High-conductivity polyanionic secondary battery cathode material and method of making same

Abstract

The application discloses a high-conductivity polyanionic secondary battery positive electrode material and a preparation method thereof, and the preparation method comprises the following steps: S1, grinding and mixing of emulsion: grinding alkali metal source, transition metal source, anion source and carbon source with water to form a uniform emulsion; S2, separation of precursor powder: drying the emulsion to realize solid-liquid separation and obtain dry precursor powder; S3, pre-crosslinking treatment of the precursor: solid-phase mixing the precursor powder and organic high-molecular fibrous compound under heating to form a pre-crosslinked precursor; and S4, high-temperature calcination: high-temperature calcination of the pre-crosslinked precursor, natural cooling and crystallization, and finally forming a high-conductivity polyanionic secondary battery positive electrode material connected by a three-dimensional conductive network. The high-conductivity polyanionic secondary battery positive electrode material and the preparation method thereof have the characteristics of high conductivity, small electrode binder dosage, good structural stability and strong system adaptability.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, specifically to a high-conductivity polyanionic secondary battery cathode material and its preparation method. Background Technology

[0002] Polyanionic materials often consist of a three-dimensional framework structure formed by the interlacing of alkali metal groups, transition metal groups, and anionic groups in a point-to-surface-to-line manner. The anions are often larger groups such as phosphate, pyrophosphate, and sulfate, which are poor conductors of electrons, and the resulting framework structure impedes electron flow. Therefore, polyanionic materials generally exhibit low electronic conductivity, high internal resistance polarization in batteries, and hindered long-cycle performance.

[0003] The underlying reason is the presence of PO4 in polyanionic materials. 3- P2O7 4- SO4 2- Anionic groups are poor conductors of electrons, resulting in high energy barriers for electron transitions and making electron transport difficult. Therefore, the more anionic groups a material contains, the lower its electronic conductivity; this is a fundamental property of polyanionic materials.

[0004] In the industrialization of polyanionic materials, two main methods are often employed to improve the electronic conductivity: first, nanostructuring, where the distance electrons travel within the particle is shortened when the primary particles reach the nanoscale, thus increasing the electron transport rate to some extent; and second, carbon coating, which involves modifying the surface of nanomaterials with a layer of inorganic carbon, utilizing the high electronic conductivity of this inorganic carbon to enhance electron transport between material particles. While nanostructuring and carbon coating can improve the electronic conductivity to some extent, they hinder long-range electron transport between material particles.

[0005] Therefore, the two methods mentioned above cannot achieve long-distance transmission of electrons between different particles, which to some extent restricts the improvement of the material's electronic conductivity, resulting in a large internal resistance of the powder and poor long-cycle performance of the battery. Summary of the Invention

[0006] The purpose of this invention is to provide a high-conductivity polyanionic secondary battery cathode material and its preparation method, which has the characteristics of high conductivity, low electrode binder dosage, good structural stability and strong system adaptability.

[0007] This invention can be achieved through the following technical solutions:

[0008] This invention discloses a method for preparing a high-conductivity polyanionic secondary battery cathode material, comprising the following steps:

[0009] S1. Emulsion grinding and mixing: Add water to alkali metal source, transition metal source, anion source and carbon source and grind to form a uniform emulsion;

[0010] S2. Precursor powder separation: The above emulsion is dried to achieve solid-liquid separation and obtain dry precursor powder.

[0011] S3. Precursor pre-crosslinking treatment: Precursor powder and organic polymer fiber compound are mixed in a solid phase under heating conditions to complete the melting, stretching and drawing processes of polymer fiber compound at the powder interface, forming a pre-crosslinked precursor.

[0012] S4. High-temperature calcination: The pre-crosslinked precursor is calcined at high temperature and then naturally cooled to crystallize, ultimately forming a high-conductivity polyanion-type secondary battery cathode material with a three-dimensional conductive network connection.

[0013] In this invention, a fiber carbonization three-dimensional conductive network construction method is used to improve the long-distance rapid electron transport between material particles, thereby reducing the internal resistance of polyanionic materials and improving their performance in batteries. The preparation process involves grinding an alkali metal source, a transition metal source, an anion source, and a carbon source with water, mixing them evenly, and then spray-drying the mixture. The dried precursor powder is then mixed and ground with a polymer fiber compound under heating conditions. The shear force generated during the grinding process depolymerizes, disperses, stretches, and fiberizes the fiber compound, forming bridges between different particles. Finally, carbonization is performed to form a conductive network, significantly improving the long-distance rapid electron transport.

[0014] Furthermore, in step S3, the heating temperature for pre-crosslinking is 100-350℃. When the temperature is below 100℃, the organic polymer fiber compound has a low degree of melting, and its chain structure is difficult to open, making it impossible to uniformly adhere and crosslink to the powder surface. When the temperature is above 350℃, the organic polymer fiber compound decomposes into carbon at high temperature, and the degree of fiber carbonization intensifies, making it easy to break during the mixing and ball milling process, thus failing to achieve the purpose of connecting between particles.

[0015] Further, in step S3, the organic polymer fiber compound is one or more of plastic compounds, rubber compounds, and adhesives; the plastic compound is one or more of polyethylene, polypropylene, polycarbonate, and polystyrene; the rubber compound is one or more of natural rubber, butyl rubber, styrene-butadiene rubber, and silicone rubber; and the adhesive compound is one or more of epoxy resin, acrylate, and phenolic resin.

[0016] Furthermore, in step S3, the solid-phase mixing method is one or more of ball milling, grinding, and sand milling. The purpose of dispersing and stretching the organic polymer fiber compound on the powder surface is achieved by solid-phase mixing through friction and shear force.

