Cobalt-bromine co-coated positive electrode material, and preparation method and use therefor

Abstract

Provided are a cobalt-bromine co-coated positive electrode material, and a preparation method and use therefor. Metal salt solutions with different concentration gradients are used, such that NFM ternary precursors with different ferronickel concentration gradient distributions in the radial direction can be prepared, and the content of the metal nickel is gradually reduced from inside to outside. Then, the surface of the ternary precursors is coated with cobalt ions and bromine ions by using an atomic layer deposition technique, so as to obtain a cobalt-bromine co-coated sodium ion battery positive electrode material having low cost, high rate and high stability.

Description

Cobalt-bromine co-coated positive electrode material and its preparation method and application Technical Field

[0001] The present application belongs to the technical field of sodium ion batteries and relates to a cobalt-bromine co-coated positive electrode material and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries and the preparation of their key materials have become a key focus of scientific, technological, and industrial development worldwide. However, the widespread application of lithium-ion batteries in energy storage is severely hampered by the limited global lithium reserves and the rising prices caused by their uneven distribution. Sodium and lithium share similar physicochemical properties and similar intercalation / exclusion mechanisms. In addition to their abundant availability, low cost, and widespread distribution, sodium-ion batteries offer safety advantages over lithium-ion batteries. They experience higher thermal runaway temperatures than lithium batteries and are more susceptible to passivation and oxidation, making them less susceptible to flammability—the primary drawback of lithium batteries. Therefore, the research and development of sodium-ion batteries has the potential to alleviate the limitations of energy storage battery development caused by lithium resource shortages. Among battery materials, the cathode material is the most critical component. However, cathode materials are prone to fracture during cycling and persistent side reactions with the electrolyte, severely compromising the battery's cycle life and rate capability. Surface coating can reduce stress, enhance liquid electrolyte wettability, lower interfacial charge transfer resistance, and mitigate side reactions, effectively optimizing the cathode material.

[0003] CN114242970A uses a coprecipitation method for bulk doping and surface coating to prepare a composite-coated precursor material containing two metal ions and two polyanions, effectively improving the capacity and cycling performance of the ternary material. CN115117325A uses a coprecipitation method to coat the surface of a ternary precursor with Co(OH)2. Subsequently, in an oxidizer, the β-Co(OH)2 coating on the surface of spherical nickel hydroxide is oxidized to highly conductive γ-CoOOH under the combined action of hot alkali and oxygen. CN115028215A uses a coprecipitation method and a wet coating process to prepare a bismuth-doped, cobalt-coated precursor material. CN115241422A uses solid-phase synthesis, sol-gel, and ball milling methods, respectively, to prepare a mixed sodium-ion battery cathode material consisting of iron-based phosphate and transition metal layered oxide. In the coating process of the above materials, doping coating, coating modification and other methods were adopted, but there was still uneven doping during the co-precipitation process, the product D50 was greater than 10μm, and small-particle products were difficult to mass-produce; the metal oxides, phosphates, and acetates coated on the surface would also partially leach into the electrolyte, resulting in poor rate performance of the material.

[0004] In view of this, the purpose of this application is to provide a sodium ion battery positive electrode material with better stability and rate performance.

[0005] Summary of the Invention

[0006] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0007] The purpose of the present application is to provide a cobalt-bromine co-coated positive electrode material and its preparation method and application. The present application pre-prepares a gradient-distributed NFM ternary precursor, and then uses atomic layer deposition technology to coat cobalt ions and bromide ions on the surface of the ternary precursor to obtain a cobalt-bromine co-coated positive electrode material for sodium ion batteries with low cost, high rate and high stability.

[0008] To achieve this goal, this application adopts the following technical solutions:

[0009] In a first aspect, the present application provides a method for preparing a cobalt-bromine co-coated positive electrode material, the preparation method comprising the following steps:

[0010] (1) nickel salt, iron salt and manganese salt are mixed in different molar ratios to prepare mixed salt solution A, mixed salt solution B and mixed salt solution C of different concentrations, mixed salt solution A, precipitant solution and complexing agent solution are injected into the bottom liquid in parallel, a one-step coprecipitation reaction is carried out, mixed salt solution A is switched to mixed salt solution B, a two-step coprecipitation reaction is carried out, mixed salt solution B is switched to mixed salt solution C, a three-step coprecipitation reaction is carried out to obtain a gradient nickel-iron-manganese precursor, wherein the nickel ion concentration in mixed salt solution A>the nickel ion concentration in mixed salt solution B>the nickel ion concentration in mixed salt solution C;

[0011] (2) coating Co ions and bromide ions on the surface of the gradient nickel-iron-manganese precursor by atomic layer deposition technology to obtain a modified precursor;

[0012] (3) The modified precursor is mixed with a sodium source, and subjected to sintering treatment to obtain the cobalt-bromine co-coated positive electrode material.

