prevent the collapse of NMC particles, which is a factor of capacity deterioration during cycling, and to obtain high durability, in the crystallization process, in addition to the main components of NMC, nickel, manganese, and cobalt, aluminum is added as an essential element. In addition, an NMC precursor is produced by adding the element M as an optional element, and the NMC precursor is converted to a metal composite oxide (hereinafter referred to as a metal composite oxide containing nickel, manganese, and cobalt as main components) in an oxidative roasting process. Also referred to as "NMC intermediate"), the NMC intermediate, which is a metal composite oxide, is mixed with a lithium compound in the mixing step to form a lithium mixture, and then the lithium mixture is treated in the firing step. was introduced and sintered at a low oxygen concentration, NMC with favorable particle strength, average particle diameter, and sulfate group concentration was obtained. As a result, by equipping NMC with high capacity and high durability, it becomes possible to manufacture lithium-ion secondary batteries that can improve cycle characteristics and suppress battery swelling under high voltage. I have perfected my invention.

That is, the first aspect of the present invention, which was made based on the above findings , is a positive electrode active for a high-strength lithium ion secondary battery used in a positive electrode of a lithium ion secondary battery having a swelling amount of 105% or less. A method for producing a substance, wherein the positive electrode active material for a lithium ion secondary battery has the general formula: Li _v Ni _1-w-x-y-z Mn _w Co _x Al _y M _z O _2+α (where 0. 95<v<1.22, 0.01≤w≤0.35, 0.01≤x≤0.50, 0.01≤y≤0.15, 0≤z≤0.10, 0≤α≤ 0.20, and M is one or more elements selected from W, V, Mg, Mo, Nb, Ti, Si, Zn, Cu, and Fe), and mainly primary particles are agglomerated. The lithium-nickel-manganese-cobalt-aluminum composite oxide composed of secondary particles has a particle strength of 100 to 230 MPa, an average primary particle diameter of 0.1 to 0.5 μm, and an average secondary particle diameter of 3 to 20 μm. , a sulfate radical concentration of 0.5% by weight or less, and at least a solution containing nickel, manganese, and cobalt, a solution containing aluminum, a solution containing an ammonium ion donor, an alkaline solution, and optionally an M element. a crystallization step of crystallizing a metal composite hydroxide by supplying and mixing a solution containing
an oxidizing roasting step of obtaining a metal composite oxide by oxidizing roasting the metal composite hydroxide obtained in the crystallization step at 400 to 900 ° C.;
A mixing step of obtaining a lithium mixture by mixing the metal composite oxide obtained in the oxidizing roasting step and a lithium compound;
a firing step of obtaining a lithium metal composite oxide by firing the lithium mixture obtained in the mixing step at 700 to 1000° C. while controlling the oxygen concentration to 0.1 to 20% by volume;
A method for producing a positive electrode active material for a high-strength lithium ion secondary battery, characterized by having

The positive electrode active material for lithium ion secondary batteries in the present invention is a lithium-nickel-manganese-cobalt-aluminum composite oxide that is relatively inexpensive, industrially easy to handle, and has high capacity and high durability. By using this, it is possible to obtain a lithium-ion secondary battery with battery characteristics that are far superior to those of conventional batteries, so its industrial value is extremely high.

1 is a schematic cross-sectional view of a coin battery used for evaluation of battery characteristics; FIG.

One embodiment of the present invention will be described in detail in the following order.
1. Positive electrode active material for lithium ion secondary battery2. 3. Manufacturing method of positive electrode active material for lithium ion secondary battery. Lithium Ion Secondary Battery The positive electrode active material for lithium ion secondary batteries and the method for producing the same in the present invention are not limited to the following description, and are based on the knowledge of those skilled in the art as long as they do not deviate from the spirit of the present invention. Various modifications can be made to the embodiment.
1. Positive electrode active material for lithium ion secondary battery The positive electrode active material for lithium ion secondary battery in the embodiment of the present invention has the general formula: Li _v Ni _{1-wxyz Mnw} Co _x Al _y M _z O _2+α (where 0.95<v<1.22, 0.01≤w≤0.35, 0.01≤x≤0.50, 0.01≤y≤0.15, 0≤z≤0. 10, 0 ≤ α ≤ 0.20, and M is one or more elements selected from W, V, Mg, Mo, Nb, Ti, Si, Zn, Cu, Fe), mainly primary The particle strength of the lithium-nickel-manganese-cobalt-aluminum composite oxide composed of secondary particles in which particles are aggregated is 100 to 230 MPa, the primary particle average particle size is 0.1 to 0.5 μm, and the secondary particle average particle size is is 3 to 20 μm, and the sulfate group concentration is 0.5% by weight or less.
In addition, the above positive electrode active material for lithium ion secondary batteries is
(1) supplying at least a solution containing nickel, manganese, and cobalt, a solution containing aluminum, a solution containing an ammonium ion donor, an alkaline solution, and optionally a solution containing element M into a reaction vessel and mixed; A crystallization step for crystallizing the metal composite hydroxide.

(2) an oxidizing roasting step for obtaining a metal composite oxide by oxidizing roasting the metal composite hydroxide obtained in the crystallization step at 400 to 900°C;

(3) A mixing step of obtaining a lithium mixture by mixing the metal composite oxide obtained in the oxidizing roasting step and a lithium compound.

