Preparation method of olivine-type sodium ferric phosphate, olivine-type sodium ferric phosphate and sodium ion battery

Abstract

The invention provides a preparation method of olivine-type sodium ferric phosphate, olivine-type sodium ferric phosphate and a sodium ion battery, and particularly relates to the technical field of sodium ion secondary batteries. The preparation method comprises the following steps: dissolving sodium propionate and sodium salt, adding olivine type iron phosphate, and grinding to obtain precursor slurry; and carrying out spray drying on the precursor slurry, and sintering at 200-400 DEG C to obtain the olivine type sodium ferric phosphate. In the preparation method provided by the invention, sodium propionate not only serves as a sodium source, but also can promote a kinetic process of a solid-phase reaction, so that purer olivine sodium ferric phosphate is prepared, and the capacity is further improved. And in order to reduce high content of ineffective carbon caused by difficult decomposition of propionate at low temperature, a proper metal oxide precursor needs to be additionally introduced to facilitate effective decomposition of carbonaceous species in the pyrolysis process, and a feasible path is provided for low-cost and large-scale preparation of the high-performance NaFePO4 material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sodium ion secondary battery, in particular to a preparation method of olivine-type sodium iron phosphate, olivine-type sodium iron phosphate and sodium ion battery. BACKGROUND

[0002] Among various kinds of sodium ion battery cathode materials, olivine-type sodium iron phosphate is one of the most concerned cathode materials due to the same stable structure characteristics as LiFePO4, smooth charge-discharge curve and high capacity.

[0003] At present, olivine structure NaFePO4 cannot be directly synthesized by solid phase sintering. The reason is related to the thermodynamic instability of olivine structure NaFePO4. It usually undergoes a crystal phase transition at a high temperature of 480℃, from olivine structure to a non-electrochemically active sodium iron phosphate structure, resulting in a sharp decline in electrochemical performance. Therefore, the mainstream synthesis method of olivine structure NaFePO4 is ion exchange method, which mainly converts olivine structure LiFePO4 into olivine structure NaFePO4 through two steps of delithiation and sodium intercalation.

[0004] In the ion exchange method, although delithiation by chemical method can be easily realized by oxidizing agent, there are significant technical problems in the sodium intercalation process: first, the existing sodium intercalation process cannot realize the complete intercalation of sodium ions at low temperature, and if the temperature is increased, the above-mentioned crystal phase transition risk will be easily triggered; second, the selection range of sodium salt used for sodium intercalation is narrow, and single sodium salt or conventional compound sodium salt cannot take into account the low-temperature reaction activity and sodium intercalation efficiency, and there is a lack of effective additives that can promote low-temperature solid phase sintering reaction and assist the complete intercalation of sodium ions. That is, low-temperature sintering cannot realize the complete intercalation of sodium ions, and it is difficult to synthesize stoichiometric olivine-type NaFePO4.

[0005] Therefore, the present application is proposed. SUMMARY

[0006] The present application aims to provide a preparation method of olivine-type sodium iron phosphate, olivine-type sodium iron phosphate and sodium ion battery, and at least one of the above technical problems in the prior art is solved.

[0007] In order to achieve the above-mentioned purpose of the present application, the following technical solutions are adopted: The first aspect of the present application provides a preparation method of olivine-type sodium iron phosphate. Sodium propionate and sodium salt are dissolved, and then olivine-type sodium iron phosphate is added for grinding to obtain a precursor slurry. The precursor slurry is subjected to spray drying, and then sintered at 200-400℃ to obtain the olivine-type sodium iron phosphate.

[0008] Further, the sodium salt comprises at least one of sodium formate, sodium carbonate, sodium bicarbonate, sodium acetate, sodium citrate, sodium oxalate.

[0009] Further, the molar ratio of the sodium propionate and the sodium salt is (0.1~1):1.

[0010] Further, the molar ratio of the olivine-type iron phosphate and sodium is 1:(1~1.2).

[0011] Further, the rotation speed of the grinding is 100~400rpm, and the time is 20~60min.

[0012] Further, the inlet temperature of the spray drying is 150~250℃, and the outlet temperature is 80~120℃.

[0013] Further, the time of the sintering is 10~25h.

[0014] Further, the heating rate of the sintering is 1~3℃ / min.

