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

Abstract

This method comprises: mixing a first solution containing a metal nitrate with a second solution containing lithium hydroxide to precipitate a metal hydroxide; thermally decomposing lithium nitrate produced from the metal nitrate and the lithium hydroxide; and recovering lithium oxide contained in the thermal decomposition product of the lithium nitrate. This method may further comprise converting lithium oxide into lithium hydroxide and reusing the lithium hydroxide.

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; thermally 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.

[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 4 is a graph showing the results of powder X-ray diffraction measurements of lithium nitrate powder obtained from the lithium nitrate aqueous solution of Example 1, and Li2O powder produced by the thermal decomposition of lithium nitrate. Figure 5A is an SEM image of nickel-cobalt-manganese composite hydroxide of Example 1. Figure 5B is an SEM image of lithium nickel-cobalt-manganese composite oxide of Example 1. Figure 6A is an SEM image of nickel-cobalt-manganese composite hydroxide of Example 2. Figure 6B is an SEM image of lithium nickel-cobalt-manganese composite oxide of Example 2.

[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, since lithium is a valuable resource, there is a need to effectively utilize the lithium contained in lithium salts produced together with metal hydroxides. Example 1 of Patent Document 1 describes recovering lithium hydroxide by treating lithium sulfate with an electrofilm process.

[0013] When metal nitrates are used as starting materials instead of metal sulfates, lithium nitrate is produced along with the metal hydroxide. Lithium nitrate is more easily decomposed than lithium sulfate. Therefore, it is difficult to efficiently convert lithium nitrate to lithium hydroxide using the electrofilm process described in Patent Document 1. In addition, since nitrate ions are more corrosive than sulfate ions, there are concerns about corrosion of components such as electrodes and films.

[0014] In view of the above circumstances, this disclosure provides a method for efficiently producing metal hydroxides using metal nitrates and lithium hydroxide.

[0015] The embodiments of this disclosure will be described below with reference to the drawings. This disclosure is not limited to the embodiments described below.

[0016] (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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] A precursor metal hydroxide is obtained through steps S1 to S3. The metal hydroxide is, for example, in powder form.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] Steps S4 to S10 are steps for producing lithium-containing metal oxides from metal hydroxides.

[0036] 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.

[0037] The drying process in step S3 and the oxidation roasting process in step S4 can be omitted. Without undergoing the drying process and the oxidation roasting process, the metal hydroxide obtained through step S2 may be provided to the mixing process in step S5. However, by undergoing the drying process and the oxidation roasting process, moisture can be removed and the oxidation number 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.

[0038] In the mixing process of step S5, a powdery metal oxide and a powdery 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 the lithium compound is adjusted in consideration of the composition of the final target lithium-containing metal oxide. Lithium nitrate as the lithium compound may include the one recovered in step S12 described later.

[0039] In the firing process of step S6, the mixture of the metal oxide and the lithium compound is fired. Through the firing process, a lithium-containing metal oxide is obtained. According to the method of this 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 this embodiment has a low impurity content and is suitable as a positive electrode material for a lithium secondary battery.

[0040] The ambient temperature in the firing process of 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 process is, for example, an oxygen atmosphere.

[0041] 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 processes from step S7 to step S10 may be carried out.

[0042] 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 can be 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.

[0043] 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.

[0044] 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 a filter paper, a centrifuge, a filter press, or the like.

[0045] 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.

[0046] The lithium-containing metal oxide is, for example, Li x Ni y 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. The lithium-containing metal oxide having such a composition is suitable as a positive electrode material for a lithium secondary battery.

[0047] FIG. 2 is a process diagram following the solid-liquid separation step shown in FIG. 1. In the solid-liquid separation step S2 of FIG. 1, the reacted mixed solution is separated into a metal hydroxide and a remaining solution. The remaining solution is an aqueous solution containing lithium nitrate and ammonia.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] Lithium nitrate may be thermally decomposed by heating the residual solution to 600 °C without recovering lithium nitrate from the residual solution. That is, the step of step S12 may be omitted. As a method of directly generating the decomposition product of lithium nitrate from the residual solution, there are a method of heating and evaporating the residual solution by a spray method, a method of adjusting the temperature of the ambient environment to a temperature not lower than the decomposition temperature of lithium nitrate, and the like.

