Iron(III) phosphate material, preparation method therefor, and use thereof

Abstract

The present invention belongs to the technical field of batteries. Disclosed are an iron(III) phosphate material, a preparation method therefor, and a use thereof. The iron(III) phosphate material comprises a carbon quantum dot core located internally and an iron(III) phosphate shell formed on the surface of the carbon quantum dot core, and the surface of the iron(III) phosphate shell is provided with a carbon coating layer formed from a carbon-containing dispersing agent. The iron(III) phosphate material is nanoscale iron(III) phosphate and has a uniform crystal size. The preparation method therefor comprises the following steps: mixing a first mixed solution containing a divalent iron salt and carbon quantum dots, a second mixed solution containing a phosphate and a dispersing agent, and an oxidizing agent to undergo a reaction to obtain iron(III) phosphate dihydrate; and annealing and calcining the iron(III) phosphate dihydrate. The iron(III) phosphate material can be further used for preparing a lithium iron phosphate positive electrode material and a battery.

Description

A kind of iron phosphate material and its preparation method and application Technical Field

[0001] The present disclosure relates to the field of battery technology, and in particular to an iron phosphate material and a preparation method and application thereof. Background Art

[0002] Currently, lithium battery cathode materials primarily include lithium cobalt oxide, lithium iron phosphate, lithium manganese oxide, and ternary materials. Compared to ternary cathode materials, lithium iron phosphate (LFP) cathode materials offer advantages such as improved safety, long cycle life, reduced pollution, and low cost, making them a key research focus. However, LFP cathode materials inherently exhibit poor electrical conductivity and a low lithium ion diffusion coefficient. Therefore, doping and coating processes are the primary development areas for LFP cathode materials.

[0003] Existing production processes for lithium iron phosphate cathode materials primarily include the ferrous oxalate process, the iron oxide red process, the fully wet process, and the iron phosphate process. These processes, when synthesizing the precursor for the lithium iron phosphate cathode material (i.e., iron phosphate), present drawbacks such as difficulty in process control, irregular iron phosphate particles, large particle size, and severe agglomeration. This, in turn, results in poor performance of the lithium iron phosphate produced using these processes as precursors.

[0004] In view of this, the present disclosure is proposed.

[0005] Summary of the Invention

[0006] The purpose of the present disclosure is to provide an iron phosphate material and a preparation method and application thereof, so as to solve or improve at least one of the above technical problems.

[0007] The present disclosure can be implemented as follows:

[0008] In a first aspect, the present disclosure provides an iron phosphate material comprising an internal carbon quantum dot core and an iron phosphate shell formed on the surface of the carbon quantum dot core, wherein the surface of the iron phosphate shell has a carbon coating layer formed by a carbon-containing dispersant.

[0009] In an optional embodiment, the iron phosphate material further has at least one of the following characteristics:

[0010] Feature 1: D of iron phosphate material 50 No more than 200nm;

[0011] Feature 2: D of carbon quantum dot core 50 10nm to 20nm;

[0012] Feature 3: The iron phosphate shell is formed in situ on the surface of the carbon quantum dot core;

[0013] Feature 4: The thickness of the carbon coating is 1-3nm;

[0014] Feature 5: The mass of the carbon coating layer does not exceed 5wt% of the iron phosphate material.

[0015] In an alternative embodiment, the D of the iron phosphate material 50 The thickness of the carbon coating layer is 20 nm to 200 nm; and / or the mass of the carbon coating layer is 1 wt% to 5 wt% of the iron phosphate material.

[0016] In a second aspect, the present disclosure provides a method for preparing an iron phosphate material according to any one of the aforementioned embodiments, comprising the following steps: mixing a first mixed solution, a second mixed solution, and an oxidant to react to obtain iron phosphate dihydrate; annealing and calcining the iron phosphate dihydrate to obtain an iron phosphate material;

[0017] The first mixed liquid includes divalent iron salt and carbon quantum dots; the second mixed liquid includes phosphate and carbon-containing dispersant.

[0018] In an optional embodiment, the preparation of carbon quantum dots includes: modifying citric acid with an organic amine in a solution environment to obtain a modified solution; heating the modified solution to crack the citric acid to obtain a carbon-containing solution; mixing the carbon-containing solution with an aqueous sodium hydroxide solution, separating the solid and the liquid, dialyzing the separated liquid phase, and drying the dialyzate obtained by dialysis.

[0019] In an optional embodiment, the mass ratio of citric acid to organic amine is 1:0.1-1:0.5.

[0020] In an optional embodiment, the mass fraction of citric acid in the modified solution is not less than 99.5%.

[0021] In an alternative embodiment, the organic amine includes at least one of ethanolamine, ethylenediamine, and polyethylenediamine.

[0022] In an optional embodiment, the heating temperature is 180° C.-280° C., and / or the heating time is 4 h-8 h.