[0015] In another preparation method of the olivine-type sodium iron phosphate, a metal oxide precursor is used to replace the sodium salt in the above preparation method; wherein the amount of the metal oxide precursor is 1~5wt% of the mass of the sodium propionate.

[0016] Further, the metal oxide comprises at least one of titanium oxide, cerium oxide, manganese oxide.

[0017] Further, the titanium oxide precursor comprises at least one of n-butyl titanate, isopropyl titanate, ethyl titanate, titanium citrate and titanium acetate.

[0018] Further, the cerium oxide precursor comprises at least one of cerium citrate, cerium acetate, cerium oxalate.

[0019] Further, the manganese oxide precursor comprises at least one of manganese acetate, manganese oxalate, manganese citrate, manganese stearate.

[0020] The second aspect of the present application provides an olivine-type sodium iron phosphate, which is prepared by the preparation method of the first aspect.

[0021] The third aspect of the present application provides a sodium-ion battery, which uses the olivine-type sodium iron phosphate of the second aspect as a positive active material.

[0022] Compared with the prior art, the present application has at least the following beneficial effects: The preparation method provided by the application takes olivine-type iron phosphate (FePO4) as raw material, and sodium salt and sodium propionate as sodium sources, so that sodium ions are completely embedded under low-temperature conditions of 200-400 DEG C. The sodium propionate not only serves as a sodium source, but also promotes the kinetic process of the solid-phase reaction, reduces the diffusion energy barrier of sodium ions, improves the embedding rate of sodium ions in the olivine-type iron phosphate, and prepares purer olivine-type sodium iron phosphate, so that the capacity is further improved. In order to reduce the high invalid carbon content caused by the difficulty of decomposition of propionate at low temperature, a proper metal oxide precursor is additionally introduced to facilitate the effective decomposition of carbonaceous species in the pyrolysis process, thereby providing a feasible path for the low-cost and large-scale preparation of high-performance NaFePO4 materials.

[0023] The olivine-type sodium iron phosphate provided by the application has a 0.1C charging specific capacity of 147.11 mAh / g, which is very close to the theoretical specific capacity (about 154 mAh / g) of the material, indicating that the embedding process of sodium ions in the crystal lattice is highly reversible and sufficient. At the same time, the material has a very high first coulombic efficiency of 97.7%, indicating that the irreversible capacity loss is very small during the first charge-discharge process, and the electrode / electrolyte interface has good stability, which is beneficial to improving the overall energy density and cycle life of the battery.

[0024] The sodium ion battery provided by the application has the advantages of the above-mentioned olivine-type sodium iron phosphate, so that the prepared sodium ion battery has the advantages of high safety, long cycle life, good rate capability and low cost, and is a new generation of electrochemical energy storage device with great application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the specific embodiments of the application or the technical solutions in the prior art, the following will briefly introduce the drawings needed to be used in the specific embodiments or the prior art description. Obviously, the drawings in the following description are some embodiments of the application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0026] Figure 1 The SEM image of the olivine-type sodium iron phosphate obtained in Example 1 is shown in the figure. Figure 2 The SEM image of the olivine-type sodium iron phosphate obtained in Comparative Example 1 is shown in the figure. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical scheme and advantages of the application more clear, the technical scheme in the embodiments of the application will be described clearly and completely in the following with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only some of the embodiments of the application, not all the embodiments.

[0028] Hereinafter, the terms "include", "have", and their conjugations, which can be used in various embodiments of the present application, merely indicate the presence of the features, numbers, steps, operations, elements, components, or combinations thereof, and do not preclude the presence or addition of one or more other features, numbers, steps, operations, elements, components, or combinations thereof.

[0029] A preparation method of an olivine-type sodium iron phosphate according to the first aspect of the present application, after dissolving sodium propionate and sodium salt, adding olivine-type iron phosphate for grinding to obtain a precursor slurry; after spray drying the precursor slurry, sintering at 200-400 DEG C to obtain the olivine-type sodium iron phosphate.

