阅读说明：本技术 一种高倍率磷酸铁锂的制备方法 (Preparation method of high-rate lithium iron phosphate ) 是由 张世庆 唐盛贺 阮丁山 唐春霞 李长东 于 2021-07-20 设计创作，主要内容包括：本发明公开了一种高倍率磷酸铁锂的制备方法,先将配好的含有铁离子和磷酸根离子的混合溶液进行一次研磨,得到一次研磨浆料,再将一次研磨浆料、锂盐、有机碳源和金属盐添加剂混合,所得混合液进行二次研磨,得到二次研磨浆料,最后将二次研磨浆料进行喷雾干燥,所得干燥物料进行动态烧结,即得磷酸铁锂。本发明用研磨时产生的热量进行结晶析出,进行物料的充分混合,再进行动态烧结,使得所制备出的产品具有更为圆润的形貌和更优良的碳包覆层,产品性能较优；该工艺在一次研磨时巧妙地利用研磨产热结晶析出物料,同时保证粒度得到很好地控制,相比于普通的“先沉淀、干燥制备得到前驱体,再进行颗粒细化处理”的传统工艺更为简单有效。(The invention discloses a preparation method of high-rate lithium iron phosphate, which comprises the steps of firstly grinding a prepared mixed solution containing iron ions and phosphate ions to obtain a primary grinding slurry, then mixing the primary grinding slurry, lithium salt, an organic carbon source and a metal salt additive, grinding the obtained mixed solution for the second time to obtain a secondary grinding slurry, finally spray-drying the secondary grinding slurry, and dynamically sintering the obtained dried material to obtain the lithium iron phosphate. The invention uses the heat generated during grinding to crystallize and separate out, fully mixes the materials, and then dynamically sinters, so that the prepared product has more round appearance and more excellent carbon coating, and the product performance is better; the process ingeniously utilizes grinding to generate heat and crystallize to separate out materials during primary grinding, and meanwhile, the granularity is well controlled, and compared with the common traditional process of firstly precipitating and drying to prepare a precursor and then carrying out particle refining treatment, the process is simpler and more effective.)

1. The preparation method of the high-rate lithium iron phosphate is characterized by comprising the following steps of:

s1: grinding the prepared mixed solution containing iron ions and phosphate ions for the first time to obtain primary grinding slurry;

s2: mixing the primary grinding slurry, lithium salt, an organic carbon source and a metal salt additive, and performing secondary grinding on the obtained mixed solution to obtain secondary grinding slurry;

s3: and carrying out spray drying on the secondary grinding slurry, and dynamically sintering the obtained dried material to obtain the lithium iron phosphate.

2. The method according to claim 1, wherein in step S1, the mixed solution is prepared as follows: dissolving waste scrap iron in an acid solution, adding an alkaline solution to adjust the pH, adding iron phosphate crystal seeds, and adding a compensating agent to perform phosphorus-iron ratio compensation to obtain the mixed solution.

3. The method according to claim 2, wherein in step S1, the acid solution is one or both of phosphoric acid and nitric acid.

4. The method according to claim 2, wherein the pH is 0.5 to 3.0 in step S1.

5. The preparation method according to claim 2, wherein in step S1, the compensating agent is one or more of phosphoric acid, monoammonium phosphate, diammonium phosphate, triammonium phosphate, ferric pyrophosphate, iron powder, ferric oxide, ferric hydroxide or ferric nitrate nonahydrate.

6. The method for preparing according to claim 1, characterized in that the equipment used for the primary grinding and/or the secondary grinding is a sand mill.

7. The method as claimed in claim 1, wherein in step S1, the primary polishing slurry has a particle size D50 of 100-1000 nm.

8. The method as claimed in claim 1, wherein in step S2, the particle size D50 of the particles in the secondary polishing slurry is 100-1200 nm.

9. The method according to claim 1, wherein in step S3, the equipment used for sintering is a rotary kiln; preferably, the temperature of the high-temperature section of the rotary kiln is controlled to be 650-850 ℃, the retention time in the high-temperature section is controlled to be 4-15h, and the pressure in the rotary kiln is controlled to be 40-300 Pa.

10. The method according to claim 1, wherein in step S3, the sintered material is further subjected to a jet milling step to control the particle size D50 of the lithium iron phosphate to 0.5 to 3.0 μm.

