Modified ferric phosphate material, preparation method therefor, and use thereof

Abstract

Provided in the present disclosure are a modified ferric phosphate material, a preparation method therefor, and the use thereof. The preparation method comprises the following steps: (1) mixing dopamine hydrochloride and F127 with a solvent, and adding trimethylbenzene, so as to obtain a nano-emulsion; and (2) adjusting the pH of the nano-emulsion, then adding an initiator to polymerize dopamine hydrochloride, adding a ferric salt for adsorption, and adding a phosphorus source to obtain a precursor; and (3) sintering the precursor to obtain the modified ferric phosphate material. The present disclosure uses the F127, TMB and dopamine to form a dendritic structure, and uses dopamine to complex Fe3+ to form ferric phosphate having a dendritic structure, which, together with ferric phosphate formed by free iron ions and ferric phosphate formed by Fe3+ that is complexed with dopamine not having the dendritic structure, constitutes ferric phosphate particles containing a carbon channel skeleton therein.

Description

A modified ferric phosphate material and its preparation method and application Technical Field

[0001] The present disclosure belongs to the technical field of battery materials and relates to a modified iron phosphate material and a preparation method and application thereof. Background Art

[0002] Lithium batteries, as the energy storage component of outdoor mobile power banks, can be called the "heart" of the power bank. Using high-quality lithium batteries not only provides safer use but also extends the life of the power bank. There are two main types of lithium batteries on the market: ternary lithium batteries and lithium iron phosphate batteries.

[0003] Among them, lithium iron phosphate, with its olivine structure, experiences minimal volume change during lithium extraction and insertion. This physical characteristic ensures excellent cycling performance and thermal stability. Furthermore, lithium iron phosphate is relatively affordable, generally around 30% cheaper than ternary batteries. Furthermore, lithium iron phosphate batteries offer significant environmental advantages. Lithium iron phosphate materials are characterized by their absence of precious metals such as cobalt and nickel, resulting in low raw material prices. Furthermore, phosphorus and iron are abundant on Earth, eliminating supply constraints.

[0004] However, due to the olivine structure of lithium iron phosphate, compared with the layered structure of the ternary positive electrode material, lithium iron phosphate can only move in one dimension. This structure has a certain impact on the insertion and extraction of lithium ions, resulting in poor conductivity.

[0005] CN113540461A discloses a method for preparing lithium iron phosphate coated with a full carbon layer, which comprises: adding a lithium source, iron phosphate, a carbon source and a solvent into a mixer in a certain proportion, stirring for 30 minutes to mix evenly; sand-milling the evenly mixed materials through a sand mill, and controlling the slurry particle size by the sand milling time; spray-drying the obtained sand-milled slurry to obtain a lithium iron phosphate precursor, and controlling the water content of the lithium iron phosphate precursor; adding a certain amount of flux to the obtained lithium iron phosphate precursor for dry mixing; crushing the obtained mixed material so that the obtained powder particle size meets the requirements; and sintering the obtained crushed material at high temperature in a nitrogen atmosphere.

[0006] CN101442117A discloses a method for preparing carbon-coated lithium iron phosphate (LiFePO4 / C), which comprises the following steps: a. weighing LiOH·H2O, reduced Fe powder and H3PO4 in a molar ratio of 1:1:1, stirring and reacting in an aqueous solution under nitrogen protection for 2 to 10 hours, then adding a carbon source to the reaction system, and spray-drying the obtained suspension reaction product through a high-speed centrifugal spray dryer to obtain a LiFePO4 / C precursor; b. transferring the above-mentioned LiFePO4 / C precursor to a tubular furnace in an inert or non-oxidizing atmosphere and treating it at a temperature of 200 to 750°C for 6 to 24 hours to obtain the carbon-coated lithium iron phosphate.

[0007] The above solution improves the conductivity of lithium iron phosphate materials by coating, but conventional carbon coating can only solve the conductivity of the lithium iron phosphate surface, the improvement effect is relatively poor, and it is easy to affect the energy density of the material.