[0030] The preparation method provided by the present application takes olivine-type iron phosphate (FePO4) as raw material, takes sodium salt and sodium propionate as sodium source, realizes complete embedding of sodium ions under low temperature condition. Sodium propionate not only serves as sodium source, but also can promote the kinetic process of solid phase reaction, reduce the diffusion energy barrier of sodium ions, improve the embedding rate of sodium ions in olivine-type iron phosphate, and prepare purer olivine-type sodium iron phosphate, so that the capacity can be further improved. In order to reduce the high invalid carbon content caused by the difficulty of decomposition of propionate at low temperature, a proper metal oxide precursor is additionally introduced to facilitate the effective decomposition of carbonaceous species in the pyrolysis process, which provides a feasible path for low-cost and large-scale preparation of high-performance NaFePO4 material.

[0031] The present application uses sodium propionate as the necessary sodium source because the thermodynamic properties of sodium propionate are special. Sodium propionate has multiple phase changes, and in the low-temperature sintering process (< 290 DEG C), it undergoes solid phase-solid phase (crystal changes from "rigid solid state" to "plastic solid state") and solid phase-liquid phase phase change processes, which helps to form dynamic ion transmission channels and micro-melting environment locally, significantly enhances the diffusion dynamics of sodium ions, and promotes the embedding of sodium ions into the olivine-type iron phosphate (FePO4) lattice. At the same time, the energy released by the phase change can reduce the activation energy of the solid phase reaction, alleviate the problem of limited ion migration caused by low temperature, thus promoting the complete sodium embedding reaction and obtaining stoichiometric NaFePO4, improving the structural integrity and sodium de-embedding reversibility of the material, and ultimately showing higher charge and discharge specific capacity and electrochemical performance.

[0032] At the same time, the selection of sodium propionate as the necessary sodium source also shows unexpected physical performance improvement. Due to the solid phase-liquid phase melting process, the sodium propionate can make the sodium iron phosphate particles stick together more tightly, so that the olivine-type NaFePO4 shows higher compaction density and lower specific surface area.

[0033] Typically but not exclusively, the sintering temperature may be, for example, 200℃, 230℃, 260℃, 290℃, 320℃, 350℃ or 400℃, or any value within the range of 200℃ to 400℃.

[0034] Further, the sodium salt includes at least one of sodium formate, sodium carbonate, sodium bicarbonate, sodium acetate, sodium citrate, sodium oxalate, which can be completely decomposed in the high-temperature sintering process, and the anion part thereof escapes in the form of gas, and finally only the sodium element is left to participate in the reaction or doped into the target material lattice without introducing any impurity element residue.

[0035] Further, the molar ratio of the sodium propionate and the sodium salt is (0.1-1):1.

[0036] If the amount of sodium propionate is too low, the propionate will be insufficient, and the sodium propionate cannot fully play the role of an auxiliary agent; if the amount of sodium propionate is too high, the propionate will be difficult to decompose on the surface of sodium iron phosphate, and the active material ratio of the material will be reduced, and the residual sodium propionate will also increase the powder resistance of the material, which is not conducive to the performance of the material.

[0037] Typically but not exclusively, the molar ratio of the sodium propionate and the sodium salt may be, for example, 0.1:1, 0.2:1, 0.4:1, 0.6:1, 0.8:1 or 1:1, or any value within the range of (0.1-1):1.

[0038] And / or, the molar ratio of the olivine-type iron phosphate and sodium is 1:(1-1.2).

[0039] Typically but not exclusively, the molar ratio of the olivine-type iron phosphate and sodium may be, for example, 1:1, 1:1.05, 1:1.1, 1:1.15 or 1:1.2, or any value within the range of 1:(1-1.2).

[0040] Further, the rotation speed of the grinding is 100-400 rpm, and the time is 20-60 min.

[0041] Typically but not exclusively, the rotation speed of the grinding may be, for example, 100 rpm, 150 rpm, 200 rpm, 250 rpm, 300 rpm, 350 rpm or 400 rpm, or any value within the range of 100-400 rpm, and the grinding time may be, for example, 20 min, 30 min, 40 min, 50 min or 60 min, or any value within the range of 20-60 min.

[0042] Further, the inlet temperature of the spray drying is 150-250℃, and the outlet temperature is 80-120℃.

