Composite cathode material, method for manufacturing the same, and use

Abstract

A composite cathode material, a method for manufacturing the same, and its use are provided. The composite cathode material comprises an internal core and a carbon coating layer covering at least a portion of the surface of the internal core and / or embedded in the internal core, wherein the internal core is made of NaFePO4 and Na 4+x Fe 3-y (PO4) 2+z The composite cathode material includes the compound shown in formula 1 of P2O7, where formula 1 assumes -0.15 ≤ x ≤ 0.8, 0 ≤ y ≤ 0.5, and -0.2 ≤ z ≤ 0.2, and the particle size of NaFePO4 is ≤ 100 nm. When this composite cathode material is applied to a battery, the battery's capacity and magnification performance are improved.

Description

[Technical Field]

[0001] The embodiments of this application relate to composite cathode materials, their manufacturing methods, and their use, and belong to the field of secondary battery technology. [Background technology]

[0002] Because sodium resources are abundant and inexpensive compared to lithium resources, research into sodium-ion batteries is increasingly being conducted within the industry. Sodium iron pyrophosphate has the advantages of low cost and excellent structural stability, and is currently considered the most promising material for industrialization as a cathode material for sodium-ion batteries. However, sodium iron pyrophosphate has low electronic conductivity, and conventional technology has mainly involved carbon coating of sodium iron pyrophosphate to increase its electronic conductivity. Even now, composite cathode materials made by carbon coating sodium iron pyrophosphate still suffer from problems such as low capacity and poor magnification performance. [Overview of the Initiative] [Problems that the invention aims to solve]

[0003] This invention provides a composite cathode material, which, when applied to a battery, improves the battery's capacity and magnification performance.

[0004] This invention provides a method for manufacturing a composite cathode material, and the above-mentioned composite cathode material can be manufactured by this manufacturing method, the manufacturing process is simple, and it is suitable for widespread use.

[0005] This invention provides a battery that, because it comprises the above-mentioned composite positive electrode material, exhibits excellent magnification performance, cycle performance, and discharge ratio capacity. [Means for solving the problem]

[0006] This application provides a composite cathode material comprising an internal core and a carbon coating layer that covers at least a portion of the surface of the internal core and / or is embedded in the internal core. The aforementioned internal core comprises NaFePO4 and the compound shown in Formula 1. Na 4+x Fe 3-y (PO4) 2+z P2O7 formula 1 In Equation 1, we set -0.15≦x≦0.8, 0≦y≦0.5, and -0.2≦z≦0.2. The particle size of NaFePO4 is assumed to be ≤100 nm.

[0007] According to the above composite cathode material, the atomic ratio of Fe to P in the composite cathode material gradually decreases from (0.9~1.1):1 from the outside to the inside, and thereafter stabilizes at (0.65-0.85):1, and / or In the composite cathode material, the atomic ratio of Fe to Na gradually decreases from (0.9-1.1):1 from the outside to the inside, and then stabilizes at (0.65-0.85):1.

[0008] According to the above composite cathode material, the mass percentage content of the carbon coating layer is 0.5-5% based on the total mass of the composite cathode material.

[0009] According to the above composite cathode material, the composite cathode material contains PO4 3- and P2O7 4- The molar ratio is (1.5-3):1.

[0010] According to the composite cathode material described above, the particle size of the internal core is 100-900 nm.

[0011] According to the above-mentioned composite cathode material, the specific surface area of ​​the composite cathode material is 5-20 m². 2 g -1 That is the case.

[0012] According to the above composite cathode material, the tap density of the composite cathode material is 1.9-2.4 g / cm³. -3 That is the case.

[0013] This application provides the above-mentioned method for manufacturing a composite cathode material, and this manufacturing method includes: A step of sequentially performing a polishing treatment and a spray drying treatment on a raw material system containing a sodium source, an iron source, a phosphorus source, and a carbon source to obtain a powder; A step of sequentially performing a first firing treatment, a second firing treatment, a third firing treatment, and a fourth firing treatment on the powder to obtain the composite cathode material. In the raw material system, the molar ratio a of sodium element, the molar ratio b of iron element, and the molar ratio c of phosphorus element satisfy 3.85 ≤ a ≤ 4.8, 2.5 ≤ b ≤ 3, and 3.8 ≤ c ≤ 4.2. In the first firing treatment, the temperature is 255 - 260 °C and the time is 1 - 2 h. In the second firing treatment, the temperature is 300 - 320 °C and the time is 3 - 5 h. In the third firing treatment, the temperature is 370 - 390 °C and the time is 1 - 2 h. In the fourth firing treatment, the temperature is 470 - 500 °C and the time is 8 - 10 h.

[0014] According to the above manufacturing method, both the sodium source and the iron source are sodium iron ethylenediaminetetraacetate.

[0015] According to the above manufacturing method, the polishing treatment includes a first polishing treatment and a second polishing treatment. The particle size of the abrasive in the second polishing treatment is smaller than the particle size of the abrasive in the first polishing treatment.

[0016] According to the above manufacturing method, in the first polishing treatment, the rotation speed is 900 - 1200 rpm and the time is 2 - 3 h, and / or In the second polishing treatment, the rotation speed is 400 - 2000 rpm and the time is 1 - 2 h.

[0017] According to the above manufacturing method, the carbon source includes an organic carbon source.

