Method for producing metal hydroxide and method for producing lithium-containing metal oxide

Abstract

The present disclosure provides a method for efficiently producing a metal hydroxide using a metal nitrate and lithium hydroxide. 　This method comprises mixing a first solution, which contains a metal nitrate, with a second solution, which contains lithium hydroxide, and precipitating a metal hydroxide. The first solution has a metal nitrate concentration higher than 1.0 mol / L but not higher than 6.0 mol / L. The second solution has a lithium hydroxide concentration higher than 1.0 mol / L but not higher than 5.0 mol / L. The metal hydroxide has a lithium atom content of, for example, 0.002-5.4 mass%. The metal hydroxide has a nitrogen atom content of, for example, 0.004-9.8 mass%.

Description

Method for producing metal hydroxides and method for producing lithium-containing metal oxides

[0001] This disclosure relates to a method for producing metal hydroxides and a method for producing lithium-containing metal oxides.

[0002] Metal oxides containing lithium and other metallic elements are typical positive electrode materials for lithium-ion batteries. These types of metal oxides can be obtained, for example, by calcining a mixture of lithium hydroxide and other metal hydroxides. Therefore, there is a need to efficiently produce high-quality metal hydroxides as precursors.

[0003] Metal hydroxides are typically produced from metal sulfates. For example, when an aqueous solution of nickel sulfate is mixed with an alkaline aqueous solution such as sodium hydroxide, solid nickel hydroxide precipitates. Metal sulfates are produced by creating an intermediate from ore using a high-pressure acid leaching method with sulfuric acid, and then removing impurities from the intermediate by methods such as solvent extraction. Alternatively, metal sulfates can be produced by dissolving a recycled material called black mass and removing impurities from the dissolved product.

[0004] Patent No. 7298004

[0005] When metal sulfates and sodium hydroxide are used as starting materials, the metal hydroxide contains sulfur and sodium. Sulfur and sodium are impurities in the final metal oxide. To reduce the sulfur content, it is necessary to thoroughly wash the metal hydroxide or metal oxide with water. In this case, the disposal method of the large amount of waste liquid generated becomes an issue. The disposal method of the sodium sulfate aqueous solution produced along with the metal hydroxide also becomes an issue.

[0006] On the other hand, if metal nitrates are used instead of metal sulfates, and lithium hydroxide is used instead of sodium hydroxide, the metal hydroxide will not contain sulfur or sodium.

[0007] This disclosure provides a method for efficiently producing metal hydroxides using metal nitrates and lithium hydroxide.

[0008] This disclosure provides a method for producing a metal hydroxide, comprising mixing a first solution containing a metal nitrate with a second solution containing lithium hydroxide to precipitate a metal hydroxide, wherein the concentration of the metal nitrate in the first solution is higher than 1.0 mol / L and 6.0 mol / L or less, and the concentration of the lithium hydroxide in the second solution is higher than 1.0 mol / L and 5.0 mol / L or less.

[0009] According to this disclosure, metal hydroxides can be efficiently produced using metal nitrates and lithium hydroxide.

[0010] Figure 1 is a process diagram showing a method for producing a metal oxide according to an embodiment of this disclosure. Figure 2 is a process diagram following the solid-liquid separation step shown in Figure 1. Figure 3 is a process diagram following the Li2O recovery step shown in Figure 2. Figure 4A is an SEM image of nickel hydroxide from Example 1. Figure 4B is an SEM image of nickel hydroxide from Comparative Example 1. Figure 5A is a cross-sectional SEM image of lithium nickel composite oxide from Example 1. Figure 5B is a cross-sectional SEM image of lithium nickel composite oxide from Comparative Example 1.

[0011] (Knowledge forming the basis of this disclosure) An embodiment of Patent Document 1 describes that metal hydroxides can be synthesized from metal nitrates instead of metal sulfates. Patent Document 1 also describes the use of an aqueous lithium hydroxide solution as the alkaline aqueous solution.

[0012] On the other hand, Patent Document 1 only describes the specific conditions for a method of synthesizing metal hydroxides from metal sulfates. The properties of metal nitrates differ from those of metal sulfates. Therefore, there is a need for technology to efficiently produce metal hydroxides using metal nitrates and lithium hydroxide.

