High-conductivity sodium-ion battery cathode material / organic conductive polymer composite and preparation method thereof

Abstract

The application discloses a high-conductivity sodium-ion battery positive electrode material / organic conductive polymer composite material and a preparation method thereof, and comprises the following steps: S1, preparation of a chain product: dissolving an organic conductive polymer monomer in water, adjusting the pH of the solution to be acidic, adding an oxidizing agent, and inducing the organic conductive polymer monomer to undergo a polymerization reaction to form a chain product; S2, preparation of a precursor slurry: adding a sodium source, an iron source and a sulfur source into the chain product solution, and after sufficient dissolution, forming a uniform precursor slurry; S3, preparation of a precursor powder: drying the precursor slurry to realize solid-liquid separation, and obtaining a dried precursor powder; S4, high-temperature sintering: calcining the precursor powder in a protective atmosphere, and obtaining Na 2+x Fe 2‑x (SO4)3 / organic conductive polymer composite positive electrode material after natural cooling. The application has the characteristics of high electronic conductivity, low specific surface area, high compaction density and excellent electrochemical performance.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sodium ion batteries, in particular to a high-conductivity sodium ion battery positive electrode material / organic conductive polymer composite material and a preparation method thereof. BACKGROUND

[0002] The performance of the positive electrode material has a significant influence on the energy density and electrochemical performance of the sodium ion battery system, and the sodium ion battery material truly suitable for batch production needs to meet the characteristics of low cost, high performance, easy processing and the like. However, the currently marketed layered oxides, prussian blue systems and polyanion materials have different performances, and there are few materials with excellent comprehensive performance.

[0003] The sulfate material is a branch of the polyanion type sodium ion battery positive electrode material, has rich resource reserves, a simple preparation process, a high voltage platform and high system energy density, and is currently positioned in the low-end power field in the market. However, the sulfate material is a high-temperature unstable phase, and when the temperature is higher than 450 DEG C, the sulfate radical in the material is easily decomposed to generate sulfur dioxide, so the sintering temperature of the material is generally low. In addition, the material is a three-dimensional framework structure formed by FeO6 octahedra and SO4 tetrahedra connected in the form of points / lines / surfaces, and because SO4 does not have conductivity, the electronic conductivity of the material is generally low. However, the high-temperature instability of the material makes it difficult to be in-situ carbon-modified through high-temperature pyrolysis, and thus the electronic conductivity is improved. At present, the commonly used method on the market is to physically mix inorganic carbon (carbon nanotubes, graphene, high-specific-surface carbon black) with the sulfate material, which will cause the specific surface of the material to be too large, and at the same time, the above inorganic carbon has a high cost, causing the sulfate material to lose its unique low-cost advantage. SUMMARY

[0004] The application aims to provide a high-conductivity sodium ion battery positive electrode material / organic conductive polymer composite material and a preparation method thereof, which have the characteristics of high electronic conductivity, low specific surface area, high compaction density and excellent electrochemical performance.

[0005] The application can be implemented by the following technical scheme:

[0006] The application discloses a preparation method of a high-conductivity sodium ion battery positive electrode material / organic conductive polymer composite material, which comprises the following steps:

[0007] S1, preparation of a chain product: dissolving an organic conductive polymer monomer in water, adjusting the pH of the solution to be acidic, adding an oxidizing agent, and inducing the organic conductive polymer monomer to undergo a polymerization reaction to form a chain product;

[0008] S2, preparation of precursor slurry: adding a sodium source, an iron source and a sulfur source into the above solution for forming a chain product, and dissolving sufficiently to form a uniform precursor slurry;

[0009] S3, preparation of precursor powder: drying the above precursor slurry to realize solid-liquid separation, and obtaining dry precursor powder;

[0010] S4, high-temperature sintering: calcining the above precursor powder in a protective atmosphere, and obtaining Na 2+x Fe 2-x (SO4)3 / organic conductive polymer composite positive electrode material after natural cooling.

[0011] In the Na 2+x Fe 2-x (SO4)3 / organic conductive polymer composite positive electrode material, the value range of x is 0≤x≤1.

[0012] In the present application, in order to improve the electronic conductivity of the sulfate material, the present application prepares a high-conductivity Na 2+x Fe 2-x (SO4)3 / organic conductive polymer positive electrode material, which is characterized in that a layer of organic conductive polymer is modified on the surface of Na 2+x Fe 2-x (SO4)3, which is a chain structure polymerized by a double-bond-containing organic compound monomer, and has electronic conductivity, and forms a three-dimensional conductive network in the Na 2+x Fe 2-x (SO4)3 particle, which greatly improves the electronic conductivity at the material interface. The process is simple, the prepared material is high in uniformity, small in specific surface, and excellent in electrochemical performance.