[0017] Furthermore, in step S4, the conditions for high-temperature calcination are: sintering temperature greater than 400°C and holding time greater than 3 hours, to ensure sufficient crystal growth of the material.

[0018] Furthermore, in step S2, the drying method is one or more of the following: low-temperature drying, vacuum drying, natural air drying, spray drying, flash drying, and high-temperature evaporation crystallization, in order to achieve solid-liquid separation.

[0019] Further, in step S1, the alkali metal source is one or more of sodium-containing compounds, potassium-containing compounds, and lithium-containing compounds. The sodium-containing compound is one or more of sodium hydroxide, sodium peroxide, sodium carbonate, sodium hydroxide, sodium formate, sodium acetate, sodium oxalate, trisodium citrate, sodium sulfate, sodium chloride, and sodium nitrate. The potassium-containing compound is one or more of potassium hydroxide, potassium carbonate, potassium chloride, potassium sulfate, potassium nitrate, potassium peroxide, potassium superoxide, and potassium bicarbonate. The lithium-containing compound is one or more of lithium carbonate, lithium bicarbonate, lithium hydroxide, lithium dihydrogen phosphate, lithium chloride, and lithium fluoride.

[0020] Further, in step S1, the transition metal source is one or more of the following: iron-containing compound, cobalt-containing compound, nickel-containing compound, and manganese-containing compound. The iron-containing compound is one or more of the following: ferric hydroxide, iron oxide, ferrous oxalate, ferrous sulfate, ferric nitrate, ferric phosphate, ferric chloride, and ferric citrate. The cobalt-containing compound is one or more of the following: cobalt oxalate, cobalt carbonate, cobalt oxide, cobalt hydroxide, cobalt chloride, cobalt nitrate, and cobalt sulfate. The nickel-containing compound is one or more of the following: nickel hydroxide, nickel nitrate, nickel oxide, nickel chloride, and nickel sulfate. The manganese-containing compound is one or more of the following: manganese oxide, manganese oxalate, manganese chloride, manganese carbonate, and manganese sulfate.

[0021] Further, in step S1, the anion source is one or more of a sulfur-containing compound, a phosphorus-containing compound, and a fluorine-containing compound; the sulfur-containing compound is one or more of sulfuric acid, sodium / potassium / lithium / ammonia sulfate, ferrous / manganese / nickel / cobalt sulfate; the phosphorus-containing compound is one or more of phosphoric acid and its alkali metal salt derivatives, phosphoric acid and its transition metal precipitates, pyrophosphate and its salt derivatives, metaphosphoric acid and its salt derivatives, polyphosphoric acid and its salt derivatives; and the fluorine-containing compound is one or more of hydrogen fluoride, ammonium fluoride, lithium fluoride, hydrogen fluoride, and lithium fluoride.

[0022] Furthermore, the carbon source is an organic carbon source and / or an inorganic carbon source. The organic carbon source is one or more of sucrose, citric acid, starch, cyclodextrin, glucose, maltose, lactose, polyvinyl alcohol, and polyacryl alcohol. The inorganic carbon source is one or more of graphene, graphite, hard carbon, carbon nanotubes, and carbon black.

[0023] Another aspect of the present invention relates to protecting a polyanion-type secondary battery cathode material, which is prepared by the above-described preparation method. Specifically, the polyanion-type secondary battery cathode material is a sodium-ion battery material or a lithium-ion battery cathode material. The sodium-ion battery cathode material is sodium iron phosphate, sodium iron pyrophosphate, sodium iron phosphate pyrophosphate, sodium vanadium phosphate, sodium vanadium fluorophosphate, sodium iron fluorophosphate, sodium iron sulfate, or sodium iron fluorosulfate. The lithium-ion battery cathode material is lithium iron phosphate, lithium iron manganese phosphate, lithium fluorinated iron phosphate, lithium fluorinated iron manganese phosphate, or lithium iron sulfate.

[0024] This invention discloses a high-conductivity polyanionic secondary battery cathode material and its preparation method, which has the following beneficial effects:

[0025] First, it has high electronic conductivity. After carbonization, the polymer fiber compound easily forms a fibrous long chain structure. The length of this chain structure ranges from a few μm to tens of μm, which can link multiple material particles at the same time, realizing the interconnection of the electronic conductive network between particles. At the same time, there are a large number of graphitized carbon layers in the carbonized structure of the compound, and electrons can be transported along the carbon layer over long distances with high efficiency, thereby improving the electronic conductivity between powders.

[0026] Secondly, the amount of electrode binder used is low. Polyanionic materials often require the addition of about 3-5% binder during electrode preparation to improve the adhesion between material particles. However, the network structure formed after carbonization of polymer fiber compounds has an adhesive effect, which can fix the particles together. This will reduce the amount of binder added during electrode preparation to a certain extent, thereby reducing the electrode preparation cost.

[0027] Third, it has good structural stability. The network structure formed after the carbonization of polymer fiber compounds has the effect of fixing particles. When these particles are made into batteries, their volume will expand / contract as sodium ions are inserted and removed, causing the particles to detach from the electrode and resulting in capacity loss. The construction of the fiber network structure effectively fixes the stability of the electrode during the material volume change process, thereby greatly improving the cycle stability of the battery.

