Preparation method and application of sodium ion positive electrode material

Abstract

The application provides a preparation method and application of a sodium ion positive electrode material, and belongs to the technical field of sodium ion batteries. Iron source, carbon source, sodium source and phosphorus source are added into deionized water in proportion, and a suspension is obtained by stirring at room temperature; the stirring is continuously carried out, a grinding aid agent is added, and after sand milling, spray drying is carried out to obtain a precursor powder; and the precursor powder is sintered in stages in an inert atmosphere to obtain a sodium iron pyrophosphate phosphate positive electrode material. The sodium ion positive electrode material has the advantages of simple operation, easy control, easy scale production, environmental friendliness, excellent electrochemical comprehensive performance and the like.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method and application of a sodium ion positive electrode material and belongs to the technical field of sodium ion batteries. BACKGROUND

[0002] Under the driving of the national strategic goal of "carbon peak and carbon neutralization", energy storage is an important part of the new power system, and plays an irreplaceable role in ensuring the smooth operation of the power system. Energy storage power stations participate in system peak regulation and frequency modulation, which can enhance the stability of the power grid, and the large-scale development has become an inevitable trend. At present, most of the energy storage systems adopt electrochemical energy storage, and the most rapid development in the electrochemical energy storage is lithium ion batteries. However, lithium ion batteries have problems such as poor safety, high cost and unstable lithium resource supply chain. Compared with lithium ion batteries, sodium ion batteries have lower unit cost, better safety and wider working temperature range, but slightly lower energy density. Therefore, in the field of energy storage with high safety requirements and cost sensitivity, sodium ion batteries have great application potential, such as in the field of two-wheeled vehicles and low-speed electric vehicles, sodium ion batteries are expected to complement and effectively replace lithium ion batteries and lead-acid batteries.

[0003] At present, the mainstream technical route of sodium ion battery positive electrode materials includes layered oxide materials, prussian blue type materials and polyanion materials, but each has limitations.

[0004] Layered oxides have the problems of irreversible phase change and poor air stability. During the deintercalation process in the layered structure, the large volume of Na + often causes irreversible changes to the material structure, resulting in degradation of battery cycle performance; layered oxides are easily hygroscopic and will absorb moisture in the air when exposed to air, which will affect the electrochemical performance.

[0005] Although the prussian blue type compound has low manufacturing cost, it has the problem of crystal water, which is difficult to control in mass production and will affect the cycle performance and safety of the battery.

[0006] The poly-anion material is an olivine structure similar to lithium iron phosphate, has high structural stability, and has the longest theoretical cycle life, and is more suitable for the energy storage market. The raw material of the poly-anion material is sodium iron phosphate pyrophosphate, which has low cost, good cycle performance (volume change < 5% during charging and discharging), high thermal stability, and is not easily affected by the environment. However, sodium iron phosphate pyrophosphate often needs to be coated with carbon to improve the electrical conductivity of the material. When mixing, an organic carbon source containing monosaccharide or disaccharide is added, and the material is prone to wall sticking during subsequent spray drying, resulting in low material yield and unstable sugar metering ratio, which ultimately affects the performance of the product. Iron oxide (Fe2O3) is the most common iron source, widely used in architectural coatings and automotive coatings, with mature preparation process, sufficient production, and low price. However, the Mohs hardness of Fe2O3 is about 7, which makes sanding difficult and requires a long sanding time, greatly reducing production efficiency. In addition, long sanding time can cause Fe2O3 to settle, affecting the sanding effect. SUMMARY

[0007] To solve the above technical problems, the present application first provides a preparation method of sodium ion positive electrode material. This process not only effectively shortens the sanding time and improves the sanding efficiency, but also improves the wall sticking phenomenon of the material, which is beneficial to improving the material yield and the stability of the product performance. The sodium ion positive electrode material can be produced in batches.

