Nano-cobalt(II) hydroxide, preparation method therefor, and use thereof

Abstract

A nano-cobalt(II) hydroxide, a preparation method therefor, and a use thereof, belonging to the technical field of lithium-ion batteries. The preparation method comprises: reacting a cobalt salt solution and a precipitant solution at 30-35 ℃, and during the reaction process, adjusting the amount of precipitant solution added so as to control the pH of the reaction system to be 13-13.5, and after the reaction is finished, obtaining a nano-cobalt(II) hydroxide slurry. The precipitant solution comprises a liquid alkali and a deflocculant, and the mass ratio of the solute in the liquid alkali to the deflocculant is 1:0.02-0.05. Carrying out the reaction at a lower temperature prevents particle agglomeration caused by intensified Brownian motion among particles, thus facilitating the synthesis of ultra-fine nano-cobalt(II) hydroxide while reducing energy consumption; when the interaction forces between molecules become stronger, the use of both a higher pH and the deflocculant allows good dispersibility to still be maintained, thus reducing the occurrence of agglomeration; and the obtained crystal grains are small in size, are not prone to agglomerate, and have good dispersibility.

Description

Nano-cobalt hydroxide and its preparation method and application Technical Field

[0001] The present disclosure relates to the technical field of lithium-ion batteries, and in particular to a nano-cobalt hydroxide and a preparation method and application thereof. Background Art

[0002] Layered high-nickel cathode materials have the advantages of high capacity and low cost, and are widely used in lithium-ion battery cathode materials. However, high-nickel cathode materials are extremely sensitive to moisture and carbon dioxide in the air, and are prone to forming residual lithium compounds, which have many effects on the subsequent slurry preparation and the electrochemical performance of the cathode materials, and even affect battery safety. Researchers usually eliminate residual lithium by coating nano-cobalt hydroxide on the surface of the cathode to improve material performance. The ideal coating layer should be thin and uniform, which requires nano-cobalt hydroxide to have a smaller size and better dispersibility. However, after the particles are refined to the nanoscale, the large amount of positive and negative charges accumulated on their surface will cause surface charge aggregation, making the nanoparticles extremely unstable. In addition, the nanoparticles have a large surface area and high surface energy, are in an energy unstable state, and are prone to agglomeration. How to prepare nano-cobalt hydroxide materials with smaller size and good dispersibility is one of the challenges facing the industry.

[0003] In view of this, the present disclosure is proposed.

[0004] Summary of the Invention

[0005] The purpose of the present disclosure includes providing a method for preparing nano-cobalt hydroxide, which can effectively avoid grain agglomeration, and the prepared grains are small in size and have good dispersibility.

[0006] The purpose of the present disclosure includes providing a nano-cobalt hydroxide.

[0007] The purpose of the present disclosure includes providing the use of nano-cobalt hydroxide in preparing positive electrode materials.

[0008] An object of the present disclosure includes providing a positive electrode material.

[0009] An object of the present disclosure includes providing a lithium-ion battery.

[0010] In order to achieve at least one of the above-mentioned objectives of the present disclosure, the following technical solutions may be adopted:

[0011] In a first aspect, the present disclosure provides a method for preparing nano-cobalt hydroxide, comprising: reacting a cobalt salt solution and a precipitant solution at 30-35° C., adjusting the amount of the precipitant solution added to control the pH of the reaction system to be 13-13.5 during the reaction, and obtaining a nano-cobalt hydroxide slurry after the reaction, wherein the precipitant solution comprises liquid caustic soda and a deflocculant, and the mass ratio of solute in the liquid caustic soda to the deflocculant is 1:0.02-0.05.

[0012] In some embodiments of the present disclosure, the deflocculant includes one or more of sodium citrate, potassium citrate, potassium tartrate, sodium tartrate, and sodium glycinate.

[0013] In some embodiments of the present disclosure, the cobalt salt solution and the precipitant solution react in a reactor filled with bottom water.

[0014] In some embodiments of the present disclosure, the volume of the kettle bottom water accounts for 30% to 45% of the total volume of the reactor.

[0015] In some embodiments of the present disclosure, the amount of the cobalt salt solution added per hour is 30% to 40% of the total volume of the reactor.

[0016] In some embodiments of the present disclosure, the cobalt salt solution and the precipitant solution are added to the reactor in parallel.

[0017] In some embodiments of the present disclosure, the cobalt salt solution and the precipitant solution are added in parallel for a time period of 0.5 h to 1.5 h.

[0018] In some embodiments of the present disclosure, during the reaction process, the stirring speed in the reactor is 300 rpm to 500 rpm.

[0019] In some embodiments of the present disclosure, before adding the cobalt salt solution and the precipitant solution, nitrogen is introduced into the reactor to replace the air in the reactor, and the nitrogen is continuously introduced during the reaction.

[0020] In some embodiments of the present disclosure, the nitrogen gas used to replace the air in the reactor is introduced for 30 min to 60 min.

[0021] In some embodiments of the present disclosure, the method for preparing nano-cobalt hydroxide further comprises filtering, washing, drying and crushing the nano-cobalt hydroxide slurry.

[0022] In some embodiments of the present disclosure, the washing comprises washing 3 to 5 times with hot pure water at 70 to 80°C.

[0023] In some embodiments of the present disclosure, the drying comprises drying in a vacuum oven at 80-90° C. for 5-10 hours.