[0008] Summary of the Invention

[0009] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0010] The purpose of the present invention is to provide a modified iron phosphate material and its preparation method and application. The present invention forms a dendritic structure by using polyoxyethylene polyoxypropylene ether F127, TMB and dopamine, and uses dopamine to modify Fe 3+ complex to form a dendritic structure of iron phosphate, and with the free iron ions to form iron phosphate and the Fe that does not form a dendritic dopamine complex 3+ The formed iron phosphate (dopamine is carbonized into a carbon skeleton after calcination) together forms iron phosphate particles with an internal carbon channel skeleton.

[0011] To achieve this purpose, the present disclosure adopts the following technical solutions:

[0012] In a first aspect, the present disclosure provides a method for preparing a modified ferric phosphate material, the preparation method comprising the following steps:

[0013] (1) dopamine hydrochloride, polyoxyethylene polyoxypropylene ether F127 (Pluronic F127, abbreviated as F127) and a solvent are mixed, and trimethylbenzene (TMB) is added to obtain a nanoemulsion;

[0014] (2) after adjusting the pH of the nanoemulsion, adding an initiator to polymerize dopamine hydrochloride, adding an iron salt for adsorption, and then adding a phosphorus source to obtain a precursor;

[0015] (3) Sintering the precursor to obtain the modified iron phosphate material.

[0016] The present invention utilizes F127, TMB and dopamine hydrochloride to polymerize to form nanoparticle emulsion, adds initiator to polymerize dopamine, and then polydopamine is reacted with Fe 3+ After the addition of phosphate, some of the Fe adsorbed by polydopamine 3+ and free Fe 3+ It can react with phosphate to form iron phosphate, which then aggregates to form large particles. In the iron phosphate precursor formed after high-temperature calcination, the TMB in the iron phosphate attached to polydopamine is removed, creating a porous structure. Dopamine hydrochloride becomes a nitrogen-doped carbon structure, and the iron phosphate on its surface forms a dendritic structure with a mesoporous iron phosphate carbon skeleton attached to the surface. This creates a network structure with internal cavity channels and nitrogen-doped carbon.

[0017] In one embodiment, the mass ratio of dopamine hydrochloride to polyoxyethylene polyoxypropylene ether F127 in step (1) is (0.3-0.8):1, for example: 0.3:1, 0.4:1, 0.5:1, 0.6:1 or 0.8:1, etc.

[0018] In one embodiment, the mass volume ratio of the polyoxyethylene polyoxypropylene ether F127 to the solvent is 1:(50-100) g / mL, for example: 1:50 g / mL, 1:60 g / mL, 1:80 g / mL, 1:90 g / mL or 1:100 g / mL, etc.

[0019] In one embodiment, the solvent comprises water and ethanol.

[0020] In one embodiment, the volume fraction of ethanol in the solvent is 30% to 60%, for example, 30%, 35%, 40%, 50% or 60%.

[0021] In one embodiment, the mixing stirring speed is 500-1000 rpm, for example, 500 rpm, 600 rpm, 800 rpm, 900 rpm or 1000 rpm.

[0022] In one embodiment, the mass volume ratio of dopamine hydrochloride to trimethylbenzene in step (1) is 1: (1 to 4) g / mL, for example: 1: 1 g / mL, 1: 1.5 g / mL, 1: 2 g / mL, 1: 3 g / mL or 1: 4 g / mL, etc., and can further be 1: (1.5 to 3) g / mL.

[0023] In one embodiment, the pH in step (2) is 1 to 2, for example, 1, 1.2, 1.5, 1.8 or 2.

[0024] In one embodiment, the initiator comprises ammonium persulfate.

[0025] In one embodiment, the molar ratio of dopamine hydrochloride to ammonium persulfate is 1:(5-15), for example, 1:5, 1:8, 1:10, 1:12 or 1:15, and can further be 1:(8-12).

[0026] In one embodiment, the iron salt in step (2) includes any one of ferric nitrate, ferric chloride or ferric sulfate, or a combination of at least two thereof.

[0027] In one embodiment, the molar ratio of iron ions to dopamine hydrochloride in the iron salt is (5-20):1, for example: 5:1, 8:1, 10:1, 15:1 or 20:1, etc., and can further be (8-15):1.

