Sodium electric precursor and preparation method and application thereof

Abstract

The invention provides a sodium electric precursor and a preparation method and application thereof. The preparation method comprises the following steps: injecting a solution A, a first complexing agent and a first precipitant into a base solution in a parallel flow manner to carry out a first-step precipitation reaction, and then injecting a solution B, a second complexing agent and a second precipitant in a parallel flow manner to carry out a second-step precipitation reaction; after the second-step precipitation reaction is finished, firstly injecting the solution A ', then injecting the solution A' and the solution C ', finally injecting the solution A', and carrying out a third-step precipitation reaction; c (solution A ') is less than c (solution A), and c (solution C') is less than c (solution C); after the third-step precipitation reaction is finished, the solution C and a third precipitator are injected in a parallel flow mode, a fourth-step precipitation reaction is carried out, and the sodium electric precursor is prepared. According to the invention, a buffer layer with gradually-changed components is constructed through a specific stepped injection mode in a third-step precipitation reaction and a sectional reaction of a low-concentration solution, so that the cycle life of the sodium-ion battery is prolonged, and the safety performance of the sodium-ion battery is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery materials, and particularly relates to a sodium battery precursor and a preparation method and application thereof. BACKGROUND

[0002] At present, the problem of energy shortage is increasingly prominent, and it is particularly important to develop new energy storage batteries such as lithium ion batteries and sodium ion batteries.

[0003] As for the sodium ion battery, it has great potential in the fields of chemical energy storage, low-speed electric vehicles, base station construction, etc. due to the advantages of low raw material cost and abundant reserves. However, the problem of relatively low energy density still needs to be solved. For the positive electrode material of the sodium ion battery, it has the advantages of high theoretical capacity, good structural stability, and smooth sodium ion migration channel, etc. However, the above-mentioned material still has problems such as rapid capacity and voltage decay during charging and discharging. Therefore, the prior art has carried out relevant research and improvement.

[0004] For example, the existing patent CN116969520A discloses a sodium battery precursor and a preparation method and application thereof, and the preparation method comprises the following steps: (1) mixing nickel salt, manganese salt and iron salt with a solvent to obtain solution A, mixing copper salt, complexing agent and solvent to obtain solution B, and mixing one or more of lithium salt, zinc salt, titanium salt or magnesium salt and solvent to obtain solution C; (2) co-currently injecting alkali solution, ammonia water and solution A into a bottom solution for one-step co-precipitation reaction, co-currently injecting ammonia water, alkali solution and solution B for two-step co-precipitation reaction; (3) co-currently injecting a precipitant solution and solution C for three-step co-precipitation reaction to obtain the sodium battery precursor. The above technical solution not only reduces the cost of the material, but also improves the sodium ion deintercalation capacity of the precursor to a certain extent, thereby improving the capacity retention rate and cycle performance of the material. However, the multi-layer structure formed by the three-step precipitation is easy to cause significant differences in composition and structure between the layers, and there are interface defects, which can easily cause stress concentration of the sodium ion battery during the cycle process, trigger micro-cracks, and finally cause the structure of the electrode material to collapse and the capacity to rapidly decay, which seriously affects the cycle life and safety performance of the battery.

[0005] Therefore, how to optimize the preparation process of the sodium battery precursor, reduce the interface defects, and alleviate the stress concentration phenomenon of the sodium ion battery during the cycle process, so as to improve the safety and reliability of the sodium ion battery, is a technical problem to be solved. SUMMARY

[0006] In view of the deficiencies of the prior art, the purpose of the present application is to provide a sodium battery precursor, a preparation method and application thereof. The present application uses a specific step-by-step injection method in the third step of the precipitation reaction, and uses a segmented reaction of a low-concentration solution to construct a composition-graded buffer layer on the surface of the product formed in the second step of the precipitation. The buffer layer can effectively weaken the interlayer stress formed in different precipitation stages, inhibit the generation and expansion of microcracks, reduce interface defects, relieve the stress concentration phenomenon of the sodium ion battery during the cycle process, and optimize the uniformity of the distribution of the doped elements by the synergistic effect of the solution A' and the solution C', inhibit the dissolution of metal ions and the decomposition of the electrolyte. In addition, the gradual buffer layer can also improve the continuity of the sodium ion migration channel and reduce the interface impedance, so that the cycle life and safety performance of the sodium ion battery are significantly improved.

[0007] To achieve this purpose, the present application adopts the following technical solutions:

[0008] In a first aspect, the present application provides a preparation method of a sodium battery precursor, which comprises the following steps:

[0009] A first nickel-iron-manganese mixed salt solution, a copper salt solution and a first doped metal salt solution are prepared, which are denoted as solution A, solution B and solution C, respectively. The solution A, a first complexing agent and a first precipitant are injected into a bottom solution for a first step of precipitation reaction, and then the solution B, a second complexing agent and a second precipitant are injected for a second step of precipitation reaction.

[0010] A second nickel-iron-manganese mixed salt solution and a second doped metal salt solution are prepared, which are denoted as solution A' and solution C', respectively, c(solution A') < c(solution A), and c(solution C') < c(solution C). After the second step of precipitation reaction, the solution A' is injected first, then the solution A' and the solution C' are injected, and finally the solution A' is injected for a third step of precipitation reaction.

[0011] After the third step of precipitation reaction, the solution C and a third precipitant are injected for a fourth step of precipitation reaction to obtain the sodium battery precursor.

[0012] The present application constructs a compositionally graded buffer layer on the surface of the product formed in the second precipitation by using a stepwise injection method in the third precipitation reaction and a segmented reaction of a low concentration solution, which can effectively weaken the interlayer stress formed in different precipitation stages, inhibit the generation and expansion of microcracks, reduce interface defects, relieve the stress concentration phenomenon of the sodium ion battery during the cycle process, and optimize the uniformity of the distribution of doped elements by the synergistic effect of solution A' and solution C', inhibit the dissolution of metal ions and the decomposition of electrolyte, and the graded buffer layer can also improve the continuity of the sodium ion migration channel and reduce the interface impedance, so that the cycle life and safety performance of the sodium ion battery are significantly improved.

