CN116409772A - Secondary growth preparation method of nano lithium iron phosphate - Google Patents

Abstract

The invention discloses a secondary growth preparation method of nano lithium iron phosphate, which comprises the following steps: carrying out hydrothermal reaction on nano lithium iron phosphate serving as a seed crystal, a two-dimensional phosphorus simple substance and a reducing agent in a lithium iron phosphate precursor solution; the lithium iron phosphate precursor solution includes an iron source, a lithium source, and a phosphorus source. According to the invention, the primary nano lithium iron phosphate is used as a seed crystal, and the two-dimensional phosphorus simple substance and the lithium iron phosphate precursor solution are introduced to perform secondary growth in the hydrothermal process, so that the preparation of the high-performance nano lithium iron phosphate material is realized. Compared with the prior art, the method is efficient and environment-friendly, does not need to use an additional organic inducer, and greatly reduces pollution in the preparation process. Meanwhile, the method has simple steps and strong controllability, and is more beneficial to industrialized production of high-performance nano lithium iron phosphate.

Description

A secondary growth preparation method of nano-lithium iron phosphate

technical field

The invention relates to the technical field of cathode materials for lithium ion batteries, in particular to a preparation method for secondary growth of nanometer lithium iron phosphate.

Background technique

Lithium iron phosphate is a lithium-ion battery cathode material with high safety, stability, cycle life and energy density, so it has been widely used in portable electronic devices, electric vehicles, energy storage systems and other fields. Compared with traditional lithium cobaltate, lithium nickelate and ternary materials, it has higher safety and environmental protection, and is more suitable for large-scale applications. However, their rate capability is poor due to their low lithium ion mobility and low electronic conductivity. At present, nanonization, doping and coating of lithium iron phosphate are important methods to improve its rate performance.

Chinese patent CN115367724A discloses a method for producing lithium iron phosphate materials using biomass agents. First, the lithium source, iron source and phosphorus source are ground to make an aqueous solution, and a mixture of biomass agent and benzenesulfonic acid is added as an additive, and then according to Proportion The materials prepared in the first two steps are mixed for hydrothermal reaction, and finally the materials are eluted to obtain lithium iron phosphate powder. Similarly, the Chinese patent CN102013490A discloses a high-rate performance lithium iron phosphate cathode material and its preparation method. The ball-milled graphite is mixed with iron salt, phosphate and lithium salt, and the secondary ball milling is carried out with anhydrous ethanol as the medium. The powder material obtained by spray-drying the slurry is then placed in a rotary furnace for atmosphere sintering to obtain a high-rate performance lithium iron phosphate cathode material. In addition, Chinese patent CN114171740A discloses a preparation method of nano-lithium iron phosphate cathode material. First, hollow nano-carbon spheres are prepared, and then mixed with lithium salt, iron salt, and phosphorus salt to form a reaction solution, which is then subjected to hydrothermal reaction under inert gas. The lithium iron phosphate precursor is obtained, and finally roasted. The above method is relatively cumbersome and lacks the controllability of the nanostructure of lithium iron phosphate, especially the dominant channel for lithium ion transmission. In addition, some impurities that cannot be removed may be introduced, which brings uncontrollable potential risks to its application. Therefore, it is urgent to develop a new method for the preparation of lithium iron phosphate to realize the regulation and control of the structure and properties of lithium iron phosphate.

Contents of the invention

In view of the above technical problems, the present invention provides a secondary growth preparation method of nano-lithium iron phosphate, using primary nano-lithium iron phosphate as a seed crystal, introducing two-dimensional phosphorus element and lithium iron phosphate precursor, and using two-dimensional phosphorus element to induce crystallization The secondary growth is carried out in the hydrothermal process to realize the control of the dominant crystal plane. The invention synthesizes a high-rate performance pure-phase lithium iron phosphate positive electrode material through a simple process, and solves the problem of impurities in the preparation process of lithium iron phosphate in the prior art. The problem.

To achieve the above object, the present invention provides the following technical solutions:

On the one hand, the present invention provides a kind of secondary growth preparation method of nano-lithium iron phosphate, comprising the following steps:

The nanometer lithium iron phosphate, the two-dimensional phosphorus element and the reducing agent are subjected to a hydrothermal reaction in a lithium iron phosphate precursor solution; the lithium iron phosphate precursor solution includes an iron source, a lithium source and a phosphorus source.

As a preferred embodiment, the reaction temperature of the hydrothermal reaction is 150°C-220°C; the holding time of the hydrothermal reaction is 150min-220min.