[0028] In one embodiment, the phosphorus source includes any one of ammonium hydrogen phosphate, ammonium dihydrogen phosphate, or ammonium phosphate, or a combination of at least two thereof.

[0029] In one embodiment, the pH of the mixed solution is 1.5 to 2.5, for example, 1.5, 1.8, 2, 2.2 or 2.5.

[0030] In one embodiment, the temperature of the sintering treatment in step (3) is 600-700°C, for example, 600°C, 620°C, 650°C, 680°C or 700°C.

[0031] In a second aspect, the present disclosure provides a modified ferric phosphate material, which is prepared by the method described in the first aspect.

[0032] The particles of the iron phosphate material prepared by the method disclosed in the present invention have voids inside. According to the iron phosphate embedding / extraction model theory, the voids in the middle are conducive to shortening the lithium ion path. At the same time, a carbon coating is formed inside the iron phosphate particles. Dopamine provides nitrogen while providing carbon, forming a nitrogen-doped carbon layer inside, forming a non-intrinsic and disordered carbon structure, further achieving an improvement in the electrical conductivity and reducing the internal resistance, and forming lithium iron phosphate particles with a common carbon coating inside and outside.

[0033] In a third aspect, the present disclosure provides a lithium iron phosphate positive electrode material, which is prepared by mixing and sintering the modified iron phosphate material as described in the second aspect with a lithium source and a carbon source.

[0034] In a fourth aspect, the present disclosure provides a positive electrode plate, wherein the positive electrode plate comprises the lithium iron phosphate positive electrode material as described in the third aspect.

[0035] In a fifth aspect, the present disclosure provides a lithium-ion battery, wherein the lithium-ion battery comprises the positive electrode sheet as described in the fourth aspect.

[0036] Compared with the prior art, the present disclosure has the following beneficial effects:

[0037] (1) The present invention uses polyoxyethylene polyoxypropylene ether F127, TMB and dopamine to form a dendritic structure, and uses dopamine to 3+ The complexation forms a dendritic structure of iron phosphate, and together with the iron phosphate formed by free iron ions and the iron phosphate formed by iron that has not formed a dendritic dopamine complex (dopamine is carbonized into a carbon skeleton after calcination), it forms iron phosphate particles with an internal carbon channel skeleton.

[0038] (2) The modified iron phosphate prepared by the method disclosed in the present invention can produce a lithium iron phosphate battery with a 0.2C discharge capacity of more than 155Ah / g, a 1C discharge capacity of more than 144Ah / g, a 3C discharge capacity of more than 130Ah / g, and a 10C discharge capacity of more than 122Ah / g. By adjusting the raw material feed amount and reaction conditions, the material can have a capacity of 164mAh / g at a 0.2C rate and a capacity of 130mAh / g at a 10C rate.

[0039] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The accompanying drawings are used to provide a further understanding of the technical solution of this article and constitute a part of the specification. Together with the embodiments of this application, they are used to explain the technical solution of this article and do not constitute a limitation on the technical solution of this article.

[0041] FIG1 is a schematic diagram of the structure of a unit dopamine polymerization model in one embodiment of the present disclosure.

[0042] FIG2 is a SEM image of the modified iron phosphate material obtained in Example 1 of the present disclosure.

[0043] FIG3 is an enlarged SEM image of the modified ferric phosphate material obtained in Example 1 of the present disclosure. DETAILED DESCRIPTION

[0044] The technical solution of the present disclosure is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present disclosure and should not be regarded as specific limitations of the present disclosure.

[0045] Example 1

[0046] This embodiment provides a modified ferric phosphate material, and the preparation method of the modified ferric phosphate material is as follows:

[0047] (1) A 50% ethanol solution was added with dopamine hydrochloride and F127 at a mass ratio of 0.5:1 (the mass volume ratio of F127 to the solvent was 80 g / mL), and the mixture was stirred at 750 rpm until it became clear. Trimethylbenzene was added at a speed of 2 rpm, and the ratio of dopamine hydrochloride to TMB was 1 g:1.5 ml to obtain a nanoemulsion;

