阅读说明：本技术 一种球形磷酸铁锂正极材料的制备方法及应用 (Preparation method and application of spherical lithium iron phosphate cathode material ) 是由 黄勇平 胡振宇 金磊 陈佳敏 邵国祥 于 2021-08-13 设计创作，主要内容包括：本发明提供了一种球形磷酸铁锂正极材料的制备方法；所述方法包括以下步骤：(1)将铁源、锂源、磷源湿法研磨,得到混合溶液A；(2)加入碳源分散于混合溶液A中,得到混合溶液B；(3)聚苯胺纤维溶解于二甲亚砜中,得到聚苯胺混合二甲亚砜的溶液；(4)将聚苯胺混合二甲亚砜的溶液分散于混合溶液B中,得到混合溶液C；(5)将混合溶液C进行喷雾干燥,得到喷雾料；(6)将喷雾料进行冷冻干燥,得到烧结前驱体；(7)将步骤(6)得到的前驱体在还原气氛条件下高温烧结得到成品。本发明通过在分散阶段引入聚苯胺导电剂,能大大增强烧结后成品的导电率；本发明工艺简单,可以有效改善正极材料的形貌,提高材料的电化学性能。(The invention provides a preparation method of a spherical lithium iron phosphate anode material; the method comprises the following steps: (1) carrying out wet grinding on an iron source, a lithium source and a phosphorus source to obtain a mixed solution A; (2) adding a carbon source to disperse in the mixed solution A to obtain a mixed solution B; (3) dissolving polyaniline fiber in dimethyl sulfoxide to obtain solution of polyaniline mixed with dimethyl sulfoxide; (4) dispersing the solution of polyaniline mixed with dimethyl sulfoxide into the mixed solution B to obtain a mixed solution C; (5) carrying out spray drying on the mixed solution C to obtain a spray material; (6) freeze-drying the spray material to obtain a sintering precursor; (7) and (4) sintering the precursor obtained in the step (6) at high temperature under the reducing atmosphere condition to obtain a finished product. According to the invention, the polyaniline conductive agent is introduced in the dispersion stage, so that the conductivity of the sintered finished product can be greatly enhanced; the method has simple process, can effectively improve the appearance of the anode material and improve the electrochemical performance of the material.)

1. A preparation method of a spherical lithium iron phosphate anode material is characterized by comprising the following steps: comprises the following steps of (a) carrying out,

(1) carrying out wet grinding on an iron source, a lithium source and a phosphorus source to obtain a mixed solution A;

(2) adding a carbon source to disperse in the mixed solution A to obtain a mixed solution B;

(3) dissolving polyaniline fiber in dimethyl sulfoxide to obtain solution of polyaniline mixed with dimethyl sulfoxide;

(4) dispersing the solution of polyaniline mixed with dimethyl sulfoxide into the mixed solution B to obtain a mixed solution C;

(5) carrying out spray drying on the mixed solution C to obtain a spray material;

(6) freeze-drying the spray material to obtain a sintering precursor;

(7) and (4) sintering the precursor obtained in the step (6) at high temperature under the reducing atmosphere condition to obtain a finished product.

2. The method for preparing the spherical lithium iron phosphate cathode material according to claim 1, wherein the method comprises the following steps: the iron source in the step (1) is ferric phosphate or ferric oxide, the lithium source is lithium carbonate or lithium nitrate, and the phosphorus source is phosphoric acid or ferric phosphate.

3. The method for preparing the spherical lithium iron phosphate cathode material according to claim 1, wherein the method comprises the following steps: in the reaction raw materials of iron, lithium and phosphorus in the step (1), the molar ratio of Li to Fe to P is (1-1.1) to (0.9-1.0) to 1.

4. The method for preparing the spherical lithium iron phosphate cathode material according to claim 1, wherein the method comprises the following steps: the carbon source in the step (2) comprises any one or combination of at least two of sucrose, glucose, starch, citric acid and polypropylene, the mass of the carbon source is 1-15 wt% of the mass of the reaction raw materials containing lithium, iron and phosphorus, and the dispersion time is 2 h.

