Spherical lithium iron phosphate precursor, preparation method and application thereof

Abstract

The application discloses a spherical lithium iron phosphate precursor, a preparation method and application thereof, and relates to the technical field of batteries. The preparation method of the spherical lithium iron phosphate precursor comprises the following steps: mixing, dissolving and reacting a lithium source, a phosphorus source and an iron source to obtain a lithium iron phosphate solution; and mixing the lithium iron phosphate solution with a surfactant, and evaporating under the condition of 90-110 DEG C to obtain a solid lithium iron phosphate precursor. The surfactant is used to form a spherical sol in a solvent, the spherical sol continuously loses water in the drying process, the precursor enters the spherical sol, and finally a spherical precursor pre-burnt product is obtained. The lithium iron phosphate is synthesized in a liquid phase, the self-assembly of the surfactant is used to make the precursor have a spherical shape, the spherical size is 50-110 nm, the sphericity is greater than 0.85, the particle is small and compact, and the spherical precursor is beneficial to the release of the electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to spherical lithium iron phosphate precursors, their preparation methods, and applications. Background Technology

[0002] Cathode materials are a crucial component of lithium-ion batteries. Currently, the most researched cathode materials include LiCoO2, LiNiO2, and LiFePO4. Lithium iron phosphate (LiFePO4) exhibits superior high-temperature performance and cycle performance, combining the advantages of various cathode materials. Furthermore, it is a green and non-toxic material due to its absence of precious metals, readily available raw materials, and low production cost.

[0003] Existing lithium iron phosphate precursors are generally prepared by mixing lithium, phosphorus, iron and carbon sources in a mixer. The mixing equipment has high requirements, and the resulting precursors have poor morphology or inconsistent shapes, which leads to poor electrochemical performance of lithium battery cathode materials.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a spherical lithium iron phosphate precursor and its preparation method, with the aim of preparing a lithium iron phosphate precursor with smaller particle size and higher sphericity.

[0006] Another objective of this invention is to provide a lithium iron phosphate cathode material and a lithium-ion battery, which aims to improve the density and uniformity of the material, thereby improving its electrochemical performance.

[0007] This invention is implemented as follows:

[0008] In a first aspect, the present invention provides a method for preparing a spherical lithium iron phosphate precursor, comprising:

[0009] A lithium iron phosphate solution is obtained by mixing and dissolving lithium, phosphorus and iron sources.

[0010] A lithium iron phosphate solution was mixed with a surfactant and evaporated at 90-110°C to obtain a solid lithium iron phosphate precursor.

[0011] In an optional embodiment, the lithium iron phosphate solution and the surfactant are mixed and dissolved, and then mixed with a carbon source to obtain a precursor solution. The precursor solution is then evaporated at 90-110°C to obtain a solid lithium iron phosphate precursor.

[0012] The surfactant is selected from at least one of sodium hexadecylbenzenesulfonate, triethanolamine, ethylene glycol, and polyethylene glycol;

[0013] Preferably, the surfactant is sodium hexadecylbenzenesulfonate / ethylene glycol.

[0014] In an optional embodiment, the mass ratio of the surfactant to the lithium iron phosphate solution is 1:(50-200); preferably 1:(60-160).

[0015] In an optional embodiment, the carbon source is selected from one or more of glucose, fructose, sucrose, citric acid, ethylene glycol, PEG, PVA, CTAB, isopropanol, propylene, acrylic acid, acrylate, acrylamide, acrylonitrile and its derivatives, graphite and carbon nanotubes, and the mass ratio of the carbon source to the lithium iron phosphate solution is 1:(3-10).

[0016] In an optional implementation, the evaporation time is controlled to be 1-7 hours during the evaporation process;

[0017] And / or, the spherical size of the spherical lithium iron phosphate precursor is 50-110 nm;

[0018] And / or, the sphericity of the spherical lithium iron phosphate precursor is greater than 0.85.