[0048] (2) adjusting the pH of the nanoemulsion to below 1.5, adding ammonium persulfate to polymerize dopamine hydrochloride, wherein the molar ratio of dopamine hydrochloride to ammonium persulfate is 1:10, and then adding ferric nitrate to the solution to complex it with polydopamine, Fe 3+ The molar ratio of ammonium phosphate to dopamine hydrochloride is 12:1, and then ammonium hydrogen phosphate is added to adjust the pH to 2 to keep the phosphate and Fe 3+ The molar ratio is 1:1, and the reaction is complete;

[0049] (3) After filtering, washing with ethanol and water, drying, calcining at 650°C, and crushing, the modified iron phosphate material is obtained. In the modified iron phosphate material, the schematic diagram of the unit dopamine polymerization model structure is shown in Figure 1 (composed of dopamine, TMB, and F127). The tree-like structure disclosed in the present invention is formed by the intertwining connection of the unit structure during the reaction process. At the same time, the dopamine complexed Fe 3+ , forming an iron phosphate with an internal tree-like structure. After the TMB in each unit structure is removed through subsequent drying and calcination processes, a porous structure is left. The SEM images of the modified iron phosphate material are shown in Figures 2-3.

[0050] Example 2

[0051] This embodiment provides a modified ferric phosphate material, and the preparation method of the modified ferric phosphate material is as follows:

[0052] (1) A 40% ethanol solution was added with dopamine hydrochloride and F127 at a mass ratio of 0.3:1 (the mass volume ratio of F127 to the solvent was 50 g / mL), and the mixture was stirred at 500 rpm until it became clear. Trimethylbenzene was added at a speed of 2 rpm, and the ratio of dopamine hydrochloride to TMB was 1:2 g / mL to obtain a nanoemulsion;

[0053] (2) adjusting the pH of the nanoemulsion to 1, adding ammonium persulfate to polymerize dopamine hydrochloride, wherein the molar ratio of dopamine hydrochloride to ammonium persulfate is 1:8, and then adding ferric nitrate to the solution to complex it with polydopamine, Fe 3+ The molar ratio of ammonium phosphate to dopamine hydrochloride is 15:1, and then ammonium hydrogen phosphate is added to adjust the pH to 1.5 to keep the phosphate and Fe 3+ The molar ratio is 1:1, and the reaction is complete;

[0054] (3) After filtering, washing with ethanol and water, drying, calcining at 600° C., and crushing, the modified iron phosphate material is obtained.

[0055] Example 3

[0056] This embodiment provides a modified ferric phosphate material, and the preparation method of the modified ferric phosphate material is as follows:

[0057] (1) A 60% ethanol solution was added with dopamine hydrochloride and F127 at a mass ratio of 0.8:1 (the mass volume ratio of F127 to the solvent was 100 g / mL), and the mixture was stirred at 1000 rpm until it became clear. Trimethylbenzene was added at a speed of 2 rpm, and the ratio of dopamine hydrochloride to TMB was 1:3 g / mL to obtain a nanoemulsion;

[0058] (2) adjusting the pH of the nanoemulsion to 2, adding ammonium persulfate to polymerize dopamine hydrochloride, wherein the molar ratio of dopamine hydrochloride to ammonium persulfate is 1:12, and then adding ferric nitrate to the solution to complex it with polydopamine, Fe 3+ The molar ratio of ammonium phosphate to dopamine hydrochloride is 8:1, and then ammonium hydrogen phosphate is added to adjust the pH to 2.5 to keep the phosphate and Fe 3+ The molar ratio is 1:1, and the reaction is complete;

[0059] (3) After filtering, washing with ethanol and water, drying, calcining at 700° C., and crushing, the modified iron phosphate material is obtained.

[0060] Example 4

[0061] The only difference between this embodiment and embodiment 1 is that the mass volume ratio of dopamine hydrochloride to trimethylbenzene is 1:1 g / mL, and other conditions and parameters are exactly the same as those in embodiment 1.

[0062] Example 5

[0063] The only difference between this embodiment and embodiment 1 is that the mass volume ratio of dopamine hydrochloride to trimethylbenzene is 1:4 g / mL, and other conditions and parameters are exactly the same as those in embodiment 1.

