Method for preparing battery positive electrode material precursor using cobalt-iron slag and its application

Abstract

This disclosure belongs to the technical field of battery positive electrode material preparation and discloses a method for preparing battery positive electrode material precursors using cobalt-iron slag. The method first involves roasting the cobalt-iron slag, acid leaching, and solid-liquid separation to produce molten iron and cobalt slag. The molten iron is then prepared into ferric phosphate dihydrate. The cobalt slag is then decontaminated to produce cobalt carbonate. Finally, calcination is performed to obtain ferric phosphate and cobalt trioxide. The ferric phosphate and cobalt oxide precursors prepared in this disclosure are both of high purity, and batteries prepared using them exhibit excellent chemical properties.

Description

Technical Field

[0001] The present disclosure belongs to the technical field of battery positive electrode material preparation, and particularly relates to a method for preparing a battery positive electrode material precursor by utilizing cobalt-iron slag and an application thereof. Background Art

[0002] With the growing number of new energy vehicles, new energy batteries require large quantities of high-value metal elements. To reduce the shortage of lithium battery materials and environmental pollution, it is crucial to find a green and pollution-free method to improve the utilization of metal resources. Lithium cobalt oxide (LCO) has become the first generation of commercial cathode materials due to its advantages such as a high discharge platform and high specific capacity. However, it contains the highly toxic and expensive cobalt element, which puts significant pressure on the environment and costs. Therefore, reducing costs and pollution in the synthesis of raw materials is one of the most pressing issues. Lithium iron phosphate batteries are highly safe and can be cycled up to 2,000 times, offering significant cost advantages. Currently, as the new energy market continues to expand, the demand for lithium cobalt oxide and lithium iron phosphate cathode materials remains significantly underdeveloped. LCO and LFP account for a significant portion of the total cost of cathode materials, while their precursors account for the majority of the cost. Therefore, reducing the cost of precursors is the primary means of reducing the cost of new energy batteries.

[0003] Cobalt-iron slag contains rich cobalt and iron resources. However, due to the large number of impurities in cobalt-iron slag, the separation of impurities is relatively difficult. At present, the separation and recovery of cobalt and iron elements in cobalt-iron slag generally adopts wet leaching separation. The cobalt liquid and iron liquid separated by wet leaching are then used as raw materials to synthesize the required precursors (such as iron phosphate and cobalt oxide precursors). On the one hand, it is difficult to ensure the purity of the metal salt solution obtained by wet leaching separation, and low purity or poor purity stability will affect the performance of the final battery. On the other hand, the process of separating the cobalt liquid and the iron liquid and then synthesizing the precursor is relatively complicated, with high production costs and low utilization rate of cobalt-iron ore.

[0004] Therefore, there is an urgent need to provide a method for utilizing cobalt-iron slag to prepare high-purity cathode material precursors and improve the utilization rate of cobalt-iron ore. Summary of the Invention

[0005] The present disclosure aims to address at least one of the technical problems existing in the aforementioned prior art. To this end, the present disclosure proposes a method for preparing battery cathode material precursors using cobalt-iron slag and its application. This method directly uses cobalt-iron leachate as raw material to prepare iron phosphate and cobalt oxide precursors, thereby improving the utilization rate of cobalt-iron ore and producing high-purity precursors.

[0006] A first aspect of the present disclosure provides a method for preparing a battery positive electrode material precursor using cobalt-iron slag.

[0007] Specifically, a method for preparing a battery positive electrode material precursor using cobalt-iron slag comprises the following steps:

[0008] S1: roasting cobalt iron slag to obtain roasted slag, then mixing it with acid solution and oxidant, leaching to obtain iron leachate; then solid-liquid separation of the iron leachate to obtain a first filtrate and cobalt slag;

[0009] S2: adding phosphoric acid to the first filtrate to obtain iron-phosphorus liquid A, mixing the iron-phosphorus liquid A with a precipitant A, and then heating to react to obtain an iron phosphate slurry, wherein the precipitant A is a carbonate and / or bicarbonate; and then solid-liquid separation of the iron phosphate slurry to obtain a filter cake B and a second filtrate;

[0010] S3: placing the filter cake B in a phosphoric acid solution for aging, followed by solid-liquid separation to obtain filter cake C, which is then washed to obtain ferric phosphate dihydrate;

[0011] S4: sintering the ferric phosphate dihydrate to obtain ferric phosphate.

[0012] In the present disclosure, the cobalt iron slag is first roasted to generate cobalt oxide and ferric oxide, and then the Fe 3+ and Co 3+ The difference in leaching solubility in acid (sulfuric acid, nitric acid, hydrochloric acid), among which the solubility of Fe3+ is much greater than that of Co 3+ , and in the acid solution, the leaching rate of Fe element is faster than that of Co element, so Fe is firstly leached through the acid dissolution process. 3+ Separated from slag, and added with oxygen-containing ligand oxidant as oxidant to inhibit Co 3+ After the cobalt and iron are separated, the Co 3+ Reduction to Co 2+ Leaching. The key to achieving good separation of cobalt and iron lies in the process of roasting and adding oxidants. Controlling the roasting and adding oxidants can reduce the cobalt content in the iron liquid (first filtrate).