[0023] In an optional embodiment, the concentration of the sodium hydroxide aqueous solution is 10 g / L-20 g / L, and the volume ratio of the carbonaceous solution to the sodium hydroxide aqueous solution is 1:1-1:2.

[0024] In an optional embodiment, the molecular weight cut-off of the dialysis bag used for dialysis is 500D-1500D.

[0025] In an optional embodiment, the drying temperature is -20°C to -60°C, and the drying time is 10 hours to 14 hours.

[0026] In an optional embodiment, the mass ratio of carbon quantum dots to divalent iron salt is 5:100 to 20:100.

[0027] In an alternative embodiment, the ferrous salt includes at least one of ferrous sulfate, ferrous nitrate and ferrous chloride.

[0028] In an optional embodiment, the molar ratio of the iron element in the ferrous salt to the phosphorus element in the phosphate is 1.1:1 to 1.5:1.

[0029] In an alternative embodiment, the phosphate includes at least one of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, and ammonium phosphate.

[0030] In an alternative embodiment, the carbonaceous dispersant comprises acrylic acid.

[0031] In an optional embodiment, the amount of carbon-containing dispersant used is 3 wt%-10 wt% of the divalent iron salt.

[0032] In an alternative embodiment, the oxidizing agent comprises hydrogen peroxide.

[0033] In an optional embodiment, the amount of the oxidant added is 1 to 1.2 times the amount of iron in the divalent iron salt on a molar basis.

[0034] In an optional embodiment, the reaction temperature is 100° C.-130° C.; and / or the reaction time is 2 h-6 h.

[0035] In an optional embodiment, the annealing calcination includes at least one of the following features:

[0036] Feature 1: The annealing temperature is 400℃-600℃;

[0037] Feature 2: Annealing and calcination time is 3h-8h;

[0038] Feature 3: Annealing and calcination are carried out under vacuum conditions.

[0039] In a third aspect, the present disclosure provides a lithium iron phosphate positive electrode material, the raw materials for preparing the lithium iron phosphate positive electrode material include the iron phosphate material of any one of the aforementioned embodiments.

[0040] In a fourth aspect, the present disclosure provides a battery comprising the lithium iron phosphate positive electrode material of the aforementioned embodiment.

[0041] The beneficial effects of the present disclosure include:

[0042] The iron phosphate material provided by the present disclosure includes a carbon quantum dot core located inside and an iron phosphate shell formed on the surface of the carbon quantum dot core, and the surface of the iron phosphate shell has a carbon coating. Among them, the carbon quantum dot core can play a role in increasing the formation rate of the iron phosphate shell and refining the particles, which is beneficial to controlling the particle size of the iron phosphate material. The carbon-containing dispersant can not only inhibit the agglomeration between the grains, but also the carbon coating formed therefrom can further limit the growth of the iron phosphate particles. By combining the carbon quantum dot core with the carbon-containing dispersant, nano-scale iron phosphate with regular morphology, uniform particles and small particle size can be obtained, and the iron phosphate material can be used as a precursor to prepare nano-scale lithium iron phosphate positive electrode materials. The preparation method of the above-mentioned iron phosphate material is simple, easy to operate, easy to control, and has good product stability, and is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0044] FIG1 is a SEM image of the iron phosphate material prepared in Example 1 of the present disclosure. DETAILED DESCRIPTION

[0045] To make the purpose, technical solutions, and advantages of the embodiments of the present disclosure more clear, the technical solutions in the embodiments of the present disclosure are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer were followed. Reagents or instruments used where the manufacturer is not specified are conventional products that can be purchased commercially.

[0046] The iron phosphate material provided by the present disclosure and its preparation method and application are described in detail below.

[0047] The present disclosure provides an iron phosphate material, which includes a carbon quantum dot core located inside and an iron phosphate shell formed on the surface of the carbon quantum dot core, wherein the surface of the iron phosphate shell has a carbon coating layer formed by a carbon-containing dispersant.

[0048] The carbon quantum dot cores described above can increase the formation rate of the iron phosphate shell and refine the particles, which helps control the particle size of the iron phosphate material, thereby obtaining nano-iron phosphate with regular morphology, uniform particles, and small particle size. This nano-iron phosphate can be used as a precursor to prepare nano-scale lithium iron phosphate cathode materials. It should be noted that nano-scale lithium iron phosphate cathode materials can shorten the transmission distance of electrons and ions, have the ability to charge and discharge at high currents, and have excellent electrochemical performance.

[0049] The carbon-containing dispersant can not only reduce the surface energy of nano-crystals, change the thickness of the double layer and increase the steric effect between grains, thereby inhibiting the agglomeration of nano-crystals; but also the carbon coating formed by it is coated on the surface of ferric phosphate dihydrate, which can further limit the growth of ferric phosphate dihydrate particles.

