Coated sodium ion precursor material as well as preparation method and application thereof

Abstract

The invention discloses a coated sodium ion precursor material as well as a preparation method and application thereof. The sodion precursor material comprises a sodion precursor inner core and a coating layer coating the surface of the sodion precursor inner core, and the coating layer comprises a lanthanum-doped manganese-based Prussian blue material. A sodium ion precursor is coated to form a coated sodium ion precursor material, a coating layer contains a manganese-based Prussian blue material of which the bulk phase is doped with lanthanum, the structure can be stabilized, an interface can be optimized, ion and electron transmission can be promoted, and under the combined action of the three mechanisms, the performance is comprehensively improved. The cycling stability, the rate capability and the thermal safety of the sodium ion battery prepared from the sodium ion precursor material are remarkably improved.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a coated sodium ion precursor material, a preparation method thereof, and uses thereof. Background Art

[0002] Sodium-ion batteries, with their excellent high- and low-temperature performance, fast-charging capabilities, and high safety, have become an emerging energy storage technology in recent years. Due to their abundant sodium resources and low cost, they have shown great potential for application in low-speed electric vehicles and large-scale energy storage. However, the energy density of sodium-ion batteries is far lower than that of ternary lithium-ion batteries. Furthermore, sodium-ion batteries are prone to phase transitions and oxygen evolution during cycling, especially at higher cutoff voltages. This can cause lattice distortion, structural collapse, and accelerated battery performance degradation, shortening cycle life, leading to poor rate performance, and low thermal safety. These factors have severely hampered the market development of sodium-ion batteries.

[0003] Sodium ion battery positive electrode materials mainly include layered metal oxides, polyanionic compounds, and Prussian blue compounds. Element doping and coating can effectively improve the performance of sodium ion battery positive electrode materials and enhance the structural stability of the material. For example, CN 117712305 A discloses a Prussian blue-coated sodium ion battery positive electrode material and its preparation method and application. The invention discloses a coating layer comprising a manganese-based layered oxide and a coating layer uniformly coated on the surface of the manganese-based layered oxide. The coating layer is a potassium-based Prussian blue material. The positive electrode material prepared therefrom has good structural stability and electrochemical performance, and can maintain a low surface alkalinity of the test alkali in the environment. However, it has the problem of easy structural collapse and manganese dissolution, which affects the performance of its electrochemical performance and cannot take into account good cycle life, rate performance and thermal safety.

[0004] Therefore, providing a strategy to improve the cycle life, rate performance and thermal safety of sodium ion positive electrode materials is a technical problem that needs to be solved urgently. Summary of the Invention

[0005] In view of the above technical problems existing in the prior art, the purpose of the present invention is to provide a coated sodium ion precursor material and its preparation method and use.

[0006] In the present invention, "comprising" means that in addition to the listed components, some unlisted components may also be contained. In some embodiments, only the listed components are contained. In this case, "comprising" can be modified to "consisting of..."

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a coated sodium ion precursor material, comprising a sodium ion precursor core and a coating layer coated on the surface of the sodium ion precursor core, wherein the coating layer comprises a lanthanum-doped manganese-based Prussian blue material.

[0009] The present invention forms a coated sodium ion precursor material by coating a sodium ion precursor. The coating layer contains a manganese-based Prussian blue material doped with lanthanum in the bulk phase, which can stabilize the structure, optimize the interface, and promote ion and electron transmission. Under the joint action of these three mechanisms, the overall performance improvement is achieved. The cycle stability, rate performance and thermal safety of the sodium ion battery prepared using the sodium ion precursor material are significantly improved. Among them, the manganese-based Prussian blue material {Na2Mn[Fe(CN)6], MnHCF} has a stable three-dimensional framework structure, can provide open deintercalation channels for sodium ions, and has excellent electrochemical properties. Furthermore, the use of lanthanum ions (La 3+ ) replaces some of the manganese sites in manganese-based Prussian blue, which can expand the lattice spacing, inhibit bulk structural distortion, relieve structural stress, reduce lattice water through ion exchange, and avoid capacity decay caused by side reactions. The use of lanthanum-doped manganese-based Prussian blue to coat the sodium ion precursor core enables the prepared sodium ion positive electrode material to fully utilize its open three-dimensional channels and cubic crystal structure to provide a rapid diffusion path for sodium ions, effectively buffering the volume change during the sodium ion insertion and extraction process (for example, <2%), reducing cracks and pulverization of the electrode material caused by repeated charge and discharge, significantly extending the cycle life, and giving the material excellent rate performance. Moreover, during the battery charge and discharge process, the lanthanum-doped Prussian blue coating can act as a "buffer layer" to disperse stress concentration, prevent particle breakage, avoid lattice structure collapse, and significantly extend the cycle life.

