Pyrophosphate ferric sodium phosphate / C composite material and preparation and application thereof in sodium ion battery

Abstract

The invention belongs to the field of sodium ion batteries, and particularly relates to a pyrophosphoric acid ferric phosphate sodium / C composite material and preparation and application thereof.The preparation method comprises the step that slurry containing a sodium source, an iron source, a phosphorus source, a carbon source and an adjusting agent is subjected to spray drying-heat treatment or spray pyrolysis treatment, and the pyrophosphoric acid ferric phosphate sodium / C composite material is prepared, the invention is characterized in that the regulator is a compound having at least one of a formula 1 # imgabs, a formula 0 #, a formula 2 # imgabs 1 # and a formula 3 # imgabs 2 #. According to the present invention, with the regulator containing the components, the phase, the crystal face, the crystal grain and the defect of the prepared material can be accidentally optimized, the charge-discharge capacity of the prepared sodium ferric pyrophosphate positive electrode material can be accidentally further improved, and the fast charge performance, the long cycle stability and the low temperature performance are significantly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium-ion battery material preparation, and specifically relates to the field of positive electrode active materials for sodium-ion batteries. Technical Background

[0002] Due to its abundant sodium resources and low cost, sodium-ion batteries have become a highly attractive low-cost and high-efficiency alternative to meet the application of large-scale energy storage technologies. As a key component of sodium-ion batteries, the positive electrode material has become a determinant of the energy density and total cost in the battery system.

[0003] As a representative of iron-based phosphate positive electrodes, Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 (NFPP) has a high theoretical capacity of 129 mAh g -1 . The Fe 2+ / 3+ redox pair provides a relatively high average voltage platform of 3.1 V, and at the same time combines the advantages of phosphates and pyrophosphates. Thanks to the large three-dimensional open Na+ diffusion channels, the NFPP iron-based mixed phosphate positive electrode exhibits extremely small volume changes and strong structural stability during charge and discharge. Compared with toxic vanadium-based and structurally unstable manganese-based phosphate compounds, the low-cost NFPP polyanion positive electrode is one of the most promising and worthy of attention positive electrode materials. However, the poor electronic conductivity and slow sodium-ion diffusion kinetics of the sodium iron pyrophosphate positive electrode material hinder the perfect performance of its excellent electrochemical properties, resulting in its rate performance and long-cycle stability not meeting people's requirements. These problems have greatly hindered the practical application of sodium iron pyrophosphate. The means to improve the material properties are mainly divided into three aspects. One is metal ion doping; the second is to control the particle size of the positive electrode material; the third is morphology design and surface coating of the material. Among many synthesis methods, the sand grinding spray method is a highly advantageous synthesis route suitable for large-scale industrial production.

[0004] For example, Chinese patent document with publication number CN118825268A discloses a polyanion positive electrode material, its preparation method and application, specifically recording a scheme for preparing the positive electrode material by subjecting a sodium source, a phosphorus source and an iron source to secondary spraying and sintering. Chinese patent document with publication number CN118943336A discloses a preparation method of a single-crystalline sodium-ion battery positive electrode material, specifically recording a preparation process of grinding the particle size of iron phosphate slurry to D90≤0.5 μm, and then adding a supplementary phosphorus source, a sodium source and a carbon source for secondary ball milling and sintering.

[0005] The Chinese patent document with the publication number CN118851132A discloses a sodium-site doped carbon-coated sodium iron pyrophosphate phosphate and its preparation method and application. It is specifically recorded that after slurrying the A source / B source, sodium source, iron source, phosphorus source and carbon source, pre-sintering at 200-400 °C in advance, and then secondary grinding, two-stage sintering is carried out to obtain the sodium-site doped carbon-coated sodium iron pyrophosphate phosphate.

