Preparation method and application of high-capacity battery active material

Abstract

The present invention discloses a method for preparing a high-capacity battery active material and its application. The method comprises mixing a ferric hydroxide colloid with a carbon source, spray-drying the resulting mixture to obtain carbon-doped nano-iron oxide, mixing the nano-iron oxide with a lithium source, sintering the mixture under an inert atmosphere, mixing the sintered material, an organic polymer, and an organic solvent, and wet-grinding the resulting ground material under a protective atmosphere. The resulting ground material is spray-dried under an inert atmosphere, and the resulting dried material is sintered under an inert atmosphere to obtain the battery active material. The present invention uses ferric hydroxide colloid as the iron source, which has good colloid dispersibility and produces small iron oxide particles, which is beneficial for the subsequent preparation of small particles of Li5FeO4. Introducing a conductive carbon source into the ferric hydroxide colloid can not only prevent the material from melting and growing, making the synthesized particles smaller, but also improve the conductive properties of the material. Adding an organic polymer during the sand milling process can form a relatively dense coating layer on the material surface, further improving the stability and conductive properties of the material.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion battery materials, and in particular relates to a preparation method of a high-capacity battery active material and application thereof. Background Art

[0002] Currently, new energy vehicles are placing increasingly higher demands on the range of their power batteries, which in turn places higher demands on the cycle capacity of power battery materials. As is well known, during the initial charge and discharge of lithium-ion batteries, due to the formation of the SEI film, lithium ions cannot be 100% returned to the positive electrode, but some lithium ions are lost. This results in the lithium-ion battery's initial charge and discharge capacity and cycle capacity being insufficiently utilized. To address this issue, ultra-high-capacity materials are often added to the positive electrode material to improve it.

[0003] Li5FeO4 has the advantage of ultra-high theoretical capacity. Adding a certain amount of Li5FeO4 to the positive electrode material can effectively improve the problem of lithium ion loss during the first charge and discharge. The current method of synthesizing Li5FeO4 still has some problems. For example, the particles of the synthetic material are too large, resulting in a long lithium ion migration path, relatively low capacity, poor conductivity, and poor stability. To address these problems, it is generally considered to reduce the size of the material by reducing the particle size of iron oxide, but it is difficult to reach the nanoscale for iron oxide, and the nano-scale iron oxide on the market is expensive and in small supply, which does not have a cost advantage. In addition, among the current carbon coating technologies, there is a method of using gaseous low-molecular-weight organic matter to vapor-phase coat the surface of the material, which can also improve the conductivity and stability of the material to a certain extent, but vapor-phase coating has high requirements for safe production and equipment, which is not conducive to industrialization. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention provides a preparation method of a high-capacity battery active material and its application.

[0005] According to one aspect of the present invention, the following steps are proposed:

[0006] S1: mixing ferric hydroxide colloid with a carbon source, and spray drying the resulting mixture to obtain carbon-doped nano-iron oxide;

[0007] S2: mixing the nano-iron oxide with a lithium source, and sintering the mixture under an inert atmosphere to obtain a sintered material;

[0008] S3: mixing the sintering material, the organic polymer and the organic solvent, performing wet grinding under a protective atmosphere, and spray drying the obtained ground material under a protective atmosphere to obtain a dry material;

[0009] S4: The dried material is sintered under an inert atmosphere to obtain the battery active material.

[0010] In some embodiments of the present invention, in step S1, the method for preparing the ferric hydroxide colloid is: slowly adding an iron salt solution to hot water, accompanied by heating and stirring, and keeping the temperature for a period of time after the addition is completed to obtain the ferric hydroxide colloid. The ferric hydroxide colloid is prepared by heating the iron salt solution in water to cause a hydrolysis reaction. Furthermore, the water is deionized water with an impurity content of ≤1000ppm; further, the concentration of the iron salt solution is 0.1-12mol / L; further, the heating temperature is above 80°C; further, the holding time after the addition is completed is above 10 minutes.

