K2feo4 composite material, and preparation method and application thereof
By forming a dense silicon oxide and titanium oxide coating layer on the surface of K2FeO4, the decomposition and stability problems of K2FeO4 material are solved, its lithium-ion and electron conduction properties are improved, and the cycle and discharge performance of the battery is enhanced.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- EVE POWER CO LTD
- Filing Date
- 2023-11-08
- Publication Date
- 2026-07-07
AI Technical Summary
K2FeO4 materials are prone to self-decomposition during cycling and react with water in the air, resulting in poor storage and cycling stability, and negatively impacting lithium-ion conductivity and electronic conductivity.
K2FeO4 is coated with silicon oxide and titanium oxide layers. A dense coating layer is formed by liquid-phase mixing and high-temperature sintering. The thickness and particle size of the coating layer are controlled to form a macroporous/mesoporous structure to promote lithium-ion transport.
It improves the storage stability and cycling performance of K2FeO4 materials, enhances lithium-ion and electron conduction properties, and improves discharge performance.
Smart Images
Figure BDA0004536621880000151
Abstract
Description
Technical Field
[0001] This invention relates to the field of battery technology, and in particular to a K2FeO4 composite material, its preparation method, and its application. Background Technology
[0002] K2FeO4 is a compound of iron in the +6 oxidation state. Due to its three-electron reduction properties, it can undergo multi-electron reduction, thus providing a high cathode capacity. Moreover, its theoretical specific capacity far exceeds that of commonly used cathode materials such as LCO, LFP, and NCM.
[0003] Although K2FeO4 exhibits high redox potential and specific capacity, its Fe content, being in the +6 oxidation state, makes it highly susceptible to self-decomposition during cycling (4K2FeO4 = 2Fe2O3 + 3O2 + 4K2O). Furthermore, K2FeO4 readily reacts with water in the air (4K2FeO4 + 10H2O = 4Fe(OH)3↓ + 8KOH + 3O2↑), making it difficult to store and resulting in poor cycling stability (only about 100 cycles). Currently, surface coating is commonly used to improve the storage and cycling stability of K2FeO4, with the coating layer primarily composed of SiO2 and Al2O3. While coated K2FeO4 electrode materials can overcome its inherent decomposition defects to some extent, the silicon oxide coating layer is at risk of detachment during long-term battery cycling, and the lithium-ion conductivity, electronic conductivity, and discharge performance of the coated K2FeO4 electrode material are negatively affected.
[0004] Therefore, there is an urgent need to provide a potassium ferrate electrode material that can overcome the inherent defects of potassium ferrate itself, improve the stability of the coating layer, and enhance the lithium-ion conductivity, electronic conductivity, and discharge performance of the potassium ferrate electrode material. Summary of the Invention
[0005] In order to overcome the intrinsic defects of potassium ferrate while improving its lithium-ion conductivity, electronic conductivity and discharge performance, this application provides a K2FeO4 composite material, its preparation method and application.
[0006] In a first aspect, this application provides a method for preparing a K2FeO4 composite cathode material, employing the following technical solution:
[0007] A method for preparing a K2FeO4 composite cathode material, the method comprising the following steps:
[0008] (1) K2FeO4, the first organic solvent and a portion of silicon source are mixed, stirred and filtered to obtain the first premix;
[0009] (2) Sinter the first premixed material in step (1) under an oxygen-containing atmosphere to obtain SiO2 modified K2FeO4 composite material;
[0010] (3) Mix the titanium source, the SiO2 modified K2FeO4 composite material, the second organic solvent and the remaining silicon source, stir and filter to obtain the second premix;
[0011] (4) Under an oxygen-containing atmosphere, the second premix in step (3) is sintered to obtain SiO2 & TiO2 modified K2FeO4 composite material;
[0012] In the preparation process, the mass ratio of silicon source, titanium source and K2FeO4 is (1.5-2):(0.5-1):5.
