Cobalt-coated sodium ion battery precursor, and preparation method and use therefor

Abstract

A cobalt-coated sodium ion battery precursor, and a preparation method and use therefor. The cobalt-coated sodium ion battery precursor sequentially comprises, from inside to outside, a core, a transition layer and an outer coating layer. The core comprises a nickel-iron-manganese precursor material. The transition layer comprises a nickel-iron-manganese-cobalt precursor material. The coating layer comprises a cobalt hydroxide material. By carrying out gradient coating of cobalt on the nickel-iron-manganese core, cobalt is sequentially increased from inside to outside, such that the surface structure stability of the nickel-iron-manganese precursor is improved, side reaction between the electrode and the electrolyte is inhibited, and the use voltage and rate capability of the sodium-ion battery are effectively improved.

Description

A cobalt-coated sodium ion battery precursor 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-coated sodium ion battery precursor and a preparation method and application thereof. Background Art

[0002] As the electric vehicle market continues to expand, demand for lithium-ion batteries is rapidly increasing. However, the uneven geographical distribution and relatively scarce lithium resources have led to rising prices in the end-market for lithium-ion batteries. Consequently, sodium-ion batteries have re-entered the market. With their abundant raw materials, low cost, and high safety, sodium-ion batteries have become a hot topic in recent years.

[0003] The energy storage mechanism of sodium-ion batteries is similar to that of lithium-ion batteries, with acceptable theoretical specific capacity (1166 mAh / g for sodium and 3860 mAh / g for lithium) and electrode potential (-2.71 V (vs. SHE) for sodium and -3.04 V (vs. SHE) for lithium). The content of sodium in the earth's crust is relatively high, at 23.6×10 3 The concentration of cobalt in sodium ion batteries is 170000 mg / kg, which is more than a thousand times that of lithium (17 mg / kg). Furthermore, it is widely distributed, especially in seawater, with abundant reserves. Its low price makes the development of sodium ion batteries promising, making it a strong competitor in the field of electrochemical energy storage. Ternary layered hydroxide materials containing nickel, cobalt, and manganese have excellent electrochemical properties and good thermal stability and are widely used in the preparation of sodium ion battery cathode materials. However, cobalt is scarce in the Earth's crust and has a high production cost, which increases the cost of sodium ion battery cathode materials.

[0004] To reduce the cost of cathode materials for sodium-ion batteries, researchers are using iron instead of cobalt to prepare a ternary layered precursor of nickel, iron, and manganese for use in cathode production. However, nickel-iron-manganese sodium battery precursors suffer from poor air stability, particle pulverization at high rates, and severe capacity decay, severely hindering the industrial development of sodium batteries.

[0005] Therefore, how to improve the stability of nickel-iron-manganese-sodium cathode precursor materials and enhance their electrochemical performance is a technical problem that needs to be solved urgently.

[0006] Summary of the Invention

[0007] 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.

[0008] In response to the shortcomings of the existing technology, the purpose of this application is to provide a cobalt-coated sodium-ion battery precursor and its preparation method and application. The sodium-ion battery positive electrode precursor material provided in this application is a nickel-iron-manganese core that is gradient-coated with cobalt, which increases from the inside to the outside. This improves the surface structural stability of the nickel-iron-manganese precursor, inhibits side reactions between the electrode and the electrolyte, and effectively improves the operating voltage and rate performance of the sodium-ion battery.

[0009] To achieve this goal, this application adopts the following technical solutions:

[0010] In a first aspect, the present application provides a cobalt-coated sodium-ion battery precursor, which comprises a core, a transition layer and an outer coating layer from the inside to the outside; the core comprises a nickel-iron-manganese precursor material; the transition layer comprises a nickel-iron-manganese-cobalt precursor material; and the coating layer comprises a cobalt hydroxide material.