[0006] In summary, although there are some sanding and spray sintering preparation processes for sodium iron pyrophosphate phosphate materials in the prior art, in the existing sanding and spray preparation processes, it is difficult to ensure that all particles can be evenly stressed during the grinding process, resulting in a non-concentrated particle size distribution, uneven distribution of each element component, poor product consistency, and affecting subsequent electrochemical performance and processing performance. The uneven distribution of Na, Fe, and P element components easily leads to the generation of heterophases of sodium iron pyrophosphate and sodium iron phosphate in the generated material, affecting the capacity performance of the material and the attenuation of the cycle performance. In addition, it is difficult to optimize the interfacial interaction between carbon and the main material in the materials prepared by the prior art, the improvement of the electrical conductivity is relatively effective, and it is difficult to meet the application requirements of low temperature, super fast charging and high rate long cycle. Summary of the Invention

[0007] Aiming at the deficiencies of the prior art, the first object of the present invention is to provide a preparation method of a sodium iron pyrophosphate phosphate / C composite material, aiming to prepare a material that meets the application requirements of low temperature, super fast charging and long cycle.

[0008] The second object of the present invention is to provide a sodium iron pyrophosphate phosphate / C composite material prepared by the above preparation method and its application in sodium ion batteries.

[0009] The third object of the present invention is to provide a sodium ion battery containing the sodium iron pyrophosphate phosphate / C composite material.

[0010] A preparation method of a sodium iron pyrophosphate phosphate / C composite material, wherein a slurry containing a sodium source, an iron source, a phosphorus source, a carbon source and an adjusting agent is subjected to spray drying-thermal treatment or spray pyrolysis treatment to obtain the sodium iron pyrophosphate phosphate / C composite material;

[0011] The adjusting agent is a compound having at least one of Formula 1, Formula 2, and Formula 3:

[0012]

[0013]

[0014] The X is a carbon chain of C 1 ~C 3 The R 1 is H or C 1 ~C 3An alkyl group, where M is H, Na or NH 4 ;

[0015] The R 2 is C 1 ~C 3 alkyl group, amino group or is

[0016] The R 3 is H, C 1 ~C 3 alkyl group, Na or NH 4 .

[0017] Innovatively, the compounds with the structures of Formula 1 to Formula 3 of the present invention are used to participate in the slurrying process of the raw materials and the subsequent heat treatment (spray pyrolysis process), which helps to optimize the nucleation of sodium iron pyrophosphate, optimize the crystal plane and surface defect structure. In addition, it can also improve the interfacial physicochemical structure between the carbon layer and sodium iron pyrophosphate and homogenize the element distribution. The research of the present invention shows that the material prepared by the preparation method can unexpectedly meet the requirements of low temperature and super fast charging applications. In addition, it can also improve the long-range cycling performance at high rates.

[0018] In the present invention, the components of the sodium source, iron source, phosphorus source, and carbon source and the ratio between the components can be reasonably adjusted as needed.

[0019] For example, the sodium source includes at least one of sodium acetate, sodium carbonate, sodium bicarbonate, trisodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium pyrophosphate, and sodium citrate.

[0020] The iron source includes at least one of iron oxide, iron phosphate, and ferrous oxalate.

[0021] The phosphorus source includes at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, trisodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, and sodium pyrophosphate.

[0022] The carbon source includes at least one of hard carbon source and soft carbon source, and further preferably includes at least one of citric acid, glucose, sucrose, fructose, lactose, phenolic resin, polyethylene glycol, polyvinyl alcohol, polyglycerol, graphene, and carbon nanotubes.

[0023] In the present invention, the regulator can cooperate with the spray heat treatment process, and can optimize the surface grains, crystal planes and surface morphology of the prepared material, which is beneficial to improving its fast charging, long cycle and low temperature performance. The research also shows that using Formula 1 as the regulator, especially Formula 1 where R 1 is an alkyl group, can obtain better performance compared with other regulators.

[0024] Preferably, the conditioner is a composite of Formula 1 and Formula 3. Further preferably, the weight ratio of Formula 1 to Formula 3 is 1:0.1 - 2; preferably 1:0.5 - 1. Research in the present invention shows that the conditioner in the preferred ratio helps to further optimize the phase, crystal grains, defects and elemental homogenization effect of the product, and helps to further optimize the low temperature, fast charging and long cycle effects of the material.

[0025] The slurry can be prepared by conventional means. For example, it can be obtained by liquid-phase sanding of a sodium source, an iron source, a phosphorus source, a carbon source, and a conditioner.

[0026] In the present invention, the solvent in the slurry includes water.