5. The method for preparing the spherical lithium iron phosphate cathode material according to claim 1, wherein the method comprises the following steps: in the step (3), the mass of the polyaniline fiber (conductive agent) is 0.5-2 wt% of the mass of the reaction raw material containing lithium, iron and phosphorus, and the mass of the dimethyl sulfoxide is 0.5-2 wt% of the mass of the reaction raw material containing lithium, iron and phosphorus.

6. The method for preparing the spherical lithium iron phosphate cathode material according to claim 1, wherein the method comprises the following steps: and (4) dispersing the solution of polyaniline fiber mixed with dimethyl sulfoxide in the mixed solution B for 2 h.

7. The method for preparing the spherical lithium iron phosphate cathode material according to claim 1, wherein the method comprises the following steps: drying by using a spray drying tower in the step (5), wherein the inlet temperature of the spray drying tower is 120-300 ℃, and the outlet temperature of the spray drying tower is 50-100 ℃;

the method for preparing the spherical lithium iron phosphate cathode material according to claim 1, wherein the method comprises the following steps:

the freeze-drying operation in the step (6) is as follows,

a. putting a material to be freeze-dried into a freeze-drying box which is cooled to minus 10 ℃ to minus 50 ℃ for 3 to 5 hours to freeze the material;

b. opening the vacuum diffusion pump, and when the pressure is reduced to 1.3-13 Pa, the ice just begins to sublimate, and the sublimated water vapor is frozen into ice crystals in the condenser; to ensure sublimation of the ice, the heating system was turned on and the shelf was heated to 30-60 ℃.

8. In the step (7), the reducing atmosphere is nitrogen, the sintering temperature is 600-800 ℃, and the sintering time is 8-10 h.

9. The spherical lithium iron phosphate cathode material obtained by the preparation method according to any one of claims 1 to 8.

10. The spherical lithium iron phosphate cathode material prepared by the preparation method according to any one of claims 1 to 9 is applied to a lithium ion battery.

Technical Field

The invention belongs to the technical field of energy storage materials, and particularly relates to a preparation method and application of a spherical lithium iron phosphate anode material.

Background

With the continuous development of human society, environmental problems are increasingly prominent, and with the rise of new energy strategies in China, lithium ion batteries are widely applied as clean energy due to the advantages of small size, high energy density, safety, environmental protection and the like since the early development of the last 90 th century.

The lithium iron phosphate serving as the lithium ion battery anode material has the advantages of wide raw material source, low price, good material thermal stability, high voltage platform, long cycle life, no toxicity, no harm, high safety and the like, is separated from a plurality of anode materials, and becomes the first choice of the power and energy storage lithium ion battery anode material at present.

However, the energy density and the cycling stability of the composite material need to be further improved to meet the market requirement, and how to improve the energy density and the cycling stability becomes a technical problem to be solved urgently.

At present, the high-temperature solid phase method needs high-temperature drying before sintering, but precursors generated after drying are easy to adhere, so that the agglomeration phenomenon of products after sintering is serious, and the overall appearance and the electrical property are influenced.

Disclosure of Invention

In view of the above, the invention aims to provide a preparation method and application of a spherical lithium iron phosphate cathode material, so as to overcome the defects of the prior art. The spray material is subjected to freeze drying before sintering, and due to volatilization of dimethyl sulfoxide, agglomeration of a precursor can be greatly reduced, and agglomeration and growth of spherical particles during sintering are reduced.

