CN114057176B - Lithium iron phosphate and its preparation methods and applications - Google Patents

Abstract

The invention discloses lithium iron phosphate and a preparation method and application thereof; the preparation method of the lithium iron phosphate comprises the following steps: (1) Ferric salt, phytic acid and phosphate are mixed and reacted in water to obtain ferric phosphate precursor liquid; (2) Filtering, drying and calcining the ferric phosphate precursor liquid to obtain ferric phosphate; (3) Mixing ferric phosphate, lithium salt and a carbon source in water, and then drying and calcining to obtain lithium iron phosphate. According to the invention, the low-temperature performance of the prepared lithium iron phosphate is obviously improved through the matched use of the phytic acid and the phosphate.

Description

Lithium iron phosphate and its preparation methods and applications

Technical field

The invention relates to the field of battery technology, and in particular to lithium iron phosphate and its preparation method and application.

Background technique

With the continuous reduction of oil resources around the world and the increasingly serious environmental pollution caused by automobile exhaust, hybrid electric vehicles (HEV) and electric vehicles (EV) have attracted much attention as substitutes for fuel-driven vehicles in the future, and mobile power systems are As one of the key components of electric vehicles. Therefore, high-performance (i.e. high specific energy, long life, safety), low-cost and environmentally friendly batteries will become the focus and hot spot of the development of the mobile power industry. Lithium-ion batteries are a new generation of green, high-energy rechargeable batteries developed to meet this demand. It has outstanding advantages such as high voltage, small size, light weight, high specific energy, no memory effect, no pollution, small self-discharge, and long life.

Since Padhi et al. reported in 1997 that lithium iron phosphate material with olivine structure can be used as the cathode material of lithium-ion batteries, it has become the most popular material at present due to its advantages such as low price, environmental protection and pollution-free, non-hygroscopicity and good thermal stability. One of the most promising cathode materials, it has attracted the attention of the majority of scientific research institutions and commercial institutions. In recent years, many scientific researchers have done a lot of research, development and improvement of this material. At present, this material has gradually moved towards commercialization and is used in the high-capacity, high-power and long-life lithium-ion battery market. Lithium iron phosphate represents the future development direction of power battery cathode materials.

At present, solid-phase synthesis is the main method for preparing commercial lithium iron phosphate. However, due to the high cost of divalent iron sources, difficulty in preservation, and the large particle size and poor uniformity of the synthesized lithium iron phosphate, it is difficult to meet the requirements of power lithium-ion batteries. need. Therefore, cheap and stable ferric iron is used as the iron source instead of divalent iron, and ferric phosphate is synthesized as the precursor to prepare lithium iron phosphate. The synthesis method of ferric phosphate is usually to react ferric chloride or ferric nitrate solution with phosphoric acid, and then decompose and volatilize hydrogen chloride or nitric acid at high temperature to obtain ferric phosphate.

However ^, lithium ^{iron phosphate causes phosphoric} acid to be Batteries using lithium iron as the cathode material have significant attenuation in charge and discharge performance at low temperatures.

Contents of the invention

The purpose of the present invention is to provide a lithium iron phosphate and its preparation method and application, which can significantly improve its low-temperature performance.

In order to achieve the above objects, the technical solution adopted by the present invention is:

The invention discloses a preparation method of lithium iron phosphate, which includes the following steps:

(1) Mix and react ferric iron salts, phytic acid, and phosphate in water to obtain iron phosphate precursor body fluid;

(2) Filter, dry, and calcine the iron phosphate precursor body fluid obtained in step (1) to obtain iron phosphate;

(3) Mix the iron phosphate obtained in step (2) with lithium salt and carbon source in water, then dry and calcine to obtain lithium iron phosphate.

As a preferred technical solution, in step (1), the trivalent iron salt includes but is not limited to one or a mixture of ferric chloride, ferric nitrate, and ferric sulfate.

As a preferred technical solution, in step (1), phosphates include but are not limited to H ₃ PO ₄ , (NH ₄ ) ₃ PO ₄ , (NH ₄ ) ₂ HPO ₄ , (NH ₄ )H ₂ PO ₄ One or a mixture of several.

As a preferred technical solution, in the step (1), the molar ratio of phytic acid to phosphate is 1:999-999:1.

As a preferred technical solution, in step (1), alkali solution is added to the reaction system to control the pH value to less than 7.

As a preferred technical solution, the alkali solution includes but is not limited to one or a mixture of ammonia water, sodium hydroxide solution, sodium acetate solution, and ammonium acetate solution.

As a preferred technical solution, in step (1), the reaction is a room temperature reaction.

As a preferred technical solution, in step (2), alkali solution is added to dilute the iron phosphate precursor body fluid before filtration or alkali solution is added to wash the iron phosphate precursor body fluid when filtering.