(4) A firing step of obtaining a lithium metal composite oxide by firing the lithium mixture obtained in the mixing step at 700 to 1000° C. while controlling the oxygen concentration to 0.1 to 20% by volume.
It is obtained by a manufacturing method having these steps (1) to (4), and is processed in the order of steps (1) to (4).
In the crystallization step (1), in addition to nickel, manganese, and cobalt, which are the main components of NMC, aluminum is added as an essential element, and an element M is added as an optional element to generate an NMC precursor, thereby obtaining an NMC precursor. is converted into a metal composite oxide in the oxidizing roasting step of (2), and the obtained NMC intermediate is mixed with a lithium compound in the mixing step of (3) to form a lithium mixture. By introducing carbon dioxide and sintering at a low oxygen concentration in the sintering step (4), NMC having favorable particle strength, average particle size, and sulfate group concentration can be obtained.
As described above, by newly equipping a battery with NMC, which has high capacity and high durability, as a positive electrode active material, it is possible to improve cycle characteristics and suppress swelling of the battery under high voltage. It becomes possible to manufacture a lithium-ion secondary battery far superior to the conventional one.
<Composition>
Nickel is an element that contributes to improving battery capacity. In order to obtain a high capacity, the range of "1-wxyz" indicating the nickel content is preferably 0.30 to 0.95, and 0.35 to 0.80. is more preferred, and 0.40 to 0.60 is particularly preferred. If the value of "1-wxyz" is less than 0.30, the battery capacity will decrease, while if it exceeds 0.95, the electronic conductivity will increase too much, causing thermal runaway due to short circuit, etc. is generated, there is a possibility that the safety of the battery cannot be sufficiently ensured.
Manganese is an element that contributes to improving thermal stability. In order to obtain better thermal stability, the range of "w" indicating the manganese content is preferably 0.01 to 0.35, more preferably 0.10 to 0.30, and 0 0.15 to 0.30 is particularly preferred. If the value of "w" is less than 0.01, no improvement in thermal stability is observed, while if it exceeds 0.35, the amount of manganese elution increases during operation at high temperatures, and the cycle characteristics deteriorate. A problem arises.
Cobalt is an element that contributes to the improvement of cycle characteristics. By including an appropriate amount of cobalt in the positive electrode active material, it is possible to provide good cycle characteristics and high durability without impairing the initial discharge capacity. The range of "x" indicating the cobalt content is preferably 0.01 to 0.50, more preferably 0.10 to 0.35, and 0.15 to 0.35. Especially preferred. If the value of "x" is less than 0.01, sufficient cycle characteristics cannot be obtained, and the capacity retention rate after cycling decreases.
Aluminum is an element that suppresses excessive electronic conductivity and greatly contributes to ensuring safety. In order to ensure excellent safety, the value of "y" indicating the aluminum content is preferably 0.01 to 0.15, more preferably 0.05 to 0.10, and 0.05 to 0.10. 06 to 0.08 is particularly preferred. If the value of "y" is less than 0.01, no improvement in safety is observed, while if it exceeds 0.15, aluminum segregates inside the particles, inhibiting lithium ion conductivity, A problem arises that the cycle characteristics deteriorate.
Furthermore, the NMC in the present invention can optionally contain the element M. By including the element M in the positive electrode active material, it becomes possible to further improve the battery characteristics such as the durability of the lithium ion secondary battery. At least one element selected from W, V, Mg, Mo, Nb, Ti, Si, Zn, Cu, and Fe can be used as the element M described above. The selection of these elements M is appropriately made according to the application of the lithium-ion secondary battery as well as the required performance. The range of "z" indicating the content of the optionally added element M is preferably 0 to 0.10, more preferably 0.02 to 0.08, and 0.04 to 0.06. is particularly preferred. When the value of "z" exceeds 0.10, the efficiency of the redox reaction decreases, and thus the battery capacity also decreases.
Further, as will be described later, the element M can be crystallized together with nickel, manganese, cobalt, and aluminum in the crystallization step and uniformly dispersed in the resulting NMC precursor particles. It may be coated on the particle surface of the NMC precursor. Furthermore, during the mixing step, it is possible to mix the lithium compound together with the NMC intermediate, and these methods may be used in combination. Regardless of which method is used, it is necessary to adjust the content so as not to deviate from the composition in the above general formula.

The evaluation method for the composition is not particularly limited, and the composition can be determined by chemical analysis techniques such as acid decomposition-ICP (inductively coupled plasma) emission spectrometry.
<Particle strength>
The particle strength is preferably 100-230 MPa, more preferably 120-200 MPa, and particularly preferably 150-180 MPa. If the particle strength is less than 100 MPa, many "cracks" may occur in the NMC particles after charging and discharging, resulting in a decrease in capacity and swelling of the battery. At that time, the filling property becomes poor, and it may become impossible to produce the positive electrode film. In addition, when a positive electrode film having poor filling properties is subjected to charge-discharge cycles, the capacity decreases significantly, resulting in extremely poor cycle characteristics.

The evaluation method for particle strength is not particularly limited, and the strength can be obtained, for example, by measuring each particle using a microcompression tester.
<Average particle size>
The average primary particle size is preferably 0.1 to 0.5 μm. This makes it possible to obtain high battery capacity and high cycle characteristics when used for the positive electrode of a battery. If the average primary particle diameter is less than 0.1 μm, high cycle characteristics may not be obtained, while if it exceeds 0.5 μm, the battery capacity and output characteristics will decrease, and sufficient battery characteristics will be obtained. may not be
Also, the average secondary particle diameter is preferably 3 to 20 μm, more preferably 6 to 12 μm. As a result, when used for the positive electrode of a battery, it is possible to achieve both high battery capacity and high fillability for the positive electrode. When the secondary particle average particle diameter is less than 3 μm, high filling properties for the positive electrode may not be obtained, while when it exceeds 20 μm, the battery capacity and output characteristics decrease, and sufficient battery characteristics cannot be obtained. sometimes not.
The evaluation method for the average particle diameter is not particularly limited, and for example, the average particle diameter can be obtained from the volume standard distribution measured using the laser diffraction/scattering method.
<Sulfate group concentration>
The sulfate radical concentration is preferably 0.5% by weight or less, more preferably 0.3% by weight or less, and particularly preferably 0.1% by weight or less. If the sulfate group concentration exceeds 0.5% by weight, the diffusion of lithium ions is inhibited and the battery capacity decreases, and the sulfate group itself hardly contributes to the charge/discharge reaction. The amount corresponding to the irreversible capacity of the battery must use an extra negative electrode material for the battery. As a result, the capacity per weight or per volume of the battery as a whole is reduced, and excess lithium is accumulated in the negative electrode as irreversible capacity, which poses a problem in terms of safety.