As a preferred embodiment, the reducing agent is ascorbic acid.

As a preferred embodiment, the iron source is a water-soluble ferrous salt, preferably ferrous sulfate heptahydrate;

Preferably, the lithium source is a water-soluble lithium salt, preferably lithium hydroxide monohydrate;

Preferably, the phosphorus source is a water-soluble phosphorus source, preferably phosphoric acid;

Preferably, the solvent of the lithium iron phosphate precursor solution is a mixed solvent of water and ethylene glycol.

As a preferred embodiment, the two-dimensional phosphorus simple substance is two-dimensional black phosphorus;

Preferably, the lateral dimension of the two-dimensional phosphorous simple substance is 0.5 μm˜100 μm, and the thickness is 1 nm˜30 nm.

As a preferred embodiment, the mass ratio of the two-dimensional phosphorus element to the nano-lithium iron phosphate as the seed crystal is 1:0.4-5;

Preferably, in the lithium iron phosphate precursor solution, the molar ratio of iron in the iron source, lithium in the lithium source, and phosphorus in the phosphorus source is 1:3-4:1-2;

Preferably, the mass ratio of the reducing agent to the iron source is 1-2:2780;

Preferably, the mass ratio of the nano-lithium iron phosphate used as the seed crystal to the iron source is 1-10:125.

In some specific embodiments, the secondary growth preparation method also includes post-treatment of washing and drying after cooling, wherein cooling can be done by natural cooling.

In the technical solution of the present invention, the mass ratio of the theoretical mass of the nano-lithium iron phosphate obtained by the above-mentioned secondary growth preparation method to the nano-lithium iron phosphate as the seed crystal is 5-200:1.

As a preferred embodiment, the nano-lithium iron phosphate used as the seed crystal is prepared by a hydrothermal method;

Preferably, the particle size of the nano-lithium iron phosphate used as the seed crystal is 30nm-200nm.

In some specific embodiments, the preparation of nano-lithium iron phosphate as a seed crystal by the hydrothermal method comprises the following steps:

A solution including a reducing agent, an iron source, a lithium source and a phosphorus source is subjected to a hydrothermal reaction. Wherein, the reducing agent is ascorbic acid; the iron source is a water-soluble ferrous salt; preferably ferrous sulfate heptahydrate; the lithium source is a water-soluble lithium salt, preferably lithium hydroxide monohydrate; the phosphorus source It is a water-soluble phosphorus source, preferably phosphoric acid; the solvent of the lithium iron phosphate precursor solution is a mixed solvent of water and ethylene glycol. The condition of the hydrothermal reaction is 150°C-220°C and heat preservation for 150min-220min.

In yet another aspect, the present invention provides nano-lithium iron phosphate obtained by the above-mentioned secondary growth preparation method.

In yet another aspect, the present invention provides the application of the above nano-lithium iron phosphate in the preparation of lithium-ion batteries, specifically, the application in the preparation of lithium-ion battery cathode materials.

The above technical solution has the following advantages or beneficial effects: the present invention uses nano-lithium iron phosphate as a seed crystal and adds two-dimensional phosphorus as a regulator to obtain lithium iron phosphate with different crystal surface exposure rates through secondary in-situ growth, Among them, the two-dimensional phosphorus element can construct a microenvironment through redox reactions to realize the secondary growth regulation of lithium iron phosphate.

Compared with the prior art, the present invention has the following advantages:

1. Innovation in the regulation mechanism: the two-dimensional phosphorus element undergoes an oxidation reaction during the hydrothermal process, and the surface is negatively charged, attracting crystal seeds and positive ions, and the local ion concentration on the surface of black phosphorus increases, thereby regulating the lithium iron phosphate on the crystal seed growth, to achieve the ultimate purpose of changing the exposure rate of the crystal face;

2. The more crystal faces of the lithium ion channel are exposed, the shorter the channel distance is, the better the performance is. The seed crystal is affected by the two-dimensional phosphorus element and can reach the channel crystal plane (010) by secondary growth. The channel distance is more Relatively shorter effect;

3. The secondary grown lithium iron phosphate material is synthesized by low-temperature hydrothermal method, with low energy consumption, simple equipment and operation, no introduction of other organic compounds, and easy elution, which is conducive to industrial production of high-performance nano-lithium iron phosphate.

Description of drawings

Fig. 1 is a scanning electron microscope image of the nano-lithium iron phosphate seed crystal prepared in Production Example 1 of the present invention.