[0018] According to the above manufacturing method, the carbon source further comprises an inorganic carbon source, The ratio of the mass of the organic carbon source to the mass of the inorganic carbon source is (12.5-30):1.

[0019] According to the above manufacturing method, the raw material system further contains a coupling agent, Based on the total mass of the aforementioned raw material system, the mass percentage content of the coupling agent is 1-3%. Preferably, the coupling agent is a titanate coupling agent.

[0020] This application provides a battery comprising the above-described composite cathode material. [Effects of the Invention]

[0021] The composite cathode material according to the present invention comprises an internal core formed of a compound shown in Formula 1 and NaFePO4 having a special particle size, and a carbon coating layer covering at least a portion of the surface of the internal core. The composite cathode material having the special composition according to the present invention exhibits excellent discharge capacity, cycle performance, and magnification performance.

[0022] The above-mentioned composite cathode material can be manufactured by the manufacturing method of the composite cathode material according to the present invention, and the manufacturing method is easy to operate and suitable for widespread use.

[0023] The battery according to this application, having the above-mentioned composite positive electrode material, exhibits excellent cycle performance, discharge ratio capacity, and magnification performance. [Brief explanation of the drawing]

[0024] To more clearly describe the embodiments of the present application or the solutions of the prior art, the drawings that may be used in the description of the embodiments or the prior art are briefly described below. Naturally, the drawings described below are some embodiments of the present application, and those skilled in the art will be able to conceive of other drawings based on these without requiring any creative effort. [Figure 1] This is an XRD diagram of the composite cathode material in Example 1 of the present application. [Figure 2] This is an XRD diagram of the composite cathode material in Example 2 of the present application. [Figure 3] This is an XRD diagram of the composite cathode material in Example 3 of the present application. [Figure 4] This is an XRD diagram of the composite cathode material in Comparative Example 1 of the present invention. [Figure 5] This is an SEM diagram of the composite cathode material in Example 1 of the present application. [Figure 6] This is an SEM diagram of the composite cathode material in Example 2 of the present application. [Figure 7] This is an SEM diagram of the composite cathode material in Example 3 of the present application. [Figure 8] This is an SEM diagram of the composite cathode material in Comparative Example 1 of the present invention. [Figure 9] This is the charge / discharge curve of the battery in Example 1 of the present invention. [Figure 10] This is the charge / discharge curve of the battery in Embodiment 2 of the present invention. [Figure 11] This is the charge / discharge curve of the battery in Embodiment 3 of the present application. [Figure 12] This is the charge / discharge curve of the battery in Comparative Example 1 of the present invention. [Modes for carrying out the invention]

[0025] To clarify the purpose, technical solution, and advantages of this application, the technical solution will be described clearly and completely below with reference to the embodiments of this application. Naturally, the embodiments described are only a part of the embodiments of this application, not all of them. A person skilled in the art will know that all other embodiments obtained based on the embodiments of this application without requiring any creative work are all within the scope of protection of this application.

[0026] In a first aspect, the present application provides a composite cathode material comprising an internal core and a carbon coating layer covering at least a portion of the surface of the internal core and / or embedded in the internal core. The internal core contains NaFePO4 and the compound shown in Formula 1. Na 4+x Fe 3-y (PO4) 2+z P2O7 Formula 1 In Formula 1, -0.15 ≦ x ≦ 0.8, 0 ≦ y ≦ 0.5, -0.2 ≦ z ≦ 0.2, and The particle size of NaFePO4 is set to be ≦ 100 nm.

[0027] It can be understood that the carbon coating layer according to the present application may cover the surface of the inner core, may cover a part of the surface of the inner core, or the carbon coating layer may be embedded in the inner core.

[0028] The composite cathode material according to the present application includes an inner core and a carbon coating layer from the inside to the outside.

[0029] The inner core includes NaFePO4 with a particle size ≦ 100 nm and the compound represented by Formula 1. The particle size of NaFePO4 refers to the average particle size of NaFePO4. NaFePO4 with a particle size ≦ 100 nm can be transformed into amorphous FePO4 during the charge and discharge of the battery, thereby effectively exerting the capacity of NaFePO4 and improving the capacity of the composite cathode material. The compound represented by Formula 1 may be Na4Fe3(PO4)2P2O7. This compound has excellent stability and contributes to the improvement of the cycle performance of the composite cathode material. The carbon coating layer can improve the electron mobility of the composite cathode material and significantly improve the conductivity of the composite cathode material. Therefore, the composite cathode material according to the present application has excellent capacity, cycle performance, and rate performance.

[0030] It is confirmed from the XPS measurement of the composite cathode material according to the present application that the signal of carbon atoms gradually attenuates from the outside to the inside of the composite cathode material according to the present application, indicating that the carbon coating layer according to the present application is on the outer surface of the composite cathode material.

[0031] In some embodiments of the present application, the composite cathode material has an atomic ratio of Fe to P that gradually decreases from (0.9-1.1):1 from the outside to the inside, and thereafter stabilizes at (0.65-0.85):1 and / or The fact that the atomic ratio of Fe to Na in the composite cathode material gradually decreases from (0.9-1.1):1 from the outside to the inside, and then stabilizes at (0.65-0.85):1, indicates that the NaFePO4 in the inner core is in close proximity to the outer surface of the composite cathode material.

