Polyanion composite positive electrode material and preparation method thereof

Abstract

The invention provides a polyanion composite positive electrode material and a preparation method thereof, the chemical formula of the polyanion composite positive electrode material is Na < 4 + x > Fe3 (PO4) 2 (P2O7) / Na4VMn (PO4) 3 (at) C, Na < 4 + x > Fe3 (PO4) 2 (P2O7) and Na4VMn (PO4) 3 are used as core materials of the anion composite positive electrode material, a carbon coating layer coats the core materials to form the polyanion composite positive electrode material, and the content of the carbon coating layer in the polyanion composite positive electrode material is 0.5 wt%-2.5 wt%. The polyanion composite positive electrode material Na < 4 + x > Fe3 (PO4) 2 (P2O7) and Na4VMn (PO4) 3 are used as core materials of the anion composite positive electrode material, the Na < 4 + x > Fe3 (PO4) 2 (P2O7) and the Na4VMn (PO4) 3 are compounded, the interface impedance is reduced, the core materials are coated with the carbon coating layer to form the polyanion composite positive electrode material, the charge and discharge of impure-phase ferric sodium pyrophosphate and ferric sodium phosphate of ferric sodium pyrophosphate are greatly reduced, and the charge and discharge of the formed material are greatly reduced. The capacity and the battery performance of the material are improved, and the rate capability is remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to a battery cathode material, in particular to a polyanion composite cathode material and a preparation method thereof. BACKGROUND

[0002] Pyrophosphate has the advantages of high energy density and high power density, and has higher thermal stability and relatively easy preparation process compared with sulfate and phosphate, and becomes the polyanion material closest to the actual application in performance. Na4Fe3(PO4)2(P2O7) as a potential sodium ion battery cathode material has the advantages of high theoretical specific capacity, low cost and environmental friendliness, and has attracted widespread attention. However, in practical application, the capacity of Na4Fe3(PO4)2(P2O7) material is quite different from the theoretical value. SUMMARY

[0003] The present application aims to overcome the deficiencies in the prior art and provide a polyanion composite cathode material and a preparation method thereof.

[0004] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: a polyanion composite cathode material, the chemical formula of the polyanion composite cathode material is Na4+xFe3(PO4)2(P2O7) / Na4VMn(PO4)3@C, -0.2≤x≤0.2, Na4+xFe3(PO4)2(P2O7) and Na4VMn(PO4)3 are used as the core material of the anion composite cathode material, and a carbon coating layer is used to coat the core material to form the polyanion composite cathode material, and the content of the carbon coating layer in the polyanion composite cathode material is 0.5wt%-2.5wt%.

[0005] The traditional physical mixing method simply mixes two polyanion materials, which has a significant influence on the performance improvement of the material. The above-mentioned polyanion composite cathode material is synthesized by high-temperature chemical method using Na4+xFe3(PO4)2(P2O7) and Na4VMn(PO4)3 and a carbon source, Na4+xFe3(PO4)2(P2O7) and Na4VMn(PO4)3 are used as the core material of the anion composite cathode material, and the two materials are compounded to form a stable interface structure with very small interface impedance, thereby improving the electrochemical performance. The above-mentioned polyanion composite cathode material Na4+xFe3(PO4)2(P2O7) and Na4VMn(PO4)3 are used as the core material of the anion composite cathode material, and a carbon coating layer is used to coat the core material to form the polyanion composite cathode material, which greatly reduces the impurity sodium pyrophosphate and sodium iron phosphate of sodium pyrophosphate iron phosphate, and the compounding of Na4+xFe3(PO4)2(P2O7) and Na4VMn(PO4)3 and the carbon coating layer form the charge and discharge of the material, reduce the interface impedance, improve the capacity and battery performance of the material, and significantly improve the rate performance.

[0006] Preferably, in the core material of the polyanionic composite cathode material, Na4+xFe3(PO4)2(P2O7) and Na4VMn(PO4)3 are formed into an interfacial bond through sintering of the source materials.

[0007] Preferably, the content of the carbon coating layer in the polyanionic composite cathode material is 1.0wt%-2.0wt%.

[0008] Preferably, the weight ratio of Na4+xFe3(PO4)2(P2O7) to Na4VMn(PO4)3 in the polyanionic composite cathode material is 1:(0.1-10).