[0024] In some embodiments of the present disclosure, the pulverizing comprises pulverizing the dried particles using a jet mill to a particle size of less than 200 nm.

[0025] In some embodiments of the present disclosure, the liquid alkali includes one or more of sodium hydroxide and potassium hydroxide.

[0026] In some embodiments of the present disclosure, the concentration of the liquid alkali is 5 to 10 mol / L.

[0027] In some embodiments of the present disclosure, the cobalt salt solution includes one or more of cobalt chloride, cobalt sulfate, and cobalt nitrate.

[0028] In some embodiments of the present disclosure, the concentration of the cobalt salt solution is 1.5 to 2.5 mol / L.

[0029] In a second aspect, the present disclosure provides a nano-cobalt hydroxide, which is prepared using the preparation method of the nano-cobalt hydroxide described in any one of the above embodiments.

[0030] In a third aspect, the present disclosure provides the use of the nano-cobalt hydroxide described in the above embodiment in preparing a positive electrode material.

[0031] In a fourth aspect, the present disclosure provides a positive electrode material, comprising a positive electrode and the nano-cobalt hydroxide as described in the above embodiment, wherein the nano-cobalt hydroxide is coated on the surface of the positive electrode.

[0032] In a fifth aspect, the present disclosure provides a lithium-ion battery comprising the positive electrode material as described in the above embodiment.

[0033] Compared with the prior art, the advantages of the present invention include:

[0034] On the one hand, the present disclosure provides a method for preparing nano-cobalt hydroxide, which uses a precipitant made of liquid caustic soda and a deflocculant mixed in a specific ratio. The deflocculant in the precipitant can form an electrical double layer on the surface of the nano-cobalt hydroxide. This Coulomb repulsion significantly reduces the attractive force that causes nanoparticles to agglomerate, thereby improving dispersibility. Furthermore, this type of deflocculant has an antioxidant effect, absorbing oxygen molecules within the system to prevent oxidation of the nano-cobalt hydroxide, which could affect product quality. The advantage of mixing a deflocculant with liquid caustic soda is that as the amount of liquid caustic soda increases during the reaction, the viscosity and oxygen content of the slurry in the system also increase. The addition of a deflocculant also increases proportionally, offsetting the negative effects of the increased amount of liquid caustic soda. This negative effect is that an increase in pH leads to stronger intermolecular interactions in the reaction system, resulting in increased viscosity and colloidal properties. This reduces the fluidity of the slurry within the reactor and weakens the local stirring intensity within the slurry, hindering the dispersion of the nano-cobalt hydroxide. The present disclosure utilizes a deflocculating agent, which can maintain good dispersion even at a pH of 13 to 13.5. On the other hand, the preparation method of nano cobalt hydroxide provided by the present disclosure controls the synthesis temperature to 30-35°C during the synthesis reaction stage. Reacting at a lower temperature can avoid the intensification of Brownian motion between particles leading to particle agglomeration, which is conducive to the synthesis of ultrafine nano cobalt hydroxide and saves energy. Liquid alkali combines the above two aspects, and the preparation method of nano cobalt hydroxide provided by the present disclosure can enable rapid nucleation of crystals, small grain size, and not easy to agglomerate, with good dispersibility. The above-mentioned nano cobalt hydroxide can be widely used in the preparation of positive electrode materials, and can achieve good coating of the positive electrode surface to eliminate residual lithium, and the obtained coating layer is thin and uniform. The lithium ion battery prepared from the above-mentioned positive electrode material has excellent performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0036] FIG1 is a SEM image of nano-cobalt hydroxide provided in Example 1 of the present disclosure at a scale of 4 μm;

[0037] FIG2 is a SEM image of nano-cobalt hydroxide provided in Example 1 of the present disclosure at a scale of 20 μm;

[0038] FIG3 is a SEM image of nano-cobalt hydroxide provided in Example 2 of the present disclosure at a scale of 4 μm;

[0039] FIG4 is a SEM image of nano-cobalt hydroxide provided in Example 3 of the present disclosure at a scale of 4 μm;

[0040] FIG5 is a SEM image of nano-cobalt hydroxide provided in Example 4 of the present disclosure at a scale of 4 μm;

[0041] FIG6 is an SEM image of nano-cobalt hydroxide provided in Comparative Example 1 of the present disclosure at a scale of 4 μm;

[0042] FIG7 is an SEM image of nano-cobalt hydroxide provided in Comparative Example 2 of the present disclosure at a scale of 4 μm;

[0043] FIG8 is an SEM image of nano-cobalt hydroxide provided in Comparative Example 3 of the present disclosure at a scale of 4 μm;

[0044] FIG9 is an SEM image of nano-cobalt hydroxide provided in Comparative Example 4 of the present disclosure at a scale of 4 μm;

[0045] FIG10 is an SEM image of nano-cobalt hydroxide provided in Comparative Example 5 of the present disclosure at a scale of 4 μm;

[0046] FIG11 is an SEM image of nano-cobalt hydroxide provided in Comparative Example 6 of the present disclosure at a scale of 4 μm;

[0047] FIG12 is an SEM image of nano-cobalt hydroxide provided in Comparative Example 7 of the present disclosure at a scale of 4 μm;

[0048] FIG13 is a SEM image of the positive electrode material coated with nano-cobalt hydroxide provided in Example 1 of the present disclosure at a scale of 4 μm;

[0049] FIG14 is an SEM image of the positive electrode material coated with nano-cobalt hydroxide provided in Comparative Example 1 of the present disclosure at a scale of 4 μm. DETAILED DESCRIPTION

[0050] The embodiments of the present disclosure will be described in detail below with reference to the examples. However, those skilled in the art will appreciate that the following examples are intended only to illustrate the present disclosure and should not be construed as limiting the scope of the present disclosure. Where specific conditions are not specified in the examples, the experiments were performed under conventional conditions or the conditions recommended by the manufacturer. Where the manufacturer of the reagents or instruments is not specified, all are commercially available conventional products.

