Method for reducing pores formed among particles during sintering of composite ferric sodium pyrophosphate

Abstract

The invention discloses a method for reducing pores formed among particles during sintering of composite ferric sodium pyrophosphate, which comprises the following steps: step 1, preparation of precursor slurry: mixing, stirring and grinding an iron source, a phosphorus source, a sodium source, a carbon source and deionized water to obtain the precursor slurry; wherein the stoichiometric ratio of the iron source to the phosphorus source to the sodium source is 3: 4: 4, and the chemical formula of the synthesized composite ferric sodium pyrophosphate is Na4Fe3 (PO4) 2P2O7; 2, carrying out spray drying on the precursor slurry to obtain a dried precursor; and step 3, loading the dried precursor in a graphite sagger, and then feeding the dried precursor into a roller kiln for sintering to obtain the composite ferric sodium pyrophosphate material. According to the invention, the solid content of the slurry is reduced to realize that the spray-dried composite phosphoric acid ferric pyrophosphate precursor forms thin-wall secondary spherical particles, and then through a unique sintering process curve, volatile components of the precursor are smoothly discharged in the sintering process, so that the composite phosphoric acid ferric pyrophosphate product without pores among particles is obtained.

Description

Technical Field

[0001] The invention relates to the field of production of composite sodium ferric phosphate pyrophosphate materials, and in particular to a method for reducing pores formed between particles of composite sodium ferric phosphate pyrophosphate during sintering. Background Art

[0002] During the large-scale mass production of composite phosphate sodium iron pyrophosphate materials, due to problems such as large loading volume and low heat transfer efficiency, the composite phosphate sodium iron pyrophosphate precursor will not be able to discharge volatiles in time during sintering, and the phase reaction will occur at the same time, resulting in larger pores between the material particles. Summary of the invention

[0003] The present invention aims to solve the above technical problems and provide a method for reducing the formation of pores between particles of composite phosphate sodium iron pyrophosphate during sintering. The specific technical scheme is as follows:

[0004] A method for reducing pores formed between particles of composite phosphate sodium iron pyrophosphate during sintering, comprising the following steps:

[0005] Step 1: Preparation of precursor slurry: Mix, stir and grind the iron source, phosphorus source, sodium source and carbon source with deionized water to obtain a precursor slurry; wherein the stoichiometric ratio of iron source: phosphorus source: sodium source is 3:4:4, and the chemical formula of the synthesized composite phosphate sodium iron pyrophosphate is Na4Fe3(PO4)2P2O7;

[0006] Step 2, spray drying the precursor slurry to obtain a dried precursor;

[0007] Step 3, the dried precursor is charged into a graphite sagger and then sent into a roller kiln for sintering to obtain a composite phosphate sodium iron pyrophosphate material;

[0008] Wherein, in step 1, the solid content of the slurry should be controlled at 10-20%;

[0009] In step 2, the spray drying air inlet temperature should be 200-250°C, the air outlet temperature should be 110-130°C, the moisture content of the precursor after drying is less than 3%, and the particle size D50 of the precursor after spray drying is between 5 and 30 μm;

[0010] In the step 3, the charge amount of the graphite sagger should be greater than 4 kg, and the sintering temperature should be set to three sintering platforms, wherein the temperature of the first sintering platform should be in the range of 150-250° C., and the platform time should be between 2 and 10 hours, the temperature of the second sintering platform should be in the range of 350-400° C., and the platform time should be between 1 and 5 hours, and the temperature of the third sintering platform should be in the range of 450-610° C., and the platform time should be between 6 and 8 hours.

[0011] In the step 3, the weight ratio of the carbon source to the composite sodium iron pyrophosphate material is 2.0%.

[0012] At the first sintering platform temperature, the water inside the material evaporates and forms water vapor and is discharged. At the second sintering platform temperature, the carbon source is carbonized to form a carbon coating on the surface of the particles. At the third sintering platform temperature, the iron source, phosphorus source, and sodium source react to form sodium ferric pyrophosphate particles. As the sintering time at this platform increases, the purity of the crystal phase gradually increases.

[0013] Wherein: the iron source is one or more of iron oxide, ferroferric oxide, ferrous oxalate, ferric phosphate and ferric nitrate.

[0014] Wherein: the phosphorus source is one or more of: ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, and phosphoric acid.

[0015] Wherein: the sodium source is one or more of sodium carbonate, sodium hydroxide, sodium oxalate and sodium bicarbonate.

[0016] Wherein: the carbon source is one or more of glucose, sucrose, starch, citric acid, maltose, asphalt and oxalic acid.

