WO2018129883A1

WO2018129883A1 - Lithium iron phosphate/carbon composite material and preparation method therefor

Info

Publication number: WO2018129883A1
Application number: PCT/CN2017/092314
Authority: WO
Inventors: 陈立鹏; 汪龙; 柳娜
Original assignee: 宁德时代新能源科技股份有限公司
Priority date: 2017-01-11
Filing date: 2017-07-09
Publication date: 2018-07-19
Also published as: CN108305991A

Abstract

A preparation method for a lithium iron phosphate/carbon composite material, comprising the following steps: 1) weighing iron powder, phosphoric acid, and an acidifying additive, and dispersing the same in deionized water; 2) heating to perform an acidification reflux reaction; 3) after the acidification reflux reaction ends, adding a lithium-containing compound and an organic carbon source to perform mixing and dispersion; 4) stirring and evaporation drying the mixture to obtain a lithium iron phosphate precursor which is composited by the organic carbon source; and 5) sintering the collected precursor, pulverizing and screening, and then obtaining the lithium iron phosphate/carbon composite material. Relative to the existing technology, said preparation method for the lithium iron phosphate/carbon composite material has the following advantages: 1) the raw materials have wide sources and are low cost; 2) the product has a good crystalline structure, few impurities, and even granularity, and has ideal electrochemical properties; 3) the preparation process is simple and practical, equipment running costs are low, and large scale industrial production is easily achieved.

Description

Lithium iron phosphate/carbon composite material and preparation method thereof

Technical field

The invention belongs to the field of lithium ion batteries, and more particularly to a lithium iron phosphate/carbon composite material and a preparation method thereof.

Background technique

As a positive electrode material for lithium ion batteries, lithium iron phosphate material has the advantages of abundant raw material source, low price, green environmental protection, high theoretical specific capacity (about 170 mAh/g), long life, good safety and thermal stability, and is currently commercialized. The preferred cathode material for automotive power batteries.

At present, the preparation of lithium iron phosphate material mainly uses high energy wet grinding equipment to grind and pulverize iron orthophosphate and lithium salt to realize nanocrystallization of lithium iron phosphate material. However, the production cost of this preparation method is high, which limits its development. The specific performances are as follows: 1) raw materials belong to specific fields of fine processing products, non-chemical application fields are bulk products, and raw material costs are high; 2) existing wet grinding The preparation of lithium iron phosphate material has higher energy consumption, but the production capacity is relatively low. 3) The equipment and auxiliary materials of the existing wet grinding process belong to wearing parts and consumables, and the production investment is large.

In view of this, it is indeed necessary to provide a lithium iron phosphate/carbon composite material which is low in cost, ideal in performance, and suitable for industrial production, and a preparation method thereof.

Summary of the invention

The object of the present invention is to overcome the deficiencies of the prior art and provide a lithium iron phosphate/carbon composite material which is low in cost, ideal in performance, and suitable for industrial production, and a preparation method thereof.

In order to achieve the above object, the present invention provides a method for preparing a lithium iron phosphate/carbon composite material, which comprises the following steps:

1) Weigh iron powder, phosphoric acid and acidification additives, and disperse in deionized water;

2) heating to carry out an acid reflux reaction;

3) after the acidification reflux reaction is completed, the lithium-containing compound and the organic carbon source are added for mixing and dispersion;

4) stirring and evaporating the mixture to obtain an organic carbon source composite lithium iron phosphate precursor;

5) The collected precursors are sintered, pulverized and sieved to obtain lithium iron phosphate/carbon composite material.

As an improvement of the preparation method of the lithium iron phosphate/carbon composite material of the present invention, in the step 1), the iron fine powder has a particle size of 5 to 30 μm, and the phosphoric acid is a concentrated phosphoric acid having a concentration of 70 to 85%. The molar ratio of the Fe fine powder to the Fe and P elements in the concentrated phosphoric acid is 1:1.

As an improvement of the preparation method of the lithium iron phosphate/carbon composite material of the present invention, in the step 1), the acidification additive is at least one of oxalic acid, citric acid, tartaric acid and oxalic acid, and the content thereof is iron fine powder. 5 to 15% of the mass.

As an improvement of the preparation method of the lithium iron phosphate/carbon composite material of the present invention, in step 1), a doping metal compound is further added, and the molar ratio of the doping metal element M to the P element in the doped metal compound is 0.005~ 0.03:1.

As an improvement of the preparation method of the lithium iron phosphate/carbon composite material of the present invention, the doping metal compound is a manganese-containing compound, a titanium-containing compound, a cobalt-containing compound, an iron-containing compound, a magnesium-containing compound, an aluminum-containing compound, and the like. One or more of a chromium compound and a cerium-containing compound, the doping metal compound is one or more of an oxide, a hydroxide, a nitrate, and an organic acid salt containing a doping element, and the organic acid salt is preferably vinegar. Acid salt, oxalate.