[0051] The endpoints of the ranges and any values ​​disclosed in this disclosure are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed herein.

[0052] The present disclosure provides a method for preparing nano-cobalt hydroxide, which comprises the following steps:

[0053] S1. Prepare cobalt salt solution and precipitant solution.

[0054] The cobalt salt solution includes, but is not limited to, one or more of cobalt chloride, cobalt sulfate, and cobalt nitrate, and the concentration of the cobalt salt solution is 1.5 to 2.5 mol / L. In some embodiments, the concentration of the cobalt salt solution can be, for example, any one of 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2.0 mol / L, 2.1 mol / L, 2.2 mol / L, 2.3 mol / L, 2.4 mol / L, and 2.5 mol / L, or a range between any two of them.

[0055] The precipitant solution includes liquid caustic soda and a deflocculant, with the mass ratio of solute to deflocculant in the liquid caustic soda being 1:0.02-0.05. The liquid caustic soda includes, but is not limited to, one or more of sodium hydroxide and potassium hydroxide, with a concentration of 5-10 mol / L. The deflocculant includes one or more of sodium citrate, potassium citrate, potassium tartrate, sodium tartrate, and sodium glycinate.

[0056] In some embodiments, the mass ratio of the solute to the deflocculant in the liquid caustic soda can be, for example, any one of 1:0.02, 1:0.03, 1:0.04, 1:0.05, or a range between any two of them. The present disclosure has found that when the mass ratio of the solute to the deflocculant in the liquid caustic soda is lower than the above range, the amount of deflocculant used is too small, which will result in the increase in the amount of liquid caustic soda when adjusting the pH, causing the intermolecular interaction force to become very strong, the viscosity to increase, the reaction system to exhibit colloidal properties, the slurry fluidity to deteriorate, and the local stirring intensity within the slurry to weaken, which is not conducive to the dispersion of nano-cobalt hydroxide. When the amount of deflocculant used is too much, the particle size does not further decrease, but it will lead to the introduction of too many organic impurities during the synthesis, resulting in increased wastewater treatment costs.

[0057] In some embodiments, the concentration of the liquid caustic soda can be, for example, any one of 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L, 10 mol / L, or a range between any two of them.

[0058] S2. Synthesis reaction.

[0059] The reactor is bottomed with pure water, and the volume of the bottom water accounts for 30% to 45% of the total volume of the reactor. Nitrogen is introduced into the reactor for 30 minutes to 60 minutes to replace the air in the reactor. At the same time, the reactor is heated, the synthesis temperature is set to 30°C to 35°C, and the stirring speed in the reactor is 300rpm to 500rpm.

[0060] A cobalt salt solution and a precipitant solution are added. The cobalt salt solution and the precipitant solution disclosed herein can be added separately or in parallel, preferably in parallel. The amount of the cobalt salt solution added per hour is 30% to 40% of the total volume of the reactor. The amount of the precipitant solution added is adjusted to control the pH of the reaction system to be 13 to 13.5. Nitrogen is continuously introduced during the reaction. The cobalt salt solution and the precipitant solution are added in parallel to the reactor for 0.5 to 1.5 hours, and then the addition of the liquid is stopped. After the reaction is completed, a nano-cobalt hydroxide slurry is obtained.

[0061] In some embodiments, the volume of the bottom water of the reactor accounts for any one of 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, and 45% of the total volume of the reactor, or a range therebetween. In the present disclosure, pure water is used as the bottom water of the reactor. Compared with solutions using liquid caustic soda as the bottom water of the reactor, the present disclosure can save caustic soda and save costs.

[0062] In some embodiments, the time for introducing nitrogen into the reactor can be, for example, any one of 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, and 60 min, or a range between any two of them. The present disclosure effectively replaces the air in the reactor by introducing nitrogen for a long time. If the nitrogen introduction time is too short, incomplete air replacement may occur.

[0063] In some embodiments, the synthesis temperature can be, for example, any one of 30° C., 31° C., 32° C., 33° C., 34° C., and 35° C., or a range between any two thereof. The use of a lower synthesis temperature in the present disclosure can avoid agglomeration of particles caused by increased Brownian motion between particles, thereby facilitating the synthesis of ultrafine nano-cobalt hydroxide and saving energy.

[0064] In some embodiments, the stirring speed can be, for example, any one of 300 rpm, 350 rpm, 400 rpm, 450 rpm, and 500 rpm, or a range between any two thereof. The present disclosure can accelerate the dispersion of particles by stirring.

[0065] In some embodiments, the amount of cobalt salt solution added per hour is any one of 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, or 40% of the total volume of the reactor, or a range therebetween. The present disclosure effectively shortens the reaction time by feeding the cobalt salt at a high flow rate, and produces a large number of crystal nuclei in the early stages of the reaction, preventing the particles from agglomerating and growing.