[0019] In an optional embodiment, the preparation process of lithium iron phosphate solution includes: mixing and dissolving lithium source, phosphorus source and iron source in a molar ratio of Li:Fe:P = (0.95-1.03):(0.95-1.03):(0.95-1.03), and then reacting at 50-70°C for 0.5-2 hours;

[0020] Preferably, the lithium source is selected from at least one of lithium carbonate, lithium hydroxide, lithium nitrate, and lithium phosphate;

[0021] Preferably, the phosphorus source is selected from at least one of ammonium phosphate, diammonium phosphate, hydrogen phosphate, lithium phosphate, phosphoric acid, and iron phosphate;

[0022] Preferably, the iron source is selected from at least one of iron oxide, ferric nitrate nonahydrate, ferric phosphate, ferric hydroxide, and ferric phosphate;

[0023] Preferably, the solvent used to dissolve the lithium source, phosphorus source and iron source is water and nitric acid, the mass fraction of nitric acid is 30%-68%, preferably 55%-65%, the volume ratio of water to nitric acid is (0.3-0.6):1, and the ratio of the total amount of solvent to the total mass of the three raw materials is 1:(1.6-6).

[0024] In an optional embodiment, the method further includes: pulverizing the solid lithium iron phosphate precursor and then sieving it using a 100-200 mesh sieve.

[0025] And / or, sintering the solid lithium iron phosphate precursor to obtain lithium manganese iron phosphate cathode material.

[0026] Secondly, the present invention also provides a spherical lithium iron phosphate precursor, which is prepared by the preparation method described in the above embodiments.

[0027] Thirdly, the present invention also provides a lithium iron phosphate cathode material, which is prepared by the spherical lithium iron phosphate precursor in the above embodiments.

[0028] Fourthly, the present invention also provides a lithium-ion battery, which is prepared by using the lithium iron phosphate cathode material described in the above embodiments.

[0029] This invention offers the following advantages: By employing surfactants to self-assemble in a solvent to form spherical sols, these spherical sols continuously lose water during drying, allowing the precursor to enter the sols and ultimately yielding spherical precursor pre-calcined products. Through the synthesis of lithium iron phosphate in the liquid phase, the self-assembly of surfactants results in a spherical precursor with a size of 50–110 nm and a sphericity greater than 0.85. The small and dense particles are beneficial for the release of electrochemical properties. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 A schematic diagram illustrating the principle of self-assembly to form spherical particles;

[0032] Figure 2 The image shows a scanning electron microscope (SEM) image of the precursor obtained in Example 2.

[0033] Figure 3 This is a schematic diagram of the sphericity test. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0035] This invention provides a method for preparing a spherical lithium iron phosphate precursor, comprising the following steps:

[0036] S1. Preparation of lithium iron phosphate solution

[0037] A lithium iron phosphate solution is prepared by mixing and dissolving lithium, phosphorus, and iron sources and reacting them.

[0038] In practice, the preparation process of lithium iron phosphate solution includes: mixing and dissolving lithium source, phosphorus source, and iron source in a molar ratio of Li:Fe:P = (0.95-1.03):(0.95-1.03):(0.95-1.03), and then reacting at 50-70℃ for 0.5-2 hours. The amount of lithium source, phosphorus source, and iron source is controlled to have an elemental molar ratio of approximately 1:1:1. The reaction at 50-70℃ will produce lithium iron phosphate.

[0039] Specifically, the molar ratio of lithium, iron, and phosphorus can be 0.95:1.00:0.95, 1.00:1.03:1.00, 1.03:1.03:1.03, etc., the reaction temperature can be 50℃, 55℃, 60℃, 65℃, 70℃, etc., and the reaction time can be 0.5h, 1.0h, 1.5h, 2.0h, etc.

[0040] In some embodiments, the lithium source is selected from at least one of lithium carbonate, lithium hydroxide, lithium nitrate, and lithium phosphate, and may be several of these, but is not limited to these raw materials. The phosphorus source is selected from at least one of ammonium phosphate, diammonium phosphate, hydrogen phosphate, lithium phosphate, phosphoric acid, and iron phosphate, and may be several of these, but is not limited to these raw materials. The iron source is selected from at least one of iron oxide, ferric nitrate nonahydrate, iron phosphate, iron hydroxide, and iron phosphate, and may be several of these, but is not limited to these raw materials.

[0041] In some embodiments, the solvents used to dissolve the lithium source, phosphorus source, and iron source are water and nitric acid. The amount of water and nitric acid used is not limited, as long as it can dissolve the raw materials well. For example, the solvent used is water and nitric acid with a concentration of 30%-68%, preferably 55%-65%, and the volume ratio of water to nitric acid is (0.3-0.6):1, such as 0.3:1, 0.4:1, 0.5:1, 0.6:1, etc. The ratio of the total amount of solvent to the total mass of the three raw materials is 1:(1.6-6), such as 1:1.6, 1:2, 1:6, etc.