[0010] Moreover, Prussian blue material has the advantages of simple synthesis, low cost, and non-toxicity, making it suitable for large-scale production.

[0011] The present invention does not specifically limit the method for forming the coating layer. The method in the prior art can be used to form a coating layer on the surface of the sodium ion precursor core. In the future, with the refinement of the coating process (such as atomic layer deposition), this technology is expected to promote the commercialization of sodium ion batteries in the fields of energy storage and power.

[0012] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0013] The doping amount of lanthanum in the lanthanum-doped manganese-based Prussian blue material is 0.5 at % to 0.2 at %, for example, it can be 0.5 at %, 0.45 at %, 0.4 at %, 0.35 at %, 0.3 at %, 0.25 at % or 0.2 at %.

[0014] Preferably, the sodium ion precursor core comprises nickel iron manganese hydroxide.

[0015] Preferably, the particle size D50 of the sodium ion precursor core is 8μm to 18μm, for example, it can be 8μm, 8.5μm, 9μm, 9.5μm, 10μm, 10.5μm, 11μm, 12.5μm, 13μm, 13.5μm, 14μm, 14.5μm, 15μm, 15.5μm, 16μm, 16.5μm, 17μm or 18μm, etc.

[0016] Preferably, the particle size D50 of the coated sodium ion precursor material is 10μm to 25μm, for example, it can be 10μm, 10.5μm, 11μm, 12.5μm, 13μm, 13.5μm, 14μm, 14.5μm, 15μm, 15.5μm, 16μm, 16.5μm, 17μm, 18μm, 18.5μm, 19μm, 20μm, 20.5μm, 21μm, 22μm, 22.5μm, 23μm, 24μm or 25μm, etc.

[0017] In a second aspect, the present invention provides a method for preparing the coated sodium ion precursor material as described in the first aspect, the preparation method comprising the following steps:

[0018] (1) adding the mixed metal salt solution, the first precipitant solution, and the first complexing agent solution to the base liquid in parallel to perform a first coprecipitation reaction to obtain a slurry of the sodium ion precursor core;

[0019] (2) Sodium ferrocyanide, a divalent soluble manganese salt, and a lanthanum salt are dissolved in water to prepare a coating solution, and the coating solution, a second precipitant solution, and a second complexing agent solution are added to a reactor containing a slurry of the sodium ion precursor core to perform a second coprecipitation reaction to obtain the coated sodium ion precursor material.

[0020] The method of the present invention is simple and controllable to operate, has low preparation cost, and is suitable for industrial production.

[0021] Preferably, the metal ions in the mixed metal salt solution in step (1) include nickel ions, divalent iron ions and manganese ions.

[0022] The present invention does not impose any specific limitation on the preparation method of the mixed metal salt solution in step (1). For example, a soluble metal salt may be added to deionized water and stirred to obtain the mixed metal salt solution.

[0023] Preferably, the metal salts include nickel salts, iron salts and manganese salts.

[0024] In one embodiment, the anion in the metal salt is at least one of sulfate, nitrate or chloride.

[0025] Preferably, the molar concentration of the metal ions in the mixed metal salt solution in step (1) is 1.5 mol / L to 2 mol / L, for example, it can be 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L or 2 mol / L.

[0026] Preferably, the base liquid in step (1) comprises water, a third precipitant and a third complexing agent, the pH of the base liquid is 10 to 11, for example, 10, 10.2, 10.3, 10.5, 10.7, 10.8 or 11, etc.; the ammonia value of the base liquid is 7 to 9 g / L (for example, 7 g / L, 7.2 g / L, 7.3 g / L, 7.4 g / L, 7.6 g / L, 7.8 g / L, 8 g / L, 8.3 g / L, 8.6 g / L, 8.8 g / L or 9 g / L, etc.), and the mass of the third complexing agent in the base liquid is The concentration of the third precipitant in the base solution is 7 g / L to 20 g / L (for example, it can be 7 g / L, 8 g / L, 9 g / L, 10 g / L, 11 g / L, 12 g / L, 13 g / L, 14 g / L, 15 g / L, 16 g / L, 17 g / L, 18 g / L, 19 g / L or 20 g / L, etc.), and the concentration of the third precipitant in the base solution is 15 g / L to 17 g / L (for example, it can be 15 g / L, 15.2 g / L, 15.5 g / L, 16 g / L, 16.3 g / L, 16.6 g / L or 17 g / L, etc.).