[0013] Further, the organic conductive polymer is one or two or more of polyaniline, polypyrrole, polythiophene, polyacetylene, polyphenylene, polyphenylene acetylene and polydiacetylene; and the organic conductive polymer monomer is one or two or more of aniline, pyrrole, thiophene, acetylene, phenylene and diacetylene.

[0014] Further, in step S1, the pH range is 1-4, and when the pH is lower than 1, the corrosion intensity to the equipment is large, which is not conducive to large-scale production, and when the pH is higher than 4, the proton hydrogen content in the solution is insufficient to support the cross-linking reaction of the organic conductive polymer monomer, affecting the polymerization effect.

[0015] Further, in step S1, the oxidizing agent is one or more of hydrogen peroxide, hydrazine hydrate, peracetic acid, sodium percarbonate, and the added molar amount of the oxidizing agent is 1-3 times the molar amount of the organic conductive polymer monomer; when the molar amount of the oxidizing agent is less than 1 times, the organic conductive polymer monomer is not fully reacted, and there are problems such as waste of raw materials; and when the molar amount of the oxidizing agent is more than 3 times, the production cost is increased due to the excess oxidizing agent, and the large amount of residual oxidizing agent also affects the crystallization of the subsequent material.

[0016] Further, in step S4, the sintering temperature is 300-450°C, and the time is ≥0.1H; when the temperature is less than 300°C, the Na 2+x Fe 2-x The crystallinity of the Na 2+x Fe 2-x The compactness of the Na 2+x Fe 2-x The Na

[0017] Further, in step S3, the drying method is one or more of spray drying, flash drying, and heating evaporation.

[0018] Further, in step S1, the acid for adjusting the pH is one or more of formic acid, acetic acid, sulfuric acid, nitric acid, citric acid, ascorbic acid, salicylic acid, and malic acid.

[0019] Further, in step S2, the sodium source is one or more of sodium formate, sodium acetate, sodium nitrate, sodium bicarbonate, sodium carbonate, sodium hydroxide, sodium sulfate, sodium citrate, and sodium ascorbate; the iron source is one or more of iron powder, ferrous sulfate, iron hydroxide, ferrous oxide, magnetite, hematite, and hydroxyl ferric hydroxide; and the sulfur source is one or more of sulfuric acid, ammonium sulfate, sodium sulfate, ferrous sulfate, and ferrous ammonium sulfate.

[0020] Further, in step S4, the protective atmosphere is one or more of nitrogen, argon, carbon monoxide, carbon dioxide, hydrogen, and helium.

[0021] Another aspect of the present application is to protect a high-conductivity sodium-ion battery cathode material / organic conductive polymer composite material, which is prepared by the above preparation method.

[0022] The application discloses a high-conductivity sodium ion battery positive electrode material / organic conductive polymer composite material and a preparation method thereof.

[0023] First, the electronic conductivity is high. Organic conductive polymers such as polyaniline, polypyrrole and polythiophene have long-range Pi electron main chain structures, and under the action of an external electric field, carriers (solitons, polarons and bipolarons) in the organic conductive polymers move along the conjugated Pi bond, so that the directional transmission of electrons is realized, and the conductivity is exhibited. The organic conductive polymers are attached to the material interface, so that the rapid conduction of electrons between material particles and between the material and the polymer is realized, thereby reducing the internal resistance polarization of the material.

[0024] Second, the specific surface area is low. The chain structure formed by the organic conductive polymer has a small specific surface area, and the relatively dense and smooth crystal structure of the sulfate also has a low specific surface area. Therefore, the Na 2+x Fe 2-x The specific surface area of the material composed of the Na

[0025] Third, the compaction density is high. The Na 2+x Fe 2-x During the sintering process of the Na 2+x Fe 2-x After the nucleation of the Na 2+x Fe 2-x The Na

[0026] Fourth, the electrochemical performance is excellent. The Na 2+x Fe 2-x The Na Specific embodiments

[0027] In order to enable those skilled in the art to better understand the technical solutions of the application, the product of the application will be further described in detail below with reference to the embodiments.

[0028] The application discloses a preparation method of a high-conductivity sodium-ion battery positive electrode material / organic conductive polymer composite material.