[0032] In this invention, the atomic ratio of Fe to P or Fe to Na in a composite cathode material can be measured using conventional measurement methods in the art. For example, the measurement can be performed using XPS or SEM-EDS to obtain the atomic ratio of Fe to P or Fe to Na in the composite cathode material.

[0033] In this application, assuming that the capacity and cycle performance of the composite cathode material are ensured, the mass percentage content of the carbon coating layer in the composite cathode material can be suitably selected so that further improvement in the magnification performance of the composite cathode material can be expected. In some embodiments of this application, the mass percentage content of the carbon coating layer is 0.5-5% based on the total mass of the composite cathode material.

[0034] In some embodiments of this application, the composite cathode material is PO4 3- and P 2 O7 4- The ratio of the content is (1.5-3):1.

[0035] In this application, P2O7 3- It is derived from the compound shown in formula 1, and PO4 3- It is derived in part from the compound shown in Formula 1, and in part from NaFePO4. 3- and P2O7 4- It can be understood that when the content ratio of the compound shown in Equation 1 and NaFePO4 is (1.5-3):1, the advantages of the compound and NaFePO4 are better utilized, and the cycle performance and capacity of the composite cathode material can be further improved.

[0036] In this application, PO4 in composite cathode materials 3- and P2O7 4- The content can be detected using a spectrophotometer.

[0037] In some embodiments of the present application, the particle size of the internal core is 100-900 nm.

[0038] The primary particles of the composite cathode material according to this application exhibit a spherical or disc-shaped form. The bonding of any two particles of the composite cathode material via a carbon coating layer can be confirmed by HRTEM.

[0039] In this application, the particle size of the internal core refers to the average particle size of the internal core. In the composite cathode material according to this application, the internal core with a particle size of 100-900 nm is connected via a carbon coating layer, and electrons and ions move through the carbon coating layer, thus contributing to an improvement in the specific capacity and magnification performance of the composite cathode material. When the particle size of the internal core is 100-900 nm, the specific surface area of ​​the composite cathode material is reduced, which can avoid slurry gelation during the manufacturing of the cathode plate and improve the coating effect on the cathode plate, further increasing the potential for industrial application of the composite cathode material.

[0040] In some embodiments, the surface contact angle of the composite cathode material according to the present invention is 35-60°.

[0041] In some embodiments, the absence of an apparent porous structure on the surface of the internal core contributes to a further reduction in the specific surface area of ​​the composite cathode material. In some embodiments of the present application, the specific surface area of ​​the composite cathode material is 5-20 m². 2 g -1 In this case, the composite cathode material can further avoid slurry gelation during the manufacturing of the cathode plate and improve the coating effect on the cathode plate.

[0042] In some embodiments of the present application, the tap density of the composite cathode material is 1.9–2.4 g / cm³. -3In this case, it contributes to improving the tap density of the positive electrode plate, and as a result, the capacitance of the positive electrode plate is improved. In some embodiments, the composite positive electrode material according to the present invention has a tap density of 2.2-2.6 g cm². -3 This can be applied to the manufacture of positive electrode plates, and batteries equipped with such positive electrode plates have superior volume-specific energy.

[0043] In a second aspect, the present application provides a method for manufacturing the above-mentioned composite cathode material, the manufacturing method being: A process to obtain powder by sequentially performing polishing and spray drying treatments on a raw material system containing a sodium source, an iron source, a phosphorus source, and a carbon source, The process includes a step of sequentially performing a first calcination treatment, a second calcination treatment, a third calcination treatment, and a fourth calcination treatment on the powder to obtain a composite cathode material, In the raw material system, the molar proportions of sodium (a), iron (b), and phosphorus (c) satisfy 3.85 ≤ a ≤ 4.8, 2.5 ≤ b ≤ 3, and 3.8 ≤ c ≤ 4.2. In the first firing process, the temperature was 255-260°C and the time was 1-2 hours. In the second firing process, the temperature was 300-320°C and the time was 3-5 hours. In the third firing process, the temperature was 370-390°C and the time was 1-2 hours. In the fourth firing process, the temperature is 470-500°C and the time is 8-10 hours.

[0044] This invention involves polishing a raw material system containing specific amounts of sodium, iron, phosphorus, and carbon sources to uniformly mix them and obtain a uniform suspension, and then spray-drying the suspension to evaporate all the water in the suspension to obtain a powder. Then, the powder is subjected to a first firing treatment at 255-260°C for 1-2 hours, the temperature is raised to 300-320°C, a second firing treatment is performed for 3-5 hours, the temperature is raised to 370-390°C, a third firing treatment is performed for 1-2 hours, the temperature is raised to 470-500°C, and a fourth firing treatment is performed for 8-10 hours to form a composite cathode material having the core housing structure of this invention.

[0045] The raw material system according to this application further contains water, and it can be understood that this application does not limit the water content in the raw material system. In some embodiments, the ratio of the total mass of the sodium source, iron source, phosphorus source, and carbon source (solid phase) to the mass of water (liquid phase) is (0.2-0.4):1, and when the Dv50 of the solid phase in the raw material system is 100-1000 nm, it contributes to improving the powder yield. In certain embodiments, the water may be ultrapure water.

[0046] In the polishing process, it is understood that a portion of the solid phase dissolves in water, while the rest forms as a suspension in the water. During their investigation, the inventors found that increasing the content of the suspension in the suspension contributes to improved powder yield, reduced raw material loss during spray drying, and lower raw material costs. In some embodiments, the powder yield can be improved when the mass percentage content of the suspension in the suspension obtained by the polishing process is 35-75%.