[0011] In some embodiments of the present invention, in step S1, the temperature of the hot water is above 80°C.

[0012] In some embodiments of the present invention, in step S1, the carbon source is at least one of carbon nanotubes, conductive carbon black, graphite powder, polyethyleneimine, glucose, or polyvinyl alcohol. Furthermore, the carbon source has a particle size Dv50 of 0.5-3 μm.

[0013] In some embodiments of the present invention, in step S1, the spray drying temperature is 180-250°C.

[0014] In some embodiments of the present invention, in step S1, the mixed material needs to be stirred during the spray drying process, and the stirring speed is 100-500 rpm.

[0015] In some embodiments of the present invention, in step S1, the amount of the carbon source added is 5%-30% of the mass of the generated nano-iron oxide.

[0016] In some embodiments of the present invention, in step S1, the BET of the nano-iron oxide is 28-58m 2 / g, particle size Dv50 is 100-700nm.

[0017] In some embodiments of the present invention, in step S2, the lithium source is at least one of lithium hydroxide monohydrate, anhydrous lithium hydroxide or lithium oxide, and the molar ratio of lithium in the lithium source to iron in the nano-iron oxide is 5.0-5.8.

[0018] In some embodiments of the present invention, in step S2, the sintering temperature is 600-900° C. Further, the sintering time is 8-36 hours.

[0019] In some embodiments of the present invention, in step S3, the organic polymer is at least one of polypyrrole, polythiophene, polyacetylene, polyphenylene or polyphenylene vinylene. Furthermore, the amount of the organic polymer added is 0.1% to 3% of the theoretical mass of the obtained battery active material.

[0020] In some embodiments of the present invention, in step S3, the organic solvent is at least one of triethanolamine, N-methylpyrrolidone, 2-hydroxyethylamine, glycerol, or di-n-amyl ether. Compared to low-flash organic solvents such as methanol and ethanol, the organic solvent selected in the present invention has a relatively higher flash point, ensuring smooth spray drying.

[0021] In some embodiments of the present invention, in step S3, the wet grinding process comprises: first, adding the sintered material to the organic solvent, performing wet coarse grinding under a protective atmosphere, and then sand milling. During the sand milling process, the organic polymer is added to obtain the ground material. Furthermore, the coarse grinding speed is 400-800 rpm, and the particle size Dv50 of the coarsely crushed material is ≤20 μm. Furthermore, the sand milling speed is 2000-3000 rpm.

[0022] In some embodiments of the present invention, in step S3, the particle size Dv50 of the grinding material is 0.5-3 μm.

[0023] In some embodiments of the present invention, in step S3, the spray drying temperature is 150-220°C.

[0024] In some embodiments of the present invention, in step S4, the sintering temperature is 200-400° C. Further, the sintering time is 2-10 hours.

[0025] In some embodiments of the present invention, in step S4, the material obtained after the sintering is sieved, and the particle size Dv50 of the obtained battery active material is 2-8 μm.

[0026] The present invention also provides application of the preparation method in preparing lithium ion batteries.

[0027] According to a preferred embodiment of the present invention, there are at least the following beneficial effects:

[0028] 1. The present invention uses ferric hydroxide colloid as the iron source. Compared with ferric hydroxide synthesized directly using an iron source and alkali solution precipitation, the colloid has better dispersibility and the resulting iron oxide particles are smaller, which is conducive to the subsequent preparation of small particles of Li5FeO4. The material synthesized by iron source and alkali solution precipitation tends to agglomerate, resulting in larger particles and a higher plateau voltage. In addition, the present invention introduces a conductive carbon source into the ferric hydroxide colloid, which can not only prevent the material from melting and growing during the sintering process, making the synthesized particles smaller, but also helps improve the conductive properties of the material.