[0064] Example 6

[0065] The only difference between this embodiment and embodiment 1 is that the molar ratio of iron ions to dopamine hydrochloride in the iron salt is 5:1, and other conditions and parameters are exactly the same as those in embodiment 1.

[0066] Example 7

[0067] The only difference between this embodiment and embodiment 1 is that the molar ratio of iron ions to dopamine hydrochloride in the iron salt is 20:1, and other conditions and parameters are exactly the same as those in embodiment 1.

[0068] Example 8

[0069] The only difference between this embodiment and embodiment 1 is that the molar ratio of dopamine hydrochloride to ammonium persulfate is 1:5, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0070] Comparative Example 1

[0071] The only difference between this comparative example and Example 1 is that triphenylamine (TMB) is not added, and other conditions and parameters are exactly the same as those in Example 1.

[0072] Comparative Example 2

[0073] The only difference between this comparative example and Example 1 is that dopamine hydrochloride is not added, and other conditions and parameters are exactly the same as those in Example 1.

[0074] Performance testing:

[0075] The modified iron phosphate material and Li2CO3 prepared in the embodiment and comparative example were loaded into a ball mill and wet-milled with anhydrous ethanol at a speed of 600 rpm for 5 h; glucose, lithium carbonate and the prepared iron phosphate precursor with a C:Li:P molar ratio of 0.05:1.05:1.0 were calcined at 600 ° C under a nitrogen atmosphere to obtain a lithium iron phosphate material. The prepared lithium iron phosphate positive electrode material was mixed with a cyclohexane solution of acetylene black and polyvinylidene fluoride (PVDF) at room temperature and pressure to form a slurry (according to the positive electrode material: acetylene black: PVDF weight ratio of 75:15:10), which was evenly coated on an aluminum foil substrate as the positive electrode of the simulated battery. The negative electrode of the simulated battery used a lithium sheet, and the electrolyte was 1 mol LiPF6 dissolved in a mixed solvent of 1L EC and DMC (volume ratio 1:1). The positive electrode, negative electrode, electrolyte, and diaphragm were assembled into a simulated battery in an argon-protected glove box. The rate test steps for the simulated battery are: first charge to 4.2V at 30mA / g, then discharge to 2.0V at the rate current. The released capacity is the discharge capacity at that rate. After the discharge is completed, discharge again at 30mA / g to 2.0V. Then proceed to the next rate test. The test results of this simulated battery are shown in Table 1:

[0076] Table 1

[0077] As can be seen from Table 1, it can be obtained from Examples 1-3 that the 0.2C discharge capacity of the lithium iron phosphate battery made from the modified iron phosphate prepared by the method described in the present disclosure can reach more than 155Ah / g, the 1C discharge capacity can reach more than 144Ah / g, the 3C discharge capacity can reach more than 130Ah / g, and the 10C discharge capacity can reach more than 122Ah / g. By controlling the raw material feeding amount and the reaction conditions, the 0.2C discharge capacity of the lithium iron phosphate battery made from the modified iron phosphate can reach 164mAh / g, the 1C discharge capacity can reach 150mAh / g, the 3C discharge capacity can reach 143mAh / g, and the 10C discharge capacity can reach 130mAh / g.

[0078] By comparison of Example 1 and Examples 4-5, it can be seen that in the preparation process of the modified iron phosphate described in the present disclosure, the mass volume ratio of dopamine hydrochloride to TMB affects its performance. The mass volume ratio of dopamine hydrochloride to TMB is controlled at 1:1.5~3g / mL, and the performance of the modified iron phosphate obtained is better. If the amount of TMB added is too large, the proportion of hollow cavities increases, resulting in a decrease in the energy density of lithium iron phosphate. If the amount of TMB added is too small, the proportion of hollow cavities decreases, the energy density is increased, and the transmission path increases.

[0079] By comparison of Example 1 and Examples 6-7, it can be seen that in the preparation process of the modified iron phosphate described in the present disclosure, the molar ratio of iron ions and dopamine hydrochloride in the iron salt will affect its performance. The molar ratio of iron ions and dopamine hydrochloride in the iron salt is controlled at 8 to 15:1, and the performance of the modified iron phosphate obtained is better. If the amount of dopamine hydrochloride added is too large, the carbon content in the obtained material is too high and the energy density is reduced. If the amount of dopamine hydrochloride added is too small, a cavity cannot be formed to shorten the lithium ion transmission path, and an effective internal carbon guide cannot be formed.

