High-solid-degree composite sodium ferric phosphate positive electrode material, preparation method thereof and battery

Abstract

The invention relates to a high-solid-degree composite sodium ferric phosphate positive electrode material, a preparation method thereof and a battery, and belongs to the technical field of sodium ion battery positive electrode material preparation. According to the preparation method, the molar ratio of Fe < 2 + > to Na < + > to P < 3 + > is (0.8-1.0): (1.0-1.3): 1; grinding the compounded raw materials with grinding beads, wherein the filling rate of the grinding beads is 60-70%; carrying out spray drying, rotational flow crushing and solidification; carrying out segmented gradient sintering; the finished product particles are prepared by sintering at three stages of different temperatures in combination with atmosphere regulation and control; and preparing coating slurry, mixing and dispersing the coating slurry and the finished product particles, and drying to obtain the composite sodium ferric phosphate positive electrode material. The solid degree and the tap density of the particles can be improved, the solid particle proportion of the obtained composite sodium iron phosphate positive electrode material is larger than or equal to 85%, and the tap density is 2.05-2.2 g / cm < 3 >.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sodium-ion battery cathode material preparation, in particular to a high-solidity composite sodium iron phosphate cathode material and a preparation method thereof and a battery. BACKGROUND

[0002] Composite sodium iron phosphate (Na4Fe3(PO4)2(P2O7)) is a new type of battery cathode material, which has the advantages of high energy density, long cycle life, and environmental friendliness, and is widely used in electric vehicles and energy storage systems.

[0003] The composite sodium iron phosphate prepared by the existing preparation method has low particle solid fraction (solid particle ratio) and tap density, and in the batch production process in the pilot stage, the 10C cycle retention rate (1500 times) is low and the batch solid fraction fluctuates greatly.

[0004] For example, the patent with publication number CN119284857A prepares sodium iron pyrophosphate phosphate by a preparation method of solid phase mixing and secondary sintering. The carbon-coated sodium iron pyrophosphate phosphate is mixed with an organic carbon source and sintered at 400-580℃ to improve the uniformity of carbon coating, but its tap density is only 1.8g / cm 3 For example, the patent with publication number CN116002650A uses a coprecipitation method to prepare Fe(OH)3 precursor, mixes it with sodium source, phosphorus source and carbon source, and then sprays and dries, and then synthesizes composite sodium iron phosphate by high temperature pyrolysis. The solid particle ratio is only 60%-70%.

[0005] Therefore, there is an urgent need for a preparation method to improve the particle solid fraction and tap density of composite sodium iron phosphate and realize batch production. SUMMARY

[0006] In view of the above analysis, the present application aims to provide a high-solidity composite sodium iron phosphate cathode material and a preparation method thereof and a battery, to solve the problem of low particle solid fraction and tap density of existing composite sodium iron phosphate.

[0007] In one aspect, the present application provides a preparation method of a high-solidity composite sodium iron phosphate cathode material, comprising the following steps:

[0008] S1: raw material ratio, according to the molar ratio: Fe 2+ : Na + : P 3+ = (0.8-1.0) : (1.0-1.3) : 1;

[0009] S2: grinding the raw materials, using grinding beads to grind the compounded raw materials, the filling rate of the grinding beads is 60-70%;

[0010] S3: spray-drying solidification by cyclone breaking;

[0011] S4: sectional gradient sintering; by sintering at three different temperatures and matching atmosphere control, the finished product particles are prepared;

[0012] S5: carbon-based material coating, prepare coating slurry, mix and disperse with finished product particles, dry to obtain composite sodium iron phosphate positive electrode material.

[0013] Further, ensure that the discharge D50≤1μm, D90≤3μm, and the particle size distribution span (D90-D10) / D50≤2.5.

[0014] Further, in step S3, the cyclone breaking device is used for breaking, and the rotating speed is 200-300rpm.

[0015] Further, in step S3, the atomization pressure is 0.85-1.2MPa, and the feeding flow rate is 10-15L / h.

[0016] Further, the average particle size of the finished product particles is 5-10μm, and the solid core proportion is ≥90%.

[0017] Further, the three different temperatures include a low-temperature section, a medium-temperature section, and a high-temperature section.