[0029] 2. After sintering to form massive Li5FeO4, the present invention performs wet grinding in an organic solvent and a protective atmosphere to prevent the material from deteriorating in the air, which can effectively reduce the particle size of the material, which is beneficial to shortening the migration path of lithium ions and thus improving the material capacity; the addition of organic polymers during the sand grinding process is to form a nano-coated carbon layer on the surface of the material. Compared with general low-molecular-weight organic matter, the organic polymers used in the present invention have large molecular chains and can form a relatively dense coating layer on the surface of the material, ensuring the coating effect, and the thickness is controllable, which can further improve the stability and conductive properties of the material; compared with vapor phase coating, the present invention has lower equipment requirements and higher safety.

[0030] 3. The high-capacity battery active material synthesized by the present invention has a simple synthesis process, low processing cost, high efficiency, and is easy to industrialize. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0032] Figure 1 Schematic diagram of the synthesis process of Example 1 of the present invention;

[0033] Figure 2 This is a SEM image of the iron oxide synthesized in Example 1;

[0034] Figure 3 This is a SEM image of Li5FeO4 synthesized in Example 1;

[0035] Figure 4 TEM image of Li5FeO4 synthesized in Example 1;

[0036] Figure 5 This is the charge-discharge curve of Li5FeO4 synthesized in Example 1;

[0037] Figure 6 This is the SEM image of Li5FeO4 synthesized in Comparative Example 1;

[0038] Figure 7 The charge-discharge curve of Li5FeO4 synthesized in Comparative Example 1;

[0039] Figure 8 This is the SEM image of Li5FeO4 synthesized in Comparative Example 2;

[0040] Figure 9 This is the charge and discharge curve of Li5FeO4 synthesized in Comparative Example 2. DETAILED DESCRIPTION

[0041] The following will clearly and completely describe the concept and technical effects of the present invention in conjunction with the embodiments to fully understand the purpose, features and effects of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0042] Example 1

[0043] This example synthesized a high-capacity battery active material Li5FeO4, see Figure 1 The specific process is:

[0044] (1) Under heating conditions of 90°C, a 3L volume, 5mol / L concentration of ferric chloride solution was slowly added to deionized water. During the addition process, the solution in the container was stirred at a stirring speed of 80rpm. After the addition was completed, the solution was kept warm for 20min to form a ferric hydroxide colloidal solution. Graphite powder was added as a carbon source material, and its Dv50 was 1.5μm. The amount of graphite powder added was 6.5% of the mass of the theoretically formed nano-iron oxide after spray drying. The stirring was continued at a stirring speed of 300rpm and spray drying was performed at a spray drying temperature of 200°C. Carbon-doped nano-iron oxide was obtained. Its morphology is shown in FIG. Figure 2 The particle size of nano-iron oxide was measured to be 560nm and the BET value was 42m 2 / g.

[0045] (2) Nano-iron oxide and lithium hydroxide were mixed at high speed in a high-speed mixer, wherein the molar ratio of lithium to iron was 5.3, the mixing speed was 600 rpm, and the mixing time was 40 min to obtain a uniformly mixed material, which was then placed in a nitrogen atmosphere for high-temperature sintering at a sintering temperature of 680° C. and a sintering time of 25 h to obtain a sintered block material;

[0046] (3) The sintered block material was subjected to a roller coarse crushing treatment with a roller gap of 1.5 mm, and was added to a 2-hydroxyethylamine solvent and subjected to wet coarse crushing under a nitrogen atmosphere. The crusher speed was 650 rpm, and the particle size Dv50 of the coarse crushed material was 12 μm. The material was then subjected to high-speed sand milling with a sand mill speed of 2600 rpm and a sand milling time of 1.5 h. The particle size of the material after sand milling was 0.9 μm. A certain amount of polythiophene was added during the sand milling process, and the addition amount was 1% of the final theoretical synthetic material mass. After the sand milling, the material was spray dried under a nitrogen atmosphere at a drying temperature of 220° C. to obtain a dry material;

[0047] (4) The dried material was sintered at a low temperature of 520°C for 10 hours. After sintering, it was sieved through a 400-mesh sieve to obtain a high-capacity battery active material, Li5FeO4. The particle size Dv50 was measured to be 4 μm.