As an improvement of the preparation method of the lithium iron phosphate/carbon composite material of the present invention, in the step 2), the acidification temperature is 50 to 150 ° C, and the acidification time is 4 to 8 hours.

As an improvement of the preparation method of the lithium iron phosphate/carbon composite material of the present invention, in the step 3), the molar ratio of the Li to the P element is 1.02:1.

As an improvement of the preparation method of the lithium iron phosphate/carbon composite material of the present invention, in the step 3), the lithium-containing compound comprises lithium carbonate, lithium hydroxide monohydrate, lithium acetate, lithium nitrate, lithium citrate, preferably one. Lithium hydroxide in water.

As an improvement of the preparation method of the lithium iron phosphate/carbon composite material of the present invention, in the step 3), the organic carbon source is one or more of maltose, glucose, sucrose, fructose, starch, phenolic resin, The amount added is 5 to 15% of the mass of the iron fine powder.

As an improvement of the preparation method of the lithium iron phosphate/carbon composite material of the present invention, in the step 5), the sintering temperature is 650 to 750 ° C, and the sintering time is 4 to 8 hours.

In order to achieve the above object, the present invention also provides a lithium iron phosphate/carbon composite material which is produced according to the method for producing lithium iron phosphate/carbon composite material of the present invention.

Compared with the prior art, the preparation method of the lithium iron phosphate/carbon composite material of the invention directly adopts the iron acid powder and phosphoric acid for acidification and reflux reaction, and then mixes the lithium salt and the carbon source, and is dried to obtain an organic carbon source composite lithium iron phosphate precursor. Finally, the sintered lithium iron phosphate/carbon composite material has the following advantages: 1) a wide range of raw materials and low cost, the raw materials involved are low-cost bulk chemical products; 2) the product has good crystal structure and less impurities. Uniform particle size, excellent electrochemical performance; 3) Simple and practical preparation process, using acid reflux reaction process to make iron powder and phosphoric acid react to produce nanoparticles, replacing traditional high-energy wet grinding and pulverization nano-processing; 4) Equipment Low operating cost, only need to support the atmospheric pressure reflux reaction device, avoid the use of high-value, difficult to maintain wet grinding equipment and auxiliary materials, easy to achieve large-scale industrial production.

DRAWINGS

The lithium iron phosphate/carbon composite material of the present invention and a preparation method thereof are described in detail below with reference to the accompanying drawings and specific embodiments, wherein:

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an XRD chart of a lithium iron phosphate/carbon composite material obtained in Example 1 of the present invention.

2 is an SEM image of a lithium iron phosphate/carbon composite material obtained in Example 1 of the present invention.

Fig. 3 is a graph showing the first discharge specific capacity of the lithium iron phosphate/carbon composite material obtained in Example 1 and Comparative Example 1 of the present invention.

detailed description

The present invention will be further described in detail below in conjunction with the drawings and specific embodiments. The specific embodiments described in the specification are to be construed as illustrative only and not limiting.

Example 1

77.18 g of iron fine powder having a D50 of 10 μm, 1.3 g of manganese dioxide, 115.29 g of concentrated phosphoric acid (85%), 3.86 g of oxalic acid and 57.65 g of deionized water were sequentially added to a three-necked flask, and dispersed at a speed of 400 rpm to obtain a suspension;

The three-necked bottle was placed in an oil bath, heated to 50 ° C, and acidified and refluxed at this temperature for 4 hours;

42.78 g of lithium hydroxide monohydrate and 3.86 g of maltose were added to the three-necked flask, and dispersed at 1500 rpm for 1 hour. After the reaction was completed, the cooling and reflux were closed;

The mixture is stirred and evaporated to obtain an organic iron source composite lithium iron phosphate precursor;

The collected precursors were sintered at 650 ° C for 4 hours, and pulverized and sieved to obtain a low-cost lithium iron phosphate/carbon composite material.

1 is an X-ray diffraction (XRD) pattern of a lithium iron phosphate/carbon composite material according to Example 1 of the present invention, and the XRD pattern shows that the lithium iron phosphate/carbon composite material obtained in Example 1 has good crystallinity and high purity, and is not There is an impurity peak. 2 is an SEM image of a lithium iron phosphate/carbon composite material according to Embodiment 1 of the present invention. As can be seen from FIG. 2, the lithium iron phosphate/carbon composite material prepared in Example 1 of the present invention is a nano particle, and the particle size thereof. evenly distributed.