[0013] It should be noted that c(solution A') refers to the total molar concentration of nickel, iron and manganese metal elements in solution A', and the same applies to the others.

[0014] In the present application, c(solution A') < c(solution A) and c(solution C') < c(solution C) can slow down the diffusion and precipitation rate of ions in the reaction system, avoid rapid agglomeration or uneven crystallization caused by excessive local ion concentration, make the third precipitation process more controllable, and be beneficial to the formation of a buffer layer structure with fine particles and uniform composition distribution. For solution A', the low concentration characteristic can weaken the deposition intensity of nickel, iron and manganese elements, and form a gradient connection with the first precipitation reaction of higher concentration, so that the nickel, iron and manganese composition of the product presents a gradual change from the inner layer to the outer layer, reducing the structural differences between the layers caused by concentration mutation. For solution C', low concentration of doped metal ions can reduce the risk of local enrichment during the precipitation process, promote the uniform embedding of doped elements in the buffer layer, avoid local structural distortion caused by high concentration doping, and enhance the regulation of doped elements on the interface stability.

[0015] In the present application, the solution A' is injected first, then the solution A' and the solution C' are injected, and finally the solution A' is injected. The gradient buffer structure of "nickel-iron-manganese transition layer-nickel-iron-manganese and doped element mixed layer-nickel-iron-manganese transition layer" is constructed by using this process route, which weakens the interface mutation, improves the structural stability, and the materials on both sides of the gradient buffer structure are the same. This symmetrical design can uniformly disperse the stress generated by volume change during the cycle process of the sodium ion battery, further inhibit the initiation and expansion of microcracks.

[0016] Preferably, the concentration of the solution A is 0.5-2 mol / L, for example, it can be 0.5 mol / L, 1 mol / L, 1.5 mol / L or 2 mol / L, etc.

[0017] Preferably, the concentration of the solution C is 0.05-0.5 mol / L, for example, it can be 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L or 0.5 mol / L, etc.

[0018] Preferably, the concentration ratio of the solution A' to the solution A is (0.15-0.25):1, for example, it can be 0.15:1, 0.2:1 or 0.25:1, etc.

[0019] In the present application, the suitable concentration ratio of the solution A' to the solution A can regulate the deposition rate and distribution density of the nickel-iron-manganese elements, so that the content variation of the nickel-iron-manganese elements presents a linear gradual change, further weakens the interfacial energy, reduces the risk of structural peeling caused by concentration difference in the cycle process, and ensures the stability of the structure.

[0020] Preferably, the concentration ratio of the solution C' to the solution C is (0.05-0.15):1, for example, it can be 0.05:1, 0.1:1 or 0.15:1, etc.

[0021] In the present application, the suitable concentration ratio of the solution C' to the solution C is conducive to realizing the progressive introduction of doped metal ions in the third step of the precipitation reaction, enhancing the regulation effect of the doped elements on the interfacial stability, and reducing stress concentration and metal dissolution in the cycle process.

[0022] Preferably, in the first doped metal salt solution, the first doped metal ion includes any one or a combination of at least two of zinc ion, titanium ion, magnesium ion or lithium ion.

[0023] Preferably, in the second doped metal salt solution, the second doped metal ion includes any one or a combination of at least two of zinc ion, titanium ion, magnesium ion or lithium ion.

[0024] Preferably, the first doped metal ion in the first doped metal salt solution and the second doped metal ion in the second doped metal salt solution are of the same type.

[0025] Preferably, the first complexing agent and the second complexing agent each independently include any one or a combination of at least two of ammonia, acetic acid, sodium citrate or ethylenediamine.

[0026] Preferably, the first precipitant, the second precipitant and the third precipitant each independently include sodium hydroxide and / or potassium hydroxide.

[0027] Preferably, the base solution includes ammonia and lye.

[0028] Preferably, the pH of the base solution is 9-13, for example, it can be 9, 10, 11, 12 or 13, etc.

[0029] Preferably, the ammonia concentration in the bottom solution is 1-10 g / L, for example, it can be 1 g / L, 2 g / L, 5 g / L, 8 g / L or 10 g / L, etc.

[0030] Preferably, the end point of the first step precipitation reaction is that the particle size D50 in the reaction system is 3-4 μm, for example, it can be 3 μm, 3.2 μm, 3.4 μm, 3.6 μm, 3.8 μm or 4 μm, etc.

[0031] Preferably, the reaction temperature of the first step precipitation reaction is 20-80℃, for example, it can be 20℃, 30℃, 40℃, 50℃, 60℃, 70℃ or 80℃, etc.

[0032] Preferably, during the first step precipitation reaction, the pH of the reaction system is 8-12, for example, it can be 8, 9, 10, 11 or 12, etc.

[0033] Preferably, the end point of the second step precipitation reaction is that the particle size D50 in the reaction system is 3.5-4.5 μm, for example, it can be 3.5 μm, 3.7 μm, 3.9 μm, 4.1 μm, 4.3 μm or 4.5 μm, etc.

[0034] Preferably, the reaction temperature of the second step precipitation reaction is 20-80℃, for example, it can be 20℃, 30℃, 40℃, 50℃, 60℃, 70℃ or 80℃, etc.

[0035] Preferably, during the second step precipitation reaction, the pH of the reaction system is 8-12, for example, it can be 8, 9, 10, 11 or 12, etc.

[0036] Preferably, the injection volume ratio of the solution A to the solution A' is 3:(0.8-1.2), for example, it can be 3:0.8, 3:0.9, 3:1, 3:1.1 or 3:1.2, etc.

[0037] Preferably, the injection volume ratio of the solution C to the solution C' is 3:(0.8-1.2), for example, it can be 3:0.8, 3:0.9, 3:1, 3:1.1 or 3:1.2, etc.

[0038] Preferably, during the re-injection of the solution A' and the solution C', the injection volume ratio of the solution A' to the solution C' is (0.5-1.5):(0.5-1.5), wherein the selected range "0.5-1.5" of the solution A' can be 0.5, 0.75, 1, 1.25 or 1.5, etc., and the selected range "0.5-1.5" of the solution C' can be 0.5, 0.75, 1, 1.25 or 1.5, etc.