[0013] The embodiments of this disclosure will be described below with reference to the drawings. This disclosure is not limited to the embodiments described below.

[0014] (Embodiment) Figure 1 is a process diagram showing a method for producing a metal oxide according to an embodiment of the present disclosure. The metal oxide is produced via a precursor metal hydroxide. The metal oxide is typically a lithium-containing metal oxide.

[0015] Before carrying out each step shown in Figure 1, the starting materials are prepared. The starting materials are a first solution containing a metal nitrate and a second solution containing lithium hydroxide. The first and second solutions are typically aqueous solutions. When the solvent is water, the effort of recovering the evaporated solvent can be omitted.

[0016] The concentration of metal nitrate in the first solution is, for example, higher than 1.0 mol / L and 6.0 mol / L or less. Alternatively, the concentration of metal nitrate in the first solution may be higher than 1.0 mol / L and 4.0 mol / L or less. The concentration of lithium hydroxide in the second solution is, for example, higher than 1.0 mol / L and 5.0 mol / L or less. The solubility of metal nitrate in water is higher than that of metal sulfate. Therefore, it is possible to adjust the concentration of metal nitrate in the first solution to within the above range. By adjusting the concentration of metal nitrate in the first solution and the concentration of lithium hydroxide in the second solution to high values, the total volume of the first and second solutions can be significantly reduced. This is advantageous for the efficient production of metal hydroxides.

[0017] The concentration of metal nitrate in the first solution is preferably 2.0 mol / L or higher. When the concentration of metal nitrate is high, metal hydroxide can be precipitated while further reducing the total volume of the first and second solutions.

[0018] The concentration of lithium hydroxide in the second solution is preferably 3.5 mol / L or higher. When the concentration of lithium hydroxide is high, metal hydroxides can be precipitated while further reducing the total volume of the first and second solutions.

[0019] Metal nitrates contain at least one metal element selected from the group consisting of, for example, Ni, Mn, Co, Al, Ca, Sr, Zr, Nb, and Ti. The composition of metal hydroxides can be controlled by selecting the type of metal element contained in the metal nitrate.

[0020] In detail, the metal nitrate may be at least one selected from the group consisting of nickel nitrate (Ni(NO3)2), manganese nitrate (Mn(NO3)2), cobalt nitrate (Co(NO3)2), aluminum nitrate (Al(NO3)3), calcium nitrate (Ca(NO3)2), strontium nitrate (Sr(NO3)2), zirconium nitrate (ZrO(NO3)2), niobium nitrate (Nb(NO3)5), and titanium nitrate (Ti(NO3)4). For example, when an aqueous solution of nickel nitrate is mixed with an aqueous solution of lithium hydroxide, nickel hydroxide is obtained as a metal hydroxide. For example, when an aqueous solution containing nickel nitrate, cobalt nitrate, and manganese nitrate is mixed with an aqueous solution of lithium hydroxide, nickel-cobalt-manganese hydroxide is obtained as a metal hydroxide. The composition of the metal hydroxide can be controlled by adjusting the atomic ratio of the metal elements in the first solution containing the metal nitrate.

[0021] As shown in Figure 1, in the precipitation step S1, the first solution and the second solution are mixed to precipitate the metal hydroxide. In the precipitation step, the pH of the mixed solution of the first and second solutions at 50°C is adjusted to, for example, 9.5 to 11.5, preferably 10 to 11.5. By adjusting the pH of the mixed solution to this range, the metal hydroxide can be precipitated efficiently.

[0022] To adjust the pH of the mixed solution of the first and second solutions, a pH adjusting agent may be added to the mixture. Ammonia is an example of a pH adjusting agent. Gaseous ammonia may be dissolved in the mixture, or an aqueous ammonia solution may be added to the mixture. Using ammonia as a pH adjusting agent avoids the contamination of metal hydroxides with metal atoms such as sodium as impurities. On the other hand, using ammonia as a pH adjusting agent results in the contamination of metal hydroxides with nitrogen atoms. However, as long as metal nitrates are used, nitrogen atoms are inevitably present in the metal hydroxides. Therefore, ammonia is desirable from the standpoint of reducing the types of impurities. In addition, ammonia is easy to recover afterward.