[0018] The temperature of the low-temperature section is room temperature-300℃, the heating rate is 3-5℃ / min, the holding time is 4-7h, the gas is nitrogen, and the flow rate is 5-8m 3 / h;

[0019] The temperature of the medium-temperature section is 300-500℃, the heating rate is 2-3℃ / min, the holding time is 2-4h, the gas is a mixture of nitrogen and argon, the N2 / Ar volume ratio is 9:1, and the flow rate is 8-10m 3 / h;

[0020] The temperature of the high-temperature section is 500-700℃, the heating rate is 1-2℃ / min, the holding time is 5-8h, the gas is argon, and the flow rate is 10-15m 3 / h.

[0021] Further, the coating slurry in S5 is carbon nanotubes and graphene, and the mass ratio of the carbon nanotubes to the graphene is 1:1-2:1.

[0022] Preferably, the tube diameter of the carbon nanotubes is 10-20nm, and the purity is ≥95%.

[0023] Preferably, the single-layer rate of the graphene is ≥90%.

[0024] Further, the solid particles of the composite sodium iron phosphate positive electrode material account for ≥ 85%, and the tap density is 2.05-2.2 g / cm 3 .

[0025] In another aspect, the application provides a high-solid composite sodium iron phosphate positive electrode material obtained by the preparation method.

[0026] A battery comprising a positive electrode material obtained by the preparation method.

[0027] Compared with the prior art, the application can achieve at least one of the following beneficial effects:

[0028] 1. The application improves the solidness and tap density of the particles by precisely controlling the raw material ratio, grinding process, spray drying, cyclone breaking, solidification, segmented gradient sintering, and carbon-based material coating, etc., to ensure that the solid particles of the obtained composite sodium iron phosphate positive electrode material account for ≥ 85%, and the tap density is 2.05-2.2 g / cm 3 ;

[0029] 2. The application can improve the consistency and stability of the material. Precise raw material ratio can ensure the completeness and uniformity of the reaction, and the grinding process can make the raw material mixture more uniform. The segmented gradient sintering can precisely control the sintering process of the particles according to the characteristics of different temperature sections, reduce the differences between batches, and thus improve the cycle retention rate and batch stability.

[0030] 3. In the application, spray drying and cyclone breaking can form a more compact structure in the drying process, and the segmented gradient sintering can precisely control the sintering process of the particles according to the characteristics of different temperature sections, further improving the solidness and tap density of the particles.

[0031] In the application, the above technical solutions can be combined with each other to achieve more preferred combination schemes. Other features and advantages of the application will be described in the subsequent specification, and some advantages will become apparent from the specification or by implementing the application. The purpose and other advantages of the application can be achieved and obtained from the specific embodiments described in the specification and the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0032] The accompanying drawings are included to provide a further understanding of the application and are incorporated herein and constitute a part of the application. The same reference numbers in the drawings indicate the same elements throughout the drawings.

[0033] Figure 1 is a low-magnification SEM morphology diagram of Example 1;

[0034] Figure 2 is a high-magnification SEM morphology diagram of Example 1;

[0035] Figure 3 is a low-magnification SEM morphology of Comparative Example 2;

[0036] Figure 4 is a high-magnification SEM morphology of Comparative Example 2;

[0037] Figure 5 is a 0.2C charge-discharge curve of different examples and comparative examples;

[0038] Figure 6 is a schematic diagram of the overall structure of a spray drying tower;

[0039] Figure 7 is a partial enlarged schematic diagram of Figure 6

[0040] Figure 8 is a formal projection view of a spray drying tower;

[0041] Figure 9 is a schematic diagram of the structure of a guide plate in a cyclone device;

[0042] Reference signs:

[0043] 1, tower body; 11, tower body section; 12, guide section; 13, discharge port; 14, air duct; 2, crushing device; 21, motor; 22, connecting rod; 23, rotating shaft; 24, blade set; 25, blade; 3, cyclone device; 31, guide plate; 311, guide pipe; 312, inner chamber; 313, injection hole. DETAILED DESCRIPTION

[0044] The preferred embodiments of the present application will be described in detail below with reference to the drawings, which form a part of this application, and together with the embodiments of the present application, illustrate the principles of the present application, but are not intended to limit the scope of the present application.

[0045] Composite sodium iron phosphate (Na4Fe3(PO4)2(P2O7)) is a new type of battery positive electrode material, which has the advantages of high energy density, long cycle life, and environmental friendliness, and is widely used in electric vehicles and energy storage systems.