[0013] In some embodiments of the present disclosure, the step of converting the cobalt slag into cobalt trioxide is further included:

[0014] (1) adding the cobalt slag to the second filtrate, and then adding a reducing agent to react to obtain Co 2+ Leachate, to the Co 2+ Adding a precipitant B to the leachate to control the pH value to 4-6.5, and then performing solid-liquid separation to obtain a third filtrate and insoluble hydroxides, wherein the precipitant B is a carbonate and / or bicarbonate;

[0015] (2) mixing the third filtrate with a precipitant C to react, controlling the pH value during the reaction to be 8.0-10.5, and then concentrating to obtain a red slurry, which is washed and dried to obtain cobalt carbonate, wherein the precipitant C is a carbonate and / or bicarbonate;

[0016] (3) Sintering the cobalt carbonate to obtain cobalt trioxide.

[0017] In some embodiments of the present disclosure, in step S1, the cobalt-iron slag is at least one of cobalt-iron ore, cobalt-iron alloy, and cobalt-iron oxide waste. The cobalt-iron slag primarily comprises FeO, Fe2O3, CoO, and CoO3, and further contains impurities such as Al2O3 and insoluble matter. The cobalt-iron slag has an Fe content of 5-35%, a Co content of 5-30%, an Al content of 0-2%, and an insoluble matter content of 2-10%.

[0018] In some embodiments of the present disclosure, in step S1, the cobalt-iron slag is ground and sieved before roasting.

[0019] In some embodiments of the present disclosure, in step S1, the calcination temperature is 500-750° C., and the calcination time is 0.5-5 h.

[0020] In some embodiments of the present disclosure, in step S1, the calcination temperature is 600-750° C., and the calcination time is 0.5-3 h.

[0021] In some embodiments of the present disclosure, in step S1, the acid solution is at least one of sulfuric acid, nitric acid, and hydrochloric acid.

[0022] In some embodiments of the present disclosure, in step S1, the molar ratio of Fe to acid in the cobalt-iron slag is 1:(1-2).

[0023] In some embodiments of the present disclosure, in step S1, the oxidant is an oxygen-containing ligand oxidant.

[0024] In some embodiments of the present disclosure, in step S1, the oxidant is selected from at least one of ferric acid, sodium ferrate, and potassium ferrate. The main reason for selecting an oxygen-containing ligand oxidant is that its electrode potential is greater than that of trivalent cobalt particles, and its oxidizing property is stronger, which can inhibit the oxidation of Co. 3+ Reduced to Co 2+ The leaching effect is better.

[0025] In some embodiments of the present disclosure, in step S1, the amount of the oxidant added is the amount required to oxidize Fe 2+ 110-130% of the theoretical molar amount. The role of excess oxidant is to ensure that Fe2+ Complete oxidation, inhibiting more Co 3+ Reduction leaching from minerals.

[0026] In some embodiments of the present disclosure, in the iron-phosphorus liquid A in step S2, the molar ratio of Fe to P is 1:(1.02-1.12).

[0027] In some embodiments of the present disclosure, in step S2, the precipitant A is selected from at least one of ammonium bicarbonate, sodium bicarbonate, potassium bicarbonate, potassium carbonate, ammonium carbonate, and sodium carbonate. Using a carbonate or bicarbonate as a precipitant can act both as a precipitant and as a foaming agent, increasing the number of pores in the iron phosphate product. The porous iron phosphate can serve as inlet and outlet channels for S and Co during the aging process, facilitating the removal of S and Co impurities. It can also reduce the diffusion channels for lithium ions after the lithium iron phosphate cathode is synthesized, thereby improving the electrochemical performance of the battery.

[0028] In some embodiments of the present disclosure, the mass concentration of the precipitant A is 8-30%.

[0029] In some embodiments of the present disclosure, the mass concentration of the precipitant A is 10-20%.

[0030] In some embodiments of the present disclosure, in step S2, the ratio of the flow rate of the precipitant added to the flow rate of the iron-phosphorus solution A is 1:(3-5). By controlling the addition rate of the precipitant, excessively high local pH values ​​can be avoided, which may hydrolyze to form Fe(OH)3 and Co(OH)2 and affect product quality.

[0031] In some embodiments of the present disclosure, in step S2, during the mixing process, the pH value is adjusted to 1.6-2.3 by controlling the amount of the precipitant A added.

[0032] In some embodiments of the present disclosure, in step S2, the reaction temperature is 70-90° C., and the reaction time is 0.5-2 h.

[0033] In some embodiments of the present disclosure, in step S3, the concentration of the phosphoric acid solution is 0.2-3 mol / L.

[0034] In some embodiments of the present disclosure, in step S3, the aging temperature is 85-95° C., and the aging time is 2-5 hours.

[0035] In some embodiments of the present disclosure, in step S3, the washing process is to wash the filter cake C until the conductivity of the washing water is ≤500 μm / cm.

[0036] In some embodiments of the present disclosure, in step S4, the sintering process of the ferric phosphate dihydrate is: heating to 550-700° C. and sintering for 3-6 hours in air, argon or nitrogen atmosphere.

[0037] In some embodiments of the present disclosure, in step (1), the reducing agent includes at least one of glucose, H2C2O4, NaSO3, CO, NH3, and SO2. The amount of the reducing agent added is Co 3+ Completely reduced to Co 2+ The reducing agent is 110%-130% of the molar amount of Co 3+ Reduction to Co 2+ , can improve Co 2+ The leaching rate is very low and no other impurities are introduced.