[0011] The sodium battery precursor material provided in the present application has a core, a transition layer and an outer coating layer, and the cobalt content in the transition layer and the outer coating layer increases successively. After the transition of the nickel-iron-manganese-cobalt transition layer, a close combination of the outer coating layer and the core is achieved, thereby improving the structural stability of the precursor material and avoiding the stress and strain concentration at the coating interface under high-rate charge and discharge conditions, which leads to the shedding and powdering of the cobalt hydroxide coating interface, thereby improving the operating voltage and rate performance of the sodium ion battery.

[0012] In this application, the core, transition layer and outer coating layer are indispensable. Without the transition layer, the problem of delamination between the coating layer and the core cannot be solved; and if the cobalt content does not increase sequentially from the inside to the outside, a good coating effect cannot be achieved; and if cobalt coating is not performed, the operating voltage and rate performance of the positive electrode material cannot be improved.

[0013] In one embodiment, the D50 of the core is 2.5 to 6 μm, for example, 2.5 μm, 3 μm, 3.1 μm, 3.2 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm or 6 μm.

[0014] In one embodiment, the difference between D50 of the particles containing the core and the transition layer and D50 of the core is 0.1 to 0.5 μm, for example, 0.1 μm, 0.1 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm or 0.5 μm.

[0015] In the present application, the difference between the D50 of the particles containing the core and the transition layer and the D50 of the core is in the numerical range of 0.1 to 0.5 μm, which can better improve the coating effect and improve the performance of the material. If the difference is too small, that is, the transition layer is too thin, it will affect the coating effect. If the difference is too large, that is, the transition layer is too thick, it will make it difficult to control the coating thickness of the outermost cobalt hydroxide layer, increasing the difficulty of coating.

[0016] In one embodiment, the difference between the D50 of the cobalt-coated sodium ion battery precursor and the D50 of the particles containing the core and the transition layer is 0.1 to 0.5 μm, for example, 0.1 μm, 0.1 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm or 0.5 μm, etc.

[0017] The sodium battery precursor material provided in this application can effectively improve its operating voltage and rate performance by regulating the particle size of the core, transition layer and precursor material and increasing the cobalt coating content.

[0018] In a second aspect, the present application provides a method for preparing a cobalt-coated sodium ion battery precursor as described in the first aspect, the preparation method comprising the following steps:

[0019] Adding nickel-iron-manganese mixed salt solution, precipitant solution and complexing agent solution in parallel to carry out the first stage of co-precipitation reaction to obtain a core structure precursor material;

[0020] Then, a cobalt salt solution is added to carry out a second stage of coprecipitation reaction with a nickel-iron-manganese mixed salt solution, a precipitant solution and a complexing agent solution to obtain a precursor material coated with a transition layer;

[0021] The addition of the nickel-iron-manganese mixed salt solution is stopped, and the cobalt salt solution, the precipitant solution and the complexing agent solution are continued to undergo the third stage of coprecipitation reaction to obtain the cobalt-coated sodium ion battery precursor.

[0022] The preparation method provided in the present application obtains a multilayer sodium electric precursor material through a three-stage co-precipitation reaction, and simultaneously realizes an increase in the cobalt content from the transition layer to the outer coating layer. While regulating the cobalt content, a nickel-iron-manganese sodium electric precursor material with stable structure and good performance is obtained. The preparation method is simple to operate and does not require a complicated processing process.

[0023] In one embodiment, the precipitant comprises any one of sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate, or a combination of at least two thereof.

[0024] In one embodiment, the complexing agent includes any one of ammonia, acetic acid, oxalic acid, citric acid, ethylenediaminetetraacetic acid or salicylic acid, or a combination of at least two thereof.

[0025] It should be noted that the precursor material provided in this application can be a hydroxide system or a carbonate system, and those skilled in the art can make adaptive adjustments based on the selection of precipitants and complexing agents; at the same time, during the reaction process, the amount of cobalt coating can be adaptively adjusted according to actual needs.

[0026] In one embodiment, the reaction temperatures of the first stage coprecipitation reaction, the second stage coprecipitation reaction and the third stage coprecipitation reaction are each independently 30-80°C, for example, 30°C, 40°C, 50°C, 60°C, 70°C or 80°C.