[0013] By sequentially coating the surface of potassium ferrate with silicon oxide and titanium dioxide, a uniform and dense first silicon oxide coating layer is formed on the surface of potassium ferrate. This prevents the potassium ferrate core from contacting air and water vapor, reducing its self-decomposition rate and thus improving its storage stability and cycle performance as a cathode material. On the other hand, the mixing of silicon and titanium sources generates a second titanium dioxide coating layer on the surface of the first silicon oxide coating layer. This second titanium dioxide coating layer not only has excellent compatibility with the first silicon oxide coating layer, ensuring a tight bond between them and guaranteeing the stability of the material interface, but also improves the overall structural stability of the coating layer during long-term battery cycling and reduces the risk of detachment. Furthermore, the macroporous / mesoporous dual-channel structure in titanium dioxide forms lithium-ion transport channels, which to some extent promotes lithium-ion transport, alleviates the influence of the first silicon oxide coating layer on the lithium-ion conductivity of potassium ferrate, and improves the electron transport capacity within the potassium ferrate electrode material, thereby significantly improving the discharge performance of the potassium ferrate electrode material.
[0014] Preferably, the mass ratio of the first part of the silicon source in step (1) to the remaining part of the silicon source in step (3) is 1:(0.5-1).
[0015] By adjusting the amount of silicon source in steps (1) and (3), the first silicon oxide coating layer can improve the stability of potassium ferrate while minimizing its negative impact on the lithium-ion conduction and electronic conduction performance of the potassium ferrate electrode material. Furthermore, the first silicon oxide coating layer is tightly connected to the second silicon titanium oxide coating layer, improving the overall stability of the coating layer. This allows the macroporous / mesoporous dual-channel structure in titanium dioxide to play its role in promoting lithium-ion transport, thereby promoting lithium-ion and electronic transport and further improving the discharge performance of the potassium ferrate electrode material.
[0016] Preferably, in steps (1) and (3), both the first organic solvent and the second organic solvent include alcohol solvents; the stirring process in steps (1) and (3) is carried out in a protective gas.
[0017] Preferably, the alcohol solvent includes at least one of methanol, ethanol, or isopropanol.
[0018] Preferably, the protective gas includes at least one of nitrogen, argon, helium, neon, krypton, and radon.
[0019] Preferably, in step (1), the stirring time during the stirring process is 4-8 hours and the stirring speed is 200-500 rpm; after the filtration operation, the filter cake is taken out and dried to obtain the first premix.
[0020] Preferably, the stirring time in step (3) is 4-6 hours and the stirring speed is 300-600 rpm; after the filtration operation, the filter cake is taken out and dried to obtain the second premix.
[0021] Preferably, the oxygen-containing atmosphere in steps (2) and (4) is oxygen and / or ozone.
[0022] Preferably, the temperature during the sintering process in step (2) is 700-900℃, the sintering time is 4-6h, and the heating rate during sintering is 5-15℃ / min.
[0023] Preferably, the temperature during the sintering process in step (4) is 700-800℃, the sintering time is 3-5h, and the heating rate during sintering is 5-10℃ / min.
[0024] By selecting a coating source capable of liquid-phase mixing and high-temperature sintering, the coating source and potassium ferrate are fully premixed in a protective gas atmosphere, ensuring that the potassium ferrate does not deteriorate. In the oxygen and / or ozone atmosphere during subsequent sintering, the decomposition of potassium ferrate at high temperatures can be avoided, which is beneficial for preparing potassium ferrate materials with excellent conductivity, cycle performance and storage performance.
[0025] Preferably, the D50 of K2FeO4 in step (1) is 10-15 μm.
[0026] By controlling the particle size of potassium ferrate particles, the deposition thickness of silicon source on the surface of potassium ferrate particles is reduced, and the upper limit of the thickness of the first silicon oxide coating layer is controlled, thereby reducing the negative impact of excessive coating layer on the lithium-ion conduction and conductivity of potassium ferrate composite materials.
[0027] Preferably, the mass ratio of K2FeO4 to the first organic solvent in step (1) is 1:(4-10).
[0028] Preferably, the mass of the second organic solvent in step (3) is the same as the mass of the first organic solvent in step (1); and the type of the second organic solvent in step (3) is the same as the type of the first organic solvent in step (1).