In order to achieve the purpose, the technical scheme of the invention is realized as follows:

a preparation method of a spherical lithium iron phosphate anode material comprises the following steps,

(1) carrying out wet grinding on an iron source, a lithium source and a phosphorus source to obtain a mixed solution A;

(2) adding a carbon source to disperse in the mixed solution A to obtain a mixed solution B;

(3) dissolving polyaniline fiber (conductive agent) in dimethyl sulfoxide to obtain solution of polyaniline mixed with dimethyl sulfoxide (which is convenient for uniform mixing with a precursor);

(4) dispersing the solution of polyaniline mixed with dimethyl sulfoxide into the mixed solution B to obtain a mixed solution C;

(5) carrying out spray drying on the mixed solution C to obtain a spray material;

(6) freeze-drying the spray material (greatly removing water and dimethyl sulfoxide) to obtain a sintering precursor;

(7) and (4) sintering the precursor obtained in the step (6) at high temperature under the reducing atmosphere condition to obtain a finished product.

In the preparation method provided by the invention, the polyaniline conductive agent is introduced in the step (4), so that the conductivity of a sintered finished product can be greatly enhanced, and the electrochemical performance of the product is improved; the spray material is freeze-dried before sintering in the step (6), so that the agglomeration and growth of spherical particles during sintering can be reduced; the carbon amount brought away by water volatilization during the sintering of the spray material is greatly reduced, and the cost of the carbon source is saved.

The following is a preferred technical solution of the present invention, but not a limitation to the technical solution provided by the present invention, and the technical objects and advantageous effects of the present invention can be better achieved and achieved by the following preferred technical solution.

Preferably, the iron source in step (1) is iron phosphate or ferric oxide, the lithium source is lithium carbonate or lithium nitrate, and the phosphorus source is phosphoric acid or iron phosphate.

Preferably, in the reaction raw material containing lithium, iron and phosphorus in step (1), the molar ratio of Li to Fe to P is (1 to 1.1): 0.9 to 1.0):1, for example, 1:0.9:1, 1.05:0.95:1, 1.1:0.9:1, 1.1:0.95:1, 1.05:1:1 or 1.1:1:1, but not limited to the above-mentioned values, and other values not mentioned in the above-mentioned range of values are also applicable.

Preferably, in the step (2), the carbon source includes any one of sucrose, glucose, starch, citric acid or polypropylene or a combination of at least two of the foregoing.

Preferably, the mass of the carbon source in step (1) is 1 to 15 wt%, such as 1wt%, 2 wt%, 3 wt%, 5wt%, 7 wt%, 9wt%, 10 wt%, 12 wt%, 14 wt% or 15 wt% of the mass of the reaction raw material containing lithium, iron and phosphorus, but not limited to the recited values, and other non-recited values within the range of the recited values are also applicable.

According to experimental research, in the step (2) of the preparation method provided by the invention, if the addition amount of the carbon source is too much, the coating layer is too thick, the internal resistance of the material is increased, and the total amount of active substances is reduced; if the adding amount of the carbon source is too small, the carbon coating is not uniform, and the conductivity of the material is influenced.

Preferably, in step (3), the mass of the polyaniline fiber (conductive agent) is 0.5 to 2 wt% of the mass of the reaction raw material containing lithium, iron and phosphorus, such as 0.5wt%, 0.75 wt%, 1wt%, 1.2 wt%, 1.5wt%, 1.7 wt%, 1.9wt%, or 2 wt%, but not limited to the recited values, and other values in the range of the recited values are also applicable; the mass of dimethyl sulfoxide is 0.5 to 2 wt% of the mass of the reaction raw material containing lithium, iron and phosphorus, for example, 0.5wt%, 0.75 wt%, 1wt%, 1.2 wt%, 1.5wt%, 1.7 wt%, 1.9wt% or 2 wt%, but is not limited to the above-mentioned values, and other values not shown in the above-mentioned value range are also applicable.