[0017] Technical principle: The present invention uses a spray drying device to dry the slurry. In the present invention, the solid content of the slurry is controlled to be relatively low (between 10% and 20%), and thin-walled hollow precursor particles can be obtained after spray drying; then, through a unique curve sintering, the precursor undergoes three processes of drainage, carbonization, and phase formation to obtain a composite phosphate sodium iron pyrophosphate finished material. Because heat is conducted from the outside to the inside during the sintering process, the drainage and exhaust are also from the outside to the inside. The thin-walled hollow precursor helps to discharge the water inside the particles during the sintering process, and avoids the carbon layer coating the surface of the particles after carbonization, which hinders the discharge of water inside the particles, causing water vapor and other volatile substances to expand inside the particles, and then discharge after expanding the gap between the particles, resulting in the formation of large pores inside the particles.

[0018] The beneficial effects of the present invention are as follows: the method of the present invention realizes the formation of thin-walled secondary spherical particles from the composite sodium ferric phosphate pyrophosphate precursor after spray drying by reducing the solid content of the slurry, and then realizes the smooth discharge of volatiles from the precursor during the sintering process through a unique sintering process curve, thereby obtaining a composite sodium ferric phosphate pyrophosphate product with no pores between particles, and the reduction of pores inside the material, which can increase the compaction density of the product and reduce the specific surface area of ​​the material. The product prepared by this technology has excellent compaction density and battery processing performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The drawings described herein are used to provide further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0020] Figure 1 The 0.2C first charge gram capacity curves of different embodiments of the present invention and comparison.

[0021] Figure 2 The 0.2C first discharge gram capacity curves of different embodiments of the present invention and comparison are shown.

[0022] Figure 3 This is the SEM electron micrograph of Comparative Example 1.

[0023] Figure 4 This is a SEM electron micrograph of Example 1. DETAILED DESCRIPTION

[0024] In order to more clearly illustrate the overall concept of the present application, a detailed description is given below in an illustrative manner in conjunction with the accompanying drawings.

[0025] Embodiment 1:

[0026] Ferric phosphate, diammonium phosphate and sodium carbonate are mixed according to the molar ratio of 3:4:4 of iron, phosphorus and sodium elements, and oxalic acid and deionized water accounting for 2% of the weight of the final product are added. The solid content of the slurry is controlled at 10%, and a precursor slurry is obtained after sand grinding.

[0027] The slurry is sent to a spray dryer for drying to obtain a precursor. The spray dryer has an air inlet temperature of 250° C. and an air outlet temperature of 110° C. to obtain a dried precursor.

[0028] The above precursor was sent to a roller kiln for sintering with a loading amount of 6 kg. A total of three sintering temperatures were set, with the first sintering temperature being 150°C and the sintering time being 6 hours, the second sintering temperature being 400°C and the sintering time being 2 hours, and the third sintering temperature being 610°C and the sintering time being 8 hours.

[0029] Embodiment 2:

[0030] Ferric phosphate, diammonium phosphate and sodium carbonate are mixed according to the molar ratio of 3:4:4 of iron, phosphorus and sodium elements, and oxalic acid and deionized water accounting for 2% of the weight of the final product are added. The solid content of the slurry is controlled at 15%, and a precursor slurry is obtained after sand grinding.

[0031] The slurry is sent to a spray dryer for drying to obtain a precursor. The spray dryer has an air inlet temperature of 250° C. and an air outlet temperature of 110° C. to obtain a dried precursor.

[0032] The above precursor was sent to a roller kiln for sintering with a loading amount of 6 kg. A total of three sintering temperatures were set, including a first sintering temperature of 200°C for 6 hours, a second sintering temperature of 350°C for 2 hours, and a third sintering temperature of 550°C for 8 hours.

[0033] Embodiment 3:

[0034] Ferric phosphate, diammonium phosphate and sodium carbonate are mixed according to the molar ratio of 3:4:4 of iron, phosphorus and sodium elements, oxalic acid and deionized water accounting for 2% of the weight of the final product are added, the solid content of the slurry is controlled at 20%, and the precursor slurry is obtained after sand grinding.

[0035] The slurry is sent to a spray dryer for drying to obtain a precursor. The spray dryer has an air inlet temperature of 250° C. and an air outlet temperature of 110° C. to obtain a dried precursor.

[0036] The above precursor was sent to a roller kiln for sintering with a loading amount of 6 kg. A total of three sintering temperatures were set, with the first sintering temperature at 250°C and a sintering time of 6 hours, the second sintering temperature at 300°C and a sintering time of 2 hours, and the third sintering temperature at 450°C and a sintering time of 8 hours.