[0066] In some embodiments, the pH of the reaction system can be, for example, any one of 13, 13.1, 13.2, 13.3, 13.4, and 13.5, or a range between any two thereof. The higher the pH of the reaction system controlled by the present disclosure, the greater the supersaturation of the precipitation system, resulting in rapid crystal nucleation and smaller grain size.

[0067] In some embodiments, the time for co-flowing the cobalt salt solution and the precipitant solution into the reactor can be controlled within a range of, for example, 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h, 1 h, 1.1 h, 1.2 h, 1.3 h, 1.4 h, or 1.5 h, or any two thereof. By limiting the above parameters, the present disclosure shortens the reaction time of the present application, thereby improving production efficiency. S3: Washing, drying, and pulverizing.

[0068] The nano-cobalt hydroxide slurry is filtered by a filter press, washed with hot pure water at 70-80° C. for 3-5 times, then dried in a vacuum oven at 80-90° C. for 5-10 hours, and finally pulverized with a jet mill to a particle size of less than 200 nm to obtain a finished nano-cobalt hydroxide product.

[0069] In some embodiments, the washing temperature may be, for example, any one of 70°C, 71°C, 72°C, 73°C, 74°C, 75°C, 76°C, 77°C, 78°C, 79°C, or 80°C, or a range between any two thereof. The number of washes may be, for example, 3, 4, or 5 times. The drying temperature may be, for example, any one of 80°C, 81°C, 82°C, 83°C, 84°C, 85°C, 86°C, 87°C, 88°C, 89°C, or 90°C, or a range between any two thereof. The drying time may be, for example, any one of 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours, or a range between any two thereof.

[0070] In the present disclosure, during the synthesis reaction stage, low-temperature synthesis is combined with a high pH value to increase the supersaturation of the precipitation system, resulting in rapid crystal nucleation and smaller grain size. Furthermore, the present disclosure utilizes a high feed flow rate, which helps shorten the reaction time, generating a large number of crystal nuclei at the initial stage of the reaction, preventing particles from agglomerating and growing. Combined with a low reaction temperature, this prevents intensified Brownian motion between particles, which can lead to particle agglomeration, facilitating the synthesis of ultrafine nano-cobalt hydroxide while also saving energy. Due to the high reaction pH, the correspondingly high concentration of liquid caustic soda also increases the intermolecular interactions, which in turn increases viscosity and exhibits colloidal properties. This can lead to poor fluidity of the slurry within the reactor and weaken the local stirring intensity within the slurry, hindering the dispersion of the nano-cobalt hydroxide. The present disclosure selects a specific deflocculating agent to be mixed with liquid caustic soda in a specific ratio. This deflocculating agent can form a double layer on the surface of the nano-cobalt hydroxide. This Coulomb repulsion significantly reduces the attractive force that causes nanoparticles to agglomerate, thereby improving dispersibility. Furthermore, this deflocculating agent has an antioxidant effect, absorbing oxygen molecules within the system to prevent oxidation of the nano-cobalt hydroxide, which could affect product quality. The advantage of mixing a deflocculant with liquid caustic soda is that as the amount of liquid caustic soda increases during the reaction, the viscosity and oxygen content of the slurry in the system also increase. Simultaneously, the amount of deflocculant added also increases proportionally, offsetting the negative effects of the increased amount of liquid caustic soda. The nano-cobalt hydroxide crystals produced using the method for preparing nano-cobalt hydroxide provided herein have a small primary particle size and excellent dispersibility.

[0071] The nano-cobalt hydroxide described above can be widely used in the preparation of positive electrode materials. Specifically, the present disclosure provides a positive electrode material comprising a positive electrode and the nano-cobalt hydroxide described above, with the nano-cobalt hydroxide coated on the surface of the positive electrode. Due to the small size and excellent dispersibility of the nano-cobalt hydroxide provided herein, the positive electrode surface can be well coated to eliminate residual lithium, and the resulting coating layer is thin and uniform. Lithium-ion batteries prepared from this positive electrode material exhibit excellent performance.

[0072] The features and performance of the present disclosure are further described in detail below with reference to the embodiments.

[0073] Example 1

[0074] This embodiment provides a nano-cobalt hydroxide, the preparation method of which comprises the following steps:

[0075] S1. Prepare solution: prepare 2 mol / L cobalt chloride solution, 8 mol / L sodium hydroxide solution and 16 g / L sodium citrate in a volume ratio of 1:1 as a precipitant solution.

[0076] S2. Synthesis of Nano-Cobalt Hydroxide: The reactor was filled with pure water as the bottom liquid, with the volume of the bottom liquid accounting for 30% of the total volume of the reactor. Nitrogen was introduced for 40 minutes, and the reactor was heated. The synthesis temperature was set to 30° C., the stirring speed was 450 rpm, and a cobalt salt solution and a precipitant solution were added in parallel, wherein the hourly flow rate of the cobalt salt was 38% of the volume of the reactor. The flow rate of the precipitant solution was adjusted to control the pH value of the reaction system to be constant at 13.3. After reacting for 1 hour, the liquid addition was stopped to obtain a nano-cobalt hydroxide slurry.

[0077] S3. Washing, drying, and crushing the nano-cobalt hydroxide slurry: The prepared slurry was pumped into a filter press, washed five times with 80°C hot pure water, dried in a vacuum oven at 90°C for 10 hours, and crushed by a jet mill to obtain a finished nano-cobalt hydroxide product with an average particle size of 165 nm. As can be seen from the SEM images provided in Figures 1 and 2, the nano-cobalt hydroxide has a small particle size and good dispersibility.

