Method for preparing high energy density lithium iron phosphate

Abstract

The application provides a preparation method of high-energy-density lithium iron phosphate and a lithium iron phosphate battery, and comprises the following steps: S1: preparing iron phosphate dihydrate with a spherical microstructure and iron phosphate dihydrate with a flaky microstructure; and S2: mixing the iron phosphate dihydrate with the spherical microstructure and the iron phosphate dihydrate with the flaky microstructure, co-calcining the mixed iron phosphate dihydrate with lithium source, and performing a crushing process. The preparation method can improve the energy density of the lithium iron phosphate.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a method for preparing high-energy-density lithium iron phosphate. Background Technology

[0002] With technological advancements, new energy sources are gaining increasing attention. Currently, the main types of new energy batteries are ternary lithium batteries, lithium iron phosphate batteries, and lithium iron phosphate batteries. Lithium iron phosphate batteries, with their advantages of high safety, long cycle life, high temperature resistance, and relatively low cost, are a crucial development direction for new energy batteries. However, inherent shortcomings and disadvantages of lithium iron phosphate batteries still exist, and improving their energy density remains a significant challenge for the industry.

[0003] Currently, the main method for preparing high-energy-density lithium iron phosphate is through the preparation of small-particle lithium iron phosphate. However, this method is cumbersome, complex to control, and has high raw material costs, making it difficult to industrialize. Summary of the Invention

[0004] In view of this, the present invention provides a method for preparing high-energy-density lithium iron phosphate, which can improve the energy density of lithium iron phosphate.

[0005] This invention provides a method for preparing high-energy-density lithium iron phosphate, the method comprising the following steps:

[0006] S1: Prepare ferric phosphate dihydrate with spherical microstructure and ferric phosphate dihydrate with flake microstructure;

[0007] S2: Iron phosphate dihydrate with a spherical microstructure is mixed with iron phosphate dihydrate with a flake microstructure, and then subjected to a co-roasting and crushing process with a lithium source to obtain lithium iron phosphate.

[0008] Furthermore, in preparing ferric phosphate dihydrate with a spherical microstructure, the method includes: forming ferric phosphate dihydrate through a sulfuric acid system.

[0009] Furthermore, in preparing ferric phosphate dihydrate with a sheet-like microstructure, the method also includes the following steps:

[0010] S11: Dissolve the ferrophosphorus material in a volatile acidic solution to obtain the original solution, and filter the original solution to obtain the filtrate;

[0011] S12: Evaporate the filtrate to remove the volatile acids in the filtrate, forming an evaporated slurry;

[0012] S13: After diluting the evaporated slurry with water, it is then subjected to precipitation, filtration, washing and drying steps to obtain ferric phosphate dihydrate with a microscopic morphology of flakes.

[0013] Furthermore, the volatile acid in the volatile acid solution has a mass fraction of 5-60%, and the molar amount of the volatile acid is 0.3-4 times the molar amount of iron in the iron phosphate material.

[0014] Furthermore, in the spherical form of the ferric phosphate dihydrate, the molar ratio of iron to phosphorus is less than 0.985, while in the flake form of the ferric phosphate dihydrate, the molar ratio of iron to phosphorus is greater than 0.985.

[0015] Furthermore, in step S2, the mass ratio of the ferric phosphate dihydrate with a sheet-like microstructure to the ferric phosphate dihydrate with a spherical microstructure is 1:1 to 1:5.

[0016] Furthermore, in step S2, the molar ratio of the amount of lithium in the added lithium source to the sum of the amounts of iron in the total iron phosphate in the spherical and flake-shaped ferric phosphate dihydrate is 1-1.08:1.

[0017] Furthermore, during step S2, the method also includes adding a carbon source during calcination, wherein the mass of the carbon source accounts for 5-10% of the total mass of iron phosphate in the dihydrate iron phosphate with a microscopic morphology of spherical and flake-like.

[0018] Furthermore, in step S2, the method further includes adding iron oxide and / or iron hydroxide to the mixture of ferric phosphate dihydrate with a spherical microstructure and ferric sulfate dihydrate with a flake-like microstructure.

[0019] Furthermore, the total amount of iron in the iron oxide and the iron hydroxide is 0.01%-0.15% of the total amount of iron in the spherical ferric phosphate dihydrate and the flake-shaped ferric sulfate dihydrate.