Preferably, in the step (4), the solution of polyaniline mixed with dimethyl sulfoxide is dispersed in the mixed solution B, and the mixing time is 2 hours;

preferably, the inlet temperature of the spray drying tower in step (5) is 120 to 300 ℃, such as 120 ℃, 130 ℃, 140 ℃, 150 ℃, 175 ℃, 200 ℃, 225 ℃, 250 ℃ or 300 ℃, but not limited to the recited values, and other values within the range of values are equally applicable, and the outlet temperature is 50 to 100 ℃, such as 50 ℃, 60 ℃, 70 ℃, 80 ℃, 90 ℃ or 100 ℃, but not limited to the recited values, and other values within the range of values are equally applicable;

preferably, in the step (6), the freeze-drying comprises the steps of,

a. putting a material to be freeze-dried into a freeze-drying box which is cooled to minus 10 ℃ to minus 50 ℃ for 3 to 5 hours to freeze the material; b. opening the vacuum diffusion pump, and when the pressure is reduced to 1.3-13 Pa, the ice just begins to sublimate, and the sublimated water vapor is frozen into ice crystals in the condenser; to ensure sublimation of the ice, the heating system was turned on and the shelf was heated to 30-60 ℃.

The temperature of the freeze drying chamber is in the range of-10 ℃ to-50 ℃, for example, -10 ℃, -20 ℃, -30 ℃, -40 ℃, -50 ℃ and the like, but is not limited to the recited values, and other values not recited in the range of values are also applicable.

The freezing time is in the range of 3-5 hours, such as 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, etc., but is not limited to the recited values, and other values not recited in the range of values are also applicable.

The pressure of the vacuum diffusion pump is in the range of 1.3 to 13 Pa, for example, 1.3Pa, 2.3 Pa, 4.3 Pa, 6.3 Pa, 8.3 Pa, 10.3 Pa, 12 Pa, 13 Pa, etc., but the pressure is not limited to the above-mentioned values, and other values not shown in the above-mentioned range are also applicable.

The shelf heating temperature is in the range of 30 ℃ to 60 ℃, for example 30 ℃, 35 ℃, 40 ℃, 45 ℃, 50 ℃, 55 ℃, 60 ℃ and the like, but is not limited to the recited values, and other values not recited in the numerical range are also applicable.

Preferably, in the step (7), the reducing atmosphere is nitrogen and/or argon; the sintering temperature is 600-800 ℃, and preferably 650-750 ℃; the sintering time is 5-8 h.

The sintering temperature is, for example, 600 ℃, 650 ℃, 700 ℃, 750 ℃, or 800 ℃, but is not limited to the recited values, and other values not recited in the numerical range are also applicable.

The sintering time is, for example, 5 hours, 6 hours, 6.5 hours, 7 hours, or 8 hours, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.

The average particle size of the lithium iron phosphate material prepared by the preparation method of the present invention is 3 to 15 μm, for example, 3 μm, 5 μm, 7 μm, 9 μm, 10 μm, 12 μm or 15 μm, but the present invention is not limited to the above-mentioned values, and other values not listed in the above-mentioned range are also applicable.

The invention also provides the spherical lithium iron phosphate material prepared by the preparation method.

The invention also provides an application of the spherical lithium iron phosphate material prepared by the preparation method in a lithium ion battery.

Compared with the prior art, the preparation method of the spherical lithium iron phosphate cathode material has the following advantages:

(1) according to the invention, the polyaniline conductive agent is introduced in the dispersion stage, so that the conductivity of the sintered finished product can be greatly enhanced, and the electrochemical performance of the product is improved; the spray material is subjected to freeze drying before sintering, so that the agglomeration of a precursor is greatly reduced, and the agglomeration and growth of spherical particles during sintering are reduced; the carbon amount brought away by water volatilization during the sintering of the spray material is greatly reduced, and the cost of the carbon source is saved.

(2) The method has simple process, can effectively improve the appearance of the anode material and improve the electrochemical performance of the material. Compared with the method without cooling and drying, after the spray material cooling and drying process is added, the material has regular secondary spherical appearance, and the circulation retention rate at 2000 weeks is improved from 85% to 93%.

Drawings

Fig. 1 is an SEM image of lithium iron phosphate obtained in example 1 of the present invention.

