Preparation method of sodium iron fluorophosphate active material for sodium ion battery

Abstract

The preparation method of the sodium iron fluorophosphate active material for the sodium-ion battery according to the present invention comprises the steps of: mixing a phosphorus source and an iron source with an adsorbent to form a powder; impregnating the above powder in an alkaline earth metal salt solution and under weakly acidic conditions; mixing the modified powder with a binder, a sodium source, and a fluorine source; and roasting and forming at a temperature below 400°C; wherein the adsorbent comprises kaolin and diatomaceous earth powder; and the binder comprises acetylene black. The impregnation of kaolin, diatomaceous earth, and the alkaline earth metal salt solution improves the adsorption capacity of phosphate particles, coats the iron source, and prevents the oxidation of the iron source during the preparation of sodium iron fluorophosphate. There is no need to strictly control the acidity and alkalinity of the solution, and the preparation is carried out with high process compatibility through simple method steps, reducing the production cost and improving the production efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion battery materials, and more specifically, to a method for preparing a sodium iron fluorophosphate active material for a sodium ion battery. Background Art

[0002] Lithium ion batteries are currently common new energy batteries, and their application and popularization have been greatly developed. However, lithium resources have low reserves in the earth's crust and limited resource quantity. On the basis of maintaining the advantageous performance of lithium ion batteries, finding materials that can be substituted and have abundant resources is one of the ways to solve the problem of resource shortage at present.

[0003] Sodium resources, which are similar to lithium in characteristics, are rich in reserves and environmentally friendly, and are an ideal large-scale electricity storage application technology.

[0004] Compared with the field of lithium ion batteries, there are still many technical problems to be overcome in the field of sodium ion batteries, and its technical maturity lags far behind that of lithium ion batteries. For example, in the existing cathode material system, materials of an iron-based system can be compounded with sodium materials to obtain battery materials with high capacity, long cycle life, and high stability.

[0005] However, iron-based system materials are prone to oxidation during the preparation process, resulting in a decrease in the overall conductivity of the composite material. In the prior art, for example, in Chinese invention patent - sodium iron fluorophosphate @C@RGO composite material and its preparation and application in sodium ion batteries, by controlling the pH within the range of 3-4 and combining with other conditions, the oxidation of the iron-based system is avoided. However, in actual production, precise control of the pH is costly, and it is not easy to monitor the overall pH change. Only point-by-point inspection can be carried out at specific points, which is likely to result in the pH system not being within the desired range. This may even lead to a decrease in the finished product rate of material preparation and a decrease in production efficiency. Summary of the Invention

[0006] Therefore, in the present invention, through the adsorption treatment of the phosphorus source and the iron source, it is expected that the iron source is first coated in the phosphorus source and the adsorbent to avoid the exposed area of the iron source and reduce oxidation. Then, through the binder, the phosphorus source, the iron source, the fluorine source, and the sodium source are complexed, and finally, the sodium iron fluorophosphate active material is prepared by impurity removal and calcination.

[0007] To achieve the above object, the specific technical solution adopted by the present invention is as follows:

[0008] The method for preparing a sodium iron fluorophosphate active material for a sodium ion battery provided by the present invention includes the following steps:

[0009] Adsorption treatment of the phosphorus source and the iron source:

[0010] Mix the phosphorus source and the iron source with the adsorbent to form a powder;

[0011] Impregnation modification:

[0012] Immerse the above powder in an alkaline earth metal salt solution under weakly acidic conditions;

[0013] Composite bonding:

[0014] Mix the modified powder with a binder, a sodium source, and a fluorine source;

[0015] Roasting and forming:

[0016] Roast and form at a temperature below 400 °C;

[0017] Among them, the adsorbent includes clay and diatomaceous earth powder;

[0018] The binder includes acetylene black.

[0019] Preferably, the particle size range of the clay powder is 2 - 10 μm.

[0020] Preferably, the particle size range of the diatomaceous earth powder is 2 - 10 μm.

[0021] Preferably, the carbon content of the acetylene black is greater than 99.5%.