[0043] Typically but not exclusively, the inlet temperature of the spray drying can be, for example, 150℃, 170℃, 190℃, 210℃, 230℃ or 250℃, or any value within the range of 150-250℃, and the outlet temperature can be, for example, 80℃, 90℃, 100℃, 110℃ or 120℃, or any value within the range of 80-120℃.

[0044] Further, the sintering time is 10-25 h.

[0045] Typically but not exclusively, the sintering time can be, for example, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, 18 h, 20 h, 22 h, 24 h or 25 h, or any value within the range of 10-25 h.

[0046] Further, the heating rate of the sintering is 1-3℃ / min, mainly to ensure uniform and controllable transformation of the precursor during pyrolysis and solid-phase reaction. The heating rate can avoid both too fast heating leading to local intense decomposition of sodium propionate and other organic sodium salts, resulting in a large amount of gas and causing particle agglomeration or structure cracking, and too slow heating prolonging the process cycle and reducing the efficiency; more importantly, under this mild heating condition, sodium propionate can orderly undergo multi-stage phase change, gradually release active sodium ions and form a short-term micro-melting state, effectively promote the uniform diffusion and embedding of sodium ions into the FePO4 lattice, and maintain the moderate decomposition of the carbon source to build a conductive network, thereby ensuring the phase purity, microstructure compactness and stability of the electrochemical performance of the final product of olivine-type NaFePO4.

[0047] Typically but not exclusively, the heating rate of the sintering can be, for example, 1℃ / min, 1.5℃ / min, 2℃ / min, 2.5℃ / min or 3℃ / min, or any value within the range of 1-3℃ / min.

[0048] The inventors have found that the use of sodium propionate as the sole sodium source can increase the carbon content of the final prepared olivine-type sodium iron phosphate, thereby affecting the performance of the specific capacity, and therefore the introduction of other sodium sources for compounding can maximize the performance of the specific capacity.

[0049] In another method for preparing olivine-type sodium iron phosphate according to the present application, a metal oxide precursor is used to replace the sodium salt in the above preparation method; wherein the amount of the metal oxide precursor is 1-5wt% of the mass of sodium propionate.

[0050] When the amount of the metal oxide precursor is too low, the decomposition of propionate and anions in the added sodium salt is not replenished, leading to the aggregation of anions on the surface of the material, and the amount of residual carbon on the surface is large, which is not conducive to the reduction of powder resistance and the improvement of capacity; when the amount of the metal oxide precursor is too high, the proportion of active substances is reduced, which directly affects the capacity of the material.

[0051] Typically but not limitedly, the amount of the metal oxide precursor may be, for example, 1 wt%, 2 wt%, 3 wt%, 4 wt% or 5 wt% of the mass of sodium propionate, or any value within the range of 1-5 wt%.

[0052] Further, the metal oxide includes at least one of titanium oxide, cerium oxide and manganese oxide.

[0053] And / or, the titanium oxide precursor includes at least one of n-butyl titanate, isopropyl titanate, ethyl titanate, titanium citrate and titanium acetate.

[0054] And / or, the cerium oxide precursor includes at least one of cerium citrate, cerium acetate and cerium oxalate.

[0055] And / or, the manganese oxide precursor includes at least one of manganese acetate, manganese oxalate and manganese stearate.

[0056] The second aspect of the present application provides an olivine-type sodium iron phosphate prepared by the preparation method of the first aspect.

[0057] The olivine-type sodium iron phosphate provided by the present application has a 0.1C charging specific capacity of 147.11 mAh / g, which is very close to the theoretical specific capacity of the material (about 154 mAh / g), indicating that the embedding process of sodium ions in the crystal lattice is highly reversible and sufficient. At the same time, the material shows a very high first coulomb efficiency of 97.7%, indicating that the irreversible capacity loss is very small during the first charge and discharge process, and the electrode / electrolyte interface has good stability, which is beneficial to improve the overall energy density and cycle life of the battery.

[0058] The third aspect of the present application provides a sodium ion battery using the olivine-type sodium iron phosphate of the second aspect as a positive electrode active material.

[0059] The sodium ion battery provided by the present application has the advantages of the above-mentioned olivine-type sodium iron phosphate, so that the prepared sodium ion battery has the advantages of high safety, long cycle life, good rate capability and low cost, and is a new generation of electrochemical energy storage device with great application prospect.