[0008] Specifically, the present application is realized by the following scheme:

[0009] A preparation method of sodium ion positive electrode material, comprising the following steps:

[0010] Step one: according to the stoichiometric ratio, respectively take sodium source, iron source, phosphorus source and carbon source, and add them into deionized water in turn, and stir and disperse at room temperature to obtain a suspension;

[0011] Step two: continuously stir, add grinding aid, keep the suspension from settling, and put the suspension into a sand mill to sand the suspension with sanding medium;

[0012] Step three: spray dry the sanded suspension to obtain a precursor powder;

[0013] Step four: put the precursor powder into a kiln, and perform a staged sintering process in an inert atmosphere to obtain a sodium ion positive electrode material.

[0014] Further, as a preferred:

[0015] In step one,

[0016] The sodium source is at least one of an organic sodium salt, an inorganic sodium salt, metallic sodium, and a sodium oxide. More preferably, the inorganic sodium salt is at least one of sodium carbonate, sodium bicarbonate, sodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, and sodium pyrophosphate; the organic sodium salt is at least one of sodium oxalate, sodium acetate, and sodium citrate; and the sodium oxide is at least one of sodium oxide and sodium peroxide.

[0017] The iron source is at least one of an inorganic iron salt, an organic iron salt, and an iron oxide. More preferably, the inorganic iron salt is at least one of ferric oxide, ferric tetroxide, ferric nitrate, ferric phosphate, and ferrous carbonate; the organic iron salt is at least one of ferrous oxalate, ferrous acetate, and ferrous carbonate; and the iron oxide is at least one of ferric oxide and ferric oxide, with ferric oxide being the most preferred.

[0018] The phosphorus source is at least one of phosphoric acid, phosphates, and pyrophosphates. More preferably, the phosphate is at least one of sodium dihydrogen phosphate, ammonium dihydrogen phosphate, disodium hydrogen phosphate, diammonium hydrogen phosphate, and sodium phosphate; and the pyrophosphate is at least one of sodium pyrophosphate, trisodium monohydrogen pyrophosphate, disodium dihydrogen pyrophosphate, and monosodium trihydrogen pyrophosphate.

[0019] The carbon source is at least one of a high-temperature carbonizable organic substance and maltodextrin. More preferably, the high-temperature carbonizable organic substance is at least one of glucose, sucrose, citric acid, stearic acid, oxalic acid, and cellulose. The maltodextrin is at least one of maltodextrins with different reducing sugar equivalents (DE values). Maltodextrins with different DE values ​​include those with a DE of 4% to 6%, where the sugar composition consists entirely of larger molecules of tetrasaccharides or higher; those with a DE of 9% to 12%, where the sugar composition comprises a lower proportion of low-molecular sugars; those with a DE of 13% to 17%, which are less susceptible to moisture and browning and have good solubility; and those with a DE of 18% to 20%, which have a certain degree of hygroscopicity, can undergo a browning reaction, and have good solubility. Maltodextrins with a lower DE value of 4% to 6% are optimal.

[0020] In step 2,

[0021] The grinding aid is one of polyethylene glycols (PEG) of varying molecular weights. More preferably, the grinding aid is any one of PEG-200, PEG-400, PEG-600, PEG-800, PEG-1000, PEG-1500, PEG-2000, PEG-3000, PEG-4000, PEG-6000, and PEG-8000, preferably PEG-2000 to PEG-8000, and most preferably PEG-4000.

[0022] The sanding medium is at least one of natural sandstone, zirconia beads, glass beads, steel beads, agate beads; the sanding medium has a diameter of 0.1-3mm, preferably 0.3-0.4mm.

[0023] The sanding machine is one of a disc type, a pin type, and a turbine type.

[0024] The sanding machine has a sanding rotation speed of 1000-2500rpm, preferably 1200-2000rpm; the sanding time is 0.5h-2h; and the particle size of the material after sanding is required to be D50 in the range of 300-500nm.

[0025] In step three, the inlet temperature of the spray drying is 150-250℃, and the outlet temperature is 90-130℃.

[0026] In step four,

[0027] The inert sintering atmosphere is one of nitrogen, nitrogen-hydrogen mixed gas, argon, and argon-hydrogen mixed gas.