[0038] In some embodiments of the present disclosure, in step (1), the sparingly soluble hydroxide is one or more of ferric hydroxide or aluminum hydroxide, and the carbonate ions react with Al and residual Fe ions to form aluminum carbonate and ferric carbonate, which are immediately hydrolyzed upon contact with water to form hydroxide. By adding a precipitant B to control the pH value to 4-6.5, solid-liquid separation can be achieved to remove aluminum and iron impurities in the cobalt solution, wherein controlling the pH value to 4-6.5 can completely precipitate Fe and partially precipitate Al, thereby preparing Al-doped cobalt carbonate.

[0039] In some embodiments of the present disclosure, in step (2), the reaction temperature is 60-80°C.

[0040] In some embodiments of the present disclosure, in step (2), the concentration is performed by filtering the clear liquid in the slurry using a concentration device when the slurry level reaches 70%-90% of the container level, stopping the filtration when the slurry is concentrated to 40%-60% of the liquid level, continuing to add materials and control the pH, and completing the concentration after multiple concentrations until the solid content of the slurry is 150-300 g / L and the particle size is 15-20 μm.

[0041] In some embodiments of the present disclosure, the precipitant B and the precipitant C are independently selected from at least one of ammonium bicarbonate, sodium bicarbonate, potassium bicarbonate, potassium carbonate, ammonium carbonate, sodium carbonate, and the like.

[0042] In some embodiments of the present disclosure, in step (3), the cobalt carbonate is sintered in an air atmosphere by first heating to 250-350°C for pre-sintering for 2-3 hours, and then heating to 600-750°C for sintering for 3-6 hours. Pre-sintering followed by high-temperature sintering helps ensure sufficient contact between the material and oxygen during the sintering process.

[0043] The second aspect of the present disclosure provides an application of the above-mentioned method for preparing a battery positive electrode material precursor using cobalt-iron slag in preparing a battery positive electrode material.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] (1) The present invention first removes part of the Fe in the cobalt iron slag by roasting. 2+ 、Co 2+ Oxidized to Fe 3+ 、Co 3+ , due to Co 3+ The leaching rate in acid solution is low, while Fe 3+ The principle of high leaching rate is that excessive oxidant is added during the leaching process to inhibit the 3+ Reduction, first leaching extract containing a small amount of Co 3+ After the iron liquid and solid-liquid separation, cobalt slag is produced, and bicarbonate or carbonate is added to the iron liquid to precipitate iron phosphate; the iron phosphate is then aged with a phosphoric acid solution. The aging process can replace the S and Co impurities in the iron phosphate, and the replacement ratio of Co can be controlled by adjusting the concentration of phosphoric acid to prepare Co-doped iron phosphate. The appropriate amount of element doping is beneficial to improving the material performance. The cobalt-iron separation process in the present disclosure does not require a high-pressure leaching process, and in the subsequent steps, cobalt slag and a reducing agent are added to the solid-liquid separation liquid after the iron phosphate synthesis to replace the Co 2+ Leaching, by adding bicarbonate or carbonate to remove impurities and then preparing cobalt carbonate, avoids the use of closed high-pressure equipment in the conventional cobalt-iron liquid separation process, reduces equipment costs and reduces safety risks.

[0046] (2) The present disclosure uses carbonate or bicarbonate as a precipitant in the synthesis process of cobalt carbonate and iron phosphate, which is beneficial to improving the electrochemical performance of the prepared positive electrode material precursor. In the synthesis process of iron phosphate, carbonate or bicarbonate is both a precipitant and a foaming agent. Since CO2 is generated by high temperature and acts on the inside of the iron phosphate, pores are formed inside and on the surface of the iron phosphate, which is beneficial to the escape of impurity S. The increase in pores on the surface and inside of the porous iron phosphate product can reduce the migration and diffusion distance of lithium ions in the preparation process of lithium iron phosphate, increase the migration channel of lithium ions, and increase the utilization rate of its own activity, thereby improving the electrochemical performance of lithium iron phosphate.

[0047] (3) The method disclosed herein for preparing battery positive electrode material precursors using cobalt iron slag directly uses cobalt iron slag as a raw material to prepare iron phosphate, a precursor of lithium iron phosphate, and cobalt oxide, a precursor of lithium cobaltate. The yields of iron and cobalt in the preparation process reach over 98% and 96%, respectively, which helps to improve the utilization rate of cobalt iron slag and reduce the cost of precursor preparation. The purity of the prepared precursors iron phosphate and cobalt oxide is relatively high, and the chemical properties of the batteries prepared using them are excellent. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is a SEM image of the iron phosphate prepared in Example 1;

[0049] Figure 2 is the XRD pattern of the iron phosphate prepared in Example 1;

[0050] Figure 3 This is a SEM image of the cobaltous oxide prepared in Example 1;

[0051] Figure 4 This is the XRD pattern of the cobaltous oxide prepared in Example 1. DETAILED DESCRIPTION

[0052] In order to make the technical solutions of the present disclosure more clearly understood by those skilled in the art, the following examples are given for illustration. It should be noted that the following examples do not limit the scope of protection claimed in the present disclosure.

[0053] Unless otherwise specified, the raw materials, reagents, or devices used in the following examples can be obtained from conventional commercial sources or by existing known methods.