[0029] By controlling the mass ratio of potassium ferrate to organic solvent, the premix can maintain a certain viscosity, which is beneficial for the premix to coat the potassium ferrate particles with a particle size of 10-15μm and generate a first silicon oxide coating layer with uniform and stable thickness. This promotes the continued uniform coating of silicon titanium oxide on the surface of the first silicon oxide coating layer, thereby reducing the negative impact of silicon oxide on the lithium-ion conduction and conductivity of the potassium ferrate electrode material.
[0030] Preferably, the silicon source includes at least one of tetraethyl silicate and tetrapropyl silicate.
[0031] Preferably, the titanium source includes at least one of titanium sulfate, tetrabutyl titanate, isopropyl titanate, and tetraethyl titanate.
[0032] By selecting appropriate silicon and titanium sources to work together, the negative impact of silicon oxide coating on the electrical conductivity of potassium ferrate composite materials can be reduced.
[0033] Secondly, this application provides a K2FeO4 composite cathode material, which adopts the following technical solution:
[0034] A K2FeO4 composite cathode material, wherein the K2FeO4 composite material is prepared by the method described above, and the K2FeO4 composite material includes a potassium ferrate core and a first silicon oxide coating layer and a second silicon titanium oxide coating layer disposed on the surface of the potassium ferrate core.
[0035] Preferably, the thickness of the first silicon oxide coating layer is 5-20 nm.
[0036] Preferably, the thickness of the second silicon titanium oxide coating layer is 5-30 nm.
[0037] By controlling the thickness of the first silicon oxide coating layer and the second silicon titanium oxide coating layer, the influence of silicon oxide on the lithium-ion conductivity and electronic conductivity of potassium ferrate electrode material can be greatly reduced.
[0038] Thirdly, this application provides a battery that adopts the following technical solution:
[0039] A battery comprising the K2FeO4 composite material described above. Detailed Implementation
[0040] To better understand and implement this invention, the technical solution will be clearly and completely described below with reference to the embodiments.
[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.
[0042] Unless otherwise stated, all numerical values for the amounts of expressed components, reaction conditions, etc., used in the specification and claims are to be understood as being modified by the term "about". Therefore, unless otherwise indicated, the numerical parameters set forth herein are approximate values that can be varied to obtain the desired performance.
[0043] The word “and / or” as used in this article refers to one or all of the elements mentioned.
[0044] The terms "include" and "contain" as used in this article cover both cases where only the mentioned elements exist and cases where other unmentioned elements exist in addition to the mentioned elements.
[0045] All percentages in this invention are weight percentages, unless otherwise stated.
[0046] Unless otherwise stated, the terms “a,” “an,” “an,” and “the” as used in this specification are intended to include “at least one” or “one or more.” For example, “a component” refers to one or more components, and therefore more than one component may be considered and may be employed or used in the implementation of the described embodiments.
[0047] Example
[0048] Example 1
[0049] 1. Preparation of K2FeO4 composite materials
[0050] A K2FeO4 composite material is prepared by the following method:
[0051] (1) At 25°C, 1 mg of tetraethyl silicate, 5 mg of K2FeO4 with a D50 of 12 μm and 35 mg of methanol were mixed and stirred for 6 h at 350 rpm in a nitrogen atmosphere. After stirring, the mixture was filtered and the filter cake was dried to obtain the first premix.
[0052] (2) The first premix obtained in step (1) is heated to 800°C at a heating rate of 10°C / min in an oxygen and ozone atmosphere and sintered for 5 hours. The first premix after sintering is cleaned with methanol and then dried to obtain a SiO2 modified K2FeO4 composite material with a first silicon oxide coating layer thickness of 12nm.
[0053] (3) At 25°C, 0.7 mg of tetraethyl silicate, 0.8 mg of tetrabutyl titanate, SiO2 modified K2FeO4 composite material and 35 mg of methanol were mixed and stirred for 5 h at 450 rpm in a nitrogen atmosphere. After stirring, the filter cake was dried to obtain the second premix.
[0054] (4) The second premix obtained in step (3) is heated to 750°C at a heating rate of 8°C / min in an oxygen and ozone atmosphere and sintered for 4 hours. The sintered second premix is cleaned with methanol and then dried to obtain a SiO2&TiO2 modified K2FeO4 composite material with a second silicon titanium oxide coating thickness of 18nm, that is, a total coating thickness of 30nm.