[0042] S2, Self-assembly molding

[0043] A solid lithium iron phosphate precursor is obtained by mixing a lithium iron phosphate solution with a surfactant and evaporating the mixture at 90-110°C. In practice, the lithium iron phosphate solution and surfactant are mixed and dissolved, then mixed with a carbon source to obtain a precursor solution. This precursor solution is then evaporated at 90-110°C to obtain the solid lithium iron phosphate precursor.

[0044] It should be noted that, as Figure 1As shown, a colloid with a specific morphology is formed by the self-assembly of a surfactant in a solvent. During the drying process, the spherical sol continuously loses water, and the precursor solution enters the spherical sol, ultimately forming a spherical precursor pre-calcined product. During the evaporation process, the evaporation time is controlled to be 1-7 hours, such as 1 hour, 3 hours, 5 hours, 7 hours, etc. The spherical size of the spherical lithium iron phosphate precursor is 50-110 nm, and the sphericity is greater than 0.85.

[0045] In some embodiments, the surfactant is selected from at least one of sodium hexadecylbenzenesulfonate, triethanolamine, ethylene glycol, and polyethylene glycol, all of which can result in smaller and more uniform precursor particles. Preferably, the surfactant is sodium hexadecylbenzenesulfonate and / or ethylene glycol, and by selecting the optimal surfactant, the uniformity of the precursor formation can be further improved.

[0046] In some embodiments, the mass ratio of surfactant to lithium iron phosphate solution is 1:(50-200); preferably 1:(60-160), such as 1:60, 1:80, 1:110, 1:150, etc. The size of the precursor particles can be adjusted by adjusting the amount of surfactant. The amount of surfactant is preferably within the above range. Too much or too little surfactant is not conducive to forming a precursor with higher uniformity.

[0047] In some embodiments, the carbon source is selected from one or more of glucose, fructose, sucrose, citric acid, ethylene glycol, PEG, PVA, CTAB, isopropanol, propylene, acrylic acid, acrylates, acrylamide, acrylonitrile and its derivatives, graphite, and carbon nanotubes. The mass ratio of the carbon source to the lithium iron phosphate solution is 1:(3-10), such as 1:3, 1:5, 1:8, 1:10, etc. Selecting any of these carbon sources is beneficial for forming precursors with higher sphericity.

[0048] S3, Crushing

[0049] The solid lithium iron phosphate precursor is pulverized and then sieved using a 100-200 mesh screen. Pulverization refers only to breaking up the clumps of the precursor. The reason for the small particle size of the precursor obtained in this embodiment is that the particles of the lithium iron phosphate precursor formed in step S2 are small, at the nanometer level, and the pulverization in S3 only breaks up the clumps without affecting the particle size of the precursor.

[0050] In some embodiments, the crushing includes coarse crushing and fine crushing, wherein coarse crushing is >3mm and fine crushing is <3mm.

[0051] This invention also provides a spherical lithium iron phosphate precursor, prepared by the above-described method, which has the advantages of small particle size, dense particle size, and high sphericity, which is beneficial to the release of electrochemical performance. Specifically, the lithium iron phosphate precursor prepared in this invention has a size of 50-110 nm and a sphericity greater than 0.85.

[0052] This invention also provides a lithium iron phosphate cathode material, which is prepared by the above-mentioned spherical lithium iron phosphate precursor. Since the precursor has a relatively ideal particle size and sphericity, it can endow the lithium iron phosphate cathode material with better performance.

[0053] Furthermore, the aforementioned lithium iron phosphate cathode material can be used to prepare lithium-ion batteries, resulting in battery materials with excellent electrochemical performance and promising market application prospects.

[0054] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0055] Example 1

[0056] This embodiment provides a method for preparing a spherical lithium iron phosphate precursor, including the following steps:

[0057] (1) Take LiOH, Fe(NO3)3·9H2O and NH4H2PO4 into beakers respectively, with amounts of 4.80g, 80.80g and 23.00g, add 6mL of water and 15mL of 60% nitric acid to dissolve them completely;

[0058] (2) Place the solution obtained in step (1) at 60°C and stir for 30 minutes. Add 0.8g of sodium cetylbenzenesulfonate and dissolve it completely. Then take 15g of carbon source (glucose) and add it to the solution. Dissolve it completely to obtain the precursor solution.

[0059] (3) Place the precursor solution obtained in step (2) at 100°C and evaporate the water for 2 hours to obtain the precursor sample.