As a preferred technical solution, in step (2), the calcination temperature is 100-800°C.

As a preferred technical solution, in step (3), the lithium salt includes but is not limited to one or a mixture of lithium carbonate, lithium hydroxide, lithium nitrate, and lithium oxalate.

As a preferred technical solution, in the step (3), the carbon source includes but is not limited to one or a mixture of glucose, sucrose, carbon nanotubes, and graphene.

The invention also discloses the application of the lithium iron phosphate prepared by the above preparation method in the cathode material of lithium ion battery.

Beneficial effects of the present invention:

The present invention uses phytic acid and phosphate to form a phosphate group as a phosphorus source, synthesizes iron phosphate with ferric iron salt, and then uses the iron phosphate as a precursor to prepare lithium iron phosphate. The present invention significantly improves the low-temperature performance of the prepared lithium iron phosphate through the combined use of phytic acid and phosphate.

Description of drawings

Figure 1 is a process flow chart for preparing iron phosphate from ferric salt;

Figure 2 is a structural diagram of a device for preparing iron phosphate from ferric iron salt;

Figure 3 is a process flow chart for preparing lithium iron phosphate from iron phosphate;

Figure 4 is a structural diagram of a device for preparing lithium iron phosphate from iron phosphate;

Figure 5 is an SEM image of lithium iron phosphate prepared in Example 1;

Figure 6 is a 0.2C discharge specific capacity diagram of the button battery made of lithium iron phosphate in Example 1 at -20°C;

Figure 7 is a 0.2C discharge specific capacity diagram of the button battery made of lithium iron phosphate in Example 2 at -20°C;

Figure 8 is a 0.2C discharge specific capacity diagram of the button battery made of lithium iron phosphate in Comparative Example 1 at -20°C.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described below in conjunction with the accompanying drawings.

Example 1

As shown in Figures 1 to 4, the following steps are used to prepare lithium iron phosphate:

(1) Add ferric chloride solution, phytic acid, (NH ₄ )H ₂ PO ₄ and ammonia water into the reaction kettle, control the molar ratio of phytic acid to (NH ₄ )H ₂ PO ₄ to 1:99, and control the molar ratio of ammonia water Add the amount to adjust the pH value of the system to about 2, then mix and stir in the reaction kettle at room temperature for 1 hour; then pump the reaction slurry into the aging kettle for aging for 1 hour, and pump the obtained iron phosphate precursor liquid into the finished product tank temporarily. live.

(2) Dilute the ferric phosphate precursor liquid obtained in step (1) with ammonia water, then pump it into a plate and frame filter for filtration, and wash until neutral; then add the wet material to a flash dryer to flash dry, and then add the rotary It is calcined in a kiln at 400°C to obtain iron phosphate.

(3) Add the iron phosphate, lithium carbonate, and glucose obtained in step (2) to a dispersion kettle filled with water to fully disperse, then add the slurry to a grinding tank for grinding, and then spray drying with spray drying equipment and sintering in a sintering furnace. Crush it with a jet mill to obtain lithium iron phosphate.

Example 2

As shown in Figures 1 to 4, the following steps are used to prepare lithium iron phosphate:

(1) Add ferric chloride solution, phytic acid, H ₃ PO ₄ and ammonia water into the reaction kettle, control the molar ratio of phytic acid and H ₃ PO ₄ to 1:99, control the addition amount of ammonia water and adjust the pH value of the system to About 2, then mix and stir the reaction at room temperature in the reaction kettle for 1 hour; then pump the reaction slurry into the aging kettle for aging for 1 hour, and the obtained iron phosphate precursor liquid is pumped into the finished product tank for temporary storage.

(2) Dilute the ferric phosphate precursor liquid obtained in step (1) with ammonia water, then pump it into a plate and frame filter for filtration, and wash until neutral; then add the wet material to a flash dryer to flash dry, and then add the rotary It is calcined in a kiln at 400°C to obtain iron phosphate.

(3) Add the iron phosphate, lithium carbonate, and glucose obtained in step (2) to a dispersion kettle filled with water to fully disperse, then add the slurry to a grinding tank for grinding, and then spray drying with spray drying equipment and sintering in a sintering furnace. Crush it with a jet mill to obtain lithium iron phosphate.

Comparative example 1

Use the following steps to prepare lithium iron phosphate:

(1) Add ferric chloride solution, H ₃ PO ₄ and ammonia water into the reaction kettle, control the amount of ammonia water added to adjust the pH value of the system to about 2, then mix and stir the reaction kettle at room temperature for 1 hour; then add the reaction slurry The material is pumped into the aging kettle for aging for 1 hour, and the obtained iron phosphate precursor liquid is pumped into the finished product tank for temporary storage.

