Sodium-supplementing Na4Fe3-a (PO4) 2P2O7 composite positive electrode material, preparation thereof and application of sodium-supplementing Na4Fe3-a (PO4) 2P2O7 composite positive electrode material in sodium ion battery

Abstract

The invention belongs to the technical field of sodium ion battery positive electrode material preparation, and particularly discloses a sodium-supplemented Na4Fe3-a (PO4) 2P2O7 composite positive electrode material, a preparation method thereof and application of the sodium-supplemented Na4Fe3-a (PO4) 2P2O7 composite positive electrode material in a sodium ion battery, the sodium-supplemented Na4Fe3-a (PO4) 2P2O7 composite positive electrode material comprises a component A and a component B, the component A is an iron vacancy active material, the chemical expression of the component A is Na4Fe3-a (PO4) 2P2O7 material, and a is more than or equal to 0.02 and less than or equal to 0.2; and the component B is a sodium supplementing agent which comprises at least one of C1-C6 sodium carboxylate, C4-C8 N-containing sodium carboxylate, benzophenone sodium, sodium oxide and sodium nickelate. According to the invention, the iron vacancy component A and the iron vacancy component B are combined, so that the capacity, the first effect and the cycling stability under high rate of the material in a total battery can be synergistically improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion battery materials, and particularly relates to the technical field of positive active materials for sodium ion batteries. Background Art

[0002] The abundance, wide distribution and low cost of sodium element make sodium ion batteries promising candidates for large-scale energy storage. Currently, the main positive electrode systems for sodium ion batteries include layered oxides, polyanion-type compounds, Prussian blue and its analogues. Among them, layered oxides have a high specific capacity, but there are multiple phase transitions during cycling, resulting in easy collapse of the structure and poor cycling performance; the problem of crystal water in Prussian blue and its analogues is difficult to solve, and gas is easily generated at high potentials. In contrast, polyanion-type compounds have an open three-dimensional framework, so they have good cycle stability, especially Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 , which has resource advantages and is environmentally friendly and suitable for large-scale energy storage, is the best choice for the positive electrode material of commercial sodium ion batteries.

[0003] However, in the commercial application system, during the first charge process of the full battery composed of Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 and hard carbon, due to the formation of the solid electrolyte interface and the low Coulomb efficiency of the existing hard carbon negative electrode, the loss of active sodium ions in the full battery system is inevitable. This will cause a decrease in capacity and deterioration of cycling performance.

[0004] In view of the problems faced by the sodium iron pyrophosphate material, the existing main idea lies in doping and coating the material. For example, the Chinese patent document with the publication number CN117374257A discloses a preparation method of a sodium iron pyrophosphate-carbon composite cathode material. The steps are as follows: S1. Perform a first heat treatment on the solid mixture 1 including ferrous oxalate and sodium dihydrogen phosphate to obtain a precursor; S2. Calcinate the mixture 2 including the precursor, sodium dihydrogen phosphate and a sodium supplement agent to obtain the sodium iron pyrophosphate-carbon composite cathode material. Another example is that the Chinese patent document with the publication number CN118790969A discloses a sodium iron pyrophosphate cathode material with low resistivity. The chemical formula of this material is Na4-xFe3-y(PO4)2(P2O7) / C, where 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, and x < y; by adjusting the content of Na vacancies and Fe defects in the sodium iron pyrophosphate cathode material with low resistivity, the conductivity is improved. In addition, the Chinese patent document with the publication number CN118610454A discloses an iron-deficient manganese-doped sodium-based cathode material, which is obtained by simultaneously introducing Mn doping and Fe vacancy defects into the iron atom positions in the Na4Fe3(PO4)2P2O7 unit cell of sodium iron pyrophosphate. Specifically, this material is Na4Fe3-3x-3yMn3x(PO4)2P2O7. This technology simultaneously introduces Mn doping and Fe vacancy defects into the iron atom positions in the unit cell of traditional sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7) to obtain Na4Fe3-3x-3yMn3x(PO4)2P2O7, thereby improving its performance.