[0055] 2. Battery manufacturing
[0056] 2.1. Preparation of the positive electrode sheet
[0057] The positive electrode slurry was prepared as follows: K2FeO4 composite material, conductive agent acetylene black, and binder PVDF were added to a vacuum mixer at a mass ratio of 97.9:0.9:1.2 and mixed. Then, NMP solvent was added to the mixed slurry, and the slurry was stirred under vacuum until homogeneous, thus obtaining the positive electrode slurry of this embodiment. The above positive electrode slurry was uniformly coated on both surfaces of the positive electrode current collector aluminum foil, air-dried at room temperature, and then transferred to an oven for further drying. After drying in the oven, a positive electrode semi-finished product was obtained. Then, the positive electrode semi-finished product was cold-pressed and cut to obtain the positive electrode sheet to be assembled.
[0058] 2.2. Preparation of negative electrode sheet
[0059] The negative electrode slurry was prepared as follows: artificial graphite, conductive agent acetylene black, thickener CMC, and binder SBR were added to a vacuum mixer in a mass ratio of artificial graphite: conductive agent acetylene black: thickener CMC: binder SBR = 96.4:1:1.2:1.4 and mixed. Then, deionized water was added to the resulting mixture, and the mixture was stirred under vacuum until homogeneous, thus obtaining the negative electrode slurry of this embodiment.
[0060] The above-mentioned negative electrode slurry is uniformly coated on both surfaces of the negative electrode current collector copper foil. After drying at room temperature, it is transferred to an oven for further drying. After drying in the oven, a negative electrode semi-finished product is obtained. Then, the negative electrode semi-finished product is cold-pressed and cut to obtain the negative electrode sheet to be assembled.
[0061] 2.3. Assembly of Lithium-ion Batteries
[0062] Commercially available polyethylene film is used as the separator for the lithium-ion battery, and a commercially available electrolyte suitable for 4.2V (upper charging voltage) battery system is used as the electrolyte. The above-mentioned positive electrode sheet, negative electrode sheet and separator are wound together to obtain bare cell. The bare cell is then packaged, injected with electrolyte, left to stand, formed and tested for capacity to obtain the finished battery.
[0063] Example 2
[0064] The difference from Example 1 lies in the preparation of the K2FeO4 composite material;
[0065] A K2FeO4 composite material is prepared by the following method:
[0066] (1) At 25°C, 1 mg of tetrapropyl silicate, 5 mg of K2FeO4 with a D50 of 15 μm and 20 mg of ethanol were mixed and stirred for 8 h at 200 rpm in an argon atmosphere. After stirring, the mixture was filtered and the filter cake was dried to obtain the first premix.
[0067] (2) The first premix obtained in step (1) is heated to 900°C at a heating rate of 5°C / min in an oxygen atmosphere and sintered for 4 hours. The first premix after sintering is cleaned with ethanol and then dried to obtain a SiO2 modified K2FeO4 composite material with a first silicon oxide coating layer thickness of 5nm.
[0068] (3) At 25°C, 0.5 mg of tetrapropyl silicate, 0.5 mg of titanium sulfate, SiO2 modified K2FeO4 composite material and 20 mg of ethanol were mixed and stirred for 6 h at 300 rpm in an argon atmosphere. After stirring, the mixture was filtered and the filter cake was dried to obtain the second premix.
[0069] (4) The second premix obtained in step (3) is heated to 800°C at a heating rate of 5°C / min in an oxygen atmosphere and sintered for 3 hours. The sintered second premix is cleaned with ethanol and then dried to obtain a SiO2&TiO2 modified K2FeO4 composite material with a second silicon titanium oxide coating layer thickness of 5nm, that is, a total coating layer thickness of 10nm.
[0070] Example 3
[0071] The difference from Example 1 lies in the preparation of the K2FeO4 composite material;
[0072] A K2FeO4 composite material is prepared by the following method:
[0073] (1) At 25°C, 1 mg of tetraethyl silicate, 5 mg of K2FeO4 with a D50 of 10 μm and 50 mg of isopropanol were mixed and stirred for 4 h at 500 rpm in a helium atmosphere. After stirring, the mixture was filtered and the filter cake was dried to obtain the first premix.