[0027] In the present invention, the molar ratio of Na, Fe, and P elements in the slurry is 3.95 - 4.05:2.86 - 3:4 - 4.1; preferably 4:2.96:4.05.

[0028] In the present invention, the carbon source is 10 - 20 wt% of the weight of the designed sodium iron pyrophosphate material.

[0029] In the present invention, the conditioner is 1 - 3 wt% of the weight of the designed sodium iron pyrophosphate material.

[0030] In the present invention, in the spray drying - heat treatment process, the inlet temperature of spray drying is 150°C - 270°C, the outlet temperature is 80°C - 130°C; the heat treatment temperature is 475 - 550°C; the heat treatment time is 8 - 20 h;

[0031] Preferably, the temperature in the spray pyrolysis process is 475 - 550°C.

[0032] The present invention also provides a sodium iron pyrophosphate / C composite material prepared by the above - mentioned preparation method.

[0033] The preparation method of the present invention can endow the prepared material with special physical and chemical characteristics, and the material prepared by the preparation method can unexpectedly significantly improve its electrochemical performance at low temperature, super fast charging and high rate.

[0034] The present invention also provides an application of the sodium iron pyrophosphate / C composite material prepared by the above - mentioned preparation method. Using it as a positive electrode active material for preparing sodium - ion batteries.

[0035] The present invention also provides a sodium - ion battery, which includes the sodium iron pyrophosphate / C composite material prepared by the preparation method of the present invention.

[0036] For the sodium - ion battery of the present invention, except for including the sodium iron pyrophosphate / C composite material of the present invention, other components and structural relationships can be known in the industry.

[0037] Beneficial effects:

[0038] In the present invention, the compounds with the structures of Formula 1 to Formula 3 are innovatively used to participate in the slurrying process of raw materials and subsequent heat treatment (spray pyrolysis process). This helps to homogenize the contact of sodium iron pyrophosphate phosphate elements, improve nucleation and control crystal grains. In addition, it can also optimize the phase and improve the interface. Research in the present invention shows that the materials prepared by the described preparation method can unexpectedly meet the application requirements of low temperature and super fast charging. In addition, it can also improve the long-range cycling performance at high rates. The method of the present invention is simple to operate, has low energy consumption, high efficiency, and has a cost advantage, and can realize large-scale industrial production. Description of the drawings

[0039] Figure 1 SEM diagram of the sodium iron pyrophosphate phosphate material obtained in Example 1;

[0040] Figure 2 Cycling diagram of 1C of the sodium iron pyrophosphate phosphate material obtained in Example 1. Detailed implementation manners

[0041] An optional preparation method of a sodium iron pyrophosphate phosphate / C composite material of the present invention comprises the following steps:

[0042] Step 1: Add a sodium source, an iron source, a phosphorus source, a carbon source, and an adjusting agent to deionized water, stir and disperse to obtain a suspension; pour the suspension into a sand mill, and obtain a sanded slurry after sanding;

[0043] Step 2: Perform spray granulation on the slurry to obtain a spray-dried precursor material;

[0044] Step 3: Sinter the precursor material under an inert atmosphere to obtain a sodium iron pyrophosphate phosphate cathode material;

[0045] In step (2), the rotation speed of the sanding is 1500 - 2500 rpm, preferably 2000 rpm, the sanding time is 2 - 10 h, preferably 6 h, and the average particle size of the sanded slurry is 100 nm - 300 nm, preferably 200 nm.

[0046] In the spray drying granulation process in step (3), the inlet air temperature is 150°C - 270°C, and the outlet temperature is 80°C - 130°C.

[0047] In step (4), the sintering conditions are: heating to 475 - 550°C; the sintering time is 8 - 20 h, and the heating rate is 2 - 5°C / min.

[0048] In step (4), the inert reducing atmosphere is one or a mixture of two or more of nitrogen, argon, and hydrogen, preferably a mixture of argon and hydrogen, and the volume percentage content of hydrogen is 1 - 5%.