[0029] S1, chain product preparation: organic conductive polymer monomers are dissolved in water, the pH of the solution is adjusted to be acidic, an oxidizing agent is added, and the organic conductive polymer monomers are induced to undergo a polymerization reaction to form a chain product;

[0030] S2, preparation of a precursor slurry: a sodium source, an iron source and a sulfur source are added to the chain product forming solution, and after being dissolved sufficiently, a uniform precursor slurry is formed;

[0031] S3, preparation of a precursor powder: the precursor slurry is dried to realize solid-liquid separation, and a dried precursor powder is obtained;

[0032] S4, high-temperature sintering: the precursor powder is calcined in a protective atmosphere, and after natural cooling, a Na 2+x Fe 2-x (SO4)3 / organic conductive polymer composite positive electrode material is obtained.

[0033] In the Na 2+x Fe 2-x (SO4)3 / organic conductive polymer composite positive electrode material, the value range of x is 0≤x≤1.

[0034] Further, the organic conductive polymer is one or two or more of polyaniline, polypyrrole, polythiophene, polyacetylene, polyphenylene, polyphenylene acetylene and polydiacetylene; and the organic conductive polymer monomer is one or two or more of aniline, pyrrole, thiophene, acetylene, phenylene and diacetylene.

[0035] Further, in step S1, the pH range is 1-4.

[0036] Further, in step S1, the oxidizing agent is one or two or more of hydrogen peroxide, hydrazine hydrate, peroxyacetic acid and sodium percarbonate, and the addition amount of the oxidizing agent is 1-3 times the molar amount of the organic conductive polymer monomer.

[0037] Further, in step S4, the sintering temperature is 300-450°C, and the time is ≥0.1H.

[0038] Further, in step S3, the drying mode is one or two or more of spray drying, flash drying and heating evaporation.

[0039] Further, in step S1, the acid for adjusting the pH is one or two or more of formic acid, acetic acid, sulfuric acid, nitric acid, citric acid, ascorbic acid, salicylic acid and malic acid.

[0040] Further, in step S2, the sodium source is one or more of sodium formate, sodium acetate, sodium nitrate, sodium bicarbonate, sodium carbonate, sodium hydroxide, sodium sulfate, sodium citrate, and sodium ascorbate; the iron source is one or more of iron powder, ferrous sulfate, iron hydroxide, ferrous oxide, magnetite, wuestite, and hydroxyl ferric hydroxide; and the sulfur source is one or more of sulfuric acid, ammonium sulfate, sodium sulfate, ferrous sulfate, and ferrous ammonium sulfate.

[0041] Further, in step S4, the protective atmosphere is one or more of nitrogen, argon, carbon monoxide, carbon dioxide, hydrogen, and helium.

[0042] Another aspect of the present application is to provide a high-conductivity sodium-ion battery cathode material / organic conductive polymer composite material.

[0043] Example 1

[0044] The present application relates to a method for preparing a high-conductivity sodium-ion battery cathode material / organic conductive polymer composite material, comprising the following steps:

[0045] S1, preparation of a chain product: dissolve an organic conductive polymer monomer in water, adjust the pH of the solution to 4, and add an oxidizing agent to induce polymerization of the organic conductive polymer monomer to form a chain product. Specifically, the organic conductive polymer monomer is aniline. The oxidizing agent is hydrogen peroxide, and the molar amount of the oxidizing agent added is 2 times the molar amount of the organic conductive polymer monomer. The acid used to adjust the pH is formic acid.

[0046] S2, preparation of a precursor slurry: add a sodium source, an iron source, and a sulfur source to the above-mentioned solution in which the chain product is formed, and after sufficient dissolution, a uniform precursor slurry is formed. The sodium source is sodium formate; the iron source is iron hydroxide and ferrous oxide; and the sulfur source is sulfuric acid and ammonium sulfate.

[0047] S3, preparation of a precursor powder: dry the above-mentioned precursor slurry to achieve solid-liquid separation, and obtain a dry precursor powder. Specifically, the drying method is spray drying.

[0048] S4, high-temperature sintering: in a protective atmosphere, calcine the above-mentioned precursor powder, and after natural cooling, obtain a Na 2+x Fe 2-x (SO4)3 / organic conductive polymer composite cathode material. Specifically, the sintering temperature is 300°C, and the time is 1H; and the protective atmosphere is nitrogen.

[0049] In the Na 2+x Fe 2-x (SO4)3 / organic conductive polymer composite cathode material, the value of x is in the range of 0≤x≤1.

