JP2024008824A - Positive electrode material for lithium ion secondary battery, and production method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for production of a positive electrode material superior in output in low SOC while keeping discharge capacity.

SOLUTION: A method for production of a positive electrode material for a lithium ion secondary battery comprises the steps of: sintering a mixture containing a lithium compound, a nickel-containing composite compound, and a molybdenum compound to gain first particles containing a lithium transition metal composite oxide, in which the ratio of a mole number of nickel to a total mole number of metal, excluding lithium in its composition is over 0.6 and below 1; and bringing the first particle into contact with a liquid medium so that the concentration of a solid content of the first particles is 20 mass% or more and 80 mass% or less, thereby removing part of a molybdenum element included in the first particles to gain second particles.

SELECTED DRAWING: None

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to a positive electrode material for lithium ion secondary batteries and a method for manufacturing the same.

Lithium transition metal composite oxides such as lithium cobalt oxide, lithium nickel oxide, nickel cobalt lithium manganate, etc. are used in the manufacturing method of positive electrode materials for lithium ion secondary batteries. A lithium-nickel composite oxide with a high proportion of nickel instead of cobalt, which is a rare resource, has the advantage of high charge/discharge capacity per unit weight. However, in a lithium-nickel composite oxide with a high nickel ratio, reduction of nickel is likely to occur, and the output may deteriorate in a low state of charge (low SOC).

Patent Document 1 states that by washing a lithium composite transition metal oxide containing tungsten with water to remove tungsten remaining on the surface, excellent capacity characteristics, life characteristics, resistance characteristics, and high temperature safety can be achieved. Are listed.

Patent Document 2 discloses that a high discharge capacity retention rate can be obtained by coating at least a portion of the surface of a lithium sodium nickel cobalt composite oxide with a lithium ion conductive oxide made of a compound containing molybdenum and lithium. Are listed.

Special table 2020-501310 JP2020-123441

Positive electrode materials for lithium ion secondary batteries, particularly positive electrode materials with a high nickel ratio such as a nickel molar ratio exceeding 0.6, are required to further improve output characteristics at low SOC. Therefore, an object of the present invention is to provide a method for manufacturing a positive electrode material that maintains discharge capacity and has better output characteristics at low SOC.

The first aspect is a method for producing a positive electrode material for a lithium ion secondary battery. A method for producing a positive electrode material for a lithium ion secondary battery involves firing a mixture containing a lithium compound, a nickel-containing composite compound, and a molybdenum compound, and determining the ratio of the number of moles of nickel to the total number of moles of metals other than lithium in the composition. a step of obtaining first particles containing a lithium-transition metal composite oxide having a particle diameter of more than 0.6 and less than 1; The method includes the step of removing a part of the molybdenum element contained in the first particles by bringing the first particles into contact with a liquid medium to obtain second particles.

The second aspect is a positive electrode material for a lithium ion secondary battery. The positive electrode material for lithium ion secondary batteries is an oxide containing lithium, nickel, and molybdenum, in which the ratio of the number of moles of nickel to the total number of moles of metals other than lithium in the composition is more than 0.6 and less than 1. The total number of moles of metals other than lithium contained in the filtered powder obtained by filtering the slurry after mixing 200 g of the oxide particles and 165 g of pure water and stirring for 30 minutes. The ratio of the number of moles of molybdenum to the total number of moles of metals other than lithium in the oxide particles before filtration is 0.55 times or more.

According to this, it is possible to provide a method for manufacturing a positive electrode material that maintains discharge capacity and has better output characteristics at low SOC.

Embodiments of the present invention will be described in detail below. However, the embodiments shown below illustrate a method for manufacturing a positive electrode material for a lithium ion secondary battery in order to embody the technical idea of the present invention, The method of manufacturing the material is not limited to this. Further, the content of each component in the composition means the total amount of the plurality of substances present in the composition, unless otherwise specified, when a plurality of substances corresponding to each component are present in the composition. The average particle size of particles such as raw materials is the center particle size of particles corresponding to 50% of the cumulative volume from the small particle size side of the particle size distribution obtained by the laser scattering method.

A method for producing a positive electrode material for a lithium ion secondary battery involves firing a mixture containing a lithium compound, a nickel-containing composite compound, and a molybdenum compound, and determining the ratio of the number of moles of nickel to the total number of moles of metals other than lithium in the composition. a step of obtaining first particles containing a lithium-transition metal composite oxide having a particle diameter of more than 0.6 and less than 1; and a step of removing a part of the molybdenum element contained in the first particles by bringing the particles into contact with a liquid medium to obtain second particles. In addition, other steps such as a preparation step for preparing a nickel-containing composite compound may be included as necessary.

A mixture containing a lithium compound, a nickel-containing composite compound, and a molybdenum compound is fired to obtain first particles containing a lithium transition metal composite oxide in which the molar ratio of nickel is more than 0.6 and less than 1. Thereafter, the second particles obtained by contacting the first particles with a liquid medium are applied to a lithium ion secondary battery to further improve output characteristics at low SOC while maintaining discharge capacity. Can be done. For example, this can be considered as follows. When obtaining second particles by bringing the first particles into contact with a liquid medium, part of the molybdenum contained in the first particles is removed, so that some molybdenum compounds are reduced in the second particles obtained. The specific surface area increases as well. Furthermore, molybdenum compounds tend to be less likely to segregate than tungsten and the like. Therefore, when a molybdenum compound is used, voids may be formed due to the molybdenum compound being removed throughout the particle during cleaning by contact with a liquid medium. As a result, when the obtained second particles are used in a battery, it is thought that the movement of lithium ions is promoted not only on the surface of the particles but also inside the particles, and the resistance is improved. Not only does the increase in specific surface area improve the output characteristics, but by removing a portion of the molybdenum, it is thought that the remaining molybdenum contributes to improving the output at low SOC while suppressing a decrease in discharge capacity. This improvement in output characteristics at low SOC is effective when the first particle contains a lithium transition metal composite oxide with a nickel ratio exceeding 0.6, and the resistance tends to increase at low SOC. It is thought that the remaining molybdenum in the first particles reduces this increase in resistance. An example of a method for manufacturing a positive electrode material for a lithium ion secondary battery (hereinafter also simply referred to as positive electrode material) will be described below.

(Preparation process)
In the preparation step, a nickel-containing composite compound is prepared. The precursor may be appropriately selected and prepared from commercially available products, or may be prepared by preparing a nickel-containing complex oxide having a desired structure by a conventional method. Here, the nickel-containing complex compound includes a complex oxide or complex hydroxide containing nickel, a complex oxide or complex hydroxide containing nickel and a metal other than nickel (for example, cobalt, manganese, aluminum, titanium, niobium, etc.) Examples include.

As a method for obtaining a nickel-containing composite compound having a desired composition, there is a method in which raw material compounds (hydroxide, carbonate compounds, etc.) are mixed according to the desired composition and decomposed into a nickel-containing composite oxide by heat treatment. A nickel-containing composite oxide is prepared as a nickel-containing composite compound by preparing a solution in which nickel is dissolved, obtaining a precursor precipitate having the desired composition by adjusting the temperature, adjusting the pH, adding a complexing agent, etc., and heat-treating the precursor precipitate. Examples include a coprecipitation method to obtain An example of a method for producing a nickel-containing composite oxide (hereinafter also simply referred to as a composite oxide) will be described below.

The method of obtaining a composite oxide by the coprecipitation method includes a seed generation step in which seed crystals are obtained by adjusting the pH etc. of a mixed solution containing metal ions at a desired composition ratio, and a seed generation step in which the generated seed crystals are grown to obtain the desired crystal. The method can include a crystallization step for obtaining a composite hydroxide having characteristics, and a step for heat-treating the obtained composite hydroxide to obtain a composite oxide.

In the seed generation step, a liquid medium containing seed crystals is prepared by adjusting the pH of a mixed solution containing nickel ions at a desired composition ratio, for example, from 11 to 13. The seed crystals can include, for example, a hydroxide containing nickel in a desired proportion. A mixed solution can be prepared by dissolving nickel salt in water at a desired ratio. Examples of nickel salts include sulfates, nitrates, hydrochlorides, and the like. In addition to the nickel salt, the mixed solution may optionally contain other metal salts in a desired composition ratio. The temperature in the seed generation step can be, for example, from 40°C to 80°C. The atmosphere in the seed generation step can be a low oxidizing atmosphere, for example, the oxygen concentration may be maintained at 10% by volume or less.

In the crystallization step, the generated seed crystals are grown to obtain a nickel-containing precursor precipitate having desired properties. The growth of the seed crystals can be carried out, for example, by adding nickel ions and optionally other metal ions to a liquid medium containing the seed crystals, while maintaining its pH in the range of, for example, 7 to 12.5, preferably 7.5 to 12. This can be done by adding a mixed solution containing. The addition time of the mixed solution is, for example, 1 hour to 24 hours, preferably 3 hours to 18 hours. The temperature in the crystallization step can be, for example, from 40°C to 80°C. The atmosphere in the crystallization step is the same as in the seed generation step.