[0053] Lithium sulfate (Li₂SO₄) does not thermally decompose at low temperatures, and it is difficult to apply the method of this embodiment to lithium sulfate.

[0054] In step S13, lithium nitrate can be heated using a heat treatment furnace equipped with exhaust facilities. The temperature inside the heat treatment furnace is adjusted to, for example, 630 °C to 750 °C. The atmosphere inside the heat treatment furnace is, for example, an air atmosphere.

[0055] In the LiOH production step 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. Thereby, effective utilization of lithium can be achieved.

[0056] FIG. 3 is a process diagram following the Li₂O recovery step shown in FIG. 2. In the Li₂O recovery step of step S13 in FIG. 2, when lithium nitrate is thermally decomposed, nitrogen oxides (NO x ) are generated together with Li₂O.

[0057] In the NO x gas recovery step of step S15 in FIG. 3, nitrogen oxides (NO x gas) contained in the decomposition product of lithium nitrate are recovered. Thereby, the load on the environment can be reduced.

[0058] The recovered NO x gas can be converted to nitric acid by a known method in step S16. For example, NO xThe gas is mixed with air and cooled to below 140°C. This causes NO to react with O2 to produce NO2. By dissolving NO2 in water, nitric acid is obtained in aqueous solution. Nitric acid may also be used as a back extractant when producing the starting material, metal nitrate.

[0059] When producing metal nitrates from materials such as ore and black mass, impurities are removed by solvent extraction. Solvent extraction is a method of separating substances using the difference in specific gravity of solvents and chelating agents. For example, between two immiscible liquids such as an aqueous solution and an oil (e.g., hexane, diethyl ether), a chelating agent is added to the oil, and the aqueous solution and oil are stirred. This allows specific metal ions, such as Ni ions, to be extracted into the oil in the form of chelate complexes. Subsequently, the acidic aqueous solution and oil are stirred so that the chelating agent detaches from the specific metal ions. This extracts the specific metal ions into the acidic aqueous solution. The nitric acid produced in step S16 can be reused as the acidic aqueous solution.

[0060] Furthermore, it is difficult to recover sulfuric acid from lithium sulfate. Therefore, when the starting material is a metal sulfate, it is difficult to reuse the sulfuric acid.

[0061] According to the method of this embodiment, it is possible to minimize the generation of waste materials during the process from starting raw materials to obtaining the target product. Therefore, the method of this embodiment is efficient from the standpoint of effective use of resources and can also contribute to reducing the burden on the environment.

[0062] (Other Embodiments) (Note) The above description of embodiments discloses the following technologies.

[0063] (Technical 1) 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; thermally decomposing lithium nitrate produced from the metal nitrate and lithium hydroxide; and recovering lithium oxide contained in the decomposition product of lithium nitrate.

[0064] According to this disclosure, metal hydroxides can be efficiently produced using metal nitrates and lithium hydroxide.

[0065] (Technology 2) A method for producing a metal hydroxide according to Technology 1, further comprising converting the lithium oxide to the lithium hydroxide and reusing it. This makes it possible to make effective use of lithium.

[0066] (Technical 3) A method for producing a metal hydroxide according to Technical 1 or 2, further comprising recovering nitrogen oxides contained in the decomposition products of lithium nitrate. This reduces the burden on the environment.

[0067] (Technical 4) A method for producing a metal hydroxide according to any one of Technical 1 to 3, 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.

[0068] (Technical 5) A method for producing a metal hydroxide according to Technical 4, 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.

[0069] (Technical 6) A method for producing a metal hydroxide according to Technical 5, further comprising separating the mixed solution into the metal hydroxide and the residual solution, and heating the residual solution to volatilize ammonia. This allows for the rapid recovery of ammonia.

[0070] (Technical 7) A method for producing a metal hydroxide according to any one of Technical 1 to 6, 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 8) A method for producing a metal hydroxide according to any one of Technical 1 to 7, 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 9) 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 8; and calcining a mixture of the metal hydroxide and a lithium compound so as to obtain a lithium-containing metal oxide.