[0027] In one embodiment, the reaction rates of the coprecipitation reaction in the first stage, the coprecipitation reaction in the second stage, and the coprecipitation reaction in the third stage are each independently 180 to 1200 rpm, for example, 180 rpm, 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm, 1100 rpm or 1200 rpm, etc.

[0028] In one embodiment, the pH values ​​of the first stage coprecipitation reaction, the second stage coprecipitation reaction, and the third stage coprecipitation reaction are each independently 6.5 to 13, for example, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5 or 13, etc.

[0029] In one embodiment, the specific surface area of ​​the core structure precursor material is ≥12m 2 / g, for example 12m 2 / g, 12.5m 2 / g、13m 2 / g、14m 2 / g、15m 2 / g、16m 2 / g、17m 2 / g、18m 2 / g、19m 2 / g, 20m 2 / g or 25m 2 / g, etc.

[0030] In one embodiment, the tap density of the core structure precursor material is ≥1.7 g / cm 3 , for example 1.7 g / cm 3 、1.71g / cm 3 , 1.72g / cm 3 , 1.73g / cm 3, 1.74g / cm 3 , 1.75g / cm 3 , 1.76g / cm 3 , 1.77g / cm 3 , 1.78g / cm 3 , 1.79g / cm 3 , 1.8g / cm 3 , 1.83g / cm 3 , 1.85g / cm 3 or 1.9 g / cm 3 wait.

[0031] The core precursor material prepared in this application has a more stable core structure and a better sphericity when the specific surface area and tap density are within the above numerical ranges, and the coating effect of the coating layer can also be improved.

[0032] In one embodiment, the D50 of the core structure precursor material is 2.5 to 6 μm, for example, 2.5 μm, 3 μm, 3.1 μm, 3.2 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm or 6 μm.

[0033] In one embodiment, during the second stage of the coprecipitation reaction, the particle size of the core structure precursor material increases by 0.1 to 0.5 μm, for example, 0.1 μm, 0.1 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm or 0.5 μm.

[0034] In one embodiment, during the coprecipitation reaction in the third stage, the particle size of the precursor material coated with the transition layer increases by 0.1 to 0.5 μm, for example, 0.1 μm, 0.1 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm or 0.5 μm.

[0035] As an optional technical solution, the preparation method includes the following steps:

[0036] A nickel-iron-manganese mixed salt solution, a precipitant solution, and a complexing agent solution are added in parallel, and a first-stage coprecipitation reaction is performed at a reaction rate of 180 to 1200 rpm at 30 to 80° C. in an environment where the pH value is maintained at 6.5 to 13, to obtain a core structure precursor material with a D50 of 2.5 to 6 μm.

[0037] The pH value is maintained at 6.5 to 13, and then a cobalt salt solution is added to carry out a second stage of coprecipitation reaction with a nickel-iron-manganese mixed salt solution, a precipitant solution, and a complexing agent solution at 30 to 80° C. and a reaction rate of 180 to 1200 rpm to obtain a precursor material coated with a transition layer;

[0038] Stop adding the nickel-iron-manganese mixed salt solution, maintain the pH value at 6.5-13, and continue to carry out the third stage of coprecipitation reaction of the cobalt salt solution, the precipitant solution and the complexing agent solution at 30-80° C. and a reaction rate of 180-1200 rpm to obtain a cobalt-coated sodium ion battery precursor;

[0039] During the second stage of the coprecipitation reaction, the particle size of the core structure precursor material increases by 0.1 to 0.5 μm; during the third stage of the coprecipitation reaction, the particle size of the precursor material coated with the transition layer increases by 0.1 to 0.5 μm.

[0040] It should be noted that in the preparation method provided in this application, the concentration and feed amount of each solution can be adaptively adjusted according to the target product.

[0041] In a third aspect, the present application provides a nickel-iron-manganese-sodium cathode material, which is obtained by mixing and sintering the cobalt-coated sodium ion battery precursor as described in the first aspect with a sodium source.