[0009] Preferably, the weight ratio of Na4+xFe3(PO4)2(P2O7) to Na4VMn(PO4)3 in the polyanionic composite cathode material is 1:(0.1-1.0).

[0010] When the weight ratio of Na4+xFe3(PO4)2(P2O7) to Na4VMn(PO4)3 in the polyanionic composite cathode material is 1:(0.1-1.0), the capacity and battery performance of the material, especially the rate performance, can be better improved.

[0011] Preferably, the weight ratio of Na4+xFe3(PO4)2(P2O7) to Na4VMn(PO4)3 in the polyanionic composite cathode material is 1:(0.1-0.5).

[0012] When the weight ratio of Na4+xFe3(PO4)2(P2O7) to Na4VMn(PO4)3 in the polyanionic composite cathode material is 1:(0.1-0.5), the capacity and battery performance of the material, especially the rate performance, can be better improved.

[0013] Preferably, the preparation method of the polyanionic composite cathode material is that the source material of Na4+xFe3(PO4)2(P2O7), the source material of Na4VMn(PO4)3, and the carbon source are mixed and sprayed in a certain weight ratio, and then sintered at a temperature of 500-550℃ for 8-15h / ℃.

[0014] Preferably, the charge transfer impedance of the polyanionic composite cathode material is in the range of 1-200Ω.

[0015] Preferably, the charge transfer impedance of the polyanionic composite cathode material is in the range of 10-100Ω.

[0016] The application also provides a preparation method of the polyanionic composite cathode material, and the method comprises the following steps: (1) Iron source, vanadium source, manganese source, dispersant, sodium source, phosphorus source and carbon source are stirred and mixed uniformly in deionized water to form a dispersion liquid, and spray drying is performed to obtain a precursor powder; (2) The precursor powder is sintered at a temperature of 500-550°C under an anaerobic atmosphere to obtain a composite positive electrode material Na4+xFe3(PO4)2(P2O7) / Na4VMn(PO4)3@C; (3) The Na4+xFe3(PO4)2(P2O7) / Na4VMn(PO4)3@C positive electrode material is air-jet milled to a set particle size range.

[0017] Preferably, in step (1), the dispersant is at least one of PVA, PEG, PVB and CMC, and the amount of dispersant is 0.5wt%-10wt% of the total weight of the substances in step (1) excluding deionized water; the amount of carbon source is 1.0wt%-5wt% of the total weight of the substances in step (1) excluding deionized water.

[0018] Preferably, the amounts of iron source, sodium source and phosphorus source satisfy the molar ratio Na:Fe:P=4+x:3:4, and -0.2≤x≤0.2.

[0019] Preferably, in step (1), the carbon source is at least one of acetylene black, graphene, ascorbic acid, conductive carbon black, glucose, sucrose, starch, maltose and ketjen black.

[0020] Preferably, in step (1), 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.

[0021] Preferably, in step (1), the phosphorus source is at least one of phosphoric acid, sodium dihydrogen phosphate, trisodium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium pyrophosphate, trisodium pyrophosphate, disodium pyrophosphate and monosodium pyrophosphate.

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

[0023] Preferably, in step (3), the sintering temperature is 500-550°C, the sintering time is 8-15h, and the heating rate is 2-5°C / min. The poly-anion composite positive electrode material of the present application is prepared by high-temperature chemical synthesis method using Na4+xFe3(PO4)2(P2O7) and Na4VMn(PO4)3 as the core material of the anion composite positive electrode material, and carbon source. Na4+xFe3(PO4)2(P2O7) and Na4VMn(PO4)3 as the core material of the anion composite positive electrode material, the two materials are compounded to form a stable interface structure with very small interface impedance, thereby improving the electrochemical performance. The poly-anion composite positive electrode material Na4+xFe3(PO4)2(P2O7) and Na4VMn(PO4)3 as the core material of the anion composite positive electrode material, and the carbon coating layer coated on the core material form a poly-anion composite positive electrode material, which greatly reduces the impurity sodium iron pyrophosphate and sodium iron phosphate of sodium iron pyrophosphate, and the combination of Na4+xFe3(PO4)2(P2O7) and Na4VMn(PO4)3, the carbon coating layer, the charge and discharge of the material, the reduction of the interface impedance, the improvement of the capacity and the battery performance, and the significant improvement of the rate performance. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The XRD pattern of the poly-anion composite positive electrode material of Example 1 of the present application.