[0073] According to this disclosure, lithium-containing metal oxides can be efficiently produced using metal nitrates and lithium hydroxide.

[0074] (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-Co-Mn nitrate mixed 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. In the Ni-Co-Mn nitrate mixed aqueous solution, the atomic ratios of nickel, cobalt, and manganese were Ni:Co:Mn = 90:5:5. The concentration of ammonia in the solution was in the range of 3.5 mol / L to 4.5 mol / L. The nickel-cobalt-manganese composite hydroxide precipitated at the bottom of the glass container by decantation was separated from the liquid phase and dried at 105°C for 12 hours. This yielded the nickel-cobalt-manganese composite hydroxide of Example 1 and a residual solution containing lithium nitrate.

[0075] Nickel-cobalt-manganese composite hydroxide was oxidized and roasted at 550°C for 4 hours. This yielded powdered nickel-cobalt-manganese composite oxide. The nickel-cobalt-manganese composite oxide was mixed with powdered LiOH and calcined at 760°C for 10 hours. This yielded lithium nickel-cobalt-manganese composite oxide.

[0076] The lithium nickel cobalt manganese 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 cobalt manganese 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 cobalt manganese composite oxide, it was dried at 160°C for 12 hours. This yielded the lithium nickel cobalt manganese composite oxide of Example 1.

[0077] The residual solution containing lithium nitrate was treated with an anion exchange resin to separate lithium ions from polyvalent ions. This yielded a highly pure aqueous solution of lithium nitrate. Using a rotary evaporator (AS ONE, ARE-V1200), water was evaporated from the obtained aqueous solution of lithium nitrate. This yielded lithium nitrate powder. The obtained lithium nitrate powder was thermally decomposed at 650°C to obtain Li₂O powder. The Li₂O powder was dissolved in pure water to obtain an aqueous solution of LiOH. Ammonia can be recovered during the evaporation of water.

[0078] (Example 2) The LiOH aqueous solution obtained in Example 1 was used as the starting material in the precipitation step (step S1 in Figure 1), and the nickel-cobalt-manganese composite hydroxide of Example 2 and the lithium-nickel-cobalt-manganese composite oxide of Example 2 were synthesized by the same method as in Example 1.

[0079] [Powder X-ray Diffraction Measurement] Powder X-ray diffraction measurements were performed on the lithium nitrate powder obtained from the lithium nitrate aqueous solution of Example 1, and the Li2O powder produced by the thermal decomposition of lithium nitrate, using an X-ray diffractometer (MiniFlex, Rigaku Corporation). The results are shown in Figure 4.

[0080] Figure 4 is a graph showing the results of powder X-ray diffraction measurements of lithium nitrate powder obtained from the lithium nitrate aqueous solution of Example 1, and Li2O powder produced by the thermal decomposition of lithium nitrate. As shown in the lower graph of Figure 4, before thermal decomposition, the sample mainly contained lithium nitrate (LiNO3). After thermal decomposition, the peak attributed to lithium nitrate disappeared, and a strong peak attributed to lithium oxide (Li2O) appeared. The sample after thermal decomposition mainly contained lithium oxide.

[0081] [Observation using a scanning electron microscope] For each of Example 1 and Example 2, the nickel-cobalt-manganese composite hydroxide and lithium-nickel-cobalt-manganese composite oxide were observed using a scanning electron microscope (SEM). The results are shown in Figures 5A to 6B.

[0082] Figure 5A is an SEM image of the nickel-cobalt-manganese composite hydroxide of Example 1. Figure 5B is an SEM image of the lithium nickel-cobalt-manganese composite oxide of Example 1. Figure 6A is an SEM image of the nickel-cobalt-manganese composite hydroxide of Example 2. Figure 6B is an SEM image of the lithium nickel-cobalt-manganese composite oxide of Example 2.