[0013] In the method described in the present application, the concentration of the nickel-manganese-iron mixed salt solution includes but is not limited to three, can be four, or can be a combination of five or more, but the feeding needs to be carried out according to the nickel concentration gradient.

[0014] This application uses metal salt solutions with different concentration gradients to prepare NFM ternary precursors with different nickel-iron concentration gradients in the radial direction, and the content of metallic nickel gradually decreases from the inside out. This can not only ensure the volume energy density of the cobalt-bromine co-coated positive electrode material, but also reduce the sodium-nickel mixing and reduce costs. Using atomic layer deposition technology, and using cobalt salts and bromides to effectively replace expensive cobalt bromide, the surface of the cobalt-bromine co-coated positive electrode material for sodium-ion batteries is coated with Co ions that increase the material rate and bromide ions that increase the material stability.

[0015] In one embodiment, the total concentration of nickel, iron and manganese in the mixed salt solution A, mixed salt solution B and mixed salt solution C in step (1) is independently 1 to 5 mol / L, for example: 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L or 5 mol / L.

[0016] In one embodiment, the precipitant solution comprises sodium hydroxide solution.

[0017] In one embodiment, the complexing agent solution comprises aqueous ammonia.

[0018] In one embodiment, the ammonia concentration in the base solution is 3 to 70 g / L, for example, 3 g / L, 10 g / L, 25 g / L, 56 g / L or 70 g / L.

[0019] In one embodiment, the pH of the base solution is 8.5 to 11.7, for example, 8.5, 9, 10, 11 or 11.7.

[0020] In one embodiment, the feed rates of the mixed salt solution A, mixed salt solution B and mixed salt solution C in step (1) are independently 2 to 50 L / h, for example, 2 g / L, 5 g / L, 10 g / L, 20 g / L or 50 g / L.

[0021] In one embodiment, the feed rate of the precipitant solution is 1 to 30 L / h, for example, 1 g / L, 5 g / L, 10 g / L, 20 g / L or 30 g / L.

[0022] In one embodiment, the feeding rate of the complexing agent solution is 0.5 to 15 L / h, for example, 0.5 g / L, 1 g / L, 5 g / L, 10 g / L or 15 g / L.

[0023] In one embodiment, the temperature of the one-step coprecipitation reaction, the two-step coprecipitation reaction and the three-step coprecipitation reaction in step (1) is independently 15-70°C, for example: 15°C, 20°C, 30°C, 50°C or 70°C.

[0024] In one embodiment, the pH of the one-step co-precipitation reaction, the two-step co-precipitation reaction, and the three-step co-precipitation reaction are independently 9 to 12, for example, 9, 9.5, 10, 11, or 12.

[0025] In one embodiment, the time for the one-step co-precipitation reaction, the two-step co-precipitation reaction and the three-step co-precipitation reaction is independently 2 to 48 hours, for example, 2 hours, 5 hours, 10 hours, 20 hours or 48 hours.

[0026] In one embodiment, the total molar ratio of the gradient nickel-iron-manganese precursor to the coated cobalt ions and bromide ions in step (2) is (95-99.7):(0.3-5), for example: 95:5, 96:4, 97:3, 98:2 or 99.7:0.3, etc.

[0027] In one embodiment, the molar ratio of the cobalt element to the bromine element is 1:(0.5-5), for example, 1:0.5, 1:1, 1:2, 1:4 or 1:5.

[0028] In one embodiment, the cobalt source includes any one or a combination of at least two of cobalt sulfate, cobalt chloride, or cobalt nitrate.

[0029] In one embodiment, the bromine source includes any one of bromine water, sodium bromide, manganese bromide, barium bromide, or magnesium bromide, or a combination of at least two thereof.