The evaluation method for the sulfate group concentration is not particularly limited. For example, the total sulfur content of NMC is analyzed by a combustion infrared absorption method or an acid decomposition-ICP emission spectroscopic analysis method, and the total sulfur content is determined. can be obtained by converting to a sulfate group (SO ₄ ²⁻ ).
2. Method for producing positive electrode active material for lithium ion secondary battery The method for producing NMC in the present invention comprises the steps (1) to (4) described below, and the steps (1) to (4) are performed in order. , is processed. Through these processes, a lithium-nickel-manganese-cobalt-aluminum composite oxide in which the sulfate group concentration is suppressed while maintaining high particle strength while controlling the primary particle average particle size and the secondary particle average particle size within the optimum range. is obtained.
(1) Crystallization Step Normally, when the NMC precursor is produced by a crystallization method, a continuous crystallization method is used. This method is a method for easily producing a large amount of NMC precursors having the same composition. NMC precursor particles generally obtained by a crystallization method are mainly composed of secondary particles in which primary particles are agglomerated. However, in this continuous crystallization method, the particle size distribution of the obtained NMC precursor particles tends to be a relatively wide normal distribution, and there is a problem that the particles do not necessarily have a uniform particle size. NMC prepared from NMC precursor particles having a wide particle size distribution as a raw material may contain fine powder of less than 3 μm when a lithium-ion secondary battery is assembled, which is likely to cause deterioration of cycle characteristics. Moreover, if the particle size distribution becomes uneven, the reaction resistance increases, which may adversely affect the battery output.
Therefore, in the crystallization process, for example, by clearly separating the "nucleation" stage and the "particle growth" stage, the particle size is homogenized to obtain an NMC precursor with a narrow particle size distribution. is preferred.
<Nucleation stage>
First, a water-soluble nickel salt, a manganese salt, and a cobalt salt are dissolved in water at a predetermined ratio to prepare a raw material solution A containing nickel, manganese, and cobalt. The nickel salt, manganese salt and cobalt salt used here are preferably sulfates. Subsequently, a water-soluble aluminum salt is dissolved in water at a predetermined ratio to prepare a raw material solution B containing aluminum. The aluminum salt used here is preferably an aluminate rather than a sulfate. Next, the prepared raw material solutions A and B and a solution containing an ammonium ion donor such as aqueous ammonia are supplied to a crystallization reaction tank while stirring to form a reaction solution in the reaction tank, and An alkali solution such as a sodium hydroxide solution is supplied at the same time to control the pH of the reaction solution to be constant.
In addition, a solution containing element M may optionally be added to raw material solutions A and B. However, if precipitation occurs by adding this solution, each raw material solution is simultaneously introduced into the reaction vessel through a separate route. supply. By controlling the addition amount of the alkaline solution so as to maintain a constant pH, it is possible to selectively generate minute "nuclei" of the NMC precursor in the formed reaction solution.
The pH of the reaction solution (based on a liquid temperature of 25° C.) is preferably 12.0 or higher, more preferably 12.0 to 14.0. As a result, minute "nuclei" of the NMC precursor can be selectively generated in the reaction solution. If the pH is less than 12.0, the growth of "nuclei" also occurs at the same time, so that the total number of "nuclei" is insufficient and the particle size tends to become coarse, resulting in a wide particle size distribution. The total number of "nuclei" can be controlled by the pH and ammonium ion concentration in nucleation and the amount of each raw material solution supplied.
The ammonium ion concentration of the reaction solution is preferably kept constant within the range of 3 to 15 g/L. When the ammonium ion concentration becomes unstable, the solubility of the metal ions also changes, which inhibits the formation of well-ordered NMC precursor particles and facilitates the formation of gel-like "nuclei," which tends to result in a broader particle size distribution. . Furthermore, when the ammonium ion concentration is less than 3 g/L, it does not function as a complexing agent, while when it exceeds 15 g/L, the NMC precursor particles are formed too densely, and the final product NMC is also dense. It is not preferable because it may become a structure and the specific surface area may decrease.
The temperature of the reaction solution is preferably set at 35-60°C. If the temperature is less than 35° C., the temperature is low and the metal ions to be supplied have insufficient solubility, nucleation easily occurs, and control of nucleation becomes difficult. On the other hand, when the temperature exceeds 60°C, volatilization loss of ammonia is accelerated, so that the concentration of ammonium ions as a complexing agent decreases, and the solubility of metal ions becomes insufficient as described above.
In addition, the crystallization time in the nucleation stage can be arbitrarily set depending on the target average particle size of the NMC precursor particles.
<Particle Growth Stage>
In the particle growth stage, the pH of the reaction solution (based on the liquid temperature of 25° C.) is controlled in the range of 10.5 to 12.0, and the alkaline solution is supplied into the reaction vessel to lower the pH than in the nucleation stage. . After the nucleation stage, by controlling the pH within this range, only the growth of the "nuclei" generated in the nucleation stage is preferentially caused, new nucleation is suppressed, and NMC precursors are produced. The width of the particle size distribution in the particles can be narrowed. When the pH is less than 10.5, the metal ions remaining in the reaction solution increase, resulting in deterioration of production efficiency. Particle size distribution tends to be wide. Moreover, when a sulfate is used in the raw material solution, the concentration of sulfate group remaining in the NMC precursor particles increases, which is not preferable. The ammonium ion concentration and temperature of the reaction solution may be controlled within the same range as in the nucleation stage.
Further, after the nucleation stage or during the particle growth stage, part of the reaction solution is discharged out of the reaction vessel to increase the concentration of the NMC precursor particles in the reaction solution. It is also possible to grow. As a result, the particle size distribution of the NMC precursor particles can be narrowed and the particle density can be increased.
In addition, by controlling the atmosphere in the reaction vessel during the nucleation stage and the particle growth stage, it becomes possible to control the NMC precursor and, in turn, the particle structure of the MNC. That is, by controlling the oxygen concentration in the reaction vessel, the size of the primary particles that constitute the NMC precursor particles can be adjusted, and the denseness of the NMC precursor particles can be adjusted. Therefore, by reducing the oxygen concentration in the reaction vessel to create a non-oxidizing atmosphere, the density of the NMC precursor particles is increased, and the NMC finally obtained is also highly dense, resulting in a solid structure. will have. On the other hand, by increasing the oxygen concentration in the reaction vessel to create an oxidizing atmosphere, the NMC precursor particles become less dense, and the finally obtained NMC has a hollow or porous structure. Become. In particular, in the early stages of the nucleation stage and the particle growth stage, the inside of the reaction vessel is made into an oxidizing atmosphere, and then controlled to be a non-oxidizing atmosphere. You can increase your sexuality. A positive electrode active material obtained from such NMC precursor particles has a hollow structure having a sufficiently large hollow portion. The size of the hollow portion can be controlled by adjusting the time of the oxidizing atmosphere and the time of the non-oxidizing atmosphere.
(2) Oxidizing Roasting Step In the oxidizing roasting step, the NMC precursor obtained in the crystallization step is heated in an oxidizing atmosphere at a temperature of 400 to 900° C. for 3 to 10 hours to convert the NMC intermediate. It is a process of obtaining The holding time at the oxidizing roasting temperature is preferably 3 to 10 hours, more preferably 5 to 7 hours. If it is less than 3 hours, the average primary particle diameter of the NMC intermediate becomes small, and the average primary particle diameter of NMC as the final product becomes 0.1 μm or less, resulting in a decrease in particle strength. On the other hand, after 10 hours, the specific surface area of the NMC intermediate becomes 2.0 m ² /g or less, and the reactivity between lithium and the transition metal deteriorates in the subsequent firing step, resulting in a decrease in battery capacity. Productivity deteriorates due to the extension of the baking time.