[0027] Preferably, in step (1) of the first coprecipitation reaction, the parameters during the process of the first coprecipitation reaction are controlled as follows: temperature is in the range of 40°C to 80°C, pH value is in the range of 10 to 11, ammonia value is in the range of 7 to 9 g / L, rotation speed is 280 rpm to 400 rpm, and reaction time is 40h to 150h. For example, the temperature can be 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C, etc.; the pH value can be 10, 10.2, 10.4, 10.5, 10.6, 10.8 or 11, etc.; the ammonia value can be 7g / L, 7.2g / L, 7.4g / L, 7.5g / L, 7.7g / L, 8g / L, 8.2g / L, 8.5g / L, 8.8g / L or 9g / L, etc.; the rotation speed can be the reaction time can be, for example, 40h, 42h, 45h, 48h, 50h, 53h, 55h, 60h, 65h, 70h, 75h, 80h, 85h, 90h, 95h, 100h, 105h, 110h, 115h, 120h, 125h, 130h, 135h, 140h, 145h or 150h, etc.

[0028] Preferably, the concentration of the coating solution in step (2) is 0.1 mol / L to 0.2 mol / L, for example, it can be 0.1 mol / L, 0.12 mol / L, 0.14 mol / L, 0.15 mol / L, 0.17 mol / L, 0.18 mol / L or 0.2 mol / L.

[0029] Preferably, the divalent soluble manganese salt in step (2) includes at least one of manganese nitrate, manganese sulfate and manganese chloride.

[0030] Preferably, the lanthanum salt in step (2) comprises lanthanum nitrate and / or hydrated lanthanum nitrate crystals.

[0031] Preferably, the parameters during the second coprecipitation reaction in step (2) are controlled as follows: temperature in the range of 40°C to 80°C, pH value in the range of 5 to 9, ammonia value in the range of 3 to 4 g / L, rotation speed in the range of 80 rpm to 200 rpm, and reaction time in the range of 10 h to 30 h. For example, the temperature can be 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C; the pH value can be 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5 or 9; the ammonia value can be 3 g / L, 3.2 g / L, 3.4 g / L, 3.5 g / L, 3.7 g / L, 3.8 g / L or 4 g / L; the rotation speed can be 80 rpm, 100 rpm, 120 rpm, 140 rpm, 160 rpm, 180 rpm or 200 rpm; the reaction time can be 10 h, 12 h, 14 h, 15 h, 16 h, 18 h, 20 h, 22 h, 24 h, 26 h, 28 h or 30 h. The pH and ammonia values ​​of the second coprecipitation reaction occurred in a lower range, resulting in a thin strip-like morphology, which provided more rapid diffusion paths for sodium ions.

[0032] Preferably, the method for preparing the coating solution in step (2) comprises: dissolving sodium ferrocyanide in water to obtain solution A, and dissolving a divalent soluble manganese salt, a lanthanum salt, and the solution A in water to obtain a coating solution. Since manganese salt and lanthanum salt solutions are usually weakly acidic, if manganese salt, lanthanum salt, and sodium ferrocyanide are directly mixed, the acidic environment will cause ferrocyanide ions [Fe(CN)6] 4- Partial hydrolysis releases highly toxic hydrogen cyanide (HCN). Therefore, it is preferred to prepare the coating solution in the above-mentioned step-by-step mixing manner.

[0033] Preferably, the concentration of sodium ferrocyanide in the solution A is 0.02mol / L to 0.15mol / L, for example, it can be 0.02mol / L, 0.03mol / L, 0.04mol / L, 0.05mol / L, 0.06mol / L, 0.07mol / L, 0.08mol / L, 0.09mol / L, 0.1mol / L, 0.11mol / L, 0.12mol / L, 0.13mol / L or 0.15mol / L, etc.