[0030] In one embodiment, the coating in step (2) is followed by aging, washing and drying.

[0031] In one embodiment, the sodium source in step (3) comprises sodium carbonate.

[0032] In one embodiment, the molar ratio of the sodium element in the sodium source to the metal element in the modified precursor is (1.02-1.2):1, for example: 1.02:1, 1.05:1, 1.1:1, 1.15:1 or 1.2:1, etc.

[0033] In one embodiment, the atmosphere of the sintering process includes oxygen.

[0034] In one embodiment, the sintering temperature is 400-1000°C, for example, 400°C, 500°C, 700°C, 900°C or 1000°C.

[0035] In one embodiment, the sintering treatment time is 4 to 30 hours, for example, 4 hours, 8 hours, 10 hours, 20 hours or 30 hours.

[0036] In a second aspect, the present application provides a cobalt-bromine co-coated positive electrode material, which is prepared by the method described in the first aspect.

[0037] In a third aspect, the present application provides a positive electrode plate, which comprises the cobalt-bromine co-coated positive electrode material as described in the second aspect.

[0038] In a fourth aspect, the present application provides a sodium ion battery, which comprises the positive electrode sheet as described in the third aspect.

[0039] Compared with the prior art, this application has the following beneficial effects:

[0040] (1) The cobalt-bromine co-coated positive electrode material for sodium ion batteries prepared in this application uses metal salt solutions with different concentration gradients to prepare an NFM ternary precursor with different nickel-iron concentration gradient distributions in the radial direction, and the content of metallic nickel gradually decreases from the inside to the outside, which can not only ensure the volume energy density of the cobalt-bromine co-coated positive electrode material, but also reduce the mixing of sodium and nickel and reduce costs.

[0041] (2) This application adopts atomic layer deposition technology, using cobalt salts and bromide for surface coating, replacing expensive cobalt bromide. Because of the use of atomic layer deposition technology, the thickness, quality, and ion deposition order of the coating layer can be effectively controlled. After coating, the cobalt-bromine co-coated positive electrode material can be prevented from contacting the electrolyte. The surface-coated cobalt ions can reduce the mixing of cations and thus improve the stability of the material. The cobalt ions with larger ionic radius increase the spacing between the Na layers and increase the transmission rate of sodium ions, thereby improving the rate performance of the material; bromide ions can form a CEI film on the electrode surface, alleviate surface side reactions, and adjust the ordered structure of the superlattice. At the same time, it can stabilize the framework structure of the anion and strengthen the stability of the Ni-O, Mn-O, and Fe-O bonds, thereby improving the stability of the material. Therefore, surface coating of Co and bromine by atomic layer deposition technology can not only improve the rate performance of the material, but also improve the stability of the material.

[0042] (3) Compared with existing similar products, the cobalt-bromine co-coated positive electrode material prepared in this application has higher capacity, better low-temperature performance, smaller self-discharge, and longer cycle life, and is fully capable of adapting to the capacity retention of batteries in low-temperature environments. Since the atomic layer deposition technology is based on surface self-limitation and self-saturation adsorption reactions, it has surface controllability. The prepared film has excellent three-dimensional conformality and large-area uniformity, which can ensure precise sub-monolayer film thickness control. Therefore, by controlling the production process during the coating of Co ions and bromide ions, especially by accurately controlling the time of the atomic layer deposition process, it is helpful to form a coating layer with controllable thickness and uniform surface coating, which can avoid contact with the electrolyte and achieve rapid diffusion of sodium ions and electronic conduction, meeting the use requirements of high-rate, high-cycle, and high-stability power batteries.

[0043] (4) The first discharge specific capacity of the battery made of the cobalt-bromine co-coated positive electrode material described in the present application can reach more than 160.6 mAh / g, the 1C rate can reach more than 156.1 mAh / g, the capacity retention rate after 300 cycles can reach more than 93.1%, the 5C rate can reach more than 134.2 mAh / g, and the capacity retention rate after 300 cycles can reach more than 90.4%. In the preparation process of the cobalt-bromine co-coated positive electrode material described in the present application, by coating its surface with Co and bromide ions, not only the rate performance of the material is effectively increased, but also it has a good capacity retention rate after 300 cycles.