[0074] (2) The first premix obtained in step (1) is heated to 700°C at a heating rate of 15°C / min in an oxygen atmosphere and sintered for 6 hours. The first premix after sintering is cleaned with isopropanol and then dried to obtain a SiO2 modified K2FeO4 composite material with a first silicon oxide coating layer thickness of 20nm.
[0075] (3) At 25°C, 1 mg of tetrapropyl silicate, 1 mg of isopropyl titanate, SiO2 modified K2FeO4 composite material and 50 mg of ethanol were mixed and stirred for 4 hours at 600 rpm in an argon atmosphere. After stirring, the filter cake was dried to obtain the second premix.
[0076] (4) The second premix obtained in step (3) is heated to 700°C at a heating rate of 10°C / min in an oxygen atmosphere and sintered for 5 hours. The sintered second premix is then cleaned with ethanol and dried to obtain a SiO2&TiO2 modified K2FeO4 composite material with a second silicon titanium oxide coating layer thickness of 30nm, that is, a total coating layer thickness of 50nm.
[0077] Example 4
[0078] The difference from Example 1 lies in the preparation of the K2FeO4 composite material;
[0079] A K2FeO4 composite material is prepared by the following method:
[0080] (1) At 25°C, 1 mg of tetrapropyl silicate, 5 mg of K2FeO4 with a D50 of 13 μm and 40 mg of ethanol were mixed and stirred for 6 h at 400 rpm in a neon atmosphere. After stirring, the mixture was filtered and the filter cake was dried to obtain the first premix.
[0081] (2) The first premix obtained in step (1) is heated to 860°C at a heating rate of 12°C / min in an ozone atmosphere and sintered for 5 hours. The first premix after sintering is cleaned with ethanol and then dried to obtain a SiO2 modified K2FeO4 composite material with a first silicon oxide coating layer thickness of 15nm.
[0082] (3) At 25°C, 0.6 mg of tetrapropyl silicate, 1 mg of tetraethyl titanate, SiO2 modified K2FeO4 composite material and 40 mg of ethanol were mixed and stirred at 500 rpm for 5.5 h in an argon atmosphere. After stirring, the mixture was filtered and the filter cake was dried to obtain the second premix.
[0083] (4) The second premix obtained in step (3) is heated to 760°C at a heating rate of 6°C / min in an oxygen atmosphere and sintered for 4.5h. The sintered second premix is cleaned with ethanol and then dried to obtain a SiO2&TiO2 modified K2FeO4 composite material with a second silicon titanium oxide coating layer thickness of 25nm, that is, a total coating layer thickness of 40nm.
[0084] Example 5
[0085] The difference from Example 1 is that in the preparation process of K2FeO4 composite material, the silicon source used in step (1) is 1.42 mg and the silicon source used in step (3) is 0.28 mg.
[0086] Example 6
[0087] The difference from Example 1 is that in the preparation process of K2FeO4 composite material, the silicon source used in step (1) is 0.74 mg and the silicon source used in step (3) is 0.96 mg.
[0088] Example 7
[0089] The difference from Example 1 is that the particle size D50 of K2FeO4 in the preparation of the K2FeO4 composite material is 8 μm.
[0090] Example 8
[0091] The difference from Example 1 is that the particle size D50 of K2FeO4 in the preparation of the K2FeO4 composite material is 18 μm.
[0092] Example 9
[0093] The difference from Example 1 is that, in the preparation process of the K2FeO4 composite material, the mass ratio of K2FeO4 to the first organic solvent is 1:2.
[0094] Example 10
[0095] The difference from Example 1 is that, in the preparation process of the K2FeO4 composite material, the mass ratio of K2FeO4 to the first organic solvent is 1:11.
[0096] Example 11
[0097] The difference from Example 1 is that the thickness of the first silicon oxide coating layer in the prepared K2FeO4 composite material is 30 nm.
[0098] Example 12
[0099] The difference from Example 1 is that the thickness of the second silicon titanium oxide coating layer in the prepared K2FeO4 composite material is 3 nm.
