CN102502562A - Preparation method of lithium iron phosphate, lithium ion battery and anode material and anode thereof - Google Patents

Abstract

The invention provides a preparation method of lithium iron phosphate, a lithium ion battery, a positive electrode material of the lithium ion battery and a positive electrode of the lithium ion battery. The preparation method of the lithium iron phosphate comprises the following steps: uniformly mixing lithium dihydrogen phosphate and an iron source to obtain a mixture material, wherein the molar ratio of lithium to iron in the mixture material is (1-1.02) to (0.98-1); the iron source includes: a ferrous iron source compound, a trivalent inorganic iron source compound, and a trivalent organic iron source compound; and then under the protection of inert gas, preheating the mixture and calcining to obtain the lithium iron phosphate powder. The method can prepare the lithium iron phosphate material with the particle size distributed in a non-normal way by one step, improves the electronic conductivity and the lithium ion conduction rate of the material, improves the tap density of the material, improves the high-rate discharge performance of the material, ensures that the material has higher volume specific capacity, and ensures that Fe in the material is in a Fe-Fe ratio state₂The content of P impurities is low.

Description

Preparation method of lithium iron phosphate, lithium ion battery, positive electrode material and positive electrode thereof

technical field

The invention relates to the field of lithium ion batteries, in particular to a preparation method of lithium iron phosphate, lithium ion batteries, positive electrode materials and positive electrodes thereof.

Background technique

Lithium iron phosphate is mainly used as the positive electrode material of lithium ion batteries. Compared with traditional lithium ion secondary battery positive electrode materials such as LiMn ₂ O ₄ with spinel structure and LiCoO ₂ with layered structure, the raw material source of lithium iron phosphate is Wider and cheaper. In addition, lithium iron phosphate also has the characteristics of large discharge capacity, high safety in use, non-toxic and environmental protection, and has attracted people's attention in recent years.

Solid-phase synthesis is the main synthesis method of lithium iron phosphate, and the prior art provides a variety of methods for preparing lithium iron phosphate by solid-phase synthesis, for example: Liu et al [Journal of PowerSources, 2006,159: 717-720] and Li ₂ CO ₃ , FeC ₂ O ₄ ·2H ₂ O, NH ₄ H ₂ PO ₄ , and acetylene black were used as raw materials, and the raw materials were mixed according to the molar ratio of Li:Fe:P of 1:1:1. After ball milling for 24 hours, the The nanoscale LiFePO4/C composite material was obtained by keeping it in a tube furnace for 15 hours, and the particle size of the obtained material was 100nm. Due to the small particle size and short lithium ion diffusion path, the rate performance of the material is improved. However, due to the poor processing performance of nano-scale materials, the requirements for coating and mixing equipment are high, and the price of raw materials is high, and the synthetic materials are relatively expensive, and the price is relatively expensive.

Wang Guan et al. [Acta Advanced Chemistry, 2007, 28: 136-139] prepared LiFePO ₄ /C composite material by carbothermal reduction method using Fe ₂ O ₃ as raw material. The research shows that the discharge specific capacity of the material at 0.1C rate is 144.8mAh/g. The method can generate a strong reducing atmosphere during the reduction process, and ferric oxide and other ferric iron compounds can be used as the iron source, thereby reducing the raw material cost. However, the particle size of the materials prepared by this method is generally in the micron level, so the synthesized materials are lower than those synthesized by the traditional high-temperature solid-state method in terms of capacity performance and rate performance.

[Acta Physicochemical Society, 2009, 25: 1504-1510] used inorganic Fe ₂ O ₃ and organic iron citrate (FeC ₆ H ₅ O ₇ 5H ₂ O) as mixed iron sources, and utilized lemon in iron citrate Acid radicals were used as carbon source and reducing agent, and high-density LiFePO ₄ /C composites were successfully prepared by solid-state-carbothermal reduction method. Material grains consist of nanoparticles and microparticles. This method is conducive to improving the uniformity of carbon coating in the material, and the rate performance retention rate of the material is better, but the initial discharge performance of the synthesized LiFePO ₄ /C composite material is poor, which is mainly due to the reduction of the atmosphere. If the amount added is too large, excessive Fe ₂ P impurities will be produced in the material.