[0028] Fourth, the system exhibits strong adaptability. By controlling the heating and grinding conditions of the precursor powder and organic polymer fiber compound, different parameters such as fiber stretching thickness and length can be precisely adjusted. Selective adaptation can be performed based on the particle size of the polyanionic material, minimizing the amount of organic polymer fiber compound used while meeting material and battery design requirements. Attached Figure Description

[0029] Figure 1 Example 1: High conductivity Na4Fe 2.91 SEM of (PO4)2P2O7 / C material;

[0030] Figure 2 Na₄Fe, as in Comparative Example 1 2.91 SEM of (PO4)2P2O7 / C material. Detailed Implementation

[0031] To enable those skilled in the art to better understand the technical solution of the present invention, the product of the present invention will be further described in detail below with reference to embodiments.

[0032] This invention discloses a method for preparing a high-conductivity polyanionic secondary battery cathode material, comprising the following steps:

[0033] S1. Emulsion grinding and mixing: Add water to alkali metal source, transition metal source, anion source and carbon source and grind to form a uniform emulsion;

[0034] S2. Precursor powder separation: The above emulsion is dried to achieve solid-liquid separation and obtain dry precursor powder.

[0035] S3. Precursor pre-crosslinking treatment: Precursor powder and organic polymer fiber compound are mixed in a solid phase under heating conditions to form a pre-crosslinked precursor;

[0036] S4. High-temperature calcination: The pre-crosslinked precursor is calcined at high temperature and then naturally cooled to crystallize, ultimately forming a high-conductivity polyanion-type secondary battery cathode material with a three-dimensional conductive network connection.

[0037] Furthermore, in step S3, the heating temperature for pre-crosslinking is 100-350°C.

[0038] Further, in step S3, the organic polymer fiber compound is one or more of plastic compounds, rubber compounds, and adhesives; the plastic compound is one or more of polyethylene, polypropylene, polycarbonate, and polystyrene; the rubber compound is one or more of natural rubber, butyl rubber, styrene-butadiene rubber, and silicone rubber; and the adhesive compound is one or more of epoxy resin, acrylate, and phenolic resin.

[0039] Furthermore, in step S3, the solid phase mixing method is one or more of ball milling, grinding, and sand milling.

[0040] Furthermore, in step S4, the conditions for high-temperature calcination are: sintering temperature greater than 400°C and holding time greater than 3 hours, to ensure sufficient crystal growth of the material.

[0041] Furthermore, in step S2, the drying method is one or more of the following: low-temperature drying, vacuum drying, natural air drying, spray drying, flash drying, and high-temperature evaporation crystallization, in order to achieve solid-liquid separation.

[0042] Further, in step S1, the alkali metal source is one or more of sodium-containing compounds, potassium-containing compounds, and lithium-containing compounds. The sodium-containing compound is one or more of sodium hydroxide, sodium peroxide, sodium carbonate, sodium hydroxide, sodium formate, sodium acetate, sodium oxalate, trisodium citrate, sodium sulfate, sodium chloride, and sodium nitrate. The potassium-containing compound is one or more of potassium hydroxide, potassium carbonate, potassium chloride, potassium sulfate, potassium nitrate, potassium peroxide, potassium superoxide, and potassium bicarbonate. The lithium-containing compound is one or more of lithium carbonate, lithium bicarbonate, lithium hydroxide, lithium dihydrogen phosphate, lithium chloride, and lithium fluoride.

[0043] Further, in step S1, the transition metal source is one or more of the following: iron-containing compound, cobalt-containing compound, nickel-containing compound, and manganese-containing compound. The iron-containing compound is one or more of the following: ferric hydroxide, iron oxide, ferrous oxalate, ferrous sulfate, ferric nitrate, ferric phosphate, ferric chloride, and ferric citrate. The cobalt-containing compound is one or more of the following: cobalt oxalate, cobalt carbonate, cobalt oxide, cobalt hydroxide, cobalt chloride, cobalt nitrate, and cobalt sulfate. The nickel-containing compound is one or more of the following: nickel hydroxide, nickel nitrate, nickel oxide, nickel chloride, and nickel sulfate. The manganese-containing compound is one or more of the following: manganese oxide, manganese oxalate, manganese chloride, manganese carbonate, and manganese sulfate.

[0044] Further, in step S1, the anion source is one or more of a sulfur-containing compound, a phosphorus-containing compound, and a fluorine-containing compound; the sulfur-containing compound is one or more of sulfuric acid, sodium / potassium / lithium / ammonia sulfate, ferrous / manganese / nickel / cobalt sulfate; the phosphorus-containing compound is one or more of phosphoric acid and its alkali metal salt derivatives, phosphoric acid and its transition metal precipitates, pyrophosphate and its salt derivatives, metaphosphoric acid and its salt derivatives, polyphosphoric acid and its salt derivatives; and the fluorine-containing compound is one or more of hydrogen fluoride, ammonium fluoride, lithium fluoride, hydrogen fluoride, and lithium fluoride.

[0045] Furthermore, the carbon source is an organic carbon source and / or an inorganic carbon source. The organic carbon source is one or more of sucrose, citric acid, starch, cyclodextrin, glucose, maltose, lactose, polyvinyl alcohol, and polyacryl alcohol. The inorganic carbon source is one or more of graphene, graphite, hard carbon, carbon nanotubes, and carbon black.

[0046] Another aspect of the present invention relates to protecting a polyanion-type secondary battery cathode material, which is prepared by the above-described preparation method. Specifically, the polyanion-type secondary battery cathode material is a sodium-ion battery material or a lithium-ion battery cathode material. The sodium-ion battery cathode material is sodium iron phosphate, sodium iron pyrophosphate, sodium iron phosphate pyrophosphate, sodium vanadium phosphate, sodium vanadium fluorophosphate, sodium iron fluorophosphate, sodium iron sulfate, or sodium iron fluorosulfate. The lithium-ion battery cathode material is lithium iron phosphate, lithium iron manganese phosphate, lithium fluorinated iron phosphate, lithium fluorinated iron manganese phosphate, or lithium iron sulfate.