If the oxidizing roasting temperature is less than 400° C., the average primary particle size of the NMC intermediate becomes smaller, so that the average primary particle size of NMC becomes less than 0.1 μm, and the particle strength decreases. On the other hand, when the temperature exceeds 900° C., the specific surface area of the NMC intermediate becomes less than 2.0 m ² /g, the reactivity between lithium and the transition metal deteriorates in the firing process, the battery capacity decreases, and the firing time increases. Productivity deteriorates due to extension.
The oxidizing roasting atmosphere is an oxidizing atmosphere, preferably with an oxygen concentration of 18 to 100% by volume. That is, it is preferably performed in an air atmosphere and in an oxygen stream. Considering the cost, it is particularly preferable to carry out the process in an air stream. If the oxygen concentration is less than 18% by volume, the oxidation is not sufficient and there is a risk of abnormal growth of primary particles.

The heating furnace used for oxidizing roasting is not particularly limited as long as it can be used in an air atmosphere and an oxygen stream, but an electric furnace that does not generate gas is preferable, batch type or continuous type. of heating furnace is used. Further, a rotary kiln or a fluidized bed roasting furnace, which has good gas replacement properties, heat exchange efficiency and productivity, is particularly preferable from an industrial point of view.
(3) Mixing step In the mixing step, the NMC intermediate obtained in the oxidizing roasting step is added to the atomic number of lithium (Li) with respect to the total atomic number (Me) of the metal elements excluding lithium (Li / Me ) is a step of mixing lithium compounds to obtain a lithium mixture so that the ratio is 0.95 to 1.20. When Li/Me is less than 0.95, the resulting lithium-ion secondary battery using NMC has a large reaction resistance of the positive electrode, resulting in a low battery output. As a result, the initial discharge capacity of the obtained NMC decreases, and the reaction resistance of the positive electrode also increases.

Although the lithium compound is not particularly limited, lithium hydroxide, lithium carbonate, or a mixture thereof can be preferably used. Considering ease of handling and stability of quality, it is more preferable to use lithium carbonate.

The NMC intermediate and lithium compound are preferably thoroughly mixed. A general mixer can be used for the mixing operation. For example, a shaker mixer, a Loedige mixer, a Julia mixer, a V blender, or the like can be used, and the NMC intermediate particles are sufficiently mixed with the lithium compound so as not to be broken.
(4) Firing step In the firing step, the lithium mixture obtained in the mixing step is fed with carbon dioxide in a low-oxygen atmosphere in which the oxygen concentration is reduced from that in the air at a temperature of 700 to 1000 ° C. for 5 to 20 hours. It is a step of obtaining NMC of the final product by heating. If the firing temperature is less than 700°C, the reaction between the NMC intermediate and the lithium compound is difficult to progress, and the diffusion of lithium into the NMC intermediate is insufficient. Since it is not aligned, the battery capacity and output characteristics are degraded. On the other hand, if the firing temperature exceeds 1000° C., intense sintering occurs between the NMC particles, forming sintered agglomerates that hinder the adjustment of the particle size by the crushing process. The fillability of the battery deteriorates greatly, resulting in a decrease in battery capacity.
The holding time at the firing temperature is preferably 5 to 20 hours, more preferably 5 to 10 hours. If the firing time is less than 5 hours, the formation of NMC will be insufficient. On the other hand, if the firing time exceeds 20 hours, the NMC particles will be violently sintered, the battery capacity will decrease, and the productivity will deteriorate due to the extension of the firing time.

The firing atmosphere is a low-oxygen atmosphere, but it is preferable to flow carbon dioxide and control the oxygen concentration to 0.1 to 20% by volume. If the oxygen concentration exceeds 20% by volume, the crystallinity of NMC may not be uniform, and an improvement in particle strength may not be observed. Crystallinity is greatly improved by growing crystals in a low-oxygen atmosphere, and an improvement in particle strength can be confirmed in a normal firing time. This is because oxygen deficiency occurs in a part of the heating furnace due to the low oxygen concentration, but starting from the oxygen deficiency part, the crystallinity is rapidly improved, contributing to the improvement of the grain strength. it is conceivable that.

The heating furnace used for firing is not particularly limited as long as it can be used in a low-oxygen atmosphere, but an electric furnace that does not generate gas is preferable, and a batch-type or continuous-type heating furnace is used.

