Method for reducing residual alkali of sodium ion battery positive electrode material through weak acid oxide composite coating

Abstract

The invention belongs to the technical field of sodium ion layered oxide positive electrode materials, and relates to a method for reducing residual alkali of a sodium ion battery positive electrode material through weak acid oxide composite coating, which comprises the following steps: 1, uniformly mixing a sodium source, a nickel-iron-manganese precursor, a lithium source and an oxide; 2, calcining the mixture in stages; 3, crushing the primary sintering material, and sieving; 4, uniformly mixing the obtained material with an acidic compound and a metal oxide compound; 5, carrying out secondary sintering on the obtained mixture; and 6, crushing the secondary sintered material, and sieving to obtain the acid / oxide composite coated sodium ion battery layered oxide positive electrode material. According to the invention, a dry mixing process is used, sintering is only needed in an air environment, and compared with a wet coating process, the process is simpler, the cost is lower, and the consumed time is shorter; through composite coating of boric acid and aluminum oxide, multiple effects of reducing residual alkali on the surface and improving the electrochemical performance of the material can be achieved while the structure and morphology of the material are not damaged.

Description

Technical Field

[0001] The invention belongs to the technical field of sodium ion layered oxide positive electrode materials and relates to a method for reducing residual alkali in sodium ion battery positive electrode materials by composite coating with weak acid oxides. Background Art

[0002] The rise of sodium-ion batteries stems from the exploration of potential alternatives to lithium-ion batteries. As the core technology in the current energy storage field, lithium-ion batteries widely support the rapid development of electric vehicles, smart homes, portable devices and other fields. However, with the expansion of the electric vehicle market and the popularization of renewable energy, the demand for energy storage has risen sharply, and the limited resources and rising prices of lithium have become prominent, prompting the industry to explore new energy storage solutions. Against this background, sodium-ion batteries have emerged with their unique advantages. They not only show high energy storage efficiency and excellent cycle stability, but also indicate broad application potential in electric vehicles and large-scale energy storage systems. When exploring the scope of sodium-ion battery cathode materials in depth, we have to mention the three major mainstream types of layered oxides, polyanions and Prussian blue. Among them, layered oxides have become the focus of scientific researchers due to their excellent energy density performance, better safety performance than lithium batteries, and excellent low-temperature resistance.

[0003] However, the poor air stability and high residual alkali content of the sodium ion layered oxide material system cannot be ignored. Specifically, when the layered oxide positive electrode material comes into contact with air, it is very easy to react with moisture (H2O) and carbon dioxide (CO2) in the environment to produce byproducts such as sodium carbonate, which in turn damages the electrochemical performance of the material. To meet this challenge, researchers have adopted an oxide coating strategy to build a barrier that effectively prevents the penetration of harmful components in the air and protects the structural stability of the sodium ion layered oxide material. On the other hand, the excessively high residual alkali content on the surface of the sodium ion layered oxide material is also a problem that needs to be solved urgently. These residual alkaline substances, such as sodium hydroxide (NaOH) and sodium carbonate (Na2CO3), will continue to release alkaline ions during the battery charge and discharge cycle, aggravating the polarization of the material and may cause gas production inside the battery, posing a threat to the battery's cycle stability and safety performance.

[0004] Existing technologies for reducing residual alkali are mainly aimed at high-nickel lithium-ion battery positive electrode materials. For high-nickel lithium-ion battery positive electrode materials, wet treatment is mostly used. While washing the residual alkali on the surface of the material with water, a layer of material that can further reduce the residual alkali on the surface of the material is coated; for sodium-ion battery positive electrode materials, because they are extremely sensitive to moisture, wet treatment is often not considered, and in industrial production, wet treatment consumes a lot of energy and is costly, making it difficult to achieve tonnage-level scale-up production. For example, in invention CN117976889A and invention CN118156479A, acidic ammonium salts and cobalt fluorosilicate, strong acid and weak base salts, are used to coat high-nickel lithium-ion ternary positive electrode materials, respectively. However, in sodium-ion batteries, the residual alkali on the surface of the material is mostly sodium carbonate, and the use of strong acid and weak base salts will react with a large amount of sodium carbonate, and may even damage the material itself. In the invention CN117936748A and the invention CN118054005A, an oxide mixture is used to coat the O3 type nickel-iron-manganese-based sodium positive electrode material, but in fact, the residual alkali reduction effect of this oxide coating is not obvious, and flocculation, gas production and other problems still occur in practical applications. In the invention CN118062908A, acidic substances such as boric acid are used to treat the material, but the introduction of boron elements to the surface does not significantly improve the cycle performance of the material, and the use of ethanol solution in the patent to clean the positive electrode material in advance will destroy the morphology and structure of the material surface, and it is difficult to scale up production. Therefore, a method for reducing surface residual alkali with simple process, low cost, short time consumption and no damage to the material structure and morphology is needed to solve the above problems. Summary of the invention