[0078] Example 2

[0079] This embodiment provides a nano-cobalt hydroxide, the preparation method of which comprises the following steps:

[0080] S1. Prepare solution: prepare 1.5 mol / L cobalt sulfate solution, 8 mol / L potassium hydroxide solution and 16 g / L potassium citrate in a volume ratio of 1:1 as a precipitant solution.

[0081] S2. Synthesis of Nano-Cobalt Hydroxide: The reactor was filled with pure water as the bottom liquid, with the volume of the bottom liquid accounting for 40% of the total volume of the reactor. Nitrogen was introduced for 30 minutes, and the reactor was heated. The synthesis temperature was set to 32° C., the stirring speed was 300 rpm, and a cobalt salt solution and a precipitant solution were added in parallel, wherein the hourly flow rate of the cobalt salt was 30% of the volume of the reactor. The flow rate of the precipitant solution was adjusted to control the pH value of the reaction system to be constant at 13.5. After the reaction was completed for 1.5 hours, the liquid addition was stopped to obtain a nano-cobalt hydroxide slurry.

[0082] S3. Washing, drying, and crushing the nano-cobalt hydroxide slurry: The prepared slurry was pumped into a filter press, washed five times with 70°C hot pure water, dried in a vacuum oven at 80°C for 10 hours, and crushed by a jet mill to obtain a finished nano-cobalt hydroxide product with an average particle size of 141 nm. As can be seen from the SEM image provided in Figure 3, the nano-cobalt hydroxide has a small particle size and good dispersibility.

[0083] Example 3

[0084] This embodiment provides a nano-cobalt hydroxide, the preparation method of which comprises the following steps:

[0085] S1. Prepare solution: prepare 2.5 mol / L cobalt nitrate solution, 8 mol / L sodium hydroxide solution and 16 g / L sodium tartrate in a volume ratio of 1:1 as a precipitant solution.

[0086] S2. Synthesis of Nano-Cobalt Hydroxide: The reactor was filled with pure water as the bottom liquid, with the volume of the bottom liquid accounting for 45% of the total volume of the reactor. Nitrogen was introduced for 60 minutes, and the reactor was heated. The synthesis temperature was set to 35° C., the stirring speed was 500 rpm, and a cobalt salt solution and a precipitant solution were added in parallel, wherein the hourly flow rate of the cobalt salt was 40% of the volume of the reactor. The flow rate of the precipitant solution was adjusted to control the pH value of the reaction system to be constant at 13. After reacting for 0.5 hours, the liquid addition was stopped to obtain a nano-cobalt hydroxide slurry.

[0087] S3. Washing, drying, and crushing the nano-cobalt hydroxide slurry: The prepared slurry was pumped into a filter press, washed three times with 80°C hot pure water, dried in a vacuum oven at 85°C for 6 hours, and crushed by a jet mill to obtain a finished nano-cobalt hydroxide product with an average particle size of 158 nm. As can be seen from the SEM image provided in Figure 4, the nano-cobalt hydroxide has a small particle size and good dispersibility.

[0088] Example 4

[0089] This embodiment provides a nano-cobalt hydroxide, the preparation method of which comprises the following steps:

[0090] S1. Prepare solution: prepare 2.5 mol / L cobalt chloride solution and 2.5 mol / L cobalt nitrate solution in a volume ratio of 1:1 as a cobalt salt solution, and mix 8 mol / L sodium hydroxide solution, 8 mol / L potassium hydroxide, 16 g / L sodium citrate and 16 g / L sodium glycinate in a volume ratio of 1:1:1:1 as a precipitant solution.

[0091] S2. Synthesis of Nano-Cobalt Hydroxide: The reactor was filled with pure water as the bottom liquid, with the volume of the bottom liquid accounting for 30% of the total volume of the reactor. Nitrogen was introduced for 40 minutes, and the reactor was heated. The synthesis temperature was set to 30° C., the stirring speed was 450 rpm, and a cobalt salt solution and a precipitant solution were added in parallel, wherein the hourly flow rate of the cobalt salt was 38% of the volume of the reactor. The flow rate of the precipitant solution was adjusted to control the pH value of the reaction system to be constant at 13.3. After reacting for 1 hour, the liquid addition was stopped to obtain a nano-cobalt hydroxide slurry.

[0092] S3. Washing, drying, and crushing the nano-cobalt hydroxide slurry: The prepared slurry was pumped into a filter press, washed five times with 80°C hot pure water, dried in a vacuum oven at 90°C for 10 hours, and crushed by a jet mill to obtain a finished nano-cobalt hydroxide product with an average particle size of 124 μm. As can be seen from the SEM image provided in Figure 5, the nano-cobalt hydroxide has a small particle size and good dispersibility.

[0093] Comparative Example 1

[0094] This comparative example is substantially the same as Example 1, except that the sodium citrate in Example 1 is omitted and only 8 mol / L potassium hydroxide solution is used as the precipitant solution.

[0095] After testing, the size of the obtained nano-cobalt hydroxide was 451 nm. Referring to the SEM image provided in FIG6 , it can be seen that the particle size of the nano-cobalt hydroxide was relatively large, the dispersion was poor, and there was agglomeration.