[0054] Example 1

[0055] A method for preparing a battery positive electrode material precursor using cobalt-iron slag comprises the following steps:

[0056] (1) 30 kg of cobalt-iron slag (wherein the mass percentage of Fe is approximately 20% and the mass percentage of Co is approximately 15%) was ground to 2 μm and passed through a 150-mesh sieve. The resulting 29.5 kg of fine slag was placed in a box furnace and calcined at 650°C for 1 hour to obtain 29 kg of calcined slag. The calcined slag was then uniformly mixed with 100 L of 1.3 mol / L sulfuric acid and 1.35 kg of ferric acid, stirred at 35 Hz, and subjected to a primary leaching at 70°C to obtain an iron leachate, which was then subjected to solid-liquid separation to obtain a first filtrate and cobalt slag.

[0057] (2) adding 12.8 kg of phosphoric acid to the first filtrate to obtain an iron-phosphorus liquid A having a molar ratio of Fe to P of 1:1.05, wherein the mass concentration of Fe is 48.86 g / L and the mass concentration of P is 24.79 g / L; adding the iron-phosphorus liquid A and 28 L of 17% by mass sodium carbonate in parallel at a flow rate of 4:1, adjusting the pH to 1.9, heating to 80° C. and stirring for 1 hour to obtain an amorphous iron phosphate slurry, and obtaining filter cake B and a second filtrate after solid-liquid separation;

[0058] (3) Filter cake B was placed in an aging kettle containing 100 L of 0.75 mol / L phosphoric acid solution and aged for 6 h to displace the Co and S impurities in the iron phosphate. After aging, solid-liquid separation was performed to obtain filter cake C. Filter cake C was washed until the conductivity of the washing water was ≤500 μm / cm, and then dried to obtain iron phosphate dihydrate powder.

[0059] (4) 10 kg of cobalt slag obtained in step (1) was put into the second filtrate, and 1 kg of glucose was added as a reducing agent to reduce the Co 3+ Reduction leaching to obtain Co 2+ leachate; after continuing to add sodium carbonate to adjust the pH to 5, the residual Fe and Al in the solution generate Fe2(CO3)3 and Fe2(CO3)3, which are hydrolyzed to generate Fe(OH)3 and Al(OH)3 precipitations, and solid-liquid separation is performed to obtain the third filtrate (cobalt solution) after impurity removal and insoluble hydroxide;

[0060] (5) A sodium carbonate solution with a mass percentage of 17% was used as the bottom liquid of the reactor (volume of 15 L). After stirring at 35 Hz and heating to 75°C, the third filtrate (cobalt solution) and sodium carbonate were added in parallel, and the pH was controlled to 9.2. When the slurry level reached 80% of the container level, the clear liquid in the slurry was filtered using a concentration device. When the concentration reached 50% of the liquid level, the filtration was stopped. The third filtrate (cobalt solution) and sodium carbonate were continued to be added in parallel and the pH value was controlled to 9.2. After multiple concentrations, the solid content of the slurry in the reactor reached 200 g / L and the particle size reached 15 μm to obtain a red slurry. The red slurry was then washed with hot water at 70°C and dried to obtain pink cobalt carbonate powder.

[0061] (6) The ferric phosphate dihydrate prepared in step (3) was heated to 580° C. in an air atmosphere and sintered for 4 h to obtain ferric phosphate. Figure 1 This is the SEM image of iron phosphate. Figure 1 It can be seen that the prepared iron phosphate is porous iron phosphate, which is beneficial to reducing the diffusion distance of Li ions, can strengthen the nanoscale size and porous advantages, and improve the electrochemical performance of lithium iron phosphate materials; Figure 2 is the XRD pattern of iron phosphate, Figure 2 The prepared iron phosphate has no impurities and good uniformity, and can be used to prepare lithium iron phosphate batteries. The cobalt carbonate powder prepared in step (5) is first sintered in air at 300°C for 2 hours, and then heated to 700°C and sintered for 4 hours to obtain cobalt tetroxide. Figure 3 This is the SEM image of cobalt tetroxide. Figure 3 The cobalt trioxide shown is uniformly spherical, well dispersed, and contains pores on the surface, which is beneficial to reducing the migration distance of lithium ions; Figure 4 is the XRD pattern of cobalt tetroxide, Figure 4 This shows that the prepared cobalt trioxide is a pure phase without impurity peaks and can be used as a precursor of lithium cobalt oxide.

[0062] Example 2

[0063] A method for preparing a battery positive electrode material precursor using cobalt-iron slag comprises the following steps:

[0064] (1) 30 kg of cobalt-iron slag (wherein the mass percentage of Fe is approximately 18% and the mass percentage of Co is approximately 15%) was ground to 5 μm and passed through a 150-mesh sieve. The resulting 29.4 kg of fine slag was placed in a box furnace and calcined at 650°C for 3 h to obtain 29 kg of calcined slag. The calcined slag was then uniformly mixed with 100 L of 1.6 mol / L sulfuric acid and 1.45 kg of ferric acid, stirred at 40 Hz, and subjected to a primary leaching at 80°C to obtain an iron leachate, which was then subjected to solid-liquid separation to obtain a first filtrate and cobalt slag.