[0050] In the present disclosure, D of the iron phosphate material 50 No more than 200nm, such as 200nm, 180nm, 150nm, 120nm, 100nm, 80nm, 50nm, 20nm or 10nm, etc., or any other value within the range of no more than 200nm. In some optional embodiments, the D of the iron phosphate material 50 It can be 20 nm to 200 nm, for example, 120 nm to 185 nm.

[0051] In the present disclosure, the carbon quantum dot core is nanometer-sized. In some embodiments, the D 50 It can be 10 nm to 20 nm, such as 10 nm, 12 nm, 15 nm, 18 nm or 20 nm, or any other value within the range of 10 nm to 20 nm.

[0052] The nanoscale carbon quantum dots, as ultrafine spherical particles, act as structural directing agents for shell growth during the ferric phosphate synthesis process, enabling in-situ growth of ferric phosphate on the nanoscale carbon quantum dots. Furthermore, as the ferric phosphate grows on the surface of the nanoscale carbon quantum dot core, it also nucleates. The nanoscale carbon quantum dots help increase the nucleation rate of the ferric phosphate and significantly refine the grains, thereby facilitating the production of nanoscale ferric phosphate materials.

[0053] It should be noted that if the D of the carbon quantum dot core 50 If the D of the carbon quantum dot core is too small, it is easy to agglomerate in the solution, which is not conducive to controlling the particle size of the iron phosphate material. 50 If the particle size is too large, the overall particle size of the iron phosphate material will be too large.

[0054] In the present disclosure, the thickness of the carbon coating layer may be 1-3 nm, such as 1 nm, 1.5 nm, 2 nm, 2.5 nm or 3 nm.

[0055] The mass of the carbon coating layer does not exceed 5wt% of the ferric phosphate material, and may be, for example, 5wt%, 4wt%, 3wt%, 2wt%, 1wt% or 0.5wt% of the ferric phosphate material, or any other value within the range of not more than 5wt%. In some optional embodiments, the mass of the carbon coating layer is 1wt%-5wt% of the ferric phosphate material.

[0056] Accordingly, the present disclosure also provides a method for preparing the above-mentioned iron phosphate material, which may include the following steps: mixing the first mixed liquid, the second mixed liquid and the oxidant to react to obtain iron phosphate dihydrate; annealing and calcining the iron phosphate dihydrate to obtain the iron phosphate material;

[0057] The first mixed liquid includes divalent iron salt and carbon quantum dots; the second mixed liquid includes phosphate and carbon-containing dispersant.

[0058] For reference, the preparation of carbon quantum dots may include: modifying citric acid with an organic amine in a solution environment to obtain a modified solution; heating the modified solution to decompose the citric acid to obtain a carbon-containing solution; mixing the carbon-containing solution with an aqueous sodium hydroxide solution, separating the solid and the liquid, dialyzing the separated liquid phase, and drying the dialyzate obtained by dialysis.

[0059] The solution environment can be a water environment. The modification of citric acid by the organic amine is mainly to increase the hydrophilicity of citric acid by providing a nitrogen source, thereby facilitating a more uniform dispersion of particles in water.

[0060] For example, the mass ratio of citric acid to the organic amine can be 1:0.1-1:0.5, such as 1:0.1, 1:0.15, 1:0.2, 1:0.25, 1:0.3, 1:0.35, 1:0.4, 1:0.45, or 1:0.5, or any other value within the range of 1:0.1-1:0.5. The organic amine can, for example but not by way of limitation, include at least one of ethanolamine, ethylenediamine, and polyethylenediamine. In some embodiments, the mass fraction of citric acid in the modified solution is no less than 99.5%.

[0061] In the present disclosure, the temperature for heating the modified solution may be 180° C. to 280° C., such as 180° C., 200° C., 220° C., 250° C., or 280° C., or any other value within the range of 180° C. to 280° C. The heating time may be 4 h to 8 h, such as 4 h, 5 h, 6 h, 7 h, or 8 h, or any other value within the range of 4 h to 8 h.

[0062] Citric acid can be decomposed by heating. The present invention modifies the solution according to the above temperature and time, which is beneficial to controlling the size of the carbon quantum dots generated by decomposition.

[0063] If the heating temperature is lower than 180°C, too few carbon quantum dots will be formed, resulting in a low yield. If the heating temperature is higher than 280°C, the carbon quantum dots will be too large. If the heating time is shorter than 4 hours, the carbon quantum dots will be poorly dispersed and have a low yield. If the heating time is longer than 8 hours, the carbon quantum dots will be unevenly distributed.

[0064] Continuing from the above, the surface of the nanocarbon quantum dots produced by high-temperature pyrolysis of citric acid contains a large number of oxygen-containing functional groups, which can effectively adsorb iron ions and increase the synthesis rate of iron phosphate. The nanocarbon quantum dots produced by pyrolysis under these conditions serve as ultrafine spherical particles and act as structural directing agents for nucleation and growth during the synthesis of iron phosphate. This allows the in situ nucleation and growth of iron phosphate on the nanocarbon quantum dots, increasing the nucleation rate and significantly refining the grains, which is conducive to the production of nanoscale iron phosphate.

