Method for coating polyanion composite material with carbon dots in situ, polyanion composite material and application of polyanion composite material
By forming a carbon dot-coated polyanionic composite material through pre-sintering and high-temperature calcination, the problems of high cost, poor safety and poor electronic conductivity of secondary battery cathode materials are solved, achieving high efficiency and stability in electrochemical performance. It is suitable for electrochemical energy storage devices such as sodium-ion batteries, sodium metal batteries and lithium-ion batteries.
Patent Information
- Application Number
- CN202511720389.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-21
- Publication Date
- 2026-02-06
AI Technical Summary
Existing cathode materials for secondary batteries suffer from problems such as high cost, poor safety, poor electronic conductivity, and unsatisfactory electrochemical kinetic performance. In particular, polyanionic compounds are structurally unstable during charge and discharge, leading to safety risks and performance limitations.
By mixing alkali metal sources, transition metal sources, non-metal sources and carbon sources, and then pre-sintering and calcining at high temperature, a polyanionic composite material with in-situ carbon dot coating is formed, which improves the structural stability and electronic conductivity of the material.
It significantly improves the specific capacity, rate performance, and cycle stability of electrochemical devices, reduces manufacturing costs, and is suitable for industrial production.
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Figure CN121484029A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of positive electrode active material technology, and more specifically, to a method for in-situ coating of carbon dots with polyanionic composite materials, the polyanionic composite materials and their applications. Background Technology
[0002] With the continuous growth of energy utilization and demand, long-life, safe, inexpensive, and efficient renewable energy storage devices are crucial for creating the energy internet of the future. Among several energy storage technologies, rechargeable batteries have become one of the most competitive options for storing energy and powering devices and vehicles due to their low cost, sufficient safety, excellent conversion efficiency, and eco-friendliness. Typically, the positive electrode active material is the core component of a rechargeable battery: it not only provides the battery with a high redox potential but also plays a key role in determining the battery's reversible capacity, operating voltage, and cost (accounting for approximately 40% of the total battery cost).
[0003] In the mainstream cathode materials for secondary batteries, layered metal oxides, polyanionic compounds, and Prussian blue analogues (PBAs) are all commercially viable candidates due to their excellent metal ion storage behavior. However, the main problems with Prussian blue analogues are concentrated on cost and safety: low yield leads to high cost, and their thermally unstable structure poses safety risks. While layered transition metal oxides offer advantages such as high capacity and good electronic conductivity, complex phase and volume changes occur during charge and discharge, accompanied by continuous oxygen release, which poses safety risks. The importance of polyanionic compounds lies in their unique structure, high operating potential, and superior cycle and thermal stability—these characteristics collectively endow the materials with reliable safety. The introduction of inert polyanions, while bringing high redox potentials, also leads to poor electronic conductivity, resulting in poor electrochemical kinetic performance and large overpotentials, hindering the practical application and development of polyanionic cathode materials. Summary of the Invention
[0004] Based on the aforementioned technical problems in the existing technology, the present invention provides a method for in-situ coating of carbon dots with polyanionic composite materials. This method uses a simple pre-sintering process to polymerize small molecule carbon sources in situ to form carbon dots with uniform size and abundant functional groups. Then, high-temperature sintering is used to obtain a composite material with a uniform surface carbon layer. The obtained composite material is used as a positive electrode active material in electrochemical devices, which can effectively improve the specific capacity of electrochemical devices and enhance their cycle performance and rate performance.
[0005] To achieve the above objectives, the technical solution of the present invention is as follows:
[0006] A method for in-situ coating of carbon dots with polyanionic composite materials includes the following steps:
[0007] S1. Mix the alkali metal source, transition metal source, non-metal source and carbon source evenly to obtain the precursor;
[0008] S2. The precursor is pre-sintered at a temperature of 150-300°C and then calcined at a temperature of 500-1000°C in a non-oxidizing atmosphere to obtain a polyanionic composite material with carbon dots in situ coated.