[0047] The present invention does not particularly limit the spray drying process, as long as the suspension can be dried and turned into a powder. In some embodiments, the spray drying process can be carried out using a spray dryer, which can have a fan temperature of 180-240°C and an outlet temperature of 80-100°C.

[0048] The yield of the powder obtained by the manufacturing method of the present invention can be set to 70-97% in order to contribute to improving the yield of the composite cathode material.

[0049] In some embodiments, the powder is subjected to a grinding process and a sieving process in sequence, and the mesh of the sieve used for the sieving process may be 250-350 mesh, so as to further improve the effect of the subsequent firing process and to obtain a composite cathode material with superior performance.

[0050] This application does not particularly limit the specific methods of the first, second, third, and fourth firing treatments, provided that the temperature and time fall within the above range. In some embodiments, the first, second, third, and fourth firing treatments may be carried out in a firing atmosphere, which may be a nitrogen gas atmosphere or a nitrogen-hydrogen gas mixed atmosphere. When the firing atmosphere is a nitrogen-hydrogen gas mixed atmosphere, the volume ratio of nitrogen gas to hydrogen gas may be 95:5. In some embodiments, the flow rate of the firing atmosphere may be 0.3-0.5 L / min so that the effect of the firing treatment is further improved and a composite cathode material with superior performance is obtained.

[0051] In this application, the heating rate for the first, second, third, and fourth firing treatments can be set to 3°C / min so that each raw material reacts sufficiently, the degree of graphitization of the carbon material improves, and the overall performance of the composite cathode material improves.

[0052] The composite cathode material can be manufactured using the method for manufacturing the composite cathode material according to this application, and this manufacturing method is easy to operate and suitable for widespread use.

[0053] The present application does not particularly limit the polishing process as long as the raw material system can be uniformly mixed. In some embodiments of the present application, the polishing process includes a first polishing process and a second polishing process. The particle size of the polishing beads in the second polishing process is smaller than the particle size of the polishing beads in the first polishing process.

[0054] This invention contributes to improving the effectiveness of the polishing process by performing the first polishing treatment using polishing beads with a large particle size, and the second polishing treatment using polishing beads with a small particle size, thereby obtaining a uniformly mixed suspension, and consequently contributing to an improvement in the overall performance of the composite cathode material.

[0055] The polishing process according to the present invention can be performed in a polishing machine, and furthermore, the present invention can further limit the specific steps of the first polishing process and the second polishing process so that further improvement in the overall performance of the composite cathode material can be expected. In some embodiments of the present invention, in the first polishing process, the rotational speed is 900-1200 rpm, the time is 2-3 hours, and / or In the second polishing process, the rotational speed is 400-2000 rpm, and the duration is 1-2 hours.

[0056] The present application does not particularly limit the sodium source, as long as sodium element is available. In some embodiments, the sodium source may be at least one of sodium dihydrogen phosphate, sodium bicarbonate, sodium carbonate, sodium pyrophosphate decahydrate, and sodium ethylenediaminetetraacetate. Furthermore, the present application does not particularly limit the iron source, as long as iron element is available. In some embodiments, the iron source may be at least one of iron(II) oxalate dihydrate, iron pyrophosphate, iron phosphate, and sodium ethylenediaminetetraacetate. Moreover, the present application does not particularly limit the phosphorus source, as long as phosphorus element is available. In some embodiments, the phosphorus source may be at least one of sodium dihydrogen phosphate, iron phosphate, iron pyrophosphate, and sodium pyrophosphate decahydrate. It is understood that when sodium ethylenediaminetetraacetate is included in the raw material system, nitrogen, iron, and sodium elements can all be introduced, which not only contributes to simplifying the manufacturing process but also enables the complexation of iron atoms and their confinement to the metal active center (suppression of elution of altered metals).

[0057] The carbon source in this application may be an organic carbon source and / or an inorganic carbon source. In some embodiments of this application, when the carbon source includes an organic carbon source, during the calcination process, the molecules of the organic material are carbonized, forming a three-dimensional network for electron transfer, achieving continuous electron transfer, and significantly improving the conductivity of the composite cathode material.

[0058] The organic carbon source relating to this application may be a conventional organic carbon source in the art. For example, the organic carbon source may be at least one of polyethylene glycol, citric acid, glucose, sucrose, melamine, and polyacrylamide.

[0059] In this invention, when the organic carbon source includes citric acid and at least one of polyethylene glycol, glucose, and sucrose, the carboxyl and hydroxyl of citric acid not only undergo an esterification reaction to form a crosslinked structure, but the citric acid can also strongly bond with the hydroxyl of at least one of polyethylene glycol, glucose, and sucrose to form a precursor polymer. During the subsequent calcination process, the precursor polymer forms a carbon skeleton, uniformly supporting an internal core on the carbon skeleton, thereby forming a composite cathode material with excellent performance.

[0060] In the present invention, when the organic carbon source is selected from at least one of melamine and polyacrylamide, nitrogen atoms can be further introduced into the system to improve the specific capacity and magnification performance of the composite cathode material.

[0061] In some embodiments of the present application, the carbon source may further include an inorganic carbon source. The ratio of the mass of the organic carbon source to the mass of the inorganic carbon source may be (12.5-30):1.

