Sodium-ion battery positive electrode material, preparation method thereof and sodium-ion battery

Abstract

The invention discloses a sodium ion battery positive electrode material, a preparation method thereof and a sodium ion battery. The sodium ion battery positive electrode material comprises a manganese-based material and a fast ion conductor polymer coating the surface of the manganese-based material, the chemical formula of the manganese-based material is NaaMnbMcO2, a is larger than or equal to 0.5 and smaller than or equal to 1.2, and blt is larger than or equal to 0.8. 1, 0lt; b is less than or equal to 0.2, c is less than or equal to 0.2, b + c is equal to 1, and M is selected from one or more of Fe, Mg, Zn, Ni, Cu, Ti, Sb, Nb, Li and Co. The surface of the manganese-based material is coated with the fast ion conductor polymer to obtain the sodium-ion battery positive electrode material, the advantages of high capacity and long circulation of the manganese-based material are reserved, meanwhile, the capability of exchanging electrons and sodium ions with electrolyte of the manganese-based material can be improved, the internal resistance of the material is reduced, and the rate capability of the material is improved; and the air stability of the sodium-ion battery positive electrode material can be improved through the coating protection effect.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium-ion batteries, and in particular, to a cathode material for a sodium-ion battery, a preparation method thereof, and a sodium-ion battery. Background Art

[0002] With the continuous transformation of the energy consumption mode, lithium-ion batteries have become the mainstream energy storage battery system due to their extensive material systems and high energy density, and have been widely used in various portable devices and electric vehicles. However, due to the low reserves of lithium resources and their uneven distribution around the world, especially the shortage of lithium carbonate ore resources in China, the cost of lithium-ion batteries has been continuously increasing. Based on the above considerations, people have turned their attention to sodium, a homologous element with rich reserves and low prices. At present, sodium-ion batteries have become a new research hotspot in new energy.

[0003] The cathode material is an important factor affecting the energy density, service life, and cost of the battery. Developing efficient cathode materials is crucial for promoting the commercialization of sodium-ion batteries. Among many cathode materials for sodium-ion batteries, the layered oxide cathode material for manganese-based sodium-ion batteries has high specific capacity and good cycle performance, and has received widespread attention from researchers. However, this material has the following defects, such as: the conductivity of the manganese-based material itself is low, and the rate performance is poor, which affects its practical application.

[0004] The invention patent with the application publication number CN 118039838 A discloses a manganese-based sodium-ion battery cathode material and a preparation method thereof. The layered manganese-based sodium-ion battery cathode material is mixed evenly with a sodium source and a phosphorus source to obtain a mixture; the mixture is subjected to low-temperature heat treatment in a reducing atmosphere; the reducing atmosphere is changed into a nitrogen atmosphere and / or an inert atmosphere, and the heat treatment temperature is increased for reaction, and then the manganese-based sodium-ion battery cathode material is obtained. This preparation method can in-situ convert a part of the surface layered manganese-based sodium-ion battery cathode material into a polyanion-type coating layer with the sodium source and the phosphorus source, thereby improving the specific capacity of the layered manganese-based cathode material, but it cannot fundamentally solve the problems of low conductivity and poor rate performance of the manganese-based material.

[0005] The invention patent with the authorization announcement number CN 102544495 B discloses a preparation method of a lithium iron phosphate-polyacetylene composite cathode material, and the steps are as follows: lithium iron phosphate is dispersed in a surfactant solution, an alkaline organic solution is added, a hydrogen-containing polyhaloolefin is added, and the reaction is carried out at a temperature of 15-30°C for 1-7 hours under argon protection, neutralized with hydrochloric acid, and the product is washed with water and then washed with acetone; finally, it is dried in a vacuum drying oven at 85-95°C for 8-12 hours to obtain the lithium iron phosphate-polyacetylene composite cathode material.