Adjustment of pH in the seed generation step and the crystallization step can be carried out using an acidic aqueous solution such as a sulfuric acid aqueous solution or a nitric acid aqueous solution, an alkaline aqueous solution such as a sodium hydroxide aqueous solution, or an aqueous ammonia solution.

In the crystallization step, it is desirable to control the particle size of the precursor precipitate. The particle size of the precursor precipitate can be controlled by adjusting the temperature, pH, stirring speed, etc. of the reaction field. Further, these conditions can be adjusted as appropriate depending on actual conditions such as the shape of the container housing the reaction field, the starting materials, and the rate at which the starting materials are introduced into the reaction field. Furthermore, it is possible to control the particle size of the precursor precipitate by adjusting the aging time after the precipitation of the precursor precipitate starts, the stirring speed, etc. The conditions at this time may also be adjusted as appropriate depending on the actual conditions, since the growth rate, shape, etc. of the particles vary depending on the shape of the reaction vessel.

In the step of obtaining the composite oxide, the composite oxide is obtained by heat-treating the precursor precipitate containing the composite hydroxide obtained in the crystallization step. The heat treatment may be performed, for example, by heating the composite hydroxide at a temperature of 500°C or lower, preferably 350°C or lower. Further, the temperature of the heat treatment may be, for example, 100°C or higher, preferably 200°C or higher. The heat treatment time may be, for example, 0.5 to 48 hours, preferably 5 to 24 hours. The atmosphere for the heat treatment may be the air or an atmosphere containing oxygen. The heat treatment may be performed using, for example, a box furnace, rotary kiln, pusher furnace, roller hearth kiln, or the like.

The resulting composite oxide may contain other metal elements in addition to nickel. Other metals include cobalt, manganese, aluminum, titanium, niobium, etc., preferably at least one selected from the group consisting of these, and at least one selected from the group consisting of cobalt, manganese, and aluminum. It is preferable to include. When the composite oxide contains other metals, the mixed aqueous solution from which the precursor precipitate is obtained may contain other metal ions in a desired configuration. Thereby, a composite oxide having a desired composition can be obtained by making the precursor precipitate contain nickel and other metals and heat-treating the precursor precipitate.

The average particle size of the composite oxide is, for example, 2 μm or more and 30 μm or less, preferably 3 μm or more and 25 μm or less. The average particle size of the composite oxide is a volume average particle size, and is a value at which the volume integrated value from the small particle size side in the volume distribution obtained by the laser scattering method is 50%.

In the nickel-containing composite compound, the ratio of the number of moles of nickel to the total number of moles of metal contained in the nickel-containing composite compound may be, for example, greater than 0.6 and less than 1. The ratio of the number of moles of nickel to the total number of moles of metals contained in the nickel-containing composite compound is preferably 0.7 or more, more preferably 0.8 or more. Further, the ratio of the number of moles of nickel to the total number of moles of metals contained in the nickel-containing composite compound may be 0.98 or less, or may be 0.95 or less. By having a nickel ratio in the nickel-containing composite compound within the above range, the discharge capacity of the positive electrode material obtained using this can be increased, while the addition or removal of molybdenum (described later) can improve output at low SOC. tends to be larger.

In the nickel-containing composite compound, the ratio of the number of moles of cobalt to the total number of moles of metals contained in the nickel-containing composite compound may be 0 or more and less than 0.4, preferably 0.01 or more, and more preferably 0.03. That's all. Further, the ratio of the number of moles of cobalt to the total number of moles of metals contained in the nickel-containing composite compound is preferably 0.2 or less, more preferably 0.1 or less. By having the cobalt ratio in the nickel-containing composite compound within the above range, the cost for manufacturing the positive electrode material can be reduced, and the effect of improving output at low SOC by adding or removing molybdenum, which will be described later, tends to be greater. There is.

The nickel-containing composite compound may be a compound containing at least nickel and cobalt. When the nickel-containing composite compound contains cobalt in addition to nickel, the ratio of the number of moles of cobalt to the total number of moles of metal contained in the nickel-containing composite compound may be 0.01 or more and less than 0.4, preferably 0. It is at least .02, more preferably at least 0.04, preferably at most 0.2, more preferably at most 0.1.

The nickel-containing composite compound may include at least one of manganese and aluminum in its composition. When the nickel-containing composite compound includes at least one of manganese and aluminum in its composition, the ratio of the total number of moles of manganese and aluminum to the total number of moles of metals contained in the nickel-containing composite compound is, for example, greater than 0, preferably is 0.01 or more, more preferably 0.03 or more. Further, the ratio of the total number of moles of manganese and aluminum to the total number of moles of metals contained in the nickel-containing composite compound may be, for example, less than 0.4, preferably 0.2 or less, more preferably 0.1 or less. be. When the ratio of manganese and aluminum in the nickel-containing composite compound is within the above range, the discharge capacity of the positive electrode material obtained using the same tends to be larger.

The nickel-containing composite compound may include other metal elements M2 than nickel, cobalt, manganese and aluminum in its composition. When the nickel-containing composite compound includes at least the metal element M2 in its composition, the ratio of the total number of moles of the metal element M2 to the total number of moles of metal contained in the nickel-containing composite compound is, for example, greater than 0, preferably 0. 001 or more, more preferably 0.003 or more. Further, the ratio of the total number of moles of the metal element M2 to the total number of moles of metals contained in the nickel-containing composite compound is, for example, 0.1 or less, preferably 0.05 or less, and more preferably 0.03 or less. Examples of the metal element M2 include sodium, potassium, magnesium, calcium, barium, yttrium, titanium, zirconium, niobium, tantalum, chromium, molybdenum, tungsten, iron, copper, zinc, cadmium, gallium, silicon, tin, phosphorus, Examples include bismuth, lanthanum, cerium, neodymium, samarium, erbium, and lutetium, and preferably at least one selected from the group consisting of silicon, zirconium, titanium, magnesium, tantalum, niobium, molybdenum, and tungsten.

The nickel-containing composite compound may be a composite oxide, and may have a composition represented by the following formula (2), for example.
Ni _{q Cor} M ¹ _s M ² _t O _2+α (2)

In formula (2), M ¹ represents at least one of Mn and Al. ^M2 is Na, K, Mg, Ca, Ba, Y, Ti, Zr, Nb, Ta, Cr, Mo, W, Fe, Cu, Zn, Cd, Ga, Si, Sn, P, Bi, La, At least one selected from the group consisting of Ce, Nd, Sm, Er, and Lu is shown. q, r, s, t and α are 0.6<q<1, 0≦r<0.4, 0≦s<0.4, 0≦t≦0.1, -1≦α≦1, q+r+s+t≦1 is satisfied. Preferably, 0.7≦q≦0.98, 0.01≦r≦0.2, 0.01≦s≦0.2, 0.001≦t≦0.05, -0.1≦α≦ It is 0.1. Also preferably, ^M2 is at least one selected from the group consisting of Si, Zr, Ti, Mg, Ta, Nb, Mo, and W.

In the step of obtaining the first particles, a mixture containing a lithium compound, a nickel-containing composite compound, and a molybdenum compound is fired, and the ratio of the number of moles of nickel to the total number of moles of metals other than lithium in the composition exceeds 0.6. contains a lithium-transition metal composite oxide with less than 1. The step of obtaining the first particles may include a mixing step and a firing step in addition to the above-mentioned preparation step.

(Mixing process)
The mixing step includes obtaining a mixture containing a lithium compound, a nickel-containing composite compound, and a molybdenum compound. The lithium compound, the nickel-containing composite compound, and the molybdenum compound may be mixed in a dry or wet manner. Mixing can be performed using, for example, a super mixer. In this mixing step, in addition to the nickel-containing composite compound and the molybdenum compound, other simple metal elements, alloys, or metal compounds may be mixed. Further, as the nickel-containing composite compound, the nickel-containing composite compound obtained in the above-mentioned preparatory step can be used, but it may also be appropriately selected from commercially available products.

Examples of the lithium compound include lithium hydroxide, lithium carbonate, and lithium oxide. The particle size of the lithium compound used for mixing is, for example, 0.1 μm or more and 100 μm or less as a volume average particle size, and preferably 2 μm or more and 20 μm or less.

The lithium compound may be mixed such that the molar ratio of lithium to the total moles of metals contained in the nickel-containing composite compound is 0.7 or more and 1.4 or less, and 0.95 or more and 1.2 or less. may be mixed with The nickel-containing composite compound and the lithium compound can be mixed using, for example, a high-speed shear mixer.

Examples of molybdenum compounds include molybdenum oxide, lithium molybdate, molybdenum chloride, molybdenum fluoride, sodium molybdate, ammonium molybdate, and the like. Among these, molybdenum oxide is preferred, and molybdenum trioxide is more preferred. When molybdenum oxide is used as a molybdenum compound, a positive electrode material with relatively few impurities can be obtained, so when a positive electrode material obtained using this is used in a battery, battery characteristics may be improved.