[0062] In this invention, when the carbon source further includes an inorganic carbon source, the inorganic carbon source penetrates the internal core, and the organic carbon source forms a carbon coating layer, and rapid electron or ion transfer is achieved through the combined action of the inorganic and organic carbon sources.

[0063] The present invention states that the inorganic carbon source is not particularly limited and may be a conventional inorganic carbon source in the art, and exemplarily, the inorganic carbon source may be cochin black and / or carbon nanotubes.

[0064] In some embodiments, when the carbon source includes both organic and inorganic carbon sources, a coupling agent can be further added, with the mass percentage content of the coupling agent being 1-3% based on the total mass of the raw material system. In some embodiments, the coupling agent may be a titanate coupling agent.

[0065] When the raw material system further contains a coupling agent, the coupling agent can promote the reaction between the organic carbon source and the inorganic carbon source, thereby better achieving rapid electron or ion transfer and improving the electrochemical performance of the battery.

[0066] In this application, the theoretical mass of sodium iron pyrophosphate can be calculated according to the amounts of sodium, iron, and phosphorus sources added and the reaction equation, and the carbon source content can be determined according to the theoretical mass of sodium iron pyrophosphate. In some embodiments, the amount of inorganic carbon source added can be 0.5-2% of the theoretical mass of sodium iron pyrophosphate, and the amount of organic carbon source added can be 8-25% of the theoretical mass of sodium iron pyrophosphate.

[0067] In a third aspect, the present invention provides a battery comprising the above-mentioned composite cathode material.

[0068] In this invention, a positive electrode slurry can be manufactured by mixing a conductive agent, an adhesive, and the above-mentioned composite positive electrode material, and the positive electrode slurry can be placed on at least one functional surface of a positive electrode current collector and dried to form a positive electrode plate.

[0069] In certain embodiments, the conductive agent may be acetylene black or conductive carbon black, the adhesive may be PVDF, the mass ratio of the composite cathode material, conductive agent, and adhesive may be 8:1:1, drying may be carried out in a vacuum oven, and the drying time may be 2 hours.

[0070] In some embodiments, the battery according to the present invention can be obtained by stacking the above-mentioned positive electrode plate, separator, and negative electrode plate to obtain an electrode assembly, placing the electrode assembly in an outer package, and injecting an electrolyte into the outer package.

[0071] The battery according to this application, having the above-mentioned composite positive electrode material, exhibits excellent cycle performance, discharge ratio capacity, and magnification performance.

[0072] The technical solution related to this application will be further described below with reference to specific embodiments.

[0073] Example 1 The battery according to this embodiment is manufactured by a method that includes the following steps.

[0074] 1. Manufacturing of composite cathode materials 1) Weigh 2 mol of sodium dihydrogen phosphate dihydrate and 1.5 mol of iron(II) oxalate dihydrate, and calculate the theoretical mass of sodium iron pyrophosphate phosphate according to the reaction equation. Then, add polyethylene glycol and melamine, dissolve in 2 L of deionized water, and perform a first polishing treatment and a second polishing treatment sequentially using a polishing machine to obtain a suspension. The suspension is then spray-dried using a spray dryer to obtain a powder. Here, the amounts of polyethylene glycol and melamine added are 25% of the theoretical mass of sodium iron pyrophosphate, and the mass ratio of polyethylene glycol to melamine is 1:1. In the first polishing process, the particle size of the polishing machine was larger than that of the polishing machine in the second polishing process. In the first polishing process, the duration was 3 hours, and the rotational speed of the polishing machine was 1000 rpm min. -1 In the second polishing process, the time was 1.5 hours, and the rotation speed of the polishing machine was 500 rpm min. -1 And, In the spray drying process, the spray dryer has a fan temperature of 210°C and an outlet temperature of 85°C. 2) The powder was placed in a tubular furnace continuously filled with nitrogen gas, and the first, second, third, and fourth calcination treatments were carried out sequentially, and a composite cathode material was obtained after cooling. Here, the nitrogen gas flow rate is 0.3 L min -1 And, In the first firing process, the temperature was maintained at 255°C for 2 hours. In the second firing process, the temperature was maintained at 300°C for 5 hours. In the third firing process, the temperature was maintained at 370°C for 2 hours. In the fourth firing process, the temperature was maintained at 470°C for 10 hours.

[0075] 2. Battery manufacturing A composite cathode material, acetylene black, and PVDF adhesive were mixed in a mass ratio of 80:10:10 to form a cathode slurry. This slurry was then applied to two functional surfaces of aluminum foil, dried, and baked in a vacuum oven for 2 hours to obtain a cathode plate. Furthermore, an electrode assembly was obtained by stacking a positive electrode plate, a separator, and a negative electrode made of metallic sodium sheet in a glove box where both the water and oxygen content were less than 0.001 ppm. Then, the electrode assembly was placed in an outer package, and electrolyte was injected into the outer package to obtain a CR 2032 button cell. Here, the separator is a Celgard membrane. The electrolyte contains NaClO4, EC, PC, and FEC, with a volume ratio of EC to PC of 1:1, a concentration of NaClO4 of 0.8 mol / L, and a mass percentage content of FEC of 7.5%.