Contents of the invention

The technical problem solved by the present invention is to provide a preparation method of lithium iron phosphate, a lithium ion battery and its positive electrode material and positive electrode. The lithium iron phosphate prepared by the above method has a higher tap density and a better rate performance, and Fe ₂ P impurity content is low.

In view of this, the present invention provides a kind of preparation method of lithium iron phosphate, comprising:

a), mix lithium dihydrogen phosphate and iron source evenly to obtain a mixed material, the molar ratio of lithium and iron in the mixed material is (1～1.02):(0.98～1); the iron source includes: divalent Iron source compounds, trivalent inorganic iron source compounds and trivalent organic iron source compounds;

b) under the protection of inert gas, heating the material mixture at 300°C-500°C for 5h-20h, cooling, and grinding to obtain a reaction precursor;

c) Under the protection of an inert gas, calcining the reaction precursor at 600° C. to 800° C. for 10 h to 40 h, cooling, and grinding to obtain lithium iron phosphate powder.

Preferably, the ferrous iron source compound is ferrous oxalate and/or ferrous acetate.

Preferably, the trivalent inorganic iron source compound is iron oxide and/or iron nitrate.

Preferably, the trivalent organic iron source compound is ferric citrate.

Preferably, the ferrous iron source compound. The molar ratio of the trivalent inorganic iron source compound to the trivalent organic iron source compound is (0.2-0.6):(0.16-0.36):(0.08-0.26).

Preferably, the mixing method in step a is high-speed ball milling.

The present invention also provides a positive electrode material for a lithium ion battery, which is the lithium iron phosphate powder prepared by the above method.

The present invention also provides a positive electrode of a lithium ion battery, comprising a substrate and a coating material placed on the surface of the substrate, and the coating material includes: the above-mentioned positive electrode material of the lithium ion battery, a conductive material and a binder.

The present invention also provides a lithium ion battery, comprising the positive electrode and negative electrode of the above lithium ion battery, a diaphragm and an electrolyte arranged between the positive electrode and the negative electrode.

The invention provides a method for preparing lithium iron phosphate. The method uses lithium dihydrogen phosphate as a lithium source, and uses divalent iron source compounds, trivalent inorganic iron source compounds and trivalent organic iron source compounds as iron sources. Preparation of lithium iron phosphate by solid-state-carbothermal reduction process. Because iron sources of different particle sizes have an impact on the particle size of the material formed after sintering, the present invention uses the above-mentioned mixed iron sources with different particle sizes to facilitate the preparation of lithium iron phosphate materials with non-normal particle size distribution in one step, small particle materials It has better rate performance, and larger particles have the advantages of higher tap density, thus improving the electronic conductivity and lithium ion conductivity of the material, as well as the tap density of the material, which not only improves the large rate of the material Discharge performance, but also make the material have a higher volume specific capacity.

Simultaneously, the introduction of the ferrous iron source in the preparation method provided by the invention reduces the amount of the trivalent inorganic iron source in the mixed iron source, reduces the reduced carbon required in the synthesis process, thereby reducing the amount of the trivalent organic iron source. The added amount can restrain excessive Fe ₂ P impurities produced after cracking, and reduce the content of Fe ₂ P impurities in the material.

Description of drawings

Figure 1 is the XRD pattern of the product prepared in Example 1 of the present invention.

Detailed ways

In order to further understand the present invention, the preferred embodiments of the present invention are described below in conjunction with examples, but it should be understood that these descriptions are only to further illustrate the features and advantages of the present invention, rather than limiting the claims of the present invention.

