A sodium iron pyrophosphate phosphate cathode material and a preparation method thereof

Abstract

The present invention provides a method for preparing a sodium iron pyrophosphate phosphate cathode material with the chemical formula Na4Fe3+x(PO4)2(P2O7)@C; -0.3 ≤ x ≤ 0.3, where C represents a carbon coating layer formed on the sodium iron pyrophosphate phosphate cathode material. In the preparation method, the carbon source of the carbon coating layer is a mixture of an organic carbon source and an inorganic carbon source. The method for preparing the sodium iron pyrophosphate phosphate cathode material of the present invention forms a carbon coating layer on the surface of the sodium iron pyrophosphate phosphate cathode material through sintering by using a carbon source composed of an organic carbon source and an inorganic carbon source, and selects the types of the organic carbon source and the inorganic carbon source and controls the weight ratio of the organic carbon source and the inorganic carbon source, so as to prepare a sodium iron pyrophosphate phosphate cathode material with a higher pure phase, reduce the content of impurity phases, improve the specific capacity and the initial efficiency of the sodium iron pyrophosphate phosphate cathode material, and have a beneficial effect on the cycle stability.

Description

Technical Field

[0001] The present invention relates to the field of cathode materials for batteries, and particularly to a sodium iron pyrophosphate phosphate cathode material and a preparation method thereof. Background Art

[0002] In sodium ion battery materials, in order to enable sodium ions to obtain a larger diffusion channel in the crystal to stabilize the crystal structure and improve the electrochemical performance of the electrode material, PO4 3- , P2O7 4- etc. are introduced into the electrode material system, and such materials are collectively referred to as polyanions.

[0003] Pyrophosphates have the advantages of high energy density and high power density. Compared with sulfates and phosphates, they have higher thermal stability and a relatively easy preparation process, making them the polyanion materials closest to practical applications at present. Currently, sodium iron pyrophosphate phosphate products on the market are basically affected by process conditions and have a small amount of impurities such as sodium iron phosphate and sodium pyrophosphate iron, resulting in serious negative impacts on the specific capacity and cycle stability of sodium iron pyrophosphate phosphate battery materials. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a sodium iron pyrophosphate phosphate cathode material and a preparation method thereof.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is: a preparation method of a sodium iron pyrophosphate phosphate cathode material, and the chemical formula of the sodium iron pyrophosphate phosphate cathode material is Na4Fe 3+x (PO4)2(P2O7)@C; -0.3 ≤ x ≤ 0.3, where C represents a carbon coating layer formed by the sodium iron pyrophosphate phosphate cathode material;

[0006] In the preparation method, the carbon source of the carbon coating layer is a mixture of an organic carbon source and an inorganic carbon source. The organic carbon source is at least one of lauric acid, sodium laurate, and maltodextrin, and the inorganic carbon source is at least one of graphite milk and Ketjen black; the weight ratio of the organic carbon source to the inorganic carbon source is 1:(0.3 - 3).

[0007] The above preparation method of the sodium iron pyrophosphate phosphate cathode material forms a carbon coating layer on the surface of the sodium iron pyrophosphate phosphate cathode material by sintering using a carbon source composed of an organic carbon source and an inorganic carbon source. Moreover, by selecting the types of the organic carbon source and the inorganic carbon source and controlling the weight ratio of the organic carbon source to the inorganic carbon source, a sodium iron pyrophosphate phosphate cathode material with a higher pure phase is prepared, the content of impurities is reduced, the specific capacity and the initial efficiency of the sodium iron pyrophosphate phosphate cathode material are improved, and it has a beneficial effect on the cycle stability. And a pure-phase sodium iron pyrophosphate phosphate cathode material can be obtained at a lower sintering temperature.

[0008] Preferably, the sodium iron pyrophosphate phosphate cathode material is prepared from an iron source, a sodium source, a phosphorus source, and a carbon source.

[0009] Preferably, the weight content of the carbon coating layer in the sodium iron pyrophosphate phosphate cathode material is 0.5% to 3%.

[0010] Preferably, the organic carbon source in the carbon source is maltodextrin and the inorganic carbon source is Ketjen black.

[0011] In the above method for preparing the sodium iron pyrophosphate phosphate cathode material, when the organic carbon source in the carbon source is maltodextrin and the inorganic carbon source is Ketjen black, the specific capacity and cycle stability of the sodium iron pyrophosphate phosphate cathode material are better.