The lithium iron phosphate/carbon composite material prepared in Example 1 was mixed with a conductive agent carbon black (Super P) and a binder PVDF at a mass ratio of 90:5:5 to form a slurry, uniformly coated on an aluminum foil current collector. The positive electrode membrane is made up, the lithium metal sheet is used as the negative electrode, the polypropylene microporous membrane is used as the separator, and the lithium hexafluorophosphate is used as the electrolyte. The half-cell is assembled in the argon-protected glove box, and the prepared half-cell is subjected to charge and discharge test. . 3 is a graph of the first discharge specific capacity of the lithium iron phosphate/carbon composite material obtained in Example 1 of the present invention, As can be seen from Fig. 3, the half-cell 0.1C first discharge specific capacity is 150 mAh/g, and the 1C first discharge specific capacity is 140 mAh/g.

The steps of the examples 2 to 5 are basically the same as those of the first embodiment, wherein the quality of the iron fine powder and lithium hydroxide monohydrate is the same as that of the first embodiment, and the use amount and preparation process parameters of the respective materials different from the first embodiment are different. See Tables 1-3 for the results of the first discharge specific capacity test of each of the examples.

Comparative example 1

77.18g iron fine powder, 1.3g manganese dioxide, 115.29g concentrated phosphoric acid (85%), 42.78g lithium hydroxide monohydrate, 3.86g oxalic acid, 3.86g maltose and 57.65g deionized water with D50 of 10μm were weighed respectively. The above raw materials were subjected to high-energy wet ball milling at a polishing rate of 1400 rpm for 4 hours; spray drying was carried out to obtain a lithium iron phosphate precursor; the precursor was sintered at 650 ° C for 4 hours, and pulverized and sieved to obtain a lithium iron phosphate/carbon composite material.

Figure 3 is a broken line diagram of the first discharge specific capacity of the lithium iron phosphate/carbon composite prepared in Comparative Example 1. As can be seen from Figure 3, Comparative Example 1 0.1C and 1C of lithium iron phosphate/carbon composite. The first discharge specific capacity was 137 mAh/g and 118 mAh/g, respectively.

Table 1, Examples 1 to 5 and Comparative Example 1 use of related substances

Table 2, Preparation Process Parameters of Examples 1 to 5 and Comparative Example 1

Table 3, first discharge specific capacity test results of Examples 1 to 5 and Comparative Example 1

According to the first discharge specific capacity results of Example 1 and Comparative Example 1, it can be seen that although the raw materials involved in the two methods are the same, the final results are different because different processes are employed. The acidizing reflow technique employed in the first to fifth embodiments of the present invention is superior to the comparative example 1 in the high energy wet ball milling technique, and the first discharge specific capacities of 0.1C and 1C of Examples 1 to 5 are higher than that of Comparative Example 1, which is better. The conductivity is also low during the preparation process using the acidified reflux technology of Examples 1 to 5. Through comparative analysis, it can be seen that the acid reflow technology is not only simple in process, but also has better performance of the prepared lithium iron phosphate/carbon composite material, and has a good market application prospect.

In combination with the above detailed description of the examples and comparative examples of the present invention, it can be seen that, compared with the prior art, the preparation method of the lithium iron phosphate/carbon composite material of the present invention is to directly carry out an acid reflux reaction using iron fine powder and phosphoric acid, and then mix the lithium salt and The carbon source, the organic iron source composite lithium iron phosphate precursor is dried, and finally the lithium iron phosphate/carbon composite material is sintered, which has the following advantages: 1) the raw material source is wide, the cost is low, and the raw materials involved are low-cost. Bulk chemical products; 2) The product has good crystal structure, less impurities, uniform particle size and excellent electrochemical performance; 3) The preparation process is simple and practical, and the acid precipitation reaction process is used to react the iron powder with phosphoric acid to prepare nanoparticles. It replaces the traditional high-energy wet grinding and pulverization nano-fabrication process; 4) The equipment has low operating cost, and only needs to support the atmospheric pressure reflux reaction device, avoiding the use of high-value, difficult-to-maintain wet-grinding equipment and auxiliary materials, and easy to realize large-scale industrial production. .

It should be noted that during the acidification reflux reaction, the acidified refluxed slurry is not a complete single substance solution form, but a nanoparticle emulsion of the mixture. The acidification reaction does not require all the reactions, and only the large particle iron powder is partially acidified, so that the large particle skeleton structure is loose and pulverized into small particles, that is, the ferrous iron and the acid in the iron powder react with each other to make the large particle powder. In order to realize the nanometerization process of large particles into small particles, the components of the small particles are ferrous oxide, Fe ₃ O ₄ , ferrous phosphate, iron phosphate and the like.