[0020] Furthermore, in step S2, the method includes mixing the spherical ferric phosphate dihydrate with the flake-shaped ferric phosphate dihydrate, followed by ball milling and dehydration.

[0021] Furthermore, in step S2, the method further includes ball milling the spherical ferric phosphate dihydrate and the flake-shaped ferric phosphate dihydrate separately, then preparing the spherical ferric phosphate dihydrate and the flake-shaped ferric phosphate dihydrate into slurries, and then spray drying and granulating the two prepared slurries.

[0022] Furthermore, the average particle size of the primary lithium iron phosphate particles is 0.1-0.3 μm, and in step S2, the particle size of the ball-milled lithium iron phosphate is D99 < 150 μm.

[0023] Furthermore, this lithium iron phosphate has Li x Fe y M z The general structural formula of PO4, wherein M is selected from one or more of Mg, Mn, S, Al, Cu, Zn, Cr, Ti, Pb, Co and Ni, y is 0.980-0.995, z is 0.0001-0.005, and x is 1.0y-1.05y.

[0024] In summary, this invention utilizes iron phosphate with different microstructures to prepare lithium iron phosphate. Because iron phosphate with different microstructures exhibits different anisotropy, the energy density of iron phosphate within the microscopic space of lithium iron phosphate can be increased after the lithium iron phosphate is prepared. Furthermore, since spherical iron phosphate has a low iron-to-phosphorus molar ratio, adding flake-shaped iron phosphate with a high iron-to-phosphorus molar ratio during lithium iron phosphate preparation further enhances the energy density of the synthesized lithium iron phosphate. The synergistic effect of different microstructures and different iron-to-phosphorus molar ratios further improves the energy density of the prepared lithium iron phosphate.

[0025] Furthermore, this method prepares ferric phosphate dihydrate using a volatile acidic solution method. The volatile acidic solution can be recycled, which reduces the amount of acidic solution lost during the process. The process is environmentally friendly, has low cost, and is easy to industrialize.

[0026] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0027] Figure 1 The diagram shows a flowchart of each step in the preparation method of high energy density lithium iron phosphate provided in an embodiment of the present invention.

[0028] Figure 2 This is a scanning electron microscope image of spherical iron phosphate.

[0029] Figure 3 This is a scanning electron microscope image of flaky iron phosphate.

[0030] Figure 4 A scanning electron microscope image of lithium iron phosphate prepared by the high energy density lithium iron phosphate preparation method provided in this embodiment of the invention.

[0031] Figure 5 The image shows the XRD pattern of iron phosphate in Example 1.

[0032] Figure 6 This is a scanning electron microscope image of lithium iron phosphate prepared using spherical iron phosphate.

[0033] Figure 7 This is a scanning electron microscope image of lithium iron phosphate prepared using flake-shaped iron phosphate. Detailed Implementation

[0034] To further illustrate the technical means and effects adopted by the present invention in order to achieve the intended purpose, the following detailed description is provided in conjunction with the accompanying drawings and preferred embodiments.

[0035] This invention provides a method for preparing high-energy-density lithium iron phosphate, which can improve the energy density of lithium iron phosphate.

[0036] Figure 1 The diagram shown is a flowchart illustrating the steps of the high-energy-density lithium iron phosphate preparation method provided in this embodiment of the invention. Figure 2 This is a scanning electron microscope image of spherical iron phosphate. Figure 3 This is a scanning electron microscope image of sheet-like iron phosphate. Figure 4 Scanning electron microscope (SEM) images of lithium iron phosphate prepared by the high-energy-density lithium iron phosphate preparation method provided in this embodiment of the invention. For example... Figures 1 to 4 As shown, the preparation method of high energy density lithium iron phosphate provided in this embodiment of the invention includes the following steps:

[0037] S1: Preparation of ferric phosphate dihydrate with spherical microstructure (see...) Figure 2 ), and ferric phosphate dihydrate with a microscopic morphology of flakes (see Figure 3 );

[0038] The aforementioned microstructure refers to the morphological characteristics of the product as observed by equipment such as optical microscopes and scanning electron microscopes. In the preparation of ferric phosphate dihydrate, the microstructure is related to the preparation method; different preparation methods result in different microstructures.

