JP6572545B2 - Method for producing coated lithium-nickel composite oxide particles - Google Patents

Description

  The present invention relates to lithium-nickel composite oxide particles having a high nickel content, and relates to a method for producing easy-to-handle coated lithium-nickel composite oxide particles with improved stability in the air atmosphere.

  In recent years, with the rapid expansion of small electronic devices such as mobile phones and notebook computers, the demand for lithium ion secondary batteries as a chargeable / dischargeable power source has increased rapidly. Lithium-cobalt oxide (hereinafter referred to as cobalt) is widely used as a positive electrode active material that contributes to charge and discharge in the positive electrode of a lithium ion secondary battery. However, by optimizing the battery design, the capacity of the cobalt-based positive electrode is improved to the same level as the theoretical capacity, and it is becoming difficult to further increase the capacity.

  Therefore, development of lithium-nickel composite oxide particles using lithium-nickel oxide having a theoretical capacity higher than that of conventional cobalt-based materials is in progress. However, pure lithium-nickel oxide has problems in safety, cycle characteristics, etc. due to its high reactivity with water, carbon dioxide and the like, and it has been difficult to use it as a practical battery. Accordingly, lithium-nickel composite oxide particles to which transition metal elements such as cobalt, manganese, iron or the like or aluminum are added have been developed as measures for improving the above problems.

  The lithium-nickel composite oxide is a composite oxide particle represented by a transition metal composition Ni0.33Co0.33Mn0.33 called a so-called ternary system in which equimolar amounts of nickel, manganese, and cobalt are added (hereinafter, referred to as “ternary system”). Ternary system) and so-called nickel-based lithium-nickel composite oxide particles (hereinafter sometimes referred to as nickel-based) having a nickel content exceeding 0.75 mol. From the viewpoint of capacity, the nickel system having a high nickel content has a great advantage over the ternary system.

However, nickel (NCA) is more sensitive to the environment than cobalt and ternary because of its high reactivity with water and carbon dioxide, and absorbs moisture and carbon dioxide (CO ₂ ) in the air. There are easy features. It has been reported that moisture and carbon dioxide are deposited on the particle surface as impurities such as lithium hydroxide (LiOH) and lithium carbonate (Li ₂ CO ₃ ), respectively, and adversely affect the positive electrode manufacturing process and battery performance.

  By the way, in the manufacturing process of a positive electrode, it passes through the process of apply | coating and drying the positive mix slurry which mixed lithium- nickel composite oxide particle | grains, a conductive support agent, a binder, the organic solvent, etc. on collectors, such as aluminum. In general, lithium hydroxide may react with a binder to rapidly increase pH and slurry viscosity and cause the slurry to gel in the positive electrode mixture slurry manufacturing process. These phenomena can cause defects and defects, and a decrease in the yield of positive electrode manufacturing, resulting in a difference in product quality. In addition, during charging and discharging, these impurities may react with the electrolytic solution to generate gas, which may cause problems in battery stability.

  Therefore, when nickel-based (NCA) is used as lithium-nickel composite oxide particles, the positive electrode manufacturing process is dry (low humidity) in a decarboxylation atmosphere in order to prevent the generation of impurities such as lithium hydroxide (LiOH). ) It must be done in the environment. Therefore, although nickel-based (NCA) has a high theoretical capacity and is promising as a material for a lithium ion secondary battery, it requires a large equipment introduction cost to maintain its manufacturing environment. There is a problem of becoming.

In order to solve such a problem, a method of coating the surface of the lithium-nickel composite oxide particles by using a coating agent has been proposed. Such coating agents are broadly classified into inorganic coating agents and organic coating agents, and inorganic coating agents include fumed silica, titanium oxide, aluminum oxide, aluminum phosphate, cobalt phosphate, and fluoride. of materials such as lithium, as the coating agent of organic, carboxymethyl cellulose, the material such as a fluorine-containing polymer has been proposed.

For example, Patent Document 1 discloses a method of forming a lithium fluoride (LiF) or fluorine-containing polymer layer on the surface of lithium-nickel composite oxide particles, and Patent Document 2 discloses a fluorine-containing polymer formed on lithium-nickel composite oxide particles. A method of forming a layer and adding a Lewis acid compound for further neutralizing impurities has been proposed. In both treatments, lithium-nickel composite oxide particles are modified to be hydrophobic by a coating layer containing a fluorine-based material, suppressing moisture adsorption and suppressing deposition of impurities such as lithium hydroxide (LiOH). Is possible.
However, the coating layer containing a fluorine-based material used for coating does not have electrical conductivity. Therefore, even if the accumulation of impurities can be suppressed, since the coating layer itself becomes an insulator, the positive electrode resistance is increased and the battery characteristics are deteriorated. Therefore, there has been a problem that the quality of the lithium-nickel composite oxide particles itself is deteriorated.