[0046] The composite sodium iron phosphate prepared by the existing preparation method has low particle solidness (the proportion of solid particles) and tap density, and in the batch production process in the pilot stage, the 10C cycle retention rate (1500 times) is low and the batch solidness fluctuates greatly.

[0047] ​For example, the patent with publication number CN119284857A relates to the preparation of sodium iron phosphate pyrophosphate, a preparation method by solid phase mixing and secondary sintering, carbon-coated sodium iron phosphate pyrophosphate is mixed with an organic carbon source and sintered at 400-580°C, improving the uniformity of carbon coating, but its tap density is only 1.8g / cm 3 . For example, the patent with publication number CN116002650A uses a coprecipitation method to prepare Fe(OH)3 precursor, which is mixed with a sodium source, a phosphorus source, and a carbon source, then spray dried, and then synthesized into a composite sodium iron phosphate by high temperature pyrolysis, with a solid particle ratio of only 60%-70%.

[0048] Therefore, the present application provides a preparation method of a high-solid composite sodium iron phosphate positive electrode material, comprising the following steps:

[0049] S1: raw material ratio, according to the molar ratio: Fe 2+ : Na + : P 3+ = (0.8-1.0) :(1.0-1.3) :1;

[0050] S2: grinding of raw materials, using grinding beads to grind the compounded raw materials, the filling rate of the grinding beads is 60-70%;

[0051] S3: spray drying, cyclone breaking and solidification;

[0052] S4: step-by-step gradient sintering; by sintering at three different temperatures and cooperating with atmosphere control, the finished product particles are prepared;

[0053] S5: carbon-based material coating, preparing a coating slurry, mixing and dispersing it with the finished product particles, and drying to obtain a composite sodium iron phosphate positive electrode material.

[0054] Compared with the prior art, the present application can improve the consistency and stability of the material by precisely controlling the raw material ratio, grinding process, spray drying, cyclone breaking and solidification, step-by-step gradient sintering and carbon-based material coating. Precise raw material ratio can ensure the completeness and uniformity of the reaction, the grinding process can make the raw material mixing more uniform, and the step-by-step gradient sintering can precisely control the sintering process of the particles according to the characteristics of different temperature sections, reducing the differences between batches and improving the cycle retention rate and batch stability. In the present application, spray drying, cyclone breaking and solidification can make the particles form a more dense structure during the drying process, and the step-by-step gradient sintering can precisely control the sintering process of the particles according to the characteristics of different temperature sections, further improving the solidness and tap density of the particles, ensuring that the solid particle ratio of the obtained composite sodium iron phosphate positive electrode material is ≥85%, and the tap density is 2.05-2.2g / cm 3 .

[0055] Specifically, the raw materials include an iron source, a sodium source and a phosphorus source, and need to be strictly formulated according to the molar ratio: Fe 2+ : Na + : P 3+ = (0.8-1.0) : (1.0-1.3) : 1.

[0056] Preferably, the iron source is one or more of iron sulfate, ferrous sulfate, ferric nitrate, ferric chloride, ferrous oxalate, ferric phosphate, ferric acetate, ferroferric oxide, ferriferrous oxide, ferric pyrophosphate.

[0057] Preferably, the sodium source is one or more of sodium carbonate, sodium hydroxide, sodium acetate, sodium citrate, sodium bicarbonate, sodium pyrophosphate, sodium acetate, sodium phosphate, sodium sulfate.

[0058] Preferably, the phosphorus source is one or more of sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium phosphate.

[0059] It should be noted that in the present application, the source of raw materials includes an iron source, a sodium source and a phosphorus source, which is relatively extensive, and only needs to be formulated according to the molar ratio: Fe 2+ : Na + : P 3+ = (0.8-1.0) : (1.0-1.3) : 1.

[0060] Specifically, the D50 of the discharge is ensured to be ≤1 μm, the D90 is ensured to be ≤3 μm, and the particle size distribution span (D90-D10) / D50 is ensured to be ≤2.5.

[0061] It should be noted that in the present application, the grinding process adopts a horizontal sand mill, and the raw materials, grinding beads and slurry are added for grinding to achieve uniform dispersion at the nanometer level. The D50 of the discharge is ensured to be ≤1 μm, the D90 is ensured to be ≤3 μm, and the particle size distribution span (D90-D10) / D50 is ensured to be ≤2.5. The particle size distribution span (D90-D10) / D50 is controlled to be below 2.5, which improves the dispersibility and reduces the particle segregation problem.