[0065] (2) adding 16.10 kg of phosphoric acid to the first filtrate to obtain an iron-phosphorus liquid A having a molar ratio of Fe to P of 1:1.10, wherein the mass concentration of Fe is 38.57 g / L and the mass concentration of P is 23.42 g / L; adding the iron-phosphorus liquid A and 38 L of 17% by mass sodium carbonate in parallel at a flow rate of 4:1, adjusting the pH to 2.3, heating to 90° C. and stirring for 1 hour to obtain an amorphous iron phosphate slurry, and obtaining filter cake B and a second filtrate after solid-liquid separation;

[0066] (3) Filter cake B was placed in an aging kettle containing 100 L of 1.50 mol / L phosphoric acid solution and aged for 6 h to displace the Co and S impurities in the iron phosphate. After aging, solid-liquid separation was performed to obtain filter cake C. Filter cake C was washed until the conductivity of the washing water was ≤500 μm / cm, and then dried to obtain iron phosphate dihydrate powder.

[0067] (4) 11 kg of cobalt slag obtained in step (1) was put into the second filtrate, and 0.5 kg of H2C2O4 was added as a reducing agent to reduce the Co 3+ Reduction leaching to obtain Co 2+ leachate; after continuing to add sodium carbonate to adjust the pH to 4.8, the residual Fe and Al in the solution generate Fe2(CO3)3 and Fe2(CO3)3, which are hydrolyzed to generate Fe(OH)3 and Al(OH)3 precipitations, and solid-liquid separation is performed to obtain the third filtrate (cobalt solution) after impurity removal and insoluble hydroxide;

[0068] (5) A sodium carbonate solution with a mass percentage of 17% was used as the bottom liquid of the reactor (volume of 15 L). After stirring at 40 Hz and heating to 75°C, the third filtrate (cobalt solution) and sodium carbonate were added in parallel, and the pH was controlled to 9.0. When the slurry level reached 80% of the container level, the clear liquid in the slurry was filtered using a concentration device. When the concentration reached 50% of the liquid level, the filtration was stopped. The third filtrate (cobalt solution) and sodium carbonate were continued to be added in parallel and the pH was controlled to 9.0. After multiple concentrations, the solid content of the slurry in the reactor reached 250 g / L and the particle size reached 12 μm to obtain a red slurry. The red slurry was then washed with hot water at 70°C and dried to obtain pink cobalt carbonate powder.

[0069] (6) The ferric phosphate dihydrate prepared in step (3) is heated to 610° C. in an air atmosphere and sintered for 3 h to obtain ferric phosphate; the cobalt carbonate powder prepared in step (5) is first sintered at 250° C. in an air atmosphere for 3 h, and then heated to 750° C. and sintered for 2 h to obtain cobalt tetroxide.

[0070] Example 3

[0071] A method for preparing a battery positive electrode material precursor using cobalt-iron slag comprises the following steps:

[0072] (1) 20 kg of cobalt-iron slag (wherein the mass percentage of Fe is approximately 30% and the mass percentage of Co is approximately 21%) was ground to 2 μm and passed through a 150-mesh sieve. The resulting 18.9 kg of fine slag was placed in a box furnace and calcined at 700°C for 0.5 h to obtain 18.5 kg of calcined slag. The calcined slag was then uniformly mixed with 100 L of 1.4 mol / L sulfuric acid and 1.22 kg of ferric acid, stirred at 45 Hz, and subjected to a primary leaching at 70°C to obtain an iron leachate. The solid-liquid separation was then performed to obtain a first filtrate and cobalt slag.

[0073] (2) adding 15.8 kg of phosphoric acid to the first filtrate to obtain an iron-phosphorus liquid A having a molar ratio of Fe to P of 1:1.08, wherein the mass concentration of Fe is 42.86 g / L and the mass concentration of P is 25.76 g / L; adding the iron-phosphorus liquid A and 23 L of 20% by mass sodium carbonate at a flow rate of 4:1 in parallel, adjusting the pH to 1.7, heating to 90° C. and stirring for 1 hour to obtain an amorphous iron phosphate slurry, and obtaining filter cake B and a second filtrate after solid-liquid separation;

[0074] (3) Filter cake B was placed in an aging kettle containing 100 L of 1.20 mol / L phosphoric acid solution and aged for 6 h to displace the Co and S impurities in the iron phosphate. After aging, solid-liquid separation was performed to obtain filter cake C. Filter cake C was washed until the conductivity of the washing water was ≤500 μm / cm, and then dried to obtain iron phosphate dihydrate powder.

[0075] (4) 10 kg of cobalt slag obtained in step (1) was put into the second filtrate, and 0.75 kg of glucose was added as a reducing agent to reduce the Co 3+ Reduction leaching to obtain Co 2+ leachate; after continuing to add sodium carbonate to adjust the pH to 5.3, the residual Fe and Al in the solution generate Fe2(CO3)3 and Fe2(CO3)3, which are hydrolyzed to generate Fe(OH)3 and Al(OH)3 precipitations, and solid-liquid separation is performed to obtain the third filtrate (cobalt solution) after impurity removal and insoluble hydroxide;

[0076] (5) A 20% by mass sodium carbonate solution was used as the bottom liquid of the reactor (volume of 15 L), stirred at 25 Hz and heated to 75°C, and the third filtrate (cobalt solution) and sodium carbonate were added in parallel to control the pH to 9.2. When the slurry level reached 80% of the container level, the clear liquid in the slurry was filtered by a concentration device. When the concentration reached 50% of the liquid level, the filtration was stopped, and the third filtrate (cobalt solution) and sodium carbonate were added in parallel to control the pH to 9.2. After multiple concentrations, the solid content of the slurry in the reactor reached 200 g / L and the particle size reached 17 μm to obtain a red slurry. The red slurry was then washed with hot water at 70°C and dried to obtain pink cobalt carbonate powder.