[0044] Still other aspects will become apparent upon reading and understanding the detailed description. DETAILED DESCRIPTION

[0045] The technical solution of the present application is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations of the present application.

[0046] Example 1

[0047] This embodiment provides a cobalt-bromine co-coated positive electrode material, and the preparation method of the cobalt-bromine co-coated positive electrode material is as follows:

[0048] (1) Nickel, iron, and manganese sulfate solutions were mixed in different molar ratios to obtain a total metal ion concentration of 2 mol / L, wherein the molar ratio of nickel, iron, and manganese in mixed salt solution A was 0.34:0.33:0.33, the molar ratio of nickel, iron, and manganese in mixed salt solution B was 0.29:0.38:0.33, and the molar ratio of nickel, iron, and manganese in mixed salt solution C was 0.24:0.43:0.33. The mixed metal salt solution A, 10 mol / L sodium hydroxide solution, and 7.5 mol / L ammonia water were added together to a base solution having a pH of 11.8 and an ammonia concentration of 25 g / L. During this process, the feed rate of the mixed metal salt solution A is controlled to be 15 L / h, the pH value of the reaction system is controlled to be between 11.0 and 11.5, and the ammonia concentration is controlled to be between 8.5 and 40 g / L by controlling the flow rate of the sodium hydroxide solution and the ammonia water, the coprecipitation reaction is carried out at a reaction temperature of 62° C., after reacting for 10 hours, the mixed metal salt solution A is replaced with the mixed metal salt solution B, and after reacting for another 34 hours, the mixed metal salt solution B is replaced with the mixed metal salt solution C, the reaction shutdown particle size is 6.0 μm, and a gradient nickel-iron-manganese precursor with different nickel-iron concentration gradient distributions is obtained;

[0049] (2) using atomic layer deposition technology to coat the surface of a gradient nickel-iron-manganese precursor, using cobalt sulfate as a cobalt source and sodium bromide as a bromine source, the prepared gradient nickel-iron-manganese precursor, cobalt sulfate, and sodium bromide are subjected to atomic layer deposition in a molar ratio of 98:1:1, and a layer of cobalt sulfate and sodium bromide are successively coated on the prepared gradient nickel-iron-manganese precursor, aged to remove sulfate and impurity elements, centrifuged and washed, and then dried at 150° C. to obtain a modified precursor;

[0050] (3) Sodium carbonate and the modified precursor were mixed evenly in a molar ratio of Na / M=1.08, calcined at 800° C. for 17 h, and ground and sieved to obtain the cobalt-bromine co-coated positive electrode material.

[0051] Example 2

[0052] This embodiment provides a cobalt-bromine co-coated positive electrode material, and the preparation method of the cobalt-bromine co-coated positive electrode material is as follows:

[0053] (1) Nickel, iron, and manganese sulfate solutions were mixed in different molar ratios to obtain a total metal ion concentration of 5 mol / L, wherein the molar ratio of nickel, iron, and manganese in mixed salt solution A was 0.34:0.33:0.33, the molar ratio of nickel, iron, and manganese in mixed salt solution B was 0.25:0.42:0.33, and the molar ratio of nickel, iron, and manganese in mixed salt solution C was 0.20:0.47:0.33. The mixed metal salt solution A, 8.5 mol / L sodium hydroxide solution, and 6 mol / L ammonia water were added together to a base solution having a pH of 11 and an ammonia concentration of 60 g / L. During this process, the feed rate of the mixed metal salt solution A is controlled to be 12 L / h, the pH value of the reaction system is controlled to be between 11.0 and 11.5, and the ammonia concentration is controlled to be between 17 and 70 g / L by controlling the flow rate of the sodium hydroxide solution and the ammonia water, the coprecipitation reaction is carried out at a reaction temperature of 52° C., after reacting for 8 hours, the mixed metal salt solution A is replaced with the mixed metal salt solution B, and after reacting for another 24 hours, the mixed metal salt solution B is replaced with the mixed metal salt solution C, the reaction shutdown particle size is 6.2 μm, and a gradient nickel-iron-manganese precursor with different nickel-iron concentration gradient distributions is obtained;