[0060] The present application will be further described by specific examples and comparative examples, but it should be understood that these examples are only for a more detailed description and should not be construed as limiting the present application in any form. The raw materials used in the examples and comparative examples of the present application are prepared according to the conventional conditions or the conditions recommended by the manufacturer, unless otherwise specified. The reagents or instruments used are all conventional products that can be purchased on the market, unless otherwise specified.

[0061] Example 1 This example provides an olivine-type sodium iron phosphate, and the specific preparation process is as follows: (1) 7.28 g of sodium propionate and 30.93 g of sodium acetate trihydrate (m 丙酸钠 : m 三水乙酸钠 = 1:2) were weighed into a beaker, 160 mL of deionized water was added, and stirred until completely dissolved.

[0062] (2) 45.25 g of olivine-type iron phosphate was added to the above solution, and after stirring uniformly, it was poured into a sand mill, and sand milling was carried out at a rotation speed of 200 rpm for 0.5 h, so that the raw materials were uniformly dispersed, to obtain a precursor slurry.

[0063] (3) The above precursor slurry was subjected to spray drying by a spray dryer, and the inlet temperature was set to 200°C and the outlet temperature was set to 100°C, to obtain a precursor powder.

[0064] (4) The precursor powder obtained above was placed in a porcelain boat, and sintered in a protective atmosphere, and the temperature was raised to 300°C at a rate of 2°C / min and kept for 12 h, to obtain an olivine-type sodium iron phosphate.

[0065] Comparative Example 1 This comparative example provides an olivine-type sodium iron phosphate, which is different from Example 1 in that only sodium propionate is used as the sodium source, and the amount of sodium propionate is 29.11 g, and the rest of the preparation method is the same as Example 1, which will not be repeated here.

[0066] Comparative Example 2 This comparative example provides an olivine-type sodium iron phosphate, which is different from Example 1 in that only sodium acetate trihydrate is used as the sodium source, and the amount of sodium acetate trihydrate is 41.24 g, and the rest of the preparation method is the same as Example 1, which will not be repeated here.

[0067] Characterization Example 1 The olivine-type sodium iron phosphate obtained from Example 1 and Comparative Example 1 was subjected to morphology analysis, and the SEM images obtained are shown in Figure 1 and Figure 2 .

[0068] From Figure 1It can be seen that the surface of the particles is smooth, and no extra impurity particles are generated, indicating that the sodium ions are well inserted, and there is no obvious undecomposed compound.

[0069] From Figure 2 It can be seen that too much sodium propionate causes the propionate to be difficult to decompose at low temperature, so that a layer of insulating coating is attached to the surface of the particles, making the powder resistance of the material abnormally large, which is not conducive to the insertion and extraction of sodium ions.

[0070] Test Example 1 1. Physical property test Tap density: tested by a powder tap density instrument, the olivine-type sodium iron phosphate sample was placed in a standard measuring cylinder, and was vibrated at a fixed vibration frequency and pressure until the volume no longer changed, and the tap density (g / cm 3 ) of the sample was calculated according to the sample mass and the final volume.

[0071] Specific surface area: determined by the nitrogen adsorption-desorption method (BET method), the adsorption amount of nitrogen of the sample was measured at liquid nitrogen temperature, and the specific surface area (m 2 / g) of the olivine-type sodium iron phosphate sample was calculated by the BET equation.

[0072] C content test: an elemental analyzer was used, the olivine-type sodium iron phosphate sample was completely burned in a high-temperature oxygen stream to convert the carbon therein into carbon dioxide, and the generated CO2 amount was quantitatively determined by infrared absorption or a thermal conductivity detector, so as to accurately obtain the mass percentage (%) of carbon elements in the material.

[0073] 2. Electrochemical performance test The olivine-type sodium iron phosphate obtained in Example 1 and Comparative Examples 1-2 was used as a positive electrode active material, and after 80 parts of the positive electrode active material, 10 parts of acetylene black, and 10 parts of a binder were dissolved in N-methyl pyrrolidone, the mixture was coated on a treated aluminum foil, and the coated aluminum foil was vacuum dried at 90°C to obtain a positive electrode sheet. Then, in an anhydrous and oxygen-free glove box, the prepared positive electrode sheet, a sodium sheet, a separator, and NC-008 (1 mol / L NaClO4 sodium salt dissolved in a volume ratio of 1:1 of ethylene carbonate (EC) and propylene carbonate (PC) and additional addition of 5% fluoroethylene carbonate (FEC)) electrolyte were assembled to form a button cell for electrochemical performance test.