[0039] In the present application, the suitable injection volume ratio of solution A' and solution C' can ensure the proportion of components in the mixed layer of nickel-iron-manganese and doping elements, guarantee the continuous and gradual composition connection of the mixed layer and the front and rear nickel-iron-manganese transition layers, avoid structural faults caused by unbalanced proportion, and enhance the structural integrity and ion migration fluency of the buffer layer as a whole.

[0040] Preferably, the end point of the third step precipitation reaction is that the particle size D50 in the reaction system is 4-5 μm, for example, it can be 4 μm, 4.2 μm, 4.4 μm, 4.6 μm, 4.8 μm or 5 μm, etc.

[0041] Preferably, the reaction temperature of the third step precipitation reaction is 20-80℃, for example, it can be 20℃, 30℃, 40℃, 50℃, 60℃, 70℃ or 80℃, etc.

[0042] Preferably, the reaction temperature of the fourth step precipitation reaction is 20-80℃, for example, it can be 20℃, 30℃, 40℃, 50℃, 60℃, 70℃ or 80℃, etc.

[0043] Preferably, during the fourth step precipitation reaction, the pH of the reaction system is 8-12, for example, it can be 8, 9, 10, 11 or 12, etc.

[0044] Preferably, during the concurrent injection of solution C and the third precipitant, an aluminum source solution is also injected.

[0045] In the present application, the injection of the aluminum source solution can make the aluminum element and the doping metal ions in solution C synergistically act to form a stable spinel structure in the shell, enhance the structural density, and further more efficiently block the penetration of electrolyte, and together with the doping metal elements, strengthen the inhibition effect on the electrolyte erosion, and improve the interface stability of the material.

[0046] Preferably, the injection amount of the aluminum source solution accounts for 0.5-1.5 mol% of the molar fraction of solution C, for example, it can be 0.5 mol%, 1 mol% or 1.5 mol%, etc.

[0047] Preferably, the aluminum source solution includes any one or a combination of at least two of aluminum nitrate solution, aluminum chloride solution or aluminum sulfate solution.

[0048] Preferably, the concentration of the aluminum source solution is 0.1-0.5 mol / L, for example, it can be 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L or 0.5 mol / L, etc.

[0049] Preferably, the preparation method of the first nickel-iron-manganese mixed salt solution comprises:

[0050] Dissolving nickel salt, iron salt and manganese salt in solvent to prepare solution A.

[0051] Preferably, the molar ratio of the nickel salt, iron salt and manganese salt is (0.2-0.45):(0.2-0.45):(0.2-0.45), wherein the selected range "0.2-0.45" of the nickel salt can be 0.2, 0.25, 0.3, 0.35, 0.4 or 0.45, etc., the selected range "0.2-0.45" of the iron salt can be 0.2, 0.25, 0.3, 0.35, 0.4 or 0.45, etc., and the selected range "0.2-0.45" of the manganese salt can be 0.2, 0.25, 0.3, 0.35, 0.4 or 0.45, etc.

[0052] For example, the nickel salt can be nickel sulfate, nickel nitrate or nickel chloride, etc., the iron salt can be iron sulfate, iron nitrate or iron chloride, etc., the manganese salt can be manganese sulfate, manganese nitrate or manganese chloride, etc., and the solvent can be deionized water, etc.

[0053] Preferably, the preparation method of the second nickel-iron-manganese mixed salt solution comprises:

[0054] Dissolving nickel salt, iron salt and manganese salt in solvent to prepare solution A'.

[0055] Preferably, the molar ratio of the nickel salt, iron salt and manganese salt is (0.2-0.45):(0.2-0.45):(0.2-0.45), wherein the selected range "0.2-0.45" of the nickel salt can be 0.2, 0.25, 0.3, 0.35, 0.4 or 0.45, etc., the selected range "0.2-0.45" of the iron salt can be 0.2, 0.25, 0.3, 0.35, 0.4 or 0.45, etc., and the selected range "0.2-0.45" of the manganese salt can be 0.2, 0.25, 0.3, 0.35, 0.4 or 0.45, etc.

[0056] For example, the nickel salt can be nickel sulfate, nickel nitrate or nickel chloride, etc., the iron salt can be iron sulfate, iron nitrate or iron chloride, etc., the manganese salt can be manganese sulfate, manganese nitrate or manganese chloride, etc., and the solvent can be deionized water, etc.

[0057] Preferably, the preparation method of the copper salt solution comprises:

[0058] Mixing copper salt and solvent to prepare solution B. For example, the copper salt can be copper sulfate, copper nitrate or copper chloride, etc., and the solvent can be deionized water, etc.

[0059] Preferably, the preparation method of the first doped metal salt solution comprises:

[0060] Solution C is prepared by mixing the first doped metal salt and a solvent. The first doped metal salt can be, for example, a sulfate, and the solvent can be, for example, deionized water.

[0061] Preferably, the method for preparing the first doped metal salt solution includes:

[0062] Solution C is prepared by mixing the second doped metal salt and a solvent. The second doped metal salt can be, for example, a sulfate, and the solvent can be, for example, deionized water.

[0063] Preferably, the preparation method includes the following steps:

[0064] (1) Dissolve nickel salt, iron salt, and manganese salt in a solvent at a molar ratio of (0.2-0.45):(0.2-0.45):(0.2-0.45) to prepare a solution A with a concentration of 0.5-2 mol / L; mix copper salt with solvent to prepare a solution B with a concentration of 0.1-0.3 mol / L (e.g., 0.1 mol / L, 0.2 mol / L, or 0.3 mol / L); mix the first doped metal salt with solvent to prepare a solution C with a concentration of 0.05-0.5 mol / L; wherein the first doped metal salt includes any one or a combination of at least two of zinc salt, titanium salt, magnesium salt, or lithium salt.