[0077] (6) The ferric phosphate dihydrate prepared in step (3) is heated to 580° C. in an air atmosphere and sintered for 4 h to obtain ferric phosphate; the cobalt carbonate powder prepared in step (5) is first sintered in an air atmosphere at 300° C. for 2 h, and then heated to 700° C. and sintered for 4 h to obtain cobalt tetroxide.

[0078] Comparative Example 1

[0079] This comparative example provides a method for preparing a traditional iron phosphate precursor.

[0080] Specifically, the preparation method comprises the following steps:

[0081] (1) Pure water, ferrous sulfate and a small amount of phosphoric acid were prepared into liquid metal A, wherein the molar concentration of Fe was 1.0 mol / L and the molar ratio of Fe to P was 0.15; based on the Fe concentration measured in liquid metal A, pure water, ammonium dihydrogen phosphate and hydrogen peroxide were prepared into precipitant B, wherein the molar ratio of Fe to P in the precipitant was 0.90 and the Fe 2+ The molar ratio of hydrogen peroxide to the precipitant is 0.7;

[0082] (2) Using 10 L of liquid metal A as the bottom liquid of the reactor, pump the precipitant B into the reactor at a rate of 1.5 mol / L, adjust the pH to 1.9, and age the slurry for 3 h after it turns white;

[0083] (3) separating the aged slurry in step (2) into a solid-liquid state to obtain a filter cake, washing the filter cake until the conductivity of the washing water is ≤500 μm / cm, and drying to obtain ferric phosphate dihydrate powder;

[0084] (4) The dihydrate iron phosphate powder is heated to 580°C in air and sintered for 4 hours to obtain high-purity anhydrous iron phosphate, which can be used to prepare lithium iron phosphate positive electrode materials.

[0085] Comparative Example 2

[0086] This comparative example provides a method for preparing a traditional lithium cobalt oxide precursor Co3O4.

[0087] Specifically, the preparation method comprises the following steps:

[0088] (1) using 1.2 mol of sulfuric acid to dissolve metallic cobalt to generate a cobalt sulfate aqueous solution with a cobalt content of 50 g / L;

[0089] (2) dissolving ammonium bicarbonate powder in water to prepare an ammonium bicarbonate solution with a concentration of 1.5 mol / L;

[0090] (3) Using ammonium bicarbonate solution as the base liquid, the prepared cobalt sulfate and ammonium bicarbonate solution are added to the reactor, stirred at 40 Hz, and then the ammonium bicarbonate solution is added at 70°C to react and generate cobalt carbonate slurry;

[0091] (4) The cobalt carbonate slurry is filtered to obtain a filter residue, which is then washed with hot water at 70°C and dried. The washed and dried filter residue is then sintered at 300°C for 2 hours, and then heated to 700°C and sintered for 4 hours to obtain the lithium cobalt oxide positive electrode precursor Co3O4.

[0092] Comparative Example 3

[0093] This comparative example provides a method for preparing a battery positive electrode material precursor using cobalt-iron slag.

[0094] The difference between this comparative example and Example 1 is that in step (1), the amount of ferric acid added in this comparative example is 0.81 kg (60% of the amount of ferric acid added in Example 1), and the rest of the preparation process is the same as Example 1.

[0095] Comparative Example 4

[0096] This comparative example provides a method for preparing a battery positive electrode material precursor using cobalt-iron slag.

[0097] The difference between this comparative example and Example 1 is that in step (2), the sodium carbonate in Example 1 is replaced by sodium hydroxide of the same concentration in this comparative example, and the rest of the preparation process is the same as that in Example 1 (steps (4) and (5) continue to use sodium carbonate to prepare cobalt carbonate), and dense iron phosphate is obtained.

[0098] Comparative Example 5

[0099] This comparative example provides a method for preparing a battery positive electrode material precursor using cobalt-iron slag.

[0100] The difference between this comparative example and Example 1 is:

[0101] Steps (1) and (2) are the same as in Example 1;

[0102] In step (3), pure water is used as the aging liquid instead of phosphoric acid solution;

[0103] Steps (4)-(6) are the same as in Example 1.

[0104] Product effect testing

[0105] 1. Finished product quality testing

[0106] Table 1 shows the physical and chemical indicators of the ferric phosphate products prepared in Examples 1, 2, 3 and Comparative Examples 1, 3, 4, and 5, and Table 2 shows the physical and chemical indicators of the cobalt oxide products prepared in Examples 1, 2, 3 and Comparative Examples 2, 3, 4, and 5. The specific data are obtained by testing with an ICP-AES analyzer. Tables 1 and 2 also list the precipitation rates of Fe and Co in the preparation, respectively, for evaluating the yield of cobalt iron, wherein the precipitation rate of Fe = (Fe concentration in the first filtrate of step (1) - residual Fe concentration in the filtrate after the reaction of step (3)) / Fe concentration in the first filtrate of step (1), and the precipitation rate of Co = (Co concentration in the first filtrate of step (4) 2+ Co concentration in the leachate - residual Co concentration after step (5) reaction / Co concentration in step (4) 2+ The concentration of Co in the leachate.