[0009] The alkali metal source includes a sodium source or a lithium source; the transition metal source includes at least one of a vanadium source, an iron source, a manganese source, and a titanium source; and the non-metal source includes at least one of a phosphorus source, a fluorine source, a sulfur source, and a silicon source.
[0010] In some embodiments, the mass of the carbon source is 5-30% of the total mass of the alkali metal source, transition metal source, non-metal source and carbon source.
[0011] In some embodiments, the temperature is increased to the pre-sintering temperature at a rate of 1-10°C / min, and the pre-sintering time is 1-5 hours.
[0012] In some embodiments, after pre-sintering, the temperature is increased to the calcination temperature at a rate of 1-10℃ / min, and the calcination time is 5-12h.
[0013] In some embodiments, the non-oxidizing atmosphere is one of argon, nitrogen, helium, or a hydrogen-argon mixture.
[0014] In some embodiments, the mixing method in step S1 includes at least one of ball milling, spray drying, and sol-gel methods.
[0015] In some embodiments, the ball milling method specifically involves mixing raw materials (alkali metal source, transition metal source, non-metal source and carbon source), adding them to a ball milling device, with a ball-to-material ratio of 1:15-20, and ball milling at a rate of 400-600 r / min.
[0016] In some implementations, the ball milling time is 5-7 hours.
[0017] In some embodiments, the spray drying method specifically involves dispersing the raw materials (alkali metal source, transition metal source, non-metal source, and carbon source) in water, followed by spray drying, controlling the inlet temperature at 180-200℃, the outlet temperature at 90-110℃, and the fan speed at 1.35-1.5 m / s. 3 / min, the peristaltic pump speed is 400-800mL / h.
[0018] In some embodiments, the raw materials are added to water at a mass ratio of 50-100:1, stirred and dispersed evenly at a stirring rate of 300-800 r / min for 1-10 h and a stirring temperature of 10-30℃.
[0019] In some embodiments, the sol-gel method specifically involves adding raw materials (alkali metal source, transition metal source, non-metal source and carbon source) to water and stirring and mixing them evenly at a temperature of 50-100°C, wherein the mass ratio of raw materials to water is 20-80:1.
[0020] In some embodiments, the sol-gel method involves a stirring rate of 300-800 r / min and a stirring time of 1-10 h.
[0021] In some embodiments, the alkali metal source includes, but is not limited to, at least one of alkali metal oxides, chlorides, sulfates, nitrates, carbonates, acetates, citrates, and phosphates. Specifically, the sodium source includes, but is not limited to, at least one of sodium metavanadate, sodium hydrogen phosphate, sodium hydroxide, sodium acetate, sodium carbonate, sodium oxalate, sodium dihydrogen phosphate, and sodium citrate. The lithium source includes, but is not limited to, at least one of lithium acetate, lithium hydroxide, lithium citrate, and lithium oxide. The transition metal source includes, but is not limited to, at least one of transition metal oxides, chlorides, sulfates, nitrates, carbonates, acetates, citrates, and phosphates. Specifically, the vanadium source includes at least one of vanadium pentoxide, vanadium trioxide, vanadium dioxide, vanadium hydroxide, ammonium metavanadate, sodium divanadate, vanadium hexacarbonyl, vanadium peroxy acid, vanadium oxysulfate, orthovanadic acid, and sodium metavanadate; the iron source includes at least one of ferric nitrate, ferric oxalate, ferric acetate, and ferric sulfate; the nonmetallic source includes at least one of nonmetallic oxides or salt compounds, specifically, the phosphorus source includes at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, metaphosphoric acid, and ammonium phosphate; the carbon source includes at least one of citric acid, glucose, sucrose, ascorbic acid, oxalic acid, stearic acid, and cellulose.
[0022] The present invention also provides a polyanionic composite material obtained by the preparation method of any of the above embodiments.