[0006] However, the hydrogen-containing polyhaloolefin is selected from any one of polyvinylidene fluoride, poly(1,2-dichloroethylene), polyvinyl chloride, polyvinylidene chloride, and their copolymers or blends. Therefore, it cannot coat polyacetylene or a housing material containing polyacetylene on lithium iron phosphate. Therefore, the problems of low conductivity and poor rate performance cannot be solved either. Summary of the Invention

[0007] To solve the above problems, in a first aspect, the present invention provides a cathode material for a sodium-ion battery, which has high conductivity, good rate performance, and good air stability and cycle stability.

[0008] The technical solution of the present invention to solve the above problems is as follows:

[0009] A cathode material for a sodium-ion battery, comprising a manganese-based material and a fast ion conductor polymer coated on the surface of the manganese-based material; the chemical formula of the manganese-based material is Na a Mn b M c O2, where 0.5 ≤ a ≤ 1.2, 0.8 ≤ b < 1, 0 < c ≤ 0.2, b + c = 1, and M is selected from one or more of Fe, Mg, Zn, Ni, Cu, Ti, Sb, Nb, Li, and Co.

[0010] Preferably, the fast ion conductor polymer is selected from at least one of sodium polyacetylene sulfonate and sodium polystyrene acetylene sulfonate.

[0011] As common general knowledge in the art, in a lithium-ion battery, by doping manganese elements, lithium iron phosphate manganese can achieve higher energy density and working voltage, but at the same time bring other problems. In addition to similar problem 1), the presence of manganese elements makes the intercalation and deintercalation of lithium ions and the movement more difficult, and the electronic conductivity and lithium ion mobility are lower, affecting the capacity and rate performance of the material; there is also problem 2) during the charge and discharge process, the crystal structure of manganese ions will undergo irreversible changes, and at the same time, manganese ions will be de-doped and deposited on the surface of the negative electrode to damage the SEI film. Therefore, the specific capacity of the material is low and decays rapidly, and the cycle performance is affected to a certain extent. It can be predicted that similar problems may also be encountered in sodium-ion batteries; in the manganese-based cathode material of sodium-ion batteries, similar problems can be effectively solved or alleviated by coating.

[0012] Under the technical framework of coating, the inventors noticed that when the conductive polymer polypyrrole is used as an electrode material, it can improve the charge-discharge performance and cycle stability of the battery. However, the performance of polypyrrole is not yet sufficient to improve the manganese-based material to a level where it can be directly applied, and it cannot withstand the high temperature of the second firing. Through root cause analysis, the conductivity of such substances is due to the presence of conjugated double bonds, and the electrons in the large π bond can flow freely. Therefore, preparing a conductive polymer with a large π bond in the main chain has become the key direction for breakthrough. Among them, the conductivity that polyacetylene can achieve is the highest among the discovered conductive polymers. However, there are also some problems with the direct application of polyacetylene. Polyacetylene is a solid and cannot be directly coated on the manganese-based cathode material, and the hard carbon coating layer prepared by conventional processes cannot form good electrical contact with the internal manganese-based material, making it difficult to exert the advantage of the high conductivity of polyacetylene.

[0013] Conductive polymer materials are divided into two major categories according to the carriers: electronic conductors and ionic conductors. Electronic conductors are represented by polyacetylene and polypyrrole. Ionic conductors are represented by the polymer complex composed of polyoxyethylene ether and polypropylene oxide ether and alkali metal salts, and ionic conduction is the main mechanism during conduction. The inventors learned in the research on improving the conductivity of the manganese-based cathode material of sodium-ion batteries that fast ion conductor polymers can effectively improve this performance. Existing technologies indicate that although fast ion conductors are solids, one of their sublattices is in a molten state, so they also have some characteristics of liquids, that is, they have the duality of solid and liquid. Therefore, coating a layer of ionic conductor on the surface of the manganese-based material has become an effective way to solve the above problems.

[0014] The applicant's research found that the conductivity of ionic conductors is mainly determined by high elasticity and polarity. At relatively high temperatures, the segments of the polymer chains in ionic conductors will relax, soften or transform into a highly elastic state, so they have some characteristics of liquids. In this non-flowing liquid, due to the ionic properties of the salts and the polar effects of the polymers, the conductivity of the manganese-based cathode material can be significantly improved.