[0062] It should be noted that in the present application, the filling rate and particle size of the grinding beads need to be strictly controlled, wherein the filling rate is controlled to be 60-70% (volume ratio), and the particle size is controlled to be The material of the grinding beads is one of zirconium oxide, silicon nitride and aluminum oxide.

[0063] Preferably, in step S1, the grinding beads are zirconium oxide grinding beads with a particle size of 0.1-0.3 μm.

[0064] Preferably, in step S1, the grinding beads are nitride silicon grinding beads with a particle size of 0.1-0.3 μm.

[0065] Preferably, in step S1, the grinding beads are alumina grinding beads.

[0066] It should be noted that in the grinding of the present application, the grinding slurry needs to be added, wherein the solid content of the grinding slurry is 25%-35wt%, the solvent is deionized water (conductivity <1 μS / cm), and the dispersant is one or more of sodium polyacrylate, sodium polycarboxylate, and sodium methylene bisnaphthalene sulfonate (dosage is 0.7%-1.3% of the total mass of the raw material).

[0067] After the grinding beads and the grinding slurry are added to the horizontal sand mill, the feeding speed of the grinding slurry needs to be controlled at 5-10 L / h, the rotation speed of the sand mill is 1000-2000 rpm (linear speed ≥10 m / s), the sand mill is circulated for 3-7 times, and the interval between each circulation is 10 min to avoid overheating of the grinding slurry.

[0068] By using the grinding method provided by the present application, the grinding energy density is improved by 30% through high filling rate design of fine beads, the single sand mill efficiency is improved by 2 times (compared with traditional process), micron-level agglomerates are completely broken, and hollow particle nucleation sites are eliminated. At the same time, the ratio of dispersant to solvent is optimized, the Fe / Na / P element distribution deviation is <1.5% (ICP-OES detection), and a homogeneous precursor is provided for subsequent solid particle growth. After grinding, the discharge D50 is ≤1 μm, the discharge D90 is ≤3 μm, the particle size distribution span (D90-D10) / D50 is ≤2.5, and nanoscale uniform dispersion is achieved. Specifically, in step S3, a cyclone crushing device is added, and the rotation speed is 200-300 rpm.

[0069] Specifically, in step S3, the atomization pressure is 0.85-1.2 MPa, and the feeding flow rate is 10-15 L / h.

[0070] It should be noted that in step S3 of the present application, a pilot-scale spray drying tower (processing capacity 50-100 kg / h) is used for spray drying and cyclone crushing of the solid particles.

[0071] Figures 6-9 .

[0072] The spray drying tower comprises a tower body 1, a crushing device 2, and a cyclone device 3; the tower body 1 is hollow, and comprises a tower body section 11 and a flow guide section 12; the tower body section 11 is cylindrical, and the flow guide section 12 is frustum-shaped; the flow guide section 12 is integrally formed with the tower body section 11, and the flow guide section 12 is located below the tower body section 11, and a discharge port 13 is arranged at one end of the flow guide section 12 away from the tower body section 11;

[0073] ​The crushing device 2 is composed of a driving assembly and a plurality of crushing assemblies, the crushing assemblies are arranged in the tower body 1, and each crushing assembly comprises a rotating shaft 23 and a blade group 24;

[0074] The driving assembly comprises a motor 21 and a connecting rod 22 connected with the motor 21, the connecting rod 22 is lapped on the upper end of the tower body 1, the connecting rod 22 is perpendicular to the axis of the tower body 1, the center of the connecting rod 22 coincides with the axis of the tower body 1, and the crushing assembly is connected on the connecting rod 22. The rotating shaft 23 and the blade group 24 constitute the crushing assembly, the rotating shaft 23 is connected on the connecting rod 22, and the rotating shaft 23 is uniformly distributed along the length direction of the connecting rod 22; the blade group 24 is rotationally connected on the end of the rotating shaft 23 away from the connecting rod 22, the blade group 24 is composed of a plurality of blades 25, and the blades 25 rotate along the axis of the rotating shaft 23. The number of the crushing assemblies is three, and the blade group 24 comprises three blades 25. The distance between the ends of adjacent blades 25 and the distance between the end of the blade 25 and the inner wall of the tower body 1 are greater than or equal to 50 mm, and the distance between the blade group 24 and the discharge port 13 on the tower body 1 is 200-300 mm.