The embodiment of the present invention discloses a preparation method of lithium iron phosphate, comprising the following steps:

a) Mix the lithium source and the iron source evenly to obtain a mixed material, the molar ratio of lithium and iron in the mixed material is (1-1.02): (0.98-1), and the iron source includes: ferrous iron source Compounds, trivalent inorganic iron source compounds and trivalent organic iron source compounds;

b) Under the protection of an inert gas, heat the mixed material at 300°C to 500°C for 5h to 20h, cool, and grind to obtain a reaction precursor;

c) Under the protection of an inert gas, calcining the reaction precursor at 600° C. to 800° C. for 10 h to 40 h, cooling, and grinding to obtain lithium iron phosphate powder.

In the above preparation method, step a is the process of preparing the material mixture. The reason why the present invention uses a mixture of ferrous iron source compound, trivalent inorganic iron source compound and trivalent organic iron source compound as the iron source is that iron sources of different particle sizes It has an impact on the particle size of the material formed after sintering. The smaller the particle size of the raw material, the easier it is to form a material with a smaller particle size during the sintering process, and the difference in the size of different types of iron sources is conducive to the preparation of lithium iron phosphate powder with different particle sizes in one step. . The particle size of the ferrous iron source compound is small, and the lithium iron phosphate material synthesized from it also has a small particle size. The particle size of the trivalent inorganic iron source compound is relatively large, and the shape of the raw material is controllable, which is conducive to the synthesis of lithium iron phosphate materials with high tap density; the trivalent inorganic iron source is conducive to obtaining good coating performance during the sintering process lithium iron phosphate material. Therefore, the above-mentioned mixed iron source is used to ensure that the products have different particle size distribution intervals, to increase the tap density of the material and to improve the rate performance of the material.

As a preferred version, the present invention controls the preferred molar ratio of ferrous iron source compound, trivalent inorganic iron source compound and trivalent organic iron source compound in the iron source to be (0.2～0.6):(0.16～0.36):(0.08～0.26 ).

Among them, the ferrous iron source compound is preferably ferrous oxalate and/or ferrous acetate. The trivalent inorganic iron source compound is preferably iron oxide and/or iron nitrate, which has relatively high volume specific energy. The trivalent organic iron source compound is preferably ferric citrate.

Among the above-mentioned materials, lithium dihydrogen phosphate is used as a lithium source and as a phosphorus source. The reason why the present invention chooses lithium dihydrogen phosphate is that: firstly, the choice of lithium dihydrogen phosphate reduces the types of raw materials that need to be mixed, which is conducive to industrial control stability. It is helpful to the stability of the synthesized material; secondly, compared with phosphoric acid such as ammonium dihydrogen phosphate, it does not produce ammonia gas and has little environmental pollution.

In the material mixture, the molar ratio of the lithium in the lithium source and the iron in the iron source is (1～1.02): (0.98～1), even if the lithium is slightly excessively processed, this is because: on the one hand, the iron content in the material is too high , and the lithium content is too low, which will cause iron atoms to occupy the vacancies of lithium atoms, thereby blocking the one-dimensional movement channel of lithium ions in lithium iron phosphate, resulting in a decrease in the diffusion rate of lithium ions, and a decrease in the discharge specific capacity and rate performance of the material; On the one hand, lithium raw materials are prone to volatilization during the high-temperature reaction process. For this reason the present invention controls the mol ratio of lithium source and iron source in the above range to ensure material discharge specific capacity and rate performance, and the present invention preferably controls the mol ratio of lithium and iron in the mixed material in the material mixture to be (1～1.02):( 0.98～0.99).

In step a, in order to mix the components in the material uniformly, the present invention preferably adopts a high-speed ball milling method for mixing. It is more preferred to use ethanol as a dispersant for wet milling, and the amount of ethanol added is preferably 1.5 to 3 times the weight of the material mixture. According to step a), each raw material is mixed to obtain a material mixture. The obtained material mixture is continued to be pretreated according to step b.