[0025] Figure 2 The XRD pattern of the poly-anion composite positive electrode material of Comparative Example 4 of the present application. DETAILED DESCRIPTION

[0026] For the purpose of better illustrating the object, technical scheme and advantages of the present application, the present application will be further described in conjunction with specific examples.

[0027] Example 1: As a poly-anion composite positive electrode material of the present application, the chemical formula is Na4+xFe3(PO4)2(P2O7) / Na4VMn(PO4)3@C, x=-0.1, Na4+xFe3(PO4)2(P2O7) and Na4VMn(PO4)3 as the core material of the anion composite positive electrode material, and the carbon coating layer coated on the core material forms a poly-anion composite positive electrode material. The content of the carbon coating layer in the poly-anion composite positive electrode material is 2.18wt%, and Na4+xFe3(PO4)2(P2O7) and Na4VMn(PO4)3 form an interface combination.

[0028] The weight ratio of Na4+xFe3(PO4)2(P2O7) to Na4VMn(PO4)3 in the poly-anion composite positive electrode material is 1:0.15.

[0029] The preparation method of the poly-anion composite positive electrode material of the present application comprises the following steps: (1) Ferric nitrate was added to deionized water as an iron source, vanadium source, manganese source, dispersant, sodium source, phosphorus source and carbon source. The mixture was stirred until the dispersion was uniform. The mixture was then milled in a sand mill at a speed of 1200 rpm for 4.5 h. The dispersant was PEG (polyethylene glycol) and the amount of dispersant was 1.5 wt% of the total weight of the added substances (excluding water). The amount of carbon source was 3 wt% of the total weight of the added substances (excluding water). The carbon source was acetylene black, the sodium source was sodium carbonate, the phosphorus source was sodium dihydrogen phosphate, the vanadium source was vanadium acetylacetonate, and the manganese source was manganese acetate tetrahydrate. After milling, the precursor powder was obtained by spray drying. The inlet air temperature of the spray drying was 250 ℃, the outlet air temperature was 120 ℃, the atomization pressure was 0.4 MPa, and the feed rate was 30 rpm. (2) The precursor powder was sintered at 550°C for 10 hours under an inert atmosphere (N2) to obtain the composite cathode material Na4+xFe3(PO4)2(P2O7) / Na3V2(PO4)3@C; (3) The sodium iron pyrophosphate cathode material was pulverized by airflow to obtain an average particle size in the range of 10~12μm.

[0030] Example 2: As a polyanion composite cathode material according to an embodiment of the present invention, the difference between this embodiment and Embodiment 1 is that the weight ratio of Na4+xFe3(PO4)2(P2O7) to Na4VMn(PO4)3 in the polyanion composite cathode material is 1:0.3.

[0031] Example 3: As a polyanion composite cathode material according to an embodiment of the present invention, the difference between this embodiment and Embodiment 1 is that the weight ratio of Na4+xFe3(PO4)2(P2O7) to Na4VMn(PO4)3 in the polyanion composite cathode material is 1:0.5.

[0032] Example 4: As a polyanion composite cathode material according to an embodiment of the present invention, the difference between this embodiment and Embodiment 1 is that the weight ratio of Na4+xFe3(PO4)2(P2O7) to Na4VMn(PO4)3 in the polyanion composite cathode material is 1:0.8.

[0033] Example 5: As a polyanion composite cathode material according to an embodiment of the present invention, the difference between this embodiment and Embodiment 1 is that the weight ratio of Na4+xFe3(PO4)2(P2O7) to Na4VMn(PO4)3 in the polyanion composite cathode material is 1:1.2.

[0034] Example 6: As a polyanion composite cathode material according to an embodiment of the present invention, the difference between this embodiment and Embodiment 1 is that the weight ratio of Na4+xFe3(PO4)2(P2O7) to Na4VMn(PO4)3 in the polyanion composite cathode material is 1:1.8.

[0035] Example 7: As a polyanion composite cathode material according to an embodiment of the present invention, the difference between this embodiment and Embodiment 1 is that the weight ratio of Na4+xFe3(PO4)2(P2O7) to Na4VMn(PO4)3 in the polyanion composite cathode material is 1:2.5.

[0036] Example 8: As a polyanion composite cathode material according to an embodiment of the present invention, the difference between this embodiment and Embodiment 1 is that the weight ratio of Na4+xFe3(PO4)2(P2O7) to Na4VMn(PO4)3 in the polyanion composite cathode material is 1:5.