[0100] Comparative Example 1
[0101] The difference from Example 1 lies in the preparation of the K2FeO4 composite material;
[0102] A K2FeO4 composite material is prepared by the following method:
[0103] (1) At 25°C, 1.7 mg of tetraethyl silicate, 5 mg of K2FeO4 with a D50 of 12 μm and 35 mg of methanol were mixed and stirred for 6 h at 350 rpm in a nitrogen atmosphere. After stirring, the mixture was filtered and the filter cake was dried to obtain the premix.
[0104] (2) The premix obtained in step (1) was heated to 800°C at a heating rate of 10°C / min in an oxygen and ozone atmosphere and sintered for 5 hours. The sintered premix was cleaned with methanol and then dried to obtain a SiO2 modified K2FeO4 composite material with a silicon oxide coating thickness of 14 nm.
[0105] Comparative Example 2
[0106] The difference from Example 1 lies in the preparation of the K2FeO4 composite material;
[0107] A K2FeO4 composite material is prepared by the following method:
[0108] (1) At 25°C, 1.7 mg of tetraethyl silicate, 5 mg of K2FeO4 with a D50 of 12 μm and 35 mg of methanol were mixed and stirred at 350 rpm for 6 h in a nitrogen atmosphere. After stirring, the mixture was filtered and the filter cake was dried to obtain a silicon-containing premix.
[0109] (2) The silicon-containing premix obtained in step (1) was heated to 800°C at a heating rate of 10°C / min in an oxygen and ozone atmosphere and sintered for 5 hours. The sintered silicon-containing premix was cleaned with methanol and then dried to obtain a SiO2 modified K2FeO4 composite material with a silicon oxide coating thickness of 14 nm.
[0110] (3) At 25°C, 0.8 mg of tetrabutyl titanate, the SiO2 modified K2FeO4 composite material obtained in step (2) and 35 mg of methanol were mixed and stirred for 5 h at 450 rpm in a nitrogen atmosphere. After stirring, the filter cake was dried to obtain silicon-titanium premix.
[0111] (4) The silicon-titanium premix obtained in step (3) is heated to 750°C at a heating rate of 8°C / min in an oxygen and ozone atmosphere and sintered for 4 hours. The sintered silicon-titanium premix is cleaned with methanol and then dried to obtain a SiO2&TiO2 modified K2FeO4 composite material with a silicon-titanium oxide coating thickness of 16nm, that is, a total coating thickness of 30nm.
[0112] Comparative Example 3
[0113] The difference from Example 1 lies in the preparation of the K2FeO4 composite material;
[0114] A K2FeO4 composite material is prepared by the following method:
[0115] (1) At 25°C, 1.7 mg of tetrapropyl silicate, 0.8 mg of tetrabutyl titanate, 5 mg of K2FeO4 with a gD50 of 12 μm and 35 mg of ethanol were mixed and stirred for 6 h at 400 rpm in an argon atmosphere. After stirring, the mixture was filtered and the filter cake was dried to obtain the premix.
[0116] (2) The premix obtained in step (1) was heated to 800°C at a heating rate of 10°C / min under an oxygen atmosphere and sintered for 5 hours. The sintered premix was then cleaned with ethanol and dried to obtain a SiO2&TiO2 modified K2FeO4 composite material with a silicon titanium oxide coating thickness of 30 nm.
[0117] Comparative Example 4
[0118] The difference from Example 1 is that in the preparation of the K2FeO4 composite material, dry mixing is used in steps (1) and (3) without the use of organic solvents.
[0119] Detection methods
[0120] I. Cyclic Performance Testing
[0121] The cycling performance of the potassium ferrate composite materials prepared in Examples 1-12 and Comparative Examples 1-4 was tested. The test method was as follows: the lithium battery was cycled at 60°C, charged at 1C constant current and constant voltage to 3.65V, cut off current 0.05C, left to stand for 30min, discharged at 1C constant current to 2.5V, left to stand for 30min, and cycled 500 times. The discharge capacity of the first cycle was Q1, the discharge capacity of the 500th cycle was Q2, and the cycle capacity retention rate was Q2 / Q1×100%. The calculation results are recorded in Table 1.