[0075] The cyclone device 3 comprises a guide plate 31, the guide plate is arranged on the inner wall of the tower body 1 and communicates with the air pipe (not shown in the figure) through the air duct 14 on the tower body 1; the guide plate 31 comprises an inner chamber 312, a guide pipe 311 and a jet hole 313; the guide pipe 311, the inner chamber 312 and the jet hole 313 are in communication, and the guide pipe 311 is inserted into the air duct 14 of the tower body 1. The guide plates 31 are uniformly arranged along the axis of the tower body 1, and the number of the guide plates 31 is four. The number of the jet holes 313 is multiple, and they are uniformly arranged. The jet direction of the axis of the jet hole 313 is opposite to the intersection of the tower body 1, and the included angle between the tangent of the intersection point of the tower body 1 and the axis of the jet hole 313 is 30°.

[0076] The movement process of the spray drying tower:

[0077] Start the motor 21, the motor 21 provides power, then drives the rotating shaft 23 to rotate along the axis of the rotating shaft 23 through the transmission device (not shown in the figure, the existing gear chain structure can be used), and then drives the blade 25 to rotate, so as to realize the crushing of the hollow particles.

[0078] The gas enters the inner chamber 312 from the air pipe along the guide pipe 311, is blown into the tower body 1 from the jet hole 313 after being uniformly and stably in the inner chamber 312, the gravity of the solid particles is greater than the buoyancy, and the solid particles are discharged from the discharge port, the hollow particles are blown up by the cyclone device 3, are crushed by the crushing device 2, and then are re-formed into new particles, so as to continuously perform the cycle, improve the solid degree, and improve the proportion of the solid particles.

[0079] The two-fluid atomizing nozzle is used for atomization, the atomization pressure is controlled to be 0.85-1.2 MPa, and the feeding flow rate of the grinding slurry is 10-15 L / h. The inlet air temperature and the outlet air temperature need to be controlled during the atomization, that is, the inlet air temperature is 220-250 DEG C (adjusted by an electric heating tube + hot air circulation system, the precision is ± 5 DEG C), and the outlet air temperature is 100-120 DEG C.

[0080] The particle forming mechanism is that the solvent on the surface of the atomized droplet is rapidly evaporated to form a shell, and the internal slurry shrinks to the center due to the temperature gradient; the blade is sheared and broken at a rotating speed of 200-300 rpm to break the hollow shell, and the high-concentration slurry (solid content ≥ 35%) is re-aggregated into a solid core under the action of surface tension, so that the average particle size of the finished product is 5-10 μm, and the solid core accounts for ≥ 90%.

[0081] Specifically, the three different temperatures include a low-temperature section, a medium-temperature section and a high-temperature section.

[0082] The temperature of the low-temperature section is room temperature-300 DEG C, the temperature increasing rate is 3-5 DEG C / min, the holding time is 4-7 h, the gas is nitrogen, and the flow rate is 5-8 m 3 / h;

[0083] The temperature of the medium-temperature section is 300-500 DEG C, the temperature increasing rate is 2-3 DEG C / min, the holding time is 2-4 h, the gas is a mixed gas of nitrogen and argon (N2 / Ar volume ratio 9:1), and the flow rate is 8-10 m 3 / h;

[0084] The temperature of the high-temperature section is 500-700 DEG C, the temperature increasing rate is 1-2 DEG C / min, the holding time is 5-8 h, the gas is argon, and the flow rate is 10-15 m 3 / h.

[0085] It should be noted that, in the application, different temperatures are used for sintering. In the low-temperature section, the temperature is controlled to be below 300 DEG C (not including the point value of 300 DEG C), the purpose is to gradually remove the residual solvent (water, ethanol, etc.) and the dispersing agent, avoid the internal pores and hollow structure of the particles caused by rapid volatilization at high temperature, and protect Fe 2+ from being oxidized. In the medium-temperature section, the temperature is controlled to be 300-500 DEG C (not including the point value of 500 DEG C), by reducing the temperature increasing rate and the mixed gas atmosphere, the preliminary bonding of Na + , Fe 2+ and pyrophosphate (P2O7 4-) framework pre-forming, providing a stable structural basis for high-temperature section crystal growth. In the high-temperature section, the temperature is controlled to be 500-700℃, and through extremely low heating rate, long holding time and high-purity argon protection, the complete growth of the composite sodium iron phosphate crystal form and the densification of the particles are realized, the internal pores are eliminated, and finally a high solid content structure is formed.