Fig. 2 is an SEM magnified view of a single lithium iron phosphate ball obtained in example 1 of the present invention.

FIG. 3 is an SEM image of a sample of comparative example 1 of the present invention.

Detailed Description

In order to better illustrate the present invention and facilitate the understanding of the technical solutions of the present invention, the present invention is further described in detail below. The following examples are merely illustrative of the present invention and do not represent or limit the scope of the claims, which are defined by the claims.

Unless defined otherwise, technical terms used in the following examples have the same meanings as commonly understood by one of ordinary skill in the art to which the present invention belongs. The test reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the experimental methods are conventional methods unless otherwise specified.

The following are typical, but non-limiting, examples of the invention.

Example 1

In this example, lithium iron phosphate was prepared as follows:

(1) grinding iron phosphate and lithium carbonate by a wet method to obtain a mixed solution A, wherein in the reaction raw materials containing lithium, iron and phosphorus, the element molar ratio of Li to Fe to P is 1:0.9: 1;

(2) adding sucrose to be dispersed in the mixed solution A to obtain a mixed solution B, wherein the mass of the sucrose is 1wt% of that of the reaction raw materials containing lithium, iron and phosphorus;

(3) dissolving polyaniline fiber (conductive agent) in dimethyl sulfoxide to obtain solution of polyaniline mixed with dimethyl sulfoxide (which is convenient for uniform mixing with a precursor);

(4) dispersing the solution of polyaniline mixed with dimethyl sulfoxide into the mixed solution B to obtain a mixed solution C, wherein the mass of polyaniline fibers (conductive agents) is 0.5wt% of that of reaction raw materials containing lithium, iron and phosphorus, and the mass of the dimethyl sulfoxide is 0.5wt% of that of the reaction raw materials containing lithium, iron and phosphorus;

(5) and (3) carrying out spray drying on the mixed solution C to obtain a spray material, wherein the inlet temperature of a spray drying tower is 260 ℃, and the outlet temperature of the spray drying tower is 80 ℃.

(6) Freeze-drying the spray material (greatly removing water and dimethyl sulfoxide) to obtain a sintering precursor, wherein the freeze-drying comprises the following steps,

a. putting a material to be freeze-dried in a freeze-drying box which is cooled to-10 ℃ for 3 hours to freeze the material; b. opening the vacuum diffusion pump, when the pressure is reduced to 1.3Pa, the ice begins to sublimate, and the sublimated water vapor is frozen into ice crystals in the condenser; in order to ensure the sublimation of the ice, a heating system is started, the shelf is heated to 30 ℃, the temperature range of the freeze-drying box is-10 ℃, and the freezing time is 3 hours;

(7) and (4) sintering the precursor obtained in the step (6) at 700 ℃ under the condition of nitrogen atmosphere to obtain a finished product.

The performance test results of the lithium iron phosphate material prepared in this example are shown in table 1.

Fig. 1 and 2 are SEM images of the product obtained in this example, and it can be seen from the images that the overall sphericity is good, the dispersion is uniform, the growth of single spherical particles is good, and the average particle size of the spherical particles is 6.5 μm.

Example 2

In this example, the raw materials and operations were the same as in example 1 except that the molar ratio of Li to Fe to P in step (3) was 1.05:1: 1.

The average particle size of the particles was 6.8. mu.m.

The performance test results of the lithium iron phosphate material prepared in this example are shown in table 1.

Example 3

This example was carried out in the same manner as in example 1 except that lithium carbonate was replaced with lithium nitrate in step (4).

The average particle size of the particles was 7.2. mu.m.

The performance test results of the lithium iron phosphate material prepared in this example are shown in table 1.

Example 4

This example was carried out in the same manner as in example 1 except that sucrose was replaced with glucose in step (5).

The average particle size of the particles was 8.7. mu.m.

The performance test results of the lithium iron phosphate material prepared in this example are shown in table 1.