Technical Field

The invention belongs to the technical field of lithium ion battery material preparation, and particularly relates to a preparation method of high-rate lithium iron phosphate.

Background

Lithium iron phosphate is an important member of the anode material of the lithium ion battery, and is always popular in the lithium ion battery industry due to excellent safety, stable long-circulating property and non-toxic and environment-friendly green characteristics. Nowadays, with the exhaustion of petroleum resources and the improvement of environmental awareness of people, renewable lithium ion batteries are deeply involved in our lives, particularly lithium iron phosphate batteries are more advanced into our lives in a high-minded posture, and commercial automobiles, energy storage base stations, various electrical equipment and the like have the shadow of lithium iron phosphate at present or in the future. The popularization and application of the popular 5G technology in the world are more dependent on the construction of a 5G base station, and the lithium iron phosphate anode material is one of the best materials for supplying energy to the base station. However, lithium iron phosphate itself has obvious disadvantages, such as low electronic conductivity and ionic conductivity, and especially poor battery rate performance limits the popularization and application of lithium iron phosphate. Therefore, in order to improve the performance of the lithium iron phosphate positive electrode material, especially the rate capability, it is one of the important research directions of the lithium iron phosphate positive electrode material.

In the process of processing and producing steel materials in a steel processing factory, a plurality of leftover materials and scrap (hereinafter, referred to as scrap iron) are often generated, the scrap iron is used as solid waste, the scrap iron is generally treated by carrying out furnace returning reconstruction and is remelted and cast into corresponding steel materials, and the treatment method is simple but has low added value.

Disclosure of Invention

The present invention is directed to solving at least one of the problems of the prior art described above. Therefore, the invention provides a preparation method of high-rate lithium iron phosphate.

According to one aspect of the invention, the invention provides a preparation method of high-rate lithium iron phosphate, which comprises the following steps:

s1: grinding the prepared mixed solution containing iron ions and phosphate ions for the first time to obtain primary grinding slurry;

s2: mixing the primary grinding slurry, lithium salt, an organic carbon source and a metal salt additive, and performing secondary grinding on the obtained mixed solution to obtain secondary grinding slurry;

s3: and carrying out spray drying on the secondary grinding slurry, and dynamically sintering the obtained dried material to obtain the lithium iron phosphate.

In some embodiments of the present invention, in step S1, the mixed solution is prepared as follows: dissolving waste scrap iron in an acid solution, adding an alkaline solution to adjust the pH, adding iron phosphate crystal seeds, and adding a compensating agent to perform phosphorus-iron ratio compensation to obtain the mixed solution. The scrap iron is used as an iron source for recycling, so that the raw material cost can be reduced by about 12 percent.

In some preferred embodiments of the present invention, the scrap iron pieces are subjected to a water immersion treatment to wash away surface residues of the scrap iron pieces before dissolution.

In some embodiments of the present invention, in step S1, the acid solution is one or both of phosphoric acid and nitric acid.

In some embodiments of the present invention, in step S1, the alkali solution is one or more of hydrogen peroxide, ammonia water or ammonium carbonate.

In some embodiments of the invention, in step S1, the pH is 0.5 to 3.0.

In some embodiments of the present invention, in step S1, the compensation agent is one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium phosphate, triammonium phosphate, ferric pyrophosphate, iron powder, iron oxide, ferric hydroxide, or ferric nitrate nonahydrate.

In some embodiments of the invention, the apparatus used for primary and/or secondary grinding is a sand mill.

In some preferred embodiments of the invention, the grinding cavity structure of the sand mill is of a bar-pin type, a turbine type or a bar-pin-turbine composite type; furthermore, the grinding cavity of the sand mill is made of high-strength wear-resistant alumina ceramic material; further, the grinding beads used by the sand mill are zirconia beads, so that the grinding efficiency is ensured, and impurities are not introduced. The grinding cavity of the sand mill is provided with a temperature control indicator, so that the crystallization temperature and the discharging condition can be well guaranteed.

In some embodiments of the invention, in step S1, the particle size D50 of the particles in the primary polishing slurry is 100-1000 nm.