[0048] Characterization test: Li5FeO4 synthesized by this method, see Figure 3 , the material particles have good uniformity; see Figure 4 The synthetic material has a good coating effect and forms an obvious coating layer.

[0049] Example 2

[0050] This example synthesizes a high-capacity battery active material Li5FeO4. The specific process is as follows:

[0051] (2) Under heating conditions at 90°C, a 3L ferric chloride solution with a concentration of 5 mol / L was slowly added to deionized water, and during the addition process, the solution in the container was stirred at a stirring speed of 80 rpm. After the addition was completed, the solution was kept warm for 20 minutes to form a ferric hydroxide colloidal solution. Carbon nanotubes were added as a carbon source material in an amount of 6.5% of the mass of the theoretically formed nano-iron oxide after spray drying, and the stirring was continued at a stirring speed of 300 rpm. Spray drying was performed at a spray drying temperature of 200°C to obtain carbon-doped nano-iron oxide.

[0052] (2) Nano-iron oxide and lithium hydroxide were mixed at high speed in a high-speed mixer, wherein the molar ratio of lithium to iron was 5.3, the mixing speed was 600 rpm, and the mixing time was 40 min to obtain a uniformly mixed material, which was then placed in a nitrogen atmosphere for high-temperature sintering at a sintering temperature of 680° C. and a sintering time of 25 h to obtain a sintered block material;

[0053] (3) The sintered block material was subjected to a roller coarse crushing treatment with a roller gap of 1.5 mm, and was added to N-methylpyrrolidone solvent and subjected to wet coarse crushing under a nitrogen atmosphere with a crusher speed of 650 rpm. It was then subjected to high-speed sand milling with a sand mill speed of 2600 rpm and a sand milling time of 1.5 h. The particle size of the material after sand milling was 0.9 μm. A certain amount of polyphenylene was added during the sand milling process, and the addition amount was 1% of the final theoretical synthetic material mass. After the sand milling, it was spray dried under a nitrogen atmosphere at a drying temperature of 220°C to obtain a dry material;

[0054] (4) The dried material is subjected to low-temperature sintering at a sintering temperature of 550°C for 10 hours. After sintering, it is sieved through a 400-mesh sieve to obtain Li5FeO4, a high-capacity battery active material.

[0055] Comparative Example 1

[0056] This comparative example synthesized a carbon-free Li5FeO4. The difference from Example 1 is that no carbon source and organic polymer were added. The specific process is as follows:

[0057] (1) Under heating conditions at 90°C, a 3L ferric chloride solution with a concentration of 5mol / L was slowly added to deionized water. During the addition process, the solution in the container was stirred at a stirring speed of 80rpm. After the addition was completed, the solution was kept warm for 20min to form a ferric hydroxide colloidal solution, which was then spray-dried at a spray drying temperature of 200°C to obtain nano-iron oxide. The particle size Dv50 of the nano-iron oxide was measured to be 890nm, and the BET value was 31m 2 / g.

[0058] (2) Nano-iron oxide and lithium hydroxide were mixed at high speed in a high-speed mixer, wherein the molar ratio of lithium to iron was 5.3, the mixing speed was 600 rpm, and the mixing time was 40 min to obtain a uniformly mixed material, which was then placed in a nitrogen atmosphere for high-temperature sintering at a sintering temperature of 680° C. and a sintering time of 25 h to obtain a sintered block material;

[0059] (3) The sintered block material was subjected to a roller coarse crushing treatment with a roller gap of 1.5 mm, and was added to a 2-hydroxyethylamine solvent. It was wet coarsely crushed under a nitrogen atmosphere with a crusher speed of 650 rpm. The particle size Dv50 of the coarsely crushed material was 12 μm. It was then subjected to high-speed sand milling with a sand mill speed of 2600 rpm and a sand milling time of 1.5 h. The particle size of the sand milled material was 1.2 μm. It was spray dried under a nitrogen atmosphere at a drying temperature of 220°C to obtain a dry material, which was passed through a 400-mesh sieve to obtain the battery active material Li5FeO4, and its particle size Dv50 was measured to be 5.2 μm.