[0022] Preferably, the sodium source is one or more combinations of sodium carbonate, sodium formate, sodium hydroxide, sodium acetate, and sodium fluoride.

[0023] Preferably, the fluorine source is one or two combinations of sodium fluoride and hydrofluoric acid.

[0024] Preferably, the phosphorus source is one or more combinations of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and sodium dihydrogen phosphate.

[0025] Preferably, the iron source is one or more combinations of iron citrate, ferrous oxalate, ferrous gluconate, iron agar lysine, iron phthalocyanine, and ferrocene.

[0026] Preferably, after the impregnation modification, the mixed powder is dried at 110 - 120 °C for 0.5 - 1.5 hours.

[0027] Preferably, the roasting procedure is as follows: 0 - 200 °C, with a heating rate of 3 °C / min and a holding time of 60 min; 200 - 400 °C, with a heating rate of 5 °C / min and a holding time of 120 min.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The impregnation of clay, diatomaceous earth and alkaline earth metal salt solution improves the adsorption capacity of phosphate particles, coats the iron source, and prevents the oxidation of the iron source during the preparation of sodium ferric pyrophosphate fluoride. It does not require strict pH control, and is prepared with high process compatibility through simple method steps, which reduces production costs and improves production efficiency.

[0030] In addition, adding acetylene black to the complexing agent has a bonding effect on the one hand, and a function of guiding and promoting carbon coating on the other hand.

[0031] The present invention will be further described below in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the XRD diagram in a preferred embodiment of the present invention.

[0033] Figure 2 This is a SEM image of a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0034] The present invention is further explained and illustrated by specific implementation modes below. It should be understood that the purpose of the following implementation modes is to make the technical solution of the present invention clearer and easier to understand, and does not limit the protection scope of the claims.

[0035] Example 1

[0036] This embodiment prepares a sodium iron pyrophosphate fluoride active material, including the following steps:

[0037] 1. Raw material activation:

[0038] Clay was crushed and industrial diatomite powder was sieved. The sieved material was taken, and 900g of clay powder and 600g of diatomite powder were weighed and mixed thoroughly. They were soaked in 4000mL of 1mol / L hydrochloric acid solution, and ultrasonically acidified for 12h. The mixture was filtered under negative pressure and washed with ultrapure water until neutral. The mixture was dried at 120℃, and then placed in a muffle furnace and calcined at 700℃ for 5h. The mixture was taken out and cooled to room temperature, and then ground through a 150-mesh sieve to obtain an activated powder.

[0039] 2. Impregnation modification:

[0040] Weigh 1000g of the activated mixed powder and mix it with diammonium phosphate and ferric citrate to 2500g. 3 mol / L calcium nitrate solution, fully mixed, magnetically stirred, supersaturated impregnation, impregnation for 10 hours, aging for 24 hours, negative pressure adsorption separation, drying at 120°C for 60 minutes, and then roasting at 450°C for 5 hours. After cooling and grinding through a 150-mesh sieve, modified diatomite modified with calcium oxide was obtained.

[0041] 3. Bonding and complexing:

[0042] The purpose of adding adhesives and complexing agents is to allow ferric citrate (in a coated state to avoid oxidation) and ammonium dihydrogen phosphate to bind to hydrofluoric acid and sodium fluoride.

[0043] The complexing agent includes acetylene black, which can effectively bond the ammonium dihydrogen phosphate and ferric citrate to hydrofluoric acid and sodium fluoride on the one hand, and guide and promote carbon coating on the other hand.

[0044] 4. Granulation, roasting and molding:

[0045] Weigh 800g of modified powder, 120g of ammonium carbonate, and 80g of sodium silicate nonahydrate respectively, mix them evenly, add 200g of water, stir to obtain mud, age for 20h, and granulate to obtain spherical particles of uniform size of 2-3mm. According to the roasting procedure: 0-200℃, heating rate of 3℃ / min, heat preservation for 60min; 200-400℃, heating rate of 5℃ / min, heat preservation for 120min. Roast the spherical particles according to the set procedure. Disc-shaped three-dimensional porous composite adsorption spherical particles can be obtained.

