Method for preparing modified nano-tricobalt tetraoxide

Abstract

A method for preparing a modified nano-tricobalt tetraoxide. The method comprises the following steps: preparing a cobalt salt solution, an alkali solution and a sintering aid; introducing an inert gas into a reaction kettle to replace air in the reaction kettle, such that a reaction is performed in the inert atmosphere, adding the cobalt salt solution and the alkali solution, and mixing and reacting same, so as to obtain a nano-cobalt hydroxide slurry having a water content of 85-90 wt%; subjecting the nano-cobalt hydroxide slurry to filter pressing, so as to obtain a press-dried nano-cobalt hydroxide slurry having a water content of 60-70 wt%; drying the press-dried nano-cobalt hydroxide slurry, so as to obtain a dried nano-cobalt hydroxide slurry having a water content of less than 10 wt%; and oxidizing and crushing the dried nano-cobalt hydroxide slurry, and mixing and modifying same with the sintering aid, so as to obtain modified nano-tricobalt tetraoxide having a water content of less than 1 wt% and a D50 of less than 1 μm. The water content of the nano-cobalt hydroxide slurry is reduced in gradient by means of the two steps of filter pressing and drying; and the sintering temperature is reduced by taking the sintering aid as a catalyst.

Description

A preparation method of modified nano-cobalt tetroxide Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a preparation method of modified nano-cobalt tetroxide. Background Art

[0002] Layered high-nickel cathode materials have advantages such as high capacity and low cost, and are widely used in lithium-ion battery cathode materials. However, as the nickel content increases, some nickel ions will be located in the place of lithium ions in the material's microstructure, resulting in the lithium ions not being fully embedded in the material's lattice structure, which aggravates the lithium-nickel mixing. At the same time, when the nickel content is greater than 80%, the nickel on the surface easily reacts with moisture and carbon dioxide in the air, forming residual lithium compounds such as lithium carbonate and lithium hydroxide on the surface of the material, which can cause negative effects such as gelation of the cathode material slurry, degradation of electrochemical performance, and gas release. In order to remove residual lithium compounds on the surface, surface coating modification is an effective means compared to the water washing process. Among them, coating the surface of high-nickel cathode materials with nano-cobalt tetroxide can effectively remove residual lithium while forming a LiCoO2 phase on the material surface, reducing the surface LiNiO2 phase content and improving the electrochemical performance of the material.

[0003] Nano-cobalt trioxide is usually sintered from nano-cobalt hydroxide. First, the nano-cobalt hydroxide particles are very small, making it difficult to completely squeeze out the water during solid-liquid separation. Second, after separation, if the filter cake has a low moisture content, it exhibits the properties of a non-Newtonian fluid, making it impossible to transport materials through mechanical extrusion, resulting in feeding difficulties and restricting industrial continuous production. If the filter cake has a high moisture content, it will increase the energy consumption of the drying process.

[0004] Summary of the Invention

[0005] Based on this, the present invention aims to provide a method for preparing modified nano-cobalt tetroxide. During the synthesis of nano-cobalt tetroxide, the nano-cobalt hydroxide slurry is first pressed and then dried, reducing energy consumption and improving production efficiency. Furthermore, during the oxidation of the nano-cobalt hydroxide slurry, it is simultaneously depolymerized and modified, simplifying the production process and further reducing energy consumption.

[0006] A method for preparing modified nano-cobalt tetroxide comprises the following steps:

[0007] Prepare cobalt salt solution, alkaline solution and sintering aid;

[0008] Inert gas is introduced into the reactor to replace the air therein, so that the reaction is carried out in an inert atmosphere, and the cobalt salt solution and the alkaline solution are added and mixed to react to obtain a nano-cobalt hydroxide slurry with a water content of 85-90wt%;

[0009] filter-filtering the nano-cobalt hydroxide slurry to obtain a dried nano-cobalt hydroxide slurry having a water content of 60 to 70 wt %;

[0010] drying the squeezed nano-cobalt hydroxide slurry to obtain a dry nano-cobalt hydroxide slurry having a water content of less than 10 wt %;

[0011] The dried nano-cobalt hydroxide slurry is oxidized and crushed, and mixed with the sintering aid for modification to obtain modified nano-cobalt tetroxide.