[0023] Specifically, the polyanionic composite material includes, but is not limited to, lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium fluorinated iron sulfate, lithium iron silicate, sodium vanadium phosphate, sodium fluorinated vanadium phosphate, sodium vanadium manganese phosphate, sodium titanium manganese phosphate, sodium vanadium iron phosphate, sodium iron phosphate, sodium iron pyrophosphate, sodium iron pyrophosphate, sodium manganese pyrophosphate, sodium manganese iron pyrophosphate, sodium iron sulfate, etc.
[0024] The present invention also provides a positive electrode active material, wherein the positive electrode active material comprises the above-mentioned polyanionic composite material.
[0025] The present invention also provides a positive electrode, wherein the positive electrode comprises the above-described positive electrode active material.
[0026] The present invention also provides an electrochemical energy storage device, which includes, but is not limited to, sodium-ion batteries, sodium metal batteries, lithium-ion batteries, lithium metal batteries, zinc-ion batteries, zinc metal batteries, etc.
[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0028] The preparation method of this invention involves pre-sintering at a specific temperature followed by high-temperature calcination. This allows small-molecule carbon sources to fully polymerize, forming carbon dots with specific structures and creating a uniform coating layer in situ. This effectively improves the structural stability and electrochemical performance of the composite material. Specifically, by strictly controlling the pre-sintering temperature, the content of surface groups and the degree of carbonization on the carbon dots can be effectively regulated, thereby affecting the subsequent sintering coating process and controlling the size of the primary particles in the composite material. This is beneficial for the nucleation of the matrix material and restricts its growth, thus reducing the bulk ion transport path. When used as an active material in electrochemical energy storage devices, it can give the devices excellent specific capacity, rate performance, and cycle stability.
[0029] This invention utilizes a small-molecule carbon source to form carbon dots in situ at a specific temperature, which not only solves the problems of scarce and expensive carbon dot sources but also ensures uniform mixing of the carbon dots with the precursor. Furthermore, the in-situ carbon dot coating strategy of this invention is universally applicable to polyanionic cathode materials, exhibiting significant effects and remarkable versatility. This method substantially improves the electronic conductivity of the material, greatly enhancing the electrochemical performance of the battery.
[0030] The preparation method of this invention has a simple process flow, short preparation time, low raw material cost, and can achieve kilogram-level preparation, making it suitable for industrial production. Attached Figure Description
[0031] Figure 1 The CLSM pattern of the powder obtained by sintering the precursor prepared in Example 1 of the present invention at 250°C for 4 hours under argon atmosphere;
[0032] Figure 2 This is a SEM image of sodium iron pyrophosphate prepared in Example 1 of the present invention;
[0033] Figure 3 The XRD pattern of sodium iron pyrophosphate prepared in Example 1 of this invention;
[0034] Figure 4 The charge-discharge curve of sodium iron pyrophosphate prepared in Example 1 of the present invention at a rate of 0.5C is shown.
[0035] Figure 5This is a long-cycle diagram of sodium iron pyrophosphate prepared in Example 1 of the present invention at a 20C rate.
[0036] Figure 6 The rate performance of sodium iron pyrophosphate prepared in Example 1 of this invention under different current density conditions is shown in the graph.
[0037] Figure 7 This is a SEM image of sodium vanadium phosphate prepared in Example 2 of the present invention;
[0038] Figure 8 The XRD pattern of sodium vanadium phosphate prepared in Example 2 of this invention;
[0039] Figure 9 The charge-discharge curve of sodium vanadium phosphate prepared in Example 2 of the present invention at a rate of 0.5C is shown.
[0040] Figure 10 This is a long-cycle diagram of sodium vanadium phosphate prepared in Example 2 of the present invention at a 50C rate.
[0041] Figure 11 The rate performance of sodium vanadium phosphate prepared in Example 2 of this invention under different current density conditions is shown in the graph.