[0015] In the above technical solution of the present invention, the structural formula of sodium polystyreneacetylene sulfonate is as follows:

[0016]

[0017] This application also provides a synthesis method of the sodium polystyreneacetylene sulfonate:

[0018] Under the conditions of an aqueous solution and nitrogen protection, phenylacetylene undergoes a polymerization reaction under the catalysis of triethylamine and cyclooctadienyl rhodium dimer chloride to synthesize polystyreneacetylene. The synthesized polystyreneacetylene is then fully reacted with a sufficient amount of concentrated sulfuric acid under heating. After the reaction ends and cools to room temperature, it is diluted, neutralized to neutral, filtered, washed, and dried to obtain the finished product of sodium polystyreneacetylene sulfonate.

[0019] Polyphenylacetylene is a conductive polymer that conducts electricity through electrons. Therefore, using it as a coating on the surface of manganese-based materials has limited effect on improving the conductivity of the cathode materials for sodium-ion batteries. To effectively improve the conductivity of the cathode materials for sodium-ion batteries, the present invention synthesizes a derivative of polyphenylacetylene - sodium polystyrene sulfonate, which is a light yellow amorphous solid at room temperature, and its measured conductivity is about 10 -4 S / cm. After applying a voltage across its two ends, a small amount of silver-white metallic sodium is deposited on the electrode, indicating that sodium polystyrene sulfonate has ionic conductivity. Considering its conductivity value, it shows that sodium polystyrene sulfonate is a fast ion conductor.

[0020] Fast ion conductors, also known as superionic conductors and sometimes called solid electrolytes, have ionic conductivities comparable to those of liquid electrolytes (10 -4 S / cm) and low ionic conduction activation energies within a certain temperature range. Coating a fast ion conductor polymer on the surface of manganese-based materials can enhance the ability of manganese-based materials to exchange electrons and sodium ions with the electrolyte, reduce the internal resistance of the materials, improve the electronic conductivity and ionic conductivity. After reducing the internal resistance, during high-rate large-current charge and discharge processes, the self-heating decreases, the internal voltage loss of the battery decreases, and the energy loss also decreases, thereby improving the rate performance of the cathode materials.

[0021] As a derivative of the conductive polymer polyphenylacetylene, sodium polystyrene sulfonate has a large benzene ring - double bond conjugated system, and the delocalized degenerate molecular orbitals formed by it provide relatively high electronic conductivity. After sulfonation modification and then alkalization, it has the ability to load and transport sodium ions, greatly improving its sodium ion conductivity, thus enabling the cathode materials to have better conductive performance. In addition, the polymer material coating can resist the structural stress generated by the materials during charge and discharge, inhibit material deformation and cracking; it can also improve the stability of the materials against air through the coating protection effect.

[0022] Preferably, the median particle size D50 of the cathode materials for sodium-ion batteries is 2 - 12 μm, and the particle size width K90 < 1.2.

[0023] In a second aspect, the present invention provides a preparation method for the above-mentioned cathode materials for sodium-ion batteries, including the following steps:

[0024] S1. Mix the sodium source, manganese source, and M source evenly to obtain a first-stage mixture;

[0025] S2. Place the first-stage mixture in an air or oxygen atmosphere and sinter to obtain manganese-based materials;

[0026] S3. Mix the manganese-based materials with the fast ion conductor polymer to obtain a second-stage mixture;

[0027] S4. Place the secondary mixture in a nitrogen or argon atmosphere and sinter to obtain the cathode material for the sodium-ion battery.

[0028] Preferably, in step S1, the sodium source is selected from one or more of sodium hydroxide, sodium carbonate, sodium bicarbonate, and sodium oxalate; the manganese source is selected from one or more of manganese oxides, carbonates, and oxalates; the M source is selected from one or more of M oxides, carbonates, and oxalates.

[0029] Preferably, in step S1, the molar ratio of sodium element, manganese element, and M element in the sodium source, manganese source, and M source is (0.5 - 1.2):(0.8 - 1):(0 - 0.2).

[0030] Preferably, in step S2, the sintering temperature is 800 - 1200 °C and the sintering time is 6 - 36 h.

[0031] Preferably, in step S3, the mass fraction of the fast ion conductor polymer in the secondary mixture is 1000 - 20000 ppm.