[0065] For reference, the concentration of the sodium hydroxide aqueous solution used for mixing with the carbon-containing solution can be 10 g / L to 20 g / L, such as 10 g / L, 12 g / L, 15 g / L, 18 g / L, or 20 g / L, or any other value within the range of 10 g / L to 20 g / L. The volume ratio of the carbon-containing solution to the sodium hydroxide aqueous solution can be 1:1 to 1:2, such as 1:1, 1:1.5, or 1:2, or any other value within the range of 1:1 to 1:2.

[0066] The function of the sodium hydroxide aqueous solution is to further remove impurities and purify the carbon quantum dot solution.

[0067] For example, the solid-liquid separation of the mixed solution obtained by mixing the carbonaceous solution with the sodium hydroxide aqueous solution can be performed by centrifugation. The centrifugal speed can be 7000 r / min-9000 r / min, such as 7000 r / min, 8000 r / min, or 9000 r / min.

[0068] After centrifugation, the supernatant is collected and transferred to a dialysis bag for dialysis. The molecular weight cut-off of the dialysis bag used for dialysis can be 500D-1500D, such as 500D, 800D, 1000D, 1200D or 1500D, and the dialysate (i.e., an aqueous solution of carbon quantum dots) is obtained by dialysis.

[0069] For reference, the temperature for drying the dialysate may be -20°C to -60°C, such as -20°C, -40°C or -60°C, and the drying time may be 10 hours to 14 hours, such as 10 hours, 12 hours or 14 hours. Exemplarily, the drying method may be freeze drying.

[0070] In the present disclosure, the mass ratio of carbon quantum dots to divalent iron salt can be 5:100 to 20:100, such as 5:100, 8:100, 10:100, 12:100, 15:100, 18:100 or 20:100, or any other value within the range of 5:100 to 20:100.

[0071] The divalent iron salt may illustratively but not limitatively include at least one of ferrous sulfate, ferrous nitrate and ferrous chloride.

[0072] It should be noted that the mixing order of the ferrous salt and the carbon quantum dots is not limited. In some embodiments, the first mixed solution can be formed by adding carbon quantum dots to the ferrous salt solution.

[0073] The molar ratio of the iron element in the ferrous salt to the phosphorus element in the phosphate can be 1.1:1 to 1.5:1, such as 1.1:1, 1.2:1, 1.3:1, 1.4:1 or 1.5:1, or any other value within the range of 1.1:1 to 1.5:1.

[0074] The phosphate may illustratively but not limitatively include at least one of diammonium hydrogen phosphate, ammonium dihydrogen phosphate and ammonium phosphate.

[0075] In the present disclosure, the carbon-containing dispersant may include acrylic acid. By adding acrylic acid as a dispersant during the synthesis of iron phosphate, it can not only reduce the surface energy of nano-crystals, change the thickness of the double electric layer and increase the steric effect between grains, thereby inhibiting the agglomeration of nano-crystals. At the same time, Fe 2+ Fe formed after oxidation by oxidants 3+ It can also serve as a catalyst to promote the oxidative polymerization of acrylic acid on the surface of ferric phosphate dihydrate particles to generate polyacrylic acid and coat the surface of ferric phosphate dihydrate, further limiting the growth of ferric phosphate dihydrate particles.

[0076] For reference, the amount of carbon-containing dispersant used can be 3wt%-10wt% of the divalent iron salt, such as 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt% or 10wt%, etc., or it can be any other value within the range of 3wt%-10wt%.

[0077] It should be noted that the order of mixing the phosphate and the carbonaceous dispersant is not limited. In some embodiments, the second mixed solution can be formed by adding the carbonaceous dispersant to the phosphate solution.

[0078] The oxidizing agent may be, for example, hydrogen peroxide, or oxygen.

[0079] For reference, the amount of the oxidant added can be 1-1.2 times, such as 1 time, 1.1 times or 1.2 times, of the iron element in the divalent iron salt in terms of molar amount.

[0080] It should be noted that the mixing order of the first mixed liquid, the second mixed liquid and the oxidant is not limited. In some embodiments, the second mixed liquid can be added to the first mixed liquid and the oxidant can be added.

[0081] In the present disclosure, the reaction temperature of the first mixed liquid, the second mixed liquid, and the oxidant can be 100° C. to 130° C., such as 100° C., 105° C., 110° C., 115° C., 120° C., 125° C., or 130° C., or any other value within the range of 100° C. to 130° C. The reaction time can be 2 h to 6 h, such as 2 h, 3 h, 4 h, 5 h, or 6 h, or any other value within the range of 2 h to 6 h.