[0023] In the precipitation process, the temperature of the mixed solution of the first and second solutions is maintained at, for example, 20°C to 90°C, preferably 40°C to 60°C. Maintaining the temperature of the mixed solution at an appropriate temperature prevents unintended evaporation of the solvent and ammonia.

[0024] In the precipitation process, the first solution and the second solution may be mixed directly, or they may be mixed by adding the first solution and the second solution to water at an appropriate temperature. In this case, it is desirable that the temperature of the first solution and the temperature of the second solution are equal. When the temperatures of the first solution and the second solution are equal, temperature control of the mixed solution is easy, and the solubility is also improved. Note that when the temperature difference between the temperature of the first solution and the temperature of the second solution is 5°C or less, their temperatures are considered to be equal.

[0025] During the precipitation process, lithium nitrate is produced along with the metal hydroxide. The lithium nitrate remains dissolved in the solvent (water) and does not precipitate.

[0026] In the solid-liquid separation step S2, the mixed solution is separated into a metal hydroxide and a residual solution using filter paper, a centrifuge, a filter press, etc. This yields a metal hydroxide as a precursor. The residual solution contains lithium nitrate and a pH adjuster.

[0027] In the drying step S3, the metal hydroxide is dried. The ambient temperature during the drying step is, for example, 105°C to 120°C. The drying time is, for example, 1 to 12 hours. The ambient atmosphere during the drying step is, for example, air. The metal hydroxide may also be air-dried naturally under air.

[0028] A precursor metal hydroxide is obtained through steps S1 to S3. The metal hydroxide is, for example, in powder form.

[0029] In this embodiment, an aqueous solution of lithium hydroxide is used as the second solution, which is an alkaline aqueous solution. More specifically, the metal element contained in the second solution only needs to be lithium as the main component, or it may be lithium alone. "Main component" means the component that is present in the largest amount by mass. "Lithium only" means that, excluding unavoidable impurities, no metal elements other than lithium have been intentionally added. The ratio of the mass of unavoidable impurities to the total mass of lithium hydroxide may be 5% or less, 3% or less, 1% or less, or 0.5% or less. Metal elements that can be impurities include sodium and potassium.

[0030] Metal hydroxides contain lithium atoms derived from lithium hydroxide. The lithium atom content in the metal hydroxide is, for example, 0.002% by mass or more and 5.4% by mass or less. When the final product is a lithium-containing metal oxide, the lithium atoms contained in the precursor are not impurities but active ingredients. Therefore, if the metal hydroxide contains lithium atoms, the amount of lithium compound used in subsequent steps (steps S5 and S6) can be reduced.

[0031] In this embodiment, a metal nitrate is used as the metal source. Therefore, the metal hydroxide contains nitrogen atoms derived from the metal nitrate and nitrogen atoms derived from ammonia as a pH adjuster. The nitrogen atom content in the metal hydroxide is, for example, 0.004% by mass or more and 9.8% by mass or less. The nitrogen atoms are contained in the metal hydroxide in the form of lithium nitrate, for example. When lithium nitrate is present between the primary particles of the metal hydroxide, nitrate ions (NO3) are formed in the calcination process (step S6) described later. - The nitrates vaporize, and tiny voids resulting from the vaporization of nitrate ions remain in the secondary particles of the metal oxide after calcination. However, the ionic radius of nitrate ions is smaller than that of sulfate ions. Therefore, metal nitrates are more advantageous than metal sulfates in increasing the density of the final product, the metal oxide.

[0032] Furthermore, when metal sulfates are used as the metal source, sulfur atoms remain in the metal hydroxide in the form of lithium sulfate. 2- Lithium sulfate does not vaporize even when heated and remains as lithium sulfate. Lithium sulfate causes a decrease in the capacity of lithium-containing metal oxides used as cathode materials.

[0033] Steps S4 to S10 are steps for producing lithium-containing metal oxides from metal hydroxides.