[0096] Comparative Example 2

[0097] This comparative example is substantially the same as Example 1, except that, in this comparative example, 8 mol / L sodium hydroxide solution and 20 g / L sodium citrate were mixed at a volume ratio of 1:1 as the precipitant solution. At this time, the mass ratio of the solute to the deflocculant in the liquid caustic soda was 1:0.0625.

[0098] After testing, the size of the obtained nano-cobalt hydroxide was 223 nm. Referring to the SEM image provided in FIG7 , it can be seen that the particle size of the nano-cobalt hydroxide was smaller and the dispersibility was better, but slightly worse than that of Example 1.

[0099] Comparative Example 3

[0100] This comparative example is basically the same as Example 1, except that, in this comparative example, 8 mol / L sodium hydroxide solution and 4 g / L sodium citrate were mixed in a volume ratio of 1:1 as the precipitant solution. At this time, the mass ratio of the solute to the deflocculant in the liquid caustic soda was 1:0.0125.

[0101] After testing, the size of the obtained nano-cobalt hydroxide was 241 nm. Referring to the SEM image provided in FIG8 , it can be seen that the particle size of the nano-cobalt hydroxide was relatively large, the dispersion was poor, and there was agglomeration.

[0102] Comparative Example 4

[0103] This comparative example is substantially the same as Example 1, except that the sodium citrate in Example 1 is replaced by the antioxidant hydrazine hydrate.

[0104] After testing, the size of the obtained nano-cobalt hydroxide was 385 nm. Referring to the SEM image provided in FIG9 , it can be seen that the particle size of the nano-cobalt hydroxide was relatively large, the dispersion was poor, and there was agglomeration.

[0105] Comparative Example 5

[0106] This comparative example is basically the same as Example 1, except that the pH of the reaction system in this comparative example is controlled to be 12.5.

[0107] After testing, the size of the obtained nano-cobalt hydroxide was 1021 nm. Referring to the SEM image provided in FIG10 , it can be seen that the particle size of the nano-cobalt hydroxide was significantly increased, the dispersion was poor, and there was obvious agglomeration.

[0108] Comparative Example 6

[0109] This comparative example is basically the same as Example 1, except that the synthesis temperature in this comparative example is controlled to be 45°C.

[0110] After testing, the size of the obtained nano-cobalt hydroxide was 271 nm. Referring to the SEM image provided in FIG11 , it can be seen that the particle size of the nano-cobalt hydroxide was relatively large, the dispersion was poor, and there was agglomeration.

[0111] Comparative Example 7

[0112] This comparative example is substantially the same as Example 1, except that the hourly flow rate of the cobalt salt in this comparative example is 20% of the volume of the reactor.

[0113] After testing, the size of the obtained nano-cobalt hydroxide was 257 nm. Referring to the SEM image provided in FIG12 , it can be seen that the particle size of the nano-cobalt hydroxide was relatively large, the dispersion was poor, and there was agglomeration.

[0114] Experimental example

[0115] The nanometer cobalt hydroxide obtained in the above examples and comparative examples is coated on the high nickel positive electrode material Ni 0.8 Co 0.1 Mn 0.1 The surface of the O2 is coated with a coating layer, and the specific method is as follows: the nano-cobalt hydroxide prepared in the experimental example is uniformly mixed with the positive electrode material according to a mass ratio of 0.01, and then sintered at a high temperature of 650 ° C to obtain Ni coated with cobalt hydroxide nanosheets. 0.8 Co 0.1 Mn 0.1 A button-type battery was assembled using O2 as the positive electrode material, a lithium sheet as the negative electrode material, and LiPF6 as the electrolyte. The charge-discharge cycle voltage ranged from 3.0 to 4.35V. The first-cycle charge-discharge capacity was tested at a current density of 0.1C, and the capacity retention was tested at a current density of 1C. The corresponding charge-discharge capacity, first-cycle efficiency, and capacity retention after 100 cycles were then tested.

[0116] The test results show that the size of the nano-cobalt hydroxide prepared in Examples 1-4 provided by the present disclosure is much smaller than that of the nano-cobalt hydroxide prepared in Comparative Examples 1-7, and the smaller the size of the nano-cobalt hydroxide, the better the electrochemical performance of the positive electrode material after coating. It can be seen that the charge and discharge capacity, first-cycle efficiency and capacity retention rate after 100 cycles of Examples 1-4 are significantly better than those of Comparative Examples 1-7.

[0117] Specifically, the sodium citrate in Example 1 was omitted in Comparative Example 1, resulting in an increase in the amount of liquid alkali when adjusting the pH in Comparative Example 1, causing the intermolecular interaction force to become very strong, the viscosity to increase, the reaction system to exhibit colloidal properties, the slurry fluidity to deteriorate, and the local stirring intensity within the slurry to weaken, which is not conducive to the dispersion of nano-cobalt hydroxide. As a result, the size of the nano-cobalt hydroxide obtained in Comparative Example 1 (451 nm) is much larger than the size of the nano-cobalt hydroxide in Example 1 (165 nm), and its charge and discharge capacity, first-week efficiency, and capacity retention rate after 100 weeks are significantly worse than those in Example 1.

[0118] In Comparative Example 2, the amount of sodium citrate used was higher than the range disclosed herein, and its size was slightly larger than that in Example 1. The charge / discharge capacity, first-cycle efficiency, and capacity retention after 100 cycles were also slightly worse than those in Example 1. However, the increased amount of sodium citrate used resulted in the introduction of excessive organic impurities during synthesis, leading to increased wastewater treatment costs.