[0042] Figure 12 The XRD pattern of sodium vanadium fluorophosphate prepared in Example 3 of this invention;
[0043] Figure 13 The CLSM image of the powder obtained by sintering the precursor prepared in Example 4 of the present invention at 200°C for 4 hours under argon atmosphere;
[0044] Figure 14 Here is a SEM image of the lithium iron phosphate prepared in Example 4 of this invention;
[0045] Figure 15 The XRD pattern of lithium iron phosphate prepared in Example 4 of this invention;
[0046] Figure 16 The charge-discharge curve of lithium iron phosphate prepared in Example 4 of this invention at a rate of 0.5C is shown.
[0047] Figure 17 The rate performance of lithium iron phosphate prepared in Example 4 of this invention under different current density conditions is shown in the graph.
[0048] Figure 18 The rate performance of sodium iron pyrophosphate prepared in Comparative Example 1 of this invention under different current density conditions is shown in the graph.
[0049] Figure 19 The graph shows the rate performance of sodium vanadium phosphate prepared in Comparative Example 2 of this invention under different current density conditions. Detailed Implementation
[0050] Numerous specific details are set forth in the following description to provide a full understanding of the invention. However, the invention can be practiced in many other ways different from those described herein, and similar modifications can be made by those skilled in the art without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.
[0051] 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.
[0052] Example 1
[0053] The carbon source used in this example is citric acid, and the synthesized system is a sodium iron pyrophosphate composite material. The synthesis is performed using a spray drying method and includes the following steps:
[0054] S1. Citric acid, ferric nitrate nonahydrate, and sodium dihydrogen phosphate dihydrate are dissolved in deionized water in a molar ratio of 3:3:4. The mass ratio of deionized water to the total mass of citric acid, ferric nitrate nonahydrate, and sodium dihydrogen phosphate dihydrate is 1:60. The mixture is stirred for 1 hour to obtain a clear precursor solution.
[0055] S2. The obtained precursor solution is spray-dried. During the spray drying process, the inlet temperature is controlled at 180℃, the outlet temperature at 100℃, and the fan speed at 1.5m. 3 The peristaltic pump was set at a speed of 400 ml / h to obtain precursor powder.
[0056] S3. The precursor powder obtained in step S2 is transferred into a tube furnace and pre-calcined at 250°C for 3 hours at a rate of 5°C / min under an argon atmosphere, and then calcined at 550°C for 10 hours at a rate of 5°C / min. After calcination, it is naturally cooled to room temperature to obtain a high-ratio performance sodium iron pyrophosphate phosphate composite material coated with citric acid-derived carbon dots (named: NFPP@CACDs250).
[0057] The pre-calcined material was subjected to CLSM testing, and the results are as follows: Figure 1 As shown;
[0058] The obtained sodium iron pyrophosphate composite material was subjected to SEM and XRD tests, and the test results are as follows: Figure 2 and Figure 3 As shown.
[0059] The obtained NFPP@CACDs250 was subjected to relevant electrochemical performance tests, and the specific methods are as follows:
[0060] Battery Assembly: Weigh 210 mg of the NFPP@CACDs obtained in this example, add 60 mg of superconducting carbon black (SP), 30 mg of polyvinylidene fluoride (PVDF), and 1.2 mL of N-methylpyrrolidone (NMP), stir to form a slurry, mix evenly, and coat it onto carbon-coated aluminum foil to form a positive electrode. In a vacuum glove box, use a sodium metal sheet as the negative electrode, Whatman GF / D as the separator, and 1 mol / L NaClO4 / DMC:EC:EMC=1:1:1+FEC(5%) as the electrolyte to assemble a CR2016 coin cell. Test its electrochemical performance. The test results are as follows: Figures 4-6 As shown
[0061] Figure 4 This is a charge-discharge curve of a half-cell fabricated using NFPP@CACDs250 at a 0.5C rate. Figure 4 The composite material prepared in this embodiment, when used as the positive electrode active material, exhibits a "slope-plateau" charge-discharge characteristic during charge-discharge, with a discharge specific capacity of 103.6 mAh / g.
[0062] Figure 5 In the study, the NFPP@CACDs250 half-cell exhibited a discharge specific capacity of 83.8 mAh / g and a retention rate of 99.7% after 5000 cycles at a current rate of 20 C, with almost no capacity decay.