[0050] Embodiment 2

[0051] The embodiment relates to a preparation method of a high-conductivity sodium ion battery positive electrode material / organic conductive polymer composite material, and the method comprises the following steps:

[0052] S1, chain product preparation: organic conductive polymer monomers are dissolved in water, the pH of a solution is adjusted to 2, an oxidizing agent is added, and a polymerization reaction of the organic conductive polymer monomers is induced to form a chain product. Specifically, the organic conductive polymer monomers are aniline and pyrrole. The oxidizing agent is peroxoacetic acid, and the added amount of the oxidizing agent is 1 times the amount of the organic conductive polymer monomers. The acid for adjusting the pH is acetic acid and sulfuric acid.

[0053] S2, preparation of a precursor slurry: a sodium source, an iron source and a sulfur source are added to the solution in which the chain product is formed, and after being dissolved sufficiently, a uniform precursor slurry is formed. The sodium source is sodium nitrate, sodium bicarbonate and sodium ascorbate. The iron source is diiron trioxide and hydroxyl ferric hydroxide. The sulfur source is ferrous sulfate and ferrous ammonium sulfate.

[0054] S3, preparation of a precursor powder: the precursor slurry is dried to realize solid-liquid separation, and a dried precursor powder is obtained. Specifically, the drying mode is flash drying.

[0055] S4, high-temperature sintering: the precursor powder is calcined in a protective atmosphere, and after natural cooling, a Na 2+x Fe 2-x (SO4)3 / organic conductive polymer composite positive electrode material is obtained. Specifically, the sintering temperature is 450°C, and the time is 0.5H. The protective atmosphere is carbon monoxide and carbon dioxide.

[0056] In the Na 2+x Fe 2-x (SO4)3 / organic conductive polymer composite positive electrode material, the value range of x is 0≤x≤1.

[0057] Embodiment 3

[0058] The embodiment relates to a preparation method of a high-conductivity sodium ion battery positive electrode material / organic conductive polymer composite material, and the method comprises the following steps:

[0059] S1, chain product preparation: organic conductive polymer monomers are dissolved in water, the pH of a solution is adjusted to 1, an oxidizing agent is added, and a polymerization reaction of the organic conductive polymer monomers is induced to form a chain product. Specifically, the organic conductive polymer monomers are aniline and pyrrole. The oxidizing agent is peroxoacetic acid, and the added amount of the oxidizing agent is 1 times the amount of the organic conductive polymer monomers. The acid for adjusting the pH is acetic acid and sulfuric acid.

[0060] S2, Preparation of precursor slurry: sodium source, iron source and sulfur source are added to the above solution for forming chain product, and after sufficient dissolution, a uniform precursor slurry is formed. The sodium source is sodium citrate, sodium ascorbate; the iron source is iron powder, ferrous sulfate; and the sulfur source is sulfuric acid, ammonium sulfate.

[0061] S3, Preparation of precursor powder: the above precursor slurry is dried to achieve solid-liquid separation, and a dry precursor powder is obtained. Specifically, the drying method is heating evaporation.

[0062] S4, high-temperature sintering: the above precursor powder is calcined in a protective atmosphere, and after natural cooling, Na 2+x Fe 2-x (SO4)3 / organic conductive polymer composite positive electrode material is obtained. Specifically, the sintering temperature is 400°C, and the time is 1H; the protective atmosphere is carbon dioxide, hydrogen, and helium.

[0063] In the Na 2+x Fe 2-x (SO4)3 / organic conductive polymer composite positive electrode material, the value range of x is 0≤x≤1.

[0064] Example 4

[0065] This embodiment relates to a preparation method of a high-conductivity sodium ion battery positive electrode material / organic conductive polymer composite material, comprising the following steps:

[0066] S1, Preparation of chain product: organic conductive polymer monomer is dissolved in water, the pH of the solution is adjusted to 2, and an oxidizing agent is added to induce polymerization of the organic conductive polymer monomer to form a chain product. Specifically, the organic conductive polymer monomer is thiophene, acetylene, and diacetylene. The oxidizing agent is hydrogen peroxide and hydrazine hydrate, and the addition amount of the oxidizing agent is 1.5 times the molar amount of the organic conductive polymer monomer; the acid for adjusting the pH is formic acid, salicylic acid, and malic acid.

[0067] S2, Preparation of precursor slurry: sodium source, iron source and sulfur source are added to the above solution for forming chain product, and after sufficient dissolution, a uniform precursor slurry is formed. The sodium source is sodium citrate, sodium ascorbate; the iron source is iron powder, ferrous sulfate; and the sulfur source is sulfuric acid, ammonium sulfate.

[0068] S3, Preparation of precursor powder: the above precursor slurry is dried to achieve solid-liquid separation, and a dry precursor powder is obtained. Specifically, the drying method is spray drying and flash drying.