[0076] Example 2 The method for manufacturing the battery according to this embodiment is generally the same as the method for manufacturing the battery according to Example 1, but there are the following differences. In the manufacturing of composite cathode materials, 0.6 mol of sodium pyrophosphate decahydrate, 0.6 mol of iron(II) oxalate dihydrate, 1.47 mol of iron phosphate, and 0.27 mol of sodium bicarbonate were weighed out, and the theoretical mass of sodium iron pyrophosphate was calculated according to the reaction equation. Then, polyethylene glycol and glucose were added. Here, the amount of polyethylene glycol and glucose added is 11.1% of the theoretical mass of sodium iron pyrophosphate, and the mass ratio of polyethylene glycol to glucose is 1:1.

[0077] Example 3 The method for manufacturing the battery according to this embodiment is generally the same as the method for manufacturing the battery according to Example 1, but there are the following differences. In the manufacturing of composite cathode materials, 1 mole of sodium pyrophosphate decahydrate, 1 mole of iron(II) oxalate dihydrate, and 2 moles of iron phosphate were weighed, and the theoretical mass of sodium iron pyrophosphate was calculated according to the reaction equation. Then, polyethylene glycol, cochin black, and titanate coupling agent were added. Here, the amount of polyethylene glycol added is 25% of the theoretical mass of sodium iron pyrophosphate, the amount of Cochin Black added is 1% of the theoretical mass of sodium iron pyrophosphate, and the amount of titanate coupling agent added is the same as the amount of Cochin Black added.

[0078] Example 4 The method for manufacturing the battery according to this embodiment is generally the same as the method for manufacturing the battery according to Example 1, but there are the following differences. In the manufacturing of composite cathode materials, Melamine was substituted with glucose, and the amounts of glucose and polyethylene glycol added were 4% and 2% of the theoretical mass of sodium iron pyrophosphate, respectively.

[0079] Example 5 The method for manufacturing the battery according to this embodiment is generally the same as the method for manufacturing the battery according to Example 1, but there are the following differences. In the manufacturing of composite cathode materials, Melamine was substituted with glucose, and the amounts of glucose and polyethylene glycol added were 20% and 6% of the theoretical mass of sodium iron pyrophosphate, respectively.

[0080] Example 6 The method for manufacturing the battery according to this embodiment is generally the same as the method for manufacturing the battery according to Example 1, but there are the following differences. In the manufacturing of composite cathode materials, In the first firing process, the temperature was maintained at 255°C for 2 hours. In the second firing process, the temperature was maintained at 300°C for 4 hours. In the third firing process, the temperature was maintained at 390°C for 2 hours. In the fourth firing process, the temperature was maintained at 500°C for 8 hours.

[0081] Example 7 The method for manufacturing the battery according to this embodiment is generally the same as the method for manufacturing the battery according to Example 1, but there are the following differences. In the manufacturing of composite cathode materials, In the first firing process, the temperature was maintained at 255°C for 2 hours. In the second firing process, the temperature was maintained at 300°C for 4 hours. In the third firing process, the temperature is maintained at 370°C for 1 hour. In the fourth firing process, the temperature was maintained at 470°C for 10 hours.

[0082] Example 8 The method for manufacturing the battery according to this embodiment is generally the same as the method for manufacturing the battery according to Example 1, but there are the following differences. In the manufacturing of composite cathode materials, 1 mole of sodium pyrophosphate decahydrate, 1.15 moles of triiron tetroxide, 2 moles of phosphoric acid, and 0.2 moles of sodium ferric ethylenediaminetetraacetate were weighed out, the theoretical mass of sodium ferric pyrophosphate was calculated according to the reaction equation, and then glucose was added. Here, in order to address the carbon source in ethylenediaminetetraacetate sodium, melamine is substituted with glucose, and the amount of glucose added is 7% of the theoretical mass of ferric pyrophosphate sodium.

[0083] Example 9 The method for manufacturing the battery according to this embodiment is generally the same as the method for manufacturing the battery according to Example 1, but there are the following differences. In the manufacturing of composite cathode materials, The polishing process is performed only once, for a duration of 4 hours, and the polishing machine rotates at 800 rpm min. -1 That is the case.

[0084] Example 10 The method for manufacturing the battery according to this embodiment is generally the same as the method for manufacturing the battery according to Example 3, but there are the following differences. In the manufacturing of composite cathode materials, The carbon sources are glucose and acetylene black, with the amounts of glucose and acetylene black added being 1% and 2% of the theoretical mass of sodium iron pyrophosphate, respectively.

[0085] Comparative Example 1 The battery manufacturing method for this comparative example is generally the same as the battery manufacturing method for Example 1, but there are the following differences. In the manufacturing of composite cathode materials, polyethylene glycol and melamine are not added.

[0086] Comparative Example 2 The battery manufacturing method for this comparative example is generally the same as the battery manufacturing method for Example 1, but there are the following differences. In step 1), the amount of polyethylene glycol and melamine added is 18% of the theoretical mass of sodium iron pyrophosphate. In step 2), the powder was placed in a tubular furnace continuously filled with nitrogen gas, and the first, second, and third calcination processes were carried out sequentially. After cooling, a composite cathode material was obtained. Here, the nitrogen gas flow rate is 0.3 L min -1 And, In the first firing process, the temperature was maintained at 255°C for 2 hours. In the second firing process, the temperature was maintained at 390°C for 5 hours. In the third firing process, the temperature was maintained at 530°C for 15 hours.

[0087] Performance measurement 1. The following performance measurements were performed on the composite cathode materials in the examples and comparative examples, and the measurement results are shown in Table 1.