[0086] Specifically, the coating slurry is carbon nanotubes and graphene, and the mass ratio of the carbon nanotubes to the graphene is 1:1-2:1.

[0087] Preferably, the carbon nanotube has a tube diameter of 10-20 nm and a purity of ≥95%.

[0088] Preferably, the graphene has a single-layer rate of ≥90%.

[0089] It should be noted that the preparation raw materials of the coating slurry mainly include carbon nanotubes and graphene, and the ratio of the two is controlled. Imbalance of the ratio will lead to incomplete conductive network, for example, too many carbon nanotube CNTs are easy to agglomerate, and too many graphene are easy to stack. The preparation raw materials of the coating slurry also include deionized water / ethanol (volume ratio 1:1), and a dispersing aid sodium carboxymethyl cellulose, the amount of which is 0.4-0.6wt% of the coating slurry.

[0090] High-shear dispersing machine (rotation speed 2000-3000 rpm, dispersion time 30-45 min) is used for dispersion treatment to ensure uniform dispersion of CNTs and graphene without obvious agglomeration. The slurry solid content (5-10wt%) can stabilize the slurry viscosity at 100-300 mPa·s, which not only ensures the fluidity during high-shear dispersion, but also forms a uniform coating layer through adsorption during the coating stage.

[0091] Specifically, in the coating process, the coating slurry and the finished particles are added to the pilot-scale horizontal mixer, the rotation speed is controlled at 80-150 rpm, and the mixing time is 50-120 min, so that the carbon slurry is uniformly adsorbed on the surface of the particles.

[0092] It should be noted that the rotation speed (80-150 rpm) and time (50-120 min) of the horizontal mixer realize the uniform adsorption of the carbon slurry on the surface of the particles. Too low rotation speed (<80 rpm) will lead to insufficient coating (no coating in some parts); too high rotation speed (>150 rpm) will cause particle breakage (especially brittle particles after sintering) due to excessive shear force.

[0093] Drying process, fluidized bed dryer (temperature 80-100℃, wind speed 1.5m / s), drying time 1-2h, control coating thickness 10-20nm, avoid carbon structure damage caused by traditional high temperature drying (>150℃). Temperature >100℃ will cause carbon material (especially graphene) pyrolysis; temperature <80℃ is not fully dried, residual solvent causes the coating layer to crack.

[0094] Coating efficiency improvement: the unique screw belt structure of the horizontal mixer improves the uniformity of coating to more than 95%, which has a significant advantage over traditional ball milling coating (uniformity 70%-80%). Synergistic enhancement of conductivity: CNTs form a conductive network, and graphene provides a two-dimensional conductive base surface, and the electrical conductivity of the composite material reaches 5.2×10 -3 S / cm, which is 48% higher than single carbon coating (3.5×10 -3 S / cm).

[0095] Single carbon material instead of mixed coating: use conductive carbon black (such as SuperP) or acetylene black instead of carbon nanotube-graphene combination, coating slurry solid content is increased to 15wt%, and uniform coating is achieved through ball milling mixing (speed 150rpm, time 90min), reducing material cost.

[0096] The application provides a battery comprising a positive electrode material, which is prepared by the method of the application.

[0097] In order to more clearly describe the application, the following examples and comparative examples are further illustrated.

[0098] Example 1

[0099] The application provides a preparation method of high-solid composite sodium iron phosphate positive electrode material, comprising the following steps:

[0100] S1: raw material ratio, mix iron sulfate, sodium dihydrogen phosphate and sodium phosphate according to the element molar ratio Fe 2+ :Na + : P 3+ =0.92:1.12:1, wherein 3kg of dispersant (30% sodium polyacrylate solution) is added;

[0101] S2: grinding of raw materials, using a horizontal sand mill for grinding: Zirconia beads (filling rate 65%), solid content 27%, feeding speed 5L / h, speed 1200rpm, circulating sand mill 5 times; discharge result: D50=0.7μm, D90=2.3μm, (D90-D10) / D50=1.8;