[0012] Preferably, the preparation method includes the following steps:

[0013] (1) After mixing the iron source, the dispersant, the sodium source, the phosphorus source, and the carbon source evenly in deionized water, perform sand grinding in a sand mill;

[0014] (2) Spray-dry the liquid after sand grinding in step (1) to obtain a precursor mixed powder;

[0015] (3) Ball-mill the precursor mixed powder in step (2);

[0016] (4) Sinter the precursor mixed powder in step (3) in an inert gas atmosphere at 500 - 550 °C for 8 - 15 h to obtain the sodium iron pyrophosphate phosphate cathode material;

[0017] (5) Air-flow crush the sodium iron pyrophosphate phosphate cathode material in step (4).

[0018] In the above method for preparing the sodium iron pyrophosphate phosphate cathode material, wet mixing is adopted followed by spray drying, and the carbon source is mixed together in the wet mixing step. After spray drying, ball milling is performed, so that the phase of the sodium iron pyrophosphate phosphate cathode material prepared after sintering is purer.

[0019] Preferably, in step (1), the dispersant accounts for 0.5 wt% - 10 wt% of the total weight of the iron source, the dispersant, the sodium source, the phosphorus source, and the carbon source, and the dispersant is at least one of PVA, PEG, PVB, and CMC.

[0020] Preferably, in step (1), after sand grinding, the average particle size of the particles is controlled to be 0.5 - 2 μm.

[0021] Preferably, in step (1), the rotational speed of the sand mill for sand grinding is 1000 - 1400 rpm, and the sand grinding duration is 3 - 6 h.

[0022] Preferably, in step (2), the inlet air temperature for spray drying is 220 - 260°C, the outlet air temperature is 110 - 140°C, the atomization pressure is 0.3 - 0.5 Mpa, and the feeding speed is 20 rmp - 40 rmp.

[0023] Preferably, in step (3), the ball-to-material ratio for ball milling = (6 - 25):1.

[0024] Preferably, the sodium source is at least one of sodium carbonate, sodium bicarbonate, sodium acetate, sodium citrate, disodium hydrogen phosphate, sodium hydrogen citrate, and sodium hydroxide.

[0025] Preferably, the phosphorus source is at least one of phosphoric acid, sodium dihydrogen phosphate, trisodium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium pyrophosphate, trisodium monohydrogen pyrophosphate, disodium dihydrogen pyrophosphate, and sodium trihydrogen monopyrophosphate.

[0026] Preferably, the iron source is iron phosphate, ferrous oxalate dihydrate, or iron(III) oxide.

[0027] Preferably, in the carbon source, the ratio of the organic carbon source to the inorganic carbon source is 1:(0.6 - 2).

[0028] The present invention also provides a sodium iron pyrophosphate phosphate cathode material prepared by the method for preparing a sodium iron pyrophosphate phosphate cathode material described in any one of the above.

[0029] The beneficial effects of the present invention are as follows: The present invention provides a sodium iron pyrophosphate phosphate cathode material and a preparation method thereof. In the method for preparing the sodium iron pyrophosphate phosphate cathode material of the present invention, a carbon source composed of an organic carbon source and an inorganic carbon source is used to form a carbon coating layer on the surface of the sodium iron pyrophosphate phosphate cathode material through sintering. Moreover, the types of the organic carbon source and the inorganic carbon source are selected and the weight ratio of the organic carbon source to the inorganic carbon source is controlled, so as to prepare a sodium iron pyrophosphate phosphate cathode material with a relatively high pure phase, reduce the content of impurity phases, improve the specific capacity and the initial efficiency of the sodium iron pyrophosphate phosphate cathode material, and have a favorable impact on the cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is an XRD pattern of the sodium iron pyrophosphate phosphate cathode material prepared by the method for preparing a sodium iron pyrophosphate phosphate cathode material of the present invention.

[0031] Figure 2 It is an XRD pattern of the sodium iron pyrophosphate phosphate cathode material prepared by the method for preparing a sodium iron pyrophosphate phosphate cathode material of the present invention.

[0032] Figure 3 It is an XRD pattern of the sodium iron pyrophosphate phosphate cathode material prepared by the method for preparing a sodium iron pyrophosphate phosphate cathode material of the present invention.

[0033] Figure 4XRD pattern of the sodium iron pyrophosphate phosphate cathode material prepared by the preparation method of the comparative example of the present invention.