[0060] (3) The precursor sample prepared in step (3) is placed in a crusher for crushing. After crushing, it is sieved with a 150-mesh sieve to obtain spherical precursor.

[0061] Example 2

[0062] This embodiment provides a method for preparing a spherical lithium iron phosphate precursor, including the following steps:

[0063] (1) Take Li2CO3, Fe2O3 and H3PO4 (85% concentration) into beakers respectively, with amounts of 7.40g, 16.00g and 23.00g, add 6mL of water and 15mL of 65% nitric acid to dissolve them completely;

[0064] (2) Place the solution obtained in step (1) at 50°C and stir for 50 min. Add 0.8 g of hexadecanetrimethylammonium bromide. After complete dissolution, take 15 g of carbon source (fructose) and add it to the solution. Dissolve it completely to obtain the precursor solution.

[0065] (3) Place the precursor solution obtained in step (2) at 90°C and evaporate the water for 2 hours to obtain the precursor sample.

[0066] (4) The precursor sample prepared in step (3) was placed in a crusher for crushing. After crushing, it was sieved through a 150-mesh sieve to obtain spherical precursors. The scanning electron microscope image of the precursors is shown below. Figure 2 As shown.

[0067] From Figure 2 As can be seen, the precursor prepared in this embodiment has a particle size of nanometers, a spherical morphology, and a uniform distribution.

[0068] Example 3

[0069] This embodiment provides a method for preparing a spherical lithium iron phosphate precursor, including the following steps:

[0070] (1) Take Li2CO3 and FePO4 in a beaker, with amounts of 7.40g and 30.2g respectively, add 6mL of water and 15mL of 60% nitric acid, and dissolve them completely;

[0071] (2) Place the solution obtained in step (1) at 70°C and stir for 20 minutes. Add 0.8g of triethanolamine and dissolve it completely. Then take 15g of carbon source (sucrose) and add it to the solution. Dissolve it completely to obtain the precursor solution.

[0072] (3) Place the precursor solution obtained in step (2) at 110°C to evaporate the water and evaporate for 2 hours to obtain the precursor sample.

[0073] (4) The precursor sample prepared in step (3) is placed in a crusher for crushing. After crushing, it is sieved with a 150-mesh sieve to obtain spherical precursor.

[0074] Example 4

[0075] This embodiment provides a method for preparing a spherical lithium iron phosphate precursor, including the following steps:

[0076] (1) Take Li3PO4, Fe2O3 and NH4H2PO4 into beakers respectively, with amounts of 7.73g, 16.00g and 15.33g, add 6mL of water and 15mL of 65% nitric acid, and dissolve them completely.

[0077] (2) Place the solution obtained in step (1) at 60°C and stir for 20 minutes. Add 0.8g of polyethylene glycol and dissolve it completely. Then take 15g of carbon source (citric acid) and add it to the solution. Dissolve it completely to obtain the precursor solution.

[0078] (3) Place the precursor solution obtained in step (2) at 100°C and evaporate the water for 2 hours to obtain the precursor sample.

[0079] (4) The precursor sample prepared in step (3) is placed in a crusher for crushing. After crushing, it is sieved with a 150-mesh sieve to obtain spherical precursor.

[0080] Comparative Example 1

[0081] The only difference from Example 1 is that the surfactant sodium hexadecylbenzenesulfonate is not added in step (2).

[0082] Experimental Example 1

[0083] The performance, particle size, and density of the precursors obtained in the test examples and comparative examples are shown in Table 1.

[0084] Table 1 shows the performance and parameter test results of the precursors obtained in the examples and comparative examples.

[0085]

[0086] Experimental Example 2

[0087] The sphericity of the precursors obtained in the test examples and comparative examples is shown in Table 2 below.

[0088] Sphericity is the ratio of the shortest diameter to the longest diameter of a spherical particle, such as... Figure 3 As shown, it is represented as:

[0089]

[0090] Table 2 shows the sphericity test results of the precursors obtained in the examples and comparative examples.

[0091] sample 1 2 3 4 5 6 average value Example 1 0.88 0.81 0.79 0.91 0.85 0.93 0.86 Example 2 0.91 0.84 0.80 0.95 0.89 0.96 0.89 Example 3 0.86 0.88 0.82 0.91 0.89 0.93 0.88 Example 4 0.79 0.84 0.91 0.85 0.87 0.90 0.86 Comparative Example 1 0.11 0.56 0.32 0.75 0.43 0.81 0.50

[0092] Note: 1-6 are the results of repeated experiments with multiple particles.