[0060] Characterization test: Li5FeO4 synthesized by this method, see Figure 6 , the material particles have good uniformity.

[0061] The particle size of the nano-iron oxide obtained in this comparative example is larger than that of Example 1. This is because graphite powder is added to the iron hydroxide colloid in Example 1, which can prevent the iron oxide from melting and growing. Therefore, the particle size of Example 1 is smaller, and the particle size of the final product is also smaller.

[0062] Comparative Example 2

[0063] This comparative example synthesized a battery active material Li5FeO4. The difference from Example 1 is that dry crushing was adopted. The specific process is as follows:

[0064] (1) The nano-iron oxide of Example 1 and lithium hydroxide were mixed at high speed in a high-speed mixer, wherein the molar ratio of lithium to iron was 5.3, the mixing speed was 600 rpm, and the mixing time was 40 min to obtain a uniformly mixed material, which was then placed in a nitrogen atmosphere for high-temperature sintering at a sintering temperature of 680° C. and a sintering time of 25 h to obtain a sintered block material;

[0065] (2) The sintered block material is subjected to a roller coarse crushing treatment with a roller gap of 1.5 mm, and is dry crushed by air flow milling. After the air flow milling, a certain amount of polythiophene is added for dry mixing, and the addition amount is 1% of the final theoretical synthetic material mass. The sintering is carried out in a nitrogen atmosphere at a sintering temperature of 520°C.

[0066] (3) The sintered material was passed through a 400-mesh sieve to obtain the battery active material Li5FeO4, and its particle size Dv50 was measured to be 8.2 μm.

[0067] Characterization test: Li5FeO4 obtained by this synthesis method, see Figure 8 , it can be seen from the figure that the particles of the material formed are relatively large.

[0068] Comparative Example 3

[0069] This comparative example synthesizes a battery active material Li5FeO4. The difference from Example 1 is that low molecular weight organic matter is used instead of high molecular weight polymer at the end. The specific process is as follows:

[0070] A sintered block material was prepared according to the process of steps (1) and (2) of Example 1, and the sintered block material was subjected to a roller coarse crushing treatment with a roller gap of 1.5 mm. The coarse crushed material was added to a 2-hydroxyethylamine solvent, and wet coarse crushing was performed under a nitrogen atmosphere. The crusher speed was 650 rpm, and the particle size Dv50 of the coarse crushed material was 12 μm. The material was then subjected to high-speed sand milling with a sand mill speed of 2600 rpm and a sand milling time of 1.5 h. The particle size of the material after sand milling was 0.9 μm. A certain amount of glucose was added during the sand milling process, and the addition amount was 1% of the final theoretical synthetic material mass. After the sand milling, the material was spray dried under a nitrogen atmosphere at a drying temperature of 220° C. to obtain a dry material.

[0071] The dried material was sintered at a temperature of 550°C for 10 hours and passed through a 400-mesh sieve to obtain the battery active material Li5FeO4.