[0065] Solution A, the first complexing agent, and the first precipitant are injected concurrently into the base liquid. A first-step precipitation reaction is carried out under stirring until the particle size D50 in the reaction system is 3-4 μm, at which point the reaction is complete. Then, solution B, the second complexing agent, and the second precipitant are injected concurrently to carry out a second-step precipitation reaction until the particle size D50 in the reaction system is 3.5-4.5 μm. The first and second complexing agents each independently comprise any one or a combination of at least two of ammonia, acetic acid, sodium citrate, or ethylenediamine. The first and second precipitants each independently comprise sodium hydroxide and / or potassium hydroxide. The base liquid comprises ammonia and an alkaline solution, with a pH of 9-13 and an ammonia concentration of 1-10 g / L. The reaction temperature for the first-step precipitation reaction is 20-80℃, and the pH of the reaction system is 8-12. The reaction temperature for the second-step precipitation reaction is 20-80℃, and the pH of the reaction system is 8-12.

[0066] (2) Dissolve nickel salt, iron salt, and manganese salt in a solvent at the same nickel-iron-manganese molar ratio as in solution A to prepare solution A', wherein the concentration ratio of solution A' to solution A is (0.15-0.25):1; mix the second doped metal salt with the solvent to prepare solution C', wherein the concentration ratio of solution C' to solution C is (0.05-0.15):1; wherein the second doped metal salt is of the same type as the first doped metal salt.

[0067] After the second precipitation reaction is completed, under continuous stirring, solution A' is first injected, followed by solutions A' and C' in a volume ratio of (0.5-1.5):(0.5-1.5), and finally solution A' is injected to carry out the third precipitation reaction until the particle size D50 in the reaction system is 4-5 μm; wherein, the injection volume ratio of solution A to solution A' is 3:(0.8-1.2); the injection volume ratio of solution C to solution C' is 3:(0.8-1.2); and the reaction temperature of the third precipitation reaction is 20-80℃.

[0068] (3) After the third precipitation reaction is completed, the solution C, the third precipitant and the aluminum source solution are injected in parallel to carry out the fourth precipitation reaction until the particle size D50 in the reaction system is 4.5-5.5 μm (for example, it can be 4.5 μm, 5 μm or 5.5 μm, etc.); wherein, the third precipitant includes sodium hydroxide and / or potassium hydroxide; the injection amount of the aluminum source solution accounts for 0.5-1.5 mol% of the molar fraction of the solution C, and the concentration of the aluminum source solution is 0.1-0.5 mol / L; the reaction temperature of the fourth precipitation reaction is 20-80℃; during the fourth precipitation reaction, the pH of the reaction system is 8-12.

[0069] (4) After the fourth precipitation reaction is completed, dry at 80-150℃ (e.g., 80℃, 100℃, 120℃ or 150℃, etc.) for 60-180 min (e.g., 60 min, 120 min or 180 min, etc.) to obtain the sodium-ion precursor.

[0070] In a second aspect, the present invention provides a sodium-electric precursor, which is prepared by the preparation method described in the first aspect.

[0071] Thirdly, the present invention provides a cathode material, which is prepared by sintering a sodium-ion precursor and a sodium source as described in the second aspect.

[0072] Fourthly, the present invention provides a sodium-ion battery, wherein the positive electrode of the sodium-ion battery includes the positive electrode material as described in the third aspect.

[0073] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0074] Compared with the prior art, the present invention has the following beneficial effects:

[0075] This invention utilizes a specific step-by-step injection method in the third-step precipitation reaction, employing a segmented reaction of a low-concentration solution, to construct a buffer layer with gradually changing composition on the surface of the product formed in the second-step precipitation. This buffer layer effectively weakens the interlayer stress formed at different precipitation stages, inhibits the generation and propagation of microcracks, reduces interface defects, and alleviates stress concentration during sodium-ion battery cycling. Furthermore, it optimizes the uniformity of dopant element distribution through the synergistic effect of solutions A' and C', inhibiting the dissolution of metal ions and electrolyte decomposition. Simultaneously, the gradually changing buffer layer enhances the continuity of sodium ion migration channels and reduces interfacial impedance, ultimately resulting in a significant improvement in the cycle life and safety performance of the sodium-ion battery. Detailed Implementation

[0076] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0077] Example 1

[0078] This embodiment provides a method for preparing a sodium-ionized precursor, the method comprising the following steps:

[0079] (1) Nickel sulfate, ferric sulfate and manganese sulfate are dissolved in deionized water in a molar ratio of 1:1:1 to prepare a solution A with a concentration of 1.5 mol / L; copper sulfate and deionized water are mixed to prepare a solution B with a concentration of 0.2 mol / L; the first doped metal salt is mixed with deionized water to prepare a solution C with a concentration of 0.2 mol / L; wherein the first doped metal salt is titanium sulfate.

[0080] Solution A, ammonia, and sodium hydroxide are injected concurrently into the base solution, and a first-step precipitation reaction is carried out under stirring until the particle size D50 in the reaction system is 3.4 μm, at which point the reaction is complete. Then, solution B, ammonia, and sodium hydroxide are injected concurrently to carry out a second-step precipitation reaction until the particle size D50 in the reaction system is 3.8 μm. The base solution includes ammonia and an alkaline solution, with a pH of 11 and an ammonia concentration of 5 g / L. The reaction temperature for the first-step precipitation reaction is 55°C, and the pH of the reaction system is 9.5. The reaction temperature for the second-step precipitation reaction is 52°C, and the pH of the reaction system is 9.8.

[0081] (2) Dissolve nickel sulfate, ferric sulfate, and manganese sulfate in deionized water at the same nickel-iron-manganese molar ratio as in solution A to prepare a solution A' with a concentration of 0.3 mol / L; mix the second doped metal salt with deionized water to prepare a solution C' with a concentration of 0.02 mol / L; wherein the second doped metal salt is of the same type as the first doped metal salt; the concentration ratio of solution A' to solution A is 0.2:1; the concentration ratio of solution C' to solution C is 0.1:1.