[0054] (2) using atomic layer deposition technology to coat the surface of a gradient nickel-iron-manganese precursor, using cobalt sulfate as a cobalt source and sodium bromide as a bromine source, the prepared gradient nickel-iron-manganese precursor, cobalt sulfate, and sodium bromide are subjected to atomic layer deposition in a molar ratio of 95:1:4, and a layer of cobalt sulfate and sodium bromide are successively coated on the prepared gradient nickel-iron-manganese precursor, aged to remove sulfate and impurity elements, centrifuged and washed, and then dried at 150° C. to obtain a modified precursor;

[0055] (3) Sodium carbonate and the modified precursor are uniformly mixed in a molar ratio of Na / M=1.05, calcined at 600° C. for 15 h, and ground and sieved to obtain the cobalt-bromine co-coated positive electrode material.

[0056] Example 3

[0057] This embodiment provides a cobalt-bromine co-coated positive electrode material, and the preparation method of the cobalt-bromine co-coated positive electrode material is as follows:

[0058] (1) Nickel, iron, and manganese sulfate solutions were mixed in different molar ratios to obtain a total metal ion concentration of 1 mol / L, wherein the molar ratio of nickel, iron, and manganese in mixed salt solution A was 0.34:0.33:0.33, the molar ratio of nickel, iron, and manganese in mixed salt solution B was 0.21:0.45:0.34, and the molar ratio of nickel, iron, and manganese in mixed salt solution C was 0.18:0.52:0.3. Mixed metal salt solution A, 8 mol / L sodium hydroxide solution, and 5 mol / L ammonia water were added together to a base solution having a pH of 9 and an ammonia concentration of 15 g / L. During this process, the feed rate of the mixed metal salt solution A is controlled to be 12 L / h, the pH value of the reaction system is controlled to be between 11.0 and 11.5, and the ammonia concentration is controlled to be between 10 and 30 g / L by controlling the flow rate of the sodium hydroxide solution and the ammonia water, the coprecipitation reaction is carried out at a reaction temperature of 42° C., after reacting for 20 hours, the mixed metal salt solution A is replaced with the mixed metal salt solution B, and after reacting for another 48 hours, the mixed metal salt solution B is replaced with the mixed metal salt solution C, the reaction shutdown particle size is 6.4 μm, and a gradient nickel-iron-manganese precursor with different nickel-iron concentration gradient distributions is obtained;

[0059] (2) using atomic layer deposition technology to coat the surface of a gradient nickel-iron-manganese precursor, using cobalt sulfate as a cobalt source and sodium bromide as a bromine source, the prepared gradient nickel-iron-manganese precursor, cobalt sulfate, and sodium bromide are subjected to atomic layer deposition in a molar ratio of 98.5:1:0.5, and a layer of cobalt sulfate and sodium bromide are successively coated on the prepared gradient nickel-iron-manganese precursor, aged to remove sulfate and impurity elements, centrifuged and washed, and then dried at 150° C. to obtain a modified precursor;

[0060] (3) Sodium carbonate and the modified precursor are uniformly mixed in a molar ratio of Na / M=1.1, calcined at 800° C. for 10 h, and ground and sieved to obtain the cobalt-bromine co-coated positive electrode material.

[0061] Example 4

[0062] The only difference between this embodiment and embodiment 1 is that the molar ratio of cobalt sulfate to sodium bromide during surface coating is 1:0.2, and other conditions and parameters are exactly the same as those in embodiment 1.

[0063] Example 5

[0064] The only difference between this embodiment and embodiment 1 is that the molar ratio of cobalt sulfate to sodium bromide during surface coating is 1:8, and other conditions and parameters are exactly the same as those in embodiment 1.

[0065] Example 6

[0066] The only difference between this embodiment and embodiment 1 is that the gradient nickel-iron-manganese precursor, cobalt sulfate, and sodium bromide are atomic layer deposited in a molar ratio of 94:3:3, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0067] Example 7

[0068] The only difference between this embodiment and embodiment 1 is that the gradient nickel-iron-manganese precursor, cobalt sulfate, and sodium bromide are atomic layer deposited in a molar ratio of 99.9:0.05:0.05, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0069] Comparative Example 1

[0070] The only difference between this comparative example and Example 1 is that the metal salt solution mixed in step (1) is only proportioned according to the nickel-iron-manganese molar ratio of 0.34:0.33:0.33, and the other conditions and parameters are exactly the same as those in Example 1.