[0034] Preferably, the molar ratio of sodium ferrocyanide, divalent soluble manganese salt and lanthanum salt in the coating solution is 1: (0.92-0.95): (0.03-0.05), wherein the selection range of divalent soluble manganese salt is "0.92-0.95", for example, it can be 0.92, 0.93, 0.94 or 0.95; the selection range of lanthanum salt is "0.03-0.05", for example, it can be 0.03, 0.04 or 0.05.

[0035] Preferably, the coating solution in step (2) further comprises a dispersant, and the dispersant comprises at least one of polyvinyl pyrrolidone, polyethylene glycol, sodium citrate and sodium lauryl sulfate.

[0036] Preferably, the amount of the dispersant added is: 1 mol to 1.5 mol (for example, 1 mol, 1.2 mol, 1.3 mol, 1.4 mol or 1.5 mol, etc.) of the dispersant per 1 L of the coating liquid.

[0037] Preferably, the first complexing agent, the second complexing agent and the third complexing agent independently comprise at least one of ammonia water, sodium fluoride, sodium citrate and sodium lactate. Wherein, "independently" means that the first complexing agent, the second complexing agent and the third complexing agent are independently selected within the above-mentioned ranges, are not affected by each other, and can be the same or different.

[0038] In a second aspect, the present invention provides a sodium ion positive electrode material, which is prepared using the coated sodium ion precursor material described in the first aspect.

[0039] In a third aspect, the present invention provides a method for preparing the sodium ion positive electrode material according to the second aspect, the preparation method comprising the following steps:

[0040] The coated sodium ion precursor material described in the first aspect is sintered to obtain the sodium ion positive electrode material.

[0041] Preferably, the sintering temperature is 750°C to 850°C, for example, it can be 750°C, 755°C, 760°C, 770°C, 780°C, 790°C, 800°C, 810°C, 820°C, 830°C, 840°C or 850°C.

[0042] Preferably, the sintering time is 10 h to 40 h, for example, it can be 10 h, 12 h, 13 h, 15 h, 17 h, 20 h, 22 h, 25 h, 26 h, 28 h, 30 h, 32 h, 33 h, 35 h, 37 h, 38 h or 40 h.

[0043] In a fourth aspect, the present invention provides a sodium ion battery, comprising the sodium ion positive electrode material described in the second aspect.

[0044] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] (1) The present invention forms a coated sodium ion precursor material by coating a sodium ion precursor. The coating layer contains a bulk-phase lanthanum-doped manganese-based Prussian blue material, which can stabilize the structure, optimize the interface, and promote ion and electron transport. Under the combined action of these three mechanisms, a comprehensive performance improvement is achieved. The sodium ion battery prepared using this sodium ion precursor material has significantly improved cycle stability, rate performance, and thermal safety.

[0047] (2) The coated sodium ion precursor material of the present invention is applied to sodium ion batteries, which can achieve high initial discharge capacity, initial coulombic efficiency, and cycle performance. The initial discharge capacity is above 145.1 mAh / g, preferably above 148.7 mAh / g; the initial coulombic efficiency is above 83.3%, preferably above 84.6%; and the capacity retention rate after 50 cycles is above 94.7%, preferably above 96.2%. DETAILED DESCRIPTION

[0048] The technical solution of the present invention is further illustrated below through specific implementation methods.

[0049] Example 1

[0050] This embodiment provides a coated sodium ion precursor material, which includes a sodium ion precursor core (nickel iron manganese hydroxide, particle size D50 is 10 μm) and a coating layer coated on the surface of the sodium ion precursor core, wherein the coating layer includes a lanthanum-doped manganese-based Prussian blue material.

[0051] The doping amount of lanthanum element in the lanthanum-doped manganese-based Prussian blue material is 0.4at%;

[0052] The particle size D50 of the coated sodium ion precursor material is 14 μm.

[0053] This embodiment also provides a method for preparing the above-mentioned coated sodium ion precursor material, comprising the following steps:

[0054] (1) Preparation of base liquid: Add pure water accounting for 1 / 2 of the total solvent in the reactor into the reactor, start stirring, introduce high-purity nitrogen, and then add precipitant (NaOH) and complexing agent (ammonia water) to make the parameters of the base liquid as follows: pH 10, ammonia value 8g / L, complexing agent concentration 8g / L, and precipitant concentration 16g / L.