[0082] Through the above reaction, the oxidant converts Fe in the divalent iron salt into 2+ Oxidized to Fe 3+ and reacts with phosphate to generate ferric phosphate dihydrate in situ on the surface of carbon quantum dots. The use of dispersant can avoid agglomeration.

[0083] If the reaction temperature is below 100°C, the reaction rate is too low, causing the iron content of the resulting ferric phosphate dihydrate to deviate from the theoretical value. If the reaction temperature is above 130°C, the trivalent iron ions will hydrolyze to form ferric hydroxide, reducing the purity of the resulting ferric phosphate dihydrate. If the reaction time is shorter than 2 hours, the reaction will be incomplete, and some residual raw materials will not participate in the reaction, resulting in insufficient purity of the ferric phosphate dihydrate. If the reaction time is longer than 6 hours, the ferric phosphate dihydrate grains will grow abnormally, and side reactions may easily occur, resulting in reduced purity of the ferric phosphate dihydrate.

[0084] In the present disclosure, the annealing temperature can be 400° C. to 600° C., such as 400° C., 450° C., 500° C., 550° C., or 600° C., or any other value within the range of 400° C. to 600° C. The annealing time can be 3 h to 8 h, such as 3 h, 4 h, 5 h, 6 h, 7 h, or 8 h, or any other value within the range of 3 h to 8 h. The annealing can be performed under vacuum conditions.

[0085] Taking polypropylene as an example of a carbon-containing dispersant, polyacrylic acid is carbonized through annealing and calcination to form a carbon coating layer.

[0086] If the annealing temperature is lower than 400°C, the carbonization reaction is not complete, resulting in reduced purity of the ferric phosphate dihydrate. If the annealing temperature is higher than 600°C, the formed ferric phosphate dihydrate crystals have more defects and reduced stability. If the annealing time is shorter than 3 hours, the crystallinity of the ferric phosphate dihydrate is reduced and the carbon layer formed is uneven. If the annealing time is longer than 8 hours, it is easy to cause the formation of impurities.

[0087] Continuing from the above, the present disclosure increases the nucleation rate of ferric phosphate dihydrate by adding nanometer-scale carbon quantum dots, and combines this with an acrylic acid autopolymerization reaction to limit grain growth. The combination of these two methods can make the nucleation rate of the grains during the synthesis of ferric phosphate dihydrate greater than the growth rate, thereby achieving effective control of particle size, facilitating the generation of nanometer-scale ferric phosphate dihydrate, and the resulting crystals are more uniform. The organic polymer on the surface of the ferric phosphate dihydrate particles, after annealing and carbonization, uniformly carbon-coates the ferric phosphate dihydrate particles, facilitating the preparation of nanometer-scale ferric phosphate materials.

[0088] In addition, the present disclosure also provides a lithium iron phosphate positive electrode material, the raw materials for preparing the lithium iron phosphate material include the above-mentioned iron phosphate material.

[0089] In some embodiments, the lithium iron phosphate cathode material provided herein is nanoscale, which can shorten the transmission distance of electrons and ions, enable high current charge and discharge capabilities, and provide excellent electrochemical performance. For example, the lithium iron phosphate cathode material can have a large discharge capacity, excellent rate charge and discharge performance, and good cycle stability.

[0090] Furthermore, the present disclosure also provides a battery containing the above-mentioned lithium iron phosphate positive electrode material, which is conducive to having better electrochemical performance.

[0091] The features and performance of the present disclosure are further described in detail below with reference to the embodiments.

[0092] Example 1

[0093] This embodiment provides an iron phosphate material, which is a carbon-coated nano-iron phosphate, denoted as LiFePO4 / C composite material. The iron phosphate material includes a carbon quantum dot core located inside and an iron phosphate shell formed in situ on the surface of the carbon quantum dot core, and the surface of the iron phosphate shell has a carbon coating layer.

[0094] The preparation method of the iron phosphate material comprises:

[0095] S1: Dissolve citric acid and ethylenediamine in deionized water at a mass ratio of 1:0.2 to obtain a modified solution with a citric acid mass fraction of 99.5%. Heat the modified solution to 230° C. and react for 6 hours to obtain a carbon-containing solution.

[0096] S2: The carbon-containing solution of S1 was mixed with a sodium hydroxide solution with a concentration of 20 g / L in a volume ratio of 1:1.5. The mixed solution was centrifuged at 8000 r / min for 10 minutes, and the supernatant was collected. The supernatant was transferred to a dialysis bag with a molecular weight cutoff of 1000D and dialyzed for 12 hours to obtain a dialysate (aqueous solution of carbon quantum dots). The dialysate was collected and transferred to a freeze dryer and freeze-dried at -40°C for 12 hours to obtain nanocarbon quantum dots.