  In patent document 3, the manufacturing method of the positive electrode active material which can suppress gas generation | occurrence | production inside a battery by making a phosphoric acid compound adhere and heat is proposed. However, in Patent Document 3, gas generation inside the battery is an issue, and it cannot be said that gelation has been sufficiently studied. Therefore, it cannot be said that the optimum conditions for producing the coated lithium-nickel composite oxide particles capable of simultaneously preventing the gelation of the slurry and maintaining the electrical characteristics of the positive electrode active material have been sufficiently studied.

JP 2013-179063 A Special table 2011-511402 gazette JP 2010-55777 A

  In view of the above-mentioned problems of the prior art, the present invention provides a coated lithium-nickel composite oxide particle that can be handled in an air atmosphere and that can provide a coating of a lithium ion conductor that does not adversely affect battery characteristics. The purpose is to provide a manufacturing method.

  In order to solve the above-described problems in the prior art, the present invention is a result of repeated studies on the coating process, more specifically, the mixing conditions of lithium-nickel composite oxide particles and phosphoric acid compounds. It has been found that by performing mixing in an oxygen atmosphere with a predetermined water vapor and carbon dioxide concentration or less, generation of impurities caused by moisture and carbon dioxide in the atmosphere can be suppressed, and gelation of the slurry due to impurities can be suppressed. It was. Therefore, it is a production method capable of producing suitable coated lithium-nickel composite oxide particles that can be handled in an air atmosphere during material handling, transportation, storage, electrode production and battery production. As a result, the present invention has been completed.

  That is, the first invention is a composite hydroxide for producing a composite hydroxide as a coprecipitate by adding an aqueous solution containing an alkaline solution to a mixed aqueous solution containing a nickel salt, a cobalt salt, and an additive metal salt. Mixing and baking a manufacturing process, a heat treatment process for heating the composite hydroxide particles manufactured by the composite hydroxide manufacturing process to obtain heat-treated particles, the heat-treated particles and lithium or / and a lithium compound To the total amount of the firing step of obtaining the lithium-nickel composite oxide particles, the lithium-nickel composite oxide particles obtained by the firing step, and the mixture of the lithium-nickel composite oxide particles and the phosphoric acid compound 2.0 mass% or more and 5.0 mass% or less of a phosphoric acid compound is mixed in an oxygen atmosphere where water vapor is 500 ppm or less and carbon dioxide is 50 ppm or less. A method of producing coated lithium-nickel composite oxide particles for a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising a coating step of obtaining coated lithium-nickel composite oxide particles by heating at a temperature of from ℃ to 300 ℃ It is.

  The second of the present invention is the method for producing coated lithium-nickel composite oxide particles according to the first invention, wherein the coating film of the coated lithium-nickel composite oxide particles in the coating step is amorphous.

  A third aspect of the present invention is the method for producing coated lithium-nickel composite oxide particles according to the first or second aspect, wherein the mixed aqueous solution in the composite hydroxide production step is a mixed aqueous solution further containing a complexing agent. It is.

The lithium-nickel composite oxide particles are a method for producing coated lithium-nickel composite oxide particles according to any one of the first to third inventions represented by the following general formula (1).
_{Li x Ni (1-y-} z) M y N z O 2 ··· (1)
(Wherein x is 0.90 to 1.20, y is 0.01 to 0.20, z is 0.01 to 0.15, 1-yz is a value exceeding 0.75, M represents at least one element selected from the group consisting of Co and Mn, and N represents at least one element selected from the group consisting of Al, In, Mg, W, Mo and Sn.)

  The coated lithium-nickel composite oxide particles produced by the production method of the present invention have excellent electrical conductivity and lithium ion conductivity, and are excellently coated with a film capable of suppressing moisture and carbon dioxide gas permeation. It is a coated lithium-nickel composite oxide particle.

  These coated lithium-nickel composite oxide particles are replaced by positive electrode manufacturing equipment that has been strictly controlled in terms of carbon dioxide gas concentration and water concentration, and can be used for manufacturing equipment that has been used in cobalt and ternary systems. It can be provided as a composite oxide positive electrode active material for an ion battery.

2 is a TEM photograph showing a coated state of coated lithium-nickel composite oxide particles according to Example 1. FIG. 4 is a TEM photograph showing a coated state of coated lithium-nickel composite oxide particles according to Comparative Example 2. FIG.

  The coated lithium-nickel composite oxide particles of the present invention and the production method thereof will be described in detail below. In addition, this invention is not limitedly interpreted by the following detailed description. In the present invention, secondary particles in which primary particles are aggregated may be referred to as lithium-nickel composite oxide particles.

[Compound of phosphoric acid and lithium]
The coated lithium-nickel composite oxide particles of the present embodiment are lithium-nickel composite oxide particles coated with a coating film of a phosphoric acid and lithium compound. By coating the coating film of phosphoric acid and lithium compound, it is possible to suppress the permeation of moisture and carbon dioxide gas. Therefore, the production | generation of the impurity which arises with the water | moisture content and carbon dioxide gas in air | atmosphere can be suppressed, and the raise of pH and slurry viscosity in a positive mix slurry manufacturing process can be suppressed.