[0049] The following are more typical cases:

[0050] Example 1:

[0051] Weigh the corresponding materials of sodium bicarbonate, iron oxide, and ammonium dihydrogen phosphate according to the molar ratio of Na, Fe, and P elements of 4:2.96:4.05. Add citric acid as the carbon source, with a weight of 15 wt% of the content of the designed sodium iron pyrophosphate material to be synthesized. Add a regulator (in this case, Formula A, with a structure of ); the regulator is 2% of the content of the designed sodium iron pyrophosphate material to be synthesized. Add deionized water and grind it in a sand mill at a speed of 2000 rpm for 4 hours to obtain a milled slurry (the average particle size of the particles in the slurry is 200 - 230 nm). Spray-dry the obtained slurry at an inlet temperature of 180 °C and an outlet temperature of 100 °C to obtain a sodium iron pyrophosphate precursor powder; place the sodium iron pyrophosphate precursor powder in a tube furnace, heat it to 550 °C at a heating rate of 2 °C / min in a hydrogen / argon mixed atmosphere (hydrogen content is 3 v%) and keep it calcined for 10 h, and then cool it with the furnace to obtain a sodium iron pyrophosphate cathode material (chemical formula Na4Fe3(PO4)2P2O7).

[0052] Example 2:

[0053] Compared with Example 1, the only difference is that the type of regulator is changed, and other operations and parameters are the same as those in Example 1. The experimental groups are as follows:

[0054] Group A: The regulator is Formula B, with a structure of:

[0055] Group B: The regulator is Formula C, with a structure of:

[0056] Group C: The regulator is Formula D, with a structure of:

[0057] Group D: The regulator is Formula E, with a structure of:

[0058] Group E: The regulator is a composition of Formula A and Formula E with a weight ratio of 1:0.5;

[0059] Group F: The regulator is a composition of Formula A and Formula D with a weight ratio of 1:0.5;

[0060] Other operations and parameters are the same as those in Example 1.

[0061] Example 3:

[0062] Compared with Example 1, the only difference is that the carbon source is glucose, which is 10% of the designed weight of sodium iron pyrophosphate, the regulator is 4% of the designed weight of sodium iron pyrophosphate; the sanding time is 6 h, the inlet temperature of spraying is 210 °C, and the outlet temperature is 110 °C; the calcination atmosphere is Ar atmosphere, the calcination temperature is 500 °C, and the heat preservation time at the calcination temperature is 14 h. Other operations and parameters are the same as those in Example 1.

[0063] Comparative Example 1:

[0064] Compared with Example 1, the only difference is that no regulator is added, and other operations and parameters are the same as those in Example 1.

[0065] Comparative Example 2:

[0066] Compared with Example 1, the only difference is that polyvinylpyrrolidone is used to replace the regulator with equal weight, and other operations and parameters are the same as those in Example 1.

[0067] Comparative Example 3:

[0068] Compared with Example 1, the only difference is that sodium dodecyl sulfate is used to replace the regulator with equal weight, and other operations and parameters are the same as those in Example 1.

[0069] Comparative Example 4:

[0070] Compared with Example 1, the only difference is that Comparative Formula A is used to replace the regulator with equal weight, and other operations and parameters are the same as those in Example 1.

[0071] Comparative Example 5:

[0072] Compared with Example 1, the only difference is that Comparative Formula B is used to replace the regulator with equal weight, and other operations and parameters are the same as those in Example 1.

[0073] Comparative Example 6:

[0074] Compared with Example 1, the only difference is that the regulator does not participate in the sanding and spraying treatment process. Instead, other components except the regulator are sanded and sprayed to obtain a precursor, and the precursor and the regulator are mixed and then subjected to subsequent calcination treatment together. Other operations and parameters are the same as those in Example 1.

[0075] Test Example: The sodium iron pyrophosphate cathode materials prepared in each example and comparative example, Super-P, and PVDF are dispersed in NMP according to a mass ratio of 8:1:1. After being ground and dispersed evenly, they are coated on an aluminum foil and dried in a vacuum oven at 100 °C to obtain a cathode electrode sheet with a surface density of 6-8 mg cm -2, with sodium metal as the negative electrode plate, a glass fiber membrane as the separator, and NaClO as the electrolyte 4 / EC+DEC (EC:DEC = 1:1 by volume), and an additive of 5% fluoroethylene carbonate (FEC) is additionally added to the electrolyte. A button battery is assembled in a glove box. During the electrochemical performance test, the charge-discharge temperature is room temperature, the test voltage range is 1.7V to 4.2V, and the current of 1C is 129mA / g. The test results are shown in Table 1.