[0047] Example 1: High conductivity Na₄Fe 2.91 Synthesis and Electrochemical Properties of (PO4)2P2O7 / C Materials

[0048] Step 1: Add sodium dihydrogen phosphate and ferric nitrate to an aqueous solution in a stoichiometric ratio of 4:2.91 as shown in the molecular formula. Add citric acid (20% by weight of total solids in the solution) as a carbon source for the reduction of ferric iron during sintering and for coating the surface layer of the material. Stir to dissolve and form a homogeneous solution.

[0049] Step 2: Spray dry the above solution, with the inlet air temperature controlled at 260℃ and the outlet air temperature controlled at 80℃ to achieve solid-liquid separation and obtain dry, light yellow spherical precursor powder.

[0050] Step 3: Heat and melt the precursor powder and polystyrene (addition amount is 5% of the weight of the precursor powder) at 300° to promote the melting, stretching, and fiberization of the polymer fiber compound, and realize its cross-linking network on the surface of the material powder.

[0051] Step 4: The pre-crosslinked polymer precursor powder is calcined at a high temperature of 500℃ for 4 hours, followed by natural cooling and crystallization to form a high-conductivity Na4Fe with a three-dimensional conductive network. 2.91 (PO4)2P2O7 / C material.

[0052] High conductivity Na4Fe 2.91(PO4)2P2O7 / C material, SurP, and PVDF5130 were mixed and homogenized at a mass ratio of 9.68:0.2:0.12, with the solid content controlled at 60%. After homogenization, a 150µm four-sided coating tool was used to coat the black paste onto aluminum foil. The film was dried in a vacuum drying oven at 100℃ for 2 hours. The peel strength of the film was tested, and the results showed that its peel strength was about 40 N / m, which was comparable to that of Comparative Example 1. This indicates that the network structure formed by the polymer fiber compound has a curing effect on the material particles, which can reduce the amount of binder used in the electrode preparation process to a certain extent. The electrode film was punched into a disc with a radius of 0.6 mm using a punching machine. Sodium metal was used as the counter electrode, 1mol / L NaClO4EC+DEC (1:1 vol%)+5% FEC was used as the electrolyte, and a PP / PE / PP three-layer separator was used. The CR2016 button cell was assembled in a glove box.

[0053] Figure 1 Na4Fe has high electrical conductivity 2.91 SEM images of the (PO4)2P2O7 / C material show that the particles are bonded together by carbon fibers, which are formed by the carbonization of a polymer fiber compound. These carbon fibers act as bridges between the particles, facilitating rapid electron transfer. Table 1 shows that the electronic conductivity of this material is 10⁻⁶. -8 The S / m ratio is approximately seven orders of magnitude higher than that of Comparative Example 1, indicating that the carbon fiber network significantly improves the electronic conductivity of the material. Table 1 shows the electrochemical performance test results for Na4Fe, which exhibits high conductivity. 2.91 The (PO4)2P2O7 / C electrode exhibits a reversible discharge capacity of 120 mAh / g at a 0.1C rate (1C = 120 mAh / g), slightly higher than the 116 mAh / g in Comparative Example 1. This difference stems from battery polarization. The carbon fiber network-modified material boasts high electronic conductivity and low internal resistance, resulting in less polarization during charge and discharge and thus higher capacity utilization. This electrode maintains 97.6% of its capacity at 10C relative to 0.1C, demonstrating excellent rate performance. This is related to the construction of the carbon fiber conductive network, which effectively improves the electrode's electronic conductivity, reduces electrode polarization, and enhances capacity utilization. Ultimately, after 1000 cycles, the electrode retains a capacity of 99.5%, showcasing excellent cycle stability. Compared to Comparative Example 1 (90.2%), the higher capacity retention of this electrode is related to the stability of its electrode structure. The carbon fiber network construction suppresses particle shedding due to volume expansion during sodium insertion / extraction, thereby improving its long-cycle stability.

[0054] Example 2 Synthesis and electrochemical properties of high-conductivity Na3V2(PO4)3 / C materials

[0055] Step 1: Add sodium dihydrogen phosphate and ammonium metavanadate to an aqueous solution in a stoichiometric ratio of 3:2 according to the molecular formula. Add glucose with a total solid content of 15% (by weight) as a carbon source for the reduction of ferric iron during sintering and the coating of the material surface layer. Stir and dissolve to form a uniform solution.

[0056] Step 2: Spray dry the above solution, with the inlet air temperature controlled at 280℃ and the outlet air temperature controlled at 90℃ to achieve solid-liquid separation and obtain a dry, dark brown precursor powder.

[0057] Step 3: Heat and melt the precursor powder and phenolic resin (addition amount is 9% of the weight of the precursor powder) at 270° to promote the melting, stretching, and fiberization of the polymer fiber compound, and realize its cross-linking network on the surface of the material powder.

[0058] Step 4: The precursor powder with pre-crosslinked polymer is calcined at high temperature to 750℃ and held for 10 hours. It is then allowed to cool and crystallize naturally to form a high-conductivity Na3V2(PO4)3 / C material with a three-dimensional conductive network.