In some embodiments of the present invention, in step S2, the molar ratio of Li, Fe, and P in the mixed solution is (0.98-1.10): (0.95-1.02): 1.

in some embodiments of the present invention, in step S2, the amount of the organic carbon source added is 10% to 70% of the mass of the lithium salt; the addition amount of the metal salt additive is 0.5-5.0% of the mass of the lithium salt.

In some embodiments of the present invention, in step S2, the lithium salt is one or more of lithium carbonate, lithium acetate, lithium hydroxide or lithium nitrate; the organic carbon source is one or more of starch, sucrose, cellulose, anhydrous glucose, monohydrate glucose, anhydrous citric acid, monohydrate citric acid, oxalic acid, chitin, polyvinyl alcohol, polyethylene glycol, polyacrylic acid, polyvinylpyrrolidone, tween 40, tween 60 or tween 80; the metal salt additive is one or more of ammonium metavanadate, chromium nitrate nonahydrate, titanium oxide, tetraethyl titanate, tetrabutyl titanate, zinc oxide, zinc nitrate, barium carbonate, aluminum oxide, aluminum nitrate, nickel oxide, magnesium oxide or magnesium carbonate.

In some embodiments of the invention, in step S2, the particle size D50 of the particles in the secondary polishing slurry is 100-1200 nm.

In some embodiments of the invention, in step S3, the dried material has a particle size D50 of 0.5 to 50 μm.

In some embodiments of the present invention, in step S3, the equipment used for sintering is a rotary kiln; preferably, the temperature of the high-temperature section of the rotary kiln is controlled to be 650-850 ℃, the retention time in the high-temperature section is controlled to be 4-15h, and the pressure in the rotary kiln is controlled to be 40-300 Pa. The rotary kiln has the continuous feeding and discharging function, can keep continuous feeding, sintering and cooling discharging, has short sintering period, few control points, convenient improvement of sintering efficiency, small occupied area of equipment, reduction of capital investment cost of plant equipment by about 10 percent, reduction of production and maintenance cost by more than 13 percent, and strong market competitiveness at the profit level.

In some embodiments of the present invention, in step S3, the sintering is performed under an inert atmosphere, preferably a nitrogen atmosphere.

In some preferred embodiments of the invention, the rotary kiln is a rotary kiln with a special material structure, a furnace tube of the rotary kiln is a high-temperature-resistant and corrosion-resistant high-nickel alloy tube, the material components comprise 20-35% of Cr and 25-55% of Ni, and a lining of the rotary kiln is a high-temperature-resistant high-strength ceramic sheet, so that the introduction of magnetic foreign matters and other impurities can be reduced; a cross rod or a stirring rod is arranged in the rotary kiln, so that dynamic sintering is enhanced, and materials are more fully sintered; a vibration hammer is arranged outside a furnace tube of the rotary kiln to prevent materials from sticking to the wall; air inlets are formed inside and outside the rotary kiln tube, and inert gas can be introduced to ensure that the materials are not oxidized at high temperature.

In some embodiments of the present invention, in step S3, the sintered material is further subjected to a jet milling process, and the particle size D50 of the lithium iron phosphate is controlled to be 0.5 to 3.0 μm. Further, the moisture content of the lithium iron phosphate is less than 1000 ppm.

According to a preferred embodiment of the present invention, at least the following advantages are provided:

1. according to the invention, the heat generated during grinding is used for crystallization and precipitation, materials are fully mixed, and then dynamic sintering is carried out, so that the prepared product has a more mellow appearance and a more excellent carbon coating layer, the product performance is excellent, compared with a commercial power product, the multiplying power performance is greatly improved, the 0.1C specific discharge capacity can reach 160mAh/g, and the first effect is stable to more than 98%; the 5.0C specific discharge capacity under the condition of high-rate charge and discharge can reach 132mAh/g, the cycling stability is good, and the lithium iron phosphate anode material belongs to a better power type lithium iron phosphate anode material product.

2. The process method ingeniously utilizes grinding to generate heat to crystallize and separate out materials during primary grinding, simultaneously ensures that the granularity is well controlled, is simpler and more effective compared with the common traditional process of firstly precipitating and drying to prepare a precursor and then carrying out particle refining treatment, and further reduces the cost.