The compound of phosphoric acid and lithium refers to a compound containing a phosphate group (PO ₄ ) and a lithium (Li) element. The compound of phosphoric acid and lithium is not particularly limited as long as it is a compound containing a phosphate group (PO ₄ ) and a lithium (Li) element. For example, trilithium phosphate (Li ₃ PO ₄ ) , Lithium dihydrogen phosphate (LiH ₂ PO ₄ ), dilithium hydrogen phosphate (Li ₂ HPO ₄ ), and the like.

  Further, the coating film of phosphoric acid and lithium compound of the coated lithium-nickel composite oxide particles is preferably amorphous. When the coating film is amorphous, the movement of lithium ions can be made preferable. Therefore, it is possible to prevent a decrease in battery characteristics such as discharge capacity due to the coating film.

  The film thickness of the phosphoric acid / lithium compound coating film is preferably 20 nm or more and 90 nm or less. When the film thickness is less than 20 nm, it tends to be difficult to suppress the generation of impurities caused by atmospheric moisture or carbon dioxide. When the film thickness exceeds 90 nm, the battery positive electrode active material tends to have a reduced discharge capacity, a reduced coulomb efficiency, and battery characteristics.

  Moreover, it is preferable that the coating amount of the compound of phosphoric acid and lithium is 2.0 mass% or more and 5.0 mass% or less with respect to the coating lithium-nickel composite oxide particle whole quantity. By setting the coating amount of the phosphoric acid and lithium compound in such a range, it is possible to prevent the generation of impurities caused by moisture and carbon dioxide in the atmosphere, and the discharge capacity and coulomb efficiency as a battery positive electrode active material. Since it does not decrease, preferable battery characteristics can be maintained.

[Lithium-nickel composite oxide particles]
The lithium-nickel composite oxide particles used in the present invention are spherical particles, and the average particle size is preferably 5 to 20 μm. By setting it as such a range, while having favorable battery performance as lithium-nickel composite oxide particle, and coexistence of the favorable lifetime of a battery (cycle characteristic), it is preferable.

  The nickel-based lithium-nickel composite oxide particles are preferably those represented by the following general formula (1).

_{Li x Ni (1-y-} z) M y N z O 2 ··· (1)
(Wherein x is 0.90 to 1.20, y is 0.01 to 0.20, z is 0.01 to 0.15, 1-yz is a value exceeding 0.75, M represents at least one element selected from the group consisting of Co and Mn, and N represents at least one element selected from the group consisting of Al, In, Mg, W, Mo and Sn.)

  The value of 1-yz (nickel content) is preferably a value exceeding 0.80, more preferably a value exceeding 0.90, from the viewpoint of capacity.

  The electrode energy densities (Wh / L) of cobalt-based (LCO), ternary (NCM), and nickel-based (NCA) are 2160 Wh / L (LiCoO 2) and 2018.6 Wh / L (LiNi 0.33 Co 0.33 Mn 0.33 Co 0, respectively. .33O2), 2376 Wh / L (LiNi0.8Co0.15Al0.05O2). Therefore, a high-capacity battery can be manufactured by using the nickel-based lithium-nickel composite oxide particles as a positive electrode active material of a lithium ion battery.

[Method for producing coated lithium-nickel composite oxide particles]
A production method for producing the coated lithium-nickel composite oxide particles will be described.

(Composite hydroxide particle production process)
The composite hydroxide particle production process is a coprecipitate obtained by adding an aqueous solution containing an alkaline solution to a mixed aqueous solution of a nickel salt such as nickel sulfate (II), a cobalt salt such as cobalt sulfate (II) and an added metal salt. Is a step of obtaining composite hydroxide particles. As the additive element used in the additive metal salt, at least one element selected from the group consisting of Al, In, Mg, W, Mo, and Sn can be used. In addition, the concentration of cobalt and the concentration of the additive element with respect to the transition metal are 10 atomic% or more and 35 atomic% or less and the concentration of the additive element is 0 atomic% or more and 35 atomic% from the viewpoint of stabilization of crystal structure and safety. The following is preferable.