[0046] Example 2

[0047] This embodiment prepares a sodium iron pyrophosphate fluoride active material, including the following steps:

[0048] 1. Raw material activation:

[0049] Clay was crushed and industrial diatomite powder was sieved. The sieved material was taken, and 900g of clay powder and 600g of diatomite powder were weighed and mixed thoroughly. They were soaked in 4000mL of 1mol / L hydrochloric acid solution, and ultrasonically acidified for 12h. The mixture was filtered under negative pressure and washed with ultrapure water until neutral. The mixture was dried at 120℃, and then placed in a muffle furnace and calcined at 700℃ for 5h. The mixture was taken out and cooled to room temperature, and then ground through a 150-mesh sieve to obtain an activated powder.

[0050] 2. Impregnation modification:

[0051] Weigh 1000g of the activated mixed powder and mix it with sodium dihydrogen phosphate and ferrous gluconate to make up to 2500g. 3 mol / L calcium nitrate solution, fully mixed, magnetically stirred, supersaturated impregnation, impregnation for 10 hours, aging for 24 hours, negative pressure adsorption separation, drying at 120°C for 60 minutes, and then roasting at 450°C for 5 hours. After cooling, grinding and sieving, modified diatomite modified with calcium oxide was obtained.

[0052] 3. Bonding and complexing:

[0053] The purpose of adding adhesives and chelating agents is to allow ferrous gluconate (in a coated state to avoid oxidation) and sodium dihydrogen phosphate to bind to hydrofluoric acid and sodium formate.

[0054] The complexing agent includes acetylene black, which can effectively bond sodium dihydrogen phosphate and ferrous gluconate to hydrofluoric acid and sodium formate on the one hand, and guide and promote carbon coating on the other hand.

[0055] 4. Granulation, roasting and molding:

[0056] Weigh 800g of modified powder, 120g of ammonium carbonate, and 80g of sodium silicate nonahydrate respectively, mix them evenly, add 200g of water, stir to make mud, age for 20h, use a sugar coating machine to granulate and form, and make uniform 2-3mm spherical particles. According to the roasting procedure: 0-200℃, heating rate of 3℃ / min, heat preservation for 60min; 200-400℃, heating rate of 5℃ / min, heat preservation for 120min. Roast the spherical particles according to the set procedure. Disc-shaped three-dimensional porous composite adsorption spherical particles can be obtained.

[0057] Example 3

[0058] This embodiment prepares a sodium iron pyrophosphate fluoride active material, including the following steps:

[0059] 1. Raw material activation:

[0060] Clay was crushed and industrial diatomite powder was sieved. The sieved material was taken, and 900g of clay powder and 600g of diatomite powder were weighed and mixed thoroughly. They were soaked in 4000mL of 1mol / L hydrochloric acid solution, and ultrasonically acidified for 12h. The mixture was filtered under negative pressure and washed with ultrapure water until neutral. The mixture was dried at 120℃, and then placed in a muffle furnace and calcined at 700℃ for 5h. The mixture was taken out and cooled to room temperature, and then ground through a 150-mesh sieve to obtain an activated powder.

[0061] 2. Impregnation modification:

[0062] Weigh 1000g of the activated mixed powder and mix it with phosphoric acid and ferrous oxalate to make up to 2500g. 3 mol / L calcium nitrate solution, fully mixed, magnetically stirred, supersaturated impregnation, impregnation for 10 hours, aging for 24 hours, negative pressure adsorption separation, drying at 120°C for 60 minutes, and then roasting at 450°C for 5 hours. After cooling and grinding through a 150-mesh sieve, modified diatomite modified with calcium oxide was obtained.

[0063] 3. Bonding and complexing:

[0064] The purpose of adding a binder and a chelating agent is to allow ferrous oxalate (in a coated state to avoid oxidation) and diammonium hydrogen phosphate to bind to sodium fluoride.

[0065] The complexing agent includes acetylene black, which can effectively bond diammonium hydrogen phosphate and ferrous oxalate to sodium fluoride on the one hand, and guide and promote carbon coating on the other hand.