[0088] 1)XRD measurement XRD measurements were performed on the composite cathode materials in the examples and comparative examples, and the measurement results are shown in Figure 1-4. Figure 1 is an XRD diagram of the composite cathode material in Example 1 of the present invention, Figure 2 is an XRD diagram of the composite cathode material in Example 2 of the present invention, Figure 3 is an XRD diagram of the composite cathode material in Example 3 of the present invention, and Figure 4 is an XRD diagram of the composite cathode material in Comparative Example 1 of the present invention. From Figures 1-4, it can be seen that the composite cathode materials in the examples and comparative examples of the present invention crystallized well, and NFPP(Na 4+x Fe 3-y (PO4) 2+z It can be confirmed that no obvious impurity peaks other than P2O7 and NFP (NaFePO4) are observed.

[0089] Rietveld analysis of the spectrum was performed to obtain the ratio of NFPP to NFP in the composite cathode material. The grain sizes of the three independent highest intensity peaks of NFPP and NFP were calculated using the Scherrer equation to determine the grain sizes of the different phases.

[0090] 2) SEM measurement SEM measurements were performed on the composite cathode materials in the examples and comparative examples, and the measurement results are shown in Figure 5-8. Figure 5 is an SEM diagram of the composite cathode material in Example 1 of the present invention, Figure 6 is an SEM diagram of the composite cathode material in Example 2 of the present invention, Figure 7 is an SEM diagram of the composite cathode material in Example 3 of the present invention, and Figure 8 is an SEM diagram of the composite cathode material in Comparative Example 1 of the present invention. From Figures 5-8, it can be seen that the composite cathode material in the examples of the present invention is bonded via a carbon coating layer, while the composite cathode material in the comparative example has a large crystal grain size and does not have a carbon coating layer.

[0091] 3) BET measurement The BET of the composite cathode materials in the examples and comparative examples was measured using a BET measuring device that uses N2 adsorption.

[0092] 4) Tap density of composite cathode material Using a cylindrical container with a diameter of 13 mm, 2 g of material was loaded, and it was pressurized to 3 T. The final sample thickness was measured, and the tap density of the material was calculated.

[0093] 5) Atomic ratio of Fe to Na (Fe / Na) or atomic ratio of Fe to P (Fe / P) The composite cathode material was measured using XPS to obtain the initial Fe-to-Na atomic ratio (Fe / Na) or Fe-to-P atomic ratio (Fe / P) from the outside to the inside of the composite cathode material, and the final stable Fe-to-Na atomic ratio (Fe / Na) or Fe-to-P atomic ratio (Fe / P), respectively.

[0094] 2. The following performance measurements were performed on the batteries in the examples and comparative examples, and the measurement results are shown in Table 2.

[0095] 1) Charge / discharge specific capacity The battery's charge / discharge range is 1.7-4.1V, and the charge / discharge current density is 1C (1C = 129mAh g). -1 The results are shown in Table 1 and Figure 9-12. Figure 9 shows the charge-discharge curve of the battery in Example 1 of the present application, Figure 10 shows the charge-discharge curve of the battery in Example 2 of the present application, Figure 11 shows the charge-discharge curve of the battery in Example 3 of the present application, and Figure 12 shows the charge-discharge curve of the battery in Comparative Example 1 of the present application. From Figures 9-12, it can be confirmed that the battery in the embodiment of the present application has excellent charge-discharge ratio capacity.

[0096] 2) Magnification performance The battery's charge / discharge range was 1.7-4.1V, with a magnification of 5C. The measurement results are shown in Table 1.

[0097] 3) Tap density of the electrode plates After the dried positive electrode plate was roller-rolled at a predetermined pressure, it was punched using a standard die. The weight and thickness of the punched electrode plate were measured, and the weight and thickness of the aluminum foil were subtracted, respectively. The tap density of the roller-rolled electrode plate was then obtained using a density calculation formula.

[0098] 4) Cycle performance The batteries were tested by cycling them 200 times under normal temperature (25°C) conditions at a 5C multiplier, and the cycle retention rate was calculated based on the cycle capacity at the initial 5C.

[0099] [Table 1] [Table 2]

[0100] From Tables 1 and 2, it can be confirmed that when the composite cathode material according to the embodiment of the present application is applied to a battery, the battery's multiplier performance, cycle performance, and discharge ratio capacity can be improved.

[0101] Furthermore, from Examples 1-11 and Comparative Example 1, it was confirmed that by using a composite cathode material comprising an internal core and a carbon coating layer, the battery's magnification performance, cycle performance, and discharge ratio capacity can be effectively improved. From Examples 1-11 and Comparative Example 2, it was confirmed that a battery with superior magnification performance, cycle performance, and discharge ratio capacity can be obtained only when the particle size of NaFePO4 in the internal core is ≤100 nm. From Examples 1 and 4-5, it was confirmed that when the mass percentage content of the carbon coating layer in the composite cathode material is 0.5-5%, a composite cathode material with appropriate BET and appropriate internal core particle size can be obtained, and when applied to a battery, a battery with superior magnification performance, cycle performance, and discharge ratio capacity can be obtained. From Examples 1 and 6-7, it was found that PO4 is included in the composite cathode material. 3- and P2O7 4- By selecting the appropriate molar ratio, a composite cathode material with an appropriate tap density can be obtained, and it has been confirmed that this composite cathode material can improve the battery's multiplier performance, cycle performance, and discharge ratio capacity. Examples 1 and 8 confirm that using sodium ethylenediaminetetraacetate as both a sodium source and an iron source in the manufacturing method can further improve the battery's multiplier performance, cycle performance, and discharge ratio capacity. Examples 1 and 9 demonstrate that by performing polishing twice, a composite cathode material with an appropriate tap density can be obtained, resulting in improved battery multiplier performance, cycle performance, and discharge ratio capacity. Examples 3 and 10 confirm that by using a carbon source containing both organic and inorganic carbon sources, and by selecting the mass ratio of the organic and inorganic carbon sources, the battery's multiplier performance, cycle performance, and discharge ratio capacity can be further improved.