  The mixed aqueous solution is made alkaline by adding an aqueous solution containing an alkaline solution. When the complexing agent is not added, the pH range of the mixed aqueous solution is preferably selected from pH = 10 to 11, and the temperature of the mixed aqueous solution is preferably in the range of 60 ° C. or higher and 80 ° C. or lower. By setting it as such a range, a reaction rate can be made into an appropriate range. Further, the solubility of Ni is preferable, and the formation of particles due to crystallization can be prevented. Crystallization in the state of exceeding pH 11 tends to form fine particles, deteriorate filterability, and make it impossible to obtain spherical particles. If the pH is less than 10, the production rate of hydroxide is remarkably slow, Ni remains in the filtrate, and the amount of precipitation of Ni tends to deviate from the target composition, making it difficult to obtain a target mixed hydroxide. Further, when the temperature of the mixed aqueous solution is less than 60 ° C., the reaction rate tends to be insufficient. Furthermore, if the temperature of the mixed aqueous solution exceeds 80 ° C., the amount of water evaporation increases, so the slurry concentration increases, the solubility of Ni decreases, and crystals such as sodium sulfate are generated in the filtrate, and the impurity concentration For example, the charge / discharge capacity of the positive electrode material tends to decrease.

  In addition to adding an aqueous solution containing an alkaline solution, it is preferable to add a complexing agent such as ammonia to the mixed aqueous solution in the composite hydroxide preparation step. The solubility of Ni can be increased by adding a complexing agent such as ammonia. When a complexing agent is used, it is preferable that pH = 10 to 12.5 is selected for the pH range of the mixed aqueous solution, and the temperature of the mixed aqueous solution is in the range of 40 ° C. or higher and 60 ° C. or lower. In the reaction tank, the concentration of the complexing agent in the aqueous reaction solution is preferably maintained at a constant value within a range of 3 g / L to 25 g / L. When the complexing agent concentration is less than 3 g / L, the solubility of metal ions cannot be kept constant, so that plate-shaped hydroxide primary particles having a uniform shape and particle size are not formed, and gel-like particles are not formed. Since nuclei are easily generated, the particle size distribution tends to be widened. On the other hand, when the ammonia concentration exceeds 25 g / L, the solubility of metal ions becomes too high, the amount of metal ions remaining in the reaction aqueous solution increases, and there is a tendency for compositional deviation and the like to occur. Further, when the ammonia concentration varies, the solubility of metal ions varies, and uniform hydroxide particles are not formed. Therefore, it is preferable to maintain a constant value. For example, the ammonia concentration is preferably maintained at a desired concentration by setting the upper and lower limits to about 5 g / L.

(Heat treatment process)
The heat treatment step is a step of obtaining heat-treated particles by heating and heat-treating the composite hydroxide particles produced in the composite hydroxide production step. The moisture contained in the composite hydroxide particles can be removed by the heat treatment step. By performing this heat treatment step, moisture remaining in the particles up to the firing step can be reduced. In addition, since the composite hydroxide particles can be converted into composite oxide particles, it is possible to prevent the ratio of the number of metal atoms and the number of lithium atoms in the produced positive electrode active material from being varied. Note that it is only necessary to remove moisture to such an extent that the ratio of the number of metal atoms and the number of lithium atoms in the positive electrode active material does not vary, so it is not necessary to convert all composite hydroxide particles to composite oxide particles. Absent. In the heat treatment step, the composite hydroxide particles may be heated to a temperature at which residual moisture is removed, and the heat treatment temperature is not particularly limited, but is preferably 105 ° C. or higher and 800 ° C. or lower. Residual moisture can be removed by heating the composite hydroxide particles to 105 ° C. or higher. In addition, if it is less than 105 degreeC, it exists in the tendency for a long time to remove a residual water | moisture content. When it exceeds 800 ° C., the particles converted into the composite oxide tend to sinter and aggregate. The atmosphere in which the heat treatment is performed is not particularly limited, and is preferably performed in an air stream that can be easily performed.

(Baking process)
The firing step is a step of obtaining lithium-nickel composite oxide particles by firing a lithium mixture obtained by mixing the heat treated particles obtained in the heat treatment step and lithium or / and a lithium compound. The heat-treated particles are composite hydroxide particles from which residual moisture has been removed in the heat treatment step, composite oxide particles converted into oxides in the heat treatment step, or mixed particles thereof. The lithium mixture is the ratio of the number of atoms of metals other than lithium in the lithium mixture (ie, the sum of the number of atoms of nickel, cobalt and added metal (Me)) to the number of atoms of lithium (Li) (Li / Me). Is preferably 0.90 to 1.20, more preferably 0.95 to 1.10. That is, it mixes so that Li / Me in a lithium mixture may become the same as Li / Me in the positive electrode active material of this invention. This is because Li / Me does not change before and after the firing step, and thus Li / Me to be mixed becomes Li / Me in the positive electrode active material.

  The lithium compound is not particularly limited, but for example, lithium hydroxide, lithium nitrate, lithium carbonate, or a mixture thereof is preferable because it is easily available. In particular, lithium hydroxide is more preferably used in consideration of ease of handling and stability of quality.

  The lithium mixture is preferably mixed well before firing. By sufficiently mixing before firing, there is no variation in Li / Me (added metal) between individual particles, and sufficient battery characteristics can be obtained.