The amount of the molybdenum compound added may be, for example, 0.5 mol % or more based on the total number of moles of metals other than lithium contained in the mixture excluding the molybdenum compound. The amount of the molybdenum compound added is preferably greater than 0.5 mol%, more preferably 0.6 mol% or more, and even more preferably 1 mol% or more, and 1.2 mol% or more. Further, the amount of the molybdenum compound added may be 5 mol% or less, preferably 2 mol% or less, more preferably 2 mol% or less, based on the total number of moles of metals other than lithium contained in the mixture excluding the molybdenum compound. , 1.8 mol% or less. If the amount of the molybdenum compound added is less than 0.5 mol%, there is a tendency that the effect of improving output characteristics will not be sufficiently obtained, while if the amount added exceeds 5 mol%, there is a risk that charge/discharge capacity and cycle characteristics may deteriorate. There is.

In the mixing step, in addition to the lithium compound, the nickel-containing composite compound, and the molybdenum compound, other simple metal elements, alloys, or metal compounds may be mixed. Other metal elements include aluminum, silicon, zirconium, titanium, magnesium, tantalum, niobium, molybdenum, tungsten, etc., and from the group consisting of aluminum, silicon, zirconium, titanium, magnesium, tantalum, niobium, molybdenum and tungsten. It may contain at least one selected type. Among them, it is preferable to include at least one selected from the group consisting of aluminum, zirconium, and tungsten as other metal elements, and each of these metal elements may be contained alone, but it is preferable that each metal compound is contained. and may contain multiple compounds. For example, a compound containing aluminum and a compound containing zirconium may be included in the mixture. Specific examples of compounds containing aluminum include aluminum oxide, aluminum hydroxide, aluminum carbonate, aluminum chloride, aluminum iodide, aluminum sulfate, and aluminum nitrate. Specific examples of compounds containing zirconium include zirconium oxide, zirconium hydroxide, zirconium fluoride, zirconium chloride, zirconium bromide, zirconium iodide, zirconium sulfide, and zirconium carbonate. Specific examples of compounds containing tungsten include tungsten oxide, lithium tungstate, tungsten fluoride, tungsten chloride, tungsten bromide, and tungsten iodide. When a compound containing aluminum is mixed, the crystal structure is stabilized, which tends to improve the safety of the resulting positive electrode material when used in batteries. When a compound containing zirconium is mixed, it is expected that the cycle characteristics of the obtained positive electrode material will be improved when used in a battery. Mixing a compound containing tungsten tends to further improve the output characteristics when the resulting positive electrode material is used in a battery.

In the mixing process, when aluminum is particularly mixed as another metal element in addition to the lithium compound, nickel-containing composite compound, and molybdenum compound, the amount added is less than 0 mol% in terms of aluminum atoms relative to the nickel-containing composite compound. The amount may be as large as 15 mol% or less. The amount of the aluminum-containing compound added is preferably greater than 0.5 mol%, more preferably 1 mol% or more, and even more preferably 1.5 mol% in terms of aluminum atoms, based on the nickel-containing composite compound. They are mixed so that the above results are achieved. Further, the amount of the aluminum-containing compound added is preferably 12 mol% or less, more preferably 8 mol% or less, still more preferably 5 mol% or less, based on the nickel-containing composite compound. Further, the aluminum-containing compound used for mixing may be a single substance or a compound.

In the mixing process, when other metal elements other than aluminum are mixed in addition to the lithium compound, nickel-containing composite compound, and molybdenum compound, the amount added is in terms of atoms of the other metal element, relative to the nickel-containing composite compound. It may be greater than 0 mol% and less than 5 mol%. The mixed form of the other metal element may be a single substance or a compound, but the amount added is preferably 0.01 mol relative to the nickel-containing composite compound in terms of atoms of the other metal element. % or more, more preferably 0.05 mol % or more, still more preferably 0.1 mol % or more. Further, the amount of the metal-containing compound added is preferably 3 mol% or less, more preferably 1 mol% or less, and even more preferably 0.5 mol%, based on the nickel-containing composite compound in terms of atoms of other metal elements. Mixed as follows:

(Firing process)
A lithium transition metal in which the ratio of the number of moles of nickel to the total number of moles of metals other than lithium in the composition is more than 0.6 and less than 1, obtained by firing a mixture containing a lithium compound, a nickel-containing composite compound, and a molybdenum compound. Contains complex oxides. Firing may be performed in the air or in an atmosphere containing oxygen.

The firing temperature is, for example, 550°C or more and 1000°C or less, preferably 700°C or more and 1000°C or less, more preferably 800°C or more and 1000°C or less, and even more preferably 850°C or more and 950°C or less. The mixture may be fired by heat treatment at a single temperature, but from the viewpoint of discharge capacity at high voltage, it is preferable to perform heat treatment at multiple temperatures. When firing by heat treatment at multiple temperatures, for example, it is desirable to hold the first temperature for a predetermined time, then further raise the temperature, and hold the second temperature for a predetermined time. The first temperature is, for example, 200°C or more and 600°C or less, preferably 400°C or more and 500°C or less, and the second temperature is, for example, 600°C or more and 950°C or less, preferably 850°C or more and 950°C or less. The heat treatment time is, for example, 0.5 to 48 hours, and when heat treatment is performed at a plurality of temperatures, each can be 0.2 to 47 hours.

The first particles may include a lithium transition metal composite oxide having a layered structure. Further, the lithium transition metal composite oxide contained in the first particles is a compound containing nickel, but may further contain cobalt or manganese. Further, the number of moles of lithium contained in the first particles may be 0.95 or more and 1.5 or less, and may be 1 or more and 1.2 or less with respect to the total number of moles of metals other than lithium. The number of moles of nickel contained in the first particles may be 0.6 or more and less than 1, and may be 0.8 or more and 0.98 or less with respect to the total number of moles of metals other than lithium. Furthermore, when cobalt is included, the number of moles of cobalt contained in the metal other than lithium may be 0.01 or more and 0.2 or less, and 0.03 or more and 0.2 or less, relative to the total number of moles of the metal other than lithium. It may be 1 or less.

In the step of obtaining the first particles, the lithium transition metal composite oxide contained in the first particles has a composition in which the ratio of moles of molybdenum to the total moles of metals other than lithium exceeds 0.005 and is 0.02. It may be the following. Moreover, the molybdenum contained in the first particles is preferably 0.006 or more, more preferably 0.01 or more, and even more preferably 0.012 or more with respect to the total number of moles of metals other than lithium in the composition. The molybdenum contained in the first particles is preferably 0.018 or less based on the total number of moles of metals other than lithium in the composition. If the content of molybdenum contained in the first particles is 0.005 or less, the effect of improving output characteristics tends to be insufficient.

The lithium transition metal composite oxide contained in the first particles may be a composite oxide, and may have a composition represented by the following formula (1), for example.
Li _p Ni _x Co _y M ¹ _z M ² _u O _2+α (1)
In formula (1), M ¹ represents at least one of Mn and Al. ^M2 is Na, K, Mg, Ca, Ba, Y, Ti, Zr, Nb, Ta, Cr, Mo, W, Fe, Cu, Zn, Cd, Ga, Si, Sn, P, Bi, La, At least one selected from the group consisting of Ce, Nd, Sm, Er, and Lu is shown. p, x, y, z, u and α are 0.95≦p≦1.5, 0.6<x<1, 0≦y<0.4, 0≦z<0.4, 0≦u ≦0.1, -0.3≦α≦0.3, x+y+z+u≦1. Preferably, 1.0≦p≦1.3, 0.7≦x≦0.98, 0.01≦y≦0.2, 0.01≦z≦0.2, 0.001≦u≦0 .05, -0.1≦α≦0.1. Also preferably, M ² is at least one selected from the group consisting of Si, Zr, Ti, Mg, Ta, Nb, Mo, and W, and more preferably, M ² contains Mo. In addition to Mo, at least one member selected from the group consisting of Si, Zr, Ti, Mg, Ta, Nb, and W may be included.

In the step of obtaining the second particles, the molybdenum element contained in the first particles is removed by contacting the first particles with a liquid medium such that the solid content concentration of the first particles is 20% by mass or more and 80% by mass or less. Including removing some. This step may include a washing step as the step of bringing the first particles into contact with the liquid medium, and may also include a boron mixing step or a heat treatment step after the washing step. For example, after bringing the first particles into contact with the liquid medium, the method may further include mixing with a boron compound and heat-treating.

(Washing process)
In the cleaning step, the first particles are brought into contact with a liquid medium to remove a portion of the molybdenum element contained in the first particles, thereby obtaining cleaning particles as second particles. The treated product after contact with the liquid medium may be subjected to dehydration treatment, drying treatment, etc., as necessary. The cleaning step is, for example, a step of removing a part of the molybdenum element contained in the first particles, and an example of the form of molybdenum contained in the first particles is lithium molybdate generated in the firing step.