[0107] Table 1 Physical and chemical indicators of ferric phosphate products

[0108]

[0109]

[0110] As shown in Table 1, the impurity content of the ferric phosphate product prepared in Example 1 is lower than that in Comparative Example 1, especially the impurity S. In Comparative Example 3, the oxidant added is insufficient to inhibit the oxidation of Co. 3+ Reduction to Co 2+ , resulting in a higher content of Co in the primary leachate 2+ , S (especially Co 2+ ), which results in excessive Co and S in the final ferric phosphate product. Comparative Example 4 replaces sodium carbonate with sodium hydroxide to obtain dense ferric phosphate, in which the content of impurity S is relatively high. Comparative Example 5 does not use phosphoric acid solution for aging in step (3), and the Co and S impurities in the obtained ferric phosphate are relatively high. The S impurity requires a higher dehydration temperature to remove.

[0111] Table 2 Physical and chemical indicators of cobalt tetroxide products

[0112]

[0113] As can be seen from Table 2, the cobalt trioxide prepared by using cobalt iron slag in the embodiment of the present disclosure has similar properties to the product prepared by the traditional method in Comparative Example 2, but directly using cobalt iron slag can make more effective use of resources.

[0114] 2. Electrochemical performance test

[0115] (1) Assembling lithium iron phosphate button batteries

[0116] Using the iron phosphate prepared in Examples 1, 2, and 3 and Comparative Examples 1, 3, 4, and 5 as raw materials, lithium iron phosphate positive electrode materials were prepared and lithium iron phosphate button cells were assembled. The specific process was as follows: iron phosphate, a lithium source, a carbon source, and a surfactant were mixed in a molar ratio of 1:1.04:0.05:0.04, and then spray-dried to synthesize lithium iron phosphate powder, which was then sintered at 750°C to obtain the lithium iron phosphate positive electrode material. The lithium iron phosphate positive electrode material, acetylene black, and PTFE were mixed in an N-methylpyrrolidone solution in a ratio of 8:1:1 to prepare a slurry. The slurry was applied to the surface of the positive electrode current collector, and graphite, acetylene black, CMC, and SBR were applied to the surface of the negative electrode current collector. The positive and negative electrode sheets were then baked at 130°C and 110°C, respectively, for 8 hours to reduce moisture. After sheeting and cutting, the negative electrode shell, lithium metal sheet, separator, gasket, spring sheet, positive electrode shell, and electrolyte were assembled in a glove box to form a lithium iron phosphate button cell.

[0117] The electrochemical performance of lithium iron phosphate button cells was tested using an electrochemical workstation and other equipment. The specific process was as follows: at room temperature (25°C), the charge and discharge voltage was 2.0-3.65V, and the initial charge and discharge rate was 0.1C. The initial discharge capacity and initial efficiency were tested. At room temperature (25°C), the charge and discharge voltage was 2.0-3.65V, and the charge and discharge rate was 1C. The cycling performance was tested for 1000 cycles at room temperature (25°C). The test results are shown in Table 3.

[0118] As shown in Table 3, the electrochemical performance of lithium iron phosphate button cells assembled using the iron phosphate prepared in Examples 1-3 is superior to that of Comparative Examples 3, 4, and 5. The iron phosphate prepared in Comparative Example 4 is dense and pore-free, which is not conducive to Li ion migration after the synthesis of lithium iron phosphate, thereby affecting the charge and discharge capacity of the material. The iron phosphate prepared directly from cobalt iron slag in the disclosed embodiments can achieve similar or even better electrochemical performance than the iron phosphate prepared by traditional methods (Comparative Example 1).

[0119] Table 3 Comparison of electrochemical performance of lithium iron phosphate batteries

[0120]

[0121] (2) Assembling lithium cobalt oxide button batteries

[0122] Lithium cobalt oxide button cells were assembled using the cobalt oxide prepared in Examples 1, 2, and 3 and Comparative Examples 2, 3, 4, and 5 as raw materials. The specific process was as follows: Co₃O₄ and LiCO₃ were mixed with a stoichiometric ratio of n(Li) / n(Co) of 1:1, sintered at 650°C for 5 hours, and then sintered at 900°C for 8 hours to synthesize lithium cobalt oxide powder. LiCoO₂, acetylene black, and PVDF were mixed in a molar ratio of 93.5:4.0:2.5 and then coated on the positive electrode current collector. A graphite negative electrode was coated on the negative electrode current collector. The positive and negative electrode sheets were then baked at 120°C and 110°C, respectively, for 8 hours to reduce moisture. After sheeting and cutting, the negative electrode shell, lithium metal sheet, separator, gasket, spring sheet, positive electrode shell, and electrolyte were assembled in a glove box to form a lithium cobalt oxide button cell.

[0123] The electrochemical performance of lithium cobalt oxide button cells was tested using an electrochemical workstation and other equipment. The specific process was as follows: Initial discharge capacity and initial efficiency were tested at room temperature (25°C), charge and discharge voltage (3.0-4.65V), and initial charge and discharge rate (0.1C). Cycling performance was also tested at room temperature (25°C), charge and discharge voltage (3.0-4.65V), and charge and discharge rate (0.5C) for 50 cycles.