[0119] The amount of sodium citrate used in Comparative Example 3 is lower than the range disclosed herein. In this case, the effect is poor due to the same reasons as in Comparative Example 1, but it is significantly better than Comparative Example 1.

[0120] In Comparative Example 4, sodium citrate was replaced by the antioxidant hydrazine hydrate. However, since hydrazine hydrate could not play a deflocculation role, the effect of Comparative Example 4 was significantly worse than that of Example 1.

[0121] The pH of the reaction system in Comparative Example 5 is significantly lower than that in Example 1. At this time, the supersaturation of the precipitation system is lower than that in Example 1, and the crystals cannot nucleate quickly, resulting in a larger grain size, which is significantly larger than the size of other comparative examples. This fully demonstrates the importance of the pH of the reaction system.

[0122] In Comparative Example 6, the synthesis temperature was increased. At this time, the Brownian motion between the particles intensified, resulting in particle agglomeration, the particle size of the nano-cobalt hydroxide increased, and the charge and discharge capacity, first-cycle efficiency, and capacity retention rate after 100 cycles were significantly lower than those in Example 1.

[0123] In Comparative Example 7, the hourly flow rate of the cobalt salt solution was reduced, resulting in a decrease in the feed amount per unit time, an extension of the reaction time, and a decrease in the amount of crystal nuclei produced in the initial stage of the reaction. In the subsequent reaction process, the particles gradually agglomerated and grew, thereby increasing the particle size of the cobalt hydroxide. The charge and discharge capacity, first-week efficiency, and capacity retention rate after 100 weeks were significantly lower than those in Example 1.

[0124] Furthermore, it can be seen from Figures 13 and 14 that the nano-cobalt hydroxide prepared in Example 1 is smaller in size, and the surface of the positive electrode material after coating presents a uniform dot-shaped coating, while the nano-cobalt hydroxide prepared in Comparative Example 1 is larger in size, and the surface of the positive electrode material after coating has obvious enrichment of the coating, which proves that the coating effect and dispersion effect of the nano-cobalt hydroxide provided in Example 1 are better.

[0125] In summary, the method for preparing nano-cobalt hydroxide provided by the present disclosure utilizes a precipitant that uses a mixture of liquid caustic soda and a deflocculant in a specific ratio. The deflocculant in the precipitant can form an electrical double layer on the surface of the nano-cobalt hydroxide. This, through Coulomb repulsion, significantly reduces the attractive force that causes nanoparticles to agglomerate, thereby improving dispersibility. Furthermore, this type of deflocculant has an antioxidant effect, absorbing oxygen molecules within the system and preventing oxidation of the nano-cobalt hydroxide, which could affect product quality. The advantage of mixing a deflocculant with liquid caustic soda is that as the amount of liquid caustic soda increases during the reaction, the viscosity and oxygen content of the slurry in the system also increase. The addition of a deflocculating agent also increases proportionally, offsetting the negative effects of the increased amount of liquid caustic soda. This negative effect is that an increase in pH leads to stronger intermolecular interactions in the reaction system, resulting in increased viscosity and colloidal properties. This reduces the fluidity of the slurry within the reactor and weakens the local stirring intensity within the slurry, hindering the dispersion of the nano-cobalt hydroxide. The present disclosure utilizes a deflocculating agent to maintain good dispersion even at a pH of 13 to 13.5. On the other hand, the preparation method of nano cobalt hydroxide provided by the present disclosure controls the synthesis temperature to 30-35°C during the synthesis reaction stage. Reacting at a lower temperature can avoid the intensification of Brownian motion between particles leading to particle agglomeration, which is conducive to the synthesis of ultrafine nano cobalt hydroxide and saves energy. Liquid alkali combines the above two aspects, and the preparation method of nano cobalt hydroxide provided by the present disclosure can enable rapid nucleation of crystals, small grain size, and not easy to agglomerate, with good dispersibility. The above-mentioned nano cobalt hydroxide can be widely used in the preparation of positive electrode materials, and can achieve good coating of the positive electrode surface to eliminate residual lithium, and the obtained coating layer is thin and uniform. The lithium ion battery prepared from the above-mentioned positive electrode material has excellent performance.

[0126] The above describes in detail the optional embodiments of the present disclosure, but the present disclosure is not limited thereto. Within the technical concept of the present disclosure, various simple variations of the technical solution of the present disclosure can be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as the contents disclosed by the present disclosure and fall within the scope of protection of the present disclosure. Industrial Applicability