[0042] In the nickel-iron-manganese-sodium cathode precursor material provided in the present application, there is no special limitation on the specific molar ratio of nickel-iron-manganese. Those skilled in the art can adaptively adjust the ratio according to different needs. At the same time, the specific molar ratio content of the nickel-iron-manganese-cobalt precursor material in the transition layer can be reasonably adjusted according to the thickness requirements and the thickness of the outer coating layer.

[0043] In one embodiment, the molar ratio of the total molar amount of metal ions in the cobalt-coated sodium ion battery precursor to the molar ratio of sodium ions in the sodium source is 1:(0.75-1.2), for example, 1:0.75, 1:0.8, 1:0.9, 1:1, 1:1.1 or 1:1.2.

[0044] In one embodiment, the sintering temperature is 600-1000°C, such as 600°C, 700°C, 750°C, 800°C, 850°C, 900°C or 1000°C, and can be optionally 700-900°C.

[0045] In one embodiment, the sintering time is 8 to 20 hours, such as 8 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 18 hours or 20 hours, and can be optionally 10 to 15 hours.

[0046] The sintering process provided in this application can also be carried out in stages, such as two-stage sintering, etc.; and during the sintering process, modification methods such as doping or coating can be performed according to actual needs. The technical solutions known to those skilled in the art are applicable to this application.

[0047] In a fourth aspect, the present application also provides a sodium ion battery, which includes the nickel-iron-manganese-sodium cathode material as described in the third aspect.

[0048] Compared with the prior art, this application has the following beneficial effects:

[0049] The sodium battery precursor material provided in the present application has a core, a transition layer and an outer coating layer, and the cobalt content in the transition layer and the outer coating layer increases successively. After the transition of the nickel-iron-manganese-cobalt transition layer, a close combination of the outer coating layer and the core is achieved, thereby improving the structural stability of the precursor material and avoiding the stress and strain concentration at the coating interface under high-rate charge and discharge conditions, which leads to the shedding and powdering of the cobalt hydroxide coating interface, thereby improving the operating voltage and rate performance of the sodium ion battery.

[0050] Still other aspects will become apparent upon reading and understanding the detailed description. DETAILED DESCRIPTION

[0051] The technical solution of the present application is further illustrated below by specific examples. Those skilled in the art should understand that the examples are only for facilitating understanding of the present application and should not be regarded as specific limitations of the present application.

[0052] Example 1

[0053] This embodiment provides a cobalt-coated sodium-ion battery precursor, which includes a core, a transition layer and an outer coating layer from the inside to the outside; the core includes a nickel-iron-manganese hydroxide precursor material; the transition layer includes a nickel-iron-manganese-cobalt hydroxide precursor material; the coating layer includes a cobalt hydroxide material; the difference between the D50 of the particles containing the core and the transition layer and the D50 of the core is 0.2 μm; the difference between the D50 of the cobalt-coated sodium-ion battery precursor and the D50 of the particles containing the core and the transition layer is 0.1 μm.

[0054] The preparation method of the cobalt-coated sodium ion battery precursor is as follows:

[0055] (1) using a nickel-iron-manganese sulfate mixed solution (nickel-iron-manganese molar ratio of 1:1:1), a cobalt sulfate solution, a sodium hydroxide solution, and an ammonia solution as reaction raw materials, and performing a coprecipitation reaction at a temperature of 50° C., a pH of 11, and a stirring rate of 500 rpm;

[0056] The coprecipitation reaction is divided into three stages:

[0057] The first stage of the coprecipitation reaction: a mixed solution of nickel-iron-manganese sulfate, a sodium hydroxide solution, and an aqueous ammonia solution were added to a reactor in parallel and coprecipitated for 70 hours to obtain a core precursor material (nickel-iron-manganese hydroxide) with a D50 of 3.2 μm.