[0069] S4, high-temperature sintering: the above precursor powder is calcined in a protective atmosphere, and after natural cooling, Na 2+x Fe 2-x(SO4)3 / organic conductive polymer composite cathode material. Specifically, the sintering temperature is 350°C, the time is 2H; the protective atmosphere is nitrogen, argon, hydrogen, helium.

[0070] In Na 2+x Fe 2-x In the (SO4)3 / organic conductive polymer composite cathode material, the value range of x is 0≤x≤1.

[0071] Example 5

[0072] This embodiment relates to a preparation method of a high-conductivity sodium ion battery cathode material / organic conductive polymer composite material, comprising the following steps:

[0073] S1, preparation of chain product: dissolve the organic conductive polymer monomer in water, adjust the pH of the solution to 3, add an oxidizing agent, and induce the organic conductive polymer monomer to undergo a polymerization reaction to form a chain product. Specifically, the organic conductive polymer monomer is aniline, pyrrole, thiophene, or acetylene. The oxidizing agent is hydrogen peroxide or hydrazine hydrate, and the addition amount of the oxidizing agent is 2.5 times the molar amount of the organic conductive polymer monomer. The acid used to adjust the pH is formic acid, acetic acid, sulfuric acid, or malic acid.

[0074] S2, preparation of precursor slurry: add a sodium source, an iron source, and a sulfur source to the above-mentioned chain product solution, dissolve thoroughly, and form a uniform precursor slurry. The sodium source is sodium formate, sodium acetate, sodium sulfate, sodium citrate, or sodium ascorbate. The iron source is ferrous oxide, magnetite, maghemite, or hydroxyl ferric hydroxide. The sulfur source is sulfuric acid or ammonium sulfate.

[0075] S3, preparation of precursor powder: dry the above-mentioned precursor slurry to achieve solid-liquid separation and obtain dry precursor powder. Specifically, the drying method is spray drying or flash drying.

[0076] S4, high-temperature sintering: calcine the above-mentioned precursor powder in a protective atmosphere, and after natural cooling, obtain Na 2+x Fe 2-x (SO4)3 / organic conductive polymer composite cathode material. Specifically, the sintering temperature is 380°C, the time is 1.5H; the protective atmosphere is carbon monoxide, carbon dioxide, hydrogen, helium

[0077] In Na 2+x Fe 2-x In the (SO4)3 / organic conductive polymer composite cathode material, the value range of x is 0≤x≤1.

[0078] Application Example 1 Na 2.4 Fe 1.8 Synthesis and electrochemical performance of (SO4)3 / polyaniline material

[0079] The present embodiment relates to a high-conductivity sodium-ion battery cathode Na 2.4 Fe 1.8 (SO4)3 / Polypyrrole composite material. The preparation method comprises the following steps:

[0080] Step 1: Dissolve aniline monomer in water, adjust the PH of the solution to 1.5 with formic acid, slowly add hydrazine hydrate (the amount of addition is 2.0 times the molar amount of aniline monomer), and induce in-situ polymerization of aniline monomer to form a dark brown slurry;

[0081] Step 2: Add sodium acetate, ferrous sulfate, and sulfuric acid to the above solution in a ratio of 2.4:1.8:1.2, fully dissolve to obtain a uniform precursor slurry;

[0082] Step 3: Spray dry the above precursor solution, with an inlet temperature of 300°C and an outlet temperature of 90°C, to remove the water in the slurry and obtain a dry precursor powder;

[0083] Step 4: Calcine the above precursor powder under a nitrogen atmosphere, with a sintering temperature of 400°C and a holding time of 10H, and then naturally cool to obtain Na 2.4 Fe 1.8 (SO4)3 / Polypyrrole cathode material.

[0084] Table 1 shows that the Na 2.4 Fe 1.8 (SO4)3 / Polypyrrole cathode material has a specific surface area of 5.6m 2 / g, which is significantly lower than the specific surface area of the materials prepared by in-situ carbonthermal reduction and inorganic carbon physical modification in the comparative examples, indicating that the Na 2.4 Fe 1.8 (SO4)3 / Polypyrrole cathode material has low porosity, and the particles formed during the sintering process of primary particles are large, and the degree of densification is high, and the Na 2.4 Fe 1.8 (SO4)3 / Polypyrrole material has a smooth surface without too many defects, and finally realizes the preparation of a low specific surface material, which significantly improves the material's end production and the performance and maintenance of its electrochemical properties.