[0012] The present invention ensures that the reaction is carried out under an inert atmosphere by introducing an inert gas into the reactor, thereby preventing the nano cobalt hydroxide slurry from being oxidized by air during synthesis. Experiments have found that the nano cobalt hydroxide slurry can still maintain fluid properties when the water content is 60-70wt%. Therefore, the present invention reduces the water content of the nano cobalt hydroxide slurry by two steps of pressure filtration and drying. The pressure filtration removes part of the free water to control the water content to 60-70wt%. The slurry with this water content can reduce the energy consumption of the subsequent drying step and also keep the slurry fluid, which is convenient for transportation to the subsequent drying equipment. The drying further removes the free water to reduce the water content to below 10wt%, which is convenient for subsequent oxidation, crushing and modification. The sintering aid acts as a catalyst to reduce the sintering temperature and reduce energy consumption. The preparation method of the modified nano cobalt tetroxide of the present invention can improve production efficiency and reduce production energy consumption.

[0013] In one embodiment, the cobalt salt solution of the present invention comprises one or more of cobalt chloride, cobalt sulfate, and cobalt nitrate, with a concentration of 1.5 to 2.5 mol / L. A cobalt salt solution with too low a concentration can affect production efficiency; since cobalt salts all have a certain solubility, a high concentration can cause dissolution difficulties.

[0014] In one embodiment, the alkaline solution of the present invention is at least one of sodium hydroxide and potassium hydroxide, with a concentration of 5 to 10 mol / L. A too low alkaline solution concentration affects production efficiency and increases wastewater discharge; a too high alkaline solution concentration increases viscosity, affecting the mixing uniformity of the slurry in the reactor and, in turn, affecting product quality.

[0015] In one embodiment, the sintering aid of the present invention is at least one of boric acid, boron oxide, and lithium oxide, with a concentration of 0.5 to 1.0 mol / L. A sintering aid concentration that is too low will not achieve the desired catalytic effect, while a concentration exceeding a certain level will not produce a superior catalytic effect and will instead result in waste.

[0016] In one embodiment, pure water is added as a base liquid before the cobalt salt solution and the alkaline solution are added to the reactor of the present invention. The base liquid accounts for 40-50% of the volume of the reactor. After the cobalt salt solution and the alkaline solution are added, the base liquid accounts for 70-80% of the volume of the reactor. The use of pure water as a base liquid allows for adjustment of the alkaline solution concentration, facilitating pH adjustment.

[0017] In one embodiment, the reaction temperature in the reactor of the present invention is 40-60° C., and the reaction pH is 12.0-12.5. Such temperature and pH are favorable for the synthesis of nano-cobalt hydroxide.

[0018] In one embodiment, the filter press of the present invention includes: injecting the nano-cobalt hydroxide slurry into a filter press, washing it 3-5 times with hot pure water at 70-80°C, squeezing it at a pressure of 0.05-1 MPa, and pressing it for 10-30 minutes. By adjusting the squeezing pressure and the pressing time, the moisture content of the slurry is controlled within an appropriate range. While the free water is rapidly removed by physical means, the nano-cobalt hydroxide retains fluid properties, facilitating uniform transportation to the drying equipment and improving production efficiency.

[0019] In one embodiment, the drying process of the present invention includes conveying the squeezed nano-cobalt hydroxide slurry to a vacuum belt dryer via a screw pump for continuous drying, wherein the screw pump has a feed frequency of 10 to 20 Hz, a drying temperature of 100 to 130° C., and a residence time of 30 to 60 minutes. The screw pump can continuously and stably pump the nano-cobalt hydroxide slurry, further reducing the moisture content of the slurry through drying to facilitate subsequent oxidation and pulverization steps.

[0020] In one embodiment, the oxidation and pulverization process described herein includes adding the dried nano-cobalt hydroxide slurry to a butterfly nest mill, setting the air inlet temperature to 250-300°C, the air outlet temperature to 150-175°C, the main engine speed to 10-20 Hz, and the feed frequency to 20-30 Hz. The butterfly nest mill contains a pulverization chamber whose primary internal component is a vertically mounted multi-stage deagglomeration wheel. During operation, the material is rapidly ultrafinely ground through pressure, shear, friction, and other forces, achieving a deagglomeration effect. By adjusting the inlet and outlet air temperatures of the butterfly nest mill, the nano-cobalt hydroxide is oxidized to cobalt tetroxide, while utilizing its deagglomeration function to effectively prevent the formation of agglomerates during oxidation.