[0093] As can be seen from Table 2, the sphericity of the precursor prepared in the embodiments of the present invention is greater than 0.85, which is a significant improvement compared to Comparative Example 1.

[0094] As can be seen from Tables 1 and 2, the precursor prepared in Comparative Example 1 without the addition of surfactant has large particle size, low sphericity, and poor electrochemical performance. In contrast, Examples 1-4 of this invention, by adding one or more surfactants to the lithium iron phosphate solution, prepared precursor particles that are small, dense, and have high sphericity, which is beneficial for the release of electrochemical performance.

[0095] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a spherical lithium iron phosphate precursor, characterized in that, include: The lithium source, phosphorus source and iron source are mixed and dissolved, and then reacted at 50-70℃ for 0.5-2h to obtain a lithium iron phosphate solution. The lithium iron phosphate solution and surfactant are mixed and dissolved, and then mixed with a carbon source to obtain a precursor solution. The precursor solution is evaporated at 90-110°C to obtain a solid lithium iron phosphate precursor. The surfactant is selected from at least one of sodium hexadecylbenzenesulfonate, triethanolamine, ethylene glycol, and polyethylene glycol. The mass ratio of the surfactant to the lithium iron phosphate solution is 1:(50-200). By employing the self-assembly of surfactants in a solvent to form spherical sols, the spherical sols continuously lose water during the drying process, and the precursor solution enters the spherical sols, ultimately forming spherical precursor pre-calcined products; the sphericity of the obtained spherical lithium iron phosphate precursor is greater than 0.

85.

2. The preparation method according to claim 1, characterized in that, The surfactant is sodium hexadecylbenzenesulfonate and / or ethylene glycol.

3. The preparation method according to claim 2, characterized in that, The mass ratio of the surfactant to the lithium iron phosphate solution is 1:(60-160).

4. The preparation method according to claim 2, characterized in that, The mass ratio of the carbon source to the lithium iron phosphate solution is 1:(3-10). And / or, the carbon source is selected from one or more of glucose, fructose, sucrose, citric acid, ethylene glycol, PEG, PVA, CTAB, isopropanol, acrylic acid, acrylate, acrylamide, acrylonitrile and its derivatives, graphite and carbon nanotubes.

5. The preparation method according to claim 2, characterized in that, During the evaporation process, the evaporation time is controlled to be 1-7 hours; And / or, the spherical size of the spherical lithium iron phosphate precursor is 50~110nm.

6. The preparation method according to claim 1, characterized in that, The lithium source, the phosphorus source, and the iron source are mixed and dissolved in a molar ratio of Li:Fe:P = (0.95-1.03):(0.95-1.03):(0.95-1.03).

7. The preparation method according to claim 6, characterized in that, The lithium source is selected from at least one of lithium carbonate, lithium hydroxide, lithium nitrate, and lithium phosphate.

8. The preparation method according to claim 6, characterized in that, The phosphorus source is selected from at least one of ammonium phosphate, diammonium phosphate, hydrogen phosphate, lithium phosphate, phosphoric acid, and iron phosphate.

9. The preparation method according to claim 6, characterized in that, The iron source is selected from at least one of iron oxide, ferric nitrate nonahydrate, ferric hydroxide, and ferric phosphate.

10. The preparation method according to claim 1, characterized in that, The solvents used to dissolve the lithium source, the phosphorus source and the iron source are water and nitric acid. The mass fraction of the nitric acid is 30%-68%, the volume ratio of water to nitric acid is (0.3-0.6):1, and the ratio of the total amount of solvent to the total mass of the three raw materials is 1:(1.6-6).

11. The preparation method according to claim 1, characterized in that, Also includes: The solid lithium iron phosphate precursor was pulverized and then sieved using a 100-200 mesh sieve. And / or, sintering the solid lithium iron phosphate precursor to obtain lithium manganese iron phosphate cathode material.

12. A spherical lithium iron phosphate precursor, characterized in that, It is prepared by the preparation method according to any one of claims 1-11.

13. A lithium iron phosphate cathode material, characterized in that, It is prepared using the spherical lithium iron phosphate precursor of claim 12.

14. A lithium-ion battery, characterized in that, It is prepared using the lithium iron phosphate cathode material as described in claim 13.

Images