Under the above sintering conditions, the NMC particles to be obtained are suppressed from forming sintered lumps due to severe sintering, but slight sintering may occur. In such a case, it is possible to further include a crushing step of crushing the obtained NMC particles. As a crushing method, known means can be used, for example, a pin mill or a hammer mill can be used. At this time, it is preferable to adjust the crushing force to an appropriate range so as not to destroy the secondary particles.
3. Lithium ion secondary battery]
Next, a lithium ion secondary battery using NMC manufactured according to the embodiment of the present invention as a positive electrode active material will be described. The above-mentioned lithium ion secondary battery (hereinafter also referred to as "secondary battery") includes components such as a positive electrode, a negative electrode, a separator, and a non-aqueous electrolytic solution, which are the same as those of a general lithium ion secondary battery.
(1) Constituent member <positive electrode>
Using the NMC described above as a positive electrode active material, for example, a positive electrode for a lithium ion secondary battery is produced as follows.

First, NMC according to the present embodiment is mixed with a conductive material and a binder, and if necessary, activated carbon and a solvent for adjusting viscosity are added, and these are kneaded to prepare a positive electrode mixture paste. . At that time, the mixing ratio of each component in the positive electrode mixture paste is also an important factor that determines the performance of the lithium ion secondary battery. For example, when the solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, the NMC content is 60 to 95 parts by mass and the conductive material is included, as in the positive electrode of a general lithium ion secondary battery. The amount can be 1 to 20 parts by weight and the binder content can be 1 to 20 parts by weight. In particular, in order to obtain a battery with a high capacity, it is more preferable to produce a highly filled positive electrode with an NMC content of 90 to 95 parts by mass.

The obtained positive electrode mixture paste is applied, for example, to the surface of a current collector made of aluminum foil and dried to scatter the solvent. If necessary, pressure may be applied by a roll press or the like in order to increase the electrode density. In this manner, a sheet-like positive electrode can be produced. The sheet-like positive electrode is cut into an appropriate size according to the intended battery and used for manufacturing the battery. The method for producing the positive electrode is not limited to the above method, and other methods may be used.

Examples of conductive materials that can be used include graphite (natural graphite, artificial graphite, expanded graphite, etc.) and carbon black-based materials such as acetylene black and ketjen black.

Binders play a role in binding NMC particles, and examples thereof include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, and cellulose resin. Alternatively, polyacrylic acid can be used.

In addition, if necessary, a solvent for dispersing NMC, a conductive material and activated carbon and dissolving a binder can be added to the positive electrode mixture. can be used. In addition, activated carbon can be added to the positive electrode mixture in order to increase the electric double layer capacity. When manufacturing a sheet-shaped positive electrode, the positive electrode mixture paste is rolled and stretched. may crack and the cycle characteristics may deteriorate. However, if the NMC of the present invention with a particle strength adjusted to 100 to 230 MPa is used as a positive electrode active material, it is possible to prevent particle cracking and a decrease in filling rate of the positive electrode active material during electrode production. Moreover, although the battery may swell due to particle cracking of the positive electrode active material, the swelling can be suppressed by using the NMC as the positive electrode active material.
<Negative Electrode>
Metallic lithium, a lithium alloy, or the like can be used for the negative electrode. In addition, a binder is mixed with a negative electrode active material capable of intercalating and deintercalating lithium ions, and an appropriate solvent is added to form a paste-like negative electrode mixture. It can then be dried and used as a compacted form to increase electrode density if desired.

Examples of negative electrode active materials include lithium-containing substances such as metallic lithium and lithium alloys, natural graphite capable of intercalating and deintercalating lithium ions, artificial graphite, calcined organic compounds such as phenolic resins, and carbon such as coke. A powder form of the substance can be used. In this case, a fluororesin such as PVDF can be used as the binder for the negative electrode in the same manner as the binder for the positive electrode, and a solvent for dispersing the active material and the binder includes N-methyl-2-pyrrolidone. of organic solvents can be used.
<Separator>
The separator is sandwiched between the positive electrode and the negative electrode, and has the function of separating the positive electrode and the negative electrode and retaining the electrolyte. As such a separator, for example, a thin film made of polyethylene, polypropylene, or the like and having a large number of fine pores can be used. do not have.
<Non-aqueous electrolytic solution>
The non-aqueous electrolytic solution is obtained by dissolving a lithium salt as a supporting salt in an organic solvent. Examples of organic solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and trifluoropropylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate and dipropyl carbonate; and ether compounds such as dimethoxyethane, sulfur compounds such as ethyl methyl sulfone and butane sultone, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate, etc., alone or in combination of two or more. can be done.

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN(CF ₃ SO ₂ ) ₂ and their composite salts can be used. In addition, the non-aqueous electrolytic solution may contain a radical scavenger, a surfactant, a flame retardant, and the like.
<Lithium ion secondary battery>
The lithium-ion secondary battery according to the embodiment of the present invention can have various shapes such as a cylindrical shape and a laminated shape. Regardless of which shape is adopted, the positive electrode and the negative electrode are laminated with a separator interposed to form an electrode body, the obtained electrode body is impregnated with a non-aqueous electrolyte, and the positive electrode current collector and the outside are impregnated. A current collector is connected to the positive electrode terminal, and the negative electrode current collector and the negative electrode terminal to the outside are connected using a current collecting lead or the like, and sealed in the battery case to complete the lithium ion secondary battery. .
<Characteristics of non-aqueous electrolyte secondary battery)
As described above, the non-aqueous electrolyte secondary battery according to the embodiment of the present invention uses the NMC according to the present embodiment as a positive electrode active material, so that the negative electrode resistance is reduced, thereby improving the battery capacity, output characteristics, and cycle performance. Excellent characteristics. Moreover, this lithium ion secondary battery is superior not only in particle strength but also in thermal stability and safety, even when compared with conventional secondary batteries using NMC particles as a positive electrode active material.