[0085] The Na 2.4 Fe 1.8(SO4)3 / Polypyrrole anode material, AB, PVDF were mixed in a mass ratio of 9.2:0.4:0.4 to prepare slurry, the viscosity of the slurry was 2900 Pa.S, the fluidity was good, and the loading distribution on the current collector was uniform during the coating process, which was related to the low specific surface area of the material. The smaller the specific surface area, the weaker the adsorption capacity of the solvent and the binder during the homogenization process, the lower the viscosity of the slurry, and the better the processability. Then, a black slurry was coated on an aluminum foil using a 150-μm four-side coater, and then the film was dried in a vacuum drying oven at 100°C for 2 hours. The electrode film was punched into a circular sheet with a radius of 0.6 mm using a punching machine, and a CR2016 button cell was assembled in a glove box using metallic sodium as the counter electrode, 1 mol / L NaClO4 EC+DEC (1:1 vol%) + 5% FEC as the electrolyte, and a PP / PE / PP three-layer separator.

[0086] The above button cell was subjected to constant current charge and discharge test, and the current density was 0.1C (1C=110mAh / g). Table 1 shows that the reversible specific capacity of the electrode is 108.2mAh / g in the voltage range of 2.0-4.5V, which is significantly higher than that of the material in the comparative example. The capacity improvement is related to the purity and crystallinity of the material itself. In the liquid phase method, the ion mixing degree is high, the crystal nucleus formed by the mutual bonding between the ions during sintering is more complete, the crystallinity is higher, the effective sodium storage site is increased, and the capacity is improved. In addition, the results in Table 1 show that the capacity retention rate of the material at 10C is 97.6% of that at 0.1C, which is better than the performance in the comparative example, showing good rate performance, which indicates that the addition of polyaniline conductive polymer reduces the internal resistance of the material and is beneficial to the improvement of the cycle stability of the material. 2.4 Fe 1.8 The modification of (SO4)3 material effectively improves the electronic conductivity of the material, increases the transmission speed of electrons between particles, reduces the polarization of the material at high rate, and thus improves the capacity utilization at high rate. Finally, the capacity retention rate of the electrode at 1C rate after 500 cycles is as high as 97.8%, which is better than the cycle stability of the material in the comparative example,

[0087] which indicates that the addition of polyaniline conductive polymer reduces the internal resistance of the material and is beneficial to the improvement of the cycle stability of the material. In addition, Na 2.4 Fe 1.8 The specific surface of (SO4)3 / polypyrrole material is small, the crystal density is high, the degree of side reaction between the material and the electrolyte at high voltage is reduced, the dissolution of the material interface is effectively inhibited, and thus the cycle stability is improved.

[0088] Comparative Example 1 Na 2.4 Fe 1.8 Synthesis of (SO4)3 / C material and its electrochemical performance

[0089] The present embodiment relates to Na 2.4 Fe 1.8 (SO4)3 / C composite material. The preparation method comprises the following steps:

[0090] Step 1: sodium acetate, ferrous sulfate, sulfuric acid are added to the above solution in a ratio of 2.4:1.8:1.2, and citric acid is added as an organic carbon source, the molar amount of which is 0.2 times that of ferrous sulfate, and a uniform precursor slurry is obtained after sufficient dissolution;

[0091] Step 2: spray dry the above precursor solution, the inlet air temperature is 300°C, and the outlet air temperature is 90°C, remove the water in the slurry, and obtain dry precursor powder;

[0092] Step 3: calcine the above precursor powder under a nitrogen atmosphere, the sintering temperature is 400°C, the holding time is 10H, and the Na 2.4 Fe 1.8 (SO4)3 / C positive electrode material is obtained after natural cooling.

[0093] Table 1 shows that the specific surface area of the material is 9.7m 2 / g, slightly larger than that of application example 1, indicating that the material has more pores, which is related to the lower pyrolysis degree of citric acid. In theory, citric acid cannot be completely and effectively cracked to form a carbon layer with high conductivity and dense coating above 500°C, and at a pyrolysis temperature of 400°C, the carboxyl and hydroxyl groups contained in citric acid cannot be effectively converted into gaseous compounds and volatilized, remaining in the material and causing the specific surface area to increase significantly.

[0094] The Na 2.4 Fe 1.8 (SO4)3 / C composite material, AB, and PVDF are mixed in a mass ratio of 9.2:0.4:0.4 to prepare a slurry, and the viscosity of the slurry is 8900Pa.S, which is higher than that of the material in application example 1, which is related to the higher specific surface area. The larger the specific surface area, the stronger the adsorption capacity of the solvent and binder in the slurry, and the more likely it is to cause the viscosity of the slurry to rise, affecting the subsequent processing of the electrode sheet. Then a 150um four-side coater is used to coat the black slurry on an aluminum foil, and then the film is dried in a 100°C vacuum drying oven for 2 hours. The electrode film is punched into a circular sheet with a radius of 0.6mm using a sheet punching machine, and a metal sodium is used as a counter electrode, 1mol / L NaClO4EC+DEC(1:1vol%)+5%FEC is used as an electrolyte, and a PP / PE / PP three-layer separator is used to assemble a CR2016 type button cell in a glove box.