Fig. 2 is a scanning electron microscope image of lithium iron phosphate prepared in comparative examples 1 and 3 of the present invention.

Fig. 3 is an X-ray diffraction pattern of lithium iron phosphate prepared in Comparative Example 1-2 and Example 1 of the present invention.

Fig. 4 is a scanning electron microscope image of lithium iron phosphate prepared in Example 1 of the present invention.

FIG. 5 is a rate performance diagram of lithium iron phosphate prepared in Comparative Example 2 and Example 1 of the present invention.

Fig. 6 is a charge-discharge curve diagram of lithium iron phosphate prepared in Example 1 of the present invention under the condition of charge and discharge at 15C.

Detailed ways

The following embodiments are only some of the embodiments of the present invention, not all of them. Therefore, the detailed description in the embodiments of the invention provided below is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative efforts belong to the protection scope of the present invention.

In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or commonly used in this industry. The methods in the following examples, unless otherwise specified, are conventional methods in the art.

Manufacturing example 1

Step 1, prepare 0.1mg/mL ascorbic acid aqueous solution, weigh 2.78g of ferrous sulfate heptahydrate and dissolve in 10mL of the above-mentioned ascorbic acid aqueous solution; weigh 1.4g of lithium hydroxide monohydrate and prepare 10mL of aqueous solution; Add 3mL of iron solution, 3mL of lithium hydroxide solution and 80μL of phosphoric acid into 12mL of ethylene glycol, and finally into the autoclave;

Step 2, heating to 180°C and keeping it warm for 60 minutes;

Step 3, after natural cooling, wash with pure water for several times and then dry to obtain nano-lithium iron phosphate seed crystals.

The nano-lithium iron phosphate seed crystal obtained in this manufacturing example is shown in FIG. 1 , and the particle size of the seed crystal is 30nm-200nm.

Comparative example 1

Step 1, prepare 0.1mg/mL ascorbic acid aqueous solution, weigh 2.78g of ferrous sulfate heptahydrate and dissolve in 10mL of the above-mentioned ascorbic acid aqueous solution; weigh 1.4g of lithium hydroxide monohydrate and prepare 10mL aqueous solution; take the Add 10 mg of seed crystal, 3 mL of ferrous sulfate solution prepared above, 3 mL of lithium hydroxide solution and 80 μL of phosphoric acid into 12 mL of ethylene glycol, and finally add it to the autoclave;

Step 2, heating to 180°C and keeping warm for 200min;

Step 3, after natural cooling, wash with pure water several times to obtain lithium iron phosphate.

As shown in FIG. 2 , in this comparative example, a pure-phase lithium iron phosphate material can be obtained, and the particles of the seed crystal become significantly larger after secondary growth. The X-ray diffraction pattern of the lithium iron phosphate material prepared in this comparative example is shown in Figure 3, and the XRD test result of the sample corresponds to the standard card.

Comparative example 2

Step 1, prepare 0.1mg/mL ascorbic acid aqueous solution, weigh 2.78g of ferrous sulfate heptahydrate and dissolve in 10mL of the above-mentioned ascorbic acid aqueous solution; weigh 1.4g of lithium hydroxide monohydrate and prepare 10mL of aqueous solution; Mix 3mL of iron solution, 3mL of lithium hydroxide solution and 80μL of phosphoric acid into 12mL of ethylene glycol, and finally add to the autoclave;

Step 2, heating to 180°C and keeping warm for 200min;

Step 3, after natural cooling, wash with pure water for several times to obtain a pure-phase lithium iron phosphate material grown once.

The XRD test pattern of the pure-phase lithium iron phosphate material obtained in this comparative example is shown in FIG. 3 .

Comparative example 3

Step 1, prepare 0.1mg/mL ascorbic acid aqueous solution, weigh 2.78g of ferrous sulfate heptahydrate and dissolve in 10mL of the above-mentioned ascorbic acid aqueous solution; weigh 1.4g of lithium hydroxide monohydrate and prepare 10mL of aqueous solution; Mix 3mL of iron solution, 3mL of lithium hydroxide solution and 80μL of phosphoric acid into 12mL of ethylene glycol containing 20mg of black phosphorus, and finally add to the autoclave;

Step 2, heating to 180°C and keeping warm for 200min;

Step 3, after natural cooling, wash with pure water for several times to obtain a pure-phase lithium iron phosphate material grown once.

As shown in Figure 2, this comparative example shows that the particle size distribution of the synthesized lithium iron phosphate is extremely uneven.