[0028] The two-stage temperature rising is used in the staged sintering treatment. More preferably, the two-stage temperature rising is first raised from room temperature to 200-350℃, and the temperature is kept for 1h-12h at a temperature rising rate of 0.5-5℃ / min, and then raised to 450-650℃, and the temperature is kept for 1h-24h at a temperature rising rate of 0.5-5℃ / min.

[0029] Meanwhile, the second aspect of the present application aims to provide the application of the above-mentioned sodium ion positive electrode material in a sodium ion battery: the above-mentioned sodium ion positive electrode material of sodium iron pyrophosphate phosphate, a binder PVDF, and a conductive agent Super P are uniformly mixed in an organic solvent at a mass ratio of 94:2.5:3.5, coated on an aluminum foil current collector, and then dried and rolled to become a positive electrode sheet; and then combined with a negative electrode sheet and a separator to form an electric core, and then injected into an electrolyte to form a sodium ion battery.

[0030] The present application has the following beneficial effects:

[0031] (1) When iron oxide is used as the iron source, the Mohs hardness is large (about 7), which leads to a large difficulty in sanding, a long sanding time, a large particle size of the sanding material, and easy settlement in the sanding process, greatly reducing the production efficiency, increasing the production cost, and affecting the sanding quality. The addition of the grinding aid polyethylene glycol in the sanding stage can greatly shorten the sanding time, on the one hand, improving the production efficiency, and on the other hand, reducing the energy consumption cost; at the same time, the particle size of the required material is ground to be smaller and more uniform, which is more conducive to the subsequent secondary granulation of spray drying, and a precursor powder with uniform particle size can be obtained.

[0032] For example, when iron oxide is used as the iron source, the sand milling time required without adding a grinding aid, such as polyethylene glycol, is not less than 2 h, and the slurry particle size is 0.5-0.8 μm; adding PEG-4000 or the like as a grinding aid can shorten the sand milling time by 50%, and at the same time, the slurry particle size after sand milling can be controlled to be 0.3-0.5 μm.

[0033] (2) When sucrose or glucose, a single-chain sugar (C6H 12 O6), is used as the carbon source, the single-chain sugar is coated on the material surface, and in the spray drying process, the intermolecular force increases due to high temperature, and the viscosity also increases, so that the sucrose or glucose, a single-chain sugar, carries a large amount of the material and adheres to the inner wall of the spray drying equipment. This seriously affects the material yield, the sugar metering ratio and the product performance, and at the same time, the equipment cleaning is difficult and has a high frequency, which greatly hinders batch production. Maltodextrin is a multi-chain polymer sugar, has a three-dimensional network structure, has strong water retention ability after absorbing water, has strong combination and adhesion, has strong film-forming property at a low DE value, and can form a soft, stretchable and heat-reversible gel. When sucrose or glucose, a single-chain sugar, is used as the carbon source, adding a certain proportion of maltodextrin with a low DE value can significantly improve the material wall sticking in the spray drying process, improve the material yield and stabilize the product performance, and at the same time, the process is simple, easy to control and green, and is conducive to industrial large-scale batch production.

[0034] (3) Sodium iron phosphate pyrophosphate has poor electronic conductivity, and a carbon coating method is often used to improve the electronic conductivity of the material to improve the electrochemical performance. The strong film-forming property of maltodextrin with a low DE value can optimize the coating effect of the carbon source, make the material surface coating more uniform, and greatly improve the electronic conductivity of the ion cathode material.

[0035] (4) The preparation method of the application has the advantages of simple operation, easy process control, simple process and easy industrial preparation, and has a good development prospect in the field of large-scale energy storage. The sodium ion battery cathode material prepared by the method of the application has good cycle stability, high specific capacity and good rate performance, and provides support for the large-scale and industrial development of the sodium ion battery cathode material. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 SEM image of the sodium ion battery cathode material prepared in Example 1, magnified by 1000 times;

[0037] Figure 2 SEM image of the sodium ion battery cathode material prepared in Example 1, magnified by 5000 times;

[0038] Figure 3 XRD image of the sodium ion battery cathode material prepared in Example 1;

[0039] Figure 4 Charge-discharge curve of the sodium-ion cathode material prepared in Example 1 as a sodium-ion battery cathode material;