[0059] High-conductivity Na3V2(PO4)3 / C material, SurP, and PVDF5130 were mixed and homogenized in a mass ratio of 9.69:0.2:0.11, with the solid content controlled at 55%. After homogenization, a 150µm four-sided coating tool was used to coat the black paste onto aluminum foil. The film was dried in a vacuum drying oven at 100℃ for 2 hours. The peel strength of the film was tested, and the results showed that its peel strength was about 55 N / m. Under the same peel strength as Comparative Example 2, the amount of binder required for electrode preparation was lower, indicating that the network structure formed by the carbonization of polymer fiber compounds is mutually cross-linked and has a fixing effect on material particles, which reduces the amount of binder used in the electrode preparation process to a certain extent, and is conducive to reducing the electrode processing cost. The electrode membrane was punched into a disc with a radius of 0.6 mm using a punching machine. Sodium metal was used as the counter electrode, and 1 mol / L NaClO4EC+DEC (1:1 vol%)+5% FEC was used as the electrolyte. The separator was a PP / PE / PP three-layer separator. The CR2016 button cell was assembled in a glove box.

[0060] Table 1 shows that the electronic conductivity of this material is 10. -9The S / m ratio is approximately four orders of magnitude higher than that of Comparative Example 2, indicating that the interconnections of the carbon fiber network at the material interface provide a large electronic conductive network, which is beneficial for significantly improving the electronic conductivity between materials. Table 1 shows the electrochemical performance test results: the reversible discharge capacity of the high-conductivity Na3V2(PO4)3 / C electrode at a rate of 0.1C (1C=125mAh / g) is 115mAh / g, slightly higher than the 112mAh / g in Comparative Example 2. This difference stems from the difference in electronic conductivity affecting the electron transport rate in the electrode, resulting in increased electrode polarization. Within a limited voltage range, some capacity is lost, indirectly proving that the modification of the carbon fiber network is beneficial to the material's capacity. The electrode retains 98.2% of its capacity at 10C relative to 0.1C, demonstrating excellent rate performance. This is related to the improvement in electronic conductivity of the material due to the construction of the carbon fiber conductive network, indicating that the reduction in internal resistance of the material has a significant effect on improving the electrode's rate performance. Finally, after 1000 cycles, the electrode retains a capacity of up to 98.7%, exhibiting excellent cycle stability. Compared with Comparative Example 2 (92.4%), the higher capacity retention of this electrode is related to the stability of its electrode structure. The construction of the carbon fiber network suppresses problems such as material pulverization and shedding caused by material volume expansion, thereby improving its long-cycle stability.

[0061] Comparative Example 1: Na₄Fe 2.91 Synthesis and Electrochemical Properties of (PO4)2P2O7 / C Materials

[0062] Step 1: Add sodium dihydrogen phosphate and ferric nitrate to an aqueous solution in a stoichiometric ratio of 4:2.91 as shown in the molecular formula. Add citric acid (20% by weight of total solids in the solution) as a carbon source for the reduction of ferric iron during sintering and for coating the surface layer of the material. Stir to dissolve and form a homogeneous solution.

[0063] Step 2: Spray dry the above solution, with the inlet air temperature controlled at 260℃ and the outlet air temperature controlled at 80℃ to achieve solid-liquid separation and obtain dry, light yellow spherical precursor powder.

[0064] Step 3: The precursor powder is calcined at a high temperature of 500℃ for 4 hours, followed by natural cooling and crystallization to obtain Na4Fe. 2.91 (PO4)2P2O7 / C material.

[0065] Na4Fe 2.91(PO4)2P2O7 / C material, SurP, and PVDF5130 were mixed and homogenized at a mass ratio of 9.45:0.2:0.35, with the solid content controlled at 60%. After homogenization, a black paste was coated onto aluminum foil using a 150µm four-sided coating tool. The film was dried in a vacuum drying oven at 100°C for 2 hours. The peel strength of the film was tested, and the results showed that its peel strength was approximately 40 N / m. Under the same peel strength, the adhesive used in this electrode was about 191.6% higher than that in Example 1, and the preparation cost of the electrode will be significantly increased compared to Example 1. The electrode film was punched into a disc with a radius of 0.6 mm using a punching machine. Sodium metal was used as the counter electrode, and 1 mol / L NaClO4EC+DEC (1:1 vol%)+5% FEC was used as the electrolyte. The separator was a PP / PE / PP three-layer separator. The CR2016 button cell was assembled in a glove box.

[0066] Figure 2 Na4Fe 2.91 SEM images of the (PO4)2P2O7 / C material show that the particles are uniformly dispersed, exhibiting irregular shapes, and point-like contacts between the particles. Table 1 shows that the electronic conductivity of this material is 10. -15 The S / m ratio is lower than that of Example 1, indicating poor electronic conductivity due to the point-like connections between particles alone. Table 1 shows the electrochemical performance test results for Na4Fe. 2.91 The (PO4)2P2O7 / C electrode exhibits a reversible discharge capacity of 116 mAh / g at a rate of 0.1C (1C = 120 mAh / g), slightly lower than that of Example 1. This indicates that the material's low electronic conductivity increases the battery's internal resistance polarization to some extent, preventing the material from effectively utilizing its capacity within a limited voltage range, resulting in low capacity utilization. The electrode's capacity retention at 10C relative to 0.1C is only 80.4%, indicating poor rate performance. This is related to the material's low electronic conductivity and high internal resistance polarization, which hinders capacity release at high current densities. Ultimately, after 1000 cycles, the electrode's capacity retention is only 90.2%, demonstrating poor cycle stability. This is related to the stability of the electrode structure, indicating that during cycling, the electrode structure experiences volume expansion due to sodium insertion / extraction, leading to pulverization and shedding, resulting in partial capacity deactivation and decreased cycle stability.