[0034] In step S4, the oxidation roasting process, the metal hydroxide is roasted. The oxidation roasting process is a process that converts metal hydroxide into metal oxide. For example, if the metal hydroxide is nickel-cobalt-manganese composite hydroxide, the nickel-cobalt-manganese composite hydroxide is converted into nickel-cobalt-manganese composite oxide through the oxidation roasting process. The ambient temperature in the oxidation roasting process is, for example, 350°C to 650°C. The roasting time is, for example, 3 hours to 12 hours. The ambient atmosphere in the oxidation roasting process is, for example, an atmospheric atmosphere.

[0035] The drying step in step S3 and the oxidative roasting step in step S4 are optional. The metal hydroxide obtained through step S2 may be provided to the mixing step in step S5 without going through the drying and oxidative roasting steps. However, by going through the drying and oxidative roasting steps, moisture can be removed and the oxidation state of the metal in the metal oxide can be appropriately controlled. As a result, the Li / Me ratio in the lithium-containing metal oxide can be accurately controlled. Me represents a metal element such as Ni.

[0036] In the mixing step S5, powdered metal oxide and powdered lithium compound are mixed. The lithium compound is at least one selected from the group consisting of lithium hydroxide, lithium carbonate, and lithium nitrate. The mixing ratio of the metal oxide and lithium compound is adjusted taking into consideration the composition of the final target product, the lithium-containing metal oxide. The lithium nitrate used as the lithium compound may include the lithium recovered in step S12, which will be described later.

[0037] In the firing step S6, a mixture of a metal oxide and a lithium compound is fired. Through the firing step, a lithium-containing metal oxide is obtained. According to the method of the present embodiment, impurities such as sulfur and sodium are not contained in the lithium-containing metal oxide. The lithium-containing metal oxide produced by the method of the present embodiment has a low impurity content and is suitable as a positive electrode material for a lithium secondary battery.

[0038] The ambient temperature in the firing step S6 is, for example, from 700°C to 920°C. The firing time is, for example, from 3 hours to 20 hours. The ambient atmosphere in the firing step is, for example, an oxygen atmosphere.

[0039] In order to impart a shape and quality suitable for a positive electrode material of a lithium secondary battery to the lithium-containing metal oxide, the steps from step S7 to step S10 may be carried out.

[0040] In the grinding step S7, the particles of the lithium-containing metal oxide are ground. Thereby, a powder of the lithium-containing metal oxide having a desired average particle size is obtained. In the grinding step, one or more grinding devices such as a jaw crusher, a roll crusher, a jet mill, and a ball mill may be used.

[0041] In the water washing step S8, the powder of the lithium-containing metal oxide is washed with water. Thereby, impurities remaining in the particles of the lithium-containing metal oxide can be removed. Examples of the impurities include lithium hydroxide and lithium carbonate.

[0042] The solid-liquid separation step S9 is a step for removing the water used for water washing. The lithium-containing metal oxide and water are separated using filter paper, a centrifuge, a filter press, or the like.

[0043] In the drying step S10, the powder of the lithium-containing metal oxide is dried. The ambient temperature in the drying step is, for example, from 150°C to 210°C. The drying time is, for example, from 5 hours to 12 hours. The ambient atmosphere in the drying step is, for example, a vacuum atmosphere.

[0044] The lithium-containing metal oxide is, for example, Li x Niy M z It has a composition represented by O2. M is at least one selected from the group consisting of Co, Mn, and Al. x, y, and z satisfy 0.98 ≤ x ≤ 1.1 and y + z = 1. A lithium-containing metal oxide having such a composition is suitable as a positive electrode material for lithium secondary batteries.

[0045] Figure 2 is a process diagram following the solid-liquid separation process shown in Figure 1. In the solid-liquid separation process of step S2 in Figure 1, the reacted mixed solution is separated into a metal hydroxide and a residual solution. The residual solution is an aqueous solution containing lithium nitrate and ammonia.

[0046] The residual solution may contain valuable metal ions such as Ni, Co, Mn, and Al. In this case, Ni and Co can be precipitated and recovered as hydroxides by adjusting the pH of the residual solution. Other metals, such as Al and Mn, can be recovered using ion exchange resins. Ion exchange resins may adsorb polyvalent metals such as Al and Mn, but not lithium ions.