[0005] The technical solution adopted by the present invention to solve the technical problem is: a method for reducing the residual alkali of the positive electrode material of a sodium ion battery by composite coating of weak acid oxides, comprising the following steps:

[0006] Step S1, mixing a sodium source, a nickel-iron-manganese precursor, a lithium source and an oxide uniformly to obtain a mixture I;

[0007] Step S2, calcining the mixture I obtained in step S1 in stages, setting the sintering temperature of the first stage to 400° C. to 800° C., and the holding time to 4 h to 8 h; setting the sintering temperature of the second stage to 800° C. to 1000° C., and the sintering time to 10 h to 20 h, and setting the heating rate to 2 to 5° C. / min, to obtain the first sintered material;

[0008] Step S3, crushing the first sintered material obtained in step S2 and sieving it, the sieving screen includes: 600 mesh to 325 mesh, to obtain a granular material; the material particle size is 5-10 microns, and the target positive electrode material can be obtained below 800 mesh;

[0009] Step S4, uniformly mixing the granular material obtained in step S3 with the acidic compound and the metal oxide composite to obtain a mixture II;

[0010] Step S5, performing secondary sintering on the mixture II obtained in step S4 to obtain a second sintered material;

[0011] Step S6, crushing the second sintered material obtained in step S5 and sieving it, the sieving screen includes: 600 mesh to 325 mesh, to obtain an acid / oxide composite-coated sodium ion battery layered oxide positive electrode material.

[0012] Preferably, in step S1, the nickel-iron-manganese precursor is Ni a Fe b Mn c (OH)2, where the values ​​of a, b, and c range from 0 to 1.

[0013] Preferably, in step S1, the sodium source includes: one or more of sodium bicarbonate, sodium carbonate, sodium phosphate, sodium nitrate, sodium citrate, sodium hydroxide, sodium oxide, sodium peroxide, anhydrous sodium sulfate, sodium carboxymethyl cellulose, and sodium lactate; the lithium source includes: one or more of lithium carbonate, lithium hydroxide, lithium acetate, lithium nitrate, lithium oxide, lithium peroxide, lithium trioxide, and lithium chloride; the oxide includes: one or more of cobalt trioxide, titanium dioxide, magnesium oxide, calcium oxide, vanadium oxide, and zinc oxide.

[0014] Preferably, in step S1, the sodium salt, nickel iron manganese precursor, lithium salt and oxide are weighed and mixed according to the molar ratio of Na:NFM:Li:oxide=(0.92-1.05):2(1-xy):x:y, wherein x=0-0.1 and y=0-0.3.

[0015] Preferably, in step S1, a high-speed mixer is used for mixing, the rotation speed of the high-speed mixer is set to 600-1200 rpm, and the mixing time is 1-3 hours.

[0016] Preferably, in step S4, the acidic compound includes: one or more of oxalic acid, citric acid, boric acid, acetic acid, carbonic acid, and silicic acid; the coating amount of the acidic compound is 0 to 1.0 wt% of the mass of the first sintered material; the metal oxide includes: one or more of titanium oxide, aluminum oxide, copper oxide, tungsten oxide, zirconium oxide, tin oxide, and niobium oxide; the coating amount of the metal oxide is 0 to 1.0 wt% of the mass of the first sintered material.

[0017] More preferably, in step S4, when the acidic compound is boric acid, the purity of the boric acid is ≥99.9%, and the particle size of the boric acid is D50=5um; when the metal oxide is aluminum oxide, the purity of the aluminum oxide is ≥99.9%, and the particle size of the aluminum oxide is D50=20nm.