[0066] 4. Granulation, roasting and forming:

[0067] Weigh 800 g of modified powder, 120 g of ammonium carbonate, and 80 g of sodium silicate nonahydrate respectively. After uniform mixing, add 200 g of water, stir to prepare a mud material, age for 20 h, and granulate and form using a sugar coating machine to obtain spherical particles with uniform size of 2 - 3 mm. According to the roasting procedure: from 0 to 200 °C, the heating rate is 3 °C / min, and keep warm for 60 min; from 200 to 400 °C, the heating rate is 5 °C / min, and keep warm for 120 min. Roast the spherical particles according to the set procedure. Disk-shaped three-dimensional porous composite adsorption spherical particles can be obtained. The XRD pattern is shown in Figure 1 , and the SEM is shown in Figure 2 .

[0068] Comparative Example 1

[0069] Take 0.015 mol of ferric nitrate nonahydrate, 0.015 mol of ammonium dihydrogen phosphate, 0.02 mol of anhydrous sodium carbonate, 0.015 mol of ammonium fluoride, and 0.03 mol (molar ratio to iron is 2:1) of ascorbic acid. Then weigh 0.15 g of RGO (equivalent to 5% of the theoretical active material), dissolve it in deionized water, and adjust the pH to 3 - 4 using sulfurous acid. Evaporate the water at 80 °C and vacuum dry at 100 °C for 4 h. Put the obtained powder into a porcelain boat and sinter at 550 °C for 12 h in an argon atmosphere. Then Na4Fe3PO4P2O7F3@C@RGO is obtained. A material with high crystal phase purity is obtained.

[0070] The composite cathode material for sodium-ion batteries and a sodium sheet are assembled into a button battery. The voltage of the material can reach 3.6 V; at a 1C rate, after 100 cycles, the discharge specific capacity is 95 mAh / g, and the capacity retention rate is above 90%.

[0071] Comparative Example 2

[0072] Take 0.015 mol of ferric nitrate nonahydrate, 0.015 mol of ammonium dihydrogen phosphate, 0.02 mol of anhydrous sodium carbonate, 0.015 mol of ammonium fluoride, and 0.045 mol (molar ratio to iron is 3:1) of ascorbic acid. Then weigh 0.15 g of RGO, dissolve it in deionized water, and adjust the pH to 3 - 4 using sulfurous acid. Evaporate the water at 80 °C and vacuum dry at 100 °C for 4 h. Put the obtained powder into a porcelain boat and sinter at 550 °C for 12 h in an argon atmosphere. Then Na4Fe3PO4P2O7F3@C@RGO is obtained.

[0073] The composite cathode material for sodium-ion batteries and a sodium sheet are assembled into a button battery. At a 1C rate, after 100 cycles, the discharge specific capacity is 92 mAh / g, and the capacity retention rate is above 90%.

[0074] Comparative Example 3

[0075] Take 0.9085 g (5 mmol) of ferrous oxalate dihydrate and 1.2121 g (10 mmol) of anhydrous sodium dihydrogen phosphate, put them into a polytetrafluoroethylene ball milling jar, add acetone and ball mill for 6 h, then dry at 50 °C in a vacuum drying oven for 2 h, and grind for 1 h to obtain the precursor powder.

[0076] Heat the precursor powder in a tubular furnace with argon flowing through it at a heating rate of 2 °C / min to 560 °C and hold for 12 h, then cool with the furnace. After grinding the obtained product, the Na2FeP2O7 material is obtained.

[0077] Adjust the sintering temperature in the above preparation method to 600 °C and 640 °C respectively, and prepare the Na2FeP2O7 material according to the same method as above.

[0078] Perform a 1C constant current charge-discharge test at room temperature, and the charge-discharge cut-off voltage is 2.0 V - 4.0 V. After testing, the initial discharge specific capacity of the comparative material is 67.58 mAh / g, the discharge capacity after 100 cycles is 65.98 mAh / g, and the capacity retention rate is 97.63%.