The liquid medium (hereinafter referred to as cleaning liquid) may contain metal ions such as sodium, if necessary. Examples include alkali metal ions such as sodium ions, lithium ions, and potassium ions, and alkaline earth metal ions such as magnesium ions. Preferably, the solution contains at least one of sodium and lithium. When the cleaning solution contains sodium ions, the content of sodium ions may be, for example, from 0.01 mol/L to 2.0 mol/L, preferably from 0.03 mol/L to 1.5 mol/L. L or less, more preferably 0.05 mol/L or more and 1.0 mol/L or less, even more preferably 0.05 mol/L or more and 0.7 mol/L or less, particularly preferably 0.1 mol/L or more and 0. .4 mol/L or less. The same applies when the cleaning liquid contains lithium ions. When both sodium ions and lithium ions are included, the total content of each ion is preferably within the above range. Further, when the cleaning liquid contains metal ions other than sodium, the content thereof may be, for example, 0.1 mol/L or less, and preferably less than 0.01 mol/L. From the viewpoint of reducing damage to the lithium transition metal composite oxide contained in the first particles, it is preferable that the cleaning liquid contains sodium, and it is preferable that the metal ions contained in the cleaning liquid be within the above range. When the content of sodium ions is 0.4 mol %/L or less, damage caused by cleaning can be particularly reduced, and battery characteristics tend to be further improved.

The contact temperature between the first particles and the cleaning liquid is, for example, 5°C or more and 60°C or less, preferably 10°C or more and 40°C or less. Further, the contact time is, for example, 1 minute or more and 2 hours or less, preferably 5 minutes or more and 30 minutes or less.

The contact between the first particles and the cleaning liquid may be carried out by adding the first particles to the cleaning liquid to prepare a slurry. The first particles may be brought into contact with the cleaning liquid such that the solid content concentration of the first particles is, for example, 20% by mass or more and 80% by mass or less, preferably 25% by mass or more and 60% by mass or less. The content is more preferably 30% by mass or more and 60% by mass or less. The solid content concentration of the first particles is the mass of the first particles/(mass of the first particles + the mass of the cleaning liquid), and for example, in the case of 20% by mass, the mass of the first particles and the cleaning liquid The ratio will be 20:80. The solid content concentration range described above tends to be more effective when the first particles are introduced into the cleaning liquid and contacted as a slurry. The contact may also be carried out by passing a cleaning liquid through the first particles held on a filter, or by passing the cleaning liquid through a dehydrated cake obtained by washing the first particles with pure water or the like and dehydrating them. You may do so. When the first particles are washed with pure water or the like and then the washing liquid is passed through the dehydrated cake obtained by dehydration, the total amount of the pure water and the washing liquid used is 0.000% relative to the mass of the first particles. It is preferably 25 times or more and 10 times or less, and more preferably 0.5 times or more and 4 times or less.

The contact between the first particles and the cleaning solution is such that the lithium contained in the second particles is The ratio of the number of moles of molybdenum to the total number of moles of metals other than lithium in the composition of the transition metal composite oxide (hereinafter referred to as molybdenum ratio) may be in the following relationship. Specifically, the value obtained by dividing the molybdenum ratio of the second particles by the molybdenum ratio of the first particles may be 0.3 or more, preferably 0.35 or more and 0.8 or less. More preferably, it is 0.4 or more and 0.7 or less, and even more preferably 0.4 or more and 0.6 or less. By bringing the first particles into contact with the liquid medium within this range during the cleaning process, it is possible to improve the output at a low SOC by removing a portion of the molybdenum element, while also reducing the damage can be reduced. These molybdenum ratios can be measured by inductively coupled plasma (ICP) emission spectroscopy. At this time, an inductively coupled plasma emission spectrometer (ICP-AES; manufactured by PerkinElmer) may be used.

The cleaning particles obtained in the cleaning step may be subjected to a drying treatment. The drying treatment only needs to be able to remove at least a portion of the water adhering to the cleaning particles, and can be performed by heating drying, air drying, reduced pressure drying, or the like. The drying temperature in the case of heating and drying may be a temperature at which water contained in the cleaning particles is sufficiently removed. The drying temperature is, for example, 80°C or higher and 300°C or lower, preferably 100°C or higher and 250°C or lower. The drying time may be appropriately selected depending on the amount of water contained in the cleaning particles. The drying time is, for example, 1 hour or more and 10 hours or less.

(Boron mixing process)
In the boron mixing step, cleaning particles and a boron compound are mixed to obtain a boron mixture. The cleaning particles and the boron compound may be mixed in a dry or wet manner. Mixing can be performed using, for example, a super mixer. Further, in this boron mixing step, in addition to the boron compound, a single substance, an alloy, or a metal compound of another metal element may be mixed. Other metal elements include aluminum, silicon, zirconium, titanium, magnesium, tantalum, niobium, molybdenum, tungsten, etc., and at least one selected from the group consisting of these is preferred.

The boron compound can be selected from at least one selected from the group consisting of boron oxide, boron oxo acids, and boron oxo acid salts. More specific examples of boron compounds include lithium tetraborate (Li ₂ B ₄ O ₇ ), ammonium pentaborate (NH ₄ B ₅ O ₈ ), and orthoboric acid (H ₃ BO ₃ ; so-called ordinary boric acid). ), lithium metaborate (LiBO ₂ ), boron oxide (B ₂ O ₃ ), etc., at least one selected from the group consisting of these is preferable, and orthoboric acid is more preferable in terms of cost.

The boron compound may be mixed with the cleaning particles in a solid state or as a solution of the boron compound. When using a boron compound in a solid state, the volume average particle diameter of the boron compound is, for example, 1 μm or more and 60 μm or less, preferably 10 μm or more and 30 μm or less.

The content of the boron compound in the boron mixture is, for example, 0.1 mol% or more as a ratio of the number of moles of boron atoms to the total number of moles of metals other than lithium in the lithium transition metal composite oxide contained in the cleaning particles. It may be mol% or less, preferably 0.1 mol% or more and 1.5 mol% or less, more preferably 0.1 mol% or more and 1.2 mol% or less.

(Heat treatment process)
In the heat treatment step, the boron mixture is heat-treated at a temperature of, for example, 100° C. or higher and 450° C. or lower to obtain a heat-treated product that is a positive electrode material. The temperature of the heat treatment may be 200°C or more and 400°C or less, preferably 220°C or more and 350°C or less, and more preferably 250°C or more and 350°C or less. The atmosphere for the heat treatment may be an oxygen-containing atmosphere or may be in the air. The heat treatment time is, for example, 1 hour or more and 20 hours or less, preferably 5 hours or more and 10 hours or less. Note that the heat-treated product obtained in the heat treatment step may be subjected to crushing treatment, classification treatment, etc. as necessary.

The heat-treated product obtained after the heat treatment preferably has a specific surface area of 1.0 m ² /g or more and 2.0 m 2 /g, more preferably 1.3 ^{m 2 /} g or more and 1.7 m ² /g. . Further, the ratio of molybdenum to the lithium transition metal composite oxide is preferably 0.004 or more and 0.02 or less, more preferably 0.005 or more and 0.01 or less.

A lithium-deficient region may be formed near the surface of the cleaning particles after the cleaning step, and desorption and insertion of lithium ions may be inhibited in the lithium-deficient region. However, by mixing a boron compound and heat-treating the cleaning particles after the cleaning process, lithium vacancies can be compensated, inhibition of desorption/insertion of lithium ions can be suppressed, and charge/discharge characteristics and cycle characteristics can be improved. Conceivable. By performing the boron mixing step and the heat treatment step on the cleaning particles in this way, the battery characteristics of the positive electrode material, which is the second particle, tend to be further improved.

The positive electrode material for a lithium ion secondary battery obtained in this manner contains lithium, nickel, and molybdenum, and the ratio of the number of moles of nickel to the total number of moles of metals other than lithium in the composition exceeds 0.6 and is 1. After mixing 200 g of oxide particles and 165 g of pure water and stirring for 30 minutes, the filtered powder contains oxide particles (second particles) containing an oxide that is less than The ratio of the number of moles of molybdenum to the total number of moles of metals other than lithium contained in the oxide particles is 0.55 or more times the ratio of the number of moles of molybdenum to the total number of moles of metals other than lithium in the oxide particles before filtration. be.