[0040] Figure 5 Charge-discharge curve of the sodium-ion cathode material prepared in Example 10 as a sodium-ion battery cathode material. DETAILED DESCRIPTION

[0041] The principles and features of the present application are described below in conjunction with the accompanying drawings, and the examples are only used to explain the present application and are not intended to limit the scope of the present application. Example 1

[0042] The preparation method of the sodium-ion cathode material in the present embodiment uses Fe2O3 as the iron source, NaH2PO4 as the sodium source and phosphorus source, and glucose and maltodextrin as the carbon source. The specific preparation process is as follows:

[0043] (1) 1197.675 g of iron oxide, 2399.18 g of sodium dihydrogen phosphate, 540.48 g of glucose, 311.685 g of maltodextrin (DE < 6%), and 62.337 g of polyethylene glycol PEG-4000 were added to 6767.0355 mL of deionized water, and the suspension was stirred at room temperature to obtain a suspension;

[0044] (2) The suspension was transferred to a sand mill for sand milling, and the suspension was continuously stirred to prevent sedimentation. About 0.3 mm zirconia beads were selected as the sand milling medium, the sand mill speed was 1300 rpm, and the sand milling time was 1 h;

[0045] (3) The sand-milled suspension was transferred to a spray dryer for spray drying, the inlet air temperature was 160℃, and the outlet air temperature was 95℃, to obtain a precursor powder;

[0046] (4) The precursor was sintered under the protection of argon-hydrogen mixed gas (5% H2). The first stage temperature was 350℃, and the holding time was 5 h. The second stage temperature was 550℃, and the holding time was 15 h. After the material cooled down, the sodium-ion cathode material was obtained.

[0047] The sodium-ion cathode material prepared in the present embodiment and the button half-cell formed by assembling the sodium-ion cathode material as a cathode material were subjected to performance detection, and the results are as follows Figures 1 to 4The prepared sodium ion positive electrode material powder is spherical in shape, and the product particle size can be controlled. The 2theta has significant peaks near 10°, 16°, 17°, 24°, 26°, 33° and 35°, indicating that the product is a relatively pure sodium iron pyrophosphate positive electrode material. The working voltage of the obtained half-cell is between 1.5V and 4.2V, the initial coulombic efficiency is >97%, the reversible capacity at 0.1C is >110mAh / g, the reversible capacity of the assembled button half-cell at 1C is >100mAh / g, and there is almost no attenuation after 300 cycles. Example 2

[0048] The settings of this example and example 1 are the same, the difference is that in step (1), the grinding aid is PEG-3000. The sanding effect is slightly worse, and under the same sanding time, the material particle size is about 5% larger. Example 3

[0049] The settings of this example and example 1 are the same, the difference is that in step (1), the grinding aid is PEG-6000. The sanding effect is not much different, and can reach the required process level, but the material price is about 10% higher, and the economic benefit is poor. Example 4

[0050] The settings of this example and example 1 are the same, the difference is that in step (1), the grinding aid is PEG-8000. The sanding effect is slightly better, and the sanding time can be shortened by about 7%, but the material price is about 30% higher, the cost is higher in industrialization and large-scale production, and the economic benefit is poor. Example 5

[0051] The settings of this example and example 1 are the same, the difference is that in step (1), the malt dextrin is malt dextrin with DE of about 12%. The results show that the spray drying wall sticking phenomenon is slight, and the overall effect is good. Example 6

[0052] The settings of this example and example 1 are the same, the difference is that in step (1), the malt dextrin is malt dextrin with DE of about 17%. The spray drying wall sticking phenomenon is slight, and the overall effect is slightly worse than example 5. Example 7

[0053] The settings of this example and example 1 are the same, the difference is that in step (1), the malt dextrin is malt dextrin with DE of about 20%. The spray drying wall sticking phenomenon is slight, and the overall effect is slightly worse than example 6. Example 8

[0054] The present example and the setting of example 1 are the same, the difference is that: step (1) without adding grinding aid polyethylene glycol PEG-4000. The sanding time required to increase more than 50%, and can not be sanding material to 0.5 μm and below, sanding effect is poor, the energy consumption is high, long time. Example 9

[0055] The present example and the setting of example 1 are the same, the difference is that: step (1) without adding malt dextrin, that is, the carbon source is only glucose. The spray drying process is easy to stick wall, material output rate is low, the product performance is poor. Example 10

[0056] The present example and the setting of example 1 are the same, the difference is that: step (1) without adding grinding aid polyethylene glycol PEG-4000, and the carbon source is only glucose without malt dextrin. The sanding effect and spray drying effect is worse than example 1.