Step b is the process of pretreating the material mixture, the main function is to predecompose the raw materials to form reactive precursors containing PO ₄ ^3- , Li ⁺ , Fe ²⁺ /Fe ³⁺ and decomposed carbon. A large amount of water, carbon dioxide, carbon monoxide and other gases will be produced in this process. The high reaction temperature and long reaction time are conducive to the full decomposition of raw materials. In the subsequent sintering process, because the regenerated gas is less, the atmosphere in the furnace is easy to control. The electrical properties of the sintered material are more stable. However, the reaction temperature is too high and the reaction time is too long, which not only wastes energy, but also causes side reactions to occur during long-term high-temperature pretreatment, which deteriorates the electrical properties of the material during the sintering stage. For this reason, the present invention controls the temperature of this step to be 300°C to 500°C, and the heating time is 5h to 20h. The heating temperature is preferably 320°C to 450°C, more preferably 340°C to 400°C. The heating time is preferably 8h to 15h.

According to step b, the materials are mixed and preheated, and then calcined according to step c. The reactions that occur during the calcination process are as follows:

LiH ₂ PO ₄ +FeC ₂ O ₄ (Fe(C ₂ H ₃ O ₂ ) ₂ )→LiFePO ₄ +H ₂ O+CO ₂ +CO

LiH ₂ PO ₄ +Fe ₂ O ₃ (Fe(NO ₃ ) ₃ )+FeC ₆ H ₅ O ₇ →LiFePO ₄ +H ₂ O+CO ₂ +CO+C

The temperature and time of calcination have an important influence on the electrochemical properties of the product. The higher the reaction temperature, the better the atomic activation energy, and the easier the raw material is to react completely to form a material with high crystallinity. The higher the crystallinity of the material, the smaller the grain size, and the material The higher the discharge specific capacity and rate performance. Under the same conditions, if the reaction temperature is too high, the crystal grains of the material will be larger, and the discharge rate performance of the material will deteriorate; if the reaction temperature is too low, the crystallization of the material will be imperfect, and the discharge performance of the material will deteriorate. However, if the reaction temperature is too high, the growth tendency of the material after crystallization is strong, and the crystal grains are easy to grow during the subsequent heat preservation process. In addition, during the reaction process, material crystallization is perfected and grain grows simultaneously, and the control of the reaction time in the present invention is used to ensure that the deterioration of electrical properties of the material due to grain crystallization tends to be perfected while grain growth is not prominent. If the reaction time is too long, the crystal grains of the material will be larger; if the reaction time is too short, the crystallization of the material will be imperfect. For this reason, the present invention controls the calcination temperature of step c to be 600° C. to 800° C. and the time to be 10h to 40h. The calcination temperature is preferably set at 650°C to 750°C, and the calcination time is preferably 20h to 30h. After calcination, the calcined product is cooled and ground to obtain lithium iron phosphate powder.

It can be seen from the above scheme that the present invention uses lithium dihydrogen phosphate as the lithium source, a mixture of ferrous iron source compound, trivalent inorganic iron source compound and trivalent organic iron source compound as the iron source, and adopts high-temperature solid-state-carbothermal reduction Process for preparing lithium iron phosphate. Because iron sources of different particle sizes have an impact on the particle size of the material formed after sintering, the present invention uses the above-mentioned mixed iron sources with different particle sizes to facilitate the preparation of lithium iron phosphate materials with non-normal particle size distribution in one step, small particle materials It has better rate performance, and larger particles have the advantages of higher tap density. While improving the electronic conductivity and lithium ion conductivity of the material, it also improves the tap density of the material, which not only improves the high rate discharge performance of the material , but also make the material have a higher volume specific capacity.