[0055] Prepare a mixed metal salt solution: dissolve nickel sulfate, ferrous sulfate, and manganese sulfate in deionized water and stir evenly to obtain a 1.5 mol / L mixed metal salt solution.

[0056] The above-mentioned mixed metal salt solution, NaOH solution and ammonia water were added to the base liquid in parallel to carry out the first coprecipitation reaction. The parameters during the first coprecipitation reaction were controlled as follows: temperature of 60°C, pH of 10, ammonia value of 8 g / L, and rotation speed of 380 rpm. After 60 hours of reaction, a slurry of a precursor with a particle size D50 of 10 μm was obtained.

[0057] (2) Preparation of coating solution: Sodium ferrocyanide was dissolved in water to obtain a solution A with a concentration of 0.1 mol / L, and a divalent soluble manganese salt, a lanthanum salt, a dispersant (polyvinyl pyrrolidone), and the solution A were dissolved in water to obtain a coating solution with a concentration of 0.15 mol / L, wherein the molar ratio of sodium ferrocyanide, divalent soluble manganese salt, and lanthanum salt was 1:0.95:0.05, and the content of the dispersant in each 1 L of the coating solution was 1 mol.

[0058] (3) The precursor slurry of step (1) was put into a reactor, and under nitrogen protection, the coating liquid, NaOH solution and ammonia water were added to the reactor in parallel to carry out a second coprecipitation reaction. The parameters during the second coprecipitation reaction were controlled as follows: temperature of 40°C, pH of 5, ammonia value of 3.5 g / L, rotation speed of 180 rpm, and reaction for 20 hours to obtain a coated sodium ion precursor material with a particle size D50 of 14 μm.

[0059] This embodiment further provides a sodium ion positive electrode material, and a preparation method thereof includes: sintering the above-mentioned coated sodium ion precursor material at 750° C. for 20 hours to obtain the sodium ion positive electrode material.

[0060] Example 2

[0061] This embodiment provides a coated sodium ion precursor material, which includes a sodium ion precursor core (nickel iron manganese hydroxide, particle size D50 is 8 μm) and a coating layer coated on the surface of the sodium ion precursor core, wherein the coating layer includes a lanthanum-doped manganese-based Prussian blue material.

[0062] The doping amount of lanthanum element in the lanthanum-doped manganese-based Prussian blue material is 0.5at%;

[0063] The particle size D50 of the coated sodium ion precursor material is 10 μm.

[0064] This embodiment also provides a method for preparing the above-mentioned coated sodium ion precursor material, comprising the following steps:

[0065] (1) Preparation of base liquid: Add pure water accounting for 1 / 2 of the total solvent in the reactor into the reactor, start stirring, introduce high-purity nitrogen, and then add precipitant (NaOH) and complexing agent (ammonia water) to make the parameters of the base liquid as follows: pH is 11, ammonia value is 9 g / L, the concentration of complexing agent is 15 g / L, and the concentration of precipitant is 15 g / L.

[0066] Prepare a mixed metal salt solution: dissolve nickel sulfate, ferrous sulfate, and manganese sulfate in deionized water and stir evenly to obtain a 1.8 mol / L mixed metal salt solution.

[0067] The above-mentioned mixed metal salt solution, NaOH solution and ammonia water were added to the base liquid in parallel to carry out the first coprecipitation reaction. The parameters during the first coprecipitation reaction were controlled as follows: temperature of 45°C, pH value of 11, ammonia value of 7 g / L, rotation speed of 400 rpm, and after 50 hours of reaction, a precursor slurry with a particle size D50 of 8 μm was obtained.

[0068] (2) Preparation of coating solution: Sodium ferrocyanide was dissolved in water to obtain a solution A with a concentration of 0.05 mol / L, and a divalent soluble manganese salt, a lanthanum salt, a dispersant (polyvinyl pyrrolidone), and the solution A were dissolved in water to obtain a coating solution with a concentration of 0.1 mol / L, wherein the molar ratio of sodium ferrocyanide, divalent soluble manganese salt, and lanthanum salt was 1:0.92:0.05, and the content of the dispersant in each 1 L of the coating solution was 1 mol.