[0047] In the ammonia recovery step S11 in Figure 2, ammonia, which is a pH adjusting agent, is recovered. Specifically, the remaining solution is heated to volatilize the ammonia. By dissolving the volatilized ammonia in water, an aqueous ammonia solution is obtained. The aqueous ammonia solution can be reused as a pH adjusting agent. In the ammonia recovery step S11, the remaining solution may also be boiled. This allows for the rapid recovery of ammonia.

[0048] In step S12, the lithium nitrate recovery step, solid lithium nitrate is recovered. That is, water is removed from the remaining solution to precipitate solid lithium nitrate. The remaining solution may be heated to remove water. The lithium nitrate recovery step in step S12 may be carried out in succession with the ammonia recovery step in step S11.

[0049] In the Li2O recovery step S13, lithium nitrate is decomposed, and Li2O contained in the decomposition products of lithium nitrate is recovered. Specifically, lithium nitrate is thermally decomposed. The decomposition temperature of lithium nitrate (LiNO3) is approximately 600°C. Since lithium nitrate decomposes at a relatively low temperature, thermal decomposition is a suitable method for recovering lithium from lithium nitrate. By recovering lithium oxide from lithium nitrate, lithium can be utilized effectively. In other words, the method of this embodiment is efficient from the viewpoint of effective resource utilization.

[0050] The lithium nitrate may be thermally decomposed by heating the remaining solution to 600°C without recovering the lithium nitrate from the remaining solution. In other words, step S12 may be omitted. Methods for directly generating the decomposition product of lithium nitrate from the remaining solution include heating and evaporating the remaining solution by spraying, and adjusting the ambient temperature to a temperature above the decomposition temperature of lithium nitrate.

[0051] Furthermore, lithium sulfate (Li2SO4) does not decompose at low temperatures, making it difficult to apply the method of this embodiment to lithium sulfate.

[0052] In step S13, lithium nitrate may be heated using a heat treatment furnace equipped with an exhaust system. The temperature inside the heat treatment furnace is adjusted, for example, to 630°C to 750°C. The atmosphere inside the heat treatment furnace is, for example, an atmospheric atmosphere.

[0053] In the LiOH production process of step S14, Li₂O is dissolved in water to produce an aqueous lithium hydroxide solution. The aqueous lithium hydroxide solution can be reused as a starting material for producing metal hydroxides. That is, lithium oxide may be converted to lithium hydroxide and reused. This makes effective use of lithium possible.

[0054] Figure 3 is a process diagram following the Li2O recovery process shown in Figure 2. In the Li2O recovery process of step S13 in Figure 2, when lithium nitrate is thermally decomposed, nitrogen oxides (NOx) are produced along with Li2O. x ) generates.

[0055] NO in step S15 of FIG. 3 x In the gas recovery step, nitrogen oxides (NO x gas) contained in the decomposition products of lithium nitrate are recovered. This can reduce the environmental load.

[0056] The recovered NO x gas can be converted to nitric acid by known methods in step S16. For example, air is mixed with the NO x gas and cooled to 140 °C or lower. Thereby, NO reacts with O2 to produce NO2. By dissolving NO2 in water, nitric acid can be obtained in the form of an aqueous solution. Nitric acid may be used as a back-extraction agent when producing the metal nitrate which is the starting material.

[0057] When producing metal nitrate from materials such as ore and black mass, impurities are removed by solvent extraction. The solvent extraction method is a method of separating substances using the difference in the specific gravity of solvents and a chelating agent. For example, among two immiscible liquids such as an aqueous solution and an oil (e.g., hexane, diethyl ether, etc.), a chelating agent is added to the oil, and the aqueous solution and the oil are stirred. Thereby, specific metal ions such as Ni ions can be extracted into the oil in the form of a chelate complex. Then, the acidic aqueous solution and the oil are stirred so that the chelating agent is removed from the specific metal ions. Thereby, the specific metal ions are extracted into the acidic aqueous solution. As the acidic aqueous solution, the nitric acid produced in step S16 can be reused.