[0122] II. Storage Performance Testing
[0123] The storage performance of the potassium ferrate composite materials prepared in Examples 1-10 and Comparative Examples 1-4 was tested. The test method was as follows: capacity calibration for 5 cycles, constant current and constant voltage charging at 1C to 3.65V, storage in a 60℃ incubator for 28 days, and standing at 25℃ for 5 hours.
[0124] Initial capacity: The average discharge capacity after 3 cycles of initial calibration;
[0125] Recovery capacity: The average discharge capacity after 3 cycles following storage and calibration;
[0126] Capacity recovery rate = recovered capacity / initial capacity × 100%; and the calculation results are recorded in Table 1.
[0127] III. Conductivity Test
[0128] The conductivity of the potassium ferrate composite materials prepared in Examples 1-12 and Comparative Examples 1-4 was tested. The test method is as follows: the internal resistance of the prepared potassium ferrate composite lithium battery was measured using an AC frequency internal resistance meter at 1 kHz, and the calculation results were recorded in Table 1.
[0129] IV. Capacity Retention Test
[0130] The rate capability of the lithium batteries prepared in Examples 1-12 and Comparative Examples 1-4 was tested. The test method was as follows: the batteries were charged to 3.65V at 1C constant current and constant voltage at 25°C and then left to stand for 30 minutes. The batteries were discharged to 2.5V at 1C and 2C constant current at 25°C, respectively. The discharge capacity at different rates was recorded. The capacity retention rate was calculated as 2C discharge capacity / 1C discharge capacity × 100%. The calculation results were recorded in Table 1.
[0131] V. Discharge Median Voltage Test
[0132] The discharge performance of the lithium batteries prepared in Examples 1-12 and Comparative Examples 1-4 was tested. The test method was as follows: the lithium batteries were cycled at 25°C, charged to 3.65V with 1C constant current and constant voltage, cut off current of 0.05C, and left to stand for 30 minutes. Then, they were discharged to 2.5V with 1C constant current and left to stand for 30 minutes. The cycle was repeated 5 times. The median voltage of the last discharge cycle was recorded, and the test data were recorded in Table 1.
[0133] Table 1
[0134]
[0135] Based on Examples 1-6, Comparative Example 1, and Table 1, it can be seen that the K2FeO4 composite material prepared in this application has excellent storage stability, can reduce the internal resistance of the cell, and improve the cycle performance of the lithium battery. This is because, on the one hand, the second silicon titanium oxide coating layer can be tightly bonded to the silicon oxide coating layer, improving the overall stability of the coating layer and the stability of the material interface, and reducing the risk of it falling off during cycling. On the other hand, the pore structure in the second silicon titanium oxide coating layer can play a promoting role in lithium-ion conduction and electron conduction, thereby significantly reducing the negative impact of silicon oxide coating on the lithium-ion conduction performance, electron conduction performance, and battery discharge performance of the K2FeO4 electrode material.
[0136] Based on Example 1, Comparative Examples 2-3, and Table 1, it can be seen that when silicon and titanium sources are used individually as coating sources to coat the surface of potassium ferrate, the electronic conductivity and discharge performance of the potassium ferrate composite material decrease significantly. This is because when silicon and titanium sources are coated on the surface of potassium ferrate, the tightness between the silicon oxide coating layer and the titanium oxide coating layer on the surface of potassium ferrate decreases, which is not conducive to improving the overall structural stability of the coating layer, increasing the risk of it falling off during battery use, and is also not conducive to the conduction of lithium ions and electrons, thus reducing the cycle performance of the lithium battery.
[0137] Based on Example 1, Comparative Example 4, and Table 1, it can be seen that the present invention uses silicon source and titanium source as coating source mixed with organic liquid phase and oxygen sintering to obtain potassium ferrate composite material with excellent lithium ion conduction performance, electronic conduction performance and electrochemical performance.