[0039] In this step, ferric phosphate material can be prepared into spherical ferric phosphate dihydrate using sulfuric acid systems such as one-step or two-step sulfuric acid processes. More specifically, it can be prepared using an ammonia-based or sodium-based sulfuric acid system to achieve the spherical morphology of ferric phosphate dihydrate.

[0040] It should be noted that this method is also the conventional preparation method for the iron phosphate required to produce lithium iron phosphate.

[0041] Preferably, in ferric phosphate dihydrate with a spherical microstructure, the molar ratio of iron to phosphorus is less than 0.985.

[0042] Preferably, in ferric phosphate dihydrate with a flake-like microstructure, the molar ratio of iron to phosphorus is greater than 0.985.

[0043] Furthermore, the preparation of ferric phosphate dihydrate with a sheet-like microstructure also specifically includes:

[0044] S11: Dissolve the ferrophosphorus material in volatile acidic solutions such as hydrochloric acid, citric acid, and organic acids, and then filter to obtain the filtrate.

[0045] In this step, the ferrophosphate material can be the ferrophosphate slag or phosphating slag after lithium extraction from lithium iron phosphate, allowing for the recycling of raw materials and cost savings. Understandably, in other embodiments, it can also be other substances containing ferrophosphate.

[0046] The mass fraction of volatile acid in the volatile acidic solution is 5-60%. The molar amount of volatile acid is 0.3-4 times the molar amount of iron in the ferrophosphate feed.

[0047] S12: Evaporate the filtrate to remove the volatile acids and form an evaporated slurry;

[0048] It should be noted that after evaporation, the volatile acids can be collected for recycling.

[0049] In this step, the evaporation temperature is 80-140℃, and the evaporation mass is 50-90% of the filtrate mass.

[0050] S13: After diluting the evaporated slurry with water, it undergoes sedimentation, filtration, washing and drying to obtain ferric phosphate dihydrate with a non-spherical microstructure.

[0051] In this step, the amount of water added for dilution is 60-110% of the slurry mass. The drying temperature is 60-140℃, and the time is 1-5 hours.

[0052] S2: Ferric phosphate dihydrate with a spherical microstructure is mixed with ferric phosphate dihydrate with a flake microstructure, and after co-calcination with a lithium source and crushing process, high energy density lithium iron phosphate is obtained.

[0053] In this step, the mass ratio of ferric phosphate dihydrate with a flake-like microstructure to ferric phosphate dihydrate with a spherical microstructure is 1:1 to 1:5.

[0054] In this step, spherical ferric phosphate dihydrate and flake-like ferric phosphate dihydrate can be directly mixed, and then ball-milled and dehydrated to form a granular mixture. The particle size D99 of the ball-milled lithium iron phosphate is <150 μm.

[0055] The dehydration and calcination temperature is 500-850℃, and the time is 1-9 hours. Preferably, the dehydration temperature is 500-650℃, and the time is 2-5 hours. Preferably, the calcination temperature is 700-850℃, and the time is 4-9 hours.

[0056] The added lithium source, such as lithium carbonate, lithium hydroxide, lithium bicarbonate, etc., has a molar ratio of lithium to total iron in ferric phosphate dihydrate with spherical and flake-like microstructures of 1.00-1.08:1.

[0057] Furthermore, a carbon source can be added during the calcination process to facilitate the reduction of ferric iron and to act as a coating agent to increase ion transport rate. The carbon source can be glucose or PEG (polyethylene glycol), and the total mass added should account for 5-10% of the total mass of ferric phosphate in the spherical and flake-shaped dihydrate.

[0058] Furthermore, the average particle size of the primary particles (i.e., unagglomerated particles) of lithium iron phosphate particles is 0.1-0.3 μm.

[0059] Furthermore, this lithium iron phosphate has Li x Fe y M z The general structural formula of PO4, wherein M is selected from one or more of Mg, Mn, S, Al, Cu, Zn, Cr, Ti, Pb, Co and Ni, y is 0.980-0.995, z is 0.0001-0.005, and x is 1.0y-1.05y.

[0060] Furthermore, during the mixing process, iron oxide and / or iron hydroxide can be added. During calcination, the addition of iron oxide or iron hydroxide allows the iron element in the iron oxide or iron hydroxide to enter the lattice of lithium iron phosphate without changing the morphology of the spherical ferric phosphate dihydrate and the plate-like ferric sulfate dihydrate. This can further increase the iron-phosphorus molar ratio in lithium iron phosphate, thereby increasing the energy density of the synthesized lithium iron phosphate.