[0032] Preferably, in step S4, the sintering temperature is 200 - 800 °C and the sintering time is 4 - 24 h.

[0033] The invention also provides a sodium-ion battery, and the cathode of the sodium-ion battery includes the above-mentioned cathode material for the sodium-ion battery.

[0034] The present invention has the following beneficial effects:

[0035] In the present invention, a fast ion conductor polymer is coated on the surface of the manganese-based material to obtain the cathode material for the sodium-ion battery, which retains the advantages of high capacity and long cycle of the manganese-based material. At the same time, it can improve the ability of the manganese-based material to exchange electrons and sodium ions with the electrolyte, reduce the internal resistance of the material, and improve the rate performance of the material; and the polymer material coating can resist the structural stress generated during charge and discharge, inhibit the deformation and cracking of the material, and also improve the air stability of the cathode material for the sodium-ion battery through the coating protection effect. Description of the Drawings

[0036] Figure 1 It is the SEM image of the cathode material for the sodium-ion battery in Example 2;

[0037] Figure 2 It is the SEM image of the cathode material for the sodium-ion battery in Example 10;

[0038] Figure 3 It is the SEM image of the cathode material for the sodium-ion battery in Comparative Example 1. Detailed Embodiments

[0039] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts are within the protection scope of the present invention.

[0040] Example 1

[0041] A preparation method of sodium polystyrene sulfonate includes the following steps:

[0042] In a reaction kettle, while introducing nitrogen to exhaust air, 100 g of phenylacetylene, 8 L of ultrapure water and 8 mL of triethylamine are successively added. After stirring evenly, 40 mL of a tetrahydrofuran solution of 25% dichlorocyclooctadienyl rhodium dimer is slowly dropped into the reaction kettle, and the reaction is carried out at room temperature for 1 h.

[0043] After the reaction is completed, a yellow crude product is obtained by filtration. Then, 1 L of tetrahydrofuran is taken to dissolve the crude product, and it is slowly dropped into 40 L of a methanol solution. A solid precipitates, and the yellow solid is obtained by filtration. After repeating this process 2 - 3 times, the product is placed in a vacuum drying oven at 45°C for 48 h to obtain a yellow solid, polystyrene acetylene.

[0044] 50 g of polystyrene acetylene is added to the reaction kettle, 5 L of concentrated sulfuric acid with a mass fraction of 98% is slowly added, the temperature is raised to 130°C, and the stirring reaction is carried out until the polystyrene acetylene is completely dissolved, and the heat preservation reaction is carried out for 24 h.

[0045] After the reaction is completed, it is cooled to room temperature, the solution is slowly dropped into 50 L of ultrapure water, and then sodium hydroxide is added to adjust the pH ≥ 9. The whole process is kept in a cold water bath to ensure that the liquid temperature does not exceed 50°C, a light yellow crude product precipitates, the solid is collected after filtration, washed with ultrapure water until the washing liquid is neutral, and the product is placed in a vacuum drying oven at 80°C for 48 h to obtain a light yellow solid, sodium polystyrene sulfonate.

[0046] Example 2

[0047] A preparation method of a cathode material for a sodium-ion battery includes the following steps:

[0048] S1. Sodium carbonate, manganese tetroxide, and iron(III) oxide are fully mixed according to a molar ratio of Na:Mn:Fe = 1:0.9:0.1 to obtain a first-stage mixture;

[0049] S2. The first-stage mixture is placed in a roller hearth furnace and sintered at 900°C for 12 h in an air atmosphere to obtain a manganese-based material NaMn 0.9 Fe 0.1 O2;

[0050] S3. The manganese-based material NaMn0.9 Fe 0.1 O2 and sodium polyphenylene sulfonate are uniformly mixed to obtain a secondary mixture, wherein the mass fraction of sodium polyphenylene sulfonate in the secondary mixture is 5000ppm;

[0051] S4. Place the secondary mixture in a roller furnace and sinter at 300° C. for 6 hours in a nitrogen atmosphere to obtain a positive electrode material for a sodium ion battery.