[0058] In the second stage of the coprecipitation reaction, a cobalt sulfate solution was added to the raw materials of the first stage simultaneously, wherein the feed rate ratio of the cobalt sulfate solution to the nickel-iron-manganese sulfate mixed solution was 1:10, and the coprecipitation reaction was carried out for 5 hours to obtain a precursor material coated with a transition layer having a D50 of 3.4 μm (i.e., the transition layer was a nickel-iron-manganese-cobalt hydroxide precursor material, and the D50 of the particles grew to 0.2 μm);

[0059] In the third stage of the coprecipitation reaction, the addition of the nickel-iron-manganese sulfate mixed solution was stopped, and the cobalt sulfate solution, sodium hydroxide solution and ammonia solution were added to the reactor in parallel for a coprecipitation reaction of 2.5 hours. The particle size was reduced to 3.5 μm (the particle size grew by 0.1 μm). The reaction was stopped to obtain a sodium-ion battery precursor with a cobalt coating amount of 10,000 ppm. The solid phase was then separated, aged, washed and dried to obtain a cobalt-coated sodium-ion battery precursor.

[0060] Example 2

[0061] This embodiment provides a cobalt-coated sodium-ion battery precursor, which includes a core, a transition layer and an outer coating layer from the inside to the outside; the core includes a nickel-iron-manganese hydroxide precursor material; the transition layer includes a nickel-iron-manganese-cobalt hydroxide precursor material; the coating layer includes a cobalt hydroxide material; the difference between the D50 of the particles containing the core and the transition layer and the D50 of the core is 0.5 μm; the difference between the D50 of the cobalt-coated sodium-ion battery precursor and the D50 of the particles containing the core and the transition layer is 0.5 μm.

[0062] The preparation method of the cobalt-coated sodium ion battery precursor is as follows:

[0063] (1) A coprecipitation reaction was carried out using a nickel-iron-manganese sulfate mixed solution (a nickel-iron-manganese molar ratio of 1:1:1), a cobalt sulfate solution, a sodium hydroxide solution, and an ammonia solution as reaction raw materials at a temperature of 40° C., a pH of 11.8, and a stirring rate of 380 rpm;

[0064] The coprecipitation reaction is divided into three stages:

[0065] The first stage of the coprecipitation reaction: a mixed solution of nickel-iron-manganese sulfate, a sodium hydroxide solution, and an ammonia solution were added to a reactor in parallel and the coprecipitation reaction was carried out for 100 hours to obtain a core precursor material (nickel-iron-manganese hydroxide) with a D50 of 6 μm.

[0066] In the second stage of the coprecipitation reaction, a cobalt sulfate solution was added to the raw materials of the first stage simultaneously, wherein the feed rate ratio of the cobalt sulfate solution to the nickel-iron-manganese sulfate mixed solution was 1:10, and the coprecipitation reaction was carried out for 10 hours to obtain a precursor material coated with a transition layer having a D50 of 6.5 μm (i.e., the transition layer was a nickel-iron-manganese-cobalt hydroxide precursor material, and the particle size grew to 0.5 μm);

[0067] In the third stage of the coprecipitation reaction, the addition of the nickel-iron-manganese sulfate mixed solution was stopped, and the cobalt sulfate solution, sodium hydroxide solution and ammonia solution were added to the reactor in parallel for a coprecipitation reaction of 5 hours. The particle size was reduced to 7 μm (the particle size grew to 0.5 μm). The reaction was stopped to obtain a sodium-ion battery precursor with a cobalt coating amount of 20,000 ppm. The solid phase was then separated, aged, washed and dried to obtain a cobalt-coated sodium-ion battery precursor.

[0068] Example 3

[0069] The difference between this embodiment and embodiment 1 is that the molar ratio of nickel, iron and manganese in the nickel, iron and manganese mixed salt solution in this embodiment is 2:4:4.

[0070] The rest of the preparation methods and parameters were the same as those in Example 1.

[0071] Example 4

[0072] The difference between this embodiment and embodiment 1 is that the difference between D50 of the particles containing a core and a transition layer in this embodiment and D50 of the core is 0.05 μm.