[0061] More specifically, iron oxide and / or iron hydroxide can be added during ball milling, and the total amount of iron in iron hydroxide and iron oxide is 0.01%-0.15% of the total amount of iron in spherical ferric phosphate dihydrate and flake-like ferric sulfate dihydrate.

[0062] In another embodiment of the present invention, during mixing, spherical ferric phosphate dihydrate and flake-shaped ferric phosphate dihydrate can be ball-milled separately, then separately prepared into slurries. The two prepared slurries are then spray-dried and granulated before mixing to complete the mixing process. This method ensures a more uniform mixing of the two materials.

[0063] More specifically, during slurry preparation, the solid content in the slurry is 15%-40% of the total slurry mass.

[0064] like Figure 4 As shown, in this embodiment, lithium iron phosphate is prepared by using iron phosphate with different microstructures. Since spherical and flake-shaped iron phosphate have different anisotropies, the different microstructures of iron phosphate can increase the energy density of iron phosphate within the microscopic space of lithium iron phosphate after preparation. Furthermore, since flake-shaped iron phosphate is easier to pulverize after ball milling than spherical iron phosphate, and the pulverized particles are smaller, these small particles can enter the gaps in the spherical iron phosphate, resulting in a smaller average particle size and higher density of the shaped lithium iron phosphate, which further improves the energy density of lithium iron phosphate within the microscopic space. Furthermore, since the iron-to-phosphorus molar ratio of spherical iron phosphate is low, adding flake-shaped iron phosphate with a high iron-to-phosphorus molar ratio during lithium iron phosphate preparation can further improve the energy density of the synthesized lithium iron phosphate. The synergistic effect of different microstructures and different iron-to-phosphorus molar ratios further enhances the energy density of the prepared lithium iron phosphate.

[0065] This method prepares ferric phosphate dihydrate using a volatile acidic solution. The volatile acidic solution can be recycled, which reduces the loss of acidic solution during the process. The process is environmentally friendly, has low cost, and is easy to industrialize.

[0066] The method described above will be explained below with specific implementation details:

[0067] Example 1:

[0068] (1) Preparation of iron phosphate dihydrate with a flake-like microstructure: Take 500g of iron phosphate residue (iron content 20%) after lithium extraction from waste lithium iron phosphate material, dissolve it with 500g of hydrochloric acid with a mass fraction of 20%, dissolve it at 80℃, react for 3h, evaporate the hydrochloric acid in the filtrate after filtering the solution at 110℃, the mass of hydrochloric acid evaporated is 80% of the original filtrate mass (hydrochloric acid recovery rate 92%), then dilute with water, the amount of dilution water added is 85% of the original filtrate mass, filter and wash the obtained slurry, dry it at 120℃ for 3h, and obtain iron phosphate dihydrate material, Fe / P (mol) = 0.995.

[0069] (2) Preparation of spherical ferric phosphate dihydrate: Ferric phosphate dihydrate was prepared in a one-step process in a sulfuric acid system (using sodium system).

[0070] (3) Preparation of lithium iron phosphate: Spherical iron phosphate dihydrate and flake iron phosphate dihydrate were ball-milled in a ball mill until the particle size D99 = 60 μm. The mixture was dehydrated at 550 °C for 3 h. Then, lithium carbonate and carbon source were added to the dehydrated material. The amount of battery-grade lithium carbonate and carbon source added was 2.5% and 8% of the mass of iron phosphate, respectively. After mixing, the material was calcined at 780 °C for 5 h to obtain high energy density lithium iron phosphate material.

[0071] Figure 5 The XRD pattern in this embodiment is derived from... Figure 5 It can be seen that the prepared flake and spherical mixed iron phosphate has good purity and crystal form, and no impurity peaks.

[0072] Example 2:

[0073] (1) Preparation of iron phosphate dihydrate with a flake-like microstructure: Take 500g of iron phosphate residue (iron content 20%) after lithium extraction from waste lithium iron phosphate material, dissolve it with 450g of hydrochloric acid with a mass fraction of 25%, dissolve it at 70℃, react for 4h, and evaporate the hydrochloric acid in the filtrate after filtration at 80℃. The mass of hydrochloric acid evaporated is 90% of the original filtrate mass (hydrochloric acid recovery rate 94%). Then dilute with water, the amount of dilution water added is 80% of the original filtrate mass. After filtering and washing, the slurry is dried at 110℃ for 2h to obtain iron phosphate dihydrate with a flake-like microstructure and Fe / P (mol) = 0.997.