Drawings

The invention is further described with reference to the following figures and examples, in which:

FIG. 1 is a SEM photograph of example 5 of the present invention;

FIG. 2 is a graph comparing the discharge curves of the same type of products in the market and example 5 of the present invention at different multiplying factors.

Detailed Description

The concept and technical effects of the present invention will be clearly and completely described below in conjunction with the embodiments to fully understand the objects, features and effects of the present invention. It is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments, and those skilled in the art can obtain other embodiments without inventive effort based on the embodiments of the present invention, and all embodiments are within the protection scope of the present invention.

Example 1

The embodiment prepares the high-rate lithium iron phosphate, and the specific process comprises the following steps:

(1) the method comprises the following steps of (1) leaching a waste scrap iron sample 1 with water to remove residues on the surface layer of scrap iron, dissolving the waste scrap iron sample in a mixed solution of 2mol/L phosphoric acid and 1.5mol/L nitric acid, adding ammonia water and hydrogen peroxide under continuous stirring to adjust the pH to 1.0, adding iron phosphate seed crystals, adding iron powder and ammonium dihydrogen phosphate as compensation agents to perform proportioning compensation, grinding for the first time with a sand mill, performing crystallization by using heat generated by sand grinding, and simultaneously controlling the discharge particle size D50 to be about 425 nm;

(2) adding the primary grinding slurry into a mixed solution of a lithium salt, an organic carbon source and a metal salt additive, carrying out secondary mixing grinding, and controlling the content of a final mixed solution Li: fe: the P molar ratio is 1.02: 0.98: 1, wherein the lithium salt is lithium carbonate, the organic carbon source is anhydrous glucose accounting for 32% of the mass of the lithium salt and citric acid monohydrate accounting for 17% of the mass of the lithium salt, the metal salt additive is titanium oxide accounting for 1.2% of the mass of the lithium salt and chromium nitrate nonahydrate accounting for 2.5% of the mass of the lithium salt, and the discharge particle size D50 of the secondary grinding slurry is 350 nm;

(3) spray drying the secondary grinding slurry, controlling the discharge particle size D50 to be about 20 mu m, putting the spray-dried material into a rotary kiln with a special material structure, continuously and dynamically sintering in a pure nitrogen atmosphere, controlling the temperature of a high-temperature section to be 790 ℃, staying for 6h in the high-temperature section, maintaining the furnace pressure to be about 150Pa, and carrying out jet milling on the sintered material, wherein the crushing particle size D50 is 1.62 mu m, the discharge moisture content is 436ppm, and the obtained material is the high-magnification lithium iron phosphate anode material.

Example 2

The embodiment prepares the high-rate lithium iron phosphate, and the specific process comprises the following steps:

(1) the method comprises the following steps of (1) immersing and washing a waste scrap iron sample 1 with water to remove residues on the surface layer of scrap iron, dissolving the waste scrap iron sample in a mixed solution of 1.5mol/L phosphoric acid and 1.0mol/L nitric acid, adding ammonia water and ammonium carbonate under continuous stirring to adjust the pH value to 2.0, then adding iron phosphate seed crystals, adding iron nitrate nonahydrate and diammonium phosphate as compensation agents to perform proportioning compensation, grinding the mixture once with a sand mill, performing crystallization by using heat generated by sand grinding, and simultaneously controlling the discharge particle size D50 to be about 550 nm;

(2) adding the primary grinding slurry into a mixed solution of a lithium salt, an organic carbon source and a metal salt additive, carrying out secondary mixing grinding, and controlling the content of a final mixed solution Li: fe: the P molar ratio is 1.0: 0.96: 1, wherein the lithium salt is lithium hydroxide, the organic carbon source is sucrose accounting for 37% of the mass of the lithium salt and tween-80 accounting for 10% of the mass of the lithium salt, the metal salt additive is tetrabutyl titanate accounting for 1.8% of the mass of the lithium salt and alumina accounting for 1.5% of the mass of the lithium salt, and the discharge particle size D50 of the secondary grinding slurry is 355 nm;

(3) spray drying the secondary grinding slurry, controlling the discharge particle size D50 to be about 25 mu m, putting the spray-dried material into a rotary kiln with a special material structure, continuously and dynamically sintering in a pure nitrogen atmosphere, controlling the temperature of a high-temperature section to be 750 ℃, staying for 9 hours in the high-temperature section, maintaining the furnace pressure to be about 200Pa, and carrying out jet milling on the sintered material, wherein the milling particle size D50 is 1.18 mu m, the moisture content is 338ppm, and the obtained material is the high-magnification lithium iron phosphate anode material.