[0069] (3) The precursor slurry of step (1) is put into a reactor, and under nitrogen protection, the coating liquid, NaOH solution and ammonia water are added to the reactor in parallel to carry out a second coprecipitation reaction. The parameters during the second coprecipitation reaction are controlled as follows: temperature of 50°C, pH value of 8, ammonia value, rotation speed of 150 rpm, and reaction for 10 hours to obtain a coated sodium ion precursor material with a particle size D50 of 10 μm.

[0070] This embodiment further provides a sodium ion positive electrode material, and a preparation method thereof includes: sintering the above-mentioned coated sodium ion precursor material at 800° C. for 15 hours to obtain the sodium ion positive electrode material.

[0071] Example 3

[0072] This embodiment provides a coated sodium ion precursor material, which includes a sodium ion precursor core (nickel iron manganese hydroxide, particle size D50 is 15 μm) and a coating layer coated on the surface of the sodium ion precursor core, wherein the coating layer includes a lanthanum-doped manganese-based Prussian blue material.

[0073] The doping amount of lanthanum element in the lanthanum-doped manganese-based Prussian blue material is 0.2 at %;

[0074] The particle size D50 of the coated sodium ion precursor material is 18 μm.

[0075] This embodiment also provides a method for preparing the above-mentioned coated sodium ion precursor material, comprising the following steps:

[0076] (1) Preparation of base liquid: Add pure water accounting for 1 / 2 of the total solvent in the reactor into the reactor, start stirring, introduce high-purity nitrogen, and then add precipitant (NaOH) and complexing agent (ammonia water) to make the parameters of the base liquid as follows: pH 10, ammonia value 7g / L, complexing agent concentration 7g / L, precipitant concentration 17g / L.

[0077] Prepare a mixed metal salt solution: dissolve nickel sulfate, ferrous sulfate and manganese sulfate in deionized water and stir evenly to obtain a 2 mol / L mixed metal salt solution.

[0078] The above-mentioned mixed metal salt solution, NaOH solution and ammonia water were added to the base liquid in parallel to carry out the first coprecipitation reaction. The parameters during the first coprecipitation reaction were controlled as follows: temperature of 80°C, pH of 10.5, ammonia value of 9 g / L, rotation speed of 280 rpm, and after 100 hours of reaction, a precursor slurry with a particle size D50 of 15 μm was obtained.

[0079] (2) Preparation of coating solution: Sodium ferrocyanide was dissolved in water to obtain a solution A with a concentration of 0.15 mol / L, and a divalent soluble manganese salt, a lanthanum salt, a dispersant (sodium lauryl sulfate), and the solution A were dissolved in water to obtain a coating solution with a concentration of 0.2 mol / L, wherein the molar ratio of sodium ferrocyanide, divalent soluble manganese salt, and lanthanum salt was 1:0.95:0.03, and the content of the dispersant in each 1 L of the coating solution was 1.5 mol.

[0080] (3) The precursor slurry of step (1) was put into a reactor, and under nitrogen protection, the coating liquid, NaOH solution and ammonia water were added to the reactor in parallel to carry out a second coprecipitation reaction. The parameters during the second coprecipitation reaction were controlled as follows: temperature of 70°C, pH value of 7, ammonia value, and rotation speed of 200 rpm. The reaction was carried out for 13 hours to obtain a coated sodium ion precursor material with a particle size D50 of 18 μm.

[0081] This embodiment further provides a sodium ion positive electrode material, and a preparation method thereof includes: sintering the above-mentioned coated sodium ion precursor material at 850° C. for 10 hours to obtain the sodium ion positive electrode material.

[0082] Example 4

[0083] The difference from Example 1 is that during the second coprecipitation, the ammonia value is 5 g / L.

[0084] Example 5

[0085] The difference from Example 1 is that during the second coprecipitation process, the pH value was 9.5.

[0086] Example 6

[0087] The difference from Example 2 is that the reaction time of the second coprecipitation is 2 h, so that the particle size D50 of the coated sodium ion precursor material is 8.2 μm.

[0088] Example 7

[0089] The difference from Example 1 is that the reaction time of the second coprecipitation is 35 h, so that the particle size D50 of the coated sodium ion precursor material is 26 μm.

[0090] Comparative Example 1

[0091] The difference from Example 1 is that no lanthanum salt is added in step (2). The precursor of this comparative example has a coating layer, and the coating layer is not doped with lanthanum.

[0092] Comparative Example 2

[0093] The difference from Example 1 is that step (2) and step (3) are not performed. The precursor of this comparative example does not have a coating layer.

