Iron-based polyanionic sodium ion battery positive electrode material and preparation method thereof

Abstract

The invention discloses a preparation method of an iron-based polyanionic sodium ion battery positive electrode material, and relates to the technical field of sodium ion batteries. The preparation method comprises the following steps: mixing a sodium source, a carbon source, isopropanol and water, and uniformly stirring to obtain a first mixed system; respectively adding a transition metal source and a phosphorus source into the first mixed system, stirring at normal temperature, and obtaining a precursor through a template method; drying the precursor according to a first preset condition to obtain a dried precursor A; sintering the precursor A for the first time according to a second preset condition to obtain a second mixed system; carrying out ball milling treatment on the second mixed system, and compounding the second mixed system with a carbon material through a ball milling method; and carrying out secondary sintering on a product compounded with the carbon material after ball milling according to a third preset condition to obtain the iron-based polyanionic sodium ion battery positive electrode material. According to the preparation method, the energy consumption is greatly reduced, the exploration of the iron-based mixed phosphate material is accelerated, and the large-scale application of the iron-based positive electrode material is facilitated.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, specifically to an iron-based polyanion sodium-ion battery cathode material and its preparation method. Background Technology

[0002] Lithium-ion batteries are used in portable devices and large-scale energy storage. However, due to the scarcity and uneven distribution of lithium resources, sodium-ion batteries, which have a similar working mechanism to lithium-ion batteries, are expected to become one of the best alternatives to lithium-ion batteries due to their abundant reserves and high safety.

[0003] Iron-based polyanionic sodium-ion battery cathode materials have attracted widespread attention due to their low cost and environmental friendliness. Among them, Na4Fe3(PO4)2P2O7 is noteworthy for its average operating voltage of 3.1 V, small volume change (<4%) during sodium intercalation / deintercalation, and moderate theoretical specific capacity (129 mAh g⁻¹). -1 With its characteristics such as [missing information], it has gradually developed into one of the cathode materials with the greatest commercial potential.

[0004] To address the issue of poor electronic conductivity, modifications using carbon materials such as citric acid, ascorbic acid, reduced graphene oxide, and carbon nanotubes can improve electronic conductivity, but improving the intrinsic electronic conductivity of the material remains challenging. Because it is easy to generate an inactive impure phase, maricite-type NaFePO4, during the synthesis process, which seriously affects its sodium storage performance, many scholars have tried to suppress the formation of impure phases through ion doping and other means, but there are still significant shortcomings. Constructing iron defects and synthesizing non-uniform compounds are effective means of synthesizing pure-phase materials. However, the above methods all involve the regulation of transition metal sites, which affects their theoretical specific capacity. Summary of the Invention

[0005] This invention proposes a method for preparing iron-based polyanionic sodium-ion battery cathode material. By carbon coating and nano-sizing, the electronic conductivity of the sodium-ion battery cathode is improved, thereby enhancing its electrochemical performance and obtaining a sodium-ion battery cathode material with high structural stability and low cost.

[0006] The technical solution of the present invention is as follows: A method for preparing an iron-based polyanionic sodium-ion battery cathode material, comprising the following steps: Step 1: Mix the sodium source, carbon source, isopropanol and water, and stir until homogeneous to obtain the first mixed system; Step 2: Add the transition metal source and phosphorus source to the first mixing system and stir at room temperature to obtain the precursor by template method; dry the precursor according to the first preset conditions to obtain the dried precursor A. Step 3: The precursor A is sintered for the first time according to the second preset conditions to obtain the second mixed system; Step four: The second mixture system is ball-milled and then combined with carbon materials by ball milling. Step 5: The product after ball milling and composite with carbon material is sintered a second time according to the third preset conditions to obtain iron-based polyanion sodium-ion battery cathode material.

[0007] As a preferred embodiment, the first preset conditions are: stirring time of 2-6 hours, rotary evaporation temperature of 65-85°C, and drying time of 0.5-2 hours.