[0037] Example 9: As a polyanion composite cathode material according to an embodiment of the present invention, the difference between this embodiment and Embodiment 1 is that the carbon coating content in the polyanion composite cathode material is 0.56wt% (the content in the sintered material was detected and calculated by a CHNS elemental analyzer).

[0038] Example 10: As a polyanion composite cathode material according to an embodiment of the present invention, the difference between this embodiment and Embodiment 1 is that the carbon coating content in the polyanion composite cathode material is 1.03 wt% (the content in the sintered material was detected and calculated by a CHNS elemental analyzer).

[0039] Example 11: As a polyanion composite cathode material according to an embodiment of the present invention, the difference between this embodiment and Embodiment 1 is that the carbon coating content in the polyanion composite cathode material is 1.48 wt% (the content in the sintered material was detected and calculated by a CHNS elemental analyzer).

[0040] Example 12: As a polyanion composite cathode material according to an embodiment of the present invention, the difference between this embodiment and Embodiment 1 is that the carbon coating content in the polyanion composite cathode material is 2.51 wt% (the content in the sintered material was detected and calculated by a CHNS elemental analyzer).

[0041] Comparative Example 1: As a comparative example of the present invention, this polyanion composite cathode material differs from Example 1 in that the chemical formula of the polyanion composite cathode material is Na4+xFe3(PO4)2(P2O7) / Na4VMn(PO4)3, meaning it does not have a carbon coating layer. The preparation method is the same as in Example 1 without the addition of a carbon source.

[0042] Comparative Example 2: As a comparative example of the present invention, this polyanionic composite cathode material differs from Example 1 in that the chemical formula of the polyanionic composite cathode material is Na₄+xFe₃(PO₄)₂(P₂O₇) / Na₃V₂(PO₄)₃@C. Specifically, sodium manganese vanadium phosphate is replaced with sodium vanadium phosphate. The preparation method is the same as in Example 1, but without the addition of a manganese source, and the proportion of carbon source material is the same as in Example 1.

[0043] Comparative Example 3: As a comparative example of the present invention, this polyanionic composite cathode material differs from Example 1 in that its chemical formula is Na₄+xFe₃(PO₄)₂(P₂O₇) / @C. Specifically, the source material sintering of the polyanionic cathode material is not added, and the preparation method is the same as in Example 1 without the addition of manganese or vanadium sources. The proportion of carbon source material is the same as in Example 1.

[0044] Comparative Example 4: As a comparative example of the present invention, the polyanionic composite cathode material differs from Example 1 in that Na4+xFe3(PO4)2(P2O7) material and Na4VMn(PO4)3 material are prepared by pre-sintering respectively. Na4+xFe3(PO4)2(P2O7) material powder, Na4VMn(PO4)3 material powder, and carbon source were sintered at 550℃ for 10 hours under an inert atmosphere (N2) to obtain a composite cathode material.

[0045] (a) Material characterization: Figure 1 The image shows the XRD pattern of the Na4+xFe3(PO4)2(P2O7) / Na4VMn(PO4)3@C material of Example 1. Figure 2 The image shows the XRD pattern of the polyanion composite cathode material in Comparative Example 4.

[0046] (II) Material Properties: I. EIS Testing Test method: Using an electrochemical workstation with a three-electrode system, ensure the coin cell and three electrodes are correctly installed, measure the open-circuit voltage (maintain for 20 min, at which point the open-circuit voltage will hardly fluctuate), and set the starting voltage based on the open-circuit voltage. Frequency range: Scan from high frequency (100kHz) to low frequency (0.01Hz). AC voltage amplitude: Set to 5mV.

[0047] II. Specific Capacity and Cyclic Stability Tests Test Method: A positive electrode sheet made from the obtained positive electrode composite material (85wt%), Super P conductive carbon black (5wt%), and polyvinylidene fluoride (10wt%) was used as the positive electrode of the sodium-ion battery. A metallic sodium sheet was used as the counter electrode. 5 vol.% of fluoroethylene carbonate was added to a 1 mol / L NaClO4 / propylene carbonate solution as the electrolyte. Glass fiber was used as the separator. The batteries were assembled into coin cells in a glove box under a high-purity argon atmosphere. Constant current charge-discharge mode was used. After 5 weeks of charge-discharge testing at a current density of 0.1C, the rate performance and cycle performance were characterized at a high rate of 1C. The test conditions were: discharge cut-off voltage of 2.0V and charge cut-off voltage of 3.6V.