[0073] During the preparation process, after obtaining a precursor material coated with a transition layer having a D50 of 3.25 μm during the second stage coprecipitation reaction, a third stage coprecipitation reaction was performed. The remaining preparation methods and parameters remained the same as in Example 1.

[0074] Example 5

[0075] The difference between this embodiment and embodiment 1 is that the difference between the D50 of the particles containing the core and the transition layer in this embodiment and the D50 of the core is 0.6 μm.

[0076] During the preparation process, during the second stage coprecipitation reaction, after obtaining a precursor material coated with a transition layer with a D50 of 3.8 μm, the third stage coprecipitation reaction was carried out, and the particle size was reduced to 4 μm, and the reaction was stopped.

[0077] The rest of the preparation methods and parameters were the same as those in Example 1.

[0078] Example 6

[0079] The difference between this embodiment and Example 1 is that the D50 of the core precursor in this embodiment is 7 μm; the difference between the D50 of the particles containing the core and the transition layer and the D50 of the core is 0.2 μm; the difference between the D50 of the cobalt-coated sodium ion battery precursor and the D50 of the particles containing the core and the transition layer is 0.1 μm.

[0080] In the preparation method, the reaction time of each coprecipitation stage is adaptively adjusted.

[0081] The rest of the preparation methods and parameters were the same as those in Example 1.

[0082] Example 7

[0083] The difference between this embodiment and Example 1 is that the D50 of the core precursor in this embodiment is 2 μm; the difference between the D50 of the particles containing the core and the transition layer and the D50 of the core is 0.2 μm; the difference between the D50 of the cobalt-coated sodium ion battery precursor and the D50 of the particles containing the core and the transition layer is 0.1 μm.

[0084] In the preparation method, the reaction time of each coprecipitation stage is adaptively adjusted.

[0085] The rest of the preparation methods and parameters were the same as those in Example 1.

[0086] Comparative Example 1

[0087] The difference between this comparative example and Example 1 is that the positive electrode precursor material provided in this comparative example does not contain a transition layer.

[0088] In the preparation method, the second stage coprecipitation reaction is not performed, and the core D50 remains unchanged.

[0089] The rest of the preparation methods and parameters were consistent with those in the example.

[0090] Comparative Example 2

[0091] The difference between this comparative example and Example 1 is that in this comparative example, the positions of the transition layer and the outer coating layer are interchanged (that is, the outer coating layer serves as the transition layer, and the transition layer serves as the outer coating layer, and the law of particle size difference remains consistent, the difference between the D50 of the particles containing the core and the new transition layer and the D50 of the core is 0.2 μm; the difference between the D50 of the cobalt-coated sodium ion battery precursor and the D50 of the particles containing the core and the new transition layer is 0.1 μm).

[0092] In the preparation method, after the first stage coprecipitation reaction, the third stage coprecipitation reaction is carried out, and finally the second stage coprecipitation reaction is carried out, and the reaction time is adaptively adjusted.

[0093] The rest of the preparation methods and parameters were the same as those in Example 1.

[0094] Comparative Example 3

[0095] The difference between this comparative example and Example 1 is that the positive electrode precursor provided in this comparative example does not include a transition layer or an outer coating layer, that is, the core structure is the positive electrode precursor material.

[0096] In the preparation method, only the first stage of coprecipitation reaction is carried out, and then the solid phase is separated, aged, washed and dried to obtain the sodium battery positive electrode precursor material.

[0097] Sodium carbonate is mixed with the sodium cathode precursor provided by Examples 1-7 and Comparative Examples 1-3 in a planetary mixer, wherein the molar ratio of sodium ions in the sodium source to metal ions in the precursor is 1:1. The mixture is then sintered at 700°C in a resistance furnace at a heating rate of 5°C / min for 18 hours to obtain the iron-based sodium cathode material.