[0074] Initial efficiency test: the battery was tested by charging and discharging at a current of 1C of 129 mA / g at room temperature. The charging and discharging voltage range was 1.8-4.2 V, and 0.1C was used for one complete charging and discharging cycle, and the obtained data are shown in Table 1.

[0075] The obtained data are shown in Table 1.

[0076] Table 1

[0077] As can be seen from Table 1, the sodium phosphate iron prepared by sodium intercalation of sodium propionate and sodium acetate has the best electrochemical performance, and the compaction and specific surface area are the best. However, all sodium propionate, although theoretically more perfect in sodium intercalation, faces the difficulty of propionate decomposition, resulting in a decrease in active material ratio and hindering the sodium ion shuttling during the charging and discharging process. Therefore, the capacity decreases. The use of all sodium acetate also has the problem of insufficient sodium intercalation, which makes it difficult to increase the capacity.

[0078] Example 2 The present embodiment provides an olivine-type sodium iron phosphate. Different from Example 1, equimolar sodium formate is used to replace sodium acetate trihydrate, and the rest of the preparation method is the same as that of Example 1, which is not repeated here.

[0079] Example 3 The present embodiment provides an olivine-type sodium iron phosphate. Different from Example 1, equimolar sodium carbonate is used to replace sodium acetate trihydrate, and the rest of the preparation method is the same as that of Example 1, which is not repeated here.

[0080] Example 4 The present embodiment provides an olivine-type sodium iron phosphate. Different from Example 1, equimolar sodium bicarbonate is used to replace sodium acetate trihydrate, and the rest of the preparation method is the same as that of Example 1, which is not repeated here.

[0081] Example 5 The present embodiment provides an olivine-type sodium iron phosphate. Different from Example 1, equimolar sodium citrate is used to replace sodium acetate trihydrate, and the rest of the preparation method is the same as that of Example 1, which is not repeated here.

[0082] Example 6 The present embodiment provides an olivine-type sodium iron phosphate. Different from Example 1, equimolar sodium oxalate is used to replace sodium acetate trihydrate, and the rest of the preparation method is the same as that of Example 1, which is not repeated here.

[0083] Test Example 2 The olivine-type sodium iron phosphates obtained in Examples 2-6 are subjected to physical performance testing and electrochemical performance testing according to the testing method of Test Example 1, and the obtained data are recorded in Table 2.

[0084] Table 2

[0085] As can be seen from Table 2, sodium formate and sodium acetate have relatively optimal electrochemical performance and lower residual carbon content, which is mainly because the acetate and formate volatilize during the sanding spray process, consuming a large amount of anions, and during the sintering process, the acetate and formate are more easily decomposed and volatilized at low temperatures, while other anions are more difficult to volatilize, especially the carbonate, which is relatively stable at this temperature, and we need a certain amount of anions to carbonize, and the excess carbon is used to reduce the ferric iron in the iron phosphate to provide better electrochemical potential energy for sodium intercalation, thereby increasing the amount of sodium intercalation, so the capacity of the carbonate is lower.

[0086] Example 7 The present example provides an olivine-type sodium iron phosphate, which is different from Example 1 in that the molar ratio of m 丙酸钠 : m 三水乙酸钠 is 0.2:1, and the remaining steps are the same as those of Example 1, which are not repeated here.

[0087] Example 8 The present example provides an olivine-type sodium iron phosphate, which is different from Example 1 in that the molar ratio of m 丙酸钠 : m 三水乙酸钠 is 1:1, and the remaining steps are the same as those of Example 1, which are not repeated here.

[0088] Example 9 The present example provides an olivine-type sodium iron phosphate, which is different from Example 1 in that the molar ratio of m 丙酸钠 : m 三水乙酸钠 is 1.5:1, and the remaining steps are the same as those of Example 1, which are not repeated here.

[0089] Test Example 3 The olivine-type sodium iron phosphates obtained in Examples 7-9 were subjected to physical performance testing and electrochemical performance testing according to the testing method of Test Example 1, and the obtained data are recorded in Table 3.