[0034] Figure 5 XRD pattern of the sodium iron pyrophosphate phosphate cathode material prepared by the preparation method of the comparative example of the present invention. Specific embodiments

[0035] To better illustrate the purpose, technical solution and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0036] Example 1

[0037] As a preparation method of a sodium iron pyrophosphate phosphate cathode material according to an embodiment of the present invention, the chemical formula of the sodium iron pyrophosphate phosphate cathode material is Na4Fe 3+x (PO4)2(P2O7)@C; x = -0.15, C represents a carbon coating layer formed by the sodium iron pyrophosphate phosphate cathode material;

[0038] The preparation method includes the following steps:

[0039] (1) After mixing the iron source, dispersant, sodium source, phosphorus source and carbon source evenly in deionized water, the solid-liquid material ratio of the solid-liquid material is 18 g of solid phase material to 92 mL of water; sand milling is carried out in a sand mill; the carbon source accounts for 3 wt% of the total weight of all raw materials of the iron source, sodium source, phosphorus source and carbon source; the carbon source is a mixture of an organic carbon source and an inorganic carbon source, and the ratio of the organic carbon source to the inorganic carbon source is 1:1; the dispersant accounts for 0.5 wt% of the total weight of the iron source, dispersant, sodium source, phosphorus source and carbon source, and the dispersant is polyvinyl alcohol (PVA); the rotation speed of the sand mill for sand milling is 1200 rpm, the sand milling time is 4 h, and the average particle size of the particles after sand milling is controlled to be 0.5-2 μm; the sodium source is sodium carbonate, the phosphorus source is sodium dihydrogen phosphate, and the iron source is ferrous oxalate dihydrate; the organic carbon source in the carbon source is maltodextrin, and the inorganic carbon source is graphite milk;

[0040] (2) Spray-drying the liquid after sand milling in step (1) to obtain a precursor mixed powder; the inlet air temperature for spray-drying is 240 °C, the outlet air temperature is 120 °C, the atomization pressure is 0.4 Mpa, and the feeding speed is 30 rmp;

[0041] (3) Ball-milling the precursor mixed powder in step (2); the ball-to-material ratio for ball-milling = (6-25):1;

[0042] (4) Heating the precursor mixed powder in step (3) to 520 °C in an inert gas atmosphere and sintering for 10 h to obtain a sodium iron pyrophosphate phosphate cathode material;

[0043] (5) Grinding the sodium iron phosphate pyrophosphate positive electrode material in step (4) by air flow.

[0044] Example 2

[0045] As a method for preparing sodium iron phosphate pyrophosphate positive electrode material according to an embodiment of the present invention, the only difference between this embodiment and embodiment 1 is that the organic carbon source in the carbon source is lauric acid, and the inorganic carbon source is Ketjen black.

[0046] Example 3

[0047] As a method for preparing a sodium iron phosphate pyrophosphate positive electrode material according to an embodiment of the present invention, the only difference between this embodiment and embodiment 1 is that the organic carbon source in the carbon source is maltodextrin, and the inorganic carbon source is Ketjen black.

[0048] Example 4

[0049] As a method for preparing a sodium iron phosphate pyrophosphate positive electrode material in an embodiment of the present invention, the only difference between this embodiment and Example 3 is that the organic carbon source in the carbon source is maltodextrin, the inorganic carbon source is Ketjen black, and the weight ratio of maltodextrin to Ketjen black is 1.5:1.

[0050] Example 5

[0051] As a method for preparing a sodium iron phosphate pyrophosphate positive electrode material in an embodiment of the present invention, the only difference between this embodiment and Example 3 is that the organic carbon source in the carbon source is maltodextrin, the inorganic carbon source is Ketjen black, and the weight ratio of maltodextrin to Ketjen black is 2:1.

[0052] Example 6

[0053] As a method for preparing a sodium iron phosphate pyrophosphate positive electrode material in an embodiment of the present invention, the only difference between this embodiment and Example 3 is that the organic carbon source in the carbon source is maltodextrin, the inorganic carbon source is Ketjen black, and the weight ratio of maltodextrin to Ketjen black is 2.5:1.

[0054] Example 7

[0055] As a method for preparing a sodium iron phosphate pyrophosphate positive electrode material in an embodiment of the present invention, the only difference between this embodiment and Example 3 is that the organic carbon source in the carbon source is maltodextrin, the inorganic carbon source is Ketjen black, and the weight ratio of maltodextrin to Ketjen black is 1:1.5.