[0098] The prepared positive electrode materials provided in Examples 1-7 and Comparative Examples 1-3 were mixed with acetylene black and polyvinylidene fluoride in a mass ratio of 8:1:1, respectively, and added to N-methyl-2-pyridine to obtain a positive electrode slurry. The positive electrode slurry was evenly applied on an aluminum foil, dried, and punched into a thin sheet to obtain a positive electrode sheet; the positive electrode sheet, elemental sodium sheet, glass fiber separator, electrolyte (sodium salt is NaClO4) gasket, shrapnel and battery shell were assembled into a button battery in an Ar gas glove box.

[0099] The sodium ion batteries provided in Examples 1-7 and Comparative Examples 1-3 were performance tested, and the test conditions were as follows: the rate performance test was conducted on a voltage platform of 3.2-4.1 V, and the battery was subjected to 300 charge and discharge tests at current densities of 1C and 5C, and the discharge specific capacity of different samples at current densities of 1C and 5C was recorded; the cycle performance test method was the capacity retention rate of different samples under 1C and 5C conditions for 300 cycles.

[0100] The test results of the above tests are shown in Table 1.

[0101] Table 1

[0102] From the data results of Examples 1, 4 and 5, it can be seen that if the transition layer is too thin, it is not conducive to improving the rate performance; and if it is too thick, it will lead to a decrease in capacity.

[0103] From the data results of Examples 1, 6 and 7, it can be seen that if the core particle size is too small, the discharge capacity will be affected; and if the core particle size is too large, the rate performance will be reduced.

[0104] From the data results of Examples 4-7, it can be seen that the sodium battery precursor material provided in this application can effectively improve its operating voltage and rate performance by regulating the particle size of the core, transition layer and precursor material and increasing the cobalt coating content.

[0105] From the data results of Example 1 and Comparative Examples 1-3, it can be seen that the order of the core, transition layer and outer coating layer, as well as the selection of material types of the sodium battery positive electrode precursor material provided by the present application must be coordinated and none of them can be missing in order to improve the operating voltage and rate performance; the lack of a transition layer of nickel, iron, manganese and cobalt makes it impossible to achieve stable adhesion of the positive electrode coating layer; and if the cobalt content decreases from the inside to the outside, not only will it fail to improve the electrochemical performance of the sodium battery, but it will seriously deteriorate the core and coating structure, and greatly reduce the electrochemical performance of the sodium battery positive electrode.

[0106] In summary, the sodium battery precursor material provided by the present application, through the coordinated cooperation of the core, transition layer and outer coating layer, the cobalt content in the transition layer and the outer coating layer increases successively, and through the transition of the nickel-iron-manganese-cobalt transition layer, a close combination of the outer coating layer and the core is achieved, thereby improving the structural stability of the precursor material, avoiding the stress and strain concentration on the coating interface under high-rate charge and discharge conditions, resulting in the shedding and powdering of the cobalt hydroxide coating interface, thereby improving the operating voltage and rate performance of the sodium ion battery.

[0107] 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 substitutions 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 cobalt-coated sodium-ion battery precursor, which sequentially includes a core, a transition layer, and an outer coating layer from inside to outside; the core includes a nickel-iron-manganese precursor material; the transition layer includes a nickel-iron-manganese-cobalt precursor material; and the coating layer includes a cobalt hydroxide material.

2. The cobalt-coated sodium-ion battery precursor according to claim 1, wherein, the D50 of the core is 2.5 - 6 μm.

3. The cobalt-coated sodium-ion battery precursor according to claim 1 or 2, wherein, the difference between the D50 of the particle containing the core and the transition layer and the D50 of the core is 0.1 - 0.5 μm; Optionally, the difference between the D50 of the cobalt-coated sodium-ion battery precursor and the D50 of the particle containing the core and the transition layer is 0.1 - 0.5 μm.

4. A preparation method of the cobalt-coated sodium-ion battery precursor according to any one of claims 1 - 3, comprising the following steps: Co-currently adding a nickel-iron-manganese mixed salt solution, a precipitant solution, and a complexing agent solution to carry out a first-stage co-precipitation reaction to obtain a core structure precursor material; Then adding a cobalt salt solution to jointly carry out a second-stage co-precipitation reaction with the nickel-iron-manganese mixed salt solution, the precipitant solution, and the complexing agent solution to obtain a precursor material coated with a transition layer; Stop adding the nickel-iron-manganese mixed salt solution, and continue to carry out a third-stage co-precipitation reaction with the cobalt salt solution, the precipitant solution, and the complexing agent solution to obtain the cobalt-coated sodium-ion battery precursor.