[0074] (2) Preparation of spherical ferric phosphate dihydrate: Ferric phosphate dihydrate with spherical microstructure was prepared by a one-step method in a sulfuric acid system (using an ammonia system).

[0075] (3) Spherical iron phosphate dihydrate and flake iron phosphate dihydrate were ball-milled in a ball mill until the particle size D99 = 110 μm. The mixture was dehydrated at 500 °C for 2 h. Lithium carbonate and carbon source were then added to the dehydrated material. The amount of battery-grade lithium carbonate and carbon source added was 2.55% and 9% of the mass of iron phosphate, respectively. After mixing, the material was calcined at 800 °C for 4 h to obtain high energy density lithium iron phosphate material.

[0076] Example 3:

[0077] (1) Preparation of iron phosphate dihydrate with a flake-like microstructure: Take 500g of iron phosphate residue (20% iron content) after lithium extraction from waste lithium iron phosphate material, dissolve it with 250g of hydrochloric acid with a mass fraction of 60%, dissolve it at 80℃, react for 3h, and evaporate the hydrochloric acid in the filtrate after filtration at 140℃. The mass of hydrochloric acid evaporated is 90% of the original filtrate mass (hydrochloric acid recovery rate 94%). Then dilute with water, the amount of dilution water added is 70% of the original filtrate mass. After filtering and washing, the slurry is dried at 135℃ for 2h to obtain iron phosphate dihydrate S1, Fe / P (mol) = 0.999.

[0078] (2) Preparation of spherical ferric phosphate dihydrate: Ferric phosphate dihydrate was prepared by a two-step method in a sulfuric acid system (using an ammonia system).

[0079] (3) Preparation of lithium iron phosphate: Spherical ferric phosphate dihydrate and flake ferric phosphate dihydrate were ball-milled in a ball mill until the particle size D99 = 140 μm. The mixture was dehydrated at 650 °C for 2 h. Then, lithium carbonate and carbon source were added to the dehydrated material. The amount of battery-grade lithium carbonate and carbon source added was 2.60% and 7% of the mass of ferric phosphate, respectively. After mixing, the material was calcined at 800 °C for 4 h to obtain high energy density lithium iron phosphate material.

[0080] Example 4:

[0081] (1) Preparation of iron phosphate dihydrate with a flake-like microstructure: Take 500g of iron phosphate residue (iron content 20%) after lithium extraction from waste lithium iron phosphate material, dissolve it with 500g of hydrochloric acid with a mass fraction of 20%, dissolve it at 80℃, react for 3h, evaporate the hydrochloric acid in the filtrate after filtering the solution at 70℃, the mass of hydrochloric acid evaporated is 80% of the original filtrate mass (hydrochloric acid recovery rate 92%), then add water to dilute it, the amount of dilution water added is 85% of the original filtrate mass, filter and wash the obtained slurry, and dry it at 120℃ for 3h to obtain iron phosphate dihydrate with a flake-like microstructure.

[0082] (2) Preparation of spherical ferric phosphate dihydrate: Ferric phosphate dihydrate with spherical morphology was prepared by a one-step method in a sulfuric acid system (using sodium system).

[0083] (3) Preparation of lithium iron phosphate: Spherical iron phosphate dihydrate and flake iron phosphate dihydrate were ball-milled in a ball mill until the particle size D99 = 60 μm. The mixture was dehydrated at 550 °C for 3 h. Then, lithium carbonate and carbon source were added to the dehydrated material. The amount of battery-grade lithium carbonate and carbon source added was 2.5% and 8% of the mass of iron phosphate, respectively. After mixing, the material was calcined at 780 °C for 5 h to obtain high energy density lithium iron phosphate material.

[0084] Example 5:

[0085] (1) Preparation of iron phosphate dihydrate with a flake-like microstructure: Take 500g of iron phosphate residue (iron content 19%) after lithium extraction from waste lithium iron phosphate material, dissolve it with 500g of hydrochloric acid with a mass fraction of 24%, dissolve it at 80℃, react for 3h, evaporate the hydrochloric acid in the filtrate after filtering the solution at 110℃, the mass of hydrochloric acid evaporated is 78% of the original filtrate mass (hydrochloric acid recovery rate 92%), then dilute with water, the amount of dilution water added is 85% of the original filtrate mass, filter and wash the obtained slurry, dry it at 120℃ for 3h, and obtain iron phosphate dihydrate material with Fe / P (mol) = 0.994.