[0058] It is difficult to recover sulfuric acid from lithium sulfate. Therefore, when the starting material is metal sulfate, it is difficult to reuse sulfuric acid.

[0059] According to the method of this embodiment, it is possible to avoid as much as possible the generation of substances to be discarded in the process from the starting material to obtaining the target product. Therefore, the method of this embodiment is efficient from the viewpoint of effective utilization of resources and can also contribute to reducing the environmental load.

[0060] (Other embodiments) (Appended notes) By the description of the above embodiments, the following technologies are disclosed.

[0061] (Technical 1) A method for producing a metal hydroxide, comprising mixing a first solution containing a metal nitrate and a second solution containing lithium hydroxide to precipitate a metal hydroxide, wherein the concentration of the metal nitrate in the first solution is higher than 1.0 mol / L and 6.0 mol / L or less, and the concentration of the lithium hydroxide in the second solution is higher than 1.0 mol / L and 5.0 mol / L or less.

[0062] According to this disclosure, metal hydroxides can be efficiently produced using metal nitrates and lithium hydroxide.

[0063] (Technical 2) The method for producing a metal hydroxide according to Technical 1, wherein the concentration of the metal nitrate in the first solution is 2.0 mol / L or higher. When the concentration of the metal nitrate is high, the metal hydroxide can be precipitated while further reducing the total amount of the first and second solutions.

[0064] (Technical 3) A method for producing a metal hydroxide according to Technical 1 or 2, wherein the concentration of lithium hydroxide in the second solution is 3.5 mol / L or higher. When the concentration of lithium hydroxide is high, the metal hydroxide can be precipitated while further reducing the total amount of the first solution and the second solution.

[0065] (Technical 4) A method for producing a metal hydroxide according to any one of Technical 1 to 3, further comprising decomposing the lithium nitrate produced from the metal nitrate and the lithium hydroxide, and recovering the lithium oxide contained in the decomposition product of the lithium nitrate. By recovering lithium oxide from lithium nitrate, lithium can be effectively utilized. In other words, the method of this embodiment is efficient from the viewpoint of effective resource utilization.

[0066] (Technical 5) The method for producing a metal hydroxide according to Technical 4, wherein the decomposition of lithium nitrate includes thermal decomposition of lithium nitrate. Since lithium nitrate decomposes at relatively low temperatures, thermal decomposition is suitable as a method for recovering lithium from lithium nitrate.

[0067] (Technical 6) A method for producing a metal hydroxide according to Technical 4 or 5, further comprising converting the lithium oxide to the lithium hydroxide. This makes it possible to make effective use of lithium.

[0068] (Technical 7) A method for producing a metal hydroxide according to any one of Technical 1 to 6, further comprising adjusting the pH of the mixed solution of the first solution and the second solution to 9.5 or more and 11.5 or less. By adjusting the pH of the mixed solution to this range, the metal hydroxide can be efficiently precipitated.

[0069] (Technical 8) A method for producing a metal hydroxide according to Technical 7, wherein the pH of the mixed solution is adjusted by adding ammonia to the mixed solution. Ammonia is desirable from the viewpoint of reducing the types of impurities.

[0070] (Technical 9) A method for producing a metal hydroxide according to any one of Technical 1 to 8, wherein the first solution and the second solution are aqueous solutions. When the solvent is water, the effort of recovering the evaporated solvent can be omitted.

[0071] (Technical 10) A method for producing a metal hydroxide according to any one of Technical 1 to 9, wherein the metal nitrate contains at least one metal element selected from the group consisting of Ni, Mn, Co, Al, Ca, Sr, Zr, Nb, and Ti. The composition of the metal hydroxide can be controlled by selecting the type of metal element contained in the metal nitrate.

[0072] (Technical 11) A method for producing a metal hydroxide according to any one of Technical 1 to 10, wherein the content of lithium atoms in the metal hydroxide is 0.002% by mass or more and 5.4% by mass or less, and the content of nitrogen atoms in the metal hydroxide is 0.004% by mass or more and 9.8% by mass or less. When lithium atoms are contained in the metal hydroxide, the amount of lithium compound used in subsequent steps can be reduced.