[0052] Example 3

[0053] The only difference from Example 2 is that in step S3, the mass fraction of sodium polyphenylene sulfonate in the secondary mixture is 19000 ppm.

[0054] Example 4

[0055] The only difference from Example 2 is that in step S3, the mass fraction of sodium polyphenylene sulfonate in the secondary mixture is 1500 ppm.

[0056] Example 5

[0057] The only difference from Example 2 is that sodium carbonate is replaced by sodium hydroxide.

[0058] Example 6

[0059] The only difference from Example 2 is that trimanganese tetraoxide is replaced by dimanganese trioxide.

[0060] Example 7

[0061] The only difference from Example 2 is that ferrous oxide is replaced by ferrous oxalate.

[0062] Example 8

[0063] The only difference from Example 2 is that in step S2, the sintering temperature is 1000°C and the time is 10 hours.

[0064] Example 9

[0065] The only difference from Example 2 is that in step S4, the sintering temperature is 700° C. and the sintering time is 4 hours.

[0066] Example 10

[0067] A sodium ion battery positive electrode material and a preparation method thereof, comprising the following steps:

[0068] S1. Sodium carbonate, manganese tetraoxide, ferric oxide and titanium dioxide are fully mixed in a molar ratio of Na:Mn:Fe:Ti=1:0.9:0.08:0.02 to obtain a primary mixture;

[0069] S2. Place the first-stage mixture in a roller hearth furnace and sinter it at 900 °C for 12 h in an air atmosphere to obtain the manganese-based material NaMn 0.9 Fe 0.08 Ti 0.02 O2;

[0070] S3. Mix the manganese-based material NaMn 0.9 Fe 0.08 Ti 0.02 O2 and sodium polystyrene sulfonate evenly to obtain a second-stage mixture, where the mass fraction of sodium polystyrene sulfonate in the second-stage mixture is 5000 ppm;

[0071] S4. Place the second-stage mixture in a roller hearth furnace and sinter it at 300 °C for 6 h in a nitrogen atmosphere to obtain the positive electrode material for sodium-ion batteries.

[0072] Comparative Example 1

[0073] A positive electrode material for sodium-ion batteries and its preparation method include the following steps:

[0074] S1. Thoroughly mix sodium carbonate, manganese tetroxide, and ferric oxide in a molar ratio of Na:Mn:Fe = 1:0.9:0.1 to obtain a first-stage mixture;

[0075] S2. Place the first-stage mixture in a roller hearth furnace and sinter it at 900 °C for 12 h in an air atmosphere to obtain the positive electrode material for sodium-ion batteries.

[0076] Comparative Example 2

[0077] The difference from Example 2 is only that in step S3, the mass fraction of sodium polystyrene sulfonate in the second-stage mixture is 600 ppm.

[0078] Comparative Example 3

[0079] The difference from Example 2 is only that in step S3, the mass fraction of sodium polystyrene sulfonate in the second-stage mixture is 50000 ppm.

[0080] Perform electrochemical performance tests on the positive electrode materials for sodium-ion batteries in Examples 2 to 10 and Comparative Examples 1 to 3. The test method is as follows: Slurry and coat the prepared positive electrode material for sodium-ion batteries together with a conductive agent and a binder on an aluminum foil to prepare a button cell positive electrode sheet, and assemble it with a sodium sheet negative electrode into a button-type sodium-ion battery. For the air stability experiment, place the electrode sheet in the air for 3 days and then assemble it with the sodium sheet negative electrode. Perform charge-discharge cycling and rate tests on the above button-type sodium-ion batteries. The test results are shown in the following table.

[0081] The conductivity of the sodium-ion battery cathode materials in Examples 2-10 and Comparative Examples 1-3 was tested. The test method was as follows: The prepared sodium-ion battery cathode material was added to a powder resistivity tester, and the pressure was increased to 1000 kg (100 MPa), and the resistivity of the cathode material was measured. The powder conductivity could be calculated.