FIG. 1 is a schematic cross-sectional view of a coin battery used for evaluation of battery characteristics. For example, when the NMC according to the embodiment of the present invention is used as a positive electrode active material to configure the 2032 type coin battery shown in FIG. 1, the initial discharge capacity is 155 mAh / g or more while maintaining the particle strength at 100 to 230 MPa. , the 500 cycle capacity retention rate can be 75% or more, and the swelling rate can be 105% or less.
<Application>
As described above, the non-aqueous electrolyte secondary battery according to the embodiment of the present invention is excellent in battery capacity, output characteristics and cycle characteristics, and small portable electronic devices (smartphones, etc.) that require these characteristics at a high level. It can be suitably used as a power supply for tablets, mini laptops, etc.). In addition, the non-aqueous electrolyte secondary battery according to the embodiment of the present invention is also excellent in safety, and not only can it be made smaller and have a higher output, but it can also simplify an expensive protection circuit. Therefore, it can be suitably used as a power source for transportation equipment that is limited in mounting space.

The present invention will be specifically described using examples, but the technical scope of the present invention is not limited by these examples. In addition, regarding the present examples, NMC (positive electrode active material) and each reagent used in manufacturing the lithium ion secondary battery are all special grade reagents manufactured by Wako Pure Chemical Industries, Ltd.
The evaluation methods in Examples (and Comparative Examples) are as follows, and the obtained evaluation results are shown in Table 1.
(1) NMC (positive electrode active material)
1) Composition The composition is obtained by subjecting 1 g of a sample to thermal decomposition treatment with an inorganic acid and adding pure water to a constant volume of 100 ml to obtain an analysis specimen solution, then diluting the analysis specimen solution as appropriate and using a multi-type ICP emission spectrometer. was measured using ICPE-9000 (manufactured by Shimadzu Corporation).
2) Particle strength Particle strength was calculated by applying a load to one NMC particle with an indenter using a micro-strength evaluation tester MCT-500 (manufactured by Shimadzu Corporation) and calculating the particle strength at the time of destruction. Specifically, the NMC particles were stationary on a silicon plate, the position was finely adjusted to match the center of the indenter, and the indenter was brought into contact with the NMC particles to the extent that a large load was not applied, and the measurement was performed. . The measurement conditions were a test force of 150 mN and a load rate of 2.0 mN/sec, and the average value of 10 particles was obtained.
3) Average Particle Size The average particle size was obtained from the volume standard distribution measured using a Microtrac MT3300EX2 (manufactured by Microtrac Bell Co., Ltd.), which is a laser diffraction/scattering type particle size distribution analyzer. By adjusting the irradiation intensity of ultrasonic waves to the sample, separate measurement of the primary particle average particle size and the secondary particle average particle size was performed.
4) Sulfate Group Concentration The sulfate group content was obtained by analyzing the total sulfur content by acid decomposition-ICP emission spectrometry, and converting the total sulfur content into sulfate groups (SO ₄ ^2- ). . For the measurement, ICPE-9000 (manufactured by Shimadzu Corporation), which is a multi-type ICP emission spectrometer, was used.
(2) Lithium-ion secondary battery 1) Initial discharge capacity The initial discharge capacity is obtained by leaving a coin battery or a small rectangular battery for about 24 hours after production, and the open-circuit voltage OCV (open-circuit-voltage) is stable. Then, the battery was charged to a cut-off voltage of 4.3 V at a current density of 0.1 mA/cm ² to the positive electrode, and discharged to a cut-off voltage of 3.0 V after resting for 1 hour. A multi-channel voltage/current generator R6741A (manufactured by Advantest Co., Ltd.) was used to measure the discharge capacity.
2) Cycle characteristics The charge/discharge test described above was repeated, and the 500-cycle capacity retention rate was calculated by measuring the 500th discharge capacity relative to the initial discharge capacity.
3) Swelling amount The swelling amount of the lithium-ion compact prismatic battery was calculated using the following formula.
Swelling amount (%) = (battery thickness after 500 cycles)/(battery thickness after 1st cycle) x 100

<Crystallization step>
First, a 60 L reaction tank is filled with half the amount of water, and while stirring in the air, the temperature inside the tank is set to 40°C, and appropriate amounts of 25 wt% sodium hydroxide solution and 25 wt% aqueous ammonia In addition, the pH of the liquid in the tank (based on the liquid temperature of 25° C.) was adjusted to 12.8, and the ammonium ion concentration was adjusted to 10 g/L. Next, a 2.0 mol/L raw material solution (metal element molar ratio of Ni:Co:Mn=55:20:25) obtained by dissolving and mixing nickel sulfate, cobalt sulfate, and manganese sulfate was added at 0.13 L/min. The solution was supplied to obtain a reaction solution. At the same time, 25% by mass sodium hydroxide solution and 25% by mass aqueous ammonia were added at a constant rate, and crystallization was performed for 2 minutes and 30 seconds while controlling the pH at 12.8 (nucleation pH). After that, nitrogen gas is supplied to reduce the oxygen concentration in the reaction tank to 2% by volume or less, and the 25% by mass sodium hydroxide solution is temporarily supplied until the pH reaches 11.6 (nuclear growth pH). After stopping and reaching a pH of 11.6, the feed of 25% by weight sodium hydroxide solution was adjusted to match the added amount of sodium aluminate solution and restarted. Crystallization was continued for 4 hours while controlling the pH at 11.6, and the crystallization was completed. After completion of crystallization, the product was washed with water, _filtered and _dried to obtain an _NMC precursor represented by _{Ni0.54Mn0.24Co0.19Al0.03} (OH) ₂ .
<Oxidizing roasting process>
The NMC precursor obtained in the crystallization step is placed in a heating container made of magnesia, and treated in an air atmosphere using a closed electric furnace under the conditions of an oxidizing roasting temperature of 400 ° C. and an oxidizing roasting time of 5 hours. After that _, the oxidized roast _was cooled to room _temperature to obtain an NMC intermediate represented by _{Ni0.54Mn0.24Co0.19Al0.03O} .
<Mixing process>
The NMC intermediate obtained in the oxidative roasting process and lithium carbonate weighed so that Li/Me = 1.03 were mixed together in a shaker mixer, TURBULA-Type T2C (manufactured by Willie & Bacchofen (WAB)). to obtain a lithium mixture.
<Baking process>
The lithium mixture obtained in the mixing step is placed in a heating container made of magnesia, and using a closed electric furnace, carbon dioxide is supplied into the furnace under the conditions of 0.5 to 20 L / min, and the oxygen concentration in the furnace is increased. 18% by volume and maintained in a low-oxygen atmosphere at a firing temperature of 850° C. and a firing time of ₁₀ hours _. An _NMC (positive _electrode active material) represented _{by 54Mn0.24Co0.19Al0.03O2} was obtained _.
<Production of battery>
52.5 mg of the obtained NMC, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene resin (PTFE) were weighed and mixed, and molded at a pressure of 100 MPa to a thickness of 100 μm, and the positive electrode shown in FIG. (Evaluation electrode) (1) was produced. Furthermore, after drying the positive electrode (1) at 120° C. for 12 hours in a vacuum dryer, a 2032 type coin battery using the positive electrode (1) was dried in a glove in an argon gas atmosphere with a controlled dew point of −80° C. Made in a box. Lithium metal or carbon with a thickness of 1 mm is used for the negative electrode (2), and ethylene carbonate ( _EC ) and diethyl carbonate (EC) and diethyl carbonate ( DEC) (manufactured by Tomiyama Pharmaceutical Co., Ltd.) was used. A polyethylene porous film having a film thickness of 25 μm was used for the separator (3). A 2032-type coin battery had a gasket (4) and a wave washer (5), and was assembled into a battery with a positive can (6) and a negative can (7).