[0102] S3: spray drying solidification by cyclone breaking; spray drying solidification by cyclone breaking was carried out in a pilot-scale spray drying tower, a cyclone device and a breaking device were added 300 mm above the discharge port, including three groups of symmetrical rotating blades, the rotating speed of the blades was 250 rpm, the atomization pressure was 0.85 MPa, and the feeding flow was 12 L / h. The inlet air temperature and the outlet air temperature need to be controlled during the atomization process, the inlet air temperature was 240 DEG C, and the outlet air temperature was 110 DEG C;

[0103] S4: sectional gradient sintering; the finished product particles were prepared by sintering at three different temperatures and cooperating with atmosphere regulation;

[0104] the low-temperature section: 280 DEG C for 5 h (from room temperature to 280 DEG C at a rate of 5 DEG C / min), the medium-temperature section: 470 DEG C for 2.5 h (from 280 DEG C to 470 DEG C at a rate of 2.5 DEG C / min), and the high-temperature section: 610 DEG C for 6 h (from 470 DEG C to 610 DEG C at a rate of 1.5 DEG C / min); the atmosphere: pure N2 (4 m 3 / h) in the low-temperature section, N2 / Ar = 9:1 (10 m 3 / h) in the medium-temperature section, and pure Ar (12 m 3 / h) in the high-temperature section;

[0105] XRD without impurity phase, and the cross-section solid particle accounted for 89% in SEM;

[0106] S5: carbon-based material coating;

[0107] The coating slurry was prepared, the mixing speed was 100 rpm, the mixing time was 45 min, the carbon nanotube: graphene = 1:1, and the solid content was 8 wt%; the carbon nanotube had a tube diameter of 10-20 nm and a purity of greater than or equal to 95%; the single-layer rate of the graphene was greater than or equal to 90%; the preparation raw material of the coating slurry further included deionized water / ethanol (volume ratio 1:1) and a dispersing aid carboxymethyl cellulose sodium, and the amount of the dispersing aid carboxymethyl cellulose sodium was 0.45 wt% of the coating slurry.

[0108] The CNTs and the graphene were uniformly dispersed without obvious agglomeration by adopting a high-shear dispersing machine (rotating speed 2300 rpm, dispersing time 40 min); the slurry solid content (5-10 wt%) could stabilize the slurry viscosity at 100-300 mPa·s;

[0109] The coating slurry and the finished product particles were added into a pilot-scale horizontal mixer, the rotating speed was controlled at 120 rpm, and the mixing time was 80 min;

[0110] The fluidized bed dryer was used to dry at 85 DEG C for 1.5 h, the air speed was 1.5 m / s, and the composite sodium iron phosphate positive electrode material was obtained after drying.

[0111] Example 2

[0112] Example 2 is substantially the same as the preparation process of Example 1, except that the sand milling process in Example 2 uses silicon nitride beads (filling rate 65%), solid content 35%, circulating sand milling 6 times, the discharge result: D50 = 0.9 μm, D90 = 2.6 μm, (D90-D10) / D50 = 1.9.

[0113] Example 3

[0114] Example 3 is substantially the same as the preparation process of Example 1, except that the sintering process in Example 3 adjusts the heating rate of the low temperature section, the medium temperature section, and the high temperature section to the lower limit.

[0115] The heating rate of the low temperature section is 3℃ / min, the heating rate of the medium temperature section is 2℃ / min, and the heating rate of the high temperature section is 1℃ / min.

[0116] Example 4

[0117] Example 4 is substantially the same as the preparation process of Example 1, except that the coating process in Example 4 uses conductive carbon black instead of carbon nanotube-graphene, and the solid content is 15wt%.

[0118] Comparative Example 1

[0119] Comparative Example 1 is substantially the same as the preparation process of Example 1, except that the sand milling process in Comparative Example 1 uses zirconia beads (filling rate 60%), only circulating sand milling 2 times, the discharge result: D50 = 2 μm, D90 = 4.5 μm, (D90-D10) / D50 = 2.6.

[0120] Comparative Example 2

[0121] Comparative Example 2 is substantially the same as the preparation process of Example 1, except that the spray drying process in Comparative Example 2 does not have a cyclone crushing device in the spray drying tower equipment.

[0122] Comparative Example 3

[0123] Comparative Example 3 is substantially the same as the preparation process of Example 1, except that the sintering process in Comparative Example 3 is single-stage sintering, room temperature-610℃ (heating rate 5℃ / min) for 6h.

[0124] Performance detection

[0125] The above examples and comparative examples are subjected to performance detection, and the specific detection results are shown in Table 1.