Example 3

The embodiment prepares the high-rate lithium iron phosphate, and the specific process comprises the following steps:

(1) the method comprises the following steps of (1) leaching a waste scrap iron sample 2 with water to remove residues on the surface layer of scrap iron, dissolving the waste scrap iron sample in a mixed solution of 2mol/L phosphoric acid and 1.2mol/L nitric acid, adding ammonia water and ammonium carbonate under continuous stirring to adjust the pH to 1.6, adding iron phosphate seed crystals, adding ferric hydroxide and phosphoric acid as compensation agents to perform proportioning compensation, grinding for the first time with a sand mill, performing crystallization separation by using heat generated by sand grinding, and simultaneously controlling the discharge particle size D50 to be about 725 nm;

(2) adding the primary grinding slurry into a mixed solution of a lithium salt, an organic carbon source and a metal salt additive, carrying out secondary mixing grinding, and controlling the content of a final mixed solution Li: fe: the molar ratio of P is 1.05: 0.97: 1, wherein the lithium salt is lithium carbonate, the organic carbon source is sucrose accounting for 38% of the mass of the lithium salt and polyvinylpyrrolidone accounting for 8.5% of the mass of the lithium salt, the metal salt additive is ammonium metavanadate accounting for 1.6% of the mass of the lithium salt and zinc nitrate accounting for 1.3% of the mass of the lithium salt, and the discharge particle size D50 of the secondary grinding slurry is 500 nm;

(3) spray drying the secondary grinding slurry, controlling the discharge particle size D50 to be about 30 mu m, putting the spray-dried material into a rotary kiln with a special material structure, continuously and dynamically sintering in a pure nitrogen atmosphere, controlling the temperature of a high-temperature section to be 760 ℃, staying the high-temperature section for 8.5h, maintaining the furnace pressure to be about 200Pa, and carrying out jet milling on the sintered material, wherein the milling particle size D50 is 1.56 mu m, the water content is 373ppm, and the obtained material is the high-magnification lithium iron phosphate anode material.

Example 4

The embodiment prepares the high-rate lithium iron phosphate, and the specific process comprises the following steps:

(1) the method comprises the following steps of (1) leaching a waste scrap iron sample 2 with water to remove residues on the surface layer of scrap iron, dissolving the waste scrap iron sample in a mixed solution of 1.8mol/L phosphoric acid and 1.5mol/L nitric acid, adding ammonia water and hydrogen peroxide under continuous stirring to adjust the pH to 1.3, adding iron phosphate seed crystals, adding iron powder and phosphoric acid as a compensation agent to perform proportioning compensation, grinding for the first time with a sand mill, performing crystallization separation by using heat generated by sand grinding, and simultaneously controlling the discharge particle size D50 to be about 720 nm;

(2) and then adding the primary grinding slurry into a mixed solution of a lithium salt, an organic carbon source and a metal salt additive, carrying out secondary mixing grinding, and controlling the content of a final mixed solution Li: fe: the P molar ratio is 1.03: 0.96: 1, wherein the lithium salt is lithium hydroxide, the organic carbon source is 37% of monohydrate glucose and 15.2% of polyacrylic acid, the metal salt additive is 1.8% of tetrabutyl titanate and 1.4% of zinc nitrate, and the discharge particle size D50 of the secondary grinding slurry is 400 nm;

(3) spray drying the secondary grinding slurry, controlling the discharge particle size D50 to be about 25 mu m, putting the spray-dried material into a rotary kiln with a special material structure, continuously and dynamically sintering in a pure nitrogen atmosphere, controlling the temperature of a high-temperature section to be 780 ℃, staying for 10h in the high-temperature section, maintaining the furnace pressure to be about 250Pa, and carrying out jet milling on the sintered material, wherein the milling particle size D50 is 1.48 mu m, the moisture content is 375ppm, and the obtained material is the high-magnification lithium iron phosphate anode material.