[0057] The positive electrode material prepared in example 10 was subjected to charge-discharge experiment, the results are shown as follows: Figure 5 The first coulomb efficiency of the obtained positive electrode material is 95.9%, and the reversible capacity reaches 103 mAh / g at 0.1C. The reversible capacity of the assembled button half cell reaches 92 mAh / g at 1C.

[0058] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a sodium ion positive electrode material, characterized in that: Here are the steps: Step 1: weigh the sodium source, iron source, phosphorus source and carbon source according to the stoichiometric ratio, add them into deionized water in sequence, and stir and disperse them at room temperature to obtain a suspension. The sodium source is at least one of sodium carbonate, sodium bicarbonate, sodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium pyrophosphate, sodium oxalate, sodium acetate, sodium citrate, sodium oxide, and sodium peroxide; The iron source is at least one of ferric oxide, ferric oxide, ferric nitrate, ferric phosphate, ferrous carbonate, ferrous oxalate, and ferrous acetate; The phosphorus source is at least one of sodium dihydrogen phosphate, ammonium dihydrogen phosphate, disodium hydrogen phosphate, diammonium hydrogen phosphate, sodium phosphate, sodium pyrophosphate, trisodium monohydrogen pyrophosphate, disodium dihydrogen pyrophosphate and monosodium trihydrogen pyrophosphate. The carbon source is a mixture of at least one high-temperature carbonizable organic matter and maltodextrin, the high-temperature carbonizable organic matter is at least one of glucose, sucrose, citric acid, stearic acid, oxalic acid, and cellulose, and the maltodextrin is maltodextrin with a DE of 4-6%; Step 2: Continue stirring and add a grinding aid to keep the suspension from settling, and place the suspension in a sand mill for sand grinding, wherein the grinding aid is a mixture of any one or more of PEG-200, PEG-400, PEG-600, PEG-800, PEG-1000, PEG-1500, PEG-2000, PEG-3000, PEG-4000, PEG-6000, and PEG-8000. The sand mill speed is 1000-2500 rpm, the sand grinding time is 0.5 h-2 h, and the particle size D50 of the material after sand grinding is required to be 300-500 nm; Step 3: spray drying the sand-milled suspension to obtain a precursor powder, wherein the inlet temperature of the spray drying is 150-250° C. and the outlet temperature is 90-130° C.; Step 4: Place the precursor powder in a kiln and sinter it in stages in an inert atmosphere to obtain a sodium ion positive electrode material. The staged sintering treatment adopts a two-stage heating method: first, heat it from room temperature to 200°C~350°C, keep it warm for 1h~12h, and the heating rate is 0.5~5°C / min. Then, heat it to 450°C~650°C, keep it warm for 1h~24h, and the heating rate is 0.5~5°C / min.

2. The method for preparing a sodium ion positive electrode material according to claim 1, wherein: During the grinding process, a sand grinding medium is added, wherein the sand grinding medium is at least one of natural sand, zirconia beads, glass beads, steel balls, and agate beads, and the diameter of the sand grinding medium is 0.1-3 mm.

3. An application of the sodium ion positive electrode material prepared by the method of claim 1, characterized in that: The sodium ion positive electrode material is evenly mixed with the binder PVDF and the conductive agent Super P in a mass ratio of 94:2.5:3.5 in an organic solvent, coated on an aluminum foil current collector, and dried and roller-pressed to form a positive electrode sheet; then it is combined with the negative electrode sheet and the separator to form a battery cell, and after being placed in a shell, the electrolyte is injected to form a sodium ion battery.

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