Simultaneously, the introduction of the ferrous iron source in the preparation method provided by the invention reduces the amount of the trivalent inorganic iron source in the mixed iron source, reduces the reduced carbon required in the synthesis process, thereby reducing the amount of the trivalent organic iron source. The added amount can restrain excessive Fe ₂ P impurities produced after cracking, and reduce the content of Fe ₂ P impurities in the material.

In addition, the present invention also realizes the uniform mixing of lithium iron phosphate with different particle sizes, which solves the problem that materials with different particle sizes are difficult to mix evenly during the physical mixing process after synthesizing lithium iron phosphate with different properties in industry.

The present invention also provides a lithium ion battery cathode material, which is the lithium iron phosphate powder prepared by the above method. The lithium iron phosphate material has high tap density and excellent rate performance.

The present invention also provides a lithium-ion battery positive electrode, which includes: a substrate and a coating material placed on the surface of the substrate, wherein the coating material includes: the above-mentioned lithium-ion battery positive electrode material, a conductive material and an adhesive.

The matrix in the above positive electrode can be made of materials well known to those skilled in the art, such as aluminum foil. The conductive material in the coating material is preferably conductive graphite, and the adhesive can be polytetrafluoroethylene, polyvinylidene chloride, polyvinyl chloride, polymethylmethacrylate or styrene-butadiene rubber.

The secondary battery positive electrode provided by the present invention can be prepared by the following method:

The positive electrode is prepared by mixing the above-mentioned positive electrode material, conductive material, and binder, dissolving them in N-methylpyrrolidone and pressing them on the substrate.

Correspondingly, the present invention also provides a lithium-ion battery, comprising: the positive electrode of the above-mentioned ion battery, the negative electrode, the diaphragm and the electrolyte disposed between the positive electrode and the negative electrode. The lithium-ion battery adopts the above-mentioned lithium iron phosphate material as the positive electrode material, and the electrochemical performance of the battery is also improved due to the high tap density and volume specific capacity of the material.

In order to further understand the present invention, the preparation method of lithium iron phosphate provided by the present invention is described below in conjunction with the examples, and the protection scope of the present invention is not limited by the following examples.

Example 1

1. Using absolute ethanol as a dispersant, mix 1.02mol lithium dihydrogen phosphate, 0.4mol ferrous oxalate, 0.255mol iron oxide and 0.09mol ferric citrate through a high-speed ball mill;

2. Place the mixed raw materials in a tubular heating furnace, feed nitrogen gas as a protective gas, raise the temperature to 350°C, keep the temperature constant for 10 hours, cool and grind to obtain the reaction precursor;

3. Put the reaction precursor obtained in step 2 into the reactor, place it in a tube furnace, pass in nitrogen as a protective gas, raise the temperature to 700°C, keep the temperature constant for 24 hours, cool with the furnace, grind, and sieve to obtain the powder It is lithium iron phosphate material.

Figure 1 is the XRD pattern of the product prepared in this example. It can be seen from the figure that lithium iron phosphate was successfully prepared, and there is no diffraction peak of Fe ₂ P in the figure, which shows that the method suppresses the formation of Fe ₂ P.

The particle size distribution of the lithium iron phosphate material prepared in this example was tested. The test results are: the lithium iron phosphate has three intervals of particle size distribution, which are respectively low diameter peak 0.2-0.1um, medium diameter peak 0.1-2um, and high diameter peak 2～10um.

Example 2

1. Using absolute ethanol as a dispersant, mix 1.02mol of lithium dihydrogen phosphate, 0.4mol of ferrous oxalate, 0.24mol of iron oxide and 0.12mol of ferric citrate through a high-speed ball mill and mix evenly;

2. Put the mixed raw materials in a tube furnace, pass in argon as a protective gas, raise the temperature to 250°C, keep the temperature constant for 10 hours, cool and grind to obtain the reaction precursor;

3. Put the reaction precursor prepared in step 2 into the reactor, place it in a tube furnace, pass in nitrogen as a protective gas, raise the temperature to 800°C, calcine at a constant temperature for 32 hours, cool with the furnace, grind, and sieve. The powder is lithium iron phosphate material.

