A high-pressure lithium iron phosphate material prepared by a differential thermal sintering process and a preparation method thereof

Abstract

The application discloses a high-pressure compact lithium iron phosphate material prepared by a differential thermal sintering process and a preparation method thereof. A lithium iron phosphate precursor is placed in a sagger, is vibrated and flattened, then the sagger is placed in a high-temperature sintering furnace, inert gas is introduced, solid-phase reaction is carried out by heating, different heating temperatures are adopted at the top and the bottom of the high-temperature sintering furnace, the heating temperature at the top is higher than that at the bottom, and after the reaction is completed, airflow crushing is carried out to obtain the high-pressure compact lithium iron phosphate material. The lithium iron phosphate material prepared by the differential thermal sintering process (controlling different heating temperatures at the top and the bottom of the high-temperature sintering furnace, and the heating temperature at the top is higher than that at the bottom) has the advantages that the temperature gradually increases from the bottom to the top, the particle size gradually increases, and the consistency of the electrochemical performance of the material is good.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium battery processing, and particularly relates to a high-compaction lithium iron phosphate material prepared by a differential thermal sintering process and a preparation method thereof. BACKGROUND

[0002] With the continuous development of the energy storage market, lithium ion batteries have formed a power + energy storage dual-track pattern. In the power aspect, various automobile enterprises are constantly pursuing the cruising range, and are currently moving from 700 kilometers to 1000 kilometers. The cruising range is also a point that consumers pay more attention to. In the energy storage market, especially in the field of household energy storage and portable power sources. Placed at home, a small footprint or used outdoors, light weight, easy to carry. Such products will have good market competitiveness. Therefore, whether it is power or energy storage, high energy density will be the direction of future development. For the improvement of energy density, the positive material is the main influencing factor. At present, the market mainly uses ternary and lithium iron phosphate. Compared with ternary positive materials, lithium iron phosphate positive materials have better advantages in safety, cycle, cost, raw materials, etc. However, lithium iron phosphate materials also have shortcomings, and the compaction density limits the improvement of energy density. How to improve the compaction density of lithium iron phosphate materials has become a research hotspot.

[0003] The current mainstream direction is to increase the compaction density of lithium iron phosphate materials through the mixing of large and small particles. For example, CN116002648A uses a hydrothermal method to prepare large and small particle lithium iron phosphate materials, and then mixes the large and small particles. CN115806283A realizes the staggered grading of large and small particles through two sintering processes. CN111392705B realizes the mixing of large and small particles by sanding different particle size precursors. The above methods can realize the mixing of large and small particles, but the difference between large and small particles is obvious, and it tends to two extremes, and the material consistency is poor. In addition, the preparation of large and small particles needs different process conditions, and then mixing, the process is complicated. SUMMARY

[0004] In view of the problems of poor consistency and complicated process of the prior art for preparing high-compaction lithium iron phosphate materials, the application provides a high-compaction lithium iron phosphate material prepared by a differential thermal sintering process and a preparation method thereof. The lithium iron phosphate material prepared by the differential thermal sintering process has gradually increasing particle size, and the consistency of the electrochemical performance of the material is good.

[0005] The application is implemented by the following technical solutions:

[0006] The application discloses a method for preparing high-compaction lithium iron phosphate material by differential thermal sintering process.

[0007] Further, the height of the sagger is greater than or equal to 100 mm, and the height of the loaded material after vibration is greater than 90 mm and less than the height of the sagger.

[0008] Further, the heating temperature at the top of the high-temperature sintering furnace is 750-810 DEG C, the heating temperature at the bottom is 700-780 DEG C, and the solid-phase reaction time is 6-10 h.

[0009] Further, the preparation method of the lithium iron phosphate precursor comprises the following steps: uniformly mixing a solvent, a lithium source, iron phosphate and a carbon source according to a proportion, sand grinding and crushing, and then spray drying to obtain the lithium iron phosphate precursor.

[0010] Further, the solvent is pure water, the lithium source is lithium carbonate, and the carbon source is one or more of sucrose, glucose, starch and polyethylene glycol; the mass ratio of the pure water, the iron phosphate, the lithium source and the carbon source is 1-3:1:0.24-0.26:0.08-0.1.

[0011] Further, the D50 particle size of the sand grinding and crushing product is 100-500 nm, and the D50 particle size of the lithium iron phosphate precursor after spray drying is 7-30 mu m.

[0012] Further, the top and the bottom of the high-temperature sintering furnace are separately controlled for heating.

[0013] Further, the inert gas is nitrogen, the inert gas is introduced from the bottom of the sintering furnace, and the waste gas is discharged from the top.

[0014] Further, the D50 particle size of the high-compaction lithium iron phosphate material is 0.7-2.5 mu m.

[0015] Further, the high-compaction lithium iron phosphate material is prepared by the differential thermal sintering process.