[0094] Comparative Example 3

[0095] The difference from Example 1 is that the manganese salt in step (2) is replaced by an iron salt.

[0096] The precursor of this comparative example has a coating layer, and the coating layer is lanthanum-doped iron-based Prussian blue.

[0097] Comparative Example 4

[0098] The difference from Example 1 is that the lanthanum salt in step (2) is replaced by magnesium.

[0099] The precursor of this comparative example has a coating layer, which is a magnesium-doped manganese-based Prussian blue. Cyclic stability, manganese is easily dissolved

[0100] Application Examples

[0101] Positive electrodes were prepared using the sodium ion positive electrode materials of Examples 1-7 and Comparative Examples 1-4, and button cells were assembled. The positive electrode was prepared by mixing the sodium ion positive electrode material, a conductive agent (Super P), and PVDF in a mass ratio of 96:2:2 in NMP to obtain a positive electrode slurry, which was then coated onto aluminum foil and dried to obtain the positive electrode. Sodium metal was used as the negative electrode, and glass fiber was used as the separator. The electrolyte was prepared by adding 0.5 mol / L of the lithium salt NaPF6 to a mixture of propylene carbonate and ethyl methyl carbonate as a solvent, and adding 3 wt% of fluoroethylene carbonate to the solvent to obtain the electrolyte.

[0102] Performance testing:

[0103] In the voltage range of 2.0 to 4.8 V, the button battery was tested for its first discharge capacity at 0.1C, its first coulombic efficiency, and its capacity retention after 50 cycles at a charge and discharge rate of 1C. The results are shown in Table 1.

[0104] Table 1

[0105]

[0106] By comparing Example 1 with Examples 4-5, it can be seen that during the second co-precipitation process, the control of ammonia value and pH value is relatively important. If the ammonia value is too high or the pH value is too high, it will affect the morphology of the precursor primary particles and reduce the diffusion rate of sodium ions, thereby reducing the electrochemical performance of the battery.

[0107] By comparing Example 1 with Examples 6-7, it can be seen that Mn 2+ Jahn-Teller distortion is prone to occur. If the coating layer is too thin (Example 6), the effect of preventing Mn dissolution is reduced, which is not conducive to structural stability. If the coating layer is too thick (Example 7), ions cannot pass through quickly, which reduces the conductivity of the battery. Therefore, if the coating layer is too thin or too thick, the electrochemical performance of the battery will be reduced.

[0108] By comparing Example 1 with Comparative Examples 1-2, it can be seen that no coating layer is provided (Comparative Example 2), and the stability is poor; a coating layer is provided and lanthanum is not doped in the coating layer (Comparative Example 1), although it still has a certain effect of stabilizing the structure, the electrochemical performance is significantly reduced.

[0109] By comparing Example 1 with Comparative Example 3, it can be seen that the redox potential of manganese in manganese-based Prussian blue is much higher than that of iron, which can effectively improve the operating voltage and energy density during the charge and discharge process. In addition, the radius of iron ions in iron-based Prussian blue is much smaller than that of lanthanum ions. The forced insertion of lanthanum will lead to a sudden increase in local lattice stress, causing phase separation and significantly reducing material performance.

[0110] By comparing Example 1 with Comparative Example 4, it can be seen that manganese-based Prussian blue doped with magnesium ions will block the electron conduction path of MnHCF, seriously affecting the material rate performance, reducing the discharge capacity, coulombic efficiency and cycle performance.

[0111] The applicant states that the present invention is intended to illustrate the detailed methods of the present invention through the above-described embodiments, but the present invention is not limited to the above-described detailed methods, that is, it does not mean that the present invention must rely on the above-described detailed methods in order to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for various raw materials in the products of the present invention, addition of auxiliary ingredients, and selection of specific methods, etc., are all within the scope of protection and disclosure of the present invention.

Claims

1. A coated sodium ion precursor material, characterized in that: The sodium ion precursor material includes a sodium ion precursor core and a coating layer coated on the surface of the sodium ion precursor core, and the coating layer includes a lanthanum-doped manganese-based Prussian blue material.