[0056] Example 8

[0057] As a method for preparing a sodium iron phosphate pyrophosphate positive electrode material in an embodiment of the present invention, the only difference between this embodiment and Example 3 is that the organic carbon source in the carbon source is maltodextrin, the inorganic carbon source is Ketjen black, and the weight ratio of maltodextrin to Ketjen black is 1:2.

[0058] Comparative Example 1

[0059] As a preparation method of sodium iron pyrophosphate phosphate cathode material for the comparative example of the present invention, the only difference between this comparative example and Example 3 is that: the carbon source is an organic carbon source, and the organic carbon source is maltodextrin.

[0060] Comparative Example 2

[0061] As a preparation method of sodium iron pyrophosphate phosphate cathode material for the comparative example of the present invention, the only difference between this comparative example and Example 3 is that: the carbon source is an inorganic carbon source, and the inorganic carbon source is Ketjen black.

[0062] Comparative Example 3

[0063] As a preparation method of sodium iron pyrophosphate phosphate cathode material for the comparative example of the present invention, the only difference between this comparative example and Example 3 is that: the organic carbon source in the carbon source is glucose, and the inorganic carbon source is Ketjen black.

[0064] Comparative Example 4

[0065] As a preparation method of sodium iron pyrophosphate phosphate cathode material for the comparative example of the present invention, the only difference between this comparative example and Example 3 is that: the organic carbon source in the carbon source is maltodextrin, and the inorganic carbon source is conductive carbon black.

[0066] Experimental method

[0067] I. Samples to be measured

[0068] The polyvinyl alcohol used in the experiment is polyvinyl alcohol 17-88 type with a molecular weight of 10,000-50,000. The rest of the materials are all chemical materials above analytical pure. The sodium iron pyrophosphate phosphate cathode materials are prepared according to the methods of Examples 1-8 and Comparative Examples 1-4, and the total amount of raw materials of iron source, dispersant, sodium source, phosphorus source and carbon source is mixed according to 5 g and then prepared. As the samples to be measured.

[0069] II. Phase purity detection

[0070] Test method: The prepared samples are subjected to XRD testing, and the test data is fitted using Fullprof software to obtain the content of different phases.

[0071] The sodium iron pyrophosphate phosphate cathode materials of Examples 1-3 and Comparative Examples 1-2 are subjected to XRD detection, and the experimental results are as Figures 1 to 5 shown, where Figure 1 is the result diagram of the sodium iron pyrophosphate phosphate cathode material of Example 1, where Figure 2 is the result diagram of the sodium iron pyrophosphate phosphate cathode material of Example 2, where Figure 3 is the result diagram of the sodium iron pyrophosphate phosphate cathode material of Example 3, whereFigure 4 It is the result diagram of the sodium iron pyrophosphate phosphate cathode material of Comparative Example 1, where Figure 5 It is the result diagram of the sodium iron pyrophosphate phosphate cathode material of Comparative Example 2.

[0072] It can be seen that the preparation method of the sodium iron pyrophosphate phosphate cathode material of the present invention prepares a sodium iron pyrophosphate phosphate cathode material with a relatively high pure phase. As shown in Table 1, it is the detection result of the purity of the sodium iron pyrophosphate phosphate cathode material of the present invention.

[0073] Table 1 Detection results of the purity of the sodium iron pyrophosphate phosphate cathode material

[0074]

[0075] III. Specific capacity and cycle stability test

[0076] Test method: The positive electrode sheet made by mixing the obtained positive electrode composite material (85 wt%), Super P conductive carbon black (5 wt%), and polyvinylidene fluoride (10 wt%) is used as the positive electrode of the sodium-ion battery. A metal sodium sheet is used as the counter electrode. 5 vol.% of fluoroethylene carbonate is added to a 1 mol / L NaClO4 / propylene carbonate solution as the electrolyte, and glass fiber is used as the separator. A button cell is assembled in a glove box under a high-purity argon atmosphere. The constant current charge-discharge mode is used. After 5 weeks of charge-discharge testing at a current density of 0.1C, it is changed to 1C high rate to characterize its rate performance and cycle performance. The test conditions are: the discharge cut-off voltage is 2.0V, and the charge cut-off voltage is 4.0V

[0077] The experimental results are shown in Table 2.