[0076] Table 1:

[0077]

[0078]

[0079] It can be seen from Examples 1 to 3 and Comparative Examples 1 to 5 that by selecting the components described in the present invention as the regulator, it can unexpectedly optimize the phase, crystal plane, crystal grains, and defects of the prepared material, and can unexpectedly further improve the charge-discharge capacity, fast charging performance, long cycle stability, and low-temperature performance of the prepared sodium iron pyrophosphate positive electrode material. In addition, it can be seen from Examples 1 and 2 that using Formula 1, especially the preferred Formula 1, as a single regulator can obtain a better physical and chemical adjustment effect of the material. In addition, combining Formula 1 and Formula 3 can further achieve synergy, which helps to further optimize the physical and chemical structure of the material and can obtain better fast charging, long cycle, and low-temperature stability and other performances.

Claims

1. A method for preparing a sodium iron pyrophosphate / C composite material, comprising spray drying-heat treatment or spray pyrolysis treatment of a slurry containing a sodium source, an iron source, a phosphorus source, a carbon source, and a regulator to obtain the sodium iron pyrophosphate / C composite material, characterized in that: The adjusting agent is a compound having at least one of Formula 1, Formula 2, and Formula 3: The X is a C1-C3 carbon chain, the R1 is H or a C1-C3 alkyl group, and the M is H, Na or NH4; The R2 is a C1-C3 alkyl, an amino or The R3 is H, C1-C3 alkyl, Na or NH4.

2. The method for preparing the sodium iron pyrophosphate / C composite material according to claim 1, characterized in that: The sodium source includes at least one of sodium acetate, sodium carbonate, sodium bicarbonate, trisodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium pyrophosphate, and sodium citrate; Preferably, the iron source includes at least one of iron oxide, iron phosphate and ferrous oxalate.

3. The method for preparing the sodium iron pyrophosphate / C composite material according to claim 1, characterized in that: The phosphorus source includes at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, trisodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, and sodium pyrophosphate.

4. The method for preparing the sodium iron pyrophosphate / C composite material according to claim 1, characterized in that: The carbon source includes at least one of a hard carbon source and a soft carbon source, and further preferably includes at least one of citric acid, glucose, sucrose, fructose, lactose, phenolic resin, polyethylene glycol, polyvinyl alcohol, polypropylene glycol, graphene, and carbon nanotubes.

5. The method for preparing the sodium iron pyrophosphate / C composite material according to claim 1, characterized in that: The adjusting agent is a compound of Formula 1 and Formula 3. More preferably, the weight ratio of Formula 1 to Formula 3 is 1:0.1-2; preferably 1:0.5-1.

6. The method for preparing the sodium iron pyrophosphate / C composite material according to claim 1, characterized in that: The slurry is obtained by liquid-phase sand milling of a sodium source, an iron source, a phosphorus source, a carbon source and a regulator; Preferably, the solvent in the slurry comprises water; Preferably, the molar ratio of Na, Fe and P elements in the slurry is 3.95-4.05:2.86-3:4-4.1; preferably 4:2.96:4.05; Preferably, the carbon source is 10-20 wt% of the weight of the designed sodium iron pyrophosphate material; Preferably, the regulator is 1 to 3 wt % of the weight of the designed sodium ferric pyrophosphate material.

7. The method for preparing the sodium iron pyrophosphate / C composite material according to claim 1, characterized in that: In the spray drying-heat treatment process, the air inlet temperature of the spray drying is 150℃~270℃, the outlet temperature is 80℃~130℃; the heat treatment temperature is 475℃~550℃; the heat treatment time is 8~20h; Preferably, the temperature in the spray pyrolysis process is 475-550°C.

8. A sodium iron pyrophosphate / C composite material obtained by the preparation method according to any one of claims 1 to 7.

9. An application of the sodium iron pyrophosphate / C composite material prepared by the preparation method according to any one of claims 1 to 7, characterized in that: It is used as positive electrode active material to prepare sodium ion batteries.

10. A sodium ion battery, characterized in that: The invention relates to a sodium iron pyrophosphate / C composite material prepared by the preparation method according to any one of claims 1 to 7.

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