[0082] After the second precipitation reaction is completed, under continuous stirring, solution A' is first injected, followed by solutions A' and C' in a 1:1 volume ratio, and finally solution A' is injected to carry out the third precipitation reaction until the particle size D50 in the reaction system is 4.2 μm; wherein, the injection volume ratio of solution A to solution A' is 3:1; the injection volume ratio of solution C to solution C' is 3:1; and the reaction temperature of the third precipitation reaction is 50℃.

[0083] (3) After the third precipitation reaction is completed, the solution C, sodium hydroxide and aluminum sulfate solution are injected in parallel to carry out the fourth precipitation reaction until the particle size D50 in the reaction system is 4.6 μm; wherein, the amount of aluminum sulfate solution injected accounts for 1 mol% of the molar fraction of the solution C, and the concentration of the aluminum sulfate solution is 0.3 mol / L; the reaction temperature of the fourth precipitation reaction is 52℃; and the pH of the reaction system is 10 during the fourth precipitation reaction.

[0084] (4) After the fourth precipitation reaction is completed, the sodium-ion precursor is dried at 120°C for 80 min to obtain the sodium-ion precursor.

[0085] Example 2

[0086] This embodiment provides a method for preparing a sodium-ionized precursor, the method comprising the following steps:

[0087] (1) Nickel sulfate, ferric sulfate and manganese sulfate are dissolved in deionized water in a molar ratio of 1:1:1 to prepare a solution A with a concentration of 1.4 mol / L; copper sulfate and deionized water are mixed to prepare a solution B with a concentration of 0.1 mol / L; the first doped metal salt is mixed with deionized water to prepare a solution C with a concentration of 0.2 mol / L; wherein the first doped metal salt is titanium sulfate.

[0088] Solution A, ammonia, and sodium hydroxide are injected concurrently into the base solution, and a first-step precipitation reaction is carried out under stirring until the particle size D50 in the reaction system reaches 3.7 μm, at which point the reaction is complete. Then, solution B, ammonia, and sodium hydroxide are injected concurrently to carry out a second-step precipitation reaction until the particle size D50 in the reaction system reaches 4.2 μm. The base solution includes ammonia and an alkaline solution, with a pH of 11 and an ammonia concentration of 5 g / L. The reaction temperature for the first-step precipitation reaction is 52°C, and the pH of the reaction system is 9.9. The reaction temperature for the second-step precipitation reaction is 52°C, and the pH of the reaction system is 9.8.

[0089] (2) Dissolve nickel sulfate, ferric sulfate, and manganese sulfate in deionized water at the same nickel-iron-manganese molar ratio as in solution A to prepare a solution A' with a concentration of 0.21 mol / L; mix the second doped metal salt with deionized water to prepare a solution C' with a concentration of 0.01 mol / L; wherein the second doped metal salt is of the same type as the first doped metal salt; the concentration ratio of solution A' to solution A is 0.15:1; the concentration ratio of solution C' to solution C is 0.05:1.

[0090] After the second precipitation reaction is completed, under continuous stirring, solution A' is first injected, followed by solutions A' and C' in a volume ratio of 0.5:1.5, and finally solution A' is injected to carry out the third precipitation reaction until the particle size D50 in the reaction system is 4.5 μm; wherein, the injection volume ratio of solution A to solution A' is 3:1.2; the injection volume ratio of solution C to solution C' is 3:1.2; and the reaction temperature of the third precipitation reaction is 52℃.

[0091] (3) After the third precipitation reaction is completed, the solution C, sodium hydroxide and aluminum sulfate solution are injected in parallel to carry out the fourth precipitation reaction until the particle size D50 in the reaction system is 5 μm; wherein, the amount of aluminum sulfate solution injected accounts for 0.5 mol% of the molar fraction of the solution C, and the concentration of the aluminum sulfate solution is 0.5 mol / L; the reaction temperature of the fourth precipitation reaction is 52℃; during the fourth precipitation reaction, the pH of the reaction system is 9.7.

[0092] (4) After the fourth precipitation reaction is completed, dry at 100℃ for 90 min to obtain the sodium-ion precursor.

[0093] Example 3

[0094] This embodiment provides a method for preparing a sodium-ionized precursor, the method comprising the following steps:

[0095] (1) Nickel sulfate, ferric sulfate and manganese sulfate are dissolved in deionized water in a molar ratio of 1:1:1 to prepare a solution A with a concentration of 1.5 mol / L; copper sulfate and deionized water are mixed to prepare a solution B with a concentration of 0.2 mol / L; the first doped metal salt is mixed with deionized water to prepare a solution C with a concentration of 0.3 mol / L; wherein the first doped metal salt is titanium sulfate.

[0096] Solution A, ammonia, and sodium hydroxide are injected concurrently into the base solution, and the first precipitation reaction is carried out under stirring until the particle size D50 in the reaction system is 3.6 μm, at which point the reaction is complete. Then, solution B, ammonia, and sodium hydroxide are injected concurrently to carry out the second precipitation reaction until the particle size D50 in the reaction system is 4 μm. The base solution includes ammonia and alkaline solution, with a pH of 11 and an ammonia concentration of 5 g / L. The reaction temperature for the first precipitation reaction is 55°C, and the pH of the reaction system is 9.8. The reaction temperature for the second precipitation reaction is 55°C, and the pH of the reaction system is 9.9.

[0097] (2) Dissolve nickel sulfate, ferric sulfate, and manganese sulfate in deionized water at the same nickel-iron-manganese molar ratio as in solution A to prepare a solution A' with a concentration of 0.375 mol / L; mix the second doped metal salt with deionized water to prepare a solution C' with a concentration of 0.045 mol / L; wherein the second doped metal salt is of the same type as the first doped metal salt; the concentration ratio of solution A' to solution A is 0.25:1; the concentration ratio of solution C' to solution C is 0.15:1.

[0098] After the second precipitation reaction is completed, under continuous stirring, solution A' is first injected, followed by solutions A' and C' in a volume ratio of 1.5:0.5, and finally solution A' is injected to carry out the third precipitation reaction until the particle size D50 in the reaction system is 4.5 μm; wherein, the injection volume ratio of solution A to solution A' is 3:0.8; the injection volume ratio of solution C to solution C' is 3:0.8; and the reaction temperature of the third precipitation reaction is 55℃.