In the positive electrode material for lithium ion secondary batteries, when 200 g of oxide particles and 165 g of pure water are mixed and the slurry is filtered after stirring for 30 minutes, the total mole of metals other than lithium in the oxide particles before filtration is The ratio of the number of moles of molybdenum to the total number of moles of metals other than lithium contained in the powder after filtration (residual molybdenum ratio) is 0.55 times or more. Further, the residual molybdenum ratio is preferably 0.6 times or more and less than 1. Positive electrode materials for lithium ion secondary batteries that have undergone a cleaning process have a relatively higher residual molybdenum ratio compared to those that have not undergone a cleaning process. It is possible to obtain output characteristics at low SOC. Note that the residual molybdenum ratio can be measured as follows. The number of moles of molybdenum relative to the total number of moles of metals other than lithium was measured using an inductively coupled plasma emission spectrometer (ICP-AES; manufactured by PerkinElmer) on positive electrode materials for lithium ion secondary batteries containing oxide particles. Measure the ratio (A). After that, 200 g of positive electrode material for lithium ion secondary batteries and 165 g of pure water were mixed, stirred for 30 minutes to prepare a slurry, and the filtered powder obtained by filtering the slurry was similarly inductively bonded. Using a plasma emission spectrometer, the ratio (B) of the number of moles of molybdenum to the total number of moles of metals other than lithium is determined. Using each measurement result, the remaining molybdenum ratio (B)/(A) can be calculated by dividing the ratio of moles of molybdenum after filtration (B) by the ratio of moles of molybdenum before filtration (A). calculate.

The second particles may include a lithium transition metal composite oxide having a layered structure. Further, the lithium transition metal composite oxide contained in the second particles is a compound containing nickel, but may further contain cobalt or manganese.

The crystallinity of the lithium transition metal composite oxide contained in the second particles may be 300 or more and 800 or less, preferably 350 or more and 700 or less, and more preferably 400 or more and 600 or less. When the crystallinity is within the above range and a certain number of grain boundaries are included in the positive electrode material, an increase in resistance can be suppressed in some cases. Further, it is more preferable that the crystallinity is 500 or more and 550 or less, and when the crystallinity is within this range, the effect of improving low SOC output when molybdenum is added and washed may be particularly large. Note that crystallinity can be determined by measuring the XRD spectrum of the positive electrode material using a powder X-ray diffractometer and using the half-value width of the peak in the (104) plane. Determining the crystallinity of a sample by fitting the XRD pattern of a crystal structure model of a lithium-transition metal compound obtained from the International Center for Diffraction Data (ICDD) and the XRD pattern obtained by measurement using the least squares method. Can be done. Specifically, it can be determined by the method described in Examples below.

The average particle diameter of the second particles is, for example, 2 μm or more and 30 μm or less, preferably 3 μm or more and 25 μm or less. The average particle size of the composite oxide is a volume average particle size, and is a value at which the volume integrated value from the small particle size side in the volume distribution obtained by the laser scattering method is 50%.

The ratio of the number of moles of nickel to the total number of moles of metals other than lithium in the composition of the lithium transition metal composite oxide contained in the second particles may be, for example, greater than 0.6 and less than 1. The ratio of the number of moles of nickel to the total number of moles of metals other than lithium is preferably 0.7 or more, more preferably 0.8 or more. Further, the ratio of the number of moles of nickel to the total number of moles of metals other than lithium may be 0.98 or less, or may be 0.95 or less. By having the nickel ratio of the lithium-transition metal composite oxide contained in the second particles within the above range, the discharge capacity of the positive electrode material obtained using the second particles can be increased, and the SOC can be lowered by adding or removing molybdenum. The improvement effect on output tends to be greater.

The lithium transition metal composite oxide contained in the second particles may have a composition in which the ratio of the number of moles of cobalt to the total number of moles of metals other than lithium is 0 or more and less than 0.4, preferably 0.01 or more. , more preferably 0.03 or more. Further, the ratio of the number of moles of cobalt to the total number of moles of metals other than lithium is preferably 0.2 or less, more preferably 0.1 or less. By having the cobalt ratio in the lithium-transition metal composite oxide contained in the second particles within the above range, the cost for manufacturing the positive electrode material can be reduced, and the output at low SOC can be improved by adding or removing molybdenum. The effect tends to be greater.

The lithium transition metal composite oxide contained in the second particles may include at least one of manganese and aluminum in its composition. When the lithium transition metal composite oxide contained in the second particles contains at least one of manganese and aluminum in its composition, the ratio of the total number of moles of manganese and aluminum to the total number of moles of metals other than lithium in the composition is: For example, it is greater than 0, preferably 0.01 or more, more preferably 0.03 or more. Further, the ratio of the total number of moles of manganese and aluminum to the total number of moles of metals other than lithium may be, for example, less than 0.4, preferably 0.2 or less, and more preferably 0.1 or less. When the ratio of manganese and aluminum in the lithium transition metal composite oxide contained in the second particles is within the above range, the discharge capacity of the positive electrode material obtained using the same tends to be larger.

The lithium transition metal composite oxide contained in the second particles may contain a metal element M2 other than nickel, cobalt, manganese, and aluminum in its composition. When the lithium-transition metal composite oxide contained in the second particles contains at least metal element M2, the lithium-transition metal composite oxide contained in the second particles has a ratio of metal element M2 to the total number of moles of metal contained in the lithium-transition metal composite oxide contained in the second particles. The ratio of the total number of moles is, for example, greater than 0, preferably 0.001 or more, and more preferably 0.003 or more. Further, the ratio of the total number of moles of metal elements to the total number of moles of metals contained in the nickel-containing composite compound is, for example, 0.1 or less, preferably 0.05 or less, and more preferably 0.03 or less. Examples of the metal element M2 include sodium, potassium, magnesium, calcium, barium, yttrium, titanium, zirconium, niobium, tantalum, chromium, molybdenum, tungsten, iron, copper, zinc, cadmium, gallium, silicon, tin, phosphorus, Examples include bismuth, lanthanum, cerium, neodymium, samarium, erbium, and lutetium, and preferably at least one selected from the group consisting of silicon, zirconium, titanium, magnesium, tantalum, niobium, molybdenum, and tungsten. More preferably, metal element M2 contains molybdenum. In addition to molybdenum, it may contain at least one member selected from the group consisting of silicon, zirconium, titanium, magnesium, tantalum, niobium, and tungsten.

The lithium transition metal composite oxide contained in the second particles may have a composition in which the ratio of the number of moles of molybdenum to the total number of moles of metals other than lithium is 0.002 or more and 0.015 or less. Moreover, the molybdenum contained in the second particles is preferably 0.003 or more, more preferably 0.0035 or more, even more preferably 0.004 or more, and Particularly preferred is .0045 or more. The molybdenum contained in the first particles is preferably 0.013 or less, more preferably 0.01 or less, even more preferably 0.008 or less, and 0.007 or less relative to the total number of moles of metals other than lithium in the composition. The following are particularly preferred. When the content of molybdenum contained in the second particles is within the above-mentioned range, there is a tendency to achieve both charge/discharge capacity and output characteristics at low SOC.

The lithium transition metal composite oxide contained in the second particles may have a composition represented by the following formula (1).
Li _p Ni _x Co _y M ¹ _z M ² _u O _2+α (1)
In formula (1), M ¹ represents at least one of Mn and Al. ^M2 is Na, K, Mg, Ca, Ba, Y, Ti, Zr, Nb, Ta, Cr, Mo, W, Fe, Cu, Zn, Cd, Ga, Si, Sn, P, Bi, La, At least one selected from the group consisting of Ce, Nd, Sm, Er, and Lu is shown. p, x, y, z, u and α are 0.95≦p≦1.5, 0.6<x<1, 0≦y<0.4, 0≦z<0.4, 0≦u ≦0.1, -0.3≦α≦0.3, x+y+z+u≦1. Preferably, 1.0≦p≦1.3, 0.7≦x≦0.98, 0.01≦y≦0.2, 0.01≦z≦0.2, 0.001≦u≦0 .05, -0.1≦α≦0.1. Also preferably, M ² is at least one selected from the group consisting of Si, Zr, Ti, Mg, Ta, Nb, Mo, and W, and more preferably, M ² contains Mo. In addition to Mo, at least one member selected from the group consisting of Si, Zr, Ti, Mg, Ta, Nb, and W may be included.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited to these Examples. In addition, the volume average particle diameter used was a value at which the volume integrated value from the small particle diameter side in the volume distribution obtained by the laser scattering method was 50%. Specifically, the volume average particle diameter was measured using a laser diffraction particle size distribution device (MALVERN Inst. MASTERSIZER 2000). The specific surface area was measured by a gas adsorption method (one point method) using nitrogen gas using a BET specific surface area measuring device (manufactured by Mountech: Macsorb). The composition was measured using an inductively coupled plasma emission spectrometer (ICP-AES; manufactured by PerkinElmer), and the crystallinity was measured as follows.

The X-ray diffraction spectrum (tube current 200 mA, tube voltage 45 kV) was measured using CuKα rays, and the diffraction peak obtained around 2θ = 44 degrees was fitted by the least squares method using the PseudoVoigt function, and the values of θ and β were determined. was calculated. Crystallinity D is calculated by the following formula (3) from the diffraction peak due to the (104) plane determined by X-ray diffraction.