[0095] The constant current charge-discharge test was carried out on the above-mentioned button cell, and the current density was 0.1C (1C = 110 mAh / g). Table 1 results show that the reversible specific capacity of the electrode is only 64.5 mAh / g in the voltage range of 2.0-4.5V, and the capacity is lower than that of the material in application example 1, which is related to the preparation of the material by carbon thermal reduction method. The organic citric acid carbon source used in this method cannot be effectively cracked at a temperature of 400°C, and the carbon formed does not have high electrical conductivity. At the same time, the incomplete pyrolysis of the carbon source will also hinder the sintering process of Na 2.4 Fe 1.8 The melting and crystallization of the (SO4)3 material affects its crystallinity and phase purity, ultimately leading to the capacity of the material to be blocked. In addition, the results of the rate performance test show that the capacity retention rate of the material synthesized by the solid-phase carbon thermal reduction method is only 56.3% at 10C relative to 0.1C, which is much lower than the performance of the material in application example 1. This is related to the incomplete pyrolysis of the organic carbon on the surface of the material, which leads to a large interface resistance, resulting in a decrease in the capacity of the material at a high rate. Finally, the results in Table 1 show that the capacity retention rate of the electrode is only 64.2% after 500 cycles at 1C in the voltage range of 2.0-4.3V. The low cycle stability of the material is caused by the incomplete pyrolysis of the organic carbon, which easily leads to an increase in side reactions between the electrolyte and the material at high voltage, affecting the interface stability of the material. On the other hand, the crystallinity and phase purity of the material are affected by the organic carbon during the sintering process, leading to uneven local volume expansion during the sodium ion extraction process, which easily induces lattice cracking and ultimately leads to a decrease in the cycle stability of the material.

[0096] Example 2 Na 2.4 Fe 1.8 Synthesis and electrochemical performance of Na

[0097] This example relates to a Na 2.4 Fe 1.8 (SO4)3 / high specific surface area carbon black composite material. The preparation method comprises the following steps:

[0098] Step 1: Sodium sulfate, ferrous sulfate are added to a ball mill jar in a ratio of 1.2:1.8, and high specific surface area carbon black is added as a conductive agent, with an addition weight of 0.12 times that of ferrous sulfate, a ball-to-material ratio of 20:1, and a grinding time of 20H;

[0099] Step 2: The above precursor powder is calcined under a nitrogen atmosphere, with a sintering temperature of 400°C and a holding time of 10H. After natural cooling, Na 2.4 Fe 1.8 (SO4)3 / high specific surface area carbon black anode material is obtained.

[0100] The results of Table 1 show that the material has a specific surface area as high as 17.8 m 2 / g, much higher than the material in application example 1, which is related to the introduction of high specific surface carbon black, which contains a large amount of micropores in its structure, which is easy to cause the specific surface of the material to be too large. On the other hand, the ball milling process will polish the raw materials very fine, and during the sintering process, these fine particles are difficult to melt and crystallize to form larger particles due to the obstruction of high specific surface carbon black, which ultimately leads to further increase of the specific surface.

[0101] Na 2.4 Fe 1.8 The Na2SO4 / high specific surface carbon black material, AB, and PVDF were mixed in a mass ratio of 9.2:0.4:0.4 to prepare a slurry, and the discharge viscosity was as high as 34000 Pa.S, the slurry flowability was poor, it was difficult to sieve, and cracks were prone to occur during coating, which was related to the large specific surface of the material, which adsorbed a certain amount of solvent and binder in the slurry, resulting in a significant decrease in flowability. Then the black slurry was coated on the aluminum foil using a 150um four-side coater, and then the film was dried in a 100℃ vacuum drying oven for 2 hours. The electrode film was punched into a circular sheet with a radius of 0.6mm using a punching machine, and a CR2016 type button cell was assembled in a glove box using sodium metal as the counter electrode, 1mol / L NaClO4EC+DEC (1:1vol%)+5%FEC as the electrolyte, and PP / PE / PP three-layer separator.