[0005] In summary, although there are some existing solutions to improve the performance of sodium iron pyrophosphate by means of doping, coating, etc., the existing improvement solutions can well improve the performance of the half-cell, but it is difficult to still show the expected technical effects in the actual full-cell system. The capacity utilization, initial efficiency, and long-term cycle stability at high rates of the full-cell of the material still need to be improved. Summary of the Invention

[0006] In view of the problems existing in the prior art, the present invention provides a sodium-supplemented Na 4 Fe 3-a (PO 4 ) 2 P 2 O 7 composite cathode material, aiming to provide a cathode material with excellent full-cell electrochemical performance.

[0007] The second object of the present invention is to provide the sodium-supplemented Na 4 Fe 3-a (PO 4 ) 2 P 2 O 7Preparation method of composite cathode material and its application in sodium-ion batteries.

[0008] The third object of the present invention is to provide a sodium-supplemented Na 4 Fe 3-a (PO 4 ) 2 P 2 O 7 Sodium-ion battery with composite cathode material and its cathode.

[0009] Existing means can well improve the performance of the sodium iron pyrophosphate material in half-cells, but there are still certain differences in the performance of half-cells and full-cells. There are few existing technologies that can truly improve its full-cell performance, especially improvement schemes for capacity utilization, initial efficiency, and long-cycle performance. To address this problem, the present invention provides the following improvement means:

[0010] A sodium-supplemented Na 4 Fe 3-a (PO 4 ) 2 P 2 O 7 Composite cathode material, including component A and component B;

[0011] The component A is an iron vacancy active material, and its chemical formula is Na 4 Fe 3-a (PO 4 ) 2 P 2 O 7 material, where 0.02 ≤ a ≤ 0.2;

[0012] Component B is a sodium supplement, which includes carboxylate of C 1 ~C 6 , carboxylate containing N of C 4 ~C 8 , sodium benzophenone, sodium oxide, sodium nickelate, or at least one of them.

[0013] The present invention innovatively combines the iron vacancy component A and the sodium supplement component B, so as to achieve synergy and solve problems such as low capacity utilization rate, unsatisfactory initial efficiency, and poor long-term cycle stability that are prone to occur in the iron vacancy component A in full cells. In the present invention, through the combination of the iron vacancy component A and component B, the capacity, initial efficiency, and cycle stability at high rates of the material in full cells can be synergistically improved.

[0014] Na 4 Fe 3-a (PO 4 ) 2 P 2 O 7In the material, a can further be 0.04 to 0.1.

[0015] The described component A is a Na 4 Fe 3-a (PO 4 ) 2 P 2 O 7 material; wherein the carbon content can be 1 to 3 wt.%. The described component A can be obtained by sintering the raw materials of the stoichiometry. Among them, a conventional carbon source is also allowed to be added to the raw materials. Each raw material and the sintering process can be well-known in the industry.

[0016] In the present invention, the components and the combined synergy of the described component A and B are the key to improving their performance in the full cell. Research also shows that further innovative optimization of their components and compounding methods helps to further improve the synergy between the two, and helps to further improve the capacity, rate and long cycle performance of the full cell.

[0017] In the present invention, preferably, the described component B is in-situ compounded on component A, and it is obtained by sintering after the reaction of the precursor raw material of component B and the surface of component A; the precursor raw materials include C 1 ~C 6 carboxylic acids, C 4 ~C 8 N-containing carboxylic acids, boric acid, phosphoric acid of at least one. Research in the present invention shows that by in-situ reacting the residual alkali on the surface of component A with the described precursor raw materials, a composite material in-situ compounded with component B can be obtained, and this material can exhibit better capacity, initial efficiency and long-term cycle stability at high rates.

[0018] In the present invention, the C 1 ~C 6 carboxylic acids are unitary, binary or polycarboxylic acids; preferably at least one of sodium acetate and sodium oxalate;

[0019] Preferably, the C 4 ~C 8 N-containing carboxylate is at least one of disodium ethylenediaminetetraacetate and tetrasodium ethylenediaminetetraacetate.