[0138] Combining Examples 1, 7-8 and Table 1, it can be seen that by adjusting the amount of silicon source in steps (1) and (3), the first silicon oxide coating layer and the second silicon titanium oxide coating layer work together to improve the interface stability of the potassium ferrate electrode material. This allows the macroporous / mesoporous dual-channel structure in titanium dioxide to play its role in promoting the transport of lithium ions, thereby promoting the transport of lithium ions and electrons, and further improving the discharge median voltage of the potassium ferrate electrode material.
[0139] Based on Examples 1, 9-10 and Table 1, it can be seen that when the mass ratio of K2FeO4 to organic solvent is too high or too low, the lithium-ion conductivity, electronic conductivity, and discharge performance of the lithium battery using potassium ferrate electrode material decrease. This is because when the mass ratio of K2FeO4 to organic solvent is too high or too low, it will affect the mixing uniformity of the premix and reduce the thickness and uniformity of the coating layer formed on the surface of K2FeO4 during the later sintering process.
[0140] Based on Examples 1, 11-12 and Table 1, it can be seen that when the particle size of K2FeO4 is too large or too small, the lithium-ion conductivity and electronic conductivity of the K2FeO4 composite material decrease, the internal resistance of the lithium battery increases, and the cycle performance decreases. This is because when the particle size of K2FeO4 is too large or too small, it is not conducive to the formation of a uniform and dense first silicon oxide coating layer and a second silicon titanium oxide coating layer, which reduces the interfacial stability between the two coating layers and between the first silicon oxide coating layer and the potassium ferrate core.
[0141] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.
Claims
1. A method for preparing a K2FeO4 composite material, characterized in that, The preparation method includes the following steps: (1) K2FeO4, the first organic solvent and the first part of the silicon source are mixed, stirred and filtered to obtain the first premix; (2) In an oxygen-containing atmosphere, the first premixed material in step (1) is sintered to obtain SiO2 modified K2FeO4 composite material; (3) The titanium source, the SiO2 modified K2FeO4 composite material, the second organic solvent and the remaining silicon source are mixed, stirred and filtered to obtain the second premix; wherein, the mass ratio of the first part of the silicon source in step (1) to the remaining part of the silicon source in step (3) is 1:(0.5-1). (4) Under an oxygen-containing atmosphere, the second premix in step (3) is sintered to obtain a SiO2&TiO2 modified K2FeO4 composite material; In the preparation process, the mass ratio of silicon source, titanium source and K2FeO4 is (1.5-2):(0.5-1):
5.
2. The method for preparing a K2FeO4 composite material according to claim 1, characterized in that, In steps (1) and (3), both the first organic solvent and the second organic solvent include alcohol solvents; the stirring process in steps (1) and (3) is carried out in a protective gas.
3. The method for preparing a K2FeO4 composite material according to any one of claims 1 or 2, characterized in that, The oxygen-containing atmosphere mentioned in steps (2) and (4) is oxygen and / or ozone.
4. The method for preparing a K2FeO4 composite material according to claim 1, characterized in that, The D50 of K2FeO4 in step (1) is 10-15 μm.
5. The method for preparing a K2FeO4 composite material according to claim 1, characterized in that, The mass ratio of K2FeO4 to the first organic solvent in step (1) is 1:(4-10).
6. The method for preparing a K2FeO4 composite material according to claim 1, characterized in that, The silicon source includes at least one of tetraethyl silicate and tetrapropyl silicate.
7. The method for preparing a K2FeO4 composite material according to claim 1, characterized in that, The titanium source includes at least one of titanium sulfate, tetrabutyl titanate, isopropyl titanate, and tetraethyl titanate.
8. A K2FeO4 composite material, characterized in that, The K2FeO4 composite material is prepared by the method described in any one of claims 1-7, and the K2FeO4 composite material includes a potassium ferrate core, a first silicon oxide coating layer and a second silicon titanium oxide coating layer disposed on the surface of the potassium ferrate core.
9. The K2FeO4 composite material according to claim 8, characterized in that, The thickness of the first silicon oxide coating layer is 5-20 nm.
10. The K2FeO4 composite material according to claim 8, characterized in that, The thickness of the second silicon titanium oxide coating layer is 5-30 nm.
11. A battery, characterized in that, The battery comprises the K2FeO4 composite material as described in any one of claims 8-10.