[0063] like Figure 6 As shown, the discharge specific capacities of NFPP@CACDs250 at different current rates of 0.5 C, 1 C, 2 C, 5 C, 10 C, 20 C, and 50 C are 103.6 mAh / g, 100.7 mAh / g, 97.8 mAh / g, 93.3 mAh / g, 89.5 mAh / g, 85.3 mAh / g, and 79.4 mAh / g, respectively. This indicates that during the low-temperature pre-calcination process at 250℃, citric acid fully polymerizes to form carbon dots, which are then coated onto the material surface during the subsequent high-temperature calcination process, resulting in the material exhibiting superior rate performance.
[0064] Example 2
[0065] The carbon source used in this example is citric acid, and the synthesis system is a sodium vanadium phosphate composite material. The synthesis was performed using a ball milling method, and specifically includes the following steps:
[0066] S1: 2 mmol vanadium pentoxide, 3 mmol sodium carbonate, 6 mmol ammonium dihydrogen phosphate and 600 mg citric acid were placed in an agate ball mill jar and ball milled at 500 rpm for 6 hours at a ball-to-material ratio of 15:1, with the ball mill rotation direction changed every 30 minutes to obtain precursor powder.
[0067] S2 The precursor powder obtained in step S1 is transferred into a tube furnace and pre-calcined at 250°C for 4 hours at a rate of 5°C / min under an argon atmosphere, and then calcined at 900°C for 8 hours at a rate of 5°C / min. After calcination, it is naturally cooled to room temperature to obtain a high-ratio performance sodium vanadium phosphate composite material coated with citric acid-derived carbon dots (named: NVP@CACDs).
[0068] The obtained high-ratio sodium vanadium phosphate composite material was subjected to SEM and XRD tests, and the test results are as follows: Figure 7 and Figure 8 As shown.
[0069] The obtained NVP@CACDs250 was subjected to relevant electrochemical performance tests, and the specific methods are as follows:
[0070] Battery Assembly: Weigh 210 mg of NVP@CACDs250 obtained in this example, add 60 mg of conductive superconducting carbon black (SP), 30 mg of polyvinylidene fluoride (PVDF), and 1.2 mL of N-methylpyrrolidone (NMP), stir to form a slurry, mix evenly, and coat it onto carbon-coated aluminum foil to form a positive electrode. In a vacuum glove box, use a sodium metal sheet as the negative electrode, Whatman GF / D as the separator, and 1 mol / L NaClO4 / PC+FEC (5%) as the electrolyte to assemble a CR2016 coin cell. Test its electrochemical performance. The test results are as follows: Figures 9-11 As shown.
[0071] Figure 9 This is a charge-discharge curve of a half-cell fabricated using NVP@CACDs250 at a 0.5 C rate, as shown below. Figure 9 The composite material prepared in this embodiment, when used as the positive electrode active material, exhibits a voltage plateau of 3.4V and a discharge specific capacity of 113.8 mAh / g during charge and discharge.
[0072] Figure 10 In the study, the NVP@CACDs250 half-cell exhibited a discharge specific capacity of 81.1 mAh / g and a capacity retention rate of 94.0% after 5000 cycles at a 50 C current rate, demonstrating a high capacity retention rate.
[0073] like Figure 11As shown, the discharge specific capacity of NVP@CACDs250 at different current rates of 0.5 C, 1 C, 2 C, 5 C, 10 C, 20 C, and 50 C are 113.8 mAh / g, 112.7 mAh / g, 111.8 mAh / g, 109.8 mAh / g, 106.1 mAh / g, 101.17 mAh / g, and 86.3 mAh / g, respectively. This indicates that during the low-temperature pre-calcination process at 250℃, citric acid fully polymerizes to form carbon dots, which are then coated onto the material surface during the subsequent high-temperature calcination process, resulting in the material exhibiting superior rate performance.