D=K’λ/(βcosθ) (3)

In the above formula, D represents crystallinity (Å), λ represents the wavelength of the X-ray source (1.54 Å in the case of CuKα), β represents the integral width (radian), and θ represents the diffraction angle (degree). ), and K' is measured using sintered Si for optical system adjustment (manufactured by Rigaku Denki Co., Ltd.), and when using the above equation (3), the crystallinity D due to the (022) plane is A value of 1000 Å is used.

[Example 1]
Preparation process A nickel-containing composite compound (composite oxide particles) having a volume average particle diameter of 10 μm and a composition of Ni:Co:Mn:=0.89:0.05:0.06 was prepared by a coprecipitation method. Obtained.

Mixing step The obtained composite oxide particles, lithium hydroxide, aluminum hydroxide, zirconium oxide, and molybdenum trioxide are mixed. The molar ratio of lithium hydroxide was adjusted to be Li:(Ni+Co+Mn):Al=1.10:0.98:0.02. Further, the amount of zirconium oxide added was adjusted to be 0.3 mol % based on the composite oxide particles. In addition, the amount of molybdenum trioxide added is set to 1.7 mol% with respect to the total amount of aluminum added in addition to nickel, cobalt, and manganese in the composite oxide particles, that is, (Ni+Co+Mn+Al):Mo = 1:0.017. A mixture was obtained by mixing composite oxide particles, lithium hydroxide, aluminum hydroxide, zirconium oxide, and molybdenum trioxide.

Firing Step The obtained mixture was heat-treated in an oxygen stream at a first temperature of 450°C for 3 hours and a second temperature of 915°C for 4 hours. After firing, pulverization is performed to create a lithium transition composition with a ratio of nickel, cobalt, manganese, and aluminum of Ni:Co:Mn:Al=0.87:0.05:0.06:0.02. First particles containing a metal composite oxide were obtained. Table 1 shows the amount of molybdenum relative to the total number of moles of metals other than lithium contained in the first particles. In each of the following Examples and Comparative Examples, the amount of molybdenum is similarly shown in each table.

Washing Step The obtained first particles were added to a sodium sulfate aqueous solution prepared to have a sodium ion concentration of 0.156 mol/L as a washing liquid to form a slurry with a solid content concentration of 55% by mass. The solid content concentration was determined by mass of first particles/(mass of first particles + mass of cleaning liquid). The slurry was stirred for 30 minutes, then drained in a funnel and separated as a cake. The separated cake was dried in air at 250°C for 10 hours to obtain washed particles.

Boron mixing step: Add orthoboric acid in an amount of 1 mol% as boron atoms to the total number of moles of metals other than lithium in the lithium-transition metal composite oxide contained in the obtained cleaning particles, and mix and stir to form a boron mixture. I got it.

Heat Treatment Step The obtained boron mixture is heat treated at 300°C in the atmosphere for 10 hours to form Li _1.04 Ni _0.863 Co _0.049 Mn _0.058 Al _0.02 Mo _0.007 Zr _0. A positive electrode material, which is a second particle, containing a lithium transition metal composite oxide considered to be ₀₀₃ O ₂ was obtained. Table 1 shows the amount of molybdenum relative to the total number of moles of metals other than lithium contained in the second particles. In each of the following Examples and Comparative Examples, the amount of molybdenum is similarly shown in each table.

[Example 2]
A positive electrode material was obtained in the same manner as in Example 1 except that the second temperature in the firing step was 935°C.

[Example 3]
In the mixing process, the molar ratio of lithium hydroxide was adjusted to be Li:(Ni+Co+Mn):Al=1.07:0.98:0.02, and the amount of molybdenum trioxide added was adjusted to the composite oxide particles. A positive electrode material was obtained in the same manner as in Example 1, except that the content was adjusted to 1.0 mol % and the second temperature in the firing step was 900°C.

[Example 4]
In the mixing process, the molar ratio of lithium hydroxide was adjusted to be Li:(Ni+Co+Mn):Al=1.07:0.98:0.02, and the amount of molybdenum trioxide added was adjusted to the composite oxide particles. A positive electrode material was obtained in the same manner as in Example 1, except that the second temperature in the firing step was adjusted to 1.2 mol% and the second temperature was 910°C.

[Comparative example 1]
A positive electrode material was prepared in the same manner as in Example 1, except that the steps after the cleaning step after the firing step were not performed.

[Comparative example 2]
In the mixing step, the molar ratio of lithium hydroxide was adjusted to be Li:(Ni+Co+Mn):Al=1.06:0.98:0.02, and the amount of molybdenum oxide added was adjusted to the composite oxide particles. A positive electrode material was obtained in the same manner as in Example 1, except that the content was adjusted to 0.5 mol% and the second temperature in the firing step was 845°C.

[Comparative example 3]
In the mixing process, adjust the molar ratio of lithium hydroxide to Li:(Ni+Co+Mn):Al=1.05:0.98:0.02, use manganese oxide instead of molybdenum trioxide, and mix manganese oxide. Li _1.05 was prepared in the same manner as in Example 1, except that the amount of Li added was adjusted to 1.0 mol % with respect to the composite oxide particles, and the second temperature in the firing step was set to 770°C. A positive electrode material containing a lithium transition metal composite oxide considered to be Ni _0.861 Co _0.048 Mn _0.068 Al _0.02 Zr _0.003 O ₂ was obtained.

[Battery characteristics evaluation]
The positive electrode materials obtained in Examples 1 to 4 and Comparative Examples 1 to 3 were evaluated for discharge capacity and output characteristics at low SOC as follows.

[Evaluation of discharge capacity]
The discharge capacity of the positive electrode materials obtained in each Example and each Comparative Example was evaluated as follows.

(Preparation of positive electrode)
92 parts by mass of the above positive electrode material, 3 parts by mass of acetylene black, and 5 parts by mass of PVDF (polyvinylidene fluoride) were dispersed and dissolved in NMP (N-methyl-2-pyrrolidone) to prepare a positive electrode slurry. The obtained positive electrode slurry was applied to a current collector made of aluminum foil, and after drying, compression molding was performed using a roll press machine so that the density of the positive electrode layer was 3.3 g/cm ³ , and the size was 15 cm ² . I cut it up and got the positive electrode.

(Preparation of negative electrode)
A negative electrode slurry was prepared by dispersing 97.5 parts by mass of artificial graphite, 1.5 parts by mass of CMC (carboxymethylcellulose), and 1.0 parts by mass of SBR (styrene butadiene rubber) in water. The obtained negative electrode slurry was applied to copper foil, dried, and further compression molded to obtain a negative electrode.

(Preparation of non-aqueous electrolyte)
EC (ethylene carbonate) and EMC (ethyl methyl carbonate) were mixed at a volume ratio of 3:7 to obtain a mixed solvent. Lithium hexafluorophosphate (LiPF ₆ ) was dissolved in the obtained mixed solvent at a concentration of 1 mol/L to obtain a non-aqueous electrolyte.

(Preparation of evaluation battery)
After attaching lead electrodes to the positive and negative current collectors, vacuum drying was performed at 120°C. Next, a separator was placed between the positive electrode and the negative electrode, and they were housed in a bag-shaped laminate pack. Next, this was vacuum dried at 60° C. to remove moisture adsorbed on each member. Thereafter, a nonaqueous electrolyte was injected into the laminate pack under an argon atmosphere, and the pack was sealed to prepare a battery for evaluation.

(aging)
The evaluation battery was charged with a charging voltage of 4.2 V, a charging current of 0.1 C (1 C is the current at which discharging ends in 1 hour), constant current and constant voltage charging (cutoff current of 0.005 C), and a discharge end voltage of 2.5 V. A constant current discharge with a discharge current of 0.1 C was performed to blend the nonaqueous electrolyte into the positive and negative electrodes.

(Measurement of discharge capacity)
After aging, perform constant current and constant voltage charging (cutoff current 0.005C) at a charging voltage of 4.2V and charging current of 0.1C, and then perform constant current discharge at a discharge end voltage of 2.5V and a discharge current of 0.1C. and measured the discharge capacity. Table 1 shows the relative discharge capacity of each Example and each Comparative Example when the value of the discharge capacity of Comparative Example 3 is set to 1.

[Evaluation of relative resistance at low SOC]
For the positive electrode materials obtained in each Example and each Comparative Example, output characteristics at low SOC were evaluated by measuring DC-IR (direct current internal resistance). The measurements were performed as follows.

(DC-IR measurement at low SOC)
A battery for evaluation was produced in the same manner as when measuring the discharge capacity, and aging was performed in the same manner using the produced battery for evaluation. The battery for evaluation after aging was placed in an environment of 25° C., and the direct current internal resistance (DC-IR) was measured. After performing constant current charging to SOC 95% at a full charge voltage of 4.2 V, the open circuit potential at SOC 95% was measured. Thereafter, pulse discharge using a specific current i was performed for 30 seconds, and the voltage V was measured after 30 seconds. The DC internal resistance was calculated from the difference between the open circuit potential and the voltage V after 30 seconds. Note that the current i was set to 0.08A. This was subjected to constant current discharge to SOC of 80%, 50%, and 5%, respectively, and DC-IR measurements were repeated at each SOC. Table 1 shows the relative resistance results of each Example and each Comparative Example, assuming that the resistance value of Comparative Example 3 at SOC of 80%, 50%, and 5% is 1.