[0021] In one embodiment, the sintering aid is added to the dried nano-cobalt hydroxide slurry during oxidation and pulverization, coating the surface of the nano-cobalt oxide. The sintering aid forms a solid solution with the positive electrode material, distorting the lattice and activating it, thereby lowering the sintering temperature. The solid solution is distributed between the nano-cobalt oxide particles, inhibiting grain growth and promoting densification. This accelerates atomic diffusion during the sintering process and promotes sintering densification.

[0022] For better understanding and implementation, the present invention is described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is an XRD pattern of modified nano-cobalt tetroxide;

[0024] Figure 2 is a SEM image of modified nano-cobalt tetroxide. DETAILED DESCRIPTION

[0025] A method for preparing modified nano-cobalt tetroxide comprises the following steps:

[0026] Prepare the solution: prepare a cobalt salt solution, an alkaline solution, and a sintering aid solution of a certain concentration. The cobalt salt can be one or more of cobalt chloride, cobalt sulfate, and cobalt nitrate, with a concentration of 1.5 to 2.5 mol / L. The alkaline solution can be one or more of sodium hydroxide and potassium hydroxide, with a concentration of 5 to 10 mol / L. The sintering aid solution can be an aqueous solution of sintering aids commonly used in positive electrode materials, such as boric acid, boron oxide, and lithium oxide, with a concentration of 0.5 to 1.0 mol / L.

[0027] Nano-cobalt hydroxide synthesis reaction: The reactor uses pure water as the bottom liquid, the volume of the bottom liquid accounts for 40-50% of the total volume of the reactor, and 5-10m 3 / min nitrogen for 30 to 60 minutes to replace the air in the reactor, start the reactor heating, set the synthesis temperature to 40 to 60°C, add cobalt salt and alkali solution, wherein the cobalt salt flow rate is 200 to 300 L / h, and the nitrogen flow rate remains unchanged during the reaction. The alkali solution flow rate is adjusted to control the reaction pH value to 12.0 to 12.5. When the liquid volume in the reactor accounts for 70 to 80%, stop adding liquid to obtain nano cobalt hydroxide slurry with a water content of 85 to 90 wt%.

[0028] Nano-cobalt hydroxide filter pressing: the nano-cobalt hydroxide slurry prepared above is pumped into a filter press, washed 3 to 5 times with 70-80°C pure water, with a pressing pressure of 0.05-1 MPa and a drying time of 10-30 min, and the moisture content of the filter cake is controlled at 60-70 wt%.

[0029] Nano-cobalt hydroxide drying: The filter cake is transported to a vacuum belt dryer through a screw pump for continuous drying. The screw pump feed frequency is 10-20 Hz, the drying temperature is 100-130°C, and the residence time is 30-60 minutes. The moisture content of the discharge is controlled to be less than 10wt%.

[0030] Oxidation, pulverization, and modification of nano-cobalt hydroxide: The dried nano-cobalt hydroxide powder is added to a butterfly nest mill for oxidation, pulverization, and modification. The inlet air temperature is set at 250-300°C, the outlet air temperature is 150-175°C, the main engine speed is 10-20 Hz, and the feed frequency is 20-30 Hz. While the nano-cobalt hydroxide material is oxidized and pulverized in the main engine, a sintering aid solution is evenly pumped into the modifier inlet on the side of the pulverization chamber at a flow rate of 5-10 L / h using a metering pump. After atomization, the sintering aid solution is coated on the surface of the nano-cobalt tetroxide, ultimately obtaining a modified nano-cobalt tetroxide powder material with a moisture content of less than 1wt% and a D50 of less than 1μm.

[0031] Example 1

[0032] The preparation method of a modified nano-cobalt tetroxide of this embodiment comprises the following steps:

[0033] Prepare solution: prepare 2 mol / L cobalt chloride solution, 8 mol / L sodium hydroxide solution, and 0.5 mol / L boric acid solution.