[0086] (2) Preparation of spherical ferric phosphate dihydrate: Ferric phosphate dihydrate was prepared in a one-step process in a sulfuric acid system (using sodium system).

[0087] (3) Preparation of lithium iron phosphate: Spherical iron phosphate dihydrate, flake-shaped iron phosphate dihydrate, and iron oxide were ball-milled in a ball mill jar. The molar amount of iron added to the iron oxide was 0.07% of the molar amount of spherical and flake-shaped iron phosphate. The mixture was ball-milled to a particle size D99 = 60 μm. The mixture was dehydrated at 550 °C for 3 h. Then, lithium carbonate and carbon source were added to the dehydrated material. The amount of battery-grade lithium carbonate and carbon source added was 2.5% and 8% of the mass of iron phosphate, respectively. After mixing, the material was calcined at 780 °C for 5 h to obtain high energy density lithium iron phosphate material.

[0088] Example 6:

[0089] (1) Preparation of iron phosphate dihydrate with a flake-like microstructure: Take 500g of iron phosphate residue (iron content 19%) after lithium extraction from waste lithium iron phosphate material, dissolve it with 500g of hydrochloric acid with a mass fraction of 24%, dissolve it at 80℃, react for 3h, evaporate the hydrochloric acid in the filtrate after filtering the solution at 110℃, the mass of hydrochloric acid evaporated is 78% of the original filtrate mass (hydrochloric acid recovery rate 92%), then dilute with water, the amount of dilution water added is 85% of the original filtrate mass, filter and wash the obtained slurry, dry it at 120℃ for 3h, and obtain iron phosphate dihydrate material with Fe / P (mol) = 0.994.

[0090] (2) Preparation of spherical ferric phosphate dihydrate: Ferric phosphate dihydrate was prepared in a one-step process in a sulfuric acid system (using sodium system).

[0091] (3) Preparation of lithium iron phosphate: The solid content of spherical iron phosphate dihydrate and flaky iron phosphate dihydrate was adjusted to 30%. After spray drying, the mixture was dehydrated at 550°C for 3 hours. Then, lithium carbonate and carbon source were added to the dehydrated material. The amount of battery-grade lithium carbonate and carbon source added was 2.5% and 8% of the mass of iron phosphate, respectively. After mixing, the material was calcined at 780°C for 5 hours to obtain high energy density lithium iron phosphate material.

[0092] Example 7:

[0093] (1) Preparation of iron phosphate dihydrate with a flake-like microstructure: Take 500g of iron phosphate residue (iron content 19%) after lithium extraction from waste lithium iron phosphate material, dissolve it with 500g of hydrochloric acid with a mass fraction of 24%, dissolve it at 80℃, react for 3h, evaporate the hydrochloric acid in the filtrate after filtering the solution at 110℃, the mass of hydrochloric acid evaporated is 78% of the original filtrate mass (hydrochloric acid recovery rate 92%), then dilute with water, the amount of dilution water added is 85% of the original filtrate mass, filter and wash the obtained slurry, dry it at 120℃ for 3h, and obtain iron phosphate dihydrate material with Fe / P (mol) = 0.994.

[0094] (2) Preparation of spherical ferric phosphate dihydrate: Ferric phosphate dihydrate was prepared in a one-step process in a sulfuric acid system (using sodium system).

[0095] (3) Preparation of lithium iron phosphate: Slurry of spherical ferric phosphate dihydrate, flaky ferric phosphate dihydrate, and iron oxide was prepared. The molar amount of iron added to the iron oxide was 0.07% of the molar amount of spherical and flaky ferric phosphate. The solid content of the slurry was 30%. After spray drying, the mixture was dehydrated at 550°C for 3 hours. Then, lithium carbonate and carbon source were added to the dehydrated material. The amount of battery-grade lithium carbonate and carbon source added was 2.5% and 8% of the mass of ferric phosphate, respectively. After mixing, the material was calcined at 780°C for 5 hours to obtain high energy density lithium iron phosphate material.