[0124] Table 4 is a comparison of the electrochemical performance of lithium cobalt oxide batteries. As can be seen from Table 4, the electrochemical performance of the lithium cobalt oxide products prepared in the examples of the present disclosure and the comparative examples is similar. The cobalt oxide prepared in the examples of the present disclosure can be used as a lithium cobalt oxide precursor, and the resulting lithium cobalt oxide batteries exhibit good electrochemical performance.

[0125] Table 4 Comparison of electrochemical performance of lithium cobalt oxide batteries

[0126]

Claims

1. A method for preparing a battery positive electrode material precursor using cobalt-iron slag, characterized in that: The following steps are involved: S1: roasting cobalt iron slag to obtain roasted slag, then mixing it with acid solution and oxidant, leaching to obtain iron leachate; then solid-liquid separation of the iron leachate to obtain a first filtrate and cobalt slag; S2: adding phosphoric acid to the first filtrate to obtain iron-phosphorus liquid A, mixing the iron-phosphorus liquid A with a precipitant A, and then heating to react to obtain an iron phosphate slurry, wherein the precipitant A is a carbonate and / or bicarbonate; and then solid-liquid separation of the iron phosphate slurry to obtain a filter cake B and a second filtrate; S3: placing the filter cake B in a phosphoric acid solution for aging, followed by solid-liquid separation to obtain filter cake C, which is then washed to obtain ferric phosphate dihydrate; S4: sintering the ferric phosphate dihydrate to obtain ferric phosphate; In step S1, the oxidant is selected from at least one of ferric acid, sodium ferrate, and potassium ferrate; the amount of the oxidant added is the amount required to oxidize Fe 2+ 110-130% of the theoretical molar amount.

2. The method according to claim 1, characterized in that The invention also includes the step of preparing the cobalt slag into cobalt trioxide: (1) adding the cobalt slag to the second filtrate, and then adding a reducing agent to react to obtain Co 2+ Leachate, to the Co 2+ Adding a precipitant B to the leachate to control the pH value to 4-6.5, and then performing solid-liquid separation to obtain a third filtrate and insoluble hydroxides, wherein the precipitant B is a carbonate and / or bicarbonate; (2) mixing the third filtrate with a precipitant C to react, controlling the pH value during the reaction to be 8.0-10.5, and then concentrating to obtain a red slurry, which is washed and dried to obtain cobalt carbonate, wherein the precipitant C is a carbonate and / or bicarbonate; (3) Sintering the cobalt carbonate to obtain cobalt trioxide.

3. The method according to claim 1, characterized in that In step S1, the cobalt-iron slag is at least one of cobalt-iron ore, cobalt-iron alloy, and cobalt-iron oxide waste; in the cobalt-iron slag, the content of Fe element is 5-35%, the content of Co element is 5-30%, the content of Al element is 0-2%, and the content of insoluble matter is 2-10%.

4. The method according to claim 1, wherein In step S1, the calcination temperature is 500-750° C., and the calcination time is 0.5-5 h.

5. The method according to claim 1, characterized in that In step S1, the acid solution is at least one of sulfuric acid, nitric acid, and hydrochloric acid; and the molar ratio of Fe in the cobalt-iron slag to the acid solution is 1:(1-2).

6. The method according to claim 1, characterized in that In step S2, the pH value of the mixture is adjusted to 1.6-2.3 by controlling the amount of the precipitant A added.

7. The method according to claim 1, characterized in that In step S2, the reaction temperature is 70-90° C., and the reaction time is 0.5-2 h.

8. The method according to claim 1, characterized in that In step S2, the precipitant A is selected from at least one of ammonium bicarbonate, sodium bicarbonate, potassium bicarbonate, potassium carbonate, ammonium carbonate, and sodium carbonate.

9. The method according to claim 1, characterized in that In step S3, the concentration of the phosphoric acid solution is 0.2-3 mol / L; the aging temperature is 85-95° C.; and the aging time is 2-5 h.

10. The method according to claim 1, characterized in that In step S4, the sintering process of the ferric phosphate dihydrate is: heating to 550-700° C. and sintering for 3-6 hours in air, argon or nitrogen atmosphere.

11. The method according to claim 2, characterized in that In step (1), the reducing agent includes at least one of glucose, H2C2O4, NaSO3, CO, NH3, and SO2.

12. The method according to claim 2, characterized in that In step (1), the amount of the reducing agent added is Co 3+ Completely reduced to Co 2+ 110%-130% of the molar amount.

13. The method according to claim 2, characterized in that In step (1), the sparingly soluble hydroxide is one or more of ferric hydroxide and aluminum hydroxide.

14. The method according to claim 2, characterized in that In step (2), the reaction temperature is 60-80°C.

15. The method according to claim 2, characterized in that The precipitant B and the precipitant C are independently selected from at least one of ammonium bicarbonate, sodium bicarbonate, potassium bicarbonate, potassium carbonate, ammonium carbonate, and sodium carbonate.

16. The method according to claim 2, characterized in that In step (3), the sintering process of the cobalt carbonate is as follows: in an air atmosphere, first heating to 250-350° C. for pre-sintering for 2-3 hours, then heating to 600-750° C. for sintering for 3-6 hours.

17. Use of the method for preparing a battery positive electrode material precursor using cobalt-iron slag according to any one of claims 1 to 16 in preparing a battery positive electrode material.

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