Example 5

In this example, lithium iron phosphate was prepared as follows:

(1) grinding ferric phosphate and lithium nitrate by a wet method to obtain a mixed solution A, wherein in the reaction raw materials containing lithium, iron and phosphorus, the molar ratio of Li to Fe to P is 1.1:0.9: 1;

(2) adding sucrose to be dispersed in the mixed solution A to obtain a mixed solution B, wherein the mass of the sucrose is 1.4 wt% of that of the reaction raw materials containing lithium, iron and phosphorus;

(3) dissolving polyaniline fiber (conductive agent) in dimethyl sulfoxide to obtain solution of polyaniline mixed with dimethyl sulfoxide (which is convenient for uniform mixing with a precursor);

(4) dispersing the solution of polyaniline mixed with dimethyl sulfoxide into the mixed solution B to obtain a mixed solution C, wherein the mass of polyaniline fibers (conductive agents) is 1.5wt% of that of reaction raw materials containing lithium, iron and phosphorus, and the mass of the dimethyl sulfoxide is 1.2 wt% of that of the reaction raw materials containing lithium, iron and phosphorus;

(5) spray drying the mixed solution C to obtain a spray material, wherein the inlet temperature of a spray drying tower is 220 ℃, and the outlet temperature of the spray drying tower is 90 ℃;

(6) freeze-drying (removing water and dimethyl sulfoxide greatly) the spray material to obtain a sintering precursor, wherein the freeze-drying comprises the following steps:

a. putting a material to be freeze-dried in a freeze-drying box which is cooled to-20 ℃ for 4 hours to freeze the material; b. opening the vacuum diffusion pump, when the pressure is reduced to 1.7Pa, the ice begins to sublimate, and the sublimated water vapor is frozen into ice crystals in the condenser; in order to ensure the sublimation of the ice, a heating system is started, the shelf is heated to 30 ℃, the temperature of the freeze-drying box is in a range of-15 ℃, and the freezing time is 4 hours;

(7) and (4) sintering the precursor obtained in the step (6) at 750 ℃ under the condition of nitrogen atmosphere to obtain a finished product.

The average particle size of the particles was 4.7. mu.m.

The performance test results of the lithium iron phosphate material prepared in this example are shown in table 1.

Example 6

In this example, lithium iron phosphate was prepared as follows:

(1) grinding ferric phosphate and lithium phosphate by a wet method to obtain a mixed solution A, wherein in the reaction raw materials containing lithium, iron and phosphorus, the molar ratio of Li to Fe to P is 1.05:0.95: 1;

(2) adding citric acid to disperse in the mixed solution A to obtain a mixed solution B, wherein the mass of the sucrose is 1.8 wt% of that of the reaction raw materials containing lithium, iron and phosphorus;

(3) dissolving polyaniline fiber (conductive agent) in dimethyl sulfoxide to obtain solution of polyaniline mixed with dimethyl sulfoxide (which is convenient for uniform mixing with a precursor);

(4) dispersing the solution of polyaniline mixed with dimethyl sulfoxide into the mixed solution B to obtain a mixed solution C, wherein the mass of polyaniline fibers (conductive agents) is 1.9wt% of that of reaction raw materials containing lithium, iron and phosphorus, and the mass of the dimethyl sulfoxide is 0.4 wt% of that of the reaction raw materials containing lithium, iron and phosphorus;

(5) spray drying the mixed solution C to obtain a spray material, wherein the inlet temperature of a spray drying tower is 290 ℃, and the outlet temperature of the spray drying tower is 80 ℃;

(6) freeze-drying the spray material (greatly removing water and dimethyl sulfoxide) to obtain a sintering precursor, wherein the freeze-drying comprises the following steps,

a. putting the material to be freeze-dried into a freeze-drying box which is cooled to-28 ℃ for 3.5h, and freezing the material; b. opening the vacuum diffusion pump, when the pressure is reduced to 1.8Pa, the ice begins to sublimate, and the sublimated water vapor is frozen into ice crystals in the condenser; in order to ensure the sublimation of the ice, a heating system is started, the shelf is heated to 50 ℃, the temperature of the freeze-drying box is in a range of-25 ℃, and the freezing time is 3.5 hours;

(7) and (4) sintering the precursor obtained in the step (6) at 710 ℃ under the condition of nitrogen atmosphere to obtain a finished product.