[0096] Comparative Example 1:

[0097] Preparation of spherical ferric phosphate dihydrate in flake form (1): Ferric phosphate dihydrate with spherical microstructure was prepared by a one-step method in a sulfuric acid system (using sodium system).

[0098] (2) Preparation of lithium iron phosphate: Spherical iron phosphate dihydrate was ball-milled in a ball mill until the particle size D99 = 60 μm. The mixture was then dehydrated at 550 °C for 3 h. Lithium carbonate and a carbon source were then added to the dehydrated material. The amounts of battery-grade lithium carbonate and carbon source added were 2.5% and 8% of the mass of iron phosphate, respectively. After mixing, the materials were calcined at 780 °C for 5 h to obtain high-energy-density lithium iron phosphate material (see...). Figure 6 ).

[0099] Comparative Example 2:

[0100] Ferric phosphate dihydrate with a spherical microstructure (1) was prepared by a one-step method in a sulfuric acid system (using a sodium system).

[0101] (2) Preparation of lithium iron phosphate: The spherical iron phosphate dihydrate was ball-milled in a ball mill until the particle size D99 = 60 μm. The mixture was dehydrated at 550 °C for 3 h. Then, lithium carbonate and carbon source were added to the dehydrated material. The amount of battery-grade lithium carbonate and carbon source added was 2.5% and 8% of the mass of iron phosphate, respectively. After mixing, the material was calcined at 780 °C for 5 h to obtain high energy density lithium iron phosphate material.

[0102] Comparative Example 3:

[0103] Preparation of spherical ferric phosphate dihydrate in flake form (1): Ferric phosphate dihydrate with spherical microstructure was prepared by a one-step method in a sulfuric acid system (using sodium system).

[0104] (2) Preparation of lithium iron phosphate: The spherical iron phosphate dihydrate was ball-milled in a ball mill until the particle size D99 = 60 μm. The mixture was dehydrated at 450 °C for 3 h. Then, lithium carbonate and carbon source were added to the dehydrated material. The amount of battery-grade lithium carbonate and carbon source added was 2.5% and 8% of the mass of iron phosphate, respectively. After mixing, the material was calcined at 780 °C for 5 h to obtain high energy density lithium iron phosphate material.

[0105] Comparative Example 4:

[0106] (1) Preparation of iron phosphate dihydrate with a flake-like microstructure: Take 500g of iron phosphate residue (iron content 20%) after lithium extraction from waste lithium iron phosphate material, dissolve it with 500g of hydrochloric acid with a mass fraction of 20%, dissolve it at 80℃, react for 3h, evaporate the hydrochloric acid in the filtrate after filtering the solution at 110℃, the mass of hydrochloric acid evaporated is 80% of the original filtrate mass (hydrochloric acid recovery rate 92%), then dilute with water, the amount of dilution water added is 85% of the original filtrate mass, filter and wash the obtained slurry, dry it at 120℃ for 3h, and obtain iron phosphate dihydrate material, Fe / P (mol) = 0.995.

[0107] (2) Preparation of lithium iron phosphate: Ferric phosphate dihydrate with a microscopic morphology of flakes was ball-milled in a ball mill until the particle size D99 = 60 μm. The mixture was then dehydrated at 550 °C for 3 h. Lithium carbonate and a carbon source were then added to the dehydrated material, with the amounts of battery-grade lithium carbonate and carbon source being 2.5% and 8% of the mass of ferric phosphate, respectively. After mixing, the materials were calcined at 780 °C for 5 h to obtain high-energy-density lithium iron phosphate material (e.g., ...). Figure 7 ).

[0108] The lithium iron phosphate batteries from the above embodiments and comparative examples were prepared, and their physicochemical parameters were tested. A comparison of the physicochemical properties of the lithium iron phosphate products prepared from the embodiments and comparative examples is shown in Table 1.

[0109] Table 1: Comparison of physicochemical parameters of lithium iron phosphate products prepared in each example and comparative example

[0110]

[0111] As can be seen from the table above, the lithium iron phosphate product prepared by the method provided by the present invention is superior to the relevant products in the comparative example in terms of initial efficiency, specific surface area, 0.2C, and compaction.