[0008] As a preferred embodiment, the second preset conditions are as follows: the process is carried out under protective gas conditions, the processing time in the tube furnace is 3-5 hours, the heating rate is 2-5℃ / min, and the sintering temperature is 300-400℃; the protective gas is any one of argon, argon-hydrogen mixture, nitrogen, and neon. The third preset condition is that the processing time in the tube furnace is 6-12 hours, the heating rate is 1-5℃ / min, and the sintering temperature is 500-650℃.

[0009] As a preferred embodiment, the sodium source is one or more of sodium carbonate, sodium acetate, sodium oxalate, sodium citrate, sodium phosphate, sodium nitrate, sodium hydroxide, sodium bicarbonate, sodium dihydrogen phosphate, and sodium chloride.

[0010] As a preferred embodiment, the iron source is at least one selected from ferrous sulfate, ferric nitrate, ferrous acetylacetone, ferric phosphate, and ferric oxide.

[0011] As a preferred embodiment, the phosphorus source is at least one selected from ferric phosphate, phosphoric acid, ammonium dihydrogen phosphate, and sodium dihydrogen phosphate.

[0012] As a preferred embodiment, the carbon source includes at least two of polyacrylic acid, citric acid, and ascorbic acid.

[0013] As a preferred embodiment, the molar ratio of the sodium source, iron source and phosphorus source is (4-4.15):3:4.

[0014] As a preferred embodiment, the carbon material used in the ball milling process in step five is any one of Ketjen black, graphene, reduced graphene oxide, single-walled carbon nanotubes, oleic acid, sucrose, polyethylene glycol, and glucose; the composite mass ratio of the carbon material to the second mixing system is 0.5%-10%.

[0015] This application also provides an iron-based polyanionic sodium-ion battery cathode material, including a cathode sheet, which is prepared from the following materials: Iron-based polyanionic sodium-ion battery cathode material prepared using the above-mentioned preparation method; Conductive additives and binders; The molar ratio of the iron-based polyanionic sodium-ion battery cathode material, conductive additive, and binder is 7:2:1 or 8:1:1. The conductive additive is any one of acetylene black, super p, and Ketjen black; The binder is any one of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), or sodium alginate (SA).

[0016] Compared with the prior art, the present invention provides an iron-based polyanionic sodium-ion battery cathode material and its preparation method, the beneficial effects of which are: 1. In the iron-based polyanionic sodium-ion battery cathode material and its preparation method, X-ray diffraction analysis shows that by controlling the sodium content, the inactive phase NaFePO4 can be significantly eliminated, and a composite structure of sodium iron pyrophosphate and sodium iron pyrophosphate can be formed, thereby stabilizing the crystal structure and significantly improving the performance.

[0017] 2. In this iron-based polyanionic sodium-ion battery cathode material and its preparation method, the discharge specific capacity of the iron-based cathode material at room temperature was found to be ≥110 mAh g through constant current charge-discharge testing. -1 Ultra-fast rate performance (achieving 60.1 mAh g⁻¹ at a current density of 200 C). -1 (Discharge specific capacity), while this iron-based cathode material also exhibits outstanding high-temperature performance and faster Na+ discharge. + Diffusion kinetics.

[0018] 3. In the iron-based polyanionic sodium-ion battery cathode material and its preparation method, according to scanning electron microscopy, the iron-based cathode material is formed by the aggregation of primary particles with a particle size of 50~60nm, mainly 200nm. Attached Figure Description

[0019] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0020] Figure 1 This is a scan image of the iron-based cathode material Na4Fe3(PO4)2P2O7 of the present invention; Figure 2 The XRD pattern of the iron-based cathode material Na4Fe3(PO4)2P2O7 of this invention is shown. Figure 3 This is a charge-discharge curve of the iron-based cathode material Na4Fe3(PO4)2P2O7 of the present invention; Figure 4 This is a scaling factor diagram of the iron-based cathode material Na4Fe3(PO4)2P2O7 of the present invention; Figure 5 This is a cycle diagram of the iron-based cathode material Na4Fe3(PO4)2P2O7 of this invention. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] The sodium site of Na4Fe3(PO4)2P2O7 was regulated using a template method, and the molecular formula is Na 4+x Fe3(PO4)2P2O7, where x=0.07, by regulating the inactive sites of this iron-based material, the formation of the inactive impure phase NaFePO4 is suppressed, forming a composite material of Na4Fe3(PO4)2P2O7 and Na2FeP2O7, thereby obtaining an iron-based polyanionic sodium-ion battery cathode material with excellent electrochemical performance.