[0074] Example 3
[0075] The carbon source used in this example is citric acid, and the synthesis system is sodium vanadium fluorophosphate composite material. It is synthesized using the sol-gel method, and specifically includes the following steps;
[0076] S1. Place 15 mmol sodium fluoride, 10 mmol ammonium metavanadate, 10 mmol ammonium dihydrogen phosphate and 1 g citric acid into a 100 ml beaker, add 50 ml deionized water, stir at 400 rpm for 12 h in an oil bath at 80 °C, and dry the resulting wet gel in a vacuum drying oven at 80 °C for 10 h to obtain the precursor powder.
[0077] S2 The precursor powder obtained in step S1 is transferred into a tube furnace and pre-calcined at 250°C for 4 hours at a rate of 5°C / min under an argon atmosphere, and then calcined at 650°C for 8 hours at a rate of 5°C / min. After calcination, it is naturally cooled to room temperature to obtain a high-ratio performance sodium vanadium fluorophosphate composite material with citric acid-derived carbon dots and carbon coating (named: NVPF@CACDs).
[0078] The obtained high-ratio sodium vanadium fluorophosphate composite material was subjected to XRD testing, and the test results are as follows: Figure 12 As shown.
[0079] Example 4
[0080] The carbon source used in this example is glucose, and the synthesized system is a lithium iron phosphate composite material. The synthesis was performed using a ball milling method, and specifically included the following steps:
[0081] S1. Place 5 mmol of ferric phosphate, 2.5 mmol of lithium carbonate and 300 mg of glucose into an agate ball mill jar, and ball mill at 500 rpm for 6 hours with a bead-to-material ratio of 15:1. During the process, change the direction of the ball mill rotation every 30 minutes to obtain the precursor powder.
[0082] S2. The precursor powder obtained in step S1 is transferred into a tube furnace and pre-calcined at 200°C for 4 hours at a rate of 5°C / min under an argon atmosphere, and then calcined at 700°C for 10 hours at a rate of 5°C / min. After calcination, it is naturally cooled to room temperature to obtain a high-rate performance lithium iron phosphate composite material (named: LFP@GluCDs200) with glucose-derived carbon dots carbon coating.
[0083] The pre-calcined material was subjected to CLSM testing, and the results are as follows: Figure 13 As shown;
[0084] The obtained high-rate lithium iron phosphate composite material was characterized by SEM and XRD, and the results are as follows: Figure 14 and 15 As shown.
[0085] The obtained LFP@GluCDs200 was subjected to relevant electrochemical performance tests, and the specific methods are as follows:
[0086] Battery Assembly: Weigh 320 mg of NVP@CACDs250 obtained in this example, add 40 mg of superconducting carbon black (SP), 40 mg of polyvinylidene fluoride (PVDF), and 1.5 mL of N-methylpyrrolidone (NMP), stir to form a slurry, mix evenly, and coat it onto carbon-coated aluminum foil to form a positive electrode. In an argon-filled glove box, use a lithium metal sheet as the negative electrode, PP as the separator, and 1 mol / L LiPF6 / DEC:DMC:EC=1:1:1+FEC(5%) as the electrolyte to assemble a CR2016 coin cell. Test its electrochemical performance. The test results are as follows: Figures 16-17 As shown.
[0087] like Figure 16 As shown, the charge-discharge curves of the half-cell fabricated by LFP@GluCDs200 at a 0.5 C rate show a voltage plateau of 3.4V and a discharge specific capacity of 146.31 mAh / g.
[0088] like Figure 17 As shown, LFP@GluCDs200 exhibits discharge specific capacities of 138.72 mAh / g, 128.62 mAh / g, 118.24 mAh / g, 99.47 mAh / g, and 86.84 mAh / g at different current rates of 1 C, 2 C, 5 C, 10 C, and 20 C, respectively. This indicates that during the low-temperature pre-sintering process at 200℃, glucose fully polymerizes to form carbon dots, which are then coated onto the material surface during the subsequent high-temperature calcination process, resulting in excellent rate performance.