Example 1

Step 1, prepare 0.1mg/mL ascorbic acid aqueous solution, weigh 2.78g of ferrous sulfate heptahydrate and dissolve in 10mL of the above-mentioned ascorbic acid aqueous solution; weigh 1.4g of lithium hydroxide monohydrate and prepare 10mL aqueous solution; take the Mix 8 mg of seed crystal, 3 mL of ferrous sulfate solution prepared above, 3 mL of lithium hydroxide solution and 80 μL of phosphoric acid into 12 mL of ethylene glycol containing 20 mg of black phosphorus, and finally add to the autoclave;

Step 2, heating to 180°C and keeping warm for 200min;

Step 3, after natural cooling, wash with pure water several times to obtain secondary grown lithium iron phosphate.

The X-ray diffraction pattern of the pure-phase lithium iron phosphate material prepared in this embodiment is shown in FIG. 3 , and the XRD test result of the sample corresponds to the standard card. It can be seen from Figure 3 that in Example 1, the exposure ratio of the (020) crystal plane to the (200) crystal plane of the XRD of the lithium iron phosphate material is larger than that of Comparative Examples 1 and 2, representing the dominant direction of lithium ion transport (010) The more exposure, the more favorable the migration of lithium ions, which contributes to the improvement of the rate performance.

FIG. 4 is a scanning electron microscope image of the lithium iron phosphate material prepared in this embodiment.

The lithium iron phosphate materials prepared in this example and Comparative Example 2 were first carbonized, and the carbonization process was carried out with reference to [Ind.Eng.Chem.Res.2017,56,10648-10657]. The button half-cell specification is CR2032, half-cell slurry preparation: mix carbonized lithium iron phosphate and superconducting carbon black (SP) at a weight ratio of 8:1, and after fully grinding, N-methylpyrrolidone of polyvinylidene fluoride (PVDF/NMP) solution was added to the ground powder. At this time, the mass ratio of carbonized lithium iron phosphate:SP:PVDF was 8:1:1, and then coated on aluminum foil, and dried at 120°C for 6h under vacuum. Afterwards, it is cut into a positive electrode sheet with a diameter of 12 mm for use. Prepare the positive electrode casing, diaphragm, shrapnel, gasket, lithium sheet, negative electrode casing and weighed positive electrode sheet. In this experiment, a lithium sheet is used as the negative electrode, and the diaphragm is a Celgard 2400 microporous membrane. Use a pipette gun to drop 3 to 4 drops of lithium hexafluorophosphate electrolyte onto the diaphragm, and install the battery in a glove box filled with argon gas. After installation, Encapsulate the battery using an electric encapsulation machine. The rate performance was tested after the half-cell was left standing for 12 hours. The charge-discharge range was 2.0-3.75V, 1C=170mA/g. Among them, the rate performance diagram of the half-cells prepared by the same method in this embodiment and Comparative Example 2 is shown in FIG. 5 . The charge-discharge curve of the half-cell prepared in this example at 15C is shown in FIG. 6 . It can be seen from the figure that the half-cell prepared in this example has good charge-discharge performance and rate performance, which is significantly better than that of Comparative Example 2.

Example 2

Step 1, prepare 0.1mg/mL ascorbic acid aqueous solution, weigh 2.78g of ferrous sulfate heptahydrate and dissolve in 10mL of the above-mentioned ascorbic acid aqueous solution; weigh 1.4g of lithium hydroxide monohydrate and prepare 10mL aqueous solution; take the Mix 50 mg of seed crystals, 3 mL of ferrous sulfate solution prepared above, 3 mL of ferrous sulfate solution, 3 mL of lithium hydroxide solution, and 100 μL of phosphoric acid into 12 mL of ethylene glycol containing 10 mg of black phosphorus, and finally add to the autoclave;

Step 2, heating to 150°C and keeping warm for 180min;

Step 3, after natural cooling, wash with pure water several times to obtain secondary grown lithium iron phosphate.

Example 3

Step 1: prepare a 0.1 mg/mL ascorbic acid aqueous solution, weigh 2.6 g of ferrous sulfate heptahydrate and dissolve it in 10 mL of the above-mentioned ascorbic acid aqueous solution; weigh 1.3 g of lithium hydroxide monohydrate to prepare a 10 mL aqueous solution; take Manufacturing Example 1 to prepare 20 mg of seed crystals, 3 mL of ferrous sulfate solution prepared above, 3 mL of lithium hydroxide solution and 80 μL of phosphoric acid were mixed and added to 12 mL of ethylene glycol containing 10 mg of black phosphorus, and finally added to the autoclave;

Step 2, heating to 180°C and keeping it warm for 220min;

Step 3, after natural cooling, wash with pure water several times to obtain secondary grown lithium iron phosphate.