As shown in Table 1, Examples 1 to 4 in which a molybdenum compound was added had reduced resistance at low SOC, that is, excellent output characteristics at low SOC, compared to Comparative Example 3 in which manganese oxide was added. Furthermore, in Comparative Example 1 in which a molybdenum compound was added and no cleaning was performed, a decrease in discharge capacity was confirmed. In Examples 1 to 4, in which a molybdenum compound was added and cleaning was performed, when comparing the first particles and the second particles, it was confirmed that the specific surface area increased and the molybdenum content (added metal content ratio) decreased. . This is thought to be because molybdenum compounds produced during the firing process, such as lithium molybdate, were removed during the cleaning process.

[Evaluation of residual molybdenum ratio]
The residual molybdenum ratio remaining after the obtained positive electrode material was brought into contact with pure water was measured. The ratio of the number of moles of molybdenum to the total number of moles of metals other than lithium ( A) was measured. A slurry was prepared by mixing 200 g of the positive electrode material obtained in the same manner as in Example 1 and 165 g of pure water and stirring for 30 minutes. The ratio (B) of the number of moles of molybdenum to the total number of moles of metals other than lithium was determined using the same inductively coupled plasma emission spectrometer for the filtered powder obtained by filtering the slurry. . Using each measurement result, the remaining molybdenum ratio (B)/(A) can be calculated by dividing the ratio of moles of molybdenum after filtration (B) by the ratio of moles of molybdenum before filtration (A). Calculated. Comparative Example 1 was also measured in the same manner, and the results are shown in Table 2.

[Example 5]
In the preparation step, composite oxide particles having a volume average particle diameter of 10 μm and a composition of Ni:Co:Mn:=0.88:0.05:0.07 are prepared and mixed by a coprecipitation method. In the process, the molar ratio of lithium hydroxide was adjusted to be Li: (Ni + Co + Mn): Al = 1.05:0.98:0.02, and in the firing process, the second temperature was set at 935 ° C. for 4 hours. A positive electrode material was obtained in the same manner as in Example 1 except for the following steps.

[Comparative example 4]
In the mixing process, lithium hydroxide was adjusted to a molar ratio of Li:(Ni+Co+Mn):Al=1.07:0.98:0.02, and tungsten oxide was used without adding molybdenum trioxide. A positive electrode material was prepared in the same manner as in Example 5, except that the amount of tungsten oxide added was adjusted to 1.7 mol % with respect to the composite oxide, and the second temperature in the firing process was set to 975°C. I got it. Relative values of SOC 80%, 50%, and 5% in Example 5 and Comparative Example 4 when the resistance value of Comparative Example 4 at SOC 80%, 50%, and 5% is set to 1, and the discharge capacity value is set to 1. The resistance and relative discharge capacity are shown in Table 3.

As shown in Table 3, it was confirmed that Example 5, in which molybdenum was added and cleaning was performed, had improved output characteristics at low SOC compared to Comparative Example 4, in which a tungsten compound was added in place of molybdenum. It was done.

[Example 6]
In the preparation step, composite oxide particles having a volume average particle diameter of 4 μm and a composition of Ni:Co:Mn:=0.88:0.05:0.07 were prepared by a coprecipitation method. In the mixing process, adjust the molar ratio of lithium hydroxide to Li: (Ni + Co + Mn): Al = 1.07: 0.98: 0.02, do not add zirconium oxide, and add the amount of molybdenum trioxide. was adjusted to 1.0 mol% with respect to the total of nickel, cobalt, manganese and aluminum, and the second temperature was set at 890 ° C. in the firing process. A positive electrode material was obtained.

[Comparative example 5]
In the mixing process, the molar ratio of lithium hydroxide was adjusted to be Li: (Ni + Co + Mn): Al = 1.05: 0.98: 0.02, and in the firing process, it was performed at a second temperature of 760 ° C. for 4 hours. A positive electrode material was obtained in the same manner as in Example 6 except for the above. Relative values of SOC 80%, 50%, and 5% in Example 6 and Comparative Example 5 when the resistance value of Comparative Example 5 is 1 and the discharge capacity value is 1 at SOC 80%, 50%, and 5%, respectively. The resistance and relative discharge capacity are shown in Table 4.

[Example 7]
A positive electrode material was obtained in the same manner as in Example 6, except that in the preparation step, composite oxide particles having a volume average particle diameter of 22 μm were prepared, and the second temperature in the firing step was 910° C.

[Comparative example 6]
A positive electrode material was obtained in the same manner as in Comparative Example 5, except that composite oxide particles having a volume average particle diameter of 22 μm were prepared in the preparation step. Relative values of SOC 80%, 50%, and 5% in Example 7 and Comparative Example 6 when the resistance value of Comparative Example 6 at SOC 80%, 50%, and 5% is set to 1, and the discharge capacity value is set to 1. The resistance and relative discharge capacity are shown in Table 5.

As shown in Tables 4 and 5, even in Examples 6 and 7 using positive electrode materials with average particle diameters of 22 μm and 4 μm, the output characteristics at low SOC were improved by adding molybdenum and washing. confirmed.

[Comparative Example 7]
In the preparation step, composite oxide particles having a volume average particle diameter of 10 μm and a composition of Ni:Co:Mn:=0.6:0.2:0.2 were prepared by a coprecipitation method. In the mixing step, lithium hydroxide was adjusted to a molar ratio of Li:(Ni+Co+Mn)=1.10:1.0, aluminum hydroxide and zirconium oxide were not added, and molybdenum trioxide was added in an amount of 1.10:1.0. The content was adjusted to 0 mol % to obtain a mixture. First particles were obtained in the same manner as in Example 1, except that the firing step was performed at a second temperature of 905° C. for 4 hours.

In the boron mixing step, the amount of orthoboric acid is 0.5 mol% as boron element and 0.25 mol% as tungsten element with respect to the total number of moles of metals other than lithium in the lithium-transition metal composite oxide contained in the second particles. A positive electrode material was obtained in the same manner as in Example 1, except that tungsten oxide was added in an amount of mol % and the heat treatment temperature was set at 400° C. in the heat treatment step.

[Comparative example 8]
In the mixing step, the molar ratio of lithium hydroxide was adjusted to be Li:(Ni+Co+Mn):Al=1.09:1.0, no molybdenum trioxide was added, and the second temperature in the firing step was 845°C. A positive electrode material was obtained in the same manner as in Comparative Example 7, except that.

[Comparative Example 9]
A positive electrode material was obtained in the same manner as Comparative Example 7 except that the cleaning step was not performed.

[Comparative Example 10]
A positive electrode material was obtained in the same manner as Comparative Example 8 except that the cleaning step was not performed. Relative resistance and relative discharge at SOC 80%, 50%, and 5% in each comparative example when the resistance value of Comparative Example 10 at SOC 80%, 50%, and 5% is set to 1, and the discharge capacity value is set to 1. The capacity is shown in Table 6.

As shown in Table 6, in Comparative Example 10 where the NiCoMn ratio was 6:2:2 and the content of nickel to metals other than lithium was 0.6 or less, in Comparative Example 9 where a molybdenum compound was added, No improvement in output characteristics was observed at low SOC, on the contrary, it was deteriorating. Further, in Comparative Example 7 in which a molybdenum compound was added and water washing was performed, no improvement in output at low SOC was observed.

[Example 8]
A positive electrode material was obtained in the same manner as in Example 2, except that the firing conditions in the firing step were set to an air atmosphere.

[Comparative Example 11]
A positive electrode material was obtained in the same manner as in Example 8, except that a slurry having a solid content concentration of 10% by mass was obtained in the washing step. SOC80%, 50%, 5% in Example 8, Comparative Example 11, and Comparative Example 1 when the resistance value of Comparative Example 1 at SOC80%, 50%, and 5% is 1, and the discharge capacity value is 1. Table 7 shows the relative resistance and discharge capacity of each.

As shown in Table 7, it was confirmed that the effect of improving output characteristics at low SOC could be obtained by performing the cleaning step under conditions such that the solid content concentration was 20% by mass or more.