It should be further noted that although in the examples of the present specification, the acidifying additive is only exemplified by oxalic acid, citric acid or oxalic acid, according to other embodiments of the present invention, the acidifying additive may also be tartaric acid or A combination of the foregoing acidifying additives. Further, although the organic carbon source has been described by taking only maltose, glucose, sucrose, and fructose as an example in the embodiment of the present invention, the organic carbon source may be starch, phenol resin or the like according to other embodiments of the present invention. A combination of organic carbon sources. Furthermore, although the compound doped with the metal element M is described by way of example only in the examples of the present invention, manganese dioxide, magnesium oxide, titanium dioxide, and cobalt trioxide, the doping metal according to other embodiments of the present invention. The compound may also be an iron-containing compound, an aluminum-containing compound, a chromium-containing compound, a cerium-containing compound or a combination of the foregoing doped metal compounds; the doping metal compound is an oxide containing a doping element, hydrogen Oxide, nitrate, organic acid salt or a combination thereof. Finally, although the lithium-containing compound is exemplified by lithium hydroxide monohydrate as an example in the embodiment of the present invention, according to other embodiments of the present invention, the lithium-containing compound may also be lithium carbonate, lithium acetate or lithium nitrate. , lithium citrate or a combination of the foregoing lithium-containing compounds.

The above embodiments may be modified and modified as appropriate by those skilled in the art in light of the above disclosure. Therefore, the invention is not limited to the specific embodiments disclosed and described herein, and the modifications and variations of the invention are intended to fall within the scope of the appended claims. In addition, although specific terms are used in the specification, these terms are merely for convenience of description and do not limit the invention.

Claims

A method for preparing a lithium iron phosphate/carbon composite material, comprising the steps of:

1) Weigh iron powder, phosphoric acid and acidification additives, and disperse in deionized water;

2) heating to carry out an acid reflux reaction;

3) after the acidification reflux reaction is completed, the lithium-containing compound and the organic carbon source are added for mixing and dispersion;

4) stirring and evaporating the mixture to obtain an organic carbon source composite lithium iron phosphate precursor;

5) The collected precursors are sintered, pulverized and sieved to obtain lithium iron phosphate/carbon composite material.
The method for preparing a lithium iron phosphate/carbon composite according to claim 1, wherein in the step 1), the iron fine powder has a particle size of 5 to 30 μm, and the phosphoric acid has a concentration of 70 to 85. % of concentrated phosphoric acid, the molar ratio of Fe to P in the iron fine powder and concentrated phosphoric acid is 1:1.
The method for preparing a lithium iron phosphate/carbon composite material according to claim 1, wherein in the step 1), the acidifying additive is at least one of oxalic acid, citric acid, tartaric acid and oxalic acid. It is 5 to 15% of the quality of iron fine powder.
The method for preparing a lithium iron phosphate/carbon composite material according to claim 1, wherein in step 1), a doping metal compound is added, and a molar ratio of the doping metal element M and the P element in the doping metal compound is further added. The ratio is 0.005 to 0.03:1.
The method for preparing a lithium iron phosphate/carbon composite according to claim 4, wherein the dopant metal compound is a manganese-containing compound, a titanium-containing compound, a cobalt-containing compound, an iron-containing compound, a magnesium-containing compound, and a One or more of an aluminum compound, a chromium-containing compound, and a cerium-containing compound, and the doping metal compound is one or more of an oxide, a hydroxide, a nitrate, and an organic acid salt containing a doping element.
The method for preparing a lithium iron phosphate/carbon composite according to claim 1, wherein in the step 2), the acidification temperature is 50 to 150 ° C, and the acidification time is 4 to 8 hours.
The method for preparing a lithium iron phosphate/carbon composite according to claim 1, wherein In the step 3), the molar ratio of the Li to the P element is 1.02:1.
The method for preparing a lithium iron phosphate/carbon composite according to claim 1, wherein in the step 3), the lithium-containing compound comprises lithium carbonate, lithium hydroxide monohydrate, lithium acetate, lithium nitrate, and citric acid. Lithium, preferably lithium hydroxide monohydrate.
The method for preparing a lithium iron phosphate/carbon composite according to claim 1, wherein in the step 3), the organic carbon source is maltose, glucose, sucrose, fructose, starch, phenolic resin or a combination thereof. The amount added is 5 to 15% of the mass of the iron fine powder.
The method for producing a lithium iron phosphate/carbon composite according to claim 1, wherein in the step 5), the sintering temperature is 650 to 750 ° C, and the sintering time is 4 to 8 hours.
A lithium iron phosphate/carbon composite material, characterized in that the lithium iron phosphate/carbon composite material is produced according to the production method according to any one of claims 1 to 10.