[0071] Comparative Example 2

[0072] The only difference between this comparative example and Example 1 is that step (2) atomic layer deposition is not performed, and other conditions and parameters are exactly the same as those in Example 1.

[0073] Comparative Example 3

[0074] The only difference between this comparative example and Example 1 is that cobalt bromide is directly used for coating in step (2), and the other conditions and parameters are exactly the same as those in Example 1.

[0075] Performance testing:

[0076] At 25°C, the cobalt-bromine co-coated positive electrode materials prepared in the above examples and comparative examples were used as the positive electrode main material, and the metal sodium sheet was used as the negative electrode to assemble CR2032 button batteries. Then, charge and discharge tests were performed in the voltage range of 1.0 to 4.5 V. The test results are shown in Table 1:

[0077] Table 1

[0078] As can be seen from Table 1, it can be obtained from Examples 1-3 that the first discharge specific capacity of the battery made of the cobalt-bromine co-coated positive electrode material described in the present application can reach more than 160.6 mAh / g, the 1C rate can reach more than 156.1 mAh / g, and the capacity retention rate after 300 cycles can reach more than 93.1%, the 5C rate can reach more than 134.2 mAh / g, and the capacity retention rate after 300 cycles can reach more than 90.4%. In the preparation process of the cobalt-bromine co-coated positive electrode material described in the present application, by coating its surface with Co and bromide ions, not only the rate performance of the material is effectively increased, but also it has a good capacity retention rate after 300 cycles.

[0079] By comparison of Example 1 and Example 4-5, it can be seen that in the preparation process of the cobalt-bromine co-coated positive electrode material described in the present application, the molar ratio of the cobalt source and the bromine source will affect its performance. The molar ratio of the cobalt source and the bromine source is controlled at 1:0.5~5, and the cobalt-bromine co-coated positive electrode material has better performance. If the proportion of cobalt ions in the coating layer is too high, it is easy to cause the modified cobalt-bromine co-coated positive electrode material to have fewer active anions, and the CEI film cannot be formed on the electrode surface, making it difficult to achieve the purpose of alleviating surface side reactions and adjusting the ordered structure of the superlattice. At the same time, the framework structure of the anion will also become unstable, which not only increases the preparation cost, but also does not improve the rate performance of the material; if the proportion of bromide ions in the coating layer is too high, the structural stability of the prepared cobalt-bromine co-coated positive electrode material is low, resulting in the collapse of the layered structure during the cycle, and the transition metal ions irreversibly migrate to the sodium layer, causing cation mixing.

[0080] By comparison of Example 1 and Examples 6-7, it can be seen that in the preparation process of the cobalt-bromine co-coated positive electrode material described in the present application, the total molar ratio of the gradient nickel-iron-manganese precursor to the cobalt source and the bromine source will affect its performance. The total molar ratio of the gradient nickel-iron-manganese precursor to the cobalt source and the bromine source is controlled at (95-99.7): (0.3-5), and the cobalt-bromine co-coated positive electrode material obtained has better performance. If the cobalt source and the bromine source are over-dosed too much during surface coating, the thickness of the coating layer will increase, which will not only fail to quickly achieve the diffusion of sodium ions, but also reduce the conductivity of electrons; if the cobalt source and the bromine source are over-dosed too little, it will not be able to protect the cobalt-bromine co-coated positive electrode material and prevent it from contacting the electrolyte, nor can it improve the cycle performance, rate performance and stability of the cobalt-bromine co-coated positive electrode material.

[0081] By comparing Example 1 and Comparative Example 1, it can be seen that the present application uses metal salt solutions with different concentration gradients to prepare NFM ternary precursors with different nickel-iron concentration gradient distributions in the radial direction, and the content of metallic nickel gradually decreases from the inside to the outside, which can not only ensure the volume energy density of the cobalt-bromine co-coated positive electrode material, but also reduce the sodium-nickel mixing and reduce costs.

[0082] By comparing Example 1 with Comparative Examples 2-3, it can be seen that the present application adopts atomic layer deposition technology and uses cobalt salts and bromides to effectively replace expensive cobalt bromide to prepare a cobalt-bromine co-coated positive electrode material for a sodium ion battery. The surface of the cobalt-bromine co-coated positive electrode material is coated with Co ions that increase the material rate and bromide ions that increase the material stability.