[0097] S3: Ferrous sulfate and ammonium dihydrogen phosphate were dissolved in deionized water at a Fe:P molar ratio of 1.2:1 to form a solution. Carbon nanoparticles (10% by weight of the ferrous sulfate) were added to the ferrous sulfate solution, and the mixture was mixed to obtain a first mixed solution. Acrylic acid (6% by weight of the ferrous sulfate) was added to the ammonium dihydrogen phosphate solution, and the mixture was mixed to obtain a second mixed solution.

[0098] S4: adding the second mixed solution to the first mixed solution and adding hydrogen peroxide in a molar amount that is 1.1 times the molar amount of iron, reacting at a temperature of 120° C. for 4 h, filtering, and washing to obtain ferric phosphate dihydrate.

[0099] S5: annealing and calcining the ferric phosphate dihydrate at 500° C. in a vacuum tube furnace for 5 h to obtain carbon-coated nano-ferric phosphate.

[0100] The SEM image of the carbon-coated nano-iron phosphate is shown in FIG1 . As can be seen from FIG1 , the prepared iron phosphate material has a regular morphology, uniform particles, and a small particle size.

[0101] The carbon-coated nano-iron phosphate 50 The D of the carbon quantum dot core is 120nm. 50 The thickness of the carbon coating layer is 15 nm, and the thickness of the carbon coating layer is 2 nm; the mass of the carbon coating layer is 2 wt % of the carbon-coated nano-iron phosphate.

[0102] Example 2

[0103] This embodiment provides an iron phosphate material, which is a carbon-coated nano-iron phosphate, denoted as LiFePO4 / C composite material. The iron phosphate material includes a carbon quantum dot core located inside and an iron phosphate shell formed in situ on the surface of the carbon quantum dot core, and the surface of the iron phosphate shell has a carbon coating layer.

[0104] The preparation method of the iron phosphate material comprises:

[0105] S1: Dissolve citric acid and ethylenediamine in deionized water at a mass ratio of 1:0.2 to obtain a modified solution with a citric acid mass fraction of 99.5%. Heat the modified solution to 180° C. and react for 8 hours.

[0106] S2: The carbon-containing solution of S1 was mixed with a sodium hydroxide solution having a concentration of 10 g / L in a volume ratio of 1:1. The mixed solution was centrifuged at 8000 r / min for 10 min, and the supernatant was collected. The supernatant was transferred to a dialysis bag with a molecular weight cut-off of 1000 D and dialyzed for 12 h to obtain a dialysate (aqueous solution of carbon quantum dots). The dialysate was collected and transferred to a freeze dryer and freeze-dried at -60°C for 12 h to obtain nanocarbon quantum dots.

[0107] S3: Ferrous sulfate and ammonium dihydrogen phosphate were dissolved in deionized water at a Fe:P molar ratio of 1.1:1 to form a solution. Carbon nanoparticles (10% by weight of the ferrous sulfate) were added to the ferrous sulfate solution, and the mixture was mixed to obtain a first mixed solution. Acrylic acid (3% by weight of the ferrous sulfate) was added to the ammonium dihydrogen phosphate solution, and the mixture was mixed to obtain a second mixed solution.

[0108] S4: adding the second mixed solution to the first mixed solution and adding hydrogen peroxide in a molar amount that is 1 times the molar amount of iron, reacting at a temperature of 100° C. for 6 h, filtering, and washing to obtain ferric phosphate dihydrate.

[0109] S5: annealing and calcining the ferric phosphate dihydrate at 600° C. in a vacuum tube furnace for 3 h to obtain carbon-coated nano-ferric phosphate.

[0110] Example 3

[0111] This embodiment provides an iron phosphate material, which is a carbon-coated nano-iron phosphate, denoted as LiFePO4 / C composite material. The iron phosphate material includes a carbon quantum dot core located inside and an iron phosphate shell formed in situ on the surface of the carbon quantum dot core, and the surface of the iron phosphate shell has a carbon coating layer.

[0112] The preparation method of the iron phosphate material comprises:

[0113] S1: Dissolve citric acid and ethylenediamine in deionized water at a mass ratio of 1:0.5 to obtain a modified solution with a citric acid mass fraction of 99.5%. Heat the modified solution to 280° C. and react for 4 hours.

[0114] S2: The carbon-containing solution of S1 was mixed with a sodium hydroxide solution with a concentration of 20 g / L in a volume ratio of 1:2. The mixed solution was centrifuged at 8000 r / min for 10 minutes, and the supernatant was collected. The supernatant was transferred to a dialysis bag with a molecular weight cutoff of 1000 D and dialyzed for 12 hours to obtain a dialysate (aqueous solution of carbon quantum dots). The dialysate was collected and transferred to a freeze dryer and freeze-dried at -20°C for 12 hours to obtain nanocarbon quantum dots.