[0020] In the present invention, component B includes component B1 and component B2; among them, component B1 includes at least one of sodium oxalate and sodium nickelate; component B2 includes at least one of sodium diacetone, sodium acetate and tetrasodium ethylenediaminetetraacetate. Research shows that through the combined component B, the sodium supplementation effect can be further optimized, and the capacity utilization rate, initial efficiency and long-term cycle effect at high rates of the defective cathode material can be further improved.

[0021] Preferably, in Component B, the weight ratio of Component B1 to Component B2 is 1:0.5 - 2.

[0022] In the present invention, the D50 of Component A is less than 25 μm, preferably 4 - 15 μm; the D50 of Component B is 2 - 5 μm.

[0023] Sodium supplementation Na 4 Fe 3-a (PO 4 ) 2 P 2 O 7 The composite cathode material has a core - shell structure, where Component B is the shell. Research in the present invention shows that under the innovative combination of Component A and B, further combined with the particle sizes of the two and the core - shell morphology, it helps to further optimize their synergy and further improve the capacity, rate performance, and long - cycle performance of the full battery.

[0024] In the present invention, sodium supplementation Na 4 Fe 3-a (PO 4 ) 2 P 2 O 7 In the composite cathode material, the content of Component B is 1 - 10 wt%; preferably 2 - 5 wt%.

[0025] The present invention also provides a preparation method of the sodium - supplemented Na 4 Fe 3-a (PO 4 ) 2 P 2 O 7 composite cathode material, which is obtained by preparing Component A and mixing it with Component B; or by subjecting the precursor raw materials of Component A and Component B to surface reaction and then sintering.

[0026] In the present invention, the steps for preparing Component A are: slurrying, spraying, and heat - treating a mixed raw material containing a carbon source and stoichiometric amounts of a sodium source, an iron source, and a phosphorus source to obtain Component A;

[0027] Preferably, the sodium source is at least one of sodium carbonate, sodium bicarbonate, sodium acetate, sodium dihydrogen phosphate, sodium phosphate, and sodium hydroxide;

[0028] Optionally, the iron source is at least one of iron phosphate, iron oxalate, iron nitrate, iron powder, iron oxide, and ferrous sulfate;

[0029] Optionally, the phosphorus source is at least one of phosphoric acid, sodium phosphate, ammonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium hydrogen phosphate, sodium dihydrogen phosphate, and iron phosphate;

[0030] Optionally, the carbon source is an organic carbon source, further being at least one of glucose, sucrose, citric acid, starch, ascorbic acid, cyclodextrin, and polyethylene glycol;

[0031] Preferably, the weight ratio of the organic carbon source to the iron source is 1:5 to 20;

[0032] In the present invention, the means of pulping can be conventional, for example, coarse grinding, sand grinding, etc. The solvent for pulping can be water or an aqueous solvent. The particle size D50 of the mixed pulp after pulping is 0.1 to 0.5 μm.

[0033] Preferably, the outlet temperature of the spraying is greater than 90 °C; further, it can be 90 to 140 °C.

[0034] Preferably, the temperature of the heat treatment is 400 to 600 °C, the heating rate is 2 to 4 °C / min, and the holding time is 4 to 15 h.

[0035] Preferably, the mixing method of component A and component B is at least one of wet ball milling, dry ball milling, and gas mixing; preferably wet ball milling. Research shows that the preferred mixing method can further improve the combined synergistic effect of component A and B, and can further optimize the capacity, initial efficiency, and long-term cycle stability at high rates of the material.

[0036] Preferably, the medium for wet ball milling includes at least one of ethanol, acetone, and glycerol.

[0037] In the present invention, the precursor raw materials include at least one of oxalic acid, boric acid, and phosphoric acid.

[0038] Preferably, the precursor raw materials are 5 wt% to 10 wt% of the weight of component A.

[0039] The sintering process is carried out in a protective atmosphere. The sintering temperature is 150 to 200 °C. The sintering time is 5 to 10 h.

[0040] The present invention also provides a positive electrode of a sodium-ion battery, including a current collector and a positive electrode material compounded on its surface. The positive electrode material includes a positive electrode active material, and the positive electrode active material includes the sodium-supplemented Na 4 Fe 3-a (PO 4 ) 2 P 2 O 7 composite positive electrode material.