[0067] Comparative Example 2: Synthesis and Electrochemical Performance of Na3V2(PO4)3 / C Material

[0068] Step 1: Add sodium dihydrogen phosphate and ammonium metavanadate to an aqueous solution in a stoichiometric ratio of 3:2 according to the molecular formula. Add glucose with a total solid content of 15% (by weight) as a carbon source for the reduction of ferric iron during sintering and the coating of the material surface layer. Stir and dissolve to form a uniform solution.

[0069] Step 2: Spray dry the above solution, with the inlet air temperature controlled at 280℃ and the outlet air temperature controlled at 90℃ to achieve solid-liquid separation and obtain a dry, dark brown precursor powder.

[0070] Step 3: The dark brown precursor powder is calcined at high temperature to 750℃ and held for 10 hours. It is then allowed to cool naturally to crystallize, thus obtaining the Na3V2(PO4)3 / C material.

[0071] Na3V2(PO4)3 / C material, SurP, and PVDF5130 were mixed and homogenized in a mass ratio of 9.48:0.2:0.32, with the solid content controlled at 55%. After homogenization, a 150µm four-sided coating tool was used to coat the black paste onto aluminum foil. The film was dried in a vacuum drying oven at 100°C for 2 hours. The peel strength of the film was tested, and the results showed that its peel strength was approximately 55 N / m. Compared with Example 2, this electrode used more adhesive at the same peel strength, resulting in higher electrode preparation costs. The electrode film was punched into a disc with a radius of 0.6 mm using a punching machine. Metallic sodium was used as the counter electrode, and 1 mol / L NaClO4EC+DEC (1:1 vol%)+5% FEC was used as the electrolyte. The separator was a PP / PE / PP three-layer separator. The CR2016 button cell was assembled in a glove box.

[0072] Table 1 shows that the electronic conductivity of this material is 10. -13The S / m ratio is lower than that of Example 2, indicating poor inter-material contact and poor continuity of the electronic conductive network, which is not conducive to the rapid transport of electrons between particles. Table 1 shows the electrochemical performance test results: the reversible discharge capacity of the Na3V2(PO4)3 / C electrode at a rate of 0.1C (1C=125mAh / g) is 112mAh / g, lower than that of Example 2. This problem stems from the low electronic conductivity of the Na3V2(PO4)3 / C material, resulting in a large polarization potential after electrode fabrication. Within a limited voltage range, the capacity will be partially lost due to polarization. The electrode's capacity retention at 10C relative to 0.1C is 82.7%, indicating poor rate performance. This is due to the low electronic conductivity of the material, which exacerbates polarization under high current density conditions, leading to more significant capacity deactivation. Ultimately, after 1000 cycles, the capacity retention rate of this electrode is only 92.4%, indicating poor cycle stability. Compared to Example 2 (98.7%), during the charging and discharging process of this electrode, the material particles repeatedly expand and contract as sodium ions are intercalated and deintercalated, and some poorly contacted areas will detach, resulting in abnormal capacity performance and accelerated attenuation.

[0073] Table 1 Performance Test Results

[0074]

[0075] Example 3

[0076] This embodiment relates to a high-conductivity polyanion-type secondary battery cathode material, the preparation method of which includes the following steps:

[0077] S1. Emulsion grinding and mixing: Add water to alkali metal source, transition metal source, anion source and carbon source and grind to form a uniform emulsion;

[0078] S2. Precursor powder separation: The above emulsion is dried to achieve solid-liquid separation and obtain dry precursor powder.

[0079] S3. Precursor pre-crosslinking treatment: Precursor powder and organic polymer fiber compound are mixed in a solid phase under heating conditions to form a pre-crosslinked precursor;

[0080] S4. High-temperature calcination: The pre-crosslinked precursor is calcined at high temperature and then naturally cooled to crystallize, ultimately forming a high-conductivity polyanion-type secondary battery cathode material with a three-dimensional conductive network connection.

[0081] In step S3 of this embodiment, the heating temperature for pre-crosslinking is 350°C; the organic polymer fiber compound is a plastic compound, and one or more of the plastic compounds are polyethylene, polypropylene, polycarbonate, and polystyrene; the solid-phase mixing method is ball milling.

[0082] In step S4 of this embodiment, the conditions for high-temperature calcination are: sintering temperature greater than 400°C and holding time greater than 3 hours, to ensure sufficient crystal growth of the material.

[0083] In step S2 of this embodiment, the drying method is low-temperature drying and vacuum drying.

[0084] In this embodiment, the alkali metal source is a sodium-containing compound, which includes sodium hydroxide, sodium peroxide, sodium carbonate, sodium hydroxide, sodium formate, sodium acetate, sodium oxalate, trisodium citrate, sodium sulfate, sodium chloride, and sodium nitrate.

[0085] In this embodiment, the transition metal source is an iron-containing compound, which may include ferric hydroxide, iron oxide, ferrous oxalate, ferrous sulfate, ferric nitrate, ferric phosphate, ferric chloride, or ferric citrate.

[0086] In this embodiment, the anion source is a sulfur-containing compound or a phosphorus-containing compound. The sulfur-containing compound is sulfuric acid, sodium sulfate, or ferrous sulfate, and the phosphorus-containing compound is phosphoric acid and its alkali metal salt derivatives.

[0087] In this embodiment, the carbon source is organic carbon, and the organic carbon source is sucrose, citric acid, starch, cyclodextrin, glucose, maltose, or lactose.