[0072] Test example

[0073] Li₅FeO₄ from Examples 1 and 2, Comparative Examples 1, 2, and 3 were fabricated into button cells, undergoing the following steps: ① Slurry preparation: 4g of the material was weighed and mixed with a conductive agent and a binder, with the material:conductive agent:binder ratio being 8:1:1. The binder used was PVDF, and the conductive agent was conductive carbon. ② Coating: Coating was performed on aluminum foil using a doctor blade. ③ Drying: Drying the coated electrode in a vacuum drying oven at 120°C for 2 hours. ④ Pressing: Pressing the dried electrode using a double-roll press. ⑤ Assembling the battery components, including the positive and negative electrode sheets, separator, and electrolyte, into button cells. The specific capacity was tested at a charging voltage of 4.25V and a charge rate of 0.1C. The results are shown in Table 1.

[0074] Table 1

[0075] Sample number Charging capacity mAh / g Example 1 705 Example 2 698 Comparative Example 1 220 Comparative Example 2 545 Comparative Example 3 621

[0076] It can be seen from Table 1 that the charging capacity of Comparative Example 3 is lower than that of Example 1. This is because the carbon coating material of Comparative Example 3 is a low-molecular organic matter, and the carbon coating layer formed is not as dense as that of Example 1, resulting in a decrease in capacity.

[0077] Figure 5 This is the charge-discharge curve of Li5FeO4 synthesized in Example 1. It can be seen from the figure that its capacity can reach 705mAh / g.

[0078] Figure 7This is the charge-discharge curve of Li5FeO4 synthesized in Comparative Example 1. It can be seen from the figure that its capacity is 220 mAh / g, which is significantly lower than the capacity of the material doped and coated with carbon source in Example 1, indicating that carbon doping and coating can greatly improve the material capacity.

[0079] Figure 9 This is the charge-discharge curve for Li5FeO4 synthesized in Comparative Example 2. The figure shows a capacity of 545 mAh / g, approximately 160 mAh / g lower than the smaller Li5FeO4 particles synthesized using wet grinding in Example 1. This indicates that wet grinding can effectively reduce the particle size of the material, thereby shortening the migration path of lithium ions and increasing the material's capacity.

[0080] While the embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to the embodiments described above. Various modifications may be made within the scope of knowledge possessed by a person skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof may be combined with one another unless there is a conflict.

Claims

1. A method for preparing a battery active material, characterized in that: The following steps are involved: S1: mixing ferric hydroxide colloid with a carbon source, and spray drying the resulting mixture to obtain carbon-doped nano-iron oxide; S2: mixing the nano-iron oxide with a lithium source, and sintering the mixture under an inert atmosphere to obtain a sintered material; S3: mixing the sintering material, the organic polymer and the organic solvent, performing wet grinding under a protective atmosphere, and spray drying the obtained ground material under a protective atmosphere to obtain a dry material; S4: sintering the dried material under an inert atmosphere to obtain the battery active material; In step S1, the preparation method of the ferric hydroxide colloid is: slowly adding an iron salt solution to hot water, accompanied by heating and stirring, and keeping the temperature for a period of time after the addition is completed to obtain the ferric hydroxide colloid; the temperature of the hot water is above 80°C.

2. The preparation method according to claim 1, characterized in that In step S1, the carbon source is at least one of carbon nanotubes, conductive carbon black, graphite powder, polyethyleneimine, glucose or polyvinyl alcohol.

3. The preparation method according to claim 1, characterized in that In step S1, the spray drying temperature is 180-250°C.

4. The preparation method according to claim 1, characterized in that In step S1, the amount of the carbon source added is 5%-30% of the mass of the generated nano-iron oxide.

5. The preparation method according to claim 1, characterized in that In step S2, the sintering temperature is 600-900°C.

6. The preparation method according to claim 1, characterized in that In step S3, the organic polymer is at least one of polypyrrole, polythiophene, polyacetylene, polyphenylene or polyphenylene vinylene.

7. The preparation method according to claim 1, characterized in that In step S3, the particle size Dv50 of the grinding material is 0.5-3 μm.

8. The preparation method according to claim 1, characterized in that In step S4, the sintering temperature is 400-600°C.

9. Use of the preparation method according to any one of claims 1 to 8 in the preparation of lithium ion batteries.

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