[0041] The present invention also provides a sodium-ion battery, including a positive electrode, a negative electrode, and a barrier layer disposed between the positive electrode and the negative electrode. The positive electrode is the positive electrode described in the present invention. The negative electrode includes a current collector and a negative electrode active material compounded on its surface. The negative electrode active material includes at least one of a carbon material, a silicon material, and a carbon-silicon composite material.

[0042] Beneficial effects:

[0043] In the present invention, the component A with iron vacancies and the sodium-supplementing component B are combined, so that synergy can be achieved, and the capacity utilization rate, initial efficiency, and long-term cycle stability of the component A with iron vacancies in the full battery can be improved. By adding some in-situ sodium-supplementing precursor components to the component A, as well as jointly controlling the compounding and structure of the components A and B, the capacity utilization rate, initial efficiency, and long-term cycle stability of the material can be further improved. Description of the drawings

[0044] Figure 1 It is a cycle schematic diagram of Example 1;

[0045] Figure 2 It is a cycle schematic diagram of Comparative Example 1; Detailed implementation manners

[0046] Example 1

[0047] A preparation method of a composite sodium pyrophosphate iron phosphate positive electrode material and a sodium-supplementing material includes the following steps:

[0048] (1) Weigh ferrous oxalate, sodium carbonate, and ammonium dihydrogen phosphate according to the molar ratio of Na:Fe:P in the raw materials being 4:2.96:4. At the same time, add glucose accounting for 15 wt% of the mass of the raw materials (referring to the iron source) as a carbon source, and disperse it in deionized water, controlling the solid content at 40%. Grind the above slurry, controlling the slurry particle size D50 = 0.3 μm.

[0049] (2) Dry the precursor slurry obtained in step (1) in a spray drying tower. Set the inlet temperature of the spray drying to 240 °C and control the outlet temperature at 100 °C to obtain the dried precursor powder. Under the protection of nitrogen, heat the obtained dried precursor powder at a heating rate of 5 °C / min to 475 °C and keep it warm for 12 h to obtain the sodium pyrophosphate iron phosphate positive electrode material (component A).

[0050] (3) Dry-grind the positive electrode material obtained in step 2 with a sodium-supplementing agent (component B, sodium oxalate in this case) to obtain a composite positive electrode material (where the content of component B is 5 wt.%). Among them, the particle size of the positive electrode material is 20 μm, and the particle size of the sodium-supplementing material is 5 μm.

[0051] (4) The obtained cathode active material, SP, and PVDF were mixed into a homogeneous slurry in a mass ratio of 90:5:5, and then coated on aluminum foil. Then, the film was dried in a vacuum drying oven at 110 °C for 4 hours. The electrode film was punched into a disc with a radius of 10 mm using a punching machine. A hard carbon negative electrode was used as the counter electrode (including a negative current collector such as copper foil and a negative electrode material composite on its surface, and the negative electrode material included a hard carbon material, PVDF, and conductive carbon black with a weight ratio of 90:5:5), 1 mol / L NaPF6 in EC+PC (1:1 vol%) + 5% FEC was used as the electrolyte, and the separator was glass fiber. A CR2016 type button battery was assembled in a glove box. The above battery was subjected to constant current charge-discharge testing, with a voltage range of 2-4 V, a test temperature of 25 °C, a test rate of 0.2C and 10C, and the initial discharge specific capacity and Coulomb efficiency at 0.2C and the capacity retention rate after 1000 cycles at 10C were tested.

[0052] Example 2

[0053] Compared with Example 1, the only difference was that the molar ratio of Na:Fe:P in step 1 was 4:2.90:4, and other conditions remained unchanged.

[0054] Example 3

[0055] Compared with Example 1, the only difference was that the sodium supplement agent in step 3 was changed, and other operations and parameters were the same as those in Example 1. The experimental groups were as follows:

[0056] Group A: The sodium supplement agent was diacetone sodium;

[0057] Group B: The sodium supplement agent was sodium oxalate + diacetone sodium with a mass ratio of 1:1;

[0058] Group C: The sodium supplement agent was sodium nickelate;

[0059] Other operations and parameters were the same as those in Example 1.