[0018] Preferably, in step S5, the secondary sintering temperature is 500° C. to 800° C., the sintering time is 4 h to 10 h, and the heating rate is set at 2 to 5° C. / min.

[0019] Preferably, in step S1, the nickel-iron-manganese precursor comprises a mixture of nickel oxide, manganese oxide and iron oxide.

[0020] The beneficial effects of the present invention are:

[0021] The present invention mixes a sodium source, a nickel iron manganese (NFM) precursor, a lithium source and an oxide in a high-speed mixer, and then performs gradient sintering on the mixture in an air atmosphere to obtain a primary sintering product. The primary sintering material and a certain amount of boric acid and aluminum oxide are then mixed in a high-speed mixer, and secondary sintering is performed in an air atmosphere to obtain a secondary sintering product, which is crushed and sieved to obtain a sodium ion battery layered oxide positive electrode material coated with boron and aluminum. Gradient sintering can control the sintering temperature and gradient so that the grain size and grain boundary inside the material are evenly distributed, thereby improving the electrochemical stability and cycle life of the material; in the composite coating, boric acid can neutralize part of the alkaline residual substances on the surface, further reducing the residual alkali of the material, and aluminum oxide can form a protective layer to prevent the material from being corroded by hydrofluoric acid, thereby improving the cyclic stability of the material; secondary sintering can re-combine part of the sodium source that has not been burned into the lattice with the oxide framework to form a sodium ion battery layered oxide positive electrode material with a higher sodium content. Therefore, the present invention uses a dry mixing process and only needs to be sintered in an air environment, which is simpler, less costly and less time-consuming than a wet coating process. Through the composite coating of boric acid and alumina, the multiple effects of reducing surface residual alkali and improving the electrochemical performance of the material can be achieved without destroying the material structure and morphology. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 2 are SEM images of the layered oxide positive electrode materials of Example 2 (a) of the present invention and Comparative Example 1 (b);

[0023] Figure 2 Graph showing the cycle performance of the layered oxide positive electrode materials in Examples 1-5 of the present invention and Comparative Examples 1-2. DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the relevant technologies in the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] refer to Figures 1-2 The purpose of this embodiment is to provide a method for preparing a layered oxide positive electrode material for a sodium ion battery with low residual alkali. The process is simple and the repeatability is high. The obtained layered oxide positive electrode material for a sodium ion battery has a higher specific capacity, better rate performance, higher air stability and longer cycle life. The specific scheme is as follows:

[0026] The preparation process includes the following steps:

[0027] S1, mixing the sodium source, nickel iron manganese precursor, lithium source and oxide in a high-speed mixer;

[0028] S2, calcining the mixture obtained in step S1 in an air atmosphere in stages, setting the first stage sintering temperature to 400°C-800°C, the holding time to 4h-8h, setting the second stage sintering temperature to 800°C-1000°C, the sintering time to 10h-20h, and setting the heating rate to 2-5°C / min, to obtain a primary sintered material;

[0029] S3, crushing the sintered product obtained in step S2 and passing it through a 400-mesh sieve;

[0030] S4, mixing the material obtained in step S3, the acidic compound and the metal oxide composite in a high-speed mixer;

[0031] S5, performing secondary sintering on the product obtained in step S4 under air atmosphere;

[0032] S6. The secondary sintered material obtained in step S5 is crushed and passed through a 400-mesh sieve to obtain an acid / oxide composite-coated sodium ion battery layered oxide positive electrode material.

[0033] In S1, the nickel-iron-manganese ternary precursor is Ni a Fe b Mn c (OH)2, wherein a, b, and c are any numbers between 0 and 1.

[0034] In S1, the sodium source in step (1) is one or more of sodium bicarbonate, sodium carbonate, sodium phosphate, sodium nitrate, sodium citrate, sodium hydroxide, sodium oxide, sodium peroxide, anhydrous sodium sulfate, sodium carboxymethyl cellulose or sodium lactate; the lithium source is one or more of lithium carbonate, lithium hydroxide, lithium acetate, lithium nitrate, lithium oxide, lithium peroxide, lithium trioxide, lithium chloride; the oxide is one or more of cobalt trioxide, titanium dioxide, magnesium oxide, calcium oxide, vanadium oxide, zinc oxide.