The particle size distribution of the lithium iron phosphate material prepared in this example was tested. The test results are: the lithium iron phosphate has a particle size distribution of three intervals, which are respectively a low diameter peak of 0.2-1um, a middle diameter peak of 1-3um, and a high diameter peak of 3 ~10um.

Example 3

1. Using absolute ethanol as a dispersant, mix 1 mol of lithium dihydrogen phosphate, 0.2 mol of ferrous oxalate, 0.36 mol of iron oxide and 0.08 mol of ferric citrate through a high-speed ball mill and mix evenly;

2. Put the mixed raw materials in a tubular heating furnace, feed nitrogen gas as a protective gas, raise the temperature to 400°C, keep the temperature constant for 5 hours, cool and grind to obtain the reaction precursor;

3. Put the reaction precursor obtained in step 2 into the reactor, place it in a tube furnace, feed nitrogen gas as a protective gas, raise the temperature to 500°C, keep the temperature constant for 40 hours, cool with the furnace, grind, and sieve the obtained powder. It is lithium iron phosphate material.

The particle size distribution of the lithium iron phosphate material prepared in this example was tested. The test results are: the lithium iron phosphate has a particle size distribution of three intervals, which are respectively a low diameter peak of 0.2-2um, a middle diameter peak of 2-4um, and a high diameter peak of 4um. ~10um.

Example 4

1. Using absolute ethanol as a dispersant, mix 1 mol of lithium dihydrogen phosphate, 0.6 mol of ferrous acetate, 0.16 mol of iron oxide and 0.08 mol of ferric citrate through a high-speed ball mill and mix evenly;

2. Place the mixed raw materials in a tubular heating furnace, pass in argon as a protective gas, raise the temperature to 300°C, keep the temperature constant for 20 hours, cool and grind to obtain the reaction precursor;

3. Put the reaction precursor obtained in step 2 into the reactor, place it in a tube furnace, feed nitrogen gas as a protective gas, raise the temperature to 650°C, keep the temperature constant for 10 hours, cool down with the furnace, grind, and sieve the obtained powder. It is lithium iron phosphate material.

The particle size distribution of the lithium iron phosphate material prepared in this example was tested. The test results are: the lithium iron phosphate has a particle size distribution of three intervals, which are respectively a low diameter peak of 0.2-3um, a middle diameter peak of 3-5um, and a high diameter peak of 5um. ~10um.

Example 5

1. Using absolute ethanol as a dispersant, mix 1 mol of lithium dihydrogen phosphate, 0.58 mol of ferrous oxalate, 0.16 mol of ferric nitrate and 0.08 mol of ferric citrate through a high-speed ball mill and mix evenly;

2. Place the mixed raw materials in a tubular heating furnace, feed nitrogen gas as a protective gas, raise the temperature to 300°C, keep the temperature constant for 20 hours, cool and grind to obtain the reaction precursor;

3. Put the reaction precursor obtained in step 2 into the reactor, place it in a tube furnace, pass in nitrogen gas as a protective gas, raise the temperature to 600°C, keep the temperature constant for 12 hours, cool down with the furnace, grind, and sieve the obtained powder. It is lithium iron phosphate powder.

The particle size distribution of the lithium iron phosphate material prepared in this example was tested. The test results are: the lithium iron phosphate has a particle size distribution of three intervals, which are respectively a low diameter peak of 0.2-4um, a middle diameter peak of 4-6um, and a high diameter peak of 6um. ~10um.