[0102] The above button cell was subjected to constant current charge and discharge test, and the current density was 0.1C (1C=110mAh / g). The results in Table 1 show that the reversible specific capacity of the electrode is 89.3mAh / g in the voltage range of 2.0-4.5V, which is slightly lower than that of the material in application example 1, indicating that the material prepared by solid phase method has low phase purity, crystallinity and active material content due to the decrease in mixing uniformity of the raw materials, resulting in a significant decrease in actual capacity. In addition, the results of the rate performance test show that the capacity retention rate of the material at 10C rate is only 93.7% compared with 0.1C, and the rate performance is poor, which is related to the low phase purity of the material. The existence of impurities produces a large number of grain boundaries, which affects the transmission between ions, causing the concentration polarization to increase at high rate, seriously hindering the rapid migration of ions, resulting in a significant decrease in the rapid charge and discharge capacity. Finally, the results in Table 1 show that the capacity retention rate of the electrode is only 87.6% after 500 cycles at 1C rate in the voltage range of 2.0-4.3V, which is a larger decrease in cycle stability compared with application example 1, which is mainly due to the large specific surface area of the material. The larger the specific surface, the higher the content of interface defects, which will accelerate the side reaction between the interface of the material and the electrolyte at high voltage, resulting in continuous deterioration of the cycle stability of the material.

[0103] Table 1 Performance test results

[0104]

[0105] The above embodiments are merely specific embodiments of the present application and are described in more detail and in a specific manner, but should not be construed as limiting the scope of the patent rights of the present application. It should be noted that, for those of ordinary skill in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, and these obvious replacement forms all belong to the protection scope of the present application.

Claims

1. A method for preparing a high-conductivity sodium-ion battery cathode material / organic conductive polymer composite material, characterized in that The method comprises the following steps: S1, preparation of a chain product: dissolving an organic conductive polymer monomer in water, adjusting the pH of the solution to be acidic, and adding an oxidizing agent to induce polymerization of the organic conductive polymer monomer to form the chain product; the pH range is 1-4, and the acid used to adjust the pH of the solution is one or more than two of formic acid, acetic acid, sulfuric acid, nitric acid, citric acid, ascorbic acid, salicylic acid, and malic acid; S2, preparation of a precursor slurry: adding a sodium source, an iron source, and a sulfur source to the solution of the chain product, dissolving sufficiently to form a uniform precursor slurry; S3, preparation of a precursor powder: drying the precursor slurry to achieve solid-liquid separation, and obtaining a dried precursor powder; S4, high-temperature sintering: the above precursor powder is calcined in a protective atmosphere, and Na 2+x Fe 2-x (SO4)3 / organic conductive polymer composite cathode material; the calcination temperature is 300-450°C, and the time is ≥0.1H; In Na 2+x Fe 2-x In the (SO4)3 / organic conductive polymer composite cathode material, the value range of x is 0≤x≤1. The organic conductive polymer is one or more than two of polyaniline, polypyrrole, polythiophene, polyacetylene, polyphenylene, polyphenyleneacetylene, and polydiacetylene; the organic conductive polymer monomer is one or more than two of aniline, pyrrole, thiophene, acetylene, phenylene, and diacetylene; The oxidizing agent is one or more than two of hydrogen peroxide, hydrazine hydrate, peracetic acid, and sodium percarbonate, and the addition amount of the oxidizing agent is 1-3 times the molar amount of the organic conductive polymer monomer.

2. The process for the preparation of high conductivity sodium-ion battery cathode material / organic conductive polymer composite as claimed in claim 1, wherein: In step S3, the drying method is one or more than two of spray drying, flash drying, and heating evaporation.

3. The process for the preparation of high conductivity sodium-ion battery cathode material / organic conductive polymer composite as claimed in claim 1, wherein: In step S2, the sodium source is one or more than two of sodium formate, sodium acetate, sodium nitrate, sodium bicarbonate, sodium carbonate, sodium hydroxide, sodium sulfate, sodium citrate, and sodium ascorbate; the iron source is one or more than two of iron powder, ferrous sulfate, iron hydroxide, ferrous oxide, magnetite, hematite, and hydroxyl ferric hydroxide; and the sulfur source is one or more than two of sulfuric acid, ammonium sulfate, sodium sulfate, ferrous sulfate, and ferrous ammonium sulfate.

4. The process for the preparation of high conductivity sodium-ion battery cathode material / organic conductive polymer composite as claimed in claim 1, wherein: In step S4, the protective atmosphere is one or more than two of nitrogen, argon, carbon monoxide, carbon dioxide, hydrogen, and helium.

5. A high-conductivity sodium-ion battery cathode material / organic conductive polymer composite material, characterized in that: The method is prepared by any one of claims 1-4.

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