[0099] (3) After the third precipitation reaction is completed, the solution C, sodium hydroxide and aluminum sulfate solution are injected in parallel to carry out the fourth precipitation reaction until the particle size D50 in the reaction system is 5 μm; wherein, the amount of aluminum sulfate solution injected accounts for 1.5 mol% of the molar fraction of the solution C, and the concentration of the aluminum sulfate solution is 0.1 mol / L; the reaction temperature of the fourth precipitation reaction is 55℃; during the fourth precipitation reaction, the pH of the reaction system is 9.8.

[0100] (4) After the fourth precipitation reaction is completed, the sodium-ion precursor is dried at 120°C for 90 min to obtain the sodium-ion precursor.

[0101] Example 4

[0102] The difference between this embodiment and Embodiment 1 is that the concentration ratio of solution A' to solution A is 0.1:1.

[0103] The remaining preparation methods and parameters are consistent with those in Example 1.

[0104] Example 5

[0105] The difference between this embodiment and Embodiment 1 is that the concentration ratio of solution A' to solution A is 0.3:1.

[0106] The remaining preparation methods and parameters are consistent with those in Example 1.

[0107] Example 6

[0108] The difference between this embodiment and Embodiment 1 is that the concentration ratio of solution C' to solution C is 0.02:1.

[0109] The remaining preparation methods and parameters are consistent with those in Example 1.

[0110] Example 7

[0111] The difference between this embodiment and Embodiment 1 is that the concentration ratio of solution C' to solution C is 0.2:1.

[0112] The remaining preparation methods and parameters are consistent with those in Example 1.

[0113] Example 8

[0114] The difference between this embodiment and embodiment 1 is that in step (2), the solution A' and solution C' with an injection volume ratio of 1:1 are replaced with the solution A' and solution C' with an injection volume ratio of 0.5:2.

[0115] The remaining preparation methods and parameters are consistent with those in Example 1.

[0116] Example 9

[0117] The difference between this embodiment and embodiment 1 is that in step (2), the solution A' and solution C' with an injection volume ratio of 1:1 are replaced with the solution A' and solution C' with an injection volume ratio of 2:0.5.

[0118] The remaining preparation methods and parameters are consistent with those in Example 1.

[0119] Example 10

[0120] The difference between this embodiment and embodiment 1 is that aluminum sulfate solution is not injected in step (3).

[0121] The remaining preparation methods and parameters are consistent with those in Example 1.

[0122] Comparative Example 1

[0123] The difference between this comparative example and Example 1 is that in step (2), after the second precipitation reaction is completed, the solutions A' and C' with a volume ratio of 1:1 are directly injected to carry out the third precipitation reaction.

[0124] The remaining preparation methods and parameters are consistent with those in Example 1.

[0125] Comparative Example 2

[0126] The difference between this comparative example and Example 1 is that, in step (2), after the second precipitation reaction is completed, the solutions A' and C' with a volume ratio of 1:1 are not injected.

[0127] The remaining preparation methods and parameters are consistent with those in Example 1.

[0128] Comparative Example 3

[0129] The difference between this comparative example and Example 1 is that step (2) is omitted.

[0130] The remaining preparation methods and parameters are consistent with those in Example 1.

[0131] Comparative Example 4

[0132] The difference between this comparative example and Example 1 is that in step (2), the concentration of solution A' is equal to the concentration of solution A.

[0133] The remaining preparation methods and parameters are consistent with those in Example 1.

[0134] Comparative Example 5

[0135] The difference between this comparative example and Example 1 is that in step (2), the concentration of solution C' is equal to the concentration of solution C.

[0136] The remaining preparation methods and parameters are consistent with those in Example 1.

[0137] Performance testing

[0138] The sodium-ion cathode precursors obtained in the above examples and comparative examples were pre-calcined at 400°C for 5 hours, then uniformly mixed with sodium carbonate powder according to the elemental ratio, and calcined at 800°C in air atmosphere for 12 hours to obtain sodium-ion cathode material. The sodium-ion cathode material, acetylene black and polyvinylidene fluoride were mixed in N-methyl-2-pyridinyl ketone at a mass ratio of 8:1:1 to prepare cathode slurry, which was then uniformly coated on aluminum foil, dried and stamped to form cathode sheet. The cathode sheet, sodium metal sheet, glass fiber separator, electrolyte (concentration 1 mol / L, solute is NaClO4, solvent is a combination of ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1), gasket, spring sheet and battery case were assembled into button battery in Ar gas glove box.

[0139] Electrochemical performance: At 25℃, within a voltage range of 2.0-4.0V, the charge / discharge current density is 10 mA·g. -1 Under these conditions, the battery was subjected to charge-discharge tests to obtain the initial discharge specific capacity. At 25°C and within a voltage range of 2.0-4.0V, the charge-discharge current density was 10 mA·g. -1 Under these conditions, the system was cycled 2000 times to perform a cycle performance test and obtain the capacity retention rate.

[0140] Safety performance: After the above cycle performance test, the fully charged battery was pressurized to 8kN at a rate of 10kN / min using a 10mm steel column (simulating moderate compression), and the phenomenon was observed after holding for 1 minute.

[0141] The test results are shown in Table 1.

[0142] Table 1

[0143]

[0144] analyze:

[0145] As shown in Table 1, this invention utilizes a specific step-by-step injection method in the third precipitation reaction to construct a buffer layer with gradually changing composition on the surface of the product formed in the second precipitation step through a segmented reaction of a low-concentration solution. This buffer layer can effectively weaken the interlayer stress formed at different precipitation stages, inhibit the generation and propagation of microcracks, reduce interface defects, and alleviate stress concentration in sodium-ion batteries during cycling. Furthermore, it can optimize the uniformity of dopant element distribution through the synergistic effect of solutions A' and C', inhibit the dissolution of metal ions and electrolyte decomposition. At the same time, the gradually changing buffer layer can also improve the continuity of sodium ion migration channels and reduce interfacial impedance, ultimately resulting in a significant improvement in the cycle life and safety performance of sodium-ion batteries.