(2) Dilute the ferric phosphate precursor liquid obtained in step (1) with ammonia water, then pump it into a plate and frame filter for filtration, and wash until neutral; then add the wet material to a flash dryer to flash dry, and then add the rotary It is calcined in a kiln at 400°C to obtain iron phosphate.

(3) Add the iron phosphate, lithium carbonate, and glucose obtained in step (2) to a dispersion kettle filled with water to fully disperse, then add the slurry to a grinding tank for grinding, and then spray drying with spray drying equipment and sintering in a sintering furnace. Crush it with a jet mill to obtain lithium iron phosphate.

Figure 5 is an SEM image of the lithium iron phosphate prepared in Example 1. It can be seen from the figure that the particle size of the lithium iron phosphate prepared in Example 1 is uniform.

The lithium iron phosphate prepared in Example 1, Example 2, and Comparative Example 1 was used as a positive electrode material. First, a positive electrode sheet was made: the positive electrode material, binder, and conductive agent were mixed into the positive electrode ingredients to obtain a uniform positive electrode slurry. The prepared positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil to obtain a positive electrode sheet. The positive electrode sheet, the negative electrode sheet and the separator are wound to prepare a lithium-ion battery core, and the electrolyte is injected to form a button battery.

Figure 6 is a diagram of the discharge specific capacity of the button battery made of lithium iron phosphate in Example 1 at 0.2C at -20°C. The specific discharge capacity at -20°C can reach 80mAh/g.

Figure 7 is a diagram of the discharge specific capacity of the button battery made of lithium iron phosphate in Example 2 at -20°C at 0.2C. The -20°C discharge specific capacity can reach 83mAh/g.

Figure 8 is a diagram of the discharge specific capacity of the button battery made of lithium iron phosphate in Comparative Example 1 at -20°C at 0.2C. The -20°C discharge specific capacity can reach 54mAh/g.

It can be seen from the above comparison that, compared with the comparative example of using only phosphoric acid, the present invention significantly improves the low-temperature performance of the prepared lithium iron phosphate through the combined use of phytic acid and phosphate.

The basic principles, main features and advantages of the present invention have been shown and described above. Those skilled in the industry should understand that the present invention is not limited by the above embodiments. The above embodiments and descriptions only illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will also have other aspects. Various changes and modifications are possible, which fall within the scope of the claimed invention. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims (11)

1. A method for preparing lithium iron phosphate, which is characterized in that it includes the following steps: (1) Mix and react ferric iron salts, phytic acid, and phosphate in water to obtain iron phosphate precursor body fluid; (2) Filter, dry, and calcine the iron phosphate precursor body fluid obtained in step (1) to obtain iron phosphate; (3) Mix the iron phosphate obtained in step (2) with lithium salt and carbon source in water, then dry and calcine to obtain lithium iron phosphate; In the step (1), the molar ratio of phytic acid and phosphate is 1:999-1:99. 2. The preparation method of lithium iron phosphate according to claim 1, characterized in that: in the step (1), the ferric salt includes but is not limited to one of ferric chloride, ferric nitrate, ferric sulfate or Several mixes. 3. The preparation method of lithium iron phosphate according to claim 1, characterized in that: in the step (1), the phosphate includes but is not limited to H ₃ PO ₄ , (NH ₄ ) ₃ PO ₄ , (NH ₄ ) ₂ HPO ₄ , (NH ₄ )H ₂ PO ₄ , or a mixture of several. 4. The preparation method of lithium iron phosphate according to claim 1, characterized in that: in the step (1), alkali liquid is added to the reaction system to control the pH value to less than 7. 5. The preparation method of lithium iron phosphate according to claim 4, characterized in that: the alkali solution includes but is not limited to one or more mixtures of ammonia water, sodium hydroxide solution, sodium acetate solution, and ammonium acetate solution. . 6. The method for preparing lithium iron phosphate according to claim 1, characterized in that in step (1), the reaction is a room temperature reaction. 7. The preparation method of lithium iron phosphate according to claim 1, characterized in that: in the step (2), alkali solution is added to dilute the iron phosphate precursor body fluid before filtering, or alkali solution is added to wash the iron phosphate precursor body fluid when filtering. 8. The method for preparing lithium iron phosphate according to claim 1, characterized in that in step (2), the calcination temperature is 100-800°C. 9. The preparation method of lithium iron phosphate according to claim 1, characterized in that: in the step (3), the lithium salt includes but is not limited to one of lithium carbonate, lithium hydroxide, lithium nitrate, and lithium oxalate. Or a mix of several. 10. The preparation method of lithium iron phosphate according to claim 1, characterized in that: in the step (3), the carbon source includes but is not limited to one or more of glucose, sucrose, carbon nanotubes, and graphene. A mixture of species. 11. Application of lithium iron phosphate prepared by the preparation method according to any one of claims 1 to 10 in lithium ion battery cathode materials.