2. The coated sodium ion precursor material according to claim 1, characterized in that The doping amount of lanthanum element in the lanthanum-doped manganese-based Prussian blue material is 0.5at% to 0.2at%; Preferably, the sodium ion precursor core comprises nickel iron manganese hydroxide; Preferably, the particle size D50 of the sodium ion precursor core is 8 μm to 18 μm; Preferably, the particle size D50 of the coated sodium ion precursor material is 10 μm to 25 μm.

3. A method for preparing a coated sodium ion precursor material according to claim 1 or 2, characterized in that: The preparation method comprises the following steps: (1) adding the mixed metal salt solution, the first precipitant solution, and the first complexing agent solution to the base liquid in parallel to perform a first coprecipitation reaction to obtain a slurry of the sodium ion precursor core; (2) Sodium ferrocyanide, a divalent soluble manganese salt, and a lanthanum salt are dissolved in water to prepare a coating solution, and the coating solution, a second precipitant solution, and a second complexing agent solution are added to a reactor containing a slurry of the sodium ion precursor core to perform a second coprecipitation reaction to obtain the coated sodium ion precursor material.

4. The preparation method according to claim 3, characterized in that The metal ions in the mixed metal salt solution of step (1) include nickel ions, divalent iron ions and manganese ions; Preferably, the molar concentration of the metal ions in the mixed metal salt solution in step (1) is 1.5 mol / L to 2 mol / L; Preferably, the base liquid in step (1) comprises water, a third precipitant and a third complexing agent, the pH of the base liquid is 10-11, the ammonia value of the base liquid is 7g / L-9g / L, the mass concentration of the third complexing agent in the base liquid is 7g / L-20g / L, and the concentration of the third precipitant in the base liquid is 15g / L-17g / L; Preferably, in step (1), the parameters of the first coprecipitation reaction are controlled as follows: temperature in the range of 40°C to 80°C, pH value in the range of 10 to 11, ammonia value in the range of 7g / L to 9g / L, rotation speed in the range of 280rpm to 400rpm, and reaction time in the range of 40h to 150h.

5. The preparation method according to claim 3 or 4, characterized in that The concentration of the coating solution in step (2) is 0.1 mol / L to 0.2 mol / L; Preferably, the divalent soluble manganese salt in step (2) includes at least one of manganese nitrate, manganese sulfate and manganese chloride; Preferably, the lanthanum salt in step (2) comprises lanthanum nitrate and / or hydrated lanthanum nitrate crystals; Preferably, the parameters during the second coprecipitation reaction in step (2) are controlled as follows: temperature in the range of 40° C. to 80° C., pH value in the range of 5 to 9, ammonia value in the range of 3 g / L to 4 g / L, rotation speed in the range of 80 rpm to 200 rpm, and reaction time in the range of 10 h to 30 h; Preferably, the method for preparing the coating solution in step (2) comprises: dissolving sodium ferrocyanide in water to obtain solution A, dissolving a divalent soluble manganese salt, a lanthanum salt, and the solution A in water to obtain a coating solution; Preferably, the concentration of sodium ferrocyanide in the solution A is 0.02 mol / L to 0.15 mol / L; Preferably, the molar ratio of sodium ferrocyanide, divalent soluble manganese salt and lanthanum salt in the coating solution is 1:(0.92-0.95):(0.03-0.05).

6. The preparation method according to any one of claims 3 to 5, characterized in that The coating solution in step (2) further comprises a dispersant, wherein the dispersant comprises at least one of polyvinyl pyrrolidone, polyethylene glycol, sodium citrate and sodium lauryl sulfate; Preferably, the amount of the dispersant added is: 1 mol to 1.5 mol of dispersant per 1 L of coating liquid.

7. The preparation method according to any one of claims 3 to 6, characterized in that The first complexing agent, the second complexing agent and the third complexing agent independently include at least one of ammonia water, sodium fluoride, sodium citrate and sodium lactate.

8. A sodium ion positive electrode material, characterized in that The sodium ion positive electrode material is prepared using the coated sodium ion precursor material according to claim 1 or 2.

9. A method for preparing the sodium ion positive electrode material according to claim 8, characterized in that: The preparation method comprises the following steps: Sintering the coated sodium ion precursor material according to claim 1 or 2 to obtain the sodium ion positive electrode material; Preferably, the sintering temperature is 750°C to 850°C; Preferably, the sintering time is 10 hours to 40 hours.

10. A sodium ion battery, comprising the sodium ion positive electrode material according to claim 8.

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