[0060] Example 4

[0061] Compared with Example 1, the only difference was that in step 3, the mixing method of component A and component B was wet ball milling, the grinding speed was 500 rpm, the ball-to-material ratio was 50:1, and the ball milling medium was acetone; other operations and parameters were the same as those in the example.

[0062] Example 5

[0063] Compared with Example 1, the difference is only that the in-situ preparation method is used for preparation. That is, in step 3, the sodium iron pyrophosphate sodium positive electrode material obtained in step 2 is pre-surface reacted with oxalic acid (the amount of oxalate is the same as that of component B in Example 1), and then the surface reaction product is separated, and then kept warm at a temperature of 160-180 °C in an Ar atmosphere for 6-7 h to obtain the in-situ sodium supplement composite material.

[0064] Example 6

[0065] Compared with Example 1, the difference is only that the slurry particle size in step 1 is controlled at D50 = 0.25 μm, the spray inlet temperature in step 2 is 220 °C, and the outlet temperature is 95 °C; the sintering temperature is 500 °C and the time is 10 h; other conditions remain unchanged.

[0066] Example 7

[0067] Compared with Example 1, the difference is only that in step 3, the mass ratio of the sodium supplement agent in the composite material is controlled at 3 wt%, and other conditions remain unchanged.

[0068] Comparative Example 1

[0069] Compared with Example 1, the difference is only that the Na:Fe:P molar ratio in step 1 is 4:3:4, and other conditions remain unchanged.

[0070] Comparative Example 2

[0071] Compared with Example 1, the difference is only that the sodium supplement treatment in step (3) is not carried out, but the component A prepared in step 3 is directly used as the active material for the test in step 4, and other conditions remain unchanged.

[0072] The test results of each case are shown in Table 1:

[0073] Table 1

[0074]

[0075] From the examples and comparative examples, it can be seen that the combination of the defective Na 4 Fe 3-a (PO 4 ) 2 P 2 O 7 material and the sodium supplement material can unexpectedly achieve synergy, improve its capacity utilization rate, improve the initial coulomb efficiency and the long cycle effect at high rates. In addition, from Examples 1 and 3, it can be seen that using the preferred sodium diacetone or a combined component containing sodium diacetone as the sodium supplement agent can further react with the defective Na 4 Fe 3-a (PO 4 )2 P 2 O 7 Material synergy combination can obtain better performance. It can also be known from Examples 1, 4 or 5 that by adopting the in-situ sodium supplementation scheme and the liquid-phase ball milling composite method, the material synergy can be further improved, which helps to further optimize the capacity utilization rate of the prepared material, improve the initial Coulomb efficiency and the long-cycle effect at high rates.

Claims

1. A sodium supplement Na4Fe 3-a (PO4)2P2O7 composite positive electrode material, characterized in that comprising component A and component B; The component A is an iron vacancy active material, and its chemical formula is Na4Fe 3-a (PO4)2P2O7 material, wherein 0.02≤a≤0.2; Component B is a sodium supplement, which includes at least one of C1-C6 sodium carboxylates, C4-C8 N-containing sodium carboxylates, sodium benzophenone, sodium oxide, and sodium nickelate.

2. Sodium supplement Na4Fe as claimed in claim 1 3-a (PO4)2P2O7 composite positive electrode material, characterized in that The component A is Na4Fe composite with carbon 3-a (PO4)2P2O7 materials; Preferably, the component B is in-situ compounded on the component A, and is obtained by sintering the precursor material of the component B and the surface of the component A; the precursor material includes at least one of C1-C6 carboxylic acids, C4-C8 N-containing carboxylic acids, boric acid, and phosphoric acid.