[0146] As can be seen from the comparison between Example 1 and Examples 4-5, if the concentration ratio of solution A' to solution A is too small, the formation efficiency of the buffer structure is low, and because the concentration is too low, it is difficult to form an effective compositional gradient connection with the second-step precipitation product, which easily leads to obvious interfacial gaps between the buffer layer and the inner layer product, weakening the suppression effect on interfacial defects. If the concentration ratio of solution A' to solution A is too large, a significant compositional gradient buffer structure cannot be formed, making it difficult to effectively alleviate interfacial stress, ultimately affecting the cycle stability and safety performance of the battery.

[0147] As can be seen from the comparison between Example 1 and Examples 6-7, if the concentration ratio of solution C' to solution C is too small, it will be difficult to form a reasonable concentration gradient with the dopant element introduced by solution C in the subsequent fourth precipitation reaction, weakening the buffer layer's buffering effect on interfacial stress and increasing the risk of interfacial defects. If the concentration ratio of solution C' to solution C is too large, it will destroy the continuous gradual change characteristics of the composition of the third precipitation product, and will also cause a sudden change in concentration with the dopant element introduced by solution C in the fourth precipitation reaction, exacerbating the concentration of interfacial stress, leading to a decrease in the structural stability of the sodium battery precursor, and ultimately affecting the cycle performance and safety reliability of the sodium-ion battery.

[0148] As can be seen from the comparison between Example 1 and Examples 8-9, if in step (2), the solution A' and solution C' with an injection volume ratio of 1:1 are replaced with the solution A' and solution C' with an injection volume ratio of 0.5:2, the volume ratio is too small, which will lead to excessive doping of metal in the constructed nickel-iron-manganese and doped element mixed layer, destroying the main structural framework of the mixed layer, weakening the stress buffering capacity of the buffer structure, and increasing the risk of interface defects; if in step (2), the solution A' and solution C' with an injection volume ratio of 1:1 are replaced with the solution A' and solution C' with an injection volume ratio of 2:0.5, the volume ratio is too large, which will not be able to give full play to the regulatory effect of the doped element on the interface stability, resulting in the exacerbation of the interface stress concentration phenomenon, affecting the overall structural stability of the sodium battery precursor, and is not conducive to improving the cycle performance of sodium-ion batteries.

[0149] As can be seen from the comparison between Example 1 and Example 10, if aluminum sulfate solution is not injected in step (3), the spinel structure crystal configuration cannot be formed by the aluminum element, which weakens the anti-penetration effect of the shell on the electrolyte and increases the probability of interface defects.

[0150] As can be seen from the comparison between Example 1 and Comparative Examples 1-2, if the third precipitation reaction is carried out by directly injecting the solutions A' and C' in a volume ratio of 1:1 after the second precipitation reaction, it is difficult to form a buffer structure with a gradual transition of components, which leads to an aggravation of interfacial stress concentration, increases the structural defects of the precursor, and is not conducive to the stability of the cycle performance of sodium-ion batteries. If the solutions A' and C' in a volume ratio of 1:1 are not injected after the second precipitation reaction, an effective buffer structure cannot be constructed, which reduces the bonding force between different layers. During cycling, the uneven stress distribution makes it easier for interfacial peeling to occur, resulting in increased battery internal resistance and accelerated capacity decay. It is difficult to effectively suppress interfacial defects and improve cycle stability.

[0151] As can be seen from the comparison between Example 1 and Comparative Example 3, if step (2) is not performed, that is, if the gradient buffer structure is not constructed, the layers of the sodium battery precursor lack smooth component transition and stress buffer region. As a result, during the charge and discharge cycle of the sodium-ion battery, with the repeated expansion and contraction of the electrode material, this stress will continue to accumulate, which will lead to structural damage such as interface cracking and interlayer peeling, seriously affecting the structural stability of the precursor, and ultimately resulting in poor cycle life and safety performance of the battery.

[0152] As can be seen from the comparison between Example 1 and Comparative Examples 4-5, if the concentration of solution A' is equal to that of solution A, it is difficult to form a compositional gradient change from the core to the buffer structure, resulting in the inability to effectively alleviate interlayer interface stress. During battery cycling, the interface is still prone to cracking due to differences in expansion and contraction, weakening the effect of the gradient buffer structure on improving structural stability. If the concentration of solution C' is equal to that of solution C, it is impossible to construct a gradual distribution of doped elements from the buffer structure to the shell, affecting the cycle life and safety performance of the sodium-ion battery.

[0153] It should be noted that the present invention is illustrated through the above embodiments, but the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a sodium-ionized precursor, characterized in that, The preparation method includes the following steps: Prepare a first nickel-iron-manganese mixed salt solution, a copper salt solution, and a first doped metal salt solution, denoted as solution A, solution B, and solution C, respectively; inject solution A, the first complexing agent, and the first precipitant in parallel into the base liquid to carry out the first precipitation reaction, and then inject solution B, the second complexing agent, and the second precipitant in parallel into the base liquid to carry out the second precipitation reaction; Prepare a second nickel-iron-manganese mixed salt solution and a second doped metal salt solution, denoted as solution A' and solution C', respectively, where c(solution A') < c(solution A) and c(solution C') < c(solution C). After the second precipitation reaction is completed, first inject solution A', then inject solution A' and solution C', and finally inject solution A' to carry out the third precipitation reaction. After the third precipitation reaction is completed, the solution C and the third precipitant are injected in parallel to carry out the fourth precipitation reaction to obtain the sodium-ion precursor.

2. The preparation method according to claim 1, characterized in that, The concentration of solution A is 0.5-2 mol / L; Preferably, the concentration of solution C is 0.05-0.5 mol / L; Preferably, the concentration ratio of solution A' to solution A is (0.15-0.25):1; Preferably, the concentration ratio of solution C' to solution C is (0.05-0.15):

1.