[0112] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing high-energy-density lithium iron phosphate, characterized in that: The method includes the following steps: S1: Prepare ferric phosphate dihydrate with a spherical microstructure and ferric phosphate dihydrate with a flake-like microstructure; when preparing ferric phosphate dihydrate with a flake-like microstructure, the method further includes the following steps: S11: Dissolve the ferrophosphorus material in a volatile acidic solution and filter it to obtain the filtrate; S12: Evaporate the filtrate to remove the volatile acids in the filtrate, forming an evaporated slurry; S13: After diluting the evaporated slurry with water, it is then subjected to precipitation, filtration, washing and drying steps to obtain ferric phosphate dihydrate with a microscopic morphology of flakes. S2: Iron phosphate dihydrate with a spherical microstructure is mixed with iron phosphate dihydrate with a flake microstructure, and then subjected to a co-roasting and crushing process with a lithium source to obtain lithium iron phosphate.

2. The method for preparing high-energy-density lithium iron phosphate according to claim 1, characterized in that: The method for preparing ferric phosphate dihydrate with a spherical microstructure includes: forming ferric phosphate dihydrate through a sulfuric acid system.

3. The method for preparing high-energy-density lithium iron phosphate according to claim 2, characterized in that: The volatile acid in the volatile acidic solution has a mass fraction of 5-60%, and the molar amount of the volatile acid is 0.3-4 times the molar amount of iron in the ferrophosphorus material.

4. The method for preparing high-energy-density lithium iron phosphate according to claim 1, characterized in that: In the spherical form of the ferric phosphate dihydrate, the molar ratio of iron to phosphorus is less than 0.985; in the flake form of the ferric phosphate dihydrate, the molar ratio of iron to phosphorus is greater than 0.

985.

5. The method for preparing high-energy-density lithium iron phosphate according to claim 1, characterized in that: In step S2, the mass ratio of the ferric phosphate dihydrate with a sheet-like microstructure to the ferric phosphate dihydrate with a spherical microstructure is 1:1 to 1:

5.

6. The method for preparing high-energy-density lithium iron phosphate according to claim 1, characterized in that: In step S2, the molar ratio of the amount of lithium in the added lithium source to the total amount of iron in the spherical ferric phosphate dihydrate and the flake-shaped ferric phosphate dihydrate is 1-1.08:

1.

7. The method for preparing high-energy-density lithium iron phosphate according to claim 1, characterized in that: In step S2, the method further includes adding a carbon source during calcination, wherein the mass of the added carbon source accounts for 5-10% of the total mass of iron phosphate in the dihydrate iron phosphate with a microscopic morphology of spherical and flake-like.

8. The method for preparing high-energy-density lithium iron phosphate according to claim 1, characterized in that: In step S2, the method further includes adding iron oxide and / or iron hydroxide to the mixture of spherical ferric phosphate dihydrate and flake-shaped ferric phosphate dihydrate.

9. The method for preparing high-energy-density lithium iron phosphate according to claim 8, characterized in that: The total amount of iron in the iron oxide and iron hydroxide is 0.01%-0.15% of the total amount of iron in the spherical ferric phosphate dihydrate and the flake-shaped ferric phosphate dihydrate.

10. The method for preparing high-energy-density lithium iron phosphate according to claim 1, characterized in that: In step S2, the method includes mixing the spherical ferric phosphate dihydrate with the flake-shaped ferric phosphate dihydrate, followed by ball milling and dehydration.

11. The method for preparing high-energy-density lithium iron phosphate according to claim 1, characterized in that: In step S2, the method further includes ball milling the spherical ferric phosphate dihydrate and the flake-shaped ferric phosphate dihydrate separately, then preparing the spherical ferric phosphate dihydrate and the flake-shaped ferric phosphate dihydrate into slurries, and then spray drying and granulating the two prepared slurries together.

12. The method for preparing high-energy-density lithium iron phosphate according to claim 1, characterized in that: The average particle size of the primary particles of the prepared lithium iron phosphate particles is 0.1-0.3 μm, and in step S2, the particle size of the lithium iron phosphate after ball milling is D99<150 μm.

13. The method for preparing high-energy-density lithium iron phosphate according to claim 1, characterized in that: The lithium iron phosphate has the general structural formula LixFeyMzPO4, where M is selected from one or more of Mg, Mn, S, Al, Cu, Zn, Cr, Ti, Pb, Co and Ni, y is 0.980-0.995, z is 0.0001-0.005, and x is 1.0y-1.05y.

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