[0034] Synthesis of nano-cobalt hydroxide: The reactor is filled with pure water, the volume of the bottom liquid accounts for 50% of the total volume of the reactor, and the volume of the bottom liquid accounts for 8m 3 Nitrogen was introduced at a rate of 1 / min for 40 min, the reactor was heated, the synthesis temperature was set to 50°C, and cobalt salt and alkali solution were added in parallel, wherein the cobalt salt flow rate was 200 L / h. During the reaction, the nitrogen flow rate was kept constant and continuously introduced, and the alkali solution flow rate was adjusted to control the reaction pH value to be constant at 12.2. When the alkali solution flowed to 72% of the volume of the reactor, the liquid addition was stopped to obtain a nano-cobalt hydroxide slurry.

[0035] Nano-cobalt hydroxide filtration: The nano-cobalt hydroxide slurry prepared above was pumped into a filter press, washed three times with 75° C. pure water, squeezed at a pressure of 1 MPa, and dried for 15 min to obtain a paste-like filter cake with a moisture content of 62.5 wt%.

[0036] Nano-cobalt hydroxide drying: The filter cake obtained by filtration was conveyed to a vacuum belt dryer by a screw pump for continuous drying. The screw pump feed frequency was 10 Hz, the drying temperature was 130° C., and the residence time was 50 min to obtain nano-cobalt hydroxide powder with a moisture content of 5 wt%.

[0037] Oxidation, pulverization, and modification of nano-cobalt hydroxide: The Diechao mill was set with an inlet temperature of 300°C, an outlet temperature of 175°C, a main engine speed of 20 Hz, and a feed frequency of 25 Hz. The nano-cobalt hydroxide powder obtained above was added to the Diechao mill feed bin. Simultaneously, a metering pump was used to uniformly pump a boric acid solution at a flow rate of 10 L / h from the modifier inlet on the side of the pulverization chamber to obtain a modified nano-cobalt tetroxide material having a moisture content of 0.52 wt%.

[0038] As shown in Figures 1 and 2, XRD showed a pure phase of Co3O4, and SEM showed that the nanosheets had uniform morphology and consistent size.

[0039] Example 2

[0040] The preparation method of a modified nano-cobalt tetroxide of this embodiment comprises the following steps:

[0041] Prepare solution: prepare 1.5 mol / L cobalt chloride solution, 6 mol / L sodium hydroxide solution, and 0.6 mol / L boric acid solution.

[0042] Synthesis of nano-cobalt hydroxide: The reactor is filled with pure water, the volume of the bottom liquid accounts for 40% of the total volume of the reactor, and the volume of the bottom liquid accounts for 5m 3 Nitrogen was introduced at a rate of 1 / min for 60 min, the reactor was heated, the synthesis temperature was set to 45°C, and cobalt salt and alkali solution were added in parallel, wherein the cobalt salt flow rate was 300 L / h. During the reaction, the nitrogen flow rate was kept constant and continuously introduced, and the alkali solution flow rate was adjusted to control the reaction pH value to be constant at 12.0. When the alkali solution flowed to 70% of the volume of the reactor, the liquid addition was stopped to obtain a nano-cobalt hydroxide slurry.

[0043] Nano-cobalt hydroxide filtration: The nano-cobalt hydroxide slurry prepared above was pumped into a filter press, washed four times with 70° C. pure water, with a pressing pressure of 0.5 MPa and a drying time of 25 min to obtain a paste-like filter cake with a moisture content of 66 wt%.

[0044] Nano-cobalt hydroxide drying: The filter cake obtained by filtration was conveyed to a vacuum belt dryer by a screw pump for continuous drying. The screw pump feed frequency was 15 Hz, the drying temperature was 100° C., and the residence time was 60 min to obtain nano-cobalt hydroxide powder with a moisture content of 8 wt%.

[0045] Oxidation, pulverization, and modification of nano-cobalt hydroxide: The Diechao mill was set with an inlet air temperature of 250°C, an outlet air temperature of 150°C, a main engine speed of 10 Hz, and a feed frequency of 20 Hz. The nano-cobalt hydroxide powder obtained above was added to the Diechao mill feed bin. Simultaneously, a metering pump was used to uniformly pump a boric acid solution at a flow rate of 8 L / h from the modifier inlet on the side of the pulverization chamber to obtain a modified nano-cobalt tetroxide material having a moisture content of 0.55 wt%.