[0083] The applicant declares that the above is only a specific implementation method of the present application, but the protection scope of the present application is not limited thereto. Technical personnel in the relevant technical field should understand that any changes or replacements that can be easily thought of by technical personnel in the relevant technical field within the technical scope disclosed in this application fall within the protection scope and disclosure scope of this application.

Claims

1. A method for preparing a cobalt-bromine co-coated positive electrode material, The following steps are involved: (1) mixing a nickel salt, an iron salt and a manganese salt in different molar ratios to prepare a mixed salt solution A, a mixed salt solution B and a mixed salt solution C of different concentrations, injecting the mixed salt solution A, a precipitant solution and a complexing agent solution into a base solution in parallel, performing a one-step coprecipitation reaction, switching the mixed salt solution A to the mixed salt solution B, performing a two-step coprecipitation reaction, switching the mixed salt solution B to the mixed salt solution C, performing a three-step coprecipitation reaction, and obtaining a gradient nickel-iron-manganese precursor, wherein the nickel ion concentration in the mixed salt solution A>the nickel ion concentration in the mixed salt solution B>the nickel ion concentration in the mixed salt solution C; (2) coating Co ions and bromide ions on the surface of the gradient nickel-iron-manganese precursor by atomic layer deposition technology to obtain a modified precursor; (3) The modified precursor is mixed with a sodium source, and subjected to sintering treatment to obtain the cobalt-bromine co-coated positive electrode material.

2. The preparation method according to claim 1, in, The total concentration of nickel, iron and manganese in the mixed salt solution A, mixed salt solution B and mixed salt solution C in step (1) is independently 1 to 5 mol / L; Optionally, the precipitant solution comprises a sodium hydroxide solution; Optionally, the complexing agent solution includes aqueous ammonia; Optionally, the ammonia concentration in the base solution is 3 to 70 g / L; Optionally, the pH of the base solution is 8.5-11.

7.

3. The preparation method according to claim 1 or 2, in, In step (1), the feed rates of the mixed salt solution A, the mixed salt solution B and the mixed salt solution C are independently 2 to 50 L / h; Optionally, the feed rate of the precipitant solution is 1 to 30 L / h; Optionally, the feeding rate of the complexing agent solution is 0.5 to 15 L / h.

4. The preparation method according to any one of claims 1 to 3, in, The temperature of the one-step coprecipitation reaction, the two-step coprecipitation reaction and the three-step coprecipitation reaction in step (1) is independently 15 to 70° C.; Optionally, the pH of the one-step coprecipitation reaction, the two-step coprecipitation reaction and the three-step coprecipitation reaction are independently 9 to 12; Optionally, the time for the one-step co-precipitation reaction, the two-step co-precipitation reaction and the three-step co-precipitation reaction is independently 2 to 48 hours.

5. The preparation method according to any one of claims 1 to 4, in, The total molar ratio of the gradient nickel-iron-manganese precursor to the coated Co ions and bromide ions in step (2) is (95-99.7):(0.3-5); Optionally, the molar ratio of the Co ions to the bromide ions is 1:(0.5-5); Optionally, the cobalt source includes any one or a combination of at least two of cobalt sulfate, cobalt chloride or cobalt nitrate; Optionally, the bromine source includes any one of bromine water, sodium bromide, manganese bromide, barium bromide, bromine or magnesium bromide, or a combination of at least two thereof.

6. The preparation method according to any one of claims 1 to 5, in, After the coating in step (2), the coating is aged, washed and dried.

7. The preparation method according to any one of claims 1 to 6, in, The sodium source in step (3) comprises sodium carbonate; Optionally, the molar ratio of the sodium element in the sodium source to the metal element in the modified precursor is (1.02-1.2):1; Optionally, the atmosphere of the sintering process includes oxygen; Optionally, the sintering temperature is 400-1000°C; Optionally, the sintering treatment time is 4 to 30 hours.

8. A cobalt-bromine co-coated positive electrode material prepared by the method according to any one of claims 1 to 7.

9. A positive electrode sheet comprising the cobalt-bromine co-coated positive electrode material as claimed in claim 8.

10. A sodium ion battery comprising the positive electrode sheet according to claim 9.

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