[0080] By comparison of Example 1 and Example 8, it can be seen that in the preparation process of the modified ferric phosphate described in the present disclosure, the molar ratio of dopamine hydrochloride to ammonium persulfate (initiator) affects its performance. The molar ratio of dopamine hydrochloride to ammonium persulfate (initiator) is controlled at 1:8 to 12, and the performance of the modified ferric phosphate obtained is better. If the amount of ammonium persulfate (initiator) added is too low, the degree of polymerization of polydopamine is small, the dendritic structure is small, the hollow structure is small, and the lithium ion transmission path is increased. If the amount is too high, it will cause waste.

[0081] From the comparison between Example 1 and Comparative Examples 1-2, it can be seen that TMB and dopamine hydrochloride play a crucial role in the formation of pore size in the iron phosphate precursor.

Claims

1. A method for preparing a modified ferric phosphate material, The following steps are involved: (1) mixing dopamine hydrochloride, polyoxyethylene polyoxypropylene ether F127 and a solvent, and adding trimethylbenzene to obtain a nanoemulsion; (2) after adjusting the pH of the nanoemulsion, adding an initiator to polymerize dopamine hydrochloride, adding an iron salt for adsorption, adding a phosphorus source, adjusting the pH of the mixed solution, and obtaining a precursor; (3) Sintering the precursor to obtain the modified iron phosphate material.

2. The preparation method according to claim 1, in, The mass ratio of dopamine hydrochloride and polyoxyethylene polyoxypropylene ether F127 in step (1) is (0.3-0.8):

1.

3. The preparation method according to claim 1 or 2, Features in, The mass volume ratio of the polyoxyethylene polyoxypropylene ether F127 to the solvent is 1: (50-100) g / mL.

4. The preparation method according to any one of claims 1 to 3, in, The solvents include water and ethanol.

5. The preparation method according to any one of claims 1 to 4, in, The volume fraction of ethanol in the solvent is 30-60%.

6. The preparation method according to any one of claims 1 to 5, in, The stirring speed of the mixing is 500-1000 rpm.

7. The preparation method according to any one of claims 1 to 6, in, The mass volume ratio of dopamine hydrochloride to trimethylbenzene in step (1) is 1:(1-4) g / mL.

8. The preparation method according to any one of claims 1 to 6, in, The mass volume ratio of dopamine hydrochloride to trimethylbenzene in step (1) is 1:(1.5-3) g / mL.

9. The preparation method according to any one of claims 1 to 8, in, The pH in step (2) is 1-2.

10. The preparation method according to any one of claims 1 to 9, in, The initiator includes ammonium persulfate; Optionally, the molar ratio of dopamine hydrochloride to ammonium persulfate is 1:(5-15).

11. The preparation method according to claim 10, in, The molar ratio of dopamine hydrochloride to ammonium persulfate is 1:(8-12).

12. The preparation method according to any one of claims 1 to 11, in, The iron salt in step (2) includes any one of ferric nitrate, ferric chloride or ferric sulfate, or a combination of at least two thereof; Optionally, the molar ratio of iron ions to dopamine hydrochloride in the iron salt is (5-20):1, and can further be (8-15):1; Optionally, the phosphorus source includes any one of ammonium hydrogen phosphate, ammonium dihydrogen phosphate or ammonium phosphate, or a combination of at least two thereof; Optionally, the pH of the mixed solution is 1.5-2.

5.

13. The preparation method according to any one of claims 1 to 12, in, The sintering temperature in step (3) is 600-700°C.

14. A modified iron phosphate material obtained by the method according to any one of claims 1 to 13.

15. A lithium iron phosphate positive electrode material prepared by mixing and sintering the modified iron phosphate material as claimed in claim 14 with a lithium source and a carbon source.

16. A positive electrode sheet comprising the lithium iron phosphate positive electrode material as claimed in claim 15.

17. A lithium ion battery comprising the positive electrode sheet according to claim 16.

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