[0035] In S1, sodium salt: nickel iron manganese precursor: lithium salt are weighed and mixed according to the molar ratio of Na: NFM: Li: oxide = (0.92 ~ 1.05): 2 (1-xy): x: y, (x = 0 ~ 0.1, y = 0 ~ 0.3).

[0036] In S1, the speed of the high-speed mixer is set to 600-1200 rpm, and the mixing time is 1-3 h.

[0037] In S4, the acidic compound is one or more of oxalic acid, citric acid, boric acid, acetic acid, carbonic acid, and silicic acid; the coating amount of the acidic compound is 0 to 1.0 wt% of the mass of the sintered product; the oxide is one or more of titanium oxide, aluminum oxide, copper oxide, tungsten oxide, zirconium oxide, tin oxide, and niobium oxide; the coating amount of the oxide is 0 to 1.0 wt% of the mass of the sintered product.

[0038] When the acidic compound is boric acid, the purity is ≥99.9% and the particle size is D50=5um; when the oxide is aluminum oxide, the purity is ≥99.9% and the particle size is D50=20nm.

[0039] In S5, the secondary sintering temperature is 500°C to 800°C, the sintering time is 4h to 10h, and the heating rate is set to 2 to 5°C / min.

[0040] The experimental results are recorded in Table 1 below:

[0041]

[0042] Table 1

[0043] In this embodiment, the material itself does not use the ternary precursor Ni a Fe b Mn c(OH)2 but using nickel, manganese, iron oxides for mixing can also obtain a primary sintered material. In the process of making secondary batteries, the use of sodium hexafluorophosphate electrolyte or other salt electrolytes can also achieve the effect of performance testing. In addition to boric acid, the weak acid in the coating agent used in this embodiment can also be a mixture of one or more of acidic substances such as oxalic acid, citric acid, acetic acid, carbonic acid, and silicic acid, and the oxide can be a mixture of one or more of titanium oxide, aluminum oxide, copper oxide, tungsten oxide, zirconium oxide, tin oxide, and niobium oxide.

[0044] In this embodiment, firstly, the material coating adopts a simple high-speed mixer to perform dry mixing process, which is different from the water-based or ethanol-based wet process in the prior art. Secondly, the coating agent is a weak acid and an oxide composite coating, the weak acid can be boric acid, and the oxide can be nano-aluminum oxide. Thirdly, the weak acid is used to react with the residual alkali on the surface, and try not to destroy the surface lattice structure of the layered positive electrode material, and the oxide is used to form a protective layer to prevent the material from being corroded by the acid substances generated in the electrolyte during the cycle and the dissolution of transition metals.

[0045] In summary, the present invention is to mix the sodium source, nickel iron manganese precursor, lithium source and oxide in a high mixer, and then gradient sinter the mixture in an air atmosphere to obtain a primary sintering product. The primary sintered material and a certain amount of boric acid and aluminum oxide are then mixed in a high mixer, and secondary sintering is performed in an air atmosphere to obtain a secondary sintering product, which is crushed and sieved to obtain a boron-aluminum composite-coated sodium ion battery layered oxide positive electrode material; the present invention uses a dry mixing process and only needs to be sintered in an air environment. Compared with the wet coating process, the procedure is simpler, the cost is lower, and the time consumption is shorter. Through the composite coating of boric acid and aluminum oxide, the multiple effects of reducing the surface residual alkali and improving the electrochemical performance of the material can be achieved without destroying the material structure and morphology.