[0046] Example 3

[0047] The preparation method of a modified nano-cobalt tetroxide of this embodiment comprises the following steps:

[0048] Prepare the solution: prepare 2.5 mol / L cobalt chloride solution, 10 mol / L sodium hydroxide solution, and 0.8 mol / L boric acid solution.

[0049] Synthesis of nano-cobalt hydroxide: The reactor is filled with pure water, the volume of the bottom liquid accounts for 45% of the total volume of the reactor, and the volume of the bottom liquid accounts for 10m 3 Nitrogen was introduced at a rate of 1 / min for 30 min, the reactor was heated, the synthesis temperature was set to 40°C, and cobalt salt and alkali solution were added in parallel, with the cobalt salt flow rate being 230 L / h. During the reaction, the nitrogen flow rate remained unchanged and continued to be introduced, and the alkali solution flow rate was adjusted to control the reaction pH value to be constant at 12.5. When the alkali solution flowed to 80% of the volume of the reactor, the liquid addition was stopped to obtain a nano-cobalt hydroxide slurry.

[0050] Nano-cobalt hydroxide filtration: The nano-cobalt hydroxide slurry prepared above was pumped into a filter press and washed five times with 80° C. pure water, with a pressing pressure of 0.05 MPa and a drying time of 30 min to obtain a paste-like filter cake with a moisture content of 69 wt%.

[0051] Nano-cobalt hydroxide drying: The filter cake obtained by filtration was conveyed to a vacuum belt dryer by a screw pump for continuous drying. The screw pump feed frequency was 20 Hz, the drying temperature was 120° C., and the residence time was 30 min to obtain nano-cobalt hydroxide powder with a moisture content of 7.6 wt%.

[0052] Oxidation, pulverization, and modification of nano-cobalt hydroxide: The Diechao mill was set with an inlet air temperature of 280°C, an outlet air temperature of 160°C, a main engine speed of 16 Hz, and a feed frequency of 30 Hz. The nano-cobalt hydroxide powder obtained above was added to the Diechao mill feed bin. Simultaneously, a metering pump was used to uniformly pump a boric acid solution at a flow rate of 5 L / h from the modifier inlet on the side of the pulverization chamber to obtain a modified nano-cobalt tetroxide material having a moisture content of 0.56 wt%.

[0053] Example 4

[0054] The preparation method of a modified nano-cobalt tetroxide of this embodiment comprises the following steps:

[0055] Prepare solution: prepare 1.6 mol / L cobalt chloride solution, 5 mol / L sodium hydroxide solution, and 1.0 mol / L boric acid solution.

[0056] Synthesis of nano-cobalt hydroxide: The reactor is filled with pure water, the volume of the bottom liquid accounts for 48% of the total volume of the reactor, and the volume of the bottom liquid accounts for 6m 3 Nitrogen was introduced at a rate of 1 / min for 50 min, the reactor was heated, the synthesis temperature was set to 60°C, and cobalt salt and alkali solution were added in parallel, with the cobalt salt flow rate being 260 L / h. During the reaction, nitrogen flow rate remained unchanged and continued to be introduced, and the alkali solution flow rate was adjusted to control the reaction pH value to be constant at 12.4. When the alkali solution flowed to 77% of the reactor volume, the liquid addition was stopped to obtain a nano-cobalt hydroxide slurry.

[0057] Nano-cobalt hydroxide filtration: The nano-cobalt hydroxide slurry prepared above was pumped into a filter press and washed four times with 70-75° C. pure water, with a pressing pressure of 0.8 MPa and a drying time of 10 min to obtain a paste-like filter cake with a moisture content of 60-62 wt%.

[0058] Nano-cobalt hydroxide drying: The filter cake obtained by pressure filtration was conveyed to a vacuum belt dryer via a screw pump for continuous drying. The screw pump feed frequency was 12 Hz, the drying temperature was 110° C., and the residence time was 40 min to obtain nano-cobalt hydroxide powder with a moisture content of 5.8 wt %.