5. The preparation method according to claim 4, wherein, the precipitant includes any one or a combination of at least two of sodium hydroxide, potassium hydroxide, sodium carbonate, or potassium carbonate; Optionally, the complexing agent includes any one or a combination of at least two of ammonia water, acetic acid, oxalic acid, citric acid, ethylenediaminetetraacetic acid, or salicylic acid; Optionally, the reaction temperature of the first-stage co-precipitation reaction, the second-stage co-precipitation reaction, and the third-stage co-precipitation reaction is independently 30 - 80 °C; Optionally, the reaction rate of the first-stage co-precipitation reaction, the second-stage co-precipitation reaction, and the third-stage co-precipitation reaction is independently 180 - 1200 rpm; Optionally, the pH value of the first-stage co-precipitation reaction, the second-stage co-precipitation reaction, and the third-stage co-precipitation reaction is independently 6.5 - 13.

6. The preparation method according to claim 4 or 5, wherein, The specific surface area of the core structure precursor material ≥ 12 m 2 / g; Optionally, the tap density of the core structure precursor material is ≥ 1.7 g / cm 3 ; Optionally, the D50 of the core structure precursor material is 2.5 - 6 μm; Optionally, during the second-stage co-precipitation reaction, the particle size of the core structure precursor material increases by 0.1 - 0.5 μm; Optionally, during the third-stage co-precipitation reaction, the particle size of the precursor material coated with a transition layer increases by 0.1 - 0.5 μm.

7. The preparation method according to any one of claims 4 - 6, wherein, the preparation method comprises the following steps: The nickel-iron-manganese mixed salt solution, precipitant solution, and complexing agent solution are added in parallel flow, and the pH value is maintained in an environment of 6.5-13. The first-stage coprecipitation reaction is carried out at 30-80 °C with a reaction rate of 180-1200 rpm to obtain a core structure precursor material with a D50 of 2.5-6 μm; In an environment where the pH value is maintained at 6.5-13, then a cobalt salt solution is added, and the second-stage coprecipitation reaction is carried out together with the nickel-iron-manganese mixed salt solution, precipitant solution, and complexing agent solution at 30-80 °C with a reaction rate of 180-1200 rpm to obtain a precursor material coated with a transition layer; Stop adding the nickel-iron-manganese mixed salt solution, and in an environment where the pH value is maintained at 6.5-13, the cobalt salt solution, The precipitant solution and the complexing agent solution continue to carry out the third-stage coprecipitation reaction at 30-80 °C with a reaction rate of 180-1200 rpm to obtain a cobalt-coated sodium-ion battery precursor; Among them, during the second-stage coprecipitation reaction, the particle size of the core structure precursor material increases by 0.1-0.5 μm; during the third-stage coprecipitation reaction, the particle size of the precursor material coated with a transition layer increases by 0.1-0.5 μm.

8. A nickel-iron-manganese-sodium cathode material for sodium-ion batteries obtained by mixing and sintering the cobalt-coated sodium-ion battery precursor according to any one of claims 1-3 with a sodium source.

9. According to the nickel-iron-manganese-sodium cathode material for sodium-ion batteries described in claim 8, wherein, The molar ratio of the total molar amount of metal ions in the cobalt-coated sodium-ion battery precursor to the sodium ions in the sodium source is 1:(0.75-1.2); Optionally, the sintering temperature is 600-1000 °C, and further optionally 700-900 °C; Optionally, the sintering time is 8-20 h, and further optionally 10-15 h.

10. A sodium-ion battery comprising the nickel-iron-manganese-sodium cathode material for sodium-ion batteries described in claim 8 or 9.

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