[0083] As shown in Figures 5A and 6A, a well-formed nickel-cobalt-manganese composite hydroxide was obtained by the method of this disclosure. No significant difference was observed between Example 1 and Example 2. That is, the reuse or non-reuse of the lithium hydroxide aqueous solution did not have a significant effect on the synthesis of the nickel-cobalt-manganese composite hydroxide.

[0084] As shown in Figures 5B and 6B, a well-formed lithium nickel cobalt manganese composite oxide was obtained by the method of this disclosure. No significant difference was observed between Example 1 and Example 2. That is, the presence or absence of reuse of the lithium hydroxide aqueous solution did not have a significant effect on the synthesis of the lithium nickel cobalt manganese composite oxide.

[0085] [Battery Fabrication] Lithium secondary batteries were fabricated using the lithium nickel cobalt manganese composite oxides of Example 1 and Example 2.

[0086] (Example 1) A positive electrode slurry was prepared by mixing and stirring lithium nickel cobalt manganese composite oxide particles from Example 1, acetylene black (AB), polyvinylidene fluoride (PVDF), and N-methylpyrrolidone (NMP) as positive electrode active materials. The mass ratio of the positive electrode active material, AB, and PVDF was positive electrode active material:AB:PVDF = 96:2:2. The positive electrode slurry was applied to the surface of an aluminum foil to form a coating film. After drying the coating film, it was rolled. This obtained a positive electrode.

[0087] A negative electrode slurry was prepared by mixing graphite, styrene-butadiene rubber (SBR) dispersion, sodium carboxymethylcellulose (CMC-Na), and water in a predetermined solid content mass ratio. The negative electrode slurry was applied to the surface of a copper foil to form a coating film. After drying the coating film, it was rolled. This obtained a negative electrode.

[0088] Ethylene carbonate (EC), fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of EC:FEC:DMC:EMC = 10:5:10:75 to prepare a non-aqueous solvent. LiPF6 was dissolved in the non-aqueous solvent to a concentration of 1.3 mol / L to obtain a non-aqueous electrolyte.

[0089] Current collector leads were attached to both the positive and negative electrodes. The positive electrode, separator (Cellguard Co., Ltd., #2320), and negative electrode were assembled and placed in a laminate film container. A non-aqueous electrolyte was poured into the container and sealed. This obtained the battery of Example 1.

[0090] (Example 2) The battery of Example 2 was fabricated in the same manner as in Example 1, except that the lithium nickel cobalt manganese composite oxide particles of Example 2 were used as the positive electrode active material.

[0091] [Charge and Discharge Test] Charge and discharge tests were performed on the batteries of Example 1 and Example 2 using the following method. Constant current charging was performed at a current of 0.2C until the voltage reached 4.3V, and constant voltage charging was performed at a voltage of 4.3V until the current reached 0.02C. After a 20-minute rest period, constant current discharge was performed at a current of 0.2C until the voltage reached 2.5V. The results are shown in Table 1.

[0092]

[0093] The charging and discharging capacities shown in Table 1 represent the ratio to the charging and discharging capacities of Example 2. As shown in Table 1, the charging and discharging capacities of the battery in Example 1 were equivalent to those of the battery in Example 2. In other words, the presence or absence of reuse of the lithium hydroxide aqueous solution did not have a significant effect on the charging and discharging capacities of the battery.

[0094] 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 with a second solution containing lithium hydroxide to precipitate a metal hydroxide; thermally decomposing lithium nitrate produced from the metal nitrate and lithium hydroxide; and recovering lithium oxide contained in the decomposition product of lithium nitrate.

2. The method for producing a metal hydroxide according to claim 1, further comprising converting the lithium oxide to the lithium hydroxide and reusing it.

3. The method for producing a metal hydroxide according to claim 1, further comprising recovering nitrogen oxides contained in the decomposition products of lithium nitrate.

4. 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.

5. The method for producing a metal hydroxide according to claim 4, wherein the pH of the mixed solution is adjusted by adding ammonia to the mixed solution.

6. The method for producing a metal hydroxide according to claim 5, further comprising: separating the mixed solution into the metal hydroxide and the remaining solution; and heating the remaining solution to volatilize ammonia.

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

8. 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.

9. 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.

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