[0073] (Technical 12) A method for producing a lithium-containing metal oxide, comprising: producing a metal hydroxide by the method described in any one of Technical 1 to 11; and calcining a mixture of the metal hydroxide and a lithium compound so as to obtain a lithium-containing metal oxide.

[0074] According to this disclosure, lithium-containing metal oxides can be efficiently produced using metal nitrates and lithium hydroxide.

[0075] (Technical 13) The lithium-containing metal oxide is Li x Ni y M z A method for producing a lithium-containing metal oxide according to Technology 12, wherein the composition is represented by O2, M is at least one selected from the group consisting of Co, Mn, and Al, and the conditions 0.98 ≤ x ≤ 1.1 and y + z = 1 are satisfied. A lithium-containing metal oxide having such a composition is suitable as a positive electrode material for lithium secondary batteries.

[0076] (Example 1) 500 mL of pure water was placed in a 3 L glass container and heated to prepare 50°C hot water. LiOH aqueous solution was added to the hot water so that the pH of the solution was in the range of 10.9 to 11.1. The concentration of LiOH in the solution was in the range of 1.0 mol / L to 5.0 mol / L. LiOH aqueous solution and ammonia aqueous solution were added to the solution while adding a 2 mol / L Ni nitrate aqueous solution at a rate of 2 mL / min so that the pH of the solution was in the range of 10.9 to 11.1. The concentration of ammonia in the solution was in the range of 3.5 mol / L to 4.5 mol / L. Nickel hydroxide precipitated at the bottom of the glass container was separated from the liquid phase by decantation and dried at 105°C for 12 hours. This obtained the nickel hydroxide of Example 1.

[0077] Nickel hydroxide was oxidized and roasted at 550°C for 4 hours to obtain powdered nickel oxide. The nickel oxide was mixed with powdered LiOH and calcined at 760°C for 10 hours to obtain lithium nickel composite oxide.

[0078] The lithium nickel composite oxide was pulverized using a ball mill (Fritsch PL-7) at 150 rpm for 1 hour. ZrO balls (5 mm in diameter) were used for pulverization. After pulverization, the lithium nickel composite oxide was washed with water at a solid-liquid ratio of 1000 g / L for 10 minutes and at a stirring speed of 200 rpm. After recovering the lithium nickel composite oxide, it was dried at 160°C for 12 hours. This yielded the lithium nickel composite oxide of Example 1.

[0079] (Comparative Example 1) Nickel hydroxide of Comparative Example 1 was prepared in the same manner as in Example 1, except that a 2 mol / L NaOH aqueous solution was used instead of a LiOH aqueous solution, a 1 mol / L Ni sulfate aqueous solution was used instead of a Ni nitrate aqueous solution, the pH of the solution was maintained in the range of 10.5 to 10.7, and a 1.8 mol / L ammonia aqueous solution was used.

[0080] Using the nickel hydroxide of Comparative Example 1, the lithium nickel composite oxide of Comparative Example 1 was prepared in the same manner as in Example 1.

[0081] [Elemental Analysis] Elemental analysis of nickel hydroxide from Example 1 and Comparative Example 1 was performed using an ICP emission spectrometer (Thermo Fisher Scientific, iCAP7400 Duo). Nickel hydroxide was weighed, and a solution was obtained by adding acid, heating, and dissolving. The solution was diluted with pure water to obtain a sample for measurement. The target elements were nickel (Ni), sodium (Na), sulfur (S), lithium (Li), and nitrogen (N). The results are shown in Table 1. In Table 1, "-" means that the value was below the detection limit.

[0082] [Measurement of Specific Surface Area] The BET specific surface area of ​​nickel hydroxide in Example 1 and Comparative Example 1 was measured using a specific surface area / pore distribution analyzer (BELSORP MINI X, manufactured by Microtrac Bell). The results are shown in Table 1.

[0083]

[0084] As shown in Table 1, the nickel hydroxide of Comparative Example 1 contained sodium and sulfur. In contrast, the nickel hydroxide of Example 1 did not contain sodium and sulfur. The nickel hydroxide of Example 1 contained lithium and nitrogen.