[0016] The application has the following beneficial effects:

[0017] The application controls different heating temperatures of the top and the bottom of the high-temperature sintering furnace (the heating temperature of the top is higher than that of the bottom) through the differential thermal sintering process, so that the temperature of the lithium iron phosphate precursor gradually increases from the bottom to the top of the sintering pot during the solid-phase reaction, and the particle size of the lithium iron phosphate also gradually increases, realizing the mixing of large and small particles in a single process flow, which is simple and does not need to prepare large particles first, then small particles, and then mix the large and small particles.

[0018] In the mixing of the traditional preparation of lithium iron phosphate materials with high compaction density, the large particles are very large, and the small particles are very small, which are two extremes, and the consistency of the electrochemical performance of the materials is poor, while the lithium iron phosphate material prepared by the differential thermal sintering process of the application has a gradually increasing temperature from the bottom to the top, and the particle size is gradually increased, and the consistency of the electrochemical performance of the material is good. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 It is a temperature distribution schematic diagram of the differential thermal sintering process sintering pot in the application;

[0020] Figure 2 It is a compaction density comparison diagram of the lithium iron phosphate materials prepared in Examples 1-3 and Comparative Example 1;

[0021] Figure 3 It is an electron microscope diagram of the lithium iron phosphate materials prepared in Comparative Example 1 and Example 3, the left diagram is Comparative Example 1, and the right diagram is Example 3. DETAILED DESCRIPTION

[0022] In order to make the personnel in the art better understand the technical solutions of the application, the technical solutions of the application will be clearly and completely described below, and other similar examples obtained by the personnel in the art without creative labor based on the examples in the application shall belong to the protection scope of the application.

[0023] Example 1

[0024] (1) Pure water, lithium carbonate, iron phosphate and glucose were added into a blender in a mass ratio of 1:1:0.24:0.09, mixed uniformly, crushed by sand milling, the slurry particle size D50 was controlled to be 360 nm, and then spray drying was carried out to obtain lithium iron phosphate precursor with D50 of 20 μm;

[0025] (2) The lithium iron phosphate precursor in step (1) was placed in a 150 mm sintering pot, and after mechanical vibration, the material height was 120 mm;

[0026] (3) Put the sagger containing the lithium iron phosphate precursor into a high-temperature sintering furnace, introduce nitrogen gas at the bottom of the high-temperature sintering furnace, and exhaust at the top, heat for solid-phase reaction, separately control heating at the top and the bottom of the high-temperature sintering furnace, the heating temperature at the top is 750°C, the heating temperature at the bottom is 700°C, and the solid-phase reaction time is 10 h;

[0027] (4) After the solid-phase reaction is completed, the sintered lithium iron phosphate is airflow crushed to obtain a high-compaction lithium iron phosphate material with a D50 particle size of 1.5 μm.

[0028] Example 2

[0029] (1) Put pure water, lithium carbonate, iron phosphate, starch, and sucrose into a mixer in a mass ratio of 3:1:0.26:0.08:0.01, mix uniformly, crush by sand milling, control the slurry particle size D50 to be 150 nm, and then spray dry to obtain a lithium iron phosphate precursor with a D50 of 10 μm;

[0030] (2) Put the lithium iron phosphate precursor in step (1) into a 300 mm sagger, mechanically vibrate and flatten, and the material height is 240 mm;

[0031] (3) Put the sagger containing the lithium iron phosphate precursor into a high-temperature sintering furnace, introduce nitrogen gas at the bottom of the high-temperature sintering furnace, and exhaust at the top, heat for solid-phase reaction, separately control heating at the top and the bottom of the high-temperature sintering furnace, the heating temperature at the top is 810°C, the heating temperature at the bottom is 780°C, and the solid-phase reaction time is 6 h, and the temperature distribution in the sagger in the differential thermal sintering process is shown in Figure 1

[0032] (4) After the solid-phase reaction is completed, the sintered lithium iron phosphate is airflow crushed to obtain a high-compaction lithium iron phosphate material with a D50 particle size of 2.0 μm.

[0033] Example 3

[0034] (1) Put pure water, lithium carbonate, iron phosphate, glucose, and polyethylene glycol into a mixer in a mass ratio of 2:1:0.25:0.09:0.01, mix uniformly, crush by sand milling, control the slurry particle size D50 to be 480 nm, and then spray dry to obtain a lithium iron phosphate precursor with a D50 of 7 μm;

[0035] (2) Put the lithium iron phosphate precursor in step (1) into a 230 mm sagger, mechanically vibrate and flatten, and the material height is 180 mm;

[0036] ​(3) Put the sagger containing the lithium iron phosphate precursor into a high-temperature sintering furnace, introduce nitrogen gas at the bottom of the high-temperature sintering furnace, and exhaust at the top, heat for solid-phase reaction, separately control heating at the top and the bottom of the high-temperature sintering furnace, the heating temperature at the top is 780℃, the heating temperature at the bottom is 730℃, and the solid-phase reaction time is 8h;

[0037] (4) After the solid-phase reaction is completed, airflow crushes the sintered lithium iron phosphate to obtain high-pressure lithium iron phosphate material with a D50 particle size of 0.7μm.