The same procedure as in Example 1 was performed except for the following conditions.
<Oxidizing roasting process>
The oxidation roasting temperature was set to 500°C.

The same procedure as in Example 1 was performed except for the following conditions.
<Oxidizing roasting process>
The oxidation roasting temperature was 600°C.

The same procedure as in Example 1 was performed except for the following conditions.
<Oxidizing roasting process>
The oxidation roasting temperature was 600°C.
<Baking process>
The oxygen concentration in the furnace was set to 0.2% by volume.

The same procedure as in Example 1 was performed except for the following conditions.
<Oxidizing roasting process>
The oxidation roasting temperature was set at 700°C.

The same procedure as in Example 1 was performed except for the following conditions.
<Oxidizing roasting process>
The oxidation roasting temperature was 800°C.

The same procedure as in Example 1 was performed except for the following conditions.
<Oxidizing roasting process>
The oxidation roasting temperature was 900°C.

The same procedure as in Example 1 was performed except for the following conditions.
<Crystallization step>
As the element M, tungsten was added so that the Z value of the general formula: Li _v Ni _{1-wxyz Mnw} Co _x Al _y M _z O _2+α was 0.03.

The same procedure as in Example 1 was performed except for the following conditions.
<Crystallization step>
As the element M, tungsten was added so that the Z value of the general formula: Li _v Ni _{1-wxyz Mnw} Co _x Al _y M _z O _2+α was 0.03.
<Oxidizing roasting process>
The oxidation roasting temperature was 600°C.

The same procedure as in Example 1 was performed except for the following conditions.
<Crystallization step>
As the element M, tungsten was added so that the Z value of the general formula: Li _v Ni _{1-wxyz Mnw} Co _x Al _y M _z O _2+α was 0.03.
<Oxidizing roasting process>
The oxidation roasting temperature was 600°C.
<Baking process>
The oxygen concentration in the furnace was set to 0.2% by volume.

The same procedure as in Example 1 was performed except for the following conditions.
<Crystallization step>
As the element M, tungsten was added so that the Z value of the general formula: Li _v Ni _{1-wxyz Mnw} Co _x Al _y M _z O _2+α was 0.03.
<Oxidizing roasting process>
The oxidation roasting temperature was 800°C.

The same procedure as in Example 1 was performed except for the following conditions.
<Crystallization step>
Molybdenum and niobium were added as _the element M so that _the Z value of the general formula: _{LivNi1 - wxyzMnwCoxAlyMzO2 +α was} 0.03. Equal amounts of molybdenum and niobium were added so that the total amount was 0.03 in Z value.
<Oxidizing roasting process>
The oxidation roasting temperature was 800°C.

The same procedure as in Example 1 was performed except for the following conditions.
<Crystallization step>
As the element M, vanadium and _magnesium were added so that the Z value of the general formula _{: LivNi1 - wxyzMnwCoxAlyMzO2 +α was} 0.06. Equal amounts of vanadium and magnesium were added so that the total amount was 0.06 in Z value.

The same procedure as in Example 1 was performed except for the following conditions.
<Crystallization step>
As the element _{M , titanium and silicon were added so that the Z value of the general formula: LivNi1-wxyzMnwCoxAlyMzO2 + α was 0.06 .} Titanium and silicon were each added in equal amounts and added so that the total amount would be 0.06 in the Z value.
<Oxidizing roasting process>
The oxidation roasting temperature was 800°C.

The same procedure as in Example 1 was performed except for the following conditions.
<Crystallization step>
Zinc, copper, and iron were added as the element _M so that _the Z value of the general formula: _{LivNi1 - wxyzMnwCoxAlyMzO2 +α was} 0.09. Equal amounts of zinc, copper, and iron were added so that the total amount would be 0.09 in the Z value.
[Comparative Example 1]
The same procedure as in Example 1 was performed except for the following conditions.
<Oxidizing roasting process>
No oxidative roasting was performed.
<Baking process>
The inside of the furnace was made into an atmospheric atmosphere (state in which the oxygen concentration exceeded 20% by volume).
[Comparative Example 2]

The same procedure as in Example 1 was performed except for the following conditions.
<Oxidizing roasting process>
The oxidation roasting temperature was 300°C.
<Baking process>
The inside of the furnace was made into an atmospheric atmosphere (state in which the oxygen concentration exceeded 20% by volume).
[Comparative Example 3]