[0090] Table 3

[0091] As can be seen from Table 3, when the amount of sodium propionate added is insufficient, although the residual carbon content is not large and the specific surface area is also low, the sodium propionate cannot fully play its role as a sodium intercalation aid, and it is difficult for sodium ions to completely intercalate into the crystal lattice at low temperatures, so the capacity is low, but continuous addition of more sodium propionate can be found that the residual carbon content increases with the increase of sodium propionate, and the capacity gradually decreases, which further indicates that too much sodium propionate is not conducive to the capacity.

[0092] Example 10 The present example provides an olivine-type sodium iron phosphate, which is different from example 1 in that the sintering temperature in step (4) is 200°C, and the rest of the preparation method is the same as example 1, which will not be repeated here.

[0093] Comparative Example 3 The present comparative example provides an olivine-type sodium iron phosphate, which is different from example 1 in that the sintering temperature in step (4) is 320°C, and the rest of the preparation method is the same as example 1, which will not be repeated here.

[0094] Comparative Example 4 The present comparative example provides an olivine-type sodium iron phosphate, which is different from example 1 in that only sodium acetate trihydrate is used as a sodium source, the amount of sodium acetate trihydrate is 41.24g, the sintering temperature in step (4) is 320°C, and the rest of the preparation method is the same as example 1, which will not be repeated here.

[0095] Test Example 4 The olivine-type sodium iron phosphate obtained in example 10 and comparative examples 3-4 is tested for physical properties and electrochemical properties according to the test method of test example 1, and the data obtained are recorded in table 4.

[0096] Table 4

[0097] As can be seen from table 4, too low a sintering temperature is not conducive to the thermodynamic diffusion of sodium ions, and the amount of sodium intercalation is insufficient, but too high a temperature will make the olivine sodium iron phosphate structure unstable, and part of the olivine sodium iron phosphate will be converted into the scorodite-type sodium iron phosphate, so the capacity will decrease slightly. Similarly, without the addition of sodium propionate, the capacity will still be lost at high temperatures.

[0098] Example 11 The present example provides an olivine-type sodium iron phosphate, which is different from example 1 in that the heating rate in step (4) is 2°C / min, and the rest of the preparation method is the same as example 1, which will not be repeated here.

[0099] Example 12 The present example provides an olivine-type sodium iron phosphate, which is different from example 1 in that the heating rate in step (4) is 3°C / min, and the rest of the preparation method is the same as example 1, which will not be repeated here.

[0100] Example 13 The present example provides an olivine-type sodium iron phosphate, which is different from example 1 in that the heating rate in step (4) is 6°C / min, and the rest of the preparation method is the same as example 1, which will not be repeated here.

[0101] Test Example 5 The physical properties and electrochemical properties of the sodium iron phosphate of olivine type obtained in Examples 11-13 were tested according to the test method of Test Example 1, and the data obtained are recorded in Table 5.

[0102] Table 5

[0103] As can be seen from Table 5, the heating rate has no effect on the compaction, specific surface area and carbon content, but the capacity weakly decreases with the increase of the heating rate, which is probably due to the rapid shrinkage of the organic anion caused by the too fast heating rate, which hinders the insertion channel of sodium ions, resulting in a small decrease in capacity.

[0104] Example 14 This example provides a sodium iron phosphate of olivine type, which is different from Example 1 in that n-butyl titanate is used to replace sodium acetate trihydrate, the addition amount of n-butyl titanate is 1.3 g, the amount of sodium propionate is 29.11 g, and the rest of the methods are the same as those of Example 1, which are not repeated here.

[0105] Example 15 This example provides a sodium iron phosphate of olivine type, which is different from Example 1 in that n-butyl titanate is used to replace sodium acetate trihydrate, the addition amount of n-butyl titanate is 0.29 g, the amount of sodium propionate is 29.11 g, and the rest of the methods are the same as those of Example 1, which are not repeated here.

[0106] Example 16 This example provides a sodium iron phosphate of olivine type, which is different from Example 1 in that n-butyl titanate is used to replace sodium acetate trihydrate, the addition amount of n-butyl titanate is 1.45 g, the amount of sodium propionate is 29.11 g, and the rest of the methods are the same as those of Example 1, which are not repeated here.