[0037] Comparative Example 1:

[0038] Ferric phosphate, diammonium phosphate and sodium carbonate are mixed according to the molar ratio of 3:4:4 of iron, phosphorus and sodium elements, and oxalic acid and deionized water accounting for 2% of the weight of the final product are added. The solid content of the slurry is controlled at 40%, and a precursor slurry is obtained after sand grinding.

[0039] The slurry is sent to a spray dryer for drying to obtain a precursor. The spray dryer has an air inlet temperature of 250° C. and an air outlet temperature of 110° C. to obtain a dried precursor.

[0040] The above precursor was sent to a roller kiln for sintering with a loading amount of 6 kg. A total of three sintering temperatures were set, with the first sintering temperature being 150°C and the sintering time being 6 hours, the second sintering temperature being 400°C and the sintering time being 2 hours, and the third sintering temperature being 610°C and the sintering time being 8 hours.

[0041] Experimental results comparison table

[0042]

[0043] Explanation of using different sintering temperatures for the precursors obtained by spray drying with different slurry solid contents: the lower the slurry solid content, the larger the hollow spheres formed, and the greater the heat loss during the conduction process, so a higher temperature is required to sinter to obtain the final product. The present invention discharges water and other volatiles through the first stage of low-temperature and long-insulation drainage, carbonizes the carbon source in the second stage, forms a carbon coating layer on the surface of the particles, improves the electronic conductivity of the material, and finally reacts at the third stage temperature to obtain a composite phosphoric acid sodium iron pyrophosphate product.

[0044] Figure 3 This is a SEM micrograph of Comparative Example 1, in which the secondary particle wall thickness is large and there are many hollow pores inside the secondary particles. The pores will lead to poor particle morphology, poor processing performance and low compaction density when preparing before the battery core.

[0045] Figure 4 This is a SEM micrograph of Example 1. The secondary particle wall thickness is small, there are no hollow pores inside the secondary particles, the material compaction density is high, and the processing performance is good when it is prepared before the battery core.

[0046] The above examples are only embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for reducing the formation of pores between particles of composite phosphate sodium iron pyrophosphate during sintering, characterized in that: The following steps are involved: Step 1: Preparation of precursor slurry: Mix, stir and grind the iron source, phosphorus source, sodium source and carbon source with deionized water to obtain a precursor slurry; wherein the stoichiometric ratio of iron source: phosphorus source: sodium source is 3:4:4, and the chemical formula of the synthesized composite phosphate sodium iron pyrophosphate is Na4Fe3(PO4)2P2O7; Step 2: spray drying the precursor slurry to obtain a dried precursor; Step 3: The dried precursor is charged into a graphite sagger and then sent into a roller kiln for sintering to obtain a composite phosphate sodium iron pyrophosphate material.

2. The method according to claim 1, characterized in that: In step 1, the solid content of the slurry should be controlled at 10-20%.

3. The method according to claim 1, characterized in that: In step 2, the spray drying air inlet temperature should be 200-250° C., the air outlet temperature should be 110-130° C., the moisture content of the precursor after drying is less than 3%, and the particle size D50 of the precursor after spray drying is between 5 and 30 μm.

4. The method according to claim 1, characterized in that: In the step 3, the charge amount of the graphite sagger should be greater than 4 kg, and the sintering temperature should be set to three sintering platforms, wherein the temperature of the first sintering platform should be in the range of 150-250° C., and the platform time should be between 2 and 10 hours, the temperature of the second sintering platform should be in the range of 350-400° C., and the platform time should be between 1 and 5 hours, and the temperature of the third sintering platform should be in the range of 450-610° C., and the platform time should be between 6 and 8 hours.

5. The method according to claim 1, characterized in that: In the step 3, the weight ratio of the carbon source to the composite sodium iron pyrophosphate material is 2.0%.

6. The method according to claim 1, characterized in that: The iron source is one or more of iron oxide, ferroferric oxide, ferrous oxalate, ferric phosphate and ferric nitrate.

7. The method according to claim 1, characterized in that: The phosphorus source is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, and phosphoric acid.

8. The method according to claim 1, characterized in that: The sodium source is one or more of sodium carbonate, sodium hydroxide, sodium oxalate and sodium bicarbonate.

9. The method according to claim 1, characterized in that: The carbon source is one or more of glucose, sucrose, starch, citric acid, maltose, asphalt and oxalic acid.

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