[0046] It should be emphasized that the above are only preferred embodiments of the present invention and do not limit the present invention in any form. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for reducing residual alkali in positive electrode materials of sodium ion batteries by composite coating of weak acid oxides, characterized in that: The preparation method comprises the following steps: Step S1, mixing a sodium source, a nickel-iron-manganese precursor, a lithium source and an oxide uniformly to obtain a mixture I; Step S2, calcining the mixture I obtained in step S1 in stages, setting the sintering temperature of the first stage to 400° C. to 800° C., and the holding time to 4 h to 8 h, so that the nickel-iron-manganese precursor is completely decomposed into nickel-iron-manganese oxide; setting the sintering temperature of the second stage to 800° C. to 1000° C., the sintering time to 10 h to 20 h, and the heating rate to 2 to 5° C. / min, to obtain the first sintered material; Step S3, crushing the first sintered material obtained in step S2 and sieving it, the sieving screen includes: 600 mesh to 325 mesh, to obtain a material with uniform particle size; Step S4, uniformly mixing the uniform particle size material obtained in step S3 with the acidic compound and the metal oxide composite to obtain a mixture II; Step S5, performing secondary sintering on the mixture II obtained in step S4 to obtain a second sintered material; Step S6, crushing the second sintered material obtained in step S5 and sieving it, the sieving screen includes: 600 mesh to 325 mesh, to obtain an acid / oxide composite-coated sodium ion battery layered oxide positive electrode material.

2. The method for reducing residual alkali in positive electrode materials of sodium ion batteries by composite coating of weak acid oxides according to claim 1, characterized in that: In step S1, the nickel-iron-manganese precursor is Ni a Fe b Mn c (OH)2, where the values ​​of a, b, and c range from 0 to 1.

3. The method for reducing residual alkali in positive electrode materials of sodium ion batteries by composite coating of weak acid oxides according to claim 1, characterized in that: In step S1, the sodium source includes: one or more of sodium bicarbonate, sodium carbonate, sodium phosphate, sodium nitrate, sodium citrate, sodium hydroxide, sodium oxide, sodium peroxide, anhydrous sodium sulfate, sodium carboxymethyl cellulose, and sodium lactate; the lithium source includes: one or more of lithium carbonate, lithium hydroxide, lithium acetate, lithium nitrate, lithium oxide, lithium peroxide, lithium trioxide, and lithium chloride; the oxide includes: one or more of cobalt trioxide, titanium dioxide, magnesium oxide, calcium oxide, vanadium oxide, and zinc oxide.

4. The method for reducing residual alkali in positive electrode materials of sodium ion batteries by composite coating of weak acid oxides according to claim 1, characterized in that: In the step S1, the sodium salt, nickel iron manganese precursor, lithium salt and oxide are weighed and mixed according to the molar ratio of Na:NFM:Li:oxide=(0.92-1.05):2(1-xy):x:y, wherein x=0-0.1 and y=0-0.

3.

5. The method for reducing residual alkali in positive electrode materials of sodium ion batteries by composite coating of weak acid oxides according to claim 1, characterized in that: In the step S1, a high-speed mixer is used for mixing, the rotation speed of the high-speed mixer is set to 600-1200 rpm, and the mixing time is 1-3 hours.

6. The method for reducing residual alkali in positive electrode materials of sodium ion batteries by composite coating of weak acid oxides according to claim 1, characterized in that: In step S4, the acidic compound includes: one or more of oxalic acid, citric acid, boric acid, acetic acid, carbonic acid, and silicic acid; the coating amount of the acidic compound is 0 to 1.0 wt% of the mass of the first sintered material; the metal oxide includes: one or more of titanium oxide, aluminum oxide, copper oxide, tungsten oxide, zirconium oxide, tin oxide, and niobium oxide; the coating amount of the metal oxide is 0 to 1.0 wt% of the mass of the first sintered material.

7. The method for reducing residual alkali in positive electrode materials of sodium ion batteries by composite coating of weak acid oxides according to claim 6, characterized in that: In step S4, when the acidic compound is boric acid, the purity of the boric acid is ≥99.9%, and the particle size of the boric acid is D50=5um; when the metal oxide is aluminum oxide, the purity of the aluminum oxide is ≥99.9%, and the particle size of the aluminum oxide is D50=20nm.

8. The method for reducing residual alkali in positive electrode materials of sodium ion batteries by composite coating of weak acid oxides according to claim 1, characterized in that: In the step S5, the secondary sintering temperature is 500° C. to 800° C., the sintering time is 4 h to 10 h, and the heating rate is set at 2 to 5° C. / min.

9. The method for reducing residual alkali in positive electrode materials of sodium ion batteries by composite coating of weak acid oxides according to claim 1, characterized in that: In the step S1, the nickel-iron-manganese precursor includes a mixture of nickel oxide, manganese oxide and iron oxide.

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