[0102] Finally, it should be noted that the above embodiments are intended to illustrate, and not limit, the technical solutions of the present application. However, the present application will be described in detail with reference to the above embodiments. Those skilled in the art will still be able to modify the technical solutions described in the above embodiments or make equivalent substitutions to some or all of their technical features, and these modifications or substitutions should be understood not to deviate from the essence of the corresponding technical solutions within the scope of the technical solutions of the embodiments of the present application.

[0103] This application claims priority to a Chinese patent application filed with the China National Intellectual Property Administration on June 29, 2023, with application number 202310793176.6, titled "Composite Cathode Material, Method for Manufacturing the Same, and Use thereof," the entirety of which is incorporated into this application by reference.

Claims

1. A composite cathode material comprising an internal core and a carbon coating layer that covers at least a portion of the surface of the internal core and / or is embedded in the internal core, The aforementioned internal core is NaFePO ４ It includes the compound shown in formula 1, Na ４＋ｘ Fe ３－ｙ (PO ４ ) ２＋ｚ P ２ O ７ Formula 1 In Equation 1, we set -0.15 ≤ x ≤ 0.8, 0 ≤ y ≤ 0.5, and -0.2 ≤ z ≤ 0.

2. NaFePO ４ Let the particle size be ≤ 100 nm. Composite cathode material.

2. The composite cathode material has an atomic ratio of Fe to P that gradually decreases from (0.9-1.1):1 from the outside to the inside, and thereafter stabilizes at (0.65-0.85):1, and / or The composite cathode material according to claim 1, wherein the atomic ratio of Fe to Na gradually decreases from the outside to the inside from (0.9-1.1):1, and thereafter stabilizes at (0.65-0.85):

1.

3. The composite cathode material according to claim 1 or 2, wherein the mass percentage content of the carbon coating layer is 0.5-5% based on the total mass of the composite cathode material.

4. Among the composite cathode materials, PO ４ ３－ and P ２ O ７ ４－ The molar ratio of is (1.2 - 2.5):

1. The composite cathode material according to any one of claims 1 - 3.

5. The particle size of the aforementioned internal core is 100-900 nm, and / or The specific surface area of ​​the composite cathode material is 5-20 m². ２ g －１ and / or, The tap density of the composite cathode material is 1.9–2.4 g / cm³. －３ The composite cathode material according to any one of claims 1 to 4.

6. A process to obtain powder by sequentially performing polishing and spray drying treatments on a raw material system containing a sodium source, an iron source, a phosphorus source, and a carbon source, A method for producing a composite cathode material according to any one of claims 1 to 5, comprising the step of sequentially performing a first calcination treatment, a second calcination treatment, a third calcination treatment and a fourth calcination treatment on the powder to obtain the composite cathode material, In the raw material system, the molar proportions of sodium (a), iron (b), and phosphorus (c) satisfy 3.85 ≤ a ≤ 4.8, 2.5 ≤ b ≤ 3, and 3.8 ≤ c ≤ 4.

2. In the first firing process described above, the temperature was 255-260°C and the time was 1-2 hours. In the second firing process described above, the temperature was 300-320°C and the time was 3-5 hours. In the third firing process described above, the temperature was 370-390°C and the time was 1-2 hours. In the fourth firing process described above, the temperature is 470-500°C and the time is 8-10 hours. Manufacturing method.

7. The manufacturing method according to claim 6, wherein the sodium source, the iron source, and the carbon source all contain sodium ethylenediaminetetraacetate.

8. The polishing process includes a first polishing process and a second polishing process. The manufacturing method according to claim 6 or 7, wherein the particle size of the abrasive in the second polishing treatment is smaller than the particle size of the abrasive in the first polishing treatment.

9. In the first polishing process described above, the rotational speed is 900-1200 rpm, the time is 2-3 hours, and / or, The manufacturing method according to claim 8, wherein in the second polishing process, the rotational speed is 400-2000 rpm and the time is 1-2 hours.

10. The manufacturing method according to any one of claims 6-9, wherein the carbon source includes an organic carbon source.

11. The carbon source further comprises an inorganic carbon source, The manufacturing method according to claim 10, wherein the ratio of the mass of the organic carbon source to the mass of the inorganic carbon source is (12.5-30):

1.

12. The aforementioned raw material system further contains a coupling agent, The manufacturing method according to claim 11, wherein the mass percentage content of the coupling agent is 1-3% based on the total mass of the raw material system.

13. The manufacturing method according to claim 12, wherein the coupling agent is a titanate coupling agent.

14. A battery comprising the composite positive electrode material according to any one of claims 1 to 5.

Images