  The firing step is a step in which the lithium mixture is fired to obtain lithium-nickel composite oxide particles. When the lithium mixture is fired in the firing step, lithium in the substance containing lithium diffuses into the heat-treated particles, so that lithium-nickel composite oxide particles are formed. Firing of the lithium mixture is performed at 700 ° C. or higher and 850 ° C. or lower, particularly preferably 720 ° C. or higher and 820 ° C. or lower. When the firing temperature is less than 700 ° C., lithium is not sufficiently diffused into the heat-treated particles, surplus lithium and unreacted particles remain, and the crystal structure tends to be insufficiently arranged. On the other hand, when the firing temperature exceeds 850 ° C., intense sintering occurs between the heat treated particles and abnormal grain growth tends to occur. Then, there is a possibility that the particles after firing become coarse and the particle form (form of spherical secondary particles described later) cannot be maintained, and when the positive electrode active material is formed, the specific surface area decreases and the positive electrode There is a tendency that the resistance increases and the battery capacity decreases. The firing time is preferably at least 3 hours or more, more preferably 6 hours or more and 24 hours or less.

  The atmosphere during firing is preferably an oxidizing atmosphere, and more preferably an atmosphere having an oxygen concentration of 18% by volume to 100% by volume. That is, firing is preferably performed in the air or in an oxygen stream. This is because if the oxygen concentration is less than 18% by volume, the composite hydroxide particles contained in the heat-treated particles cannot be sufficiently oxidized, and the crystallinity of the lithium-nickel composite oxide particles may be insufficient. Because there is sex. Considering battery characteristics in particular, it is preferable to carry out in an oxygen stream.

[Coating process]
In the coating step, the lithium-nickel composite oxide particles obtained in the firing step are mixed with a phosphoric acid compound in an atmosphere from which water vapor and carbon dioxide have been removed, and reacted with the surface. This is a step of covering the covering film. When the composite oxide obtained in the firing step is dispersed in water, high alkalinity is exhibited. This is because lithium present on the outer surface of the particles is eluted to produce lithium hydroxide. Since lithium on the outer surface is extremely reactive, it reacts with water vapor and carbon dioxide in the atmosphere. This water vapor or carbon dioxide causes deformation of the battery container when the battery is assembled, and the fired composite oxide is mixed in an oxygen atmosphere with water vapor of 500 ppm or less and carbon dioxide of 50 ppm or less. In this way, the lithium and phosphate compound on the surface of the particles react quickly by bringing the composite oxide and phosphoric acid compound that remain in the oxidized state immediately after firing into contact, thereby producing a phosphoric acid and lithium compound. To do. Note that the oxygen concentration in the oxygen atmosphere is preferably 18% by volume or more and 100% by volume or less.

  A phosphoric acid compound refers to a compound having a structure containing a phosphate group. By bringing the composite oxide and the phosphoric acid compound into contact with each other, lithium and the phosphoric acid compound on the surface of the particles react quickly to form a phosphoric acid and lithium compound. Examples of the phosphoric acid compound include ammonium dihydrogen phosphate, diammonium hydrogen phosphate, lithium phosphate, and mixtures thereof.

  The phosphoric acid compound is mixed in an amount of 2.0% by mass or more and 5.0% by mass or less based on the total amount of the mixture of the lithium-nickel composite oxide particles and the phosphoric acid compound. If it is less than 2.0% by mass, the coating amount of the phosphoric acid and lithium compound is not sufficient, and it becomes difficult to suppress the gelation of the slurry due to the impurities. If it exceeds 5.0% by mass, the coating amount of the phosphoric acid and lithium compound is too large, which affects the electrical characteristics of the positive electrode active material and reduces the initial discharge capacity of the battery.

  Further, the mixture of the lithium-nickel composite oxide particles and the phosphoric acid compound is heated at a temperature of 120 ° C. or higher and 300 ° C. or lower. By heating at such a temperature, moisture and carbon dioxide adhering to and accompanying the phosphoric acid compound can be removed. Therefore, gelation of the slurry due to impurities can be suppressed. However, when exposed to a high temperature of 400 ° C. or higher, the reaction is accelerated by the high energy, but it becomes easy to crystallize when cooled. As crystallization progresses, the mobility of lithium is lost, and the battery performance decreases. In addition, when exposed to a high temperature of 400 ° C. or higher, the formed compound causes excessive aggregation and unevenness of the coating film, resulting in insufficient coverage of the entire particle by the coating film, and thus the exposed composite oxide It is difficult to suppress gelation by the particle surface. Therefore, it is most preferable that the temperature at which the phosphoric acid / lithium compound is generated be 120 ° C. or more and 300 ° C. or less, the water vapor is 500 ppm or less and the carbon dioxide is 50 ppm or less, and the atmosphere is in an oxygen stream.

  Examples of the present invention will be specifically described below with reference to comparative examples. However, the present invention is not limited only to the following examples.