[0107] Example 17 This example provides a sodium iron phosphate of olivine type, which is different from Example 1 in that n-butyl titanate is used to replace sodium acetate trihydrate, the addition amount of n-butyl titanate is 2 g, the amount of sodium propionate is 29.11 g, and the rest of the methods are the same as those of Example 1, which are not repeated here.

[0108] Example 18 This example provides a sodium iron phosphate of olivine type, which is different from Example 14 in that cerium oxide is used to replace n-butyl titanate, and the rest of the methods are the same as those of Example 14, which are not repeated here.

[0109] Example 19 This example provides a sodium iron phosphate of olivine type, which is different from Example 14 in that manganese acetate is used to replace n-butyl titanate, and the rest of the methods are the same as those of Example 14, which are not repeated here.

[0110] Test Example 6 The olivine-type sodium iron phosphate obtained in Examples 14-19 was subjected to physical property testing and electrochemical property testing according to the test method of Test Example 1, and the data obtained are recorded in Table 6.

[0111] Table 6

[0112] As can be seen from Table 6, the addition of titanium element can effectively reduce the carbon content of the overall material, indicating that titanium helps to decompose residual sodium propionate, and different amounts of addition have different effects. When the amount of addition is too low, the improvement effect on the overall is not obvious, and when the amount of addition is too large, the excess titanium will form titanium oxide, reducing the purity of the active substance, thereby slightly reducing the capacity. When manganese and cerium are used, the decomposition-promoting effect on carbon is poor due to the different effects of different metal elements, and the overall capacity is lower than that before modification.

[0113] Finally, it should be noted that the above-described examples are merely specific embodiments of the present application, which are used to illustrate the technical solutions of the present application, but not to limit it. The protection scope of the present application is not limited thereto. Although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that any person skilled in the art can modify or easily think of changes to the technical solutions recorded in the foregoing examples, or make equivalent replacements to some technical features thereof, within the technical range disclosed by the present application. Such modifications, changes or replacements do not make the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for producing sodium iron phosphate of olivine type, characterized by, After dissolving sodium propionate and sodium salt, adding olive-type iron phosphate to grind to obtain a precursor slurry; After spray drying the precursor slurry, sintering at 200-400℃ to obtain the olive-type sodium iron phosphate.

2. The production method according to claim 1, characterized by, The sodium salt includes at least one of sodium formate, sodium carbonate, sodium bicarbonate, sodium acetate, sodium citrate, and sodium oxalate.

3. The production method according to claim 1, characterized by, The molar ratio of the sodium propionate to the sodium salt is (0.1-1):

1. And / or, the molar ratio of the olive-type iron phosphate to sodium is 1:(1-1.2).

4. The production method according to any one of claims 1 to 3, characterized by, The rotation speed of the grinding is 100-400rpm, and the time is 20-60min.

5. The preparation method according to any one of claims 1 to 3, characterized in that, The inlet temperature of the spray drying is 150-250℃, and the outlet temperature is 80-120℃.

6. The preparation method according to any one of claims 1 to 3, characterized in that, The sintering time is 10-25h. And / or, the heating rate of the sintering is 1-3℃ / min.

7. A method for producing sodium iron phosphate of olivine type, characterized by, Using a metal oxide precursor to replace the sodium salt in the preparation method of any one of claims 1-6; The amount of the metal oxide precursor is 1-5wt% of the mass of the sodium propionate.

8. The preparation method according to claim 7, characterized in that, The metal oxide includes at least one of titanium oxide, cerium oxide, and manganese oxide. And / or, the titanium oxide precursor includes at least one of n-butyl titanate, isopropyl titanate, ethyl titanate, titanium citrate, and titanium acetate. And / or, the cerium oxide precursor includes at least one of cerium citrate, cerium acetate, and cerium oxalate. And / or, the manganese oxide precursor includes at least one of manganese acetate, manganese oxalate, and manganese stearate.

9. A sodium iron phosphate of olivine type, characterized in that, The preparation method of any one of claims 1-8 is used to prepare.

10. A sodium-ion battery, characterized in that, The olive-type sodium iron phosphate of claim 9 is used as a positive electrode active material.

Images