[0088] Example 4

[0089] This embodiment relates to a high-conductivity polyanion-type secondary battery cathode material, the preparation method of which includes the following steps:

[0090] S1. Emulsion grinding and mixing: Add water to alkali metal source, transition metal source, anion source and carbon source and grind to form a uniform emulsion;

[0091] S2. Precursor powder separation: The above emulsion is dried to achieve solid-liquid separation and obtain dry precursor powder.

[0092] S3. Precursor pre-crosslinking treatment: Precursor powder and organic polymer fiber compound are mixed in a solid phase under heating conditions to form a pre-crosslinked precursor;

[0093] S4. High-temperature calcination: The pre-crosslinked precursor is calcined at high temperature and then naturally cooled to crystallize, ultimately forming a high-conductivity polyanion-type secondary battery cathode material with a three-dimensional conductive network connection.

[0094] In step S3 of this embodiment, the heating temperature for pre-crosslinking is 250°C; the organic polymer fiber compound is a plastic compound or a rubber compound, wherein one or more of the plastic compounds are polyethylene, and the rubber compounds are natural rubber, butyl rubber, styrene-butadiene rubber, or silicone rubber; the solid-phase mixing method is grinding.

[0095] In step S4 of this embodiment, the conditions for high-temperature calcination are: sintering temperature greater than 400°C and holding time greater than 3 hours, to ensure sufficient crystal growth of the material.

[0096] In step S2 of this embodiment, the drying method is natural air drying or spray drying.

[0097] In this embodiment, the alkali metal source is a potassium-containing compound or a lithium-containing compound. The potassium-containing compound is potassium hydroxide, potassium carbonate, potassium chloride, or potassium sulfate, and the lithium-containing compound is lithium carbonate or lithium bicarbonate.

[0098] In this embodiment, the transition metal source is an iron-containing compound or a manganese-containing compound. The iron-containing compound is ferric hydroxide, iron oxide, or ferrous oxalate, and the manganese-containing compound is manganese oxide or manganese oxalate.

[0099] In this embodiment, the anion source is a phosphorus-containing compound or a fluorine-containing compound. The phosphorus-containing compound is pyrophosphate and its salt derivatives, and the fluorine-containing compound is hydrogen fluoride, ammonium fluoride, lithium fluoride, or lithium fluoride.

[0100] In this embodiment, the carbon source is an inorganic carbon source, such as graphene, graphite, hard carbon, carbon nanotubes, or carbon black.

[0101] Example 5

[0102] This embodiment relates to a high-conductivity polyanion-type secondary battery cathode material, the preparation method of which includes the following steps:

[0103] S1. Emulsion grinding and mixing: Add water to alkali metal source, transition metal source, anion source and carbon source and grind to form a uniform emulsion;

[0104] S2. Precursor powder separation: The above emulsion is dried to achieve solid-liquid separation and obtain dry precursor powder.

[0105] S3. Precursor pre-crosslinking treatment: Precursor powder and organic polymer fiber compound are mixed in a solid phase under heating conditions to form a pre-crosslinked precursor;

[0106] S4. High-temperature calcination: The pre-crosslinked precursor is calcined at high temperature and then naturally cooled to crystallize, ultimately forming a high-conductivity polyanion-type secondary battery cathode material with a three-dimensional conductive network connection.

[0107] In step S3 of this embodiment, the heating temperature for pre-crosslinking is 100°C; the organic polymer fiber compound is a plastic compound, a rubber compound, or an adhesive, wherein one or more of the plastic compounds are polyethylene or polypropylene, the rubber compounds are styrene-butadiene rubber or silicone rubber, and the adhesive compounds are epoxy resin, acrylate, or phenolic resin; the solid phase mixing method is sand milling.

[0108] In step S4 of this embodiment, the conditions for high-temperature calcination are: sintering temperature greater than 400°C and holding time greater than 3 hours, to ensure sufficient crystal growth of the material.

[0109] In step S2 of this embodiment, the drying method is spray drying and high-temperature evaporation crystallization.

[0110] In this embodiment, the alkali metal source is a sodium-containing compound, a potassium-containing compound, or a lithium-containing compound. The sodium-containing compound is sodium hydroxide, the potassium-containing compound is potassium hydroxide, potassium carbonate, potassium chloride, potassium sulfate, potassium nitrate, or potassium peroxide, and the lithium-containing compound is lithium carbonate, lithium bicarbonate, or lithium hydroxide.

[0111] In this embodiment, the transition metal source is an iron-containing compound, a cobalt-containing compound, a nickel-containing compound, or a manganese-containing compound. The iron-containing compound is iron hydroxide or iron oxide. The cobalt-containing compound is cobalt oxalate, cobalt carbonate, cobalt oxide, cobalt hydroxide, or cobalt chloride. The nickel-containing compound is nickel hydroxide, nickel nitrate, nickel oxide, or nickel chloride. The manganese-containing compound is manganese oxide or manganese oxalate.

[0112] In this embodiment, the anion source is a sulfur-containing compound or a phosphorus-containing compound. The sulfur-containing compound is sulfuric acid, sodium / potassium / lithium / ammonia sulfate, ferrous / manganese / nickel / cobalt sulfate, and the phosphorus-containing compound is phosphoric acid and its alkali metal salt derivatives, phosphoric acid and its transition metal precipitates, pyrophosphate and its salt derivatives, metaphosphoric acid and its salt derivatives, polyphosphoric acid and its salt derivatives.

[0113] In this embodiment, the carbon source is an organic carbon source and an inorganic carbon source. The organic carbon source is sucrose, citric acid, starch, cyclodextrin, glucose, maltose, and lactose, while the inorganic carbon source is carbon nanotubes and carbon black.

[0114] The above embodiments are merely specific examples of the present invention, and their descriptions are quite specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these obvious substitutions all fall within the protection scope of the present invention.