Example 1
Nickel sulfate, cobalt sulfate, and sodium aluminate are dissolved in water, and a sodium hydroxide solution is added with sufficient stirring. The molar ratio of nickel (Ni), cobalt (Co), and aluminum (Al) Ni: Co: Al = 81.5: 15: 3.5 Composite hydroxide particles were obtained as a coprecipitate. The produced coprecipitate was filtered, washed with water, dried, then heated to 700 ° C. in the atmosphere and held for 6 hours, and then heat-treated by furnace cooling to room temperature to obtain heat-treated particles.

The heat-treated particles and lithium hydroxide / hydrate salt commercially available as lithium or / and a lithium compound are sufficiently mixed so that the molar ratio is Li: (Ni + Co + Al) = 103: 100, and is heated to 500 ° C. in an oxygen stream. The temperature was raised to 500 ° C. and held for 3 hours, then heated to 745 ° C. and held for 12 hours, and then cooled in the furnace to room temperature, so that the transition metal composition Li _1.03 Ni _0.82 Co _{0 .15} Lithium-nickel composite oxide particles represented by Al _0.03 were obtained.

The lithium-nickel composite oxide particles are taken out so as not to be exposed to the outside air, and in an oxygen atmosphere (99.9 vol% oxygen, 495 ppm water vapor, 30 ppm carbon dioxide) as an atmosphere from which water vapor and carbon dioxide have been removed. Crushed. Then, 25 g of the pulverized lithium-nickel composite oxide particles and 0.6 g of ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ) were sufficiently mixed. This mixture was kept in an oxygen stream at 300 ° C. for 4 hours and cooled to room temperature, and then taken out from the furnace to obtain coated lithium-nickel composite oxide particles of Example 1. In addition, when elemental analysis was performed on the coating film by the EDX image, it was presumed that the phosphoric acid and lithium compound was coated because the phosphorus element was detected.

  The coated lithium-nickel composite oxide particles coated with the phosphoric acid and lithium compound were used as the coated lithium-nickel composite oxide particles according to Example 1, and the air stability test, gelation test, and battery described below were used. Characteristic tests (charge / discharge test, coulomb efficiency) were conducted.

(Example 2)
The coated lithium-nickel composite oxide particles of Example 2 were obtained in the same manner as in Example 1 except that the amount of ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ) was 1.2 g in Example 1. Various evaluations were made.

(Example 3)
Be the same as any addition to the temperature for heating the mixture of the composite oxide and ammonium dihydrogen phosphate and 120 ° C. Example 2 In Example 2, it was as in Example 3.

(Comparative Example 1)
Except not adding and mixing ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ) in Example 1, everything was the same as Example 1 to obtain lithium-nickel composite oxide particles of Comparative Example 1, and various evaluations were made. went.

(Comparative Example 2)
Various evaluations were made as Comparative Example 2 except that the amount of ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ) in Example 1 was changed to 1.8 g.

(Comparative Example 3)
In Example 1, except that the composite oxide was 100 g and the amount of ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ) was 0.8 g, all were the same as Example 1, and Comparative Example 3 was used. went.

(Comparative Example 4)
In Example 1, except that the temperature at which the mixture of the composite oxide and ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ) was heated was 700 ° C., all was the same as Example 1, and Comparative Example 4 was used. Evaluation was performed.

(Comparative Example 5)
In Example 1, the temperature of heating the mixture of the composite oxide and ammonium dihydrogen phosphate was 120 ° C., and the atmosphere was in the air (20% by volume of oxygen, 19000 ppm of water vapor, and 400 ppm of carbon dioxide). Various evaluations were made in the same manner as Example 1 as Comparative Example 5.

(Comparative Example 6)
Various evaluations were made as Comparative Example 6 except that the atmosphere in the Example 1 was air (20% by volume of oxygen, 19000 ppm of water vapor, and 400 ppm of carbon dioxide).

<Gelification test>
The change in the viscosity of the positive electrode mixture slurry with time was measured by preparing a positive electrode mixture slurry in the following order, and observing the increase in viscosity and gelation.

  As a compounding ratio, the respective mass ratios of lithium-nickel composite oxide particles: conductive aid: binder: N-methyl-2-pyrrolidone (NMP) according to Examples and Comparative Examples are 45: 2.5: 2. It weighed so that it might become 5:50, and also after adding 1.5 mass% water, it stirred with the autorotation and revolution mixer, and obtained the positive mix slurry. The obtained slurry was stored in an incubator at 25 ° C., the change with time was stirred with a spatula, the viscosity increase and the degree of gelation were confirmed for each of the Examples and Comparative Examples, and stored until complete gelation. Table 1 shows the number of days until gelation.