[0089] Comparative Example 1
[0090] The method used in this comparative example is the same as that in Example 1, except that there is no pre-sintering process or the pre-sintering temperature is different. The specific steps are as follows:
[0091] S1. Citric acid, ferric nitrate nonahydrate, and sodium dihydrogen phosphate dihydrate are dissolved in deionized water in a molar ratio of 3:3:4. The mass ratio of deionized water to the total mass of citric acid, ferric nitrate nonahydrate, and sodium dihydrogen phosphate dihydrate is 1:60. The mixture is stirred for 1 hour to obtain a clear precursor solution.
[0092] S2. Spray dry the obtained precursor solution with an inlet temperature of 180℃, an outlet temperature of 100℃, a fan speed of 100%, and a peristaltic pump speed of 20% to obtain precursor powder.
[0093] S3. The precursor powder obtained in step S2 is transferred into a tube furnace and pre-calcined at 350°C for 3 hours (or without pre-calcination) at a rate of 5°C / min under an argon atmosphere. Then, it is calcined at 550°C for 10 hours at a rate of 5°C / min. After calcination, it is naturally cooled to room temperature to obtain a high-ratio performance sodium iron pyrophosphate phosphate composite material coated with citric acid-derived carbon dots (named NFPP@CACDs350 and NFPP@CA, respectively).
[0094] like Figure 18 As shown, the discharge specific capacities of NFPP@CA without pre-sintering at different current rates of 0.5 C, 1 C, 2 C, 5 C, 10 C, 20 C, and 50 C are 96.3 mAh / g, 94.5 mAh / g, 91.7 mAh / g, 85.6 mAh / g, 78.1 mAh / g, 66.4 mAh / g, and 43.4 mAh / g, respectively. In contrast, the discharge specific capacities of NFPP@CACDs350 are 97.9 mAh / g, 94.8 mAh / g, 91.4 mAh / g, 86.4 mAh / g, 82.4 mAh / g, 78.1 mAh / g, and 72.2 mAh / g, respectively. This is because after pre-sintering, citric acid undergoes a violent carbonization reaction at a pre-sintering temperature of 350°C, destroying the carbon dot structure of the citric acid.
[0095] Comparative Example 2
[0096] The method used in this comparative example is the same as that in Example 2, except that there is no pre-sintering process or the pre-sintering temperature is different. The specific steps are as follows:
[0097] S1: 2 mmol vanadium pentoxide, 3 mmol sodium carbonate, 6 mmol ammonium dihydrogen phosphate and 600 mg citric acid were placed in an agate ball mill jar and ball milled at 500 rpm for 6 hours at a bead-to-material ratio of 15:1, with the ball mill rotation direction changed every 30 minutes during the process to obtain the precursor.
[0098] S2 The precursor obtained in step S1 is transferred into a tube furnace and pre-calcined at 350°C for 4 hours (or without pre-calcination) at a rate of 5°C / min under an argon atmosphere, and then calcined at 900°C for 8 hours at a rate of 5°C / min. After calcination, it is naturally cooled to room temperature to obtain high-ratio performance sodium vanadium phosphate composite materials with citric acid-derived carbon dots and carbon coating (named: NVP@CACDs350 and NVP@CA, respectively).
[0099] Electrochemical performance tests were performed on the NVP@CACDs350 and NVP@CA obtained in this comparative example. The test results are as follows: Figure 19 As shown.
[0100] like Figure 19 As shown, the discharge specific capacities of NVP@CA at different current rates of 0.5 C, 1 C, 2 C, 5 C, 10 C, 20 C, and 50 C are 110.5 mAh / g, 107.7 mAh / g, 104.6 mAh / g, 97.3 mAh / g, 87.69 mAh / g, 75.84 mAh / g, and 58.46 mAh / g, respectively. In contrast, the discharge specific capacities of NVP@CACDs350 are 112.1 mAh / g, 109.8 mAh / g, 107.6 mAh / g, 102.7 mAh / g, 96.8 mAh / g, 88.3 mAh / g, and 74.1 mAh / g, respectively. Clearly, the high-rate performance of sodium vanadium phosphate synthesized using citric acid as a carbon source without pre-sintering is far inferior to that of sodium vanadium phosphate composites synthesized after pre-sintering at lower temperatures.