Claims

1. A method for preparing a high-conductivity polyanionic secondary battery cathode material, characterized in that... Includes the following steps: S1. Emulsion grinding and mixing: Add water to alkali metal source, transition metal source, anion source and carbon source and grind to form a uniform emulsion; S2. Precursor powder separation: The above emulsion is dried to achieve solid-liquid separation and obtain dry precursor powder. S3. Precursor pre-crosslinking treatment: Precursor powder and organic polymer fiber compound are mixed in a solid phase under heating conditions to form a pre-crosslinked precursor; the heating temperature for pre-crosslinking is 100-350℃; the organic polymer fiber compound is one or more of plastic compounds, rubber compounds, and adhesives; the plastic compound is one or more of polyethylene, polypropylene, polycarbonate, and polystyrene; the rubber compound is one or more of natural rubber, butyl rubber, styrene-butadiene rubber, and silicone rubber; the adhesive compound is one or more of epoxy resin, acrylate, and phenolic resin. S4. High-temperature calcination: The pre-crosslinked precursor is calcined at high temperature and then naturally cooled to crystallize, ultimately forming a high-conductivity polyanion-type secondary battery cathode material with a three-dimensional conductive network connection.

2. The method for preparing the high-conductivity polyanionic secondary battery cathode material according to claim 1, characterized in that: In step S3, the solid phase mixing method is one or more of ball milling, grinding, and sand milling.

3. The method for preparing the high-conductivity polyanionic secondary battery cathode material according to claim 1, characterized in that: In step S4, the conditions for high-temperature calcination are: sintering temperature greater than 400℃ and holding time greater than 3 hours.

4. The method for preparing the high-conductivity polyanionic secondary battery cathode material according to claim 1, characterized in that: In step S2, the drying method is one or more of the following: low temperature drying, vacuum drying, natural air drying, spray drying, flash drying, and high temperature evaporation crystallization.

5. The method for preparing the high-conductivity polyanionic secondary battery cathode material according to claim 1, characterized in that: In step S1, the alkali metal source is one or more of sodium-containing compounds, potassium-containing compounds, and lithium-containing compounds. The sodium-containing compound is one or more of sodium hydroxide, sodium peroxide, sodium carbonate, sodium hydroxide, sodium formate, sodium acetate, sodium oxalate, trisodium citrate, sodium sulfate, sodium chloride, and sodium nitrate. The potassium-containing compound is one or more of potassium hydroxide, potassium carbonate, potassium chloride, potassium sulfate, potassium nitrate, potassium peroxide, potassium superoxide, and potassium bicarbonate. The lithium-containing compound is one or more of lithium carbonate, lithium bicarbonate, lithium hydroxide, lithium dihydrogen phosphate, lithium chloride, and lithium fluoride.

6. The method for preparing the high-conductivity polyanionic secondary battery cathode material according to claim 1, characterized in that: In step S1, the transition metal source is one or more of the following: iron-containing compound, cobalt-containing compound, nickel-containing compound, and manganese-containing compound. The iron-containing compound is one or more of the following: ferric hydroxide, iron oxide, ferrous oxalate, ferrous sulfate, ferric nitrate, ferric phosphate, ferric chloride, and ferric citrate. The cobalt-containing compound is one or more of the following: cobalt oxalate, cobalt carbonate, cobalt oxide, cobalt hydroxide, cobalt chloride, cobalt nitrate, and cobalt sulfate. The nickel-containing compound is one or more of the following: nickel hydroxide, nickel nitrate, nickel oxide, nickel chloride, and nickel sulfate. The manganese-containing compound is one or more of the following: manganese oxide, manganese oxalate, manganese chloride, manganese carbonate, and manganese sulfate.

7. The method for preparing the high-conductivity polyanionic secondary battery cathode material according to claim 1, characterized in that: In step S1, the anion source is one or more of sulfur-containing compounds, phosphorus-containing compounds, and fluorine-containing compounds; the sulfur-containing compound is one or more of sulfuric acid, sodium / potassium / lithium / ammonia sulfate, and ferrous / manganese / nickel / cobalt sulfate; the phosphorus-containing compound is one or more of phosphoric acid and its alkali metal salt derivatives, phosphoric acid and its transition metal precipitates, pyrophosphate and its salt derivatives, metaphosphoric acid and its salt derivatives, and polyphosphoric acid and its salt derivatives; and the fluorine-containing compound is one or more of hydrogen fluoride, ammonium fluoride, lithium fluoride, and hydrogen fluoride. The carbon source is an organic carbon source and / or an inorganic carbon source. The organic carbon source is one or more of sucrose, citric acid, starch, cyclodextrin, glucose, maltose, lactose, polyvinyl alcohol, and polyacryl alcohol. The inorganic carbon source is one or more of graphene, graphite, hard carbon, carbon nanotubes, and carbon black.

8. A polyanion-type secondary battery cathode material, characterized in that: The positive electrode material of the polyanion-type secondary battery, prepared by any one of claims 1-7, is a sodium-ion battery material or a lithium-ion battery material. The sodium-ion battery positive electrode material is sodium iron phosphate, sodium iron pyrophosphate, sodium iron pyrophosphate, sodium vanadium phosphate, sodium vanadium fluorophosphate, sodium iron fluorophosphate, sodium iron sulfate, or sodium iron fluorosulfate. The lithium-ion battery positive electrode material is lithium iron phosphate, lithium iron manganese phosphate, lithium fluorinated iron phosphate, lithium fluorinated iron manganese phosphate, or lithium iron sulfate.

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