Example 6

1. With absolute ethanol as a dispersant, 1mol of lithium dihydrogen phosphate, 0.2mol of ferrous oxalate, 0.2mol of ferrous acetate, 0.14mol of ferric nitrate, 0.1mol of ferric oxide and 0.26mol of ferric citrate are used as a dispersant with ethanol, Mixed evenly by high-speed ball mill;

2. Put the mixed raw materials in a tubular heating furnace, feed nitrogen gas as a protective gas, raise the temperature to 300°C, keep the temperature constant for 15 hours, cool and grind to obtain the reaction precursor;

3. Put the reaction precursor obtained in step 2 into the reactor, place it in a tube furnace, pass in nitrogen gas as a protective gas, raise the temperature to 650°C, keep the temperature at a constant temperature for 14 hours, and after cooling with the furnace, grind and sieve the obtained powder. It is lithium iron phosphate powder.

Using the lithium iron phosphate materials prepared in Examples 1 to 6 as positive electrode materials, CR2016 button-type experimental batteries were made according to the following method, and the numbers were A, B, B, D, E, F:

1. Mix the positive electrode material with conductive graphite super P and binder PVDF at a ratio of 8:1:1, dissolve in N-methylpyrrolidone (NMP), stir evenly, dry, pulverize, and press on aluminum mesh to make Positive sheet.

2. Dry the positive electrode sheet prepared in step 1 in a vacuum oven at 130°C for 5 hours, and place the dried positive electrode sheet, the negative electrode prepared from metal lithium sheet, the polypropylene separator, and the electrolyte in a room filled with high-purity argon Assemble in a glove box to obtain a CR2016 button-type experimental battery. The supporting electrolyte in the electrolyte is LiPF ₆ , the solvent is a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 1:1, and the concentration of the electrolyte is 1mol/L.

The 0.1C first discharge specific capacity and tap density of the above six CR2016 button-type experimental batteries were tested, and the test results are listed in Table 1.

Table 1 The first discharge specific capacity and tap density of the battery at 0.1C

From the above results, it can be seen that the lithium iron phosphate material prepared by the method provided by the present invention has higher tap density and volume specific capacity, and less Fe2P impurities.

The descriptions of the above embodiments are only used to help understand the method and core idea of the present invention. It should be pointed out that for those skilled in the art, without departing from the principle of the present invention, some improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention will not be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (9)

1. A preparation method for lithium iron phosphate, comprising: a) Mix lithium dihydrogen phosphate and iron source evenly to obtain a mixture material, the molar ratio of lithium and iron in the mixture material is (1～1.02):(0.98～1); the iron source includes: divalent Iron source compounds, trivalent inorganic iron source compounds and trivalent organic iron source compounds; b) Under the protection of an inert gas, heat the mixture material at 300°C to 500°C for 5h to 20h, cool, and grind to obtain a reaction precursor; c) Under the protection of an inert gas, calcining the reaction precursor at 600° C. to 800° C. for 10 h to 40 h, cooling, and grinding to obtain lithium iron phosphate powder. 2. The preparation method according to claim 1, characterized in that, the ferrous source compound is ferrous oxalate and/or ferrous acetate. 3. The preparation method according to claim 1, characterized in that, the trivalent inorganic iron source compound is iron oxide and/or iron nitrate. 4. The preparation method according to claim 1, characterized in that, the trivalent organic iron source compound is ferric citrate. 5. The preparation method according to claim 1, characterized in that, the molar ratio of the ferrous iron source compound, the trivalent inorganic iron source compound and the trivalent organic iron source compound is (0.2～0.6): (0.16～ 0.36): (0.08～0.26). 6. The preparation method according to claim 1, characterized in that the mixing method in step a is high-speed ball milling. 7. A lithium ion battery cathode material, characterized in that it is lithium iron phosphate powder made by the method according to claim 1. 8. A lithium-ion battery positive electrode, characterized in that it comprises a substrate and a coating material placed on the surface of the substrate, the coating material comprising: the lithium-ion battery positive electrode material, conductive material and binding agent according to claim 7 . 9. A lithium ion battery, characterized in that it comprises: the positive pole of the lithium ion battery according to claim 8, the negative pole, and a diaphragm and electrolyte solution arranged between the positive pole and the negative pole.

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