[0085] The specific surface area of ​​the nickel hydroxide in Example 1 was significantly higher than that of the nickel hydroxide in Comparative Example 1.

[0086] [Observation using a scanning electron microscope] Nickel hydroxides from Example 1 and Comparative Example 1 were observed using a scanning electron microscope. The results are shown in Figures 4A and 4B. Figure 4A is an SEM image of the nickel hydroxide from Example 1. Figure 4B is an SEM image of the nickel hydroxide from Comparative Example 1. As shown in Figure 4A, the surface of the nickel hydroxide from Example 1 had a structure in which primary particles were densely superimposed. In contrast, as shown in Figure 4B, the surface of the nickel hydroxide from Comparative Example 1 had a structure in which primary particles were more coarsely superimposed compared to Example 1.

[0087] The cross-sections of the lithium nickel composite oxide particles of Example 1 and Comparative Example 1 were observed using a scanning electron microscope. The results are shown in Figures 5A and 5B. Figure 5A is a cross-sectional SEM image of the lithium nickel composite oxide of Example 1. Figure 5B is a cross-sectional SEM image of the lithium nickel composite oxide of Comparative Example 1. As shown in Figures 5A and 5B, the voids in the cross-section of the lithium nickel composite oxide particles of Example 1 were smaller than the voids in the cross-section of the lithium nickel composite oxide particles of Comparative Example 1.

[0088] The technology described herein is useful for the production of metal oxides and their precursors, metal hydroxides.

Claims

1. A method for producing a metal hydroxide, comprising mixing a first solution containing a metal nitrate and a second solution containing lithium hydroxide to precipitate a metal hydroxide, wherein the concentration of the metal nitrate in the first solution is higher than 1.0 mol / L and 6.0 mol / L or less, and the concentration of the lithium hydroxide in the second solution is higher than 1.0 mol / L and 5.0 mol / L or less.

2. The method for producing a metal hydroxide according to claim 1, wherein the concentration of the metal nitrate in the first solution is 2.0 mol / L or higher.

3. The method for producing a metal hydroxide according to claim 1, wherein the concentration of lithium hydroxide in the second solution is 3.5 mol / L or more.

4. A method for producing a metal hydroxide according to claim 1, further comprising: decomposing the lithium nitrate produced from the metal nitrate and the lithium hydroxide; and recovering the lithium oxide contained in the decomposition product of the lithium nitrate.

5. The method for producing a metal hydroxide according to claim 4, wherein the decomposition of the lithium nitrate includes thermal decomposition of the lithium nitrate.

6. The method for producing a metal hydroxide according to claim 4, further comprising converting the lithium oxide to the lithium hydroxide.

7. The method for producing a metal hydroxide according to claim 1, further comprising adjusting the pH of the mixed solution of the first solution and the second solution to 9.5 or more and 11.5 or less.

8. The method for producing a metal hydroxide according to claim 7, wherein the pH of the mixed solution is adjusted by adding ammonia to the mixed solution.

9. The method for producing a metal hydroxide according to claim 1, wherein the first solution and the second solution are aqueous solutions.

10. The method for producing a metal hydroxide according to claim 1, wherein the metal nitrate contains at least one metal element selected from the group consisting of Ni, Mn, Co, Al, Ca, Sr, Zr, Nb, and Ti.

11. A method for producing a metal hydroxide according to claim 1, wherein the content of lithium atoms in the metal hydroxide is 0.002% by mass or more and 5.4% by mass or less, and the content of nitrogen atoms in the metal hydroxide is 0.004% by mass or more and 9.8% by mass or less.

12. A method for producing a lithium-containing metal oxide, comprising: producing a metal hydroxide by the method described in claim 1; and calcining a mixture of the metal hydroxide and a lithium compound so as to obtain a lithium-containing metal oxide.

13. The lithium-containing metal oxide is Li x Ni y M z A method for producing a lithium-containing metal oxide according to claim 12, having a composition represented by O2, where M is at least one selected from the group consisting of Co, Mn, and Al, and satisfying 0.98 ≤ x ≤ 1.1 and y + z = 1.

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