[0115] S3: Ferrous sulfate and ammonium dihydrogen phosphate were dissolved in deionized water at a Fe:P molar ratio of 1.5:1 to form a solution. Carbon nanoparticles (20% by weight of the ferrous sulfate) were added to the ferrous sulfate solution, and the mixture was mixed to obtain a first mixed solution. Acrylic acid (10% by weight of the ferrous sulfate) was added to the ammonium dihydrogen phosphate solution, and the mixture was mixed to obtain a second mixed solution.

[0116] S4: adding the second mixed solution to the first mixed solution and adding hydrogen peroxide in a molar amount 1.2 times that of the iron, reacting at a temperature of 130° C. for 2 h, filtering, and washing to obtain ferric phosphate dihydrate.

[0117] S5: annealing and calcining the ferric phosphate dihydrate at 400° C. in a vacuum tube furnace for 8 h to obtain carbon-coated nano-ferric phosphate.

[0118] Comparative Example 1

[0119] The difference between this comparative example and Example 1 is that no carbon quantum dots are added to the first mixed solution, and accordingly no S1 and S2 are present.

[0120] Comparative Example 2

[0121] The difference between this comparative example and Example 1 is that no acrylic acid is added to the second mixed liquid.

[0122] Comparative Example 3

[0123] The difference between this comparative example and Example 1 is that carbon quantum dots are added to the first mixed liquid and acrylic acid is not added to the second mixed liquid.

[0124] Comparative Example 4

[0125] The difference between this comparative example and Example 1 is that lignin is used to replace citric acid.

[0126] Comparative Example 5

[0127] The difference between this comparative example and Example 1 is that during the preparation of carbon quantum dots, ethylenediamine was not used to modify citric acid.

[0128] Comparative Example 6

[0129] The difference between this comparative example and Example 1 is that an equal amount of trimethyloctadecylammonium bromide is used instead of acrylic acid.

[0130] Comparative Example 7

[0131] The difference between this comparative example and Example 1 is that an equal amount of glucose is used instead of acrylic acid.

[0132] Performance testing

[0133] The iron phosphate materials prepared in Examples 1-3 and Comparative Examples 1-7 were respectively prepared into positive electrode sheets in the following manner and assembled into button batteries.

[0134] Preparation method: Weigh the iron phosphate material and lithium carbonate at a molar ratio of P:Li of 1:1, and sucrose with a 10% mass fraction of iron phosphate, mix them evenly, calcine them at 720°C for 6 hours under a nitrogen atmosphere, and naturally cool them to room temperature to finally obtain the lithium iron phosphate positive electrode material. The lithium iron phosphate positive electrode material lithium iron phosphate, conductive agent (Super P), and binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 90:5:5, added to the solvent N-methylpyrrolidone (NMP), stirred into a uniform positive electrode active material slurry, and the slurry is evenly coated on the positive electrode current collector aluminum foil and dried to obtain the positive electrode sheet.

[0135] Assembly Method: Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of 1:1:1 to create an electrolyte solution with a LiPF6 concentration of 1.0 mol / L. A 2025 button-type battery was assembled using a polyethylene film (PE) as the separator and a lithium metal sheet as the negative electrode.

[0136] The electrochemical performance of the button cell was tested, and charge and discharge tests were performed at room temperature from 2V to 3.75V. The results are shown in Table 1.

[0137] Table 1 Test results

[0138] It can be seen from Table 1 that the iron phosphate material provided in this embodiment has a relatively small particle size, and the corresponding lithium iron phosphate positive electrode material has good electrochemical properties.

[0139] Among them, it can be seen from Comparative Example 1 and Comparative Example 1 that the addition of carbon quantum dots can play a role in refining particles. By comparing Example 1 and Comparative Example 2, it can be seen that the addition of acrylic acid is beneficial for controlling the particle size of the material, which may be because it can reduce particle agglomeration. At the same time, it provides a carbon coating source. By comparing Example 1 and Comparative Example 3, it can be seen that by combining carbon quantum dots and acrylic acid, the size of iron phosphate can be better controlled, which is conducive to the production of uniform nano-iron phosphate particles, and thus significantly improves the electrochemical performance of the material.

[0140] In summary, the iron phosphate material provided by the present disclosure has a regular morphology, uniform particles, and a small particle size at the nanometer level. The iron phosphate material can be used to prepare nanometer-level lithium iron phosphate positive electrode materials, which have good electrochemical properties. Industrial Applicability

[0141] The iron phosphate material disclosed herein has a regular morphology, uniform particles, and a small particle size, enabling the preparation of nanoscale lithium iron phosphate cathode materials. This nanoscale lithium iron phosphate cathode material shortens electron and ion transmission distances, enables high-current charge and discharge capabilities, and exhibits excellent electrochemical performance. The preparation method for this iron phosphate material is simple, easy to operate, and control, resulting in a stable product suitable for industrial production.

Claims

1. A kind of iron phosphate material, characterized in that, the iron phosphate material includes a carbon quantum dot core located inside and an iron phosphate shell formed on the surface of the carbon quantum dot core, and the surface of the iron phosphate shell has a carbon coating layer formed by a carbon-containing dispersant.