The average particle size of the particles was 9.4. mu.m.

The performance test results of the lithium iron phosphate material prepared in this example are shown in table 1.

Comparative example 1

This comparative example is a blank control without lyophilization.

The average particle size of the particles was 18.7. mu.m.

The performance test results of the lithium iron phosphate material prepared in the comparative example are shown in table 1.

Fig. 3 is an SEM image of the product obtained in this example, and it can be seen that the spherical particles are seriously adhered, which greatly affects the overall morphology and electrical properties.

The performance test method comprises the following steps:

the lithium iron phosphate materials prepared in the examples and the comparative examples were subjected to the following performance tests:

(1) testing the size of the whisker: measuring the diameter and the length of the sample whisker by using an electronic scanning microscope;

(2) electrochemical testing: the lithium iron phosphate material prepared by the invention is prepared into a positive pole piece, the negative pole is a graphite negative pole, the diaphragm is Celgard2400, and the electrolyte is 1mol/L LiPF₆And a mixed solution of dimethyl carbonate and ethyl methyl carbonate (the volume ratio is 1:1: 1) is assembled into the 18650 cylindrical single battery. The preparation process of the positive pole piece comprises the following steps: mixing a positive electrode material, a conductive agent acetylene black and a binder PVDF according to the mass percentage of 94:3:3, taking N-methyl pyrrolidone as a solvent, preparing slurry, coating the slurry on an aluminum foil, and drying in vacuum to obtain the positive electrode piece. The preparation process of the negative pole piece comprises the steps of carrying out negative pole batching on graphite, a thickening agent CMC, a binder SBR and conductive carbon powder according to the weight ratio of 95:1:2:2 in a water system to obtain uniform negative pole slurry, and uniformly coating the prepared negative pole slurry on a negative pole current collector Cu foil and cooling to obtain the negative pole piece. Under the condition of normal temperature, the prepared cylindrical battery is tested on a LAND battery test system of Wuhan Jinnuo electronic Limited company, the charging and discharging voltage interval is 2.0-3.65V, the first discharging specific capacity and the 2000 th cyclic discharging specific capacity of the battery are tested under the current density of 1C, the 2000 th cyclic capacity retention ratio is calculated, and the 2000 th cyclic capacity retention ratio = 2000 th cyclic discharging specific capacity/first discharging specific capacity.

The test results are shown in table 1 below:

TABLE 1 test results

Item	Average particle size (nm)	1C specific first discharge capacity (mAh/g)	Specific discharge capacity (mAh/g) of 2000 th cycle	Capacity retention at 2000 cycles (%)
					Example 1	6.5	156.4	147.0	93.98
Example 2	6.8	158.7	149.9	94.45
					Example 3	7.2	156.1	146.9	94.10
Example 4	8.7	157.6	148.3	94.10
					Example 5	4.7	157.2	147.5	93.83
Example 6	9.4	156.8	146.4	93.37
					Comparative example 1	18.7	136.0	101.1	74.34

As can be seen from table 1, the lithium iron phosphate materials prepared in embodiments 1 to 6 of the present invention have good electrochemical properties, because the spherical lithium iron phosphate is obtained by freeze drying and high-temperature sintering in the preparation method of the above embodiments, which can significantly improve the electrochemical properties of the materials.

As can be seen from table 1, comparative example 1 has lower first discharge specific capacity, 2000 th cycle discharge specific capacity and 2000 th cycle capacity retention ratio than example 1 because freeze-drying was not added to comparative example 1.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.