[0082] Table 1: Data table of electrochemical performance test of Examples 2-10 and Comparative Examples 1-3

[0083]

[0084] As can be seen from Table 1, compared with Comparative Example 1 without adding sodium polystyrene sulfonate, the first-cycle discharge specific capacity, 10C capacity retention rate, 100-cycle capacity retention rate, conductivity, and capacity retention rate after 3 days of air storage of the sodium-ion battery cathode materials in Examples 2-10 were all improved. This indicates that coating sodium polystyrene sulfonate on the surface of the manganese-based material can improve the capacity, conductivity, rate performance, cycle stability, and air stability of the sodium-ion battery cathode material.

[0085] It can also be seen from Table 1 that the first-cycle discharge specific capacity, rate performance, cycle retention rate, conductivity, and air stability of Examples 2-10 were better than those of Comparative Examples 2 and 3. This shows that compared with adding too little (600 ppm) sodium polystyrene sulfonate in Comparative Example 2 and adding too much (50,000 ppm) sodium polystyrene sulfonate in Comparative Example 3, coating an appropriate amount (1000-20,000 ppm) of sodium polystyrene sulfonate on the surface of the manganese-based material in the examples of the present invention can effectively improve the capacity, rate performance, and cycle stability of the sodium-ion battery cathode material, while maintaining high conductivity and air stability.

[0086] From Figure 1 、 Figure 2 、 Figure 3 It can also be seen that the particle size of the sodium-ion battery cathode material obtained in Example 2 of the present invention is uniform and the edges are round, which is better. While the sodium-ion battery cathode material in Comparative Example 1 is in the shape of long and thin rods and is prone to breakage, which is significantly worse.

Claims

1. A sodium ion battery positive electrode material, characterized in that: It includes a manganese-based material and a fast ion conductor polymer coated on the surface of the manganese-based material; the chemical formula of the manganese-based material is Na a Mn b M c O2, where 0.5 ≤ a ≤ 1.2, 0.8 ≤ b < 1, 0 < c ≤ 0.2, b + c = 1, and M is selected from one or more of Fe, Mg, Zn, Ni, Cu, Ti, Sb, Nb, Li, and Co.

2. The sodium ion battery positive electrode material according to claim 1, characterized in that The fast ion conductor polymer is selected from at least one of sodium polyacetylene sulfonate and sodium polyphenylene acetylene sulfonate.

3. The sodium ion battery positive electrode material according to claim 1, characterized in that The median particle size D50 of the sodium ion battery positive electrode material is 2 to 12 μm, and the particle size width K90 is less than 1.

2.

4. The method for preparing the positive electrode material for a sodium ion battery according to any one of claims 1 to 3, characterized in that: The steps include: S1, mixing the sodium source, manganese source and M source evenly to obtain a primary mixture; S2, placing the primary mixed material in air or oxygen atmosphere and sintering to obtain a manganese-based material; S3, mixing the manganese-based material and the fast ion conductor polymer uniformly to obtain a secondary mixture; S4. Place the secondary mixture in a nitrogen or argon atmosphere and sinter to obtain a positive electrode material for a sodium ion battery.

5. The preparation method according to claim 4, characterized in that: In step S1, the sodium source is selected from one or more of sodium hydroxide, sodium carbonate, sodium bicarbonate, and sodium oxalate; the manganese source is selected from one or more of manganese oxides, carbonates, and oxalates; and the M source is selected from one or more of M oxides, carbonates, and oxalates.

6. The preparation method according to claim 4, characterized in that: In step S1, the molar ratio of the sodium element, the manganese element and the M element in the sodium source, the manganese source and the M source is (0.5-1.2):(0.8-1):(0-0.2).

7. The preparation method according to claim 4, characterized in that: In the step S2, the sintering temperature is 800-1200° C., and the sintering time is 6-36 hours.

8. The preparation method according to claim 4, characterized in that: In step S3, the mass fraction of the fast ion conductor polymer in the secondary mixture is 1000-20000 ppm.

9. The preparation method according to claim 4, characterized in that: In the step S4, the sintering temperature is 200-800° C., and the sintering time is 4-24 hours.

10. A sodium ion battery, characterized in that: The positive electrode of the sodium ion battery comprises the positive electrode material of the sodium ion battery according to any one of claims 1 to 3.

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