[0048] Table 1. Specific capacity and cycle stability of polyanion composite cathode materials

[0049] Depend on Figure 1 and Figure 2 The XRD patterns show that the polyanion composite cathode materials of Example 1 and Comparative Example 4 have the same composition. However, according to EIS detection, the interfacial impedance of the polyanion composite cathode material of Comparative Example 4 is much larger than that of the polyanion composite cathode material of Example 1. This indicates that in the core material of the polyanion composite cathode material of Example 1, the source material sintered Na4+xFe3(PO4)2(P2O7) and Na4VMn(PO4)3 form a better interfacial bond.

[0050] As shown in Table 1, the polyanion composite cathode materials Na4+xFe3(PO4)2(P2O7) and Na4VMn(PO4)3 of the present invention are used as the core materials of the anion composite cathode material. The carbon coating layer coats the core materials to form the polyanion composite cathode material. The composite of Na4+xFe3(PO4)2(P2O7) and Na4VMn(PO4)3, and the carbon coating layer, improve the charge and discharge performance of the material, reduce the interface impedance, improve the capacity and battery performance of the material, and significantly improve the rate performance.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A polyanion composite cathode material, characterized in that, The chemical formula of the polyanion composite cathode material is Na4+xFe3(PO4)2(P2O7) / Na4VMn(PO4)3@C, -0.2≤x≤0.

2. Na4+xFe3(PO4)2(P2O7) and Na4VMn(PO4)3 are used as the core material of the anion composite cathode material. The carbon coating layer coats the core material to form the polyanion composite cathode material. The carbon coating layer content in the polyanion composite cathode material is 0.5wt%~2.5wt%.

2. The polyanion composite cathode material according to claim 1, characterized in that, In the core material of the polyanion composite cathode material, the source material Na4+xFe3(PO4)2(P2O7) and Na4VMn(PO4)3 form an interface bond through sintering.

3. The polyanion composite cathode material according to claim 1, characterized in that, The carbon coating content in the polyanion composite cathode material is 1.0 wt% to 2 wt%.

4. The polyanion composite cathode material according to claim 1, characterized in that, In the polyanion composite cathode material, the weight ratio of Na4+xFe3(PO4)2(P2O7) to Na4VMn(PO4)3 is 1:(0.1~10).

5. The polyanion composite cathode material according to claim 1, characterized in that, The weight ratio of Na4+xFe3(PO4)2(P2O7) to Na4VMn(PO4)3 in the polyanionic composite cathode material is 1: (0.1~1.0).

6. The polyanion composite cathode material according to claim 1, characterized in that, The preparation method of the polyanion composite cathode material is as follows: Na4+xFe3(PO4)2(P2O7) source material, Na4VMn(PO4)3 source material and carbon source are mixed and sprayed in a weight ratio, and then sintered at a temperature of 500~550℃ for 8~15h.

7. The polyanion composite cathode material according to claim 1, characterized in that, The charge transfer impedance of the polyanion composite cathode material ranges from 1 to 200 Ω.

8. The method for preparing the polyanion composite cathode material according to any one of claims 1 to 7, characterized in that, The method includes the following steps: (1) The iron source, vanadium source, manganese source, dispersant, sodium source, phosphorus source and carbon source are stirred and mixed in deionized water to form a dispersion, and spray dried to obtain precursor powder; (2) The precursor powder was sintered at a temperature of 500℃~550℃ in an oxygen-free atmosphere to obtain the composite cathode material Na4+xFe3(PO4)2(P2O7) / Na4VMn(PO4)3@C; (3) Grind the Na4+xFe3(PO4)2(P2O7) / Na4VMn(PO4)3@C cathode material into a set particle size range.

9. The method for preparing the polyanion composite cathode material according to claim 8, characterized in that, In step (1), the dispersant is at least one of PVA, PEG, PVB, and CMC, and the amount of dispersant used is 0.5wt% to 10wt% of the total weight of substances other than deionized water in step (1); the amount of carbon source used is 1.0wt% to 5wt% of the total weight of substances other than deionized water in step (1). The amounts of iron, sodium, and phosphorus sources should conform to the molar ratio Na:Fe:P = 4 + x: 3: 4, where -0.2 ≤ x ≤ 0.2.

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