From Table 1, while it took 3 days for the slurry according to Example 1 and Example 2 to completely gel, the slurry according to Comparative Example 1, Comparative Example 3, Comparative Example 5 and Comparative Example 6 It took 8 hours (within 1 day) to completely gel. From this, the slurry according to the example is such that lithium hydroxide (LiOH), lithium carbonate (Li ₂ CO ₃ ) and the like are obtained by coating the lithium-nickel composite oxide particle surface with a compound of phosphoric acid and lithium. It was confirmed that the generation of impurities can be suppressed, and the gelation of the slurry and the increase in the slurry viscosity due to the reaction between these impurities and the binder can be prevented. On the other hand, Comparative Example 1 in which the phosphoric acid and lithium compound was not coated, and ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), which is a phosphoric acid compound in the coating step, was 2.0% by mass with respect to the total amount of the mixture. Comparative Example 3 in which only a small amount is mixed, Comparative Example 4 in which the coating process is performed in an atmosphere exceeding 300 ° C., or ammonium dihydrogen phosphate which is a lithium-nickel composite oxide particle and a phosphate compound in the coating process In Comparative Example 5 in which mixing with (NH ₄ H ₂ PO ₄ ) was performed in an air atmosphere (oxygen 20 volume%, water vapor 19000 ppm, carbon dioxide 400 ppm), gelation and increase in slurry viscosity occurred. It was confirmed. This is presumed that impurities such as lithium hydroxide (LiOH) and lithium carbonate (Li ₂ CO ₃ ) were generated in Comparative Examples 1, 3, 4, 5, and 6.

<Battery characteristics evaluation>
A nonaqueous electrolyte secondary battery for evaluation (lithium ion secondary battery) was produced by the following procedure, and battery characteristics were evaluated.

[Manufacture of secondary batteries]
The battery characteristics of the coated lithium-nickel composite oxide particles were evaluated by preparing a coin-type battery and a laminate-type battery, and measuring the charge / discharge capacity and the Coulomb efficiency with the coin-type battery.

(A) Positive electrode The coated lithium-nickel composite oxide particles according to the obtained Examples and Comparative Examples were mixed with acetylene black as a conductive auxiliary agent and polyvinylidene fluoride (PVdF) as a binder. It mixed so that mass ratio might be 85: 10: 5, and it was made to melt | dissolve in N-methyl-2-pyrrolidone (NMP) solution, and produced the positive mix slurry. This positive electrode mixture slurry was applied to an aluminum foil with a comma coater, heated at 100 ° C., and dried to obtain a positive electrode. The obtained positive electrode was passed through a roll press to apply a load, and a positive electrode sheet with an improved positive electrode density was produced. This positive electrode sheet was punched out to have a diameter of 9 mm for coin type battery evaluation, and cut out to be 50 mm × 30 mm for a laminate cell type battery, and each was used as an evaluation positive electrode.

(B) Negative electrode Graphite as a negative electrode active material and polyvinylidene fluoride (PVdF) as a binder are mixed so that the mass ratio of these materials is 92.5: 7.5, and N-methyl-2 A negative electrode mixture paste was obtained by dissolving in a pyrrolidone (NMP) solution.

  The negative electrode mixture slurry was applied to a copper foil with a comma coater in the same manner as the positive electrode, heated at 120 ° C., and dried to obtain a negative electrode. The obtained negative electrode was passed through a roll press to apply a load, and a negative electrode sheet with improved electrode density was produced. The obtained negative electrode sheet was punched out so as to have a diameter of 14 mm for a coin type battery, and cut out so as to be 54 mm × 34 mm for a laminated cell type battery, and each was used as a negative electrode for evaluation.

(C) Coin battery and laminate cell type battery The produced electrode for evaluation was dried at 120 ° C. for 12 hours in a vacuum dryer. And using this positive electrode, a 2032 type coin battery and a laminate cell type battery were produced in a glove box in an argon atmosphere in which the dew point was controlled at −80 ° C. For the electrolyte, ethylene carbonate (EC) and diethyl carbonate (DEC) 3: 7 (manufactured by Toyama Pharmaceutical Co., Ltd.) using 1M LiPF ₆ as a supporting electrolyte and a glass separator as a separator were used for each evaluation battery. Was made.

<< Charge / Discharge Test >>
The produced coin-type battery is allowed to stand for about 24 hours after assembly, and after the open circuit voltage OCV (Open Circuit Voltage) is stabilized, the cut-off voltage is set at a current density of 0.2 C in a constant temperature bath at 25 ° C. The battery was charged until it reached 3V. A charge / discharge test was conducted to measure the discharge capacity when discharged until the cut-off voltage reached 3.0 V after a 1-hour rest, and the initial discharge capacity (mAh / g) and Coulomb efficiency were determined. The evaluation results are shown in Table 1.