[0059] Oxidation, pulverization, and modification of nano-cobalt hydroxide: The Diechao mill was set with an inlet air temperature of 260°C, an outlet air temperature of 165°C, a main engine speed of 12 Hz, and a feed frequency of 22 Hz. The nano-cobalt hydroxide powder obtained above was added to the Diechao mill feed bin. Simultaneously, a metering pump was used to uniformly pump a boric acid solution at a flow rate of 6 L / h from the modifier inlet on the side of the pulverization chamber to obtain a modified nano-cobalt tetroxide material having a moisture content of 0.55 wt%.

[0060] The above-described embodiments represent only a few implementations of the present invention. While their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. In other embodiments of the present invention, for example, the inert gas may not be nitrogen but may be neon, argon, or the like; for example, the cobalt salt flow rate in different reactors may not necessarily be within the range of 200 to 300 L / h; and for example, the sintering aid flow rate in different butterfly-nest mills may not necessarily be within the range of 5 to 10 L / h.

Claims

1. A method for preparing modified nano-cobalt tetroxide, comprising the following steps: Prepare cobalt salt solution, alkaline solution and sintering aid; Introducing an inert gas into the reaction kettle to replace the air therein, so that the reaction is carried out in an inert atmosphere, adding the cobalt salt solution and the alkaline solution for mixed reaction, and obtaining a nano cobalt hydroxide slurry with a water content of 85-90wt%; The nano cobalt hydroxide slurry is subjected to filter pressing to obtain a squeezed-dried nano cobalt hydroxide slurry having a water content of 60 to 70 wt %; Drying the squeezed nano-cobalt hydroxide slurry to obtain a dry nano-cobalt hydroxide slurry having a water content of less than 10 wt %; The dried nano cobalt hydroxide slurry is oxidized and crushed, and mixed with the sintering aid for modification to obtain modified nano cobalt tetroxide.

2. The method for preparing modified nano-cobalt tetroxide according to claim 1, characterized in that: The cobalt salt solution is one or more of cobalt chloride, cobalt sulfate and cobalt nitrate, and the concentration is 1.5-2.5 mol / L.

3. The method for preparing modified nano-cobalt tetroxide according to claim 1, characterized in that: The alkaline solution is at least one of sodium hydroxide and potassium hydroxide, and the concentration is 5-10 mol / L.

4. The method for preparing modified nano-cobalt tetroxide according to claim 1, characterized in that: The sintering aid is at least one of boric acid, boron oxide and lithium oxide, and the concentration is 0.5-1.0 mol / L.

5. The method for preparing modified nano-cobalt tetroxide according to claim 1, characterized in that: Before adding the cobalt salt solution and the alkaline solution into the reactor, pure water is first added as a base liquid, and the base liquid accounts for 40-50% of the volume of the reactor; after adding the cobalt salt solution and the alkaline solution, the base liquid accounts for 70-80% of the volume of the reactor.

6. The method for preparing modified nano-cobalt tetroxide according to claim 1, characterized in that: In the reactor, the reaction temperature is 40-60° C., and the reaction pH is 12.0-12.

5.

7. The method for preparing modified nano-cobalt tetroxide according to claim 1, characterized in that: The filter pressing comprises: putting the nanometer cobalt hydroxide slurry into a filter press, washing it 3 to 5 times with hot pure water at 70 to 80° C., with a pressure of 0.05 to 1 MPa and a filter pressing time of 10 to 30 minutes.

8. The method for preparing modified nano-cobalt tetroxide according to claim 1, characterized in that: The drying comprises: conveying the squeezed nano cobalt hydroxide slurry to a vacuum belt dryer through a screw pump for continuous drying, wherein the screw pump feed frequency is 10-20 Hz, the drying temperature is 100-130° C., and the residence time is 30-60 min.

9. The method for preparing modified nano-cobalt tetroxide according to claim 1, characterized in that: The oxidation and pulverization comprises: adding the dry nano cobalt hydroxide slurry into a butterfly nest mill, setting the air inlet temperature to 250-300° C., the air outlet temperature to 150-175° C., the main engine speed to 10-20 Hz, and the feed frequency to 20-30 Hz.

10. The method for preparing modified nano-cobalt tetroxide according to claim 1, characterized in that: The sintering aid is added to the dried nanometer cobalt hydroxide slurry while being oxidized and crushed, so that the sintering aid is coated on the surface of the nanometer cobalt tetroxide.

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