Example 5

The embodiment prepares the high-rate lithium iron phosphate, and the specific process comprises the following steps:

(1) the method comprises the following steps of (1) leaching a waste iron scrap sample 2 with water to remove residues on the surface layer of the iron scrap, dissolving the waste iron scrap sample in a mixed solution of 1.6mol/L phosphoric acid and 1.5mol/L nitric acid, adding ammonia water and hydrogen peroxide under continuous stirring to adjust the pH to 1.1, adding iron phosphate seed crystals, adding iron powder and ammonium dihydrogen phosphate as compensation agents to perform proportioning compensation, grinding for the first time by using a sand mill, performing crystallization by using heat generated by sand milling, and simultaneously controlling the discharge particle size D50 to be about 950 nm;

(2) adding the primary grinding slurry into a mixed solution of a lithium salt, an organic carbon source and a metal salt additive, carrying out secondary mixing grinding, and controlling the content of a final mixed solution Li: fe: the molar ratio of P is 1.04: 0.98: 1, wherein the lithium salt is lithium carbonate, the organic carbon source is sucrose accounting for 33% of the mass of the lithium salt and polyethylene glycol accounting for 13.8% of the mass of the lithium salt, the metal salt additive is titanium oxide accounting for 1.2% of the mass of the lithium salt and magnesium carbonate accounting for 1.7% of the mass of the lithium salt, and the secondary grinding slurry discharge particle size D50 is 330 nm;

(3) spray drying the secondary grinding slurry, controlling the discharge particle size D50 to be about 20 mu m, putting the spray-dried material into a rotary kiln with a special material structure, continuously and dynamically sintering in a pure nitrogen atmosphere, controlling the temperature of a high-temperature section to be 770 ℃, staying the high-temperature section for 9 hours, maintaining the furnace pressure to be about 150Pa, and carrying out jet milling on the sintered material, wherein the milling particle size D50 is 1.64 mu m, the water content is 406ppm, and the obtained material is the high-magnification lithium iron phosphate anode material.

Test examples

The electrical property test was performed as follows: 3-5g of the lithium iron phosphate positive electrode material prepared in examples 1-5, and the corresponding PVDF (polyvinylidene fluoride) and SP carbon were weighed in the following proportion of 92: 5: 3, dispersing and pulping in NMP (N-methyl pyrrolidone), uniformly coating on a flat aluminum foil, baking in a baking oven to dry, rolling and punching into a positive wafer with the diameter of 15mm, and assembling the button cell in a dry inert gas glove box by taking a metal lithium sheet as a negative electrode material, taking a polypropylene microporous membrane as a diaphragm and taking 1mol/L lithium hexafluorophosphate dissolved in a mixed solution of ethylene carbonate and diethyl carbonate as an electrolyte. And controlling the test voltage range to be 2.0-3.8V to carry out button cell test. The same battery assembly and testing was performed on the same type of product on the market, and the test results are shown in table 1.

TABLE 1

As can be seen from table 1, the product performance of examples 1 to 5 is superior, and compared with a commercially available power type product, the rate capability is greatly improved, the 0.1C specific discharge capacity can reach 160mAh/g, the first effect is stable at more than 98%, the 5.0C specific discharge capacity can reach 132mAh/g under the high-rate charge and discharge condition, and the cycle stability is good, and the product belongs to a superior power type lithium iron phosphate positive electrode material product.

Table 2 shows the results of ICP measurements of the cleaned scrap iron pieces.

TABLE 2

As can be seen from Table 2, the scrap iron mainly contains C and Ni in a relatively outstanding manner, but does not affect the performance of the final product.

Fig. 1 is an SEM image of lithium iron phosphate obtained in example 5, and it can be seen from the image that the obtained material particles are round and uniform, the carbon coating layer is good, and the material particles play an important role in stabilizing the electrical properties.

Fig. 2 is a comparison graph of discharge curves of the lithium iron phosphate prepared in example 5 and the commercial products of the same type at different rates, and it can be seen from the graph that the discharge specific capacities of 0.1C and 5.0C in example 5 are both significantly better than those of the commercial products.

The embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the gist of the present invention. Furthermore, the embodiments of the present invention and the features of the embodiments may be combined with each other without conflict.