The same procedure as in Example 1 was performed except for the following conditions.
<Oxidizing roasting process>
The oxidation roasting temperature was set to 1000°C.
<Baking process>
The inside of the furnace was made into an atmospheric atmosphere (state in which the oxygen concentration exceeded 20% by volume).
[Comparative Example 4]

The same procedure as in Example 1 was performed except for the following conditions.
<Crystallization step>
As the element M, tungsten was added so that the Z value of the general formula: Li _v Ni _{1-wxyz Mnw} Co _x Al _y M _z O _2+α was 0.03.
<Oxidizing roasting process>
No oxidative roasting was performed.
<Baking process>
The inside of the furnace was made into an atmospheric atmosphere (state in which the oxygen concentration exceeded 20% by volume).
[Comparative Example 5]

The same procedure as in Example 1 was performed except for the following conditions.
<Crystallization step>
As the element M, tungsten was added so that the Z value of the general formula: Li _v Ni _{1-wxyz Mnw} Co _x Al _y M _z O _2+α was 0.03.
<Oxidizing roasting process>
The oxidation roasting temperature was 300°C.
<Baking process>
The inside of the furnace was made into an atmospheric atmosphere (state in which the oxygen concentration exceeded 20% by volume).
[Comparative Example 6]

The same procedure as in Example 1 was performed except for the following conditions.
<Crystallization step>
As the element M, tungsten was added so that the Z value of the general formula: Li _v Ni _{1-wxyz Mnw} Co _x Al _y M _z O _2+α was 0.03.
<Oxidizing roasting process>
The oxidation roasting temperature was set to 1000°C.
<Baking process>
The inside of the furnace was made into an atmospheric atmosphere (state in which the oxygen concentration exceeded 20% by volume).
[Comparative Example 7]

The same procedure as in Example 1 was performed except for the following conditions.
<Crystallization step>
Molybdenum and niobium were added as _the element M so that _the Z value of the general formula: _{LivNi1 - wxyzMnwCoxAlyMzO2 +α was} 0.03. Equal amounts of molybdenum and niobium were added so that the total amount was 0.03 in Z value.
<Oxidizing roasting process>
No oxidative roasting was performed.
<Baking process>
The inside of the furnace was made into a large atmosphere (state in which the oxygen concentration exceeded 20% by volume).
(Comparative Example 8)

The same procedure as in Example 1 was performed except for the following conditions.
<Crystallization step>
Zinc, copper, and iron were added as the element _M so that _the Z value of the general formula: _{LivNi1 - wxyzMnwCoxAlyMzO2 +α was} 0.09. Equal amounts of zinc, copper, and iron were added so that the total amount would be 0.09 in the Z value.
<Oxidizing roasting process>
No oxidative roasting was performed.
<Baking process>
The inside of the furnace was made into an atmospheric atmosphere (state in which the oxygen concentration exceeded 20% by volume).

[Comprehensive evaluation]
As can be seen from Table 1 above, in the NMC of Examples 1 to 15, the conditions such as the oxidizing roasting temperature and the firing atmosphere were all within the preferable range in the manufacturing process, so the particle strength and the primary particle average The particle size, secondary particle average particle size, and sulfate radical concentration all showed favorable values. This result indicates that the optimum positive electrode active material for lithium ion secondary batteries has been developed in order to obtain excellent lithium ion secondary batteries with improved safety in addition to discharge capacity and durability. there is Therefore, using the NMCs of Examples 1 to 15, lithium ion secondary batteries were produced and their characteristics were evaluated. The swelling ratio was 105% or less, which was also a very good value.
On the other hand, the NMC of Comparative Examples 1 to 8 did not undergo the oxidizing roasting process in the manufacturing process, and the conditions such as the oxidizing roasting temperature were not preferable, so in addition to the particle strength, the primary particles Any one of the average particle size, the average particle size of the secondary particles, and the concentration of sulfate radicals did not reach a sufficient value. Moreover, using the NMCs of Comparative Examples 1 to 8, lithium ion secondary batteries were produced and their characteristics were evaluated. It was far inferior to the examples.

1 positive electrode (evaluation electrode)
2 negative electrode (lithium metal or carbon)
3 Separator 4 Gasket 5 Wave washer 6 Positive electrode can 7 Negative electrode can

Claims (1)

A method for producing a positive electrode active material for a high-strength lithium ion secondary battery used in the positive electrode of a lithium ion secondary battery having a swelling amount of 105% or less,
The positive electrode active material _for a high-strength lithium ion secondary battery has _a general formula _{: LivNi1 -wxyzMnwCoxAlyMzO2 + α} (where 0.95<v<1. 22, 0.01 ≤ w ≤ 0.35, 0.01 ≤ x ≤ 0.50, 0.01 ≤ y ≤ 0.15, 0 ≤ z ≤ 0.10, 0 ≤ α ≤ 0.20; M is represented by one or more elements selected from W, V, Mg, Mo, Nb, Ti, Si, Zn, Cu, and Fe) Lithium nickel consisting mainly of secondary particles in which primary particles are aggregated The manganese-cobalt-aluminum composite oxide has a particle strength of 100 to 230 MPa, an average primary particle diameter of 0.1 to 0.5 μm, an average secondary particle diameter of 3 to 20 μm, and a sulfate ion concentration of 0. .5% by weight or less,
By feeding and mixing at least a solution containing nickel, manganese and cobalt, a solution containing aluminum, a solution containing an ammonium ion donor, an alkaline solution and optionally a solution containing element M into a reaction vessel , a crystallization step of crystallizing the metal composite hydroxide;
an oxidizing roasting step of obtaining a metal composite oxide by oxidizing roasting the metal composite hydroxide obtained in the crystallization step at 400 to 900 ° C.;
A mixing step of obtaining a lithium mixture by mixing the metal composite oxide obtained in the oxidizing roasting step and a lithium compound;
and a firing step of obtaining a lithium metal composite oxide by firing the lithium mixture obtained in the mixing step at 700 to 1000° C. while controlling the oxygen concentration to 0.1 to 20% by volume. A method for producing a positive electrode active material for a high-strength lithium ion secondary battery, characterized by:

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