From Table 1, the initial discharge capacity of the coin-type battery according to Example 1 is 197.1 mAh / g, the coulomb efficiency is 92.7%, and the initial discharge capacity of the coin-type battery according to Example 2 is 194.8 mAh / g. The Coulomb efficiency is 92.5%, and good battery identification can be maintained. On the other hand, the initial discharge capacity of the coin-type battery according to Comparative Example 2 in which the amount of the phosphoric acid compound exceeds 5.0 mass% is 185.6 mAh / g, and the coulomb efficiency is 91.6%. Compared to the example, the initial discharge capacity is decreased. This is considered to have influenced the electrical characteristics of the positive electrode active material because the coating amount was too large. In addition, the Coulomb efficiency of the coin-type battery according to Comparative Example 5 in which the mixing in the coating process is performed in an air atmosphere (oxygen is 20% by volume, water vapor is 19000 ppm, carbon dioxide is 400 ppm) is 91.8%, and Comparative Example 6 The coulomb efficiency of the coin-type battery according to the present invention is 91%, and a decrease in coulomb efficiency is seen compared to the example. This is because the mixing in the coating process was carried out in an air atmosphere of over 500 ppm of water vapor and over 50 ppm of carbon dioxide (20% by volume of oxygen, 19000 ppm of water vapor, and 400 ppm of carbon dioxide), so lithium hydroxide (LiOH), carbonic acid It is considered that impurities such as lithium (Li ₂ CO ₃ ) are generated, causing a problem in the stability of the battery.

  Table 1 shows the thickness of the particle surface obtained by TEM observation of the lithium phosphate compound in Examples 1 to 3 and Comparative Examples 1 to 3. FIG. 1 shows a TEM photograph showing the coated state of the coated lithium-nickel composite oxide particles according to Example 1, and FIG. 2 shows the coated state of the coated lithium-nickel composite oxide particles according to Comparative Example 2. The TEM photograph which showed was shown. As shown in FIG. 1, in Example 1, the outer surface of the particle different from the material of the particle was in the form of a coating film having a thickness of about 40 nm. Moreover, it was confirmed from the EDX image that the coating film contains phosphorus. As shown in FIG. 2, in Comparative Example 2, the phosphor-containing material similarly covers the outer surface of the particle with a thickness of about 100 nm. Moreover, in the XRD measurement, no peak other than the peak attributed to lithium nickelate was observed in any sample, and it was confirmed that the generated compound was amorphous.

  Further, Table 1 shows the results obtained by dispersing 2.5 g of the lithium-nickel composite oxide particles of Examples and Comparative Examples in 50 ml of ion-exchanged water and measuring the hydrogen ion concentration (pH). Comparative Example 1 shows a value exceeding pH 12, suggesting that lithium derived from the lithium-nickel composite oxide particles is present on the outer surface of the particles. In general, lithium and phosphoric acid form a lithium phosphate compound such as trilithium phosphate or dilithium monohydrogen phosphate, and this reaction is considered to occur on the surface of the composite oxide particles. Lithium on the surface of the composite oxide particles stabilizes by forming a compound with phosphoric acid, which reduces the pH value when dispersed in water and lowers the pH that causes gelation. I understand that

Claims (4)

A composite hydroxide production step of producing a composite hydroxide as a coprecipitate by adding an aqueous solution containing an alkaline solution to a mixed aqueous solution containing a nickel salt, a cobalt salt, and an additive metal salt;
A heat treatment step of heating the composite hydroxide particles produced by the composite hydroxide production step to obtain heat treated particles;
A calcining step of obtaining lithium-nickel composite oxide particles by mixing and calcining the heat treated particles and lithium or / and a lithium compound;
Phosphoric acid compound of 2.0% by mass or more and 5.0% by mass or less with respect to the total amount of the lithium-nickel composite oxide particles obtained by the firing step and the mixture of the lithium-nickel composite oxide particles and the phosphoric acid compound And a coating step of mixing in an oxygen atmosphere with water vapor of 500 ppm or less and carbon dioxide of 50 ppm or less and heating at a temperature of 120 ° C. or more and 300 ° C. or less to obtain coated lithium-nickel composite oxide particles. A method for producing coated lithium-nickel composite oxide particles for a positive electrode active material for an electrolyte secondary battery.   The method for producing coated lithium-nickel composite oxide particles according to claim 1, wherein the coating film of the coated lithium-nickel composite oxide particles in the coating step is amorphous.   The method for producing coated lithium-nickel composite oxide particles according to claim 1 or 2, wherein the mixed aqueous solution in the composite hydroxide production step is a mixed aqueous solution further containing a complexing agent. The method for producing coated lithium-nickel composite oxide particles according to any one of claims 1 to 3, wherein the lithium-nickel composite oxide particles are represented by the following general formula (1).
_{Li x Ni (1-y-} z) M y N z O 2 ··· (1)
(Wherein x is 0.90 to 1.20, y is 0.01 to 0.20, z is 0.01 to 0.15, 1-yz is a value exceeding 0.75, M represents either Co, or Co and Mn , and N represents at least one element selected from the group consisting of Al, In, Mg, W, Mo, and Sn.)