[0038] Comparative Example 1

[0039] (1) Put pure water, lithium carbonate, iron phosphate, glucose, and polyethylene glycol in a ratio of 2:1:0.25:0.09:0.01 into a blender, mix uniformly, control the slurry particle size D50 to be 360nm by sand milling and crushing, and then obtain lithium iron phosphate precursor with a D50 of 20μm by spray drying;

[0040] (2) Put the lithium iron phosphate precursor in step (1) into a 150mm sagger, mechanically vibrate to 120mm in height after leveling;

[0041] (3) Put the sagger containing the lithium iron phosphate precursor into a high-temperature sintering furnace, introduce nitrogen gas at the bottom of the high-temperature sintering furnace, and exhaust at the top, heat for solid-phase reaction, separately control heating at the top and the bottom of the high-temperature sintering furnace, the heating temperature at the top is 780℃, the heating temperature at the bottom is 730℃, and the solid-phase reaction time is 8h;

[0042] (4) After the solid-phase reaction is completed, airflow crushes the sintered lithium iron phosphate to obtain high-pressure lithium iron phosphate material with a D50 particle size of 1.5μm.

[0043] The tap density and discharge gram capacity of the lithium iron phosphate material prepared in Comparative Example 1 and Examples 1-3 under different pressures were tested, the tap density comparison chart of the lithium iron phosphate material powder is shown in Figure 2 , the discharge gram capacity test results of the lithium iron phosphate material are shown in Table 1 below, and the electron microscope images of the lithium iron phosphate material prepared in Comparative Example 1 and Example 3 are shown in Figure 3 , wherein the left image is the lithium iron phosphate material prepared in Comparative Example 1, and the right image is the lithium iron phosphate material prepared in Example 3.

[0044] Table 1 Comparison of discharge gram capacity of lithium iron phosphate material prepared in Examples 1-3 and Comparative Example 1

[0045] .

Claims

1. A method for preparing high-pressure lithium iron phosphate materials using differential thermal sintering, characterized in that, The lithium iron phosphate precursor was placed in a sagger and vibrated to flatten it. Then the sagger was placed in a high-temperature sintering furnace, inert gas was introduced, and the furnace was heated to carry out a solid-phase reaction. The top and bottom of the high-temperature sintering furnace were heated at different temperatures, with the top heating temperature being higher than the bottom heating temperature. After the reaction was completed, the furnace was subjected to air jet pulverization to obtain high-pressure compacted lithium iron phosphate material. The height of the sagger is ≥100mm, and the loading height after vibration and leveling is greater than 90mm and less than the height of the sagger. The high-temperature sintering furnace has a top heating temperature of 750-810℃, a bottom heating temperature of 700-780℃, and a solid-phase reaction time of 6-10 hours.

2. The method for preparing high-pressure lithium iron phosphate materials using the differential thermal sintering process according to claim 1, characterized in that, The preparation method of the lithium iron phosphate precursor is as follows: the solvent, lithium source, iron phosphate and carbon source are mixed evenly in proportion, crushed by sand milling, and then spray dried to obtain the lithium iron phosphate precursor.

3. The method for preparing high-pressure lithium iron phosphate materials using the differential thermal sintering process according to claim 2, characterized in that, The solvent is pure water, the lithium source is lithium carbonate, and the carbon source is one or more of sucrose, glucose, starch, and polyethylene glycol; the mass ratio of the pure water, iron phosphate, lithium source, and carbon source is 1-3:1:0.24-0.26:0.08-0.

1.

4. The method for preparing high-pressure lithium iron phosphate materials using the differential thermal sintering process according to claim 2, characterized in that, The D50 particle size after milling is 100~500nm, and the D50 particle size of the lithium iron phosphate precursor after spray drying is 7~30μm.

5. The method for preparing high-pressure lithium iron phosphate materials using the differential thermal sintering process according to claim 1, characterized in that, The top and bottom of the high-temperature sintering furnace are heated separately.

6. The method for preparing high-pressure lithium iron phosphate materials using the differential thermal sintering process according to claim 1, characterized in that, The inert gas is nitrogen, which is introduced from the bottom of the sintering furnace and discharged from the top.

7. The method for preparing high-pressure lithium iron phosphate materials using the differential thermal sintering process according to claim 1, characterized in that, The D50 particle size of the high-pressure lithium iron phosphate material is 0.7-2.5 μm.

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