The disclosure herein may include the following aspects.
(Aspect 1)
A lithium transition metal in which the ratio of the number of moles of nickel to the total number of moles of metals other than lithium in the composition is more than 0.6 and less than 1, obtained by firing a mixture containing a lithium compound, a nickel-containing composite compound, and a molybdenum compound. Obtaining first particles containing a composite oxide;
Part of the molybdenum element contained in the first particles is removed by contacting the first particles with a liquid medium such that the solid content concentration of the first particles is 20% by mass or more and 80% by mass or less. and obtaining second particles. A method for producing a positive electrode material for a lithium ion secondary battery.
(Aspect 2)
The lithium transition metal composite oxide contained in the second particles has a composition in which the ratio of the number of moles of nickel to the total number of moles of metals other than lithium is 0.7 or more and less than 1. A method for producing a positive electrode material for a next battery.
(Aspect 3)
According to aspect 1 or 2, the lithium transition metal composite oxide contained in the second particles has a composition in which the ratio of the number of moles of nickel to the total number of moles of metals other than lithium is 0.8 or more and less than 0.95. A method for producing a positive electrode material for a lithium ion secondary battery.
(Aspect 4)
The method for producing a positive electrode material for a lithium ion secondary battery according to aspect 1, wherein the lithium transition metal composite oxide contained in the second particles is represented by the following compositional formula (1).
Li _p Ni _x Co _y M ¹ _z M ² _u O _2+α (1)
(0.95≦p≦1.5, 0.6<x<1, 0≦y<0.4, 0≦z<0.4, 0≦u≦0.1, -0.3≦α≦ 0.3, x+y+z+u≦1, M ¹ represents at least one of Mn and Al. M ² represents Na, K, Mg, Ca, Ba, Y, Ti, Zr, Nb, Ta, Cr, Mo, W , Fe, Cu, Zn, Cd, Ga, Si, Sn, P, Bi, La, Ce, Nd, Sm, Er, and Lu.)
(Aspect 5)
In the step of obtaining the first particles, the lithium transition metal composite oxide contained in the first particles has a composition in which the ratio of moles of molybdenum to the total moles of metals other than lithium exceeds 0.005 and is 0. .02 or less, the method for producing a positive electrode material for a lithium ion secondary battery according to any one of aspects 1 to 4.
(Aspect 6)
Any of aspects 1 to 5, wherein the lithium transition metal composite oxide contained in the second particles has a composition in which the ratio of the mole number of molybdenum to the total number of moles of metals other than lithium is 0.004 or more and 0.015 or less. The method for producing a positive electrode material for a lithium ion secondary battery according to item 1.
(Aspect 7)
The method for producing a positive electrode material for a lithium ion secondary battery according to any one of aspects 1 to 6, wherein the step of obtaining the first particles includes firing the mixture at a temperature of 800° C. or higher and 1000° C. or lower.
(Aspect 8)
The lithium ion secondary battery according to any one of aspects 1 to 7, wherein in the step of obtaining the second particles, after the first particles are brought into contact with a liquid medium, the first particles are further mixed with a boron compound and heat treated. Method for producing positive electrode material for use.
(Aspect 9)
The method for producing a positive electrode material for a lithium ion secondary battery according to any one of aspects 1 to 8, wherein the nickel-containing composite compound is a composite oxide containing at least nickel and cobalt.
(Aspect 10)
The method for producing a positive electrode material for a lithium ion secondary battery according to any one of aspects 1 to 9, wherein the liquid medium is a solution containing at least one of sodium and lithium.
(Aspect 11)
The composition of the lithium transition metal composite oxide contained in the second particle with respect to the ratio of the number of moles of molybdenum to the total number of moles of metals other than lithium in the composition of the lithium transition metal composite oxide contained in the first particle. The method for producing a positive electrode material for a lithium ion secondary battery according to any one of aspects 1 to 10, wherein the ratio of the number of moles of molybdenum to the total number of moles of metals other than lithium is 0.35 or more and 0.8 or less. .
(Aspect 12)
oxide particles containing an oxide containing lithium, nickel and molybdenum, the ratio of the number of moles of nickel to the total number of moles of metals other than lithium in the composition being more than 0.6 and less than 1;
Ratio of the number of moles of molybdenum to the total number of moles of metals other than lithium contained in the filtered powder obtained by mixing 200 g of the oxide particles and 165 g of pure water and stirring the slurry for 30 minutes. is 0.55 times or more the ratio of the number of moles of molybdenum to the total number of moles of metals other than lithium in the oxide particles before filtration.
(Aspect 13)
The positive electrode material for a lithium ion secondary battery according to aspect 12, wherein the ratio of the number of moles of molybdenum to the total number of moles of metals other than lithium contained in the oxide particles is 0.004 or more and 0.015 or less.

Claims (14)

A lithium transition metal in which the ratio of the number of moles of nickel to the total number of moles of metals other than lithium in the composition is more than 0.6 and less than 1, obtained by firing a mixture containing a lithium compound, a nickel-containing composite compound, and a molybdenum compound. Obtaining first particles containing a composite oxide;
Part of the molybdenum element contained in the first particles is removed by contacting the first particles with a liquid medium such that the solid content concentration of the first particles is 20% by mass or more and 80% by mass or less. and obtaining second particles. A method for producing a positive electrode material for a lithium ion secondary battery. The lithium ion according to claim 1, wherein the lithium transition metal composite oxide contained in the second particles has a composition in which the ratio of the number of moles of nickel to the total number of moles of metals other than lithium is 0.7 or more and less than 1. A method for producing a positive electrode material for a secondary battery. 2. The lithium-transition metal composite oxide contained in the second particles has a composition in which the ratio of the number of moles of nickel to the total number of moles of metals other than lithium is 0.8 or more and less than 0.95. A method for producing a positive electrode material for lithium ion secondary batteries. The method for producing a positive electrode material for a lithium ion secondary battery according to claim 1, wherein the lithium transition metal composite oxide contained in the second particles is represented by the following compositional formula (1).
Li _p Ni _x Co _y M ¹ _z M ² _u O _2+α (1)
(0.95≦p≦1.5, 0.6<x<1, 0≦y<0.4, 0≦z<0.4, 0≦u≦0.1, -0.3≦α≦ 0.3, x+y+z+u≦1, M ¹ represents at least one of Mn and Al. M ² represents Na, K, Mg, Ca, Ba, Y, Ti, Zr, Nb, Ta, Cr, Mo, W , Fe, Cu, Zn, Cd, Ga, Si, Sn, P, Bi, La, Ce, Nd, Sm, Er, and Lu.) In the step of obtaining the first particles, the lithium transition metal composite oxide contained in the first particles has a composition in which the ratio of moles of molybdenum to the total moles of metals other than lithium exceeds 0.005 and is 0. The method for producing a positive electrode material for a lithium ion secondary battery according to claim 1 or 2, wherein the positive electrode material for a lithium ion secondary battery is .02 or less. 3. The lithium transition metal composite oxide contained in the second particles has a composition in which the ratio of the number of moles of molybdenum to the total number of moles of metals other than lithium is 0.004 or more and 0.015 or less. A method for producing the positive electrode material for a lithium ion secondary battery as described above. 6. The lithium-transition metal composite oxide contained in the second particles has a composition in which the ratio of the number of moles of molybdenum to the total number of moles of metals other than lithium is 0.004 or more and 0.015 or less. A method for producing a positive electrode material for lithium ion secondary batteries. The method for producing a positive electrode material for a lithium ion secondary battery according to claim 1 or 2, wherein the step of obtaining the first particles includes firing the mixture at a temperature of 800°C or higher and 1000°C or lower. The positive electrode material for a lithium ion secondary battery according to claim 1 or 2, wherein the step of obtaining the second particles includes further mixing with a boron compound and heat-treating the first particles after contacting the first particles with a liquid medium. Production method. The method for producing a positive electrode material for a lithium ion secondary battery according to claim 1 or 2, wherein the nickel-containing composite compound is a composite oxide containing at least nickel and cobalt. The method for producing a positive electrode material for a lithium ion secondary battery according to claim 1 or 2, wherein the liquid medium is a solution containing at least one of sodium and lithium. The composition of the lithium transition metal composite oxide contained in the second particle relative to the ratio of the number of moles of molybdenum to the total number of moles of metals other than lithium in the composition of the lithium transition metal composite oxide contained in the first particle. The method for producing a positive electrode material for a lithium ion secondary battery according to claim 1 or 2, wherein the ratio of the number of moles of molybdenum to the total number of moles of metals other than lithium is 0.35 or more and 0.8 or less. oxide particles containing an oxide containing lithium, nickel and molybdenum, the ratio of the number of moles of nickel to the total number of moles of metals other than lithium in the composition being more than 0.6 and less than 1;
Ratio of the number of moles of molybdenum to the total number of moles of metals other than lithium contained in the filtered powder obtained by mixing 200 g of the oxide particles and 165 g of pure water and stirring the slurry for 30 minutes. is 0.55 times or more the ratio of the number of moles of molybdenum to the total number of moles of metals other than lithium in the oxide particles before filtration. The positive electrode material for a lithium ion secondary battery according to claim 13, wherein the ratio of the number of moles of molybdenum to the total number of moles of metals other than lithium contained in the oxide particles is 0.004 or more and 0.015 or less.