[0078] Table 2 Specific capacity and cycle stability of the sodium iron pyrophosphate phosphate cathode material

[0079]

[0080]

[0081] As can be seen from Table 2, for the preparation method of the sodium iron pyrophosphate phosphate cathode material of the present invention, by using a carbon source composed of an organic carbon source and an inorganic carbon source to form a carbon coating layer on the surface of the sodium iron pyrophosphate phosphate cathode material through sintering, and by selecting the types of the organic carbon source and the inorganic carbon source and controlling the weight ratio of the organic carbon source and the inorganic carbon source, a sodium iron pyrophosphate phosphate cathode material with a relatively high pure phase is prepared, reducing the content of impurity phases and improving the specific capacity and cycle stability of the sodium iron pyrophosphate phosphate cathode material. In particular, when the organic carbon source in the carbon source is maltodextrin and the inorganic carbon source is Ketjenblack, the phase of the prepared sodium iron pyrophosphate phosphate cathode material is purer, and the specific capacity and cycle stability of the sodium iron pyrophosphate phosphate cathode material are improved.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing sodium iron pyrophosphate positive electrode material, characterized in that: The chemical formula of the sodium iron phosphate pyrophosphate positive electrode material is Na4Fe3+x(PO4)2(P2O7)@C; -0.3≤x≤0.3, C represents the carbon coating layer formed by the sodium iron phosphate pyrophosphate positive electrode material; the weight content of the carbon coating layer in the sodium iron phosphate pyrophosphate positive electrode material is 0.5% to 3%; In the preparation method, the carbon source of the source material of the carbon coating layer is a mixture of an organic carbon source and an inorganic carbon source, wherein the organic carbon source is maltodextrin and the inorganic carbon source is ketjen black; the weight ratio of maltodextrin to ketjen black is 2:(3-4).

2. The method for preparing the sodium iron phosphate pyrophosphate positive electrode material according to claim 1, characterized in that: The preparation method comprises the following steps: (1) mixing an iron source, a dispersant, a sodium source, a phosphorus source and a carbon source in deionized water and grinding the mixture in a sand mill; (2) spray drying the liquid after sand milling in step (1) to obtain a precursor mixed powder; (3) ball milling the precursor mixed powder of step (2); (4) sintering the precursor mixed powder of step (3) at 500-550° C. for 8-15 h in an inert gas atmosphere to obtain a sodium iron pyrophosphate positive electrode material; (5) Grinding the sodium iron phosphate pyrophosphate positive electrode material in step (4) by air flow.

3. The method for preparing the sodium iron phosphate pyrophosphate positive electrode material according to claim 2, characterized in that: In step (1), the dispersant accounts for 0.5wt% to 10wt% of the total weight of the iron source, dispersant, sodium source, phosphorus source and carbon source, and the dispersant is at least one of PVA, PEG, PVB and CMC.

4. The method for preparing the sodium iron phosphate pyrophosphate positive electrode material according to claim 2, characterized in that: In step (1), the average particle size of the particles after sand grinding is controlled to be 0.5 to 2 μm.

5. The method for preparing the sodium iron phosphate pyrophosphate positive electrode material according to claim 2, characterized in that: In step (2), the inlet air temperature of the spray drying is 220-260° C., the outlet air temperature is 110-140° C., the atomization pressure is 0.3-0.5 MPa, and the feed speed is 20 rpm-40 rpm; in step (3), the ball-to-material ratio of the ball mill is (6-25):

1.

6. The method for preparing sodium iron phosphate pyrophosphate positive electrode material according to claim 2, characterized in that: The sodium source is at least one of sodium carbonate, sodium bicarbonate, sodium acetate, sodium citrate, disodium hydrogen phosphate, disodium hydrogen citrate, and sodium hydroxide; the phosphorus source is at least one of phosphoric acid, sodium dihydrogen phosphate, trisodium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium pyrophosphate, trisodium monohydrogen pyrophosphate, disodium dihydrogen pyrophosphate, and monosodium trihydrogen pyrophosphate; the iron source is ferric phosphate, ferrous oxalate dihydrate, or ferric oxide.

7. The sodium iron phosphate pyrophosphate positive electrode material prepared by the method for preparing the sodium iron phosphate pyrophosphate positive electrode material according to any one of claims 1 to 6.

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