[0079] Verification Example 1

[0080] Respectively take the materials prepared in Example 1 and Comparative Examples 1 - 3 to make button cells, and perform a constant current charge-discharge test at 1C at room temperature using a Neware battery test system. The test voltage range is 1.5 - 4.2 V, and the test results are shown in Table 1 below.

[0081] Table 1 Charge-discharge test results (1C, room temperature)

[0082]

[0083] The key technical points of Comparative Examples 1 and 2 are to maintain a pH of 3 - 4 and relatively strict temperature control conditions. In Comparative Example 3, the oxidation of the iron source was not controlled, lacking effective protective technical means, resulting in weak performance of the prepared sodium iron pyrophosphate cathode material.

[0084] Specifically, the comparison is as follows:

[0085] The discharge capacity of the cathode materials prepared in Comparative Examples 1 and 2 after 100 cycles is 39.7% higher than that of Comparative Example 3.

[0086] The capacity retention rates of Comparative Examples 1 - 3 and Example 1 are basically at the same level.

[0087] Compared with Comparative Examples 1 and 2, after 100 cycles, the discharge capacity and capacity retention rate of Example 1 are basically at the same level. However, Example 1 does not require strict control of the pH environment, and at the same time, the preparation temperature condition is lower, which makes the preparation environment compatibility of the sodium iron pyrophosphate cathode material better and the preparation cost lower.

[0088] The present invention is described by way of examples, but does not constitute a limitation to the present invention. With reference to the description of the present invention, other variations of the disclosed examples, such as those easily conceivable by professionals in the art, should fall within the scope defined by the claims of the present invention.

Claims

1. A preparation method of sodium iron fluorophosphate active material for sodium-ion batteries, characterized in that: Adsorption treatment of phosphorus source and iron source: Mix the phosphorus source and iron source with an adsorbent to form a powder. Impregnation modification: Impregnate the above powder in an alkaline earth metal salt solution under weakly acidic conditions. Composite bonding: Mix the modified powder with a binder, a sodium source, and a fluorine source. Calcination and molding: Calcine and mold at a temperature below 400 °C. Wherein, the adsorbent includes kaolin and diatomite powder. The binder includes acetylene black.

2. The preparation method of sodium iron fluorophosphate active material for sodium-ion batteries according to claim 1, characterized in that: The particle size range of the kaolin powder is 2 - 10 μm.

3. The preparation method of sodium iron fluorophosphate active material for sodium-ion batteries according to claim 1, characterized in that: The particle size range of the diatomite powder is 2 - 10 μm.

4. The preparation method of sodium iron fluorophosphate active material for sodium-ion batteries according to claim 1, characterized in that: The carbon content of the acetylene black is greater than 99.5%.

5. The preparation method of sodium iron fluorophosphate active material for sodium-ion batteries according to claim 1, characterized in that: The sodium source is one or a combination of sodium carbonate, sodium formate, sodium hydroxide, sodium acetate, and sodium fluoride.

6. The preparation method of sodium iron fluorophosphate active material for sodium-ion batteries according to claim 1, characterized in that: The fluorine source is one or a combination of sodium fluoride and hydrofluoric acid.

7. The preparation method of sodium iron fluorophosphate active material for sodium-ion batteries according to claim 1, characterized in that: The phosphorus source is one or a combination of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and sodium dihydrogen phosphate.

8. The preparation method of sodium iron fluorophosphate active material for sodium-ion batteries according to claim 1, characterized in that: The iron source is one or a combination of ferric citrate, ferrous oxalate, ferrous gluconate, lysine iron agar, phthalocyanine iron, and ferrocene.

9. The preparation method of sodium iron fluorophosphate active material for sodium-ion batteries according to claim 1, characterized in that: After the impregnation modification, the mixed powder is dried at 110 - 120 °C for 0.5 - 1.5 hours.

10. The preparation method of sodium iron fluorophosphate active material for sodium-ion batteries according to claim 1, characterized in that: The procedure for calcination and molding: 0 - 200 °C, heating rate is 3 °C / min, holding for 60 min; 200 - 400 °C, heating rate is 5 °C / min, holding for 120 min.

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