3. Sodium supplement Na4Fe as claimed in claim 1 3-a (PO4)2P2O7 composite positive electrode material, characterized in that The C1-C6 carboxylic acid is a monobasic, dibasic or polybasic carboxylic acid; preferably at least one of sodium acetate and sodium oxalate; Preferably, the C4-C8 sodium N-carboxylate is at least one of disodium ethylenediaminetetraacetate and tetrasodium ethylenediaminetetraacetate; Preferably, component B includes component B1 and component B2; wherein component B1 includes at least one of sodium oxalate and sodium nickelate; and component B2 includes at least one of sodium diacetone, sodium acetate, and tetrasodium ethylenediaminetetraacetate.

4. Sodium supplement Na4Fe as claimed in claim 1 3-a (PO4)2P2O7 composite positive electrode material, characterized in that The D50 of component A is less than 25 μm, preferably 4-15 μm; the D50 of component B is 2-5 μm; Sodium Supplement Na4Fe 3-a The (PO4)2P2O7 composite positive electrode material has a core-shell structure, wherein the component B is a shell.

5. The sodium supplement Na4Fe according to any one of claims 1 to 4 3-a (PO4)2P2O7 composite positive electrode material, characterized in that Sodium Supplement Na4Fe 3-a In the (PO4)2P2O7 composite positive electrode material, the content of component B is 1 to 10 wt%, preferably 2 to 5 wt%.

6. A sodium supplement Na4Fe according to any one of claims 1 to 5 3-a The method for preparing a (PO4)2P2O7 composite positive electrode material is characterized in that: Component A is prepared and mixed with component B to obtain the composite material; or the composite material is obtained by sintering the composite material after surface reaction of the precursor materials of component A and component B.

7. Sodium supplement Na4Fe as claimed in claim 6 3-a The method for preparing a (PO4)2P2O7 composite positive electrode material is characterized in that: The steps of preparing component A are: slurrying, spraying and heat treating a mixed raw material containing a carbon source and a stoichiometric sodium source, an iron source and a phosphorus source to obtain the component A; Preferably, the sodium source is at least one of sodium carbonate, sodium bicarbonate, sodium acetate, sodium dihydrogen phosphate, sodium phosphate, and sodium hydroxide; Optionally, the iron source is at least one of ferric phosphate, ferric oxalate, ferric nitrate, iron powder, ferric oxide, and ferrous sulfate; Optionally, the phosphorus source is at least one of phosphoric acid, sodium phosphate, ammonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, and iron phosphate; Optionally, the carbon source is an organic carbon source, further at least one of glucose, sucrose, citric acid, starch, ascorbic acid, cyclodextrin, and polyethylene glycol; Preferably, the weight ratio of the organic carbon source to the iron source is 1:5-20; Preferably, the outlet temperature of the spray is greater than 90°C; Preferably, the heat treatment temperature is 400-600° C., the heating rate is 2-4° C. / min, and the holding time is 4-15 h.

8. Sodium supplement Na4Fe as claimed in claim 7 3-a The method for preparing a (PO4)2P2O7 composite positive electrode material is characterized in that: Preferably, the mixing method of component A and component B is at least one of wet ball milling, dry ball milling, and gas mixing; Preferably, the medium for wet ball milling includes at least one of ethanol, acetone, and glycerol; The precursor raw material includes at least one of oxalic acid, boric acid and phosphoric acid; Preferably, the precursor material is 5wt%-10wt% of the weight of component A; The sintering process is carried out in a protective atmosphere, the sintering temperature is 150-250°C, and the sintering time is 5-10 hours.

9. A positive electrode of a sodium ion battery, comprising a current collector and a positive electrode material composited on the surface of the current collector, wherein the positive electrode material comprises a positive electrode active material, characterized in that: The positive electrode active material comprises the sodium supplement Na4Fe according to any one of claims 1 to 4 3-a (PO4)2P2O7 composite positive electrode material or sodium supplemented Na4Fe prepared by the preparation method according to any one of claims 5 to 8 3-a (PO4)2P2O7 composite positive electrode material.

10. A sodium ion battery, comprising a positive electrode, a negative electrode and a barrier layer disposed between the positive electrode and the negative electrode, characterized in that: The positive electrode is the positive electrode according to claim 9.

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