2. The iron phosphate material according to claim 1, characterized in that, the iron phosphate material also has at least one of the following characteristics: Feature 1: The D of the iron phosphate material 50 is not more than 200 nm; Feature 2: The D of the carbon quantum dot core is 50 from 10 nm to 20 nm; Characteristic three: the iron phosphate shell is formed in situ on the surface of the carbon quantum dot core; Characteristic four: the thickness of the carbon coating layer is 1-3 nm; Characteristic five: the mass of the carbon coating layer does not exceed 5 wt% of the iron phosphate material.

3. The iron phosphate material according to claim 2, characterized in that, The D of the iron phosphate material 50 is 20 nm to 200 nm; and / or, the mass of the carbon coating layer is 1 wt% - 5 wt% of the iron phosphate material.

4. A preparation method of the iron phosphate material according to any one of claims 1-3, characterized in that, comprises the following steps: mixing and reacting a first mixed solution, a second mixed solution and an oxidant to obtain iron phosphate dihydrate; annealing and calcining the iron phosphate dihydrate to obtain the iron phosphate material; wherein, the first mixed solution includes a divalent iron salt and carbon quantum dots; the second mixed solution includes phosphate and a carbon-containing dispersant.

5. The preparation method according to claim 4, characterized in that, the preparation of the carbon quantum dots includes: modifying citric acid with an organic amine in a solution environment to obtain a modified solution; heating the modified solution to cause the cleavage of citric acid to obtain a carbon-containing solution; mixing the carbon-containing solution with an aqueous sodium hydroxide solution, separating the solid and liquid, dialyzing the separated liquid phase, and drying the dialysate obtained by dialysis.

6. The preparation method according to claim 5, characterized in that, the mass ratio of the citric acid to the organic amine is 1:0.1-1:0.

5.

7. The preparation method according to claim 5, characterized in that, the mass fraction of the citric acid in the modified solution is not less than 99.5%.

8. The preparation method according to any one of claims 5-7, characterized in that, the organic amine includes at least one of ethanolamine, ethylenediamine and polyethylene diamine.

9. The preparation method according to any one of claims 5-8, characterized in that, the heating temperature is 180°C-280°C, and / or the heating time is 4h-8h.

10. The preparation method according to any one of claims 5-9, characterized in that, the concentration of the aqueous sodium hydroxide solution is 10 g / L-20 g / L, and the volume ratio of the carbon-containing solution to the aqueous sodium hydroxide solution is 1:1-1:

2.

11. The preparation method according to any one of claims 5-10, characterized in that, the cut-off molecular weight of the dialysis bag used for dialysis is 500D-1500D.

12. The preparation method according to any one of claims 5-11, characterized in that, the drying temperature is -20°C to -60°C, and the drying time is 10h-14h.

13. The preparation method according to any one of claims 4-12, characterized in that, the mass ratio of the carbon quantum dots to the divalent iron salt is 5:100 to 20:

100.

14. The preparation method according to claim 13, It is characterized in that the divalent iron salt includes at least one of ferrous sulfate, ferrous nitrate and ferrous chloride.

15. The preparation method according to any one of claims 4-12, It is characterized in that the molar ratio of iron element in the divalent iron salt to phosphorus element in the phosphate is 1.1:1 to 1.5:

1.

16. The preparation method according to any one of claims 4-15, It is characterized in that the phosphate includes at least one of diammonium hydrogen phosphate, ammonium dihydrogen phosphate and ammonium phosphate.

17. The preparation method according to any one of claims 4-16, It is characterized in that the carbon-containing dispersant includes acrylic acid.

18. The preparation method according to any one of claims 4-17, It is characterized in that the dosage of the carbon-containing dispersant is 3wt%-10wt% of the divalent iron salt.

19. The preparation method according to any one of claims 4-18, It is characterized in that the oxidant includes hydrogen peroxide.

20. The preparation method according to claim 19, It is characterized in that in terms of molar amount, the addition amount of the oxidant is 1 to 1.2 times that of the iron element in the divalent iron salt.

21. The preparation method according to any one of claims 4-20, It is characterized in that the reaction temperature is 100°C-130°C; and / or, the reaction time is 2h-6h.

22. The preparation method according to any one of claims 4-21, It is characterized in that the annealing calcination includes at least one of the following characteristics: Characteristic one: the temperature of the annealing calcination is 400°C-600°C; Characteristic two: the time of the annealing calcination is 3h-8h; Characteristic three: the annealing calcination is carried out under vacuum conditions.

23. A lithium iron phosphate cathode material, It is characterized in that the preparation raw materials of the lithium iron phosphate cathode material include the iron phosphate material according to any one of claims 1-3.

24. A battery, It is characterized in that it contains the lithium iron phosphate cathode material according to claim 23.

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