Example 4

Step 1, prepare 0.1mg/mL ascorbic acid aqueous solution, weigh 2.78g of ferrous sulfate heptahydrate and dissolve in 10mL of the above-mentioned ascorbic acid aqueous solution; weigh 1.3g of lithium hydroxide monohydrate and prepare 10mL aqueous solution; Mix 15 mg of seed crystal, 3 mL of ferrous sulfate solution prepared above, 3 mL of lithium hydroxide solution and 100 μL of phosphoric acid into 12 mL of ethylene glycol containing 5 mg of black phosphorus, and finally add it to the autoclave;

Step 2, heating to 150°C and keeping warm for 220min;

Step 3, after natural cooling, wash with pure water several times to obtain secondary grown lithium iron phosphate.

Example 5

Step 1, prepare 0.1mg/mL ascorbic acid aqueous solution, weigh 2.78g of ferrous sulfate heptahydrate and dissolve in 10mL of the above-mentioned ascorbic acid aqueous solution; weigh 1.4g of lithium hydroxide monohydrate and prepare 10mL aqueous solution; take the Mix 70 mg of seed crystal, 3 mL of ferrous sulfate solution prepared above, 3 mL of lithium hydroxide solution and 100 μL of phosphoric acid into 12 mL of ethylene glycol containing 30 mg of black phosphorus, and finally add it to the autoclave;

Step 2, heating to 220°C and keeping warm for 220min;

Step 3, after natural cooling, wash with pure water several times to obtain secondary grown lithium iron phosphate.

The above is only a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications are also possible. It should be regarded as the protection scope of the present invention.

Claims (10)

1. A secondary growth preparation method of nano-lithium iron phosphate, characterized in that, comprising the steps: The nanometer lithium iron phosphate, the two-dimensional phosphorus element and the reducing agent are subjected to a hydrothermal reaction in a lithium iron phosphate precursor solution; the lithium iron phosphate precursor solution includes an iron source, a lithium source and a phosphorus source. 2. The secondary growth preparation method according to claim 1, characterized in that, the reaction temperature of the hydrothermal reaction is 150°C-220°C; the holding time of the hydrothermal reaction is 150min-220min. 3. The secondary growth preparation method according to claim 1, wherein the reducing agent is ascorbic acid. 4. secondary growth preparation method according to claim 1, is characterized in that, described iron source is water-soluble ferrous salt, is preferably ferrous sulfate heptahydrate; Preferably, the lithium source is a water-soluble lithium salt, preferably lithium hydroxide monohydrate; Preferably, the phosphorus source is a water-soluble phosphorus source, preferably phosphoric acid; Preferably, the solvent of the lithium iron phosphate precursor solution is a mixed solvent of water and ethylene glycol. 5. The secondary growth preparation method according to claim 1, wherein the two-dimensional phosphorus simple substance is two-dimensional black phosphorus; Preferably, the lateral dimension of the two-dimensional phosphorous simple substance is 0.5 μm˜100 μm, and the thickness is 1 nm˜30 nm. 6. The secondary growth preparation method according to claim 4, characterized in that the mass ratio of the two-dimensional phosphorus element to the nano-lithium iron phosphate as the seed crystal is 1:0.4-5; Preferably, in the lithium iron phosphate precursor solution, the molar ratio of iron in the iron source, lithium in the lithium source, and phosphorus in the phosphorus source is 1:3-4:1-2; Preferably, the mass ratio of the reducing agent to the iron source is 1-2:2780; Preferably, the mass ratio of the nano-lithium iron phosphate used as the seed crystal to the iron source is 1-10:125. 7 . The secondary growth preparation method according to claim 1 , characterized in that, the secondary growth preparation method further comprises post-treatments of washing and drying after cooling down. 8 . 8. The secondary growth preparation method according to claim 1, wherein the nano-lithium iron phosphate as the seed crystal is prepared by a hydrothermal method; Preferably, the particle size of the nano-lithium iron phosphate used as the seed crystal is 30nm-200nm. 9. The nano-lithium iron phosphate obtained by the secondary growth preparation method described in any one of claims 1-8. 10. The application of nano-lithium iron phosphate according to claim 9 in the preparation of lithium-ion batteries is characterized in that it is used in the preparation of lithium-ion battery cathode materials.

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