3. The preparation method according to claim 1 or 2, characterized in that, In the first doped metal salt solution, the first doped metal ion includes any one or a combination of at least two of zinc ions, titanium ions, magnesium ions, or lithium ions. Preferably, in the second doped metal salt solution, the second doped metal ion includes any one or a combination of at least two of zinc ions, titanium ions, magnesium ions, or lithium ions; Preferably, the first doped metal ion in the first doped metal salt solution is the same type as the second doped metal ion in the second doped metal salt solution; Preferably, the first complexing agent and the second complexing agent each independently comprise any one or a combination of at least two of ammonia, acetic acid, sodium citrate, or ethylenediamine; Preferably, the first precipitant, the second precipitant, and the third precipitant each independently comprise sodium hydroxide and / or potassium hydroxide; Preferably, the base liquid includes ammonia and an alkaline solution; Preferably, the pH of the base solution is 9-13; Preferably, the ammonia concentration in the base solution is 1-10 g / L.

4. The preparation method according to any one of claims 1-3, characterized in that, The endpoint of the first precipitation reaction is that the particle size D50 in the reaction system is 3-4 μm. Preferably, the reaction temperature of the first precipitation reaction is 20-80℃; Preferably, during the first precipitation reaction, the pH of the reaction system is 8-12; Preferably, the endpoint of the second precipitation reaction is that the particle size D50 in the reaction system is 3.5-4.5 μm; Preferably, the reaction temperature for the second precipitation reaction is 20-80℃; Preferably, during the second precipitation reaction, the pH of the reaction system is 8-12.

5. The preparation method according to any one of claims 1-4, characterized in that, The injection volume ratio of solution A to solution A' is 3:(0.8-1.2); Preferably, the injection volume ratio of solution C to solution C' is 3:(0.8-1.2); Preferably, during the re-injection of solution A' and solution C', the injection volume ratio of solution A' to solution C' is (0.5-1.5):(0.5-1.5); Preferably, the endpoint of the third precipitation reaction is: the particle size D50 in the reaction system is 4-5 μm; Preferably, the reaction temperature of the third precipitation reaction is 20-80℃.

6. The preparation method according to any one of claims 1-5, characterized in that, The reaction temperature for the fourth step of precipitation is 20-80℃; Preferably, during the fourth precipitation reaction, the pH of the reaction system is 8-12; Preferably, during the co-flow injection of solution C and the third precipitant, an aluminum source solution is also injected; Preferably, the amount of aluminum source solution injected accounts for 0.5-1.5 mol% of the molar fraction of solution C. Preferably, the concentration of the aluminum source solution is 0.1-0.5 mol / L.

7. The preparation method according to any one of claims 1-6, characterized in that, The preparation method includes the following steps: (1) Dissolve nickel salt, iron salt, and manganese salt in a solvent at a molar ratio of (0.2-0.45):(0.2-0.45):(0.2-0.45) to prepare a solution A with a concentration of 0.5-2 mol / L; mix copper salt with a solvent to prepare a solution B with a concentration of 0.1-0.3 mol / L; mix the first doped metal salt with a solvent to prepare a solution C with a concentration of 0.05-0.5 mol / L; wherein the first doped metal salt includes any one or a combination of at least two of zinc salt, titanium salt, magnesium salt, or lithium salt. Solution A, the first complexing agent, and the first precipitant are injected concurrently into the base liquid. A first-step precipitation reaction is carried out under stirring until the particle size D50 in the reaction system is 3-4 μm, at which point the reaction is complete. Then, solution B, the second complexing agent, and the second precipitant are injected concurrently to carry out a second-step precipitation reaction until the particle size D50 in the reaction system is 3.5-4.5 μm. The first and second complexing agents each independently comprise any one or a combination of at least two of ammonia, acetic acid, sodium citrate, or ethylenediamine. The first and second precipitants each independently comprise sodium hydroxide and / or potassium hydroxide. The base liquid comprises ammonia and an alkaline solution, with a pH of 9-13 and an ammonia concentration of 1-10 g / L. The reaction temperature for the first-step precipitation reaction is 20-80℃, and the pH of the reaction system is 8-12. The reaction temperature for the second-step precipitation reaction is also 20-80℃, and the pH of the reaction system is 8-12. (2) Dissolve nickel salt, iron salt, and manganese salt in a solvent according to the same nickel-iron-manganese molar ratio as in solution A to prepare solution A', wherein the concentration ratio of solution A' to solution A is (0.15-0.25):1; mix the second doped metal salt with the solvent to prepare solution C', wherein the concentration ratio of solution C' to solution C is (0.05-0.15):1; wherein the second doped metal salt is of the same type as the first doped metal salt; After the second precipitation reaction is completed, under continuous stirring, solution A' is first injected, followed by solutions A' and C' in a volume ratio of (0.5-1.5):(0.5-1.5), and finally solution A' is injected to carry out the third precipitation reaction until the particle size D50 in the reaction system is 4-5 μm; wherein, the injection volume ratio of solution A to solution A' is 3:(0.8-1.2); the injection volume ratio of solution C to solution C' is 3:(0.8-1.2); the reaction temperature of the third precipitation reaction is 20-80℃; (3) After the third precipitation reaction is completed, the solution C, the third precipitant and the aluminum source solution are injected in parallel to carry out the fourth precipitation reaction until the particle size D50 in the reaction system is 4.5-5.5 μm; wherein, the third precipitant includes sodium hydroxide and / or potassium hydroxide; the amount of aluminum source solution injected accounts for 0.5-1.5 mol% of the molar fraction of the solution C, and the concentration of the aluminum source solution is 0.1-0.5 mol / L; the reaction temperature of the fourth precipitation reaction is 20-80℃; during the fourth precipitation reaction, the pH of the reaction system is 8-12; (4) After the fourth precipitation reaction is completed, dry at 80-150℃ for 60-180 min to obtain the sodium-ion precursor.

8. A sodium-ionized precursor, characterized in that, The sodium-ion precursor is prepared by the preparation method according to any one of claims 1-7.

9. A positive electrode material, characterized in that, The cathode material is prepared by sintering the sodium-ion precursor and sodium source as described in claim 8.

10. A sodium-ion battery, characterized in that, The positive electrode of the sodium-ion battery includes the positive electrode material as described in claim 9.

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