[0101] Comparative Example 3
[0102] The method used in this comparative example is the same as that in Example 3, except that there is no pre-sintering process or the pre-sintering temperature is different. The specific steps are as follows:
[0103] S1. Place 5 mmol of ferric phosphate, 2.5 mmol of lithium carbonate and 300 mg of glucose into an agate ball mill jar, and ball mill at 500 rpm for 6 hours with a bead-to-material ratio of 15:1. During the process, change the direction of the ball mill rotation every 30 minutes to obtain the precursor.
[0104] S2. The precursor obtained in step S1 is transferred into a tube furnace and pre-calcined at 350°C for 4 hours (or without pre-calcination) at a rate of 5°C / min under an argon atmosphere. Then, it is calcined at 700°C for 10 hours at a rate of 5°C / min. After calcination, it is naturally cooled to room temperature to obtain a high-rate performance lithium iron phosphate composite material with glucose-derived carbon dots carbon coating (named: LFP@GluCDs350, LFP@Glu).
[0105] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0106] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the 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 modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.
Claims
1. A method for in-situ coating of carbon dots with polyanionic composite materials, characterized in that, Includes the following steps: S1. Mix the alkali metal source, transition metal source, non-metal source and carbon source evenly to obtain the precursor; S2. The precursor is pre-sintered at a temperature of 150-300°C and then calcined at a temperature of 500-1000°C in a non-oxidizing atmosphere to obtain a polyanionic composite material with carbon dots in situ coated. The alkali metal source includes a sodium source or a lithium source; the transition metal source includes at least one of a vanadium source, an iron source, a manganese source, and a titanium source; and the non-metal source includes at least one of a phosphorus source, a fluorine source, a sulfur source, and a silicon source.
2. The method for in-situ carbon dot coating of polyanionic composite materials according to claim 1, characterized in that, In step S1, the mixing method includes at least one of ball milling, spray drying, and sol-gel method.
3. The method for in-situ carbon dot coating of polyanionic composite materials according to claim 2, characterized in that, The ball milling method specifically involves mixing the raw materials and adding them into a ball milling device at a ball-to-material ratio of 1:15-20, and milling at a rate of 400-600 r / min.
4. The method for in-situ carbon dot coating of polyanionic composite materials according to claim 2, characterized in that, The spray drying method specifically involves dispersing the raw material in water, followed by spray drying, controlling the inlet temperature at 180-200℃, the outlet temperature at 90-110℃, and the fan speed at 1.35-1.5m / s. 3 / min, the peristaltic pump speed is 400-800mL / h.
5. The method for in-situ carbon dot coating of polyanionic composite materials according to claim 2, characterized in that, The sol-gel method specifically involves adding the raw material to water and stirring and mixing it evenly at a temperature of 50-100℃, wherein the mass ratio of the raw material to water is 20-80:
1.
6. The polyanionic composite material obtained by the method according to any one of claims 1-5.
7. The polyanionic composite material according to claim 6, characterized in that, The polyanionic composite material includes lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium fluorinated iron sulfate, lithium iron silicate, sodium vanadium phosphate, sodium fluorinated vanadium phosphate, sodium vanadium manganese phosphate, sodium titanium manganese phosphate, sodium vanadium iron phosphate, sodium iron phosphate, sodium iron pyrophosphate, sodium iron pyrophosphate, sodium manganese pyrophosphate, sodium manganese iron pyrophosphate, and sodium iron sulfate.
8. A positive electrode active material, characterized in that, Including the polyanionic composite material as described in claim 6 or 7.
9. A positive electrode, characterized in that, Includes the positive electrode active material as described in claim 8.
10. An electrochemical energy storage device, characterized in that, Includes the positive electrode as described in claim 9.