[0023] A method for preparing an iron-based polyanionic sodium-ion battery cathode material includes the following steps: (1) The template method described herein specifically involves mixing a sodium source, a carbon source, isopropanol, and water. After the carbon source reacts with the sodium source, it coagulates in a mixed solution of isopropanol and water to form a homogeneous and stable colloid, thus obtaining a first mixed system. The sodium source is sodium carbonate, and the carbon source is polyacrylic acid. Specifically, 20 ml of 0.1 g of [amount missing] ml ... -1 A polyacrylic acid solution was prepared by mixing 40 ml of water and 0.6359 g of sodium carbonate, and then 200 ml of isopropanol was added dropwise to form a homogeneous and stable colloidal solution.

[0024] (2) Subsequently, the transition metal source and phosphorus source were added to the first mixing system and stirred at room temperature, and dried by rotary evaporation to obtain the precursor; wherein, the stirring time was 4h; the rotary evaporation temperature was 80℃; the drying time was 0.5h; the transition metal source was ferric nitrate nonahydrate with a mass of 3.636g; the phosphorus source was ammonium dihydrogen phosphate with a mass of 1.3803g.

[0025] (3) The dried precursor is sintered for the first time to obtain the second mixed system, wherein the sintering temperature is 350℃ and the sintering time is 4 hours.

[0026] (4) The second mixed system was combined with carbon material by ball milling and then sintered for a second time to obtain iron-based mixed phosphate cathode material. The ball milling speed was 500 rad / min, the ball milling time was 6 hours, the second sintering temperature was 550℃, the sintering time was 8 hours, the carbon material was Ketjen Black, and the mass ratio of the second mixed system to the carbon material was 100:3.

[0027] According to another aspect of the present invention, the present invention also relates to an iron-based polyanionic sodium-ion battery cathode material obtained by a method for preparing an iron-based sodium-ion battery cathode material, wherein the iron-based cathode material is a nanoscale spherical particle with a particle size of 40 nm.

[0028] Figure 1 This is a scanning image of the iron-based cathode material Na4Fe3(PO4)2P2O7 of the present invention; as can be seen from Figure 1, the material is a loose structure composed of nano-sized particles with a particle size of mainly 200 nm.

[0029] Figure 2 The image shows the XRD pattern of the iron-based cathode material Na4Fe3(PO4)2P2O7 of this invention. As can be seen from Figure 2, after Na site regulation, no characteristic peaks related to the inactive phase maricite type NaFePO4 appeared, while obvious characteristic peaks of active Na2FeP2O7 were detected, ultimately forming a heterocomposite material of Na4Fe3(PO4)2P2O7 and Na2FeP2O7.

[0030] Figure 3 The image shows the charge-discharge curves of the iron-based cathode material Na4Fe3(PO4)2P2O7 of this invention. A constant current charge-discharge test was performed at a current density of 0.1 C, and after five cycles, the initial discharge specific capacity was close to the theoretical specific capacity of 129 mAh g. -1 This indicates that through carbon recombination and Na site regulation, the electronic conductivity of Na4Fe3(PO4)2P2O7 is significantly improved, the inactive phase components are completely eliminated, and the sodium storage performance is fully utilized.

[0031] Figure 4 This is the rate performance diagram of the iron-based cathode material of the present invention. Thanks to the elimination of inactive components and the composite with carbon materials, the rate performance of the material is greatly improved, achieving a current density of 60.1 mAh g⁻¹ even at an ultra-high current density of 200 C. -1 The specific discharge capacity.