[0127] The present invention provides a method for preparing nano-cobalt hydroxide. Liquid caustic soda and a deflocculant are mixed in a specific ratio as a precipitant. The deflocculant in the precipitant forms a double electrical layer on the surface of the nano-cobalt hydroxide. This, through Coulomb repulsion, significantly reduces the attractive force that causes nanoparticles to agglomerate, thereby improving dispersibility. Furthermore, this type of deflocculant has an antioxidant effect, absorbing oxygen molecules within the system to prevent oxidation of the nano-cobalt hydroxide, which could affect product quality. The advantage of mixing a deflocculant with liquid caustic soda is that as the amount of liquid caustic soda increases during the reaction, the viscosity and oxygen content of the slurry in the system also increase. The addition of a deflocculant also increases proportionally, offsetting the negative effects of increased liquid caustic soda. This negative effect is that an increase in pH leads to stronger intermolecular interactions in the reaction system, resulting in increased viscosity and colloidal properties. This reduces the fluidity of the slurry within the reactor and weakens the local stirring intensity within the slurry, hindering the dispersion of the nano-cobalt hydroxide. The present invention utilizes a deflocculant to maintain good dispersion even at a pH of 13 to 13.5. On the other hand, the preparation method of nano cobalt hydroxide provided by the present disclosure controls the synthesis temperature to 30-35°C during the synthesis reaction stage. Reacting at a lower temperature can avoid the intensification of Brownian motion between particles leading to particle agglomeration, which is conducive to the synthesis of ultrafine nano cobalt hydroxide and saves energy. Liquid alkali combines the above two aspects, and the preparation method of nano cobalt hydroxide provided by the present disclosure can enable rapid nucleation of crystals, small grain size, and not easy to agglomerate, with good dispersibility. The above-mentioned nano cobalt hydroxide can be widely used in the preparation of positive electrode materials, and can achieve good coating of the positive electrode surface to eliminate residual lithium, and the obtained coating layer is thin and uniform. The lithium ion battery prepared from the above-mentioned positive electrode material has excellent performance.

Claims

1. A method for preparing nano cobalt hydroxide, characterized in that: It includes: The cobalt salt solution and the precipitant solution are reacted at 30-35° C. During the reaction, the amount of the precipitant solution added is adjusted to control the pH of the reaction system to be 13-13.

5. After the reaction is completed, nano cobalt hydroxide slurry is obtained. The precipitant solution includes liquid alkali and a deflocculating agent. The mass ratio of the solute in the liquid alkali to the deflocculating agent is 1:0.02-0.

05.

2. The method for preparing nano cobalt hydroxide according to claim 1, wherein The deflocculating agent includes one or more of sodium citrate, potassium citrate, potassium tartrate, sodium tartrate and sodium glycinate.

3. The method for preparing nano-cobalt hydroxide according to any one of claims 1 to 2, characterized in that: The cobalt salt solution and the precipitant solution react in a reaction kettle filled with bottom water.

4. The method for preparing nano cobalt hydroxide according to claim 3, wherein The volume of the kettle bottom water accounts for 30% to 45% of the total volume of the reactor.

5. The method for preparing nano-cobalt hydroxide according to any one of claims 3 to 4, characterized in that: The amount of the cobalt salt solution added per hour is 30% to 40% of the total volume of the reactor.

6. The method for preparing nano-cobalt hydroxide according to any one of claims 3 to 5, characterized in that: The cobalt salt solution and the precipitant solution are added to the reactor in parallel.

7. The method for preparing nano cobalt hydroxide according to claim 6, wherein The cobalt salt solution and the precipitant solution are added in parallel for a time period of 0.5 h to 1.5 h.

8. The method for preparing nano-cobalt hydroxide according to any one of claims 3 to 7, characterized in that: During the reaction process, the stirring speed in the reactor is 300 rpm to 500 rpm.

9. The method for preparing nano-cobalt hydroxide according to any one of claims 3 to 8, characterized in that: Before adding the cobalt salt solution and the precipitant solution, the method further comprises introducing nitrogen into the reactor to replace the air in the reactor, and continuously introducing the nitrogen during the reaction process.

10. The method for preparing nano-cobalt hydroxide according to claim 9, characterized in that: The nitrogen gas used to replace the air in the reactor is introduced for 30 to 60 minutes.

11. The method for preparing nano-cobalt hydroxide according to any one of claims 1 to 10, characterized in that: The method for preparing the nano-cobalt hydroxide further comprises filtering, washing, drying and crushing the nano-cobalt hydroxide slurry.

12. The method for preparing nano-cobalt hydroxide according to claim 11, characterized in that: The washing comprises washing with 70-80° C. hot pure water for 3-5 times.

13. The method for preparing nano-cobalt hydroxide according to any one of claims 11-12, characterized in that: The drying comprises drying in a vacuum oven at 80-90° C. for 5-10 hours.

14. The method for preparing nano-cobalt hydroxide according to any one of claims 11 to 13, characterized in that: The pulverizing includes using a jet mill to pulverize the dried particles to a particle size of less than 200 nm.

15. The method for preparing nano-cobalt hydroxide according to any one of claims 1 to 14, characterized in that: The liquid alkali includes one or more of sodium hydroxide and potassium hydroxide.

16. The method for preparing nano-cobalt hydroxide according to any one of claims 1 to 15, characterized in that: The concentration of the liquid alkali is 5-10 mol / L.

17. The method for preparing nano-cobalt hydroxide according to any one of claims 1 to 16, characterized in that: The cobalt salt solution includes one or more of cobalt chloride, cobalt sulfate and cobalt nitrate.

18. The method for preparing nano-cobalt hydroxide according to any one of claims 1 to 17, characterized in that: The concentration of the cobalt salt solution is 1.5-2.5 mol / L.

19. A nano-cobalt hydroxide, characterized in that: The nano-cobalt hydroxide is prepared by the preparation method of the nano-cobalt hydroxide according to any one of claims 1 to 18.

20. Use of the nano cobalt hydroxide as claimed in claim 19 in preparing positive electrode materials.

21. A positive electrode material, characterized in that It comprises a positive electrode and the nano-cobalt hydroxide as claimed in claim 19, wherein the nano-cobalt hydroxide is coated on the surface of the positive electrode.

22. A lithium ion battery, characterized in that: It comprises the positive electrode material as claimed in claim 21.

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