[0126] Table 1 Performance detection results

[0127]

[0128]

[0129] In combination with Examples 1-4 and Comparative Examples 1-3, and with reference to Table 1 and Figures 1-6 It can be seen that, by using the preparation method provided by the present application, the solid particles of the high-solid-content composite sodium iron phosphate positive electrode material obtained account for more than 89%, the tap density is more than 2.08 g / cm 3 The above 10C cycle retention rate (1500 times) is more than 95.8%, and the production of each batch is relatively stable, with a solid content fluctuation of less than 5.5%. The 0.2C charge gram capacity is more than 116.71 mAh / g, the 0.2C discharge gram capacity is more than 106.74 mAh / g, and the 0.2C coulombic efficiency is more than 91.46%.

[0130] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A method for preparing a high solidity composite sodium iron phosphate cathode material, characterized in that, The method comprises the following steps: S1 : Raw material proportioning, according to the molar ratio: Fe 2+ : Na + : P 3+ = (0.8-1.0) : (1.0-1.3) : 1; S2: grinding the raw materials, wherein the compounded raw materials are ground by using grinding beads, and the filling rate of the grinding beads is 60-70%; S3: spray drying and solidification by cyclone crushing; S4: subsection gradient sintering, wherein the finished product particles are prepared by sintering at three different temperatures and cooperating with atmosphere control; S5: carbon-based material coating, wherein the coating slurry is prepared, mixed and dispersed with the finished product particles, and dried to obtain the composite sodium iron phosphate positive electrode material.

2. The method for preparing a high-solidity composite sodium iron phosphate cathode material according to claim 1, characterized in that, The discharge D50 is ensured to be ≤1 μm, the D90 is ensured to be ≤3 μm, and the particle size distribution span (D90-D10) / D50 is ensured to be ≤2.

5.

3. The method for preparing a high-solidity composite sodium iron phosphate cathode material according to claim 1, characterized in that, In step S3, the crushing is performed by a cyclone crushing device, and the rotating speed is 200-300 rpm.

4. The method for preparing a high-solidity composite sodium iron phosphate cathode material according to claim 1, characterized in that, In step S3, the atomization pressure is 0.85-1.2 MPa, and the feeding flow rate is 10-15 L / h.

5. The method for preparing a high-solidity composite sodium iron phosphate cathode material according to claim 1, characterized in that, The average particle size of the finished product particles is 5-10 μm, and the solid core ratio is ≥90%.

6. The method of claim 1, wherein the high-density composite sodium iron phosphate cathode material is prepared by the steps of: mixing a sodium source, an iron source, and a phosphorus source to form a mixture; and heating the mixture to a temperature of 600-800°C for 1-10 hours in a non-oxidizing atmosphere. The three different temperatures include a low-temperature section, a medium-temperature section and a high-temperature section. The temperature of the low-temperature section is room temperature-300 DEG C, the temperature increasing rate is 3-5 DEG C / min, the holding time is 4-7h, the gas is nitrogen, and the flow rate is 5-8m 3 / h. The temperature of the medium temperature section is 300-500℃, the temperature rising rate is 2-3℃ / min, the holding time is 2-4h, the gas is the mixed gas of nitrogen and argon, the volume ratio of N2 / Ar is 9:1, and the flow rate is 8-10m 3 / h. The temperature of the high-temperature section is 500-700℃, the temperature rising rate is 1-2℃ / min, the holding time is 5-8h, the gas is argon, and the flow rate is 10-15m 3 / h.

7. The method for preparing a high-solidity composite sodium iron phosphate cathode material according to claim 1, characterized in that, The coating slurry in S5 is carbon nanotubes and graphene, and the mass ratio of the carbon nanotubes to the graphene is 1:1-2:

1. Preferably, the tube diameter of the carbon nanotubes is 10-20 nm, and the purity is ≥95%. Preferably, the single-layer rate of the graphene is ≥90%.

8. The method of claim 1, wherein the high-density composite sodium iron phosphate cathode material is prepared by the steps of: The solid particles of the composite sodium iron phosphate positive electrode material account for ≥ 85%, and the tap density is 2.05-2.2 g / cm 3 . ​ 9. A high solidity composite sodium iron phosphate cathode material, characterized in that, The method is obtained by any one of claims 1-8.

10. A battery, characterized by The positive electrode material is obtained by any one of claims 1-8.

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