[0032] Figure 5 This is a cycling diagram of the iron-based cathode material of the present invention; due to its robust heterogeneous composite structure, the material achieves an ultra-long cycle life of 10,000 cycles at a current density of 50C.

[0033] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing an iron-based polyanionic sodium-ion battery cathode material, characterized in that, The method comprises the following steps: Step one, mix sodium source, carbon source, isopropyl alcohol and water, stir evenly to obtain a first mixed system; Step two, add transition metal source and phosphorus source to the first mixed system respectively, stir at room temperature, and obtain a precursor by a template method; dry the precursor according to a first preset condition to obtain a dried precursor A; Step three, sinter the precursor A according to a second preset condition to obtain a second mixed system; Step four, perform ball milling treatment on the second mixed system, and compound the second mixed system with a carbon material by a ball milling method; Step five, sinter the product after the ball milling and the carbon material compounding according to a third preset condition to obtain an iron-based polyanionic sodium ion battery positive electrode material.

2. The method for preparing an iron-based polyanionic sodium-ion battery cathode material according to claim 1, characterized in that, The first preset condition is that the stirring time is 2-6h, the rotary evaporation temperature is 65-85℃, and the drying time is 0.5-2h.

3. The method according to claim 1, characterized in that, The second preset condition is that the treatment is performed under a protective gas condition, the treatment time in a tube furnace is 3-5h, the heating rate is 2-5℃ / min, and the sintering temperature is 300-400℃; the protective gas is any one of argon, argon-hydrogen mixed gas, nitrogen and neon; The third preset condition is that the treatment time in a tube furnace is 6-12h, the heating rate is 1-5℃ / min, and the sintering temperature is 500-650℃.

4. The method for preparing an iron-based polyanionic sodium-ion battery cathode material according to claim 1, characterized in that, The sodium source is one or two or more of sodium carbonate, sodium acetate, sodium oxalate, sodium citrate, sodium phosphate, sodium nitrate, sodium hydroxide, sodium bicarbonate, sodium dihydrogen phosphate and sodium chloride.

5. The method for preparing an iron-based polyanionic sodium-ion battery cathode material according to claim 1, characterized in that, The iron source is at least one of ferrous sulfate, ferric nitrate, acetylacetone ferrous, ferric phosphate and iron oxide.

6. The method for preparing an iron-based polyanionic sodium-ion battery cathode material according to claim 1, characterized in that, The phosphorus source is at least one of ferric phosphate, phosphoric acid, ammonium dihydrogen phosphate and sodium dihydrogen phosphate.

7. The method for preparing an iron-based polyanionic sodium-ion battery cathode material according to claim 1, characterized in that, The carbon source includes at least two of polyacrylic acid, citric acid and ascorbic acid.

8. The method for preparing an iron-based polyanionic sodium-ion battery cathode material according to claim 1, characterized in that, The molar ratio of the sodium source, the iron source and the phosphorus source is (4-4.15):3:

4.

9. The method for preparing an iron-based polyanionic sodium-ion battery cathode material according to claim 1, characterized in that, The carbon material used in the ball milling process in step five is any one of Ketjen black, graphene, reduced graphene oxide, single-walled carbon nanotube, oleic acid, sucrose, polyethylene glycol and glucose; the compounding mass ratio of the carbon material to the second mixed system is 0.5%-10%.

10. An iron-based polyanionic sodium-ion battery cathode material comprising a cathode sheet, characterized in that, The positive electrode sheet is prepared from the following materials: The iron-based polyanionic sodium ion battery positive electrode material prepared by the method according to any one of claims 1-9; A conductive additive and a binder; wherein The molar ratio of the iron-based polyanionic sodium ion battery positive electrode material, the conductive additive and the binder is 7:2:1 or 8:1:1; The conductive additive is any one of acetylene black, super p and Ketjen black; The binder is any one of polyvinylidene fluoride PVDF, sodium carboxymethyl cellulose CMC or sodium alginate SA.

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